HUT77646A - Microencapsulation process and product - Google Patents

Description

PUBLICATION LITERATURE

DANUBIA Patent and Trademark Office Ltd.

Budapest

Microencapsulation process and product obtained

The present invention relates to a process for the microencapsulation of various materials, in particular pesticidal agents, by which wet and dry formulations can be obtained. In particular, the present invention relates to the encapsulation of materials from which the product obtained can be diluted with water to obtain aqueous pesticidal formulations which can be applied by conventional spraying.

Encapsulation of various pesticidal agents, plant growth regulators and other substances used in this field has been of particular interest in recent years. For safety and ease of application, it is particularly advantageous to market such materials in the form of aqueous dispersions which are readily dispersible in water and applied in the desired area.

In recent years, various proposals have been made for the microencapsulation of various pesticidal substances. For example, U.S. Pat. No. 5,160,530 (Griffin) discloses microcapsulation of pesticides (e.g., trifluralin) in which the active ingredient is molten, the bulk material is combined with a film-forming polymer such as polyvinyl alcohol (PVA), and The material thus obtained is emulsified and spray-dried.

85977-2506E OE / Hoj • · • · · · · ····

US-A-4 244 836 (Hoechst) discloses a similar method for encapsulating pesticides by spray-drying a dispersion containing the active ingredient and PVA.

Although certain systems are suitable for the methods described above, they have several drawbacks, such as diffusion of the active ingredient in the product, which results in crystallization of the active ingredient in the PVA matrix, and in particular undesirable polymorphs of the melted active ingredient in the former method. may develop when cooled to ambient temperature.

Another method for encapsulation is described in US-A-4 936 901 (Monsanto), in which the microcapsules containing the active ingredients are prepared by contacting a surface polycondensation reaction, such as an isocyanate / polyamine reaction. The resulting contact surfaces are then spray-dried polymerized microcapsules. It is mentioned in the publication that PVA may be used as a suspension adjuvant in the spray drying step. However, the process provides microcapsules with non-controllable release characteristics. Furthermore, certain active ingredients tend to diffuse out of the contact surfaces from polymerized microcapsules during storage and thus crystallize (at ambient temperature for solid active ingredients). Another difficulty with this method is that each product obtained has low release characteristics because of the large particle size distribution and the thick polymer wall.

• ··· ··

Another problem with this reference is that it does not at all deal with the preparation of microcapsules from which the active ingredient is released rapidly, the resulting products generally having a sustained or delayed release. Frequently controlled release formulations are required to provide a rapid "knock-down", followed by sustained release of the remaining active ingredient. Quick release capsules generally require small size (volume mean diameter,

VMD (less than 5 µm) or required to have an extremely thin polymer wall. None of the systems disclosed in US-A-4,906,901 have the small particle size commonly required to achieve a rapid knock-down effect. The only information in the publication about particle size is that the particle size distribution (not VMD) is 1-50 μ. Surfactants that are of importance in the art are those that would not be suitable for the preparation of capsules having a VMD of less than 5 µm.

It is also known, for example, from EP-A-611 253, US-A-5 332 584 and US-A-5 324 584 that PVA is used as a surfactant or protective colloid in pesticidal encapsulation processes. However, it is not mentioned in those publications that PVA is actively involved in the design of the wrapper so that it can influence and provide an effective control over the release characteristics of the microcapsules.

• · ··

It has been found that by incorporating PVA into the contacting surface polycondensation system in the manufacture of microcapsules, the resulting capsules are spray-dried in the presence of PVA and optionally in the presence of additional PVA which may be the same or different as that used in the microcapsulation step. microcapsules may be prepared which have improved storage stability, particularly with respect to the leaching of the active ingredient from the microcapsules, especially if the microcapsules are small in size (e.g., less than 5 µm).

Accordingly, the present invention relates to a process for preparing an encapsulated material, wherein the microcapsules are formed by contacting a surface polycondensation reaction, the resulting microcapsules are spray-dried in the presence of polyvinyl alcohol (PVA), in which the PVA is present during the surface polycondensation reaction.

As mentioned above, additional PVA may be added to the mixture containing the microcapsules prior to the spray drying step, and this PVA is preferably different from the PVA used in the surface polycondensation step.

The degree of polymerization of PVA used in the microcapsulation step may be in the range of 50-5000 and the degree of hydrolysis in the range of 70% to 100%. Desirable PVA characteristics include being an emulsifier prior to the polycondensation step, in order to help stabilize the capsules during their formation and to facilitate the wettability of the capsules during spray drying for final use. These requirements may not be optimal

I · «·· Satisfied with a single PVA grade. A good compromise is found with a material having a degree of polymerization of ca.

300 and a degree of hydrolysis of ca. 88%.

An additional PVA may be added prior to the dewatering step and is selected mainly because of its poor solubility against the encapsulated material and its ease of wetting in cold (and possibly hard) water. Chemically modified PVAs, such as sulfonated or carboxylated PVA derivatives, are particularly preferred for this purpose.

Surface polycondensation can be performed to form microcapsules by any method known to those skilled in the art.

In a preferred embodiment, the contacting surface (hereinafter surface) polycondensation reaction is conducted in the presence of PVA using polyisocyanate and polyamine. Because PVA is present during the polycondensation reaction that forms the wall of the microcapsules, and because its surfactant provides both a sufficiently high concentration and a preferential orientation at the oil / water interface, PVA containing the hanging -OH groups reacts with the isocyanate and thus polyurethane groups are incorporated into the polymer microcapsule wall. The permeability of polyurethane polymers is completely different from that of polyurea, which is formed during the reaction of polyisocyanate with polyamine. Other surface polycondensation reactions that may be employed include the isocyanate / polyol, isocyanate / water and isocyanate / acid chloride reactions.

Examples of encapsulating materials include:

• · «·

pesticidal substances: amitraz phosalone azinfoz ethyl phospholipids azinfoz methyl phosmet benzoximate promecarb bifenthrin quinalphos binapacryl resmethrin bioresmethrin temephos klórpirifoz tetramethrin klórpirifoz methyl xylylcarb cianofoz acrinathrin cyfluthrin allethrin cypermethrin benfuracarb bromofoz biollethrin bromopropylate bioalletrin S butakarboxim bioresmethrin butoxikarboxin buprofezin chlordimeform chlorfenvinphos chlorobenzilate klórfsurazuron Chlorpropylate chlormephos klórfoxim cycloprothrin fenamifoz Betacyfluthrin fenobucarb cyhalothrin gamma-HCH kambda-cyhalothrin methidathion alpha-cypermethrin deltamethrin beta-cypermethrin dicofol cyphenothrin dioxabenzafoz demeton-S-methyl

• i «e η ι • · *« · · »9» · 0 »* * ··» dioxacarb endosulfan

EPNetiofencarb dinobuton tetradifon tralometer

N-2,3-dihydro-3-methyl

-l, 3-thiazol-2-ylidene-2,4

parathion-methyl -xilidén fentiokarb fenpropathrin fenthion fenvalerate flucythrinate flufenoxuron tau fluivalinát formothion hexaflumuron hydroprene izofenfoz isoprocarb isoxathion malathion mefozfolán methoprene methoxychlor mevinphos diklórvoz disulfoton edifenphos empenthrin esfenvalerate ethoprophos etofenprox etrimphos fenazaquin fenitrothion phenothrin phenthoate pirimifoz ethyl pirimifoz methyl profenofoz Propaphos Propargite propetamfozpiraklofoz tefluthrin terbufoz tetraklorinfosz tralomethrin triazofoz pyraclofoz tefluthrin terbufoz tetrachlorinphos tralomethrin r · * * * ·· *

permethrin triazophos fungicidal substances: benalaxyl biteranol Bupyrimate ciprokozanol carboxin tetraconazole dodemorph difenoconazol dodine dimethomorph fenarimol diniconazole ditalimfoz ethoxyquin myclobutanil etridiazole nuarimol fenpropidin oxycarboxin fluchloralin penconazole flusilazole prochloraz imibenzkonazol tolklofoz methyl myclobutanil tridimefon propiconazole triadimenol pyrifenox azaconazole tebuconazole epoxiconazole tridemorph fenpropimorph triflumizole herbicidal substances: 2,4-D esters bifenox 2,4-DB esters bromoxynil esters acetochlor bromoxynil acionifen butachlor aiaklór butamifoz anilofos butralin benfluralin butoxide

·· ♦ »·« »· ·» · · ·

benfuresate carbetamide bensulide klómitrofen benzoylpropethyl Chloropropham cinmethylin flurochloraline haloxifop clethodim ethoxyethyl clomazone haloxyfop-methyl clopyralid esters ioxynil esters CMPP esters isopropalin cycloate MCPA esters cycloxydim mecoprop-P esters desmedipham metolachlor dichloroprop esters monalide diclofop-metildietatil naprop amide dimethachlor nitrofen dinitramin oxadiazon ethalfluralin oxyfluorfen ethofumesate pendimethalin fenobucarb phenisopham fenoxaprop ethyl phenmedifam fluazifop pichloram esters fluazifop-P pretilachlor fluchloralin profluoralin flufenoxim propachlorto flumetralin propanil flumetralin propakizafop fluorodiphen pyridate fluoroglycofen ethyl quizalofop-P fluoroxypyr esters triclopyr esters

- 10 flurecol butyl tridiphan trifluralin

Other pesticides, such as nitrapyrin, which inhibits nitrification, may also be used. The compositions of the present invention may further comprise a mixture of two or more pesticides, which in some cases form a eutectic mixture having a lower melting point than the individual components.

Pesticides may also be organic soluble derivatives of pesticidal compounds which are difficult or non-soluble in the organic material itself.

The amount of active ingredient is generally 30-90% by weight, preferably 60-85% by weight, more preferably 75-80% by weight based on the total weight of the spray-dried composition.

As mentioned above, the process of the invention is particularly advantageous for producing small particle size microcapsules having a VMD of 5 µm or less, in particular 2 µm or less. The main advantage of such small capsules is that their specific surface area is larger in weight than larger particles and thus have a higher release rate and better knock-down effect. Further, such small capsules are more capable of penetrating the soil or various grass surfaces than larger capsules and can be more effectively applied in such areas. An additional benefit of small capsules is that as the VMD value decreases, it is possible to maintain an increased amount of · ·

- 11 supercooled active ingredients in liquid form. In this way, it is possible to formulate a capsule without the use of a solvent, the core of which is a liquid, which has environmental benefits and may have a higher active ingredient content.

Capsules containing liquid cores obtained from supercooled melts have various advantages and one of the most important features of the compositions of this invention is that the liquid core is released faster than the solid. This, in combination with the small particle size, significantly increases the rate of drug release. Another advantage of such a core is that it does not crystallize and thus does not cause the capsule to collapse, which on the one hand leads to premature release and on the other hand renders the formulation unstable upon storage. A third advantage of the active ingredient being in the liquid state is that it cannot form a biologically less potent polymorphic form by crystallization, which is a problem that is otherwise present, for example, in the process of US-A-5 160 530.

Obviously, if the active ingredient is dissolved in a solvent, this problem will not be encountered. Any water-insoluble solvent may be used if this solvent appears to be acceptable. Examples of such solvents are aromatic solvents, especially alkyl-substituted benzenes such as xylene or propylbenzene fractions, mixed naphthalenes and alkylnaphthalene fractions; mineral oils; kerosene; dialkyl amides of fatty acids, in particular dimethyl amides of fatty acids such as dimethyl amide of caprylic acid; chlorinated aliphatic and aromatic hydrocarbons such as 1,1,1-trichloroethane or chlorobenzene; glycol derivatives

Esters of 12 such as acetate of diethylene glycol, n-butyl, ethyl or methyl ether, acetate of dipropylene glycol methyl ether, ketones such as isophorone and trimethylcyclohexanone (dihydroisophorone) and acetate products such as hexyl or heptyl acetate. Preferred organic liquids are xylene, propylbenzene fractions, alkyl acetates and alkylnaphthalene fractions.

An advantage of the encapsulation process, in which the encapsulation reaction is carried out in the presence of PVA, is that the amount of polyurethane and polyurea in the capsule wall can be controlled with some precision by varying the time before the polyamine is added. Because these two polymers provide different diffusion properties to the encapsulated material, varying the ratio of polyurethane / polyurea provides another independent method of controlling the rate of drug release by controlling the wall thickness and size of the capsule.

In another embodiment, the solvent may be a polymerizable monomer such as an ethylene double bond monomer (e.g., styrene, α-methylstyrene, (m) ethyl methacrylate, vinyl halide, or acrylonitrile), which is polymerized in a subsequent step and thus forming a matrix core in the capsule, which represents an additional control of drug release.

A further advantage of the encapsulation method carried out in the presence of PVA is that due to the hanging OH groups, PVA is chemically bound to the capsule wall during the wrapping reaction. Terminally connected PVA (tails) via such a bond is double bonded PVA (loops) and serially bonded

- 13 PVAs (trains) develop. In the presence of uncoupled PVA, particularly in the spray drying step, the resulting product may have a disadvantage. Concentration (PVA, capsules and other added materials such as salts) increases rapidly during spray drying. The aim is to form a water-soluble polymer of uniform thickness around the capsules and to convert it into a film upon drying. Obviously, flocculation may occur if the concentration increases during the drying process. Thus, capsule-to-capsule contact may occur, leading to irreversible coagulation. The presence of loops and trains can provide protection against all these processes, which otherwise cause poor re-wetting and colloidal instability. They also have the additional advantage of allowing substantial amounts of electrolyte to be added to the capsule suspensions, which promote rapid, re-wettability of the dried product, as described, for example, in EP-A2-568379. Higher concentrations of any electrolyte in conventional capsule suspensions generally lead to irreversible coagulation of the capsules.

A further advantage of the encapsulation process of the present invention is that it allows the preparation of dry formulations containing two or more active ingredients which would otherwise produce a product which is chemically or physically unstable when directly formulated (i.e. without encapsulation of one or the other). These agents may be encapsulated separately, but in another preferred embodiment, one or more of these agents (or some portion of one) is encapsulated by the process of the present invention and the remainder is not encapsulated. In this way, the non-encapsulated active ingredient is directly bioavailable, whereas the encapsulated material is released much more slowly. The amount of material used in these various forms will vary depending on the particular application method and will generally be in the range of 0.1 to 99.9% by weight of the encapsulated material.

The microcapsules of the present invention are prepared by mixing, under high shear mixing, a solution or melt of the active ingredient (e.g., a pesticide), PVA (in aqueous solution) and a surface polycondensation agent (e.g., isocyanate).

PVA acts as an emulsifier and in some systems no additional emulsifier is required. However, it may be desirable to add an additional emulsifier of known type to produce small particle size emulsions. Once the desired particle size emulsion has been achieved; then adding the other polymeric crosslinking agent (e.g., polyamine) to complete the surface polycondensation reaction.

As mentioned above, the preferred reagent for the polycondensation reaction is polyamine, which is generally a water-soluble reactive polyamine such as diethylenetriamine or tetraethylene pentamine. These amines react with the isocyanate on the contact surfaces as soon as they are added to the emulsion. Occasionally, a more controlled reaction may be achieved by using either a water-soluble amine salt or an oil-soluble amine salt in the aqueous phase or dissolved in the oil phase at an early stage of the reaction, for example, prior to emulsification. Because they are salts, they do not react immediately with the isocyanate, but they react immediately when the pH is adjusted to release the free amine, whereby crosslinking occurs.

High shear mixing can be carried out batchwise or continuously. In the former case, the time of addition of the reactive amine or the time of release of the amine is controlled by the time required for the formation of an emulsion having the appropriate particle size distribution (obviously dependent on the size of the batch). the addition or release of the amine can be carried out at any time by simple addition of a point, thereby completely controlling the urea / urethane ratio.

As mentioned above, the PVA used in the process of the invention can be added at the start of the reaction to form microcapsules. However, it is generally preferred that the additional PVA is added after the microcapsules have formed but before spray drying. The ratio of the amount of PVA added in the second stage to the initial amount present is usually at least 0.5: 1.

Other conventional additives, such as emulsifiers, dispersants, disintegrants, salts and film-forming polymers, may also be added.

The following examples illustrate preferred embodiments of the present invention and illustrate some of the characteristics of these examples. Thus, Figure 1 shows the relationship between crystallization and VMD and Figure 2 shows the effect of crystallization on the residue.

Example 1

An emulsion was prepared by high shear mixing from an aqueous 20% PVA solution (GLO3, Nippon Goshei, degree of hydrolysis 88%, degree of polymerization about 300) at 55 ° C in a water bath. The molten chlorpyrifos mixture is mixed with polymeric isocyanate (Voranate M220) in the amounts indicated below and then added to the PVA solution in the water bath with vigorous shear mixing.

Chlorpyrifos technical 93.9 g

Voranate M220 4.7 g

GLO3 12 g as a 15% w / w solution

Diethylenetriamine 1.25 g dissolved in 65 g water

For samples of approximately 100 g, a mixing time of 30 seconds is sufficient to reduce the VMD to less than 1 μιη for a larger sample (500 g) of approx. 90 seconds required for approx. To provide a VMD of about 1 pm.

Once the desired VMD is achieved, diethylenetriamine is added under high shear mixing.

The reaction between the isocyanate and the polyamine and PVA yields microcapsules containing the active ingredient dispersed in the aqueous phase.

To prepare the dry product, the wet capsule (5 kg) is mixed with 0.855 kg GLO3 (as a 21% aqueous solution) and deionized water is added so that the viscosity of the suspension is suitable for spray drying.

I

- 17 (usually about 100 mPas). By spray-drying the microcapsule suspension, a dry product is obtained which has a concentration of ca. Contains 75% by weight of chlorpyrifos. The additional amount of PVA is such that the ratio in the dry product is about. 66% should be the first PVA and 33% the next PVA. The spray drying temperature is 120-150 ° C and the outlet temperature is 65-80 ° C. The product obtained is slightly greyish in color and is free of particulate matter and has a water content of ca. 0.5%. The wet capsule product has a particle size (vmd) and the dry product has a particle size when dispersed in water of approx. 1 pm.

Examination of the rate of release

The release rate of the product was investigated by spraying a 1000 ppm diluent onto a glass slide and measuring the amount of residue at 20 ° C in a constant stream of air after 24 hours. For the product of Example 1, the residue is 95% on the glass plate.

Example 2

Wet capsules were prepared as described in Example 1 but using a continuous in-line mixer according to the following composition:

93.9 g 2.94 g

16.8 g as a 21% w / w solution

1.56 g dissolved in 65 g water

The resulting wet capsule phase (5 kg) is then mixed with 200 g of 10% carboxylated PVA solution (Trade Mark KM118),

Clopyrophos technical Voranate M220 GLO3

Diethylenetriamine

18 and then spray-dried to give approx. 75% by weight of product containing chlorpyrifos are obtained. The wettable capsule product has a particle size (VMD) and a dry product has a particle size of about 2 to about 60 mg when dispersed in water. 0.6 μ. In a glass plate residue test, only 30% of this product remains after a 24 hour storage period, indicating the extent to which the release characteristics can be controlled by the present invention.

The main differences between Examples 1 and 2 are:

(i) In Example 1, more isocyanates were used, resulting in a thicker wall than in Example 2.

(ii) In Example 1, its value is greater than in Example 2, so the contact area is proportionally smaller.

(iii) Since Example 2 was continuous and Example 1 was intermittent as in Example 2 earlier than in Example 1.

(iv) Due to the increased particle size (VMD = 1 µm), the product of Example 1 is more crystalline than that of Example 2, which is ca. 10% in solid form as compared to Example 2 where VMD is 0.55 µm and crystallinity is 3%.

Each of these factors provides a faster release of the product of Example 2 compared to the product of Example 1, which is clear from the fact that much less drug remains in Example 2 than in Example 1. The relationship between the percentage crystallization and the percentage of material remaining on the glass plate after 24 hours is shown in Figure 2.

- 193-6. examples

Further formulations were prepared essentially as described in Example 1 and the amounts were varied according to the data summarized in Table 1 below (amounts in grams). Table 1 shows how easily the release characteristics can be controlled.

Table 1

Example number 3 4 5 6 chlorpyrifos 42.29 42.29 48.59 48.59 Voranate 7.09 7.09 0.79 0.79 GLO3 2.00 12.00 2.00 12.00 Water 38.00 28.00 38.00 28.00 Diethylenetriamine 1.91 1.91 0.21 0.21 Water 8.71 8.71 10.41 10.41 particle Size 10.91 0.48 9.05 0.96 Release rate% residual after 24 hours 86 81 64 5

All of these wet capsule systems were mixed with GL03 to give a 75% chlorpyrifos product and then spray dried as described above. For a comparative study, a methyl-containing nonionic surfactant (Atlox 4849B) was used to directly substitute PVA in Example 6 to achieve a particle size of 0.45 µm. This product is then atomized • · • · · ♦ · »

We dried it, but it failed because of waxy precipitation in the equipment.

Each of them is 1-6. In the case of the product of the invention according to Examples 1 to 4, spray drying was carried out at high yield and the product obtained was stable for storage.

7-9. examples

Three products are prepared according to the following composition:

Chlorpyrifos technical 95.06 g

Voranate M220 2.94 g

GLO3 7.54 g

Water 30.16 g

The material was emulsified at 50 ° and diethylenetriamine (1.91 g) dissolved in 77.7 g water was added.

In these examples, the time before administration of triethylene triamine was varied so as to vary the ratio of polyurea to polyurethane in the capsule wall. This was measured by infrared techniques. The release rates of the three different formulations were determined as described above.

Table 2

Example number Prior to DETA administration (minutes) Particle- size micron Urea: urethane ratio release speed (% residue) 7 immediately 0.62 2.94: 1 85 8 1 minute 0.68 2.36 70 9 6 minutes 0.74 1.69 55

It is apparent from the above data that altering the urea-urethane ratio in this manner is a useful means of controlling the release characteristics of the product. Various products were prepared in a similar manner, with varying release rates, corresponding to values ranging from 100% to 10% after 24 hours, which were achieved by varying the urea to urethane ratio as described above.

Example 10

Chloropyrophos-methyl is dissolved in an aromatic solvent (Solvesso 200) and then encapsulated in the following composition:

Chlorpyrifos-methyl Solvesso 200 Voranate M-229 GLO3

Diethylene triamine g (technical) g 1 g g (in 10% aqueous solution)

0.3 g dissolved in 9.7 g water

The resulting wet capsule has a phase particle size (VMD) of 1.72 µm. The product is then mixed with an amount of PVA solution (GLO3) such that the dry product is ca. Contain 50% by weight of chlorpyrifos-methyl after spray drying to obtain a free flowing powder containing 50% by weight of chloropyrophos-methyl in the encapsulated product. This product is stable for storage and is easily released from small capsules for administration of water. Addition of the product to water yields a particle size (VMD) of 1.66 µm, which indicates that such a product is capable of regaining its wet capsule size upon addition to water.

-2 211. example

The chlorpyrifos-containing product is prepared with different particle size distributions and stored at ambient temperature. Chlorpyrifos has a melting point of 40-42 ° C. At ambient temperature, such an encapsulated product would be expected to crystallize over time. The incidence of crystallization can be determined by Differential Scanning Calorimetry (DSC) and the endothermic melting point is used to detect the amount of product in the crystalline state. Using this method, it has surprisingly been found that very small amounts of chlorpyrifos crystallized in the system of the invention compared to the product of US-A-5 160 530, in which chlorpyrifos was emulsified in a PVA solution and then dried by spray drying. Figure 1 illustrates the dependence of crystallization on non-particle size (vmd) formulations of the present invention compared to the product prepared according to US-A 5 160 530 ("Griffin Example"). It can be seen that in the Griffin exemplary product, the degree of crystallization is about. 30% at a VMD of 0.4 µm, while for such a particle size the expected value for the material encapsulated by the process of the invention would be about 3%. This clearly shows the surprising stability of the metastable liquid state. The effect of crystallization (and thus indirectly on particle size) on the amount of residual material is shown in Figure 2. There is very little crystallization of the product according to the invention (max. 15%

2.2 pm vmd), but Griffin shows 30%

The product of Example -23 (where the vmd is actually 0.4 µm for the emulsion).

Claims (18)

Patent claims A process for preparing an encapsulated material comprising forming the microcapsules containing the material by contacting a surface polycondensation reaction, then spray-drying and spray-drying the capsules in the presence of polyvinyl alcohol (PVA), characterized in that . 2. The process of claim 1 further comprising adding PVA to the mixture containing the microcapsules prior to the spray drying step. 3. The process of claim 2, wherein the additional PVA added prior to the spray drying step is different from the PVA used in the surface polycondensation reaction. 4. The process according to any one of claims 1 to 4, wherein the first addition of PVA has a degree of hydrolysis of 70 to 100% and a degree of polymerization of at least 50. 5. The process of claim 4, wherein the first degree of PVA hydrolysis is about 1 to about 10 percent. 88% and a degree of polymerization of ca. 300th 6. A process according to any one of claims 1 to 3, wherein the second PVA is carboxylated or sulfonated PVA. 7. Process according to any one of claims 1 to 3, characterized in that the microcapsules are formed by reaction between polyisocyanate and polyamine. -25 * · »* • * · · ** · ϊ ϊ · · · · · · · · · · · · · · 8. A process according to any one of claims 1 to 4, wherein the amount of encapsulated material is 30-95% by weight relative to the spray-dried microcapsules. 9. The process of claim 8, wherein the amount of encapsulated material is 60-85% by weight relative to the spray-dried microcapsules. 10. The process of claim 9, wherein the amount of encapsulated material is 75-80% by weight relative to the spray-dried microcapsules. 11. A process according to any one of claims 1 to 4, wherein the spray-dried microcapsules have a volume average particle size (vmd) of 5 µm or less. The process of claim 11, wherein the spray-dried microcapsules have a vmd of 2 µm or less. 13. A process according to any one of claims 1 to 4, wherein the material to be encapsulated is in the form of a solvent solution. 14. A process according to any one of claims 1 to 4, wherein the pesticidal agent is encapsulated. 15. A microcapsule by encapsulating the active ingredient by a surface polycondensation reaction, produced by spray drying the product obtained in the presence of polyvinyl alcohol (PVA), characterized in that the surface polycondensation reaction is carried out in the presence of PVA. 16. The microcapsule according to claim 15, wherein the encapsulated material is present in the microcapsule in a liquid state. I The microcapsule according to claim 15 or 16, characterized in that it contains at least two different pesticides. 18. The microcapsule according to claim 17, wherein the at least two different pesticides are encapsulated separately. The microcapsule according to claim 17 or 18, characterized in that it contains both relatively slow and relatively fast release microcapsules.