MELT-BLOWN DEPTH FILTER, PROCESS AND MACHINE OF MAKING IT

A tubular depth filter element has three or more concentric zones. Each zone is made of an essentially continuous melt blown filament. The filament of an outer zone preferably has a larger diameter than the filaments of other zones. The outer zone overlaps with at least 85%, and preferably all, of another zone. Optionally, one or more additional filaments may traverse through all of zones. The depth filter element is made by spraying filaments onto a rotating mandrel to form a filament mass in contact with a conical press roller. The filaments are sprayed from three or more nozzles which are spaced apart along the length of the mandrel. One of the filaments is formed in a spray pattern that is angled towards an adjacent spray pattern so as to overlap with at least 50 or 85%, and preferably all, of the adjacent spray pattern.