JP2008257924A - Insulated wire, and transformer using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an insulated wire satisfying a requirement for improvement of heat resistance, and also having superior chemical resistance. <P>SOLUTION: This insulated wire has a conductor and at least one layer of insulating layer to coat the conductor, and a polyphenylene sulfide resin composition containing 85 mass% of a polyphenylene sulfide resin (A-1), obtained by blending a high-viscosity polyphenylene sulfide resin (A-1) having a melt viscosity of 500-3,000N sec/cm<SP>2</SP>at 300°C, with low-viscosity polyphenylene sulfide resin (A-2), having a melt viscosity of 50N sec/cm<SP>2</SP>or higher which is lower than the melt viscosity of the high-viscosity polyphenylene sulfide resin at 300°C. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an insulated wire having at least one insulating layer, preferably composed of three or more insulating layers, and a transformer using the same.

The structure of the transformer is defined by IEC standard (International Electrotechnical Communication Standard) Pub. That is, in these standards, at least three insulating layers (the enamel film covering the conductor is not recognized as an insulating layer) are formed between the primary winding and the secondary winding in the winding or the insulation. The thickness of the layer is 0.4 mm or more, and the creepage distance between the primary winding and the secondary winding is 5 mm or more, and 3000 V is applied to the primary side and the secondary side, depending on the applied voltage. It is sometimes prescribed that it can withstand more than 1 minute.
Under such a standard, conventionally, as a transformer occupying the mainstream, a structure as illustrated in the sectional view of FIG. 2 has been adopted. In this transformer, an enamel-covered primary winding 4 is wound in a state in which insulation barriers 3 for securing a creeping distance are arranged at both ends of the peripheral surface of the bobbin 2 on the ferrite core 1. An insulating tape 5 is wound on at least three layers on the primary winding 4, and an insulating barrier 3 for securing a creepage distance is further disposed on the insulating tape, and then an enamel-coated secondary winding 6. Is a wound structure.

However, in recent years, a transformer having a structure not including the insulating barrier 3 or the insulating tape layer 5 as shown in FIG. 1 has been used in place of the transformer having the cross-sectional structure shown in FIG. . Compared with the transformer having the structure shown in FIG. 2, this transformer can be reduced in size as a whole, and has the advantage that the winding work of the insulating tape can be omitted.
When the transformer shown in FIG. 1 is manufactured, the primary winding 4 and the secondary winding 6 to be used have at least three insulating layers 4b (6b) on the outer periphery of one or both of the conductors 4a (6a). , 4c (6c), 4d (6d) are required in relation to the IEC standard.

  As such a winding, an insulating tape is wound around the outer periphery of the conductor to form a first insulating layer, and an insulating tape is further wound thereon to form a second insulating layer and a third insulating layer. Are formed in order to form an insulating layer having a three-layer structure in which layers are separated from each other. In addition, it is also known that a fluororesin is sequentially extruded and coated on the outer periphery of a conductor instead of an insulating tape to form a total of three insulating layers (see, for example, Patent Document 1).

However, in the case of the above-described insulating tape winding, the winding work is unavoidable, so the productivity is remarkably low, and therefore the wire cost is very high.
Further, in the case of the above-mentioned fluororesin extrusion, the insulating layer is formed of a fluororesin, so that it has an advantage of good heat resistance, but the cost of the resin is high, and the resin is pulled at a high shear rate. Therefore, it is difficult to increase the production speed due to the property that the appearance state deteriorates, and there is a problem that the cost of the electric wire becomes high as in the case of the insulating tape winding.

  In order to solve these problems, a modified polyester resin which controls crystallization and suppresses a decrease in molecular weight as the first and second insulating layers is extruded on the outer periphery of the conductor, and a polyamide resin is used as the third insulating layer. Has been put to practical use (see, for example, Patent Documents 2 and 3). Furthermore, with the recent miniaturization of electrical and electronic equipment, there is concern about the effects of heat generation on the equipment. Polyethersulfone (hereinafter referred to as “PES”) resin is extrusion coated as a multilayer insulated wire that achieves higher heat resistance. Have been proposed (see, for example, Patent Document 4).

  However, it cannot be said that such a multilayer insulated wire can sufficiently meet the demands for improving the performance of future transformers that are becoming increasingly severe. The multilayer insulated wire using the PES resin proposed above realizes high heat resistance of at least heat-resistant type F (155 ° C.) satisfying the IEC 60950 standard, but there is a concern that the chemical resistance is poor.

Until now, there has not been known an insulated wire having excellent chemical resistance while maintaining heat resistance of heat resistance F or higher. In order to satisfy the heat resistance of heat class F or higher, super engineer plastics such as polyphenylene sulfide (hereinafter also referred to as “PPS”) resin, PES resin, and polyetherimide (hereinafter referred to as “PEI”) resin are used, or A method such as filling with an inorganic filler is conceivable. However, amorphous resins such as PES resin and PEI resin have a drawback that they can sufficiently satisfy heat resistance but are very weak in chemical resistance. PPS resin, which is a crystalline resin, is excellent in chemical resistance, but has poor elongation characteristics and is not suitable for use alone as a wire material. On the other hand, by using the PPS described in Patent Document 5, it is possible to make the electric wire sufficiently flexible, but a rubber component is added to this PPS, and the heat resistance is B type (130 ° C.). It will drop to. Further, when the inorganic filler is filled, the flexibility is remarkably lowered, and there is a possibility that a serious defect as an electric wire such as the coating resin is broken in the winding process.
Therefore, there is a demand for a multilayer insulated wire having both high heat resistance higher than heat resistance type F and excellent chemical resistance.
Japanese Utility Model Publication No. 3-56112 US Pat. No. 5,606,152 JP-A-6-223634 JP-A-11-176244 Japanese Patent Application No. 2003-502842

  In order to solve the above-described problems, an object of the present invention is to provide an insulated wire that satisfies the high heat resistance requirement of the heat resistant type F and also has excellent chemical resistance. Furthermore, an object of the present invention is to provide a transformer having excellent electrical characteristics and high reliability, which is formed by winding an insulated wire excellent in heat resistance and chemical resistance.

  As a result of intensive studies, the present inventors have found that an insulating layer is made of a mixture of a high-viscosity PPS resin having a specific melt viscosity and a low-viscosity PPS resin mixed with a plurality of PPS resins having different melt viscosities. It was found that the electric wire can have both heat resistance and elongation characteristics. The above object of the present invention has been achieved by the insulated wires shown below and a transformer using the insulated wires.

That is, the present invention provides the following insulated wires and transformers.
(1) An insulated wire having a conductor and at least one insulating layer covering the conductor, wherein at least one of the insulating layers has a melt viscosity of 500 to 3000 N · sec / m ^{2 at} 300 ° C. The high viscosity polyphenylene sulfide resin (A-1) in FIG. 5 has a melt viscosity at 300 ° C. of 50 N · sec / m ² or more, and is lower than the melt viscosity at 300 ° C. of the high viscosity polyphenylene sulfide resin (A-1). An insulated wire comprising a PPS resin composition comprising 85% by mass or more of a polyphenylene sulfide resin (A) blended with a low-viscosity polyphenylene sulfide resin (A-2) on the side.
(2) The PPS resin composition is a resin dispersion containing a thermoplastic elastomer (B), the PPS resin (A) as a continuous layer, and the thermoplastic elastomer (B) as a dispersion layer. The insulated wire according to (1).
(3) The insulated wire according to (2), wherein the PPS resin composition contains 15 parts by mass or less of the thermoplastic elastomer (B) with respect to 100 parts by mass of the PPS resin (A). .
(4) The thermoplastic elastomer (B) is a resin (B-1) containing at least one functional group selected from the group consisting of an epoxy group, an oxazolyl group, an amino group, and a maleic anhydride residue. The insulated wire according to (2) or (3), characterized in that:
(5) Item (2) or (3), wherein the thermoplastic elastomer (B) is an ethylene copolymer (B-2) having a carboxylic acid or a metal salt of a carboxylic acid in the side chain. Insulated wires.
(6) The PPS resin resin (A) is the high-viscosity PPS resin (A-1) and the low-viscosity PPS resin (A-2) is 90: 10-50 in (A-1) :( A-2). : The insulated wire according to any one of (1) to (5), which is blended at a mass ratio of 50.
(7) An insulated wire having a conductor and at least two insulating layers covering the conductor, wherein polyester is used for the innermost layer closest to the conductor. (1) to (6) An insulated wire given in any 1 paragraph.
(8) A transformer comprising the insulated wire according to any one of (1) to (7).

  The multilayer insulated wire of the present invention sufficiently satisfies the heat resistance of the IEC60950 standard heat-resistant type F and has excellent chemical resistance, so that it has sufficient strength even in the step of impregnating chemicals after winding. An even wider selection is possible.

  The insulated wire of the present invention is an insulated wire comprising a conductor and at least one insulating layer that covers the conductor, and at least one of the insulating layers includes a high-viscosity PPS resin (A-1), A PPS resin composition comprising 85% by mass or more of a PPS resin (A) blended with a low-viscosity PPS resin (A-2) is used.

The melt viscosity at 300 ° C. of the high viscosity PPS resin (A-1) used in the present invention is 500 N · sec / m ² or more. If the molecular weight is smaller than this, sufficient elongation characteristics cannot be obtained even with a PPS blend polymer. Further, since the extremely difficult to mold the high molecular weight occurs, the melt viscosity are those in 500~3000N · sec / ^{m 2,} preferably in the 8000~2000N · sec / ^{m 2,} 800~ More preferably, it is 1500 N · sec / m ^2, and most preferably about 1000 N · sec / m ² .

The melt viscosity at 300 ° C. of the low-viscosity PPS resin (A-2) used in the present invention is 50 N · sec / m ² or more, and is on the lower viscosity side than the high-viscosity PPS used for blending. Sufficient elongation characteristics cannot be obtained with a molecular weight of 50 N · sec / m ² or less. Melt viscosity at 300 ° C. of low viscosity PPS resin (A-2) is preferably in the 50~500N · sec / ^{m 2,} more preferably in the 100~400N · sec / ^{m 2,} about 200 N · sec / M ² is most preferred.
As conditions for measuring these viscosities, a capillary viscometer was used, and measurement was performed at a use temperature of 300 ° C. and a use die L / D = 40/1. As an example of an apparatus capable of measurement, there is Capillograph 1C (trade name) manufactured by Toyo Seiki Co., Ltd.

The blend ratio in the PPS resin (A) is preferably 10 to 50 parts by mass of the low viscosity PPS resin (A-2) with respect to 90 to 50 parts by mass of the high viscosity PPS resin (A-1). When there are too many ratios of high-viscosity PPS resin (A-1), fluidity | liquidity is low and workability may become very scarce. Moreover, when there are too few ratios of high-viscosity PPS resin (A-1), an elongation characteristic may fall large. The blend ratio is preferably 20 to 40 parts by mass of the low viscosity PPS resin (A-2) with respect to 80 to 60 parts by mass of the high viscosity PPS resin (A-1).
As a PPS type, any of a cross-linked type, a semi-linear type, and a linear type may be used, but as a PPS resin used in the present invention, for example, DIC FZ2100 (manufactured by Dainippon Ink and Chemicals, trade name) is used as a high molecular weight PPS resin A typical example of the low molecular weight PPS resin is DSP C-106 (trade name, manufactured by Dainippon Ink & Chemicals, Inc.).

The PPS resin composition used in the present invention contains the above PPS resin (A) in an amount of 85% by mass or more, preferably 90 to 95% by mass or more.
The component other than the PPS resin (A) that can be included in the PPS resin composition is not particularly limited as long as it does not impair the object of the present invention. It is preferable because there is no concern about the deterioration of property.

  In the present invention, the PPS resin composition is preferably a resin dispersion containing the thermoplastic elastomer (B), the PPS resin (A) as a continuous layer, and the thermoplastic elastomer (B) as a dispersion layer. By adding the thermoplastic elastomer (B), further improvement in flexibility is expected. The content of the thermoplastic elastomer (B) in the present invention is preferably 15 parts by mass or less, more preferably 4 to 13 parts by mass with respect to 100 parts by mass of the PPS resin (A). Addition of 15 parts by mass or less is expected to further improve flexibility without impairing heat resistance.

In one preferred embodiment of the present invention, the thermoplastic elastomer (B) is selected from the group consisting of an epoxy group, an oxazolyl group, an amino group and a maleic anhydride residue as the functional group having reactivity with the polyester resin. It is a resin (B-1) containing at least one group. Among them, it is particularly preferable to contain an epoxy group. The resin (B-1) preferably has 0.05 to 30 parts by mass and more preferably 0.1 to 20 parts by mass of the functional group-containing monomer component in the same molecule. If the amount of the monomer component containing the functional group is too small, the effect of the present invention is hardly exerted, and if it is too large, a gelled product is easily generated due to overreaction with the polyester resin (A).
Such a resin (B-1) is preferably a copolymer comprising an olefin component and an epoxy group-containing compound component. Moreover, the copolymer which consists of at least 1 or more types of component, an olefin component, and an epoxy-group containing compound component among an acrylic component or a vinyl component may be sufficient.

  Representative examples of the above (B-1) include ethylene / glycidyl methacrylate copolymer, ethylene / glycidyl methacrylate / methyl acrylate terpolymer, ethylene / glycidyl methacrylate / vinyl acetate ternary copolymer. Examples of the polymer include ethylene / glycidyl methacrylate / methyl acrylate / vinyl acetate quaternary copolymer. Of these, ethylene / glycidyl methacrylate copolymer and ethylene / glycidyl methacrylate / methyl acrylate terpolymer are preferred. Examples of commercially available resins include Bond First (manufactured by Sumitomo Chemical Co., Ltd., trade name) and Rotada (manufactured by Atofina Corp., trade name).

  (B-1) may be any of a block copolymer, a graft copolymer, a random copolymer, and an alternating copolymer. Resin (B-1) is, for example, an ethylene / propylene / diene random copolymer, an ethylene / diene / ethylene block copolymer, a propylene / diene / propylene block copolymer, or a styrene / diene / ethylene block copolymer. Polymer, styrene / diene / propylene block copolymer, styrene / diene / styrene block copolymer, partially epoxidized diene component or epoxy-modified compound such as glycidyl methacrylic acid It may be a thing. These copolymers are also preferably hydrogenated in order to increase the thermal stability.

  In another preferred embodiment of the present invention, the thermoplastic elastomer (B) is an ethylene copolymer (B-3) in which a carboxylic acid or a metal salt of a carboxylic acid is bonded to a side chain of polyethylene. This ethylene copolymer functions to suppress crystallization of the polyester resin.

  Examples of the carboxylic acid to be bonded include unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid, and unsaturated dicarboxylic acids such as maleic acid, fumaric acid, and phthalic acid. Examples of the metal salt include salts with Zn, Na, K, Mg and the like. As such an ethylene copolymer, for example, a resin generally called an ionomer in which a part of a carboxylic acid of an ethylene-methacrylic acid copolymer is converted into a metal salt (for example, Himiran; trade name, Mitsui Polychemical Co., Ltd.) ), Ethylene-acrylic acid copolymer (for example, EAA; trade name, manufactured by Dow Chemical Company), ethylene-based graft polymer having a carboxylic acid in the side chain (for example, Admer; trade name, manufactured by Mitsui Petrochemical Industries, Ltd.) ).

  Further, by selecting a polyester resin for the layer closer to the conductor than the layer using the PPS resin, extremely good solderability can be imparted. While satisfying the high heat resistance of heat-resistant type F, it can also have solderability.

As the polyester resin used in the present invention, those obtained by ester reaction of an aromatic dicarboxylic acid or a dicarboxylic acid in which a part thereof is substituted with an aliphatic dicarboxylic acid and an aliphatic diol are preferably used. For example, polyethylene terephthalate (PET) resin, polybutylene terephthalate (PBT) resin, polyethylene naphthalate (PEN) resin and the like can be given as representative examples. Commercially available resins that can be preferably used in the present invention include polyethylene terephthalate ( PET-based resins are Viropet (trade name, manufactured by Toyobo Co., Ltd.), Belpet (trade name, manufactured by Kanebo Co., Ltd.), and Teijin PET (trade name, manufactured by Teijin Limited). Examples of the polyethylene naphthalate (PEN) resin include Teijin PEN (trade name, manufactured by Teijin Ltd.), and examples of the polycyclohexanedimethylene terephthalate (PCT) resin include Ekter (trade name, manufactured by Toray Industries, Inc.). A rod run (trade name, manufactured by Unitika Co., Ltd.), which is a liquid crystalline polyester, is also suitable. In the polyester resin of the present invention, a blend of polyester resins, the above thermoplastic elastomer, commonly used additives, inorganic fillers, processing aids, colorants, and the like are also added as long as the required properties are not impaired. be able to.

  The conductor used in the present invention is a metal (eg, copper, aluminum, etc.) bare wire (single wire), an insulated wire in which an enamel coating layer or a thin insulating layer is provided on the bare metal wire, or a plurality of bare metal wires or A multi-core stranded wire obtained by twisting a plurality of enamel insulated wires or thin insulated wires can be used. The number of stranded wires of these stranded wires can be arbitrarily selected depending on the high frequency application. In addition, when the number of cores (elements) is large (for example, 19-, 37-elements), it may not be a stranded wire. When not a stranded wire, for example, a plurality of strands may be simply bundled substantially in parallel, or the bundle may be twisted at a very large pitch. In any case, it is preferable that the cross section is substantially circular.

  In the insulated wire of the present invention, when the insulating layer has three layers, the outer periphery of the conductor is extrusion coated with the first insulating layer having a desired thickness, and then the outer periphery of the first insulating layer is formed. The second insulating layer having a desired thickness is extrusion-coated, and the insulating layer is sequentially extruded. The total thickness of the extruded insulating layer formed in this way is preferably in the range of 60 to 180 μm for the three layers. This means that if the total thickness of the insulating layer is too thin, the resulting multi-layer insulated wire has a large decrease in electrical characteristics and may be unsuitable for practical use. Conversely, if it is too thick, it is unsuitable for downsizing. This may be difficult. A more preferable range is 70 to 150 μm. In addition, the thickness of each of the three layers is preferably 20 to 60 μm.

  The insulated wire of the present invention can be used without any particular change to a transformer using a conventionally known insulated wire. In particular, the insulated wire of the present invention having three insulating layers can be suitably used as the primary winding 4 and the secondary winding 6 of the transformer having the structure shown in FIG.

  EXAMPLES Next, although this invention is demonstrated further in detail based on an Example, this invention is not limited to these.

Examples 1 to 10 and Comparative Examples 1 and 2
The resin composition for forming the insulating layer was prepared by melting and mixing the materials shown in Table 1 with a twin screw extruder for kneading, further cooling with water and cutting into pellets with a pelletizer.
An annealed copper wire having a wire diameter of 1.0 mm was prepared as a conductor. The composition of the resin for extrusion coating of each layer shown in Table 1 (the numerical value of the composition indicates parts by mass) and the thickness. In the case of a single layer, one layer is sequentially extruded and coated on a conductor for insulation. An electric wire was manufactured.
About the obtained insulated wire, various characteristics were tested by the following specifications. The appearance was observed with the naked eye.

A. Flexibility Wrap tightly 10 times so that the wire is in contact with the wire itself, observe with a microscope, and pass if no abnormalities such as cracks or crazing are seen in the film (shown as ○ in Table 1) Moreover, although it is not as abnormal as a crack or crazing, it is indicated by Δ when the wrinkle or the like is changed on the surface of the electric wire, and rejected (shown by x in Table 1). It was.
B. Electrical heat resistance It evaluated by the following test method based on the appendix U (electric wire) of 2.9.4.4 term of IEC standard 60950.
A multi-layer insulated wire is wound around a mandrel with a diameter of 10 mm for 10 turns while applying a load of 118 MPa (12 kg / mm ² ), type F: heated at 240 ° C. for 30 minutes, and then a voltage is applied at 3000 V for 1 minute to short circuit. And F type pass (indicated by ◯ in Table 1). (Decision is evaluated at n = 5. If even one is NG, it is rejected (indicated by x in Table 1)).
C. Chemical resistance A wire wound with 20D as a winding process was immersed in xylene, styrene, ethanol, and isopropyl alcohol solvent for 30 seconds, dried and then observed on the surface of the sample to determine whether cracks or crazing had occurred. In Table 1, the case where cracks and crazing did not occur was indicated as "O", and the case where crazing occurred was indicated as "X".

In Table 1, “-” means not added. In addition, pass / failure 好 ま し い is particularly preferable, ◯ is preferable, and × indicates inappropriate.
Each resin shown in the table is as follows.
PPS (molecular weight peak 35000): DIC FZ2100 (manufactured by Dainippon Ink & Chemicals, Inc., trade name) polyphenylene sulfide resin PPS (molecular weight peak 20000): DSP C-106 (manufactured by Dainippon Ink & Chemicals, trade name) polyphenylene sulfide resin Ethylene / Glucidyl methacrylate / Methyl acrylate copolymer: Bond First (trade name, manufactured by Sumitomo Chemical Co., Ltd.)
Ethylene copolymer: High Milan 1855 (trade name, manufactured by Mitsui DuPont)
Polyester: Rod run (made by Unitika Ltd., trade name) Liquid crystal polyester resin 15 parts by mass and Teijin PET TR8550 (Teijin Ltd., trade name) Polyethylene terephthalate resin 85 parts by mass PES: Sumika Excel 4100 (trade name, manufactured by Sumitomo Chemical Co., Ltd.) ) Polyethersulfone resin In addition, the first layer, the second layer, and the third layer are coated in order from the conductor. In the case of a three-layer structure, the third layer is the outermost layer.

From the results shown in Table 1, the following became clear.
In Comparative Example 1, the electrical heat resistance was satisfactory, but the PES resin, which is weak in chemical properties, was used for the outermost layer, and the chemical resistance was not satisfactory. In Comparative Example 2, the amount of the epoxy group-containing resin added was large and the electrical heat resistance was poor. On the other hand, in Examples 1-9, all of the electrical heat resistance, chemical resistance, and wire appearance satisfied the acceptance criteria. In Example 10, since the blend ratio of the low-viscosity PPS resin was increased and the elongation rate was decreased, the flexibility of the electric wire was reduced as a result. However, other characteristics such as heat resistance met the acceptance criteria.

It is sectional drawing which shows the example of the transformer of a structure which uses a 3 layer insulated wire as a coil | winding. It is sectional drawing which shows an example of the transformer of the conventional structure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ferrite core 2 Bobbin 3 Insulation barrier 4 Primary winding 4a Conductors 4b, 4c, 4d Insulating layer 5 Insulating tape 6 Secondary winding 6a Conductors 6b, 6c, 6d Insulating layer

Claims (8)

An insulated wire having a conductor and at least one insulating layer covering the conductor, wherein at least one of the insulating layers has a high melt viscosity at 300 ° C. of 500 to 3000 N · sec / m ^2. Viscosity polyphenylene sulfide resin (A-1) has a melt viscosity at 300 ° C. of 50 N · sec / m ² or more, and is lower than the melt viscosity at 300 ° C. of the high viscosity polyphenylene sulfide resin (A-1). An insulated wire comprising a polyphenylene sulfide resin composition containing 85% by mass or more of a polyphenylene sulfide resin (A) blended with a low viscosity polyphenylene sulfide resin (A-2).   The polyphenylene sulfide resin composition is a resin dispersion containing a thermoplastic elastomer (B), the polyphenylene sulfide resin (A) as a continuous layer, and the thermoplastic elastomer (B) as a dispersion layer. The insulated wire according to claim 1.   The insulated wire according to claim 2, wherein the polyphenylene sulfide resin composition contains 15 parts by mass or less of the thermoplastic elastomer (B) with respect to 100 parts by mass of the polyphenylene sulfide resin (A).   The thermoplastic elastomer (B) is a resin (B-1) containing at least one functional group selected from the group consisting of an epoxy group, an oxazolyl group, an amino group, and a maleic anhydride residue. The insulated wire according to claim 2 or 3.   The insulated wire according to claim 2 or 3, wherein the thermoplastic elastomer (B) is an ethylene copolymer (B-2) having a carboxylic acid or a metal salt of a carboxylic acid in a side chain.   The polyphenylene sulfide resin (A) is composed of the high-viscosity polyphenylene sulfide resin (A-1) and the low-viscosity polyphenylene sulfide resin (A-2) at 90:10 to 50 in (A-1) :( A-2). The insulated wire according to any one of claims 1 to 5, wherein the insulated wire is blended at a mass ratio of 50.   It is an insulated wire which has at least 2 layers of insulation layers which coat | cover a conductor and the said conductor, Comprising: Polyester is used for the innermost layer nearest to a conductor, In any one of Claims 1-6 characterized by the above-mentioned. Insulated wire as described.   A transformer comprising the insulated wire according to any one of claims 1 to 7.

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