WO2002060770A1 - Method for manufacturing a liquid packaging container emptying opening - Google Patents

Abstract

The object of the invention is a method for manufacturing a pour opening in packaging container for a liquid substance. In the method a first hole of predetermined size and shape is formed in the base layer (2) made of fibre-based material of a packaging laminate (1), after which the surface of the base layer is laminated on one side with at least one first thermoplastic layer (4) to form a surface film. In accordance with the invention a second hole of predetermined size and shape is formed in the surface film at the location of the first hole, the edges (5) of which second hole are inside the edges of the first hole (3), the surface opposite to at least one first thermoplastic layer of the base layer is laminated with at least one further thermoplastic layer (6), the hole in the surface layer is furnished with a pull tab (7), and the further thermoplastic layer (6) and the pull tab (7) attached on opposite sides of the hole penetrating the surface layer and the base layer are joined together in the area of the hole by application of heat and pressure in such a way that the parts of the first and the second thermoplastic layers (4,6) covering the first hole are heated to softening temperature and treated in such a way that they are shaped so as to enclose between them the raw edge (5) of the hole in the base layer.

Description

Method for manufacturing a liquid packaging container emptying opening

Background of the invention

The object of invention is a method for manufacturing a pour opening in a packaging container for a liquid substance, which container is either partially or fully manufactured from packaging laminate comprising layers of fibre-based material and thermoplastic, and which opening is furnished with a removable pull tab.

Disposable liquid packaging containers are nowadays used increasingly for packaging liquid food products, such as milk, juice and wine. Usually, these packaging containers are manufactured from pre-fabricated laminated packaging material comprising abase layer made of liquid packaging board, which is covered, at least on one side and usually on both sides, with thin liquid- and gas-tight thermoplastic layers, such as polyethylene layers.

In addition, liquid packaging containers are generally furnished with some kind of opening device, for example with an indication for tearing or cutting or with a removable pull tab that is attached over the pour opening in a liquid- and gas-tight manner. Typical examples of liquid packaging containers furnished with opening devices of this kind are found, for example, in U.S. Patent No. 5 653 383 and in the published application EP 155 600.

An opening device comprising a pour opening that has been pre-pierced in the packaging material and a removable pull tab that is attached in a liquid- and gas-tight manner over the opening, has many advantages in that it is easy to use, it can be attached to the packaging material beforehand, and it is economical costwise. However, when packaging liquid fill materials, special attention must be paid to ensure that the raw edge of the packaging laminate exposed in the piercing is carefully isolated from the fill material, because otherwise the fill material is absorbed into the fibrous base layer, which impairs the tightness, strength and appearance of the laminate. Therefore, in order to prevent absorption, it is usual, that, in addition to the removable pull tab, the pour opening is provided with an inner thermoplastic layer that is placed on the side of the laminate against the fill material and covers both the pour opening and the area around it. This covering layer is thus joined to the pull tab via the pour opening in such a way that the covering layer tears off when the pull tab is removed, enabling the emptying of the fill material through the pour opening. However, the raw edge previously sealed by the covering layer is thereby exposed again, and some fill material will be absorbed into the fibrous base layer during emptying. This is not, however, desirable for hygienic and aesthetic reasons.

When packaging sterile fill materials, such as sterile milk and sterile juice, aseptic packages are used mainly having the above-described structures. The packaging laminate, however, comprises one or more additional layers in order to improve gas tightness. The gas barrier used for this is usually aluminium foil or thermoplastic, for example polyethylene. In this case it is especially important to avoid contact between the fill material and the metal, and not only during storage in a closed container, but also during the emptying phase and when the remaining fill material is stored in an open container. This applies especially to acid fill materials, such as juice and wine, because contact between these fill materials and metal causes a chemical change that affects the taste of the product.

The earlier solutions used to avoid the above-mentioned problems in aseptic packaging containers furnished with a removable pull tab have been very complex and comprised an inner covering layer, the purpose of which was to prevent the fill material from coming into contact with the raw edge of the pour opening and to make sure that a sufficient gas barrier is formed between the fill material and said raw edge. The weakness of earlier solutions has been the fact that separate tabs, fitted only at the location of the hole in the base laminate, have been used as an inner covering layer. hi addition, solutions have also been presented in which both the outer and inner covering layers have been laminated over the whole base laminate. Solutions of this kind involve, among other things, problems with the opening system of the package, which are due to the thick film that is formed over the hole. On the other hand, it has been proposed that the thick film formed over the hole can be weakened at the points where the film is supposed to tear when the pour opening is opened. A structure of this kind is presented, for example, in the pubhshed application EP 686567. However, such weakening of the film essentially impairs the gas tightness of the package, which is by no means recommendable when the object is expressly to secure a sufficient gas barrier between the fill material and 1he packaging laminate's raw edge as well as between the fill material and the surrounding gas, such as air. The Finnish Patent No. 104 811 presents a solution in which both the outer and inner covering layer are laminated over the whole base laminate. The solution presented in the said Finnish Patent No. 104 811 differs from the above-mentioned published patent application EP 686 567, among other things, in that the hole forming the pour opening is formed before the pull tab is attached. Such solutions, in which the removable pull tab alone serves the purpose of ensuring the gas barrier between the fill material and the gas surrounding the package, involve several problems as regards achieving a sufficient gas barrier. In addition, to acquire a sufficient gas barrier, the pull tab must be secured very tightly to the packaging laminate, which makes it more difficult to open the package. One significant weakness of previous solutions has been that the base material, that is the so-called base laminate, has comprised a layer of fibre-based material and at least one thermoplastic layer laminated onto that. In this base laminate a hole has been formed for the pour opening, after which additional thermoplastic layers have been laminated in order to enclose the raw edge of the layer of fibre-based material containing the base laminate. This means that the thermoplastic layer in the base laminate has not played any part in sealing the raw edge, and thus the material could not be used optimally, and secondly, due to the additional layers, the containers were unnecessarily thick. Such structures are presented, for example, in the pubhshed application EP 686567, U.S. Patent No. 5 653 383, and FI Patent No. 104 811. The solutions described in the above-mentioned U.S. Patent No. 5 653 383 also involve various problems both in the opening arrangement itself and in the general structure of the packaging material. When both the sealing of the raw edge and the pull tab itself are executed by means of tabs fitted only at the location of the hole in the base laminate, the opening when sealed becomes so much thicker than the rest of the packaging laminate that 1he rolls in which packaging material are stored become unfit for use. On the other hand, sealing the raw edge with a separate tab means that the packaging laminate in which the hole for the pour opening has been pierced should in itself meet the gas and liquid tightness requirements placed on the package, at least as regards the outer surface, because the tab in question does not play any part in meeting these requirements. Such a tab, if used for sealing the raw edge, will in addition have to be aligned with the hole in the packaging laminate and attached to the edges of the hole, which makes the manufacture a complex process that demands precision in this respect too.

Brief description of the invention

It is an object of the present invention to present a method for manufacturing a pour opening, which method does not involve the above-mentioned problems. The present invention thus relates to a method for manufacturing a pour opening in a packaging container intended for a liquid substance, which container is partly or wholly manufactured from packaging laminate comprising layers of fibre-based material and thermoplastic, and which opening is furnished with a removable pull tab, in which method a first hole of predetermined size and shape is formed in the base layer of fibre-based material of the packaging laminate, after which the surface of the base layer is laminated on one side with at least one first thermoplastic layer to form a surface film.

The method in accordance with the present invention is characterised in that a second hole of predetermined size and shape is formed in the surface film at the location of the first hole, the edges of which second hole are inside the edges of the first hole, that the surface opposite to at least one first thermoplastic layer of the base layer is laminated with at least one further thermoplastic layer, that the hole in the surface layer is furnished with a pull tab, and that the second thermoplastic layer and the pull tab attached to the opposite sides of the hole penetrating the surface layer and the base material, are joined together in the area around the hole by the application of heat and pressure in such a way that the parts of the first and second thermoplastic layers covering the first hole are heated to softening temperature and treated in such a way that they are shaped and enclose between them the raw edge of the hole in the base layer.

This method has several essential advantages. One of the most central advantages is that the base layer made of fibre-based material does not need to be separately laminated with a gas- and Uquid-tight thermoplastic layer and a thermoplastic layer for sealing the raw edge, since all the layers laminated on that side of the base layer made of fibre-based material that forms the exterior surface of the packaging, play a part in sealing the raw edge. In addition, a thermoplastic layer laminated on the base material and any further layers laminated on top of the said thermoplastic layer can be optimised as regards their properties. Thus the thermoplastic layer to be laminated onto the surface of the base material can be chosen so mat it provides optimal adhesion to the base layer made of fibre-based material, even if this is achieved at the expense of other properties such as gas and liquid tightness. These other properties can then be obtained by laminating a further thermoplastic layer on top of the first thermoplastic layer. It is a known fact that the films possessing the best barrier properties adhere best to layers of thermoplastic rather than to layers of fibre-based material such as board. Therefore, of the thermoplastic layers that play a part in sealing the raw edge, the one closest to the raw edge is the thermoplastic layer that adheres optimally to the base layer made of fibre-based material. Moreover, all the films laminated on top of the layer of fibre-based material play a part in sealing the raw edge, and these other films used in sealing the raw edge can now better be selected for properties that are important for sealing the raw edge with the highest possible degree of gas and liquid tightness. Furthermore, the layer used in sealing the raw edge can be laminated in a fully conventional manner, as it is now intended to cover the base laminate entirely, and no special solutions are needed for aligning the said layer with respect to the hole in the base laminate.

One essential advantage achieved by this method is an excellent gas barrier between the fill material and the gas surrounding the packaging. According to this method, the interior surface of the packaging laminate is laminated with an unbroken thermoplastic layer that is not perforated at any stage of manufacture. Therefore, this unbroken layer can be laminated from a material that has excellent barrier properties, and an excellent gas barrier can be obtained without further barrier layers. Preferably the thermoplastic layer that forms the interior surface of the packaging laminate is extruded in the form of a polyethylene film or a multi-laminated barrier structure comprising an ethylene/alpha-olefin. The polyethylene film is preferably of low-density polyethylene (PE-LD). The multi-laminated barrier structure may comprise, for example, five layers extruded simultaneously by the same extruder. In this case, for instance, the film placed against the base layer of fibre-based material can be made of polyethylene, for example PE-LD. The multi- laminated barrier structure preferably also comprises a layer of an ethyl/vinyl alcohol copolymer. To improve or to obtain barrier properties, if the other thermoplastic layers lack this property, the first thermoplastic layer forming the surface layer may comprise some suitable barrier plastic, such as an ethylene/alpha-olefin.

Preferably the thermoplastic layer that forms the surface layer of the packaging laminate is extruded as a polyethylene film or as a multi-laminated barrier structure comprising an ethylene/alpha-olefin. The polyethylene film is preferably low-density polyethylene (PE-LD). The multi-laminated barrier structure may comprise, for example, five layers extruded simultaneously by the same extruder, h this case the film placed against the base layer made, for example, of fibre- based material, may be polyethylene, such as PE-LD, and the second film to be laminated on top of this film may comprise over 50%, e.g. 80%, of ethylene/alpha-olefin, while the rest is PE-LD. The other layers of the multi-laminated barrier structure in question may, for example, be polyethylene (PE) or polypropene (PP). The multi-laminated barrier structure in question may also comprise layers of adhesion agents. This enables optimal adhesion to the base layer made of fibre-based material and also good barrier properties, in such a way that the thermoplastic layer creating the barrier properties is not the outermost layer that is in contact with the product to be packed.

In the method according to the invention, two holes are formed, of which the first hole, larger in size, is formed in the base material, and a second hole, smaller in size, is formed in the surface film. The second hole of predetermined size and shape formed in the surface film is formed at the location of the first hole, in such a way that the edges of the second hole are inside the edges of the first hole.

The forming of both holes can be performed in a more conventional manner, for example by die cutting. What is essential is that, when forming the second hole, the surface film is left to partly cover the hole in the base material, and that this part of the surface film covering the hole in the base material is sufficient to seal the raw edge together with the thermoplastic layer laminated on the other side of the base material, when they are heated to softening temperature and treated in such a way that they are shaped to seal between them in a gas and liquid tight manner the raw edge of the hole in the base layer. According to the invention, the sealing of the opening is performed by both an inner thermoplastic layer and a removable pull tab attached on the outside. The pull tab is attached by application of heat and pressure in the area of the hole in such a way that it is attached tightly to the unbroken thermoplastic layer on the inside of the package. When removing the removable pull tab, the inner unbroken thermoplastic layer of the package will tear at the location of the hole formed in the first thermoplastic layer, attached to the pull tab, in such a way that a pour opening is formed, but the raw edge of the base laminate will still remain sealed.

A short description of the figures The invention will be illustrated in more detail by reference to the appended drawings, in which Figure 1 shows in cross-section one exemplary embodiment of a pour opening according to the invention and Figure 2 shows in cross-section one exemplary embodiment of the pour opening according to the invention at different phases of manufacture. Figure 3 shows a cross- section of the multi-laminated barrier structure in one exemplary embodiment of the pour opening according to the invention.

Detailed description of preferred embodiment

Figure 1 shows the packaging laminate 1, the phases of manufacture of which are shown in Figure 2, A-G. Figure 2 A shows the base layer 2 made of fibre-based material, through which layer a hole has been pierced, the surrounding raw edge of which is indicated by the number 3 (Figure 2 B). Thereafter the base layer has been laminated on one side with a thermoplastic layer in order to form a surface film 4 (Figure 2 C). Then a hole has been made in the surface film 4, the edges 5 of which hole are on the inside of the hole made in the base layer (Figure 2 D). The base layer has then been laminated, on the side opposite to the surface layer, with a thermoplastic layer 6, in order to form the inner layer of the packaging laminate (Figure 2 E). Finally, the hole made in the surface layer is covered with a removable pull tab 7 (Figure 2 F), which is then by application of heat and pressure pressed tightly together with the inner surface 6 of the packaging laminate (Figure 2 G). Thereby the pull tab 7 and the thermoplastic layer 6 forming the inner surface adhere to each other tightly. Simultaneously the thermoplastic layers 4 and 6 are also pressed together and fuse together, covering the raw edge 3 so as to make it gas and liquid tight. The package can be opened by removing the removable pull tab 7, whereby the drinking hole is formed in the packaging laminate between the dotted lines 8 indicated in Figure 1. Thus the thermoplastic layers 4 and 6 remain to protect the raw edge 3 of the base layer made of fibre-based material. To improve or to obtain barrier properties, in case the other thermoplastic layers lack this property, the first thermoplastic layer 4 forming the surface layer may comprise some suitable barrier plastic such as an ethylene/alpha-olefin.

Preferably the thermoplastic layer 4 forming the surface layer of the packaging laminate 1 is extruded to form a polyethylene film or a multi-laminated barrier structure comprising an ethylene/alpha-olefin. The polyethylene film is preferably of low-density polyethylene (PE-LD). The multi-laminated barrier structure may comprise, for example, five layers extruded simultaneously using the same extruder. In this case, for example, the film coming into contact with the base layer of fibre-based material may be polyethylene, such as PE-LD, and the other film laminated on top of this film may comprise over 50%, e.g. 80%, of ethylene/alpha-olefin, while the rest is PE-LD. In this way optimal adhesion to the base layer of fibre-based material is obtained, as well as good barrier properties, in such a way that the thermoplastic creating the barrier properties is not the outermost layer that is in contact with the packaged product. The other layers of the said multi-laminated barrier structure may, for example, be of polyethylene (PE) or polypropylene (PP). The said multi-laminated barrier structure may also comprise layers of adhesion agent. A preferred adhesion agent is the Admer® adhesive resin produced by Mitsui Chemicals.

A preferred embodiment in accordance with the invention is shown by the way of an example in Table 1 and Figure 3, in which the base layer made of fibre-based material is marked with the letter a, the first thermoplastic layer 4 fprming the surface layer is marked with the letters b - f, and the further thermoplastic layer 6 forming the inner layer of the packaging laminate is marked with the letters g - k. Table 1 shows the material of each of the layers of the packaging laminate and their preferred amounts. Table 1

While the preferred embodiment of the present invention has been disclosed herein, it will be appreciated that the described structure of the invention may be modified to some extent without departing from the scope of protection as found in the appended patent claims.

Thus the thermoplastic layer formed on the surface of the base layer may also include, before perforation, more than one thermoplastic layer or, for example, a barrier layer of duminium. The number and nature of the layers is above all determined on the basis of the intended use of the package. Similarly the nature and number of the layers to be laminated on the inner surface of the base laminate is above all determined on the basis of the desired properties of the package in question. The layer composition of the ready-made packaging laminate is naturally optimised so that it meets the desired requirements, both as regards the packaging laminate itself and as regards the sealing of the raw edge of the hole made in the packaging laminate. In the method according to the invention, the layers necessary for the sealing of the raw edge are used to optimal advantage in the other parts of the packaging laminate as well, whereby it is possible to avoid using unnecessary and thus, from the point of view of a specific use, extra thermoplastic layers.

Claims

Claims

1. Method for manufacturing a pour opening in packaging container for a liquid substance, which container is either partially or fully manufactured from a packaging laminate consisting of layers of fibre-based material and thermoplastic, and which opening is furnished with a removable pull tab, in which method a first hole of predetermined size and shape is formed in the base layer (2) made of fibre-based material of the packaging laminate (1), after which the surface of the base layer is laminated on one side with at least one first thermoplastic layer (4) to form a surface film, characterisedin that a second hole of predetermined size and shape is formed in the surface film at the location of the first hole, the edges (5) of which second hole are inside the edges of the first hole (3), the surface opposite to at least one first thermoplastic layer of the base layer is laminated with at least one further thermoplastic layer (6), the hole in the surface layer is furnished with a pull tab (7), and the further thermoplastic layer (6) and the pull tab (7) attached on opposite sides of the hole penetrating the surface layer and the base layer are joined together in the area of the hole by the application of heat and pressure, in such a way that the parts of the first and the second thermoplastic layers (4, 6) covering the first hole are heated to softening temperature and treated in such a way that they are shaped so as to enclose between them the raw edge (5) of the hole in the base layer.

2. A process in accordance with patent claim 1, char cte ised in that at least one first thermoplastic layer (4) is extruded to form a multi-laminated barrier structure comprising an α-olefin.

3. A process in accordance with patent claim 2, characterised in that polyethylene is extruded to form a layer that comes into contact with the base layer (2) of fibre- based material in the multi-laminated barrier structure .

4. A process in accordance with either of patent claims 2 or 3, characterised in that polypropylene is extruded to form at least one of the layers of the said multi-laminated barrier structure.

5. A process in accordance with any of patent claims 1-4, characterised in that the said at least one further thermoplastic layer (6) is extruded to form a multi-laminated barrier structure.

6. A process in accordance with patent claim 5, characterisedin that polyethylene is extruded to form the layer that comes into contact with the base layer (2) made of fibre-based material in the multi-laminated barrier structure.

7. A process in accordance with patent claim 5 or 6, characterised in that an ethyl/vinyl alcohol copolymer is extruded to form at least one layer of the said multi-laminated barrier structure.

8. A process in accordance with patent claims 1-7, characterised in that the first and the second holes are formed by die-cutting.