| 摘要 |
<p>A filter which has a high accuracy, little pressure loss and a long lifetime as compared with a conventional filter. In a filter comprising aggregate of nonwoven fibers, at least two layers of aggregate of nonwoven fibers, i.e. a prefiltration layer and a microfiltration layer are provided, the diameter of the fibers constituting the prefiltration layer being set gradually smaller in the filtering direction, at least not less than 10 wt.% of the fibers constituting the microfiltration layer comprising fibers the diameter of which is smaller than a minimum diameter of the fibers of the prefiltration layer.</p> |
