CLEANING COMPOSITIONS

Abstract: A cleaning composition, suitably in the form of a personal washing bar contains fatty acyl isethionate and by weight of the composition at least 0.002% of each of an antioxidant, a sequestering agent for iron and a sequestering agent for copper. The presence of the antioxidant and the sequestering agents improves the shelf life of the products.

Description: This invention relates to cleaning compositions containing fatty acyl isethionate as at least part of detergent active present. The compositions may in particular be in the form of bars for personal washing. Bars containing fatty acyl isethionate as the main detergent active have been marketed commercially for a number of years, and have achieved considerable acceptance in North America. There have also been numerous proposals for bars in which fatty acyl isethionate is used in admixture with other detergent active(s) which may be soap. Bars containing substantial amounts of isethionate have a distinctive odour; and it is known that the quality of the fatty acid used in production of the isethionate needs to be controlled in order to control the odour of the freshly-made product. Provided that this quality control is done, the fresh product can have an acceptable odour despite being subjected to high temperature during the process of manufacture. The commercially made product, with an acceptable odour when freshly made, has a shelf life which is generally satisfactory. Such a requirement must be the case for a product which has been accepted by consumers. We have now appreciated however the products containing fatty acyl isethionate, and having an acceptable odour when produced, nevertheless can have a tendency to develop an undesirable odour on prolonged storage at ambient temperature. We consider that it would be desirable to ameliorate this tendency, so as to enhance the shelf life of such products. We believe that the cause of this hitherto unrecognised defect is a process of autoxidation after production. Without being bound by this belief as to the cause, the present invention resides in a finding that the shelf life of products containing fatty acyl isethionate can be improved by the incorporation into such products of small quantities of each of an antioxidant, a sequestrant for iron and a sequestrant for copper. It is essential to this invention that all three of these items are present. GB patent specification 1 081 233 (Bierre) teaches the use of a stabiliser for an antioxidant for soaps and synthetic detergents formed by mixing EDTA with a mixture of diethylene glycol and polyethylene glycol. GB patent specification 1 169 551 (Unilever Limited) teaches the use of 0.02% EHDP and 0.02% EDTA by weight in soap bars to improve their short-term storage properties. The specification suggests that fatty acyl isethionate can be present. In a first aspect the invention provides a process of producing a cleaning composition which contains detergent active including at least 40% by weight of the composition fatty acyl isethionate, which comprises preparing the fatty acyl isethionate from isethionate and free fatty acid under an inert atmosphere and flash cooling the product, subsequently, incorporating into the composition at least 0.002% by weight of the composition of each of an antioxidant, a sequestering agent for iron and a sequestering agent for copper. Products obtained by a process in which the antioxidant and sequestering agents are added after the flash cooling step are surprisingly stable as compared with products in which these ingredients are added prior to the flash-cooling step. The fatty acyl compound used to manufacture the isethionate is maintained under an inert atmosphere, for example it is sparged with nitrogen or some other gas which does not react with it, prior to reaction to form the fatty acyl isethionate. It should then be maintained under an atmosphere of such gas until the isethionate formation step has been carried out. Sparging with nitrogen will generally consist in bubbling the nitrogen through fatty acyl-containing precursor compound while the latter is in a liquid form. The fatty acyl compound normally used is coconut fatty acid. The antioxidant used should be a compound able to suppress reactions proceeding via a free radical mechanism, and will generally be a free radical scavenging agent. Many such compounds are available. The antioxidant is added after the fatty acyl isethionate has been formed and any other high temperature steps have been carried out. Suitably it is incorporated in the composition and maintained at a temperature below 170°C. A preferred antioxidant is 2,6-di-t-butyl-4-methylphenol referred to hereinafter as BHT. A preferred level of addition of this compound is 200 ppm (0.02% by weight) based on the fatty acyl-containing precursor. A preferred sequestering agent for copper is ethylene diamine tetra acetic acid (EDTA) or a soluble salt thereof such as its tetra sodium salt or mixtures thereof. Such agents are known to enhance the activity of iron in accelerating autoxidation, but can be used successfully provided there is a satisfactory sequestering agent for iron present. The two sequestering agents are then acting synergistically. The preferred sequestering agent for iron is 1-hydroxyethane-1,1-diphosphonic acid (EHDP) or a soluble salt thereof or mixtures thereof. This sequestering agent can be used successfully even when the cleaning composition is superfatted. If the composition does not contain free fatty acid then an alternative possibility for the sequestering agent for iron is magnesium trisilicate. These preferred sequestering agents are added after the fatty acyl isethionate has been formed and any other high temperature processing steps have been carried out. Suitably the sequestering agents are incorporated in the composition and maintained at a temperature below 170°C. The quantity of the antioxidant, and of each sequestering agent should be sufficient to be effective. As indicated above, the amount is at least 0.002% by weight of the composition and it is preferred to use a greater amount so that the composition contains at least 0.005% or at least 0.01% of each sequestering agent. The stoichiometric equivalent of 0.02% tetrasodium EDTA is 33 ppm copper. The stoichiometric equivalent of 0.02% EHDP (as pure acid) is 54 ppm iron. These quantities are well above the amounts of contaminating copper and iron which we have been able to detect in fatty acyl isethionate-containing bars as currently marketed. The total quantity of antioxidant plus sequestering agents will normally be below 1% by weight of the composition and indeed normally less than 0.1% by weight. Fatty acyl isethionates normally used in cleaning compositions have 8 to 18 carbon atoms in the fatty acyl group. Particularly preferred is coconut fatty acyl. The coconut fatty acyl may have been hardened, that is to say the amount of olefinic unsaturation reduced, in well known manner. The detergent actives present in a cleaning composition bar may consist exclusively or substantially exclusively of fatty acyl isethionate and soap. For example the amount of any other detergent active may be less than 2% of all detergent active present. Weight ratios of soap to fatty acyl isethionate may range from 10:90 to 95:5, preferably 15:85 to 60:40, and may be in the range 10:90 to 35:65 or 25:75. As taught in US Patent 2 894 912 (Geitz) fatty acyl isethionate provides at least 40%, preferably from 48%, up to 53% by weight of the composition. If acyl isethionate and soap are not the only detergent actives present they may nevertheless constitute most of the detergent active present, e.g. more than three quarters of it with the weight ratio of soap to acyl isethionate still being within the range as being within the range as indicated above. This invention is particularly applicable when fatty acyl isethionate constitutes at least the majority of detergent active present. A superfatted composition may contain more than 5% free fatty acid. In a composition which is preponderantly fatty acyl isethionate, together with some soap, the amount of superfatting acid may be more than equivalent to the amount of soap, so that soap is converted into its acid form to a substantial degree. In a compositions which contains a small amount of soap, the soap used may contain some additive to prevent deterioration of its own odour, but of course the amount will be diluted on mixing with fatty acyl isethionate. Generally a separate addition of the antioxidant and sequestrants of this invention will be required. The present invention may in particular be applied when the fatty acyl isethionate has been prepared by reaction of C₈-C₁₈ fatty acyl compound, usually the fatty acid itself with an isethionate at temperatures in excess of 100°C. The addition of EDTA and EHDP to fatty acyl isethionate can conveniently be carried out by periodically dosing a small quantity of each of these materials into a tank where the fatty acyl isethionate is mixed with other ingredients of a cleaning composition. Both materials can be added in the form of aqueous solution and since the amounts which are added are small the increased water content of the composition is not significant. However, the two sequestering agents need to be added to the fatty acyl isethionate through separate pipework because if solutions of them are allowed to mix together before mixing with other material, there is a tendency for solids to crystallise out from the mixed solution. The composition suitably admixed with for example soap and any other conventional additive e.g. dye, perfume, free fatty acid, sodium isethionate is suitably worked and formed into for example bars. Embodiments of the present invention will now be described by way of example only with reference to the following Examples. In each of the examples coconut fatty acid was reacted to form sodium fatty isethionate by the process described in US patent specification No. 3320292. In outline the process comprises reacting a concentrated solution of sodium isethionate with coconut fatty acid in the presence of zinc oxide acting as catalyst. The reaction mixture is maintained at a temperature of about 232°C under a nitrogen blanket in order to remove water and allow the reaction to proceed. The resulting product is stripped to remove residual free coconut fatty acid. Stearic acid can be added at this stage in order to retain fluidity. The stripped product is then flash cooled, suitably by admixing with for example sodium isethionate solution. Other ingredients, in particular soap, can then be admixed. For bars the mixture can then be rolled, milled, plodded and stamped. Example 1 (not according to the invention) Coconut fatty acid was reacted to form sodium fatty isethionate by the process of patent specification US 3220292. The process was carried out in slightly different ways to provide experimental and control products. For the experimental material the coconut fatty acid was sparged with nitrogen before reaction and the sparged material thereafter kept under a nitrogen atmosphere throughout all the reaction process steps carried out at elevated temperatures. BHT was included in the coconut fatty acid used for the experimental material, so as to provide 200 ppm BHT in the fatty acid. After flashcooling tetrasodium EDTA and EHDP were added to the experimental material to provide 0.02% by weight of each in the mixture. The control material was prepared in the same way from the same batch of fatty acid but without nitrogen sparging, and without the additions of BHT, EDTA salt and EHDP. The experimental and control product materials were both processed into unperfumed and perfumed bars which were subjected to storage tests. To assess storage stability, the bars were wrapped in a conventional wrapping used for bars for personal washing, and stored for twelve weeks at room temperature (20°C), 28°C and 38°C. Odour was assessed by a human tester and rated on a scale as follows: 1. Excellent 2. Good ie standard for a commercial product 3. Fair 4. Poor 5. Unsatisfactory All bars were rated 1 or 2 prior to storage. The general condition of the bars was also noted. To assist in standardising the results observed at one time with the results at another time e.g. after storage, the tester was provided with reference samples which were stored under refrigerated conditions so that these reference samples should undergo minimal change in odour. Even so, it should be appreciated that any ratings of 1, 2 or 3 are not truly absolute but rather are comparative between the experimental and control materials at the time of the test. Results are set out in the following Table I. Example 2 (not according to the invention) The preparation of sodium fatty acyl isethionate, processing of the product into bars and storage testing of those bars was carried out in the same way as for Example 1. As in Example 1 the control bars are prepared without nitrogen sparging and without any BHT, EDTA or EHDP. A first experimental material was prepared while employing nitrogen sparging and adding the BHT to the coconut fatty acid. A second experimental material was also prepared while employing nitrogen sparging and the addition of BHT, to the fatty acid before reaction: additionally tetra sodium EDTA and EHDP were added to this second experimental material after the reaction had been carried out. The bars were wrapped, subjected to storage under various conditions, and tested in the same manner as for Example 1. The experiment was then repeated but with no control material (lacking nitrogen sparging and all of BHT, EDTA and EHDP), and making perfumed bars only. The storage tests were used to compare the materials with and without EDTA and EHDP. The results of the storage tests for the first run of this example and the repetition are set out in Table II below. It can be seen from the Tables that the provision of nitrogen sparging prior to reaction and addition of BHT to the coconut fatty acid before reaction produced only a marginal improvement in the odour rating whereas if this was combined with addition of EDTA and EHDP, there was a clearly observable improvement. Example 3 The preparation of sodium fatty acyl isethionate and processing of the product into bars was carried out in the same way as for Example 1. In the present example five different processing regimes were followed with regard to the use of the sequestering and antioxidant agents in order to compare the effect of the presence of the sequestering agents and the antioxidant when used separately and when used together and the point of addition of the antioxidant. The products were prepared from the same coconut and stearic fatty acid production (ex Emery Chemicals Toronto) in order to ensure equivalence in the initial odour and chemical composition of the raw materials. All batches were produced with nitrogen sparging during the heat-up and reaction stages and during the stripping and flash cooling stages. The five different regimes followed were: A. 200 ppm BHT added to the coconut fatty acid raw material (equivalent to 75 ppm BHT on a finished product basis). B. 0.02% Na₄EDTA and 0.02% EHDP added to the flashed cooled sodium fatty isethionate base. C. A combination of A. and B. D. 0.02% Na₄EDTA, 0.02% EHDP and 0.0075% BHT (75 ppm BHT on a finished product basis) added to the flash cooled sodium fatty isethionate base (process according to the present invention). E. A control product, with no initiation or propagation inhibitors, except 15 ppm of BHT normally contained in the stearic acid. All the regimes were absent of the standard 30 ppm BHT which had been added in the previous examples. When produced each bar was packaged in standard cartons and wraps. For the product of each regime some bars were stored at room temperature and some at a raised temperature (38°C). After one month the bars stored at 38°C were analysed by gas chromatography and mass spectroscopy. The results of the analyses are summarised in Table III below. The chromatographs for the control (ie unpreserved) product E indicate significant peaks of low molecular weight aldehydes and hydrocarbons, which are attributable to the result of oxidative degeneration (ie autoxidation) of unsaturated fatty acids. The two principal contributors to the malodour are isopentanal/pentanal and hexanal. The addition of 200 ppm of BHT alone to the coconut fatty acids (sample A) offered little improvement, as significant levels of isopentanal and hexanal were still present. However methyl pentenes and hexane were substantially eliminated. The products (samples B, C and D) prepared with the two chelating agents were significantly more stable than the control product or the product with BHT only. The low molecular weight hydrocarbons, isopentanal/pentanal, and the methyl pentenes were all minimised or eliminated from all bars containing Na₄EDTA and EHDP. A comparison of samples C and D, which each contain all three agents but differ in their point of addition of BHT, shows that sample C is less stable than sample D. Thus the most stable product was that which was prepared with Na₄EDTA, EHDP and BHT added after flash cooling as virtually all the identifiable low molecular weight aldehydes and hydrocarbons were eliminated.

Claims: A process for preparing a cleaning composition which contains detergent active including at least 40% by weight of the composition fatty acyl isethionate characterised in that the process comprises: (a) preparing the fatty acyl isethionate from isethionate and free fatty acid under an inert atmosphere and flash cooling the product and, (b) subsequently, incorporating into the composition at least 0.002% by weight of the composition of an antioxidant, at least 0.002% by weight of the composition of a sequestering agent for iron and at least 0.002% by weight of the composition of a sequestering agent for copper. A process according to claim 1 wherein the sequestering agents are incorporated in the cleaning composition and maintained at a temperature below 170°C. A process according to claim 1 or claim 2 wherein the antioxidant is incorporated in the cleansing composition and maintained at a temperature below 170°C. A process according to any one of claims 1 to 3 wherein the antioxidant is a free radical scavenging agent. A process according to any one of the claims 1 to 4 wherein the sequestering agent for copper is selected from the group comprising ethylene diamine tetra acetic acid, a soluble salt thereof and mixtures thereof. A process according to any one of claims 1 to 4 wherein the sequestering agent for iron is selected from the group comprising 1-hydroxyethane-1,1-diphosphonic acid, a soluble salt thereof, magnesium trisilicate and mixtures thereof. A process according to any one of the claims 1 to 6 wherein the sequestering agents are added separately to the composition. A process according to any one of claims 1 to 7 including incorporating soap into the composition. A process according to any one of claims 1 to 8 including forming the composition into bars. Product obtainable by the process of any of claims 1 to 9.

Inventors: WATSON, DOUGLAS R.
Applicants: UNILEVER N.V., UNILEVER PLC
Application year: 1987
Main classification: C11D1
IPC codes: C11D17, C11D10, C11D3, C11D1