Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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UHLM 205--PCT--PFF/WG~7
SELF-VENTING BAG AND METHOD FOR FILLING IT
The invention relates to a self-venting bag for filling with fincly
dividëd material such as powders, grains, flakes, fibers,
especially materials of light bulk weight.
The packing of granular, powdered or fibrous materials has in
recent years become increasingly mechanized and automated,
especially for the purpose of saving labor and time and of using
automatic packing machines. This mechanization and automation
creates requirements for the bags or sack-like packaging media,
some of which conflict with one another.
For example, in automatic packing machines it is desired always to
shorten the cycle time of the apparatus and hence to increase the
utilization and effectiveness of the machinery which often requires
considerable investment. An impediment to this is that in the
packing process air or other gaseous substances are aarried with
the materials, which inflate the bags and the trapped air can
escape only slowly. Attempts have been made in all kinds of ways
to remedy this problem, for example by designing the automatic
packing machines with air escape vents on the filler spout of valve
bag fillers, or by the creation of small holes in the bag material-
-the so-called "needling" of the material, so that the result is
a eelf-venting bag.
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UHLM 2 0 5 -PCT-PFF/WGW
This has not produced a satisfactory solution of the problem
because, for example in the case of automatic valve-bag filling
machines the difficulty involved in removing the air necessary for
the movement and control of the materials being packed is great,
apparatus for the purpose is troublesome, and ventilation problems
are created because when the air is removed finely divided material
is carried with it and trapping it is difficult. In the case of
needling the material of which the self-venting bag is made, there
are limits to the openings for the escape of the air, because in
the needling of, for examplel film material or kraft paper, the
penetration of finely divided material such as flour must be
prevented. ~ery small holes, on the other hand, clog too rapidly,
so that the intended effect of removing entrained air quickly i5
not achieved.
These problems are especially great in the case of materials in
powder or fiber form of great specific surface area, because the
powders or fibers bind a great amount of air -to-themselves. Flour,
cellulose powders, silica gels, textile fibers, down, and similar
materials are typical examples. The adhesion of air or other gases
that are sometimes used in packaging has the additional advantage
that the bags first remain puffed up like balloons and are
difficult to carry and stack, but on the other hand they are
UHLM 2 05-PCT-PFF/WGW
insufficiently filled, much package space is wasted, and because
of the empty space the bags are unsightly and hard to transport and
stack.
There is therefore an urgent need for a self-venting bag which does
not have these disadvantages, permits time-saving and space-saving
filling of bags, allows full use to be made of the space offered
by the shape of the bag, and makes the bags easier to transport and
stack in a safe and space-saving manner. Furthermore the bag must,
of course, have sufficient strength to withstand the filling
pressure of an automatic filler as well as the weight of the
material being bagged. Since these problems are especially severe
in the case of valve bags, since short time cycles are desirable
when filling them, the invention will be further explained below
in connection with a valve bag, but will not be limited to this
special example. The self-venting bay is important and
advantageous even in the case of other methods of filling bags,
such as filling bags from screw conveyors, or even shoveling the
material into they by hand.
Since the problems pointed out exist to a special degree in the
case of finely divided materials of low specific weight, as
mentioned before, the invention will be explained also with
UHLM 205-PCT-PFF/WGW
reference to examples of this kind. The advantages, however, exist
also in the case of other materials such as Portland cement.
Surprisingly, the characteristics and qualities outlined above ca-n
be achieved and the stated problem can be solved with a self-
venting bag which consists wholly or partially of nonwoven fabric
that is permeable to air and gas, and whose air and gas
permeability is so great that air or gases which blow back during
filling can escape through the nonwoven fabric.
What particular characteristics of air permeability and other
properties must be provided by the nonwoven fabric required for
making the bag in accordance with the invention depends on a number
of interlinked and interdependent factors. This has to do on the
one hand with a whole series of factors relating to the material
being bagged, such as particle siæe, specific weight, temperature,
net content and weight, and any chemical and physical aggressivity
~hat might be involved. The nonwoven fabric of a bag for cement
of very great specific weight and a comparatively high temperature
produced by the milling that precedes bagging will of course
require greater strength rating, greater thickness and greater
weight per unit area than a bag to be filled with down or silica-
gel.
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ll~LM 205-PCT-PFF/WGW
On the other hand, the properties of the nonwoven material used are
interr~lated, such as air permeability, weight per unit area,
thickness of the nonwoven material, its pore size and the number
of pores, the kind of nonwoven material used, and the binding of
its fibers or the bonding method used, so that for these properties
only wide ranges can be given within which a choice must be made
for the particular purpose.
As regards air permeability, one preferred range is 100 to 3000
l/m2/s, measured in accordance with DIN 53887, and the range from
400 to 2000 l/m2/s has proven especially advantageous for most
materials to be bagged and most nonwoven materials. At an air
permeability below 100 l/m2/s, an excessively high pressure builds
up even with this outstandingly appropriate material, and the bag
can be damaged. At higher air permeability than 3000 l/m2/s the
nonwoven material is either too thin or its pores are too large,
or both, and then it no longer protects its contents against
external influences and lets finely divided contents leak out,
i.e., creates dust, and no longer even has the necessary strength.
With regard to the desirable weight per unit area, the limits are
30 to 200 g/m2 for the nonwoven material, preferably 40 to 150 g/m2.
Here, again, the contents, the package size, the manner of packing,
and the like, have an influence. It is evident that if the bags
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UHLM 205-PCT-PFF/WGW
are filled by hand the requirements regarding strength are
substantially less stringent than when the bags are filled at a
comparatively high filling pressure and a short cycle time.
The thickness of the nonwoven material is also related to and
dependent upon the other factors. It is best in the range of 0.1
to 1.5 mm, preferably 0.2 to 1 mm. A comparatively thin nonwoven
material must have high strength ratings in order to withstand the
stress of filling and of the handling and storaye of the filled
bag.
An additional influencing factor is the pores present in the
nonwoven material as regards their size and density. It is these
pores that ultimately determina the air permeability and hence
suitability for fast self-venting. Most of all their size,
however, has a decisive influence on the permeability of the bag
and the prevention of raising dust when the bag is being filled and
during the later handling of the filled bag. Here it is mainly the
maximum pore size that is the limiting factor, which for most of
the materials mentioned in the beginning should preferably not be
greater than 150 micrometers. In the case of the pore size there
is also the often-mentioned interrelation with other
characteristics of the nonwoven material, and it is evident that
a thin nonwoven material with relatively large pores has a greater
UHLM 205--PCT--PFF/WGW
tendency to be dusty than a thicker one with pores of the same size
or a greater number of medium and smaller pores, because in the
case of a thicker nonwoven material the probability that a small
particle of the ~ill might be filtered out and thus prevented from
emerging is multiplied.
From all this it can be concluded that decisive importance is to
be attributed to the characteristics of the nonwoven fabric as the
sole material or the material of predominant area. The great
variety of characteristics available in the field of nonwoven
materials, on the other hand, is what makes this ]cind of fabric so
appropriate to the solution of the stated problem and so adaptable
to the great variety of materials to be contained, to bagging
methods and to bagging apparatus.
The term, "nonwoven fabric," is to be broadly understood, and
covers all materials which to any considerable extent contain
textile fibers of a length between 3 mm and 50 mm which are
randomly deposited wet or dry, and bonded in many different ways,
e.g., mechanically by needling or chemically by binding agents
and/or thermally by heat treatment. For this new and important
group of fabrics, which assumes an intermediate position between
paper and woven and knit fabrics, the term, "nonwoven fabric," has
established itself generally. Also to be included in this group
U~ILM 205-PCT- PFF/WGW
of fabrics are spun-bonded materials; these are synthetic materials
such as polyesters which, in the process of their fabrication from
the melt, i.e., when the filaments or fibers issue from a
spinneret, are laid down in different directions and adhere to one
another while still in the plastic state to produce tha fabric.
What distinguishes the nonwoven fabricss is that paper consists of
short fibers based on cellulose or mechanical wood pulp with fiber
lengths up to 2 mm. Included in the term "nonwoven fabrics" are
also products which contain, in addition to textile fibers, a
considerable proportion of cellulose or mechanical wood pulp fibers
which are the basis of paper manufacture. Such an admixture not
only makes a nonwoven less expensive, but also the shorter
cellulose and pulp fibers serve simultaneously as a kind of binding
fibers for the longer textile fibers which are the essence of the
nonwoven fabrics.
The material basis of the textile fibers or filaments contained in
the nonwoven fabric is also extremely broad and runs from natural
fibers such as cotton, through staple fiber, i.e., cellulose
converted to fibers, to synthetic materials on the basis of
polyester, polyamide, polypropylene and inorganic materials such
as rock wool and glass fibers. Which nonwoven fabric is selected
for the self-venting bag depends entirely on the material to be
bagged, the filling method, and the apparatus used for the purpose.
UHLM 205-PCT-PFF/WGW
It is, however, precisely the great number of nonwoven fabric
varian~s and qualities that are on the market that, in addi~ion to
the all-important easy and rapid venting, makes the nonwoven
fabrics so outstandingly suited as material for a self-venting bag.
There is a custom-made nonwoven fabric available for nearly every
need.
The high strength of these nonwoven fabrics is, of course, a very
great advantage, and those having a dry longitudinal and transverse
tensile strength between 80 and 400 Nm have proven especially
valuable and suffice for most materials, and for the common bag
sizes and fill weights.
As already explained, the wall of the self-venting bag does not
necessarily consist entirely of nonwoven material, and it may be
expedient in the case of certain fill materials or stresses to make
parts of it, such as the mouth or bottom area, of other materials.
At least half of the bag walll however, can best consist of
nonwoven material in order to achieve the fast-venting effect.
The most decisive advantage of the self-venting bag, however, is
that, especially in the case of automatic filling machines, it
permits rapid venting, shorter cycling time and a large packed
content. It is therefore outstandingly suitable as a valve bag.
Therefore, one preferred method of filling such a nonwoven bag
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llHLM 205-PCT-PFF/WGW
consists in filling it with a feed pressure of 0.~ to 1.0 bar, and
thus the bag can be filled more quickly and densely. The rapid
venting through the nonwoven bag wall especially facilitates the
refilling of the bag, and one preferred variant process consists
in shaking and/or knocking the bag after the first filling and
adding considerable amounts of fill after this compacting
operation, so that ultimately a tightly packed bag utilizing the
full bag capacity will be obtained, or the bag can be made of
smaller dimensions for the same fill weight as beEore. The result
is therefore a filled bag that is easy to handle and stack. These
properties can be further enhanced and improved i~ the ~illed bag,
after filling and closing, is carried in another preferred process
variant through belts preferably engaging the broad flat sides of
the bag, or else is pressed between platens so that residual air
is forced out, and the full bag will thus be given a largely oblong
shape that i5 easy to stack and carry on pallets.
It is a considerable advantage that the self-venting bag in
accordance with the invention is also less problematical as regards
disposal and environmental concerns. The common valve bags of
paper consist usually of two paper plies and one plastic layer
between them, and therefore they cannot be recycled but must either
be burned or dumped, thereby placing more stress on the
environment. The bag according to the invention, however, since
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U~ILM 205-PCT-PFF/WG~1
in its preferred embodiment it consists only of nonwoven material,
can be-shredded to the fibers which can be made again into nonwoven
material for the same or a different purpose.
The nonwoven ba~ permits an additional, especially advantageous
embodiment of the invention by having a closure extending
preferably over the entire width of the bag at the end opposite
the fill opening, serving the double purpose of:
a. permitting easy emptying of the bag without having to
cut away its closure, as in the case of cutting away the
upper part of a valve bag.
b. making it possible, therefore, to re-use the bag for the
same purpose, and hence
a considerable saving of the bag material required for a certain
amount of goods, and a greatly reduced problem as regards disposal
and the environment.
At the same time two properties of nonwoven materials have a
beneficial effect: The good air permeability of the nonwoven
material facilitates the emptying of the filled bag, because no
vacuum builds up as would be the case with a conventional, sewn
film bag. Secondly, on account of its textile nature, it is very
well suited for sewing such a closure, preferably a tape, and the
danger of ripping or bursting does not exist.
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UE~LM 205-PCT-PFF/WG~
The additional closure permitting repeated reuse can be the zip
closure known in connection with pacXaging bags. Especially
preferred is a hook-and-loop closure on account of its simplicity
of operation. The closure is best created when the self-venting
bag is manufactured.
What follows is a rough sketch of this preEerred further
development of the invention and the hook-and-loop closure,
although this additional embodiment of the invention is not limited
to a reusable bag in this form.
In Figures I to IV the individual steps are shown for the
preparation of a reusable bag provided with a hook-and-loop
closure. The bag 1 of nonwoven fabric has a fill opening 2. In
the case of a valve bag this fill opening 2 is closed with a valve
closure with a lateral opening for the introduction of a filler
spout .
The end of bag 1 opposite the fill opening 2 has the flaps 3, 4
and 5, which are folded over at right anyles and when glued or
stitched form the bottom of the self-venting bag 1. The middle
flap 3 of th~ one wide, slightly longer side terminates in the
stitched-on loop strip 7 which, together with the hook strip 6
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IJ~LM 205-PCT-PFF/WGW
stitched at the lower part of the other wide side forms the hook-
and-loop closure when the bag is full.
In the following table a number of nonwovens are listed in regard
to their composition, the type of bonding, the unit weight, the
thickness and the air permeability, as well as the materials packed
in them. All of these examples constitute preferred embodiments.
All valve bags were able to be filled at a filling pressure between
0.8 and 1 bar in 6 to 10 seconds to the fill weiyht given in the
table, without marked raising of dust. After ~ogging the filled
bag, the contents could be compressed to the fill weight given in
the next column.
~ -
Dc) lZ h~ O O O
_ V ` -- N N
U. V~ '--
. _
C v . . ~ `t U~ `t 1`- N ~
._ N N _ ~ _ _ _ _ N
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a V E 1 ~ ~ ,, ~ ~ ~ q
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V
O U~ o O o
~ c~ E
G t~, _
O ~ .0 N ~0 O ~1 10 N 00
CO O O O O O O O
CO O UO~ ~ ~ ~t
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.c@ ~ ~ ~ æ E n E ~ CX v
O~ ~ C L ~ ~ c ~ c ._ ._ L
~ a. z ~ 3 ~ ~1
C~ ) O
V ~ o~ O
C C ~ _ ~ N ~ ~V N
-- O O r~ C ._ 0 ~
~C~ oi ~t o $ C~ o ~ii ~ ~D ~ IU ~U V X X
; N ~X ~ X ~ ~ ~ ~ Y ~ Y ~ ~ 3~
Z ~ . 1~ t~ ~ O I-- U~ m n.
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