DE2330500C2 - Liquid packaging and device for producing this packaging - Google Patents

Description

The invention relates to a packaging for liquids made of cardboard or paper as a carrier material for the packaging, which is impermeable to liquids at least on its inside and essentially consists of a tubular packaging sleeve which is produced by connecting two side edges of the carrier material by means of a butt weld seam over the entire length of the side edges, the open tube ends of the packaging being pressed together and closed by transverse weld seams.

In many types of liquid packaging, the tubular packaging sleeve is formed by welding the two opposite side edges of a paper web together.

A first type of welding along the free edges of the carrier material is done in such a way that, to form a tube - seen in cross-section - the inside of one end is placed slightly overlapping the outside of the other end and is welded to it by pressing. This creates a thickened strip along the weld seam because two layers of the carrier material are welded together. When welding in this way, it is also important to ensure that the free edge of the carrier material that will be inside the tube is properly covered with plastic, otherwise the liquid would penetrate the carrier material and cause the packaging to leak.

In another type of packaging, the two inner sides of the plastic-coated carrier material are welded together along their free edges. In this case, too, a thickened strip is created because two layers of carrier material are welded on top of each other. The point at which the weld ends towards the interior is particularly at risk with this type of welded connection. It is essential that this opening is filled perfectly with plastic, otherwise cracks and leaks will occur when the packaging is filled and the carrier material layers are pulled apart. The tensile stress in the latter type of welded connection is largely perpendicular to the plane of the welded surface, i.e. the tensile strength is considerably lower than that which can be achieved in the direction of the plane of the welded material surfaces.

Both types of connection described above have the disadvantage that all welds that run transversely to the weld seam described first - for example the weld seams on the bottom and top of the packaging, which run transversely to the longitudinal weld seams on the sides - are difficult to seal. This is because the transverse weld seam must run across areas with two layers of carrier material as well as four layers of carrier material. At those points where the longitudinal weld seam is made as described above, the area with the four layers of material lying on top of each other is created after folding or double-folding. It is obvious that perfect sealing during welding is particularly difficult at the transition points between the areas with two layers of material and those with four layers of material. Good and even heating and thus even welding cannot often be achieved because the contact pressure of the welding jaws is difficult at the transition points mentioned.

The two types of connection mentioned above also have the disadvantage that the necessary overlap means that material is wasted, at least in the area of the thickened strip. Since the packaging described above is a mass-produced item in large quantities, saving the strips on the connecting seams would have a significant effect.

Instead of superimposing narrow strips on the side edges, the CH-PS 3 79 397 already discloses the joining of these side edges of the carrier material by means of a butt weld seam which extends over the entire length of the side edges. The packaging described here is similar to that described in more detail at the beginning. The purpose of the butt weld seam in the known packaging is to create a packaging sleeve with a practically uniform wall thickness, also across the longitudinal seam, so that the finished package is free of tensile stresses which are directed perpendicular to the longitudinal direction of the seam. The uniform wall thickness in the seam zone as well as in the rest of the packaging sleeve achieves a certain inherent rigidity which is not particularly important in general production. of liquid packs. In the known case, the butt weld ends flush with the surface, and there is therefore a risk that the interfaces that are free of plastic coating are not completely covered by the plastic added during the welding process. Gaps or cracks in places are enough to give moisture or liquid penetrating the paper web from the outside or inside the opportunity to soften the paper. To avoid this risk, separate plastic films have been placed on the critical lines. However, this is an uneconomical measure.

Another disadvantage of the known butt weld seam in one embodiment is that between the two free end edges the supplied plastic is so thin that this layer cannot adequately absorb the tensile forces that are always exerted when filling a liquid package.

Other embodiments shown in the publication have the disadvantage that the end edges have to be machined in a complex manner, so that layers are removed and overlapping areas can form, which overall, after being placed on top of one another, give the uniform wall thickness again.

The object of the invention is to improve the packaging described in more detail at the outset in such a way that the two side edges of the carrier material, which run close to one another and parallel to one another without contact or overlap, are connected in a liquid-tight manner and have a high tensile strength during use.

This object is achieved according to the invention in that the butt weld seam, viewed in cross section, has a profile that extends beyond the inner and outer edge areas of the free end edges. This allows the plastic to be brought precisely to the critical points, whereby it is not important that the wall thickness of the material remains constant overall and in particular across the seam zone. During butt welding, the plastic can even swell slightly beyond the edge areas, so that this results in a welded connection with high tensile strength and absolute tightness.

By butt welding with the properties mentioned above, the disadvantageous overlapping of the layers along the edges described above can be avoided.

Viewed in cross-section, it can be, for example, a double-T profile, in which plastic material is also pressed out parallel to the edge areas next to the free end edges and cast there, so that tensile forces acting in a direction transverse to the longitudinal sealing seam are also well absorbed. If a sufficient amount of plastic is used, the crossbars of the T can also be deliberately made sufficiently long in order to maintain the good tensile properties of the weld according to the invention.

Because the butt weld extends over the entire height of the side wall of the packaging, it is also possible to produce packages from an endless tube of carrier material, so that the butt weld can also be produced continuously. When applying the cross welds, the sealing difficulties mentioned at the beginning no longer occur because there is no thickened strip along the weld.

In an advantageous embodiment of the invention, the two edges of the carrier material in the finished butt weld seam are approximately 1 mm apart. This makes the seam particularly elastic, which advantageously increases the tensile strength. Polyethylene, for example, is used as the plastic.

From DD-PS 18 081 a device for producing a tubular packaging casing of the type described above is known, which consists of a transport device for feeding the carrier web, which is formed by two counter-rotating rollers with parallel axes of rotation. The known device also has a device for folding a carrier web into a tube that encloses one roller, the free end edges of the carrier web being guided in the area of the rollers, and it has a device for welding the carrier web in the area of its free end edges. However, the known device is only suitable for forming completely overlapping web edges, the two rollers merely being pressure rollers. The outer surface of the rollers is not only adapted to each other but also to the tube with a circular cross-section that runs between them. Consequently, the outer roller, i.e. the roller arranged outside the packaging tube, has ends with a larger radius than in the middle area. Due to the larger radius, these curved surfaces on the outside have a higher peripheral speed than the surface areas in the middle. As a result, a certain amount of friction in the area of the overlap seam cannot be avoided during operation.

In order to produce the packaging described at the beginning, the object of the invention is therefore to modify and improve the device known from the publication discussed above so that a butt weld seam can be produced in a suitable manner. This object related to the device is achieved according to the invention in that the rollers are designed as externally profiled hollow rollers, the interior of which is provided with inlet and outlet lines for cooling liquid and that the outlet opening of an extruder delivering liquid plastic opens into the intake gap of the rollers, in which the free end edges of the carrier web are guided opposite one another at a short distance.

The extruder with filling container and filling pipe is arranged so that its outlet opening is fixed directly in front of the rollers in the running direction of the carrier webs. The butt weld seam can advantageously be produced in a single operation. The liquid welding material, once produced from the plastic granulate by heating, is pressed directly between the correspondingly guided free edges of the carrier webs without the need for repeated heat supply. Immediately after the liquid plastic is introduced between the free edges of the carrier material and after the weld connection with the coating of the carrier material, the butt weld seam according to the invention is profiled and cooled.

The new device is simple and creates functionally reliable welded joints with greater tensile strength without overlapping of the carrier layers.

By cooling the rollers, they can also be kept relatively small, and despite their design as hollow rollers, their strength and operational reliability are not adversely affected.

Further advantages, features and possible applications of the present invention will become apparent from the following description of a preferred embodiment in conjunction with the drawings. It shows

Fig. 1 shows in cross section a first type of welded joint according to the prior art,

Fig. 2 a second type of welded joint according to the prior art,

Fig. 3 the butt weld seam according to the invention in cross section,

Fig. 4 the device for producing the tubular packaging sleeve from carrier material coated on both sides with a continuous butt weld seam,

Fig. 5 a top view of the finished welded packaging tube at section A of Fig. 4 and

Fig. 6 is a sectional view through the manufacturing device of Fig. 4.

In the following packaging, which is given only as an example, both according to the prior art and according to the invention, it is assumed that the carrier material 1 is a paper web coated on both sides with polyethylene.

In Fig. 1 to 3 the butt weld seam is shown in cross section, with the carrier material 1 shown partially broken off. The known welded joints according to Fig. 1 and 2 have two partially overlapping carrier material layers which are welded together by prior heating. As mentioned above, in the embodiment according to Fig. 1 it is essential that the free narrow edge of the carrier material is sufficiently coated with plastic at point 2 so that liquid from the interior 3 of the tube does not penetrate into the paper and make the packaging leaky. According to Fig. 2, care must be taken to ensure that there is a good coating of plastic at point 4 because the tensile forces in the direction of the parts shown with solid lines are mainly concentrated at this point 4 and this is where the risk of leakage is most likely to arise. The tensile strength of the known welded joints is considerably lower in the direction of the arrows shown with solid lines than in the arrows shown with dashed lines.

Fig. 3, on the other hand, shows the butt weld according to the invention in cross section. The two free edges 5 and 6 of the carrier material 1 are connected to one another with the double-T butt weld profile 7. This profile represents the butt weld seam. The two edges 5 and 6 of the carrier material 1 are located at a distance of approximately 1 mm in the finished butt weld seam 7 shown in Fig. 3.

Of course, deviations are possible here, i.e. the distance can also be 0.5 to 1.5 mm. In special embodiments, the two edges can also lie completely against each other, so that almost no polyethylene is arranged between them. Nevertheless, one can then speak of a butt weld seam, because the narrow edges are butt-jointed. The edge areas on the outside and inside of the 60 carrier material 1 are firmly connected to the polyethylene of the weld seam 7 to form a unit, so that absolute tightness is guaranteed. While a double-T profile is shown in Fig. 3, other types of profile, for example a single T or similar, are of course also possible. On the other hand, it is not necessary for the butt weld seam to form an exact profile, rather the polyethylene material can be applied so that it flows laterally and merges continuously - without edges.

The continuous operation is shown schematically in the device shown in Fig. 4 for producing a package made from a continuous tube. The above-mentioned device for folding a carrier web into a tube shape is not shown because this is common and known in the packaging industry. For this reason, it is easy to imagine how the paper tube, which is open above the rollers 10 and 11 shown in Fig. 4, is closed below the rollers. A plan view from the left of the tube in Fig. 4 is shown in Fig. 5, with the carrier material broken off on all four sides. It can be seen that the packaging made from such a tube has a butt weld seam 7 running over the entire height of its side wall.

The two rollers 10 and 11 according to Fig. 4 have axes of rotation 12 and 13 arranged parallel to one another and are designed as hollow rollers. As indicated by the arrows 14 , they are driven in opposite directions. Fig. 6 shows inlet and outlet lines 15 and 16 through which cooling liquid 17 is fed into the interior of the hollow rollers 10 and 11. The granulate is fed from the filling pipe 19 arranged in the mandrel 18 into the extruder 20 , where it is liquefied and pressed into the filling pipe 22 by the screw 21. The outlet opening 23 of the extruder 20 is located directly in front of the rollers 10 and 11 as seen in the direction of travel of the carrier material web 1. At the point designated 25 in Fig. 6, the liquid polyethylene is pressed between and around the free edges of the free ends of the carrier web 1 which are to be welded together. The grooves 26 arranged in the rollers 10 and 11 ensure that the melting polyethylene is formed into the desired profile, whereby the plastic is simultaneously cooled and hardened.

In the embodiment shown in Fig. 6, it is conceivable that the carrier material 1 is guided around the mandrel in which the one roller and also the extruder 20 are arranged, in order to form the tube for liquid packaging described above.

In a special embodiment similar to the system shown in Fig. 6, a filling tube for the liquid to be introduced into the packaging tube can also be arranged in the mandrel 18 in approximately the shape of the filling tube 19. This results in a particularly compact machine in which not only the carrier material web is formed into a tube and sealed by butt welding, but also filled with liquid directly underneath.

Claims (3)

1. Packaging for liquids made of cardboard or paper as a carrier material for the packaging, which is impermeable to liquids at least on its inside and essentially consists of a tubular packaging sleeve which is produced by connecting two side edges of the carrier material by means of a butt weld seam over the entire length of the side edges, the open tube ends of the packaging being pressed together and closed by transverse weld seams, characterized in that the butt weld seam ( 7 ) has a profile extending beyond the inner and outer edge regions of the free end edges ( 5 , 6 ) when viewed in cross section. 2. Packaging according to claim 1, characterized in that the two edges ( 5 , 6 ) of the carrier material ( 1 ) in the finished butt weld seam ( 7 ) are at a distance of approximately 1 mm. 3. Device for producing the tubular packaging casing according to claim 1 or 2, consisting of a transport device for feeding the carrier web, which is formed by two counter-rotating rollers with parallel axes of rotation, a device for folding a carrier web into a tube enclosing one roller, the free end edges of the carrier web being guided in the region of the rollers, and a device for welding the carrier web in the region of its free end edges, characterized in that the rollers ( 10 , 11 ) are designed as externally profiled hollow rollers, the interior of which is provided with inlet and outlet lines ( 15 , 16 ) for cooling liquid, and that the outlet opening ( 23 ) of an extruder ( 20 ) delivering liquid plastic opens into the intake gap of the rollers ( 10 , 11 ), in which the free end edges ( 5 , 6 ) of the carrier web ( 1 ) meet one another at a slight Distance from each other.