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
  • D04H5/00—Non woven fabrics formed of mixtures of relatively short fibres and yarns or like filamentary material of substantial length
  • D04H5/06—Non woven fabrics formed of mixtures of relatively short fibres and yarns or like filamentary material of substantial length strengthened or consolidated by welding-together thermoplastic fibres, filaments, or yarns
• • 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
  • D04H5/00—Non woven fabrics formed of mixtures of relatively short fibres and yarns or like filamentary material of substantial length
  • D04H5/08—Non woven fabrics formed of mixtures of relatively short fibres and yarns or like filamentary material of substantial length characterised by the method of forming fleeces or layers, e.g. reorientation of fibres or yarns
• • 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
  • B01D39/163—Other self-supporting filtering material ; Other filtering material of organic material, e.g. synthetic fibres the material being fibrous of synthetic origin sintered or bonded
• • 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
• • 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
  • D04H3/016—Non-woven fabrics formed wholly or mainly of yarns or like filamentary material of substantial length characterised by the fineness
• • 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
  • D04H3/03—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 at random
• • 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
  • D04H3/08—Non-woven fabrics formed wholly or mainly of yarns or like filamentary material of substantial length characterised by the method of strengthening or consolidating
  • D04H3/16—Non-woven fabrics formed wholly or mainly of yarns or like filamentary material of substantial length characterised by the method of strengthening or consolidating with bonds between thermoplastic filaments produced in association with filament formation, e.g. immediately following extrusion
• • 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]
  • Y10T442/608—Including strand or fiber material which is of specific structural definition
  • Y10T442/614—Strand or fiber material specified as having microdimensions [i.e., microfiber]
  • Y10T442/625—Autogenously bonded
• • 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]
  • Y10T442/626—Microfiber is synthetic polymer
• • 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
• • 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]
  • Y10T442/69—Autogenously bonded 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]
  • Y10T442/696—Including strand or fiber material which is stated to have specific attributes [e.g., heat or fire resistance, chemical or solvent resistance, high absorption for aqueous compositions, water solubility, heat shrinkability, etc.]

Definitions

• the present invention relates to nonwoven fibrous webs comprising a combination of continuous oriented meltspun fibers and separately prepared micro fibers.
• Nonwoven fibrous webs used as filtration media often comprise two or more kinds of fibers, each having a different average diameter so the web can filter particles of a broad range of sizes.
• the different kinds of fibers lie in different layers of the web.
• One example taught in Healy, U.S. Patent Application Publication No. US 2004/0035095 is a filtration web comprising a layer of microf ⁇ bers having diameters between about 0.8 and 1.5 micrometers meltblown onto a spunbond web (see paragraphs [0009] through [0012]).
• a problem with such a web is that such small micro fibers, exposed on the top of the web, are very fragile and easily crushed by normal handling or contact with some object.
• SMS webs comprising a layer of spunbond fibers, a layer of meltblown micro fibers, and another layer of spunbond fibers.
• the multilayer nature of such webs increases their thickness and weight, and also introduces some complexity in manufacture.
• micro fibers are incorporated into a nonwoven fibrous web that comprises a coherent matrix of meltspun fibers. It has been found that a stream of micro fibers, including a stream consisting only of very fine microf ⁇ bers having a median diameter of one or two micrometers or less, can be merged with a stream of meltspun fibers, whereupon the micro fibers are captured by the stream of meltspun fibers and dispersed among the meltspun fibers. Also, by the present invention the collected meltspun fibers are bonded, preferably by an autogenous thermal bonding step, to form a coherent matrix that is self-sustaining in which the microfibers are reliably held and protected so the web can be handled and used with minimal loss or crushing of microfibers. Preferably the meltspun fibers are oriented fibers comprised of a semicrystalline polymeric material, thus adding to the mechanical or physical properties of the web.
• the present invention provides a nonwoven fibrous web that comprises a matrix of continuous meltspun fibers bonded to a coherent self-sustaining form, and separately prepared microfibers dispersed among the meltspun fibers, most often in an amount accounting for at least one weight-percent of the fibers of the web.
• a web as described has a number of beneficial and unique properties.
• a useful finished product can be prepared that consists only of a single layer, but comprises a mixture of microfibers and larger fibers, with broadened filtration capability and increased fiber surface area.
• Such a single-layer product offers important efficiencies - product complexity and waste are reduced by eliminating laminating processes and equipment and by reducing the number of intermediate materials.
• webs of the invention can be quite economical. Also, if the fibers of the web all comprise the same polymeric composition, the web can be fully recyclable.
• a web of the invention can be used in a variety of forms - e.g., it can be molded or pleated, as well as being used in its collected form.
• the web is given an even more greatly increased fiber surface area, with such beneficial effects as improved filtration and thermal or acoustic insulating performance.
• Performance such as filtration and insulation performance can be tailored to a particular use by using fibers of different diameters.
• pressure drops of webs of the invention are kept lower, because the larger meltspun fibers physically separate and space apart the microfibers.
• micro fibers are fibers having a median diameter of 10 micrometers or less; "ultrafine microfibers” are microfibers having a median diameter of two micrometers or less; and “submicron microfibers” are microfibers having a median diameter one micrometer or less.
• an array of submicron microfibers it means the complete population of microfibers in that array, or the complete population of a single batch of microfibers, and not only that portion of the array or batch that is of submicron dimensions.
• Continuous oriented meltspun fibers herein refers to essentially continuous fibers issuing from a die and traveling through a processing station in which the fibers are permanently drawn and at least portions of the polymer molecules within the fibers are permanently oriented into alignment with the longitudinal axis of the fibers ("oriented" as used with respect to fibers means that at least portions of the polymer molecules of the fibers are aligned along the longitudinal axis of the fibers).
• Microfibers herein refers to 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.
• "Separately prepared microfibers” means a stream of microfibers produced from a micro fiber- forming apparatus (e.g., a die) positioned such that the microfiber stream is initially spatially separate (e.g., over a distance of about 1 inch (25 mm) or more from, but will merge in flight and disperse into, a stream of larger size meltspun fibers.
• Automatic bonding is defined as bonding between fibers at an elevated temperature as obtained in an oven or with a through-air bonder without application of solid contact pressure such as in point-bonding or calendering.
• Molecularly same polymer refers to polymers that have essentially the same repeating molecular unit, but which may differ in molecular weight, method of manufacture, commercial form, etc.
• All the fibers of the web are said to be unoriented to give good isotropic properties (column 13, lines 47-49). There is no teaching of a web comprising a coherent matrix of continuous oriented thermally bonded meltspun fibers, with micro fibers dispersed among the meltspun fibers.
• Bodaghi et al U.S. Patent No. 5,993,943 teaches small-diameter oriented meltblown fibers, including fibers that can average less than one micrometer (micron) in diameter) to which non-oriented meltblown fibers may be added; but there is no teaching of a coherent matrix of bonded meltspun fibers in which meltblown microf ⁇ bers are dispersed.
• a filter element that comprises a porous molded web that contains thermally bonded staple fibers and non-thermally bonded electrically charged microfibers, the porous molded web being retained in its molded configuration, at least in part, by bonds between the staple fibers at points of fiber intersection.
• Figure 1 is a schematic overall diagram of apparatus of the invention for forming a nonwoven fibrous web according to the invention.
• FIG. 2 is an enlarged side view of a processing chamber for preparing fibers useful in a web of the invention, with mounting means for the chamber not shown.
• Figure 3 is a top view, partially schematic, of the processing chamber shown in
• Figure 4 is an enlarged view of a portion of the apparatus shown in Figure 1.
• Figure 5 is a schematic enlarged and expanded view of a heat-treating part of the apparatus shown in Figure 1.
• Figure 6 is a perspective view of the apparatus of Figure 5.
• Figure 7 is a histogram showing the distribution of fibers in a web of Example 11.
• Figures 1-6 show an illustrative apparatus for carrying out the invention as part of a direct- web production method and apparatus.
• Figure 1 is a schematic overall side view;
• Figures 2 and 3 are enlarged views of fiber-forming portions of the Figure 1 apparatus;
• Figures 4 and 5 are enlarged views of other portions of the apparatus shown in Figure 1 ;
• Figure 6 is a perspective view of apparatus as shown in Figures 1 and 5.
• a stream 1 of continuous oriented meltspun fibers is prepared in fiber-forming apparatus 2 and directed toward collection apparatus
• meltblown fibers emanating from meltb lowing apparatus 101 On its course between the fiber- forming apparatus 2 and the collection apparatus 3, the stream 1 is intercepted by a stream 100 of meltblown fibers emanating from meltb lowing apparatus 101.
• the two streams merge as discussed in more detail below and become deposited on the collection apparatus as a blended web of the oriented continuous meltspun fibers and the meltblown fibers.
• a second meltblowing apparatus 101a could be used to introduce meltblown fibers on both sides of the meltspun stream.
• the fiber-forming apparatus 2 in Figure 1 is a preferred apparatus for use in the invention.
• fiber-forming material is brought to an extrusion head 10 — in this illustrative apparatus, by introducing a polymeric fiber- forming material into a hopper 11, melting the material in an extruder 12, and pumping the molten material into the extrusion head 10 through a pump 13.
• solid polymeric material in pellet or other particulate form is most commonly used and melted to a liquid, pumpable state, other fiber-forming liquids such as polymer solutions can also be used.
• the extrusion head 10 may be a conventional spinnerette or spin pack, generally including multiple orifices arranged in a regular pattern, e.g., straightline rows.
• Filaments 15 of fiber-forming liquid are extruded from the extrusion head and conveyed to a processing chamber or attenuator 16.
• the distance 17 the extruded filaments 15 travel before reaching the attenuator 16 can vary, as can the conditions to which they are exposed.
• quenching streams 18 of air or other gas are presented to the extruded filaments to reduce the temperature of the extruded filaments 15.
• the streams of air or other gas may be heated to facilitate drawing of the fibers.
• a first air stream 18a blown transversely to the filament stream which may remove undesired gaseous materials or fumes released during extrusion
• a second quenching air stream 18b that achieves a major desired temperature reduction.
• quenching streams may be used; for example, the stream shown as 18b in Figure 1 could itself comprise more than one stream to achieve a desired level of quenching.
• the quenching air may be sufficient to solidify the extruded filaments 15 before they reach the attenuator 16.
• the extruded filaments are still in a softened or molten condition when they enter the attenuator.
• no quenching streams are used; in such a case ambient air or other fluid between the extrusion head 10 and the attenuator 16 may be a medium for any change in the extruded filaments before they enter the attenuator.
• the filaments 15 pass through the attenuator 16, and eventually exit onto a collector 19 where they are collected as a mass of fibers 20, as discussed in more detail below.
• the collector 19 is generally porous and a gas-withdrawal device 14 can be positioned below the collector to assist deposition of fibers onto the collector.
• the distance 21 between the attenuator exit and the collector may be varied to obtain different effects.
• the filaments are lengthened and reduced in diameter and polymer molecules in the filaments become oriented, i.e., at least portions of the polymer molecules within the fibers become aligned with the longitudinal axis of the fibers. In the case of semicrystalline polymers, the orientation is generally sufficient to develop strain-induced crystallinity, which greatly strengthens the resulting fibers.
• the representative attenuator 16 includes slanted entry walls 27, which define an entrance space or throat 24a of the attenuation chamber 24.
• the entry walls 27 preferably are curved at the entry edge or surface 27a to smooth the entry of air streams carrying the extruded filaments 15.
• the walls 27 are attached to a main body portion 28, and may be provided with a recessed area 29 to establish a gap 30 between the body portion 28 and wall 27.
• Air may be introduced into the gaps 30 through conduits 31 , creating air knives (represented by the arrows 32) that increase the velocity of the filaments traveling through the attenuator, and that also have a further quenching effect on the filaments.
• the attenuator body 28 is preferably curved at 28a to smooth the passage of air from the air knife 32 into the passage 24.
• the angle ( ⁇ ) of the surface 28b of the attenuator body can be selected to determine the desired angle at which the air knife impacts a stream of filaments passing through the attenuator.
• the air knives may be disposed further within the chamber.
• the attenuation chamber 24 may have a uniform gap width (the horizontal distance 33 on the page of Figure 2 between the two attenuator sides is herein called the gap width) over its longitudinal length through the attenuator (the dimension along a longitudinal axis 26 through the attenuation chamber is called the axial length).
• the gap width may vary along the length of the attenuator chamber.
• the attenuation chamber is defined by straight or flat walls; in such embodiments the spacing between the walls may be constant over their length, or alternatively the walls may slightly diverge or converge
• the length of the attenuation chamber 24 can be varied to achieve different effects; variation is especially useful with the portion between the air knives 32 and the exit opening 34, sometimes called herein the chute length 35.
• the angle between the chamber walls and the axis 26 may be wider near the exit 34 to change the distribution of fibers onto the collector; or structure such as deflector surfaces, Coanda curved surfaces, and uneven wall lengths may be used at the exit to achieve a desired spreading or other distribution of fibers.
• the gap width, chute length, attenuation chamber shape, etc. are chosen in conjunction with the material being processed and the mode of treatment desired to achieve desired effects. For example, longer chute lengths may be useful to increase the crystallinity of prepared fibers. Conditions are chosen and can be widely varied to process the extruded filaments into a desired fiber form.
• the meltb lowing apparatus 101 can be of known structure and operated in known ways to produce meltblown micro fibers for use in the invention.
• An early description of the basic meltb lowing method and apparatus is 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.
• Polypropylene is generally the preferred material for forming meltblown fibers, but many other materials can be used, including generally any of the materials useful for forming the meltspun fibers. It is usually preferred in the case of webs that are to be electrically charged that both the meltspun fibers and the meltblown fibers be made of an electrically chargeable material.
• Preferred materials include polypropylene, polycarbonate, polymethyl pentene, and copolymers of cyclic olefins; others are polyethylene and polylactic acid polymers.
• the distance 107 in Figure 4 from the exit of the die 102 to the centerline of the meltspun stream 1 is preferably about 2 to 12 inches (5 to 25 centimeters) and preferably about 6 or 8 inches (about 15 or 20 centimeters) or less for very small micro fibers
• the stream 100 of meltb lown fibers is preferably disposed at an acute angle ⁇ to the stream 1 of meltspun fibers, so that a vector of the meltb lown stream 100 is directionally aligned with the stream 1.
• ⁇ is between about 0 and 45 degrees and more preferably between 10 and 30 degrees.
• the amount of molecular material of the phase susceptible to undesirable (softening- impeding) crystal growth is not as great as it was before treatment.
• the amorphous- characterized phase is understood to have experienced a kind of cleansing or reduction of molecular structure that would lead to undesirable increases in crystallinity in conventional untreated fibers during a thermal bonding operation.
• Treated fibers of the invention are capable of a kind of "repeatable softening,” meaning that the fibers, and particularly the amorphous-characterized phase of the fibers, will undergo to some degree a repeated cycle of softening and resolidifying as the fibers are exposed to a cycle of raised and lowered temperature within a temperature region lower than that which would cause melting of the whole fiber.
• repeatable softening is indicated when a treated web (which already generally exhibits a useful bonding as a result of the heating and quenching treatment) can be heated to cause further autogenous bonding of the fibers.
• the cycling of softening and resolidifying may not continue indefinitely, but it is generally sufficient that the fibers may be initially bonded by exposure to heat, e.g., during a heat treatment according to the invention, and later heated again to cause re-softening and further bonding, or, if desired, other operations, such as calendering or re-shaping.
• the invention is most commonly practiced by collecting a web on a continuous screen-type collector such as the belt-type collector 19 in Figure lor a screen-covered drum.
• a web can be collected by aiming the merged stream of meltspun and meltblown fibers into the gap between two collectors, as shown and described in Olson et al., WO 2004/046443, whereupon a web having a C-shaped configuration of fibers is obtained.
• a web could be prepared from the submicron fibers themselves, such a web would be flimsy and weak. But by incorporating the submicron fibers in a coherent bonded oriented fiber matrix a strong and self-supporting web or sheet material can be obtained.
• Preferably webs of the invention have a Gurley stiffness of at least 200 mg, especially when intended to be used in devices such as pleated filters.
• meltspun fibers of Example 4 were measured with scanning electron microscopy (SEM) and found to have a median diameter (44 fibers measured) of 15 micrometers.
• the meltspun fibers of Examples 1-3 were estimated to have a median fiber diameter of approximately 11 micrometers (based on similar samples).
• polypropylene having a melt flow index of 350 (Fina
• meltblown fibers were measured with SEM and found to have a median fiber diameter of 1.13 micrometers, and the meltblown fiber stream had a width such as to be present at a width of about 12 inches (about 30 centimeters) in the collected web on the collection belt 19. Essentially 100% of the meltblown fibers were captured within the meltspun stream.
• the web of one example (Example 4) was cross-sectioned and micro fibers were found to be distributed through the full thickness of the web.
• the webs of Examples 1-3 had a ratio of about 64 parts by weight of meltspun fibers and 36 parts by weight meltblown fibers.
• the web of Example 4 had a ratio of about 82 parts by weight of meltspun fibers and 18 parts by weight meltblown fibers.
• the combined stream of meltspun and meltblown fibers was collected on a 20- mesh stainless steel collection belt (19), which moved at a rate of 29 fpm (about 8.8 meters/minute) for Examples 1-3 and 47 fpm (about 14.3 meters/minute) for Example
• the challenge stream comprised particles generated from a 2% NaCl solution in a concentration of 19-25 mg/m 3 .
• the automatic filter tester was run with the heater on and particle neutralizer on. Results are given in Table 2. The last column gives the total weight collected on the filter from the challenge stream up to the time of maximum penetration.
• Samples F and H are most preferred because they exhibit penetration and pressure drop loading results very similar to the standard multilayer commercial respirator.
• Sample S is also a most preferred sample because it is run at significantly higher total process throughput, has low initial pressure drop, and has maximum penetration of less than 5%.
• Other preferred samples in Table 2 include the A, G, I, and T samples, because they exhibit initial pressure drop of less than 10 mm H 2 O, maximum penetrations of less than 5%, and moderate NaCl challenge at maximum penetration (meaning that they do not plug up too rapidly).
• x position means the distance 107 on Fig. 4 of the drawings). Samples were also hydrocharged in the manner described in Examples 1-4.
• a critical parameter in determining if a filter web is suitable for use as a self-supporting pleated filter is the stiffness of the web; adequate stiffness is necessary to initially form and later retain the pleated shape.
• the filter media property is being described and not the filter property, i.e. that the media itself is not reinforced by wire, mesh, or stiffening layers even if the filter construction may have wire, glue, or frame reinforcement to strengthen the entire filter.
• the exemplary webs of the invention were compared to the flat web properties of a commercially available HVAC filter, namely a 2-inch-deep (50 mm) pleated filter with 5 mm pleat spacing, the filter media being a three-layer laminate including a 17 gsm polypropylene spunbond coverweb, a 40 gsm electrostatically charged meltblown filter media, and a 90 gsm polyester spunbond stiffening layer.
• the web used to make the commercial pleated filter was tested in the flat condition before folding into a pleated form.
• the key targeted properties of the exemplary webs of the invention include a Gurley stiffness of greater than 600 mg (to achieve the stated two-inch pleat depth of the commercial filter) and similar penetration (efficiency) as the commercial filter.
• Examples 5-13 are all about 100 gsm, which is considerably less than the current commercial [multilayer product] laminate solution of approximately 150 gsm. Further evaluation was performed by load-testing Examples 5-13 as flat filters with NaCl on a TSI 8130 Automatic Filter Tester (approximately 0.075 ⁇ m diameter particles).
• the flat media was tested with the collector side of the web both up and down to examine whether fiber intermixing and/or the collection surface affected the loading behavior. Samples were loaded to maximum penetration at 60 lpm (10 cm/s face velocity) flowrate, and the tests were then stopped. Particles were generated from a 2% NaCl solution in a concentration of about 16-23 mg/m 3 . The automatic filter tester was run with the heater on and particle neutralizer on. Results are in Table 5.
• Samples Example 9 and 10 webs tested “down” are the most preferred samples because they have initial pressure drop closest to the comparison, lower initial penetration, higher initial quality factor, and lower maximum penetration, all with similar pressure drop rise as a function of challenge.
• the Example 12 web is also a most preferred sample because it has slightly lower initial pressure drop, somewhat higher maximum penetration, but almost 3X the mass challenge at maximum penetration for nearly equal pressure drop rise - equating to a better-loading filter.
• the hydrocharged Samples 9 and 11 tested “up” and Samples 5, 8, 11, and 13 tested “down” are also preferred samples because they have moderate pressure drop, low initial penetration, moderate to high initial quality factors, and maximum penetration less than the control.
• Sample 12 is the overall most preferred sample due to the balance of flat media physical properties and filtration performance.
• Example 11 was submitted for analysis with a scanning electron microscope, and the meltblown fibers were found to have a median diameter of 0.65 micrometers, a mean diameter of 0.88 micrometers, and a standard deviation of 0.67 micrometers; the maximum diameter was 4.86 micrometers and the minimum was 0.20 micrometers.
• the sample size was 151 meltblown fibers and 28 meltspun fibers; all fibers less than 10 microns in diameter were assumed to be meltblown fibers.
• a histogram of the size distribution is pictured in Figure 7, with fiber diameter in micrometers plotted along the abscissa and frequency plotted along the ordinate.
• the surface area of the meltblown micro fibers was determined as about 51% of the total web surface area, and the surface area of the submicron fibers was determined as about 23% of the total web surface area.
• the submicron fibers of Example 11 were captured with essentially 100% efficiency during the web formation process, and the resulting bonded web had adequate strength and integrity for normal handling.
• Samples 1-13 While a specific construction is compared in these experiments, the deep body of information included in Samples 1-13 illustrate that the present invention can be tuned and used for numerous pleated filter applications, including but not limited to low to high MERV ratings for HVAC filter applications, room air purifier filters, cabin air filters, automotive intake filters, and many general or specific pleated filter uses.
• meltblown web Example Cl
• the meltblown web consisted only of polypropylene fibers having an effective fiber diameter of 5.5 micrometers, the web basis weight was 106 gsm, and the web had a solidity of 5.4%. Results are reported in Table 6, where "t" is time in hours.
• webs of the invention had a compaction of less than 10%. Even a compaction of 20% would be markedly better than the compaction exhibited by the meltblown web.

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• 2006
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