| 摘要 |
PROBLEM TO BE SOLVED: To provide an electret exhibiting excellent filtration characteristics, by effectively exhibiting charging effect due to physical effect of ultrasonic vibration in electrification of a structure of thermoplastic resin and suppressing structural injuries in the process of electrification of the structure. SOLUTION: The electret is obtained by a method and an electrification device therefor, in which method, a structure comprising a thermoplastic resin is treated with ultrasonic waves through a polar liquid, wherein the distance between the ultrasonic generator and a restricting element set opposite to the generator is made <150 times of the thickness of the structure under 20 g/cm<SP>2</SP>compression weight. COPYRIGHT: (C)2005,JPO&NCIPI
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