WO2002044315A1

WO2002044315A1 - Cleaning compositions

Info

Publication number: WO2002044315A1
Application number: PCT/EP2001/013831
Authority: WO
Inventors: Jelles Vincent Boskamp; Rahul Dominic Vas Bhat
Original assignee: Unilever N.V.; Unilever Plc; Hindustan Lever Ltd
Priority date: 2000-11-24
Filing date: 2001-11-26
Publication date: 2002-06-06
Also published as: AU2002220733A1

Abstract

A tablet, or a region such as a layer of a tablet, is compacted from a particulate cleaning composition comprising particles which are a mixture of: (i) a water-insoluble, water-swellable material which expands to at least twice its original volume on contact with water; and (ii) other material acting as a carrier therefor, wherein the carrier material is either water-dispersible and present in an amount in the particles which exceeds the amount of material (i), or, it is a starch or a derivative thereof obtainable by chemical treatment of starch which increases its water-solubility. Process for making a tablet comprising said particles.

Description

CLEANING COMPOSITIONS

This invention relates to cleaning compositions in the form of tablets. These tablets are intended to disintegrate when placed in water and thus are intended to be consumed in a single use. The tablets may be suitable for use in machine dishwashing, the washing of fabrics or other cleaning tasks.

Detergent compositions in tablet form and intended for fabric washing have been described in a number of patent documents including, for example EP-A-711827, WO-98/42817 and WO-99/20730 (Unilever) and are now sold commercially. Tablets of composition suitable for machine dishwashing have been disclosed in EP-A-318204 and US-A-5691293 and are sold commercially. Tablets have several advantages over powdered products: they do not require measuring and are thus easier to handle and dispense into the washload, and they are more compact, hence facilitating more economical storage.

Tablets of a cleaning composition are generally made by compressing or compacting a composition in particulate form. Although it is desirable that tablets have adequate strength when dry, yet disperse and dissolve quickly when brought into contact with water, it can be difficult to obtain both properties together. Tablets formed using a low compaction pressure tend to crumble and disintegrate on handling and packing; while more forcefully compacted tablets may be sufficiently cohesive but then fail to disintegrate or disperse to an adequate extent in the wash. Tableting will often be carried out with enough pressure to achieve a compromise between these desirable but antagonistic properties. However, it remains desirable to improve one or other of these properties without detriment to the other so as to improve the overall compromise between them. Thus, if the speed of disintegration can be improved without reducing the strength, the manufacturer may choose to compact the particulate composition more forcefully and thereby make stronger tablets which disintegrate at the same speed as before.

If a tablet contains organic surfactant, this tends to function as a binder, plasticising the tablet. However, it can also retard disintegration of the tablet by forming a viscous gel when the tablet comes into contact with water. Thus, the presence of surfactant can make it more difficult to achieve both good strength and speed of disintegration: the problem has proved especially acute with tablets formed by compressing powders containing surfactant and built with insoluble detergency builder such as sodium aluminosilicate (zeolite) . It is known to include materials whose function is to enhance disintegration of tablets when placed in wash water. For example, our EP-A-838519 mentioned above teaches the use of sodium acetate trihydrate for this purpose. A number of documents have taught that the disintegration of tablets of cleaning composition can be accelerated by incorporating in the tablet a quantity of a water-insoluble but water-swellable material serving to promote disintegration of the tablet when placed in water at the time of use. Such documents include EP-A-466484, EP-A-482627 and WO-A-98/40463.

A number of materials are known as swelling disintegrants . In recent years there has been some interest in materials which absorb many times their own volume of water when they become wet. Sometimes referred to as "super absorbers", these materials have been used in sanitary products for absorbing fluids. They have also been proposed as disintegrants because their high water absorption causes swelling.

WO 98/03064 discloses a disintegrant composition containing a so-called super disintegrant together with a co-disintegrant . In an example tablets are made from a cleaning composition of alkaline inorganic salts, mixed with microcrystalline cellulose, cross-linked sodium carboxymethyl cellulose, silica and magnesium stearate.

WO98/40463 discloses detergent tablets containing a disintegrant which has a high water-absorbing capacity. This disintegrant is used in the form of granules, which may be co- granules containing other material, so that the disintegrant with high water-absorbing capacity provides from 20 to 100% of the granules .

WO 98/55575 discloses detergent tablets which incorporate disintegrating granules which contain 10 to 95% cellulose and 5 to 90% of a second material which may be a microcrystalline cellulose or a functional constituent of a detergent composition.

WO 00/77152 (Unilever) discloses detergent tablets comprising water insoluble, water swellable disintegration material which is cellulosic and from a plant source other than timber.

WO 98/55582 (Unilever) discloses detergent tablets comprising water insoluble, water swellable polymeric disintegration material and highly soluble disintegration promoting materials.

EP-A-1 043 389 (Dalli-Werke GmbH) discloses disintegrant granules comprising cellulose and a (co) polymer of (meth) acrylic acid or its salts for cleaning tablets.

WO 98/55582 (Unilever) discloses detergent tablets having at least two distinct regions and comprising swelling disintegrant particles in a greater concentration in one of the regions . GB-A-2339574 discloses a disintegrating component for use in detergent composition including tablets consisting of a wicking agent and a water-swellable agent in an intimate mixture. It is preferred that the water-swellable agent provides a majority of this mixture. Various water-swellable agents are suggested including cross-linked polymers. The wicking agents disclosed are cellulosic. In a number of examples the water-swellable agent is cross-linked carboxymethyl cellulose, intimately mixed with a lesser quantity of a cellulose carrier. These examples also appear in GB-A-2339575.

A coated detergent tablet comprising Nymcel™ disintegrant in the coating mixture is disclosed in EP-A-896 053.

According to a first aspect of the present invention there is provided a tablet of compacted cleaning composition, wherein the composition of the tablet, or a discrete region thereof, comprises 0.5% or 1% to 10 % by weight of disintegrant particles which comprise a mixture of: (i) a water-insoluble, water-swellable material which expands to at least twice its original volume on contact with water; and (ii) other material acting as a carrier therefor, which material is water-dispersible as a colloidal dispersion and further wherein the amount by weight of carrier material (ii) exceeds the amount of material (i) present in the disintegrant particles. Preferably, according to this aspect of the invention the water-insoluble, water-swellable material is an organic polymer .

According to a second aspect of the present invention there is provided a tablet of compacted cleaning composition, wherein the composition of the tablet, or a discrete region thereof, comprises 0.5% or 1% to 10 % by weight of disintegrant particles which comprise a mixture of:

(i) a water-insoluble, water-swellable material which expands to at least twice its original volume on contact with water; and

(ii) other material acting as a carrier therefor, which is either starch or a derivative of starch obtainable by chemical treatment of starch which increases its water-solubility.

Generally in this aspect of the invention the amount of carrier material (ii) exceeds the amount of material (i) .

Tablets of the present invention disintegrate faster in static water than tablets which do not contain the required disintegrant particles.

We have found that water-swellable disintegrant materials capable of swelling to at least double their volume are effective to bring about tablet disintegration at the time of use. However, if such materials are used on their own, their elasticity in the dry state causes difficulty, and tablets made with them can expand and break after stamping.

It has therefore proved desirable to use such material in a mixture with a carrier.

The use of disintegrant particles which contain a dispersible carrier is a distinctive feature of this invention. We have found two advantages. Firstly, disintegrant particles which contain a water-insoluble carrier material can leave residues of this carrier material on the fabrics or other articles which are cleaned using the composition. A dispersible carrier ameliorates this disadvantage. Secondly, the cellulosic materials which have commonly been used as carriers are slow to degrade after use. Consequently they add to the environmental burden caused by waste water.

By contrast, water-dispersible materials are in general more rapidly biodegradable and do not constitute such a burden on the environment .

It is desirable that the carrier material is used in a substantially greater quantity than the swellable, insoluble disintegrant. The carrier material should be hydrophilic and capable of absorbing at least some water even in the absence of the swelling disintegrant. Preferred materials are organic compounds with hydroxy groups. It is also preferred that a carrier material does not expand to more than twice its volume on contact with water, before it disperses.

The ability of a material to disperse in water may be observable visually. Of course a simple test for dispersion or dissolution is to agitate a quantity of the material with water and then leave the mixture to settle. If the material has dispersed as a colloid, it will be present in the supernatant liquor above any remaining solid.

Some materials disperse slowly in water, but nevertheless do so, and are more rapidly degradable than materials which do not disperse at all. Materials which disperse slowly may be distinguished from those which do not disperse by making a dispersion in urea solution (e.g. 6 Molar urea solution) which accelerates dispersion by interrupting hydrogen bonding.

A material which is dispersible as a colloidal suspension may be characterised by ability to increase the viscosity of water upon dispersion.

According to a further aspect the present invention provides a process for making a tablet of compacted particulate cleaning composition, which process comprises the steps of mixing disintegrant particles which comprise a mixture of: (i) a water-insoluble, water-swellable material which expands to at least twice its original volume on contact with water; and (ii) other material acting as a carrier therefor, which is water-dispersible as a colloidal dispersion or which is either starch or a derivative obtainable by chemical treatment of starch which increases its water-solubility, with other constituents of a particulate cleaning composition to form a particulate cleaning composition and placing a quantity of the particulate cleaning composition within a mould and compacting that composition within the mould.

Detailed Description

Forms of this invention, preferred and optional features, and materials which may be used, will now be discussed in greater detail. The sole drawing is a cross-sectional view of a testing apparatus .

Except in the operating and comparative examples, or where otherwise explicitly indicated, all numbers in this description indicating amounts of material or conditions of reaction, physical properties of materials and/or use are to be understood as modified by the word "about." All amounts are by weight, unless otherwise specified.

A tablet of this aspect of the invention may be either homogeneous or heterogeneous. In the present specification, the term "homogeneous" is used to mean a tablet produced by compaction of a single particulate composition, but does not imply that all the particles of that composition will necessarily be of identical composition. The term "heterogeneous" is used to mean a tablet consisting of a plurality of discrete regions, for example layers, inserts or coatings, each derived by compaction from a particulate composition. In a heterogeneous tablet according to the present invention, each discrete region of the tablet will preferably have a mass of at least 5g.

The study of water-swellable disintegrant materials has largely taken place in connection with pharmaceutical tablet formulations . One parameter which may be used to characterise such materials is their increase in volume when placed in contact with water. Some materials are capable of absorbing, and being swelled by, a volume of water which is considerably in excess of their own volume.

An apparatus for measuring increase in volume is illustrated in "The Mechanisms of Disintegrant Action", Kanic & Rudnic, Pharmaceutical Technology, April 1984, pages 50-63. This article also refers to papers describing other apparatus.

A swellable disintegrant used in this invention swells to at least twice its original volume on contact with water. It may be preferred that the disintegrant swells to at least 10 or 15 times its original volume on contact with water. A number of water-insoluble, water-swellable materials are known to be useful as tablet disintegrants, in particular for pharmaceutical tablets. A discussion of such materials is found in "Drug Development and Industrial Pharmacy", Volume 6, pages 511-536 (1980) .

Suppliers of water-swellable disintegrant materials include J Rettenmaier & Sόhne in Germany and FMC Corporation in USA.

Such swelling materials are mostly polymeric in nature and many of them are of natural origin. Materials which swell strongly are often chemically modified forms of natural materials such as Primo el™ and Explotab™ both of which are sodium carboxymethyl starch also known as sodium starch glycolate; cellulose derivatives, for example Courlose™ and Nymcel™ sodium carboxymethyl cellulose, Ac-di-Sol™ cross-linked modified cellulose, and cross-linked cellulose. Of these types of material cross-linked carboxymethyl cellulose, cross-linked starch, cross-linked cellulose, carboxymethyl starch, starch glycolate are especially preferred.

Various synthetic organic polymers can also swell strongly on contact with water for example, cross-linked polyvinylpyrrolidone and cross-linked polyacrylate. Cross-linked cellulose fibres are preferably cross-linked in substantially individualised form, i.e. the cellulosic fibres have primarily intrafibre cross-linked bonds. Such fibres can be made by a dry cross-linking process such as described in US- A-3224926, or aqueous solution, as described in US-A-3241553 , or non-aqueous solution cross-linking, as described in US-A- 4035147. Preferably the cellulose is cross-linked with dialdehydes (as described in US 4689118 or US-A-4822453 ) , epichlorohydrin, formaldehyde or by carboxylic acids (e.g. US- A-5137537), most preferably citric acid: or cross-linked polyacrylate .

Another parameter which characterises swellable materials is the force which they exert if they are allowed to take up water whilst confined within an enclosure.

We have found that materials and particles which swell on contact with water are effective as disintegrants if there is a rapid development of force when they come into contact with water.

We have carried out measurements using a relatively simple piece of apparatus shown in the attached drawing, together with an Instron materials testing machine.

The apparatus consists of a cylinder (10) with internal diameter 25mm and a length of 20mm. This cylinder is perforated by a ring of holes (12) adjacent one end. There are 36 of these holes, each 1mm diameter, with centres 2.5mm from the end of the cylinder.

This end of the cylinder is glued to the base of a glass container (14) of internal diameter 73mm.

To test a sample of a powdered disintegrant, 1.5 grams of the disintegrant is placed in the cylinder and gently tapped so that it forms a level bed (16) which is usually 6mm to 10mm deep depending on the bulk density of the powder.

A plunger (18) of the Instron machine is moved into the upper part of the cylinder, over this powder bed.

Under computer control of the Instron machine the plunger is applied to the top of the powder bed (16) with a force of 1 Newton .

50ml of distilled water at 22 °C is tipped into the annular space (20) around the cylinder. This water passes through the holes (12) into the powder bed. The Instron machine is programmed to hold the plunger in position against the swelling bed of powder, and the force required for this is recorded.

The significant parameter is the maximum slope of a graph of expansion force against time . Measurement of swelling can be recorded with the same apparatus. The plunger is again applied to the top of a bed of the dry powder, and pressed against it with a force of 1 Newton. 50ml of water is poured in as before. The Instron machine is programmed to allow expansion of the bed of powder, while maintaining a force on it of 1 Newton. Displacement of the plunger is recorded.

It is preferred that the strongly swelling material, if tested by itself, shows a development of expansion force which exceeds 1.5 Newton/second.

The development of swelling force has also been measured for a number of materials by C.Caramella et al published in International Journal of Pharmaceutical Technology and Production Manufacturing Volume 5 (2) pages 1 to 5, 1984, as set out in the following table.

Carrier Materials

The particles containing the super-disintegrant also contain a carrier material which is water-dispersible. Preferred are those compounds which are also hydrophilic, as it is theorised that such hydrophilic materials help to draw water into the particles containing the super-disintegrant.

It is also preferred that the carrier material swells to a lesser extent on contact with water before dissolving or dispersing. Preferably, the carrier material swells to no more than twice its original volume, more preferably not more than 1.5 times its original volume.

The carrier material can be a single material or a mixture thereof .

Suitable water-dispersible materials form colloidal dispersions in water at 20°C and may include starches, for example maize, rice and potato starches, pregelatinised starch, and starch derivatives obtained by chemical treatment of the starch (so- called chemical modification) in a manner which increases the water-solubility of the starch. For a particle to be colloidal at least one dimension thereof is below lμ .

Starch and starch derivatives are water-dispersible. They show some swelling in water before they disperse. Pregelatinised starches may also form colloidal suspensions, e.g. from amylose and/or amylopectin.

An advantage of starch as a carrier material is that it is inexpensive and easy to process into disintegrant granules.

The mean particle sizes of starches are generally quite small; for example native starches are substantially spherical or oyster shaped and have mean particle sizes such as; amaranth starch 1 to 3 m, wheat starch 2 to 45 m, rich starch 5 to 15μm, potato starch 25 to 45 m.

Disintegrant Particles

As mentioned above, we have found that disintegrant particles which contain a high proportion of material (s) able to swell to several times the dry volume are excessively elastic. They lead to tablets which are not dimensionally stable during dry storage. By contrast, disintegrant particles which contain a minority of such material mixed with a majority of carrier which does not swell so much, can provide effective disintegration, with more stability of the tablet between manufacture and use . Preferred disintegrant particles contain from 60%, better from 75% or 90% up to 99.9% by weight of a carrier material which is water-soluble or is water-dispersible together with from 0.01 or 0.1% to 20%, better 0.1 to 10% by weight of water-insoluble material which swells on contact with water to more than twice, possibly more than three or four times its volume.

Water-insoluble materials which display limited swelling, typical as carrier materials in known disintegrant particles, may be included in a minority proportion, e.g. up to 20% by weight of the disintegrant particles, if desired. Preferably, however, such materials are used in amounts below 5% ^'by weight of the disintegrant particles or are completely absent.

Optionally, the disintegrant particles can contain from 0.5% or 1% up to 15% or even 25% by weight of a polymeric binder. Generally, a polymer used for this purpose will be solid at 25°C. It is preferred that the polymer binder material should melt at a temperature of at least 35°C, better 40°C or above, which is above the range of ambient temperatures in many temperate countries. For use in hotter countries it will be preferably that the melting temperature is somewhat above 40°C, so as to be above the ambient temperature. Some polymers which may be used are solids at temperatures up to 100°C, that is to say they retain a solid appearance even though they are in an amorphous state. They may soften and melt to a mobile liquid on heating further, or may decompose without melting on heating sufficiently in excess of 100°C. Such polymers will generally be added as a powder during the course of granulation. Another possibility would be addition as a solution in a volatile organic solvent, but that is not preferred.

Other polymers which may be used melt to liquid form at temperatures not exceeding 80°C and may be sprayed as molten liquid onto the surfactant and builder mixture during the course of granulation.

Organic polymers are in general amorphous solids. A significant parameter characterising amorphous solids is their glass transition temperature. When an amorphous hydrophilic polymer absorbs moisture, the moisture acts as a plasticiser and lowers the glass transition temperature of the polymer. Suitable polymers may have a glass transition temperature, when anhydrous, which is from 300 to 500K (i.e. approximately 25°C to 225°C) but may be incorporated in a moisture-containing state so that their glass transition temperature is lower.

Preferred polymer materials are synthetic organic polymers especially polyethylene glycol . Polyethylene glycol of average molecular weight 1500 (PEG 1500) melts at 45°C and has proved suitable. Polyethylene glycol of higher molecular weight can also be used (PEG 4000 melts at 56°C and PEG 6000 at 58°C) . Other possibilities are polyvinylpyrrolidone, and polyacrylate and water-soluble acrylate copolymers .

The amount of water-soluble polymer included in the particles which also contain organic surfactant and detergency builder is preferably between 0.5 or 1% and 15% or 20% by weight of the particles, possibly at least 1.5 or 3% by weight. Further preferred is that the amount is not over 7 or 10% by weight. Alternatively, the amount of water-soluble polymer present may be defined in terms of the whole composition of the tablet or region thereof, in which case, it is desirably present in an amount of between 0.5 and 10% by weight, more preferably at least 1, 2 or 5% by weight. Possibly the amount of polymer does not exceed 7% by weight of the whole composition.

If further water-soluble polymer is incorporated into the composition as a separate ingredient, i.e. not in particles with organic surfactant and detergency builder, the total amount present should fall within the limits expressed above in terms of the whole composition.

It is preferred that the components of the particle are in intimate contact with each other. This may be achieved in a homogeneous particle (i.e. one which has substantially the same composition throughout) by dry mixing the components of the particles in the desired proportions and then compacting the mixture into particles. Mixing of the materials can be carried out by standard apparatus for mixing particulate solids. Other ingredients can be incorporated at this stage. If a polymeric binder is incorporated, it can be added in particulate form during this mixing operation. Alternatively, if it can be melted, the molten polymer can be sprayed on to the mixture or on to one particulate ingredient of the mixture.

Compaction of the mixture can be brought about by forcing it between a pair or rollers using any suitable operating conditions. One suitable apparatus, a roller compactor, has a feed screw which delivers the mixture to the nip of the rollers. The speed of the feed screw, and hence the amount of material delivered to the nip of the rollers should be high enough to force an unbroken stream of material through the rollers, but not so high that the material is converted into a dough.

Manufacturers of roller compactors and also milling machinery include Hosokawa Bepex located at Heilbronn, Germany, Alexanderwerk located at Remschied, Germany and Fitzpatrick located at Elmhurst, USA.

Alternatively a laboratory punch tabletting machine (for example a Carver Laboratory Tablet Press) may be used to tablet the disintegrant granule particle mixture to a tablet which is subsequently milled and sieved to separate material of the desired particle size.

An alternative approach is to form particles of the carrier material (and optionally the PEG binder) by conventional means, and subsequently apply a coating of the swellable disintegrant material. This coating can be applied by suspending the disintegrant in a solvent in which it does not swell appreciably, and then spraying this onto a fluidised bed of the carrier particles, with evaporation of the solvent.

The particles containing swellable disintegrants and carrier preferably have an average particle side of at least 250 m, better at least 400μm up to lOOOμm. More preferred is that 95% by weight of the particles have a size in the range of from 350μm or 500im to 710 m or lOOOμm. It is also preferred that not more than 5% of the disintegrant particles have a size less than 350,um.

Surfactant Compounds

Compositions which are compacted to form tablets, or discrete regions thereof, in accordance with this invention may contain one or more organic detergent surf ctants. In a fabric washing composition, these preferably provide from 5 to 50% by weight of the composition of the tablet or region thereof, more preferably from 8 or 9% by weight of the composition up to 35% or 40% by weight. If the tablet is composed of more than one discrete region, then these preferred amounts of surfactant may apply to the tablet as a whole.

Surfactant may be anionic (soap or non-soap) , cationic, zwitterionic, amphoteric, nonionic or a combination of these.

Anionic surfactant may be present in an amount from 0.5 to 50% by weight, preferably from 2% or 4% up to 30% or 40% by weight of the tablet composition.

In a machine dishwashing composition, organic surfactant is likely to constitute from 0.5 to 8%, more likely from 0.5 to 5% of the composition of the tablet or region thereof and is likely to consist of nonionic surfactant, either alone or in a mixture with anionic surfactant.

Synthetic (i.e. non-soap) 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 Cs-Cis; olefin sulphonates; alkane sulphonates; dialkyl sulphosuccinates; and fatty acid ester sulphonates.

Primary alkyl sulphate having the formula; ROS0₃ ^" M⁺ in which R is an alkyl or alkenyl chain of 8 to 18 carbon atoms especially 10 to 14 carbon atoms and M⁺ is a solubilising cation, is commercially significant as an anionic surfactant.

Linear alkyl benzene sulphonate of the formula;

where R is linear alkyl of 8 to 15 carbon atoms and M⁺ is a solubilising cation, especially sodium, is also a commercially significant anionic surfactant.

Frequently, such linear alkyl benzene sulphonate or primary alkyl sulphate of the formula above, or a mixture thereof will be the desired anionic surfactant and may provide 75 to 100 wt% of any anionic non-soap surfactant in the composition.

In some forms of this invention the amount of non-soap anionic surfactant lies in a range from 5 to 20 or 25 wt% of the tablet or region thereof.

It may also be desirable to include one or more soaps of fatty acids . These are preferably sodium soaps derived from naturally occurring fatty acids, for example, the fatty acids from coconut oil, beef tallow, sunflower or hardened rapeseed oil . Suitable nonionic surfactant compounds which may be used include in particular the reaction products of compounds having a hydrophobic group and a reactive hydrogen atom, for example, aliphatic alcohols, acids, amides or alkyl phenols with alkylene oxides, especially ethylene oxide.

Specific nonionic surfactant compounds are alkyl (C8-22) phenol- ethylene oxide condensates, the condensation products of linear or branched aliphatic Cs-₂₀ primary or secondary alcohols with ethylene oxide, and products made by condensation of ethylene oxide with the reaction products of propylene oxide and ethylene-diamine .

Especially preferred are the primary and secondary alcohol ethoxylates, especially the C₉_n and C₁₂-₁₅ primary and secondary alcohols ethoxylated with an average of from 5 to 20 moles of ethylene oxide per mole of alcohol.

In certain forms of this invention the amount of nonionic surfactant lies in a range from 4 to 40%, better 4 or 5 to 30% by weight of the composition of the tablet or region thereof. Many nonionic surfactants are liquids . These may be absorbed onto particles of the composition prior to compaction into tablets. Amphoteric surfactants which may be used jointly with anionic or nonionic surfactants or both include amphopropionates of the formula:

O CH₂CH₂OH

II I

RC— NH-CH₂CH₂— N-CH₂CH₂C0₂Na

where RCO is a acyl group of 8 to 18 carbon atoms, especially coconut acyl .

The category of amphoteric surfactants also includes amine oxides and also zwitterionic surfactants, notably betaines of the general formula;

where R₄ is an aliphatic hydrocarbon chain which contains 7 to 17 carbon atoms, R₂ and R₃ are independently hydrogen, alkyl of 1 to 4 carbon atoms or hydroxyalkyl of 1 to 4 carbon atoms such as CH₂OH, Y is CH₂ or of the form CONHCH₂CH₂CH₂ (amidopropyl betaine) ; Z is either a COO^" (carboxybetaine) , or of the form CHOHCH₂S0₃ - (sulfobetaine or hydroxy sultaine) .

Another example of amphoteric surfactant is amine oxide of the formula;

where R_x is Cχo to C₂o alkyl or alkenyl; R₂, R₃ and R₄ are each hydrogen or Ci to C alkyl, while n is from 1 to 5.

Cationic surfactants may possibly be used. These frequently have a quaternised nitrogen atom in a polar head group and an attached hydrocarbon group of sufficient length to be hydrophobic .

A general formula for one category of cationic surfactants is;

where each R independently denotes an alkyl group or hydroxyalkyl group of 1 to 3 carbon atoms and R denotes an aromatic, aliphatic or mixed aromatic and aliphatic group of 6 to 24 carbon atoms, preferably an alkyl or alkenyl group of 8 to 22 carbon atoms and X^" is a counterion.

The amount of amphoteric surfactant, if any, may possibly be from 3% to 20 or 30% by weight of the tablet or region of a tablet; the amount of cationic surfactant, if any, may possibly be from 1% to 10 or 20% by weight of the tablet or region of a tablet .

Water-softening agent A composition which is compacted to form tablets or tablet regions may contain a so-called water-softening agent which serves to remove or sequester calcium and/or magnesium ions in the water. In the context of a detergent composition containing organic surfactant a water-softening agent is more usually referred to as a detergency builder.

When a water-softening agent is present, the amount of it is likely to lie in a broad range from 5 better 15 wt% up to 98%wt of the tablet composition. In detergent tablets the amount is likely to be from 15 to 80%, more usually 15 to 60% by weight of the tablet.

Water-softening agents may be provided wholly by water soluble materials, or may be provided in large part or even entirely by water-insoluble material with water-softening properties.

Alkali metal aluminosilicates are strongly favoured as environmentally acceptable water-insoluble softening agents (detergency builders) for fabric washing, and are preferred in this invention. Alkali metal (preferably sodium) aluminosilicates may be either crystalline or amorphous or mixtures thereof, having the general formula: 0.8 - 1.5 Na₂O.Al₂0₃. 0.8 - 6 Si0₂. xH₂0

These materials contain some bound water (indicated as XH2O) and are required to have a calcium ion exchange capacity of at least 50 mg CaO/g. The preferred sodium aluminosilicates contain 1.5-3.5 Si0₂ units (in the formula above). Both the amorphous and the crystalline materials can be prepared readily by reaction between sodium silicate and sodium aluminate, as amply described in the literature.

Suitable crystalline sodium aluminosilicate ion-exchange materials are described, for example, in GB 1429143 (Procter & Gamble) . The preferred sodium aluminosilicates of this type are the well known commercially available zeolites A and X, the newer zeolite P described and claimed in EP 384070 (Unilever) and mixtures thereof. This form of zeolite P is also referred to as "zeolite MAP". One commercial form of it is denoted "zeolite A24" available from Ineos Silicas, UK.

Conceivably a detergency builder could be a layered sodium silicate as described in US 4664839. NaSKS-6 is the trademark for a crystalline layered silicate marketed by Hoechst (commonly abbreviated as "SKS-6"). NaSKS-6 has the delta- Na₂Si0₅ morphology form of layered silicate. It can be prepared by methods such as described in DE-A-3 , 417 , 649 and DE-A-

3,742,043. Other such layered silicates, such as those having the general formula NaMSi_xθ₂χ₊ι.yH₂0 wherein M is sodium or hydrogen, x is a number from 1.9 to 4, preferably 2, and y is a number from 0 to 20, preferably 0 can be used.

The less preferred category of water-soluble phosphorus- containing inorganic softeners includes the alkali-metal orthophosphates, metaphosphates, pyrophosphates and polyphosphates . Specific examples of inorganic phosphate detergency builders include sodium and potassium tripolyphosphates, orthophosphates and hexametaphosphates .

Non-phosphorus water-soluble detergency builders may be organic or inorganic. Inorganics that may be present include alkali metal (generally sodium) carbonate; while organics include polycarboxylate polymers, such as polyacrylates, acrylic/maleic copolymers, and acrylic phosphonates, monomeric polycarboxylates such as citrates, gluconates, oxydisuccinates, glycerol mono- di- and trisuccinates, carboxymethyloxysuccinates , carboxymethyloxymalonates , dipicolinates and hydroxyethyliminodiacetates .

Tablet compositions preferably include polycarboxylate polymers, more especially polyacrylates and acrylic/maleic copolymers which have some function as water-softening agents and also inhibit unwanted deposition onto fabric from the wash liquor. Bleach System

Tableted compositions according to the invention may contain a bleach system. This preferably comprises one or more peroxy bleach compounds, for example, inorganic persalts or organic peroxyacids, which may be employed in conjunction with activators to improve bleaching action at low wash temperatures. If any peroxygen compound is present, the amount is likely to lie in a range from 10 to 85% by weight of the composition of the tablet or region thereof. If the tablet contains surfactant and detergency builder, the amount of peroxygen compound bleach is unlikely to exceed 25%wt of the composition of the tablet or region thereof.

Preferred inorganic persalts are sodium perborate monohydrate and tetrahydrate, and sodium percarbonate, advantageously employed together with an activator. Bleach activators, also referred to as bleach precursors, have been widely disclosed in the art. Preferred examples include peracetic acid precursors, for example, tetraacetylethylene diamine (TAED) , now in widespread commercial use in conjunction with sodium perborate; and perbenzoic acid precursors. The quaternary ammonium and phosphonium bleach activators disclosed in US 4751015 and US 4818426 (Lever Brothers Company) are also of interest. Another type of bleach activator which may be used, but which is not a bleach precursor, is a transition metal catalyst as disclosed in EP-A-458397, EP-A-458398 and EP-A-549272. A bleach system may also include a bleach stabiliser (heavy metal sequestrant) such as ethylenediamine tetramethylene phosphonate and diethylenetriamine pentamethylene phosphonate.

Water-Soluble Disintegration-Promoting Particles A tablet or a region of a tablet may contain water-soluble particles to further promote disintegration. It may be preferred that such particles make up from 10 to 50% by weight of the composition of the tablet or region thereof.

Such soluble particles typically contain at least 50% (of their own weight) of one or more salts which is other than soap or organic surfactant and which has a solubility in deionised water of at least 10 g/lOOg at 20°C.

More preferably this water-soluble salt is selected from either:

• compounds with a water-solubility exceeding 50 g/lOOg in water at 20°C; or

• sodium tripolyphosphate, containing at least 50% of its own weight of the phase I anhydrous form, and which is partially hydrated so as to contain water of hydration in an amount which is at least 1% by weight of the sodium tripolyphosphate in the particles.

As will be explained further below, these disintegration- promoting particles can also contain other forms of tripolyphosphate or other salts within the balance of their composition.

If the material in such water-soluble disintegration-promoting particles can function as a detergency builder, (as is the case with sodium tripolyphosphate) then of course it contributes to the total quantity of detergency builder in the tablet composition.

The quantity of water-soluble disintegration-promoting particles may be from 10% up to 30 or 40% by weight of the tablet or region thereof. The quantity may possibly be from 12% up to 25 or 30% or more.

A solubility of at least 50 g/lOOg of deionised water at 20°C is an exceptionally high solubility: many materials which are classified as water soluble are less soluble than this.

Some highly water-soluble salts which may be used are listed below, with their solubilities expressed as grams of solid to form a saturated solution in a litre of water at 20°C:- Material Water Solubility (g/lOOg)

Sodium citrate dihydrate 72 Potassium carbonate 112 Sodium acetate 119 Sodium acetate trihydrate 76 Magnesium sulphate 7H₂0 71

By contrast the solubilities of some other common materials at 20°C are:-

Material Water Solubility (g/lOOg)

Sodium chloride 36 Sodium sulphate decahydrate 21.5 Sodium carbonate anhydrous 8.0 Sodium percarbonate anhydrous 12 Sodium perborate anhydrous 3.7 Sodium tripolyphosphate anhydrous 15

Preferably this highly water soluble salt is incorporated as particles of the material in a substantially pure form (i.e. each such particle contains over 95% by weight of the salt) . However, the said particles may contain salt of such solubility in a mixture with other material, provided the salt(s) of the specified solubility provide at least 50% by weight of these particles. As such a salt dissolves it leads to a transient local increase in ionic strength which can assist disintegration of the tablet by preventing nonionic surfactant from swelling and inhibiting dissolution of other materials.

A preferred material is sodium acetate in a partially or fully hydrated form.

Another possibility which is less preferred is that the said particles which promote disintegration are particles which contain sodium tripolyphosphate with more than 50% (by weight of the particles) of the anhydrous phase I form, and which is partially hydrated so as to contain water of hydration in an amount which is at least 1% by weight of the sodium tripolyphosphate.

Sodium tripolyphosphate is very well known as a sequestering builder in detergent compositions. It exists in a hydrated form and two crystalline anhydrous forms . These are the normal crystalline anhydrous form, known as phase II which is the low temperature form, and phase I which is stable at high temperature. The conversion of phase II to phase I proceeds fairly rapidly on heating above the transition temperature, which is about 420°C, but the reverse reaction is slow. Consequently phase I sodium tripolyphosphate is metastable at ambient temperature. A process for the manufacture of particles containing a high proportion of the phase I form of sodium tripolyphosphate by spray drying below 420°C is given in US-A-4536377.

These particles should also contain sodium tripolyphosphate which is partially hydrated. The extent of hydration should be at least l%wt of the sodium tripolyphosphate in the particles.

It may lie in a range from 1 to 4%wt, or it may be higher. Indeed fully hydrated sodium tripolyphosphate may be used to provide these particles.

The remainder of the tablet composition used to form the tablet or region thereof may include additional sodium tripolyphosphate. This may be in any form, including sodium tripolyphosphate with a high content of the anhydrous phase II form.

Suitable material is commercially available. Suppliers include Rhone-Poulenc, France and Rhodia, UK.

Alternatively a highly water soluble material, such as urea, may be used instead of the highly soluble salts mentioned above. In this case the highly soluble material may be used in the same amounts and in the same manner as for the highly soluble salt. Other Ingredients

Tablets of the invention may also contain one of the detergency enzymes well known in the art for their ability to degrade and aid in the removal of various soils and stains. Suitable enzymes include the various proteases, cellulases, lipases, amylases, and mixtures thereof, which are designed to remove a variety of soils and stains from fabrics. Examples of suitable proteases are Maxatase (Trade Mark) , as supplied by Gist- Brocades N.V., Delft, Holland, and Alcalase (Trade Mark), and Savinase (Trade Mark) , as supplied by Novo Industri A/S,

Copenhagen, Denmark. Detergency enzymes are commonly employed in the form of granules or marumes, optionally with a protective coating, in amount of from about 0.1% to about 3.0% by weight of the composition of the tablet or region thereof; and these granules or marumes present no problems with respect to compaction to form a tablet.

The tablets of the invention may also contain a fluorescer (optical brightener) , for example, Tinopal (Trade Mark) DMS or Tinopal CBS available from Ciba-Geigy AG, Basel, Switzerland. Tinopal DMS is disodium 4, 4 'bis- (2-morpholino-4-anilino-s- triazin-6-ylamino) stilbene disulphonate; and Tinopal CBS is disodium 2 , 2 ' -bis- (phenyl-styryl) disulphonate.

An antifoam material is advantageously included if organic surfactant is present, especially if a detergent tablet is primarily intended for use in front-loading drum-type automatic washing machines. Suitable antifoam materials are usually in granular form, such as those described in EP 266863A (Unilever) . Such antifoam granules typically comprise a mixture of silicone oil, petroleum jelly, hydrophobic silica and alkyl phosphate as antifoam active material, sorbed onto a porous absorbed water-soluble carbonate-based inorganic carrier material. Antifoam granules may be present in an amount up to 5% by weight of the composition of the tablet or region thereof .

It may also be desirable that a tablet of the invention includes an amount of an alkali metal silicate, particularly sodium ortho-, eta- or disilicate. The presence of such alkali metal silicates at levels, for example, of 0.1 to 10 wt%, may be advantageous in providing protection against the corrosion of metal parts in washing machines, besides providing some measure of building and giving processing benefits in manufacture of the particulate material which is compacted into tablets. A composition for fabric washing will generally not contain more than 15 wt% silicate. A tablet for machine dishwashing will frequently contain at least 20 wt% silicate.

Further ingredients which can optionally be employed in fabric washing detergent tablets of the invention include anti- redeposition agents such as sodium carboxymethylcellulose, straight-chain polyvinyl pyrrolidone and the cellulose ethers such as methyl cellulose and ethyl hydroxyethyl cellulose, fabric-softening agents; heavy metal sequestrants such as EDTA; perfumes; and colorants or coloured speckles.

Bulk Density While the starting particulate composition may in principle have any bulk density, the present invention may be especially relevant to tablets of detergent composition made by compacting powders of relatively high bulk density, because of their greater tendency to exhibit disintegration and dispersion problems. Such tablets have the advantage that, as compared with a tablet derived from a low bulk density powder, a given dose of composition can be presented as a smaller tablet.

Thus the starting particulate composition may suitably have a bulk density of at least 400 g/litre, preferably at least 500 g/litre, and possibly at least 600 g/litre.

A composition which is compacted into a tablet or tablet region may contain particles which have been prepared by spray-drying or granulation and which contain a mixture of ingredients. Such particles may contain organic detergent surfactant and some or all of the water-softening agent (detergency builder) which is also present in a detergent tablet.

Granular detergent compositions of high bulk density prepared by granulation and densification in a high-speed mixer/granulator, as described and claimed in EP-A-340013 (Unilever) , EP-A-352135 (Unilever) , and EP-A-425277 (Unilever) , or by the continuous granulation/densification processes described and claimed in EP-A-367339 (Unilever) and EP-A- 390251 (Unilever) , are inherently suitable for use in the present invention.

The separate particles containing the highly-swelling material required for this invention are preferably mixed with the remainder of the particulate composition prior to compaction.

Particle Size Control

Particle sizes can be controlled in the manufacturing process of the particles included in the composition. Oversize particles are usually removed by sieving (for example by a Mogensen screen) at the end of the production process, followed by milling and recycling of the removed oversize fraction. Undersize particles can also be removed by sieving, or if the manufacturing process employs a fluidised bed, undersized particles can be removed in that fluidised bed.

Tableting

Tableting entails compaction of a particulate composition. A variety of tableting machinery is known, and can be used. Generally it will function by stamping a quantity of the particulate composition which is confined in a die. Tableting may be carried out at ambient temperature or at a temperature above ambient which may allow adequate strength to be achieved with less applied pressure during compaction. In order to carry out the tableting at a temperature which is above ambient, the particulate composition is preferably supplied to the tableting machinery at an elevated temperature. This will of course supply heat to the tableting machinery, but the machinery may be heated in some other way also.

If any heat is supplied, it is envisaged that this will be supplied conventionally, such as by passing the particulate composition through an oven, rather than by any application of microwave energy.

The size of a tablet will suitably range from 10 to 160 grams, preferably from 15 to 60 g, depending on the conditions of intended use, and whether it represents a dose for an average load in a fabric washing or dishwashing machine or a fractional part of such a dose. The tablets may be of any shape. However, for ease of packaging they are preferably blocks of substantially uniform cross-section, such as cylinders or cuboids. The overall density of a tablet for fabric washing preferably lies in a range from 1040 or 1050g/litre preferably at least HOOg/litre up to 1400g/litre. The tablet density may well lie in a range up to no more than 1350 or even 1250g/litre. The overall density of a tablet of some other cleaning composition, such as a tablet for machine dishwashing or as a bleaching additive, may range up to 1700g/litre and will often lie in a range from 1300 to 1550g/litre.

Product forms and proportions The present invention may especially be embodied as a tablet for fabric washing. Such a tablet will generally contain, overall, from 5 to 50% by weight of organic surfactant and from 5 or 10% to 80% by weight of detergency builder which is a water softening agent. Water-soluble disintegration promoting particles may be present in an amount from 5% to 25% by weight of the composition. Peroxygen bleach may be present and if so is likely to be in an amount not exceeding 25% by weight of the total composition.

The invention may be embodied as tablets whose principal or sole function is that of removing water hardness. In such tablets the water-softening agents, especially water-insoluble aluminosilicate, may provide from 50 to 98% of the tablet composition. A water-soluble supplementary builder may well be included, for instance in an amount from 2% to 30wt% of the composition, or may be considered unnecessary and not used.

Water-softening tablets embodying the invention may include some surfactant .

The invention may be embodied as tablets for machine dishwashing. Such tablets typically contain a high proportion of water soluble salts, such as 50 to 95% by weight, at least some of which, exemplified by sodium citrate and sodium silicate, have water-softening properties.

Both water-softening and machine dishwashing tablets may include nonionic surfactant which can act as a lubricant during tablet manufacture and as a low foaming detergent during use. The amount may be small, e.g. from 0.2 or 0.5% by weight of the composition up to 3% or 5% by weight.

Tablets for use as a bleaching additive will typically contain a high proportion of peroxygen bleach, such as 25 to 85% by weight of the composition. This may be mixed with other soluble salt as a diluent. The composition of such a tablet may well include a bleach activator such as tetraacetylethylene diamine (TAED) . A likely amount would lie in the range from 1 to 20% by weight of the composition.

The invention will be further exemplified by the following examples. Further examples within the scope of the present invention will be apparent to the person skilled in the art.

Example 1

A detergent base powder, incorporating organic surfactants and detergency builder was made using known granulation technology. It had the following composition, which is shown both as weight percentages of the base powder and as parts by weight .

The amount of zeolite MAP (zeolite A24) in the table above is the amount which would be present if it was anhydrous. Its accompanying small content of moisture is included as part of the moisture and minor ingredients. Sodium carboxymethyl cellulose^' is a commonly used water soluble antiredeposition polymer. A number of further ingredients were added to this base powder resulting in the following composition:

Disintegrant granules were made by dry mixing Maize starch (Rocquette, France) , cross-linked carboxymethyl cellulose (Nylin XL-50D - FMC, USA) and PEG 1500 in the proportions shown in the table below, compacted together using a small scale roller compactor (Pharmapaktor L 200/50, Hosokawa Bepex), milled using an impact mill (Siebmeuhle FC 200, Hosokawa Bepex) and sieved to result in particles with particle sizes in the range 355 to lOOO m.

Three formulations for making detergent tablets were used. Formulation A was the complete formulation above with no added disintegrant, formulation B was 42.5 g of the complete formulation above plus 2.13 g of disintegrant particle I, and formulation C was 42.5 g of the complete formulation above plus 2.13 g of disintegrant particle II.

These formulations were compacted with variable force in a laboratory press (Specac Air press) to produce cylindrical tablets.

The strength of the tablets, in their dry state as made on the press, was determined as the force needed to break the tablet, measured using an Instron type universal testing instrument to apply compressive force on a tablet diameter (i.e. perpendicular to the axis of a cylindrical tablet) . The applied force F was progressively increased until the tablet breaks, whereupon the force at failure F_max in Newtons is recorded. A further measure of the strength of the tablets is their diametrical fracture stress σ calculated from the equation:

πDt

where σ is the diametrical fracture stress in Pascals, F_max is the applied load in Newtons to cause fracture, D is the tablet diameter in metres and t is the tablet thickness in metres.

The disintegration of the tablets (t₉o)was tested by placing a tablet on a wire gauze with 1cm by 1cm holes and then immersed into a beaker of water (1 litre) at 10°C, and the time taken for 90% by weight of the tablet to fall through the gauze is measured.

The results given below are the averages over three tablets tested.

Claims

1. A tablet of compacted particulate cleaning composition, characterised in that the composition of the tablet or a discrete region thereof comprises 0.5 to 10% by weight of disintegrant particles which comprise a mixture of:

(i) a water-insoluble, water-swellable material which expands to at least twice its original volume on contact with water, and

(ii) other material acting as a carrier therefor, which material is water-dispersible as a colloidal dispersion, and further wherein the amount by weight of carrier material

(ii) exceeds the amount of material (i) present in the disintegrant particles.

2. A tablet of compacted particulate cleaning composition, characterised in that the composition of the tablet or a discrete region thereof comprises 0.5 to 10% by weight of disintegrant particles which comprise a mixture of:

(ii) other material acting as a carrier therefor, which is either starch or a derivative obtainable by chemical treatment of starch which increases its water-solubility.

3. A tablet according to either of claim 1 or claim 2, wherein the water-insoluble, water-swellable material is an organic polymer.

4. A tablet according to claim 3, wherein the water- insoluble, water-swellable material is selected from cross- linked carboxymethyl cellulose, cross-linked polyvinylpyrrolidone, cross-linked starch, cross-linked cellulose, carboxymethyl starch, starch glycolate and cross- linked polyacrylate .

5. A tablet according to any one claims 1 to 4, wherein the disintegrant particles comprise 0.01 to 20% by weight of the water-insoluble, water-swellable disintegrant.

6. A tablet according to any one of the preceding claims, wherein the carrier material comprises from 60 to 99.9% by weight of the disintegrant particles.

7. A tablet according to any one of the preceding claims, wherein the carrier material is hydrophilic.

8. A tablet according to any one of the preceding claims in which the disintegrant particles consist of 0.01 to 20% by weight of the water-insoluble, water-swellable material, 1 to 15% by weight of a polymeric binder and 60 to 99.9% of the carrier material .

9. A tablet according to any one of the preceding claims, wherein 95% by weight of the disintegrant particles have a particle size in the range of from 350μm to lOOOμm.

10. A tablet according to any one of the preceding claims, wherein the tablet, or discrete region thereof, further comprises organic surfactant and detergency builder.

11. A tablet according to claim 10, wherein the tablet, or discrete region thereof, comprises 5 to 50% by weight organic surfactant and 10 to 80% by weight of detergency builder.

12. A tablet according to either claim 10 or claim 11, wherein the detergency builder is sodium aluminosilicate.

13. A tablet according to any one of the preceding claims wherein the tablet has a density of between 1040g/l and 1400g/l.

14. A process for making a tablet of compacted particulate cleaning composition, which process comprises the steps of mixing disintegrant particles which comprise a mixture of:

(i) a water-insoluble, water-swellable material which expands to at least twice its original volume on contact with water; and (ii) other material acting as a carrier therefor, which is water-dispersible as a colloidal dispersion or which is either starch or a derivative obtainable by chemical treatment of starch which increases its water-solubility, with other constituents of a particulate cleaning composition to form a particulate cleaning composition and placing a quantity of the particulate cleaning composition within a mould and compacting that composition within the mould.