Electret fiber sheet and method of producing same

Abstract

An electret fiber sheet has polarized charges on its surface and preferably has charges in ordered orientation across it. The polarized charges are present in an amount of at least 7.times.10.sup.-11 C/cm.sup.2. Such sheets are formed to have a dust collecting efficiency. Sheets having an amount of polarized charge even as high as this are nevertheless stable when they have a maximum orientation energy of depolarization of at least 0.2 eV. Such an electret sheet can be obtained by a process comprising placing a fiber sheet between a non-contact type voltage-application electrode and an earth electrode confronting each other and supplying electricity (voltage>3 kV; current density>1.times.10.sup.-6 mA/cm.sup.2) between the electrodes, provided that the fiber sheet has a weight less than 80 g/m.sup.2 and a covering factor at least 60%. The electret fiber sheet is useful in a variety of applications, such as filter materials, especially for collection of micro dust; clothing and furniture apparel for industrial clean rooms; adsorbing materials; and medical materials such as masks and collectors of bacillus.

Dependencies are inferred from the claim text.