Detergent powders and process for preparing them

Abstract: Dispensing of certain spray-dried detergent powders in automatic washing machines is substantially improved by the incorporation of 0.1-6.0% by weight of a hydrophobic additive having a contact angle to water of at least 75° and a melting point of 30-100°C. The additive may be included in the slurry from which the powder is prepared, or sprayed, preferably dispersed in nonionic surfactant, onto the powder. The preferred additive is paraffin wax.

Description: TECHNICAL FIELD The present invention relates to detergent powders prepared at least in part by spray-drying and intended for use in drum-type front-loading washing machines. The invention is of especial applicability to powders containing no, or reduced levels of, phosphate builders and to powders of high bulk density. BACKGROUND In recent years the trend in detergent compositions has been towards reducing or eliminating phosphate builders. The replacement of sodium tripolyphosphate as a builder in detergent powders by its most popular zero-phosphate substitute, crystalline sodium aluminosilicate (zeolite), has led to a number of difficulties with the structure and physical properties of the powder. One such problem that has been encountered is the tendency of zeolite-built powders to dispense less well in front-loading automatic washing machines than do their phosphate-built counterparts; a higher proportion of the powder dosed into the machine is left behind in the dispenser, leading to product wastage and clogging. This problem is especially marked at low wash temperatures. The tendency towards poor dispensing has been exacerbated by the recent trend in the detergents industry towards higher bulk density powders. We have now found that the dispensing behaviour of those powders that are especially prone to this problem may be substantially improved by including in the powders low levels of certain paraffin waxes, either via the slurry or by subsequent spray-on. Surprisingly, the incorporation of the materials via the slurry also improves powder structure and raises the bulk density. DEFINITION OF THE INVENITON In a first aspect, the invention comprises a spray-dried detergent powder as defined by claim 1. In a second aspect, the invention provides a process for the preparation of a detergent powder, the process being as defined by claim 7. PRIOR ART FR-A-2 257 680 discloses phosphate containing granular detergent compositions which include a microcrystalline paraffin wax as a foam control agent. It is generally mentioned in this document that suitable waxes appear to be those which can be solubilized by the surfactant employed. Further examples of detergent compositions containing foam control systems that include hydrocarbon waxes are given in EP-A-87 233, EP-A-109 247 and EP-A-206 522 (Unilever); GB 1 492 939, GB-B-2 040 982, EP-A-8 829, EP-A-8 830 and JP-A-56 034797 (Procter & Gamble); DE-A-3 436 194, US 4 590 194 and EP-A-150 386 (Henkel). US 4 196 104 (Procter & Gamble) discloses spraying an antistatic composition comprising a quaternary ammonium compound and a paraffin wax (as dispersion inhibitor) onto detergent base granules. DETAILED DESCRIPTION OF THE INVENTION The first aspect of the invention is a detergent powder prepared at least in part by spray-drying. The composition of the invention may be a fully formulated detergent composition prepared wholly by spray-drying; a spray-dried base to which other ingredients may be admixed to form a finished product; or a finished product of that type, comprising a spray-dried base in admixture with other ingredients. As essential ingredients, the detergent powder of the invention contains at least 5% by weight of one or more anionic and/or nonionic surfactants, from 20 to 80% by weight of crystalline or amorphous aluminosilicate detergency builder, and a specified paraffin wax that influences its dispensing behaviour in a particular manner. The composition of the invention may also contain any of the materials conventionally included in detergent compositions. These are described in more detail below. The surfactant component The total amount of surfactant present in the composition of the invention will generally range from 5 to 40% by weight, more preferably from 10 to 30% by weight and especially from 12 to 20% by weight. These figures are typical for fully formulated detergent compositions, and where a spray-dried base forms only part of such a composition the surfactant content of that base, as a percentage, may of course be higher. The invention relates to compositions containing anionic surfactant. When such powders are prepared by spray-drying, the high-foaming anionic surfactant tends to cause "puffing" (entrainment of air) in the slurry, so that highly porous particles are formed in the spray-drying tower. These particles may be very crisp and free-flowing, but may be of lower bulk density than desired. Surprisingly, the incorporation in the slurry of a paraffin wax, in accordance with the present invention, has been found to result in an increase in bulk density. The amount of anionic surfactant present is at least 5% by weight, and may suitably be in the range of from 5 to 30% by weight, preferably from 5 to 10% by weight, these figures again being based on a fully formulated detergent composition. Anionic surfactants are well known to those skilled in the art. Examples include alkylbenzene sulphonates, particularly sodium linear alkylbenzene sulphonates having an alkyl chain length of C 8 -C 15 ; primary and secondary alkyl sulphates, particularly sodium C 12 -C 15 primary alcohol sulphates; olefin sulphonates; alkane sulphonates; dialkyl sulphosuccinates: and fatty acid ester sulphonates. Preferably, the composition of the invention also contains one or more nonionic surfactants. Nonionic surfactants that may be used include the primary and secondary alcohol ethoxylates, especially the C 12 -C 15 primary and secondary alcohols ethoxylated with an average of from 3 to 20 moles of ethylene oxide per mole of alcohol. The weight ratio of anionic surfactant to nonionic surfactant is preferably at least 0.67:1, more preferably at least 1:1, and most preferably within the range of from 1:1 to 10:1, in order to obtain the optimum detergency and foaming properties appropriate for front-loading automatic washing machines. These ratios of course apply to fully formulated products. A spray-dried base that is to form only part of a product may contain a lower proportion of, or no, nonionic surfactant, the balance of the nonionic surfactant being added after the spray-drying tower. The paraffin wax The characterising feature of the composition of the present invention is the presence of a low level (0.1-6.0% by weight) of a paraffin wax. The hydrophobicity of this material is expressed in terms of its contact angle to water, which must be at least 75°, preferably at least 85°. The melting point of the paraffin wax is also important: it appears that the wax should be solid at ambient temperature but liquid at slurry-processing temperature (generally in the range of from 60 to 100°C). The melting point of the paraffin wax should lie within the range of from 30 to 100°C, preferably from 40 to 80°C, more preferably within the range of from 50 to 60°C. Paraffin oil liquid at ambient temperature has been found to be ineffective in the context of the present invention, and also tends to give wet, sticky powders with unacceptable flow properties. It is also essential that the paraffin wax be substantially insoluble in anionic and nonionic surfactants : the microcrystalline waxes of FR-A-2 257 680 and GB 1 492 939 (Procter & Gamble) are stated to be chosen for their solubility in the surfactant present, and are unsuitable for use in the present invention for that reason as well as for the reason that their melting points are too high. The paraffin wax is preferably present in an amount of from 0.2 to 4% by weight. In a fully formulated product the optimum level for paraffin wax appears to be from 0.3 to 2% by weight. Incorporation of the paraffin wax The composition of the invention is prepared by a process which includes the step of spray-drying an aqueous crutcher slurry. This slurry will normally contain all those desired ingredients sufficiently heat-stable to survive the spray-drying process, notably anionic surfactants, builders, inorganic salts, sodium silicate, Polymers and fluorescers. More heat-sensitive ingredients can be postdosed to, or sprayed onto, the spray-dried base. There are two methods by means of which the paraffin wax characteristic of the invention may be incorporated. It may be included in the slurry, in which case it is preferably used in an amount of from 0.2 to 4.0% by weight, more preferably from 0.3 to 2.0% by weight, based on the final powder including any postdosed ingredients. It may be advantageous to premix the paraffin wax with surfactant, especially nonionic surfactant, before admixture with other slurry ingredients. It has surprisingly been found that incorporation of paraffin wax via the slurry not only improves dispensing behaviour, but also improves powder structure and, when anionic surfactant is present, also raises the bulk density. Flow properties are not detrimentally affected. The second method by which the paraffin wax may be incorporated in a detergent composition of the invention is by spraying it in liquefied form onto the spray-dried powder. If the final product is to include postdosed solid ingredients, for example, sodium perborate, bleach activator granules, enzyme granules or antifoam granules, the paraffin wax should be sprayed on after addition of those ingredients so as to cover the whole powder. If desired, the paraffin wax may be melted and sprayed directly onto the powder. The paraffin wax is then preferably used in an amount of from 2.0 to 6.0% by weight, more preferably from 3.0 to 4.0% by weight. According to a preferred embodiment of the invention, however, the paraffin wax is premixed with nonionic surfactant to form a coating composition which may then be sprayed onto the detergent powder. Lower levels of the paraffin wax, for example, 0.2 to 4.0%, preferably 0.3 to 2.0%, are then found to be effective. The coating composition consists essentially of 2-50% by weight of the paraffin wax and 50-98% by weight of nonionic surfactant. The coating composition desirably contains 8-15% by weight of paraffin wax and 85-92% by weight of nonionic surfactant. The paraffin wax, and if necessary the nonionic surfactant, are melted to form the coating composition, which is applied as a liquid, suitably at a temperature of 40-60 ° C. The coating composition should be substantially free of other ingredients that might interfere with the beneficial effect of the paraffin wax on dispensing. Dispensing behaviour It is an essential feature of the detergent powder of the invention that the incorporation as specified above of a paraffin wax should bring about an improvement in dispensing behaviour. Dispensing is assessed by means of a standard test using a Philips (Trade Mark) AWB 126/7 washing machine using a 100 g powder dose and a water fill of 5 litres at 20°C flowing in over a period of 1 minute. The dry weight of powder remaining in the dispenser, in grams, then represents the weight percentage of powder not dispensed into the machine (the residue). It will be appreciated that this test is stringent, using a low water inlet temperature and flow rate, and a machine with a drawer-type dispenser which is particularly vulnerable to high residues and clogging. According to the invention, the incorporation of the paraffin wax should effect a reduction in the residue of at least 10 percentage points, preferably at least 20 percentage points. For the purposes of comparison, a powder having essentially the same composition but with an inorganic salt (sodium carbonate or sodium sulphate) to make up the difference should be used. Clearly an improvement of this magnitude can only be observed if the control powder exhibits poor dispensing properties. The present invention is therefore especially applicable to powders which, without the paraffin wax, give dispenser residues of at least 10%, more especially at least 20%, by weight. That is especially likely to be the case if the powder is a zero-phosphate composition built with crystalline (zeolite) or amorphous sodium aluminosilicate; if it contains less than 10% sodium silicate; or if it has a bulk density of 450 g/litre or more, preferably 600 g/litre or more. Optional components As indicated previously, the detergent powder of the invention can contain any of the ingredients conventionally present in compositions intended for the washing of fabrics in front-loading automatic washing machines. Examples of such components include inorganic and organic detergency builders, other inorganic salts, bleaches, fluorescers, polymers, lather control agents, enzymes and perfumes. If desired, the powder of the invention may contain one or more soaps of fatty acids, in addition to the non-soap anionic surfactant mentioned above. The powder will also contain one or more detergency builders. The invention is of especial applicability to zero-phosphate powders containing from 20 to 80 % by weight of crystalline (zeolite) or amorphous aluminosilicate. Other supplementary, builders may also be present, for example, polycarboxylate polymers such as polyacrylates, acrylic-maleic copolymers, or acrylic phosphinates; momomeric polycarboxylates such as nitrilotriacetates and ethylene diamine tetraacetates; inorganic salts such as sodium carbonate; and many other materials familiar to the skilled detergent formulator. If desired, the powder of the invention may contain sodium silicate. High levels of silicate can in themselves have a beneficial effect on dispensing, as well as on powder structure and prevention of machine corrosion, but are undesirable in powders containing aluminosilicate because the two components react together to form insoluble siliceous species. The present invention enables the dispensing behaviour of zeolite-built powders to be improved without a corresponding increase in the level of insoluble material. Accordingly, the invention relates to powders containing less that 10% by weight, more especially less than 5% by weight, of sodium silicate. Other materials that may be present in the powder of the invention include fluorescers, antiredeposition agents, inorganic salts such as sodium sulphate, enzymes, lather control agents, bleaches, bleach activators, and bleach stabilisers. These may be included in the spray-dried base powder or postdosed according to their known suitability for undergoing spray-drying processes and their compatibility with other slurry ingredients. The invention is further illustrated by the following non-limiting Examples, in which parts and percentages are by weight unless otherwise stated. EXAMPLES Examples 1 to 4 Zero-phosphate detergent base powders containing various amounts of paraffin wax (melting point 52-54°C) or paraffin oil were prepared, by slurry-making and spray-drying, to the following nominal composition: Parts Sodium linear alkylbenzene sulphonate 9.0 Nonionic surfactant 1.0 Zeolite (anhydrous) 24.0 Acrylic/maleic copolymer 4.0 Sodium carbonate 2.0 Minor ingredients 0.83 Moisture 10.0 Paraffin wax 0, 0.25, 0.5, 1.0, 2.0 or paraffin oil 1.0 Total 51-53 parts To the base powder were postdosed the following ingredients: Parts Burkeite/nonionic surfactant adjunct 13.0 Sodium perborate monohydrate 8.0 TAED granules 3.0 Dequest 0.2 Enzyme granules 0.6 Lather control granules 3.0 Sodium alkaline silicate 5.0 Sodium carbonate 5.4 Sodium sulphate to 100.0 The following table shows the six compositions prepared, their dispenser residues measured in accordance with the defined test given above, and their powder properties: A 1 2 3 4 B Paraffin wax 0 0.25 0.5 1.0 2.0 0 Paraffin oil 0 0 0 0 0 1.0 Sodium sulphate 11.65 11.32 10.87 10.62 9.82 10.62 Dispenser residue 42 20 0 0 0 33 Bulk density (g/l) 680 609 755 724 685 Dynamic flow rate 109 111 109 109 90 Compressibility (%) 34 16 24 25 21 It will be noted that even the low level of 0.25 parts of paraffin wax effected a substantial improvement in dispensing behaviour, and no dispenser residues at all were observed when higher levels of paraffin wax were used. The higher levels also brought about increases in bulk density, and improvements in powder structure (compressibility) were observed at all levels. The dispensing and powder properties of the spray-dried base powders of Examples 2-4 and Comparative Example A were also examined. The full formulations of these base powders were as follows: A 2 3 4 Sodium LAS 17.96 17.67 17.59 17.30 Nonionic surfactant 1.99 1.96 1.95 1.92 Zeolite (anhydrous) 47.89 47.13 46.89 46.17 Copolymer 7.89 7.85 7.82 7.70 Sodium carbonate 3.99 3.93 3.91 3.85 Minor ingredients 1.66 1.63 1.62 1.60 Moisture 18.53 18.85 18.27 17.61 Paraffin wax 0 0.98 1.9 3.85 Total 100.0 100.0 100.0 100.0 The full formulation of the base powder of Comparative Example B was identical to that of Example 3, except that the paraffin wax was replaced by paraffin oil. The dispensing residues of the base powders, determined by the test described above, and their powder properties were as follows: A 2 3 4 Dispenser residue (%) 46 0 0 0 Bulk density (g/l) 540 585 525 586 DFR (ml/s) 108 115 117 109 Compressibility (% v/v) 36 29 31 30 The dispenser residue of the base powder of Comparative Example B was 15%. Example 5 Zero-phosphate detergent powders similar to those of Examples 1-4 but containing a higher level of anionic surfactant were prepared, to the following formulations (in weight %): Spray-dried base powder C 5 Sodium linear alkylbenzene sulphonate 11.1 11.1 Nonionic surfactant 1.2 1.2 Zeolite (anhydrous) 24.0 24.0 Acrylic/maleic copolymer 4.0 4.0 Sodium carbonate 2.0 2.0 Sodium alkaline silicate 0.5 0.5 Sodium sulphate 1.3 1.3 Minor ingredients 0.83 0.83 Paraffin wax (m.pt. 52-54°C) 0 1.0 Moisture 9.50 9.95 Postdosed ingredients Burkeite/nonionic surfactant adjunct 16.09 16.09 Sodium perborate monohydrate 8.0 8.0 TAED granules 3.0 3.0 Dequest 0.75 0.75 Enzyme granules 0.5 0.5 Lather control granules 2.4 2.4 Sodium carbonate 3.27 3.27 Sodium sulphate 11.43 9.98 Total 100.0 100.0 The dispensing and powder properties of these products were as follows: C 5 Dispenser residue (%): of base 80 0 of whole product 55 3 Bulk density (g/l) 660 648 Dynamic flow rate (ml/s) 91 97 Compressibility (% v/v) 10 17 With this product, which already exhibited a very high bulk density and excellent powder properties, no further improvement in these respects resulted from the inclusion of paraffin wax in the base powder. A marked improvement in dispensing behaviour was, however, observed. Examples 6 to 8 A zero-phosphate detergent base powder similar to that of Comparative Example A was prepared, by slurry-making and spray-drying, to the following formulation: Parts % Sodium linear alkylbenzene sulphonate 9.0 18.37 Nonionic surfactant 1.0 2.04 Zeolite (anhydrous) 24.0 48.98 Acrylic/maleic copolymer 4.0 8.16 Sodium carbonate 2.0 4.08 Minor ingredients 0.83 1.69 Moisture 8.17 16.68 Samples of this base powder were post-sprayed with molten paraffin wax (melting point 52-54°C) in various amounts, as shown in the table below. The dispensing properties of the samples, and of the base powder without wax spray-on (Comparative Example D), are also shown in the table. D 6 7 8 Paraffin wax sprayed on: parts 0 0.3 1.0 2.0 % 0 0.61 2.0 3.92 Dispenser residue (%) 37 12 10 1 It will be seen that the sprayed-on paraffin wax effected a substantial reduction in dispenser residues: at the 2 parts (3.92%) level these were negligibly low. Examples 9 to 11 The procedure of Examples 6 to 8 was repeated, but this time the paraffin wax was melted and dispersed in liquid nonionic surfactant, and the coating composition thus obtained was sprayed onto the base powder. The three coating compositions used were as follows, the parts being on the same basis as those of the base powder D, and the percentages being based on the coating composition: Parts % Example 9: Paraffin wax 0.3 9.1 Nonionic surfactant 3.0 90.9 Example 10: Paraffin wax 1.0 25.0 Nonionic surfactant 3.0 75.0 Example 11: Paraffin wax 2.0 40.0 Nonionic surfactant 3.0 60.0 Dispensing and powder properties were as follows: D 9 10 11 Wax/nonionic spray-on: Total (parts) 0 3.3 4.0 5.0 Total (% on base powder) 0 6.31 7.55 9.26 Dispenser residue (%) 37 0 0 0 Bulk density (g/ml) 450 512 Dynamic flow rate (ml/s) 108 105 Compressibility (% v/v) 27 21 Comparison with Examples 6 to 8 shows that when the paraffin wax was pre-dispersed in nonionic surfactant it was effective at a lower level in improving dispensing behaviour. Bulk density and compressibility were improved even at the low level of 0.3 parts (0.61%) of paraffin wax.

Claims: A spray-dried detergent powder being substantially free from inorganic phosphate and comprising at least 5% by weight of one or more anionic surfactants, from 20 to 80% by weight of crystalline or amorphous aluminosilicate detergency builder, no more than 10% by weight of alkali metal silicate, and from 0.1 to 6.0% by weight of a paraffin wax which is water-insoluble and substantially insoluble in anionic and nonionic surfactants and has a melting point within the range of from 30 to 100°C and a contact angle to water of at least 75°, characterised in that the powder is obtainable by a process including the step of spray-drying an aqueous slurry of detergent ingredients, the paraffin wax being either incorporated in the slurry or sprayed onto the spray-dried powder and in that the powder is substantially free of paraffin oil. A powder as claimed in claim 1, characterised in that the paraffin wax has a contact angle to water of at least 85°. A powder as claimed in claim 1 or claim 2, characterised in that the paraffin wax has a melting point within the range of from 40 to 80°C. A powder as claimed in any preceding claim, characterised in that the amount of paraffin wax incorporated in the powder is within the range of from 0.2 to 4.0% by weight. A powder as claimed in any preceding claim, characterised in that it has a bulk density of at least 450 g/litre. A powder as claimed in claim 5, characterised in that it has a bulk density of at least 600 g/litre. A process for the preparation of a detergent powder being substantially free from inorganic phosphate and comprising at least 5% by weight of one or more anionic surfactants, from 20 to 80% by weight of crystalline or amorphous aluminosilicate detergency builder no more than 10% by weight of alkalimetal silicate and 0.1 to 6.0% by weight based on the powder of a paraffin wax which is water-insoluble and substantially insoluble in anionic and nonionic surfactants and has a melting point within the range of from 30 to 100°C and a contact angle to water of at least 75°, the process including the step of spray-drying an aqueous slurry, characterised in that the paraffin wax is either incorporated in the slurry or sprayed onto the spray-dried powder and in that the powder is substantially free of paraffin oil. A process as claimed in claim 7, characterised in that the paraffin wax is incorporated via the slurry, in an amount of from 0.2 to 4.0% by weight based on the powder. A process as claimed in claim 8, characterised in that the paraffin wax is premixed with nonionic surfactant before admixture with other slurry ingredients. A process as claimed in claim 7, characterised in that the paraffin wax in liquefied form is sprayed onto the spray-dried powder, in an amount of from 0.2 to 4.0% by weight on the powder thus obtained. A process as claimed in claim 10, characterised in that it incorporates spraying onto the powder a coating composition consisting essentially of: (i) from 2 to 50% by weight of the paraffin wax dispersed in (ii) from 50 to 98% by weight of nonionic surfactant, the percentages being on the coating composition. A process as claimed in claim 11, characterised in that the coating composition consists essentially of from 5 to 30% by weight of paraffin wax and from 70 to 95% by weight of nonionic surfactant. A process as claimed in claim 12, characterised in that the coating composition consists essentially of from 8 to 15% by weight of paraffin wax and from 85 to 92% by weight of nonionic surfactant.

Inventors: APPEL PETER WILLEM, KIELMAN HENDRIK SIMON, LIEM SEENG DJIANG, WAAS MARCO, APPEL, PETER WILLEM, KIELMAN, HENDRIK SIMON, LIEM, SEENG DJIANG, WAAS, MARCO
Applicants: UNILEVER NV, UNILEVER PLC, UNILEVER N.V.
Application year: 1989
Main classification: C11D3
IPC codes: C11D17, C11D3, C11D11