Note: Descriptions are shown in the official language in which they were submitted.
~ 09 44 0 2
Background of t e Invention
This invention relates to encapsulation and particu-
larly to the method of production of small or minu~e capsules
constituted by a skin or a thin wall of organic polymer composi-
tion enclosing a water-immiscible material, such as an organic
li~uid. More particularly, thi~ invention relates to the pro-
. duction of improved discrete polyurea microcapsules containing
various core materials by the addition of solvents to the
organic phase. T~e improvement can be the resu}t of either or
both effects as noted by (l) *he formation of di8tinct polymer
walls by e~luding water from the organic phase and (2) selec-
tively contxolling wall porosity. The process of this inven~ion
is directed to the production of such capsules, wherein micro-
capsu~ polymer wall solvents or non-solvents are included in
the organic phase prlor to microew apsulat~on.
Reference i8 made to Belgian Patent No. 796~746,
a8signed to Stauffer Chemical Company, published September 14,
,.
1973. The sforementioned patent describes a method for encap-
sulatlng various water-immiscibIe màterials employing an organic
isocyanate intermediate to form a polyurea cap~ule enclosure
around~a water-immiscible material dispersed in an aqueou~
cont~nuou~ phase.
Gapsules of this nature and description have a variety
of uses~ such as for containing d~es, inks, chemical reagents,
~. ~
25~ ~ pharmac~euticals, flavoring materials, fertili~ers, fungicides,
bactericides, pesticides, such as herbicides, insecticides and
the like, which substances can be dissolved, suspended or other-
wise dispersed in or as the core material to be enclosed by the
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1094402
capsule. The material to be encapsulated can be employed in the
ini.ial dispersion at a temperature above its melting point,
or dis~olved o~ dispersed in suitable water-immiscible organic
solvent. The nature of the water-immiscible material to be
encapsulated can be organic or inorganic in origin. Once encap-
sulated, the liquid or other form is pxPserved until it is
released by some means or instrumentality that breaks, crushes,
melts, dissolve~ or otherwise removes the capsu~ skin, or until
release by diffusion is effected under suitable conditions. An
important specific aspect of this invention, toge~her with other
features and advantages contèmplated by the invention, is the
novel method!or selectively controlling wall porosity and
formation of distinct polyurea walls by preventing water from
entering the organic phase dùring the polymerization involving
the reactlon between polyisocyanate monomers.
Efective encapsulation by interfacial polymerization
by a`n organic isocyanate intermediate can be accomplished in a
proces~ which utilizes two substantially immiscible liquid ,
one tenmed an aqueous phase and the other termed an organic
phase, which compr~ses es~ablishing a physical di~persion of
~20 the organic phase in the aqueous phase. Said organic phase
contains the isocyanate intermediate for the pclyurea capsule
~kin or enclosure. The interfacial polymerization, as i~ i~
termed, ~nvol~es hydrolysis of an isocyanate monomer to form an
amhne, which in turn reacts with another isocyanate monomer to
form the polyurea enclosure. Capsules fo~med in this manner
can range in size from about 0.5 microns to about 100 microns.
-3-
1094~02
Certain organic materials and material termed '~ater-
immiscible", are capable of dissolving an appreciable amount of
water. When this takes place during the formation of the poly-
urea microcapsule wall on the surface of the droplet, there will
be an increased proportion of polymer formation throughout the
core material. Whereas water is essential to the system em-
ploying organic polyisocyanates to prepare polyurea walls,
inclusion of water in the water-immiscible material in the cap-
sule core is not desirable. The presence and amount of water in
the organic or water-immiscible m~terial to be encapsulated will
depend upon the nature of thé material. By this invention, it
is possible ~o exclude water from the core material or organic
pha~e, thereby provide improved discrete polyurea microcapsules
with distinct well-formed walls.
The art has for some time been in need of improved
microcapsules which can control more closely the loss of the
active core material. Prior methods required the penmeability
of the microcapsule wall to be controlled by varying its thick-
ness and cross-linking density. Alsv desirable, and heretofore
difficult to æcomplish, i8 the prevention of water from entering
the orga~ic phase during the formation of polyurea microcapsules
containing certain organic materials which d~ssolve undesirable
amounts of water.
Summary of the In~ention
Therefore, it is an ob3ect of the present invention
to provide a novel microencapsulating process and novel products
produced thereby which products are characterized by optimized
rate of release characteristics by formation of polyurea walls
~09~40Z
and by selectively controlling wall porosity.
It is another object of this invention to provide a novel
system of microencapsulation employing a preferred solvent which
by virtue of good polymer solvent characteristics, causes a re-
duction in the pore size of the microcapsule wall. Conversely,
by the use of a poor polymer solvent, the permeability of the
capsule wall can be increased by increasing the pore size of the
microcapsule wall.
It is a further object of this invention to provide micro-
capsules having improved rate-release controlling capabilities.
Said rate of release being a consequence of the diffusive per-
meability of the resulting microcapsule wall.
Another object of the invention is to provide an improved
process for obtaining discrete microcapsules with thin walls
and relatively impervious to the loss of core material until the
desired release time and conditions. Said process is highly
versatile and affords a controlled means for achieving a large
; number of variations in the wall thickness, permeability, polymeric
compositions and release characteristics of the products produced
therewith.
Other objects of this invention will be apparent to those
skilled in the art on reading the instant specification.
In accordance with the present teachings, a process is
provided for the formation of improved discrete polyurea micro-
capsules which have distinct polyurea walls formed from the inter-
facial polymeri~ation of a pol~isocyanate and an aqueous phase
wherein the addition to the organic phase of a solvent during the
microencapsulation comprises the steps of adding to an organic
phase comprising water-immiscible material to be encapsulated,
a solvent capab]e of excluding water from the organic phase, and
--5--
D
~.0~440;;~
polyisocyanate, forming a dispersion of the organic phase in
the aqueous phase comprising water~ a surfactant and a protective
colloid and formation of the distinct polyurea polymer walls.
In accordance with a further embodiment of the present
teachings, an improved polyurea microcapsule is provided which
contains a water-immiscible material in the microcapsule core
which comprises a distinct polyurea polymer wall and a core which
comprises a water-immiscible material and a solvent capable of
excluding water from the microcapsule core.
The a~ove have been achieved by forming polyurea micro-
capsules while employing a good polymer solvent in the core
together with the active ingredient. Conversely, increased
-Sa-
. . .
109 440 ~
permeability can be achieved using a poor p~lymer solvent. ~-
That is, the permeability o the microcapsule wall, to control
the porosity of the wall7 is by the inclusion o~ microcaps~le
polymer wall solvents and non-solvents in the organic pha~e
thereof prior to microencapsulatlon. Accordingly, the encap-
sulation proces~ is basically as described in Belgian Patent
~o~ 796,746; however, it has bee~ found that the choice of
organic sol~ent included in the core o the capsules can impart
the desired effect of pore slze reduction or increase, as well
o as, exclusion o water from the core material, i.e. ac~ive ~=
materia~
~ The choice of solvents generally ~ large, depending ~r
; upon the particular monomer system that i~ utiLized for the
~ ~ production of the por~us poLymeric mlcrocapsule wall. The sol-
L5 vent should not be such a good solvent for the polymer that it
is completely miscible in all proportions, nor should the sol- ~-
f.~
vent be a material which 1~ a non-solvent for the monomer.
General b~ materials which are complete b soluble result in a
polymer product which has no apparent pore size and is swollen
by the solvent, whereas microcapsules having polymeric walls
psoduced by the use of non-solvents have pore sizes that are r~
too large to be o practical utility. Suitable solvents for
; the practice of thl~ iivention can be an undiluted or unmlxed
~ solvent, hawe~er, suItable solvents are readily prepared by
; 25 admixing the solvents and non-~olvents or alternatively, by
seIecting a suitable solvent having the desired characteristics.
Sultable solvents an~ m~xtures of solvents are readily
determined for the prepara~ion o a speciic polymer system by
. , .
-6-
~- .
' ' ~
. . . ~ . : ~
1091~40Z
use of the relationship: = O~ 0.8, wherein is the solu-
bility parameter for the solvent system and O is the solu-
bility parameter for the polymer. Low porosity polymers
are obtained when the solubility paræme~er fal1s within this
range. The solubility paræmeters are discussed in "Some
Fæ tors Af~ecting the Solubility of Polymers", by P.A. Small,
~ournal of Applied Chemistry 3, 71 (1953) and also by Harry
Burnell in the "Interchemical Review", 14, 3-16 31-46 ~1955).
For mixed solvents the value of is readily calculated by
additive averaging on a weight ~asis.
Particularly beneficial and advan~ageous in ~he prac-
tice of ~he present invention is the utilization of the solvent,
xylene, as a solvent. Xylene as a solvent in the core of poly-
urea microcapsules has been found to be exceedingly beneficial.
Loss of core material can be decreased by forming a ~istinct
and tighter, i.e. more dense, compact, hell structuresto
decrease permeability. --
- Within the preferred practice of the present invention,
core material can be effectively microencap~ulated by interfacial
polymerization of an organic isocyanate intermediate in a process
which utilizes two substantially immi~cible liquids, one termed
an aqueous phage and the other termed an orgaNc phase, and
which comprises establishing a physical dispersion of the
organic phase in the aqueou~ phase. Said organic phase contain-
25- ing the organic isocyanate intermediate for the polyurea capsule
skin or enclosure, the active ingredient and polymer solvent
The interfacial pol~meriæation to form the capsular wall involves
10 9 44 0 2
hydrolysis of an isocyanate monomer to form an amine which in
turn reacts with another isocyanate monomer to form the polyurea
enclosure. The addition of no other reactant i~ required once
the dispersion establishing drop~s of the organic phase within
a continuous liquid phase, i.e. aqueous phase, has been accom-
plished. Thereafter, and preferably with moderate agitation of
the dispersion, the formation of the polyurea capsule skin or
enclosure around the dispersed Qrganic droplets is~brought abou~
by heating the continuous liquid phase or by introducing a
catalytic amount of a basic amhne or other agent capable of
increasing the ra~e of isocyanate hydroly~i~, such as tri-n-butyl
tin acetate, ~pt~onally ~n addition adjusting the pH of the dis-
persion~ thereby effecting the desired condensation re æ tion at
the interface b~ween the organic droplets and the continuous
phase.
In this fashion, fully satisfactory, discrete micro-
capsules are formed having a skin or outer wall consisting of
the polyurea produ~ed by the reaction and containing the encap-
sulated core material and polymer solvent. Within the process
of the invention the reaction which forms the skin or enclosure
for the capsule generally is complete~ such that`essentially no
unreacted poly~socyanate remains. If a good polymer solvent is
used in the core, the pore size of the microcapsule wall will be
reduced and therefore there will be a reduction in the permeabil-
i~y of the wall. If a poor polymer solvent i8 used, the wall
will be more porous and the permeability will be increased. It
is not necessary to separate the capsule~ for desired utiliza-
tion, i.e. the encapsulated material may be directly usable,
depending upon the intended utilizati~n. However, s~ch separa-
tion prior to utilization may be carried out by any of the normal
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~09440Z
separation processes involving, for example, settling, filtra-
tion or skimming of the collect~d capsules, washing and if
desired, drying. The product from the process of this invention
is particularly suitable for direct agricultural pesticidal
applicat~ons, additional agents can bP added such as thickeners,
bioc~des, surfac~ants snd dispersants to improve storage stability
and ease of application. The initial dispersion of the organic
phase in ~he aqueous phase may be assisted with an appropriate
emul~ifying or dispersing agent and the control of the size and
uniformity of the ultimate capsules is readily effected by any
; convenient method to dispersé one liquid into another
Improved microcapsules having polyurea walls were pre-
pared in accordance with the method of the present invention~
The i~vention is further illustrated, but not limited, by the
following examples.
EXAMPLE I
The use of the polymer solvent technique of the pre-
sent invent~on was applied to the encapsulation of the herbi-
cide EPT ~ (EPTC), S-ethyl dipropyl thiocarb~mate. The purpose
was to decrease the loss of the active ingredlent by making the
wall less permeable, and to eliminate inc~eased water penetra-
tion into the core material. Xylene was chosen as a good sol-
vent for aromatic polyurea wall.
Microcapsules typically were prepared as follows:
Water (300 cc) containing 2.0 per cent of neutralized
poly-(methyl vinyl ether/maleic anhydride) protective colloid
and 0.3 per cent linear alcohol ethoxylate emulsifier were
_g_
.. .
~og L/~ 4 oz
placed into an open reactor ves~el. In a separate container
270 g. S-ethyl dipropylthioca~bamate ~an herbicide), 68 g.
xylene, 18.2 g. polymethylene polyphenyliso yanate (PAPI) and
9.1 g. tolylene diisocyanate (TDI 80% 2,4 and 20% 2,6) were
mixed together. This mixture was then added to the reactor
vessel and emulsified with a high shear ~tirrer. The resulting
partiole range was about 5 to abnut 30 p. Only mild agitation
was required for the balance of the reæ tion. The temperature
of the reactants was raised to 50C~ over a 20 minute period.
The temperature was maintained at 50C. for 2 hours 40 mi~utes.
.
There was dispersed 3.5 g. Attagel 40 ~attapulgite
clay), 14.0 g. sodium tripolyphosphate and 0.35 g. Dowcide G
(sodium pentachlorophena`te) into the microcapsule dispersion
w~th high shear stirrer. The pH wa~ adju~ted to 11.0 with 3.5
ml. 50 per cent sodium hydroxide.
This formulation disperses very well ~n water and
discrete capsules are observed under a microscope. These cap-
sules h~3:ve a wall content of about 7.5 per cent.
The prepared material~ were bioassayed by determining
per cent gra8g control after 24 hour~ delayed incorporat~on.
During the 24 hour period, EPTC normal~y evaporates, thereb~
providing substantially decreased herbicidal efficacy. This is
compared be~ween samples and an emulsifiable concentrate as a
control check. All materials were appl;ed at an effective: rate
Or 1 lb/acre a.~. The results of the~e experiments appear in
Table I.
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1(19440Z
TABLE I
Wet S~
~r
Ratio Ratio 1 lb/Acre
Formulation% Wall in PAPI EPTC d 1 d .
crocapsule T~ r~ne 0 hr
EPTC 6* 99 42
EPTC 2** 25 2.0 All EPTC98 80
EPTC 3** 17 2.0 All EPTC99 35
EPTCa 3** 7.5 2.0 4.0 99 96
~PTC 3** 7.5- 2.0 9.0 g9 96
EPTC 3** T 7.5 2,0 19.0 99 97
EPTC 2** 15 2.0 4.0 99 98
* - Emulsifiable Concentrate (non-microcapsule system)
** ~ M~crocapsule Dispersion
a - Prepared in illustrat~ve examples
These results show that the volatility 1095 of EPTC
from the microcapsule increases markedly as the per cent wall
is reduced from 25 per cent to 17 per cent in the absence of
xylene. However, wi~h the ~ylene present, exc~llent delayed
incorporation wet soil activ~ty was achieved even with the
7.5 per ce~t wall system. The xylene reduces the pore size in
the polyurea wall and therefore r~du~es its permeability to EPTC.
A5 the xylene content in the thin wall (7.5% wall) micro-
capsule was reduced a le~s distinct wall was provided. In the
thin wal~ microcap~ules when the xylene content was reduced to
zero it was impossible to form a dîscrete microcapsule with a
distinct wall.
~09440Z
EXAMPLE II
In the same manner as Example I, the herbicide
R0-NEE ~, Cycloate, S-ethyl cyclohexyl ethylthiocarbamate,
was microencapsulated. The purpose using the procedure of the
present application was to reduce vaporization loss. The fol-
lowing T~.ble II summarizes the formulations and results of the
tests.
TABLE II
Formu- Wet Soil Bioassay
SAM- lat~on % Grass_Cont ~ I lb/A~
PLE lb/Gal~ % PAPI R0-N~E ~ ~ }~
No. R0-NEE~ Wall TDI ~ylene 0 Hour Z4 Hour
1* 4 7.5 2.0 - 51 39
2* 3 7.5 2.0 4.0 17 28
3* 3 15.0 2.0 4.0 4 3
4* 4 15.0 2.0 - 51 49
; 5** 6E - - - 42
* - 1-4- Microcapsule Dicpersion
** - Emulsifiable Concentrate (non-microcapsule sys~em)
Fonmulations 1 and 4 are comparable to R0-NEE ~ 6E
ia herbicidal activity and display excellent wet soil persistence
over the 6E formulation. Samples 2 and 3 contain xylene in the
organlc phase. This causes the wall to be less porous and
terefore less permeable to the herbicide. The low per cent of
grass control for samples 2 and 3 upon immediate incorporation
demons~rates the effect of the xylene in the organic phase during
microencapsulation to produce a less porous and hence a less
permeable wall.
~12
109 LJJ~ 40Z
.
EXAMPLE III
E~erimental Procedure
. A 4 gram ~ample of ~he R-2o458 (4-ethylphenyl geranyl
ether epoxide) microcapsule formulation ~containing approxi-
mately 10% R-20458), was d~lute~ to 100 m7. with deionized
water, and then 2 ml. of this suspension was diluted to 2
S liters, with deionized water, producing a 4 ppm R-20458 solution
if all the toxicant was released from the capsules. At 0, 15,
60, and 120 minutes a 250 ml. sample was removed from the agi-
tated suspension~ the microcapsules removed by filtration, and
the filtratetanalyzed for ~-20458. Two filtration methods were
used in ~wo separate tests. The susp2nsion was filtered through
a Millipore filter, 0.6S micron, using a fresh filter each ~ime,
or was filtered through a fresh Celite 454 filter cake on a
vacuum funnel. Both operations were carried out under a slight
vacuum; the filtration of 250 ml. taking only one to ~wo min~te~
for either method.
' -13 `
Yj
109440Z
TABLE III
The R-20458 content of water suspensions of R-20458 microcapsules
Samp le
No. 1 2 3 4 5
Per cent wall 7.5 25 7.5 7.5 7.5
PAPI/TDI 2.0 2 2.0 2.0 2.0
Solvent - - xylene 1,1,1- Eth~lene
tri- dic loride
chloro-
ethan
(Solvent/ (2) (2) ~2) 0
R-20458 tech.)
Sample - ppm R-20458
t3 o , 0.2(.6)a 0.1 0.1 0.1 0.1
t = 15 min. 1.1(1.2) 0.1 0.1 0.1 0.1
t - 60 min. 1.5(1.8) 0.1 0.1 0.1 0.1(0.1)
,
t = 120 min. 1.8(2.2)0.1 0.1 0.1 0.17(0.2)
a 3 First value from Millipore~filtration procedure and second
value in ( ) from Celite filtration proceture. Only one
value shown ~ the values were the same in both procedures.
The insect ~uvenile hormone readily passed through the
microcapsule with 7.5 per cent wall~ but was stopped by the
mi~rocapsule with 25 per cent wall and by the solvent-containing
. ~
walls formed duri:ng the micrsencapsulation procedures with a sol-
5~ ~ vent present in the organic phase.
EXAMPLE~I~
In the same manner as Examp~e I, microcapsule formula-
tions of thioc arbamate herbicide and antidote therefor~ EPTC
and N~N-diallyl dichloracetamide, were produc~d and bioassayed
on wet soil. The bioassay was to establish per cent grass
- 14 - ~
~0 ~40 ~
control and per cent corn injury for comparison to immediate in-
corporation and 24 hour delayed incorporation. I~ accordance
with the previous disclosure hereinabove, the presence of a
solvent, such as xylene, in the microcapsule during wall forma-
tion in the encapsulation system reduces the size of the micro-
pores in the polyurea wall, and thereby reduces the permeability
of organic molecules through the microcapsule waLl.
~,:
. , :
. ~ .
-15-
lQ9'~40;2
c ~1 ~ o
~ i~ ~
O ~ a~
C C~ ~ ~
C ~ o~ o
o ~ ~ ~ o o ~ ~ o o
~--' ~
a 1~ æ
~ 10~l ~
C
~ c ~
~ ~ ~ _~ o
= ~ ' ' ;~
", o ~ ~ o ~
~1 ~ ~ 1 ~
~ Ei ~15 3 r~
_~ ,~
,~ ` +
~ . ~ ¦ - i Ç
C ~ o o o o o I ~o
: ~C ~ ,,5s,,
. o o ~,j~, C ~
,, Z
--16--
109440Z
This test indicates that reducing the xylene or solvent
eontent within the microcapsule, will cause increased volatility
loss of the antidote component.
As is apparent from the foregoing specification, the
method of the present invention is susceptible of being embodied
with various altera~ions and modification~ which may differ
particularly from those that have been descrlbed in the preceding
specification and description. For this reason, it is to be
fully under~tood that a11 of the foregoing ~s intended to be
merely illustrative and is not to be con~trued or ~nterpreted
as being res~rictive or otherwise limiting of ~he present inven-
tion, excepting as it is set forth and de~ined in the hereto
appended claims.
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