Cleaning compositions for solid surfaces – auxiliary compositions – Cleaning compositions or processes of preparing – Heterogeneous arrangement
Reexamination Certificate
2000-03-30
2002-07-02
Gupta, Yogendra N. (Department: 1751)
Cleaning compositions for solid surfaces, auxiliary compositions
Cleaning compositions or processes of preparing
Heterogeneous arrangement
Reexamination Certificate
active
06413927
ABSTRACT:
The present invention relates to a process for stabilising particulate alkali metal percarbonate, and particularly to a coating process therefor, to the particulate percarbonate having improved stability so produced and to washing or bleaching compositions containing the same.
It is well known that particulate alkali metal percarbonates, including sodium percarbonate in particular, can be used as bleach additives for addition to detergent compositions, and as bleaching compounds in detergent powder mixtures, eg for domestic clothes washing or in dishwashing compositions. In comparison with alkali metal perborate tetrahydrate, they have the advantage of dissolving more rapidly at temperatures in the range of 20° C. to 40° C., which is becoming increasingly beneficial in view of the trend towards lower clothes washing temperatures and the use of a bleach activator in conjunction with the bleach. Another advantage of percarbonates is that they are environmentally friendly. However, percarbonates have a known disadvantage of decomposing more quickly than sodium perborate tetrahydrate during storage in the powdered state, particularly if stored in a damp atmosphere and in washing or detergent compositions. Moreover, other constituents of washing compositions such a alkaline builders are known to accelerate the rate of decomposition of percarbonates.
In order to improve the stability of percarbonates, and particularly sodium percarbonate, it has been proposed to treat the surface or the surface layer of the percarbonate particles with a wide range of materials, and in particular to coat or encapsulate the percarbonate with those materials. A wide range of organic and/or polymer compounds such as paraffins, carboxylic acids, polyols, vinyl resins etc. and inorganic compounds such as silicates, borates, perborates, boric acids, carbonates, chlorides, sulphates and phosphates have been proposed as coating materials. There remains, however, a continuing need to locate alternative or improved means for improving the stability of percarbonates.
In WO 95/18065, Solvay Interox has disclosed the use of complexes of boric acid with polyols or hydroxycarboxylic acids as coating agents for percarbonates, including, without any particular emphasis, complexes of boric acid with saccharides. Research has shown that coating agents incorporating boric acid or borates are amongst the most effective coating agents for stabilising percarbonate, including their complexes with the polyol/hydroxycarboxylic acids, but some potential customers for percarbonates dislike the presence of boron possibly because they fear that its use in bleaching or washing compositions may be prohibited or curtailed. Accordingly, it remains desirable for producers of percarbonate to continue to try to develop boron-free coating materials.
In the course of devising the instant invention, a number of the organic materials were tested which had been contemplated in WO 95/180650 in complexes with the oxyboron compound. Amongst those materials, saccharides were tested and it was found that there was a substantial difference between them in their performance at stabilising the percarbonate, and particularly when the percarbonate is incorporated in detergent or washing compositions. In particular, it was found that lactose, alternatively called milk-sugar, provided relatively poor stability when employed in a low proportion, even though it was alleged by Sunstar KK et al in JP 60116625 that a peroxide (5% potassium persulphate and 26% sodium percarbonate) coated with 15-25% milk sugar showed good stability in an artificial teeth cleaning composition.
The present invention provides a process for stabilising a particulate alkali metal percarbonate by coating it with an effective amount of a coating material characterised in that the coating material comprises not more than 5% by weight, based on the coated material of a non-reducing oligomeric saccharide.
Herein by the term effective amount is meant an amount such that the rate of decomposition of percarbonate is reduced in comparison with the corresponding uncoated percarbonate, for example when stored in an atmosphere at 80% relative humidity and 32° C. in the presence of its own weight of zeolite 4A as described hereinafter.
Herein, during the coating process, the coating material is brought into contact with the particulate percarbonate, and especially suitably in the form of an aqueous solution.
Without being bound by any theory, it is believed that the effectiveness of coatings obtained in the present process may be assisted by the ability of solutions of the selected non-reducing oligomeric saccharides to spread easily across the surface of the percarbonate and thereby create a barrier or layer from even small amounts of coating agent that prevents or reduces interaction between the percarbonate core and the environment, be it water vapor in the local atmosphere and/or other particulate materials in for example detergent compositions in which percarbonate is incorporated as a bleach. However, easy spreadability of a solution of the coating a gent in practice is believed to contribute only a part of the overall explanation as to how or why the selected coatings are so effective, because other sugars such as lactose are likewise capable of spreading across the surface, but do not exhibit the same performance.
The non-reducing oligomeric saccharide is preferably a disaccharide, and particularly sucrose. It will be recognized that as employed herein, a reference to sucrose includes the molecule itself and any polymeric derivatives that are derivable during processes for applying a coating to percarbonate. For example, during some processes for applying a coating and in most processes for drying a coated percarbonate, it is normal practice to contact the percarbonate particles with a hot gas, which may encourage polymerization. For the avoidance of doubt, the derivatives of sucrose, if any, that arise during such coating or drying processes are encompassed within the instant invention.
It will be recognized that the term oligomeric saccharide excludes starch and like extremely high molecular weight materials.
The sucrose or other non-reducing oligomeric saccharide need not constitute all the coating agent. Indeed, it is preferable for the coating agent to further comprise at least one co-coating agent which can be a salt of a carboxylic or organophosphonic acid, but which advantageously is an inorganic salt. The salt may be employed as such or in the instance of for example carboxylic acids can be incorporated in the solution employed for coating as the corresponding acid which is neutralized by contact with the percarbonate during the coating process. By so employing a co-agent, it is possible either to increase the total coating level without increasing the amount of sucrose or other non-reducing oligomeric saccharide that is coated onto the percarbonate or to achieve the same total weight of coating but with a smaller proportion of sucrose or other non-reducing oligomeric saccharide. In some preferred embodiments of the present invention, the non-reducing oligomeric saccharide provides a minor fraction of the total weight of coating agent.
It will also be understood that although oligomeric saccharides can be employed in a small amount as a coating agent on an oxidizing agent such as sodium percarbonate safely, ie as demonstrated by low heat emission in a standard test, the use of significantly larger amounts result in much greater heat emission which demonstrates that the product is much less safe than uncoated material. Accordingly, it is of practical significance that the proportion of sucrose or other non-reducing oligomeric saccharide employed in the present invention be severely restricted. The potential oxidative interaction between sodium percarbonate and a oligomeric saccharide accordingly represents a major difference between sodium percarbonate and other detergent ingredients like zeolites as such or bearing absorbed additives which do not undergo such oxidative intera
Baker Daniel R.
Horne Graham R.
James Alun P.
Gupta Yogendra N.
Larson & Taylor PLC
Petruncio John M
Solvay ( Societe Anonyme)
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