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Description  |
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This invention relates to the encapsulation of active ingredient
(especially detergent enzyme) within polymeric material so as to protect
the active ingredient from the ambient environment, for instance
atmospheric moisture when the product is exposed to the air, or the liquid
phase of a liquid detergent when the product is incorporated in such a
detergent.
Numerous ways of protecting active ingredient from the ambient environment
are known. Some rely on a wholly liquid system. In U.S. Pat. No.
4,801,544, aqueous micelles of enzyme and surfactant are emulsified into a
hydrocarbon solvent. In U.S. Pat. No. 4,906,396, enzyme is dispersed in a
hydrophobic fluid, such as a silicone oil.
More usually, the enzyme is protected by a solid phase. In U.S. Pat. No.
4,090,973, solid surfactant is used. Often, however, a polymeric material
is used. The enzyme or active ingredient may be dispersed in a polymeric
matrix or it may be encapsulated by a polymeric shell formed around a core
containing the active ingredient.
The solid polymeric material can be made by polymerisation of monomeric
material in the presence of the active ingredient, but this is generally
undesirable and normally the solid polymer of the matrix or shell is
formed by depositing solid polymer from a solution of polymer. The polymer
can remain chemically unchanged during the deposition from dissolved to
solid form, the deposition being due primarily to a change in the solvent
composition or properties. Alternatively, deposition can be caused by,
accompanied by or followed by a chemical change in the polymer, such as
neutralisation, complexing with another polymer, or cross linking. The
formation of a solid polymer shell in this manner from a solution of
polymeric material is generally termed coacervation.
Typical techniques for forming a polymer shell are described in, for
instance, GB 1,275,712, 1,475,229 and 1,507,739, DE 3,545,803 and U.S.
Pat. No. 3,591,090.
A particular problem arises when the active ingredient is an enzyme,
especially an enzyme suitable for incorporation in detergents, because of
the difficulty of preventing the enzyme losing activity before use.
Many different ways of encapsulating enzymes have been proposed. Some do
not include coacervation. For instance GB 1,377,725 contacts atomised
droplets of an aqueous slurry of enzyme with particles of starch. However
there is a risk that the resultant coating will be discontinuous. It is
therefore preferred to form the coating or matrix by deposition of solid
polymer from a solution of polymer in which the enzyme is dispersed, i.e.
by coacervation.
For instance in U.S. Pat. No. 3,838,007 droplets of enzyme dispersed in an
aqueous solution of, for instance, gelatin are dispersed into water and
then cross linked, to give cross linked particles of the gelatin
containing the enzyme.
In JP-A-61254244, a typical process comprises mixing enzyme powder and
silica into an aqueous solution of polyvinyl alcohol or other suitable
polymer, dispersing the aqueous suspension into a non-aqueous liquid and
adding acetone, so as to deposit the polymer as a wall around the enzyme
particles. The product is said to have a particle size of around 50 to
2,000 um.
In U.S. Pat. No. 4,898,781, a dispersion is formed of enzyme powder in
propylene glycol and aqueous polyvinyl alcohol and this dispersion is then
converted into particles by various techniques. In one technique, the
dispersion is introduced as droplets into an aqueous solution of cross
linking agent, thereby solidifying by cross linking the polyvinyl alcohol.
In another technique, the dispersion is dispersed into a hydrophobic
solvent and then heated so as to drive off water and solidify the
polyvinyl alcohol. The products are said to have a size of 20 to 1,000 um.
Other techniques are described. JP-A-63105098 includes similar process
description and many of the examples are identical. It proposed that the
particles of enzyme in a covering of polyvinyl alcohol should be
homogeneously dispersed in a liquid or gel detergent.
EP-A-356,240 (and U.S. Pat. No. 5,035,900) describes processes for
encapsulating enzyme or other biologically produced material in a matrix
of polymeric material by mixing the polymeric material with an aqueous
liquor containing the biologically produced material (as a fermentation
liquor or plant extract), dispersing this mixture in a water immiscible
liquid and azeotroping the dispersion. The product can either be
relatively coarse beads that can be recovered or a stable dispersion of
small particles in the water immiscible liquid. Although this is a very
useful recovery technique and provides some protection to the enzyme,
additional stabilisation is desirable.
In EP-A-356,239 (which is equivalent to part of the disclosure in U.S.
application Ser. No. 734,545, now U.S. Pat. No. 5,324,445 of 23rd Jul.
1991) we have described various compositions and processes primarily
intended for the encapsulation of enzymes for liquid and other detergents.
One type of product described therein comprises particles having a core
comprising matrix polymer containing the enzyme, oil around the core and a
polymer shell around the oil.
In particular, particles of a matrix polymer containing an active
ingredient can be formed as a dispersion in oil and this dispersion can
then be dispersed in an aqueous solution of an encapsulating polymer or
blend of polymers and polymer deposition can then be caused to occur
around the oil particles that contain the particles of matrix polymer that
contain the active ingredient.
As explained in EP 356,239, it can be desirable for the matrix polymer to
be a salt formed between ammonia or other volatile amine and a polymer
derived from ethylenically unsaturated carboxylic acid. The matrix polymer
can be formed or introduced as an aqueous solution of the salt with a
volatile amine and this dispersion can then be subjected to azeotroping to
drive off water and the volatile amine, so as to solidify the polymer
wholly or partially in the free acid form. The solid polymer will be less
hydrophilic than the starting amine salt and so will provide some
impermeability to protect the encapsulated enzyme from moisture. The
combination of this relatively impermeable matrix, the outer polymer
shell, and the intervening oil would be expected to provide excellent
stability to the enzyme. Although the system does give significant
improvements, there is still some loss of activity.
It would be desirable to be able to provide coacervated particles that
could more reliably protect any active ingredient in the matrix from
exposure to moisture during manufacture and subsequent storage.
A particulate composition according to the invention comprises particles
having
a substantially anhydrous core comprising one or more particles of a matrix
polymer containing active ingredient and
a layer of hydrophobic oil around the matrix polymer particle or particles,
and
a shell of polymer around the oil layer,
wherein the solid matrix polymer is sufficiently hydrophobic that it will
partition preferentially into the oil rather than into water.
By referring to partitioning into "water", we are referring in particular
to the partitioning of the solid matrix polymer into the aqueous solution
from which the shell polymer was formed. In many instances, the
partitioning properties into ordinary water do, however, give a useful
guide.
If the encapsulating polymer was deposited from a neutral solution, then it
is more convenient to define the matrix polymer as partitioning into the
oil in preference to water, but if the encapsulating polymer was mixed
with the dispersion in the form of an alkaline solution then the relative
partitioning effect should be determined with respect to an alkaline
solution corresponding to the alkalinity of that solution in order to
allow for any solubilisation of the polymer by salt formation with the
alkali of the encapsulating solution.
A process according to the invention for producing encapsulated particles
comprises
providing an aqueous solution of encapsulating polymeric material that can
be caused to deposit as a solid shell about particles dispersed in the
solution,
providing a substantially anhydrous dispersion in oil of particles of a
matrix polymer containing active ingredient,
dispersing this substantially anhydrous dispersion of matrix polymer
particles containing active ingredient in oil into the aqueous solution,
and causing a solid polymer shell to form around droplets of the matrix
particles in oil, wherein the matrix polymer partitions into the oil in
preference to the aqueous solution of encapsulating polymeric material.
The invention is based on our realisation that, even though the matrix
polymer in EP 356,239 was relatively non-hydrophobic, it was considerably
more hydrophilic than the oil with the result that the aqueous solution of
encapsulating polymer and the matrix polymer particles were attracted to
one another with undesirable consequences. Since the formation of the
dispersion generally involved homogenising the polymer-in-oil dispersion
into the aqueous solution encapsulating polymer, the act of forming the
dispersion was able to result in intimate and prolonged contact between
the polymer particles and the aqueous solution.
It seems that during this contact there can be migration of water from the
solution into the matrix polymer, with the result that, even though the
polymer particles had been dried by azeotroping, the particles that were
then encapsulated within the outer shell contained trapped moisture. This
can be undesirable for enzymes and other active ingredients.
Also, there can be some migration of the enzyme or active ingredient out of
the matrix polymer and into the aqueous solution, thereby losing the
benefit of trapping the enzyme initially in the matrix polymer.
Finally, because of the attraction of the aqueous solution to the matrix
polymer, the encapsulating polymer could tend to deposit direct on to the
matrix polymer, without any oil trapped between the matrix polymer
particle and the encapsulating polymer shell. Since the oil is capable of
hindering the inward migration of moisture, this also was undesirable.
In the invention, we use a matrix polymer that is so hydrophobic that it
partitions preferentially into the oil rather than into the aqueous
solution of encapsulating polymer.
This therefore reduces the risk of moisture migrating from the aqueous
solution into the matrix, and it reduces the risk of enzyme or active
ingredient migrating out of the matrix into the aqueous solution. Because
the aqueous solution is incompatible with both the hydrophobic oil and the
matrix polymer there is increased tendency for the encapsulating shell to
be formed around a layer of oil, rather than in direct contact with a
matrix polymer particle. Finally, the increased hydrophobic properties of
the matrix polymer reduce still further the tendency for migration of
moisture into the polymer.
In a preferred process of the invention, the substantially anhydrous
dispersion of particles of the matrix polymer in oil is made by providing
a dispersion in oil of an aqueous solution of matrix polymeric material
containing enzyme or other active ingredient, subjecting this dispersion
to distillation to provide a substantially anhydrous dispersion in oil of
particles of matrix polymer containing active ingredient, and during or
after the distillation converting the polymer solution into a solid
polymer.
The initial aqueous solution of matrix polymeric material can be made by
dissolving the polymeric material in water or other aqueous solution in
which it is soluble, and dispersing or dissolving-the active ingredient in
the solution. In another process, the dispersion is made by reverse phase
polymerisation of a water soluble monomer or monomer blend in the presence
of the active ingredient.
The conversion of the droplets of polymer solution into solid polymer
particles can be brought about by various techniques. For instance, it can
be due merely to evaporation of solvent. It can be due to chemical
modification even though solidification may include another cause. This
modification should produce a polymer that is insoluble in water and that
will partition into the oil in preference to the aqueous solution of
encapsulating material.
One form of chemical modification can involve cross linking, for instance a
cross linking agent can be included in the polymer solution and will cause
cross linking during or after the azeotroping.
Another, and preferred, form of chemical modification comprises converting
a polymer that is in salt form into free base or free acid form. Thus a
polymer containing amino groups can be present initially as a water
soluble salt but can be insolubilised by conversion to the free base, or
polymer that is in anionic soluble salt form can be insolubilised by
conversion to the free acid. Such conversion can be partial or complete.
Preferably the salt forming moiety is volatile with the result that
conversion to the free acid or free base can be achieved during
distillation. Amine (including ammonium) salts of anionic polymer are
preferred. The modification normally occurs during or after azeotroping
and renders the matrix less permeable, e.g. to liquid detergent
concentrate.
Another way of converting the matrix polymer to solid form is by selecting
a hydrophobic polymer from the class known as "low critical solution
temperature" (LCST) polymers. The process by which these can be used for
the matrix is substantially the same as the process by which they can be
used for forming the encapsulating shell, and this is described in more
detail below. In brief, a characteristic of such polymers is that they can
be insolubilised by heating to a critical temperature (for instance as can
happen during the distillation stage) and a depressant for the temperature
of insolubilisation (for instance a water miscible non-solvent or an
electrolyte) can be added to stabilise the solid form at a lower
temperature. This is all described in more detail below.
Other coacervating techniques can be used.
In this specification, and in particular in the following discussion of the
formation of the polymer shell, we use the term "coacervation" and
"coacervating polymer" in the general sense described above, namely any
mechanism by which a polymer can be converted from a solution form to a
solid, encapsulating, form. Accordingly, for convenience, we refer below
to the encapsulating polymer as a coacervating polymer and we refer to the
aqueous solution of this as an aqueous coacervating solution.
By saying that the matrix polymer partitions into the oil in preference to
the aqueous solution of coacervating polymer, or other water phase, we
mean that the polymer particles will be preferentially attracted to the
oil phase rather than to the aqueous phase. One simple way of
demonstrating whether or not the matrix polymer does preferentially
partition into the oil phase is to incorporate some water soluble dye into
the matrix polymer and then to disperse vigorously a dispersion of the
dyed polyer particles in the oil into the aqueous phase, and then to allow
the dispersion to phase separate. If substantially all the dye has
remained in the polymer particles, this shows that there was substantially
no contact between the polymer particles and the water, and that the
polymer particles therefore partition preferentially into the oil phase.
However if the water phase is significantly dyed, this shows that the
polymer particles have partitioned significantly or preferentially into
the aqueous phase.
The oil can be any hydrophobic, water immiscible, liquid. Examples are
aliphatic, cycloaliphatic, aromatic and naphthenic oils, vegetable oils
and silicone oils.
Because the oil is hydrophobic, and because the matrix polymer also is
hydrophobic and is attracted to the oil in preference to the water, a film
or larger amount of oil is held around each polymer particle during the
formation of the coacervate, and the coacervate coating is formed as an
outer shell around this inner shell of oil. This has two significant
advantages:
Firstly, there is little or no direct contact between the aqueous
coacervating phase and the substantially anhydrous matrix polymer. As a
result, there is little or no opportunity for water to migrate into the
substantially anhydrous matrix polymer during the formation of the
coacervate coating or for active ingredient in the matrix polymer to
migrate out into the coacervating solution. In particular, the
coacervation can be conducted without raising the moisture content of the
matrix polymer.
Secondly, the active ingredient in the matrix polymer is protected from its
surroundings not only by the outer coacervate coating but also by the
inner layer of hydrophobic oil. Thus even if the coacervate coating has a
tendency to allow permeation by moisture, the inner shell of hydrophobic
oil between the coacervate and the matrix polymer will reduce or eliminate
any risk of transfer of moisture from outside the particle to the matrix
polymer or transfer of water soluble active ingredient in the matrix
polymer to outside the coacervate coating.
In order that the polymer does partition preferentially into oil, it is
necessary for it to be much more hydrophobic than, for instance, the
acrylic acid-ammonium acrylate polymer proposed in EP 356239.
As mentioned above, the matrix polymer is generally provided by
insolubilising a polymer that was initially provided as an aqueous
solution. Any modification that achieves this insolubilisation can be used
but preferably the modification is reversible so that the polymer can then
be solubilised when it becomes necessary to facilitate release of active
ingredient from within the particles into water. The modification can be
achieved chemically or physically. When the modification is achieved
chemically, the initially soluble polymer is preferably a copolymer of
water soluble ionic monomer with water insoluble monomer, in which event
the reversible insolubilisation will preferably comprise converting some
or all of the ionic monomer groups to free acid or free base monomer
groups.
Suitable monomers are ethylenically unsaturated monomers. Ionic monomers
are preferably anionic monomers groups that include sulphonic or,
preferably, carboxylic acid groups. Preferred monomers include methacrylic
and acrylic acids. The anionic groups may be present in the soluble
polymer as alkali metal or amine salts and may be converted to free
carboxylic acid groups in the insolubilisation reaction. This can be
achieved by acidification with hydrochloric acid or other suitable acid
but preferably the anionic group is present as a salt of a volatile amine
(e.g., ammonia) and the acidification is achieved by heating the polymer
sufficient to volatilise the ammonia or other amine. This heating can
occur during the distillation step. Although anionic groups are preferred
as the ionic groups, cationic groups such as dialkylaminoalkyl
(meth)-acrylate or amide acid addition or quaternary ammonium salt can be
used.
The ionic groups must be copolymerised with hydrophobic water insoluble
monomer. Suitable hydrophobic ethylenically unsaturated monomers are
hydrocarbon monomers such as styrene and alkyl-substituted styrenes, alkyl
acrylates and methacrylates (for instance methacrylate) and vinyl acetate.
The amount of hydrophobic monomer will generally be from 40 to 95% by
weight, with the balance to 100% being the ionic monomer. However small
amounts (e.g., up to 20%) of other monomers that are neither ionic nor
hydrophobic may be included, an example being vinyl pyrrolidine.
The matrix polymeric material can be made by solution polymerisation in the
organic solvent or by oil-in-water emulsion polymerisation, followed by
addition of sufficient alkali to solubilise the aqueous polymer in the
conventional manner. Active ingredient can be dispersed or dissolved in
the polymerising mixture before polymerisation, but preferably is
dispersed or dissolved into a solution of the polymeric material after
polymerisation. The polymer can be made as a water soluble salt by reverse
phase polymerisation, e.g., in the hydrophobic oil that is used in the
encapsulation process.
If the polymer was not formed as a reverse phase emulsion, the resultant
solution of polymer containing active ingredient can be dispersed into the
desired hydrophobic oil (or the polymer can be dispersed in the oil and
the active ingredient then added) in the presence of suitable dispersion
stabiliser that can be a water-in-oil emulsifier and/or an amphipathic
polymeric stabiliser. Suitable emulsifiers, stabilisers and oils are
described in, for instance, EP 128,661, EP 284,366 and EP 284,367.
Emulsification can be achieved by homogenisation with a Silverson or other
homogeniser.
The dispersion of aqueous polymer and active ingredient in oil can
subsequently be subjected to distillation under reduced pressure until
substantially all the water has been removed. If the active ingredient is
temperature sensitive, the reduced pressure should be sufficiently low
that the distillation occurs at a safe temperature, for instance below
30.degree. C. Anionic monomer is preferably present as ammonium salt, in
which event the dispersion can be heated briefly to a temperature and for
a time sufficient to drive off most of the ammonia but insufficient to
damage any heat-sensitive active ingredient in the matrix polymer.
The resultant dispersion of dry polymer particles in oil can then be
dispersed into an aqueous solution of coacervating polymeric material, for
instance by emulsification using a Silverson homogeniser. The particle
size can be controlled in known manner by appropriate selection of the
emulsification conditions and generally is below 20 .mu.m, usually below
10 .mu.m, although if desired the process can be used to make larger
particles, e.g., up to 100 um or 500 um. The size will usually be above
0.3 .mu.m, e.g. up to 3 .mu.m
If the particle size of the resultant oil-in-water dispersion is small,
each oil droplet may only contain one particle of matrix polymer, with the
result that the core of the final product comprises a single matrix
polymer particle surrounded by some oil. However each droplet, and
therefore each core, often includes several matrix polymer particles
dispersed in oil.
Coacervation can be by any known technique, for instance any of those
mentioned or used in EP 356,239, but is preferably by use of "low critical
solution temperature" (LCST) polymers. Coacervation can be brought about
solely by heating as described in U.S. Pat. No. 3,244,640 but preferably
coacervation is brought about by heating followed by the addition of a
depressant. In particular, a process for encapsulating by coacervation
particles each comprising matrix polymer (containing active ingredient)
and an outer layer of oil can be performed as described in our Application
filed today Ser. No. 08/196,230, now abandoned that claims priority from
British Application 9110407.5. This process comprises
providing an aqueous solution of a LCST polymer that has a temperature of
reversible insolubilisation (TRI) in that solution of T1,
forming a dispersion of the particles in that solution at a temperature T2
that is below T1,
heating the dispersion to a temperature above T1 and thereby precipitating
the LCST polymer as a coascervate around the particles, then
adding a TRI depressant to the solution and thereby reducing the
temperature of reversible insolubilisation of the LCST polymer in that
solution to a temperature T3 that is lower than T1, and
either cooling the dispersion to a temperature between T3 and T1 and
maintaining the dispersion at a temperature between T3 and T1,
or separating the particles from the dispersion while at a temperature
above T3.
The TRI depressant, and its amount, are selected to give the desired
depression in the temperature of reversible insolubilisation. Preferably
it is an electrolyte.
A wide variety of electrolytes can be used but since satisfactory results
are obtained with simple inorganic salts, it is generally preferred to use
them as part or all of the electrolyte. Suitable salts include sodium,
potassium, ammonium, calcium, magnesium and aluminium salts, particularly
of carbonate, sulphate, chloride and nitrate. Some or all of the
electrolyte can be anionic surfactant, for instance of the type
conventionally present in a liquid detergent concentrate.
Typical amounts of salt that should be added are 2 to 30% based on the
aqueous composition, or such as to give a 15:1 to 1:15 weight ratio of
polymer:salt. The amount is preferably sufficient for T3 to be at least
5.degree. C. below the anticipated lowest temperature of storage. As
mentioned, some electrolyte can be present in the initial solution,
typically in an amount of 0 to 5% based on the initial solution, provided
this does not depress T1 too much.
Generally T1 is at least 5.degree. C. higher than the anticipated
temperature of usage, for instance the temperature of the dilution water
into which the particles are to be dissolved.
Although we prefer to use an electrolyte for depressing the reversible
insolubilisation temperature, any other material that has the desired
depressant effect can be used. Generally they can all be characterised as
being water-miscible non-solvents (in the absence of significant amounts
of water) for the relevant LCST polymer. Examples include organic liquids
such as lower alcohols, glycols and non-ionic surfactants. Particular
examples are ethanol, glycerol, ethylene glycol, mono propylene glycol and
ethoxylated octyl or nonyl phenol surfactants.
The LCST polymer can be a naturally occurring polymer such as certain
cellulose derivatives, such as the methyl, hydroxy propyl, and mixed
methyl/hydroxy propyl cellulose ethers. However it is generally preferred
for the LCST polymer to be a synthetic polymer formed by polymerisation of
what can be termed an LCST monomer either as a homopolymer or as a
copolymer with a hydrophilic monomer that is present in an amount
insufficient to cause T1 to be unacceptably high. Suitable LCST monomers
include N-alkylacrylamide, N,N-dialkylacrylamide, diacetone acrylamide,
N-acryloylpyrrolidine, vinyl acetate, certain (meth) acrylate esters
(especially hydroxypropyl esters), styrene, and various other vinyl
monomers, especially N-vinylimidazoline and the like.
When the LCST polymer is a copolymer, the comonomer is usually hydrophilic
and can be non-ionic or ionic. Suitable non-ionic monomers include
acrylamide, hydroxyethyl acrylate, vinyl pyrollidone, or hydrolysed vinyl
acetate.
Anionic or cationic monomer can be used in place of or in addition to the
non-ionic comonomer to form a copolymer or terpolymer with the LCST
monomer respectively. Suitable anionic monomers include ethylenically
unsaturated carboxylic or sulphonic acid monomers, for example (meth)
acrylic acid and alkaline salts thereof, and 2-acrylamido methyl propane
sulphonic acid. Suitable cationic monomers include dialkylaminoalkyl
(meth)acrylates and acrylamides as acid addition or quaternary ammonium
salts, for example dialkylaminoethyl (meth)acrylate acid addition salts.
One beneficial effect resulting from the use of cationic or anionic
comonomer or termonomer is that their presence can prevent the coagulation
and subsequent phase separation of the encapsulated particles which may
occur in particularly high salt environments such as may exist in certain
detergents.
The method relies upon the reversible insolubilisation by temperature
change of an LCST polymer to form a coacervate coating, followed by the
addition of a TRI depressant to modify the properties of the coating in a
beneficial manner. Since the initial insolubilisation is by temperature
change, this can be conducted homogeneously througout the composition and
so can yield very uniform coacervation.
An essential modification of the coating is that the TRI depressant reduces
the temperature of reversible insolubilisation of the coating. This means
that the temperature of the solution can be cooled below the temperature
at which the coacervate coating was first formed without the coating being
solubilised. This permits handling, storage and recovery at ambient
temperatures.
Another modification is that the addition of the TRI depressant can tend to
change other physical properties of the coating of the LCST polymer. In
particular, it is easily possible to select an LCST polymer that forms a
much harder and less permeable coating in the presence of an added
electrolyte (as the TRI depressant) than in its absence. Thus the addition
of the electrolyte will generally both reduce the temperature of
reversible insolubilisation of the polymer and will render the coating
much harder and less permeable than it would be in the absence of the
electrolyte.
However, the effect is reversible since when the concentration of TRI
depressant is sufficiently reduced, the temperature of reversible
insolubilisation will then rise again to, or at least towards, the initial
temperature T1 of reversible insolubilisation. Also, if the TRI depressant
hardened the coating, the coating may tend to revert to its original
softer and more permeable texture.
The temperature T1 of reversible insolubilisation of the LCST polymer is
the temperature at which the polymer will become insoluble if the solution
containing the polymer is heated past T1 or will become soluble if
insoluble polymer in that aqueous solution is cooled below that
temperature. The temperature of reversible insolubilisation is generally
reasonably abrupt, but may extend over a few degrees or more. Naturally T3
must be sufficiently low that any range for T1 does not significantly
overlap the range for T3, which is the corresponding temperature for the
polymer in the aqueous solution containing the TRI depressant. It should
be noted that T1 and T3 relate to the polymer in the particular aqueous
solution in which it exists. Thus, in the invention, the initial aqueous
solution can contain some electrolyte or other TRI depressant in which
event T1 in that solution will generally be lower than it would be if the
initial solution had been free of electrolyte or other depressant, but
additional electrolyte or other depressant is then added to reduce the
temperature of reversible insolubilisation to T3.
T1 is generally at least 25.degree. C. and often at least 30.degree. C. and
frequently is in the range 45.degree. to 80.degree. C. but can be as high
as 100.degree. C. Some polymers require the presence of some electrolyte
in order to bring T1 in the initial solution down to a convenient value,
e.g. below 100.degree. C.
T3 is generally at least 5.degree. C. lower than T1 and is preferably at
least 10.degree. C. and often at least 20.degree. C. below T1. When the
particles are to be stored in aqueous electrolyte, T3 should be below the
probable storage temperature. Preferably T3 is 0.degree. C., that is to
say the coating will never dissolve in liquid water, but higher values of
T3, such as 5.degree. C. or even 10.degree. C., can be acceptable in many
instances.
Irrespective of how the coacervation of the shell is achieved, the choice
of coacervate shell must be such as to allow eventual release of active
ingredient from within the matrix when the product is exposed to selected
conditions, whilst preventing release prior to that stage. For instance,
if the particles are in the form of dry powder the coacervate shell should
reduce ingress of ambient moisture sufficient to prevent significant
deactivation of the active ingredient but upon exposure to dilution water
or an appropriate chemical reagent (for instance dilute alkali), the shell
should permit adequate permeation through the shell and from the matrix
into the surrounding liquor.
When the composition is in the form of a dispersion in liquid, the shell
should prevent permeation of that liquid through the shell but should be
capable of permitting permeation when the liquid is changed, for instance
when it is diluted. When, as is preferred, the composition is in the form
of a liquid detergent in which the encapsulated particles are dispersed,
the shell should be such as to prevent substantially permeation of the
alkaline liquid through the shell but should be such as to permit
permeation by wash water, often warm wash water, when the liquid detergent
is diluted in wash water.
Suitable coacervating polymers can be the LCST polymers mentioned above and
the coacervating polymers that have previously been proposed for, for
instance, the coacervate shell around enzyme particles, especially enzyme
particles that are to be dispersed into a liquid detergent. Suitable
materials are described in, inter alia, EP-A-356239. Cross linked pva is
suitable.
A wide variety of active ingredients can be encapsulated by the described
technique including dyes (for pressure sensitive paper), agricultural
chemicals, perfumes, flavours, condiments, essential oils, bath oils,
bleaching agents, and enzymes. Suitable agricultural chemicals are water
insoluble pesticides (e.g. herbicides and insecticides) that would
otherwise need to be formulated as, for instance, an emulsifiable solution
in oil. The invention is of particular value when applied to the
encapsulation of enzymes, and in particular detergent enzymes, i.e.
enzymes of the type that are useful for inclusion in laundry or other
detergent compositions.
When the particle size is small, e.g. below 20 um, the particulate
composition is generally provided as a dispersion in the liquid medium,
for instance a liquid detergent. When the particle size is larger, for
instance above 50 um and especially above 100 um, the particles can be
recovered as dry particles.
The liquid or dry composition can be substantially storage stable due to
the protection provided by the matrix polymer, the oil layer and the
encapsulating coacervate shell. Upon mixing with water, or other
appropriate change in the ambient conditions, the outer shell
disintegrates or swells sufficient to allow penetration of the oil layer
and release of the active ingredient from within the matrix, possibly
after chemical reversion of that matrix to render it more hydrophilic. For
instance, if, as is preferred, the matrix polymer is the acid form of an
anionic polymer, exposure to alkaline wash water will tend to solubilise
it.
Suitable proportions of active ingredient: matrix polymer are 1:100 to
1:0.5 on a dry weight basis, whilst the matrix/active
ingredient:coacervate polymer ratio is generally from 1:60 to 5:1 on a dry
weight basis. The amount of oil encapsulated within the particles is
generally from 20 to 97% based on the dry weight of the particles.
When the active ingredient is an enzyme for detergents and the composition
is a liquid detergent, its formulation can be conventional for
enzym | | |
