Cleaning compositions for solid surfaces – auxiliary compositions – Cleaning compositions or processes of preparing – For cleaning a specific substrate or removing a specific...
Reexamination Certificate
1999-03-30
2001-10-23
Gupta, Yogendra (Department: 1751)
Cleaning compositions for solid surfaces, auxiliary compositions
Cleaning compositions or processes of preparing
For cleaning a specific substrate or removing a specific...
C510S367000, C252S186270, C423S415200
Reexamination Certificate
active
06306811
ABSTRACT:
This invention concerns sodium percarbonate and compositions containing it, especially detergent compositions which contain additionally a constituent thereof which interacts destructively with sodium percarbonate.
Detergent compositions, and specifically particulate detergent compositions intended for general purpose household fabric washing or for specialist uses such as nappy sanitisation or dishwashing often contain in addition to one or more surfactants, a builder, a bleach and optionally fillers/processing aids and minor amounts of a number of other adjuvants including one or more chosen from an optical bleach, complexing agents, perfumes, and colours. Traditionally, the builder was selected from inorganic phosphates such as sodium tripolyphosphate in view of the beneficial properties of phosphates in fabric washing, but phosphates have been shown to cause or contribute to eutrophication, and one source of phosphates is the effluent from domestic or industrial fabric washing. Consequently, and in response to increasingly stringent legislation in various countries, the detergents industry in more recent years has sought alternatives to phosphates, of which one very important class of replacement builders comprises zeolites.
The bleach constituent usually comprises a peroxygen compound, of which one favoured example comprises sodium carbonate peroxyhydrate in view of its solubility and other characteristics. This compound has commonly been called sodium percarbonate, and is so referred herein. However, sodium percarbonate can interact destructively with other detergent constituents resulting in progressive decomposition of the percarbonate and hence its loss of bleaching power during storage and transportation of the composition and the problem is especially evident when the detergent builder comprises zeolites.
A number of proposals have been made to overcome or ameliorate the problem of sodium percarbonate decomposition in zeolite-built detergent compositions. In general, the proposals relate to two methods. In one method, as exemplified by EP-A-0451893 to Unilever, a particle size distribution of the sodium percarbonate is selected in accordance with a given formula. In effect, the formula favours a mean particle size of at least 400 microns and a narrow particle distribution. Such a method employs simply the gross external dimensions of the percarbonate to indicate which are superior and which are inferior particles to employ. However, sodium percarbonate generally has a porous or irregular outer layer so that the gross dimensions do not directly control the effective surface area of the percarbonate. The regularity and porosity of the external surface of sodium percarbonate varies depending upon its method of manufacture, and this is a further and very important factor which directly affects the effective surface area and the stability of the percarbonate.
A second and frequently described method of improving the stability of sodium percarbonate is to coat the surface of the percarbonate with a surface layer of material which physically interposes itself between the surface of the percarbonate and any other particulate constituents of the composition. The effectiveness of the coating at retarding or ameliorating the rate and extent of percarbonate decomposition depends on the nature of the material employed for the coating and the integrity of the coating. Whilst a number of coating materials have been described which are beneficial in retarding decomposition in zeolite-built detergent compositions, including particularly coatings containing sodium borates in U.S. Pat. No. 4526698 to Kao Soap, these do not teach the reader anything about the inherent stability of the uncoated percarbonate. Likewise, in WO 95/15291 to Kemira, there is described the use of carbon dioxide gas in contact with damp percarbonate during the coating operation to improve the resultant stability of the resultant coated percarbonate. As with the Kao Soap disclosure, this provides no teaching on the stability of the uncoated percarbonate.
The continuing desire to incorporate both zeolites and sodium percarbonate in a detergent composition, and especially in concentrated or ultra-concentrated detergent compositions means that there remains a continuing need to find yet more and/or better ways to improve the stability of percarbonate and/or determine how to select appropriately from the various manufacture methods for sodium percarbonate, the product which exhibits improved or optimised stability.
In addition, however, at least in some parts of the world, a significant fraction of washing compositions or bleach additive compositions are built with a major proportion of non-zeolite builder or even without any zeolite builder, so that it would also be commercially advantageous to improve or optimise the stability of sodium percarbonate incorporated in such compositions too.
It is a first object of at least some aspects of the present invention to provide other and/or improved detergent compositions containing both sodium percarbonate and a zeolite.
It is a further object of the present invention in at least certain other aspects to identify a method of selecting sodium percarbonate which is intrinsically suited for incorporation in built compositions.
According to the present invention, there is provided a detergent composition which contains a zeolitic builder and sodium percarbonate characterised in that the sodium percarbonate intrinsically has a mean particle size of from 500 to 1000 microns and not more than 20% by weight of below 350 microns and has a moisture pick-up when measured in a test conducted in a humidity room at 80% relative humidity and 32° C. after 24 hours of not greater than 30 g/1000 g sample.
Herein, “intrinsically” when employed in conjunction with sodium percarbonate or “intrinsic sodium percarbonate” both indicate dry sodium percarbonate which has been obtained from a crystallisation or other manufacturing process without a subsequent coating or surface treatment that has to interpose a layer of non-sodium percarbonate material between itself and some other constituent of the composition. It will be recognised that the properties of particulate sodium percarbonate can be modified by subsequent treatments, but that it remains advantageous to select as core material, sodium percarbonate that has good stability intrinsically.
According to a further aspect there is provided a process for selecting sodium percarbonate for incorporation in a builder-containing composition characterised by conducting in either order the steps of
1) measuring its particle size distribution, determining its mean particle size and the weight fraction below 350 microns, and rejecting from step 1 material which has a mean particle size outside the range of from 500 to 1000 microns or contains more than 20% by weight of below 350 microns; and
2) measuring the extent to which moisture is picked up by the material in a test conducted for 24 hours at 32C and 80% relative humidity and rejecting material which picks up more than 30 g moisture per 1000 g material, the retained material meeting acceptable standards intrinsically for sodium percarbonate in regard to its particle size and moisture pick-up.
By selecting intrinsic sodium percarbonate which simultaneously has a desirable particle size distribution and a suitable moisture pick-up in the specified tests, it is possible to identify sodium percarbonate which has a superior stability in a built composition such as especially a zeolite-built detergent composition when compared for example with the incorporation of commercially available uncoated percarbonate which meets neither or only one of the selected parameters.
It will be recognised that it is possible to produce and isolate varied sodium percarbonate products having the same or similar particle size distribution, but a widely differing moisture pick-ups by the choice of manufacturing process and by appropriate selection of conditions/operating parameters within the chosen manufacturing process. Su
Deli Pier-Luigi
Horne Graham R.
James Alun P.
Pardini Romano
Parvaneh Soraya
Gupta Yogendra
Larson & Taylor PLC
Petruncio John M.
Solvay Interox
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