CA1048217A - Method of manufacturing an electrically insulated coil - Google Patents

Abstract

Abstract of the Disclosure A method of manufacturing an electrically insulated coil having excellent insulation characteristics and high reliability using a vacuum-pressure impregnation process comprises the step of selective-ly effectively combining epoxy resins, curing agents and curing accelerators employed as a mica bonding agent and an impregnant.

Description

104B'~17 This învention relates to a method of manufacturing an electrical-ly insulated coil using a vacuum-pressure impregnation process.
Recently, as a result of applylng a high voltage and large capacitance to an electric appliance, high electrical intensity and mechanical strength are demanded of an electrically insulatea coil for use with such an electric appliance.
Conventionally, as the method of manufacturing an electrically insulated coil capable of satisfying such demand there has been adoptea a vacuum-pressure impregnation process which comprises winding a mica sheet or tape around a coil, subjecting said coil as a whole to vacuum-desiccation to remove the solvent, water content or the like, subsequently vacuum-impregnating a non-solvent resin such as poly-; ester, epoxy resin or the like into space portions within the insula-tion body of the coil, thereafter applying a pressure to the resultant coil, and solidifying the non-solvent resin. Where the electrically insulated coil is manufactured utilizing the foregoing process, use is made o~ ~1) compounds (thermoplastic bituminous material), (2) un-saturated polyester, ~3) epoxy resins or the like, as the impregnant while use i9 made of the corresponding materials to those constituting - 20 said impregnant, as the mica bonding agent. The above enumerated material (1) has a defect in heat-resistance, and the material (2) has a defect in heat-resistance and water-resi.stance, respectively.
Accordingly, ~he materials (1) and (2) have recen~ly been little in u~e, and the last-mentioned epoxy resins (3) having high water-resistance and excellent electrical characteristics have principally been adopted. ~owever, the combinations o~ curing agents and curing accelerators and the types of epoxy resins result in a wide variety of range. Where, therefore, the epoxy resins are employed as the ~`~
impregnant, combinations made by taking only the properties of such materials into consideration do not serve as those fully satisfying the necessary requirements for the manufacturing steps~ -For this reason, an insulated coil of highly reliable quality :

can not easily be obtained with the result that the chaxacteri~tic of the coil so produced frequently pres~nt3 a high degree of varia-tion to become a cause of coil accidentsO :~
This invention has been achieved in view of the aforeaaidcircumstances, and is intended to provide a meth~ of manufacturing a highly reliable, electrically insulated coll of excellent quality having the characteristics enabling the coil manufacturing steps (press~remolding and solidi~ying steps) to be ~tably carried out.
That is, the characterizing feature of th~ inv~ntion resides in that in the manufacture of an electrical insulation coil by the vacuum-pressur~ Lmpregnation proce~s employing epoxy resins the above object has been attained by selectively effectively combining epoxy resins, curing agent~ and curing accelerator~ used as the ~ Lmpregnant and the mica bonding agentO
- The method o~ manufacturing an electric~ ly insulated coil according to the invention will now be describedO A mica tape ~: ~oated with a varnish (mica bonding agent) containing 0.3 to 105 weight parts or preferably 003 to loO weight parts of boron tri-fluoride serie~ latçnt curing agent based on 100 weight Earts of 20 ~poxy resin is wound around a coil, and the result~nt coil is sub-~ected to preliminary desiccation by vacuum-hea~ingO The amount of varnish used as said mica bonding agent is preferred to account for 10 to 20~ of the sum amount of mica and rein~orcing materialO A
mica tape coated with such mica bonding agent remains ~table, high-ly flexible due to little soli~ification, highly operable and dur-able for long use, and further is not af~ected by the heating (up ~ :
to about 90C)"per~vrmed for preliminarily desiccating said resultant coilO
Next, an impregnation resin consisting of acid anhydride 3 ~exies curing agen~ and cyc1oaliphatic epoxy resin is impregnated .

~ 1048Z~7undar vacuum-pressure into the preliminarily de~iccated oilO Sub-sequently, the coil impregnated i9 fa~tened with a metal pad applied thereto and i9 subjected to 301i~ification, thereby obtaining a final coil product~ At this time, though the impregnation resin itself is low in viscosity and accordingly low in solidification speed, it reaches the mica tape layar and i9 mixed with the mica bonding agent to become integral therewith, so that the boron tri-fluoride serie~ latent curing agent contained in tha mica bonding agent concurrently acts on the impregnation res in as a curing ~ ?
accelerator. For thi~ reason~ the solidif ication speed i8 effective-ly ad3us ted during the solidification stap to form an ideal in- :~:
sulation body with the aid of the fastening forceO
A3 the epoxy re~in of the mica bonding agent a bisphenol epichlorohydrin series epoxy resin (~or example, Epikotes 828 and 1001 manufactured under such trade names by Shell Chemical Company or DER 331 and DER 661 manu~actured under ~uch trade name3 by ~ow ~.
: Ch#mical Company~ i~ preferably u~ed in a single or mixed form.
Further) as the boron trifluoride series latent curing agent complex æalts ~uch as BF3-monoethylamine, BF3-piperidineJ ~F3-benzylamine or the like are suitable. Further, as the acid anhydride ~eries curing agent acid anhydrides such as hexahydronaphthalic anhydride, methy?hexahydrophthali~ anhydride, methyltetrahydxophthalic anhy-dri~c, methylnadic anhydride or the like preferably are respectively used in a ~ingle or mixed ~orm~ Further, as the cycloaliphatic epoxy resinJ Chis30nox 221 (manufactured under such trade ~ame by Chi~o Company) and a glycidyl epoxy type epoxy resin (for example, XB-2610 manufactured under such trade name by Ciba Geigy Company) :
can be employed~ In addition, $ox ~he purpose of decreaæing the LmprsgnatiOn viscosity of the ~pregnant, an epoxy series rsacti~e JO diluent (for example, butylglycidy~ether or arylglycidylether) can ~ _ 3 _ :
" , ., ~ , . . . . .

~48~
be added to the impregnant ~9 required~
As above describedJ bacau~e of a good adaptability between the mica bonding agent and impregnation re~in a3 selectively efect-ively mutually combined the electrically insulated coil manufactured by the above-mentioned method has an axcellent electrical, mechani-cal and thermal characteri~tic~ and i~ mainta~ned highly reliable in qualityO

- 3a -' -: . , . .: , This invention will be more fully understood by re~erence to the concrete example which ~ollows.
Example Five types of varnishes (a 50% solution of methylethylketon) were first prepared each of which has such a resin composition as is ~ ?
shown in the respective columns of examples 1 to 3 and controls 1 -~ and 2 of Table 1. The varnish so prepared was coated on a mica sh~et consisting of a bonded mica paper or flake mica and glass reinorcing material as a lining material to obtain a mica tape. The mica tape was wound around a coil whose elemental wire is previously insulated, and the resultant coil was introduced into an impregnation tank and was subjected to preliminary vacuum desiccation under a tamperature of 70C to 80C and under a pres~ure of 0.3 mm Hg. Subsequently, said coil was cooled to normal temperature and was vacuum impregnated : with an impregnation resin consisting of acid anhydride and cyclo-aliphatic epoxy resin, and thereafter was ~ubjected to a pressure of 7 kg/cm2 for 15 hours.
Thereafter, said coil was taken out of the impregnation tank, .~ and a metal pad was applied to the taken-out coil. The resultant .: .
~ 20 coil was wound with a thermal shrinkable tape such as shrinkable polyester tape and was gradually heated for solidi~ication, and thereafter was finally heated ~or 20 hours at a temperature of 150C
to obtain a final product, iOe~ ~ an electrically insulated co~ lo : The coil thus obtained has such electrical characteristics as presented in Table 2. The respective coils obtained from the examples :
1, 2 and 3 had a prescribed dimension and a good insulation layer `~
~ having a uniform thicknessO On the other hand, the surface of the insulation layer of the coi7 according to the control 1 was coloured ::
whitish, which indicates that the impregnation resin flows out from the surface of the insulation ~ayer and accordingly is not held :` thereinO The coil according to the control 2 presented a good appearance but the insulation layer thereof failed to be sufficiently compressed to have a somewhat lar~er thickness. When this coil was : ' ' ; - 4 -16~4~2~7' cut off, an impre~nation resin layer proved to be formed thick between the insulation layers and to have innumerabl~ small cracks.
Since, in the insulated coil of the invention, the boron tri fluoride series latent curing agent affects the suitability of the coil itself~ the addition amount thereof is of greak importance.
Namely, as apparent from the results of the examples 1 to 3 and controls 1 and 2, it i5 when 0O3 to 1~5 weight parts or preferably 0.3 to loO wei~ht part of said latent curing agent based on 100 weight parts of epoxy resin was added thereto that a good result is obtained~ Where a solid cyclo-aliphatic epoxy resin (for ex~mple, LT
580 manufactured under such trade name by Ciba Geigy Company) was used as the mica bonding agent, the reaction of the mica bonding agent with the impregnation resin, when the ormer was mixed with the latter~ was promoted due to the high reactivity of boron tri-fluoride series latent curing agent and cyclo-alipha~ic epoxy resin, so that a result similar to the control 2 was obtained to present a low suitabilityO
: Table 1 .

_ Example 1 Example 2 Example 3 Control 1 Control 2 . = ~ : . .............. ~ _ 70 weight 60 weight 60 weight 70 weight 60 weight part of part o part of part o~ part o Compo- DER 331 828 Ep kote Epikote Ep kote nents of A
mica 30 weight 40 weight 40 weight 30 weight 40 weight bo di part of part of part of part of part of n ng DER 661 DEN 4~8 DEN 438 Epikote DEN 438 agent 1001 _ . .
0O3 weight loO weight 1O5 weight 3 weight B part of part of part o~ _ part of BF3-mono- BF3- BF3- BF3-. _ ethylamine piperidine piperidlne plperidine A Epoxy resîn B Boron fluoride series latent curing agent ~:
.

.

~4i~7 Table 2 _ ~ tanS ~ an ~` ~ tan (5' - Voltage Mica bonding Initial Initial Initial BDV sndurance a~ent u~ed value~ value ~ ~alue ~ KV/mm characteristics E/ ~ E 1.5E
__ _ _ _ . .. _ ., . - __ Example 1 0.02 0.05 0.11 2600800<

2 0.01 0.02 0.09 27.01000~

3 0.~2 0.03 0.28 25.07<
Control 1 O33 1.33 1.70 19.0_ o. 18 o . 55 o. 78 17. 5 20r ~ 3~o In the above ~abl~ 2~ E represent~ the rated voltage, the initial value i8 the value of the tan ~ at the nonionization time : when it doe~ not ri~e, in the case where the low voltage as applied is gradually increased in mea~uring the tan ~ value, BDV is the insulation braakd~wn voltage~ and the voltage endurance characteris-tic is the length of time required for the ~oltage having ~ vo}tage inclination of 9.5 KV/mm to be applied until the insulated condition .. . .
i5 broken-downO

:~ A~ above de~cribed, a highly reliable electrically insulated coil of excellent quality ha~ing ths characteristic3 enabling the coil manufacturing ~teps (pressuremolding and 301idiEying steps) to ; be stably carried out can be ob~ained, in the present method o~

~ manuacturing an electrically insulated coi} by vacuum-pressure . .
.~ impregnation proces~ employing epoxy resin~, by selectiv~ly effe~tive~
ly combining epoxy resin~, curing agent~ and curing accelerator~

: u~ed a~ the Lmpregnant and the mica bonding agent.
~ hough~ as heretofore mentioned, the coil, to which th~ mica bonding agant and the impregnant are only applied, pre3ents9 as it i9, a sufficient per~srmance, the mutual adaptability between the mica bonding agent and impregnant can further be increased by pre-~4~
~.iously applying, befor~ the mica bonding agent is coated on themica tape, an uncured epoxy powder containing therein a curing agent which is ~olid at normal tempsrature as an adhe-~ive between the mica sheet and the reinforcing material. This i~ because the respective solidification spe2ds of the impregnation resin ~nd the mica bonding agent within the insulation layer are kept con-stant by said previous application of said powder. ~amely~ within the mica layer there wi}l be attainad the distribution of a small amount of Lmpregnation re~in and a large amount of mica bonding agent while between the mica layer~ there will be created a layer having the distribution of a ~mall amount of adhesive and a large amount of LmpregnatiOn resin. Accordingly, in any portions of the mica layer section the solidification is properly advanced due to the presence of curing agent, i.e~, the boron trifluoride serie~
latent curing agent within the mica layer and the latent curing agent contained in the powder between the mica layers, so that a uniform insulation layer having good suitability is formed during the solidification stepO
In case of the oregoing uncured epoxy powder containing curing agent therein, fo~ example, a bisphenol series solid epoxide (Epikote~ 1001, 1004 and 1007 manufactured under such trad~ names by Shell Chemical Company) i9 de3irable as said epoxide re3in~ and, for example9 th~ latent cu~ing agent in the said powder such as anhydride dicyandiamide, diamino-diphenylmethane or imidazole~ is .
: suitable as said curing agent. The amount of said powder bet~eon mica sheet and reinforcing materials is preferred to account for 3 to 12 weight % of the adhesive powder based on the sum amount of mica sheet and reinforcing materialO ~he reason i~ that in case of le88 than 3 weight % the solidification promoting action be-.
. . . . .

~34~ 7 tween the Lmpreynation r~sin and said powder i~ rsndered ineffec-tive whereas in ca~e of more than 12 weight % the action of said powder i9 rendered too effective to render tha re~ultant mica tape inflexible with the result that its resin impregnability and operability are decreased to render it unsuitable.
FurtherJ by applying, in addition to ~aid previous application treatment ~or said powder, a mica layer flow-preventing agent to the mica tape there can be obtain~d a more highly reliable insulated coil., That is, where no mica layex flow-preventing agent i~ app-10 lied to the mica tape, it often happen~ that when the mica tapeof the coil after completion of resin impregnation is pre3se* by ~ingers~ the mica layer is displacedO ~his produces the pos~ibili- ;
ty that in case of the manufacture of an elongate, large coil a mica layer flow takes place due to the molding pressure during the solidification ~tep performed after a metal pad i~ applied to an unfinished coil, which undesirably affects the characteristics o the coil after ~olidification. Such mica layer flow-preventing agent application is performed by using a~ small an amount of normal temperature ~olidifiable epoxy resin composit.ion as Oo l to 1 weight ~ based on the 8um amount o, for example, mica tape and reinforcing material. A coil wound with a mica tape subjected to previous application as the mica layer fl~w-preventing agent of 0.5~ of ~`
normal temperature solidifiabLe epoxy resin composition ~onsisting :
of 100 parts of Epikote 828 and 13 parts of triethylenetetramine based on tha ~um amount of mica tape and r~inforcing material presented no mica layer flow and had good characteristics after solidified.
There will now be described a concreta example of the method of producing a mica tape.
3~ i Tha f ir~t step (Bondin~ step utilizir~g the epoxy powder):

.

1~8Z~L7 An epoxy resin o~ EPX 1346 is applied to a gla~s cloth having a fiber thickne~3 of 30 m at the rate of 8g per square meter o~ the glass cloth, and the resultant glass cloth i9 fused to a not-dehydrated, bonded mica paper having a thickness o~ Ool mm by a heated roll kept at a temperature range of 125 ~ 5~ at a speed of 2 m/minO Thi~ extent of thermal hi~tory, however~ does not cause the ~olidification of the EPX 1346~ which permits th0 EPX
1346 to remain effective as the reaction promoting agent for the impregnating resin . .
The second step (Mica layer fl~w-preventing ~tep 3:
A varnish consisting of 0.1 kg of Epikote 828, Ool kg of TTA
~txiethylenetetramine), 6075 kg of ~oluene and 2.25 kg of methanol i9 coated as the mica layer flow-preventing agent on the mica ~heet obtained in the first step, so as to permit the varni~h thu~ u~ed to amount to 50 + 5 g/m20 The resultant mica sheet3 after passed through a drying stove kept at 60C at a speed of 2 m/min., is allowed to ~tand overnight, thereby to cause the mica layer flow-preventing agent to be fully solidifiedG
The third s~ep (St~p for coatiny the bonding agent):
A varnish con~iqting o~ 6 kg o~ Epikote 828, 4 kg of DEN 438, 0005 kg o B~3 piperidine, 706 kg o~ methylethylk~ton and 204 kg o~ toluene i8 coated as the mica bondi~g agent on the mica sheet obtained in the second step, so a9 to permit the varnish thus used to amount to 80 ~ g/m20 The resultant mica sheet i9 passed through a drying 9 tove kept a~ 80 to 90C at a speed of 1 m/minO and is thereby dried to obtain a desired mica tapeO
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Claims (3)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of manufacturing an electrically insulated coil comprising impregnating a cyclo-aliphatic epoxy resin containing acid anhydride into a coil wound with a mica tape which is obtained by coating a mica sheet consisting of a mica and backing material with a resin material containing 100 weight parts of epoxy resin and 0.3 to 1.5 weight parts of boron trifluoride series latent curing agent, pressure-molding the resultant coil and solidifying the same.

2. A method of manufacturing an electrically insulated coil according to claim 1, wherein an uncured powdered epoxy resin containing a curing agent, solid at normal temperature, is previously applied to an interface between the mica and the backing material and heated to fusion-bond the mica and the backing material.

3. A method of manufacturing an electrically insulated coil according to claim 1, wherein the mica sheet is previously treated with a mica layer flow-preventing agent.