The present invention relates to aerated low density cast detergent bars. The invention particularly relates to a process for preparing aerated low density cast detergent bars wherein the ■ air has been stabilised in the formulation, and the bar does not stick to the mould and is easy to demould.

Solid detergent bars/cakes are usually produced by shear working/homogenisation of the formulation, followed by extrusion and stamping. However this procedure is only suitable for detergent bar formulations which are thermoplastic, or which are not shear sensitive. The formulations that are shear sensitive and which can be melted at reasonable temperatures are generally produced by the process of casting. In the manufacture of detergent compositions by casting, the formulated system is taken to a fluid state by raising the temperature, filled into moulds, and then cooled.

The water content in the detergent bars is generally maintained around 5 % to 40 %. If gases such as air can be entrapped in the detergent bar, the apparent density of the bar can be reduced, and it enables the manufacture of larger size bars for a given weight. 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. The entrapment of air or gas into the soap bar also improves the in-use properties such as feel, lather etc. The problems that have to be addressed while preparing aerated cast bars include the stability of air in the bar. Further, one has to ensure that the bar can be easily removed from the mould.

US5972860 (Kao Corporation, 1999) discloses a framed aerated detergent bar essentially incorporating inorganic salts and non-ionic, surfactants, and a process for the production of such bars wherein air in the form of fine bubbles is whipped into the formulation, ensuring that the bubbles are stabilised.

US5194172 (P&G, 1990) and US5219487 (P&G, 1992) disclose aerated freezer bar compositions, and processes for making the same.

W02002/083832 (Unilever) describes a. process for preparing an ultra low-density, cast-dehydrated detergent bar composition, which process' comprises a step • of essentially ■ dehydrating the rigid bar to bring down the moisture level to enable entrainment of air in the range 1 % to 90 % .by volume of the composition.

Our co-pending application 328/MUM/2003 describes a process for the preparation of an aerated solid shaped cast detergent composition comprising the step of adding fatty alcohol prior to .or after incorporation of air or gas intc the melt for stabilisation of the air in. the composition. The above prior art generally teaches compositions and processes to manufacture aerated detergent bars which either require special equipment to provide mechanical agitation for whipping air into the formulation, or the use of ' freezing temperatures, or require addition of extra ingredients like inorganic salts/nonionic surfactants which affect the us.er properties.

The prior art document WO2002/083832 requires the essential step of dehydration, which process requires careful process control measures. In many cases the cast detergent bar sticks to the mould, and the bar is difficult to demould. It has now been found that aerated cast detergent bars of very low density having excellent stability of the entrapped air/gas in the bar can be obtained, at the same time ensuring easy demoulding of the bars, all these advantageous properties being obtained while ensuring the essential bar properties like high lather, low mush and cracking and a smooth and mild feel in use. The present inventors have found that this can be attained by the novel step of addition of certain ingredients at a particular stage of the process.

It is thus the basic object of the present invention to be able to provide for a process for the manufacture of a low ■density detergent bar composition .by incorporating air into the formulation during processing.

It is another object of the present invention to be able to provide for a process for the manufacture of a low density detergent bar composition by incorporating air and stabilising it in the formulation during processing and storage, at the same time maintaining the physical and in use properties of the bar.

It is yet anther object of the present invention to be able . to provide for a process for the manufacture of a low density detergent bar composition by incorporating air which in addition to remaining stable in the formulation during processing and storage and maintaining the physical and in- use properties of the bar, does not stick to the mould, thereby enabling easy demoulding of the bar.

According to a first aspect of the present invention there is provided a process for the manufacture of an aerated solid shaped detergent composition comprising: i. 20 % to 60 % of detergent active; ii. 30 % to 60 % of water and/or polyhydric alcohol; iii. 3 % to 10 % of alkali metal salt of fatty acid of carbon chain length in the range of 14 to 22 and an oil, ■ all components by weight of the composition, which process comprises the steps of: i. preparation of a melt of the detergent composition to be cast; • ii. incorporation of . an alkali metal salt of fatty acid of carbon chain length in the range of 14 to -22 and the oil into the melt; iii. incorporation of air or gas into the said melt; iv. ' mixing the melt in a high shear mixer; • v. pouring the said melt into a mould; vi. cooling the mould to promote solidification of the composition; and vii. demoulding the solidified-shaped article.

It is particularly preferred that the alkali metal salt of fatty acid of carbon chain length in the range of 14 to 22 and the oil are present in a weight ratio in the range of 1:3 to 3:1.

It is an essential part of the process that, the 3 % to 10 % of one or more of alkali metal salts of fatty acid of carbon chain length in the range of 14 to 22 and an oil are incorporated into the formulation prior to the incorporation of air or gas. Alkali metal salt of fatty acid of carbon chain length in the range of 14 to 22 is hereinafter referred to as λinsoluble soap' for the sake of brevity. These ingredients, along with the others listed, help in stabilising the air. in the product while ensuring the physical and in-use properties of the bar, and at the same time help ensure that the bar does not stick to the mould, thereby enabling easy demoulding of the bar. The process is particularly but not exclusively suitable for manufacturing shaped detergent articles such as soap tablets for personal wash. • ■ The detergent active used in the process may be soap or non- soap surfactants, and is present in an amount of 20 % to 60 %,. preferably 20 % to 55 %, more preferably 25 % to 50 % by weight of the composition. The detergent active is preferably an anionic surfactant. The detergent active may be generated by neutralising the acid precursor of the active with an alkali, or preformed active may be used. The detergent active is mixed with water and or other solvents and heated to form a melt. Any suitable composition that can be converted into a melt at elevated temperatures may also be employed in the process. It is preferred that the anionic surfactant is a soap. Non-soap detergent, if present, is preferably incorporated at 1 % to 10% by weight of the composition.

The term total fatty matter, usually abbreviated to TFM, is j used to denote the percentage by weight of fatty acid and triglyceride residues present in soaps, without taking into account the accompanying cations.

For a soap having 18 carbon atoms, an accompanying sodium cation will generally amount to about 8 % by weight. Other cations may be employed as desired, for example zinc, potassium, magnesium, alkyl ammonium and aluminium.

The term soap denotes salts of carboxylic fatty acids. The ■ soap may be derived from any of the triglycerides conventionally used in soap manufacture - consequently the carboxylate anions in the soap may contain from 8 to 22 carbon atoms.

The soap may be obtained by saponifying a fat and/or a fatty acid. The fats or oils generally used in soap manufacture may be such as tallow, tallow stearines, palm oil, palm stearines, soya bean oil, fish oil, caster oil, rice bran oil, sunflower oil, coconut oil, babassu oil, palm kernel oil, and others. In the above process, the fatty acids are — 1 —

derived from oils/fats selected from coconut, rice bran, groundnut, tallow, palm, palm kernel, cotton seed, soybean, castor etc. The fatty acid soaps can also be synthetically ■ prepared (e.g. by the oxidation of petroleum or by the hydrogenation of carbon monoxide by the Fischer-Tropsch process) . Resin acids, such as those present in tall oil, may be used. Naphthenic acids are also suitable.

A typical fatty acid blend consists of 5 % to 30 % coconut fatty acids and 70 %■ to 95 % fatty acids ex-hardened rice bran oil. Fatty acids derived from other suitable oils/fats such as groundnut, soybean, tallow, palm, palm kernel, etc. may also be used in other desired proportions.

The composition according to the invention will preferably comprise detergent actives' which are generally chosen from anionic, nonionic, cationic, zwitterionic detergent actives or mixtures thereof. Suitable examples of detergent-active compounds are compounds commonly used as. surface-active agents given in the well-known textbooks such as "Surface Active Agents", Volume I by Schwartz and Perry and "Surface Active Agents and Detergents", Volume II by Schwartz, Perry and Berch or "Handbook of Surfactants", M.R. Porter, Blackie Publishers, 1991.

Non-soap detergent, if present, is preferably incorporated at 1 % to 10 % by weight of the composition. Polyhydric alcohols suitable for the invention include poly (ethylene glycol), propylene glycol, glycerol and sorbitol. Especially preferred is a mixture of PEG, Propylene glycol and sorbitol. The polyhydric alcohol is suitably added a) before saponification or b) before and after saponification.

Poly(ethylene glycol) used in the invention preferably has a molecular weight of from 200 to 1500.

The polyhydric alcohol is present in an amount of from 20 % to 50 %, more preferably from 20 % to 45 %, and most preferably from 30 % to 40 % by weight of the total detergent composition.

One or more insoluble soap (e.g. alkali metal salt of fatty acid of carbon chain length in the range of 14 to 22) is present in the composition prepared by the process of the invention. These compounds are herein referred to as ^insoluble' soaps for the sake of brevity. It is preferred that the insoluble soaps used are saturated. The carbon chain length of these soaps are preferably in the range of 16 to 20 most preferably 18. Sodium stearate is a highly preferred insoluble soap.

These insoluble soaps are added after melting of the detergent actives whether used from preformed sources or prepared by neutralisation of the detergent active precursor, but before aeration of the melt.

One or more oils are present in the composition prepared by the process of the invention. The oils are preferably those having high degree of unsaturation. More preferably they have an iodine value higher than 90. The oils which may be used include vegetable oils like sunflower oil, coconut oil, rice bran oil, ground nut oil, mustard oil, safflower oil, palm oil, soya bean oil, corn oil, olive oil, petroleum oils such as mineral oil, petrolatum and synthetic oils like silicone oil. The oils are added to the composition before the step of aeration.

The total amount of insoluble soaps and oils is in the range of 3 % to 10 %. It is preferred that the ratio of the insoluble soaps to the oils is in the range of 1:4 to 4:1, more preferably 1:3 to 3:1, even more preferably 2:3 to 1:1.

Free fatty acids are preferably included in the composition of the invention. The free fatty acids may have carbon chain length in the range of 8 to 22, more preferably a carbon chain length of 16 or 18. The free fatty acids are preferably present in an amount of 0.5 % to 10 %, more preferably 0.5 % to 8 % by weight of the composition. These free fatty acids are preferably added after the aeration step.

Conventional ingredients used in detergent formulations may suitably be incorporated in the formulation. Some of the ingredients which may be included in the composition ■ prepared by the process of the invention include builders, inorganic particulates, fillers, benefit agents and other minor additives. The benefit agents which may be included are moisturisers and humectants. Examples of these are Carbopol 934, ethoxylated castor oil, paraffin oils, lanolin and its derivatives. Silicone compounds such as silicone surfactants like DC3225C (Dow Corning) and/or silicone emollients, silicone oil (DC-200 Ex-Dow Corning) may also be included. Sun-screens such as 4-tertiary butyl-4 ' -methoxy dibenzoylmethane (available under the trade name PARSOL 1789 from Givaudan) and/or 2-ethyl hexyl methoxy cinnamate (available under the trade name PARSOL MCX from Givaudan) or other UV-A and UV-B sun-screens may be used.

Water soluble glycols such as propylene glycol, ethylene glycol, glycerol, may be employed at levels upto 10 %. Examples of other minor additives include enzymes, antiredeposition agents, fluorescers, colour, preservatives, perfumes, bleaches, bleach precursors, bleach stabilisers, sequestrants, soil release agents (usually polymers) and other polymers may optionally be incorporated up to 10 wt%.

For the process of making the bars according to the invention the detergent active is either generated by neutralising the acid precursor of the detergent active, or by using preformed detergent actives. The detergent active along with other ingredients that form the composition of the bar is converted into an isotropic solution by raising the temperature. The oil and the insoluble soap are then added to the mix. Air or gas is incorporated into the composition before pouring it into a mould. The mould is cooled suitably to bring about rigidification of the composition. The solidified composition is demoulded and if required cut into tablets. The process of the invention will now be described with reference to comparative examples of conventional processes, as well as a non-limiting examples of the process according to the invention.

Examples

Example 1

A one kilogram batch of aerated soap bar was prepared by the procedure as given below.

Initially fatty acid was charged along with part of the polyol mixture into the reactor and was melted at 70-800C. After the fat charge was melted, it was neutralised using sodium hydroxide at 85-9O0C. After neutralisation, the minor ingredients such as preservatives etc were added. The rest of the polyol mixture was then added. Finally, sodium lauryl sulphate (SLS) and water were added, and the melt was mixed until the SLS is dissolved. The sodium stearate and sunflower oil were than added to the mix and mixed well.

The melt was then transferred to another vessel, and was mixed under high shear using a Silverson.mixer. While mixing, air was passed at a fixed flow rate into the melt for a period of 20 minutes. The aerated melt was then poured into a mold. Upon solidification, the bar was demolded. The ease with which the bar could be demoulded was noted. The composition of the batch is given in Table 1 with the physical and in-use properties. These properties were measured as given below. Determination of Density

The density of the detergent bar was measured by weighing a piece in air and in water. The ratio of the weight in air to weight in water is the density of the bar.

Determination of hardness

The hardness of the bar was rated based on the feel of the bar and given a rating of very soft, soft, good and excellent, and was correlated with hardness measured using the penetration test, where the penetration of a sharp rod in the bar under known weight is determined.

Determination of In-use properties

The in-use properties in terms of feel and lather were determined through sensory perception, and was rated as okay, good, very good and excellent. - The composition details .of the batch of Example 1 along with the physical and in-use properties are summarized in Table 1. Table 1

Comparative Examples A to E

Several formulations were prepared as comparative examples of aerated soap bars which were prepared by processes outside the scope of the invention.

Comparative Example A

An aerated soap bar was prepared as described for Example 1, except that sodium stearate was not used.

Comparative Example B An aerated soap bar was prepared as described for Example 1 except that sunflower oil was not used.

Comparative Example C

An aerated soap bar was prepared as described for Example 1 except that the sodium stearate was prepared by addition of equivalent amount of stearic acid before neutralisation.

Comparative Example D

An aerated soap bar was prepared as described for Example 1 except that sodium stearate was added after aeration.

Comparative Example E

An aerated soap bar was prepared as described for Example 1 except that sodium stearate and sunflower oil were added at a total of 2 %.

The composition details of the batch of Comparative Examples A to E along with the physical and in-use properties are summarized in Table 2. Table 2

Example 2 An aerated soap bar was prepared as described in Example 1, where additionally 4 % stearic acid was added after aeration. The data is summarized in Table 3.

Table 3

The examples demonstrate that bars prepared by the process within the invention (Examples 1 and 2) show excellent stability, have acceptable user properties and are easy to demould while the bars prepared outside the invention (Comparative Examples A to E) do not satisfy at least one of the desired properties.