EP0397597A1 - Package and its heating respectively its sterilization method - Google Patents

Abstract

The package for a filling (38) which can be heated with microwaves can be sealed in an airtight manner and is made up of at least two parts; it is designed, in particular as a container, dish (16) or bag. The package can be reversibly stretched and/or deformed. One part of it consists of a bare or coated aluminium sheet, and the other of a sterilisable sheet (22) which is transparent to microwaves. To sterilise the filling, a package is continuously heated by exposure to microwaves at a temperature between 100 and 130 DEG C without applying a counter pressure, and cooled with water and then by allowing to stand. <IMAGE>

Description

The invention relates to an airtight sealable, at least two-part package for microwavable contents, in particular a container, a bowl or a bag. The invention further relates to a method for heating or sterilizing packs.

For energy-saving heating or sterilizing in microwave ovens, microwave-transparent containers made of a plastic or glass are used according to the known prior art.

The common microwave frequencies are in the UHF range, i.e. between 300 and 3000 MHz, with wavelengths of 100 - 10 cm. For industrial and medical applications, various frequencies in the mentioned range are reserved in the international frequency allocation plan. However, the frequency of 2450 MHz is used practically exclusively for microwave ovens, which has a wavelength of 12.25 cm in free space.

Microwaves cannot penetrate metal, they are reflected on metallic surfaces without heating them up. On the other hand, many non-metallic materials such as glass, ceramics, porcelain, paper and plastics are permeable to microwaves. The passage through these materials with practically no release of energy means that there is little or no heating.

Between the two extremes mentioned are many organic materials, in particular non-frozen water-containing foods, which relate the microwave energy relatively absorb well and are therefore suitable for heating by means of microwaves. The explanation lies in the molecular structure with dipoles that are particularly pronounced in water. These are stimulated by microwaves to move very quickly, which generates frictional heat.

In addition to the heating or sterilization of food in solid and liquid form, other applications are also important, for example the sterilization of pharmaceuticals.

The inventors have set themselves the task of creating a package of the type mentioned at the outset and a method for heating or sterilizing them which allow better use of the energy content of the microwaves and therefore result in stronger and more uniform heating.

With regard to the device, the object is achieved according to the invention in that the package is designed to be elastically expandable and / or deformable and consists partly of a bare or coated aluminum foil, and partly of a sterilizable foil that is permeable to microwaves.

With such a package, the known, favorable properties of an open aluminum package are used, which reflects the microwave rays on the inside, as a result of which the filling material is heated more strongly and more uniformly with a predetermined energy content. In addition, the better thermal conductivity of an aluminum packing compared to plastics is used by heating the contents evenly.

Known sterilizable aluminum packs have so far only been accessible for energy-saving heating by means of microwaves if the lid has been removed. This ent of course, every possibility for sterilization falls.

The package according to the invention is preferably designed such that the container, the shell, is designed as a single or multiple compartment shell, or the first half of the bag is made of aluminum foil, the lid or the second half of the bag is made of a stretchable, essentially organic material.

Here and in other respects, aluminum foil refers to a rolled thin aluminum layer in the foil or thin strip area, which consists of pure aluminum or a wrought aluminum alloy. Depending on the thickness and use, the aluminum foil can be bare, lacquered and / or laminated with at least one further foil, which consists of plastic or paper. Internal plastic layers prevent any reaction between aluminum and the contents. External plastic or paper layers prevent damage to thin aluminum foils and make labeling easier.

The bottom of the container or the shell made of aluminum foil can be designed to be deformable, in particular as a foldable membrane. This can at least partially compensate for the pressure generated in the package during sterilization.

The lid or the second half of the bag, which are permeable to microwaves, preferably consist of a multilayer laminate, in particular of an inner heat seal layer, a barrier and an outer layer.

With the heat seal layer, the lid or the second half of the bag is fixed or peelable (peelable) to the container, the shell or the first half of the bag made of or with an aluminum foil. Good for heat seal layers Suitable materials are polypropylene (PP), polyethylene (PE), oriented polypropylene (oPP) and polyethylene terephthalate (PET), which can be used individually or as a copolymer or as mixtures. In practice, the heat seal layer normally has a thickness of 2-70 µm.

A pack that can be kept as a preserve has a middle layer, which is referred to as a barrier and lies between the sealing and outer layers. According to a first variant, this consists of organic material, such as polyethylene vinyl alcohol (EVOH) or polyvinylidene chloride (PVDC). According to a second variant, an extremely thin inorganic coating, for example made of a glass, an oxide or oxide mixtures, in particular silicon oxide, can be used as a barrier. These multi-layer barriers of only a few hundred 10⁻¹⁰ m have their own stretchability.

The outer layer of the lid or the second half of the bag, which is relevant for the elastic expansion, preferably consists of polypropylene (PP), oriented polypropylene (oPP), a polyamide (PA), an oriented polyamide (oPA) and / or polyethylene terephthalate (PET). This layer is applied in a thickness familiar to the person skilled in the art.

With regard to the sterilization of the contents of a package, the object is achieved according to the invention in that the package is continuously heated to a temperature between 100 and 130 ° C. without the application of counter pressure by the action of microwaves and cooled by water and then left to stand.

Since there is no back pressure during sterilization in a microwave oven, preferably at 121 ° C., the increased vapor pressure inside the package causes deformation and / or expansion, the latter practically exclusively with the organic material. Thanks to the reflection of the microwaves on the inner wall of the packing part with the aluminum layer the product is heated faster and more evenly. Throughput can be increased significantly. After cooling, the containers return to their original shape.

The method according to the invention for heating the contents of a package without sterilization is characterized in that the lid or the second half of the bag is perforated before use, and the package is heated in the microwave oven without lifting off the lid or the second half of the bag.

The perforation is preferably carried out immediately before use and can also be done with kitchen appliances that are used in other ways, for example with a sausage cutter.

The steam pressure generated during heating in a microwave oven can be continuously compensated for by escaping steam thanks to the perforation.

The contents of a heated single or multi-compartment shell, also known as a menu shell, can keep the heat better thanks to the lid that has not been removed and can be made available to the consumer in an absolutely hygienic manner. In this case, a cover that is also optically transparent is particularly advantageous because the contents can be checked superficially before dispensing.

• - Fig. 1 einen Mikrowellenofen mit einem Behälter, in per­spektivischer Darstellung,
• - Fig. 2 einen Teilschnitt durch eine Schale,
• - Fig. 3 einen Teilschnitt durch einen Beutel,
• - Fig. 4 einen Schnitt durch eine Eingefachschale, vor und nach dem Sterilisieren,
• - Fig. 5 einen Schnitt durch eine Eingefachschale während des Sterilisierens.

The invention is explained in more detail with reference to the exemplary embodiments shown in the drawing, which are also the subject of subclaims. They show schematically:

• 1 shows a microwave oven with a container, in a perspective view,
• 2 shows a partial section through a shell,
• 3 shows a partial section through a bag,
• - Fig. 4 shows a section through a single shell, before and after sterilizing,
• - Fig. 5 shows a section through a single tray during sterilization.

The microwave oven 10 shown in FIG. 1 has an overhead, invisible magnetron tube with a dome made of ceramic material. When switched on, this magnetron sends out microwaves which are characterized by beams 12.

The microwaves are reflected by the inner and outer walls of an aluminum container 14 located in the microwave oven and by the inner walls of the oven. The contents in the container 14 are omitted for the sake of clarity, the microwave-permeable container lid is also optically transparent and therefore not visible. Due to the microwaves reflected in the interior of the container, the contents are heated faster and more evenly.

The outer region of an aluminum shell 16 shown in FIG. 2 has a horizontally encircling sealing edge 18. The outer wall 15 of the shell 16 or the underside of the sealing edge 18 is protected with an applied lacquer 20.

The microwave-permeable cover 22 consists of an outer layer 24, a barrier 26 and a sealing layer 28 forming the inner layer.

In the present example, the outer layer consists of a 25 µm thick oPA layer, the barrier consists of a 30 µm thick EVOH layer and the sealing layer consists of a 60 µm thick PP mixture.

The outer region of a bag 30 shown in FIG. 3 comprises a first bag half 32 and a second bag half 34 sealed thereon.

The outside of the aluminum foil 15 belonging to the first bag half 32 is laminated with printed paper 36. The barrier 26 lying between the sealing layer 28 and the outer layer 24 of the second bag half 34 consists of a quartz glass layer (SiO _x ) about 500 x 10⁻¹⁰ m (500Å) thick.

Both the lid 22 according to FIG. 2 and the second half of the bag 34 from FIG. 3 are expandable under increased pressure, such as that prevailing during sterilization. The sealing seams are designed so that they do not tear when stretched.

During the cooling process, the lid and the second bag half 34 re-form into the original shape or length due to the inherent stresses in the material.

The aluminum shell 16 shown in FIG. 4 contains a filling material 38. The shell is closed airtight with a cover 22 sealed onto the sealing edge 18.

Fig. 5 shows the same container during sterilization in a microwave oven. At elevated temperature, vigorous development of water vapor 40 has started. The cover 22 is stretched by the pressure and bulges outwards. The seal seams remain intact.

Because of the high pressure, the bottom 42 of the can has bulged slightly.

During cooling, the shell returns to the dimensions shown in FIG. 4.

Claims (10)

1. A hermetically sealable, at least two-part package for microwaves (12) heatable filling (38), in particular container (14), shell (16) or bag (30),
characterized in that
that the package is designed to be reversibly expandable and / or deformable and consists partly of a bare or coated aluminum foil (15) and partly of a sterilizable film (22, 34) that is permeable to microwaves. 2. Package according to claim 1, characterized in that the container (14), the shell (16) or the first half of the bag (32) made of an aluminum foil (15), the lid (22) or the second half of the bag (34) made of a stretchable , consists essentially of organic material. 3. Pack according to claim 1 or 2, characterized in that the bottom (42) of the container (14) or the shell (16) made of an aluminum foil (15) is deformable, preferably as a foldable membrane. 4. Pack according to one of claims 1-3, characterized in that the lid (22) or the second half of the bag (34) made of a multilayer laminate, preferably a heat seal layer (28), a barrier (26) and an outer layer (24 ) consists. 5. Pack according to claim 4, characterized in that the solid or peelable heat seal layer (28) consists of a preferably 2-70 µm thick layer of polypropylene, polyethylene, oriented polypropylene and / or Polyethylene terephthalate exists. 6. Pack according to claim 4 or 5, characterized in that the barrier (26) consists of preferably 5-50 µm thick polyethylene vinyl alcohol or polyvinylidene chloride. 7. Package according to claim 4 or 5, characterized in that the multilayer barrier (26) consists of a few hundred 10⁻¹⁰ m thick glass or oxide, preferably silicon oxide. 8. Package according to one of claims 4-7, characterized in that the outer layer (24) consists of polypropylene, oriented polypropylene, a polyamide, an oriented polyamide and / or polyethylene terephthalate. 9. A method for sterilizing the contents of a package according to any one of claims 1-8, characterized in that it is continuously heated to a temperature between 100 and 130 ° C without the application of a back pressure by the action of microwaves and is cooled by water and subsequent standing. 10. A method for heating the filling material, in particular a food, a package, according to one of claims 1-8, characterized in that the lid (22) or the second half of the bag (34) perforates before heating, and the package without lifting the Lid (22) or the second bag half (34) is heated in a microwave oven (10).

Images