Cleaning compositions for solid surfaces – auxiliary compositions – Cleaning compositions or processes of preparing – Solid – shaped macroscopic article or structure
Reexamination Certificate
1999-10-07
2001-10-30
Gupta, Yogendra N. (Department: 1751)
Cleaning compositions for solid surfaces, auxiliary compositions
Cleaning compositions or processes of preparing
Solid, shaped macroscopic article or structure
C510S141000, C510S315000, C510S323000, C510S361000, C510S377000, C510S398000, C510S434000, C510S446000, C510S477000, C510S488000, C510S507000, C510S511000
Reexamination Certificate
active
06310028
ABSTRACT:
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. Another possibility is that they could be embodied 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.
Detergent compositions in tablet form have been described in a number of documents such as GB 911204 (Unilever), US 3953350 (Kao), and others subsequently. Such tablets are sold commercially. 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. It is necessary to compromise between speed of disintegration at the time of use and strength during handling before use.
EP 0 838 519 discloses the use of sodium acetate trihydrate to enhance the speed of disintegration of tablets, without detriment to tablet strength.
Other disclosures relevant to sodium acetate or hydrated salts in tablets include WO 90/02165 which mentions a range of materials including sodium acetate 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.
EP-A-711827 teaches that speed of disintegration of tablets can be improved by including a highly water-soluble citrate.
WO 96/06156 mentions that hydrated materials are useful when making tablets with the aid of microwave radiation to cause sintering.
Sodium acetate trihydrate is normally produced by a crystallisation process, so that the crystallised product contains 3 molecules of water of crystallisation for each sodium and acetate ion pair.
We have now found that sodium acetate in partially hydrated form, for example, produced by a spray-drying or granulation route, can be used in place of crystallised material and surprisingly, it enhances the speed of disintegration of tablets without loss of strength.
Broadly, the present invention provides a tablet of a compacted particulate composition wherein the tablet or a region thereof contains a water-softening agent and the composition also includes sodium acetate which is partially hydrated.
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 partially hydrated sodium acetate may be at least 5 or 7% by weight of the composition, often at least 10% or 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. Smaller amounts down to 2% by weight of the composition may be employed, especially in conjunction with a second material which promotes disintegration.
Accordingly, the present invention provides a tablet of a compacted particulate composition wherein the tablet or a region thereof comprises from 15 to 93% by weight of a water-softening agent characterised in that the tablet or said region thereof contains 2 to 35% by weight of partially hydrated sodium acetate.
It is possible that the partially hydrated sodium 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.
It is also possible that the partially hydrated sodium acetate is used in conjunction with crystalline sodium acetate trihydrate, as described in EP 838 519. Thus a tablet composition might contain from 2% or 5% up to 20% or more of partially hydrated sodium acetate, accompanied by 2% or 5% to 20% by weight of crystalline sodium acetate trihydrate.
Accordingly, certain forms of the present invention provide a tablet of a compacted particulate composition wherein the tablet or a region thereof comprises from 15 to 93% by weight of a water-softening agent characterised in that the tablet or said region thereof contains 2 to 35% by weight of sodium acetate which is partially hydrated, optionally accompanied by crystallised sodium acetate trihydrate or by sodium citrate dihydrate, provided that the total quantity of sodium acetate and sodium citrate dihydrate is from 7 to 50% by weight of the tablet or said region thereof.
In another aspect, this invention provides the use of partially hydrated sodium acetate in a tablet of compacted particulate composition or a region thereof, to enhance the disintegration of the tablet in water.
This invention utilises partially hydrated sodium acetate, to promote disintegration of a tablet in water.
It is strongly preferred that the partially hydrated sodium acetate and/or mixture thereof with sodium citrate dihydrate or sodium acetate trihydrate(if any) have a mean particle size of above 250 &mgr;m, and preferably above 300 &mgr;m (0.3 mm), to facilitate flow and handling of the particulate composition prior to and during compaction. The particle size will probably have a mean value less than 2 mm, preferably less than 1 mm. Poor powder flow is disadvantageous, inter alia, in that it leads to irregular filling of dies and inconsistent tablet weight and strength.
Partially Hydrated Sodium Acetate
Two methods of obtaining partially hydrated sodium acetate will be described here.
Spray Drying
The sodium acetate solution which is spray-dried may be a heated concentrated solution of sodium acetate, which itself may be made by the direct neutralisation of acetic acid in caustic soda. The solution of sodium acetate obtained by the neutralisation of the acetic acid with caustic soda, can be readily concentrated by heating, for example by heating with steam.
The spray drying can then be carried out in a spray drying tower using a counter current of unheated and non-dried air, although the use of heated and/or dried air is also possible.
Even though such spray-drying could lead to the trihydrate of sodium acetate, it is controllable to ensure that it leads to a product which is not fully hydrated to the trihydrate. The extent of hydration (ratio of water to acetate molecules) of the sodium acetate may be higher than 2.0, or 2.5, and particularly higher than 2.6 or 2.7. The hydration is less than 3.0, and usually less than 2.9, and particularly less than 2.8.
The spray-dried sodium acetate may have a bulk density of at least 400 g/liter, preferably at least 500 g/liter, and advantageously at least 700 g/liter.
Spray-dried sodium acetate with slightly less than 3 molecules of water of hydration per acetate ion can be bought from Albright & Wilson (Product Code: 020010), and this has a hydration of 2.76, an average particle size of between 330 and 370 &mgr;m, and a bulk density of between 730 and 930 g/liter.
Direct Granulation
An alternative method of producing partially hydrated sodium acetate requires the neutralisation of acetic acid (in either its glacial form or diluted in water) by solid sodium carbonate in a mixer/granulator. The degree of hydration of the sodium acetate can be controlled by the concentration of the solution of acetic acid or by the addition of water to the mixer/granulator. The product of this granulation process may contain some sodium carbonate,
Boyer Charles
Gupta Yogendra N.
Mitelman Rimma
Unilever Home & Personal Care USA Division of Conopco, Inc.
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