Dispersion having an insecticidal action
The invention relates to a dispersion having an
insecticidal action, a process for its preparation and its
use.
DE 3835592 discloses the use of hydrophobic SiC>2 for
combating, for example, sucking insects. Such materials
are applied by dusting on.
However, because of the dust nuisance (industrial hygiene)
during application of these materials, this procedure is
finding ever less acceptance by the user. The aqueous
dispersions comprising only a hydrophobic silica and water
which are also described in DE 3835592, however, do not
show an adequate stability.
US 5830512 describes a dispersion in which an adequate
stability is achieved by addition of hydrophilic
substances, such as, for example, silicas. However, the
active hydrophobic component is diluted by a hydrophilic
substance as a result of this. Furthermore, only a very
low stability of the dispersion of hours to a few days is
achieved.
It is known from EP 1 250 048 to stabilize the dispersion
of hydrophobic silicon dioxide by gelling additives, such
as xanthan gum, sodium alginates or neutralized
carboxyvinyl polymers, mixtures of these additives also
being possible.
In interplay with the hydrophobic SiO2 particles and
incorporated air, these gelling additives moreover have
the effect of a significant structural viscosity.
A pronounced structural viscosity offers advantages in
application by spraying on: During the spraying process,

the viscosity of the dispersion under the shear forces
acting on it is relatively low. After the drops of
dispersion have impinged on the surface to be covered, the
viscosity rises again sharply, so that dripping/running
off from perpendicular surfaces in particular is avoided.
The essential feature according to EP 1 250 048 is that in
addition to the hydrophobic SiO2 particles to be dispersed,
large amounts of air are also incorporated. In
conventional dispersing processes, this cannot be avoided
without the use of wetting surfactants and defoamers.
Thus, a density of only 0.6 g/1 is stated in Example 1.
Approx. 40 % of the volume is therefore air.
To achieve an adequate activity, a minimum mass must be
applied to the surfaces to be sprayed. If only approx.
60 % of the volume of the spraying equipment can be made
use of per spraying operation, this means a significantly
reduced efficiency of the staff performing the
application.
The transportation and packaging costs and the disposal
costs of the packaging required are adversely higher by
this proportion.
An approx. 40 % larger storage area must also be taken
into account during storage.
Furthermore, a homogeneous, bubble-free covering of
surfaces to be treated cannot be achieved with a
dispersion containing air.
The invention provides a dispersion comprising, in
addition to water, 0.5 to 20 wt.% of hydrophobic silica,
0.01 to 10 wt.% of a gelling or viscosity-increasing
additive, 0.1 to 1 wt.% of a preservative and 0 to 1 wt.%
of a surface-active substance.
The water content can be 68 to 99.4 wt.%.

The specific density of the dispersion can be greater than
0.6 g/ml, preferably 0.7 to 1.02 g/ml.
A pyrogenically prepared, hydrophobized silica can be
employed as the hydrophobic silica. It can have a BET
surface area of 20 to 600 m2/g.
The gelling or viscosity-increasing additive can be a
biopolymer, such as, for example, xanthan gum, sodium
alginate, carob bean flour, pectin, agar, carrageens,
alginates and/or neutralized carboxyvinyl polymer, or
mixtures of these substances.
Preservatives which are approved for foodstuffs can be
employed as preservatives. These can be:
sorbic acid, sodium sorbate, potassium sorbate, calcium
sorbate, benzoic acid, sodium benzoate, potassium
benzoate, calcium benzoate, PHB ethyl ester, PHB ethyl
ester sodium salt, PHB propyl ester, PHB propyl ester
sodium salt, PHB methyl ester, PHB methyl ester sodium
salt, sulfur dioxide, sodium sulfite, sodium hydrogen
sulfite, sodium disulfite, potassium disulfite, calcium
disulfite, calcium hydrogen sulfite, biphenyl,
orthophenylphenol, sodium orthophenylphenolate,
thiabendazole, nisin, natamycin, formic acid, sodium
formate, calcium formate, hexamethylenetetramine, dimethyl
dicarbonate, propionic acid, sodium propionate, calcium
propionate, potassium propionate
Compounds which are also approved are:
nitrates, nitrites, carbon dioxide, chlorine and chlorine
dioxide
Ionic, nonionic and anionic surfactants can be employed as
surface-active substances.
The invention also provides a process for the preparation
of the dispersion according to the invention, which is
characterized in that the individual components are

dispersed successively or together into the water and in
this procedure the individual components are deaerated
before and/or during the addition or the dispersion is
deaerated during the individual dispersing steps.
In one embodiment of the invention, the deaeration can be
carried out by means of application of a vacuum.
Surprisingly, a stable and active dispersion which does
not contain extensive amounts of air can be achieved
according to the invention. This deaerated dispersion can
be achieved by dispersion of previously deaerated
hydrophobic SiO2. A subsequent deaeration of the
dispersions is indeed technically possible, but can be
achieved only with a high outlay because of the increased
viscosity of the homogeneous aqueous phase (gelling agent
as an additive). At least the greatest possible portion of
the air dispersed in can be removed by deaeration measures
before or during the dispersing.
In principle, any dispersing process which either renders
possible prior deaeration of the powder to be dispersed
and also prevents dispersing in of air during the
dispersing is suitable.
One embodiment of the deaeration and dispersing is the
utilization of a vacuum dissolver. A procedure is possible
here in which water and the gelling additive are
predispersed briefly, the entire amount of hydrophobic SiO2
is then added to the surface of the solution, without
stirring, the container is evacuated and only then is the
dispersing in of the hydrophobic SiO2 started.
A PSI Mix® from NETZSCH can also perform this deaeration
of the powder.
In order to remove residual microbubbles, deaeration
units, such as the NETZSCH DA-VS vacuum deaerator from

NETZSCH, a vacuum thin film rotary process, can be
employed.
The dispersion according to the invention can be employed
as insecticides, for example, against
Housedust mite: Dermatophagoides pteronyssinus
Poultry mite: Dermanyssus gallinae
Rust-red flour beetle: Tribolium castaneum
Grain weevil: Sitophilus granarius
Indian meal moth: Plodia interpunctella
Wheat aphid: Schiazaphis graminum.
Example 1
477.5 g completely demineralized water are initially
introduced into a double-walled dispersing container of
the CDS vacuum dispersing system with a DISPERMAT®
dissolver from VMA-GETZMMIN GMBH, 7.5 g xanthan gum are
added, the container is evacuated (water pump) and the
components are dispersed/dissolved at 2,000 rpm, toothed
disc of 7 0 mm diameter, for 15 min.
15 g AEROSIL® R 202 are then added, the container is
evacuated and the substance is incorporated into the
mixture at 800 rpm.
Since air is desorbed by this process and the bubbles
formed lead to an increase in volume, the evacuation
process must be interrupted several times in order to
allow coalescence of the air bubbles and thus an easier
deaeration. This operation is repeated until no further
increase in volume of the dispersion produced takes place
in vacuo. Dispersing is then carried out in vacuo at
3,500 rpm for 15 min.

At a concentration of 3 % SiO2 and 1.5 % xanthan gum, a
density of approx. 0.95 g/ml can be achieved with this
method. Theoretically, it should be possible to achieve a
density of 1.02. This difference can be explained by the
formation of some microbubbles.
Such microbubbles result from the release of desorbed air
constituents, after competing adsorption has taken place,
by a "fine deaeration", for example with the aid of a
NETZSCH DA-VS vacuum deaerator the density of approx. 1.02
can be achieved.
Example 2
476.5 g completely demineralized water are initially
introduced into a double-walled dispersing container of
the CDS vacuum dispersing system with a DISPERMAT®
dissolver from VMA-GETZMANN GMBH, 1 g lecithin is added,
the container is evacuated briefly (water pump) and the
components are dispersed/dissolved at 2,000 rpm, toothed
disc of 70 mm diameter, for 1 minute.
7.5 g xanthan gum are then added, the container is
evacuated (water pump) and the components are dispersed/
dissolved at 2,000 rpm, toothed disc of 70 mm diameter,
for 15 min. 15 g AEROSIL® R 202 are then added, the
container is evacuated and the substance is incorporated
into the mixture at 800 rpm.
Since air is desorbed by this process and the bubbles
formed lead to an increase in volume, the evacuation
process must be interrupted several times in order to
allow coalescence of the air bubbles and thus an easier
deaeration. This operation is repeated until no further
increase in volume of the dispersion produced takes place
in vacuo. Dispersing is then carried out in vacuo at
3,500 rpm for 15 min.

At a concentration of 3 % SiO2, 1.5 % xanthan gum and 0.2 %
lecithin, a density of approx. 1.0 g/ml can be achieved
with this method.
Due to the presence of a surface-active substance, the
wetting of the hydrophobic silica is improved, as a result
of which easier deaeration is achieved.
Theoretically, it should be possible to achieve a density
of 1.02. This difference can be explained by the formation
of some microbubbles. Such microbubbles result from the
release of desorbed air constituents, after competing
adsorption has taken place, by a "fine deaeration", for
example with the aid of a NETZSCH DA-VS vacuum deaerator
the density of approx. 1.02 can be achieved.
Conventional additives for preserving, such as sorbic
acids/sorbates, benzoic acid/benzoates, propionic acid,
parabens (para-hydroxybenzoic acid esters) and/or
Acticide® MV (Thor), can be added to the dispersions
produced.
Example 3
The activity was tested in Petri dishes. In this test,
filter papers having a diameter of 8.4 cm were coated on
one side, with the aid of a doctor blade, with a layer
thickness of 200 µm of the substance to be tested and,
after drying, were placed in Petri dishes of plastic
having a diameter of 9 cm. The mites (poultry mite,
Dermanyssus gallinae) were placed in the centre of the
treated surface using a fine brush. After application of
the mites, the Petri dishes were closed and the lid was
additionally secured with Parafilm. The activity tests
were evaluated after 24 hours.

All the tests were conducted at a relative atmospheric
humidity of 40 % and a temperature of 2 6oC. The activity
on the mites was determined by counting under a
stereomicroscope. A distinction was made between dead
mites, severely damaged mites (severe excitation, mostly
lying on the back and unable to run) and living mites in
per cent compared with the controls.
The activity was investigated on materials which were
produced in accordance with Example 2, dispersions for
which other hydrophobic Aerosil types were employed
instead of Aerosil® R202 additionally being tested.
0.1 % sorbic acid, 0.1 % potassium sorbate and 0.2 %
propionic acid were added as preservatives during the
preparation.
A batch without the addition of AEROSIL® was used as a
control sample, all the other additives, including the
preservatives, being identical.


Comparison example
477.5 g completely demineralized water are initially-
introduced into a double-walled dispersing container of
the CDS vacuum dispersing system with a DISPERMAT®
dissolver from VMA-GETZMANN GMBH, 7.5 g xanthan gum are
added and the components are dispersed/dissolved at
2,000 rpm, toothed disc of 70 mm diameter, for 15. 15 g
AEROSIL® R 202 are then added and incorporated into the
mixture at 800 rpm. After the incorporation of the
AEROSIL® R 202, dispersing is then carried out at
3,500 rpm for 15 min. The dispersion obtained has a
density of only 0.6 g/m1.

WE CLAIM:
1. Deaerated dispersion comprising, in addition to water, 0.5 to 20 wt.% of
hydrophobic silica, 0.01 to 10 wt.% of a gelling or viscosity-increasing additive,
0.1 to 1 wt.% of a preservation and 0 to 1 wt.% of a surface-active substance,
characterized in that it has a specific density of greater than 0.6 g/ml and that it is
obtainable by a process in that the individual components are dispersed
successively or together into the water and in this procedure the individual
components are deaerated before and/or during the addition or the dispersion is
deaerated during the individual dispersing steps.
2. Process for the preparation of a deaerated dispersion comprising, in addition
to water, 0.5 to 20 wt.% of hydrophobic silica, 0.01 to 10 wt.% of a gelling or
viscosity-increasing additive, 0.01 to 1 wt.% of a preservative and 0 to 1 wt.% of
a surface-active substance, which has a specific density of greater than 0.6 g/ml,
wherein the individual components are dispersed successively or together into
the water and in this procedure the individual components are deaerated before
and/or during the addition or the dispersion is deaerated during the individual
dispersing steps.

3. Process for the preparation of the dispersion as claimed in claim 2, wherein
the deaeration is carried out by means of application of a vacuum.

Deaerated dispersion comprising, in addition to water, 0.5 to 20 wt.% of
hydrophobic silica, 0.01 to 10 wt.% of a gelling or viscosity-increasing additive,
0.1 to 1 wt.% of a preservation and 0 to 1 wt.% of a surface-active substance,
characterized in that it has a specific density of greater than 0.6 g/ml and that it is
obtainable by a process in that the individual components are dispersed
successively or together into the water and in this procedure the individual
components are deaerated before and/or during the addition or the dispersion is
deaerated during the individual dispersing steps.