Note: Descriptions are shown in the official language in which they were submitted.
- 2 ~ 1 O 57 1 9 2
This invention relates to the preparation of improved
pesticide formulations containing very high concentrations
of the pesticidally active ingredient.
The active component of most pesticides is a well-
de~ined chemical compound, but in agricultural applications
it is usually impracticable to apply this compound
directly because of the problems inherent in securing
uniform distribution over large areas of the small
amounts required (typically 1 kg per hectare). Hence,
in practice the compound is generally diluted with
relatively large volumes of water to facilitate spray
application over these large areas. However, in most
instances the low water solubility of the active ingredient
makes it difficult for the user to prepare such spray
solutic)ns by direct dissolution or suspension, and
therefore the product is normally formulated with
carefully selected carriers and surface-active agents
to ensure that the formulation will rapidly disperse
in water to give a product having good spraying characteristics.
The development and production of such a ~ormulated
product which will not only have the necessary physical
properties but also a satisfactory stability under field
conditions allied with good biological performance requires
a high level of expertise and quality control, and it is
therefore rarely practicable for each end-user to purchase
the active ingredient, carrier and surface-active agent
- 3- ~057~9Z
in order to produce his own formulation on the spot.
Accordingly almost all pesticides are sold as formulations
containing carrier and surface-active agent in addition
to the active ingredient, which can be applied either
directly (e.g. with granule~) or after suitable
dilution with water (e.g. wettable powders, emul'sifiable
concentrates, suspension concentrates, etc.) The
~inal choice of formulation type will be dictated
by the intended application of the product and the
physical properties of the active ingredient, for
example granules being chosen for localized application
whilst dilute sprays are used for treatment of large
, areas.
In order to provide a formulation having acceptable
physical properties it is normally necessary to
include not only surface-active agents but also
a carrier, which may be a liquid, as in the case
of an emulsifiable concentrate, or solid as in the
case of a wettable powder. Without the use of such
a carrier severe technical problems can arise in
producing an acceptable formulation; ~or example
any attempt to prepare a wettable powder without
a solid carrier, or filler, results in an inadequate
mix of the surface-active ingredients with the active
ingredient, overheating of the mill with smearing
of the toxicant over the mill surfaces and inadequate
4 -
105719Z
attrition leading to insufficiently small particle
size. However, the presence o~ this carrier inevitably
increases both raw material and transport costs
although it has no intrinsic value to the customer.
Clearly it would be advantageous if the quantity
of carrier could be substantially reduced or even
eliminated, and it has now been found according
to the subJect o~ the preæenb invention that this
can be achieved by preparing formulatio~sin the
presence o~ a liquid which is then removed by sublimation.
The present invention therefore provides a
process for the preparation of a pesticide formulation
containing at least 80% by weight o~ pesticidally
toxic material, which comprises ~reezing an intimate
mixture containing the pesticidal toxicant, at least
one sur~ace-active agent and a sublimable liquid
medium, reducing the pressure above the ~rozen mixture
to below the triple point pressure o~ the liquid,
and removing the medium as a gas whilst maintaining
the pressure below that at which the medium can
exist in liquid form. It should be appreciated that
the pestioidally ef~ective material may contain
other components in addition to the toxicant designed
to enhance the biological ef~ect o~ the toxicant,
~or example an oil may be added to facilitate herbicidal
activity or a synergist to enhance insectioidal
- 5 ~ ' 1 0 S 71 9 Z
activity. Also polymers may be added to control
the release o~ toxicant.
The es~ential criterion required of the liquid
medium is that it possesses a triple point at which
gas, liquid and solid are in equilibrium and at
pressures below that Or the triple point it exists
solely in the solid and gaseous phases, since it
is then possible at suitably reduced pressure to
remove the medium from the ~rozen mixture via the
gas phase without the medium melting into a liquid
phase. Under these conditions, the removal of the
medium can be ef~ected without destroying the intimate
association of the toxicant and surface-active agent,
and thereby can yield a carrier-free product having
acceptable physical properties. The removal o~ the
medium from the frozen mixture is accomplished by
allowing it to gain heat, whilst maintaining the
pressure below that at which the medium can exist
in the liquid state, and maintaining a condensing
surrace near to the ~rozen mixture at a temperature
below that Or the mixture. Under the~e condition~
the medium evaporates rrom the frozen mixture as
a gas and iB collected as a solid on the condensing
surrace. The rate at which this gas phase transfer
f medium ~rom rrozen mixture to condensing surrace
takes place is dependent primarily on the pressure
- 6- 105719Z
and the temperature ~ the frozen mixture, lower
pressures and higher temperatures increasing the
rate of transfer.
For reasons of practical convenience it is
preferred to use as the sublimable liquid medium
a material which is liquid at room temperature and
which can be ~rozen by the use of readily available
materials such as solid carbon dioxide or other
conventional re~rigerants. Thu~ water i9 a particularly
convenient sublimable liquid medium, although organic
liquids such as benzene and dioxane can also be
used under appropriate conditions. When water is
used the ~reezing is suitably effected by a mixture
of solid carbon dioxide and, for example, acetone,
and the water removal (freeze-drying) is generally
carried out at a pressure below 1 Torr (the triple
point pressure of water being 4,6 Torr) using a
condenser cooled to below minus 30C and allowing
the frozen mixture to warm to above 0C, preferably
around room temperature or even hlgher.
The surfaoe-active agent may be an emulsi~ying
agent or a dispersing agent or a wetting agent;
it may be nonionic, ampholytic, cationic or anionic.
Any o~ the surface-active agents usually applied
in ~ormulating herbicides or insecticides may be
used. Examples of suitable surface-active agents
.
1057192
are the sodium or calcium salts of polyacrylic acids
and lignin sulphonic acids, the condensation products
of fatty acids or aliphatic amines or amides containing
at least 12 carbon atoms in the molecule with ethylene
oxide and/or propylene oxide; fatty acid esters
of glycerol, sorbitan, sucrose or pentaerythritol;
condensates of these with ethylene oxide and/or
~opylene oxide, condensation products of fatty alcohols
or alkyl phenols for example p-octylphenol or p-octylcresol,
with ethylene oxide and/or propylene oxide; sulphates
or sulphonates of these condensation products; alkali
or alkaline earthmetal salts, preferably sodium
salts, of sulphuric or sulphonic acid esters containing
at least 10 carbon atoms in the molecule, for example
sodium lauryl sulphate, sodium secondary alkyl sulphates,
sodium salts of sulphonated castor oil, and sodium
; alkylaryl sulphonates such as sodium dodecylbenzene
sulphonate; and polymers of ethylene oxide and copolymers
of ethylene oxide and propylene oxide.
The toxicant used in the process of this invention
may be any pesticide which i~ solid under normal
temperatures (e~g. 20-25C) and atmospheric pressure,
and its intimate mixture with the sublimable liquid
medium and surface-active agent may be accomplished
in a variety o~ ways. Thus in one embodiment the
medium may be chosen so that it is one capable of
1057192
dissolving the toxicant, when the requisite intimate
admixture is readily achieved sirlply by stirring
the resulting solution. This procedure may be applied
using either water or a suitable organic liquid
as the sublimable solvent, but in either case it
is desirable for the solution to be frozen rapidly
in order to minimize the growth of large crystals
which would require crushing prior to subliming
o~f the liquid medium.
,10 In a second embodiment the medium may be chosen
so that the toxicant dissolves to only a limited
extent, water usually being the medium of choice
since the majority of pesticides are insoluble ~or
only slightly ~oluble) in water. In this embodiment
the solid toxicant is mixed with the water (or other
medium) and appropriate sur~ace-active agents and
then subjected to a suitable milling process (e.g.
in a slow or high speed stirrer grinder) which ensures
that
the solid particles of toxicant are su~ficiently
small to permit their regular coating by the sur~aoe-
aotive agents present in the mixture. Pre~erabl,y
the par~ticle size should be reduced to below 100
microns, and desirably below 10 microns. The amount
of water present during the milling process is not
critical, because effectively all the water is removed
- 9 -
lOS7~92
during the subsequent freeze-drying step. However,
if the water content of the slurry produced by milling
is less than 50%, it is sometimes found that the
freeze-dried product forms as a crust which requires
further milling to yield an acceptable product.
Therefore it i8 preferable to adjust the proportion
of water to minimize the crust formation during
drying.
When the slurry formed by milling solid toxicant
with a non-solvent medium and surface-active agents
is frozen, the dispersed ~olid particles are locked
into place in the resultant ice matrix. Thus, when
the pressure is reduced and the water sublimes away,
the toxicant particles, together with the surface-active
agent, do not agglomerate as the volume of mixture
i i8 reduced. The resulting dry, powdery product containing
only toxicant and ~urface-active agents, is termed
a "Technical ~Concentrate", and possesses physical
properties closely resembling those of a conventional
wettable powder, although having no solid filler
and therefore a much higher toxicant content.
This retention Or the spatial relationships
Or the slurry components during the freeze-drying
makes possible a rurther a~pect of this second embodiment
or the invention, namely the production Or a freeze-
dried suspension concentrate which can be reconstituted
- lo - 1057192
without loss of physical properties merely by addition
of water. According to this aspect of the invention,
the toxicant is milled together with water which
may contain, in addition to the more conventional
surface-active agents, a suspending agent, such
as a protective colloid or thixotropic agent, and
optionally also dissolved
organic solidsor inorganic salts to raise the density
of the suspending liquid and thereby assist in preventing
sedimentation, the resulting mixture is frozen and
the water removed therefrom at a pressure sufficiently
low to preclude the formation of liquid water. With
suitable choice of the ingredients, the milling
can yield a stable, non-sedimenting, flowable product
containing up to 50-60% of toxicant. It is normally
impracticable to use a lesser amount of water (or
other suspending medium) without impairing the physical
properties of the suspension concentrate, whilst
any attempt to remove the water subsequently by
conventional means results in a similar detrimental
ePfect. However, the removal of the water by ~reeze-drying,
according to the process of the present invention,
yields a dry powdery product which retains latent
the physical properties required to produce a stable
9uspension and can therefore be reconstituted by
addition of water into acceptable suspension concentrates
:
1057192
of any convenient toxicant concentration, or alternatively
directly into sprayable suspensions
Additionally, a ~chnical concentrate can be
reconstituted into a suspension concentrate by mixing
with water containing the appropriate extra ingredients
needed to make a stable suspension concentrate.
; Alternatively, if the toxicant r~quires the addition
of an oil for optimum activity, for example, in
the post-emergence use of triazine herbicides, the
technical concentrates can be mixed directly with
an emulsion of the oil in water.
It will be appreciated that the process of
this invention is applicable to the preparation
of products containing mixtures of toxicants. These
may be toxicant materials which are either both
soluble or both substantially insoluble in the sublimable
li~uid medium, or it may often be convenient to
prepare a product containing, for example, both a
soIuble and an insoluble pesticide. In the last
situation, the proc~re followed is precisely that
described earlier for the formulation of insoluble
toxicants except that the sublimable liquid medium
in which the insoluble toxicant is milled contain8
additionally a dissolved quantity of the soluble
toxi¢ant.
The invention is further described in the following
ex~mples.
- 12 - lOS719Z
Example I Preparation of Technical Concentrates
A blend comprising 190g. "Gardona"'insecticide
(technical material containing 98.5% wt. 2-chloro-1-
(2, 4, 5-trichlorophenyl) vinyl dimethyl phosphate),
5g. Orota~731 SD (sodium salt of condensed aryl
sulphonic acid), 5g. Vanisperse-:-CB (sodium lignin
sulphonate) and 200g. water was charged to an attritor
and ground until the particle size was in the range
of 1-2 microns. After blending, the slurry was run
out of the attritor into a round-bottomed 2 litre
flask, which was rotated in a solid carbon dioxide/
acetone freezing bath ~til the slurry formed a uniform
coating of frozen solid over the entire internal surface
of the flask.
The flask was then connected by a manifold connector
to a freeze-drying unit, evacuated to a pressure of
about 0.5 Torr and exposed to ambient temperature (20C)
whilst the condenser in the freeze-drying ~it was
maintained at about -35~C. About 6 hours is required to
complete the drying of a 500g. batch of slurry, and
the completion of the drying stage can be recognized
by the external surfaces Or the flask reaching room
temperature (during the drying the heat uptake required
to sublimate the water maintains a cooling effect on
the flask). The flask was then removed from the drying
unit and the resultant technical concentrate was poured
out as a free flowing powder,
"Trademark
~ - 13 - 1057~9Z
Follo~ling a similar procedure, technical concentrates
were also prepared with the following toxicants:-
"Torque"-~(trineophyl tin oxide/hydroxide) 97Z wt.
(98% pure technical material)
Marasperse7~CBOS-3 1.5% wt.
(Sodium lignosulphonate)
DuponaI'ME 1.5% wt.
(Sodium lauryl sulphate)
"Bladex't`(Cyanazine - 99% pure technical) 96% wt.
Aerosol OTB~ 2% wt
(Sodium dioctyl sulpho-succinate)
Vanisperse-`~CB 2% wt.
Bladex~ 13%
MCPA 82%
Vanisperse'~CB 2.0%
Empice~ LZ 2,0%
(Sodium lauryl sulphate)
The physical properties of three o~ these technical
concentrates are summarized in the following Table l.
~Tradcmark
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- 1 5 - ~057192
Example II Pre~aration of Freeze-Dried Sus~ension
Concentrate
3 . 5 kg of 3/8~' diameter + 3.5 kg of 1/4~' diameter
steartite media were charged to an attritor. t~ith the
impeller rotating at 80 rpm, 10g Vanisperse7'CB, 3g Kelzan~
XC (a modified polysaccharide), 3g Orotan~ SN and water
to 910g were added to the mill. After five minutes 450g
BLADEX~was incorporated and the im~eller s~eed increased
to 245 rpm and the milling continued for 4~ hours.
The mill was emptied whilst running at 80 rpm. The
density of the formulation was determined ald found
to be o.85 g/l indicating extreme aeration. After de-
aeration, which was achieved with a Silverson stirrer
fitted with an axial ~low head, the density was found
to have increased to 1.07 g/kg.
The product was then divided into two equal portions,
to one the requisite weight of mono-ethylene glycol (9%)
was blended, this sample was then called 'Standard
BLADE~'SC' and the physico-chemical properties examined.
The results were used as a standard a~ainst which a
freeze dried and reconstituted suspension concentrate
was compared. The remaining half of the SC was freeze-
dried by the process described in Example I.
When dry the concentrate formed a crust which coated
the internal surface of the flask. This crust broke
into small piecea when the flask was ~ently tapped
~'Trademark
- 1 6 - 1057192
and was reduced to a fine powder by a sin~le nass
throu~h a hammer mi11. The free~e-dried concentrate
was subsequently reconstituted by blending in the
ratios 48% dried SC: 43% water and 9% mono-ethylene
glycol using a Silverson stirrer fitted with an
axial f'low head. The method of reconstitution ensured
that any air entrapped in the dry powder was not
retained in the SC.
The physico-chemical pro~erties of the reconstituted
Bladex~SC were compared against those of the standard
Bladex~SC, and the results are shown in Table 2.
7'-Trademark
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~Trademark
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- 1 8 - ~.05719Z
Exam,rle III
The biological activity of the Bladex'technical
concentrate, Standard suspension concentrate and
freeze dried suspension concentrate was assessed
in comparative tests a~!ainst peas, rye grass and
mustard, and comparisons Or standard Garden~75%
wettable r,owder with 94% technic~;l concentrate were
made using Spodoptera Littoralis. The results of
these tests are shown in the following tables 3
and 4, the standards being a wettable powder
containing 50% by weight of Bladex~'
~Trademark
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19
10571~Z
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1057192
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- 21 - 1057192
Example ~V
A freeze-dried suspension concentrate of Bladex'
was prepared followin~ the same procedure, and usin~
the same in~redients, as in Example II. A solution
in water of the potassium salt of MCPA was also
freeze dried, and 298~ of this product (equivalent
to 250g MCPA acid) were mixed with 68~ of the dried
Bladex`sus~ension concentrate, 3~ Kelzan7~XC and
3g Orota~SN to provide a formulation which could li
be reconstituted by the addition of water into a
sprayable formulation containing a mixture of Bladex~
:~ and MCPA.
~Trademark
21
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..... . . .. . . ... . . .. . . .
