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, in 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, in order to produce aqueous pesticidal compositions, which can be applied by conventional spray techniques.
• regulators, and the like is a field which has attracted increasing interest in recent years.
• US-A-5160530 (Griffin. discloses a process for encapsulating pesticides (for example trifluralin), by melting the active material, and combining the melted material with a film-forming polymer, such as a
• PVA polyvinylalcohol
• US-A-4244836 discloses a similar method of encapsulating pesticidal materials, by spray drying a dispersion of the active material and a PVA.
• US-A-4936901 discloses an alternative method of encapsulation, in which microcapsules containing the active material are formed by means of an interfacial polycondensation reaction, involving an
• Rapid release capsules are generally required to be small in size (typically with a volume mean diameter (VMD) less than 5 micrometres) or have extremely thin polymer shell walls. None of the systems prepared in US-A-4936901 have the small particle size normally required to provide rapid knock-down. The only information about particle size given in the reference is that particle the size distribution (not the VMD) is from 1-50 microns. The surfactants taught as essential to the reference are of a kind which would not be suitable for the formation of such capsules with a VMD of less than 5 micrometres.
• microcapsules and subsequently spray drying the resulting microcapsules in the presence of the PVA and optionally a further quantity of PVA which may be the same or different from the one adopted in the microencapsulation step, microcapsules can be obtained which show improved storage stability, especially to the leaching of the active
• microcapsules 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 be 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 in the microencapsulation step may be one with a degree of polymerisation of from 50 to 5,000, and a degree of hydrolysis of from ⁇ 0% to 100%. Desirable characteristics for the PVA are that it should be an efficient emulsifier prior to the polycondensation step, that it can assist the stabilisation of the capsules wnilst they are forming, and also that it can assist the re-wetting of the capsules after spay drying when they are ultimately used. These requirements are not all optimally met in 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 which may be added prior to the spray drying step is mainly selected on the basis of its poor solvent qualities for the encapsulated material, and for its ease of re-wetting in cold (and possibly hard) water.
• Chemically modified PVAs, such as the sulphonated or carooxylated PVAs, are particularly useful for this purpose.
• microcapsules may be carried out by any of the various methods known to those skilled in the art.
• the interfacial layer In a preferred embodiment, 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 may be a pesticidal material, for example
• 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 of 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 enhanced release rate and better knock-down.
• such small capsules can penetrate soil or surface grass thatch better than larger capsules, and so are more efficacious in certain applications where such soil or thatch mobility is needed.
• Yet another benefit of such small capsules is that, as the VMD decreases, it is possible to retain greatly increased amounts of supercooled active in the liquid form. It is thus possible to produce in a reliable manner liquid core capsules without the use of solvents, which in turn gives environmental advantages, as well as higher active loadings in the final product.
• 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 chlorobenzene, 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 dipropyleneglycol, ketones such as isophorone and trimethylcyclohexan
• An advantage of the encapsulation method in 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 polvurea in the capsule wall can be controlled with some accuracy. Since these two polymers have very different diffusivities for the
• this ratio of poiyurethane/polyurea provides a further, independent method for controlling the release rate of the active, in 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
• PVA unsaturated monomer
• 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 said actives may be separately encapsulated, but in an
• one or more of the active materials may be encapsulated by the method in 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 in such different forms will vary dependent upon the particular application but in general terms, each such material may constitute from 0.1 to 99.9% by weight of the total of the encapsulated material.
• microcapsules in accordance with the invention may be prepared by high shear mixing of a solution or a melt containing the active material (eg. pesticide) the PVA (as an aqueous solution) , and one of the materials for
• the PVA acts as an emulsifier, and in some systems, no further emulsifier may be required. It is desirable however to add additional emuisifiers, which may be of generally known type in order to produce the desired emulsion of small particle size.
• additional emuisifiers which may be of generally known type in order to produce the desired emulsion of small particle size.
• 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 emuisification) . By virtue of the fact that they are salts, they do not immediately react 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 (inline).
• the time of addition or release of the reactive amine is governed by the processing time required to form the emulsion with the correct particle size distribution (which clearly is paten size dependent), whilst in the latter case, the interfacial reaction can be petter controlled, since the amine can be added/released at any desired time simply by choice of injection point in the process stream, thus giving essentially complete control over the urea/urethane ratio.
• 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 2 illustrates the effect of crystaliinity on residuality.
• An emulsion was prepared by high shear mixing of an aqueous 20% w/w PVA solution (GLO3, Nippon Gohsei, 88% hydrolysed, degree of polymerisation approximately 300) maintained at 55 °C in a water bath.
• Molten chlorpyrifos was mixed with a polymeric isocyanate (VORANATE M220) in the amount shown oelow, and the mixture added to the PVA solution in the water bath, under high shear.
• the diethylene- triamine was added under high shear.
• the further PVA was such as to provide a ratio of approximately 66 percent of the first PVA, and 33 percent of the further PVA in the dry product.
• the spray drying was carried out using an inlet temperature of from 120°C to 150°C, and an outlet 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 the wet capsule product and of the cry product when put into water and allowed to disperse were both about 1 micrometre.
• the release rate of the product was tested by spraying a dilution containing 1000 ppm by weight of active material onto glass slides and measuring the amount left after storing the slides in a fixed temperature environment at 20°C with constant air-flow for 24 hours.
• the product from Example 1 gave a residual figure of 95% retained on the glass slide.
• 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.
• a carboxylated PVA Trade Mark KM118
• VMD particle size
• Example 1 has more isocyanate, and therefore
• Example 1 has a larger VMD than Example 2, and so has a proportionately lower interfacial area. (iii) Because Example 2 was made in-line, and Example I was made by a batch process, the amine was added earlier in Example 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).
• Chlorpyrifos-methyl was dissolved in an aromatic solvent (Solvesso 200) and then encapsulated using the tecnnigue above, using the following recipe. Chlorpyrifos-methyl 42g (technical)
• This wet capsule phase had a particle size (vmd) of 1.72 microns.
• the product was mixed with sufficient PVA solution (GL03) to produce a dry product containing
• 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.
• 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.
• 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

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Life Sciences & Earth Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Dispersion Chemistry (AREA)
• General Health & Medical Sciences (AREA)
• Health & Medical Sciences (AREA)
• Pest Control & Pesticides (AREA)
• Dentistry (AREA)
• Wood Science & Technology (AREA)
• Zoology (AREA)
• Environmental Sciences (AREA)
• Engineering & Computer Science (AREA)
• Toxicology (AREA)
• Plant Pathology (AREA)
• Agronomy & Crop Science (AREA)
• Agricultural Chemicals And Associated Chemicals (AREA)
• Manufacturing Of Micro-Capsules (AREA)

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Citations (5)

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• 1995
  • 1995-01-19 GB GBGB9501017.9A patent/GB9501017D0/en active Pending
  • 1995-11-30 NZ NZ297679A patent/NZ297679A/xx not_active IP Right Cessation
  • 1995-11-30 CA CA002209630A patent/CA2209630A1/en not_active Abandoned
  • 1995-11-30 BR BR9510518A patent/BR9510518A/pt not_active IP Right Cessation
  • 1995-11-30 EP EP95941498A patent/EP0804284A1/en not_active Ceased
  • 1995-11-30 WO PCT/US1995/015543 patent/WO1996022159A1/en not_active Application Discontinuation
  • 1995-11-30 CZ CZ972125A patent/CZ212597A3/cs unknown
  • 1995-11-30 HU HU9800551A patent/HUT77646A/hu not_active Application Discontinuation
  • 1995-11-30 PL PL95321376A patent/PL321376A1/xx unknown
  • 1995-11-30 KR KR1019970704896A patent/KR19980701505A/ko not_active Application Discontinuation
  • 1995-11-30 JP JP52224096A patent/JP4155411B2/ja not_active Expired - Lifetime
  • 1995-11-30 CN CN95197380A patent/CN1096882C/zh not_active Expired - Lifetime
  • 1995-11-30 AU AU42900/96A patent/AU716412B2/en not_active Expired
  • 1995-11-30 UA UA97073815A patent/UA48160C2/uk unknown

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