Improved Resin-rich Mica Tape

Abstract

Resin-rich mica tapes comprising one or more than one layer of mica paper and one or more than one layer of a nonmetallic inorganic fabric, in particular a glass fabric, which are pre-impregnated with an impregnation resin composition comprising an epoxy resin with more than one epoxy group, which is solid or semisolid at ambient temperature, a latent curing agent for said epoxy resin, about 5 to about 20% by weight of hexagonal boron nitride of a particle size (D50) of equal or less than about 3 μm, about 0.05 to about 1% by weight of a wetting agent and a suitable solvent which is removed after pre-impregnation of the mica tape with the impregnation resin mixture are useful to prepare electrical insulations with excellent thermal conductivity and dielectric dissipation factor.

Claims

1.-14. (canceled)

15. A resin-rich mica tape comprising at least one layer of mica paper and at least one layer of a nonmetallic inorganic fabric, wherein the mica paper and nonmetallic inorganic fabric each contain an impregnation resin composition comprising (i) an epoxy resin having more than one epoxy group, (ii) a latent curing agent for said epoxy resin, (iii) hexagonal boron nitride of a particle size (D50) of equal or less than about 3 μm, and (iv) a wetting agent.

16. The resin-rich mica tape according to claim 15, wherein said impregnation resin composition comprises: about 59 to about 89.95% by weight of the epoxy resin; about 5 to about 20% by weight of the hexagonal boron nitride; about 0.05 to about 1% by weight of the wetting agent; and about 5 to about 20% by weight of a solvent, wherein the solvent is removed after being impregnated into the mica paper and nonmetallic inorganic fabric.

17. The resin-rich mica tape according to claim 16, wherein the wetting agent is present in an amount from about 0.075 to about 0.75% by weight based on the impregnation resin composition.

18. The resin-rich mica tape according to claim 15, wherein the wetting agent is selected from (i) alkyl or alkenyl (ether) phosphates and (ii) reaction products of phosphoric acid or polyphosphoric acids with polyethyleneglycol mono(C.sub.1-C.sub.4alkyl)ether and cyclic lactones.

19. The resin-rich mica tape according to claim 15, wherein the wetting agent is selected from compounds having the following formula ##STR00008## wherein R1 is a linear or branched alkyl or alkenyl group containing 4 to 22 carbon atoms; R2 and R3 are independently selected from hydrogen or a linear or branched alkyl or alkenyl group containing 4 to 22 carbon atoms; and m, n and p are each 0 or a number in a range of from 1 to 10.

20. The resin-rich mica tape according to claim 15, wherein the wetting agent is selected from reaction products of phosphoric acid or a polyphosphoric acid with block copolymers of the following formula:
RO(C.sub.2H.sub.4O).sub.m(PES).sub.n—H wherein R is a linear or branched C.sub.1-.sub.4alkyl, PES is a polyester derived from a cyclic lactone; m is from about 5 to about 60; n is from about 2 to about 30.

21. The resin-rich mica tape according to claim 15, wherein the epoxy resin is a solid or semisolid epoxy novolac.

22. The resin-rich mica tape according to claim 15, wherein the latent curing agent is a complex of boron trifluoride with an amine selected from aliphatic, araliphatic, cycloaliphatic and heterocyclic amines having 2 to 10 carbon atoms and one or two primary, secondary, or tertiary amino groups.

23. The resin-rich mica tape according to claim 22, wherein the amine of the boron trifluoride complex is selected from ethylamine, diethylamine, trimethylamine, isopropylamine, di-secondary butylamine, benzylamine, isophoronediamine, and piperidine.

24. The resin-rich mica tape according to claim 15, wherein the latent curing agent is present in an amount of 0.05 to 5% by weight based on the epoxy resin.

25. The resin-rich mica tape according claim 16, wherein the solvent is an aprotic solvent having a boiling point below about 100° C.

26. The resin-rich mica tape according to claim 25, wherein the solvent comprises ethyl acetate or methylethylketone.

27. A process for the manufacture of a resin-rich mica tape, comprising: a) placing at least one layer of mica paper on top of a layer of nonmetallic inorganic fabric to form a pre-laminate, b) impregnating the pre-laminate with an impregnation resin composition comprising (i) an epoxy resin having more than one epoxy group, (ii) a latent curing agent for said epoxy resin, (iii) hexagonal boron nitride of a particle size (D50) of equal or less than about 3 μm, (iv) a wetting agent, and (v) a solvent, c) removing the solvent, and, optionally cooling the impregnated pre-laminate.

28. A process for the manufacture of a resin-rich mica tape, comprising: a) individually impregnating a mica paper and a nonmetallic inorganic fabric with an impregnation resin composition comprising (i) an epoxy resin having more than one epoxy group, (ii) a latent curing agent for said epoxy resin, (iii) hexagonal boron nitride of a particle size (D50) of equal or less than about 3 μm, (iv) a wetting agent, and (v) a solvent; b) removing the solvent and, optionally, cooling the impregnated mica paper and nonmetallic inorganic fabric; c) placing at least one layer of the impregnated mica paper on top of a layer of the impregnated inorganic fabric to form a pre-laminate, and d) impregnating the pre-laminate with an additional amount of the impregnation resin composition and thereafter removing the solvent and, optionally, cooling the impregnated pre-laminate.

Description

Example 1

Reference Without Boron Nitride

[0119] An impregnation resin mixture is prepared based on 50.0 g Araldite® EPN 1138 N80 which is mixed with 1.38 g Aradur®HZ 5933 in 5.0 g methylethylketone.

[0120] 100×100 mm of calcined mica paper of a grammage of 120 g/m.sup.2 are impregnated with 0.7 g of the impregnation resin mixture. The solvent is removed by heating the mica paper sample in an oven for 1 min at 120° C. A layer of glass fabric style 771 (grammage: 32 g/m.sup.2) is then applied to the impregnated mica paper and an additional 0.7 g of the impregnation resin mixture is applied and the sample dried at 120° C. for 2 min.

[0121] Specimens of hand samples are prepared by curing in a heated press at 160° C. for 4 h.

[0122] For comparative experiments of production samples the commercial standard resin-rich mica tape Calmicaglas® 0409 (supplier: Isovolta) is used.

[0123] Test bars are wrapped on an iron core. The tape width is 25 mm, taping tension is 70 N. 16 half-lapped layers are taped. The test bars are cured in a heated press to a insulation thickness of 2.0 mm. Pressure is applied after a 7 min preheating phase. Curing is conducted at 160° C. for 1 h.

Example 2

Reference With BN (Type 1) But Without Wetting Agent

[0124] The samples are prepared as follows:

[0125] A resin mixture is prepared based on 5.0 g LME 11007 (a mixture of 500 g Araldite® EPN 1138 N80 with 100 g BN(type1) which is further mixed with 1.25 g Aradur® HZ 5933 and 5.0 g methylethylketone.

[0126] 100×100 mm of calcined mica paper of a grammage of 120 g/m.sup.2 are impregnated with 0.7 g of the impregnation resin mixture. The solvent is removed by heating the mica paper sample in an oven for 1 min at 120° C. A layer of glass fabric style 771 (grammage: 32 g/m.sup.2) is then applied to the impregnated mica paper and an additional 0.7 g of the impregnation resin mixture is applied and the sample dried at 120° C. for 2 min.

[0127] Specimens of hand samples are prepared by curing in a heated press at 160° C. for 4 h.

[0128] The mica paper specimens showed optical defects in form of bubbles on the surface. The glass/mica laminates exhibited voids also between the layers.

Example 3

According to the Invention With BN (Type 1) and Wetting Agent

[0129] The samples are prepared as follows:

[0130] A resin mixture was prepared based on 50.0 g LME 11033 (a mixture of 500 g Araldite® EPN 1138 N80 with 100 g BN(type1) and 1.0 g Byk® W996 wetting agent) which is further mixed with 1.25 g Aradur® HZ 5933 and 5.0 g methylethylketone.

[0131] 100×100 mm of calcined mica paper of a grammage of 120 g/m.sup.2 are impregnated with 0.7 g of the impregnation resin mixture. The solvent is removed by heating the mica paper sample in an oven for 1 min at 120° C. A layer of glass fabric style 771 (grammage: 32 g/m.sup.2) is then applied to the impregnated mica paper and an additional 0.7 g of the impregnation resin mixture is applied and the sample dried at 120° C. for 2 min.

[0132] Specimens of hand samples are prepared by curing in a heated press at 160° C. for 4 h. The aspect is good.

[0133] To test the processability and properties under standard production conditions, a sample production is conducted on production machines. The resin content is adjusted to 100 g/m.sup.2. In production process the mica paper and glass fabric are impregnated simultaneously in one step and the solvent is removed to yield the mica tape.

[0134] Test bars are wrapped on an iron core. The tape width is 25 mm; taping tension is 70 N. 16 half-lapped layers are taped. The test bars are cured in a heated press to an insulation thickness of 2.0 mm. Pressure is applied after a 7 min preheating phase. Curing is conducted at 160° C. for 1 h. The aspect is good.

Comparison of the Properties of the Samples Obtained in Comparative Examples 1 and 2 Versus the Samples of Example 3 According to the Invention

[0135] The dielectric dissipation factor (tan(δ)) of the cured hand samples at room temperature (RT) and at 155° C. are determined according to IEC 60250 in Tettex instrument using a guard ring electrode at 400 V/50 Hz. Furthermore, the thermal conductivity at 90° C. of the hand samples is measured using an Anter Unitec device and the voids in the pressed material are detected with optical microscope.

[0136] The thickness of the production samples is determined according to IEC 60371-2, the voltage endurance of these samples according to IEEE 1053 and the breakdown voltage according to IEC 60243-1.

[0137] The results are shown in the following table:

TABLE-US-00001 Example 1 Example 2 Example 3 (comparative) (comparative) (invention) Hand tan(δ) at ≈1.6 1.1 1.0 samples RT [%] tan(δ) at 5 31.7 5 155° C. [%] Thermal 0.24 0.35 0.4 conductivity at 90° C. [Wm.sup.−1K.sup.−1] Voids in no yes no pressed material Production Thickness 0.18 — 0.18 samples [mm] Voltage 28.96 — 90 endurance [h] (15 kV/mm) Breakdown 62.4 — 54.9 voltage [kV]

[0138] It can be seen that the thermal conductivity of the samples unsurprisingly increases with the addition of the boron nitride. The dielectric dissipation factor of the samples, on the other hand, while comparable at room temperature, significantly increases at 155° C., when only the hexagonal boron nitride powder is added to the impregnation resin mixture of Example 1, so that this impregnation resin composition would be inoperative in technical practice. Surprisingly however this increase of the dielectric dissipation factor disappears again, when a wetting agent is added in addition to the boron nitride powder according to the present invention as shown be Example 3.

[0139] Surprisingly, the voltage endurance of the insulating material according to the invention is significantly increased in comparison to the conventional material without boron nitride.

Example 4

According to the Invention With BN (Type 2) and Wetting Agent

[0140] The samples are prepared as follows:

[0141] A resin mixture is prepared by mixing 500 g of Araldite® EPN 1138 N80 with 100 g BN(type2) and 1.0 g Byk® W996 wetting agent with a high shear mixer at ambient temperature for 55 min.

[0142] 50 g of this mixture is further mixed with 1.25 g Aradur® HZ 5933 and 5.0 g methylethylketone.

[0143] 100×100 mm of calcined mica paper of a grammage of 120 g/m.sup.2 are impregnated with 0.7 g of the impregnation resin mixture. The solvent is removed by heating the mica paper sample in an oven for 1 min at 120° C. A layer of glass fabric style 771 (grammage: 32 g/m.sup.2) is then applied to the impregnated mica paper and an additional 0.7 g of the impregnation resin mixture is applied and the sample dried at 120° C. for 2 min.

[0144] Specimens of hand samples are prepared by curing in a heated press at 160° C. for 4 h.

[0145] The aspect is of the pressed sample is good with no voids. The thermal conductivity at 90° C. of the hand sample is 0.39 Wm.sup.−1 K.sup.−1, measured using an Anter Unitec device.

Example 5

According to the Invention With BN (Type 5) and Wetting Agent

[0146] The samples are prepared as follows:

[0147] A resin mixture is prepared by mixing 500 g of Araldite® EPN 1138 N80 with 100 g BN (type5) and 1.0 g Byk® W996 wetting agent with a high shear mixer at ambient temperature for 5 minutes.

[0148] 50 g of this mixture is further mixed with 1.25 g Aradur® HZ 5933 and 5.0 g methylethylketone.

[0149] 100×100 mm of calcined mica paper of a grammage of 120 g/m.sup.2 are impregnated with 0.7 g of the impregnation resin mixture. The solvent is removed by heating the mica paper sample in an oven for 1 min at 120° C. A layer of glass fabric style 771 (grammage: 32 g/m.sup.2) is then applied to the impregnated mica paper and an additional 0.7 g of the impregnation resin mixture is applied and the sample dried at 120° C. for 2 min.

[0150] Specimens of hand samples are prepared by curing in a heated press at 160° C. for 4 h.

[0151] The aspect is of the pressed sample is good with no voids. The thermal conductivity at 90° C. of the hand sample is 0.38 Wm.sup.−1 K.sup.−1, measured using an Anter Unitec device.