GB2063289A - Low phosphate spray-dried powders - Google Patents

Abstract

Spray-dried detergent powders containing less than 20% by weight of the composition of a phosphate salt, and more than 20% by weight of anionic synthetic detergent compound, can be rendered crisp and free-flowing by addition of bentonite or kaolin clays to the crutcher slurry.

Description

SPECIFICATION Process for preparing spray-dried powders This invention relates to detergent powders and to processes for making them.

Sodium tripolyphosphate, although an extremely effective detergency builder, is becoming increasingly expensive and has become a target for legislation designed to protect the environment. For these reasons there has recently been a move towards detergent powders containing lower levels of phosphates in generai and sodium tripolyphosphate in particular than were used ten years ago.

One of the difficulties inherent in such detergent powders containing only low levels of sodium tripolyphosphate is that it is difficult to prepare crisp, free-flowing powders by the normal spray-drying process. This problem is exacerbated if a relativel high proportion of detergent active compund is present.

We have now discovered that crisp, free-flowing spray-dried detergent powders can be prepared from aqueous detergent slurries containing relatively low levels of sodium tripolyphosphate and relatively high levels of detergent active compound, if bentonite or kaolin is included in the slurry.

Bentonite, which is a colloidal clay formed by weathering of volcanic ash has been suggested for use in detergent compositions previously. It has detergent properties and consequently has been suggested as an auxiliary detergent-active compound during times of oil and fat shortages. It is mentioned as being an inorganic builder and a filler in the standard work on detergents, Schwarz and Perry's "Surface Active Agents" and it has recently been suggested for forming an adjunct with liquid nonionic surfactants in US Patent No. 3,849,327. Certain of the examples in British Patent No. 1 485,31 6 also contain bentonite, although it is not said what the purpose of this is.

Kaolin, or china clay, is essentially a hydrated aluminium silicate. It is believed to be derived from felspar. Like bentonite, it has been suggested for use in detergent compositions, for example in United States Patent No. 3,983,078 and United States Patent No. 4,166,039, where it is treated as an equivalent of bentonite.

In accordance with the present invention there is provided a crisp, free-flowing detergent powder comprising (i) a detergent active component consisting essentially of an anionic detergent active compound in an amount greater than about 20% by weight of the composition, (ii) a detergency builder of which less than 20% by weight of the composition is a phosphate salt, and (iii) from 1 to 1 5% by weight of bentonite or kaolin.

In a second aspect, the invention provides a process for preparing a crisp, free-flowing detergent powder which comprises forming an aqueous slurry comprising a detergent active component consisting essentially of an anionic detergent active compound in an amount greater than 13% by weight, a detergency builder of which less than 13% by weight, based on the weight of the slurry, is a phosphate salt and from 0.610% by weight of bentonite or kaolin.

Bentonite is essentially a clay and so has a lattice structure containing exchangeable cations. We prefer to use bentonites in which the exchangeable cation is sodium and/or calcium.

The nature of the anionic detergent active compound is not criticai. The compound can be any surface-active material which is suitable for use in detergent formulations. Examples of such materials are primary and secondary alkyl sulphate salts, secondary alkane sulphonate salts, olefine sulphonate salts and alkylaryl sulphonate salts, especially the sodium salts of these compounds. Mixtures of these compounds can also be used, but mixtures of anionic detergent active compounds with nonionic surfactants are excluded from the scope of the invention.

As already stated, the anionic detergent active compound should be present in the detergent compositions of the invention in an amount greater than about 20% by weight of the composition, desirably about 2030% by weight. Compositions containing less anionic detergent active compound than about 20% are insufficiently detersive at low temperatures in the absence of large amounts of phosphate and compositions containing more than about 30% of anionic detergent active component are difficult to process and are also too costly to be commercially viable.

Whilst the nature of the detergency builder is not critical, it will be preferable, because of the absence of large quantities of phosphate, to use builder components which are relatively efficient. As has been said, the maximum level of phosphate, whether present as orthophosphate, pyrophosphate or tripolyphosphate, is 20% by weight of the composition, as when using higher amounts of phosphate salt than this it is possible to prepare satisfactory spray-dried powders without the use of bentonite.

Provided that this iimitation is complied with, then the buider may include any of the compounds which are suitable for use as detergency builders. Examples of these include alkali metal carbonates, especially sodium carbonate, alkyl metal amine carboxylates, such as sodium nitrilotriacetate and sodium ethylenediamine tetraacetate, alkali metal ether carboxylates, such as sodium oxydiacetate, sodium carboxymethyloxysuccinate, sodium carboxymethyloxymalonate and homologues thereof, alkali metal citrates, alkali metal mellitates and salts of polymeric carboxylic acids, such as sodium polymaleate, copolyethylenemaleate, polyitaconate and polyacrylate. When sodium carbonate is used as a detergency builder, it is advantageous to have present some calcium carbonate having a surface area of at least about 10 m2/g, as described in UK Patent 1,437,950.

Another type of detergency builder which can be used, either alone or in admixture with other builders, is a cation exchange material, especially a sodium aluminosilicate such as described in UK Patent 1,429,143 or in Netherlands Patent Application 7,403,381. Preferred materials of this type have the formula (Na2O)0711 A12 3(Si 2)1.3--3.3 and may be amorphous or crystalline, with some bound water usually in an amount of about 1030% depending on the drying conditions used. Such sodium aluminosilicate materials should, of course, be very finely divided so as to minimise deposition on the fabrics during washing.

The total amount of the detergency builder which is used in the composition as a whole is normally from about 10% up to about 60% by weight of the composition, preferably about 15% to about 50%, and the ratio by weight of the detergency builders to the detergent active compounds which are used is generally from about 3:1 to about 1:2 parts by weight.

The detergent compositions of the invention may also include any of the conventional optional additives in the amounts usually employed in detergent compositions. Examples of these additives include lather controllers, anti-redeposition agents such as sodium carboxymethylcellulose, oxygenreleasing bleaching agents such as sodium perborate and sodium percarbonate, per-acid bleach precursors such as tetraacetylethylenediamine, chlorine-releasing bleaching agents such as trichloroisocyanuric acid and alkali metal salts of dichloroisocyanuric acid, fabric softening agents such as quaternary ammonium salts, anti-ashing aids, starches, slurry stabilisers such as copolyethylenemaleic anhydride and copolyvinylmethylether-maleic anhydride, usually in salt form, inorganic salts such as sodium silicates and sodium sulphate and, usually present in very minor amounts, fluorescent agents, perfumes, enzymes such as proteases and amylases, germicides and colourants. The detergent compositions usually have an alkaline pH, generally in the region of pH 9-11, which is achieved by the presence of alkaline salts, especially sodium silicates such as the meta-, neutral or alkaline silicates, preferably at levels up to about 15% by weight.

The invention is illustrated by the following Examples in which parts and percentages are by weight except where otherwise indicated.

EXAMPLE 1 Three crutcher slurries of the following formulations were spray-dried: % by weight A B C Sodium dodecylbenzene sulphonate 19.0 19.0 19.0 Sodium tripolyphosphate 15.0 15.0 15.0 Sodium silicate 12.0 12.0 12.0 Sodium carboxymethyl cellulose 0.6 0.6 0.6 Sodium sulphate 45.4 40.4 35.4 Bentonite nil 5.0 10.0 Water and minor components to 100.0 100.0 100.0 The flow rate of each of the resulting powders was measured by a standard technique with the results shown in Table 1.

TABLE 1 Powder Dynamic Flow Rate (ml/sec) A nil B 80 C 80 EXAMPLE 2 In a second experiment three further crutcher slurries were prepared and spray-dried. The slurries had the following formulation: % by weight D E F Sodium dodecylbenzene sulphonate 20.0 20.0 20.0 Sodium carbonate 56.0 54.0 46.0 Sodium silicate 10.0 10.0 10.0 Sodium carboxymethyl cellulose 0.6 0.6 0.6 Sodium sulphate and minor components nil 4.4 4.4 Bentonite nil 2.0 10.0 Water -balance to 100- The resultant spray-dried powders were packed into non-laminated cardboard cartons and stored at a temperature of 280C and at 70% relative humidity. After a storage period of four weeks, the cartons were opened and an examination was made of the condition of the powder.

Powder D was almost totally caked and felt very soft. Powder F showed little or no caking and felt crisp, and Powder E was half-caked.

EXAMPLE 3 In a third experiment four further crutcher slurries were prepared and spray-dried. The slurries had the following formulations: % by weight G H I J Sodium dodecylbenzene sulphonate 28.0 28.0 28.0 28.0 Sodium orthophosphate 16.0 16.0 16.0 16.0 Sodium silicate 10.01 10.0 10.0 10.0 Sodium carbonate 20.0 20.0 20.0 20.0 Sodium sulphate 20.0 20.0 20.0 15.0 Kaolin 0 5.0 10.0 0 Bentonite O 0 0 5.0 Water and minor components to 100 100 100 100 Spray-dried powders H, I and J containing bentonite or kaolin were noticeably crisper than the control powder G. In a test to determine the cohesiveness of the powders, a sample of each was placed in turn in a cylindrical vessel having removeable side walls. The powder was compressed by placing a weight on the surface of the column, and the weight and the side walls of the vessel were then removed leaving a free-standing column of powder. Weights were then placed on the column of powder until collapse occurred.

The results are shown in the table, the high loading accepted by powder G, the control powder without either kaolin or bentonite, showing the cohesiveness of the powder.

TABLE 2 Cohesion Value (kg) Powder G 5.0 Powder H 2.0 Powdery 1.0 Powder J 3.0 The increased crispness, or lack of cohesion, in the powders of the invention is evident from the table.

The above Examples demonstrate the benefit in respect of flow and caking properties which is derived from the use of bentonite in accordance with this invention.

Claims (8)

1. A process for preparing a crisp, free-flowing detergent powder which comprises forming an aqueous slurry comprising a detergent active component consisting essentially of an anionic detergent active compound in an amount greater than 13% by weight, a detergency builder of which less than 13% by weight, based on the weight of the slurry, is a phosphate salt and from 0.6 to 10% by weight of bentonite or kaolin, and spray-drying it.

2. A process according to claim 1 in which the slurry comprises bentonite.

3. A process according to claim 1 or claim 2 wherein the slurry comprises 2030% by weight of the anionic detergent active compound.

4. A crisp, free-flowing detergent powder comprising (i) a detergent active component consisting essentially of an anionic detergent active compound in an amount greater than about 20% by weight of the composition, (ii) a detergency builder of which less than 20% by weight of the composition is a phosphate salt, and (iii) from 1 to 15% by weight of bentonite or kaolin.

5. A detergent powder according to claim 4 comprising from 1 to 15% by weight of bentonite.

6. A detergent powder according to claim 4 or claim 5 comprising from 20 to 30% by weight of the anionic detergent active component.

7. A process in accordance with claim 1 substantially as hereinbefore described in any one of the examples.

8. A detergent powder in accordance with claim 4 substantially as hereinbefore described in any one of the Examples.