JP7016860B2 - Insulated wire - Google Patents

Description

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

In an electric device having a high applied voltage, for example, a motor used at a high voltage, a high voltage is applied to an insulated wire constituting the electric device, and a partial discharge (corona discharge) is likely to occur on the surface of the insulating layer. When the occurrence of corona discharge causes a local temperature rise, ozone generation, ion generation, etc., dielectric breakdown occurs at an early stage, and the life of the insulated wire and thus the electrical equipment is shortened. Therefore, an insulated wire used for an electric device having a high applicable voltage is required to have excellent insulation, mechanical strength, and the like, as well as an improvement in the corona discharge starting voltage.

As a device to raise the corona discharge start voltage, it is effective to reduce the dielectric constant of the insulating layer. In order to reduce the dielectric constant of the insulating coating, a heat-curing film (insulating coating) is made of an insulating varnish containing a coating resin and a pyrolytic resin that decomposes at a temperature lower than the baking temperature of the coating resin. (See JP-A-2012-224714). In this insulated wire, pores are formed in the heat-cured film by utilizing the fact that the thermally decomposable resin is thermally decomposed at the time of baking the coating resin and the portion becomes pores, and the insulating wire is insulated by the formation of pores. Achieves a low dielectric constant of the coating.

Further, in the insulated wire provided with the insulating layer including such pores, the mechanical strength in the thickness direction of the insulating layer is lowered, so that the insulating layer is thick in order to achieve both low dielectric constant and mechanical strength. An insulated wire composed of three or more pore layers divided in a direction and in which the pore ratio of these three or more pore layers changes stepwise has been proposed (see JP-A-2016-91865).

Japanese Unexamined Patent Publication No. 2012-224714 Japanese Unexamined Patent Publication No. 2016-91865

The insulated wire according to one aspect of the present invention is an insulated wire having a linear conductor and an insulating layer coated on the outer peripheral surface of the conductor, and the insulating layer is an inner pore layer having a plurality of pores. And an outer pore layer arranged outside the inner pore layer and having a plurality of pores, 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 schematic cross-sectional view of the insulated wire which concerns on 1st Embodiment of this invention. It is a schematic cross-sectional view of the insulated wire which concerns on 2nd Embodiment of this invention. It is a schematic cross-sectional view of the hollow forming particle contained in the varnish used for forming the insulating electric 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 this 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, there is a disadvantage that the mechanical strength is lowered and the insulating property, particularly the dielectric breakdown strength after heating for a long time is lowered.

Therefore, it is an object of the present invention to provide an insulated electric wire having excellent insulating properties and mechanical strength.

[Effect of this disclosure]
The insulated wire of the present disclosure is excellent in insulating property and mechanical strength.

[Explanation of Embodiment of the present invention]
(1) The insulated wire according to one aspect of the present invention is an insulated wire including a linear conductor and an insulating layer coated on the outer peripheral surface of the conductor, and the insulating layer has a plurality of pores. The inner pore layer and the outer pore layer arranged outside the inner pore layer and having a plurality of pores are provided. In the insulating layer, the independent porosity in the pores is 80% by volume or more, and the inner side. 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, the insulating layer contains pores, and the independent pore ratio in the pores of the insulating layer is equal to or higher than the above value. Can be increased and has excellent insulation. Further, the insulated wire is provided with an inner pore layer and an outer pore layer, and by setting the porosity of each within the above range, the effect of suppressing the mechanical strength can be reduced, and the mechanical strength of the insulating layer as a whole can be improved. Excellent. Here, the "independent porosity" means a value obtained by a measurement method described later. Further, "porosity" means a percentage of the volume of pores to the volume including 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. It is a value obtained by the formula (W1-W2) × 100 / W1 from the mass W1 when there is no pore obtained by multiplying 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 conductor and suppress a decrease in the volumetric efficiency of the coil when forming the coil or the like.

(3) The insulating layer may include another pore layer having a plurality of pores on the outside of the outer pore layer, and the porosity of the other pore layer is 1% by volume or more and 10% by volume or less. The average thickness of the other pore layers is preferably 3 μm or more and 10 μm or less. By further providing another pore layer having the above configuration on the outside of the outer pore layer, it is possible to improve the durability of the insulated wire while maintaining the mechanical strength of the insulating layer as a whole.

(4) It is preferable that an outer shell is provided at the peripheral edge 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 thermal decomposition of the core of the hollow forming particles of the core shell structure, and the shell is present as an outer shell in the peripheral portion of the pores, so that the formed pores vary in size and shape. Insulation and mechanical strength are further improved because the size is smaller and the independent porosity is improved. The core-shell structure refers to a structure in which the material forming the core of the particles and the material of the shell surrounding the core are different.

(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 the insulating property and heat resistance. The "main component" is a component having the highest content, for example, a component contained in an amount of 50% by mass or more.

(6) It is preferable that the plurality of pores are oblate spheroids, 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 plurality of pores. The pores are oblate spheroids, 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, so that the pores abut against each other in the direction perpendicular to the conductor surface. It becomes difficult and the independent porosity in the insulating layer can be increased. The "flat sphere" means a sphere whose minor axis is 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, and as a result, the flexibility, wear resistance, scratch resistance, and work resistance of the insulated wire are improved. It is possible to effectively enhance such characteristics.

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

[Insulated wire]
[First Embodiment]
The insulated wire 1 of FIG. 1 includes a linear conductor 2 and an insulating layer 3 coated on the outer peripheral surface of the conductor 2. The insulating layer 3 is composed of 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 rectangular cross section, but may be a round wire having a circular cross section or a stranded wire obtained by twisting a plurality of strands.

As the material of the conductor 2, a metal having high conductivity and high mechanical strength is preferable. Examples of such metals include copper, copper alloys, aluminum, aluminum alloys, nickel, silver, iron, steel, stainless steel and the like. The conductor 2 is a material obtained by forming these metals in a linear shape, or a material having a multilayer structure in which such a linear material is coated with another metal, for example, nickel-coated copper wire, silver-coated copper wire, or copper-coated aluminum. Wires, copper-coated steel wires and the like can be used.

As the lower limit of the average cross-sectional area of the conductor 2, 0.01 mm ² is preferable, and 0.1 mm ² is more preferable. As the upper limit of the average cross-sectional area of the conductor 2, 20 mm ² is preferable, 10 mm ² is more preferable, and 5 mm ² is further preferable. If the average cross-sectional area of the conductor 2 is less than the above lower limit, the volume of the insulating layer 3 with respect to the conductor 2 may increase, and the volumetric efficiency of the coil or the like formed by using the insulated wire 1 may decrease. 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 diameter of the insulated wire 1 may be unnecessarily increased.

<Insulation layer>
As shown in FIG. 1, the insulating layer 3 is composed of 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 wire having a rectangular cross section of the conductor, it is necessary to increase the average thickness of the insulating layer 3. As the lower limit of the average thickness of the inner pore layer 3a, 3 μm is preferable, and 5 μm is more preferable. 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 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, 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 above lower limit, the inner pore layer 3a having a large effect of maintaining the mechanical strength may become 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, which has 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.

In the case of a so-called square wire 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, more preferably 100 μm. The upper limit of the average thickness of the outer pore layer 3b is preferably 160 μm, more preferably 130 μm. In the case of a round wire having a circular cross section 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, more preferably 20 μm. The upper limit of the average thickness of the outer pore layer 3b is preferably 160 μm, more preferably 130 μm. If the average thickness of the outer pore layer 3b is less than the above lower limit, the outer pore layer 3b, which has a large effect of contributing to lower dielectric constant, may become 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, which has a small effect of maintaining the mechanical strength, may become 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 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, more preferably 30 μm. The upper limit of the average thickness of the insulating layer 3 is preferably 300 μm, more preferably 200 μm. On the other hand, in the case of a so-called square wire 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, more preferably 100 μm. The upper limit of the average thickness of the insulating layer 3 is preferably 400 μm, more preferably 300 μm. If the average thickness of the insulating layer 3 is less than the above lower limit, the insulating layer 3 may be torn and the insulation of the conductor 2 may be insufficient. If the average thickness of the insulating layer 3 exceeds the above upper limit, the volumetric efficiency of the coil or the like formed by using the insulated wire 1 may decrease.

The resin as the main component of the resin composition forming the insulating layer 3 (inner pore layer 3a and outer pore layer 3b) is not particularly limited, and is, for example, polyvinyl formal, thermosetting polyurethane, thermosetting acrylic, epoxy, thermosetting polyester. Thermosetting resins such as thermosetting polyesterimide, thermosetting polyesteramideimide, aromatic polyamide, thermosetting polyamideimide, thermosetting polyimide, for example, polyetherimide, polyether ether ketone, polyether sulfone, polyamideimide, Thermoplastic resin such as polyimide can be used. Here, the "main component" is a component having the highest content, for example, a component contained in an amount of 50% by mass or more. The resin as the main component of the resin composition forming the inner pore layer 3a and the outer pore layer 3b may be of the same type or may be of a different type.

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

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 above lower limit, the dielectric constant of the insulating layer 3 may not be 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, it may not be possible to secure sufficient mechanical strength of the insulating layer 3.

The lower limit of the independent porosity in the pores 4 of the insulating layer 3 is 80% by volume, more preferably 85% by volume, 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 property and mechanical strength of the insulated wire tend to decrease. The independent porosity of the pores 4 contained in the inner pore layer 3a and the independent porosity of the pores 4 contained 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 through a resin composition having an insulating property between the pores and the 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). This is the volume% of the total pores of those that are not open to each other (independent pores). The independent porosity (% by volume) can be calculated by binarizing the independent pores and 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, more preferably 1 μm. The upper limit of the average diameter of the pores 4 is preferably 10 μm, more preferably 8 μm. If 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. When the average diameter of the pores 4 exceeds the above upper limit, it becomes difficult to make the distribution of the pores 4 uniform in each layer of the inner pore layer 3a and the outer pore layer 3b, and the distribution of the dielectric constant may be easily biased. The average diameter of the pores 4 contained in the inner pore layer 3a and the outer pore layer 3b may be different.
Here, the "average diameter of pores" means a value obtained by calculating and averaging the diameters of true spheres corresponding to the volumes of pores of, for example, 30 pores 4 contained in the insulating layer 3. The volume of the pores 4 can be determined by observing the cross section of the insulating layer 3 with a scanning electron microscope. The average diameter of the pores 4 can be changed depending on 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.

The plurality of pores 4 are covered with an outer shell. The outer shell is composed of a shell 7 in which the core 6 of the hollow forming particles 5 having the core shell structure shown in FIG. 3 is removed to form a hollow shell. That is, the outer shell is derived from the shell 7 of the hollow forming particles 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 oblate spheroids. Further, although an external force is likely to act in the direction perpendicular to the surface of the conductor 2, if the minor axis of the pores 4 is oriented in the vertical direction, it becomes difficult for the pores to come into contact with each other in the vertical direction, so that the independent pores are independent pores. The rate can be improved. Therefore, it is preferable that the proportion of the pores 4 whose minor axis is oriented in the direction perpendicular to the surface of the conductor 2 is large. The lower limit of the ratio of the number of pores 4 whose minor axis is oriented 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 proportion of the pores 4 whose minor axis is oriented perpendicular to the surface of the conductor 2 is less than the above lower limit, the number of pores in contact with each other increases, and the independent porosity may decrease.
Here, "the minor axis of the pores is oriented in the direction perpendicular to the conductor surface" means that the angle difference between the minor axis of the pores and the direction perpendicular to the conductor surface is 20 degrees or less.

As the lower limit of the average 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, 0.2 is preferable, and 0.3 is more preferable. The upper limit of the average of the above ratios is preferably 0.95, 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 varnish baking, so that the flexibility of the insulated wire 1 may decrease. When the average of the above ratios exceeds the above upper limit, when the porosity is increased, the pores are likely to come into contact with each other in the thickness direction (direction perpendicular to the surface of the conductor 2) of the insulating layer 3 on which an external force is likely to act. The independent porosity may be low. The minor axis and the major axis of the pores 4 can be determined by observing the cross section of the insulating layer 3 with a scanning electron microscope. The ratio can be adjusted by changing the pressure applied to the hollow forming particles 5 due to shrinkage of the resin composition contained in the varnish during baking. The pressure applied to the hollow-forming particles 5 can be changed, for example, depending on 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" is the cross section including the minor axis and the major axis of, for example, 30 pores 4 contained in the insulating layer 3. The ratio of the length of the minor axis to the major axis in is calculated and means the average value.

The lower limit of the average major axis of the pores 4 is not particularly limited, but is preferably 0.1 μm, more preferably 1 μm, for example. As the upper limit of the average of the major axis, 10 μm is preferable, and 8 μm is more preferable. 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 becomes difficult to make the distribution of the pores 4 in the insulating layer 3 uniform, and the distribution of the dielectric constant may be easily biased.
Here, the "average of the major axis of the pores" means a value obtained by averaging the major axis of, for example, 30 pores 4 included in the insulating layer 3.

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

The insulating layer 3 may include an outer shell without defects. Depending on the conditions under which the thermally decomposable resin of the core 6 flows out to the outside of the shell 7, a defect may not be formed in the shell 7 (outer shell). Further, the insulating layer 3 may include pores 4 that are not covered with the outer shell.

[Manufacturing method of insulated wire]
Next, a method of manufacturing the insulated wire 1 will be described. The method for manufacturing the insulated wire 1 is a hollow including a resin composition forming the insulating layer 3, a core 6 containing a thermally decomposable resin as a main component, and a shell 7 having a thermal decomposition temperature higher than the thermal decomposition temperature of the thermal decomposition resin. The inner pore layer 3a including the pores 4 is formed by a step of diluting the forming particles 5 to prepare varnishes having different contents of the hollow forming particles 5 (varnish preparation step) and by applying and baking the varnish on the outer peripheral surface of the conductor 2. The step of forming (inner pore layer forming step) and the coating and baking of the conductor 2 forming the inner pore layer 3a of the varnish having a larger content of the hollow forming particles 5 than the varnish forming the inner pore layer 3a on the outer peripheral surface. A step of forming the outer pore layer 3b including the pores 4 (outer pore layer forming step) is provided.

<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 varnish 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 porosities of the inner pore layer 3a and the outer pore layer 3b are different from each other, here, two types of varnishes for the inner side and the outer side having different contents of the hollow forming particles 5 are prepared. As the inner and outer varnishes, the same type of resin composition for forming the insulating layer 3 to be diluted with a solvent may be used, or different varnishes may be used.

(Resin composition)
The resin composition is a composition containing a main polymer, a diluting 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, or thermosetting. Polyester precursors, thermosetting polyesterimide precursors, thermosetting polyesteramideimide precursors, thermosetting polyamideimide precursors, polyimide precursors and the like can be used. When a thermoplastic resin is used as the main polymer, for example, polyetherimide, polyetheretherketone, polyethersulfon, polyamideimide, polyimide and the like can be used. Among these, the polyimide precursor and the 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 the insulating varnish can be used. Specifically, for example, polar organic solvents such as N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-dimethylformamide, dimethylsulfoxide, tetramethylurea, hexaethylphosphate triamide, and γ-butyrolactone are used. First, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; esters such as methyl acetate, ethyl acetate, butyl acetate and 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 chlorphenol; Examples thereof include tertiary amines, and these organic solvents are used alone or in combination of two or more.

Further, the resin composition may contain a curing agent. Examples of the curing agent include titanium-based curing agents, isocyanate-based compounds, blocked isocyanates, urea and melamine compounds, amino resins, acetylene derivatives, alicyclic acid anhydrides such as methyltetrahydrophthalic anhydride, aliphatic acid anhydrides, and aromatics. Acid anhydride and the like are exemplified. These curing agents are appropriately selected depending on the type of the main polymer contained in the resin composition used. For example, in the case of a polyamide-imide type, 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-based compound include aromatic diisocyanates such as tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), p-phenylenedi isocyanate, and naphthalene diisocyanate; hexamethylene diisocyanate (HDI), 2,2,4-trimethylhexanediisocyanate, and lysine. An aliphatic diisocyanate having 3 to 12 carbon atoms such as diisocyanate; 1,4-cyclohexane diisocyanate (CDI), isophorone diisocyanate (IPDI), 4,4'-dicyclohexylmethane diisocyanate (hydrogenated MDI), methylcyclohexanediisocyanate, isopropyridene dicyclohexyl -4,4'-diisocyanate, 1,3-diisocyanatomethylcyclohexane (hydrogenated XDI), hydrogenated TDI, 2,5-bis (isocyanatomethyl) -bicyclo [2.2.1] heptane, 2, Alicyclic isocyanate with 5 to 18 carbon atoms such as 6-bis (isocyanatomethyl) -bicyclo [2.2.1] heptane; aromatic ring such as xylylene diisocyanate (XDI) and tetramethylxylylene diisocyanate (TMXDI). An aliphatic diisocyanate having the above; examples thereof include 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, tolylen-2,4-diisocyanate, tolylen-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, butyrolylated melamine and the like. Examples of the acetylene derivative include ethynylaniline and ethynylphthalic anhydride.

(Hollow forming particles)
As shown in FIG. 3, the hollow-forming particles 5 have a core 6 containing a pyrolyzable resin as a main component and a shell 7 having a higher pyrolysis temperature than the pyrolysis 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. Therefore, 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 when the temperature is raised from room temperature at 10 ° C./min under an air atmosphere and the mass reduction rate becomes 50%. The pyrolysis temperature can be measured, for example, by measuring the thermal weight using a thermogravimetric-differential thermal analyzer (“TG / DTA” of SII Nanotechnology Co., Ltd.).

The thermally decomposable resin used for the core 6 of the hollow forming particles 5 is not particularly limited, but for example, one end or a part of polyethylene glycol, polypropylene glycol or the like is alkylated, (meth) acrylated or epoxidized. Compounds; (meth) acrylics having an alkyl group having 1 or more and 6 or less carbon atoms such as methyl poly (meth) acrylate, ethyl poly (meth) acrylate, propyl poly (meth) acrylate, and butyl poly (meth) acrylate. Polymers of acid esters; polymers of modified (meth) acrylates such as urethane oligomers, urethane polymers, urethane (meth) acrylates, epoxy (meth) acrylates, ε-caprolactone (meth) acrylates; poly (meth) acrylic acids; these Cross-linked product: Polystyrene, cross-linked polystyrene and the like. Among these, a polymer of a (meth) acrylic acid ester having an alkyl group having 1 or more and 6 or less 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. Examples of the polymer of such a (meth) acrylic acid ester include polymethylmethacrylate (PMMA).

The shape of the core 6 is preferably spherical. In order to make the shape of the core 6 spherical, for example, spherical pyrolytic resin particles may be used as the core 6. When spherical pyrolytic 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, still more preferably 1 μm, for example. The upper limit of the average particle size of the resin particles is preferably 15 μm, more preferably 10 μm. If the average particle size 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 becomes difficult to be uniform, and the distribution of the dielectric constant becomes difficult. May be prone to bias. Here, the average particle size of the resin particles means the particle size indicating the highest volume content ratio in the particle size distribution measured by the laser diffraction type particle size distribution measuring device.

As the main component of the shell 7, a material having a higher pyrolysis temperature than the pyrolysis 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 it imparts elasticity to the shell 7 and easily improves the insulating property and heat resistance. Here, the "fluorine resin" means that at least one of the hydrogen atoms bonded to the carbon atom constituting the repeating unit of the polymer chain is a fluorine atom or an organic group having a fluorine atom (hereinafter, also referred to as "fluorine atom-containing group"). ) Replaced by. The fluorine atom-containing group is one in which at least one of the hydrogen atoms in the 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 be done. The shell 7 may contain metal as long as the insulating property is not impaired.

The resin as the main component 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 type of resin as the main polymer of the resin composition is used as the main component resin of the shell 7, the pyrolysis temperature is higher than that of the pyrolytic resin, so that even if the pyrolytic resin is gasified, the shell 7 Since the resin as the main component is not easily thermally decomposed, the independent pore ratio in the pores 4 can be increased. In the insulated wire formed of such a varnish, the presence of the outer shell of the pore 4 may not be confirmed 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, it is possible to make it difficult for the shell 7 to be integrated with the above resin composition. Therefore, when a resin of the same type as the main polymer of the resin composition is used. The independent porosity in the pores 4 is higher than that in the pores 4.

The lower limit of the average thickness of the shell 7 is not particularly limited, but is preferably 0.01 μm, more preferably 0.02 μm, for example. The upper limit of the average thickness of the shell 7 is preferably 0.5 μm, 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 decrease. If the average thickness of the shell 7 exceeds the above upper limit, the volume of the pores 4 becomes too small, so that the porosity of the insulating layer 3 may not be increased more than a predetermined value. The shell 7 may be formed of one layer or may be formed of a plurality of layers. When the shell 7 is formed of a plurality of layers, the average of the total thicknesses of the plurality of layers may be within the above range.
Here, the "average thickness of the shell" means a value obtained by averaging the thicknesses of the shells 7 for, for example, 30 hollow-forming particles 5.

The upper limit of the CV value of the hollow forming particles 5 is preferably 30%, more preferably 20%. When the CV value of the hollow forming particles 5 exceeds the above upper limit, the insulating layer 3 contains a plurality of pores 4 having different sizes, so that the distribution of the dielectric constant may be easily biased. The lower limit of the CV value of the hollow forming particles 5 is not particularly limited, but is preferably 1%, for example. If the CV value of the hollow-forming particles 5 is less than the above lower limit, the cost of the hollow-forming particles 5 may become too high. Here, the “CV value” means a variable variable defined in JIS-Z8825 (2013).

As shown in FIG. 3, the hollow forming particles 5 may be configured such that the core 6 is formed of one pyrolytic resin particle, or the core 6 is formed of a plurality of pyrolytic resin particles and has a shell. The resin of 7 may be configured to cover these plurality of pyrolytic resin particles.

Further, the surface of the hollow forming particles 5 may be smooth without unevenness as shown in FIG. 3, or unevenness 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. The upper limit of the resin solid content concentration of the varnish is preferably 50% by mass, more preferably 30% by mass. If the resin solid content concentration of the varnish is less than the above lower limit, the thickness that can be formed by one application of the varnish becomes small, so that the number of repetitions of the varnish application step for forming the insulating layer 3 having a desired thickness is increased. This may increase the time of the varnish application process. If the resin solid content concentration of the varnish exceeds the above upper limit, the varnish may thicken and the storage stability of the varnish may deteriorate.

Further, in addition to the hollow forming particles 5, a pore forming agent such as a pyrolytic particle may be mixed with the varnish for forming pores. Further, for pore formation, a varnish may be prepared by combining diluting solvents having different boiling points. 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 the outer shell includes pores that are not covered with the outer shell, the presence of the pores covered with the outer shell can increase the independent porosity in the pores 4.

<Inner pore layer forming process>
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. 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 the portion of the inner pore layer 3a where the thermally decomposable resin was present.

If the inner pore layer 3a of the desired thickness cannot be formed by one 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.

<Outer pore layer forming process>
In the outer pore layer forming step, the outer peripheral surface of the conductor 2 on which the inner pore layer 3a is formed is coated with the outer varnish having a larger content of the heat-decomposable resin than the inner varnish prepared in the varnish preparation step. By baking, the outer pore layer 3b is formed on the outer side of the inner pore layer 3a formed on 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 the portion of the outer pore layer 3b where the thermally decomposable resin was present.

If 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 insulating electric wire 1, the insulating layer contains pores, and the independent pore ratio in the pores of the insulating layer 3 is equal to or higher than the above value. It can be made and has excellent insulation. Further, the insulated wire 1 includes an inner pore layer and an outer pore layer, and by setting the porosity of each within the above range, the effect of suppressing the mechanical strength can be reduced, and the mechanical strength of the insulating layer as a whole can be improved. Excellent.

[Second Embodiment]
The insulated wire 1 of FIG. 2 includes a linear conductor 2 and an insulating layer 3 coated on the outer peripheral surface of the conductor 2. The insulating layer 3 is composed of 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. The inner pore layer 3a, the outer pore layer 3b, and the other pore layer 3c each have a plurality of pores 4. The independent porosity in the pores 4 of the insulating layer 3 is 80% by volume or more, more preferably 85% by volume or more, 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 contained in the other pore layer 3c may be different from the independent porosity of the pores 4 contained in the inner pore layer 3a or the independent porosity of the pores 4 contained in the outer pore layer 3b. .. In this case, it is preferable that the independent porosity in the pores 4 is within the above range also in the other pore layers 3c.

The insulated wire 1 of FIG. 2 has a different configuration of the insulating layer 3 from the insulated wire 1 of FIG. As the conductor 2, the inner pore layer 3a and the outer pore layer 3b of the insulated wire 1 of FIG. 2, the same conductors as the conductor 2, the inner pore layer 3a and the outer pore layer 3b of the insulated wire 1 of FIG. 1 can be used. The explanation is omitted.

As the lower limit of the porosity of the other pore layer 3c, 1% by volume is preferable, and 3% by volume is more preferable. The upper limit of the porosity of the other pore layer 3c is preferably 10% by volume, more preferably 8% by volume. If the porosity of the other pore layer 3c is less than the above lower limit, the dielectric constant of the insulating layer 3 may not be sufficiently lowered, and the corona discharge start voltage may not be sufficiently improved. If the porosity of the other pore layer 3c exceeds the above upper limit, it may not be possible to secure sufficient mechanical strength of the insulating layer 3.

As the lower limit of the average thickness of the other pore layer 3c, 3 μm is preferable, and 5 μm is more preferable. The upper limit of the average thickness of the other pore layer 3c is preferably 10 μm, 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 may become too thin and the mechanical strength of the insulating layer 3 may not be maintained. When the average thickness of the other pore layers 3c exceeds the above upper limit, the other pore layers 3c, which have a small effect of reducing the dielectric constant, may become too thick and the dielectric constant of the insulating layer 3 may not be sufficiently lowered.

[Manufacturing method of insulated wire]
Next, a method of manufacturing the insulated wire 1 of FIG. 2 will be described. The insulated wire 1 of FIG. 2 can be manufactured, for example, by the same method as the manufacturing method of the insulated wire 1 of the first embodiment of FIG.

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

<Other stomatal layer formation steps>
In the other pore layer forming step, a varnish for another pore layer 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 coating, it is baked to form another pore layer 3c on the outside of the outer pore layer 3b formed on the conductor 2. At the time of baking, the thermally decomposable resin contained in the other pore layer varnish is thermally decomposed, and pores 4 are generated in the portion of the other pore layer 3c where the thermally decomposable resin was present.

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

[Other embodiments]
It should be considered that the embodiments disclosed this time are exemplary in all respects and not restrictive. The scope of the present invention is not limited to the configuration of the above-described embodiment, but is indicated by the scope of claims and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

That is, in the first and second embodiments, the insulated wire in which the insulating layer is composed of two or three pore layers has been described, but further, as an insulated wire in which the insulating layer is composed of four or more pore layers. May be good. By increasing the number of pore layers constituting the insulating layer, it becomes easier to finely adjust the dielectric constant and the mechanical strength of the entire insulating layer. Further, an insulated wire may be formed in which the insulating layer is composed of one or two pore layers by using pore layers having different porosities in the thickness direction.

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

The heat-expandable microcapsules have a core material (inclusion) made of a heat-expanding agent and an outer shell that encloses the core material. The heat-expanding agent of the heat-expandable microcapsules may be any one that expands or generates a gas by heating, and the principle thereof is not limited. As the thermal expansion agent for the heat-expandable microcapsules, 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 chlorofluorocarbons such as trichlorofluoromethane are preferably used. Further, as the chemical foaming agent, a substance having thermal decomposability such as azobisisobutyronitrile that generates _N2 gas by heating is preferably used.

The expansion start temperature of the thermal expansion agent of the heat-expandable microcapsule, that is, the boiling point of the low boiling point 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 heat-expandable microcapsule described later. More specifically, as the lower limit of the expansion start temperature of the thermal expansion agent of the heat-expandable microcapsules, 60 ° C. is preferable, and 70 ° C. is more preferable. The upper limit of the expansion start temperature of the thermal expansion agent of the heat-expandable microcapsules is preferably 200 ° C, more preferably 150 ° C. If the expansion start temperature of the heat-expanding agent of the heat-expandable microcapsules does not reach the above lower limit, the heat-expandable microcapsules may unintentionally expand during manufacturing, transportation, or storage of the insulated wire. If the expansion start temperature of the heat-expanding agent of the heat-expandable microcapsules exceeds the above upper limit, the energy cost required for expanding the heat-expandable microcapsules may become excessive.

The outer shell of the heat-expandable microcapsules is formed of a stretchable material capable of forming a microballoon containing the generated gas by expanding without breaking when the heat-expanding agent is expanded. As a material for forming the outer shell of the heat-expandable microcapsules, a resin composition containing a polymer such as a thermoplastic resin as a main component is usually used.

The thermoplastic resin which is the main component of the outer shell of the heat-expandable microcapsule is formed of a monomer such as vinyl chloride, vinylidene chloride, acrylonitrile, acrylic acid, methacrylic acid, acrylate, methacrylate, and styrene. A polymer or a copolymer formed from two or more kinds of monomers is preferably used. As an example of a preferable thermoplastic resin, vinylidene chloride-acrylonitrile copolymer is mentioned, and the expansion start temperature of the thermal expansion agent in this case is 80 ° C. or higher and 150 ° C. or lower.

Further, in the above embodiment, the structure in which the pores contained in the insulating layer are formed by the thermal decomposition of the thermally decomposable resin has been described, but for example, the pores may be formed by a hollow filler. When the pores are formed of the hollow filler, for example, the resin composition forming the insulating layer and the hollow filler are kneaded, and the kneaded material is coated on the conductor by extrusion molding to manufacture an insulated electric wire.

When the pores are formed by the hollow filler, the hollow portion inside the hollow filler becomes the pores contained in the insulating layer. Examples of the hollow filler include a shirasu balloon, a glass balloon, a ceramic balloon, an organic resin balloon and the like. When flexibility is required for the insulated wire, an organic resin balloon is preferable among these. Further, in the case of an insulated wire in which mechanical strength is important, a glass balloon is preferable because it is easy to obtain and is not easily damaged.

Further, in the above embodiment, the structure in which the pores contained in the insulating layer are formed by the thermal decomposition of the thermally decomposable resin has been described, but for example, the structure may be such that the pores are formed by using a phase separation method. As an example of using the phase separation method, a thermoplastic resin is used as the resin for forming the insulating layer, 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 the air, and the solvent is extracted and removed with another volatile solvent to form pores.

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 to enhance the adhesion between the layers and to reinforce the low dielectric constant of the insulating layer, and can be formed by, for example, a known resin composition.

When the inner intervening layer is provided between the conductor and the insulating layer, the resin composition forming the inner intervening layer contains, for example, one or more resins among polyimide, polyamide-imide, polyesterimide, polyester and phenoxy resins. It is good. Further, 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, and as a result, the insulating electric wire can be used. Properties such as flexibility, wear resistance, scratch resistance, and work resistance 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. Further, a commercially available liquid composition (insulating varnish) may be used as each resin contained in the resin composition forming the inner intervening layer.

Further, as the resin composition for forming the inner intervening layer, the same kind of resin as the above-mentioned resin as the main component of the resin composition of the insulating layer may be used as the main component. Further, the inner intervening layer may contain a plurality of pores. Since the inner intervening layer contains a plurality of pores, the inner intervening layer can also contribute to the reduction of the dielectric constant of the insulating layer. However, in this case, it is more preferable that the porosity of the inner intervening layer is smaller than the porosity of the insulating layer. Further, the inner intervening layer may be formed of a plurality of layers, and the porosities of the plurality of layers may be different from each other.

Further, in the insulated wire, a protective layer having further insulating properties may be laminated on the outer peripheral surface side of the insulating layer. As the resin composition forming the protective layer, a resin composition having the same type as the resin listed as the main component of the resin composition of the insulating layer described above can be used. The protective layer may or may not contain pores. When the protective layer contains pores, the protective layer can also contribute to the reduction of the dielectric constant of the insulating layer. However, in this case, it is more preferable that the porosity of the protective layer is smaller than the porosity of the insulating layer. On the other hand, when the protective layer does not contain pores, the insulating property is excellent, so that the insulating property of the insulated wire is further improved. Further, the protective layer may be formed of a plurality of layers including pores, and the porosities of the plurality of layers may be different from each other.

Further, in the insulated wire, a further layer such as a primer layer may be provided between the conductor and the insulating layer. The primer layer is a layer provided for enhancing the adhesion between layers, and can be formed by, for example, a known resin composition.

When a primer layer is provided between the conductor and the insulating layer, the resin composition forming the primer layer may contain, for example, one or more resins among polyimide, polyamide-imide, polyesterimide, polyester and phenoxy resins. good. Further, 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 improved. , Scratch resistance, work resistance and other characteristics can be effectively enhanced.

Further, the resin composition forming the primer layer may contain other resins such as epoxy resin, phenoxy resin, melamine resin and the like together with the above resin. Further, a commercially available liquid composition (insulating varnish) may be used as each resin contained in the resin composition forming the primer layer.

The lower limit of the average thickness of the primer layer is preferably 1 μm, more preferably 2 μm. The upper limit of the average thickness of the primer layer is preferably 30 μm, more preferably 20 μm. If the average thickness of the primer layer is less than the above lower limit, sufficient adhesion to the conductor may not be exhibited. If the average thickness of the primer layer exceeds the above upper limit, the diameter of the insulated wire may be unnecessarily increased.

Hereinafter, the present invention will be described in more detail by way of 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))
A resin composition was prepared by diluting the main polymer with this solvent using polyimide as the main polymer and N-methyl-2-pyrrolidone as the solvent. Next, core-shell particles having a core of PMMA particles and a shell of silicone having an average particle diameter of 3 μm were used as the hollow-forming particles, and an amount of the insulating layer having a pore ratio of 10% by volume was dispersed in the resin composition by a calculated value. Varnish (A) was prepared.

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

[Manufacturing 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 square conductor with a cross section of 2 mm x 2 mm, and use a die with an opening similar to the conductor and the inside of the baking furnace. It 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) was applied to the outer peripheral surface of the inner pore layer as an outer varnish, and the die was passed through a die having an opening similar to a conductor and a baking furnace at a speed of 6 m / min at 350 ° C. It was baked for 1 minute to form an insulating film. The coating of the outer varnish, passing through the die, and baking were repeated 30 times to form the outer pore layer, and the insulated wire (No. 1) was manufactured.

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 square conductor with a cross section of 2 mm x 2 mm, and use a die with an opening similar to the conductor and the inside of the baking furnace. It 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) was applied to the outer peripheral surface of the inner pore layer as an outer varnish, and the die was passed through a die having an opening similar to a conductor and a baking furnace at a speed of 6 m / min at 350 ° C. It was baked for 1 minute to form an insulating film. The application of the outer varnish, passing through the die, and baking were repeated 28 times to form the outer pore layer. Further, a varnish (A) is applied to the outer peripheral surface of the outer pore layer as a varnish for another pore layer, and the varnish (A) is passed through a die having an opening similar to a conductor and a baking furnace at a speed of 6 m / min to 350 ° C. Was baked for 1 minute to form another pore layer, and an insulated wire (No. 2) was manufactured.

No. in Table 1 The insulated wire shown in 3 was manufactured as follows. Using a vertical coating facility, varnish (B) is applied to the outer peripheral surface of a square conductor with a cross section of 2 mm x 2 mm, and a die with an opening similar to the conductor and a baking furnace at a speed of 6 m / min. It was passed and baked at 350 ° C. for 1 minute to form an insulating film. The application 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]
The obtained No. 1 to No. For the insulated wire of 3, the pore ratio of each layer, the independent pore ratio in the pores, the dielectric constant of the insulating layer, the corona discharge start voltage, the dielectric breakdown voltage, the dielectric breakdown voltage after long-term heating, and the post-press film thickness reduction rate are determined. Evaluation was performed according to the following method. The evaluation results are shown in Table 1.

(Porosity of each layer)
Each of the formed layers (inner pore layer, outer pore layer, other pore layer and pore layer) was separated from the conductor in a cylindrical shape, and the mass W2 of each tubular layer was measured. Further, the apparent volume V1 was obtained from the outer shape of each tubular layer, and V1 was multiplied by the density ρ1 of the material of each layer to calculate the mass W1 when there were no pores. From these W1 and W2 values, the porosity was calculated by the following formula.
Porosity = (W1-W2) x 100 / W1 (volume%)

(Independent porosity in the pores)
The cross section of each layer obtained by peeling into a tubular shape is observed with a scanning electron microscope (SEM), and the layers are not opened to each other by an insulating resin composition between the adjacent pores (independent). The independent porosity (% by volume) in the pores was calculated by binarizing the pores) and the pores other than the independent pores.

(Dielectric constant of insulating layer)
No. 1 to No. The dielectric constant ε of the insulating layer 3 was measured for the insulated wire of 3. FIG. 4 is a schematic diagram for explaining a method for measuring the dielectric constant. In FIG. 4, the insulated wires are designated by the same reference numerals as those in FIG. First, silver paste P was applied to three places on the surface of the insulated wire, and the insulating layer 3 on one end side of the insulated wire was peeled off to expose the conductor 2 to prepare a measurement sample. Here, the coating lengths of the silver paste P applied to the three places on the surface of the insulated wire in the longitudinal direction of the insulated wire were set to 10 mm, 100 mm, and 10 mm in order along the longitudinal direction. Two silver pastes P coated with a length of 10 mm are grounded, and the capacitance between the 100 mm long silver paste P applied between these two silver pastes and the exposed conductor 2 is LCR. It was measured with a 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)
The measurement was performed using a partial discharge tester (“KPD2050S” manufactured by Kikusui Electronics Co., Ltd.). The surfaces of the two insulated wires were brought into close contact with each other over a length of 100 mm so that there was no gap, and the electrodes were connected between the two conductors. The voltage was boosted at a frequency of 60 Hz at 25 ° C., and the voltage when a partial discharge of 100 pC or more occurred was read. It was carried out at n = 5, and evaluated by the average value.

(Dielectric breakdown voltage)
Measurement was performed using a dielectric breakdown tester (FAITH's "BREAK-DOWN TESTER" CONTROL UNIT F81501 ""). No. 1 to No. An aluminum foil having a width of 10 mm was wound around the insulated wire of No. 3, and one of the electrodes was connected to the conductor and the other was connected to the aluminum foil. The voltage was boosted at a boost speed of 500 V / sec, and the voltage when a current of 15 mA or more flowed was read. It was carried out at n = 5, and evaluated by the average value.

(Insulation breakdown voltage after heating for a long time)
No. 1 to No. After storing the insulated wire of No. 3 in a constant temperature room at 220 ° C. in an air atmosphere for 2000 hours, the dielectric breakdown voltage was measured by the above method.

(Rate of reduction in film thickness after pressing)
No. 1 to No. The insulated wire of No. 3 was installed in the press processing machine so that the press pressure was applied to a part of the insulating wire in the longitudinal direction thereof. A load (N) obtained by pressing pressure (MPa) × pressing area (mm ² ) was applied so as to have a predetermined pressing pressure, and after the load became stable, pressing was performed for 10 seconds. The average thickness T1 of the insulating layer at the pressed portion and the average thickness T2 of the insulating layer at the unpressed portion were measured, and from the measured values of T1 and T2, (T2-T1) × 100 / T2 (%). The rate of decrease in film thickness after pressing was calculated by the formula of. The reduction rate of the film thickness after pressing was measured by setting the pressing pressures 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 No. 2, the porosity of the inner pore layer is 1% by volume or more and 10% by volume or less, 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 of No. 2 has a high dielectric breakdown voltage after being heated for a long time, a low rate of decrease in film thickness after pressing, and is excellent in insulating properties and mechanical strength. On the other hand, No. The insulated wire of No. 3 did not have the above-mentioned layer structure, and the dielectric breakdown voltage after heating for a long time and the rate of decrease in film thickness after pressing were deteriorated.

1 Insulated wire 2 Conductor 3 Insulated 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)

An insulated wire having a linear conductor and an insulating layer coated on the outer peripheral surface of the conductor.
The insulating layer comprises 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 or more and 10% by volume or less.
The porosity of the outer pore layer is 25% by volume or more and 50% by volume or less .
An outer shell is provided on the peripheral edge of the plurality of pores, and the outer shell is derived from a shell of hollow forming particles having a core shell structure.
An insulated wire whose main component is a pyrolytic resin whose core is the hollow-forming particles . 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 the average thickness of the outer pore layer is 80 μm or more and 160 μm or less. The insulating layer includes another pore layer having a plurality of pores on the outside of the outer pore layer, the porosity of the other pore layer is 1% by volume or more and 10% by volume or less, and the average thickness is 3 μm. The insulated wire according to claim 1 or 2, which is 10 μm or less. The insulated wire according to claim 1, claim 2 or claim 3, wherein at least a part of the outer shell is defective. The insulated wire according to any one of claims 1 to 4 , wherein the main component of the outer shell is silicone. The plurality of pores are oblate spheroids,
The insulated wire according to any one of claims 1 to 5, wherein 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 plurality of pores. The insulated wire according to any one of claims 1 to 6, wherein a primer layer is provided between the conductor and the insulating layer.

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