FORM 2 THE PATENTS ACT 1970 [39 OF 1970] COMPLETE SPECIFICATION [See Section 10] "NOVEL MICROCAPSULES" SYNGENTA LIMITED, a British company of Fernhurst, Haslemere, Surrey GU27 3JE, Great Britain, The following specification particularly describes the nature of the invention and the manner in which it is to be performed:- NOVEL MICROCAPSULES FIELD OF THE INVENTION This invention relates to capsules of the nano and micron size (collectively, microcapsules) and to a process for their production. More particularly, this invention relates to encapsulated droplets of a liquid material that is substantially insoluble in water, and where the encapsulating shell has surface modifying compounds contained therein, thereby forming a modified capsule wall having a number of advantages. Further, this invention relates to the processes for the production of such capsules, including intermediate processes, and methods for their use. BACKGROUND OF THE INVENTION The use of microcapsules for both the slow or controlled and fast or quick release of liquid, solid and solids dissolved or suspended in solvent is well known in the chemical art, including the pharmaceutical specialty chemical and agricultural industries In agriculture, these release techniques have improved the efficiency of herbicides, insecticides, fungicides, bactericides and fertilizers. Non-agricultural uses have included encapsulated dyes, inks, pharmaceuticals, flavoring agents and fragrances. The material used informing the wall of the microcapsule is typically taken from resin intermediates or monomers. The wall tends to be porous in nature, and may release the entrapped material to the surrounding medium at a slow or controlled rate by diffusion through the wall. The capsules may be alternatively designed so as to quickly release the material to the surrounding medium by modifying the cross-linkage in the wall. Further, the encapsulated material may be released in either a controlled or quick manner by means of a trigger mechanism built into the wall, wherein the trigger may be environmentally sensitive allowing quick breakdown of the wall under certain conditions. In addition to providing controlled or quick release, the walls also serve to facilitate the dispersion of water-immiscible liquids into water and watersxmtaining media such as wet soil. Droplets encapsulated in mis manner are particularly useful in agriculture. Various processes for microencapsulating material have been previously developed. These processes can be divided into three broad categories - physical, phase separation and interfacial reaction methods. In the physical methods category, microcapsule wall material and core particles are physically brought together and the wall material flows around the core particle to form the microcapsule. In the phase separation category, microcapsules are formed by emulsifying or dispersing the core material m an uranisdble continuous phase in which the wall material is dissolved and caused to physically separate from the continuous phase, such as by coacervation, and deposit around the core particles. In the interracial reaction category, the core material is emulsified or dispersed in an immiscible continuous phase, and then an interacial polymerization reaction is caused to take place at the surface of the core particles thereby forming microcapsules. The above processes vary in utility. Physical methods, such as spray drying, spray chilling and humidized bed spray coating, have limited utility for the microencapsulation of products because of volatility losses and pollution control problems associated with evaporation of solvent or cooling, and because under most conditions not all of the product is encapsulated nor do all of the polymer particles contain product cores. Phase separation techniques suffer from process control and product loading limitations. It may be difficult to achieve reproducible phase separation conditions, and it may be difficult to ensure that the phase-separated polymer will preferentially wet the core droplets. Interfacial polymerization reaction methods have proven to be the most suitable processes for use in the agricultural industry for the microencapsulation of pesticides. There are various types of mterfacial reaction techniques. In one type of interfacial condensation polymerization microencapsulation process, monomers from the oil and aqueous phases respectively ate brought together at the oil/water interface where they react by condensation to form the microcapsule wall ("two phase polymerisation"). In general such reactions involve the condensation of an isocyanate moiety on one monomer with a second moiety such as an amine on a second monomer. In another type of polymerization reaction, the in situ interfacial condensation polymerization reaction, all of the wall-forming monomers or pre-polymers are contained in one phase (the oil phase or the aqueous phase asthe case may be). In one process the oil is dispersed into a continuous or aqueous phase solution comprising water and a surface-active agent. The organic phase is dispersed as discrete droplets throughout the aqueous phase by means of emulsification, with an interface between the discrete organic phase droplets and the surrounding continuous aqueous phase solution being formed. In situ condensation of the wall-forming materials and curing of the polymers at the organic-aqueous phase interface 5 may be initiated by heating the emulsion to a temperature between of about 20° C to about 85° C and optionally adjusting the pH. The heating occurs for a sufficient period of time to allow substantial completion of in situ condensation of the monomers or pre-polymers to convert the organic droplets to capsules consisting of solid permeable polymer shells enclosing the organic core materials. 10 Many such in situ condensations involve isocyanate moieties. For example one type of microcapsule prepared by in situ condensation and found in the art, as exemplified in U.S. Patent No. 4,285,720 is a polyurea microcapsule which involves me use of at least one polyisocyanate such as polymethylene polyphenylenejsocyanate (PMPPI) and/or tolylene dusocyanate (TDI) as the waU-forming material. In the creation of polyurea microcapsules, 15 the wall-forming reaction is initiated by heating the emulsion to an elevated temperature at which point the isocyanate groups are hydrolyzed ar the mteriace to fbnn amines, which in turn react with unhydrolyzed isocyanate groups to form the polyurea microcapsule wall. Isocyanates may undergo many types of chemical transformations such as homo-polymerisation, oligomerisation, cycloaddition, insertion and nucleopbilic reactions as 20 described in the text H. Ulrich, CHEMISTRY AND TECHNOLOGY OF ISOCYANATES, John Wiley &. Sons, Chichester, United Kingdom (1996). In the context of microcapsule wall formation, nucleopbilic reactions are the most important Typical micleopbiles include carboxyl, thiol, active methylene, hydroxyl and amino groups. The use of isocyanates in which the -NCO group is 'masked' is well known in 25 isocyanate polymer chemistry. For example, the -NCO group may be reacted with various molecules (BH) to give blocked isocyanates (RNHCOB) as described in Wicks & Wicks, PROGRESS IN ORGANIC COATINGS, Vol. 36. pp. 148-72 (1999). The blocked isocyanates may be de-blocked by further reaction with nucleophiles: RNCO + BH -> R-NH-CO-B 30 R-NH-CO-B +NuH -> R-NH-CO-Nu + BH While we do not exclude the use of blocked isocyanates in the present invention, that approach is not preferred as it nonnally requires relatively high (>100"C) temperatures for the deblocking reaction, and as the blocking agents are released into the medium. A further type of microcapsule prepared by in situ condensation which does not involve the reaction of isocyanate groups is exemplified in U.S. patents 4,956,129 and 5,332,584. These microcapsules, commonly termed "aminoplasf' microcapsules, are prepared by the self-condensation of etherified urea-formaldehyde resins or prepolymers in which from about 50 to about 98% of the methylol groups have been etberified with a C4-Cw alcohol (preferably n-butanol). The prepolymer is added to or included in the organic phase of an oil/water emulsion. Self-condensation of the prepolymer takes place under the action of heat at low pH. To form the microcapsules, the temperature of the two-phase emulsion is raised to a value of from about 20°C to about 90°C, preferably from about 40°C to about While we do not exclude the use of blocked isocyanates in the present invention, that approach is not preferred as it normally requires relatively high (>100°C) temperatures for the deblocking reaction, and as the blocking agents are released into the medium. A further type of microcapsule prepared by in situ condensation which does not involve the reaction of isocyanate groups is exemplified in U.S. patents 4,956,129 and 5,332,584. These microcapsules, commonly termed "arainoplasr" microcapsules, are prepared by the self-condensation of ctherified urea-formaldehyde resins or prepolymers in which from about SO to about 98% of the methylol groups have been etberified with a C4-C,D alcohol (preferably n-butanol). The prepolymer is added to or included in the organic phase of an oil/water emulsion. Self-condensation of the prepolymer takes place under the action of heat at low pH. To form the microcapsules, the temperature of the two-phase emulsion is raised to a value of from about 20°C to about 90*C, preferably from about 40°C to about 90°C, most preferably from about 40°C to about 60°C. Depending on the system, the pH value may be adjusted to an appropriate level For the purpose of this invention a pH of about 1.5 to 3 is appropriate. Microcapsules produced by such in situ condensation have the benefits of high pesticide loading and low manufacturing costs, as well as a very efficient membrane and no reactive residue remaining in the aqueous phase. Regardless of the type of process utilized, the final encapsulated products may be packaged and used in a number of forms. For instance, they may be used in the form of a suspension of microcapsules in a liquid such as water or another aqueous medium (generally termed a suspension concentrate). Alternatively they may be packaged and used as dried microcapsules (for instance, produced from suspensions of microcapsules in liquids by techniques such as by spray drying, flat plate drying, drum drying or other drying methods). In yet a third way, they may be combined into other solid formulations such as granules, tapes or tablets containing microcapsules. All of these types of formulations are generally used by adding them to a liquid medium (usually water) in equipment such as a spray tank for agricultural use. Liquid media, whether that packaged with the microcapsules in suspension concentrate form, or that used in a spray tank or other application equipment, often has various ingredients in addition to water, including wetters, dispersants, emulsifiers, protective colloids or colloid stabilizers and surface active agents or surfactants. The protective colloids are sed in processes for the preparation of the microcapsules and serve to prevent agglomeration of the oil droplets prior to encapsulation, or of the capsules after wall formation, as well as aiding the re-dispersing of the capsules upon settling. The surfactants perform various functions depending upon the type of surfactant used. These include varying the permeability of the wall, aiding in dispersing the capsules, acting as a wetter, reducing or eununatmg foaming, affecting the adhesiveness of the capsule to the surface to which it is applied, and so forth. Primarily, the surfactants act as free, non-bound emulsifiers in the preparation of the precursor emulsion. However, under certain conditions the protective colloids, surfactants and emulsifiers can become desorbed or otherwise separated (to varying degrees) from the microcapsules so that they do not continue to perform their functions as effectively. SUMMARY OF THE INVENTION It has been discovered that one or more waU-modrfying compounds (termed "surface-modifying agents") can, by virtue of reaction with the wall-forming materials, be incorporated in the microcapsule wall to create a modified microcapsule surface with built-in surfactant and/or colloid sfrfojl'*^ properties. The preferred compounds in this invention . have weak or nonexistent surface activity and/or colloid stabilizing properties in and of themselves but contain within the molecular structure one or more moieties that are capable of imparting surface activity. PRIOR ART US Patent No 6,022,501 (assigned to American Cyanamid Company) discloses pH-sensrtive microcapsules obtained by introducing apolyacidhalide into the emulsion during the formation of a polyamide, polyester, polyamide/polyester or cross-linked amino resin microcapsule wall such mat free carboxylic acid groups are incorporated in the shell wall. Such microcapsules are stable at pH values from about pH 1 to pH 5.5 and release then-contents at pH values greater than about 5.5. U.S. Patent No. 5,925,464 (assigned to Dow AgroSciences) discloses a method of encapsulating pesticidal materials, in which microcapsules containing the active material are formed by means of an interfocial polycondensation reaction, involving an isocyanate/polyamme reaction in the presence of a polyvinyl alcohol ("PVA"). This reference mentions that the PVA, having pendant -OH groups, reacts with the isocyanate to incorporate polyurethane groups into the polymeric microcapsule walls. U.S. Patent No. 6,020,066 (assigned to Bayer AG) discloses a process for forming microcapsules having walls of polyureas and poryiminoureas, wherein the walls axe characterized in that they consist of reaction products of crosslinking agents containing NHj groups with isocyanates. The crosslinking agents necessary for wall formation include di- or polyamines, diols, polyols, pdytunctional amino alcohols, guanidme, guanidine salts, and compounds derived therefrom. These agents are capable of reacting with the isocyanate groups at the phase interface in order to form the wall BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 generally illustrates the effect upon redispersibility of wall-modified microcapsules. Fig. 2 generally illustrates the effect upon permeability, or release rate, of wall-modified microcapsules. DETAILED DESCRIPTION OF THE INVENTION It has been found that, by use of the concepts of this invention in the above-mentioned conventional microcapsule processes, it is possible to produce a modified chemical structure that alters the properties of me capsule. The process employs surface modifying compounds that generally exhibit little or no type of surface activity, but contain one or more moieties that are capable of imparting surface activity when the compound is chemically altarhrd to the microcapsule wall. Thus, when such compounds are incorporated into the wall of the capsules, capsules with enhanced properties are formed. In its simplest form, the microcapsule of the present invention is comprised of a core material encapsulated by a wall formed from one or more monomer or oligomer or polymer compounds, wherein the wall has been modified to incorporate one or more agents which affect the properties of the capsule. Thus according to the present invention mere is provided a microcapsule ccxoprising an encapsulated material enclosed within a solid permeable sheU of a polymer resm wherein the polymer resin has incorporated therein at least one surface modifying compound wherein said surface modifying compound is sdectedfroin compounds having a formula (T), (IT), (HI) (PO),(EO)t-X OB) wherein R*, r and s are as defined in relation to formula (VI) above. When -Z is a block copolymer, structure (LA) has the formula R4.-0(PO)(>(EO),(PO)!-X o>emanethiol hydrochloride [(CH3)2n(H)CH2CH2SH] CT and 3-mercaptopropionic acid [HSCH2CH2CO2H] and salts thereof. WhenY1 is ring structure group such as an aryl group the substituents Xand Z in formula (IA) may be direct substituents in the ring for example:- Z (ID) If X and Z are adjacent substituents capable of reacting together such as carboxyate and/or sulphonate they may form a cyclic anhydride capable of ring-opening under the reaction conditions. An example of such & compound is 2-sulphobenzoic acid anhydride. In structure (H) where two groups X are at distal ends of the molecule, -Z- may be an oxyetbylene containing polymer and there is a direct bond between-Z-arid each-X. Thus one preferred structure (II) has the formula:- wherein a and b are independently from 0 to 3000 or more preferably from 0 to 2000, provided that a is not 0 and the total of a +■ b is Horn, about 7 to about 3000 or more preferably from about 10 to about 2000 and EO and PO represent oxyerhylene and oxypropylene respectively which may be arranged in random or block formation. More preferably, a and b are independently from 0 to200, provided that the total of a + b is from about 10 to about 200. Preferably a is greater than b, for example it is preferred that a is at least 4 times greater than b. When -Z- represents an ethylene oxide, propylene oxide block copolymer, the compound may have the structure X-{PO)..(EO)k. (PO)e-X* (HB) wherein a', b1 and c arc independently from 0 to 2000, provided that V is not 0 and the total of a' + b' + c is from about 7 to about 3000 or more preferably from about 10 to about 2000 and EO and PO represent oxyethylene and oxypropylene respectively. Preferably b' is greater than the sum of a' + c, for example at least 4 times greater than the sum of a*+ c. Preferably a', b' and c are independently from 0 to200, provided that the total of a' + b3 + c is from about 10 to about 200. The groups X and X* may be thesame or different but are conveniently the same. An example of a compound of formula (1IB) wherein the terminal -OH groups are replaced by -*JH, is JEFFAMINE ED2003 [HjNCHMeCa^-CPOX-CEO),,-(PO).-NHJ, where a+c=2.5 and b=41, available from Huntsman. Alternatively -Z- in structure QX) may be quaternary arnmoimim. Thus for example a further preferred structure (U) has the formula (EC)R14 wherein Ru and Ru, which may be the same or different are hydrogen Ct to C^ straight or branched chain alkyl; aryl for example phenyl; or C, to C4 aralkyl, for example benzyl, wherein each aryl group may be optionally substituted by conventional sobstituents such as C, to C4 alkyl, nitro and halo and wherein Y4 and Y4' which may be the same or different are -*r } FAX: 013. wherein R,, and R, are independently C, to Cl0 straight or branched chain alkyl linking gtoups optionally substituted by halogen or ether, for example C5 to C4 alkoxy and (Lj), is a polyoxyalkyene group such as polyoxyethylene or more preferably polyoxypropylene or pofyoxybutyiene; n is from 2 to 20, preferably from 4 to 10 and A- is a suitable anion. It is preferred that both RM and R1S are not hydrogen at the same time. An example of a surface modifying compound of formula (JLC) is a benzoxonium chloride such as that illustrated in Example IS or an amino oxyethylene diol such as that illustrated in Example 19. Structure (III), where two X groups are at distal ends of the molecule and Z is a pendant group, may in one embodiment take the form:- X-YrC(Z)(R«)-Y2'-X' (1IIA) wherein Rj is hydrogen or more preferably a C, to C4 alkyl group optionally substituted by ether, for example C, to C4 alkoxy or halogen and Y2 and Y2\ which may be same or different are independently -RrCL,),- or -Rr ' ' wherein Ry, and*, are independently C, to Cl0 straight or branched chain alkyl linking groups optionally substituted by halogen or ether, for example C, to C4 alkoxy and (L,)B is a polyoxyalkyene group such as polyoxyethylene or more preferably polyoxypropylene or polyoxybutylene; n is from 2 to 20, preferably from 4 to 10. Compounds of formula QUA) are illustrated by (i) the propoxylated derivative of 1,4- butanediol-3-sodiosulphonate (ii) dimemylolpropionic acid ("DMPA") and (iii) dimethylol butyric acid COMBA") *£^,N* DMPA(R = M8) DMBA(R-E0 When the moiety linking X and Z is a ring structure group such as an aryl group, the substituents X and Z in formula (III) may be direct subsuments in the ring for example:-X An example of a compound of structure (MB) is illustrated by esters of 5-sodiosulphoisophthalate (SSI?A) where the groups Rj, which may be the same or different, are a hydrocarbyl moiety having 1-30 carbon atoms optionally linked or substituted by one or more halo, amino, ether or thioether groups or combinations of these. Preferably R, is a C4 to Ca straight or branched chain alkyl group. SOaNa Alternatively the groups X and Z may be joined to the ring structure via linking groups, for example the compound of structure (III) may have the formula (IHC)> rac wherein Y3, Y3' and Y3" may individually represent a direct link between X or Z (as the case may be) and the ring structure or may represent one of the linking groups described above. In particular, Y3, Yj' and Y" may independently have the definitions for Y3 given above. Alternatively Y3, Y3' and Ys" may independently be a group -(L^R* where L, is an ester linking group -C(0)-O, R, is an oxyethylene, oxypropylene or oxybutylene group or polyoxyefhylene, polyoxypropylene or polyoxybutylene group having a degree of polymerisation from 2 to 20. In one embodiment Y3'' represents a direct link between Zand the aryl ring and -Yj- and -Y3'- are both -(L2)R as herein defined wherein R, is oxyethylene and X is -OH. An example of a compound of formula me is Qv) bis(2-hydroxyemyl>5-soidiosulphoisojihthalate CECrSSIPA"). FAX:01344 A further preferred class of compound of structure III has the formula HID:- wherein Rl 0 is a C, to C, straight ox branched chain aUcyl group and the two groups X and JT, which may be the same or different, may be attached to the same carbon atom in the alkyl Jiain ox to different carbon atoms in the alkyl chain, -Lr a linking group which is - R,- wherein R, and L2 are as defined above and Rn is a Cj to C, alkyl group. Compounds of formula (IVA) are represented tor example by SO-Na H ' Raechig Poly-EPS S20-Na (i) PolyGPS 520 available from Raschig wherein -Y- is polyoxyproph/eoe and Y* is a C, alkyl group, (ii) fiie Michael adduct of Jeffamine 1000M (available from Huntsman) and ethylhydroxyethylacrylate wherein Z is a methyl-capped polyoxy etbylene-coutaining polymer linked directly to -NH- and V is a group -Rir(La)- Rj- as defined above in which R» is oxyeihylene [MeOEOnPOBNHCHiCH2COOCH2CH;OH where n is about 18 and m is about 3] (iii) the ethoxylated adduct of Jeffamine Ml 000 wherein Z is a methyl-capped polyoxyethylene-containing polymer linked directly to -NH- and Y is a polyoxyethylene group [MeOEO JO^NHCCHaCHjO)^]. Structure (V) is illustrated by me sulfonate polyester polyol prepared by reacting sodium sulphoisophthalic acid, adipic acid, cyclohexane di methanol, methoxy-polyethylene glycol (mw 750) and trhnethylol propane to give a product having a hydoxyl number in me range offrom 150 to 170. There may be a variation in the structural composition of the product depending on the conditions used. It will be appreciated by those skilled in the art that the reaction will produce a complex mixture of molecules and the structure (V) should not therefore be taken as an exact representation of the sulphonate polyester polyol. Typically however me sulphonate polyester polyol will have at least two terminal -OH groups whilst the sulphonate group provides the -Z group. Structural variations however may mean that the number of moieties -X are average rather than absolute or an exact integer and in particular on average there may not be exactly three -X groups. The polymer wall materials of this invention may be any polymer system conventionally used in microcapsule wall-formation or suitable for such use. Examples include wall materials made by a wide variety of isocyanate polymerisation reactions forming for example polyurea and polyurethane resins, non-isocyanate systems such as polyester, polythioester, polyamide polysulfonamide, polyphosphonamide, polycarbonate and porysiloxane polymers, and the self-condensation of an optionally etherified urea-formaldehyde prepolymer- The use of such polymer resins as wall-forming materials in the manufacture of microcapsules will be familiar to those skilled in the art but the reactions involved may be conveniently summarised as follows wherein the structures in parenthesis illustrate a short¬hand notation for the functional groups produced on polymerisation and are not polymeric structures in themselves:- For the purposes of the present invention however the polymer resin is preferably formed either by an in situ or two phase polymerisation reaction of an isocyanate moiety or alternatively by the condensation of an optionally etherified urea-formaldehyde prepolymer including both self-condensation Qj cross-linking with a suitable agent Tiros according to a further aspect of the present invention there is provided a microcapsule having enhanced dispersibility comprising an encapsulated material enclosed within a solid permeable shell of a polymer resin having incorporated therein at least one surface modifying compound having one to eight functional moieties capable of reacting with at least one isocyanate group present on thxwaUfonning material, which imparts surface activity when incorporated and wherein said surface modifying compound is selected from compounds having the formula 0) (ID (III) (IV) (V) wherein Z is a moiety that contributes to modifying the surface properties of said microcapsule and each X is, independently, a functional moiety capable of reacting with isocyanate and the moieties designated by lines linking the X and Z functional groups have a molecular weight of between SO and 4000, and may be optionally substituted aryl, hydrocarbyl, or heterocyclic unitSj ox combinations thereof, optionally containing internally linked amino, ether, thioether, acetal, ester, tbioester, amide, sulphonamide, methane, urea, carbonate, siloxane, or phoBphonafaide jjTfujps or combinations thereof. Thus in one aspect of the present invention the solid permeable shell of polymer resin is made by isocyanate polymerisation and the surface modifying compound reacts with the isocyanate moiety in the wall forming material. Such wall-forming processes involving either an in situ or two phase polymerisation reaction of an isocyanate moiety will be fiamiliar to those skilled in the art and may be used in the process of the present invention. Suitable isocyanates include, inter alia, aromatic isocyanates such as isomers of tolylene diisocyanate, isomers and derivatives of phenylene diisocyanate, isomers and derivatives of biphenylene diisocyanates, polymemyleoepolyphenyleneisocyanates (PMPPI), aliphatic acyclic isocyanates such as hexamethylene diisocyanate (HMDI), cyclic aliphatic isocyaoates such as i isophoronediisocyanate (IPDI) and trimers of HMDI. Mixtures of isocyanates may also be used. Methods of varying the permeability and thickness of the wall are well known to those skilled in the art and include the type and. amount of waU-forming material and the degree of cross-linking used The present invention may be directed to microcapsule systems having a wall which presents either a signified material Thus tor example microcapsules of the present invention will not generally release the core material until after application to the desired target or utility, almough for some applications the microcapsule wall may be designed to be ruptured on or immediately after application. Alternatively the microcapsules of the present invention may be designed to release core material slowly over a period of time or may be sufficiently robust or to be dried and then re-dispersed. In general it is preferred that the weight ratio of the wall material to the microcapsule (core plus wall) is greater than 1% by weight. Typically the weight ratio will be from 1% to 70% or more specifically from 3% to 15%. The chemistry of microcapsule wall formation from isocyanate molecules with a functionality of 2 or more typically involves reaction with a molecule having two or more functional groups capable of reaction with the isocyanate group. Established preparative methods for predominantly polyurea microcapsules typically involve reaction of the isocyanates with amino-groups. Thus typical isocyanate wall-forming reactions include the reaction with an amine moiety to form a polyurea or with adiior tri glycol to form a polyurethane. The isocyanate molecules are usually contained within the oil phase in the above described processes. The amino groups may be either generated in situ in the oil phase at the oil-water interface as described for example in U.S. Patent No. 4,285,720, incorporated herein by reference, or may be added through the aqueous phase as described for example in U.S. Patent No. 4,280,833, incoiporated herein by reference. Cross-linking may be accomplished by the inclusion of isocyanates having a functionality of greater than 2, or by adding amine compounds such as diemylenetriamine with a functionality of greater than 2. More specifically as described in U.S. Patent No. 4,285,720, a polyurea microcapsule involves the use of at least one polyisocyanate such as polymethylene polypfoenyleneisocyanate (PMPPI) and/or tolylene diisocyanate (TDI) as the wall-forming material. In the in situ creation of such polyurea microcapsules, the wall-forming reaction is initiated by heating the emulsion to an elevated temperature at which point some isocyanate groups are hydrolyzed at the interface to form amines, which m turn react wim unhydrotyzed isocyanate groups to form the polyurea microcapsule wall. The present invention is also applicable to variations in conventional walKorming processes. For example the incorporation of acetal containing structures to form acid-triggerable microcapsules is described in PCT Patent Application WO 00/05952. Catalysts may be used to promote reaction between isocyanates and nucleophiles, particularly when the nucleophile or the isocyanate is relatively unreactivc. When such reaction is accomplished in a homogeneous oil phase, catalysts such as dibutyltin dilaurate are suitable. When such reaction is accomplished at the interface of an oil-in-water emulsion, phase transfer catalysts such as those described in U.S. Patent No. 4,140,516 are suitable. Whilst the isocyanate-based process of the present invention is generally applicable to a wide range of isocyanate wall-forming reactions such as those described above, the in situ polyurea process such as that described in U.S. Patent No. 4,285,720 and the two phase process such as that described for example in US Patent No 4,280,833 are generally most conveoient According to a still former aspect of the present invention mere is provided in a process for the production of microcapsules by self-condensation of an optionally ethcrificd urea-fbimaldehyde prepolymer, wherein an emulsion is prepared in which the discontinuous phase contains the prepolymer and one or more materials to be encapsulated, and wherein microcapsules are formed by self-condensation of the prepolymer adjacent to the interface between the discontinuous phase and the continuous phase of the emulsion, the step comprising reacting the prepolymer, before and/or after preparation of the emulsion, with a surface-modifying agent selected from compounds having the formula X-z X—z-X x I x X-X-z X—|—z X (i) oo (i«> («v) (V) whereXis OH, SH,orNHA, A is hydrogen or C,-C4 alkyl and Z is a moiety that contributes to modifying the surface properties of a microcapsule shell produced by self-condensation of the prepolymer, and the moieties designated by lines linking the X and Z functional groups have a molecular weight of between SO and 4000, and may be optionally substituted aryl, hydroearbyl, or heterocyclic units optionally containing internally linked amino, ether, thioether, acetal, ester, tbioester, amide, sulnhonamide, urethane, urea, carbonate, siloxane, or phosphonamide groups or a combination thereof In addition to self-condensation of the optionally etherified urea-formaldehyde prepolymer, the scope of the present invention also includes the optional inclusion of a cross-finking agent providing cross-linking condensation between the pre-polymer and the cross-linking agent Thus preferred materials utilized in forming the wall of the microcapsules of this invention also include optionally etherified urea-formaldehyde resins, (urea-formaldehyde prepolymers). Preferably they are etherified and comprise urea-fcrmaldehyde prepolymers or resins in which the methylol (-CH^OH) groups have been etherified by reaction with an alcohol, preferably a C4-C,0 alkanol, most preferably n-butanoL Preferably from about 50 to about 98% and most preferably from about 70 to about 90 % or from about 70 to about 95%, of the methylol groups in the prepolymer have been etherified. Etherified urea-formaldehyde prepolymers suitable for use in the invention include those available, for instance, under the Beetle trademark from American Cyanamid, the Resimene trademark from Solutia, and the Beckamine trademark from Reichold Chemicals. Processes for production of aminoplast microcapsules in the present invention are described in U.S. patents 4,956,129 and 5332,584, which are hereby incorporated herein by reference. La general, the chemistry is believed to involve the self-condensation of the etherified urea-formaldehyde prepolymer. Cross-linking and other wall-modifying agents such as pentaerythritol and pentaerythritol derivatives may be included in the process to provide additional cross-linking. Other suitable cross-linking agents include those containing hydroxyl, amine and thiol functional groups, particularly polythiols. One particularly useful 5 cross-linking agent described in the above-mentioned U.S. patents is pentaerythritol tetrakis (3-mercaptopropionate), sold under the trademark Mercaptacetate Q-43 Ester. The exact nature of the wall chemistry of these microcapsules is not known for certain, and we do not wish to be bound by theory. However, it is believed that self-condensation or cross-linking of methylol and/or etherified methy lol groups in the 10 prepolymer involves the formation of new either and/or thioether and/or -NCH^N- groups. It will be appreciated that the chemistry of the reaction of the group-X with the wall-forming material will vary as between the various isocyanate systems and aminoplast systems and different surface-modifying agents may be preferred depending on the wall-forming system used. Isocyanate systems will be considered first 15 Tne surface rnc^lifymgajrorwur^ functional groups (designated as X) capable of reacting with wall forming material, in this instance with isocyanate. The reactions of the rooiety X with isocyanates are illustrated herein below using structure (IA) for simplicity although the reactions of the remaining structures correspond accordingly. For example, carboxylic acids react with isocyanates to 20 form mixed anhydrides that rapidly eliminate carbon dioxide with the formation of carboxylic amides: RNCO + Z-Y-CO2H -> [RNHCOOCO-Y-Z1] -> Z-Y-CONHR+ C02 Thiol, hydroxyl and amino groups react with isocyanates to form respectively thiocarbamate, urethane, and urea linkages: 25 RNCO+Z-Y-SH ■ KNHCO-S- Y-Z thiocarbamate linkage RNC0 + Z-Y-0H -> RNHC0-O-Y-Z urethane linkage RNCO + Z-Y-NHA^RNH-CO-NA-Y-Z urea linkage ■While any functional group of the above types may be used to introduce surface modifying compounds into the microcapsule walls of the present invention, hydroxyl and 30 amino groups are particularly preferred unless a slower reaction is desired as discussed below. The preferred groups are chosen on the basis of the process and on the desired properties of the microcapsule wall as is discussed in greater detail below. The reactivity of the functional group with the isocyanate influences the process of choice. For example, the reaction with amines is very fast, allowing modification from an agent in the aqueous phase with waU-fonrung materials in the oil phase. In contrast, the reaction with alcohols or thiols is much slower and may compete less favourably with hydrolysis of the isocyanate if the surface modifying compound is introduced from the aqueous phase. Reaction of isocyanates with these molecules is thus more readily accomplished in the oil phase. The stoichiometry of the reaction of the surface-modified compound and the isocyanate will detennine the degree of polymerization of the resulting surface modifying jyimpnW to be incorporated into the wall. For example, with only a slight excess of the total isocyanate moieties over the total -X moieties for difunctional (i.e. with two groups X) surface modifying compounds and difunctional isocyanates, relatively high molecular weight material may be produced. In certain instances, this product may be soluble in the aqueous phase and thciefbre may not be readily available for incorporation into the wall. Such a case may arise, for example, with a diol surface modifying compound or prepolvma carrying several sulphonate groups. At higher ratios of isocyanate to surface modifying compound, lower degrees of polymerization result It will be appreciated however that in any event the polymer initiating groups of the waU-forming material, for example the isocyanate groups, should not be fully reacted with surface modifying compound since wall-formation cannot then take place. Whilst in some situations wall formation may take place in competition with the reaction between isocyanate and the surface modifying compound even at stoichiometrics of about 1:1, it is preferred that there is an excess of (total) isocyanate groups over (total) groups -X Thus for example in me reaction between ft difunctional isocyanate wall-forming material such as TDI and a difunctional surface modifying compound (i.e. a surface modifying compound having two groups -X) such as dimethylorpropionic acid (DMPA) molar ratios of TDI'JDMPA of from 4:1 to 15 :1 are preferred. When the surface modifying compound is added via he aqueous phase, the degree of modification may be altered by changing the mass in ihe aqueous phase whilst keeping the amount of isocyanate the same. Typically, the surface modifying compounds of the present invention have molecule weights of about 2000 or less. It may be preferred to have molecular weights of less than 10,000 in prepolymers that have been reacted with the surface modifying compound(s). Thus in general the preferred ratio of the total moiety(ies) -NCO in the wall-forming material to the total reactive moietyCies) -X in the surface modifying compound is from 2 :1 to 25 :1 and more preferably from 4 :1 to 15 ; 1. Thus for example when a difunctional isocyanate (such as TDI) is reacted with a difunctional surface modifying compound (such as DMPA) this ratio remains 2:1 to 25 ; 1 and more preferably from 4:1 to IS : 1 on a molar basis, whilst for PMPPI (a multifunctional typically isocyanate with an average functionality of 2.7) reacted with a monofuncuonal surface modifying compound such as MeOPEG, this equates to molar ratios of PMPPI: MeOPEG of from 0,75 :1 to 9.3 :1 and more preferably from 1.5:1 to 5.6:1. Where more than two functional groups (X) are present in either the surface modifying compounds or the isocyanates, it is possible to generate cross-linking reactions. These reactions may be undesirable if they occur before the wall-formation proper takes place. When two functional groups are present ra the surface mcKlifymg ocnnpou^ with a difunctional isocyanate will result ma linear cbmi-extenQ^ surface modified molecule. The use of excess difunctional isocyanate in the reaction controls the degree of polymerization of the isocyanate extended product. It may be preferred to have alpha-omega isocyanate terminated molecules. In order to minimize or avoid cross-linking until the desired moment, isocyanates having a functionality of greater than2 are preferably added to the oil after the chain extension reaction and before emulsification. When one functional group (-X) is present in the surface modifying compound, it imry he preferred to react this molecule with an isocyanate having a functionality of greater man or equal to two. Thus for example MeOPEG may suitably be reacted with PMPPI. The unreacted isocyanate groups can then be used to polymerize by chain extension with other wall-farming materials. Surface modifying compounds having two or more functional groups (-X) may be used if the level of cross-linking with isocyanates prior to wall formation takes place can be controlled. This may be achieved, for example, by reacting surface modifying compounds having a functionality of only slightly greater than 2 with an excess of afunctional isocyanate prior to the optional addition of isocyanates having a functionality greater than 2 to the oil phase after the chain extension reaction and before emulsification, Such a situation, employing the sulphonate polyester pojyol Ulustrated by structure (V) is described in Example 6 below. Alternatively, surface modifying compounds with a functionality greater man 2 may be mixed with isocyanates having a functionality greater than or equal to 2 , provided that the reaction between the surface modifying compoimd and isocyanate molecules can be inhibited until the oil has been emulsified in water. In terms of the aminoplast system, the surface-modifying agents of the present invention contain one or more functional groups (designated as -X) capable of reacting with methylol and etherified methylol groups. Their reactions with the waU-fbrming urea formaldehyde prepolymers axe illustrated herein below using structure (IA) for simplicity although the reactions of the remaining structures correspond accordingly. Far example, hydroxyl groups of a surface-modifying agent are believed to react with methylol or ether groups in me prepotymer to form ether linkages: >NCH20R + HO- Y-2 -»■ >NCH2-0-Y-Z + ROH where R is hydrogen (forming a methylol group) or (C4-C]0) alkyl (forming an ether group). Note, however, mat under cextain conditions this reaction may be reversible and me product containing a new ether linkage >NCH,-0-Y-Z may not be sufficiently stable under the process ccwidrdons. Amino groups in a surface-moctifying agent are believed to react with methylol or ether groups in the prepolymer to form amino linkages: >NCH,OR + AHN-Y-Z -* >NCHjNA-Y,-Z + ROH where A is hydrogen or C,-C4 alkyl. This reaction is expected to be less reversible than the above emer-proclucing reaction, and the products more stable. Thiol groups in a surface-modifying agent are believed to react with the methylol or ether groups in the prepolymer to form thioemer linkages: >NCH20R+HS-Y-Z -► >NCH,-S-Y-Z + ROH FP This reaction is expected to be less reversible than the above ether producing reaction and the products more stable. In general therefore it is preferred that-X is an amino or in particular a thiol group when an aminoplast system is used The reactivity of the functional group in the surface-modifying agent with the prepolymer irtfluemvis the choice of process as well as of the surface-modifying compound. FoTe«rap\e>theTeaxtionwi1ih1^ modification from a surface modifying compound in the aqueous phase with wall-forming materials in the oil phase. The stoichiometry of the reaction of the surface modifying compound with the alkylated urea-fonnaldehyde pre-polymer will depend on: (i) the structure and molecular weight of both the modifier and the resin, (ii) the required degree of modification, (iii) the mechanism of the reaction. Commercial alkylated U-F resins are available in a range of molecular weights and degrees of alkylation. For the purpose of illustration only a simplified representation of a repeat unit in the resins used in this invention is given by the formula - [NfCHPR^O-N(CH20R>CHJ.- where R is hydrogen (forming a methylol group) or C&- (fonning a butyl ether group) and nhas a value between 1 and 1000. The surface modifying compounds are reacted with the-OR groups as described above in a ratio which is preferably determined by routine oqjerimentation and where sufficient of the OR groups are reacted so as to impart surface-active properties to the modified resin, with sufficient OR groups remaining to enable self-condensation or cross-Unking reactions to form the microcapsule walL If an excess of OR groups are reacted the modified resin may become water soluble and thus unavailable for incorporation into the capsule wall For a given molecular weight, the greater the hydrophiheity of the surface modifying agent the lower will be the stoichiometric ratio of agentOR groups necessary to impart surface-active properties. For example, and in general for a given molecular weight a lower stoichiometric ratio of agentOR groups would be required for sulphonate containing man carboxylate containing surface modifying agents. For a given structural type of surface modifying agent such as a methoxy-poryefhylene glycol MeO(EO)«- the higher the molecular weight (value of m) the lower will be be the ratio of agentOR groups necessary to impart surface-active properties. In addition, the preferred stoichiometric ratio of agentOR groups may depend on the relative reactivity of the surface-modifying agent with methylol and with butyl ether groups on the resin. It has been round convenient to estimate the amount of surface modifying compound used based roughly on the number of theoretical U-F repeat units (where the degree of alkylation is as defined by the supplier of the resin) in a given molecular weight of the alkylated U-F resin. Preferred stoichiometric mole ratios surface modifying agent:U-F repeat unit are between 1:40 to 1:4. The choice erf the preferred surface modifying compound for use with any given microcapsule wall-forming system will depend on a range of factors. Thus for example in the isocyanate polyurea system mere are practical advantages in addition of the surface modifying compound through the aqueous phase, for which process it is preferred that -X is amino. On the other hand there are other advantages in (he pre-reaction of isocyanate with the surface modifying compound, and in particular it is an advantage that the course of reaction can be monitored using infra-red analysis. When -X is thiol or hydroxy it is preferred that's the reaction with isocyanate takes place before emnlsfication, Clearly however the ease and convenience of the reaction of the surface modifying compound with the isocyanate group(s) is not the only factor to be considered. Once reaction has taken place the nature of the surface modification provided by the remainder of the surface modifying compound becomes key. In commercial terms the cost of the surface modifying compound is also a factor to be considered. The nature of the core material is not critical to the scope of me present invention and any material suitable for microencapsulation may be used as core material. The benefits of the present invention may however be of particular relevance to specific core materials and applications. For example the microcapsules of the present invention will find particular utility in applications for which microcapsule stability, aggregation and re-dispersibihty tend to present problems. The core material is typically a liquid and, in the case of agricultural products, may be comprised of one or more pesticides, or, in the case of non-agricuhural products, may be comprised of inks, dyes, biological actives, pharmaceuticals or other products. For agricultural products, the core may be an organic solution, typically immiscible with water, comprising one or more pesticides as the active ingredient, including insecticides, herbicides, fungicides and biocides. The pestiddernay be a liquid, a solid pesticide that has Ff been dissolved in a solvent tbat is immiscible with water, or a sohd suspended in the organic solution that may have within h another pesticide. The organic solution may also have an photostabilising protectant suspended or dissolved within it. Any agrochemical which is suitable fox microencapsulation may be used, but by way of illustration only, examples of suitable herbicides are s-triazines, e.g., atrazine, simazine, rxopazine, cyprozine; Sulphonylureas e.g., chlorsuliuron, chlorimuronethyl, metsulfuron-methyl, thiameturon-methyl; foramsulfuron, iodosulfom and Triketones e.g., sulcotrione. Another suitable compound is the fungicide ^rneuiyl^-^d^^anoplienQxy^yrmudin' 4-yloxy)pharyl]-3-methoxypropenoate. Examples of suitable insecticides include permemxin, cypermcthrin, deltarnjethrin, fenvalerate, cyflumrin, resroethrin, aUethrin, etofenprox tefluthrin and lambd^-cyhalomrin. Hie liquid in which the solid is suspended may suitably be a second herbicide, especially a thiocarbamate or a haloacetanilide, and preferably acetochlor. The ■ ^ haloacetanilides, particularly the subclass generally known as a-chloroacetanilides, are a well-known class of hcrbicidal agents and have been used and proposed for use in a number of crop and non-crop applications. Some of the better known members of mis class include a-^Woro^-etlryl-N^2-methoxy-l-inemylemyl>Bcetanilide (metolachlor), N-butoxymethyl-CrtbJoro-2^6MiemylacetaniIide (butachlor), a-chloro-2',6'-diethyl-N-mefcoxymsthylaceti>Tiilide (alachlor), 2K;bJorc-N'(e^oxymethyl)^^thyls5-acetotoluidide (acetochlor) and a-chloro^N-isopropylacetanilide (propachlor). Many other compounds of this type are disclosed in numerous patents. The fhiocaxbamates are a well known class of herbicide which includes Molinate (S-ethyl hexabydio-lH-azepine-l-carbothioate); Butylate (S-ethyl diisqburylmiocarbamate); EPTC (ethyl dqiropylthiolcarbamate); Triallate (2,3,3-trichloroallyl-diisc^opylthiolcarbamate); Diallate (cia-l-ttan3-2^-djchloroallyl-diisopi^ylthiolcarbamate); and Vernolate (S-propyl dipropyltbiolcarbamate). When the liquid is an herbicide, the microcapsules of the invention suitably contain 0.1-55% by weight of biologically active compounds. The liquid may alternatively be any organic solvent that is immiscible with water, and is polar enough to dissolve the monomers, oligomers or prepolymers used to form the walls of the rraoocapsules Suitable solvents arewellknown to mose skilled in the art By way of illustration, examples of such solvents are aromatic compounds such as xylenes or naphthalenes, especially Sofveaso 200; aliphatic compounds such as aliphatic or cycloaliphatic hydrocarbons, for example hexane, heptane and cyclohexane; alkyl esters such as alkyl acetates for example Exxate 700 or Exxate 1000 and such as alkyl phthalates for example diethyl phthalate and dibutylphthalate; ketones such as cyclohexanone or acetophenone; chlorinated hydrocarbons; and vegetable oils. The solvent may be a mixture of two or more of the above solvents. A safener for either herbicide may be present, and paany such safeners or antidotes are well knovvn in the art Preferred types for use with haloacetanilide herbicides include dichloroacetamides such as dichlonnid (N,N-diaUyl dicbioroax»tarnide)^1S-trhneuyl-3^chloroacetyl oxazobdine (R-29148),N-dichloroacetyl-l -oxaa2aspiro(4,5]decane(AD 67) 4 dichloroacey benzoxazine (CGA-154281); 1 p ynmidin-6(2H)»one and N^13^oxolan-2-yl-methyI>N^2-propenyl>2^^chloroacetamide (PPG-1292). These and other dichloroacetamides are described, for instance, in U.S. Pat. Nos. 4,124,372; 4,256,481; 4,294,764; 4,448,960; 4,601,745; 4,618,361; 4,708,735 and 4,900,350. Additional known types of safeners or antidotes include certain oxime derivatives (U.S. Pat Nos. 4,070^89 and 4,269,775, for instanoeX thiazole carboxylic acids and derivatives (U.S. Pat. No. 4,199,506 for instance), haloacyhetrahydroisoqiiiTinlines (U.S. Pat No. 4,755,218, for example), aryl cyclopropane carbonrtriles (U.S. Pat No. 4,859,232, for example) and 1,8-naphthalic acid, its anhydride and derivatives. Safeners or antidotes, when included, will usually be contained in the organic or water-immiscible phase. When a pbotostabilising protectant is used in mis uwentkm, ft is preferably titanium dioxide, zinc oxide, or a mixture of titanium dioxide and zinc oxide. In general, the photostabilising protectant is used in an amount of from about 0.1 to about SO weight %, preferably fiom about 1 to about 10 weight %, with respect to the organic phase. Mixtures of titanium dioxide and zinc oxide will contain these two substances in a weight ratio of from about 1:10 to about 10:1. Biologically active materials suitable for the present invention that are subject to degradation or decomposition by ultraviolet light and therefore requiring a protectant include the pyrethroidfi and pyremtms. Many of the pyrethroids known to be susceptible to degradation by ultravoilude pennethrin, cypennethrin, deltamethrin, fenvalerale, cyfluthrin, resmelhrm, aUethrin, etofenprox, and lambda-cyhalothrin. Other biologically active materials that axe known to be susceptible to degradation or decomposition by ultraviolet light include the herbicides triflnralin, ioxynil and napropamide, the insecticides piruniphos-mefhyl and chlorpyrifos and the fungicide azoxystrobin. Microcapsules of this invention may contain two or more ultraviolet light sensitive biologically active materials. The liquid utilized in this invention may be a liquid biologically active material which itself is susceptible to degradation by ultraviolet light, or a biologically active material which is not normally so susceptible (but in which there is suspended a second biologically active material which is light-sensitive), or an organic solvent which is immiscible in water and in which the ultraviolet light sensitive material is suspended or dissolved. The liquid, in any case, should be sufficiently polar to dissolve the prepolymer or prepolymers used to form the microcapsule wall Capsule suspensions of the present invention may also be produced containing two materials that may be incompatible with each other, with one material encapsulated and the other contained in the aqueous phase of the suspension. Such combination products are storage stable and enable, for example, the production of a combination pesticidal product wherein incompatible pesticides may be applied together. Those skilled in the art will be readily able to apply conventional processes for the preparation of microcapsules according to the invention in non-agrochemical fields including but not limited to encapsulated dyes, inks, pharmaceuticals, flavouring agents and fragrances. Oil-in-water techniques are generally more suitable although the present invention also includes water-in-ofl microencapsulation techniques. Conventional solvents may be used for the oil phase such as those described above in connection with microcapsules for agrochemtcal use. According to a further aspect of the present invention there is provided a modified process &r the encapsulation of a dispersed material within a solid permeable shell of a polymer resin formed by polymerisation of a wall-forming material which comprises incorporating a surface modifying compound having a formula (3), (H), (HI), (IV) or (V) as hereinbefore defined into the polymer resin. The incorporation of the surface modifying wonpoundm the polymer resm wall of the microcapsule may take place at various stages during the microencapsulation process. FA: Process^ One process for preparing such microcapsules comprises pre-reacting the surface modifying compound and a. wall-farming material (for example a monomer, oligomer or prepolymar) in an organic phase, for example: (a) reacting a surface-modifying compound or agent with at least one wall-forming material thereby forming a modified surface-active intermediate; (b) preparing an organic solution or oil phase ciornphsii^ me material to be encapsulated, the modified surface-active intermediate, and, optionally, additional waU-forming material; (c) creating an emulsion of me organic solution in a continuous phase aqueous solution comprising water and, optionally, a protective colloid, wherein the emulsion comprises discrete droplets of the organic solution dispersed throughout the continuous phase aqueous solution, with an interface formed between the discrete droplets of organic solution and the aqueous solution; and either (d) outsmgtejinr polymerization and/or curing of the modified wall-forming material in the organic solution of the discrete droplets at the interface with the aqueous solution by heating me emulsion for a sufficient period of time andoptionally adjusting the pH to a suitable value to allow substantial completion of wall formation, thereby converting the organic solution droplets to capsules consisting of solid, permeable, modified polymer shells enclosing the material, or as an alternative to (d) (e) causing polymerization at the oU-water interface material added through, the aqueous continuous phase and capable of reacting with the wall forming materials) in the discontinuous oil phase. In stage (a) above the pre-reacuon of the surface modifying compound and the wall-farming material to form the surface-active intenriediaternay either take place ra phase to be encapsulated or in a different or separate organic phase from which the modified surface-active intennftdiate may optionally be isolated before use in stage (b). In stage (d) above and in corresponding stages of the processes described below, aminoplast systems generally required adjustment of the pH. Adjustment of the pH is sometimes also used in isocyanate systems. : Process 1 above is suitable for bow aminoplast and isocyanate waU-foiming systems. The functionality of the wall-forming material and the surface modifying compound respectively should preferably be such that their reaction does not lead to excessive cross-linking such that the emulsification or subsequent wall-forming reactions are adversely affected. Thus for example for reaction with difunctional isocyanates mono- or difuncdonal surface modifying compounds are preferred. For reaction with isocyanates having a functionality greater man 2, monoronctional surface modifying compounds are preferred. For reaction with polyiunctional alkylated urea-formaldehyde resins monofunctional surface modifying compounds are also preferred. Certain intermediates produced by reaction of the waU-fonning material and the surface-modifying compound in step (a) are novel, as is the process for their preparation, and both the intermediates and processes for their preparation constitute further aspects of this invention Process 2 A second process for preparing such wall-modified microcapsules cornprises preparing an organic solution or oil phase comprismg the material to be encapsulated, the surface modifying compound and the wall-forming material, and allowing the surface modifying compound to react with the wall-forming material under the conditions of me in situ polymerization and/or curing, for example; a) preparing an organic solution or oil phase comprising the material to be encapsulated, the surface modifying compound and the waU-forrning material b) creating an emulsion of die organic solution in a continuous phase aqueous solution comprising water and, optionally, a protective colloid, wherein the emulsion comprises discrete droplets of the organic solution dispersed throughout the continuous phase aqueous solution, with an interface formed between the discrete droplets of organic solution and the aqueous solution; and either c) causing in situ polymerization and/or curing of the modified wall-forming material in the organic solution of the discrete droplets at the interface with the aqueous solution by heating the emulsion for a sufficient period of time and optionally adjusting the pH to a suitable value to allow substantial completion of wall formation, thereby FP converting the organic solution droplets to capsules consisting of solid, permeable, modified polymer shells enclosing the material; or optionally in addition to (c) (d) causing polyrneri?ation at the oil-water interface by bringing together a wall forming material added through the aqueous continuous phase and capable of reacting with the wall forming materials) in the discontinuous oil phase. Process (2) above is suitable for both the isocyanate and aminoplast wall-forming systems. The functionality of the wall-forming material and the surface modifying compound is not critical. Preferably the reactivity of the group(s) -X with the waU-forming material are such mat incorporation of the surface modifying compound into the wall material takes place at the oil-water interface before or at the same time as wall formation and the reaction product of the surface modifying compound and the wall-forming material remains at the interface rather than dissolving in the aqueous phase. Process 3 la a third process, the surface modifying compound may be incorporated in the aqueous phase rather than the organic phase. Thus a third process for preparing wall-modified microcapsules comprises: (a) preparing an organic solution or oil phase comprising the material to be ericar^ulated and the wall-forming material; (b) creating an emulsion of the organic solution in a continuous phase aqueous solution comprising water and the surface-modifying compound(s), wherein the emulsion comprises discrete droplets of the organic solution dispersed throughout the continuous phase aqueous solution, with an interface formed between the discrete droplets of organic solution and the aqueous solution; and (c) causing fej^ polymerization and/or curing of me waU-forming material so that the surface-rnodifying molecule(s) is incorporated mtoth^waU by beating nV emulsion for a sufficient period of time and optionally adjusting the pH to a suitable value, to allow substantial completion of wall formation, thereby converting the organic solution droplets to capsules consisting of solid, permeable, modified polymer shells m^Ue4 by shear and amount of cmulsifier used to make the emulsion. High levels of surfactants, which normally work by adsorption at me intermce, can often adversely affect the integrity of the microcapsule wall. The present invention resides in both the process for preparing such rnicrocapsules and me microcapsules thus formed. One aspect of this invention describes microcapsule wall compositions having one or more surface modifying compounds bonded therein. These compounds may be anionic, FA cationic, zwiterionic, and/or nonionic in nature ox various combinations of the same depending on the nature of the group Z. Charged agents may or may not be switchable between ionized and non-ionized forms. The presence of ionic groups at the surface of microcapsules provides a means of charge repulsion between adjacent particles and this aids colloid stability of the formulation. Charge repulsion may be between either separately positive or negative groups. Examples of positively charged groups -Z include quaternary ammonium. Examples of negatively charged groups -Z include sulphonate, carboxyl and phosphonate. Colloid stabilization may alternatively be effected by non-charged hydrophilic moieties that maintain stability by preventing particles from interacting by steric repulsion. Examples of such moieties include oxyethylene- containing polymers. The surface-modifying compounds may further serve to change the properties of the microcapsule wall such that the capsules may, for example, become more or less adhesive to a particular surface . The preferred method of stabilization will depend upon the desired application of the microcapsule product For example, positively charged structures may adherc-rtrrmgly to negatively charged biological material such as foliage and soil. The invention is further illustrated by the following examples; however such examples should not be interpreted as a limitation on the invention: Exemplification, of Capsule Formation - EXAMPLE 1 Incorporation of an anionic sulfonate diol into the polyurea walls of microcapsules cemtaining Acetochlor using Process (1) above. This experiment demonstrated that a sulfonate diol can be incorporated into microcapsule walls by attachment to tolylene diisocyante (TDI") in the oil phase prior to encapsulation. A sulfonate diol of the following formula - wherex +y = 3,4 or 6, was reacted with tolylene diisocyanate ("TDI") forming a chain-extended surface modifying compound according to the following reaction - H(PO)„0 ^ ^^ * S03Na NCO o The sulfonate diol was dissolved in methylene chloride (CKUCy and gradually added at room temperature to a methylene chloride solution of TDI while stirring. The mixture was heated to 35°C and analyzed by an Ht spectrometer to monitor the progress of the reaction which was indicated by the diminishing of the -OH stretching peak at 3400 cm'1 and the increasing of me polyurethane (-O-CO-NH-) peaks at 1720 cm"1 (C=0) and 3300 cm"1 (-NH-). After reaction, the methylene chloride was removed by increasing the temperature of the solution to 40°C. In order to rmnimi>* possible polymerization reactions, excess amounts of TDI were used in the reaction. The molar ratios of the sulfonate diol/TDI used were 1:3 and 1:5 (the stoichiometric ratio is 1:2). The chain-extended TDI sulfonate diol (1.35g) was added to an organic phase comprising a solution of the pesticide acetochlor (23.65g), (dichlormid (KN-diallyl-2,2-diduoioaeetamide)) (3.93g), polymethylene polyphenylene isocyanate ("PMPPT) (l-S2g), and Atiox 3409/Atlox 3404 emulsifier (0,95g). This organic phase was then added to a separate aqueous phase comprised of water and either OVo, 1% or 2% REAX100M (a lignosulfonate available from Westvaco) as a protective colloid, and stirred at a fixed speed and time for each level of REAX 100M, thereby creating an oil-in-water emulsion. The emulsion was heated causing polymerization of the waU-fbrming material wim sulfonate groups attached therein, thereby forming microcapsules averaging from 4.5 to 32 microns in diameter, depending upon the amount of protective colloid found within die aqueous phase. Microcapsules formed with the sulfonate group derived from reaction of the surface modifying compound and the wan-fanning znataial were compared against microcapsules ' § prepared following the same process, but without the incorporation of the surface modifying compound. The compositions (la and lc below) containing surface modifying compounds had a greater emulsrfication effect than the compositions (lb and Id below) without the surface modifying compounds, and required less energy for emulsification whilst producing smaller emulsion particles, and consequentially, smaller microcapsules as shown below - Composition Presence of Sulfonate Wall-Modifying Compound % Protective Colloid in Aqueous Phase Agitation Emulsion Particle Size (Microns) State of Microcapsule Dispersion la Yes 2% 3000 rpm, 0.5 min 4.5 Fully dispersed lb No 2% 3000 rpm, 1.0 min 32 Fully dispersed lc Yes 1% 3000 rpm, 3.0 min 10 Fully dispersed Id Ho 1% 3000 rpm, 3.0 min 28 Fully dispersed le Yes 0% 3000rpm, 3.0 min 25 Fully dispersed If No 0% 3000 rpm, 3,0 min 25 Agglomerated and Gelled A dispersant, such as lignosulfonate or polyvinyl alcohol, is generally required in the rxncroencapsulation process to stabilize the particles, fa the presence of the sulfbnate-containingwall modifying compound, a rnicrocapsulc formulation can be maa^wrthc^ using any protective colloid, reflecting the dispersant function of the sulfonate moiety, as illustrated in the example above (Composition le). In contrast, formulations made in the absence of a protective colloid, Le., without the incorporated surface modifying compound, gelled during reaction (If). These results reflect the dispersant function of the sulfonate moiety due to the charges built into the wall through surface modification according to the invention. In the example the release rate of Acetochlor and dichlonnid (N,N-diallyl-2,2-dichloroacetamide) was not affected by the incorporation of the surface modifying compound. EXAMPLE 2 Incorporation of an anionic sulfonate diamine (Poly-EPS 520-Na) into the polyurea walls of microcapsules containing Acetochlor using Process (3) above. This experiment demonstrated that an anionic sulfonate diamine can be incorporated into microcapsule walls via reaction from the aqueous phase, thereby improving dispersibility and redispersibility of the capsules as well as affecting the release characteristics of the capsules. A sulfonate diamine of the following formula - ^ ° L ^ TrK^ ^f>T ^^ ^SO,Na H 3 commercially available from Raschig as Poly-EPS 520-Na, was used to prepare acetochlor-conlaining microcapsules. However, instead ofpre-reacting the sulfonate diamine with TDI and then adding to the organic phase, the diamine was dissolved in the aqueous phase. Microcapsule formulations were thee prepared as in Example 1 above with and without Reax 100M (protective colloid) in the aqueous phase of the formulation. The reaction between -NH2 and/or -NH- and -OCN at the oil/water interface allowed the compound containing the sulfonate groups to chemically bond to the microcapsule wall. The sulfonate diamine wall-modified microcapsules showed significant dispersant function. In the presence of the sulfonate diamine in the aqueous phase, well-dispersed strong microcapsules were formed without the use of the protective colloid Reax 100M. In contrast, in the absence of the protective colloid Reax 100M and the sulfonate diamine surface modifying compound, oil particles were recombined during the reaction and a glue¬like gel was formed. With respect to the release rate of Acetochlor from the microcapsules, small amounts of sulfonate diamin» in the aqueous phase that were chemically bonded to the wall, e.g., 3.0% sulfonate diamine, reduced the release rate of the microcapsules. In contrast, larger amounts of sulfonate ^«min»s e.g., 6.0%, increased the release rate of Acetochlor. EXAMPLE 3 Incorporation of an anionic sulfonate diamine (Poly-EPS-520-Na) into the polyurea walls of microcapsules containing Lambda-cyhalothrm usuu> Process 3 above. The use of certain water soluble polymers which coat microcapsules during spray drying and which aid redispersion is known in the art and is exemplified in EP 0869712 which is incorporated herein by reference. This experiment demonstrated that an anionic sulfonate diamine can be incorporated into microcapsule walls via reaction from the aqueous phase, markedly improving redispersibUity of spray-dried capsules without the need for a polymeric coating, as well as improving the storage stability of those capsules. Wall-modified microcapsule suspensions containing Lambda-cyhalothrin were prepared as described in Example 2 above. The lambda-cyhalothrin microcapsules produced had a typical wall of approximately 7.5 weight percent of the microcapsule. The capsule suspensions were diluted in equal ratios with water and then spray-dried using a Buchi Mini Spray Drier unit. The spray-drying conditions were as follows: Air Spray Rate 600 Inlet Temperature 140°C Outlet Temperature 70°C Feed Rate Adjusted between 3 and 5 ml/nun in order to maintain outlet temp The ability of the dry powder to spontaneously redisperse when added to water was assessed. The particle distribution and size was evaluated by adding the dry product to water in a vial that was inverted 10 times. The resulting dispersion was men screened by optical microscope and an LS-Coultcr particle size analyzer. The test was carried out at initial day and after storage ofthe dry product in a sealed combiner at 50°C for three days, 10 days and three weeks respectively. The results ofthe surface modified capsules versus non-surface modified capsules are given in the Table below: Additives (Based on Dry Product) RedispersionTest- Average Particle Size Distribution' Polymer Dispersant Wetter Salt Initial Day 3 Days at50°C 10 Days at 50°C 3 Weeks at50°C Non-Surface Modified Capsules None 15% LomarD 1.5% Gcrapon T-T7 10% CaCIj 37.3 microns 63.3 microns 64.5 microns 40.2 microns Surface Modified Capsules None 15% LomarD 1.5% Gerapon T-77 10% CaCl2 4.0 microns 5.1 microns 9.0 microns 8.8 microns * mean microcapsule diameter Was approximately 2.5 microns. Hie above results shows that wall modified microcapsules significantly improve redispcrsibflity of spray dried capsules versus non-modified capsules. EXAMPLE 4 Incorporation of a nonionic polyoxyalkylene molecule into foe walla of polyurea microcapsules containing Acetocblor using Process (3) above. This experiment demonstrated that a nonionic polyoxyalkylene molecule can be incorporated into microcapsule walls via reaction from the aqueous plwse, thereby unprovmg redisrjersibUity of the capsules and affecting the release characteristics of the capsules. A polyoxyau^ler* molecute of te where PO is propylene oxide, EO is ethylene oxide, y + z =5, and x = 39.S (commercially available as Jeffiunine ED2003 from Huntsman) was used to prepare AcetochlcrPOiNHa, where EO and PO designate respectively -CHJCHJO- and -CHMeCH,0- groups. Reaction with HEA gives the adduct MeOE01^03NHCH2CH2CXX^i3CH3OH in which the -NH- and -OH groups can react with isocyanate groups. A solution of the above steric stabilizer (0.7g) and dibutyltin dihuirate (0. Ig) in Acetochlor (20g) was added at room temperature over 10 minutes to a stirred solution of tolylene 2,4-dusocyanate (4g) in Acetochlor (20g). The mixture was heated at SO°C for 1.5 hours to give the 'oil' phase that was emulsified using a Silverson stirrer into a solution of Reax 10OM (0.7g) and Terghol XD (0.7g) in water (42.9g) cooled to 8°C. The temperature rose to about 14°C. The emulsion was paddle stirred at SO'C for 3 hours to give about 5 micron diameter microcapsules. The capsule suspension was spray dried and the dry powder was tested for redispersibility as described in Example 11. EXAMPLE 6 Incorporation of a sulfonate stabilizer into the walls of poiyurea microcapsules containing Acetochlor using Process (1) above. A sulfonate ("SSIPA") polyester polyol was prepared by reacting sodium sulphoisophthalic acid, adipic acid, cyclohexane dimethanol, methoxy-poryethyiene glycol (mw 720) and trunefhylol propane to give a product having a hydroxyl number in the range of from 150 to 170. A solution of the above sodium sulfonate polyol (0.2g) and dibutyltin dilaurate (O.lSg) in Acetochlor (30g) was added at room temperature over 10 minutes to a stirred solution of tolylene 2,4-diisocyanate (4g) in Acetochlor (lOg). The mixture was heated at 50°C for 2 hours then cooled to room temperature and polymethylene poryphenylene-isocyaoate (0.13g) was added to give me oil phase. The oil was emulsified using a Silverson stirrer into a solution of Reax 100M (0.7g) and Tergitol XD (0.7g) in water (42.9g) cooled to 10*C. The emulsion was paddle stirred at 50°C for 3 hours to give about 5 micron diameter microcapsules which were smooth, spherical, strong with no leakage on drying and were re-suspendable in water. The capsule suspension was spray dried and the dry powder was tested for redispersibility as described in Example 11. EXAMPLE7 Incorporation of dimethylol propionic acid ("DMPA") into the walls of poryurea microcapsules containing Acetochlor using Process (1) above. This experiment demonstrated that dimethylol propionic acid ("DMPA") piOCHjCMeCCOjH^H^OH] can be incorporated into microcapsule walls in a formulation containing a free emulsifier and colloid stabiliser. A solution of DMPA (O.lSg, 1.12mmoI) and dibutyltin dilaurate (O.lSg) in Acetochlor (Sg) and dimethylacetamide (0.5g) was added to a stirred solution of tolylene 2,4-diisocyanate (TDI, 2.4 g, 13.79mmoI) in Acetochlor (lOg). The mixture was heated at 55°C for 2 hours, and men cooled to room temperature when polymethylene polypheaylen©-isocyanate (O.lSg) was added to give the 'oil' phase. The oil was emulsified using a Silverson stirrer into a solution of Rcax 100M (0.6g) and Tergitol XD (0.6g) in water (32.3 g) cooled to 8°C. The emulsion was paddle-stirred at 50°C for 3 hour6, giving robust microcapsules which did not leak on drying and which were re-suspendable in water. EXAMPLE 8 Incorporation of dimethylol butyric acid ("DMBA") into the walls of polyuica microcapsules contaming Acctochlor using Process (1) above. This experiment demonstrated that DMBA can be incorporated Into microcapsule walls in a formulation containing a free emulsifier and colloid stabiliser. A solution of dimethylol butyric acid (DMBA, O.lSg) and dibutyltin dilaurate (O.Ig) in Acetochlox (1 Og) was added to a stirred solution of tolylene 2,4-diisocyanate (TDI, 2.4 g, 13.79mmol) in Acetochlor (1 Og). The mixture was heated at 5S°C for 2 hours then cooled to room temperature whenpolymethylene polyphenylene-isocyanate (O.lSg) was added to give the 'oil' phase. The oil was emulsified using a Silveison stirrer into a solution of Reax 1 OOM (0.6g) and Tergitol XD (0.6g) in water (32.3 g) cooled to 8°C. The emulsion was paddle stirred at 50°C for 3 hours to give robust microcapsules mat did not leak on drying and were re-suspendable in water. EXAMPLE 9 Incorporation of dimethylol propionic acid (DMPA) into the walls of poryurea mi/>rrM>^p«T)ly(memylenepolyphenylenc isocyanate) (PMPPI) and tolylene dnsocyanate (TDI) at 50*C. Example 25a: Zone of Protection Test: The test procedure was similar to that described for Example 24. The extent of damage by com root worms was assessed one month after planting as a function of plant heights and the rating system developed by Dr. James Oleson at Iowa State University. Resutey The distances from the point source at which damage began are collected in the following Table which shows that Formulation E (nanocapsules with sulphonate surface modification) gave the highest zone of protection in this test. 77-wni j-oaco on: 47 &11AAA1 "?CCQ FAX:01 Formulation Distance (cm) from centre where . damage begins (1/2 node destroyed) A 4.75 B 5.61 C 3.37 D 6.4 E 6.75 F 5.18 Example 25b: Root Box Test (aimulation of seed treatment on com seed). For this test 1 mL of the test fotmulation was pipetted on to each of 10 seeds sown in a large root box enclosed in a greenhouse. The trial was infested on days 1 and 14 at a level of 600 eggs/ft to more closely simulate the field by allowing for a variety of growth stages of rootworm to be attacking the roots at the same time. At infestation, Didbrojica eggs were suspended in 0.18% agar solution and pipetted into 1-1.5" deep divots approximately 2-3" from the base of the plants on both sides of the row. The divots were covered with loose soil and the test was irrigated after infesting to keep the eggs from desiccating. Due to a pipette problem, half of the fourth replication was infested at 10 times the specified level at first infestation. However, statistical analysis indicates that the fourth replication did not have an inordinately large amount of root damage. The rating methods used m this trial are the linear rating system developed by Dr. James Oleson at Iowa State University. numbernode? Q^srfQye^on'wSetsof. comjifenil; ■',^J:^:'^i, *D *E *F **Tefluihrm 3G in fbrrow ** Tefluthrin 3G - T band (applied in bands on both sides of furrow) 0.617 0.316 0.557 0.485 (ferraers will tolerate 0.5) 0.155 'NGENTA Untreated check I 1.830 (plant in danger of falling over) I *Tefluthrin microcapsule formulations pipetted on to seed **Tefluthrin 3G - commercial Tefluthrin 3% granular formulation (moutmoriUonite clay) applied dry Formulation £ (nanocapsule with sulphonate surface modification) which was applied directly to seed again gave the highest soil mobility in this seed treatment simulation test It was superior to the commercial standard granule distributed in furrow but not quite as good as the commercial standard grannie distributed in bands on either side of the furrow. EXAMPLE 26 Examples 26a-l. Incorporation of a polyoxyethylene modifying agent into the walls of arninoplast capsules. These experiments demonstrated that a polyoxyemylene modifying agent (Jeffamine 1000M) can be reacted with an emerified urea-formaldehyde resin (Beetle 80) to give a product with surface active properties which can be incorporated into the walls of lambda-cyhalothrin containing arninoplast microcapsules. Example 26a: Incorporation of a polyoxyethylene modifying agent into an etherified urea-faunaldehyde resin. Beetle 80 (9.0g), Jeffamine 1 DOOM (0.5,1.0 or 2.0g) and p-mluenesulphonic acid (0.03g) were dissolved in toluene and refhrxed for 6.5h. The mixture was cooled and filtered to remove undissolved p-tDluenesulphonic acid, and the toluene was evaporated to give an oily liquid. Jeffarnine 1000M [MeOEOl9P03NK2 where EO and PO designate -CH2CH20- and -CHMeCH20- groups respectively] is available from Huntsman. The emerified urea-formaldehyde resin Beetle 80 is available from American Cyanamid; 94% of the metbylol groups in the prepolymer have been emerified with n-butanol. Examples 26b-g (Formation of stable emulsions): These experiments demonstrated that the modified resin from Example 26a has enhanced emulsification properties. Emulsion-in-water (EW) formulations were prepared using the modified resin from Example 26a, and were compared with EWs of the same composition but in which the Jegarnine lOOOM and prepolymer had not been reacted prior to emuiaficanon. FAX:C Compositions, chosen to reflect typical precursor mixtures for miaocansules, are detailed in the table below. The modified resin (or Beetle 80 and Jeffamine 1000M) and pentaerythritol tetrakis 3-mercaptopropionate (otherwise known as Q43) were dissolved in Solvesso 200 (aromatic solvent available from Exxon) to give an organic phase (oil) that was emulsified into a solution of Petro BAF (a sodium alkyl naphthalene sulphonate available from Cognis) in water using a Stiverson mixer. The pH of the emulsions was adjusted to 2.0-2.2 by the drop wise addition of a 10:1 dilution of sulphuric acid. Example 26b 26c 26d 26e 26f 26g Solvesso 200 (grams) 31.09 31.09 26.74 26.74 17.34 17.34 Q43 (grams) 0.82 0.82 0.71 0.71 0.46 0.46 Beetle 80 (grams) 7.36 7.36 6.97 6.97 4.76 4.76 Jeframine 1000M (grams) 1.64 1.64 0.77 0.77 0.26 0.26 Petro BAP (grains) 0.03 0.03 0.03 0.03 0.02 0.02 Water (grams) 40.94 40.94 35.21 35.21 22.84 22.84 Pre-reactkm of Beetle 80 & Jef&mine 1000M Yes No Yes No Yes No EW stable upon acidification Yes No Yes No Yes No The emulsions prepared using the modified resins (Examples 26b, d and f) were stable for several days at ambient temperature, whereas those prepared using Beetle 80 and Jeffamine 1000M that had not been pre-reacted (Examples 26c, e and g) broke down immediately upon acidification. This indicates that the modification of Beetle 80 with Jeffamine 1000M results in the generation of a product with enhanced emnlsification and colloid stabilising properties. Examples 26h~l. These experiments demonstrated that the modified resin from Example 26a can be incorporated using Process (1) above into the walls of lambda-cyhalomrin containing microcapsules in the presence of a free colloid stabiliser, but without the use of a free emulsifier. FAX:013444136 Capsule suspension (CS) formulations were prepared according to the table below in which the modified resin described in example 26a was incorporated into the microcapsule walls. Umbda-cyhalothrin, Q43 and the modified resin were dissolved in Solvesso 200 to give the internal oil phase. Petro BAF and Lamar D (a sodium naphthalene sutphonate ! available from Cognis) were dissolved in water, and the pH of this solution was reduced to 2.0-2,2 by drop wise addition of a 10:1 dilution of sulphuric acid to give the continuous aqueous phase. The oil phase was emulsified into the aqueous phase, then the emulsion was paddle stirred at 55°C for 3 hours. In each case spherical capsules were produced with good wall strength and integrity i (capsule sizes in the range 13-18?ra). Example 26h 26i 26j 26k 261 lambda-cyhalothrin (grams) 5.00 5.00 5.00 5.00 5.00 Solvesso 200 (grams) 8.04 8.04 8.04 8.02 7.91 Q43 (grams) 0.38 0.38 0.38 0.94 0.94 Beetle 80 (grams) 1.50 1.50 1.50 0.94 0.94 Jeffamine 1000M (grams) 0.08 0.08 0.08 0.10 0.21 ?et»BAF (grams) 0.05 0.05 0.05 0.05 0.05 lomarD (grams) 1.10 0.50 0.25 1.00 1.00 Water (grams) 33.85 34.55 34.70 33.95 33.95 EXAMPLE 27 Incorporation of an anionic mercaptoaflcane carboxylate modifier into the walls of nninoplast microcapsules using Process (1) above in the presence of a colloid stabiliser. A solution of Beetle 80 (5.0 g), 3-mercaptopropionic acid (0.14 g) and trichloroacetic acid (0.05 g) in Solvesso 200 (60.0 g) was heated at 50 °C for 3 hours. Q43 (0.31 g) was added to a portion of me Beetle 80 solution (12.19 g) and the resulting oil was emulsified into an aqueous phase comprising PetroBAF (0.06 g, O.S % to oil) and Gohseaol GL03 (1.0 g of a 15% aq. solution.) in water (total mass 37.5 g, 25% solids) using a Silverson mixer at 7.5 Krpm for 2 min. The emulsion, with droplets of 5.3 ?m in diameter, was heated at 50 °C for 3 hours to give microcapsules of similar diameter. EXAMPLE 28 Incorporation of an aromatic suhphonate modifier into the walls of aminoplast microcapsules using Process (1) above. This experiment demonstrated thai 2-sulfbbenzoic acid cyclic anhydride can be reacted with an alkylated urea-formaldehyde resin using Process 1 to give a surface-active intermediate that could be incorporated into the walls of aminoplast microcapsules hi the presence of a colloid stabiliser. Beetle 80 (5.0 g) was added to a solution of 2-sulfobenzoic acid cyclic anhydride (0.15 g or 0.30 g, 3 or 6 mol % w.r.t U-F repeat units) in acetophenone (60.0 g) along with anhydrous triethylamine (0.11 mL). The solution was heated to 50 °C for 3 hours at which time no peaks due to cyclic anhydride could be seen in the IB. spectrum. Q43 (0.31 g or 0.15 g) was added to a portion of the Beetle 80 solution (12.19 g) in which. 6 % of U-F units had been reacted with 2-sulfobenzoic acid cyclic anhydride. This organic phase was emulsified using a Sitverson mixer at 7.5 Krpm for 1 min into water at pH 2.8-3.0. Gohsenol OL03 (2 % on oil) and optionally PctroBAF (0.5% on oil) were cither dissolved in me water before emulsification, or were added to the aqueous phase after emulsification such that the entire aqueous phase was 37.5 g (25 % wt/wt internal phase). The emulsion was heated at 50 °C for 3 hours to give microcapsules. No wall formation occurred when PetxoBAF was omitted from the emulsioa The modified U-F resins were shown to be surface active as follows. A sample (4.0 g) of the above solutions was separately emulsified into water (6.0 g) using an Ystral mixer at 2 Krpm for 2 min. The 3 % modified resin stabilised the emulsion for >1 hour at pH 10.5 but not at pH 2.2. The 6 % modified resin stabilised the emulsion, having a PSD (D[v,0.S]) of 2.0 ?m, for > 1 hour at pH 3.0. Emulsions at pH 3.0 prepared from a lOwttot % solution of unmodified Beetle 80 (not reacted with 2-sulfobenzoic acid cyclic anhydride) in acetophenone were unstable. Similarly unstable were emulsions of me same unmodified Beetle 80 solution in water containing 2-sulfobenzoic acid (the hydrolysis product of the cyclic anhydride) at an amount corresponding to that used in the modification reaction. This shows that the surface activity exhibited by the 6 % modified U-F resin is not due to inherent surface activity of the resin itself, or of a hydrolysis product of the cyclic anhydride, or of the cyclic anhydride itself which is quickly hydrolysed during emulsification into acidic water. EXAMPLE 29 FAX:013444 Incorporation of an anionic znercaptoalkane sulphonate modifier into the walls of aminoplast microcapsules containing lambda-cyhalothrin using Process (3) above. This experiment demonstrated mat an anionic metcaptoalkane sulphonate could be built into aminoplast capsule walls. 2-Mercaptoethancsulphonic acid sodium salt is commercially available from Aldrich, and abbreviated here as "MESNA". An organic phase was prepared by dissolving lambda-cyhalotbria (5g), Beetle 1050-10 (2.025g) and pentaerythritol tetrakis 3-mercaptopropionate (022$, Q43) in Solvesso 200 (15.2Sg). This oil was emulsified into a solution of Gohsenol GL03 (O.Sg) in water (25.45g) using a Silverson stirrer, men Petto BAF (0.05g) and a 50% aqueous solution of MESNA (O.Sg) were added. The pH of the emulsion was reduced to 2.8 by the drop wise addition of sulphuric acid (10:1 aqueous solution), and then the emulsion was paddle stirred at 55°C for 3 hours. Finally the pH of the capsule suspension was adjusted to 6.5 by the drop wise addition of ammonia (1:1 aqueous solution). This resulted in 5.7um microcapsules which maintained their integrity upon drying, and which had a zeta potential of-21.1 +/- 2.8roV (compared to a zeta potential of-12.4 +/-2.0mV for equivalent microcapsules ntnn which the modifier was omitted). EXAMPLE 30 Incorporation of a catianic quaternary ammonium alkylamine into the walls of aminoplast microcapsules containing lambda-cyhalothrin using Process (3) above. This experiment demonstrated that a catianic quaternary ammonium alkylamine modifier could be built into aminoplast capsule walls. An organic phase was prepared by dissolving lambda*;yhalothriii (5g), Beetle 1050-10 (2.025g) and pentaerymritol tetrakis 3-mercaptopropionate (0.225& Q43) in Solvesso 200 (15.25g). This oil was emulsified into a solution of Gohsenol GL03 (0.25g), Petro BAF (0.05g) and (2-ammoemyl)trimethylammomum chloride hydrochloride (0.55g) in water (26.4g) using a Silverson mixer. The pH of the emulsion was reduced to 1.9 by dropwise addition of sulphuric acid (10:1 aqueous solution), and then the emulsion was paddle stirred at 55°C for 3 hours. Finally the pH of the capsule suspension was adjusted to 5.7 by the drop wise addition of ammonia (1:1 aqueous solution). This resulted in 7.9um microcapsules which maintained their integrity upon drying, and which had a zeta potential of -13 +/- FAX:013 2.2mV (compared to a zeta potential of-12.4 +/- 2.0mV for equivalent microcapsules from which the modifier was omitted). Although this invention has been described with respect to specific embodiments, the details hereof are not to be construed as limitations, for it will be apparent that various, equivalents, changes and modifications may be resorted to without parting from the spirit and scope of the invention, and it is understood that such equivalent embodiments are intended to be included within the scope of the inventioa. 27-NOU-2002 20:53 01344413669 97>: P.60 WE CLAIM: 1. A microcapsule comprising an encapsulated material enclosed within a solid permeable shell of a polymer resin of the kind such as herein described wherein (a) said polymer resin is made by isocyanate polymerisation and the polymer resin has at least one surface modifying compound of the kind such as herein described having a moiety — X as defined below which reacts with the isocyanate moiety in the wall forming material; or wherein (b) said polymer resin is made by the polymerisation of a urea formaldehyde prepolymer in which the methylol (-CH2OH) groups have optionally been partially etherified by reaction with a C4-C10 alkanol, and the polymer resin has at least one surface modifying compound having a moiety —X as defined below which reacts with the methylol or etherified methylol moieties in the urea formaldehyde wall forming material; and wherein said surface modifying compound is selected from compounds having a formula (IA), (IB), (IC), (ID), (IIA), (IIB), (IIC), (IIIA), (IIIB), (IIIC), (HID) or (IVA) X-Yi-Z (IA) RrO(PO)r(EO)s-X (IB) R4-0(PO)r.(EO)s.(PO)t-X (IC) z (ID) X-(EO)a(PO)b-X' (HA) X-(POV(EO)b>(PO)c-X' (nB) ?I5 ~Y;-N-Y4—x A Ru X-Y2-C(Z)(R6)-Y2'-X' (BSA X (IIIB) (HC) (NIC) X. X / R 10 -R 11 (HID) X-Y-NH-Y'-Z (rvA) or wherein the surface modifying compound is a sulfonate polyester polyol prepared by reacting sodium sulphoisophthalic acid, adipic acid, cyclohexane dimethanol, methoxypolyethylene glycol (with an average molecular weight of 750) and trimethylol propane to give a product having a hydroxyl number in the range of from 150 to 170; and wherein in formulae (IA) to (IVA) above Z if present is sulphonate, carboxylate, phosphonate, phosphate, quaternary ammonium, betaine, oxyethylene or an oxyethylene- containing polymer; and each X or X' is, independently, hydroxyl, thiol, a group —NHA wherein A is hydrogen or Ci to C4 alkyl or a group -CO-OR where R is hydrogen or a hydrocarbyl moiety having 1-30 carbon atoms optionally linked or substituted by one or more halo, amino, ether or thioether groups or combinations of these; and wherein in the surface modifying compound of formula (IA) Yi is a moiety linking X and Z and is a straight or branched alkyl chain containing from 1 to 20 carbon atoms or is naphthyl, cyclopentyl or cyclohexyl; and wherein in the surface modifying compound of formula (IB) R4 is an end-capping group which is Ci to C4 alkyl, r and s are independently from 0 to 3000, provided that s is not 0 and the total of r + s is from 7 to 3000 and EO and PO represent oxyethylene and oxypropylene respectively which may be arranged in random or block formation; and wherein in the surface modifying compound of formula (IC) R4' is an end-capping group which is Ci to C4 alkyl, r', s' and t are independently from 0 to 2000, provided that s is not 0 and the total of r' + s' + t is from 7 to 3000 and EO and PO represent oxyethylene and oxypropylene respectively; and wherein in the surface modifying compound of formula (ID) X and Z are as defined above or if X and Z are adjacent substituents capable of reacting together they may form a cyclic anhydride capable or ring-opening under the reaction conditions; and wherein in the surface modifying compound of formula (IIA) a and b are independently from 0 to 3000, provided that a is not 0 and the total of a + b is from 7 to 3000 and EO and PO represent oxyethylene and oxypropylene respectively which may be arranged in random or block formation; and wherein in the surface modifying compound of formula (IIB) a', b' and c are independently from 0 to 2000, provided that b is not 0 and the total of a' + b' + c is from 7 to 3000 and EO and PO represent oxyethylene and oxypropylene respectively; and wherein in the surface modifying compound of formula (IIC) Ri4 and R15, which may be the same or different, are hydrogen Ci to C20 straight or branched chain alkyl; aryl; or Ci to C4 aralkyl, wherein each aryl group may be optionally substituted by Ci to C4 alkyl, nitro or halo and Y4 and Y4' which may be the same or different are -Rs- or -R7-(Ll)n- wherein R7 and Rs are independently Ci to C10 straight or branched chain alkyl linking groups optionally substituted by halogen or Ci to C4 alkoxy and (Li)n is a polyoxyalkyene group, n is from 2 to 20 and A-is a suitable anion; and wherein in the surface modifying compound of formula (IIIA) R6 is hydrogen or a Ci to C4 alkyl group optionally substituted by ether or halogen and Y2 and IV, which may be same or different are independently -R7-(Li)n- or -Rs- wherein R7 and Rs are independently Ci to C10 straight or branched chain alkyl linking groups optionally substituted by halogen or Ci to C4 alkoxy and (Li)n is polyoxyethylene, polyoxypropylene or polyoxybutylene, n is from 2 to 20; and wherein in the surface modifying compound of formula (IIIB), X and Z are as previously defined; and wherein in the surface modifying compound of formula (IIIC), Y3, Y3' and Y3" individually represent a direct link between X, X' and Z respectively and the ring structure or may be a group where L2 is an ester linking group —C(0)-0, R9 is oxyethylene, oxypropylene or oxybutylene or polyoxyethylene, polyoxypropylene or polyoxybutylene having a degree of polymerisation from 2 to 20; and wherein in the surface modifying compound of formula (HID), Rio is a Ci to Cs straight or branched chain alkyl group and the two groups X and X', which may be the same or different, may be attached to the same carbon atom in the alkyl chain or to different carbon atoms in the alkyl chain, -L5- is a linking group which is -(Li)n- or -Rs- wherein Rs, and (Li)n are as defined above in relation to formula (IIIA) and Rn is Ci to C4 alkyl; and wherein in the surface modifying compound of formula (IVA), Y and Y' are independently a straight or branched chain Ci to Cio alkyl group, a polyoxyethylene, polyoxypropylene or polyoxybutylene polymer chain of formula -(Li)n- as defined above or a group -(L2J-R9 -as defined above. 2. A microcapsule as claimed in claim 1 wherein when -Z is sulphonate, carboxylate, phosphonate or phosphate it is present as a salt providing the -Z" anion; or when -Z is quaternary ammonium it has the structure [-NRiR2R3]+A'-wherein Ri, R2 and R3 are independently hydrogen or Ci to C4 alkyl and A'- is a suitable inorganic or organic anion provided that not more than one of Ri, R2 and R3 is hydrogen; or when -Z is oxyetheylene or an oxyethylene-containing polymer, it is an oxyethylene polymer or is a random or block oxyethylene/oxypropylene copolymer containing an oxyethylene to oxypropylene mole ratio of greater than 1. 3. A microcapsule as claimed in claim 1 or 2 wherein the polymer resin is made by isocyanate polymerisation and the isocyanate wall forming material is tolylene diisocyanate or an isomer thereof, phenylene diisocyanate or an isomer thereof, biphenylene diisocyanate or an isomer thereof, polymethylenepolyphenyleneisocyanate (PMPPI), hexamethylene diisiocyanate (HMDI) or a trimer thereof or isophoronediisocyanate (IPDI). 4. A microcapsule as claimed in claim 3 wherein the proportions of the surface modifying chemical relative to the wall forming material are such that there is an excess of total isocyanate groups present in the wall forming material over total groups —X. 5. A microcapsule as claimed in claim 4 wherein the mole ratio of the total moiety(ies) —NCO in the wall-forming material to the total reactive moiety(ies) —X in the surface modifying compound is from 2:1 to 25:1. 6. A microcapsule as claimed in claim 1 or 2 wherein the polymer resin is made by the polymerisation of a urea formaldehyde prepolymer and the mole ratio of the surface modifying agent to the number of urea-formaldehyde repeat units in the urea formaldehyde prepolymer is between 1:40 to 1:4. 7. A modified process for the encapsulation of a dispersed material within a solid permeable shell of a polymer resin formed by polymerisation of a wall-forming material which comprises (a) when said polymer resin is made by isocyanate polymerisation, incorporating therein at least one surface modifying compound as claimed in claim 1 having a moiety — X as defined in claim 1 which reacts with the isocyanate moiety in the wall forming material; or (b) when said polymer resin is made by the polymerisation of a urea formaldehyde prepolymer in which the methylol (-CH2OH) groups have optionally been partially etherified by reaction with a C4-C10 alkanol, incorporating therein at least one surface modifying compound as claimed in claim 1 having a moiety —X as defined in claim 1 which reacts with the methylol or etherified methylol moieties in the urea formaldehyde wall forming material. 8. A process as claimed in claim 7 comprising a) reacting the surface-modifying compound with at least one wall-forming material thereby forming a modified surface-active intermediate; b) preparing an organic solution or oil phase comprising the material to be encapsulated, the modified surface-active intermediate, and, optionally, additional wall-forming material; c) creating an emulsion of the organic solution in a continuous phase aqueous solution comprising water and, optionally, a protective colloid, wherein the emulsion comprises discrete droplets of the organic solution dispersed throughout the continuous phase aqueous solution, with an interface formed between the discrete droplets of organic solution and the aqueous solution; and either d) causing in situ polymerization and/or curing of the modified wall-forming material in the organic solution of the discrete droplets at the interface with the aqueous solution by heating the emulsion for a sufficient period of time and optionally adjusting the pH to a suitable value to allow substantial completion of wall formation, thereby converting the organic solution droplets to capsules consisting of solid, permeable, polymer shells enclosing the material and formed from the surface modifying compound; or as an alternative to (d) e) causing polymerization at the oil-water interface by bringing together a wall forming material added through the aqueous continuous phase and capable of reacting with the wall forming material(s) in the discontinuous oil phase. 9. A process as claimed in claim 7 comprising a) preparing an organic solution or oil phase comprising the material to be encapsulated, the surface modifying compound and the wall-forming material; b) creating an emulsion of the organic solution in a continuous phase aqueous solution comprising water and, optionally, a protective colloid, wherein the emulsion comprises discrete droplets of the organic solution dispersed throughout the continuous phase aqueous solution, with an interface formed between the discrete droplets of organic solution and the aqueous solution; and either c) causing in situ polymerization and/or curing of the modified wall- forming material in the organic solution of the discrete droplets at the interface with the aqueous solution by heating the emulsion for a sufficient period of time and optionally adjusting the pH to a suitable value to allow substantial completion of wall formation, thereby converting the organic solution droplets to capsules consisting of solid, permeable, modified polymer shells enclosing the material; or as an alternative to (c) (d) causing polymerization at the oil-water interface by bringing together a wall forming material added through the aqueous continuous phase and capable of reacting with the wall forming material(s) in the discontinuous oil phase. A process as claimed in claim 7 comprising a) preparing an organic solution or oil phase comprising the material to be encapsulated and the wall-forming material; b) creating an emulsion of the organic solution in a continuous phase aqueous solution comprising water and the surface-modifying compound(s), wherein the emulsion comprises discrete droplets of the organic solution dispersed throughout the continuous phase aqueous solution, with an interface formed between the discrete droplets of organic solution and the aqueous solution; and c) causing in situ polymerization and/or curing of the wall-forming material so that the surface-modifying molecule(s) forms the wall by heating the emulsion for a sufficient period of time and optionally adjusting the pH to a suitable value, to allow substantial completion of wall formation, thereby converting the organic solution droplets to capsules consisting of solid, permeable, modified polymer shells enclosing the material. A process as claimed in claim 7 comprising a) preparing an organic solution or oil phase comprising the material to be encapsulated and a first wall-forming material(s); b) creating an emulsion of the organic solution in a continuous phase aqueous solution comprising water and the surface-modifying compound(s), wherein the emulsion comprises discrete droplets of the organic solution dispersed throughout the continuous phase aqueous solution, with an interface formed between the discrete droplets of organic solution and the aqueous solution whereupon the surface modifying compound(s) react at the interface with wall forming material from the organic phase; and c) causing polymerization at the oil-water interface by bringing together a second wall forming material added through the aqueous continuous phase and capable of reacting with the first wall forming material(s) in the discontinuous oil phase. 12. A process as claimed in claim 7 wherein there is employed a combination of the processes claimed in claims 8 to 11. 13. The reaction product of a surface modifying compound as claimed in claim 1 and an isocyanate wall forming material or a urea formaldehyde prepolymer in which the methylol (-CH2OH) groups have optionally been partially etherified by reaction with a C4-C10 alkanol. 14. A microcapsule as claimed in any one of claims 1 to 6 wherein the encapsulated material is an agrochemical, an ink, a dye, a biologically active material or a pharmaceutical. 15. A process as claimed in any one of claims 7 to 12 wherein the encapsulated material is an agrochemical, an ink, a dye, a biologically active material or a pharmaceutical. 16. A method for modifying the soil mobility of an agrochemical which comprises encapsulating the agrochemical in a process as claimed in any of claims 7 to 12. Dated this 2nd day of December, 2002 (RANJNA MEHTA-DUTT) OF REMFRY 8B SAGAR ATTORNEY FOR THE APPLICANTS