Process to prepare a soap bar

Technical field

The invention relates to a soap bar comprising lower amount of total fatty matter as compared to traditional soaps.

Background and prior art

Soap bars have conventionally been used for cleaning purposes whether for personal cleaning purposes or for fabric cleaning purposes. These bars are traditionally prepared with total fatty matter (TFM) of 72-78 weight percent. Soaps are generally prepared by saponification of oils of or by neutralization of a fatty acid mixture with an alkali. A traditional soap with such a high amount of total fatty matter provides sufficient cleaning and good bar integrity during storage and use.

However, the high amount of fatty matter used to make the bar, tends to add to the cost due to the high cost of the raw material viz. fatty acid mixture or the oils. It has been determined in the past that this high level of total fatty matter is not necessarily required for the cleaning purposes. Often, a large percentage of the fatty matter happens to be insoluble soap of stearic acid or palmitic acid origin. Sufficient cleaning can be obtained with much lower amount of total fatty matter. Efforts to prepare bar with lower amount of fatty matter have adversely effected the other user desirable properties like bar integrity, mush, and rate of wear.

In order to provide structural integrity to the bars prepared with lower TFM, various structuring technologies have been developed. IN177828 (Hindustan Lever Ltd. 1997) relates to an improved process for preparing a low TFM content detergent bar

with high water content comprising 25 to 70% by weight of colloidal aluminium hydroxide formed in situ in the particle size range of 0.1 to 25 μm and 15 to 52% by weight water, and other minor ingredients.

Another structuring technology has been disclosed in the past in IN187129 (Hindustan Lever Ltd. 1997) . This technology relates to a shaped detergent composition for laundry washing comprising soap, water and alumino-silicate formed in-situ wherein the fatty matter of the soap has an iodine value of at least 60 wherein the alumino-silicate is produced from selected precursor materials.

It is desirable to develop alternative soap bar structuring technologies to enable greater flexibility in preparing bars to a wider range of raw materials and processing conditions. In this effort the present inventors have surprisingly found that a unique and selective process of preparing soap bars by forming calcium silicate in situ provides for much better structuring as compared to similar processes known in the art.

WO2003040283 (Unilever) describes a detergent bar comprising from 5% to 60% detergent active and 2 to 20% of a structuring system being the reaction product of at least two different polyvalent metal ions with sodium silicate wherein one of the metal ions is calcium or magnesium and the other being selected from boron, aluminium, zinc, calcium and magnesium.

WP98/38269 (Procter and Gamble) describes a process for making a synthetic laundry detergent bar composition having improved physical properties wherein a calcium salt and siliceous material complex is formed insitu.

Although the above two publications describe calcium silicate structuring in combination with other structuring technologies, they do not teach the unique selective order in which the reactants have to be added in the soap making process in order to get the desired benefits. Furthermore, the present inventors have determined that a selected class of calcium compounds having specific water solubility when used in the formation of calcium silicate in situ provides for much better structuring of the bar.

It is thus an object of the invention to provide for low TFM soap bar which can be prepared to more effectively utilize the raw material thereby enabling higher flexibility in manufacture and raw material utilization.

Summary of the invention

Thus, according to the present invention there is provided a process for preparing a low TFM soap bar having from 30% to 70% by weight of soap, said process comprising the steps of • mixing sodium silicate with soap followed by the step of

• mixing a sparingly water soluble calcium compound to form calcium silicate in situ and

• plodding and forming the resulting mixture into a bar

Detailed description of the invention

The invention provides for a low total fatty matter (TFM) detergent bar that gives good cleaning while retaining all the user desired properties, especially bar integrity. The invention provides for a selective process hitherto not known that provides for good soap bar structuring. By selective process is meant that the order in which the reactants are

added is critical in achieving the desired results. If the reactants are added in any other order the results are inferior. In the present invention, the soap in fluid state is used for preparing the soap bar. Soap may be prepared fresh by saponification of oil or neutralisation of fatty acid or fatty acid mixtures before proceeding with the process of the invention, or soap which is pre-prepared may be melted in the desired reaction vessel for the process of the invention. The process of the invention comprises selectively adding first the sodium silicate to the soap solution/dispersion before adding the calcium compound that is sparingly soluble water. If the calcium compound that is sparingly soluble in water, is added to the soap solution/dispersion before the sodium silicate is added, the desired improved results will not be obtained.

Another highly preferred criterion for forming the soap bar of the invention is the selection of calcium compounds having low water solubility. By sparingly water soluble calcium compound is meant a calcium compound that has a water solubility less than 2 g/litre at 25°C. Calcium compounds that fall within this criterion which can be effectively used in the process of the invention include calcium hydroxide, calcium sulphate, calcium carbonate, more preferably calcium hydroxide or calcium sulphate. The sparingly water soluble calcium compound is preferably added in the process of the invention in amounts in the range of 0.01 to 10% by weight of the soap bar prepared.

The sodium silicate used in the process is preferably alkaline sodium silicate i.e. having a general chemical formula Na2<0.2Siθ2. The sodium silicate is generally available as a solution in water having a solids content of 40 to 50%, the balance being water. The sodium silicate (on dry weight basis) is preferably added in amounts in the range of 0.1 to 20 % by

weight of the soap bar being prepared. Thus if sodium silicate having a solids content of 42 weight % is added, then this solution is added in amounts in the range of about 0.25 to 50% by weight of the soap bar being prepared.

It is desirable that the process of the invention is carried out at temperatures in the range of 25 to 9O ⁰ C, more preferably in the range of 70 to 85 ⁰ C.

When applying the process of the invention, a soap bar having from 30 to 70%, more preferably 40 to 55% soap by weight of the bar is prepared. The fatty matter in soap is generally denoted by measuring the total fatty matter, usually abbreviated to TFM. TFM is used to denote the percentage by weight of fatty acid and triglyceride residues present in soaps without taking into account the accompanying cations. In view of the above soap level of the soap bar prepared according to the invention, the TFM level of said soap bar is approximately from 25 to 65% by weight.

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, castor oil, rice bran oil, sunflower

oil, coconut oil, babassu oil, palm kernel oil, and others. In the above process the fatty acids are 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.

Tallow fatty acids can be derived from various animal sources and generally comprise about 1-8% myristic acid, about 21-32% palmitic acid, about 14-31% stearic acid, about 0-4% palmitoleic acid, about 36-50% oleic acid and about 0-5% linoleic acid. A typical distribution is 2.5% myristic acid, 29% palmitic acid, 23% stearic acid, 2% palmitoleic acid, 41.5% oleic acid, and 3% linoleic acid. Other similar mixtures, such as those from palm oil and those derived from various animal tallow and lard are also included.

Coconut oil (CNO) refers to fatty acid mixtures having an approximate carbon chain length distribution of 8% C8, 7% ClO, 48% C12, 17% C14, 8% C16, 2% C18, 7% oleic and 2% linoleic acids (the first six fatty acids listed being saturated) . Other sources having similar carbon chain length distributions, such as palm kernel oil and babassu kernel oil, are included within the term coconut oil.

Fatty acid:

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 soap bar of the invention is well structured when the bar has water in the range of 15 to 40% by weight of the bar.

The process of the invention may be carried out in any mixer conventionally used in soap manufacture. Preferably a high shear kneading mixer is used. 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.

Optional ingredients:

Synthetic surfactants: The soap bar of the invention may optionally comprise synthetic surface active agents or surfactants which may be chosen from anionic, cationic, amphoteric, non-ionic or zwitterionic types. When present they are generally in amount not higher than 15 weight percent.

Water insoluble particulates: The bar of the invention may include certain amounts of inorganic particulates which provide different functionalities e.g. talc, calcite, clays or natural particulates like starch. When present, water insoluble particulates may be present in amounts in the range of 1 to 20% by weight of the soap bar.

Alumino-silcate structuring: The soap bar may optionally be additionally structured using inorganic particulate structurant alumino silicate. It is preferably generated in situ using a source of monomeric aluminium to condense with silicate anion.

The preferable components used for the generation of the structurant are aluminium sulphate and alkaline sodium silicate. It is also possible to incorporate readily available sodium alumino-silicate into the formulation. The alumino- silicate is preferably present in an amount in the range of 0.5 to 6% by weight of the soap bar.

Other optional benefit agents: When the soap bar of the invention is used for personal cleaning purposes benefit agents which impart beneficial functionality to the skin/hair are optionally included e.g. moisturisers, emollients, sunscreens, or anti ageing compounds. Examples of moisturisers and emollients include humectants like polyols, glycerol, cetyl alcohol, carbopol, 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 also be incorporated. Water soluble glycols such as propylene glycol, ethylene glycol, glycerol, may be employed at levels up to 10%.

Other additives such as one or more water insoluble particulate materials e.g. polysaccharides such as starch or modified starches and cellulose may be incorporated. Minor additives include colour, preservatives and perfumes, may optionally be incorporated.

When the soap bar is used for fabric cleaning applications, it may optionally include one or more builders. The builders are

preferably selected from one or more of sodium carbonate, zeolite, sodium silicate and sodium tripolyphosphate . Additionally other optional ingredients in the powder form e.g. fillers like sodium chloride or sodium sulphate are incorporated. Other optional ingredients that may be used to provide improved user properties include anti-redeposition agents, fluorescers or whitening agents, enzymes.

The invention will now be illustrated with reference to the following non-limiting examples.

Examples :

Comparative Example-A

Soap bars having a TFM of 49% were prepared using the following procedure.

Fatty acids blend consisting of 90% of a mixture of oleic and hysteric acids and 10% lauric acid were neutralized in the crutcher at 8O ⁰ C. The water content in the soap was about 25%.

Comparative Example - B

A soap batch was made in the sigma mixer at 80 C. The batch size was 2 kg. The neat soap as made in Comparative Example A was used. 1413 g of soap was taken. 255 g of water was added to the soap mass. The calcium silicate in this example was prepared by first adding 100 g of calcium hydroxide (HA-20 commercial grade) to the soap mix. After the mixture had been sufficiently mixed for 15 minutes at 8O ⁰ C, 238 grams of a solution of alkaline silicate (having 42% solids content) was mixed to the soap mass at 8O ⁰ C for 15 minutes. The final water content of the soap bar was about 37%.

Example - 1

A soap bar as prepared in Comparative Example - B was prepared except that the sequence of addition of sodium silicate and HA- 20 was reversed i.e. the sodium silicate was added to the soap mass before the calcium hydroxide i.e. HA-20 was added.

All the samples were measured for rigidity using a CSL500 Carrimed Rheometer. The results are indicated in Figure -1.

The data in Table-1 indicates that the soap bar prepared by the process of the invention provides for far superior rigidity as compared to the soap bars of the prior art.

Foam Stability:

Foam was generated from the soap bars of Comparative Example - B and Example -1. The procedure used was as follows. 25 grams per litre (gpl) of soap solution was prepared and foam was generated by whipping in a blender. The volume of the foam was monitored over time and the data is summarized in Figure-2.

The data in Figure - 2 indicates that the initial foam volume of the soap bar as per the invention is comparable to that of the prior art. However the foam volume of the soap of the invention decays faster with time as compared to that of the prior art. This indicates better rinsability of the soap composition of the invention as compared to that of the prior art thereby leading to lower water usage for rinsing.

Effect of using water soluble calcium salt Example -2 A soap bar as per Example -1 was prepared except that the final water content of the soap bar was about 32%.

Comparative Example-C

A soap bar as per Example-2 was prepared except that equivalent amount of calcium chloride (which is a highly water soluble calcium compound) was used instead of calcium hydroxide. The final water content of the soap bar was also 32%.

Comparative Example-D

A soap bar as per Comparative Example-A (Without any silicate structuring) was prepared as a control sample except that the final water content of the bar was about 32%.

The rigidity of the soap bars were measured and the data is shown in Figure-3.

The data in Figure-3 indicates that the soap bar as per the invention (Example-2) is far more rigid as compared to bars prepared as per the prior art processes.