Electrical Insulation System Based on Epoxy Resins for Generators and Motors

Abstract

Disclosed is an anhydride-free insulation system for current-carrying construction parts of an electric engine which comprises:

(A) a mica paper or mica tape for wrapping parts of said electric engine that are potentially current-carrying during operation of the engine, which mica paper or mica tape is impregnable via vacuum pressure impregnation with a thermally curable epoxy resin formulation and comprises one or more thermally activatable sulfonium salt initiators for the homopolymerisation of the epoxy resins present in said said thermally curable epoxy resin formulation or a mixture thereof in an amount sufficient to homopolymerize the epoxy resin taken up by the mica paper or mica tape and the construction part of the engine during the vacuum pressure impregnation step;
(B) a thermally curable bath formulation for the vacuum pressure impregnation comprising (i) a polyglycidyl ether or a mixture thereof, and (ii) a cycloaliphatic epoxy resin comprising at least two epoxy groups, which are fused to a cycloaliphatic ring, or a mixture thereof,
which formulation is substantially or, preferably, entirely free of thermally activatable curing initiators for the epoxy resin formulation.

Claims

1.-16. (canceled)

17. An insulation system comprising: (a) a mica paper or mica tape containing one or more thermally activatable sulfonium salt initiators; and (b) a thermally curable epoxy bath formulation comprising: (i) a polyglycidyl ether, and (ii) a cycloaliphatic epoxy resin comprising at least two epoxy groups, which are fused to a cycloaliphatic ring, wherein the thermally curable epoxy bath formulation is substantially free of thermally activatable sulfonium salt initiators, and wherein the insulation system is substantially free of anhydrides.

18. The insulation system according to claim 17, wherein the one or more thermally activatable sulfonium salt initiators are present in the mica paper or mica tape in an amount from about 0.01 to about 10 g/m.sup.2 of the mica paper or mica tape.

19. The insulation system according to claim 17, wherein the one or more thermally activatable sulfonium salt initiators are selected from the compounds of formula I to IV: ##STR00004## wherein: A is C.sub.1-C.sub.12alkyl, C.sub.3-C.sub.8cycloalkyl, C.sub.4-C.sub.10cycloalkylalkyl or phenyl, which is unsubstituted or substituted by one or more substituents selected from C.sub.1-C.sub.8alkyl, C.sub.1-C.sub.4alkoxy, halogen, nitro, phenyl, phenoxy, C.sub.1-C.sub.4alkoxycarbonyl or C.sub.1-C.sub.12alkanoyl; Ar, Ar.sup.1 and Ar.sup.2, independently of one another, are phenyl or naphthyl, which is unsubstituted or substituted by one or more substituents selected from C.sub.1-C.sub.8alkyl, C.sub.1-C.sub.4alkoxy, halogen, nitro, phenyl, phenoxy, C.sub.1-C.sub.4alkoxycarbonyl or C.sub.1-C.sub.12alkanoyl; and Q.sup. is SbF.sub.6.sup., AsF.sub.6.sup. or SbF.sub.5(OH).sup..

20. The insulation system according to claim 17, wherein the polyglycidyl ether is a diglycidylether of phenolic compounds.

21. The insulation system of claim 20, wherein the polyglycidyl ether is a diglycidylether of phenolic compounds having the formula: ##STR00005## wherein the R groups are independently selected from hydrogen or methyl group and n is a number equal or greater than zero.

22. The insulation system according to claim 17, wherein the cycloaliphatic epoxy resin is selected from diepoxides of dicyclohexadiene or dicyclopentadiene, bis(2,3-epoxycyclopentyl) ether, 1,2-bis(2,3-epoxycyclopentyloxy)ethane, 3,4-epoxycyclohexyl-3,4-epoxycyclohexane-carboxylate, and 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate.

23. The insulation system according to claim 17, wherein the thermally curable epoxy bath formulation comprises the polyglycidyl ether and the cycloaliphatic epoxy resin in a weight ratio between about 5:1 and about 1:10.

24. The insulation system according to claim 17, wherein the thermally curable epoxy bath formulation has a viscosity of not more than about 75 mPa.Math.s at 60 C.

25. The insulation system according to claim 17, wherein the thermally curable epoxy bath formulation further comprises micro particles, nano particles or a mixture thereof and, optionally, a wetting agent.

26. A mica paper or a mica tape comprising one or more thermally activatable sulfonium salt initiators.

27. The mica paper or mica tape of claim 26, wherein the one or more thermally activatable sulfonium salt initiators is present in an amount of about 0.01 to about 10 g/m.sup.2 of the mica paper or mica tape.

28. The mica paper or mica tape according to 26, wherein the one or more thermally activatable sulfonium salt initiators is dibenzyl-phenyl-sulfonium hexafluoroantimonate.

29. A method of manufacturing electrically insulated parts, comprising (a) wrapping a part with a mica paper or mica tape containing one or more thermally activatable sulfonium salt initiators, (b) contacting the part wrapped in mica paper or mica tape with a thermally curable epoxy bath formulation comprising (i) a polyglycidyl ether, and (ii) a cycloaliphatic epoxy resin comprising at least two epoxy groups, which are fused to a cycloaliphatic ring, wherein the thermally curable epoxy bath formulation is substantially free of thermally activatable sulfonium salt initiators, (c) subjecting the part wrapped in mica paper or mica tape and the thermally curable epoxy bath formulation to a vacuum impregnation process such that the mica paper or mica tape is impregnated with at least a portion of the thermally curable epoxy bath formulation; and (d) subjecting the part wrapped in mica paper or mica tape impregnated with at least a portion of the thermally curable epoxy bath formulation to heat sufficient to cure the thermally curable epoxy bath formulation.

30. The method of claim 29, wherein the part wrapped in mica paper or mica tape impregnated with at least a portion of the thermally curable epoxy bath formulation is heated in step (d) to a temperature between about 60 C. to about 200 C. for a time sufficient to cure the thermally curable epoxy bath formulation in the mica paper or mica tape.

Description

EXAMPLES

[0068] The following Examples serve to illustrate the invention. Unless otherwise indicated, the temperatures are given in degrees Celsius, parts are parts by weight and percentages relate to percent by weight (weight percent). Parts by weight relate to parts by volume in a ratio of kilograms to litres.

(A) Description of inqredients used in the Examples: [0069] CY 179-1: bis-(epoxycyclohexyl)-methylcarboxylate, supplier: Huntsman, Switzerland; [0070] MY 790-1 CH: distilled bisphenol A diglycidyl ether (BADGE), epoxy eq.: 5.7-5.9 eq./kg, supplier: Huntsman, Switzerland; [0071] PY 306 bisphenol F diglycidyl ether (BFDGE), epoxy eq.: 6.0-6.4 eq./kg, supplier: Huntsman, Switzerland; [0072] HY 1102: methylhexahydrophthalic acid anydride (MHHPA), supplier: Huntsman, Switzerland; [0073] XD 4410: one-component epoxy-based VPI-resin based on BADGE, Bisphenol F diglycidyl ether (BFDGE) and 2,3-epoxypropyl-o-tolylether, supplier Huntsman, Switzerland; [0074] DY 9577: curing accelerator for epoxy anydride hardener systems based on borontrichloride-octyldimethylamine adduct (1:1), supplier: Huntsman, Switzerland; [0075] DY 073-1: curing accelerator for epoxy anydride hardener systems based on a tertiary amine; [0076] ZK RT 1507: Dibenzyl-phenyl-sulfonium-SbF6, supplier: Huntsman, Switzerland; [0077] PC Propylene-carbonate: supplier: Huntsman

[0078] Mica tapes are composed of mica paper, optionally containing one or more additives or resins for consolidation of the mica paper, and a light-weight glass fabric made from E-glass or a polymer film that is adhered to the mica paper with a non-reactive or reactive adhesive for mechanical support. Following tapes were used in the Examples:

[0079] New inventive mica tape containing ZK RT 1507, supplier: Isovolta, Austria; Poroband ME 4020: mica tape containing zinc naphthenate, supplier: Isovolta, Austria; Poroband 0410: mica tape without accelerator, supplier: Isovolta, Austria.

(B) Comparison of Properties of Comparative and Inventive Formulations without Tape:

a) Comparative Example 1 (MY 790-1 CH/HY 1102/DY 9577/DY 073)

[0080] This comparative example is performed in order to compare the properties of the cured neat resins (without mica tape). For curing of the Comparative Example 1, small amounts of the curing accelerators DY 9577 and DY 073-1 are used instead of Zn naphthenate (contained in typical commercially available-tapes) because Zn-naphthenate is quite difficult to get homogenously dispersed in the epoxy/anhydride mixture.

[0081] To test the bath stability at 23 C., 1 kg of MY 790-1 CH and 1 kg of HY 1102 are mixed together in a steel vessel with an anchor stirrer at ambient temperature for 5 minutes. This mixture is then kept in an inert glass bottle for the storage test regarding bath stability at 23 C. for 80 days.

[0082] The viscosity of the mixture is determined before and after the storage at a measurement temperature of 60 C. While the initial viscosity at 60 C. is 32 mPas, the viscosity increased during the storage time of 80 days by 12%.

[0083] To test all the other properties of the cured material, to 1 kg of the mixture described above as replacement for the Zn naphthenate that normally would promote the curing of impregnated tape, 0.8 g of DY 9577 and 0.2 g of DY 073-1 are added and mixed for another 10 minutes. This mixture is then cast in to moulds in the corresponding thicknesses to prepare plates for the various tests. After pouring the material to the moulds, these are put into an oven for 16 hours at 90 C. and 10 hours at 140 C.

b) Comparative Example 2 (XD 4410)

[0084] This example relates to a homopolymerisable aromatic epoxy system containing the catalyst in the composition (one-component system). It does normally go along with mica-tapes free of catalyst.

[0085] The commercial product Araldite XD 4410 is directly used to check the storage stability at 23 C. over 409 days. XD 4410 exhibits a viscosity of 78 mPas (initial at 60 C.) and an increase of less than 6% during 409 days.

[0086] The reactivity of this mixture is checked with a gel timer at 80 C. and 140 C.

[0087] To produce plates for the other tests, it is poured into moulds of corresponding thicknesses to prepare plates for the various tests. After pouring the material into the moulds, these are put to an oven for 4 hours at 125 C. and 12 hours at 170 C.

c) Inventive Example 1

[0088] The inventive example 1 of thermally curable bath formulation (B) for an insulation system according to the invention system is a mixture of 848.5 g resin CY 179-1 and 151.9 g MY 790-1 CH (prepared at ambient temperature).

[0089] The stability of this bath formulation is checked during 20 hours storage at 100 C. The initial viscosity is 40.4 mPas and the viscosity after storage 40.2 mPas.

[0090] To produce test plates without a mica tape 0.5 g of ZK RT 1507 are dissolved in 99.5 g propylene carbonate.

[0091] 198 g of the above described thermally curable bath formulation are mixed with 2 g of the mentioned solution of ZK RT 1507 in propylene carbonate.

[0092] The reactivity of this mixture is checked with a gel timer at 80 C. and 140 C.

[0093] To produce plates for the other tests, the formulation is poured into moulds of corresponding thicknesses to prepare plates for the various tests. After pouring the material into the moulds, these are put into an oven for 30 min at 80 C., 30 min 130 C. and 10 hours at 150 C.

d) Inventive Example 2

[0094] The inventive example 2 of thermally curable bath formulation (B) for an insulation system according to the invention system is a mixture of 495 g resin CY 179-1 and 495 g MY 790-1 CH (prepared at ambient temperature).

[0095] The stability of this bath formulation is checked during 20 hoursstorage at 100 C. The initial viscosity is 65.4 mPas and the viscosity after storage 65.4 mPas.

[0096] To produce test plates without a mica tape 0.5 g of ZK RT 1507 are dissolved in 99.5 g propylene carbonate (LME11135).

[0097] 198 g of the above described thermally curable bath formulation are mixed with 2 g of the mentioned solution of ZK RT 1507 in propylene carbonate.

[0098] The reactivity of this mixture is checked with a gel timer at 80 C. and 140 C.

[0099] To produce plates for the other tests, the formulation is poured into moulds of corresponding thicknesses to prepare plates for the various tests. After pouring the material into the moulds, these are put into an oven for 30 min at 80 C., 30 min 130 C. and 10 hours at 170 C.

e) Inventive Example 3

[0100] The inventive example 3 of thermally curable bath formulation (B) for an insulation system according to the invention system is a mixture of 848.5 g resin CY 179-1 and 151.5 g PY 306 (prepared at ambient temperature).

[0101] The stability of this bath formulation is checked during 20 hoursstorage at 100 C. The initial viscosity is 35.6 mPas and the viscosity after storage 35.8 mPas.

[0102] To produce test plates without a mica tape 0.5 g of ZK RT 1507 are dissolved in 99.5 g propylene carbonate.

[0103] 198 g of the above described thermally curable bath formulation are mixed with 2 g of the mentioned solution of ZK RT 1507 in propylene carbonate.

[0104] The reactivity of this mixture is checked with a gel timer at 80 C. and 140 C.

[0105] To produce plates for the other tests, the formulation is poured into moulds of corresponding thicknesses to prepare plates for the various tests. After pouring the material into the moulds, these are put into an oven for 30 min at 80 C., 30 min 130 C. and 10 hours at 170 C.

f) Test Results

[0106] The results of the afore-mentioned tests with the curable epoxy bath formulations of Comparative Examples 1 and 2 as well as the Inventive Examples 1, 2 and 3 are summarized in Table 1 below (data determined without tape, just for illustrating the properties of the epoxy matrix of such insulation systems).

TABLE-US-00001 TABLE 1 Comparative Comparative Inventive Inventive Inventive Example 1 Example 2 Example 1 Example 2 Example 3 MY 790-1 100 15 49.5 HY 1102 100 XD 4410 100 CY 179-1 84 49.5 84 PY 306 15 ZK RT 1507, 1 1 1 0.5% in PC DY 9577 0.16 DY 073-1 0.04 Working possible very good very good very good very good hygiene anhydride contact Viscosity at 32 78 40.4* 65.4* 35.6* 60 C. [mPa .Math. s] Viscosity 12% <6% very good very good very good increase of (80 days)** (409 days) formulation when stored at 23 C. Viscosity of 34.2** n.a. 40.2* 65.4* 35.8* formulation at 60 C. after 20 h storage at 100 C. Storage tank yes no no no no cooling needed Number of 2 1 1 1 1 components to mix Gelation time n.a. >>1000 16 40 14 21 20 at 80 C. Gelation time n.a. 30 1 30 1 30 140 at 140 C. Glass 144 C. 130 C. 171 C. 150 C. 151 C. transition temperature T.sub.g Cure 16 h(90 C.)/ 4 h(125 C.)/ 0.5 h(80 C.)/ 0.5 h(80 C.)/ 0.5 h(80 C.)/ conditions 10 h(140 C.) 12 h(170 C.) 0.5 h(130 C.)/ 0.5 h(130 C.)/ 0.5 h(130 C.)/ 10 h(150 C.) 10 h(170 C.) 10 h(170 C.) Dissipation 8% 12% 1.8% 4% 2.5% factor tan at 155 C. 5% weight 390 C. 400 C. 415 C. 415 C. 410 C. loss at (TGA 20 K/min) Tensile 45 Mpa ca. 45 Mpa 34 Mpa 38 Mpa 30 Mpa strength Elongation at 1.75% ca. 2% 1.1% 1.2% 1% break Thermal H F H H H insulation class rating *without ZK RT 1507 **without DY 9577 and DY 073-1 T.sub.g determined according to ISO 6721/94; Dielectric dissipation factor tan determined according to IEC 60250; 5% weight loss at (TGA 20 K/min): The indicated temperature is the temperature, for which the weight loss is just reaching 5% during heating a sample with a heating rate of 20 K/min. Tensile strength and elongation at break determined at 23 C. according to ISO R527

(C) Preparation of Mica Paper and Mica Tapes According to the Invention and Application Tests Thereof:

[0107] A mica paper sheet based on uncalcined mica flakes with an areal weight of 160 g/m.sup.2 is cut in a rectangular shape of the size 200100 mm. For mica paper impregnation a solution of LME 11135 (=0.5 wt % ZK RT 1507 in PC) in methyl ethyl ketone (MEK) is prepared which contains 10.5 wt % of LME11135 (=525 mg ZK RT 1507). The mica sheet is impregnated with 2.0 g of the solution and the solvent is removed in an oven at 85 C. for 1 min. The mica paper thus prepared contains 52.5 mg/m.sup.2 ZK RT 1507.

[0108] The treated mica paper is either used as it is or is combined with a glass fabric. In that case a glass fabric style 792 (23 g/m.sup.2, 2615 5.5 tex/5.5 tex), which has previously been coated with 3 g/m.sup.2 of an epoxy/acrylic resin mixture, is adhered to the mica tape using a solid epoxy resin having a melting point around 100 C. For this purpose the solid epoxy resin is evenly dispersed on the treated mica paper. Then the glass fabric is laid on top. The specimen is put into a heated press to melt the epoxy resin (130 C. for 30 s). The glass fabric and the mica paper stick together after removing from the press.

[0109] The obtained mica paper sheets and glass/mica specimens are cut in halfs to give 100100 mm samples. 4 layers of mica paper are piled with each 1.5 g evenly distributed impregnation resin between the layers giving a total resin weight of 4.5 g.

[0110] The impregnated specimens are used for monitoring the dissipation factor tan during cure in a Tettex instrument or are cured in a heated press. Cure in the Tettex instrument and tan measurement is conducted at 155 C.

[0111] Cure in the hot press is conducted following the following temperature cycle: 90 C. at 2 bar for 2 h-130 C. at 2 bar for 2 h-180 C., no pressure for 10 h.

[0112] The cured composites are subjected to tan measurement at 155 C.

[0113] The results of the afore-mentioned tests with the curable epoxy bath formulations of Comparative Example 1 (not containing DY9577 and 073-1) with Poroband ME 4020 (Reference system 1) and Comparative Example 2 with Poroband 0410 (Reference System 2) as well as the Inventive Example 1 are summarized in Table 2 below.

TABLE-US-00002 TABLE 2 Inventive System Reference Reference Exam- Exam- Exam- System 1 System 2 ple 1 ple 2 ple 3 Dissipation factor 4.4% 22.8% 3.7% 6.8% 2.5% tan (at 155 C.) Dissipation factor tan determined according to IEC 60250 in a Tettex instrument using a guard ring electrode at 400 V/50 Hz;

(D) Conclusions from the Examples Above

[0114] a) Conclusions Based on the Comparisons without Tape:

[0115] Regarding the first critical aspect of working hygiene, the anhydride-free inventive example is better than the classical anhydride-based reference, because it is does not contain a respiratory sensitizer and therefore is not regarded as a SVHC.

[0116] While the anhydride-based reference is quite low viscous, the existing anhydride-free solution according to Comparative Example 2 (XD 4410) is relatively high viscous and hence more difficult to impregnate into the mica-tape and the windings. The inventive bath formulations have a viscosity level quite similar to the anhydride-based reference and can impregnate better than the anhydride-free reference bath formulation based on XD 4410.

[0117] Regarding the bath stability, the anhydride-based reference builds up the viscosity at 23 C. during only 80 days already by 12%. To overcome this issue, a cooled storage is normally applied. The anhydride-free reference bath formulation (XD 4410) is quite stable and therefore does not need a cooling. Surprisingly the bath systems according to the invention based on CY 179-1 and aromatic resins are quite stable as there was virtually no change in viscosity even when treating the material for 20 hours at 100 C. Hence also no cooling would be typically required for the inventive bath composition.

[0118] A further advantage of the inventive system over the traditional reference is that there is no need for mixing the 2 components when refreshing the bath as it can be applied as one-component product (assuming a pre-mix of CY 179-1 and MY 790-1 CH to be delivered. As there is no anhydride that may partly evaporate during the application process out of the bath and hence impacting the optimal mixing ratio with the reference, this issue does not happen with the inventive example resulting in a better quality consistency.

[0119] The reactivity of the inventive product is moderate at temperatures up to 80 C. but very high at temperatures around 140 C. This means that this system is quite latent and therefore stable at storage temperature but highly reactive at higher temperature.

[0120] The one component reference according to Comparative Example 2 is also quite slow at 80 C., however it is still slow at high curing temperature (gel time of 30 min at 140 C.).

[0121] The T.sub.g of the inventive system is slightly higher. That is positive, as there is more distance to the application critical temperature of 155 C.

[0122] The most positive and surprising finding is that the dielectric dissipation factor tan at 155 C. is even lower and hence better than that of the anhydride-based reference containing a tertiary amine or boron trichloride-octyldimethylamine adduct as curing accelerator.

[0123] A dielectric dissipation factor tan of >10% at 155 C. is the main issue of the anhydride free reference example (XD 4410) of Comparative Example 2 and the reason why such systems could not be used for class H application, although it would be even better temperature stable according to the weight loss short term experiment given in the table. In this respect the inventive example is at least as stable as the unmodified reference.

[0124] So as a conclusion the new inventive insulation system surprisingly eliminates all issues of traditional insulation system for vacuum pressure impregnation, the anhydride/SVHC/REACH issue as well the issues of already known anhydride-free systems such as high viscosity, low reactivity at high temperature, limitation to class F and a too high dielectric dissipation factor tan of more than 10%.

b) Conclusions Based on the Comparisons of Impregnated Mica Paper and Mica Tapes

[0125] In comparison to state of the art insulation systems the tan values of the inventive system can reach significantly lower values. This can be the basis for a higher workload. Because less energy is lost and converted to heat, the thermal stress on the material shall be lower. Because the viscosity of all inventive resins is low, the impregnability is good also at room temperature.

[0126] Also the compatibility with polyester-polyols could be proven which can be used for mechanical enhancement of the impregnated mica paper and glass/mica combination. The presence of polyester-polyol led to identical tan values.