EP0772671A1

EP0772671A1 - Method for preparing co-granules, co-granules thus obtained and use thereof as a component in detergent compositions

Info

Publication number: EP0772671A1
Application number: EP95926948A
Authority: EP
Inventors: Theo Jan Osinga
Original assignee: Joseph Crosfield and Sons Ltd; Crosfield Ltd
Current assignee: Ineos Silicas Ltd
Priority date: 1994-07-19
Filing date: 1995-07-14
Publication date: 1997-05-14
Anticipated expiration: 2015-07-14
Also published as: EP0772671B1; GB9414576D0; ATE248214T1; DE69531621D1; AU3115095A; WO1996002621A1

Abstract

Method for preparing co-granules in particular for a diswashing detergent composition, at least comprising a salt of a di-, tri- or tetracarboxylic acid and an inorganic salt, which method comprises preparing a solution or a slurry of the ingredients, drying the mixture, compacting the dried product, and breaking up and sieving the compacted product, co-granules obtainable by said method, and detergent composition comprising such co-granules.

Description

Method for preparing co-granules, co-granules thus obtained and use thereof as a component in detergent compositions.

The present invention in the first place relates to a method for preparing co-granules, which are useful in detergent compositions. More particularly such co-granules are suitable for automatic dishwashing compositions.

The term "granule" is to be interpreted broadly and is intended to comprise various particulate forms such as granulate, coarse powder, tablets and noodles. Dishwashing compositions frequently consist of granules of one particular inorganic compound such as e.g. alkali silicate and these compositions often contain the other ingredients in the form of different particles e.g. of organic compounds etc. The granules, frequently silicate granules often dissolve only with difficulty. They lead to the formation of fines (dust) . Moreover segregation of different types of granular components (e.g. bleach system and enzymes or other usual ingredients) can take place. The problems are aggravated by the fact that silicate granules having a molar ratio Si0₂/Na₂0 between 1.8 and 3.0 and a moisture content of below about 22% by weight dissolve only with considerable difficulty. Moreover, alkali silicate granules with ahomogeneous distribution ofmoisture are difficult to obtain. Usually less moisture is present in the outer skin than in the inside, which is a consequence of drying and which reduces solubility during use.

Preparation of granules of builders e.g. phosphate replacing builders like di-, tri- or tetracarboxylic acid is difficult and therefor relatively expensive.

In this respect mention is made of EP-A-0574 685 (Haarmann & Reimer Corp.) which relates to a method for the production of detergent builder formulations comprising granules of citric acid or an alkali metal salt thereof in combination with a detergent builder. Citric acid or a salt thereof is spray granulated from its partially purified fermentation broth in order to form free flowing granules. Detergent builders may be added to the fermentation broth or introduced during spray granulation in order to form granules which include such detergent builders.

Another method for preparing co-granules useful in detergent compositions is known inter alia from EP-A-0 421 664 (Rohm and Haas Company) disclosing a method for preparing a polymer containing granulate containing 20% by weight of polymer and at least 20% by weight of a water soluble inorganic compound. Such compounds are preferably sulphates, carbonates or silicates. Also other phosphate replacing builders may be present such as zeolites, carbonates, nitrilotriacetic acid, citric acid, tartaric acid, salts there of, phosphonates etc. The examples disclose granules containing polymer and sodium sulphate or sodium carbonate.

The object of the present invention is to provide a method for preparing co-granules having a good solubility in water, giving less fines during handling, having a more even distribution of moisture, and preventing segregation of at least those ingredients included in the co-granules, which can be conveniently prepared.

According to the invention this object is achieved by amethod for preparing co-granules, at least comprising a salt of a di-, tri- or tetracarboxylic acid and an inorganic salt, which process comprises preparing a solution or a slurry of the ingredients, drying themixture and compacting the dryproduct.

Usually a slurry is prepared in water and the mixture is dried by means of suitable drying techniques, like a turbine dryer e.g. a Turbogranulation dryer ex. Vomm-Turbo Technology, VOMM IMPIANTI E PROCESSI S.r.l., Milan, Italy. In EP-A-0 526 978 it is disclosed that silicates can be simultaneously dried and granulated in this dryer. However, this dryer is less suited for the combined drying and granulation to produce co-granules containing substantial quantities of organic ingredients in conjunction with silicate. Due to the high attrition between the rotating blades and the film formed on the wall during the granulation phase, local overheating can cause partial decomposition of the organic ingredients, leading to (local-) coloring.

Drying can also conveniently be achieved by spray drying the slurry by a conventional technique using a spray tower in which the slurry is atomized and dried in a hot air stream. The conditions in the spray tower, when drying silicate or mixtures, containing silicate can be controlled in such a manner, that the bulk density, the particle size and shape can be optimised.

In order to achieve maximum solubility it is preferred to produce a powder product consisting of either small particles

(below 100 microns) or hollow spheres with a particle size up to approximately 400 micron. After drying the resulting powder can be granulated, optionally after milling in a granulation process, e.g. using a Lδdige plow share mixer. For granulation usually a small amount of moisture is added.

The powders obtained in a turbine dryer generally have a wider particle size distribution as part of the product is gathering at the wall creating larger particles. Furthermore it will be very difficult to produce hollow spherical particles in a turbine dryer. Hollowparticles havingbetter accessability and consequently better solubility.

Furthermore powder particles obtained in a turbine dryer are less homogeneously dried as a result of their larger particles being more effectively dried at the outside and as a result of the difference in residence time betweenparticles remaining in the gas stream and those sticking on the (heated) wall of the dryer .

Consequently fluidized bed drying results in a more even distribution of moisture and in better accessable particles.

It is also possible to spray the slurry onto fine particles while drying to form gradually growing granules. This can be performed in e.g. an AGT-unit for continuous drying and granulationexGlatt-GmbH/Process Technology, Binzen, Lδrrach, Germany.

Another possibility is to spray the slurry in a rotary drum granulator onto fines building up coarser particles followed by, or in conjunction with drying. The spray-on techniques lead to granules with a homogenous distribution of moisture and consequently a better solubility.

Such granules however comprise a relatively poor attrition resistance and provide a considerable dust problem during handling thereof. Further disadvantages of such processes are that it is extremely difficult to avoid caking of the product leading to large lumps. These processes also lead to more massive particles with less homogeneous distribution of the residual moisture, leading to worse dissolution.

If however, according to the invention the dried powder or the dried granulated product is subjected to a compacting treatment, an excellent product can be obtained, which shows no dust problem as a consequence of the high attrition resistance with a more homogeneous distribution of moisture, minimising the risk of segregation in the detergent compositions and in which the use of separate builders can be avoided. The product obtained shows no dust problems as a consequence of the high attrition resistance and also has a relatively high bulk density. Preferably compaction is performed at a temperature between 0 and 90°C and more preferably between 20 and 50 °C. The pressure depends on the method of compaction, i.e. the device used and the material which is to be compacted.

In a preferred embodiment the moisture content of the dried product before compaction is adjusted to at least 5-25% (w/w) , which further improves the bulk density and attrition resistance of the end product.

Compacting per se is known in the art. In this respect reference is made to US-A-3 875 282 (Stauffer) , US-A-3 931 036 (Philadelphia Quartz) and US-A-2 463 680 ( yandotte) .

Compacting can be performed by a number of methods, however for the present method it is preferred that compaction is performed by passing the dry mixture through rollers forming a film. Such a film will expediently have a thickness of 1-10 mm. Compaction can also expediently be performed by making tablets.

Compaction can be carried out between 2 rollers in a continuous process as offered by the firmAlexanderwerke AG in Remscheid, Germany or in a tabletting operation.

The effectiveness of the compaction process depends on the pressure exerted on the powder layer/film and the temperature.

In anAlexanderwerke unit, the pressure is exertedhydrolically on one of the rollers. The powder is pressed through the rollers and the dosing rate determines the thickness of the film, which is normally a few millimeters only. The minimum pressure needed to granulate the powders in a standard

Alexanderwerke unit having rollers with a diameter of 48 cm and a length of 26 cm is about 130 bar. The maximum pressure the equipment tolerates is slightly above 200 bar. The temperature is controlled by internal cooling of the rollers. The temperature range that can be used is between 0 and 80% and preferably 20-50°C. To provide granules with the desired particle size it is preferred to break up the compacted product and to sieve.

Advantageously the fines resulting from said sieve operation are returned to the dried product before compaction and the resulting oversize particles are returned to the breaking step. Although it is also possible to return the fines to the starting slurry. The oversize particles can advantageously be returned to the breaking operation.

The salt of a di-, tri- or tetracarboxylic acid is particularly an alkali metal salt of an acid like citric acid, mellitic acid, oxydisuccinic acid, carboxymethoxysuccinic acid, malonic acid, dipicolinic acid, alkenyl succinic acid etc. Part of the di-, tri- and tetracarboxylic acid e.g.30% can be replaced by a lower hydroxymonocarboxylic acid e.g. lactic acid.

In a preferred embodiment of the invention the organic salt comprises an alkali metal salt of a di-, tri- or tetracarboxylic acid. Partial salts of the carboxylic acid in which one or more of the hydrogen ions of the carboxylic groups are replaced by metal ions are particularly useful. Especially sodium and potassium salts can be used with good results for the purpose of this invention. Potassium salts are sometimes preferred because of their higher solubility. The use of alkali metal citrate, especially sodium citrate in the co-granules according to the present invention is preferred. The use of sodium oxydisuccinate is also preferred.

The inorganic salt of the co-granules comprise preferably an alkali metal silicate. The use of sodium silicate with a Si0₂/Na₂0 molar ratio of 1.0 to 3.3, preferably 1.8 to 2.8 is particularly recommended. Alkali metal disilicates, in particular sodium disilicate is used with special advantage.

In another preferred embodiment of the invention the co- granules further comprise at least one polymeric compound being either an acid and/or a salt of a polycarboxylic acid polymer or a polypeptide. Suitable polycarboxylic acid polymers comprise e.g. awater-soluble homopolymer or copolymerhaving a molecular weight of at least 500. It may be derived from a monocarboxylic acid or from a di-, tri- or polycarboxylic acid. The polymer will normally be used in the form of its water-soluble alkali metal salt form. One group of polymer materials found to be of value comprises homopolymers derived from a monomer of the formula:

COOM R2

whereinRj is hydrogen, hydroxyl, C'-C alkyl or alkoxy, acetoxy, or -CH₂COOM; R² is hydrogen, C^l-C* alkyl or -COOM and M is an alkalimetal. Examples of this group include the sodium and potassiumsalts of polyacrylic, polymethacrylic, polyitaconic, polymaleic and polyhydroxyacrylic acids and also the hydrolysis products of the corresponding polymerised acid anhydrides. Thus the polymer obtained by hydrolysis of maleic anhydride falls within this group. Suitable polypeptides which can be incorporated in the co-granules according to the present invention are e.g. polyaspertate and polyglutamate.

A second group of suitable polymeric materials comprises the copolymers of two or more carboxylic monomers of the above formula. Examples of this group include the sodium and potassium salts of copolymers of maleic anhydride with acrylic acid, methacrylic acid, crotonic acids, itaconic acid and its anhydride and/or aconitic acid. A third group of suitable polymeric materials comprises the copolymers of one carboxylic monomer of the above formula and two or more non-carboxylic acid monomers such as ethylene, propylene, styrene, alpha- methylstyrene, acrylonitrile, acrylamide, vinylacetate, methylvinylketone, acrolein and esters of carboxylic acid monomers such as ethyl acrylate and methacrylate.

It is also advantageous if the co-granule further comprises at least one inorganic salt of the group consisting of alkali metal tripolyphosphate, alkali metal carbonate/bicarbo- nate/sesquicarbonate, alkali metal sulphate. (One of the advantages of incorporating such an inorganic salt is that it increases the solubility of the co-granule because these salts dissolve rapidly and thereby convert the co-granule to an open sponge-like structure so that the surface area of the granule is increased which leads to an increase of the solubility of the remaining solid material consisting especially of silicate) .

Most of the salts also act as a builder reinforcing detergent activity. Non-phosphate inorganic salts as various carbonates especiallyalkali metal carbonate/bicarbonate/sesquicarbonate are preferred. In the co-granule the inorganic salts are usually present in the form of their lower stable hydrate(s) .

In the method according to the invention the solution or slurry is preferably prepared by adding di-, tri- or tetracarboxylic acid to a solution containing the inorganic salt, neutralising the carboxylic acid with alkali, optionally having further ingredients as to obtain a solution or slurry with a water content of 30-60 % (w/w) , which solution or slurry is subsequently dried and compacted. The various ingredients of the solution or slurry can be used in the form of solid dry or hydrated forms, to which water is added.

An other aspect of the invention provides co-granules obtainable by the method according to the invention.

Preferably said co-granules have a bulk density of at least 700 g/dm³, morepreferably above 800 g/dm³, andmostpreferably a bulk density between 900 g/dm³ and 1200 g/dm³. High bulk densities are desirable at present, to be able to provide final detergents compositions with a relatively high specific weight.

The particle size of the co-granules according to the present invention is not critical however, it is preferred that the co-granules have an average particle size of 100 to 1500 micrometer, more preferably an average particle size of 400-900 micrometer and a Rosen Rammler N-value above 2.5. Particle size determination and the definition and determination of the Rosen Rammler N-value is described in detail in "Small Particle Statistics" by Herdan, C; second revised edition; Butterworth, London 1960, in particular page 86-101. Graph paper according to DIN 1171 (new) is often used to determine the N-value.

Preferred compositions of the co-granules according to the invention are:

5-90% (w.w.) alkali metal silicate;

5-90% (w.w.) alkali metal salt of di-, tri- or tetracarboxylic acid;

0-20% (w.w.) polymer;

0-40% (w.w.) alkali metal tripolyphosphate; 0-40% (w.w.) alkali metal (bi)carbonate, or sesquicarbonate;

0-10% (w.w.) organic phosphonate;

0-60% (w.w.) alkali metal sulphate;

5-25% (w.w.) moisture.

2_^

5-95% (w.w.) alkali metal silicate;

0-60% (w.w.) alkali metal salt of di-, tri- or tetracarboxylic acid; 5-60% (w.w.) polymer; 0-40% (w.w.) alkali metal (bi) carbonate; 5-25% (w.w.) moisture. The organic phosphonates which can be present in the co- granules according to the present invention are e.g. the various organic polyphosphonates, e.g. of the Dequest^® range, which are especially added to phosphate-free machine dishwashing compositions. A drawback of these polymers is that some of them are not quite biodegradable and therefore environmentally less acceptable. Therefore some of the polyphosphonates, whilst being effective, are less acceptable as being P-containing products.

3__,

20-50% (w.w.) alkali metal silicate,-

40-75% (w.w.) alkali metal salt of di-, tri- or tetracarboxylic acid; 1-9% (w.w.) polymer;

1-36% (w.w.) alkali metal tripolyphosphate,-

1-36% (w.w.) alkali metal (bi)carbonate, or sesquicarbonate,-

0-37% (w.w.) alkali metal sulphate,-

0-9% (w.w.) organic phosphonate,- 0-5% (w.w.) of minor ingredients,-

5-25% (w.w.) moisture.

Under minor ingredients are here to be understood compounds like, the well-known enzyme stabilizers such as the polyalcohols, e.g. glycerol, and borax; anti-scaling agents,^• crystal-growth inhibitors, threshold agents,- thickening agents,- perfumes and dyestuffs and the like. Also a small amount of low- to non-foaming nonionic surfactant, which includes any alkoxylated nonionic surface-active agent wherein the alkoxy moiety is selected from the group consisting of ethylene oxide, propylene oxide and mixtures thereof, is preferably used to improve the detergency and to suppress excessive foaming due to some protein soil. However, an excessive proportion of nonionic surfactant should be avoided. Normally, an amount of 0.1 to 5% by weight, preferably from 0.5 to 4% by weight, is quite sufficient. Examples of suitable nonionic surfactants for use in the invention are the low- to non-foaming ethoxylated straight- chain alcohols of the Plurafac^® RA series, supplied by the Eurane Company; of the Lutensol^® LF series, supplied by the BASF Company and of the Triton^® DF series, supplied by the Rohm & Haas Company.

The present invention in a third aspect provides a detergent composition comprising co-granules according to the invention. Preferably such as detergent composition comprises at least 40% of co-granules according to the invention and a bleach system and/or an enzyme system.

The bleach system and/or an enzyme system is then usually added in the form of separate particles which may have the same particle size distribution as the co-granules; also it is usually advantageous if the bulk density of these particles is comparable to that of the co-granules.

Preferably the detergent composition consists for at least 50% of co-granules according to the invention, and less than 30% of a bleach system and an enzyme system.

Enzymes are used for many purposes in various fields where biochemical reactions occur. In general, an enzyme can be described as a catalyst capable of permitting a biochemical reaction to quickly occur and can be classified according to the type of reaction they catalyze. Enzymes are characterized by a high specificity, that is to say, each enzyme can catalyze a single reaction of one substance or a very small number of closely related substances.

Examples of enzymes suitable for use in the cleaning compositions of this invention include lipases, peptidases, amylases (amylolytic enzymes) and others whichdegrade, alter or facilitate the degradation or alteration of biochemical soils and stains encountered in cleansing situations so as to remove more easily the soil or stain from the object being washed to make the soil or stain more removable in a subsequent cleansing step. Both degradation and alteration can improve soil removability. Well-known andpreferred examples of these enzymes are proteases, lipases and amylases. Lipases are classified as EC class 3, hydrolases, subclass EC 3.1, preferably carboxylic ester hydrolases EC 3.1.1. An example thereof are lipases EC 3.1.1.3 with the systematic name glycerol ester hydrolases. Amylases belong to the same general class as lipases, subclass EC 3.2, especially EC 3.2.1 glycose hydrolases such as 3.2.1.1 alpha-amylase with the systematic name alpha-1,4-glucan-4-glucanohydrolase,- and also 3.2.1.2, beta-amylase with the systematic name alpha-1,4-glucan maltohydrolase. Proteases belong to the same class as lipases and amylases, subclass EC 3.4, particularly EC 3.4.4. peptide peptido-hydrolases such as EC 3.4.4.16 with the systematic name subtilopeptidase A.

Obviously the foregoing classes should not be used to limit the scope of the invention. Enzymes servingdifferent functions can also be used in the practice of this invention, the selection dependingupon the composition of biochemical soil, intended purpose of a particular composition, and the availability of an enzyme to degrade or alter the soil.

Lipases, sometimes called esterases, hydrolyse fatty soils. Lipases suitable for use herein include those of animal, plant and microbiological origin. Suitable lipases are also found in many strain of bacteria and fungi. For example, lipases suitable for use herein can be derived from Pseudomonas, Aspergillus, Pneumococcus, Staphylococcus, Toxins, Mycobacterium Tuberculosis, Hycotorula Lipolytica, and Sclerotiniamicroorganisms, and canbemade using recombinant DNA manufacturing techniques.

Suitable animal lipases are found in the body fluids and organs of many species. A preferred class of animal lipase herein is the pancreatic lipase.

Lipase can be employed in the present cleaning compositions in an amount from about 0.005% to about 10%, preferably from 0.01 to 5% of the cleaning composition, on a pure enzyme basis.

The enzymes most commonly used in machine dishwashing compositions are amylolytic enzymes.

The amylolytic enzymes for use in the present invention can be those derived frombacteria of fungi. Preferred amylolytic enzymes are those prepared and described in British patent specification No. 1,296,839, cultivated from the strains of Bacillus lichenifozmis NCIB 8061, NCIB 8059, ATCC 6334, ATCC 6598, ATCC 11 945, ATCC 8480 and ATCC 9945 A. Examples of such amylolytic enzymes are amylolytic enzymes produced and distributed under the trade name of SO-95^® or Termamyl^® by Novo Industri A/S, Copenhagen, Denmark. These amylolytic enzymes are generally presented as granules andmay have enzyme activities of from about 2 to 10 Maltose units/milligram.

The amylolytic activity can be determined by the method as described by P. Bernfeld in "Method of Enzymology", Vol. I (1955) , page 149.

The compositions of the invention preferably also contains a proteolytic enzyme.

Examples of suitable proteolytic enzymes are the subtilisins which are obtained from particular strains of B. subtilis and B. licheniformis, such as the commercially available subtilisins Maxatase ^® suppliedbyGist-Brocades N.V. , Delft, Holland, and Alcalase^®, supplied by Novo Industri A/S, Copenhagen, Denmark.

Particularly suitable is a protease obtained from a strain of Bacillus having maximum activity throughout the pH range of 8-12, being commercially available from Novo Industri A/S under the registered trade names of Esperase^® and Savinase^®. The preparation of these and analogous enzymes is described in GB-A-1 243 784.

Another suitable protease useful herein is a fairly recent commercial product sold by Novo Industri A/S under the trade name Durazym^®, as described in WO-A-89/06279. The enzymes are generally presented as granules, e.g. marumes, prills, T-granules etc. , and may have enzyme activities of from about 500 to 1700 glycine units/milligram. The proteolytic activity can be determined by the method as described by M.L. Anson in "Journal of General Physiology", Vol. 22 (1938), page 79 (one Anson Unit/g = 733 Glycine Units/milligram) .

All these enzymes can each be present in a weight percentage amount of from 0.2 to 5% by weight, such that for amylolytic enzymes the final composition will have amylolytic activity of from 10² to 10⁶ Maltose units/kg, and for proteolytic enzymes the final composition will have proteolytic enzyme activity of from 10⁶ to 10⁹ Glycine Units/kg.

The detergent composition may also comprise a bleach system encapsulated or not. The bleach system may be a chlorine- or bromine-releasing agent or a peroxygen compound. Among suitable reactive chlorine- or bromine-oxidizing materials are heterocyclic N-bromo- and N-chloro imides such as trichlorosio-cyanuric, tribromoisocyanuric, dibromoisocyanuric and dichloroisocyanuric acids, and salts thereof with water- solubilizing cations such as potassium and sodium. Hydantoin compounds such as l,3-dichloro-5,5-dimethylhydantoin are also quite suitable.

Dry, particulate, water-soluble anhydrous inorganic salts are likewise suitable for use herein such as lithium, sodium or calciumhypochlorite and hypobromite. Chlorinated trisodium phosphate is another suitable material. Chloroisocyanurates are, however, the preferred bleaching agents. Potassium dichloroisocyanurate is sold by Monsanto Company as ACL-59^®. Sodium dichloroisocyanurates are also available from Monsanto as ACL-60^®, and in the dihydrate form, from the Olin Corporation as Clearon CDB-56^®, available in powder form (particle diameter of less than 150 microns) ,- mediumparticle size (about 50 to 400 microns) ,- and coarse particle size (150- 850 microns) . Very large particles (850-1700 microns) are also found to be suitable.

Organic peroxy acids or the precursors therefor may also be utilized in the bleach system. The peroxyacids usable in the present invention are solid and, preferably, substantially water-insoluble compounds. By "substantially water-insoluble" is meant herein a water-solubility of less than about 1% by weight at ambient temperature. In general, peroxyacids containing at least about 7 carbon atoms are sufficiently insoluble in water for use herein.

Typical monoperoxy acids useful herein include alkyl peroxy acids and aryl peroxyacids such as:

(i) peroxybenzoic acid and ring-substitutedperoxybenzoic acids, e.g. peroxy-alpha-naphthoic acid;

(ii) aliphatic and substituted aliphatic monoperoxy acids, e.g. peroxylauric acid and peroxystearic acid;

(iii) phthaloyl amido peroxy caproic acid (PAP) .

Typical diperoxy acids useful therein include alkyl diperoxy acids and aryldiperoxy acids, such as:

(iv) l,12-diperoxydodecanedioic acid (DPDA) ,-

(v) l,9-diperoxyazelaic acid; (vi) diperoxybrassylic acid; diperoxysebacic acid and diperoxyisophthalic acid;

(vii) 2-decyldiperoxybutane-l,4-dioic acid.

Peroxyacid bleach precursors are well known in the art. As non-limiting examples can be named N,N,N' ,N' -tetraacetyl ethylene diamine (TAED) , sodium nonanoyloxybenzene sulphonate (SNOBS), sodium benzoyloxybenzene sulphonate (SBOBS) and the cationic peroxyacid precursor (SPCC) as described in US-A-4 751 015.

Inorganic peroxygen-generating compounds are also suitable for preparing the co-granules of the present invention. Examples of these materials are salts of monopersulphate, perborate monohydrate, perborate tetrahydrate, and percarbonate.

If desirably, a bleach catalyst, such as the manganese complex, e.g. Mn-Me TACN, as described in EP-A-0 458 397, or the sulphonimines of US Patents 5,041,232 and 5,047,163, can be incorporated.

For chlorine bleaches the amount used in the co-granules of the invention may vary within the range of about 0.5% to about 3% as available chlorine (Av Cl) . For peroxygen bleaching agents a suitable range will be from 0.5% to 3% av 0 (available oxygen) .

Finally the invention is a fourth aspect relates to the use of a co-granule according to the invention as a component in detergent compositions, more preferably in dishwashing compositions. More in particular the invention provides non- irritant detergent compositions in which the amount of peroxygen bleach, protease and surfactant taken together is at most 20%, more in particular between 10 and 19.95% (w.w.) of the total composition. In the following the invention will be illustrated by a number of examples not to be interpreted as limiting the invention. All parts and percentages mentioned are on a weight basis unless indicated otherwise.

EXAMPLES

1. Preparation of solutions/slurries for spray-drying

The following solutions were produced:

la. Starting from anhydrous citric acid.

Composition:

Dry basis As Is

(kg) (kg)

Citric acid. Oaq. 189.5 189.5

Water 189.5

NaOH (50%) 118.5 237

Sokalan CP 5 (40%)* 21.6 54

Sodium silicate (45%)** 150.8 335

Total 480.41005

*) Sokalan CP-5 is a copolymer (of acrylic acid and maleic acid) sold by BASF in Germany

**) The sodium silicate used had a mol ratio Si0₂/Na₂0 of 2.0

The citric acid was first mixed with water and under stirring and cooling it was neutralised by slowly adding caustic soda. The solution was kept at about 70°C while successively the polymer and the silicate liquor were added. The solution obtained was clear at 70°C. lb. Starting from sodiumcitrate.2aq.

Composition:

Dry basis AS IS

(kg) (kg)

Sodiumcitrate.2aq. 254.6 290.2

Water 325.8

Sokalan CP-5 (40%)* 21.6 54

Sodiumsilicate (45%) ** 150.8 335

Total 4271005

In this case the citrate was dissolved under stirring in water, which was preheated at 70°C. The polymer and the silicate solution were then added. The solution was again clear.

2. Spray-drying

Spray-drying was carried out in a co-current manner in a standard spray-tower. The gas was pre-heated to max. 230°C and the solution was introduced (sprayed) at about 70°C in order to save energy/maximize capacity.

The spraying conditions were as follows:

Gas temperature inlet 200 - 230°C Gas temperature exit 120 - 140°C Temperature solution 65 - 75°C

It was found, that at outlet temperatures above 140°C the material leaving the tower was still slightly plastic. Therefore for the compositions used, this seemed to be the maximum practical temperature.

The powders obtained varied in properties as summarized below, which could be adjusted by varying the conditions within the ranges given. Bulk density (g/cm³) : 200 - 680

Free moisture content (%, w.w.)*: 7- 12

Particle size: 90% below 250 micrometers.

*) Free moisture content is measured at 160°C in an IR (Infrared) METTLER Balans, as marketed by the German firm METTLER. The time of measurement at 160°C is 7 minutes.

3. Compaction

Compaction was carried out in a standard compaction-roller unit as marketed by the firm Alexanderwerke AG in Remscheid, Germany. Type: Walzenpresse Type WP 480 x 260 V.

The equipment consists of 2 rollers. The powder was pressed between the rollers by a screw. The powderflow could be controlled by the screw. The pressure of the rollers was controlledhydrolycally as the upper rollerwas not in a fixed position. The maximum pressure was about 150 t, which is equivalent to a hydrolic pressure of about 200 bar and about 6 t per cm length of the roller.

The rollers rotated at a speed of 14 - 18 revolutions per min.

The rollers were kept at about 25°C by water cooling.

During the experiments, the hydrolic pressure was varied between 130 and 170 bar.

It was found, that 135 bar was about the minimum pressure acceptable for the product composition and the temperature chosen. At higher temperatures, the pressures can be reduced.

The sheet formed was broken down and sieved, using sieves of 200 and 1200 micrometers. The finer particles were returned to the compactor and the larger particles were returned to the breaker.

Products obtained:

Bulk density (g/cm³) : 870 - 900

Attrition test (fluid bed) (%,w.w.)* 3.6 - 5.2 *) Dissolution time at 20 °C ** O'SO'-l^O¹ Particles below 200 micrometers 0 - 0.2% (w.w.) Particles above 1000 micrometers ID - 25 % (w.w.) N Value (Rosen Rammler) 3.5 - 4.5

*) The attrition test was carried out in a fluid bed under standard conditions (air flow rate, time, amount of product used) . The amount of finer particles formed

(particle size below 200 micrometer) was measured and given as % by weight.

**) The dissolution time is the time needed for complete dissolution in water at 20 °C and at a 5% (w.w.) concentration.

Comparative test

Above reported results are excellent as can be concluded from the fact, that standard granular sodium silicate with a mol . ratio Si0₂/Na₂0 2.0 produced according to the same process, i.e. : Spray-drying a solution of the sodiumsilicate (pre-heated at 70°C) under the same conditions as above and compacted under the same conditions had the following properties:

Bulk density (g/cm³) : 770 - 820

Attrition test (fluid bed) (% w.w.)* : 10 - 30 Dissolution time at 20 °C ** : 3'- 5"

In case the same silicate solution was dried and granulated simultaneously in the Tubro-Dryer, following results were obtained:

Bulk density (g/cm³) : 850 - 950

Attrition test (fluid bed) (% w.w.)* : 4 - 8

Dissolution time at 20 °C ** : 7' - 10'

Claims

C L A I M S

1. Method for preparing co-granules for incorporation in detergent compositions, at least comprising a salt of a di-, tri- or tetracarboxylic acid and an inorganic salt, which method comprises preparing a solution or a slurry of the ingre- dients, drying the mixture, compacting the dried product and breaking up and sieving the compacted produc .

2. Method according to claim 1, characterised in that com¬ paction is performed at a temperature between 0 and 90 °C.

3. Method according to claim l or 2, characterised in that the moisture content of the dried product before compaction is adjusted to at least 5-25 % (w/w) .

4. Method according to one or more of claims 1-3, characte¬ rised in that compaction is performed by passing the dried mixture through rollers.

5. Method according to one or more of claims 1-4, characte¬ rised in that compaction is performed by making tablets.

6. Method according to one or more of claims 1-5, characterised in that the fines resulting from breaking up and sieving are returned to the dried product before compaction and the resulting oversized particles are returned to the breaking step.

7. Method according to one or more of claims 1-6, charac¬ terised in that the organic salt comprises an alkali metal salt of a di-, tri- or tetracarboxylic acid.

8. Method according to claim 7, characterised in that the alkali metal salt of a di-, tri- or tetracarboxylic acid comprises an alkali metal citrate.

9. Method according to claim 7, characterised in that the alkali metal salt of a di-, tri- or tetracarboxylic acid comprises an alkali metal oxydisuccinate.

10. Method according to one or more of claims 1-6, charac- terised in that the inorganic salt comprises an alkali metal silicate.

11. Method according to claim 10, characterised in that the alkali metal silicate is sodium silicate with an Si0₂/Na₂0 molar ratio of 1.0 to 3.3, preferably 1.8 to 2.8.

12. Method according to claim 10 or 11, characterised in that the alkali metal silicate is alkali metal disilicate.

13. Method according to one or more of the preceding claims, characterised in that the co-granules further comprise at least one polymeric compound, being either an acid and/or a salt of a polcarboxylic acid polymer or a polypeptide.

14. Method according to one or more of the preceding claims, characterised in that the co-granules further comprise at least one inorganic salt of alkali metal tripolyphosphate, alkalimetal carbonate/bicarbonate/sesquicarbonate oralkali metal sulphate.

15. Method according to one or more of the preceding claims, characterised in that the slurry is prepared by adding di-, tri- or tetracarboxylic acid to a solution containing the inorganic salt, neutralising the carboxylic acidwith alkali, optionally adding further ingredients, as to obtain a solution or a slurry with a water content of 30 - 60 % (w/w) .

16. Co-granules obtainable by the method according to one or more of the claims 1-15.

17. Co-granules according to claim 16, characterised by having a bulk density of at least 700 g/dm³, preferably above 800 g/dm³.

18. Co-granules according to claim 17, characterised in that the bulk density of the co-granules is between 900 g/dm³ and 1200 g/dm³.

19. Co-granules according to one or more of claims 16-18, characterised in that the average particle size of the co- granules is 100 to 1500 μm.

20. Co-granules according to claim 19, characterised in that the average particle size of the co-granules is comprised between 400 and 900 μm and that the Rosen Rammler N-value thereof is above 2.5.

21. Detergent composition comprising co-granules according to one or more of claims 16-20.

22. Use of a co-granules according to one or more of claims 16-20 as a component in detergent compositions.