EP1516916A1

EP1516916A1 - Detergent compositions

Info

Publication number: EP1516916A1
Application number: EP04077150A
Authority: EP
Inventors: Leandre Naddeo; Peter Iwan Stuut; Gilbert Martin Verschelling
Original assignee: Unilever PLC; Unilever NV
Current assignee: Unilever PLC; Unilever NV
Priority date: 2003-09-19
Filing date: 2004-07-27
Publication date: 2005-03-23

Abstract

A method of preparing a cleaning tablet which has a plurality of discrete regions with differing compositions, characterised in that at least one first region of the tablet is a solid region of compacted particulate material and at least one second region of the tablet is a sprayed region and said method comprising the steps of (a) compressing a particulate composition to form said first region of compacted particulate material; (b) subsequently spraying a liquid composition onto the upper surface of said first region wherein the spraying is limited to said upper surface; and (c)solidifying said liquid composition to form said second phase of the cleaning tablet.

Description

This invention relates to cleaning compositions in the form of tablets. For use in fabric washing or machine dishwashing. The invention also relates to a process for the preparation of a cleaning composition in the form of tablets.
Detergent compositions in tablet form have advantages over powdered products in that they do not require measuring and are thus easier to handle and dispense into the washload.
Tablets of a cleaning composition are generally made by compressing or compacting a quantity of the composition in particulate form.
Tablets comprising two or more separate regions have also been described. For example WO 01/42416 describes the production of multi-phase moulded bodies comprising a combination of core moulded bodies and a particulate premix. WO 00/61717 describes a detergent tablet which is characterised in that at least part of its outer surface is semi-solid. WO 00/04129 describes a multi-phase detergent tablet comprising a first phase in the form of a shaped body having at least one mould therein and a second phase in the form of a particulate solid compressed within said mould. WO 99/24549 describes a detergent tablet comprising a compressed solid body and a non-compressed gelatinous portion mounted in a mold of said body.
EP 71644 describes the spray-coating of a detergent tablet with polyethylene glycol to form a coating surrounding the tablet. EP 1035198 describes the coating of detergent tablets using meltable materials.
There have been a number of proposals for tablets which are subdivided into separate regions (e.g. layers) which differ in their composition.
WO 99/35225 relates to moulded bodies with two solid phases wherein one phase of no more than 40 vol% of the moulded body contains more than 80wt% of the total of an active substance contained in the moulded body with an ingredient from the group of surfactants.
The present invention aims to provide an alternative process for the production of multi-phase cleaning tablets comprising a compressed phase and a second preferably smooth phase. In particular the process of the present invention is advantageous in that it does not require the presence of pre-prepared molds in the tablet surface and hence the tablets can be easily prepared without the need of a specific equipment for the formation of such molds. Furthermore the process of the invention is advantageous in that it does not require a separate step for the pre-preparing of the second phase and hence does not require separate steps e.g. for the casting, extrusion or otherwise performing of the smooth parts.
It has now been found that it is possible to apply a phase for example a smooth phase to a pre-compressed phase of a cleaining tablet without the need of coating said pre-compressed phase in its entirety. In particular it has been found that the spraying of a second phase onto the upper surface of a first region of compressed particulate material leads to a cleaining tablet with distinctive regions e.g. layers without substantive processing problems such as an undesired egree of clotting of the nozzle or dripping or flowing of said second phase. In particular it has also been found that the use of relatively high surfactant levels in said second phase allows the spraying of said phase onto the pre-compressed phase thereby avoiding substantial processing problems.
According to a first aspect of the present invention there is provided a method of preparing a cleaning tablet which has a plurality of discrete regions with differing compositions, characterised in that at least one first region of the tablet is a solid region of compacted particulate material and at least one second region of the tablet is a sprayed region and said method comprising the steps of (a) compressing a particulate composition to form said first region of compacted particulate material(said region preferably having a substantially flat upper surface);(b) subsequently spraying a liquid composition onto the upper surface of said first region; and (c)solidifying said liquid liquid composition to form said second phase of the cleaning tablet.
The regions of the tablet are possibly separate layers within a tablet. Especially the first region preferably is a layer of compacted particulate material, preferably having a substantially flat upper surface, whereupon the second region has been sprayed. Preferably said second sprayed region covers a substantial part of the upper surface of the first region, e.g. preferably at least 65%, more preferred at least 75%, most preferred more than 90% or even substantially all of the upper surface of the first region is covered by the second sprayed region.
For the purpose of the invention the term upper surface refers to one of the main sides of the cleaning tablet which by placing the tablet on a flat surface could be classified as the upper surface. Spraying generally will be limited to one outer side of the cleaning tablet, preferably the main (e.g. upper) side.
Such a sprayed region may therefore substantially look like a separate layer of the cleaning tablet. Occasionally however the sprayed nature of said second region may lead to a slightly domed shape of said second region whereby its thickness at the centre of the tablet is greater than the thickness at the edges of the second region.
Preferably the first region has a weight of from 10 to 50 grams, more preferred from 15 to 40 grams. Preferably the second region has a weight of 0.5 to 15 grammes, more preferred 1 to 10 grammes, most preferred 2 to 6 grammes.
The second region of the tablet is a sprayed, preferably smooth region. For the purpose of this invention the term smooth phase refers to compositions which are on the one hand solid enough to retain their shape at ambient temperature and on the other hand smooth in appearance. Smooth textures are generally of low or no porosity and have -at normal viewing distance- the appearance of a continuous phase for example as opposed to porous and particulate appearance of a compacted particulate material. Sprayed smooth regions however may have small irregularitis in their upper surface for example caused by uneven solidification of the sprayed droplets or by the inclusion of small air bubbles into the region. Generally however the sprayed region is still smooth in appearance and is clearly distinguishable from the generally uneven apperance of compacted particulate materials.
WO99/24549 describes the use of non-compressed gelatinous portions mounted in a mold as a smooth phase. These tablets must be made with specific equipment to ensure the appropriate mold formation. WO 00/61717 describes (in the example) the preparation of a compressed particulate tablet on top of which a (non-compressed) layer was made by pouring a mixture of nonionic and PEG followed by hardening. This method of preparation is disadvantageous because it requires a very long hardening step in the tablet mould, during which the tablet mould cannot be used for further production.
Preferably the sprayed region is both a smooth region and a semi-solid region. For the purpose of this invention the term semi-solid refers to compositions which are one the one hand solid enough to retain their shape at ambient temperature but which are neither completely solid.
A suitable test to check if a composition can be considered as semi-solid can be described as follows:
A cylindrical tablet with a diameter of 45 mm and a height of 20 mm is compressed radially between the plates of a material testing machine until the tablet fractures. At the starting position the plates contact the tablet but do not apply force to it. Force is applied, to compress the tablet, the vertical speed of the upper plate is 25 mm/minute. The testing machine measures the applied force (F), and also the displacement (x) of the plates towards each other as the tablet is compressed. The distance (y) between the plates before force is applied, which is the diameter of the tablet, is also known. At failure, the tablet cracks and the applied force needed to maintain the displacement drops. Measurement is discontinued when the applied force needed to maintain the displacement has dropped by 25% from its maximum value. The displacement at failure (x_f) is also measured.
A graph of force (F) against displacement (x) can be made. The maximum force is the force at failure (F_f). The break energy is the area under the graph of force against displacement, up to the point of break and is given by the equation:
wherein E_b is the break energy in mJoules, x is the displacement in metres and F is the applied force in Newtons at displacement x and x_f is the displacement at failure.
Semi-solid compositions are characterised by a ratio of F_f to E_b of less than 1.0, more preferred from 0.1 to 0.9, most preferred from 0.2 to 0.6, while traditional tablets of compacted particulate materials are generally characterised by a ratio of F_f to E_b of more than 1, more generally more than 1.25 or even more than 1.5 up to say 6.
In an advantageous embodiment of the invention said second region comprises from 40-100 wt% of surfactants (based on the total weight of the second region), more preferred from 50-95 wt%, most preferred the second region is predominantly constituted by surfactants e.g. more than 60 wt% for example 70 to 90 wt%. It has been found that the combination of a separate sprayed, smooth or semi-solid first region and these high surfactant levels provide very good dispersing and cleaning properties to the tablet.
Preferably the surfactants in the sprayed region comprise a combination of anionic surfactants and non-soap non-ionic surfactants in a weight ratio of from 5 : 1 to 1 : 5, more preferred 3 : 1 to 1 : 3, more preferred 2 : 1 to 1: 2. Further surfactants, for example cationic surfactants may equally be present for example at a level of 0.1 to 10 wt% based on the weight of the smooth or semi-solid part. Also advantageously the smooth or semi-solid region may comprise soap for example at a level of 0.1 to 10 wt% based on the weight of the smooth or semi-solid part.
Also advantageously the second region of the tablet may comprise diluent materials for example polyethyleneglycol, (mono-)propyleneglycol or di-propylene glycol. Preferably the level of these diluents is from 0 to 40 wt%, more preferred 2 to 30, most preferred 10-25 wt% based on the weight of the region.
The second phase preferably comprises no or only low levels of water. Preferably the level of water is less than 20 wt % based on the weight of the phase, more preferred less than 15 wt%, most preferred from 5 to 12 wt%. Most preferably the second phase is substantially free from water, which means that apart from low levels of moisture (e.g. for neutralisation or as crystal water) no additional added water is present.
Preferably the total weight of surfactants in the sprayed region is from 0.5 to 10 grammes, more preferred from 1 to 5 grammes.
In a preferred embodiment of the invention the first region of compacted material comprises no or only low levels of surfactants. Preferably the level of surfactants in the first region is less than 10 wt%(based on the total weight of the tablet or even less than 10% wt based on the weight of the first region), more preferred from 0 to 9 wt%, most preferred from 1 to 8 wt%.
The first region of the tablet is a solid region prepared by compression of a particulate composition.
Although the first region may comprise surfactant materials, this region preferably comprises ingredients of the tablet other than surfactants. Examples of these ingredients are for example builders, bleach system, enzymes etc. Preferably the builders in the tablet are predominantly present in the first region. Preferably the bleach system is predominantly present in the first region. Preferably the enzymes are predominantly present in the first region. For the purpose of this invention, unless stated otherwise, the term "predominantly present" refers to a situation wherein at least 90 wt% of an ingredient is present in the first region, more preferred more than 98 wt%, most preferred substantially 100 wt%.
The above description of the tablet has been given with reference to a tablet constituted by two regions. It will however be understood that each of the regions may be composed of a limited number of discrete regions.
In addition to the sprayed region and the solid compacted region the cleaning tablets of the invention may optionally comprise further regions, for example the tablet may be partly or wholly coated.
Cleaning tablets according to the invention are preferably manufactured by a process comprising the steps of:
(a) inserting a particulate composition into a tablet mould
(b) compression of the particulate composition to form a compressed tablet;
(c) removal of the compressed tablet from the tablet mould;
(d) spraying a liquid composition onto the upper surface of said compressed tablet to form a smooth phase on top of said compressed tablet.
In a preferred embodiment of the invention the particulate composition is compressed in step (b) at a force of 0.1 to 20 kN/cm². After the compression the compressed tablet is preferably removed from the tablet mould. This removal has the clear advantage that the spraying step takes place outside the tablet mould thereby significantly reducing the degree of contamination of the tablet mould by the molten composition.
Optionally the upper surface of the compressed composition may be treated with one or more materials e.g. barriers or adhesives before application of the second region thereto.
The spraying step d preferably preferably involves the preheating of the material to an elevated temperature for example from 50 to 150 C, more preferably from 60 to 140 C, most preferably from 70 to 130 C. The liquid, preferably molten material is then sprayed onto the compressed tablet. Generally normal spraying equipment can be used for this purpose, for example one or more spraying nozzles can be positioned above the surface of the compressed tablet followed by spraying the liquid, preferably molten composition onto the tablet. Preferably the spraying involves the formation of relatively small droplets of liquid material. Especially preferable the mean diameter of said molten droplets is from 0.01 to 5 mm, more preferred from 0.015 to 1 mm, most preferred from 0.02 to 0.4 mm , whereby the mean diameter refers to the diameter wherein half the material is present in droplets smaller than the mean diameter and the other half in droplets having greater mean diameters.
Solidification of the liquid material may be accomplished by any sutiable method e.g. cooling, gellation or by removal of shear. Preferably the solidification involves the cooling of the liquid phase, preferably to ambient temperature.
Generally the liquid composition to be sprayed may be under a light over-pressure e.g. from 0.1 to 10 bar, more preferred from 0.2 to 5 bar over air to ensure the appropriate flow of the droplets through the nozzle until the surface of the compressed tablet. The use of a spraying process to form the second, preferably smooth phase has several advantages, for example the use of a spraying process generally leads to a good adherence of the smooth phase to the compressed phase and may generally lead to a reduced or even an absence of the need for an adhesive between the compressed phase and the sprayed phase. Furthermore the spraying of the second phase onto the compressed phase surprisingly often leads to an attractive shiny upper surface of the smooth phase. Also advantageously the spraying of the liquid material onto the compressed tablet leads to the rapid removal of shear, the rapid gelling of gelation agents (if present) and rapid cooling of the liquid material, therewith causing quick solidification and avoiding the need for long waiting times and also significantly reducing the amount of liquid material that drips from the tablet. Preferably the sprayed layer has an average thickness of from 0.5 to 5 mm, more preferred 1 to 4 mm, for example 1.5 to 3 mm.
Preferably the liquid material to be sprayed onto the compressed tablet will (just before spraying) have a viscosity of 0.1 Pa.s to 12 Pa.s and a yield stress of 5 to 80 Pa. These viscosities can for example be determined via the method as described in EP 1,032,642.
Preferably the tablet of the invention is packed into a suitable packaging material after production. Due to the efficient process the time-span for the production can be short, for example the time for the process starting at step (a) until the packaging of the tablet may be less than 5 minutes, preferably even less than 2 minutes.
In a preferred embodiment the invention relates to a cleaning tablet comprising a first compressed phase and a second phase sprayed onto the upper surface of the compressed phase. Generally sprayed layers can be distinguished from cast or molded layers by the substantial absence of sharp ridges or corners caused by molds or extrusion equipment. Generally sprayed layers are formed by the flowing together of the sprayed droplets and have clearly rounded edges. Sometimes sprayed layers are equally characterised by slight irregularities in the surface caused by the flowing together of the sprayed droplets and sometimes by the inclusion of small air bubbles during solidification.
Another advantage of the method of the invention is that it can be carried out in a normal tablet press without the need of adaptation of the shape of the pressing surfaces and without long waiting times e.g. for hardening. Also the cleaning tablets produced by a method of the invention generally do not need substantial indentations in its surface (e.g. moulds, indents or cavities) to retain the sprayed phase. Generally the upper surface of the compressed phase can be substantially flat, therewith avoiding the need to use complicated equipment to produce said tablet and also avoiding weaknesses in the tablet due to uneven surfaces etc.
A tablet of this invention may be intended for use in machine dishwashing. Such a tablet is likely to contain surfactant in a low concentration such as 0.5 to 2 wt% based on the whole tablet, although higher concentrations ranging up to 10 wt% may be used. Such will typically contain salts, such as over 60 wt%, often over 85 wt% of the tablet.
Water-soluble salts typically used in machine dishwashing compositions are phosphates (including condensed phosphates) carbonates and silicates, generally as alkali metal salts. Water soluble alkali metal salts selected from phosphates, carbonates and silicates may provide 60 wt% or more of a dishwashing composition.
Another preferred possibility is that a tablet of this invention will be intended for fabric washing. In this event the tablet will be likely to contain at least 2 wt%, probably at least 5 wt%, up to 40 or 50 wt% surfactant based on the whole tablet, and from 5 to 80 wt% detergency builder, based on the whole tablet.
Materials, which may be used in tablets of this invention, will now be discussed in more detail.

Surfactant Compounds

Compositions, which are used in tablets of the invention, will contain one or more 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% 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.
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 C₈-C₁₅; olefin sulphonates; alkane sulphonates; dialkyl sulphosuccinates; and fatty acid ester sulphonates.
Primary alkyl sulphate having the formula ROSO₃ ^- 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 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_8-20 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 C_9-11 and C_12-15 primary and secondary alcohols ethoxylated with an average of from 5 to 20 moles of ethylene oxide per mole of alcohol.
In some fabric washing tablets 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 whole tablet.
Many nonionic surfactants are liquids. These may be absorbed onto particles of the composition.
In a machine dishwashing tablet the surfactant may be wholly nonionic, in an amount below 5 wt% of the whole tablet although it is known to include some anionic surfactant and to use up to 10 wt% surfactant in total.

Detergency Builder

A composition, which is used in tablets of the invention, will contain from 5 to 80%, more usually 15 to 60% by weight of detergency builder. This 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. Water-insoluble detergency builder may be present as 5 to 80 wt%, better 5 to 60 wt% of the composition.
Alkali metal aluminosilicates are strongly favoured as environmentally acceptable water-insoluble 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 Na₂O.Al₂O₃. 0.8 - 6 SiO₂. xH₂O
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 SiO₂ 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 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.
Conceivably a water-insoluble 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-Na₂SiO₅ 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_xO_2x+1.yH₂O 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.
Water-soluble phosphorous-containing inorganic detergency builders, include the alkali-metal orthophosphates, metaphosphates, pyrophosphates and polyphosphates. Specific examples of inorganic phosphate builders include sodium and potassium tripolyphosphates, orthophosphates and hexametaphosphates.
Non-phosphorous 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 and hydroxyethyliminodiacetates.
At least one region (preferably the first region) of a fabric washing tablet preferably include polycarboxylate polymers, more especially polyacrylates and acrylic/maleic copolymers which can function as builders and also inhibit unwanted deposition onto fabric from the wash liquor.

Bleach System

Tablets according to the invention may contain a bleach system in at least one region of a tablet, preferably in the second region. 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 25% by weight 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.
As indicated above, if a bleach is present and is a water-soluble inorganic peroxygen bleach, the amount may well be from 10% to 25% by weight of the composition.

Other Detergent Ingredients

The detergent tablets of the invention may also contain (preferably in the second region) 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; and these granules or marumes present no problems with respect to compaction to form a tablet.
The detergent tablets of the invention may also contain (preferably in the first region) 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 (preferably in the first region), 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, absorbed 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 detergent 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 tablet for fabric washing will generally not contain more than 15 wt% silicate. A tablet for machine dishwashing will often contain more than 20 wt% silicate. Preferably the silicate is present in the first region of the tablet.
Further ingredients which can optionally be employed in a region of a fabric washing detergent of the invention tablet (preferably the first region) 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.
Further ingredients, which can optionally be used in tablets of the invention, preferably in the second region are dispersing aids. Examples of suitable dispersing aids are water-swellable polymers (e.g. SCMC) highly soluble materials (e.g. sodium citrate, potassium carbonate or sodium acetate) or sodium tripolyphospate with preferably at least 40% of the anhydrous phase I form.

Particle Size and Distribution

The first region of a detergent tablet of this invention, is a preferably 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 is especially relevant to tablets 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 perhaps at least 600 g/litre.
Tableting machinery able to carry out the manufacture of tablets of the invention is known, for example suitable tablet presses are available from Fette and from Korch.
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.
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 preferably lies in a range from 1040 or 1050gm/litre up to 1600gm/litre.
Preferably the diameter of the first phase is substantially the same as the diameter of the second phase. For the purpose of the invention "substantially the same diameter" means that the diameter of the first phase differs less than 5 mm with the diameter of the second phase, more preferably less than 3mm or even less than 1mm.

Example 1

A detergent powder was made of the following composition by pregranulating the granule ingredients, followed by post-dosing the rest of the ingredients

Ingredient	Parts by weight
granules
Na-las	1.1
Nonionic 7EO	0.5
Soap (C16-C18)	0.1
Zeolite A24	2.4
NaAc3aq	0.3
Light soda ash	0.4
SCMC (68%)	0.1
Moisture/minors	0.4
Post-dose
EAG (17% silicone)	3.0
Fluorescer (15%)	2.2
STP HPA	28.3
STP LV	34.0
Na-disilicate (80%)	3.8
TAED (83%)	4.3
Percarbonate	16.9
Dequest 2047	1.9
Minors/ enzymes/color	to 100

The second phase of the tablet was produced of the following composition:

Ingredient Parts by weight

Na-las 39.1

Nonionic 7EO 33.5

C16-C18 soap 7.3

Di-propylene glycol to 100
The mixture was heated to 80°C to provide a molten liquid composition, which can be sprayed through a conventional spraying nozzle.
The tablets were made as follows:
25grammes of the powder are inserted into a 45 mm die of a tabletting machine, optionally followed by a flattening step, the material is compressed at 6kN/cm² Into a single tablet, followed by ejection of the tablet.
The ejected tablets are positioned on a moving belt above which a spraying nozzle was positioned at a height of 15 cm. The used nozzle was a double nozzle from spraying systems. The pre-nozzle was aSSCO 40100 nozzle, the spray nozzle was a SSC0134255.45 nozzle, the total being a 2 phase, full cone nozzle with an air over pressure of 0.5 bar. The liquid flow was set at 35 gram/minute.
As soon as the tablet was in such a position that the spraying nozzle was located substantially above the center of the tablet, about 5 grams of the molten composition was sprayed onto the upper tablet surface. The spraying takes place in 8 seconds to deposit 5 gram of gel. During and after the spraying, the molten composition cools to ambient temperature while forming itself into a smooth continuous phase located substantially over the entire upper surface of the compressed tablet. The cooling step takes less than 20 seconds, followed by packaging the tablets 2 by two in a flow-wrap of plastic film. The smooth phase had a shiny glancy type appearance. The thickness of the smooth phase was about 3 mm.
The tablets of the invention show fast dispersing of the compacted powder region during the washing process therewith allowing the early release of e.g. builder components into the washing liquor. The smooth or semi-solid part shows delayed dispersing therewith providing the surfactants at a later stage during the washing process.

Claims

A method of preparing a cleaning tablet which has a plurality of discrete regions with differing compositions, characterised in that at least one first region of the tablet is a solid region of compacted particulate material and at least one second region of the tablet is a sprayed region and said method comprising the steps of (a) compressing a particulate composition to form said first region of compacted particulate material; (b) subsequently spraying a liquid composition onto the upper surface of said first region wherein the spraying is limited to said upper surface; and (c)solidifying said liquid composition to form said second phase of the cleaning tablet.
A method according to claim 1 wherein the first region is substantially free from indents, molds and cavities.
A method according to claim 1 or 2 wherein the upper surface of the first region is substanially flat.
A method according to claim 1, wherein the compressed phase is produced in a tablet mould and wherein the compressed phase is removed from said mould prior to the spraying of the liquid composition thereon.
A method according to claim 1, wherein the liquid which is sprayed onto the tablet is a molten liquid and preferably has a temperature of from 50 to 150 C, more preferred 70 to 150 C.
A method according to claim 1, wherein the liquid is sprayed onto the tablet in the form of droplets having a mean diameter of 0.01 to 5 mm.
A cleaning tablet comprising a first compressed phase and a second phase sprayed onto the upper surface of the first compressed phase, wherein said phases are separate layers within the tablet.
A cleaning tablet according to claim 7, wherein the sprayed phase comprises 40-100 wt% of surfactants.
A cleaning tablet according to claim 7, wherein the sprayed phase has a weight of from 0.5 to 15 grammes.
A cleaning tablet according to claim 7, comprising a barrier or adhesive layer between the compressed phase and the sprayed phase.
A cleaning tablet according to claim 7, wherein the sprayed phase is a smooth phase.
A cleaning tablet according to claim 7 wherein the sprayed phase has an average thickness of from 0.5 to 5 mm.