Patent ID: 8709139

Claim:
A ply for use in a HEPA filter element, comprising: a first carrier layer, said first carrier layer comprising first polypropylene fibers having a core/mantle structure, said mantle comprising metallocene catalyzed polypropylene, said core comprising pure polypropylene wherein melting of said mantle fibers occurs without the core structure being impaired, said first polypropylene fibers being electrostatically charged for stabilization; and a second precipitation layer, said second precipitation layer comprising second polypropylene fibers, where said second polypropylene fibers are at least in part electrostatically charged and wherein said precipitation layer includes nanofibers selected from polyamide, polyacrylonitrile, polycarbonate or polypropylene; wherein: said first carrier layer and said second precipitation layer are configured as nonwoven fabrics such that at least certain regions are free of glass fibers; and said first carrier layer and said second precipitation layer are bonded such that at least a portion of said first polypropylene fibers and said second polypropylene fibers are at least partially melted and bond together to form a composite that passes through said first carrier layer and said second precipitation layer and said filter element includes regions capable of bending or pleating.