A kind of varnish

with high temperature and humidity resistance

for resistor was obtained by condensation of epoxy resin

acid anhydride and glycol with proper nano-SiO

2

added at 80℃.The investigation was conducted in the electrical performance

structure

thermal stability

mechanical robustness

humidity resistance for varnish and failure analysis of resistor resisting humidity.Infrared spectra（IR）（analysis） shows more compact and steady inter-crosslinked network structure is formed in the modified undercoat polymer with nano-SiO

2

added

and molecule polarity of the polymer becomes smaller

which makes the appetencies between the polymer and water molecules weaker. Hence

such undercoat is of excellent performance desired.The SEM picture of impact tests reveals solidifying polymer with nano-SiO

2

presents itself gliding fracture

which concludes nano-SiO

2

can improve the toughness of epoxy resin.When the mass fraction of nano-SiO

2

is about 2.79×10

-2

the property of high temperature and humidity resistance for varnish is best

with varying ratio of resistance with such undercoat painted is less than one in a thousand.