CA1169242A - Containers for use in electrostatic spraying - Google Patents

Abstract

ABSTRACT
A liquid container adapted to form part of apparatus for electrostatic spraying, the apparatus including a power supply, high voltage generator having input and output terminals, a spray nozzle at least part of the surface of which is electrically conductive, an electrode disposed adjacent the nozzle and insulated therefrom, with electrical connections for connecting the power supply to the input terminals of the generator and the electrode to one output terminal of the generator and the nozzle to the other output terminal of the generator; the container comprising:
a body having an orifice for delivering liquid;
mounting means for locating the container on the apparatus in a position in which the orifice can deliver liquid to the spray nozzle, the mounting means including a conductor or conductors forming part of the electrical connections for the apparatus; and closure sealing means for closing the orifice prior to the location of the container on the apparatus and so that the orifice is opened when and only when the container is mounted on the apparatus.

Description

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CONT~INERS FOR USE IN ELECTROSTATIC SPRAYING

his invention relates to containers, and in .. _ particular to containers for use in the electrostatic spraying of liquids.
In ourr Canadian Patelit No. 1071937 issued February 19, I980, ~we have descri~ed an apparatus for the .
electrostatic spraying of liquids. This apparatus is of simple construction, with a low power requirement (it has no moving part~ 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 crops.
Electrostatic spraying of crops also has advantages in promoting even coating of plants, with spray ~eing 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~Patënt ~o. 1071937 comprises essentially a discharge nozzle; an 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 passing through the nozzle.
This apparatus is particularly suitable for the application of pesticides at low or ultra-low volume (t~pically at a spray application rate in the range 0.5 to 10 litres spray liquid per hectare). Low and ultra-low volume 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 one disadvantage. Of necessity, they must use relatively concentrated pesticidal compositions. Such compositions frequently have a greater or lesser degree of human S~

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toxicity, and for this reason it is desirable 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. Desirably it should be able ~o spray pesti,cides of several different 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 afoxesaid Canadian Patent No. 1071937, useful and convenient 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 position 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 cIeaning 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 i5 to provide containers suitable for use in electrostatic spraying apparatus of the kind described in aforesaid Canadian ''~
' 30 Patent No. 1071937 ~ ~which enable a number of the problems outlined aboue to be mitigated or overcome.
According to the present invention in its broadest aspect, we provide a liquid container adapted to form part of apparatus for electrostatic spraying, the appa-ratus including a power source, a high voltage generator, a spray nozzIe at least part of the surface of which is `\\

~ ~ 69~ 2 electrically conductive, an electrode disposed adjacent the nozzIe and insulated therefrom with eIectxical connections for connecting the power source to the input _ terminals of the yenerator, the electrode to one output terminal and the nozzle to the other output terminal of the generator; the container hauing an orifice for delivering liquid, mounting means for locating the container on the apparatus in a position in which the oxifice can deliver liq`uid to the spray nozzle, the 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 fox 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-cation, the term 'conducting surface' is intended toinclude a semi-conducting surface.
- Prior to mounting on the spraying apparatus, the ; container orifice obviously requires to be sealed against the emission of liquid. Onè or more conventional sealing - 25 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 apparatus. Such opening may take place during such locationl or subsequently: furthermore, the opening may be actuated mechanically or electrically.
Thus, 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 orifice of the container. The container orifice may be sealed by a valve, e.g. a spxing biassed ball valve which is opened during mounting by contact with a detent on the apparatus , .

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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 ~e accomplished by use of an electrostatic valve. Such a valve may be spring-biassed 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 fox liquid to be electrostatically sprayed, suitable for mounting on a holder carrying a high voltage generaLor, the container having: a spray nozzle at least part of the surface of which is electrically conductive; an orifice for delivering liquid to the nozzle; an elec~rode dis-posed about the nozzle and insulated therefrom; mounting means for locating the container on the holder; separate electrical connections from the nozzle and the electrode to separate contacts on the mounting means so placed that when the container is located on the holder by the mounting means each contact can make electrical connection - with one output terminal of the high voltage generator;
and a seal for closing the orifice prior to location on the holder.
We further provlde a holder suitable for receiving a container according to the invention which comprises 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 ge~erator.
A further teature of the inventlon is the sprayer .

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f ormed 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 genexator at or near earth potential. Such means may be a conductor for connection-to earth, for example, a trailing earth wire dependant from the holder. Where such means are provided, it is preferred that the earthed terminal of the high voltage generator is arranged f or 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.
I~ desired, one of the two electri~al 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.
i -- For most efficient operation the container also requires a mean~ of equalising the external and internal : 20 pressure during spraying, for example an air vent, Gr non-rigid walls.
Containers according to the invention may be filled ` with properly formulated spray liquid by the manufacturer, and after the containers are closed, the spray liquid will remain uncontaminated until it is actually sprayed.
There is 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 refilling; or 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 2 ~ ~

containers (nozæle, electrode, contacts and connections) may be provided by metal inserts, or (for all parts except the contacts) by application of conductive metallic ~ coatings or paints to the container surface or by the use of paxtly~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. ~ccordingly, in a different aspect the invention provides a container for liquid 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 of 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 term~nal'of ~ the high voltage generator; and a seal for closing the orifice prior to location on the holder. It is fur~her preferred that the container he 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 therefrom, the nozzle and the elec-trode being disposed to be electrically connected via contacts on the mounting means to opposite terminals of 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 no~zIe, or bo~h, on the holder. In a particularly convenient arrangement, the mounting means on the container has three electrical contacts, one f'or connecting one pole of the power source to a first input terminal of the genexator; one for connecting the noz'zle to a first output terminal of ~ ;11 69~

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 connection to earth.
One suitable form of power source is an electrical storage battery. The amount of electrical energy required to atomise liquid is remarkably low. A typical example may be considered: a vessel containing 500 ml of li~uid to be sprayed at a rate of 0.5 ml per second, with o a droplet size of about 100 microns, and a charge to mass ratio of 5 x 10 3 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 10 volts and an output voltage of 20 kilovolts. Thus the required cell rating is only 4 milliampere hours, at about 10 volts. This capacity is considerably less than that of most readily available torch batteries. If the containers are to be discarded after use, batteries of the necessary rating can be made cheaply on a large ~: scale; alter~atively, small quickly rechargeable batteries may be used. An example of another form of power source which may be used in the invention is a solar cell. Suitable high voltages for use in the invention range from about 1 to about 30 kilovolts, and most conveniently from abcut 5 to about 20 kilovolts.
A specific embodiment of the invention will now be described with reference to the drawings, in which:
Figure 1 is a perspective view of a container according to the invention;
~ Figure 2 is an end ~iew of a container according to - the mvention;
- Figure 3 is a vertical section through the container on the line AA of Figure 2;
Figure 4 is a plan view of the holder;
Figure 5 is a pla~ view of thç collar of the con-tainer;

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, Figure 6 is a circuit diagram of the circuit formed when the container is mounted on the holder.
Figure 7 is a vertical section through the neck of ''~ a second container according to the invention.
Figure 3 is a vertical section through the neck of a third container according to the invention.
Figure 9 is a plan view of plate 54 shown in Figure 8.
With reference generally to Figure's 1 to 3 and 5, lo the container comprises a generally flask-shaped body (1) of blow-moulded high density polyethylene, the neck of which is in liquid-tight sealed engagement with a collar (2) injection-moulded from polyacetal. It contains a solution (40) of 10% ~y weight of an insecticide in an aromatic hydrocarbon solvent. The collar (2) ;s 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 external diameter is somewhat less than that of the internal diameter of the cylinder (4). The plug (5) is held in place within.the cylinder (4~ by outwardly projecting lugs (6). It"thus ;' forms, in coo'peration with the cylinder (4~, an annular - channel (7) of capillary dimensions through which spray liquid may pass. The plug (5) is also provided with a central bore carrying a polythene capillary tube (8) which extends upwardly into the ~ody (1) of the con-tainer. The annular nozzle 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 ; 30 in Figure 3). Within the container on the upper surface Of the collar (2~ is carried a 10 volt battery ~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 or electrical leakage. The positive pole o the battery (10) is connected to a brass contact stud (11l on the - outer wall of the collar (2) by a strip (12) of elec-1 ~ ? 2 '1 ~
g _ . trically conductive paint, passing from the battery ~10) up over the rim of the collar (2~ and down the outside thereof. The negative pole of the battery (10~ is con-. _ nected, by a similar conductive strip (13~, to a second brass contact stud (14). Stud (~4~ 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 conductivP rim (17~ is con-nected by an electrically conductive paint strip (18), passing down the inside of the cylinder (4~ and over the top rim of the collar, to a third brass contact stud (19) on the outside of the collar (2~. To prevent current leakage through the spray liquid, the conductive strips (12), (13~ and (18) are protected within the body (1~ of the container by insulating varnish. A projecting key (20) is also formed on the outside of collar (2).
With reference now principally to Figure 4, the~
holder for the container comprises a body ~21) suitable - for hol~ing in the hand carrying a variable high voltage generator (223 (233P, 0~20 kilovolts, 200 microamp module, ex Brandenburg Limited). The body (21) is of generally - 25 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 (251, (26~ and (27~ are mounted on the inside of the ring (23~ so as to be able to contact studs (11), (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' positionl leads via a conductor (30) to the input terminal of the high ~oltage generator (22). Stud (26~
is connected via an insulated electrical conductor (31) to a conductor (32) for connection to earth: the con-ductor (32) is a metal wire with a bared end for trailing ; 1 ~ 69~

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 (22~. The _ negative output terminal (35) of the generator (22~ is connected to the earth wire t32~.
- In operation, the container~is placed in an upright pos~tion, and the sealing cap (9~ removed. The ring t23) of the holder is then placed over the collar (2~ of the containerl over which it is a push fit, and the two o 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: (11) 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)0 The switch (29) is at once turned to the 'on' position. This permits current flow from the battery (10~ via contacts (11) and (25) to the generator (22); and this in ~urn causes a high potential (conveniently 15 kilovolts) to be conveyed from the terminal (34) via contacts (27) and (19) to the electrically conducting surface (17) of the cylinder (4). Meanwhile the electrically conducting surface (16) of the cylinder (3) is earthed, via contacts (14) and (26) and earth wire (32). An intense electro- -static field is thereby created between the two con-ducting sur~aces (17) and (16~, which causes liquid eme~ging adjacent to the surface (17) to atomise, and be projected downw æ dly as a fine spray, of controlled particle size towards any desired target. As the liquid passes out of the container through the annular channel (7~, the decreasing pressure within the cont~iner 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.

g~2 Various modifications to the foregoing ap~aratus will be apparent to those skilled in the art. The''con-tainer illustrated is intended to be disposable.' However, reusable con~ainers may 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 forconnection 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 resistance.
- 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 ~: 20 pathway has high resistance, we have found that it'-is generally adequate. Experlments 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 dif~erent from that of earth, relative to the potential on the nozzle of several thousand voltsO The current flowing through the operator is so small that there is no danger to him whatever, nor 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 which ~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 th'e container are " . I:f~9~12 oonveniently adapted for holding in the hand; but they may also be carried on vehicles such as tractors 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 whic~ the spray nozzle is not integral with the container. In this case, a relati~ely large container can supply several spray nozzles; and electrical power may be supplied from 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 i5 mounted a simple mechanical ball valve, comprising a ball (42) ; urged against a seat (4~) by a compression spring (44) mounted against stops (45). Prior to location on the spraying apparatus or holder (46), the ball valve prevents li~uid 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 an electrical connection in the apparatus (46), permittiny the supply of an appropriate high potential to the spray-head.
Figure 8 shows an alternative ~orm of valve 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 within the port (51) of plate (50) and closes it against passage of 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 I 7 6 ~

low~r and upper surfaces respectively, with a thin layer of a dialectric ~epoxide resin). Contacts (58) and (59) 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 spraying apparatus (not shown) in fluid-tight engagement with a conduit leading to an electrostatic spray~head. Contacts ~58~ 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 p~tential 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, and neither can - 20 potential be transmitted to the electrostatic`spray-head.

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TWR/vmc 21 Aug 79

Claims (5)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A liquid container adapted to form part of apparatus for electrostatic spraying, the apparatus including a power supply, high voltage generator having input and output terminals, a spray nozzle at least part of the surface of which is electrically conductive, an electrode disposed adjacent the nozzle and insulated therefrom, with electrical connections for connecting the power supply to the input terminals of the generator and the electrode to one output terminal of the generator and the nozzle to the other output terminal of the generator;
the container comprising:
a body having an orifice for delivering liquid;
mounting means for locating the container on the apparatus in a position in which the orifice can deliver liquid to the spray nozzle, the mounting means including a conductor or conductors forming part of the electrical connections for the apparatus; and closure sealing means for closing the orifice prior to location of the container on the apparatus and so that the orifice is opened when and only when the container is mounted on the apparatus.

2. A liquid container as recited in Claim 1 wherein said closure sealing means comprises means for re-closing automatically when the container is removed from the apparatus.

3. A liquid container as recited in Claim 2 wherein said closure sealing means comprises an electrostatic valve.

4. A liquid container adapted to form part of apparatus for electrostatic spraying, the apparatus including a power supply, high voltage generator having input and output terminals, a spray nozzle at least part of the surface of which is electrically conductive, an electrode disposed adjacent the nozzle and insulated therefrom, with electrical connections for connecting the power supply to the input terminals of the generator and the electrode to one output terminal of the generator and the nozzle to the other output terminal of the generator;
the container comprising:
a body having an orifice for delivering liquid;
mounting means for locating the container on the apparatus in a position in which the orifice can deliver liquid to the spray nozzle, the mounting means including a conductor or conductors forming part of the electrical connections for the apparatus; and closure sealing means for closing the orifice prior to the location of the container on the apparatus, and so that the orifice is automatically re-closed when the container is removed from the apparatus.

5. A liquid container as recited in Claim 4 wherein said closure sealing means comprises an electro-static valve.