EP1389230A1

EP1389230A1 - Cleaning compositions

Info

Publication number: EP1389230A1
Application number: EP01994642A
Authority: EP
Inventors: Erik Christiaan Unilever Res Vlaardingen BERDEN; Wouter Laurens Ijdo; Michel Jan Unilever Research Vlaardingen RUIJTER; Harmannus Unilever Research Vlaardingen TAMMES; Mark c/o Wageningen Univ en Research VAN DER VEEN
Original assignee: Unilever PLC; Vas Bhat Rahul Dominic; Unilever NV
Current assignee: Unilever PLC; Vas Bhat Rahul Dominic; Unilever NV
Priority date: 2000-11-24
Filing date: 2001-11-01
Publication date: 2004-02-18
Also published as: AU2002224833A1; WO2002042402A1

Abstract

The invention provides a tablet of compacted particulate detergent composition including organic surfactant, detergency builder and other constituents, wherein the composition of the tablet or a discrete region thereof consists of (i) from 1% to 15% by weight of disintegrant particles containing water-swellable, water-insoluble disintegrant material (ii) a balance from 85 to 99% by weight of further component particles and wherein the particle sizes and size distributions are such that: the mean particle size of the disintegrant particles (i) is not more than 1.4 times the mean particle size of the further component particles (ii); and at least 90% by weight of the further component particles (ii) have a size greater than 350Fm.The tablets have good disintegration and strength 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 in a single use. The tablets may be suitable for use in machine dishwashing, the washing of fabrics or other cleaning tasks.

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

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

If a tablet contains organic surfactant, this can function as a binder, plasticising the tablet. However, it can also retard disintegration of the tablet by forming a viscous gel when the tablet comes into contact with water. Thus, the presence of surfactant can make it more difficult to achieve both good strength and speed of disintegration: the problem has proved especially acute with tablets formed by compressing powders containing surfactant and built with insoluble detergency builder such as sodium aluminosilicate (zeolite) .

It is known to include materials whose function is to enhance disintegration of tablets when placed in wash water. For example, our EP-A-838519 mentioned above teaches the use of sodium acetate trihydrate for this purpose.

In our EP-A-466484 and corresponding US-A-5360567 it is taught that the particles of a detergent composition used for compaction into tablets should have their size confined within a limited range of particle size. Fine particles smaller than 200 m are excluded. The bulk of the composition should be particles with sizes confined within a size range spanning no more than 700μm and located within a broader range from 200 m to 2000 m. The document also teaches that a binder material which functions as a disintegrant can advantageously be used by applying it to the surface of other particles. Results set out in the Examples of this document show that in the absence of such a binder, faster dissolution of tablets occurs when the particle sizes in the composition are restricted to a narrow range of small sizes - 250 to 500 m. When binder material (cross-linked polyvinyl pyrrolidone) was used on the surface of particles there was a considerable improvement in the speed of disintegration of tablets, but it was still the case that small particle sizes gave more rapid disintegration of tablets.

In our EP-A-522766 and corresponding US-A-5407594 a material which functions as a binder and disintegrant is applied to the surface of particles which are not restricted to the same narrow size range, although particles smaller than 200 m are again excluded.

WO-A-98/40463 teaches the use of a cellulosic swelling disintegrant in the form of granules with a particle size in a range from 300μm to 1600.m. In an example, the swelling disintegrant particle size was such that more than 90% was in a size range from 200 to 2000_ium. The same was true of the remainder of the detergent composition.

Inferior results - a slower speed of disintegration - were observed in a comparative example with small particle size (lOOμm) swelling disintegrant.

Consistent with this, in our WO-A-98/55590 it is taught that a water-swellable but insoluble disintegrant should preferably have a particle size of at least 500 m. In one example, 3% of disintegrant sieved to a size range of 800- 1400μm displayed a tablet strength and speed of disintegration which were slightly superior to those with 5% of the same disintegrant sieved to a size range of 470- 800 m.

The apparent conclusions are (i) that the detergent composition should avoid particles smaller that 200μm but a size range slightly above this will be satisfactory, and (ii) that swelling disintegrant particles have most effect if they are relatively large.

In surprising contrast with these prior disclosures, we have found that a swelling disintegrant is most efficacious if it has a particle size which approximates to that of the remainder of the detergent composition, while also imposing a somewhat different boundary on particle size.

So, according to a first aspect of this invention, there is provided a detergent tablet in which a discrete region or the entire tablet consists of compacted particulate detergent composition including organic surfactant, detergency builder and other constituents, wherein the composition of the tablet or a discrete region thereof consists of

(i) from 1% to 15% by weight of disintegrant particles containing water-swellable, water-insoluble disintegrant material (ii) a balance from 85 to 99% by weight of further component particles characterised in that the particle sizes and size distributions are such that: the mean particle size of the disintegrant particles (i)is not more than 1.4 times, better not more than 1.3 times the mean particle size of the further component particles (ii) ; and at least 90% by weight of the further component particles (ii) have a size greater than 350 m.

Tablets made from a composition in accordance with the above requirements exhibit faster disintegration in water, whilst retaining their strength, compared to tablets in which the particle size distributions fall outside those defined above .

If the invention is employed in a region of a tablet rather than the whole of the tablet, that region will have the advantage of faster disintegration while retaining strength.

This advantage of faster disintegration at equivalent strength offers the tablet manufacturer the possibility of tablets of satisfactory strength which dissolve more rapidly than other tablets, or alternatively the possibility of raising the force applied during tablet compaction, so as to obtain tablets of greater strength with the same speed of disintegration as other tablets. Of course, the manufacturer may also choose some intermediate position with some increase in both strength and speed of disintegration. Forms of this invention, preferred and optional features, and materials which may be used, will now be discussed in greater detail. The drawing is a cross-sectional view of a piece of apparatus used in testing.

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

Particle Sizes The particles sizes referred to are the particle sizes of the constituents of the particulate detergent composition before compaction to form detergent tablets.

It is preferred that at least 90% by weight of the disintegrant particles (i) also have a size greater than 350 m.

In compositions according to the invention the mean particle size of the disintegrant particles (i) is not more than 1.4 times, preferably not greater than 1.3 or even 1.2 times, the mean particle size of the further component particles (ii) . Possibly the mean particle size of the disintegrant particles (i) is not greater than the mean particle size of the further component particles (ii) . It is also preferred that the mean particle size of the disintegrant particles (i) is at least 0.5 better at least 5 0.7 times the mean particle size of the further component particles (ii) .

It is further preferred that the mean particle size of the further component particles (ii) is in a range of 500 to 10 1200μm.

The preferred particle size distribution of the further component particles (ii) about the mean particle size can be defined in relation to upper and lower thresholds, XT_J

15 and X_L respectively. In the preferred size distribution, 90% by weight of the particles have size between the upper and lower thresholds, no more than 5% by weight of the particles have a size less than the lower threshold (X_L) and no more than 5% by weight of the particles have a size

20 larger than the upper threshold (X_u) where the upper threshold X_u is not more than 1200μm larger than the lower threshold X_L. It is more preferred that the lower threshold (X_L) is at least 350μm and the upper threshold (Xu) is less than 1500μm or 2000 m. Even more preferred is

25 a lower threshold of at least 700 or 900μm.

Techniques for the manufacture of particulate materials in average sizes from 350μm to 1500μm are well known Particle sizes can be varied, when required, by modifying the process parameters in manufacturing particulate materials .

For example, adjustable parameters in agglomeration processes include the liquid to solids ratio in the mixture which is being granulated, operating temperature and residence time in the mixer which is carrying out granulation.

Particle size range can be controlled by removing oversized and undersized particles. Oversized particles are usually removed by a sieving operation, and may then be milled and recycled to an earlier stage of the manufacturing process.

Undersize particles can also be removed by sieving, or if the manufacturing process employs a fluidised bed, they can be entrained in the gas stream from the bed.

"Mean particle size" refers to the value d₅₀, which is the aperture of a (theoretical) sieve through which 50 weight % of the powder passes (see Particle Size Measurement by T Allen, 2^nd Edition, Chapman & Hall, 1975) .

Water-Swellable Material

A number of water-insoluble, water-swellable materials are known to be useful as tablet disintegrants, in particular for pharmaceutical tablets. Discussion of such materials is found in "Drug Development and Industrial Pharmacy", Volume 6, pages 511-536 (1980) . In tablets of the invention such materials may be included in an amount of 0.1 or 0.5% to 10% by weight of the tablet or discrete region thereof. Such materials may be mixed with each other, or mixed with other materials as carriers. If these water-swellable materials are included as part of disintegrant particles, these particles may be present in an amount of 1 to 10% by weight of the tablet or region thereof .

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

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™ or Explotab™, both of which are sodium starch glycolate also known as sodium carboxymethyl starch; 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, microcrystalline cellulosic fibres cross-linked cellulose; 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.

The study of water-swellable disintegrant materials has largely taken place in connection with pharmaceutical tablet formulations. One parameter which may be used to characterise such materials is their increase in volume when placed in contact with water. Some materials are capable of absorbing, and being swelled by, a volume of water which is considerably in excess of their own volume. Thus, they may swell to more than double their dry volume . An apparatus for measuring increase in volume is illustrated in "The Mechanisms of Disintegrant Action", Kanic & Rudnic, Pharmaceutical Technology, April 1984, pages 50-63. This article also refers to papers describing other apparatus.

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

An apparatus for measuring both of these parameters is described in EP-A-333104. A sample of material is pressed against a sintered glass disc. The force by which it is pressed against the disc is measured by means of a load cell . The sample is allowed to take up water or aqueous solution through the sintered glass disc.

The supply for this water or aqueous solution is a reservoir which has been placed on a balance. The force on the load cell and the weight lost from the reservoir are monitored over a period of time. We have found that materials and particles which swell on contact with water are effective as disintegrants if thee is a rapid development of force when they come into contact with water.

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

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

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

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

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

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

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

The significant parameter is the maximum slope of a graph of expansion force against time.

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

Disintegrant particles may consist of a carrier material which absorbs some water. And may swell on initial contact with water mixed with a minor proportion of another material which swells more strongly than the carrier material on contact with water. It may take up more water than the carrier material, or swell more rapidly or both. The proportions may be from 75% or 90% up to 99.9% of the carrier material and from 0.1 up to 10%, of the more strongly swelling material.

Optionally up to 15% or 20% of a water-soluble synthetic organic polymer is present as a binder.

It is preferred that the strongly swelling material, if tested, by itself, has ability to absorb at least twice possibly at least 2.5 or 3 times its own volume of water and has a development of expansion force which exceeds 1.5 Newton/second.

The development of swelling force has been measured for a number of materials, as set out in the following table.

The more strongly swelling material may come from a category referred to as a super-disintegrant . Such super disintegrants tend to be cross-linked synthetic or natural polymers and include cross-linked forms of carboxymethyl cellulose, cellulose, starch, polyvinylpyrrolidone and polyacrylate . The carrier materials are preferably selected from compounds which contain hydroxy groups . A carrier material may itself be a water-insoluble, and somewhat water-swellable material. Such materials include starches, for example, maize, rice and potato starches, celluloses, microcrystalline cellulosic fibres and some synthetic organic polymers. Disintegrant particles may also contain up to 15% or 20% by weight of a water-soluble polymer which acts as a binder, e.g. polyethylene glycol .

Specifically, a super-disintegrant may take up more than twice its own volume of water, while a carrier for it takes up less water by volume than the super-disintegrant.

Such disintegrant particles may be made by mixing the swellable disintegrant with the carrier material, then compacting the mixture, and if necessary comminuting the compacted mixture into disintegrant particles. Preferably these have a particle size in a range from 250 to 1000 microns.

Mixing of these materials can be carried out by standard apparatus for mixing particulate solids. Other ingredients can be incorporated at this stage. If a polymeric binder is incorporated, it can be added in particulate form during this mixing operation. Alternatively, if it can be melted, the molten polymer can be sprayed on to the mixture or on to one particulate ingredient of the mixture. Compaction of the mixture can be brought about by forcing it between a pair of rollers. Suitable apparatus - a roller compactor - has a feed screw which delivers the mixture to the nip of the rollers. The speed of the feed screw, and hence the amount of material delivered to the nip of the roller should be high enough to force an unbroken stream of material through the rollers, but not so high that the material is converted into a dough.

The sheet material which issues from the rollers is next broken up and milled to the required particle size.

Manufacturers of both roller compactor and milling machinery include Hosakawa Beper located at Heilbronn, Germany, Alexanderwerk located at Remschied, Germany and Fitzpatrick located at Elmhurst, USA.

Surfactant Compounds

Compositions which are compacted to form tablets of this invention, or discrete regions thereof, contain one or more organic detergent surfactants. In a fabric washing composition, these preferably provide from 5 to 40% by weight of the composition of the tablet or region thereof, more preferably from 8 or 9% by weight of the composition up to 30% or 35% by weight. If the tablet is composed of more than one discrete region, then these preferred amounts of surfactant may apply to the tablet as a whole. This organic surfactant forms part of the further component particles (ii) which make up the balance if the composition. Surfactant may be anionic (soap or non-soap) , cationic, zwitterionic, amphoteric, nonionic or a combination of these .

In fabric laundry tablets, anionic surfactant may be present in an amount from 0.5 to 40% by weight, preferably from 2% or 4% up to 30% or 35% by weight of the tablet or region thereof .

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 composition of the tablet or region thereof and is likely to consist of nonionic surfactant, either alone or in a mixture with anionic surfactant . Synthetic (i.e. non-soap) anionic surfactants are well known to those skilled in the art. Examples include alkylbenzene sulphonates, particularly sodium linear alkylbenzene sulphonates having an alkyl chain length of Cβ-Cis; olefin sulphonates; alkane sulphonates; dialkyl sulphosuccinates; and fatty acid ester sulphonates.

Primary alkyl sulphate having the formula

R0S0₃ ^" M⁺ in which R is an alkyl or alkenyl chain of 8 to 18 carbon atoms especially 10 to 14 carbon atoms and M⁺ is a solubilising cation, is commercially significant as an anionic surfactant .

Linear alkyl benzene sulphonate of the formula

where R is linear alkyl of 8 to 15 carbon atoms and M⁺ is a solubilising cation, especially sodium, is also a commercially significant anionic surfactant. Frequently, such linear alkyl benzene sulphonate or primary alkyl sulphate of the formula above, or a mixture thereof will be the desired anionic surfactant and may provide 75 to 100 wt% of any anionic non-soap surfactant in the composition.

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

It may also be desirable to include one or more soaps of fatty acids . These are preferably sodium soaps derived from naturally occurring fatty acids, for example, the fatty acids from coconut oil, beef tallow, sunflower or hardened rapeseed oil .

Suitable nonionic surfactant compounds which may be used include in particular the reaction products of compounds having a hydrophobic group and a reactive hydrogen atom, for example, aliphatic alcohols, acids, amides or alkyl phenols with alkylene oxides, especially ethylene oxide.

Specific nonionic surfactant compounds are alkyl (C₈.₂₂) phenol-ethylene oxide condensates, the condensation products of linear or branched aliphatic C₈-₀ primary or secondary alcohols with ethylene oxide, and products made by condensation of ethylene oxide with the reaction products of propylene oxide and ethylene-diamine . Especially preferred are the primary and secondary alcohol ethoxylates, especially the C₉_ ₁ and C1₂-₁5 primary and secondary alcohols ethoxylated with an average of from 5 to

20 moles of ethylene oxide per mole of alcohol. In certain forms of this invention the amount of nonionic surfactant lies in a range from 4 to 40%, better 4 or 5 to

30% by weight of the composition of the tablet or region thereof. Many nonionic surfactants are liquids. These may be absorbed onto particles of the composition forming part of the other particles (ii) , prior to compaction into tablets.

Amphoteric surfactants which may be used jointly with anionic or nonionic surfactants or both include amphopropionates of the formula:

O CH₂CH₂OH

II I

RC— NH-CH₂CH₂— N— CH₂CH₂C0₂Na

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

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

where R₄ is an aliphatic hydrocarbon chain which contains 7 to 17 carbon atoms, R₂ and R₃ are independently hydrogen, alkyl of 1 to 4 carbon atoms or hydroxyalkyl of 1 to 4 carbon atoms such as CH₂0H, Y is CH₂ or of the form CONHCH₂CH₂CH₂ (amidopropyl betaine) ; Z is either a COO^"

(carboxybetaine) , or of the form CHOHCH₂S0₃ - (sulfobetaine or hydroxy sultaine) .

Another example of amphoteric surfactant is amine oxide of the formula

where R_x is Cι₀ to C₂₀ alkyl or alkenyl; R₂, R₃ and R₄ are each hydrogen or Ci to C₄ 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.

Detergency builder

The composition which is compacted to form a tablet or a discrete tablet regions also contains a detergency builder which serves to remove or sequester calcium and/or magnesium ions in the water.

When a detergency builder is present, the amount of it is likely to lie in a broad range from 10 better 15 wt% up to 80% of the tablet composition. The amount is more likely to be from 15 to 70%, more usually 15 to 60% by weight of the tablet.

Detergency builders 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 detergency builders for fabric washing, and are preferred in this invention. Alkali metal (preferably sodium) aluminosilicates may be either crystalline or amorphous or mixtures thereof, having the general formula : 0 . 8 - 1 . 5 Na₂O .Al₂0₃ . 0 . 8 - 6 Si0₂. xH₂0

These materials contain some bound water (indicated as xH₂0) 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 units (in the formula above) . Both the amorphous and the crystalline materials can be prepared readily by reaction between sodium silicate and sodium aluminate, as amply described in the literature.

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

Conceivably a detergency builder could be a layered sodium silicate as described in US 4664839. NaSKS-6 is the trademark for a crystalline layered silicate marketed by Hoechst (commonly abbreviated as "SKS-6") . NaSKS-6 has the delta-Na₂Si0₅ morphology form of layered silicate. It can be prepared by methods such as described in DE-A-3,417, 649 and DE-A-3, 742, 043. Other such layered silicates, such as those having the general formula NaMSi_xθ2_X+ι.yH₂0 wherein M is sodium or hydrogen, x is a number from 1.9 to 4, preferably 2, and y is a number from 0 to 20, preferably 0 can be used.

The less preferred category of water-soluble phosphorus- containing inorganic softeners includes the alkali-metal orthophosphates, metaphosphates, pyrophosphates and polyphosphates . Specific examples of inorganic phosphate detergency builders include sodium and potassium tripolyphosphates, orthophosphates and hexametaphosphates . Non-phosphorus water-soluble detergency builders may be organic or inorganic. Inorganics that may be present include alkali metal (generally sodium) carbonate; while organics include polycarboxylate polymers, such as polyacrylates, acrylic/maleic copolymers, and acrylic phosphonates, monomeric polycarboxylates such as citrates, gluconates, oxydisuccinates, glycerol mono- di- and trisuccinates, carboxymethyloxysuccinates, carboxymethyloxymalonates, dipicolinates and hydroxyethyliminodiacetates .

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

Bleach System

Tableted compositions according to the invention may contain a bleach system, which would form part of the further component particles (ii) . This preferably comprises one or more peroxy bleach compounds, for example, inorganic persalts or organic peroxyacids, which may be employed in conjunction with activators to improve bleaching action at low wash temperatures. If any peroxygen compound is present, the amount is likely to lie in a range from 10 to 85% by weight of the composition of the tablet or region thereof. If the tablet contains surfactant and detergency builder, the amount of peroxygen compound bleach is unlikely to exceed 25% of the composition of the tablet or region thereof. Preferred inorganic persalts are sodium perborate monohydrate and tetrahydrate, and sodium percarbonate, advantageously employed together with an activator. Bleach activators, also referred to as bleach precursors, have been widely disclosed in the art. Preferred examples include peracetic acid precursors, for example, tetraacetylethylene diamine (TAED) , now in widespread commercial use in conjunction with sodium perborate; and perbenzoic acid precursors . The quaternary ammonium and phosphonium bleach activators disclosed in US 4751015 and US 4818426 (Lever Brothers Company) are also of interest. Another type of bleach activator which may be used, but which is not a bleach precursor, is a transition metal catalyst as disclosed in EP-A-458397, EP-A-458398 and EP-A- 549272. A bleach system may also include a bleach stabiliser (heavy metal sequestrant) such as et ylenediamine 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 (i) as required by this invention, and would form part of the further component particles (ii) . It may be preferred that such particles make up from 3%, better from 5% or 10% to 50% by weight of the composition of the tablet or region thereo .

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

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

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

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

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

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

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

A solubility of at least 50g/100g of deionised water at 20°C is an exceptionally high solubility: many materials which are classified as water soluble are less soluble than this. Materials of such high solubility may be used in amounts from 3%, possibly from 5% or 10% up to 30% by weight of the tablet.

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 lOOg of deionised 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 7H₂0 71

By contrast the solubilities of some other common materials at 20°C are:- Material Water Solubility (g/lOOg)

Sodium chloride 36

Sodium sulphate decahydrate 21.5

Sodium carbonate anhydrous 8.0

Sodium percarbonate anhydrous 12 Sodium perborate anhydrous 3.7

Sodium tripolyphosphate anhydrous 15

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

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

These particles should also contain sodium tripolyphosphate which is partially hydrated. The extent of hydration should be at least 1% by weight of the sodium tripolyphosphate in the particles. It may lie in a range from 1 to 4%, or it may be higher. Indeed fully hydrated sodium tripolyphosphate may be used to provide these particles .

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

Suitable material is commercially available. Suppliers include Rhone-Poulenc, France and Albright & Wilson, UK.

Other Ingredients

Tablets of the invention may also contain one of the detergency enzymes well known in the art for their ability to degrade and aid in the removal of various soils and stains. Suitable enzymes include the various proteases, cellulases, lipases, amylases, and mixtures thereof, which are designed to remove a variety of soils and stains from fabrics. Examples of suitable proteases are Maxatase (Trade Mark), as supplied by Gist-Brocades N.V. , Delft, Holland, and Alcalase (Trade Mark) , and Savinase (Trade Mark) , as supplied by Novo Industri A/S, Copenhagen, Denmark. Detergency enzymes are commonly employed in the form of granules or marumes, optionally with a protective coating, in amount of from about 0.1% to about 3.0% by weight of the composition of the tablet or region thereof; and these granules or marumes present no problems with respect to compaction to form a tablet.

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

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

It may also be desirable that a tablet of the invention includes an amount of an alkali metal silicate, particularly sodium ortho-, 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, fabric- softening agents; heavy metal sequestrants such as EDTA; perfumes; and colorants or coloured speckles.

Bulk Density

While the starting particulate composition may in principle have any bulk density, the present invention may be especially relevant to tablets of detergent composition made by compacting powders of relatively high bulk density, because of their greater tendency to exhibit disintegration and dispersion problems. Such tablets have the advantage that, as compared with a tablet derived from a low bulk density powder, a given dose of composition can be presented as a smaller tablet. Thus the starting particulate composition may suitably have a bulk density of at least 400 g/litre, preferably at least 500 g/litre, and possibly at least 600 g/litre.

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

Granular detergent compositions of high bulk density prepared by granulation and densification in a high-speed mixer/granulator, as described and claimed in EP 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.

The separate particles (i) of the water-insoluble, water- swellable disintegration-promoting material required for this invention, and any optional water-soluble particles to promote disintegration, are preferably mixed with the remainder of the particulate composition prior to compaction.

A proportion of the further component particles (ii) preferably consist of 25 to 75% by weight of organic surfactant, 25 to 75% be weight of detergency builder, and 0 to 50% by weight of other materials. The proportion of other particles with this defined composition is preferably such that these articles comprise from 30 to 99% by weight of the tablet or region thereof .

Tableting

Tableting entails compaction of a particulate composition.

A variety of tableting machinery is known, and can be used. Generally it will function by stamping a quantity of the particulate composition which is confined in a die.

Tableting may be carried out at ambient temperature or at a temperature above ambient which may allow adequate strength to be achieved with less applied pressure during compaction. In order to carry out the tableting at a temperature which is above ambient, the particulate composition is preferably supplied to the tableting machinery at an elevated temperature. This will of course supply heat to the tableting machinery, but the machinery may be heated in some other way also.

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

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

Example 1

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

The amount of zeolite MAP (zeolite A24) in the table above is the amount which would be present if it was anhydrous. Its accompanying small content of moisture is included as part of the moisture and minor ingredients. Sodium carboxymethyl cellulose is a commonly used water soluble antiredeposition polymer.

A number of further ingredients were added to this base powder resulting in the following composition:

This resulting composition was sieved into various fractions: 355 -lOOOμm, 500-710μm and 1000-1400μm.

Nylin LX-16 is a water-insoluble compacted cellulosic disintegrant obtained commercially from FMC. It was sieved before use into the fractions 500-710μm and 1000-1400μm. Formulations for making detergent tablets were made by combining 5 parts by weight of a sieved fraction of Nylin LX-16 with 100 parts per weight of a sieved fraction of the detergent composition, as detailed in the following table.

These compositions were compacted with variable force in a laboratory press (Instron 5866) to produce cylindrical tablets with a weight, of approximately 40 grams.

The strength of the tablets, in their dry state as made on the press, was determined as the force needed to break the tablet, measured using an Instron type universal testing instrument to apply compressive force on a tablet diameter (i.e. perpendicular to the axis of a cylindrical tablet). The applied force F was progressively increased until the tablet breaks, whereupon the force at failure F_max in Newtons is recorded. Also the displacement at fracture was measured and the break energy, which is the area under a force-over-displacement graph up to failure, was calculated (Eb in milliJoules) . A further measure of the strength of the tablets is their diametrical fracture stress DFS calculated from the equation: where DFS is the diametrical fracture stress in Pascals, P is the applied load in Newtons to cause fracture, D is the tablet diameter in metres and t is the tablet thickness in metres. Generally it is preferred that tablets have a DFS of at least 14kPa, better at least 20 kPa and possibly at least 25kPa.

The disintegration of 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 (AWB 126/127) . 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 were then removed, dried at 100°C for 24 hours to give constant weight and weighed again.

1 - no residue after the ingress of 4.6 litres of water

2 - no residue after the ingress of 3.9 litres of water

In this example option D was comparative . The mean particle size of its disintegrant was more than 1.4 times the mean particle size of the remainder of the composition.

Option C was within the invention, but was less preferred because the mean particle size of its disintegrant particles was less than 0.7 times the mean particle size of the remainder of the composition.

Example 2

A very similar formulation to that above was made, except using Arbocel Al, a water-insoluble cellulosic disintegrant obtained from wood pulp, available from J Rettenmaier & Sδhne. Both the detergent composition and the Arbocel were sieved to 500-710μm fraction, combined in the same proportion as above, and made into 40 gram tablets using varying compaction forces. The tablets were tested as in Example 1, with results as follows.

Claims

1. A tablet of compacted particulate detergent composition including organic surfactant, detergency builder and other constituents, wherein the composition of the tablet or a discrete region thereof consists of

(i) from 1% to 15% by weight of disintegrant particles containing water-swellable, water-insoluble disintegrant material (ii) a balance from 85 to 99% by weight of further component particles characterised in that the particle sizes and size distributions are such that: the mean particle size of the disintegrant particles (i)is not more than 1.4 times the mean particle size of the further component particles (ii) ; and at least 90% by weight of the further component particles (ii) have a size greater than 350μm.

2. A tablet according to claim 1 wherein at least 90% by weight of the disintegrant particles (i) also have a size greater than 350μm.

3. A tablet according to claim 1 or claim 2 wherein the mean particle size of the disintegrant particles (i)is at least half the mean particle size of the further component particles (ii) .

4. A tablet according to claim 1 or claim 2 wherein the mean particle size of the disintegrant particles (i) is at least 0.7 times the mean particle size of the further component particles (ii) .

5. A tablet according to any one of the preceding claims wherein the mean particle size of the further component particles (ii) is in a range from 500 to 1200μm.

6. A tablet according to any one of the preceding claims wherein the particle size distribution of the particles

(ii) is such that

• at least 90% of the particles (ii) have a size greater than a lower threshold X_L but less than an upper threshold X₀ where Xu is not more than 1200μm larger than X_L

• no more than 5% of the particles (ii) have a size smaller than the lower threshold X_L

• no more than 5% of the particles (ii) have a size larger than the upper threshold Xu.

7. A tablet according to claim 6 wherein the lower threshold X_L is at least 350μm and the upper threshold Xu is not more than 2000μm.

8. A tablet according to any one of the preceding claims wherein the composition of the tablet or discrete region thereof contains from 5 to 40% by weight of organic surfactant, and from 10 to 80% by weight of detergency builder, both of which are contained within the further component particles (ii) .

9. A tablet according to claim 8 wherein the further component particles (ii) include or comprise an amount which is from 30 to 99% by weight of the composition of the tablet or region thereof, of particles which themselves consist a mixture of 25 to 75% by weight of an organic surfactant, 25 to 75% of detergency builder, and 0 to 50% of other materials.

10. A tablet according to any one of the preceding claims wherein the particles (ii) include 10 to 50% by weight of the composition of particles which contain more than half of their own weight of material which is other than soap or organic surfactant and which has a solubility in deionised water of at least lOg/lOOg at 20°C.

11. A tablet according to claim 10 wherein the said material is a salt with a solubility of at least 50 g/lOOg of deionised water at 20°C.

12. A tablet according to any one of the preceding claims wherein the particles (ii) include3 to 30% by weight of the composition of particles which contain more than half of their own weight of material which is other than soap or organic surfactant and which has a solubility in deionised water of at least 50g/l00g at 20°C.

13. A tablet according to any one of the preceding claims wherein the detergency builder comprises aluminosilicate.

14. A tablet according to any one of the preceding claims wherein the disintegrant particles (i) contain from 0.001 to 10% of their own weight of a water-insoluble material which swells to at least double its own volume on contact with water, optionally from 1 to 15% or 20% of a water soluble binder and a balance to 99.999% of other material.