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Title:
INSULATING METHOD AND INSULATED METAL PRODUCT
Document Type and Number:
WIPO Patent Application WO/2004/098794
Kind Code:
A1
Abstract:
It is an object of the present invention to provide an insulating method in which an insulating film having a high dielectric breakdown voltage can be attained in a simple manner, and an insulated metal product obtained thereby. An insulating method comprising steps of: (I) forming a first insulating film on the surface of an article to be treated by using an insulating coating; and (II) forming a second insulating film at an area of a coating defect of the first insulating film formed in said step (I) by cationic electrodeposition using a cationic electrocoating, wherein said cationic electrocoating contains a resin composition of which a hydratable functional group is reduced directly by an electron and passivated, resulting in deposition of a film.

Inventors:
Kawanami, Toshitaka (G608, 1-12 Matsuodai 2-chome, Inagawach, Kawabe-gun Hyogo 61, 66602, JP)
Sakamoto, Hiroyuki (11-501-608, Koyochonaka 5-chome Higashinada-k, Kobe-shi Hyogo 32, 65800, JP)
Tanaka, Hidenori (14-17, Inabaso 1-chome Amagasaki-shi, Hyogo 64, 66000, JP)
Morichika, Kazuo (5-51-504, Makitacho Takatsuki-shi, Osaka 55, 56908, JP)
Saito, Takao (17-9, Midorigaoka 2-chome Toyonaka-shi, Osaka 02, 56000, JP)
Application Number:
PCT/JP2004/006678
Publication Date:
November 18, 2004
Filing Date:
May 12, 2004
Export Citation:
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Assignee:
NIPPON PAINT CO., LTD. (1-2 Oyodokita 2-chome, Kita-ku Osaka-shi, Osaka 11, 53185, JP)
Kawanami, Toshitaka (G608, 1-12 Matsuodai 2-chome, Inagawach, Kawabe-gun Hyogo 61, 66602, JP)
Sakamoto, Hiroyuki (11-501-608, Koyochonaka 5-chome Higashinada-k, Kobe-shi Hyogo 32, 65800, JP)
Tanaka, Hidenori (14-17, Inabaso 1-chome Amagasaki-shi, Hyogo 64, 66000, JP)
Morichika, Kazuo (5-51-504, Makitacho Takatsuki-shi, Osaka 55, 56908, JP)
Saito, Takao (17-9, Midorigaoka 2-chome Toyonaka-shi, Osaka 02, 56000, JP)
International Classes:
B05D5/12; B05D1/36; B32B15/08; C25D13/00; C25D13/06; H01B7/00; H01B7/02; H01B13/00; H01B13/16; H01B17/60; H01L21/312; (IPC1-7): B05D5/12; B05D1/36
Foreign References:
JP2001205183A2001-07-31
JP2000191958A2000-07-11
JP2000189891A2000-07-11
JP2001096221A2001-04-10
JP2001276722A2001-10-09
JP2001121074A2001-05-08
Attorney, Agent or Firm:
Yasutomi, Yasuo (Chuo BLDG, 4-20 Nishinakajima 5-chome, Yodogawa-k, Osaka-shi Osaka 11, 53200, JP)
Download PDF:
Claims:
CLAIMS
1. An insulating method comprising steps of: (I) forming a first insulating film on the surface of an article to be treated by using an insulating coating; and (II) forming a second insulating film at an area of a coating defect of the first insulating film formed in said step (I) by cationic electrodeposition using a cationic electrocoating, wherein said cationic electrocoating contains a resin composition of which a hydratable functional group is reduced directly by an electron and passivated, resulting in deposition of a film.
2. The insulating method according to Claim 1, comprising a step of: (X) molding the article to be treated, having the first insulating film, after said step (I) and before said step (II).
3. The insulating method according to claim 2, wherein the area of a coating defect occurs due to said step (X).
4. The insulating method according to any of Claims 1 to 3, wherein the step (I) of forming a first insulating film is performed by a dice technique or a felt technique.
5. The insulating method according to any of Claims 1 to 4, wherein the insulating coating contains a polyamideimide resin or a polyamide resin.
6. The insulating method according to any of Claims 1 to 5, wherein the resin composition has a sulfonium group and a propargyl group.
7. The insulating method according to any of Claims 1 to 6, wherein the resin composition has an epoxy resin as a skeleton.
8. An insulated metal product which is obtained by the insulating method according to any of Claims 1 to 7.
Description:
DESCRIPTION INSULATING METHOD AND INSULATED METAL PRODUCT TECHNICAL FIELD The present invention relates to an insulating method and an insulated metal product.

BACKGROUND ART It is often required to insulate a product by forming insulating films on the surface of the product in the field of electric and electronic equipment. Such a surface insulating is generally carried out by using insulating coatings containing organic resins such as various synthetic resins and natural resins.

As an insulating coating used for forming such an insulating film, there are known, for example, coatings of aromatic polyamide resin, polybenzimidazole resin, polyamide-imide resin and polyimide resin as disclosed in Japanese Kokai Publication 2000-235818. However, in an insulating film formed by applying such an insulating coating, it may be impossible to attain an adequate insulating property due to a film defect such as pin holes and the like, and an area of a coating defect, produced through molding an article to be treated after forming the insulating film, such as cracks and the like.

In addition, since such an insulating coating is generally applied by a dice technique or a felt technique, it could be applied only to ones having a relatively simple shape such as a plate form or a rod form and was difficult to application to an article to be treated having a complex shape. In order to improve such a respect, an insulating method in which an insulating film is formed on an article to be treated having such a simple shape that coating by a dice technique or a felt technique can be conducted and then this coated article is molded

is conceivable. However, if insulating is performed on a product by this method, the resulting product becomes insufficient in an insulating property in the case where an insulating film is broken by a physical force during molding.

Thus, there has been desired the development of an insulating method by which it is possible to give coating readily even to an article to be treated having a complex shape and to provide a high insulating property for an article to be treated.

SUMMARY OF THE INVENTION In view of the above-mentioned circumstances, it is an object of the present invention to provide an insulating method in which an insulating film having a high dielectric breakdown voltage can be attained in a simple manner, and an insulated metal product obtained thereby.

The present invention provides an insulating method comprising steps of: (I) forming a first insulating film on the surface of an article to be treated by using an insulating coating; and (II) forming a second insulating filmat an area of a coating defect of the first insulating film formed in said step (I) by cationic electrodeposition using a cationic electrocoating, wherein said cationic electrocoating contains a resin composition of which a hydratable functional group is reduced directly by an electron and passivated, resulting in deposition of a film.

Preferably, the insulating method comprises a step of: (X) molding the article to be treated, having the first insulating film, after said step (I) and before said step (II).

The area of a coating defect occurs, for example, due to said step (X).

Preferably, the step (I) of forming a first insulating film is performed by a dice technique or a felt technique.

Preferably, the insulating coating contains a polyamide-imide resin or a polyamide resin.

Preferably, the resin composition has a sulfonium group and a propargyl group.

Preferably, the resin composition has an epoxy resin as a skeleton.

The present invention also provides an insulated metal product which is obtained by the insulating method.

DETAILED DESCRIPTION OF THE INVENTION Hereinafter, the present invention will be described in detail.

The insulating method of present invention comprises the steps of: (I) forming a first insulating film on the surface of an article to be treated by using an insulating coating; and (II) forming a second insulating film at an area of a coating defect of the first insulating film formed in the step (I) by cationic electrodeposition using a cationic electrocoating.

That is, the insulating method is a method of obtaining an insulating film having an excellent dielectric breakdown voltage by forming the second insulating film at areas of film defects such as a crack and a pin hole existing in the first insulating film formed using a cationic electrocoating.

Further, in the step (II), a cationic electrocoating having a high throwing power and an excellent insulating property is used ; therefore, insulating can be efficiently performed. In addition, since a cationic electrocoating is used, a coating material does not adhere to anareawhere a defect of the insulating film is not produced. Accordingly, the present invention is also excellent in that an abundance of resin is not unnecessarily used.

Since the cationic electrodeposition in the step (II) is suitably applied even to an article to be treated, having a complex shape, the step (II) is performed and the second insulating film can be formed even if the article to be treated is molded after thestep (I) andbeforestep (II). Theobtainedsecondinsulating film allows a defect such as a crack to be repaired; therefore,

the insulating film having a high dielectric breakdown voltage can be attained.

The insulating coating used in the step (I) is not particularly limited as long as it is a coating capable of forming an insulating film having a high insulating property, and examples thereof may include various conventionally known insulating coatings formed by containing organic resins such as polyvinyl formal resin, polyamide resin, polyimide resin, polyamide-imide resin, polyester-imide resin, polyester resin, polyurethane resin and epoxy resin.

Examples of an insulating coating formed by containing the above-mentioned polyvinyl formal resin may include a coating containing a polyvinyl formal resin and a phenol resin and, as <BR> <BR> acommerciallyavailableproduct, PVFS7-24 (madebyTotokuToryo<BR> Co. , Ltd.) and the like are suitably used.

Examples of an insulating coating formed by containing the above-mentionedpolyamide resinmay include aramid (aromatic polyamide) coatings, nylon MXD 6 coatings and the like. In particular, aramid coatings are preferred in point of heat resistance, mechanical strength and the like.

Examples of an insulating coating formed by containing the above-mentioned polyimide resin may include total aromatic polyimide coatings and the like and, as a commercially available <BR> <BR> product, Pyre-ML (made by DuPont K. K. ), TORAYNEECE 3000 (made<BR> by Toray Industries, Inc. ) and the like are suitably used.

Examples of an insulating coating formed by containing the above-mentioned polyamide-imide resin may include a coating <BR> <BR> prepared by reacting tricarboxylic anhydride with diisocyanate, and the like and, as a commercially available product, NEOHEAT <BR> <BR> AI (made by Totoku Toryo Co. , Ltd. ) and the like are given.

Examples of an insulating coating formed by containing the above-mentioned polyester-imide resin may include a coating prepared by further reacting imide-dicarboxylic acid, which is a reaction product of tricarboxylic anhydride and diamine, with a polyhydric alcohol and, as a commercially available product,

NEOHEAT 8600A (made by Totoku Toryo Co. , Ltd. ) and the like are given.

Examples of an insulating coating formed by containing the above-mentioned polyester resin may include alkyd resin coatings, especially, glycerine-modified alkyd resin coatings, tris (hydroxyethyl) isocyanurate (THEIC) -modified alkyd resin coatings, and the like and, as a commercially available product, NEOHEAT 8200K1 (made by Totoku Toryo Co. , Ltd. ) and the like are given.

Examples of an insulating coating formed by containing the above-mentioned polyurethane resin may include a coating prepared by reacting diisocyanate with a polyester resin, and the like and, as a commercially available product, TPU F1 (made by Totoku Toryo Co. , Ltd. ) and the like are given.

Examples of an insulating coating formed by containing the above-mentioned epoxy resin may include a coating containing a bisphenol A type epoxy resin and a phenolic resin, and the like and, as a commercially available product, CEMEDINE 110 (made by CEMEDINE Co. , Ltd. ) and the like are given. Among the insulating coatings described above, the insulating coating formed by containing the above-mentioned polyamide-imide resin or polyamide resin is preferred in that the obtained insulating film has a higher dielectric breakdown voltage.

The step (I) of forming the first insulating film by using the above-mentioned insulating coating can be performed by a conventionally known method such as an application and baking of the above-mentioned insulating coating. As a method of applying the above-mentioned insulating coating, a dice technique and a felt technique are preferred.

As described above, since the method of applying the above-mentioned insulating coating by the dice technique or felt technique requires to conduct an ironing step after the application of the insulating coating, this method can be suitably applied to an article to be treated, which has such a simple shape that ironing can be carried out, but is difficult

to the application to an article to be treated having a complex shape. Thus, when after the above-mentioned insulating coating was applied to an article to be treated, the article to be treated was molded to produce a defect such as cracks, it was difficult to repair the area of a coating defect by applying the above insulatingcoatingagain. Inaddition, thismethodhadaproblem also in that in repairing, only one ironing was insufficient and two or more ironing was necessary to attain an adequate insulating film; therefore, a production efficiency is deteriorated, but the present invention improves such a problem.

The dice technique is a method in which an insulating coating is allowed to adhere to the surface of an article to be treated by passing an article to be treated through an insulating coating or contacting the article with a roller provided with an insulating coating on its surface and, then, the article to be treated is subjected to ironing using a dice and thereby the insulating coating is applied to the overall surface of the article to be treated. The dice technique is applied to the case where an article to be treated has a relatively large size, namely, it is a flat and rectangular conductive wire being thick and wide.

The felt technique is applied to the case of a flat and rectangular conductive wire having a relatively small size, namely, being thin and narrow, but it has a feature that it can be applied regardless of the size of the flat and rectangular conductive wire in contrast to the dice technique and is mainly employed in a horizontal baking oven. This felt technique is a method in which an insulating coating is allowed to adhere to the surface of an article to be treated by passing an article to be treated through an insulating coating or contacting the article with a roller provided with an insulating coating on its surface and, then, the article to be treated is subjected to ironing using a felt and thereby the insulating coating is applied to the overall surface of the article to be treated.

Next, the flat and rectangular conductive wire, to which the

insulating coating has been applied, is guided into a baking oven and the insulating coating is dried and cured to provide an insulating film.

The insulating method of the present invention can be suitably applied to the case of having the step (X) of molding an article to be treated after the step (I) and before the step (II). When an article to be treated having the first insulating film formed in the step (I) is molded, this may produce cracks and the like in the first insulating film and deteriorate the insulating property. By performing the step (II) after molding an article to be treated according to the insulating method of the present invention, a defect such as cracks produced in the first insulating film can be repaired. In addition, since the step (II) is the cationic electrodeposition using a cationic electrocoating, it is possible to give coating readily even to an article to be treated having a complex shape.

The term"molding"used herein refers to bending in the form of V character or U character.

The insulating method of the present invention executes the step (II) of forming the second insulating filmby performing cationic electrodeposition using a cationic electrocoating, and the cationic electrocoating used in the step (II) contains a resin composition of which a hydratable functional group is reduced directly by an electron and passivated, resulting in deposition of a film. The insulating film having a high dielectric breakdown voltage can be attained by repairing an area of a coating defect of the first insulating film and forming the second insulating film, being an electrodeposited filmhaving an insulating property, in the step (II).

The mechanism of deposition on the cathode as caused by voltage application in the step (II) is represented by the following formula (1), and the insulating film is passivated to be deposited by providing the hydratable functional group in the resin composition (substrate; expressed by"S"in the formula) with an electron on the cathode.

That is, when the reaction represented by the formula (1) occurs, the hydratable functional group existing in the resin composition in the cationic electrocoating is directly reduced on the cathode, resulting in insolubilization and deposition.

Since the film deposited according to this mechanism has a higher dielectric breakdown voltage than a film obtained by using an usual cationic electrocoating, it can attain an excellent insulating film.

In the insulating method of the present invention, the above-mentioned resin composition preferably has a sulfonium group and a propargyl group because throwing power and an insulating property of an electrodeposited film become excellent.

By using the resin composition having a sulfonium group and a propargyl group, an insulating film having a higher dielectric breakdown voltage can be obtained.

The resins composing the above resin composition may contain both a sulfonium group and a propargyl group in each molecule, but it does not necessarily do so. Thus, for example, the resins may have only either the sulfonium group or the propargyl group in each molecule. In the latter case, however, the whole resin composition has both of these two kinds of curable functional groups. That is, the above resin composition may comprise any resin containing sulfonium group andpropargyl group, a mixture of a resin having only a sulfonium group (s) and a resin having only a propargyl group (s), or a mixture of all of these kinds of resins. It is herein defined in the above sense that the resin composition has both sulfonium and propargyl groups.

The sulfonium group is a hydratable functional group in the resin composition. When an electric voltage or current exceeding a certain level is applied to the sulfonium group in the electrodeposition step, the group is subjected to an

electrolytic reduction on the electrode ; thereby, the ionic group disappears and the sulfonium group can be irreversibly passivated.

It is considered that, in this electrodeposition step, the electrode reaction provoked generates the hydroxide ion, and the sulfonium group holds the hydroxide ion, with the result that an electrolytically generated base is formed in the electrodeposited film. This electrolytically generated base can convert the propargyl group existing in the electrodeposited film and being low in reactivity upon heating to the allene bond high in reactivity upon heating.

The resin to act as the skeleton of the above-mentioned resin composition is not particularly limited, but an epoxy resin is suitably used because of a high insulating property of the epoxy resin.

As the above-mentioned epoxy resin, there are suitably used those having at least two epoxy groups in a molecule, including, for example, polyepoxy resins such as epi-bis-epoxy resins ; modifications thereof obtained by extending its chain with diol, dicarboxylic acid, diamine or the like; epoxidized polybutadiene; novolak phenol polyepoxy resins; novolak cresol polyepoxy resins; polyglycidyl acrylate; polyglycidyl ethers of aliphaticpolyolsorpolyetherpolyol ; andpolyglycidylesters of polybasic carboxylic acids. In particular, novolak phenol polyepoxy resins, novolak cresol polyepoxy resins and polyglycidyl acrylate are preferred because of the ease of polyfunctionalization for enhancing curability. In addition, part of the above-mentioned epoxy resin maybe amonoepoxy resin.

Preferably, the resin composition includes a resin having the epoxy resin as a skeleton and has a number-average molecular weight of 500 (lower limit) to 20000 (upper limit). When it <BR> <BR> is less than 500, the coating efficiency in the electrodeposition step will be poor, and when it exceeds 20000, a good film cannot be formed on the surface of a substrate. As for the number-average molecular weight, a more preferable molecular

weight can be selected in accordance with the resin skeleton.

In the case of novolak phenol epoxy resins and novolak cresol epoxy resins, for example, the lower limit is preferably 700 and the upper limit is preferably 5000.

Preferably, the sulfonium group content in the resin composition is within a range of 5 milli moles (lower limit) to 400 milli moles (upper limit) per 100 g of the solid matter in the resin composition provided that the total content of the sulfonium and propargyl groups conditions to be mentioned later herein are satisfied. When this content is less than 5 milli moles per 100 g of the solid matter, curability cannot be adequately exerted, and hydratability and bath stability are deteriorated. When it exceeds 400 milli moles per 100 g of the solid matter, the film deposition on the surface of a substrate becomes poor. As for the sulfonium group content, a more preferable content can be selected in accordance with the resin skeleton employed. In the case of novolak phenol epoxy resins and novolak cresol epoxy resins, for example, the above lower limit is preferably 5 milli moles, more preferably 10 milli moles per 100 g of the solid matter in the resin composition. In addition, the above upper limit is preferably 250 milli moles, more preferably 150 milli moles per 100 g of the solid matter in the resin composition.

The propargyl group of the resin composition acts as a curable functional group in the cationic electrocoating.

Preferably, the propargyl group content in the resin composition is within a range of 10 milli moles (lower limit) to 495 milli moles (upper limit) per 100 g of the solid matter in the resin composition provided that the total content of the sulfonium and propargyl groups conditions to be mentioned later herein are satisfied. When this content is less than 10 milli moles per 100 g of the solid matter, curability cannot be sufficiently exerted, and when it exceeds 495 milli moles per 100 g of the solid matter, the hydration stability in the case of being used as an electrocoating may be affected. As for the

propargyl group content, a more preferable content can be selected in accordance with the resin skeleton employed. In the case of novolak phenol epoxy resins and novolak cresol epoxy resins, for example, the above lower limit is more preferably 20 milli moles and the above upper limit is more preferably 395 millimoles, perlOOgof the solidmatter in the resin composition.

The total content of the sulfonium and propargyl groups, in the above resin composition, is preferably 500 milli moles or less per 100 g of the solid matter in the resin composition.

When this content exceeds 500 milli moles per 100 g of the solid matter, aresinmaynotbe attainedin factor adesiredperformance may not be attained. As for the total content of the sulfonium and propargyl groups, in the above resin composition, a more preferable content can be selected in accordance with the resin skeleton employed. In the case of novolak phenol epoxy resins and novolak cresol epoxy resins, for example, the total content is more preferably 400 milli moles or less per 100 g of the solid matter in the resin composition.

Part of the propargyl group in the resin composition may be converted to an acetylide. An acetylide is a salt-like acetylated metal compound. As for the content of the propargyl group to be converted to an acetylide in the resin composition, preferably, the lower limit is 0. 1 milli mole and the upper limit is 40 milli moles, per 100 g of the solid matter in the resin composition. When this content is less than 0.1 milli mole per 100 g of the solid matter, the effect of the conversion to an acetylide are not sufficiently exerted, and when it exceeds 40 milli moles, per 100 g of the solid matter, the conversion to an acetylide is difficult. As for this content, amore preferable range can be selected in accordance with the metal species employed.

A metal contained in the propargyl group converted to an acetylide is not particularly limited as long as it presents a catalytic action, and example thereof may include transition metals such as copper, silver and barium. If considering the

conformity with an environment, copper and silver are preferable, and copper is more preferable from the viewpoint of the availability. When copper is used as the above-mentioned metal, the content of the propargyl group to be converted to an acetylide in the above resin composition is more preferably 0. 1 to 20 milli moles per 100 g of the solid matter in the resin composition.

By converting part of the propargyl group in the above resin composition to an acetylide, a curing catalyst can be introduced into the resin. When the resin composition is prepared in this manner, it is unnecessary to use an organic transitionmetal complex which is generally difficult to dissolve or disperse in organic solvents and water and is possible to introduce even a transition metal easily through conversion to an acetylide, and therefore even a hard-to-dissolve transition metal compound is applicable to a coating composition without restraint. Further, the occurrence of an organic acid salt as an anion in the electrocoating bath, which is encountered when a transition metal organic acid salt is used, can be avoided and, furthermore, the metal ion will not be removed through ultrafiltration, hence the bath management and the design of electrocoatings become easy.

The resin composition may contain a carbon-carbon double bond where desired. Since the above-mentioned carbon-carbon double bond has high reactivity, curability can be further enhanced.

Preferably, the content of the above-mentioned carbon-carbon double bond is within a range of 10 milli moles (lower limit) to 485 milli moles (upper limit), per 100 g of the solid matter in the resin composition provided that the total content of the propargyl group and carbon-carbon double bond conditions to be mentioned later are satisfied. When this content is less than 10 milli moles per 100 g of the solid matter, an improvement in curability by addition of the carbon-carbon double bond cannot be adequately exerted, and when it exceeds 485 milli moles per 100 g of the solid matter, the hydration

stability in the case of being used as an electrocoating may be affected. As for the content of the carbon-carbon double bond, a more preferable content can be selected in accordance with the resin skeleton employed. In the case of novolak phenol epoxy resins and novolak cresol epoxy resins, for example, the lower limit is preferably 20 milli moles and the upper limit is preferably 375 milli moles, per 100 g of the solid matter in the resin composition.

When the resin composition contains the above carbon-carbon double bond, the total content of the above propargyl group and the above carbon-carbon double bond is preferably within a range of 80 milli moles (lower limit) to 450 milli moles (upper limit), per 100 g of the solid matter in the above resin composition. When this content is less than 80 milli moles per 100 g of the solid matter, curability may become insufficient, and when it exceeds 450 milli moles per 100 g of the solid matter, the sulfonium group content becomes less and a dielectric breakdown voltage may become insufficient.

As for the total content of the propargyl group and the carbon-carbon double bond, a more preferable content can be selected in accordance with the resin skeleton employed. In the case of novolak phenol epoxy resins and novolak cresol epoxy resins, for example, the lower limit is more preferably 100 milli moles and the upper limit is more preferably 395 milli moles, per 100 g of the solid matter in the resin composition.

In addition, when the resin composition contains the above carbon-carbon double bond, the total content of the sulfonium group, the propargyl group and the carbon-carbon double bond is preferably 500 milli moles or less per 100 g of the solid matter in the resin composition. When this content exceeds 500 milli moles per 100 g of the solid matter, a resin may not be attained in fact or a desired performance may not be attained.

As for the total content of the sulfonium group, the propargyl group and the carbon-carbon double bond, a more preferable content can be selected in accordance with the resin skeleton

employed. In the case of novolak phenol epoxy resins and novolak cresol epoxy resins, for example, the total content is more preferably 400 milli moles or less per 100 g of the solid matter in the resin composition.

The above resin composition can favorably be produced, for example, by the step (i) of reacting an epoxy resin having at least two epoxy groups in a molecule with a compound having a functional group capable of reacting with the epoxy group and a propargyl group to obtain an epoxy resin composition containing a propargyl group and the step (ii) of reacting the residual epoxy groups in the epoxy resin composition having a propargyl group (s) obtained in the step (i) with a sulfide/acid mixture to introduce the sulfonium group.

The above-mentioned compound having a functional group capable of reacting with the epoxy group and a propargyl group (hereinafter, referredtoas"compound (A)") maybe, for example, a compound having both a functional group capable of reacting with the epoxy group, such as a hydroxyl or carboxyl group, and a propargyl group. As specific examples, there may be given propargyl alcohol and propargylic acid. In particular, propargyl alcohol is preferable from the viewpoint of its availability and good reactivity.

For providing the above resin composition with a carbon-carbon double bond as required, a compound having a functional group capable of reacting with the epoxy group and a carbon-carbon double bond (hereinafter, referred to as "compound (B)") may be used in combination with the compound (A) in the step (i). As the compound (B), a compound having both a functional group capable of reacting with the epoxy group, such as a hydroxyl or carboxyl group, and a carbon-carbon double bond may be used. Specifically, when the group capable of reacting with the epoxy group is a hydroxyl group, examples of the compound (B) may include 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate,

hydroxybutyl methacrylate, allyl alcohol, methacrylic alcohol, and the like. When the group capable of reacting with the epoxy group is a carboxyl group, examples of the compound (B) may include acrylic acid, methacrylic acid, ethacrylic acid, crotonic acid, maleic acid, phthalic acid, itaconic acid; half esters such as maleic acid ethyl ester, fumaric acid ethyl ester, itaconic acid ethyl ester, succinic acid mono (meth) acryloyloxyethyl ester, and phthalic acid mono (meth) acryloyloxyethyl ester; synthetic unsaturated fatty acids such as oleic acid, linolic acid, ricinolic acid, and the like ; and nature-derived unsaturated fatty acids such as linseed oil, soybean oil, and the like.

In the step (i), the epoxy resin having at least two epoxy groups in a molecule is reacted with the compound (A) to obtain an epoxy resin composition containing a propargyl group (s) or reacted with the compound (A) and the compound (B) as required to obtain an epoxy resin composition containing a propargyl group (s) and carbon-carbon double bond. In the latter case, in the step (i), the compound (A) and compound (B) may be mixed together in advance and then subjected to reaction, or the compound (A) and compound (B) may be separately subjected to reaction. In addition, the functional group reacting with the epoxy group which the compound (A) has and the functional group reacting with the epoxy group which the compound (B) has may be the same or different.

When, in the step (i), the compound (A) and compound (B) are subjected to reaction with the epoxy resin, the portion between both compounds to be blended may be selected so as to attain the desired content of specified functional groups, for example, the above-mentioned contents of the propargyl group and carbon-carbon double bond.

As for the reaction conditions in the step (i), the reaction is generally carried out at room temperature or 80 to 140°C for several hours. In addition, publicly known ingredients, which are required for the progress of the reaction, such as a catalyst and/or solvent may be used as required. The completion of the

reaction can be checked by measuring an epoxy equivalent, and the functional group introduced can be identified by analysis of nonvolatile content and instrumental analysis of the resin composition obtained. The reaction product thus obtained generally occurs as a mixture of epoxy resins having one or more propargyl groups, or a mixture of epoxy resins having one or more propargyl groups and one or more carbon-carbon double bonds.

In this sense, there can be obtained the resin composition having a propargyl group (s), or a propargyl group and carbon-carbon double bond through the step (i).

In the step (ii), the residual epoxy groups in the epoxy resin composition containing a propargyl group, obtained in the step (i), are reacted with a sulfide/acid mixture to introduce a sulfonium group. This introduction of the sulfonium group can be effected by the method which comprises causing the sulfide/acid mixture to react with the epoxy group to conduct introduction of the sulfide and conversion thereof to the sulfonium group or the method which comprises introducing a sulfide and then converting the introduced sulfide to a sulfonium group with an acid, an alkyl halide such as methyl fluoride, methyl chloride or methyl bromide, or the like, if necessary, followed by anion exchange. From the viewpoint of the availability of the reactant, the method using a sulfide/acid mixture is preferred.

The above-mentioned sulfide is not particularly limited, and examples thereof may include aliphatic sulfides, aliphatic-aromatic mixed sulfides, aralkyl sulfides, cyclic sulfides and the like. Specific examples thereof may include diethyl sulfide, dipropyl sulfide, dibutyl sulfide, dihexyl sulfide, diphenyl sulfide, ethyl phenyl sulfide, tetramethylene sulfide, pentamethylenesulfide, thiodiethanol, thiodipropanol, thiodibutanol, 1- (2-hydroxyethylthio)-2-propanol, 1- (2-hydroxyethylthio)-2-butanol, 1-(2-hydroxyethylthio)-3-butoxy-1-propanol, and the like.

The above-mentioned acid is not particularly limited, and

examples thereof include formic acid, acetic acid, lactic acid, propionic acid, boric acid, butyric acid, dimethylolpropionic acid, hydrochloric acid, sulfuric acid, phosphoric acid, N-acetylglycine, N-acetyl- (3-alanine and the like.

The mixing ratio between the sulfide and acid in the above sulfide/acid mixture is generally and preferably about 100/40 to 100/100 as expressed in terms of sulfide/acid mole ratio.

'The reaction in the step (ii) canbecarriedout, forexample, by mixing the epoxy resin composition having a propargyl group, obtained in the step (i), and the above sulfide/acid mixture in an amount selected so as to give the above-mentioned sulfonium group content, for instance, with water in an amount of 5 to 10 moles per mole of the sulfide used and stirring the mixture generally at 50 to 90°G for several hours. A residual acid value of 5 or less may serve as a criterion in determining the reaction to be completed. The introduction of sulfonium group in the resin composition obtained can be identified by potentiometric titration.

The same procedure can be used also in the case where the sulfide is first introduced and then converted to the sulfonium group. By introducing the sulfonium group after introduction of the propargyl group, as described above, the sulfonium group can be prevented from being decomposed due to heating.

In the case of converting part of the propargyl group in the above resin composition to an acetylide, the conversion to the acetylide can be carried out by the step of reacting the epoxy resin composition, containing a propargyl group, obtained in the step (i) with a metal compound to thereby convert part of the propargyl group in the above epoxy resin composition to the corresponding acetylide. The above-mentioned metal compound is preferably a transition metal compound capable of giving an acetylide, and examples thereof may include complexes or salts of such transition metals as copper, silver and barium.

Specific examples thereof may include acetylacetonato-copper, copper acetate, acetylacetonato-silver, silver acetate, silver

nitrate, acetylacetonato-barium, and barium acetate. In particular, copper or silver compounds are preferable from the viewpoint of the conformity with an environment, and copper compoundsare more preferable becauseoftheir ready availability.

For example, acetylacetonato-copper is suitably used in view of the ease of bath control.

As for the reaction conditions of converting part of the propargyl group to an acetylide, the reaction is generally carried out at 40 to 70°C for several hours. The progress of the reaction can be checked by the coloration of the resulting resin composition and/or the disappearance of the methine proton signal on a nuclear magnetic resonance spectrum. Thus, the time when the propargyl group-derived acetylide in the resin composition arrives at a desired level is determined and, at that time, the reaction is terminated. The reaction product obtained is generally a mixture of epoxy resins with one or more propargyl groups converted to an acetylide. A sulfonium group can be introduced, by the step (ii), into the thus obtained epoxy resin composition with part of the propargyl group converted to an acetylide.

The step of converting part of the propargyl group in the epoxy resin composition to an acetylide and the step (ii) can be carried out under common reaction conditions, so that both steps can be carried out simultaneously. The method of carrying out both steps simultaneously can advantageously simplify the production process.

In this way, the resin composition containing a propargyl group and a sulfonium group, and optionally containing a carbon-carbon double bond and/or a propargyl group-derived acetylide as required can be produced while preventing the sulfonium group from being decomposed. Incidentally, acetylides in a dry state are explosive but the reaction is carried out in an aqueous medium and the desired substance can be obtained in the form of an aqueous composition. Therefore, there arises no safety problem.

Since the cationic electrocoating comprises the resin composition and the resin composition itself is curable, it is not always necessary to use a curing agent. However, for further improving the curability, a curing agent may be used. Examples of the curing agent may include compounds having a plurality of at least one species of propargyl groups and carbon-carbon double bonds, for example compounds obtained by adding a compound containing a propargyl group, such as propargyl alcohol, or a compound, containing carbon-carbon double bond, such as acrylic acid to polyepoxide such as a novolak phenol or pentaerythritol tetraglycidyl ether.

It is not always necessary to use a curing catalyst in the cationic electrocoating. However, when a further improvement in curability is required depending on the curing reaction conditions, a transition metal compound in general use may be appropriately added as required. Such compound is not particularly limited, and examples thereof may include complexes or compounds formed by combining a ligand, such as cyclopentadiene or acetylacetone, or a carboxylic acid such as acetic acid, with transition metals such as nickel, cobalt, manganese, palladium and rhodium. The amount of the above curing catalyst to be added is preferably from 0.1 milli mole (lower limit) to 20 milli moles (upper limit) per 100 g of the resin solid matter in the cationic electrocoating.

An amine may further be blended in the cationic electrocoating. By the addition of the amine, the conversion of the sulfonium group to a sulfide by electrolytic reduction in the process of electrodeposition is increased. The amine is not particularly limited, and examples thereof may include amine compounds such as primary to tertiary monofunctional or polyfunctional aliphatic amines, alicyclic amines and aromatic amines. In particular, water-soluble or water-dispersible ones are preferable. Examples of the amines may include alkylamines having 2 to 8 carbon atoms such as monomethylamine, dimethylamine, trimethylamine, triethylamine, propylamine, diisopropylamine

and tributylamine; monoethanolamine, dimethanolamine, methylethanolamine, dimethylethanolamine, cyclohexylamine, morpholine, N-methylmorpholine, pyridine, pyrazine, piperidine, imidazoline, imidazole and the like. These may be used alone or two or more of them may be used in combination. In particular, hydroxy amines such as monoethanolamine, diethanolamine and dimethylethanolamine are preferred from the view point of excellent dispersion stability in water.

The above amine can be directly blended in the cationic electrocoating. While in the conventional neutralized amine type electrocoating, the addition of a free amine results in deprivation of the neutralizing acid in the resin, hence inmarked deterioration of the stability of the electrocoating solution, no such bath stability trouble will arise in the present invention.

The amount of the above amine to be added is preferably 0. 3 meq (lower limit) to 25 meq (upper limit) per 100 g of the resin solid matter in the cationic electrocoating. When this amount is less than 0. 3 meqper 100 g, the f ilm thickness retention may become insufficient. When it exceeds 25 meq per 100 g, the effects proportional to the addition amount can no longer be obtained ; this is not economical. The lower limit is more preferably 1 meq per 100 g, and the upper limit is more preferably 15 meq per 100 g.

In the cationic electrocoating, there may also be incorporated an aliphatic hydrocarbon group-containing resin composition. The incorporation of the aliphatic hydrocarbon group-containing resin composition results in an improvement in the shock resistance of the coating films obtained. As the aliphatic hydrocarbon group-containing resin composition, there may be mentioned those containing, per 100 g of the solid matter in the resin composition, 5 to 400 milli moles of a sulfonium group, 80 to 135 milli moles of an aliphatic hydrocarbon group containing 8 to 24 carbon atoms and optionally containing an unsaturated double bond in the chain thereof and 10 to 315 milli

moles of at least one of a propargyl group and organic groups containing 3 to 7 carbon atoms and having a terminal unsaturated double bond on condition that the total content of the sulfonium group, the aliphatic hydrocarbon group containing 8 to 24 carbon atoms and optionally containing an unsaturated double bond in the chain thereof and the propargyl group and organic groups containing 3 to 7 carbon atoms and having a terminal unsaturated double bond is not more than 500 milli moles per 100 g of the solid matter in the resin composition.

When such an aliphatic hydrocarbon group-containing resin <BR> <BR> composition is incorporated in the above cationic electrocoating,<BR> the resin solidmatter in the cationic electrocoating preferably contains, per 100 g thereof, 5 to 400 milli moles of sulfonium group, 10 to 300 milli moles of the aliphatic hydrocarbon group containing 8 to 24 carbon atoms and optionally containing an unsaturated double bond in the chain thereof and a total of 10 to 485 milli moles of the propargyl group and organic groups containing 3 to 7 carbon atoms and having a terminal unsaturated double bond, and the total content of the sulfonium group, the aliphatic hydrocarbon group containing 8 to 24 carbon atoms and optionally containing an unsaturated double bond in the chain thereof, the propargyl group and the organic groups containing 3 to 7 carbon atoms and having a terminal unsaturated double bond is not more than 500 milli moles per 100 g of the resin solid matter in the cationic electrocoating, and the content of the aliphatic hydrocarbon group containing 8 to 24 carbon atoms and optionally containing an unsaturated double bond in the chain thereof is 3 to 30% by weight relative to the resin solid matter in the electrocoating.

When the aliphatic hydrocarbon group-containing resin <BR> <BR> composition is incorporated in the above cationic electrocoating and the sulfonium group content level is lower than 5 milli moles per 100 g, any satisfactory curability cannot be attained and, further, the hydratabilityandbath stability will be poor. When it exceeds 400 milli moles per 100 g, the deposition of films

on the surface of the substrate worsens. When the content of the aliphatic hydrocarbon group containing 8 to 24 carbon atoms and optionally containing an unsaturated double bond in the chain thereof is less than 80 milli moles per 100 g, the shock resistance will not be improved to a satisfactory extent and, when it exceeds 350 milli moles per 100 g, the resin composition becomes dif f icult to handle. When the total content of the propargyl group and the organic groups containing 3 to 7 carbon atoms and having a terminal unsaturated double bond is less than 10 milli moles per 100 g, no satisfactory curability can be manifested on the occasion of combined use of another resin and/or another curing agent and, when it exceeds 315 milli moles per 100 g, the shock resistance will not be improved to a satisfactory extent. The total content of the sulfonium group, the aliphatic hydrocarbon group containing 8 to 24 carbon atoms and optionally having an unsaturated double bond in the chain thereof, the propargyl group and the organic groups containing 3 to 7 carbon atoms and having a terminal unsaturated double bond is not more than 500 milli moles per 100 g of the solid matter in the resin composition.

When it exceeds 500 milli moles, any corresponding resin cannot be obtained in actuality or the desired performance characteristics cannot be obtained in some instances.

The above-mentioned cationic electrocoating may further contain another components used in an ordinary cationic electrocoating as required. The above-mentioned another component is not particularly limited, and examples thereof may include a pigment, a rust preventive, a pigment dispersion resin, a surfactant, an antioxidant and an ultraviolet absorber.

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 pigment is not particularly limited, and examples thereof may include coloring pigments such as titanium dioxide, carbon black and red iron oxide; rust-preventive pigments such

as basic lead silicate and aluminum phosphomolybdate; and extender pigments such as kaoline, clay and talc. Examples of therustpreventive, specifically, mayincludecalciumphosphite, zinc calcium phosphite, calcium-carrying silica, calcium-carrying zeolite, and the like. The total amount of the above-mentioned pigments and rust preventives to be added ispreferably0% byweight (lower limit) to 50 % by weight (upper limit) in terms of the solid matter in the cationic electrocoating.

The pigment dispersion resins are used to stably disperse the pigments in the cationic electrocoating. The pigment dispersion resins are not particularly restricted but include those pigment dispersion resins which are in general use. A pigment dispersion resin containing a sulfonium group and an unsaturated bond within the resin may also be used. Such pigment dispersion resin containing a sulfonium group and an unsaturated bond can be obtained, for example, by the method comprising reacting a sulfide compound with a hydrophobic epoxy resin obtained by reacting a bisphenol-based epoxy resin with a half-blocked isocyanate, or reacting the resin with a sulfide compound in the presence of a monobasic acid and a hydroxyl group-containing dibasic acid. The pigment dispersion resins can also stably disperse the rust preventives containing no heavy metal in the cationic electrocoating.

The cationic electrocoating can be prepared, for example, by admixing the resin composition with the above-mentioned other ingredients as required and dissolving or dispersing the resulting composition in water. On the occasion of use in the electrodeposition step, the bath solution/dispersion prepared preferably has a nonvolatile matter content of 5 % by weight (lower limit) to 40 % by weight (upper limit). The preparation is preferably carried out in such a way that the contents of the propargyl group, carbon-carbon double bond and sulfonium group in the electrocoating may not deviate from the respective ranges indicated above referring to the resin composition.

In the insulating method according to the present invention, the step (II) can be performed using an electrodeposition apparatus in which the usual cationic electrodeposition can be carried out. For example, the electrodeposition can be carried out using a cationic electrodeposition apparatus which comprise electrodeposition means, washing means and heating means combined in that order. In this way, the insulating film having the high dielectric breakdown voltage can be obtained in an efficient manner. Examples of the electrodeposition apparatus which can be used may include a horizontal electrodeposition apparatus in which electrodeposition is carried out while an article to be coated is pulled horizontally, and a vertical electrodeposition apparatus in which an article to be coated is introduced into the electrocoating bath from the bottom thereof and pulled out from the top of the electrocoating bath.

The above-mentioned electrodeposition means is aimed to form a film on the surface of an article to be coated by cationic electrodeposition using a cationic electrocoating. The above-mentioned electrodeposition means is not particularly limited as long as it is one capable of conducting cationic electrodeposition.

In operating the electrodeposition means, the method comprising, for example, immersing an article to be coated in the cationic electrocoating for utilizing the article as a cathode, and applying a voltage generally within the range of 50 to 450 V between the cathode and an anode may be given as an example. When the voltage applied is lower than 50 V, the dielectric breakdown voltage may be possibly lowered and insufficient electrodeposition will result. When it exceeds 450 V, the electricity consumption uneconomically increases.

When the cationic electrocoating is used and a voltage within the range is applied, a uniform film can be formed on the whole material surface without any rapid increase in film thickness in the process of electrodeposition. In ordinary cases, a bath temperature of the cationic electrocoating in applying the above

voltage is preferably 10 to 45°C.

The above-mentioned washing means is intended for washing the article with the cationic electrocoating adhering thereto to remove the electrocoating bath liquid. The washing means is not particularly restricted but may be any the conventional washing apparatus. For example, there may be given an apparatus in which the electrodeposited article is washed using, as a washing liquid, the filtrate obtained by ultrafiltration of the electrocoating bath liquid. As the above-mentioned heating means, there may be specifically given a hot air drying oven, a near-infrared heating oven, a far-infrared heating oven, and an induction heating oven, for instance.

The step (II) can also be performed using the electrocoating bath in which an electrocoating is stirred with a mixing apparatus utilizing a low frequency vibration in the above-mentioned electrodeposition step. Since a crack or pin hole may have a pore or a shape like a thin groove, it is preferred to perform the above-mentioned electrodeposition step in the electrocoating bath in which an electrocoating is stirred with the above-mentioned low frequency vibration mixer in that the cationic electrocoating composition is adequately agitated and a resin film is adequately formed in the pore portion.

In such a case, a washing step in the step (II) can also be performed using a washing bath in which agitation is conducted with the low frequency vibration mixer.

The insulating method according to the present invention uses a cationic electrocoating to form the second insulating film on the first insulating film formed in the step (I). By performing the step (I) and the step (II), a defect of the first insulating film, such as a pin hole and a crack can be repaired with the second insulating film and the insulating film having a high dielectric breakdown voltage can be attained.

An article to be coated, to which the insulating method of the present invention is applicable, is not particularly limited as long as it exhibits conductivity through which

cationic electrodeposition can be conducted, and examples thereof may include metals such as iron, copper, aluminum, gold, silver, nickel, tin, zinc, titanium and tungsten, and alloys containing these metals. In particular, a substance consisting of metals such as copper, gold, aluminum and iron, or alloys based on these metals are preferable.

The present invention also provides an insulated metal product which is obtained by the insulating method. Since the insulated metal product has the insulating film obtained by the insulating method, it can be suitably used even for uses where a higher dielectric breakdown voltage is required.

The insulating method of the present invention comprises the step (I) of forming the first insulating film by using an insulating coating, and the step (II) of forming the second insulating film on the first insulating film formed in the step (I) by cationic electrodeposition using a cationic electrocoating, wherein the cationic electrocoating contains a resin composition of which a hydratable functional group is reduced directly by an electron and passivated, resulting in deposition of a film. Since in the insulating method, the step (II) is further performed using a cationic electrocoating containing the above-mentioned resin composition after the step (I) is performed, the insulating film having a high dielectric breakdown voltage canbe attainedby repairing an area of a coating defect of the first insulating film with the second insulating film. In addition, since the second insulating film in the present invention is formed by the cationic electrodeposition, it can be applied even to the molded article to be treated having a complex shape. Therefore, insulated metal products obtained by the insulating method of the present invention have the high insulating properties even after being molded and therefore can be suitably used to applications requiring the higher dielectric breakdown voltage.

EXAMPLES

Hereinafter, the present invention will be described more specifically by way of examples, but the present invention is not limited to these examples. Further, in examples,"part (s)" refers to"part (s) by weight"unless otherwise specified.

Production Example 1 Production of an epoxy resin composition having a sulfonium group and a propargyl group Inaseparableflaskprovidedwithastirrer, athermometer, a nitrogen gas inlet tube and a reflux cooling tube, 100. 0 parts of EPOTOHTO YDCN-701 with an epoxy equivalent of 200.4 (cresol novolak type epoxy resin made by Tohto Kasei Co., Ltd.), 23.6 parts of propargyl alcohol and 0.3 part of dimethylbenzylamine were put, and the mixture was heated to 105°C and reacted at that temperature for 3 hours to obtain a resin composition containing a propargyl group with an epoxy equivalent of 1580.

Acetylacetonate-copper (2. 5 parts) was added thereto, and the reaction was allowed to proceed at 50°C for 1.5 hours. It was verified that part of the terminal hydrogens of the added propargyl groups was disappeared by proton (1H) NMR (propargyl converted to acetylide equivalent to 14 milli moles per 100 g of the resin solid matter).

1- (2-hydroxyethylthio)-2, 3-propanediol (10. 6parts), 4. 7parts of glacial acetic acid and 7.0 parts of deionized water were added thereto, and the reaction was allowed to proceed for 6 hours while maintaining the temperature at 75°C. After verification that the residual acid value is 5 or less, 43.8 parts of deionized water was added to give an intended resin composition solution. This solution had a solid matter content of70. 0% byweightandthesulfoniumvalueof28. Omillimoles/100 g varnish. The number-average molecular weight (determined by GPC on the polystyrene equivalent basis) was 2443.

Production Example 2 Production of a cationic electrocoating To 142.9 parts of the epoxy resin composition obtained

in Production Example 1 was added 157. 1 parts of deionized water, and the mixture was stirred in a high-speed rotary mixer for 1 hour and then 373.3 parts of deionized water was further added and this aqueous solution was adjusted so as to have a solid matter content of 15 % by weight to obtain a cationic electrocoating.

Example 1 The copper round electric wire having a round shape in the cross-sectional profile (15cm in length, 0.2 mm in diameter) was degreased with SURF POWER (made by NIPPON PAINT Co., Ltd.) at a treatment temperature of 45°C for a treatment time of 60 seconds. The degreased electric wire was further washed with water by spraying for 30 seconds. NEOHEAT AI (insulating coating containing polyamide-imide resin, made by Totoku Toryo<BR> Co. , Ltd. ) was applied to this wire and then heated at 190°C for 25 minutes. By repeating this cycle of applying the insulating coating and heat setting 3 times, the first insulating film was formed.

By subjecting the resulting wire, on which the first insulating film was formed, to the following electrodeposition means, washing means and heating means, a second insulating film was formed on the surface of this round wire.

(Electrodeposition means) The wire after water washing was immersed in the cationic electrocoating obtained in Production Example 2, stored as an electrocoating bath liquid in an electrocoating bath, and cationic electrodeposited at a bath temperature of 30°C for 5 seconds with a voltage of 100 V being applied (with the wire as the cathode and the counter electrode as the anode).

(Washing means) The wire obtained after immersion period of cationic electrodeposition was washed with water by spraying for 30 seconds to remove the cationic electrocoating adhering to the wire.

(Heating means)

The wire after washing was heated in a hot air drying oven at 190°C for 25 minutes to form the second insulating film and give an insulated wire.

Comparative Example 1 An insulated wire was obtained by following the same procedure as in Example 1 except for not forming the second insulating film.

Example 2 After forming the first insulating film by following the same procedure as in Example 1, the coated round electric wire was subjected to bending in the form of V character. Then, the second insulating film was formed on this molded wire in the same manner as in Example 1 to obtain an insulated wire.

Comparative Example 2 An insulated wire was obtained by following the same procedure as in Example 2 except for not forming the second insulating film.

(Evaluation) The insulated wires obtained in Examples 1 and 2 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 Dielectric breakdown voltage (kV) Example 1 8. 2 Example 2 8.1 Comparative Example 1 4. 1 Comparative Example 2 O) ) Cracks were produced at a bent portion.

It is shown from Table 1 that the insulated wire obtained in Example 1 had higher dielectric breakdown voltage than that obtained in Comparative Example 1. In addition, the dielectric breakdown voltage of the insulated wire obtained in Comparative Example 2 was deteriorated in comparison with that obtained in Comparative Example 1. However, the insulated wire obtained in Example 2 had higher dielectric breakdown voltage than that obtained in Comparative Example 2. Thus, it is understood that excellent insulating films were formed by the insulating method of the present invention.

INDUSTRIAL APPLICABILITY The insulating method according to the present invention has the constitution, so that by forming the second insulating film, an insulating film can be repaired and, therefore, the insulating film having a high insulating property can be attained even though a defect occurs in the first insulating film. Further, the method of forming the second insulating film in the present invention can be suitably applied even to the molded article to be treated having a complex shape because it is conducted by the cationic electrodeposition. In addition, since the insulatedmetal products, obtainedbyusing the insulatingmethod of the present invention, have the above insulating films, they can be suitably used to applications requiring higher dielectric breakdown voltage.