WO2000069750A1

WO2000069750A1 - Film, especially for packaging purposes, and packaging

Info

Publication number: WO2000069750A1
Application number: PCT/EP2000/004256
Authority: WO
Inventors: Horst-Ditmar Gröne
Original assignee: Groene Horst Ditmar
Priority date: 1999-05-14
Filing date: 2000-05-11
Publication date: 2000-11-23
Also published as: MXPA01011717A; CA2373304A1; DE19922065A1; AU5065400A; BR0010523A

Abstract

The invention relates to a film, especially for packaging purposes, which essentially consists of a hardened foam that is at least partially provided with an open-pored structure. Liquid can be stored in the pores of said foam. According to the invention, the pore size of the foam increases at least in sections and with an increasing distance from a first surface (8) of the film and a second surface (10) of the film, whereby said second surface is opposite the first surface.

Description

Foil, in particular for packaging purposes, and packaging

The present invention relates to a film, in particular for packaging purposes, which essentially consists of a cured foam having at least partially an open-pore structure, in the pores of which a liquid can be stored, and a packaging, in particular for liquid-containing foods such as meat or the like consists essentially of a thermoformed or deformed container for holding a good.

Such films serve as the starting material for the production of packaging in the form of a tray for the storage of foodstuffs, in particular those which contain relatively large amounts of liquid. Such packaging is intended for smaller portions of meat, fish, poultry and the like intended for end consumers, which contain high proportions of blood and water that accumulates in the packaging after being packaged. Since such blood-water mixtures have a negative influence on the overall appearance of the packaged product, packagings have been proposed which absorb such mixtures - at least in part -. In a known packaging tray, a paper insert is arranged between two layers of plastic, such as polystyrene. Through several holes in the inner layer of plastic facing the packaged product, the liquid, for example a previously mentioned mixture of blood and water, can get between the two layers and be sucked up by the paper insert. This packaging generally achieves satisfactory results, but is relatively complex and therefore expensive to manufacture.

Another known packaging consists of a liquid-absorbent foam made of plastic, which has an open-pore structure on the side of the product and a closed-pore structure on the outer side facing away from the product or is provided with a cover film which is impermeable to liquid, so that liquid does not come out of the packaging can leak. Liquid can be stored in the pores of the foam. Such packaging is made from a film produced by extrusion by deep drawing.

A special method for producing such a film as the starting material for the packaging can achieve a pore structure which is characterized in that the size of the pores decreases starting from an outer surface of the film, i.e. that relatively large pores are formed in the area of the surface and increasingly smaller pores with increasing distance from the surface. In the known packaging, the surface with the large pores is arranged on the inside of the packaging on the product side. In the area of the large pores, the liquid storage capacity of the cured foam for absorbing liquid is greater than in the area of smaller pores. Consequently, in the known packaging, liquid is stored to a much greater extent on the side of the product, or in other words the inside of the packaging, than in regions of the packaging which are further away from the surface.

Another problem arises due to the structure of the packaging described above. The liquid stored in the film is regular, especially at relatively large quantities of stored liquid are visible to an observer from the inside of the packaging, which considerably disturbs the overall aesthetic impression of the packaging, especially when the liquid is a dark mixture of water and blood. In order to reduce this negative aesthetic effect, it has been proposed to produce particularly thick-walled packaging or to choose dark colors for the packaging materials. However, dark colors for the packaging materials are only used in about 30% of all packaging, while in 70% of the packaging of the type in question, light colors are desirable and are accordingly also used; the problem described above is therefore of great importance in the case of these primarily used light-colored packaging materials.

To increase the absorption capacity for liquid, it has also been proposed to provide a particularly thick film as the starting material for the packaging. The ratio of absorption capacity to volume of the packaging material can, however, be improved.

It is therefore the object of the present invention to provide a film and a packaging which avoids the disadvantages of the prior art, has a high liquid storage capacity and also ensures an attractive visual impression when in particular dark liquids or large quantities of liquid are taken up.

The invention solves this problem in a packaging of the type mentioned in that the pore size of the foam increases at least in sections with increasing distance from a first surface of the film, and that the pore size of the foam with increasing distance from a second surface opposite the first surface Foil also increases at least in sections.

The film and packaging according to the invention has a high liquid absorption capacity and ensures that liquid absorbed is not or only very much is slightly visible from the outside, even if the liquid has a relatively dark color - in relation to the color of the packaging material. According to the invention, the size of the pores increases with increasing distance from both outer surfaces, while the size of the pores near the surfaces is relatively small. As a result, the liquid is essentially stored in the interior of the film and not in the edge regions, since in the region of the pores with larger average pore sizes there is greater liquid storage capacity than in the region of smaller pore sizes. Due to the increased liquid storage inside the film, it is not perceivable or negligible for a viewer that liquid has accumulated within the pores of the foam. Even with dark liquids and when using a light foam, it is difficult or impossible for an observer to see from the outside that liquid is present in the film. This is a considerable advantage over the known packaging. The film according to the invention has a very high specific liquid absorption capacity - based on the mass - and ensures that liquid accumulates at a distance from the outer surfaces of the film and thus primarily inside the film.

A particularly preferred embodiment of the film according to the invention is characterized in that the film is essentially impermeable to liquids in the region of the first and second surfaces. The liquid impermeability in the area of the surfaces on the one hand ensures that absorbed liquid cannot escape from the film, that is to say cannot escape from a packaging produced with the film according to the invention. On the other hand, absorbed liquid will not run back into the interior of the packaging. The liquid enters the film from the interior of the packaging in that, in accordance with a particularly preferred development of the invention, openings are provided in the area of the first or second surface in the liquid-impermeable area, through which openings liquid can reach the area of the open-pore structure. In addition, the liquid-impermeable areas additionally provide an "optical barrier", so that liquid stored in the film is not recognizable from the outside, i.e. does not shine through the film.

In a further alternative embodiment of the invention it is provided that a cover film is attached to the first surface and / or the second surface. The cover film can be a thin film which may be made of a different material and which is sealed, glued or welded onto the film according to the invention. This results in additional sealing of the film against gases and liquids and an improved overall visual impression of the packaging, since dark liquids in particular are not visible from the outside.

According to a further preferred embodiment of the invention it is provided that the film is composed of two layers which are preferably sealed, welded or glued to one another in mirror symmetry. This has a great advantage in terms of production, because two separate layers can first be produced, which are then permanently connected to one another. The separate layers can - for example - be produced to produce the pore structure according to the invention by extruding a liquid plastic as the starting material for the foam through an extrusion nozzle, expanding it to form cells or open-pore structures and then expanding it from one side, for example the outside of a tubular one Film web is cooled so that pores of very small size are formed in the area of the cooled surface or even an area without a pore structure is formed, while pores of larger diameter are formed on the opposite inside of the film.

The invention is described below using an exemplary embodiment and a manufacturing method with reference to the accompanying drawings. Show it:

1 is a schematic representation of an essentially clear a film made of a foam in a cross-sectional view;

2 shows a schematic representation of the film according to the invention to illustrate the pore structure and liquid absorption capacity;

3 shows a schematic illustration of an alternative embodiment of the film according to the invention;

4 shows a film according to the invention during manufacture in a schematic view; and

Fig. 5 shows a device for producing a film according to the invention in a side view.

The film according to the invention, shown schematically in a cross-sectional view in FIG. 1, consists of a foam having an open-pore structure, which consists of a plastic such as polystyrene with additives or other plastics suitable for producing a foam. The film is the starting material for the production of a packaging according to the invention in the form of a shell representing a container, in the interior of which foods such as meat or the like are placed and which is sealed airtight and liquid-tight with a cover film. However, the film can also be used for other purposes.

The film according to the invention is composed of two identical layers 2, 4, which are sealed to one another in the exemplary embodiment, but can alternatively also be welded, glued or otherwise attached to one another. The film is essentially mirror-symmetrical with respect to a contact surface 6 between the layers 2, 4. Both layers 2, 4 are essentially impermeable to liquids in the region of their surfaces 8 and 10, which form a first surface 8 or opposite second surface 10 of the composite film. In the area of the surfaces 8, 10 there is an essentially closed structure without pores is present, which results from the manufacturing process explained in more detail below. With increasing distance X starting from the surfaces 8, 10, the middle increases the size of the pores 3 of the cured foam, as can be seen from the illustration.

Fig. 2 illustrates the liquid absorption capacity of the film according to the invention schematically by the distances of the lines 1 2, 14, measured along the straight lines running parallel to the surface 8 or 10. In the edge region 16 of the layer 2 or edge region 18 of the layer 4 adjacent to the surfaces 8 and 10, the film is impermeable to liquid and there is no liquid absorption capacity. With increasing distance X from the surface 8 or 10, the liquid absorption capacity increases due to the increasing sizes of the pores 3 - approximately linearly - to a maximum in the area 20 near the center of the film and the contact area 6 between the two layers 2, 4. Then the liquid absorption capacity drops sharply with a further increasing distance X from the surface 8 or 10 and a decreasing distance to the contact area 6. Liquid absorbed by the film is therefore essentially stored inside the film. From the outside, the liquid stored in the pores of the film is not or only slightly recognizable.

The alternative exemplary embodiment of the film according to the invention shown in FIG. 3 has a fundamentally similar open-pore structure to the exemplary embodiment described above; Identical parts or structures are provided with the same reference symbols, and reference is made to the above descriptions in order to avoid repetition. In addition, a cover film 22, 24 is bonded to the layers 2 and 4 in the area of the surfaces 8 and 10, respectively. The cover films 22, 24 consist of a liquid-impermeable plastic. The two layers 2, 4 are welded together in the contact area 6. In a manner not shown, instead of the two layers 2, 4, only one layer 2 could be connected to a cover film; a cover film increases the strength of the film and thus the packaging. After the film has been produced, in both of the above-described exemplary embodiments, perforations are formed in the region of the surface 8 or 10, which face the interior in the subsequent packaging, through which liquid can get into the pores of the open-cell foam from the outside in order to enter the Pores to be stored. These openings are punched in, for example. In the case of the first exemplary embodiment (FIGS. 1 and 2), the perforations will completely penetrate the edge region 1 6. In the case of the exemplary embodiment according to FIG. 3, the perforations will completely penetrate both the cover film 22 and the adjacent region 26 of the layer 2, so that liquid can get into the pores 3 through the perforations.

A method and a device for producing a film according to the invention is described below with reference to FIGS. 4 and 5.

Fig. 4 illustrates schematically the connection of two layers 2, 4 by welding or gluing. For welding, a heating device (not shown) for heating the inner sides of the layers 2, 4 is arranged relative to the layers 2, 4 in such a way that the inner sides of the layers 2, 4 are heated in such a way that they are then joined together by welding. Alternatively, an adhesive application device can be provided for applying adhesive to the inner sides of the layers 2 and 4. By means of mechanical devices (not shown), for example roller guides, the two layers 2 and 4 are pressed against one another after the heating or application of adhesive, so that they permanently bond to one another.

5 illustrates an apparatus and further the method for producing a film according to the invention. Liquid plastic, for example polystyrene, exits the extrusion nozzle from a stationary-mounted extrusion device 30 with an annular extrusion nozzle and expands under high pressure and forms a tubular web 32. During expansion, a foam with an essentially open-pore structure is formed. A so-called air shower (not shown) is arranged outside the tubular web 32 has a plurality of air outlet nozzles from which air flows for cooling the tubular web 32 emerge. In the area of the outer surface of the tubular web 32, due to the air currents, the tubular web 32 is cooled more than on the inner surface of the tubular web 32, where cooling takes place in the ambient air. Because of this uneven cooling of the tubular web 32, a pore structure forms in the hardening foam, which was previously described with reference to FIGS. 1 to 3.

The tubular web 32 is conveyed along the outer surface of a so-called cooling mandrel 34, which is continuously cooled from the inside with a liquid, for example water. During the contact of the tubular web 32 on the outer surface of the cooling mandrel 34, the web 32 continues to cool.

A cutting device 36 with two rotating cutting knives is attached downstream to the cooling mandrel 34 and cuts through the tubular web 32 at two opposite locations in a middle plane, so that the tubular web 32 results in two separate webs or layers 2, 4 (see figures above). which are "laid flat" or transferred to flat layers 2, 4 due to a positive guidance with the aid of a total of two cylindrical rollers 38. The rollers 38 are rotatably mounted on a frame 40.

With the help of the rollers 38 rotatably mounted on the frame 40, the layers 2, 4 are deflected and pressed together by means of the rollers 42.

Two radiators 44 fastened to the frame 40 in a manner not shown heat the respective inside of the layers 2, 4 (cf. FIG. 4) with radiant heat, so that the surface of the layers 2, 4 is brought into a flowable state. The two layers 2, 4 are then sealed in the contact area 6 between the layers 2, 4 using the rollers 42. The finished film according to the invention is then wound up in a manner not shown. After complete cooling, the film is unwound and deep-drawn to produce a packaging according to the invention and then cut into separate packaging, each of which has a bowl-shaped container.

Claims

Expectations

1 . Film, in particular for packaging purposes, consisting essentially of a cured foam having at least partially an open-pore structure, in the pores of which a liquid can be stored, characterized in that the pore size of the foam at least in sections with increasing distance from a first surface (8) the film increases, and that the pore size of the foam increases at least in sections with increasing distance from a second surface (1 0) of the film opposite the first surface (8).

2. Film according to claim 1, characterized in that the film in the region of the first and second surfaces (8, 10) is substantially impermeable to liquids.

3. A film according to claim 2, characterized in that the film in the liquid-impermeable area (1 6) has openings through which liquid can get into the area of the open-pore structure.

4. A film according to claim 2 or 3, characterized in that a cover film (22, 24) on the first surface (8) and / or the second surface (1 0) is attached.

5. Film according to one of claims 1 to 4, characterized in that it is composed of two layers (2, 4), which are preferably sealed, welded or glued to one another in mirror symmetry.

6. Packaging, in particular for liquid-containing foods such as meat or the like, which essentially consist of a thermoformed or deformed from a film Containers for receiving a good, characterized by a film according to at least one of the above

Expectations.