JP7340037B2 - Filtration media containing a polyamide nanofiber layer - Google Patents

Description

priority claim
[0001] This application claims priority to US Provisional Application No. 62/841,485, filed May 1, 2019, the contents and disclosure of which are incorporated herein by reference in their entirety.

FIELD OF THE INVENTION [0002] The present invention relates to filtration media comprising at least one layer of polyamide nanofiber nonwoven fabric, and methods of making the at least one layer using a polyamide having a relative viscosity of 2 to 200 by a meltblowing process.

[0003] Common filtration processes remove particulate matter from fluids, including air or other gas streams, or liquid streams such as hydraulic fluids, lubricants, fuels, water streams or other fluids. Such filtration processes require mechanical strength, chemical and physical stability of the microfiber and substrate materials. Filtration media can be exposed to a wide range of temperature conditions, humidity, mechanical vibration and shock, and reactive and non-reactive, abrasive or non-abrasive particulate matter entrained in the fluid stream. The filter may be removed for inspection and cleaned with an aqueous or non-aqueous cleaning composition. Such media are often made by spinning or meltblowing fine fibers and then forming an interlocking web of microfibers on a porous substrate. In the meltblowing process, the fibers can form physical bonds between the fibers to join the fiber mat into a unified layer. Such materials can then be fabricated into desired filter formats such as cartridges, flat discs, canisters, panels, bags and pouches. Within such structures, the media can be pleated, rolled, or otherwise positioned substantially on the support structure.

[0004] Existing filtration media are described in the art. For example, US Pat. No. 6,746,517 describes the use of fine filters or fibers having fiber diameters of about 0.0001 to 0.5 microns made by electrospinning fine fibers using conventional techniques. disclose.

[0005] US Patent No. 7,115,150 discloses a filter arrangement for fog removal comprising a generally pleated barrier medium treated with a deposit of fine fibers. Filter arrangements may take the form of tubular radial sealing elements; tubular axial sealing elements; forward flow air cleaners; backflow air cleaners; can have multiple layers of

[0006] US Patent No. 6,716,274 discloses a filter arrangement for an industrial air cleaner comprising a normally pleated barrier media treated with a deposit of fine fibers. The medium is particularly advantageous in high temperature (greater than 60° C.) operating environments.

[0007] U.S. Patent Nos. 6,955,775; 7,070,640; 7,179,317; 7,270,693; Nos. 8,366,797, 8,709,118, and 9,718,012 disclose improvements that can be made from improved polymeric materials in the form of microfiber and nanofiber structures. Disclosed are polymeric and fibrous materials made from polystyrene. Microfiber and nanofiber structures can be used in a variety of useful applications including the production of filter materials.

[0008] US Patent No. 8,512,432 discloses a composite filtration media structure comprising a base substrate comprising a nonwoven synthetic fabric formed from a plurality of fibers in a spunbond process. The base substrate has a filtration efficiency of about 35% to less than 50% measured according to EN 1822 (1998) test procedure. A nanofiber layer is deposited over the base substrate. The composite filtration media structure has a minimum filtration efficiency of about 70% measured according to EN 1822 (1998) test procedure.

[0009] US Patent Application Publication No. 20070074628 discloses a coalescing filtration medium for removing liquid aerosols, oil and/or water from gas streams. The medium contains a nanofiber web of at least one nanofiber layer of continuous substantially polyolefin-free polymeric nanofibers, each nanofiber layer having an average fiber diameter of less than about 800 nm and at least about 2 It has a basis weight of .5 g/m ² . A nanofiber web of nanofiber layers was made by electroblowing a solution of nylon 6,6 polymer.

[0010] Various designs of filtration media are also described in the art. For example, US Pat. No. 7,877,704 described replaceable filter elements containing multiple filtration media and related filtration systems, techniques and methods. As disclosed, the filter element includes an outer filtration medium and an inner filtration medium. The outer filtration media is operable to remove particulate matter present in the fluid stream and/or coalesced water contained in the fluid stream. The inner filtration media is operable to remove particulate matter from the fluid stream, separate water from the fluid stream, and remove particulate matter from the fluid stream.

[0011] U.S. Patent No. 8,784,542 discloses a polymeric fiber having a basis weight of 0.01 to 50 g/ ^m2 and a porosity of 60 to 95% and having a number average fiber diameter in the range of 50 to 600 nm. Disclosed is a nanofiber membrane layer comprising a nanoweb made of nanofibers and comprising a polymer composition comprising a semi-crystalline polyamide having a C/N ratio of up to 5.5. The present invention also relates to water and air filtration devices comprising such nanofiber membrane layers.

[0012] Multilayer structures have also been described. For example, US Pat. No. 8,308,834 discloses a composite filtration media comprising a base substrate comprising a nonwoven synthetic fabric formed from a plurality of fibers by a spunbond process. The base substrate has a minimum filtration efficiency of about 50% measured according to ASHRAE 52.2-1999 test method. A nanofiber layer is deposited on one side of the base substrate. The composite filtration media construction has a minimum filtration efficiency of about 75% measured according to ASHRAE 52.2-1999 test method.

[0013] EP-A-2321029 discloses a multi-component filtration medium comprising at least two different materials, at least one of which is a low melting component, a composite filtration comprising fine fibers supported by the multi-component filtration medium A medium is disclosed wherein the fine fibers are formed from a polymeric material, have an average fiber diameter of less than about 500 nm, and the fine fibers are thermally bonded to the multi-component filtration media with a low temperature melting component.

[0014] US Patent No. 8,679,218 discloses a filtration medium having multiple layers. As disclosed, the filtration media includes a nanofiber layer adhered to another layer. The layer to which the nanofiber layer is adhered is formed of multiple fiber types (eg, fibers that make up structures with different breathability and/or pressure drops). The disclosed nanofiber layers can be adhered to single-phase or multi-phase layers. The disclosed nanofiber layers can be manufactured with a meltblown process. Filtration media can optionally be devised to have advantageous properties including high dust particle capture efficiency and/or high dust holding capacity.

[0015] Various methods of making filter components are disclosed in the art. For example, US Patent Application Publication No. 2015/0157971 discloses a filtration barrier comprising at least one barrier layer comprising polymeric nanofibers interwoven with microfibers, and at least one substrate layer comprising polymeric microfibers. . Filtration barriers can be made by an electrospinning process.

[0016] As indicated above, polymeric membranes, including nanofiber and microfiber nonwovens, are known in the art and are used for a variety of purposes, including, for example, filtration media and clothing applications. Known techniques for forming microporous polymeric structures include xerogel and airgel film formation, electrospinning, meltblowing, and centrifugal spinning using rotating spinnerets and biphasic spinning through fine channels using a propellant gas. There is polymer extrusion.

[0017] U.S. Patent Application Publication No. 2014/0097558 discloses a method of manufacturing a filtration medium, such as a personal protective mask or respirator, comprising a convex mold that may be shaped, for example, in the shape of a human face. An electrospinning process is included to form the nanofibers thereon. See also US Patent Application Publication No. 2015/0145175. WO2014/074818 discloses nanofiber meshes and xerogels used to selectively filter target compounds or elements from liquids. Also described are methods of forming nanofiber meshes and xerogels, methods of processing liquids using nanofiber meshes and xerogels, and methods of analyzing target compounds or entities using nanofiber meshes or ten xerogels. be done.

[0018] Despite the wide variety of techniques and materials that have been proposed, conventional filtration media suffer from many deficiencies in terms of manufacturing cost, processability and product properties.

[0019] In some embodiments, the present disclosure is a filtration media comprising a nanofiber nonwoven layer, wherein the nanofiber nonwoven layer is spun into nanofibers having an average fiber diameter of less than 1 micron (1000 nanometers). Filtration media comprising a polyamide having a relative viscosity of 2 to 200 formed into layers. The nanofiber nonwoven layer may comprise polyamide spun into nanofibers having an average fiber diameter of less than 1 micron (1000 nanometers) and formed into a layer, the layer having a melting point of 225° C. or higher. Filters can be air filters, oil filters, bag filters, liquid filters, or respiratory filters such as face masks, surgical masks or personal protective equipment. In some aspects, the polyamide can be nylon 6,6. In a further aspect, the polyamide can be nylon 6,6 and nylon 6 derivatives, copolymers, blends or alloys. In some aspects the polyamide is a high temperature nylon. In some aspects, the polyamide is a long chain aliphatic nylon selected from the group consisting of N6, N6T/66, N612, N6/66, N11, and N12, where "N" means nylon, "T ” refers to terephthalic acid. The nanofiber nonwoven layer can have an Air Permeability Value of less than 200 CFM/ft ² . In some aspects, the nanofiber nonwoven layer has an air permeability value of 50 to 200 CFM/ft ² . Nanofibers may have an average fiber diameter of 100 to 907 nanometers, such as 300 to 700 nanometers or 350 to 650 nanometers. Nonwoven products may have a basis weight of 150 grams/m ² (gsm) or less, such as from 5 to 150 gsm or from 10 to 125 gsm. The filtration media may further include a scrim layer. In some aspects, a nanofiber nonwoven layer can be spun onto the scrim layer. In a further aspect, the nanofiber nonwoven layer can be spun onto layers other than the scrim layer. In some aspects, the nanofiber nonwoven layer is sandwiched between the scrim layer and at least one other layer. In a further aspect, the nanofiber nonwoven layer is sandwiched between at least two layers other than the scrim layer. In yet another aspect, the nanofiber nonwoven layer is the outermost layer. The filtration medium may further include at least one additional layer, and the nanofiber nonwoven layer may be spun onto one of the at least one additional layer. The relative viscosity of the polyamide of the nanofiber nonwoven layer can be reduced by at least 20% compared to the polyamide prior to spinning to form the layer.

[0020] In some embodiments, the present disclosure is a method of making a filtration medium comprising a polyamide nanofiber layer comprising: (a) providing a spinnable polyamide polymer composition, wherein the polyamide (b) melt spinning the polyamide polymer composition into a plurality of nanofibers having an average fiber diameter of less than 1 micron (1000 nanometers); and (c) the nanofibers Forming on an existing filtration media layer, wherein the polyamide nanofiber layer has an average nanofiber fiber diameter of less than 1000 nanometers.

[0021] In some embodiments, the present disclosure is a method of making a filtration media comprising a polyamide nanofiber layer comprising: (a) providing a spinnable polyamide polymer composition; melt spinning the article into a plurality of nanofibers having an average fiber diameter of less than 1 micron (1000 nanometers); wherein the fiber layer has an average nanofiber fiber diameter of less than 1000 nanometers and a melting point of 225° C. or higher. Polyamide nanofiber layers can be melt spun by melt blowing through a die into a high velocity gas stream. The polyamide nanofiber layer can be melt-spun by 2-phase propellant-gas spinning, which involves extruding a polyamide polymer composition in liquid form through a fiber-forming channel with a pressurized gas. A polyamide nanofiber layer can be formed by collecting nanofibers on a moving belt. In some aspects, the polyamide composition comprises nylon 6,6. In a further aspect, the polyamide composition comprises nylon 6,6 and nylon 6 derivatives, copolymers, blends or alloys. In yet another aspect, the polyamide comprises HTN. In some aspects, the polyamide is a long chain aliphatic nylon selected from the group consisting of N6, N6T/66, N612, N6/66, N11, and N12, where "N" means nylon, "T ” refers to terephthalic acid. The polyamide nanofiber layer can have a basis weight of 150 gsm or less. The filtration media may further include a scrim layer. In some aspects, a polyamide nanofiber layer can be spun onto the scrim layer. In a further aspect, the polyamide nanofiber layer can be spun onto layers other than the scrim layer. In yet another aspect, the polyamide nanofiber layer can be sandwiched between the scrim layer and at least one other layer. In yet another aspect, the polyamide nanofiber layer can be sandwiched between at least two layers other than the scrim layer. In some aspects, the polyamide nanofiber layer is the outermost layer. In some aspects, the filtration medium may further include at least one additional layer, and the nanofiber nonwoven layer may be spun onto one of the at least one additional layer. The relative viscosity of the polyamide of the polyamide nanofiber layer can be reduced by at least 20% compared to the polyamide prior to spinning to form the layer.

[0022] The present invention will now be described in detail with reference to the drawings, in which like numerals indicate like parts.

[0023] Fig. 4 is a separate schematic representation of a two-phase propellant gas spinning system useful in connection with the present invention; FIG. 2 is a separate schematic diagram of a two-phase propellant gas spinning system useful in connection with the present invention; [0024] Fig. 5 is a photomicrograph at 5Ox magnification of nanofiber nylon 66 melt-spun into a nonwoven having an RV of 7.3. [0025] FIG. 4 is a photomicrograph at 8000× magnification of nanofibers of the grade nylon 66 of FIG. 3 melt-spun into a nonwoven having an RV of 7.3.

[0026] Overview
[0027] The present invention relates to a filtration medium that includes a layer of nanofiber nonwoven fabric that includes, in part, a polyamide. Polyamides can have melting points above 225°C. Polyamides may have a relative viscosity of 2 to 200, such as 2 to 100, 2 to 60, 20 to 50, 20 to 13, 13 to 20, or 2 to 12. Polyamides can be spun or meltblown into nanofibers with an average fiber diameter of less than 1000 nanometers (1 micron) and formed into nonwoven products. A nanofiber nonwoven layer comprising polyamide can then be incorporated into the filter. The layer is providing a spinnable polyamide polymer composition capable of being meltblown, wherein the polyamide has a relative viscosity of 2 to 200; (b) the polyamide polymer composition is in liquid form; spinning or meltblowing into a plurality of nanofibers having an average fiber diameter of less than 1 micron by a process involving two-phase propellant gas spinning comprising extruding the polyamide polymer composition of of into a plurality of nanofibers having an average fiber diameter of less than 1 micron; Subsequently (c) it can be made by forming the nanofibers into an article. The general steps of meltblowing technology are illustrated in FIGS.

[0028] A particularly preferred polyamide is nylon 6,6

and nylon 6,6 and nylon 6

including copolymers, blends, and alloys of
[0029] Other embodiments include, but are not limited to, nylon 6,6 or nylon derivatives, copolymers, blends and alloys containing or made from nylon 6 or copolymers with repeating units as described above. Including N6T/66, N612, N6/66, N11, and N12, where "N" refers to nylon and "T" refers to terephthalic acid. Another preferred embodiment comprises High Temperature Nylon ("HTN") and blends, derivatives or copolymers containing them. Another preferred embodiment also includes long chain aliphatic polyamides made with long chain diacids and blends, derivatives or copolymers containing them.

[0030] The present disclosure may be understood by reference to Figures 1 and 2, which illustrate a two-phase propellant gas spinning process useful for making nanofibers, and a general meltblowing technique, respectively. In particular, disclosed herein is a method of making a nanofiber nonwoven product in which the nonwoven is melt spun by meltblowing through a spinneret into a high velocity gas stream. More specifically, the nonwoven fabric is melt spun by two-phase propellant gas spinning, which involves extruding a polyamide polymer composition in liquid form through a fiber-forming channel with a pressurized gas.

[0031] Definitions and test methods
[0032] The terms used herein have their ordinary meanings consistent with the definitions below. gsm means basis weight in grams per square meter, RV means relative viscosity, and so on.

[0033] Percentages, parts per million (ppm), etc., mean weight percent or parts by weight based on the weight of the composition, unless otherwise indicated.
[0034] Exemplary definitions and test methods are further described in US Patent Application Publication Nos. 2015/0107457 and 2015/0111019. For example, the term "nanofiber nonwoven" means a web of numerous essentially randomly oriented fibers in which the overall repeating structure cannot be discerned by the naked eye in the arrangement of the fibers. The fibers can be bonded together or entangled endlessly to impart strength and integrity to the web. The fibers can be staple fibers or continuous fibers and can comprise a single material or multiple materials as combinations of different fibers or similar fibers each comprising a different material. Nanofiber non-woven products are mainly composed of nanofibers. By "predominantly" is meant greater than 50% of the fibers in the web are nanofibers. The term "nanofiber" means fibers having a number average fiber diameter of less than 1000 nm or 1 micron. For non-round cross-section nanofibers, the term "diameter" as used herein means the largest cross-sectional dimension.

[0035] Basis weight is determined by ASTM D-3776 and may be reported in gsm (g/m2).
[0036] "Consisting essentially of" and similar terms refer to the listed ingredients and exclude other ingredients that materially alter the basic novel properties of the composition or article. Unless otherwise indicated or readily apparent, a composition or article consists essentially of the enumerated or listed ingredients when the composition or article contains 90% or more by weight of the enumerated or listed ingredient. That is, the term excludes more than 10% unlisted components.

[0037] Unless otherwise indicated, the test method for determining average fiber diameter is that of Hassan et al. , J20 Membrane Sci. , 427, 336-344, 2013.

[0038] Air permeability is measured using an Air Permeability Tester available from Precision Instrument Company, Hagerstown, MD. Air permeability is defined as the flow rate of air through a sheet of material under a specified pressure head at 23±1° C. and is typically 0.50 in. Expressed as cubic feet per square foot per minute at a water pressure of (12.7 mm), in units of cm ³ per square cm per second or elapsed time per unit area of sheet for a given volume. The above instrument can measure transmission from 0 to approximately 5000 cubic feet per minute per square foot of test area. For purposes of comparing transmittance, it is convenient to express values normalized to a 5 gsm basis weight. This is done by measuring the sample's air permeability value and basis weight (usually at 0.5″ H2O) and then multiplying the actual air permeability value by the ratio of the actual basis weight to 5. For example, , if a 15 gsm basis weight sample has a value of 10 CFM/ ^ft2 , then its normalized 5 gsm air permeability value is 30 CFM/ ^ft2 .

[0039] As used herein, polyamide composition and similar terms mean compositions containing polyamides, including copolymers, terpolymers, polymer blends, alloys and derivatives of polyamides. Additionally, as used herein, "polyamide" means a polymer having as components a polymer containing linkages of amino groups of one molecule and carboxylic acid groups of another molecule. In some aspects, polyamide is the component present in the highest amount. For example, 40 wt. % Nylon 6, 30 wt. % polyethylene, and 30 wt. % polypropylene is referred to herein as a polyamide because the nylon 6 component is present in the greatest amount. Furthermore, 20 wt. % Nylon 6, 20 wt. % Nylon 66, 30 wt. % polyethylene, and 30 wt. % polypropylene are also referred to herein as polyamides because the nylon 6 and nylon 66 components are the components present in the largest amount overall. A suitable alloy may include, for example, 20% nylon 6, 60% nylon 6,6 and 20% polyester by weight.

[0040] Representative polyamides and polyamide compositions are described in Kirk-Othmer, Encyclopedia of Chemical Technology, Vol. 18, pp. 328371 (Wiley 1982), the disclosure of which is incorporated by reference.

[0041] Briefly, polyamides are products that contain repeating amide groups as an integral part of the main polymer chain. Linear polyamides are of particular interest and can be formed by condensation of difunctional monomers as is well known in the art. Polyamide is often referred to as nylon. Although generally considered condensation polymers, polyamides can also be formed by addition polymerization. This method of preparation is particularly important for some polymers whose monomers are cyclic lactams (ie nylon 6). The individual polymers and copolymers and their preparation are disclosed in the following patents: U.S. Pat. Nos. 4,760,129; 5,504,185; 5,543,495; 5,698,658. 6,011,134; 6,136,947; 6,169,162; 7,138,482; 7,381,788; , 759,475.

[0042] A particularly preferred class of polyamides for some applications is Glasscock et al. , High Performance Polyamides Fulfill Demanding Requirements for Automotive Thermal Management Components, (DuPont), http://www2. dupont. com/Automotive/en_US/assets/downloads/knowledg e%20center/HTN-whitepaper-R8. pdf containing high temperature nylon (HTN). Such polymers typically contain one or more of the structures shown below:

[0043] The relative viscosity (RV) of a polyamide refers to the ratio of solution or solvent viscosities measured by a capillary viscometer at 25°C (ASTM D 789). For this purpose the solvent is formic acid containing 10% by weight water and 90% by weight formic acid. The solution is 8.4 wt% polymer dissolved in solvent.

[0044] Relative viscosity (ηr) is the ratio of the absolute viscosity of the polymer solution to that of formic acid:
ηr=(ηp/ηf)=(fr×dp×tp)/ηf
(Wherein, dp = density of formic acid-polymer solution at 25 ° C., tp = average outflow time s for formic acid-polymer solution, ηf = absolute viscosity of formic acid kPa × s (E + 6 cP), fr = viscometer tube coefficient (tube factor) mm2/s(cSt)/s=ηr/t3).

[0045] A typical calculation for a 50 RV specimen:
ηr=(fr×dp×tp)/ηf
(In the formula,
fr = Viscometer tube factor, typically 0.485675 cSt/s dp = Density of polymer-formic acid solution, typically 1.1900 g/ml tp = Mean outflow time for polymer-formic acid solution, typically 135.00 s
η = absolute viscosity of formic acid, typically 1.56 cP,
ηr = (0.485675 cSt/s x 1.1900 g/ml x 135.00 s)/1.56 cP = giving an RV of 50.0).
The term t3 is the runoff time of the S-3 calibrated oil used in the determination of the absolute viscosity of formic acid required by ASTM D789.

[0046] Additional embodiments of the present invention include the production of layers of filtration media having an average fiber diameter of less than 1 micron and comprising polyamide nanofibers having an RV of 2 to 200. In this alternate embodiment, preferred RV ranges include 2-200, 2-100, 2-60, and 5-60. The nanofibers are then converted into nonwoven webs. As RV increases beyond about 20 to 30, operating temperature becomes a more important parameter to consider. Above the range of about 20 to 30 RV, the temperature must be carefully controlled so that the polymer melts for processing purposes. Methods or examples of melting techniques are described in US Pat. No. 8,777,599, as are heating and cooling sources that can be used with the apparatus to independently control the temperature of the fiber manufacturing apparatus. Non-limiting examples include resistance heaters, radiant heaters, cooling or heating gas (air or nitrogen), or conductive, convective, or radiant heat transfer mechanisms.

[0047] Although reducing RV is generally not a desirable practice when spinning nylon 6,6, it can actually be an advantage in the production of nanofibers. In certain aspects of the invention, it has been found advantageous to melt-spun nylon 6,6 at as low an RV as possible to achieve the smallest filament diameters in the production of nanofiber filaments. Increasing the process temperature by only a small amount reduces the viscosity. Advantageously, it is possible to reduce the viscosity of nylon 6,6 by adding moisture to depolymerize the polymer. This is one advantage over addition polymers such as polypropylene. In some aspects, the RV of the polyamide nanofiber layer is at least 20% greater than the RV of the polyamide prior to forming the spun or meltblown layer, such as at least 25%, at least 30%, at least 35%, at least 40%, or at least 45% lower.

[0048] Non-limiting examples of polymers include polyamides, polypropylene and copolymers, polyethylene and copolymers, polyesters, polystyrenes, polyurethanes, and combinations thereof. Thermoplastic and biodegradable polymers are also suitable for meltblowing or meltspinning into the nanofibers of the present invention. As described herein, the polymer is melt spun or melt blown, preferably by two-phase propellant gas spinning, e.g., the polyamide polymer composition in liquid form is forced through the fiber-forming channel with pressurized gas. push out.

[0049] Other polymeric materials that can be used in the nanofibers of the present invention are addition and condensation polymer materials such as polyolefins, polyacetals, polyamides (already mentioned), polyesters, cellulose ethers and esters, polyalkylene sulfides, Including polyarylene oxides, polysulfones, modified polysulfone polymers and mixtures thereof. Preferred materials falling within these generic classes are polyamide, polyethylene, polybutylene terephthalate (PBT), polypropylene, poly(vinyl chloride), polymethyl methacrylate (and other acrylics), polystyrene, and copolymers thereof (e.g. ABA type block copolymers), poly(vinylidene fluoride), poly(vinylidene chloride), polyvinyl alcohol in crosslinked and uncrosslinked forms with varying degrees of hydrolysis (87% to 99.5%). Addition polymers tend to be glassy (Tg above room temperature). This is the case for polyvinyl chloride and polymethyl methacrylate, polystyrene polymer compositions or alloys, or the low crystallinity of polyvinylidene fluoride and polyvinyl alcohol materials. The nylon copolymers embodied herein are made by combining various diamine compounds, various diacid compounds and various cyclic lactam structures in a reaction mixture and then randomly placing monomeric materials within the polyamide structure. It can be made by forming nylon. For example, a nylon 6,6-6,10 material is a nylon made from hexamethylenediamine and _C6 and _C10 blends of diacids. Nylon 6-6,6-6,10 is a nylon made by copolymerizing a blend of ε-aminocaproic acid, hexamethylenediamine and C ₆ and C ₁₀ diacid materials.

[0050] Block copolymers are also useful in the process of the present invention. The choice of solvent swell agent in such copolymers is important. The solvent chosen is such that both blocks are soluble in that solvent. One example is ABA (styrene-EP-styrene) or AB (styrene-EP) polymers against methylene chloride solvent. If one component is not soluble in that solvent, a gel will form. Examples of such block copolymers are Kraton® type styrene-b-butadiene and styrene-b-hydrogenated butadiene (ethylene propylene), Pebax® type ε-caprolactam-b-ethylene oxide, Sympatex® ) polyester-b-ethylene oxide and polyurethanes of ethylene oxide and isocyanate.

[0051] Polyvinylidene fluoride, syndiotactic polystyrene, copolymers of vinylidene fluoride and hexafluoropropylene, polyvinyl alcohol, polyvinyl acetate, amorphous addition polymers such as poly(acrylonitrile) and its copolymers with acrylic acid and methacrylate, Addition polymers such as polystyrene, poly(vinyl chloride) and its various copolymers, poly(methyl methacrylate) and its various copolymers are soluble at low pressures and temperatures and can be solution spun relatively easily. It is publicly known. It is envisioned that these can be melt spun according to the present invention as one method of making nanofibers.

[0052] There are substantial advantages to forming polymeric compositions that include two or more polymeric materials in a polymer blend, alloy format, or crosslinked chemically bonded structure. Such polymer compositions alter polymer attributes, such as improving polymer chain flexibility or chain mobility, increasing overall molecular weight, and providing reinforcement through the formation of a network of polymeric materials. This is believed to improve physical properties.

[0053] In one embodiment of this concept, two related polymeric materials can be blended for beneficial properties. For example, high molecular weight polyvinyl chloride can be blended with low molecular weight polyvinyl chloride. Similarly, high molecular weight nylon materials can be blended with low molecular weight nylon materials.

[0054] In some embodiments, such as those described in US Pat. No. 5,913,993, a small amount of polyethylene polymer is blended with a nylon compound used to form a nanofiber nonwoven with desirable characteristics. can be The addition of polyethylene to nylon enhances certain properties such as softness. The use of polyethylene also lowers production costs and further facilitates downstream processing such as bonding to other fabrics or itself. An improved fabric can be made by adding a small amount of polyethylene to the nylon feedstock used to produce the nanofiber meltblown fabric. More specifically, the fabric is made by forming a blend of polyethylene and nylon 6,6, extruding the blend into a plurality of continuous filaments, directing the filaments through a die to meltblown the filaments, and can be produced by depositing on a collecting surface such that a web is formed.

[0055] The polyethylene useful in the process of this embodiment of the invention preferably has a melt index of from about 5 grams/10 min to about 200 grams/10 min, more preferably from about 17 grams/10 min to about 150 grams/10 min. The polyethylene should preferably have a density of from about 0.85 grams/cc to about 1.1 grams/cc, most preferably from about 0.93 grams/cc to about 0.95 grams/cc. Most preferably, the polyethylene has a melt index of about 150 and a density of about 0.93.

[0056] The polyethylene used in the process of this embodiment of the invention may be added at a concentration of about 0.05% to about 20%. In preferred embodiments, the concentration of polyethylene is from about 0.1% to about 1.2%. Most preferably polyethylene is present at about 0.5%. The concentration of polyethylene in fabrics produced according to the described method is approximately equal to the percentage of polyethylene during the manufacturing process. Thus, the percentage of polyethylene in the fabric of this embodiment of the invention typically ranges from about 0.05% to about 20%, preferably about 0.5%. Thus, fabrics typically contain from about 80 to about 99.95 weight percent nylon. The filament extrusion process can be performed at about 250°C to about 325°C. Preferably, the temperature range is from about 280°C to about 315°C, but can be lower if nylon 6 is used.

[0057] The blend or copolymer of polyethylene and nylon can be formed in any suitable manner. Typically, the nylon compound is nylon 6,6, but other polyamides of the nylon family can be used. Mixtures of nylons can also be used. In one particular example, polyethylene is blended with a mixture of nylon 6 and nylon 6,6. Polyethylene and nylon polymers are commonly supplied in the form of pellets, chips, flakes, and the like. The desired amount of polyethylene pellets or chips can be blended with the nylon pellets or chips in a suitable mixing device such as a rotary drum tumbler or the like, and the resulting blend fed into the feed hopper of a conventional extruder or spunbond spinning line. can be introduced. Blends or copolymers can also be produced by introducing suitable mixtures into a continuous polymerization spinning system.

[0058] Additionally, different species of common polymer genera can be blended. For example, a high molecular weight styrene material can be blended with a low molecular weight high impact polystyrene. Nylon-6 materials can be blended with nylon copolymers such as nylon-6; 6,6; 6,10 copolymers. Additionally, polyvinyl alcohol with a low degree of hydrolysis, such as 87% hydrolyzed polyvinyl alcohol, can be blended with fully or super-hydrolyzed polyvinyl alcohol with a degree of hydrolysis of 98 to 99.9% or more. . All of these materials in the blend can be crosslinked using any suitable crosslinking mechanism. Nylon can be crosslinked using a crosslinker reactive with the nitrogen atoms of the amide bonds. Polyvinyl alcohol materials may be used with hydroxyl-reactive substances such as monoaldehydes such as formaldehyde, urea, melamine-formaldehyde resins and analogues, boric acid and other inorganic compounds, dialdehydes, diacids, urethanes, epoxies and other known crosslinkers. can be crosslinked using an agent. Cross-linking technology is a well-known and understood phenomenon in which cross-linking reagents react to form covalent bonds between polymer chains to substantially improve molecular weight, chemical resistance, overall strength and resistance to mechanical degradation.

[0059] Nanofibers can be made of polymeric materials or polymers plus additives. One preferred embodiment of the present invention is a polymer blend comprising a first polymer and a second, different polymer (different in polymer type, molecular weight or physical properties), which is conditioned or treated at elevated temperatures. The polymer blend can be reacted to form a single chemical species or can be physically mixed into a blended composition by an annealing process. Annealing involves physical changes such as crystallinity, stress relaxation or orientation. The preferred materials are chemically reacted into a single polymeric species such that Differential Scanning Calorimeter (DSC) analysis shows that the single polymeric material is susceptible to high temperatures, high humidity and difficult actuation. It appears to exhibit improved stability when exposed to conditions. Nanofibers of this class of materials can have diameters of about 0.01 to 5 microns. Preferred materials for use in the blended polymer system include nylon 6; nylon 66; nylon 6-10; nylon (6-66-610) copolymers and other linear generally aliphatic nylon compositions.

[0060] Certain embodiments of making the nanofiber nonwovens of the present invention are generally by two-phase spinning or meltblowing through a spinning channel using a propellant gas as described in US Pat. No. 8,668,854. The process involves two-phase polymer or polymer solution flow and pressurized propellant gas (usually air) into narrow, preferably converging channels. The channel is generally preferably annular in shape. It is believed that the polymer is sheared by the gas stream in narrow, preferably converging channels, creating polymer film layers on both sides of the channel. These polymer film layers are further sheared into fibers by the propellant gas stream. Again, a moving collector belt can be used and the basis weight of the nanofiber nonwoven is controlled by adjusting the speed of the belt. Collector spacing can also be used to control the fineness of the nanofiber nonwoven. The process is better understood with reference to FIG.

[0061] FIG. 1 schematically illustrates the operation of a system for spinning nanofiber nonwovens, including a polymer feed assembly 110, an air feed 1210, a spinning cylinder 130, a collector belt 140 and a take-up reel 150. FIG. In operation, a polymer melt or solution is fed to spinning cylinder 130 and forced by high pressure air through narrow channels in the cylinder to shear the polymer into nanofibers. Details are provided in the aforementioned US Pat. No. 8,668,854. Throughput rate and basis weight are controlled by belt speed. Optionally, functional additives such as charcoal, copper, etc. can be added with the air feed if desired.

[0062] In an alternative construction of the spinneret used in the system of Figure 1, the particulate material is described by Marshall et al. may be added at a separate inlet as seen in U.S. Pat. No. 8,808,594.

[0063] Yet another method that may be used is meltblowing the polyamide nanofiber webs of the present invention (Figure 2). Meltblowing involves extruding a polymer into a relatively high velocity, typically hot gas stream. To produce suitable nanofibers, Hassan et al. , J Membrane Sci. , 427, 336-344, 2013 and Ellison et al. , Polymer, 48 (11), 3306-3316, 2007, and International Nonwoven Journal, Summer 2003, pg 21-28, careful selection of orifice and capillary geometry and temperature is required.

[0064] In some aspects, the polyamide nanofibers are meltblown. Meltblowing is advantageously less expensive than electrospinning. Meltblowing is a type of process developed for the formation of fibers and nonwoven webs; fibers are formed by extruding a molten thermoplastic polymeric material, or polymer, through a plurality of small holes. The resulting molten threads or filaments become a converging high velocity stream of gas that attenuates or draws the filaments of molten polymer to reduce their diameter. The meltblown fibers are then carried by a high velocity gas stream and deposited on a collecting surface or formed into wires to form a nonwoven web of randomly distributed meltblown fibers. The formation of fibers and nonwoven webs by meltblowing is well known in the art. 3,704,198; 3,755,527; 3,849,241; 3,978,185; See 4,100,324; 4,118,531; and 4,663,220.

[0065] U.S. Patent No. 7,300,272 discloses a fiber extrusion pack for extruding molten material to form a mass of fibers wherein each divided distribution plate is layered within the fiber extrusion pack. a number of segmented distribution plates arranged in a stack to form a distribution network in which features on the segmented distribution plates deliver molten material to orifices in the fiber extrusion pack Form. A split distribution plate includes a set of plate segments each having a gap disposed between adjacent plate segments. Adjacent edges of the plate segments are shaped to form a reservoir along the gap, and a sealing plug is positioned within the reservoir to prevent molten material from escaping through the gap. The sealing plug can be formed by molten material leaking into the gap, collecting and solidifying within the reservoir, or by placing plug material within the reservoir of the puck assembly. This pack can be used to make nanofibers with the meltblown system described in the previously mentioned patent.

[0066] Such meltblowing can form a polyamide nanofiber web having an oxidative degradation index ("ODI") from 214 to 4162 ppm. ODI is measured using gel permeation chromatography (GPC) with a fluorescence detector. The instrument is calibrated with a quinine external standard. 0.1 grams of nylon is dissolved in 10 mL of 90% formic acid. This solution is then analyzed by GPC with a fluorescence detector. The detector wavelength for ODI is 340 nm for excitation and 415 nm for emission. Additionally, such meltblowing can produce a thermal degradation index (“TDI”) of 26-1129 ppm. TDI is measured the same as ODI except that the detector wavelength for TDI is 300 nm excitation, 338 nm emission. Meltblowing can also produce relative viscosities as described herein. TDI and ODI test methods are also disclosed in US Pat. No. 3,525,124.

[0067] Filtration media
[0068] The polyamide nanofibers described herein are advantageously used in a variety of filtration media applications such as air filters, oil filters, bag filters, liquid filters, breathing filters, fuel filters, hydraulic oil filters, etc. . Polyamide nanofibers are not typically considered the only layer in filters, but are envisioned to be used in addition to traditional filters or to replace one or more layers in traditional filters. be done. A polyamide nanofiber layer is also referred to as a nanofiber nonwoven layer comprising polyamide.

[0069] Filtration parameters
[0070] One general parameter specific to filtration media is the "efficiency" of the filtration medium. Efficiency is the propensity of a medium to trap particulate matter as opposed to allowing the particulate matter to pass through the medium instead of being filtered. Another common characteristic is the pressure drop across the medium, which is often traditionally related to the porosity of the medium. Pressure drop is related to how restrictive the filtration media is to fluid flow. Larger pore sizes typically allow greater fluid flow, but unfortunately typically result in more particulate matter passing through. As a result, efficiency often conflicts with pressure drop. In particular, while it is often desirable to capture large amounts of particulate matter, such high efficiencies often have the undesirable effect of increasing the restrictiveness of the medium and thus the pressure drop across the medium. This shortens the life of the filter.

[0071] Efficiency often refers to the initial efficiency, ie, the efficiency of the filtration media after manufacture but before it is loaded with particulate matter prior to use. During use, the filtration media picks up and traps particulate matter within the media as a dust cake and/or otherwise by catching it. These filtered particulate matter plug larger pores in the media, thereby preventing smaller particles from passing through the pores, thereby increasing the efficiency of the media over time to an operating efficiency greater than the initial efficiency. However, by blocking the fluid flow path, such filtered particulate matter also increases the pressure drop across the medium by removing or partially clogging the fluid path, thereby reducing fluid flow. be more restrictive.

[0072] Typically, filter life is determined by the pressure drop (delta P) across the filter. In one embodiment, Delta P may be 0.5 to 10 _mmH2O , such as 0.5 to 5 _mmH2O or 0.5 to 3 _mmH2O . As more and more particles are filtered out of the fluid stream and captured by the filtration medium, the filtration medium becomes more restrictive to the fluid flow. As a result, the pressure drop across the filtration media is higher. Ultimately, the medium becomes too restrictive, resulting in an insufficient amount of fluid flow for a given application's fluid requirements. Filter change intervals are calculated to approximately coincide with such occurrences (eg, before insufficient fluid flow conditions are reached). Filter change intervals can also be determined by a sensor that measures the pressure drop load across the media.

[0073] In general, electrospun nanofiber media are expected to provide superior filtration efficiency. The reason for this is that smaller diameter nanofibers can be packaged together without increasing the overall solidity of the medium, given the fact that smaller fibers occupy less volume than larger fibers. It is from. Thus, electrospun nanofiber media can effectively trap fine particles that filtration media made of coarse fibers, such as meltblown fiber filtration media, cannot. However, larger sized particles can quickly plug the pores on the upstream surface of the electrospun nanofiber media, thereby increasing the pressure drop of the filtration media to unacceptable levels and reducing filter life. . Multiple layers of filtration media comprising polyamide nanofiber layers improve filter life by allowing smaller particles to be trapped within the depth of the melt-spun polyamide nanofiber layers. while maintaining high filtration efficiency.

[0074] Polyamide nanofibers offer several advantages over traditional filter materials, including filters containing polypropylene layers. Surprisingly and unexpectedly, forming a polyamide nanofiber layer by meltblowing results in increased strength, higher melting point, specific It has been discovered that increased chemical resistance in liquids, smaller pore sizes, and lower melt flow indices are obtained. By incorporating polyamide nanofibers into filters, the cost of producing filters can be reduced due to the melt spinning process compared to other processes such as electrospinning. Polyamide nanofibers also have increased filtration efficiency compared to traditional filter materials due to their small pore size. Filters with polyamide nanofiber layers may also have reduced weight compared to traditional filters, and even the layers of construction of the filter may be simplified due to the increased efficiency seen by using polyamide nanofibers. An additional advantage of using polyamide nanofibers is that, as described below, for pleated filters, polyamide nanofibers can be combined with a scrim or substrate, which compares favorably with traditional filters. is to allow less energy to be used during pleating due to the less time and lower temperatures used during the pleating process. Finally, the inclusion of a layer of polyamide nanofibers generally does not require resizing of equipment specifically made to work with the filter, such as the canister surrounding the filter.

[0075] Filtration media layer
[0076] Filtration media generally include several layers, each layer providing different filtration characteristics. One such layer is a scrim layer, such as a reinforcing layer. In some aspects, the scrim layer is selected to have a significant filtration capacity and efficiency. However, in other aspects, the scrim layer may or may not have low filtration capacity or efficiency. The scrim layer may have a thickness of 0.1 to 0.81 mm, such as 0.2 to 0.3 mm, or about 0.25 mm. The scrim layer may have a basis weight of 5 to 203 gsm, such as 5 to 60 gsm, 15 to 45 gsm, or any value in between. The fibers of the scrim layer may have a median fiber diameter of 1 to 1000 microns, such as 1 to 500 microns, 1 to 100 microns, or any value in between. Thickness, basis weight, and median fiber diameter can be selected based on the type of filtration media in which the scrim will be used. Generally, the scrim has a Frazier air permeability of 111 CFM to 1675 CFM, e.g. can have The filtration efficiency of the scrim layer was characterized by comparing the number of dust particles with particle sizes ranging from 0.3 μm to 10 μm on the upstream and downstream faces of the scrim measured using a PALAS MFP-2000 (Germany) instrument. can be The filtration efficiency of the scrim selected for the scrim layer in one embodiment is measured using ISO fine dust with a dust concentration of 70 mg/m ³ , a sample test size of 100 ² cm, and a face velocity of 20 cm/s. Suitable scrims may be selected from widely commercially available scrims or may be formed by a spunbonding or carding or batting process or another process using suitable polymers. Suitable polymers for the scrim include, but are not limited to, polyesters, polypropylenes, polyethylenes and polyamides such as nylon or combinations of two or more of these polymers. For example, suitable scrims for the scrim layer are available from Berry Plastics, formerly Fiberweb Inc. of Old Hickory, Tennessee, or Cerex Advanced Fabrics, Inc. of Cantonment, Florida, among others. It is available in various thicknesses from suppliers including More than one scrim layer may be incorporated into the filtration media.

[0077] An additional layer within the filtration media is a polyamide nanofiber layer. In some aspects, this layer is spun or meltblown directly onto one or more scrim layers. In some embodiments, the polyamide nanofiber layer is at least 1 mm thick, typically 1.0 mm to 6.0 mm, preferably 0.07 mm to 3 mm, in one embodiment about 0.13 mm thick; m ² ), such as a basis weight of less than 120 gsm, or a basis weight of less than 100 gsm. For ranges, the basis weight may be 5 to 150 gsm, such as 10 to 150 gsm, 10 to 120 gsm or 10 to 100 gsm. The fibers of the polyamide nanofiber layer have a median fiber diameter of 1 nanometer to 1000 nanometers as described herein and are less than 1000 nanometers, such as less than 907 nanometers, less than 900 nanometers, 800 nanometers It can be less than a meter, less than 700 nanometers, less than 600 nanometers, or less than 500 nanometers. With respect to the lower limits, the average fiber diameter of the nanofibers of the fibrous layer of the nonwoven is at least 100 nanometers, at least 110 nanometers, at least 115 nanometers, at least 120 nanometers, at least 125 nanometers, at least 130 nanometers, at least 150 nanometers, It may have an average fiber diameter of at least 300 nanometers or at least 350 nanometers. In one embodiment, the filtration efficiency of the polyamide nanofiber layer is measured using a PALAS MFP-2000 (Germany) instrument. can be characterized by comparing

[0078] As used herein, the term "layer" does not require complete coverage of the surface from which the polyamide nanofibers are spun. A layer may cover the entire surface area of the underlying layer, or may cover less than 99%, such as less than 90%, less than 80%, less than 70% or less than 60% of the surface area. In some aspects, the polyamide nanofiber layer may cover at least 5%, such as at least 10%, at least 20%, at least 30%, or at least 40% of the surface area of the underlying layer. In terms of range, the polyamide nanofiber layer may cover 5 to 100% of the spun layer, such as 5 to 99%, 10 to 90%, 20 to 80%, 30 to 70%, or 40 to 60%. The same applies to the layers spun onto the polyamide layer.

[0079] In addition to the scrim layer and the polyamide nanofiber layer, conventional layers may also be included. Such conventional layers may be formed by melt spinning or electrospinning.
[0080] Further description of conventional filtration media layers is disclosed in some of the references disclosed in the background section of this application. In some aspects, additional layers include polyvinyl chloride (PVC), polyolefins, polyacetals, polyesters, cellular ethers, polyalkylene sulfides, polyarylene oxides, polysulfones, modified polysulfone polymers and polyvinyl alcohols, polyamides, polystyrene , polyacrylonitrile, polyvinylidene chloride, polymethylmethacrylate, and polyvinylidene fluoride.

[0081] Solvents used in the polymeric solution for electrostatic spinning of fine fibers include acetic acid, formic acid, m-cresol, trifluoroethanol, hexafluoroisopropanol, chlorinated solvents, alcohols, water, ethanol, isopropanol, acetone, and N-methylpyrrolidone, and methanol. The solvent is appropriately selected according to polymer solubility and desired fine fiber size. For example, a mixture of formic acid and acetic acid can be used with polyamide, also commonly known as nylon, to produce nylon fine fibers that can have an average fine fiber diameter of less than 100 nanometers.

[0082] As described above, in some aspects, the polyamide nanofiber layer is melt spun directly onto the scrim layer. In certain embodiments, no solvent is used when creating the layer of nanofiber filaments. One or more additional layers may then be deposited on top of the polyamide nanofiber layer, for example two more layers, three more layers, four more layers, or five or more layers. In a further aspect, additional layers can be deposited on the side of the scrim layer opposite the polyamide nanofiber layer. In still further aspects, one or more additional scrim layers may be included in the filter. The polyamide nanofiber layer may also be included more than once. In yet another aspect, the polyamide nanofiber layer is not melt spun directly onto the scrim layer, but instead is melt spun onto a different layer. In still yet another embodiment, the scrim layer is omitted and the filter is composed of a polyamide nanofiber layer and other layers described herein. In each of the aspects described above, the polyamide nanofiber layers are sandwiched between other meltspun layers, between electrospun layers, or between meltspun and electrospun layers. can get caught.

[0083] In another aspect of the invention, one or more layers can be combined to create a filtration medium of greater thickness. The additional layers also increase the dirt holding capacity of the media. Interestingly, the fabric efficiency does not increase significantly when more layers are added. This is because the mean flow pore size does not change substantially with the addition of layers, and smaller particles that pass through the first layer continue to pass through the other layers. Layering fabrics provides thicker media and increases the dirt holding capacity of the media, but does not dramatically increase filtration efficiency. Gradient filters can be made by adding another layer of higher filtration efficiency. This gradient filter provides higher filtration efficiency.

[0084] While the above description applies broadly to various applications of filtration media, further description of specific types of filters is provided below.
air filter
[0085] Polyamide nanofiber layers as described herein may be used in air filters. Air filters can be useful in applications including building air circulation systems, vehicles, vacuum cleaners, face masks, respirator filters, and other applications requiring filtered air. Fluid streams such as air and gas streams often carry particulate matter. It is necessary to remove some or all of the particulate matter from the fluid stream. For example, air intake flow to cabins of motorized vehicles, air in computer disk drives, HVAC air, applications with clean room ventilators and filter bags, barrier fabrics, fabrics, air to engines or generators of motorized vehicles. gas streams directed to gas turbines; and air streams to various combustion furnaces often contain particulate matter. For cabin air filters, it is desirable to remove particulate matter for passenger comfort and/or aesthetics. Air and intake air flow to engines, gas turbines and combustion furnaces require particulate matter removal as particulate matter can cause substantial damage to the internal workings of the various mechanisms involved. . In other cases, product gases or off-gases from industrial processes or engines may contain particulate matter. Before such gases can or should be vented to the atmosphere through various downstream equipment, it would be desirable to obtain substantial removal of particulate matter from those streams. .

[0086] Some general understanding of the basic principles and issues of air filter design is through consideration of the following types of filtration media: surface loading media; and depth media. can be understood. Each of these types of media has been well studied and each is widely available. Some principles related to these are described, for example, in US Pat. Nos. 5,082,476; 5,238,474; and 5,364,456. The complete disclosures of these three patents are incorporated herein by reference.

[0087] In some aspects, the polyamide nanofibers can be formed on and adhered to the filter substrate. Natural and synthetic fiber substrates such as spunbond fabrics, nonwovens of synthetic fibers and nonwovens made from blends of cellulose, synthetic and glass fibers, nonwoven and woven glass fabrics, plastic screens such as extrusions and perforations of organic polymers. Opened UF and MF membrane materials can be used. The sheet-like substrate or cellulosic nonwoven web can then be formed into a filter structure that is placed in a fluid stream, including an air stream or a liquid stream, for the purpose of removing suspended or entrained particulate matter from the stream. The shape and structure of the filter material is up to the design engineer. One important parameter of the formed filter element is its resistance to the effects of heat, humidity or both. An important aspect of the filtration media of the present invention is the ability of the filtration media to survive in contact with warm moist air. Polyamide nanofibers in contact with such a hot moist air stream should retain more than 50% of the fibers unchanged for filtration purposes after being exposed to air having a temperature of 60° C. and a relative humidity of 100% for 16 hours. is. One aspect of the filtration media of the present invention is testing the ability of the filtration media to survive immersion in warm water for a significant period of time. Immersion tests show that polyamide nanofibers survive hot, moist conditions and survive washing of filter elements in aqueous solutions that can contain substantial proportions of strong detergent surfactants and substances of strong alkalinity. can provide valuable information about the ability to Preferably, the polyamide nanofibers of the present invention are capable of surviving after immersion in hot water while retaining at least 50% or even at least 75% of the fibrils formed on the surface of the substrate as an active filter component. can. Retention of at least 50% polyamide nanofibers can maintain substantial fiber efficiency without loss of filtration capacity or increased back pressure. A typical polyamide nanofiber filtration layer has a thickness in the range of 0.001 to 5 microns, such as 0.01 to 3 microns, and a polyamide nanofiber basis weight of about 0.01 to 240 micrograms/cm ^{2 .} is in the range of The polyamide nanofiber layer formed on the filter substrate should be substantially uniform in both filtration performance and fiber arrangement. Substantial uniformity means that the fibers have sufficient coverage of the substrate to have at least some measurable filtration efficiency across the coated substrate. Adequate filtration can occur with wide variations in fiber add-on. Thus, polyamide nanofiber layers may vary in fiber coverage, basis weight, layer thickness or other measures of fiber add-on and still be well within the bounds of the present invention. Even relatively small add-ons of fine fibers can add efficiency to the overall filter structure.

[0088] Filter "lifetime" is typically defined according to a selected limiting pressure drop across the filter. The pressure rise across the filter defines life at a level defined for its application or design. Since this pressure rise is a result of load, longer life is usually directly related to higher capacity for systems of equal efficiency. Efficiency is the propensity of a medium to trap rather than pass particulate matter. In general, the more efficient a filtration medium is in removing particulate matter from a gas stream, generally the more rapidly the filtration medium (assuming other variables are held constant). Approaching differential "lifetime" pressures. In this application, the term "unchangeable for filtration purposes" means maintaining efficiency sufficient to remove particulate matter from a fluid stream as required for the chosen application.

[0089] Paper filter elements are a widely used form of surface loading media. Generally, the paper element comprises a dense mat of cellulose, synthetic or other fibers oriented across a gas stream carrying particulate matter. The paper is generally permeable to gas streams and is constructed with sufficiently small pore sizes and suitable porosity to prevent the passage of particles larger than a selected size. As the gas (fluid) passes through the filter paper, the upstream surface of the filter paper operates by diffusion and interception to capture and retain particles of a selected size from the gas (fluid) stream. Particles are collected as a dust cake on the upstream face of the filter paper. Over time, the dust cake also begins to act as a filter, increasing efficiency. This is sometimes referred to as "seasoning" and is the development of an efficiency greater than the initial efficiency.

[0090] Simple filter designs such as those described above are subject to at least two types of problems. First, failure of the system occurs as a result of a relatively simple flaw, namely a paper break. Second, particulate matter quickly accumulates as a thin dust cake or layer on the upstream face of the filter, increasing pressure drop. Various methods have been applied to increase the "life" of surface loaded filter systems such as paper filters. One method is to provide the media with a pleated structure to increase the surface area of the media encountered by the flow of the gas stream compared to a flat, non-pleated structure. Although this increases filter life, it is still substantially limited. For this reason, the surface loading media primarily has relatively low velocities through the filtration media, generally no higher than about 20-30 feet per minute (1 foot = 0.3048 m), typically on the order of about 10 feet per minute or less. There are applications where speed is a concern. The term "velocity" in this context is the average velocity through the medium (ie flow volume per medium area).

[0091] In general, as air flow velocity through fluted paper media is increased, filter life is reduced at a rate proportional to the square of the velocity. Therefore, when a pleated paper surface-loaded filter system is used as a particulate filter for systems requiring substantial flow of air, a relatively large surface area is required for the filtration media. For example, a typical cylindrical pleated paper filter element for an over-the-highway diesel truck is about 9-15 inches in diameter, about 12-24 inches long, and about 1-2 inches deep. It has folds. Therefore, the filtration surface area (one side) of the media is typically 30 to 300 square feet.

[0092] In many applications, particularly those involving relatively high flow rates, an alternative type of filtration media, sometimes commonly referred to as "depth" media, is used. A typical depth medium includes relatively thick tangles of fibrous material. Depth media is generally defined in terms of its porosity, density or percent solids. For example, a 2-3% solid media is a depth media mat of fibers arranged such that approximately 2-3% of the total volume comprises fibrous material (solids) and the remainder is air or gas space. be.

[0093] Another useful parameter for defining depth media is fiber diameter. If the percent solids is held constant, but the fiber diameter (size) is reduced, the pore size or inter-fiber space is reduced, i.e. the filter becomes more efficient, trapping smaller particles more effectively do.

[0094] A typical conventional depth media filter is a deep, relatively constant (or uniform) density media, i.e., the solidity of the depth media remains substantially constant throughout its thickness. system. "Substantially constant" in this context means that the density varies relatively little, if any, over the depth of the medium. For example, such fluctuations may be the result of slight compression of the outer engagement surface by the container in which the filtration media is placed.

[0095] A gradient density depth media arrangement has been developed. Some such arrangements are described, for example, in US Pat. Nos. 4,082,476; 5,238,474; and 5,364,456. In general, a depth media arrangement can be designed to provide a "load" of particulate matter substantially throughout its volume or depth. Therefore, such an arrangement can be designed to load a higher amount of particulate matter relative to a surface-loaded system when sufficient filter life is reached. However, since relatively low solids media are generally desirable for substantial loads, the trade-off for such an arrangement was efficiency. Gradient density systems, such as those of the above-mentioned patents, are designed to provide substantial efficiency and longer life. In some instances, surface loading media are utilized as "polish" filters in such arrangements.

[0096] The filtration media construction of the present invention includes a first layer of permeable coarse fibrous media or substrate having a first surface. A first layer of polyamide nanofiber media is secured to the first surface of the first layer of permeable coarse fibrous media and a second layer of polyamide nanofibers is secured to the substrate. The first layer of preferably permeable coarse fibrous material comprises fibers having an average fiber diameter of at least 10 microns, typically and preferably from about 12 (or 14) to 30 microns. Also preferably, the first and second layers of permeable coarse fibrous material have a basis weight of about 200 gsm (grams per meter ² or g/m ² ) or less, preferably about 0.50 to 150 gsm, most preferably at least 8 gsm. Including medium with quantity. The first layer of preferably permeable coarse fibrous media is at least 0.0005 inches (12 microns) thick, typically and preferably about 0.001 to 0.030 inches (25-800 microns) thick. thickness.

[0097] In some arrangements, the first layer of permeable coarse fibrous material, as assessed by the Frazier Permeability Test independently of the rest of the structure, is at least 1 meter/min, typically and preferably Including materials that exhibit a transmittance of about 2-900 meters/min (about 0.03-15 m-sec ^-1 ). When referring to efficiencies herein, unless otherwise specified, 0.78μ monodisperse polystyrene spherical particles are used as described herein according to ASTM-1215-89 at 20 fpm (6.1 meters/min). Refers to efficiency when measured.

[0098] In some aspects, the layer of polyamide nanofibers fixed to the first surface of the layer of permeable coarse fibrous media is a layer of nano- and microfiber media, and the fibers are about 2 microns or less. generally and preferably have an average fiber diameter of less than about 1 micron, typically and preferably less than 0.5 micron and within the range of about 0.05 to 0.5 micron. Also preferably, the first layer of fine fibrous material secured to the first surface of the first layer of permeable coarse fibrous material is about 30 microns or less, more preferably 20 microns or less, most preferably about It has an overall thickness of no greater than 10 microns, and typically and preferably within a thickness of about 1 to 8 times (more preferably no greater than 5 times) the fine fiber average fiber diameter of the layer.

[0099] Some aspects include filtration media broadly defined within the overall filter structure. Some preferred arrangements for such use include media arranged in a cylindrical pleated configuration, with the pleats generally extending longitudinally, ie, in the same direction as the long axis of the cylindrical pattern. With such an arrangement, the media can be embedded in the end caps in the same manner as conventional filters. Such an arrangement may include typical conventional purpose upstream liners and downstream liners if desired.

[0100] In some applications, the media of the present invention may be used with other types of media, such as conventional media, to improve overall filtration performance or life. For example, the media of the present invention may be laminated to conventional media, utilized in a stacked arrangement; or incorporated (as an essential feature) within a media structure that includes one or more regions of conventional media. It can also be used upstream of such media for good loading; and/or downstream of conventional media as a high efficiency abrasive filter.

[0101] Some arrangements of the present invention may also be utilized in liquid filter systems, ie, where the particulate matter to be filtered is carried in a liquid. In certain applications, such as hot fluids, the melting point of nylon nanofiber fabrics offers certain advantages. The melting point of the nylon nanofiber fabric may be 223°C to 360°C, such as 225°C to 350°C. Also, some arrangements of the present invention may be used in mist collectors, such as devices for filtering fine mist from air.

[0102] Various filter designs are shown in patents that disclose and claim various aspects of filter constructions and constructions used with filter materials. U.S. Pat. No. 4,720,292 discloses a radial seal design for a filter assembly having a generally cylindrical filter element design, the filter element being a relatively soft rubber seal having a cylindrical, radially inwardly facing surface. It is sealed with a similar end cap. US Pat. No. 5,082,476 discloses a filter design using a depth media comprising a foam substrate having a pleated component combined with the microfiber material of that invention. US Pat. No. 5,104,537 relates to filter structures useful for filtering liquid media. Liquid is entrained within the filter housing, passes through the exterior of the filter into the inner annular core, and then returns to active use within the structure. Such filters are extremely useful for filtering hydraulic fluids. US Pat. No. 5,613,992 shows a typical diesel engine air intake filter construction. This structure draws air, which may contain entrained moisture, from the outer surface of the housing. Air passes through the filter, but moisture can pass through the bottom of the housing and out of the housing. U.S. Pat. No. 5,820,646 discloses a Z filter construction, which requires fluid flow to pass through at least one layer of filtration media in a "Z" shaped passageway to obtain adequate filtration performance. It uses a specific pleated filter design that contains blocked passages with . Filtration media formed into a pleated Z-shape can contain the fine fiber media of the invention. US Pat. No. 5,853,442 discloses a baghouse structure with filter elements that can contain the fine fiber structure of that invention. U.S. Pat. No. 5,954,849 is useful in processing air having a high dust load to filter dust from air streams after processing workpieces that typically produce a significant dust load in the ambient atmosphere. Figure 2 shows a dust collector structure; Finally, US Design Patent No. 425,189 discloses a panel filter using a Z filter design.

[0103] The media can be polyester synthetic media, media made from cellulose, or blends of these types of materials. One example of cellulose media that can be used is: basis weight of about 45-55 lbs. /3000 ft ² (84.7 g/m ² ), eg, 48-54 lbs. /3000 ft ² ; about 0.005 to 0.015 inches thick, such as about 0.010 inches. (0.25 mm); frazier permeability about 20-25 ft/min, such as about 22 ft/min (6.7 m/min); pore size about 55-65 microns, such as about 62 microns; wet tensile strength at least about 7 lbs/in, eg 8.5 lbs. /in (3.9 kg/in); mechanical burst strength of about 15-25 psi, eg, about 23 psi (159 kPa). Cellulose media can be treated with fine fibers, eg, fibers having a size (diameter) of 5 microns or less, and in some instances submicron. Various methods can be utilized to apply the fine fibers to the medium if it is desired to use them. Some such approaches are characterized, for example, in US Pat. No. 5,423,892, column 32, lines 48-60. More specifically, such methods are disclosed in U.S. Pat. Nos. 3,878,014; 3,676,242; 3,841,953; 849,241. Sufficient fines are typically applied until the resulting media construction has an individual test of 50 to 90% and an overall efficiency of greater than 90% tested according to SAE J726C using SAE fine dust.

[0104] Examples of filter structures that can be used are described in US Patent No. 5,820,646. In another example embodiment, the grooved structure (not shown) includes tapered flutes. By "tapered" is meant that the flute widens along its length such that the downstream opening of the flute is larger than the upstream opening. Such filter structures are described in US Application Serial No. 08/639,220, which is incorporated herein by reference in its entirety. Details regarding fine fibers and their materials and manufacture are disclosed in US Application Serial No. 09/871,583, which is incorporated herein by reference.

[0105] Various filter designs are shown in the patents that disclose and claim various aspects of filter construction and structures used with filter materials. US Pat. No. 7,008,465 discloses a filter design that can be used in wet-dry vacuums. U.S. Pat. No. 4,720,292 discloses a radial seal design for a filter assembly having a generally cylindrical filter element design, the filter element being a relatively soft, rubber-like seal having a cylindrical, radially inwardly facing surface. are sealed by the end caps of the US Pat. No. 5,082,476 discloses a filter design using a depth media comprising a foam substrate having a pleated component combined with the microfiber material of that invention. US Pat. No. 5,104,537 relates to filter structures useful for filtering liquid media. Liquid is entrained within the filter housing, passes through the exterior of the filter and into the inner annular core before returning to active use within the structure. Such filters are extremely useful for filtering hydraulic fluids. US Pat. No. 5,613,992 shows a typical diesel engine air intake filter construction. The structure draws air, which may contain entrained moisture, from the outer surface of the housing. Air passes through the filter, but moisture can pass to the bottom of the housing and out of the housing. U.S. Pat. No. 5,820,646 describes a blocked passageway that requires fluid flow to pass through at least one layer of filtration media in a "Z" shaped passageway for adequate filtration performance. Disclosed is a Z-filter structure that uses a particular pleated filter design that includes: Filtration media formed into a pleated Z-shape can contain the fine fiber media of the invention. US Pat. No. 5,853,442 discloses a baghouse structure having filter elements that can contain the fine fiber structure of that invention. Berkhoel et al. U.S. Pat. No. 5,954,849 to Ambient Air for filtering dust from an air stream after processing a workpiece that produces a substantial dust load in the ambient atmosphere, useful in treating air that typically has a high dust load. Figure 2 shows a dust collector structure; Finally, Gillingham, US Design Patent No. 425,189, discloses a panel filter using a Z filter design.

oil filter
[0106] Oil filters intended for use in combustion engines traditionally include filtration media having fibers derived from wood pulp. Such wood pulp fibers are typically 1 to 7 millimeters long and 15 to 45 microns in diameter. Natural wood pulp has been a preferred raw material for producing filtration media primarily due to its relatively low cost, processability, various mechanical and chemical properties, and end-use durability. The filtration media are pleated to increase the filtration surface area transversely to the direction of oil flow.

[0107] U.S. Patent No. 3,288,299 discloses a two-sided oil filter cartridge in which part of the flow is through a surface-type filter element, such as pleated paper, and the remaining flow is through a depth-type filter element. of filter elements, such as thick fibrous masses. An oil filter and adapter is disclosed in US Pat. No. 3,912,631.

[0108] A typical oil filter includes a pleated filtration media with a backing structure. Conventional filtration media exhibit low stiffness and have poor mechanical strength in terms of tensile strength and burst strength. Therefore, the filtration media is used with metal mesh or other types of pleated configurations when used in end applications.

[0109] Nevertheless, due to their low mechanical strength, filtration media tend to rupture over time when exposed to engine oil at temperatures encountered in combustion engines, eg, 125 to 135°C.

[0110] Filtration media products made primarily of wood pulp are still an excellent choice for most automotive and heavy-duty oil filtration applications, but the media may be subject to a variety of chemical, thermal, and mechanical impacts in the end-use environment. There is an increasing market demand for oil filtration products that exhibit increased strength and durability over time when exposed to stress. This demand arises from both the more severe end-use conditions to which the media are exposed as well as the increasing demand for filtration media that can be safely used in end-use applications for increasingly longer periods of time without bursting or failing.

[0111] A long-standing and widely used solution to this need has been to incorporate some minor amount of synthetic fibers, typically PET polyester, in amounts of about 5-20%. The result of this reinforcing fiber feature is higher media strength and enhanced chemical properties due to the superior chemical, thermal, and mechanical durability of the synthetic fiber itself when the media is exposed to the end-use environment. and mechanical durability.

[0112] There are alternative technical solutions based primarily on non-natural fibers described in the art for air filters. US Pat. No. 7,608,125 describes about 20-60 wt. % glass fiber, about 15-60 wt. % polymer fibers and about 15-40 wt. % binder is disclosed. The binder of this disclosure is a latex modified with melamine formaldehyde.

[0113] US Patent Application Publication No. 2012/0175298 discloses a HEPA filter comprising a nonwoven web of two different fiber compositions. The first fibrous component is formed from at least 20% by weight of the web of polyester, polyamide, polyolefin, polylactide, cellulose ester, polycaprolactone fibers. The second fiber can be composed of cellulose fibers (Lyocell) or glass or a combination of the two. Additionally, there are binder components formed from acrylic polymers, styrenic polymers, vinyl polymers, polyurethanes, and combinations thereof.

[0114] US Patent Application Publication No. 2013/0233789 discloses a glass-free nonwoven fuel filtration media comprised of a blend of staple synthetic fibers and fibrillated cellulose fibers.

[0115] US Pat. disclose. In fact, known filtration media containing a high proportion of synthetic fibers cannot be pleated or self-supporting on their own, but are pleated together using some sort of additional mechanical support layer, such as a plastic or wire mesh backing. should be reinforced.

[0116] Media made with high levels of synthetic fibers typically have a tendency to drape and lack sufficient stiffness and stiffness, causing the pleats to collapse without additional support. The 100% synthetic media disclosed in the art cannot maintain grooved patterns such as corrugations or pleated structures due to the thermal and mechanical properties of synthetic fibers. The fibrous media of the present invention is readily grooveable, ie, corrugable and pleatable. And this material can retain most of its original groove depth (or corrugation depth) even after long exposure times in hot engine oil having a temperature of, for example, 140°C. This feature also contributes to the extended operational life of the fibrous media.

[0117] Some oil filters can also omit expensive backing materials, allowing for more easily grooved (or corrugated) and pleatable filters. The end result is the ability to produce filters from this fibrous media without a supporting backing material while also achieving significantly higher burst strength than is possible with traditional types of oil filtration media containing wood pulp, aided by glycol. excellent resistance to decay and excellent dust filtration capacity and particle removal efficiency.

[0118] By incorporating a polyamide nanofiber layer into the oil filter, some of the above problems may be alleviated due to the above-mentioned benefits of the polyamide nanofiber layer.
[0119] Like the other filtration media described herein, the oil filter is typically a multi-layer filter. Representative thermoplastic fibers suitable for additional layers within the oil filter include polyesters (e.g., polyalkylene terephthalates such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.), polyalkylenes (e.g., polyethylene, polypropylene etc.), polyacrylonitrile (PAN), as well as additional polyamide layers (nylon, eg, nylon-6, nylon 6,6, nylon-6,12, etc.). Preferred are PET fibers that exhibit good chemical and thermal resistance, properties that are important for use as media oil filters.

[0120] In certain embodiments, the thermoplastic synthetic fibers are selected from fibers having an average fiber diameter of 0.1 μm to 15 μm, such as 0.1 μm to 10 μm, and an average length of 1 to 50 mm, such as 1 to 20 mm. In general, fibers with a length greater than 5 mm, especially greater than 10 mm are preferred for good burst strength. In the context of the present invention, "silica-like fibers" primarily mean "glass" fibers, such as microglass fibers.

[0121] Such fibers generally have an aspect ratio (ratio of length to diameter) of 1,000 to 1. In one embodiment, the glass fibers have an average fiber diameter of 0.1 μm to 5 μm and an aspect ratio of 1,000 to 1. In particular, glass fibers may have an average fiber diameter of 0.4 to 2.6 μm. Glass fibers are preferably included in an amount sufficient to improve the efficiency of the fibrous media as a filter. In one embodiment, the synthetic fibers are 30 wt. %, preferably 20 wt. Contains up to % glass fiber. Synthetic fibers are 30 wt. % or less or 20 wt. % glass fibers, but this amount is sufficient to produce fibrous media for filter examples. Typically, prior art synthetic filtration media contain large amounts of glass fibers in order to achieve sufficient filtration efficiency of gases or liquids even at high temperature conditions, such as 150°C. However, the use of less glass fibers in the claimed fibrous media may provide the fibrous media with superior filtration properties in terms of particle removal efficiency and hot oil burst strength. In a particularly preferred embodiment there are at least two types of glass fibers, namely a first group of fibers with an average fiber diameter of less than 1 μm and a second group of fibers with an average fiber diameter of 2 μm or more. The weight ratio of the two groups of fibers is generally 1:100 to 100:1, especially about 1:10 to 10:1. The synthetic fibers may also comprise up to 40%, preferably up to 30% by weight of regenerated cellulosic material such as Lyocell or viscose or combinations thereof, based on the total weight of the fibres.

[0122] The filtration media may be contained in canisters, such as single or dual canisters. Each canister may have an inlet and an outlet for respectively introducing oil flow and removing filter oil. The filtration media within each canister may be different to allow for different filtration capabilities. For example, a first canister contains a filter housing for full channel filtration, while a second canister contains a filter housing for reduced channel filtration. US Patent Application Publication No. 2008/0116125 describes such dual canisters in detail.

bag filter
[0123] Bag filters are described in the art, for example, in US Patent No. 7,318,852 and US Patent Application Publication No. 2009/2055226. Dust collectors, also known as baghouses, are widely used to filter particulate matter from industrial effluents or offgases. Once filtered, the cleaned off-gas can be vented to the atmosphere or recycled. Such baghouse dust collector structures generally include one or more flexible filter banks supported within a cabinet or similar structure. In such filter cabinets and banks, the filter bags are generally fixed within the cabinet and maintained in a position such that the waste liquid efficiently passes through the bags to remove entrained particulate matter. A filter bag secured within a cabinet is typically supported by a structure that separates upstream and downstream air and supports the filter bag to maintain efficient operation.

[0124] More specifically, in so-called "baghouse filters", particulate matter is removed from a gas stream as the stream is directed through a filtration medium. In a typical application, the filtration medium generally has a sleeve-like tubular shape and is arranged such that the gas stream deposits the particles to be filtered on the exterior of the sleeve. In this type of application, the filtration media is periodically cleaned by subjecting the media to a pulsed reverse flow, which removes filtered particulate matter from the exterior of the sleeve and into the lower portion of the baghouse filter structure. act to collect U.S. Pat. No. 4,983,434 illustrates baghouse filter construction and prior art filter laminates.

[0125] Separation of particulate matter impurities from industrial fluid streams is often accomplished using woven fabric filters. These fabric-based filtration media remove particulate matter from fluids. When the resistance to flow or pressure drop across the fabric caused by the accumulation of particulate matter on the filter becomes appreciable, the filter must be cleaned and the particulate cake removed.

[0126] Characterizing filter bag types by cleaning method is common in the industrial filtration market. The most common types of cleaning techniques are reverse air, shaker and pulse jet. Backwash and shaker techniques are considered low energy cleaning techniques.

[0127] The backwash technique is a gentle backflow of air through a filter bag that collects dust inside. Backflow crushes the bag and bursts the dust cake out the bottom of the bag into the hopper. The shaker mechanism also cleans filter cake that collects inside the bag. The top of the bag is attached to a vibrating arm that creates a sine wave within the bag to dislodge the dust cake. Pulse-jet cleaning technology uses short pulses of compressed air that enter the top of the interior of the filter tube. The pulsed cleaning air aspirates secondary air as it passes through the tube venturi and the resulting air mass violently expands the bag and shakes off the collected dust cake. The bag typically folds back to the cage support and begins collecting particulate matter again.

[0128] Of the three cleaning techniques, pulse jet is the most stressful to the filtration media. In recent years, however, industrial process engineers have increasingly opted for pulse jet baghouses.

[0129] The need for chemically resistant filtration media that is thermally stable at high temperatures (up to 200°C) in the baghouse narrows the selection of filtration media for pulse jet applications to few viable candidates. Common high temperature fabrics include polytetrafluoroethylene (PTFE), fiberglass, or polyimide (polyimide is stable for continuous use up to 260°C). The effects of high temperatures combined with the effects of oxidizing agents, acids or bases tend to prematurely fail glass fiber and polyimide media. Therefore, it is preferred to use PTFE. A commercially available PTFE fabric is PTFE fiber supported needle felt. These felts typically weigh 20-26 oz/ ^yd2 and are reinforced with a multifilament woven scrim (4-6 oz/yd2). Felt is made of staple fibers (usually 6.7 denier/filament, or 7.4 dtex/filament) and is 2-6 inches long. This product functions similarly to many other felt media in that the primary dust cake "seasons" the bag. This seasoning, sometimes called in-depth filtration, causes the media to filter more efficiently, but has the disadvantage that the pressure drop across the media increases during use. Eventually the bag will confuse or clog and the bag must be washed or replaced. In general, the media have low filtration efficiency, are distracting, and are not dimensionally stable at elevated temperatures (shrinkage).

[0130] Another type of structure designed for high temperatures is described in US Patent No. 5,171,339. A bag filter is disclosed that includes a bag retainer with a filter bag. The filter bag fabric comprises a felt laminate of poly(m-phenylene isophthalamide), polyester or polyphenylene sulfide fibers needled with a thin non-woven fabric of poly(p-phenylene terephthalamide) fibers; ) The fabric is placed on the surface of the filter bag that is first exposed to the hot particle-carrying gas stream. The poly(p-phenylene terephthalamide) fabric can have a basis weight of 1 to 2 oz/yd2.

[0131] Bilayer products of a porous expanded PTFE (ePTFE) membrane laminated to a woven porous expanded PTFE fiber fabric have also been used. Commercial success of this product has not materialized for several reasons, but primarily due to the non-permanent woven fiber fabric backing on the pulse jet cage support. The woven yarn slips on itself, creating excessive stress in the membrane, resulting in cracking of the membrane.

[0132] Nonwoven fabrics have been advantageously used in the manufacture of filtration media. Generally, nonwoven fabrics used in this type of application are entangled and consolidated by mechanical needle punching, sometimes referred to as "needle felting". This entails repeated insertion and withdrawal of barbed needles through the fibrous web structure.

[0133] US Patent No. 4,556,601 discloses hydroentangled nonwoven fabrics that can be used as heavy duty gas filters.

[0134] US Patent No. 6,740,142 discloses nanofibers used in baghouse filters. The flexible bag is at least partially covered with a layer having a basis weight of 0.005 to 2.0 grams per square meter (gsm) and a thickness of 0.1 to 3 microns. The layer contains polymeric fibrils of about 0.01 to about 0.5 microns in diameter, but is limited in basis weight due to limitations in the processes used to produce it.

[0135] In some aspects, the filter has a basis weight of greater than about 0.1 gsm, or greater than about 0.5 gsm, or greater than about 5 gsm, or even greater than about 10 gsm and no greater than about 90 gsm. can include a filtration medium comprising a nanoweb layer stabilized at a The filtration media further includes a substrate to which the nanowebs are bonded in face-to-face relationship. Advantageously, the nanoweb layer is disposed on the upstream face or side of the filter bag, ie the surface first exposed to the hot particle-carrying gas stream.

[0136] In a further embodiment, the filter is a composite of a first substrate layer having a thermally stabilized nanoweb bonded in face-to-face relationship, and a second substrate layer bonded to the nanoweb layer. wherein the nanoweb is positioned upstream of the filter bag, ie, the surface of the filter bag that is first exposed to the hot particle-carrying gas stream, and the nanoweb has a basis weight greater than about 0.1 gsm. In some cases the second substrate layer is advantageously arranged between the nanoweb and the first substrate layer, in other cases the nanoweb layer is arranged between the first and second substrate layers. is desirable.

[0137] Polymers useful for electroblowing or meltblowing the nanofiber webs of the present invention are polyamides (PA), preferably polyamide 6, polyamide 6,6, polyamide 6,12, polyamide 11, polyamide 12, polyamide 4, 6. Polyamides selected from the group consisting of semi-aromatic polyamides, high temperature polyamides and any combination or blend thereof. Polyamides (PA) used in making the blend compositions of the present invention are well known in the art. Representative polyamides include, for example, the molecular weights described in U.S. Pat. Nos. 4,410,661; 4,478,978; 4,554,320; Included are at least 5,000 semi-crystalline and amorphous polyamide resins.

[0138] Polyamides, such as copolymers of adipic acid, isophthalic acid and hexamethylenediamine, or blends of polyamides, obtained according to the present invention by copolymerization of two of the above polymers, terpolymerization of the above polymers or their component monomers Mixtures can also be used, for example mixtures of PA6,6 and PA6. Preferably, the polyamide is linear and has a melting or softening point above 200°C.

[0139] Such polyamides formed by electrospinning may be used in addition to polyamide nanofiber layers of the present invention formed by melt spinning. The polyamides used to spin the fibers contain thermal stability additives such as antioxidants. Antioxidants suitable for use in the present invention are substances that are soluble in the spinning solvent along with the polyamide if the polyamide is spun from solution. Examples of such materials are copper halides and hindered phenols. By "hindered phenol" is meant a compound whose molecular structure contains a phenolic ring bearing an alkyl group on one or both of the carbon atoms cis to the hydroxyl moiety. Alkyl groups are preferably tertiary butyl moieties and both adjacent carbon atoms carry tertiary butyl moieties.

[0140] Antioxidants include, but are not limited to: phenolic amides such as N,N'-hexamethylenebis(3,5-di-(tert)-butyl-4-hydroxyhydrocinnamamide ) (Irganox 1098); amines such as various modified benzenamines (eg Irganox 5057); phenolic esters such as ethylenebis(oxyethylene)bis-(3-(5-tert-butyl-4-hydroxy-m-tolyl). )-propionate (Irganox 245) (all available from Ciba Specialty Chemicals Corp., Tarrytown, N.Y.); a mixture of organic or inorganic salts such as cuprous iodide, potassium iodide, and zinc octadecanoate. (available from Ciba Specialty Chemicals Corp., Tarrytown, N.Y. as Polyad 201) and (available from Polyad Services Inc., Earth City, Mo. as Polyad 1932-41), copper acetate, potassium bromide, and a mixture of calcium salts of octadecanoic acid; hindered amines such as 1,3,5-triazine-2,4,6-triamine, N,N′″-[1,2-ethane-diyl-bis[[[4,6 -bis-[butyl(1,2,2,6,6-pentamethyl-4-piperidinyl)amino]-1,3,5-triazin-2-yl]imino]-3,1-propanediyl]]bis[ N′,N″-dibutyl-N′,N″-bis(1,2,2,6,6-pentamethyl-4-piperidinyl) (Chimassorb 119 FL), 1,6-hexanediamine, N,N′- Bis(2,2,6,6-tetramethyl-4-piperidinyl)-polymer with 2,4,6-trichloro-1,3,5-triazine, reaction product with N-butyl-1-butanamine and N- Butyl-2,2,6,6-tetramethyl-4-piperidinamine (Chimassorb 2020), and poly[[6-[(1,1,3,3-tetramethylbutyl)amino]-1,3,5 -triazine-2,4-diyl][2,2,6,6-tetramethyl-4-piperidinyl)imino]-1,6-hexanediyl[(2,2,6,6-tetramethyl-4-piperidinyl ) imino]]) (Chimassorb 944) (all from Ciba Specialty Chemicals Corp.). , Tarrytown, N.L. Y. polymeric hindered phenols, such as 2,2,4-trimethyl-1,2-dihydroxyquinoline (Ultranox 254, Crompton Corporation, a subsidiary of Chemtura Corporation, Middlebury, Conn., 06749); hindered phosphites, such as bis (2,4-di-t-butylphenyl) pentaerythritol diphosphite (Ultranox 626 from Crompton Corporation, a subsidiary of Chemtura Corporation, Middlebury, Conn., 06749); ) phosphite (Irgafos 168 of Ciba Specialty Chemicals Corp., Tarrytown, NY); 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid (Fiberstab PA6, Ciba Specialty Chemicals Corp.); . Co., Inc., Tarrytown, N.Y.), and combinations and blends thereof.

[0141] Antioxidants used as stabilizers may be from 0.01 to 10% by weight, especially from 0.05 to 5% by weight of the polyamide layer formed by electrospinning.
[0142] The substrate layer of the bag filter can be made of various conventional fibers such as cellulosic fibers such as cotton, hemp or other natural fibers, inorganic fibers such as glass fibers, carbon fibers or organic fibers such as polyesters, polyimides, polyamides, polyolefins. , or other conventional fibrous or polymeric materials and mixtures thereof.

[0143] The substrate layer of the filter bags of the present invention can be woven or non-woven. In woven bags, the fibers are typically formed into an interlocking mesh of fibers in a typical woven format. Nonwoven fabrics are typically made by loosely forming fibers with no particular orientation and then bonding the fibers to a filter fabric. One aspect of constructing the elements of the present invention involves using felt media as the substrate. Felt is a compacted porous nonwoven fabric made by arranging separate natural or synthetic fibers and compressing the fibers into a felt layer using commonly available felting techniques known to those skilled in the art.

[0144] Fibers are typically used that yield woven fabrics that exhibit excellent resilience and resistance to the effects of air passage and particulate matter entrapment. The woven fabric can have chemical particulate matter stability and can be stable to varying temperatures of the air passing through the baghouse and the particulate matter entrained on the filter surface. can.

[0145] The filter structure of the present invention is typically maintained in its useful open shape by supporting the substrate plus nanoweb layer composite to a suitable support structure, such as a retainer at the neck of the bag, or a support structure. can be placed inside the bag. Such supports may be formed from linear members in the form of windings or structures such as cages. Alternatively, the support can comprise a perforated ceramic or metal structure that mimics the shape of the bag. If the support structure contacts the filter substrate over a significant percentage of its surface area, the support structure should be permeable to the passage of air through the structure, increasing the pressure drop across the filter bag. shouldn't. Such a support structure can be configured to contact the entire interior of the filter bag and maintain the filter bag in an efficient filtering configuration or configuration.

[0146] The process by which the nanoweb layer is combined with the substrate to produce the composite structure is not particularly limited. The nanofibers of the nanoweb layer can be physically entangled within the substrate layer or joined by intermingling the fibers of the nanoweb layer with the fibers of the substrate, such as by thermal bonding or ultrasonic lamination or bonding. be able to.

[0147] Thermal methods of bonding the substrate layer to the nanoweb layer or nanoweb plus substrate layer include calendering. "Calendering" is the process of passing a web through a nip between two rolls. The rolls may contact each other or may be fixed or with a variable gap between the roll surfaces.

[0148] Advantageously, in the calendering process, a nip is formed between a soft roll and a hard roll. A "soft roll" is a roll that deforms under pressure applied to hold two rolls together in the calender. A "rigid roll" is a roll with a surface that does not undergo deformation under the pressure of the process that has a significant effect on the process or product. A "blank" roll is one that has a smooth surface within the capabilities of the process used to manufacture it. Unlike point-bonding rolls, there are no dots or patterns that intentionally create a pattern on the web as it passes through the nip. The stiff roll in the calendering process used in the present invention can be patterned or plain.

[0149] Adhesive lamination can be performed in conjunction with calendering or by applying pressure to the laminate by other means at low temperatures, such as room temperature, in the presence of a solvent-based adhesive. Alternatively, hot melt adhesives can be used at elevated temperatures. Those skilled in the art will readily recognize suitable adhesives that can be used in the process of the present invention.

[0150] Examples of methods of entangling fibers according to such physical bonding are needlepunching and waterjet processing, otherwise known as hydroentangling or spunlacing. As disclosed in U.S. Pat. Nos. 3,431,611 and 4,955,116, needle punching (or needling) essentially forces individual fibers in small bundles through a card batt of fibers. and forcing it through a number of perforations such that a cohesive fabric structure is formed.

[0151] In the process of making the filters of the present invention, it is desirable to needlepunch (or waterjet) the dense layer (substrate) side of the nonwoven. Needle-punching on the high-density layer side reduces pore collapse or deformation associated with twisting, as well as undesirable pore size, compared to when needle-punching is performed on the low-density layer (nanoweb) side. By reducing the expansion, the initial loss of cleaning efficiency for smaller particles can be reduced. It is preferred to set the number of needles per unit area (number of perforations) in the range of about 40 to about 100 perforations/cm 2 in order to limit undesirable expansion of pore size and to provide sufficient twisting action. Additionally, no more than about 25% of the surface area of the low density layer should be perforated.

[0152] Freshly spun nanowebs may comprise nanofibers produced primarily or exclusively by electrospinning, such as classical electrospinning or electroblowing, and in some circumstances by meltblowing or other such suitable processes. Classical electrospinning is a technique described in US Pat. No. 4,127,706 in which high voltage is applied to polymers in solution to create nanofibers and nonwoven mats. However, the overall throughput in the electrospinning process is too low to be commercially viable in forming higher basis weight nanowebs.

[0153] An "electric blow" process is disclosed in WO 03/080905. A stream of polymeric solution containing polymer and solvent is fed from a storage tank to a series of spin nozzles in the spinneret, through which a high voltage is applied and the polymeric solution is expelled. On the other hand, compressed air, which may optionally be heated, is emitted from air nozzles arranged at or around the face of the spinning nozzle. A polymeric solution is advanced to help form a fibrous web, which is collected on a grounded porous collection belt above the vacuum chamber. The electroblowing process enables the formation of nanowebs of commercial size and quantity in relatively short times at basis weights greater than about 1 gsm and even as high as about 40 gsm or greater.

[0154] The substrate can be placed on a collector to collect and combine the spun nanofiber web on the substrate. Examples of substrates can include various nonwovens such as meltblown nonwovens, needlepunched or spunlaced nonwovens, woven fabrics, knitted fabrics, paper, etc., without limitation as long as the nanofiber layer can be added onto the substrate. can be used for Nonwovens can comprise spunbond fibers, dry or wet laid fibers, cellulosic fibers, meltblown fibers, glass fibers, or blends thereof. Alternatively, the nanoweb layer can be deposited directly onto the felt substrate.

[0155] To lower the Tg of the fiber polymer, it can be advantageous to add plasticizers known in the art to the various polymers described above. Suitable plasticizers will depend on the electrospun or electroblown polymer as well as the particular end use into which the nanoweb will be introduced. For example, nylon polymers can be plasticized with water or even residual solvent from electrospinning or electroblowing processes. Other art known plasticizers that can be useful in lowering polymer Tg include, but are not limited to, aliphatic glycols, aromatic sulphanamides, phthalates selected from the group consisting of, but not limited to, dibutyl phthalate, dihexyl phthalate, dicyclohexyl phthalate, dioctyl phthalate, diisodecyl phthalate, diundecyl phthalate, didodecanyl phthalate, and diphenyl phthalate; The Handbook of Plasticizers, edited by George Wypych, 2004 Chemtec Publishing, incorporated herein by reference, discloses other polymer/plasticizer combinations that can be used in the present invention.

liquid filter
[0156] Liquid filtration media are often used to filter microorganisms. Biopharmaceutical manufacturing is constantly looking for ways to streamline operations, combine and eliminate steps, and reduce the time it takes to process each batch of pharmaceutical drug substance. At the same time, market and regulatory pressures are driving down the cost of manufacturing biopharmaceuticals. Since bacteria, mycoplasma and virus removal represent a significant percentage of the total cost of purification of drug substances, measures to increase the filtration throughput of porous membranes and reduce the purification process time are in great demand.

[0157] With the introduction of new pre-filtration media and the corresponding increase in bacterial, mycoplasma and virus-retaining filter throughput, feedstream filtration is becoming flux limited. Therefore, a dramatic improvement in the permeability of bacteria, mycoplasma and virus retention filters would have a direct beneficial impact on the cost of the bacteria, mycoplasma and virus filtration process.

[0158] Filters used for liquid filtration can generally be classified as either fibrous nonwoven media filters or porous film membrane filters.
[0159] Porous film membrane liquid filters or other types of filtration media can be unsupported or used with porous substrates or supports. Porous film liquid filtration membranes, typically having pore sizes smaller than the porous fibrous nonwoven media, are (a) fine particles in which the particulate matter filtered from the liquid typically ranges from about 0.1 micron (μm) to about 10 μm. Filtration (MF); (b) ultrafiltration (UF), in which the particulate matter filtered from the liquid typically ranges from about 2 nanometers (nm) to about 0.1 μm; and (c) filtered from the liquid It can be used for reverse osmosis (RO) where particulate matter typically ranges from about 1 Å to about 1 nm.

[0160] The retrovirus-retaining membrane is usually considered to be on the open end of the ultrafiltration membrane.
[0161] High permeability and high reliable retention are two desirable parameters for liquid filtration membranes. However, there is a trade-off between these two parameters, and for the same type of liquid filtration membrane, greater retention can be achieved at the expense of permeability. Inherent limitations of conventional processes for making liquid filtration membranes prevent membranes from exceeding a certain threshold of porosity, thus limiting the amount of permeability that can be achieved for a given pore size.

[0162] Fibrous nonwoven liquid filtration media include, but are not limited to, nonwoven media formed from spunbond, meltblown or spunlaced continuous fibers; hydroentangled nonwovens formed from carded staple fibers and the like; media, and/or combinations thereof. Fibrous nonwoven media filters typically used for liquid filtration generally have pore sizes greater than about 1 μm.

[0163] Nonwoven materials are widely used in the manufacture of filtration products. Pleated membrane cartridges typically include a nonwoven material as a drainage layer (e.g., U.S. Pat. Nos. 6,074,869, 5,846,438, and 5,652,050, each to Pall Corporation). and U.S. Pat. No. 6,598,749, assigned to Cuno Inc., now 3M Purification Inc.).

[0164] Nonwoven microporous materials, such as EMD Millipore Corporation, of Billerica, Mass. Biomax ® ultrafiltration membranes by Co., Ltd. can also be used as support screens for adjacent porous membrane layers disposed therebetween.

[0165] Nonwoven microporous materials also include a support scaffold to increase the strength of the porous membrane placed over the nonwoven microporous structure, such as Milligard™ filters, also available from EMD Millipore Corporation. can be used as

[0166] The nonwoven microporous material is also " It can also be used as a "coarse prefiltration". Porous membranes usually provide a very critical biosafety barrier or structure with well-defined pore sizes or molecular weight cutoffs. Critical filtration is characterized by the expected and identifiable assurance of high removal of microorganisms and viral particles (usually >99.99% as defined by specific tests). Critical filtration is relied upon to ensure the sterility of liquid drug and liquid biopharmaceutical formulations at multiple stages of manufacture as well as at the point of use.

[0167] Meltblown and spunbond fibrous media are often referred to as "traditional" or "conventional" nonwovens. The fibers of these traditional nonwovens are usually at least about 1,000 nm in diameter, so the effective pore size of traditional nonwovens is greater than about 1 micron. Traditional nonwoven manufacturing methods typically result in highly non-uniform fiber mats.

[0168] Historically, the randomness of the formation of conventional nonwoven mats, such as by meltblowing and spunbonding, has led to the general assumption that nonwoven mats are unsuitable for very serious filtration of liquid streams; Filtration devices incorporating conventional nonwoven mats typically use these mats for prefiltration purposes only to increase the capacity of the porous critical filtration membranes placed downstream of the conventional nonwoven mats.

[0169] Another type of nonwoven includes electrospun nanofiber nonwoven mats, which, like "traditional" or "conventional" nonwovens, are generally unsuitable for critical filtration of liquid streams. (see, for example, Bjorge et al., Performance assessment of electrospun nanofibers for filter applications, Desalination, 249, (2009), 942-948).

[0170] Electrospun polymeric nanofiber mats are highly porous, with "pore" size approximately linearly proportional to fiber diameter and porosity relatively independent of fiber diameter. The porosity of electrospun nanofiber mats typically ranges from about 85% to 90%, resulting in dramatically improved permeation compared to dip-cast membranes with similar thickness and pore size ratings. A nanofiber mat exhibiting properties is obtained. The porosity advantage of electrospun polymeric nanofiber mats over porous membranes is amplified in the smaller pore size range typically required for virus filtration due to the reduced porosity of UF membranes mentioned above. Become so.

[0171] Electrospun nanofiber nonwoven mats are produced by spinning a polymer solution or melt using an electric potential rather than the meltblown wet or extrusion manufacturing processes used to make conventional or traditional nonwoven fabrics. be. Fiber diameters typically obtained by electrospinning range from 10 nm to 1,000 nm, one to three orders of magnitude smaller than conventional or traditional nonwovens.

[0172] The electrospun nanofiber mat places the dissolved or melted polymeric material adjacent to the first electrode, and the dissolved or melted polymeric material is drawn as fibers from the first electrode toward the second electrode. is formed by applying a potential such that In the process of making electrospun nanofiber mats, the fibers are not laid down in the mat by blown hot air or other mechanical means that can produce a very broad pore size distribution. Rather, the electrospun nanofibers form a highly uniform mat due to mutual electrical repulsion between the electrospun nanofibers.

[0173] WO 2010/107503, assigned to EMD Millipore Corporation, teaches that nanofiber mats with specific thicknesses and fiber diameters provide an improved combination of liquid permeability and microbial retention. The thinnest sample taught has a transmittance of 4,960 lmh/psi at 55 μm thickness, but neither a method for determining retention assurance nor the level of assurance achieved is described. In general, nanofiber mats provide 2-10 times better permeability than corresponding porous membranes of comparable retention, a result of nanofiber mats with higher porosity (typical wet-cast porous membranes). about 90% vs. 70-80% for the active membrane).

[0174] Electrospun nanofiber mats can be made by depositing fibers onto a conventional spunbonded nonwoven (an example of a face-to-face interface between a nonwoven and a nanofiber layer is available from Elmarco sr. and US Patent Application Publication No. 200910199717, assigned to Clarcor Inc., each of which is hereby incorporated by reference in its entirety). In each of these approaches, surface roughness of the supporting nonwoven can propagate into the nanofiber layer and potentially compromise retention properties by causing potential non-uniformities in the nanofiber structure.

[0175] Jirsak et al. U.S. Pat. No. 7,585,437, issued to No. 7,585,437, teaches a nozzle-free method of producing nanofibers from a polymer solution using electrostatic spinning and an apparatus that implements the method.

[0176] Nano Technics Co., which is incorporated herein by reference in its entirety. LTD. WO 2003/080905, assigned to , teaches an electroblowing process in which a stream of polymeric solution containing polymer and solvent is fed from a storage tank to a series of spinning nozzles in a spinneret to which high A voltage is applied through which the polymeric solution is expelled. Compressed air, optionally heated, is released from air nozzles located in or around the plane of the spinning nozzle. The compressed air aids in the formation of a nanofiber web by guiding the blow gas stream generally downward as it envelops and advances the newly released polymeric solution, which is placed above the vacuum chamber in a grounded porosity. Collected on a collection belt.

[0177] Schaefer et al. US Patent Application Publication No. 2004/0038014 teaches a nonwoven filtration mat comprising one or more layers of a collection of fine polymeric microfibers and nanofibers formed by electrostatic spinning for filtering contaminants.

[0178] Green, US Patent Application Publication No. 2009/0199717, teaches a method of forming an electrospun fiber layer on a substrate layer, wherein a significant amount of electrospun fibers is less than 100 nanometers (nm) has a fiber diameter of

[0179] Bjorge et al. in Desalination 249 (2009) 942-948 teaches electrospun nylon nanofiber mats having nanofiber fiber diameters of about 50 nm to 100 nm and a thickness of about 120 μm. The bacterial LRV measured on untreated fibers is 1.6-2.2. Bjorge et al. intentionally conclude that the bacteria removal efficiency of nanofiber electrospun mats is unsatisfactory.

[0180] Gopal et al. teaches electrospun polyethersulfone nanofiber mats in Journal of Membrane Science 289 (2007) 210-219, where the nanofibers have a diameter of about 470 nm. During liquid filtration, the nanofiber mat functions as a filter screen to filter out particles larger than 1 micron (μm) and as a depth filter (eg, pre-filter) for particles smaller than 1 micron.

[0181] Aussawasathien et al. in Journal of Membrane Science, 315 (2008) 11-19 teaches electrospun nanofibers with diameters of about 30 nm to 110 nm used for the removal of polystyrene particles with diameters of about 0.5 μm to 10 μm.

[0182] One reason research has investigated collection electrode properties is to control the orientation of the nanofibers collected on the electrode. Li et al. is Nano Letters, vol. 5, no. 5 (2005) 913-916 described the introduction of an insulating gap into the collecting electrode and the effect of the area and geometry of the introduced insulating gap. They showed that nanofiber assembly and alignment could be controlled by varying the collection electrode pattern.

[0183] Several methods have been published that focus on geometric surface properties such as roughness. For example, US Patent Application Publication No. 2011/0305872 describes altering the surface roughness of a substrate by grafting a polymer layer to alter the binding properties of a biologic on the substrate. An optical surface metrology method using an Olympus LEXT OLS4000 laser confocal microscope to determine the surface roughness of a substrate has been described.

[0184] Critical filtration applications that achieve higher microbial retention on their own are not sufficient, but it is necessary to do so in a reliable manner with high assurance. To predict retention assurance, statistical methods such as censored data regression are often used to analyze lifespan data for lifespan-shortened reliability (Blanchard, (2007), Quantifying Sterilizing Membrane Retention Assurance, BioProcess International, v.5, No. 5, pp. 44-51).

[0185] US Patent Application Publication No. 2014/0166945 discloses a liquid filter comprising a porous polymeric nanofiber layer on a support, wherein at least on the surface of the support facing the polymeric nanofiber layer, the surface squared The square root height is less than about 70 microns. This publication discloses various polymers that can be used for the nanofiber layer and support.

[0186] Electrospun nanofibers can be made from a wide variety of polymers and polymeric compounds, including thermoplastic and thermoset polymers. Suitable polymers include, but are not limited to, nylon, polyimide, aliphatic polyamide, aromatic polyamide, polysulfone, cellulose, cellulose acetate, polyethersulfone, polyurethane, poly (urea urethane), polybenzimidazole (PBI ), polyetherimide, polyacrylonitrile (PAN), poly(ethylene terephthalate), polypropylene, polyaniline, poly(ethylene oxide), poly(ethylene naphthalate), poly(butylene terephthalate), styrene-butadiene rubber, polystyrene, poly(vinyl chloride ), poly(vinyl alcohol), poly(vinylidene fluoride), poly(vinyl butylene), polymethyl methacrylate (PMMA), copolymers, derivative compounds and blends and/or combinations thereof.

[0187] Non-limiting examples of single- or multi-layered porous substrates or supports include smooth nonwovens. In another non-limiting example, a smooth nonwoven substrate has a substantially uniform thickness. Smooth nonwovens are made from various thermoplastic polymers such as polyolefins, polyesters, polyamides, and the like.

[0188] The uniformity of the nonwoven substrate of the composite filtration media that captures or collects the electrospun nanofibers can determine, at least in part, the properties of the nanofiber layer of the final composite filtration structure obtained. For example, the smoother the surface of the substrate used to collect the electrospun nanofibers, the more uniform the resulting nanofiber layer structure.

[0189] The smoothness of the supporting nonwoven is characterized by geometric smoothness, or lack of rough surface features having dimensions greater than one fiber diameter of the nonwoven, and low hair depth, i.e., fibers and/or protruding beyond the surface. Or related to a small number of loops. Geometric smoothness can be readily measured by several common techniques such as mechanical and optical surface measurements, visible light reflection (gloss metrology) and other techniques known to those skilled in the art.

[0190] In some aspects, the electrospun nanofiber layer is bonded to a smooth nonwoven substrate. Bonding can be accomplished by methods well known in the art, such as, but not limited to, thermal calendering between heated smooth nip rolls, ultrasonic bonding, and through-gas bonding. The bonding of the electrospun nanofiber layer to the nonwoven substrate increases the strength of the composite, as well as the compression resistance of the composite, and the resulting composite filtration media makes the composite filtration platform a useful filter shape and size. It can withstand the forces associated with forming on the filter or when installing the composite filtration platform on the filtration device.

[0191] In other embodiments of the composite liquid filtration platform, the physical properties of the porous electrospun nanofiber layer, such as thickness, density, and pore size and shape, are similar to those of the nanofiber layer. It can work depending on the bonding method used between the nonwoven substrate. For example, thermal calendering can be used to reduce the thickness and increase the density, reduce the porosity of the electrospun nanofiber layer, and reduce the pore size. This in turn reduces the flow rate through the composite filtration media for a given differential pressure applied.

[0192] In general, ultrasonic bonding bonds a smaller area of the electrospun nanofiber layer than thermal calendering, and thus has less effect on the thickness, density and pore size of the electrospun nanofiber layer.

[0193] Bonding with hot gas or hot air generally has the least effect on the thickness, density and pore size of the electrospun nanofiber layer, so this bonding method is desirable to maintain higher fluid flow rates. would be preferred in some applications.

[0194] When thermal calendering is used, care should be taken not to overbond the electrospun nanofiber layers so that the nanofibers melt and no longer retain their structure as individual fibers. There must be. In extreme cases, overbonding can result in complete melting of the nanofibers and formation of a film. One or both of the nip rolls used are heated to about ambient temperature, eg, from about 25°C to about 300°C. The porous nanofiber media and/or porous support or substrate can be compressed between nip rolls at pressures ranging from about 0 lb/in to about 1000 lb/in (178 kg/cm).

[0195] Calendering conditions, such as roll temperature, nip pressure and line speed, can be adjusted to achieve the desired solidity. Generally, application of higher temperature, pressure, and/or residence time at elevated temperature and/or pressure results in increased solidity.

[0196] Other mechanical steps, such as drawing, cooling, heating, sintering, annealing, winding, unwinding, etc., are optionally included in the overall process of forming, shaping, and making the desired composite filtration media. good too.

breathing filter
[0197] US Patent Application Publication No. 2014/0097558 discloses that various types of respiratory filters are known in the art. Personal protective equipment (PPE), specifically disposable face masks, may need to comply with certain regulations during design and manufacture. The user's ability and ease of breathing while wearing the mask and the fit and comfort of the user wearing the mask may be considered. Due to the disposable nature of the mask, a low cost manufacturing process is desirable. Certain regulatory standards must be met. For example EN 149:2001 in Europe or 42 CFR part 84 or ISO 17420 in the USA. Under these regulations PPE is a Class III product in accordance with PPE directives in Europe or other parts of the world. PPE, such as disposable masks or reusable cartridges, may contain filtration media that may be made of meltblown fibers and/or microglass materials. Filtration by a mask is achieved when airborne particles are trapped in a matrix of fibers contained in the filter media of the mask.

[0198] Nanofibers formed by electrospinning a polymer solution can be functionalized by adding another substance to the polymer solution. Additional functionalizers may be operable to remove gases and may include one or more chemicals that may trap gases (where gases are volatile organic chemicals (VOCs), acids Steam, carbon dioxide ( _CO2 ), nitric oxide (NO), nitrogen dioxide ( _NO2 ), ozone ( _O3 ), hydrogen cyanide (HCN), arsine ( _AsH3 ), hydrogen fluoride (HF), chlorine dioxide ( ClOC ₂ ), ethylene oxide (C ₂ H ₄ O), formaldehyde (CH ₂ O), methyl bromide (CH ₃ Br), and/or phosphine (PH3)). In certain embodiments, the functionalized material is a biocide (i.e., a chemical substance capable of deterring, rendering harmless, or exerting a control effect on harmful organisms by chemical or biological means). or microbes), viricides (i.e., physical or chemical agents that inactivate or kill viruses) and/or bactericides (i.e., substances that kill bacteria, such as disinfectants, antiseptics, or antibiotics) can include one of In other embodiments, the functionalized nanofibers may be used to remove humidity, control temperature, indicate end of life, indicate clogged material, and/or provide a fresh odor inside the mask. may be operable to

[0199] The filtration layer may be formed directly on the support layer rather than being formed separately. The filtration layer may contain one or more types of fibers made from the same or different polymeric fiber-forming materials. The majority of the fibers in the filtration layer are formed from fiber-forming materials capable of receiving sufficient electret charge and maintaining adequate charge separation. A preferred polymeric fiber-forming material is a non-conductive resin having a volume resistivity of 1014 ohm-centimeters or greater at room temperature (22° C.). The resin may have a volume resistivity of about 1016 ohm-centimeters or greater. Resistivity of polymeric fiber-forming materials can be measured according to standardized test ASTM D 257-93. Some examples of polymers that may be used are thermoplastic polymers containing polyolefins such as polyethylene, polypropylene, polybutylene, poly(4-methyl-1-pentene) and cyclic olefin copolymers, and combinations of such polymers. Other polymers that can be used but can be difficult to charge or can lose charge rapidly include polycarbonates, block copolymers such as styrene-butadiene-styrene and styrene-isoprene-styrene block copolymers, polyesters such as polyethylene. There are terephthalates, polyamides, polyurethanes, as well as other polymers familiar to those skilled in the art. Some or all of the filtration layer fibers can be made from multicomponent fibers, such as splittable fibers, if desired. Suitable multicomponent (eg, bicomponent) fibers include side-by-side, sheath-core, segmented pie, islands in the sea, tipped and segmented ribbon fibers. be. If splittable fibers are used, splitting can be done using various techniques familiar to those skilled in the art, such as carding, air jets, embossing, calendering, hydroentangling or needle punching. or be facilitated. The filtration layer preferably consists of monocomponent fibers of poly-4-methyl-1-pentene or polypropylene, or of poly-4-methyl-1-pentene or polypropylene of layered or core-sheath construction, for example having poly-4-methyl-1-pentene or polypropylene on the outer surface. - Manufactured from bicomponent fibers of 4-methyl-1-pentene and polypropylene. Most preferably, the filtration layer is made from polypropylene homopolymer monocomponent fibers because of polypropylene's ability to retain a charge, especially in moist environments. Additives may be added to the polymer to enhance filtration performance, electret chargeability, mechanical properties, aging resistance, coloration, surface properties or other desired characteristics. Typical additives include fillers, nucleating agents (e.g. MILLAD™ 3988 dibenzylidene sorbitol available from Milliken Chemical), electret charge enhancing additives (e.g. tristearylmelamine, and various photostabilizing agents). (e.g. CHIMASSORB™ 119 and CHIMASSORB 944 from Ciba Specialty Chemicals), curing initiators, curing agents (e.g. poly(4-methyl-1-pentene)), surfactants and surface treatments (e.g. Jones et al. fluorine atoms to improve filtration performance in oil mist environments as described in U.S. Pat. processing). The types and amounts of such additives are familiar to those skilled in the art. For example, electret charge enhancing additives generally contain about 5 wt. %, more typically about 2 wt. present in amounts less than %. The polymeric fiber-forming material also preferably contains substantially no components such as antistatic agents that can significantly increase electrical conductivity or otherwise interfere with the fiber's ability to accept and retain an electrostatic charge. Not included.

[0200] Filtration layers can have various basis weights, fiber sizes, thicknesses, pressure drops and other characteristics, and can be sufficiently brittle to not be roll-to-roll processable. The filtration layer can have a basis weight ranging, for example, from about 0.5 to about 300 g/m2 (gsm), from about 0.5 to about 100 gsm, from about 1 to about 50 gsm, or from about 2 to about 40 gsm. Relatively low basis weights, such as about 2, 5, 15, 25 or 40 gsm are preferred for filtration layers. The fibers in the filtration layer can have a median fiber size of less than about 10 μm, less than about 5 μm, or less than about 1 μm, for example. Filtration layer thickness can be, for example, from about 0.1 to about 20 mm, from about 0.2 to about 10 mm, or from about 0.5 to about 5 mm. A nanofiber filtration layer (eg, a coarse textured support layer) applied to several support layers at very low basis weights does not change the overall media thickness. Filtration layer basis weight and thickness can be controlled or adjusted, for example, by varying collector speed or polymer throughput.

[0201] The support layer is sufficiently robust that a filtration layer can be formed on the support layer and the resulting media optionally further converted using roll-to-roll processing equipment. The support layer can be formed from a variety of materials and can have a variety of basis weights, thicknesses, pressure drops and other characteristics. For example, the support layer can be a nonwoven web, woven fabric, knit, open cell foam or perforated membrane. A nonwoven fibrous web is a preferred support layer. Suitable fibrous precursors for making such nonwoven webs include the polymeric fiber-forming materials described above and other polymeric fiber-forming materials that do not readily accept or retain an electrostatic charge. The support layer may also be formed from natural fibers or from blends of synthetic and natural fibers. If made from a nonwoven web, the support layer may be formed from molten thermoplastic polymer using, for example, meltblowing, melt spinning or other suitable web processing techniques, carding or from a Rando-Webber machine. It may be formed from natural fibers or blends of synthetic and natural fibers using deposition, or may be formed using other techniques familiar to those skilled in the art. If made from a woven web or knit, the support layer is formed, for example, from microdenier continuous filament or staple fiber yarns (i.e., yarns having a denier per filament (dpf) of less than about 1) and is well known to those skilled in the art. It can be processed into a woven or knitted support fabric using any suitable processing technique. The support layer can have a basis weight ranging, for example, from about 5 to about 300 gsm, more preferably from about 40 to about 150 gsm. The thickness of the support layer can be, for example, from about 0.2 to about 40 mm, from about 0.2 to about 20 mm, from about 0.5 to about 5 mm, or from about 0.5 to about 1.5 mm.

[0202] In addition to the polyamide nanofiber layer, additional layers can be added to the disclosed media if desired. Typical additional layers are familiar to those skilled in the art and include protective layers (eg, anti-abrasion layers, anti-irritation layers, and other cover layers), reinforcement layers and adsorption layers. Adsorptive particles (eg, activated carbon particles or alumina particles) can also be introduced into the medium using methods familiar to those skilled in the art.

[0203] Hydrocharging of the disclosed multilayered media can be performed using a variety of techniques, for example, by impinging, soaking, or condensing a polar fluid onto the media, followed by drying, resulting in a be electrified. Representative patents describing hydrocharging are U.S. Pat. Nos. 5,496,507 and 5,908,598; 6,375,886; 6,454,986; and 6,743,464. Water is preferably used as the polar hydrocharging liquid and the medium is preferably exposed to the polar hydrocharging liquid using a jet or droplet stream of liquid provided by suitable spray means. Apparatuses useful for hydraulically entangling fibers are generally useful for carrying out hydrocharging, although actuation in hydrocharging occurs at lower pressures than are commonly used in hydroentangling. U.S. Pat. No. 5,496,507 describes a representative apparatus in which a jet or stream of water droplets impinge on a medium with sufficient pressure to provide a filtration-enhancing electret charge to the medium that is subsequently dried. Let me. The pressure required to achieve optimum results depends on the type of nebulizer used, the type of polymer from which the filtration layer is formed, the thickness and density of the media, and whether pretreatments such as corona charging precede hydrocharging. may vary depending on how it was performed. Generally, pressures in the range of about 69 to about 3450 kPa are suitable. Preferably, the water used to provide the droplets is relatively pure. Distilled or deionized water is preferred over tap water.

[0204] The disclosed media may be subjected to other charging techniques, such as electrostatic charging (e.g., US Pat. Nos. 4,215,682, 5,401,446 and 6,119, before or after hydrocharging). , 691), tribocharging (described, for example, in U.S. Pat. No. 4,798,850) or plasma fluorination (described, for example, in U.S. Pat. No. 6,397,458). may be provided. Corona charging followed by hydrocharging and plasma fluorination followed by hydrocharging are preferred combined charging techniques.

[0205] Additional respiratory filters have been described, for example, in fibrous air filtration webs, such as U.S. Patent Nos. 4,011,067; 4,215,682; 4,729,371; 4,798,850; 5,401,466; 5,496,507; 6,119,691; 6,315,806; 6,397,458; 6,554,881; 6,562,112; 6,627,563; 6,673,136; 6,716,274; 6,743,273; and 6,827,764; and Tsai et al. , Electrospinning Theory and Techniques, 14th Annual International TANDEC Nonwovens Conference, Nov. 9-11, 2004. Other fibrous webs are described, for example, in US Pat. Nos. 4,536,361 and 5,993,943.

embodiment
[0206] The present disclosure includes the following embodiments:
[0207] Embodiment 1: A filtration medium comprising a nanofiber nonwoven layer, wherein the nanofiber nonwoven layer is spun into nanofibers having an average fiber diameter of less than 1 micron (1000 nanometers) and formed into a layer. A filtration medium comprising a polyamide having a relative viscosity of 2 to 200.

[0208] Embodiment 2: The nanofiber nonwoven layer comprises polyamide spun into nanofibers having an average fiber diameter of less than 1 micron (1000 nanometers) and formed into a layer, the layer having a melting point of 225°C or higher. An embodiment according to embodiment 1, comprising:

[0209] Embodiment 3: An embodiment according to embodiment 1 or 2, wherein the filter is an air filter, oil filter, bag filter, liquid filter, or respiratory filter.
[0210] Embodiment 4: An embodiment according to embodiment 1 or 2, wherein the polyamide is nylon 6,6.

[0211] Embodiment 5: An embodiment according to embodiment 1 or 2, wherein the polyamide is nylon 6,6 and a derivative, copolymer, blend or alloy of nylon 6.
[0212] Embodiment 6: An embodiment according to embodiment 1 or 2, wherein the polyamide is high temperature nylon.

[0213] Embodiment 7: The polyamide is a long chain aliphatic nylon selected from the group consisting of N6, N6T/66, N612, N6/66, N11, and N12, where "N" means nylon; An embodiment according to embodiment 1 or 2, wherein T" refers to terephthalic acid.

[0214] Embodiment 8: An embodiment according to any of Embodiments 1-7, wherein the nanofiber nonwoven layer has an air permeability value of less than 200 CFM/ ^ft2 .
[0215] Embodiment 9: An embodiment according to any of Embodiments 1-8, wherein the nanofiber nonwoven layer has an air permeability value of 50 to 200 CFM/ ^ft2 .

[0216] Embodiment 10: An embodiment according to any of Embodiments 1-9, wherein the nanofibers have an average fiber diameter of 100 to 907 nanometers, such as 300 to 700 nanometers or 350 to 650 nanometers.

[0217] Embodiment 11: An embodiment according to any of Embodiments 1-10, wherein the nonwoven product has a basis weight of 150 GSM or less.
[0218] Embodiment 12: An embodiment according to any of Embodiments 1-11, wherein the filtration media further comprises a scrim layer.

[0219] Embodiment 13: An embodiment according to Embodiment 12, wherein the nanofiber nonwoven layer is spun onto the scrim layer.
[0220] Embodiment 14: An embodiment according to Embodiment 12, wherein the nanofiber nonwoven layer is spun onto a layer other than a scrim layer.

[0221] Embodiment 15: An embodiment according to embodiment 12, wherein the nanofiber nonwoven layer is sandwiched between the scrim layer and at least one other layer.
[0222] Embodiment 16: An embodiment according to embodiment 12, wherein the nanofiber nonwoven layer is sandwiched between at least two layers other than the scrim layer.

[0223] Embodiment 17: An embodiment according to embodiment 12, wherein the nanofiber nonwoven layer is the outermost layer.
[0224] Embodiment 18: According to any of Embodiments 1-11, wherein the filtration medium further comprises at least one additional layer, and the nanofiber nonwoven layer is spun onto one of the at least one additional layer. embodiment.

[0225] Embodiment 19: A practice according to any of Embodiments 1-18, wherein the relative viscosity of the polyamide within the nanofiber nonwoven layer is reduced by at least 20% compared to the polyamide prior to spinning to form the layer. form.

[0226] Embodiment 20: A method of making a filtration medium comprising a polyamide nanofiber layer comprising: (a) providing a spinnable polyamide polymer composition, wherein the polyamide has a relative viscosity of 2 to 200; (b) melt spinning the polyamide polymer composition into a plurality of nanofibers having an average fiber diameter of less than 1 micron (1000 nanometers); and (c) the nanofibers on an existing filtration media layer. wherein the polyamide nanofiber layer has an average nanofiber fiber diameter of less than 1000 nanometers.

[0227] Embodiment 21: A method of making a filtration medium comprising a polyamide nanofiber layer, comprising: (a) providing a spinnable polyamide polymer composition; and (c) forming the nanofibers on an existing filtration media layer, wherein the polyamide nanofiber layer is 1000 nanometers. having an average nanofiber fiber diameter of less than and a melting point of 225° C. or higher.

[0228] Embodiment 22: An embodiment according to Embodiment 20 or 21, wherein the polyamide nanofiber layer is melt-spun by melt-blowing through a die into a high-velocity gas stream.
[0229] Embodiment 23: The polyamide nanofiber layer is melt spun by two-phase propellant gas spinning comprising extruding a polyamide polymer composition in liquid form through a fiber forming channel with pressurized gas, Embodiment 20 or an embodiment according to 21.

[0230] Embodiment 24: An embodiment according to any of Embodiments 20-23, wherein the polyamide nanofiber layer is formed by collecting the nanofibers on a moving belt.
[0231] Embodiment 25: An embodiment according to any of embodiments 20-24, wherein said polyamide composition comprises nylon 6,6.

[0232] Embodiment 26: An embodiment according to any of embodiments 20-24, wherein said polyamide composition comprises nylon 6,6 and derivatives, copolymers, blends or alloys of nylon 6.

[0233] Embodiment 27: An embodiment according to any of embodiments 20-24, wherein said polyamide comprises HTN.
[0234] Embodiment 28: The polyamide is a long chain aliphatic nylon selected from the group consisting of N6, N6T/66, N612, N6/66, N11, and N12, wherein "N" means nylon; An embodiment according to any of embodiments 20-24, wherein "T" refers to terephthalic acid.

[0235] Embodiment 29: An embodiment according to any of embodiments 20-28, wherein the polyamide nanofiber layer has a basis weight of 150 GSM or less.
[0236] Embodiment 30: An embodiment according to any of embodiments 20-29, wherein the filtration medium further comprises a scrim layer.

[0237] Embodiment 31: An embodiment according to any of embodiments 20-30, wherein the polyamide nanofiber layer is spun onto the scrim layer.
[0238] Embodiment 32: An embodiment according to embodiment 31, wherein the polyamide nanofiber layer is spun onto a layer other than a scrim layer.

[0239] Embodiment 33: An embodiment according to embodiment 31, wherein the polyamide nanofiber layer is sandwiched between the scrim layer and at least one other layer.
[0240] Embodiment 34: An embodiment according to embodiment 31, wherein the polyamide nanofiber layer is sandwiched between at least two layers other than the scrim layer.

[0241] Embodiment 35: An embodiment according to embodiment 31, wherein the polyamide nanofiber layer is the outermost layer.
[0242] Embodiment 36: According to any of Embodiments 20-31, wherein the filtration medium further comprises at least one additional layer, wherein the nanofiber nonwoven layer is spun onto one of the at least one additional layer. embodiment.

[0243] Embodiment 37: An embodiment according to any of Embodiments 20-36, wherein the relative viscosity of the polyamide within the polyamide nanofiber layer is reduced by at least 20% compared to the polyamide prior to spinning to form the layer.

[0244] The present disclosure will be further understood by the following non-limiting examples.

Example 1
[0245] Nylon 6,6 was melt-spun onto a moving drum at two basis weights using the procedure and apparatus described in US Pat. No. 8,668,854 (generally shown in FIG. 1). It was spun into a nonwoven fabric. An extruder with a high compression screw and running at 20 RPM with a temperature profile of 245°C, 255°C, 265°C, and 265°C was used. The polymer temperature was 252° C. and air was used as gas. A higher basis weight sample was made by the same process but with the nanofibers spun onto the scrim. Here, the scrim is simply the neutral article of the invention used to add integrity to the nanofiber webs of the invention. The resin had a relative viscosity of 7.3. To ensure that the viscosity of the low RV resin remained constant, the polymer was made with an excess of about 5% adipic acid.

[0246] The average fiber diameter, basis weight, and air permeability of the nonwoven fabric were determined according to Hassan et al. The article J Membrane Sci. , 427, 336-344, 2013. Water vapor transmission rate was also measured (g/m ² /24hr).

[0247] The results and details are shown in Table 1 and the nonwovens produced are shown in the photomicrographs of FIGS. The nonwoven had an average fiber diameter ranging from 470 nm to 680 nm (average 575 nm).

[0248] As can be seen from Table 1, the melt spun nanofiber nonwovens of the present invention had an average fiber diameter of 570 for an RV of 7.3. Air permeability was about 182.8 CFM/ft ² and water vapor permeability averaged about 1100 g/m ² /24 hr.

[0249] Polyamides made into nanofibers with RV greater than about 20-30 have higher molecular weights than those with lower RV values. The resulting polymer properties can differ from polymers with RV values less than 20, especially in terms of elasticity, strength, thermal or chemical stability, appearance, and/or surface properties, among others. It would be desirable to use a mixture of lower and higher molecular weight polymers in the nonwoven web. Lower molecular weight polymers fibrillate more readily and can result in fibers of varying diameters. If the polymers are not blended, separate nozzles may be utilized for different molecular weight polymers.

[0250] For polyamides having an RV greater than 20-30 and less than 200, a significant number of fibers within the fibrous layer of the nonwoven have an average fiber diameter of less than 1 micron, more preferably about 0.1 to 1 micron, or More preferably, it can be from 0.1 to about 0.6 microns. The resulting nonwoven has an average fiber diameter of less than 1 micron.

[0251] In one embodiment of the present invention, the advantage is that two related polymers with different RV values (both less than 200 and having average fiber diameter less than 1 micron) are blended for desired properties. can be considered.

Example 2
[0252] The nanofibers of the present invention were made using the meltblown process with the pack described in US Patent No. 7,300,272. 36RV nylon 6,6 was melt spun and pumped into a meltblown die. Moisture levels in the resin ranged from about 0.2% to about 1.0%. A four zone extruder was used at temperatures ranging from 233 to 310°C. Die temperatures ranging from 286 to 318°C were used. Heated air was used as the gas for the meltblowing process. The nanofibers were obtained from Cerex Advanced Fabrics, Inc.; It was deposited on a 10 grams per square meter (gsm) thermally bonded nylon spunbond scrim commercially available under the trademark PBN-II.RTM. Other spunbonded fabrics can be used. Other fabrics such as polyester spunbond fabrics, polypropylene spunbond fabrics, nylon meltblown fabrics or other fabrics, knits, needlepunches, or other nonwovens can be used. No solvents or adhesives were used. Various fabrics were made with layers of nanofibers. The basis weight of the nanofiber layer ranged from about 0.7 gsm to about 23 gsm. The average fiber diameters of these nanofiber layers ranged from about 0.36 microns to about 0.908 microns. The relative viscosities of these nanofiber layers ranged from about 22 to about 31. Starting RV ranged from 34 to 37 and about 36. Efficiencies of these fabrics ranged from about 2.71% to about 76.7% as measured using a TSI 8130 with a 0.3 micron challenge fluid. The average pore size of these fabrics ranged from about 4.5 microns to about 84.1 microns. Air permeabilities for these fabrics ranged from 21 to 1002 cfm/ft ² .

Example 3
[0253] Resins with an RV ranging from 34 to 37 were used with the puck described in US Patent No. 7,300,272 to make nanofibers with an RV of about 16.8. This is a reduction in RV from resin to fabric of about 17.2 to 20.2 RV units. The resin contained about 1% moisture by weight and was passed through a small extruder with four zones with a temperature range of 233-310°C. A die temperature of about 308° C. was used.

Example 4
[0254] Resins with an RV ranging from 34 to 37 were used with the puck described in US Patent No. 7,300,272 to make nanofibers with an RV of about 19.7. This is a reduction in RV from resin to fabric of about 14.3 to 17.3 RV units. The resin contained 1% moisture by weight and was run on a small extruder with four zones ranging in temperature from 233 to 310°C. A die temperature of about 277° C. was used.

Example 5
[0255] Resins in the RV range from 34 to 37 were used and blended with 2% Nylon 6. Nanofibers with an RV of about 17.1 were made using the puck described in US Pat. No. 7,300,272. This is a reduction in RV from resin to fabric of about 16.9 to 19.9 RV units. The resin contained 1% moisture by weight and was run on a small extruder with four zones ranging in temperature from 233 to 310°C. A die temperature of about 308° C. was used. Other blends or copolymers of nylon can be used. In a preferred embodiment, a blend of nylon 6 and nylon 6,6 can be used. These blends of nylon 6 and nylon 6,6 have melting points between the melting point of nylon 6 of about 220°C and the melting point of nylon 6,6 of about 260°C.

Example 6
[0256] Three to six layers of nanofiber nonwovens were combined to make higher basis weight and thickness media. Each layer was manufactured by Cerex Advanced Fabrics, Inc. of Cantonment, Florida. It contained a web of nylon 6,6 nanofibers on a 10 gsm nylon spunbond scrim available under the trademark "PBN-II" from Epson. Four different webs with different basis weights listed in Table 2 (13.3, 21.2, 13.2, and 20.2) were used. Table 2 shows the basis weight, filtration efficiency measured using the TSI 8130 with a 0.3 micron challenge fluid, average flow pore size, and average pressure drop (PD) measured by the TSI 8130. Duplicate samples were measured to report the average for average flow pore size, efficiency and pressure drop.

[0257] The fabrics had basis weights ranging from 13.2 gsm to 127.2 gsm and mean flow pore sizes ranging from 3.9 to 5.8 microns and 63.5% to 80.2 as measured by the TSI instrument previously described. It had a filtration efficiency in the % range.

Example 7 - Bacterial and Particulate Filtration Efficiency Test
[0258] Two sample filters were prepared using a web of polyamide 66 nanofibers. Filter 1 had a basis weight of 8.2 gsm and its nanofibers had an average fiber diameter of 612 nm and a median fiber diameter of 440 nm. The air permeability was 72.1 cfm/ft ² , the average flow pore diameter was 7.2, and the bubble point was 28.1 microns. Filter 2 had a basis weight of 11.1 gsm and its nanofibers had an average fiber diameter of 621 nm and a median fiber diameter of 469 nm. The air permeability was 39.2 cfm/ft ² , the average flow pore diameter was 5.9, and the bubble point was 25.7 microns. Each filter was approximately 20 mm thick. Each filter had dimensions of about 174 mm by about 178 mm.

[0259] Filter 1 and Filter 2 were tested for bacterial filtration efficiency (BFE) and particle filtration efficiency (PFE). Filter 1 and Filter 2 were compared against a reference filter made with three layers of polypropylene-spunbond/meltblown/spunbond.

[0260] A BFE test was performed to determine the filtration efficiency of the test filters by comparing the bacterial control counts upstream of the test filters to the bacterial counts downstream. A nebulizer was used to aerosolize a suspension of Staphylococcus aureus and deliver it to the test article at a constant flow rate (28.3 L/m) and fixed air pressure (2.8 x 103 CFU). . Condition parameters were 85% ± 5% relative humidity and 21°C ± 5°C for a minimum of 4 hours. Challenge delivery was maintained at 1.7-3.0×10 ³ colony forming units (CFU) with a mean particle size (MPS) of 3.0±0.3 μm. The aerosol was drawn through a 6-stage biological particle Andersen sampler for collection. This test method conforms to ASTM F2101-19 and EN 14683:2019, Annex B.

[0261] A pressure drop (delta P) test was performed to determine the air permeability of the test filter articles by measuring the air pressure difference across the test article at a constant flow rate using a manometer. The Delta P test meets EN 14683:2019, Annex C and ASTM F2100-19.

[0262] PFE testing was performed to evaluate the non-living particle filtration efficiency (PFE) of test filter articles (11.1 gsm, 8.2 gsm, and standard). Monodisperse polystyrene latex spheres (PSL) were atomized (atomized), dried and passed through the test filter article. Particles passing through the test filter article were counted using a laser particle counter.

[0263] The test filter was placed in the system and a 1 minute count was made. One minute control counts were made before and after each test article with no test filter article in the system and the counts were averaged. A control count was performed to determine the average number of particles delivered to the test filter article. Filtration efficiency was calculated using the number of particles that penetrated the test filter article and compared to the average of the control values.

[0264] The procedure used the basic particle filtration method described in ASTM F2299 with some exceptions. Specifically, the procedure incorporated an unneutralized challenge. In practical use, this challenge represents a more natural state, since the particles carry an electrical charge. Unneutralized aerosols are also prescribed in the FDA Guidance Document for Surgical Face Masks.

[0265] The results of the BFE and PFE tests are shown in Table 3. The results shown in Table 3 are average results. For the 8.2 gsm meltblown polyamide and polypropylene standards, five samples were averaged. Four samples were averaged for the 11.1 and 11.1 gsm meltblown polyamides.

[0266] Both the 11.1 gsm and 8.2 gsm meltblown polyamide 66 nanofibers showed similar favorable PFE to the standard. Advantageously, 11.1 gsm also outperformed BFE while improving (reducing) delta P compared to the standard. This is a significant and unexpected improvement. Similarly, the 8.2 gsm meltblown polyamide 66 nanofibers showed a significantly lower delta P, although the BFE was only slightly lower. The meltblown nanofibers of the present invention can provide functional efficiency with improved performance compared to polypropylene standards.

[0267] Although the invention has been described in detail, modifications within the spirit and scope of the invention will be readily apparent to those skilled in the art. Such modifications are also considered part of the invention. In view of the above discussion, the relevant knowledge in the art, and the references cited above in connection with the background of the invention, the disclosures of which are hereby incorporated by reference in their entirety, no further description is deemed necessary. Additionally, in view of the foregoing discussion, it should be understood that aspects of the invention and portions of various embodiments may be combined or interchanged in whole or in part. Furthermore, as will be appreciated by those skilled in the art, the above description is merely exemplary and is not intended to limit the invention. Finally, all mentioned patents, publications and applications are hereby incorporated by reference in their entirety.
The present invention includes the following embodiments.
[1] A filtration medium comprising a nanofiber nonwoven layer, wherein the nanofiber nonwoven layer is spun into nanofibers having an average fiber diameter of less than 1 micron (1000 nanometers), and the relative viscosity formed in the layer is A filtration medium comprising 2 to 200 polyamides.
[2] A filtration medium comprising a nanofiber nonwoven layer, wherein the nanofiber nonwoven layer comprises polyamide spun into nanofibers having an average fiber diameter of less than 1 micron (1000 nanometers) and formed into a layer. , a filtration medium in which the layers have a melting point of 225° C. or higher.
[3] The filtration media of [1] or [2], wherein the filter is an air filter, oil filter, bag filter, liquid filter, or respiratory filter.
[4] The filtration medium of [1] or [2], wherein the polyamide is nylon 6,6.
[5] The filtration media of [1] or [2], wherein the polyamide is nylon 6,6 and a derivative, copolymer, blend or alloy of nylon 6.
[6] The filtration media of [1] or [2], wherein the polyamide is high temperature nylon.
[7] the polyamide is a long chain aliphatic nylon selected from the group consisting of N6, N6T/66, N612, N6/66, N11, and N12, where "N" means nylon and "T" is terephthal; The filtration medium of [1] or [2], which refers to acid.
[8] The filtration media of any of [1]-[7], wherein the nanofiber nonwoven layer has an air permeability value of less than 200 CFM/ft ² .
[9] The filtration media of any of [1]-[8], wherein the nanofiber nonwoven layer has an air permeability value of 50 to 200 CFM/ft ² .
[10] The filtration medium of any one of [1] to [9], wherein the nanofibers have an average fiber diameter of 100 to 907 nanometers.
[11] The filtration media of any of [1]-[10], wherein the nonwoven product has a basis weight of 150 GSM or less.
[12] The filtration medium of any one of [1] to [11], wherein the filtration medium further comprises a scrim layer.
[13] The filtration media of [12], wherein the nanofiber nonwoven layer is spun onto the scrim layer.
[14] The filtration media of [12], wherein the nanofiber nonwoven layer is spun onto a layer other than the scrim layer.
[15] The filtration media of [12], wherein the nanofiber nonwoven layer is sandwiched between the scrim layer and at least one other layer.
[16] The filtration media of [12], wherein the nanofiber nonwoven layer is sandwiched between at least two layers other than the scrim layer.
[17] The filtration media of [12], wherein the nanofiber nonwoven layer is the outermost layer.
[18] Any of [1] to [11], wherein the filtration medium further comprises at least one additional layer, wherein the nanofiber nonwoven layer is spun onto one of the at least one additional layer. filtration media.
[19] The filtration medium of any one of [1] to [18], wherein the relative viscosity of the polyamide of the nanofiber nonwoven layer is reduced by at least 20% compared to the polyamide prior to spinning to form the layer. .
[20] A method of making a filtration medium comprising a polyamide nanofiber layer, comprising:
(a) providing a spinnable polyamide polymer composition, wherein the polyamide has a relative viscosity of 2 to 200;
(b) melt spinning the polyamide polymer composition into a plurality of nanofibers having an average fiber diameter of less than 1 micron (1000 nanometers); and
(c) forming nanofibers on an existing filtration media layer, wherein the polyamide nanofiber layer has an average nanofiber fiber diameter of less than 1000 nanometers;
A method, including
[21] A method of making a filtration medium comprising a polyamide nanofiber layer, comprising:
(a) providing a spinnable polyamide polymer composition;
(b) melt spinning the polyamide polymer composition into a plurality of nanofibers having an average fiber diameter of less than 1 micron (1000 nanometers); and
(c) forming nanofibers on an existing filtration media layer, wherein the polyamide nanofiber layer has an average nanofiber fiber diameter of less than 1000 nanometers and a melting point of 225° C. or higher;
A method, including
[22] The method of making the filtration media of [20] or [21], wherein the polyamide nanofiber layer is melt-spun by melt-blowing through a die into a high-velocity gas stream.
[23] The polyamide nanofiber layer is melt spun by two-phase propellant gas spinning, which involves extruding a polyamide polymer composition in liquid form through a fiber-forming channel with pressurized gas, [20] or [21]. A method of making a filtration medium according to .
[24] A method of making a filtration media according to any of [20] to [23], wherein the polyamide nanofiber layer is formed by collecting nanofibers on a moving belt.
[25] The method of making a filtration medium according to any one of [20] to [24], wherein the polyamide composition comprises nylon 6,6.
[26] The method of making a filtration media of any of [20] to [24], wherein the polyamide composition comprises nylon 6,6 and derivatives, copolymers, blends or alloys of nylon 6.
[27] The method of making a filtration medium according to any one of [20] to [24], wherein the polyamide comprises HTN.
[28] The polyamide is a long chain aliphatic nylon selected from the group consisting of N6, N6T/66, N612, N6/66, N11, and N12, wherein "N" means nylon and "T" is A method of making a filtration medium according to any of [20] to [24], which refers to terephthalic acid.
[29] A method of making a filtration media according to any of [20] to [28], wherein the polyamide nanofiber layer has a basis weight of 150 GSM or less.
[30] The method of making the filtration medium of any of [20] to [29], wherein the filtration medium further comprises a scrim layer.
[31] The method of making the filtration media of any of [20]-[30], wherein the polyamide nanofiber layer is spun onto the scrim layer.
[32] The method of making the filtration media of [31], wherein the polyamide nanofiber layer is spun onto a layer other than the scrim layer.
[33] The method of making the filtration media of [31], wherein the polyamide nanofiber layer is sandwiched between the scrim layer and at least one other layer.
[34] The method of making the filtration media of [31], wherein the polyamide nanofiber layer is sandwiched between at least two layers other than the scrim layer.
[35] The method of making the filtration media of [31], wherein the polyamide nanofiber layer is the outermost layer.
[36] Any of [20] to [31], wherein the filtration medium further comprises at least one additional layer, and wherein the nanofiber nonwoven layer is spun onto one of the at least one additional layer. A method of making a filtration medium.
[37] Producing the filtration media of any of [20] to [36], wherein the relative viscosity of the polyamide in the polyamide nanofiber layer is reduced by at least 20% compared to the polyamide prior to spinning to form the layer. how to.

Claims (11)

A filtration media comprising 3 to 6 nanofiber nonwoven layers on a nylon spunbond scrim, each nanofiber nonwoven layer being spun into nanofibers having an average fiber diameter of less than 1 micron (1000 nanometers). , a polyamide having a relative viscosity of 2 to 200 as measured by ASTM D 789, a pressure drop of the filtration media of 0.5 to 10 mm H ₂ O (4.9 to 98.06 Pa) , and 3 to 6 nanometers. A filtration medium wherein each of the fiber nonwoven layers has a basis weight of 2-40 gsm . 2. The filtration media of claim 1, wherein the filter is an air filter, oil filter, bag filter, liquid filter, or respiratory filter. 2. The filtration media of claim 1, wherein the polyamide is nylon 6,6. 2. The filtration media of claim 1, wherein the polyamide is nylon 6,6 and nylon 6 derivatives, copolymers, blends or alloys. 2. The filtration media of claim 1, wherein the polyamide is high temperature nylon. The polyamide is a long chain aliphatic nylon selected from the group consisting of N6, N6T/66, N612, N6/66, N11, and N12, where "N" means nylon and "T" means terephthalic acid The filtration medium of claim 1. 7. The filtration media of any of claims 1-6, wherein the nanofiber nonwoven layer has an air permeability value of less than 200 CFM/ft ^<2> . 8. The filtration media of any of claims 1-7, wherein the nanofiber nonwoven layer has an air permeability value of 50 to 200 CFM/ft ^<2> . 9. A filtration medium according to any preceding claim, wherein the nanofibers have an average fiber diameter of 100 to 907 nanometers. 10. The filtration media of any of claims 1-9, wherein the nonwoven product has a basis weight of 150 GSM or less. 11. The filtration medium of any of claims 1-10, wherein the relative viscosity of the polyamide of the nanofiber nonwoven layer is reduced by at least 20% compared to the polyamide prior to spinning to form the layer.

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