To make it possible to retain an electric charge on polyethylene itself by charging at a room temperature, by a method wherein an electret is formed by the material containing an ethylene random copolymer formed by ethylene having specific density and meltflow rate and α olefin having specific carbon number.
An ethylene based random copolymer is a random copolymer of ethylene and α-olefin of 3 to 20 C. Its density is 0.890 to 0.940 g/cm3, and its meltflow rate(MFR) under the load of 2.16 kg at 190°C is 0.1 to 100 g/10 min. in an ASTMD 1238 method. The quantity of α-olefin in the random copolymer should be 0.1 to 30 mol%. An electret is formed by molding and processing the material containing 1 wt.% or more of the above-mentioned ethylene random copolymer, the electret is brought into the state of an electret by charging, and the electret is manufactured by post processing according to circumferences.
TANAKA MUTSUHIRO
AKUNE TAKASHI
