A thermally bonded filtration media that can be used in high temperature conditions in the absence of any loss of fiber through thermal effects or mechanical impact on the fiber components is disclosed. The filter media can be manufactured and used in a filter unit or structure, can be placed in a stream of removable fluid, and can remove a particulate load from the mobile stream at an increased temperature range. The combination of bi-component fiber, other filter media fiber, and other filtration additives provides an improved filtration media having unique properties in high temperature, high performance applications.

An air filter medium includes a collection layer, an air-permeable adhesive layer, and a porous fluorine resin membrane in this order from upstream to downstream of the filter medium. An initial pressure drop of the filter medium at a permeate flow rate of 5.3 cm/sec is 250 Pa or less. When a test is performed in which polydisperse polyalphaolefin particles having a peak in number in a particle size range of 0.1 to 0.2 μm are allowed to pass through the filter medium at a concentration of 0.2 to 0.5 g/m.sup.3 and a linear velocity of 5.3 cm/sec, the holding amount is 43.0 g/m.sup.2 or more from a moment when the holding amount reaches 20 g/m.sup.2 to when a moment the pressure drop reaches PD.sub.1+120 Pa, where PD.sub.1 is the pressure drop of the filter medium at the moment when the holding amount reaches 20 g/m.sup.2.

Fine fiber products including fiber webs, as well as related assemblies, systems and methods, are described. In some embodiments, fiber webs described herein may include fine fibers and relatively low amounts of degraded polymer formed during a fiber extrusion process. The fiber webs may be used for filter media applications.

A nanofiber nonwoven product is disclosed which comprises a polyamide with a relative viscosity from 2 to 330, spun into nanofibers with an average diameter of less than 1000 nanometers (1 micron). In general, the inventive products are prepared by: (a) providing a polyamide composition, wherein the polyamide has a relative viscosity from 2 to 330; (b) melt spinning the polyamide composition into a plurality of nanofibers having an average fiber diameter of less than 1 micron, followed by (c) forming the nanofibers into the product.

The electret-treated sheet includes: a core layer (A) which is a porous film containing at least a thermoplastic resin; a surface layer (X) disposed on one side of the core layer (A); and a back surface layer (Y) disposed on the other side of the core layer (A), the surface layer (X) and the back surface layer (Y) each having a charged outermost surface, wherein the electret-treated sheet has a water vapor permeability coefficient of 0.1 to 2.5 g.Math.mm/m.sup.2.Math.24 hr; the core layer (A) has a pore aspect ratio of 5 to 50 and an average pore height of 2.5 to 15 μm; the surface layer (X) and the back surface layer (Y) each have a thickness of 5 to 200 μm; and the surface layer (X) includes a heat seal layer (B) including the outermost surface, wherein the heat seal layer (B) has a melting point of 50 to 140° C.

Articles and methods relating to filter media are generally provided. In some embodiments, a filter media has an irregular surface structure. For instance, the filter media may comprise a plurality of peaks that are irregular in one or more ways. A ratio of a peak height standard deviation to an average peak height may be greater than or equal to 0.05, and/or a ratio of a peak spacing standard deviation to an average peak spacing may be greater than or equal to 0.08. In some embodiments, a filter media comprises a non-woven fiber web having a layer thickness of greater than 0.3 mm and/or a stiffness of less than or equal to 100 mg.

A melt-blown nonwoven fabric includes polybutylene terephthalate, in which an intrinsic viscosity of the melt-blown nonwoven fabric is 0.45 dl/g or more and 0.60 dl/g or less.

A filter comprising a nanofiber nonwoven product is disclosed which comprises a polyamide with a relative viscosity from 2 to 330, spun into nanofibers with an average diameter of less than 1000 nanometers (1 micron). In general, the inventive products are prepared by: (a) providing a polyamide composition, wherein the polyamide has a relative viscosity from 2 to 330; (b) melt spinning the polyamide composition into a plurality of nanofibers having an average fiber diameter of less than 1 micron, followed by (c) forming the nanofibers into the product.

A nanofiber based multi-layer filtration material suitable for use in providing air filtration to a user's respiratory system may be provided. as an air filtration garment and/or other air filterina devices such as a face mask, mask and garments or the like. The laminate includes a one or more fabric layer adjacent to one or more nanofiber layers.

Non-woven fiber webs and articles (e.g., filter media) comprising non-woven fiber webs are generally described. In some embodiments, a non-woven fiber web described herein formed via certain non-wetlaid processes may exhibit enhanced physical properties. For example, a non-woven fiber web may be subjected to a carding (e.g., cross-lapped carding) process. In some cases, the non-woven fiber webs described herein may be calendered to further enhance their physical properties.