GB2263282A - Soap compositions - Google Patents

Abstract

Hard soap, which has a fatty matter content intermediate between laundry soap and toilet soap, is made with a glycerol content in the range of 6.2 to 10% by weight and a non-soap electrolyte content in the range 0.4 to 1.5% by weight. The soap content defined as total fatty matter content is 61 to 67% by weight. The glycerol may be incorporated into the soap composition by leaving in the composition the glycerol which is formed during saponification. Soap of this composition has properties which are satisfactory for a conventional opaque hard soap.

Description

SOAP COMPOSITIONS This invention relates to the manufacture of soap.

Soap bars are traditionally manufactured to fit within one of three categories, referred to as "toilet soap", "laundry soap" and "hard soap". All are normally opaque.

Toilet soap is made with a relatively high content of soap and is used for personal washing. Laundry soap is made with a lower content of soap and a higher content of moisture. It is principally used for the hand washing of fabrics.

"Hard Soap" is a product falling in between the categories of laundry soap and toilet soap. It is used, at least in some countries, both for laundry and for personal washing. It has a soap content intermediate between the levels of soap contained in toilet soap and in hard soap.

The present invention relates to a product which is intended to resemble, and be used in place of, traditional "hard soap".

Conventional modern soap bar manufacture from triglycerides (i.e. fats) entails saponification with sodium hydroxide followed by separation of the glycerol produced in the reaction.

There are, however, processes which do not entail separation of glycerol. These are the so-called "cold process saponification" and "semi-boiled saponification" methods. In both of these the mixture from the reaction is cast into bars by pouring it into frames and allowing it to set. The soaps produced by these saponification methods tend to be too soft and sticky to process with the equipment used in the conventional procedure of plodding and stamping as is used for conventional glycerol-freed soap.

Consequently casting, which leads to a harder product, has often been the only way to form such soap into bars, despite poor throughput and inherent difficulty in stamping the soap into desired bar shapes. Soap produced by these routes has often been of poor quality and sometimes has incorporated inexpensive fillers which can render the soap bars excessively hard but of even lower quality.

There have been proposals to add glycerol deliberately to soap. However, addition of glycerol in this way leads to soft and sticky soap which is difficult to make into bars without additional processing steps or formulation ingredients. Confirmation of this is found in EP-A-89714 (Procter & Gamble) whose opening pages mention the difficulties associated with adding glycerol at the normal stage for the introduction of additives.

Addition of glycerol, or other materials, has frequently been proposed for the purpose of producing soap-based product with special features which can be sold for a relatively high price. In particular, some processes deliberately add glycerol after making the soap or else leave glycerol in the composition in order to produce translucent soap. Such translucent soap products are usually intended for personal washing, as an alternative to a traditional toilet soap, even though the soap content may be below the customary level for a toilet soap.

Additional processing steps have generally been utilised, such as the application of shear work in a cavity transfer mixer as described in EP-A-90649 (Unilever).

Cations other than sodium and/or solvents other than glycerol are frequently used in these translucent bars.

Translucent soaps generally have in-use properties which would be regarded as poor for an ordinary opaque soap.

However, these can be tolerated in translucent soaps which are commercially viable because they are visually attractive. For instance, in a test for mush formation, bars are used for four days, left overnight and then assessed for surface hardness by prodding and assigning a numerical score for the depth and area of indentation. In this test a conventional opaque bar of sodium soap scored 5.

A translucent bar incorporating some potassium ions and with glycerol added after soap-making had a score of 16, which would be unacceptable for an opaque soap.

We have now found that soap with properties which are satisfactory for a conventional opaque hard soap can be made by a procedure which leads to a glycerol-containing formulation. The formulation needs to lie within specified constraints.

According to a first aspect of this invention there is provided a soap composition which, aside from any non-soap particulates comprises: a total fatty matter content from 61 to 67% by weight; 6.2 to 10% by weight glycerol; from 0.4 to 1.5% by weight non-soap electrolyte, with water included in the balance to 100%.

It is possible to add modest proportions of insoluble particulate filler into a soap composition. It acts as a solid diluent without serious effect on rheology.

Consequently the above percentages are based on the weight of the composition excluding any dispersed non-soap particulates.

A composition according to this invention may, if desired, be substantially free of particulate filler.

Alternatively some particulate filler may be included.

Possible fillers include kaolin, silica and starch.

The amount of particulate filler which is included will generally not exceed 20% by weight of the total composition.

Particle size desirably lies in a range from 0.1 to 20u, and should not exceed lOOp because a gritty feel is apparent as particle size increases above about 20p.

The composition may well consist substantially only of the constituents which have already been mentioned, including filler (if any). Consequently the quantity of non-particulate material in the composition which is other than the said soap, glycerol, electrolyte and water may be not in excess of 5% by weight, better not over 3% by weight, based on the weight of the composition excluding dispersed non-soap particulates. Non-soap surfactant will not normally be included.

The term "total fatty matter", usually abbreviated to TFM, is a conventional way to express the concentration of soap (plus any free fatty acid present). It denotes the percentage by weight of fatty acid residues present without taking into account the accompanying cations.

The accompanying cations will generally constitute 5 to 8% by weight so that the quantity of soap, reckoned as anhydrous will generally lie in the range 66 to 76% by weight, and usually 68.5 to 75% by weight based on the weight of the composition excluding any dispersed non-soap particulates.

The term "soap" denotes salts of monocarboxylic 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. Possibly at least 90% by weight of the soap will have carboxylate anions with 12 to 18 carbon atoms.

The soap may be exclusively sodium soap or almost entirely so. Thus the soap may be at least 93%, 95% or even 98% by weight sodium soap.

Hard soap does not normally incorporate free fatty acid, giving a superfatted bar, in contrast with conventional practice for some toilet soaps. If any free fatty acid is present it may well be less than 5% or even 3% by weight of the composition. Any free fatty acid which is present contributed to the total fatty matter (TFM).

Glycerol left in the composition after saponification will constitute from 6.2 to 10% by weight, usually 6.5 to 9.5% by weight based on the composition excluding any non soap particulates. It may lie in the even narrower range of 8 to 9.5%.

The hardness of the composition will be affected both by the quantity of water-soluble electrolyte present and by the charge/size ratio of the anion(s). An electrolyte with a small anion will harden the soap more, for a given weight of electrolyte than if the anion is large.

The amount of electrolyte should be adjusted so as to be high enough to avoid softness and stickiness without becoming so high as to over harden the product. In the latter case undue cracking of soap bars during handling would be likely. Suitable levels of sodium chloride generally lie in the range 0.5 to 1.0% based on the composition excluding any non-soap particulates. For sodium carbonate the range is likely to be 0.7 to 1.5% by weight.

For reasons of economy in production it is preferred that at least a majority of the electrolyte is a sodium chloride or sodium carbonate or a mixture of the two.

Accordingly preferred soap bars according to this invention have a composition, which, aside from any non-soap particulates, lies within the ranges: total fatty matter 61 to 67% by weight accompanying cations 5 to 8% glycerol 6.5 to 9.5% sodium chloride/sodium carbonate 0.5 to 1.5% The hardness of a soap bar can be quantified by measuring the yield stress of the bar. Measurement of yield stress is described inter alia in Elementary Rheology by GW Scott Blair, Academic Press, London 1969 and Rheometry: Industrial Application Ed. K. Walters Research Studies Press (a division of John Wiley & Sons Ltd) New York 1980.

Soap bars of this invention preferably have a yield stress at 30"C of at least 0.9 x 10-5 Nm-2, more preferably at least 1.3 x 10-5 Nm-2.

The bars of this invention will usually be opaque bars, since they are intended to substitute for conventional opaque hard soap bars. Any bar containing particulate filler will inevitably be opaque.

Manufacture of soap compositions according to this invention is preferably carried out by a process in which triglycerides are saponified with alkali and the resulting mixture is processed into bars without freeing the soap from the glycerol produced in the reaction.

Therefore a second aspect of this invention provides a process for making a soap composition as any set forth above, comprising saponifying triglycerides with alkali, especially sodium hydroxide, incorporating electrolyte, and plodding and stamping the mixture into bars while retaining in the mixture the glycerol produced by the saponification.

The process may also include a drying step and possibly a milling step. Some fatty acids may be included with the triglycerides if desired but the weight of fatty acid will generally be less than the weight of triglyceride, for instance no more than one quarter the weight of triglyceride. The triglyceride may be fats or oils generally used in soap manufacture such as tallow, tallow stearines, palm oil, palm stearines, soya bean oil, rice bran oil, coconut oil, babassu oil and palm kernel oil.

The triglycerides may be in accordance with the normal practice for toilet soap of using a mixture of triglyceride sources so as to obtain a desired mixture of alkyl chain lengths. Typical is 60-90t non-lauric fat/oil such as tallow and 10-40% lauric oil such as coconut. A conventional combination is 80% tallow 20% coconut.

However, the invention is applicable to less usual possibilities such as 95% or even 100% coconut oil, or at the opposite extreme wholly non-lauric fat/oil.

The alkali used for saponification will preferably be aqueous sodium hydroxide solution. A suitable concentration range is 30 to 50% w/w. The amount of alkali should desirably be enough to effect complete saponification so as to avoid leaving traces of unreacted fat in the product.

The reaction is preferably carried out at a temperature in a range from 70 to 95"C.

Drying is best carried out using apparatus which brings about some shearing and fragmentation of the mixture.

Possibilities are to employ flash cooling and drying, or drying and cooling on a surface which is scraped to remove the dried mixture in the form of chips.

The process of saponification may be carried out as a batch process. The process is well suited to this because it is possible to employ simple plant with a low capital cost. It can also be implemented as a continuous process, using a high shear mixer which is combined with a reactor.

The subsequent processing after drying can include the conventional steps of plodding and then stamping the soap into bar form. Additives such as perfume can be added before milling/plodding. Incorporation of filler (if any) is preferably done just before or at a milling stage, so that milling comminutes and distributes the filler.

Examples of the invention will now be described.

Examples 1 to 4 illustrate saponification only. For these examples the reaction was carried out in a pilot plant. The reaction vessel was a crutcher of 250kg size fitted with a jacket for regulating temperature, a stirrer for agitating the contents and an observation port. The crutcher had a bottom outlet with a valve to close the outlet. Two vessels were provided for preparation of liquids to be run into the crutcher. Pipes led from bottom outlets of these vessels to inlet valves above the crutcher. Downstream of these valves the pipes led into the top of the crutcher so as to deliver above the stirrer in the crutcher.

Example 1 120Kg of a tallow/coconut oil mixture (ratio 90:10) containing 7% free fatty acid was heated to 80"C in the crutcher. 59Kg of 30.7% w/w sodium hydroxide solution was added over a period of 20 minutes. The contents of the crutcher was stirred throughout. 20 minutes after the end of the caustic soda addition 0.9Kg of salt (dissolved in water) was added. After completion of the reaction and full mixing of salt with the soap mass a full analysis was carried out. This showed nearly full saponification (0.25% unsaponified) had taken place and no free caustic soda was detected.

Example 2 Example 1 was repeated, varied in that the oil was initially heated to 90"C. All of the sodium hydroxide was mixed with the salt and the mixture was added over 60 minutes. At the end of this time the reaction mixture was stirred for a further 40 minutes.

Examples 3 and 4 Fully refined palm oil and (separately) fully refined tallow were both saponified successfully, using the procedure of Example 2.

Example 5 A number of hard soap compositions were prepared, commencing with saponification of an 90:10 tallow/coconut mixture by the procedure of Example 1. The resulting liquid soap masses were each dried using a vacuum flash drier so as to have total fatty matter contents as set out in the table below. Sodium chloride was included at a concentration of 0.5% by weight. None of the compositions contained particulate filler.

Drying of the mixtures produced by the saponification reaction was carried out using a vacuum flash drier. The entire mixture was dried, without removal of glycerol. The dried compositions were milled, plodded and stamped into bars. The processability of these compositions was noted.

Where possible the yield stress of the resulting bars were measured. Results are given in Table 1 below.

Yield stress quantifies the hardness of a soap bar, as mentioned above. The yield stress of the bars at a specified temperature was determined by measuring the length of a cast made by a weighted cheese wire within a specified time. A horizontally braced cheese wire of diameter d cm suspended from a counterbalanced and freely pivotable arm was brought into contact with a freshly prepared bar of soap at the specified temperature. A corner edge of the soap was positioned under the wire such that when a weight W gm was placed on the arm directly above the cheese wire, the length of cut L cm made by the wire increases to the limit where the stress exerted by the wire equals the resistance of the bar. The stress exerted by the wire at this limit is equal to the yield stress of the soap bar. The time taken to reach this limit was of the order of 30 seconds.In practice a standard 1 minute cut time was allowed in each case.

For a bar having an orthogonal corner edge in transverse cross section the yield stress of the bar was calculated using the following formula: Yield stress = 38 x W98.1 Nm-2 8 x Ld Results for some bars produced by a conventional soap making procedure are included for comparison.

Table 1 Formulation TFM NaCl Yield Stress Processability No. % % (Nm-2 x 105) at 30 C 1 58 0.5 0.48 Unprocessable, too soft and sticky 2 59.5 0.5 1.20 Acceptable 3 62 0.5 1.68 Acceptable 4 66 0.5 2.10 Acceptable 5 68* 0.5 0.95 Poor, softer and stickier than products 2, 3 and 4 * Conventionally produced soap.

It can be seen from Table 1 that bars in accordance with the invention, having a total fatty matter content from 61 to 67% and with 0.5t electrolyte present give bars whose yield stress values are acceptable.

Claims (12)

1. A soap composition comprising: a total fatty matter content from 61 to 67% by weight;

6.2 to 10% by weight glycerol; 0.4 to 1.5% by weight non-soap electrolyte; the balance to 100% including water, the above percentages being based on the weight of the composition excluding any dispersed non-soap particulates.

2. A composition according to claim 1 wherein at least 95% of the soap is sodium soap.

3. A composition according to claim 1 or claim 2 including water-insoluble non-soap particulate filler in an amount from 1 to 20% by weight based on the total composition, the filler having a particle size in the range from O.lp to lOOP.

4. A composition according to claim 1 or claim 2 which is substantially free of particulate filler.

5. A composition according to any one of the preceding claims wherein the content of further non-aqueous material(s) other than any particulate filler as specified in claim 3 is not more than 3% by weight based on the weight of the composition excluding any dispersed non-soap particulates.

6. A composition according to any one of the preceding claims with a composition comprising: total fatty matter 61 to 67% by weight accompanying cations 5 to 8% glycerol 6.5 to 9.5% electrolyte 0.5 to 1.5% the balance to 100% including water, the above percentages being based on the weight of the composition excluding any dispersed non-soap particulates, and at least a majority of the electrolyte being sodium chloride, sodium carbonate or a mixture thereof.

7. A composition according to claim 6 in which the quantity of electrolyte is 0.5 to 1.0% by weight.

8. A composition according to claim 6 or claim 7 in which at least 90% of the electrolyte by weight, is sodium chloride or sodium carbonate.

9. A composition according to any one of the preceding claims which is opaque.

10. A composition according to any one of the preceding claims wherein the content of free fatty acid (if any) does not exceed 5% by weight of the composition.

11. A process for making a composition according to any one of the preceding claims, comprising saponifying triglycerides with alkali and incorporating electrolyte, and plodding and stamping the mixture into bars while retaining in the mixture the glycerol produced by the saponification.

12. A process according to claim 11 which, between saponification and plodding includes a step of drying the mixture produced by saponifying while also breaking the mixture into fragments.