Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reissue Patent
2000-10-13
2002-07-02
Foelak, Morton (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S081000, C521S139000, C521S146000, C521S060000
Reissue Patent
active
RE037780
ABSTRACT:
TECHNICAL FIELD
In 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 INVENTION
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.
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 182 139, GB-A-1 168 925, EP-A-0 544 562, in patent FR 2 688 474, and in utility model DE 9013898.8.
The absorbent layer may simply be fixed to the internal surface of a tray of plastics material or interposed between two sheets of plastics material, of which that which is in contact with the food has holes through which the liquid released by the food is conveyed towards the interposed absorbent layer.
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 made of a single material, generally expanded polystyrene, which can isolate the liquid exuded from the food, causing it to descend by gravity into a space formed between two sheets of the aforesaid plastics material by passing through holes formed in the sheet on which the food is placed are also known. Examples of these trays are given in patent applications EP-A-0 574 819 and WO 94/00366.
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. Moreover, the blood can easily return the sheet which is in contact with the food as a result of the inversion or simply the inclination of the tray.
The technical problem upon which the present invention is based is that of providing a tray which is made solely of plastics material and which itself has the capacity to absorb liquids, particularly aqueous liquids, released by foods, thus preventing the problems set out above with reference to the trays of the prior art.
A partial solution to the aforementioned technical problem was offered in patent application EP 0 090 507, which describe a “fast food” container produced from a composite structure constituted by two superimposed sheets of which one is a normal sheet of closed-cell expanded plastics material and the other is a sheet of substantially open-cell plastics material which has the ability to absorb condensed steam coming from the foods present in the container.
The sheet of substantially open-cell plastics material constitutes the inner layer of the container which is in direct contact with the food.
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.
According to application EP 0 090 507, the open-cell sheet is produced, by the mixing of polystyrene with an excess of a chemical nucleating and expanding agent such as sodium bicarbonate/citric acid, in an extruder having a single mixing chamber and a single screw, the molten mixture being brought to a temperature of 196-204° C. immediately before extrusion.
SUMMARY OF THE INVENTION
The technical problem set out above is solved, according to the present invention, by a method of producing substantially open-cell 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 from 65% of polystyrene, and from 0.2 to 10% of a nucelating 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.
Simply “polystyrene” means polystyrene as such, that is, not incorporating hydrocarbons.
The percentage is given herein should be understood as the weight relative to the total weight of the mixture if not specified otherwise.
In order to increase the absorption capacity of the sheet, a quantity of from 5 to 10% by weight of the aforesaid nucleating agent, relative to the total weight of the mixture, is preferably used.
The aforesaid mixture preferably has a content of from 1 to 7% by weight, relative to the weight of the mixture, of aliphatic hydrocarbon with 4-6 carbon atoms and the hydrocarbon is preferably pentane.
The density of the final expanded sheet can be modified by variation of the percentage of polystyrene and, in particular, increases with increases in the aforesaid percentage.
Moreover, there are various types of polystyrene incorporating aliphatic hydrocarbons with 4-6 carbon atoms on the market, which incorporate different quantities of hydrocarbon; the density of the sheets produced from these products decreases as the hydrocarbon content increases.
The aforesaid nucleating agent is preferably selected from the group comprising sodium bicarbonate, citric acid, talc, sodium carbonate, Hydrocerol® and gypsum. This nucleating agent need not necessarily have chemical expanding properties, whereas this constituted an essential condition in the method according to EP-A-0 090 507.
The aliphatic hydrocarbon with 4-6 carbon atoms is preferably constituted by pentane.
In order to give the sheet according to the invention a better capacity to absorb aqueous liquids, a quantity of at least one surfactant variable from 0.2 to 10%, and preferably from 1 to 4% of the total weight of the mixture is added to the starting mixture.
The at least one surfactant may be selected from the anionic, cationic and non-ionic surfactants in common use, and is preferably a salt of a sulphonic acid of formula R—SO
3
H or of a sulphuric ester of formula R—OSO
3
H, in which R is selected from the group comprising alkyl and alkylaryl, with an alkali metal or an alkaline-earth metal.
A surfactant which has been found particularly useful for the purposes of the present invention is the aliphatic sulphonate marketed by the firm NOVACROME with the name HOSTASTAT SYSTEM E 3904®.
It is advantageous, in order further to increase the capacity of the sheet to absorb aqueous liquids, to add a quantity of up to 30%, preferably from 10% to 20%, of the mixture, of a shock-resistant polystyrene, preferably a dispersion of polybutadiene in polystyrene such as, for example, ENICHEM's product EDISTIR SR 550®.
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° C. instead of 196-204° C.): this has the favourable consequence of a considerable energy saving, an improvement in the aesthetic ch
Lanzani Federico
Mauri Renato
Foelak Morton
Nixon & Vanderhye P.C.
Sirap-Gema S.p.A.
LandOfFree
Method for the production of substantially open-cell... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for the production of substantially open-cell..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for the production of substantially open-cell... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2824388