PACKAGING CONTAINER AND METHOD OF PRODUCING THE SAME

Abstract: The invention concerns a packaging container consisting of at least one inner layer (2) and one outer layer (1), said layers being held together only by mechanical anchoring means (4, 5, 6) which means comprises at least one substantially dovetail-shaped portion formed on one of said layers (2).

Description: Packaging container and method of producing the same Field of the invention The invention relates to a packaging container and method of producing a packaging container comprising at least one inner layer and one outer layer, wherein said inner and outer layers are held together by mechanical anchoring means, said mechanical anchoring means comprising at least one portion formed on one of said layers. Such a container is known from SE 350 943 or SE 353 876 for example. Background to the invention Containers of the above mentioned type are often formed as an inner plastics tray and an outer cardboard tray and are foreseen with a flange at the upper edge of the inner tray to which a reclosable lid can be fitted. A typical application for such a container is as a container for margarine or dairy products such as cheese spreads for example. However, these containers have the disadvantage that the various handling procedures carried out on them such as ejection from the mould, filling, closing and further operations, require that the inner and outer layers need to be securely held together to prevent separation e.g. due to flexing. The solution normally adopted is to heat seal the layers together, often with the addition of a hot melt adhesive. Due to the increased concern for the environment, it is desirable to make containers which are readily recyclable. Containers of the above type are however unsuitable since the material of the outer layer (normally fibrous) cannot easily be separated from the plastics inner layer. Clearly a need exists for a container which has an inner layer readily suitable for product storage, which can easily be combined with an outer layer which is strong, on which one can easily print and which allows separation for recycling but which still ensures secure attachment for processing purposes. In particular it is preferred that the inner layer has very little stiffness and that the required stiffness is provided by the outer layer. As a solution to these problems a container has been proposed in our Swedish application SE 9100905-0, not prior published, wherein an inner plastics layer is secured to an outer cardboard stiffening layer by means of rivet type projections formed on the inner member which project through and are of slightly larger dimension than the cut- outs provided in the outer cardboard layer. In one embodiment the rivet-like projections are assisted at each of the corners by a larger projection which has a lower edge overlapping an upper edge portion of the outer layer. After further development of the container it is now realised that a secure attachment between the layers can be provided if the projections also provide lateral anchoring as well as vertical anchoring between the layers without requiring the use of rivet-type projections. The container according to the invention has the features defined in claim 1. The invention also concerns a method for forming such a container, the essential features of the method being defined in claim 12. Preferred features of the invention are defined in the dependent claims. Whilst the invention is described with reference to a dovetail-shaped anchoring portion in its most preferable form it is clear that the expression dovetail-shaped as used in the claims is not restricted to this preferred form. Thus, other examples, such as will be described later with regard to Fig.7, may also be considered as dovetail- shaped. According to a preferred embodiment of the invention, in which the dovetail-shaped portion has at least one sloping side which overlaps the outer layer, the lateral anchoring is enhanced. Not only does the resulting package look more attractive than the rivet type, but it can more easily be ejected from the mould and also more easily separated into inner and outer elements for recycling since the overlapping portions do not need to fully encompass the cut-out in the outer layer. Whilst it is not a strict necessity, the anchoring is further enhanced if the overlapping dovetail part(s) are also in pressure contact with the other layer, thus reducing to a minimum the possibility of the outer layer separating from the inner layer during processing. Recycling is a simple procedure. The outer part is merely pulled away from the inner part, whereby the overlapped portions of the outer layer deform sufficiently to spring past the dovetail projections. The most common method of manufacturing the container is to pressure and/or vacuum form the inner layer inside the already erected blank which is positioned in a female mould element. A preferable form of carrying out the method would then be as follows. A pre-cut and pre-printed blank of material (most normally being a fibrous material such as cardboard sheet and having the necessary folding denotations marked thereon) is transported to the empty female mould. A vacuum is applied , via appropriate tubing, to openings in the female mould surface. The cardboard blank is introduced into the mould, thus being erected by folding the side and end panels about the base portion along the folding denotations. A sheet or foil of plastics material, for example polypropylene, is brought to the mould and heated. Then it is lowered onto the mould and is pressed and/or drawn into the inside of the blank so as not only to cover it from the inside but also to be drawn into the dovetail-shaped recesses in the mould itself. The plastic is thereby, normally along both sides of the sloping side portions and the base edge of the dovetail (in its most preferred orm) , made to overlap the cardboard outer layer and thus anchors it. The combined container unit is then ejected from the mould for further processing. Whilst pressure forming is most preferred, it is clear that other methods could be used such as vacuum forming, injection moulding, or thermoforming using a male mould in addition. Clearly also other materials, such as PVC or polystyrene, could be used instead of polypropylene for the inner layer, but despite the smaller softening interval of polypropylene, polypropylene is preferred due to its environmental profile. Brief description of the drawings Fig.l depicts one embodiment of a finished container according to the invention; Fig.2 depicts a- view of one half of a symmetrical pre-cut blank foreseen with folding denotations for use as an outer layer of the container according to Fig.l; Fig.3 is a sectional view along line A-A in Fig.l; Fig.4 is a sectional view along line B-B in Fig.l; Fig.5 is an enlarged end view of the dovetail-shaped projection of Fig.4 in overlapping relation to the outer layer; Fig.6 is an enlarged end view of a second embodiment of the dovetail-shaped projection in overlapping relation to the outer layer. Fig.7 depicts a schematic representation of other dovetail- shaped anchoring means which can be used in accordance with the invention. Description of a preferred embodiment The container of Fig.l consists of two layers, an inner layer 2 generally of a thermoformable material such as polypropylene, polystyrene or PVC for example and an outer layer generally of a non-thermoformable material such as cardboard. The outer layer will generally be printed with a description of the product and other information. Several plies may also be included in either of the layers if this is desired. On the interior side of the view shown in Fig.l (see for example the left-hand end) , the contours of the outer layer (e.g. the upper edge 9 or the end flap border 7) are visible in the inner layer. This is due to the manner of producing the container, whereby the plastics material of the inner layer- 2 has adapted its contour closely to the shape of the inside of the blank. The upper edge 9 of the outer layer is here shown to be slightly below the upper edge 3 of the inner layer 2. This is normally the case since, for easy moulding of the inner layer, the upper edge 9 must not project above the edge 3, which corresponds to the upper edge of the mould. Hence due to the tolerances which have to be allowed for, the upper edge 9 is normally slightly below the edge 3 by the order of 0 to 2 millimetres. Dovetail-shaped projections 4, 5 and 6 are positioned at the corners, ends and sides of the container respectively. As is show , the size of the dovetails may vary, such that larger projections are provided in the corners and smaller ones at the sides and ends. In particular it has been found useful to use a dovetail-shaped projection with a larger base at each of the corners to allow easier de-stacking when the final containers are to be filled after they have been transported to the filling location. De-stacking is assisted by the larger base portions at these locations since the base will rest on the flange upper surface of the container below it and thus will provide a sufficiently large air gap between one container and the next. Larger base portions could also be provided at the ends and/or sides if desired. Reference numeral 3 indicates a closing flange to which a reclosable lid is normally applied. The flange also has the purpose of covering the upper cut edge 9 of the outer blank from normal view. For this reason the dovetail cut-outs are normally made in the upper edge 9 of the erected outer layer blank 1. With the use of the dovetail-shaped projections and cut¬ outs of the present invention it has been found that to keep the container intact for processing the end panels "c" (see Fig.2) merely need to be folded up over the outside of the ends 7 of the side panels "b" and held in place by the dovetail anchoring means in order to have a container which is adequately secure for further processing without the need for any additional holding means. Consequently no folding of the end panel over the end of the side flaps or hot melt adhesive between parts of the end and side panels is required. This is of particular advantage since with these other types of construction the outer layer blank must generally be assembled before insertion into the mould. The general form of the outer layer blank is depicted in Fig.2. The blank- is symmetrical and thus only one half is shown. The blank thus comprises side panels "b" and end panels "c" joined to a base panel "a" via fold lines (indicated in dashed lines). Dovetail-shaped cut-outs 4' ', 5 and 6" are made in the upper edge (when erected) of the blank and these will approximately align with recesses in the mould when the blank is positioned therein. In the corner regions, fold lines 11 are foreseen on the outer surface of the outer layer for allowing the corner region to conform to a rounded shape. Fig.3 shows a sectional view along line A-A in Fig.l,. whereby the dovetail section 4 at the corner can be seen protruding from the inner layer 2. The dovetail portion 4 includes a lower edge portion 4' which overhangs the upper edge 9 of the outer layer. Whilst it is not shown as such, it would normally also be in contacting relationship therewith to provide additionally secure attachment. Similarly Fig.4 shows a view along the line B-B in Fig.l, being the dovetail section 5 at one end of the container. It will be seen that the dovetail section differs from that in Fig.3 in two main aspects. Firstly the outer surface of the dovetail is divided into two principal regions of different slope by a line 5' and secondly the lower edge of the dovetail only has a small overlap. Clearly however the base edge of the dovetail projection does not have to have any overlap at all but could be approximately flush with the upper edge 9 of the outer container blank or even spaced therefrom as shown in Figure 6. Figures 5 and 6 depict two enlarged views of different embodiments of dovetail-shaped projections 4 formed on the inner layer and corresponding dovetail cut-outs in the outer layer blank. The upper edge flange 3 has been removed for clarity. The embodiments differ from eachother mainly in that Fig.5 has the cut-out border 10 of the outer layer positioned totally inside the outer border of the dovetail- shape section formed on the inner layer, such that the dovetail projection overlaps the outer layer along the whole length of the sloping sides and the lower edge, whereas Fig.6 depicts a situation where only a portion of the sloping sides of the dovetail projection 4 overlaps the outer layer, since the upper edges of the cut-out border 10' are visible. Additionally the lower edge of the cut out is slightly below the lower edge of the projection. However it is clear that the lower edge of the dovetail projection may be flush with the cut-out, overlap it or be above it, - whichever is desired. Additionally it is shown in Fig.5 that, apart from the two principal sloping surfaces at an angle to eachother and divided by the line 5 ', there are formed two additional sloping surfaces 20. The combination of these sloping surfaces 20 with the principal surfaces of the portion 5 has been found to be the optimum shape for assisting ejection from the mould after forming. Such a dovetail shape is however normally only used at the ends and sides, but not at the corners, since the corner portions do not generally present difficulties with respect to ejection, due to the curvature present. Fig.7 shows three further possibilities, seen only schematically of course, of possible dovetail-shaped mechanical anchoring means in accordance with the invention. Whilst several embodiments have been depicted and described, it is to be understood that many variations of the invention are possible within the scope of the appended claims. In particular it is noted that the material thicknesses of the various layers may vary greatly.

Claims: Claims 1. A packaging container comprising at least one inner layer (2) and one outer layer (1) , wherein said inner and outer layers are held together by mechanical anchoring means (4,5,6), said mechanical anchoring means (4,5,6) comprising at least one portion formed on one of said layers (2), characterized in that said portion is substantially dovetail-shaped and in that at least one side of the dovetail-shaped portion overlaps at least a portion of the other (1) of said layers. 2. A packaging container according to claim 1, characterized in that said at least one side is a sloping side of a dovetail-shaped portion. 3. A packaging container according to either of claims 1 or 2, characterized in that the inner layer (2) comprises a thermoformable material and the outer layer (1) comprises a non-thermoformable material, preferably cardboard, said at least one dovetail-shaped portion (4,5,6) being formed on said inner layer (2) . 4. A packaging container according to any of claims 1 to 3, characterized in that said dovetail-shaped portion formed on one of said layers has two sloping sides each of which overlaps the other layer. 5. A packaging container according to any preceding claim, characterized in that there are a plurality of said dovetail-shaped portions formed on the inner layer, positioned at the corners and/or on the side and/or ends of said packaging container. 6. A packaging container according to any of claims 1 to 5, characterized in that the outer layer (1) is foreseen with shaped cut-outs (4' ' ,5' ' ,6' ') which are slightly smaller than the dovetail-shaped portions (4,5,6) on the inner layer (2) . 7. A packaging container according to any preceding claim, characterized in that the lower edge portion (4') of the dovetail-shaped portion (4) formed on said one layer (2) overlaps part of said other layer (1) . 8. A packaging container according to claim 6, characterized in that the cut-outs are positioned along the upper edge (9) of the outer layer (1) . 9. A packaging container according to any preceding claim, characterized in that the outer layer (1) is formed from a folded and erected cardboard blank, the blank having a base (a) , side panels (b) and two end panels (c) , the said end panels (c) each being a single layer flap folded about the base (a) over the respective ends (7) of the side panels (b) and anchored in position only by said dovetail-shaped portion (5) on the inner layer (2) . 10. A packaging container according to any preceding claim, characterized in that the base edge of the shaped portion extends outwardly from the surface of the container on which it is formed by a sufficient amount in order to provide a ledge to assist de-stacking of a stack of containers. 11. A packaging container according to any preceding claim, characterized in that some or all of the dovetail- shaped portions are provided with two principal surfaces of differing slope, said principal surfaces intersecting along a line (5') . 12. A method of producing a packaging container wherein a blank of a foldable material, preferably cardboard, having preferably dovetail-shaped cut-outs therein is introduced into a female mould and wherein the - 5 female mould has correspondingly shaped recesses which substantially align with said cut-outs in the folded and erected blank, and wherein a plastics material is introduced inside the erected blank, said plastics material thereby covering at least the whole of the inside of the 10 blank and entering into the recesses in the mould, and wherein the outer layer is anchored to the inner layer by at least one of the sides of the dovetail-shaped portions formed on the inner layer. 13. A method according to claim 12, wherein the 15 plastics material is introduced into the erected blank and recesses by pressure and/or vacuum-forming a plastics sheet which has been preheated. 14. A method according to either of claims 13 or 14, wherein the blank is brought to the female mould in a flat 20 condition and is folded and erected by being introduced into said female mould.

Inventors: HAGELQVIST PER, HOLMBERG YNGVE, LUGNER ANDERS, NIDEBORN KARL, HAGELQVIST, PER, HOLMBERG, YNGVE, LUGNER, ANDERS, NIDEBORN, KARL
Applicants: AKERLUND & RAUSING AB, HAGELQVIST PER, HOLMBERG YNGVE, LUGNER ANDERS, NIDEBORN KARL, AB AAKERLUND & RAUSING
Application year: 1993
Main classification: B65D5
IPC codes: B29C51, B31B1, B31B7, B65D5, B65D25