| 摘要 |
<p>1,046,142. Polyethylene terephthalate electret. PHILIP MORRIS Inc. Jan. 20, 1965 [Jan. 21, 1964], No. 2570/65. Heading H1M. An electret is formed from a polyethylene terephthalate body by heating the body to 90-170‹ C. for at least a minute, subjecting the body at this temperature to an electric field of 0À5-300 kilovolts per centimetre for 0.15 sees. to 1000 hours, cooling the body in the electric field and removing it from the field. The body may be in the form of a film or disc or it may be doughnut, dumb-bell or pyramid shaped. It may contain minor amounts of other materials, e.g. it may be coated with silicone resin or P.T.F.E., or may contain semi-conductors or ferro electrics such as barium or calcium titanate. Several disc-shaped bodies may be formed into electrets in a single operation, the individual discs being orientated with flat surfaces parallel and separated by aluminium foil. The formed electret may be stored wrapped in aluminium foil. The electrets of the invention can be employed in electrostatic filters, dosimeters, microphones, electrometers and vibration meters.</p> |
