GB920868A - Process for making minute capsules and pre-mix compositions for use therein - Google Patents

Abstract

Minute capsules, each composed of a gelled polymeric-material wall enclosing a nucleus of a water-immiscible solid are prepared by placing in water one or more hydrophilic, film-forming, polymeric materials, at least one of which is temperature gellable and a phaseseparation inducing material, at a temperature below the gelling temperature of the said polymeric material, raising the temperature of the system formed to a point where at least part of the polymeric material becomes associated with water to form a liquid coacervate phase and adding the nucleus material at any time during the foregoing steps whereby the dispersed coacervate deposits on the dispersed nucleus material to form a liquid coacervate wall around each unit of nucleus material, and cooling the system with agitation to below the gelling point of the deposited coacervate material to form capsules which may subsequently be hardened by treatment with an aldehyde or other cross-linking agent. Suitable polymeric materials are gelatin alone and in combination with a natural or synthetic polymeric material which has a negative charge with respect to gelatin at its isoelectric point, e.g. gum arabic, polyethylene maleic anhydride, polyvinyl methyl ether maleic anhydride, polymethacrylic acid or mixtures thereof. The phase-separation inducing material may be a salt or a material which causes an alteration in the pH of the polymer dispersion. Possible nucleus materials are waterdispersable solids which are wettable by the liquid polymer wall material, e.g. powdered magnetic iron oxide, pigments, crystalline or amorphous powders, e.g. dyes and medicines, specific examples being; pyromellitic anhydride, carvone, riboflavin, ZnS and BaSO4.ALSO:Minute capsules, each composed of a gelled polymeric material wall enclosing a nucleus of a water-immiscible solid or liquid or a solid dissolved or dispersed in a water-immiscible liquid are prepared by placing on water one or more hydrophilic, film-forming, polymeric materials, at least one of which is temperature gellable and a phase-separation inducing material, at a temperature below the gelling temperature of the said polymeric material, raising the temperature of the system formed to a point where at least part of the polymeric material becomes associated with water to form a liquid coacervate phase and adding the nucleus material at any time during the foregoing steps whereby the dispersed coacervate deposits on the dispersed nucleus material to form a liquid coacervate wall around each unit of nucleus material, and cooling the system with agitation to below the gelling point of the deposited coacervate material to form capsules which may subsequently be hardened by treatment with an aldehyde or other cross-linking agent. Suitable polymeric materials are gelatin alone and in combination with a natural or synthetic polymeric material which has a negative charge with respect to gelatin at its isoelectric point e.g. gum arabic, polyethylene maleic anhydride, polyvinyl methyl ether maleic anhydride, polymethacrylic acid or mixtures thereof. The phase-separation inducing material may be a salt or a material which causes an alteration in the pH of the polymer dispersion. Possible nucleus materials are waterdispersible solids and liquids (including solutions or dispersions of solids in liquids) which are wettable by the liquid polymer wall material, e.g. animal, vegetable, mineral and synthetic oils, powdered magnetic iron oxide alone or suspended in an oil, pigments, pigmented oils e.g. inks, crystalline or amorphous powders e.g. dyes and medicines, specific examples being hexane, trichlorodiphenyl, pyromellitic anhydride, carvone, riboflavin, ZnS and BaSO4. The invention also comprises pre-mix compositions for use in the above process comprising the polymeric material, phase separation inducing material and, optionally, nucleus material in proportions such that the pre-mixes may be dispersed in water below the gelling temperature of the polymeric material and the above process performed without the addition of further material apart from nucleus material if not present in the pre-mix.