Envelopes – wrappers – and paperboard boxes – Paperboard box – With closure for an access opening
Reexamination Certificate
2000-01-04
2003-04-29
Rada, Rinaldi I. (Department: 3721)
Envelopes, wrappers, and paperboard boxes
Paperboard box
With closure for an access opening
C493S134000, C493S142000, C493S287000, C493S341000, C493S394000
Reexamination Certificate
active
06554182
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a packaging container for the cold storage of liquid foods, for retaining superior flavour and aroma properties in the packed product, the container being of the type which is produced by fold forming and sealing of a planar, substantially rectangular or quadratic packaging container blank comprising side wall panels, top panels and bottom panels, for the formation of a tubular blank with a longitudinal sealing joint between the overlapping longitudinal incision edges of the packaging container blank, the tubular blank thereafter being given the desired bottom and top closures by fold forming and sealing of the bottom and top panels, respectively, of the packaging container blank, the packaging container blank being produced from a laminated packaging material comprising a core layer of paper or paperboard, an outer, aroma barrier layer of PET and a gas barrier layer disposed between the core layer and the aroma barrier layer. The present invention also relates to a method of producing such packaging containers.
BACKGROUND ART
Use has long been made within the packaging industry of packages of a single-use nature (so-called single-use disposable packages) for packing and transporting products such as liquid foods. A very large group of these single-use disposable packages is produced from laminated packaging material based on an interjacent core layer of paper or paperboard and outer laminate layers of some thermosealable plastic possessing superior liquid barrier properties, normally such as low density polyethylene (LDPE).
Depending on what food product is to be packed, i.e. its composition and storage sensitivity, its shelf-life, additional laminate layers—or laminate layers of other types than LDPE—may be included in the laminate structure. Examples of such additional or other laminate layers may be material layers possessing superior gas barrier properties, such as an aluminium foil or a layer of polyamide or of copolymers of ethylene and vinyl alcohol. Certain food products, such as juice, moreover place more stringent requirements to the effect that the packaging material possess superior aroma barrier properties, i.e. prevent flavour deterioration as a result of non-polar flavour and aroma substances being absorbed from the packed product into the packaging material. At the same time as the package must afford the product the best possible product protection properties, production of such single-use packages must also be simple and rational in order to be economically viable.
Within the prior art technology, polyethylene terephthalate (PET) has often been proposed as a material possessing superior aroma barrier properties, suitable for the inside layer in a packaging container for direct contact with the packed product, as opposed to, for example, LDPE. PET possesses extremely good barrier properties against essential oils such as D-limonen and other non-polar flavour and nutrient substances in, for example, orange juice and is, therefore, a highly desirable material for this purpose. However, PET suffers from the major drawback in employment as the innermost laminate layer in a packaging container for direct contact with the packed product in that it is difficult to thermoseal at rational production speeds, in particular on sealing of the longitudinal joints in a packaging container produced from a sheet-shaped packaging laminate blank in which the longitudinal edges of the sheet-shaped blank overlap one another and are exposed such that the outside of the inner edge is sealed against the inside of the outer edge. In rational production of conventional packaging containers, such longitudinal joint sealing takes place at very high speeds, in that the sheet-shaped blanks in rapid sequence are advanced, reformed and longitudinally sealed by means of thermosealing into tubular packaging container blanks. The term “tubular” is hereafter taken to signify tubes of both circular and quadratic or rectangular cross section. For thermosealing of PET, it is necessary that the pressure from the sealing jaws is maintained during the heating process, at least up to approximately 165° C., which takes roughly 0.5 sec. However, the available stay time during the sealing process on sealing of longitudinal joints, i.e. the time during which the pressure from the sealing jaws is maintained, is only approx. 0.01 sec., and thereby insufficient. On the other hand, sealing of the top and bottom of the same packaging containers takes place intermittently in connection with the product being filled into the container, which permits longer stay times in the sealing operation proper, and thereby makes for thermosealing by means of surface fusion between two PET layers.
Attempts have been made to overcome these difficulties in various manners, for example by employing a modified PET which facilitates thermosealing. From, for example, European Patent Application EP 0 237 235, it is known that glycol-modified PET, so-called PETG, may be thermosealed. However, a serious drawback inherent in this glycol-modified PET is that it results in a more brittle material layer with less flexibility and durability and is thus not as desirable in a packaging laminate as normal, amorphous, non glycol-modified PET. Moreover, nor can thermosealing take place using PETG at such high production speeds as are actually desirable.
One method of attempting to circumvent the difficulties of longitudinally sealing normal PET by means of thermosealing has been instead to seal the longitudinal lap joints by means of hot melt glue sealing, by applying a hot melt glue along one edge and then compressing it with the other edge in the lap joint between the two edges. However, it has not hitherto been possible to achieve rational sealing speeds using this technique. It has not hitherto been possible to use hot melt glue application at acceptable speeds, and serious problems have been encountered with large spillage of hot melt glue and with the fact that the application of the hot melt glue becomes uneven, with tacky outflows as a result. Another difficulty in the striving to produce a packaging container possessing superior aroma barrier properties is that such a hot melt glue sealed longitudinal joint is not durable in cold storage. Such a packaging container has thus not hitherto been capable of being stored for a lengthy period of time with good liquid-, gas-, and aroma barrier properties, because of the fact that the hot melt glue sealed longitudinal joint becomes untight.
In respect of liquid-, gas-, and aroma barrier properties, such incision edges of the sheet-shaped packaging blank which are freely exposed to the packed product create problems in that gas and liquid molecules, like non-polar flavour substances, are slowly absorbed in the packaging material through the thus freely exposed incision edges.
Another drawback is that configurationally stable, strong and durable packaging containers according to the prior art technology normally require larger quantities of the materials included in the package in order to achieve improved stability and improved barrier properties, despite lengthy cold storage, and thus command a higher price.
Hence, it has not hitherto been possible in the prior art technology, in a cost effective and rational manner to longitudinally joint seal and produce fold-formed packaging containers from sheet-shaped blanks of a paper-based packaging laminate with inside layers of PET which possess retained superior gas and aroma barrier properties also in the lengthy cold storage of liquid foods.
OBJECTS OF THE INVENTION
One object of the present invention is therefore to realise a novel packaging container of the type described by way of introduction without the attendant problems of the type intimately to the prior art technology.
A further object of the present invention is to realise a configurationally stable packaging container possessing superior gas and aroma barrier properties for packing and lengthy cold storage of liquid foods, from a sheet-sh
Borgström Rolf
Magnusson Tommy
Burns Doane Swecker & Mathis L.L.P.
Desai Hemant M.
Tetra Laval Holdings & Finance S.A.
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