U.S. patent application number 10/005743 was filed with the patent office on 2003-06-05 for helically crimped, shaped, single polymer fibers and articles made therefrom.
Invention is credited to Brown, Kurtis Lee, Quinn, Christopher Bryan, Shelley, Jeffrey David, Sykes, Samuel L..
Application Number | 20030104748 10/005743 |
Document ID | / |
Family ID | 21717489 |
Filed Date | 2003-06-05 |
United States Patent
Application |
20030104748 |
Kind Code |
A1 |
Brown, Kurtis Lee ; et
al. |
June 5, 2003 |
Helically crimped, shaped, single polymer fibers and articles made
therefrom
Abstract
There is provided a nonwoven fabric for use in personal care
absorbent articles where the fabric is made from single polymer,
helically crimped fibers. Such a fabric provides economical
production since it uses only one polymer. These fabrics have
superior void volume and resilience and are useful in a number of
applications, including as outercovers, liners, surge layers and
even as an absorbent core.
Inventors: |
Brown, Kurtis Lee;
(Alpharetta, GA) ; Quinn, Christopher Bryan;
(Duluth, GA) ; Shelley, Jeffrey David; (Appleton,
WI) ; Sykes, Samuel L.; (Atlanta, GA) |
Correspondence
Address: |
KIMBERLY-CLARK WORLDWIDE, INC.
401 NORTH LAKE STREET
NEENAH
WI
54956
|
Family ID: |
21717489 |
Appl. No.: |
10/005743 |
Filed: |
December 3, 2001 |
Current U.S.
Class: |
442/352 ;
442/327; 442/359 |
Current CPC
Class: |
D04H 1/55 20130101; D04H
1/544 20130101; Y10T 442/635 20150401; D04H 1/555 20130101; D04H
11/08 20130101; Y10T 442/60 20150401; Y10T 442/627 20150401 |
Class at
Publication: |
442/352 ;
442/327; 442/359 |
International
Class: |
D04H 001/00; D04H
003/00; D04H 005/00; D04H 013/00; D04H 001/06 |
Claims
What is claimed is:
1. A nonwoven fabric for use in personal care absorbent articles
comprising single polymer, helically crimped fibers.
2. The nonwoven fabric of claim 1 wherein said polymer is selected
from the group consisting of polyolefins, polyamides, polyesters,
rayon, acrylics, superabsorbents, and regenerated cellulose.
3. The nonwoven fabric of claim 2 wherein said polymer is
polyolefin.
4. The nonwoven fabric of claim 3 wherein said polyolefin is
polypropylene.
5. The nonwoven fabric of claim 1 wherein said fabric is bonded by
a method selected from the group consisting of thermal point
bonding, point unbending, through air bonding, ultrasonic bonding
and hydroentangling.
6. The nonwoven fabric of claim 5 wherein said fabric is bonded by
thermal point bonding.
7. The nonwoven fabric of claim 5 wherein said fabric is bonded by
through air bonding.
8. The nonwoven fabric of claim 5 wherein said fabric is bonded by
hydroentangling.
9. The nonwoven fabric of claim 1 wherein said fibers are staple
fibers.
10. The nonwoven fabric of claim 1 wherein said fibers are
continuous fibers.
11. The nonwoven fabric for personal care absorbent articles of
claim 1 wherein said article is selected from the group consisting
of diapers, training pants, absorbent underpants, adult
incontinence products, bandages and other wound care products and
feminine hygiene products.
12. An absorbent core for personal care absorbent articles
comprising helically crimped fibers made from a superabsorbent
polymer.
13. A loop material for a hook and loop fastener wherein said loop
material comprises single component helically crimped fibers.
14. The loop material of claim 13 wherein said loop material is
bonded with a point unbonded pattern.
Description
BACKGROUND OF THE INVENTION
[0001] This invention concerns polymer fibers and articles that may
be made using such fibers. More particularly, these fibers may be
used in absorbent articles that are useful in personal care
products like disposable sanitary napkins, diapers, training pants,
incontinence garments, wound care products and the like. These
articles typically have a structure including a body side liner, a
liquid impervious outer layer or "baffle", and an absorbent core
between the liner and the baffle.
[0002] Crimped fibers have been found to be useful in materials for
personal care products because of their ability to give increased
thickness to the materials, as well as other properties.
[0003] Bicomponent fibers have previously been used to produce
crimped fibers. The fibers may have one side made from one polymer
and another side made from a different polymer and are also used as
binder fibers. Other options include having one polymer comprise
the center area of the fiber and another the outer area though
symmetrical fibers are less attractive for crimping. Still another
option is to produce a fiber having legs or lobes with different
polymers making up different parts of the legs or lobes (U.S. Pat.
No. 5,707,735). These fibers perform adequately but are relatively
expensive to produce, since they are made from more than one
polymer. The equipment to produce these fibers is also relatively
more expensive and complicated, as compared to single polymer
fibers, since multiple channels must be machined into the fiber
spinneret plate.
[0004] Mechanical crimping of single component fibers is another
option known in the art, though this is a slow and cumbersome
manufacturing process. The type of crimp induced by mechanical
crimping, generally by passing fibers between intermeshing rollers,
is usually a zig-zag crimp in only one plane.
[0005] Despite past development of absorbent structures, there
remains a need for improved absorbent structures that can
adequately reduce leakage from absorbent products, such as feminine
hygiene products and infant care products, and be simpler to
manufacture and still more cost effective. There is a need for an
absorbent structure that can provide improved handling of liquid
surges by more effectively intaking, distributing and retaining
repeated loadings of liquid. There remains a need for materials to
be made economically and quickly for use in such absorbent
structures, where the materials are made using helically crimped
fibers. Such materials should have liquid handling properties
superior to those made from previously used fibers.
SUMMARY OF THE INVENTION
[0006] In response to the discussed difficulties and problems
encountered in the prior art, a new structural material comprising
a nonwoven web having good bulk and resilience properties to allow
for more efficient liquid handling is provided. This is achieved by
a material for use in personal care absorbent articles wherein the
material is made with single component fibers having a helical
crimp. A variety of polymers may be used to produce the nonwoven of
this invention including polyolefins, polyamides, polyesters,
rayon, acrylics, superabsorbents, and regenerated cellulose, though
polyolefin is preferred and most preferably polypropylene. The
nonwoven fabric maybe bonded by thermal point bonding, point
unbending, through air bonding with the use of a binder, ultrasonic
bonding and hydroentangling. The nonwoven fabric of this invention
may be used in a variety of personal care products, including
diapers, training pants, absorbent underpants, adult incontinence
products, bandages and other wound care products and feminine
hygiene products. The nonwoven fabric of this invention maybe used
as a surge material, a hoop component of a hook and loop fabric,
and as an absorbent core, an outercover, a liner, a filtration
media, and wipers, among other things.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a diagram of an apparatus for manufacturing
spunbond fibers.
[0008] FIG. 2 is a cut-away side view of dual capillaries for fiber
production.
[0009] FIG. 3 is a cross-sectional view of dual capillaries for
fiber productions showing the differential shape of the
capillaries.
[0010] FIG. 4 is a cut-away side view of a capillary for producing
a homofilament spunbond fiber.
DEFINITIONS
[0011] As used herein, the following terms have the definitions
ascribed to them.
[0012] The term "disposable" includes being disposed of after use
and not intended to be washed and reused.
[0013] As used herein, the term "nonwoven fabric or web" means a
web having a structure of individual fibers or threads which are
interlaid, but not in an 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, 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 useful are usually expressed in microns. (Note that to
convert from osy to gsm, multiply osy by 33.91). As used herein,
the term "spunbonded fibers" refers to small diameter fibers which
are formed by extruding molten thermoplastic material as filaments
from a plurality of fine, usually circular capillaries of a
spinneret 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., 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. No. 3,338,992 and
U.S. Pat. No. 3,341,394 to Kinney, U.S. Pat. No. 3,502,763 to
Hartmann, and U.S. Pat. No. 3,542,615 to Dobo et al. Spunbond
fibers are generally not tacky when they are deposited onto a
collecting surface. Spunbond fibers are generally continuous and
have average diameters (from a sample of at least 10) larger than 7
microns, more particularly, between about 10 and 30 microns. The
fibers may also have shapes such as those described in U.S. Pat.
No. 5,277,976 to Hogle et al., U.S. Pat. No. 5,466,410 to Hills,
and U.S. Pat. No. 5,069,970 and U.S. Pat. No. 5,057,368 to Largman
et al., which describe hybrids with unconventional shapes.
[0014] As used herein the term "conjugate fibers" refers to fibers
which have been formed from at least two polymers extruded from
separate extruders but spun together to form one fiber. Conjugate
fibers are also sometimes referred to as multicomponent or
bicomponent fibers. The polymers are usually different from each
other though conjugate fibers may be monocomponent fibers. The
polymers are arranged in substantially constantly positioned
distinct zones across the cross-section of the conjugate fibers and
extend continuously along the length of the conjugate fibers. The
configuration of such a conjugate fiber may be, for example, a
sheath/core arrangement wherein one polymer is surrounded by
another or may be a side by side arrangement, a pie arrangement or
an "islands-in-the-sea" arrangement. Conjugate fibers are taught in
U.S. Pat. No. 5,382,400 to Pike et al. and may be used to produce
crimp in the fibers by using the differential rates of expansion
and contraction of the two (or more) polymers.
[0015] As used herein the term "biconstituent fibers" refers to
fibers that have been formed from at least two polymers extruded
from the same extruder as a blend. The term "blend" is defined
below. Biconstituent fibers do not have the various polymer
components arranged in relatively constantly positioned distinct
zones across the cross-sectional area of the fiber and the various
polymers are usually not continuous along the entire length of the
fiber, instead usually forming fibrils or protofibrils which start
and end at random. Biconstituent fibers are sometimes also referred
to as multiconstituent fibers.
[0016] As used herein the term "blend" means a mixture of two or
more polymers while the term "alloy" means a sub-class of blends
wherein the components are immiscible but have been compatibilized.
"Miscibility" and "immiscibility" are defined as blends having
negative and positive values, respectively, for the free energy of
mixing. Further, "compatibilization" is defined as the process of
modifying the interfacial properties of an immiscible polymer blend
in order to make an alloy.
[0017] "Single polymer fibers" means fibers made from one polymer
from one extruder. A nonwoven web of single polymer fibers may have
only the single polymer fibers or may be a blend of single polymer
fibers and other fibers. Such a web may also have a layer of single
polymer fibers and layers of other types of fibers as well. A
single polymer fiber may also be made from differing polymers along
its length and as a biconstituent fiber blend but not as a
conjugate fiber. This means that at any point in the fiber (except
for a small area of transition) the fiber is made from only one
polymer, though this may not be the same polymer as in another
section along the fibers' length.
[0018] As used herein, the term "bonded carded web" refers to webs
made from staple fibers which are sent through a combing or carding
unit, which breaks apart and aligns the staple fibers in the
machine direction to form a generally machine direction-oriented
fibrous nonwoven web. Such fibers are from a few millimeters to
centimeters in length and are usually purchased in bales which are
placed in a picker which separates the fibers prior to the carding
unit. Once the web is formed, it is then bonded by one or more of
several known bonding methods. One such bonding method is powder
bonding, wherein a powdered adhesive binder is distributed through
the web and then activated, usually by heating the web and adhesive
with hot air. Another suitable bonding method is pattern bonding,
wherein heated calender rolls or ultrasonic bonding equipment are
used to bond the fibers together, usually in a localized bond
pattern, though the web can be bonded across its entire surface, if
so desired. Another suitable and well-known bonding method,
particularly when using bicomponent staple fibers, is through-air
bonding, where one of the components acts as a binder.
[0019] As used herein, the term "hot air knife" or HAK means a
process of pre- or primarily bonding a just produced microfiber,
particularly spunbond, web in order to give it sufficient integrity
for further processing, but does not mean the relatively strong
bonding of secondary bonding processes like TAB, thermal bonding
and ultrasonic bonding. A hot air knife is a device which focuses a
stream of heated air at a very high flow rate at the nonwoven web
immediately after its formation. This rate is generally from about
1000 to about 10000 feet per minute (fpm) (305 to 3050 meters per
minute), or more particularly from about 3000 to 5000 feet per
minute (915 to 1525 m/min). The air temperature is usually in the
range of the melting point of at least one of the polymers used in
the web, generally between about 200 and 550.degree. F. (93 and
290.degree. C.) for the thermoplastic polymers commonly used in
spunbonding. The control of air temperature, velocity, pressure,
volume and other factors helps avoid damage to the web while
increasing its integrity. The HAK's focused stream of air is
arranged and directed by at least one slot (or closely spaced
holes) serving as the exit for the heated air towards the web, with
the slot running in a substantially cross-machine direction over
substantially the entire width of the web. Since the foraminous
wire onto which microfiber web polymer is formed generally moves at
a high rate of speed, the time of exposure of any particular part
of the web to the air discharged from the hot air knife is less a
tenth of a second and generally about a hundredth of a second. The
HAK is further described in U.S. Pat. No. 5,707,468, commonly
assigned.
[0020] As used herein "thermal point bonding" involves passing a
fabric or web of fibers to be bonded between a heated calender roll
and an anvil roll. The calender roll is usually, though not always,
patterned in some way so that the entire fabric is not bonded
across its entire surface, and the anvil roll is usually flat. As a
result, various patterns for calender rolls have been developed for
functional as well as aesthetic reasons. One example of a pattern
has points and is the Hansen Pennings or "H&P" pattern with
about a 30% bond area with about 200 bonds/square inch as taught in
U.S. Pat. No. 3,855,046 to Hansen and Pennings. The H&P pattern
has square point or pin bonding areas wherein each pin has a side
dimension of 0.038 inches (0.965 mm), a spacing of 0.070 inches
(1.778 mm) between pins, and a depth of bonding of 0.023 inches
(0.584 mm). The resulting pattern has a bonded area of about 29.5%.
Another typical point bonding pattern is the expanded Hansen
Pennings or "EHP" bond pattern which produces a 15% bond area with
a square pin having a side dimension of 0.037 inches (0.94 mm), a
pin spacing of 0.097 inches (2.464 mm) and a depth of 0.039 inches
(0.991 mm). Another typical point bonding pattern designated "714"
has square pin bonding areas wherein each pin has a side dimension
of 0.023 inches, a spacing of 0.062 inches (1.575 mm) between pins,
and a depth of bonding of 0.033 inches (0.838 mm). The resulting
pattern has a bonded area of about 15%. Yet another common pattern
is the C-Star pattern wnich has a bond area of about 16.9%. The
C-Star pattern has a cross-directional bar or "corduroy" design
interrupted by shooting stars. Other common patterns include a
diamond pattern with repeating and slightly offset diamonds with
about a 16% bond area and a wire weave pattern looking as the name
suggests, e.g. like a window screen, with about a 19% bond area.
Typically, the percent bonding area varies from around 10% to
around 30% of the area of the fabric laminate web. As in well known
in the art, the spot bonding holds the laminate layers together as
well as imparts integrity to each individual layer by bonding
filaments and/or fibers within each layer.
[0021] As used herein "pattern unbonded" or interchangeably "point
unbonded" or "PUB", means a fabric pattern having continuous bonded
areas defining a plurality of discrete unbonded areas as
illustrated in U.S. Pat. No. 5,858,515 to Stokes et al. The fibers
or filaments within the discrete unbonded areas are dimensionally
stabilized by the continuous bonded areas that encircle or surround
each unbonded area, such that no support or backing layer of film
or adhesive is required. The unbonded areas are specifically
designed to afford spaces between fibers or filaments within the
unbonded areas.
[0022] "Hydrophilic" describes fibers or the surfaces of fibers
which are wetted by the aqueous liquids in contact with the fibers.
The degree of wetting of the materials can, in turn, be described
in terms of the contact angles and the surface tensions of the
liquids and materials involved. Equipment and techniques suitable
for measuring the wettability of particular fiber materials can be
provided by a Cahn SFA-222 Surface Force Analyzer System, or a
substantially equivalent system. When measured with this system,
fibers having contact angles less than 90.degree. are designated
"wettable" or "hydrophilic", while fibers having contact angles
equal to or greater than to 90.degree. are designated "nonwettable"
or hydrophobic.
[0023] As used herein, the term "personal care product" or
"personal care absorbent product" means diapers, training pants,
absorbent underpants, adult incontinence products, bandages and
other wound care products and feminine hygiene products.
TEST METHODS
[0024] Compression test: The compression test measures the
resistance to compression and resiliency of a material. This
relatively simple test uses a Compressometer from the Frazier
Precision Instrument Co., Inc., 210 Oakmont Avenue, Gaithersburg,
Md. 20760 and is performed generally according to the US Department
of Commerce, Bureau of Standards Research Paper RP561 published in
the Bureau of Standards Journal of Research, Vol. 10, June 1933, p.
705-713. The Compressometer has a foot of 2.54 cm (one inch) in
diameter under which the sample is placed. Force is applied to the
sample vertically and is monitored by a dial indicator. The
thickness is measured at 0.1 psi load and at a number of pressures
as the load is increased to 3 psi. After reaching 3 psi, the
thickness is measured as the load is gradually reduced, in order to
provide a resiliency measurement.
[0025] Opacity: This test measures the light transmittance through
a sample material. The test equipment is a HunterLab Color
Difference Meter model D25, available from HunterLab of Naperville
Ill., 60540. The test specimen must be large enough to cover the
0.5 inch (1.27 cm) test aperture or port and the sample tested at
one position, in this case testing the anvil side of the sample,
turned 90 degrees and re-tested and the results averaged.
[0026] Peel Test: The peel force value measures the force needed to
peel apart a hook and loop fastening system at approximately a 180
degree angle and can be determined in accordance with standard
procedure ASTM D5170, approved Sep. 15, 1991 and published November
1991; with the following particulars. The loop material to be
tested is cut into a rectangle, 76 mm (3 inch) by 152 mm (6 inch)
with the longer dimension in the cross-machine direction. The loop
material is placed under the clamping plate of a rolidown machine.
The hook material is placed on top of the loop material and
attached by the rolidown machine using a 2 kg roller. A suitable
rolidown machine is part number HR-100 available from Chemsultants
International, of Mentor, Ohio. During the engagement of the
fastener components, the roller is rolled over the test specimen
through one cycle in the direction of the cross-wise "width" of the
sample. In addition, the initial peel by hand to "raise the loops"
is omitted. After the hook and loop are properly attached, the
combination is placed in the testing apparatus, an Instron Model
2712-004 tensile tester with 102 mm (4 inch) rubberized grip faces
(Instron Corporation, Canton Mass. 02021). The hook base is
inserted in the upper grip and the loop in the lower in such a
manner that the movement of the grips away from each other will
result in the peeling apart of the two materials. Slack is removed
and the machine is started. The tester is set with a crosshead
speed of 500 mm/min. and a gage length of 76 mm. Measurements are
begun at 10 mm and end at 46 mm and are in grams. The reported
value of a peel test result is a peal load value employing MTS
TESTWORKS software with a peak criteria of 2%. Additionally, the
peel force value is normalized to be stated in terms of force per
unit length of the "width" dimension of the fastener component on
the test specimen, such as grams per inch or grams per centimeter.
The MTS TESTWORKS software is available from MTS Systems
Corporation, a business having offices in Eden Prairie, Minn.
[0027] Shear: The shear test is used to test the force necessary to
pull a hook and loop fastener apart. A rolldown machine
(Cheminstruments Inc.) having a 2 kg weight, is used to engage the
hook and loop material. The samples were then inserted into an
Instron TM tester with a crosshead speed of 250 mm/min and pulled
apart in a manner similar to that used in the peel test. The sample
width used was 2.54 cm (1 inch) and the hook used was VELCRO.RTM.
HTH-851 though other hooks like 3M's CS-600 may be used, as long as
all samples are tested with the same hook.
[0028] Tensile: The tensile test measures the peak and breaking
loads and peak and break percent elongations of a fabric. This test
measures the load (strength) in grams and elongation in percent. In
the tensile test, two clamps, each having two jaws with each jaw
having a facing in contact with the sample, hold the material in
the same plane, usually vertically, separated by 7.6 cm (3 inches)
and move apart at a specified rate of extension. Values for strip
tensile strength and strip elongation are obtained using a sample
size of 3 inches by 15.2 cm (6 inches), with a jaw facing size of
2.54 cm (1 inch) high by 3 inches wide, and a constant rate of
extension of 300 mm/min. The Sintech 2 tester, available from the
Sintech Corporation, 1001 Sheldon Dr., Cary, N.C. 27513, the
Instron Model TM, available from the Instron Corporation, 2500
Washington St., Canton, Mass. 02021, or a Thwing-Albert Model
INTELLECT II available from the Thwing-Albert Instrument Co., 10960
Dutton Rd., Phila., Pa. 19154 may be used for this test. Results
are reported as an average of three specimens and may be performed
with the specimen in the cross direction (CD) or the machine
direction (MD).
[0029] Bulk (thickness) The caliper of a material is a measure of
thickness and is measured at 146.3 grams per square centimeter
(0.05 psi) with a Starret-type bulk tester, in units of
millimeters.
DETAILED DESCRIPTION
[0030] This invention relates to personal care absorbent articles
such as disposable sanitary napkins, diapers, incontinence
garments, and the like. The materials of this invention may also
find application as wipers and in the area of filtration. Nonwoven
fabrics prepared with single polymer, helically crimped fibers
provide improved properties in a number of areas useful for these
articles.
[0031] Absorbent articles typically have at least a liquid
permeable body side liner, a liquid impervious baffle, and an
absorbent core between the liner and baffle. Filters and wipes may
be single layer fabrics or may have multiple layers with different
specialized properties.
[0032] Nonwoven materials such as carded webs and spunbond webs
have been used as the body side liner in absorbent products. Open,
porous liner structures have been employed to allow liquid to pass
through them rapidly and help keep the wearer's skin separated from
the wet absorbent pad beneath the liner. Some structures have
incorporated zoned surfactant treatments in selected areas of the
liners to increase the wettability of the selected regions and
thereby control the amount of liquid wet-back onto a wearer's
skin.
[0033] The outer cover or baffle is designed to be impermeable to
liquid in order to keep the clothing or bedding of the wearer from
becoming soiled. The impermeable baffle is often made from a thin
film and is generally made from plastic, though other materials may
be used. Nonwoven webs, films or film coated nonwoven webs may be
used as the baffle as well. The baffle may optionally be composed
of a vapor or gas permeable, microporous "breathable" material,
that is permeable to vapors or gas yet substantially impermeable to
liquid.
[0034] Absorbent articles have employed various types of absorbent
cores composed of superabsorbents and/or cellulosic fibers.
Particular absorbent garments may be configured with absorbent
gelling particles and may include a multi-layer absorbent core
arrangement having varying compositions.
[0035] In addition, other layers of material, such as those
constructed with thick, lofty fabric structures, have been
interposed between the liner and absorbent pad for the purpose of
reducing wet-back, distributing liquid and providing a reservoir or
"surge" holding ability.
[0036] Helically crimped fibers may be produced by a number of
means. FIG. 1 shows an apparatus of the general type used for
manufacturing filaments or fibers according to the co-assigned
patent applications. Apparatus 10 has a first extruder assembly 12
for producing spunbond fibers in accordance with known methods
(also see U.S. Pat. No. 5,382,400 to Pike et al.). A spinneret 14
is supplied with molten polymer resin from a resin source (not
shown). The spinneret 14 produces fine denier fibers from the exit
16, which are quenched by an air stream supplied by a quench blower
18. The air stream may differentially cool one side of the fiber
stream more than the other side, thus causing bending and crimping
of the fibers. Crimping creates a softer fabric by, for example,
reducing the straightness of the fibers between bond points created
in the thermal bonding step. Various parameters of the quench
blower 18 can be controlled to control the quality and quantity of
crimping. Fiber composition and resin selection also determine the
crimping characteristics imparted.
[0037] The filaments are drawn into a fiber drawing unit or
aspirator 20 having a Venturi tube/channel 22, through which the
fibers pass. The tube is supplied with temperature controlled air,
which attenuates the filaments as they are pulled through the fiber
drawing unit 20 in their plastic state. The attenuated fibers are
then deposited onto a foraminous moving collection belt 24 and
retained on the belt 24 by a vacuum force exerted by a vacuum box
26. The belt 24 travels around guide rollers 27. As the fibers move
along on the belt 24, a compaction roll 28 above the belt, which
operates with one of the guide rollers 27 beneath the belt,
compresses the spunbond mat so that the fibers have sufficient
integrity to go through the manufacturing process. A hot air knife
may be used as an alternative to the compaction roll.
[0038] A layer of meltblown fibers, comprised of from 1 to about 10
microns in diameter, preferably less than 5 micron diameter, may be
introduced on top of the spunbond layer from a windup roll 30 of
previously manufactured meltblown fibers. Alternatively, it is also
possible to form meltblown fibers and deposit them as formed
directly on the spunbond layer. The meltblown fibers are formed of
resin which is preferably a thermoplastic polymer such as, but not
limited to, polyolefins, polyesters, polyamides, polyurethanes,
copolymers and mixtures thereof.
[0039] A second layer of spunbond fibers may be made by a spunbond
apparatus 32 in a manner similar to that described for spunbond
apparatus 12; i.e., a spinneret 34 produces filaments which are
quenched and crimped by a quench blower 36 and attenuated by an
aspirator 38. The fibers deposited on the meltblown layer are then
compressed by a second compaction device 40 to form a three layer
laminate comprised of spunbond-meltblown-spunbound fibers 42 (the
SMS laminate).
[0040] Spunbond nonwoven fabrics are generally bonded in some
manner as they are produced in order to give them sufficient
structural integrity to withstand the rigors of further processing
into a finished product. Bonding can be accomplished in a number of
ways such as hydroentanglement, needling, ultrasonic bonding,
adhesive bonding, stitchbonding, through-air bonding and thermal
bonding. A preferred method is by thermal bonding. The SMS laminate
42 is moved off the belt 24 and passed between a nipped pair of
thermal bond rolls 44 and 46. Bond roll 44 is a conventional smooth
anvil roll. Bond roll 46 is a conventional pattern roll having a
plurality of pins 48. The pins create bond points within the fabric
matrix. The number and size of bond points are related to fabric
stiffness; i.e., higher bond areas or more bond points per unit
area produce a stiffer fabric. The SMS laminate is passed between
the rolls 44 and 46 and the pins 48 imprint a pattern on the SMS
laminate 42 by pressing on the anvil roll 44 where the nip pressure
is controlled for uniformity.
[0041] The rolls 44 and 46 can be heated to more efficiently form
fiber bonds. The rolls 44 and 46 may be heated to different
temperatures. The optimal temperature range and roll differential
depends on the denier, fiber composition, web mass and web density
and whether monocomponent or conjugate fibers are used. For
monocomponent polypropylene fibers having approximately a 3 dpf,
produced at about 500 feet per minute, the temperature range is
about 270.degree. F. (132.degree. C.), to about 340.degree. F.
(171.degree. C.), with a preferred differential between pattern and
anvil roll of about 10.degree. F. (5.5.degree. C.) to about
30.degree. F. (17.degree. C.). For monocomponent polypropylene
fibers having approximately a 1 dpf at the same production speed,
the temperature range is about 240.degree. F. (115.degree. C.) to
about 290.degree. F. (143.degree. C.), with a preferred
differential of about 40-50.degree. F. (22-28.degree. C.). The
overall temperature range is lower for smaller denier fibers
because heat transfer is more efficient. For a given raw material,
the temperature range stays generally the same, but shifts warmer
or cooler, depending on conveyor speed which significantly impacts
web mass and density. Preferably, the pattern roll is heated to a
higher temperature than the anvil. The lower temperature on the
anvil roll 44 reduces the possibility of fiber glazing and
secondary fiber-to-fiber bonding between the bond points. The
result of this differential bond roll temperature is that secondary
fiber-to-fiber bonds are reduced without affecting the integrity of
the primary bonds, therefore improving fabric drape.
[0042] After the laminate 42 passes through the bond rolls 44 and
46, it is optionally passed to a neck stretching assembly 50,
comprising a pair of nipped rolls 52 and 54. The rolls 52 and 54
run under tension at a controlled speed faster than the speed of
the bond rolls 44 and is 46, thus stretching the SMS laminate 42 in
the same direction as the path of the fabric, known as the machine
direction. Neck stretching breaks fiber-to-fiber bonds and strains
fibers between bond points, thereby reducing fabric stiffness. The
rolls may be heated or cooled as needed to achieve desired mat
properties and dimensional stability.
[0043] The neck stretched SMS laminate 42 is then optionally passed
to an unnecking assembly 56 and a collection roll 66 as known to
those skilled in the art such as has been generally set forth in
U.S. Pat. No. 5,810,954 to Jacobs et al.
[0044] The method according to U.S. patent provisional application
60/257,973 (docket no. 15272) uses a single, shaped capillary for
inducing differential shear between the polymer flowing in a
substantially hemispherical, or half round, half of the capillary
and the polymer flowing in the non-hemispherical, or shaped, half
of that capillary. The method may further include differential or
directed quenching of the filaments, with the directed quenching
air aimed at the shaped portion of the fiber.
[0045] The single, shaped capillary has a cutaway portion which is
not more than 25 percent of the entire cross-sectional area of the
substantially round circumference of the capillary. It is believed
that removal of less than 25 percent of the cross sectional area of
the capillary aids in the retention of substantially circular
cross-section, while inducing the necessary shear differential
between the round and non-round halves of the capillaries, and so
provides for a robust fiber.
[0046] It is believed that other shapes like an "X" or "Y" shape or
a multi-lobal shape, made from a single polymer and subjected to a
differential quench treatment, as taught in U.S. patent application
60/257,983, for example, will also produce satisfactory fibers.
[0047] U.S. patent application Ser. No. 09/747,278 (docket 15274)
teaches the production of single polymer crimped fibers by joining
polymer streams exiting through a dual capillary spinneret design.
The capillaries share a parallel border where they are adjacent
each other and are specifically shaped to maximize induced shear.
Differentially induced shear in the different polymer streams
results in differential tensions in the joined halves of the
filament. The filaments may further be subjected to differential or
directed quenching which provides for setting the crimps in the
filaments to further induce the crimp. The filaments may also be
desirably drawn out in the spinning processing to achieve a
substantially round shape which results in a robust and predictable
filament.
[0048] As shown in FIG. 2, the die tip 70 defines a polymer supply
passage 72 that terminates in further passages defined by
counterbores 74 which are connected to capillaries 76. While
schematic in nature, it will be appreciated that FIG. 2 shows dual
capillaries 76 which are individual passages formed in the die tip
70. The differential capillary shapes are more clearly seen in FIG.
3. Generally, it is preferred that the capillaries of the present
invention have a length to width ratio of between about 4:1 to
about 12:1; and more preferably between about 6:1 to about 10:1,
with length being defined in the direction of polymer flow and
width being the capillary diameter.
[0049] Accordingly, each fiber is produced by the two capillaries
of a dual capillary design. FIG. 3 details an exemplary embodiment
of these dual capillary designs. It is believed that the use of
differently shaped capillaries to produce a single fiber causes the
side of the fiber with increased shear to have a lower viscosity
and lower melt strength, with subsequently higher orientation
within that segment of the fiber. Differential polymer structure
between the two capillaries is further believed to result in
differential cooling rates between fiber segments, further helping
to produce crimp.
[0050] As seen in FIG. 3, the dual capillary design 112 has a first
capillary 114 and a second capillary 116. The first capillary 114
has an outside border 118 and an inside border 120 located adjacent
the second capillary 116 at a distance sufficiently close to cause
polymer extrudate from the first and second capillaries to meld or
conjoin into a single fiber. The outside border 118 is arcuate and
extends over about 120 degrees. The inside border 120 is also
arcuate and extends over about 120 degrees but has a smaller radius
than the outside border. The second capillary 116 is shown as
substantially circular such that its inside border 122, facing and
adjacent the first capillary 114, is arcuate. The second capillary
distal border 124, that is distal from the first capillary, is of
course also arcuate. The second capillary, though shown as
circular, may be substantially elliptical if desired.
[0051] U.S. patent application Ser. No. 09/746,858 (docket no.
16170) teaches the production of single polymer crimped fibers by
joining polymer streams from two capillaries, each having different
length to diameter ratios (L/D) with the joined streams exiting
through a single outlet, or hole, in the meltspun die head. Due to
the different capillary structures, differently induced shear in
the different polymer streams results in differential polymer
orientation, crystallinity percentage and resultant differential
tensions in the joined halves of the filament. The filaments may
further be subjected to quenching which provides for setting the
crimps in the filaments to further induce the crimp. The filaments
in one embodiment retain a substantially round shape by exiting
through a round hole thus resulting in a more robust and
predictable filament although the fiber shape need not be so
limited.
[0052] FIG. 4, details a portion of an exemplary die head 80 as set
up for polypropylene homofilament spunbond crimped filament
production. A counter bore 82 is located in the die head between
the polymer supply channel 84 and the extrusion, or knife, edge 86,
thus having its longitudinal axis in, or defining, the direction of
polymer flow, as indicated by arrow 88. The counter bore 82 does
not reach, or open to, the knife edge 86. In the direction of
polymer flow, the counter bore 82 has a first channel 90 of about
4.00 mm diameter adjacent and connected to the polymer supply
channel 84. The first channel 90 leads to a first conical feed
chamber 92 whose wall slopes inwardly and downwardly by about 2.16
mm at a 60 degree angle to lead to a second, narrower, channel 94
of about 1.50 mm diameter and 7.43 mm length. The second channel 94
ends in a second conical feed chamber 96 whose walls also slope
inwardly at about 60 degrees to end in a flat bottom about 0.54 mm
in from the knife edge 86.
[0053] The first capillary 98 of about 0.60 mm diameter is
connected to the first feed chamber 92 at about the midpoint
thereof and extends parallel to the counter bore long axis to open
to the air at the knife edge 86, for a total length of about 6.36
mm.
[0054] The second capillary 100 of about 0.20 mm diameter and 0.30
mm length is connected to the second feed chamber 96 conical wall
and extends downwardly at about a 45 degree angle to connect with
the first capillary 98 at about 0.41 mm above the knife edge, or
first capillary exit hole 102.
[0055] In this embodiment the first capillary has an L/D ratio of
about 10 to 1 and the second capillary has an L/D ratio of about
1.5 to 1. The L/D ratio of the capillaries may be varied to achieve
the desired durability, processability and percentage of
crystallinity within the fiber. Crystallinity percentage represents
the amount, or percent, of crystals formed in the polymer chain.
The capillaries or the exit hole may be shaped rather than round to
induce further crimping.
[0056] It is believed that the higher shear produced in the polymer
by travel through the shorter, narrower, second capillary will
lower the viscosity of the polymer melt and induce higher polymer
chain orientation than polymer travel through the larger, wider
first capillary. The polymer in the first capillary will have a
higher viscosity and lower polymer chain orientation, resulting in
a more amorphous polymer stream. As the commingled polymer stream
exits the spinneret into the air, it is preferably quenched on both
sides to fix the orientation of the extrudate. The highly oriented
side will shrink to a greater degree, causing crimping of the
fiber.
[0057] U.S. provisional patent application 60/257,982 (docket no.
15620) teaches the treatment of helically crimped homofilaments
with sufficient hot air flow to accelerate the fibers' natural
tendency to crimp. This also sets the crimps without substantial
melt bonding or relaxation of the crimped fibers in order to retain
the lofty structure of this layer of the laminate. Various other
layers may then be bonded, such as by thermal point bonding, to
create a laminate which retains the essential characteristics of
each layer. The layers may, for example, be bonded together with
sufficient integrity to create a laminate that will withstand high
speed web transfer processing without harm to the processing
equipment or the material. This process preferably uses a hot air
knife, a device now known to those skilled in the art and described
in U.S. Pat. No. 5,707,468 to Arnold et al, to which has been
attached a diffuser mechanism which can end in a plate with
multiple perforations for escape of the hot air, rather than as a
concentrated line in the HAK.
[0058] The dwell time, air temperature, and flow rates of the hot
air knife are adjusted according to polymer type and fiber
morphology of the crimped fibers. An exemplary homofilament
polypropylene helical spunbond layer has been treated with desired
results by diffuse airflow. The flow rate was about 275 meters per
minute or mpm (900 feet per minute or fpm) over a 45.72 cm
(eighteen inch) length in the machine direction at between 61 and
366 mpm (200 and 1200 fpm) material traversal rates. Further
satisfactory results were obtained with a diffuser plenum extending
20.32 cm (eight inches) in the machine direction, at air
temperatures of between 132-143 degrees C. (270-290 degrees F.), at
an airflow rate of between 213 and 259 mpm (700 and 850 fpm),
supplied at a distance of 2.54 cm (one inch) from the forming wire,
and material traversal rates of between 91 and 244 mpm (300 fpm and
800 fpm).
[0059] U.S. provisional patent application 60/257,972 (docket no.
15814) teaches a first layer of nonwoven filaments deposited onto a
forming belt, or foraminous wire, an optional intermediate layer,
and a layer of lofty nonwoven filaments such as e.g., helically
crimped homofilaments deposited over the first layer and any
in-place intermediate layers. The first layer is treated, such as
by known hot air knife treatment, to bond the first layer into a
web with sufficient integrity to withstand high speed web transfer
handling. The optional intermediate layer may or may not be heat
treated depending on fiber type, desired laminate functionality, or
morphology, or the like. The layer of lofty nonwoven filaments is
treated in-line on the forming belt with sufficient heat to set the
crimps without substantial melt bonding or crimp relaxation of the
crimped fibers in order to retain the lofty structure of this layer
of the laminate. The various web layers, i.e., the first layer for
mechanical integrity, the second lofty, helical crimped, layer, and
any intermediate layers are then bonded, such as by thermal point
bonding, to retain the essential characteristics of each layer and
bond the layers together with sufficient integrity to create a
laminate that will withstand high speed web transfer processing
without harm to the processing equipment or the material. It will
be understood that manufacturing speeds will be dependent on the
materials being formed, but the present invention should have few
practical limits in this regard and may accommodate web speeds by
way of example only, in the range of 200 to 2000 feet per minute.
It has been found that the crimps of a single component crimped
thermoplastic fiber web may be crystallized, or set, to retain
their loft through low applications of heat as in U.S. Pat. No.
6,123,886 to Slack. Slack teaches a method of making a substantial
helical crimp in a continuous filament by generating turbulence in
thermoplastic material intended to form the filament while it is at
its glass transition phase temperature and maintaining the
turbulence while the polymer crystallizes. This treatment, however,
does little to increase the integrity of the web for modern,
high-speed, line-transfer manufacturing, and, as taught in Slack,
is a slow, off-line process unsuitable for economical manufacture
rates.
[0060] The crimped fiber laminate material made in this manner can
be useful for high loft and high bulk applications such as the loop
portions of hook and loop fasteners. The fibers may be designed to
produce fabric of good softness and drape while keeping sufficient
bulk and loft to aid in the cloth like feel.
[0061] The materials of this invention may be made from synthetic
polymers. Synthetic fibers include those made from polyolefins,
polyamides, polyesters, rayon, acrylics, superabsorbents,
LYOCELL.RTM. regenerated cellulose and any other suitable synthetic
fibers known to those skilled in the art. Many polyolefins are
available for fiber production, for example polyethylenes such as
Dow Chemical's ASPUN.RTM. 6811A liner low density polyethylene,
2553 LLDPE and 25355 and 12350 high density polyethylene are such
suitable polymers. The polyethylenes have melt flow rates,
respectively, of about 26, 40, 25 and 12.
[0062] Fiber forming polypropylenes include Exxon Chemical
Company's ESCORENE.RTM. PD 3445 polypropylene and Himont Chemical
Co.'s PF304. Other polyolefins are also available.
[0063] A number of examples were prepared using different fibers,
in order to test the fabrics of the invention. The fibers used were
helically crimped single polymer fibers made according to U.S. Pat.
No. 6,123,886, helically crimped bicomponent fiber,, and
mechanically crimped polypropylene fibers.
[0064] The helically crimped single polymer fibers (Fiber 1) had a
denier of 7 and were made from polypropylene. These fibers were
produced as continuous fibers and subsequently cut into staple
lengths of approximately 50 mm.
[0065] The bicomponent crimped fibers (Fiber 2) had a denier of
about 6 and were made from polypropylene and polyethylene. These
fibers were cut into staple lengths of 50 mm.
[0066] The mechanically crimped fibers (Fiber 3) also had a denier
of about 6 and were cut into staple lengths of about 50 mm.
[0067] Each of the fibers was processed into a nonwoven web
according to known bonded carded web processes at two different
basis weights. All webs were bonded with a point un-bonded pattern.
The six nonwoven webs were tested for bulk, shear and peel
strength, compression, resilience and density. The results are
given in Table 1. In Table 1, basis weight is given in grams per
square meter, bulk in mm, shear and peel were measured in the cross
machine direction and are in grams, compression is given in mm for
a test using a 2.54 cm (1 inch) diameter foot at a pressure of
292.7 gram-centimeter squared (0.1 psi), the resilience is the
difference between the load and unload heights and the density is
given in grams per cubic centimeter.
1 TABLE 1 Fiber 1 Fiber 1 Fiber 2 Fiber 2 Fiber 3 Fiber 3 Basis
weight 48.5 31.9 52.3 23.3 51.2 26.8 Bulk 13.7 8.6 9.4 5.1 7.6 4.6
Shear 2724 2510 2493 2390 2914 2593 Peel 76 28 48 45 51 49
Compression 1.12 0.58 0.71 0.33 0.66 0.41 (load) Compression 0.71
0.38 0.48 0.15 0.51 0.25 (unload) Resilience 0.64 0.65 0.68 0.46
0.77 0.63 Density 0.0035 0.0037 0.0056 0.0046 0.0067 0.0059
[0068] As can be seen from Table 1, the shear and peel
characteristics of the single polymer helically crimped fiber web
are superior to that of the bicomponent crimped fibers, except for
the shear of fiber 1 at 31.9 gsm. The bulk was much greater for the
single polymer helically crimped fiber web, indicating an advantage
in fluid handling applications in personal care products, as well
as in hook and loop fastening applications as a loop material. The
high bulk and good resilience of the single polymer helically
crimped fiber web also indicates a high void volume (and low
density), also a positive indicator for a successful fluid handling
layer.
[0069] Another example was performed using helically crimped fibers
but made according to the spunbonding process. The fibers used were
single component helically crimped spunbond fibers and helically
crimped bicomponent fibers.
[0070] The helically crimped single polymer fibers (Fiber 4) had a
denier of 7 and were made from polypropylene. These fibers were
made according to U.S. patent provisional application 60/257,973
and had about 25 percent of the cross sectional area of the
capillary removed to induce shear.
[0071] The bicomponent crimped fibers (Fiber 5) had a denier of
about 6 and were made from polyethylene and polypropylene in a
side-by-side configuration. These fibers were made according to
U.S. Pat. No. 5,382,400 to Pike et al.
[0072] Each of the fibers was processed into a nonwoven web
according to known spunbonding processes at two different basis
weights. All webs were thermally bonded using a point un-bonded
pattern. The four nonwoven webs were tested for shear and peel
strength, percent opacity, machine directional tensile strength,
cross-machine tensile strength, compression and resilience using
the procedures herein. The results are given in Table 2. In Table
2, basis weight is given in grams per square meter, shear and peel
were measured in the cross machine direction and are in grams,
compression is given in mm for a test using a 2.54 cm (1 inch)
diameter foot at a pressure of 292.7 gram-centimeter squared (0.1
psi) and the resilience is the difference between the load and
unload heights.
2 TABLE 2 Fiber 4 Fiber 4 Fiber 5 Fiber 5 Basis weight 48.8 23.4
52.5 25.4 Shear 1210 585 872 993 Peel 115 58 161 176 Opacity 55.4
38.8 44.8 25.3 Compression 0.61 0.36 0.58 0.41 (load) Compression
0.46 0.23 0.41 0.23 (unload) Resilience 0.75 0.64 0.70 0.56 Tensile
MD 12.4 8.2 7.7 2.5 Tensile CD 8.1 5.0 3.7 1.1
[0073] The resilience of the single component helically crimped
fibers was greater than that of the bicomponent fibers, especially
if normalized for basis weight, as were the tensile strengths. The
opacity of the single component helically crimped fibers was also
greater, indicating the possible application for this fabric where
stain hiding properties are desired, such as in an outercover or
liner for personal care products.
[0074] Tenacity testing of the fibers 4 and 5 made at about 4.7
denier, revealed a tenacity in gm/denier of 1.9 and 1.4
respectively, showing the fibers according to the invention to be
stronger than comparable crimped bicomponent fibers.
[0075] The testing of the single polymer helically crimped fiber
webs indicates that they will be good surge materials in personal
care products. Surge control materials are provided to quickly
accept an incoming insult and either absorb, hold, channel or
otherwise manage the liquid so that it does not leak outside the
article. The surge layer may also be referred to as an intake
layer, transfer layer, transport layer and the like. A surge
material must typically be capable of handling an incoming insult
of between about 60 and 100 cc at a volumetric flow rate of from
about 5 to 20 cc/sec, for infants, for example.
[0076] Superabsorbent polymers may also be used to produce single
polymer helically crimped fibers for use in the nonwoven webs of
this invention. Superabsorbents are normally used in particulate
form in absorbent cores since they absorb many times their weight
in liquid. A particular problem for prior absorbent cores using
particulate superabsorbents has been "gel blocking", a condition
whereby the superabsorbent particles swell and impede or prohibit
entry of additional liquid to be absorbed. Particulate
superabsorbent may also leak from the product much more easily than
fibrous superabsorbent. The large void volume and good resilience
associated with helically crimped fibers should alleviate the
problem of gel blocking to a large degree, maintaining open pores
in the absorbent structure for continued liquid intake for a longer
period of time than conventional absorbent cores.
[0077] Superabsorbents that are useful in the present inventions
can be chosen from classes based on chemical structure as well as
physical form. These include superabsorbents with low gel strength,
high gel strength, surface cross-linked superabsorbents, uniformly
cross-linked superabsorbents, or superabsorbents with varied
cross-link density throughout the structure. Superabsorbents may be
based on chemistries that include but are not limited to acrylic
acid, iso-butylene/maleic anhydride, polyethylene oxide,
carboxy-methyl cellulose, poly vinyl pyrrollidone, and poly vinyl
alcohol. The superabsorbents may range in rate from slow to fast.
The superabsorbents must be capable of being made into a fiber. The
superabsorbents may be in various degrees of neutralization.
Neutralization occurs through use of counter ions such as Li, Na,
K, Ca. Examples of superabsorbents obtained from Camelot are
designated FIBERDRI.RTM. 1241 and FIBERDRI.RTM. 1161. Examples of
these types of superabsorbents obtained from Technical Absorbents,
Ltd. are designated as OASIS.RTM. 101 and OASIS.RTM. 111. Another
Example included in these types of superabsorbents is obtained from
Chemtall Inc. and is designated FLOSORB.RTM. 60 Lady. Another
Example included in these types of superabsorbents is obtained from
Sumitomo Seika and is recognized as SA60N Type 2. Additional types
of superabsorbents not listed here which are commonly available and
known to those skilled in the art can also be useful in the present
inventions.
[0078] The nonwoven fabrics of this invention may be made with
various physical parameters dependent upon its end use. The fabric
may be made with a basis weight, for example, from about 20 to 80
gsm for liqhter weight applications and from 80 to 150 gsm for
heavier weight applications. Lighter weight applications include,
for example, liners, loop materials and outercovers and heavier
weight applications include surge and absorbent core materials,
filtration media, and wipers. The density of the web may be varied
from about 0.002 to 0.05 g/cm.sup.3. The degree of crimp may be
controlled using the variables of quench temperature, L/D ratio,
shape of capillary, type of polymer, and polymer flow rate. The
denier of the fiber used to make the nonwoven web of this invention
may also be adjusted in order to change the behavior of the web.
The denier will affect, for example, the wicking properties of the
web. The properties of the web may be affected also by chemical
treatments. These treatments include anti-statics and surfactant
designed to change the hydrophilicity of the fibers.
[0079] As will be appreciated by those skilled in the art, changes
and variations to the invention are considered to be within the
ability of those skilled in the art. Examples of such changes are
contained in the patents identified above, each of which is
incorporated herein by reference in its entirety to the extent it
is consistent with this specification. Such changes and variations
are intended by the inventors to be within the scope of the
invention.
* * * * *