Patent GB-518189-A (GB)
Title: Improvements in or relating to the coating of fruit, vegetables, nuts, eggs and like perishable produce prior to marketing
IPC: A23B7/16
Filed: 1938-08-17
Abstract: 518,189. Preserving perishable produce; synthetic resin compositions. DU PONT DE NEMOURS & CO., E. I. Aug. 17, 1938, No. 24284. Convention date, Aug. 26, 1937. [Class 49] [Also in Group IV] Citrus fruit, apples, tomatoes, and other fruit, nuts, vegetables, eggs and other perishable produce are prepared and preserved for marketing by coating their entire surface with a resinous protective film by treatment with an aqueous emulsion of an emulsion-polymer-resin prepared by polymerizing an emulsion of a polymerizable monomeric compound. Compounds used include those containing a substituted ethylene group, e.g., vinyl compounds such as vinyl esters and styrene, and the acrylie compounds such as acrylic acid esters, nitriles, amides and the corresponding alpha- and #-homologues. In particular, esters of acrylic acid and of alpha-substituted acid, e.g., methyl, ethyl, propyl and butyl acrylates and methyl, ethyl, propyl, butyl, isobutyl and methoxyethyl methacrylates alone or in suitable combinations are used. The properties of the film may be modified by adding to the aqueous emulsion substances for improving the film-forming properties, decreasing porosity, reducing desiccation and varying the hardness, toughness, adhesiveness &c. of the film. Plasticizers used include phthalic acid esters, e.g., dibutyl phthalate, and phthalates' prepared from mixtures of alcohols containing 4-8 carbon atoms. The plasticizer is preferably dissolved in a monomeric ester prior to emulsification and polymerization ; sufficient is added to produce a softening temperature which will cause the resin particles to adhere to one another and form a continuous film on drying. Emulsifying agents used include those obtained by sulphating, to give sulphonic acids or sulphuric acid esters, straight chain alcohols of more than 7 carbon atoms, or esters or ethers of unsaturated alcohols containing more than 7 carbon atoms, e.g., sodium decyl sulphate or the sodium salt of octadecanediol mono-acetate sulphate. Other emulsifying agents used include soaps, sulphonic acids and quaternary ammonium compounds, e.g., lauryl piperidinium bromide and cetyl trimethyl ammonium bromide. To reduce the porosity of the films, dammar gum, ester gum and other gummy material or natural or artificial waxy or resinous material, e.g., Asiatic wax or a modified alkyd resin, such as diethylene glycol coconut oil modified alkyd resin, are included preferably in the monomeric ester prior to emulsification and polymerization. The hardness, toughness, pliability and adhesiveness of the coatings may be modified using suitable inter-polymeric combinations, e.g., polymerization of mixtures of monomeric methyl and butyl methacrylate produces a resin having properties intermediate those of the resins prepared from the individual monomeric compounds. An inter-polymer of vinyl acetate and chloride with 75-90 per cent. of the chloride may be used. Oil-soluble dyes may be added to the emulsion to enhance the colour of the produce. Fungicidal action may be obtained by using methacrylate-polymer-resin or by adding to the emulsion borax, boric acid, sodium borate and like water-soluble and also oil-soluble fungicides. Examples of the coating compositions giving proportions which may be used are included. In one example, a mixture of dammar, benzoyl peroxide, butyl and methyhnetacrylate monomers and dibutyl phthalate is filtered through cotton and added to water containing sodium octadecanediol mono-acetate sulphate, shaken thoroughly, recycled for three minutes in a colloid mill and heated for forty-eight hours at 65‹C. to effect polymerization. Fruit may be dipped in or sprayed with this emulsion. In coating oranges and similar produce emulsions containing about 8.5 per cent. of solids may be used, but higher concentrations may be employed, e.g., apples, tomatoes &c. may be coated with a relatively heavy transparent film which may be stripped off prior to use.