| 摘要 |
PROBLEM TO BE SOLVED: To provide an electret filter whose collection efficiency is hard to deteriorate.SOLUTION: An electret filter includes: a first fiber layer containing a first fiber which is easily charged by a fact that a mass of oil solution adhered to a fiber surface is equal to or less than 0.2 mass% as a main constitution fiber; and a second fiber layer containing a second fiber which is hard to be charged by a fact that the mass of oil solution adhered to the fiber surface is more than 0.2 mass % as a main constitution fiber. Since the first fiber layer is excellent in collection efficiency of dust since the first fiber layer includes excellent electret performance, and the second fiber layer can prevent deterioration of the collection efficiency of dust in the first fiber layer by holding the first fiber layer at an approximate insulated state. Thus, the collection efficiency of the electret filter is hard to deteriorate. |
