Epoxy resin composition

1. A method for insulating electrical or electronic components comprising the steps

(i) applying a heat curable composition that is stable at room temperature to one or more electrical or electronic components; and

(ii) curing the curable composition at a temperature greater than 60° C., wherein the curable composition comprises:

(a) 10-40% by weight, based on the total amount of components (a)+(b)+(c)+(d), of a cationically polymerisable cycloaliphatic epoxy resin,

(b) an initiator for the cationic polymerisation,

(c) a microparticle filler with an average particle size of 5-25 μm comprising at least one of an angular amorphous silica, an angular aluminium oxide or an angular semi-metal nitride, carbide or hydroxide, and

(d) a silica nanoparticle,

to provide a material having a glass transition temperature greater than 180° C., wherein component (b) is a mixture comprising:

(b1) a quaternary ammonium salt with an aromatic heterocyclic cation having one or two nitrogen atoms and a non-nucleophilic anion selected from BF 4 − , PF 6 − , SbF 6 − , SbF 5 OH − , BX p Y q − or CF 3 (CF 2 ) m SO 3 − , wherein

p and q are 0, 1, 2, 3 or 4, provided that p+q=4,

X denotes halogen or hydroxyl,

Y represents phenyl or naphthyl which are unsubstituted or substituted by fluoro, trifluoromethyl, trifluoromethoxy, nitro or cyano, and

m is 0 or an integer from 1 to 17; and

(b2) a 1,2-ethanediol substituted by four aromatic radicals.

2. The method according to claim 1 , wherein the component (b2) is a compound of formula (5)

wherein R 8 , R 9 , R 10 and R 11 independently of the other are phenyl that is unsubstituted or substituted by C 1 -C 12 alkyl, C 1 -C 12 alkoxy, C 7 -C 36 aralkyl, C 6 -C 36 aryl, C 3 -C 15 alkoxyalkyl, C 1 -C 12 alkylthio, C 1 -C 12 alkylcarbonyl, halogen, nitro or cyano, and R 12 and R 13 independently of the other are hydrogen or C 1 -C 12 alkyl.

3. The method according to claim 1 , wherein the total amount of microparticle filler (c) and nanoparticle filler (d) of the curable composition is 60 to 90% by weight, based on the total amount of components (a), (b), (c), and (d).

4. The method according to claim 1 , wherein the amount of nanoparticle filler (d) in the curable composition is 2 to 20% by weight, based on the total amount of components (a), (b), (c), and (d).

5. The method according to claim 1 , wherein the one or more electrical or electronic components are selected from printed circuit boards, stators, rotators, bushings, transformers, and/or switchgears.

6. An insulated electrical and electronic component obtained by the method according to claim 1 .

7. A method for insulating electrical or electronic components comprising the steps

(i) applying a heat curable composition that is stable at room temperature to one or more electrical or electronic components; and

(ii) curing the curable composition at a temperature greater than 60° C. to provide a material having a glass transition temperature greater than 180° C., wherein the curable composition comprises:

(a) 10-40% by weight, based on the total weight of components (a)+(b)+(c)+(d)+(e), of a cationically polymerisable cycloaliphatic epoxy resin,

(b) a curing accelerator selected from tertiary amines, urea derivatives, unsubstituted or substituted imidazoles, and one or more complexes of amines with boron trichloride or boron trifluoride,

(c) a microparticle filler with an average particle size of 5-25 μm comprising at least one of an angular amorphous silica, an angular aluminium oxide or an angular semi-metal nitride, carbide or hydroxide, and

(d) a silica nanoparticle filler and

(e) an initiator for the cationic polymerization comprising:

(b1) a quaternary ammonium salt with an aromatic heterocyclic cation having one or two nitrogen atoms and a non-nucleophilic anion selected from BF 4 − , PF 6 − , SbF 6 − , SbF 5 OH − , BX p Y q − or CF 3 (CF 2 ) m SO 3 − , wherein

p and q are 0, 1, 2, 3 or 4, provided that p+q=4,

X denotes halogen or hydroxyl,

Y represents phenyl or naphthyl which are unsubstituted or substituted by fluoro, trifluoromethyl, trifluoromethoxy, nitro or cyano, and

m is 0 or an integer from 1 to 17; and

(b2) a 1,2-ethanediol substituted by four aromatic radicals.

8. An insulated electrical and electronic component obtained by the method according to claim 7 .