GB938729A - Improvements in and relating to electrically non-conducting films - Google Patents

Abstract

Foods, particularly greasy foods, may be wrapped or packaged in an electrically non-conducting film which has an organic thermoplastic heat-seal coating, the coating having incorporated therein a cationic surface-active agent in an amount sufficient to confer anti-static properties sufficient to lower the electrostatic propensity to no more than 5 kilovolts/foot with a charge decay half time of no more than 5 seconds. By "electrically non-conducting film" is meant a film which accumulates electrostatic charges on its surface and includes film, which may be biaxially oriented and heat set, of cellulose ester, polyethylene terephthalate and similar polyester, vinylidene chloride copolymer, crystallizable polymers and copolymers of a -olefines, including ethylene, having preferably between 2 and 6 carbon atoms in the molecule and particularly propylene which is at least 75% insoluble in boiling n-heptane, e.g. isotactic polypropylene. The film may be chemically surface-treated to improve the adhesion of the heat seal coating before the latter is applied, e.g. by corona discharge, ozone, ionizing radiation in the presence of oxygen, or chemically oxidizing agents, e.g. halogens, potassium permanganate and chromic acid. The coating may be of copolymers of vinylidene chloride with, for example, acrylonitrile, methyl or ethyl acrylates, vinyl chloride, acrylic and methacrylic acids; vinyl acetate copolymers which may conveniently contain other monomers, e.g. itaconic and citraconic acids; gelatine, polyvinyl alcohol, acetate or acetal, e.g. butyral; copolymers of butadiene with acrylonitrile, ethyl or methyl acrylates, vinylidene chloride, vinyl chloride, acrylic or methacrylic acids, or vinyl acetate; copolymers of methyl methacrylate and methacrylic acid; copolyesters of terephthalic acid and another dicarboxylic acid, e.g. an aliphatic dicarboxylic acid, with alkylene glycols particularly ethylene glycol; and N-alkoxy methyl polyamides. The cationic surface-active agent may be an amine or phosphonium salt such as a quaternary ammonium or phosphonium salt, the quaternary residue being attached to at least one long chain of carbon atoms which may have other atoms besides carbon atoms, e.g. oxygen or nitrogen atoms, in the chain or substituted on to it, and may contain at least eight carbon atoms. The long chain of carbon atoms may be an alkyl group derived from a fatty acid or alcohol, the condensate of formaldehyde or of an alkylene oxide or glycol, e.g. ethylene or propylene oxide, or a polymeric residue to which one or more quaternary ammonium or phosphonium residues are attached. The cationic surface-active agent may be the salt of a strong acid, a betaine having a chain as above attached to the betaine nucleus, polymers of acrylic acid derivatives in which the monomer has the formula CH2=C(R)CO.NH.(CH2)N+R113X-or CH2=C(R).CO.O.(CH2)nN+R113X-and compounds of formula <FORM:0938729/VI/1> and particularly compounds having the formula R1-N+R113X-; <FORM:0938729/VI/2> R1CO.N+H(CH2)nN+R113X-; or R1.CO.O(CH2)n.N+R113X-; where R is hydrogen or methyl, R1 is a long chain of carbon atoms as above, preferably C10 to C24 normal-alkyl or alkenyl, or an ethylene oxide condensate having 5 to 40 ethylene oxide residues in the chain, R11 is an alkyd or alkenyl residue which may be substituted with hydroxyl or aryl groups, or a long chain of carbon atoms as in the case of R1, n is from 1 to 10, preferably 3, and X- is an anion. N-stearoyl (g ) amino propyl dimethyl b -hydroxy ethyl ammonium salt is particularly effective. The coating may be applied from an aqueous dispersion and the cationic surface-active agent may be an emulsifying agent for the dispersion. The coating may contain an additive in addition to and other than a cationic surface-active agent, e.g. anti-oxidants, dyes, pigments, lubricants, anti-blocking agents, ultra-violet light stabilizers and slip agents such as starch, talc, zinc oxide, calcium and magnesium carbonates, diatomaceous earth, silica, kaolin, titanium dioxide, triferric tetroxide, and other inorganic oxides, carbonates, silicates, aluminates and aluminosilicates, finely dispersed polypropylene and polyvinyl chloride (particle size 0.1 to 20 microns), unsaturated and saturated fatty acid amides, such as palmitamide, stearamide, distearamide and alkylene distearamides such as methylene and ethylene distearamide; hydroxylated fatty acid amides such as hydroxystearamide, hydrogenated castor oil, ester-type waxes, ether waxes and other hard waxes. The food may be heated in the package and stored. Specification 715,914 is referred to.