Process for preparing coated alkali metal percarbonate, coated alkali metal percarbonate obtainable by this process, its use in detergent composition, and detergent compositions containing it
AssigneeSolvay (Societe Anonyme)
InventorsGrahm R. Horne, Alun P. James, Juan-Teva Carlier, Manfred Mathes
Life of this patent
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Abstract
A process for preparing coated particulate alkali metal percarbonate in which coating is carried out by mixing percarbonate with a solid particulate coating agent and optionally with an aqueous liquid, so that the amount of water present during mixing does not exceed 12% of the total weight of the mixture. Coated alkali metal percarbonate obtainable by this process and its use as active bleach in detergent compositions.
Claims21
1- A process for preparing coated alkali metal percarbonate in which coating is carried out by mixing alkali metal percarbonate with at least one solid particulate coating agent in an amount of less than 15% of the total weight of the mixture and optionally with an aqueous liquid, so that the amount of water present during mixing is at least 1.5% of the total weight of the mixture and does not exceed 12% by weight of the total weight of the mixture.
2- The process according to claim 1, wherein the amount of water does not exceed 10%, preferably 8% of the total weight of the mixture.
3- The process according to claim 1 or 2, without carrying out, before mixing, a preliminary preparation of a solution or a slurry of the coating agent.
4- The process according to any one of claims 1 to 3, wherein the solid coating agent comprises boric acid.
5- The process according to claim 4, wherein the coating agent contains at least 96% by weight of boric acid, preferably 100% by weight.
6- The process according to any one of claims 1 to 5, wherein the amount of coating agent is at most 7% of the total weight of the mixture.
7- The process according to any one of claims 4 to 6, wherein the coating agent is used in such a quantity that the coated alkali metal percarbonate contains from 0.1 to 0.5, preferably from 0.15 to 0.3% by weight of boron.
8- The process according to any one of claims 1 to 7, wherein the solid particulate coating agent has a mean diameter of at most 500 μm, preferably at most 250 μm.
9- The process according to any one of claims 1 to 8, wherein the coating is carried out by using dry particles of alkali metal percarbonate containing less than 1.5% by weight of water.
10- The process according to claim 9, comprising:
- (1) Preparing an aqueous slurry of alkali metal percarbonate particles in a crystallizer or crystallizer-classifier;
- (2) Separating the alkali metal percarbonate particles from the aqueous slurry to form a wet cake of alkali metal percarbonate particles;
- (3) Drying the wet cake of alkali metal percarbonate particles to form dry alkali metal percarbonate particles containing less than 1.5% by weight of water;
- (4) Mixing the dry alkali metal percarbonate particles with the solid coating agent in the presence of an amount of water which does not exceed 12% of the total weight of the mixture, to form wet coated alkali metal percarbonate particles;
- (5) Drying the wet coated alkali metal percarbonate particles to form dry coated PCS particles containing less than 1.5% by weight of water;
- (6) Collecting the dry coated alkali metal percarbonate particles.
11- The process according to claim 10, wherein step (4) is carried out by first mixing the dry alkali metal percarbonate particles with the solid coating agent, and then adding water to this mixture.
12- The process according to claim 10, wherein step (4) is carried out by mixing the dry alkali metal percarbonate particles simultaneously with water and the solid coating agent.
13- The process according to claim 9, wherein the dry alkali metal percarbonate particles are obtained by fluid bed granulation.
14- The process according to any one of claims 1 to 8, wherein the coating is carried out by using wet particles of alkali metal percarbonate.
15- The process according to claim 14, comprising:
- (1) preparing an aqueous slurry of alkali metal percarbonate particles in a crystallizer or a crystallizer-classifier;
- (2) separating the alkali metal percarbonate particles from the aqueous slurry to form a wet cake of alkali metal percarbonate particles containing less than 12% by weight of water;
- (3) mixing the wet cake of alkali metal percarbonate particles with the solid coating agent and optionally with dry alkali metal percarbonate particles, to form a wet cake of coated alkali metal percarbonate particles;
- (4) drying the wet cake of coated alkali metal percarbonate particles to form dry coated alkali metal percarbonate particles;
- (5) collecting the dry coated alkali metal percarbonate particles.
16- Coated alkali metal percarbonate obtainable by the process according to any one of claims 1 to 15, wherein the solid particulate coating agent solely consists of boric acid.
17- The coated alkali metal percarbonate according to claim 16, presenting a surface structure which is substantially in the form of plates when analysed with scanning electron microscopy (SEM) at a magnification of about 10.000.
18- The coated alkali metal percarbonate according to claim 17, wherein the surface structure measured with SEM at a magnification of about 10.000 is essentially free of needles.
19- The coated alkali metal percarbonate according to any one of claims 16 to 18, having one or more of the following properties:
- (a) a mean diameter from 500 to 1200 μm;
- (b) an Avox from 12 to 14.8%;
- (c) a bulk density from 0.8 to 1.2 g/cm3;
- (d) a 90% dissolution time from 0.5 to 3 min;
- (e) an attrition from 0.05 to 5%;
- (f) a thermal stability from 0.1 to 12 μW/g;
20- Use of the coated alkali metal percarbonate of any of the claims 16 to 19 in detergent compositions.
21- Detergent compositions containing the coated alkali metal percarbonate of any of claims 16 to 19 as active bleach constituent and a builder.