ELECTRET FILTER AND PRODUCTION OF PLEATED ELECTRET FILTER

PROBLEM TO BE SOLVED: To obtain an electret filter which is free from entanglement by pleating and allows the efficient execution of pleating by combining thin layers made of materials which are not electreted to one or both surfaces of an electret filter material by Coulomb force. SOLUTION: The electret filter medium 1 made of stock subjected to an electreting treatment, such as non-woven fabric formed by using fibers subjected to the electreting treatment, is used. The thin layers consisting of the materials which are not electreted, such as non-woven fabrics formed by using the non- electreted fibers, i.e., the non-electreted thin layers 2, are combined by the Coulomb force on one or both surfaces of the electret filter medium 1. The electret filter obtd. in such a manner does not entangle with feed teeth, etc., and does not require the interruption of work at the time of pleating with a pleating machine, thereby contributing to an increase in a working speed. The filter is not fixed as the Coulomb force is utilized and, therefore, the pleating is smoothly executed.