U.S. patent application number 10/007328 was filed with the patent office on 2002-07-04 for novel process to prepare microencapsulated formulations.
Invention is credited to Wang, Wenhua W..
Application Number | 20020086045 10/007328 |
Document ID | / |
Family ID | 22320792 |
Filed Date | 2002-07-04 |
United States Patent
Application |
20020086045 |
Kind Code |
A1 |
Wang, Wenhua W. |
July 4, 2002 |
Novel process to prepare microencapsulated formulations
Abstract
Provided is a method of encapsulating a chemical agent
comprising: (a) combining particles of a chemical agent and an
encapsulation effective amount of a first encapsulating agent in an
aqueous solvent and (b), converting the first encapsulating agent
to a polymer to form encapsulated particles of the chemical
agent.
Inventors: |
Wang, Wenhua W.; (Levittown,
PA) |
Correspondence
Address: |
FMC Corporation
Patent Administrator
1735 Market Street
Philadelphia
PA
19103
US
|
Family ID: |
22320792 |
Appl. No.: |
10/007328 |
Filed: |
November 8, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10007328 |
Nov 8, 2001 |
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09437938 |
Nov 10, 1999 |
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6387385 |
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60108189 |
Nov 12, 1998 |
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Current U.S.
Class: |
424/408 |
Current CPC
Class: |
B01J 13/22 20130101;
B01J 13/18 20130101; B01J 13/06 20130101 |
Class at
Publication: |
424/408 |
International
Class: |
A01N 025/34 |
Claims
What is claimed:
1. A method of encapsulating a chemical agent comprising: (a)
combining, in an aqueous solvent, particles of a chemical agent
suspended in the aqueous solvent and an encapsulation effective
amount of a first encapsulating agent; and (b) converting the first
encapsulating agent to an encapsulating polymer, thereby forming
encapsulated particles of the chemical agent.
2. The method of claim 1, wherein the converting of step (b) is:
(i) where the first encapsulating agent is a polymer, changing the
pH of the aqueous solvent to precipitate the polymer; or (ii) where
the first encapsulating agent comprises water-dispersible
oligomers, polymers, or mixtures thereof, forming the precipitated
polymer from the encapsulating agent.
3. The method of claim 2, wherein the converting is according to
(ii) and the converting process further comprises heating the
combined particles and first encapsulating agent to at least about
40.degree. C.
4. The method of claim 3 wherein the encapsulating polymer is
selected from the group consisting of: ureformaldehyde resin,
melamine formaldehyde resin, phenol formaldehyde resin, resorcinol
formaldehyde resin, butylated urea formaldehyde resin,
polyisocyanate, glycoluril formaldehyde resin, and
poly(methylolacrylamide).
5. The method of claim 4 wherein the polyisocyanate comprises
residues derived from an alkylene diisocyanate.
6. The method of claim 5 wherein the alkylene diisocyanate is
hexamethylene diisocyanate.
7. The method of claim 2, wherein the converting is according to
(ii) and wherein the first encapsulating agent forms an
encapsulating polymer selected from the group consisting of:
polyisocyanates, formaldehyde copolymers, a polyacrylamide, and
phenoxy resin.
8. The method of claim 2, wherein the converting is according to
(i) and the method further comprises: (c) reacting the
encapsulating polymer with a first curing agent.
9. The method of claim 8, wherein reacting comprises heating to a
temperature of at least 40.degree. C.
10. The method of claim 8 wherein the first curing agent is an
inorganic or organic salt having a multivalent cation.
11. The method of claim 10 wherein the first curing agent is
selected from the group consisting of: calcium chloride, calcium
carbonate, magnesium chloride, calcium lignosulfonate, calcium
alkylbenzene sulfonate, and calcium stearate.
12. The method of claim 11 wherein the first curing agent is
calcium lignosulfate.
13. The method of claim 9 wherein the first curing agent is
selected from the group consisting of: diamines, silanes,
aldehydes, polyhydroxides, epoxides, diepoxides, or water soluble
amino resins.
14. The method of claim 13 wherein the first curing agent is
formaldehyde.
15. The method of claim 8 further comprising: (d) combining the
encapsulated particles of step (c) with a second encapsulating
agent.
16. The method of claim 15, further comprising heating the
combination of step (d) to a temperature of at least about
40.degree. C.
17. The method of claim 15 wherein the second encapsulating agent
forms a second encapsulating polymer selected from the group
consisting of: formaldehyde copolymers, polyisocyanates, a
polyacrylamide, and phenoxy resin.
18. The method of claim 17 wherein the second encapsulating polymer
is selected from the group consisting of: ureformaldehyde resin,
melamine formaldehyde resin, polyisocyanates, phenol formaldehyde
resin, resorcinol formaldehyde resin, butylated urea formaldehyde
resin, glycoluril formaldehyde resin, and methylolacrylamide.
19. The method of claim 18 wherein the polyisocyanate comprises
residues derived from an alkylene diisocyanate.
20. The method of claim 19 wherein the alkylene diisocyanate is
hexamethylene diisocyanate.
21. The method of claim 1, wherein the particles have an size
ranging from about 1 .mu.m to about 100 .mu.m.
22. The method of claim 1, wherein the viscosity of the suspension
does not significantly increase during the converting of step
(b).
23. The method of claim 1 wherein the converting is effected by
lowering the pH of the aqueous solvent.
24. The method of claim 23 wherein the first encapsulating agent is
a polymer selected from the group consisting of: polyanhydrides,
polyanhydride acids, polyanhydride salts, polyanhydride esters,
styrene maleic anhydride copolymers and hydrolysis and
neutralization products thereof, polysaccharides, acrylic acid
polymers, polyacrylamides, acrylic polymers,
hydrophobically-modified polyacrylic acids, and salts of alkyl
naphthalene sulfonate polymers.
25. The method of claim 24 wherein the first encapsulating agent is
selected from the group consisting of: maleic anhydride copolymer
disodium salt, styrene maleic anhydride copolymer amide ammonium
salt, styrene maleic anhydride copolymer ammonium salt, poly(methyl
vinyl ether-co-maleic anhydride), N-methylolacrylamide, and
poly(vinyl chloride-co-vinyl acetate-co-hydroxyl acrylate).
26. The method of claim 23 wherein the pH is lowered by adding an
acid selected from the group consisting of: hydrochloric acid,
hydrobromic acid, hydroiodic acid, sulfuric acid, perchloric acid,
phosphoric acid, acetic acid, trifluoroacetic acid, citric acid,
and 2,2,2-trifluoroethanol.
27. The method of claim 26 wherein the acid is acetic acid.
28. The method of claim 1 wherein the chemical agent is a bioactive
agent.
29. The method of claim 28 wherein the bioactive agent is a
pesticide.
30. The method of encapsulating a chemical agent according to claim
2 wherein the converting is according to (ii) and the change in pH
is a decrease in pH, effected by addition of acid, to less than
about 6 and further comprising adding a curing agent, which is a
calcium salt, and heating the resulting mixture to a temperature
above about 40.degree. C.
31. The method of claim 30 further comprising the steps of
combining the product of claim 31 with a water-dispersible
polyisocyanate based on hexamethylene diisocyanate and heating the
resulting combination to a temperature above about 40.degree. C.
Description
[0001] This application claims benefit of U.S. Provisional
Application No. 60/108,189, filed Nov. 12, 1998.
[0002] The present invention relates to improved formulations of
solid chemical agents. In particular, the invention relates to
encapsulated or capsule suspension (CS) formulations of particles
of solid chemical agent compositions, such as pesticides, and more
particularly it pertains to the coating of solid particles with
polymer film(s) in an aqueous environment.
[0003] It is known that solid materials can be microencapsulated by
solvent evaporation, solvent extraction, coacervation, in-situ
polymerization, and spray-drying. However, these microencapsulation
processes tend to involve either the use of organic solvents which
are often toxic or hazardous to either the environment or the
personnel involved, or the processes are complicated and difficult
to apply on a commercial scale. As a result, there are but a few
methods by which solid insoluble chemical agents can be safely and
efficiently microencapsulated.
[0004] The present invention provides encapsulating techniques that
are water-based and hence economical and environmentally friendly.
By avoiding organic solvents, the costs and dangers of recycling
such materials are avoided. The method can be conducted in
relatively simple equipment using relatively simple process
steps.
[0005] A surprising observation is that encapsulation can be
conducted with an encapsulating agent that can be transformed into
an insoluble form and which, in the insoluble form, can coat the
solid material. Further, the process of encapsulation can
unexpectedly be conducted in an aqueous suspension without
agglomerating the particles of solid material.
SUMMARY OF THE INVENTION
[0006] The present invention relates to encapsulated or capsule
suspension (CS) formulations of chemical agents that are coated
with a first encapsulating agent and then optionally double-coated
with a second encapsulating agent. The particles of the
encapsulated formulation preferably have a particle size from about
1 .mu.m to about 100 .mu.m; more preferably from about 1 .mu.m to
about 30 .mu.m. The compositions of the present invention are of
the type commonly referred to by skilled artesians as
microencapsulated.
[0007] The present invention also relates to methods for preparing
the formulations of chemical agents. The method of the invention
involves encapsulation of chemical agents according to the
following steps: (a) providing a dispersion or suspension, in an
aqueous solvent, of particles of a chemical agent (such as a
bioactive agent), a water-soluble or water dispersible first
encapsulating agent, which also has wetting agent characteristics,
and optionally an antifoam agent; (b) converting the first
encapsulating agent to an encapsulating polymer that coagulates or
precipitates from the aqueous solvent on and around the particles
of the chemical agent, thereby forming encapsulated particles of
the chemical agent.
[0008] In preferred embodiments, the encapsulated particles remain
in suspension. The process can involve a step (c) of reacting the
precipitated encapsulating polymer with a first curing agent.
Certain embodiments involve the further steps of (d) optionally
agitating the dispersion while adding to it, either neat or in an
aqueous solution or dispersion, a second encapsulating agent and;
(e) optionally curing the second encapsulating agent by raising the
temperature. In one embodiment, all of the above steps are carried
out with the particles suspended in the aqueous solvent.
[0009] The process has two particularly preferred embodiments.
Where the first encapsulating agent is a polymer, the converting
step (b) comprises changing the pH of the aqueous solvent to
precipitate the polymer. Where the first encapsulating agent
comprises dispersible oligomers or dispersible polymers, the
converting step (b) comprises forming the precipitated polymer from
the first encapsulating agent.
[0010] In one particular embodiment where pH change is used in the
converting step, the first encapsulating agent is a polymer having
pendant functional groups derived from carboxylic acid anhydride
functional groups, for example, an ammonium salt of a carboxamic
acid. In this embodiment, derivatives of copolymers of styrene and
maleic anhydride are particularly useful.
[0011] In another particular embodiment where converting involves
forming the precipitated polymer, the first encapsulating agent is
a water-dispersible polyisocyanate or a polymerizable oligomer of a
suitable resin such as the oligomers that result from partial
condensation of formaldehyde with, for example, phenol, urea, or
melamine.
[0012] The encapsulated particles are, optionally, further treated
with heat alone or heat in combination with a curing agent, of
which calcium lignosulphate is but one example. In some
embodiments, the encapsulated particles are subjected to a second
encapsulation procedure in which the encapsulating agent is the
same as or different from the encapsulating agent used in the first
encapsulation. When two encapsulation procedures are carried out,
the conversion in the second procedure is advantageously effected
by forming the encapsulating polymer from the encapsulating
agent.
DEFINITIONS
[0013] Aqueous solvent: is water or a mixture of water and an
organic solvent that is freely miscible with water. Ethanol is but
one example of an organic solvent that can be mixed with water to
form an aqueous solvent. Preferably, water comprises at least about
50% v/v, more preferably about 95% v/v, of the aqueous solvent.
[0014] Average particle size shall mean that at least about 50% of
the particles shall have a diameter within .+-.5% of the diameter
cited, where diameter is measured by light scattering using an
instrument, such as a Laser Scattering Particle Size Distribution
Analyser, Horiba Instrument Corp., Irvine, Calif.
[0015] Bioactive agent: is a substance such as a chemical that can
act on a cell, virus, organ or organism, including but not limited
to drugs (i.e. pharmaceuticals) and pesticides, to create a change
in the functioning of the cell, virus, organ or organism. In one
embodiment of the invention, the method of the invention is applied
to bioactive agents that are organic molecules having molecular
weight of about 500 or less or to polymeric species such as
proteins, nucleic acids, and the like. A "pesticide" is a molecule
or combination of molecules that repels, retards, or kills pests,
such as, but not limited to, deleterious or annoying insects,
weeds, worms, fungi, bacteria, and the like, and can be used for
crop protection, edifice protection, turf protection, or protection
of a person; pesticide as used herein also refers to growth
regulators, either used to encourage growth of a desired plant
species or retard growth of an undesired pest.
[0016] Chemical agent: is an organic or inorganic compound, such as
a compound to be used as a reactant in a synthetic or preparative
process, as a reagent in an analytical method, a dye, a bioactive
agent, and the like.
[0017] Encapsulating effective amount: is an amount of
encapsulating agent which, used in a method of the present
invention, is sufficient to form a coating on or admixture with at
least 90% of the particles of chemical agent, where the coating or
admixture is a functional amount.
[0018] Encapsulating agent: is a monomeric, oligomeric, or
polymeric substance soluble or dispersible in an aqueous solvent
under at least one set of conditions and which can be converted to
an insoluble form by appropriate changes in process conditions or
chemical form. Upon such conversion, an encapsulating agent forms a
coating on or intimate solid admixture with particles dispersed or
suspended in the aqueous solvent in which the encapsulating agent
is dissolved.
[0019] Functional amount: is an amount of an encapsulant which, for
example, slows release of the encapsulated agent, reduces the
toxicity of the agent to mammals, stabilizes the form of the agent,
inhibits crystallization of the agent, reduces the volatility of
the agent, or produces any other benefit of coating a chemical
agent with a polymer or admixing the chemical agent with the
polymer.
[0020] Microparticles: are particles of chemical agent having
average diameter from about 1 .mu.m to about 1000 .mu.m.
[0021] Significant increase in viscosity: an increase of about 50%
or more in the Brookfield viscosity, as measured by a Brookfield
viscometer, Brookfield Engineering Labs Inc., Stoughton, Mass., is
considered significant. In general, an increase in Brookfield
viscosity of between about 100 cp and about 200 cp is considered
significant.
DETAILED DESCRIPTION OF THE INVENTION
[0022] The encapsulation method of the present invention is
carried-out according to one of several possible embodiments. The
encapsulation process, in any embodiment, can include adding one or
more additives, such as xanthan gum; a bactericide, for example
1,2-benzisothiazolin-3-on- e (available from ICI Americas Inc.,
Talleyville, Del.); an amphoteric surfactant, for example
laurimionodipropionate (available from Rhone-Poulenc Inc.,
Louisville, Ky. as Proxel.RTM. GXL); an inert dye, for example
Tricon Green 18800 (available from Tricol Colors, Elmwood Park,
N.J.); or an ionic dispersing agent such as an alkyl naphthalene
sulfonate.
[0023] In a particularly preferred embodiment, the particles of
chemical agent are microparticles that are dispersed throughout and
remain suspended in an aqueous solvent and the process is
carried-out in a high speed mill, such as an intermittent-type
attritor mill, in which the first encapsulating agent also
functions as a wetting agent.
[0024] A typical recipe according to the present invention will
ordinarily contain from about 5 to about 60, preferably about 20 to
about 50, weight percent of chemical agent, from about 1 to about
20, preferably about 5 to about 10, weight percent of a first
encapsulating agent relative to the weight percent of the chemical
agent to be encapsulated, and if any is used, about 0.05 to about
1, preferably about 0.1 to about 0.9, weight percent of a antifoam
agent. Antifoam agents, if any are used, may include but are not
limited to polydimethyl siloxanes.
[0025] The present invention is useful for, among other things,
encapsulating chemical agents that are solid pesticides. The term
pesticide includes but is not limited to herbicides, insecticides,
acaricides, fungicides, nematicides, ectoparasiticides, and growth
regulators. Solid pesticides that can be microencapsulated by the
present invention include, but are not limited to, carbamates,
ureas, triazines, triazoles, uracils, organophosphates,
morpholines, dinitroanilines, acylalaninies, pyrethroids, and
organochlorines. Examples of solid pesticides that can be use in
the present invention include but are not limited to carbofuran,
azinphos-methyl, sulfentrazone, carfentrazone-ethyl, cypermethrin,
cyromazine, beta-cyfluthrin, endosulfan, and phosmet. When the
solid pesticide is a herbicide, the formulations of the present
invention control the release of the herbicide causing the
herbicide to be released at a lower rate.
[0026] The encapsulating polymers or resins used as encapsulating
agents in the present invention should preferably possess wetting
agent characteristics and, in one embodiment, be pH sensitive so
that when the pH is acidic they become water-insoluble and
precipitate on the hydrophobic surface of the particles, but when
the pH is basic the polymer is soluble in aqueous solvent. By
possessing wetting agent characteristics and being pH sensitive,
the encapsulating agent serves as both a wetting agent and a
coating material. Activity as a wetting agent is evidenced by the
stability over time of the particle size and viscosity of a
suspension of particles of the chemical agent in an aqueous solvent
in which an encapsulation effective amount of the encapsulating
agent is dissolved and converted to a form that can be expected to
encapsulate the particles. This indication of wetting agent
character is particularly meaningful when a curing agent is present
that can be expected to crosslink the encapsulating agent. However,
wetting agent characteristics are also important when no curing
agent is used.
[0027] Polymers or resins useful as first encapsulating agents in
one embodiment of the present invention where the converting step
involves pH change include polyanhydrides, in particular copolymers
of maleic anhydride, as well as the acids, salts, and esters
derived therefrom. The copolymer of methyl vinyl ether and maleic
anhydride available from ISP, Wayne N.J. under the trademark
Agrimer.RTM. VEMA is another example of a commercially available
polyanhydride. Polymers formed from simultaneous or sequential
hydrolysis and neutralization of styrene maleic anhydride
copolymers (for example styrene maleic anhydride copolymer disodium
salt, styrene maleic anhydride copolymer amide ammonium salt, and
styrene maleic anhydride copolymer ammonium salt exemplify polymers
derived from maleic anhydride copolymers). A particularly preferred
encapsulating agent in this regard is the ammonium salt of the
carboxamic acid derived from a styrene-maleic anhydride copolymer
(i.e. styrene maleic anhydride copolymer amide ammonium salt)
available from Solutia, Springfield Mass., as Scripset.RTM. 720.
Still other polymers useful as encapsulating agents when the
converting step involves pH change include polysaccharides; acrylic
polymers, including polymers of acrylic acid or acrylamide;
hydrophobically-modified polyacrylic acids; and phosphate esters,
their acids and sodium salts; N-methylolacrylamide; and (vinyl
chloride/vinyl acetate/hydroxyl acrylate) copolymer.
[0028] In one embodiment, encapsulation is effected by changing pH.
For example, in certain embodiments using polymers that incorporate
carboxylate groups, the pH of the aqueous particle suspension can
be adjusted downward to a pH of from about 4 to about 7, preferably
about 6. After adjusting the pH by the addition of the acid and,
optionally, a first curing agent, the dispersion is optionally
cured by heating to a temperature in the range of, for example,
about 40.degree. to about 90.degree. C., preferably about
50.degree. to about 80.degree. C., for, for example, about 10
minutes to about five hours, preferably about 10 minutes to about
two hours.
[0029] Wet-milling, when employed, typically uses high-shear
milling. The time that the aqueous microparticle dispersion is
wet-milled is not critical, but is usually about 15 to about 50
minutes. Factors that influence the particles' size, which
determines the eventual size of the microcapsules, and the
stability of the suspension, include the speed and length of
milling, the type and amount of encapsulating agent, temperature,
and viscosity, as well as the presence of xanthan gum and alkyl
naphthalene sulfonate dispersing agent, when these are used.
Selection of the appropriate microcapsule size to achieve the
purposes of the invention requires a balance between competing
factors. In general, decreasing the amount of the first
encapsulating agent gives smaller particle size and, when decreased
beyond a certain amount, the particle size will increase and the
coating of the microcapsule may not be as uniform. Increasing the
amount of the first encapsulating agent can yield better coating
uniformity but, beyond a certain amount, can yield larger particle
size due to agglomeration. In preferred embodiments of the
invention, these parameters are selected to give a functional
amount of encapsulation while minimizing the amount of
agglomeration occurring in the encapsulation process.
[0030] In one embodiment of the present invention, the average size
of the microcapsules is about 1 .mu.m to about 100 .mu.m,
preferably about 1 .mu.m to about 30 .mu.m. The operating
conditions to yield microcapsules of a desired size will depend on
a variety of factors, including, where applicable, the size of the
starting particles, the wet-milling equipment used, the amount of
encapsulating agent and curing agent used, the number of coating
steps applied, and the like. For example, a smaller particle size
generally results when less encapsulating agent is used and longer
wet-milling time is used. In light of the present specification,
adjustment to determine the proper conditions to achieve
encapsulations within the scope of the present invention is well
within the skill of the art.
[0031] The amount of acid added, when used, can, for example in
certain embodiments, range from about 0.05 to about 5.0, preferably
about 0.1 to about 3.0, weight percent relative to the total weight
of the formulation, although this range can vary with the type of
encapsulating agent used and the type of acid used. In general, the
weight of acid added is sufficient to bring the pH of the aqueous
solvent to between about 4 and about 6. Acids that may be useful in
certain embodiments of the present invention are either protic
acids or Lewis acids. Examples of protic acids or Lewis acids that
may be used include but are not limited to hydrochloric acid,
hydrobromic acid, hydroiodic acid, sulfuric acid, acetic acid,
perchloric acid, trifluoroacetic acid, and 2,2,2-trifluoroethanol.
A preferred acid is acetic acid.
[0032] By way of example, first curing agents that may be used in
accordance with certain embodiments of the present invention are
the divalent salts, of lignosulfonates, alkylbenzene sulfonates,
and stearates. Also useful as first curing agents are diamines,
silanes (e.g. vinyltriisopropoxysilane), aldehydes, polyhydroxides,
epoxides, and water soluble amino resins. Further examples of
suitable divalent salts, include but are not limited to calcium
chloride, calcium carbonate, magnesium chloride, calcium
lignosulfonate, calcium alkylbenzene sulfonate, and calcium
stearate. An example of a suitable diamine is
2-methylpentamethylene diamine (available from DuPont, Willmington,
Del., as Dytek.RTM.) A). An example of a suitable water soluble
amino resin is Cymel.RTM. 1141, available from Cytec, W. Paterson
N.J. A preferred and economical first curing agent is calcium
lignosulfonate. When one is used, the amount of the first curing
agent added typically ranges from about 0.5 to about 10, preferably
about 1 to about 5, weight percent present relative to the total
weight of the formulation. The amount of first curing agent used
varies with the type of curing agent used. For example, when
calcium lignosulfonate is the first curing agent, relatively more
first curing agent is used compared to the case where calcium
chloride is the first curing agent.
[0033] In certain embodiments where the converting step comprises
forming the encapsulating polymer, the encapsulating agents are
water dispersible oligo- or polyisocyanates or water soluble or
dispersible resins such as formaldehyde copolymers,
polyacrylamides, and phenoxy resins. Examples of formaldehyde
copolymers, polyacrylamides, and phenoxy resins that may be used in
the present invention are urea-formaldehyde resins,
melamine-formaldehyde resins, phenol-formaldehyde resins,
resorcinol-formaldehyde, butylated urea/formaldehyde,
glycoluril-formaldehyde resins, and methylolacrylamide. Preferred
among these encapsulating agents are melamine-formaldehyde resins,
polymethylolacrylamide, and, in particular, water-dispersible
polyisocyanates. Particularly preferred water-dispersible polymeric
or oligomeric isocyanates are those based on an alkylene
diisocynate in which the alkylene group can optionally comprise a
ring structure. A particularly preferred water dispersible
oligomeric or polymeric diisocyanate comprises residues of
hexamethylene diisocyanate (e.g. Bayhydur XP-7063; Bayer
Corporation, Pittsburgh, Pa.).
[0034] In certain preferred embodiments, these encapsulating
polymers are used in a second encapsulation step, and so the
encapsulating agents that form the polymers are "second
encapsulating agents." When used in a second encapsulation step,
the amount of the encapsulating agent added, if any is used,
typically ranges from about 0.5 to 10, preferably about 1 to about
5, weight percent relative to the total weight of the encapsulated
material.
[0035] Where the encapsulating agents of the above paragraph are
used in a second encapsulation step, preferably the encapsulating
agent is added more gently than is preferred in some embodiments of
the first encapsulation. For example, stirring can be used.
Stirring is preferably continued while the encapsulating agent is
cured by heating to a temperature of about 40.degree. to about
80.degree. C., preferably about 70.degree. C., for, for example, 10
minutes to ten hours, preferably one to four hours.
[0036] The amounts of post encapsulation additives to be added are
similar for all embodiments and typically would be selected from
one or more of about 0.003 to about 0.5, preferably about 0.005 to
about 0.3, weight percent of xanthan gum; about 0.01 to about 0.1,
preferably about 0.01 to about 0.08, weight percent of one or more
bactericides; up to about 0.05, preferably up to about 0.04, weight
percent of an inert dye; and up to about 7 weight percent of one or
more surfactants, each weight percent relative to the weight of the
formulation after addition of the additives.
[0037] In certain embodiments, the suspension of chemical agent in
aqueous solvent, with or without curing agent, is filtered to
remove particles having an average particle size greater than a
selected amount, such as about 100 .mu.m. The filtering step, for
example, can be used to ensure that at least 90% of the
microencapsulated particles have a particle size not greater that
about 30 .mu.m.
[0038] The formulations of the present invention are prepared in
accordance with the procedures shown in the examples below. The
examples serve only to illustrate the invention and should not be
interpreted as limiting since further modifications of the
disclosed invention will be apparent to those skilled in the art.
All such modifications are deemed to be within the scope of the
invention as defined in the claims.
EXAMPLE 1
Preparation of a 250 Grams/Liter Carbofuran Capsule Suspension (250
CS) Formulation
[0039] A mixture of 20.0 grams of a 25% aqueous styrene maleic
anhydride copolymer amide ammonium salt solution (Scripset.RTM.
720), Solutia, Springfield, Mass., 100.0 grams of carbofuran (FMC
Corporation, Chicago, Ill.), 0.5 gram of a 100% polydimethyl
siloxane antifoam agent (Dow Corning.RTM. 1520, Dow Corning
Corporation, Midland, Mich.), and 90.0 grams of distilled water was
wet-milled for 30 minutes at high speed in an intermittent-type
attritor mill (Union Process Type B Attritor Mill, Union Process,
Inc., Akron, Ohio). After this time, the aqueous microparticle
dispersion was filtered into a one liter stainless steel beaker. To
the filtrate was added 4.0 grams of calcium chloride and 65.0 grams
of water. The pH of the mixture was adjusted to 5.7 by adding 0.8
gram (20 drops) of acetic acid. The suspension was then heated to
50.degree. C. where it was stirred at about 200 to 350 rpm for one
hour using an overhead paddle-type stirrer. After this time, 10.0
grams of a partially methylated melamine-formaldehyde resin
(Cymel.RTM. 385, Cytec Industries Inc., West Paterson, N.J.) were
added. Upon completion of addition, the formulation was heated to
70.degree. C. where it stirred for one hour. At the conclusion of
this period, 20.0 grams of aqueous 1% xanthan gum (Keizan.RTM. S,
Monsanto, St. Louis, Mo. and 10.0 grams of an nonionic polymeric
surfactant (Atlox.RTM. 4913, ICI Americas Inc., Wilmington, Del., a
subsidiary of Imperial Chemical Industries Surfacants) were added
to the formulation. The formulation after mixing for thirty minutes
had a viscosity of 336 cps.
EXAMPLE 2
Preparation of a 250 Grams/Liter Carbofuran Capsule Suspension (250
CS) Formulation
[0040] A mixture of 20.0 grams of a 25% aqueous styrene maleic
anhydride copolymer amide ammonium salt solution (Scripset.RTM.
720), 100.0 grams of carbofuran, 1.0 gram of a 100% polydimethyl
siloxane antifoam agent (Dow Corning.RTM. 1520), and 90.0 grams of
distilled water was wet-milled for 30 minutes at high speed in an
intermittent-type attritor mill (Union Process Type B Attritor
Mill, Union Process Inc., Akron, Ohio). After this time, the
aqueous microparticle dispersion was filtered into a one liter
stainless steel beaker. The pH of the filtrate (the dispersion) was
adjusted to 5.4 by adding a pre-blended solution of 8.0 grams of a
calcium lignosulfonate (Norlig.RTM. 11 DA, LignoTech USA,
Rothschild, Wis.) 0.8 gram (20 drops) of acetic acid, and 65.0
grams of distilled water. The suspension was heated to 70.degree.
C. where it was agitated for about one hour using an overhead
paddle-type stirrer. After this time, 6.0 grams of
N-methylolacrylamide (Cylink.RTM. NMA-LF, Cytec Industries Inc.,
West Paterson, N.J.) were added. Upon completion of addition, the
formulation was heated to 70.degree. C. where it stirred for one
hour. At the conclusion of this period, 10.0 grams of aqueous 1%
xanthan gum (Kelzan.RTM. S) and 10.0 grams of an nonionic polymeric
surfactant (Atlox.RTM. 4913) were added to the formulation. The
formulation after mixing for ten minutes had a viscosity of 82
cps.
EXAMPLE 3
Preparation of a 250 Grams/Liter Carbofuran Capsule Suspension (250
CS) Formulation
[0041] A mixture of 30.0 grams of a 25% aqueous styrene maleic
anhydride copolymer amide ammonium salt solution (Scripset.RTM.
720), 100 grams of carbofuran, 1.0 gram of a 100% polydimethyl
siloxane antifoam agent (Dow Corning.RTM. 1520), and 90.0 grams of
distilled water was wet-milled for 25 minutes at high speed in an
intermittent type attritor mill (Union Process Type B Attritor
Mill, Union Process, Inc., Akron Ohio). After this time, the
aqueous microparticle dispersion was filtered into a one liter
stainless steel beaker. The pH of the filtrate (the dispersion) was
adjusted to 5.6 by adding a pre-blended solution of 8.0 grams of a
calcium lignosulfonate (Norlig.RTM. 11 DA), 1.2 grams (30 drops) of
acetic acid, and 65.0 grams of distilled water. The suspension was
heated to 70.degree. C. where it was agitated at about 200 to 350
rpm for about two hours using an overhead paddle-type stirrer.
After this time, 10.0 grams of aqueous 1% xanthan gum (Kelzan.RTM.
S) and 10.0 grams of an nonionic polymeric surfactant (Atlox.RTM.
4913) were added to the formulation. The formulation was agitated
for about ten additional minutes.
EXAMPLE 4
Preparation of a 250 Grams/Liter Carbofuran Capsule Suspension (250
CS) Formulation
[0042] A mixture of 40.0 grams of an aqueous 25% styrene maleic
anhydride copolymer amide ammonium salt solution (Scripset.RTM.
720), 96.0 grams of carbofuran, 1.0 gram of a 100% polydimethyl
siloxane antifoam agent (Dow Corning.RTM. 1520), and 90.0 grams of
distilled water was wet-milled for 20 minutes at high speed in an
intermittent-type attritor mill (Union Process Type B Attritor
Mill, Union Process Inc., Akron Ohio). After this time, the aqueous
microparticle dispersion was filtered into a one liter stainless
steel beaker. The pH of the filtrate (the dispersion) was adjusted
to 5.9 by adding a pre-blended solution of 8.0 grams of a calcium
lignosulfonate (Norlig.RTM. 11 DA), 2.0 grams (50 drops) of acetic
acid, and 65.0 grams of distilled water. The suspension was
agitated at about 25.degree. C. for one hour and about 200-350 rpm
using an overhead paddle-type stirrer type stirrer and then 10.0
grams of water-dispersible polyisocyanate (Bayhydur.RTM. XP-7063,
Bayer Corp., Pittsburgh, Pa.) were added. Upon completion of
addition, the formulation was heated to 60.degree. C. where it was
agitated for about 1.5 hours. At the conclusion of this period,
about 40.0 grams of aqueous 1% xanthan gum (Keizan.RTM. S) and a
total of 25.0 grams of lignosulfonate sodium salt (15.0 grams of
Lignosol.RTM. SFX-65L and 10.0 grams of Marasperse.RTM. B-22, both
available from LignoTech USA, Rothschild, Wis.) were added to the
formulation. The formulation after mixing for ten minutes had a
Brookfield viscosity of 208 cps.
[0043] While this invention has been described with an emphasis
upon preferred embodiments, it will be obvious to those of ordinary
skill in the art that variations in the preferred devices and
methods may be used and that it is intended that the invention may
be practiced otherwise than as specifically described herein.
Accordingly, this invention includes all modifications encompassed
within the spirit and scope of the invention as defined by the
claims that follow.
* * * * *