CA1087043A - Anaerobic resin curing system - Google Patents

Abstract

ANAEROBIC RESIN CURING SYSTEM

ABSTRACT OF THE DISCLOSURE
Anaerobic resins are cured in a gaseous atmosphere which does not contain oxygen. An insulated conductor is placed in a vacuum and is impregnated with an anaerobic resin under pressure. The conductor is then placed in a non-oxygen containing atmosphere, such as nitrogen, which cures the resin.

Description

BACKGROUND OF THE IN VENTION
Conductors for use as coils ln g~ner-'ors and motors are ~nsulated using the VPI (vacuum-pres~ure impreg-nat~on) process by wrapping with rnica t2Pe~ tn-~ with a glass binding tape to hGld the brittle mlca tape onO The wrapped conductor is placed in a ~acuum then ir a resin under pressure~ It is removed and heated in arl oven tO CUL e the resin.
While this system is used commercially, ~t re-quires a great deal of energy.for t`he baking ovens bPcause the copper ln the coils must be heated along w~th the resin.
Run-off of the resln durlng cure can occur~ and mechan1cal stresses in the resin can be induced by expanslon of the copper during cure and its subsequent contractlon during cooling.
Anaerobic resins are resins which will not cure in the presence of oxygen, but will cure when placed between two oxygen-impervious surfaces, and therefore they are commonly used as adheslves.
PRIOR ART
U.S. Patent No. 3,539,438 discloses ~rapping a --1-- , ., ,` ,. ' , , ' , ' ' ' ,' ' .' ! ` ' .. 1 ' . ., . ; ' ; ~, .. . . ' ' ' . ' . .

46,427 ~87043 . .
.'.: `' conductor with mica paper and impregnatin~ wlth a non- -anaerobic acrylic resin.
Anaerobic resins are disclosed in U.S. Patent Nos. 3,616,040; 3,634,379; 3,775,385; 3,855,040; 3,880,956, `
3,041,322; 3,125,480, 3,203,941; 3,3OO,547; 3,419,512;

2,8g5,950; 3,043,820; 3,046,262; 3,218,305; 3,435,012; and

3,720,656. ~`~
SUMMARY OF THE INVENTION
We have found that insulated conductors impreg-nated with anaeroblc resins will not cure in a vacuum, which is an advantage in the VPI process, but can be cured by con-tact with a gaseous atmosphere which does not contaln oxy-gen. This means that the resins can be cured at room temp-erature, thus avoiding the problems previously encountered with heat-cured resins. Electrical properties are comparable to the heat-cured resins now in use, except at high voltages.
Unlike electron beam and UV cured resins, anaeroblc resins cured under a gas cure in depth, down to 6 lnches or more.
DESCRIP~ION OF THE INVENTION
Figure 1 is an isometric vlew in section of an insulated condu¢tor impregnated with an anaerobic resln.
Figure 2 is a diagram of an apparatus for con-tinuously coating a wire using the curing system of the invention.
In Figure 1, a conductor 1 is covered with several layers of mica tape insulation 2 and one layer of woven organic tape insulation 3, which holds the mica insulation ;

in place. An anaerobic resin 4 impregnates the insulatlon and forms an outer coating.
In Figure 2, a conductor 5 passes ~rom capstan 6 .

46,427 ,, ~37~43 into bath 7 of an anaerobic resin 8. The wire then passes over sheave 9 into closed tank 10. An inert gas flQws into the tank from conduit 11. As the wire passes over sheaves 12 in the tank it is cured, then leaves the tank and is wound on capstan 13.
An anaero~ic resin is a resin which will not cure in the presence of oxygen, but wlll cure at room temperature ~ u~R~
when placed between~oxygen-impervious surfaces. Solventless anaerobic resins are required for the VPI process. Most anaerobic reslns are acryllcs, such as diacrylates, which polymerize by addition through a double bond. Commonly used acryllc anaerobic resins include tetraethylene glycol dimethacrylate and tetraethylene glycol diacrylate. An acrylic anaerobic resin may contain a reactive comonomer such as ethyl methacrylate, styrene, or 2-ethylhexyl acry-late. An organic peroxide free radical initiator such as cumene hydroperoxide or t-butyl perbenzoate is o~ten used to initi.ate cure. An accelerator, usually a tertiary amine such as N,N-dimethyl-p-toluidine~ and a coaccelerator, usually an organic sulfimide such as benzoic sulflmide, may be present to reduce curing time. The free radical initi-ator can be stabilized with a free radical stabilizer such as hydroquinone. The hereinbefore cited patents describe many anaerobic resins ~amiliar to the art which may be used in this invention.
The conductor is preferably copper because it is most widely used for electrlcal insulation and it is known to accelerate the cure of anaerobic reslns, though other metals can also be usedO
The primary insulation is preferably mica, espec-- ` 46,427 :~871D4;3 :~

ially for high voltages, as lt has excellant electrical properties. Glass, asbestos, Nomex~ a polyamide belleved to be made from meta phenylene diamine and isophthaloyl chlo-ride, sold by Dupont), and other types of insulation could also be used, either alone, in mixtures, or in mixtures wlth mica. Mica lnsulation is usually made with a polyester backing to hold the mica together. The insulation may be a tape which is wrapped around the conductor, the amount of insulation depending upon the voltage drop across the in-sulation. Mica insulation is preferably impregnated wlthabout 3 to 30% (preferably about 5 to about 12%, by welght based on the mica weight), of a polymer which is coreactive with the anaerobic resin, in order to insure a better bond.
Polyesters, acryllcs, polybutadienes, or other unsaturated monomers may be used as co-reactive resins.
The VPI process is the preferred method of in-sulating a conductor because it leaves very few air gaps in the insulation, but other methods may also be used. The wrapped conductor is placed in a tank which is then evac-uated. The anaeroblc resin is admltted under pressure,usually at least about 46 psi, though about 90 to about 100 psi is preferred. The resin should saturate the lnsulation.
Typically, the insulation will contain about 5 to about 35%
(by weight based on the insulation weight) of the anaerobic resin, though about 20 to about 30% is preferred. The resin is permitted to drain from the wrapped conductor and is ;
cured by contact with a gas which does not contain any significant amount of oxygen. This may be accomplished in the same tank or the wrapped conductor may be cured in a separate tank. Nitrogen, carbon dioxide, or rnixtures of 46,427 ~137~3 ;;

.
these two gases is preferred as it is inexpensive, sa~e, and easy to handle, but other inert gases (other than oxygen) may also be used. It has been found that if nitrogen is used to cure an acrylic resin the rates of cure are optimum at a nitrogen flow rate of about 6 to about 20 lpm (liters per minute) . . ..
The following examples further illustrate this invention.
Example I
. .
The following table gives varlous anaeroblc resin compositions whlch were prepared and tested for gel time and storage stability.

:

46, 427 170~L3 ,~ , . ~: .
o ~ o ~ In o o o o o o ' ~) ., C ~ ~ 0 3 ~ Ln ~-1 0 0 0 0 0 0 O ~ ~ ~ ~ A ~ A ~ /~ ~ ;;
~ ,a t;i '') Z N ,~ ~ ~ 3 3 V ~1 .
o o o ': ~ L~ ~ O U~
~ ~ ~ tr) ' ~ t~ ~ ~) O O O ~ O O
..

o 30 ~ 3 3 3 J ' ~
O, O O 0 O' ,, O O O O O O
`. ~ P ' , ' ' , I ' ,' ` ' ~' , 8 o ~ ", ,~, o o o~ ~
o ~ ' , ' ' ~-, . ' .

3 3 3 O 3 3 3 3 .=r 3 ~ '`.
~ ~ O O O ~i O O O ~0 0 0 0 ~ ' ' .`:
... ,9~
~ '~
O O O O ' O O O O O O
N N N N N N ~ N N N

. ' . ', , ' ' .

46,427 ~ .
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Samples of the above resins were llmited to about ~ :
50 gms due to the high exotherm pro~uced during cure. The .
storage stability tests, which determine storage time until visual gelling occurs, were carried out on samples of about 50 g of resin stored in 4 ozO glass ~ars or polyethylene containersO Because of the uncertain effects of the fluores~
cent lighting in the laboratory on the resin stabillties, ~:
the samples were stored in the dark. Periodically, gel times were run ~under N2 flow) on khe samples to check for `~
10 retention of cure reactivity during storageO :~
The gel time measurements (i,e~, time required for visual gelling to occur) were made on 10 g samples ln 2 inch diameter alumlnum dishesO It was found that the ordinary laboratory vacuum was insufficient to gel the samples within a reasonable timeO However, rapid gelation was achieved by placing the samples in a desiccator and passing nitrogen through the desiccator~ The following table gives the .
results of testing resin number 10.
Cure Condition Gel Time at 25C
Air 48 hours N2 stream (13 lpm) 30 to 60 minutes ~acuum 24 hours At the end of 24 hours, a very small amount of gel :~
(about 7% of the resin) was observed at the bottom of the alumlnum dlsh of the sample placed ln the v~cuum.
The followlng table gives the results of slmllar tests performed on resin number 9O

46,427 ~ 7~43 '.:

Cure Condltion Gel Time_at 25C
C2 (13 lpm) 20 minutes N2 (5 psi static) 7 to 8 hours Air (13 lpm) ~ 2 days 2 (13 lpm) > 2 days Pressurized C02 at 50 psi also produced a rapi~
cure. Static nitrogen or carbon dioxide under pressure results in a slower cure than does a flow of nitrogen or carbon dloxide at atmospheric pressure, but requ~res smaller ,;~
lO quantities of gas. ~ ;
Using a similar procedure, the effect of the nitrogen flow rate on resin number 9 was determinedO The following table gives the results.
Flow Rate (lpm) Gel Time (hours) 1062 7.5 3025 4~C
6050 2.0 1300 1.5 2000 3.0 26.0 4,0 The above table shows khat a flow rate of about 6 to about 20 lpm is critical to obtaining a rapid cure at pressure of about one atmosphereO

Example II
.
Power factor data were obtained on mica composites impregnated with the most promising anaerobic resins, resin numbers 8 and 90 Two types of composite were prepared, one (sample A) was made by brushing an anaerobic resin on a B piece of "raw" mica paper t"Cogemica" sold by Cogebi CoO), (4 inO x 4 in~) about 20 mils thick, and the other type of 46,427 ;

;-.
sample (sample B) was fabricated by brushlng the anaerobicsover a polyester-impregnated mica tape wrapped 6 layers thick (i.e., 3 wrappings half-lapped~ on copper tubes (8 in long, 0.5 in. od). Because of the very fluid nature ( <3.0 cps) of these anaerobic resins it was observed that rapid and thorough penetration of these mica products occurred.
The samples were gelled under a stream of N2 (13.0 liters/min.) at room temperature and it was noted that the copper tube samples exhibited rapid gel under these condi-tions (i.eO ~30 minO). To establish the extent of cure ofthe anaerobic resins in these composites and the necessity (or not) for a heat post-treatment o~ these materials, it was decided to bake one set of these samples for 4 hours at 135C after the initial room temperature cure, It was felt that a comparison of the electrical data obtained from these two sets of samples would determine whether or not an additional heat treatment is necessary to obtain full cure wlth these anaerobic materials.
Power factor measurements were recorded at 25C
and 150C. The copper tube samples were also measured at 1, 1O5, and 2 kV at both temperatures to evaluate the ef~ect of voltage on the power factors of these mica composites.
Power factor data obtained with copper tubes wrapped with the Sample B mica tape and impregnated with two of the anaerobic resins are shown in the following table.

_g_ :

' ~
46,427 ~871D43 Heat Cure? % Power Factor ~100 x tan~) j Temperature (4 hours Applied Voltage Resin (C) _at 135C) ~ ~ 1.5 2.0 9 25 Yes 2 3 2.322 59 150 Yes 28 3 28 9 31 9 ~
~ _ ~-No 2.32 2.32 2.5 ~ ;
8 Yes 2.48 2.492.52 ~-~

150 No 27.9 28.9 31.1 Yes 34.2 35.7 37.7 The results for resin number g at 150C show that thé sample, which did not have any heat treatment after the initial cure, has sllghtly higher power factor values than the sample whlch had heat treatment. However, both samples showed similar power factor values at 25C.
For resin number 8, the sample with the additional heat treatment exhibits somewhat higher power factor values at 150C than the sample that did not have the additional cure. The room temperature values for both samples, however, remain the same. It is dlfficult, on the basls of these data, to say whether an additional heat postcure is necessary for these anaerobic materials to achieve full cure. Never-theless, it may be significant that all four samples showed very similar room temperature power factor values.
Although no attempt was made to identlfy the optimum mica tape for these anaerobic impregnants, the power factor values in these composites using the Sample B mica tape are not considered to be excessively high. Although the values (i.e. 32-37% at 150C and 2 kV) would be un- !
acceptably high for high voltage applications, they would be suitable for low voltage equipment insulation ~e.g., <13.8 kV).

46,427 `

' ~L~87~g3 ' : ~`
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Dlelectric strength measurements were carried out on mlca composites made wlth Sample A lmpregnated with resin number 8. The samples were tested under an aliphatic hydro-carbon transformer oil sold by Westinghouse Electric Corp-oration under the trademark "WEMCO C" at room temperature using a voltage rise o~ 1 kV/secO Power factor and dlelectric constant data obtained with the Sample A composites uslng -resin number 10 are summarized in the f'ollowing table.
_ Power Dielectric Test Temper- Cure Capacitance Factor % Constant ature tC) Conditions (pF) _100 x tan ~) tE') _ 16 hrs at 25C36.3 o.89 3.4 under N2 Same + 4 hrs at 58.4 1.6 502 135C in air ;
16 hrs at 25C138O6 4.8 12.9 150 under N2 --Same + 4 hrs at 94.2 23.0 8.4 135C in air Once agaln there appears to be an interesting dif-f'erence between the sample which had the additional heat treatment and the one that did not. The power f'actor of' the ~ ;
room temperature cured sample, measured at 150C was much lower than that of' the other one. The rea~ons f'or these dlfferences are not very clear at this time; however, both samples would be consldered as having acceptably low power ~actor and dielectric constant values for insulatlon up to a voltage Or about 13.8 kV.
The following table shows the dielectric strength for the two samples used ln the previous table. The mea-surements were made at an N2 flow rate of 13.0 lpm under "WEMCO C" oil at 25C using a voltage rise of 1 kV/sec.
- Both composite samples were used in the previous power L~6,427 87o43 factor measurements and probably experienced 1 hour at 150C
before being tested for dielectric strength. ~ ;~
Composite Breakdown Dielectrlc Thickness Voltage Strength re Condition (mils) (kV; rms) (volts/mil) Overnight (16 hours) 21 16.0 765 at 25C in N2 stream . _ _ , Same + 4 hours at 20 16.5 ~30 135~ in air . _. _ _ Same + 4 hours at 20 18.5 935 135C in air -The sample which had the additional elevated temperature cure would appear to have somewhat higher di-electric strength than the room temperature cured sample~
However, both composites would seem to have higher dielec-tric strengths than those of epoxy resin impregnated mlca composites of similar thicknesses, Typically, the epoxy-mica composites show values of 400-600 volts/mil compared with 700-900 volts/mil for the anaerobic resin samples.
Example III
To lllustrate the importance of curlng these reslns under a stream of N2, the following experiment was carried out. Four copper tubes were wrapped with Sample B
mica tape as described previously. One set (2) of these samples was impregnated with resin number 5 and the ot,her with resin number 80 One of' each set was allowed to cure in an N2 stream (flow rate 13 lpm) for 32 hours, then both sets were left in air for two weeks. The cure conditions and resin retention for each of these samples is shown in the following table.

46, 427 37a~43 ": '~' ' ., .

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P~ a) Oo o ,~
a)o ta ~ ~ co O
~; ~ o ,~
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~o ~, a) o ~ ~ oc~
~ t- ~ ~ ' ~
I--1 ." ~ ,.
U~ :` :

orl N
Z Z '~
V
a) " :.
0~ ~ ~ ~ :, ~:4 ~ ~1 r lCJ~
. , , rl bl o~
Q,~3:

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Q" 3 bO--`
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V ~ L~

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p:; z r~
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- 1 3 - :~

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The resins had been stored two months at room temperature ln polyethylene bottles prior to being usedO
~he resin "run-off" from the samples cured under N2 was f'ound to be negligibleO
Power factor measurements at 1 kV were then carried out on these four samples at 25C. The results are shown in the following table.
_ _ .
Powe r Factor (100 x tan ~ ) at 60 Hz _ Sample At 150C after At 25C after 10No. At 25C3 days at 150C 3 days at 150C
Bl 25.6 30.2 1O4 B2 ` 3.5 23 1 1.2 B3 4c5 2508 1.8 `
B4 32.8 23.9 1.8 .
Samples B2 and B3, which had been allowed to cure ;
in the N2 stream, showed much lower power factor values than the ones which had been left in air. This was not too sur-prlsing since the latter two samples were stlll very tacky, even after two weeks. The others were firm and tack-free a~ter a ~ew hours in N2.
To lllustrate this lack of cure ln Samples Bl and BL, all ~our specimens were postcured 3 days at 150C and the power factors remeasured at 25C and also at 150C.
These data are also shown ln the above table. At room temperature all four samples gaue simllar values tbetween 1.2% and 1.8%) and also at 150C (23.1 to 30.2%).
Thus, the indication ls that the samples exposed ; ;
to the N2 stream were more fully cured than the ones left in air.

46,427 .. ' '' ~L~87043 For a typical Class F motor, an addit.lonal heat treatment of the materials would not appear to be necessary slnce full cure could be obtained after the coils have been wound inko a stator because the operating temperature of the ~ ;
motor would be high enough to bring about a full cure.
Also, the winding of partially cured coils (assum-ing resin is non-tacky) might be advantageous since the mica insulation would still retaln an appreciable degree of flex-ibility. Conventionally made coils are sometimes stlff and 10 difficult to wind without cracking the lnsulation. ~,

Claims (28)

We claim:

1. An article comprising a conductor covered with insulation which is impregnated with a cured anaerobic resin.

2. An article according to Claim 1 wherein said insulation is selected from the group consisting of mica, glass, asbestos, organic resins, and mixtures thereof.

3. An article according to Claim 2 wherein said insulation is mica.

4. An article according to Claim 1 wherein said insulation contains about 3 to about 30% by weight based on said insulation weight) of an organic resin co-reactive with said anaerobic resin.

5. An article according to Claim 1 wherein said anaerobic resin is an acrylic resin.

6. An article according to Claim 5 wherein said acrylic resin is modified with styrene.

7. An article according to Claim 1 wherein the amount of said anaerobic resin is about 5 to 35% (by weight based on the weight of said insulation).

8. An article according to Claim 1 wherein said conductor is copper.

9. A method of forming a cured, resinous coating on an article comprising applying an anaerobic resin to said article in the presence of oxygen, and placing said article in a gaseous atmosphere which does not contain oxygen.

10. A method according to Claim 9 wherein said gaseous atmosphere is selected from the group consisting of nitrogen, carbon dioxide, and mixtures thereof.

11. A method according to Claim 9 wherein said anaerobic resin is an acrylic resin.

12. A method according to Claim 9 wherein said article is a conductor covered with insulation.

13. A method according to Claim 12 wherein said insulation is mica and said conductor is copper.

14. A method according to Claim 12 wherein said insulated conductor is placed in a vacuum, then immersed into said anaerobic resin under pressure.

15. A method according to Claim 14 wherein said pressure is about 45 to about 100 psi.

16. A method of continuously insulating wire com-prising passing said wire through an anaerobic resin, thence through a gaseous atmosphere which does not contain oxygen.

17. A method according to Claim 16 wherein said gaseous atmosphere is selected from the group consisting of nitrogen, carbon dioxide, and mixtures thereof.

18. A method according to Claim 16 wherein anaerobic resin is an acrylic resin.

19. A method according to Claim 16 wherein said anaerobic resin is solventless.

20. A method according to Claim 16 wherein said anaerobic resin includes an accelerator.

21. A method according to Claim 20 wherein said accelerator is benzoic sulfimide.

22. An article according to Claim 1 wherein said conductor is a wire.

23. An article according to Claim 1 wherein said conductor is a motor or generator coil.

24. A method according to Claim 9 wherein said anaerobic resin is solventless.

25. A method according to Claim 9 wherein said anaerobic resin includes an accelerator.

26. A method according to Claim 25 wherein said accelerator is benzoic sulfimide.

27. A method according to Claim 9 wherein said conductor is a motor or generator coil.

28. A method according to Claim 9 or 11 wherein said gaseous atmosphere which does not contain oxygen is nitrogen at a flow rate of about 6 to about 20 liters per minute.