Note: Descriptions are shown in the official language in which they were submitted.
104543~
BACKGROUND OF THE INVENTION
This invention relates to biaxially oriented striped
nonwoven fabrics and a method for making same, and more part-
icularly, to a method of making a nonwoven fabric having al-
ternating high fiber density and low fiber density striped
portions, and fiber mixtures of both long and short fiber
lengths, said fabric having substantially biaxial orientation
of fibers throughout the fabric.
Nonwoven fabrics are now used for a variety of purposes
in a number of industries. These fabrics have been made tradi-
tionally by methods such as carding, garnetting, air-laying
and the like. Nonwoven webs have been made to have most of the
fibers therein oriented in the machine direction; other non-
woven webs have been made to have some cross orientation; and
still other webs have been produced having a randomized fiber
distribution. However, sutstantially all of these webs are
lacking in any surface character or natural decorative effect.
Nowhere in the art, heretofore, has a nonowoven fabric been
made in an unlayered structure having a striped construction
wherein half of the stripes have a high fiber density and the
other half of the stripes are of low fiber density; further-
more, no fabrics have yet been made in such a strip3d m~er, for
example wherein a majority of the fibers in the high fiber
density stripes are oriented in a direction parallel to stripes
(machine direction~, while a majority of the fibers in the low
fiber density stripes are oriented in a direction substantially
perpendicular to the stripes (cross direction). No method has
yet been devised for manufacturing such a fabric with at least
two types of orientation disposed thereon simultaneously.
Furthermore, it has been discovered that while the bi-
axially oriented nonwoven fabric described above has been very
satisfactory in many respects, efforts have been undertaken to
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104~43~
attempt to reduce the cost of raw materials therein, while
increasing the bulk, softness, feel and look of the resulting
nonwoven fabric. Thus, a papermaker's method for making this
nonwoven, using short paper fibers, will reduce costs dramati-
cally.
The invention provides a method of making biaxially
oriented nonwoven fabrics having areas of low fiber density
and high fiber density wherein a majority of the fibers in
said low fiber density areas are oriented in a direction sub-
stantially normal to the fibers in the directly adjacent highfiber density areas and a majority of the fibers in said high
fiber density areas that lies directly adjacent said low fiber
density areas are oriented in a direction substantially parallel
with the contours of the configuration of the low fiber density
area comprising: preparing a stock of blended long and short
fibers, said long fibers being at least one-half inch in length
or more and said short fibers being less than one-half inch in
length; maintaining said stock of fibers in an agitated state;
causing a flow of said stock to pass into a headbox, and
stabilizing same therein; passing said stabilized stock flow onto
moving fourdrinier screen having fluid-impervious resist areas
thereon; causing a majority of said long and said short fibers
in said stock flow to locate outside said fluid-impervious
resist areas, said majority of fibers that lie directly adja-
cent said fluid-impervious resist areas orienting themselves in
a direction substantially parallel with the contours of said
resist areas; simultaneously causing a minority of said long
and short fibers in said stock flow to locate across said fluid-
impervious resist areas, said minority of said long and short
fibers orienting themselves in a substantially cross direction
normal to the axis of said fluid-imperious resist areas; secur-
ing said biaxially oriented nonwoven fabric in said orientation
B
1045431
as described herein; carrying said biaxially oriented nonwoven
fabric on said moving fourdrinier screen toward a pick-up means
fGr collecting the thusly formed fabric; and, collecting said
fabric on said pick-up means. The nonwoven fabric with long and
short fibers therein can have a striped patterned construction
manufactured into it, which would be able to be produced with
relatively inexpensive short fibered materials, The nonwoven
fabric may have alternating stripes of high fiber density and
low fiber density, wherein a majority of the fibers in the high
fiber density stripes are oriented in the machine direction while
a majority of the fibers in the low fiber density stripes are
oriented in the cross direction. The direction of the stripes
may run across the fabric or at some other angle that is bias
to the angle of the direction of travel of the fabric.
By placing lines of fluid-impervious materials on or
over the moving fourdrinier screen, an unlayered nonwoven fabric
having, for example, alternating stripes of high fiber density
areas can be produced by papermaking techniques wherein substan-
tially all of the fibers in the high fiber density stripes are
oriented in the direction of the fluid-impervious lines, and
substantially all of the fibers in the low fiber density stripes
are oriented in a direction substantially normal to that direc-
tion. Since the short fibers are of insufficient length (pre-
ferably 1/4") to bridge the fluid-impervious lines or areas,
most of them will be deposited with substantially their full
length within impervious areas on the collection screen so as to
form "twistless ribbon strands". These areas also contain a ma-
jority of the long fibers from a stock flow being fed thereto,
while a lesser number of the long fibers bridge across the re-
sist lines or areas and remain in a generally cross direction tothese resist areas or lines. A majority of the bridging long fi-
bers have at least a portion of their length included in adjacent
1~45431
high density areas. The nonwoven fabric can be bound together
in a number of ways, including the use of thermoplastic fibers
as some of the short fibers therein, so that upon heating said
thermoplastic fibers, they will bond the long bridging fibers
at their ends where they are incorporated into the stripes but
leave the bridging fiber itself substantially free of binder
between the stripes, thus enhancing the drape and softness in
these areas, while increasing the bulk of the high fiber density
areas.
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1045431 - ~-
BRIEF DESC~IPTIO`~J ~_T~E DP~_`JGS
Figure 1 shows a plan view of a nonwoven fabric made with
the process of this invention.
Figure 2 is a flo~7 chart outlining the steps of the
process of this invention.
DESCRIPTION OF THE PT'~EFERRE:D EMBODIM~,NTS
Referring to ~igure 1 of the drawings, there is shown an
unlayered non~70ven fabric 10 having alternating high fiber density
stripes 11 and low fiber density stripes 12. As can be seen in
the drawing, the majority of the fibers in the high fiber density
stripes 11 are oriented in a direction that substantially follows
the direction of a moving fourdrinier screen upon which such a
fabrlc is made (machine direction), that is to say, that those
fibers are aligned substantially parallel to the length of the
fabric. However, the majority of the fibers in the low fiber
density stripes 12 are oriented in a direction that is substan-
tially across the width of the fabric 10 (cross direction
orientation), that is to say, these fibers are aligned sub-
stantially normal to the fibers in the high fiber density stripes
11 and in bridging relationship with those stripes. These
alternating striped portions of varying orientation are formed
simultaneously as described below.
A non~70ven fabric such as shown in Figure 1 can be made by
papermaking techniques wherein a stock of blended fibers
comprising long fibers and short fibers are prepared and held
in a chest at a particular consistency, ~hile being agitated
to prevent settling and separation of the solids. The stock can
then flo~7 to an inlet distribution s~stem ~Jhere the flow spreads
to the full machine ~7idth, discharging the stoc]; into the headbo~,
~here the flow bccomes stabilized. ~t this point, the stabilized
stock flow can then pass onto a moving fourdrinier ~7ire screen.
~4~431
The fourdrinier screen has fluid-impervious resist areas
placed thereoll in various confiyurations, for example, continuous
and parallel stripes. Thus, as the stock flow passes onto the
fourdrinier screen, a majority of both the long and short fibers
are drawn to the areas thereon outside the fluid-impervious
resist areas, or in the case of the example, in between the
fluid-impervious stripes. This, of course, would be espeially
true of the short fibers since they would not be subject to
forces of more than one of the areas outside of the fluid-impervious
areas and would not attempt to bridge a fluid-impervious area.
P~ather, because of the movement of the fourdrinier screen, they
will be increasingly drawn to the pervious portion of the screen
and will be oriented in the direction of the fluid-impervious
stripes, or parallel to the machine direction of the formed web.
Simultaneously, a minority of the fibers, especially the
long fibers, will be subject to the forces of at least two
fluid-pervious areas, thereby causing some of the long fibers to
bridge across a fluid-im2ervious area. Thus, such fibers will
be oriented in a direction substantially normal to the axis of
2~ the fluid-impervious resist areas.
If the striping bars or fluid-impervious resist areas
are disposed fairly close together so that the distance between
the bars is less than a flber length, and preferably less than
one-half the length of a long fiber, the fibers that do not
bridge the striping bars will be carried into a high fiber -
density stripe or the pervious area that lies between the
striping bars. As described earlier herein, a high fiber density
stripe formed by a majority of the fibers is therefore induced
to have a primary orientation along the axis of the striping bar.
104~431
The long fibers are, for the purposes of this invention,
at least one-half inch in length or more. The short fibers
used herein may be paper fibers, cotton linters, short thermo-
plastic fibers, or the like, or combinations thereof, so long
as the fibers are less than one-half inch in length. If short
thermoplastic binder fibers are used, either alone or with other
short fibers, then they too will be drawn into the high fiber
density stripes and, when activated, will bond the long bridging
fibers at their ends where thev are incorporated into the stripes,
but will leave the bridging fiber itself substantially free of
binder between the high fiber density stripes, thus enhancing
drape and softness in those areas, and in the total fabric.
For the purposes of this invention, these high fiber density
areas comprising long and short fibers are referred to as twistless
ribbon strands herein, and sho~ld have at least one strand width
I in spacing between the strands, but not so much space that the
long fibers are not able to bridge thereacross. While it is
true that some short fibers will be ~ound in the low fiber
density areas mixed in with the long bridging fibers, a majority
of the short fibers will be disposed within the twistless ribbon
strands. Therefore, the low fiber density stripes will have a
lower total fiber length per unit of area of short fibers therein
than the twistless ribbon strands. Furthermore, most of the
long bridging fibers will have at least a portion of their length
in adjacent strands, connecting the twistless strands, thereby
forming the nonwoven fabric.
In all but the lightest weight fabrics, the top of the
fabric, that is the portion of the fabric furthest removed from
the fourdrlnier screen, appears to be covered by a minor portion
of long and short fibers positioned generally across the entire
104S431
wid-th of the webs. ~s the fibers in the stoc~ flow position
themselves on the fourdrinier screen and fluid-impervious resist
areas, and become increasingly thick and pass off tne striping
bars, the fluid-borne fibers become less generally controlled
by the water's diverging action between fluid pervious and
impervious areas, and then fall on the uppermost portions of the
tnusly formed fabric in a some~hat randomized fashion. The
web at this point can best be described as having high and low
fiber density stripes having a somewhat randomized covering
portion of long and short fibers integrated therewith. ~lowever,
a majority of the fibers are still positioned in a striped
fashion and in an orientation parallel to the length of the web.
If the striping bars are moved closer together and arranged
so that they are spaced on, for example 3/4 inch centers, it
becomes apparent that a much more pronounced ribbed structure
is formed. By "ribbed structure", it is meant that the high
fiber density stripes have so many fibers therein that this portion
of the web structure becomes almost semi-circular in its con-
struction, ~Ihile the low fiber density areas remain rather flat.
This arrangement could well be described as being a wash-board
configuration. The fabrics produced by this invention have a
variety of uses and could be used as disposable curtains or drapes'
decorative narrow ribbons and for florist ribbons; sweatbands;
cling type bandages; disposable tablecloths and the like.
Of course, other designs of striping bars can be used in
different arrangements to produce similarly biaxially oriented
nonwoven fabrics. For example, impervious resist areas can be
designed into the fourdrinier screen as a substitute for the
striping bars. Resist areas can also be formed in the shape of a
star, or the like, directly on the screen, so that as the portion
5431
of the screen carrying the fluid~impervious resist areas passes
through the apparatus, and the fibers have been deposited
thereon and run over the suction roll, the biaxial orientation
of fibers will occur on and around the resist areas on the screen
producing a rather uniaue fabric. The resist areas will be
covered by fibers in a manner as to produce low fiber density areas
wherein the fibers are oriented in a direction substantially
across each of the finger-like extensions on the star, or normal
to the particular configuration, for example, while the area of
the fabric web directly adjacent the resist area will have
fibers oriented in a direction substantially parallel with the
contours of the configuration of the resist area, and the fibers
on the rest of the web not affected by resist areas will have
a random, cross or machine orientation as desired. Other con-
figurations could also be made on the screen to produce other
similar biaY.ially oriented patterns thereof.
If the length of the striping bars blocking the screen is
reduced so that they do not extend so far as to cover the entire
screen collecting surface, then a substantially random web will
be formed on the unblocked screen surface causing a random web
to become superimposed over and integrally connected with the
striped web. The proportion of web weight that is striped and
has been biaxially oriented, to tAe proportion of superimposed
web that is random can, of course, be varied by adjusting the
proportion of the screen that is blocked by the striping bars.
Of course, as stated and described herein earlier, resist
areas may also be placed at any other angles, other than parallel
or normal to the direction of travel of the screen to produce
fabriss witn stripes at a bias to the direction of travel of
3~ the fabrics.
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~045431
Since it is obvious that many rnodifications and embodiments
can be made in the above-d2scribed i.nvention without chanying
the spirit and scope of the invention, it is intend~d that this
invention not be limited by anything other than the appended
claims.
