CA2044014A1 - Self-venting bag and method for filling it - Google Patents

Abstract

Abstract of the Disclosure The self-venting bag for filling with finely divided materials consists wholly or partially of air- and gas-permeable nonwoven fabric whose air and gas permeability is so great that air or gas that is compressed by the filling can escape through the nonwoven fabric.

Description

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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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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 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 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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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 ~4~4 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 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.

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 _g_ 0 ~ 4 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 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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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 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.

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Claims (15)

1. Self-venting bag for filling with finely divided goods such as powders, grains, flakes, fibers, especially goods of low specific weight, characterized in that the bag consists wholly or partially of an air- and gas-permeable nonwoven fabric whose air and gas permeability is so great that air or gases compressed by the filling can escape through the nonwoven fabric.

2. Self-venting bag according to claim 1, characterized in that the bag wall consists at least to one-half of an air- and gas-permeable nonwoven fabric.

3. Self-venting bag according to either of claims 1 and 2, characterized in that the nonwoven fabric has an air permeability of 100 to 3000 1/m2/s.

4. Self-venting bag according to claim 3, characterized in that the nonwoven fabric has an air permeability of 400 to 2000 l/m2/s.

5. Self-venting bag according to any one of claims 1 to 4, characterized in that the weight per unit area of the nonwoven fabric amounts to 30 to 200 g/m2.

6. Self-venting bag according to claim 5, characterized in that the weight per unit area of the nonwoven fabric is 40 to 150 g/m2.

7. Self-venting bag according to any one of claims 1 to 6, characterized in that the thickness of the nonwoven fabric amounts to 0.1 to 1.5 mm.

8. Self-venting bag according to claim 7, characterized in that the thickness of the nonwoven fabric amounts to 0.2 to 1.0 mm.

9. Self-venting bag according to any one of claims 1 to 8, characterized in that the maximum pore size in the nonwoven fabric is 150 micrometers.

10. Self-venting bag according to any one of claims 1 to 9, characterized in that it has at its end opposite its opening a closure for emptying the bag.

11. Self-venting bag according to claim 10, characterized in that the closure is a hook-and-loop closure.

12. Self-venting bag according to any one of claims 1 to 11, characterized in that the bag is a valve bag.

13. Process for filling a nonwoven bag according to any one of claims l to 12, characterized in that the filling is performed with a feed pressure of 0.8 to 1.0 bar.

14. Process for filling a nonwoven bag according to any one of claims 1 to 12, characterized in that, after shaking and/or knocking the filled bag an after-filling is performed.

15. Process according to either of claims 13 or 14, characterized in that the filled bag is passed through rollers and/or pressed by platens.