METHOD FOR MANUFACTURING A CONTAINER

Abstract

The method for manufacturing a container, comprising a substantially rigid outer container and an easily deformable inner bag of thermoplastic materials not forming a welded connection with each other, with a container opening and at least one wall opening in the outer container, through which pressure equilibrium occurs in the space between the inner bag and the outer container, wherein a preform consisting of at least two tubes is co-extruded and placed between the open halves of a finishing mold and the finishing mold is closed, when the preform is of the length required for manufacturing the container, wherein excess material is removed from the base region of the container to be manufactured and a weld seam is formed, having a base weave of welded material from the outer container,in which the welded base seam of the inner bag is held and supported in the axial direction and the preform is inflated by a pressure means in coupling with the wall of the finishing mold and removed from the finishing mold, is characterized by the following steps: a) removing a section of the base weave of the outer container so that a section of the base seam of the inner container is exposed to the outside; b) raising the exposed section of the base seam towards the outer container so that an opening is produced between the base seam of the inner bag and the outer container; c) introducing a pressure means into the opening, whereby the inner bag is separated from the outer container on both sides; d) supplying a pressure means at the container opening so that the inner bag is reattached to the outer container.

Description

The invention relates to a method for manufacturing a container comprising a substantially rigid outer container and an easily deformable inner bag made of thermoplastic materials, which do not form a welded connection with each other. The outer container has a container opening, and the inner container has at least one wall opening through which pressure equilibrium occurs in the space between the inner bag and the outer container when the inner bag contracts as a result of the discharge of its contents. In the method, a preform consisting of at least two layers is co-extruded and placed between the open halves of a finishing mold. The finishing mold is closed when the preform has reached the length required for manufacturing the container.Excess material in the base region of the container to be manufactured is removed, and a weave of welded material is formed projecting outward from the outer container. The welded base seam of the inner bag is then secured and held in the axial direction within this weave. The preform is then inflated by a pressure medium, usually compressed air, in contact with the wall of the finishing mold and removed from the mold. BACKGROUND OF THE INVENTION The different types of thermoplastic materials of the outer container and the inner bag do not form a welded connection but adhere to each other with considerable adhesive forces when the container is manufactured by a coextrusion process according to the method described above. Before such a container is ready for use—that is, before it is filled with a liquid or, for example, gel-like contents, which is gradually discharged, for example, by means of an airless pump or, in the case of a tightly sealed container, by compression—the inner bag must be separated from the outer container wall and then reapplied. This can occur by applying reduced pressure to the inner bag through the container opening, which then contracts abruptly. The inner bag, whose base seam is attached to the base fabric of the outer container, thus separates from the outer container in a more or less uncontrolled manner; it is also possible for the inner bag to separate only on one side. A pressure medium, usually compressed air, is then introduced into the inner bag through the container opening to reapply it to the outer container so that the inner bag can reach the planned filling volume. A method for releasing the inner bag from the outer container is described in DE102006012487 B4, in which at least one wall opening is formed by drilling or penetrating the wall of the outer container with a drill or piercing needle. After the outer container wall is fully penetrated, compressed air is introduced into the space between the container and the inner bag. As a result, the inner bag separates from the outer container wall, whereby compressed air is supplied into the space between the inner bag and the outer container until a predetermined pressure value is measured in the inner bag, the container opening having been previously sealed. This procedure does not also ensure that the inner bag separates evenly from the outer container on both sides. / αο / ηη / ζζηζ / Β / γίΛΐ When the inner bag is not substantially and uniformly separated from the outer container wall, a relatively large subatmospheric pressure develops within the inner bag as a consequence of the discharge of packing material, despite the pressure-balancing openings in the outer container wall. The greater this subatmospheric pressure, the greater the permeation through the very thin wall of the inner bag and the risk of it becoming permeable. If the subatmospheric pressure in the inner bag becomes too high, it can also impair the functionality of the pump, which is typically provided, preventing some of the container's contents from being discharged. BRIEF DESCRIPTION OF THE INVENTION The object of the present invention is to provide a method in which the inner bag can be uniformly separated from the outer container and reapplied to the outer container. A device with which this method can be performed also needs to be specified. These objects are resolved according to the invention by the features of claims 1 and 8. The advantageous embodiments of the invention are characterized in the dependent claims. The method according to the invention provides, as the first step, that a small section of the base weave of the outer container is removed so that a section of the base seam of the inner bag held in the base weave is exposed to the outside. It is preferable to cut the base weave section; for this purpose, a circular cutter is particularly advantageous. This cut should be located in the center of the weld seam, viewed along its length. The cut is made transversely across the weld seam and only deep enough to prevent the inner bag from becoming permeable. The next step in the method involves lifting or pressing the exposed section of the base seam against the outer container, thereby creating an opening between the base seam of the inner bag and the outer container. This opening, formed on both sides of the base seam of the inner bag, is then filled with a pressure medium during or after the lifting of the base seam. This pressure medium flows down both sides of the inner bag to the neck region of the container, thus separating the inner bag from the outer container on both sides. Compressed air is preferably used as the pressure medium. The exposed section of the base seam can be lifted by any suitably shaped tool, whereby a pin-shaped blow mandrel is used with particular advantage as the tool, through which the pressure medium can be blown into the opening simultaneously. In the method according to the invention, the inner bag is completely separated on both sides with a minimal cycle time, without damage occurring to the inner bag, such as spaced fracture or the disadvantageous formation of folds. The concluding stage of the method according to the invention consists of supplying a pressure medium to the container opening, which is known per se, so that the inner bag is reattached to the outer container, specifically without lasting deformation of the inner bag during the separation process, i.e., without the formation of folds and without trapping air between the inner bag and the outer container. The outer container and the inner bag may each consist of one or more layers, which do not form a welded connection with each other during coextrusion. The outer container frequently includes an oxygen diffusion barrier layer. This oxygen diffusion barrier is cut in the method according to the invention only in a single, small portion of the weld seam, where the container has its greatest material thickness. This results in extremely low oxygen diffusion occurring only in the inner bag. Since only a small central section of the container's weld seam is cut and this line is precisely limited, especially when using a circular cutter, the inner bag remains reliably held with its base seam welded to the undamaged region of the outer container's base weave on both sides so that the inner bag is fixed to the outer container in the axial direction and can contract only in the radial direction when the container's contents are distributed. The method according to the invention was carried out in a bottle-shaped container with a capacity of 12.5 cm³ with the following preferred details: the weld seam was cut over a length of approximately 4 mm with a cutting depth of approximately 3 mm in the middle of the 27 mm long weld seam using a circular cutter in a single cut, which was made perpendicular to the weld seam. The separating tool had a pin-like blow-off mandrel with a length of approximately 7 mm, whereby the mandrel was inserted approximately 2.5 mm. The air pressure nozzles in the mandrel had a diameter between 0.5 mm and 1.5 mm, depending on the adhesion of the inner bag. As a result, the uniform, complete separation of the inner bag from the outer container and the smooth reattaching of the inner bag are achieved in significantly reduced work steps. The cutting length of the weld seam and the cutting depth should be varied appropriately with other bottle types. BRIEF DESCRIPTION OF THE FIGURES Figures 1 to 3 show the steps in the method according to the invention in a purely schematic manner. DETAILED DESCRIPTION OF THE INVENTION Figure 1 is a vertical cross-sectional view, centered through a vessel, including a rigid outer vessel 1 and an inner coupling bag 2. The vertical section extends in the longitudinal direction centrally through the base weld seam 3, in which the base weld seam 4 of the inner vessel 2 is clamped into the base weave 5 of welded material of the outer vessel 1. In Figure 2, a section 6 of the base weave 5 is cut with a circular cutter, which is not shown, so that a section 7 of the base seam 4 of the inner bag 2 is exposed to the outside. Figure 3 shows that the exposed section 7 of the base seam 4 is lifted into the container by a mandrel 8, thereby creating an opening between the base seam 4 of the inner bag 2 and the outer container 1, into which compressed air is introduced, thereby separating the inner bag 2 from the inner wall of the outer container 1 on both sides of the weld seam 3. An apparatus according to the invention for carrying out the method includes a mounting device for the vessel to be processed, a cutting device with a circular cutter, which removes a section of the weld seam from the vessel fixed in position in the mounting device in a single cut, and a separating device, which includes a separating pin, which is connected to a compressed air source and is advanced and thus forced to the weld seam in the vessel.

Claims

1. A method for manufacturing a container comprising a substantially rigid outer container and an easily deformable inner bag of thermoplastic materials not forming a welded connection with each other, with a container opening and at least one wall opening in the outer container, through which pressure equilibrium occurs in the space between the inner bag and the outer container, wherein a preform consisting of at least two tubes is co-extruded and placed between the open halves of a finishing mold and the finishing mold is closed, when the preform is of the length required for manufacturing the container, wherein excess material is removed from the base region of the container to be manufactured and a weld seam is formed, having a base weave of welded material from the outer container,wherein the welded base seam of the inner bag is held and supported in the axial direction and the preform is inflated by a pressure means in coupling with the wall of the finishing mold and removed from the finishing mold, characterized by the following steps: a) removing a section of the base weave of the outer container so that a section of the base seam of the inner container is exposed to the outside; b) raising the exposed section of the base seam towards the outer container so that an opening is produced between the base seam of the inner bag and the outer container; c) introducing a pressure means into the opening, whereby the inner bag is separated from the outer container on both sides; d) supplying a pressure means at the container opening so that the inner bag is reattached to the outer container.

2. The method according to claim 1, further characterized in that the section of the base frame is cut.

3. The method according to claim 2, further characterized in that a circular cutter is used for cutting the base frame section.

4. The method in accordance with any of claims 1 because a central section of the base frame is removed or cut.

5. The method in accordance with any of claim 1 because compressed air is used as the pressure medium.

6. The method in accordance with any of claims 1 to 3, further characterized by 4, further characterized by 5, further characterized in that the exposed section of the base seam is lifted by a tool.

7. The method according to claim 6, further characterized in that a blow mandrel is used as the tool, through which the pressure medium is blown into the opening.

8. An apparatus for carrying out the method according to any of claims 1 to 7, characterized by a mounting device, in which a container to be processed can be fixed, a cutting device with a circular cutter, which is positioned to advance, and a separating device, with a blow mandrel, which is mounted to advance and which is connected to a compressed air source.