| 摘要 |
<p>An electret made of styrene-type polymer (e.g., polystyrene), having a volume resistivity of at least 1016 ohm-cm and a glass transition temperature above 50.degree.C, and containing not more than 1% by weight of electron-donor impurities and not more than 0.5% by weight of electron-acceptor impurities, said electret being capable of retaining at least 75% of its charge after exposure to a temperature of 50.degree.C and a relative humidity of 100% for 100 days.</p> |
