CA1169241A - Holder for electrostatic spraying - Google Patents

Abstract

ABSTRACT
A holder adapted to form part of apparatus for electrostatic spraying, the apparatus including a power supply, high voltage generator, 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, and a liquid spray container having an orifice for delivering liquid to the spray nozzle and mounting means for locating the container on the apparatus including a conductor or conductors completing said electrical connections; the holder having a body carrying the high voltage generator, and mounting means complementary to the mounting means on the container provided with an electrical contact or contacts complementary to the conductor or conductors on the container.

Description

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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

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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 9~ 1

- 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; - .

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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.

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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 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

Claims (5)

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

1. A holder adapted to form part of apparatus for electrostatic spraying, the apparatus including a power supply, high voltage generator, 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 and a liquid spray container having an orifice for delivering liquid to the spray nozzle and mounting means for locating the container on the apparatus including a conductor or conductors completing said electrical connections; the holder having a body carrying the high voltage generator, and mounting means complementary to the mounting means on the container provided with an electrical contact or contacts complementary to the conductor or conductors on the container; said holder adapted to be carried on a vehicle.

2. A holder as claimed in Claim 1, wherein the contact on the holder mounting means serves to connect one terminal of the high voltage generator to the conductive surface of a nozzle forming part of the container.

3. A holder as claimed in either of Claims 1 or 2 being provided with a conductor for connection to earth of the electrode disposed adjacent the nozzle.

4. A holder as claimed in Claim 1 further characterized in that the holder carries means for opening the container seal.

5. A holder as claimed in Claim 4 wherein said means comprises a projection to enter the container mouth and lift a moveable closure element off a valve seat.