US 20050130540 A1
Multicomponent spunbond filaments including a core of superabsorbent polymer surrounded by a thermoplastic polymer sheath that is liquid permeable. The superabsorbent polymer in the filament core absorbs liquids that penetrate through liquid pathways defined in the filament sheath to the core. The spunbond filaments are suitable for forming an absorbent core of an article that absorbs liquids, such as a disposable hygienic article used for absorbing aqueous body fluids.
1. A non-woven web formed from a plurality of multicomponent filaments, each filament comprising:
a liquid-pervious sheath region comprising a melt-processable thermoplastic polymer; and
a core region encased within said sheath region, said core region comprising a melt-processable superabsorbent polymer capable of absorbing liquid that penetrates through said sheath region to said core region.
2. The nonwoven web of
3. The nonwoven web of
4. The nonwoven web of
5. The nonwoven web of
6. The nonwoven web of
7. The nonwoven web of
8. The nonwoven web of
9. The nonwoven web of
10. A product formed from the nonwoven web of
11. The product of
12. A method of manufacturing a nonwoven web, comprising:
heating a thermoplastic polymer to a flowable state;
heating a superabsorbent polymer to a flowable state;
combining the thermoplastic polymer and the superabsorbent polymer to form a plurality of multicomponent filaments each having a liquid-pervious sheath region including the thermoplastic polymer and a core region including the superabsorbent polymer; and
collecting the plurality of multicomponent filaments to form a nonwoven web.
13. The method of
adding a concentration of superabsorbent polymer granules to the superabsorbent polymer.
14. The method of
adding a concentration of superabsorbent polymer agglomerates to the superabsorbent polymer.
15. The method of
distributing the superabsorbent polymer along a length of each of the plurality of multicomponent filaments in a plurality of discrete portions with adjacent ones of the plurality of discrete portions being separated by one of a plurality of voids into which the superabsorbent polymer may expand after liquid is absorbed.
16. The method of
forming a plurality of liquid pathways extending through the sheath region.
17. The method of
adding a pathway-promoting agent to the thermoplastic polymer.
The invention relates generally to methods for manufacturing spunbond nonwoven webs and, more particularly, to methods for manufacturing spunbond nonwoven webs from multicomponent filaments incorporating a melt-processable superabsorbent polymer core.
Nonwoven webs and their manufacture from melt-processable thermoplastic polymers has been the subject of extensive development resulting in a wide variety of materials converted for numerous commercial and consumer applications, such as disposable hygienic articles. Nonwoven webs consist of a sheet of overlapped and intermingled filaments or fibers of melt-processable thermoplastic polymers manufactured using, for example, spunbond processes. A spunbond process generally involves distributing one or more thermoplastic polymers in a spin pack for extrusion as a dense curtain of semi-solid filaments from a spinneret of the spin pack. The descending curtain of filaments is cooled by a cross-flow of cooling air and the individual filaments are attenuated by a drawing device or aspirator. Spunbond filaments are generally lengthwise continuous and have average diameters in the range of about 10 to 20 microns. The filaments discharged from the drawing device are deposited on a collector, such as a forming belt or a forming drum, as a continuous length nonwoven web, which is slit and shaped for use.
Disposable hygienic articles commonly incorporate an absorbent core containing a superabsorbent polymer (SAP) capable of absorbing several times its weight of aqueous body fluids while retaining the absorbed fluids under moderate pressure. SAP's contain water-insoluble, cross-linked chain molecules that are capable of forming a hydrogel when hydrated by aqueous body fluids. The degree of polymer crosslinking of the SAP affects the absorbent capacity and gel strength of the hydrogel. In a physical property tradeoff, an SAP having high gel strength generally possesses a low absorption capacity, and an SAP having a high absorption capacity typically possesses low gel strength. Generally, SAP's characterized by a low absorbent capacity are incapable of absorbing a sufficient amount of fluid for practical use in a disposable hygienic article. To be useful in a disposable hygienic article, the SAP must have adequately high absorption capacity and the hydrogels formed therefrom must have adequately high gel strength.
In a conventional arrangement, the absorbent core includes granules of SAP that are dispersed in a porous matrix of cellulose fibers. The swelling of the SAP granules occurs in such a way that a very high absorption rate is observed shortly after an aqueous body fluid is introduced. However, the swollen SAP granules tend to close the open spaces in the SAP-fiber matrix, which slows or prevents the entry of aqueous body fluids by reducing porosity and permeability. Subsequent amounts of aqueous body fluids that can no longer penetrate into the interior of the absorbent core may leak from the hygienic article. As SAP granules embedded deeper in the absorbent core are shielded, the total storage capacity of the absorbent core is effectively reduced. This surface-limiting blocking phenomenon is particularly acute for low gel strength SAP's of high absorbency. Another disadvantage of conventional absorbent cores arises because the matrix of cellulose fibers is bulky, which conflicts with consumer demand for thin diapers. Yet another disadvantage of conventional absorbent cores is that the SAP granules tend to leak when a weight-bearing load is applied to the absorbent core.
It would be desirable, therefore, to arrange a superabsorbent polymer in an absorbent core of a hygienic article with a configuration that enhances the total storage capacity.
The invention provides a nonwoven web and a product formed using the nonwoven web each of which includes a plurality of multicomponent filament. Each filament features a liquid-permeable or liquid-pervious sheath region and a core region encased within the sheath region. The sheath region comprises a melt-processable thermoplastic polymer and the core region comprises a melt-processable superabsorbent polymer capable of absorbing liquid that penetrates through said sheath region to said core region. The nonwoven web may be used to fabricate products or articles, such as an absorbent core for a hygienic article.
In another aspect, the invention is directed to a method of manufacturing a nonwoven web that includes heating a thermoplastic polymer to a flowable state, heating a superabsorbent polymer to a flowable state, and combining the thermoplastic polymer and the superabsorbent polymer to form multicomponent filaments. Each multicomponent filament has a liquid-pervious sheath region including the thermoplastic polymer and a core region including the superabsorbent polymer. The filaments are collected to form a nonwoven web.
In accordance with the principles of the invention, the superabsorbent polymer (SAP) in the core of the multicomponent filaments is mechanically strengthened by the presence of the sheath of liquid-pervious or liquid-permeable thermoplastic polymer. This strengthening permits the SAP to be characterized by lower gel strength and, therefore, a higher absorbency than in conventional absorbent cores for hygienic articles and other fluid-absorbing items featuring SAP granules dispersed in a cellulose fiber matrix. Because the SAP is confined in the core of the multicomponent filaments, the effect of surface-limited blocking on liquid absorption is significantly reduced and the SAP is more efficiently utilized for absorbing liquids. As compared with absorbent cores of conventional SAP-fiber matrices, an absorbent core including the multicomponent filaments of the invention requires a reduced amount of SAP to achieve an equivalent total storage capacity. Therefore, the absorbent core may be manufactured at a reduced cost. By eliminating the matrix of cellulose fibers found in conventional absorbent cores, hygienic articles and other fluid-absorbing items may be made thinner. The polymer sheath surrounding the SAP core also assists for preventing leakage under a weight-bearing load.
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.
The invention is directed to methods for boosting the effectiveness of superabsorbent polymers (SAP's) used for absorbing large quantities of aqueous body fluids. To that end, the SAP is incorporated as a core region of multicomponent spunbond filaments encased in a porous thermoplastic polymer sheath. Although the filaments will be described herein as being formed using an exemplary meltspinning apparatus, it should be understood that modifications to the exemplary meltspinning apparatus described herein could be made without departing from the intended spirit and scope of the invention.
With reference to
Each set of metering pumps 16, 18 pumps metered amounts of the corresponding polymers at corresponding volumetric flow rates to a spin pack 20, which contains flow passageways that cooperate for combining the polymers. Spin packs are familiar to persons of ordinary skill in the art and, therefore, are not described here in detail. Generally, spin pack 20 includes flow passageways arranged to separately direct the polymers to a spinneret 22, in which the polymers are combined. The spinneret 22 includes spinning orifices (not shown) arranged in rows from which a dense curtain of filaments 24 each constituted collectively by the two polymers is discharged. An exemplary spin pack 20 is disclosed in U.S. Pat. No. 5,162,074, the disclosure of which is hereby incorporated by reference herein in its entirety. The shape of the spinning orifices in spinneret 22 can be selected to accommodate the cross-section desired for the extruded filaments 24, such as round, oval, trilobal, triangular, dog-boned, or flat.
The descending curtain of filaments 24 is quenched to accelerate solidification by a cross-flow of cooling air from a quench blower 25. The filaments 24 are drawn into a filament-drawing device 26 that directs high velocity sheets of process air in a downwardly direction generally parallel to the length of the filaments 24. Because the filaments 24 are extensible, the converging, downwardly-directed sheets of high-velocity process air apply a downward drag that attenuates the filaments 24. Other exemplary filament-drawing devices 26 are disclosed in U.S. patent application Ser. No. 10/072,550, U.S. Pat. No. 4,340,563, and U.S. Pat. No. 6,182,732, the disclosures of which are hereby incorporated herein by reference in their entirety.
The filaments 24 discharged from filament-drawing device 26 are propelled toward a formaminous or porous collector 28, such as a moving screen belt. The filaments 24 deposit in a substantially random manner as substantially flat loops on the collector 28 to collectively form a nonwoven web 30. The collection device 28 moves in a machine direction, represented by the arrow labeled MD, parallel to the length of the nonwoven web 30. The width of the nonwoven web 30 deposited on collector 28 is substantially equal to the width of the curtain of filaments 24.
An air management system 32 positioned below the collector 28 supplies a vacuum that is transferred through the collector 28 to attract the filaments 24 onto the collector 28. The air management system 32 disposes 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 spunbonding apparatus, not shown but similar to spunbonding apparatus 10, and meltblowing apparatus (not shown) may be provided 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 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 reference to
The sheath 34 is pervious or permeable to liquids or hydrophilic so that liquids can penetrate to the core 36 for absorption by the constituent SAP. The sheath 34 provides a mechanical support that strengthens the core 36 after an amount of a liquid is absorbed to form a hydrogel. As a result, a low gel strength and high absorbency SAP may be used in the core 36 of filament 24 for boosting the total storage capacity for liquids. Specifically, the SAP in the core 36 may exhibit an absorbency exceeding about 50 grams of saline per gram of SAP. Absorbency is a measure of the mass or volume of fluid that a given amount of SAP will absorb before saturation. Gel strength indicates the tendency of the hydrogel, once formed from the SAP, to deform or flow under an applied pressure or stress. The recipe or chemistry of the SAP may be altered to increase or decrease the rate of absorption while maintaining a high absorbency. Increases or decreases in the thickness of the sheath 34 may be used to regulate the absorption rate of the SAP core 36. Typically, the filaments 24 contain at least about 50% by weight of SAP. The SAP in core 36 forms a hydrogel that expands volumetrically after absorbing liquid. As a result, filament 24 will expand in a radial dimension after liquid absorption. The SAP in core 36 retains the absorbed liquids under moderate applied pressures.
With reference to
The pathways 40 are introduced into the sheath 38 by various different techniques including, but not limited to, adding a pathway-promoting agent to the polymer of the sheath 38. In certain embodiments of the invention, the pathways 40 may be introduced in sheath 38 by conventional phase separation methods. For example, the pathways 40 may be formed by mixing the thermoplastic polymer with a diluent or plasticizer, quenching in a liquid medium to induce phase separation, and washing away the diluent to leave behind an interconnected porous structure. Pathways 40 may also be formed in sheath 38 by introducing a blowing agent or a swelling agent into the thermoplastic polymer before the filaments 24 are formed. Another technique for forming pathways 40 in sheath 38 is to add a filler material, such as a concentration of particulate filler like calcium carbonate, capable of initiating pathway formation to the sheath polymer. Alternatively, pathways 40 may be introduced into the polymer forming sheath 38 by introduction of an additive, such as polyethylene glycol as disclosed in U.S. Pat. No. 6,623,853, the disclosure of which is hereby incorporated by reference herein in its entirety.
With reference to
With reference to
With reference to
The absorbent core 64 includes filaments 24 in accordance with the principles of the invention capable of absorbing large quantities of aqueous body fluids and retaining the absorbed body fluids under moderate applied pressures. The absorbent core 64 may be formed in its entirety from filaments 24, from a commingled mixture of filaments 24 and other non-absorbent spunbond filaments, or from a multi-ply laminate structure in which nonwoven web 30 forms one layer. The absorbent capacity of the absorbent core 64 may be optimized for the intended use of the hygienic article 58.
After a limited number of soilings by aqueous body fluids is absorbed by the absorbent core 64, the hygienic article 58 is intended to be discarded. The invention contemplates that hygienic article 58 may be any item used to absorb and contain aqueous body fluids, and more specifically refers to devices that are placed against or in proximity to the body of the wearer to absorb and contain the various aqueous body fluids discharged from the wearer. For example, hygienic article 58 may be a diaper, a catamenial pad, a feminine hygiene product such as tampons and sanitary napkins, absorbent underpants, an incontinence pad, a training pant and the like, as well as a wipe, a bandage, a wound dressing, and other articles. The invention contemplates that various other consumer and commercial articles or applications that require a heightened level of liquid absorption may incorporate the multicomponent filaments 24 of the invention. As examples, the multicomponent filaments 24 of the invention may be used to for protecting power and communication cables from moisture, in agriculture to increase the capability of soil to retain moisture and nutrients, for treating and containing wastewater, and in the hygienic packaging of food products.
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 applicant 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 applicant's general inventive concept. The scope of the invention itself should only be defined by the appended claims,