Mehrschichtiger Filter und Verfahren zu dessen Herstellung

摘要

The invention refers to a composite filter for filtering a stream of ambient air comprising at least one non-prebonded upstream tier and one non-prebonded downstream tier, wherein the ratio of absolute pore volume of upstream tier to downstream tier RAPV > 2, and the absolute projected fiber coverage of upstream tier and of downstream tier APFC > 95%. Further, the invention refers to a method of making such a composite filter comprising the steps of (a) laying down a filtration material onto a support to form the upstream non-prebonded tier, (b) depositing onto the upstream tier the downstream non-prebonded tier, and (c) bonding the tiers to form a composite filter having a unitary stratified structure.