Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02482107 2006-06-30
HIGHLY COMPRESSED FILTER TOW BALE AND METHO[)
FOR THE PRODUCTION THEREOF
The invention pertains to a packaged, highly compressed bale of filtE~r tow in
block form without any interfering bulges or constrictions in the top or
bottom of the
bale and to a process for its production.
In the production of fiber tow for use in making filter rods for the cigarette
industry, the tow is laid in so-called "filling cans". During this process,
the filter tow
is distributed in uniform layers over the cross-sectional area of the can by
the
movements of a laying unit, which moves alternately in the lengthwise and
crosswise direction. As a result, a large number of layers are laid on i:op of
each
other until the filter tow package has reached the desired weight and height
in the
can. Package weights of several hundred kilograms are conventional in this
area.
A highly compressed bale and a process for the optimal filling of a can for
the
purpose of avoiding consequent processing problems is described in WO
02/32,238 A2.
The content of the can which has been filled in this way is then compressed
in the direction in which the layers were superimposed. After it has been
compressed, the filter tow package is wrapped with packaging material while
still
inside the pressing device and therefore still under compressive stress. The
pressing device is ttien opened completely, so that the filter tow package,
now
called the "bale", is held together by the packaging material. Conventional
packaging materials include cardboard, which is held mechanically together by
strapping or by an acihesive, and synthetic fabric, which is closed by, for
example,
a Velcro fastening. An example of a glued package is described in German
Utility
Patent No. 76-35,849.1. Information on a filter tow package wrapped with
synthetic fabric can be found in the company prospectus "Some Useful
Information
about the Reusable Packaging for Rhodia Filter Tow", published by RHODIA
Acetow GmbH, Engesserstrasse 8, D-79108 Freiburg. The two latter types of
packaging require no additional strapping.
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CA 02482107 2006-06-30
The types of packaging described above which do not make use of any
strapping suffer from the problem that, after the pressure on the bale has
been
released at the end of the pressing operation, the elastic restoring force of
the
compressed filter tow leads to a pressure on the packaging, this pressure
being
exerted primarily in the direction opposite that in which the bale was
compressed.
This leads to an increase in the volume of the package and thus to undesirable
bulges at the top and bottom of the bale. If the measures described in WO
02/32,238 A2 are taken, these bulges do not interfere with the intended use of
the
filter tow, but they do prevent the filter tow packages from being stackeci
securely.
This problem is solved in the state of the art either by stacking the bales on
their
sides or by the use of special pallets, such as those described in the Rhodia
publication cited above. Problems associated with the bursting-open of the
packages because of excessive internal pressure also occur frequently.
A solution to the difficulties associated with strapping is described in US-A
4,577,752. In cases where filter tow which has been packaged with straps is
used
as intended, the bulges are less of a problem than the constrictions, which
cause
the variations in puff resistance described in WO 02/32,238 A2. And even
strapped bales can burst open. It is also standard practice in the packaging
of filter
tow to use inliners between the filter tow and the above-mentioned
mechanically
supportive packaging materials. The inliner protects the filter tow from
contamination, especially from odor contamination, and from the diffusion of
water
vapor into and out of the package. The inliner usually consists of three
pieces,
which are laid loosely inside the external packaging.
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CA 02482107 2008-05-06
The task of the invention is to provide a highly compressed bale of filter
tow in ideal block form without the bulges which interfere with the transport
of
the bales and without the constrictions in the top and bottom of the bale
which
interfere with the pay-out of the filter tow, where the compressive load to
which
the packaged filter tow is subjected is reduced, so that in particular the
bursting-
open of the package under the effect of internal pressure can be almost
completely avoided. The task of the invention is also to provide a
corresponding
packaging process.
These tasks are accomplished according to the invention by a block-
shaped bale of filter tow and by a process as claimed hereinafter.
So, the object of the invention is a packaged, highly compressed bale of
filter tow in block form without interfering bulges or constrictions in the
top and
bottom of the bale, wherein:
(a) the bale has a packing density of at least 300 kg/m3;
(b) the bale is completely wrapped by a mechanically self-supporting,
elastic packaging material, where this material has one or more joints which
are
air-tight with respect to convection;
(c) the top and bottom of the bale are so flat that, when the unopened
bale is placed on a horizontal surface, a flat plate completely covering the
bale
can be pressed onto the top of the bale by a force of 100 N acting in the
normal
direction on the center of the bale with the result that, within the largest
rectangle which can be inscribed in a vertical projection of the bale onto the
pressed-on plate, at least 90% of the area of the top surface of the bale
which is
located within the inscribed rectangle is no more than 40 mm away from the
flat
plate; and
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CA 02482107 2008-05-06
(d) the bale has a height of at least approximately 900 mm.
More specifically, the object of the invention as claimed is a packaged,
highly compressed bale of filter tow in the form of a block without
interfering bulges or constrictions in the top or bottom surface of the bale,
said bale of filter tow comprising:
- a plurality of layers of filter tow material defining an upper side and
a lower side of the bale, said filter tow material having a packing density
of at least 300 kg/m3; and
- a resilient elastic packaging material fully enclosing said bale in a
mechanically self-supporting manner, wherein said packaging material
has one or more joints which are air-tight with respect to convection,
wherein said upper side and said lower side of the bale are substantially
planar, the planarity of said upper and lower sides being defined, such
that when said lower side of a bale is placed on a horizontal surface, a
flat plate can be pressed onto said upper side of said bale by a force of
100 N acting in the normal direction on a center of said bale wherein
within the largest rectangle which can be inscribed in a vertical projection
of said bale onto the pressed-on plate, at least 90% of the area of said
upper side of said bale which is located within the inscribe rectangle is
less than 40 mm from the plate;
wherein said bale has a height of at least 900 mm;
wherein, in the packaged bale, a negative pressure of at least 0.01 bar
relative to an outside pressure is present at least immediately after the
bale has been packaged, wherein said packaging material maintains said
negative pressure and equalizes pressure gradients at said upper and
lower sides of the bale, and
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CA 02482107 2008-05-06
wherein said negative pressure reduces the pressure which the elastic
restoring force of the filter tow material exerts on the packaging from the
inside such that said planarity of said upper and lower sides is achieved
without any additional wrapping straps or transport packaging of
cardboard or synthetic fabric.
At least after packaging, a negative pressure of at least 0.01 bar versus
the outside pressure is present in the bale.
The disadvantages of the transport packaging normally used today have
already been discussed above in the description of the state of the art. It is
especially the bulges at the top and bottom of the bales which interfere with
transport in two layers. This problem has been solved in the past by
transporting the bales not in their so-called working position but rather in a
sideways storage position. Two additional work steps are required to do this,
however; namely, the bale must be turned 90 before transport and then turned
back into the working position after transport. The constrictions which are
formed by strapping are also a source of trouble. Even when the bale is used
as
intended, these constrictions cause considerable variations in the puff
resistance of the filter rods produced from the filter tow. More than 5% of
the
filter rods produced from a bale are affected by these variations. The greater
the packing density of the bale, the greater the severity of these two
problems.
The problems occur as soon as the packing density exceeds 300 kg/m3.
After a series of failed experiments, the surprising discovery was made
that it is possible to prepare a block-shaped bale without the bulges which
interfere with transport and without the constrictions which interfere with
the
intended use of the filter tow by sealing the packaging air-tight during the
packaging process. On the basis of practical considerations, therefore, a bale
according to Claim 1 is completely wrapped with a mechanically self-
supporting,
elastic packaging material, this material having one or more joints which are
air-
tight with respect to convection.
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Upon a preliminary, superficial analysis, it might appear that the bale
according to the invention is a vacuum-packed bale and thus a vacuum package
such as that familiar to all consumers on the basis of daily experience. This
is
not the case, however. The goal to be achieved with the block-shaped bale
according to the invention is to create a defined shape. The air-tight
packaging
has the task
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CA 02482107 2006-06-30
of absorbing and equalizing the pressure gradients which occur at the top and
bottom of the bale during the production process. It turned out that it was no
longer necessary to impose requirements on the packaging with respect to its
mechanical strength, its permeability to air and moisture, etc. It was found
instead
that the bale according to the invention would retain its properties even if
the
previously air-tight material were to be perforated over large areas after the
packaging process. On the basis of practical considerations, such ari
aciditional
measure will not be taken.
The geometry of the bale according to the invention is described by feature
(c) of Claim 1. The distance of the individual points on the top surface of
the bale
from the plate can be determined, for example, by using a transparent plate
and by
determining the distances between the individual points and the plate by
measuring the reflections. As an alternative, any other continuous method of
distance measurement can also be used. Within the scope of the principle
according to the invention, it is especially preferred for 90% of the area of
the top
surface of the bale which lies within the previously mentioned inscribed
rectangle to
be no more than approximately 25 mm, preferably no more than approximately 10
mm, away from the flat plate.
In regard to the packing volume of the bale, it is has been found
advantageous for the bale to have a volume of more than 0.9 m3 and/or for the
packing density to be more than 350 kg/m3 and especially to be less than 800
kg/m3. In connection with the loading of the packages into containers, it is
has
been found to be especially suitable for the bale to have the form of a block
with a
height of at least approximately 900 mm, preferably of at least approxirnately
970
mm. In this case the bales can be stacked in double layers in the container.
Packaged blocks with heights of 970-1,200 mm are especially favorable, since
such blocks can be placed in the form of individual stacks in the containers.
It is
also possible to produce much taller bales, which reduces the packaging work
relative to the amount of fibers to be packaged. In cases where the packaged
material is filter tow, these large packages offer the advantage that, whc:n
the filter
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CA 02482107 2008-05-06
is used to produce cigarette filters in a filter rod machine, it is necessary
to
replace the bale only rarely.
The packaging wrapper is preferably made of a plastic film. The
convectively air-tight joint is made as a convectively air-impermeable seam,
which is advantageously designed as a heat-sealed overlapping or finned seam.
The film consists preferably of polyethylene, especially LDPE, of modified
polyethylene (LLDPE), or of a laminated film including a layer of polyamide
and
a layer of polyethylene. For advertising and aesthetic purposes, colored or
printed film can be used as the packaging film. This is especially advisable
when the filter tow to be packaged is sensitive to light. The film can also be
provided with adhesive labels, which provide information on the content of the
package, for example. Another possibility of allowing the package to convey
information is to impress a relief into it, which is visible through the film,
which
conforms tightly to the surface of the package as a result of negative
pressure.
In addition to the name of the product, the relief can also contain a company
and/or customer logo. The film preferably has properties which make it a
reliable transport packaging material. This is why films with thicknesses in
the
range of 100-400 pm are used in particular. If desired, a transport packaging
of
cardboard, synthetic fabric, etc., can be placed around the film after the
package
wrapping or film itself has been sealed, that is, after the block-shaped bale
has
been completed. This transport packaging can then be strapped as well. As a
result, the mechanical stability of the packaging is increased, so that
thinner and
therefore less expensive film can be used. It must be emphasized, however,
that transport packaging of this type is not mandatory within the scope of the
invention.
The process for packaging a filter tow bale according to the invention
comprises the following steps:
(a) the filter tow is prepared in compressed form;
(b) the compressed filter tow is wrapped with packaging film;
(c) the package wrapper is sealed in an air-tight manner; and
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CA 02482107 2008-05-06
(d) the load on the wrapped bale is released; and
(e) a negative pressure which is at least approximately 0.01 bar versus
the outside pressure is produced inside the packaging wrapper from which the
load has been released, wherein said packaging wrapper maintains said
negative pressure and equalizes pressure gradients at upper and lower
sides of the wrapped bale, and wherein said negative pressure reduces
the pressure which the elastic restoring force of the filter tow material
exerts on the packaging from the inside such that said planarity of said
upper and lower sides is achieved without any additional wrapping straps
or transport packaging of cardboard or synthetic fabric. When the load on
the bale, which has been sealed air-tight, is released, a negative pressure
develops inside the package wrapper, which is preferably at least 0.01 bar and
which according to an especially advantageous method is in the range of 0.15-
0.7 bar.
Because of the air-tight seal of the package wrapper, the negative
pressure thus produced inside the region surrounded by the wrapper can be
maintained. This negative pressure reduces the pressure which the elastic
restoring force of the flexible material exerts on the packaging from the
inside.
For this reason, the bulges which normally develop on the filter tow bales
according to the state of the art are avoided. It thus becomes much easier to
stack the packaged bales thus produced. Because the mechanical pressure
acting from the inside on the packaging is reduced (by the negative pressure),
the risk of failure or the tendency of the packaging to rip open is also
reduced. A
higher packing density can thus also be achieved, which leads to the advantage
of more compact packages and thus to the ability to reduce the storage and
transport volumes. In particular it is possible in this way to make optimal
use of
the holding capacity of containers, in which such packaged filter tow is
stored.
The provision of filter tow in compressed form is usually accomplished
with the help of known pressing devices. The process according to the
invention
can be conducted in such a way that the quantity of filter tow intended for
the
package is first mechanically compressed in the pressing device and then
7
CA 02482107 2008-05-06
wrapped with the package wrapper. In this case the package wrapper is sealed
while it is still inside the pressing device. This embodiment offers the
advantage
that the entire process is completed at a single location.
It is also possible to compress the filter tow at a separate station as a
preparatory step. In this case, the precompressed filter tow is provided with
"auxiliary packaging", which can consist of retaining clamps, for example, and
then
7a
CA 02482107 2006-06-30
sent to the packaging station, where the auxiliary packaging is removed, the
compressed filter tow is wrapped with the package wrapper, the negative
pressure
is produced, and the package wrapper is sealed air-tight. This embodimerit
offers
the advantage that the pressing device can have greater availability, because
the
entire process is not completed at its location. In addition, the duration of
the
pressing cycle is decreased, and there are more degrees of freedom available
with
respect to the application of the package wrapper, because the compressed bale
is
accessible from all sides in the packaging station.
In contrast to the state of the art, the use of the process according to the
invention makes it possible to eliminate the inliner intended to protect the
bale from
contamination and water vapor, because these tasks are already accomplished by
the wrapper used as packaging.
The negative pressure required initially in the process according to the
invention can be obtained in various ways. According to an especially simple
embodiment, the negative pressure is generated by the expansion of the
compressed filter tow material. After the filter tow has been wrapped in the
compressed state with the package wrapper and this has been sealed air-tight,
the
external pressure on the packaged material is released. As a result, the
material
expands inside the package under the action of its own elastic restoring
force.
Because of the increase in the volume of the package, a negative pressure
develops inside the region surrounded by the wrapper. The packeige size is
preferably selected so that the compressed filter tow cannot expand
completely,
that is, so that the filter tow inside the wrapper is still compressed to a
certain
degree inside the package even after its partial expansion. This embodiment
has
the advantage that no additional means are required to generate the negative
pressure. It therefore represents an especially low-cost possibility.
According to another embodiment, which can be used as an alternative or
as an addition to the previously described variant, the negative pressure is
produced by exhausting air from the interior area surrounded by the wrapper.
In
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CA 02482107 2006-06-30
this way, a vacuum higher than the "natural" vacuum described above can be
obtained. It is also possible by this method to adjust the desired negative
pressure
with a high degree of accuracy.
The air can be exhausted by means of, for example, one or more vacuum
pumps. These are first connected on the suction side to the intE:rior' of the
otherwise air-tight package and then put into operation. After the desirf:d
riegative
pressure has been reached, the pumps are disconnected from the package, and
the exhaust connection points in the packaging wrapper are sealed air-tighi:
again.
A combination of the two previously described embodiments offers the
advantage that the evacuation times can be kept short, because the riegative
pressure is obtained by two different measures, which can be performed
simultaneously. In addition, the necessary compression forces are smaller,
because a larger packing height can be selected, where the term "packing
height"
refers to the height of the filter tow bale after it has been sealed air-tight
in the
device used to compress the filter tow. Finally, it is possible in this way to
regulate
the height of the filter tow bale with good accuracy. As a result, external
influences
such as those associated in particular with the seasons, with titer, and vvith
weight,
etc., can be moderated.
In the process according to the invention, a negative pressure of
approximately 0.15 bar to 0.7 bar below ambient pressure is preferably
produced.
This corresponds to an absolute pressure of approximately 0.85-0.3 bair inside
the
film-wrapped volume. The vacuum in question is therefore in the "Iow vacuum"
range, which is usually completely sufficient for the process accorcling to
the
invention. A negative pressure of approximately 0.2-0.4 bar, corresporiding to
an
absolute pressure of approximately 0.8-0.6 bar, has proven to be especially
suitable. The choice of the concrete range for the negative pressure depends
on
various parameters, especially on the type and quantity of the material to be
packaged, on the desired packing density, on the package wrapper used, etc. In
principle, it must be remembered that the stronger the vacuum or negative
9
CA 02482107 2006-06-30
pressure, the more compact the packages which can be obtained. Increasing the
negative pressure also has the effect of reducing the bulges. It must also be
taken
into consideration, however, that choosing a higher vacuum Ieads to a
disproportionate increase in the time required to achieve that desired
negative
pressure.
As far as the packaging wrapper used in the process according to the
invention is concerned, it should be selected so that the desired stability of
the
produced negative pressure over time and the desired mechanical stability of
the
packaging are guaranteed. Depending on the type of packaged material and on
the manner in which it is used, the desired stability over time will usually
vary
between a few days and several months or even years. Accordingly, filrns with
different air permeabilities can be used.
According to one embodiment, preferably a film of polyethylene or modified
polyethylene such as LLDPE or LDPE can be used as the package wrapper. LDPE
is low-density polyettiylene, which is produced under high pressure; LLDPE is
the
designation for low-density polyethylene with a linear structure. A plsistic
film of
this type offers the advantage that it is a pure material and can be obtained
at low
cost. A sheet of polyethylene, however, is not very strong and is therefore
suitable
especially for relatively low packing densities and small quantities of
packaged
material. Because of the relatively high permeability to air of standard
polyethylene
film, it is more suitable for uses in which the storage time does not exceed a
few
weeks.
As an alternative, it is possible advantageously to use a laminated filrn made
of polyamide and polyethylene as the package wrapper. This laminate is
characterized by a very low degree of permeability to air and by high
strength,
which means that the negative pressure can be kept constant over a long
period.
The polyamide layer preferably represents approximately 1/3 of the laminate,
the
polyethylene layer approximately 2/3.
CA 02482107 2006-06-30
The gas permeability of the package wrapper or film to air is preferably less
than 10,000 cm3/(m`' * d"' bar), preferably less than 200 cm3/(m2 * d" bar),
and
even more preferably less than 20 cm3/(m2 * d * bar). These values are
measured
according to DIN 53,380-V at 23 C and 75% relative humidity. As a result, it
can
be guaranteed that the vacuum will last for a sufficient length of time and
that the
package will not become loose and will remain as compact as possible. This
range, furthermore, is covered by standard commercial films (e.g., PA-PE
laminates). It must be emphasized that no air is transported by convection
through
the film; mass transport occurs only via diffusion across the film. The values
indicated for permeability are based on a composition analogous to ambient air
(approximately 78% N2, 21 % 02, 1% other gases). The only important values are
those pertaining to the permeability for oxygen and nitrogen. In addition to
films, it
is also possible within the scope of the present invention to use other air-
tight
materials which fulfill the above conditions.
The permeability of the film or other wrapping material to water vapor' should
preferably be less than 5 g/(m2 * d), preferably less than 2 g/(m2 * d),
measured
according to DIN 53,122, Part 2, at 23 C and 85% relative humidity. The
permeability to water vapor is not relevant to the shape-giving function of
the
packaging, but a packaging which is impermeable not only to air but also to
water
vapor offers the advantage that the product moisture content of the filter tow
remains preserved by such a packaging. This is very important in the case of
filter
tow. Thus the moisture content will equalize over the bale, and there will be
no
exchange of moisture with the environment. Polyethylene films with a thickness
of
100 pm have an approximate water vapor permeability of 1 g/(m2 * d).
In regard to the mechanical strength, the package wrapper or film should
advisably have a tear strength of at least approximately 10 N/15 mm,
preferably of
more than 100 N/15 mm, and even more preferably of more than 200 N/15 mm,
measured according to DIN EN ISO 527-3. Each of the cited values pertains to
the
minimum tear strength value in the longitudinal and transverse directions of
the
film. The concrete selection with respect to tear strength will be made as a
function
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CA 02482107 2006-06-30
of whether or not the film-wrapped bale will be repackaged for transport. In
this
context, possible materials include PE with a tear strength of 15-30 N/15 rnm
at a
thickness of 100 pm and PA6 with a tear strength of 150-300 N/15 rrim at a
thickness of 100 pm.
In general, plastic films with air-barrier layers such as layers of polyamide,
polyester, or ethylene-vinyl alcohol copolymer (EVOH) or with a metal oxide
coating such as a coating of SiOX, aluminum oxide, etc., and aluminuni foils
have
been found to be especially advantageous. This list of films is not to be
considered
exhaustive, however. Because of the impermeability of the film to air, aroma
protection, that is, protection against the intrusion of aromas from the
outside, is
also afforded, which can be advantageous for various types of packaged
materials.
A certain toughness is important for the mechanical stability of the film.
This
property is offered especially by polyamide.
One possibility of obtaining an air-tight seal of the package wrapper or film
is
to weld or to heat-seal it. Accordingly, the selected film should preferably
be
weldable or heat-sealable. In this regard, favorable film materials are those
with
low melting points. For example, polyolefins such as polyethylerie and
polypropylene or copolymers with ethylene and propylene such as EVA, LLDPE,
etc., can be mentioned here. Materials which satisfy the prerequisite of
weldability
or heat-sealability are called the "sealing layer" in the following. A film
can consist
possibly of a sealing layer of this type alone or of a laminate consistinca
of'
one or
more sealing layers and additional layers, which are designed to provide, for
example, the mechanical strength.
To ensure that the packaging can be opened easily, the sealing layers can
be "peelable"; that is, they can be sealed in an inhomogeneous manner. An
inhomogeneous sealing layer of this type can be produced in various ways, such
as by adding polybutylene at certain points to the sealing layer or by sealing
polypropylene against LLDPE. Another possibility of facilitating the opening
process consists in providing a tear-open strip in the packaging film. This
12
CA 02482107 2006-06-30
=
possibility is especially intended for films of low toughness. Finally,
projecting
corners or the like can be provided, which are intended to be cut off when
package
is to be opened. After the projecting corner has been cut off, air can pass
into the
interior of the package, and the package becomes loose. Then it can be opened
easily with a film-cutting knife without causing damage to the package
conte:nts.
As an alternative, the packaging wrapper or film can be sealed by an
adhesive. This embodiment offers the advantage that there is no need for a
heat-
sealing device. Of course, other suitable methods for sealing the packaging
film
can also be used as long as they provide the desired properties with respect
to
leak-tightness and also with respect to mechanical tensile strength requirecl
for the
area of application in question.
The heat-sealing or welding can be accomplished, for example, in such a
way as to form an overlapping seam. An overlapping seam can absorb
comparatively high tensile forces and thus hold the packaged material together
reliably even in the freshly packaged state and even if the package should
have a
leak and thus the full elastic restoring force of the material acts on the
packaging
from the inside. This type of closure is thus very secure, and the film in
this case
should advisably have a heat-sealing layer on both sides (or consist
exclusively of
such a heat-sealing layer).
According to another embodiment, the welding or heat-sealirig can be
accomplished in such a way as to form a finned seam, which is known to the
expert
in the area of film processing. This offers the advantage of being easy to
produce
from the outside, but the ability of such a seam to withstand tensile stresses
is less
than that of the overlapping seam.
The packaging wrapper or film can be designed in the form of, for example,
a one-piece bag. The prepared filter tow in this case is wrapped in a manner
similar to that in which a piece of candy is wrapped. As an alternative, the
film can
consists of a bottom, a top, and a circumferential collar. In this case, the
overall
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-
length of the joint seams is increased, because the individual parts must be
joined
together. According to another preferred embodiment, the film packaging
consists
of a top and a bottom, which can possibly be fabricated, that is, deep-drawn
or
made into a bag, etc., before use. Finally, there is also the possibility of
cutting the
film into two interlocking pieces in tennis ball fashion. It would also be
possible to
imagine other suitable ways of designing a film packaging within the scope of
the
invention.
If desired, the final sealing of the package wrapper or film, 1:hat is, the
completion of the film packaging, can be followed by repackaging thE: bale
with
cardboard, synthetic fabric, etc., which is placed around the film. This has
the
result of increasing the mechanical strength of the packaging, so that thinner
and
thus less expensive films can be selected. It must be emphasized, however,
that
repackaging of this type is not mandatory within the scope of the invention.
When external repackaging is used as described above, it is possible for the
film packaging to be designed intentionally with less air-tightness, so that
the
negative pressure is equalized within one to two days with respect to the
ambient
pressure. In other words, the package "loses" its vacuum within this period.
The
packaged filter tow thus expands into the external packaging, but in
comparison
with filter tow packaged according to a process of the state of the art, its
has less
pronounced bulging at the top and bottom of the package.
The film used in the process according to the invention preferably has a
thickness of approximately 100-400 pm, where a range of 200-300 pm and
especially of 250-300 pm has proven to be especially suitable. The exact
thickness of the film used will be selected as a function of the size and the
weight
of the fiber material to be packaged, of the degree of compression, that is,
of the
packing density, and of the type of film material used. As already explained
above,
a somewhat thinner film can possibly be selected when additional external
packaging, especially an outer packaging of cardboard, is used.
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The compressible filter tow to be packaged is thus in particular made
available in the optimal block form. As a result, packages can be obtained
which
are especially easy to stack and to handle and easy to store. The filter tow,
which
is in the form of cables, is preferably laid in layers, one on top of the
other, as
already described in connection with the process according to the state of the
art.
The invention is explained in greater detail below on the basis of a preferred
embodiment with reference to the attached drawing:
- Figures 1 a-1 c show the individual steps of an embodiment of the process
according to the invention;
- Figures 2a and 2b show an elaborated form of the package obtained
according to the process of the invention;
- Figure 3a shows a graph, which represents the change over time in the
properties of a package obtained according to the process of the invention
with the
use of polyethylene film;
- Figure 3b shows a graph similar to that of Figure 3a, which applies to a
laminated film of polyethylene and polyamide;
- Figure 4a shows various curves which illustrate the relationship between
the packing height and the height of the bale for various negative pressures;
and
- Figure 4b shows various curves which illustrate the relationship between
additional vacuum and the height of the bale at elevated temperature and
reduced
air pressure.
A bale of a compressible, flexible, fibrous material 1, which is filter tow in
the
present case, is wrapped with a film 2 and introduced into a pressing device
3, as
can be seen in Figure 1 a. In the pressing device 3, which is able to exert a
pressure of, for example, 300-400 tons, the bale is compressed to the desired
packing height . Then the film 2 is sealed air-tight except for small area,
which
serves as a connection point for the suction hose of a vacuum pump 4, such as
a
sliding vane rotary pump or the like. The interior of the region wrapped by
the film
2 is then evacuated by the vacuum pump 4 to a desired negative pressure. Once
this has been reached, the hose of the vacuum pump is disconnected from the
film,
CA 02482107 2006-06-30
and the connecting point is sealed air-tight. As previously mentioned, the use
of a
vacuum pump can be omitted if only a small degree of negative lpre ssure is
desired, such as that which can be obtained by the expansion of the bale.
In the next step, shown in Figure 1 b, the pressing device 3 is opened. The
bale thus expands again to the extent allowed by the size of the film
packaging.
The filter tow bale in its finished packaging can now be removed from the
pressing
device and is in a state in which it can be transported and stored, as
indicated in
Figure 1 c. The height of the packaged bale depends on various factors,
iricluding
the strength of the vacuum which was produced.
Figures 2a and 2b show another stage of the process according to the
invention, namely, the optional provision of the packaged filter tow bale with
external packaging 5. This can be provided in particular for the purpose of
transport and can consist, for example, of light-weight cardboard. These types
of
outside packaging materials are known to the expert and thus do not need to be
explained in detail here.
Figures 3a and 3b show graphs which represent the change over time in the
properties of packages produced by the process according to the inverition
based
on the use of a film of polyethylene and of a laminated film of
polyetl''lylene and
polyamide The polyethylene film of Figure 3a has a gas permeability of
approximately 600 mI/(m2 * d * bar), whereas the gas permeability of the
laminated
film of Figure 3b is only about 10 ml/(m2 * d * bar). As can be deriwed from a
comparison of the two graphs, the negative pressure produced in the case of
the
laminated film remains essentially constant over the course of several hundred
days, as does the height of the bale. In contrast, the negative pressure in
the case
of the bale wrapped in polyethylene film has already decreased by half after
only a
little more than 100 days, whereas the height of the bale has increased by
more
than 10 cm in the same time period. If the bales are to be stored for up to
two
years or more, the laminated film is therefore to be preferred despitE: its
higher
cost.
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As can be seen in Figure 4a, the height of the bale can be decreased by
increasing the strength of the vacuum. Three different curves are sl-iown in
the
figure. The one at the top shows the achievable height of the bale as a
function of
the packing height without the use of a vacuum pump. The curve in the middle
shows the results obtained when an additional vacuum of 0.1 bar is applied,
and
the curve at the bottom shows the results obtained with an additional vacuum
of
0.1 bar. Filter tow of type 3Y35 with a bale weight of 580 kg was processed at
a
pressure of 370 tons. Under these conditions, an additional vacuum of !0.1 bar
can
be produced reliably in about 60 seconds.
Figure 4b shows the height of the bale under modified ambient conditions as
a function of the strength of the additional vacuum, where the air temperature
was
approximately 40 C and the pressure of the ambient air was approximately 0.05
bar higher than in the example of Figure 4a. It can be seen that the height of
the
bale increases at lower air pressures and higher temperatures.
A laminated film of polyethylene and polyamide with a thickriess of
approximately 200 pm was used in the exemplary embodiment described above.
The film was heat-sealed by hand with a sealing device, where a collar part
was
joined to a top and a bottom element, each of which was pretrimmed in the
press.
The pressing force was 370 tons in all cases. The packaging costs could be
considerably reduced by means of the process according to the invention.
According to another experiment, a bale of the same weight with a packing
height of 900 mm was wrapped in a laminated film of polyamide and
polyel:hylene,
which was then welded shut. After the pressing device was opened, the height
of
the bale was 970 mm. There were no bulges anywhere in the packaged bale. By
virtue of the increase in the volume of the air inside the bale, a negative
pressure
of 0.12 bar, corresponding to an absolute pressure of 0.88 bar, was reached.
This
negative pressure was achieved without the help of a vacuum pump.
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In another experiment, a bale of the same weight with a packirig height of
900 mm was wrapped in a laminated film of polyamide and polyethylene, which
was then welded shut. The interior of the package was evacuated by means of a
vacuum pump to a negative pressure of 550 bars, corresponding to an absolute
pressure of 450 bars. After the pressing device was opened, the height of the
bale
increased to approximately 930 mm. The pressure in the interior of ttie
package
was calculated at 0.42 bar, corresponding to a negative pressure of 0.58 bar.
Again, there were no bulges in the packaged bale.
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