A TEARING STRIP, A METHOD OF MANUFACTURING SUCH STRIP AND A PACKAGE PROVIDED WITH THE TEARING STRIP

Abstract: A tearing strip of the delaminating type intended for attach­ ment to opposite insides of a package. The strip has such a layer structure that, relative the inside of the package, it has a melted-together seal while internally the strip has layers which are not fully melted together. The strip comprises a central, strong layer (21) and a first (22, 23) and second (24, 25) layer arrangement. The first layer arrangement (22, 23) has a well reproducable, high seal strength relative the central layer. However, the second layer arrangement (24, 25) is "peelable" relative the first layer arrangements (22, 23) or more likely internally between two layers (25, 24). In contrary the second layer arrangement has a well reproducable, high sealing strength relative the inside (26, 27) of the package.

Description: The present invention relates to a tearing strip arranged between two internal surfaces of a package. The invention further relates to a method of manufacturing such a strip. There are a great variety of known solutions providing opening facilities for packages, flexible packages, cardboard packages, bottles and tubes of plastics or plastics laminate, etc. So called flexible packages frequently use what is called "peelable layers". The specific characteristics of such layers which, so to say, delaminate at command and which are used for providing opening means, frequently are obtained by means of heat sealing of thermoplastic materials of polyolefine type and of such a characteristic that the materials are incompatible in terms of heat sealing. More simplified the materials may be defined as material which do not melt together when heat activated at a certain temperature, but give a certain bond. As far as pouches of plastics or plastic laminate or polyethylene coated cardboard packages are concerned there are a great number of prior art tearing strips. However, such known strips lack a structure for making the concept commercially useful. This depends on several factors, for instance the previous lack of a basic concept for manufacturing of strips. One prior art solution of the tearing open problem by using tearing strips, as described in EP-A-0083441, utilizes a central strong layer having a primer on both sides thereof and at the outside thereof there are polyethylene layers at both primer layers. The strip is sealed between two opposite inside surfaces of a package, at a pouring opening region thereof, such that a perfect strain resisting seal is obtained between said inside surface and the two polyethylene layers. However, the seal between the primer layers and each adjacent polyethylene layer is made peelable. So, when pulling the strip for tearing up the package at the pouring region thereof, the product inside the package may be exposed to the primer layers or at least residues of such. Additionally, the creation of a peelable layer, by using primer and reduced heat, and at the same time providing a perfect full-strength seal between polyethylene/polyethylene, is a very difficult task. One object of the invention is to eliminate said lack and offer an alternative which is an optimum in terms of production as well as handling. Another object is to eliminate all product harmful residues, for instance primer, from the strip and the opening of the package after the strip has been removed. The present invention provides a tearing strip, arranged between two internal surfaces of a package in the region of a pouring opening, said tearing strip comprising a grip portion protruding from the package which is arranged to be pulled to expose said pouring opening, said tearing strip comprising a central, strong layer, a pair of first layer arrangements on either side of said central layer, the first layer arrangements having a high sealing strength relative to the central layer, and a pair of second layer arrangements on either side of said pair of first layer arrangements, said pair of second layer arrangements having a material layer which, in terms of heat sealing, is incompatible to said pair of first layer arrangements and is indirect contact with and peelably sealed to said pair of first layer arrangements or internally between two layers forming said second layer arrangements, said pair of second layer arrangements having a high sealing strength relative to the internal surfaces of said package. In a preferred embodiment, the internal surfaces of the package comprise polyethylene or a coating of polyethylene, the central layer comprises a polyethylenetherephtalat layer (PETP), the said first layer arrangement comprises a first polyethylene layer and a primer layer between the polyethylene layer and the polyethylenetherephtalat layer, and the second layer arrangement comprises a second polyethylene layer and a layer X which in terms of heat sealing is incompatible to polyethylene. Examples of preferred layers X are layers of polypropylene or polyamide. In one preferred embodiment the central layer has a thickness within the range 20-50 µm and the rest of the layers of the strip have the following surface weights: Primer layer 0.8 g/m² TH, the first polyethylene layer 14 g/m², X-layer 10 g/m² and the second polyethylene layer 11 g/m². In a specifically preferred embodiment the first and the second polyethylene layers and the layer X are coextruded. The invention also provides a method for manufacturing a tearing strip for use in a package of the above-mentioned type, intended for attachment to opposite internal surfaces of said package in the region of a pouring opening, to present a grip portion protruding from the package and arranged for being gripped to remove the tearing strip from the package and exposing the said pouring opening, wherein at each side of a central, strong layer there is applied a primer, and that on the respective primer coated side there are coextruded layers of polyethylene ― X ― polyethylene, where X is a layer which is incompatible, in terms of heat sealing, to polyethylene. The present invention will now be exemplified with reference to the accompanying drawings, where Fig. 1 in a perspective view shows a cardboard package of the "gable top" type having a tearing strip according to the invention, Fig. 2 is a partial section along the cross seal of the package in fig. 1, Fig. 3 schematically shows, in an exaggerated scale as in fig. 2, the tearing strip removed from the cross seal. The package 10 in fig. 1 is a package of the gable top type manufactured from plastics coated cardboard, where at least the inside of the package is coated by plastics, generally by a coating of polyethylene. The package 10 may be intended to be used with any type of pourable product, powder, liquid, etc. In a manner known per se the package 10 has a planar bottom closure 11 and the four side walls 12-15 of the package are assembled in a known manner to form a container casing. At the top there is arranged a top closure 16 which is of the so called gable top type and comprises a crosswisely extending seal 17, where the cardboard material is heat sealed, innerside to innerside along the whole length of the cross seal 17, except the section thereof where the tearing strip 18 is inserted. In figs. 2 and 3, this tearing strip has been shown with an exaggerated thickness; in practice the heat sealing operation normally used for obtaining a cross seal is not disturbed. The thickening of material possibly caused by the strip is easily compensated by corresponding recesses in the sealing jaws. The purpose is, that the strip 18 and the outer portion 19 thereof in fig. 1 inserted in the end seal, should be used for opening up the section thereof where the strip is inserted. The strip is designed such that a delamination occurs when the strip is gripped at the portion 19 and this portion is pulled in the direction of the arrow 20. The strip delaminates "internally" at such an operation. Thus, it is not the question of a bad seal between the strip and the insides of the packaging materials, but a solution to the sealing problem which does not effect the tightness obtainable by a complete and perfect heat seal along the entire section or length of the crosswise seal or closure 17. For this specific purpose the strip has a unique structure and comprises basically a central, strong layer 21, in the actual embodiment consisting of a 36 µm thick polyethylenetherephtalat film. Symetrically, at both sides of this central layer 21 there are a first and a second layer arrangements. In the actual case the first layer arrangement comprises two layers, one layer 22 consisting of a primer, and another layer 23 consisting of polyethylene. The adhesion or attachment between the polyethylene layer 23 and the central layer 21 gives a well reproducable, high strength seal. This type of layer structure, as such, is very common in packaging applications and further details thereof are unnecessary in this context. The so called second layer arrangement according to the present invention does also comprise two layers, one first layer 24, which temporarily may be identified as a layer consisting of the composition X, and a second layer 25 of polyethylene. The material of the layer X is so elected, that when using the heat sealing operation intended for the seal 17, there is obtained, as mentioned, an adequate seal between the polyethylene layers 26, 27 of the packaging material and between the layer 25 and a respective layer 26, 27, however, not between the layer 24 of the material X and the adjacent polyethylene layer 25, 23. For this purpose the layer 24 in the actual embodiment is a polypropylene layer. In fig. 3 it is shown how the strip 18 is removed from the crosswise seal 17 and how it has left a pouring opening 28. As mentioned, the strip 18 is externally coated by polyethylene layers 25. Said layers 25 are shown broken through at the tearing up surfaces 29, 30. As previously mentioned, however, the seal between the outer layer 25 of the strip 18 and the polypropylene layer 24 of the strip is of the type "not melted together", meaning that there is a delamination at the boarder surface 31 between each polyethylene layer 25 and the polypropylene layer 24 inside such layer. This delamination effect means that, as soon as the strain in the polyethylene layer 25, i.e. the tearing strain, exceeds the level necessary for tearing up the polyethylene layer and what is needed for delamination, said delamination occurs and leaves portion 25a of the polyethylene outer layer at the inside of the packaging material. Inside the polyethylene layer 25 there is a polypropylene layer, and this layer is partially exposed when the strip is torn. It should be observed, that the primer coating or the primer layer never is exposed and thus has no possibility of effecting the contents of the package. In the embodiment according to figs. 1-3, there were obtained especially advantageous opening characteristics when using the following composition of material: a central layer 21 of polyethylenetherephtalat having a thickness of 36 µm, outer polyethylene layers 25 having a surface weight of 11 g/m², a polyethylene layer 24 having a surface weight of 10 g/m², inner polyethylene layers 23, 24 having a surface weight of 14 g/m² and primer having a surface weight of 0.8 g/m TH. Tests were also made with polyamide and acceptable results were obtained. The manufacture of the strip was carried out in such a manner that each side of a polyethylenetherephtalat film of the said thickness was coated by a primer, whereafter in an extruder, in successive stations there were coextruded layers of polyethylene ― X ― polyethylene of said thickness, first on one side of the polyethylenetherephtalat layer and then on the second side. Although the invention has been described in connection with cardboard packaging, it is realised that the tearing strip is useful also in connection with packages of so called flexible type, i.e. pouches or corresponding of plastics or plastics laminate, as well as packages of tray type, where the strip may be inserted between the closure and the tray to allow simple initiating of the tearing off of the closure by the grip portion thereof and the internal delamination characteristics.

Claims: 1. A tearing strip (18), arranged between two internal surfaces of a package (10) in the region of a pouring opening, said tearing strip (18) comprising a grip portion (19) protruding from the package which is arranged to be pulled to expose said pouring opening, said tearing strip (18) comprising a central, strong layer (21), a pair of first layer arrangements (22, 23) on either side of said central layer (21), the first layer arrangements having a high sealing strength relative to the central layer, and a pair of second layer arrangements (24, 25) on either side of said pair of first layer arrangements, said pair of second layer arrangements having a material layer which, in terms of heat sealing, is incompatible to said pair of first layer arrangements and is in direct contact with and peelably sealed to said pair of first layer arrangements or internally between two layers forming said second layer arrangements, said pair of second layer arrangements having a high sealing strength relative to the internal surfaces of said package. 2. A tearing strip according to claim 1, wherein the internal surfaces of the package consist of polyethylene or a polyethylene coating, that the central layer (21) comprises a polyethylenetherephtalat layer, that said first layer arrangement (22, 23) comprises a first polyethylene layer (23) and a primer layer (22) between said polyethylene layer and polyethylenetherephtalat layer, and that the second layer arrangement (24, 25) comprises a second polyethylene layer (25) and a layer X, which in terms of heat sealing, is incompatible to polyethylene. 3. A tearing strip according to claim 2, wherein the layer X comprises polypropylene or polyamide. 4. A tearing strip according to claim 3, wherein the central layer has a thickness of the range 20-50 µm, preferably 35 µm and that the remaining layers of the strip have the following surface weights, the primer layer 0.8 g/m² TH, the first polyethylene layer 14 g/m², the X layer 10 g/m², and the second polyethylene layer 11 g/m². 5. A tearing strip according to claim 2, wherein the first and second polyethylene layers and the layer X form a coextruded structure. 6. A method of manufacturing a tearing strip (18) for use in a package (10) according to any one or any of the preceding claims, intended for attachment to opposite internal surfaces of said package in the region of a pouring opening to present a grip portion (19) protruding from the package and arranged for being gripped to remove the tearing strip from the package and exposing the said pouring opening, wherein at each side of a central, strong layer (21) there is applied a primer (22), and that on the respective primer coated side there are coextruded layers polyethylene ― X ― polyethylene, where X is a layer which is incompatible, in terms of heat sealing, to polyethylene.

Inventors: PERSSON, BENGT
Applicants: AB AKERLUND & RAUSING
Application year: 1989
Main classification: B65D5
IPC codes: B65D75, B65D77, B65D5