EP0495230B1 - Recyclable tray-like container with absorbent means - Google Patents

Abstract

The invention relates to a container (1) of single-layer construction and made of a film of foamed plastic. For the purpose of better mechanical stability and better stacking and unstacking capability, the container has a padded edge (3) which is recessed in the manner of a gripping trough at least on one side, preferably on two opposite sides. Furthermore, the invention relates to an absorbent means (5, 6, 7, 8) for containers, which comprises a highly moisture-absorbent polymer (8). The packaging trays according to the invention are recyclable without problems with and without the absorbent means according to the invention. <IMAGE>

Description

The invention relates to a tray-shaped packaging container made of a plastic foam film for receiving liquid-secreting packaging material with a tray bottom and upwardly directed side walls, which merge into a circumferential, closed edge bead, and with an insert plate arranged at a distance from the tray bottom in the interior of the packaging container Perforations is equipped, and forms a cavity between the inside of the shell bottom and the insert plate, in which liquid-absorbent material is arranged and a tool for its production.

Packaging containers of this type are used to hold food that emits liquid, especially larger pieces of meat, the liquid being absorbed by an absorber system.

From FR-A - 2.614.877 a packaging container or a packaging tray according to the preamble of claim 1 is known, in which capsules, granules, cellulose fibers, cellulose layers, liquid-absorbing polymers or in the cavity between the tray bottom and a perforated insert plate other hydrophilic material is arranged.

DE-A-34 23 518 discloses a liquid absorbent pad for use in individual meat packs, in which numerous solid bodies or pellets are distributed to accommodate the weight of the packaged meat. The bodies or pellets are distributed in a liquid-absorbing material which is easily compressible and therefore normally presses the liquid absorbed back into the packaging tray under the pressure of the meat above. The bodies or pellets consist of liquid, non-absorbent plastic.

From GB-PS 1,168,925 a three-layer packaging tray is known, which has a perforated bottom film. Through the openings, the liquid collecting in the bowl can flow into an underlying, moisture-absorbing intermediate layer. The outer film surrounds the intermediate layer on the underside of the packaging tray and is connected to the bottom film on the edge of the tray. However, this shell has the disadvantage that it is not recyclable, since the moisture-absorbing intermediate layer cannot be separated from the shell, or only with considerable effort.

The packaging tray of AT-PS 327 783 is also constructed in three layers, namely from an inner and an outer film and an intermediate layer of liquid-absorbent material. It is produced by thermoforming the layers on top of each other. The absorbent layer is also located in the area of the shell walls, but is there due to the strong expansion in the area of the walls during thermoforming torn. It is obvious that this method can only be carried out if the absorbent layer has a relatively small thickness, but this has the disadvantage that its ability to absorb moisture is very poor. This bowl is also not recyclable.

The packaging container described in EP-A-0 090 507, on the other hand, is constructed in two layers. Its inner surface has an open-cell, foamed polymer structure that is only suitable for holding condensed liquid droplets. This container is not suitable for absorbing large amounts of moisture.

DE-A-34 06 399 describes a packaging container which is constructed from two superimposed thermoformed plastic foam foils which are welded to one another in the region of the side walls and which extend at a distance from one another in the region of the base part, the inner film in the region of the base part is provided with holes for draining liquid. The two foils form a free cavity in the area of the base part and lie directly against one another in the area of the side walls. Although this container has a relatively large, free cavity for holding liquid, it does not have an absorber system. The stackability and unstackability of these trays is unsatisfactory and needs improvement.

A major disadvantage of all of these known packaging containers is the absorption capacity of the absorption material, which is far too low. For example, a usually six-layer layer of cellulose wadding with a size of 7x10 cm can absorb a maximum of only about 8 to 10 g of liquid. If a piece of frozen meat is now packaged in such a packaging tray and then kept ready for sale in a refrigerated display case, up to 10% of the filling weight, or up to 50 g for a piece of meat of 500 g, can be released into meat juice. Such an amount exceeds the absorption capacity the absorption layer by far. Another disadvantage of the packaging containers with the absorption system according to the prior art is that these containers cannot be recycled or can only be recycled with considerable effort. This is mainly due to the fact that the liquid suction filters - usually cellulose wadding - are glued to the bottom of the trays or are enclosed between two layers of film in the packaging and are therefore virtually impossible to remove by machine. However, such trays can only be easily returned to the manufacturing process if the product is uniform, ie if the suction filter and any adhesive present are separated from the tray beforehand. Even the slightest residue from these suction filters (cellulose or similar) or adhesive residues lead to inferior recycled film and can even lead to a failure of the film extruder.

It is therefore an object of the present invention to provide a bowl-shaped packaging container which can hold a substantially larger amount of liquid which escapes from the packaged food than known packaging containers and which is sufficiently mechanically stable against pressure and shock and is easy to stack and unstack leaves. In addition, the entire system, consisting of the absorber system and packaging container, should be recyclable.

This object is achieved by a packaging container according to claim 1 in such a way that there are balls in the cavity which are coated with a liquid superabsorbent polymer or that the liquid absorbent material is formed from a flexible, liquid-permeable plastic bag in which liquid superabsorbent polymer is enclosed, or consists of a liquid superabsorbent polymer coating on the inside of the insert facing the cavity.

The one-layer, dimensionally accurate packaging container with a beaded edge is made of a single plastic foam film, preferably by deep drawing using male / female tools manufacture containers. All post-expandable plastic foam films can be used as plastic foam films. These plastic foam films are produced by foaming plastic films, the foaming (pre-foaming) being able to be brought about both chemically, ie for example by releasing CO ₂ during a chemical reaction of two compounds, and physically, ie for example by thermal expansion of an added propellant gas such as butane . These pre-expanded foils can be expanded later by re-heating them (post-expansion). For example, pre-expanded plastic films made of polypropylene (PP), in particular polyvinylidene oxide (PPO), polyethylene terephthalate (PET), but preferably physically pre-expanded polystyrene films (PS) can be used. The bowl-shaped packaging container shows the typical basic shape, which comprises a container bottom with a usually flat outer surface and a flat inner bottom surface as well as upwardly directed side walls which are usually slightly inclined away from the bottom surface. In contrast to trays of this type based on film according to the prior art, which have side walls which end in an outward-facing flange edge, the trays according to the invention have a widened, beaded edge, preferably with a straight edge directed from the side surfaces to the bottom extends parallel to the side surfaces and the bottom surface. The bead improves the mechanical stability of the shells. This increases the stiffness of the trays, so that, for example, crushing of the trays when packaged with food is reduced and even largely prevented. Because of this bead, the packaging containers according to the invention can be stacked very well and, above all, unstacked. The mechanical unstacking of conventional trays with a flange edge, in particular those with a multilayer film structure, leads in practice repeatedly to the fact that several trays are gripped at once or the The gripper arm moves between two connected film layers of a tray, both of which lead to a malfunction in the operational process.

In the shells according to the invention, this is firstly due to an extremely high dimensional accuracy, i.e. Reproducibility of the outer dimensions of the shells, in conjunction with the bead edge, which is extremely advantageous in this regard, is achieved, and secondly, the single-layer film structure of the shell has a positive effect. The stackability or unstackability can be further improved if the packaging container according to the invention is provided with at least one recessed grip in the bead area. Two recessed grips are preferably attached on two opposite sides.

The cut profile of the bead can be designed in different geometrical ways. Elliptical, in particular circular, rectangular, square or triangular sectional profiles have proven to be expedient. The bead is massive, i.e. all over, filled with foil material.

According to a further embodiment of the packaging container according to the invention, the inner surfaces of the side walls have a circumferential, step-shaped shoulder at a distance from the tray bottom, on which the insert plate is removably supported. A cavity is created between this perforated insert plate and the shell bottom, into which, for example, a moisture-absorbing agent made of a superabsorbent polymer can be added. The separately produced insert plate can be dimensioned so that it is loosely inserted, clamped or, if desired, glued into the shell. The insert plate is preferably made of the same material as the packaging container.

a.

durch die im Patrizenwerkzeug integrierte Schnittplatte kann auf den separaten Stanzschritt, in dem die tiefgezogenen Schalen ausgestanzt werden, verzichtet werden;

b.

die Maßgenauigkeit der resultierenden Schalen ist wesentlich höher, da Stanzfehler, welche durch ungenaues Einziehen der tiefgezogenen Folienbahn in ein separates Stanzwerk unvermeidlich sind, nicht mehr auftreten (Formen und Schneiden in einem Arbeitsgang);

c.

die Ränder der Schalen sind glatt und geschlossen;

d.

auch kaschierte und eingefärbte Folienbahnen können problemlos in dem erfindungsgemäßen Verfahren verwendet werden.

The packaging containers according to the invention are produced in a deep-drawing process using die and male tools, the male tool containing an integrated cutting plate. This manufacturing process offers the following advantages over the conventional deep-drawing process followed by a stamping step for film-based trays:

a.

the cutting plate integrated in the male tool eliminates the need for a separate stamping step in which the deep-drawn shells are punched out;

b.

the dimensional accuracy of the resulting shells is significantly higher since punching errors, which are inevitable due to inaccurate drawing of the deep-drawn film web into a separate punching unit, no longer occur (forming and cutting in one operation);

c.

the edges of the shells are smooth and closed;

d.

Laminated and colored film webs can also be used without problems in the process according to the invention.

The packaging containers according to the invention are produced on the basis of the known thermoforming production method for single-layer or multi-layer plastic trays with a flange edge. A 1 to 5 mm thick heated film made of pre-expanded, extruded, rigid plastic, preferably an extruded polystyrene foam film, is pressed from a male mold into a female mold. This process is supported by applying a double-sided vacuum. The heating leads to a further foaming of the already pre-expanded film material and thus to an increase in volume. At the same time, the fitting is made by means of the in the male tool Integrated cut plate cut out of the protruding film (waste) and the trays finally separated.

The optionally perforated insert plates are produced by customary methods, for example by punching them out of appropriate foils.

The single-layer packaging containers according to the invention described above are easy to recycle. In order to use them as packaging containers for foods containing liquids, the containers contain a liquid absorbent. Accordingly, the bowl-shaped packaging containers are equipped with liquid superabsorbent materials, but can also be equipped with the usual suction filters, such as paper layers or cellulose layers. However, as already mentioned above for trays according to the prior art, this results in the problem of poorer, if not impossible, reuse (recyclability) of the containers used (uneconomical separation of container and suction filter).

In order to overcome this disadvantage, according to the present invention, a moisture superabsorbent polymer which is not harmful to food law is used as the suction filter in the containers. Of course, the use of these special polymers is not limited solely to the packaging containers according to the invention, but also extends to those packaging containers according to the prior art in which, for example, cellulose layers have been used for this purpose.

According to the invention, all natural or synthetic polymers can be used as moisture superabsorbent polymers which have a multiple of their (dry) own weight of moisture - preferably water - can take up and preferably do not give up even under increased pressure or only release it to a small extent. Gum arabic, gelatin or alkali alginates (Irish moss, Na alginate) may be mentioned as examples of polymers which are suitable in principle but are not preferred. Preferred are polymers which absorb 10 to 2000 times, in particular 100 to 1200 times, very particularly preferably 300 to 700 times their own mass of moisture. Their moisture absorption capacity should be in the range from 1 to 100 ml / g, preferably 10 to 90 ml / g, particularly preferably 30 to 70 ml / g.

Polyacrylates which are modified, for example with starch, are preferably used. In particular, the alkali metal salts, preferably the sodium salts, of these compounds are used, which are commercially available, for example, under the name ^(R) SANWET (Hoechst AG, Frankfurt, SANYO Chemical Industries, Ltd., Tokyo).

These superabsorbent polymers effectively prevent the leakage of liquid that has accumulated in the packaging containers. In order to prevent excessive moisture excretion from the filling material, the direct contact of the superabsorbent polymers with the filling material can be avoided. This is done, for example, by introducing the polymer into the cavity of packaging trays with a double bottom. To relieve pressure which is exerted by the filling material on the floor and thus also on the liquid superabsorbent polymer, the double floor can be supported with spacers. These spacers can be incorporated, for example, in the insert plate or in the tray base. Cylindrical stamps which protrude as elevations above the shell bottom have proven to be expedient, the height of the stamp corresponding to the distance between the shell bottom and the insert plate.

For example, the polymer can be attached to the back of the insert - on the side facing the cavity - or on the bottom of the bowl itself, or small balls, such as polystyrene foam balls, are coated with the polymer and then filled into the cavity or on the floor attached to the shell or on the side of the insert facing the cavity of the shell. In the latter case, in which coated balls are attached to the inside of the insert plate, the insert plate can also be inserted loosely into the shell and does not need to be additionally supported by a circumferential, step-shaped heel. The balls also directly bring about the desired pressure relief. In a preferred embodiment, the moisture superabsorbent polymer is accommodated in a flexible, moisture-permeable container, for example in a plastic bag. Here too there is the possibility - for pressure relief - to fill the bag with the balls coated with the polymer, preferably polystyrene foam balls, or to fill the polymer and the balls separately into the bag. The bag can be made from conventional plastic films, for example from PVC or polyolefins, such as polypropylene or polyethylene, or from polystyrene films. It has proven to be extremely advantageous to manufacture the flexible container from a plastic which - depending on the temperature - is water-soluble, that is to say, for example, dissolves in warm water. This behavior can be advantageous both when manufacturing the bags (eg welding with steam), attaching the bags to the bottom of the shell (gluing by "dissolving" with warm water) and recycling ("washing out" the prey). Washing out proves to be an advantage in that the used trays taken back, including the plastic bag, can first be shredded and then the bag material can be dissolved in a water bath and separated from the tray material, which is not possible with conventional trays with, for example, cellulose suction filters.

A preferred film material for the bag, in addition to polystyrene, is polyvinyl alcohol (PVAL film); For example, the different types of Mowiol ^(R) are suitable (Hoechst AG, Frankfurt / Main). The temperature range of the water solubility can be set by a suitable choice of the composition of the film material.

In order to increase the moisture permeability of the bag used to the desired level, the film bag can, for example, be needled, that is to say provided with small holes.

The plastic bag is expediently filled with uncoated balls made of polystyrene foam or balls coated with liquid superabsorbent polymer, in order to relieve the pressure on the bottom of the shell.

Preferred embodiments of the invention are explained in more detail in the following figures.

Figures 1a and 1b show a bowl-shaped packaging container 1 with a bowl bottom 2 in section, without an internally circumferential stepped shoulder 5 and outside with an edge bead 3, which is interrupted to form two recessed grips 4 on the narrow sides, with Fig. 1a a cross section and Fig 1b represent a longitudinal section.

FIG. 2 shows a perspective view of a bottom view of the packaging container according to FIG. 1.

3 shows a packaging container according to the invention in cross section with circumferential shoulder 5 in the bottom area for the distant fixing of an insert plate 6 provided with perforations.

Fig. 4 shows a perspective view, partially in section, of a packaging container 1 with a bead 3, recessed grip 4, paragraph 5, insert plate 6 with perforations and a cavity which is formed by the tray bottom 2 and the insert plate 6.

5 the male and female tools for producing the packaging container according to the invention are shown. The male tool 9 contains ventilation channels 13 and an integrated cutting plate 10, which corresponds to the cutting edge 21 of the die 11. The die tool 11 contains the groove 15 necessary for the formation of the edge bead 3 as well as lugs 14 projecting into this groove for the formation of the grip recesses 4. For clarification, there is a shaped workpiece between the die and die tool - a bowl-shaped packaging container 1 with bottom 2 and with edge bead 3 and recessed grip 4 - and corresponding film protrusions (waste 12).

FIG. 6 shows a combination of the male and female tool corresponding to FIG. 5 in the closed position. The male tool additionally has a step plate 16, which is used to form the shoulder 5.

7 shows a preferred embodiment of a packaging container 1 with a circumferential step-shaped shoulder 5, shelf 6 and a liquid absorber system 18 located in the cavity 8. This liquid absorber system shown consists of a PVAL bag which contains a liquid, highly absorbent polymer and spacer balls 17.

FIG. 8 shows an embodiment of a packaging system in which the packaging container 1 does not contain a step 5, but the insert plate 6 is kept at a distance by pressure-relieving polystyrene foam balls 17. The liquid-absorbing polymer is located either as a coating on the spacer balls 17 or on the side of the insert plate 6 pointing into the cavity 8.

FIG. 9 shows a longitudinal section through a finished product packaging with packaging container 1 according to FIG. 4, including filling with food 19 and packaging film 20.

Claims (18)

1. A tray-like packaging container (1) comprising a plastic foam sheet for receiving liquid-secreting product (19) to be packaged, having a tray base (2) and upwardly directed side walls, which merge into a peripheral closed edge bead (3), having an insert sheet (6), which is provided with perforations (7), is arranged at a distance from the tray base (2) in the interior of the packaging container (1) and forms between the inner side of the tray base (2) and the insert sheet (6) a hollow space (8) in which liquid-absorbent material is arranged, wherein there are in the hollow space (8) beads (17) which are coated with a liquid-superabsorbent polymer, or wherein the liquid-absorbent material is formed by a flexible, liquid-permeable plastic bag (18) in which liquid-superabsorbent polymer is enclosed, or comprises a liquid-superabsorbent polymer coating on the inner side of the insert sheet (6) facing into the hollow space (8).
2. The tray-like packaging container as claimed in claim 1, wherein the inner surfaces of the side walls have at a distance from the tray base (2) a peripheral step-shaped shoulder (5), on which the insert sheet (6) removably rests.
3. The tray-like packaging container as claimed in claim 1, wherein arranged in the hollow space (8) are beads on which the insert sheet (6) loosely rests and which relieve the tray base (2) of the pressure of the product to be packaged.
4. The tray-like packaging container as claimed in claim 3, wherein the beads are fastened on the tray base (2) or on the inner side of the insert sheet (8) facing into the hollow space (8).
5. The tray-like packaging container as claimed in claim 3, wherein the beads are loosely filled in the hollow space (8).
6. The tray-like packaging container as claimed in claim 1, wherein the edge bead (3) has at least one recessed grip (4).
7. The tray-like packaging container as claimed in claim 1, wherein the edge bead (3) is elliptical, circular, square, rectangular or triangular in cross-section.
8. The tray-like packaging container as claimed in claim 1, wherein the plastic foam sheet is a polystyrene foam sheet.
9. The tray-like packaging container as claimed in claim 1, wherein the insert sheet (6) is made from the same material as the packaging container.
10. The tray-like packaging container as claimed in claim 1, wherein the liquid-absorbent beads (17), which are coated with a liquid-superabsorbent polymer, consists of polystyrene foam.
11. The tray-like packaging container as claimed in claim 1, wherein, for relieving the pressure on the tray base (2), the plastic bag (18) contains uncoated beads of polystyrene foam or is filled with beads (17) coated with liquid-superabsorbent polymer.
12. The tray-like packaging container as claimed in claim 11, wherein the plastic sheet of the bag (18) is a sheet which is water-soluble at elevated temperatures.
13. The tray-like packaging container as claimed in claim 11, wherein the plastic sheet of the bag (18) is a polyvinyl alcohol or polystyrene sheet.
14. The tray-like packaging container as claimed in claim 1, wherein the liquid-absorbent material (17; 18) is a polymer which absorbs liquid 10 to 2000 times its own mass.
15. The tray-like packaging container as claimed in claim 14, wherein the polymer has a liquid absorption capacity of 1 to 100 ml/g.
16. The tray-like packaging container as claimed in claim 14, wherein the liquid-absorbent polymer is a polyacrylate, in particular a sodium polyacrylate.
17. A mold for producing a tray-like packaging container as claimed in one or more of claims 1, 2, 6, 7, wherein it comprises a male mold (9) with venting channels (19) and integrated die plate (10) and a female mold (11), which has a groove (15) for the edge bead (3) of the packaging container (1) with protruding-in lugs (14) for forming the recessed grips (4), and wherein the die plate (10) corresponds to a cutting edge (21) of the female mold (11) and cuts out the packaging container (1) from a plastic foam sheet in the same operation as the molding of the packaging container.
18. The mold as claimed in claim 17, wherein the male mold (9) has a stepped plate (16), which forms a step-shaped shoulder (5) in the packaging container (1).

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