WO1998016621A2

WO1998016621A2 - Microcapsules

Info

Publication number: WO1998016621A2
Application number: PCT/GB1997/002810
Authority: WO
Inventors: Mark Alexander France
Original assignee: Warwick International Group Limited
Priority date: 1996-10-11
Filing date: 1997-10-13
Publication date: 1998-04-23
Also published as: GB9621297D0; WO1998016621A3; AU4632297A

Abstract

A process for encapsulating a solid detergent component using an oil-in-water emulsion and forming a polymer film at the oil/water interface by condensation polymerisation. TAED is the preferred detergent component and the microcapsules formed by the process may be used in liquid formulations such as isotropic or structured detergents which may contain hydrogen peroxide or a source of hydrogen peroxide. The coating improves the storage stability of the microcapsule.

Description

MICROCAPSULES

This invention relates to microcapsules and more particularly, this invention relates to microcapsules of solid material. This invention also relates to a process for producing microcapsules through an interracial polymerization reaction.

Background of the Invention

Micro encapsulation is the envelopment of small solid particles, liquid droplets, or gas bubbles with a coating, usually a continuous coating. Many terms are used to describe the contents of a microcapsule such as active agent, active core, core material, fill, internal phase, nucleus, and payload. The coating material used to form the outer surface of the microcapsule is called a coating, membrane, shell, or wall. It may be an organic polymer, hydrocolloid, sugar, wax, metal or inorganic oxide. Microcapsules usually fall in the size range of between 1 and 2000 microns, although smaller and larger sizes are known

Complex coacervation and interracial polymerization are two well known processes for the formation of microcapsules. Complex coacervation is carried out in aqueous solution and is used to encapsulate water-immiscible liquids or water-insoluble solids. In the complex coacervation of gelatin and gum Arabic, for example, the water-immiscible substance to be encapsulated is dispersed in a warm, gelatin solution Gum Arabic and water are added, the pH of the aqueous phase adjusted to about 4, and a liquid complex coacervate of gelatin and gum Arabic is formed. As long as the coacervate adsorbs on the substance being encapsulated, a coating of complex coacervate surrounds the dispersed droplets or particles of water-insoluble substances to form microcapsules. The gelatin is then crosslinked, typically with an aldehyde such as formaldehyde or glutaraldehyde. A variety of other crosslinking agents are known including polyfunctional c^rbodiimides, anhydrides and aziridines. Micro encapsulation of solid actives such as Tetraacetylethylenediamine (TAED) is described in co-pending WO95/14077. In interfacial polymerization reactions, the fill is typically a liquid rather than a solid. Interfacial polymerization involves the porycondensation of two or more reagents at the interface between two immiscible liquid phases to form a polycondensate film that encapsulates the disperse phase. The reagents diffuse together and rapidly polymerize at the interface of the two phases to form a thin coating. The degree of polymerization can be controlled by the reactivity of the reagents chosen, their concentration, the composition of either phase vehicle, and by the temperature of the system.

Microcapsules produced through interfacial polymerization having shell walls composed of polyamides, polyureas, polyurethanes, and polyesters are known; see US Patent Nos 3,516,941, 3,860,565, 4,056,610, and 4,756,906. In some instances the shell walls of these conventional irύcrocapsules are very porous and consequently disperse their fill too rapidly for some applications. Therefore, the microcapsules may have to be post-crosslinked with such crossl iking agents as poryfunctional aziridines. The crosslinking provides shell walls with greater structural integrity and reduced porosity. Of course, an obvious disadvantage to post-crosslinking or curing is that it adds another step to the microcapsule production process.

Interfacial polymerization was described as long ago as 1959 by Morgan and Kwelek "Interfacial Polycondensation II Fundamentals of Polymer Formation at Liquid Interfaces", Journal of Polymer Science, Vol XL, Pages 299-327, (1959). A further general description by Morgan can be found in "Condensation Polymers" Vol 6 of Polymer Reviews, published by Intersdence Publishers in 1965. For additional information see "Micro encapsulation, Processes and Application", IE. Vandegaer. ed. Plenum Press, New York and London 1974, pp 1-37 and 89-94. Also W. Sliwka, Agnew. Che . Internat. Edit., Vol. 14, No. 8, pp 539-550, 1975 and "Capsule Technology and Micro encapsulation", M. Gutcho, ed., Noyes Data Corporation, Park Ridge, New Jersey, 1972.

Encapsulation by condensation of a pair of complementary, direct-acting, polycondensate-forming intermediates at the interface between two substantially immiscible liquids is a technique that is extensively patented and widely used. For example in the formation of the rupturable microcapsules of toner used in carbonless copy paper. The technique has also been proposed for encapsulation of dyes, inks, chemical reagents, pharmaceuticals, flavourings, pesticides, herbicides and peroxides. The vast majority of the published literature is concerned with systems for encapsulation of spherical liquid droplets. Only a minority of disclosures address the possibility of encapsulating solid materials.

US 3 575 882 (Penwalt Corporation) addresses a problem which occurs in use of the water in oil systems. Apparently the polymer grows from the interface into the organic phase. If the organic phase is the discontinuous phase this is not a problem, but with the reverse situation the polymer grows outwards into the continuous organic phase. This is said to be a problem because the polymer then tends to be unprotected by the normal liquid or soluble dispersing agents. This is because these agents tend to stay at the original interface. Since, with outward polymer growth this eventually forms the inner polymer surface, the outer polymer surface is unprotected and is tacky and subject to agglomeration. The inventive aspect of this patent is the use of a unique class of colloids to protect the outer polymer surface in water in oil systems. Whilst the encapsulation is primarily for preservation of droplets in the liquid state, it is contemplated that the process may be used for enclosing liquid bodies which may be converted, within the capsule, to other, e.g. solid, form.

The use of the technique of interfacial polymerization in the detergents industry has not met with much success. In GB 1551 142 (P&G) it is proposed to encapsulate a rinse conditioner with poryamide or polyester. The rinse conditioner has to be melted to be a liquid and then mixed with the oily reactant and added as a liquid to the aqueous phase. GB 1 136 303 (Wallace and Tieman) describes an improved encapsulation process which is capable of encapsulating solids by interfacial polymerisation The solids are either suspended in the dispersed liquid phase or are liquids which are converted to solids by further reaction subsequent to encapsulation.

US 3492 380 describes a polymer shell which is resistant to acid pH but dissolves at alkaline pH. An example reacts ethylene diamine with a phosphorous derivative of bisphenol A US 3954 666 provides for encapsulation of ferromagnetic materials. Although these are solids the capsules remain solvent filled with the freely divided solids in suspension in the liquid. The microcapsules are semi- permeable to perform the catalysis which is the object of this invention.

EP 0463 412 (Xerox) provides a toner microcapsule which may be magnetic and contain solid material. The particle size diameter of the solids is stated to be from about 0.1 to 8 microns. The volume average diameter of the toner microcapsules is said to be from 10 to about 17 microns. Each capsule contains a plurality of solid actives within a polymer resin. The capsule walls are formed using polyisocyanates, polysilicones and amines. Free radical polymerization initiators are included.

EP 148 149 (Monsanto) discloses the use of an emulsifier in the aqueous continuous phase. The emulsifier is selected from sulphonated naphthalene formaldehyde condensates, sulphonated polystyrene derivatives and functionalised oligomers. To avoid unwanted agglomeration, the emulsion is preferably formed before addition of the second shell wall component to it. Examples of sulphonated naphthalene-formaldehyde condensates are given as "Tamol'® SN the sodium salt of condensed naphthalene sulphonic acid from Rohm and Haas and "Daxad" 11G, 16, 17 and 19 the sodium salt of polymerized alkyl naphthalene sulphonic acid from Grace, Akzo "Blancol"N, the sodium salt of sulphonated naphthalene-formaldehyde condensate from GAF Corporation

In US 4 439 510 a method for encapsulation of liquid ink is disclosed. Albumin is used as an emulsion stabiliser. It is either used in spray dried form or is denatured with enzyme catalysed hydrolysis, addition of sodium lauryi sulphate or use of hydrogen peroxide or other oxidising agents.

The use of emulsifiers is also disclosed in GB 1554 957 (Stauffer Chemical Company) which relates to coating of solid materials, but eschews the known interfacial polymerization technique. Thus highlighting the long standing technical prejudice against the use of interfacial polymerization for coating of solid materials.

EP 454 980 uses organic methyl cellulose or hydroxylated methyl cellulose as emulsifiers for pigments in a monomer core which is subsequently polymerised as a unit.

In US 5225 278 Span® 80 surfactant/sorbitan monooleate is used to stabilise a continuous hydrophobic organic phase whilst the aqueous phase contains the active biocidal liquid and a solution of diethyl sulphosuccinate. Further examples use the diethyl sulphosuccinate in an aqueous continuous phase. In the latter case no surfactant is added to the organic phase.

US 5 215 847 (Xerox) generally teaches the use of an emulsifier or surfactant to disperse and stabilise subparticles formed in the organic phase in the aqueous medium prior to encapsulation Tylose is used in the examples.

According to the present invention there is provided a method of encapsulating an active solid core having an average particle size in the range l-3000μ, preferably l-1000μ, comprising the steps of dispersing the core in water together with a first nonionic surfactant with HLB > 9 and a water soluble first reagent which is a precursor of a polycondensate which is less soluble in water than the first reagent, then bringing the dispersion into contact with an oil phase solution or dispersion of a water insoluble second reagent which is also a precursor of the polycondensate, the oil phase further comprising a second nonionic surfactant with HLB < 9, the contact time being sufficient to allow a coating of the polycondensate to form on the core, and finally isolating the coated core by a drying process.

The process is especially suitable for encapsulating solid detergent components and may use an oil-in- water emulsion and form a film of polycondensate at the oil/water interface by condensation polymerisation.

The polycondensate film protects the detergent component from both hydrolytic and perhydrolytic degradation, allowing the microcapsules to be used in isotropic or structured HDLD's with or without peroxide or persalts.

Preferably the polycondensate is selected from the group comprising polyamide, polyester, polysulphonamide, polyurea, polyurethane and mixtures thereof

Advantageously the oil is immiscible with water, has a density of 500-2000 kg/m³; preferably 800- lSOOkg/m^3, and is selected from: polar and non polar low molecular weight organic protic solvents such as chloroform; cyclohexane; toluene and mixtures thereof, and non-polar medium molecular weight oils such as vegetable, mineral and silicone oils.

The Oil Phase desirably comprises a mixture in the ratio Cyclohexane : Chloroform 4:1 v/v. Aherr-arivery it may comprise a light grade mineral oil or a surfactant may be used as the oil phase.

For Poryamides the best products (in terms of physical properties) are obtained when a cyclohexane/ chloroform mixture is used. Mineral oil tends to produce excessive aggregation of capsules. Polyesters are less sensitive to the type of oil used.

The Oil : Water Ratio is desirably in the range 1:5 to 1 :20, preferably it is 1 : 12. At less than a 1:5 ratio there exists the possibility that the emulsion could undergo localised phase inversion to produce water-in-oil emulsion.

The detergent component may be selected from the group comprising bleach activators, enzymes, and OBAs. Preferably the detergent component is TAED.

It is preferred that surfactants chosen to match the HLB of the oil/water emulsion are added to the oil and water phases to aid the growth of the polycondensate.

The term polycondensate is used to define all the reaction products possible from the techniques of interfacial polymerization including cross-linked condensates. Examples of polycondensates are polyamide, porysulphonamide, polyester, polycarbonate, polyurethane and polyurea; also copolymers such as polyurea with polyamide. More specific instances of polycondensate reactants are: diamines or polyamines in the aqueous phase and diacid or polyacid chlorides in the organic phase to give capsule walls which are polyamides. Diamines or polyamines in the aqueous phase and bischloroformates or polychloroformates in the organic phase give a polyurethane capsule wall. Diamines or polyamines in the aqueous phase and disulphonyl or polysulphonyl chlorides in the organic phase give a porysulphonamide capsule wall. Diamines or polyamines in the aqueous phase and chloroformyl chloride (phosgene) in the organic phase give a polyurea capsule wall. Diols or polyols in the aqueous phase and dϋsocyanate or polyisocyanates also produce a polyurea capsule wall. Diols and Polyols in the aqueous phase can be used with diacid or polyacid chlorides in the organic phase to give polyester capsule walls. Use of bischloroformates, polychloroformates or phosgene in the organic phase gives a polycarbonate capsule wall.

Usually, interfacial polymerization involves first producing droplets of the discontinuous phase which contain one reactant or group of reactants. This may be accomplished by dispersion. The second reactant or group of reactants is then added to the continuous phase, usually by adding a quantity of the reactant dissolved in a small quantity of the liquid which forms the continuous phase. It is common to add a dispersing agent to the continuous phase. The dispersing agent should ideally modify the outer surface of the eventual capsule in such a way that the capsules do not stick together. Commercially useful dispersing agents may be selected from emulsifiers such as sulphonated polymers and functionalised oligomers. Poly vinyl alcohols may be used in conjunction with these emulsifiers as a codispersant.

Commercially available examples of sulphonated polymers with molecular weights above about 1,000 and an equivalent weight per acid group between about 150 and about 750, as for example, sulphonated polystyrene are Versa® TL 500 and TL 600, sulphonated polystyrene manufactured by National Starch and Chemical Corporation. Versa-TL 500 has an average molecular weight of 500,000; Versa-TL 600 has an average molecular weight of 600,000.

Examples of "Functionalised oligomers" which are low molecular weight block co-polymers terminated at one end by a bulky water insoluble group, which gives the molecule surfactant like character. Such materials are polyionic and polymeric in nature and are commercially available under the tradename 'Tolywet"; they are available as the water soluble potassium, amine salts or the free acid form from Uniroyal. Such functionalised oligomers and their preparation are described in U.S. Patent Nos 3,498,942, 3,498,943, 3,632,466, 3,777,382, 3,668,230, 3,776,874 and 3,839,405.

The range of emulsifier concentration found most acceptable in the system will vary from about 0.5% to about 15% and preferably from about 2% to about 6% based on the weight of the water- immiscible material and more preferably from about 2% to about 4% and most preferably 2% relative to the weight of the water-immiscible material.

The thickness or strength of the capsule walls can be selected or controlled by reaction conditions and by the choice of the reactants. For instance, in production of polyamide or polyester capsules by reaction of a diacid chloride 'with a diamine or dioL suitably reactive tri or otherwise poly- functional acid chloride, amine or -ol can be used to give cross-linking so as to strengthen the capsule skin by forming a three dimensional polymer network. The thickness of the polymer wall can be adjusted by varying the concentration of reactants or the contact time between the liquids after addition of the second reactant, or group of reactants.

A wide variety of organic solvents may be employed as a continuous phase liquid, some Examples being mineral oil, xylene, benzene, carbon disulphide, carbon tetrachloride, pentane, and the like. The invention contemplates that other continuous phase liquids may be employed, that will cause outward polymer growth away from the aqueous droplets, provided they will serve the function of a solvent for the condensate-forming reactant and will form an interface with the aqueous body to be encapsulated.

Examples of di-functional acid-derived compounds are sebacoyl chloride, ethylene bischloroformate, phosgene, terephthaloyl chloride, adipoyl chloride, azelaoyl chloride (azelaic acid chloride), and 1,3- benzenesulphonyl dichloride. C_g straight chain aliphatic dichlorides are preferred. Also C ₆aromatic acid dichlorides especially 1,2 and 1,4 substituted. Polyfunctional compounds of this type are exemplified by trimesoyl trichloride, 1,2,4,5-benzene tetracid chloride, citric acid chloride, 1,3,5- benzene trisulphonyl chloride, and 1,3,5-benzene trischloroformate. C₆ trifunctional 1,3,5 substituted ring compounds are preferred. Also copolymers of C₈ straight chain and C aromatic ring compounds. Intermediates similarly useful in the organic phase also include diisocyanates and polyisocyanates, for example toluene dϋsocyanate, hexamethylene dϋsocyanate and polymethylene polyphenylisocyanate, e.g. PAPI (The Carwin Co.).

As examples of suitable diols for use as intermediates in the aqueous phase, there may be named bis- phenol A [^-bisφ.p^'-dihydroxy diphenyl) propane], hydroquinone, resorcinol, and various glycols such as ethylene glycol, hexanediol, dodecanediol, and the like. Polyfunctional alcohols of this character, e.g. triols, are exemplified by pyrogallol (1,2,3-benzenetriol), phloroglucinol dihydrate, pentaerythritol, trimethylolpropane, 1.4,9, 10-tetrahydroxyanthracene, 3,4-dihydroxyanthranol, diresorcinol, tetrahydroxyquinone, and anthralin. Diols with from 5 to 12, preferably nearer to 12 carbon atoms in the chain are preferred.

Suitable diamines and polyamines are usually selected as soluble er se or in soluble salt form where such reactant is to be included in the aqueous phase, are ethylene diamine, diethylene triamine, phenylene diamine, toluene diamine, hexamethylene diamine, and piperazine, and substances which are understood to be capable of significant cross-linking effect, such as 1,3,5-benzenetriarnine trihydrochloride, 2,4,6-triamino toluene trihydrochloride, tetraethylene pentamine, pentaethylene hexamine, polyethylene imine, 1,3,6-triaminonaphthalene, 3,4,5-triamino-l,2,4-triazole, and melamine 1,4,5,8-tetraamino anthraquinone. To the extent that the reactant to be used in the aqueous phase may be insoluble or have limited solubϋity in water per se, it may be used in a form or with appropriate co-operating substances to render it, in effect, soluble. Thus certain amines may be used in hydrochloride or other salt form, while a compound of little or no water solubility (by itself) such as bisphenol A may be used in a composition appropriately adjusted, as with alkali, to afford such solubility. Alternatively, a hydrophilic substitute for water may be employed, as for example methanol, provided the reactant is soluble therein. In either case the ϋquid forming the droplets is termed "aqueous" herein Diamines with between 2 and 6 carbon atoms in the chain are preferred. C₆ aromatic 1,3 substituted diamines may also be used with good effect. Also trifunctional amines with C_j methylene groups.

For the diamines, diols, and acid dichlorides there is a general preference for the higher methylene content in the chain as this decreases the permeability of the polymer film. Likewise there is a preference for chains containing aromatic units over aliphatic chains.

In practical operation, normal precautions are taken to avoid unwanted reaction or modification of the substances employed. For example, care should preferably be taken to keep the organic phase, containing the diacid chloride or equivalent intermediate as dry as possible and in isolation from the atmosphere, to avoid hydrolysis. When the aqueous phase to be encapsulated is first distributed as droplets in a body of organic solvent, the diacid chloride is thereafter added in a further quantity of such solvent. This last-mentioned solution of the acid chloride should also, of course, be kept as dry as possible untϋ actual addition and reaction.

In some cases, when dispersion is employed to distribute the aqueous droplets within the organic ϋquid, the agitation employed to establish that dispersion can be reduced as, and after, the second reactant is added to the organic ϋquid continuous phase. Such reduction of agitation being of advantage to avoid any tendency to rupture the capsules as they form At this stage of the process after the droplets have been estabϋshed by dispersion, a chief requirement may simply be for good circulation to effectuate reaction with little or no agitation, but conditions may nevertheless warrant maintaining significant agitation as and after the second intermediate or reactant is added, for instance to maintain suspension of the finely divided solid agent in the continuous phase ϋquid, and satisfactory results have been achieved where the same moderately strong degree of agitation (used to produce the dispersion of droplets) is continued throughout the process. A hi-shear stirrer head used between 300 and 600 rpm has been found to provide the optimum degree of shear for this process.

While for the most part the polycondensation occurs rapidly at room temperature appropriate higher or lower temperatures may be employed if desirable. Likewise, conventional co-operating reagents or additions for adjustment of alkalinity or other pH or like characteristics may be used. For instance such substances as sodium hydroxide, sodium carbonate and sodium bicarbonate, utilised with amines and -ols for the usual reasons known in connection with these polycondensation reactions.

An encapsulated active must be recoverable. For many purposes it is sufficient to rupture the shell wall using force. Other release mechanisms may use shells that aϋow diffusion in of a material which reacts with the active to form products of greater volume, thereby rupturing the shell from within, changes in pH of the environment, either due to addition of chemicals, transfer of the capsule or dilution, may also weaken or destabiϋse the shell. Where TAED is used as the soϋd active the level may be varied between 95% to 20% with corresponding polycondensate levels of 80% to 5% based on dry product. Higher TAED loadings are beneficial in terms of reduced solid loadings in final product. Many ϋquid systems will not support TAED microcapsules with less than 40% active content because this would give too high a soϋds loading to attain the required TAED level.

Surfactant levels may vary between 16% to 77% with respect to the total oil phase (including acid dichloride where used).

Variations of surfactant level has a different effect on the yield of polyamide prepared depending upon the acid dichloride used. This supports a reaction mechanism in which the surfactant alters the partitioning of the diamine between the oil and water phases, and also effects the permeation of diamine through the primary polymer membrane. The different effects of surfactant concentration seen with different acid dichloride monomers indicates the effect of polyamide crystallinity upon film permeabiϋty to diamine; thus affecting the polymer yield produced.

The Surfactant Chemistry can also be altered as described above. Span 85 and Tween 20 are two non-ionic surfactants which may be used with good effect. A mixture of Marlon AS3 and Synperonic A7 may be used as an anionic and non-ionic mixture.

The rnicrocapsules prepared according to the method of this invention may be employed in a variety of environments where either protection or delayed release or a combination thereof is required. When the microcapsule is intended for use in a structured ϋquid additional phase stabiϋty may be obtained if an inorganic salt is included in the system by dissolving it in the aqueous phase. Preferred salts are Potassium Chloride, Sodium Citrate and quaternary amines.

The microcapsules may either be used as they are or they may be post-coated by a different method, such as coacervation. The material to be encapsulated may likewise already have been microencapsulated by a different method. Such multiple coated particles may give the required degree of impermeability in combination with the release characteristics needed for appϋcations ^■where detergent additives are to be protected and released in an environment containing a peroxygen bleach.

General preparative method

In one general preparative method according to the invention the technique used is as follows:

Stage 1.

The core material to be encapsulated is dispersed in a suitable non-solvent, usually an oil or low molecular weight organic solvent, using a high shear stirrer. A surfactant of suitable hydrophilic- lypophiϋc balance (HLB <9) is additionally added to help disperse the core.

Stage 2.

An aqueous solution of a polyfunctional amine is prepared and added to the oil dispersion of the core material. The aqueous phase may additionally include a surfactant of suitable HLB ( >9). The combination of agitation at moderate shear and surfactant mixes produces an oil in water emulsion.

Stage 3.

Using the same non-solvent or oϋ as in stage 1, a solution or dispersion of a polyfunctional acid chloride is prepared. The solution/dispersion characteristics depend on the acid chloride solubility in the chosen oil. The volume of this solution/dispersion is sufficiently low so as not to significantly disrupt the oil/water ratio produced in stage 2. Typically less than 10% of the volume of oil used in stage 1 is required here.

Stage 4.

The acid chloride dispersion is then added drop-wise, whereupon the acid chloride and amine react at the oil-water interface to form an amide and liberate hydrogen chloride (in aqueous solution). This reaction proceeds until a primary membrane is formed around the spherical oil droplets containing the core material.

Stage 5. The primary membrane inhibits further reaction of monomers. It is beϋeved that surfactant increases the mobility of the amine, allowing it to dissociate between the oil and water phases and hence to maintain some reaction As the secondary membrane forms so the reaction slows further and as such Interfacial Polymerisation (IP) could be classed as a self limiting polymerisation. The time allowed for polymerisation will dictate the film thickness and porosity and can vary from 1 minute to 12 hours or more.

Stage 6.

The microcapsules produced are isolated by filtration, washed in water and dried in a fluid bed dryer.

The invention wiU now be further described with reference to the foUowing non-limiting examples.

Examples

Four processing routes and an uncoated control were used to determine the optimum process to get different degrees of stability in the resulting microcapsule. For each route the stability of the resulting microcapsule was measured and the appearance of the microcapsule was assessed visually using scanning electron microscopy (SEM). The results are given in Table 1 below.

Stability Data

The HPLC% data represents samples stored in alkaline peroxide-containing Heavy Duty Liquid

Detergent (HDLD) at pH 9.5 under static conditions for 24 hours. The sample is then extracted into acetonitrile : water (15:85) mix, diluted, and analysed by HPLC. The stability data (%HPLC) is thus quoted as percent TAED remaining after 24 hours storage. All samples start with 4% TAED w/w with respect to HDLD, as determined by conventional assay. The relevant comparison with uncoated micronised TAED gives average values in the range 10-20% TAED remaining after 24 hours.

Route A

Deionised water (500g) was used to disperse TAED (142g) using Tween 20 (10.2g) as a dispersing agent. Hexamethylenediamine (HDA 5.2g) was dissolved in this dispersion whilst stirring at 300 rpm, using a high shear stirrer blade.

Meanwhile the oil phase was prepared by dispersing Span 85 in chloroform (8g) and cyclohexane (32g). This oil phase was then added to the aqueous dispersion of TAED with agitation to form the required oil-in-water emulsion. The sebacoyl dichloride (lg) and phthaloyl dichloride (lg) were dissolved in a mixture of chloroform (lg) and cyclohexane (4g), and added drop-wise to the above oil-in-water emulsion, initiating polymerisatioa The TAED content of the microcapsule (anhydrous) was 95%.

Route B

TAED powder dispersed in water with Tween 20 (hydrophiϋc surfactant) added to stabilise the TAED dispersion - by acting as a wetting agent essentially. The acid dichloride is dissolved in the discontinuous oil phase with hydrophobic surfactant Span 85. This oil solution is added with agitation to the preformed aqueous dispersion of TAED to produce a surfactant stabilised oil-in- water emulsion.

The diamine is dissolved in water, this solution being added drop-wise to the oil-in-water emulsion, the rate of polymerisation is dictated by the diamine addition rate.

Individual capsule size is <500 μm. Route C

TAED is dispersed in the oil phase with the hydrophobic surfactant. Diamine solution is prepared with the addition of Tween 20 hydrophiϋc surfactant. This is added to the oil dispersion to produce the oil-in-water emulsion. Acid dichloride is dissolved into further oil phase and added dropwise to the emulsion Product obtained consists of aggregated capsules in the form of very hard spheres of ca 100 μm.

Route D

TAED is dispersed in the discontinuous oil phase cyclohexane containing the dissolved acid dichloride and the hydrophobic surfactant Span 85. A large volume of water is then added with a hydrophilic surfactant, Tween 20, to produce an oil-in-water emulsion. Aqueous diamine solution is then prepared and added dropwise to the emulsion. Product obtained as individual capsules in the form of a free flowing powder of ca. 100 μm.

Table 1

Unlike Route D, Route B requires the TAED to be dispersed in water initially. With the same interfacial reaction of precursors it may be considered that the TAED would not be coated by Route B. However, SEM analysis and stability data provide strong evidence that the TAED is coated.

Route C was clearly the best of the four routes based on physical properties, in that hard discrete spheres were obtained. SEM and stability analysis confirm that a coating has been deposited around the TAED. This route was predicted as being the least successful due to competing mechanisms of droplet coalescence and monomer reaction, but has been demonstrated here to be the best route; in terms of overall physical properties. This is surprising.

Addition of acid dichloride in Route A was predicted to produce good encapsulation, though not as good as Route D. Results confiπn that encapsulation has occurred, with individual crystal coating apparent by SEM; capsule particle size is generally <100 μm. Routes A and C in which the water insoluble acid chloride is added to the other components, including the TAED and the water soluble reagent, is seen to give a consistent result in these tests with an isotropic ϋquid. The data using isotropic ϋquids strongly suggests that Route D is not satisfactory. This is contrary to prediction. However, we have found that in a more aggressive structured Uquid environment the preferences may not follow the same order. Thus, because Route D provides a thick coating and gives a process which causes a low level of degradation of the TAED by reaction during the process, this route has been selected as a preferred route for production of TAED microcapsules for structured ϋquids.

Claims

1. A process for encapsulating a solid detergent component using an oil-in-water emulsion and forming a polymer film at the oil/water interface by condensation polymerisation.

2. A process according to claim 1 in which the polymer film is selected from the group comprising polyamide, polyester, polysulphonamide, polyurea, and polyurethane.

3. A process according to claim 1 in which the oil is immiscible with water, has a density of 500-2000 kg/m³, preferably 800-1500 kg/m³; and is selected from: polar and non polar low molecular weight organic protic solvents such as chloroform; cyclohexane; toluene and mixtures thereof; and non-polar medium molecular weight oils such as vegetable, mineral, and siϋcone oil.

4. A process according to claim 1 in which the detergent component is selected from the group comprising bleach activators, enzymes, and OBAs.

5. A process according to claim 1 in which the detergent component is TAED.

6. A process according to claim 1 in which surfactants chosen to match the HLB of the oil/water emulsion are added to the oil and water phases to aid the growth of the polymeric film.

7. A process for encapsulating an active solid core having an average particle size in the range l-3000μ, preferably 1-lOOOμ, comprising the steps of dispersing the core in water together with a first nonionic surfactant with HLB > 9 and a water soluble first reagent which is a precursor of a polycondensate which is less soluble in water than the first reagent, then bringing the dispersion into contact with an oil phase solution or dispersion of a water insoluble second reagent which is also a precursor of the polycondensate, the oil phase further comprising a second nonionic surfactant with HLB < 9, the contact time being sufficient to allow a coating of the polycondensate to form on the core, and finally isolating the coated core by a drying process.

8. A microcapsule produced by a process according to any of the preceding claims.

9. An isotropic ϋquid detergent composition containing from 0.5 to 15% of a microcapsule according to claim 8.

10. A structured ϋquid composition containing from 0.5 to 30% of microcapsules according to claim 8.