Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
For years, the nonwoven industry has attempted to produce a carded
nonwoven fabric that has good cross direction strength. Generally, the
fibers in carded webs are allgned in a direction substantially parallel to
the direction of the web within the carding machine normally used to make
nonwoven fabrics. Consequently, the machine direction strength of a carded
web generally is a high multiple of the cross direction strength. A further
complication is that the conventional processing oE bonded nonwoven fabrics
consists of a set of stages--conveying, saturating, drying, winding, etc.-
all of which impose a further drafting and parallelizing effect on the
fibrous web. In this "normal" multi-stage bonding operatlon, tensile
strength ratios will be found which are 10 to 20 to 1, machine direction to
cross direction strengths.
Attempts to bring the so-called MD/CD ratio closer to 1 have
included the use of a cross-laying device, whereby a full-width web of
oriented fibers is mechanically pleated back and forth across a conveyor belt
to build up a composite batt in which the average angular displacement of the
fibers is alternated. Such devices are slow, cumbersome and are suitable
, only for batts of substantial thickness where fold marks and overlap ridges
are not objectionable.
Another expedient used in the prior art to achieve better tensile
, strength ratios is to disperse the fibers in more or less random orientation
into an air stream, from which they are collected on a conveyer screen with
the aid of suction. Such devices, however, are expensive, and while
satisfactory at speeds of around 10 yards per minute, they produce webs of
poorer quality at speeds of over 15 yards per minute, due to clumping and
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poor dispersion of Eibers.
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It is with improvements in the art of producing fibrous webs and
nonwoven fabrics of more nearly equalized machine (longitudinal) direction
and cross (lateral) direction tensile strengths, as well as producing
aesthetically pleasing and different nonwoven fabrics, that this invention
is concerned.
Accordingly, it ls an object of the present invention to produce a
nonwoven fabric, initially made from a carding machine, that has an improved
MD/CD strength ratio and to provide a method of making such a fabric.
SUMMARY OF THE NVENTION
The invention provides a biaxially oriented nonwoven fabric oE
fibers having adjacent and alternating striped areas of low fiber density
and areas of high fiber density, a majority of the fibers in said low fiber
density areas being uniformly distributed therein and oriented in a direction ~ ~.
substantially normal to the axis of the striped area and, a majority of the
fibers in the high fiber density area that lies directly adjacent to low ;`
: fiber density areas being uniformly distributed therein and oriented in a
:~ direction substantially parallel with the stripes of the low fibers density
area, the improvement comprising a majority of the fibers in said low fiber
density area are pulled straight thereacross, while a majority of the fibers
in said high fiber density area are accordian folded in a manner as to have
the fiber segments therein aligned substantially parallel to each other; said
` fabric having a machine direction to cross direction tensile strength ratio
of less than 2 to 1.
From another aspect, the invention comprises a method of making a
biaxially oriented nonwoven fabric having a machine direction to cross
direction tensile strength ratio of less than 2 to 1 comprising: preparing
a carded web of textile fibers; sandwiching said web between a tensioned
screen and a set of spaced-apart impervious striping bars in a manner as to
have said striping bars face a means for applying a fluid force; causing
said fibers between said striping bars to be straightened thereacross at 90
to said strlping bars; simultaneously causing the remaining portions of said
fibers to become accordian folded under said striping bars, while leaving
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substantially all of the fibers originally under said striping bars to remain
in a substantially parallelized manner along the length of said striping
bars; removing said thusly treated web from said screen and striping bars;
binding said web so as to fix the orientation of said web; and collecting
said thusly finished web.
As hereinafter disclosed a carded web disposed on a relatively
fine mesh screen has finger-like striping bars placed over the web with the
axis of the bars disposed at approximately 90 to the carded web's fiber
orientation. A hydroforming process, wherein water is sprayed over the
assembly, rearranges the fibers in the web. The fibers in the low fiber
density areas have their fibers straight and highly oriented in the machine
direction so as to maximize the MD strength per unit of fabric weight in the
light or low fiber density area. By drawing the fibers very straight in these
low density stripes, more of the individual fiber's length is available for
folding into fiber segments lying in the cross direction in the high fiber
- density stripes. These fiber segments that are hydraulically moved from the
low fiber density areas to the high fiber density areas are accordian folded,
resulting in a higher CD orientation of the fiber segments in the high density
areas than was present in the original web. The resulting nonwoven fabric
advantageously has, not only good aesthetic appeal but, a nearly equal cross
direction strength and machine direction strength.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 shows a plan view of a portion of the biaxially oriented
nonwoven fabric of this invention;
Figure 2 shows a plan view of a normal textile fiber in its relaxed
state;
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Figure 3 shows a plan view of ~he fiber shown in
Figure 2 after being rearranged by fluid forces as des-
cribed in this invention;
Figure 4 shows a portion of a nonwoven fabric of
this invention, wherein the f:ibers of the web are
alternatingly drawn straight and accordian folded;
Figure 5 shows a perspective view of the apparatus
of ~his inven~ion that is used to produce the nonwoven
;~ fabric of this invention;
Figure 6 shows a side view of the drum and hydro-
. forming portion of the apparatus shown in Figure 4;
Figure 7 shows a photograph of one of the fabrics
made in this invention; and
. Figure 8 shows a sectional view of the nonwoven
web of this invention between a tensioned screen and
another screen having the striping bars as an integral
part thereof.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
. A nonwoven fabric 10 has alternating stripes of
: 20 high fiber density areas 11 and low iber density areas
. 12, as shown in Figure 1. A majority of the fibers in
the high fiber density stripes 11 are rather uniformly
distributed therein and are oriented in a direction
substantially parallel with the contours of the stripes,
and a majority of the fibers in the low fiber density
areas~l2 that lies directly adjacent the high fiber
density areas 11 are sub~tantially uniformly distributed
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therein, and are oriented in a direction substantially
normal to ~he axis of the stripe. Such a nonwoven
material is described in my co-pending application,
UOS. Serial ~umber 506,843, filed on September 17,
l974, of common assignee.
This fabric has particularly ~ood hand and feel,
as well as a very high aesthetic appeal to those
skilled in the art. However, like other nonwoven
products, this material has a rather high tensile
strength ratio in favor of the machine direction strength.
U.S. 2,862,25l describes a method and apparatus
for producing foraminous fabrics. This patent describes
a method and apparatus for using fluid forces to rearrange
a layer of fibrous material into a foraminous unitary
nonwoven fabric structure comprising spaced interconnected
packed fibrous portions of s~arting material and openings
or apertures arranged in a predetermined pattern which are
separated by the interconnected packed portions. A layer
of starting material having individual fibrous elements
which are capable of movement under the influence of an ~ i~
- applied fluid force is positioned between xigid means
having apertures thereon and a tensioned screen having
foramina thereon that are smaller than the apertures.
A stream of water, from a jet spray, or the like, is
then caused to flow through the web thereby rearranging
the individual fibrous elements into a patterned,
apertured nonwoven web.
It has now been discovered that an aesthetically
pleasing, striped nonwoven fabric can bP made from a
carded web to have a machine direction to cross direction
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tensile strength ratio that approaches uni-ty. ~ carde~
web or a cross stretched carded web is passed through
an apparatus ~uite similar to that described in
U.S. 2,862,251; however, instead of positioning the
fibrous web between the apertured rigid means and the
tensioned screen, the carded web is placed between a
tensioned screen and a drum having spaced-apart striping .-~
bars disposed thereon. Thus, when streams of a fluid,
such as water, are passed through the thusly positioned
web, the fluid forces push the ends of the fibers located
between the striping bars to the area under the bars,
thereby causing the fibers in these newly formed low
fiber density areas to be drawn very straight. Simul-
taneously, when this action takes place, the fiber
segments that are h~draulically moved from the thin or
low fiber density sections to the thicker or hi~h fiber
density sections are accordian folded when pushed
together by forces on either side of a striping bar,
thereby resulting in a higher cross direction orientation
of the fiber se~ments in the high fiber density areas
than was present in the original carded web. Accordingly,
a fabric is produced having the high-fiber density stripes
running across the fabric to maximiæe the cross direction
strength.
Figures 2, 3 and 4 show, in an exag~erated manner,
how the fluid forces act on an individual fiber. For
example, Figure 2 shows a normal individual fiber 20 as
being a series of cursive twists and turns, and having
substantially no "straight" areas therein. IIoweverr
~igure 3 simulates in an exagerrated manner what the
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same fiber might look like after being subjected to the
fluid forces with the striping bars used in this inven-
tion, wherein the fiber segments be~ween striping bars
used herewith are drawn straight, such as at 21, while
the portions of the fiber above the striping bars become
pushed together in an accordian fold, as shown by 22.
Therefore, as shown in Figure 4, the fibers 21 in the low
fiber density areas have their fibers straight and highly
oriented in the machine direction of the carded web so as
to maximize the MD strength per unit of fabric weight in
the low fiber density areas, while the fiber segments 22
in the high fiber density areas are accordian folded
resulting in a higher CD orientation--the MD/CD strength
ratis thereby comes close to unity.
The cross direction strength can be ~urther enhanced
when an overall saturation binder technique is then used
on the web. For example, when binder is added to the still
wet web, and suction is applied to remove excess binder,
a majority of the binder in the low fiber density areas
passes through the web. Consequently, more binder is
present in the thick or high density areas than in the
low fiber density areas, thereby producing a further
enhancement of the CD strength.
Of course, striping bars of varying widths can be
used, and the number o striping bars per inch can be
varied while still producing the novel nonwoven fabric
of this invention. This is shown in the examples outlined
herein.
It should be noted that fibers or fiber segments
forced to lie in a narrow band or stripe must become
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increasingly oriented along the axis of that stripe as
the stripe width decreases. Eor example, in a hypothe-
tical stripe of only a few fi.ber diameters width, any
fiber segment of reasonable length would be forced into
a cross-direction orientation of absolute precision
with its axis only a few fiber diameters in variation
from a straight line. While this example may be diffi-
cult to produce, it does demonstrate this geometric
principle.
As mentioned earlier herein, the actual production
of this fabric can be made with apparatus described in
U.S. 2,862,251. However, instead o the foraminous drum
having apertures thereon, a drum has been ~ade having
striping bars thereacross. Figures 5 and 6 show a carded
web 31 being sandwlched between a tensioned screen 32 and
the striplng bars 33 disposed on the drum 34. Fluid jets,
such as water jets 35, are mounted on shaft 36 so that as
the carded web 31 passes through this sandwich it is hit
by the jets of water in a striking zone in a manner that
rearranges the ibers in the web as described herein above.
As the fluid force passes through the thusly positioned
web, it pushes the fibers located between the striping bars
to the area under the bars, thereby causing the fiber.s in
these newly formed low fiber density areas to be drawn
very straight~ being pulled in opposite directions toward
the adjacent high fiber density areas under the bars. At
- the same time, when this action takes place, the fiber
segments that are hydraulically moved from the low fiber
density areas to the high fiber density areas become
somewhat accordian folded, thereby resulting in a higher
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cross direction orientation of the fiber segments in
the high Eiber density areas than was present in the
original carded web.
The drum 34, cradled as by freely moving rollers
38, can then carry the thusly treated web past suction
box 37, which ~urther aids in rearranging the fibers
in the web as well as removing the excess water there-
from. A suction box 39 can also be positioned directly
behind the drum at the point where the ~ater is being
passed through the striping bars, ~eb and screen. Of
course, it is not necessary to use water as the fluid
force; other fluids such as gas or air or the like can
be used with similar although possibly somewhat less
desirable results. For example, if the web contains a
;~ proportion of thermoplastic ibers therein, then it ~ ~
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might be desirable to use live steam as the fluid to
rearrange the fibers, thereby producing a thermoplastic
bonded fabric at the same time as the rearrangement of
the web takes place.
~he fluid force exerted by the water jets or
nozzles should preferably produce a water flow rate of
approximately lOcc/sec per inch of width per bank of
nozzles, using 6 banks of nozzles. The nozzles can be
conventional solid cone nozzles in overlapping relation,
such as used and described in U.S. 2,862,251. ~lso, the
water pressures and delivery capabilities can be as
described in the above-mentioned patent. However, when
this system is used with the striping bar apparatus
described above, a pulling action is exerted on the fibers
in the low density areas between the bars, while the above-
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described accordian folding action takes place simultane-
ously under the bars~ This is opposed to the results
achieved and described in U.S. 2,862,251, wherein uniformly
apertured fabrics are formed having spaced interconnected
packed fibrous portions of startin~ material and apertures
arranged in a predetermined pattern which are separated by
interconnected packed portions in yarn-like bunales. The
dif~erence in fiber structure achieved above unexpectantly
results in a much stronger ~abric in all directions--i.e.,
a nonwoven fabric possessing a tensile strength ratio that
approaches unity.
Figure 7 shows a photograph of the striped fabric
of this invention. As can be observed in this photograph,
the low fiber density areas have a majori~y o its fibers
drawn relatively straight between the high fiber density
stripes. While in the high fiber density stripes, the
"accordian folds" are not as pronounced as in Figure 3,
it is urged that this is the mechanism taking place in
those stripes that gives the particular fiber orientation
described. Furthermore, although"apertures" are present
in the web, they appear in a random fashion thereon and
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are not surrounded by yarn-like bundles of fibers.
The following are illustrative examples of fabrics
produced with this invention:
EXAMPLE I
A carded web weighing 12.28 gms/sq. yrd. was made
in the convelltional manner using 3 denier 1 9/16" type
40 F.~C rayon fibers. The MD/CD tensile strength ratio
of such webs is over 10 to 1. The carded web is then
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put through the apparatus described above wherein the
striping bar mechanism is made of 1/8" w?ide metal
striping bars that are positione?d on the drum on 1/4"
centers. The web is hit with water droplets having a
flow rate of approximately lOcc/sec per inch of width
per bank of solid cone type spray nozzles using six
banks of nozzles. rrhe web continues on the drum, is
suctioned to remove excess water, and is then overall
saturated with HA 8 binder (tradenar.le for an acrylic
lP binder composition sold by Rohm & Haas). The resulting?
striped nonwoven fabric would have a machine direction
tensile strength oE 1.95 pounds per inch of width and
a cross direction tensile strength of 1.15 pounds per
inch of width--an MD~CD ratio or about 1.7 to 1. This
is an improvement in the strength ratio over the carded
-- web of 5.84 times.
EXAMPLE II
~ carded web weighing 20 grams/sq. yd. was prepared
in the same manner and of the same fiber material as that
previously described in the above example. Again, the
~tD/CD ratio of this material being in excess of 10 to 1.
This web was treated in the same manner as in Example I
and under the same conditions, also using the HA 8 binder.
The resulting striped fabric would have a machine direction
tensile strength of 2.4 pounds per inch of width and a
cross direction tensile strength of 2.1 pounds per inch
of width--an MD/CD ratio of about 1.14 to 1. This is an
improvement in the strength ratio over the carded web of
more than eight times.
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Although all the figures and discussions for making
the nonwoven fabric of this invention utilize a drum
having fairly rigid striping bars thereon, Figure 8 shows
another embodiment of the apparatus used to make this
fabric. A tensioned screen 54 serves as a backing for web
~;~ 53. The web is sa~dwiched between screen 54 and another
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screen 51 having striping bars 52 as an integral part
thereof. These striping bars 52 can either be imprinted
on the screen or woven into the screen. If the water
spray enters from direction A, then you will still have
the same action as described above herein with the drum.
However, if the water spray enters from direction B, then
the-fibers will be washed away from the impervious striped
areas 52 and into the open areas between the stripes--this
is the r~verse of our previous discussion and examples.
In addition to the obvious advantage of increased
strength ratios in the fabric of this invention, it should
also be pointed out that aue to the structure of the
fabric (i.e., alternating stripes of high and low fiber
density) the low fiber density stripes act as "hinges" of
a sort thereby greatly enhancing the feel and drape of
the fabric.
While it is described in the two examples that the
web is made of rayon fibers, it should be pointed out
that any other fibers used by those skilled in the art
of nonwoven fabrics could also be utilized in this inven-
tion. For example, as described herein earlier, thermo-
plastic fibers could be used in forming the web and could
later be subjected to iive steam to bind the web and
rearrange the fibers simultaneously. Further, a carded
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web could be made from continuous filaments of reshuffled
spread tow web and could also be utilized in this process
with similar results.
The water pressures and flow rates mentioned herein
are preferred, however, it is possible to use pressures in
the range of 20 PSIG to 10,000 PSIG. For example, high
pressure water streams can be used, as described in
U.S. 3,485,706 to produce these striped fabrics. These
pressures range up to 5,000 pounds per square inch gage.
The striped fabric produced thereby will not require any ~;
further bonding agents, while still having an MD/CD that
approaches unity. ;~
In the description of this invention, it has been
stated that a carded web is used as a starting material,
however, if a CD strength that is higher than the MD
strength is the desired end product, then a random web
can be used initially and will result in a nonwoven that
has an MD/CD ratio of less than one.
It should also be noted at this time that a cross-
stretched carded web could be used with similar and perhapsmore advantageous results.
It is obvious that many modifications and embodiments
can be made in the above-described invention without
changing the spirit and scope of the invention; for example,
as noted above, a screen with impervious striping bars ;-
woven into or imprinted on the screen could be used instead
o~ striping bars over the web. However, it is intended
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that this invention not be limited by anything other than
the appended claims.
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