Note: Descriptions are shown in the official language in which they were submitted.
~ ~69~1
~ .
HOLDER FOR :~:LECTROSTATIC SPRAYING
;'
, This invention relates to container~, and in
_
particular to containers for use in the electrostatic
spraying of liquids.
In our r- Canadian~Patent ~o~, 10~/1937 lssùed February
..... _ .. .__ .. _ . . . _ .,. .. _. ............... ;
5 .-I9, 1980, ~~ .`~we have described an apparatus for the
electrostatic spraying of liquids. This apparatus is of
simple constructi.on, with a low power requirement ~it has
no moving parts and can readily be run off dry cells); it
: is thus particularly suited for use as a hand held
sprayer in applications where large power sources are not
readily available: for example, in spraying cropsO
Electrostatic spraying of crops also has advantages in
promoting even coating of plants, with spray being
: attracted around behind foliage instead of coating only
exposed surfaces; and in reducing spray drift, which is
at best wasteful and at worst hazardous to the environment.
The apparatus disclosed in~above Canadian Patent No. 1071937 .
- comprises essentially a discharge~nozzle; ah electrode
disposed around the nozzle; a container for supplying
liquid to be sprayed to the nozzle; and a high voltage
generator for applying a high voltage to the electrode,
the electrode being earthed. In this way a strong elec-
. tric field may be produced between the nozzle and the
electrode, sufficient to atomise liquid passin~ through
. 25 the nozzle.
: This apparatus is p?rticularly.suitable for the
application of pesticides at low or ultra-low volume
(t~pically at a spra~ application rate in.the range 0.5 to
; 10 litres spray liquid per hectare~. Low and ultra-low
volwne spraying have several recognised advantages, as
well as being especially suitable where water is not
readily available as a spray. diluent, but they also have
i one disadvantage. Of necessity, they must use relatively
concentrated pesticid21 compositions. Such compositions
frequently have a greater or lesser degree of human
I 1 69~''L 1
- 2 - .
toxicity 9 and for this reason it is desir.able that they
should be handled as little as possible. ~ parti,cular
danger is the decantation of poisonous liquids into
- beverage bottles.
A pesticide sprayer, to provide the best service,
must be reliable and adaptable. ~esirably.it should be
able to spray pesti.cides of several dif~erent kinds.
Different pesticides come in different formulations,
having different electrical properties, and requiring to
be sprayed in differing droplet sizes to give optimum
effect. In the apparatus of our aforesaid Canadian
Patent No. 1071937, useful and convenien
control over droplet size and spraying properties can be
provided by varying the applied voltage; but the size of
the nozzle and the relative size and positiGn of the
surrounding electrode may also require adjustment to suit
the formulation being sprayed. It is often difficult to"~'' '
do this reliably in the field., Also,. pesticide sprayers
(spray-tanks and spray-lines) normally require careful
,- 20 cleaning between application of different pesticides;
otherwise, for example, traces of,herbicide may damage
crops being sprayed against fungal attack. The need for
such cleaning is increased when formulations are to be
. sprayed electrostatically, since contamination may affect
their electrical prope~ties. Thorough cleaning may
damage nozzles, leading to incorrect.spray application.
The object of the present .invention is to provide
containers suitable for use in electrostatic spraying
apparatus'.of the-kind described in aforesaid Canadian ''~'
3p Patent No. 1071937 ,`which enable a
nu,mber of the problems outlined above to be mitigated or
overcome.
According to the present invention in,its bro~adest
zspect, w,e provide a liquid container adapted to form
part of apparatus for electrostatic spraying, the appa-
ratus including a power s.ource, a high voltage generator,
a spray nozzle at least part of the surface of which is
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- 3 -
electrically co~ductive, an electrode disposed adjacent
the nozzle and insulated therefrom with electrical
connections for connecting the power source to the input
_ terminals of the generatorl the electrode to on output
~S terminal and the nozzle to the other output terminal of
the genexatox; the container hauing an orifice for
delivering liquid, mounting means for locating the
container on the apparatus in a position in which the
orifice can deliver liq`uid to the spray nozzle, ~he
mounting means including a conductor or conductors
- completing said electrical connections; and a closure or
seal for closing the orifice prior to location of the
container on the apparatus.
We further provide apparatus for electrostatic
spraying as defined above, suitable for receiving a
container according to the invention; and we further
provide a sprayer formed by the combination of a con-
tainer according to the invention mounted upon apparatus
according to the invention. Throughout this specifi-
- 20 cation, the texm 'conducting surface' is intended to
include a semi-conducting surface. ~
Prior to mounting on the spxaying apparatus, the
container orifice o~viously requires t~ be sealed against
the emission of liquid. One or more cor,v`entional sealing
means may be employed, for example a screw cap or a metal
foil seal over the orifice, or both. According to a
preferred feature of the invention, the container seal is
adapted to be opened when, and preferably only when,
located on the spraying àpparatus. Such opening may take
place during such location, or subsequently: furthermore,
the opening may be actuated mechanically or electrically.
T~us, during the action of mounting the container on .to
the spraying apparatus, a knife or spike on the apparatus
may cut or pierce a metal foil over the orlfice of the
container. The container orifice may be sealed by a
valve, e.g. a spring-biassed ball valve which is opened
during mounting by contact with a detent on .he apparatus
.
4 _ ,
With such a system the. container orifice is automatically
closed on removal from the apparatus which is particularly
useful when the container still contains'liquid. The
same desirable end may also be accomplished by use of an.
electrostatic ~alve. Such a valve may be spring-~iassed
shut, and opened only by application of potential from
the high voltage generator when the container is mounted
on the apparatus.. The electrostatic valve is partic-
ularly convenient because the container remains sealed
lo even after being mounted on the apparatus, until the
. current is switched on.
In a narrower aspect of our invention, the spray
nozzle forms part of the container rather than of the
apparatus on which it is mounted. Thus, further ,
according to the present invention we provide a container
for liquid to be electrostatically sprayed, suitable for
- mounting on a holder carrying a high voltage generator,
the container having: a spray.nozzle at least part of the
surface of which is electrically conducti~e; an orifice
-20 for delivering liquid to the nozzle; an electrode' dis-
posed about the nozzle and insul'ated therefrom; mounting
' . means for locating the container on the holder; separate
- electrical connections from the nozzle and the electrode -
to separate contacts on the mounti~g means so placed that
when the container is located ~n the'holder by the
mounting means each contact can make electrical connection
with.one output terminal of the' high voltase generator;
and a seal for closing the orifice,.prior to locatio,n on
the holder.
We further provide a holder suitable ,for receiving
a .container according to the,invention which compr~ses a
body carrying a high voltage generator, and mounting
means complementary to the mounting means on the container
provided with separate electrical contacts complementary . '
to those.on the container for electrical connection to
separate terminals of the high voltage generator.
A further feature of the invention is the sprayer
_ 5 _
formed by the combination of a container according to the
invention mounted upon a holder according to the invention.
Preferably means are provided for maintaining one
terminal of the high voltage generator at or near earth
potential. Such means may be a conductor for connection
to earth, for example, a trailing earth wire dependant
îrom the holder. Where such means are provided, it is
preferred that the earthed terminal of the high voltage
generator is arranged for connection to the container
electrode rather than to the nozzle. Charging of the
spray is then by direct contact, rather than by
induction, and there is a stronger electrostatic field
transporting the spray to its (earthed) target.
If desired, one of the two electrical connections
between the contacts on the container and the high
voltage generator terminals may be through earth; though
a more direct connection is sometimes convenient.
For most efficient operation the container also
re~uir~s a means of equalising the external and internal
pressure during spraying, fox example an air vent, ~r
non-rigid walls.
Containers according to the invention may be filled
with properly formulated spray liquid by the manufacturer,
and after the ~ontainers are closed, the spray li~uid
will remain uncontaminated until it is actually sprayed.
There i5 no need to clean spray-tanks (or even spray-
lines or nozzles, if the nozzle forms part of the con-
tainer) to avoid contamination, so.~different products can
be sprayed successively without undue loss of time.
Toxic hazards through handling by operators are minimised;
errors by field operators in mixing and dilution pro-
cedures are eliminated. After use, the containers
according to the invention may be returned to the manu-
facturer for re~illing; OE may be discarded. Containers
may be made from one or more elements of plastics material
by, for example, injection moulding or blow moulding, or
a combination of the two. The conducting elements of the
~ ~ ~9~ ~
- 6 - .-
containers (nozzle, electrode, contacts and connections)
may be provided by metal inserts, or (for all parts
except the contacts) by application of ccnductive metallic
~~ coatings or paints to the container surface or by the use
of partly-conducting plastics.
It is possible to provide the energy source for the
high voltage generator in the holder. It may be preferred
however to provide it in the container. Accordingly, in
a different aspect the invention provides a container for
liguid to be electrostatically sprayed, suitable for
mounting on a holder carrying a high voltage generator
the container being provided with: an orifice for
delivering liquid to a spray nozzle; a power source
capable o. providing sufficient electrical energy to
atomise electrostatically the actual or intended contents
thereof; mounting means for locating the container on the
holder; and separate electrical connections from the
poles o the power source to separate contacts on the
; mounting means so placed that when the container is
- 20 located on the holder by the mounting means~each contact
can make electrical connection with one input terminal of
. the high voltage generator; and a seal for closing the
; orifice prior to location on the holder. It is further.
preferred that the container be provided with a spray
nozzle at least part of the surface of which is electri-
cally conductive and an electrode disposed about the
. nozzle and insulated therefromj the nozzle and the elec-
trode being disposed to be electrically connected via
contacts on the mou~ting means to opposite terminals of
~o the high voltage generator when the container is located
on the holder; but a sometimes convenient alternative is
to provide such an electrode, or such a nozzle, or both,
on the holder. In a particularly convenient arrangement,
~ the mounting means on the container has three electrical . .
- 35 contacts; one for connecting one pole of the power
; source to a first input terminal of the generator; one
- for connecting the nozzle to a first output terminal of
,
- 1 1 6 9 ~ 4 1
7 _ .
the generator; and one for connecting the second pole of
the power source and the electrode to a conductor on the
holder connected to the second input and output terminals
-- of the generator, and capable of connecti.on to earth
One suitable form of power source is an electrical
storage battery. Th.e amount of electrical energy
required to atomise liquid is remarkably low. A typical
example may be cons.idered: a vessel containing 500 ml of
liquid to be sprayed at a rate of 0.5 ml per second, with
a droplet size of about lOO microns, and a charge to mass
ratio of 5 x 10 coulombs per kilogram. The current
carried by droplets atomising from the nozzle is thus 2.5
microamperes. The spraying time will be 1000 seconds
(just over quarter of an hour) at an input current of,
typically, 15 milliamperes, an input voltage of about lO
volts and an output voltage of 20 kilovolts. ~hus the
required cell rating is only 4 milliampere hours, at
about lO volts. This capacity is considerably less than
that of most readily available torch batteries. If the
: 20 containers are to be discarded after use, batteries of
the necessary rating can be made cheaply on a large
scale; alternatively, small quickly rechargeable
batteries may be used. An example of another form of
power source which may be used in the invèntion is a .
solar cell~ 5uitable high voltages for use in the
invention range from about 1 to about 30 kilovolts, and
most conveniently from about 5.to about 20 kilovolts.
A specific embodiment of the invention wiil now be
described with reference to the drawings, in which:
3~ Figure 1 is a perspective ~iew of a container
according to the invention;
Figure 2 is an end yiew of a container according to
the invention;
Figure 3 is a vertical section through the container
35 on t~e line AA of Figure 2;
Figure 4 is a plan view of the holder;
Figure 5 is a plan view of the collar of the con-
tainex; - .
6~4 ~
. . .
Figure 6 is a cir.cuit diagram of the circuit formed
when the container is mounted on the holder.
' Figuxe 7 is a vertical section through the.neck of
a second container according to the inventionO
Figure 8 is a vertical section through the neck of a
third container, according to th~ invention.
Figure 9 is a plan view of plate 54 shown in Figure'
8.
With.reference generally to Figures 1 to 3 and,5,
the container comprises a generally flask-shaped body (1)
of blow-moulded high density polyethylene, t,he neck of
which is in li~uid-tight sealed engagement with a collar
(2) injection-moulded from polyacetal. It contains a
solution (40) of 10~ by weight of an insecticide in an
: 15 aromatic hydrocarbon solvent. The collar.(2) is formed
: , of two concentric cylinders (3) and (4), joined near their ,~
ends to form an annulus. Within the inner cylinder (4)
is a polyacetal plug (5), whose.externaI diameter is
:~ somewhat less than that of ~he internal diameter of the
.
': ~o cylinder (4). ~he plug:(5) is held in place within.,.the
cylinder (4) by outwardly projecting lugs (6). .It''thus
forms, in cooperation with the cylinder (4), an annular
.
:~ channel (7) of capillary dimensions through whlch spray
liquid ma~ pass. The plug t5) is also provided with a
central bore carrying a polythene capillary tube (.8)
which extends upwardly into the body (1) Oc the con-
, tainer. The annular no~zle formed by the combination of
the plug (5) and the cylinder (4) is closed against
- liquid leakage, by sealing cap-(,9~ (shown in position only
in Figure 3). Within the container on the upper sur~ace
,. . Of the collar (,2.) is carried a 10 ~olt bat,tery ~10).
This battery is specially constructed, and contains
sufficient electrical energy to atomise the liquid in the
container, with,an extra margin of 50~ ,to allow .for '
electric,al leakage. The positive pole of the battery ,.
(10) is connected to a brass contact stud (11~ on the
outer wall of the collar t2) by a strip (,12). o~ elec-
~ 3 692~ ~
_ g
trically conductive paint, passing from the battery ~lO)up over the rim of the collax (2~ and down the outside
thereof. The negative pole of the battery ~lO~ is con-
nected, by a similar conductive stxip (13~, to a second
brass contact stud (14), Stud (~4l is also connected, by
a similar conductive strip (15), to the rim tl6) of the
cylinder (3~. This rim (16~ is itself coated with
electrically conductive paint, to form an annular con-
ductor. Similarly, the rim ~17) of the inner cylinder
lo (4) is coated with electrically conductive paint to form
an annular conductor. The conductive rim (17) is con-
nected by an electrically conductive paint strip (18),
passing down the inside of the cylinder t~) and over the
top rim of the collar, to a third brass contact stud (l9)
- on the outside of the collar (2). To pre~ent current
leakage through the spray liquid, the conductive strips
(12), (13) and (18) are protected within the body (l) o
the container by insulating varnish. A projecting key
(20) is also formed on the outside of collar (2).
- 20 With reference now principaLly to Figuxe 4, the
holder for the container comprises a body (21) suiLable
for holding in the hand carrying a variable high voltage
generator (22) (233P, 0-20 kilovolts, 200 microamp module,
ex Brandenburg Limited). The body (21~ is of generally
elongated form, and terminates in a ring (23), the inside
of which is adapted to receive the collar (2) of the
container. A key way (24) corresponds to the key (20) on
the collar (2). Brass contacts (26), (26~ and (27~ are
mounted on the inside of the ring (23~ so as to be able
3o to contact studs (11) r (14) and (19~ on the container,
respectively. Stud (25) is connected by an insulated
electrical conductor (28) to a switch (29~, which, in the
'on' position, leads via a conductor (30) to the input
terminal of the high voltage generator (22). Stud (26)
is connected via an insulated electrical conductor (31
to a conductor (32) fo~ connection to earth: the con-
ductor (32) is a metal wire wlth a baxed e~d for trailing
.9 2 ~1 ~
-- 10 -- .,
along the ground. The stud (27) connects via an insu-
lated electrical conductor ~33~ to the positive high
voltage output terminal (34) of the generator (221. The
_ negative output terminal (35) of the generator (22~ is
connected to the earth wire (32~.
In operation, the container~is placed in an upright
position, and the sealing cap (9~ removed. The ring (231
of the holder is then placed over the collar ~2) of the
containerl over which it is a push fit, and the two
mating parts are pushed together~ The ring t23) grips
the collar (2) sufficiently tightly to hold the container
in position; the key (20) on the container cooperates
with the key way (24) to hold the container in a position
in which the following pairs of contacts touch~ and
(25); (14) and (26); and (19) and (27~. The circuit so
formed is shown in Figure 6. The holder is now used to
- invert the container over the target to be sprayed, and
liquid starts to drip from the channel (7~. The switch
(29) is at once turned to the 'on' position. This
- 20 permits current flow from the battery (10) via contacts
(11) and (25) to the generator (22); and this in turn
causes a high potential (con~eniently 15 kilovolts) to be
- conveyed from the terminal (~4) via contacts (27) and
(19) to the electrically conducting surface (17) of the
cylinder (4). Meanwhile the electrically conducting
surface (16) of the cylinder ti) is earthed, via contacts
(14) and (26) and earth wire (32). An intense electro-
static field is thereby created between the two con-
ducti~g surfaces (17? and (1~), which causes liquid
emerging adjacent to the sur~ace (17) to atomise, and be
projected downwardly as a fine spray, of controlled
particle size towards any desired target. As the liquid
passes out of the container through the annular channel
(71, the decreasing pressure within the conta~ner is
equalised by air passing up through the central capillary
tube (8). Spraying is stopped by turning off the switch
(29) and turning the container mouth upwards.
2 ~ ~
Various modifications to the foregoing apparatus
will be apparent to those skilled in the art. The con-
tainer illustrated is intended to be disposable.
However, reusable containers ma~ also be made, conven-
iently with rechargeable batteries~ For reusable con-
tainers, it may be found necessary to make the nozzle and
electrode, as well as other electrical connections, of
metal rather than merely of a conductive coating or
paint; and for this reason such reusable containers are
o substantially more expensive.
The device described includes a conductor for
connection to earth in the form of a trailing bare metal
wire. This has the disadvantage that it may become
caught up or tangled. The device works best with an
earth connection; but it need not be of low resistancet
The conductor for connection to earth may be, for example,
-~ a metallised strip along the handle of the holder. When
the operator grasps the handle, an electrical pathway to
earth is formed through the operator's body. Though this
pathway has high resistance, we have found that it is
generally adequate. Experiments have shown that, with an
~ arrangement of this kind, the voltage on the container
- electrode may be up to about one or two hundred volts
above that of earth, even when the operator is wearing
rubber boots in relatively dry conditions. Such a voltage
on the electrode is little different rrom that of earth,
relative to the potential on th~ nozzle of several
thousand volts. The current flowi~ through the operator
is so small that ther:e i9 no danger to him whateYer~ nor
; 30 can he even feel anything.
The apparatus of the invention has been described
with particular reference to its use in pesticide -
spraying, in particular of compositions comprising
pesticides in organic liquid carriers, for whlch ~t has
special advantages. However, it also has advantages in
respect to spraying of coatings or paints, for example by
the home decorator. Holders for t~e container are
.
1 1~92~1
- 12 -
conveniently adapted for holding in the hand; but they
may also be carried on vehicles such as txactors or
aircraft, when they may support more than one container.
~ ~ It may however be preferred to use, in tractors or air-
craft, a form of the invention in which the spray nozzle
is not integral with the contalner. In this case, a
relati~ely large container can supply several spray
nozzles; and electrical power may be supplied rom
batteries or generators carried in the vehicle.
Figures 7, 8 and 9 illustrate two other closure
devices which may be used in the containers of the
invention. Both are illustrated in containers in which
the spray nozzle is not integral. In Figure 7, the
container (40) has a neck (41) in which is mounted a
simple mechanical ball valve, comprising a ball ~42)
urged against a seat (43) by a compression spring (44)
mounted against stops (45). Prior to location on the
spraying apparatus or holder (46), the ball valve prevents
liquid leaving the container (40). On locating the
: 20 container (40) on the apparatus (46), the b~all (42) is
forced inwards away from the seat (43) by a finger (47),
permitting liquid to flow from the container (40) into
the apparatus (46), for delivery to an electrostatic
spray-head (not shown). At the same time, contacts (48)
on the mouth of the neck (41) complete a~ electrical
connection in the apparatus (46), permitting the supply
of an appropriate high potential to the spray-head.
Figure 8 shows an alternative ~orm.of val~e in a similar
container; this valve is operated electrostatically.
The valve comprises a metal plate (50) with a central
port (51) mounted in the neck (52) of the container (53).
Below the plate (50) is a second plate (54), shown in
plan in Figure 9-. It has a central boss ~-55?- which fits
wit~in the port (51) of plate (501 and closes it against
passage o~ liquid. Plate (54) has peripheral slots (56),
and is urged against plate (50) by a compression spring
; (57). Metal plates (50) and (54) are coated, on their
.
IJ~92~
, - 13 -
lower and upper surfaces respectively, with a thin layer
of a dialectric ~,epoxide resin). Contacts (,58) and (S9)
on the outside of the neck (52~ are electrically connected
via the metal plates (50) and (54). In operation, the
container (53) is mounted on a s~raying apparatus Cnot
shown) in fluid-tight engagement with a conduit leading
to a~ electrostatic spray-head. Contacts t58l and ~59~
are thereby connected respectively to the output terminal
of a high voltage generator and to the conducting surface
of the electrostatic spray-head, A potential of about
20 kilovolts is thus applied to plates (50) and (54).
This potential forces the plates apart by electrostatic
repulsion against the action of the spring (57), and
liquid flows from the container (53) through the port
(51) and slots (56) into the apparatus for delivery to
the spray-head. At the same time the spray-head receives
a'potential appropriate to atomise the liquid being
delivered to it. Without the container on the apparatus,
the electrostatic valve cannot open r and neither can
~ 20 potential be transmitted to the electrostatic spray-~ead.
.: . - , .
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TWR/vmc
21 Aug 79
