GB1476682A - Bleaching formulation - Google Patents

Abstract

1476682 Coated bleaching formulations P P G INDUSTRIES INC 15 May 1974 [16 May 1973] 21462/74 Heading B2E [Also in Divisions B8 and D1] A bleaching formulation is in the form of an encapsulated core wherein the core comprises particles of a solid organic per acid in admixture with particles of a dispersing agent substantially more water-soluble than the organic per acid, the core being substantially completely encapsulated with a water dispersable material comprising a hydrated or non- hydratable inorganic salt and capable, in the absence of the free water, of preventing contact of the per acid with substances such as alkali capable of causing its decomposition. The dispersing agent may be the same as or different from the encapsulating material, but is in general of weakly basic or acidic character. It may be a hydrated or non-hydratable organic or inorganic salt, a double salt or an organic acid which may also function as a sequestering agent and detergent builder, many suitable substances being specified. A hydrated salt if used is preferably such as to give up at least part of its water of hydration below 150‹C and is preferably present in an amount sufficient to provide at least 0.1 part by weight of water of hydration per part by weight of the organic per acid. Specified encapsulating materials include sodium phosphate, sodium sulphate, magnesium sulphate, magnesium ammonium sulphate, sodium aluminium sulphate, potassium aluminium sulphate, ammonium aluminium sulphate, aluminium nitrate, aluminium sulphate, and aluminium magnesium nitrate, in hydrated form. Non-hydratable salts which may be used in the encapsulating materials include potassium sulphate, potassium hydrogen sulphate, potassium dihydrogen phosphate, sodium nitrate and ammonium acid sulphate. A binding agent capable of forming a gel with water, e.g. magnesium aluminium silicate, polyvinyl alcohol, soluble starch, hydroxypropyl cellulose, hydroxyethyl cellulose, polyvinyl pyrrolidone, casein, zein or agar, may be mixed with the encapsulating salt to provide a cohesive coating. Many per acids are specified, but diperisophthalic acid is preferred. The encapsulated core is preferably substantially spherical and ranges in size from 0.1 to 5 mm in diameter. The cores may be prepared by blending the dispersing agent with an aqueous slurry of the per acid, freezing the mixture into a thin sheet and breaking the sheet into particles of the desired size or by feeding the slurry through an atomising device and freezing the liquid droplets as they are formed. Alternatively die extrusion or pelletising techniques may be used. The core particles are then encapsulated in a static or fluidised bed.