WO1996033258A1

WO1996033258A1 - Stabilised aqueous suspensions of bleach containing perborate particles

Info

Publication number: WO1996033258A1
Application number: PCT/EP1996/001643
Authority: WO
Inventors: William John Nicholson; William Paul Haslop
Original assignee: Albright & Wilson Uk Limited
Priority date: 1995-04-20
Filing date: 1996-04-19
Publication date: 1996-10-24
Also published as: AU5690296A

Abstract

An aqueous based bleach composition with high retention of available oxygen on storage comprises water, solid particles of sodium perborate and dissolved sodium metaborate at pH sufficiently high to maintain a stabilising concentration sodium metaborate in the solution.

Description

Stabl H sed aqueous suspensions of bleach containing perborate particles.

The present invention relates to stabilised aqueous suspensions of bleach and in particular to bleach stably suspended in aqueous liquid laundry detergents.

Introduction

Laundry detergents, at least in Europe, have conventionally consisted of powders which have included three main cleaning agents: (i) Surfactants to remove hydrophobic soil by making it dispersible in water; (ii) Builders to assist the surfactant by removing calcium from the water and maintain alkalinity, and by assisting in soil suspension; and (iii) an oxidising bleach to remove oxidisable stains, and act as a disinfectant, hereinafter referred to as bleach. Historically the bleach which has been used in almost all powders is sodium perborate, although other organic persalts e.g. sodium percarbonate have also been employed.

The invention applies to perborate, as the bleach, particularly sodium perborate monohydrate or tetrahydrate.

The stability of the bleach in an aqueous detergent composition is typically measured by determining the available oxygen content of a sample which has been stored under controlled conditions. The stability of the bleach may be expressed in terms of its half life, or in terms of the % available oxygen retention over a given time.

References herein to borax refer to the salt disodium tetraborate, Na₂B₄O₇, and its hydrates. For convenience, where the context permits or requires, the term may embrace other sodium borate salts intermediate between sodium orthoborate, Na₃BO₃ and sodium metaborate whose empirical formula is NaBO₂. Such salts may for example include pyroborate and pentaborate. However, all references to borax in the examples are to sodium tetraborate decahydrate. Prior Art

For more than thirty years manufacturers have tried to formulate aqueous liquid laundry detergents containing all the aforesaid three main cleaning agents. Thus, for example, GB 855 893 suggests formulations containing hydrogen peroxide bleach. However the compositions evolve oxygen rapidly after a few days storage.

More recently the successful development of structured surfactants capable of suspending builders has given rise to further attempts to introduce persalt bleaches, such as perborate, into aqueous based detergent compositions. Generally the bleaches are incorporated as the solid material rather than being present in solution in the aqueous medium. However peroxy salt bleaches are rapidly decomposed by moisture.

There have been a number of proposals to incorporate a bleach into aqueous based detergent compositions by coating it with a water insoluble, typically polymeric coating , so as to isolate it, physically, from the aqueous medium in an attempt to inhibit its decomposition (see for example W095/14077). In practice it has not been found possible to stabilise bleach reliably for sufficiently long to be commercially acceptable by this method, while permitting the release of the bleach in the wash.

Another approach has been to incorporate a water-miscible solvent into aqueous based detergent compositions so as to maintain the solubility of the bleach within defined limits thus attempting to avoid the decomposition of the bleach upon dissolution (for example EP-0-293-040).

Another known method of inhibiting the breakdown of oxidising bleaches is to use silicate, either alone or in the presence of carbonate (for example, WO91/12307).

A further approach has been to effect in situ crystallisation of a perborate bleach by converting sodium perborate monohydrate to the corresponding tetrahydrate, or by converting a borate to a perborate in a aqueous liquid detergent composition. An example of this approach is EP-0-294,904. Generally the compositions of the aforesaid application include water miscible organic solvents so as to control the solubility of the bleach, with the weight average particle diameter of the bleach upon formation being required to be between 0.5 to 20 micrometers in order to provide sufficient stability. EP-0-294,904 refers to the term "in situ recrystallisation" as relating to processes whereby perborate particles are formed from larger particles or from solution in the presence of the water/anionic surfactant/detergent builder matrix. The term is stated to encompass chemical reactions, such as for example, the formation of sodium perborate by the reaction of stoichiometric amounts of hydrogen peroxide and sodium metaborate or borax.

Problem

All the foregoing prior attempts to incorporate bleach in aqueous based detergents have been unsuccessful due to the decomposition, usually rapid, of bleach in the presence of water or of other bleach incompatible components. It is well known that the decomposition of peroxides is generally more rapid at higher pH values (which are preferred for laundry detergents in order to achieve good soil removal) and may be hazardous since very rapid evolution of oxygen can cause bottles to explode, or the contents to expand to form a voluminous foam or even give rise to a fire hazard. Even a relatively small evolution of oxygen in a sealed bottle is potentially disastrous. Thus even if an effective coating method could be devised, there would be safety concerns if a proportion of particles were defective or damaged during handling or storage. So far bleach half lives of up to 35 days (extrapolated) have been reported in the literature ( WO91/12307). This is inadequate for commercial purposes. The above patent also quotes bleach stability of up to 95% after four weeks which is still undesirably low.

Therefore, the numerous attempts to stabilise bleach in liquid laundry detergents have failed to provide an appropriate level of stability (i.e. available oxygen retention of the bleach), with the result that a commercially acceptable product has not hitherto been available. Those attempting to incorporate bleach have generally tried to avoid high pH, in order to minimise decomposition, but even at neutral pH the decomposition rate has proved unacceptable. Discovery

We have now discovered that bleaches, such as sodium perborate, may be stabilised in an aqueous medium by maintaining a sufficient amount of a dissolved metaborate in the medium. By this means the rate of decomposition has been reduced sufficiently to give a half life in excess of 2.5 years. This meets the requirement for a commercial product.

The bleach is inherently unstable in aqueous media. We believe that it disproportionates with time into hydrogen peroxide and sodium metaborate, and that the latter is converted to other borate salts under normal conditions of pH. The hydrogen peroxide decomposes rapidly in solution to oxygen and water. We believe that the disproportionation is an equilibrium reaction and that the presence of metaborate in solution shifts the equilibrium in favour of perborate and so inhibits the disproportionation of the latter. The equilibrium shift lowers the concentration of hydrogen peroxide in solution and hence the rate of evolution of oxygen. By controlling the amount of metaborate present in solution an advantageous equilibrium between the bleach, hydrogen peroxide and metaborate is established and maintained, thereby maintaining the stability of the bleach in the aqueous medium. The metaborate may be added to the aqueous medium as such or may be produced in situ e.g. by the reaction of alkali with borax or orthoborate. However since the reaction of alkali with borax is slow compared with the decomposition of hydrogen peroxide at the high pH required, it is not recommended to try to form the metaborate in this way in the presence of the perborate.

Maintenance of metaborate in the solution requires a high pH, which would normally be expected to cause rapid decomposition of peroxide. Surprisingly, alkaline metaborate solutions containing solid perborate are relatively stable, showing negligible loss of oxygen after several months storage.

Embodiments

Our invention provides an aqueous based composition containing particles of solid alkali metal or alkaline earth metal perborate, and a dissolved alkali metal or alkaline earth metal metaborate, at a pH sufficient to maintain a stabilising concentration of the metaborate in the aqueous medium.

In particular the invention provides a liquid laundry detergent composition comprising : water; sufficient surfactant and dissolved electrolyte to form a pourable solid-suspending structured surfactant system; and particles of solid sodium perborate suspended in said structured system; wherein in at least part of said dissolved electrolyte consists of sodium metaborate in a concentration sufficient to inhibit the disproportionation of sodium perborate and the composition has a pH sufficiently high at least to maintain said concentration.

According to a further embodiment our invention provides a method of stabilising sodium perborate in the presence of water which comprises introducing sodium metaborate into said water prior to addition of perborate thereto at pH sufficient to maintain said metaborate.

Perborate

The perborate is used in amounts greater than its solubility in the composition and preferably greater than its solubility in water. For instance quantities greater than 0.1% by weight of the composition, more usually greater than 1 %, eg. at least 4% preferably more than 6% more preferably greater than 10% most preferably greater than 12% are envisaged. We do not exclude the use of quantities of perborate up to eg. 70%, but such quantities are not normally required in current practice in detergent formulations. Typically the perborate is present in concentrations below 50%, more usually below 30%, especially below 25% e.g. below 20%. A typical range would be 10 to 20% by weight based on the total weight of the composition e.g. 13 to 18%. It is generally preferred to add the bleach as sodium perborate monohydrate but sodium perborate tetrahydrate may also be used. It is especially preferred to use finely milled perborate. It is possible to form the perborate in situ from metaborate or borax and hydrogen peroxide or a peroxy hydrate such as percarbonate or perpyrophosphate. Metaborate

The equilibrium may be established by the addition of an alkali or alkaline earth metal metaborate, preferably sodium metaborate to the aqueous medium. The dissolved metaborate is generally present in the aqueous medium in quantities greater than 0.5%, based on the total weight of the composition, more usually more than 1%, eg. at least 2%, especially greater than 2.5%, typically more than 3%, preferably more than 4%, most preferably more than 5%. In certain circumstances the metaborate may be present in an amount above its solubility level in the aqueous medium, although this is not normally advantageous. However, the metaborate may, in principle, provide enchanced protection at any concentration up to saturation. The stability of the perborate is roughly proportional to the metaborate concentration. The upper level is determined by cost and environmental considerations. The concentration of metaborate does not usually exceed 18% by weight and is more commonly less than 15%, typically less than 12%, especially less than 10% e.g. less than 8%. Concentrations in the range 3 to 12% by weight based on the total weight of the composition generally give cost effective stabilisation of the perborate e.g. 4.5 to 10% especially 5 to 9%. Where the metaborate is to be formed in situ by the reaction of alkali with borax or orthoborate, the borax or orthoborate is preferably added to the aqueous medium in an amount sufficient to provide the above preferred levels of metaborate. Where the metaborate is to be formed in situ the dissolved boron components of the composition will typically comprise predominantly metaborate although some borax and/or alkali may also be present. However it is preferred that the metaborate is not formed in this way in the presence of the perborate since the high pH causes substantial evolution of oxygen due to decomposition of hydrogen peroxide before sufficient metaborate to stabilise the system has formed.

Therefore, according to a particular embodiment of the invention there is provided a method of making stabilised aqueous perborate which comprises adding solid perborate to an aqueous solution of sodium metaborate. pfl

The composition has a pH sufficient to maintain the borate species present substantially as metaborate. If the pH is substantially above the minimum required to prevent the conversion of metaborate to borax, the stability of the bleach may be impaired. The pH should be above 10, preferably above 10.5 more preferably above 10.8 most preferably above 10.9, usually above 11 especially above 1 1.2 e.g. above 11.3. For best results a pH above 11.5 is preferred. Generally pH values above 13.5 are too caustic for normal detergent use and may accelerate the decomposition of the bleach. For the same reasons we prefer that the pH is less than 13. A typical range is 11 to 12.5, e.g. 11.8 to 12.4. Alkalinity is preferably maintained by addition, if required of sodium hydroxide, but other bases of sufficient strength may be employed, e.g. an alkaline sodium silicate. Sodium carbonate and sodium tripolyphosphate may also be used to contribute alkalinity.

The compositions generally have a less strongly alkaline dilution pH, e.g. on dilution with water to form a wash liquor containing 2% by weight of the composition based on the weight of the wash liquor, the pH is typically in the range 9 to 12 eg. 9.5 to 1 1.5 especially 10 to 11.

Surfactant

The aqueous based composition is preferably an aqueous based detergent composition containing surfactant. Alternatively the composition may for instance be a perborate slurry for use as a domestic bleach or for supply to industry, which preferably contains surfactant as structuring medium to support the bleach..

Typically the aqueous detergent composition comprises a structured surfactant such as a mobile spherulitic or lamellar (G-)phase in which a surfactant mesophase is interspersed with an aqueous electrolyte solution to provide a solid-suspending structure capable of stably suspending particles of perborate and of any solid builder. Such structured surfactants include reticular lamellar phases and spherulites such as are described, for example, in GB 2 123 846, GB 2 153 380, and GB 2 205 852. The bleach may be suspended in the mobile lamellar or spherulitic phases which may be formed by adding electrolyte to a surfactant solution which includes relatively high concentration of a highly soluble surfactant, such as an ether sulphate, as described in GB 2 245 280 or in No. GB-2 259.519. Structured surfactant may also be prepared by adding silicate to a composition containing a sulpho acid, as described in WO91/10720.

Any of the surfactants, builders, electrolytes, minor ingredients and/or methods taught in any of the foregoing specifications or in WO 91/12307 may be utilised in the preparation of compositions according to the present invention, subject to chemical compatibility with the perborate. Thus we prefer not to include strong reducing agents, and, as far as possible, to exclude transition metal ions as these are known to catalyse the decomposition of the bleach. We prefer to include complexants for transition metal ions such as phosphonates, especially amino phosphonates, and amino carboxylates.

Alternatively the perborate may be suspended by other known means such as polymeric thickeners or dispersants, bentonite or by milling to form a colloidal dispersion.

Surfactant is thus a preferred but not an essential component of the composition. The presence of relatively high concentrations of surfactant may help to protect the bleach. The surfactant concentration, based on the total weight of the composition, is usually greater than 2% desirably more than 3%, preferably more than 5%. The maximum concentration of surfactant could be as high as 70% but is as usually less than 60%, more commonly less than 50%, typically less than 30% e.g. 4 to 20%. Particularly preferred are surfactant concentrations between 5 and 15% based on the total weight of the composition.

The detergent compositions of the invention may comprise anionic, cationic, non-ionic, amphoteric or zwitterionic surfactants or mixtures thereof.

The anionic surfactant may comprise alkyl ether sulphate which is preferably the product obtained by ethoxylating a natural fatty or synthetic C₁₀-₂₀ (e.g. a C ₁₂-,₄) straight or branched chain saturated or unsaturated alcohol with from 1 to 20, preferably 2 to 10 e.g. 3 to 4 ethyleneoxy groups, optionally stripping any unreacted alcohol, reacting the ethoxylated product with a sulphating agent and neutralising the resulting alkyl ether sulphuric acid with a base. The term also includes alkyl glyceryl sulphates, and random or block copolymerised alkyl ethoxy/propoxy sulphates.

The anionic surfactant may alternatively or additionally comprise C ₆-₂₀ alkyl benzene sulphonates especially linear alkyl benzene sulphonates, C₁₀-₂₀ e.g. C ₁₂-₁₈ alkyl sulphates,

Cg-₂o e.g. C ₁₀-₁₈ saturated or unsaturated, straight or branched chain aliphatic soaps such as dodecanoates, myristates, stearates, oleates, linoleates, Iinolenates and palmitates and coconut and tallow fatty acids and their water soluble salts, olefin sulphonates, paraffin sulphonates, taurides, isethionates, ether sulphonates, aliphatic ester sulphonates eg, acyl glyceryl sulphonates, alkyl ether carboxylates, sulphosuccinates sulphosuccinamates and salts of alkyl phosphonic acids.

The cation of the anionic surfactant is typically sodium but may alternatively be potassium, lithium, calcium, magnesium, ammonium, or alkyl ammonium having up to 6 aliphatic carbon atoms including isopropylamine, monoethanolammonium, diethanolammonium, and triethanolammonium.

The detergent compositions of the invention preferably contain one or preferably more, non-ionic surfactants. These preferably comprise alkoxylated, e.g. ethoxylated, C₈-₂₀ preferably C ₁₂-_I8 alcohols, alkoxylated with 2 to 20 especially 2.5 to 15 alkyleneoxy groups.

The alcohol may be fatty alcohol or synthetic e.g. branched chain alcohol.

Preferably the non-ionic surfactant has an HLB of from 6 to 15, especially from 7 to 16 e.g. from 8 to 15.5. We particularly prefer mixtures of two or more non-ionic surfactants having a weighted mean HLB in accordance with the above values. Other alkoxylated non-ionic surfactant which may be present include C₆-_l6 alkylphenol alkoxylates, alkoxylated fatty acids, alkoxylated amines, alkoxylated alkanolamides and alkoxylated alkyl sorbitan and/or glyceryl esters. The alkylene oxide in the non-ionic alkoxylates is, in each case preferably ethylene oxide, but may alternatively be propylene oxide or a mixture of ethylene oxide and propylene oxide.

Other non-ionic surfactants which may be present include amine oxides, fatty alkanolamides such as coconut monoethanolamide, and coconut diethanolamide, alkylpolyglycosides and alkylaminoethyl fructosides and glucosides.

The detergent formulations of the invention may optionally comprise minor amounts of amphoteric and or cationic surfactants, for example betaines, imidazolines, amidoamines, quaternary ammonium surfactants and especially cationic fabric conditioners having two long chain alkyl groups, such as tallow group.

Builder

Detergent formulations according to our invention preferably contain builders. "Builder" is used herein to mean a compound which assists the washing action of a surfactant by ameliorating the effects of dissolved calcium and or magnesium.

Generally builders also help maintain the alkalinity of wash liquor. Typically builders include sequestrants and complexants such as sodium tripolyphosphate, potassium pyrophosphate, trisodium phosphate, sodium ethylenediamine tetracetate, sodium citrate or sodium nitrilotriacetate, ion exchangers such as zeolites and precipitants such as sodium or potassium carbonate and such other alkalis as sodium silicate. The preferred builders are sodium tripolyphosphate and zeolite. The builder is usually present at least partly as solid particles suspended in the composition. While amounts of builder of 50% of the total weight of the composition or more are possible, the builder level is usually under 40% more commonly less than 30%. Amounts are preferably greater than 5% especially greater than 10 e.g. 12 to 25% by weight based on the total weight of the composition. Hydrotropes and Solvents

Where appropriate, detergent compositions of our invention may optionally contain small amounts of hydrotropes such as sodium xylene sulphonate, sodium toluene sulphonate or sodium cumene sulphonate, e.g. in concentrations up to 5% by weight based on the total weight of the composition, preferably not more than 2%, e.g. 0.1 to 1%. Hydrotropes tend to break surfactant structure and cause instability of structured surfactants. They also add to the cost of the formulation, without improving its performance and it is therefore preferred to use the minimum amounts consistent with effectiveness. Hydrotropes are primarily useful for increasing the water solubility of less soluble components and for lowering the viscosity of liquid formulations, especially if the detergent contains surfactants in structured form. Hydrotropes are not normally required in formulations of the present invention and are preferably absent.

If required, liquid detergent compositions of the invention may contain organic solvents. However, like hydrotropes, solvents tend to break surfactant structure, and they add to the cost of the formulation. They are moreover undesirable on environmental grounds. We therefore prefer that the compositions contain less than 6%, more preferably less than 5% most preferably less than 3%, especially less than 2%, more especially less than 1%, e.g. less than 0.5% by weight of solvents such as water miscible alcohols or glycols, based on the total weight of the composition. Solvents, other than water are preferably absent.

Detergent Ancillary Ingredients

The composition may contain detergent ancillary ingredients typically in amounts up to 10% eg. 1 to 9%, usually 2 to 8% by weight total, based on the total weight of the composition. Ancillary ingredients may include stain removers in addition to the bleach. These may include chelants such as phosphonates, and/or enzymes and photoactive bleaches. Phosphonates have the advantage of chelating transition metals such as iron, which helps to stabilise the bleach. Examples include acetodiphosphonates, amino tris (methylene phosphonates), ethylenediamine tetrakis (methylene phosphonates), diethylenetriamine pentakis (methylene phosphonates) and higher member of the series. Enzymes include proteases, lipases, amylases, cellulases and/or decarboxylases.

The detergent ancillary ingredients preferably also comprise conventional detergent additives such as antiredoposition agents (typically sodium carboxymethyl cellulose), optical brighteners, sequestrants, antifoams, such as silicone antifoams, enzyme stabilisers such as polyvinyl alcohol or polyvinyl pyrrolidone, preservatives, dyes, pigments, perfumes, fabric conditioners, e.g. cationic fabric softeners such as ditallowyl dimethyl ammonium salts, or clays such as bentonite, opacifiers and/or bleach activators such as terra acety lethy lenediamine .

Encapsulation of the bleach and/or any bleach activators e.g. in waxes, gum or polymers may also be used to give auxiliary protection, such protection is not essential to the present invention.

The invention is further illustrated with reference to the following examples :-

Example 1

A spherulitic base composition was prepared comprising by active weight: % by weight (based on the total weight of the composition)

6.9% Sodium C_{1 -14} linear alkyl benzene sulphonate^*1

8.9% Sodium C_I2.₎₈ alkyl 3 mole ethoxy sulphate'²

2.8% C₉., , alkyl 2.5 mole ethoxylated alcohol^*3

4.6% potassium carbonate

2.5% sodium silicate ( 1.6 Na₂0 : 1 SiO₂)

4.6% borax decahydrate

0.1% disodium EDTA

0.3% silicon defoamer

2.8% Potassium citrate monohydrate balance water To the above base composition was added :-

4.6% sodium perborate monohydrate.

The composition had a pH of 12.03.

The sample was stored at ambient laboratory temperature for 12 months, covered with a distendable membrane, which did not distend significantly during the storage period. The % available oxygen retention is shown below in Table 3:

TABLE 3 : - % available oxvgen retained for Example 3

Storage Period % Available Oxygen retained

O Days 100%

7 Days 99%

2 Months 96%

8 Months 93%

Sodium neutralised 'NANSA' 1392 is based upon a feedstock having the typical alkyl distribution; C₁₀ (8.9%), C„ (33.7%), C_I2 (31%), C₁₃ (24%) and C₁₄ (2.0%) and is available commercially from Albright & Wilson UK Limited. 'NANSA' is a registered trademark of Albright & Wilson UK Limited.

This was available commercially from Albright & Wilson UK Limited as 'EMPIMIN' KSN 70. 'EMPIMIN' is a registered trademark of Albright & Wilson UK Limited. The feedstock alcohol which was used to produce the 'EMPIMIN' KSN 70 as used in Examples 1, 2, 3, 5 and 6 was based on a non-synthetic C,₂.₁₈ alcohol 3 mole ethoxylate (i.e. 'EMPILAN' KC3 for which see Example 4 ^*7). The present commercially available equivalent is 'EMPIMIN' KSN 70 XW which was used in Example 4, this product is based upon a blended synthetic feedstock having the typical alkyl distribution; C₉(2%), C₁₀ (4.7%), C„ (4.3%), C_I3 (60.4%) and C_l5 (28.4%). ^*3 Available commercially as 'DOBANOL' D91-2.5. 'DOBANOL' is a trademark.

Example 2

A spherulitic base composition was prepared comprising (by active weight based on the total weight of the composition):

% bv weight

6.0% Sodium C₁₂-C₁₄ linear alkyl benzene sulphonate ^*5

11.6% Sodium C₉-C₁₅ alkyl 3 mole ethoxy sulphate ^*6

2.5% C₁₂-C_lg alcohol 3 mole ethoxylate ^*7

3.8% Potassium carbonate

2.5% Sodium silicate (1.6 Na₂0: 1 Si0₂)

3.8% Borax decahydrate

0.1% Disodium EDTA

0.3% Silicon defoamer

2.3% Potassium citrate monohydrate balance water

The spherulitic base composition was stable to centrifuging at 18,000 'g' for 5 minutes and had a viscosity of 940cps @ 21sec-l.

To the above composition was added 5% ^w/_w sodium perborate monohydrate. The product had a pH of 12.02.

An initial available oxygen determination gave a result of 0.78%. The sample showed good stability when stored at 30°C for 20 days and retained an excellent level of available oxygen (0.76%, 97.4% of original result).

^*5 The product used in the preparation of Example 2 is available commercially as

'NANSA' 1364. The feedstock has the typical alkyl distribution C₁₀ (13%), C„ (31%), C₁₂ (34%) C₁₃ (21%) and C„ (0.6%). ^*6 The grade used in the preparation of Example 2 is available commercially as

'EMPIMIN' KSN27 XW. The product is based upon the blended synthetic alcohol feed stock as detailed in Example 1 ^*2.

•7 Available commercially as 'EMPILAN' KC3. 'EMPILAN' is a registered trademark of Albright & Wilson UK Limited.

Examples 3 and 4

The following compositions, in which all proportions are percentages by weight based on the total weight of the composition, were prepared :

Ex 3 Ex 4

Cj₂-i₄ linear alkyl benzene sulphonate - 4.4

C_.o-₁₄ ^alkyl 3 mole ethoxysulphate 1.52 3.1

C_.2-₁₈ alkyl 3 mole ethoxylate 3.83 -

Sodium metaborate tetrahydrate 9.6 13.1

C_.2-₁₄ alkyl betaine 2.3 1.9

Silicone antifoam 0.3 0.25

C_.2-₁₄ alkylthiol capped polymaleate 0.2 -

Optical brightener 0.05 -

Sodium tripolyphosphate 16.0 14.8

Sodium perborate monohydrate 18.0 14.8

Water balance balance pH 12 12.08 pH at 2% wt/wt dilution. 10.5

Both formulations were stable and pourable. Comparative Example

Example 1 was repeated but in the absence of sodium silicate and carbonate. The sample which had a pH of 10 was stored at 30°C but exhibited rapid evolution of oxygen almost immediately and had bubbled out of its container within 2 days. This demonstrates the importance of high pH in stabilising the compositions of the invention, contrary to the prejudice in the art.

Procedure for determination of persalts in detergents / % available oxygen retention

The available oxygen content of the above examples was determined by the following method for the determination of persalts in detergents and hence used to determine the % Available Oxygen retention.

1. A 20g aliquot of the sample was weighed to the nearest 0.0 lg (weight = M)

2. The aliquot was transferred with rinsing to a 2000ml beaker and 1000ml of deionised water at 35-40°C was added to the aliquot.

3. The diluted aliquot was then mixed under high shear for exactly 3 minutes, followed by standing for 2 minutes to allow deaeration.

4. 20ml of mixed reagent (see below) was immediately pipetted into the deaerated sample of 3, followed by titration with 0.1N potassium permanganate until a faint pink colour appears which lasts for at least 15 seconds. (The titration value = V).

5. Calculation of available oxygen contents.

Active oxygen content = V x 0.1 x 1.60 %

M The result obtained at day 0 for each sample was taken as the 100% available oxygen figure, with subsequent results expressed as a percentage of that figure.

5. The mixed reagent used in 4 was prepared by dissolving in 1000ml of 5N H₂SO₄: 50g A1₂(S0₄)₃.16H₂0, 5g Bi(NO₃)₃.5H₂0, 5g MnSO₄.4H₂O.

Claims

C AIMS

1. An aqueous based composition containing particles of solid alkali metal or alkaline earth metal perborate, and a dissolved alkali metal or alkaline earth metal metaborate, at a pH sufficient to maintain a perborate-stabilising concentration of metaborate in the aqueous medium.

2. A composition according to claim 1 wherein said perborate is sodium perborate and said metaborate is sodium metaborate.

3. A composition according to either of claims 1 and 2 comprising water; sufficient surfactant and dissolved electrolyte to form a pourable solid-suspending structured surfactant system; and particles of solid perborate suspended in said structured surfactant system; wherein said metaborate constitutes at least part of said dissolved electrolyte.

4. A composition according to any foregoing claims containing from 0.1 to 70% by weight based on the total weight of the composition of perborate.

5. A composition according to claim 4 containing from 1 to 50% by weight based on the total weight of the composition of perborate.

6. A composition according to claim 5 containing from 10 to 20% by weight, based on the total weight of the composition, of perborate.

7. A composition according to any foregoing claim containing from 2.5 to 18% by weight based on the total weight of the composition of metaborate.

8. A composition according to claim 7 containing from 3 to 12% by weight based on the total weight of the composition of metaborate.

9. A composition according to foregoing claim having a pH from 10.5 to 13.5.

10. A composition according to claim 9 having a pH from 11 to 13.

11. A composition according to any foregoing claim containing from 2 to 60% by weight based on the total weight of the composition of surfactant.

12. A composition according to claim 1 1 containing from 4 to 20% by weight of surfactant.

13. A composition according to any foregoing claim containing from 5 to 30% by weight based on the total weight of the composition of builder.

14. A composition according to claim 13 wherein said builder is sodium tripolyphosphate zeolite, sodium carbonate, sodium silicate and//or sodium citrate.

15. A composition according to any foregoing claim containing up to 10% by weight total based on the total weight of the composition of detergent ancillary ingredient selected from chelants,, enzyme, photoactive bleaches, antiredeposition agents, optical brighteners, sequestrants, antifoams, enzyme stabilisers, preservatives, dyes, pigments, perfumes, fabric softeners, clays, opacifiers and bleach activators.

16. A method of making a composition according to any foregoing claim which comprises adding a perborate to an aqueous solution containing a metaborate.

17. A method according to claim 16 wherein said aqueous solution to which said perborate is added contains at least 2.5% by weight based on the weight and said solution of sodium metaborate.

18. A method according to either of claims 16 and 17 wherein said aqueous solution contains from 3 to 50% by weight of surfactant and sufficient dissolved electrolyte to form a structured surfactant capable of suspending said perborate.