US20070216059A1 - Apparatus and methods for producing split spunbond filaments - Google Patents

Abstract

A spunbonding apparatus capable of producing multicomponent spunbond filaments. The spunbonding apparatus includes a spunbonding apparatus comprises a spinneret discharging multicomponent filaments and a filament-drawing device applying a first force that is effective to attenuate the filaments. A force applicator stationed between the spinneret and the filament-drawing device is operative for applying a second force to the filaments that promotes filament splitting. Splitting may occur before the filaments enter the filament-drawing device, within the filament-drawing device, and/or after discharge from the filament-drawing device.

Description

FIELD OF THE INVENTION
• The invention relates generally to melt-spinning apparatus and methods, and more particularly, to a spunbonding apparatus and methods for forming slit spunbond filaments.
BACKGROUND OF THE INVENTION
• Melt-spinning technologies are used for forming nonwoven webs of meltblown and/or spunbond filaments or fibers composed of one or more thermoplastic polymers such as polyethylene, polypropylene, and polyester. Nonwoven webs are fashioned into many consumer and industrial products, including disposable hygienic articles, disposable protective apparel, fluid filtration media, and household durables.
• Spunbonding processes generally involve pumping one or more molten thermoplastic polymers through a spin pack that distributes, filters, combines, and finally extrudes continuous filaments of the constituent thermoplastic polymer(s) through an array of thousands of spinneret orifices in a spinneret. After extrusion, the spunbond filaments are drawn or stretched by, for example, an impinging high-velocity airflow that accelerates the filament velocity and then quenched to cause solidification. The drawn spunbond filaments are propelled toward a forming zone and collected on a moving collector to form the spunbond nonwoven web.
• Multicomponent spunbond filaments consist of two or more thermoplastic polymers that have separate flow paths that are manipulated as the molten thermoplastic polymers pass through the spin pack. Multicomponent fibers enable a manufacturer to take advantage of the material-specific properties of different thermoplastic polymers simultaneously, often with synergistic results.
• Meltblown processes are formed by extruding a molten thermoplastic polymer through a plurality of die capillaries as molten fibers and impinging the molten fibers with high velocity air streams that attenuate the molten fibers to reduce their diameter. 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, which may be continuous or discontinuous, are generally smaller than ten microns in average diameter and may be as small as one to five microns or less. Spunbond filaments, which are typically in the one to three denier range as determined by their application, are significantly larger than meltblown filaments.
• Many nonwoven web structures are currently produced using spunbond and meltblown filaments or a composite of both filament types. Generally, nonwoven webs of meltblown filaments include tortuous fluid paths and may be appropriate for use as a barrier material. However, meltblown nonwoven webs lack sufficient web tensile strength or bonding to be used independently for products that experience high abrasion or contact with a user's skin. To solve that dilemma, the nonwovens industry often uses nonwoven webs of spunbond filaments with enhanced strength and abrasion resistance properties either in combination with meltblown nonwoven webs or as a substitute for meltblown nonwoven webs.
• Another difficulty associated with barrier materials of meltblown filaments is that the throughput of meltblown processes is significantly less than the throughput of spunbond processes. Consequently, multiple beams of meltblown filaments must be deposited to form a laminate barrier structure. Meltblown filaments are formed from spinnerettes having between 1000 and 4000, typically 1200 and 2000, filament outlets per meter. In contrast, spunbond filaments are formed from spinnerettes having 4000 to 8000 filament outlets per meter. Additionally, throughput per outlet is generally greater for spunbond processes than for meltblown processes. However, spunbond filaments are too large in diameter for use as, for example, a barrier material.
• Multi-component spunbond filaments having an appropriate arrangement of regions of different thermoplastic polymers (e.g., a segmented pie arrangement or a side-by-side arrangement) may be split to define smaller individual filaments each consisting of one region. After these filaments are collected as a nonwoven web, the filaments in the nonwoven web may be divided by a mechanical based approach involving a hydroentangling (or spunlacing) process that impinges the nonwoven web with fine water jets under high pressure to prompt filament division along the boundaries between different multicomponent regions. When mechanical action is used to split multicomponent filaments, the thermoplastic polymers are selected to bond poorly with each other to facilitate subsequent division. Another type of multi-component spunbond filaments have an appropriate arrangement of regions of different thermoplastic polymers (e.g., a island in the sea arrangement) that may be separated to define smaller individual filaments each consisting of one region. After these filaments are collected as a nonwoven web, the filaments in the nonwoven web may be separated by a chemical based approach that involves wetting the nonwoven web with a solvent that selectively dissolves the sea thermoplastic polymer in the multi component filaments leaving the islands of the other thermoplastic polymer as the smaller individual filaments
• Among the disadvantages of these conventional processes for splitting multicomponent spunbond filaments is that the wet nonwoven web must be dried to remove solvent or water after processing. This introduces an additional processing step between web production and fashioning the nonwoven web into a consumer or industrial product. In addition, the solvent used in chemical processes creates a waste stream that must be either recycled or discarded.
• It would be desirable, therefore, to provide a spunbonding apparatus and methods capable of forming smaller diameter filaments that overcomes these and other disadvantages of conventional apparatus and methods.
SUMMARY
• In one embodiment of the present invention, a spunbonding apparatus comprises a spinneret adapted to discharge a plurality of multicomponent filaments that move in a downwardly direction away from the spinneret and a filament-drawing device positioned below the spinneret. The filament-drawing device is adapted to pneumatically attenuate the multicomponent filaments, each of which has at least two polymer regions. The spunbonding apparatus further includes a force applicator effective to divide at least some of the multicomponent filaments into the at least two polymer regions to form smaller filaments. The force applicator may direct an air stream to impinge the multicomponent filaments between the spinneret and the filament-drawing device. Alternatively, the force applicator may include a roller contacting the plurality of multicomponent filaments. The spunbonding apparatus further includes a collector for collecting the smaller filaments. Splitting may occur before the filaments enter the filament-drawing device, within the filament-drawing device, and/or after discharge from the filament-drawing device.
• In another aspect of the invention, a method of forming a spunbond nonwoven web includes forming a plurality of multicomponent filaments each having at least two polymer regions and pneumatically attenuating the multicomponent filaments. The method further includes applying a dividing force to the moving plurality of multicomponent filaments effective for dividing the at least two polymer regions of at least some of the filaments to provide smaller filaments and collecting the smaller filaments to form the spunbond nonwoven web.
• Among other advantages, one benefit of a split multicomponent filament is that the constituent regions are smaller than traditional spunbond filaments. This provides a structure that may be used as a substitute for traditional meltblown filaments in forming nonwoven webs, such as nonwoven webs used as barrier materials. The ability to produce spunbond filaments with a smaller fiber diameter, in accordance with the present invention, also addresses the deficiency in the throughput of traditional meltblowing processes by providing a small filament at a greater throughput characteristic of spunbond processes that may be used as a substitute or replacement for meltblown filaments.
• These and other objects and advantages of the present invention shall become more apparent from the accompanying drawings and description thereof.
BRIEF DESCRIPTION OF THE FIGURES
• The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description given below, serve to explain the principles of the invention.
• FIG. 1 is a diagrammatic side view of a spunbonding apparatus in accordance with an embodiment of the invention;
• FIG. 1A is a diagrammatic perspective view of a portion of the spunbonding apparatus ofFIG. 1;
• FIG. 2 is a cross-sectional view of a filament discharged from the spinneret of the spunbonding apparatus ofFIG. 1;
• FIG. 3 is a diagrammatic side view of a filament splitting in accordance with the principles of the invention;
• FIG. 4 is a diagrammatic perspective view of a spunbonding apparatus in accordance with another embodiment of the invention;
• FIG. 5 is a diagrammatic side view of a filament splitting in accordance with the principles of the invention; and
• FIG. 6 is a diagrammatic perspective view of a spunbonding apparatus in accordance with yet another embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
• With reference toFIGS. 1 and 1A, aspunbonding apparatus10 is equipped with a pair ofextruders12,14 each coupled to receive amounts of a solid melt-processable thermoplastic polymer from a corresponding one of a pair ofhoppers11,13.Extruder12 converts one solid melt-processable thermoplastic polymer (polymer A) into a molten state. The molten polymer A is transferred fromextruder12 under pressure and at an elevated temperature suitable for melt processing from theextruder12 to at least onemetering pump16.Extruder14 converts another solid melt-processable thermoplastic polymer (polymer B) into a molten state. The molten polymer B is transferred under pressure and at an elevated temperature suitable for melt processing from theextruder14 to at least onemetering pump18.
• Metering pumps16,18 pump metered amounts of the corresponding one of molten thermoplastic polymers throughseparate distribution chambers17,19 extending through adie body25 to aspin pack20. Thespin pack20 and diebody25 form components of a spin beam assembly that extends in the cross-machine direction of theapparatus10 and, thus, defines the width (typically several meters) of anonwoven web30. Thespin pack20 is heated and supported by the surroundingdie body25.
• Thespin pack20 containsflow passageway plates38 that cooperate for distributing and combining the two molten thermoplastic polymers received from thedistribution chambers17,19. Heat transferred from thedie body25 to thespin pack20 maintains the two molten thermoplastic polymers in theflow passageway plates38 at a temperature suitable for melt processing and providing an extrudable melt. Theflow passageway plates38 convey the combined thermoplastic polymers to aspinneret22 from which a curtain offilaments24 is discharged from an array of discharge openings (not shown) distributed across an outlet surface of thespinneret22.
• Quench ducts27, which are positioned below thespinneret22 and flanking thespinneret22, direct a lowvelocity cross flow21 of cooling air at the descending curtain offilaments24. Thecross flow21 of cooling air quenches thefilaments24 by reducing the filament temperature to accelerate solidification. A blower (not shown) and an air chilling device or air temperature reduction (i.e., air conditioning) device supplies a flow of cooling air to the quenchducts27.
• A filament-drawingdevice26 is also positioned below thespinneret22 and receives the descending curtain of quenchedfilaments24. Thefilaments24 are directed into a draw jet or filament-drawingdevice26 along with entrained ambient air from the environment above and surrounding the filament-drawingdevice26. A blower (not shown) supplies process air, which may be heated, to a supply manifold of the filament-drawingdevice26. Generally, the filament-drawingdevice26 includes avertical passage31, which is illustrated with an exaggerated width for clarity, defined between manifold segments and in which thefilaments24 are impinged by convergingsheets35a,bof high velocity process air. Theprocess air sheets35a,bare introduced into thevertical passage31 throughslots33a,bdefined in the opposite sidewalls of thevertical passage31. Theprocess air sheets35a,bare discharged from theslots33a,bin a downwardly direction generally parallel to the length of thefilaments24.
• Because thefilaments24 are extensible, thesheets35a,bof high-velocity process air apply a downward drag or pneumatic force that creates longitudinal tension to attenuate thefilaments24. Exemplary filament-drawingdevices26 are disclosed in U.S. Pat. Nos. 4,340,563, 6,182,732 and 6,799,957, the disclosures of which are hereby incorporated herein by reference in their entirety. Other types of filament-drawingdevices26 are contemplated by the invention as usable with thespunbonding apparatus10.
• A descending curtain ofattenuated filaments24 is discharged from filament-drawingdevice26 and propelled toward a movingporous collector28. Thefilaments24 are deposited in a substantially random manner as substantially flat loops on thecollector28 to aggregately formnonwoven web30. The width of thenonwoven web30 deposited oncollector28 is approximately equal to the width of the curtain offilaments24. Thecollector28 is traveling in a machine direction (MD) relative to thespunbonding apparatus10 and filament-drawingdevice26.
• Positioned below thecollector28 is anair management system32 that supplies a vacuum transferred through thecollector28 for attracting thefilaments24 onto thecollector28 and disposing of the high-velocity process air discharged from the filament-drawingdevice26 so that filament laydown is relatively undisturbed. Exemplaryair management systems32 are disclosed in U.S. Pat. No. 6,499,982, the disclosure of which is hereby incorporated by reference herein in its entirety.
• Additional meltspinning apparatus (not shown) may be provided either downstream or upstream ofspunbonding apparatus10 for depositing one or more additional spunbond and/or meltblown nonwoven webs of either monocomponent or multicomponent filaments either as a substrate for receivingnonwoven web30 or onto an exposed surface ofnonwoven web30. An example of such a multilayer laminate in which some of the individual layers are spunbond and some meltblown is a spunbond/meltblown/spunbond (SMS) laminate made by sequentially depositing onto a moving forming belt first a spunbond fabric layer, then a meltblown fabric layer and last another spunbondlayer containing filaments24.
• With continued reference toFIGS. 1 and 1A,spunbonding apparatus10 further includes a pair ofair knives40a,blocated generally in the open space between thespinneret22 and the filament-drawingdevice26 and below the quenchducts27.Air knife40adirects a flat sheet or stream of process air, generally indicated byreference numeral42a, with a high velocity towards and against the flow offilaments24 on a downstream side of thefilaments24.Air knife40bdirects a flat sheet or stream of process air, generally indicated byreference numeral42b, with a high velocity towards and against the flow offilaments24 on an upstream side of thefilaments24. Downstream and upstream are defined in relation to the machine direction and relative to the curtain offilaments24. The high velocity streams42a,bof process air from theair knives40a,bimpinge thefilaments24 and apply a force to thefilaments24 between thespinneret22 and filament-drawingdevice26 and before thefilaments24 enter the filament-drawingdevice26.
• Each of theair knives40a,btransforms or amplifies a relatively low flow of compressed air to deliver the corresponding one of the high velocity process air streams42a,b.Air knife40aincludes an internal air plenum (not shown) coupled by a feed conduit41awith a source of compressed air, such as a standard centrifugal blower.Air knife40aincludes an outlet44a, such as a single elongate slot or a line of shorter aligned slots, from which theair stream42ais discharged. Alternatively, the outlet44aofair knife40amay include a plurality of densely-spaced orifices, or any other suitable structure for discharging the corresponding process air stream as a high velocity stream42. Theair knife40amay also include a Coanda surface that defines a guide for directing the high velocity stream discharged from the outlet44a.Air knife40bhas a construction identical or similar to theconstruction air knife40aand, accordingly, also includes a feed conduit41bandoutlet44bsimilar to the feed conduit41aand outlet44aas described above forair knife40a.
• Suitable air knives40a,bfor use in the present are commercially available from various vendors including but not limited to EXAIR Corporation (Cincinnati, Ohio), which sells air knives under the Super Air Knife trade name. The invention contemplates that theair knives40a,bmay be replaced by multiple air jets (not shown). The invention also contemplates that, although twoair knives40a,bare depicted inFIG. 1, more than two air knives, each similar or identical toair knives40a,bor even a single air knife, similar or identical to either of theair knives40a,b, may be used to provide additional high velocity air streams, similar to high velocity air streams42a,b, that impinge thefilaments24.
• With reference toFIG. 2, the constituent thermoplastic polymers inmulticomponent filaments24 are arranged indistinct regions24a,bacross the cross-section of thefilament24 and are coupled cohesively along an interface24calong which at least tworegions24a,bcontact or otherwise confront.Regions24a,bextend substantially along the entire length of thefilament24 and thefilaments24 are each substantially continuous and uninterrupted.
• Theregions24a,bmay have any cross-sectional profile that is capable of being split by an applied force. For example, thefilaments24 may have a circular or circular eccentric side-by-side configuration, an oval configuration, a trilobal configuration, a triangular configuration, a dog-boned configuration, a segmented pie or wedge configuration, or a flat ribbon-like configuration. Advantageously, the thermoplastic polymers are immiscible to promote splitting along the interface24cbetween each set ofadjacent regions24a,bconstituted by the different polymers. The interface24cwill define a shear line once splitting is initiated.
• The invention contemplates that additional thermoplastic polymers may be combined with these two thermoplastic polymers in thespin pack20 to formmulticomponent filaments24 with more than two constituent thermoplastic polymers and more than a single interface, similar to interface24c, along which splitting may occur. After splitting is induced, thesemulticomponent filaments24 may partially split in that certain regions may remain bonded together in pairs or groups with intact, bonded interfaces.
• The melt-processable thermoplastic polymers inregions24a,bare usually different from each other, althoughmulticomponent filaments24 may comprise separate components of similar or identical polymeric materials. The two melt-processable thermoplastic polymers may be of different composition, or have different melt flow rates and the same composition. The polymers inregions24a,bmay each be selected from among any commercially available spunbond grade of a wide range of thermoplastic polymer resins, copolymers, and blends of thermoplastic polymer resins including, but not limited to, polyolefins, such as polyethylene and polypropylene, polyesters, nylons, polyamides, polyvinyl acetate, polyvinyl chloride, polyvinyl alcohol, and cellulose acetate. Additives such as surfactants, colorants, anti-static agents, lubricants, flame retardants, antibacterial agents, softeners, ultraviolet absorbers, polymer stabilizers, and the like may also be blended with either thermoplastic polymer. Each constituent thermoplastic polymer may be identical in base composition and differ only in additive concentration.
• With reference toFIGS. 1, 1A,2, and3, the air streams42a,bfrom theair knives40a,beach apply a force to thefilaments24 that is effective for weakening or breaking the cohesive force along interface24cof at least a portion of thefilaments24 before thefilaments24 enter into the inlet to the filament-drawingdevice26. The force applied by each of the air streams42a,bfromair knives40a,b, respectively, acts along a line that differs from the line of action of the attenuation force applied by the filament-drawingdevice26. Generally, each of theair knives40a,brepresents a force applicator operative for applying a force along a line non-parallel or non-collinear with the attenuation force applied to thefilaments24 by thefilament drawing device26, which is along the length of thefilaments24.
• Specifically, the air streams42a,bare directed to impinge thefilaments24 at an angle, α, less than 180° and greater than 0° to anaxis47 aligned with a direction of motion of thefilaments24, which is along the length of thefilaments24. As a result, the air streams42a,btransfer momentum to thefilaments24 to generate the force that promotes division or splitting at the interface24cbetweenregions24a,b. The attenuation force transferred from the filament-drawingdevice26 to thefilaments24 is a tensile force acting parallel toaxis47. The operation of the filament-drawingdevice26 may also encourage splitting forfilaments24 characterized by weakened cohesion along interface24c.
• The resolved splitting-promoting force transferred from the air streams42a,bto thefilaments24 has a vector component acting along a line that is perpendicular to the line of action of the attenuation force (i.e., axis47). Another vector force component of the splitting-promoting force acts parallel to the attenuation force and, as a result, does not contribute significantly to the filament splitting in this embodiment of the invention. If the air stream impingement angle relative toaxis47 is equal to 90°, the splitting-promoting force only has a vector component applied along a line that is perpendicular to the line of action of the attenuation force.
• Filaments24 that experience a loss of cohesion will divide or partition into the constituent regions25a,b, which have a reduced cross-sectional area. Although the invention is not so limited, the invention contemplates that substantially all of thefilaments24 may split along their respective interfaces24cand into constituent regions25a,bbefore entering into the filament-drawingdevice26. However, the force applied to thefilaments24 may weaken, but not break, the cohesive force along the interface24cof another portion of thefilaments24 before thefilaments24 enter thefilament drawing device26.
• Thefilaments24 are stretched taut in the space between thespinneret22 and the filament-drawingdevice26 and are non-touching when contacted by the air steams42a,bfrom theair knives40a,b. The impinging high velocityprocess air sheets35a,binside the filament-drawingdevice26 cause attenuation of thefilaments24. Theprocess air sheets35a,bmay also cause some or all of theintact filaments24 with reduced cohesion to split inside the filament-drawingdevice26 and/or additional attenuation of thesplit filaments24. Additional splitting may occur ofintact filaments24 with reduced cohesion after thefilaments24 are discharged from the filament-drawingdevice26 and before thefilaments24 impact thecollector28. The air velocity of the air streams35a,bto which thefilaments24 are exposed inside the filament-drawingdevice26 is adjusted to select a spinning speed that does not cause a significant number of thefilaments24, which are reduced in diameter by splitting induced by the air streams42a,bfromair knives40a,b, to break during attenuation.
• In use, two thermoplastic polymers are melted inextruders12,14 and are subsequently combined to formfilaments24.Filaments24 in the descending curtain extruded fromspinneret22 are attenuated by the operation of the filament-drawingdevice26 and are quenched by cooling air from quenchducts27. The air streams42a,bfrom theair knives40a,bapply a force to thefilaments24 before thefilaments24 enter into the filament-drawingdevice26. This force, which acts along a line that differs from the line of action (i.e., axis47) of the tensile force applied by the filament-drawingdevice26, is effective for weakening or breaking the cohesive force along interface24cof at least a portion of thefilaments24.Filaments24 that lose cohesive will divide or partition into the constituent regions25a,b, which have a reduced cross-sectional area in comparison with theintact filament24, before collection oncollector28.
• With reference toFIG. 4 in which like reference numerals refer to like features inFIGS. 1,1A and in an alternative embodiment of the present invention, theair knives40a,b(FIGS. 1,1A) may be replaced by a set ofrollers45,46 positioned between thespinneret22 and the filament-drawingdevice26 and beneath the quenchducts27. Therollers45,46 are arranged on opposite sides of the curtain offilaments24 and physically contact the descendingfilaments24 before thefilaments24 enter the filament-drawingdevice26. Therollers45,46 may be offset vertically so that each of therollers45,46 may be positioned closer to the center-plane of the descending curtain offilaments24.
• Therollers45,46 are each driven rotationally in a direction that opposes the downward movement of thefilaments24. This operates to increase the mechanical drag applied to thefilaments24 and increases the tension between therollers45,46 and the filament-drawingdevice26. As a result,rollers45,46 each represent a force applicator that is operative for applying a tensile force acting along a line that is parallel to the line (i.e., axis47) of the attenuation force applied to thefilaments24 by thefilament drawing device26. The tensile force applied by therollers45,46 is effective for promoting splitting of thefilaments24, but is believed to supply negligible attenuation because of quenching before thefilaments24reach rollers45,46. Therollers45,46 may be chilled so that the curved surfaces contacted by thefilaments24 are cooled. The invention contemplates that only one of therollers45,46 may be present or that more than two rollers may be used to apply tension to thefilaments24 effective to promote filament splitting.
• With reference toFIG. 5, filament splitting is promoted by the tensile force applied to thefilaments24 because of the speed difference introduced by therollers45,46.Region70 of the transit path forfilaments24 is defined above the control points defined byrollers45,46. Inregion70, thefilaments24 are attenuated and have a first velocity.Region72 of the transit path for thefilaments24 is defined betweenrollers45,46 and the filament-drawingdevice26. Inregion72, the filament-drawingdevice26 maintains the tension on thefilaments24 and thefilaments24 have a second velocity greater than the first velocity inregion72. The difference in velocity promotes splitting due to the tensile force applied to thefilaments24 is in a direction parallel to the direction in which the attenuation force is applied to thefilaments24 by the filament-drawingdevice26.
• With reference toFIG. 6 in which like reference numerals refer to like features inFIG. 1, and in an alternative embodiment of the present invention, thespunbonding apparatus10 may include a set ofrollers48,50,52 positioned on one side of the descending curtain offilaments24 and another set ofrollers54,56,58 positioned on the opposite side of the descending curtain offilaments24. The rollers48-58 are positioned vertically between thespinneret22 and the filament-drawingdevice26. A portion of thefilaments24 is threaded throughrollers48,50,52 and another portion of thefilaments24 is threaded throughrollers54,56,58.Rollers48,50,52 androllers54,56,58 redirect the path of thefilaments24 and, in doing so, apply a force to thefilaments24 that imparts mechanical drag that is effective to cause filament splitting before thefilaments24 enter the filament-drawingdevice26. The force applied byrollers48 and54 causes the majority of the filament attenuation.
• The invention contemplates that different numbers of rollers may be included in each set of rollers. For example, each roll set may include a set of four individual rollers about which thefilaments24 are threaded and directed.
• Each of the rollers48-58 is capable of driven rotation about a central axis. In one embodiment of the present invention,rollers50 and56 will have a slightly faster angular velocity or speed thanrollers48 and54, respectively, which to create tension in thefilaments24 and applies a tensile force that breaks the cohesive force of the interface24cbetween thefilament regions24a,band initiate the splitting.Rollers52 and58 will maintain the same speed asrollers50 and56, respectively, or be rotated with a slightly faster speed thanrollers50 and56. Although not wishing to be bound by theory, the tension is believed to provide a minor contribution to filament attenuation during splitting but the split attenuated filament size should return after the tension applied betweenrollers48 and50 and the tension applied betweenrollers54 and56 is released. The filament-drawingdevice26 is believed to provide a minor contribution to attenuation and operates primarily to distribute thefilaments24 across thecollector28.
• With reference toFIGS. 5 and 6, filament splitting is promoted by the tensile force applied to thefilaments24 because of the speed difference betweenroller48 androller50 and the speed difference betweenroller54 androller56. For example, inregion70 above the control point defined byroller48 and betweenroller48 and thespinneret22, thefilaments24 are attenuated and have a first velocity. Inregion72 betweenrollers48 and50, the split-promoting tensile force is applied to thefilaments24, which are sufficiently quenched such that significant permanent attenuation does not occur inregion72. Filament tension is maintained inregion72 by thedownstream roller52 and the filament-drawingdevice26. After exitingregion72, the tension applied byrollers48,50 is released and thefilaments24 are believed to reassume their split attenuated size inregion70. Similar considerations apply torollers54,56, and58.
• Alternatively and with renewed reference toFIG. 6, all rollers48-58 may be driven at the same angular velocity or speed that is lower than the filament draw speed or spinning speed of the filament-drawingdevice26. In this instance, a tensile force is applied tofilaments24 in transit betweenroller52 and the filament-drawingdevice26 because therollers48,50,52 increase the tension betweenroller52 and the filament-drawingdevice26. Similarly, a tensile force is applied tofilaments24 in transit betweenroller58 and the filament-drawingdevice26 because therollers54,56,58 increase the tension betweenroller58 and the filament-drawingdevice26. These tensile forces promote filament splitting, as described with regard toFIG. 5, and act along a line (i.e., axis47) parallel with the attenuation force applied by the filament-drawingdevice26. Splitting may occur before thefilaments24 enter the filament-drawingdevice26, within the filament-drawingdevice26, and/or after discharge from the filament-drawingdevice26.
• With continued reference toFIG. 6,optional air knives60,62 may be provided that generateair sheets64,66, respectively, that impinge thefilaments24 in the space between thespinneret22 and the filament-drawingdevice26.Air knives60,62 are typically similar in construction to airknives40a,b.Air knife60 supplies a stream orsheet64 of high velocity process air that impinges thefilaments24 in a direction that angled relative to the direction of motion of thefilaments24 betweenrollers48 and50. Theair sheet64 promotes splitting of thefilaments24 to which a tensile force is applied betweenrollers48 and50. Similarly,air knife62 supplies a stream orsheet66 of high velocity process air that impinges thefilaments24 in a direction that angled relative to the direction of motion of thefilaments24 betweenrollers54 and56. Theair sheet66 promotes splitting of thefilaments24 to which a tensile force is applied betweenrollers54 and56.
• Generally, theoptional air knives60,62 each represent a force applicator that is operative for applying a force along a line non-parallel or non-collinear with the attenuation force applied to thefilaments24 by the filament-drawingdevice26, which acts along the length of the filaments24 (i.e., axis47). Specifically, theair sheets64,66 are directed to impinge thefilaments24 perpendicular (i.e., 90°) to the direction of motion of thefilaments24 betweenrollers48 and50 and betweenrollers54 and56, respectively, or at an angle, α, less than 180° and greater than 0° to the motion direction. As a result, theair sheets64,66 transfer momentum to thefilaments24 to generate the force that promotes division or splitting at the interface24cbetweenregions24a,b.
• The resolved splitting-promoting force has a vector component acting along a line that is perpendicular to the line of action of the attenuation force, which is parallel to length of the filament andaxis47. The resolved vector component of the force imparted by theair sheets64,66 parallel to the attenuation force does not contribute significantly to the filament splitting. If the air sheet impingement angle is at 90° to theaxis47, the splitting-promoting force only has a vector component applied along a line that is perpendicular to the line of action of the attenuation force and theaxis47.
• The attenuation force transferred from therollers50,52,56,58 and the filament-drawingdevice26 to thefilaments24 is a tensile force applied along the direction of motion and directed along the length of thefilaments24.
• The attenuation force is believed to further develop the filament splitting promoted by theair sheets64,66. Splitting may occur before thefilaments24 enter the filament-drawingdevice26, within the filament-drawingdevice26, and/or after discharge from the filament-drawingdevice26.
• While the present invention has been illustrated by a description of various embodiments and while these embodiments have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicants' general inventive concept. The scope of the invention itself should only be defined by the appended claims, wherein we claim:

Claims (17)

1. A spunbonding apparatus comprising:

a spinneret adapted to discharge a plurality of multicomponent filaments that move in a downwardly direction away from said spinneret, each of the multicomponent filaments having at least two polymer regions;

a filament-drawing device positioned below said spinneret, said filament-drawing device adapted to pneumatically attenuate the multicomponent filaments;

a force applicator directing an air stream impinging the multicomponent filaments between said spinneret and said filament-drawing device, said air stream effective to divide at least some of the multicomponent filaments into the at least two polymer regions to form smaller filaments; and

a collector for collecting the smaller filaments.

2. The spunbonding apparatus ofclaim 1 wherein said force applicator includes an air knife directing said air stream at an impingement angle greater than 0° and less than 180° relative to the multicomponent filaments.

3. The spunbonding apparatus ofclaim 1 further comprising:

a first driven roller contacting the multicomponent filaments; and

a second driven roller spaced from said first driven roller, said second driven roller contacting the multicomponent filaments, and said air stream impinging the multicomponent filaments between said first driven roller and said second driven roller.

4. The spunbonding apparatus ofclaim 3 wherein said force applicator includes an air knife directing said air stream at the multicomponent filaments between said first driven roller and said second driven roller.

5. The spunbonding apparatus ofclaim 4 wherein said air stream intersects the multicomponent filaments at an impingement angle greater than 0° and less than 180° relative to the multicomponent filaments between said first driven roller and said second driven roller.

6. A spunbonding apparatus comprising:

a spinneret adapted to discharge a plurality of multicomponent filaments that move in a downwardly direction away from said spinneret, each of the multicomponent filaments having at least two polymer regions;

a filament-drawing device positioned below said spinneret, said filament-drawing device adapted to pneumatically attenuate the multicomponent filaments;

a force applicator including a first roller contacting the plurality of multicomponent filaments between said spinneret and said filament-drawing device, said first roller effective to divide at least some of the multicomponent filaments into the at least two polymer regions to form smaller filaments; and

a collector for collecting the smaller filaments.

7. The spunbonding apparatus ofclaim 6 wherein said first roller is driven, and said force applicator further includes a second roller spaced from said first driven roller, said second roller being driven and contacting the multicomponent filaments.

8. The spunbonding apparatus ofclaim 7 wherein said first roller is separated from said second roller in a direction perpendicular to the downwardly direction in which the multicomponent filaments are moving.

9. The spunbonding apparatus ofclaim 7 wherein said first roller is separated from said second roller in a direction parallel to the downwardly direction in which the multicomponent filaments are moving.

10. A method of forming a spunbond nonwoven web, comprising:

forming a plurality of multicomponent filaments each having at least two polymer regions;

pneumatically attenuating the multicomponent filaments;

applying a dividing force to the moving plurality of multicomponent filaments effective for dividing the at least two polymer regions of at least some of the filaments to provide smaller filaments; and

collecting the smaller filaments to form the spunbond nonwoven web.

11. The method ofclaim 10 wherein applying the dividing force further comprises:

acting with the second force on the moving plurality of multicomponent filaments along a line perpendicular to the first force.

12. The method ofclaim 10 wherein the plurality of multicomponent filaments travel in a downward direction, and applying the dividing force further comprises:

directing an air stream toward the multicomponent filaments at an angle that is less than 180° and greater than 0° relative to the downward direction.

13. The method ofclaim 10 wherein applying the dividing force further comprises:

intersecting the multicomponent filaments with at least one roller to apply the dividing force.

14. The method ofclaim 10 wherein applying the dividing force further comprises:

intersecting the multicomponent filaments with a plurality of rollers rotating at different angular velocities to apply the dividing force.

15. The method ofclaim 10 wherein applying the dividing force further comprises:

intersecting the multicomponent filaments with a plurality of rollers rotating at a uniform angular velocity to apply the dividing force.

16. The method ofclaim 10 wherein the filaments are substantially attenuated before the dividing force is applied.

17. The method ofclaim 16 further comprising:

quenching the filaments with a flow of cooling air before the dividing force is applied.

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