Cleaning compositions for solid surfaces – auxiliary compositions – Cleaning compositions or processes of preparing – For cleaning a specific substrate or removing a specific...
Reexamination Certificate
2000-06-06
2002-04-30
Douyon, Lorna M. (Department: 1751)
Cleaning compositions for solid surfaces, auxiliary compositions
Cleaning compositions or processes of preparing
For cleaning a specific substrate or removing a specific...
C510S294000, C510S298000, C510S334000, C510S349000, C510S441000, C510S446000, C510S448000, C510S507000
Reexamination Certificate
active
06380141
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to compositions in the form of tablets, containing a water-softening agent. These tablets may be embodied as detergent compositions for use in fabric washing, or as water-softening tablets, which could be used in fabric washing jointly with a composition containing detergent active, or could possibly be used in other applications, e.g. in machine dishwashing as an anti-limescale product. The invention is concerned with tablets which are intended to disintegrate, usually in less than 15 minutes, when placed in water, so that the tablets are consumed when carrying out a single washing operation.
BACKGROUND AND SUMMARY OF PRIOR ART
Detergent compositions in tablet form are described, for example, in GB 911204 (Unilever), U.S. Pat. No. 3953350 (Kao), JP 60-015500A (Lion), JP 60-135497A (Lion) and JP 60-135498A (Lion); and are solid commercially in Europe. Tablets have several advantages over powdered products: they do not require measuring and are thus easier to handle and dispense into the washload, and they are more compact, hence facilitating more economical storage.
Detergent tablets are generally made by compressing or compacting a detergent powder, which includes detergent active and detergency builder. EP-A-522766 explains that difficulty has been found in providing tablets which have adequate strength when dry, yet disperse and dissolve quickly when added to wash water. The problem has proved especially difficult with compositions containing insoluble aluminosilicate as detergency builder, but the problem also arises with tablets which contain sodium tripolyphophate as the detergency builder.
This prior document teaches that at least some particles of the composition should be coated with a binder which helps to hold the tablet together and allows a tablet to be made using a lower compaction pressure. The binder can also function as a disintegrant.
U.S. Pat. No. 4,642,197 teaches that the effect of selected tablet disintegration agents in a washing additive tablet may be enhanced by the addition of not more than 7% by weight of an alkali metal salt of short-chain organic mono- or polycarboxylic acid. Sodium acetate and sodium citrate are named.
EP-A-482627 teaches that a detergent composition for compaction into tablets with improved solubility should include potassium carbonate together with nonionic surfactant.
EP-A-711827 teaches that speed of disintegration of tablets can be improved by including a highly water-soluble citrate. Tablet compositions exemplified in that document include sodium citrate dihydrate and also polyethylene glycol as an organic polymeric binder. This document also mentions that sodium acetate can be included in a composition as a lubricant to aid tableting. The trihydrate of sodium acetate is not named. The amount of lubricant is not stated, but it would be appropriate to include only a small amount.
WO 90/02165 mentions a range of materials including sodium acetate trihydrate as tableting aids, preferably used as a small percentage of the composition and preferably of fine particle size. A range of possible functions is attributed indiscriminately to these tableting aids.
SUMMARY OF THE INVENTION
Surprisingly, we have now found that the speed of disintegration of tablets can be enhanced by including sodium acetate trihydrate. This material has been found to be more effective than some other materials, including sodium citrate dihydrate, even without polymeric binder present. Moreover, we have found that sodium acetate trihydrate can be included without detriment to tablet strength. Indeed we have observed enhancements in tablet strength. Potassium acetate has also been found to be remarkably effective.
In a first aspect, the present invention provides a tablet of a compacted particulate composition wherein the tablet or a region thereof comprises first particles which contain a water-softening agent and second particles which contain sodium acetate trihydrate, potassium acetate or a mixture of them, where the second particles are separate from but mixed with the first particles.
The amount of water-softening agent will generally be at least 15% by weight of the composition. Depending on the function for which the tablets are intended the amount may range up to 90 or 93% by weight. In significant forms of this invention there is at least 15%, by weight of the composition, of a water-insoluble water softening agent.
The amount of the sodium acetate trihydrate or potassium acetate or mixture of the two is 10% by weight of the composition, often at least 13% by weight. The amount will not exceed 35% by weight of the composition and frequently will not exceed 25% or 30% by weight of the composition.
It is possible that the sodium acetate trihydrate or potassium acetate might be used jointly with sodium citrate dihydrate because sodium citrate dihydrate may function as a water-soluble water softening agent/detergency builder as well as enhancing the speed of disintegration of a tablet in water. Thus the composition of a tablet or region thereof might contain from 10% up to 20% or more of sodium acetate trihydrate or potassium acetate or a mixture of the two, accompanied by 5% to 20% by weight of sodium citrate dihydrate.
The invention includes a process for making tablets by mixing particles containing the water-softening agent with second particles containing the crystalline salt and then compacting the resulting composition to form a tablet or a region of a tablet.
We have now found, however, that when sodium acetate trihydrate, potassium acetate and mixtures thereof are handled on a commercial scale, they have a tendency to cake into inconvenient lumps even though they are simple crystalline solids. We have found that this problem, which we believe has not previously been recognised, can be reduced by applying finely divided particulate material to the exterior of the crystals. Moreover, the benefit of improved speed of disintegration is substantially retained.
Accordingly, in another aspect, this invention provides a process for the production of a tablet of a compacted particulate composition by mixing.
(i) first particles containing a water-softening agent, and
(ii) second particles containing a water-soluble crystalline salt selected from sodium acetate trihydrate, potassium acetate and mixtures thereof
and compacting the resulting mixed composition into tablets or regions of tablets, characterised by the presence of particles of another substance at the surface of the crystals of the said crystalline salt (ii) before it is mixed with the water softening agent (i).
In a second aspect this invention provides a tablet of compacted particulate composition containing a water-softening agent mixed with a crystalline salt selected from sodium citrate dihydrate, sodium acetate trihydrate, potassium acetate and mixtures thereof characterised by particles of another material at the surface of the crystals of the said crystalline salt.
The process may include a step of application of particles of material to the surface of crystals of the crystalline salt. However, this step may be carried out by the manufacturer of the salt, at the place and time of its production, prior to transport to the place where the tablets are made by mixing and compaction.
DETAILED DESCRIPTION AND EMBODIMENT
This invention utilises crystals of sodium acetate trihydrate, potassium acetate or mixture of them, preferably bearing particles of another substance at the surface of the crystals of the said salt, in a tablet of compacted particulate composition or a region thereof, to enhance the disintegration of the tablet in water.
The amount of the sodium acetate trihydrate, potassium acetate or mixture of them, is at least 10% by weight of the composition, often at least 13% by weight. It will generally not exceed 35% by weight of the composition and frequently will not exceed 25% or 30% by weight of the composition.
Although potassium acetate is very effective, it is hygroscopic. We have found it easier to use sodium acetate trihydrat
Douyon Lorna M.
Mitelman Rimma
Unilever Home & Personal Care USA , division of Conopco, Inc.
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