Note: Descriptions are shown in the official language in which they were submitted.
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HYDROENY'AriGLEMENT OF
CONTINUOUS ['OLYMEE~ F~
-
Tecb~Fldd
7'ha present inveotion tclatcs geneialfy to a method for
hydroentanglemettt of continuously extruded, osscntially cndicss
t]tertnoplastic
polyaur filamcats. the apparatus for carrying oat the method, and pmducts
[0 prod.uc.cd t!>ercby. Tha polyczoric filamcllts can be provided in the focm
of one
or zswe ,puubonded ptectusor web3, orthe process can be practiced in-line with
an associated spuabondiag apparatas. Fabrics ontbodying the proscnt invention
raay compriso lamiaaEons of differing pofymaic tilattcnts, auch as Eilaments
cxhibiting sipificantly diffedng bonding totnperatures. Additionalty, fa#trics
having ralativcly high basis weights can be formed from ptural slwnbond
precursor wcbs.
$ackgrouod QfThe levention
Nonwoven fabrics are used in a wide variety of applications, where the
e.ngineered qualities of the fabrics can be advantageously amployed. These
" of fabrics differ from traditional woven or Imitted fabrics in that the
fibcrs
or filanmcnts of the fabric are integratcd into a coherent wob without
traditional
textilc processcs. Entat-gkttteat of the fibers or filaments of the fabric
provide
the fabcic with tho dcsircd integrity, with the selected eatanglenient proccss
pCrrnitting fabrics to be pattemcd to achicve desired asrsthetics, and
physical
x5 characteriskics.
The term'hydcbentanglement" gcncrally refers to a proccss that was
d_velopcai as a possible substitute for a conventionat weaving proee,5s_ In a
hydcvcntangtcment process, small, high intensity jets of watu are impinged on
a
layer of loosc fibers or F laittenta, with the fibers or filaments bcing
supported on
an unyielding perforaled surface, such as a wira screen or perforated drum.
The
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liquid jets cause the fibers, being relatively short and having loose ends, to
become rearranged, with at least some portions of the fibers becoming tangled,
wrapped, and/or knotted around each other. Depending on the nature of the
support surface being used (e.g., the size, shape and pattern of openings), a
variety of fabric arrangements and appearances can be produced, such as a
fabric
resembling a woven cloth or a lace.
The term "spunbonding" re:7ers to a process in which a thermoplastic
polymer is provided in a raw or pellet form and is melted and extruded or
"spun"
through a large number of small orifices to produce a bundle of continuous or
essentially endless filaments. These filaments are cooled and drawn or
attenuated and are deposited as a loose web onto a moving conveyor. The
filaments are then partially bonded, typically by passing the web between a
pair
of heated rolls, with at least one of the rolls having a raised pattern to
provide a
bonding pattern in the fabric. Of the various processes employed to produce
nonwovens, spunbonding is the most efficient, since the final fabric is made
directly from the raw material on a single production line. For nonwovens made
of fibers, for example, the fibers must be first produced, cut, and formed
into
bales. The bales of fibers are then processed and the fibers are formed into
uniform webs, usually by carding, and are then bonded to make a fabric.
Hydroentangled nonwoven fabrics enjoy considerable commercial
success primarily because of the variety of fiber compositions, basis weights,
and surface textures and finishes which can be produced. Since the fibers in
the
fabric are held together by knotting or mechanical friction, however, rather
than
by fiber-to-fiber fusion or chemical adhesion, such fabrics offer relatively
low
tensile strength and poor elongation. In order to overcome these problems,
proposals have been advanced to entangle the fibers into an already existing
separate, more stable substrate, such as a preformed cloth or array of
filaments,
where the fibers tend to wrap around the substrate and bridge openings in the
separate substrate. Such processes obviously involve the addition of a
secondary
fabric to the product, thereby increasing the associated effort and cost.
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Another method for improving strength prope[ties is to impregnate the
fabria with adhesive, usually by dipping the fa6ric into an ad4csive bath with
subsequent drying of the fabric_ In addition to adding cost and effort to the
process, however, addition of an adhesive may undesirably affect other
properties of the final produCi. For instafiee, treatntent with an adhesive
rnay
affect the aff'utity of tttc web for a dye, or may otherwise cau$e a deeiinc
in
aestfietic properties such as hand and drape as a Yrsult of increased
stiffness.
Because of the above discussod probleau associated with hydrocntanglc<d
webs, thee hydroctttamgfing ptactice as known by those slcilled in tha art
hcrctofore hss beert principatly limitcd only to staple ftbers, to prcbonded
wcbs,
or lo filaments ofonly an eatrenely small diameter. The hydroentanglernent of
webs of filaraents that are continuous, ofrel.ttively large diameter, or
higher
deaier has heretofore not been considered feasible. Convcntional wisdom ; r?
wiggcsft that long, large diattoter, continuous filamcnts would dissipate
energy
i 5 supplied by entangling watexjets, and ihereby resist entang{emeat. An
additional factor sug&esting that continuous ftlaments coald not be
sufficiently
hydroentangled to farcn a stable, cohesive fabric is that as the filaments arc
continuous they do not have loose frcc ends requaod for wrapping and knotting.
Yet anothcr problcm in thc hydroentangling process as prescntly known and
practiced in the industry is assoiated with production spced linsitations.
Presently known methods and apparatuses for hydroentangliag f~laments are not
abla to achieve tates of production equal to tiwse of spunbonding filament
production.
VaTious prior art patents disciose teehniques for manufacturing
nonwoven fatxics by hydroontanglement. U.S. iG'atert No. 3,485,706, to Frvans,
discloses melhods and apparatus for fortnation
ot'inonwovcn fabrics by hydroentanglement. This patent describes the fiber
physics involved in the production of such fabdcs, noting that entangled
fibcrs
vrithin the fabrics aro restrained from tnovemait by intecartion with
tltemsclves
and with okher fibers in the fabrios. Such interaction is stated as being
caused by
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the manner in which the fibers are interengaged so as to cause them to
interlock
with one another. This patent is principally directed toward the entanglement
of
fibers, but reference is made to entanglement of continuous filament webs. It
is
believed that the tested samples comprised loose filament webs, and were
subjected to laboratory scale treatments that did not appropriately model
continuous processing of filamentary webs. It is additionally noted that this
patent does not distinguish between fiber entangling physics of the staple or
textile length fiber examples set forth therein, and that of the continuous
filament examples. It is believed that when subjected to the testing described
in
the patent, the fabric samples did not provide results that would define
differences in their construction. Use of cut hand sheets of spunbond webs is
believed to have rendered the filaments thereof in a discontinuous form.
Additionally, fiber ends of the cut edges were not constrained, as would be
the
case during hydroentanglement of an intact continuous filament web. As a
consequence, it is believed that the continuous filaments referred to in this
patent
were actually more in the nature of long staple fibers, and as such, responded
to
the energy of water jets as staple fibers, that is, recoiling and wrapping
around
one another. U.S. Patent No. 3,560,326, to Bunting, Jr., et al., is believed
to be
similarly limited in its teachings, and thus it is not believed that this
patent
meaningfully distinguishes between the fiber entangling physics of relatively
short fibers (i.e., staple or textile length), and continuous filament
examples set
forth therein.
U.S. Patent No. 4,818,594, to Rhodia, contemplates hydroentanglement
of fibers having diameters on the order of 0.1 to 6 microns, which by virtue
of
their micron-sized diameters are clearly formed by melt-blowing, as opposed to
spunbonding.
U.S. Patent No. 5,023,130, to Simpson et al., discloses the use of
plexifilamentary fibrous webs which are known in the art as being
instantaneously bonded during production. This patent is limited to the use of
a
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very fine mesh forming screen, and the use of water jet pressures that are in
excess of 2,000 psi in the initial forming stations.
U.S. Patent No. 5,369,858, to Gilmore et al., discloses a nonwoven fabric
comprising at least one layer of textile fibers or net polymeric filaments,
and at
least one web of melt-blown microfibers, bonded together by hydroentangling.
This patent specifically contemplates that a spunbonded fabric is employed as
a
substrate for entangling of secondary melt-blown or carded webs, with the
patent
further contemplating formation of apertures of two differing sizes in the
fabric.
As is recognized in the art, the use of particular types of polymeric fibers
or filaments can be desirable depending upon the desired physical
characteristics
of the nonwoven fabric formed from the fibers or filaments. In particular,
polyethylene filament webs are desirable for application such as facings,
coverstock, and similar applications because of the softness and drapeability
the
polyethylene provides. A drawback associated with the use of polyethylene
filament webs for such applications is the low tensile strength the filaments
exhibit. Polypropylene or polyester filament webs are typically strong in
comparison to polyethylene, but products formed from polypropylene or
polyester filament are relatively stiff in comparison to polyethylene filament
products.
It can be difficult to combine polyethylene webs with other stronger webs
to produce a product that is both soft and strong. Bonding temperature
differences ordinarily make it difficult or impossible to thermally bond a web
that might be produced in a continuous process that includes, for example, two
filament beams, one producing polyethylene and the other producing
polypropylene. A temperature selected to bond the polyethylene is insufficient
to bond the polypropylene portion. While it is possible to thermally bond the
luy ers using two thermal bonding steps, thermally bonding the polypropylene
as
a first step undesirably stiffens the polypropylene. The polyethylene layer
added
to such a web thus exhibits undesirable stiffness. The resultant laminated
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product would consist of the polyethylene layer and a relatively stiff
reinforcing
layer.
As noted above, various methods for making nonwoven fabrics are well-
known. In general, these fabrics are made from bonded fibers or filaments, or
combinations thereof. In spunbonding, a thermal plastic polymer is melt-
extruded into a plurality of continuous filaments and deposited on a conveyor.
The filaments are then continuouslN, thermally point-bonded to one another
using calender rolls. As also noted, formation of nonwoven fabrics by
hydroentanglement entails the use of high intensity, fine jets of water which
are
impinged on a web, causing the fibers to entangle and form a coherent
mechanically bonded structure.
In spunbonding, it is known that the tensile strength of the fabric of a
given basis weight can be increased by decreasing the size of the filament. In
addition, the uniformity of a fabric of a given basis weight also generally
increases with reduced filament size. However, reduced filament causes a
reduction of production output and efficiency, whether or not the web is
formed
as a single layer, or in multiple layers.
In hydroentanglement, the fiber web that is initially deposited consists of
individual unbonded fibers, and the web therefore tends to be fragile. For
this
reason, the pressure of the initial water jets impacting the web must be kept
low
to avoid excessive fiber displacement, with subsequent jets operating at
higher
pressures used to more significantly entangle the fibers. This requirement of
"pre-entangling" the web with low initial pressure jets decreases the
efficiency
of the entangling process. One known method proposed for resolving this
problem is to support the upper exposed surface of the unbonded web with a
perforated screen during entanglement, but disadvantageously involves the use
of additional equipment.
In addition, conventional hydroentanglement fabrics as they presently
exist are not considered durable, in the sense that they are not launderable.
Also,
conventional fabrics cannot be subjected to modern jet dyeing processes which
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involve high flow rates of the treating liquid. These limitations limit the
commercial applications of such fabrics and thereby significantly affect their
economic value. Proposals have been advanced to treat the finished fabric with
a curable binder. This, however, increases the processing effort and cost of
the
product. Further, the binder may have an adverse effect on the final fabric
properties, such as softness and drapeability, as well as the ability to dye
the
fabric.
Heretofore, durable, launderable nonwoven fabrics have traditionally
relied upon relatively high levels of thermal bonding, surface treatments to
bond
the surface of the fabrics, or stitch bonding techniques to provide a
stabilizing
network for tying down fiber ends. U.S. Patents No. 5,192,600 and No.
5,623,888 disclose stitch bonding technology for the production of nonwoven
fabrics, with the bulky fabrics described therein stated as being useful in a
variety of apparel and industrial end uses. U.S. Patents No. 5,288,348 and No.
5,470,640 disclose high loft, durable nonwoven fabrics which are produced by
serial bonding of layers, followed by an all-over surface bonding with a
greater
bond area than any of the intermittent bonding steps.
U.S. Patent No. 5,587,225 describes the use of hydroentangling to bind
an interior layer of cellulosic short fibers to outer layers of crimped
continuous
filaments. While the end product is described as "knit-like" and durable, the
product is intended to survive only one laundry cycle, losing up to 5% of the
original basis weight during the first washing. While the spunbond outer
layers
are described as being prebonded, the use of crimped continuous filaments is
specifically contemplated, with reliance on the cnmped configuration to assist
in
the retention of short, cellulosic fibers in the entangled matrix. It will be
appreciated that the crimping process requires either a mechanical step, or
the
use of bi-component fibers which develop latent crimp as an aspect of
processing, and thus the use of standard spunbond fabrics is not contemplated.
Additionally, this patent contemplates the use of a short staple fiber inner
layer
to increase the opacity and visual uniformity of the final product.
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The present invention further contemplates a process for formation of a
laminated nonwoven fabric, comprising polymeric filament layers exhibiting
differing properties. There is, therefore, an as yet unresolved need in the
industry for a process of hydroentangling continuous filaments of relatively
large denier, that is, filaments having diameters greater than those generally
achieved by melt-blowing formation. Also, there is a heretofore unresolved
need in the industry for a hydroentangled nonwoven fabric comprised of
continuous filaments of relatively large denier. Further, there is an
unresolved
need in the industry for an apparatus for producing a nonwoven web comprised
of hydroentangled continuous filaments of relatively large denier, and for a
method and apparatus for hydroentanglement capable of rates of production '
substantially equal to spunbonding production rates. A further aspect of the
present invention contemplates production of highly durable, dyeable nonwoven
fabric made of hydroentangled continuous filaments. The process employs
spunbonded webs that are fully stabilized by thermal point bonding with high
pressure jets utilized to separate the filaments from the thermal bond points,
freeing the filaments for entangling by water jets. Notably, the process
contemplates use of multiple prebonded spunbond layers to form a composite
web of substantial basis weight, up to 600 g/m2 (grams per square meter).
Summary Of The Invention
The present invention comprises a process for making a nonwoven fabric
in which a large number of continuous or essentially endless filaments of
about
0.5 to 3 denier are deposited on a three-dimensional support to form an
unbonded web, which is then continuously and without interruption subjected to
hydroentanglement in stages by water jets to form a fabric. The present
invention further entails the production of nonwoven fabrics from a plurality
of
polymeric webs, wherein the polyme;=ic filaments of the webs exhibit differing
physical properties, such as differing bonding temperatures. Additionally, the
present invention contemplates the production of hydroentangled nonwoven
fabrics from conventional spunbond webs of polymeric filaments, with the use
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of plural precursor spunbond webs facilitating production of hydroentangled
nonwoven fabric having a wide variety of basis weights, up to 600 gm/Z.
The hydroentanglement process of the present invention is capable of
production rates substantially equal to those of the spunbonding process. The
present invention also provides a nonwoven fabric comprised of hydroentangled
continuous filaments of 0.5 to 3 denier, wherein the filaments are
interengaged
by a matrix of packed continuous complex loops or spirals, with the filaments
being substantially free of any breaking, wrapping, knotting, or severe
bending.
The present invention further comprises an apparatus for making a nonwoven
fabric, comprising means for depositing continuous filaments of 0.5 to 3
denier
on a moving support, and at least one successive group of water jets for
hydroentangling the filaments wherein the filaments are interengaged by
continuous complex loops or spirals, with the filaments being substantially
free
of any wrapping, knotting, or severe bending.
The preferred nonwoven fabric of the present invention comprises a web
of continuous, substantially endless polymer filaments of 0.5 to 3 denier
interengaged by continuous complex loops or spirals, with the filaments being
substantially free of any wrapping, knotting, breaking, or severe bending. The
terms "knot" and "knotting" as used in the description and claims of this
irivention are in reference to a condition in which adjacent filaments in a
hydroentangled web pass around each other more than about 360 to form
mechanical bonds in the fabric.
The fabric of the invention, because of the unique manner in which the
filaments are held together, provides excellent tensile strength and high
elongation. This is a most surprising result, as it is well-known in the
industry
that with the exception of elastic nonwoven fabrics, there is an inverse
re:ationship between tensile strength and elongation values. High strength
fabrics tend to have lower elongation than fabrics of comparable weight and
lower tensile strength.
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The surprising high elongation and high tensile strength combination of
the present fabric and process results from the novel filament entanglement.
As
opposed to fiber knotting and extensive wrapping of the prior art, the
physical
bonding of the continuous filaments of the present invention is instead
characterized by complex meshed coils, spirals, and loops having a high
frequency of contact points. This novel filament mechanical bonding provides
high elongation values in excess of 90% and more typically in excess of 100%
in
combination with high tensile strength as the meshed coils and loops of the
invention disengage and filaments straighten and elongate under a load.
Knotted
fibers of the prior art, on the other hand, tend to suffer fiber breakage
under load,
resulting in more limited elongation and tensile strengths.
The effect of the novel packed loops of the fabric and process of the
invention also results in a distinctive and commercially advantageous uniform
fabric appearance. The individual fiber wrapping and knotting of prior art
hydroentangled fabrics leads to visible streaks and thin spots. The complex
packing of the loops and coils of the present invention, on the other hand,
provides better randomization of the filaments, resulting in a more consistent
fabric and better aesthetics. Because the novel packing of the filaments of
the
invention is substantially free of loose filament ends, the fabric of the
invention
also advantageously has high abrasion resistance and a low fuzz surface.
The preferred process of the present invention includes melt-extruding at
least one layer of continuous filaments of 0.5 to 3 denier onto a moving
support
to form a precursor web, continuously and without interruption pre-entangling
the web with at least one pre-entanglement water jet station having a
plurality of
water jets, and finally entangling the filament web on a three-dimensional
image
transfer device with at least one entanglement water jet station to form a
coherent web. The pre-entangling water jets are preferably operated at a
hydraulic pressure of between 100-5,000 psi, while the entangling water jets
are
operated at pressures of between 1,000-6,000 psi. Hydraulic pressures used
will
depend on the basis weight of the fabric being produced, as well as on
qualities
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desired in the fabric, as will be discussed in detail below. Use of plural
precursor webs which are laminated by hydroentanglement on a three-
dimensional image transfer device is also contemplated.
Contrary to conventional wisdom, it has been found that an unbonded
web of continuous and essentially endless filaments of relatively large denier
may be produced on a modern high speed spunbond line. Such a web may be
produced as the continuous filaments have sufficient curvature and mobility,
while being somewhat constrained along their length, to allow entanglement in
the unique manner of the invention. The dynamics of the interengaged packed
loops of the fabric of the invention are thus entirely different from the
hydroentanglement of staple fibers of the same denier.
The preferred apparatus of the present invention comprises a means for
continuously depositing substantially endless filaments of 0.5 to 3 denier on
a
moving support to form a web, and at least one water jet station for
hydroentangling the filament web. Preferably, at least one preliminary water
jet
pre-entangling station is also provided. The moving support preferably
comprises a porous single or dual wire, or a forming drum. An additional water
jet station and an additional forming drum may further be provided in the
preferred embodiment of the apparatus for impinging a pattern on the fabric.
Also, a preferred apparatus embodiment may further comprise means for
introducing a second component web, such as staple fibers, pulp, or melt-blown
webs, to the web of the invention, as a subsequent step.
A further aspect of the present invention contemplates a process for
making a laminated nonwoven fabric, wherein each of the lamination comprises
substantially continuous polymeric thermoplastic filaments. Plural precursor
webs are provided, with hydroentangling of the precursor webs on a three-
dimensional image transfer device acting to interengage the filaments of
adjacent ones of the webs to form respective plural laminations of the
nonwoven
fabric. This aspect of the invention can be advantageously employed for
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formation of nonwoven fabrics wherein the thermoplastic filaments of each of
the webs exhibit differing properties.
In particular, the present process contemplates that the thermoplastic
filaments of each web exhibit a bonding temperature which differs
significantly
from the bonding temperature of the filaments of an adjacent one of the webs.
This aspect of the invention more particularly contemplates that one of the
precursor webs comprises polyethylene filaments having a denier of about 2 to
5, with this precursor web comprising from about 40% to 90% of the weight of
the resultant nonwoven fabric. The use of polyethylene filaments desirably
provides the resultant nonwoven fabric wich softness and drapeability. An
adjacent one of the precursor webs comprises thermoplastic filaments selected
from the group consisting of polypropylene and polyester, wherein the
filaments
have a denier of about 0.5 to 3. The one or more adjacent webs can be selected
for their strength characteristics, with it further contemplated that the
nonwoven
fabric can be provided with two exterior polyethylene filament laminations,
and
an intermediate lamination formed from differing polymeric filaments, such as
polypropylene or polyester.
In accordance with a further aspect of the present invention, conventional
spunbond webs, that is, thermally point bonded webs of thermoplastic
filaments,
serve as starting materials or precursor webs for the process and product of
the
irlvention. The substrate, spunbond webs are entirely stable and can, for
example, be handled without losing their integrity and cohesiveness in
operations such as winding, unwinding, slitting, and conveying under tension.
At least two spunbond webs are provided in a layered fashion, preferably in a
continuous or semi-continuous process, for example, from a series of supply
rolls to form a composite web of substantial basis weight, up to 600 g/mZ. The
fabric of the invention is preferably produced from a polyester (PET,
polyethylene terephthalate) spunbond substrate. As such, the fabrics are
highly
durable, and can be dyed in standard textile dyeing and finishing processes.
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At least one side of the layered web structure is subjected to fine water
jets operated at high pressure. Notably, the force of the water jets causes
the
previously formed thermal point bonds within the substrate or precursor
spunbond webs to be substantially entirely broken such that the web filaments
become loose filaments, and are simultaneously entangled by the water jets
with
loosened filaments from other web layers. It is notable that the bond points
themselves are split, rather than the filaments breaking loose from the bond
points at the entry site. In this manner, substantially continuous filaments
are
maintained and free fiber ends are not created by the process. The creation of
substantially continuous filaments from the spunbonded webs is desirably
effected, rather than breakage of the thermal bonds in the spunbond webs which
would form relatively short, fiber-like segments of the filaments.
The entanglement of the continuous filaments on a three-dimensional
image transfer device results in a cohesive, durable fabric in which the
filaments
form a complex arrangement of packed loops and spirals that is substantially
free of filament breakage. Also, the structure is substantially free of any
knotting or wrapping of fibers at sharp angles, normally found in conventional
hydroentangled fabrics made from staple length fibers or pulp.
The prebonded or partially entangled webs can be treated on a apertured
forming surface or roll having a three-dimensional surface pattern in order to
rearrange the filaments and impart a pattern to at least one side of the
fabric..
Preferably, both sides of the layered structure are subjected to water jets.
The resulting fabrics of the present invention are very durable and strong
in comparison with conventional hydroentangled fabrics. If the fabrics are
made
from spunbond polyester substrate webs, for example, they can be subjected to
the rigors of a jet dyeing process. The fabrics can thereby advantageously
%place many standard woven textiles at a significantly lower cost. Depending
on the desired end use, very high basis weight fabrics can be produced having
a
number of layers and basis weights up to 600 g/mZ.
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In a further embodiment of the invention, the initial spunbond webs can
be produced in a highly efficient, high speed operation, as the raw polymer is
converted into a stable point bonded web in a continuous operation.
Advantageously, this process of the invention does not require low pressure
pre-
entanglement jets, thereby improving the efficiency of the process.
Due to the high durability and strength of the fabric, many finishing
processes are facilitated. The fabric can be subjected to multiple uses and is
launderable. Despite being durable, the fabrics of the present invention also
exhibit desirable aesthetic qualities and in this respect are comparable to
conventional and more expensive nonwoven fabrics. Also, layering of the stable
substrate webs allows use of smaller sized filaments, with the result that the
final
fabric has a higher strength and better uniformity than a fabric of the same
basis
weight comprised of larger filaments.
The above brief description sets forth rather broadly the more important
features of the present invention so that the detailed description that
follows may
be better understood, and so that the present contributions to the art may be
better appreciated. There are, of course, additional features of the
disclosure that
will be described hereinafter which will form the subject matter of the claims
appended hereto. In this respect, before explaining the several embodiments of
the disclosure in detail, it is to be understood that the disclosure is not
limited in
its application to the details of the construction and the arrangements set
forth in
the following description or illustrated in the drawings. The present
invention is
capable of other embodiments and of being practiced and carried out in various
ways, as will be appreciated by those skilled in the art. Also, it is to be
understood that the phraseology and terminology employed herein are for
description and not limitation.
Brief Description Of The DraH inLs
FIGURE 1 is a schematic view of one embodiment of the invention;
FIGURE 2 is a schematic view of another embodiment of the invention;
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FIGURE 3A is a schematic view of another embodiment of the
invention;
FIGURE 3B is a schematic view of another embodiment of the invention;
FIGURE 3C is a schematic view of another embodiment of the invention;
FIGURE 3D is a schematic view of another embodiment of the
invention;
FIGURE 4 is a schematic view of another embodiment of the invention;
FIGURE 5A is a schematic view of another embodiment of the
invention;
FIGURE 5B is a schematic view of another embodiment of the invention;
FIGURE 6 is a 30x photomicrograph of an embodiment of the fabric of
the invention;
FIGURE 7 is a 200x photomicrograph of an embodiment of the fabric of
the invention;
FIGURES 7A to 7C are views showing modeling of interloop entangling
in accordance with the present invention;
FIGURE 8 is a l Ox photomicrograph of a prior art hydroentangled staple
fiber web;
FIGURES 8A and 8B are views showing modeling free fiber end
wrapping and entangling;
FIGURE 9 is a schematic view of an apparatus for practicing a process
further embodying the present invention, wherein plural precursor webs are
employed for production of a nonwoven fabric;
FIGURES 10 is a diagrammatic view of a three-dimensional image
transfer device;
FIGURE 10A is a cross-sectional view taken along lines A-A of
FIGURE 10;
FIGURE l OB is a cross-sectional view taken along lines B-B of FIGURE
10;
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FIGURE l OC is a perspective view of the three-dimensional image
transfer device shown in FIGURE 10;
FIGURE 11 is a diagrammatic view of a three-dimensional image
transfer device;
FIGURE 1 lA is a cross-sectional view taken along lines A-A of
FIGURE 11;
Chart 1 shows Grab Tensile strength for various webs;
Chart 2 shows Tensile pounds /% Elongation at Peak Tensile;
Chart 3 shows Grab Tensile pounds for 6 inch x 4 inch samples for
various webs; and
Table 1 compares measured values between various nonwoven fabrics of
the invention and various prior art nonwoven fabrics.
Detailed Description
Turning now to the drawings, FIGURE 1 illustrates a first embodiment of
the process and apparatus of the invention. Continuous filaments 2 are melt-
extruded, drawn, and then deposited by beam 4 on moving porous support wire
6 winding on rollers 7 to form an unbonded filament web 8. After drawing,
filaments 2 have a denier of between about 0.5 to 3, with a most preferred
denier
of 1 to 2.5, and are preferably comprises of a melt-extruded thermoplastic
polymer, such as polyester, polyolefin (such as polypropylene), or polyamide.
As filaments 2 are continuously extruded, they are substantially endless.
Deposited, unbonded filament web 8 is relatively fragile, thin, and easily
disturbed. Web 8 may be comprised of more than one layer of filaments 2. The
dominant orientation of filaments 2 is in the machine-direction, with some
degree of overlap in the cross-direction. If desired, a variety of techniques
may
be employed to encourage further separation of individual filaments 2 and
greater randomness in the cross-direction. These techniques may include, but
are not limited to, impinging filaments 2 with air currents, electrostatic
charging,
or contact with solid objects. Also, as is well-known in the art, vacuum may
be
drawn through support wire 6 in the area of depositing filaments 2.
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Web 8 is continuously and substantially without interruption advanced to
pre-entangling station 10 for pre-entanglement with a plurality of individual
pre-
entangling jets 12 that direct water streams of a hydraulic pressure onto web
S.
Preferably, pre-entangling station 10 comprises from one to four sets of pre-
entangling jets 12, with one to three most preferred. Preferred pre-entangling
jets 12 operate at hydraulic pressures between 100 to 5,000 psi, and have
orifice
diameters ranging from 0.004 to 0.008 inches, with 0.005 to 0.006 inches most
preferred. Jets 12 further have a hole orifice density of from 10 to 50 holes
per
inch in the cross-direction, with at least 20 per inch most preferred. The
number
of individual jet streams per jet 12 will vary with the width of web 8; jet 12
will
extend substantially across the width of web 8, with individual jet streams at
a
density of 10 to 50 per inch. The pressures of individual pre-entangling jets
12
may vary as desired depending on fabric basis weight and desired pattern. For
pre-entangling a web 8 with a basis weight of no greater than 50 gm/m2, for
instance, a preferred pre-entangling station 10 will comprise three individual
sets
of jets 12 operating sequentially at pressures of 100, 300, and 800 psi. A
preferred pre-entangling station 10 for a web 8 of a basis weight greater than
50
gm/m2 will comprise three individual sets of water jets 12 operating
respectively
at pressures of 100, 500, and 1,200 psi.
During pre-entanglement, web 8 is supported on moving support 14,
which may comprise a forming drum, or as illustrated, a single or dual wire
mesh rotating about rollers 15. Because filaments 2 are substantially endless
and
of considerable denier, support 14 need not be of fine mesh as may be required
for shorter or finer fibers of the prior art. For high pre-entanglement
hydraulic
pressures associated with heavier basis weight fabrics, supporting web 8 on a
rotating forming drum is preferred. The purpose of pre-entanglement is to
create
sc:ne cohesiveness in web 8 so that web 8 can be transferred and will not be
destroyed by the energy of subsequent high pressure hydroentanglement. After
pre-entangling, web 8 is observed to have minimal entanglement and low
strength values.
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After pre-entangling, the continuously moving web 8 is next subjected to
high pressure hydroentangling. High pressure hydroentangling may be achieved
at a hydro-entanglement station that comprises a plurality of sets of w-ater
jets
16. High pressure jets 16 for entangling preferably are directed at the
"backside"
of web 8 opposite the "frontside" onto which pre-entangling jets were
directed.
Or, as shown in FIGURE 1, high pressure jets 16 may alternately be directed at
one and then the opposite side of web 8. High pressure water jets 16 operate
at
hydraulic pressures of between 1,000 to 6,000 psi. For webs of basis weight at
or below 50 gm/rnZ, one to four sequentially high pressure jets 16 are
preferred,
operating a pressures between 1,000 to 2,000 psi, with 1,600 psi most
preferred.
For webs of basis weight great er than 50/gm/m2, one to four sequential high
pressure jets 16 are preferred operating a pressures between 3,000 and 6,000
psi.
Preferred high pressure jets 16 have an orifice diameter of from 0.005 to
0.006
inches, and have a hole orifice density of from 10 to 50 holes per inch in the
cross-direction, with at least 20 per inch most preferred. The number of
individual jet streams will vary with the width of web 8; jets impinge web 8
across substantially its entire width with individual streams at a density of
10 to
50 holes per inch.
When high pressure hydroentanglement is carried out at hydrostatic
pressures greater than 1,600 psi, web 8 is preferably supported on rotating
forming drum 18. Drums 18 preferably have a patterned three-dimensional
surface 19 to control the X-Y spatial arrangement in the plane of filaments 2,
as
well as in the Z-direction (web thickness).
Both pre-entanglement jets 12 and entanglement jets 16 may be supplied
by a common remote water supply 20, as illustrated in FIGURE 1. Water
temperature may be ambient. Spacing between both pre-entanglement jets 12
and entanglement jets 16 and web 8 is preferably between I to 3 inches. It is
also noted that the distance between individual jet stations, and hence the
time
elapsed between impinging web 8 with jet streams, is not critical. In fact,
web 8
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may be stored after pre-entangling with pre-cntanglement jets 12 for later
entangicmrxrt, although Ihe prefe.rred pracess is continuoug_
A major lirttitation in prior art practices is tfic ability to operwto a
h)-droentangletnent Gne for a web of fibers at a b,igh rate of spccd such aS
the
iine speed of a modern spudboad line. The usc of high water prcsstaes and
hencc high energy levcls would be expecxcd to cause the fiber to be driven
excessively into screens of stnnderd mesh size, or to cause wmdue displacement
of the fibers. Yt has been found, in accordance with the present invention,
that
much higher energies can be used in tha cntanglernent station whita using
standard mesh size scrocas, allowing for an increase in line speeds
conrparable
to the normal line speed of the sprmbond line. Thus, then is no need for an
aocunuutator or other rncan$ to act as a'buffer" batwr.on filamont praduction
and
f=inal entaatgled web output or for suppoR screcas of finc rne.sh as may be
recluircd by proccsscs and apparatuscs of the prior art. As an exarnple of the
above, 3 denier polyproprlene filament webs aro subjected to an energy of 1.5
to
z.horsepowcr houts per pound (liP-hr/lb) in the high pt+essm entanglement
stations. Other exarnplcs are 0.4 to 0.75 HP-hr/lb for 1.7 denier
po[ypropylcnc
and 0.3 to 0.5 HP-hrflb for 2 denier polyester filaments. lf a final
pattetning
operation is cmplvyed, the emrgy levels arc approximately double those
described above.
FIGURE 2 shows anothcr embodimont of thc apparatus and proccss of
th.e invention. In this embodiment, pre-entaagling statidn 10 is comprised of
two individual sets of pre-entangling water jets 12, and web 8 is supportcd
ttu'ough pre-cntangling on porous forming drum 30. Use of forming dnun 30 is
prefcrred for webs of a basis weight over 50 gnatrrt', when hig}icr ptv-
cntangling
hydraulic pressures are used. As discussed, forming drum 30 preferably has a
thrcc-dimcnsional forrmng surface 32.
A preferred foriming drum and a method for using aro dcsciibcd in U.S.
Patents No. 5,244,711 and No. 5,098,764.
In ftse references, an apertured drum is pfovided with a three-dimensional
image
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tzansfer device having a sutface in the form of pyramids, with the dramago
agerttares being located at the base of the pyramids. Many other confgeuations
for the surfaoe of the drum sre also feasible. Although these references
disclose the hydroentanglement of staple fibers to producG knotted, aperttired
fabrics, it
has been found that these drUrn,s may likewise be used with the continuous pn:-
entar-gled filament webs of the present invenpon.
In the following examples, reference to a "20 x 20" image refers to a
rccttlicear fotmdtl$ pattecn in the fonrti of a pytamidal asray, laaving 20
lines per
inch by 20 lines per inch, configarccl in ac.cordattce with the pyramidal amy
iIIastrated in FIGURE.13 .of U.S. Patent No. 5,098,754' .=. a,
The imago ditl'dred in that mid-pyrairud draio holes are omitted.
Drain liaies are present at each cwner of the pyramids (i.e., fonr holes wound
each pyraniid). The pyramid height is 0.025 inches, and drain holes have a
diatneter of 0.02 inches. Drainage araa is 12.5% of the snrface area.
R,eference to 33 x 2$" forming surfar,e rcfers to a tlu-ee-limensional
image trensfer device conSgared in accordaace with the pyramidal ffiray
illustrated in FIGU1tE 13 of U.S. Patent No. 5,098,764, having 331ines per
inch
(MD) by 28 lines per inch (CD), with drain holes present at each camer of the
pyramid_
Reference to a"tricot" forming surface refers to a three-dimensional
image transfer device configured in accordance with the teaehinga of U.S.
Patent
No. 5,585,017.
FIGURE 3 shows additional embodimants of the pre-entanglernent
portion of the process and apparatus of the present invention. In FIGURE M.
Calendet 40 povides light thermal bonding to web 8 prior to pre-antanglement
at
pre-entaegling station 10. Preferred calender 40 comprises heated rouers 42
and
44, with surfacc 45 of roller 42 haviug a pattern for embossing on web S.
FIGURE 3B shows pre-entangtement station 10 entangling web 8 with web 8
supported by forming wire 6. Note that forming drum 30 is used to restrain
forming wirc 6. f'1GURE 3C,shows web 8 being supporLed 6etween fonning
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wire 6 and a second wire 46 rotating about rollers 48. Also, as shown in
FIGURE 3D, pre-entangling station 10 may be positioned directly in line with
filament attenuator 4 with web 8 supported by forming wire 6.
FIGURE 4 shows another embodiment of the apparatus and process of
the invention, further comprising pattern imparting station 50. Pattern
imparting
station 50 comprises rotating pattern drum 54, with three-dimensional surface
56, and pattern water jets 52. A plurality of jets 52 are provided, each with
a
plurality of individual jet streams, operating at pressures that may be varied
depending on the basis weight of the web and the detail of the pattern to be
embossed. Generally jets 52 operate at 2,000 to 3,000 psi for webs of a basis
weight less than 50 gm/mZ, and at 3,000 to 6,000 psi for heavier webs.
FIGURES 5A and 5B show additional embodiments of the apparatus and
process of the invention where a secondary web is introduced. The secondary
web may comprise carded staple fibers, melt-blown fibers, synthetic or organic
pulps, or the like. FIGURE 5A shows roller 60 dispensing secondary web 62
upstream of attenuator 4, so that filaments 2 will be deposited onto secondary
web 62. Secondary web 62 is thus entangled with filaments 2 through
downstream pre-entangling station 10 and downstream entangling jets 16.
FIGURE 5B shows secondary web 62 being dispensed from unroller 66
downstream of entangling jets 16, and upstream of patterning station 50.
Secondary web 62 and web 8 are entangled in this embodiment at patterning
station 50.
The preferred nonwoven fabric of the present invention comprises a web
of continuous, substantially endless polymer filaments of 0.5 to 3 denier,
with
1,2 to 2.5 denier most preferred, interengaged by continuous complex loops or
spirals, with the filaments being substantially free of any wrapping,
knotting,
b. eaking, or severe bending. As discussed infra the terms "knot" and
"knotting"
as used herein are in reference to a condition in which adjacent fibers or
filaments pass around each other more than 360 to form mechanical bonds in
the fabric. Knotting occurs to a substantial degree in conventional
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hydroentangled fabrics made from staple fibers, or those prepared with a scrim
or net and staple fibers.
The hydroentangled continuous webs of substantially endless tilaments
that comprise the fabric of the present invention, on the other hand, are
substantially free from such knotting. The mechanical bonding of the fabric of
the present invention is characterized by enmeshed coils, spirals, and loops
having a high frequency of contact points to provide high tensile strength,
while
the coils and loops are capable of release at higher load. This results in
high
cross-direction elongation values for the fabric of the invention that are
preferably in excess of 90%, and more preferably in excess of 100%. A
preferred machine direction elongation value is at least 75%. The combination
of high elongation and tensile strength is a novel and surprising result as
conventional hydroentangled fabrics because of fiber knotting have an inverse
proportional relationship between tensile strength and elongation: high
strength
fabrics tend to have lower elongation than fabrics of comparable weight with
lower tensile strength. The preferred fabric of the present invention, on the
other
hand, enjoys a proportional relationship between elongation and tensile
strength:
as fabric elongation increases, in either the CD (cross-direction) or MD
(machine-direction), tensile strength (in the same direction) likewise
increases.
The nonwoven fabric of the present invention is preferably comprised of
a polyamide, polyester, or polyolefin such as polypropylene. In addition, the
fabric of the invention may comprise secondary component webs including, but
not limited to, webs comprising staple polymer fibers, wood or synthetic pulp
and melt-blown fibers. The secondary web components may comprise between
5% and 95% by weight of the fabric of the invention. Also, the fabric of the
invention may comprise a surface treatment such as an antistat, anti-
microbial,
binder, or flame retardant. The fabric of the invention preferably has a basis
weight of between about 20 and 450 gm/mz.
FIGURE 6 is a photomicrograph of an embodiment of the fabric of the
invention at 30 x magnification. This fabric sample is comprised of 1.7 denier
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polypropylene continuous fibers with a fabric basis weight of 68 gm/m?. As
evident in the photomicrograph, the fabric of the invention has filament
mechanical bonding characterized by winding interengaged spiral coils and
loops, and is substantially free of filament knotting or breaking. FIGURE 7 is
a
photomicrograph of the same sample at 200 x magnification. The three-
dimensional characteristics of the interengaged loops and spirals is more
clearly
shown by the increased magnification of FIGURE 7. FIGURES 7A, 7B, and 7C
are views of modeling of filaments showing interloop entangling,
representative
of the type of filament entangling of fabrics formed in accordance with the
present invention.
FIGURES 6 and 7 are contrasted with FIGURE 8, which is a
photomicrograph of a hydroentangled web of the prior art comprised of staple
PET/Rayon fibers. As can be seen in FIGURE 8, the hydroentangled web of the
prior art shows numerous free fiber ends, as well as a high occurrence of
fibers
wrapped about one another and otherwise knotted. FIGURES 8A and 8B are
views of modeling of wrapping, entangling, and knotting of free fiber ends, as
would be characteristic of prior art fabrics formed from staple fibers and the
like.
The appearance and properties of the fabric are believed to be unique as
the continuous filaments are substantially immobile in the fabric and do not
substantially individually reduce in length along the filament axis or in the
general cross- or machine-directional width of the fibrous web during the
hydroentanglement process. In contrast, during the hydroentanglement of staple
fibers, the loose ends of the fibers allow them to freely alter their spatial
arrangement in the web, in the process of wrapping around themselves or
neighboring fibers, forming knots from the interlaced fibers. This wrapping
and
knotting can lead to observable strEaks and thin spots. The complex packing of
the loops and coils of the fabric of the present invention, on the other hand,
provides better randomization of the filaments, resulting in a more consistent
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fabric and better aesthetics. The fabric of the invention this has a
distinctive and
commercially advantageous uniform fabric appearance.
The nonwoven fabric of the present invention may further comprise a
secondary chemical treatment to modify the surface of the final fabric. Such
treatments may comprise spray, dip, or roll applications of wetting agents,
surfactants, fluorocarbons, antistats, antimicrobials, flame retardants, or
binders.
Further, the fabric of the present invention may comprise a secondary web
entangled with the web of the invention, such a secondary web may comprise
prefabrics, pulps, staple fibers or the like, and may comprise from 5 to 95%
on a
weight basis of the composite fabric.
After the final entanglement steps, the fabric is dried using methods well
known to those skilled in the art, including passage over a heated dryer. The
fabric may then be wound into a roll. In order to achieve the superior
physical
properties of the product of the present invention, no additional bonding,
such as
thermal or chemical bonding, is required.
The fabrics of the present invention have many applications. They may,
for example, be used in the same applications as conventional fabrics. In
particular, the nonwoven fabric of the present invention may find particular
utility in applications including absorbent articles, upholstery, and durable,
industrial, medical, protective, agricultural, or recreational apparel or
fabrics.
A first sample fabric of the invention was prepared using the process and
apparatus generally described infra and shown in FIGURE 1. The sample was
prepared using 2.2 denier polypropylene filament, with a web basis weight of
32
gm/mZ. The sample was prepared using three pre-entanglement jets 12 of
FIGURE 1 operating sequentially at 100, 300, and 800 psi; and with three
entanglement jets 16 operating sequentially at 1,200, 1,600, and 1,600 psi. To
demonstrate the effect of each stage of entanglement, grab tensile strength
was
measured after initial filament deposit, pre-entanglement, and entanglement,
with the results shown in Chart 1. The profound effect of the high pressure
entanglement jets is demonstrated in the results.
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A second sample fabric of the invention was likewise prepared with 2.2
denier polypropylene filament of a basis weight of 132 gm/m2. The fabric was
prepared using the apparatus and process as described infra and shown in
FIGURE 1, with the pre-entanglement jets operating sequentially at 25, 500,
and
1,200 psi. Two entanglement jets were used operating at 4,000 psi. The results
of grab tensile and elongation testing of these samples are presented in Chart
2.
It is noted that the sample prepared using two entanglement jets showed better
properties.
A third sample fabric of the invention with a 68 gm/m2 basis weight was
made using the apparatus as generally shown in FIGURE 1 using polypropylene.
For comparison, a"control" fabric of the same basis weight and denier was
prepared using the apparatus as shown in FIGURE 1, but with short staple
fibers
replacing the continuous filaments of the present invention. Grab tensile
strengths of the two fabrics were tested, with results shown in Chart 3. The
superiority of the fabric of the invention over the more traditional
hydroentangled staple fiber fabric is clearly shown.
In order to further define the fabric of the invention and its various
advantages, a first series of fabrics of the invention were prepared using the
process and apparatus as described herein. It is noted that the fabrics of the
present invention may be referred to as "SpinlaceT"'", which is a trademark of
the
Polymer Group, Inc. A second series of fabrics was prepared for comparison,
consisting of hydroentangled carded staple fibers entangled by a traditional
hydroentanglement process. The fabrics of the first and second series were
both
of basis weights between about 34 and 100 gm/m2, and both were made using
polypropylene fibers and filaments of similar denier. The fabrics of the first
and
second series were then tested according to standard methods as known by those
skilled in the art for basis weight, d nsity, abrasion resistance (Taber-
abrasion
resistance is measured by pressing the fabric down upon a rotating abrasion
disc
at a standard load), grab tensile, strip tensile, and trapezoid tear. The test
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methods used and characteristics tested for are descried generally in U.S.
Patent
No. 3,485,706 to Evans, herein incorporated by reference.
Three other qualities were also tested, including entanglement
completeness (a measure of the proportion of the fibers that carry the stress
when tensile forces are applied, see below), entanglement frequency (a measure
of the surface stability, entanglement frequency per inch of fiber, see
below),
and fiber interlock (a measure of how the fibers resist moving when subjected
to
tensile forces, see below). Results of testing are presented in Table 1. Note
that
"Apex" is a trademark of the Polymer Group, Inc., and as used in the Table
refers to a pattern drum having a three-dimensional surface (i.e., a three-
dimensional image transfer device). Also, the "flatbed and roll"
process/pattern
is most preferred.
Fiber Interlock Test: The fiber interlock value is the maximum force in
grams per unit fabric weight needed to pull apart a given sample between two
hooks.
Samples are cut '/z inch by 1 inch (machine-direction or cross-direction),
weighed, and marked with two points one-half inch apart symmetrically along
the midline of the fabric so that each point is 1/4 inch from the sides near
an end
of the fabric.
The eye end of a hook (Carlisle six fishhook with the barb ground off, or
a hook of similar wire diameter and size) is mounted on the upper jaw of an
Instron tester so that the hook hangs vertically from the jaw. This hook is
inserted through one marked point on the fabric sample. The second hook is
inserted through the other marked point on the sample, and the eye end of the
hook is clamped in the lower jaw of the Instron. The two hooks are now
opposed but in line, and hold the samples at one-half inch interhook
distances.
The Instron tester is set to elongate the sample at one-half inch per
minute (100% elongation per minute) and the force in grams to pull the sample
apart is recorded The maximum load in grams divided by the fabric weight in
grams per square meters is the single fiber interlock value.
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The fabric of the invention preferably has a fiber interlock value of at
least 15.
Entanglement Frequenc /y Completeness Tests: In these tests, nonwoven
fabrics are characterized according to the frequency and completeness of the
fiber entanglement in the fabric, as determined from strip tensile breaking
data
using an Instron tester.
Entanglement frequency is a measure of the frequency of occurrence of
entanglement sites along individual lengths of fiber in the nonwoven fabric.
The
higher the value of entanglement frequency, the greater is the surface
stability of
the fabric, i.e., the resistance of the fabric to the development of piling
and
fuzzing upon repeated laundering.
Entanglement completeness is a measure of the proportion of fibers that
break (rather than slip out) when a long wide strip is tested. It is related
to the
development of fabric strength.
Entanglement frequency and completeness are calculated from strip
tensile breaking data, using strips of the following sizes:
Strip Width (in.) Instron Gage Length (in.) Elongation Rate (in./min.)
0.8 ("wo") 0 0.5
0.3 (1.5 5
1.9 ("wZ") 1.5 5
In cutting the strips from fabrics having a repeating pattern or ridges or
lines or
high and low basis weight, integral numbers of repeating units are included in
the strip width, always cutting through the low basis weight proportion and
attempting in each case to approximate the desired width closely. Specimens
are
tested using an Instron tester with standard rubber coated, flat jaw faces
with the
gage lengths and elongation rates ' isted above. Average tensile breaking
forces
from each width are correspondingly reported at To, TI, and T2. It is observed
that:
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T2 Ti To
W2 Wi wo
It is postulated that the above inequalities occur because:
(1) there is a border zone of width D at the cut edges of the long
gauge length specimens, which zone is ineffective in carrying stress; and
(2) with zero gauge length, fibers are clamped jaw-to jaw and ideally
all fibers carry stress up to the breaking point, while with long gauge
lengths,
some poorly-entangled fibers slip out without breaking. A measure of the
proportion of stress-carrying fibers is called C.
Provided that D is less than '/2 w,, then:
Ti - T2 - C To
w1- 2D wi- 2D Wo
and D and C are:
D wITz - wzT,
=
2(Tz - T)
C= T2-Ti x wa
w2 - wi To
In certain cases D may be nearly zero and even a small experimental
error can result in the measured D being negative. For patterned fabrics,
strips
are cut in two directions: A in the direction of pattern ridges or lines of
highest
basis weight (i.e., weight per unit area), and B in the direction at 90 to
the
direction specified in A. In unpatterned fabrics any two directions at 90
will
suffice. C and D.are determined separately for each direction and the
arithmetic
means of the values for both directions are determined separately for each
direction and the arithmetic means of the values for both directions C and D
are calculated. C is called the entanglement completeness.
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When C is greater than 0.5, D is a measure of the average distance
required for fibers in the fabric to become completely entangled so that they
cannot be separated without breaking. When C is less than 0.5, it has been
found that D may be influenced by factors other than entanglement.
Accordingly, when C is less than 0.5, calculation of D as described above may
not be meaningful.
From testing various samples, it is observed that the surface stability of a
fabric increases with increasing product of D-' and the square root of fiber
denier d. Since 1.5 denier fibers are frequently used, all deniers are
normalized
with respect to 1.5 and entanglement frequency f per inch is defined as:
f =(D-'-~W 1.5)
If the fabric contains fibers of more than one denier, the effective denier d
is
taken as the weighted average of the deniers.
If the measured D turns out to be zero or negative, it is proper to
assume that the actual D is less than 0.01 inch andf is therefore greater than
(100N[d- 1.5) per inch.
The fabric of the invention preferably has a fiber entanglement frequency
off of at least 10.0, and a fiber interlock completeness of at least 1.00, and
a
fiber interlock value of at least 15.
As shown in Table 1, for the SpinlaceT"" fabrics of the invention the
entanglement completeness values trend higher than for the hydroentangled
staple fiber webs (HET). It is believed that these superior properties are a
result
of the complexity of the interengaged loop and spiral matrix formed by the
continuous filaments. Grab tensile values for SpinlaceT"" are about two times
that of the hydroentangled staple fiber webs. Trap tear values for all of the
SpinlaceT"' fabrics exceed those of the traditional fabrics. It is believed
that this
is a result of the randomness of the fiber matrix of the SpinlaceT"~ fabrics
that
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confounds the fault lanes that more quickly lead to failures in this test for
other
fabrics. This is also further evidenced that the complex entangling of the
continuous filaments of the SpinlaceT"' fabrics of the present invention
comprises substantially superior and distinct mechanical bonding and
disengagement from that of the traditional entangling of cut staple fibers.
Strip tensile values are highest for the SpinlaceT~~ fabrics, regardless of
sample basis weight. Note the nov,-l high elongation values that are in
combination with the high tensile of the SpinlaceT"". This is in agreement
with
the observations of the fabrics during testing. During testing, SpinlaceT""
fabric
test samples were observed to initially resist the applied tensile stress, and
then
to gradually release the tension by disentanglement of the filament from the
complex matrix structure. Tests of traditional fabrics, on the other hand,
were
observed to experience fiber and bond breakage, leading to shorter elongation
values. As discussed infra, the concomitant high strength and high elongation
of
the fabric of the present invention represents an unexpected and novel
property.
A further aspect of the present invention contemplates a process of
noaking a laminated nonwoven fabric, wherein the fabric comprises plural
laminations each comprising a web of substantially continuous polymeric
thermoplastic filaments. As is characteristic of the fabrics discussed
hereinabove, each of the web of the laminated nonwoven fabric is substantially
free of filament ends intermediate end portions of the web. This aspect of the
invention contemplates that adjacent ones of the webs of the laminated fabric
can exhibit different properties. In particular, it is contemplated that the
polymeric filaments of adjacent laminations of the fabric exhibit differing
bonding temperatures, with hydroentanglement of the laminations acting to
integrate and unify the laminations without resort to heat bonding or the
like.
The various lamination can there;fore be selected for other desirable
properties,
such as softness, strength, etc., without specific concern regarding the
compatibility of the various laminations for integration by heat bonding or
similar processes.
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Thus, this aspect of the invention contemplates manufacture of nonwoven
fabric laminate with improved softness of hand produced by treating continuous
filament webs with high pressure waterjets. A relatively strong nonwoven
fabric with improved softness and hand is produced through hydroentanglement
of continuous filament layers. One layer of the fabric may comprise
polyethylene filaments, while the second layer may comprise polyester,
polypropylene, or a like filament that provides the resultant fabric with the
desired strength. This aspect of the invention contemplates an improved
nonwoven fabric comprising layers of polyethylene filament, and
polypropylene, polyester, or a similar relatively stronger filament web. The
webs are bonded together using high pressure water jets in accordance with
processes disclosed hereinabove, including an arrangement such as disclosed in
FIGURES 5A and 5B, wherein a secondary web is introduced in conjunction
with formation of a primary web. A fabric embodying this aspect of the present
invention is strong in comparison to a fabric having a similar weight
comprising
a 100% polyethylene web. The fabric is soft compared to similar basis weight
fabrics made from 100% polypropylene, polyesters, or like polymers. The
material embodying this aspect in the invention comprises plural laminations,
and may comprise two laminations wherein a polyethylene filament layer
presents a surface having hand similar to a 100% polyethylene web.
The present process contemplates that plural precursor webs are
provided, wherein each of the precursor webs comprises substantially
continuous polymeric thermoplastic filaments. If the present process is
practiced in-line with an associated spunbonding apparatus, one or all of the
plural precursor webs may be provided in the form of unbonded filaments. In
contrast, at least one of the precursor webs may comprise spunbonded fabric
including lightly thermally bonded filaments. A precursor web provided in this
form is broken down into its constituent filaments under the influence of the
high pressure hydroentangling water jets, which break the thermal bonds formed
in the precursor web. The use of relatively lightly bonded precursor spunbond
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webs is presently preferred, since the action of the high pressure water jets
on
the lightly bonded web tends to break the web into its constituent filaments,
without breaking of the filaments into relatively shorter length fiber-like
elements.
Fabrics formed in accordance with this aspect of the present invention
may be patterned or non-patterned. The percentage of the nonwoven fabric that
is polyethylene is preferably about 40% to 90% by weight of the fabric, with
75% polyethylene being presently preferred. Basis weight of the nonwoven
fabric can range from about 15 to 80 g/mz, with the preferred basis weight
being
about 30 g/mz. The filament of the polyethylene portion of the fabric can be
varied from about 2 to 5, with 3.5 denier being presently preferred. The
remainder of the fabric weight may comprise one or more laminations formed
from filaments other than polyethylene, such as polyester, polypropylene, or
other thermoplastic polymer filaments. The denier of the filaments of these
one
or more laminations of the fabric is preferably about 0.5 to 3, with a denier
of
1.5 being presently preferred. The presently preferred polymer for the
strengthening laminations is polypropylene.
In accordance with the processes disclosed hereinabove, precursor webs
are treated on one or both sides with high pressure water jets. The degree of
hydroentangling required is that corresponding to a level which is sufficient
to
laminate the plural webs together. Greater levels of hydroentangling energy
are
desirable to stabilize the surfaces of the laminations to prevent fuzziness in
the
resultant fabric.
Example 1
A hydroentangling apparatus configured in accordance with the present
disclosure included entangling manifolds having orifice jets each 0.0059
inches
in diameter, spaced at 33.33 per inch along the length of the manifold. A 20 x
20 three-dimensional image transfer device was employed. A 17 g/m2, 1.7
denier polypropylene filament web, and a nominal 27 g/mz, nominally 3.5 denier
polyethylene web were combined at a processing speed of 40 feet per minute.
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Entangling treatments consisted of three rows of orifices directed against the
two
precursor webs on one side of the webs. The entangling pressure of the three
entangling manifolds of the apparatus were successively provided at 600,
2,000,
and 3,000 psi for the orifice jets. Total energy input was 1.8 horsepower-
hour/pound.
It is contemplated that the process of the present invention for
manufacture of laminated nonwoven fabric can be practiced in different ways.
The fabric can be produced by providing precursor webs which are unwound
from rolls, and directed into an entangling system. Alternatively, one or more
of
the precursor webs may be manufactured in a continuous process from an
associated spunbonding apparatus. It is presently preferred that lightly
thermally
point bonded precursor rolls, having the desired basis weight, be provided,
with
one layer comprising polyethylene. The precursor webs are unwound and
subjected to hydroentanglement treatment. Thermal point bonds of the
strengthening filament web should be sufficiently weak so as to break apart
into
filaments under the forces of the hydroentangling jets, rather than resulting
in
breakage of the substantially continuous filaments themselves. In a continuous
...
process, a minimum of two extruding beams are required, one for the
polyethylene filament web, and one for the associated strengthening polymeric
filament precursor web. A single polymer extrusion system can be
advantageously employed by using an un-winder, and introducing the second
precursor web via unwinding.
As will be appreciated, more than two plural laminations can be provided
for the present nonwoven fabric. By way of example, two polyethylene
precursor webs, and one polypropylene precursor web, can be provided to
produce a polyethylene/polypropylene/polyethylene laminated nonwoven fabric
thdt has a soft feel on both of the exterior polyethylene surfaces. This type
of
product, exhibiting polyethylene on both of its exterior surfaces, can be
advantageously employed in products requiring assembly bonding, such as
disposable diapers. Finished products in accordance with the present invention
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are soft and pliable, in comparison to point bonded and latex bonded fabrics
having the same basis weights.
A further aspect of the present invention discloses a process of making a
highly durable, dyeable nonwoven fabric made of hydroentangled continuous
filaments. The process employs spunbonded webs that are fully stabilized by
thermal point bonding. High pressure water jets, as generally described
hereinabove, are utilized to separate filaments from the thermal bond points,
freeing the filaments from entangling by the water jets. The process
advantageously employs multiple spunbond precursor webs or layers to form a
composite web of substantial basis weight, up to 600 g/m2. The resultant
fabric
is preferably produced form polyester (PET, polyethylene terephthalate)
spunbond substrate. As a result, the fabrics are highly durable, and can be
dyed
in standard textile dyeing and finishing processes.
Thermally bonded spunbond layers, preferable comprising polyester, are
employed as feedstock for a high-pressure hydroentangling process. The
resultant fabric is a high basis weight nonwoven web, from 50 to 600 g/m2,
with
the desirably uniform appearance and durability of a traditional woven or
knitted
textile of similar basis weight. The advantages of this process, and the
resultant
fabric, over other purportedly durable nonwoven webs include: the low cost of
spunbond webs versus other nonwoven webs; the speed of the manufacturing
process based on the ability to use highly stabilized (thermally point bonded)
continuous filaments webs as feedstock; and the durability and dyeability of
the
fmished nonwoven fabric, with the fabric exhibiting adequate strength at lower
basis weights compared to standard textiles.
Advantages of the present process over traditional knitting and weaving
processes include the low cost of the nonwoven feedstock, and the high speed
of
the spunbond and entangling processes, versus the speed of knitting or weaving
looms. The basis weight of the finll fabric product is controlled by the
weight
of the feedstock layer and the number of layers used.
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FIGURE 9 shows a series of in-line unwind rolls 21 for providing a
plurality of superimposed layers 41 of spunbond fabric. The term "spunbond" is
used herein refers to commercially available fabrics comprising thermally
point
bonded thermoplastic polymer continuous or endless filaments. As is well-
known in the art, these fabrics are made by melting and continuously melt-
extruding a thermoplastic polymer through a large number of small openings.
The filaments are cooled and attenuated or elongated either mechanically or
pneumatically, such as in a slot attenuator having a high flow of air, and are
deposited on a porous moving conveyor, typically with the aid of suction
beneath the conveyor in the area of deposit. Preferably, the filaments are
uncrimped, since this may adversely affect subsequent processing. The web is
then passed between heated calender rolls, one being engraved, to cause
thermal
point bonding of a portion of the intersecting filaments. The web, which is
now
cohesive and stable, can be wound up into rolls and/or slit. Slitting may be
required, for example, if the width of the spunbonding apparatus is greater
than
the operational width of the hydroentanglement apparatus.
The basis weights of the individual spunbond webs 41 is not critical and
is primarily.selected to provide a resultant layered basis weight of the
desired
value, depending on the end use of the finished fabric. For example, for final
basis weights of 50 to 100 g/m'-, the feedstock prebonded webs 41 can be in
the
order of 15 to 25 g/mZ. For finished products having a basis weight in excess
of
100 g/mz, heavier basis weight feedstock fabrics 4 may be used. For instance,
webs of a basis weight of 50 to 75 g/m2 may be used to produce final fabrics
having a basis weight of 250 to 600 g/mz.
The thermoplastic polymers employed to make the prebonded webs 41
may comprise polyolefins, polyamide, and polyesters, with polyesters most
preferred. The preferred range of filament deniers is from about 0.2 to 3.0,
with
about 1.5 being most preferred.
The total point bonds of the precursor fabric 4 are important to allow
handling and subsequent treatment. Thermal point bonds may be provided by a
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catender having spaced raised areas to provide a plttrality of spaeed bond,
points
in the web with uabonded filaments tlterebatweern. The total thermal bond
points can occupy from 5% to 45% of fabric area, with 1Q Y4 to 30'r6 being
most
preferred. If the bonding is too low, tho webwill ba unstable, and if the
bonding
is too high, tlu f'abric becomes too stiff.
At least two laym of the prebonded spunbond fabric 41 arc employcd
and unwound fiom rolls 21 as recluired. FIGURE 1 illustratcs a total of six
fabrics 4 being dispensed from six rolls'2I for entat-g[ement Also, additional
layers of prebonded layers of nonwoven fabrics or other typcs may be included
such as meltblown webs and nonwoven fabrics made from staple fibers_
11x individual spunbond webs 44 are layered or superitinposed on one
another to form unbvnded laminate 61. Unbonded laminate 61 is passed over
roalcrs 81 and 101 to at least one hydraentanglcmeat statlons, generally
indicated
at 12 1. With the axcepdoms noted herein, this s-tation can be that shows and
described in U.S.1'atesds No. 5,674,587 and No. 3,485,705...,
Unbonded layer lamiztate web 61 may be suppotted an a flat
porous tnoving surface but is prefcrably supported on a rotating porous drum
141 as shown.
As shown, drum 141 rotates in a counterclockwise direction Drum 141
rnay be in the farrn of a relatively rigid woven wire screen or rnay be
constructeci
frdnr a solid cylindrieal member which has been drilled to provide drainage
openings. Drunt 141 carries unbonded lanvnate 61 wtder at least ono and
prrefaably a plurality of water jet stations 16L 181, and 201, in which fine
columnar jets of wator are impinged on the outwardly facing layer_ The encrgy
of these jets causes the thecmal point bonds of the individual layas 41 to
become substantially completely disrupted, thtraby frecing the individual
c,pqtinuous filaments. The jast further cause ttie freed filamcnts S'om each
of the
layers to etttattgle with othcr &ced filamcnts from others of the layers 41 to
providc a final aohesive, unifonn web rosistanoe to delamination. Unlike
conveotionsl webs of loose fibers, the prebonded layers of filaments 41 are
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relatively dense and compact and have less void volume, providing for more
efficient transfer of hydraulic energy.
As shown schematically, hydroentanglement apparatus 121 includes
features well-known in the art, including a water supply line 221 for
supplying
water at high pressure to entangling jets 161, 181, and 201. Also, the
interior of
drum 141 may be provided with a suction zone beneath the drum surface to
remove and recycle excess water (not illustrated).
The energy generated by each manifold or jet 161, 181, and 201 is
proportional to the number of orifices per unit linear length, the pressure of
the
liquid in the manifold, and the volumetric flow; and is inversely proportional
to
the speed of passage and the weight of the fabric being produced. The distance
between jets 161, 181, and 201 and the top surface of the fabric 41 is on the
order of 0.5 to 3 inches, preferably I to 3 inches, the upper limit being
dictated
by the tendency of the jet stream to diverge and lose energy.
Since standard entanglement equipment is employed, many of the above
parameters are known or fixed, and in the case of the present invention, the
major parameters are jet pressures and jet orifice diameters for line speeds
on the
order of 125 meters per minute or greater.
The operating pressure of initial jet manifold 161 impinging the fabric
layers 41 is greater than 1,500 psi and preferably greater than 2,000 psi,
which is
higher than prior art methods have allowed for. It has been surprisingly found
that initial pressures of up to about 4,500 psi may be employed without any
adverse effects. Such high pressures are believed to be possible due to the
stable
nature of thermally bond webs 41. It is also noted that if desired, a porous
screen may be employed over the outwardly facing layer of the fabric to better
hold the fabric against the drum, but this is not required.
If the desired final basis weight of the ultimate entangled fabric is on the
order of 50 to 100 g/m2, jet 16, 18, and 20 orifice diameter is preferably on
the
order of 0.005 to 0.006 inches. For heavier fabrics, orifice diameters are
preferably greater. For example, for fabrics having a basis weight of 100 to
600
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g/m2, preferred orifice diameter is 0.008 to 0.009 inches are employed to
provide
a higher level of energy.
The initial high hydraulic pressure surprisingly does not cause any
substantial breakage of the individual filaments, which would
disadvantageously
tend to cause loss of strength in the final composite. The high pressure,
however, does cause substantially complete disruption of the thermal bond
points, such that the fabrics are temporarily converted to webs of loose
continuous filaments, while at the same time the filaments within each layer
41
and between the layers 41 are being entangled. Stated conversely, the thermal
bond points hold the filaments in position to prevent excessive displacement
during initial entanglement.
It is known that fabrics of the same basis weight having a small denier
have a greater tensile strength than fabrics with a large denier. Thus, the
present
process can employ multiple layers of small denier prebond fabrics to produce
higher basis weight entangled fabrics with exceptional strength.
It will be appreciated that the thermally point bonded, continuous
filament fabrics, can vary in basis weight, filament denier, and degree of
thermal
point bonding. Various types of these fabrics can be employed as the initial
feedstock 41 and may be used in a variety of combinations to provide special
effects for end use applications. For example, a heavier fabric can be
combined
with a lighter fabric wherein the heavier fabric serves as a backing and the
lighter fabric serves as a decorative or outwardly facing surface.
Although not essential, the layered and entangled fabric of the present
invention is preferably subjected to'.Zydroentanglement on both sides. If the
fabric is subjected to entanglement on only one side, the side facing the drum
or
forming surface will generally have a lesser degree of entanglement and thus
have lower abrasion resistance, although this is sometimes not an important
factor.
As shown in FIGURE 9, after exiting entanglement station 121, the
resultant entangled and cohesive fabric web 241 may be fed around a lead roll
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261 to treat irs reverse side at a second hydroaotangling station 281
comprising a
porous drum 30 l, which in the embodiment shown, rotates in a clockwise
direction. The station 281 include9 at least one and preferably a plurality of
wat:rx jet ntianifolds 321, 341, 361 and 381, spaced sequentially araund a
portion
of tila circumference of the roll. This step inamm tla; dograe ofentanglement
but also urges exposed loops of ftlameats back through tho notmal plane of the
web 241. 'Fhe jets 321-381 prGFerably operate at a higher prc:5ure than the
jets
of ihe 6rst series, pre6erably in camess o# 3,L100 psi and most pmfenbly in
excess
of 4,500 psi. As disoussed genexalty above, orifice size and opaating
pressures
lo of'jets at both entanglement station,9 121 and 281 depend on substrato
ttt6z=ic
basis weigttts, desired final fabclc basis weiglii, wd line speed.
The second forming drum 301 may be;of the sanla general type as the
first drum, or it may be different. In ordcr to Wly a variety of stufxce
finishes,
topography and appeartntces, it is possible to employ a dtutn or a roll which
has
15 a solid uneven surface, such as engraved or debossed areas. Planar and roll
fabric fotming devices'of this nat+ue are known in tho art and tnay be
employed.
for exaasple, to provide a fabric with apertures to raseamble vacious types of
woven fabrics, or a variety of surFace textures in a three-dimensional
pattern.
fj The relevant methods and oquipment requirettiealts $re showtt and desan'bod
in
20 U.S. Patent Nos. 5,244,711, No. 5,098,764, No. 5,674,587 and No- 5,674,591.
After the hydroentanglelnent tfeatment is cozRtlctad, the web is
transferred to a porous moving conveyor 401 and passed over suction boxes 421
to debater the web.
25 The web may then be passed tlmsugh an opt3onai treatrm,>tt stadoa 441
for the purpose of applying topical treatxt'tents; usually in liquid form to
the web.
Various agents are latown and can be applied, including flame retarding
agents,
agents to improve dycablifity, agents to improve sofhmt,, and ageats to alter
svrface activiry, such as rcpellants and surfactants. While curable binders
can be
30 applied, these are not required, and in many applications, the fabric is
pteferably
CA 02434432 2007-11-30
WO 021055778 k'Ct7rJS41J01277
free of binders- The web is then psssed through a dryer 461 and wound up on a
rfl]l 481.
A significnnt advantage ofthe prt:sent invention is the ability to produce
extremely durable nonwoven fabrics at alhigh basis weight rangc, in the ordar
of
50 to 600 ghn~.
The fabrics of the present invention can be converted into a wide variety
of end use products, such as upholstery, apparel, pads, covers, and the like.
In a preferrod step of the procen of dtt: invenNon wherein polyester
substrate webs 4 have be= used, the result=t r.ahertmt web 241 of the
invention
may also be jet dyed (not illtlstrated) tning modern jet dying tecbniqttes,
which
involve high liquid flow rates to obtain good uniforniity and reduced dwell
time.
The following tab]e illuserates tiae physici,l properties of three diffierent
polyester
:~ w... _fabrics of the prescnt invention before and after being subjected to
jet.dyeingA,,, ;.~..: ,.. r
The "oetagon/squart;" pattern is configured in accor+dance with FIOURES 10 to
10C, which illustratc a three-dimensional image treasfer device. The
"hetringbone" pattern is confgured in accordance with U.S. Patent No.
5,736,Z 19 to Suchr, anid as specifically
configured in accordance with FIGURES i 1 and 11,A..
F,ffoct of kt Dyeing On Plyaiod Propertiea
~wk Grab Temile, kg Grab Elne~atiqp, i6
Psttern
. $liA'- MD CD MD CD
1nitiAl 188 47 33 72.1 110
Herri"gbO e PogtJct-Dyc 234 53 34 67 12S
Process
Initial 140 33 21 61,7 125
Pott ]et-IYya 180 33 25 63 133
Proccss
lnitial 184 46 34 74.4 117
aetagoeJsquare Post Jet-Dyc 229 53 34 70.5 123
Process
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From these examples, it will be noted that the basis weight of the fabric
increased, which is presumably due to uptake of the dye and to some degree of
fabric shrinkage. It is also noteworthy that the physical properties,
especially the
tensile strength values, show improvement.
Unlike hydroentangled fabrics of the prior art made from fibers, the
fabrics of the present invention exhibit a unique physical structure and
mechanical bonding mechanism. Microscopic examination of the fabric reveals
that the thermal point bonds which existed in the original spunbond feedstock
are substantially absent, and therefore, thermal bonds do not play a role in
the
strength of the fabric. Moreover, and somewhat surprisingly, the process of
the
invention does not cause significant breakage of the filaments themselves,
such
that they remain continuous. In addition, since the continuous filaments don't
have loose ends which allows substantial mobility and substantial knotting and
wrapping, the filaments through the process of the invention become arrange
din
a unique fashion. The resulting structure is in the form of a complex matrix
of
filament loops which are packed and are characterized by an absence of infra-
and inter-filament knotting and wrapping. Since the matrix is. continuous and
interconnected throughout the fabric, the fabric is extremely durable.
From the foregoing, it will be observed that numerous modifications and
variations can be effected without departing from the true spirit and scope of
the
novel concept of the present invention. It is to be understood that no
limitation
with respect to the specific embodiment illustrated herein is intended or
should
be inferred. The disclosure is intended to cover, by the appended claims, all
such modifications as fall within the scope of the claims.
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