Transparent soap

Description

[0001] The application relates to a transparent soap composition. Transparent soap, particularly transparent toilet soap, is a known product. However, the manufacture of transparent soap was complicated and involved expensive techniques like mixing with high shear mixers or, for example, addition of alcohol as a solvent for the soap. Also it has often been necessary to incorporate considerable amounts of special components like resin fatty acid soap, lanolin or suchlike.

[0002] A recent development in this field is disclosed in GB-A-2 126 603 (Colgate Palmolive Co.) in which lanolin (fatty acids) are incorporated in the soap mixture and in which, as appears from the examples, a mixture of tallow fat and coconut oil soap was prepared in the classical manner by boiling, to which the other ingredients such as lanolin (fatty acid), possibly polyol etc. are added. Subsequently, to this soap composition, which contains about 0.5% sodium chloride as well as glycerol, are therefore added lanolin (fattty acid), etc. The sodium chloride present serves to salt out the soap and also imparts the required hardness to the soap tablet to be made. In the description of the British patent specification it is also mentioned incidentally on page 6, line 29, that the soap can also be prepared by continuous saponification of fatty acid, whereafter, evidently, the further components like, for example, lanolin are incorporated.

[0003] For simple processing according to the British specification, it would be desirable to feed all components directly into a device which effects direct saponification of fatty acids, but then the complication occurs that the lanolin saponifies, which spoils its activity.

[0004] The invention now provides a transparent soap composition which can be prepared, in a simple manner, by means of direct saponification of fatty acid and this composition differs from that according to British patent specification (GB-A-) 2 126 603 in that there is no lanolin (fatty acid) present and the amount of sodium chloride is less than 0.2%, while the soap tablet manufactured therefrom is of excellent transparency and also, for example, sufficiently hard and has excellent foaming characteristics.

[0005] Accordingly, the application provides a transparent soap of the following composition:

A: 55-79.5% (ww) alkali metal or tertiary amine (soap of a fatty acid mixture consisting of :
90-70%, preferably 85-70% (ww) C₁₆-C₂₂ fatty acids and
10-30%, prefrably 15-30% (ww) C₁₀-C₁₄ fatty acids;

B: 7-20% (ww) of a thermostable polyol, i.e. a polyol not discolouring appreciably at 150°C;

C: 0.5-7.5% (ww) free C₁₀-C₂₂ fatty acids;

D: 12-20% (ww) water;

E: less than 0.2% (ww) NaCl;

F: Up to 2% of usual components like perfume, dye, stabilizer, etc.

[0006] The soap composition is preferably as follows:

A: 64-78%

B: 8-15%

C: 2- 5%

D: up to 16%, preferably at least 12%

E: less than 0.1% (ww) NaCl.

[0007] Although, as a rule, transparent soap also contains potassium and/or triethanolamine soap, according to the present invention excellent results have already been obtained with predominantly or even exclusively sodium soap. Triethanol amine soaps are preferably applied in amounts below 15% (ww).

[0008] As C₁₀-C₁₄ fatty acids, normally coconut fatty acids or palmkernel fatty acids are used; as C₁₆-­C₂₂ fatty acids (saturated or unsaturated), tallow and/or palm oil fatty acids are very suitable and these are advantageously partially replaced so as to contain up to 40% of branched chain monocarboxylic acids. Suitable branched chain monocarboxylic acids are conveniently obtained as a by-product of the polymerization of unsaturated fatty acids. The branched chain monocarboxylic acids have short side-chains (C₁-C₃) distributed over the carbon chain with a statistic preference for the centre carbon atoms.

[0009] In the first place, sugar alcohols like e.g. sorbitol, mannitol, and so-called (poly)glycols derived from C₂-C₃ glycols having a molecular weight between 62 and 1200 are considered as thermostable polyol; also other C₃-C₆ polyols containing 3-6 hydroxyl groups polyols like trimethylolpropane, trimethylolethane, glycerol can be used.

[0010] As unsaponified fatty acid starting material, C₁₀-­C₂₂ fatty acids, particularly C₁₀-C₁₄ fatty acids, are particularly suitable. They can be added as such, but saponification can also be carried out with a smaller than stoechiometric amount of alkali metal hydroxide. The saponification takes place at temperatures of 20-160°C and at atmospheric or super-­atmospheric pressure. The saponification can take place in an autoclave which is operated atmospherically or under pressure, or in a unit specially designed for saponification. As far as the hydroxide is concerned, it is preferable that, predominantly or even exclusively, sodium hydroxide is used. Adding potassium hydroxide brings no or little improvement and, in any case, increases the price of the product. As usual components, perfume, stabilizers and dyes must be considered. These ingredients should be chosen judiciously, because they can cause opacity. However, from the prior art suitable components for transparent soaps are already known.

[0011] The present invention also provides a simple process for preparing transparent soaps, in which a fatty acid mixture of C₁₆-C₁₈ and C₁₀-C₁₄ fatty acids and possibly other components in a suitable ratio to each other is saponified, completely or not completely, and, after addition of the other components B and C as defined above, is dried to a water content of 12-20% and the material thus obtained is processed, preferably with a standard soap-processing unit, to transparent soap tablets. This equipment, for example, consists of a mixer in which the perfume and dye are mixed with the soap granules, a refiner-plodder and a vacuum-plodder, in which, at the outlet, an extruded bar of soap is formed that is cut into billets and stamped to tablets.

Example I

[0012] 2000 gram of a mixture consisting of 80% tallow fatty acids (substantially consisting of about 24% palmitic acid, 20% stearic acid, 2% myristic acid and 40% oleic acid and homologues thereof) and 20% coconut fatty acids (mainly consisting of about 5% capric acid, 50% lauric acid, 20% myristic acid, 11% palmitic acid and 10% oleic acid) were mixed and heated to 60°C. Hereafter, this mixture was saponified at 100°C by adding it to 1105 g aqueous sodium hydroxide (27.6% solution in water) in an autoclave. After 10 minutes, 464 g sorbitol solution (70% in water), 75 g technical lauric acid (93% pure), 42 g polyethylene glycol with an average molecular weight (M) of 400 and 12.5 ml aqueous solution of the Na salt of ethane-1-hydroxy-­1,1-diphosphonic acid (EHDP) (30% in water) were added to this so-called "neat soap". After thorough mixing of these components, the whole mixture was dried to a water content of 16%. The NaCl content was smaller than 0.01% (mainly from the technical grade sodium hydroxide), the free fatty acid content 5.3%. After processing to noodles, the visual transparency thereof was good. The noodles were fed into a plodder; a continuous bar was obtained, which was cut and stamped, yielding soap tablets. Such an uncoloured soap tablet of 2 cm thickness absorbed only 40% of a white light beam.

Example II

[0013] In a manner analogous to that described in Example I, a transparent soap was prepared in which the 42 g polyglycol was replaced by 40 g polyethyleneglycol (M = 1000) and drying was carried out to a water content of 18%; the NaCl content was also below 0.01%. The transparency of this soap was slightly better than that of the above Example.

Example III

[0014] In a manner analogous to that described in Example I, a transparent soap composition was prepared. Now, however, not 75 g technical lauric acid was added, but 42 g, and this resulted in a transparent soap composition with 0.01% NaCl and 3% free fatty acid content. In this case the light absorption was appreciably lower than that obtained according to Example 1, namely 25%.

Example IV

[0015] According to a process analogous to that of Example 1, a fatty acid mixture consisting of 62% straight chain C₁₆-C₂₂ monocarboxylic (= fatty) acid, 22% (ww) C₁₀-C₁₄ fatty acids and 16% (ww) branched chain C₁₈-C₂₂ fatty acids (by-product of the polymerization of fatty acids) were saponified with 97% of the stoechiometric amount of sodium hydroxide. Further processing was identical with that of Example 1 but no fatty acid was added after saponification. The NaCl content was below 0.01%; the light absorption was 20%.

Claims

1. A transparent soap composition, characterized in that it contains the following ingredients:

A: 55-79.5% (ww) alkali metal or tertiary amine soap of a fatty acid mixture consisting of
90-70% (ww) C₁₆-C₂₂ fatty acids and 10-30% (ww) C₁₀-C₁₄ fatty acids;

B: 7-20% (ww) of a thermostable polyol;

C: 0.5-7.5% (ww) free C₁₀-C₂₂ fatty acids;

D: 12-20% (ww) water;

E: less than 0.2% (ww) NaCL;

F: Up to 2% of conventional components like perfume, dye, stabilizer, etc.

2. A composition according to claim 1, characterized in that the percentages are:

A: 64-78%

B: 8-15%

C: 2- 5%

D: 12-16%

E: less than 0.1% (ww) NaCl.

3. Composition according to claim 1 or 2, characterized in that the soap contains sodium soap.

4. Composition according to any one of the claims 1-3, characterized in that the C₁₆-C₂₂ fatty acid groups comprise up to 40% (ww) of branched chain monocarboxylic acids.

5. Composition according to any one of the claims 1-3, characterized in that the soap also comprises triethanolamine soap.

6. Composition according to any one of the claims 1-5, characterized in that it contains 0.01-2 wt.% ethane-1-hydroxy-1,1-diphosphonic acid or a salt thereof.

7. Composition according to any one of the claims 1-6, characterized in that the polyol comprises a sugar alcohol.

8. Composition according to any one of the claims 1-7, characterized in that the polyol component comprises sorbitol.

9. Compositions according to any one of the claims 1-8, characterized in that the polyol component comprises a glycolpolyether having a molecular weight between 200 and 600.

10. Process for preparing a transparent soap composition according to any one of the claims 1-9, characterized in that a fatty acid mixture of C₁₆-­C₂₂ and C₁₀-C₁₄ fatty acids is saponified, completely or not completely, and, after addition of the other components B and possibly C, is dried to a water content of 12-20% and the material obtained is processed in a manner known per se with standard soap processing apparatus to transparent soap tablets.