Patent Application
20070216059
The invention relates generally to melt-spinning apparatus and methods, and more particularly, to a spunbonding apparatus and methods for forming slit spunbond filaments.
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.
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.
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.
With reference to
Metering pumps 16, 18 pump metered amounts of the corresponding one of molten thermoplastic polymers through separate distribution chambers 17, 19 extending through a die body 25 to a spin pack 20. The spin pack 20 and die body 25 form components of a spin beam assembly that extends in the cross-machine direction of the apparatus 10 and, thus, defines the width (typically several meters) of a nonwoven web 30. The spin pack 20 is heated and supported by the surrounding die body 25.
The spin pack 20 contains flow passageway plates 38 that cooperate for distributing and combining the two molten thermoplastic polymers received from the distribution chambers 17, 19. Heat transferred from the die body 25 to the spin pack 20 maintains the two molten thermoplastic polymers in the flow passageway plates 38 at a temperature suitable for melt processing and providing an extrudable melt. The flow passageway plates 38 convey the combined thermoplastic polymers to a spinneret 22 from which a curtain of filaments 24 is discharged from an array of discharge openings (not shown) distributed across an outlet surface of the spinneret 22.
Quench ducts 27, which are positioned below the spinneret 22 and flanking the spinneret 22, direct a low velocity cross flow 21 of cooling air at the descending curtain of filaments 24. The cross flow 21 of cooling air quenches the filaments 24 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 quench ducts 27.
A filament-drawing device 26 is also positioned below the spinneret 22 and receives the descending curtain of quenched filaments 24. The filaments 24 are directed into a draw jet or filament-drawing device 26 along with entrained ambient air from the environment above and surrounding the filament-drawing device 26. A blower (not shown) supplies process air, which may be heated, to a supply manifold of the filament-drawing device 26. Generally, the filament-drawing device 26 includes a vertical passage 31, which is illustrated with an exaggerated width for clarity, defined between manifold segments and in which the filaments 24 are impinged by converging sheets 35a,b of high velocity process air. The process air sheets 35a,b are introduced into the vertical passage 31 through slots 33a,b defined in the opposite sidewalls of the vertical passage 31. The process air sheets 35a,b are discharged from the slots 33a,b in a downwardly direction generally parallel to the length of the filaments 24.
Because the filaments 24 are extensible, the sheets 35a,b of high-velocity process air apply a downward drag or pneumatic force that creates longitudinal tension to attenuate the filaments 24. Exemplary filament-drawing devices 26 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-drawing devices 26 are contemplated by the invention as usable with the spunbonding apparatus 10.
A descending curtain of attenuated filaments 24 is discharged from filament-drawing device 26 and propelled toward a moving porous collector 28. The filaments 24 are deposited in a substantially random manner as substantially flat loops on the collector 28 to aggregately form nonwoven web 30. The width of the nonwoven web 30 deposited on collector 28 is approximately equal to the width of the curtain of filaments 24. The collector 28 is traveling in a machine direction (MD) relative to the spunbonding apparatus 10 and filament-drawing device 26.
Positioned below the collector 28 is an air management system 32 that supplies a vacuum transferred through the collector 28 for attracting the filaments 24 onto the collector 28 and disposing of the high-velocity process air discharged from the filament-drawing device 26 so that filament laydown is relatively undisturbed. Exemplary air management systems 32 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 of spunbonding apparatus 10 for depositing one or more additional spunbond and/or meltblown nonwoven webs of either monocomponent or multicomponent filaments either as a substrate for receiving nonwoven web 30 or onto an exposed surface of nonwoven web 30. 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 spunbond layer containing filaments 24.
With continued reference to
Each of the air knives 40a,b transforms or amplifies a relatively low flow of compressed air to deliver the corresponding one of the high velocity process air streams 42a,b. Air knife 40a includes an internal air plenum (not shown) coupled by a feed conduit 41a with a source of compressed air, such as a standard centrifugal blower. Air knife 40a includes an outlet 44a, such as a single elongate slot or a line of shorter aligned slots, from which the air stream 42a is discharged. Alternatively, the outlet 44a of air knife 40a may include a plurality of densely-spaced orifices, or any other suitable structure for discharging the corresponding process air stream as a high velocity stream 42. The air knife 40a may also include a Coanda surface that defines a guide for directing the high velocity stream discharged from the outlet 44a. Air knife 40b has a construction identical or similar to the construction air knife 40a and, accordingly, also includes a feed conduit 41b and outlet 44b similar to the feed conduit 41a and outlet 44a as described above for air knife 40a.
Suitable air knives 40a,b for 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 the air knives 40a,b may be replaced by multiple air jets (not shown). The invention also contemplates that, although two air knives 40a,b are depicted in
With reference to
The regions 24a,b may have any cross-sectional profile that is capable of being split by an applied force. For example, the filaments 24 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 interface 24c between each set of adjacent regions 24a,b constituted by the different polymers. The interface 24c will define a shear line once splitting is initiated.
The invention contemplates that additional thermoplastic polymers may be combined with these two thermoplastic polymers in the spin pack 20 to form multicomponent filaments 24 with more than two constituent thermoplastic polymers and more than a single interface, similar to interface 24c, along which splitting may occur. After splitting is induced, these multicomponent filaments 24 may partially split in that certain regions may remain bonded together in pairs or groups with intact, bonded interfaces.
The melt-processable thermoplastic polymers in regions 24a,b are usually different from each other, although multicomponent filaments 24 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 in regions 24a,b may 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 to
Specifically, the air streams 42a,b are directed to impinge the filaments 24 at an angle, α, less than 180° and greater than 0° to an axis 47 aligned with a direction of motion of the filaments 24, which is along the length of the filaments 24. As a result, the air streams 42a,b transfer momentum to the filaments 24 to generate the force that promotes division or splitting at the interface 24c between regions 24a,b. The attenuation force transferred from the filament-drawing device 26 to the filaments 24 is a tensile force acting parallel to axis 47. The operation of the filament-drawing device 26 may also encourage splitting for filaments 24 characterized by weakened cohesion along interface 24c.
The resolved splitting-promoting force transferred from the air streams 42a,b to the filaments 24 has a vector component acting along a line that is perpendicular to the line of action of the attenuation force (i.e., axis 47). 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 to axis 47 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.
Filaments 24 that experience a loss of cohesion will divide or partition into the constituent regions 25a,b, which have a reduced cross-sectional area. Although the invention is not so limited, the invention contemplates that substantially all of the filaments 24 may split along their respective interfaces 24c and into constituent regions 25a,b before entering into the filament-drawing device 26. However, the force applied to the filaments 24 may weaken, but not break, the cohesive force along the interface 24c of another portion of the filaments 24 before the filaments 24 enter the filament drawing device 26.
The filaments 24 are stretched taut in the space between the spinneret 22 and the filament-drawing device 26 and are non-touching when contacted by the air steams 42a,b from the air knives 40a,b. The impinging high velocity process air sheets 35a,b inside the filament-drawing device 26 cause attenuation of the filaments 24. The process air sheets 35a,b may also cause some or all of the intact filaments 24 with reduced cohesion to split inside the filament-drawing device 26 and/or additional attenuation of the split filaments 24. Additional splitting may occur of intact filaments 24 with reduced cohesion after the filaments 24 are discharged from the filament-drawing device 26 and before the filaments 24 impact the collector 28. The air velocity of the air streams 35a,b to which the filaments 24 are exposed inside the filament-drawing device 26 is adjusted to select a spinning speed that does not cause a significant number of the filaments 24, which are reduced in diameter by splitting induced by the air streams 42a,b from air knives 40a,b, to break during attenuation.
In use, two thermoplastic polymers are melted in extruders 12, 14 and are subsequently combined to form filaments 24. Filaments 24 in the descending curtain extruded from spinneret 22 are attenuated by the operation of the filament-drawing device 26 and are quenched by cooling air from quench ducts 27. The air streams 42a,b from the air knives 40a,b apply a force to the filaments 24 before the filaments 24 enter into the filament-drawing device 26. This force, which acts along a line that differs from the line of action (i.e., axis 47) of the tensile force applied by the filament-drawing device 26, is effective for weakening or breaking the cohesive force along interface 24c of at least a portion of the filaments 24. Filaments 24 that lose cohesive will divide or partition into the constituent regions 25a,b, which have a reduced cross-sectional area in comparison with the intact filament 24, before collection on collector 28.
With reference to
The rollers 45, 46 are each driven rotationally in a direction that opposes the downward movement of the filaments 24. This operates to increase the mechanical drag applied to the filaments 24 and increases the tension between the rollers 45, 46 and the filament-drawing device 26. As a result, rollers 45, 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., axis 47) of the attenuation force applied to the filaments 24 by the filament drawing device 26. The tensile force applied by the rollers 45, 46 is effective for promoting splitting of the filaments 24, but is believed to supply negligible attenuation because of quenching before the filaments 24 reach rollers 45, 46. The rollers 45, 46 may be chilled so that the curved surfaces contacted by the filaments 24 are cooled. The invention contemplates that only one of the rollers 45, 46 may be present or that more than two rollers may be used to apply tension to the filaments 24 effective to promote filament splitting.
With reference to
With reference to
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 the filaments 24 are threaded and directed.
Each of the rollers 48-58 is capable of driven rotation about a central axis. In one embodiment of the present invention, rollers 50 and 56 will have a slightly faster angular velocity or speed than rollers 48 and 54, respectively, which to create tension in the filaments 24 and applies a tensile force that breaks the cohesive force of the interface 24c between the filament regions 24a,b and initiate the splitting. Rollers 52 and 58 will maintain the same speed as rollers 50 and 56, respectively, or be rotated with a slightly faster speed than rollers 50 and 56. 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 between rollers 48 and 50 and the tension applied between rollers 54 and 56 is released. The filament-drawing device 26 is believed to provide a minor contribution to attenuation and operates primarily to distribute the filaments 24 across the collector 28.
With reference to
Alternatively and with renewed reference to
With continued reference to
Generally, the optional air knives 60, 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 the filaments 24 by the filament-drawing device 26, which acts along the length of the filaments 24 (i.e., axis 47). Specifically, the air sheets 64, 66 are directed to impinge the filaments 24 perpendicular (i.e., 90°) to the direction of motion of the filaments 24 between rollers 48 and 50 and between rollers 54 and 56, respectively, or at an angle, α, less than 180° and greater than 0° to the motion direction. As a result, the air sheets 64, 66 transfer momentum to the filaments 24 to generate the force that promotes division or splitting at the interface 24c between regions 24a,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 and axis 47. The resolved vector component of the force imparted by the air sheets 64, 66 parallel to the attenuation force does not contribute significantly to the filament splitting. If the air sheet impingement angle is at 90° to the axis 47, 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 the axis 47.
The attenuation force transferred from the rollers 50, 52, 56, 58 and the filament-drawing device 26 to the filaments 24 is a tensile force applied along the direction of motion and directed along the length of the filaments 24.
The attenuation force is believed to further develop the filament splitting promoted by the air sheets 64, 66. Splitting may occur before the filaments 24 enter the filament-drawing device 26, within the filament-drawing device 26, and/or after discharge from the filament-drawing device 26.
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:
