A METHOD AND DEVICE FOR SEALING A FOOD PACKAGE

Abstract: A method and a device for sealing a thermoplastic food package, comprising a container base (1) and a reusable cover (4) to be applied to the base. The cover (4) of the package is manufactured and mounted as a sandwich construction of at least two generally planar thermoplastic parts (8, 9), namely an oxygen permeability determining, lower part (8) and a covering part (9), the covering part having a somewhat larger size or area than the lower part (8), so that when the parts are mounted, the covering part (9) forms a projecting portion (10), which is used for hermetically sealing the package in that it is applied against the edge of the container base (1), whereafter the edge is heated together with the projecting portion.

Description: JEPPSSON PAC AB A METHOD AND DEVICE FOR SEALING A FOOD PACKAGE The present invention relates to a method and a device for sealing a thermoplastic food package, comprising a container base and a reusable cover to be applied to the base Packages of this kind are today used above all as containers for cooking fat, different kinds of pates and soft cheese, but also other uses are of course possible. Such food stuffs are presently packed for a comparatively limited quality keeping term, usually up to a few months. Especially for the product liver paste, which usually is prepared (i.e. is pasteurised by heating) after the package with its content has been sealed for sale, the said term for the product is very clearly dependent on the tightness of the package above all regarding oxygen, because the presence of this substance is a prerequisite for the micro¬ bial growth which sooner or later will make the contained product unsuitable as food. Before the product has reached this latter stadium, however, a process connected with the oxygen permeability of the package has since long gone on. If the oxygen permeability of any part of the package hereby is substantially higher than for the rest of the package, a colour change in the surface area of the product will occur at this area, which the critical consumer can interpret as a proof that the product is too old, in spite of the fact that this is not the case. The problem is especial because in this case the cover of the package has an increased permeability, which is a consequence of that covers known for the purpose have properties which are felt to be desirable. This is a problem which may seem trivial but which in spite of that still has not found its solu¬ tion. The oxygen permeability is generally speaking a direct function of the thickness of the package or the cover, which may lead to the conclusion that the thickness of the cover simply has to be increased. However, this is not the case, because this leads to consequential problems both with regard to the sealing of the package before sale, which usually and up till now has occurred by means of a simple contact welding or heating process, and with regard to the phenomenon that producers of food stuffs packed in the actual way most often are obliged to give certain information about the contained product and usually also are interested in profiling their product in one way or another, which at packages of this type almost always at least is done by printing different informative messages on the cover. In other words there is a conflict in that on the one hand it is desirable to increase the thickness of the pack¬ age cover and on the other hand that it is desired to print profiling or informative messages. This is not possible for printing technique reasons. A thicker cover also leads to a necessity to shift from the simple contact welding/heating process mentioned above to more complicated dielectrical methods, which is not desirable for cost reasons. As has been suggested above, it is difficult - or even impossible - to apply a message, independent of whether this is infor- mative or decorative, with a conventional method (printing) on a cover, which is manufactured in a thermoplastic in a thickness satisfactory for the oxygen permeability. The object of the present invention is therefore to accomplish a method and a device as defined above, whereby a distribution of the oxygen permeability for the entire packaging product is possible, at the same time as the possibility with printed messages on above all package- covers as well as the possibility also in the future to make use of contact welding/heating are maintained. This is according to the present invention attained in that the cover is manufactured and mounted as a sandwich construction of at least two generally planar thermoplastic parts, namely an oxygen permeability determining, lower part and a covering part, the covering part having somewhat larger size or area than the lower part, so that when the parts are mounted the covering part forms a projection por¬ tion, which hermetically seals the package in that the packing edge is contact heated, after the projecting por- tion of the covering part has been applied, the projecting portion of the covering part being heat/sealed to the pack¬ age container. By the fact that all parts of the package are manu¬ factured of the same thermoplastic, the package will satis- fy high criteria with regard to the ability to contain pro¬ ducts and will easily be recovered at the end of its utili¬ zation cycle, which is a great advantage, as package manu¬ facturers presently to a greater degree are obliged to take care of packages that they earlier have manufactured. The invention will be further described below under reference to an embodiment shown on the attached drawings, in which Fig. 1 is a side-view of a foodstuff-package with cover, Fig. 2 is a plan view of the cover in Fig. 1, Fig. 3 is a side view of only the cover along one of its longitudinal sides, Fig. 4 is a cross-section along the line IV-IV in Fig. 2, and Fig. 5 is a cross-section along the line V-V in Fig. 1. Fig. 1 shows a foodstuff-package with a base 1 and a cover 4, viewed from one of its longitudinal sides 2, the package 1, 4 having a stiffening flange 3 along substan- tially its entire opening. The cover 4, which appears with slightly thicker lines in the upper right corner 5 of the figure, is further described below. In order to obtain a generally even wall thickness of the base 1 it is injection moulded, the preferred thickness being about 0.5 mm. The material in the base 1 is preferably polypropylene, but also other thermoplastic materials, such as styrene or polyester, may well be used. It also appears from the figure that one of the upper corners of the base 1 has a recess 6. This recess is per see well known in the art and has the purpose of enabling a simple removal of the cover 4 from the base 1. Fig. 2 is a plan view of the cover 4 in an applied condition. The cover 4, which is a sandwich construction (to be described below) , has on its upper side a number of projections 7, which belong to the lower part 8 of the cover, which part is injection moulded to a thickness of about 0.5 mm like the package base 1. At the formation of the sandwich construction the projections 7 are intended to determine the position for and fix a covering part 9 of thermoplastic material, which has a thickness of between 0.1 and 0.2 mm and which has two main purposes: on the one hand to enable a simple application, preferably by four colour printing, of different types of messages (infor a- tive or profiling) on the cover surface 10, which is vis¬ ible in the mounted condition, on the other hand on the reverse surface (facing inwards against the package) carry a thermoplastic binder or lacquer, which at a contact heat- welding is intended to hermetically seal the base possibly before final preparation but above all before distribution and sale. A dotted line in Fig. 2 is intended to show that the covering part 9 has a portion 11 which projects outside or over the lower part 8 of the cover, at which portion 11 the flange 3 of the package base 1 is hermetically sealed by heating, preferably contact welding. The welding is so performed that the actual surfaces during about one second are heated to about 150°C under application of a low pres¬ sure from the outside of the respective details, at the same time as the package base 1 and the projecting portion 11 of the covering part 9 are in contact with each other. As appears from Figs. 3-5, the lower part 8 has a shape which corresponds to the flange/edge 3 of the lower part 1, whereby the package may be closed in a simple hy¬ gienic way after the first removal of the hermetical seal- ing with the projecting portion 11. Fig. 3 shows the com¬ pleted cover with the covering part 9 in a side view. It appears clearly that the projections 7 in this condition penetrate the covering part 9. This is however of low importance, because the covering part adheres to the entire lower part of the cover, whereby the lower part 8 of the cover will be determining for the oxygen permeability of the cover. Fig. 4 is an enlargement of the edge portion of the completed cover 8, 9 in a partial section. Finally, Fig. 5 shows how the completed cover 8, 9 co-operates with the package base 1, and it appears on one hand that the co-operation is such that closure and opening of the package is facilitated, after the hermetical sealing has been broken, on the other hand that normal hygienical requirement on such closures can be fulfilled in a simple way. It should also be mentioned that the package base 1 of course also preferably is provided with some kind of deco¬ ration or information. This may be applied by means of a label or in any other suitable way. The invention shall not be limited by the description above but is only limited by the appended claims.

Claims: CLAIMS 1. A method for sealing a thermoplastic food package, comprising a container base (1) and a reusable cover(4) to be applied to the base (1) , characterized in that the cover (4) is manufactured and mounted as a sandwich construction of at least two generally planar thermoplastic parts (8, 9) , namely an oxygen permeability determining, lower part (8) and a covering part (9) , the covering part having a somewhat larger size or area than the lower part (8) , so that when the parts are mounted the covering part (9) forms a projecting portion (10) , which is used for hermetically sealing the package in that it is applied against the edge of the container base, whereafter the edge is heated together with the projecting portion. 2. A method according to claim 1, characterized in that the side of the covering part (9) facing the lower part (8) when mounted wholly or partly is coated with a thermoplastic lacquer before mounting. 3. A method according to claim 2, characterized in that the container base (1) as well as the lower part (8) are manufactured by injection moulding. 4. A method according to any of the preceding claims, characterized in that the heating is performed during about one second up to a temperature of about 150°C. 5. A device for sealing a thermoplastic food package, comprising a container base (1) and a reusable cover (4) to be applied to the base (1) , characterized in that the cover (4) is compounded for forming a sandwich construction, which comprises at least two generally planar thermoplastic parts (8, 9) , namely a lower part (8) and a covering part (9) , which has a portion (11) projecting past the lower part, said projecting portion (11) - when the package has been sealed - is intended to form the sealing during transport and sales together with a thermoplastic lacquer, whereas the lower part is intended to form an oxygen permeability lowering and secondary consumer sealing part.

Inventors: ANDERSSON SVEN, ANDERSSON, SVEN
Applicants: ANDERSSON SVEN, JEPPSON PAC AB, ANDERSSON, SVEN
Application year: 1997
Main classification: B65B7
IPC codes: B65D43, B65D51