Washing composition containing soap

Abstract

 A washing composition, especially a fabric washing powder containing substantial proportions of soap. At least 10% by weight of the composition is a soap of an unsaturated fatty acid in order to take advantage of the superior solubility properties of such soaps. The composition also contains a water-soluble surface-active compound containing a nitrogen atom which is either positively charged or capable of taking a positive charge in aqueous solution. This compound counteracts the deposition of scale on heater elements. Examples of such compounds are quaternary ammonium salts and lecithin.

Description

[0001] This invention relates to a washing composition containing soap.

[0002] Our British Patent Application No 7936514 describes and claims soap powder containing from 15 to 60% by weight of soap, 35 to 95% by weight of the soap being derived from unsaturated fatty acids having 14 or more carbon atoms, examples of which are oleic, linoleic and linolenic acids.

[0003] We have now gained experience with compositions of this type and also with compositions of other types, for instance those containing down to 10% by weight of soap and those containing large proportions of unsaturated fatty acids having 14 or more carbon atoms and have found that there can be problems with deposits of scale on heater coils. Scalihg of heater coils is a well-known problem but it appears to be particularly severe with the compositions described.

[0004] We have now discovered how to prevent or substantially reduce build up of heater scale in the circumstances described: the solution is to include a small percentage of a water-soluble surface-active compound containing a nitrogen atom which is positively charged or capable of protonation in aqueous solution.

[0005] According to the present invention there is provided a washing composition for use at elevated temperature comprising at least 10% by weight of a soap of an unsaturated fatty acid having 14 or more carbon atoms characterised by containing upto 5% by weight of a water-soluble surface-active compound containing a nitrogen atom which is either positively charged or capable of taking a positive charge in aqueous solution, preferably quaternary ammonium salt, a sulphobetaine or an amine oxide.

[0006] These nitrogen compounds have been suggested for use in washing compositions before. In particular, surface-active quaternary ammonium salts have been suggested for inhibiting dye-transfer, in combination with anionic. and nonionic surfactants, for imparting softness benefits and for inhibiting autoxidation during spray-drying of detergent slurries containing nonionic surfactants. They have not however, as far as is known to us, been suggested in combination with the narrowly-defined soap compositions specified herein.

[0007] The quaternary ammonium salts which are preferred in the compositions of the invention are dodecyltrimethylammonium halide, tetradecyltrimethylammonium halide, hexadecyltrimethylammonium halide or sulphate. Of these halides the chloride and bromide are preferred for reasons of practicality.

[0008] More complex compounds containing a quaternised nitrogen atom; such as lecithin and lysolecithin may also be used.

[0009] The quaternary ammonium salts will preferably be present in an amount of from 0.1-5% by weight.

[0010] Groundnut oil is the preferred source of unsaturated fatty acids containing 14 or more carbon atoms, since this is high in oleic acid content and relatively low in linolenic acids. There are a number of other oils relatively rich in oleic acid. They include, but are not confined to, soyabean oil, sunflower oil, rapeseed oil, and cottonseed oil. Because these oils are rather prone to oxidation (due to their high linoleic/linolenic contents) they are best used together with a suitable antioxidant. Besides the naturally-occurring oils, certain commercially available technical grade fatty acids can be used also.

[0011] For best results we specify oils which are free from linolenic acid and prefer to use oils which provide a fatty acid composition in the final soap powder which contains a total of no more than 50% by weight of linoleic and linolenic acids. When the total content of these acids is from 20 to 50% by weight we recommend the use of a suitable antioxidant. We have found ethane-l-hydroxy-1, 1-disphos- phonic acid or ethylene diamine tetraacetic acid, or a mixture thereof, to be suitable antioxidants.

[0012] In order to obtain good solubility from soap powders included within this invention it is preferable to choose a mixture of fatty acids whose water-soluble sodium salts have a Krafft temperature of from 10-35°C, preferably no higher than 25°C.

[0013] Krafft temperature is defined by Lloyd I Osipow in 'Surface Chemistry, Theory and Industrial Application', published by Rheinhold of New York, 1962, and this definition is adopted for the purposes of this specification. To summarise the definition, the Krafft temperature can be regarded as the temperature above which there is a rapid increase in solubility of the surfactant in question due to formation of micelles.

[0014] The fabric washing compositions of the invention may, and usually will, contain a detergency builder compound. Any detergency builder may be used, either a phosphate- based builder such as sodium tripolyphosphate, sodium pyrophosphate or sodium orthophosphate, or a mixture thereof, or any one of the compounds which has been suggested recently as a result of pressure from those wishing to reduce phosphate contents of effluents. Typical of these are sodium citrate, alumino-silicates, both crystalline and amorphous, and a host of organic chelating compounds, prominent amongst which are nitrilotriacetic acid, which has been used commercially in some countries, alkenyl succinate salts and salts of carboxymethyloxy- succinic acid. These detergency builder compounds can be used in any desired combination so that the desired calcium/magnesium binding capacity is achieved at the level of phosphorus, if any, which is permitted or required.

[0015] Bearing in mind that soap formulations are to a large extent self-building, the amount of detergency builder compound required will normally be between 5 and 25% by weight of the whole powder formulation when the amount of soap is between 10 and 60% by weight, as is preferred..

[0016] The detergency builder which is preferred, for reasons of cost-effectiveness, is sodium tripolyphosphate. When this substance is used, the weight ratio, water-soluble salt of C12-C22 fatty acids: sodium tripolyphosphate may be from 10:1 to 1:3, preferably 9:1 to 3:1.

[0017] The fabric washing compositions of the invention may contain other materials in conventional amounts. For example, they may contain a bleaching material, either an oxygen bleach such as sodium perborate or sodium percarbonate, desirably with a precursor such as tetraacetylethylene diamine or a chlorine bleach such as sodium di- or tri-chloroisocyanurate, or mixtures thereof. These materials may be present in amounts of from 10 to 30% by weight of the powder, preferably 15 to 25%, when the bleaching material is sodium perborate or sodium percarbonate alone and from 5 to 20% by weight when it is a chlorine bleach such as sodium dischloroisocyanurate. When a bleach precursor is present it will desirably be at a level of from 0.2 to 3.5% by weight, and the oxygen bleach will be present at a reduced level, typically 5 to 20% by weight in the case of sodium perborate and 5 to 15% by weight in the case of sodium percarbonate.

[0018] Antiredeposition agents, such as sodium carboxymethyl cellulose, fillers such as sodium sulphate or sodium carbonate, corrosion inhibitors such as sodium silicate, lime soap dispersants such as nonionic surfactants, alkanolamides and alkali metal ether sulphates, optical brightening agents, coloured speckles and perfumes, may also be present in amounts varying from 0.1 to 15%, preferably 0.1 to 5% by weight. Moisture may be present in an amount of up to 15%.

[0019] The soap powder may be made by any of the conventional methods known to those skilled in the art, which include slurry-making, spray-drying, spray-cooling, dry-dosing and spraying of fatty acids directly onto solid components of the powders.

[0020] The invention will be further illustrated by reference to the following Example.

Example

[0021] A solution containing 4 gms/litre of a spray-dried/ cooled soap powder having the composition

in water 22° German hardness was placed in a washing machine having a weighed heater element. The solution was heated to 75°C maintained at that temperature for one hour and then discarded. That procedure was repeated 4 times, after which the heater element was dried -and re-weighed to determine the amount of scale deposited.

[0022] The whole process was then repeated using a number of different compounds. The compounds used, the concentration used and the weight of scale deposited is shown in Table 1.

[0023] It can be seen that the three surface-active quaternary ammonium compounds and the sulphobetaine, produce a dramatic reduction in the amount of scale deposited on heater elements.

Claims

1. A washing composition for use at elevated temperature comprising at least 10% by weight of a soap of an unsaturated fatty acid having 14 or more carbon atoms characterised by containing up to 5% by weight of a water-soluble surface-active compound containing a nitrogen atom which is either positively charged or capable of taking a positive charge in aqueous solution.

2. A washing composition according to Claim 1 characterised in that the surface-active compound containing a nitrogen atom comprises a quaternary ammonium salt.

3. A washing composition according to Claim 1 or Claim 2 characterised in the surface-active compound containing a nitrogen atom comprises a sulphobetaine.

4. A washing composition according to any one of the preceding claims characterised in that the surface-active compound containing a nitrogen atom comprises an amine oxide.

5. A washing composition according to Claim 2 characterised in that the quaternary ammonium salt comprises dodecyltrimethyl ammonium, hexadecyltrimethylammonium or tetradecyltrimethylammonium halide or sulphate.

6. A washing composition according to Claim 1 characterised^kin that the compound containing a nitrogen atom comprises lecithin or lysolecithin.

7. A washing composition according to any of Claims 2, 5 or 6 characterised in that the quaternary ammonium salt is present in an amount of from 0.1 to 5% by weight.

8. A washing composition according to any one of the preceding claims wherein the soap has a Krafft temperature of from 10-35°C.

9. A washing composition according to any one of the preceding claims wherein the soap contains no more than 50% by weight of linoleic and linolenic acids.

10. A washing composition according to Claim 9 wherein the soap contains 20 to 50% by weight of linoleic and linolenic acids, and an antioxidant.