GB2362161A - Detergent tablets - Google Patents

Abstract

A laundry detergent tablet comprised of a compressed particulate material. The tablet, or a region thereof contains at least one surface active agent, at least one builder, and an alkali metal silicate of the formula xSiO<SB>2</SB>:M<SB>2</SB>O where M is an alkali metal and x is at least 2.2.

Description

DETERGENT TABLETS The present invention relates to detergent tablets for

use in laundering operations, particularly but not exclusively domestic laundering.

In recent years, there has been a trend to the use of laundry detergent formulations in the form of tablets. Such tablets are more convenient to use than washing powders since they (the tablets) do not need to be "measured-out" and can easily be introduced into a domestic washing machine without spillage. The tablet may be introduced into the drum or dispensing drawer of such machine.

It is necessary that the tablets are able to disintegrate in water in an appropriate time scale to allow the various "active components" of the tablet to become dissolved or dispersed in the wash liquor. Thus, for example, a tablet to be introduced in the dispensing drawer of a domestic washing machine must be capable of dissolving the relatively short time during which water in introduced into that drawer. For a tablet to be introduced into the drum of a washing machine, a longer dissolution time will be acceptable.

The tablets must also be of acceptable storage stability.

Such tablets are produced by compression of a particulate mixture which generally comprises a builder (which may be water soluble or water insoluble), a surface active agent system optional (but usually desirable) and ancillary components such as a bleach, bleach activator, enzymes etc. as well known in the art. The surface active agent system may for example comprise a mixture of ionic and anionic surface active agents.

Frequently the tablets also contain an alkali metal silicate of the formulae XSi02:M20 where m is an alkali metal (usually sodium) and x=2 as a source of alkalinity for the wash liquor, as a corrosion inhibitor and as a sequestrant.

2 The present invention relates to improvements in detergent tablets which incorporate an alkali metal silicate, particularly with regard to dissolution and storage stability thereof According to the present invention there is provided a laundry detergent tablet comprised of a compressed particulate material, said tablet or a region thereof containing at least one surface active agent, at least one builder, and an alkali metal silicate of the formula XSi02:M20 where M is an alkali metal and x is at least 2.2.

Tablets in accordance with the invention may have the composition as defined in the previous paragraph throughout the tablet. Alternatively his composition may be provided in a region of the tablet, e.g. a layer.

We have found that the use of alkali metal silicate form which x is at least 2.2 provide improvements in dissolution of the tablets and also the storage stability of such tablets as compared to those incorporating an alkali metal silicate for which x is 2.0. Tablets in accordance with the invention display improved properties compared to the prior art silicatecontaining tablets with regard to use of the tablets in the drawer of an automatic domestic washing machine. Furthermore the tablets of the invention have excellent storage properties and are less prone to swelling and cracking than the prior art silicate-containing tablets.

The alkali metal silicate may be incorporated in the tablet (or region thereof) during manufacture either in the form of a liquid so as to act as a binder. More preferably however the silicate is incorporated as a solid.

Preferably the alkali metal silicate is sodium silicate (i.e. M= sodium). Alternatively M may be potassium.

Preferably x in the above formula is at least 2.3, more preferably at least 2.4, even more preferably at least 2.5 and still more preferably at least 2.6. Preferably x is not greater than 3.4, more preferably not greater then 3.2, even more preferably not 3 greater than 3.0, still more preferably not greater than 2.8, and most preferably not greater 2.7. A particularly preferred value for x is about 2.65.

A suitable silicate is available under the designation Pyramid G86 from Crosfield Ltd.

The amount of the alkali metal silicate incorporated in the tablet or region thereof is preferably in the range of 1% to 15% (preferably 2% to 10%) by weight of the tablet or region as appropriate.

The invention is applicable particularly, but by no means exclusively to tablets which incorporate a water insoluble, water swellable disintegrant. In particular, the present invention renders it possible to produce tablets which are intended for dosing into the dispensing drawer of a domestic washing machine and which dissolve rapidly therein during the time that water is passed into the dispensing drawer. Tablet formulations may be produced which leave a residue of less than 1% by weight of the tablet in the drawer after the addition of water thereto has terminated.

Instead of providing the tablets in the dispensing drawer of a washing machine, it is possible for them to be provided in the drum. It is also possible for the tablets to be provided in a dosing device.

It is particularly preferred that (prior to compaction of the tablet or region thereof) the disintegrant has an average particle size of 30gm to 1500gm. For example, the disintegrant may have a particle size of 50[tm to 500gm, preferably 50tm to 400gm, more preferably 100ptm to 300gm, and even more preferably 300[im to 350ttm. Alternatively, the disintegrant may have a particle size of 500[Lm to 1200[im, more preferably 600[tm to 1000[im, and even more preferably 800trn to 10OOgm Typically the amount of the disintegrant present in the tablet (or region thereof) will be in the range 0.5% to 9% by weight, more preferably 1% to 5% by weight.

4 Most preferably the disintegrant is a cellulose based material. Such cellulose based material may for example comprise both crystalline and amorphous cellulose. Examples of suitable materials are disclosed, for example, in WO-A-9855575 (Henkel), WO-A-9840462 (Herzog). The cellulose may be a cross-linked modified cellulose e.g. AC-DI-SOL and/or may comprise micro crystalline cellulose fibres (e.g. HANFLOC).

The cellulose based material may be a cellulose derivative which may be cross-linked, e.g. a cross-linked carboxymethyl cellulose.

Examples of granular disintegrants that may be used are available under the trade marks NILYN (ex FMC), grade LX16 which is an internally crosslinked carboxymethyl cellulose, and ARBOCEL TF 04515 (ex Rettenmaier).

The disintegrant may be a cellulose derivative, for example a sodium carboxymethyl cellulose. Examples include COURLOSE and NYMCEL.

Further examples of disintegrants which may be used include various starches such as potato, rice, corn or maize starch. The disintegrant may be a starch derivative, e.g. carboxymethyl starch such as available under the trade mark PRIMOGEL or a sodium starch glycolate such as available under the trade mark EXPLOTAB.

It is also possible for the disintegrating agent to be a clay. Such clays are generally of the "lamellar type" and may for example be a smectite such as a Laponite, Bentonite, Montmorrillonite, Hectorite or Saponite. For example, the clay may be a Sodium Montmorrillonite, a Sodium Hectorite, a Sodium Saponite, a Calcium Montmorrillonite or a Lithium Hectorite.

Furthermore, it is possible for the disintegrating agent to be a synthetic polymer, for example a cross-linked polyvinyl pyrrolidone, POLYPLASDONE XL or KOLLIDON XL.

It will be appreciated that certain of the abovedescribed disintegrants will provide additional benefits during a laundering operation, e.g. a clay may contribute to fabric softening properties and synthetic polymers may act to prevent deposition of dyes.

As an alternative to the use of a water insoluble, water swellable disintegrant, it is possible for the tablet (or region thereof) to incorporate a highly water soluble salt to promote disintegration.

The tablet may incorporate a fabric softening agent which may for example be a clay. The fabric softening clay preferably has a particle size of at least 500 gm.

The fabric softening clay may be any such clay having fabric softening properties used in laundry detergent formulations. Such clays are generally of the %amellar type" and are such that the layers "separate" to become deposited on the garments being washed. The clay may for example be a smectite such as a Laponite, Bentonite, Montmorrillonite, Hectorite or Saponite. For example, the clay may be a Sodium Montmorrillonite, a Sodium Hectorite, a Sodium Saponite, a Calcium Montmorrillonite or a Lithium Hectorite.

The clay preferably has a moisture content of less then 15%, more preferably less than 12%, by weight.

Generally the amount of clay used as a fabric softener in the detergent tablets or region thereof will be 5% to 20% by weight.

The clay may be used in conjunction with a cationic and/or amide surfactant to help delamination of the clay and absorption thereof onto the garments being laundered. The cationic surfactant may for example be a quaternary ammonium salt having one long chain (e.g. C8-22) alkyl group and three short chain (e.g. Cl-4) alkyl groups. A suitable cationic surfactant is coco trimethyl ammonium chloride. The 6 amide surfactant may contain at least one long chain (e.g. C8-22) alkyl group and may for example be stearyl stearamide. A suitable clay formulation may contain 20-30% by weight of the formulation (i.e. clay plus surfactants) of amide surfactant and 1-2% cationic surfactant.

The fabric softening agent may be an organic compound.

One class of organic fabric softening agents are amides of the formula Cn112n+l - C-NC.. H2m,l 11 0 where n and m are the same or different and are in the range 8 to 22, more preferably 10 to 20. If the alkyl groups are branched then they preferably include a chain of at least 8 carbon atoms.

A particularly preferred amide for use in the invention is stearyl stearamide.

Alternatively, or additionally, the organic fabric softening agent may be a quaternary ammonium salt having one long chain (e.g. C8-22) alkyl group and three short chain (e.g. Cl-4) alkyl groups. A suitable cationic surfactant is coco trimethyl ammonium chloride.

It is particularly preferred that the quaternary ammonium salt be used in combination with the above described amides in which case the quaternary ammonium salt may suitably be employed in an amount of up to 5%, more preferably 1 to 2%, by weight of the clay.

Further organic fabric softening agents which may be used include amine and/or amide fanctionalised silanes.

7 Tablets in accordance with the invention also incorporate at least one builder. Generally the builder will be present in the tablets (or region thereof) in an amount of 10% to 70% by weight, more preferably 20% to 50% by weight.

The builder may be a water soluble salt and a wide range of such salts known as builders in the art may be employed in the present invention. It is particularly preferred that the builder is an alkali metal phosphate or an alkali metal phosphate or an alkali metal carbonate. A particularly preferred builder for use in the invention is sodium triphosphate for example of the type, or of a type similar to that, disclosed in EP-A-0 839 906. Alternatively the builder may be sodium carbonate.

Alternatively the builder may be a water insoluble material, e.g. a zeolite, which may be in a powder or granular form. The Zeolite may for example be Zeolite MAP (e.g. as available under the designation DUOCIL A24 (e.g. Crosfield Ltd).

The surface active agent present in the tablet may for example be a nonionic, anionic, cationic or amphoteric surface active agent, or appropriate mixtures of such surface active agents.

If a non-ionic surface active agent is used then it may be a liquid, solid or a mixture thereof.

The term liquid surface active agent as used herein means a surface active agent having a viscosity of less then 1 Pa s at 2TC. Preferably any non-ionic liquid surface active agent in the tablet (or region thereof) has a viscosity of less then 0.5 Pas at 2TC.

If a liquid non-ionic surface active agent is to be included in the tablet then it may for example an alcohol ethoxylate. The alcohol residue (which may be of a primary or secondary alcohol) may for example comprise 8 to 18 carbon atoms and be ethoxylated with an average of 3 to 20 moles of ethylene oxide per mole of alcohol.

8 Suitable liquid non-ionic surface active agents are available from ICI under the designations SYNPERONIC A3 and SYNPERONIC A7. Mixtures of the A7 and A3 active agents may also be used. Also suitable are LUTENSOL A03 and LUTENSOL A07 (ex BASF).

Examples of solid non-ionic surface active agents which may be used in the tablets of the invention include alkyl(C8-22)P0lyglycosides. The preferred glycoside employed in the present invention is a glucoside (i.e. based on glucose), functionalised with a primary alcohol (e.g. C12-CM). More preferably the glucoside is in the form of a polyglucoside, with a preferred degree of polymerisation of between 1-2, most preferably about 1.4.

It is preferred that solid non-ionic surface active agent is used in the form of particles or granules containing at least 30% by weight, more preferably at least 40% by weight of solid non-ionic surface active agent.

A suitable polyglycoside is available under the name Glucopan (Henkel), preferably used as Glucopon G50 granules (50% APG Glucon, 50% sulphate).

Anionic surface active agents for use in the invention may comprise at least one alkyl sulphate, most preferably a C8-22 alkyl sulphate. For preference, the alkyl group of the alkyl sulphate has 8-16 carbon atoms. The alkyl sulphate may be a single compound or may comprise a mixture of alkyl sulphates of different chain lengths. For preference the alkyl groups are primary alkyl groups and preferably straight chain. The alkyl sulphate is preferably an alkali metal alkyl sulphate, the preferred alkali metal being sodium.

A suitable alkyl sulphate for use in the invention is available under the trade mark SULPHOPON, e.g. SULPHOPON 121 8GI (a Cl 2-18 alkyl sulphate).

As an alternative to an alkyl sulphate, the anionic surface active agent may be an alkyl ether sulphate, preferably one in which the alkyl group has 8-22 carbon j 9 atoms. It is particularly preferred that the alkyl ether sulphate is an alkyl (C8-22) ethoxylated (nA to 5, preferably 2 or 3) sulphate.

The alkyl group of the ether sulphate may be as described for the alkyl sulphate.

Further Examples of anionic surface active agents which may be used include alkylaryl sulphonates (e.g. alkylbenzene sulphonates, (e.g. Nansa HS80, HS85 and HS90 ex Albright & Wilson) alpha olefin sulphonates and ether carboxylates.

A suitable amphorteric surface active agent is a betaine.

Preferred betaines may be either of the formula (I) or (II).

R' 1 W-N-'--CH2-COO- (I) 1 W R' i WCONI1CH2CH2C112N - -CH2C00- In the above formula, R' and R may be the same or different C, -4 alkyl groups whereas W is an alkyl group having 8-22 carbon atoms, more preferably 12 to 18 carbon atoms e.g. mixed Clo to C14.

The preferred betaine for use in the tablet of the invention is cocoamidopropyl betaine (also known as cocodimethyl acetic acid betaine (CAS Registry No.66455-296). Further betaines which may be used are lauryl dimethyl betaine (CAS Registry No. 683-10-3), cocoa dimethyl amidopropyl betaine (CAS Registry No. 61789- 40-0) and the products identified as CAS Registry Nos. 70851-07-09 and 4292-10-8.

An alternative amphoteric surface active agent for use in the tablet of the invention is a glycinate of the formula WNHCH2C02H where W is as defined above.

A further glycinate which may be used is of the formula R 3_ N-(CH2)3 N-CH2CO2Na CH2C02Na n CH2CO2Na In which R3 is as defined above (more preferably C12-22) and n is 1 to 3.

Other suitable materials are as given in chapter I of "Amphoteric Surfactants", e.g. Lomax Ed, Marcel Decker, New York 1996.

It is preferred that the tablet (or region thereof) does not contain more than 3% by weight of liquid non-ionic surface active agent. Thus, for example the tablet may not contain any liquid non-ionic surface active agent but it is generally preferred that the tablet (or region thereof) contains at least 0.5% by weight of liquid non-ionic surface active agent. Preferably the tablet (or region thereof) does not contain more than 2. 5%, more preferably not more than 2%, even more preferably not more than 1.75% and most preferably not more than 1.5% by weight liquid non-ionic surface active agent.

11 We have found that amounts of liquid surface active agent of not more than 1.5% by weight (although preferably more than 0.5% by weight) improve the solubility of the tablet.

With these low amounts of liquid non-anionic surface active agent, it is preferred that the tablet (or region thereof) contains at least 5% by weight at least one solid surface active agent. Preferably the amount of the solid surface active agent is in the range 5% to 25% by weight, more usually 5% to 15% by weight.

To compensate for the low level of liquid non-ionic surface active agent, it is generally preferred that at least a proportion of the solid surface active agent in the tablet (or region thereof) is a non-ionic surface active agent. Most preferably the total amount of non-ionic surface active agent present in the tablet is at least 2.5%, preferably at least 3%, more preferably at least 4% and even more preferably at least 5% of the weight of the tablet or region thereof.

It is also preferred that at least a proportion of the solid surface active agent in the tablet (or region thereof) is provided by an anionic surface active agent. Typically the amount of such an anionic agent will generally be at least 5% by weight of the tablet (or region) more typically at least 8% (and at most 250/0) and generally in the range 10% to 15 %, more preferably 10% to 13%, of the same weight basis.

It is preferred that solid anionic surface active agent is used is used in the form of particles or granules containing at least 70%, more preferably at least 80% and even more preferably at least 90% by weight of anionic surface active agent.

It is also possible for at least a portion of the solid surface active agent to be provided by a cationic surface active agent although in this case there will generally be no anionic surface active agent present in the tablet.

12 The tablet may incorporate a bleach, for example an activated bleaching system. Such a system may comprise a hydrogen peroxide precursor (e.g. sodium percarbonate, sodium perborate monohydrate or sodium perborate tetrahydrate) together with a bleach activator.

The activator may be an N-acyl compound, particularly one having two or more N-acyl groups. Thus, for example, the activator may be tetraacetyl ethylene diamine (TAED) as conventionally used as a activator in detergent tablets.

Alternatively, the bleach activator may be an ester of a polyhydric alcohol having at least 5 carbon atoms and at least 3 hydroxyl groups esterified with C2-5acyl groups, the polyhydric alcohol residue of said activator not having substituents with 6 or more carbon atoms. Such an activator may have an HLB value of at least 7, more preferably at least 9, and even more preferably at least 11. The HLB value may be as high as 14 or 15.

The alcohol residue of the activator preferably has a maximum of 12 carbon atoms and a minimum of five hydroxyl groups esterified with C2-5 acyl groups. Examples of suitable alcohols are sugar and sugar derived alcohols such as sorbitol, glucitol, mannitol, glucose and sucrose.

For preference, the acyl groups in the activator are aliphatic acyl groups. It is preferred that the acyl group has two or three carbon atoms and is most preferably the acetyl group.

Specific examples of bleach activator which may be used in the tablets of the invention include hexa acetyl sorbitol, hexa acetyl mannitol, penta acetyl glucose and octa acetyl sucrose. Particularly preferred are hexa acetyl sorbitol and hexa acetyl mannitol which may be used in admixture, e.g. as disclosed in EP-A-0 525 239. Further Examples are compounds having nitrogen atoms in the basic carbohydrate skeleton, e.g. the peracetylated forms of N-methyl gluxconamide, N-methyl glucamine and glucopyronosyl amine.

13 Further details of the activators are disclosed in EP-A-0 869 170.

The amount of bleach activator incorporated in the tablet of the invention will generally be in the range of 0.5% to 10% by weight of the total formulation, more preferably 1 % to 8% and even more preferably 2% to 4% on the same basis.

The preferred bleaching system for use in the invention comprises a hydrogen peroxide precursor compound and the bleach activator as defined above which is capable of reacting with the hydrogen peroxide to generate a peracid. The hydrogen peroxide precursor compound may, for example, be an inorganic persalt e.g. a perborate (in the monohydrate and/or tetrahydrate form), a percarbonate or a persulphate. The alkali metal salts of these compounds are preferred, particularly sodium and potassium salts. Alternatively the bleaching agent may be a ureahydrogen peroxide complex.

The amount of hydrogen peroxide precursor compound present in the formulation of the invention is preferably such as to provide 0.5% to 3% by weight active oxygen, especially 1.0% to 2.5% by weight.

The tablet may incorporate at least one enzyme.

The enzyme may, for example, be a protease, amylase, lipase or cellulase (or mixtures thereof) such as commonly used in detergent formulations. Examples of suitable enzymes are available under the names Opticlean, Savinase, Esperase; TermamyI, Maxamayl, Lipomax, Lipolase; Celluzyme and Carezyme. The amount of enzyme incorporated in the tablet will depend on activity but will typically be 0.1 to 3%. This level is particularly suitable for Savinase 6.0T, Termamy]. 60T, Celluzyme 0.7T and Lipomax.

The tablets of the invention may be mass-produced on a number of tabletting machines. Models that may be used include the Europharma Machinery (UK) 14 generally work by having a rotating circular turret with arrays of punches that compress the tablets from above and below. Tablets may be produced that are single or dual or multi- layer or of the tablet-in- tablet type and variations thereof. The cycle for producing dual layer tablets consists of filling the die with the powder that will make up one of the layers, followed by filling of the powder of second layer.

Machines specially designed for dual layer operation usually have a small amount of pre-compression between filling the die with the powders of the first and second layers. This gives a sharper definition between the two layers which may be more aesthetically pleasing, particularly if the two layers are of different colours.

The press should have a control to regulate the applied force used in the main compression. The applied pressure should typically be about 0. 5 to 10 tons per 44nun diameter (or equivalent pressure per square min). The pressure applied is a crucial part of the tabletting operation as inadequate pressure will give a tablet which dissolves too slowly. The tablet strength may be monitored by use of equipment to measure its breaking strength such as the Holland CT5 automatic compression tester (see below).

It will be appreciated that the tablet may incorporate additional components as conventionally included in laundry detergent formulations. One example of such an additional component is a soap which may be used in an amount up to 5% by weight as a processing aid. Further Examples include anti-foam agents, sequestrants (e.g. of the phosphonate type), whiteness maintenance agents (e.g. CMC, polyoxyethylene terephthalate, polyethylene terephthalate), colourants (e.g. dyestuffs), perfume, flow control agents (e.g. a sulphate) flow enhancer (e.g. a zeodite), pH regulators (e.g. a carbonate or bicarbonate), anti-corrosion agents, dye transfer inhibitors (e.g. PVP) and optical brighteners (e.g. Tinopal CBS- X and Tinopal DMS-X). These components may, for example, each be present in amounts up to 1 % by weight of the formulation.

The fabric softening agent may be an organic fabric softening agent which is nitrogen containing compound having at least a degree of positive charge on the nitrogen atom.

The invention will be further described with reference to the following nonlimiting Examples.

Examples

Tablets of various compositions (see below) where produced and evaluated using the following procedures.

Beaker Test Tablets (44mm diameter, 18mm height, 40g) are placed on an open wire stand (40mm diameter, 5cm. high) in a beaker containing water at 300C. The time taken for the bulk of a tablet to fall from the stand was measured. A time of 30 seconds or less indicates suitability of the tablet for the testing in the dispensing drawer of a domestic washing machine.

Washina Machine Drawer Tests Two tablets are placed on their circular faces and side-by-side, in the main (first) dispensing drawer (clean and dry) of a washing machine (drawer empty). Two washing machines are used; a Hotpoint Ultima 1200 washing machine set at 40'C normal cotton wash and a Bosch 20001 set for a 40'C wool wash. A tablet was said to have passed the drawer test if less than 1% of the tablets, by weight when dry, was left in the drawer.

CoWression Test This was conducted on an Instron 5543 materials tester.

16 Example 1

2Kg batches of each of the following formulations 1(a)-(e) (all containing clay as a fabric softner) were prepared by admixture of the various components in the amounts shown. Formulations I(b), (d) and (e) are in accordance with the invention whereas 1(a) and 1(c) are comparative.

Component 1(2) Iffi) I(C) 1(d) W0 (Comparative) (Comparative) STP 40.50 40.50 40.50 40.50 40.50 2SiO2:Na20 5.00 0.00 5.00 0.00 0.00 12.65SiO2:Na20 0.00 10.00 0.00 5.00 10.00 2 FAS granules 11.00 11.00 11.00 11.00 11.00 Non-ionic granules 2.00 2.00 2.00 2.00 2.00 3 Non-ionic 1.00 1.00 1.00 1.00 1.00 Granular Cellulose based disintegrant 3.00 3.00 3.00 3.00 3.00 T.A.E.D. 3.00 3.00 3.00 3.00 3.00 4 Ancillary Components 2.14 2.14 2.14 2.14 2.14 Sodium Percarbonate 16.00 16.00 16.00 16.00 16.00 Clay 1 16.36 11.36 0.00 0.00 0.00 6Clay 2 0.00 0.00 16.36 16.36 11.36 Total % 100.00 100.00 100.00 100.00 100.0 Pyramid G86 ex Crosfields 2C 12-18 alkyl sulphate 3C 13-15 alkyl ethoxylate (7EO) 4 Optical Brightener, Dequest 2016D, Antifoam, Enzymes 5 Laundrosil PR 2 10 (ex Sud Chemie) 6 Laundrosil DGA (ex Sud Chemie)

Tablets were prepared from 40g samples of the above formulations using a laboratory hand press with a cylindrical die having a diameter of 44mm using a range of compaction pressures to produce tablets having a height of 18mm.

17 For each of the tablets produced, the beaker dissolution times were measured as described above and the compression force of the tablets (across the diameter thereof) was measured on the Instron 5543 materials tester.

Formulation I(a) -CoMparative Pressure Max Load Beaker time Hotpoint Bosch Tons N No. fills No. fills 1 7. 13 1.5 15. 15 2 29 18 Pass on 2"" fill Pass on 2"' fill 3 52 20 Pass on 3"' fill Pass on 2"' fill Formulation l(b) -Invention Pressure Max Load Beaker time Hotpoint Bosch Tons N No. fills No. fills 1 13 15 1.5 24 16 2 29 17 Pass on Is' fill Pass on I" fill 3 49 19 Pass on 2'4 fill Pass on 2"' fill It will be appreciated from the data given in the two foregoing Tables that formulation I(b) in accordance with the invention gives higher tablet strength at the same compaction force and better disintegration in the machine drawer.

18 Formulation I(c) -Comparative Pressure Max Load Beaker time Hotpoint Bosch Tons N No. fills No. fills 1 8 12 1.5 18 15 Pass on 2"' fill Pass n 2"' fill 2 29 17 Pass on 2 nd fill Pass on 34 fill 3 47 22 Formulation l(d)- Invention Pressure Max Load Beaker time Hotpoint Bosch Tons N No. fills No. fills I 11 12 1.5 20 14 Pass on 2"' fill Pass on I" fill 2 29 16 Pass on 2'a fill Pass on I" fill 3 44 18 Formulation I(e)- InventionPressure Max Load Beaker time Hotpoint Bosch Tons N No. fills No. fills 1 12 15 1.5 19 17 Pass on 2'6 fill Pass on 2' fill 2 28 19 Pass on 2'4 fill Pass on 2nd fill 3 50 21 Pass on 3" fill Pass on 2" fill It will be appreciated from the data given for formulation I(c) (Comparative) and formulation I(d) (Invention) that the use of the 2.65 ratio silicate gives slightly faster tablets disintegration in the beaker test and much better results in the Bosch machine. Increasing the level of silicate at the expense of clay (formulation I(c)) gave no additional benefit.

19 Example 2

The storage stability of tablets produced as described in Example I from formulations I(c), I(d) and I(e) was investigated and the results compared with those for a further formulation I(f) which corresponds with I(c) but excluding silicate and increasing the ST? level to 45.5%.

The storage stability tests were conducted under ambient conditions for unwrapped tablets and also tablets "flow-wrapped" in a polypropylene based film having a Moisture Vapour Transmission Rate (at 3 8'C, 90% RH) of 5. 0 g m-2 24hf 1 and an Oxygen Transmission Rate (at 23'C, 0% RH) of 15 cm 3 m-2 24hr-1.

After 7 weeks the height of the tablets was measured (ef original height of l8mm) and the tablets examined for degree of cracking (if any).

The results are shown in the following Tables.

UNVPED TABLETS Formulations Invention/ Height Appearance Comparative I(C) Comparative 20.8mm Significant Cracking (but tablet whole) l(d) Invention 18.7mm As New I(e) Invention 19.7mm As New Comparative 19.7mm Very Slightly Cracked PPED TABLETS

Formulations Invention/ Height Appearance Comparative I(C) Comparative 20.7mm Significant Cracking (but tablet whole) l(d) Invention 18.8nun As New l(e) Invention 19.5mm As New Iffi Comparative 19.7mm Very Slightly Cracked As will be seen from the above results, tablets in accordance with the invention (formulations 1(d) and (e)) remained as new after 7 weeks storage both in the wrapped and unwrapped conditions and exhibited less swelling than the two comparative tablets. The comparative formulation l(c) containing 2SiO2:Na20 exhibited significant cracking both in the wrapped and unwrapped conditions and swelled significantly more than the formulations in accordance with the invention. In fact, comparative formulation I(c) gave poorer results than the comparative formulation Iffi which do not contain any silicate at all.

Example 3

Using the procedures described in Example 1, 40g tablets were produced from the following "Clay free" formulations ll(a) and (b). Formulation II(a) is comparative whereas ll(b) is in accordance with the invention.

21 Component Il(a) II(b) (Comparative) STP 41.50 41.50 2M2:Na20 5.00 0.00 12.65Si02:Na20 0.00 5.0 2 FAS granules 11.00 11.0 Non-ionic granules 2.00 2.0 3 Non-ionic 1.80 1.80 Granular Cellulose based disintegrant 6.5 6.5 T.A.E.D. 3.00 3.0 4Ancillary 0.65 0.65 Components Percarbonate 18.0 18.0 Na-carbonate 9.80 9.80 Total % 100.00 100.0 Pyramid G86 ex Crosfields 2C12-18 alkyl sulphate 3C 13-1s alkyl ethoxylate (7E0) 40 ptical Brightener, Dequest 2016D, Antifoam

The tablets thus produced were tested according to the same procedures employed in Example 1.

Formulation Wa) - CoLnparative Pressure Max Load Beaker time Hotpoint Bosch Tons N No. fills No. fills 1 4 17 2 11 18 3 20 21 Pass on 2"' fill Pass on 2"' fill 4 31 22 Pass on 2" fill Pass on 3"" -fill 51 22 22 Formulation Il(b) - Invention Pressure Max Load Beaker time Hotpoint Bosch Tons N No. fills No. fills 1 3 18 2 13 18 Pass on I" fill Pass on I" fill 3 20 19 Pass on 2"t fill Pass on I'fill 4 30 19 It will be seen from the results given in the proceeding two Tables that the formulation in accordance with the invention 11(b) gives faster beaker dissolution times as well as improved "in-draw" dissolution, particularly in the Bosch machine.

11 23

Claims (17)

Claims

1. A laundry detergent tablet comprised of a compressed particulate material, said tablet or a region thereof containing at least one surface active agent, at least one builder, and an alkali metal silicate of the formula XSi02:M20 where M is an alkali metal and x is at least 2.2.

2. A tablet as claimed in claim 1 wherein the alkali metal is sodium.

3. A tablet as claimed in claim 1 or 2 wherein x is at least 2.3.

4. A tablet as claimed in claim 3 wherein x is at least 2.4.

5. A tablet as claimed in claim 4 wherein x is at least 2.5.

6. A tablet as claimed in claim 5 wherein x is at least 2.6.

7. A tablet as claimed in any one of claims I to 6 wherein x is at most 3. 4.

8. A tablet as claimed in any one of claims I to7 wherein x is about 2.65.

9. A tablets as claimed in any one of claims I to 8 wherein the amount of the alkali metal silicate incorporated in the tablet or region thereof is in the range 3% to 15% (preferably 1% to 10%) by weight of the tablet or region as appropriate.

10. A tablet as claimed in any one of claims 1 to 9 wherein the builder is water soluble.

11. A tablet as claimed in claim 10 wherein the builder is sodium tripolyphophate.

12. A tablet as claimed in any one of claims I to 9 wherein the builder is water insoluble.

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13. A tablet as claimed in claim 12 wherein the builder is zeolite.

14. A tablet as claimed in any one of claims 1 to 13 incorporating a fabric softening clay.

15. A tablet as claimed in any one of claims 1 to 14 containing 0.5% to 3% by weight of a liquid non-ionic surface active agent and 5% to 25% by weight of a solid surface active agent.

16. A tablets as claimed in any one of claims 1 to 15 incorporating a water insoluble, water swellable disintegrant.

17. A tablet as claimed in claim 16 wherein the disintegrant is a cellulose based disintegrant.