Compositions for use in impregnation of paper bushings

Abstract

The disclosure relates to a curable mixture for use in impregnation of paper bushings comprising a resin mixture of a bisphenol-A-diglycidylether (BADGE) and a bisphenol-F-diglycidylether (BFDGE), methyltetrahydrophthalic anhydride (MTHPA) as hardener, and an accelerator selected from the group consisting of tertiary alkylamine aminoethylalcohols and corresponding ethers thereof as well as paper bushings impregnated with such mixture and uses of such mixture.

Claims

1. A curable mixture comprising (i) a resin mixture comprising a bisphenol-A-diglycidylether (BADGE) and a bisphenol-F-diglycidylether (BFDGE), (ii) methyltetrahydrophthalic anhydride (MTHPA), and (iii) an accelerator selected from N,N,N′-trimethyl-N′-hydroxyethyl-bisaminoethyl ether, N-(3-dimethylaminopropyl)-N, N-diisopropanolamine, N,N-bis(3-dimethylaminopropyl)-N-isopropanolamine, and a mixture thereof wherein the curable mixture contains less than 0.2 pbw of the accelerator based on 100 pbw of the resin mixture.

2. The curable mixture according to claim 1, wherein the epoxy index according to ISO 3001 of the BADGE is in the range between 3 and 5 eq/kg.

3. The curable mixture according to claim 2, wherein the epoxy index according to ISO 3001 of the BADGE is in a range between 3.5 and 4.5 eq/kg.

4. The curable mixture according to claim 1, wherein the epoxy index according to ISO 3001 of the BFDGE is in a range between 5 and 6.45 eq/kg.

5. The curable mixture according to claim 4, wherein the epoxy index according to ISO 3001 of the BFDGE is in a range between 5.3 and 6.3 eq/kg.

6. The curable mixture according to claim 1, wherein the BADGE and the BFDGE are present in the resin mixture at a weight ratio between 1:10 and 10:1.

7. The curable mixture according to claim 1, wherein the curable mixture contains MTHPA in an amount corresponding to 80 wt. % to 120 wt. % of the stoichiometric amount based on the resin mixture.

8. The curable mixture according to claim 7, wherein the curable mixture contains MTHPA in amount corresponding to the stoichiometric amount based on the resin mixture.

9. The curable mixture according to claim 1, wherein the curable mixture contains the accelerator in an amount ranging from 0.01 to 0.10 pbw based on 100 pbw of the resin mixture.

10. A paper bushing impregnated with a curable mixture according to claim 1.

11. The paper bushing according to claim 10, wherein the paper bushing is a bushing for high-voltage application.

12. A curable mixture comprising (i) a resin mixture comprising a bisphenol-A-diglycidylether (BADGE) and a bisphenol-F-diglycidylether (BFDGE), (ii) methyltetrahydrophthalic anhydride (MTHPA), and (iii) N,N,N′-trimethyl-N′-hydroxyethyl-bisaminoethyl ether wherein the curable mixture contains less than 0.2 pbw of N,N,N′-trimethyl-N′-hydroxyethyl-bisaminoethyl ether based on 100 pbw of the resin mixture.

13. A paper bushing impregnated with a curable mixture according to claim 12.

14. The paper bushing according to claim 13, wherein the paper bushing is a bushing for high-voltage application.

Description

EXAMPLES

Comparative Example 1 (BADGE/MHHPA/BDMA)

(1) 200 g of Araldite® MY 740 resin were put in a metal reactor. Then 180 g of Aradur® HY 1102 hardener and 0.1 g Accelerator DY 062 accelerator were added. The components were then mixed with an anchor stirrer at ambient temperature for about 15 min. Finally, the reactor was subjected to a vacuum to remove all or substantially all bubbles from the mixture.

(2) This mixture was then analyzed to determine its viscosity and gel time.

(3) A portion of the mixture was then cast into molds (preheated to 80° C.) to prepare test specimens for the mechanical and electrical tests.

(4) The molds were treated according to a curing program as indicated in the table below.

(5) After cooling to ambient temperature, Tg, mechanical and electrical properties were determined according to standard procedures as specified hereunder.

Comparative Example 2 (XB 5860/Aradur® HY 1235 Hardener)

(6) 200 g of XB 5860 were put in a metal reactor. Then 170 g of Aradur® HY 1235 hardener were added. The components were then mixed with an anchor stirrer at ambient temperature for about 15 min. Finally, the reactor was subjected to a vacuum to remove all or substantially all bubbles from the mixture.

(7) This mixture was then analyzed to determine viscosity and gel time.

(8) A portion of the mixture was then cast into molds (preheated to 80° C.) to prepare test specimens for the mechanical and electrical tests.

(9) The molds were treated according to a curing program as indicated in the table below.

(10) After cooling to ambient temperature, Tg, mechanical and electrical properties were determined according to the same standard procedures as in Comparative Example 1.

Comparative Example 3 (Araldite® MY 740 Resin/Aradur® HY 918-1 Hardener/0.05 pbw BDMA)

(11) 200 g of Araldite® MY 740 resin were put in a metal reactor. Then 170 g of Aradur® HY 918-1 hardener and 0.1 g Accelerator DY 062 accelerator were added. The components were then mixed with an anchor stirrer at ambient temperature for about 15 min. Finally, the reactor was subjected to a vacuum to remove all or substantially all bubbles from the mixture.

(12) This mixture was then used to determine viscosity and gel time.

(13) A portion of the mixture was then cast into molds (preheated to 80° C.) to prepare test specimens for the mechanical and electrical tests.

(14) The molds were treated according to a curing program as indicated in the table below.

(15) After cooling to ambient temperature, Tg, mechanical and electrical properties were determined according to the same standard procedures as in Comparative Example 1.

Comparative Example 4 (Araldite® MY 740 Resin/Aradur® HY 918-1 Hardener/0.2 pbw BDMA)

(16) 200 g of Araldite® MY 740 resin were put in a metal reactor. Then 170 g of Aradur® HY 918-1 hardener and 0.4 g Accelerator DY 062 accelerator were added. The components were then mixed with an anchor stirrer at ambient temperature for about 15 min. Finally, the reactor was subjected to a vacuum to remove all or substantially all bubbles from the mixture.

(17) This mixture was then used to determine viscosity and gel time.

(18) A portion of the mixture was then cast into molds (preheated to 80° C.) to prepare test specimens for the mechanical and electrical tests.

(19) The molds were treated according to a curing program as indicated in the table below.

(20) After cooling to ambient temperature, Tg, mechanical and electrical properties were determined according to the same standard procedures as in Comparative Example 1.

Example 1

(21) 160 g of Araldite® GY 280 resin and 40 g of Araldite® GY 281 resin were put in a metal reactor. Then, 180 g of Aradur® HY 918-1 hardener and 0.14 g JEFFCAT® ZF 10 accelerator were added. The components were then mixed with an anchor stirrer at ambient temperature for about 15 min. Finally, the reactor was subjected to a vacuum to remove all or substantially all bubbles.

(22) This mixture was then used to determine viscosity and gel time.

(23) A portion of the mixture was then cast into molds (preheated to 80° C.) to prepare test specimens for the mechanical and electrical tests.

(24) The molds were treated according to a curing program as indicated in the table below.

(25) After cooling to ambient temperature, Tg, mechanical and electrical properties were determined according to the same standard procedures as in Comparative Example 1.

(26) The formulations as well as the results of the various measurements are shown in the table below.

(27) TABLE-US-00001 Comparison 1 Comparison 2 Comparison 3 Comparison 4 Inventive 1 MY 740 100 100 100 HY 1102 90 DY 062 0.05 0.05 0.2 XB 5860 100 HY 1235 85 GY 281 80 GY 280 20 HY 918-1 85 85 90 Jeffcat ZF 10 0.07 Critical Requirement Viscosity at 25° C./mPas <800 745 600 700 700 680 Viscosity at 40° C./mPas <250 255 160 126 Geltime  80° C. >10 h 20 h 58 min 17 h 27 h 18 min 7 h 20 min 13 h 51 min 120° C. >50 min 1 h 23 min 2 h 28 min 55 min Cure: 12 h 80° C. + 6 h/100° C + 12 h 80° C. + 12 h 80° C. + 12 h 80° C. + 16 h 130° C. 12 h/140° C 16 h 130° C. 24 h 120° C. 16 h 130° C. tensile strength/Mpa better than 67 45 90 96 comp. 1 elongation at break/% 2.7 1.4 5.3 4.9 Bend Notch KIC better than 0.59 0.75 0.64 comp. 1 GIC 114 95 117 Tg/° C. 120-135 123/126 125-135 104 120-130 121/123 tan delta    <0.3% 0.34% 0.40% 0.29% (50 Hz, 25° C.) Dielect const 3.3 3.3 3.3 (50 Hz, 25° C.) Contains MHHPA no yes yes no no no Contains HHPA no no yes no no no Toxic components no yes no yes yes no

(28) Tensile strength and elongation at break were determined at 23° C. according to ISO R527.

(29) Flexural strength were determined at 23° C. according to ISO 178.

(30) K.sub.IC (critical stress intensity factor) in MPa.Math.√{square root over (m)} and G.sub.IC (specific break energy) in J/m2 were determined at 23° C. by bend notch experiment.

(31) Tg was determined according to ISO 6721/94.

(32) Tan delta was measured according to IEC 60250.

(33) Comparative Example 1 shows the most widely used system in industry: BADGE/MHHPA/BDMA. The main problems of Comparative Example 1 are the REACH issues about MHHPA and the fact that the accelerator BDMA is regarded to be toxic. Further, there is a desire to reduce the tan delta as required by new standards and further reduce the viscosity for more easy impregnation.

(34) Comparative Example 2 is a system that avoids the toxicity issues of BDMA, but also contains MHHPA. Therefore, it is no solution to the main issue. Further it has an even higher tan delta compared to Comparative Example 1.

(35) The most simple idea to the person skilled in the art of formulation RIP systems might be just to exchange BADGE/MHHPA/BDMA with MTHPA instead of MHHPA. Comparative Example 3, however, shows that this would not work because the Tg would be by far too low.

(36) By increasing the amount of BDMA, the Tg may be increased to the desired level, however, then the reactivity is increased too much and such systems would be by far too reactive to be useful for the targeted applications, such as for example, impregnation systems for resin impregnated paper bushings (the reaction enthalpy would be released too quickly to let it disappear and thus the material temperature would rise too high which leads to overheating and cracks).

(37) Example 1 of the present disclosure shows a way that works in all respects. Combining selected types of BADGE and BFDGE to form a resin mixture and curing the resin mixture with MTHPA, accelerated by a small amounts (<0.2%) of tertiary alkylamine aminoethylalcohols or ethers thereof, such as the preferred catalyst JEFFCAT® ZF 10 accelerator, instead of BDMA, results in a cost efficient system that is low viscous, sufficiently low reactive (to prevent overheating in the final application), resulting in a Tg>120° C., providing the desired low tan delta of <0.3%, and free of materials currently labeled as toxic substances by, such as MHHPA and free bisphenol A. Being free of such toxic materials should render the presently disclosed composition as REACH compliant. Additional, the presently disclosed composition delivers a better mechanical profile than the presently most widely used system of Comparative Example 1.

(38) The above-disclosed subject matter is to be considered illustrative, and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments, which fall within the true scope of the present disclosure. Thus, to the maximum extent allowed by law, the scope of the present disclosure is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description.