ELECTRET PRODUCTION PROCESS Russian patent published in 1996 - IPC

FIELD: filters, such as those used for cleaning oil-containing waste water, air cleaning; manufacture of electret condenser microphones and telephones. SUBSTANCE: polyethylene base electret production process involves its evaporation on its substrate in layer-by-layer manner: polyethylene, sodium nitrite or potassium sodium tartrate, or potassium dihydrophosphate, or ammonium hydrosulfate, then polyethylene layer of 300-500 mcm in thickness, thickness of sodium nitrite or potassium sodium tartrate, or potassium dihydrophosphate, or ammonium hydrosulfate being 10-50 mcm; each time upon polyethylene layer evaporation, heat treatment is carried out at 180-200 C for 30-40 min, this procedure being followed by cooling down in corona discharge field at 25-45 kV for 60-90 s. EFFECT: improved charge value and its time stability.