The present invention relates to a process of preparing transparent soaps in which a soap is subjected to mechanical working and shear. The invention also relates to the transparent soap thus obtained.

Transparent and translucent soaps have an aesthetic appeal to the consumer and have been associated with purity -and hence with "naturalness". The essential difference between transparent and translucent soap is related to the relative quality of the light transmitted. By "transparent" is understood having the property of transmitting light without appreciable scattering, so that objects placed behind a transparent soap bar are entirely visible and can easily be discerned.

By "translucent" is understood having the property of allowing light to pass through partially or diffusely so that objects placed behind a translucent soap bar cannot clearly be distinguished (therefore also called partly transparent or semi-transparent) .

In the present specification and the attached claims the translucency is evaluated by measuring the light transmission of a slice of soap having a thickness of 18.5 mm before and after the preparation according to the present invention, using a reflectometer according to Dr B. Lange, Type LMG 008. The result is expressed as a percentage of the light transmission of a matted glass standard. The transmission of the matted glass standard compared to air is 8.3% and this transmission of the standard is taken as 100%.

Although for coloured soap there is some dependence on the colour, this difference can be neglected for non-coloured soap bars or tablets.

There are two basic manufacturing methods for making translucent and/or transparent soaps, the one route is

called the "solvent method" and the other the "mechnical working" method.

In the "solvent method", a dried conventional type of toilet soap in solid form is dissolved in boiling ethanol, or the saponification is effected in an ethanol-water mixture. If a clear solution is obtained, the major part of the ethanol is removed by evaporation to form a clear, viscous soap solution. This is poured into moulds and cooled. The solidified soap is pressed out into the desired shape and is placed for many weeks in conditioning rooms. During conditioning more water and alcohol is evaporated and consequently the final product becomes firm. The. disadvantages of this process are the long duration of the process and all the disadvantages of working with volatile and toxic solvents, which also from an ecological point of view is disadvantageous.

Another method used is the so-called "semi-boiled" process, in which a suitable blend of fatty materials is reacted with a strong solution of sodium hydroxide in a closed mixing vessel. Only water vapour is allowed to escape and upon completion of the saponification process, the liberated glycerol is retained in the final soap. After addition of the required other ingredients, the final warm and viscous soap solution is poured into moulds for rapid cooling, which enhances transparency. Hereafter the products are shaped (stamped) and packaged.

The "mechanical working" methods involve some sort of intensive mechanical working or shearing of a cooled and partially dried soap base. It is usual to add effective amounts of crystallization inhibitors to the liquid soap before drying in order to enhance translucency. Translucency is only achieved after mechanical working or shearing to a considerable degree, e.g. by mixing in a Z- blade mixer, or by multiple milling using 3, 4 or 5-rolled steel mills, or by using a cavity transfer mixer. Such processes have been described in United States Patent

Specification US-A-2,970,116 (Lever Brothers Company) and European Patent Specification EP-B-0,090,649 (Unilever). One of the disadvantages of this method is that shear- sensitive additives under the prevailing conditions of temperature and pressure can be seriously reduced in quality, so that their performance in the final product is far from optimal. Moreover the bars obtained are translucent and usually not transparent and there are limitations in the production in that the soap needs extensive recycling over the production line in order to get the right temperature and the required amount of shear. Also the soap tends to stick to the stamping dies.

It has now been found during extensive experiments that the physical transition from opaque to transparent or vice versa constitutes a delicate equilibrium, which appears to be dependent on the soap formulation, on the amount of mechanical working and shear imparted to the soap, and in particular it has been found that a specific heat treatment (preferably after the mechanical working) of the translucent soap obtained will induce transparency in the translucent soap.

With regard to the soap formulation, the minimum requirement is the presence of alkali metal soaps of saturated and unsaturated monocarboxylic or fatty acids having from 8 to 24 carbon atoms, polyhydric alcohol and water. The presence of specific crystallization modifiers has also appeared to be very beneficial for the obtainable degree of transparency. The transparency can also noticeably be enhanced by the presence of some perfumes or fragrants. In some instances the degree of mechanical working can even be less, if certain perfumes are added to the formulation. With regard to the mechanical energy and shear imparted to the soap, it has been observed that the degree of mechanical working and shear should be such as to induce the optimal translucency and dependent on the soap

formulation the soap extrusion temperature should be from 40°C to 50°C.

The heat treatment according to the present invention given to the translucent soap preferably after mechanical working and shear is effected such that the temperature of the soap is brought to a core temperature between 45°C and 65°C, preferably between 55°C and 65°C.

The heat treatment is preferably effected by means of microwave heating, but it is also possible to effect the heat treatment already during the mechanical working.and high shear e.g. in a twin-screw extruder.

It is known from British Patent Specification GB-A- 2,203,752 (S. Fox) to manufacture a floating soap by incorporating a certain amount of water into soap and irradiating the shaped, water containing soap with microwave irradiation to a temperature of 100° to 200°C for a period of 1 to 3 minutes. There is no reference whatsoever to translucency or transparency, however. In United States Patent Specification US-A-4,885,108 (Colgate-Palmolive Comp.) soap bars are heated in a closed container (optionally after having removed brand names by shaving) to 100°-120°F (37°-49°C) for sufficient time to soften the bar, after which the softened bar is formed into its required shape and size. There is no indication of translucency or transparency, however, nor is there any suggestion to these properties.

The present invention therefore relates to a process of preparing transparent or translucent soap, in which a soap is subjected to sufficient mechanical working and shear so as to induce translucency, which is characterized by the steps of:

(a) subjecting a soap composition, comprising from 60% to 80% by weight of an alkali metal soap of

saturated and unsaturated monocarboxylic or fatty acids having from 8 to 24 carbon atoms, from 5% to 20% by weight of at least one polyhydric-alcohol and from 5% to 20% by weight of water (all percentages based on the total composition) to mechanical working and shear so as to impart translucency, and

(b) subjecting the translucent soap obtained to a heat treatment in which the temperature of the soap is brought to a core temperature of from 45°C to -65°C, and

(c) cooling the soap.

The soap composition may also comprise up to 20% by weight of the total composition of at least one sugar or at least one at least partially hydrogenated sugar, up to 25% by weight of the total composition of a crystallization modifier and up to 20% by weight of the total composition of hydrotropes, and surfactants. Finally, the soap composition may also comprise functional additives.

The soap comprises a mixture of soluble soaps and insoluble soaps. By "soluble" soaps are to be understood throughout this specification and the attached claims: the salts of saturated monocarboxylic acids or fatty acids having from 8 to 14 carbon atoms and additionally the salts of oleic acid and polyunsaturated monocarboxylic or fatty acids having from 8 to 22 carbon atoms. By "insoluble" soaps are to be understood throughout this specification and the attached claims: the salts of saturated monocarboxylic or fatty acids having from 16 to 24 carbon atoms. The salts of the monocarboxylic or fatty acids are preferably sodium salts, but small amounts of potassium soaps, ammonium soaps or alkanolamine soaps may also be present. The selection of the soaps depends on availability and cost, but suitable soaps are derived from coconut oil, palm kernel oil, tallow, hydrogenated tallow, palm oil, and the like and mixtures thereof. It is preferred to use soaps prepared

from 70-80% tallow and 20-30% coconut oil, palm oil and/or palm kernel oil.

The polyhydric alcohol to be used in the soap composition according to the present invention may be glycerol, polyethylene glycols, propylene glycol and mixtures of polyhydric alcohols. Preferably, from 5% to 15% by weight of the total composition of polyhydric alcohol is used.

The soap composition may also comprise up to 25% by weight of the total composition of a crystallization modifier, such as hydroxystearic acid, dimerized and/or trimerized fatty acid, elaidic acid, iso-stearic acid and their alkali metal soaps. The use of hydrogenated monomer fraction ("isostearic acid") as obtained in the polymerization of unsaturated fatty acids is preferred (for a method of preparing such acid; see United States Patent US-A-2,812,342 (Peters)).

Finally, the soap composition according to the present invention may also comprise up to 20% by weight of the total composition of hydrotropes, such as triethanolamine, a ine soaps and surfactants.

Also effective amounts of functional additives may be present. The functional additive may be selected from the group consisting of antioxidants, such as tocopherols, BHA, BHT and the like; chelating agents, such as EDTA and the like; colouring agents; deodorants; dyes; emollients, such as cosmetic oils; enzymes; foam boosters, which may be selected from anionic, a photeric, nonionic and certain cationic surfactants, such as sodium cocoyl isethionate, sodium lauryl ether sulphate and the like; foam stabilizers; germicides; lathering agents; moisturizers; optical dyes; pearlescers; perfumes; sequestering agents; skin conditioners, such as dimerized fatty acids; solvents such as propylene glycol, glycerol, sorbitol, and the like;

stabilizers; superfatting agents, such as fatty acids; UV absorbers and mixtures of these functional additives.

The functional additives may be used in any desired quantity to effect the desired functional characteristics, and usually minor amounts from about 0.01% by weight up to 10% by weight are used. Some of the additives may be used in larger amounts, however.

With regard to the mechanical working and shear imparting treatment, the moisture content of the soap can be adjusted to within the limits required for translucency and then the soap is subjected to mechanical working and shear e.g. in a Z-blade mixer, on a roller mill or in a cavity transfer mixer (preferably as described in European Patent

Specification EP-B-0,090,649) so as to impart the optimal translucency. But any other effective method, known per se may be used. The effect of the subsequent heat treatment according to the present invention is optimal, when the soap has received sufficient mechanical working and shear i.e. has reached optimal translucency allowed by the formulation.

The heat treatment according to the present invention may be applied to formed (translucent) soap bars or tablets, but it may also be applied to soap noodles before they are converted into the desired shape and size. In general the heat treatment is effected such that the core temperature of the soap reaches a value between 45° and 65°C, preferably from 55°C and 65°C. Preferably the heat treatment is effected by means of microwave heating using microwave ovens with a frequency of e.g. 915 MHz or 2450 MHz. In another embodiment the mechanical working and shear imparting treatment and the heat treatment are effected simultaneously.

The present invention also relates to the translucent or transparent soap obtained by the process according to the present invention. This soap may be in the form of noodles or in finished tablet or bar form of regular or irregular shape and any required size. When in bar form, there may have been inserted into the bar a plastic toy, animal or other phantasy figure.

The process according to the present invention is now illustrated by the following examples.

Examples I-III

Three soap compositions were prepared, starting with the following formulations (all percentages are percentages by weight) :

The mixture of the sodium soap was brought into a mixer, and after mixing the composition was passed through standard soap manufacture apparatus in 30 to 45 minutes, care being taken that the temperature of the soap mass did not exceed 40-45°C

The soap was extruded and converted, into bars and some of these were put into a standard microwave oven, operating at 2450 MHz, at a setting of 15% of the maximum power. In 10 seconds the core temperature of the bars was 60°C. At this moment the bars were taken out of the oven and allowed to cool to 20°C. An excellent transparent soap bar was obtained having the following translucency (TL) values:

Example IV

A soap composition was prepared of 60% by weight of sodium soap of tallow fatty acids, 20% by weight of sodium soap of palm kernel fatty acids, 4.2% by weight of sodium stearate and 10% by weight of sodium iso-stearate. Of this mixture 70.9% by weight was mixed with 4.2% by weight of sorbitol, 5.8% by weight of glycerol, 15% by weight of water and 2.5% by weight of free fatty acids. The soap mixture was converted into bars having a translucency value of 76.2% and then heated (both as described in Examples I-III) after which the bars had a translucency value of 105.5%

Example V

A soap composition was prepared of 47.7% by weight of sodium soap of tallow fatty acids, 11.9% by weight of sodium soap of palm kernel fatty acids, 15% by weight of the sodium salt of laurylethersulphate having an average of 3 moles of ethylene oxide, 7% by weight of glycerol, 18% by weight of water and 0.4% by weight of sodium chloride. The soap mixture was converted into bars as described in Examples I-III, and these had a translucency value of 76.4%. After heating as described in Examples I-III, the translucency value was 89.8%.

Example VI

A soap composition was prepared as described in Example II, but now 1.5% by weight of perfume were added. After formation into bars, the translucency value was 17.2% and after the heat treatment as described in Example 2, the translucency value was 60.1%.