Patent GB-837923-A (GB)
Title: Method of packaging comestibles
IPC: B65D81/24
Filed: 1957-12-13
Abstract: Foamed sheets of styrene polymers may be produced by extruding a styrene polymer in which there has been incorporated a foaming agent for polystyrene and, preferably in the proportion 0.2 to 2.0% based upon the weight of the polymer, an alkaline earth metal sulphate having an average particle size of less than 5 microns; the presence of the sulphate is stated to reduce the pore size of the foamed sheets.  Preferred foaming agents are aliphatic and cycloaliphatic hydrocarbons which have a boiling point between 10 DEG  and 80 DEG C.  The extrudible material may be prepared by homogeneously dispersing the alkaline earth metal sulphate throughout the styrene polymer, preferably before incorporating the foaming agent. Alternatively the styrene polymer having incorporated a foaming agent may be intimately admixed with a finely divided alkaline earth metal sulphate, or a particulate styrene polymer incorporating a foaming agent may be coated with an aqueous solution of a water-soluble alkaline earth metal salt and the wet particulate material treated with an aqueous solution of a sulphate.  According to an example, five pounds of polystyrene beads of 20 to 40 U.S. standard mesh size having 6% of pentane incorporated are coated first with an aqueous solution containing 21 grams barium chloride and then with an aqueous solution containing 14 grams sodium sulphate.  They are then washed with water to free them from sodium chloride and dried; the beads have approximately 1% barium sulphate deposited upon their surface. The beads were fed to a conventional screw-type extruder operating at 325 DEG  F. and at a die pressure of 400 lb/inch2.  The resulting foamed polystyrene sheet has a substantially uniform cell size of 0.014 inch.  Interpolymers, containing a predominant proportion of styrene, with the conjugated 1.3 dienes, alpha-beta unsaturated monocarboxylic acids and their functional derivatives, and divinyl benzene or a blend of the styrene polymer with another polymer e.g. a rubbery diene polymer, or a graft polymer obtained by dissolving a rubbery diene polymer in monomeric styrene and subsequently polymerizing the mixture, may be employed.  All or part of the styrene may be replaced by a homologue of styrene such as alpha-methyl-styrene, ortho, meta- or para-methylstyrene, ortho-, meta- or para-ethylstyrene or 2.4-dimethylstyrene.  The styrene polymers employed preferably have a molecular weight of 40,000 to 80,000 as determined by the Standinger method.ALSO:Cellular sheets of styrene polymers are produced by extruding a styrene polymer in which has been incorporated a volatile expanding agent, e.g. hydrocarbons boiling between 10 DEG  and 80 DEG C, and an alkaline with metal sulphate of particle size less than 5 microns and in a proportion of 0,2 to 2,0% by weight of the polymer.  The sulphate reduces the pore size of the sheets. Particulate styrene polymer incorporating the expanding agent may be coated with the sulphate by a double decomposition reaction, washed, dried and extruded at 325 DEG F.ALSO:A comestible which is subject to deterioration at room temperature and may be preserved under cold storage, e.g. meat, fish or poultry, is placed in a tray formed of a foamed styrene polymer, the comestible and tray are wrapped in a thin transparent, heat-sealable film of thermoplastic material having low water vapour transmission characteristics, and the resulting package is sealed. The tray is preferably formed from a foamed styrene polymer having a density less than 10 lbs. per cubic foot, a closed cell structure of which the majority of the cells has a diameter less than 0.05 inch and, when formed solely of the polymer, a thickness of at least 0.03 inch.  The polystyrene foam may be laminated with paper, a film of plastic material or metal foil, e.g. a laminate of an 0.01 inch thick sheet of polystyrene foam and a sheet of paper 0.004 inch thick may be employed.  A number of examples of suitable thermoplastic wrapping films are given.  Blends of styrene polymers with another polymer may be employed (Group V).