Abstract:
Improved method for producing an electrically insulated conductive body such as coils, etc. for use in electrical apparatuses and appliances, wherein an electrically conductive body is immersed in an electrodeposition paint liquid prepared by dispersing into water mica powder as an inorganic insulative substance and water-dispersion varnish as an organic insulative substance, thereby forming an electro-deposited layer on the electrically conductive body by electrophoresis, followed by drying the electro-deposited layer coated on the electrically conductive body under heat, then the dried electro-deposited conductive body is immersed in a water-soluble resin solution containing therein a curing agent, followed by drying the resin coating under heat, and finally the resin-coated, electro-deposited conductive body is impregnated with an impregnating resin, followed by heat-setting the resin as impregnated.

Description:
This application is a continuation of application Ser. No. 370,907, filed Apr. 22, 1982, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a novel method for producing an electrically insulated conductive body by utilization of electrophoresis. The method according to the present invention is particularly suited for production of electrically insulated conductive bodies such as coils, etc. used in electrical apparatuses and appliances. 
     2. Description of the Prior Arts 
     Production of the electrically insulated conductive bodies such as a coil, etc. for use in electrical apparatuses and appliances has heretofore been done by impregnating the coil made of electric conductor, which is wound together with inorganic-organic composite type porous insulating material, with an impregnating resin containing therein curing agent, curing catalyst, curing accelerator, and so on, followed by heat-setting the impregnated resin. 
     Such conventional method, however, has various disadvantages such that a great deal of man power is required for winding the porous insulating material together with the electric conductor, which inevitably lower the working efficiency; the socalled &#34;dropping phenomenon&#34; takes place due to lowered viscosity in the resin composition when the impregnated resin is to be cured under heat; in view of the fact that the impregnating resin contains the curing agent, a curing catalyst, and a curing accelerator as its composition, the resin tends to be cured when left over a long period of time, hence its usable period of time is inevitably restricted; and, for the preceding reason, maintenance and control of the storage vessel for the impregnating resin is rather complicated. 
     The present inventors have so far developed various methods for forming an electro-deposited insulating layer by electrophoresis using electrodeposition paint consisting of mica and water-dispersion varnish (vide: Laid-Open Japanese Patent Application No. 89178/76 and No. 114602/76), the methods being capable of dispersing with winding the electrical conductor together with the porous insulating material, which has been one of the disadvantages in the abovementioned conventional method for its production. 
     These forming methods, however, have such a disadvantage that the mechanical strength of the electrolytically deposited insulating layer at a stage prior to its impregnation with the impregnating resin is weak, which weakness causes cracks and tear-offs to occur in it when the insulating layer is fitted inside a slot of an iron core. 
     As the result of diligent and strenuous researches conducted in an attempt to remove the defects in such forming methods as well as those remaining in the conventional methods, the present inventors have discovered that all of the abovementioned defects could be solved by immersing the electrolytically deposited insulating layer, after its formation, into an aqueous solution added in advance with the curing accelerator, based on which discovery they completed the present invention. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide an improved method for producing an electrically insulated conductor body free from all the afore-mentioned defects. 
     It is another object of the present invention to provide an improved method for producing an electrically insulated conductive body free from various disadvantages inherent in the conventional methods, which has been solved by immersing an electro-deposited layer in a water soluble resin solution added in advance with a curing accelerator. 
     More particularly, according to the present invention, there is provided a method for producing an electrically insulated conductive body, which comprises steps of immersing an electrically conductive body into an electro-deposition paint obtained by dispersing into water mica as an inorganic insulative substance and water-dispersion varnish as an organic insulative substance, forming an electro-deposited layer on the electrically conductive body by electrophoresis, drying the electrically conductive body coated with the electro-deposited layer under heat, further immersing the dried electro-deposited conductive body into a water-soluble resin solution containing therein a curing agent, followed by drying the resin coating under heat, and then impregnating the electrically insulated conductive body with an impregnating resin, followed by heat-setting the resin as impregnated. 
     With the above-described method according to the present invention, there would accrue various advantages such that the electro-deposited layer has a remarkably improved mechanical strength even prior to its impregnation treatment with the impregnating resin; no cracks and tear-offs appear in the electro-deposited layer, which tend to occur at the time of fitting the insulating layer onto the iron core; any complicated and uneconomical aspects can be eliminated in maintenance and control of the resin storing vessel for keeping the impregnating resin added with the curing agent, curing accelerator, etc. in an appropriate viscosity, as has been experienced in the conventional methods; no dropping phenomenon occurs with the impregnating resin when it is to be heat-set; and adhesive property of the impregnating resin to the adhesion surface improves. As the result, there can be obtained the electrically insulated conductive body which is supple and remarkably stable in quality. 
     The foregoing objects, other objects, and the specific manner of preparing the electro-deposited insulating layer according to the present invention will become more apparent and understandable from the following detailed description thereof along with several preferred examples. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The water-dispersion varnish for use in the present invention may be of any kind that is capable of electrolytic deposition. As the suitable examples, there can be enumerated acryl type water-dispersion varnish, epoxy ester type water-dispersion varnish, and so forth. Mica powder to be used should preferably have a particle size that does not pass through a 20-mesh sieve, but passes through a 200-mesh sieve, particularly, 35-mesh sieve. A mixing quantity of the water-dispersion varnish and the mica powder should preferably be 5 to 30 parts by weight of the water-dispersion varnish to 100 parts by weight of the mica powder in consideration of the impregnating property of the impregnating resin at the post-stage of the manufacturing process of the electrically insulated conductor. 
     For the water-soluble resin to be used in the present invention, arcyl type resins and epoxy ester type resins, for example, are suitable, the concentration of which may be from 1 to 10% by weight, or preferably, from 1 to 6% by weight. For the curing accelerator to be contained in the water-soluble resin, any of water-soluble curing accelerators may be suited for the purpose. Examples of such curing accelerators are triethanol amine and other organic amines, and 2-ethyl-4-methylimidazole (2E4MZ) and other imidazoles. The concentration of the curing accelerator in the mixture ranges from 2 to 20% by weight, or preferably, from 3 to 10% by weight. For the impregnating resin to be used in the ultimate stage of the manufacturing process, any of the well-known thermosetting resin used in electrical apparatuses and appliances in general may be used without limitation. 
     With a view to enabling those skilled in the art to put the method for producing the electrically insulated conductor into practice according to the present invention, there will be presented an actual example of preparing the water-dispersion varnish for electrolytic deposition, several preferred examples of manufacturing the electrically insulated conductors according to the present invention, and a comparative example. It should, however, be noted that the present invention is not limited to these examples alone, but any changes and modifications may be made in the components and their mixing ratio within the ambit of the present invention as set forth in the appended claims. 
     EXAMPLE OF PREPARING WATER-DISPERSION VARNISH FOR ELECTRODEPOSITION 
     From a mixture of the following ingredients, there was obtained acid-added epoxy resin having an acid value of from 30 to 60. 
     
         ______________________________________Ingredients         Parts (by wt.)______________________________________EPIKOTE 1001 (bisphenol type               100epoxy resin, a product ofShell Chemical Company)Tetrahydrophthalic anhydride               25Ethylene glycol      6______________________________________ 
    
     The thus obtained epoxy resin was dispersed in warm water containing ammonia, from which water-dispersion varnish having a pH value of from 7.0 to 8.0 was obtained by blowing nitrogen gas into the liquid, and other methods. 
     EXAMPLE 1 
     Mica powder of a particle size which was passable through a 35-mesh sieve and had been well washed with deionized water was mixed with the abovementioned water-dispersion varnish consisting of bisphenol type epoxy resin (EPIKOTE 1001) and tetrahydrophthalic anhydride and ethylene glycol as the principal constituents in a mixing quantity of 100 parts by weight of mica powder with respect to 10 parts by weight of the resin component in the water-dispersion varnish. To this mixture, deionized water was added and agitated sufficiently, thereby preparing uniformly dispersed electrodeposition paint liquid containing therein a total non-volatile substance at a ratio of 15% by weight to the total paint liquid. 
     A coil for an induction motor fabricated by bundling strands, on which glass fibers were wound in advance by mechanical means, was immersed in the electrodeposition paint liquid thus prepared, and then a direct current voltage of 100 volts was applied for 20 seconds across opposite electrodes at an interpole distance of 50 cm between them, thereby forming on the coil the electro-deposited layer consisting of mica and a resin component in the water-dispersion varnish. 
     Subsequently, the coil, on which the electro-deposited layer was formed, was immersed in a 2% conc. acryl type water-soluble resin added with 5% conc. triethanolamine as the curing accelerator. Thereafter, the coil was heated for 15 minutes at 150° C. for drying, thereby forming a coating film of 1.0 mm thick on it. 
     The thus coated coil was further subjected to the vacuum-impregnation with epoxy resin consisting of 100 parts by weight of EPON 828 (a product of Shell Chemical Company) not containing therein the curing accelerator and 98 parts by weight of HN 2200 (a product of Hitachi Kasei Kogyo K.K.), followed by heating the same for 5 hours at 150° C. to set, thereby manufacturing the electrically insulated conductive body for the induction motor. 
     The electrically insulated conductive body thus obtained did not cause the dropping phenomenon of epoxy resin, and exhibited highly stable quality. 
     EXAMPLES 2 TO 7 
     The same procedures as in Example 1 above were followed except for use of the components, their mixing ratio, and heat-setting time as shown in the following Table 1, thereby obtaining the electrically insulated conductive body for the induction motor. 
     COMPARATIVE EXAMPLE 
     Mica powder which was passable through a 35-mesh sieve and which had been well washed with deionized water was admixed into the abovementioned water-dispersion varnish composed of bisphenol type epoxy resin (EPIKOTE 1001) and tetrahydrophthalic anhydride and ethylene glycol in a quantity of 100 parts by weight thereof with respect to 15 parts by weight of the resin component in the water-dispersion varnish. Then, deionized water was added to the mixture and the whole batch was sufficiently agitated, thereby preparing uniformly dispersed electro-deposited paint liquid containing therein the total non-volatile component of 15% by weight with respect to the paint liquid as a whole. 
     Into the thus prepared electrodeposition paint liquid, there was immersed a coil for an induction motor fabricated by bundling strands, on which glass fiber was wound in advance by mechanical means. After the immersion, a direct current voltage of 100 volts was applied for 20 seconds across opposite electrodes at an interpole distance between them of 50 cm, thereby forming on the coil the electro-deposited layer consisting of mica and a resin component in the water-dispersion varnish. 
     The electro-deposited layer was then heated for 15 minutes at 150° C. to dry, whereby a coating film of 1.0 mm thick was obtained. The thus obtained coil was immersed in epoxy resin liquid (EPON 828: HN 2200=100: 98 parts by weight) added with 1 part by weight of zinc octylate (Oct.-Zn) as a curing catalyst, followed by the vacuum-impregnation of the coil with epoxy resin. Thereafter, the resin-coated coil was heated for 10 hours at 150° C. to set the resin, thereby obtaining the electrically insulated conductive body for the induction motor. 
     The following Table 1 also indicates, for each example, the breakdown voltage (BDV) and the dielectric loss tangent (tan δ) of the electrolytically deposited insulating coating on the coil at its initial stage and after it was subjected to thermal deterioration for 16 days at 250° C., with a view to evaluating the characterstics of the electrically insulated conductive body obtained in the Comparative Example and Examples 1 through 7, respectively. Incidentally, a reference to &#34;GP-5&#34; in the column of &#34;Impregnating Resin&#34; in Table 1 is a tradename of unsaturated polyester resin produced by Ryoden Kasei K.K. 
     
                                           TABLE 1__________________________________________________________________________Example Comparative          Exp. 1 Exp. 2 Exp. 3  Exp. 4__________________________________________________________________________Electrolytically   Mica powder          Mica powder                 Mica powder                        Mica powder                                Mica powderdeposited paint   (100)  (100)  (100)  (100)   (100)(paint by wt.)   Epoxy ester          Epoxy ester                 Epoxy ester                        polyester type                                Epoxy ester   type water-          type water-                 type water                        water-disper-                                type water-   dispersion          dispersion                 dispersion                        sion varnish                                dispersion   varnish (15)          varnish (10)                 varnish (20)                        (10)    varnish (20)Water-soluble   --     Acryl type                 Acryl type:                        Acryl type                                Acryl typeresin &amp; curing water-soluble                 water-soluble                        water-soluble                                water-solubleaccelerator    resin (2.0)                 resin (3.0)                        resin (4.0)                                resin (5.0)(%)            Triethanol                 benzyldi-                        Potassium per-                                Benzoyl          amine (5.0)                 methyl amine                        sulfate (5.0)                                peroxide(3.0)                 (10.0)Impregnating   EPON 828          EPON 828                 EPON 828                        GP-5    GP-5resin   (100)  (100)  (100)(part by wt.)   HN 2200          HN 2200                 HN 2200   (98)   (98)   (98)   Oct.-Zn(1.0)Heating-setting   10      5      4      6       6time (hr.)CharacteristicsInitialBDV (kv)   over 50          over 50                 over 50                        over 50 over 50tan δ (%)   0.3    0.2    0.2    0.2     0.2After deterio-rationBDV (kV)   46     48     48     35      38tan δ (%)   7.0    4.0    4.2    13.0    12.8__________________________________________________________________________        Example Exp. 5 Exp. 6  Exp. 7__________________________________________________________________________        Electrolytically                Mica powder                       Mica powder                               Mica powder        deposited paint                (100)  (100)   (100)        (paint by wt.)                Epoxy ester                       Epoxy ester                               Epoxy ester                type water-                       type water-                               type water-                dispersion                       dispersion                               dispersion                varnish (10)                       varnish (15)                               varnish (15)        Water-soluble                Acryl type                       Acryl type                               Epoxy ester        resin &amp; curing                water-soluble                       water-soluble                               type water-        accelerator                resin (2.0)                       resin (2.0)                               soluble resin        (%)     2E4MZ (3.0)                       Tris(dimethyl-                               (2.0)                       aminomethyl)                               Dimethylamino-                       phenol (4.0)                               methyl phenol                               (5.0)        Impregnating                EPON 828                       EPON 828                               GP-5        resin   (100)  (100)   (unsaturated        (part by wt.)                HN 2200                       HN 2200 polyester                (98)   (98)    resin)        Heating-setting                 5      5       5        time (hr.)        Characteristics        Initial        BDV (kV)                over 50                       over 50 over 50        tan δ (%)                0.2    0.2     0.2        After deterio-        ration        BCF (kV)                48     48      36        tan δ (%)                2.0    4.0     12.6__________________________________________________________________________