U.S. patent application number 10/022180 was filed with the patent office on 2003-06-19 for uniform distribution of absorbents in a thermoplastic web.
Invention is credited to Clark, Darryl Franklin, Liu, Yuelong, Matela, David Michael.
Application Number | 20030114066 10/022180 |
Document ID | / |
Family ID | 21808224 |
Filed Date | 2003-06-19 |
United States Patent
Application |
20030114066 |
Kind Code |
A1 |
Clark, Darryl Franklin ; et
al. |
June 19, 2003 |
Uniform distribution of absorbents in a thermoplastic web
Abstract
A web of thermoplastic multicomponent substantially continuous
fibers is thoroughly and evenly mixed with absorbent materials
prior to deposition on the forming wire to result in superior
adherence of the absorbents to the thermoplastic components and
hence result in superior performance of the web. The multicomponent
fibers have a low melting point sheath which can be fully activated
to melt and wet the absorbent particles. The web can then be
densified and cooled, securing the absorbents to the web with
hardened flow joints and enabling the web to carry high loadings of
absorbent while maintaining good web integrity.
Inventors: |
Clark, Darryl Franklin;
(Hendersonville, NC) ; Liu, Yuelong; (Alpharetta,
GA) ; Matela, David Michael; (Alpharetta,
GA) |
Correspondence
Address: |
PAULEY PETERSEN KINNE & ERICKSON
2800 WEST HIGGINS ROAD
SUITE 365
HOFFMAN ESTATES
IL
60195
US
|
Family ID: |
21808224 |
Appl. No.: |
10/022180 |
Filed: |
December 13, 2001 |
Current U.S.
Class: |
442/361 ;
442/364; 442/401; 442/417 |
Current CPC
Class: |
Y10T 442/641 20150401;
D01F 8/14 20130101; Y10T 442/637 20150401; D04H 3/14 20130101; D01F
8/06 20130101; Y10T 442/681 20150401; Y10T 442/699 20150401; D01F
8/12 20130101; D01F 8/10 20130101 |
Class at
Publication: |
442/361 ;
442/364; 442/417; 442/401 |
International
Class: |
D04H 001/00; D04H
003/00; D04H 005/00 |
Claims
We claim:
1. A method of making an absorbent nonwoven web, comprising: a)
producing a mass of thermoplastic substantially continuous
sheath-core or side-by-side multicomponent filaments by entraining
molten thermoplastic polymers into a first air stream and drawing
and containing the filaments in a fiber distribution unit; b)
introducing an absorbent material via a second air stream into the
fiber distribution unit at a point above a divergence zone of the
mass of filaments in the fiber distribution unit; c) allowing the
mass of filaments and absorbent material to mix in the fiber
distribution unit and collecting the mixture onto a forming wire in
a uniform distribution of filaments and absorbent material; d)
running the collected mass of filaments and absorbent material
through a heater at a time and temperature sufficient to soften the
sheath of the filaments; and e) densifying the softened mass of
filaments and the absorbent material.
2. The method of making an absorbent nonwoven web of claim 1,
further including passing the collected mass of filaments and
absorbent material through a heater at a time and temperature
sufficient to fully activate the sheaths of the multicomponent
filaments to a liquid state and densifying the heated mixture at a
pressure and time sufficient to contact at least a majority of the
pulp fibers to the fully activated mass of multicomponent
filaments.
3. The method of making an absorbent nonwoven web of claim 1,
further including cooling the densified mass of filaments and
absorbent material.
4. The method of making an absorbent nonwoven web of claim 1,
wherein the substantially continuous multicomponent filaments are
spunbond.
5. The method of making an absorbent nonwoven web of claim 1,
wherein the substantially continuous multicomponent filaments are
spunbond polyethylene-polypropylene sheath-core filaments.
6. The method of making an absorbent nonwoven web of claim 5,
wherein the substantially continuous spunbond multicomponent
filaments crimp upon the application of heat.
7. The method of making an absorbent nonwoven web of claim 1,
wherein the substantially continuous multicomponent filaments are
meltblown.
8. The method of making an absorbent nonwoven web of claim 1,
wherein the sheaths of the substantially continuous multicomponent
filaments contain polar functional groups selected from the group
including: maleic anhydride modified Polyethylene such as EPOLENE
C-16, and Polypropylene such as Exxelor P01020.
9. The method of making an absorbent nonwoven web of claim 1,
wherein a core material of the substantially continuous spunbond
multicomponent filaments is selected from a group including
polyester (PET or PBT), nylon or Polypropylene.
10. The method of making an absorbent nonwoven web of claim 1,
wherein a sheath material comprises a wettable polymer selected
from a group consisting of polyvinyl acetates, saponified polyvinyl
acetates, saponified ethylene vinyl acetates, and combinations
thereof.
11. The method of making an absorbent nonwoven web of claim 1,
wherein the mixture comprises an absorbent in about 5-97% by weight
of the pulp fibers and about 3-95% by weight of the substantially
continuous multicomponent filaments.
12. The method of making an absorbent nonwoven web of claim 1,
wherein the mixture comprises an absorbent in about 35-95% by
weight of the pulp fibers and about 5-65% by weight of the
substantially continuous multicomponent filaments.
13. The method of making an absorbent nonwoven web of claim 1,
wherein the mixture comprises an absorbent in about 50-95% by
weight of the pulp fibers and about 5-50% by weight of the
substantially continuous multicomponent filaments.
14. The method of making an absorbent nonwoven web of claim 1,
wherein the mixture comprises an absorbent in about 5-90% by weight
of a superabsorbent material.
15. The method of making an absorbent nonwoven web of claim 14,
wherein the mixture comprises an absorbent in about 10-60% by
weight of the superabsorbent material.
16. The method of making an absorbent nonwoven web of claim 14,
wherein the mixture comprises an absorbent in about 20-50% by
weight of the superabsorbent material.
17. The method of making an absorbent nonwoven web of claim 1,
wherein the step of introducing a plurality of an absorbent via a
second air stream into the fiber distribution unit at a point above
a divergence zone of the mass of filaments in the fiber
distribution unit occurs in the drawing zone of the fiber
distribution unit at a point where the filaments have not
hardened.
18. The method of making an absorbent nonwoven web of claim 1,
wherein the step of introducing a plurality of an absorbent via a
second air stream into the fiber distribution unit at a point above
a divergence zone of the mass of filaments in the fiber
distribution unit occurs above the point of cyclonic airstream
formation in the fiber distribution unit.
19. The method of making an absorbent nonwoven web of claim 1,
further comprising: activating the sheaths of the filaments at
between 160.degree. F.-300.degree. F., for about 0.5 to about 20
seconds.
20. The method of making an absorbent nonwoven web composite of
claim 1, wherein the forming wire bears the collected mass through
the heater.
21. An absorbent article comprising: a) a cover sheet serving as
the exterior layer of the article; b) a top sheet serving as the
interior layer of the article; c) a primary liquid retention layer
having: i) a mass of thermoplastic substantially continuous at
least partially sheath-core multicomponent filaments having a
plurality of absorbent particles in a uniform distribution of
filaments, ii) with a majority of the absorbent particles joined to
sheaths of the multicomponent filaments by hardened flow joints;
and iii) the primary liquid retention layer further being a
densified web.
22. The absorbent article of claim 21 wherein the primary liquid
retention layer is a densified web of from about 0.05 g/cc to about
0.5 g/cc.
23. An absorbent nonwoven web comprising: a) a mass of
thermoplastic, substantially continuous, at least partially
sheath-core, multicomponent filaments having a plurality of
absorbent particles in a uniform distribution throughout the mass
of filaments; b) with a majority of the absorbent particles joined
to sheaths of the multicomponent filaments by hardened flow joints;
and c) the mass of thermoplastic, substantially continuous, at
least partially sheath-core, multicomponent filaments with the
plurality of absorbent particles in a uniform distribution
throughout the mass of filaments further being densified.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to nonwoven web composites having a
very uniform distribution of thermoplastic bicomponent continuous
filaments and absorbents throughout the web.
[0002] Bicomponent nonwoven filaments are known in the art
generally as thermoplastic filaments which employ at least two
different polymers combined together in a heterogeneous fashion.
Instead of being homogeneously blended, two polymers may, for
instance, be combined in a side-by-side configuration, so that a
first side of a filament is composed of a first polymer "A" and a
second side of the filament is composed of a second polymer "B."
Alternatively, the polymers may be combined in a sheath-core
configuration, so that an outer sheath layer of a filament is
composed of a first polymer "A," and the inner core is composed of
a second polymer "B." Other heterogeneous configurations are also
possible.
[0003] Bicomponent filaments have been disclosed in combination
with carbon particles, zeolites, ion exchange resins, carbon
fibers, sterilizing fibers, and/or gas adsorbing fibers for use in
specialized filters. U.S. Pat. No. 5,670,044, issued to Ogata et
al., discloses the use of bicomponent meltblown filaments in these
combinations, for use in cylindrical filters. In that case, the
bicomponent filaments contain high and low melting polymers. The
filaments of the filter are stacked and bonded together by melting
only the lower melting component.
[0004] Pulp fibers have been employed in certain absorbent
applications to enhance the absorbency. U.S. Pat. No. 4,530,353,
issued to Lauritzen, discloses pulp fibers in combination with
staple length bicomponent fibers used in the manufacture of
absorbent bandages. In that case, the fibers also contain high and
low melting polymers. The staple length fibers are bonded together
by melting only the lower melting component. U.S. Pat. No.
4,902,559, issued to Escheway et al., discloses mixing
substantially continuous thermoplastic filaments with absorbents,
including superabsorbents, before the filaments are deposited on
the forming wire.
[0005] There is a need or desire for an absorbent nonwoven web
composite which exhibits a high degree of absorbency and a very
even distribution of the thermoplastic fibers and the absorbents
throughout the web. There is a further need to achieve a high
degree of absorbent particle loading and attachment to the
thermoplastic components of the nonwoven web to economically and
efficiently make highly absorbent webs for personal care absorbent
articles. This need exists for diapers, training pants, wipes, and
other personal care absorbent articles where comfort, strength, and
absorbent performance are all important.
SUMMARY OF THE INVENTION
[0006] The present invention is directed to an improved absorbent
nonwoven web composite suitable for use in personal care absorbent
articles, and is intended to encompass such personal care absorbent
articles constructed using the improved composite. The absorbent
nonwoven web composite includes a web of substantially continuous
length bicomponent thermoplastic nonwoven filaments having a very
even distribution of absorbent particles through the web in
relation to the thermoplastic fibers to which the absorbent
particles are attached. It is further desirable that a web of the
present invention have a high weight percent quantity of absorbents
such as pulp fibers or superabsorbents, or both, secured within the
continuous filament web. A method for easily obtaining an even
distribution of thermoplastic fibers and absorbent particles is
taught. A method of obtaining the high loading by bonding the
absorbents to fully activated, or liquid, portions of the
thermoplastic bicomponent, and densifying the fully activated web
is further disclosed.
[0007] In particular, during formation, or mixing, or both, of the
components of the web, particular techniques are used within a
fiber distribution unit (FDU) in order to ensure the proper
distribution of components so that the absorbents are evenly
distributed and may thereby be efficiently attached at high
percentage rates to the thermoplastic filaments of the web when
deposited on the forming wire and subsequently processed.
[0008] Specifically, in the making of thermoplastic fibers, whether
spunbond, or meltblown, the fibers are drawn by an airstream in the
FDU. It has been discovered that by introducing the absorbent
material, or particles, in a stream of fluid, e.g. air, to
commingle with the thermoplastic fibers at a point in the FDU above
where the fibers begin to diverge within the FDU and cyclonic fluid
streams are produced, the fibers will not separate to a great
degree from the absorbent particulates during transit to the
forming wire. This technique results in a more homogenous mixture
and even distribution of the thermoplastic and absorbent
components. Because the components are more evenly distributed,
subsequent processing of the commingled components, i.e. the
precursor web, to form an absorbent nonwoven web, such as by
heating the web, results in a greater number and more even
distribution of the absorbent particles being adhered to the
thermoplastic matrix of the web. Thus the performance of the web as
a fluid distribution or retention means for a personal care
absorbent article is enhanced.
[0009] The substantially continuous bicomponent filaments,
especially when of the sheath-core variety, provide an effective
amount of liquid outer core area during formation of the web for
surface bonding to the absorbents and a more substantial frame work
for the resultant web than would be the case with staple
thermoplastic filaments alone. Further, because they remain uncut,
the substantially continuous bicomponent filaments are believed to
provide better distribution of liquids than staple length
filaments, which are chopped into relatively short lengths.
Desirably, in certain aspects or embodiments, the polymers in the
bicomponent filaments are selected so that at least one of the
polymers provides strength and durability, and at least one of the
polymers provides softness, to the nonwoven web.
[0010] More desirably, the sheath will have a lower melting than
the polymer of the core, allowing the sheath to reach a state of
complete, or full, activation, i.e., become liquid, without
necessarily flowing, during processing of the web in order to
maximally wet the absorbents and bind them to the web with hardened
flow joints when the web is cooled to again set, or recrystallize,
the sheath of the bicomponent fiber. During the time of full
activation, the web is further densified, such as by running
through a nip between two calender, or compression, rollers to
further ensure a greater contact between the activated sheath and
the absorbent particles and provide a web which is suitably
compressed and thin for use in personal care products. The
absorbents, such as pulp fibers, superabsorbent particles, or the
like, are better contained within the matrix of continuous
filaments having strength and durability and thus may constitute up
to about 97% by weight of the absorbent nonwoven web composite
through practice of the present invention.
[0011] It is thus a feature and advantage of the invention to
provide an improved absorbent nonwoven web composite capable of
containing high absorbent loadings within a continuous filament
matrix as suitable for use as a primary liquid retention mechanism
in a personal care product.
Definitions
[0012] "Absorbent particles" refers to absorbent materials such as
pulp or superabsorbents, or other material, and in any form,
whether fibers, granules, or other shapes, that can be processed
according to the dictates of the present invention.
[0013] "Air-laying" is a well-known process by which a fibrous
nonwoven layer can be formed. In the air-laying process, bundles of
small fibers having typical lengths ranging from about 3 to about
19 millimeters (mm) are separated and entrained in an air supply
and then deposited onto a moving forming screen, usually with the
assistance of a vacuum supply. The randomly deposited fibers then
are bonded to one another using, for example, hot air or a spray
adhesive. Air-laying is taught in, for example, U.S. Pat. No.
4,640,810 to Laursen et al. Air-laying may include coform
deposition which is a known variant wherein pulp or other absorbent
fibers are deposited in the same air stream onto the forming
screen. The screen may also be referred to herein as a forming
wire. Air-laying may include multibank deposition which is know in
the art to be a technique whereby multiple spray heads for the
various fibers or components are located in series along the
machine direction of the forming wire to serially deposit the same
or different materials in layers onto the forming wire.
[0014] The term "bicomponent filaments" or "bicomponent fibers"
refers to fibers which have been formed from at least two polymers
extruded from at least two separate extruders but spun together to
form one fiber and may also be referred to herein as "conjugate" or
"multicomponent" fibers. "Bicomponent" is not meant to be limiting
to only two constituent polymers unless other specifically
indicated. The polymers are arranged in substantially constantly
positioned distinct zones across the cross-section of the
bicomponent fibers and extend continuously along the length of the
bicomponent fibers. The configuration of such a bicomponent fiber
may be, for example, a sheath-core arrangement wherein one polymer
is surrounded by another, or may be a side-by-side, A/B,
arrangement or an A/B/A, side-by-side (-by-side), arrangement.
Bicomponent fibers are generally taught in U.S. Pat. No. 5,108,820
to Kaneko et al., U.S. Pat. No. 5,336,552 to Strack et al., and
U.S. Pat. No. 5,382,400 to Pike et al. For two component fibers,
the polymers may be present in ratios of 75/25, 50/50, 25/75 or any
other desired ratios. Conventional additives, such as pigments and
surfactants, may be incorporated into one or both polymer streams,
or applied to the filament surfaces.
[0015] The term "microfibers" means small diameter fibers having an
average diameter not greater than about 75 microns, for example,
having an average diameter of from about 1 micron to about 50
microns, or more particularly, having an average diameter of from
about 1 micron to about 30 microns. Another frequently used
expression of fiber diameter is denier, which is defined as grams
per 9000 meters of a fiber. For a fiber having circular
cross-section, denier may be calculated as fiber diameter in
microns squared, multiplied by the density in grams/cc, multiplied
by 0.00707. A lower denier indicates a finer fiber and a higher
denier indicates a thicker or heavier fiber. For example, the
diameter of a polypropylene fiber given as 15 microns may be
converted to denier by squaring, multiplying the result by 0.89
g/cc (an assumed polypropylene density for this example) and
multiplying by 0.00707. Thus, a 15 micron polypropylene fiber has a
denier of about 1.42 (152.times.0.89.times.0.00- 707=1.415).
Outside the United States the unit of measurement is more commonly
the "tex," which is defined as the grams per kilometer of fiber.
Tex may be calculated as denier/9.
[0016] The term "nonwoven fabric" or "nonwoven web" means a web
having a structure of individual fibers or threads which are
interlaid, but not in a regular or identifiable manner as in a
knitted fabric. Nonwoven fabrics or webs have been formed from many
processes such as, for example, meltblowing processes, spunbonding
processes, air-laying processes, and bonded carded web processes.
The basis weight of nonwoven fabrics is usually expressed in ounces
of material per square yard (osy) or grams per square meter (gsm)
and the fiber diameters are usually expressed in microns. (Note
that to convert from osy to gsm, multiply osy by 33.91).
[0017] The term "meltblown fibers" means fibers formed by extruding
a molten thermoplastic material through a plurality of fine,
usually circular, die capillaries as molten threads or filaments
into converging high velocity heated gas (e.g., air) streams which
attenuate the filaments of molten thermoplastic material to reduce
their diameter, which may be microfiber diameter. Thereafter, 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. Such a process is disclosed for
example, in U.S. Pat. No. 3,849,241 to Butin et al. Meltblown
fibers are microfibers which may be continuous or discontinuous,
are generally smaller than 10 microns in diameter, and are
generally self bonding when deposited onto a collecting
surface.
[0018] The term "pulp fibers" refers to fibers from natural sources
such as woody and non-woody plants. Woody plants include, for
example, deciduous and coniferous trees. Non-woody plants include,
for instance, cotton, flax, esparto grass, milkweed, straw, jute
hemp, and bagasse.
[0019] The term "polymer" generally includes without limitation
homopolymers, copolymers (including, for example, block, graft,
random and alternating copolymers), terpolymers, etc., and blends
and modifications thereof. Furthermore, unless otherwise
specifically limited, the term "polymer" shall include all possible
geometrical configurations of the material. These configurations
include, but are not limited to isotactic, syndiotactic and atactic
symmetries.
[0020] "Personal care product" or "personal care absorbent article"
means diapers, wipes, training pants, absorbent underpants, adult
incontinence products, feminine hygiene products, wound care items
like bandages, and other like articles.
[0021] The term "spunbond fibers" refers to small diameter fibers
which are formed by extruding molten thermoplastic material as
filaments from a plurality of fine capillaries of a spinneret
having a circular or other configuration, with the diameter of the
extruded filaments then being rapidly reduced as by, for example,
in U.S. Pat. No. 4,340,563 to Appel et al., and U.S. Pat. No.
3,692,618 to Dorschner et al., U.S. Pat. No. 3,802,817 to Matsuki
et al., U.S. Pat. Nos. 3,338,992 and 3,341,394 to Kinney, U.S. Pat.
No. 3,502,763 to Hartman, U.S. Pat. No. 3,502,538 to Petersen, and
U.S. Pat. No. 3,542,615 to Dobo et al. Spunbond fibers are quenched
and generally not tacky when they are deposited onto a collecting
surface. Spunbond fibers are generally continuous and usually have
average diameters larger than meltblown fibers, and more
particularly, generally between about 10 and 30 microns. A
particularly suitable bicomponent polyethylene/polypropylene fiber
for processing according to the present invention is disclosed in
U.S. Pat. No. 5,336,552 to Strack et al. and U.S. Pat. No.
5,382,400 to Pike et al.
[0022] The term "substantially continuous filaments" or
"substantially continuous fibers" refers to filaments or fibers
prepared by extrusion from a spinneret, including without
limitation spunbond and meltblown fibers, which are not cut from
their original length prior to being formed into a nonwoven web or
fabric. Substantially continuous filaments or fibers may have
average lengths ranging from greater than about 15 cm to more than
one meter, and up to the length of the nonwoven web or fabric being
formed. The definition of "substantially continuous filaments" (or
fibers) includes those filaments or fibers which are not cut prior
to being formed into a nonwoven web or fabric, but which are later
cut when the nonwoven web or fabric is cut.
[0023] The term "superabsorbent material" refers to a water
swellable, water-insoluble organic or inorganic material capable,
under the most favorable conditions, of absorbing at least about 10
times its weight, preferably at least about 30 times its weight in
an aqueous solution containing 0.9% by weight sodium chloride at
room temperature and pressure.
[0024] The term "staple fibers" means fibers which are natural or
cut from a manufactured filament prior to forming into a web, and
which have an average length ranging from about 0.1-15 cm, more
commonly about 0.2-7 cm.
[0025] The term "through-air bonding" or "TAB" means a process of
bonding a nonwoven, for example, a bicomponent fiber web in which
air which is sufficiently hot to melt one of the polymers of which
the fibers of the web are made is forced through the web. The air
velocity is often between 100 and 500 feet per minute and the dwell
time may be as long as 20 seconds. The melting and resolidification
of the polymer provides the bonding. Since TAB requires the melting
of at least one component to accomplish bonding, it is generally
restricted to webs with two components such as bicomponent fiber
webs or webs containing an adhesive fiber or powder.
[0026] Words of degree, such as "about", "substantially", and the
like are used herein in the sense of "at, or nearly at, when given
the manufacturing and material tolerances inherent in the stated
circumstances" and are used to prevent the unscrupulous infringer
from unfairly taking advantage of the invention disclosure where
exact or absolute figures are stated as an aid to understanding the
invention.
[0027] "Online" refers to a continuous process for forming an
integral web on a single forming line, as opposed to a material
constructed from multiple webs formed on multiple lines and then
put together as component pieces.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a schematic illustration of an exemplary
embodiment of the apparatus and method for making a nonwoven
absorbent web according to the present invention.
[0029] FIG. 2 is a schematic illustration of a fiber distribution
unit (FDU) according to the present invention.
[0030] FIG. 3 is a schematic view of a personal care absorbent
article having a cutaway of the body side liner to illustrate
utilization of a nonwoven absorbent web according to the present
invention.
DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS
[0031] The present invention is directed to an absorbent composite
nonwoven web composite including substantially continuous
bicomponent thermoplastic filaments and absorbents adhered to the
filaments in an even distribution throughout the web. Desirably,
the absorbent nonwoven web composite contains a high loading by
weight percent of absorbent.
[0032] The substantially continuous bicomponent thermoplastic
filaments may have any of the bicomponent configurations described
above and are desirably in the 15-25 micron diameter range.
Desirably, the filaments have either of an A/B or A/B/A
side-by-side configuration, or a sheath-core configuration. More
desirably, a sheath-core configuration is used to provide the
maximum amount of lower melting point sheath polymer material with
which to contact, wet, and secure, the absorbent particles or
fibers also contained in the web. The substantially continuous
filaments are most typically spunbond filaments, although some
meltblown microfibers may be added to the web, for various reasons,
as farther discussed below. Alternatively, bicomponent meltblown
filaments may be used in some embodiments of the invention. Other
processes for forming substantially continuous filaments may also
be employed. The filaments may further be crimped, using techniques
available to persons skilled in the art. For example, the
aforementioned PRISM fibers may be made to crimp during transit to,
or upon arrival at the forming wire, resulting in a web of
substantially crimped thermoplastic fiber, resulting in a random
and thorough distribution of thermoplastic fiber throughout the
structure of the web.
[0033] The substantially continuous bicomponent filaments contain
at least two thermoplastic polymers. The substantially continuous
bicomponent filaments contain a first polymer which melts before
the second polymer. For ease of explanation the first polymer will
be referred to hereinafter as the sheath polymer, and the second
polymer will be referred to as the core polymer, although it will
be understood that the filaments need not be sheath-core
configuration according to some aspects of the present invention.
The sheath polymer may contribute one or more desirable properties
beyond its low melting point and wettability of the absorbents in
its liquid state. For example, polar functional groups may be added
to the sheath polymer to aid in the attachment of the absorbent
fibers thereto. Some examples of polymers with suitable polar
functional groups are maleic anhydride modified polyethylene such
as EPOLENE C-16, from Uniroyal Chemical of Middlebury, Conn. and
polypropylene such as Exxelor PO 1020, from ExxonMobil Chemical of
Houston, Tex. Polymers may also be provided in the sheath which
have high wettability for liquid water distribution within the
web.
[0034] Also, the core polymer may contribute one or more additional
desirable properties beyond its strength and durability. The
bicomponent filaments may include more than two distinct polymers,
with each polymer contributing unique properties. For example, the
bicomponent filaments may include a distinct polymer blend having
desirable properties, adjacent to another distinct polymer or
polymer blend. Additives, such as pigments and hydrophilic
modifiers, may be incorporated into one or both polymers, or
applied to the filament surfaces.
[0035] Examples of core polymer components suitable for use in the
present invention may include, without limitation: polypropylene,
polybutylene terephthalate, polyethylene terephthalate, or Nylon.
Other polymers may include, without limitation: polypropylene
homopolymers, polypropylene copolymers containing up to about 10%
ethylene or another C.sub.4-C.sub.20 alpha-olefin comonomer, high
density polyethylenes, linear low density polyethylenes in which
the alpha-olefin comonomer content is less than about 10% by
weight, polyamides, polyesters, polycarbonates,
polytetrafluoroethylenes, and other high tensile materials.
Generally, a first polymer can be said to contribute durability to
bicomponent filaments when a nonwoven web made from bicomponent
filaments containing a first polymer and a second polymer
withstands a tensile load which is at least about 10% greater, and
preferably at least about 30% greater, than a similar nonwoven web
made from similar filaments containing the second polymer
alone.
[0036] Examples of sheath polymer components which contribute a low
melting point and good wetting of the absorbent particles within
the web may include, without limitation: polyethylene,
polypropylene, fluropolyolefins or polybutylenes. Other polymers
may include, without limitation: high pressure (branched) low
density polyethylenes, linear low density polyethylenes in which
the alpha-olefin comononer content is more than about 10% by
weight, copolymers of ethylene with at least one vinyl monomer (for
example, ethylene vinyl acetate), copolymers of ethylene with
unsaturated aliphatic carboxylic acids (including ester derivatives
thereof) and copolymers of any two alpha-olefins having 2-20 carbon
atoms wherein the content of each of the two comononers exceeds 10%
by weight of the copolymer (including, for instance,
ethylene-propylene rubbers). Also included are thermoplastic
polyurethanes, A-B and A-B-A' block copolymers where A and A' are
thermoplastic end blocks and B is an elastomeric block.
[0037] Examples of polymers which contribute wettability to a
thermoplastic nonwoven web include, without limitation: polyamides,
polyvinyl acetates, saponified polyvinyl acetates, saponified
ethylene vinyl acetates, and other hydrophilic materials. A polymer
generally contributes to the wettability of bicomponent filaments
if a droplet of water positioned on a nonwoven web made from
bicomponent filaments containing first and second polymers has a
contact angle which is a) less than 90 degrees measured using ASTM
D724-89, and b) less than the contact angle of a similar nonwoven
web made from similar filaments containing only the first polymer.
When used as an outer layer in a sheath-core bicomponent filament
web, the hydrophilic polymer imparts surface wettability to the
entire web.
[0038] The pulp fibers may be any high-average fiber length pulp,
low-average fiber length pulp, or mixtures of the same. Preferred
pulp fibers include cellulose fibers. The term "high average fiber
length pulp" refers to pulp that contains a relatively small amount
of short fibers and non-fiber particles. High fiber length pulps
typically have an average fiber length greater than about 1.5 mm,
preferably about 1.5-6 mm. Sources generally include non-secondary
(virgin) fibers as well as secondary fiber pulp which has been
screened. The term "low average fiber length pulp" refers to pulp
that contains a significant amount of short fibers and non-fiber
particles.
[0039] Examples of high average fiber length wood pulps include
those available from the U.S. Alliance Coosa Pines Corporation
under the trade designations Longlac 19, Coosa River 56, and Coosa
River 57. The low average fiber length pulps may include certain
virgin hardwood pulp and secondary (i.e., recycled) fiber pulp from
sources including newsprint, reclaimed paperboard, and office
waste. Mixtures of high average fiber length and low average fiber
length pulps may contain a predominance of low average fiber length
pulps. For example, mixtures may contain more than about 50% by
weight low-average fiber length pulp and less than about 50% by
weight high-average fiber length pulp. One exemplary mixture
contains about 75% by weight low-average fiber length pulp and
about 25% by weight high-average fiber length pulp.
[0040] The pulp fibers may be unrefined or may be beaten to various
degrees of refinement. Crosslinking agents and/or hydrating agents
may also be added to the pulp mixture. Debonding agents may be
added to reduce the degree of hydrogen bonding if a very open or
loose nonwoven pulp fiber web is desired. One exemplary debonding
agent is available from the Quaker Oats Chemical Company,
Conshohocken, Pa., under the trade designation Quaker 2008. The
addition of certain debonding agents in the amount of, for example,
1-4% by weight of the pulp, may reduce the measured static and
dynamic coefficients of friction and improve the abrasion
resistance of the thermoplastic continuous polymer filaments. The
debonding agents act as lubricants or friction reducers. Debonded
pulp fibers are commercially available from Weyerhaeuser Corp.
under the designation NB 405.
[0041] In another highly advantageous embodiment, a quantity of a
superabsorbent material is combined with the substantially
continuous bicomponent thermoplastic polymer filaments, to improve
the absorbency of the absorbent nonwoven web composite, with or
without pulp fibers.
[0042] The superabsorbent materials can be natural, synthetic and
modified natural polymers and materials. In addition, the
superabsorbent materials can be inorganic materials, such as silica
gels, or organic compounds such as cross-linked polymers. The term
"cross-linked" refers to any means for effectively rendering
normally water-soluble materials substantially water insoluble but
swellable. Such means can include, for example, physical
entanglement, crystalline domains, covalent bonds, ionic complexes
and associations, hydrophilic associations, such as hydrogen
bonding, and hydrophobic associations or Van der Waals forces.
[0043] Examples of synthetic superabsorbent material polymers
include the alkali metal and ammonium salts of poly(acrylic acid)
and poly(methacrylic acid), poly(acrylamides), poly(vinyl ethers),
maleic anhydride copolymers with vinyl ethers and alpha-olefins,
poly(vinyl pyrrolidone), poly(vinylmorpholinone), poly(vinyl
alcohol), and mixtures and copolymers thereof. Further
superabsorbent materials include natural and modified natural
polymers, such as hydrolyzed acrylonitrile-grafted starch, acrylic
acid grafted starch, methyl cellulose, chitosan, carboxymethyl
cellulose, hydroxypropyl cellulose, and the natural gums, such as
alginates, xanthum gum, locust bean gum and the like. Mixtures of
natural and wholly or partially synthetic superabsorbent polymers
can also be useful in the present invention. Other suitable
absorbent gelling materials are disclosed by Assarsson et al. in
U.S. Pat. No. 3,901,236 issued Aug. 26, 1975. Processes for
preparing synthetic absorbent gelling polymers are disclosed in
U.S. Pat. No. 4,076,633 issued Feb. 28, 1978 to Masuda et al. and
U.S. Pat. No. 4,286,082 issued Aug. 25, 1981 to Tsubakimoto et
al.
[0044] Superabsorbent materials may be xerogels which form
hydrogels when wetted. The term "hydrogel," however, has commonly
been used to also refer to both the wetted and unwetted forms of
the superabsorbent polymer material. The superabsorbent materials
can be in many forms such as flakes, powders, particulates, fibers,
continuous fibers, networks, solution spun filaments and webs. The
particles can be of any desired shape, for example, spiral or
semi-spiral, cubic, rod-like, polyhedral, etc. Needles, flakes,
fibers, and combinations may also be used.
[0045] When used, the superabsorbent material may be present within
the absorbent nonwoven composite in an amount from about 5 to about
90 weight percent based on total weight of the absorbent nonwoven
composite. Preferably, the superabsorbent constitutes about 10-60%
by weight of the absorbent nonwoven web composite, more preferably
about 30-40% by weight. Superabsorbents are generally available in
particle sizes ranging from about 20 to about 1000 microns.
Examples of commercially available particulate superabsorbents
include SANWET.RTM. IM 3900 and SANWET.RTM. IM-5000P, available
from Hoescht Celanese located in Portsmouth, Va., DRYTECH.RTM.
2035LD available from Dow Chemical Co. located in Midland, Mich.,
and FAVOR.RTM. 880, available from Stockhausen, located in
Greensborough, N.C. An example of a fibrous superabsorbent is
OASIS.RTM. 101, available from Technical Absorbents, located in
Grimsby, United Kingdom. The superabsorbents may be added using the
same techniques described for combining the pulp fibers and
continuous bicomponent nonwoven filaments.
[0046] Various improvements and alternative embodiments are also
considered to be within the scope of the invention. In one
embodiment, the continuous bicomponent thermoplastic filaments are
combined with other thermoplastic filaments in addition to the
absorbents. For instance, the continuous bicomponent thermoplastic
filaments may include a mixture of bicomponent spunbond filaments
and higher melting point meltblown filaments. In this embodiment,
the meltblown filaments may be effective in creating or maintaining
fluid channels within the web beyond that inherent in using the
spunbond filaments.
[0047] In another embodiment, the continuous bicomponent filaments
may be spunbond and mixed with meltblown fibers which have a
relatively low melting point. The composite web may thus be formed
by combining three or more streams of bicomponent spunbond
filaments, lower melting meltblown filaments and pulp fibers. The
meltblown filaments may still be hot and tacky when the pulp fibers
are introduced, and may fuse with the pulp fibers to help
consolidate the structure. Meltblown microfibers, which typically
have diameters much smaller than spunbond fibers, may in effect
serve as an additional binder or adhesive for the pulp fibers. The
meltblown fibers are desirably in the 2-10 micron diameter
range.
[0048] In another embodiment, side-by-side bicomponent filaments
having the ability to crimp are used as thermoplastic filaments.
The substantially continuous crimped bicomponent filaments may be
in the form of meltblown microfibers, or be spunbond filaments.
Crimped bicomponent filaments can be used with or without other
thermoplastic filaments in a nonwoven web to provide enhanced bulk
and lower web density.
[0049] FIG. 1 is a schematic diagram illustrating methods and
apparatus of this invention for producing fully activated
bicomponent webs with high absorbent loading, the ability to
maintain density after bonding, increased stiffness and good
mechanical properties, low polymer levels and the concomitant
ability to maintain wettability due to low polymer content.
[0050] As shown in FIG. 1, two polymers A and B are spunbond with
known thermoplastic fiber spinning apparatus 21 to form bicomponent
side-by-side, or more desirably, sheath-core, morphology fibers 23.
The fibers may, for example, be a PE/PBT/PE side-by-side in A/B/A
morphology, or a PE/PP sheath-core morphology, in the range of 15
to 25 microns. The fibers 23 are then traversed through a fiber
distribution unit (FDU) 25. According to one embodiment of the
present invention, the absorbent components such as pulp fibers,
superabsorbents, or both, may be added to the FDU 25 by a separate
entrainment as at 24 in the upper half of the FDU, or at a point
above the divergence of the thermoplastic fibers, as further
explained below, thereby aiding in the efficient distribution of
the absorbents within the thermoplastic fiber mass over that of
typical random air-laying processes of separate fiber and absorbent
streams applied directly to a forming wire 27. Addition of the
absorbent particles at a point below the fiber divergence point has
been found to result in segregation of the elements in non-uniform
distribution at the forming wire 27 with the absorbent particulates
aggregating at the margins of the web on the forming wire.
[0051] Dependent upon the personal care product application, the
amount of absorbent may be between about 3 weight percent and about
97 weight percent pulp fibers with the remainder being
thermoplastic fibers, and desirably between about 35 weight percent
and about 95 weight percent pulp fibers, with between about 5
weight percent to 65 weight percent thermoplastic fiber. Desirably
in some applications, such as in fluid transfer layers of infant
care, adult care, and feminine care absorbent products, or in
personal wipe products such as baby wipes, vaginal wipes, etc.,
where maintaining low moisture is more important than absorbent
capacity, a ratio of about 30-40 weight percent pulp fibers to
about 60-70 weight percent thermoplastic fibers may result in a
suitable distribution of absorbent. Some applications, such as
absorbent core materials for infant care, adult care, and feminine
care absorbent products, and the like may, use a higher pulp
content where the amount of absorbent may desirably be between
about 50 weight percent and about 95 weight percent pulp fibers and
with between about 5 weight percent to 65 weight percent
thermoplastic fiber. In some applications, such as where special
emphasis is placed on fluid retention, the amount of superabsorbent
may comprise between about 5 weight percent and about 90 weight
percent of total mass, in some cases desirably between about 10
weight percent and about 60 weight percent of total mass, and in
some cases more desirably between about 20 weight percent and about
50 weight percent of total mass.
[0052] The thermoplastic fibers 23 are left in a substantially
continuous state and are deposited on a moving forming wire 27.
Deposition of the fibers is aided by an under-wire vacuum supplied
by a negative air pressure unit, or below wire exhaust, 29.
Additional thermoplastic fibers, e.g. meltblown fibers, may be
added to the wire 27, as at depositing head 28, or entrained into
the FDU 25, as indicated by phantom line 30. The meltblown fibers
may be, e.g., homofilament or bicomponent, desirably in the
diameter range of 2 to 10 microns, and may be of higher or lower
melting point than the sheath polymer of the spunbond bicomponent
fibers, as discussed above.
[0053] The fibers 23 are then heated to soften the sheath polymer
of the bicomponent fibers making it tacky so that the absorbent
particles may adhere to the thermoplastic fibers. In one
embodiment, the commingled mass of bicomponent fibers and absorbent
particulates may be heated to fully activate the sheath polymer to
a liquid state whereby the sheath polymer may wet the absorbent
particulates and form hardened flowjoints upon cooling to secure
the absorbent particulates within the web. The heating may be done
by traversal under one of a hot air knife (HAK) or hot air
diffuser, as indicated at 33, and will be appreciated to be used in
the alternative under normal circumstances. A conventional hot air
knife includes a mandrel with a slot that blows a jet of hot air
onto the nonwoven web surface. Such hot air knives are taught, for
example, by U.S. Pat. No. 5,707,468 to Arnold, et al. A hot air
diffuser is an alternative which operates in a similar manner but
with lower air flow over a greater surface area and thus generally
uses correspondingly lower air temperatures to maintain the
integrity of the web.
[0054] If necessary of desired, the web 37 is then transported to a
through air bonding (TAB) unit 39 to soften the sheath polymer or
fully activate the sheath polymer of the bicomponent fibers to a
liquid state where it can flow onto, or wet, the absorbent
components of the web. It will be appreciated that the TAB unit 39
may be used in the alternative as the sole heat activation means
for the web and may offer a better range of sheath polymer
activation control than the hot air knife of diffuser 33. Care
should be taken to minimize flow of the melted sheath polymer
beyond that needed to wet the absorbents. Desirably the web is
subjected to between about 160.degree. F. and about 300.degree. F.
for a period of time between about 0.5 to about 20 seconds to
achieve full activation of polymer component A of the
multicomponent meltblown filaments. More preferably, the time
period is between about 1 to about 10 seconds and most preferably
about 4-7 seconds. However, the type of polymer and the oven
temperature will govern the actual time the need to melt or soften
the sheath polymer component.
[0055] While the sheath polymer is still soft, or fully activated
if desired, it is then densified, such as by compression through a
nip formed by two calender rolls 41. Densification is desirable in
a preferred embodiment to between about 0.05 g/cc and 0.50 g/cc,
and more desirably to between about 0.05 g/cc and 0.20 g/cc for use
in some personal product applications. The calender rolls 41 may,
but need not, provide point bonding of the web and may be heated to
maintain softness or full activation of the sheath polymer during
densification. Alternatively, the calender rolls 41 may be cooled
to provide a means for removing heat from the web in order to
solidify the sheath polymer which has adhered to the absorbent
material. Alternatively, the densified web 40 is fixed to capture
the absorbent particulates and prevent further bonding or collapse
of the web by a forced air cooling unit 44 pulling ambient air
through the web, or the like. The stabilized and densified web 40
can then be collected on a winding roll 43 or the like for later
use.
[0056] Referencing FIG. 2, the thermoplastic fiber spinning
apparatus 21 forms bicomponent side-by-side, or more desirably,
sheath-core, morphology fibers 23, which then enter the FDU 25. The
bicomponent fibers 23 enter the FDU 25 in molten form and are drawn
in a drawing zone 51 and solidify over the course of the drawing
zone 51 to individual filaments. In the drawing zone the
bicomponent fibers are held in a roughly cylindrical formation
within the walls of the drawing chute 53 of the FDU. At the
divergence point 55 of the FDU 23, the walls of the FDU become
conical and the solidified filaments spread out, or diverge, from
one another in an increasingly conical vortex, or cyclonic motion,
57 until they are deposited on the forming wire 27. The person
having ordinary skill in the art will appreciate that the
bicomponent fibers will solidify and begin to diverge and circulate
in cyclonic fashion during their transit through the FDU whether or
not a conical wall portion is provided in the FDU, due to the force
of the fluid-entrained absorbent particulates as at 24.
[0057] At a point above where the bicomponent fibers 23 begin to
diverge, the absorbent particles are entrained, as at 24, into the
flow of the bicomponent fibers. It has been found that entrainment
of the absorbent particles below the divergence point 55 will not
result in adequate admixture of the absorbent particles and the
bicomponent fibers due to the vortex motion within the lower half
of the FDU.
[0058] The absorbent nonwoven composite of the invention thus
provides a high loading of absorbent particles in a densified web
of stable and desirable physical properties. The web can be used in
a wide variety of absorbent products including, in particular,
personal care absorbent articles. Personal care absorbent articles
include diapers, training pants, swim wear, absorbent underpants,
baby wipes, adult incontinence products, feminine hygiene products,
and the like. For example, referencing FIG. 3, a diaper 61 may have
a cover sheet 67 serving as the exterior layer of the article
facing away from a wearer's skin; a top sheet 63 serving as the
interior layer of the article facing towards a wearer's skin; and a
primary liquid retention layer 65 therebetween as constructed from
a web of the present invention. The absorbent nonwoven composite
can also be used in absorbent medical products, including without
limitation underpads, bandages, absorbent drapes, and medical wipes
which contain alcohol and/or other disinfectants, and household
wipes and mops of the wet or the dry variety.
[0059] While the embodiments of the invention described herein are
presently considered preferred, various modifications and
improvements can be made without departing from the spirit and
scope of the invention. The scope of the invention is indicated by
the appended claims, and all changes within the meaning and range
of equivalents are intended to be embraced therein.
* * * * *