Background of the Invention Fabric washing compositions contain, as an essential ingredient, a surfactant system whose role is to assist in removal of soil from the fabric and its suspension in the wash liquor. Detergent bars require an acceptable physical strength so that they retain their structural integrity during handling, transport and use. The hardness of the bars, at the time of manufacture and subsequently, is an especially important property. Commercially available detergent bars contain detergent active components and detergent builders, fillers, structurants, hardeners together with optional components for example abrasives, perfumes, colour and bleaching agents.

The water content in the detergent bars is generally maintained around 6%. The binders and fillers used in non-soap detergent NSD bars are typically minerals and the low moisture content coupled with the use of high proportion of minerals result in NSD bars with high density making them considerably smaller. If gases such as air, oxygen, nitrogen or carbon dioxide can be entrapped in the detergent bar the bulk density of the bar can be reduced and it enables the manufacture of larger bars. It is also possible to entrap sufficient air in order to make the bars float in the washing solution. The concept of entrapment of air or gas has been achieved more particularly for soap bars as it is an advantage to have the bars float in the bath tub.

DE-A-19 826 430 discloses a process for continuous manufacture of floating soap, of adjustable foam density, in which molten soap at 75-90 degrees C, gas and additive

materials such as colour and perfume, are fed to a closed mixing system, which is preferably a high-shear multiple pin unit. The foam density is controlled by the agitator rotational speed/degree of shear and the operating pressure, which should be sufficient for transfer to downstream processing units. Raw aerated soap is continuously discharged from a nozzle, and is fed either to moulds or via a cooling belt to a soap press. The gas can be air, carbon dioxide or nitrogen, etc. and is typically added at a rate of 0.5-1.0 g/cm3 soap; perfume and colour addition is typically 2-5% w/w of the feed soap.

The object of the present invention is to provide a novel process for the manufacture of low density detergent bars by entrapping gas that is generated by the decomposition of the component of the detergent formulation during extrusion.

WO-A-9744434, WO-A-0017308 disclose the use of peroxygen beaches such as perborates and percarbonates in detergent bar compositions. These are used as a source of active oxygen in the formulations. But in these cases care is taken to see that the compounds do not decompose during the process of manufacture but are available during use. Usually the product is conveyed to a two stage vacuum plodder operating at high vacuum so that entrapped air is removed.

EP-A-90 648, discloses a device such as cavity transfer mixer to introduce gas into the detergent material. The device has two closely spaced mutually displaceable surfaces each having a pattern of cavities which overlap during movement of surfaces so the material moved between the surfaces traces a path through cavities alternatively in each surface so that the bulk of the material passes through the shear zone in the material generated by displacement of the surfaces.

Definition of the invention Thus, according to the present invention there is provided a process for preparing a non-granular solid detergent composition with entrapped gas bubbles, the composition comprising the ingredients: from 5% to 80% by weight of detergent active;

from 5% to 30% by weight of water; from 0% to 30% by weight, preferably from 1 % to 30% detergency builder ; and optionally, one or more other ingredients; which process comprises the steps of : admixture of the ingredients and from 0.1% to 10%, preferably from 1% to 5% by weight of the composition of a chemical blowing agent that decomposes at a temperature in the range from 50°C to 90°C, to generate a gas optionally in presence of water, said chemical blowing agent being incorporated whilst the admixture is at temperature below 50°C ; extruding the resultant mix at a temperature of from 50°C to 90°C ; and optionally cooling the resultant extrudate, converting it into billets and forming tablets.

Detailed description of the invention It is preferable that the mixture containing the chemical blowing agent does not encounter a temperature of 50°C or higher before the mass reaches the extruder.

The raise in the temperature above the decomposition temperature of the chemical blowing agent helps in releasing the gas which gets entrapped in the bar formulation during extrusion and enables the preparation of low density bars.

It is possible that the temperature of the mass is raised to 60-90°C just before feeding into the extruder but it is preferred that the detergent composition does not encounter a temperature of 50°C higher until it is in the extruder. As a preferred aspect of the invention, the temperature of the extruder is raised to 60-90°C so that the generation of the gas takes place only in the extruder. It is particularly preferred that the temperature of the extruder is maintained at a temperature range 60-75°C.

As a preferred aspect of the invention, the temperature of the bar coming out of the extruder should be cooled down to-45°C by way of either cooling the die or by passing it through a cooling tunnel.

Processing The steps of mixing and extrusion use conventional mixing and extrusion apparatus.

The step comprising cooling of the extrudate, conversion to billets and forming tablets (bars) is optional but also involves use of typical apparatus, including conventional die stampers.

Thus, the invention can be carried out in any mixer conventionally used in soap/detergent manufacture and is preferably a high shear kneading mixer. The preferred mixers include ploughshare mixer, mixers with kneading members of sigma type, multi wiping overlap, single curve or double arm. The double arm kneading mixers can be of overlapping or tangential in design. Alternatively the invention can be carried out in a helical screw agitator vessel or multi head dosing pump/high shear mixer and spray drier combinations as in conventional processing.

The composition that can be processed by the above process to entrap the gas in order to reduce the density of the bar is any conventional detergent composition comprising detergent active, builder, structurants etc but containing 0.1-10% a chemical blowing agent that decomposes to generate a gas at a temperature range 50-90°C optionally in presence of water.

We may also claim the intermediate extrudable composition containing the blowing agent, before the release of the gas. Thus, a second aspect of the present invention provides an intermediate extrudable composition comprising: from 5% to 80% by weight of detergent active; from 0.1% to 10%, preferably from 1% to 5% by weight of a chemical blowing agent that decomposes at a temperature in the range of from 50°C to 90°C to generate a gas, optionally in the presence of water; from 5% to 30% by weight of water; from 0% to 30%, preferably from 1 % to 30% by weight of detergency builder ; and

optionally, one or more other ingredients.

Further, the blowing agent may be lost completely from the composition after release of the gas or it may leave a residue. Thus, a third aspect of the present invention provides a solid non-granular detergent composition comprising :- from 5% to 80% by weight of detergent active; the residue of a chemical blowing agent; from 5% to 30% by weight of water; from 0% to 30%, preferably from 1% to 30% by weight of detergency builder ; and optionally, one or more other ingredients.

Chemical blowing agents : Chemical blowing agents used in the formulation are those that decompose at temperatures in the range 50-90°C and generate a gas. A few examples of such compounds are sodium perborate, hydrogen peroxide and other per-oxy compounds, certain azo compounds which give out nitrogen on decomposition for e. g. 1,1-azobis- isobutyronitrile, 2,2-azobis (2,4-dimethyl-valenonitrile), 2,2-azobis (4-methoxy-2,4- dimethylvalenonitrile) and several others listed in"Polymeric materials encyclopaedia"Vol. 1, CRC Press, edited by J. C. Salamone, bicarbonates which give C02 on heating, or di-isocyanates which give C02 by reacting with water and boro-hydrides which give out hydrogen.

The level at which the chemical blowing agent is incorporated in the composition is in the range 0.1 to 10% by weight but preferably in the range 1-5%.

Detergent Active: The detergent active used in the process may be selected from one or more soap and/or one or more non-soap surfactants. The composition according to the invention will preferably comprise detergent actives which are generally chosen from

both anionic and nonionic detergent actives. Other actives such as cationic, amphoteric and zwitterionic surfactants may also be used. Examples of suitable detergent-active species are given in the following well-known textbooks: (i)"Surface Active Agents", Volume 1 by Schwarz and Perry, (ii)"Surface Active Agents and Detergents", Volume 11 by Schwartz, Perry and Berch, (iii)"Handbook of Surfactants", M. R. Porter, Chapman and Hall, New York, 1991.

Builders The detergency builder used in the formulation is preferably inorganic and suitable builders include, for example, alkali metal aluminosilicates (zeolites), alkali metal carbonate, sodium tripolyphosphate (STPP), tetrasodium pyrophosphate (TSPP), citrates, sodium nitrilotriacetate (NTA) and combinations of these. Builders are suitably used in an amount ranging from 1 to 30% by wt.

Inorganic particulates : Inorganic particulate phase is not an essential ingredient of the formulation but may be incorporated especially for hard surface cleaning compositions. Preferably, the particulate phase comprises a particulate structurant and/or abrasive which is insoluble in water. In the alternative, the abrasive may be soluble and present in such excess to any water present in the composition that the solubility of the abrasive in the aqueous phase is exceeded and consequently solid abrasive exists in the composition.

Suitable inorganic particulates can be selected from, particulate zeolites, calcites, dolomites, feldspars, silicas, silicates, other carbonates, bicarbonates, sulphates and . polymeric materials such as polyethylene.

The most preferred inorganic particulates are calcium carbonate (as Calcite), mixtures of calcium and magnesium carbonates (as dolomite), sodium hydrogen carbonate, borax, sodium/potassium sulphate, zeolite, feldspars, talc, kaolin and silica.

Calcite, talc, kaolin, feldspar and dolomite and mixtures thereof are particularly preferred due to their low cost and colour.

Other addivitives : Other additives such as one or more water insoluble particulate materials such as polysaccharides such as starch or modified starches and cellulose may be incorporated.

Minor additives: Conventional ingredients preferably selected from enzymes, antiredeposition agents, fluorescers, colour, preservatives and perfumes, also beaches, bleach precursors, bleach stabilisers, sequestrants, soil release agents (usually polymers) and other polymers may optionally be incorporated up to 10 wt%.

The invention will now be illustrated by the following non-limiting examples.

Examples Process for preparation of the Detergent bars: Different formulations as described in Table 1 and 2 were prepared and analysed for bar density.

Soap bars: a. Conventional Process: A batch of 2 Kg bar was prepared by taking 1.82 Kg of soap cleanse containing approximately 32% water, along with 60 gms of soda ash, 20 gms of sodium sulphite, 94 gms of alkaline sodium silicate and 6 gms of minors such as colour and perfume, mixing them thoroughly in a sigma mixer at ambient temperature of approximately 25°C, followed by plodding in the conventional manner at a temperature of approximately 45°C (example 1). A similar batch was prepared but with the addition of approximately 40g of sodium perborate which was compensated by soda ash.

The dough was plodded at approximately 45°C (example 2).

b. Process according to the invention: A batch similar to the one mentioned above in example 2 was prepared in the mixer.

However, temperature in the plodder was maintained at 65°C (example 3). These bars were cooled to about 45°C by cooling the plodder cone/die using chilled water. c. Process in which the temperature of the dough was high : A batch similar to the one mentioned above in example 2 was prepared in the mixer but the mixing was carried out at high temperature of 65°C, thus the dough was aerated during mixing. This dough was then plodded in the conventional manner (example 4).

Analysis of the density of the bar: The density of the bar is measured by the standard method and calculated using the formula Density (grams/cm3) = Weight of bar (grams) Volume in cm3

Table 1 Composition (% wt) Example 1 Example 2 Example 3 Example 4 TFM 59 59 59 59 Moisture32 32 32 32 Alkaline silicate 4.7 4.7 4.7 4.7 Sodium perborate-2 2 2 Soda ash 3 1 1 1 Sodium sulphite 1 1 1 1 Minors (color/perfume) 0.3 0.3 0.3 0.3 Property Density (g/cc) 1.13 1.13 0.96 1. 11

Data in Table 1 above shows that there is significant reduction in bar density when perborate is added to the formulation and is decomposed in the extruder the way it is described in the invention (example 3 against example 1). Simple addition of perborate to the bar in a conventional manufacturing process does not give the benefit since the blowing agent does not decompose (example 2). On the other hand, if the gas is allowed to be generated in the mixer itself, then also there is no appreciable density reduction for the bar (example 4).

Non-soap (NSD) Bars: c. Conventional process A batch of 6 Kg detergent bar was prepared by taking 1.2 Kg of linear alkyl benzene sulphonic acid in a sigma mixer and neutralising it with 600 g of sodium carbonate.

Other ingredients such as 720 g of STPP builder, 150 g of aluminum sulphate, 120 g of boric acid, 210 g of alkaline sodium silicate, approximately 3 Kg of fillers, water and minor ingredients were then added. These were thoroughly mixed in a sigma mixer operating at ambient temperature of approximately 25°C and plodded in a conventional manner at approximately 45°C (example 5). d. Process according to the invention: A batch similar to the one mentioned above in example 5 was prepared with the addition of approximately 120 g of sodium perborate in the mixer at the end, thoroughly mixing it at ambient temperature, and then plodding it at 70°C (example 6).

Table 2 Composition % wt. Ex 5 Ex 6 Detergent Active 20 20 (LAS) Builders (STPP) 13 13 Soda 6 6 2. 5 2. 5 Boric acid 2 2 Sodium silicate 3.5 3. 5 Calcite to 100 to 100 China clay 8.33 8.33 Conventional minor 2 2 ingredients % Moisture 10 10 Sodiumperborate-2 BarProperties Density (g/cc) 1.85 1.5

Data presented in Table 2 show that addition of perborate to the NSD bar formulation and decomposing it in the extruder in the manner described in the invention leads to significant reduction in bar density.