MICROENCAPSULATION
The present invention relates to a novel process for making microcapsules and to
microcapsules made by the process. It also relates to a process for the use of the
microcapsules.
Microcapsules are small capsules which comprise a wall which surrounds an
encapsulated material, generally a liquid. They may be used for protecting the encapsulated
material from the external environment, for example from degradation by air or light
(especially u.v. radiation). They may also be used to isolate hazardous materials within the
microcapsule to make them safer to handle or use. Microcapsules are known to be used for
agrochemicals, particularly insecticides such as lambda c)thalothrin, to protect them from
degradation by UV light and to provide controlled release following application.
Certain known microcapsules are made by interfacial polymerisation. In such a
process a solution is first formed of a first monomer, such as a polyisocyanate, in a waterinsoluble
liquid to be encapsulated. The solution may also contain a biologically active
ingredient. This solution is then dispersed in water "together with surfactants to form an
emulsion. A suitable second monomer such as a polyamine is added to the water and this
reacts with the first monomer at the surface of the emulsion droplets to make a cross-linked
polymer, in this example a polyurea, which forms a microcapsule wall around the droplets.
Known first and second monomers also include polyisocyanate and polyol to make a
polyurethane wall, polyfunctional acid halide and polyamine to make a polyamide wall and
polyfunctional acid halide and polyol to make a polyester wall.
There are disadvantages of these types of microcapsules. Polymeric capsule walls of
this known type provide poor protection for the contents from UV light. Also, the surfactant
which is used to form the emulsion may lead to a problem when later handling the dispersion
of microcapsules because it may cause foaming.
In one known approach, photoprotectants form part or all of the microcapsule wall
materials and thus provide a shield for the capsule, thereby protecting any photosensitive
active ingredient that is present within the capsules. For example CA2133779 shows that
lignosulphonates and the like can be used in combination with a protein such as a high bloom
gelatin to form a capsule wall that improves the resistance of agriculturally active substances,
such as pesticides, to U.v. light degradation. The capsule wall formed by the interaction of
these components is durable and has a u.v. protectant as an integral part ofits structure.
Moy describes in EP539142Al the use of colloidal inorganic particles, particularly
those of silica and zirconium dioxide, to make microcapsules by coacervation or by
interfacial polymerisation methods. The process involves the formation of so called
Pickering emulsions and the thermoset microcapsule wall comprises the inorganic particles.
Moy does not contemplate the use of surface-modified particles, not the use of cross-linkers
to form the capsule wall.
Co-pending international application PCT/GB2007/003374 is concerned with light
protecting particles which are chemically bonded to the microcapsule wall but does not
contemplate microcapsule walls formed from light protecting particles themselves.
The present invention provides an aqueous dispersion of microcapsules having a
cross-linked particulate inorganic wall in an aqueous medium. In a further aspect, these
microcapsules may be further modified by adding, to the aqueous medium, a material which
will further react with any remaining cross-linker. For example, when the cross-linker is a
polyisocyanate, a polyamine such as diethylentriamine may be added. This causes further
cross-linking and polymer fonnation at the microcapsule particulate inorganic wall and may
be used to modify the durability of the capsules or permeability of the capsule walls to give,
for example, a longer release time under given conditions.
Brief Description of the Drawings:
The invention will be better understood with reference to the detailed description
when considered in conjunction with non-limiting examples and the accompanying drawings.
Figure 1 is a light microscope image of the clay dispersion of Example 1.
Figure 2 is a light microscope image of the Pickering emulsion of Example 2.
Figure 2a is a light microscope image showing that the emulsion droplets collapse on drying
in air on a glass slide.
Figure 2b is a light microscope image showing the affect of addition of 5% by weight
Synperonic ™ NP8 to a Pickering emulsion.
Figure 3 is a light microscope image of the microcapsules of Example 3.
Figure 3a shows a stable microcapSUle dispersion of Fig. 3.
Figure 3b shows the microcapsules of Fig. 3 after the addition of SynperonicTM NP8.
Figure 4 is a Scanning Electron Microscope image of the capsules of Example 4.
Figure 5 is a light microscope image of the capsules of Example 5.
Figure 5a is a light microscope image showing a stable microcapsule dispersion (Example 5)
on drying on a glass microscope slide in air.
Figure 5b is a light microscope image showing an unbroken capsule dispersion (Example 5)
after the addition ofSynperonic™ NP8.
Figure 6a is a light microscope image of Example 6a.
Figure 6b is a Scanning Electron Microscope image of Example 6b.
Figure 6c is a Scanning Electron Microscope image of Example 6c.
Figure 6d is a light microscope image of Example 6d.
Figure 6e shows release curves for formulations prepared according to Examples 6a to 6d.
Figure 7 is a Scanning Electron Microscope image of Example lla.
Figure 8 is a Scanning Electron Microscope image of Example lIb.
Figure 9 shows the results of a c9mparative study of capsules prepared according to
Examples lla and lIb.
Figure 10 shows the release rate of dimethylphthalate [DMP] into water of capsules prepared
according to Example 12.
Figure 11 is a light microscope image of capsules prepared according to Example 13 in their
original dispersion.
Figure 12 is a light microscope image of capsules prepared according to Example 13 in a
dispersion formed from a redispersion after drydown.
The present invention relates to a new process for making microcapsules which does
not require surfactant and which provides microcapsules having an increased, relatively high
level of protection from u.v.light for the contents; the present invention involves the use of
surface-modified particulate inorganic material to form microcapsule walls where a crosslinker
is used to react with a reactive functional group on the surface-modified material such
that each microcapsule wall is a cross-linked wall. The present invention does also allow
surfactants to be used in the same formulation as a Pickering emulsion based system.
Pickering emulsions are often destabilized by surfactants but in the present invention, crosslinking
of the interfacial particles prevents this from occurring and surfactants may be safely
added to the system once the interfacial cross-linking has occurred. Therefore, suitably,
adjuvants may be built-in to microcapsule compositions of the present invention.
Microcapsules of the present invention are suitable for controlled release applications
(for instance, controlled release of an active ingredient from within the core of the
microcapsules). The controlled release rate may be tailored through the present invention.
Another aspect of the present invention is that the cross-linked systems may be easily
modified through addition of an extra cross-linking molecule (for example, a water
dispersible isocyanate orpolyfunctional cross-linker, such as diethylenetriamine [DETA]) to
the outer (external or continuous) phase of the dispersion such that the release rate of any
active ingredient from within the core of the capsule maybe varied to give a desired release
rate profile. The opportunity to use extra cross-linking molecules means that it is possible to
strengthen an existing layer in a single-layered capsule or to fOlm multi-layered capsules.
The microcapsules of the present invention may be made by a process comprising:
i) fonning a solution of a cross-linker in a liquid;
ii) fonning a slurry of a surface-modified particulate inorganic material in an aqueous
medium;
iii) dispersing the solution of step i) into the slurry of step ii) to fonn a Pickering
emulsion and causing or allowing the cross-linker to react with a reactive functional group on
the surface-modified particulate inorganic material so as to fonn a cross-linked microcapsule
wall.
Steps (i) and (ii) may be carried out in any order.
A slurry is a suspension of a solid in a liquid; in this invention, the slurry fonned in
step ii) is a suspension of cross-linkable, surface-modified inorganic particles in an aqueousbased
medium. It has been found that it is possible to disperse the solution of sJep i) into the
slurry of step ii) without using additional surfactants. This is because the particles of surfacemodified
inorganic material tend to accumulate at the interface between the solution droplets
and the aqueous continuous phase and reduce the corresponding surface energy. This effect
is known as a 'Pickering Emulsion'. The use of this combination of a Pickering Emulsion
with a cross-linkable particulate inorganic material and a cross-linker allows for a
particularly simplified process.
The liquid used in step i) comprises material to be encapsulated. I:ri one embodiment,
the liquid comprises an active ingredient which is to be encapsulated, optionally together
with a solvent, particularly if at room temperature the active ingredient is a solid, or of high
viscosity. Therefore, when present, the active ingredient may be the liquid, a part of the
liquid, dissolved in the liquid, dispersed in the liquid or is a solid complex of an
agrochemical with a molecular complexing agent and is dispersed in the liquid. The liquid is
suitably substantially insoluble in water, more suitably it has a solubility in water at 20°C of
less than 10g/1 and most suitably less than 5g/1. The liquid must dissolve the cross-linker so
as to form. a solution.
Any active ingredient encapsulated within the core of the microcapsules is suitably
less than 10% by weight soluble in water and more suitably less than 1 % by weight soluble in
water; and most suitably less than 0.1 % by weight soluble in water.
A wide range of active materials (active ingredients) may be encapsulated
including inks, flavours, cosmetics, perfumes, sunscreens, fragrances, adhesives, sealants,
phase change materials, biocides, oilfield chemicals (including corrosion and scale
inhibitors), flame retardants, food additives (including vitamins, ingredients, probiotics and
antioxidants), active agents that may be included in detergent, fabric softeners and other
household products (such as bleaches, enzymes and surfactants), active agents that may be
included in textiles (such as insect repellents, antimicrobial agents, skin softeners and
medically active compounds), active agents that may be included in coatings (such as fire
retardant, flame retardant, antifouling, antibacterial, biocidal, scratch resistant and abrasion
resistant compounds) and biologically active compounds (such as pharmaceuticals and
agrochemicals). Suitably the active material is an agrochemical such as a herbicide,
fungicide or insecticide. Many such agrochemicals are known and are described in The
Pesticide Manual 14th edition published by the British Crop Protection Council in 2006. The
invention is also suitable for encapsulating a solid complex of an agrochemical with a
molecul~ complexing agent including, for example, a complex of 1-MCP and acyclodextrin.
The invention is most useful for agrochemicals that are subject to degradation
when exposed to sunlight, in particular pyrethroid insecticides such deltamethrin,
tralomethrin:, cyfluthrin, alphamethrin, zeta-cypermethrin, fenvalerate, esfenvalerate,
acrinathrin, allethrin, bifenthrin, bioallethrin, bioresmethrin, cycloprothrin, beta-cyfluthrin,
cyhalothrin, beta-cypennethrin, cyphenothrin, empenthrin, etofenprox, fenpropathrin,
flucythrinate, tau-fluvalinate, phenothrin, prallethrin, resmethrin, tefluthrin, tetramethrin, and
lambda-cyhalothrin; suitably lambda-cyhalothrin.
Suitably, microcapsules of the present invention may be used in wall-boards or
plasterboards in buildings, and may be used in improving cement compositions and processes
for making cementitious materials.
The active ingredient is suitably a pharmaceutical compound or an agrochemical;
more suitably it is an agrochemical.
Suitably, the ~chemica1 is a fungicide, insecticide, herbicide or growth regulator,
used for controlling or combating pests 'such as fungi, insects and weeds or for controlling
the growth of useful plants. The agrochemical may also be used in non-agricultural
situations [for example public health and professional product purposes, such as termite
barriers, mosquito nets and wall-boards].
Further suitable applications include, without limitation:
Sustained release or controlled release usages, for example: pharma, for example acid
resistant capsules (oral delivery past low pH in the stomach), protection of labile actives,
pseudo-zero order release through capsule wall and Ostwald-ripening resistant emulsion
formulations; cosmetics; perfumes, for example slowing down evaporation of top-notes or
sustained release and minimising overpowering odours; capsules having affinity for cellulose
and trapped on textile surface during laundering; flavours, for example light stabilised to
prevent oxidation; self-healing coatings, for example capsule bursts to release a resin that
repairs damage; carbonless copy paper; novel, double taste and texture food, for example
capsule which dissolves in the mouth and releases a new taste; pressure sensitive adhesives;
sealants; nutrition (for example increased bioavailability of complex molecules and
protection of sensitive molecules such as vitamins, probiotics and other food additives); toner
inks with photosensitivity or thermal sensitivity; textile coatings, for example, for improving
permeability properties; antifouling coatings; surface protective coatings, for example, for
improving scratch or abrasion resistance; and construction materials, for example wallboards,
plasterboards and cements. Example of capsules that are dried out, include, for
example, various mineral blends to fonn a ceramic upon calcination; low density fillers for
polymers or paints; insulating materials; low density propp ants; light reinforcing particles,
for example for wood-fibre composites; recyclable pigments, for example low density
allowing easy flotation separation; and energy buffers, for example use in a void in spheres to
provide a 'crash barrier' with adsorption of energy. Capsules of the present invention may be
of novel size or shape, for example: creation of plate or rod shape capsules; and use of
metallic particles resulting in conductive capsules, or having a metallic nature, for example
plasmon absorbance.
A solution suitable for use in step i) may be made by stirring a liquid and a crosslinker
together. Heating and mechanical agitation may be used to aid or accelerate
dissolution of the cross-linker. Similar techniques may be used to mix or dissolve an active
ingredient with any solvent that is optionally included.
Examples of particulate inorganic materials are oxy-compounds [that is, oxygen
based compounds] of at least one of calcium, magnesium, aluminium and silicon (or
derivatives of such materials), such as silica, silicates, marble, clays and talc. Particulate
inorganic materials may be either naturally occurring or synthesised in reactors. The
particulate inorganic material may be a mineral chosen from, but not limited to, kaolin,
bentonite, alumina, limestone, bauxite, gypsum, magnesium carbonate, calcium carbonate
(either ground or precipitated), perlite, dolomite, diatomite, huntite, magnesite, boehmite,
palygorskite, mica, vemriculite, hydrotalcite, hectorite, halloysite, gibbsite, kaolinite,
montmorillonite, illite, attapulgite, laponite and sepiolite; suitably it may be chosen from
kaolin, bentonite, alumina, limestone, bauxite, gypsum, magnesium carbonate, calcium
carbonate (either ground or precipitated), perlite, dolomite, diatomite, huntite, magnesite,
boehmite, sepiolite, palygorskite, mica, vermiculite, illite, hydrotalcite, hectorite, halloysite
and gibbsite. Further suitable clays (for example aluminosilicates) include those comprising
the kaolinite, montmorillonite or illite groups of clay mineral. Other specific examples are
attapulgite, laponite and sepiolite.
In one aspect of the invention, the particulate inorganic material is kaolin clay.
Kaolin cia):" is also referred to as china clay or hydrous kaolin, and is predominantly mineral
kaolinite (AhShOs(OH)4), a hydrous aluminium silicate (or aluminosilicate).
The particulate inorganic material suitably has a particle size distribution wherein the
median diameter (dso) is less than or equal to 10p.m, as measured by determining the
sedimentation speeds of the dispersed particles of the particulate material under test through
a standard dilute aqueous suspension using a SEDIGRAPHTM, for example SEDIGRAPIfTM
5100, obtained from Micromeritics Corporation, USA. Suitably, the particulate inorganic
material has a dso less than or equal to Sp.m. More suitably, the particulate inorganic material
has a dso less than or equal to 2p.rn. Yet more suitably, the particulate inorganic material has
a dso less than or equal to 1 p.rn. In increasing suitability, the particulate inorganic material
has a dso less than or equal to 0.9, 0.8, 0.7, 0.6,0.5,0.4, or O.3/Lm. In other aspects, the
particulate inorganic material has a dso less than or equal to O.2p.m, for example less than or
equal to O.lSJ,tID or less than or equal to 0.12fL1D. or less than or equal to O.lfLID.
In one aspect, at least about 90% of the particles of the particulate inorganic material
by weight are smaller than about 21LfIl, for example at least about 95% or 98% are smaller
than about 2fL1D.. Suitably, at least about 90% of the particles by weight are smaller than
about 1pm, for example at least about 95% or 98% are smaller than about IJL!Il. More
suitably, at least about 75% of the particles by weight are smaller than about 0.2S,um, for
example at least about 80% or 82% are smaller than about O.25pm. In another aspect, the
particulate inorganic material has a particle size distribution of (i) at least about 90% of the
particles by weight less than about 2pm, for example at least about 95% or 98%; (ii) ~t least
about 90% of the particles by weight are less than about l~ for example at least about 95%
or 98%; and (iii) at least about 75% ofthe particles by weight are less than about O.2Spm, for
example at least about 80% or 82%; and particulate inorganic material of such particle size
distributions may also have dso values at the smaller end of the range, for example at least
about 98% of the particulate inorganic material by weight is smaller than about 2p,m, at least
about 98% is smaller than about l/Lm, at least about 82% is smaller than about O.25Jml, and
the dso value of the particulate inorganic material is less than or equal to 0.12#LID .
For finer particulate inorganic material (for example having adso less than or equal to
2p,m), the material may be derived through classification, including methods such as gravity
sedimentation or elutriation, use of any type of hydro cyclone apparatus or, for example, a
solid bowl decanter centrifuge or a, disc nozzle centrifuge. The classified particulate
inorganic material may be dewatered in one of the ways known in the art, for example
filtration (including filter press), centrifugation or evaporation. The classified, dewatered
material may then be thermally dried (for example, by spray drying).
Surface-modified means that the inorganic particle surface has been (chemically)
modified so as to have cross-linkable, reactive functional groups. The surface of the particles
may be modified using modifying agents selected from a wide variety of chemicals, with the
general structure X ---Y ---2, in which X is a chemical moiety with a high affinity for the
particle surface; Z is a (reactive) chemical moiety with a desired fWlctionality; and Y is a
chemical moiety that links X and Z together. The tenn 'high affinity' relates to chemical
moieties that are either chemically bonded or strongly physisorbed to the particle surface;
suitably they are chemically bonded.
X may be, for example, an alkoxy-silane group such as tri -ethoxysilane or trimethoxysilane,
which is particularly useful when the particles have silanol (SiOH) groups on
their surface. X may also be, for example, an acid group (such as a carboxylic or an acrylic
acid group) which is particularly useful when the particles have basic groups on their surface.
Y may be any chemical group that links X and Z together, for example a polyamide, a
polyester or an alkylene chain; more suitably it is an alkylene chain; and even more suitably
it is a C2-6 a1kylene chain, such as ethylene or propylene.
Reactive groups Z may be selected from any groups, preferably different from Y,
which can be used to react with a cross-linker so as to cross-link the surface modified
particulate inorganic material. Examples of Z are epoxy groups, carboxylic groups,
unsaturated groups such as acrylic or vinyl groups and, suitably, amine groups.
Suitable examples of surface modification rely on reaction of clay with aminosilanes,
such as aminopropyltrimethoxysilane. The silane groups react with the clay so as to give free
amine groups attached to the clay surface. An extensive range of silanes exists, able to
modify surfaces with functionality appropriate for use in a range of polymer systems.
The reactive groups Z are reacted with a cross-linker so as to form a capsule wall.
Cross-linkers are compounds that have at least two reactive groups that will react with the
reactive groups on the surface-modified particles. Examples of cross-linkers that may be
used to react with amine groups on a clay particle are polyisocyanates. Polyisocyanates
provide a well-known class of cross-linker and include diisocyanates (such as toluene
diisocyanate, hexamethylene diisocyanate and isophorone diisocyanate); isocyanates with, on
average, more than two isocyanate groups (such as polymethylenepolyphenylene isocyanate);
and many others including prepolymers of diisocyanates such as their reaction products with
trimethylol propane and other simple polyols sold as Desmodur™ resins from Bayer.
Examples of cross-linkers that may be used to react with epoxy groups; with
carboxylic groups; or with unsaturated groups such as acrylic or vinyl groups will be familiar
to the person skilled in the art.
In one embodiment, clay is reacted with a suitable modifying agent, in the range of
from 0.1 to 30% of the modifying molecule based on the weight of the clay (suitably in the
range of from 0.1 to 20% and most suitably the range is from 0.1 to 10% by weight).
The aqueous medium suitable for use in step ii) mostly comprises water, for example
by weight it is more than 80% water; and suitably more than 90% water. Optionally, the
aqueous medium also comprises water miscible solvents, antifreeze agents or additional
surfactants, although as mentioned above, these are not necessary. It has been found that
surfactants may interfere with the formation of a Pickering emulsion and so it is preferred not
to include surfactants at this stage.
A slurry suitable for use in step ii) may be made by agitating the particulate inorganic
material in the aqueous medium using a mechanical stirrer (for example a Rotor/stator,
Ystral™ or Ultra Turrax™) or by ultrasonic agitation. Suitably the slurry is agitated until the
solution is added to it and the dispersion step is carried out.
In step iii), the solution may be dispersed in the slurry by conventional means such as
ultrasonic dispersers or, suitably, high speed mechanical dispersers such as a Rotor/stator
mixer, Y straI1M or Ultra Turrax TM. The dispersion process is camed out for a period between
30 seconds and 20 minutes.
The dispersion step iii) results in a dispersion of the solution in the slurry which is
. stabilised as a Pickering emulsion by the surface-modified particulate inorganic material.
This emulsion comprises droplets of the solution which are surrounded by and stabilised by
the particles of the inorganic material. The cross-linker in the solution reacts with the
reactive functional groups on the particulate inorganic material so as to form a cross-linked
microcapsule wall. This reaction can be carried out simply by allowing the dispersion to
stand at ambient temperature. Alternatively, the dispersion may be heated. The amount of
time and the optimum temperature may be established by routine experimentation.
Typically, when the particulate inorganic material is surface-modified so as to have amine
groups on its surface and the cross-linker is a polyisocyanate, stirring the dispersion at
between 15 and 25°C for an hour is sufficient to complete the reaction.
The weight ratio of inorganic particle to solution phase will be from 1 :0.1 to 1 :40;
suitably from 1:1 to 1:20.
The cross-linker may be used at a rate of from 0.1 to 30% w/w of the oil phase, more
suitably from 0.5 to 20% and most suitably from 1 to 10%.
The reaction may be controlled by pH, temperature, addition of an electrolyte or by
the use of a catalyst.
The process results in a dispersion of microcapsules in an aqueous medium. These
microcapsules may be further modified by the addition to the aqueous medium of a material
which will further ~eact with any remaining cross-linker. For example, when the cross-linker
is a polyisocyanate, a polyamine such as diethylentriamine may be added. This causes
further cross-linking and polymer formation at the microcapsule wall and may be used to
modify the durability of the capsules or permeability of the capsule walls to give, for
example, a longer release time under given conditions.
The microcapsules may be isolated by drying, for example spray drying, to ~orm a
powder or may be used as the dispersion in the aqueous medium. When the microcapsules
are isolated, they may be used dry or they may be redispersed in water before use.
The microcapsules made according to this process are new. According to the present
invention there is provided a microcapsule comprising an encapsulated material surrounded
by a wall, characterised in that the wall comprises a particulate inorganic material that has
been surface-modified and cross-linked.
The invention is illustrated by the following Examples. The particulate inorganic
material used in the Examples is a tabular (so called "blocky", flat or plate-like shape)
ultrafine kaolin, having a dso of 0.121JID and a particle size distribution with at least 98% of
the particles by weight smaller than llJID and at least 82% smaller than 0.25p.m.
In these Examples, D[ 4,3] is the volume mean diameter of the relevant particles,
capsules or droplets as obtained by laser light scattering of a diluted sample in a Malvern
Mastersizer™ 2000.
EXAMPLE 1
This Example illustrates the preparation of a surface-modified clay dispersion.
Clay particles (ultrafine tabular Kaolin sourced in the USA, obtained from Jmerys) were
surface modified by the addition of 1.6% by weight aminopropyltriethoxysilane. The
surface-modified particles were then added to water and dispersed with an Ultrasonic Probe
(Sonics and Materials, Vibra CeU™, with micro tip - hereinafter referred to as an illtrasonic
Probe) operated under the following conditions: 50% Duty cycle; Output Control 4; for
6 minutes. The composition is given in Table 1.
Table 1 (Table Removed)
Results: Size of clay dispersion: D[ 4,3] = 4.4JLm.
Figure 1 is a light microscope image of the clay dispersion of Example 1.
EXAMPLE 2
This Example illustrates the preparation of a simple Pickering emulsion.
Initially, Solvesso™ 200ND (aromatic oil from Exxon) was dispersed dropwise into the
continuous phase of a modified Kaolin dispersion prepared according to Example 1, under
high shear mixing with an Y straITM high shear mixer (type XI020) with a two-pronged TI0
head (hereinafter referred to as an Y straITM high she~r mixer) operated at about SOOOrpm.
The concentrations of the ingredients used are given in Table 2.
Subsequent high shear mixing by the Ystral™ high shear mixer operated at about 20000rpm
for 2 minutes produced an oil in water [OIW] Pickering emulsion.
Table 2
Results: Size of emulsion droplets: D[ 4,3] = 13JLm.
Figure 2 is a light microscope image of the Pickering emulsion ofEx~ple 2.
Figure 2a is a light microscope image showing that the emu1sion droplets collapse on drying
in air on a glass slide; the emulsion has broken.
Figure 2b shows that the addition of S% by weight Synperonic'I'M NP8 to the Pickering
emulsion causes the emulsion to break after 4 days, as shown by light microscopy.
- J..J -
EXAMPLE 3
This Example illustrates the preparation of a single-layered capsule suspension.
A solution of 5% w/w Suprasec TM 5025 (polymethylene polyphenylene isocyanate; PMPI)
was prepared in Solvesso™ 200ND. Meanwhile, extra water was added to a surfacemodified
Kaolin dispersion prepared according to Example I and then to this dispersion, the
Solvesso TM 200ND plus Suprasec TM 5025 solution was added dropwise with mixing by a
Y stral™ high shear mixer operated at about 5000rpm. The concentrations of the ingredients
used are given in Table 3.
Subsequently, an oil in water [O/W] emulsion was prepared,by high shear mixing with the
Ystral™ high shear mixer at about 20000rpm for 2 minutes, which then developed into a
microcapsule system as a cross-linking reaction took place.
Table 3 (Table Removed)
Results: Size of microcapsules: D[4,3] = 20µm.
Figure 3 is a light microscope image of the microcapsules of Example 3. After ageing for at
least 1 day, the microcapsules did not collapse upon drying on a glass microscope slide [see
light microscope image, Figure 3a, which shows a stable microcapsule dispersion]
demonstrating that the wall had increased mechanical strength compared to the simple
emulsion of Example 2. Addition of5% w/w Synperonic™ NP8 did not cause the emulsion
to break after a period of 1 week [see light microscope image, Figure 3b, taken after the
addition ofSynperonic™ NP8 and showing unbroken capsule dispersion] demonstrating that
cross-linking anchored the surface-modified clay at the interface such that it was not
displaced by the surfactant. Pickering emulsions are usually incompatible with surfactants
(as shown in Figure 2b); cross-linking the particles allows them to be used with surfactants.
EXAMPLE 4
This Example illustrates the preparation of a two-layered capsule suspension. Bayhydur™
3100 [polyisocyanate based on hexamethylene diisocyanate modified with a polyether chain
for water dispersibilty (from Bayer )] was dispersed in water by shaking and then the
resultant Bayhydur'IM 3100 solution was added dropwise to a single-layered capsule
suspension prepared according to Example 3 with mixing from a Y straI'IM high shear mixer
at about 5000rpm throughout the dropwise addition.
The resultant capsule suspension was then mixed with the Ystral™ high shear mixer at about
20000rpm for 2 minutes. The composition is given in Table 4.
Table 4 (Table Removed)
Result: The capsules remained intact during dry down and examination in a Scanning
Electron Microscope, see Figure 4, showing they had good mechanical strength. The
Bayhydur™ 3100 can be seen as spheres attached to the outside of the capsule walls. The
capsules were sufficiently strong for them to survive high shear mixing at 20000rpm for
2 minutes with an Ystr;UTM high shear mixer.
EXAMPLES
This Example illustrates the preparation of a single-layered capsule suspension with
diethylenetriamine; it is similar to Example 3 but it has a second cross-linker.
A 25% w/w solution ofdiethylenetriamine (DETA) was prepared in water and then this
aqueous DETA solution was added dropwise to a single-layered capsule suspension prepared
according to Example 3 with mixing from an YstraI™ high shear mixer at about SOOOrpm.
This capsule suspension was then mixed by the Ystral™ high shear mixer at about 20000rpm
for 2 minutes. The composition is given in Table 5.
Table 5 (Table Removed)
Result: Size of capsules: D[4,3] = 21pm.
Figure 5 is a light microscope image of the capsules of Example 5.
The capsules remained intact during either dry-down on a glass microscope slide or drydown
plus examination in a scanning electron microscope [SEM], demonstrating that they
have good mechanical strength. The fact that there is no capsule collapse under SEM
conditions demonstrates that the presence of the second cross-linker has enhanced the
mechanical strength of the capsules compared to these of Example 3. The capsules were
sufficiently strong for them to survive high shear mixing at 20000rpm for 2 minutes with the
Y stral™ high shear mixer.
Figure Sa is a light microscope image showing a stable microcapsule dispersion (Example 5)
on drying on a glass microscope slide in air.
Figure 5b is a light microscope image showing an unbroken capsule dispersion (Example 5)
after the addition ofSynperonic™ NP8.
EXAMPLE 6
This Example compares the release rate of non-cross-linked and cross-linked Pickering
emulsions, compared to a polymer-stabilized emulsion.
Example 6a
This Example illustrates preparation of a simple Pickering emulsion.
A 50% by weight solution of dimethylphthalate in Solvesso™200ND was dispersed
dropwise into a surface-modified Kaolin dispersion prepared according to Example 1, under
high shear mixing with an Ystral™ high shear mixer at about 5000rpm throughout the
dropwise addition and an OIW emulsion was then prepared by high shear mixing with the
Y stral™ high shear mixer at about 20000rpm for 2 minutes. The composition is given in
Table 6a.
(Table Removed)
Result: Size of droplets: D[4,3] = 43µml.
Figure 6a is a light microscope image of Example 6a.
Example 6b
This Example illustrates the preparation of a single•layered capsule suspension with
diethylenetriamine containing dimethylphthalate prepared by an Ultrasonic process.
A 10% w/w Suprasec™ 5025,45% w/w dimethyl phthalate and 45% w/w Solvesso TM2 0 OND
solution was dispersed dropwise into a surface-modified kaolin dispersion prepared
according to Example 1, under agitation with an Ultrasonic Probe;
and then an OIW emulsion was prepared by high shear mixing with the Ultrasonic Probe for
2 minutes, under the following conditions: 50% Duty cycle, Output Control 4. To this
emulsion, a 25% w/w diethylenetriamine solution was added under mixing with the
Ultrasonic Probe. The full composition is given in Table 6b.
Table 6b (Table Removed)
Result: Size of capsules: D[ 4,3] = 146JID1. (This size is very large, the reason being that, as
seen in Figure 6b, the capsules are sticking together). Figure 6b is a Scanning Electron
Microscope image of Example 6b.
Example6c
This Example illustrates the preparation of a single-layered capsule suspension with
diethylenetriamine containing dimethylphthalate, prepared with the high shear Y stral™ (or
Ultra Turrax™) process of example 2.
A 10% w/w Suprasec™ 5025, 45% wlw dimethyl phthalate and 45% w/w Solvesso™200ND
solution was dispersed dropwise into a surface-modified kaolin dispersion prepared
according to Example 1, under high shear mixing with an Ystral™ high shear mixer at about
5000rpm; and an OIW emulsion was then prepared by high shear mixing with the Y stral™
high shear mixer at about 20000rpm for 2 minutes. A 25% w/w diethylenetriamine solution
was then added to the emulsion under mixing with the Y stral™ high shear mixer at about
5000rpm and an OIW emulsion was then prepared by high shear mixing with the Ystral™
high shear mixer at about 20000rpm for 2 minutes. The full composition is identical to that
given in Table 6b; the difference between Example 6b and Example 6c lies in the preparation
processes; ultrasonic and Y stral processes respectively.
Result: Size of capsules: D[4,3] = 33~.
Figure 6c is a Scanning Electron Microscope image of Example 6c.
Example6d
This Example illustrates the preparation of a Mowiol™ 4-88 emulsion.
A 50% by weight solution of dimethyl phthalate in Solvesso ™ 200ND was dispersed
dropwise into a 2% w/w solution ofMowiol™ 4-88 (88% hydrolysed poly(vinyl acetate).
MW ca. 28,000Dalton), under high shear mixing with an Ystral™ high shear mixer. An
O/W emulsion was then prepared by high shear mixing with the Ystral™ high shear mixer,
the speed of which was adjusted to yield a droplet size about 20pm. The full composition is
given in Table 6d.
Table 6d (Table Removed)
Result: Size of droplets: D[ 4,3] = 17 µm.
Figure 6d is a light microscope image of Example 6d.
Example6e
This Example provides release rate data for formulations prepared according to Examples 6a
to 6d.
Approximately 1 to 1.Sg of each of the four formulations described in Examples 6a-6d was
diluted by a factor of 10 into water. Each of these solutions was placed in dialysis tubing and
sealed in. Each dialysis tube was placed in ca. 100m! of water and was then left on rollers in
a temperature controlled room [temperature of20(+1-2tCJ. At suitable intervals, the UV
absorbance of the water phase was measured at 276nm with a Perkin Elmer™ uv
spectrophotometer. This process allowed the release of dimethyl phthalate [DMP] into water
to be followed with time. Release curves shown below in Figure 6e show that fast release
was seen for dimethyl phthalate from the PV A stabilized emulsion (Example 6d) and from
the unreacted clay stabilized emulsion (Example 6a). The rate of release was greatly reduced
when the clay had been reacted with Suprasec™ 5025 (Example 6b) or with
diethylenetriamine (Example 6c).
EXAMPLE 7
This Example illustrates the preparation of a pre-dispersed surface-modified clay slurry.
30g of surface-modified clay particles (as described in Example 1) were de-agglomerated
(with a J&K mill) for 30 seconds prior to the addition of an equal weight of water. The
slurry was homogenised using a Flack-Tek dispersing unit for 30 seconds. The slurry was
later diluted with water to the desired concentration of 50% by weight for use ~ the
following Examples.
EXAMPLE 8
Examples 8, 9 and 10 illustrate the preparation of a single-layered capsule suspension
containing a pesticide, lambda-cyhaIothrin dissolved in Solvesso 200ND prepared with the
high shear Ystral™ process. A Suprasec™ 5025, lambda-cyhalothrin and Solvesso™200ND
solution was dispersed dropwise into a surface-modified kaolin dispersion prepared
according to Example 7, under high shear mixing with an Y straI™ high shear mixer at about
2000rpm; and an OIW emulsion was then prepared by high shear mixing with the Y stral™
high shear mixer at about 2000rpm for 1 minute. A 25% w/w diethylenetriamine solution
was then added to the emulsion under mixing with the Ystral™ high shear mixer at about
5000rpm and an OIW emulsion was then prepared by high shear mixing with the Y stral™
high shear mixer at about 20000rpm for 2 minutes. This emulsion formed a single-layer
capsule dispersion. The full composition is given in Table 7.
Table 7 (Table Removed)
EXAMPLE 9
Example 9 is an example of a capsule product containing both a cross-linked bound clay
particle and an extra polyurea binding layer. It was prepared by taking the emulsion of
Example 8 and treating it with diethylenetriamine (cross-linker) in the quantities given in
Table 8 and mixing under low shear to homogenise the product
Table 8 (Table Removed)
EXAMPLE 10
Example lOis an example of a capsule product containing both a cross-linked bound clay
particle and an extra polyuretha,ne binding layer. It was prepared by taking the emulsion of
Example 8 and treating it with glycerol (cross-linker) and DABCO (catalyst) in the quantities
given in Table 9 and mixing under low shear to homogenise the product.
Table 9 (Table Removed)
Product from Example 8 50
nAB CO is (+-)-(E)-1-(2,6,6-trimethyl-2-cyclohexen-l-yl)-2-buten-I-one.
Examples 8, 9 and 10 immediately provided fluid dispersions that did not change on
overnight standing. Further cross-linking was effected by heating the samples at 50°C for 2
hours but the physical characteristics ofthe products did not change.
To test the compatibility of these products with further added components, an oil-in-water
emulsion of a isoparaffinic oil (Isopar TM M) was prepared. Isopar M was dispersed dropwise
into a 5% w/w solution of Gohsenol™ GL05 (88% hydrolysed poly(vinyl acetate», under
high shear mixing with an YstrallM high shear mixer. An O/w emulsion was then prepared
by high shear mixing with the Y stral TM high shear mixer, the speed of which was adjusted to
yield a droplet size about lOpm. The full composition is given in Table 10.
Table 10
(Table Removed)
Equal volumes of samples of each of Examples 8, 9 and 10 were then each independently
mixed with an equal volume of the Isopar M emulsion. All the samples remained fluid both
immediately and after standing for 24hours, demonstrating the compatibility of products of
the invention with an added oil-in-water emulsion.
EXAMPLE 11
This Example provides data on enhancement seen in the photostability of lambda-cyhalothrin
when trapped within Pickering capsules.
Example lla
This Example illustrates the preparation of a single-layered capsule suspension with
diethylenetriamine containing lambda cyhalotbrin prepared ~ith the high shear Y stral™
process. A 10% w/w Suprasec™ 5025,47.5% w/w lambda cyhalotbrin and 47.5% w/w
Solvesso™200ND solution was dispersed dropwise into a surface-modified kaolin dispersion
prepared according to Example 7, under high shear mixing with an Y stral™ high shear mixer
at about 5000rpm; and an OIW emulsion was then prepared by high shear mixing with the
Ystral™ high shear mixer at about 20000rpm for 2 minutes. This emulsion formed a single
layer capsule dispersion. A 25% w/w solution of diethylenetriamine (DETA) was prepared
in water and then this aqueous DETA solution was added dropwise to the single-layered
capsule suspension with mixing from an Ystral™ high shear mixer at about 5000rpm. This
capsule suspension was then mixed by the Y stral™ high shear mixer at about 20000rpm for
2 minutes. The full composition is given in Table 11.
Table 11 (Table Removed)
Result: Size: D[4, 3] = 31.7J.tm.
Figure 7 is a Scanning Electron Microscope image of Example Ila.
Example lIb
This Example illustrates the preparation ofa single-layered capsule suspension with
diethylenetriamine containing lambda cyhalothrin prepared by the Ultrasonic process.
A 10% w/w Suprasec™ 5025, 45% wlw lambda cyhalothrin and 45% w/w
Solvesso TM200ND solution was dispersed dropwise into a surface-modified kaolin dispersion
prepared according to Example 7, under agitation with an Ultrasonic Probe; and then an OIW
emulsion was prepared by high shear mixing with the Ultrasonic Probe for 2 minutes; wider
the following conditions: 50% Duty cycle, Output Control 4. This emulsion formed a single
layer capsule dispersion. To this capsule suspension, a 25% w/w diethylenetriamine solution
was added under mixing with the Ultrasonic Probe. The full composition is given below in
Table 12. (Table Removed)
Result: Size of capsules: D[ 4,3] = 171J.Ul1 (this is large due to aggregation of the capsules in
the instrument, the electron micrograph shows the capsule size to be smaller).
Example 11c
Capsules according to Examples 11 a and 11 b were each assessed against commercially
available capsules [Karate Zeon 1M] in a comparative study to determine the extent of
protection provided by each of the capsules to lambda-cyhalothrin against U.v.
photo degradation.
For each capsule type, samples of microcapsules were spread on glass slides and exposed to a
xenon lamp (simulating sunlight) for up to three days. Using standard techniques, the
microcapsules were analysed to determine the amount oflambda-cyhalothrin present in the
formulations at the initiation of exposure to ultraviolet light and the amount remaining at
various time periods during the three days' exposure.
The results are shown in Figure 9. The capsules of the present invention clearly provide
better u. v. protection to lambda-cyhalothrin than does the current commercial product.
EXAMPLE 12
This Example illustrates the preparation of a single-layered capsule suspension with
diethylenetriamine containing dimethyl phthalate (which is an example of a volatile organic
molecule) prepared with the high shear Ystral™ process. A 10% w/w Suprasec™ 5025,
47.5% w/w dimethyl phthalate and 47.5% w/w Solvesso™200ND solution was dispersed
dropwise into a surface-modified kaolin dispersion prepared according to Example 7, under
. high shear mixing with an Ystral1M high shear mixer at about 500Orpm; and an OIW
emulsion was then prepared by high shear mixing with the Y stral™ high shear mixer at
about 20000rpm for 2 minutes. This emulsion formed a single layer capsule dispersion. The
composition is given in Table 13.
Table 13 (Table Removed)
A 25% w/w solution of diethylenetriamine (DETA) was prepared in water and then varying
amounts ofthis solution were added dropwise to the single-layered capsule suspension with
mixing from an Ystral™ high shear mixer at about 5000rpm) to give a range ofDETA
concentrations (0-1.3% by weight) in the final dispersions. Each capsule suspension was then
mixed by the Ystral™ high shear mixer at about 20000rpm for 2 minutes. The full
composition is given in Table 14.
Table 14 (Table Removed)
Approximately 1 to 1.S g of each of these capsule fonnulations was diluted by a factor of 10
into water. Each of these dilutions was placed in dialysis tubing and sealed in. Each dialysis
tube was placed in about 100ml of water and was then left on rollers in a temperature
controlled room [temperature of20(+1-2)°C]. At suitable intervals, the UV absorbance of the
water phase was measured at 276nm with a Perkin Elmer™ UV spectrophotometer. This
process allowed the release of dimethylphthalate [DMP] into water to be followed with time;
see Figure 10, which shows that increasing the DETA loading decreases the rate of release of
DMP from the capsules, showing that the rate of release is readily controlled by the loading
of DETA used in the formulation.
EXAMPLE 13
This Example illustrates the preparation of a single-layered capsule suspension with
diethylenetriamine containing mefenoxam prepared with the high shear Ystral™ process.
The capsule dispersion was found to show good redispersion properties after drying down to
a dry deposit. A S% w/w Suprasec™ S025, 47.S% w/w, mefenoxam and 47.S% w/w
Solvesso TM200ND solution was dispersed dropwise into a surface-modified kaolin dispersion
prepared according to Example 7, under high shear mixing with an Ystral™ high shear mixer
at about 5000rpm; and an O/W emulsion was then prepared by high shear mixing with the
Ystral™ high shear mixer at about 20000rpm for 2 minutes. This emulsion formed a single
layer capsule dispersion. A 2S% w/w solution of diethylenetriamine (DETA) was prepared
in water and then this aqueous DETA solution was added dropwise to the single-layered
capsule suspension with mixing from an Ystral™ high shear mixer at about 5000rpm. This
capsule suspension was then mixed by the Ystral™ high shear mixer at about 20000rpm for
2 minutes. The full composition is given in Table 15. (Table Removed)
Result: Size of capsules: D[4,3] = 13.7IA-m.
This formulation gave capsules that were stable on dry down, and the capsules in the aqueous
dispersion were stable over a period of 9 months at ambient temperature. A sample of this
dispersion was allowed to dry down in a plastic tray in a fume hood for 3 days, after which it
was found to redisperse readily in water with gentle agitation. Figure 11 shows the capsules in
their original dispersion and Figure 12 shows them in the dispersion formed from the
redispersion after dry down. The capsules appeared to have lost some of the more volatile
Solvesso TM 200ND through evaporation, but the capsules remained essentially intact and
showed facile redispersion.

WE CLAIMS
1. A process for making microcapsules comprising;
i) forming a solution ofa cross-linker in a liquid;
ii) forming a slurry of a surface-modified particulate inorganic material in an aqueous medium; and
iii) dispersing the solution of step i) in the slurry of step ii) and causing or allowing the cross-linker to react with the surface-modified particulate inorganic material so as to form a cross-linked microcapsule wall.
2. A process as claimed in claim 1 in which the liquid is substantially insoluble in water.
3. A process as claimed in claim 2 in which the liquid has a solubility in water at 20°C of less than 10g/l.
4. A process as claimed in claim 1, 2 or 3 in which the liquid comprises an active material which is an agrochemical.
5. A process as claimed in claim 4 in which the active material is an insecticide.
6. A process as claimed in claim 5 in which the insecticide is a pyrethroid.
7. A process as claimed in claim 6 in which the pyrethroid is lambda-cyhalothrin.
8. A process as claimed in anyone of the preceding claims in which the particulate inorganic material comprises an oxy-compound ofat least one of calcium, magnesium, aluminium and silicon; or a derivative ofsuch a compound.
9. A process as claimed in claim 8 in which the particulate inorganic material is or is derived from silica, a silicate, marble, a clay or talc.
10. A process as claimed in claim 9 in which the particulate inorganic material is a clay.
11. A process as claimed in anyone ofclaims 1 to 7 in which the particulate inorganic material is a mineral selected from kaolin, bentonite, alumina, limestone, bauxite, gypsum, magnesium carbonate, calcium carbonate, perlite, dolomite, diatomite, huntite, magnesite, boehmite, palygorskite, mica, vermiculite, hydrotalcite, hectorite, ha1loysite, gibbsite, kaolinite, montmorillonite, illite, attapulgite, laponite and sepiolite.
12. A process as claimed in any ofthe preceding claims in which the particulate inorganic material has a median diameter (d50) less than or equal to 10 µm.
13. A process as claimed in anyone of claims 1 to 11 in which the particulate inorganic material has a particle size distribution where at least about 90% ofthe particles by weight are smaller than about 2 µm..
14. A process as claimed in anyone ofclaims 1 to 11 in which the particulate inorganic material has a particle size distribution where at least about 90% of the particles by weight are less than about 2JDll, at least about 90% ofthe particles by weight are less than about 2µm and at least about 75% of the particles by weight are less than about 0.25µm

15. A process as claimed in anyone of the preceding claims in which the particulate inorganic material particle surface has been modified so as to have reactive groups by reaction with a chemical ofthe general structure X---Y --Z, in which X is a chemical moiety with a high affinity for the particle surface; Z is a reactive chemical moiety; and Y is a chemical moiety that links X and Z together.
16. A process as claimed in claim 15 in which X is an alkoxy-silane group.
17. A process as claimed in claim 15 or 16 in which Y is a C2-6 alkylene chain.
18. A process as claimed in claim 15, 16 or 17 in which Z is an amine group.
19. A process as claimed in anyone of the preceding claims in which the surfacemodified particulate inorganic material is clay which has been surface-modified with an amino-silane.
20. A process as claimed in anyone ofthe preceding claims in which the cross-linker is a . polyisocyanate.
21. A process as claimed in anyone of the preceding claims where the cross-linked microcapsule wall is modified through addition ofan extra cross-linking molecule.
22. A process as claimed in anyone ofclaims 1 to 21 in which the particulate inorganic material is natural.
23. A process as claimed in anyone of claims 1 to 21 in which the particulate inorganic material is synthetic.
24. A microcapsule comprising an encapsulated material surrounded by a wall, characterised in that the wall comprises a particulate inorganic material that has been surface-modified and cross-linked.
25. A microcapsule as claimed in claim 24 which contains an active ingredient encapsulated within the core ofthe microcapsule.
26. A microcapsule as claimed in claim 25 where the active ingredient is an agrochemical.
27. Use of microcapsule as defined in claim 24,25 or 26 in a conrtrolled crelease application.
28. Use of a microcapsule as defined in claim 24,25 or 26 for protecting encapsulated material from the external environment.
29. Use of a micriocapsule as defined in claim 26 for controlling or combating pests.