MIXER

FIELD OF THE INVENTION

The present invention relates to the field of making soap bars, particularly to a process for making high-moisture soap bars using ploughshare mixers.

BACKGROUND OF THE INVENTION

Conventional toilet soaps generally include predominantly soap (e.g., >70 % TFM, Total Fatty Matter), 10 to 13 % water and the usual additives (e.g., soda, salt, dyes and perfumes). These bars are typically produced by mixing soap and/or other synthetic surfactants with useful additives, followed by milling, plodding and stamping. Soap bars are produced on a commercial scale by two well known processes; a comparatively newer ploughshare mixer (PSM) process and a relatively older crutcher/Mazzonni/ Spray drier process.

Plodded soap bars are produced by subjecting the neutralized soap to various finishing steps. Prior to conversion, the soap is first dried from a moisture level of approximately 30 % to a level in the range of about 10 % to about 14 %. Next, the dried soap is generally sent to a simple paddle-type mixer where a variety of additives can be introduced. From this mixer the soap is then sent either directly to a refiner or optionally to a three-roll mill and then to the refiner. Both the refiner and the mill subject the soap to compression and an intense shearing action. After refining, the soap is compressed into a dense, coherent form in a plodding operation which forms solid portions which are suitable for stamping into bars. The drying step is necessary to remove the "gummy" texture and excessive pliability of the soap mass which exist typically at higher moisture levels.

In the production of plodded bars, drying to from about 10 % to about 14 % moisture is necessary to permit the soap mass to be processed through the finishing equipment.

Drying on a commercial basis is achieved by several different methods. One procedure employs a water-chilled roll in combination with a second feed roll to spread molten, neutralized soap into a thin, uniform layer. The cooled soap is then scraped from the roll to form chips and dried to a specific moisture level in a tunnel dryer. Soap chips already having a low moisture level (about 10 % to 1 1 %) are further dried by repeatedly conducting the chips through close-set water cooled steel rolls (i.e., three-roll mill) in the procedure known as milling, which has been already described. A modern technique for the drying of soap is known as spray drying. This process directs molten soap to the top of a tower via spray nozzles. The sprayed soap hardens and then dries in the presence of a current of heated air. Vacuum may be applied to facilitate removal of water.

Therefore, typically the moisture level of plodded soap bars is maintained in the range of about 10 % to about 14 %.

The Mazzoni /Spray Drying process essentially involves a step of vacuum drying. In this process, first a saponified soap mix having excess moisture is made. Then the unwanted moisture is removed. Although this process is extremely energy intensive due to the need for removal of excess moisture, just like spray-drying, this process remains the favoured process for making soap bars containing up to and around 14 to 16 % moisture. The earlier BLS-Mazzoni/ Spray drying system consisted of multi-head metering pump followed by high shear mixer and a residence time vessel. The function of the metering pump is to facilitate a stoichiometric addition rate of caustic, distilled fatty acid (DFA), brine and water to the mixer. From the pump-head; caustic, brine and water combine and go through a heat exchanger where the temperature rises up to about 90°C. The DFA separately goes through one heat exchanger where the temperature rises to about 95°C.

Both the streams from heat exchangers are fed to the suction of Supraton high shear mixer. After mixing, the mixture goes through the residence time vessel where the complete reaction takes place. This soap goes through the back pressure control valve, which provides pressure enough to prevent flashing of water from soap in the line and the reaction vessel and after this the product goes to appropriate pans. From the pans the neat soap is taken in the crutchers where preservatives and other ingredients are added. From crutchers, soap goes to series of heat exchangers for a temperature rise up to 140°C, and then to a flash chamber where soap is dried.

In a typical PSM process which is designed for bars with 10 % to 14 %, moisture; distilled fatty acids are first neutralised (saponified) by caustic soda. Thereafter, glycerine, common salt and other ingredients are added. The mix thus obtained is made to pass through a multi-screw assembly and then the viscous liquid mass, whose viscosity is generally around 80,000 to 120,000 cPs is made to fall on rotating chilled rolls. When the viscous material falls on the chilled rolls, flakes of soap are formed. These flakes are then conveyed to a noodler plate. As the name suggests, the material emerging from this plate is in the form of noodles. These noodles, which generally contain 10 % to 14 %, preferably 10 % to 12 % moisture are milled, plodded and given the characteristic definitive shapes of commercial soap bars. With the addition of 4 % to 5 % glycerine, it is possible to prepare soap noodles having only up to 17 % moisture. Glycerine lends hardness to the noodles. When an attempt was made to make soap bars with more than 20 % moisture through a conventional in PSM process, the viscosity of the saponified mass reduced drastically, making it difficult to flow in a controlled manner through the hardware involved in the process.

The prices of palm and other oils which are used in soap industry are ever- increasing and the oils and fatty acids obtained therefrom are very often in short supply. Therefore soap manufacturers are constantly devising new methods to reduce the oil content in their products. One way to do this is to add a lot of fillers, such as bentonite, clay and fuller's earth to the bars. However, bars with fillers are not popular with consumers and they are also difficult to process. Another approach is to increase the moisture content of the bars. However, with the Mazzoni process, making bars with 20 % or more moisture is not an

economically viable option because the manufacturer has to begin with initial moisture content of upwards of 30 % to be able to end at final moisture content of 20 % or more. The power consumption of this process is substantial.

Typically, however, incorporating higher levels of water (e.g. 20 % or more) introduces many process and product related problems. Process related problems include production of soft soap mass which is difficult to mill, plod and stamp. For these reasons, the soap bars sold in some countries generally contain only 12 to 13 % moisture.

US 2002016271 AA and WO 0246341 A1 (Unilever) discloses use of borax and borate compounds in soap bars which have more than 20 % moisture. Boron and its compounds have quite a few documented adverse effects on plant, human and animal life. Therefore manufacturers are now moving away from boron based technologies. While WO'341 also discloses a comparative "non borate" process for making bars, in the process reported therein, soap noodles

containing approximately 30% moisture content are mixed with 6 grams of soda ash, 6 gms of sodium sulphite and 60 gms of alkaline silicate in a sigma mixer. The dough is then plodded using a single screw extruder. The bars made by this process are soft, i.e. have high penetration value.

WO9209679A1 (P&G) discloses a process for making rigid framed soap bars (i.e. melt cast bars) having high moisture. Fatty acid precursor, propylene glycol, sodium chloride, and added water are mixed and heated. Caustic solution is added and the mixture is stirred until smooth forming an aqueous molten liquid comprising from 15% to 94% water and from 5.5% to 75% soap. The molten liquid mixture is poured into shaped molds and cooled to form shaped bars. It is also disclosed that when the process is used for making conventional plodding or freezer process, then very soft bars or no bars are formed. Therefore, a limitation of the process disclosed in this application is that is applies only to melt-cast bars. Similarly, in US'271 also, the bars are made by mixing from pre-neutralised soap noodles with other bar ingredients.

CN1 182789A (P&G, 1998) discloses a process for producing a high moisture laundry bar having improved firmness. The process comprises preparing a premix of 75 to 90% neat soap, 3 to 20% added water, 1 to 10% electrolyte salt and forming the mixture into a shaped bar. Although the process results in soap bars having high moisture, the premix that is prepared in accordance with this disclosure contains pre-saponified soap which is mixed with water to further make bars.

Therefore, there still remains a need for a process which allows for production of high-moisture (more than 20 % moisture) soap bars (or their precursor, i.e.

noodles) by the Ploughshare mixer. SUMMARY OF THE INVENTION

We have now determined that the problem of reduced viscosity faced in conventional PSM process can be solved by changing the sequence of addition of ingredients into the mixer at the time of saponification.

Disclosed is a process for making milled and plodded soap composition having at least 20 wt% moisture; the process having a step of saponification of oil or fatty acids in the presence of added water, wherein at least 60 % of added water is added before or simultaneously with the saponification.

The invention will now be explained in more details.

DETAILED DESCRIPTION OF THE INVENTION

The ploughshare mixer is very commonly used in processes requiring granulation of detergent powders and to produce powders by dry neutralisation. Typically, the ploughshare mixer does the following tasks in the powder mixing process; mixing of ingredients, agglomeration and de-agglomeration of particles, unification of the mean particles sizes and layering of material. Until recently, such mixers were not used for making soap bars.

A typical process involves neutralisation/saponification of fatty acids with e.g. caustic soda. This step is continued i.e. caustic soda is added until the acid is completely neutralised. When the saponification is over, glycerine, chelators, common salt, sodium sulphate and some other minors are added. The resultant mass is extruded through a noodler plate.

A typical plough share mixer is primarily designed for powder mixing but is also an efficient mixer for soap saponification at moisture content of 15 % to 20 %. The main parts of the mixer are a jacketed barrel, axial rotating shaft through the centre of the barrel (longitudinally), plough-shaped blades mounted on the axial shaft, and chopper. The ploughs and the high-speed chopper are the mixing elements. Since the gap between the plough surface and the barrel is 3 to 8 mm, the material gets sheared significantly while mixing. A typical mixer has barrel volume of 60 litres, plough rpm of 200 and chopper rpm of 3000. The plough area to barrel volume is approximately 0.002 cm ^"1 . A basic process has been described in IN187194 (Hindustan Lever Limited) This is a batch type process in which DFA and alkali are introduced by gravity flow over a period of 8 to 10 minutes and mixing takes place after which, ethylene di-amine-tetra acetic acid (EDTA)/ ethane-1 -hydroxy-1 , 1 -diphosphonate (EHDP) dosing takes place for 10 minutes. While using PSM technology, the temperature of the soap mass would be kept from 90°C to 100°C. After the mixing phase, the blower is switched on which supplies ambient air for cooling the soap mass and removes the moisture. The final product is received at 80 to 85°C with less than 15 % moisture, as in the BLS-Mazzoni process. PSM technology enables reduction in steam consumption when compared to the BLS-Mazzoni process. For the purpose of drying, a blower is installed which increases electricity consumption in the manufacturing process.

Viscosity of saponified mass is generally 80,000 to 100,000 cP (at 25°C). This viscosity is necessary for downstream processing. However, when an attempt was made to increase the moisture content of the mass by addition of water, the viscosity of the saponified mass reduced. For example, in order to get soap noodles having 24 % moisture, when necessary amount of added water was added to the mixer, the resultant mix was found to have a viscosity of about 4000 to 10,000 cP. The term "added water" is used to distinguish this water from the water of neutralisation which is generated in-situ when distilled fatty acids are saponified with an alkali. Some ingredients such as caustic soda also contain water. The drastic and uncontrolled reduction in viscosity was not conducive for the process. The drop in viscosity affects the flow of the saponified mass through the multi-screw conveyer and the chilled roll mills making it difficult to adjust the flow rate of the mass to such a level where heat exchange at the chilled rolls is proportional to the flow.

It was found that the mass was found to flow from the multi-screw conveyer and chilled roll without any resistance leading to over flow from the chilled roll. In a factory where all operations are automatic and electronically controlled, any manual intervention, such as opening and closing of gates and valves, is not a technical feasible option.

In order to bring the flow of the low viscosity saponified mass under some degree of control, a holding tank can be fitted between the plough share mixer and the chilled rolls. The tank helps in ensuring a steady supply of saponified mass to the chilled drum in a controlled manner. However, installation of such holding tanks is not possible in all manufacturing set-ups because in some factories, there is not much space between the mixer (PSM) and the chilled rolls. Installation of holding tanks also involves capital expenditure. A further problem with holding tanks is that it is difficult to synchronise the speed at which the holding tank is emptied with a typical PSM batch cycle time which is 20 to 30 minutes. Many times it may so happen that the holding tank has only partially emptied but the next batch of saponified mass is ready for further processing.

For the reasons explained above, the PSM process is generally not considered suitable for making soap bars with higher moisture content (generally 20 % or more). On the other hand, in a conventional toilet soap manufacturing process by the crutcher route, saponified mass having about 30 % moisture is dried down to about 14 to 17 % moisture. This is achieved by raising the temperature of neat soap from 90 to 95°C to 140 to 145°C by passing through a heat exchanger/heat exchangers followed by spray-drying under vacuum (approximately 100 mm Hg pressure). This process is generally not recommended for making soap bars with more than 20 % moisture. The reasons have been explained earlier.

However, surprisingly, it has been found that if at least 60 % of added water that was otherwise added to the saponified mass is added before or at the time of, i.e. simultaneously with saponification, preferably along with an electrolyte having an ion common with the soap that is formed then the viscosity of the saponified mass increased to 80,000 to 120,000 cPs. The electrolyte can be added separately or it can be mixed with the water. It is preferred that the electrolyte is added as an aqueous solution, i.e. mixed with the added water.

Preferably at least 80 % of added water is added before 80% saponification. Most preferably all of the added water is added before 80% saponification. Preferred electrolytes include sodium halides especially sodium chloride, potassium halides especially potassium chloride and lithium halides, especially lithium chloride. Other less preferred electrolytes include nitrates, nitrites, sulphate, sulphites, chlorates, carbonates, bicarbonates and acetates of sodium, potassium or lithium. It was observed that direct addition of sodium sulphate to the mixer as a solid (solid dosing) had a limitation. Addition of excess sodium sulphate in this form lead to products (soap bars) which showed crystal growth on storage. Such a phenomenon is not desirable.

Therefore, in the case of sodium sulphate it is especially preferred that this electrolyte is added in the form of an aqueous solution. On the other hand, addition of sodium chloride in any form did not pose any problems. Other preferred features of the soap composition

The soap composition has at least 20 % moisture. More preferably, moisture content of the soap composition is 20 % to 32 %, preferably 22 to 30 % and most preferably 24 % to 26 %. Moisture content can be determined by any means, such as by drying at 105°C. It is preferred that free alkali content of the noodles is 0.01 % to 0.1 %. It is preferred that Iodine value of the soap composition is 30 to 60 g l ₂ /100 g, more preferably 35 to 50 g l ₂ /100 g and most preferably 40 to 45 g l ₂ /100 g.

The soap composition so formed is generally further processed. The soap base is in the form of a viscous liquid which is dried and plodded into homogenized noodles or chips. The soap noodles/chips are then processed into finished products such as bars/tablets.

The process disclosed herein is used for making soap composition. A particularly preferred form of the soap composition is bars. Another preferred form is noodles or chips. The process disclosed herein is for making milled and plodded soap compostion in the form of bars or noodles, or the like. This process is unsuited for making framed bars, or freezer bars or melt-cast soap bars.

Further processing

Milling is meant the homogenization of the soap in the sense of eliminating granules of abnormal size and hardness contained in soap paste, thus making it uniform and of a very fine grain by touch. Soap milling can be effected either by making the material pass through mesh nets by successive extrusions (a relatively modem process) or by making it pass through successive rolling cylinders having different peripheral speeds (a traditional process). Milling involves feeding pressurized soap continuously from a chamber and under pressure into a nip of adjustable dimensions.

The nip is formed between a pair of rolls counter-rotating at different peripheral speeds and detaching milled soap from the rolls.

The invention will now be explained in details with the help of non-limiting exemplary embodiments. EXAMPLES

EXAMPLE 1 : Effect of addition of water at different stages

The aim of this experiment was to find out the effect of addition of timing of added water at different stages (2 stages). In order to rule out the possibility of any other cause and effect, an identical formulation was processed in two ways. In the first case, all of the added water was added to saponified mass (i.e. after 100 % saponification step was over) and in the second case, equal quantity of water was added simultaneously with the addition of fatty acids and caustic soda, i.e. before saponification. In the second case, all of sodium chloride was added along with the water. The fat charge of non-lauric to lauric soaps was fixed at 85/15, the Iodine value was in the range of 38 to 43 g/100 g. The Total Fatty Matter of resultant soap composition in noodle form, in either case was 50 wt%. Table 1

In Table 2 a formulation sheet is shown for a batch size of 1650 kg, which (after processing) gives the soap noodles with the composition of Table 1 .

Table 2

In the comparative experiment, the sequence of addition of ingredients was as follows.

First the sodium chloride was added into an empty PSM mixer. Then the chopper and the plough were started. The fatty acids and caustic soda were added together next, followed by glycerine, water and sodium sulphate. This step of addition of the fatty acids to the sodium sulphate lasted for 12 minutes.

Thereafter, the minor ingredients were added in about 1 minute. The contents were mixed for 10 minutes. In the second experiment done in accordance with the disclosed invention, sodium chloride and water were added to the mixer first and mixed for some time. The total duration for addition and mixing was 3.5 minutes. Thereafter, the fatty acids and caustic soda were added, followed by glycerine and sodium sulphate. This second step was for 8 minutes. Finally the minors were added and the contents were mixed as done before.

The total time taken was same for both the experiments. The measured viscosity of the liquid mass is shown in Table 3.

Table 3

Experiment Viscosity cP at 25 deg C

Comparative 4000

Second 100,000