Coating processes – Particles – flakes – or granules coated or encapsulated – Fluidized bed utilized
Reexamination Certificate
2002-01-09
2003-11-04
Douyon, Lorna M. (Department: 1751)
Coating processes
Particles, flakes, or granules coated or encapsulated
Fluidized bed utilized
C423S415200, C510S441000
Reexamination Certificate
active
06641866
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to granular coated sodium percarbonate for detergent and its manufacturing process, and more particularly to granular coated sodium percarbonate and its manufacturing process, wherein the surface of said sodium percarbonate establishes a multiple coating layer by being internally coated with a specific composition containing alkali metal silicate while externally coated with a specific composition containing alkali metal sulfate on upper part of said internally coated layer thus providing said sodium percarbonate an excellent dissolving rate in water as well as a good storage stability, preventing it from caking during delivery or storage, and being ultimately utilized as an effective detergent bleach containing zeolite as its detergent builder.
2. Description of the Related Art
Sodium percarbonate when dissolved in water can eventually release the sodium carbonate and hydrogen peroxide, which are known to be environmentally safe and do not harm textiles when bleaching clothes and thus has been used as an oxygenated bleaching agent. The conventional powder type detergents generally contain sodium percarbonate in along with zeolite, a detergent builder, which accelerates the decomposition of sodium percarbonate. Therefore, it has been quite customary to coat the surface of sodium percarbonate with borate, silicate, sulfate or carbonate when it is used together with zeolite in order to increase stability.
With the introduction of energy conservation wave to protect the global environment, the way of wash has been also changing from hot temperature wash to either warm or cold wash and in some areas washing has been traditionally carried out at room temperature. However, if the dissolution rate of sodium percarbonate is poor the sodium percarbonate is hardly well dissolved during the wash cycle and thus either released into the sewage or remained in the clothes without exhibiting effective bleaching or sterilization. Therefore, it is shown that the dissolving speed plays a crucial role in effective utilization of sodium percarbonate.
There are roughly two different methods in manufacturing sodium percarbonate; i.e., the crystallization process and the fluidized bed spray granulation process. The crystallization process is a traditional standard wet method of that crystallizes crystal sodium percarbonate by the reaction between two solutions of sodium carbonate and hydrogen peroxide. The fluidized bed spray granulation process is a method that can increase the size of granular particles of seed by spraying said two solutions of sodium carbonate and hydrogen peroxide in fluidized bed processor by using small sodium percarbonate particles as a seed.
The crystallization process is a very complicated process that necessitates the steps of solubilization and purification of sodium carbonate in along with the granulation process to adjust the size of produced sodium percarbonate. However, the sodium percarbonate thus obtained have either non-spherical shapes or rough surface inappropriate for surface coating. In the case of the fluidized bed spray granulation process, hot blast of gas is essential to evaporate huge amount of water and the high energy consumption makes it uneconomical.
GB Pat. No. 1,538,893 disclosed a traditional coating method to increase the stability of sodium percarbonate by mixing sodium sulfate and sodium silicate. Sodium silicate is an effective coating material used in increasing the stability of sodium percarbonate, however, it has a low dissolving speed in water generally and also shows a caking during the delivery or storage. Further, when sodium silicate, as a coating material, is located at the outermost of the coating films, i.e., exposed on the surface, the caking becomes more accelerated. Sodium carbonate can also cause sodium percarbonate to be caked, and the single coating mixed with sodium carbonate, sodium sulfate and sodium silicate as disclosed in the GB Pat. No. 1,538,893 has the disadvantage of generating the caking as sodium silicate and sodium carbonate are exposed on the surface. In the case of the coated sodium percarbonate disclosed in the GB Pat. No. 1,538,893, the stability of said sodium percarbonate is worse than that of sodium perborate and the improvement in stability is also not noticeable as compared to uncoated sodium percarbonate. Therefore, the single coating method as described in the GB Pat. No. 1,538,893 is not desirable because of the ineffectiveness in increasing stability. Moreover, the current powder detergents distributed in the market contain zeolite which is known to accelerate the decomposition of sodium percarbonate, and thus the sodium percarbonate disclosed in the GB Pat. No. 1,538,893 is not recommended to use.
The drawbacks of coated sodium percarbonate are also mentioned in other prior art; i.e., U.S. Pat. No. 5,935,708 described that the coated sodium percarbonate showed a caking because the outermost coating layer of the coated sodium percarbonate consists mainly of sodium carbonate, and U.S. Pat. No. 5,902,682 pointed out that coated sodium percarbonate in general have a rapid decomposition of active oxygen and thus multi-coating is more preferred. U.S. Pat. Nos. 5,462,804 and 5,902,682 both disclosed the method to improve the stability of sodium percarbonate by coating in common with silicate, magnesium sulfate, and alkali metal salts such as carbonate, bicarbonate, and sulfate in a sequential order or simultaneously. Adding silicate or carbonate to magnesium sulfate generates insoluble magnesium silicate (MgSiO
3
) or magnesium carbonate (MgCO
3
) and once said insoluble coating films are formed on the surface of sodium percarbonate they can block the permeation of moisture into sodium percarbonate. However, said insoluble coating films are water-insoluble and thus procrastinating the rate of dissolution of sodium percarbonate. U.S. Pat. No. 5,462,804 mentioned about the effect of improved dissolution rate but the level of increased dissolution rate cannot be measured because the specific temperature to measure the rate of dissolution is not identified, and U.S. Pat. No. 5,902,682 does not describe anything about the rate of dissolution. Both of the above-mentioned U.S. patent used silicate and magnesium sulfate as coating substances thus resulting the low dissolution rate of sodium percarbonate. In addition, the outermost coating layer consists of either carbonate or silicate, or the mixture of carbonate, silicate, and magnesium sulfate, all of which incur the caking during the storage of sodium percarbonate. Caking can take place both in a packing container and a storage tank of sodium percarbonate., and the caking makes the free flowing and convey of sodium percarbonate quite troublesome.
U.S. Pat. No. 5,714,201 disclosed a method of restricting the modulus of SiO
2
/Na
2
O of sodium silicate used in coating or manufacturing of sodium percarbonate to 1.5-2.3 in order to improve the dissolving speed. The above-mentioned modulus of sodium silicate can much influence the dissolution rate)of sodium percarbonate, and in general the greater the modulus of SiO
2
/Na
2
O, the slower the rate of dissolution of sodium percarbonate.
Here, the rate of dissolution of sodium percarbonate is influenced by the modulus of SiO
2
/Na
2
O if the content of sodium silicate is more than 1 wt % of sodium percarbonate, however, there is almost no influence by the modulus if the content of sodium silicate is less than 1 wt %. Moreover, the sodium percarbonate is well dissolved when manufactured using sodium silicate having low modulus of SiO
2
/Na
2
O of sodium silicate because the hydrophilic Na
2
O content increases; however, the sodium percarbonate absorbs moisture from the environment when stored for long period of time and results in caking. Therefore, it is more preferred to reduce the content of sodium silicate rather than adjusting the modulus of SiO
2
/Na
2
O of sodium silicate to enhance the dissolving speed of sodium percarbonate. The U.
Kim Yong Il
Lee Jong Pill
Lee Sang Hwa
Shur Sun Ki
Douyon Lorna M.
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Oriental Chemical Industries Co., Ltd.
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