Method for producing encapsulated sodium percarbonate particles

#The present application is US national stage of international application, PCT/EP2008/065920 which had an international filing date of Nov. 20, 2008, and which was published in German under PCT Article 21(2) on Jun. 25, 2009. Priority is claimed to European application EP 07123598.0, filed on Dec. 19, 2007 which is hereby incorporated by reference in its entirety.

#The invention provides a process for producing coated sodium percarbonate particles by spray application of a sodium sulfate-containing aqueous solution onto sodium percarbonate particles in a fluidized bed and simultaneous evaporation of water, wherein the sodium sulfate-containing aqueous solution is prepared using sodium sulfate and sodium percarbonate-containing dust.

#Sodium percarbonate is increasingly being used as a bleaching constituent in detergents and cleaning compositions. For this application, sodium percarbonate must have sufficient storage stability in detergent and cleaning composition formulations, since there is otherwise undesired loss of active oxygen and hence of bleaching action in the course of storage of the detergents and cleaning compositions. Sodium percarbonate is moisture-sensitive and decomposes in detergent and cleaning composition formulations under the action of moisture with loss of active oxygen. To produce detergents or cleaning compositions, sodium percarbonate is therefore typically used in coated form, in which case the coating layer prevents the action of moisture on the coated sodium percarbonate particles.

#To produce the coated sodium percarbonate particles, sodium percarbonate particles which have been produced from aqueous hydrogen peroxide solution and aqueous sodium carbonate solution by fluidized bed buildup granulation by the process described in EP-B 0 716 640, and had a mean particle diameter x50 of 0.70 mm and a fines fraction smaller than 0.2 mm of less than 2% by weight, were used. The coating layer was applied to these particles by the process described in paragraph [0021] of EP-B 0 863 842, by spray application of a 20% by weight aqueous solution of the coating materials in a fluidized bed at a fluidized bed temperature of 60° C. and simultaneous evaporation of water. In total, 4% by weight in each case of coating materials, calculated without water of crystallization, relative to the total amount of sodium percarbonate particles and coating materials used, were sprayed on.

#The dust 1 used in examples 2, 3 and 4 to produce the coating material solutions was separated from the air discharged from a production plant for coating sodium percarbonate particles with sodium sulfate in a fluidized bed. The dust 2 used in examples 5, 6 and 7 was separated from the air discharged from a production plant for producing sodium percarbonate particles by fluidized bed buildup granulation. The composition of the two dusts is depicted in table 1.

#In example 8, the solution of the coating materials was prepared by dissolving 20 parts by weight of sodium sulfate in 80 parts by weight of an aqueous solution which was obtained in a scrubber in which dust was separated from the air discharged from a production plant for coating sodium percarbonate particles with sodium sulfate in a fluidized bed and from the air discharged from a production plant for producing sodium percarbonate particles by fluidized bed buildup granulation. The solution from the scrubber contained a total of 6.1% by weight of dissolved solids.