Patent GB-980123-A (GB)
Title: Heat-shrinkable enveloping materials
IPC: C08L27/08
Filed: 1962-12-17
Abstract: An interpolymerized composition comprising 74-90% by weight interpolymerized vinylidene chloride, 4-22% by weight interpolymerized vinyl chloride and 2-10% by weight of at least one other interpolymerized monomer selected from (i) C1-C8 alkyl esters of acrylic or methacrylic acids, (ii) acrylonitrile, or (iii) methacrylonitrile, is used in making heat-shrinkable films. Preferably the interpolymer composition contains 80-90% by weight vinylidene chloride, 8-16% by weight vinyl chloride, and 2-10% of the other interpolymerized monomer. Specified alkyl esters include methyl, ethyl, N-propyl, N-butyl, and 2-ethylhexyl acrylates and methacrylates.  The interpolymer is made by polymerizing a mixture of the monomers in aqueous emulsion, suitably with potassium persulphate or sodium hydrogen sulphite as redox catalyst, until polymerization is at least about 80% complete, and recovering the interpolymer from the resulting latex - like dispersion.  The interpolymer is mixed with a small proportion of plasticizer and with a heat stabilizer, and extruded as a tubular film.  Plasticizers mentioned include dibutyl sebacate, dioctyl sebacate, dibutyl phthalate, dioctyl phthalate, and tricresyl phosphate.  Heat stabilizers mentioned include tetrasodium pyrophosphate, trisodium phosphate, 3(2-xenoxy)-1,2-epoxy-propane, and an epoxidized glyceride of specified properties.ALSO:A heat-shrinkable, heat-sealable, flexible enveloping material comprises a transversely and longitudinally oriented film composed of an interpolymerized composition, comprising 74-90% by weight interpolymerized vinylidene chloride, 4-22% by weight interpolymerized vinyl chloride and 2-10% by weight of at least one other interpolymerized monomer selected from (i) p  C1-C8 alkyl esters of acrylic or methacrylic acids, (ii) acrylonitrile, or (iii) methacrylonitrile.  The material is relatively impervious to water and to water vapour, and is used to pack foods with liquid components (e.g. meat and gravy or fruit in syrup) as well as hydrous foods, e.g. raw meat, fresh fruit and vegetables, without danger of dehydration during storage either at moderate temperatures or under dehydrating conditions of storage in a refrigerator or freezer.  The material, in the form of a tubular film, may be cut to the desired length, and containers or pouches prepared by heat-sealing one end of each length of cut tube.  Containers may be made with projections or pockets or other special shapes by welding the flattened tube along contour lines e.g. to fit the legs or carcasses of animals. Packaging is effected by placing the article to be protected in the container so made, removing air from the package, sealing the open end e.g. by heat-sealing or by twisting and tying, and heating the sealed package to about 85 DEG C. to shrink the bag about the enclosed article, e.g. by immersing the sealed package in hot water for 10 secs.-1 min. Foods which may be so preserved include cuts of meat roasts, legs, quarters and whole carcasses of lambs and chickens, fruit and vegetables.  Foods which do not require refrigeration for their satisfactory preservation, e.g. cheese, fish, smoked and spiced meats, e.g. bacon, ham and salami, may be protected from dehydration or contamination by moulds or bacteria by packaging as described above.  Non-edible materials e.g. leather, may be protected from deterioration in hot moist climates by the same method.