GB2281070A - Tetrasodium pyrophosphate tris peroxyhydrate - Google Patents

Abstract

Stable, novel and highly effective peroxyhydrates of condensed phosphates, in particular tetrasodium pyrophosphate tris peroxyhydrates are provided. Said peroxyhydrates may be further stabilised by treatment thereof with an acidic gas or vapour and/or by encapsulation of granules containing the peroxyhydrate with suitable encapsulants including film forming polymers and oils. Additionally, a pH modifier, such as an acid buffer or acid releasing agent may be added to said granules to protect them from excessively alkaline environments as found in most washing powders. The peroxyhydrates provided, are effective oxidising bleaches finding particular application in detergent formulations. Detergent compositions, especially laundry detergent and dishwashing powder compositions containing the peroxyhydrate, are also provided.

Description

OXIDISING BLEACH The present invention relates to a novel oxidising bleach, and in particular to peroxy hydrates of condensed phosphates, which are stable to storage.

Technical Background The introduction of synthetic detergents in the 1940's led to a demand for an effective bleach which would be incorporated into detergent powders to deal with oxidisable stains. For many years the two principal bleaches in common use had been sodium hypochlorite, present in "bleaching powder", and hydrogen peroxide. The former was too aggressive toward dyes to be useful in most laundry applications, while the latter was an unstable liquid which could not easily be incorporated into detergent powders.

The solution to the problem was sought in peroxy salts and in the peroxy hydrates of various inorganic salts. A number of salts can form crystals containing hydrogen peroxide in place of, or as well as, water of crystallisation. Particularly desirable would have been a perphosphate or peroxy hydrate of a phosphate or, preferably, of a condensed phosphate, since the condensed phosphates are needed in the detergent formulations as builders to enhance the efficiency of surfactant. It proved impossible to make stable perphosphate salts cost effectively, however, and for this reason a great deal of research was carried out and published during the 1950's, on peroxy hydrates of phosphates and condensed phosphates, and in particular of pyrophosphate and tripolyphosphate which are the builder salts most commonly used in detergents. However, no satisfactory peroxyhydrate could be found.The products were insufficiently stable.

The only convenient inorganic peroxyhydrates to be prepared were the compounds which are commonly referred to as sodium percarbonate and sodium perborate. The former is usually considered to be the peroxyhydrate of sodium carbonate. The latter has been described by some authorities as a peroxyhydrate of sodium metaborate and has been generally adopted as the most cost effective bleach for use in laundry detergent powders for the last thirty years. A major reason why perborate is preferred is that it is generally considered to be relatively stable on storage, compared to the percarbonate which tends to lose available oxygen after a short time. The greater stability of perborates compared with percarbonates has led to the view that perborates are peroxy salts rather than peroxy hydrates.It has been generally accepted that phosphates and condensed phosphates are not capable of providing a satisfactory detergent bleach, in conjunction with hydrogen peroxide, because the resulting peroxyhydrates exhibit very poor storage stability, especially in humid conditions, which has been perceived as substantially worse than that of percarbonate. For this reason little or no further work in the area has been attempted. The field has long been regarded as having been thoroughly investigated and shown to be a "blind alley".

A number of techniques are known for increasing the stability of peroxides.

It is well known that transition metal ions catalyse the evolution of oxygen from peroxides, and that sequestrants such as ethylenediamine tetracetic acid, which chelate such ions can inhibit peroxide decomposition.

Moisture is also known to accelerate decomposition. To improve the stability of percarbonates and perborates it is known to coat them with dessicants such as silica which can protect the peroxide against moisture for several weeks until they become saturated.

Encapsulation has also been used to protect bleach, using peroxide compatible encapsulants.

It is also known that peroxides tend to be less stable the higher the pH.

They break down comparatively rapidly in strongly alkaline environments.

Maintaining the peroxide in acid or an acid buffered medium, therefore, often improves storage properties.

Certain of the above techniques of stabilisation have been applied to the protection of percarbonate and also perborate, although, in general, it has not been considered necessary to apply them to the latter which has been regarded as sufficiently stable for most practical purposes. There has been little point, in practice, in applying such techniques to perphosphates since the accepted view has been that the perphosphates were too inherently unstable in comparison with percarbonates and perborates to be considered as practical bleaches. This perception has led to those skilled in the art largely ignoring the possibility of using the above stabilisation techniques with phosphate based products. The few attempts to use stabilising techniques on peroxy phosphate have only served to confirm that they are not of practical utility.

It has been apparent for many years that sodium perborate is not an ideal bleach. The metaborate ion in itself does not perform any sufficiently useful function in the wash to justify its inclusion for any reason other than the bleaching action of the peroxide for which it serves as a vehicle.

Moreover borate ion is particularly undesirable on environmental grounds.

A particular problem arises in dishwashing powders. These commonly include a chlorinating bleach such as hypochlorite. However, chlorinating bleaches are increasingly subject to environmental objections. An environmentally acceptable alternative is therefore desirable.

The object of the present invention is to provide a bleaching agent based on condensed phosphate which can be readily and economically prepared and which has a stability on prolonged storage, which is at least comparable to that of sodium percarbonate and preferably to that of sodium perborate.

A further object of the invention is to provide dishwashing powders that are not dependent on chlorinating agents for their bleaching/antiseptic activity.

Prior Art The prior art on peroxyhydrates of alkali metal condensed phosphates deals with sodium tripolyphosphate in substantial detail, but the peroxyhydrates were all very unstable. Work on pyrophosphates focused on the bisperoxyhydrate of tetra sodium pyrophosphate.

GB990172, filed in 1961 describes a method of making the bisperoxyhydrate of sodium pyrophosphate by a process which entailed adding to hydrogen peroxide one third of a molar proportion of pyrophosphate (i.e. an amount equivalent to a trisperoxyhydrate) thereby obtaining a viscous liquid which was then added to a further one sixth of a molar proportion of solid pyrophosphate, based on the number of moles of hydrogen peroxide (i.e. a total sufficient to form the bisperoxyhydrate). The product takes up a major portion of the water as water of crystallisation, forming an octahydrate. The heat of peroxyhydration is sufficient to evaporate most of the residual water to leave a solid product containing little or no free water.

The above patent claimed the use of hydrogen peroxide at concentrations between 45% and 75% by weight, but only exemplified the use of a 60% wt/wt hydrogen peroxide. When the pyrophosphate is added to 60% hydrogen peroxide as described in the specification, in the specified mole ratio of 1 to 3, the product is a syrupy liquid, which we believe comprises a mixture of bis peroxyhydrate and excess peroxide. On addition of the liquid to the further quantity of pyrophosphate the bis (peroxyhydrate) octahydrate of tetrasodium pyrophosphate (Na4 P2 07.2 (H202).8H20) is formed. This product takes up the free water in the liquid as water of crystallisation, as well as taking up the peroxide. The product may be heated to remove the water of crystallisation, leaving the anhydrous bisperoxyhydrate.

However, even the anhydrous bisperoxyhydrate is not sufficiently stable or effective to be acceptable as a bleach in detergent powders or to compete with perborate. The hydrated bisperoxyhydrate is even less stable than the anhydrous salt.

US 3,037,838 describes the preparation of a phosphate containing from 0.5 to 2.5 moles H202 by spraying dilute hydrogen peroxide onto solid pyrophosphate.

Some references have been made in the literature to a trisperoxyhydrate of pyrophosphate. For example, as long ago as 1914, DRP 293786 described a method for making sodium pyrophosphate peroxyhydrate which involved vacuum dehydration of mixtures of pyrophosphate and hydrogen peroxide at low temperatures. The method is difficult, expensive and potentially hazardous.

The product was far too difficult to make by this method for it to be considered as a potential candidate for a commercial bleach. The trisperoxyhydrate was therefore ignored outside academic circles.

DE 2622761 describes the use of various heterocylic compounds as stabilisers for inorganic peroxides. An example of such peroxide which is quoted is sodium pyrophosphate peroxyhydrate. No method of preparation of the latter compound is given and the stability of the product quoted in the examples establishes that it is totally unsuitable for commercial exploitation. Even in the presence of the stabiliser the pyrophosphate peroxyhydrate is substantially inferior to unprotected perborate.

The aforesaid US 3,037,838 refers to various stabilisers for peroxy phosphate including, for instance, citrate and silica. EP0 163 362 and EPO 040 091 describe coating detergent granules containing sensitive ingredients.

The Invention We have now discovered a simple method of making tetra sodium pyrophosphate trisperoxyhydrate. We have further discovered that the product is substantially more stable than any of the other peroxyhydrates of phosphates or condensed phosphates which have so far been examined. In particular we have discovered compositions comprising sodium pyrophosphate trisperoxyhydrate and certain stabilisers which compositions are stable and easily prepared and which offer a cost effective and environmentally preferable alternative to sodium perborate as a bleach in laundry detergent compositions.In particular we have discovered that when one molar proportion of alkali metal pyrophosphate is added to about three molar proportions of hydrogen peroxide at a hydrogen peroxide concentration greater than about 65% and preferably greater than 70% by weight based on the weight of peroxide and water, a relatively stable trisperoxyhydrate of the pyrophosphate solidifies.

The latter product is relatively cheap to prepare and is sufficiently stable and yet sufficiently active as a bleach, to be useful in detergent compositions as a more environmentally acceptable replacement for sodium perborate. The product does not absorb all the residual water, as in the prior art, but forms a paste which must be dried eg by heating.

We have further discovered that the presence of sodium tripolyphosphate in the sodium pyrophosphate when it is peroxidised significantly reduces the stability of the product. Sodium pyrophosphate is normally prepared by neutralising phosphoric acid with sufficient sodium to form an ortho phosphate having an atomic ratio of total sodium to total phosphorus corresponding to that of sodium pyrophosphate namely 2 to 1 (in other words disodium hydrogen phosphate).

This product is calcined to prepare the pyrophosphate. In practice commercial sodium pyrophosphate normally contains traces of tripolyphosphate which is formed whenever the ratio of sodium to phosphorus is below 2.

We have discovered that sodium pyrophosphate prepared by calcining di sodium hydrogen orthorphosphate in admixtures with up to 5% by weight of trisodium orthophosphate based on the total weight of orthophosphate, provides a more stable product on reaction with concentrated hydrogen peroxide than does normal commercial tetra sodium pyrophosphate.

We have further discovered that the stability of sodium pyrophosphate trisperoxyhydrate may be improved by treating the solid product with an acidic gas or vapour. This treatment is particularly useful in conjunction with a coating step in which the solid particles either before or after treatment with the acid gas are subjected to a coating or encapsulation with a stabiliser.

According to our invention there is provided a method for the manufacture of tetra sodium pyrophosphate trisperoxyhydrate which comprises adding from 0.1 to 0.9, preferably 0.2 to 0.35, most preferably 0.3 to 0.33 molar portions of tetra alkali metal pyrophosphate per mole of hydrogen peroxide to an aqueous hydrogen peroxide containing from 65% to 90% preferably 68% to 85% eg 68% to 78% especially 70% to 75% by weight peroxide, said concentration being sufficient to precipitate a trisperoxyhydrate and/or higher peroxyhydrates of the pyrophosphate, and evaporating water from the resulting paste sufficiently to form a dry product.

According to a preferred modification, the sodium pyrophosphate is substantially free from sodium tripolyphosphate but contains up to 10% based on the weight of pyrophosphate of sodium orthophosphate.

According to a second embodiment our invention provides a method for the preparation of a peroxyhydrate of sodium pyrophosphate which comprises the steps of (i) partially neutralising orthophosphoric acid with a quantity of sodium base adapted to provide greater than two and up to 2.1 gram ions of sodium per gram mole of phosphoric acid; (ii) calcining said partially neutralised orthophosphoric acid at a temperature and for a time sufficient to form a product consisting essentially of tetra sodium pyrophosphate and trisodium orthophosphate; (iii) reacting said product of step (ii) with a hydrogen peroxide solution having a concentration of hydrogen peroxide by weight based on the weight of the solution greater than 65%; and (iv) evaporating water from the product of step (iii) to provide a substantially anhydrous tetrasodium pyrophosphate tris peroxyhydrate.

According to a preferred modification, the step (iii) is performed in the presence as stabiliser of a polyphosphonate, phosphono carboxylate and/or a hydroxy carboxylate, which stabiliser sequesters iron.

According to a third embodiment a particulate solid sodium pyrophosphate trisperoxyhydrate is contacted with an acidic gas or vapour (not oxidisable by peroxide) and preferably the solid particles are coated either before or preferably after said contacting step with a peroxide stabiliser or encapsul ent.

According to a fourth embodiment the invention provides a bleach composition comprising a granular, substantially anhydrous peroxyhydrate of tetrasodium pyrophosphate containing more than 2.5 moles H202 per mole of pyrophosphate and a stabilising system comprising: (A) a sequestrant of iron ions comprising at least one polyphosphonate, phosphonocarboxylate, or hydroxy carboxylate, such as a citrate, a gluconate or preferably, an acetodiphosphonate or, most preferably, an alkyl aminophosphonate of the formula R2N-CH2 P03M2, where each R is a CH2 P03M2 group, a [(CH2)XNCH2P03M2]y P03M2 group or a C2 20 alkyl, hydroxyalkyl or carboxyalkyl group where x is 2 or 3 and y is 1 to 6 and M is a cation such that said aminophosphonate is water soluble, said sequestrant being present in said granules in admixture with said peroxyhydrate or as a coating thereon in an amount effective to inhibit the decomposition of said peroxyhydrate; and optionally (B) an inert dessicant such as silica, sodium sulphate, magnesium sulphate or calcium chloride, said dessicant being present in said granules or, preferably, as a coating on the surface of said granules in an amount sufficient to inhibit the decomposition of said peroxyhydrate; (C) an encapsulant such as a wax, a compatible non-ionic surfactant, a silicone, a phospholipid, a fatty alcohol or a fatty acid, said encapsulant forming protective capsules around said granules, (D) a pH regulating agent which tends to maintain an acidic environment incorporated in, or preferably, coated on said granule, and/or (E) a spacer coating which consists of a substantially inert solid such as sodium sulphate, and which is sufficiently thick to prevent contact between the granule and any destabilising particles present.

According to a fifth embodiment the invention provides a detergent powder composition comprising from 2% to 90% by weight of surfactant based on the total weight of the composition, from 4% to 70% by weight builder based on the total weight of the composition, from 0% to 70% by weight of a filler or diluent based on the total weight of the composition, up to 20% by weight of detergent ancillary ingredients based on the total weight of the composition, and from 0.5% to 90% by weight, based on the total weight of the composition, of granules each comprising at least 2% by weight based on the total weight of the granule of substantially anhydrous tetra sodium pyrophosphate trisperoxyhydrate, and a stabilising system comprising : (A) an effective amount between 0.001to 100% by weight, based on the total weight of the peroxyhydrate, of a sequestrant for iron, intimately mixed with or coated around said trisperoxyhydrate; and optionally (B) from 0.01 to 20% by weight, based on the total weight of the granule, of an inert dessicant mixed into or coated on the granule; (C) a peroxide-compatible encapsulant sufficient to form a protective coating around said granules, (D) a pH modifying agent which tends to maintain acidic environment, incorporated in or, preferably, coated on, said granule and/or (E) a spacer coating which comprises a substantially inert solid and which is of sufficient thickness to inhibit or prevent contact between the granule and its neighbours.

According to a sixth embodiment the invention provides the use of tetrasodium pyrophosphate trisperoxyhydrate in dishwashing compositions.

According to a seventh embodiment the invention provides a dishwashing composition comprising: from 0.05 to 3% by weight or surfactant; from 15 to 60% by weight of builder selected from condensed phosphates and zeolites; from 15 to 60% by weight of sodium silicate, at least part of said builder comprising sufficient tetrasodium pyrophosphate trisperoxyhydrate to provide from 0.05 to 5% by weight available oxygen; and, optionally, up to 60% by weight of inert diluents.

The Phosphate The peroxyhydrate is prepared from tetra sodium pyrophosphate. The literature teaches that the peroxyhydrates of orthophosphate and of the higher condensed phosphates are all too unstable to be considered, as are the peroxyhydrates of acid sodium pyrophosphate. Potassium pyrophosphate peroxyhydrate is deliquescent. We particularly prefer that the sodium pyrophosphate used in our invention to prepare the peroxyhydrate should not contain appreciable amounts of sodium tripolyphosphate.

Sodium condensed phosphates are normally prepared by partially neutralising orthophosphoric acid with a sodium base such as sodium carbonate or sodium hydroxide and heating the resulting "orthomix" in a calciner such as a rotary kiln or a fluidised bed. Neutralisation with two equivalents of base forms the di sodium hydrogen phosphate which yields tetrasodium pyrophosphate on calcining, whereas 1.5 equivalents of base give a mixture of monosodium and disodium phosphate which yields sodium tripolyphosphate on calcining.

Normal commercial sodium pyrophosphate contains traces of tripolyphosphate because the orthomix is commonly slightly "under neutralised" giving traces of monosodium dihydrogen phosphate as well as di sodium hydrogen phosphate.

We have found that such traces of tripolyphosphate reduce the stability of the peroxyhydrate and we prefer to slightly "over neutralise" to form traces of trisodium phosphate which persist in the calcined product. Preferably the mole ratio of sodium to phosphonic acid in the orthophosphate is as close to 2 as can be consistently achieved in commercial practice without falling below 2 e.g. less than 2.1 preferably less than 2.01.

The Hydrogen Peroxide The hydrogen peroxide is a concentrated solution containing more than 65%, more preferably more than 67% most preferably more than 68%, especially more than 70% eg 70 - 75% by weight of hydrogen peroxide.

The concentration is selected to ensure formation of a substantial proportion of solid tris and/or higher peroxyhydrate, on addition of the appropriate amount of pyrophosphate. The concentration is the main determinant of the peroxyhydrate formed. Typically concentrations of 70% or higher form the tris peroxyhydrate, concentrations between 65% and 70% form mixtures of bis and tris and concentrations below 65% form bis. Only the tris peroxyhydrate is sufficiently stable. The relative proportions of pyrophosphate to hydrogen peroxide are preferably substantially 1:3 molar.

However the use of higher proportions to obtain mixed bis/tris peroxyhydrates, or mixtures containing pyrophosphate eg up to 1:2.5 molar, or of lower proportions e.g. 1:4 or 1:10 molar, to obtain higher peroxyhydrates are within the scope of the invention.

The Reaction Conditions The condensed phosphate may be added to the peroxide at such a rate that the heating of the mixture, by the exothermic peroxyhydration reaction is maintained below 900c more preferably below 70"c, most preferably below 65"C, eg below 550c especially below 50"c.

On completion of the reaction the pasty product may be dried, eg by heating to an appropriate temperature such as 1000c and/or by evacuation and/or exposure of the product to a stream of dry gas such as air or nitrogen, with sufficient agitation when required. Optionally the drying may be effected, at least partially, by allowing the exothermic reaction mixture to heat up to 100"C.

The reaction preferably takes place in the presence of a sequestrant for iron such as those discussed in the next subsequent paragraph.

The Seguestrant The hydrogen peroxide used in the reaction preferably contains, as a stabiliser, a sequestrant such as an amino polycarboxylate (e.g. ethylene diaminetetracetate), phosphonate (e.g. aceto disphosphonate or nitrilotriacetate), a phosphono carboxylate (such as phosphonosuccinate and its teleomers) or a hydroxy carboxylate such as citrate or gluconate.

If not already present in the hydrogen peroxide we prefer that an effective proportion of a sequestrant for iron should be added to the reaction mixture and/or otherwise incorporated in the product. Especially preferred are phosphonates, phosphonocarboxylates and hydroxycarboxylates. Most preferred are the amino methylene carboxylates such as anino tris (methylene phosphonate) and ethanolamine bis (methylenephosphonate). Of these the most preferred are the polyalkylene polyamine methylenephosphonates of the series (X2PO3CH2)2N[(CH2)nNCH2P03X2] mCH2PO3X2 where each n, which may be the same or different, is 2 or 3, mis from 1 to 8, preferably 2 to 5, and Xis an alkali metal, preferably sodium.Most preferred examples include triethylenetetramine hexakis (methylenephosphonate), ethylenediamine tetrakis (methylenephosphonate), diethylenetriamine pentakis (methylene phosphonate), tetraethylenepentamine heptakis (methylenephosphonate), and pentaethylenehexamine octokis (methylenephosphonate).

Mixtures of sequestrants, e.g. phosphonates and citrates or phosphonates and EDTA are especially effective. Mixtures of (a) a polyalkylene polyamine phosphonate (b) a hydroxy carboxylate and (c) and amine polycarboxylate are particularly preferred.

The quantity of sequestrant should be sufficient effectively to inhibit the loss of available oxygen from the peroxyhydrate, eg from 0.001 to 5% by weight based on the total weight of aqueous peroxide solution used in the preparation, or from 0.005 to 50% based on the total amount of peroxyhydrate formed. The sequestrant is preferably intimately mixed with the peroxyhydrate and is most preferably dissolved in the hydrogen peroxide solution used to prepare the peroxyhydrate.

Dessicants The stabiliser system for the peroxyhydrate product may comprise a dessicant in addition to a sequestrant. Dessicants have been commonly used to stabilise perborates and percarbonates, however, in relation to the products of the present invention they have a disadvantage. They are only effective until they become saturated with moisture. Thereafter most dessicants become slightly hygroscopic, and this actually accelerates the decomposition of peroxy pyrophosphates. Unless the product is not required to withstand prolonged storage under humid conditions, therefore, we prefer that dessicants be absent.The dessicant, if present, may for example be finely divided silica, sodium sulphate, magnesium sulphate, magnesium metasilicate, anhydrous tetrasodium pyrophosphate, calcium chloride or any other readily hydratable, but preferably non-deliquescent compound which is compatible with peroxides. The dessicant may be present in proportions of from 0.001% to 20% based on the weight of the granule. The amount required depends on the way in which the dessicant is included in the granule. Best protection is obtained when the granule is coated with the dessicant. The dessicant, when applied as a coating can inhibit and delay decomposition due to humidity for a limited period of time, until the dessicant is fully hydrated.We prefer that the granules are at least sufficiently coated with dessicant to withstand a temperature of 30"C and a relative humidity of 80% for 20 days without losing more than 5% by weight of the total available oxygen. For example the granules may be sprayed with sodium silicate and an acid such as sulphuric, hydrochloric or phosphoric in a fluidised bed or rotary drum mixer.

Encapsul ati on We may also, optionally but preferably, encapsulate the granule in a protective coating, typically a film forming polymer or an oil. For example we may use water insoluble oils such as silicones (eg. polydimethyl siloxane) or heavy duty mineral oils, water soluble encapsulants such a proteins (eg. gelatin or casein), gums (e.g. gum acacia, gum tragacanth, gum benzoin or guar gum) cellulose derivatives such as methyl cellulose, carbohydrates such as starch, dextrin or maltose, ethoxylated non-ionic surfactants such as fatty alcohol ethoxylates, polyvinyl alcohol or polyvinyl pyrrolidone, phospholipids such as lecithin, polyacrylates or poly maleates or low melting encapsulants, such as waxes, petroleum jelly, fatty alcohols or fatty acids.It is especially preferred that the encapsulant material is selected to avoid the possibility of contacting the peroxyhydrate salts with certain organic compounds which under certain conditions may result in vigerous and possibly exothermic decomposition of the peroxyhydrate. Such organic compounds are those known in the art to produce decomposition of peroxy salts.

The peroxyhydrate may be coated using any of the known techniques of encapsulation, for example the granules may be dispersed in a molten wax or other low melting coating agent or in a solution of the encapsulant in a volatile solvent and the mixture spray cooled (prilled), or spray evaporated respectively. Alternatively the particles may be coated in a pan granulator or marumeriser. Where a non ionic surfactant is used as part of the formulation into which the bleach is incorporated, it is especially preferred to add the bleach to the dry components of the formulation, other than non-ionic surfactant, and then spray the molten surfactant onto the composition in a fluidised bed or rotary drum mixer.

pH Modifier A particularly preferred form of stabiliser is a pH modifier which protects the peroxy pyrophosphate from exposure to an excessively alkaline environment. Most washing products are alkaline, and some require to be highly alkaline, e.g. pH greater than 10 and sometimes greater than 11, in order to be fully effective.

The pH modifier maybe a (preferably solid) acid buffer or acid releasing agent such as citrate buffer, disodium pyrophosphate or preferably tetracetyl ethylenediamine. The pH modifier may be mixed into or preferably coated on the surface of the granule. It is particularly preferred to encapsulant the granule in a low melting film former such as a non-ionic surfactant, contact the encapsulated granule with finely powdered pH modifier while still tacky and cool to form a coated granule.

Acid Treatment We prefer that the particles of peroxyhydrate should be contacted with an acidic gas or vapour such as hydrogen chloride or carbon dioxide. Although it is possible to use reducing gases such as sulphur dioxide we prefer to use oxidising gases, or gases which are not readily susceptible to oxidation by peroxides. We may for example use chlorine, chlorine dioxide, sulphur trioxide, phosphorus oxychloride vapour or nitric oxide.

We particularly prefer that the acid treatment be carried out in conjunction with a coating step in which the particle is coated with a stabiliser as hereinbefore described e.g. a sequestrant, dessicant, encapsulant or pH modifier. Preferably the coating is applied after acid treatment of the surface of the particle.

The Soacer Coating A spacer coating is a substantially inert coating which is sufficiently thick to prevent contact between the granule and neighbouring, potentially destabilising, particles.

The spacer coating typically constitutes more than 20% of the total weight of the granule, e.g. 25 to 60% especially 30 to 50%. The coating is typically formed from inert materials such as sodium sulphate, but may optionally comprise, or be used in conjunction with, any of the other stabilisers described herein.

The Granule The peroxyhydrate-containing granules of the invention may optionally contain other peroxide-compatible detergent ingredients such as peroxide-compatible surfactants, builders, fillers, and other ingredients including soil suspending agents, such as sodium carboxymethyl cellulose, fabric conditioners such as bentonite, bleach activators such as tetra acetylethylenediamine or foam modifiers such silicone antifoams.

We prefer that any builder comprises sodium citrate, a phosphonate, tetra sodium pyrophosphate or zeolite. Phosphates or condensed phosphates other than tetrasodium pyrophosphate may be present but may reduce the stability of the peroxyhydrate. Sodium silicate, which has been recommended in, e.g.

DE2622761 as a bleach stabiliser, should preferably not be present in the granule in appreciable amounts, since it tends to destabilise sodium pyrophosphate tri speroxyhydrate.

The Detergent Formulation (a) Surfactant The detergent formulations of the invention typically contain from 2% to 90% by weight of surfactant, more usually 3% to 70% eg 4% to 60% especially 5% to 50%, preferably 6% to 40%, more preferably 7% to 30%, most preferably 10% to 25%.

For example the surfactant may be, or may comprise, one or more anionic surfactants such as an alkyl benzene sulphonate, alkyl sulphate, alkyl ether sulphate, paraffin sulphonate, olefin sulphonate, alkyl ester sulphonate, alkylphenyl sulphate, alkyl phenyl ether sulphate, alkyl sulphosuccinate, alkyl sulphosuccinamate, alkyl isethionate, alkyl sarcosinate soap, alkyl ether carboxylate alkyl ether polycarboxylate, alkyl tauride, alkyl phosphate, alkyl ether phosphate or alkyl or thiol capped polyelectrolytes such as an alkylthiol capped polymaleic acid.All references to "alkyl" groups in this context refer to C8 to 22 straight or branched chain alkyl or alkenyl groups. "Ether" refers to glyceryl, mono- or poly ethyleneoxy, mono or poly propyleneoxy, mixed ethyleneoxy/ propyleneoxy, and mixed glyceryl ethyleneoxy, glyceryl/propyleneoxy and glyceryl/ethyl eneoxy/propyl eneoxy.

The cation of the aforesaid anionic surfactants is usually sodium but may also be potassium or mono-, di- or tri-alkylolamine. Less commonly the cation may be lithium, ammonium, calcium, magnesium, zinc or a mono- di- or tri- alkyl amine such as isopropylamine or trimethyl amine.

The surfactant may also be, or may comprise, one or more nonionic surfactants such as the polyalkoxylated derivatives of alcohols, carboxylic acids, alkyl phenols, alkylamines, alkanolamides, or glyceryl or sorbitan esters, wherein each compound has an "alkyl" group as hereinbefore defined, and the polyalkylene oxy group comprises from 1 to 50 ethyleneoxy and/or propyleneoxy groups.

Alternatively the nonionic surfactant may be an alkanolamide, eg a mono- or di- alkanolamide, a lactobionamide, an alkylpolyglycoside or an amine oxide, or an alkyl or thiol capped polyvinyl alcohol or polyvinylpyrrolidone, or a sugar ester.

The surfactant may be, or may comprise, one or more amphoteric surfactants such as a betaine or sulphobetaine, and/or one or more cationic surfactants such as an alkyl trimethyl ammonium, alkyl pyridinium, alkyl dimethylbenzylammonium, alkyl isoquinolinium, alkyl imidazoline or alkylamido amine. The counter ion of the cationic surfactant may typically be chloride, methosulphate, formate, acetate, citrate, lactate, tartrate or bromide.

Mixtures of anionic surfactants and nonionic surfactants are particularly favoured: mixtures of anionic and/or nonionic surfactants with amphoteric surfactants are also favoured, as are mixtures of cationic with amphoteric surfactants, with or without nonionics.

Mixtures of anionic with cationic surfactants are not normally favoured.

(b) Builder The detergent composition typically contains up to 90% by weight of builder, in addition to the peroxyhydrate, which also functions as a builder in the formulation.

Most commonly the detergent formulation contains from 1% to 80% builder, eg 5% to 75%, more usually 10% to 70%, preferably 15% to 60%, more preferably 20% to 50%, most preferably 25% to 40% by weight based on the total weight of the composition.

The builder may be any substances that assists the action of the surfactant by ameliorating the effects of calcium in the wash liquor and/or maintaining alkalinity in the wash.

The builder may for example be, or may comprise, an alkali metal orthophosphate or condensed-phosphate, especially sodium tripolyphosphate, tetrasodium or tetrapotassium pyrophosphate or sodium tetraphosphate, or a phosphonate, zeolite, citrate, ethylenediamine tetracetate, nitrilotriacetate, silicate or carbonate.

(c) Deterqent Ancillary Inqredients For convenience the term "detergent ancillary ingredients" will be used herein to include all those ingredients other than surfactant, oxidising bleach, builder and any filler or diluent, which have been or may be used to enhance the performance, appearance, pourability, stability, fragrance or ease of use of detergent compositions.The term includes, for instance, soil suspending agents such as sodium carboxymethyl cellulose, optical brighteners, enzymes, photoactive bleaches, chelating agents, sequestrants, buffers, foaming agents, foam stabilisers, antifoams, preservatives, biocides, bleach activators, enzyme stabilisers, hydrotropes, polymers, dyes, vegetable oils, mineral oils, pigments, fragrances, abrasives, perfume enhancers and fabric conditioners, including cationic fabric conditioners and inorganic fabric conditioners such as bentonite.

Compositions of the invention preferably contain soil suspending agents such as sodium carboxymethyl cellulose typically in proportions of from 0.01% to 3% by weight based on the weight of the composition, especially 0.1% to 2% eg 0.5% to 1.5%.

The compositions preferably contain optical brighteners, which are fluorescent dyes, in proportions of from 0.01% to 3% by weight based on the weight of the composition, preferably 0.1% to 2%, eg 0.5% to 1%.

The compositions typically contain fragrances, dyes, pigments and/or preservatives in a total proportion of from 0.1% to 5% by weight, eg 0.5% to 3% by weight based on the total weight of the composition.

The compositions of the invention may also comprise conventional amounts of bleach activators such as tetracetylethylenediamine, foam control agents such as silicone antifoams and/or mineral oils where the compositions are intended for use in front loading washing machines, or foam boosters where the products are intended for hand washing or use in top loading washing machines.

The composition of the invention may also contain enzymes such as proteases, lipases, amylases, decarboxylases and or cellulases in effective amounts. Detergent ancillary ingredients are normally present in a total concentration below 10% by weight based on the total composition.

(d) Filler Compositions of the invention may contain inert fillers or diluents such as sodium sulphate. Sodium sulphate is normally added to detergent powders to obtain a free-flowing product. The amount is not usually critical but frequently lies within the range 10% to 60% by weight of the composition.

The peroxyhydrates of the invention may also be included in anhydrous or concentrated liquid formulations which may contain solvents such as polyethylene glycol, ethanol or isopropanol.

(e) Bleach The pyrophosphate tris(peroxyhydrate) may be present in any desired amount, eg 0.1% to 90%, preferably 3% to 50%, especially 4% to 20%, by weight based on the weight of the composition. Compositions for pre-soaking stained fabrics may contain higher proportions e.g. 80 to 90% or more.

It is possible, though not usually advantageous to include other oxidising bleaches such as sodium perborate in the formulation.

Dishwash Powders The invention therefore provides novel antomatic dishwash powders. The latter typically comprise : low levels of surfactant typically of from 0.05 to 3% by weight preferably 0.1 to 2%, e.g. 0.2 to 1% ; high levels of builder such as sodium tripolyphosphate or zeolite (e.g. 10 to 50% preferably 15 to 40% by weight) and of alkali such as sodium silicate (e.g.

10 to 50%, preferably 15 to 40% by weight); bleach (e.g. 0.05 to 50% by weight of available oxygen, preferably 0.1 to 3% especially 0.2 to 2%) ; usually a filler such as sodium sulphate in a proportion of e.g. O to 60% preferably 10 to 40% by weight especially 20 35%; and the balance typically substantially water.

The invention will be illustrated by the following examples: Example 1 1 molar equivalent of tetrasodium pyrophosphate was added slowly to 3.1 molar proportions of a 70% by weight hydrogen peroxide solution stabilised with 1% of sodium triethylene tetramine hexakis (methylene phosphonate).

The rate of addition was such as to maintain the temperature below 60"c.

The stirred mixture became at first a solution and then a thick paste as the addition of pyrophosphate progressed.

When all the pyrophosphate had been added the pasty product was dried at 1000C for 1 hour. The product was found by analysis to be Na4 P2 O7.3H202.

Example 2 The product of Example 1 was added at a level of 16% by weight, based on the total weight of the final composition (which is equivalent to 2% by weight active oxygen based on the total weight of the composition) to the following formulation in which all % are by weight based on the total weight of the formulation: Linear sodium alkyl benzene sulphonate 8.0 (mean length of alkane chain: C11.5) Ethoxylated tallow alcohol (14 EO) 2.9 Sodium soap (chain length C12-22) 3.5 Sodium tripolyphosphate 43.7 Sodium silicate (SiO2/Na2O = 2.3:1) 7.5 Magnesium silicate 1.9 Carboxymethylcellulose 1.2 Ethylenediaminetetra-acetic acid (tetrasodium salt) 0.2 Sodium sulphate 21.0 Optical brightener for cotton (dimorpholinostilbene type) 0.2 Moisture 9.9 The formulation gave good laundry performance with particularly good effects on bleachable stains.

Example 3 Samples of sodium perborate tetrahydrate, sodium percarbonate, sodium pyrophosphate tris peroxyhydrate (unstabilised) and of sodium pyrophosphate trisperoxyhydrate according to Example 1 (with 1% by weight phosphonate) were stored at 30"C in a moist (80% humidity) atmosphere. Available oxygen retained by the samples was measured at weekly intervals, and recorded in the following table.

Sample 1 - Perborate tetra-hydrate (NaB03.4H20) Sample 2 - Percarbonate (Na2C03.1.5H2O2) with silica coating.

Sample 3 - Perphosphate (Na4P207.3H202) Sample 4 - Perphosphate + 1% diethylene triamine pentakis (methyl enephosphonate) TABLE 1

Test Loss of Available Oxygen (%) Duration (days) Sample 1 Sample 2 Sample 3 Sample 4 7 0 6.2 6.7 2.9 14 O 0 4.0 6.6 4.4 21 0 5.3 13.6 6.4 28 1.0 5.87 18.8 13.1 35 17.7 23.2 29.9 21.4 42 18.8 26.3 30.4 16.0 50 20.8 23.6 30.4 22.1 EXAMPLE 4 The following formulations A and B were prepared by spray drying the ingredients other than bleach and non-ionic surfactant. The bleach was dry mixed with the formulation and the non-ionic melted and sprayed onto the composition in a rotary drum mixer providing a protective coating on the particles. All proportions other than bleach are percentages by weight based on total weight.

A B C12-16 alkyl betaine 2.12 2.85 C12-14 alkyl 8 mole ethoxylate 3.5 4.0 C12-14 alkyl 3 mole ethoxylate 3.5 4.0 Sodium tripolyphosphate 21.7 29.49 Sodium carbonate 10.0 10.0 Sodium silicate 4.25 4.97 Tetracetyl ethylene di amine - 3.0 Optical brightener 0.26 0.24 Sodium carboxymethyl cellulose 0.74 1.42 Diethylenetriamine pentakis (methyl enephosphonate) 0.27 0.95 Borax Silicone antifoam 1.06 0.95 Bleach (as % by weight available oxygen) 1.6 2.0 Moisture 6.03 3.24 Sulphate Balance Balance Samples of formulation A were prepared containing 16% by weight of sodium perborate tetrahydrate, 10.7% sodium perborate monohydrate, 11.86% sodium percarbonate and 12.7% of sodium pyrophosphate trisperoxyhydrate, respectively. Those proportions were calculated to provide, in each case, 1.6% by weight of available oxygen based on the total weight of the formulation.

Samples of formulation B contained respectively 20%, 13.3%, 14.82% and 15.88% of the above bleaches, to provide in each case 2% by weight available oxygen.

Samples were stored in three different environments : (i) 300C at 75% relative humidity (ii) 30 C sealed jar (iii) Open jar in laboratory ambient atmosphere.

All samples were stored for up to 56 days, portions being withdrawn at intervals and tested for detergency on bleachable cloths using a launderometer.

The results are set out in the following tables : TABLE 2 (Formulation A) % DETERGENCY WHEN STORED AT 30 C/75% RH

DAY SPB SPB SPC SPPP STORAGE tetra mono 0 41.7 43.1 42.7 40.6 7 43.3 41.7 43.1 35.3 14 43.5 42.6 38.8 31.6 28 41.5 41.7 31.8 25.1 56 39.6 38.8 16.8 16.3 TABLE 3 (Formulation B) % DETERGENCY WHEN STORED AT 3? C/75% RH

DAY SPB SPB SPC SPPP STORAGE tetra mono 0 46.8 48.7 48.6 48.6 7 47.7 47.1 44.7 40.6 14 45.5 46.2 40.2 34.8 28 45.3 44.7 32.3 29.3 56 41.8 38.6 23.6 22.2 TABLE 4 (Formulation A) % DETERGENCY WHEN STORED AT 3t C-closed jar

DAY SPB SPB SPC SPPP STORAGE tetra mono 0 42 43.2 45.2 41.5 7 46.3 47.1 44.7 36.7 14 45 44.1 45.5 33.5 28 46.2 47.2 39.7 24.6 56 44.7 45.7 35.7 18.6 TABLE 5 (Formulation B) X DETERGENCY WHEN STORED AT 30. C-closed jar

DAY SPB SPB SPC SPPP STORAGE tetra mono 0 49.1 49.6 50.5 49.2 7 50.6 52 49.1 45.3 14 50 50.6 49.5 41.7 28 52.3 49.6 47.1 39.3 56 47.1 47.8 41.8 34.3 TABLE 6 (Formulation A) % DETERGENCY WHEN STORED AT R.T. - opened jar

DAY SPB SPB SPC SPPP STORAGE tetra mono 0 42.7 42.7 43.8 42.2 7 43.2 44.1 43.5 38.3 14 42.8 45.5 42.2 37.6 28 43.5 43 42.6 34.8 56 45.2 46.3 48.1 38.3 TABLE 7 (Formulation B) % DETERGENCY WHEN STORED AT R.T. - opened jar

DAY SPB SPB SPC SPPP STORAGE tetra mono 0 48.7 49.5 50.2 49.3 7 49.5 49.6 50.3 47.7 14 50.5 50.7 50.6 48.5 28 48.3 49.1 48.7 47 56 51.8 51.6 51.8 47.7 All evaluations were based on average performance on four cotton test cloths stained respectively with red wine, tea, coffee and beetroot.

Example 5 Particles of tetra sodium pyrophosphate tri peroxyhydrate (300 to 1000 micron) were aglomerated with molten fatty alcohol ethoxylate and coated with finely powdered pH modifier.

The coated granules were added to the detergent formulation of example 1 and a total available oxygen level of 2% based on the total weight of the powder.

The formulations were tested at 30"C and 80% relative humidity.

TABLE 8 Sample e Loss of available Oxygen (%)

Day 3 Day 4 Day 7 Day 8 Day 11 Day 15 Perphosphate (uncoate) - 23 - - 85 100 Perphosphate (67%)+ TAED (13%) + noionic (19%) - 27 37 - - 63 Perphosphate (75%) + disodium pyrophosphate (10%) +nonionic (15%) 27 - - 69 89 100 Perphosphate (75%) sodium bicarbonate (10%) + nonionic (15%) 25 - - 88 96 100 Example 6 A dishwash powder had the formulation Wt% Sodium dodecylbenzene sulphonate 0.8 Sodium tripolyphosphate 30 Sodium silicate 38 Sodium Sulphate 20 Tetra sodium pyrophosphate trisperoxyhydrate 9 Water balance The product was a free flowing powder with good dishcleaning properties and good storage characteristics.

Example 7 3109 of anhydrous TSPP was charged to a Niro-Aeromatic Strea-1 fluid bed spray granulator. The TSPP was fluidised with drying air at 40"C. 1909 of 70% Hydrogen peroxide (containing 59 of Briquest 543-45-AS) was top sprayed through an atomising nozzle onto the fluidised bed at a rate of lOg/min. The product was dried for 20 minutes after spraying was completed. A granular product was produced with an available oxygen content equivalent to that produced by the process described in Example 1.

Claims (10)

1. A method for the manufacture of tetra sodium pyrophosphate trisperoxyhydrate which comprises adding from 0.1 to 0.9, molar portions of tetra alkali metal pyrophosphate per mole of hydrogen peroxide to an aqueous hydrogen peroxide containing from 65% to 90% by weight peroxide, said concentration being sufficient to precipitate a trisperoxyhydrate and/or higher peroxyhydrates of the pyrophosphate, and evaporating water from the resulting paste sufficiently to form a dry product.

2. A method according to Claim 1 wherein the sodium pyrophosphate is substantially free from sodium tripolyphosphate but contains up to 10% based on the weight of pyrophosphate of sodium orthophosphate.

3. A method for the preparation of a peroxyhydrate of sodium pyrophosphate which comprises the steps of (i) partially neutralising orthophosphoric acid with a quantity of sodium base adapted to provide greater than two and up to 2.1 gram ions of sodium per gram mole of phosphoric acid; (ii) calcining said partially neutralised orthophosphoric acid at a temperature and for a time sufficient to form a product consisting essentially of tetra sodium pyrophosphate and trisodium orthophosphate; (iii) reacting said product of step (ii) with a hydrogen peroxide solution having a concentration of hydrogen peroxide by weight based on the weight of the solution greater than 65%; and (iv) evaporating water from the product of step (iii) to provide a substantially anhydrous tetrasodium pyrophosphate tris peroxyhydrate.

4. A method according to Claim 3 wherein the step (iii) is performed in the presence as stabiliser of a polyphosphonate, phosphono carboxylate and/or a hydroxy carboxylate, which stabiliser sequesters iron.

5. A method of stabilising particles of solid sodium pyrophosphate trisperoxyhydrate wherein said particles are contacted with an acidic gas or vapour.

6. A method according to Claim 5 wherein said particles are coated before and/or after said contacting with a peroxide stabiliser or encapsulant.

7. A bleach composition comprising a granular, substantially anhydrous peroxyhydrate of tetrasodium pyrophosphate containing more than 2.5 moles H202 per mole of pyrophosphate and a stabilising system comprising: (A) a sequestrant of iron ions comprising at least one polyphosphonate, phosphonocarboxylate, or hydroxy carboxylate, said sequestrant being present in said granules in admixture with said peroxyhydrate or as a coating thereon in an amount effective to inhibit the decomposition of said peroxyhydrate; and optionally (B) an inert dessicant, said dessicant being present in said granules or, as a coating on the surface of said granules in an amount sufficient to inhibit the decomposition of said peroxyhydrate, (C) an encapsulant, said encapsulant forming protective capsules around said granules, (D) a pH regulating agent which tends to maintain an acidic environment incorporated in, or coated on, said granule and/or (E) a spacer coating which comprises a substantially inert solid and is sufficiently thick to prevent or inhibit contact between the granule and neighbouring particles.

8. A detergent powder composition comprising from 2% to 90% by weight of surfactant based on the total weight of the composition, from 4% to 70% by weight builder based on the total weight of the composition, from 0% to 70% by weight of a filler or diluent based on the total weight of the composition, up to 20% by weight of detergent ancillary ingredients based on the total weight of the composition, and from 0.5% to 90% by weight, based on the total weight of the composition, of granules each comprising at least 2% by weight based on the total weight of the granule of substantially anhydrous tetra sodium pyrophosphate trisperoxyhydrate, and a stabilising system comprising : (A) an effective amount between 0.001 to 100% by weight, based on the total weight of the peroxyhydrate, of a sequestrant for iron, intimately mixed with or coated around said trisperoxyhydrate; and optionally (B) from 0.01 to 20% by weight, based on the total weight of the granule, of an inert dessicant mixed into or coated on the granule, (C) a peroxide-compatible encapsulant sufficient to form a protective coating around said granules, (D) a pH modifying agent which tends to maintain acidic environment, incorporated in or, preferably, coated on, said granule, and/or (E) a spacer coating which comprises a substantially inert solid and which is sufficiently thick to inhibit contact between the granule and neighbouring particles.

9. The use of sodium pyrophosphate trisperoxyhydrate in dishwashing compositions.

10. A dishwashing composition comprising: from 0.05 to 3% by weight of surfactant; from 15 to 60% by weight of builder selected from condensed phosphates and zeolites; from 15 to 60% by weight of sodium silicate, at least part of said builder comprising sufficient tetrasodium pyrophosphat trisperoxyhydrate to provide from 0.05 to 5% by weight available oxygen; and, optionally, up to 60% by weight of inert diluents.