DETERGENT COMPOSITIONS

Abstract: Tablets of detergent composition are compacted using relatively movable mould parts, at least one of which bears an elastomeric layer to contact the composition. This enhances permeability at the tablet surface and hence the speed of water uptake and speed of dissolution/disintegration at the time of use. Compaction is carried out with sufficient pressure to form tablets containing from 20 to 35 % air by volume. Tablets of the invention take up water rapidly upon immersion, such that at least 65 % of the air space within the tablet is filled with water within 30 seconds.

Description: DETERGENT COMPOSITIONS This invention relates to the manufacture of detergent compositions in the form of tablets intended to be consumed when washing a single load of laundry. When manufacturing a detergent composition for fabric washing there are a number of possible options. Such compositions have for many years been manufactured in particulate form, commonly referred to as powders. Detergent compositions can also be manufactured as liquids. Tablets, to which this invention relates, are yet another possibility. When formulating a detergent composition there is scope to make both qualitative and quantitative choices concerning the ingredients. Anionic detergent actives are the most commonly used, usually together with nonionic detergent actives. Amongst the anionic detergent actives which are commercially available, linear alkylbenzene sulphonate and primary alkyl sulphate are commonly used. There has been a trend for particulate detergent compositions to be manufactured with a bulk density higher than 650 g/litre which is a departure from older practice when bulk densities were customarily lower Detergent compositions in tablet form have, potentially at least, several advantages over powder products. They do not require the user to measure out a volume of powder or liquid. Instead one or several tablets provide an appropriate quantity of composition for washing a single load in a washing machine or possibly by hand. They are thus easier for the consumer to handle and dispense. Detergent compositions in tablet form are generally made by compressing or compacting a detergent powder which includes both detergent active and detergency builder. It is desirable that tablets have adequate strength when dry, yet disperse and dissolve quickly when added to wash water. There have been a number of disclosures relating to the manufacture of detergent tablets which have both strength and rapidity of disintegration in water, for example EP-A- 522766. GB-A-1080066 teaches that tablets should have void space between particles in order to allow penetration of water into the tablet at the time of use. The teaching of this document is that the void volume should be from 35 to 60% of the total tablet volume. US-A-3081267 teaches that void space within a tablet and communicating with external air should be from 40 to 60% by volume of the tablet. Both of these documents teach that after the tablets are made by compaction of the particulate detergent composition the tablets should be sprayed on their exterior with water, which is then allowed to dry. The effect of this is to cause partial hydration and dissolution at the exterior of the tablets thus cementing material together at the tablet exterior. This must of course reduce porosity in the region of the tablet surface . These two documents date from 1963-1966. In more recent documents there has been disclosure of tablets of lower void volume and in Example 6 of EP 711828 tablets are disclosed which have porosities corresponding to 30% or 20% of air in the tablet volume. We have now found that a good rate of dissolution/disintegration in a wash liquor and low residues on fabric can be achieved by compacting a particulate detergent composition to give a tablet with porosity in the range 17 or 20 up to 35% air by volume in the tablet and with a permeable exterior such that water rapidly penetrates into the tablet upon immersion. We have found that the use of mould parts surfaced with elastomer is useful in enhancing permeability at a tablet exterior, frequently giving a useful improvement compared to all-steel mould parts. Consequently, in a first aspect, this invention provides a method for the manufacture of tablets of detergent composition, comprising compacting a particulate composition in a mould consisting of a plurality of mould parts which are movable relative to each other, at least one of the mould parts having an elastomeric coating on a surface area which contacts the composition, using sufficient pressure to form tablets containing from 20 to 35% air by volume, preferably from 23 to 30 or 33% air by volume . Determination of porosity The porosity of a tablet is conveniently expressed as the percentage of its volume which is air (i.e. empty space) . The air content of a tablet can be calculated from the volume and weight of the tablet, provided the true density of the solid content is known. The latter can be measured by compressing a sample of the material under vacuum with a very high applied force, then measuring the weight and volume of the resulting solid object. Elastomers Preferably the elastomer layer on one or more mould parts has a thickness of at least 300μm (0.3mm), better at least 400μm (0.4mm) or at least 500μm (0.5mm). Elastomers are polymers which are deformable, but return to approximately their initial dimensions and shape upon release of the deforming force. Generally they are polymers with long flexible chains, with some cross-linking between chains so as to form a cross-linked network structure.; The network structure restrains the movement of the macro-molecular chain molecules and as a result recovers rapidly after deformation. The term "elastomeric" includes materials as defined in ISO (International Standard Organisation) 1982 as an "elastomer", or "rubber". Also included in the definition of "elastomeric" materials according to the invention are thermoplastic elastomers and copolymers and blends of elastomers, thermoplastic elastomers and rubbers. At low temperature, elastomers are hard and brittle. Then with increasing temperature an elastomer goes through a rubbery phase after softening and retains its elasticity and elastic modulus until its decomposition temperature is reached. The material should of course be in its rubbery state at the operating temperature of the press. Preferably the elastomeric material according to the invention is selected from those classes described in American Society for Testing and Materials D1418 which include : - 1. Unsaturated carbon chain elastomers (R Class) including natural rubbers and butadiene acrylonitrile copolymer, e.g. "Perbunan" ex Bayer. 2. Saturated carbon chain elastomers (M Class) including ethylene-propylene types, e.g. "Nordel" ex DuPont and fluorine containing types, e.g. "Viton" ex DuPont. 3. Substituted silicone elastomers (Q Class), e.g. as available from Dow Corning. 4. Elastomers containing carbon, nitrogen and oxygen in the polymer chain (U Class), e.g. polyurethane ex Belzona. Additional materials, for example fillers, can be incorporated in the elastomeric material to modify its mechanical and processing properties. The effects of filler addition depends on the mechanical and chemical interaction between the elastomeric material and the filler. Fillers can be used to improve tear resistance for example. Suitable fillers include carbon blacks; silicas; silicates; and organic fillers such a styrene or phenolic resins. Other optional additives include friction modifiers and antioxidants . An elastomeric coating can be applied to mould surfaces as a solution in organic solvent. The solvent is allowed to evaporate, leaving a coating of the elastomer on the mould surface . The coating solution may be applied by spraying, or by brushing on as if it were paint. A thermoplastic elastomeric material may be applied to a mould surface as a melt, and allowed to cool. Once again application may be by brushing or spraying onto the mould surface . When an elastomeric material requires cross-linking, this may be in situ on a mould surface by incorporating a cross- linking agent in the coating material before it is applied, but "curing" the material so as to bring about the cross- linking after application to the mould surface. An elastomeric coating applied as a liquid, either as a solution or as a melt, will generally be relatively thin, probably with a thickness less than 500μm, for example in the range from 250μm to 500μm. Suitable elastomeric coatings can be obtained from materials such as liquid silicone rubbers such as Silastic 9050/50 P A+B (ex Dow Coming) which after curing has a modulus of elasticity about 2-3 Mpa; and polyurethane, for example Belzona PU221, as hereinafter defined, which after curing has a modulus of elasticity of about 9MPa, and Belzona 2131 (MP Fluid Elastomer) , a 2 part product based on a diphenylmethane 4 , 4 ' -diisoanate (MDI) system with a phenylmecuric neodecanoate catalyst . An elastomeric coating may alternatively be provided by a piece of pre- formed, elastomer such as disc, cut from a sheet of elastomer and secured to the die surface with adhesive. Pre-formed elastomer sheet will likely have a thickness of at least 500μm, often at least 700μm, as in a range from 0.7 to about 2.0mm. Even thicker layers could possibly be used, eg up to about 3.0mm. Mould parts, to which an elastomeric layer is applied in accordance with this invention, will generally be metallic, most usually steel. Other rigid materials such as ceramics may possibly be used. A mould surface may be subjected to pre-treatment to improve the bond strength between the surface and the elastomeric layer. The aim of pre-treatment is to remove weak boundary layers, for example weak oxides on metals; optimise the degree of contact between surface and coating and/or alter the surface topography such that the bondable surface area is increased, and to protect the surface before bonding to it. Notably a surface may be treated by mechanical abrasion - techniques include wire brushing abrasion papers, and blasting techniques such as water, grit, sand or glass bead blasting. The application of elastomer layers to dies will generally involve removing the dies from the press, and it may be convenient to maintain a stock of dies in readiness for use - which is reasonably practicable for industrial production. Adhesives suitable for securing an elastomer layer to a rigid mould surface include two-part epoxy resin and one- part cyanoacrylate types. Two-part epoxy resin adhesive is sold under the trade mark "Araldite" by Ciba Geigy Plastics, Duxford, England. Water uptake The speed with which water can penetrate into a tablet, which indicates whether interior porosity is open to the exterior through a permeable surface layer, can be assessed by a test of tablet wetting on partial immersion. The following procedure is suitable: A tablet is weighed, then supported on a wire mesh support within a container which is larger than the tablet . (The wire mesh support exposes more of the tablet surfaces than exposed than would be the case if the tablet was simply resiting on the base of the container.) Demineralised water, with coloured ink or dye dissolved in it, is poured into the container until it covers three quarters of the tablet surface. After 30 seconds the tablet is lifted out of the water, held for 5 seconds to allow water to drain off its surfaces, and weighed again. The increase in tablet weight is of course the weight of water taken up, and a measure of the speed with which water is taken up through capillary action. This volume of water is then expressed as a percentage of the air volume within the tablet . The part of the tablet which was not immersed in water is inspected visually. If the void space within the tablet has become completely (or nearly completely) filled with water, then this part of the tablet will have become coloured with the dye in the water. If water has not penetrated fully into the tablet, the immersed surface of the tablet will be coloured by the dye, but part of the - surface which remained dry will also remain free of dye. Fig. 5 of the drawings illustrates the application of this test to a cylindrical tablet with a radius of 22cm and a height of 20cm. A cylindrical dish 30 is used. A piece of wire mesh, aperture width 0.5cm, is cut and shaped to provide a stand 32 within the dish. The tablet 34 for test is weighed and placed so that one flat face rests on this stand. Water containing a trace of black ink is poured into the dish almost up to a level 36, very close to the upper flat face 38 of the tablet, which is approximately 25% of the tablet surface and remains exposed to air. After a set time, usually 30 seconds, the tablet is removed, allowed to drain, and re-weighed. If the pores within the tablet did not fill completely with water, a circle at the centre of the face 38 of the tablet retains the original white colour of the tablet, while the rest of the tablet has the black colour of the ink. It may be possible to support tablets in more than one orientation for partial immersion. If so, the orientation found to give greatest water uptake should be adopted for the test of wetting. In practice, the extent of tablet wetting is not greatly affected by variation in the percentage surface are exposed to water, so that a useful result can be obtained when the percentage of the tablet surface covered by the water is anywhere from 70 to 80%. It is desirable that in this test, at least 65%, better at least 80% of the void space within the tablet is filled with water within 30 seconds. In a second aspect therefore, this invention provides a tablet compacted from a particulate detergent composition to give a tablet porosity in the range 20 to 35% air by volume, and such that at least 65% of the air space within the tablet is filled with water within 30 seconds, upon partial immersion such that three quarters of the tablet surface is in contact with water. Factors affecting porosity and wetting Tablets are made by compacting a quantity of particulate detergent composition in a mould having parts which are movable relative to each other and are forced together to compact the composition into a tablet. For any chosen composition, the porosity of tablets, i.e. their percentage air volume, varies inversely with the pressure applied to compact the composition into tablets while the strength of the tablets varies with the pressure applied to compact them into tablets. Thus the greater the compaction pressure, the stronger the tablets but the smaller the air volume within them. The amount of pressure needed to obtain a porosity in the range from 25 to 35% can be found by making tablets with varying amounts of applied force, and measuring the porosity of the tablets- obtained. We have found that a number of features of a particulate detergent composition can assist in obtaining tablets which are permeable at their exterior as well as having internal porosity. It is desirable that the particulate composition has high bulk density. This is desirably at least 650gm/litre, better at least 700 to 750gm/litre. It is desirable that the proportion of fine particles, in the particulate composition is low or zero. Thus it desirable has a content of fine having particle size 200μm or less, which is less than 5% by weight of the composition. As is well known, fines can be removed by sieving. It is helpful to incorporate into the particulate composition a binder material. Preferred is that at least some of the particles of the detergent composition have the binder material applied to their surface. Then, when the composition is compacted, this coating serves as a binder distributed within the composition. It is strongly preferred that the binder is water-soluble and that it serves as a disintegrant by disrupting the structure of the tablet when the tablet is immersed in water, as taught in our EP-A-522766. The binder material should melt at a temperature of 35 °C, better 40 'C or above, which is above ambient temperatures in many temperate countries. For use in hotter countries it will be preferable that the melting temperature is somewhat above 40 °C, so as to be above the ambient temperature . For convenience the melting temperature of the binder material should be below 80 °C. Preferred binder materials are synthetic organic polymers of appropriate melting temperature, especially polyethylene glycol . Polyethylene glycol of average molecular weight 1500 (PEG 1500) melts at 45°C and has proved suitable. Polyethylene glycols of molecular weight 4000 and 6000 melt at about 55 °C and 62 °C respectively. Other possibilities are polyvinylpyrrolidone, and polyacrylates and water-soluble acrylate copolymers. The binder may suitably be applied to the particles by spraying, e.g. as a solution or dispersion. The binder is preferably used in an amount within the range from 0.1 to 10% by weight of the tablet composition, more preferably at least 1%, better at least 3%. It is preferred that the amount is not more than 8% or even 6%. As an alternative to use of a binder material, the composition may be formulated to be somewhat sticky. If the anionic detergent active is alkyl benzene sulphonate, particulate compositions are generally more sticky than when primary alkyl sulphate is used. The stickiness of a detergent composition can also be increased by spraying onto it a small amount of water or an organic liquid - perfume can be used for this . It can prove beneficial to stamp tablets at a temperature which is above ambient, although not above the melting point of any binder material, as taught by our EP-A-711828. By adopting some, or all, of these expedients, and adjusting the compaction pressure, we have found that it is possible to make tablets with the required porosity and permeable exterior, using conventional steel dies. However, a permeable exterior can more easily be obtained if at least one of the mould parts used in compacting a detergent composition is provided with an elastomeric surface in accordance with the first aspect of this invention. Compositions The particulate composition which is compacted may be a mixture of particles of individual ingredients, but usually will comprise particles which themselves contain a mixture of ingredients. Such particles containing a mixture of ingredients may be produced by a granulation process and may be used alone or together with particles or single ingredients. A detergent composition will normally contain detergent active and detergent builder. Other ingredients are optional, but usually there will be some other ingredients in addition to the detergent active and detergency builder. The amount of detergent active in a bar or tablet is suitably from 2 to 60wt% and is preferably from 5 or 8wt% up to 40 to 50wt%. Detergent-active material present may be anionic (soap or non-soap) , cationic, zwitterionic, amphoteric, nonionic or any combination of these. Anionic detergent-active compounds may be present in an amount of from 0.5 to 40 wt%, preferably from 2 or 4% to 30 or 40 wt%, more preferably from 8 to 30 wt% . Synthetic (i.e. non-soap) anionic surfactants are well known to those skilled in the art. Examples include alkylbenzene sulphonates, 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 especially sodium, is commercially significant as an anionic detergent active. Linear alkyl benzene sulphonate of the formula F /= XJ ■ so, M 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 detergent active. Frequently, such linear alkyl benzene sulphonate or primary alkyl sulphate of the formula above, or a mixture thereof will be the desired anionic detergent and may provide 75 to 100wt% of any anionic non-soap detergent in the composition. In some forms of this invention, the amount of non-soap anionic detergent lies in a range from 0.5 to 15 wt% of the composition. It may also be desirable to include one of 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 detergent 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 either alone or with propylene oxide. Specific nonionic detergent compounds are alkyl (C 8 _ 22 ) phenol-ethylene oxide condensates, the condensation products of linear or branched aliphatic C 8 _ 20 primary or secondary alcohols with ethylene oxide, copolymers of ethylene oxide and propylene oxide, and products made by condensation of ethylene oxide with the reaction products of propylene oxide and ethylene-diamine . Other so-called nonionic detergent compounds include long-chain amine oxides, tertiary phosphine oxides, and dialkyl sulphoxides . Especially preferred are the primary and secondary alcohol ethoxylates, especially the C 10 _ 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 detergent lies in a range from 2 to 40%, better 3, 4 or 5 to 30% by weight of the composition, yet more preferably from 3, 4 or 5% up to 10 or 15% by weight. Since the nonionic detergent compounds are generally liquids, these may be absorbed on a porous carrier. Preferred carriers include zeolite, sodium perborate monohydrate and Burkeite (spray-dried sodium carbonate and sodium sulphate as disclosed in EP 221776 (Unilever) . Products of this invention also include detergency builder and this may be provided by water-soluble salts or by water- insoluble material. Examples of water-soluble builders are sodium tripolyphosphate, pyrophosphate and orthophosphate; soluble carbonates, e.g. sodium carbonate; and organic builders containing up to six carbon atoms, e.g. sodium tartrate, sodium citrate, trisodium carboxymethyloxysuccinate . In particular phosphate or polyphosphate detergency builder may provide at least 5% by weight, often at least 10% by weight of the overall composition. Alkali metal (preferably sodium) aluminosilicates are water- insoluble builders. They may be incorporated in amounts of up to 60% by weight (anhydrous basis) of the composition, and may be either crystalline or amorphous of mixtures thereof, having the general formula: 0.8 - 1.5 Na 2 O.Al 2 0 3 0.8 - 6 SiO- These materials contain some bound water 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) . Suitable crystalline sodium aluminosilicate ion-exchange detergency builders 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 novel zeolite P described and claimed in EP 384070 (Unilever) and mixtures thereof. Zeolite P of this type is available from Crosfield, Warrington UK under their designation "Zeolite A24" . Other builders may also be included in the detergent composition as necessary or desired. Water-soluble builders may be organic or inorganic . Inorganic builders that may be present include alkali metal (generally sodium) carbonate; while organic builders 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 , hydroxyethyliminodiacetates; and organic precipitant builders such as alkyl- and alkenylmalonates and succinates, and sulphonated fatty acid salts. Especially preferred supplementary builders are polycarboxylate polymers, more especially polyacrylates and acrylic/maleic copolymers, suitably used in amounts of from 0.5 to 15 wt%, especially from 1 to 10 wt%; and monomeric polycarboxylates, more especially citric acid and its salts. The total amount of detergency builder will generally lie in a range from 5 to 80wt% of the composition. The amount may be at least 10 or 15wt% and may lie in a range up to 50 or 60wt%. Detergent compositions which are compacted into shaped articles 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 1 to 30% by weight of the composition. Perphthalimido perhexanoic acid and perdodecanoic acid are two examples of organic peroxyacids. Typically these can be used as 1 to 6% 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. Typically persalt is used as 5 to 30% by weight of a composition, while activator is 1 to 10% by weight of the composition. Other ingredients may also be present in the overall composition. These include sodium carboxymethyl cellulose, colouring materials, enzymes, fluorescent brighteners, germicides, perfumes and bleaches. Sodium alkaline silicate may be included, although the amount of this or at least the amount added as an aqueous liquid, is preferably restricted so as to keep to a particulate mixture prior to compaction. We have found it desirable that the particulate composition which is compacted should have a bulk density of at least 650 g/litre, preferably at least 700 g/litre, and advantageously at least 750 g/litre. Granular detergent compositions of high bulk density can be prepared by granulation and densification in a high-speed mixer/granulator, as described and claimed in EP 340013A (Unilever) , EP 35213SA (Unilever) , and EP 425277A (Unilever) , or by the continuous granulation/densification processes described and claimed in EP 367339A (Unilever) and EP 390251A (Unilever) . An embodiment of apparatus for tablet manufacture will be described by way of example with reference to Figs. 1 to 4 of the accompanying drawings in which: - Fig. 1 is a vertical cross-section through a tablet press illustrating its general arrangement; Figs. 2, 3 and 4 are similar cross-sections showing stages in the cycle of operations of the tablet press; and Fig. 5 illustrates a test procedure for water uptake. The invention can be put into effect using a conventional stamping press. A suitable press will generally have a pair of mould parts which move relatively towards and away from each other to compact particulate material between them. They may move within a surrounding sleeve or similar structure. A suitable arrangement, as illustrated in GB-A-2276345 is shown in Figs . 1 to 4 of the accompanying drawings . The apparatus is a tabletting press, whose structure incorporates a tubular sleeve 10 into which fit a lower punch 12 and an upper punch 14. The sleeve 10 defines a mould cavity 16 closed at its bottom by the lower punch 12. In use a particulate composition is supplied, to this cavity by means of a filling shoe 18 which slides on the upper surface 20. Initially the filling shoe advances to the position shown in Fig. 2 with the upper punch 14 raised. A particulate composition falls from the filling shoe to fill the cavity 16 above the lower punch 12. Next as seen in Fig. 3 the filling shoe withdraws and the upper punch 14 is pressed down into the cavity 16 thus compacting the particulate composition in the cavity to form a shaped article such as a tablet. Next, as shown in Fig. 4, the upper punch 14 is raised and the lower punch 12 is also raised until the tablet 22 lies at a level with the surface 20. After this the filling shoe 18 advances, pushing the tablet 22 away as it does so while the lower punch descends to the position shown in Fig. 2 for the cycle of operations to be repeated. The upper punch 12 and the lower punch 14 preferably each have an elastomeric layer over their faces which come into contact with the detergent composition. The sleeve 10, which also forms part of the mould, is made of steel and is not surfaced with elastomer. The punches 12,14 and also tablets compacted in the mould make sliding contact with this sleeve. EXAMPLE 1 A detergent powder with the following composition was prepared: Granulated Components % by weight coconut primary alkyl sulphate 1.4 coconut alcohol 3E0 7.6 coconut alcohol 6E0 4.8 zeolite A24 29.3 soap 2.9 sodium carboxymethyl cellulase 0.8 sodium carbonate 0.3 water 5.3 Postdosed Components PEG 1500 4.3 sodium percarbonate (borosilicate coated) 19.5 TAED granule 4.2 perfume 0.6 antifoam, fluorescer and heavy metal sequestrant 4.0 sodium citrate 15.0 The materials listed as "granulated components" were mixed in a Fukae (Trade Mark) FS-100 high speed mixer-granulator . (Continuous granulation equipment could also be used, as could other machinery for granulating in batches.) The soap was prepared in situ by neutralisation of fatty acid with sodium hydroxide . The mixture was granulated and densified to give a powder of bulk density greater than 750 g/litre and a mean particle size of approximately 650μm. The powder was sieved to remove fine particles smaller than 180μm and large particles exceeding 1700μm. The remaining solids were then mixed with the powder in a rotary mixer, after which the perfume was sprayed on, followed by the PEG. The PEG was sprayed at about 80 °C onto the powder which was at about 22-26 °C (slightly above ambient because of frictional heating during granulation) . Detergent tablets were prepared by compaction of 50g quantities of the detergent powder formulation using apparatus as illustrated in Figs. 1 to 4. The -tablets were of circular cross-section having a diameter of 4.5 cm and a thickness of approximately 2.5 to 3.1 cm. Compaction of the detergent powder, to make tablets, was carried out using either plain steel top and bottom punches, or alternatively punches which had an elastomer layer on their faces which contact the detergent composition. More specifically, one set of punches was given a polyurethane coating painted on as a solvent solution and providing a thickness of approximately 250μm after evaporation of solvent. Another set of punches was provided with a 1mm thick elastomer layer cut from sheet and glued on to the steel punches . With each set of punches 100 tablets were produced after which the top punch was inspected. With steel punches, the top punch was found to have 0.3 to 0.6g of powder firmly adhering to it, and producing indentations in the tablet surfaces. With both sets of punches bearing an elastomeric layer, the top punch was found to have only about 0.0lg of powder adhering to it . This was a light dusting which was easily removed. If a larger quantity of tablets was to be made, it would be possible to run the press for an extended period without needing frequent stops to clean the punches . The flat surfaces of tablets made with these punches were inspected visually. It was apparent that when tablets were made with steel punches the first tablets produced had smooth faces. After running the press for some time the tablets had rougher surfaces but the roughness was attributable entirely to material which had become adhered to the dies. By contrast when tablets were made using dies surfaced with elastomer 1mm thick the surfaces were rougher than the surfaces of either of the first tablets made with steel dies and tablets made with dies having a thin elastomer coating. In the case of tablets made using dies with the thick elastomer coating in accordance with the present invention the individual particles of the composition could still be discerned at the surface of the tablets . The tablets were tested to determine their density and porosity as described above. The extent to which they wetted on partial immersion - as illustrated in Fig. 5 - was tested as described above. The strength of the tablets was determined by the following test of their diametral fracture stress. The test procedure is applicable to cylindrical tablets and is carried out using a testing machine with flat faces which can be urged together by a measured force, such as an Instron Universal Testing Machine . The cylindrical tablet was placed between the platens of an Instron Machine, so that the platens contact the curved surface of the cylinder at either end of a diameter through the tablet . The sample tablet is then compressed diametrically, suitably by advancing the platens of the machine towards each other at a slow rate such as lcm/min until fracture of the tablet occurs at which point the applied load required to cause fracture is recorded. The diametral fracture stress is then calculated from the following equation: 2P δo= ■ π Dt where δ Q is the diametral fracture stress Pascal (Pa) , P is the applied load in Newtons (N) to cause fracture, D is the tablet diameter in metres (M) and t is the tablet thickness, also in metres (M) . For any given tablet composition, tablet strength varies inversely to the air volume expressed as percentage of the whole volume. If tablets have a shape which is not cylindrical, their diametral fracture stress is defined as the diametral fracture stress of cylindrical tablets having the same composition and percentage air volume. We have found it desirable in this invention that tablets should have a DFS of at least 6KPa, better at least 8KPa or 10 KPa. DFS will usually not need to exceed 25 or 30KPa, and a range of 10 to 25 or 30KPa is particularly preferred. Values of DFS up to at least 60KPa may be used, however. The results obtained were as follows: DFS Water Diameter of uptake (gm) dry core (mm) Thick elastomer (1mm) 12.4 9.3 11.2 Thin elastomer (250μm) 12.5 7.8 20.3 No elastomer 10.3 8.1 17.9 Uptake of water by the tablets made using the dies surfaced with thick elastomer was calculated to be approximately 100% of the available porosity (void space) in the tablets. The density of the tablets was determined as 1210g/litre. EXAMPLE 2 Three detergent powders of the following composition were prepared by the same procedure as in Example 1 : Granulated Components Parts by weight coconut primary alkyl sulphate 1.4 coconut alcohol 5EO 11.7 zeolite A24 27.7 soap 2.7 sodium carboxymethyl cellulase 0.8 sodium carbonate 0.3 water 8.8 Postdosed Components PEG 1500 variable sodium perborate tetrahydrate 18.5 TAED granule 4.0 perfume 0.4 antifoam, fluorescer and heavy metal sequestrant 4.0 sodium citrate 14.2 sodium polyacrylate 1.6 The amounts of polyethylene glycol (PEG) sprayed onto the powders were 1%, 4% and 13% by weight of the composition. The higher levels of PEG gave sticker powders. These powders were sieved to remove particles smaller than 200μm then compacted into tablets using a steel dies within a steel collar, and varying levels of applied force. Tablets of suitable strength and porosity were obtained as set out in the following table. It can be seen from this table that the use of the stickier powders enabled the production of tablets of greater strength using less applied pressure. These tablets gave good results in the test of water uptake. EXAMPLE 3 The detergent composition used in Example 2, containing 4% PEG was sieved to remove particles smaller than 200μm and compacted into tablets using plain steel dies and (separately) using dies surfaced with elastomer. Various levels of compaction force were employed with each set of dies . Elastomer A was 1mm thick and had elastic modulus of 0.72MPa. Elastomer B was 1mm thick and had elastic modulus 9.83MPa. The tablets were tested to determine their density, strength and water uptake . The results are tabulated below. Various periods of time were used in the water uptake test, as stated. In some instances the test was carried out twice with different periods of partial immersion. By comparing results at similar porosity and strength, it can be seen that tablets with similar density, porosity and strength had greater water uptake when made with elastomer- faced dies . EXAMPLE 4 Two batches of detergent composition as set out in Example 2 (referred to below as batch A and batch B) were stamped into tablets using a Korsch tableting press. The tablets were tested to determine their density, porosity and water uptake on partial immersion. The values for water uptake differed: this was attributed to differing contents of fine particles (<200μm) in the batches of detergent composition. Tablets were also made from the following detergent composition, prepared in a similar way and referred to as composition C. Granulated Components % by weight coconut primary alkyl sulphate 1.5 coconut alcohol 5EO 13.1 zeolite A24 31.0 soap 3.1 sodium carboxymethyl cellulase 0.8 sodium carbonate 0.3 water 8.8 Postdosed Components PEG 1500 4.0 sodium perborate tetrahydrate 22.6 TAED granule 4.0 perfume 0.4 antifoam, fluorescer and heavy metal sequestrant 4.0 sodium polyacrylate 1.6 Tablets from each batch were used to wash a set of 48 black test cloths. Washing was carried out in a Miele automatic washing machine operated on a wool-washing cycle. The washed cloths were examined for traces of tablet, visible as white residue particles on the black cloth. The tablets with greatest water uptake gave lowest residues as shown by the results in the following table: Tablets % void fill Number of cloths showing residues (s) Batch A 100 16 Batch B 77 21 Comp C 55 34

Claims: CLAIMS : 1. A method for the manufacture of tablets of detergent composition, comprising compacting a particulate composition in a mould consisting of a plurality of mould parts which are movable relative to each other, at least one of the mould parts having an elastomeric coating on a surface area which contacts the composition, using sufficient pressure to form tablets containing from 20 to 35% air by volume. 2. A method according to claim 1, wherein the tablets contain from 20 to 33% air by volume. 3. A method according to claim 1 wherein the tablets contain from 23 to 30% air by volume. 4. A method according to claim 1, claim 2 or claim 3, wherein the elastomeric layer has a thickness of at least 400μm. 5. A method according to any one of the preceding claims wherein the tablets are such that at least 65% of the void space within the tablet is filled with water within 30 seconds, upon partial immersion such that three quarters of the tablet surface is in contact with water. 6. A method according to claim 5, wherein the tablets are such that at least 80% of the void space within the tablet is filled with water within 30 seconds, upon partial immersion such that three quarters of the tablet surface is in contact with water. 7. A method according to any one of the preceding claims wherein the particulate composition contains from 5 to 40% by weight of detergent active, from 10 to 60% by weight of detergency builder, and optionally other ingredients. 8. A tablet compacted from a particulate detergent composition to give a tablet porosity in the range 20 to 35% air by volume, and such that at least 65% of the air space within the tablet is filled with water within 30 seconds, upon partial immersion such that three quarters of the tablet surface is in contact with water. 9. A tablet according to claim 8, such that at least 80% of the void space within the tablet is filled with water within 30 seconds, upon partial immersion such that three quarters of the tablet surface is in contact with water. 10. A tablet according to claim 8 or claim 9 with a porosity in the range 20 to 33% air by volume.

Inventors: ADAMS MICHAEL JOHN, BONNELL SARA JANE, WATSON SIMON ANDREW, WRAIGE DOUGLAS, ADAMS, MICHAEL, JOHN, BONNELL, SARA, JANE, WATSON, SIMON, ANDREW, WRAIGE, DOUGLAS
Applicants: UNILEVER NV, UNILEVER PLC, UNILEVER N.V.
Application year: 1998
Main classification: C11D17
IPC codes: B30B11, B30B15, C11D17