A Process for the Preparation of Insulation Systems for Electrical Engineering, the Articles Obtained Therefrom and the Use Thereof

Abstract

A process for the preparation of insulation systems for electrical engineering by automatic pressure gelation (APG) or vacuum casting, wherein a multiple component thermosetting resin composition is used, said resin composition comprising (A) at least one epoxy resin, (B) at least one carboxylic acid anhydride curing agent, and (C) 2,4,6-tris(dimethylaminomethyl)phenol,
provides encased articles exhibiting good mechanical, electrical and dielectrical properties, which can be used as, for example, insulators, bushings, switchgears and instrument transformers.

Claims

1. A process for the preparation of insulation systems for electrical engineering by automatic pressure gelation (APG) or vacuum casting, wherein a multiple component thermosetting resin composition is used, said resin composition comprising (A) at least one epoxy resin, (B) at least one carboxylic acid anhydride curing agent, and (C) 2,4,6-tris(dimethylaminomethyl)phenol.

2. The process according to claim 1, wherein the said at least one epoxy resin (A) is a diglycidylether of a bisphenol or a cycloaliphatic epoxy resin.

3. The process according to claim 2, wherein the said at least one epoxy resin (A) is a diglycidylether of bisphenol A.

4. The process according to any one of claims 1-3, wherein the said at least one carboxylic acid anhydride curing agent (B) is phthalic anhydride, tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, hexahydrophthalic anhydride or methylhexahydrophthalic anhydride.

5. The process according to any one of claims 1-4, wherein the multiple component thermosetting resin composition additionally contains (D) a filler.

6. The process according to claim 5, wherein the multiple component thermosetting resin composition contains silica flour as component (D).

7. The process according to any one of claims 1-6, wherein the thermosetting resin composition contains components (A) and (B) in amounts of 0.4-1.6 acid anhydride equivalents per epoxy equivalent.

8. The process according to any one of claims 1-7, wherein the thermosetting resin composition contains 0.05-3.0 parts by weight of 2,4,6-tris(dimethylaminomethyl)phenol based on 100 parts by weight of epoxy resin.

9. The process according to claim 1, wherein the multiple component thermosetting resin composition is prepared by mixing components (A), (B), (C) and optionally (D) and subsequently degassing the mixture by application of vacuum.

10. The process according to claim 9, wherein the mixture containing components (A), (B), (C) and optionally (D) is heated to 40-80? C. prior to the application of vacuum.

11. The use of a multiple component thermosetting resin composition comprising (A) at least one epoxy resin (B) at least one carboxylic acid anhydride curing agent, and (C) 2,4,6-tris(dimethylaminomethyl)phenol for the preparation of insulation systems for electrical engineering by automatic pressure gelation (APG) or vacuum casting.

12. An article obtained by the process according to any one of claims 1 to 10.

13. Use of the article according to claim 12 for medium and high voltage switchgear applications and as medium and high voltage instrument transformers.

Description

EXAMPLE 1

[0054] In a heatable steel vessel 100 g of ARALDITE? CY 228 is mixed with 85 g of ARADUR? HY 918 and 0.7 g TDMAMP. The mixture is heated to about 60? C. for about 5 min while slightly stirring with a propeller stirrer. Under stirring 345 g of silica W12 is added in portions and the mixture is heated up to 60? C. under stirring for about 10 minutes. Then the mixer is stopped and the vessel is carefully degassed under vacuum (about 1 min). The reactivity of this mixture is measured at various temperatures using a gel norm gel timer equipment.

[0055] The main part of the mixture is poured into a 140? C. hot steel mold (treated with mold release agent QZ13) to prepare plates of thickness 4 mm or 10 mm thick, respectively (for determination of mechanical properties respectively the thermal conductivity). The mold is then cured in an oven at 140? C. for 10 hours. Afterwards, the mold is taken out of the oven and opened and the 4 mm plates are taken out and let cool down to ambient temperature.

EXAMPLE 2

[0056] In a heatable steel vessel 100 g of ARALDITE? CY 228 is mixed with 85 g of ARADUR? HY 918-1 and 0.7 g TDMAMP. The mixture is heated to about 60? C. for about 5 minutes while stirring slightly with a propeller stirrer. Under stirring 345 g of silica W12 is added in portions and the mixture is heated up to 60? C. under stirring for about 10 minutes. Then the mixer is stopped and the vessel is degassed carefully under vacuum (about 1 minute). The reactivity of this mixture is measured at various temperatures using a gel norm gel timer equipment.

[0057] The main part of the mixture is poured into a 140? C. hot steel mold (treated with mold release agent QZ13) to prepare plates of thickness 4 mm or 10 mm thick, respectively (for determination of mechanical properties respectively the thermal conductivity). The mold is then put to an oven at 140? C. for 10 hours for curing. Afterwards, the mold is taken out of the oven and opened and the 4 mm plates are taken out and let cooled down to ambient temperature.

COMPARATIVE EXAMPLE 1

[0058] In a heatable steel vessel 100 g of ARALDITE? CY 228 is mixed with 85 g of ARADUR? HY 918 and 0.8 g DY 062. The mixture is heated to about 60? C. for about 5 min while slightly stirring with a propeller stirrer. Under stirring 345 g of silica W12 is added in portions and the mixture is heated up to 60? C. under stirring for about 10 minutes. Then the mixer is stopped and the vessel is carefully degassed under vacuum (about 1 min).

[0059] The reactivity of this mixture is measured at various temperatures using a gel norm gel timer equipment.

[0060] The main part of the mixture is poured into a 140? C. hot steel mold (treated with mold release agent QZ13) to prepare plates of thickness 4 mm or 10 mm thick, respectively (for determination of mechanical properties respectively the thermal conductivity). The mold is then cured in an oven at 140? C. for 10 hours. Afterwards, the mold is taken out of the oven and opened and the 4 mm plates are taken out and let cool down to ambient temperature.

COMPARATIVE EXAMPLE 2

[0061] In a heatable steel vessel 100 g of ARALDITE? CY 228 is mixed with 85 g of ARADUR? HY 918-1 and 0.8 g DY 062. The mixture is heated to about 60? C. for about 5 min while slightly stirring with a propeller stirrer. Under stirring 345 g of silica W12 is added in portions and the mixture is heated up to 60? C. under stirring for about 10 minutes. Then the mixer is stopped and the vessel is carefully degassed under vacuum (about 1 min). The reactivity of this mixture is measured at various temperatures using a gel norm gel timer equipment.

[0062] The main part of the mixture is poured into a 140? C. hot steel mold (treated with mold release agent QZ13) to prepare plates of thickness 4 mm or 10 mm thick, respectively (for determination of mechanical properties respectively the thermal conductivity). The mold is then cured in an oven at 140? C. for 10 hours. Afterwards, the mold is taken out of the oven and opened and the 4 mm plates are taken out and let cool down to ambient temperature.

COMPARATIVE EXAMPLE 3

[0063] In a heatable steel vessel 100 g of ARALDITE? CY 228 is mixed with 85 g of ARADUR? HY 918 and 1 g DY 070. The mixture is heated to about 60? C. for about 5 min while slightly stirring with a propeller stirrer. Under stirring 345 g of silica W12 is added in portions and the mixture is heated up to 60? C. under stirring for about 10 minutes. Then the mixer is stopped and the vessel is carefully degassed under vacuum (about 1 min). The reactivity of this mixture is measured at various temperatures using a gel norm gel timer equipment.

[0064] The main part of the mixture is poured into a 140? C. hot steel mold (treated with mold release agent QZ13) to prepare plates of thickness 4 mm or 10 mm thick, respectively (for determination of mechanical properties respectively the thermal conductivity). The mold is then cured in an oven at 140? C. for 10 hours. Afterwards, the mold is taken out of the oven and opened and the 4 mm plates are taken out and let cool down to ambient temperature.

TABLE-US-00002 TABLE 2 Formulations and Test Results Components Ex. 1 Ex. 2 Comp. Ex. 1 Comp. Ex. 2 Comp. Ex. 3 ARALDITE? CY 228 100 g 100 g 100 g 100 g 100 g ARADUR? HY 918 85 g 85 g 85 g ARADUR? HY 918-1 85 g 85 g DY 062 0.8 g 0.8 g DY 070 1.0 g TDMAMP 0.7 g 0.7 g W 12 345 g 345 g 345 g 345 g 345 g Gel time at 140? C. 4 min 30 s 4 min 30 s 4 min 20 s 4 min 30 s 3 min 20 s T.sub.g/? C. 117 111 115 117 120 Tensile strength/MPa 82 80 85 77 Elongation at break 1.00% 0.90% 0.85% 0.90% Flexural strength/MPa 119 116 120 122 100.6 K.sub.1C/MPa .Math. ?m 2.10 2.30 2.05 2.10 1.92 G.sub.1C/J/m.sup.2 343 377 350 343 316 CTE 33.2 34.9 33.1 37.2 TC/W/mK 1.02 1.05 0.95 0.99 SCT/? C. ?39 ?18 ?21 0 Vapor pressure/mbar 0.001 0.001 3.0 3.0 0.5 T.sub.g (glass transition temperature) was determined according to ISO 6721/94. Tensile strength and elongation at break were determined at 23? C. according to ISO R527. Flexural strength was determined at 23? C. according to ISO 178. K.sub.1C (critical stress intensity factor) and G.sub.1C (specific break energy) were determined at 23? C. by double torsion experiment (Huntsman-internal method). CTE (coefficient of thermal expansion) was determined according to DIN 53752. TC (thermal conductivity) was determined according to ISO 8894. SCT: Crack index (simulated crack temperature) was calculated based on T.sub.g, G.sub.1C, CTE and elongation at break according to the description given in WO 2010/112272.

EXAMPLE 4

[0065] An iron part is placed in a mould and encapsulated with a formulation according to Example 1 in the APG process and cured for 10 h at 140? C. The cured encapsulated part is subjected to a thermal cycle test.

COMPARATIVE EXAMPLE 4

[0066] An iron part of same geometry than the part used in Example 4 is placed in a mould and encapsulated with a formulation according to Comparative Example 1 in the APG process and cured for 10 h at 140? C. The cured encapsulated part is subjected to a thermal cycle test. The average crack temperature (based on a set of 20 samples each) is 14 K higher than that of the product of Example 4.

[0067] The combination widely used today in APG processes with slightly different hardeners is described in Comparative Examples 1 and 2. Such systems are toxicologically questionable in those cases where the customer is handling BDAM as a separate component and is adding the accelerator at the end of the mixing and degassing process into the well degassed mixture of anhydride and filler, what is advisable due to the relatively high vapor pressure of BDMA. The simulated crack temperature (calculated from T.sub.9, CTE, elongation at break and G.sub.1C) as a measure for the thermal cycle crack performance results in ?21 and 0? C. respectively.

[0068] Comparative Example 3 shows that the substitution of BDMA as accelerator with the less toxic 1-methylimidazole results in more brittle systems with a tendencially higher T.sub.9, lower toughness (lower G.sub.1C), lower strength and a lower elongation at break.

[0069] Inventive Examples 1 and 2 distinguish from Comparative Examples 1 and 2 only with respect to the curing accelerator. The inventive advantages are: [0070] TDMAMP is toxicologically unproblematic. [0071] Due to the lower vapor pressure it is possible to add the accelerators at an earlier step of the mixing and degassing process and thus there is no need of interrupting the process to add the accelerator at a later step. There is only a very low tendency to distill off the accelerator during the mixing and degassing step. [0072] Both inventive examples show the much better SCT values (?18 K better for both examples compared to the comparative examples). [0073] A further advantage of the inventive formulations is the slightly better thermal conductivity. [0074] The use of TDMAMP as catalyst is more effective: 0.7 pbw of TDMAMP results in the same reactivity as 0.8 pbw of BDMA. [0075] In comparison to 1-methylimidazole a longer pot-life (gel time) is achieved by application of TDMAMP. [0076] The APG process provides cured products showing lower average crack temperature.