JP7685481B2 - Insulated wire and method for manufacturing the same - Google Patents

Description

This disclosure relates to an insulated electric wire and a method for manufacturing an insulated electric wire. This application claims priority to Japanese Application No. 2020-073067, filed on April 15, 2020, and incorporates by reference all of the contents of said Japanese application.

An insulated electric wire is known that includes a linear conductor and an insulating layer that covers the conductor. The insulated electric wire is preferably used, for example, as a coil for a motor, a transformer, or the like. International Publication No. 2013/073397 discloses that the variation in thickness of the insulating layer in the insulated electric wire is suppressed, thereby improving the adhesion between the conductor and the insulating layer.

International Publication No. 2013/073397 JP 2008-097888 A

The insulated electric wire of the present disclosure is an insulated electric wire including a linear conductor having a first surface, a second surface opposite the first surface, a third surface, and a fourth surface opposite the third surface, and an insulating layer covering the conductor, wherein the insulating layer has a first insulating layer directly in contact with the conductor and one or more upper insulating layers covering the first insulating layer, wherein the first insulating layer has a first covering portion covering the first surface, a second covering portion covering the second surface, a third covering portion covering the third surface, and a fourth covering portion covering the fourth surface, wherein in a cross section perpendicular to the longitudinal direction of the insulated electric wire, the layer thickness of the first covering portion is represented by Ta, the layer thickness of the second covering portion is represented by ta, the layer thickness of the third covering portion is represented by Tb, and the layer thickness of the fourth covering portion is represented by tb, and the ratios Ta/ta and Tb/tb are all 1.6 or less.

The method for manufacturing an insulated wire disclosed herein includes a linear conductor having a first surface, a second surface opposite the first surface, a third surface, and a fourth surface opposite the third surface, and an insulating layer coating the conductor, the method for manufacturing the insulated wire includes a step of preparing the conductor and an insulating varnish, a step of coating the conductor with the first insulating layer, and a step of stacking the upper insulating layer on the first insulating layer, the coating step includes a step of applying the insulating varnish to the conductor, a step of adjusting the thickness of the insulating varnish applied to the conductor, and a step of baking the insulating varnish onto the conductor, and the step of adjusting the thickness is carried out by passing the conductor coated with the insulating varnish through an opening of a coating die such that the distance between the inner wall of the opening and the conductor is 0.040 mm or less.

FIG. 1 is a perspective view showing a longitudinal direction of an insulated electric wire according to the present embodiment. FIG. 2 is a diagram illustrating a cross section perpendicular to the longitudinal direction of the insulated wire according to the present embodiment. FIG. 3 is a process diagram of the method for producing an insulated electric wire according to the present embodiment.

[Problem to be solved by the present disclosure]
In response to the demand for smaller coils, there is a need to wind an insulated electric wire around a smaller core at a high density and high speed. In this case, it is necessary to further strengthen the adhesion between the conductor and the insulating layer so that the insulating layer covering the outer surface of the conductor is maintained without being destroyed even if a large stress is applied to the insulated electric wire during winding. Therefore, based on the strict requirements for performance in recent years, there is a strong demand for the development of an insulated electric wire with further strengthened adhesion between the conductor and the insulating layer.

An object of the present disclosure is to provide an insulated wire having improved adhesion between a conductor and an insulating layer, and a method for manufacturing the same.
[Effects of the present disclosure]

According to the present disclosure, it is possible to provide an insulated electric wire having improved adhesion between a conductor and an insulating layer, and a method for manufacturing the same.
[Description of the embodiments of the present disclosure]

The present inventors conducted intensive research to solve the above-mentioned problems and completed the present disclosure. Specifically, they focused on suppressing the variation in thickness of the first insulating layer, which is in direct contact with the conductor, among the insulating layers that cover the linear conductor in an insulated wire. As a result, they discovered that in an insulated wire with a uniform thickness of the first insulating layer, the adhesion between the conductor and the insulating layer is improved compared to conventional methods, and arrived at the present disclosure.

First, the embodiments of the present disclosure will be listed and described.
[1] An insulated wire according to one aspect of the present disclosure includes: a linear conductor having a first surface, a second surface opposite the first surface, a third surface, and a fourth surface opposite the third surface; and an insulating layer covering the conductor, wherein the insulating layer has a first insulating layer directly contacting the conductor and one or more upper insulating layers covering the first insulating layer, the first insulating layer having a first covering portion covering the first surface, a second covering portion covering the second surface, a third covering portion covering the third surface, and a fourth covering portion covering the fourth surface, wherein, in a cross section perpendicular to a longitudinal direction of the insulated wire, a thickness of the first covering portion is represented by Ta, a thickness of the second covering portion is represented by ta, a thickness of the third covering portion is represented by Tb, and a thickness of the fourth covering portion is represented by tb, and the ratios Ta/ta and Tb/tb are all 1.6 or less. In an insulated wire having such characteristics, the variation in thickness of the first insulating layer is suppressed, and therefore the adhesion between the conductor and the insulating layer can be improved.

[2] Either the ratio Ta/ta or the ratio Tb/tb may be 1.4 or less. This can improve the adhesion between the conductor and the insulating layer.

[3] The ratios Ta/ta and Tb/tb may each be 1.4 or less. This can further improve the adhesion between the conductor and the insulating layer.

[4] The cross-sectional shape of the conductor in the cross section may be rectangular. This allows the insulated wire to be wound around the core at high density.

[5] A method for producing an insulated wire according to one embodiment of the present disclosure includes a linear conductor having a first surface, a second surface opposite the first surface, a third surface, and a fourth surface opposite the third surface, and an insulating layer coating the conductor, the method for producing the insulated wire includes a step of preparing the conductor and an insulating varnish, a step of coating the conductor with the first insulating layer, and a step of stacking the upper insulating layer on the first insulating layer, the coating step includes a step of applying the insulating varnish to the conductor, a step of adjusting a thickness of the insulating varnish applied to the conductor, and a step of baking the insulating varnish onto the conductor, and the step of adjusting the thickness is performed by passing the conductor coated with the insulating varnish through an opening of a coating die such that the distance between the inner wall of the opening and the conductor is 0.040 mm or less. The manufacturing method for an insulated wire having such characteristics makes it possible to coat a conductor with a first insulating layer having reduced variation in thickness, thereby making it possible to manufacture an insulated wire having improved adhesion between the conductor and the insulating layer.

[Details of the embodiment of the present disclosure]
Hereinafter, an embodiment of the present disclosure (hereinafter also referred to as "the present embodiment") will be described in more detail. In the drawings used to explain the present embodiment, the same reference numerals represent the same or corresponding parts. Furthermore, the scale of the drawings is appropriately adjusted to facilitate understanding of each component, and the scale of each component shown in the drawings does not necessarily match the scale of the actual component.

In this disclosure, the notation "A~B" means the upper and lower limits of a range (i.e., greater than or equal to A and less than or equal to B). If no unit is specified for A and a unit is specified only for B, the units of A and B are the same.

[Insulated wire]
Hereinafter, an insulated wire according to the present embodiment will be described with reference to FIGS.
FIG. 1 is a perspective view showing a longitudinal direction of an insulated electric wire according to the present embodiment.
Fig. 2 is a diagram illustrating a cross section perpendicular to the longitudinal direction of the insulated wire according to the present embodiment. As shown in Figs. 1 and 2, the present embodiment is an insulated wire 1 including a linear conductor 11 and an insulating layer 20 that covers the conductor 11. The insulating layer 20 has a first insulating layer 21 that is in direct contact with the conductor 11, and one or more upper insulating layers 22 that are disposed on the first insulating layer 21. In the description of the present embodiment, a case will be illustrated in which the cross-sectional shape of the conductor 11 in the cross section of the insulated wire 1 is a rectangular shape, as shown in Figs. 1 and 2.

In the insulated wire according to the present embodiment, the first insulating layer has a first covering portion, a second covering portion, a third covering portion, and a fourth covering portion as portions covering two pairs of opposing surfaces of the conductor. The first insulating layer has first opposing surfaces of the first covering portion and the second covering portion, and second opposing surfaces of the third covering portion and the fourth covering portion as portions covering the two pairs of opposing surfaces of the conductor. In the insulated wire, when the thickness of the first covering portion is represented by Ta, the thickness of the second covering portion is represented by ta, the thickness of the third covering portion is represented by Tb, and the thickness of the fourth covering portion is represented by tb in a cross section perpendicular to the longitudinal direction of the insulated wire, the ratios Ta/ta and Tb/tb are all 1.6 or less.
Either the ratio Ta/ta or the ratio Tb/tb may be 1.4 or less. In the insulated wire 1 having such a feature, the variation in the thickness of the first insulating layer 21 is suppressed, and therefore the adhesion between the conductor 11 and the insulating layer 20 can be improved.
The ratios Ta/ta and Tb/tb may both be 1.4 or less. The adhesion between the conductor 11 and the insulating layer 20 can be further improved. The reason why the adhesion between the conductor 11 and the insulating layer 20 in the insulated wire 1 is improved will be described later.

<Conductor>
The insulated wire 1 according to the present embodiment includes a linear conductor 11 as described above. The conductor 11 is an electric conductor. The material of the conductor 11 is preferably a metal having high electrical conductivity and high mechanical strength. Specific examples of the material include copper, copper alloy, aluminum, aluminum alloy, nickel, silver, soft iron, steel, and stainless steel. The conductor 11 may be a wire formed from these metals in a linear shape, a coated wire in which the surface of the wire is coated with another metal, or a twisted wire in which a plurality of wires are twisted together. Examples of the coated wire include nickel-coated copper wire, silver-coated copper wire, silver-coated aluminum wire, and copper-coated steel wire, but are not limited thereto.

The shape of the conductor 11 can be appropriately selected depending on the intended use and electrical characteristics of the insulated wire 1 .
In this embodiment, in order to wind the insulated wire 1 around the core at high density, the cross-sectional shape of the conductor 11 is rectangular.
The diameter or outer circumferential length of the conductor 11 is not particularly limited, and can be appropriately selected depending on the intended use and electrical characteristics of the insulated wire 1 .

Here, in this disclosure, "flat corner", which is one of the cross-sectional shapes of conductor 11, includes rectangles and squares, and also includes shapes in which the four corners of these rectangles and squares are chamfered or have a radiused (R) shape.

The lower limit of the cross-sectional area of the conductor 11 may be 0.01 ^mm2 . If the cross-sectional area of the conductor 11 does not satisfy 0.01 ^mm2 , the ratio of the volume of the insulating layer 20 to the conductor 11 becomes large, and the volume efficiency of the coil formed using the insulated wire 1 may decrease. The upper limit of the cross-sectional area of the conductor 11 may be 20 ^mm2 . If the cross-sectional area of the conductor 11 exceeds 20 ^mm2 , it becomes necessary to thicken the insulating layer 20 in order to sufficiently improve the insulation of the insulated wire 1, and as a result, the diameter of the insulated wire 1 increases, which tends to make it difficult to wind the insulated wire 1 around the core at a high density.
The lower limit of the cross-sectional area of the conductor 11 may be 0.1 ^mm2 . If the cross-sectional area of the conductor 11 is less than 0.1 ^mm2 , the conductor resistance during current flow may be large, which may cause heat loss. The upper limit of the cross-sectional area of the conductor 11 may be ^{10 mm2} . If the cross-sectional area of the conductor 11 is more than 10 ^mm2 , it may be difficult to bend the coil formed using the insulated wire 1.

<Insulating layer>
As described above, the insulated wire 1 according to this embodiment includes the insulating layer 20 that covers the conductor 11. The insulating layer 20 has a first insulating layer 21 that is in direct contact with the conductor 11, and one or more upper insulating layers 22 that are disposed on the first insulating layer 21.

Examples of the resin constituting the insulating layer 20 include thermosetting resins such as polyvinyl formal resin, polyurethane resin, alkyl resin, epoxy resin, phenoxy resin, polyester resin, polyesterimide resin, polyesteramideimide resin, polyamideimide resin, and polyimide resin, and thermoplastic resins such as polyetherimide resin, polyetheretherketone resin, polyethersulfone resin, and polyimide resin. These resins may be used alone or in combination of two or more.
The insulating layer 20 may be made of a thermosetting polyimide resin, which can improve the strength and heat resistance of the insulating layer 20.

The first insulating layer 21 and the upper insulating layer 22 constituting the insulating layer 20 may both be formed by selecting the same type of resin from the various resins mentioned above, or may each be formed by selecting different types of resin.

The lower limit of the thickness of the insulating layer 20 (the total thickness of the first insulating layer 21 and the upper insulating layer 22) may be 5 μm. If the thickness of the insulating layer 20 is less than 5 μm, the insulating layer 20 tends to easily break, and the insulation of the conductor 11 may be insufficient.
The upper limit of the thickness of the insulating layer 20 may be 200 μm. If the thickness of the insulating layer 20 exceeds 200 μm, the volumetric efficiency of a coil or the like formed using the insulated wire 1 tends to decrease.

The thickness of the insulating layer 20 means the average value of the thickness of the insulating layer 20 covering the two pairs of opposite surfaces (upper, lower, left, and right surfaces) of the conductor 11. Specifically, the insulated electric wire 1 is cut along a surface perpendicular to its longitudinal direction, and the cross section is polished to prepare the measurement surface. Next, the measurement surface is imaged using a digital microscope VHX-7000 (manufactured by Keyence Corporation) to obtain an image. Finally, the thickness of the insulating layer 20 covering the two pairs of opposite surfaces of the conductor 11 in the image is calculated by, for example, selecting one location each from the upper, lower, left, and right surfaces of the conductor 11, measuring the thickness of the insulating layer 20 at a total of four locations, and calculating the average value from the values obtained, which can be used as the thickness of the insulating layer 20.

(First insulating layer)
The first insulating layer 21 is an insulating layer that is in direct contact with the conductor 11. In the present disclosure, the first insulating layer 21 means an insulating layer formed by baking based on an insulating varnish applied so as to be in direct contact with the conductor 11 as described later. The first insulating layer 21 has a first covering portion, a second covering portion, a third covering portion, and a fourth covering portion as portions that cover two pairs of opposing surfaces of the conductor 11. The first insulating layer has a first opposing surface of the first covering portion and the second covering portion, and a second opposing surface of the third covering portion and the fourth covering portion as portions that cover two pairs of opposing surfaces of the conductor.

<Thickness of first insulating layer (Ta, ta, Tb, tb)>
In this embodiment, in a cross section perpendicular to the longitudinal direction of the insulated wire 1, the thickness of the first covering portion of the first insulating layer 21 is represented by Ta, the thickness of the second covering portion by ta, the thickness of the third covering portion by Tb, and the thickness of the fourth covering portion by tb, and the ratios Ta/ta and Tb/tb are all 1.6 or less. For example, in Fig. 2, Ta represents the thickness of the first insulating layer 21 covering the lower surface of the conductor 11, ta represents the thickness of the first insulating layer 21 covering the upper surface of the conductor 11, Tb represents the thickness of the first insulating layer 21 covering the left surface of the conductor 11, and tb represents the thickness of the first insulating layer 21 covering the right surface of the conductor 11.

Here, in this disclosure, Ta is greater than or equal to ta (Ta≧ta), and Tb is greater than or equal to tb (Tb≧tb). That is, of the two pairs of opposing surfaces (first opposing surface, second opposing surface), the side with the thicker layer on the first opposing surface is the first covering portion, and the side with the thinner layer is the second covering portion. Also, the side with the thicker layer on the second opposing surface is the third covering portion, and the side with the thinner layer is the fourth covering portion.

In this case, in this embodiment, the ratios Ta/ta and Tb/tb are both 1.6 or less.
The ratios Ta/ta and Tb/tb may both be 1.4 or less, or may be 1.1 or less. Ideally, the ratios Ta/ta and Tb/tb are both 1.0. In these cases, the adhesion between the conductor and the insulating layer can be further improved.

The first insulating layer 21, in which the ratios Ta/ta and Tb/tb are both 1.6 or less, can be obtained, for example, by passing a conductor 11 coated with insulating varnish as described below through the opening of a coating die so that the distance between the inner wall of the opening of the coating die and the conductor is 0.040 mm or less.

In the field of technology related to insulated electric wires, there has been no idea of suppressing the variation in the thickness of the insulating layer (first insulating layer) that is in direct contact with the conductor. On the other hand, in the present disclosure, when the ratios Ta/ta and Tb/tb of the first insulating layer 21 of the insulated electric wire 1 are both 1.6 or less, the adhesion between the conductor 11 and the insulating layer 20 is even better than that of conventional insulated electric wires. The reason for this is not clear in detail, but is thought to be as follows.

In the insulating layer (first insulating layer) that is in direct contact with the conductor, for example, there may be a portion (hereinafter also referred to as a "thickened portion") that is thicker than the layer thickness of the first facing surface and the layer thickness of the second facing surface. In this case, the adhesion between the conductor and the thickened portion tends to decrease. This is because it is presumed that the thickened portion may not be baked sufficiently due to insufficient heat input during baking of the insulating varnish or difficulty in volatilizing and dissipating the solvent of the insulating varnish. Therefore, in order to obtain sufficient adhesion between the conductor and the insulating layer, it is presumed that it is important to have no thickened portion in the first insulating layer 21 that is in direct contact with the conductor 11.

From the above, it is considered that excellent adhesion can be achieved between the conductor 11 and the insulating layer 20 when the variation in the layer thickness of the first insulating layer 21 is suppressed so that the thickened portion described above does not exist, and when the ratios indicated by Ta/ta and Tb/tb are both 1.6 or less.

<Method of measuring thickness (Ta, ta, Tb, tb) of first insulating layer>
The thicknesses (Ta, ta, Tb, tb) of the first insulating layer can be measured by the same method as the method for measuring the thickness of the insulating layer 20 described above. First, an image is obtained in the same manner as the method for measuring the thickness of the insulating layer 20. Next, one location each is selected from the top, bottom, left and right surfaces of the conductor 11 in the image, and the thicknesses of the first insulating layer 21 at these four locations in total, in other words, the thicknesses Ta, ta, Tb and tb of the first covering portion, the second covering portion, the third covering portion and the fourth covering portion, can be measured to determine the thicknesses.

(Upper insulating layer)
The upper insulating layer 22 is one or more insulating layers disposed on the first insulating layer 21. The upper insulating layer 22 can be laminated on the first insulating layer 21 by a conventionally known method, as described later. The specific number of upper insulating layers 22 disposed on the first insulating layer 21 can be appropriately selected depending on the intended use, electrical characteristics, etc. of the insulated wire 1, but typically 1 to 100 upper insulating layers 22 can be disposed on the first insulating layer 21.

The thickness of the upper insulating layer 22 can be determined as the difference between the thickness of the insulating layer 20 and the thickness of the first insulating layer 21 obtained by the measurement method described above. When the insulated wire 1 is observed using a fluorescent microscope that measures the thickness of the insulating layer 20, the interface between the upper insulating layer 22 and the first insulating layer 21 can be clearly identified in a cross section perpendicular to the longitudinal direction of the insulated wire 1. Furthermore, when the upper insulating layer 22 is made up of multiple layers, the interfaces between the multiple layers can also be clearly identified.

<Adhesion between conductor and insulating layer>
In the insulated wire 1 according to this embodiment, the adhesion between the conductor 11 and the insulating layer 20 can be evaluated by the following method. First, the insulated wire 1 is obtained by the manufacturing method described below. Next, two opposing incisions are made in the insulating layer 20 of the insulated wire 1 using a cutter knife in parallel to the longitudinal direction of the insulated wire 1 so as to reach the conductor 11. Here, the distance between the two incisions is 1.0 mm.

Next, one end of the two incisions in the longitudinal direction is raised with tweezers, and this raised portion is set in a predetermined position on a tensile testing machine (5 kg load cell, manufactured by Shimadzu Corporation). The peel strength is then determined by pulling the peelable portion at a tensile speed of 100 mm/min. The peel strength (unit: N/mm) thus obtained can be evaluated as the adhesion between the conductor 11 and the insulating layer 20. As a result, it can be evaluated that the higher the peel strength value, the better the adhesion between the conductor 11 and the insulating layer 20.

[Method of manufacturing insulated wire]
Hereinafter, the method for producing an insulated wire according to this embodiment will be described with reference to FIG.
From the viewpoint of producing the insulated wire 1 according to the present embodiment with a high production yield, for example, the method for producing the insulated wire 1 according to the present embodiment is a method for producing the insulated wire 1 including a linear conductor 11 and an insulating layer 20 covering the conductor 11, the insulating layer 20 having a first insulating layer 21 in direct contact with the conductor 11 and one or more upper insulating layers 22 disposed on the first insulating layer 21. The method for producing the insulated wire 1 includes a step of preparing the conductor 11 and an insulating varnish (first step), a step of covering the conductor 11 with the first insulating layer 21 (second step), and a step of stacking the upper insulating layer 22 on the first insulating layer 21 (third step).

The coating process (second process) includes a process of applying an insulating varnish to the conductor 11 (process A), a process of adjusting the thickness of the insulating varnish applied to the conductor 11 (process B), and a process of baking the insulating varnish onto the conductor 11 (process C). The thickness adjustment process (process B) is performed by passing the conductor 11 to which the insulating varnish is applied through the opening of the coating die so that the distance between the inner wall of the opening and the conductor 11 is 0.040 mm or less. The manufacturing method of the insulated wire 1 having such characteristics can coat the conductor 11 with the first insulating layer 21 with reduced variation in layer thickness, thereby manufacturing the insulated wire 1 with improved adhesion between the conductor 11 and the insulating layer 20. Each process included in the manufacturing method of the insulated wire 1 according to this embodiment will be described in detail below.

<First step>
The first step is to prepare the conductor 11 and the insulating varnish (S11). The conductor 11 can be prepared, for example, by purchasing a commercially available product. Alternatively, the conductor 11 can be prepared by casting, elongating, drawing into a wire shape, and softening the metal described above as the material for the conductor 11. The insulating varnish can be prepared by diluting the resin described above as the material for the insulating layer 20 or a resin precursor thereof with a solvent. The resin solids concentration in the insulating varnish can be a conventional concentration known for the purpose of manufacturing this type of insulated wire.
The lower limit of the resin solid content in the insulating varnish may be 15% by mass. If the resin solid content is less than 15% by mass, the thickness of each layer after baking may become thin, which may result in reduced productivity.
The upper limit of the resin solid content concentration in the insulating varnish may be 50% by mass. If the resin solid content concentration exceeds 50% by mass, the applied insulating varnish becomes thick, and there is a risk of foaming of the coating during baking.
In addition, when the insulating varnish contains a resin precursor, the resin solids concentration means the concentration of the resin precursor.

Here, the insulating varnish may contain a curing agent in addition to the above-mentioned solvent, resin or its resin precursor, and may further contain fillers, various additives, etc.

As the solvent, known organic solvents can be used. Specifically, polar organic solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, tetramethylurea, hexaethylphosphoric triamide, and γ-butyrolactone; ketone-based organic solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; ester-based organic solvents such as methyl acetate, ethyl acetate, butyl acetate, and diethyl oxalate; ether-based organic solvents such as diethyl ether, ethylene glycol dimethyl ether, diethylene glycol monomethyl ether, ethylene glycol monobutyl ether (butyl cellosolve), diethylene glycol dimethyl ether, and tetrahydrofuran; hydrocarbon-based organic solvents such as hexane, heptane, benzene, toluene, and xylene; halogen-based organic solvents such as dichloromethane and chlorobenzene; phenol-based organic solvents such as cresol and chlorophenol; and amine-based organic solvents such as pyridine. These organic solvents can be used alone or in combination of two or more.

As the curing agent, one that has the function of curing the resin in step B described below or the function of promoting polymerization of the resin precursor can be used. Specific examples include alicyclic acid anhydrides such as methyltetrahydrophthalic anhydride, aliphatic acid anhydrides, aromatic acid anhydrides, imidazole, triethylamine, titanium compounds, isocyanate compounds, blocked isocyanates, urea, melamine compounds, and acetylene derivatives. These curing agents are appropriately selected depending on the type of resin or resin precursor in the insulating varnish.

Examples of the titanium compounds include tetrapropyl titanate, tetraisopropyl titanate, tetramethyl titanate, tetrabutyl titanate, and tetrahexyl titanate. Examples of the isocyanate compounds include aromatic diisocyanates such as tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), p-phenylene diisocyanate, and naphthalene diisocyanate; aliphatic diisocyanates having 3 to 12 carbon atoms such as hexamethylene diisocyanate (HDI), 2,2,4-trimethylhexane diisocyanate, and lysine diisocyanate; 1,4-cyclohexane diisocyanate (CDI), isophorone diisocyanate (IPDI), 4,4'-dicyclohexylmethane diisocyanate (hydrogenated MDI), and methyl diisocyanate. Examples of the isocyanate include alicyclic isocyanates having 5 to 18 carbon atoms, such as tetramethylcyclohexane diisocyanate, isopropylidenedicyclohexyl-4,4'-diisocyanate, 1,3-diisocyanatomethylcyclohexane (hydrogenated XDI), hydrogenated TDI, 2,5-bis(isocyanatomethyl)-bicyclo[2,2,1]heptane, and 2,6-bis(isocyanatomethyl)-bicyclo[2,2,1]heptane; aliphatic diisocyanates having an aromatic ring, such as xylylene diisocyanate (XDI) and tetramethylxylylene diisocyanate (TMXDI); and modified products thereof.

Examples of the blocked isocyanate include diphenylmethane-4,4'-diisocyanate (MDI), diphenylmethane-3,3'-diisocyanate, diphenylmethane-3,4'-diisocyanate, diphenylether-4,4'-diisocyanate, benzophenone-4,4'-diisocyanate, diphenylsulfone-4,4'-diisocyanate, tolylene-2,4-diisocyanate, tolylene-2,6-diisocyanate, naphthylene-1,5-diisocyanate, m-xylylene diisocyanate, p-xylylene diisocyanate, etc. Examples of the melamine compound include methylated melamine, butylated melamine, methylolated melamine, butyrolated melamine, etc. Examples of the acetylene derivative include ethynylaniline, ethynylphthalic anhydride, etc.

<Second process>
The second step is a step of coating the conductor 11 with the first insulating layer 21 (S12). The second step includes a step of applying an insulating varnish to the conductor 11 (step A), a step of adjusting the thickness of the insulating varnish applied to the conductor 11 (step B), and a step of baking the insulating varnish onto the conductor 11 (step C).

(Process A)
Step A is a step of applying the insulating varnish prepared in step 1 to the conductor 11 .

(B process)
Step B is a step of adjusting the thickness of the insulating varnish applied to the conductor 11. Furthermore, step B is performed by passing the conductor 11 coated with the insulating varnish through an opening of a coating die so that the distance between the inner wall of the opening and the conductor 11 is 0.040 mm or less.
That is, in step B, a coating die having an opening is used to adjust the thickness of the insulating varnish applied to the conductor 11 .

(C process)
Step C is a step of baking the insulating varnish onto the conductor 11. In step C, the first insulating layer 21 is formed by baking to be in direct contact with the conductor 11. Specifically, the conductor 11 to which the insulating varnish has been applied through steps A and B is placed in a baking furnace, and the insulating varnish is baked onto the conductor 11. This causes the solvent in the insulating varnish to gasify and the resin to solidify, thereby forming the first insulating layer 21 in direct contact with the conductor 11. In this case, since the insulating varnish is applied to the conductor 11 with a uniform thickness through step A, the thickness of the first insulating layer 21 formed in direct contact with the conductor 11 is also uniform, thereby making it possible to suppress variations in the layer thickness.

The baking temperature and time of the insulating varnish in the baking furnace can be appropriately selected according to the type of resin in the insulating varnish from among the temperature and time conditions known for the purpose of producing this type of insulated electric wire.

<3rd process>
The third step is a step of laminating the upper insulating layer 22 on the first insulating layer 21 (S13). In the third step, the application of the insulating varnish and the baking of the insulating varnish are repeated until the insulating layer 20 reaches a predetermined thickness, thereby laminating one or more upper insulating layers 22 on the first insulating layer 21. The method of applying and baking the insulating varnish can be a conventionally known method. Furthermore, by applying and baking the insulating varnish in accordance with the above-mentioned steps A and B, it is possible to laminate the required number of upper insulating layers 22 on the first insulating layer 21.

In this disclosure, an insulating layer obtained by applying an insulating varnish once and baking the insulating varnish is referred to as a "single-layer" insulating layer, and an insulating layer obtained by applying an insulating varnish multiple times and baking the insulating varnish is referred to as a "multiple-layer" insulating layer.
In the present disclosure, an insulating layer obtained by applying an insulating varnish once and baking it once is referred to as a "single-layer" insulating layer, whereas an insulating layer obtained by repeatedly applying an insulating varnish once and baking it once multiple times is referred to as a "multiple-layer" insulating layer.

<Action and effect>
As described above, it is possible to manufacture an insulated wire 1 including a linear conductor 11 and an insulating layer 20 covering the conductor 11, the insulating layer 20 having a first insulating layer 21 in direct contact with the conductor 11 and one or more upper insulating layers 22 disposed on the first insulating layer 21. In the insulated wire 1 manufactured by the above-described manufacturing method, variation in the thickness of the first insulating layer 21 is suppressed.

In the insulated wire 1, the first insulating layer 21 has a first coating portion, a second coating portion, a third coating portion, and a fourth coating portion as portions that cover two pairs of opposite surfaces of the conductor 11. The first insulating layer 21 has a first opposite surface of the first coating portion and the second coating portion, and a second opposite surface of the third coating portion and the fourth coating portion as portions that cover two pairs of opposite surfaces of the conductor. In a cross section perpendicular to the longitudinal direction of the insulated wire 1, when the layer thickness of the first coating portion is represented by Ta, the layer thickness of the second coating portion is represented by ta, the layer thickness of the third coating portion is represented by Tb, and the layer thickness of the fourth coating portion is represented by tb, the ratios represented by Ta/ta and Tb/tb are all 1.6 or less. This makes it possible to provide an insulated wire 1 with improved adhesion between the conductor 11 and the insulating layer 20.

The present disclosure is explained in more detail below with reference to examples, but the present disclosure is not limited to these.

[Measurement and evaluation method]
First, the measurement and evaluation methods used in the present examples will be described.

<Measurement of thickness (Ta, ta, Tb, tb) of first insulating layer>
The thicknesses of the first insulating layer in the first coating portion, second coating portion, third coating portion and fourth coating portion were measured in accordance with the method for measuring the thickness (Ta, ta, Tb, tb) of the first insulating layer described above, thereby determining the values of Ta and ta, and Tb and tb (units: μm).

<Measurement and evaluation of adhesion between conductor and insulating layer>
The adhesion between the conductor and the insulating layer was measured according to the above-mentioned method for measuring the adhesion between the conductor and the insulating layer, and the adhesion was then evaluated based on the following criteria.
A: The peel strength value is 1.0 N/mm or more.
B: The peel strength value is 0.5 N/mm or more and less than 1.0 N/mm.
C: The peel strength value is less than 0.5 N/mm.

<Measurement and Evaluation of Variation in Thickness of Insulation Layer>
First, each sample (insulated wire) described later was cut at 50 cm intervals in the longitudinal direction along a plane perpendicular to the longitudinal direction to obtain 30 cross sections. Four points (one point each on the upper, lower, left and right sides) were selected at equal intervals on the outer peripheral surface of the conductor appearing in each cross section, and the thickness of the insulating layer at the four points and its average thickness (4 points x 30 cross sections = average thickness of 120 points) were obtained. Next, the average thickness was substituted into the following formula to obtain the variation rate of the thickness of the insulating layer. In the following formula, σ indicates standard deviation. In the following formula, even if the average thickness is about the same, the larger the deviation (4σ) value, the larger the variation in the thickness.
Variation rate (%)=(4σ/average film thickness)×100.

Next, the variation rate of the thickness of the insulating layer of each sample obtained based on the above formula was evaluated based on the following criteria: If the variation rate exceeds 20%, it is considered that the uniformity of the thickness of the insulating layer is low and the adhesive strength between the conductor and the insulating layer is insufficient.
OK: The variation rate of the insulating layer is 20% or less.
NG: The variation rate of the insulating layer exceeds 20%.

[Manufacture of insulated wire]
<Sample 1>
An insulated electric wire according to the present disclosure was produced as a prototype by manufacturing according to the following procedure.

(1st step)
First, an insulating varnish was prepared by diluting a polyamic acid (polyamide precursor) with a weight average molecular weight of 37,500 with N-methyl-2-pyrrolidone (solvent). In the insulating varnish, the content of polyamic acid in the solvent was the same as in the conventional method. Furthermore, a linear conductor 11 was produced by casting, stretching, wire drawing, and softening copper, so that the cross-sectional shape that appears when cut along a plane perpendicular to the longitudinal direction has a rectangular shape (cross-sectional area: 5 ^mm2 ) as shown in Figure 2.

(Second process)
Next, the conductor 11 was immersed in the insulating varnish to apply the insulating varnish to the conductor 11 (step A), and the conductor 11 coated with the insulating varnish was passed through the opening of a coating die having a shape similar to the cross-sectional shape of the conductor 11 (step B). At this time, the maximum distance between the conductor 11 and the inner wall of the opening of the coating die was 0.027 mm. Furthermore, the conductor coated with the insulating varnish by passing through steps A and B was baked in a baking furnace (step C). The baking temperature of the insulating varnish in the baking furnace was 450° C., and the baking time was 30 seconds. Thus, a first insulating layer 21 in direct contact with the conductor 11 was formed.

(3rd step)
Next, the above-mentioned application of the insulating varnish and baking of the insulating varnish were repeated on the first insulating layer 21, thereby laminating the upper insulating layer 22 on the first insulating layer 21. Specifically, the insulating varnish was applied on the first insulating layer 21, and the first insulating layer 22 was passed through an opening of a coating die having a shape similar to the cross-sectional shape of the conductor 11, thereby forming a first layer of the upper insulating layer 22 on the first insulating layer 21. Next, the insulating varnish was applied on the first layer of the upper insulating layer 22, and the above-mentioned baking treatment was performed to form a second layer of the upper insulating layer 22, and this operation was repeated several times. As a result, the insulating layer 20 having a total of 25 layers, including the first insulating layer 21 and the upper insulating layer 22, was formed on the conductor 11, thereby obtaining the insulated wire 1.

<Samples 2 to 4>
An insulated wire was produced in the same manner as Sample 1, except that the maximum distance between the conductor and the inner wall of the opening of the coating die when the conductor passed through the opening of the coating die was as shown in Table 1.

[Evaluation of insulated wire]
For the insulated wires of Samples 1 to 4, the ratios Ta/ta and Tb/tb calculated from the thicknesses (Ta, ta, Tb, tb) of the first insulating layer 21, the adhesion between the conductor and the insulating layer, and the percentage of variation in the thickness of the insulating layer 20 were determined. The results are shown in Table 1. Table 1 also shows the maximum distance between the conductor and the inner wall of the opening of the coating die when the conductor was passed through the opening of the coating die in step A of the second process. Samples 1 to 3 are insulated wires of the examples, and Sample 4 is an insulated wire of the comparative example.

<Consideration>
In samples 1 to 3, the ratios Ta/ta and Tb/tb were all 1.6 or less. In this case, samples 1 to 3 were superior in adhesion between the conductor and the insulating layer to sample 4, in which either the ratio Ta/ta or Tb/tb exceeded 1.6. All samples 1 to 4 were rated OK (20% or less) in terms of the variation in thickness of the insulating layer.

The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is indicated by the claims, not by the embodiments and examples described above, and is intended to include the meaning equivalent to the claims and all modifications within the scope.

REFERENCE SIGNS LIST 1 insulated wire 11 conductor 20 insulating layer 21 first insulating layer 22 upper insulating layer Ta thickness of first covering portion ta thickness of second covering portion Tb thickness of third covering portion tb thickness of fourth covering portion

Claims (5)

An insulated wire including: a linear conductor having a first surface, a second surface opposite to the first surface, a third surface, and a fourth surface opposite to the third surface; and an insulating layer covering an outer peripheral surface of the conductor,
the insulating layer includes a first insulating layer directly contacting the outer circumferential surface and one or more upper insulating layers disposed on the first insulating layer;
the first insulating layer has a first covering portion covering the first surface, a second covering portion covering the second surface, a third covering portion covering the third surface, and a fourth covering portion covering the fourth surface,
In a cross section perpendicular to a longitudinal direction of the insulated wire, when a thickness of the first covering portion is represented by Ta, a thickness of the second covering portion is represented by ta, a thickness of the third covering portion is represented by Tb, and a thickness of the fourth covering portion is represented by tb, the ratios Ta/ta and Tb/tb are all 1.6 or less and satisfy the relationships Ta≧ta and Tb≧tb,
The insulated wire , wherein the first insulating layer and the upper insulating layer are formed from the same type of resin . The insulated wire according to claim 1, wherein either one of the ratios Ta/ta and Tb/tb is 1.4 or less. The insulated wire according to claim 1, wherein the ratios Ta/ta and Tb/tb are both 1.4 or less. The insulated wire according to any one of claims 1 to 3, wherein the cross-sectional shape of the conductor in the cross section is rectangular. a linear conductor having a first surface, a second surface opposite to the first surface, a third surface, and a fourth surface opposite to the third surface; and an insulating layer covering an outer circumferential surface of the conductor, the insulating layer having a first insulating layer directly in contact with the outer circumferential surface and one or more upper insulating layers disposed on the first insulating layer;
the first insulating layer has a first covering portion covering the first surface, a second covering portion covering the second surface, a third covering portion covering the third surface, and a fourth covering portion covering the fourth surface,
a thickness of the first covering portion is represented by Ta, a thickness of the second covering portion is represented by ta, a thickness of the third covering portion is represented by Tb, and a thickness of the fourth covering portion is represented by tb in a cross section perpendicular to the longitudinal direction, and ratios of Ta/ta and Tb/tb are all 1.6 or less and satisfy relationships Ta≧ta and Tb≧tb ,
The method for producing the insulated wire comprises the steps of:
providing the conductor and an insulating varnish;
coating the outer circumferential surface with the first insulating layer;
laminating the upper insulating layer on the first insulating layer;
The coating step includes:
applying the insulating varnish to the outer peripheral surface;
and baking the insulating varnish onto the conductor.
a coating step of coating the conductor with the insulating varnish through an opening of a coating die such that a distance between an inner wall of the opening and the outer circumferential surface of the conductor is 0.040 mm or less.

Images