Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Patent
1997-08-08
1999-07-20
Nutter, Nathan M.
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
42840221, 42840224, 4272133, 42721331, 42721332, 42721333, 42721334, 264 41, 264 43, 264 432, 264 433, 264 46, 264 47, B01J 1316
Patent
active
059254645
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the microencapsulation of various materials, in particular pesticidal materials, to produce both wet and dry formulations. In particular, 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.
The encapsulation of pesticides, plant growth regulators, and the like is a field which has attracted increasing interest in recent years. For safety and ease of distribution, it is particularly convenient to supply such materials in the form of aqueous dispersions of dry solids, which can be dispersed easily in water for field application.
Various proposals have been made in recent years for the microencapsulation of various pesticidal materials. For example, U.S. Pat. No. 5,160,530 (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 polyvinylalcohol (PVA). The materials are then emulsified together and spray dried.
U.S. Pat. No. 4,244,836 (Hoechst) discloses a similar method of encapsulating pesticidal materials, by spray drying a dispersion of the active material and a PVA.
Although for some systems, 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 (particularly in the Griffin method) that undesired polymorphs of the molten active material may he produced upon cooling to ambient temperature.
U.S. Pat. No. 4,936,901 (Monsanto) discloses an alternative method of encapsulation, in which microcapsules containing the active material are formed by means of an interfacial polycondensation reaction, involving an isocyanate/polyamine reaction. The resulting interfacially polymerised microcapsules are subsequently spray dried. This reference mentions that PVA may be used as a suspension adjuvant in the spray drying step. Again, this method results in the production of microcapsules with uncontrollable release characteristics. Also, some active materials show a tendency to diffuse out of the interfacially polymerised microcapsules during storage, thus producing crystallisation (in the case of actives normally solid at ambient temperatures). Another difficulty with this method is that the products which result all have slow release characteristics, because of their large particle size distribution and thick polymer wall.
One particular problem which this reference does not address at all is the production of microcapsules which provide rapid release of the active material, rather than sustained or delayed release. Often a controlled release formulation will be required to produce a rapid biological effect ("knock-down") followed by a sustained release ("residuality") of the active. Rapid release capsules are generally required to be small in size (typically with a volume mean diameter (VMD) less than 5 micrometers) or have extremely thin polymer shell walls. None of the systems prepared in U.S. Pat. No. 4,936,901 have the small particle size normally required to provide rapid knock-down. The only information about particle size giver in the reference is that 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 micrometers.
It is known furthermore from, for example EP-A-0611253, U.S. Pat. No. 5,332,584 and U.S. Pat. No. 5,324,584 to use PVAs as surfactants or protective colloids in pesticide encapsulation processes. These references do not suggest however that the PVA takes an active part In shell wall formation, such that it can influence and permit effective control over the release characteristics of the microcapsules produced.
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U.S. application No. 08/960,937, Mulqueen et al., filed Oct. 30, 1997.
U.S. application No. 08/615,326, Mulqueen et al., filed Aug. 2, 1996.
Lubetkin Steven D.
Mulqueen Patrick Joseph
Smith Geoff
Dow AgroSciences LLC
Nutter Nathan M.
Osborne D. Wendell
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