JP7805979B2 - Enameled wire and its manufacturing method - Google Patents

Description

The present invention relates to enameled wire and its manufacturing method.

Enameled wire is used in a wide variety of applications, including motors and transformers. In recent years, as various devices have become smaller and more powerful, there has been an increase in the use of coils wound with enameled wire, which are forced into narrow spaces (such as stator slots). In such applications, enameled wire is required to have high mechanical strength.
An enameled wire is composed of a conductor and an enamel resin layer covering the conductor. Increasing the adhesive strength between the conductor and the enamel resin layer is crucial for improving the mechanical strength and performance of the enameled wire. One method proposed for improving adhesiveness between the conductor and the enamel resin layer is to precisely control the imide group concentration in the polyimide enamel resin layer (Patent Document 1). Another proposal for improving the strength of the enameled wire is to further precisely control the content of polyimide resin skeletons in the enamel resin layer (Patent Document 2).

JP 2012-233123 A Patent No. 6614953

However, the type of enamel resin is limited to polyimide in the methods described in Patent Documents 1 and 2. Furthermore, as described in Patent Document 2, the adhesion between the conductor and the enamel resin layer is evaluated based on the content of imide structures in the enamel resin layer, making it difficult to control the content.
The present invention has been made in view of the above-mentioned problems, and its main object is to provide a method for efficiently producing an enameled wire that has high adhesion between the conductor and the enamel resin layer simply by adding an additive, and to provide an enameled wire obtained by this method.

That is, the present invention provides:
A method for manufacturing an enameled wire having a conductor and an enamel resin layer covering the conductor,
providing the conductor;
a step of applying a varnish containing an enamel resin or a precursor thereof, polyethylene glycol having a number average molecular weight of 400 or more and 600 or less, and a solvent around the conductor;
baking the varnish;
Including,
The amount of the polyethylene glycol in the varnish is 1% by mass or more and 10% by mass or less relative to the amount of the enamel resin or its precursor.
To provide a method for manufacturing an enameled wire.

The present invention further comprises:
An enameled wire having a conductor and an enamel resin layer covering the conductor,
the enamel resin layer is a cured film of a varnish containing an enamel resin or a precursor thereof and polyethylene glycol having a number average molecular weight of 400 or more and 600 or less, and the amount of the polyethylene glycol is 1% by mass or more and 10% by mass or less with respect to the enamel resin or precursor thereof;
Provide enameled wire.

The method of the present invention makes it possible to efficiently produce enameled wire with high adhesion between the conductor and the enamel resin layer simply by adding a certain amount of polyethylene glycol as an additive.

FIG. 1A is a cross-sectional view of an enameled wire according to one embodiment of the present invention, and FIG. 1B is a cross-sectional view of an enameled wire according to another embodiment of the present invention. FIG. 1 is a schematic diagram of an apparatus for carrying out a peel twist test in the Examples. FIG. 1 is a schematic diagram of an apparatus for conducting a break float test in the Examples. FIG. 2 is a schematic diagram for explaining a method for determining the breakage float length in the examples.

As described above, in recent years, there has been a demand for improved adhesion between the conductor and the enamel resin layer in various enameled wires.
In response to these demands, the inventors have found through extensive research that adding polyethylene glycol with a number-average molecular weight of 400 to 600 to the varnish used to form the enamel resin layer, and further adjusting the amount of polyethylene glycol to 1% by mass to 10% by mass relative to the amount of the enamel resin or its precursor, can significantly increase the adhesive strength between the conductor and the enamel resin layer. The reason why the use of the above varnish improves the adhesiveness between the conductor and the enamel resin layer is thought to be as follows.
Normally, the adhesion between a conductor and an enamel resin is achieved by a strong bond between them. However, with a typical conductor, an oxide film or other coating forms on the surface between the time of production and the time of coating with an enamel resin layer. Therefore, even if an enamel resin layer is formed on the conductor, the conductor and the enamel resin do not bond strongly, and sufficient adhesion is not achieved. In contrast, when the above-mentioned varnish is used, the polyethylene glycol in the varnish reduces the metal oxide present on the surface of the conductor and removes the coating at the same time as the enamel resin layer is formed. This is thought to result in a strong bond between the conductor and the enamel resin, resulting in high adhesion strength.
This method is not limited to a specific type of enamel resin, making it useful for producing various types of enameled wires. Furthermore, it is not necessary to precisely adjust the deposition conditions for the enamel resin layer.

The following describes in detail an enameled wire and a method for manufacturing the same according to one embodiment of the present invention. However, the enameled wire and method for manufacturing the same according to the present invention are not limited to the embodiment described below.

As shown in FIG. 1A, the enameled wire 1 of this embodiment has a conductor 3 and an enamel resin layer 5 that covers the conductor 3.
The conductor 3 is the same as that in conventional enameled wires, and is preferably a copper wire. The copper in the copper wire may be a tough pitch material or the like, but is preferably low-oxygen copper with an oxygen content of 30 ppm or less, more preferably low-oxygen copper or oxygen-free copper with an oxygen content of 20 ppm or less, and even more preferably oxygen-free copper (MiDIP (registered trademark)) with an oxygen content of 10 ppm or less. If the copper is low-oxygen copper or oxygen-free copper, voids that cause electrical resistance are less likely to occur when the conductors 3 of multiple enameled wires 1 are welded together.
On the other hand, the conductor 3 may be an aluminum wire or an aluminum alloy wire. When a high current value is required for the enameled wire 1, the conductor 3 is preferably made of pure aluminum with a high purity (for example, 99.00% or higher).

The size and shape of the cross section of the conductor 3 are not particularly limited and may be appropriately selected depending on the application. The cross section of the conductor 3 may be circular as shown in Fig. 1A or rectangular as shown in Fig. 1B. The cross section of the conductor 3 may also be other shapes, such as a hexagon.
The cross-sectional size of the conductor 3 is selected appropriately depending on the application. When the cross section is circular, its diameter is usually about 0.3 mm or more and 3 mm or less. When the cross section is rectangular, its long side is usually about 1 mm or more and 5 mm or less, and its short side is about 0.4 mm or more and 3 mm or less. When the cross section is rectangular, it is preferable that the corners are chamfered.

On the other hand, the enamel resin layer 5 is a layer that coats the conductor 3 and is a layer that mainly contains enamel resin, but may contain components other than enamel resin as long as the purpose and effect of this embodiment are not impaired. The enamel resin layer 5 is a film formed by applying and baking a varnish, which will be described later in the manufacturing method, i.e., a cured film of the varnish. In this specification, "enamel resin" refers to a resin that has insulating properties and can be baked to form a coating around the conductor 3.
The type of enamel resin is selected appropriately depending on the application of the enameled wire 1. Examples of enamel resins include polyvinyl formal resin, polyurethane resin, polyester resin, polyesterimide resin, polyamideimide resin, and polyimide resin. The enamel resin layer 5 may contain only one of these resins or two or more of them. If heat resistance is required for the enameled wire, the enamel resin is preferably a resin containing polyimide bonds, and polyimide resin is more preferred. The structure of the polyimide resin is not particularly limited, but from the perspective of heat resistance, polyimide resins obtained from aromatic tetracarboxylic dianhydride and aromatic diamine are preferred. For example, polyimide resins obtained from pyromellitic acid and diaminodiphenyl ether are preferred.

Examples of components contained in the enamel resin layer 5 other than the enamel resin include pigments, dyes, various additives, and the like.
The thickness of the enamel resin layer 5 is appropriately selected depending on the application of the enameled wire 1, but is usually 10 μm or more and 60 μm or less.

The method for producing the enameled wire will now be described.
First, the conductor described above is prepared. The conductor may be manufactured by any known method, and may be adjusted to a desired shape and size by wire drawing.

On the other hand, a varnish containing an enamel resin or its precursor, polyethylene glycol having a number-average molecular weight of 400 to 600, and a solvent is prepared. The type of enamel resin or its precursor contained in the varnish is appropriately selected according to the type of enamel resin. For example, when the enamel resin is a polyimide resin, the varnish preferably contains a polyimide precursor (such as polyamic acid or polyamideimide).
The type of solvent used in the varnish is selected appropriately depending on the type of enamel resin or its precursor. For example, for varnishes containing polyimide precursors, it is preferable to use aprotic polar organic solvents such as N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and γ-butyrolactone as the solvent. The varnish may contain only one solvent or two or more solvents.
The varnish further contains polyethylene glycol having a number-average molecular weight of 400 to 600. The amount of polyethylene glycol in the varnish may be 1% by mass to 10% by mass relative to the amount of the enamel resin or its precursor. For example, a commercially available polyethylene glycol manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. (molecular weight 400, 600) can be used as the polyethylene glycol, and this commercially available product was used here.
The method for preparing the varnish is not particularly limited, and a resin-containing varnish containing a solvent and an enamel resin or its precursor may be prepared, and a predetermined amount of polyethylene glycol may be added to the resin-containing varnish. In this case, after mixing the resin-containing varnish and polyethylene glycol, it is preferable to stir or disperse the mixture so that the polyethylene glycol is uniformly dispersed.

Next, varnish is applied around the conductor. The varnish can be applied by a known method. For example, the conductor is inserted into a die having an opening slightly larger than the cross section of the conductor and having a shape similar to the cross section of the conductor, and the varnish is applied inside the die while the conductor is moved in one direction.
After application of the varnish, the varnish is baked. Baking of the varnish can be performed by a known method, and may be performed in a vertical furnace or a horizontal furnace. The baking temperature is appropriately selected depending on the type of enamel resin and its precursor in the varnish. For example, if the varnish contains an enamel resin, the temperature may be any temperature at which the solvent in the varnish can be removed. On the other hand, if the varnish contains a precursor of an enamel resin, the varnish must be heated at a temperature at which the precursor can react. For example, if the varnish contains a polyimide precursor, a temperature at which the polyimide precursor is imidized is selected.
The baking time is appropriately selected depending on the amount of solvent in the varnish and the type of enamel resin.
It is preferable that the thickness of the film formed by one application and baking of varnish is 1 μm or more and 6 μm or less, and it is preferable to produce an enamel resin layer by applying and baking varnish multiple times (for example, 10 or more times) until the desired thickness is achieved.

The present invention will be explained in more detail below using examples. However, the scope of the present invention is not limited in any way by these examples, and modifications to the embodiments are possible without departing from the spirit of the present invention.

[Example 1]
In the following examples and comparative examples, the correlation between the number average molecular weight of polyethylene glycol added to the varnish and the adhesion between the enamel resin layer and the conductor was examined.

(Example 1-1)
As the conductor, a round wire conductor (oxygen-free copper, MiDIP (registered trademark)) having a circular cross section (diameter 1.0 mm) was prepared.
Separately, a polyimide precursor varnish containing a polyimide precursor obtained from pyromellitic dianhydride (PMDA) and diaminodiphenyl ether (DDE), and a solvent (mainly N-methyl-2-pyrrolidone and N,N-dimethylformamide) was prepared. Polyethylene glycol with a number-average molecular weight of 400 was added to the polyimide precursor varnish and mixed uniformly to obtain a varnish. The amount of polyethylene glycol added was 1 part by mass per 100 parts by mass of the resin solids content of the polyimide precursor varnish.
The conductor was inserted into a die for applying varnish, and while the conductor was moved in one direction, varnish was applied inside the die and baked at 400° C. The varnish application and baking were repeated 10 to 15 times to obtain an enameled wire with an enamel resin layer 30 μm thick.

(Example 1-2)
An enameled wire was obtained in the same manner as in Example 1-1, except that the number average molecular weight of the polyethylene glycol added when preparing the varnish was changed to 600.

(Comparative Example 1-1)
An enameled wire was obtained in the same manner as in Example 1-1, except that polyethylene glycol was not added when preparing the varnish.

(Comparative Example 1-2)
An enameled wire was obtained in the same manner as in Example 1-1, except that the number average molecular weight of the polyethylene glycol added when preparing the varnish was set to 1,000.

(evaluation)
The enameled wires produced in the above examples and comparative examples were subjected to a peel twist test and a breakage lift test as follows. The results are shown in Table 1.

Peel Twist Test Five 35 cm long test pieces were taken and fixed with the device shown in Figure 2 at a gauge length of 250 mm using fixing parts 311 and 312 to prevent sagging of the test piece 10. A cutter was then inserted into the enamel resin layer of the test piece 10 in the longitudinal direction, and one side of the layer was peeled off. One end of the test piece 10 was then rotated in the same direction at a speed of 30 to 60 revolutions per minute to twist the test piece 10, and the number of revolutions until further peeling of the coating was counted. The values shown in Table 1 are the average of five runs.

Breaking Lift Test Five 35 cm long test pieces were prepared and tested using the tensile testing machine shown in Figure 3 with a gauge length of 250 mm. Both ends of the test piece 10 were fixed to the fixing parts 411 and 412. One of the fixing parts (fixing part 412 in this case) was then stretched at a rate of 300 mm/min until the test piece 10 broke. The breaking lift length of the enamel resin layer was measured for each broken test piece 10. Figure 4 shows a schematic diagram of the broken part of the test piece 10. The breaking lift length is the length of the region where the conductor 3 and the enamel resin layer 5 overlap but are not in close contact with the conductor 3. If both test pieces 10 have regions where the conductor 3 and the enamel resin layer 5 are not in close contact with each other, as shown in Figure 4, the coating lift length is the sum of the coating lift lengths A and B. The values shown in Table 1 are the average of five tests.

·result

As shown in Table 1, when the varnish was applied without adding polyethylene glycol, the peel twist test result was 46.4 times and the fracture float was 6.6 mm (Comparative Example 1-1). In contrast, when polyethylene glycol with a number-average molecular weight of 400 to 600 was added to the varnish, the peel twist test result improved by about 1.2 times and the fracture float was reduced to less than half (Examples 1-1 and 1-2). In other words, it can be said that adding polyethylene glycol with a number-average molecular weight of 400 to 600 significantly improved the adhesion between the enamel resin layer and the conductor.
When polyethylene glycol with a number average molecular weight of 1000 was added, the results of the fracture lift test were good, but the results of the peel twist test were almost the same as when polyethylene glycol was not added (Comparative Example 1-2). In other words, it can be said that polyethylene glycol with this molecular weight did not sufficiently improve the adhesion between the enamel resin layer and the conductor.

[Example 2]
In the following examples and comparative examples, the correlation between the amount of polyethylene glycol added to the varnish and the adhesion between the enamel resin layer and the conductor was examined.

(Example 2-1)
An enameled wire was produced under the same conditions as in Example 1-1, except that the amount of polyethylene glycol in the varnish was 1% by mass relative to the amount of the polyimide precursor.

(Example 2-2)
An enameled wire was obtained in the same manner as in Example 2-1, except that the amount of polyethylene glycol in the varnish was 5% by mass relative to the amount of the polyimide precursor.

(Example 2-3)
An enameled wire was obtained in the same manner as in Example 2-1, except that the amount of polyethylene glycol in the varnish was 10% by mass relative to the amount of the polyimide precursor.

(evaluation)
The enameled wires produced in the above Examples and Comparative Examples were subjected to a peel twist test and a breakage lift test. The test methods were the same as those described above. The results are shown in Table 2.

·result

As shown in Table 2, when enameled wires were produced by adding 1% to 10% by mass of polyethylene glycol to the polyimide precursor, the peel twist test results exceeded 50 cycles and the break float test results were 3.2 mm or less. However, as the amount of polyethylene glycol increased, the peel twist test results tended to decrease (Example 2-3). Therefore, it was considered appropriate for the amount of polyethylene glycol to be 10% by mass or less relative to the mass of the enamel resin or its precursor.

The enameled wire manufacturing method of the present invention makes it possible to efficiently manufacture enameled wires with high adhesion between the conductor and the enamel resin layer. This manufacturing method is useful for manufacturing various types of enameled wires for a variety of applications.

REFERENCE SIGNS LIST 1 Enameled wire 3 Conductor 5 Enameled resin layer 10 Test piece 311, 312, 411, 412 Fixing portion

Claims (2)

A method for manufacturing an enameled wire having a conductor and an enamel resin layer covering the conductor,
providing the conductor;
a step of applying a varnish containing an enamel resin or a precursor thereof, polyethylene glycol having a number average molecular weight of 400 or more and 600 or less, and a solvent around the conductor;
baking the varnish;
Including,
the amount of the polyethylene glycol in the varnish is 1% by mass or more and 10% by mass or less relative to the amount of the enamel resin or its precursor,
The enamel resin is a polyimide resin.
Manufacturing method of enameled wire. An enameled wire having a conductor and an enamel resin layer covering the conductor,
the enamel resin layer is a cured film of a varnish containing an enamel resin or a precursor thereof and polyethylene glycol having a number average molecular weight of 400 or more and 600 or less, and the amount of the polyethylene glycol is 1% by mass or more and 10% by mass or less with respect to the enamel resin or precursor thereof,
The enamel resin is a polyimide resin.
Enamelled wire.