NO172037B - SELF-SUSTAINABLE PRODUCT CONTAINER AND PROCEDURE AND APPARATUS FOR MANUFACTURING SUCH CONTAINERS - Google Patents

Description

The present invention relates to a self-supporting product container, comprising a concave inner part with an enveloping outer edge part and a first, product-absorbing cavity section, as well as a concave outer part with an enveloping outer edge part and a second cavity section that occupies the first cavity section, the respective outer edge parts of the inner part and the outer part abutting each other and are joined together, while the cavity sections are otherwise arranged at a distance from each other everywhere.

The packaging of foodstuffs for sale to consumers has been given increasing attention, to ensure that the foodstuffs reach the consumer in the best possible condition. This has led to vacuum packaging and, more recently, to packaging in a controlled or modified atmosphere. There is also a growing demand that foodstuffs packaged in this way must be delivered in self-supporting, trough-shaped containers in which the food can be heated or cooked in conventional ovens or in microwave ovens. It is obvious that the materials used should not, in themselves or in any other way, cause contamination of the packaged food products. Materials that have the desired physical stiffness and thermal stability may, however, be not suitable for conventional differential pressure thermoforming and will often function unsatisfactory as a barrier, at least in the case of controlled or modified atmosphere packaging. It is therefore particularly difficult, if not impossible, to produce containers that meet all requirements, at a reasonable price. It is an aim to remedy the above-mentioned difficulties regarding food packaging.

This purpose is achieved according to the invention by a product container of the kind indicated at the outset, in that the inner part and the outer part are made of different thermoformable plastic materials which have different heat deformation-strength properties suitable for the use of containers as a cooking package. The fact that the inner and outer parts are made of mutually different materials contributes to an economically reasonable production. Preferably, one of the inner part and the outer part is more resistant to heat deformation than the other.

The invention also relates to a method and an apparatus for producing the self-supporting product container, as specified in the subsequent claims 4 and 7 respectively. Advantageous embodiments of the method and the apparatus are specified in claims 5, 6 and 8, 9 respectively.

The inner and outer parts can, e.g. by thermoforming under differential pressure, produced as containers or troughs with an open upper end and each separately with a bottom from which rise up side walls that are bent to create the respective outer flanges. The design can be carried out separately, as the parts are then brought together, or mostly simultaneously and mutually reversed, as the cavity section of the inner part is then turned into the cavity section of the other part.

If different materials are used, the outer part can be made of a relatively cheap material, even cardboard or paper-based material, which will give the container the desired physical properties including stiffness, while the inner layer consists of a non-polluting barrier material such as e.g. will allow the creation of a controlled/modified atmosphere in the pressure chamber above a food product. The materials' resistance to heat deformation can be different, as when cooking in a microwave oven it is required that the inner part must withstand higher heat (for example 120°C) than the outer part, for example 50-60°C), while on the other hand the outer part, when cooking in a normal oven, must withstand a higher temperature (for example 200-220°C) than the inner part (for example 120°C).

When using physically strong and rigid outer parts, the inner parts can be made of flexible material. However, the opposite is also possible, e.g. for use in a normal oven, i.e. where the inner part is physically load-bearing and the outer part is physically weaker, even flexible, but with high resistance to heat deformation, which applies to polycarbonate. The material thickness of each part can generally be kept to a reasonable minimum, with consequent cost savings. Flexibility in each part will obviously be able to contribute to resistance to shock/impact/vibration.

A product container of this kind will normally be provided with a cover which generally extends over the inner part of the container and is sealed to it, and which in many cases

extends continuously around the container.

Such a cover can be in the form of a layer, for example a cloth or a film, and interaction with the inner part can result in the contents being tightly packed and effectively encapsulated and suspended with the help of the inner part in the outer part. Alternatively, two uncovered containers facing each other can be used. In order to be joined or connected to each other, these can be connected in effectively common edge sections.

The inner and outer parts can be fused or sealed to each other at the same time as a cover layer is applied. If a controlled or modified atmosphere is required, a suitable, impermeable material is used as a cover layer. It can be advantageous, at least for foodstuffs, that the cover layer is peelably attached to the inner part, e.g. in the case of "prepared food-11 packages, so that a corner can be opened for the release of steam during cooking, and/or for easy removal after cooking. A seal of suitable strength can also serve as a safety mechanism, by being broken by excessive pressure increase in unperforated containers.

The peeling of a cover layer can be facilitated if the layer is loose in a corner of the container where the inner and outer parts are glued together. Slicing or strongly indenting the inner and outer parts in a corner or along an edge can also contribute to the removal of the cover layer, in a "break and tear" manner.

Continuous production can be carried out by thermoforming two thin sheets or layers in a machine, but prefabricated parts or a combination can also be used. The inner part itself can be filled with a product and sealed with an overlying layer, before it is introduced into the outer part.

In a suitable device, starting materials for inner and outer parts are joined together in a practical way, at least until a cover is glued on, with the help of a chain conveyor which grips oppositely located, overlapping edge parts. For food packaging, a covering layer that is impermeable to gas, steam, aroma or flavourings, and which can be made of clear, opaque or text-printed material, is preferred,

usually polymer.

In connection with the application and/or sealing of the cover layer, the inner part can be gas blown, or gas can be introduced if necessary for a controlled or modified atmosphere in the pressure chamber between the inner part and the cover layer, and in any case the inner part can have controlled penetration properties, e.g. in the event that the space between the inner part and the outer part also contains an atmosphere useful in connection with or in relation to the pressure chamber atmosphere.

The invention is described in more detail below with reference to the accompanying drawings, in which: Figure 1 shows a partially cut-away perspective view of a food container according to the invention.

Figure 2 shows a schematic section of the container.

Figure 3 shows a schematic drawing which indicates the various parts of a machine and which illustrates the process steps in a method for manufacturing a food container. Figure 4 shows a simplified section of a container which is designed to protect the contents from physical damage. Figure 5 shows a schematic diagram illustrating the process steps in the manufacture of a container, where the material in the inner and outer parts is combined before manufacture. Figure 6 shows a schematic diagram of another system for producing filter containers. Figure 7 shows a schematic diagram illustrating precautions for the passage of gas to and from both sides of the inner parts. Figure 8 shows a diagram illustrating the turning of the inner parts in the thermoforming station.

A food container 1 comprises an inner part and an outer part 3 and 5, respectively, where the inner part 3 is equipped with cavity sections 13 which are largely occupied in their entirety in a cavity 11 in the outer part 5. As shown, the parts have the form of a trough with open upper sides and with each its outer flange 7 and 9, respectively. The flange 7 on the inner part 3 overlaps and rests against the flange 9 on the outer part 5, and thereby supports the part 3. The cavity sections 13 are thus occupied, with mutual distance everywhere, in the cavity 11 of the outer part. Different materials are common for parts 3 and 5.

One of the parts 3 and 5, which may be fully formed, may be physically robust and in itself largely rigid and shape-resistant in ovens, while the other part may be physically weaker and even flexible, although this is in no way of significant importance . However, it is preferred that the inner part has properties that protect against pollution and loss of the desired atmosphere, and for example consists of a pollution-protecting material that is impermeable to controlled/modified atmospheres. Of particular interest is the use of plastic/polymer materials that can be formed by thermoforming techniques under the influence of differential pressure.

The distance that is maintained over all between the two parts 3 and 5 can be advantageously used as an insulating heat barrier or for protection against blows or shocks.

The inner part 3 according to Figure 1 has two cavity sections 13, although a single cavity section (shown with broken lines) will occur more often.

In a version suitable for use in a microwave oven, the inner part 3 consists of a flexible layer of material which can withstand the temperatures, usually up to 120°C, which occur in the food products during cooking. A suitable material consists of a co-extruded multilayer film of polyethylene/glue/nylon/glue/polyethylene with a thickness of, for example, 50-100 microns. The outer part 5 can be made of a material which is only dimensionally stable against heat effects up to temperatures of 50-60°C. A suitable starting material consists of a multilayer layer of styrene/glue/polyethylene which is co-extruded with a thickness of, for example, 500 microns.

In practice, the outer part 5 will have such a temperature that it can be held manually without difficulty, even if the contents of the inner part are at the boiling point.

The use of high-quality, relatively expensive barrier material (e.g. non-polluting and gas-impermeable) for the inner part 3 does not have to contribute significantly to physical robustness, although this may be the case for the outer part 5, which can nevertheless consist of a much cheaper material whose non-polluting properties are less important and which may also be gas permeable. The barrier material should prevent any escape of gas, flavouring, aroma and steam.

In another version for use in a normal oven, the outer part 5 consists of a material that will withstand contact with oven shelves at temperatures of 200-220°C, while the inner part 3, due to the gap 11, can be made of a material that only need to withstand the food temperature, usually 120°C, as the food acts as a heat jacket. In this case, it may be preferable for economic reasons to make the inner part 3 of a physically strong or robust material and the outer part 5 of a weaker, even flexible material. A suitable material for the inner part is a polypropylene/glue/nylon/glue/polypropylene laminate, e.g. with a thickness of 500 microns. A suitable material for the outer part is a thin and flexible polycarbonate sealing layer with a thickness of 50-100 microns. Under the influence of gas pressure between the inner part and the outer part, a flexible outer part can be expanded and safely placed at a distance from the inner part, typically by the heat developed during the preparation process expanding gas in the gap 11, whereby a distance is created between the inner part and the outer part. For the design of the parts, it can be advantageous that the amount of gas in the gap 11 is adjusted in such a way that the outer part will expand just sufficiently when heated. Flutes or grooves may be arranged in the inner part against a smooth outer part.

When manufacturing a packaged food product, the inner part and the outer part 3 and 5 respectively will usually be glued together continuously along their outer flanges 7 and 9, either before or simultaneously with the sealing of an overlying cover 20.

Figure 3 shows a manufacturing method whereby two material webs 51 and 52 are fed into respective thermoforming units 55 and 57, for the production of inner parts 59 of the material web 51 and outer parts 61 of the web 52. Each of the thermoforming units 55 and 57 typically comprises a heating element 56 for heating a material web which is forced against the element and thereby becomes deformable, and a mold 58 into which the heated material web is introduced and forced into contact with the mold 58 under the influence of differential pressure. The designed shape will be maintained during cooling. The plate 56 and the mold 58 can be moved up and down during introduction of the material path. After the thermoforming, the two designed material webs are brought together in a combining step 63, whereby the inner parts 59 are introduced into respective, trough-shaped outer parts 61.

The assembled parts are forwarded to a product filling station 64. Transport can take place using paired chain conveyors or the like. (not shown) which engages the mutually superimposed edge flanges of the two designed material webs. A conveyor with spring-loaded side grippers for holding the edges of the material web 52 can also collect the material web 51 at the station 63, and can serve for the extraction of both material webs and their continuation through the thermoforming unit, etc. However, a separate conveyor section can be used for advancing the material path for the inner part through the associated thermoforming unit.

The product filling station is followed by a sealing station in which a cover layer 65 unwound from a roll 67 is placed over the open upper side of the container. This layer is also removed preferably with the help of the first conveyor. Mechanical means can be used to hold the cover layer and the two parts to the necessary extent, while the section that occupies the product, at least if this consists of foodstuffs, is gas-flushed if necessary before the cover layer is sealed in position, usually with heat. All necessary air pumping and gas purging is preferably carried out in the sealing station. Unwanted distortion of the inner parts can thereby be avoided by reducing the pressure in the gap between the inner part and the outer part. The gap can be flushed using different gases used for the product section. Figure 7 schematically shows how provision is made for diversion to both sides of the inner layer 3 and/or for the introduction of a desired atmosphere within the final seal, as the materials in the inner and outer layers are perforated, to be brought into alignment with the respective channels which are indicated by the arrows x and y respectively and which lead to the cavities above and below the inner part. The materials are then cut to produce complete containers 71.

Containers consisting of separate shells, as described, can be used for products other than food either as shock/vibration-resistant packaging for transport, or for display, e.g. when using transparent material at least as covers.

Figure 4 shows a split shell container 90 which accommodates and retains one or more products 92, 94 which are thereby protected to a significant extent against impact and/or vibration. A contact-establishing cover material can thereby be used or, as shown, a clamshell-shaped container with an upper and

lower part components 9 6 and 98 of the above shape and connected along an edge 99. The upper part is shown in a detached position with a broken contour line at A. Each component comprises an outer part 100, usually made of relatively rigid material, and an inner part 102, both of which can be transparent.

The two components 96 and 98 can consist of separate and separated shell containers which are joined and fixed in an appropriate manner. Alternatively, alternating components 92 and 94 in a continuous row can be cut in pairs, end to end. Multiple formations can also be produced with the components side by side, and in any case in such cases adjacent formations for upper part and lower part, with cavities of different and desired shapes, can be produced without difficulty.

Figure 5 shows the simultaneous production of inner and outer parts of material webs 130 and 132 which, placed on top of each other, are simultaneously fed into a forming machine 134, preferably with a small space into which compressed gas can be introduced. The material web is simultaneously advanced to a heating and forming station 110 where they are heated, aligned and thermoformed. Two forms are arranged, one of which 112, preferably a hollow form for the outer material web and the other 114, likewise a hollow form, for the inner material web. From a pipe 115, pressure can be supplied between the material webs, so that these can be more easily adapted to the shape of the respective molds, usually in conjunction with a vacuum source which is connected to the interior of the molds. The material webs are preferably cooled by being brought into contact with the mold walls.

The two material webs can be connected along their edges by bringing their overlying edge parts together, for example after the initial design of the inner and outer parts, while they are still in the mold. If it consists of flexible material, the inner part can be turned after forming, as shown at 121, either by transfer of pressure (mechanical or hydraulic) or during filling with a product.

It may possibly be preferred that the turning is carried out in the mold by introducing pressure between the part 120 and the associated mold 114, see the broken lines in Figure 5, and as can be seen from Figure 8 where the inner part is shown with solid lines 120 in the forming position, and with broken lines 120' in the inverted position, ready to be filled with a product. The part can be turned under the influence of pressurized gas which is introduced through a channel 121.

The thus produced shell container component can then be moved to successive stations in the machine (unless simple product container parts are produced for later filling), which comprise a filling station 123, a station 125 for attaching and sealing the upper cover layer and a cutting station 127. A desired atmosphere can be created in the finished container, either in the pressure chamber above the product or between the inner and outer shells. The inner and outer parts can be perforated for diversion and/or gas purging and/or atmospheric introduction, as shown in figure 7.

Another, alternative manufacturing method is shown in Figure 6. In this case, the inner and outer parts are joined together after the inner part, as shown, has been filled and even after the filled inner part has been covered. The outer part can then be sealed to the filled inner part in station 140. After the thermoforming as shown at 141, the inner part material is advanced to a filling station 142, after which a cover layer is sealed to the filled container at 153. The filled container can be gas purged before it is finally sealed. The container is then brought together with the thermoformed outer part 150, preferably after the filled inner part has been separated from the material web, and the filling can actually take place completely separately, e.g. at a distance from the zone where the final joining with the outer material path takes place. The fitting and sealing of the cover can alternatively be carried out after the filled inner part has been joined with the outer part, so that all three material webs can be joined in a single sealing process. The other stations can be as previously described.

With suitable material designs, the upper part material can form a tearable seal together with the inner part material. If all three material layers are glued together, the inner part material and the outer part material can also be cut through at one corner flange of the container, to create a break-tear system.

The above describes the use of a barrier material, chosen because of its impermeability, for the inner part. It should be noted that many, if not all, so-called impermeable materials are permeable to a certain, albeit very small, degree. It is further assumed that an inner part material with a deliberately desired permeability can be advantageously used, for example for gas exchange through the inner part.

Moreover, the containers in question can be shaped as desired, including deeper ones, e.g. for beverages or soups etc, also triangular e.g. for sandwiches etc. The presence of a fluid, usually a gas, but possibly a liquid, between the inner and outer parts contributes to advantageous combinations of thermal insulation and physical shock-absorbing effect, especially for microwaveable foods.

Claims (9)

1. Self-supporting product container, comprising a concave inner part (3) with an enveloping outer edge part (7) and a first, product-receiving cavity section (13), as well as a concave outer part (5) with an enveloping outer edge part (9) and a second cavity section that occupies it first cavity section, in that the respective outer edge parts of the inner part and the outer part lie against each other and are joined, while the cavity sections are otherwise arranged with a mutual distance everywhere, characterized in that the inner part (3) and the outer part (5) are made of different thermoformable plastic materials that have different heat deformation -fastness properties suitable for the use of containers as a cooking seal. 2. Container according to claim 1, characterized in that the inner part (3) is more resistant to heat deformation than the outer part. 3. Container according to claims 1-2, characterized in that the outer part (5) is more resistant to heat deformation than the inner part (3). 4. Method for manufacturing the self-supporting product container according to one of claims 1 to 3, characterized by process steps comprising the manufacture of a first part (3) of plastic and with an enclosing outer edge part (7) and a product-absorbing cavity section (13), manufacture of a second part (5) of plastic and with an enclosing outer edge portion (9) and a cavity section which occupies the product receiving cavity section (13) with mutual distance (11) over all, and joining of the first and the second part along the outer edge portions of the parts, with the first part innermost and the second part outermost in relation to the container as a whole. 5. Method according to claim 4, characterized in that the first and second parts are produced from thin sheet materials made of plastic with different thermoformable plastic materials that have different heat deformation-strength properties suitable for use in containers such as a cooking package and are brought together in a sealing station (63, 110 , 150). 6. Method according to claim 4, characterized in that the first and second parts (3, 5) are produced from thin sheet materials of plastic with different heat deformation-strength properties suitable for the use of containers as a cooking pack under the influence of differential pressure in a thermo-forming station (10 ). 7. Apparatus for producing the self-supporting product container according to one of claims 1-3, characterized by means (55, 57, 110, 114) which are to form the first and the second container part (3, 5) of plastic and each with its own enclosing outer edge parts (7, 9) and receiving cavity sections (13), where the cavity section (13) in the first part (3) is arranged for receiving a product and the cavity section in the second part (5) occupies the product receiving cavity section (13) in the first part (3) with mutual distance everywhere, and means (63, 110, 150) for joining the first and the second part (3, 5) along the outer edge portions (7, 9) of the parts. 8. Apparatus according to claim 7, characterized by separate forming stations (55, 57) for the first and second part (3, 5), and a joining station (63) where the parts are brought together. 9. Apparatus according to claim 7, characterized by a single forming station (110) with mutually opposite form chambers (112, 114) for forming the first and second parts (3, 5) largely simultaneously in opposite directions, and a device -ning for turning the cavity section (13) in the first part (3).