Method for the production of substantially open-cell polystyrene sheet

Abstract

A method of producing a substantially open-cell, expanded polystyrene sheet, comprising the steps of:forming a mixture comprising from 30 to 95% of polystyrene incorporating an aliphatic hydrocarbon with 4-6 carbon atoms, from 0 to 65% of polystyrene, and from 0.2 to 10% of a nucleating agent,mixing the mixture obtained and melting it by heating inside an extruder,bringing the mixture to a temperature of 130-150° C. in the final portion of the extruder,extruding the mixture in a lower-pressure atmosphere to produce an expanded sheet, which has a low density and a high capacity to absorb aqueous liquids, particularly if a surfactant is added to the starting mixture, and which, when coupled with two films of plastics material gives rise to a laminate suitable for the production, by thermoforming, of trays of foods which may release aqueous liquids.

Description

TECHNICAL FIELDIn general, the present invention relates to the packaging of food products, particularly foods such as, for example, meat or fish, which may release blood or other liquids.In particular, the invention relates to a tray comprising a sheet of substantially open-cell, low-density polystyrene having the capacity to absorb liquids, particularly aqueous liquids, and to a method of producing it.BACKGROUND OF THE INVENTIONIn the packaging of foods which may release blood, such as meat or fish, there is a problem in providing packages which can isolate and hide the blood released by the food, since it has been found that is presence and visibility inside the package renders the latter unattractive to the purchaser.Amongst the solutions proposed for this problem in the prior art, the simplest consists of the provision of a tray provided with a pad or layer of absorbent material, generally paper. Solutions of this type are described, for example, in patent applications EP-A-O 1...

AI Technical Summary

Benefits of technology

In comparison with the closest prior art (EP-A-0 090 507), the present method has the advantage of providing a substantially open-cell sheet with a considerably lower density, for a given percentage of open cells, which can therefore absorb a larger volume of liquid for a given weight.

Moreover, the method according to the present invention is carried out at a lower temperature than the aforementioned method of the prior art (130-150.degree. C. instead of 196-204.degree. C.): this has the favourable consequence of a considerable energy saving, an improvement in the aesthetic characteristics of the skin, and better workability of the sheet.

The density of the expanded sheet can easily be adjusted upon the basis of the quantity of polystyrene resin incorporating pentane included in the starting mixture and can be reduced to values of 50 g / l when the polystyrene resin used in the starting mixture is constituted exclusively by polystyrene resin incorporating aliphatic hydrocarbon with 4-6 carbon atoms.

Moreover, the water-repellency of the sheet prevents the blood exuded from the food from wetting the inner surface of the tray creating unpleasant marks, and facilitates its penetration into the underlying absorbent layer through the holes.

The use of the substantially open-cell expanded sheet produced by the method described above as an absorbent pad for conventional polystyrene trays also solves the problem connected with the difficulty in recycling the materials and a considerable reduction in costs is achieved.

Problems solved by technology

In the packaging of foods which may release blood, such as meat or fish, there is a problem in providing packages which can isolate and hide the blood released by the food, since it has been found that is presence and visibility inside the package renders the latter unattractive to the purchaser.

The trays mentioned above have the disadvantage of being made of materials of different kinds, that is, expanded plastics, generally polystyrene, and paper or similar hydrophilic materials, which are difficult to separate from one another so that there is little or no chance of their being recycled.

Moreover, owing to the presence of the paper, the production cost of these trays is considerably greater than that of conventional non-absorbent trays.

Trays of the type described above have the disadvantage of necessarily having quite large holes in order to allow the blood to descend by the gravity and, for this reason, leave the blood which has collected in the space easily visible.

The aforesaid open-cell sheet has a high density (150-450 g / l), however, and its ability to absorb water is not adequate for the purposes of the present invention.

The open-cell sheet produced according to the method of the aforementioned patent application also has an irregular surface which impairs the appearance of the tray to a certain extent.

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