GB2322329A

GB2322329A - Packaging Materials

Info

Publication number: GB2322329A
Application number: GB9703415A
Authority: GB
Inventors: Deborah Walker
Original assignee: Lawson Mardon Packaging UK Ltd
Current assignee: Amcor Packaging UK Ltd
Priority date: 1997-02-19
Filing date: 1997-02-19
Publication date: 1998-08-26
Also published as: GB9703415D0

Abstract

A packaging material comprises a semi-rigid first layer (11) and an second layer (15) of high impact polystyrene/polypropylene alloy or of a high impact polystyrene/polyethylene alloy. The second layer (15) is bonded to the first layer, for example by means of an adhesive layer (13) or a lamination process. Such a material can be formed into packages by conventional thermoforming processes and can be used for packaging food to be heated in a microwave oven.

Description

PACKAGING MATERIALS The present invention relates to packaging materials, in particular to a packaging material suitable for use in a microwave oven.

There has recently been an increase in demand for packaged food to be supplied in self-supporting containers in which the food can be heated or cooked in microwave ovens. One conventional form of microwave oven tray is formed from CPET (crystalline polyester).

Such trays are initially produced from material in an uncrystalline form which is crystallised during the forming process. In order to crystallise the material, the tray must be formed in a tool heated to around 1750C and then cooled in a second tool to allow rigidity to set in. Accordingly, manufacture of CPET trays requires relatively large and complex processing equipment, specifically designed for that purpose.

Another material that is used for microwave trays is polypropylene. However, this material has a very narrow temperature window in which it is stable, and therefore requires specialised materials handling equipment and processing machinery to form the trays.

A relatively straightforward, and well known, system for forming plastics trays in general is the socalled thermoforming system. In this system, the tray is produced from a semi-rigid substrate web material stored on a large roll. The continuous sheet of material is fed through heating and forming, filling and sealing stages to form a continuous series of filled sealed packages. The individual trays can then be separated from one another for distribution. Such a system enables fast production of sealed food products.

However, conventional thermoform materials, particularly PVC or APET (polyvinyl chloride or amorphous polyester) are not suitable for use in a microwave oven since they soften at temperatures lower than that used during microwave cooking (1000C) and so a food package produced from these materials will lose its rigidity and collapse.

It is therefore desirable to produce trays from a material which can be processed using conventional thermoform equipment, and which has the required properties to enable such packages to be used in microwave ovens.

According to the present invention there is provided a packaging material comprising a first layer of a flexible plastics material bonded to a second layer of high impact polystyrene/polyethylene alloy or of high impact polystyrene/polypropylene alloy.

A material embodying the present invention can be formed into food trays using a conventional thermoforming method, but is still able to be used in a microwave. Accordingly, the complexity and cost of the equipment required to form microwaveable packages is reduced.

For a better understanding of the present invention and to show how the same may be carried into effect, reference will now be made by way of example to the accompanying drawings, in which: Figures lA and 1B are a part cross-sectional views of materials embodying the present invention; Figure 2 shows a food package made from the material shown in Figure 1A or IB; Figure 3 shows schematically a process for forming the material shown in Figure 1B; and Figure 4 shows schematically a process for forming the package shown in Figure 2.

Figure 1A shows a packaging material la having a first layer 11 and a second layer 15 which is joined to the first layer 11. The two layers 11 and 15 can be joined by an extrusion lamination process. The first layer is of a flexible material, for example polyethylene (PE) or ethylene vinyl alcohol coextruded polyethylene. The second layer 15 is of an alloy of high impact polystyrene and polyethylene (HIPS/PE).

The second layer 15 is semi-rigid, so that the material la as a whole behaves in a semi-rigid manner.

Alternatively, the second layer can be of high impact polystyrene/polypropylene alloy (HIPS/PP), which is also semi-rigid.

Figure 1B shows another packaging material ib embodying the present invention. The material ib is identical to the material la of Figure 1A, with the exception that the two layers are joined by means of an adhesive layer 13.

The materials la and 1b can be from 200 microns to 1000 microns in thickness, and are preferably produced in the form of a long continuous film for storage on a roll prior to use by a packaging manufacturer. The laminate material formed is generally intended for sale to food packaging and package preforming companies for formation into packages for food use.

Figure 2 shows a perspective view of a package 18 manufactured from the material shown in Figure 1A or 1B. The package 18 comprises a sealing web 181 to which a sealing layer (not shown) is attached when the package is completed, and a tray 183 for holding a product, for example food. The package can be formed in a conventional thermoforming process as will be described in more detail below.

The package 18 can be successfully heated in a microwave oven without excessive deformation, because of the rigidity of the HIPS/PE (or HIPS/PP) alloy layer in the material la, ib.

The HIPS/PE alloy layer is particularly suited to use in a microwave oven because the polyethylene has good high temperature stability.

The polyethylene layer is used in order to provide the package with gas barrier properties, or so that a top web can produce a hermetically sealed package.

Figure 3 is a schematic diagram of a process suitable for forming the laminate material ib shown in Figure 1B. A feed roll 20 carries a rolled supply of polyethylene (PE) sheet 11. The polyethylene sheet 11 is fed, via a roller 23 to a pair of rollers 24. The rollers 24 operate to transfer adhesive 22 from a vat 25 to one side of the polyethylene sheet 11. The adhesive 22 is carried from the vat 25 by the lower roller onto the sheet 11. A series of rollers 26 then carries the continuous sheet 11 through a drying oven 28 to steel and rubber combining rollers 32 and 34 respectively.

A second feed roll 30 carries a continuous sheet of material for use as the second layer 15 of Fig. lb.

This material is supplied to the laminating process at the combining rollers 32 and 34.

The steel roller 32 and the rubber roller 34 urge the second layer 15 into contact with the adhesive layer 13 carried on the polyethylene layer 11. In this way a laminate material as shown in Figure 1b is formed. The laminate material lb is then transferred to a chilling roller 36 where it cools, before being stored on a storage roller 38. When the storage roller 38 is full, it can be detached from the process equipment for supply to a thermoforming process.

Figure 4 shows schematically a process for thermoforming packages, which are then filled, sealed and dispatched. The laminate material 1 (la or ib Figures 1A and 1B) is supplied in the form of a roll 41 and is fed into the equipment via a series of rollers 42.

At station A the material 1 is formed into a package 45 by means of upper and lower dies 43 and 44.

The material is heated in station A, so that it deforms into the shape of the package 45 determined by the dies 43 and 44. Usually this package would be an open tray, for example as shown in Figure 2. The material 1 is then indexed on so that the package 45 is fed to station B, and a new portion of material is drawn into station A. Alternatively, the process can be stopped after station A and the open tray packages dispatched to a food manufacturer for filling and sealing At station B, the package 45 is loaded with a product, so as to form a filled package 46.

Repeated indexing on of the material 1 draws the package 45 through stations C to F.

At station C the filled package 46 is sealed by heat sealing a sheet of material 471 over its open top surface. The material 471 is provided by a mechanism 47 including a feed roller carrying the material. The heat sealing is accomplished by means of heated pressure plates 48. The material 471 is not necessarily the same material as used for the base of the tray.

At stations D and E the individual packages are cut from the strip of material, by means of cutter wheels 49.

Finally, at station F, the completed sealed package is ejected in the direction of arrow 50 for storage and distribution.

The formed trays, when heat sealed, can produce a hermetically sealed pack which can be peelable or nonpeelable, and is also capable of being gas flushed.

The completed pack is suitable for use in a microwave oven and is generally capable of withstanding full power of a typical microwave oven for approximately six minutes without undue distortion.

Claims

1. A packaging material comprising a first layer of a flexible plastics material bonded to a second layer of high impact polystyrene/polyethylene alloy or of high impact polystyrene/polypropylene alloy.

2. A material as claimed in claim 1, wherein the first layer is of polyethylene.

3. A material as claimed in claim 1 or 2, wherein the second layer is bonded to the first layer by means of an intermediate adhesive layer.

4. A material as claimed in claim 1 or 2, wherein the first and second layers are bonded by an extrusion lamination process.

5. A material as claimed in any one of claims 1 to 4, wherein the first layer is of ethylene vinyl alcohol co-extruded polyethylene.

6. A material as claimed in any one of claims 1 to 4, wherein the first layer is of polypropylene.

7. A material as claimed in any one of claims 1 to 4, wherein the first layer is of polyethylene.

8. A material as claimed in any one of claims 1 to 4, wherein the first layer is of polyester.

9. A package for use in a microwave oven, the package being manufactured from a material as claimed in any one of the preceding claims.

10. A package as claimed in claim 9, wherein the material is such that when the package is heated in a microwave oven the shape of the package is not substantially affected.

11. A package as claimed in claim 9 or 10, in the form of an open tray.

12. A packaging material substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.

13. A package substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.