CLEANING COMPOSITIONS

Abstract: The invention provides a tablet of compacted particulate cleaning composition containing at least one cleaning ingredient which is selected from the group consisting of organic surfactants, water softening agents and bleaches, wherein a water-swellable, water-insoluble disintegration-promoting material is present at a greater concentration in at least one zone adjacent a tablet surface than in an interior zone which is more remote from any surface of the tablet. A method of producing the tablet is also provided. The tablets exhibit an advantageous balance of strength and good disintegration properties.

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 n a single use. The tablets may be suitable for use m machine dishwashing, the washing of fabrics or other cleaning tasks. Detergent compositions m 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 containing bleach for use as an additive to a fabric washing liquor have been disclosed m US-A-4013581 (Huber/Procter and Gamble) . Tablets containing a water softening agent, for use as an additive in cleaning, are sold commercially and are one form of tablet disclosed in EP-A-838519 (Unilever) . 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. If a tablet contains organic surfactant, this functions 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) . In our published applications WO 98/46719 and WO 98/46720 we have taught that the speed of disintegration of tablets can be improved by stamping with dies (also known as punches) which bear a surface of an elastomeric material. This leads to an improved porosity at the tablet surface. 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-98/40463. EP-A-979,863 (filing date 13 August 1998, but only published 16 February 2000) discloses the inclusion of water swellable disintegrants in tablet coatings. WO 98/55583 discloses tablets with the concentration of a water-swellable polymeric material varying in different regions of the tablet to cause them to disintegrate at different rates. WO 98/55590 discloses a cleaning tablet composition comprising a water-swellable polymer in a concentration greater in at least one other region of a tablet to promote disintegration of the regions at different rates. The region may be a layer or a core or inset (or shell or coating around such inset) . In the present invention, such a disintegration-promoting material is incorporated within a tablet but is not distributed uniformly. We have found that the speed of disintegration of a tablet can be increased by concentrating water-swellable disintegrant adjacent to one or more tablet surfaces, even when the tablets have been stamped using elastomeric-surfaced dies. So, according to a first aspect of this invention, there is provided a tablet of compacted particulate cleaning composition containing at least one cleaning ingredient which is an organic surfactant, a water softening agent or a bleach, wherein a water-swellable disintegration- promoting material is present at a greater concentration in at least one zone adjacent a tablet surface than in an interior zone which is more remote from any surface of the tablet. According to a particularily preferred form of the first aspect, the water swellable disintegration-promoting material is in a form of particles with a mean particle size in a range from 250 - 1,500 micrometers. The water-swellable material may be cellulose or a material which contains cellulose mixed with other materials. However, other materials including starch are known to be effective as water-swellable disintegration-promoting materials, and these may also be used in accordance with this invention. This invention is particularly applicable when the tablets contain both surfactant and detergency builder, as in tablets for fabric washing. In a second aspect this invention provides a process for making a tablet by placing a quantity of a particulate cleaning composition within a mould and compacting that composition within the mould, characterised by placing a smaller quantity of a water-swellable disintegration- promoting material, or a composition incorporating such a material, in the mould before, after, or both before and after the said quantity of cleaning composition, so that this disintegration-promoting material lies in one or more zones of the tablet adjacent to one or more mould surfaces. This quantity of disintegration promoting material will then be absent from a further zone of the tablet formed from the quantity of cleaning composition. Forms of this invention, preferred and optional features, and materials which may be used, will now be discussed in greater detail. Water-S ellable Material A number of water-insoluble, water-swellable materials are known to be useful as tablet disintegrants, in particular for pharmaceutical tablets. Although insoluble, these materials are generally dispersible in water. A discussion of such materials is found in "Drug Development and Industrial Pharmacy", Volume 6, pages 511-536 (1980). Such materials are mostly polymeric in nature and many of them are of natural origin. Such disintegrants include starches, for example, maize, rice and potato starches and starch derivatives, such as Primojel™, carboxymethyl starch and Explotab™, sodium starch glycolate; celluloses, for example, Arbocel®-B and Arbocel®-BC (beech cellulose) , Arbocel®-BE (beech-sulphite cellulose) , Arbocel®-B-SCH (cotton cellulose), Arbocel®-FIC (pine cellulose) as well as further Arbocel® types from Rettenmaier and cellulose derivatives, for example Courlose™ and Nymcel™, sodium carboxymethyl cellulose, Ac-di-Sol™ cross-linked modified cellulose, and Hanfloc™ microcrystalline cellulosic fibres; and various synthetic organic polymers. Cellulose-containing fibrous materials originating from timber may be compacted wood pulps. So-called mechanical pulps generally incorporate lignin as well as cellulose whereas chemical pulps generally contain cellulose but little of the original lignin remains. Pulp obtained by a mixture of chemical and mechanical methods may retain some but not all of the original lignin. Suppliers of water-swellable disintegrant materials include Rettenmaier in Germany and FMC Corporation in USA. The overall quantity of water-swellable disintegration- promoting material in the tablet is preferably between 0.1 and 20% by weight, especially between 0.5 and 5% by weight. The water-insoluble, water-swellable material which is incorporated into a tablet composition preferably has a mean particle size in a range from 250μm to l,500μm, more preferably from 700μm to l,100μm. Surfactant Compounds Compositions which are compacted to form tablets or tablet regions of this invention may contain one or more organic detergent surfactants. In a fabric washing composition, these preferably provide from 5 to 50% by weight of the overall tablet composition, more preferably from 8 or 9% by weight of the overall composition up to 40%, 49% or 50% by weight. 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 4.5% of the overall composition 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 C 8 -Cι 5 ; olefin sulphonates; alkane sulphonates; dialkyl sulphosuccinates; and fatty acid ester sulphonates. Primary alkyl sulphate having the formula; ROS0 3 " 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 composition. 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 (C 8 - 22 ) phenol-ethylene oxide condensates, the condensation products of linear or branched aliphatic C 8 -2o 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 Cg-n and Cι 2 _ 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. 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 CH 2 CH 2 OH II I RC—NH—CH 2 CH 2 —N—CH 2 CH 2 C0 2 Na 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 R 4 is an aliphatic hydrocarbon chain which contains 7 to 17 carbon atoms, R 2 and R 3 are independently hydrogen, alkyl of 1 to 4 carbon atoms or hydroxyalkyl of 1 to 4 carbon atoms such as CH 2 OH, Y is CH 2 or of the form CONHCH 2 CH 2 CH 2 (amidopropyl betaine) ; Z is either a COO " (carboxybetaine) , or of the form CHOHCH 2 S0 3 - (sulfobetaine or hydroxy sultaine) . Another example of amphoteric surfactant is amine oxide of the formula O R 2 II I R—C—N (CH 2 ) n —N- ) R 4 R 3 where R x is Cι 0 to C 2 o alkyl or alkenyl; R 2 , R and R 4 are each hydrogen or Ci to C 4 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 h 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. The particles of water-swellable material may be mixed with surfactant, so that they do not end up floating on top of the wash liquor. It is suitable for this purpose to spray them with a liquid anionic surfactant such as Aerosil OT, which is the sodium salt of sulphosuccinic acid (2- ethylhexyl) ester. Such a surfactant may be sprayed on in a quantity which is from 0.01 to 10% of the weight of the water-swellable particles, preferably from 0.01 to 0.5% of their weight. 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 (detergency builder) is present, the amount of it is likely to lie in a broad range from 5%, preferably 15 wt% up to 98% 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. Alkali metal (preferably sodium) aluminosilicates may be either crystalline or amorphous or mixtures thereof, having the general formula: 0.8 - 1.5 Na 2 0.Al 2 0 3 . 0.8 - 6 Si0 2 . xH 2 0 These materials contain some bound water (indicated as xH 2 0) 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 Si0 2 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 alummosilicate 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 m 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". Conceivably a water-insoluble water-softener (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-Na 2 Si0 5 morphology form of layered silicate. It can be prepared by methods such as described m DE-A-3, 417 , 649 and DE-A-3, 742, 043. Other such layered silicates, such as those having the general formula NaMSι x 0 2x+ ι yH 2 0 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 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 tπpolyphosphates, orthophosphates and hexametaphosphates . Non-phosphorus water-soluble water-softening agents 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. The water-soluble builders may be present in the amount srated above, in particular in amounts of from 10 - 80% by weight . 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. If the tablet contains surfactant and detergency builder, the amount of peroxygen compound bleach is unlikely to exceed 25% of the composition. 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 promote disintegration. These would be in addition to the water-swellable, water-insoluble particles concentrated in surface zones of the tablet as required by this invention. Such soluble particles typically contain at least 40% (of their own weight) of one or more materials selected from • compounds with a water-solubility exceeding 50 grams per 100 grams water phase I sodium tripolyphosphate • sodium tripolyphosphate which is partially hydrated so as to contain water of hydration in an amount which is at least 0.5% by weight of the sodium tripolyphosphate in the particles. It is especially preferred that said soluble particles are selected from urea, salts with a water-solubility exceeding 50 gm per 100 gms water, and mixtures thereof. As will be explained further below, these dismtegration- 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 dismtegration- 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 3 or 5% up to 30 or 40% by weight of the tablet or region thereof. The quantity may possibly be from 8% up to 25 or 30% or more. However, it is within this invention that the amount of such water-soluble disintegration-promoting particles is low, below 5% of the tablet or region, reliance being placed on insoluble swellable particles. One possibility is that these particles contain at least 40% of their own weight, better at least 50%, of a material which has a solubility in deionised water at 20°C of at least 50 grams per 100 grams of water. These particles may provide material of such solubility in an amount which is at least 7 wt% or 12 wt% of the composition of the tablet or discrete region thereof. A solubility of at least 50 grams per 100 grams of 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 materials which may be used are listed below, with their solubilities expressed as grams of solid to form a saturated solution in 100 grams of water at 20°C:- Material Water Solubility (g/lOOg) Sodium citrate dihydrate 72 Potassium carbonate 112 Urea >100 Sodium acetate 119 Sodium acetate trihydrate 76 Magnesium sulphate 7H 2 0 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 material is incorporated as particles of the material in a substantially pure form (i.e. each such particle contains over 95% by weight of the material) . However, the said particles may contain material of such solubility in a mixture with other material, provided that material of the specified solubility provides at least 40% by weight of these particles. A preferred material is sodium acetate in a partially or fully hydrated form. It may be preferred that the highly water-soluble material is a salt which dissolves in water in an ionised form. 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. Another possibility is that the said particles which promote disintegration are particles containing sodium tripolyphosphate with more than 40% (by weight of the particles) of the anhydrous phase I form. 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. Particles which contain this phase I form will often contain the phase I form of sodium tripolyphosphate as at least 50% or 55% by weight of the tripolyphosphate in the particles . Suitable material is commercially available. Suppliers include Rhone-Poulenc, France and Albright & Wilson, UK. Another possibility is that the particles which promote disintegration are particles which contain at least 40 wt% (by weight of the particles) of phase I sodium tripolyphosphate which is partially hydrated. The extent of hydration should be at least 0.5% by weight of the sodium tripolyphosphate in the particles. It preferably lies in a range from 0.5 to 4% by weight of the particles, or it may be higher. Indeed fully hydrated sodium tripolyphosphate may be used to provide these particles. It is possible that the particles contain at least 40 wt% sodium tripolyphosphate which has a high phase I content but is also sufficiently hydrated so as to contain at least 0.5% water by weight of the sodium tripolyphosphate. 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. 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, a ylases, 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 Savmase (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; 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, Tmopal (Trade Mark) DMS or Tmopal CBS available from Ciba-Geigy AG, Basel, Switzerland. Tmopal DMS is disodium 4, 'bis- (2- morpholιno-4-anιlιno-s-tπazιn-6-ylamιno) stilbene disulphonate; and Tmopal 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. It may also be desirable that a tablet of the invention includes an amount of an alkali metal silicate, particularly sodium ortho-, meta- 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, fabnc- softening agents; heavy metal sequestrants such as EDTA; perfumes; and colorants or coloured speckles. Particle Size and Distribution A tablet of this invention, or a discrete region of such a tablet, is a matrix of compacted particles. Preferably the particulate composition has an average particle size in the range from 200 to 2000 μm, more preferably from 250 to 1400 μm. Fine particles, smaller than 180 μm or 200 μm may be eliminated by sieving before tableting, if desired, although we have observed that this is not always essential. 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 340013A (Unilever) , EP 352135A (Unilever) , and EP 425277A (Unilever) , or by the continuous granulation/densification processes described and claimed in EP 367339A (Unilever) and EP 390251A (Unilever) , are inherently suitable for use in the present invention. Preferably, separate particles of the water-insoluble, water-swellable disintegration-promoting material required for this invention, and any optional water-soluble particles to promote disintegration, are mixed with the remainder of the particulate composition prior to compaction. 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 surfactant and from 5 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. In another type of tablet formulation, the tablet may contain from 0-5% by weight of surfactant, from 0.1-20% by weight of said water-swellable disintegration-promoting particles and either from 50-98% by weight of water- softening agent or from 25 to 85% by weight of a bleach. 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 this 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 overall quantity of disintegration-promoting water- swellable material within a tablet may well be from 0.5 to 15% preferably from 1% to 8% or 10% by weight of the whole tablet. 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. In order to provide water-swellable disintegrant adjacent to surfaces of the tablet it can be put into a tableting mould before the remainder of the composition or after the remainder of the composition, or both, but before the mould is closed. In one possible procedure a small quantity of disintegrant- promoting particulate material is placed in a tableting mould, the cleaning composition for the bulk of the tablet is then placed in the mould, a small further quantity of disintegrant is added to the mould on top of the composition already in the mould and then the mould is closed and the contents compacted into a tablet. The resulting tablet will have a greater concentration of disintegrant adjacent to opposite tablet surfaces than within the tablet interior. The surface zone or zones of the tablet in which the water- swellable disintegrant is concentrated do not need to be one or more layers with defined boundaries. The water- swellable disintegrant which is concentrated at one or more surface zones will generally be mixed at the surface zone with some of the cleaning composition which also provides an interior zone where there is less of the water-swellable disintegrant . Consequently, water-swellable disintegrant which is to be concentrated adjacent a tablet surface could be put into a tableting mould concurrently with some of the cleaning composition but before the majority of it. It could be put into a tableting mould after the majority of the cleaning composition but concurrently with the last part of the cleaning composition. Furthermore both methods of addition can be used concurrently. This invention can be utilised in tablets made with two separate layers of respective different cleaning compositions . The sequence of addition to the mould might then be (i) a small quantity of swellable disintegrant, (ii) cleaning composition for one layer of the tablet, (iii) cleaning composition for the second layer of the tablet, (iv) a small additional quantity of water-swellable disintegrant . Although the surface zone(s) containing water-swellable disintegrant do not need to be distinct layers of the tablet, this is nevertheless possible. So a further possibility is that the water-swellable disintegrant is incorporated in a cleaning composition used to form a layer of the tablet adjacent to a surface or two layers adjacent two opposite surfaces of the tablet, while a further layer which provides the tablet interior contains a lesser concentration of the disintegrant or none at all. The mould in which the tablet is formed may be provided by an aperture within a rigid structure and a pair of punches movable towards each other within the aperture to compact a composition within the aperture. A tableting machine may have a rotary table defining a number of apertures each with a pair or associated dies which can be driven into an apertures. Each die may be provided with an elastomeric layer on its surface which contacts the tablet material, as taught in WO 98/46719 or WO 98/46720. 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 1050gm/lιtre preferably at least llOOgm/litre up to 1400gm/lιtre . The tablet density may well lie in a range up to no more than 1350 or even 1250gm/lιtre . 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 1700gm/lιtre and will often lie in a range from 1300 to 1550gm/lιtre . The accompanying drawings illustrate the formation of a tablet in accordance with this mvention. Figure 1 is a diagrammatic section of a tableting mould Fig. 2 is a cross-sectional view of a tablet formed in such a mould. Figs. 3, 4 and 5 illustrate the filling of the mould so as to form a three-layer tablet. Fig. 6 is a cross-sectional view of a tablet formed by the procedure shown in Figs. 3, 4 and 5. Referring to Fig. 1, the mould is defined by a cylindrical aperture 10 in a rotary tablet 12 of a tableting machine. Associated with the aperture 10 are a lower punch 14 and an upper punch 16 which can be driven into the aperture 10 so as to compress between them any composition placed in the aperture. A tablet in accordance with this invention can be made by placing a small quantity of water-swellable disintegrant within the aperture 10 so that it lies on the upper face of the lower punch 14. The mould is then filled with a composition for the tablet, a further small quantity of water-swellable disintegrant is placed onto the upper surface of the composition within the aperture 10, the punch 16 is then driven down to close the mould and the two punches are driven together to compact the contents of the mould into a tablet as shown in Fig. 2 which has flat upper and lower faces 22 where the water-swellable disintegrant will be concentrated. The interior of the tablet and its cylindrical surface 28 are formed solely by the cleaning composition, but at the flat faces 22 the cleaning composition is mixed with the water-swellable disintegrant which was put in the mould before and after the cleaning composition. Figs. 3 onwards illustrate a slightly different procedure, also embodying the invention. At a first station shown in Fig. 3 the lower punch 14 is raised to be slightly below the upper surface of the rotary table 12. The space above the lower punch 14 is filled with a composition 24 containing water-swellable disintegrant together with other constituents . At a subsequent station the lower punch 14 is lowered to the position shown in Fig.4 creating a space above the composition 24 which is filled with a further composition 26 in which either the water-swellable disintegrant is absent or it is present at a lesser concentration than in composition 24. Next at a third station shown by Fig. 5 the lower punch 14 is lowered further and more of the composition 24 is filled into the top of the cavity within the rotary table 12. Then as before the upper punch 16 which has not been shown in Figs. 3 to 5 is lowered to close the cavity and the punches 14, 16 are driven together to form a three layer tablet as illustrated diagrammatical in Fig. 6. In the tablet of Fig. 6 as in the tablet of Fig. 2 there is a greater concentration of water-swellable disintegrant adjacent to surfaces 22 of the tablet than in the interior of the tablet which has the same composition as regions adjacent to the cylindrical surface 28 of the tablet. Example A detergent base powder, incorporating organic surfactants, a small percentage of crystalline sodium acetate trihydrate, and zeolite MAP 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. The base powder and other ingredients were mixed together as set out in the following table, to form compositions indicated as A and B. Arbocel Al is a water-insoluble cellulosic disintegrant obtained from wood pulp. It was sieved before use and the fraction which was used had a particle size in the range 500-710 micrometers. Formulation A was compacted in a laboratory press to produce cylindrical tablets with a weight of approximately 40 grams. The moveable dies had elastomer on their faces which contacted the composition placed in the mould. Formulation B was also used to make tablets using the same press and mould parts. However, the procedure followed was that a quantity of Arbocel equal to 0.25% of the formulation was sprinkled into the empty mould so as to lie on the upper surface of the lower punch as described earlier with reference to Fig. 1, then the formulation B was placed in the mould cavity and finally a further quantity of Arbocel Al again in a quantity equivalent to 0.25% of the total composition was sprinkled on top of the composition before the upper punch was driven into the mould to compact the composition to a tablet. Thus tablets of formulation A and tablets from formulation B had identical overall composition but in the case of the tablets from formulation B there was a greater concentration of Arbocel Al adjacent the upper and lower surfaces of the tablets than in the tablet interior. The tablets were tested by placing two previously weighed tablets of each type in a washing machine dispenser. The dispenser was of a type used in Philips washing machines. Water at 10°C flowing at a rate of 5 litres per minute was passed through the dispenser for a period of one minute, the residue of the tablets remaining in the dispenser was then removed, re-weighed, dried at 100°C for 24 hours to give constant weight and weighed again. With tablets of formulation A, residue collected from the dispenser tray and dried to constant weight was found to be more than 80% of the original weight of the tablet placed in the dispenser tray. By contrast with tablets from formulation B where a small quantity of the Arbocel was concentrated adjacent the upper and lower surfaces of the tablets, the residue recovered from the tray and dried to constant weight was less than 15% of the original weight of the tablets. Thus, under identical conditions, tablets in accordance with the invention disintegrated to a much greater extent.

Claims: CLAIMS : 1. A tablet of compacted particulate cleaning composition containing at least one cleaning ingredient which is an organic surfactant, a water softening agent or a bleach, wherein a water-swellable, water-insoluble disintegration-promoting material is present at a greater concentration in at least one zone adjacent a tablet surface than in an interior zone which is more remote from any surface of the tablet. 2. A tablet according to claim 1 wherein the water- swellable disintegration-promoting material contains cellulose . 3. A tablet according to claim 1 of claim 2 wherein the overall quantity of water-swellable disintegration- promoting material in the tablet is between 0.1 and 20% by weight of the tablet. 4. A tablet according to any one of the preceding claims wherein the water-swellable disintegration-promoting material is in the form of particles with a mean particle size in a range from 250 to 1,500 micrometers. 5. A tablet according to any one of the preceding claims wherein the water-swellable disintegration-promoting material is in the form of particles with a mean particle size in a range from 700 to 1,100 micrometers. 6. A tablet according to any one of the preceding claims wherein the tablet contains from 5 to 50% by weight of surfactant and from 5 to 80% by weight of water-softening agent . 7. A tablet according to any one of claims 1 to 5 wherein the tablet contains from 0 to 5% by weight of surfactant, from 0.1 to 20% by weight of said water-swellable disintegration-promoting particles and either from 50 to 98% by weight of water-softening agent or from 25 to 85% by weight of a bleach. 8. A tablet according to any one of the preceding claims which also contains water-soluble disintegration-promoting particles containing at least 40% (by weight of the particles) of one or more materials selected from, • compounds with water-solubility exceeding 50 grams per 100 grams water • phase I sodium tripolyphosphate sodium tripolyphosphate which is partially hydrated so as to contain water of hydration in an amount which is at least 0.5% by weight of the sodium tripolyphosphate in the particles. 9. A tablet according to claim 8 wherein the water- soluble disintegration-promoting particles contain at least 40% (by weight of the particles) of one or more compounds selected from urea, salts with a water-solubility exceeding 50gm per lOOgms water, and mixtures thereof. 10. A tablet according to claim 9 wherein said water- soluble disintegration-promoting particles in the tablet or region thereof contain at least 40% (by weight of the particles) of phase I sodium tripolyphosphate which is partially hydrated so as to contain water of hydration in a range from 0.5 to 4% by weight of these particles. 11. A tablet according to claim 8, claim 9 or claim 10, wherein the tablet contains from 8 to 25 wt% of said water- soluble disintegration-promoting particles. 12. A tablet according to any one of the preceding claims wherein the tablet contains water-insoluble detergency builder in an amount from 5 to 98% by weight of the tablet or said region thereof. 13. A tablet according to any one of claims 1 to 11 which contains from 10 to 80% by weight of water-soluble detergency builder. 14. A tablet according to any one of the preceding claims which contains 8 to 49% by weight of surfactant. 15. Process for making a tablet as claimed in any one of the preceding claims, which comprises placing a quantity of particulate cleaning composition within a mould and compacting that composition within the mould, characterised by placing a smaller quantity of a water-swellable, water- insoluble disintegration-promoting material, or a composition incorporating such a material, in the mould before, after or both before and after the said quantity of cleaning composition, so that the disintegration promoting material lies in one or more zones of the tablet adjacent one or more mould surfaces . 16. A process according to claim 15 wherein the mould has an aperture within a rigid structure and a pair of punches movable towards each other within the cavity to compact a composition within the aperture.

Inventors: CALLAGHAN IAN, JANSSEN ROGER, CALLAGHAN, IAN, JANSSEN, ROGER
Applicants: LEVER HINDUSTAN LTD, UNILEVER NV, UNILEVER PLC, HINDUSTAN LEVER LTD, UNILEVER N.V.
Application year: 2000
Main classification: C11D17
IPC codes: C11D3, C11D17