Abstract: An electret filter made of a resin whose angle of contact upon wetting with pure water is no smaller than 95 degrees, as well as an electret filter made of a resin whose angle of contact upon wetting with pure water has been adjusted to no smaller than 95 degrees by addition of silicone oil. Those electret filters have high trapping efficiency and their ability to trap particulates, especially cigarette smoke, will not deteriorate even if they are continuously used. Therefore, they can advantageously be used as filter media in many applications such as home and industrial air conditioners, air cleaners, fan heaters, vacuum cleaners, and air conditioning systems for common equipment.

Abstract: A film electret and an electret filter that contain a polar high-molecular weight compound and that provides a TSDC curve having a homocharge peak temperature of at least 95.degree. C. and a heterocharge peak temperature of at least 80.degree. C.

Abstract: A highly efficient, reliable method is provided for producing an electret filter having an excellent collection efficiency. In this method, a film containing a resin material with high molecular weight is formed and split to form split yarns. The split yarns are then subjected to a charging treatment, and the electret filter is produced from the charged split yarns.

Abstract: Provided herein is a process for preparing an electret filter which comprises feeding a non-woven fabric composed of an electrically charged web of synthetic fibers through a nip of co-operating embossing and flat rolls under pressure and at a temperature below a softening temperature of said synthetic fibers, thereby subjecting the surface of said non-woven fabric to partical fusion bonding and integration.