JP2016091865A - Insulated electric wire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an insulated electric wire which can achieve both of keeping of a mechanical strength and reduction in a dielectric constant.SOLUTION: An insulated electric wire includes a linear conductor, and an insulation layer covered on the outer peripheral surface side of the conductor. The insulation layer contains a pore, and a porosity of the insulation layer becomes the maximum in the central portion in the thickness direction and becomes small on the inner surface side and the outer surface side. The porosity of the insulation layer may be continuously inclined. The insulation layer is formed of three or more pore layers which are divided in the thickness direction, and the porosity of the three or more pore layers may be gradually changed. The porosity of the pore layer in the central portion in the thickness direction in the three or more pore layers is preferably 5 vol.% or more and 80 vol.% or less, and the porosity of the pore layer on the innermost surface side and the outermost surface side is preferably 0.01 vol.% or more and 10 vol.% or less. An average diameter of the pore is preferably 0.1 μm or more and 10 μm or less. An average thickness of the insulation layer is preferably 15 μm or more and 300 μm or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an insulated wire.

  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) is likely to occur on the surface of the insulating coating. 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.

  As a device for increasing the corona discharge starting voltage, it is effective to lower the dielectric constant of the insulating coating. In order to reduce the dielectric constant of an insulating coating, a heat-cured film (insulating coating) is formed by 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. ) Has been proposed (see JP 2012-224714 A). In this insulated wire, pores are formed in the heat-cured 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 insulating coating is realized.

JP 2012-224714 A

  In the above conventional insulated wire, the mechanical strength of the insulating coating is reduced due to the formation of pores. However, since the pores are distributed substantially uniformly in the insulating coating, the insulating coating is uniformly distributed in the thickness direction of the insulating coating. Mechanical strength decreases. Therefore, the ratio of the decrease in the mechanical strength in the thickness direction of the insulating coating with respect to the increase in the porosity in the insulating coating is large, and the mechanical strength tends to be impaired along with the lower dielectric constant of the insulating coating. It is difficult to maintain the mechanical strength.

  This invention is made | formed based on the above situations, and it aims at providing the insulated wire which can make maintenance of mechanical strength and low dielectric constant compatible.

  An insulated wire according to an aspect of the present invention made to solve the above problems is an insulated wire comprising a linear conductor and an insulating layer coated on an outer peripheral surface side of the conductor, and the insulating layer Includes pores, and the porosity of the insulating layer is maximized at the central portion in the thickness direction and is decreased on the inner surface side and the outer surface side.

  The insulated wire of the present invention can maintain both mechanical strength and a low dielectric constant.

It is a typical sectional view of an insulated wire concerning a first embodiment of the present invention. It is a figure which shows the porosity in the thickness direction of the insulating layer of the insulated wire of FIG. It is a typical sectional view of an insulated wire concerning a second embodiment of the present invention. It is a figure which shows the porosity in the thickness direction of the insulating layer of the insulated wire of FIG.

[Description of Embodiment of the Present Invention]
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 side of the conductor, the insulating layer including pores, and the insulating layer The porosity becomes maximum at the central portion in the thickness direction, and decreases on the inner surface side and the outer surface side.

  In the insulated wire, since the insulating layer includes pores, the insulating layer can have a low dielectric constant, and the corona discharge starting voltage is improved. In addition, the insulated wire has a maximum porosity in the central portion in the thickness direction and decreases on the inner surface side and the outer surface side, so that the mechanical strength is suppressed by including pores on the inner surface side and the outer surface side of the insulating layer. The action can be reduced, the mechanical strength on the inner surface side and the outer surface side is hardly lowered, and the mechanical strength of the entire insulating layer can be maintained. Here, “porosity” means the percentage of the volume of the pores relative to the volume including the pores of the insulating layer. “Thickness direction central portion” means a region including the center in the thickness direction of the insulating layer, for example, a region within 30% of the average thickness of the insulating layer from the center in the thickness direction of the insulating layer.

  The porosity of the insulating layer may be continuously inclined. Thus, since the mechanical strength of the insulating layer does not change intermittently in the thickness direction of the insulating layer by continuously inclining the porosity of the insulating layer, the mechanical strength of the insulating layer is easily maintained. Here, “the porosity is continuously inclined” means a state where the porosity is monotonously changing in the thickness direction, and a portion where the porosity does not change may be included in a part thereof.

  The insulating layer may be composed of three or more pore layers divided in the thickness direction, and the porosity of these three or more pore layers may change stepwise. As described above, the insulating layer is composed of three or more pore layers divided in the thickness direction, and the porosity of these three or more pore layers is changed stepwise to maintain the mechanical strength and reduce the low dielectric constant. It is possible to easily form an insulating layer that realizes efficiency.

  Among the three or more pore layers, the porosity of the pore layer at the central portion in the thickness direction is preferably 5% by volume or more and 80% by volume or less, and the porosity of the pore layers on the innermost surface side and outermost surface side is 0%. It is preferably 0.01% by volume or more and 10% by volume or less. Thus, by setting the porosity of the pore layer in the central portion and the porosity of the innermost surface side and the outermost surface side pore layer within the above range, the insulating layer of the insulating layer is more reliably reduced by the central pore layer. The dielectric constant can be realized, and the mechanical strength of the insulating layer can be more reliably maintained by the pore layers on the innermost surface side and the outermost surface side. Here, the “porosity layer at the center in the thickness direction” means that the porosity is the highest among the porosity layers disposed in a region within 30% of the average thickness of the insulating layer from the center in the thickness direction of the insulating layer. Means the pore layer.

  The average diameter of the pores is preferably 0.1 μm or more and 10 μm or less. Thus, by making the average diameter of the pores within the above range, generation of corona discharge in the insulating layer can be suppressed, and the corona discharge start voltage can be maintained at a high value more reliably. Here, the “average diameter of the pores” means the average value of the diameters of the true spheres corresponding to the volume of the pores for all the pores included in the insulating layer. Therefore, when the insulating layer is composed of a plurality of pore layers, the “average pore diameter” means the average value of pores included in all pore layers.

  The average thickness of the insulating layer is preferably 15 μm or more and 300 μm or less. Thus, by making the average thickness of the insulating layer within the above range, the conductor can be reliably insulated and a decrease in the volumetric efficiency of the coil when forming the coil or the like can be suppressed.

[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.

[First embodiment]
The insulated wire 1 shown in FIG. 1 includes a linear conductor 2 and an insulating layer 3 covered on the outer peripheral surface side of the conductor 2. The insulating layer 3 includes an inner surface side pore layer 3a, a central portion pore layer 3b, and an outer surface side pore layer 3c that are divided in the thickness direction. The insulating layer 3 includes pores 4, and the porosity of the insulating layer 3 is maximized in the central pore layer 3b and is small in the inner surface side pore layer 3a and the outer surface side pore layer 3c.

<Conductor>
The conductor 2 is, for example, a round wire having a circular cross section, but may be a square wire having a square 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 conductivity and high mechanical strength. Examples of such metals include copper, copper alloys, aluminum, 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. In contrast, the upper limit of the average cross-sectional area of the conductor 2 is preferably 10 mm ^2, 5 mm ² is more preferable. 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. Conversely, 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. There is.

<Insulating layer>
As shown in FIG. 1, the insulating layer 3 includes an inner surface side pore layer 3a, a central portion pore layer 3b, and an outer surface side pore layer 3c that are divided in the thickness direction.

  Each of the inner surface side pore layer 3a, the central portion pore layer 3b, and the outer surface side pore layer 3c includes a plurality of pores 4. Here, the porosity of the central pore layer 3b laminated at the central portion in the thickness direction is larger than the porosity of the inner surface side pore layer 3a and the porosity of the outer surface side pore layer 3c. That is, the porosity of the insulating layer 3 is maximum at the central portion in the thickness direction and is small on the inner surface side and the outer surface side.

  In each of the inner surface side pore layer 3a, the central portion pore layer 3b, and the outer surface side pore layer 3c, the plurality of pores 4 are distributed substantially uniformly, and the porosity of the insulating layer 3 is as shown in FIG. 2 in the thickness direction. To change. Thus, the porosity of the insulating layer 3 changes stepwise in the thickness direction.

  As a minimum of average thickness of insulating layer 3, 15 micrometers is preferred and 30 micrometers is more preferred. On the other hand, the upper limit of the average thickness of the insulating layer 3 is preferably 300 μm, and more preferably 100 μm. If the average thickness of the insulating layer 3 is less than the lower limit, the insulating layer 3 may be broken and the conductor 2 may not be sufficiently insulated. Conversely, when the average thickness of the insulating layer 3 exceeds the above upper limit, the volume efficiency of a coil or the like formed using the insulated wire 1 may be lowered.

  The lower limit of the average thickness of the inner surface side pore layer 3a is preferably 5% with respect to the average thickness of the insulating layer 3, and more preferably 10%. On the other hand, the upper limit of the average thickness of the inner surface side pore layer 3a is preferably 40%, more preferably 35%, with respect to the average thickness of the insulating layer 3. When the average thickness of the inner surface side pore layer 3a is less than the lower limit, the inner surface side 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. On the contrary, when the average thickness of the inner surface side pore layer 3a exceeds the upper limit, the inner surface side 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. There is.

  The lower limit of the average thickness of the central pore layer 3b is preferably 20% with respect to the average thickness of the insulating layer 3, and more preferably 30%. On the other hand, the upper limit of the average thickness of the central pore layer 3b is preferably 90% and more preferably 80% with respect to the average thickness of the insulating layer 3. When the average thickness of the central pore layer 3b is less than the lower limit, the central 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 reduced. is there. On the contrary, when the average thickness of the central pore layer 3b exceeds the upper limit, the central 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. is there.

  The lower limit of the average thickness of the outer surface side pore layer 3c is preferably 5% with respect to the average thickness of the insulating layer 3, and more preferably 10%. On the other hand, the upper limit of the average thickness of the outer surface side pore layer 3c is preferably 40% and more preferably 35% with respect to the average thickness of the insulating layer 3. When the average thickness of the outer surface side pore layer 3c is less than the lower limit, the outer surface side 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. On the contrary, when the average thickness of the outer surface side pore layer 3c exceeds the upper limit, the outer surface side 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 reduced. There is.

  The resin as the main component of the resin composition for forming the insulating layer 3 (the inner surface side pore layer 3a, the central portion pore layer 3b and the outer surface side pore layer 3c) is not particularly limited, but for example, polyvinyl formal, thermosetting polyurethane , Thermosetting resins such as thermosetting acrylic, epoxy, thermosetting polyester, thermosetting polyester imide, thermosetting polyester amide imide, aromatic polyamide, thermosetting polyamide imide, thermosetting polyimide, and polyether imide, polyphenylene ether, A thermoplastic resin such as polyethersulfone 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, it is good also considering the resin of the main component of the resin composition which forms the inner surface side pore layer 3a, the center part pore layer 3b, and the outer surface side pore layer 3c as the same kind, or a different kind.

  Moreover, you may make the resin composition which forms the insulating layer 3 (the inner surface side pore layer 3a, the center part pore layer 3b, and the outer surface side pore layer 3c) contain a hardening | curing agent with the said resin. Curing agents include titanium-based curing agents, isocyanate compounds, blocked isocyanates, urea and melamine compounds, amino resins, alicyclic acid anhydrides such as methyltetrahydrophthalic anhydride, aliphatic acid anhydrides, and aromatic acid anhydrides. Etc. are exemplified. These curing agents are appropriately selected according to the type of resin 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.

  Examples of the titanium-based curing agent include tetrapropyl titanate, tetraisopropyl titanate, tetramethyl titanate, tetrabutyl titanate, and tetrahexyl titanate. Examples of the isocyanate compound include aromatic diisocyanates such as tolylene diisocyanate (TDI), diphenylmethane isocyanate (MDI), p-phenylene diisocyanate, and naphthalene diisocyanate, hexamethylene diisocyanate (HDI), 2,2,4-trimethylhexane diisocyanate, C3-C12 aliphatic diisocyanate such as lysine diisocyanate, 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 XD ), Hydrogenated TDI, carbon such as 2,5-bis (isocyanatomethyl) -bicyclo [2,2,1] heptane, 2,6-bis (isocyanatomethyl) -bicyclo [2,2,1] heptane Examples thereof include aliphatic diisocyanates having an aromatic ring such as alicyclic isocyanate, 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, 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. Is exemplified. Examples of the melamine compound include methylated melamine, butylated melamine, methylolated melamine, and butyrololized melamine.

  As described above, the porosity of the inner surface side pore layer 3a is smaller than the porosity of the central portion pore layer 3b. The lower limit of the porosity of the inner surface side pore layer 3a is preferably 1% by volume, and more preferably 2% by volume. On the other hand, the upper limit of the porosity of the inner surface side pore layer 3a is preferably 10% by volume, more preferably 8% by volume. When the porosity of the inner surface side 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. On the other hand, when the porosity of the inner surface side pore layer 3a exceeds the upper limit, there is a possibility that sufficient mechanical strength of the insulating layer 3 cannot be ensured.

  As a minimum of the porosity of the center part pore layer 3b, 5 volume% is preferable and 10 volume% is more preferable. On the other hand, the upper limit of the porosity of the central pore layer 3b is preferably 80% by volume, more preferably 60% by volume. When the porosity of the central 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. On the other hand, when the porosity of the central pore layer 3b exceeds the upper limit, there is a possibility that sufficient mechanical strength of the insulating layer 3 cannot be ensured.

  As described above, the porosity of the outer surface side pore layer 3c is smaller than the porosity of the central portion pore layer 3b. The lower limit of the porosity of the outer surface side pore layer 3c is preferably 0.01% by volume, and more preferably 1% by volume. On the other hand, the upper limit of the porosity of the outer surface side pore layer 3c is preferably 10% by volume, more preferably 8% by volume. When the porosity of the outer surface side 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 start voltage may not be sufficiently improved. On the contrary, when the porosity of the outer surface side pore layer 3c exceeds the upper limit, there is a possibility that sufficient mechanical strength of the insulating layer 3 cannot be ensured.

  The porosity of the inner surface side pore layer 3a and the porosity of the outer surface side pore layer 3c may be the same or different. The porosity of the insulating layer 3 of the insulated wire is such that the porosity of the outer surface side pore layer 3c is smaller than the porosity of the inner surface side pore layer 3a, as shown in FIG. Since the mechanical strength increases as the porosity decreases, the porosity of the outer surface side pore layer 3c is thus smaller than the porosity of the inner surface side pore layer 3a in that the strength of the outer surface of the insulated wire 1 is increased. Is preferred.

  The lower limit of the average diameter of the pores 4 is preferably 0.1 μm and more preferably 1 μm. On the other hand, the upper limit of the average diameter of the pores 4 is preferably 10 μm, more preferably 8 μm. When the average diameter of the pores 4 is less than the above lower limit, the occurrence of corona discharge in the insulating layer 3 may not be sufficiently suppressed. Conversely, when the average diameter of the pores 4 exceeds the upper limit, it is difficult to make the distribution of the pores 4 within each of the inner surface side pore layer 3a, the central portion pore layer 3b, and the outer surface side pore layer 3c uniform, There is a risk that the distribution tends to be biased. The average diameter of the pores 4 included in each of the inner surface side pore layer 3a, the central portion pore layer 3b, and the outer surface side pore layer 3c may be different.

[Insulated wire manufacturing method]
Next, the manufacturing method of the said insulated wire 1 is demonstrated. The method for manufacturing the insulated wire 1 includes diluting a resin that forms the insulating layer 3 and a thermally decomposable resin that is thermally decomposed at a temperature lower than the baking temperature of the resin, and a plurality of varnishes having different contents of the thermally decomposable resin. A step of preparing the inner surface side pore layer 3a including the pores 4 by applying and baking the varnish on the outer peripheral surface of the conductor 2 (an inner surface side pore layer forming step), and an inner surface side The central portion in the thickness direction including the pores 4 is formed by applying and baking the outer surface of the conductor 2 on which the inner surface side pore layer 3a of the varnish having the pyrolytic resin content larger than that of the varnish in which the pore layer 3a is formed. Step of forming the central pore layer 3b (center pore layer forming step), and conductor having the central pore layer 3b of the varnish having a smaller content of the thermally decomposable resin than the varnish forming the central pore layer 3b Application to the outer peripheral surface side of 2 And forming an outer side pore layer 3c comprising pores (outer surface side-porous layer forming step) by fine baking.

<Varnish preparation process>
In the varnish preparation step, the resin forming the insulating layer 3 and the thermally decomposable resin are diluted with a solvent to prepare a varnish. A plurality of types of varnishes having different contents of the thermally decomposable resin are prepared as varnishes for forming the inner surface side pore layer 3a, the central portion pore layer 3b and the outer surface side pore layer 3c, respectively. As shown in FIG. 2, since the porosity of the inner surface side pore layer 3a, the central portion pore layer 3b, and the outer surface side pore layer 3c is different from each other, here, the content of the pyrolyzable resin is different for the inner surface side and the central portion. And three kinds of varnishes for the outer surface side are prepared. In addition, the same kind may be used as resin which forms the insulating layer 3 diluted with a solvent for the inner surface side, the center part, and the outer surface side, and different things may be used.

  As the thermally decomposable resin, for example, resin particles that thermally decompose at a temperature lower than the baking temperature of the resin forming the insulating layer 3 are used. The baking temperature of the resin forming the insulating layer 3 is appropriately set according to the type of resin, but is usually about 200 ° C. or higher and 350 ° C. or lower. Accordingly, the lower limit of the thermal decomposition temperature of the thermally decomposable resin used for the varnish is preferably 200 ° C., and the upper limit is preferably 300 ° C. Here, the thermal decomposition temperature means a temperature at which the temperature is increased from room temperature to 10 ° C./min in a nitrogen 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 Nano Technology Co., Ltd.).

  The heat-decomposable resin used in the varnish is not particularly limited, but for example, a compound obtained by alkylating, (meth) acrylated or epoxidizing one or both ends or part of polyethylene glycol, polypropylene glycol or the like, poly (meta) ) Alkyl ester polymer of 1 to 6 carbon atoms of (meth) acrylic acid, such as methyl acrylate, poly (meth) ethyl acrylate, poly (meth) acrylic acid propyl, poly (meth) acrylic acid butyl, urethane oligomer , Urethane polymer, urethane (meth) acrylate, epoxy (meth) acrylate, polymer of modified (meth) acrylate such as ε-caprolactone (meth) acrylate, poly (meth) acrylic acid, cross-linked products thereof, polystyrene, cross-linked polystyrene Etc. Among these, a crosslinked product of a (meth) acrylic polymer is preferable, and a crosslinked poly (meth) acrylate is more preferable. Further, it is preferable that the thermally decomposable resin can be uniformly distributed as an island phase of fine particles in the sea phase of the resin forming the insulating layer 3. Accordingly, the thermally decomposable resin used for the varnish is preferably a resin that is excellent in compatibility with the resin forming the insulating layer 3 and is formed into a spherical shape, and specifically, a crosslinked resin.

  The crosslinked poly (meth) acrylic polymer can be obtained, for example, by polymerizing a (meth) acrylic monomer and a polyfunctional monomer by emulsion polymerization, suspension polymerization, solution polymerization, or the like.

  Here, as the (meth) acrylic monomer, acrylic acid, methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, dodecyl acrylate, stearyl acrylate, acrylic acid 2 -Ethylhexyl, tetrahydrofurfuryl acrylate, diethylaminoethyl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, n-octyl methacrylate , Dodecyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, diethylaminoethyl methacrylate and the like.

  Examples of the polyfunctional monomer include divinylbenzene, ethylene glycol di (meth) acrylate, trimethylolpropane triacrylate, and the like.

  In addition to the (meth) acrylic monomer and the polyfunctional monomer, other monomers may be used as the constituent monomer of the crosslinked poly (meth) acrylic polymer. Other monomers include glycol esters of (meth) acrylic acid such as ethylene glycol mono (meth) acrylate and polyethylene glycol mono (meth) acrylate, alkyl vinyl ethers such as methyl vinyl ether and ethyl vinyl ether, vinyl acetate and vinyl butyrate Vinyl esters, N-alkyl substituted (meth) acrylamides such as N-methylacrylamide, N-ethylacrylamide, N-methylmethacrylamide and N-ethylmethacrylamide, nitriles such as acrylonitrile and methacrylonitrile, styrene, p -Styrene monomers, such as methylstyrene, p-chlorostyrene, chloromethylstyrene, and α-methylstyrene.

  When using the resin particles to be thermally decomposed, the resin particles are preferably spherical. The lower limit of the average particle diameter of the resin particles is preferably 0.1 μm, more preferably 0.5 μm, and even more preferably 1 μm. On the other hand, the upper limit of the average particle diameter of the resin particles is preferably 100 μm, more preferably 50 μm, further preferably 30 μm, and particularly preferably 10 μm. The resin particles are thermally decomposed when the resin forming the insulating layer 3 is baked to form pores in the existing portions. Therefore, when the average particle diameter of the resin particles is less than the lower limit, pores may not be easily formed in the insulating layer 3. On the contrary, when the average particle diameter of the resin particles exceeds the upper limit, the surface of the insulating layer 3 may be easily uneven. Here, the average particle size of the resin particles means a particle size showing the highest content ratio in the particle size distribution measured with a laser diffraction particle size distribution measuring device.

  As a minimum of content of the heat decomposable resin in the said varnish, 5 mass parts is preferable with respect to 100 mass parts of resin which forms the insulating layer 3, 10 mass parts is more preferable, 15 mass parts is more preferable. On the other hand, the upper limit of the content of the thermally decomposable resin in the varnish is preferably 350 parts by weight, more preferably 150 parts by weight, and still more preferably 90 parts by weight with respect to 100 parts by weight of the resin forming the insulating layer 3. When content of the said heat decomposable resin is less than the said minimum, there exists a possibility that the dielectric constant of the insulating layer 3 cannot fully be reduced. On the contrary, when the content of the thermally decomposable resin exceeds the upper limit, there is a possibility that sufficient mechanical strength of the insulating layer 3 cannot be ensured.

  As the solvent for dilution, 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, and γ-butyrolactone 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, and tertiary amines such as pyridine. These organic solvents may be used alone or in combination of two or more. Used.

  In addition, as a minimum of the resin solid content density | concentration of the varnish prepared by diluting with these organic solvents, 15 mass% is preferable and 22 mass% is more preferable. On the other hand, the upper limit of the resin solid content concentration of the varnish is preferably 50% by mass, and more preferably 28% by mass. When the resin solid content concentration of the varnish is less than the above lower limit, the amount of application at one time when the varnish is applied is reduced, so that the inner surface side pore layer 3a, the central portion pore layer 3b or the outer surface side pores having a desired thickness There is a possibility that the number of repetitions of the varnish application process for forming the layer 3c increases and the time of the varnish application process becomes longer. On the contrary, when the resin solid content concentration of the inner surface side varnish exceeds the upper limit, the storage stability of the varnish may be deteriorated due to thickening of the varnish, and the adhesion property at the time of varnish application may be deteriorated. is there.

<Inner surface side pore layer forming step>
In the inner surface side pore layer forming step, the inner surface side pore layer 3a is formed on the surface of the conductor 2 by applying the inner surface side varnish prepared in the varnish preparation step to the outer peripheral surface of the conductor 2 and then baking it. At the time of baking, the thermally decomposable resin contained in the inner surface side varnish is thermally decomposed, and pores 4 are generated in portions where the thermally decomposable resin is present in the inner surface side pore layer 3a.

  When the inner surface side pore layer 3a having a desired thickness cannot be formed by one-time application and baking of the inner surface side varnish, the inner surface side pore layer 3a formed on the surface of the conductor 2 has a predetermined thickness. Repeat application and baking of varnish.

<Center part pore layer formation process>
In the center part pore layer forming step, the center having a larger content of the thermally decomposable resin than the inner surface side varnish prepared in the varnish preparation step is further provided on the outer peripheral surface of the conductor 2 on which the inner surface side pore layer 3a is formed. After applying the part varnish, the central part pore layer 3b is formed outside the inner surface side pore layer 3a formed on the conductor 2 by baking. At the time of baking, the thermally decomposable resin contained in the central varnish is thermally decomposed, and pores 4 are generated in portions where the thermally decomposable resin exists in the central pore layer 3b.

  When the central pore layer 3b having a desired thickness cannot be formed by one application and baking of the central varnish, the application and baking of the central varnish are repeated until the central porous layer 3b reaches a predetermined thickness. Do.

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

  When the outer surface side pore layer 3c having a desired thickness cannot be formed by one application and baking of the outer surface side varnish, the application and baking of the outer surface side varnish are repeated until the outer surface side pore layer 3c reaches a predetermined thickness. Do. The insulated wire 1 is obtained by forming the outer surface side pore layer 3c having a predetermined thickness.

  Since the porosity of the insulating layer 3 of the insulated wire 1 is different from the porosity of the inner surface side pore layer 3a and the porosity of the outer surface side pore layer 3c as shown in FIG. 2, the inner surface side varnish and the outer surface side varnish. In the case of manufacturing an insulated wire in which the porosity of the inner surface side pore layer 3a is equal to the porosity of the outer surface side pore layer 3c, the inner surface side pore layer 3a and the outer surface side pore layer 3c are formed. The same kind of varnish can be shared. In this case, since the kind of varnish to adjust decreases, the manufacturing cost of an insulated wire can be reduced.

[advantage]
In the insulated wire 1, when the insulating layer 3 includes the pores 4, the dielectric constant of the insulating layer 3 can be reduced and the corona discharge starting voltage can be improved. In addition, the insulated wire 1 has the insulating layer 3 having a maximum porosity in the central pore layer 3b at the central portion in the thickness direction, and becomes smaller in the inner pore layer 3a and the outer pore layer 3c. 3 can reduce the mechanical strength suppressing effect by including the pores 4 on the inner surface side and the outer surface side, the mechanical strength on the inner surface side and the outer surface side is hardly lowered, and the mechanical strength of the insulating layer 3 as a whole can be maintained. .

  Further, in the insulated wire 1, since the insulating layer 3 is composed of the inner surface side pore layer 3a, the central portion pore layer 3b and the outer surface side pore layer 3c having different porosities, the thickness of each pore layer can be easily adjusted. It is easy to adjust the dielectric constant and mechanical strength of the insulating layer in a well-balanced manner.

[Second Embodiment]
The insulated wire 11 in FIG. 3 includes a linear conductor 12 and an insulating layer 13 that covers the outer peripheral surface of the conductor 12. The insulating layer 13 includes pores 14, and the porosity of the insulating layer 13 is continuously inclined so as to be maximized at the central portion in the thickness direction and to be small on the inner surface side and the outer surface side in the thickness direction.

  The insulated wire 11 in FIG. 3 differs from the insulated wire 1 in FIG. 1 in the configuration of the insulating layer 13. Since the conductor 12 of the insulated wire 11 can be the same as the conductor 2 of the insulated wire 1, the description thereof is omitted.

<Insulating layer>
The insulating layer 13 includes a plurality of pores 14 as shown in FIG. As shown in FIG. 4, the porosity of the insulating layer 13 is continuously inclined in the thickness direction, maximized at the central portion in the thickness direction, and decreased on the inner surface side and the outer surface side.

  As a minimum of average thickness of insulating layer 13, 30 micrometers is preferred and 50 micrometers is more preferred. On the other hand, the upper limit of the average thickness of the insulating layer 13 is preferably 100 μm, and more preferably 80 μm. If the average thickness of the insulating layer 13 is less than the above lower limit, the insulating layer 13 may be broken and insulation of the conductor 12 may be insufficient. Conversely, when the average thickness of the insulating layer 13 exceeds the above upper limit, the volume efficiency of a coil or the like formed using the insulated wire 11 may be lowered.

  As the main component resin of the resin composition forming the insulating layer 13, the same type of resin as that described above as the resin of the insulating layer 3 in FIG. 1 can be used. In addition, the resin composition forming the insulating layer 13 may contain the same type of curing agent as that included in the resin composition forming the insulating layer 3.

  The lower limit of the average porosity at the central portion in the thickness direction of the insulating layer 13 is preferably 5% by volume, and more preferably 10% by volume. On the other hand, the upper limit of the average porosity at the central portion in the thickness direction is preferably 60% by volume, more preferably 50% by volume. When the average porosity in the central portion in the thickness direction is less than the lower limit, the dielectric constant of the insulating layer 13 is not sufficiently lowered, and the corona discharge start voltage may not be sufficiently improved. On the contrary, when the average porosity in the central portion in the thickness direction exceeds the upper limit, there is a possibility that sufficient mechanical strength of the insulating layer 13 cannot be ensured. Here, the “thickness direction central portion” means a region within 30% of the average thickness of the insulating layer 13 from the thickness direction center of the insulating layer 13, and “the average porosity in the thickness direction central portion” is Is an average value of the porosity in the region defined as the central portion in the thickness direction.

  The lower limit of the porosity on the inner surface side of the insulating layer 13 is preferably 1% by volume, and more preferably 2% by volume. On the other hand, the upper limit of the porosity on the inner surface side is preferably 10% by volume, more preferably 8% by volume. When the porosity on the inner surface side is less than the lower limit, the dielectric constant of the insulating layer 13 is not sufficiently lowered, and the corona discharge start voltage may not be sufficiently improved. On the other hand, when the porosity on the inner surface side exceeds the upper limit, there is a possibility that sufficient mechanical strength of the insulating layer 13 cannot be ensured. Here, “the porosity on the inner surface side” means the average porosity in a region within 10% of the average thickness of the insulating layer 13 in the thickness direction from the inner surface of the insulating layer 13.

  As a minimum of the porosity of the outer surface side of insulating layer 13, 1 volume% is preferred and 2 volume% is more preferred. On the other hand, the upper limit of the porosity on the outer surface side is preferably 10% by volume, more preferably 8% by volume. When the porosity on the outer surface side is less than the lower limit, the dielectric constant of the insulating layer 13 is not sufficiently lowered, and the corona discharge start voltage may not be sufficiently improved. On the contrary, when the porosity on the outer surface side exceeds the upper limit, there is a possibility that sufficient mechanical strength of the insulating layer 13 cannot be ensured. Here, “the porosity on the outer surface side” means an average porosity in a region within 10% of the average thickness of the insulating layer 13 in the thickness direction from the outer surface of the insulating layer 13.

  The lower limit of the average diameter of the pores 14 is preferably 0.1 μm, and more preferably 1 μm. On the other hand, the upper limit of the average diameter of the pores 14 is preferably 10 μm, and more preferably 8 μm. When the average diameter of the pores 14 is less than the lower limit, it may be difficult to generate the pores 14. On the other hand, when the average diameter of the pores 14 exceeds the upper limit, it is difficult to continuously incline the porosity in the thickness direction and the bias distribution tends to be biased, so that the corona discharge starting voltage is difficult to improve. There is a risk.

[Insulated wire manufacturing method]
Next, a method for manufacturing the insulated wire 11 will be described. The said insulated wire 11 can be manufactured by the method similar to the manufacturing method of the insulated wire 1 of 1st embodiment, for example.

  Specifically, in the varnish preparation step, various types of varnishes having different pyrolyzable resin contents are prepared. When preparing these varnishes, the same kind of resin is used as the resin for forming the insulating layer for any varnish.

  Next, a plurality of layers are sequentially formed on the outer peripheral side of the conducting wire 12 with different varnishes by the same method as in the inner surface side pore layer forming step, the central portion pore layer forming step, and the outer surface side pore layer forming step. At this time, the plurality of layers are formed by sequentially using varnishes having a small difference in the content of the thermally decomposable resin. Since each varnish uses the same kind of resin as the resin for forming the insulating layer, the plurality of layers formed on the outer peripheral side of the conducting wire 12 are integrated during baking, and the insulated wire 11 shown in FIG. Is obtained.

[advantage]
In the insulated wire 11, since the porosity of the insulating layer 13 is continuously inclined in the thickness direction, the mechanical strength does not change intermittently in the thickness direction of the insulating layer 13. Easy to maintain.

[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. The

  In other words, in the first embodiment, the insulated wire is described in which the insulating layer is composed of 3 pore layers. However, the porosity is maximized at the central portion and gradually decreases on the inner surface side and outer surface side. As long as each pore layer is provided, the insulated wire may be an insulated wire including four or more pore layers. 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 thermally expandable microcapsule has a core material (inner package) 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 thermal expansion microcapsule, that is, the boiling point of the low-boiling liquid or the thermal decomposition temperature of the chemical foaming agent is set to be equal to or higher than the softening temperature of the outer shell of the thermal expansion 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. On the other hand, 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 production, transportation or storage of the insulated wire. On the other hand, when the expansion start temperature of the thermal expansion agent of the thermally expandable microcapsule exceeds the above upper limit, the energy cost required for expanding the thermally expandable microcapsule may be excessive.

  On the other hand, the outer shell of the thermally expandable microcapsule is formed of a stretchable material that can expand without breaking when the thermally expandable 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.

  Examples of the thermoplastic resin used as the main component of the outer shell of the thermally expandable microcapsule are formed from monomers such as vinyl chloride, vinylidene chloride, acrylonitrile, acrylic acid, methacrylic acid, acrylate, methacrylate, and styrene. A polymer formed from two or more types of monomers is 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.

  Moreover, although the said embodiment demonstrated the structure in which the pore contained in an insulating layer was formed by thermal decomposition of a thermally decomposable resin, it is good also as a structure which formed the said pore with the hollow filler, for example. In the case where the pores are formed with a hollow filler, for example, the insulated wire can be produced by kneading the resin composition forming the insulating layer and the hollow filler and coating the kneaded material on the conductor by extrusion molding.

  When the pores are formed by 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 the insulated wire where mechanical strength is important, a glass balloon is preferable because it is easily available and is not easily damaged.

  Moreover, although the said embodiment demonstrated the structure in which the pore contained in an insulating layer was formed by thermal decomposition of a thermally decomposable resin, it is good also as a structure which formed the said pore using the phase-separation method, for example. 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.

  For example, in the 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 an inner intervening layer is provided between the conductor and the insulating layer, the resin composition forming the inner intervening layer is, for example, one or more kinds of resins selected from polyimide, polyamideimide, polyesterimide, polyester and phenoxy resin. It is good to include. In addition, the resin composition forming the inner intervening layer may contain an additive such as an adhesion improver. By forming the 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, abrasion resistance, scratch resistance, and workability can be effectively enhanced.

  Further, the resin composition forming the inner intervening layer may contain other resins, for example, an epoxy resin, a phenoxy resin, a melamine resin, and the like together with the 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 for 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.

  Further, for example, 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.

  Since the insulated wire according to the present invention can maintain both mechanical strength and a low dielectric constant, it can be suitably used to form a coil, a motor, and the like.

DESCRIPTION OF SYMBOLS 1,11 Insulated electric wire 2,12 Conductor 3,13 Insulating layer 3a Inner surface side pore layer 3b Center part pore layer 3c Outer surface side pore layer 4,14 Pore

Claims (6)

An insulated wire comprising a linear conductor and an insulating layer coated on the outer peripheral surface side of the conductor,
The insulating layer includes pores;
An insulated wire in which the porosity of the insulating layer is maximized at the central portion in the thickness direction and decreases on the inner surface side and the outer surface side.   The insulated wire according to claim 1, wherein the porosity of the insulating layer is continuously inclined. The insulating layer is composed of three or more pore layers divided in the thickness direction,
The insulated wire according to claim 1, wherein the porosity of these three or more pore layers changes stepwise.   Among the three or more pore layers, the porosity of the pore layer at the central portion in the thickness direction is 5% by volume or more and 80% by volume or less, and the porosity of the pore layer on the innermost surface side and outermost surface side is 0.01% by volume. The insulated wire according to claim 3, wherein the content is 10% by volume or less.   The insulated wire according to any one of claims 1 to 4, wherein an average diameter of the pores is 0.1 µm or more and 10 µm or less.   The insulated wire according to any one of claims 1 to 5, wherein an average thickness of the insulating layer is 15 µm or more and 300 µm or less.

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