Note: Descriptions are shown in the official language in which they were submitted.
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The present invention is an improvement in a process for
the manufacture of non-woven structures in which a part of the
border zones of the non-woven is folded toward the inner part
after a slight pre-consolidation and prior to the main consoli
dation of the sheet. This process is applicable especially
to the manufacture of non-woven fabrics made from filaments
and spunbonded fabrics. It makes it possible for the manufac-
turer to avoid waste material as a consequence of trim~.ing the
border zones of non-woven fabrics.
lQ In the manufacture of spunbond fabrics, for example, fresh-
ly spun filaments are first suhmitted to draw~ng with gas jet,
and are thereafter spread across a moving surface by means of
electrostatic charge or of stationary or movable deflectors
of of other devices to form a non-woven fabric~ Processes of
this kind are disclosed, for example in German Offenlegungs-
schrift No. 24 60 755.
In order to obtain the desired width of a non-wo~en ab~ic,
several non-woven websorstrips issueing from the individual deposlt-
ing units are laid down in parallel manner in overlapping posi-
tion. ~n this kind of laydown there are formed border zones
with reduced weight per square unit in comparison with the cen-
tral zones, if no measures are undertaken to influence those
parts which form the border zones in a different manner than
those which form the central part.
German Auslegeschrift No. 16 35 585 disclosesa process ~or
the preparation of non-woven webs o continuous f~laments, whI:ch
comprises forwarding a number of untwisted strands o~ colitinuous
filaments by an adequate number of stationary jets, spreadin~
2q the filaments by electrosta.ic chaxge and deposIt~ng them ~ n a
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moving collec~ing surface in the form of overlapping ribbons to
' form a wide non-wo~en structure. This publication also teaches
that adjacent strips must generally overlap by 50 %1 67 ~, 75 %
or 80 % in order to form a uniform non-woven structure. This
publication moreover mentions that for removing both border
zones with low weight per square unit, the non-woven webs must
be trimmed the more the larger the degree of o~erlapping. For
webs of rectangular cross-secti.on and a degree of overlapping of
50 %, the total quantity or both border zones which must be cut
1~ off in order to leave a uniform utiiizable web, corresponds to
the output of one jet. With a degree of overlapping of 67 %,
the quantity to be cut off corresponds to the output of two jets,
with a degree of overlapping of 75 %Jto the output of three jets
and with a degree of overlapping of 80 %,to the output of four
~ets.
Furthermore, the smaller the width of a non-woven web, the
higher the percentage of material to be cut off.
The waste material obtained as a consequence of cutting the
border zones of the non-woven web is uneconomic.
20Possibilities of reducing the ~uantity of material to be .
cut off, consist in influencing the ~ilaments to be deposited
in the depositing positions near the border by means of guide
plates, pegs or air nozzles or by predetermined direct7~oning of
the suctionining air at the perforated laydown belt in a manner
to make them arrange uniformly also in the border zones so
that there is obtained the Same weight pex sq-uare unit in
These zones as in the central.zones. This method, however, ~ives
~ise to strUctures in the de~osited non-~oVen web in the border
29 zone which diffex fxo~ that in the central part ~hich has not
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- been influenced. It is quite natural that the quality of the
web is deteriorated by this measure since the properties of the
web in the border zones are different from those in the central
part. Furthermore, these measures insure no sufficiently rec-
tilinear borders and even in this case it cannot be avoided to
cut off a certain part of the border zone.
The object of the present invention was, consequently, to
provide a process which does not show these disadvantage~- and
which makes it possible to transfer completely the filamentary
1 a material employed into utilizable non-woven web of hi~h quali-
ty.
This problem could be solved by the present invention by
determining the basis weight distribution I which is a measure
of weight per unit area and ordinarily expressed in terms of
grams per square metertof the border zones and thereatex fold-
ing a part of the border zone toward the central part such that
the resulting web has a uniform basis weight diatribution.
Optionally the web is slightly consolidated prior to
folding the borders to the center for example by calendering.
The width of the part of the border zone which is folded
inside depends on the mass distribution in this zone. In
order to determine the width, the basis weight distribution in
the border zone must be measured and thereafter a part o the
border zones it folded towards the center such that the result-
ing web has a uniform basis weight distribution.
If in the ideal case the basis weight in the border zones
diminishes in linear manner to the edges, the width of the
part of the bo~der zone to be folded to ~he center corresponds
29 to half the width of the border zone.
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In practice this ideal case is not given very often. How-
ever, it has become apparent surprisingly that even in those
cases where the basic weight distribution in the border zone
deviates from this ideal distribution, very good results can
still be obtained, that is to say that the basis weight uni-
formity which is usually given in the central part of non-
woven fabrics, can be achieved with the process of the inven-
tion also in the border zones.
By folding the border zone of the web to the center, not
only the basis weight of this zone approaches that of the to-
tal web, but moreover the edges of the web are straightened
surprisingly.
Furthermore it was found surprisingly that frequently a
second consolidation of the folded web by calendering suffices
~5 to counteract a subse~uent delamination of the ~olded border
zone.
The border zones are preferably folded towards the center
continuously while the non-woven web moves in the direction of
its longitudinal axis.
When the web to be folded in its border zone consists of
little extensile materlal or when the border zone should not
or must not be stretched during the folding process , the web
is guided, according to the invention, about in the middle o
the zone, where the folding process takes place,in deviation
from the linear direction~at an angle, this angle being inclin-
ed towards that level towards which the folding of the border
zones towards the center takes place, that is to say since the
border zones of the web are in most cases folded upwards in
29 practice, the total web is inclined upwards.
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The angle by which the guidance of the web through the fold-
ing zone deviates from the linear direction is
- 2 arc sin BR
L
BR denoting the width of the individual border zones of the web
and L the length of the web within the :Eolding zone. As a gene-
ral rule the angle will not exceed 70 to 90 C, an angle parti- : -
cularly preferred corresponding to the formula
a ~ 2 arc sin R
1Q L
When the material of the web is very elastic and when the
border zones of the web are very narrow, it may be operated at
smaller angles or a guidance of the web at an angle.in the
folding zone may even be dispensed with.
After having folded the border zones of the non-wo~en web,
the latter is consolidated. For the final consolidat.ion of the
web, further methods may be employed, in addition to calender-
ing, for example the consolidation by means of binding agents or
by needling.
The web prepared according to the invention shows a very
good uniformity until the edge of the border zone and unobjec-
tionably rectilinear edges. For these reasons, trimming of
the border zones may be dispensed with and there is no waste
material.
The invention will be illustrated, by way of example, in
the accompanying d.rawings and in the description referring to
the drawings.
In the drawings
29 Figure 1 represents a ~chematic cross section in vertical direc-
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tion to the longitudinal axis of a single web of a
single depositing unit of a plant for the manufacture
of spunbond fabrics, which web has been deposited on
a collecting surface (not shown);
Figure 2 is in four parts, i.e. a, b, c, and d, to show cross-
sections of non-woven fabrics which are composed of
several webs deposited one beside another as well as
in an overlapping position;
Figure 3 represents a cross-section of a web prepared initially
like that shown in Figure 2b and with the border zones
folded towards the center;
Figure 4 represents steps a, b, c, d, and e of a process of folding
a border zone of a web using schematic cross-sections
in vertical direction to the longitudinal axis of the
web;
Figure 5 is a flow scheme in elevation of the process of fold-
ing the border zones;
Figure 6 is a diagrammatic representation of the basis weight
distribution of the web with the borders not being
folded, transversely to the direction of run of the
web;
Figure 7 is a diagrammatic representation of the basis weight
distribution of the web with the borders folded accord-
ing to the invention;
Figure 8 is a diagrammatic representation of the basis weight
distribution in the border zone of a further web with
the border zone not being folded; and
Figure 9 is a diagrammatic representation of the web with the
border zones b~ing folded according to -the invention.
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R~ference is first made to Figure 1, which shows a
cross-section transversely to the longitudinal axis of a web
1 issuing from a single depositing unit.
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Several webs or strips of non-woven fabrics issuing
from single depositing units must be deposited one beside the
other overlappingly, for the preparation of wide non-woven
structures. Possibilities of arranging strips of this type
within the structure of non-woven fabrics of relatively great
width are shown in Figure 2, parts a to d. In these repre-
sentations the adjacent strips within the structure of the non-
woven fabric touch only at their surface. However, as it has
been mentioned particularly in German Offenlegungsschrift No.
24 60 755, the strips arranged one upon the other may also
penetrate each other by their layers of individual filaments
or of filament bundles. Those zones of the non-woven fabrics
which are located outside of both dotted vertical lines 2
constitute the border zones of the fabrics. They have a lower
basis weight than the central zones of the non-woven fabrics
of uniform basis weight or their basis weight is reduced to
the border. The arrows visible in Figure 2c at regular inter-
vals mean to say that the basis weight decreases from the
center to the border in linear manner. -
Non-woven fabrics of different structure, the basis
weight of which likewise decreases to the border, are further-
more known or imaginable. Fabrics of this kind may also be
used for the process of the invention.
-~ Figure 3 represents the non-woven fabric of Figure 2b
with the border zones being folded.
Figure ~ is a cross-sectional view in vertical direction
with respect to the longitudinal axis of the non-woven fabric
of the individual stages of the process of folding the border
zones. Figure 4a shows the fabric 3 with the border zones not
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1~D8379~3
being folded and with the calender rolls ~ and 5. The border
zone of the fabric to be folded is forwarded to the first bar 6,
which lifts the border zone 7 of ~he fabric.
Further bars are arranged at equal distances (Figure 4c, d),
which further lift the border,zone and press it inwards and
downwards or fold it. The fabric with the border zone being
folded is thereafter drawn off by the pair of rolls 8 and 9 or is
calendered as it is illustrated in Figure 4e.'
Figure 5 is a side ~iew of the folding process~ The un
folded non-woven fabric 3 is forwarded in the direction of the
arrow to the folding zone by the calender rolls 4 and 5. The
numerals 6 denote the folding bars, 7 the border to be folded
and 10 a deflection bar. The length of this de~lection bar
corresponds approximately to the desired width of the non-w,,oyen
fabric with the border zones being folded. The deflection b~r
is located approximately in the middle of the ~olding zone, the
latter being limited by two draw-off rolls 8 and 9 of the calen-
der. In the course of the folding process the web is deviated
by the angle a around the bar 1~. Thus the foldlng process is
facilitated. The web wi~h the borders being folded 3 is then
drawn-off and calendered by the rolls 8 a,nd 9, passed through
a needlin~ device 11 and wound u~ on a devicewhich is not shown.
The method of folding the borders and the device employed
in the present invention are given by way o~ example only.
The following example illustrate tne invention:
E X ~ M P L E 1: '
~ilaments were ~roduced f,rom molten polyethylene terephtha-
late by two spinn~rets each having seventy holes, the filaments
29 were collected to ~orm two bundles and stretched by air n~zzles.
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The titer of the individual filaments was about 8 dtex.
Either filament bundle accelerated down by the air nozzles
was forwarded to a rotating deflection device, by which they
were deposited upon a collection sufrace moving with constant
velocity~to form a strip. Both overlapping strips formed a
non-woven fabric which was thereafter pre-consolidated by ca-
lendering at 140 C. At an arbitrarily selected point of the
web, the basis weight gradient shown in Figure 6 was measured
photometrically in transverse direction with respect to the
direction of movement of the web. In the diagram D denotes
the weight per square meter, X denotes the coordinate trans- -
versely with respect to the direction oE run of the web. As
it can be seen from the curve in Figure 6~the weight per square
meter D of the web ranges between 0 g at the border of the web
and 150 g near the center of ~le web.The total width of the web
was 72 cm. By the devices shown in Figures ~ and 5 14.~ cm of
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the left border zone and 12.6 cm of the right one of the web
were folded into the center. Thereafter the web was submitted
to a second consolidation process by calendering at 140 ~.
The basis weight of the web with the borders being folded, de-
termined at the same position, was in the range of from 100 g
per square meter and 162 g per square meter, the average basis
weight being about 137 g per square meter (cf. Figure 7). The
web thus formed had a uniform structure and linear edges which
had not to be trimmed and thus there was no waste material.
E X A M P L E 2:
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Figure ~ shows the basis weight gradient of the border
of a further non-woven fabric. After having folded the border
29 zone according to the invention and after having consolidated
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the non-woven fabric a second time, the basis weight gxadient
shown in Figure 9 was measured. In this case, the basis
weight was measured at two positions of the non-woven fabric.
This non-woven fabric had also a uniform appearance and
a smooth border so that trimming of the borders could be dispens-
ed with.
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