GB2322100A - Absorbent tray for packaging meat and other foods - Google Patents

Abstract

A two or three layer foamed plastic tray comprising of a base layer with closed foam cells attached to a secondary layer with open foamed cells to absorb juices, blood and/or other liquids. An optional third solid layer with perforations with the purpose of hiding the absorbed fluids may be present.

Description

Absorbent tray for packaging meat and other foods.

The market for meat, fish and poultry and other fresh, chilled or frozen foods, is dominated in most developed countries, today, by the supermarkets.

These supermarkets, in the main, pre-package the foods into portions within trays or containers. The trays or containers are then sealed with either stretch wrap or with a heat sealed film.

In the UK, many countries in Europe and in North America, the trays or containers are predominantly made from foamed plastic sheet typically made from polystyrene.

The process, used to make these trays or containers involves, typically, the extrusion of the polystyrene together with a nucleating agent and a blowing agent which is, typically, pentane or butane gas. The resulting foam structure contains, typically, closed cells which, for the shelf life of the product, prevents the absorption of, or the passing through by, liquids. The process also, typically, involves creating a "skin" on one or both sides of the foam. The "skin" is made by collapsing the cells next to the surface by the application of a cold surface and/or cold air being directed at a point, directly after extrusion of the molten material. See figure 1.

The advantages of the foam material are several. Firstly, the foam is extremely light and the material cost is therefore low. Secondly, the foam structure makes the tray structurally rigid and prevents bending or collapsing.

Thirdly, the foam structure gives the tray thermal insulation properties which are advantageous for fish food.

One of the problems with pre-packing fresh meat and certain other fresh foods is that these foods can exude liquids such as juices and/or blood.

These juices and/or blood are known to be not attractive to consumers if they can be seen easily through the clear plastic wrap or film at the point of purchase.

To absorb these juices and/or blood food processors typically use ah absorbent pad made from natural or plastic fibres. These pads are placed under the meat or foods so that they, typically, cannot be seen and absorb the juices and/or blood. The problems with these absorbent pads.are that they are expensive and can be overlooked by the consumer who may cook the meat or food without realising that the pad is stuck to the bottom of the food.

This latter problem has partly been solved by gluing the pad to the tray but this makes the overall packaging even more expensive.

One product that exists today is a foamed trays which sandwiches an absorbent tissue between two layers of foam of which the upper layer, in contact with a meat or food, is perforated to allow the juices to drain through to the absorbent layer.

The process for making this structure is a continuous one, and, as a result, the absorbent layer is exposed, typically, at the ends of the tray. While this layer absorbs the liquid it tends to pull the liquid by capillary action to the edges of the tray and this is perceived to be unattractive to the consumer.

This invention relates to an absorbent tray for the packaging of meat and other foods.

According to the present invention the trays are moulded, typically by thermoforming or vacuum forming, from extruded material made of, typically, polystyrene or other polymer materials. The sheet will consist of two or more layers of which the foamed layer closest to the meat or other foods will be of an open cell structure which acts as a sponge to absorb juices, blood or other liquids. A solid layer with perforations may also be included between the meat and the open cell foam so that the open cell foam layer still absorbs the liquid once it has passed through the perforations of the solid layer. Below the open cell foamed layer there may be one or more layers of closed cell foam which, because of its rigidity, supports and strengthens the open cell layer.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows a typical cross section of a meat tray; Figure 2 shows a typical cross section of closed cell foam; Figure 3 shows a typical cross section of two layers of foam of which the upper layer is open cell foam and the lower layer is closed cell foam: Figure 4 shows a similar cross section to figure 3 but includes a perforated solid layer on top of the open cell foam layer.

Figure 5 shows a typical cross section similar to figure 4 but illustrates how the open cell foam is crushed to the edge of the tray to form a solid layer; Figure 6 shows a cross section of a thermoforming mould to form the tray and shows metal punches to form the perforations in the top solid layer of the tray.

The cross section shown in Fig. 2 is typical of the foam structure in a meat tray. The cells, 2, are ideally spherical and each cell closed and containing a mixture of gases. The outer cells, 1, are frequently partly collapsed by the application of cold temperature and/or pressure.

The cells, 3, as shown in Fig. 3 are open cells of which parts of the walls between adjacent cells are open. This open cell foam is extruded separately to the closed cell foam, 2. During the extrusion process a very small percentage of nucleating agent is added to the raw material at the beginning of the extruder similar to the process used for closed cell foam manufacture.

Carbon dioxide gas with or without Iso-Pentane, Pentane or Butane is injected under pressure into the melt stream of the material. Between the point at which this gas is injected and the extrusion die, a combination of water or steam and aromatic or halogenated hydrocarbon gases are injected under pressure into the melt stream. The aromatic or halogenated hydrocarbon gases are intended to attack the material in the cell walls and to cause them to rupture and thereby connecting the cells together in an open formation.

The water or steam is under considerable pressure and when the material is extruded out of the dye and therefore into normal atmospheric pressure the steam expands rapidly and further ruptures the cell walls.

The resulting foam structure of the open cell layer then acts as a sponge for any liquids that come into contact with its open face.

An alternative to the injection of the aromatic or halogenated gases is a hydrocarbon oil suspended in the steam mixture which will also attack the polystyrene material.

A further embodiment of the invention is the lamination of a thin solid film, 4, onto the upper surface of the open cell foam. When the foam sheet is thermoformed between the male mould, 7, and the female mould, 8, the film is perforated by metal punches in the male mould. These perforations, 5, allow liquid to pass through to the open cell foam where it is absorbed and distributed by capillary action. To avoid the capillary action taking the liquid to the edge of the tray the open cell foam is collapsed and compressed at the edge, 6. The film, 4b, at the edge is not perforated.

Claims (5)

Claims

1. A tray for packaging meat and fresh food compromising of two or more layers of which at least one layer is made from extruded foam with closed cells and at least another layer is made from extruded foam with a majority of open cells made from a mixture of crystal polystyrene and a nucleating agent and a blowing agent such as Iso-Pentane, Pentane or Butane or Carbon Dioxide or a mixture of these together with water or steam and together with an aromatic or halogenated hydrocarbon liquid, the combination of which creates the rupturing of the cells to absorb liquids by capillary action.

2. A tray made from foam similar to that in claim 1 in which the secondary polymer in the open cell layer or layers is high impact polystyrene, high density polyethylene, low density polyethylene or polypropylene.

3. A tray similar to that in claim 1 in which the aromatic or halogenated hydro carbon is replaced with a hydrocarbon oil.

4. A tray similar to that in claims 1, 2 or 3 in which a solid film layer of polystyrene or other polymer is laminated or extrusion coated onto the surface of the open cell foam layer and which the film is perforated during the moulding process so as to allow liquids to pass through to the open cell foam layer.

5. A tray similar to that in claims 1, 2, 3 & 4 in which pressure and/or heat is applied so as to collapse the open cells into a solid layer to prevent the capillary action in the open cells at the edges of the tray.