WO2002053697A1

WO2002053697A1 - A process for the production of cleaning agents

Info

Publication number: WO2002053697A1
Application number: PCT/GB2001/005769
Authority: WO
Inventors: Giorgio Franzolin; Antonio Cordellina; Luca Rosa-Fauzza
Original assignee: Reckitt Benckiser N.V.; Reckitt Benckiser (Uk) Limited
Priority date: 2001-01-08
Filing date: 2001-12-24
Publication date: 2002-07-11
Also published as: ES2337443T5; DE60140821D1; EP1349914B1; EP1349914B2; ATE452178T1; GB2370843A; ES2337443T3; GB0100412D0; EP1349914A1

Abstract

A laundry cleaning agent is made by pelletising a flowable tower spray powder and a flowable zeolitic powder in a pellet mill to form a premix composed of pellets with a substantial zeolite content; and post-mixing the pellets with further ingredients. The resulting particulate material may be used as such, but is preferably pressed to form laundry tablets. When manufactured by this method, the laundry tablets may have an exceptional combination of beneficial properties, namely very high density, high zeolite content and a low amount of disentegrant, all of which would normally lead disintegration time; and yet, unexpectedly, the tablets exhibit a short disintegration time, and other valuable properties.

Description

A PROCESS FOR THE PRODUCTION OF CLEANING AGENTS

This invention relates to a solid laundry cleaning agent and its manufacture. The invention relates in particular to a laundry cleaning agent in pressed block form

(hereinafter "laundry tablet") , but is also applicable to particulate laundry cleaning agents (hereinafter "washing powder"). Although discussion of the invention will focus on laundry tablets, washing powders are also of interest and share many of the advantages of the invention, that apply to laundry tablets .

A known laundry tablet comprises about 10% of a sodium (linear C₈-i5 alkyl) benzene sulfonate, about 6 wt% of zeolite, about 12% of sodium carbonate, about 15% of sodium; citrate dihydrate, about 20% of an amorphous silicate, present as a builder, about 10% of a cellulosic disintegrant and about 27% of additional ingredients (weight/tablet weight) . Such a tablet is formed by simple dry mixing of a typical tower base powder with all the other ingredients, followed by tabletting the mixture in a standard tabletting machine, such as a Korsch rotating press.

This procedure and product is satisfactory but suffer from certain limitations. In particular, it would be advantageous to be able to incorporate a higher proportion of zeolite. However, higher proportions of zeolite in powder _ form would be expected to lead to unacceptably long disintegration times. It would also be advantageous to use a lower proportion of the disintegrant, which is an expensive component and one which is without benefit in terms of cleaning action. However, even small reductions would be expected to lead to unacceptably long disintegration times, especially with increasing zeolite proportion. Further, it would be advantageous to use a lower proportion of - or no - amorphous silicate, which is also expensive. Still further, it would be advantageous to offer smaller tablets with the same cleaning power. It would be desirable therefore to be able to make tablets of higher ^: density provided that the disintegration time was still acceptably short. This is not an easy matter. Simply applying a higher compression force during tabletting achieves a higher density but at the expense of disintegration time, which may soon become unacceptable.

One possible approach was to consider using extruded particles which would then be mixed with further ingredients and pressed to form tablets. This approach is the subject of a number of patent applications of the company Henkel, of which we may mention EP-B-486592, by way of example. In EP-B-486592 there is described a process for the production of compacted granules for use in detergents. A homogenous premix, to which a plasticizer and/or lubricant is added, is extruded through perforated dyes under high pressure to form strands which are cut into pieces. There is preferably an unbound water content in the premix, preferably up to 12% by weight, more preferably up to 10% by weight and most preferably in the range from about 4 to 8% by weight. The premix may be of a tower powder. Zeolite is mentioned as a possible drying powder, to prevent the granules from sticking together, and as a possible premix component, albeit not in very high amounts. When we attempted in our experimental work to evaluate this extrusion process using the types of laundry agents of interest to us, with a high proportion of zeolite, we did not find it to be of any potential use. The materials we wished to form into granules seemed insufficiently plastic to extrude well; indeed our extruder was damaged by the attempt .

We have now determined that, to our surprise, pelletisation - as distinct from extrusion - can be used as a key step in the manufacture of advantageous laundry tablets . Those laundry tablets can achieve the aims noted above ^;- thus, they can be of high density; be small tablets; have high zeolite content; have low disintegrant content; fast disintegration; and have a low or no amorphous silicate content. Aside from advantageous laundry tablets the present invention offers the prospect of advantageous washing powders, with high bulk density, high zeolite content and low or no amorphous silicate content.

In accordance with a first aspect of the present invention there is provided a method of making a solid laundry cleaning agent, comprising the steps of pelletising a flowable tower spray powder and a flowable zeolitic powder in a pellet mill to form a premix comprising pellets with a zeolite content of at least 30% (weight of zeolite/weight of pellets) ; and mixing (hereinafter also called post-mixing) the pellets with the other ingredient (s) (hereinafter also called post-mixing ingredients) of the solid laundry cleaning agent. Preferably the tower spray powder is made up of the following constituents (weight/weight of tower spray powder) :

20-60% anionic surfactant; 0-15% processing aid; 0-25% further zeolite; 12-45% inorganic alkali metal, preferably sodium, salt; and 0-20% additional constituent (s) .

More preferably, the tower spray powder comprises 30-50% of one or more anionic surfactant .

Preferred anionic surfactants for the tower spray powder include (but are not limited to) alkali metal salts, ammonium salts, amine salts, aminoalcohol salts or magnesium salts of one or more of the following compounds: alkylsulphonates, alkylamide sulphonates, alkylarylsulphonates, olefinsulphonates, alkylamide sulphonates, alkyl sulfosuccinates, alkyl ether sulfosuccinates, alkylamide sulfosuccinates, alkyl sulfosuccinamate, alkyl sulfoacetates, acyl sarconsinates, acyl isothionates and N-acyl taurates. Generally, the alkyl or acyl group in these various compounds comprises a carbon chain containing 8 to 22, preferably, 12 to 20, carbon atoms .

Other anionic surfactants which may be used include salts

(having cations as described above) of fatty acids, individually or as mixtures, including salts of oleic and stearic acids, and of acids of palm kernel oil, coconut oil and tallow; and lactylates whose acyl group contains 8 to 20 carbon atoms. Especially useful are solid soaps, and preferably solid alkali metal salts of C₁₆._la saturated fatty acids, especially of tallow fatty acids, as these are useful also as processing aids. An especially preferred anionic surfactant for use in the present invention is an alkali metal, preferably sodium, salt of a (C₈-i5 - preferably C₉-ι₃ - linear alkyl) benzene sulphonic acid (hereinafter 8-15 LAS and 9-13 LAS) .

Preferably an alkali metal salt of an alkylbenzene sulphonic acid (for example an LAS) is present in the pellets, preferably wholly derived from the tower spray powder.!

Preferably an alkali metal salt of an alkylbenzene sulphonic acid (for example an LAS) is not present in the zeolitic powder which is to be pelletized. Preferably no anionic surfactant is present in the zeolitic powder which is to be pelletized.

Preferably an alkali metal ^• salt of an alkylbenzene sulphonic acid (for example an LAS) is not present in the post-mixed ingredients to be mixed with the pellets.

Preferably the pellets do not contain any anionic sulphate surfactant .

Preferably the post-mixed ingredients include an anionic sulphate surfactant, suitably providing 2-10%, preferably 3-7%, of the final cleaning agent (weight/weight) . Suitable anionic sulphate surfactants may include alkyl sulphates, alkyl ether sulphates, alkylamidoether sulphates, alkylaryl polyether sulphates, monoglyceride sulphates. Especially preferred are alcohol sulphates. Generally an alkyl group in these sulphate compounds is a C₈-22, preferably C12-20, alkyl group. A processing aid may be included, in the tower spray and/or the zeolitic powder and/or in the post-mixed ingredient (s) , in order to improve the efficiency of a later pelletisation step and/or of a later tabletting step, where provided. A suitable processing aid preferably functions as a plasticizer or lubricant. Examples include a soap, preferably a solid soap; a nonionic surfactant; an acrylic polymer or copolymer, for example an acrylic/ maleic anhydride copolymer; starch or a derivative thereof; gelatin; polyvinyl alcohol; and water. Preferred are a soap; a nonionic surfactant; an acrylic polymer or copolymer; and water.

Suitable nonionic surfactants include alkoxylated alcohols, particularly alkoxylated fatty alcohols. These include ethoxylated and propoxylated fatty alcohols, as well as ethoxylated and propoxylated alkyl phenols, both having alkyl groups, suitably linear or secondary, of from 7 to 18, more preferably 8 to 16 carbon chains in length, and an average of 2 to 20 moles, preferably 2 to 10, most preferably 4 to 6 moles of alkylene oxide per mole of alcohol or phenol . Ethoxylated compounds are generally preferred.

Another class of nonionic surfactants that may be used are sorbitan esters of fatty acids, typically fatty acids having _ from 10 to 24 carbon atoms, for example sorbitan mono oleate .

Other classes of nonionic surfactants that may be used are amine oxides and polyhydroxy fatty acid amides. Preferably the processing aid, where provided, is present in an amount of from 1-10%, preferably 2-8%, more preferably 3-5% (weight/weight of cleaning agent) :

The tower spray powder may include further zeolite, but this is not essential. When there is thus an input of further zeolite, the further zeolite preferably provides 4-30%, more preferably 6-20%, of the cleaning agent (weight/weight) . Preferably, when there is a further input of zeolite it is less than the input of zeolite from the zeolite powder added to the tower spray powder.

Suitable inorganic sodium salts may be selected from sodium silicate, sodium carbonate and sodium sulphate. Advantageously each of these salts is present, and each, preferably, is in the range 4-15%, most preferably 5-12% (calculated as anhydrous amount) .

Additional constituents of the tower spray powder may be selected from a stabilizer, particularly for a per compound or an enzyme. Suitable stabilizers are salts of polyphosphonic acids, such as 1-hydroxyethane-1, 1- diphosphonic acid (HEDP) , diethylenetriaminopentamethylene phosphonic acid (DETPMP) , ethylenediaminotetramethylene phosphonic acid (EDTMP) and aminotrimethylene phosphonic acid (ATP) .

Another useful additional . constituent of the cleaning agent is an optical brightener, for example a suitable stilbene . compound, in particular diaminostilbene disulfonic acid or a derivative thereof, especially an alkali metal salt. An optical brightener may conveniently be delivered via the tower spray powder. Another possible additional constituent of the cleaning agent is a soil redeposition inhibitor, for example one or more of polyvinyl pyrollidone, carboxymethyl-cellulose- sodium salt (CMC) or methylcellulose (MC) . A soil redeposition inhibitor may conveniently be delivered via the tower spray powder.

Preferably the additional constituents of the tower spray powder do not comprise in total more than 10% of the tower spray powder (weight/weight) . Typically each individual additional constituent will not comprise more than 2% of the tower spray powder (weight/weight) .

Preferably the flowable zeolitic powder comprises at least 80 wt% zeolite, and preferably at least 90 wt% zeolite. It may in certain useful embodiments be constituted substantially entirely by zeolite. When it is not, it may be zeolite admixed with a processing aid, for example as defined above.

In this specification references to "zeolite" are to substantially virgin zeolite, including bound water of crystallisation and any atmospherically absorbed unbound water that may be present, but not including deliberately added materials. "Zeolitic powder" denotes zeolite (as just defined) and also such a material containing deliberately added material (s) .

Definitions which refer to the weight or weight ratio of zeolitic powder are made with reference to the zeolite (as defined above) in the zeolitic powder, unless otherwise stated. It should be noted that both the tower spray powder and the flowable zeolitic powder are preferably macroscopically dry when delivered to the pellet mill. Preferably, both are free-flowing. The amount of liquid components present (if any) must not be such that the respective powders become damp, or sticky, or prone to form lumps. Zeolite for use in the present invention is desirably stored in conditions which discourage water take-up from the atmosphere; for example it can be stored in closed or sealed plastic sacks.

We believe that the invention can be applied using any type of zeolite, including zeolite MAP, zeolite X and zeolite P. Other suitable types are the natural materials analcite, chabazite, heulandite, stilbite, faujasite, natrolite and thomsite. Preferred zeolite for use in the present invention, however, is zeolite A.

The tower spray powder and the zeolitic powder are preferably mixed upstream of the pellet mill in a separate unit, for example a vertical mixer/granulator, a horizontal mixer/granulator or a tumbler unit, all of which are conventional . Preferably, no heating is provided during this step.

Preferably the zeolite content of the pellets is at least 35%, more preferably at least 40%. Most preferably, it is at least 45% and, especially, at least 50%.

Preferably, the zeolite content of the pellets does not exceed 80%, more preferably 70%, most preferably the zeolite content of the pellets does not exceed 65%. We have found that using the feed materials defined above, pelletisation in a standard pellet mill, e.g. a Kahl mill or a UMT mill, is efficient and unproblematic. This was unexpected given the failure we encountered in trying to extrude such materials.

Further information on pellet mills is readily available. Examples of patents concerning rotary pellet mills include DE 3813081, DE 3806945 and DE 3432780.

Preferably external heat is not provided in the pelletising step. We have found that the temperature of the material being pelletised rises moderately, typically to temperatures in the range 30-55°C, without detriment.

For the pelletisation step, the tower spray powder and the flowable zeolitic powder, as defined above, are preferably mixed together without any further material .

The pellets which are products of the pellet mill are chopped strands, "shaved" from the outer wall of the pellet mill as pelletisation proceeds. Based on our work to date it does not seem necessary from a technical standpoint to treat the pellets in any way before mixing them with post-mixed ingredients, to form the end laundry cleaning agent . However, they could if wished, primarily for aesthetic reasons, be given a simple mechanical treatment in a "ploughshare" shovel mixer, to reduce their mean aspect ratio, to be as close as possible, what may be considered to be the aesthetic ideal, 1:1 (pellet length:maximum diameter) . We have found it easy to reduce the mean aspect ratio of the as-formed pellets, by feeding them straight from the pellet mill into the shovel mixer, preferably when the pellets are still warm.

Alternatively or additionally pellets may be spheronized. Preferably, however, the pellets are not spheronized.

Alternatively or additionally pellets may be dusted with a powder to aid flowability. This could suitably be zeolite, for example zeolite A. Preferably, however, the pellets are not dusted.

Suitably the mean aspect ratio of the pellets used in the post-mixing is in the range 0.5-5:1, more preferably 0.8- 3:1 (pellet length:maximum diameter). Preferably the pellets are circularly cylindrical and so the aspect ratio denotes length: diameter. Preferably the pellets from the pellet mill are given a mechanical treatment to reduce their mean aspect ratio, to be within this range.

The pellets are intended as a universal base material to which the post-mixing ingredient (s) can be added, for example to make a heavy duty laundry detergent product, or a color care laundry detergent product. Thus, the pellets themselves preferably do not contain any of the "specialist" ingredients which are characteristic of such products. In particular, the pellets preferably do not contain any enzymes, bleaching compounds or bleach activators .

The post-mixing ingredient (s) will depend on the target use for the laundry cleaning agent - for example for general purpose laundry,- for heavy duty/white clothes; or for colored clothes. Typically the ratio of the pellets to the post-mixing ingredient (s) is in the range of 20-80 : 80-20 (weight/weight) . Preferably the ratio is in the range of 40-70 : 60-30. Most preferably, the ratio is in the range 50-60 : 50-40.

The post-mixing ingredient (s) suitably include one or more of the following: a surfactant, for example an anionic and/or nonionic surfactant; sodium bicarbonate; sodium carbonate; sodium citrate; an anti-foaming agent; an enzyme; a bleaching agent; a bleach activator; a stabilizer, for example of the phosphonate type as defined above; a soil release polymer; a soil redeposition inhibitor; an optical brightener; a fabric softener; a colorant; and a fragrance.

Generally the surfactant component of the post-mixing ingredient (s) is relatively small, suitably making up not more than 10% of the total weight of post-mixing ingredient (s) . As mentioned above the post-mixing ingredients may include an alcohol sulphate and this is preferably the only anionic surfactant component, and preferably the only surfactant component, in the post- mixing ingredient (s) . In the case of a heavy duty cleaning agent the major complement of post-mixing ingredient (s) is a bleaching agent, for example sodium percarbonate, and a bleach activator, for example' TAED; together preferably constituting at least 50% of the weight of post-mixing ingredient (s) . In the case of cleaning agents for coloured clothes one or more enzymes, for example, protease, amylase and cellulase, may comprise at least 2% of the weight of post-mixing ingredient (s) . At least 40% of the weight of post-mixing ingredient (s) may be made up of sodium bicarbonate and/or sodium carbonate and/or sodium citrate.

A particulate laundry cleaning agent may be made by simple mixing of the pellets and the post-mixing ingredient (s) , for example in a tumbler unit . The bulk density of the resulting particulate material is typically high, suitably at least 750g/l, preferably at least 800 g/1. Although such particulate material is itself of potential utility as a washing powder, preferred laundry cleaning agents of the present invention are laundry tablets. Therefore, the invention preferably includes the step, after the step of mixing the pellets with the other ingredients, of pressing the particulate material to form a tablet. As is commonplace the tablet may be formed with two or more layers of different composition, thereby keeping apart any materials which it would be undesirable to mix prior to use - for example a bleach and a bleach activator; or bleach and enzymes .

Pressing the pellets and other ingredients to form tablets is a straightforward step, using standard equipment, for example a commercially available Korsch or Bonals press. It is preferred that when tablets are to be produced, one of the post-mixing ingredient (s) is a disintegrant, for example a rapidly water-swellable material, especially a water-swellable cellulosic material. However, whereas we have previously found it necessary to incorporate at least 10% of a disintegrant in tablets, the tablets made in accordance with the present invention we find that a smaller amount can be employed perfectly adequately. Preferably the disintegrant provides less than 10% of the total weight of the tablets of the present invention and preferably not more than 8%.

We have found that by means of the present invention tablets of very high density may be produced. This is significant because, for a given cleaning power, the

^• tablets are smaller than prior tablets, and this brings about several significant advantages. For example, they may fit in washing machine drawers whereas larger tablets do not .

Preferably the tablets produced in accordance with the present invention have a density of at least 1 kg/1. More preferably, the tablets have a density of at least 1.1 kg/1 and most preferably at least 1.15 kg/1.

Preferably the tablets have a hardness of at least 50 N, preferably at least 80 N, as measured by a dynamometer as the maximum force required to break the upper surface of the tablet when a perpendicular force is applied to the centre of ^' it, by a vertically orientated cylinder of diameter 0.5cm.

Preferably the tablets have a disintegration time of not more than 30 seconds, more preferably not more than 25 seconds, most preferably not more than 20 seconds, as measured by a standard method in which a laundry tablet is placed in a stainless steel mesh ladle, with mesh holes approximately 5mm x 5mm, and then successively lowered into and raised from a transparent tank containing 800 ml water at 20°C at a frequency of 60 immersions per minute. When no solid residue of the tablet can be seen within the ladle, the time is recorded ("disintegration time") . Preferably the pellets, and the other ingredients of the washing powder or of the particulate material to be tabletted, are of size such that at least 90 wt% thereof are in the size range 150-1200 μm, more preferably in the size range 250-1000 μm (as determined by standard mesh test, employing ASTM sieves and a Retsch vibrator with predetermined amplitude and working time) .

If necessary the pellets and/or the particulate material resulting from the post-mixing may be graded, and overly large or small particles removed, for example for recycling.

When manufactured by the method described herein it will be appreciated that the laundry tablets may have an exceptional combination of beneficial properties, namely high density, high zeolite content and a low amount of disintegrant (all of which would normally lead to long disintegration time) ; and yet, unexpectedly, exhibit a short disintegration time.

Prior tablets have contained large amounts of silicates as builders. Solid laundry cleaning agents made using the present invention, whether washing powders or laundry tablets, do not require such high amounts of such silicates. Preferably the- content of silicon-containing compounds (not including zeolite) in the laundry cleaning agent is less than 10%, more preferably less than 5%. In certain embodiments the cleaning agent may be substantially free of silicon-containing compounds (except for the zeolite) . Preferably the solid laundry cleaning agents of the present invention contain no phosphate detergents.

Preferably the amount of surfactants in the cleaning agent is at least 10% by weight. Preferably it does not exceed 30%, more preferably 25%, by weight.

Preferably the zeolite content of the cleaning agent is at least 15% by weight, more preferably at least 20%, most preferably at least 25%, and, especially at least 30%.

In accordance with a second aspect of the invention there is provided a solid laundry cleaning agent comprising: a premix of a flowable tower spray and a flowable zeolitic powder formed into pellets in a pellet mill, the resulting pellets having a zeolite content of at least 30% (weight of zeolite/weight of pellets) ; and other ingredients mixed with the premix to form the cleaning agent, the zeolite content of the cleaning agent being at least 15% (weight of zeolite/weight of cleaning agent) .

In accordance with a third aspect of the present invention there is provided a cleaning agent in tablet form, made up of pellets and additional ingredients (which include a disintegrant) mixed and pressed together, the pellets being formed in a pellet mill from a macroscopically dry tower spray powder and a macroscopically dry zeolitic powder, the pellets having a zeolite content of at least 30% (weight of zeolite/weight of pellets) , the cleaning agent in tablet form having a zeolite content of at least 15%, a content of silicon-containing compounds of 0-10% (not including zeolite) and a disintegrant content of less than 10% (weight percentages/weight of the tablet) ; and a density of at least 1 kg/1, a hardness (as defined herein) of at least 50 N and a disintegration time (as defined herein) of not more than 30 seconds.

The invention will now be further described with reference to the following non-limiting examples.

Preparation of Tower Spray Powder

A tower spray powder having the following ingredients was prepared in the conventional manner, in a vertical tower, from an aqueous slurry.

Preparation of Pellets A

The tower spray powder was produced in standard manner. The soap was in the form of powder waste from soap production. The tower spray powder was mixed in equal weight with dry, virgin zeolite A powder (MICOLAN 1) , in a tumbler mixer. The zeolite had been stored in sealed plastic sacks and nothing was added to it before the mixing. The mixed material was fed into a Kahl pellet mill operated at 100 rpm to yield circularly cylindrical pellets, 1.3mm in diameter and approximately 8-10mm in mean length. The temperature of the pellets as they issued from the pellet mill was about 30-40°C. They were passed directly to a Lδdige batch mixer, in which a short treatment with rotating ploughshare shovels reduced the mean length of the pellets to approximately 2 -4mm. At this point they were graded using a sieve, to remove powder for recycling.

With the zeolite A also in the tower spray powder, zeolite A made up 64.1% of the weight of Pellets A.

Production of Pellets B

Production was the same as for Pellets A, but instead of dry, virgin zeolite A being used as the zeolitic powder, zeolitic powder was used, made up of 90% of the dry, virgin zeolite A and 10% soap as described above (weight :weight) . This zeolitic powder was mixed in equal weight with the tower spray powder.

Thus, the resultant Pellets B were made up of the following weight proportions:

50:45:5, tower spray ingredients : zeolite A added to the tower spray powder : soap.

With the zeolite A in the tower spray powder, zeolite A made up 59.1% of the weight of Pellets B. Production of High Density Washing Powder for Coloreds

Pellets A as described above were post-mixed with the following ingredients in a standard tumbler mixer in the proportions stated to yield a high density washing powder intended for washing colored fabrics .

Preparation of Laundry Tablet for Coloreds

The ingredients set out in the table below were mixed together in a standard tumbler mixer, fed repetitively to a Korsch tablet press, and pressed into white monolayer tablets of circularly cylindrical shape, having the following characteristics: Size - 22mm height x 44mm diameter

Density - 1.17 kg/1

Hardness - 90N (measured as described above)

Disintegration time - 20 seconds (measured as described above)

Weight: 37.5g

Production of Laundry Tablets for Heavy Duty/Whites

This tablet was composed of two layers, produced in standard manner in a Korsch press. The two layers are made up as follows .

(weight percentages stated)

The silicate builder had a ratio of SiO₂:Na₂0 of 2.85:1 (weight :weight) . The resulting two layer disc-shaped tablet had the following characteristics.

Size - 22mm height x 44mm diameter

Density - 1.15 kg/1

Hardness - 100N (measured as described above)

Disintegration time - 15 seconds (measured as described above)

Weight: 37.5g Production of Washing Powder for Heavy Duty/Whites

Pellets B as described above were mixed together with further ingredients in a standard tumbler mixer in the proportions stated below to yield a high density washing powder intended for washing heavily soiled white fabrics.

(weight percentages stated)

Claims

Claims :

1. A method of making a solid laundry cleaning agent, comprising the steps of pelletising a flowable tower spray powder and a flowable zeolitic powder in a pellet mill to form a premix comprising pellets with a zeolite content of at least 30% (weight of zeolite/weight of pellets) ; and mixing the pellets with the other ingredient (s) of the solid laundry cleaning agent.

2. A method as claimed in claim 1 wherein the pellets have a zeolite content of at least 40%.

3. A method as claimed in claim 1 or 2 wherein the zeolitic content of the pellets does not exceed 80%.

4. A method as claimed in any of claims 1 to 3 wherein the zeolitic powder is a substantially pure zeolite or is a zeolite admixed with up to 20% of a processing aid (weight of processing aid/weight of zeolitic powder including processing aid) , but such that the zeolitic powder remains in flowable powder form.

5. A method as claimed in claim 4 wherein said zeolitic powder comprises up to a 10% of a said processing aid, the processing aid being selected from a nonionic surfactant; an acrylic polymer or copolymer; starch or a derivative thereof; gelatin; polyvinyl alcohol; soap; and water.

6. A method as claimed in claim 4 or 5, wherein the processing aid is in solid form.

7. A method as claimed in claim 6, wherein the processing aid is a sodium and/or potassium soap of a fatty acid selected from a tallow fatty acid, coconut oil fatty acid, palm kernel oil fatty acid, oleic acid and stearic acid, ^' the soap being in particulate form.

8. A method as claimed in claim 4 wherein the zeolitic powder is a substantially pure zeolite.

9. A method as claimed in any preceding claim wherein said zeolitic powder comprises zeolite A.

10. A method as claimed in any preceding claim wherein the tower spray product is made up of the following constituents (weight of constituents/weight of tower spray powder) :

20-60% anionic surfactant (s)

0-15% processing aid(s) 0-25% further zeolite (s)

12-45% inorganic alkali metal salts (s)

0-20% additional constituent (s)

11. A method as claimed in any preceding claim comprising the step, after pelletisation, of mechanically treating the pellets to reduce their aspect ratio.

12. A method as claimed in any preceding claim wherein the ratio of pellets to said other ingredient (s) is in the range 20-80: 80-20 (weight of pellets/weight of said other ingredients) .

13. A method as claimed in claim 12 wherein the ratio of pellets to said other ingredient (s) is in the range 40-70: 60-30.

14. A method as claimed in any preceding claim wherein said other ingredient (s) include one or more of the following: a surfactant; sodium bicarbonate; sodium carbonate; sodium citrate; an antifoaming agent; an enzyme; a bleaching agent; a bleach activator; a stabilizer; a soil release polymer; a soil redeposition inhibitor; a fabric softener; a colorant; and a fragrance.

15. A method as claimed in any preceding claim wherein the resulting particulate material has a bulk density of at least 750 g/1.

16. A method as claimed in any preceding claim comprising the step, after said mixing step, of pressing the particulate material to form a tablet.

17. A method as claimed in claim 16 wherein said other ingredient (s) include a disintegrant.

18. A method as claim in claim 16 or 17 wherein the tablet has a density of at least 1 kg/1.

19. A method as claimed in claim 16 wherein the tablet has a density of at least 1.1 kg/1.

20. A solid laundry cleaning agent prepared by a method as claimed in any preceding claim.

21. A solid laundry cleaning agent comprising: a premix of a flowable tower spray and a flowable zeolitic powder formed: into pellets in a pellet mill, the resulting pellets having a zeolite content of at least 30% (weight of zeolite/weight of pellets) ; and other ingredients mixed with the premix to form the cleaning agent, the zeolite content of the cleaning agent being at least 15% (weight of zeolite/weight of cleaning agent) .

22. A cleaning agent in tablet form, made up of pellets and additional ingredients (which include a disintegrant) mixed and pressed together, the pellets being formed in a pellet mill from a macroscopically dry tower spray powder and a macroscopically dry zeolitic powder, the pellets - having a zeolite content of at least 30% (weight of zeolite/weight of pellets) , the cleaning agent in tablet form having a zeolite content of at least 15%, a content of silicon-containing compounds of 0-10% (not including zeolite) and a disintegrant content of less than 10% (weight percentages/weight of the tablet) ; and a density of at least 1 kg/1, a hardness (as defined herein) of at least 50 N and a disintegration time (as defined herein) of not more than 30 seconds.