WO2004099325A1

WO2004099325A1 - Insulating coating composition and insulated wire

Info

Publication number: WO2004099325A1
Application number: PCT/JP2004/006676
Authority: WO
Inventors: Toshitaka Kawanami; Hiroyuki Sakamoto; Hidenori Tanaka; Kazuo Morichika; Takao Saito
Original assignee: Nippon Paint Co., Ltd.
Priority date: 2003-05-12
Filing date: 2004-05-12
Publication date: 2004-11-18
Also published as: JP2004339251A; TW200506018A

Abstract

It is an object of the present invention to provide an insulating coating composition capable of attaining an insulating film having a high dielectric breakdown voltage, and an insulated wire coated therewith, which has a high insulating property and occupancy ratio. An insulating coating composition comprising a crosslinked resin particle and at least one insulating resin selected from the group consisting of polyvinyl formal resin, polyamide-imide resin, polyamide resin, polyimide resin and polyester-imide resin.

Description

DESCRIPTION

INSULATING COATING COMPOSITION AND INSULATED WIRE

TECHNICAL FIELD

The present invention relates to an insulating coating composition and an insulated wire.

BACKGROUND ART It is often required to form insulating films in the application areas such as electric and electronic equipment. Such insulating films are generally attainedbyusing insulating coatings containing organic resins such as various synthetic resins and natural resins. An example of an article to be coated, which is required to form such an insulating film, may include an electric wire having edges such as a rectangular wire. When such an electric wire having edges is used as amagnet wire, it has the performances superior to a conventional round electric wire in that since the wire increases in an occupancy ratio and can be wound in higher density, the size and the weight of the magnet can be reduced; amore strongmagnetic force canbe attained; an electric current becomes large; and a heat releasing property is excellent . As an insulating coating used for forming such an insulating film, there are known, for example, coatings comprising aromatic polyamide resin, polybenzimidazole resin, polyamide-imide resin and polyimide resin as disclosed in Japanese Kokai Publication 2000-235818. However, when an electric wire having edges, such as a rectangularwire, is coatedusing the above-mentioned insulating coating, the film thickness of an insulating film formed on the edge becomes thin; consequently, an insulated wire having a adequate insulating property may not be attained. Further, since the film thickness of the insulating film formed on the edge becomes thin, the cross-sectional profile of the obtained insulatedwire becomes different fromthe profile of an article to be coated; consequently, the occupancy ratio may not be sufficiently enhanced.

Therefore, there has been desired the development of an insulating coating composition, which can form an insulating film with a sufficient film thickness also on edges and attain an insulating film having a high insulating property when it is applied to an article to be coated having edges.

SUMMARY OF THE INVENTION In view of the above-mentioned circumstances, it is an object of the present invention to provide an insulating coating composition capable of attaining an insulating film having a high dielectric breakdown voltage, and an insulated wire coated therewith, which has a high insulating property and occupancy ratio.

The present invention is directed to an insulating coating composition comprising a crosslinked resin particle and at least one insulating resin selected from the group consisting of polyvinyl formal resin, polyamide-imide resin, polyamide resin, polyimide resin and polyester-imide resin.

Preferably, the content of the crosslinked resin particle is 0.5 to 40% by weight relative to the resin solid matter in ^"the coating composition.

The present invention is also directed to an insulated wire having edges, which is coated with the above-mentioned insulating coating composition.

Preferably, in the insulated wire having edges, an article to be coated is an electric wire of a rectangular wire or a square wire.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows an example of a schematic view of a cross section of an insulated wire coated with an insulating coating composition of the present invention.

Fig. 2 shows an example of a schematic view of a cross section of an insulated wire obtained in the case of using no crosslinked resin particle.

EXPLANATION OF THE NUMERICAL SYMBOLS 1 rectangular wire 2 insulating film

3 insulated wire

4 edge

5 insulated wire

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the present invention will be described in detail .

The insulating coating composition of the present invention comprises: a crosslinked resin particle; and at least one insulating resin selected from the group consisting of polyvinyl formal resin, polyamide-imide resin, polyamide resin, polyimide resin and polyester-imide resin, and can attain an insulating film having a dielectric breakdown voltage higher than that of an insulating film formed from a conventional insulating coating.

That is, since the insulating film, formed by applying the above-mentioned insulating coating composition, is coated uniformly throughout the whole surface, thickness of the film does not become thin at edges; therefore, it has an excellent dielectric breakdown voltage in comparison to an insulating film obtained by only applying a conventional insulating coating.

The above-mentioned crosslinked resin particle has a functionofproviding a thixotropicproperty for a coating. Thus, in baking and curing the applied film to form an insulating film, it can form an insulating film, which is coated in a sufficient thickness, on the edges of an article to be coated. As a result, it can attain an insulating film having a high dielectric breakdown voltage.

The above-mentioned crosslinked resin particle is not particularly restricted and examples thereof may include a compound obtained by a so-called emulsion method in which a polymerizable monomer is crosslinked in an aqueous medium while being emulsion polymerized in the presence of a resin having a emulsifying power and an initiator, and a compound obtained by a so-called NAD method in which a polymerizable monomer is crosslinked while being copolymerized in a mixed solution of an organic solvent and a dispersion-stable resin soluble in the organic solvent, which are methods well known to those skilled in the art. Herein, when the crosslinked resin particle is obtained by the NAD method, a substance, which includes the polymerizable monomer crosslinked through copolymerization and the dispersion-stable resin, is referred to as a crosslinked resin particle.

In addition, in the case where the insulating coating composition of the present invention is used in the form of an organic solvent, the crosslinked resin particle obtained by the above-mentioned NAD method can be contained in the insulating coating composition as it is, but when the crosslinked resin particle is obtained by the above-mentioned emulsion method, a crosslinked resin particle, obtained by eliminating water content through substituting a solvent for, azeotropically distilling, centrifuging, filtering or drying the obtained crosslinked resin particle to convert the crosslinked resin particle to an organic solvent type, can be contained in the insulating coating composition.

It is preferredthat the above-mentioned crosslinkedresin particle has specifically a volume-average particle diameter within the range from 0.05 μm as a lower limit to 1 μm as an upper limit. When it is less than 0.05 μm, coating of the edges may become insufficient. When it exceeds 1 μm, an appearance of the insulating film may be deteriorated. More preferably, the lower limit is 0.07 μm and the upper limit is 0.5 μm. This volume-averageparticle diameter canbe controlledby adjusting, for example, the composition or the polymerization conditions of apolymerizablemonomer . The above-mentionedvolume-average particle diameter can be determined, for example, by a laser-light-scattering method and the like.

The. insulating coating composition of the present invention preferably contains the crosslinked resin particle obtained in a manner described above in an amount of 0.5 to 40% by weight relative to the resin solid matter in the coating composition. When the above-mentioned content of the crosslinked resin particle is less than 0.5% by weight, coating of the edges may become insufficient. When it exceeds 40% by weight, an appearance of the insulating filmmaybe deteriorated. More preferably, the above-mentioned lower limit is 1% by weight and the above-mentioned upper limit is 30% by weight.

As the insulating coating composition of the present invention, there can be used at least one insulating resin selected from the group consisting of polyvinyl formal resin, polyamide-imide resin, polyamide resin, polyimide resin and polyester-imide resin.

Among them, the above-mentioned insulating resin is preferably a polyamide-imide resin or a polyamide resin in that the obtained insulated wire has a higher dielectric breakdown voltage.

Examples of an insulating coating comprising the above-mentioned polyamide-imide resin may include a coating prepared by reacting tricarboxylic anhydride with diisocyanate andNEOHEATAI (made by Totoku Toryo Co . , Ltd.) as a commercially available product.

Examples of an insulating coating comprising the above-mentioned polyamide resin may include aramid (aromatic polyamide) coatings, nylon MXD 6 coatings and the like. In particular, aramid coatings are preferred in view of heat resistance, mechanical strength and the like.

The above-mentioned insulating coating composition may further contain another components used in ordinary insulating coating as required. The above-mentioned another component is not particularly limited, and examples thereof may include a pigment, a rust preventing agent, a pigment dispersion resin, a surfactant, an antioxidant, an ultraviolet absorber and the like. However, when the above-mentioned components are used, it is preferred to adjust the amount of the component to be blended paying attention to the retention of a dielectric breakdown voltage.

The insulating coating composition of the present invention is suitably applicable to an article to be coatedhaving edges and can be suitably applied particularly to an electric wire having a small curvature of edges in the cross-sectional profile, which is considered to be difficult to coating. In addition, the curvature used in this description refers to one, which is represented by (a radius of a curve of the edge/a length of a shorter side of two sides containing the edge) x 100 with respect to the edge and two sides containing the edge in a cross section of the electric wire.

The article to be coated with the insulating coating compositionof thepresent inventionis notparticularlylimited, and examples thereof may include metals such as iron, copper, aluminum, gold, silver, nickel, tin, zinc, titaniumandtungsten, and alloys containing these metals.

A method of coating the insulating coating composition of the present invention is not particularly limited, and examples thereof may include well-known methods such as coating and baking. Examples of the coating method may include a dice technique, a felt technique and the like.

The above-mentioned insulating coating composition can be suitably used particularly for producing an insulated wire having edges. The above-mentioned insulated wire has a high dielectric breakdown voltage since the insulating film is formed with a substantially uniform thickness throughout the whole surface of the article to be coated, that is, the whole surface including the edges by the action of the crosslinked resin particle. Therefore, the insulated wire, having edges coated with this insulating coating composition, can be suitably used as one having the high dielectric breakdown voltage. Such the insulated wire having edges also constitutes an aspect of the present invention.

Furthermore, the article to be coated, in the insulated wire having edges of the present invention, is preferably an electric wire of a rectangular wire or a square wire, which has a rectangular shape or square shape in the cross-sectional profile respectively. When the electric wire of a rectangular wire or a square wire is coated using the insulating coating composition of the present invention, an occupation ratio of the article to be coated can be retained because of a less change in a shape; consequently, the occupation ratio of the obtained insulated wire can be improved. Therefore, it is possible to improve the performances of the insulated wire in comparison to the case of using a round electric wire having the same volume .

An example of a conceptual view of the insulating film obtainedbyusing the insulating coating composition, containing crosslinked resin particles, of the present invention is shown in Fig. 1. Fig. 1 shows an insulated wire 3 which is obtained by forming an insulating film 2, prepared from the insulating coating composition containing crosslinked resin particles, on a rectangular wire 1. The insulating film 2 formed by using the insulating coating composition of the present invention is formed in a sufficient thickness even on the edge 4 of the rectangularwire 1. Accordingly, the insulatedwire 3, obtained by using the insulating coating composition of the present invention, can be suitably used even for use where a higher dielectric breakdown voltage is required. Furthermore, the insulated wire 3, which is^" formed by using the insulating coating composition of the present invention, is small in a change in a shape and its cross-sectional profile retains a rectangular shape . Therefore, when the insulated wire 3 is used in a bundle, a void area is less because of a rectangular wire and a high occupation ratio can be retained. On the other hand, Fig.2 shows an example of a conceptual view of the insulated wire obtained by forming an insulating filmusing an insulating coating containing no crosslinked resin particle. The insulating film 2, obtained when a coating containing no crosslinked resin particle is used, is not formed in a sufficient thickness on the edge 4 of the rectangular wire 1. Consequently, the insulated wire 5, obtained by using the insulating coating containing no crosslinked resin particle, has a lower dielectric breakdown voltage in comparison to the insulated wire obtained by using the insulating coating composition, containing crosslinked resin particles, of the present invention. Furthermore, the insulated wire 5, which is formed by using the coating containing no crosslinked resin particle, is large in a change in a shape and its cross-sectional profile has mild edges and approaches a round shape . Therefore, when the insulated wire 5 is used in a bundle, a void area becomes large and a high occupation ratio cannot be retained.

By applying the insulating coating composition of the present invention, it is possible to obtain a filmhaving auniform film thickness and to significantly enhance the dielectric breakdown voltage in comparison to an insulating film obtained by only applying a conventional insulating coating. Further, when the article to be coated is an electric wire of a rectangular wire or a square wire, it is possible to retain the occupancy ratio of the obtained insulatedwire . Thereby, when the obtained insulatedwire is used, for example, as amagnet wire, an electric current becomes larger or the number of turns of a coil becomes less because of an increase in the cross-sectional area of the wire. Therefore, in the magnet, the reduction of its size and weight canbe achieved; a strongermagnetic force canbe attained; electrical resistancebecomes less; andaheat releasingproperty is enhanced. Therefore, the insulating film, obtained by using the insulating coating composition of the present invention, has the high dielectric breakdown voltage and the insulated wire having the above-mentioned insulating film can be suitably used in various applications.

EXAMPLES Hereinafter, the present invention will be describedmore specifically by way of examples, but the present invention is not limited to these examples . In the examples, "part (s) " means "part(s) by weight", unless otherwise specified.

Production Example 1

Production of an acrylic resin 1 having an epoxy group Butyl cellosolve (120 parts) was put in a reaction container and heated under stirring at 120°C. A mixed solution of 2 parts of tert-butylperoxy-2-ethylhexanoate and 10 parts of butyl cellosolve, and a monomer mixture consisting of 40 parts of glycidyl methacrylate, 150 parts of 2-ethylhexylmethacrylate, 50 parts of 2-hydroxyethyl methacrylate and 65 parts of n-butyl methacrylate were added dropwise thereto over 3 hours. This mixture was aged for 30 minutes and, then, a mixed solution of 0.5 part of tert-butylperoxy-2-ethylhexanoate and 5 parts of butyl cellosolve was added dropwise thereto over 30 minutes. Further, the resulting mixture was aged for 2 hours to obtain the solution of an acrylic resin 1 having an epoxy group with a non-volatile content of 42%. The number-average molecular weight, measuredby gel permeation chromatography (GPC) in terms of polystyrene, of this acrylic resin 1 having an epoxy group was 11000.

Production Example 2

Production of a quaternizing agent 1

Isophorone diisocyanate (220 parts) , 40 parts of methyl isobutyl ketone and 0.22 part of dibutyltin dilaurate were put in a reaction container, and 135 parts of 2-ethylhexanol was added dropwise thereto at 55°C. Thereafter, the mixture was reacted at 60°C for 1 hour to obtain a half-blocked isocyanate solution. This solution was further heated to 80°C and a mixed solution of 90 parts of N,N-dimethylaminoethanol and 10 parts of methyl isobutyl ketone was added dropwise thereto over 30 minutes. After recognizing that an isocyanate group disappearedusing infrared spectrumanalysis, themixed solution was cooled to room temperature to obtain tertiary a ine having a blocked isocyanate group. This solution was neutralized by adding 180 parts of a 50% aqueous solution of lactic acid to obtain a solution of a quaternizing agent 1.

Production Example 3 Production of a quaternizing agent 2

A solution of a quaternizing agent 2 was obtained by following the same procedure as in Production Example 2 except for using 160 parts of triethylene glycol monomethyl ether in place of 135 parts of 2-ethylhexanol used as a block agent and changing the amount of methyl isobutyl ketone as a solvent from 40 parts to 25 parts.

Production Example 4

Production of an acrylic resin 1 having an ammonium group Butyl cellosolve (120 parts) was put in a reaction container and heated under stirring at 120°C. A mixed solution of 2 parts of tert-butylperoxy-2-ethylhexanoate and 10 parts of butyl cellosolve, and a monomer mixturesi, consisting of 15 parts of glycidyl methacrylate, 50 parts of 2-ethylhexyl methacrylate, 40 parts of 2-hydroxyethyl methacrylate and 15 parts of n-butyl methacrylate were added dropwise thereto over 3 hours . This mixture was aged for 30 minutes and, then, a mixed solution of 0.5 part of tert-butylperoxy-2-ethylhexanoate and 5 parts of butyl cellosolve was added dropwise thereto over 30 minutes. Thereafter, the resulting mixture was further aged for 2 hours and cooled. This acrylic resin 2 having an epoxy group had the number-average molecular weight of 12000 and the weight-average molecular weight of 28000, measured by GPC. By adding 7 parts of N,N-dimethylaminoethanol and 15 parts of a 50% aqueous solution of lactic acid to this acrylic resin 1 and heating under stirring at 80°C, the acrylic resin 1 was quaternized. Heating was stopped at the point in time when an acid value reached 1 or less and a viscosity rise stopped to obtain the solution of an acrylic resin 1 having an ammonium group with anon-volatile content of 30%. The number of ammonium groups per a molecule of this acrylic resin 1 having an ammonium group was 6.0.

Production Example 5 Production of an acrylic resin 2 having an ammonium group

By adding 100 parts of the solution of the quaternizing agent 1 produced in Production Example 2 to 240 parts of the acrylic resin 1 having an epoxy group produced in Production Example 1 and heating under stirring at 80°C, the mixture was quaternized. Heating was stopped at the point in time when an acidvalue reached 1 or less andaviscosityrisewas not recognized to obtain the solution of an acrylic resin 2 having an ammonium group with a non-volatile content of 39% . The number of ammonium groups per a molecule of this acrylic resin 2 having an ammonium group was 8.5.

Production Example 6

Production of an acrylic resin 3 having an ammonium group

The solution of an acrylic resin 3 having an ammonium group with a non-volatile content of 36% was obtained by following the same procedure as in Production Example 5 except for using 80 parts of the solution of the quaternizing agent 2 produced in Production Example 3 in place of 100 parts of the solution of the quaternizing agent 1. The number of ammonium groups per a molecule of this acrylic resin 3 having an ammonium group was 4 . 0 .

Production Example 7

Production of a crosslinked resin particle 1 In a reaction container, 20 parts of the acrylic resin 1 having an ammonium group, produced in Production Examples 4, and 270 parts of ion-exchanged water were put, and the mixture was heated under stirring at 75°C. An aqueous solution of 1.5 parts of 2, 2 ' -azobis (2- (2-imidazoline-2-yl) propane) neutralized wholly with acetic acid was added dropwise thereto over 5 minutes. The mixed solution was aged for 5 minutes and, then, 30 parts of methyl methacrylate was added dropwise thereto over 5 minutes. The mixture was further aged for 5 minutes, and preemulsion, which was obtained by adding an α, β-ethylenicallyunsaturatedmonomermixture consistingof 170 parts of methyl methacrylate, 40 parts of styrene, 30 parts of n-butyl methacrylate, 5 parts of glycidyl methacrylate and 30 parts of neopentyl glycol dimethacrylate to a mixed solution of 70 parts of the acrylic resin 1 having an ammonium group and 250 parts of ion-exchanged water under stirring, was added dropwise thereto over 40 minutes. This mixture was aged for 60 minutes and, then, cooled to obtain an aqueous dispersion of a crosslinked resin particle 1. The resulting aqueous dispersion of the crosslinked resinparticle 1 had a non-volatile content of 35%, a pH of 5.0 and a volume-average particle diameter of 100 nm. The aqueous dispersion of the crosslinked resin particle 1 was mixed with xylene to form a mixture and xylene was substituted for water being a solvent of the mixture while the mixture was azeotropically distilled in an evaporator to obtain a dispersion of a crosslinked resin particle 1 in xylene .

Production Example 8

Production of a crosslinked resin particle 2

In a reaction container, 20 parts of the acrylic resin 2 having an ammonium group, produced in Production Examples 5, and 300 parts of ion-exchanged water were put, and the mixture was heated under stirring at 75°C. An aqueous solution of 1 part of 2, 2 ' -azobis (2- (2-imidazoline-2-yl) propane) neutralized wholly with acetic acid was added dropwise thereto over 5 minutes. The mixed solution was aged for 5 minutes and, then, 25 parts of methyl methacrylate was added dropwise thereto over 5 minutes. The mixture was further aged for 5 minutes and, then, preemulsion, which was obtained by adding an α, β-ethylenicallyunsaturatedmonomermixture consisting of 140 parts of methyl methacrylate, 30 parts of styrene, 25 parts of n-butyl methacrylate, 5 parts of glycidyl methacrylate and 25 parts of neopentyl glycol dimethacrylate to a mixed solution of 55 parts of the acrylic resin 2 having an ammonium group and 270 parts of ion-exchanged water under stirring, was added dropwise thereto over 40 minutes. This mixture was aged for 60 minutes and, then, cooled to obtain an aqueous dispersion of a crosslinked resin particle 2. The resulting aqueous dispersion of the crosslinked resinparticle 2 had a non-volatile content of 30%, apH of 5.5 and a volume-average particle diameter of 100 nm. The aqueous dispersion of the crosslinked resin particle 2 was mixed with xylene to form a mixture and xylene was substituted for water being a solvent of the mixture while the mixture was azeotropically distilled in an evaporator to obtain a dispersion of a crosslinked resin particle 2 in xylene .

Production Example 9

Production of a crosslinked resin particle 3

An aqueous dispersion of a crosslinked resin particle 3 was obtained by following the same procedure as in Production Example 8 except that in place of the acrylic resin 2 having an ammonium group used as an emulsifier, the same amount of the acrylic resin 3 having an ammonium group was used. The resulting aqueous dispersion of the crosslinked resin particle 3 had a non-volatile content of 30 %, a pH of 5.5 and a volume-average particle diameter of 90 nm. The aqueous dispersion of the crosslinked resin particle 3 was mixed with xylene to form a mixture and xylene was substituted for water being a solvent of the mixture while the mixture was azeotropically distilled in an evaporator to obtain a dispersion of a crosslinked resin particle 3 in xylene.

Production Example 10

Production of a crosslinked resin particle 4

An aqueous dispersion of a crosslinked resin particle 4 was obtained by following the same procedure as in Production

Example 8 except for changing the amount of neopentyl glycol dimethacrylate in the α, β-ethylenically unsaturated monomer mixture from 25 parts to 40 parts. The resulting aqueous dispersion of the crosslinked resinparticle 4 had anon-volatile content of 30%, a pH of 5.0 and a volume-average particle diameter of 150 nm. This aqueous dispersion was mixed with xylene to formamixture andxylenewas substituted forwaterbeing a solvent of the mixture while the mixture was azeotropically distilled in an evaporator to obtain a dispersion of a crosslinked resin particle 4 in xylene.

Production Example 11

Production of a crosslinked resin particle 5 using an emulsifier other than an acrylic resin having an ammonium group Hexadecyltrimethylammonium chloride (7 parts) was put in a reaction container as an emulsifier and dissolved in 300 parts of ion-exchanged water, and the dissolved solution was heated under stirring at 75°C. An aqueous solution of 1 part of 2,2' -azobis (2- (2-imidazoline-2-yl) propane) neutralized whollywith acetic acidwas addeddropwise thereto over 5minutes . The mixed solution was aged for 5 minutes and, then, 10 parts ofmethyl methacrylate was added dropwise thereto over 5 minutes . The mixture was further aged for 5 minutes, and preemulsion, which was obtained by adding an , β-ethylenically unsaturated monomer mixture consisting of 140 parts of methyl methacrylate, 30 parts of styrene, 25 parts of n-butyl methacrylate, 5 parts of glycidyl methacrylate and 25 parts of neopentyl glycol dimethacrylate to a mixed solution of 22 parts of hexadecyltrimethylammonium chloride and 270 parts of ion-exchanged water under stirring, was added dropwise thereto over 40 minutes . This mixture was aged for 60 minutes and, then, cooled to obtain an aqueous dispersion of a crosslinked resin particle 5, which had a non-volatile content of 30%, a pH of 5.2 and a volume-average particle diameter of 120 nm. This aqueous dispersion was mixed with xylene to form a mixture and xylene was substituted for water being a solvent of the mixture while the mixture was azeotropically distilled in an evaporator to obtain a dispersionof a crosslinkedresinparticle 5 inxylene .

Production Example 12

Production of a non-crosslinked resin particle

In a reaction container, 20 parts of the acrylic resin 1 having an ammonium group, produced in Production Examples 4, and 300 parts of ion-exchanged water were put, and the mixture was heated under stirring at 75°C. An aqueous solution of 1 part of 2, 2 ' -azobis (2- (2-imidazoline-2-yl) propane) neutralized wholly with acetic acid was added dropwise thereto over 5 minutes . The mixed solution was aged for 5 minutes and, then, 10 parts of methyl methacrylate was added dropwise thereto over 5 minutes. The mixture was further aged for 5 minutes, and preemulsion, which was obtained by adding an α, β-ethylenically unsaturated monomer mixture containing no poly (meth) acrylate, consisting of 140 parts of methyl methacrylate, 30 parts of styrene, 25 parts of n-butyl methacrylate and 5 parts of glycidyl methacrylate, to an aqueous solution of 55 parts of the acrylic resin 1 having an ammonium group and 270 parts of ion-exchanged water under stirring, was added dropwise thereto over 40 minutes. This mixture was aged for 60 minutes and, then, cooled to obtain an aqueous dispersion of a non-crosslinked resin particle. The resulting aqueous dispersion of the non-crosslinked resin particle had a non-volatile content of 32.8%, a pH of 5.0 and a volume-average particle diameter of 106 nm. This aqueous dispersion was mixed with xylene to form a mixture and xylene was substituted for water being a solvent of the mixture while the mixture was azeotropically distilled in an evaporator to obtain a dispersion of a non-crosslinked resin particle in xylene.

Production Example 13 Production of an insulating coating composition

The dispersion of a crosslinked resin particle 1 in xylene obtained in Production Example 7 was added to NEOHEAT Al (polyamide-imide resin coating, made by Totoku Toryo Co . , Ltd. , resin solid matter in the coating composition: 40% by weight) in such a way that the amount of this dispersion is 20% by weight relative to coating resin solid matter, and the mixture was stirred for 1 hour with a mixer. Thereafter, xylene was added to the mixture in such a way that the concentration of the solid matter is 15% by weight to obtain an insulating coating composition.

Production Examples 14 to 17

Production of insulating coating compositions

Respective insulating coating compositions were obtained by followingthe sameprocedure as in ProductionExample 13 except for using the dispersions of crosslinked resin particles 2 to

5 inxylene obtained in ProductionExamples 8 to 11, respectively, in place of the dispersion of a crosslinked resin particle 1 in xylene obtained in Production Example 7

Production Example 18

Production of a coating composition

A coating composition was obtained by following the same procedure as in Production Example 13 except for using the dispersionof anon-crosslinkedresinparticle inxylene obtained in Production Example 12 in place of the dispersion of a crosslinked resin particle 1 in xylene obtained in Production Example 7.

Examples 1 to 5

Each insulating coating composition obtained in Production Examples 13 to 17, respectively, was applied to a rectangular copper wire having edges (cross section: square, size: 0.3 mm x 0.3 mm, curvature: 10%) and, then, heated at 190°C forδminutes. Byrepeatingthis cycleof applying the insulating coating composition and heat setting 10 times, an insulating film was formed and each of insulated wires 1 to 5, corresponding to Production Examples 13 to 17, respectively, was obtained.

Comparative Example 1

An insulated wire was obtained by following the same procedure as in Example 1 except for using NEOHEAT Al as an insulating coating composition.

Comparative Example 2

An insulated wire was obtained by following the same procedure as inExample 1 except forusing the coating composition obtained in Production Example 18 as an insulating coating composition. [Evaluation]

The insulated wires obtained in Examples 1 to 5 and Comparative Examples 1 and 2 were evaluated on a dielectric breakdown voltage using a withstand voltage insulation tester (Model 8525, manufactured by Tsuruga Electric Co . ) by the metal foil method according to JIS C 3003. The results are shown in Table 1. Table 1

As is clear from Table 1, the insulated wires obtained in Examples had dielectric breakdown voltage higher than those obtained in Comparative Examples.

INDUSTRIAL APPLICABILITY The insulating coating composition of the present invention has the above-mentioned constitution, so that it can attain an insulating film having a high dielectric breakdown voltage. The above-mentioned insulating coating composition is suitably used for coating an electric wire having edges such as a rectangularwire or a square wire, and can attain an insulated wire having a high dielectric breakdown voltage. In addition, since the above-mentioned insulated wire becomes higher in a occupancy ratio, it can improve its performances compared with the case of coating using an insulating coating containing no crosslinked resin particle, and can be suitably used as, for example, amagnetwire. Therefore, the insulatedwire, obtained by using the insulating coating composition of the present invention, can be suitably used in various applications as one having the high dielectric breakdown voltage.

Claims

1. An insulating coating composition comprising a crosslinked resin particle and at least one insulating resin selected from the group consisting of polyvinyl formal resin, polyamide-imide resin, polyamide resin, polyimide resin and polyester-imide resin.

2. The insulating coating composition according to Claim 1, wherein the content of the crosslinked resin particle is 0.5 to 40% by weight relative to the resin solid matter in the coating composition .

3. An insulated wire having edges, which is coated with the insulating coating composition according to Claim 1 or 2.

4. The insulated wire having edges according to Claim 3, wherein an article to be coated is an electric wire of a rectangular wire or a square wire.