Patent ID: 8153702

Claim:
A method of producing an electret material comprising the steps: a) providing a polymeric dielectric material, b) electrically charging said polymeric dielectric material, whilst maintaining relative humidity conditions around said material at a relative humidity within a user-defined range, wherein charging occurs by a method selected from (i) heating said polymeric dielectric material to a temperature above the melting temperature or glass transition temperature of said material, subjecting said material to an electric field and cooling said material in the presence of said electric field to a temperature below said melting temperature or glass transition temperature, (ii) corona charging, (iii) subjecting said material to an electron beam or ion beam, (iv) contact electrification, and (v) combinations of any of the foregoing, wherein said polymeric dielectric material is a hydrophobic polymer having a water uptake <0.1 wt. %, wherein said relative humidity conditions of step b) are maintained at <5%, or said polymeric dielectric material is a water-insoluble polymer having a water uptake in the range of from 0.1 wt. % to 3 wt. %, wherein said relative humidity conditions of step b) are maintained at a range of from 20% to 40%, or wherein said polymeric dielectric material is a water-soluble or hydrophilic or polyelectrolytic polymer having a water uptake >3wt. %, wherein said relative humidity conditions of step b) are maintained at <5%.