EP0804284A1 - Procede et produit de micro-encapsulation - Google Patents

Procede et produit de micro-encapsulation

Info

Publication number
EP0804284A1
EP0804284A1 EP95941498A EP95941498A EP0804284A1 EP 0804284 A1 EP0804284 A1 EP 0804284A1 EP 95941498 A EP95941498 A EP 95941498A EP 95941498 A EP95941498 A EP 95941498A EP 0804284 A1 EP0804284 A1 EP 0804284A1
Authority
EP
European Patent Office
Prior art keywords
microcapsules
pva
encapsulated
product
interfacial polycondensation
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
EP95941498A
Other languages
German (de)
English (en)
Inventor
Patrick Jospeh Mulqueen
Steven Duff Lubetkins
Geoff Smith
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Corteva Agriscience LLC
Original Assignee
DowElanco LLC
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by DowElanco LLC filed Critical DowElanco LLC
Publication of EP0804284A1 publication Critical patent/EP0804284A1/fr
Ceased legal-status Critical Current

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J13/00—Colloid chemistry, e.g. the production of colloidal materials or their solutions, not otherwise provided for; Making microcapsules or microballoons
    • B01J13/02—Making microcapsules or microballoons
    • B01J13/06—Making microcapsules or microballoons by phase separation
    • B01J13/14—Polymerisation; cross-linking
    • B01J13/16—Interfacial polymerisation
    • A—HUMAN NECESSITIES
    • A01—AGRICULTURE; FORESTRY; ANIMAL HUSBANDRY; HUNTING; TRAPPING; FISHING
    • A01N—PRESERVATION OF BODIES OF HUMANS OR ANIMALS OR PLANTS OR PARTS THEREOF; BIOCIDES, e.g. AS DISINFECTANTS, AS PESTICIDES OR AS HERBICIDES; PEST REPELLANTS OR ATTRACTANTS; PLANT GROWTH REGULATORS
    • A01N25/00—Biocides, pest repellants or attractants, or plant growth regulators, characterised by their forms, or by their non-active ingredients or by their methods of application, e.g. seed treatment or sequential application; Substances for reducing the noxious effect of the active ingredients to organisms other than pests
    • A01N25/26—Biocides, pest repellants or attractants, or plant growth regulators, characterised by their forms, or by their non-active ingredients or by their methods of application, e.g. seed treatment or sequential application; Substances for reducing the noxious effect of the active ingredients to organisms other than pests in coated particulate form
    • A01N25/28—Microcapsules or nanocapsules
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J13/00—Colloid chemistry, e.g. the production of colloidal materials or their solutions, not otherwise provided for; Making microcapsules or microballoons
    • B01J13/02—Making microcapsules or microballoons
    • B01J13/04—Making microcapsules or microballoons by physical processes, e.g. drying, spraying
    • B01J13/043—Drying and spraying

Definitions

  • This invention relates to the microencapsulation of various materials, m particular pesticidal materials, to produce both wet and dry formulations.
  • the invention relates to encapsulating such materials so that the encapsulated product can be diluted in water, m order to produce aqueous pesticidal compositions, wnich can be applied by conventional spray tecnmques .
  • US-A-5160530 discloses a process for encapsulating pesticides (for example trifluralm; , by melting the active material, and combining the melted material with a film- orming polymer, such as a polyvmylalcohol (PVA) . The materials are then emuisifiec. together and spray dried.
  • pesticides for example trifluralm; , by melting the active material, and combining the melted material with a film- orming polymer, such as a polyvmylalcohol (PVA) .
  • PVA polyvmylalcohol
  • US-A-4244836 discloses a similar method of encapsulating pesticidal materials, by spray drying a dispersion of the active material and a PVA.
  • the processes disclosed by these references are useful, they suffer from a number of disadvantages, for example that the active material can diffuse within the product leading to crystallisation of the active material in the PVA matrix, and also articularly m the Griffin method) that undesired pciymorphs of the molten active material may be produced upon cooling to ambient temperature.
  • US-A-4936901 discloses an alternative method of encapsulation, m which microcapsules contamm ⁇ the active material are formed by means of an interfacial polycondensation reaction, involving an lsocyanate/polyamme reaction. The resulting mterfacially polymerised microcapsules are subsequently spray dried.
  • PVA may be used as a suspension adjuvant n tne spray drying step. Again, this me hoc results in tne production of microcapsules with uncontrollable release characteristics.
  • microcapsules can be obtained which show improved storage stability, especially to the leaching of the active material from the resulting microcapsules, particularly when the microcapsules are small in size, (for example less than 5 micrometer) .
  • a process for preparing an encapsulated material comprises forming microcapsules containing the material by an interfacial polycondensation reaction, and spray drying the resulting microcapsules in the presence of a polyvinylalcohol (PVA) , wherein the PVA is present during the interfacial polycondensation reaction forming the microcapsules.
  • PVA polyvinylalcohol
  • a further quantity of PVA which may preferably oe one which is different from the one used in the interfacial polycondensation step, may be added to the mixture containing the microcapsules, prior to the spray drying step.
  • the PVA employed m tne microencapsulation step may be one with a degree of polymerisation of from 50 to 5,000, and a degree of hydrolysis cf from ⁇ 0% to 100%. Desirable characteristics for the PVA are that it should be an efficient emulsif er prior to the polycondensation step, that t can assist the stabilisation of the capsules wnilst tney are forming, and also that t can assist tne re- wetting cf tne capsules after spay drying when they are ultimately used. These requirements are not all optimally met m a single PVA grade. A good compromise has been found to be a material having a degree of polymerisation of about 300, and a degree of hydrolysis of about 88%.
  • the additional PVA whicn may be added prior to the spray drying step s mainly selected on the basis of its poor solvent qualities for tne encapsulated material, and for its ease cf re-wettmg m cold (and possibly hard) water.
  • Chemically modified PVAs, suc.i as the sulphonated or carooxylated PVAs, are particularly useful for this purpose .
  • the interfacial polycondensation to form the microcapsules may be carried out by any of the various methods known to those skilled in the art.
  • the interfacial polycondensation reaction in the presence of the PVA is carried out using a polyisocyanate and a polyamine.
  • the PVA is present during the polycondensation reaction which forms the microcapsule walls, and because its surfactant nature ensures both a high concentration and preferred orientation at the oil/water interface, the PVA, having pendant -OH groups, reacts with the isocyanate to incorporate polyurethane groups into the polymeric microcapsule walls.
  • the permeability of polyurethane polymers is quite different from that the of the polyurea which is formed by reaction of the polyisocyanate with the polyamine.
  • Other interfacial polycondensation reactions which may be employed are, for example isocyanate/polyol , isocyanate/water, and isocyanate/acid chloride reactions.
  • the material which is encapsulated mav be a oesticidal material, for example amitraz pnosa one azinphos-ethyl phosfolan azinphos-methyl phosmet benzoximate promecarb bifenthrin quinalphos binapacryl resmethrin bioresmethrin temephos chlorpyrifos tetramethrin chlorpyrifos-methyl xylylcarb cyanophos acrinathrin cyfiuthrin allethrin cypermethrin benfuracarb bromophos bioallethrin bromopropylate bioallethrin S butacarboxim bioresmethrin butoxycarboxin buprofezin chlordimeform chlorfenvinphos chlorobenzilate chlorflurazuron chloropropylate chlormephos chlorophoxim cycloprothrin fenamiphos
  • 2,4-DB esters bromoxynil esters acetochlor bromoxynil aclonifen butachlor alachlor butamifos anilophos butralin benfluralin butylate benfuresate carbetamide bensulide chlornitrofen benzoylprop- thyl chiorpropham cinmethylin flurochloralin haloxyfop clethodim ethoxyethyl clomazone haloxyfop-methyl clopyralid esters ioxynil esters CMPP esters isopropalin cycloate MCPA esters cycloxydim mecoprop-P esters desmedipham metolachlor dichlorprop esters monalide diclofop-methyldiethatyl napropamide dimethachlor nitrofen dinitramine oxadiazon ethalfluralin oxyfiuorfen ethofumesate pendimethalin feno
  • compositions of the invention may also incorporate mixtures of two or more pesticides which may in some embodiments form a eutectic mixture having a melting point lower than that cf the separate components .
  • the pesticide may be an organosoluble derivative of a pesticidal compound which is itself poorly organosoluble or insoluble.
  • the active material may be present in amounts of, for example, from 30 to 90 weight percent, preferably from 60 to 85 more preferably from 75 to 80 weight percent based on the spray dried formulation.
  • the method of the invention is particularly advantageous for the production of microcapsules having a small particle size, for example having a VMD of 5 micrometer or less, particularly 2 micrometer or less.
  • the chief advantages of such small capsules are that they provide a higher surface area to mass ratio than larger particles, and thus give an ennance release rate and better knock-down. Further, such small capsules can penetrate soil or surface grass thatch better than larger capsules, and so are more efficacious in certain applications where sucn so l or thatch mobility is needed.
  • sucn small capsules is that, as the VMD decreases, it is possible to retain greatly increased amounts cf supercooled active m the liquid form. It s tnus possible to produce a reliable manner liquid core capsules witnout tne use of solvents, wnich m turn gives environmental advantages, as well as higner active loadings m the final product.
  • a liquid core in capsules made with a supercooled molten active has several advantages, of which the most significant from point of view of the present invention is that a liquid core will general release it active more rapidly than will a solid. This combined with small particle size gives a significant increase m active release rate.
  • a second advantage is that the core does no crystallise, thus causing rupture of the capsules, which can lead both to premature release, and to formulation instability on storage.
  • a third advantage of retaining th active m the liquid state is that there is no possibility of producing a biologically less active polymorph during crystallisation - a problem which is addressed in another way in US-A-5160530 (Griffin) .
  • any water-insoluble solvent may be employed if a solvent is deemed desirable.
  • typical solvents are aromatic solvents, particularly alkyl substituted benzenes such as xylene or propyl benzene fractions, and mixed naphthalene and alkyl naphthalene fractions; mineral oils; kerosene, dialkyl amides of fatty acids, particularly the dimethyl amides of fatty acids such as the dimethyl amide of caprylic acid; chlorinated aliphatic and aromatic hydrocarbons such as 1, 1, 1-trichloroethane and chiorobenzene, esters of glycol derivatives, such as the acetate cf the n-butyl, ethyl, or methyl ether of diethyleneglvcol, the acetate of the methyl ether of dipropyleneglycoi, ketones such as isophorone and trimethylcyclohexan
  • An advantage of the encapsulation method which the PVA is present during the encapsulation reaction is that by altering the time before the addition of the polyamine, the amount of polyurethane and pol urea in the capsule wall can be controlled with some accuracy. Since these two polymers have very different diffusivities for the encapsulated material, this ratio cf poiyurethane/polyurea provides a further, independent method for controlling the release rate of the active, addition to the control provided by varying capsule wall thickness and capsule size.
  • the solvent may be a polymerisable monomer for example an ethylenically unsaturated monomer (such as styrene, alphamethlystyrene, (m) ethylmethacrylate, a vinyly halide, or acrylonitrile) which is subsequently polymerised to give a matrix core to the capsules, thus adding further to the control of the release rate of the active.
  • ethylenically unsaturated monomer such as styrene, alphamethlystyrene, (m) ethylmethacrylate, a vinyly halide, or acrylonitrile
  • a further advantage of the encapsulation method in accordance with the invention is that it permits the production of dry compositions containing two or more active materials, where the materials are such that direct formulation of the materials (ie, without encapsulation of one or both of them) would lead to a product which is chemically or physically unstable.
  • the sai actives may be separately encapsulated, but an alternative and preferred embodiment, one or more of the active materials (or some portion of a single active material) may be encapsulated by the metnod accordance with the invention, and the balance not encapsulated. In this way, the unencapsulated active material is immediately biologically available upon application, whereas the encapsulated material is released more slowly.
  • the amount of each material employed sucn different forms will vary dependent upon the particular application but m general terms, each such material may constitute from 0.1 to 99.9% oy weight of tne total cf tne encapsulated material.
  • the microcapsules accordance with the invention may be prepared by nign shear mixing of a solution or a melt containing the active material (eg. pesticide) the PVA (as an aqueous solution 1 , and one of tne materials for producing the interfacial polycondensation (eg. isocyanate) .
  • the PVA acts as an emulsifier, and m some systems, no furtner emulsifier may be required. It is desirable however to add additional emuisifiers, which may be of generally known type order to produce tne desired emulsion of small particle size.
  • tnen the other polymeric cross- linker is added (eg. polyamine) , to complete the interfacial polycondensation.
  • a preferred reactant for the polycondensation is a polyamine, which is usually a water soluble, reactive polyamine, such as diethylene triamine or tetraethylene pentamine. These amines start to react with the isocyanate at the interface as soon as they are added to the emulsion. More complete control can sometimes be achieved by using either a water-soluble amine salt, or an oil-soluble amine salt, dissolved respectively in the aqueous phase or the oil phase at an- early stage in the process (for example, before emuisif cation) . By virtue cf the fact that they are salts, they do not immediately reac t with the isocyanate, out do so promptly when the pH is adjusted to liberate the free amine, whereupon cross- linking occurs .
  • a polyamine which is usually a water soluble, reactive polyamine, such as diethylene triamine or tetraethylene pentamine.
  • the high shear mixing can be performed on a batch of the ingredients, or may be conducted continuously (in ⁇ line, 1 .
  • the time of addition or release of tne reactive amine is governed by the processing time required to form the emulsion wit the correct particle size distribution 'whicn clearly s paten size dependent ⁇ , wniist m tne
  • tne interfacial reaction can oe petter controlled, since tne amme can be added/released at any desired time simply by choice cf injection point the process stream, thus giving essentially complete control over tne urea/urethane ratio.
  • tne PVA employed m the process cf the invention may be added at the outset, for formation cf the microcapsules. Usually, however, it is preferable to add additional PVA after microcapsule formation, but before spray drying.
  • the ratio of the amount of PVA added at the second stage to that added initially present is typically at least 0.5:1.
  • emulsifiers emulsifiers, dispersants, disintegration aids, salts and film-forming polymers.
  • Figure 1 illustrates tne dependence of crystaliinity on VMD
  • Figure 2 illustrates the effect of crystaliinity on residuality.
  • An emulsion was prepared by high shear mixing of an aqueous 20% w/w PVA solution (GL03, Nippon Gohsei, 88% hydroiysed, degree of polymerisation approximately 300) maintained at 55°C a water bath.
  • Molten chlorpyrifos was mixed witn a polymeric isocyanate (VORANAT ⁇ M220j tne amount shown oelow, and tne mixture added to the PVA solution in the water bath, under hi ⁇ h shear.
  • the wet capsule phase was then mixed (5kg) with 0.855kg GL03 as a 21% aqueous solution together with deionised water to adjust the suspension viscosity to an appropriate level for spray drying (conveniently about 100 mPas..
  • the icrocapsule suspension was spray-dried producing a dry product 5 containing approximately 75% w/w cnlorpy ⁇ fos .
  • the further PVA was such as to provide a ratio of approximately 66 percent of the first PVA, and 33 percent of tne furtner PVA the dry product.
  • the spray drying was carried out using an inlet temperature of from 120°C to 150°C, and an outlet C temperature of from 65°C to 85°C.
  • the product was a slightly off white free flowing powder with a water content of approximately 3.5 percent.
  • the particle size (vmd) of tne wet capsule product and cf the cry product wnen put nto water and allowed to disperse were botn about 1 5 micrometre.
  • the release rate of the product was tested by spraying 0 a dilution containing 1000 ppm by weignt of active material onto glass slides and measuring the amount left after storing the slides m a fixed temperature environment at 20°C with constant air-flow for 24 hours.
  • the product from Example 1 gave a residual figure cf 95% retained on the 5 glass slide.
  • Diethylenetriamme 1.56g dissolved 65g water This wet capsule phase (5kg) was then mixed with 200g of a 10% solution of a carboxylated PVA (Trade Mark KM118) and spray-dried as described above to produce a dry product containing approximately 75% w/w chlorpyrifos .
  • the particle size (VMD) cf the wet capsule product and the dry product when put into water and allowed to disperse was about 0.6 micron.
  • a glass slide residue test with this product showed only 30% remaining after a 24 hour storage period, illustrating the control over the release characteristics possible with this invention.
  • Example 1 has more isocyanate, and therefore thicker walls than Example 2.
  • Example- 1 has a larger VMD than Example 2, and so has a proportionately lower interfacial area.
  • Example 2 was made in-line, and Example I was made by a batch process, the amine was added earlier in Exampl ' e 2 than in Example 1.
  • compositions were prepared by the same genera method as in Example 1, by varying the amounts of the materials as shown in Table 1 (amounts are in grams) .
  • Table 1 illustrates the ease with which release characteristics may be controlled.
  • Chlorpyrifos-methyl was dissolved an aromatic solvent (Solvesso 200) and then encapsulated using the tecnn ⁇ ue above, using tne following recipe.
  • This wet capsule phase had a particle size (v d) of 1.72 microns.
  • the product was mixed with sufficient PVA solution (GL03) to produce a dry product containing approximately 50% w/w chlorpyrifos-methyl when spray dried as above to give a free-flowing powder containing about 50% w/w chlorpyrifos-methyl as an encapsulated product.
  • This product was stable on storage, releasing the small capsules readily on addition to water.
  • the product on addition to water produced a particle size (vmd) of 1.66 microns, demonstrating the ability of such products to disperse back to the wet capsule size distribution on addition to water.
  • a series of products containing chlorpyrifos were prepared with different particle size distributions and these products were stored at ambient temperature .
  • Chlorpyrifos has a melting point of about 40-42 deg C. At ambient temperature, such encapsulated products would be expected to crystallise over a period of time. The occurrence of crystallisation can be determined by the use of Differential Scanning Calorimetry (DSC) where the melting-point endotherm can be used to indicate how much of a product is in the crystalline state. Using this technique it was found that surprisingly very little chlorpyrifos crystallised in the systems of the invention, as compared to a product prepared according to US-A-516053C (Griffin) in which chlorpyrifos was emulsified in a solution of PVA and then spray-dried to produce a dry product .
  • DSC Differential Scanning Calorimetry
  • Figure 1 illustrates the dependence of the measured crystaliinity on particle VMD, for a number of compositions in accordance with the invention, as compared with the corresponding Example produced according to US-A-5160530 ("Griffin Example”) .
  • the Griffin Example has a degree of crystaliinity of about 30%, with a VMD of 0.4 micrometres, whilst the expected value for a material of this size encapsulated in accordance with the invention would be about 3%.
  • the encapsulation results in a surprising stabilisation of the metastable liquid state.
  • the effect of crystaliinity (and thus, indirectly, of particle size) on residuality is illustrated in Figure 2.

Abstract

Cette invention concerne la micro-encapsulation de divers matériaux, notamment de matériaux pesticides, afin d'obtenir des préparations sèches ou en solution. Cette invention concerne en particulier l'encapsulation de ces matériaux par l'incorporation d'un alcool de polyvinyle à un système de polycondensation interfaciale afin d'obtenir des microcapsules. Celles-ci seront ensuite séchées par atomisation en présence de l'alcool de polyvinyle, voire même d'une quantité supplémentaire d'un alcool de polyvinyle pouvant être ou non le même que celui employé lors de l'étape d'encapsulation. Le produit ainsi encapsulé peut ensuite être dilué dans l'eau afin d'obtenir des compositions pesticides aqueuses qui pourront être appliquées par les techniques de pulvérisation traditionnelles.
EP95941498A 1995-01-19 1995-11-30 Procede et produit de micro-encapsulation Ceased EP0804284A1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
GB9501017 1995-01-19
GBGB9501017.9A GB9501017D0 (en) 1995-01-19 1995-01-19 Microencapsulation process and product
PCT/US1995/015543 WO1996022159A1 (fr) 1995-01-19 1995-11-30 Procede et produit de micro-encapsulation

Publications (1)

Publication Number Publication Date
EP0804284A1 true EP0804284A1 (fr) 1997-11-05

Family

ID=10768235

Family Applications (1)

Application Number Title Priority Date Filing Date
EP95941498A Ceased EP0804284A1 (fr) 1995-01-19 1995-11-30 Procede et produit de micro-encapsulation

Country Status (14)

Country Link
EP (1) EP0804284A1 (fr)
JP (1) JP4155411B2 (fr)
KR (1) KR19980701505A (fr)
CN (1) CN1096882C (fr)
AU (1) AU716412B2 (fr)
BR (1) BR9510518A (fr)
CA (1) CA2209630A1 (fr)
CZ (1) CZ212597A3 (fr)
GB (1) GB9501017D0 (fr)
HU (1) HUT77646A (fr)
NZ (1) NZ297679A (fr)
PL (1) PL321376A1 (fr)
UA (1) UA48160C2 (fr)
WO (1) WO1996022159A1 (fr)

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* Cited by examiner, † Cited by third party
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GB9615158D0 (en) * 1996-07-19 1996-09-04 Dowelanco Process for preparing storage-stable pesticide dispersion
US20020197469A1 (en) 1998-10-26 2002-12-26 Richard Roy Clikeman Particles and a process for preparing the same
JPH11322587A (ja) * 1998-05-18 1999-11-24 Sumitomo Chem Co Ltd 常温で固体の生理活性物質のマイクロカプセル化方法およびこの方法により得られるマイクロカプセル組成物
FR2867395B1 (fr) † 2004-03-15 2006-06-16 Rhodia Chimie Sa Emulsion sechee, son procede de preparation, et ses utilisations
CN101856019A (zh) * 2010-06-04 2010-10-13 广东省粮食科学研究所 一种新型储粮害虫缓释杀虫剂及其制备方法
TWI556737B (zh) * 2011-02-11 2016-11-11 陶氏農業科學公司 改良的殺蟲劑配方
BR102012027933A2 (pt) * 2011-11-01 2015-11-17 Dow Agrosciences Llc composições pesticidas estáveis
CA2879854C (fr) 2012-07-27 2021-07-20 Fmc Corporation Formulations de clomazone
AU2018234835B2 (en) * 2017-03-17 2023-01-12 Corteva Agriscience Llc Microencapsulated nitrification inhibitor compositions
CN111972422B (zh) * 2019-05-21 2022-10-25 江苏龙灯化学有限公司 一种含有微胶囊的除草组合物及其制备方法和用途
CN110876378A (zh) * 2019-12-11 2020-03-13 利民化学有限责任公司 一种智能微胶囊悬浮剂及其制备方法

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GB1538075A (en) * 1975-03-24 1979-01-10 Champion Paper Co Ltd Formation of microcapsules by interfacial cross-linking and microcapsules produced thereby
EP0214936B1 (fr) * 1985-09-13 1992-07-08 Ciba-Geigy Ag Procédé de préparation de microcapsules
HU208218B (en) * 1986-07-09 1993-09-28 Monsanto Co Pesticidal granulated compositions dispersible in freely flowing water and process for producing same
US5225118A (en) * 1990-08-15 1993-07-06 Boise Cascade Corporation Process for manufacturing polyurea microcapsules and product therefrom
US5283153A (en) * 1992-04-15 1994-02-01 Xerox Corporation Encapsulated toner processes
KR100313589B1 (ko) * 1993-02-09 2002-11-29 노바티스 아게 미세캡슐의 제조방법

Non-Patent Citations (1)

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Also Published As

Publication number Publication date
AU4290096A (en) 1996-08-07
CN1096882C (zh) 2002-12-25
CN1173145A (zh) 1998-02-11
JP4155411B2 (ja) 2008-09-24
CZ212597A3 (en) 1997-12-17
MX9705484A (es) 1997-10-31
JPH11500346A (ja) 1999-01-12
HUT77646A (hu) 1998-07-28
NZ297679A (en) 1999-11-29
GB9501017D0 (en) 1995-03-08
WO1996022159A1 (fr) 1996-07-25
AU716412B2 (en) 2000-02-24
KR19980701505A (ko) 1998-05-15
UA48160C2 (uk) 2002-08-15
CA2209630A1 (fr) 1996-07-25
PL321376A1 (en) 1997-12-08
BR9510518A (pt) 1998-07-07

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