Plastic coated paper container with cut edges protected against moisture

Abstract: A packaging container comprising a packaging material including a paper substrate (13), an intermediate layer, an outermost layer (15) and an innermost layer (14) and having opposite side edges which overlap each other so that the outermost layer and the innermost layer of the packaging material face each other. A bending portion (19) is interposed between the outermost layer (15) and the innermost layer (14) by folding the bending portion joined with these layers. The outermost layer and the intermediate layer are made of resins which have compatibility with each other. The bending portion is formed by projecting the intermediate layer and the innermost layer from one side edge of the paper substrate and the outermost layer.

Description: BACKGROUND OF THE INVENTION FIELD OF THE INVENTION: The present invention relates to a packaging container according to the preamble of claim 1. DESCRIPTION OF THE RELATED ART: Conventionally, packaging containers used for holding liquid foods such as soft drinks and milk have been manufactured in a manner in which a web-like packaging material is formed into a brick-like shape, for example. Fig. 1 is a sectional view of a conventional packaging material. As shown in this drawing, a packaging material 11 is composed of a paper substrate 13, a layer 14 which is the innermost layer when the packaging material 11 is shaped into a package container (hereinafter simply referred to as the "innermost layer"), a layer 15 which is the outermost layer when the packaging material 11 is shaped into a package container (hereinafter simply referred to as the "outermost layer"), a gas barrier layer 16 formed between the paper substrate 13 and the innermost layer 14, and an adhesive layer 27. The paper substrate 13 is made of paperboard or a similar material, and the gas barrier layer 16 is bonded thereto by the adhesive layer 27. The opposite side edges of the packaging material 11 are overlapped with each other and then joined together by heat fusion in the longitudinal direction to obtain a tubular packaging material. The tubular packaging material is then continuously transferred downward while a liquid food is supplied into it from its top. Then, the tubular material is pressed from both sides thereof and is sealed laterally at predetermined intervals so as to obtain pillow shaped containers, which are then formed into a brick-like shape. A strip tape 25 is adhered to the sealed portion longitudinally extending along the inner surface of each packaging container (hereinafter referred to as "longitudinal sealing portion") to prevent air from entering the packaging container from a side edge of the packaging material 11 and to prevent liquid food from permeating the paper substrate 13. Packaging containers, the packaging material 11 of which has the innermost layer 14 made of a polyolefin resin, do not have sufficient ability to maintain the flavors of foods. This is because liquid foods contained in the containers contact the polyolefin resin, which adsorbs flavoring ingredients of the liquid foods over time. In order to increase the flavor-retaining ability of each container, the polyolefin resin layer may be coated with a non-olefin flavor-retaining resin which serves as the innermost layer 14. In this case, the strip tape 25 is made of a non-polyolefin resin which can be easily joined to the above-described flavoring-retaining resin by heat fusion. The strip tape 25 is adhered to the longitudinal sealing portion using heat and pressure. When the innermost layer 14 of the web-like package material is made of a flavor-retaining resin, the resin is joined to a polyolefin resin forming the outermost layer 15 when the overlapped side edges of the packaging material 11 are fused and joined in the longitudinal direction. However, since the flavor-retaining resin and the polyolefin resin are difficult to join with each other, only a poor seal can be obtained. This problem can be solved by joining the flavor-retaining resin and the polyolefin resin by fusion after activating the sealing portion of the surface of the flavor-retaining resin by a corona discharge treatment, an ozone treatment, or a flame treatment, or by joining the flavor-retaining resin and the polyolefin resin by fusion at a high temperature. However, a sufficient seal cannot be obtained even when the flavor-retaining resin is subjected to corona discharge treatment, ozone treatment or flame treatment. When the flavor-retaining resin and the polyolefin resin are fused at a high temperature to join them together, the manufacturing costs increase due to the necessity of an apparatus for high-temperature fusion. It is possible to join the flavor-retaining resin forming the innermost layer 14 and the polyolefin resin forming the outermost layer 15 with an adhesive made of an ethylene - vinyl acetate copolymer (EVA), polyethylene chloride, or the like. In this case, however, steps for applying the adhesive to the packaging material 11 and drying it are additionally required, increasing the complexity and costs in the production process and making the work troublesome. JP 1 241 434, Patent Abstract of Japan, vol.013, no.577 (M-910), Dezember 20, 1989 discloses a bending portion formed by bending the entire packaging material at the overlapping side edges wherein said bending portion is inserted between said outermost layer and said innermost layer of said packaging material by piling up said packaging material and wherein said bending portion is joined by thermal welding with flame treatment with said outermost layer and said innermost layer. GB 2 124 997 A discloses a packaging material including a paper substrate, an intermediate layer, an outermost layer and an innermost layer and having opposite side edges which overlap each other such that said outermost layer and said innermost layer of said packaging material face each other, wherein said intermediate layer and said outermost layer are made of resins which are thermally compatible with each other, and a bending portion formed by projecting said intermediate layer and said innermost layer from one side edge of said packaging material such that said intermediate layer and said innermost layer project from the edges of said paper substrate and said outermost layer, wherein said bending portion is inserted between said outermost layer and said innermost layer of said packaging material by folding said bending portion and wherein said bending portion is joined by heat fusion with said outermost layer and said innermost layer, and wherein said outermost layer is joined to said intermediate layer of said bending portion. Both the innermost and outermost layers are heat-sealable resin layers. SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-described problems of conventional packaging containers, especially to join the flavor-retaining resin forming the innermost layer 14 and the polyolefin resin forming the outermost layer 15, and to provide a packaging container which has an enhanced sealing performance and which reduces production costs. The object is solved according to the characterizing features of claim 1. Preferred embodiments of the present invention are claimed and disclosed within the subclaims. A packaging container according to another aspect of the present invention includes a packaging material having a paper substrate, an intermediate layer, an outermost layer, and an innermost layer. The opposite side edges of the packaging material are overlapped with each other so that the outermost layer and the innermost layer of the packaging material face each other. The intermediate layer and the innermost layer of the packaging material are projected from the side edges of the paper substrate and the outermost layer to form a bending portion which extends along the sealing portion. The bending portion is inserted between the outermost layer and the innermost layer of the packaging material by folding the bending portion and is joined to those layers by heat fusion. The outermost layer and the intermediate layer of the packaging material are made of resins which are compatible with each other. With this structure, resins which are compatible with each other are melted and joined to each other to form a longitudinal sealing portion, thereby providing an enhanced heat sealing performance. The side edge of the packaging material located inside the packaging container is covered with the bending portion. Accordingly, liquid food is prevented from permeating the paper substrate through the edge of the packaging material, and so the packaging container has an enhanced durability. In addition, the operation for adhering a strip tape to the inner surface of the packaging container along the longitudinal sealing portion becomes unnecessary. In a packaging container according to another aspect of the present invention, the innermost layer of the packaging material is preferably a non-olefin flavor-retaining resin. In this case, since liquid food in the packaging container contacts the flavor-retaining resin, the flavor ingredients of the liquid food are not absorbed thereby, resulting in an enhanced flavor retainability. The outer surface of the paper substrate is covered by the heat absorbing layer along the longitudinal sealing portion. Accordingly, when infrared rays are irradiated to the longitudinal sealing portion, the heat absorbing layer is locally heated to a high temperature due to the radiant heat, so that the intermediate layer and the outermost layer can be easily fused and joined to each other without causing color changes in the remaining printed surface. BRIEF DESCRIPTION OF THE DRAWINGS The structures and features of packaging containers according to the present invention will become clear by referring to the accompanying drawings, in which: Fig. 1 is a sectional view of a conventional packaging material; Fig. 2 is a sectional view of a packaging material according to a second embodiment of the present invention. DESCRIPTION OF PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the accompanying drawings. Next, a second embodiment of the present invention will be described. Fig. 2 is a sectional view of a packaging material according to the second embodiment of the present invention. As shown in Fig. 2, a packaging material 11 is composed of a paper substrate 13 as a base layer, an innermost layer 14, an outermost layer 15, a gas barrier layer 16 formed between the paper substrate 13 and the innermost layer 14, and an adhesive layer 27 as an intermediate layer. The paper substrate 13 is made of paperboard or the like, and the gas barrier layer 16 is adhered to the paper substrate 13 by the adhesive layer 27. A resin compatible with the outermost layer 15 is used to form the adhesive layer 27. An aluminum foil is used for the gas barrier layer 16. The innermost layer 14 is formed of a flavor-retaining resin which is coated on the inner surface of the gas barrier layer 16. The outermost layer 15 is formed of a polyolefin resin which is coated on the outer surface of the paper substrate 13. Examples of the flavor-retaining resin include non-olefin resins such as polyester resins, polyamide resins, polyvinylidene chloride resins, ethylene - vinyl alcohol copolymers, polyvinyl chloride resins, epoxy resins, polyurethane resins, polyacrylate resins, polyacrylonitrile resins, and polycarbonate resins. A molten flavor-retaining resin is extruded as a film from an unillustrated extruder, and is then superposed on the inner surface of the gas barrier layer 16. A small amount of an additive such as nitrocellulose may be optionally added in the molten flavor-retaining resin. In the present embodiment, polyester is used as the flavor-retaining resin. Since the liquid food comes into contact with the flavor-retaining resin, the flavor ingredients of the liquid food are not absorbed thereby. As a result, an enhanced flavor retainability can be obtained. Examples of the polyolefin resin include polyethylene, polypropylene, low-density polyethylene, and linear low-density polyethylene. In the present embodiment, polyethylene is used for the polyolefin resin. Therefore, polyethylene is also used for the adhesive layer 27. A packaging container for carrying liquid food can be obtained by forming the web-like packaging material 11 into, for example, a brick-like shape. In detail, the opposite side edges of the packaging material 11 are overlapped with each other and are joined by heat fusion in the longitudinal direction to obtain a tubular packaging material. The obtained tubular material is continuously transferred downward while a liquid food is supplied into it from the top. Then, the tubular material is pressed from both sides thereof and is sealed laterally at predetermined intervals to obtain pillow shaped containers, which are then formed into a brick-like shape. Since the innermost layer 14 is made of a flavor-retaining resin, it is difficult to join the innermost layer 14 to the outermost layer 15 by heat fusion in order to join the opposite side edges of the packaging material 11 in the longitudinal direction. Also, it becomes difficult to fuse and join facing surfaces of the innermost layer 14. To overcome these problems, the packaging container according to the present embodiment employs a structure in which a bending portion 19 integratedly extended from the packaging material 11 is disposed between the innermost layer 14 and the outermost layer 15 at the longitudinal sealing portion to prevent the outermost layer 15 from coming into direct contact with the innermost layer 14. The opposite side edges of the packaging material 11 are joined via the bending portion 19. The bending portion 19 is formed by extending the innermost layer 14, the gas barrier layer 16 and the adhesive layer 27 from one side edge of the packaging material 11 such that they project from the end surfaces of the paper substrate 13 and the outermost layer 15 by a predetermined amount. Therefore, the bending portion 19 has a laminated structure formed by the innermost layer 14, the gas barrier layer 16 and the adhesive layer 27. Before the packaging material 11 is sterilized with hydrogen peroxide, the bending portion 19 is bent outward and folded, and the adhesive layer 27 and the outermost layer 15 are brought into contact with each other and fused for joining together. In this case, black ink 31 serving as a heat absorbing layer is applied to the outer surface of the paper substrate 13 along the longitudinal sealing portion. Accordingly, when infrared rays are irradiated to the longitudinal sealing portion, the black ink 31 is locally heated to a high temperature due to the radiant heat, so that the adhesive layer 27 and the outermost layer 15 can be easily fused and joined to each other without causing color changes in the remaining printed surface. Subsequently, both side edges of the packaging material 11 are fused and joined to each other in the longitudinal direction. Since the bending portion 19 has been folded outward and the adhesive layer 27 has been joined to the outermost layer 15 at the bending portion 19, one lateral end portion of the innermost layer 14 comes into contact with the other lateral end portion of the innermost layer 14, so that an enhanced sealing performance can be obtained. As described above, the sealing performance can be improved by interposing the bending portion 19 of the packaging container between the innermost layer 14 and the outermost layer 15 along the longitudinal sealing portion. Since the packaging material 11 has a web-like shape, the paper substrate 13 is exposed to the liquid food in the packaging container at a side edge. In the present embodiment, the paper substrate 13 is prevented from being exposed to the liquid food by covering the exposed side edge with the bending portion 19. Accordingly, it is not necessary to adhere a strip tape to the inner surface of the packaging container along the longitudinal sealing portion. As a result, it is possible to simplify the production process and to reduce costs.

Claims: A packaging container comprising: a packaging material (11) including a paper substrate (13), an intermediate layer (16, 27), an outermost layer (15) and an innermost layer (14) and having opposite side edges which overlap each other such that said outermost layer (15) and said innermost layer (14) of said packaging material (11) face each other, wherein said intermediate layer (16, 27) and said outermost layer (15) are made of resins which are thermally compatible with each other, and a bending portion (19) formed by projecting said intermediate layer (16, 27) and said innermost layer (14) from one side edge of said packaging material (11) such that said intermediate layer (16, 27) and said innermost layer (14) project from the edges of said paper substrate (13) and said outermost layer (15), wherein said bending portion (19) is inserted between said outermost layer (15) and said innermost layer (14) of said packaging material (11) by folding said bending portion (19), and wherein said bending portion (19) is joined by heat fusion with said outermost layer (14) and said innermost layer (15), wherein said outermost layer (15) is joined to said intermediate layer (27) of said bending portion (19), characterized in that said innermost layer (14) and said outermost layer (15) are made of resins which are difficult to join to each other by heat fusion, and a heat absorbing layer (31) is formed in the outer surface of said paper substrate (13) to enhance the heat sealing performance. A packaging container as claimed in claim 1, characterized in that , said innermost layer (14) of said packaging material (11) is made of a non-olefin flavor-retaining resin. A packaging container as claimed in claim 1 or 2, characterized in that , said outermost layer (15) of said packaging material (11) is made of a polyolefin resin.

Inventors: IKENOYA TADAKATSU, ONO KAZUYA, IKENOYA, TADAKATSU, ONO, KAZUYA
Applicants: TETRA LAVAL HOLDINGS & FINANCE, TETRA LAVAL HOLDINGS & FINANCE SA
Application year: 1995
Main classification: B65D5
IPC codes: B32B27, B65D5, B31B1