Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D39/00—Filtering material for liquid or gaseous fluids
  • B01D39/14—Other self-supporting filtering material ; Other filtering material
  • B01D39/16—Other self-supporting filtering material ; Other filtering material of organic material, e.g. synthetic fibres
  • B01D39/1607—Other self-supporting filtering material ; Other filtering material of organic material, e.g. synthetic fibres the material being fibrous
  • B01D39/1623—Other self-supporting filtering material ; Other filtering material of organic material, e.g. synthetic fibres the material being fibrous of synthetic origin
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D39/00—Filtering material for liquid or gaseous fluids
  • B01D39/08—Filter cloth, i.e. woven, knitted or interlaced material
  • B01D39/083—Filter cloth, i.e. woven, knitted or interlaced material of organic material
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2239/00—Aspects relating to filtering material for liquid or gaseous fluids
  • B01D2239/02—Types of fibres, filaments or particles, self-supporting or supported materials
  • B01D2239/025—Types of fibres, filaments or particles, self-supporting or supported materials comprising nanofibres
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2239/00—Aspects relating to filtering material for liquid or gaseous fluids
  • B01D2239/06—Filter cloth, e.g. knitted, woven non-woven; self-supported material
  • B01D2239/065—More than one layer present in the filtering material

Definitions

• the present invention relates to air filtration media, for filtering particulate material from gas streams and in particular mist laden gas streams.
• Gas phase filtration has traditionally been accomplished by tow, medium and high efficiency pleatabie composite filter media which include either a tow, medium or high efficiency fibrous filtration layer of randomly oriented fibers; and one or more permeable stiffening layers which enable the composite filter media to be pleated and to sustain its shape.
• Such filtration devices serve as vehicle passenger compartment air filters, high performance engine air filters and engine oil filters.
• ASHRAE American Society of Heating Refrigeration and Air
• pleatabie filters and the like typically use a pleated high efficiency filtration media for the filtration element.
• Pleatabie composite filtration media made of a nanofiber high efficiency layer and a more permeable spunbound fiber stiffening layer have been shown to give good flux/barrier properties (i.e. high efficiency and tow pressure drop).
• the dust-loading capacity is tower than the desired value in certain industrial HVAC applications when filters are challenged with very small dust particles, which can occur when the HVAC system is designed and constructed to have lower efficiency pre-filters in front of the high-efficiency final fitters.
• the scrim is typically made of nonwoven webs of fiber diameter of 14 to 30 microns which can pre-filter out particles larger than about 5 microns in size. The remaining particles will reach the thin nanofiber layer and quickly fill up the pores and plug up the filters. As the result, filter resistance increases rapidly and thus shortens filter life. Attempts have been made to increase the dust-loading capacity by increasing the basis weight and thickness of the scrim layer but the results are still unsatisfactory for the more demanding situations.
• One object of the present invention is to provide such a filter medium and a method for use of the same.
• a method for the filtration of particulate matter from flowing air comprising the steps of providing a flow of air laden with a water mist and containing particles that are to be filtered and passing the air flow through a filtration medium.
• the medium has an upstream side and a
• downstream side relative to the flow of air and comprises a nanoweb layer downstream of and in fluid contact with a hydrophobic nonwoven web.
• nonwoven as used herein means a web comprising of a multitude of fibers.
• the fibers can be bonded to each other or can be unbonded.
• the fibers can comprise a single material or can comprise a multitude of materials, either as a combination of different fibers or as a combination of similar fibers each comprised of different materials. Similar fibers that are each composed of a plurality of materials can be "bicomponent" (with two materials) or multicomponent.
• nonwoven fibrous web or just “nonwoven web” is used in its generic sense to define a generally planar structure that is relatively flat, flexible and porous, and is composed of staple fibers or continuous filaments.
• nonwovens For a detailed description of nonwovens, see "Nonwoven Fabric Primer and Reference Sampler by E. A. Vaughn, ASSOCIATION OF THE NONWOVEN FABRICS INDUSTRY, 3d Edition (19d2).
• the nonwovens may be carded, spun bonded, wet laid, air laid and melt blown as such products are well known in the trade.
• Nonwoven as used herein further refers to a web having a structure of individual fibers or threads that are interlaid, but not in an identifiable manner as in a knitted fabric.
• Nonwoven fabrics or webs have been formed from many processes such as for example, meKbtowing processes, spunbonding processes, and bonded carded web processes.
• the basis weight of nonwoven fabrics is usually expressed in ounces of material per square yard (osy) or grams per square meter (gsm) and the fiber diameters useful are usually expressed in microns. (Note that to convert from osy to gsm, multiply osy by 33.91).
• Meltblown fibers'' means fibers formed by extruding a molten
• thermoplastic material through a plurality of fine, usually circular, die capillaries as molten threads or filaments into converging high velocity heated gas (e.g., air) streams which attenuate the filaments of molten thermoplastic material to reduce their diameter.
• heated gas e.g., air
• the meltblown fibers are carried by the high velocity gas stream and are deposited on a collecting surface to form a web of randomly dispersed meltblown fibers.
• meltblown fibers are microfibers which may be continuous or discontinuous, are generally smaller than about 0.6 denier, and are generally self-bonding when deposited onto a collecting surface.
• a "meltblown web” is a nonwoven web that comprises meltblown fibers.
• spunbonded fibers refers to fibers formed by extruding molten
• Spunbond fibers are generally continuous and often have average deniers larger man about 0.3, more particularly, between about 0.6 and 10.
• a "spunbond web * is a web that comprises spunbond fibers.
• SMSN* refers to a multilayer structure comprising a spunbond web plus a meftbtowrt web plus a nanoweb in that order.
• MSN refers to a meltblown web plus a spunbond web plus a nanoweb in that order.
• hydrophobic is used in its conventional sense of "repelling water.
• a “hydrophobic nonwoven web” is a web that comprises fibers with a hydrophobic surface.
• the surface may be hydrophobic by virtue of the material of the fiber, for example the fiber may be constructed entirely of a potyotefin, as pofyolefins would be considered to be intrinsically hydrophobic.
• the fiber may also be spun from a hydrophiiic material such as potyamide or polyester, and have a hydrophobic coating.
• the fiber may be spun from polyamide or polyester, and have a coating thereon of a surfactant, and in particular a fluorosurfactant.
• a material that is capable of "repelling water” is therefore meant a hydrophobic material that resists wetting by aqueous media, an agent comprising fluorine and carbon atoms being preferred.
• the hydrophiiic material can be at least partially coated with a fluorinated material.
• the fluorinated material is selected from the group consisting of ZonyKD D fabric fluoridizer consisting of fluorinated methacrylate copolymers or Zonyl® 8300 fabric protector consisting of fluorinated acryiate copolymers.
• the treatment of fabrics with such fluorinated polymers and oligomers is common in the trade and is not limited to these chemicals. One skilled in the art will be able to choose a suitable treatment.
• the water-repellent coating employed in the invention can therefore be any agent that repels water and that can be applied to the hydrophilic web, an agent comprising fluorine and carbon atoms being preferred.
• a preferred water- repellent coating of the invention is one comprising a fluoropolymer, and especially a mixture of fluoroacryiate polymers, e.g., OLEOPHOBOL SM® from Ciba Spezialitatenchemie Pfersee GmbH, Langweid, Germany.
• the coating may be applied to the fiber in a variety of ways. One method is to apply the neat resin of the coating material to the stretched high modulus fibers either as a liquid, a sticky solid or particles in suspension or as a fluidized bed.
• the coating may be applied as a solution or emulsion in a suitable solvent which does not adversely affect the properties of the fiber at the temperature of application.
• a suitable solvent which does not adversely affect the properties of the fiber at the temperature of application.
• suitable solvent any liquid capable of dissolving or dispersing the coating polymer may be used, preferred groups of solvents include water, paraffin oils, aromatic solvents or hydrocarbon solvents, with illustrative specific solvents including paraffin oil, xylene, toluene and octane.
• the techniques used to dissolve or disperse the coating polymers in the solvents will be those conventionally used for the coating of similar elastomeric materials on a variety of substrates.
• any method is suitable in principle that allows the water-repeilant agent in the chosen formulation to be uniformly distributed on the surface of the fiber.
• the water-repellent agent formulation can be applied as a thin film on a roller and the hydrophilic fiber passed through the film.
• the water-repellent agent formulation can be sprayed on to the hydrophilic fiber.
• the water-repellent agent formulation can also be applied to the fiber using a pump and a pin, slit or block applicator.
• the application of coating can be effected by passing the hydrophilic web over a roller immersed in a bath containing the aqueous emulsion of the water- repellent agent
• the drying of the coated web is performed within suitable ranges of temperature.
• the parameter ranges for temperature and drying time are also determined by the requirements of the selected application method. If the water- repellent agent is applied on the web in the web spinning process, for example, after the fiber has left the wash bath, the ranges of temperature and drying time will be determined by the spinning speed and the structural features of the spinning facility.
• the fibers may further be a bicomponent structures in which the outer surface is spun from a hydrophobic material such as a polyolefin.
• polymers that would be considered hydrophobic are polymers that comprise only carbon and hydrogen, or carbon, hydrogen and fluorine, for example polyolefins, fluoropolymers and poiyviny!idene f!uoiide.
• polymers that would be considered non hydrophobic are polyamides and polyesters.
• a meltbtown or a spunbond nonwoven fibrous web that is useful in embodiments of the invention may comprise fibers of polyethylene,
• the fibers usually include staple fibers or continuous filaments.
• nanofibers refers to fibers having a number average diameter less than about 1000 nm, even less than about 800 nm, even between about 50 nm and 500 nm, and even between about 100 and 400 nm.
• diameter refers to the greatest cross-sectional dimension.
• a "scrim * is a support layer and can be any structure with which the filter medium can be bonded, adhered or laminated.
• the scrim layers useful in the present invention are spunbond nonwoven layers, but can be made from carded webs of nonwoven fibers, meft blown nonwoven layers, woven fabrics, nets, and the like. Scrim layers useful for some filter applications require sufficient stiffness to hold pleat shape.
• a scrim as used in the present invention should have an open enough structure to not interfere with the dust holding structure of the medium.
• two or more webs being "in a face to face relationship" is meant that the surface of any one web is located essentially parallel to the surface of one or more other webs and in such a way that the web surfaces at least partially overlap.
• the webs need not be bonded to each other, but they may be partially or totally bonded to each other over at least a portion of the surfaces or edges.
• Two or more webs are in "fluid contact * with each other when during normal end use, all of the fluid that impinges on one of them is expected to impinge on the second web. Not all of the surface area of the two or more webs need be in physical contact with fluid, but all of the fluid is expected to pass through both webs.
• water misf herein is meant a two phase gas liquid system comprising a very fine water droplet dispersed in air or gas stream.
• the mist can be created by the gas or air and water being discharged through water nozzles that create very fine droplets such that the droplets are small enough to be transported by the air or gas stream without undergoing coalescence into a continuous phase during transportation in the air stream.
• Droplets are typically of the order of 18 to 50 microns in diameter.
• nanofiber web and “nanoweb” as used herein are
• nonwoven webs that comprise nanowebs and may consist entirely of nanoftbers.
• the present invention is directed to a method for the filtration of particulate matter from flowing air that avoids substantial increase in operating pressure during periods when air is saturated with water and a mist is formed.
• the method comprises the steps of providing a flow of air laden with a water mist and also containing particles that are to be filtered, and passing the air flow through a filtration medium.
• the medium has an upstream side and a downstream side relative to the flow of air and comprises a nanoweb layer downstream of and in fluid contact with a hydrophobic nonwoven web.
• the hydrophobic nonwoven web may be of any nonwoven construction known to one skilled in the art, and in particular may be a meltblown web or a spunbond web.
• the primary purpose of the nanoweb is for particle filtration.
• the function of the nanoweb is not to coalesce the water mist, and the nanoweb remains at least partially dry after the medium has been exposed to mist laden air for 30 minutes.
• the pressure drop across the medium under exposure to a water mist in an air stream rises by a factor of no more than 10 after exposure to the water mist for 3 minutes.
• the hydrophobic web can be in actual contact with the nanoweb or a second web that is either hydrophobic or hydrophilic can be situated between the hydrophobic web and the nanoweb.
• the hydrophobic web or the second web if in contact with the nanoweb, can be bonded over at least a portion of its surface with the nanoweb.
• the hydrophobic web or the second web can further be point bonded to the nanoweb, meaning that the bonding between the nanoweb and the hydrophobic web or second web can be in discrete points over the plane of the webs.
• the filtration data are taken from a test in which a flat-sheet media with a circular opening of 11.3 cm diameter is subjected to a 0.5-hour, continuous loading of a sodium chloride aerosol with a mass mean diameter of 0.26 micron, an air flow rate of 40 liter/min corresponding to a face velocity of 6.67 cm/s, and an aerosol concentration of 16 mg/m 3 .
• Filtration efficiency and initial pressure drop are measured at the beginning of the test and the final pressure drop is measured at the end of the test. Pressure drop increase is calculated by subtracting the initial pressure drop from the final pressure drop.
• the filter medium employed in the method of the invention therefore comprises at least two nortwoven layers, one of which is a nanofiber web and a second upstream hydrophobic nonwoven layer in fluid contact with the nanofiber web.
• the ratio of the mean flow pore size of the hydrophobic web layer to that of the nanofiber web is between about 1 to about 10, preferably between about 1 to about 8, and more preferably between about 1 and about 6.
• the hydrophobic web. whether meftblown, spunbond, or any other web, and the nanoweb of the present invention are in fluid contact with each other and may also be in physical contact with each other. They may also be bonded to each other by some kind of bonding means.
• Bonding means in the context of this invention refers to the manner in which lamination of two webs into a composite structure is accomplished. Methods that are suitable in the context of this invention are exemplified by, but not limited to, ultrasonic bonding, point bonding, vacuum lamination, and adhesive lamination. Those skilled in the art are familiar with the various types of bonding, and are capable of adapting any suitable bonding means for use in the invention.
• Ultrasonic bonding typically entails a process performed, for example, by passing a material between a sonic horn and an anvil roil such as illustrated in U.S. Patent Nos.4,374,888 and 5,591,278, hereby incorporated herein in their entirety by reference.
• the various layers that are to be attached together are simultaneously fed to the bonding nip of an ultrasonic unit.
• a variety of these units are available commercially. In general, these units produce high frequency vibration energy that melt
• thermoplastic components at the bond sites within the layers and join them together Therefore, the amount of induced energy, speed by which the combined components pass through the nip, gap at the nip, as well as the number of bond sites determine the extent of adhesion between the various layers.
• Very high frequencies are obtainable, and frequencies in excess of 18,000 Hz are usually referred to as ultrasonic, depending on the desired adhesion between various layers and the choice of material, frequencies as low as 5,000 Hz or even lower may produce an acceptable product.
• Point bonding typically refers to bonding one or more materials together at a plurality of discrete points.
• thermal point bonding generally involves passing one or more layers to be bonded between heated rolls, for example, an engraved pattern roll and a smooth calender roll.
• the engraved roll is patterned in some way so that the entire fabric is not bonded over its entire surface, and the calender roll is usually smooth.
• various patterns for engraved roils have been developed for functional as well as aesthetic reasons.
• Adhesive lamination usually refers to any process that uses one or more adhesives that are applied to a web to achieve a bond between two webs.
• the adhesive can be applied to the web by means such as coating with a roll, spraying, or application via fibers. Examples of suitable adhesives are given in U.S. Patent No.6,491,776, the disclosure of which is incorporated herein by reference in its entirety.
• the ratio of the mean flow pore sizes of the hydrophobic layer to the nanoweb layer are preferably related to the desired overall efficiency of the media at a given particle size, which can be controlled by the pore size of the nanoweb.
• the ratio of the mean flow pore size of the hydrophobic web layer to that of the nanofiber web is between about 1 to about 3 when the total media has an efficiency of greater than about 60%.
• the ratio of the mean flow pore size of the hydrophobic web layer to that of the nanofiber web is between about 2 to about 4 when the media has an efficiency of greater than about 70%.
• the ratio of the mean flow pore size of the hydrophobic web layer to that of the nanofiber web is between about 4 to about 6 when the media has an efficiency of greater than about 80%.
• the medium employed in the method of the invention may also be defined by the pore size of the hydrophobic web layer.
• the filter media may comprise a nanofiber web with a number average fiber diameter of less than one micron and an upstream meltbtown web layer in a face to face relationship with the nanofiber web where the mean flow pore size of the meltblown web layer is between about 12 to about 40 microns, preferably between about 15 to about 25 microns and more preferably between about 18 to about 22 microns.
• the medium employed in the method of the invention may also comprise a nanofiber web with a number average fiber diameter of less than one micron and an upstream meltblown web layer in a face to face relationship with the nanofiber web where the ratio of the mean flow pore size of the meltblown web layer to a given particle size is between about 50 and about 154 when the media has an efficiency of between 50% and 99.97% when impinged upon by particles of the given particle size.
• the ratio of the mean flow pore size of the meltblown web layer to a given particle size is between about 57 and about 96 when the media has an efficiency of between 50% and 99.97% when impinged upon by particles of the given particle size.
• the ratio of the mean flow pore size of the meltblown web layer to a particle size is between about 69 and about 85 when the media has an efficiency of between 50% and 99.97% when impinged upon by particles of the given particle size.
• the medium employed in the method of the invention may also demonstrate low efficiency changes upon being exposed to particles in an air stream.
• the filter media may exhibit an efficiency drop when filtering particles of size 0.26 microns of less than 5 % over 0.5 hours in a test in which a flat-sheet media with a circular opening of 11.3 cm diameter is subjected to a sodium chloride aerosol with a mass mean diameter of 0.26 micron, an air flow rate of 40 liter/min corresponding to a face velocity of 6.67 cm/s, and an aerosol
• the medium employed in the method of the invention in any of its embodiments may also exhibit low pressure drops when exposed to particles in an air stream.
• the filter media may exhibit pressure drop increase of less than 200 Pa when filtering particles of size 0.26 microns over 0.5 hours in a test in which a flat-sheet media with a circular opening of 11.3 cm diameter is subjected to a sodium chloride aerosol with a mass mean diameter of 0.26 micron, an air flow rate of 40 liter/min corresponding to a face velocity of 6.67 cm/s, and an aerosol concentration of 16 mg/m 3 .
• the basis weight of the hydrophobic web layer may be greater than about 10 gsm, preferably 15 gsm and more preferably 20 gsm or 30 gsm.
• the efficiency of the hydrophobic layer may be greater than about 50%, preferably greater than about 55% and more preferably greater man about 60%.
• the hydrophobic layer may comprise a melt blown polymeric web.
• the nanofjber web may comprise a nonwoven web made by a process selected from the group consisting of electroblowing, electrospinning, centrifugal spinning and melt blowing.
• the nanoweb may have a basis weight of greater than about 2 grams per square meter (gsm), and preferably greater than about 3 gsm, and more preferably greater than about 5 gsm.
• the media may further comprise a scrim support layer in contact with either the nanofiber web or the upstream layer.
• the medium employed in the method of the invention also may have resistance to the permeability decrease that may occur when a media is loaded with dust and exposed to moisture in the form of humidity.
• the present media when loaded sodium chloride aerosol with a mass mean diameter of 0.26 micron to a final resistance of between 150 and 300 Pa, the present media may exhibit a permeability loss of less than about 25% when exposed for 8 hours and air with a relative humidity of 96% at 25°C.
• the invention is further directed to a method of filtering gas, including air, comprising the step of passing the air through a media fitting any of the disclosed descriptions above.
• the as-spun nanoweb may comprise primarily or exclusively nanofibers, advantageously produced by electrospinning, such as classical electrospinning or electro-blowing, and in certain circumstances, by meltblowing or other such suitable processes.
• electrospinning such as classical electrospinning or electro-blowing
• meltblowing or other such suitable processes.
• Classical etectrospinning is a technique illustrated in U.S. Patent No.4,127,706. incorporated herein in its entirety, wherein a high voltage is applied to a polymer in solution to create nanofibers and nonwoven mats.
• total throughput in electrospinning processes is too low to be commercially viable in forming heavier basis weight webs.
• the "electroWowing” process is disclosed in World Patent Publication No. WO 03/080905, incorporated herein by reference in its entirety.
• a stream of polymeric solution comprising a polymer and a solvent is fed from a storage tank to a series of spinning nozzles within a spinneret, to which a high voltage is applied and through which the polymeric solution is discharged.
• compressed air that is optionally heated is issued from air nozzles disposed in the sides of, or at the periphery of the spinning nozzle.
• the air is directed generally downward as a blowing gas stream which envelopes and forwards the newly issued polymeric solution and aids in the formation of the fibrous web, which is collected on a grounded porous collection belt above a vacuum chamber.
• the electroblowing process permits formation of commercial sizes and quantities of nanowebs at basis weights in excess of about 1 gsm, even as high as about 40 gsm or greater, in a relatively short time period.
• Nanowebs can also be produced for the invention by the process of centrifugal spinning.
• Centrifugal spinning is a fiber forming process comprising the steps of supplying a spinning solution having at least one polymer dissolved in at least one solvent to a rotary sprayer having a rotating conical nozzle, the nozzle having a concave inner surface and a forward surface discharge edge; issuing the spinning solution from the rotary sprayer along the concave inner surface so as to distribute said spinning solution toward the forward surface of the discharge edge of the nozzle; and forming separate fibrous streams from the spinning solution while the solvent vaporizes to produce polymeric fibers in the presence or absence of an electrical field.
• a shaping fluid can flow around the nozzle to direct the spinning solution away from the rotary sprayer.
• the fibers can be collected onto a collector to form a fibrous web.
• Nanowebs can be further produced for the medium employed in the method of the invention by melt processes such as melt blowing.
• nanofibers can include fibers made from a polymer melt. Methods for producing nanofibers from polymer melts are described for example in U.S.6,520,425; U.S. 6,695,992; and U.S.6,382,526 to the University of Akron, U.S.6,183,670; U.S. 6,315,806; and U.S.4,536,361 to Torobin et al., and U.S. publication number 2006/0084340.
• a substrate or scrim can be arranged on the collector to collect and combine the nanofiber web spun on the substrate, so that the combined fiber web is used as a high-performance filter, wiper and so on.
• the substrate may include various nonwoven cloths, such as mertblown nonwoven cloth, needle-punched or spunlaced nonwoven doth, woven cloth, knitted cloth, paper, and the like, and can be used without limitations so long as a nanofiber layer can be added on the substrate.
• the nonwoven cloth can comprise spunbond fibers, dry-laid or wet-laid fibers, cellulose fibers, melt blown fibers, glass fibers, or blends thereof.
• Polymer materials that can be used in forming the nanowebs of the invention are not particularly limited and include both addition polymer arid condensation polymer materials such as, polyacetal, polyamide, polyester, polyotefins, cellulose ether and ester, polyalkylene sulfide, potyarylene oxide, polysulfone, modified polysulfbne polymers, and mixtures thereof.
• Preferred materials that fail within these generic classes include, poly (vinyichloride), polymethylmethacrylate (and other acrylic resins), polystyrene, and copolymers thereof (including ABA type block copolymers), poly (yinylidene fluoride), poly (vinylidene chloride), polyvinylalcohol in various degrees of hydrolysis (87% to 99.5%) in crosslinked and non-crosslinked forms.
• Preferred addition polymers tend to be glassy (a T 9 greater than room temperature). This is the case for polyvinylchloride and polymethylmethacrylate, polystyrene polymer compositions or alloys or low in crystallinity for polyvinylldene fluoride and polyvinylalcohol materials.
• polyamide condensation polymers are nylon materials, such as nyton-6, nylon-6, 6, nylon 6, 6-6, 10, and the like.
• any thermoplastic polymer capable of being meltblown into nanofibers can be used, including polyotefins, such as polyethylene, polypropylene and porybutylene, polyesters such as poly (ethylene terephthalate) and polyamides, such as the nylon polymers listed above.
• Suitable plasticizers will depend upon the polymer to be electrospun or electroblown, as well as upon the particular end use into which the nanoweb will be introduced.
• nylon polymers can be piasticized with water or even residual solvent remaining from the ltectrospinning or electroblowing process.
• Other known-in-the-art plasticizers which can be useful in lowering polymer T 9 include, but are not limited to aliphatic glycols, aromatic hydroxide
• sulphanomides including but not limited to those selected from the group consisting of dibutyl phthalate, dihext phthalate, dicyctohexy! phthalate, dioctyl phthalate, diisodecyl phthalate, diundecyi phthalate, didodecanyl phthalate, and diphenyl phthalate, and the like.
• the Handbook of Plasticizers edited by George Wypych, 2004 Chemtec Publishing, incorporated herein by reference, discloses other polymer/plasticizer combinations which can be used in the present invention.
• ASHRAE dust and ISO fine dust are typically used as test aerosol in dust holding capacity test for filters as well as filter media.
• size of these two types of dust are not reflective of the size of dust which high efficiency air filters are challenged with in field applications, especially when pre-fifters are used to remove large particles.
• Our field measurement in an air handling system with pre-fifters indicates that particles larger than 3 microns are rare and between 0.3 to 10 microns size range, about 60% particle by mass falls between 0.3 to 0.5 micron size range. Therefore existing dust holding test using ASHRAE and ISO fine test aerosol does not accurately predict filter media dust holding capacity in real life situation.
• a fine particle dust-loading test was developed which uses test aerosol with a mass mean diameter of 0.26 micron.
• a 2 wt% sodium chloride aqueous solution was used to generate fine aerosol with a mass mean diameter of 0.26 micron, which was used in the loading test
• the air flow rate was 40 liter/min which
• the aerosol concentration was about 16 mg/m 3 .
• Filtration efficiency and initial pressure drop are measured at the beginning of the test and the final pressure drop is measured at the end of the test.
• Pressure drop increase is calculated by subtracting the initial pressure drop from the final pressure drop.
• Filtration media air flow permeability is commonly measured using the Frazier measurement (ASTM D737). In this measurement, a pressure difference of 124.5 /m2 (0.5 inches of water column) is applied to a suitably clamped media sample and the resultant air flow rate is measured as Frazier permeability or more simply as "Frazier".
• Frazier permeability is reported in units of ft3/min/ft2. High Frazier corresponds to high airflow permeability and tow Frazier corresponds to low air flow permeability.
• the objective of the humidity test is to study the effect of relative humidity on filtration media loaded with dust or aerosol.
• Flat sheet media samples were loaded with fine aerosol of NaCI (as described above) to a final resistance between 150 to 300 Pa.
• the samples were conditioned at 25°C at different relative humidity for at least 8 hours. Air permeability of the sample was measured and recorded immediately after samples were removed from the conditioning chamber.
• Designation F 316 using a capillary flow porosimeter (model number CFP-
• 34RTF8A-3-6-L4 Porous Materials, Inc. (PMI), Ithaca, NY).
• Individual samples (8, 20 or 30 mm diameter) were wetted with low surface tension fluid (1 ,1 ,2,3,3,3- hexafluoropropene, or "Galwick," having a surface tension of 16 dyne/cm).
• Galwick low surface tension fluid
• Each sample was placed in a holder, and a differential pressure of air was applied and the fluid removed from the sample.
• the differential pressure at which wet flow is equal to one-half the dry flow (flow without wetting solvent) is used to calculate the mean flow pore size using supplied software.
• Bubble Point refers to the largest pore size.
• the moistures tester is an apparatus that contains an air chamber used to test the effects of water to simulate rain drops or water mist on filtration media.
• a sample of media is secured to the front, outside plane of the air chamber. Then, airflow is generated around the water nozzles and towards the media within the air chamber. Pressure differential between inside and outside of the air chamber is measured with pressure gauges. This value is recorded and the water nozzles are turned on. The water is left on for six minutes and pressure differential are taken at suitable intervals until the media is dry..
• an 18 cm by 18 cm sample of media is prepared. The sample is secured and sealed to outside of the air chamber perpendicular to the nozzle water stream using clamps. Air flow rate was 63 !iter/min which
• Water is turned on for six minutes and fine water mists are generated by 3 water spray nozzles. The media is exposed to the water mists.. The water flow rate was set at 70 ml/min. Every thirty seconds a pressure measurement is recorded until media dries out or pressure remains constant.
• a 24% solution of polyamide-6, 6 in formic acid was spun by etectrobtowing as described in WO 03/080905 to form nanowebs.
• the number average fiber diameters were approximately 350 nm.
• spunbond nonwoven webs were obtained made of polypropylene (68 grams per square meter (gsm) basis weight. Xavan® made by DuPont) and polyethylene terephthalate (PET) (70 gsm basis weight, F5070 style made by Kofon Co. in Korea) respectively. Melt blown webs were 23 gsm fine fiber webs made by DelStar Co. located in Middletown, Delaware.. Spunbond plus meltblown plus nanoftber (i.e. SMN) laminates were constructed by laminating to a 30 gsm spunbond polyethylene terephthalate (PET) scrim., C3030 style made by Kolon Co. in Korea.
• PET polyethylene terephthalate
• Example 3 was an MSN structure in which the M (a 20 gsm melt blown web made by DelStar Co. located in Middletown, Delaware) and the S (a 70 gsm spunbond PET web, F5070 style made by Kolon Co. in Korea) or example 2 were reversed. Table 3 shows the pressure buildup comparison between examples 2 and 3.
• numbers 1 and 3 had a hydrophobic web facing the air stream, in one case a spunbond and in one case a melt blown web.
• the data show the effectiveness of the invention in preventing pressure buildup by moisture.
• the melt blown web in the example 2 is hydrophobic and is upstream of nanoweb layer, the pressure increased is significantly high due to the hydrophilic spunbond non woven facing the air stream.
• the spunbond nonwoven is hydrophilic in the example 3 and is directly upstream of nanoweb layer and the pressure increased is significantly lessened due to hydrophobic melt blown nonwoven facing the air stream.

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• Chemical & Material Sciences (AREA)
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• Engineering & Computer Science (AREA)
• Textile Engineering (AREA)
• Filtering Materials (AREA)
• Nonwoven Fabrics (AREA)
• Separation Using Semi-Permeable Membranes (AREA)
• Filtering Of Dispersed Particles In Gases (AREA)

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• 2010
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