Cleaning compositions for solid surfaces – auxiliary compositions – Cleaning compositions or processes of preparing – With oxygen or halogen containing chemical bleach or oxidant...
Reexamination Certificate
1999-07-06
2001-05-29
Gupta, Yogendra (Department: 1751)
Cleaning compositions for solid surfaces, auxiliary compositions
Cleaning compositions or processes of preparing
With oxygen or halogen containing chemical bleach or oxidant...
C510S442000, C252S186270, C252S186320
Reexamination Certificate
active
06239095
ABSTRACT:
INTRODUCTION AND BACKGROUND
The present invention relates to a process for the preparation of coated peroxygen compounds, in particular coated sodium percarbonate with an increased active oxygen stability.
Many peroxygen compounds, also called active oxygen compounds, such as sodium percarbonate (2 Na
2
CO
3
.3H
2
O
2
) and sodium perborate monohydrate and tetrahydrate, are used as the active oxygen component in detergents, bleaching compositions and cleaning compositions. Because of the inadequate storage stability of sodium percarbonate in a warm-humid environment and in the presence of various components of detergents and cleaning compositions, sodium percarbonate must be stabilized against the loss of active oxygen (Oa). An essential principle of the stabilization consists of surrounding the sodium percarbonate particles with a coating of components having a stabilizing action.
Various substances and substance combinations which are applied in one or more layers to a core of sodium percarbonate have been proposed for stabilizing sodium percarbonate. Examples of coating components are: hydrate-forming inorganic compounds, such as sodium sulfate, magnesium sulfate, alkali metal carbonates and bicarbonates, and furthermore alkali metal silicates, alkali metal and alkaline earth metal borates and alkali metal and magnesium salts of organic carboxylic acids, such as fatty acids and citric acid. Coating of sodium percarbonate and other peroxygen compounds is at present chiefly carried out in fluidized bed processes, wherein a solution of the coating components is applied to seeds in a fluidized bed and water is evaporated off. Reference is made to DE-OS 24 17 572, German Patent 26 22 610 (corresponds to U.S. Pat. No. 4,105,827), WO 95/02555 and WO 97/19890 by way of example.
In the known fluidized bed coating of sodium percarbonate, 0.5 to 25 wt.% of coating components is applied. Although the stability increases as the amount of coating increases, the active oxygen content also decreases. There is accordingly an interest in minimizing the content of coating components in coated sodium percarbonate, while maintaining a good stability in detergents. While fluidized bed coating has proved to be superior to other coating processes, for example coating in a mixer with subsequent drying, the inventors of the present application have demonstrated by dyeing experiments that coating using a fluidized bed reactor with a conventional inflow base, for example a perforated or sieve base or so-called Conidurboden®, is incomplete both in a discontinuous procedure and quite so in a continuous procedure. This deficiency, which manifests itself in an inadequate stability of the active oxygen compound, can be overcome only by applying a thicker coating layer, although at the expense of a low active oxygen content.
An object of the present invention was accordingly to coat active oxygen compounds, in particular sodium percarbonate, in a fluidized bed, in such a way that a higher storage stability can be obtained for a given amount of coating than in the case with conventional methods.
SUMMARY OF THE INVENTION
The above and other objects of the invention can be achieved by spraying an aqueous solution containing one or more coating components on to particles of sodium percarbonate in a fluidized bed chamber and then drying by flowing a fluidizing gas through the inflow base of the fluidized bed chamber in the temperature range of 30 to 70° C.
It is a feature of the invention that a radial inflow tray is used for this purpose wherein the passage openings allow the fluidized bed gas to emerge in the region of the openings at an angle of less than 35°, measured with respect to the horizontal, in the form of aligned partial streams, and further wherein the spray nozzles are arranged such that the spray pulse points in the same direction as the pulse of the fluidizing gas.
The process of the invention has been found to be suitable for the preparation of coated peroxygen compounds in general, and in particular for the production of coated sodium percarbonate with an increased active oxygen stability. The desired results intended to be obtained herein can be achieved by using fluidized bed coating apparatus as described herein and by spraying of an aqueous solution comprising one or more coating components on to particles of the peroxygen compound. A variety of coating components can be used but the most common one is sodium sulfate. A fluidized bed chamber of the design described herein is used. Drying by means of a fluidizing gas flowing through the inflow base of the chamber at a fluidized bed temperature in the range from 30 to 70° C. is an important parameter. Of particular importance is that a radial inflow tray is used, the passage openings of which allow the fluidizing gas to emerge in the region of the opening into the chamber at an angle of less than 35°, measured with respect to the horizontal, in the form of directed partial streams. In this configuration the spray nozzles are arranged such that the pulses of the sprayed compound are oriented in the same direction as the pulses of the injected fluidizing gas.
According to a particularly preferred embodiment, the coating is carried out discontinuously in a circular reactor with a circular inflow base of lamellae overlapping like turbine blades and nozzles aligned in the inflow base in the direction of rotation of the fluidized bed. Due to the powerful spin of the partial streams, the particles are mixed thoroughly in this reactor and the particles are forced to pass repeatedly through the spray cones of the nozzles.
Using a fluidized bed apparatus with the features according to the claims, it has been possible to achieve a surprisingly higher storage stability for a given amount of coating in an unexpected manner. Using sodium sulfate as the only coating agent, it is therefore possible to achieve the stability level of sodium perborate monohydrate with an amount of coating of between 3 and 7 wt. % sodium sulfate. The smaller the average particle diameter of the material to be coated, the higher the amount of coating chosen, and vice versa.
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patent: 4105827 (1978-08-01), Brichard
patent: 4171280 (1979-10-01), Maddox et al.
patent: 4178351 (1979-12-01), Klebe et al.
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patent: 4970804 (1990-11-01), Hüttlin
patent: 5258133 (1993-11-01), Chapple
patent: 5312557 (1994-05-01), Onda et al.
patent: 5681807 (1997-10-01), Honig et al.
patent: 5902783 (1999-05-01), Lagnemo et al.
patent: 2166281 (1995-01-01), None
patent: 2417572 (1974-11-01), None
patent: 2622610 (1986-09-01), None
patent: 3839723 (1989-07-01), None
patent: 3806537 (1989-09-01), None
patent: 97/19890 (1997-06-01), None
WO 95/02555, Jan. 26, 1995.
Bertsch-Frank Birgit
Bewersdorf Martin
Kaiser Lothar
Kohlen Rainer
Overdick Ralph
Degussa-Huls Aktiengesellschaft
Gupta Yogendra
Petruncio John M
Smith , Gambrell & Russell, LLP
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