Background of the invention Cleansing compositions for machine and hand dish wash were, for a long time, available in the form of powders and bars. However, such compositions presented some problems to the users. Powders were often found to contain lumps as a result of caking due to humidity or agglomeration leading to poor in-use performance. The advent of liquids presented a new user friendly format which eliminated at least some problems. However, liquids were also expected to meet certain requirements and stability was one of them.

Aqueous dishwash compositions are now used in many countries and their use is expected to increase in the coming years. Such compositions usually contain about 50 to 70 wt% water. The balance is usually made up of anionic surfactants, in particular alkylbenzene sulphonates and ethoxylated sulphates, some amount of magnesium sulphate for grease removal, perfume, colour and other additives. Some products may also contain an alkaline ingredient like sodium carbonate.

However, in view of the high water content they are considered unsustainable.

This led to the rise of concentrated (but dilutable) forms of such aqueous compositions. Such compositions have significantly more surfactant content and consequently lesser water. The concentrated products need to be diluted with water before use.

For such concentrated compositions, thermal stability is very important. However it is observed that the viscosity of such compositions often varies with change in temperature. Such changes are not desirable because during storage and

transportation, the compositions invariably get exposed to extreme and rapidly changing temperatures. Thermal stability tests are done to check beforehand whether the compositions meet the stringent requirements or not. Samples are exposed to low temperature for a long time and then allowed to equilibrate with room temperature.

Although minor variations in viscosity are expected and are allowable; drastic reduction or drastic increase is a technical problem and more so if the changes are irreversible. Such changes in viscosity not only directly affect the in-use performance but also affect the user's sense of judgement at the time of dilution of the concentrated product. Any under-diluted or over-diluted product may not have the right balance of ingredients.

Therefore stable and consistent viscosity is important. In other words, for the concentrated product to find consumer acceptance, its viscosity should not change substantially in response to fluctuating temperatures.

In US5602092 B (Colgate-Palmolive, 1997), this problem is solved by thickening the composition with polymeric stabilising agents. In US4260528 B (Lever Brothers, 1981 ) the composition contains a natural, biopolymeric or synthetic gum thickener along with polyhydric alcohol and urea. The gum provides thickening while the urea and polyhydric alcohol provide stability and controlled flow which is further aided by adjustment of pH. In US6277803 B (Colgate-Palmolive, 2001 ) which discloses carbonate free compositions, amine oxides are used for the purpose of stability.

The compositions of GB1 164854 (Cook et.al., 1969) are stabilised by way of metal salts like chlorides and sulphates of Zinc, Magnesium, Aluminium and Calcium.

The compositions of EP2770044 A1 (Unilever, 2014) are lamellar gels having alkyl benzene sulphonate and (poly)ethoxylated alkyl sulphate in the ratio of 4:1 to 1 :1. They are free of any alkali, in particular, sodium carbonate. The compositions contain at least 1 wt% amine oxide and 1 to 12 wt% electrolyte with at least 2 wt% performance additives.

US4692275 A (Unilever, 1987) discloses powder detergent compositions with a mixed surfactant system containing a Cs-Cis alkylbenzene sulphonate and C12-C18 alcohol ethoxysulphate. The total surfactant content is up to 20 wt% and the ratio of sulphonate to sulphate is from 3.5:1 to 1.5:1 .

An alkaline material such as sodium carbonate is included in aqueous concentrated dishwash compositions in order to increase the pH and provide enough reserve alkalinity for better degreasing. It helps to include high levels of sodium carbonate in order to formulate a stable concentrated cleansing product. However the benefits tend to be offset by instability and none of the prior art discussed earlier provide a useful solution for alkaline compositions.

Summary of the invention

We have determined that the ill effects of extreme temperature on the viscosity of compositions which contain sodium carbonate can be minimised by maintaining select ratios between the alkyl benzene sulphonate and the (poly)ethoxylated sulphate.

In accordance with a first aspect is disclosed a concentrated aqueous cleansing composition comprising:

(i) 14 wt% to 35 wt% of a mixed anionic surfactant system containing alkyl

benzenesulphonate (a) and (poly)ethoxylated sulphate (b);

(ii) at least 12 wt% sodium carbonate; and,

(iii) total non-carbonate builder content less than 1 wt%, wherein ratio of (a) to (b) is from 1 :1 to 3:1 parts by weight.

In accordance with a second aspect is disclosed an aqueous cleansing composition comprising one part by weight of the composition of the first aspect and one to three parts by weight of water.

The invention will now be explained in details. Detailed description of the invention

The term "dish" as used herein means any utensil involved in food preparation or consumption which may be required to be washed to free them from food particles and other food residues, greases, proteins, starches, gums, dyes, oils and burnt organic residues.

The mixed anionic surfactant system The concentrated aqueous cleansing compositions of the invention comprise 14 wt% to 35 wt% of a mixed anionic surfactant system containing alkyl benzenesulphonate and (poly)ethoxylated sulphate .

The surfactants assist in removing soil and grease from utensils and also assist in maintaining the soil in solution or suspension in the wash liquor.

It is preferred that the alkylbenzene sulphonate is a linear alkylbenzene sulphonate having alkyl chain length of C8-C20. Generally the counter ion for anionic surfactants is an alkali metal, typically sodium, although instead of alkali metals, other amine based counter ions can also be present.

Preferred linear alkyl benzene sulphonate surfactants include sodium salt of alkyl benzene sulphonates with an alkyl chain length of from 8 to 15, more preferably 12 to 14.

The mixed anionic surfactant system also has a (poly)ethoxylated sulphate. General formula of such surfactants is RO(C2H40) _x SO3 ^" M ⁺ where R is an alkyl chain having from 10 to 22 carbon atoms, saturated or unsaturated, M is a cation which makes the compound water-soluble, especially an alkali metal, ammonium or substituted ammonium cation, and x averages from 1 to 15. Preferably R is an alkyl chain having from 12 to 16 carbon atoms, M is sodium and x averages from 1 to 3, preferably x is 1 ; This is the anionic surfactant sodium lauryl ether sulphate (SLES). It is the sodium salt of lauryl ether sulphonic acid in which the predominantly C12 lauryl alkyl group has been ethoxylated with an average of 1 mole of ethylene oxide per mole.

The ratio of (a):(b), i.e., the ratio of the total amount of alkyl benzene sulphonate to the total amount of (poly)ethoxylated sulphate is from 1 :1 to 3:1 parts by weight.

Preferred compositions according to the invention have 15 wt% to 35 wt% of the mixed anionic surfactant system. More preferred compositions have 15 wt% to 30 wt%. When the total amount of anionic surfactant is more than 35 wt% or less than 12 wt%, there is no appreciable change in viscosity of the composition as a function of temperature.

Sodium carbonate

The concentrated aqueous cleansing compositions according to the invention comprise at least 12 wt% of sodium carbonate. Preferably the amount of sodium carbonate is 14 wt% to 50 wt% and more preferably it is 14 wt% to 40 wt%. Optimally the amount of sodium carbonate is 14 wt% to 25 wt%.

Sodium carbonate provides high pH and high reserve alkalinity which is useful for degreasing.

Non-carbonate builder:

These are builders other than sodium carbonate.

Compositions comprising the total non-carbonate builder content should be less than 1 wt%. The primary function of a builder is to regulate the hardness of water so as to reduce the extent of scum. Preferably the non-carbonate builder is a zeolite, phosphate, pyrophosphate, silica, succinate, carboxylate, malonate, polycarboxylate, nitrilo triacetic acid, citric acid or a salt thereof, a soap or an acetate. The non-carbonate builders usually provide some degree of stability to the compositions. Therefore when the compositions contain more than 1 wt% non-carbonate builder, there is not much difference between the initial and final viscosity of the compositions. Water insoluble particles:

It is preferred that the concentrated aqueous cleansing compositions of the invention comprises very limited amount of, i.e., up to 2 wt% insoluble particulate matter other than the non-carbonate builder. Such particulate matter may include an abrasive or may even be a silicate like sodium silicate. The compositions may contain one type of particulate matter or a mixture of different particles while still being inside the range of up to 2 wt% of the total composition. Whenever such particles are present, it is preferred that Moh's index of such particulate matter is in the range of 2.5 to 6.0. The particulate matter could be one or more of clay, calcite, dolomite, olive stone, feldspar, apatite, fluorite and hematite, kyanite, magnetite, orthoclase and pumice. Whenever present, the average particle size of such particles is 0.5 μηη to 400 μηη, more preferably 10 μηη to 200 μηι.

Other preferred ingredients: Water:

The concentrated aqueous cleansing compositions in accordance with the invention comprise 40 wt% to 80 wt% water. More preferred compositions comprise 50 wt% to 75 wt% water. Optimal compositions have 60 wt% to 75 wt% water.

Further surfactants

The concentrated aqueous cleansing compositions of the invention may further comprise other surfactants over and above the mixed anionic surfactant system described earlier. However, such additional surfactants may have no influence or limited influence on the viscosity profile of the composition. The compositions of this invention may comprise further surfactants selected from amphoteric, zwitterionic and nonionic surfactants and combinations thereof. Cationic surfactants are not preferred. Such additional surfactants preferably are surfactants other than anionic surfactants because the compositions already contain significant amount of anionic surfactants for cleaning performance. Examples of such further surfactants suitable for inclusion herein can be found in "Surface Active Agents" Vol. 1 , by Schwartz & Perry, Interscience 1949, Vol. 2 by Schwartz, Perry & Berch, Interscience 1958, in the current edition of "McCutcheon's Emulsifiers and Detergents" published by Manufacturing Confectioners Company or in "Tenside-Taschenbuch", H. Stache, 2nd Edn., Carl Hauser Verlag, 1981.

Other Optional Ingredients

The concentrated aqueous cleansing compositions of the invention may optionally comprise other ingredients, such as fragrances, preservatives and colorants, foam boosting agents, preservatives (e.g. bactericides), pH buffering agents,

polyelectrolytes, anti-oxidants, anti-corrosion agents, anti-static agents.

The compositions may further comprise colorants, pearlisers and/or opacifiers.

Viscosity, pH and other properties

The viscosity of the concentrated aqueous cleansing compositions according to the invention is in the range of 500 cp to 10000 cp. Preferably the viscosity is in the range of 700 cP to 10000 cP and more preferably it is in the range of 800 cP to 10000 cP. Upon dilution with one to three parts by weight water, the concentrated aqueous cleansing composition forms a ready-to-use dish wash liquid. This is particularly useful against greasy soil. This diluted composition is non-gelling.

Viscosity of the diluted aqueous cleansing composition is in the range of 100 cP to 4000 cP. Preferably it is in the range of 300 cP to 2000 cP. More preferably it is in the range of 500 cP to 1200 cP. The viscosity measurements are done at 25 °C at a shear rate from 1 s ^"1 to 50 s ^~ A Haake ^® AR1000 Rheometer with cone and plate assembly is used for the

measurements but any equivalent machine may be used. Generally the viscosities of concentrated compositions tend to increase or decrease under hot or cold conditions. For this reason, such compositions are often subjected to thermal stability studies. The studies are conducted as follows:

The initial viscosity of the compositions is measured at room temperature (25 °C). This viscosity is usually measured as soon as the compositions are prepared. Thereafter the compositions are exposed to low temperature for some time and then allowed to equilibrate again with the room temperature as above. Viscosity is measured again (final viscosity). Ideally, there should be no difference between the initial and the final viscosity. However that is not the case because usually there is a difference. The comparison can be indicated in a number of ways but usually it is quite common to indicate it as percentage recovery. Recovery of 100% is ideal but any recovery falling within the range of 99 % to 70 % (of the initial viscosity) is still considered to be normal and acceptable. As an illustration, if the initial viscosity is 1000 cP and the final viscosity is 750 cP, it would be considered to be acceptable because the recovery is 75%. However if the final viscosity is 600 cP then the recovery is 60 % which is outside the range.

The pH of the concentrated aqueous cleansing compositions according to the invention is in the range of 1 1 to 13.

Method and use:

The method of cleaning any hard surface such as soiled dishes using the diluted form of the concentrated composition is not different from the usual method. In particular, such a method would include a step of contacting a soiled plate with an efficacious amount of the composition preferably with the help of a scrubber or implement such as sponge, scouring pad or cloth, followed by scrubbing and later by rinsing with water. Alternatively the concentrated aqueous cleansing compositions of the invention, or its diluted variant, may be made available to users in the form of a pre-impregnated implement. The concentrated aqueous cleansing compositions according to the invention are formulated to permit easy viscosity control by the consumer upon dilution with water. The cleaning liquid may be sold in concentrated form and, upon dilution by the consumer, display stable viscosity over a wide range of activity levels, the activity levels reducing with increased dilution. The concentrated aqueous cleansing compositions can easily be diluted by the consumer at home by combining with water and inverting or gently shaking the container, which reliably forms a homogeneous non-gelling diluted composition.

While the concentrated aqueous cleansing compositions according to the invention are generally suitable for use in dish wash applications for manual or machine assisted cleaning, the compositions may also be used for other related applications like fabric cleaning and general hard surface cleaning.

The invention will now be explained with the help of non-limiting examples.

Examples

Example-1 : Effect of ratio and the amount of mixed anionic surfactant system A series of concentrated aqueous dish wash compositions containing from 18 wt% to 35 wt% of the mixed anionic surfactant system were made. In order to prevent any unfavourable interaction of surfactants, the compositions were formulated with only two anionic surfactants; Na-LAS was the alkyl benzenesulphonate (a) and SLES 1 EO was the (poly)ethoxylated sulphate (b). The total amount of sodium carbonate was kept constant but in order to ascertain the effect of ratio between the said surfactants, the ratio was varied from 1 :1 to 3.5:1 parts by weight as described hereinafter. All the compositions did not contain any non-carbonate builder. Further, all the compositions were free of insoluble particulate matter other than the builder. Some compositions were outside the invention and some were inside. The compositions were prepared in a standard manner well known in the art. Details are provided in table 1.

Table 1

The viscosity was measured at 25°C at shear rate from 1 s ^"1 to 50 s ^_ as soon as the compositions were prepared. This was recorded as the initial viscosity.

Thereafter, all the compositions were stored at 5 °C for 12 hours and then immediately thawed for 3 hours, i.e., kept at 25°C so as to equilibrate with the room temperature. The viscosity of each composition was then measured again under variable shear rate as above. This was recorded as the final viscosity and these two values were used to determine the extent of "recovery" of viscosity.

The data applicable to all the compositions outside the invention is as follows: Table 2 summarises the viscosity profile of composition 1. Table 2

The recovery was significantly below the acceptable minimum of 70%.

Table 3 summarises the viscosity profile of composition 2. Table 3

In this case also the data indicates that the average recovery is significantly below the acceptable minimum of 70%. The viscosity profile of composition 3 is summarised in table 4.

Table 4

It is clear that there is no appreciable drop in viscosity when the ratio is 3.5:1 and total amount of surfactant is 35 wt%. There is at least 70 % recovery of viscosity at all shear rates.

The viscosity profile of composition 4 is summarised in table 5.

Table 5

Viscosity/cP

Shear rate/ s ^"1 % recovery

Initial Final

1.0 6222 6386 102

1.5 4228 4669 1 10

2.5 2976 3378 1 13

3.9 2123 2470 1 16

6.3 1548 1803 1 16

10.0 1 141 1314 1 15

15.8 855.5 963.1 1 12

25.1 650.3 718.8 1 10

39.8 501.6 544.7 108

50.0 442.9 476.6 107 It is clear that at low levels of sodium carbonate, there is not any appreciable drop in viscosity. In other words, when the amount of sodium carbonate is around 5 wt%, there is no problem which needs to be solved because there is virtually no difference between the initial and the final viscosity.

Finally, the data pertaining to composition 5 which also is outside the invention (in view of sodium silicate) is shown in table 6.

Table 6

It is clear that there is no drop in viscosity at the ratio of 3.5:1 and further in the presence of sodium silicate. There is at least 70 % recovery. The data pertaining to viscosity of the compositions within the scope of the invention (i.e., compositions 6, 7, 8 and 9) is shown below.

Data for composition 6 is summarized in table 7.

Table 7

Viscosity/cP

Shear rate/ s ^"1 % recovery

Initial Final

1.0 13880 1 1760 84.7

1.5 9755 9072 93.0

2.5 6948 6768 97.4

3.9 5020 4758 94.8

6.3 3670 3162 86.2

10.0 2723 2162 79.4 15.8 2046 1557 76.1

25.1 1562 1 183 75.7

39.8 1212 927 76.5

50.0 1074 825.4 76.9

The recovery was at least 70%. This can be attributed to the ratio of a:b which was 2:1.

The data pertaining to composition 7 is summarized in table 8. In this case the ratio was 1 :1 and the total amount of anionic surfactant was 24 wt%.

Table 8

The minimum recovery was close to 90%.

The data pertaining to composition 8 is summarized in table 9 below. In this case the ratio was 2:1. The total amount of anionic surfactant was 18 wt%. Table 9

The data indicates about 90% recovery. It was much more than the minimum level of 70%.

Finally, the data pertaining to composition 9 is summarised in table 10. The ratio of a:b was 1 :1 and the total amount of anionic surfactant was 18 wt%.

Table 10

In this case also the recovery was close to 90%.