WO2018180080A1 - Insulated electric cable - Google Patents

Abstract

An insulated electric cable according to one embodiment of this invention is an electric cable comprising a linear conductor and an insulating layer which is coated on the outer peripheral surface of the conductor, wherein the insulating layer is equipped with an inner porous layer having a plurality of pores, and an outer porous layer which is positioned on the outside of the inner porous layer and which has a plurality of pores. In the insulating layer, the independent porosity of the pores is at least 80% by volume, the porosity of the inner porous layer does not exceed 10% by volume, and the porosity of the outer porous layer falls within the range of 25% by volume to 50% by volume (inclusive).

Description

Insulated wire

The present invention relates to an insulated wire.
This application claims priority based on Japanese Patent Application No. 2017-071395 filed on Mar. 31, 2017, and incorporates all the content described in the above Japanese application.

In an electric device having a high applied voltage, such as a motor used at a high voltage, a high voltage is applied to an insulated wire constituting the electric device, and partial discharge (corona discharge) easily occurs on the surface of the insulating layer. When a local temperature rise, ozone generation, ion generation, or the like is caused by the generation of corona discharge, dielectric breakdown occurs at an early stage, and the life of the insulated wire and thus the electrical equipment is shortened. For this reason, the insulated wire used for the electric equipment with a high applied voltage is also required to improve the corona discharge starting voltage in addition to excellent insulation and mechanical strength.

An effective way to increase the corona discharge starting voltage is to reduce the dielectric constant of the insulating layer. In order to realize a low dielectric constant of the insulating coating, a heat-cured film (insulating coating) with an insulating varnish containing a coating film constituent resin and a thermally decomposable resin that decomposes at a temperature lower than the baking temperature of the coating film constituent resin. There has been proposed an insulated wire that forms a wire (see JP 2012-224714 A). In this insulated wire, pores are formed in the thermosetting film by utilizing the fact that the thermally decomposable resin is thermally decomposed during baking of the coating film constituting resin and the portions become pores. Low dielectric constant of the film is realized.

In addition, an insulated wire provided with such an insulating layer containing pores has a reduced mechanical strength in the thickness direction of the insulating layer. Therefore, in order to achieve both low dielectric constant and mechanical strength, the insulating layer has a thickness. There has been proposed an insulated wire that is composed of three or more pore layers divided in the direction and in which the porosity of these three or more pore layers changes in a stepwise manner (see Japanese Patent Application Laid-Open No. 2016-91865).

JP 2012-224714 A JP 2016-91865 A

An insulated wire according to an aspect of the present invention is an insulated wire including a linear conductor and an insulating layer coated on an outer peripheral surface of the conductor, and the insulating layer includes an inner pore layer having a plurality of pores. And an outer pore layer having a plurality of pores disposed on the outer side of the inner pore layer, and in the insulating layer, the independent porosity in the pores is 80% by volume or more, and the inner pore layer The porosity is 1% by volume or more and 10% by volume or less, and the porosity of the outer pore layer is 25% by volume or more and 50% by volume or less.

It is a typical sectional view of an insulated wire concerning a first embodiment of the present invention. It is a typical sectional view of an insulated wire concerning a second embodiment of the present invention. It is typical sectional drawing of the hollow formation particle contained in the varnish used for formation of the insulated wire which concerns on embodiment of this invention. It is a schematic diagram for demonstrating the measuring method of the dielectric constant in an Example.

[Problems to be solved by the present disclosure]
According to the insulated wires described in Patent Document 1 and Patent Document 2, it is possible to further increase the porosity of the insulating layer in order to promote the reduction of the dielectric constant of the insulating layer. However, when the porosity is increased, the mechanical strength is lowered, and there is a disadvantage that the insulation, particularly the dielectric breakdown strength after long-time heating is lowered.

Therefore, an object is to provide an insulated wire excellent in insulation and mechanical strength.

[Effects of the present disclosure]
The insulated wire of the present disclosure is excellent in insulation and mechanical strength.

[Description of Embodiment of the Present Invention]
(1) The insulated wire which concerns on 1 aspect of this invention is an insulated wire provided with a linear conductor and the insulating layer coat | covered on the outer peripheral surface of the said conductor, Comprising: The said insulating layer has several pores. An inner pore layer and an outer pore layer disposed outside the inner pore layer and having a plurality of pores, wherein the insulating layer has an independent porosity of 80% by volume or more in the pores, The porosity of the pore layer is 1% by volume or more and 10% by volume or less, and the porosity of the outer pore layer is 25% by volume or more and 50% by volume or less.

In the insulated wire, since the insulating layer includes pores, and the independent porosity in the pores in the insulating layer is equal to or higher than the above value, the dielectric breakdown voltage is maintained even after heating for a long time due to small variation in pore size. Can be increased, and the insulation is excellent. In addition, the insulated wire includes an inner pore layer and an outer pore layer, and by making each porosity within the above range, the mechanical strength suppressing action can be reduced, and the mechanical strength of the entire insulating layer can be reduced. Excellent. Here, “independent porosity” refers to a value obtained by a measurement method described later. The “porosity” means a percentage of the volume of the pores with respect to the volume including the pores of each layer constituting the insulating layer, and the density ρ1 of the material of each layer is added to the apparent volume V1 calculated from the outer shape of each layer. This is a value obtained from the equation (W1−W2) × 100 / W1 from the mass W1 when there is no pore obtained by multiplication and the actual mass W2 of each layer.

(2) The average thickness of the inner pore layer is preferably 3 μm or more and 15 μm or less, and the average thickness of the outer pore layer is preferably 80 μm or more and 160 μm or less. By setting the average thickness of each layer within the above range, it is possible to reliably insulate the conductors and to suppress a decrease in volumetric efficiency of the coil when forming the coil or the like.

(3) The insulating layer may be provided with another pore layer having a plurality of pores outside the outer pore layer, and the porosity of the other pore layer is 1% by volume or more and 10% by volume or less. Preferably, the average thickness of the other pore layer is preferably 3 μm or more and 10 μm or less. By providing another pore layer having the above configuration outside the outer pore layer, the durability of the insulated wire can be improved while maintaining the mechanical strength of the entire insulation layer.

(4) It is preferable that an outer shell is provided at the periphery of the plurality of pores, and the outer shell is derived from a shell of hollow-forming particles having a core-shell structure. The pores of the insulating layer are formed by the thermal decomposition of the core of the hollow-forming particles having a core-shell structure, and the shells are present as outer shells around the pores, so that the pores formed vary in size and shape. Since it becomes smaller and the independent porosity is improved, the insulation and mechanical strength are further improved. The core-shell structure refers to a structure in which the material forming the core of the particle is different from the material of the shell surrounding the core.

(5) The main component of the outer shell is preferably silicone. If the main component of the outer shell is silicone, it is easy to impart elasticity to the outer shell and improve insulation and heat resistance. The “main component” is a component having the largest content, for example, a component contained in an amount of 50% by mass or more.

(6) The plurality of pores are flat spheres, and in a cross section including a minor axis and a major axis of the plurality of pores, an average ratio of a minor axis length to a major axis is preferably 0.95 or less. The pores are flat spheres, and the average ratio of the length of the minor axis to the major axis is 0.95 or less in the cross section including the minor axis and the major axis of the pores. It becomes difficult and the independent porosity in an insulating layer can be made high. The “flat sphere” refers to a sphere having a minor axis smaller than the major axis when the maximum diagonal length passing through the center of gravity is the major axis and the minimum diagonal length passing through the center of gravity is the minor axis.

(7) A primer layer may be provided between the conductor and the insulating layer. By forming a primer layer between the conductor and the insulating layer, the adhesion between the conductor and the insulating layer is improved. As a result, the flexibility, wear resistance, scratch resistance and workability of the insulated wire are improved. The characteristics such as can be effectively improved.

[Details of the embodiment of the present invention]
Hereinafter, an insulated wire and a method for manufacturing an insulated wire according to an embodiment of the present invention will be described with reference to the drawings.

[Insulated wire]
[First embodiment]
An insulated wire 1 in FIG. 1 includes a linear conductor 2 and an insulating layer 3 that covers the outer peripheral surface of the conductor 2. The insulating layer 3 includes an inner pore layer 3a and an outer pore layer 3b disposed outside the inner pore layer 3a. The inner pore layer 3a and the outer pore layer 3b each have a plurality of pores 4, and the independent porosity in the pores 4 in the insulating layer 3 is 80% by volume or more.

<Conductor>
The conductor 2 is, for example, a square wire having a square cross section, but may be a round wire having a circular cross section or a stranded wire obtained by twisting a plurality of strands.

The material of the conductor 2 is preferably a metal having high electrical conductivity and high mechanical strength. Examples of such a metal include copper, copper alloy, aluminum, aluminum alloy, nickel, silver, iron, steel, and stainless steel. The conductor 2 is a material in which these metals are formed in a linear shape, or a multilayer structure in which such a linear material is coated with another metal, such as a nickel-coated copper wire, a silver-coated copper wire, or a copper-coated aluminum. Wire, copper-coated steel wire, etc. can be used.

The lower limit of the average cross-sectional area of the conductor 2, preferably 0.01 mm ^2, 0.1 mm ² is more preferable. The upper limit of the average cross-sectional area of the conductor 2 is preferably 20 mm ^2, more preferably 5 mm ² and more preferably 10 mm ^2. When the average cross-sectional area of the conductor 2 is less than the lower limit, the volume of the insulating layer 3 with respect to the conductor 2 is increased, and the volume efficiency of a coil or the like formed using the insulated wire 1 may be reduced. When the average cross-sectional area of the conductor 2 exceeds the above upper limit, the insulating layer 3 must be formed thick in order to sufficiently reduce the dielectric constant, and the insulated wire 1 may be unnecessarily increased in diameter.

<Insulating layer>
As shown in FIG. 1, the insulating layer 3 includes an inner pore layer 3a and an outer pore layer 3b.

The inner pore layer 3a and the outer pore layer 3b each include a plurality of pores 4. In each of the inner pore layer 3a and the outer pore layer 3b, the plurality of pores 4 are distributed substantially uniformly.

In the case of a so-called square line having a rectangular cross section of the conductor, it is necessary to increase the average thickness of the insulating layer 3. The lower limit of the average thickness of the inner pore layer 3a is preferably 3 μm and more preferably 5 μm. The upper limit of the average thickness of the inner pore layer 3a is preferably 15 μm, more preferably 10 μm, and even more preferably 8 μm. In the case of a round wire having a circular cross section of the conductor or a stranded wire obtained by twisting a plurality of strands, the average thickness of the insulating layer 3 can be reduced. In this case, the lower limit of the average thickness of the inner pore layer 3a is preferably 2 μm and more preferably 5 μm. The upper limit of the average thickness of the inner pore layer 3a is preferably 15 μm, more preferably 10 μm, and even more preferably 8 μm. When the average thickness of the inner pore layer 3a is less than the lower limit, the inner pore layer 3a having a large effect of maintaining the mechanical strength becomes too thin, and the mechanical strength of the insulating layer 3 may not be maintained. When the average thickness of the inner pore layer 3a exceeds the above upper limit, the inner pore layer 3a having a small effect of lowering the dielectric constant becomes too thick, and the dielectric constant of the insulating layer 3 may not be sufficiently lowered.

In the case of a so-called square line having a rectangular cross section of the conductor, it is necessary to increase the average thickness of the insulating layer 3. The lower limit of the average thickness of the outer pore layer 3b is preferably 80 μm, and more preferably 100 μm. The upper limit of the average thickness of the outer pore layer 3b is preferably 160 μm, and more preferably 130 μm. In the case of a round wire having a circular cross section of the conductor or a stranded wire obtained by twisting a plurality of strands, the average thickness of the insulating layer 3 can be reduced. In this case, the lower limit of the average thickness of the outer pore layer 3b is preferably 10 μm, and more preferably 20 μm. The upper limit of the average thickness of the outer pore layer 3b is preferably 160 μm, and more preferably 130 μm. When the average thickness of the outer pore layer 3b is less than the above lower limit, the outer pore layer 3b having a large effect of contributing to the reduction of the dielectric constant becomes too thin, and the dielectric constant of the insulating layer 3 may not be sufficiently lowered. When the average thickness of the outer pore layer 3b exceeds the above upper limit, the outer pore layer 3b having a small effect of maintaining the mechanical strength becomes too thick, and the mechanical strength of the insulating layer 3 may not be maintained.

The average thickness of the insulating layer 3 varies depending on the shape of the conductor. In the case of a round wire having a circular cross section of the conductor or a stranded wire obtained by twisting a plurality of strands, the average thickness of the insulating layer 3 can be reduced. In this case, the lower limit of the insulating layer 3 is preferably 15 μm, and more preferably 30 μm. As an upper limit of the average thickness of the insulating layer 3, 300 micrometers is preferable and 200 micrometers is more preferable. On the other hand, in the case of a so-called square line having a rectangular cross section of the conductor, it is necessary to increase the average thickness of the insulating layer 3. In this case, the lower limit of the insulating layer 3 is preferably 83 μm, and more preferably 100 μm. As an upper limit of the average thickness of the insulating layer 3, 400 micrometers is preferable and 300 micrometers is more preferable. When the average thickness of the insulating layer 3 is less than the above lower limit, the insulating layer 3 may be broken and the conductor 2 may be insufficiently insulated. When the average thickness of the insulating layer 3 exceeds the upper limit, the volume efficiency of a coil or the like formed using the insulated wire 1 may be lowered.

The resin as the main component of the resin composition forming the insulating layer 3 (the inner pore layer 3a and the outer pore layer 3b) is not particularly limited. For example, polyvinyl formal, thermosetting polyurethane, thermosetting acrylic, epoxy, thermosetting polyester , Thermosetting resins such as thermosetting polyester imide, thermosetting polyester amide imide, aromatic polyamide, thermosetting polyamide imide, thermosetting polyimide, etc., for example, polyether imide, polyether ether ketone, polyether sulfone, polyamide imide, A thermoplastic resin such as polyimide can be used. Here, the “main component” is a component having the largest content, for example, a component contained in an amount of 50% by mass or more. In addition, the resin of the main component of the resin composition which forms the inner pore layer 3a and the outer pore layer 3b may be the same type or different types.

The lower limit of the porosity of the inner pore layer 3a is 1% by volume, and more preferably 2% by volume. The upper limit of the porosity of the inner pore layer 3a is 10% by volume, and more preferably 8% by volume. When the porosity of the inner pore layer 3a is less than the lower limit, the dielectric constant of the insulating layer 3 is not sufficiently lowered, and the corona discharge starting voltage may not be sufficiently improved. When the porosity of the inner pore layer 3a exceeds the above upper limit, sufficient mechanical strength of the insulating layer 3 may not be ensured.

The lower limit of the porosity of the outer pore layer 3b is 25% by volume, preferably 30% by volume. The upper limit of the porosity of the outer pore layer 3b is 50% by volume, preferably 40% by volume, and more preferably 38% by volume. When the porosity of the outer pore layer 3b is less than the lower limit, the dielectric constant of the insulating layer 3 is not sufficiently lowered, and the corona discharge starting voltage may not be sufficiently improved. If the porosity of the outer pore layer 3b exceeds the above upper limit, sufficient mechanical strength of the insulating layer 3 may not be ensured.

The lower limit of the independent porosity in the pores 4 in the insulating layer 3 is 80% by volume, more preferably 85% by volume, and still more preferably 90% by volume. The upper limit of the independent porosity in the pores 4 is, for example, 100% by volume. When the independent porosity in the pores 4 is less than the above lower limit, the insulating properties and mechanical strength of the insulated wires tend to decrease. The independent porosity of the pores 4 included in the inner pore layer 3a and the independent porosity of the pores 4 included in the outer pore layer 3b may be different. In this case, in each of the inner pore layer 3a and the outer pore layer 3b, the independent porosity in the pores 4 is preferably within the above range.

The independent porosity in the pores 4 is determined by using a resin composition having insulating properties between adjacent pores when the cross section of the sample of each layer constituting the insulating layer 3 is observed with a scanning electron microscope (SEM). Therefore, it is the volume% with respect to the total pores of those not opening each other (independent pores). The independent porosity (volume%) can be calculated by binarization so as to distinguish the independent pores from the pores other than the independent pores in the SEM photograph of the cross section of the insulating layer.

The lower limit of the average diameter of the pores 4 is preferably 0.1 μm and more preferably 1 μm. The upper limit of the average diameter of the pores 4 is preferably 10 μm, and more preferably 8 μm. When the average diameter of the pores 4 is less than the above lower limit, the generation of corona discharge in the insulating layer 3 may not be sufficiently suppressed. When the average diameter of the pores 4 exceeds the upper limit, it is difficult to make the distribution of the pores 4 in each of the inner pore layer 3a and the outer pore layer 3b uniform, and the distribution of the dielectric constant may be easily biased. The average diameter of the pores 4 included in each of the inner pore layer 3a and the outer pore layer 3b may be different.
Here, the “average diameter of the pores” means a value obtained by calculating and averaging the diameters of true spheres corresponding to the volume of the pores of, for example, 30 pores 4 included in the insulating layer 3. The volume of the pores 4 can be obtained by observing the cross section of the insulating layer 3 with a scanning electron microscope. Further, the average diameter of the pores 4 can be changed depending on the kind of the material as the main component of the resin composition, the thickness of the insulating layer 3, the material of the hollow forming particles 5, the baking conditions, and the like.

The plurality of pores 4 are covered with an outer shell. The outer shell is constituted by a shell 7 which is hollowed by removing the core 6 of the hollow-forming particle 5 having the core-shell structure shown in FIG. That is, the outer shell is derived from the shell 7 of the hollow-forming particle 5 having a core-shell structure. In addition, at least a part of the plurality of outer shells has a defect.

The plurality of pores 4 are flat spheres. In addition, external force is likely to act in the direction perpendicular to the surface of the conductor 2, but if the minor axis of the pore 4 is oriented in the vertical direction, the pores are difficult to contact each other in the vertical direction. The rate can be improved. Therefore, the larger the proportion of the pores 4 whose minor axis is oriented in the direction perpendicular to the conductor 2 surface, the better. The lower limit of the ratio of the number of pores 4 whose minor axis is oriented in the direction perpendicular to the surface of the conductor 2 with respect to the total number of pores 4 is preferably 60%, more preferably 80%. If the ratio of the pores 4 whose minor axis is oriented in the direction perpendicular to the surface of the conductor 2 is less than the lower limit, the pores that contact each other between the pores may increase and the independent porosity may be lowered.
Here, “the short axis of the pores is oriented in the direction perpendicular to the conductor surface” means that the angle difference between the short axis of the pores and the direction perpendicular to the conductor surface is 20 degrees or less.

The lower limit of the ratio of the length of the minor axis to the major axis in the cross section including the minor axis and the major axis of the pore 4 is preferably 0.2, and more preferably 0.3. The upper limit of the average of the above ratio is preferably 0.95, and more preferably 0.9. If the average of the above ratios is less than the above lower limit, it is necessary to increase the amount of shrinkage in the thickness direction during baking of the varnish, which may reduce the flexibility of the insulated wire 1. When the average of the above ratios exceeds the upper limit, when the porosity is increased, the pores easily come into contact with each other in the thickness direction (perpendicular to the surface of the conductor 2) of the insulating layer 3 where external force is likely to act. Independent porosity may be lowered. The short diameter and long diameter of the pores 4 can be obtained by observing the cross section of the insulating layer 3 with a scanning electron microscope. In addition, the said ratio can be adjusted by changing the pressure added to the hollow formation particle 5 by the shrinkage | contraction at the time of baking of the resin composition contained in a varnish. The pressure applied to the hollow forming particles 5 can be changed depending on, for example, the type of the material that is the main component of the resin composition, the thickness of the insulating layer 3, the material of the hollow forming particles 5, the baking conditions, and the like.
Here, “the average of the ratio of the length of the minor axis to the major axis in the cross section including the minor axis and the major axis of the pores” means, for example, a section including the minor axis and the major axis of 30 pores 4 included in the insulating layer 3. The ratio of the length of the minor axis to the major axis is calculated and averaged.

The lower limit of the average major axis of the pores 4 is not particularly limited, but is preferably 0.1 μm, for example, and more preferably 1 μm. The upper limit of the average of the major axis is preferably 10 μm, and more preferably 8 μm. If the average of the major axis is less than the lower limit, the insulating layer 3 may not have a desired porosity. If the average of the major axis exceeds the upper limit, it is difficult to make the distribution of the pores 4 in the insulating layer 3 uniform, and there is a risk that the distribution of the dielectric constant tends to be biased.
Here, the “average of the major diameters of the pores” means a value obtained by averaging the major diameters of, for example, 30 pores 4 included in the insulating layer 3.

The plurality of outer shells present at the peripheral edges of the plurality of pores 4 have at least some defects. The pores 4 and the outer shell are derived from hollow forming particles 5 having a core 6 mainly composed of a thermally decomposable resin as shown in FIG. 3 and a shell 7 having a higher thermal decomposition temperature than that of the thermally decomposable resin. That is, when the varnish containing the hollow forming particles 5 is baked, the thermally decomposable resin that is the main component of the core 6 is gasified by thermal decomposition and scattered through the shell 7 to form the pores 4 and the outer shell. At this time, the passage of the thermally decomposable resin in the shell 7 exists in the outer shell as a defect. The shape of the defect varies depending on the material and shape of the shell 7, but cracks, cracks and holes are preferred from the viewpoint of enhancing the communication preventing effect of the outer shell of the pores.

Note that the insulating layer 3 may include an outer shell having no defect. Depending on the outflow conditions of the thermally decomposable resin of the core 6 to the outside of the shell 7, there is a case where no defect is formed in the shell 7 (outer shell). The insulating layer 3 may include pores 4 that are not covered by the outer shell.

[Insulated wire manufacturing method]
Next, the manufacturing method of the insulated wire 1 is demonstrated. The method of manufacturing the insulated wire 1 includes a hollow including a resin composition that forms the insulating layer 3, a core 6 mainly composed of a thermally decomposable resin, and a shell 7 having a thermal decomposition temperature higher than the thermal decomposition temperature of the pyrolytic resin. A step of diluting the forming particles 5 to prepare varnishes having different contents of the hollow forming particles 5 (varnish preparation step) and an inner pore layer 3a including the pores 4 by applying and baking the varnish on the outer peripheral surface of the conductor 2 Step of forming (inner pore layer forming step), and coating and baking on the outer peripheral surface of the conductor 2 in which the inner pore layer 3a of the varnish having a larger content of the hollow forming particles 5 than the varnish in which the inner pore layer 3a is formed is formed And a step of forming the outer pore layer 3b including the pores 4 (outer pore layer forming step).

<Varnish preparation process>
In the varnish preparation step, the resin composition forming the insulating layer 3 and the hollow forming particles 5 are diluted with a solvent to prepare a varnish. As the varnishes for forming the inner pore layer 3a and the outer pore layer 3b, a plurality of types of varnishes having different contents of the hollow-forming particles 5 are prepared. As shown in FIG. 1, since the porosity of the inner pore layer 3a and the outer pore layer 3b is different from each other, two kinds of varnishes for the inner side and the outer side having different contents of the hollow forming particles 5 are prepared here. The inner and outer varnishes may be the same or different as the resin composition for forming the insulating layer 3 diluted with a solvent.

(Resin composition)
The resin composition is a composition containing a main polymer, a diluent solvent, a curing agent, and the like. The main polymer is not particularly limited, but when a thermosetting resin is used, for example, a polyvinyl formal precursor, a thermosetting polyurethane precursor, a thermosetting acrylic resin precursor, an epoxy resin precursor, a phenoxy resin precursor, a thermosetting A polyester precursor, a thermosetting polyesterimide precursor, a thermosetting polyesteramideimide precursor, a thermosetting polyamideimide precursor, a polyimide precursor, or the like can be used. Further, when a thermoplastic resin is used as the main polymer, for example, polyetherimide, polyetheretherketone, polyethersulfone, polyamideimide, polyimide and the like can be used. Among these, a polyimide precursor and a polyimide are preferable in that the varnish can be easily applied and the strength and heat resistance of the insulating layer 3 can be easily improved.

As the diluting solvent, a known organic solvent conventionally used for insulating varnish can be used. Specifically, polar organic solvents such as N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-dimethylformamide, dimethyl sulfoxide, tetramethylurea, hexaethylphosphoric triamide, γ-butyrolactone and the like are used. First, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone; esters such as methyl acetate, ethyl acetate, butyl acetate, diethyl oxalate; diethyl ether, ethylene glycol dimethyl ether, diethylene glycol monomethyl ether, ethylene glycol monobutyl ether (butyl cellosolve) ), Ethers such as diethylene glycol dimethyl ether and tetrahydrofuran; hydrocarbons such as hexane, heptane, benzene, toluene and xylene Halogenated hydrocarbons such as dichloromethane and chlorobenzene; phenols such as cresol and chlorophenol; tertiary amines such as pyridine and the like. These organic solvents may be used alone or in combination of two or more. Used.

Further, the resin composition may contain a curing agent. Curing agents include titanium-based curing agents, isocyanate compounds, blocked isocyanates, urea and melamine compounds, amino resins, acetylene derivatives, alicyclic acid anhydrides such as methyltetrahydrophthalic anhydride, aliphatic acid anhydrides, and aromatics. An acid anhydride etc. are illustrated. These curing agents are appropriately selected according to the type of main polymer contained in the resin composition to be used. For example, in the case of polyamideimide, imidazole, triethylamine and the like are preferably used as the curing agent.

In addition, examples of the titanium-based curing agent include tetrapropyl titanate, tetraisopropyl titanate, tetramethyl titanate, tetrabutyl titanate, and tetrahexyl titanate. Isocyanate compounds include aromatic diisocyanates such as tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), p-phenylene diisocyanate, naphthalene diisocyanate; hexamethylene diisocyanate (HDI), 2,2,4-trimethylhexane diisocyanate, lysine C3-C12 aliphatic diisocyanates such as diisocyanates; 1,4-cyclohexane diisocyanate (CDI), isophorone diisocyanate (IPDI), 4,4′-dicyclohexylmethane diisocyanate (hydrogenated MDI), methylcyclohexane diisocyanate, isopropylidene dicyclohexyl -4,4'-diisocyanate, 1,3-diisocyanatomethylcyclohexane (hydrogenated XDI , Hydrogenated TDI, 2,5-bis (isocyanatomethyl) -bicyclo [2.2.1] heptane, 2,6-bis (isocyanatomethyl) -bicyclo [2.2.1] heptane, etc. Examples thereof include 5-18 alicyclic isocyanates; aliphatic diisocyanates having an aromatic ring such as xylylene diisocyanate (XDI) and tetramethylxylylene diisocyanate (TMXDI); 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, and 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 thereof include compounds in which a blocking agent such as dimethylpyrazole is added to an isocyanate group. Examples of the melamine compound include methylated melamine, butylated melamine, methylolated melamine, and butyrololized melamine. Examples of acetylene derivatives include ethynylaniline, ethynylphthalic anhydride, and the like.

(Hollow-forming particles)
As shown in FIG. 3, the hollow-forming particles 5 include a core 6 mainly composed of a thermally decomposable resin and a shell 7 having a higher thermal decomposition temperature than that of the thermally decomposable resin.

(core)
As the thermally decomposable resin used as the main component of the core 6, for example, resin particles that thermally decompose at a temperature lower than the baking temperature of the main polymer are used. The baking temperature of the main polymer is appropriately set according to the type of resin, but is usually about 200 ° C. or higher and 600 ° C. or lower. Accordingly, the lower limit of the thermal decomposition temperature of the thermally decomposable resin used for the core 6 of the hollow forming particles 5 is preferably 200 ° C., and the upper limit is preferably 400 ° C. Here, the thermal decomposition temperature means a temperature at which the temperature is increased from room temperature to 10 ° C./min in an air atmosphere and the mass reduction rate becomes 50%. The thermal decomposition temperature can be measured, for example, by measuring the thermogravimetry using a thermogravimetry-differential thermal analyzer (“TG / DTA” manufactured by SII Nanotechnology Inc.).

The heat-decomposable resin used for the core 6 of the hollow-forming particles 5 is not particularly limited. For example, one or both of polyethylene glycol and polypropylene glycol, or both ends or parts thereof are alkylated, (meth) acrylated or epoxidized. Compound; (meth) acrylic having an alkyl group having 1 to 6 carbon atoms such as poly (meth) acrylate methyl, poly (meth) ethyl acrylate, poly (meth) acrylate propyl, poly (meth) acrylate butyl, etc. Polymers of acid esters; urethane oligomers, urethane polymers, urethane (meth) acrylates, epoxy (meth) acrylates, polymers of modified (meth) acrylates such as ε-caprolactone (meth) acrylate; poly (meth) acrylic acid; these Cross-linked product: polystyrene, cross-linked polystyrene And the like. Among these, a polymer of (meth) acrylic acid ester having an alkyl group having 1 to 6 carbon atoms is preferable in that it is easily thermally decomposed at the baking temperature of the main polymer and easily forms pores 4 in the insulating layer 3. An example of such a polymer of (meth) acrylic acid ester is polymethyl methacrylate (PMMA).

The shape of the core 6 is preferably spherical. In order to make the shape of the core 6 spherical, for example, spherical heat-decomposable resin particles may be used as the core 6. When spherical heat-decomposable resin particles are used, the lower limit of the average particle diameter of the resin particles is not particularly limited, but is preferably 0.1 μm, more preferably 0.5 μm, and even more preferably 1 μm. The upper limit of the average particle diameter of the resin particles is preferably 15 μm, and more preferably 10 μm. If the average particle diameter of the resin particles is less than the above lower limit, it may be difficult to produce the hollow forming particles 5 having the resin particles as the core 6. When the average particle diameter of the resin particles exceeds the above upper limit, the hollow-forming particles 5 having the resin particles as the core 6 become too large, so that the distribution of the pores 4 in the insulating layer 3 is difficult to be uniform, and the dielectric constant distribution. There is a risk that bias is likely to occur. Here, the average particle diameter of the resin particles means a particle diameter showing the highest volume content in the particle size distribution measured with a laser diffraction particle size distribution measuring device.

As the main component of the shell 7, a material having a higher thermal decomposition temperature than the thermally decomposable resin is used. Further, as the main component of the shell 7, one having a low dielectric constant and high heat resistance is preferable. Examples of such a material used as the main component of the shell 7 include resins such as polystyrene, silicone, fluororesin, and polyimide. Among these, silicone is preferable in that elasticity is imparted to the shell 7 and insulation and heat resistance are easily improved. Here, the “fluororesin” is a fluorine atom or an organic group in which at least one hydrogen atom bonded to a carbon atom constituting the repeating unit of the polymer chain has a fluorine atom (hereinafter also referred to as “fluorine atom-containing group”). ). The fluorine atom-containing group is a group in which at least one hydrogen atom in a linear or branched organic group is substituted with a fluorine atom, and examples thereof include a fluoroalkyl group, a fluoroalkoxy group, and a fluoropolyether group. Can do. Note that the shell 7 may contain a metal as long as the insulating property is not impaired.

The main resin of the shell 7 may be the same as or different from the main polymer of the resin composition contained in the varnish. For example, even when the same resin as the main polymer of the resin composition is used as the main resin of the shell 7, the thermal decomposition temperature is higher than that of the thermally decomposable resin. Since the main component resin is difficult to thermally decompose, the independent porosity in the pores 4 can be increased. The insulated wire formed of such a varnish may not be able to confirm the presence of the outer shell of the pores 4 even when observed with an electron microscope. By using a resin different from the main polymer of the resin composition as the main component resin of the shell 7, the shell 7 can be made difficult to be integrated with the resin composition, and therefore the same type of resin as the main polymer of the resin composition is used. In comparison with, the independent porosity in the pores 4 is increased.

Although there is no restriction | limiting in particular as a minimum of the average thickness of the shell 7, For example, 0.01 micrometer is preferable and 0.02 micrometer is more preferable. The upper limit of the average thickness of the shell 7 is preferably 0.5 μm, and more preferably 0.4 μm. If the average thickness of the shell 7 is less than the above lower limit, the independent porosity in the pores 4 may be lowered. If the average thickness of the shell 7 exceeds the above upper limit, the volume of the pores 4 becomes too small, and the porosity of the insulating layer 3 may not be increased beyond a predetermined level. The shell 7 may be formed of one layer or a plurality of layers. When the shell 7 is formed of a plurality of layers, the average of the total thickness of the plurality of layers may be within the range of the thickness.
Here, the “average thickness of the shell” means, for example, a value obtained by averaging the thickness of the shell 7 for 30 hollow forming particles 5.

The upper limit of the CV value of the hollow forming particles 5 is preferably 30% and more preferably 20%. If the CV value of the hollow forming particles 5 exceeds the above upper limit, the insulating layer 3 includes a plurality of pores 4 having different sizes, so that the distribution of the dielectric constant is likely to be biased. In addition, although there is no restriction | limiting in particular as a minimum of the CV value of the hollow formation particle 5, For example, 1% is preferable. If the CV value of the hollow forming particles 5 is less than the lower limit, the cost of the hollow forming particles 5 may be too high. Here, the “CV value” means a variable defined in JIS-Z8825 (2013).

In addition, as shown in FIG. 3, the hollow forming particles 5 may have a configuration in which the core 6 is formed by one thermally decomposable resin particle, or the core 6 is formed by a plurality of thermally decomposable resin particles, It is good also as a structure which 7 resin coat | covers these some thermally decomposable resin particles.

Further, the surface of the hollow forming particle 5 may be smooth without irregularities as shown in FIG. 3, or irregularities may be formed.

Further, the lower limit of the resin solid content concentration of the varnish prepared by diluting with an organic solvent and dispersing the hollow-forming particles 5 is preferably 15% by mass, more preferably 20% by mass. As an upper limit of the resin solid content concentration of a varnish, 50 mass% is preferable and 30 mass% is more preferable. When the resin solid content concentration of the varnish is less than the above lower limit, the thickness that can be formed by a single varnish application is reduced, and therefore the number of repetitions of the varnish application step for forming the insulating layer 3 having a desired thickness is reduced. There is a risk that the time for the varnish application process will be increased. When the resin solid content concentration of the varnish exceeds the upper limit, the storage stability of the varnish may be deteriorated due to thickening of the varnish.

In addition to the hollow forming particles 5, a pore forming agent such as a thermally decomposable particle may be mixed with the varnish for forming pores. In addition, varnish may be prepared by combining diluting solvents having different boiling points for pore formation. The pores formed by the pore-forming agent and the pores formed by the combination of diluting solvents having different boiling points are difficult to communicate with the pores derived from the hollow-forming particles 5. Therefore, even when pores that are not covered with the outer shell are included, the presence of the pores covered with the outer shell can increase the independent porosity in the pores 4.

<Inner pore layer forming step>
In the inner pore layer forming step, the inner varnish prepared in the varnish preparation step is applied to the outer peripheral surface of the conductor 2 and then baked to form the inner pore layer 3a on the surface of the conductor 2. During baking, the thermally decomposable resin contained in the inner surface side varnish is thermally decomposed, and pores 4 are generated in the portion where the thermally decomposable resin exists in the inner pore layer 3a.

When the inner pore layer 3a having a desired thickness cannot be formed by a single application and baking of the inner varnish, the inner varnish is applied and baked until the inner pore layer 3a formed on the surface of the conductor 2 has a predetermined thickness. Repeat.

<Outside pore layer forming step>
In the outer pore layer forming step, after applying the outer varnish having a larger content of the thermally decomposable resin than the inner varnish prepared in the varnish preparation step to the outer peripheral surface of the conductor 2 in which the inner pore layer 3a is formed, By baking, the outer pore layer 3b is formed outside the inner pore layer 3a formed in the conductor 2. At the time of baking, the thermally decomposable resin contained in the outer varnish is thermally decomposed, and pores 4 are generated in portions where the thermally decomposable resin exists in the outer pore layer 3b.

When the outer pore layer 3b having a desired thickness cannot be formed by one application and baking of the outer varnish, the outer varnish is repeatedly applied and baked until the outer pore layer 3b has a predetermined thickness.

[advantage]
In the insulated wire 1, the insulating layer includes pores, and the independent porosity in the pores in the insulating layer 3 is equal to or higher than the above value. Therefore, the dielectric breakdown voltage may be increased due to small variation in pore size. And has excellent insulation. Moreover, the insulated wire 1 is provided with an inner pore layer and an outer pore layer, and by making each porosity within the above range, the mechanical strength suppressing action can be reduced, and the mechanical strength of the entire insulation layer can be reduced. Excellent.

[Second Embodiment]
An insulated wire 1 in FIG. 2 includes a linear conductor 2 and an insulating layer 3 that covers the outer peripheral surface of the conductor 2. The insulating layer 3 includes an inner pore layer 3a, an outer pore layer 3b disposed outside the inner pore layer 3a, and another pore layer 3c disposed outside the outer pore layer 3b. Each of the inner pore layer 3a, the outer pore layer 3b, and the other pore layer 3c has a plurality of pores 4. The independent porosity in the pores 4 in the insulating layer 3 is 80% by volume or more, more preferably 85% by volume or more, and still more preferably 90% by volume or more. The upper limit of the independent porosity in the pores 4 is, for example, 100% by volume.
The independent porosity in the pores 4 included in the other pore layer 3c may be different from the independent porosity of the pores 4 included in the inner pore layer 3a or the independent porosity of the pores 4 included in the outer pore layer 3b. . In this case, also in the other pore layers 3c, it is preferable that the independent porosity in the pores 4 is within the above range.

2 is different from the insulated wire 1 in FIG. 1 in the configuration of the insulating layer 3. Since the conductor 2, the inner pore layer 3a, and the outer pore layer 3b of the insulated wire 1 of FIG. 2 can be the same as the conductor 2, the inner pore layer 3a, and the outer pore layer 3b of the insulated wire 1 of FIG. Description is omitted.

The lower limit of the porosity of the other pore layer 3c is preferably 1% by volume, and more preferably 3% by volume. The upper limit of the porosity of the other pore layer 3c is preferably 10% by volume, more preferably 8% by volume. When the porosity of the other pore layer 3c is less than the lower limit, the dielectric constant of the insulating layer 3 is not sufficiently lowered, and the corona discharge starting voltage may not be sufficiently improved. When the porosity of the other pore layer 3c exceeds the above upper limit, there is a possibility that sufficient mechanical strength of the insulating layer 3 cannot be ensured.

The lower limit of the average thickness of the other pore layer 3c is preferably 3 μm, and more preferably 5 μm. The upper limit of the average thickness of the other pore layer 3c is preferably 10 μm, and more preferably 8 μm. When the average thickness of the other pore layer 3c is less than the above lower limit, the other pore layer 3c having a large effect of maintaining the mechanical strength becomes too thin, and the mechanical strength of the insulating layer 3 may not be maintained. When the average thickness of the other pore layer 3c exceeds the upper limit, the other pore layer 3c having a small effect of reducing the dielectric constant becomes too thick, and the dielectric constant of the insulating layer 3 may not be sufficiently lowered.

[Insulated wire manufacturing method]
Next, the manufacturing method of the insulated wire 1 of FIG. 2 is demonstrated. The insulated wire 1 of FIG. 2 can be manufactured by the method similar to the manufacturing method of the insulated wire 1 of 1st embodiment of FIG. 1, for example.

Specifically, it can be manufactured by performing the following other pore layer forming step after the outer pore layer forming step in the method of manufacturing the insulated wire 1 of the first embodiment.

<Other pore layer forming step>
In another pore layer forming step, another pore layer varnish having a smaller content of the thermally decomposable resin than the outer varnish prepared in the varnish preparation step is further applied to the outer peripheral surface of the conductor 2 on which the outer pore layer 3b is formed. After the application, the other pore layer 3c is formed outside the outer pore layer 3b formed in the conductor 2 by baking. At the time of baking, the thermally decomposable resin contained in the other varnish for the pore layer is thermally decomposed, and the pores 4 are generated in the portions where the thermally decomposable resin exists in the other pore layer 3c.

When another pore layer 3c having a desired thickness cannot be formed by one application and baking of another pore layer varnish, the other pore layer varnish is applied until the other pore layer 3c reaches a predetermined thickness. Repeat baking. By forming another pore layer 3c having a predetermined thickness, the insulated wire 1 can be obtained.

[Other Embodiments]
The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is not limited to the configuration of the embodiment described above, but is defined by the scope of the claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of the claims.

That is, in 1st and 2nd embodiment, although the insulating layer demonstrated the insulated wire comprised by the pore layer of 2 or 3, As an insulated wire comprised further, the insulating layer was comprised of 4 or more pore layers. Also good. By increasing the number of pore layers constituting the insulating layer, it becomes easier to finely adjust the dielectric constant and mechanical strength of the entire insulating layer. Moreover, it is good also as an insulated wire with which an insulating layer is comprised by the porous layer of one layer or two layers using the pore layer from which a porosity differs in thickness direction.

In the above embodiment, the production method for generating pores using a thermally decomposable resin has been described. However, instead of the thermally decomposable resin, a foaming agent or a thermally expandable microcapsule is mixed with the varnish, and the foaming agent or heat It is good also as a manufacturing method which forms pores by an expandable microcapsule. For example, in the above manufacturing method, a resin for forming an insulating layer diluted with a solvent is mixed with a thermally expandable microcapsule to prepare varnishes for each pore layer, and these varnishes are applied to the outer peripheral surface of a conductor and An insulating layer may be formed by baking. During baking, the thermally expandable microcapsules contained in the varnish expand or foam, and pores are formed by the thermally expandable microcapsules.

The heat-expandable microcapsule has a core material (including inclusion) made of a thermal expansion agent and an outer shell that wraps the core material. The thermal expansion agent of the heat-expandable microcapsules may be any one that expands or generates a gas by heating, and the principle thereof does not matter. As the thermal expansion agent of the thermally expandable microcapsule, for example, a low boiling point liquid, a chemical foaming agent, or a mixture thereof can be used.

As the low boiling point liquid, for example, alkanes such as butane, i-butane, n-pentane, i-pentane and neopentane, and freons such as trichlorofluoromethane are preferably used. As the chemical foaming agent, a material having thermal decomposability such as azobisisobutyronitrile that generates N ₂ gas by heating is preferably used.

The expansion start temperature of the thermal expansion agent of the thermally expandable microcapsule, that is, the boiling point of the low-boiling liquid or the thermal decomposition temperature of the chemical foaming agent is equal to or higher than the softening temperature of the outer shell of the thermally expandable microcapsule described later. More specifically, the lower limit of the expansion start temperature of the thermal expansion agent of the thermally expandable microcapsule is preferably 60 ° C, more preferably 70 ° C. The upper limit of the expansion start temperature of the thermal expansion agent of the thermally expandable microcapsule is preferably 200 ° C., and more preferably 150 ° C. When the expansion start temperature of the thermal expansion agent of the thermally expandable microcapsule is less than the lower limit, the thermally expandable microcapsule may expand unintentionally during manufacture, transportation or storage of the insulated wire. When the expansion start temperature of the thermal expansion agent of the thermally expandable microcapsule exceeds the above upper limit, the energy cost necessary for expanding the thermally expandable microcapsule may be excessive.

The outer shell of the thermally expandable microcapsule is formed of a stretchable material that can expand without breaking when the thermal expansion agent expands to form a microballoon containing the generated gas. As a material for forming the outer shell of the thermally expandable microcapsule, a resin composition mainly composed of a polymer such as a thermoplastic resin is usually used.

The thermoplastic resin used as the main component of the outer shell of the thermally expandable microcapsule is formed from monomers such as vinyl chloride, vinylidene chloride, acrylonitrile, acrylic acid, methacrylic acid, acrylate, methacrylate, styrene, etc. Polymers formed from two or more types of monomers are preferably used. An example of a preferred thermoplastic resin is a vinylidene chloride-acrylonitrile copolymer. In this case, the expansion start temperature of the thermal expansion agent is 80 ° C. or higher and 150 ° C. or lower.

In the above embodiment, the structure in which the pores included in the insulating layer are formed by the thermal decomposition of the thermally decomposable resin has been described. However, for example, the pores may be formed by a hollow filler. When the pores are formed with a hollow filler, an insulated wire can be produced by, for example, kneading a resin composition that forms an insulating layer and a hollow filler, and covering the conductor with the kneaded product by extrusion molding.

When the pores are formed with the hollow filler, the hollow portion inside the hollow filler becomes the pores included in the insulating layer. Examples of the hollow filler include shirasu balloons, glass balloons, ceramic balloons, and organic resin balloons. When flexibility is required for the insulated wire, an organic resin balloon is preferable among them. In the case of an insulated wire in which mechanical strength is important, a glass balloon is preferable because it is easily available and is not easily damaged.

In the above-described embodiment, the structure in which the pores included in the insulating layer are formed by thermal decomposition of the thermally decomposable resin has been described. As an example of using the phase separation method, a thermoplastic resin is used as the resin for forming the insulating layer, and it is homogeneously mixed with a solvent and applied to the outer peripheral surface of the conductor in a heated and melted state. Then, the resin and the solvent are phase-separated by immersion in an insoluble liquid such as water or cooling in air, and the pores are formed by extracting and removing the solvent with another volatile solvent.

Further, for example, in an insulated wire, a further layer such as an inner intervening layer may be provided between the conductor and the insulating layer. The inner intervening layer is a layer provided for enhancing the adhesion between the layers or reinforcing the lower dielectric constant of the insulating layer, and can be formed of, for example, a known resin composition.

When providing the inner intervening layer between the conductor and the insulating layer, the resin composition forming the inner intervening layer includes, for example, one or plural kinds of resins among polyimide, polyamideimide, polyesterimide, polyester, and phenoxy resin. Good. In addition, the resin composition forming the inner intervening layer may contain an additive such as an adhesion improver. By forming an inner intervening layer between the conductor and the insulating layer with such a resin composition, it is possible to improve the adhesion between the conductor and the insulating layer. Properties such as flexibility, wear resistance, scratch resistance, and workability can be effectively enhanced.

Further, the resin composition forming the inner intervening layer may contain other resins such as epoxy resin, phenoxy resin, melamine resin and the like together with the above resin. Moreover, you may use a commercially available liquid composition (insulation varnish) as each resin contained in the resin composition which forms an inner intervening layer.

Further, as the resin composition forming the inner intervening layer, the same kind of resin as the main component of the resin composition of the insulating layer described above may be used as the main component. Furthermore, the inner intervening layer may include a plurality of pores. When the inner intervening layer includes a plurality of pores, the inner intervening layer can also contribute to a decrease in the dielectric constant of the insulating layer. However, in this case, the porosity of the inner intervening layer is more preferably smaller than the porosity of the insulating layer. The inner intervening layer may be formed of a plurality of layers, and the porosity of the plurality of layers may be different from each other.

In the insulated wire, a protective layer having an insulating property may be further laminated on the outer peripheral surface side of the insulating layer. As a resin composition which forms a protective layer, what has as a main component the same kind as resin mentioned as a main component of the resin composition of the insulating layer mentioned above can be used. The protective layer may contain pores or may not contain pores. When the protective layer includes pores, the protective layer can also contribute to a decrease in the dielectric constant of the insulating layer. In this case, however, the porosity of the protective layer is more preferably smaller than the porosity of the insulating layer. On the other hand, when the protective layer does not include pores, the insulation of the insulated wire is further improved since the insulation is excellent. Further, the protective layer may be formed of a plurality of layers including pores, and the porosity of the plurality of layers may be different from each other.

In the insulated wire, a further layer such as a primer layer may be provided between the conductor and the insulating layer. A primer layer is a layer provided in order to improve the adhesiveness between layers, for example, can be formed with a well-known resin composition.

When a primer layer is provided between the conductor and the insulating layer, the resin composition forming the primer layer includes, for example, one or more kinds of resins selected from polyimide, polyamideimide, polyesterimide, polyester, and phenoxy resin. Good. Moreover, the resin composition forming the primer layer may contain an additive such as an adhesion improver. By forming a primer layer between the conductor and the insulating layer with such a resin composition, the adhesion between the conductor and the insulating layer is improved, and as a result, the flexibility and wear resistance of the insulated wire are increased. It is possible to effectively enhance the characteristics such as scratch resistance and process resistance.

Further, the resin composition forming the primer layer may contain other resins, for example, an epoxy resin, a phenoxy resin, a melamine resin, etc. together with the above resin. Moreover, you may use a commercially available liquid composition (insulation varnish) as each resin contained in the resin composition which forms a primer layer.

The lower limit of the average primer layer thickness is preferably 1 μm, more preferably 2 μm. As an upper limit of the average thickness of a primer layer, 30 micrometers is preferable and 20 micrometers is more preferable. There exists a possibility that sufficient adhesiveness with a conductor cannot be exhibited as the average thickness of a primer layer is less than the said minimum. If the average thickness of the primer layer exceeds the above upper limit, the insulated wire may unnecessarily increase in diameter.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[Preparation of varnish]
Varnish (A) and varnish (B) were prepared as follows.
(Varnish (A))
Using polyimide as the main polymer and N-methyl-2-pyrrolidone as the solvent, a resin composition was prepared by diluting the main polymer with this solvent. Next, core-shell particles having a core of PMMA particles and a shell of silicone having an average particle diameter of 3 μm are used as hollow-forming particles, and the resin composition is dispersed in such an amount that the calculated porosity of the insulating layer is 10% by volume. Varnish (A) was prepared.

(Varnish (B))
Using polyimide as the main polymer and N-methyl-2-pyrrolidone as the solvent, a resin composition was prepared by diluting the main polymer with this solvent. Next, core-shell particles having a core of PMMA particles and a shell of silicone having an average particle diameter of 3 μm are used as hollow-forming particles, and the calculated amount of the insulating layer having a porosity of 30% by volume is dispersed in the resin composition. Varnish (B) was prepared.

[Manufacture of insulated wires]
No. in Table 1 The insulated wire shown in 1 was manufactured as follows. Using a vertical coating facility, apply varnish (A) as an inner varnish to the outer peripheral surface of a rectangular conductor with a cross section of 2 mm x 2 mm, and inside a die and a baking furnace having openings similar to the conductor The film was passed at a speed of 6 m / min and baked at 350 ° C. for 1 minute to form an inner pore layer. Next, varnish (B) is applied to the outer peripheral surface of the inner pore layer as an outer varnish, and is passed through a die having an opening portion similar to the conductor and a baking furnace at a speed of 6 m / min. Baking was performed for 1 minute to form an insulating film. Application of the outer varnish, passing through the die, and baking were repeated 30 times to form an outer pore layer, and an insulated wire (No. 1) was produced.

No. in Table 1. The insulated wire shown in 2 was manufactured as follows. Using a vertical coating facility, apply varnish (A) as an inner varnish to the outer peripheral surface of a rectangular conductor with a cross section of 2 mm x 2 mm, and inside a die and a baking furnace having openings similar to the conductor The film was passed at a speed of 6 m / min and baked at 350 ° C. for 1 minute to form an inner pore layer. Next, varnish (B) is applied to the outer peripheral surface of the inner pore layer as an outer varnish, and is passed through a die having an opening portion similar to the conductor and a baking furnace at a speed of 6 m / min. Baking was performed for 1 minute to form an insulating film. The outer pore layer was formed by repeating the application of the outer varnish, passing through a die, and baking 28 times. Furthermore, varnish (A) was applied to the outer peripheral surface of the outer pore layer as another pore layer varnish, and passed through a die having an opening portion similar to the conductor and a baking furnace at a speed of 6 m / min. Was baked for 1 minute to form another pore layer to produce an insulated wire (No. 2).

No. in Table 1. The insulated wire shown in 3 was manufactured as follows. Varnish (B) is applied to the outer peripheral surface of a rectangular conductor having a cross section of 2 mm × 2 mm using a vertical coating equipment, and a die having an opening similar to the conductor and a baking furnace at a speed of 6 m / min. It was passed through and baked at 350 ° C. for 1 minute to form an insulating film. Coating of varnish, passing through a die, and baking were repeated 34 times to form a pore layer, and an insulated wire (No. 3) was manufactured.

[Evaluation]
No. obtained 1-No. For the insulated wires of 3, the porosity of each layer, the independent porosity in the pores, the dielectric constant of the insulating layer, the corona discharge starting voltage, the dielectric breakdown voltage, the dielectric breakdown voltage after long-time heating, and the thickness reduction rate after pressing, Evaluation was performed according to the following method. The evaluation results are shown in Table 1.

(Porosity of each layer)
Each formed layer (inner pore layer, outer pore layer, other pore layer and pore layer) was peeled off from the conductor in a cylindrical shape, and the mass W2 of each cylindrical layer was measured. Further, the apparent volume V1 was obtained from the outer shape of each cylindrical layer, and the mass W1 when there was no pore was calculated by multiplying V1 by the density ρ1 of the material of each layer. From the values of W1 and W2, the porosity was calculated by the following formula.
Porosity = (W1-W2) × 100 / W1 (volume%)

(Independent porosity in pores)
A cross section of each layer obtained by peeling into a cylindrical shape is observed with a scanning electron microscope (SEM), and is not opened to each other by interposing an insulating resin composition between adjacent pores (independent Binarization was performed so as to distinguish pores other than independent pores, and the independent porosity (volume%) in the pores was calculated.

(Dielectric constant of insulating layer)
No. 1-No. For the insulated wire 3, the dielectric constant ε of the insulating layer 3 was measured. FIG. 4 is a schematic diagram for explaining a dielectric constant measurement method. In FIG. 4, the same code | symbol as FIG. 1 is attached | subjected to the insulated wire. First, a silver sample P was applied to three places on the surface of the insulated wire, and a measurement sample was prepared in which the conductor 2 was exposed by peeling off the insulating layer 3 on one end side of the insulated wire. Here, the coating length in the longitudinal direction of the insulated wire of the silver paste P applied to the three places on the surface of the insulated wire was 10 mm, 100 mm, and 10 mm in order along the longitudinal direction. The two silver pastes P applied at a length of 10 mm are grounded, and the capacitance between the silver paste P applied at a length of 100 mm between these two silver pastes and the exposed conductor 2 is determined as LCR. Measured with meter M. The dielectric constant ε of the insulating layer 3 was calculated from the measured capacitance and the average thickness of the insulating layer 3. The dielectric constant ε was measured at n = 3 after heating at 105 ° C. for 1 hour, and the average value was obtained.

(Corona discharge start voltage)
Measurement was performed using a partial discharge tester (“KPD2050S” manufactured by Kikusui Electronics Corporation). The surfaces of the two insulated wires were brought into close contact with each other over a length of 100 mm, and electrodes were connected between the two conductors. The voltage was increased at 25 ° C. at a frequency of 60 Hz, and the voltage when a partial discharge of 100 pC or more occurred was read. It implemented by n = 5 and evaluated by the average value.

(Dielectric breakdown voltage)
The measurement was made using a dielectric breakdown tester (“BREAK-DOWN TESTER“ CONTROL UNIT F8150-1 ”from FAITH). No. 1-No. An aluminum foil having a width of 10 mm was wound around the insulated wire No. 3, and one electrode was connected to a conductor and the other was connected to the aluminum foil. The voltage was increased at a voltage increase rate of 500 V / sec, and the voltage when a current of 15 mA or more flowed was read. It implemented by n = 5 and evaluated by the average value.

(Dielectric breakdown voltage after prolonged heating)
No. 1-No. After the insulated wires 3 were stored at 220 ° C. in a thermostatic chamber under an air atmosphere for 2000 hours, the dielectric breakdown voltage was measured by the above method.

(Thickness reduction rate after pressing)
No. 1-No. The insulated wire 3 was installed in a press machine so that a pressing pressure was applied to a part of the longitudinal direction. A load (N) obtained by pressing pressure (MPa) × pressing area (mm ² ) was applied so as to obtain a predetermined pressing pressure, and the pressing was performed for 10 seconds after the load was stabilized. The average thickness T1 of the insulating layer at the pressed location and the average thickness T2 of the insulating layer at the non-pressed location are measured. From the measured values of T1 and T2, (T2-T1) × 100 / T2 (%) The thickness reduction rate after pressing was calculated by the following formula. The thickness reduction rate after pressing was measured with the pressing pressure set to 50 MPa, 100 MPa, and 200 MPa, respectively. The average thicknesses T1 and T2 of the insulating layer were measured at three points in the cross-sectional direction of the insulated wire, and the average value was used.

From the results in Table 1, No. 1 and no. In the insulated wire of 2, the porosity of the inner pore layer is 1% by volume or more and 10% by volume or less, and the porosity of the outer pore layer is 25% by volume or more and 50% by volume or less, and the independent pores in the pores in the insulating layer The rate is 80% by volume or more. No. 1 and no. It can be seen that the insulated wire No. 2 has a high dielectric breakdown voltage after heating for a long time, a low film thickness reduction rate after pressing, and is excellent in insulation and mechanical strength. On the other hand, no. The insulated wire No. 3 did not have the above layer structure, and the dielectric breakdown voltage after heating for a long time and the film thickness reduction rate after pressing deteriorated.

DESCRIPTION OF SYMBOLS 1 Insulated electric wire 2 Conductor 3 Insulating layer 3a Inner pore layer 3b Outer pore layer 3c Other pore layer 4 Pore 5 Hollow forming particle 6 Core 7 Shell M LCR meter P Silver paste

Claims (7)

1. An insulated wire comprising a linear conductor and an insulating layer coated on the outer peripheral surface of the conductor,
   The insulating layer includes an inner pore layer having a plurality of pores, and an outer pore layer disposed outside the inner pore layer and having a plurality of pores,
   In the insulating layer, the independent porosity in the pores is 80% by volume or more,
   The porosity of the inner pore layer is 1% by volume to 10% by volume,
   An insulated wire in which the porosity of the outer pore layer is 25% by volume or more and 50% by volume or less.
2. The average thickness of the inner pore layer is 3 μm or more and 15 μm or less,
   The insulated wire according to claim 1, wherein an average thickness of the outer pore layer is 80 µm or more and 160 µm or less.
3. The insulating layer includes another pore layer having a plurality of pores outside the outer pore layer, the porosity of the other pore layer is 1% by volume to 10% by volume, and the average thickness is 3 μm. The insulated wire according to claim 1 or 2, which is 10 µm or less.
4. The insulated wire according to claim 1, 2 or 3, wherein an outer shell is provided at a peripheral portion of the plurality of pores, and the outer shell is derived from a shell of hollow-forming particles having a core-shell structure.
5. The insulated wire according to claim 4, wherein a main component of the outer shell is silicone.
6. The plurality of pores are flat spheres,
   The insulated wire according to any one of claims 1 to 5, wherein an average ratio of a length of a minor axis to a major axis is 0.95 or less in a cross section including a minor axis and a major axis of the plurality of pores.
7. The insulated wire according to any one of claims 1 to 6, further comprising a primer layer between the conductor and the insulating layer.

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