Classifications

• • D—TEXTILES; PAPER
  • D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
  • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
  • D04H3/00—Non-woven fabrics formed wholly or mainly of yarns or like filamentary material of substantial length
  • D04H3/02—Non-woven fabrics formed wholly or mainly of yarns or like filamentary material of substantial length characterised by the method of forming fleeces or layers, e.g. reorientation of yarns or filaments
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D46/00—Filters or filtering processes specially modified for separating dispersed particles from gases or vapours
  • B01D46/52—Particle separators, e.g. dust precipitators, using filters embodying folded corrugated or wound sheet material
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D39/00—Filtering material for liquid or gaseous fluids
• • 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
• • D—TEXTILES; PAPER
  • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
  • D01D—MECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
  • D01D5/00—Formation of filaments, threads, or the like
  • D01D5/08—Melt spinning methods
  • D01D5/082—Melt spinning methods of mixed yarn
• • D—TEXTILES; PAPER
  • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
  • D01D—MECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
  • D01D5/00—Formation of filaments, threads, or the like
  • D01D5/08—Melt spinning methods
  • D01D5/098—Melt spinning methods with simultaneous stretching
  • D01D5/0985—Melt spinning methods with simultaneous stretching by means of a flowing gas (e.g. melt-blowing)
• • D—TEXTILES; PAPER
  • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
  • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
  • D01F6/00—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof
  • D01F6/02—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from homopolymers obtained by reactions only involving carbon-to-carbon unsaturated bonds
  • D01F6/04—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from homopolymers obtained by reactions only involving carbon-to-carbon unsaturated bonds from polyolefins
  • D01F6/06—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from homopolymers obtained by reactions only involving carbon-to-carbon unsaturated bonds from polyolefins from polypropylene
• • D—TEXTILES; PAPER
  • D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
  • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
  • D04H1/00—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres
  • D04H1/40—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties
  • D04H1/54—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties by welding together the fibres, e.g. by partially melting or dissolving
  • D04H1/56—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties by welding together the fibres, e.g. by partially melting or dissolving in association with fibre formation, e.g. immediately following extrusion of staple fibres
• • 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
  • B01D2239/0604—Arrangement of the fibres in the filtering material
  • B01D2239/064—The fibres being mixed
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T442/00—Fabric [woven, knitted, or nonwoven textile or cloth, etc.]
  • Y10T442/60—Nonwoven fabric [i.e., nonwoven strand or fiber material]
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T442/00—Fabric [woven, knitted, or nonwoven textile or cloth, etc.]
  • Y10T442/60—Nonwoven fabric [i.e., nonwoven strand or fiber material]
  • Y10T442/608—Including strand or fiber material which is of specific structural definition
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T442/00—Fabric [woven, knitted, or nonwoven textile or cloth, etc.]
  • Y10T442/60—Nonwoven fabric [i.e., nonwoven strand or fiber material]
  • Y10T442/608—Including strand or fiber material which is of specific structural definition
  • Y10T442/614—Strand or fiber material specified as having microdimensions [i.e., microfiber]
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T442/00—Fabric [woven, knitted, or nonwoven textile or cloth, etc.]
  • Y10T442/60—Nonwoven fabric [i.e., nonwoven strand or fiber material]
  • Y10T442/608—Including strand or fiber material which is of specific structural definition
  • Y10T442/614—Strand or fiber material specified as having microdimensions [i.e., microfiber]
  • Y10T442/619—Including other strand or fiber material in the same layer not specified as having microdimensions
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T442/00—Fabric [woven, knitted, or nonwoven textile or cloth, etc.]
  • Y10T442/60—Nonwoven fabric [i.e., nonwoven strand or fiber material]
  • Y10T442/68—Melt-blown nonwoven fabric
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T442/00—Fabric [woven, knitted, or nonwoven textile or cloth, etc.]
  • Y10T442/60—Nonwoven fabric [i.e., nonwoven strand or fiber material]
  • Y10T442/681—Spun-bonded nonwoven fabric

Definitions

• This invention relates to meltblown webs and meltb lowing equipment.
• Patents or applications relating to nonwoven webs, their manufacture and articles made therefrom include U.S. Patent Nos. 3,981,650 (Page), 4,100,324 (Anderson), 4,118,531 (Hauser), 4,536,440 (Berg), 4,547,420 (Krueger et al), 4,931,355 (Radwanski et al.), 4,988,560 (Meyer et al.), 5,227,107 (Dickenson et al.), 5,374,458 (Burgio) 5,382,400 (Pike et al.
• JP 2001-049560 (Nissan Motor Co. Ltd.), JP 2002- 180331 (Chisso Corp. '331) and JP 2002-348737 (Chisso Corp. '737); and U.S. Patent Application Publication Nos. US2004/0097155 Al (Olson et al.) and US2005/0217226 Al (Sundet et al. '226).
• Shaped filtration articles such as molded respirators or pleated furnace filters are sometimes made using nonwoven webs made from multicomponent (e.g., bicomponent) fibers.
• Fig. Ia through Fig. Ie depict five popular bicomponent fiber configurations, which may be referred to respectively as “2-layer” or “side-by-side” (Fig. Ia), “islands in the sea” (Fig. Ib), “solid segmented pie” (Fig. Ic), “hollow segmented pie” (Fig. Id) and “sheath-core” (Fig. Ie).
• Shaped filtration articles may also be formed by adding an extraneous bonding material (e.g., an adhesive) to a filtration web, with consequent limitations due to the chemical or physical nature of the added bonding material including added web basis weight and loss of recyclability.
• an extraneous bonding material e.g., an adhesive
• Existing methods for manufacturing shaped filtration articles such as molded respirators or pleated furnace filters generally involve some compromise of web or article properties and one or more of the disadvantages mentioned above.
• 3,981 ,650 (Page) describes a meltb lowing die equipped with two die cavities each fed a different polymer from a separate extruder.
• the use of two extruders adds cost and complexity, and the use of two polymers can provide the other disadvantages mentioned above.
• Mikami also includes a comparative example in which 5 nozzles are set between a larger nozzle on each side of the row of smaller nozzles, and says that a nonwoven fabric made using such a nozzle arrangement or made using only one smaller nozzle disposed between adjacent larger nozzles will have a narrower fiber distribution and shorter service life.
• the invention provides in one aspect a porous monocomponent nonwoven web containing a meltb lown bimodal mass fraction/fiber size mixture of intermingled continuous micro fibers and larger size fibers of the same polymeric composition, wherein there are at least five times as many microfibers as larger size fibers and wherein a histogram of the mass fraction of fibers vs. fiber size exhibits a larger size fiber mode greater than 10 ⁇ m.
• the invention provides in another aspect a process for forming a monocomponent nonwoven web comprising flowing fiber- forming material through a die cavity having larger size orifices and at least five times as many smaller size orifices to form filaments, using air or other fluid to attenuate the filaments into fibers and collecting the attenuated fibers as a nonwoven web containing a meltblown bimodal mass fraction/fiber size mixture of intermingled continuous micro fibers and larger size fibers of the same polymeric composition, wherein there are at least five times as many microfibers as larger size fibers and wherein a histogram of the mass fraction of fibers vs. fiber size exhibits a larger size fiber mode greater than 10 ⁇ m.
• the disclosed nonwoven webs have a number of beneficial and unique properties. Both the larger size fibers and the microfibers may be highly charged.
• the larger size fibers can impart improved moldability and improved stiffness to the molded or shaped matrix.
• the microfibers can impart increased fiber surface area to the web, with beneficial effects such as improved filtration performance.
• filtration and molding properties can be tailored to a particular use.
• pressure drops of the disclosed nonwoven webs are kept lower, because the larger fibers physically separate and space apart the microfibers.
• the microfibers and larger size fibers also appear to cooperate with one another to provide a higher particle depth loading capacity.
• the disclosed webs have additional uses aside from filtration.
• Fig. Ia through Fig. Ie respectively show cross-sectional schematic views of several bicomponent fiber configurations
• FIG. 2 is a schematic side view of an exemplary process for making a monocomponent nonwoven web containing micro fibers and larger size fibers of the same polymeric composition
• Fig. 3 is an outlet end perspective view of an exemplary meltblowing die having a plurality of larger and smaller orifices
• FIG. 4 is a perspective view, partially in section, of a disposable personal respirator having a deformation-resistant cup-shaped porous monolayer matrix disposed between inner and outer cover layers;
• FIG. 5 is a perspective view of pleated filtration media
• Fig. 6 is a graph showing % NaCl penetration and pressure drop for Run Nos.
• Fig. 7 and Fig. 8 are photomicrographs of the Run No. 6-8F flat web and the
• Fig. 9 and Fig. 10 are histograms of fiber count (frequency) vs. fiber size in ⁇ m for the Run No. 6-8F flat web and the Run No. 6-8M molded matrix of Example 6;
• Fig. 11 is a graph showing % NaCl penetration and pressure drop for Run No. 7- IM of Example 7;
• Fig. 12, Fig. 13 and Fig. 15 are histograms of mass fraction vs. fiber size in ⁇ m
• Fig. 14 and Fig. 16 are histograms of fiber count (frequency) vs. fiber size in ⁇ m, for a series of webs of Example 10;
• Fig. 17 is a graph showing Deformation Resistance DR for a series of molded matrices of Example 10.
• porous means air-permeable.
• the term "monocomponent" when used with respect to a fiber or collection of fibers means fibers having essentially the same composition across their cross-section; monocomponent includes blends (viz., polymer alloys) or additive-containing materials, in which a continuous phase of uniform composition extends across the cross-section and over the length of the fiber.
• the term "of the same polymeric composition” means polymers that have essentially the same repeating molecular unit, but which may differ in molecular weight, melt index, method of manufacture, commercial form, etc.
• the term "size" when used with respect to a fiber means the fiber diameter for a fiber having a circular cross section, or the length of the longest cross-sectional chord that may be constructed across a fiber having a non-circular cross-section.
• the term "continuous" when used with respect to a fiber or collection of fibers means fibers having an essentially infinite aspect ratio (viz., a ratio of length to size of e.g., at least about 10,000 or more).
• mode when used with respect to a histogram of mass fraction vs. fiber size in ⁇ m or a histogram of fiber count (frequency) vs. fiber size in ⁇ m means a local peak whose height is larger than that for fiber sizes 1 and 2 ⁇ m smaller and 1 and 2 ⁇ m larger than the local peak.
• bimodal mass fraction/fiber size mixture means a collection of fibers having a histogram of mass fraction vs. fiber size in ⁇ m exhibiting at least two modes.
• a bimodal mass fraction/fiber size mixture may include more than two modes, for example it may be a trimodal or higher-modal mass fraction/fiber size mixture.
• bimodal fiber count/fiber size mixture means a collection of fibers having a histogram of fiber count (frequency) vs. fiber size in ⁇ m exhibiting at least two modes whose corresponding fiber sizes differ by at least 50% of the smaller fiber size.
• a bimodal fiber count/fiber size mixture may include more than two modes, for example it may be a trimodal or higher-modal fiber count/fiber size mixture.
• bonding when used with respect to a fiber or collection of fibers means adhering together firmly; bonded fibers generally do not separate when a web is subjected to normal handling.
• nonwoven web means a fibrous web characterized by entanglement or point bonding of the fibers.
• the term "monolayer matrix" when used with respect to a nonwoven web containing a bimodal mass fraction/fiber size mixture of fibers means having (other than with respect to fiber size) a generally uniform distribution of similar fibers throughout a cross-section of the web, and having (with respect to fiber size) fibers representing each modal population present throughout a cross-section of the web.
• Such a monolayer matrix may have a generally uniform distribution of fiber sizes throughout a cross-section of the web or may, for example, have a depth gradient of fiber sizes such as a preponderance of larger size fibers proximate one major face of the web and a preponderance of micro fibers proximate the other major face of the web.
• the term "attenuating the filaments into fibers” means the conversion of a segment of a filament into a segment of greater length and smaller size.
• the term "meltblown" when used with respect to a nonwoven web means a web formed by extruding a fiber-forming material through a plurality of orifices to form filaments while contacting the filaments with air or other attenuating fluid to attenuate the filaments into fibers and thereafter collecting a layer of the attenuated fibers.
• meltblown fibers means fibers prepared by extruding molten fiber- forming material through orifices in a die into a high-velocity gaseous stream, where the extruded material is first attenuated and then solidifies as a mass of fibers.
• meltblown fibers have sometimes been reported to be discontinuous, the fibers generally are long and entangled sufficiently that it is usually not possible to remove one complete meltblown fiber from a mass of such fibers or to trace one meltblown fiber from beginning to end.
• meltblowing die means a die for use in a meltblowing process.
• microf ⁇ bers means fibers having a median size (as determined using microscopy) of 10 ⁇ m or less; "ultrafme microf ⁇ bers” means microf ⁇ bers having a median size of two ⁇ m or less; and "submicron microf ⁇ bers” means microf ⁇ bers having a median size one ⁇ m or less.
• an array of submicron micro fibers it means the complete population of micro fibers in that array, or the complete population of a single batch of micro fibers, and not only that portion of the array or batch that is of submicron dimensions.
• the term "charged” when used with respect to a collection of fibers means fibers that exhibit at least a 50% loss in Quality Factor QF (discussed below) after being exposed to a 20 Gray absorbed dose of 1 mm beryllium-filtered 80 KVp X-rays when evaluated for percent dioctyl phthalate ( % DOP) penetration at a face velocity of 7 cm/sec.
• self-supporting means a web having sufficient coherency and strength so as to be handleable by itself using reel-to-reel manufacturing equipment without substantial tearing or rupture.
• King Stiffness means the force required using a King Stiffness Tester from J. A. King & Co., Greensboro, North Carolina to push a flat-faced, 2.54 cm diameter by 8.1 m long probe against a molded cup-shaped respirator prepared by forming a test cup-shaped matrix between mating male and female halves of a hemispherical mold having a 55mm radius and a 310 cm ⁇ volume. The molded matrices are placed under the tester probe for evaluation after first being allowed to cool.
• the disclosed monocomponent monolayer web contains a bimodal mass fraction/fiber size mixture of micro fibers and larger size fibers.
• the micro fibers may for example have a size range of about 0.1 to about 10 ⁇ m, about 0.1 to about 5 ⁇ m or about 0.1 to about 1 ⁇ m.
• the larger size fibers may for example have a size range of about 10 to about 70 ⁇ m, about 10 to about 50 ⁇ m or about 15 to about 50 ⁇ m.
• fiber size in ⁇ m may for example have a micro fiber mode of about 0.1 to about 10 ⁇ m, about 0.5 to about 8 ⁇ m or about 1 to about 5 ⁇ m, and a larger size fiber mode of about 10 to about 50 ⁇ m, about 10 to about 40 ⁇ m or about 12 to about 30 ⁇ m.
• the disclosed web may also have a bimodal fiber count/fiber size mixture whose histogram of fiber count (frequency) vs. fiber size in ⁇ m exhibits at least two modes whose corresponding fiber sizes differ by at least 50%, at least 100%, or at least 200% of the smaller fiber size.
• the microfibers may also for example provide at least 20% of the fibrous surface area of the web, at least 40% or at least 60%.
• the web may have a variety of Effective Fiber Diameter (EFD) values, for example an EFD of about 5 to about 40 ⁇ m, or of about 6 to about 35 ⁇ m.
• EFD Effective Fiber Diameter
• the web may also have a variety of basis weights, for example a basis weight of about 60 to about 300 grams/m ⁇ or about 80 to about 250 grams/m ⁇ .
• the web may have a variety of Gurley Stiffness values, for example a Gurley Stiffness of at least about 100 mg, at least about 200 mg, at least about 300 mg, at least about 500 mg, at least about 1000 mg or at least about 2000 mg.
• the disclosed molded matrix preferably has a King Stiffness greater than 1 N and more preferably at least about 2 N or more.
• a King Stiffness greater than 1 N and more preferably at least about 2 N or more.
• Deformation Resistance DR preferably is at least about 75 g and more preferably at least about 200 g.
• the disclosed molded respirator When exposed to a 0.075 ⁇ m sodium chloride aerosol flowing at 85 liters/min, the disclosed molded respirator preferably has a pressure drop less than 20 mm H2O and more preferably less than 10 mm H2O. When so evaluated, the molded respirator also preferably has a % NaCl penetration less than about 5%, and more preferably less than about 1%.
• the flat web from which such a molded matrix may be formed preferably has an initial filtration quality factor QF of at least about 0.4 mm'l H2O and more preferably at least about 0.5 mm " ' H2O.
• the disclosed web preferably has a Gurley Stiffness before pleating of at least about 100 mg, and may have a Gurley Stiffness before pleating of at least about 200 mg or at least about 300 mg.
• a Gurley Stiffness before pleating of at least about 100 mg
• a Gurley Stiffness before pleating of at least about 200 mg or at least about 300 mg.
• the disclosed pleated filter preferably has an average initial sub-micron efficiency of at least about 15% at a 1.52 meters/sec (300 ft/min) face velocity, and may have an average initial sub-micron efficiency of at least about 25 % or at least about 50%.
• the flat web from which such a pleated filter may be formed preferably has an initial filtration quality factor QF of at least about 0.3, and more preferably at least about 0.4.
• Fig. 2 illustrates an apparatus 200 for making a porous monocomponent nonwoven web containing a bimodal fiber count/fiber size mixture of intermingled continuous micro fibers and larger size fibers of the same polymeric composition.
• Liquefied fiber-forming polymeric material fed from hopper 202 and extruder 204 enters meltblowing die 206 via inlet 208, flows through die cavity 210, and exits die cavity 210 through a row (discussed below in connection with Fig. 3) of larger and smaller size orifices arranged in line across the forward end of die cavity 210 and through which the fiber- forming material is extruded as an array of filaments 212.
• a set of cooperating gas orifices (also discussed below) through which a gas, typically heated air, is forced at very high velocity, attenuate the filaments 212 into fibers 214.
• the fibers 214 land against porous collector 216 and form a self-supporting nonwoven meltblown web 218.
• Fig. 3 shows meltblowing die 206 in outlet end perspective view, with the attenuating gas deflector plates removed.
• Die 206 includes a projecting tip portion 302 with a row 304 of larger orifices 306 and smaller orifices 308 which define a plurality of flow passages through which liquefied fiber- forming material exits die 206 and forms the filaments 212.
• Holes 310 receive through-bolts (not shown in Fig. 3) which hold the various parts of the die together.
• the larger orifices 306 and smaller orifices 308 have a 2: 1 size ratio and there are 9 smaller orifices 308 for each larger orifice 306.
• ratios of larger: smaller orifice sizes may be used, for example ratios of 1.5:1 or more, 2:1 or more, 2.5:1 or more, 3:1 or more, or 3.5:1 or more.
• Other ratios of the number of smaller orifices per larger orifice may also be used, for example ratios of 5 : 1 or more, 6:1 or more, 10:1 or more, 12:1 or more, 15:1 or more, 20:1 or more or 30: 1 or more.
• meltblowing may be found in Wente, Van A. "Superfine Thermoplastic Fibers," in Industrial Engineering Chemistry, Vol. 48, pages 1342 et seq. (1956), or in Report No. 4364 of the Naval Research Laboratories, published May 25, 1954, entitled “Manufacture of Superfine Organic Fibers” by Wente, V. A.; Boone, C. D.; and Fluharty, E. L.; in U.S. Patent No. 5,993,943 (Bodaghi et al); and in copending U.S. Patent
• the disclosed nonwoven webs may have a random fiber arrangement and generally isotropic in-plane physical properties (e.g., tensile strength). In general such isotropic nonwoven webs are preferred for forming cup-shaped molded respirators.
• the webs may instead have an aligned fiber construction (e.g., one in which the fibers are aligned in the machine direction as described in the above-mentioned Shah et al. U.S. Patent No. 6,858,297) and anisotropic in-plane physical properties. If such anisotropic nonwoven webs are employed to form pleated filters, the pleat rows may if desired be aligned with respect to one or more anisotropic properties of interest so as to reduce pleat deformation at high face velocities.
• the polymer may be essentially any thermoplastic fiber-forming material capable of providing a nonwoven web.
• the polymer may be essentially any thermoplastic fiber-forming material which will maintain satisfactory electret properties or charge separation.
• Preferred polymeric fiber- forming materials for chargeable webs are non-conductive resins having a volume resistivity of 1014 ohm- centimeters or greater at room temperature (22° C). Preferably, the volume resistivity is about 1()16 ohm-centimeters or greater. Resistivity of the polymeric fiber-forming material may be measured according to standardized test ASTM D 257-93.
• Polymeric fiber- forming materials for use in chargeable webs also preferably are substantially free from components such as antistatic agents that could significantly increase electrical conductivity or otherwise interfere with the fiber's ability to accept and hold electrostatic charges.
• Some examples of polymers which may be used in chargeable webs include thermoplastic polymers containing polyolefms such as polyethylene, polypropylene, polybutylene, poly(4-methyl-l-pentene) and cyclic olefin copolymers, and combinations of such polymers.
• polymers which may be used but which may be difficult to charge or which may lose charge rapidly include polycarbonates, block copolymers such as styrene-butadiene-styrene and styrene-isoprene-styrene block copolymers, polyesters such as polyethylene terephthalate, polyamides, polyurethanes, and other polymers that will be familiar to those skilled in the art.
• the fibers preferably are prepared from poly-4- methyl-1 pentene or polypropylene. Most preferably, the fibers are prepared from polypropylene homopolymer because of its ability to retain electric charge, particularly in moist environments.
• Electric charge can be imparted to the disclosed nonwoven webs in a variety of ways. This may be carried out, for example, by contacting the web with water as disclosed in U.S. Patent No. 5,496,507 to Angadjivand et al., corona-treating as disclosed in U.S. Patent No. 4,588,537 to Klasse et al., hydrocharging as disclosed, for example, in
• Additives may be added to the polymer to enhance the web's filtration performance, electret charging capability, mechanical properties, aging properties, coloration, surface properties or other characteristics of interest.
• Representative additives include fillers, nucleating agents (e.g., MILLADTM 3988 dibenzylidene sorbitol, commercially available from Milliken Chemical), electret charging enhancement additives (e.g., tristearyl melamine, and various light stabilizers such as CHIMASSORBTM 119 and CHIMASSORB 944 from Ciba Specialty Chemicals), cure initiators, stiffening agents (e.g., poly(4-methyl-l-pentene)), surface active agents and surface treatments (e.g., fluorine atom treatments to improve filtration performance in an oily mist environment as described in U.S. Patent Nos.
• nucleating agents e.g., MILLADTM 3988 dibenzylidene sorbitol, commercially available from Milliken Chemical
• electret charging enhancement additives e.g., tristearyl melamine, and various light stabilizers such as CHIMASSORBTM 119 and CHIMASSORB 944 from Ciba
• Fig. 4 shows in partial cross-section an exemplary cup-shaped disposable personal respirator 400.
• Respirator 400 includes inner cover web 402, monocomponent filtration layer 404, and outer cover layer 406.
• Welded edge 408 holds these layers together and provides a face seal region to reduce leakage past the edge of respirator 400.
• Fig. 5 shows in perspective view an exemplary pleated filter 500 made from the disclosed monocomponent filtration layer 502 which has been formed into rows of spaced pleats 504.
• filter 500 may be used as is or may be reinforced with a suitable support (e.g., an expanded metal screen) and optionally mounted in a suitable frame (e.g., a metal or cardboard frame) to provide a replaceable filter for use in e.g., HVAC systems.
• a suitable support e.g., an expanded metal screen
• a suitable frame e.g., a metal or cardboard frame
• the increased stiffness of pleated filter 500 (arising from the presence of the larger diameter fibers in the disclosed monocomponent filtration layer) is believed to contribute to increased resistance of pleated filter 500 to pleat deformation at high filter face velocities.
• further details regarding the construction of filter 500 will be familiar to those skilled in the art.
• the disclosed nonwoven webs may be formed into these and other finished articles using methods and additional elements that will be familiar to those having ordinary skill in the art.
• flat web properties such as basis weight, web thickness, solidity, EFD, Gurley Stiffness, Taber Stiffness, pressure drop, initial % NaCl penetration, % DOP penetration or the Quality Factor QF before shaping, and to monitor shaped (e.g., molded or pleated) matrix properties such as King Stiffness, Deformation Resistance DR, pressure drop or average initial submicron efficiency.
• molding properties may be evaluated by forming a test cup-shaped matrix between mating male and female halves of a hemispherical mold having a 55mm radius and a 310 cm ⁇ volume.
• EFD may be determined (unless otherwise specified) using an air flow rate of
• Gurley Stiffness may be determined using a Model 4171 E GURLEYTM Bending Resistance Tester from Gurley Precision Instruments. Rectangular 3.8 cm x 5.1 cm rectangles are die cut from the webs with the sample long side aligned with the web transverse (cross-web) direction. The samples are loaded into the Bending Resistance Tester with the sample long side in the web holding clamp. The samples are flexed in both directions, viz., with the test arm pressed against the first major sample face and then against the second major sample face, and the average of the two measurements is recorded as the stiffness in milligrams. The test is treated as a destructive test and if further measurements are needed fresh samples are employed.
• Taber Stiffness may be determined using a Model 150-B TABERTM stiffness tester (commercially available from Taber Industries). Square 3.8 cm x 3.8 cm sections are carefully vivisected from the webs using a sharp razor blade to prevent fiber fusion, and evaluated to determine their stiffness in the machine and transverse directions using 3 to 4 samples and a 15° sample deflection.
• Percent penetration, pressure drop and the filtration Quality Factor QF may be determined using a challenge aerosol containing NaCl or DOP particles, delivered (unless otherwise indicated) at a flow rate of 85 liters/min, and evaluated using a TSITM Model 8130 high-speed automated filter tester (commercially available from TSI Inc.).
• the particles may generated from a 2% NaCl solution to provide an aerosol containing particles with a diameter of about 0.075 ⁇ m at an airborne concentration of about 16-23 mg/m ⁇ , and the Automated Filter Tester may be operated with both the heater and particle neutralizer on.
• the aerosol may contain particles with a diameter of about 0.185 ⁇ m at a concentration of about 100 mg/m ⁇ , and the Automated Filter Tester may be operated with both the heater and particle neutralizer off.
• the samples may be exposed to the maximum NaCl or DOP particle penetration at a 13.8 cm/sec face velocity for flat web samples or an 85 liters/min flowrate for a molded or shaped matrix before halting the test.
• Calibrated photometers may be employed at the filter inlet and outlet to measure the particle concentration and the % particle penetration through the filter.
• An MKS pressure transducer (commercially available from MKS Instruments) may be employed to measure pressure drop ( ⁇ P, mm H2O) through the filter. The equation:
• AP may be used to calculate QF.
• Parameters which may be measured or calculated for the chosen challenge aerosol include initial particle penetration, initial pressure drop, initial Quality Factor QF, maximum particle penetration, pressure drop at maximum penetration, and the milligrams of particle loading at maximum penetration (the total weight challenge to the filter up to the time of maximum penetration).
• the initial Quality Factor QF value usually provides a reliable indicator of overall performance, with higher initial QF values indicating better filtration performance and lower initial QF values indicating reduced filtration performance.
• Deformation Resistance DR may be determined using a Model TA-XT2i/5
• Texture Analyzer (from Texture Technologies Corp.) equipped with a 25.4 mm diameter polycarbonate test probe.
• a molded test matrix (prepared as described above in the definition for King Stiffness) is placed facial side down on the Texture Analyzer stage.
• Deformation Resistance DR is measured by advancing the polycarbonate probe downward at 10 mm/sec against the center of the molded test matrix over a distance of 25 mm. Using five molded test matrix samples, the maximum (peak) force is recorded and averaged to establish the DR value.
• Average initial submicron efficiency may be determined by installing the framed filter into a test duct and subjecting the filter to potassium chloride particles which have been dried and charge-neutralized.
• a test face velocity of 300 ft/min (1.52 meters/sec) may be employed.
• An optical particle counter may be used to measure the concentration of particles upstream and downstream from the test filter over a series of twelve particle size ranges or channels. The particle size ranges in each channel are taken from ASHRAE standard 52.2 ("Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size"). The equation:
• Capture efficiency (%) — - - - x 100 upstream particle count
• the capture efficiency values for each of the four submicron channels may be averaged to obtain a single value for "average initial sub-micron efficiency".
• the test velocity, efficiency and pressure drop results are usually all reported.
• the disclosed nonwoven webs may be used for a variety of molded respirator shapes and for a variety of filter configurations, including HVAC (e.g., furnace) filters, vehicle cabin filters, clean room filters, humidifier filters, dehumidif ⁇ er filters, room air purifier filters, hard disk drive filters and other flat or pleatable supported or self- supporting filtration articles.
• HVAC e.g., furnace
• the disclosed nonwoven webs may if desired include one or more additional layers other than the disclosed monocomponent web.
• molded respirators may employ inner or outer cover layers for comfort or aesthetic purposes and not for filtration or stiffening.
• one or more porous layers containing sorbent particles may be employed to capture vapors of interest, such as the porous layers described in U.S. Patent Application Serial No.
• the extruder had a 20/1 length/diameter ratio and a 3/1 compression ratio.
• a Zenith 10 cc/rev melt pump metered the flow of polymer to a 10 in. (25.4 cm) wide drilled orifice meltb lowing die whose original 0.012 in. (0.3 mm) orifices had been modified by drilling out every 21st orifice to 0.025 in. (0.6 mm), thereby providing a 20:1 ratio of the number of smaller size to larger size holes and a 2:1 ratio of larger hole size to smaller hole size.
• the line of orifices had 25 holes/inch (10 holes/cm) hole spacing.
• Patent No. 5,496,507 (Angadjivand et al. '507) and allowed to dry.
• Table IA Set out below in Table IA are the Run Number, basis weight, EFD, web thickness, initial pressure drop, initial NaCl penetration and Quality Factor QF for each web at a 13.8 cm/sec face velocity.
• the Table IA webs were next molded to form cup-shaped molded matrices for use as personal respirators.
• the top mold was heated to about 235° F (113° C)
• the bottom mold was heated to about 240° F (116° C)
• a mold gap of 0.050 in. (1.27 mm) was employed and the web was left in the mold for about 9 seconds.
• the matrix Upon removal from the mold, the matrix retained its molded shape.
• Table IB Set out below in Table IB are the Run Number, King Stiffness, initial pressure drop, and the initial (and for Run Nos. 1-lM and 1-4M, the maximum loading) NaCl penetration values for the molded matrices.
• Fig. 6 is a graph showing % NaCl penetration and pressure drop for the molded matrices of Run Nos. 1-lM and 1-4M. Curves A and B respectively are the % NaCl penetration results for Run Nos. 1-lM and 1-4M, and Curves C and D respectively are the pressure drop results for Run Nos. 1-lM and 1-4M. Fig. 6 shows that the molded matrices of Run Nos. 1-lM and 1-4M provide monocomponent, monolayer molded matrices which pass the N95 NaCl loading test of 42 C.F.R. Part 84.
• Example 2 Example 2
• Table 2A webs were next molded using the method of Example 1 to form cup-shaped molded matrices for use as personal respirators.
• Table 2B are the Run Number, King Stiffness, initial pressure drop, and initial NaCl penetration for the molded matrices.
• Table 3 A webs were next molded using the method of Example 1 to form cup-shaped molded matrices for use as personal respirators.
• Table 3B are the Run Number, King Stiffness, initial pressure drop, and initial NaCl penetration for the molded matrices.
• Table 4A webs were next molded using the method of Example 1 to form cup-shaped molded matrices for use as personal respirators.
• Table 4B are the Run Number, King Stiffness, initial pressure drop, and initial NaCl penetration for the molded matrices.
• Table 5 A webs were next molded using the method of Example 1 to form cup-shaped molded matrices for use as personal respirators.
• Table 5B are the Run Number, King Stiffness, initial pressure drop, and initial NaCl penetration for the molded matrices.
• Table 6A The Table 6A webs were next molded using the method of Example 1 to form cup-shaped molded matrices for use as personal respirators. Set out below in Table 6B are the Run Number, King Stiffness, initial pressure drop, and initial NaCl penetration for the molded matrices. Table 6B
• the Run No. 6-8F flat web and 6-8M molded matrix were analyzed using scanning electron microscopy (SEM), at magnifications of 50 to l,000X made using a LEO VP 1450 electron microscope (from the Carl Zeiss Electron Microscopy Group), operated at 15 kV, 15 mm WD, 0° tilt, and using a gold/palladium-coated sample under high vacuum.
• Fig. 7 and Fig. 8 are photomicrographs of the Run No. 6-8F flat web and the Run No. 6-8M molded matrix. Histograms of fiber count (frequency) vs.
• Fig. 9 and Fig. 10 are histograms of fiber count (frequency) vs. fiber size for the Run No. 6-8F flat web and the Run No. 6-8M molded matrix of Example 6. Further details regarding the fiber size analyses for these webs are shown below in Table 6C: Table 6C
• Table 7A The Table 7A webs were next molded using the method of Example 1 to form cup-shaped molded matrices for use as personal respirators. Set out below in Table 7B are the Run Number, King Stiffness, initial pressure drop, and initial NaCl penetration for the molded matrices. Table 7B
• Fig. 11 is a graph showing % NaCl penetration and pressure drop for the molded matrix of Run No. 7- IM. Curves A and B respectively are the % NaCl penetration and pressure drop results. Fig. 11 and the data in Table 7B show that the molded matrix of Run No. 7- IM provides a monocomponent, monolayer molded matrix which passes the N95 NaCl loading test of 42 C.F.R. Part 84.
• Example 8 [0084] Using the method of Example 3, webs were made from EXXON PP3746G polypropylene to which had been added 0.8 % CHIMASSORB 944 hindered amine light stabilizer from Ciba Specialty Chemicals as an electret charging additive and then hydrocharged with distilled water. Set out below in Table 8A are the Run Number, basis weight, EFD, web thickness, initial pressure drop, initial NaCl penetration and Quality Factor QF for each web.
• Table 8 A webs were next molded using the method of Example 1 to form cup-shaped molded matrices for use as personal respirators.
• Table 8B are the Run Number, King Stiffness, initial pressure drop, and the initial (and, for Run No. 8- 3M, the maximum loading) NaCl penetration values for the molded matrices.
• the respirators included a blown microf ⁇ ber outer cover layer web, a PE85-12 thermoplastic nonwoven adhesive web from Bostik Findley, the flat web of this Example 9, another PE85-12 thermoplastic nonwoven adhesive web and another blown microf ⁇ ber inner cover layer web.
• the layers were formed into a cup-shaped respirator using a mold like that described above but having a ribbed front surface.
• the resulting molded respirators were evaluated according to ASTM F- 1862-05, "Standard Test Method for Resistance of Medical Face Masks to Penetration by Synthetic Blood (Horizontal Projection of Fixed Volume at a Known Velocity)", at test pressures of 120 mm Hg and 160 mm Hg.
• the 120 mm Hg test employed a 0.640 sec.
• the 160 mm Hg test employed a 0.554 sec. valve time and a 0.052 MPa tank pressure.
• the respirators passed the test at both test pressures.
• Table 9 Set out below in Table 9 are the Run Number, and the basis weight, EFD, thickness, initial pressure drop and initial NaCl penetration for the molded monocomponent web.
• a single screw extruder with a 50 mm diameter screw and a lOcc melt pump were used to supply the die with 100% TOTAL 3868 polypropylene.
• the die also had a 0.20 mm air slit width, a 60° nozzle edge angle, and a 0.58 mm air lip opening.
• a fine mesh screen moving at 1 to 50 m/min was employed to collect the fibers.
• Table 1OA The other operating parameters are shown below in Table 1OA:
• Fig. 12 is a histogram of mass fraction vs. fiber size in ⁇ m for the 200 gsm web.
• the web exhibited modes at 2 and 7 ⁇ m. Local peaks also appeared at 4 and 10 ⁇ m.
• the 4 ⁇ m peak did not have a larger height than fiber sizes 2 ⁇ m smaller and 2 ⁇ m larger and did not represent a mode
• the 10 ⁇ m peak did not have a larger height than fiber sizes 2 ⁇ m smaller and did not represent a mode.
• the web did not have a larger size fiber mode greater than 10 ⁇ m.
• the 200 gsm web was molded using the general method of Example 2 to form a cup-shaped molded matrix. The heated mold was closed to a 0.5 mm gap and an approximate 6 second dwell time was employed. The molded matrix was allowed to cool, and found to have a King Stiffness value of 0.64 N.
• Fig. 13 is a histogram of mass fraction vs. fiber size in ⁇ m for the 200 gsm web. The web exhibited modes at 4, 10, 17 and 22 ⁇ m. Local, non-modal peaks also appeared at 8 and 13 ⁇ m. As shown in Fig. 13, the web had larger size fiber modes greater than 10 ⁇ m.
• Fig. 14 is a histogram of fiber count (frequency) vs. fiber size in ⁇ m for the same 200 gsm web.
• the 200 gsm web was molded using the general method of Example 2 to form a cup-shaped molded matrix.
• the heated mold was closed to a 0.5 mm gap and an approximate 6 second dwell time was employed.
• the molded matrix was allowed to cool, and found to have a King Stiffness value of 0.98 N, a value that was not greater than 1 N.
• the die tip for this latter die had been modified to provide a row of larger and smaller sized orifices with a greater number of smaller orifices between larger orifices than disclosed in Mikami et al.
• the larger orifices had a 0.63 mm diameter (Da)
• the smaller orifices had a 0.3 mm diameter (Db)
• the orifice diameter ratio R (Da/Db) was 2.1, there were 9 smaller orifices between each pair of larger orifices and the orifices were spaced at 25 orifices/in. (9.8 orifices/cm).
• a single screw extruder with a 50 mm diameter screw and a lOcc melt pump were used to supply the die with polymer.
• the die also had a 0.76 mm air slit width, a 60° nozzle edge angle, and a 0.86 mm air lip opening.
• a fine mesh screen moving at 1 to 50 m/min and the operating parameters shown below in Table 1OC were employed to collect webs at 60, 100, 150 and 200 gsm:
• Fig. 15 is a histogram of mass fraction vs. fiber size in ⁇ m for the 200 gsm 100 MFR web. The web exhibited modes at 15, 30 and 40 ⁇ m. As shown in Fig. 15, the web had a larger size fiber mode greater than 10 ⁇ m.
• Fig. 16 is a histogram of fiber count (frequency) vs. fiber size in ⁇ m for the same 200 gsm web.
• Fig. 17 shows a plot of Deformation Resistance DR values vs. basis weight.
• Curves A, B, C and D respectively show webs made according to Table 1OA (37 gsm, 5:1 Db/Da ratio), Table 1OB and Table 1OC (37 gsm) and Table 1OC (100 gsm).
• Table 1OD and Fig. 17 webs made according to Mikami et al. Comparative Example 5 using a polymer like the 40 melt flow rate polymer employed by Mikami et al. had relatively low Deformation Resistance DR values.
• Employing a higher melt flow rate polymer than the Mikami et al. polymer or using a die with a greater number of smaller orifices per larger orifice than the Mikami et al. dies provided webs having significantly greater Deformation Resistance DR values.

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