AT508982A1 - METHOD FOR CLOSING A BAG - Google Patents

Description

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The invention relates to a method for closing a bag body of a fabric of monoaxially stretched polymer, in particular polyolefin or polypropylene tapes, in which at least two fabric layers are connected by means of a extending over the width of the bag body seam, and a bag made of a fabric of monoaxial stretched polymer, in particular polyolefin or polypropylene tapes, which is closed on one or both sides.

The invention further relates to a device for closing a bag body made of a web of monoaxially stretched polymer, in particular polyolefin or polypropylene tapes, in particular for carrying out the method according to the invention, with a feed device for feeding the bag body to a closing station.

For the packaging of goods, in particular bulk goods, various types of bags are used. The invention relates to sacks, which consist of a fabric of monoaxially stretched polymer, in particular polyolefin or polypropylene tapes. These tapes are prepared by stretching polymer, in particular polyolefin or polypropylene films usually to 4 to 10-fold, whereby the molecular chains are aligned in the ribbon longitudinal direction and have in this direction about 6 to 10 times the strength of the original film. The ribbon width is usually about 1.5-10 mm, the thickness 20-80 jum.

A rough classification of such bags is made by the distinction in pillow and box shape.

A pillow form of sacks usually arises by assembling the floors with a textile seam or a weld. Pillow-shaped bags are supplied as semi-finished, open-top bags or as tubing on a roll. Part-ready-made open-topped bags are usually closed after filling.

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Sacks produced from tubing are assembled directly on the filling line, a so-called FFS system (Form, Fill and Seal), through a seam on the bottom and, after filling, are also closed by a seam. In the case of a textile seam with a needle, the circumstance is disadvantageous in that the bag contents can escape via the seam fixations. In addition, the seam perforation of the fabric causes weaknesses, so that the sack can tear at the seam. In addition, machine-making the needle-punched fabric involves a number of problems, such as the risk of needle breakage and tearing of the suture used for the suture. Another disadvantage is the limited sewing speed of the sewing head, so that with currently available machines a processing of only about a maximum of about 40 to 45 bags per minute is possible. As an alternative to the textile seam, in the case of film bags, a weld can be applied to the bottom in an analogous manner to the textile seam described above and to the top after filling.

In connection with a box-shaped bags already various methods for closing the floors have become known. Most of the folded floor according to the prior art is adhesively bonded with a multi-component adhesive, since polypropylene and polyethylene materials from which the fabric usually consists, can be glued only with difficulty. In addition to the cumbersome bonding procedure, the known adhesives have other disadvantages such as low durability, brittleness due to temperature changes and loss of adhesion due to moisture. In WO 95/30598 Al an improved method is described in which at least one sack end, in particular a bottom surface, via an intermediate layer of, in particular thermoplastic, plastic, in particular polyolefin, preferably polypropylene material by the action of heat with a cover sheet of tissue of monoaxially oriented polymer, in particular polyolefin, pre- • ·········· ··················································································· 3- is polypropylene tapes, is connected and in which only the outer surface area, in particular less than 30% of the material thickness of the tissue bands, from the bottom surface and cover sheet due to the heat disoriented molecules, wherein in the rest of the material region, the molecular orientation is present. A disadvantage of this method is the control and limitation of the effect of heat such that actually only the outer surface area is heated accordingly and affected by a disorientation of the molecules. Regions of tissue with disoriented molecules have significantly lower strength compared to regions of molecules oriented by the orientation of the material.

The invention now aims to make the bag closure such that the material of the bag is weakened by the closure as little as possible, so that the closed bag does not tear even under high mechanical loads, especially in the region of the seal. In addition, a significantly higher throughput rate is to be made possible in comparison to the production of a conventional sewn closure seam. Furthermore, the process reliability is to be increased, the maintenance of the machines reduced, the production costs minimized and the optical advantages of the product ensured. The invention relates in particular to sacks with a pillow shape.

To solve this problem, the method of the aforementioned type according to the invention is characterized in that the seam is designed as a weld, wherein the welding comprises at least one Ultraschallverschweißungsschritt. The ultrasonic welding allows in this case to obtain defined welds in a simple manner, so that the affected by the welding portion of the fabric can be reduced in the weld region. In particular, if, as corresponds to a preferred development, the ultrasonic welding to form a plurality of spaced apart -4- welds is made, the tissue is only partially weakened by the weld, the strength between the individual welds is entirely retained. Since the orientation of the molecular chains is lost only to a small extent by the ultrasound welding, the tissue hardly suffers loss of strength. Preference is given to proceeding such that the welds are arranged in several rows, wherein the welds of a row are arranged on the welds of an adjacent row on gap. The staggered arrangement of the welds effectively prevents the formation of crack propagation lines.

In plastic ultrasonic welding, heat is supplied to the tapes of the fabric to be welded by high-frequency mechanical vibrations at the welds, whereby the material is melted or at least softened. In this case, the joining force and the ultrasonic vibration have the same effective direction. The introduced longitudinal waves cause a pressure threshold stress in the material and in the joining zone, which leads to a plasticization of the plastic. At the end of energy absorption, the material at the welds cools down under pressure and creates a durable, mechanically stable connection.

The weld extends according to the invention across the width of the bag body, so that due to the weld, the relevant side of the bag is substantially completely closed. For bags with a valve that arises, for example, by turning a corner at the bag end inward, the welding is also made on the - correspondingly reduced due to the chosen corner - width of the bag body and extends accordingly also on the embossed fabric.

An advantage of the method according to the invention is that it does not cause tissue damage caused by needle perforation. • · · t ···· ····································································

There are weak points. In addition, the ultrasonic welding is associated with low cost and is characterized by a high operating speed. Significantly more bags per minute can be sealed with the method according to the invention than with the methods known from the prior art. The welded joint is not subject to aging or embrittlement. There are also simple disposal options, since the bag consists exclusively of sorted material.

However, there is a risk in a welded seam produced by ultrasonic welding of the type mentioned that a peeling load acting on the weld, in which the interconnected fabric layers are pulled apart in a direction transverse to the fabric surface, leads to a detachment of the welded joint. It should therefore be noted in principle that such a welded joint is only subjected to shear, i. only subjected to a load parallel to the tissue surface. For this purpose, a preferred development of the method according to the invention provides that a flat end section of the bag body having at least one open end is folded over and that the ultrasonic welding step comprises ultrasonically welding the folded end section to the bag body. By the assignment of the end portion of the weld seam is no longer exposed to peel stress, so that the seam can withstand very high mechanical loads. This is the case in particular when, as is the case with a preferred development, the folded-over end section is merely connected, in particular welded, to the fabric layer of the bag body facing the folded-over end section.

Alternatively, the procedure is also such that the welding of the two fabric layers of the end section takes place by means of ultrasonic welding in the unfolded state of the flat end section, after which the welded end section ··· · · · · · · · · · · · · · · · ······················································································ 6 - is folded and that the folded end portion is finally connected to the bag body. The bonding can be done for example by gluing, in particular extrusion bonding or by hot air welding.

In order to avoid a welding together of the folded layer facing the fabric layer and the folded end portion facing away from the fabric layer of the bag body is advantageously inserted into the bag body, a release layer or applied a release layer. The separating layer preferably has a higher thermal conductivity than the sack tissue. The separating layer, in particular a metal-containing separating layer, is preferably applied by a coating method. The release layer used here is preferably a metal-containing paint. Due to the metal content, such a separating layer leads to heat dissipation, so that the fabric layer of the bag body facing away from the folded-over end section is subject to less or substantially no heat input. The heat input via the oscillatory body that can be excited to form ultrasonic vibrations preferably takes place on the folded-over end section.

A peel load of the welded joint is always effectively prevented, if, as corresponds to a preferred development, starting from the top due to the assignment coming to lie fabric layer only a number of directly superimposed layers of fabric by ultrasonic welding is connected to each other, which increased by one half of Total number of fabric layers corresponds.

According to a further aspect of the invention, a bag of the type mentioned is provided, which is inventively designed such that at least one closed side has a folded end portion, which is connected only to the folded end portion facing the fabric layer of the bag body, in particular ultrasonically welded. ·····

Preferred developments are defined in the subclaims and relate essentially to the features already mentioned in connection with the method according to the invention.

According to a further aspect of the invention, a device for closing a bag body of a fabric of uniaxially stretched polymer, in particular polyolefin or polypropylene tapes, in particular for carrying out the method according to the invention is provided which comprises a feeding device for feeding the bag body to a closing station. According to the invention, the device is developed in such a way that the closing station comprises an ultrasonic welding station.

The invention will be explained in more detail with reference to an embodiment schematically illustrated in the drawing.

1 shows a schematic cross-section of a tubular fabric for producing a bag according to the invention, FIG. 2 shows the fabric with folded end section, FIG. 3 shows the end section in a welded state, FIG. 4 shows a view according to the arrow IV of FIG. 3 and FIG 5 is an enlarged view of the area V of FIG.

In Fig. 1, a bag 1 is shown from a tubular fabric in a flat state, the open end 2 is to be closed to produce a bag with pillow shape. In the initial state according to FIG. 1, two fabric layers 3 and 4 can be seen. If it is a bag with side folding, which is readily possible in the context of the present invention, four layers of fabric are present in the side folding. The invention will be explained below but only with reference to a bag without side folding.

For closing the open end 2 of the bag 1, the procedure is as follows. As shown in FIG. 2, first of all, as shown in FIG. Is, the corresponding end section 5 is folded over on the bag body, so that in the area of the assignment a total of four layers of fabric on each other come to rest, namely the layers 3, 4, 6 and 7. Between the fabric layers 3 and 4, a release layer 8 is arranged. The separating layer may be a coating which is applied at least either on the side of the fabric layer 4 facing the fabric layer 3 or on the side of the fabric layer 3 facing the fabric layer 4. The separating layer 8 prevents the subsequent ultrasonic welding that the fabric layers 3 and 4 are permanently connected to each other and the fabric layer 3 is damaged.

In Fig. 2, an ultrasonic welding apparatus is shown schematically, comprising an anvil 9 and a sonotrode 10. For welding, the fabric layers 3, 4, 6 and 7 are clamped between the anvil 9 and the sonotrode 10 by the anvil 9 and the sonotrode 10 accordingly the arrows 11 are moved to the section to be welded. The sonotrode is set in ultrasonic vibration, whereby a welding is effected at the contact points of the sonotrode 10 on the tissue. The fabric layers 4, 6 and 7 are welded together. The release layer 8 prevents a permanent connection of the fabric layers 3 and 4. If the fabric layers 3 and 4 stick together after the welding process despite the release layer 8, so there is no permanent connection between these fabric layers 3 and 4 due to the release layer 8, but it can These two layers of fabric can be separated without further manual intervention without damaging the material of the fabric. Alternatively, the fabric layers are possibly separated from each other when filling the bag due to the weight of the filling material.

Fig. 3 shows the bag end in the closed state. Because the fabric layers 3 and 4 are not connected to one another, the weight of the product does not act in the sense of a peel load on the connections 4 to 6 and 6 to 7, but rather

In the sense of a shear load. The connections can absorb very high shear loads, so that the bag closure is maintained even at high loads.

4 shows the bag closure in a view according to the arrow IV of FIG. 3, wherein it can be seen that the weld is in the form of a weld extending over the entire width of the bag 1. However, the ultrasonic seam is not formed as a continuous seam, but includes, as is apparent from the detailed view of FIG. 5, a plurality of staggered welds 13. The staggered arrangement of the welds 13 causes the affected by the welding Ribbons are not weakened on their entire width by the structural change of the molecules caused by the welding. Due to the grid-like arrangement of the welds 13 a stable connection of the fabric layers is achieved without affecting the strength of the fabric as a whole decisively.

To maintain a sufficient strength, it is sufficient if the sum of the areas of the welds 13 is less than 50%, preferably less than 25%, in particular less than 15% of the surface of the weld 12.

The open end 3 can be closed after filling the bag 1 in the same manner as previously described in connection with the closure of the open end 2.

Claims (15)

1. Patent 1. The method for sealing a bag body made of a fabric of monoaxially stretched polymer, in particular polyolefin or polypropylene tapes, in which at least two fabric layers are connected by means of a seam extending over the width of the bag body, characterized in that the seam is performed as a weld, wherein the Welding comprises at least one ultrasonic welding step. 2. The method according to claim 1, characterized in that a at least one open end having flat end portion of the bag body is folded over and that the ultrasonic welding step comprises the ultrasonic welding of the folded end portion with the bag body. 3. The method according to claim 2, characterized in that the folded end portion is welded only to the folded end portion facing fabric saw of the bag body. 4. The method according to claim 2 or 3, characterized in that to avoid a Zusammeneinanderverschweißens the folded end portion facing fabric layer and the folded end portion facing away from the fabric layer of the bag body in the bag body inserted a release layer or a release layer is applied. 5. The method according to claim 4, characterized in that the release layer is applied by a coating method. 6. The method according to any one of claims 2 to 5, characterized in that starting from the lying on top of the assignment at the top fabric saw only a number ·· · - 11 -unagely superimposed layers of fabric by ultrasonic welding is connected to each other, which increased by one Half of the total number of fabric layers corresponds. 7. The method according to any one of claims 1 to 6, characterized in that the ultrasonic welding is carried out to form a plurality of spaced welds. 8. The method according to claim 7, characterized in that the welds are arranged in a plurality of rows, wherein the welds of a row to the welds of an adjacent row are arranged on the gap. 9. sack made of a fabric of monoaxially stretched polymer, in particular polyolefin or polypropylene tapes, which is closed on one or both sides, characterized in that at least one closed side has a folded end portion (5) which only with the folded end portion ( 5) facing the fabric layer (4) of the bag body (1) connected, in particular ultrasonically welded. 10. Sack according to claim 9, characterized in that to avoid a Zusammeneinanderverschweißens the folded end portion (5) facing the fabric layer (4) and the folded end portion (5) facing away from fabric layer (3) of the bag body (1) in the bag body (1 ) a release layer (8) is inserted or a release layer (8) is applied. 11. Sack according to claim 10, characterized in that the separating layer has a higher thermal conductivity than the sack tissue. 12. Sack according to one of claims 9 to 11, characterized in that, starting from the lying on top of the assignment at the top fabric layer (7) only one An ··· tl ·· ···· tt »· ·· · ···························································································································································································································· - Number of directly superimposed layers of fabric (7,6,4) in particular by ultrasonic welding is connected to each other, which corresponds to the increased by one half of the total number of fabric layers. 13. Sack according to one of claims 9 to 12, characterized in that the ultrasonic welding (12) has a plurality of spaced-apart welds (13). 14. Sack according to claim 13, characterized in that the welds (13) are arranged in a plurality of rows, wherein the welds (13) of a row to the welds (13) of an adjacent row are arranged on the gap. 15. An apparatus for closing a bag body of a fabric of monoaxially stretched polymer, in particular polyolefin or polypropylene tapes, in particular for carrying out the method according to one of claims 1 to 8, with a feed device for feeding the bag body (1) to a closing station, characterized in that the closing station comprises an ultrasonic welding station (9, 10). Herwig Worff through Vienna, on 2 November 2009 Haffrer / mid Reschmann Patentanwälte OG