Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PLANT AND METHOD FOR DRYLY PRODUCING A NON-WOVEN FIBRE WEB OF SHORT AND LONG
FI
BRES, A COTTON FIBRE WEB CONTAITIING COTTON LINTERS PULP (CLP)
The invention relates to a method for dryly producing a non-
woven fibre web of at least relatively short and relatively
long fibres.
The invention also relates to a plant for dryly producing a
non-woven fibre web by means of two air-lay stations placed
one after the other and each comprising at least one fibre
feed duct to feed fibres to the station from a fibre source,
at least one air-lay forming head connected to the fibre feed
duct and at least partly defined by a perforated screen, and a
suction box for successively sucking fibres in the forming
head through the screen.
The invention moreover relates to a non-woven fibre web
produced by means of the method and the plant for dryly
producing a non-woven fibre web.
Finally, the invention relates to the use of Cotton Linters
Pulp (CLP), which is a relatively inexpensive by-product
derived from the seed coats of the cotton plant, for dryly
producing a relatively inexpensive non-woven air laid cotton
fibre web.
The air-lay technique is known from e.g. GB Patent No. 1 499
687 which describes a plant for dryly producing a non-woven
fibre web. This plant has an air-lay forming head in form of .a
box which is defined by a perforated base at the bottom. Above
the base is rows of rotating wings which distribute the fibres
during operation into flows across the perforated base. Below
this is placed an air-permeable forming wire which is running
endlessly during operation for accommodating fibres which are
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drawn through the openings of the perforated base by the
negative pressure in a suction box placed under the forming
wire.
This plant is well suited for producing a non-woven fibre web
of like fibres or at least of fibres on the whale having the
same configuration. If the fibre web is to be made of fibres
having substantially different lengths, the plant can however
not function optimally, and the fibre web produced cannot
obtain a completely satisfactory quality.
These disadvantages can be assigned to the fact that it is not
possible to dimension the openings of the base so that they
are suited for both the relatively short' and the relatively
long fibres. It is therefore necessary to choose openings
having a size which is between the optimum sizes for each of
the two types of f fibres . The openings will then easily be too
large for the short fibres and too small for the long ones.
GB No. 2 031 970'describes an air-lay plant having several
forming heads of the above-mentioned type placed in a row one
after another above a joint forming wire. By means of this
arrangement, the plant is able to operate with both short and
Tong fibres with good results. Fibres of one specific length
are then distributed from a forming head having base openings
which are suited for exactly this fibre length. Layered fibre
webs can be produced by means of this' technique as it also is
desired in some cases. The known plant is however not suited
for producing homogeneous fibre webs of fibres of different
lengths.
The last-named problem has been tried solved by placing the
forming heads on top of each other in stead of in a row one
after the other. Such a plant is described in the patent
specification WO 96/10663. In this case, the plant has three
forming heads. The uppermost one is supplied with SAP (Super
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Absorbent Powder) and has a base with openings that exactly
fit the size of the SAP. The middle forming head is supplied
with short cellulose fibres and has a base that exactly fits
the size of these short fibres, and the lowest forming head is
supplied with long thermobinding fibres and has a base that
exactly fits the size of these long fibres.
The base of the upper forming head forms an upper delimitation
to the middle forming head, and the base of this head forms an
upper delimitation to the lowest forming head.
The openings in the base of the lowest forming head are so
large that the SAP and the cellulose fibres can pass through
the openings simultaneously'with the thermobinding fibres, and
the openings in th'e base of the middle forming head 'are so
large that the SAP can pass through these openings
simultaneously with the cellulose fibres.
Below the base of the lowest forming head is an air-permeable
forming wire which is running endlessly during operation, and
below this a suction box which is joint to all three forming
heads.
When the plant is running, the SAP is driven via the openings
in the base of the upper forming head down into the middle
forming head, the SAP and the cellulose ffibres are driven via
the openings in the base of the middle forming head down into
the lowest forming head, and the SAP, the short cellulose
fibres and the long thermobinding fibres are driven via the
openings in the base of the lowest forming head down in a
layer onto the forming wire.
The SAP and the short cellulose fibres are first~mixed in the
middle forming head and then the long thermobinding fibres in
the lowest forming head. By means of this mixing, a homogenous
fibre web should be obtainable.
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However, it is difficult to control the different air flows of
the process such that the resulting fibre web obtains an
acceptable homogeneity.
This is among other things due to the fact that the air flows
inevitably will interfere with each other. Thus, air is
simultaneously blown in on both sides of the base of both the
upper and the middle forming head, and the negative pressure
from the suction box furthermore has to propagate to the base
of the middle forming head via the openings in the base of the
lowest forming head and to the base of the upper forming head
via the openings in the middle forming head. At the same time,
the SAP, the short cellulose fibres and the long thermobinding
fibres are moving in the opposita direction through the
openings of the respective bases, said openings are thereby
randomly blocked to the flow of the air to a greater or
smaller extent.
When the forming heads are placed on top of each other instead
of in a row after each other, the plant will furthermore be
disproportionately high. Therefore, the plant known from the
patent specification WO 96/10663 can rarely find room in
existing buildings, and new buildings for .the plant will
normally look quite out of place in an otherwise harmonious
group of buildings. Furthermore, the great height means that
it is difficult to inspect the plant and control the 'process
in this plant.
Today, dryly-produced fibre webs are used extensively for many
different purposes, of which napkins, toilet paper, diapers,
sanitary napkins and products for people suffering from
incontinence can be mentioned.
In order to be able to keep the prices of these products at a
commercially acceptable level, a large part of the fibres that
form part of the air-laid fibre product are normally
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inexpensive cellulose fibres which can be mixed with e.g.
thermobinding fibres depending on the application purpose just
as the products also can contain SAP (Super Absorbent Powder)
to increase the ability of the products to absorb liquids.
However for some purposes, products are wanted that are
substantially softer than the products that are based on
cellulose fibres.
Such a very soft, non-woven fibre product can be produced by
utilising cotton fibres instead of cellulose fibres. Due to
the high price of the cotton fibres, the resulting products
will however be to expensive for practical application.
The production of cotton leaves a by-product called Cotton
Linters Pulp (CLP) and consisting of short residual fibres
from the seed coats of the cotton plants.
This by-product is far less expensive than common cotton '.
fibres. It is therefore possible to use it for producing a
very soft, non-woven cotton fibre web which, considering the
quality, would be able to compete on price with fibre webs
based on cellulose filares.
However, CLP consists of fibres that are very fine and very
short and also has a large content of unopened fibres or nits.
The above known plants and methods can therefore not be used
with a satisfactory result to produce a nits-free, homogenous,
non-woven fibre web of CLP-fibres and thermobinding fibres.
The object of the invention is to provide a method and a plant
of the kind mentioned in the opening paragraph, by means of
which a homogenous, nits-free, non-woven fibre web can 'be
produced on the basis of CLP-fibres and thermobinding fibres.
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A second object of the invention is to provide a non-woven
fibre web of the kind mentioned in the opening paragraph, that
has a homogenous and substantially nits-free structure.
A third object of the invention is to provide a use of Cotton
Linters Pulp (CLP) as base material for dryly producing a non-
woven cotton fibre web.
The novel and unique features of the method according to the
invention are the fact that a first air flow with short fibres
from a fibre source is generated, that the first air flow is
made to pass a first perforated screen having openings of a
size that mainly allow opened, but not unopened short fibres
to pass, that the first air flow is made to pass an air-
permeable first forming wire running endlessly during
operation and during this retaining a non-woven layer of short
fibres, that a second air flow with short fibres from the
fibre layer on the first forming layer is generated, that a
third air flow with long fibres from a fibre source of long
fibres is generated, that the second and third air flow are
made to pass a second perforated screen having openings of a
size that allow both short and long fibres to pass, that the
second and third air flow are made to pass an air-permeable
second forming wire running endlessly during operation, and
are made to settle as a fibre layer on the second forming
wire, and that a non-woven fibre web is made of this fibre
layer upon further treatment.
By using this method, a non-woven fibre web of short and long
fibres obtains a homogenous structure which at the same time
is nits-free when the unopened short fibres or nits are
extracted from the first perforated screen.
The novel and unique features of the plant according to the
invention are the fact that a separate fibre source belongs to
each" station, that the first station has a fibre collector
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placed under the screen of its at least one forming head, that
the second station has a forming wire placed under the screen
of its at least one forming head, and that the two stations
are connected by at least one conveyor for conveying fibres
from the fibre collector of the first station to the forming
head of the second station.
When the screen openings of the first station have a size that
fit the short fibres which e.g. can be CLP-fibres, and the
screen openings of the second station have a size that fit the
long fibres which e.g. can be thermobinding fibres, the plant
can be utilised for producing a non-woven fibre web having a
homogenous structure.
The first station is them fed short fibres whereas the second
station is fed both long fibres and short fibres having passed
the screen openings of the first station. The short and long
fibres thereby obtain being carefully mixed in the second
station and can thereby form a fibre layer having a homogenous
structure on the forming wire of the second station.
By means of the above arrangement, unopened fibres or nits. can
selectively be extracted from the first station so that the
resulting fibre web also becomes at least essentially free of
nits .
The conveyor connecting the first and the second station
together can be a belt conveyor but can in an advantageous
embodiment be a fibre feed duct connecting the fibre collector
of the first station to the forming head of the second
station. By means of a fan generating an air flow through the
fibre feed duct, the fibres are sucked from the fibre
collector of the first station up into the fibre feed duct in
order to then via this being blown 'into the forming head of
the second station.
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The fibre collector of the first station can be of any
expedient kind.
In an advantageous embodiment the fibre collector can quite
simply be the suction box of the first station whereby the
extraction from the suction box takes place by means of the
fibre feed duct which connects the two stations.
In a second advantageous embodiment the fibre collector can be
a forming wire which then acts as a travelling filter for
filtering off the short fibres from the air flow through the
screen openings of the first station.
The novel and unique features of the fibre web according to
the invention are the fact that it comprises a mixture of
thermobinding fibres and CLP-fibres screened of unopened
fibres or nits, and that it has a homogenous and nits-free
structure. Such a web has an extraordinarily great softness
which is wanted for many purposes. Furthermore, fibre webs on
cotton basis are good for the skin and non-allergenic.
The novel and unique features of the use according to the
invention are to use CLP as base material to produce a non-
woven air-laid cotton fibre web together with thermobinding
fibres.
A cotton fibre web based on conventional cotton fibres will be
to expensive for practical application due to the relatively
high price of these fibres. By using CLP as base material
instead, an inexpensive product is obtained having the same
advantages of the cotton fibre web based on conventional
cotton fibres.
However, the CLP fibres are relatively short and weak. The
strength of the web is therefore obtained by binding the
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fibres together by means of thermobinding fibres using the
method and plant according to the invention.
An especially good strength is obtained according to the
invention when the thermobinding fibres are bicomponent fibres
of the kind that each has a core consisting of a rather strong
material anal that is surrounded by an outer coating having a
lower melting point than the core.
During the production of the fibre web, the outer coating will
melt readily and effectively together with both each other and
the short and weak CLP fibres, and especially in nodal points
whereby the advantageous properties of the CLP cotton fibres
are' completely maintained whereas the core of the bicomponent
fibres transfers its great strength to the cotton fibre web.
The 'invention will be explained in greater detail below,
describing'only exemplary embodiments with reference to the
drawing, in which
Fig. 1 is a diagrammatic view of a first embodiment of a plant .
according to the invention,
fig. 2 is a diagrammatic view of a'second embodiment of a
plant according to the invention,
fig. 3 is a diagrammatic view of a third embodiment of a plant
according to the invention, and
fig. 4 is a diagrammatic view of a fourth embodiment of a
plant according to the invention.
In the following the invention is described on the assumption
that a homogenous and nits-free cotton fibre web of CLP-fibres
and thermobinding fibres is to be made.
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CLP has very fine and short fibres and also a large content of
unopened fibres or nits. Therefore, it has so far not been
possible in practice to use CLP for producing a cotton fibre
web of satisfactory quality.
The fine and short CLP-fibres are bound to the thermobinding
fibres in a manner known per se in order to thereby give the
fibre web the necessary strength. The resulting cotton fibre
web is relatively inexpensive to produce and has a very soft
structure. There is thus a considerable market for such a
product.
The plant according to the invention in fig. 1 has a first
air-lay station 1 for CLP-fibres and a second air-lay station
2 for both thermobinding fibres and CLP-fibres which have been
screened of nits in the first station. If the thermobinding
fibres are mixed with unscreened CLP-fibres, the result is,a
fibre web of unsatisfactory quality.
The main components of the first station 1 is a hammer mill 3
for defibrat.ing CLP from a roller 4, and a first forming head
5 having a first perforated base 6, a first set of rotatable
wings 7 placed in rows above the base 6, and a first suction
box 8 placed under the base 6.
ln~hen the first station is operating, the forming head 5 is
supplied with defibrated fibres from the hammer mill 3 via
first feed duct 9 having a first feed fan 10.
The wings 7 are sweeping the supplied CLP-fibres across the
base 8 in continuous flows. During this, the fibres are sucked
successively down into the suction box 8 via the openings 11
of the base 8 by a second feed fan 12 which is connected to
the suction box via the second feed duct 13.
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The openings 11 of the base 8 are arranged with a size ,that
allows the fine, short CLP-fibres to pass but not, the coarser
nits.
A return fan 14 serves for returning the nits to the hammer
mill 3 via a return duct 15 where the nits can be opened.
The screened fibres are collected in the suction box which
thus simultaneously acts as fibre collector.
The main components of the second station 2 are a fibre source
16 with a bale breaker 17 for breaking up the thermobinding
fibres from a bale of thermobinding fibres 18, and a second
forming head 19 having a second perforated base 20, a second
set of rotatable wings 21 placed in rows above the base 20, a
forming wire 22 placed under the base 20, and a second suction
box 23 placed under the forming wire 22 and via a suction duct
24 connected to a fan 25 for creating a negative pressure in
the suction box.
When the second station is operating, the second forming head
19 is supplied with screened CLP-fibres from the first suction
box 8 via the second feed duct l3 by means of the second feed
fan 12:
The second forming head 19 is simultaneously supplied with
thermobinding fibres from the fibre source 16 via a third feed
duct 26 with a third feed fan 27.
In the second forming head 19, the supplied with CLP-fibres
are mixed with the supplied thermobinding fibres. The second
set of wings 21 are sweeping the now mixed fibres across the
second perforated base 20 in continuous flows. During this,
the fibres are sucked successively down into a layer on the
forming wire 22 via the openings 28 of the base by means of
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the fan 25 which is connected to the suction box 23 via the
suction duct 24.
The openings 28 of the second base 20 are arranged with a size
that allow both CLP-fibres and thermobinding fibres to pass.
Thereby, a fibre layer of CLP-fibres and-thermobinding fibres
is made on the forming wire 22, said fibre layer has a
homogenous and nits-free structure. In a known subsequent
process (not shown), the fibre layer is finally converted into
the desired fibre web which among other things can be dust
bonded by means of of a layer of latex.
The plant according to the invention shown in fig. 2
corresponds essentially to the one shown in fig. 1 and
referred to above. Like parts are therefore designated by the
same reference numerals.
In this case, the fibre collector of the first station is
however a forming wire 29 acting as a travelling filter for
filtering off the CLP-fibres from the air flow through the
base openings 11 of the first station 1.
The CLP-fibres are sucked successively down onto the forming
wire 29 via the openings 11 of the first base by means of a
fan 30 which is connected to the suction box 8 via a suction
duct 31. An evenly distributed CLP-fibre layer 32 settling on
the forming wire 29 is successively conveyed with this wire
towards the inlet openings 33 of the second feed duct 13 and
supplied in a continuous flow into the second forming head 19
via the second feed duct 13 by means of the second feed fan
12.
This solution has especially the advantage that the feeding of
screened CLP-fibres in the second forming head 19 is
controlled very accurately, and that the resulting cotton
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fibre web therefore can obtain a very uniform structure in the
longitudinal direction.
The plant according to the invention shown in fig. 3
corresponds essentially to the one shown in fig. 2 and
referred to above. Like parts are therefore designated by the
same reference numerals.
In this embodiment both stations use a known forming head in
form of a drum-shaped screen 41 having horizontal brushes 42
for distributing the fibres over the screen. Each station has
two forming heads.
Moreover, the functioning of the embodiment shown in fig. 3 of
a plant according to the invention corresponds to the one
shown in fig. '2 and referred to above and will therefore not
be mentioned any further here.
Fig. 4 is a very diagrammatic view of a plant according to the
invention having a first station 34 with one forming head,35
for CLP-fibres placed above a forming wire 36, and a second
station 37 with three forming heads 38a,b,c for screened CLP-
fibres and other fibres placed above a joint forming wire 39.
The two stations are connected to a fibre conveyor 40 for, as
indicated by the arrows, conveying screened CLP-fibres from
the forming wire 36 of the first station 34 into the forming
heads 38a,b,c of the second station.
This plant can be used for producing cotton fibre webs having
a composition that varies in dependence of the fibres with
which the different forming heads of the second station are
supplied with.
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For example, the plant can be used for producing laminated
cotton fibre webs, and cotton fibre webs that also comprises a
powder for example SAP, and synthetic fibres such as PET.
Two different, known forming heads are mentioned above and
shown in the drawing that can form part of a plant according
the invention. However, this is only to be taken as an example
as the plant within the scope of the invention can function
with any other kind of forming head just as two or several
different types of forming heads can form part of the same
plant.
The invention is furthermore described on the'assumption that
the short fibres forming part of the fibre web according to
the inventions are CLP.
This is also only to be taken as an example as the method and
the plant according to the invention advantageously can, be
used to produce fibre webs having a content of other types of
short fibres, for example cellulose fibres.
The first air-lay station of the plant can furthermore have
more than one forming head for short fibres.
The first station can thus have one forming head for short
cellulose fibres and a second for CLP-fibres whereby a
homogenous, nits-free, non-woven cotton fibre web can be
produced that has an acceptable softness and is relatively
inexpensive.
A web having the advantageously soft properties of the
relatively short and weak CLP fibres and the advantageously
great strength of the thermobinding fibres can for example be
obtained with the following compositions.
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Example 1. A fibre web consisting of 60 weight percentage CLP
fibres and 40 weight percentage thermobinding fibres.
Example 2. A fibre web consisting of 95 weight percentage CLP
fibres and 5 weight percentage bicomponent fibres.
Example 3. A fibre web consisting of a multilayer; for example
a three-layer product where the top and base layer consist of
60 weight percentage CLP-fibres and 40 weight percentage
bicomponent fibres. The middle layer consists of 95 weight
percentage CLP-fibres and 5 weight percentage bicomponent
fibres but can just as well comprise SAP, SAF or pulp within
the scope of the invention.
