U.S. patent application number 10/736281 was filed with the patent office on 2005-06-16 for multicomponent spunbond filaments having a melt-processable superabsorbent polymer core.
This patent application is currently assigned to Nordson Corporation. Invention is credited to Crane, Patrick L..
Application Number | 20050130540 10/736281 |
Document ID | / |
Family ID | 34653854 |
Filed Date | 2005-06-16 |
United States Patent
Application |
20050130540 |
Kind Code |
A1 |
Crane, Patrick L. |
June 16, 2005 |
Multicomponent spunbond filaments having a melt-processable
superabsorbent polymer core
Abstract
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.
Inventors: |
Crane, Patrick L.;
(Dawsonville, GA) |
Correspondence
Address: |
WOOD, HERRON & EVANS, LLP (NORDSON)
2700 CAREW TOWER
441 VINE STREET
CINCINNATI
OH
45202
US
|
Assignee: |
Nordson Corporation
Westlake
OH
44145-1148
|
Family ID: |
34653854 |
Appl. No.: |
10/736281 |
Filed: |
December 15, 2003 |
Current U.S.
Class: |
442/364 ;
428/373; 428/374; 428/375; 428/397; 428/399 |
Current CPC
Class: |
D01F 8/02 20130101; D04H
3/00 20130101; Y10T 428/2933 20150115; D01F 8/04 20130101; D01D
5/082 20130101; D01D 5/088 20130101; Y10T 428/2931 20150115; Y10T
428/2976 20150115; D01F 8/10 20130101; Y10T 428/2929 20150115; Y10T
428/2973 20150115; Y10T 442/641 20150401 |
Class at
Publication: |
442/364 ;
428/373; 428/374; 428/375; 428/397; 428/399 |
International
Class: |
D04H 001/00 |
Claims
Wherein I claim:
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 claim 1 wherein said superabsorbent polymer
is an acrylate-based material.
3. The nonwoven web of claim 2 wherein said acrylate-based material
is polyacrylate.
4. The nonwoven web of claim 1 wherein said sheath region includes
a plurality of liquid pathways through which liquid penetrates to
said core region.
5. The nonwoven web of claim 3 wherein said plurality of liquid
pathways are formed by adding a pathway-promoting agent to said
thermoplastic polymer when said plurality of multicomponent
filaments are formed.
6. The nonwoven web of claim 1 wherein said core region has a
length, said superabsorbent polymer being distributed along said
length in a plurality of discrete portions with adjacent ones of
said plurality of discrete portions separated by one of a plurality
of voids into which said superabsorbent polymer may expand after
the liquid is absorbed.
7. The nonwoven web of claim 1 wherein said superabsorbent polymer
has an absorbency exceeding about 50 grams of saline per gram of
superabsorbent polymer.
8. The nonwoven web of claim 1 wherein said superabsorbent polymer
comprises a superabsorbent polymer matrix containing at least one
of a plurality of superabsorbent polymer granules and a plurality
of superabsorbent polymer agglomerates.
9. The nonwoven web of claim 1 wherein said melt-processable
superabsorbent polymer comprises at least 50 weight percent of each
of the plurality of filaments.
10. A product formed from the nonwoven web of claim 1.
11. The product of claim 10 wherein said product is a hygienic
article.
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 claim 12 further comprising: adding a
concentration of superabsorbent polymer granules to the
superabsorbent polymer.
14. The method of claim 12 further comprising: adding a
concentration of superabsorbent polymer agglomerates to the
superabsorbent polymer.
15. The method of claim 12 wherein combining the thermoplastic
polymer and the superabsorbent polymer further comprises:
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 claim 12 wherein combining the thermoplastic
polymer and the superabsorbent polymer further comprises: forming a
plurality of liquid pathways extending through the sheath
region.
17. The method of claim 16 wherein forming the plurality of
pathways further comprises: adding a pathway-promoting agent to the
thermoplastic polymer.
Description
FIELD OF THE INVENTION
[0001] 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.
BACKGROUND OF THE INVENTION
[0002] 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.
[0003] 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.
[0004] 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.
[0005] 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.
SUMMARY
[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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
[0010] 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.
[0011] FIG. 1 is a side view of a spunbonding apparatus for forming
a plurality of filaments in accordance with the principles of the
invention;
[0012] FIG. 2 is a perspective view of a portion of a
multicomponent spunbond filament formed by the spunbonding
apparatus of FIG. 1;
[0013] FIG. 3 is a cross-sectional view of the multicomponent
spunbond filament of FIG. 2;
[0014] FIG. 4 is a cross-sectional view of a portion of a
multicomponent spunbond filament in accordance with an alternative
embodiment of the invention;
[0015] FIGS. 5A and 5B are cross-sectional views of a portion of an
alternative embodiment of a multicomponent spunbond filament in
accordance with the principles of the invention;
[0016] FIG. 6 is a cross-sectional view similar to FIG. 4 of a
portion of a multicomponent spunbond filament in accordance with an
alternative embodiment of the invention; and
[0017] FIG. 7 is a perspective view of a hygienic article having an
absorbent core including multicomponent spunbond filaments in
accordance with the principles of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] 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.
[0019] With reference to FIG. 1, a spunbonding apparatus 10 is
equipped with a screw extruder 12 that converts a solid
melt-processable polymer into a molten state and transfers the
molten polymer under pressure to a set of metering pumps 16.
Another screw extruder 14 converts another solid melt-processable
polymer into a molten state and transfers the molten polymer under
pressure to a set of metering pumps 18. Pellets of the solid
polymers are placed in hoppers 11, 13 and fed to the corresponding
one of screw extruders 12, 14 for melting and transfer.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] 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.
[0025] With reference to FIGS. 2 and 3 and in accordance with the
principles of the invention, filaments 24 are multicomponent
filaments including a sheath 34 of a melt-processable thermoplastic
polymer concentrically surrounding a core 36 formed from a
melt-processable SAP, including but not limited to acrylate-based
materials such as polyacrylate or, more specifically, sodium
polyacrylate which is a sodium salt of polyacrylic acid. The
thermoplastic polymer forming sheath 34 may be selected from among
any commercially available spunbond grade of a wide range of
polymer resins, copolymers, and blends of polymer resins,
including, without limitation, polyolefins, such as polyethylene,
polypropylene, nylons, polyamides, polyesters, polyvinyl acetate,
polyvinyl chloride, polyvinyl alcohol, and cellulose acetate. The
core 36 may be concentrically arranged with the sheath 34 as
depicted in FIGS. 2 and 3 or, alternatively, may be eccentric or
offset from the sheath axial centerline. The core 36 may also be
distributed in multiple isolated cores within sheath 34 in an
islands-in-the-sea configuration.
[0026] 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.
[0027] With reference to FIG. 4 in which like reference numbers
refer to like features in FIG. 3, a sheath 38 of filament 24 may be
formed under melt-spining conditions such that an outer surface
includes multiple pathways 40 each extending radially through the
sheath thickness. The pathways 40 are direct passageways
penetrating the sheath 38 and may be present as fractures in the
sheath 38. Alternatively, the pathways 40 may include a plurality
of interconnecting interstices that communicate with the outside
and inside of the sheath 38. Because of the presence of pathways
40, liquids are able to more readily permeate or pervade the sheath
38 with a higher permeation rate and reach the SAP core 36 more
efficiently for absorption.
[0028] 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.
[0029] With reference to FIGS. 5A and 5B, filament 24 may be
meltspun under conditions that form a central, axially-extending
lumen in which the SAP is distributed in discrete, spaced-apart
portions 42 surrounded by a sheath 44. Adjacent portions 42 are
separated by one of multiple axially-extending voids 46. When
liquid is absorbed, the portions 42 expand volumetrically or swell
to at least partially fill the axially-extending voids 46, as shown
in FIG. 5B, which reduces the volume of the voids 46. The portions
42 may be arranged with regular axial spacing or may have a less
periodic arrangement. The arrangement consisting of portions 42 of
SAP separated by voids 46 may be formed by controlling the relative
volumetric flow rates of sheath polymer and SAP to the spin pack,
such as spin pack 20 (FIG. 1) so that the flow rate of the sheath
polymer is less than a flow rate required to has a structure in
which the SAP core is uninterrupted by voids.
[0030] With reference to FIG. 6, filament 24 may include a core 48
constituted by an SAP matrix 50 containing SAP granules 52 and/or
SAP agglomerates 54 and a sheath 56 surrounding the core 48. The
effect of the dispersion of SAP granules 52 or SAP agglomerates 54
in the SAP matrix 50 is to increase the gel strength at the expense
of a slight reduction in absorbency. The SAP granules 52 or SAP
agglomerates 54 are added along with the solid-phase SAP to the
appropriate one of the hoppers 11, 13 (FIG. 1).
[0031] With reference to FIG. 7, a disposable hygienic article 58
generally includes a top sheet 60, a back sheet 62, an absorbent
core 64 separating the top sheet 60 from the back sheet 62, and a
fluid acquisition and transfer layer 66 separating the absorbent
core 64 from the top sheet 60. The top sheet 60, which is intended
to be placed adjacent to the wearer's skin when the hygienic
article 58 is worn, is fluid pervious so that aqueous body fluids
may readily penetrate through its thickness to the absorbent core
64. Fluid acquisition and transfer layer 66 distributes aqueous
body fluids transferred from top sheet 60 to the underlying
absorbent core 64. The nonporous, hydrophobic back sheet 62
prevents aqueous body fluids absorbed in the absorbent core 64 from
wetting the wearer's clothing, such as pants, pajamas and
undergarments. Fastener elements 68 on the back sheet 62 cooperate
with complementary fastener elements 70 on corresponding attachment
tabs 72 extending laterally from the back sheet 62 for attaching
the hygienic article 58 to a wearer.
[0032] 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.
[0033] 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.
[0034] 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,
* * * * *