WO2006094511A2

WO2006094511A2 - An electrostatic spraying apparatus utilizing triboelectrification

Info

Publication number: WO2006094511A2
Application number: PCT/DK2006/000140
Authority: WO
Inventors: Kristiane Østergaard JENSEN
Original assignee: Rådet For Agroindustri
Priority date: 2005-03-11
Filing date: 2006-03-10
Publication date: 2006-09-14
Also published as: EP1866097A2; WO2006094511A3; DK1866097T3; DE602006010837D1; WO2006094511B1; ATE450315T1; EP1866097B1

Abstract

An electrostatic spraying apparatus, which uses induction to charge different kinds of materials such as pesticides, paint, water or other liquids, has been developed. The electrostatic spraying system depends on a new type of spray apparatus that provides a stream of electrostatic charged droplets. The charged droplets are forced towards the target by the use of air. In the apparatus a positively or negatively charged object is placed relatively to the fluid. The charged object induces a charge in the fluid before and when the fluid reaches the droplet-forming zone. The fluid gets thereby either negatively or positively charged. The object is charged by triboelectrification. The object can be a nylon pipe. The nylon pipe gets positively charged when a cobber ring slides up and down on the nylon pipe because electrons are transferred from the nylon pipe to the copper ring.

Description

An electrostatic spraying apparatus utilizing triboelectrification

Field of invention

Present invention relates to electrostatic spraying devices in general, and in particular to induction-charging systems.

Background of the invention

Today electrostatic spraying systems are widely used in the industry to coat different objects. There are different ways of charging liquids or powders among these should corona, induction and contact be mentioned. For agricultural purposes the induction method is the most suitable since this method only requires a voltage around 2 KV to charge pesticides. It can, therefore, be used in the more uncontrolled environment around a field sprayer without causing danger to the operator. Most induction charging systems use an electrode to charge the liquids. An example of such a system is US 4004733. In this system the liquid is charged by an induction electrode place closed to the droplet-forming zone. The electrode has a low potential relatively to the rest of the nozzle (several hundred to several thousands volts). The voltage of the electrode is provided by a power supply. Other examples of such electrostatic spraying apparatus may be found in: WO84/0343, GB2210216, US5765761, and US 5704554. A disadvantage with these solutions is the need for a power supply, possibly a high voltage power supply, which in turn necessitates shielding or similar protective measures. Additionally, the working environment becomes more hazardous and complicated, in particular because agricultural working conditions may be quite severe with humidity, temperatures and even physical impacts.

During the last 15 years increasing concern regarding pesticides effects on humans and wildlife have resulted in strict regulations regarding the use of pesticides. The farmers have thereby faced a new challenge namely to reduce the amount of pesticide used without reducing the yield. A possible solution to this problem is to minimize the amount of pesticide lost to the surroundings. The loss of pesticide to the surroundings depends of the drift and the fall off. The smaller droplets used the greater amount of pesticide will drift away and never hit the target plant. Big droplets are more resistant to drift, but the heavy droplets might fall off the target plants and the area covered will also be greatly reduced when big droplets are used instead of small. An optimal nozzle must, therefore, provide droplets that don't drift away and don't fall off when they hit the target. Hence, an improved electrostatic spraying apparatus would be advantageous, and in particular a more efficient and/or simple electrostatic spraying apparatus would be advantageous.

Summary of the invention

Accordingly, the invention preferably seeks to mitigate, alleviate or eliminate one or more of the above-mentioned disadvantages singly or in any combination. In particular, it may be seen as an object of the present invention to provide an electrostatic spraying apparatus that solves the above-mentioned problems of the prior art with the power supply and/or associated problems therewith.

This object and several other objects are obtained in a first aspect by an electrostatic spraying apparatus that comprises: - a housing having a front end and a rear section, the rear section having an inlet for a fluid, preferably a pressurised fluid,

- fluid conduction means for conducting the fluid from the inlet to or near the front end,

- droplet forming means for providing a droplet stream from the fluid at an outlet at the front end of the housing, - at least one air outlet, said at least one air outlet being positioned substantially circumferential or adjacent to the fluid outlet for assisting the displacement of the formed droplet steam in a preferred direction, and

- a first member and a second member capable of being relatively displaced during mutual physical contact so as to establish a charge transfer by triboelectricification from the first member to the second member, wherein at least the first member or the second member is positioned relative to the fluid conduction means so as to electrostatically induce a charge in the fluid.

The invention is particularly but not exclusively advantageous for obtaining an improved electrostatic spraying apparatus with by obviating the need for a power supply to generate the necessary voltage for electrostatic spraying. The present invention may further solve the above-mentioned spraying problems with by using small electrostatic charged droplets that are assisted by air towards the target. The air-assist prevents the drift and forces the droplets down to the crops where the electrostatic force afterwards become dominating. The small droplets are attracted to the crops by the electrostatic force and the result is a homogenously deposit of the pesticide droplets on the crops. The present invention may be applied to spray pesticides on the soil, to spray pesticides on plants, to spray pesticides on plants in greenhouses, to charge paint, to charge water in sprinkler systems and in any kind of process involving electrostatic charging of a material.

In particular, the first member or the second member may be positioned relative to the fluid conduction means so as to electrostatically induce a charge in the fluid before the fluid reach the outlet.

Preferably, at least the first member or the second member may be positioned relative to the fluid conduction means so as to electrostatically induce a charge in the fluid when the fluid reaches the outlet.

In particular, the fluid conduction means and/or the droplet forming means may comprise a conducting element, the conducting element providing an additional electrical contact from the fluid to an electron reservoir such as ground. Preferably, the conducting element may have a section positioned substantially within the fluid conduction means.

Preferably, a conducting element may provide an additional electrical contact from the fluid to an electron reservoir, the conducting element being positioned outside of the housing, more preferably the conducting element may be in electrical contact to a reservoir containing the fluid.

Preferably, the first member and the second member may be capable of being reciprocating displaced by a motive force, the motive force may be any kind of motive force, e.g. electrical actuator, hydraulic actuator, pneumatic actuator, combustion actuator etc.

In a preferred embodiment, the first member may comprise a substantially tubular section and the second member may comprise a substantially ring-shaped section so that the first and second member has corresponding shapes of fitting relationship.

Preferably, the first member and/or the second member may comprise an electrically insulating material such as PVC, acetate rayon, polyester, polyurethane elastomer, celluloid, dacron, orlon, polystyrene, styrene, acrylic, SARAN, polyethylene, polypropylene, KELF, silicon, polytetrafloroethylene, teflon, polyvinyl chloride, or silicone rubber. Other insulating materials may also be applied. Preferably, the first member and/or the second member comprises an electrically conducting materials such as Cu, Ag, Au, Ni, Zn, Al, Cr, Mn, Fe, Co or any alloys thereof. In a second aspect the present invention relates to an electrostatic spraying apparatus comprising:

- a housing having a front end and a rear section, the rear section having an inlet for a fluid, preferably a pressurised fluid. - fluid conduction means for conducting the fluid from the inlet to or near the front end,

- droplet forming means for providing a droplet stream from the fluid at an fluid outlet at the front end of the housing, and

The first and second aspect of the present invention may each be combined with the other aspect. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

Detailed description In present invention, a new type of electrostatic spray apparatus has been developed. The apparatus uses triboelectrification to establish a charge transfer between two objects and the objects are thereby charged. One of the charged objects is placed relatively to the fluid conduction means and the charged object induces a charge in the fluid. At the end of the apparatus droplets are made and after the droplets leave the apparatus an air-stream forces the droplets towards the target. The apparatus can be used to charge pesticides, paint, water or any kind of material that can be charged by induction.

Triboelectrification is a process where charge is transferred between solids that touch each other. When two materials touch, electrons are transferred from one material to the other and when they are afterwards separated the materials will have an excess charge. The most common known experiment to demonstrate triboelectrification is to rub a plastic rod with a rabbit fur. The rabbit fur gets positively charged while the plastic rod gets negatively charged and the rabbit fur will afterwards attract negatively charged objects and repel positively charged objects. Another common known experiment is to scuff ones shoes across a nylon carpet. The person gets thereby charged to around 3.5 KV and when he afterwards touches something that can conduct like a metal doorknob or another person he will discharge and feel an unpleasant shock. Charging of solids, triboelectrification, can happen between two insulating materials, two conducting materials, between one insulating and one conducting material and between two pieces of the same material.

When two insulating materials or one insulator and one conductor are rubbed against each other electrons are transferred between the materials and insulators will have an excess charge after separation on the areas that have been in contact with the other material. If the conductor is insulated it will also keep its excess charge after separation. When two metals are rubbed against each other, electrons will also move across the interface, but the metals have to be separated extremely quickly in order to create static electricity. Two identical surfaces, macroscopically speaking, that are rubbed against each other can also exchange charge if the contact takes place between a small area of one surface and a larger area of the other.

There exits triboelectric series that show the tendency of various materials to give up electrons when they come in contact with another material. A material will be positively charged when it is rubbed with a material placed lower on the list, while it will be negatively charged when it's rubbed with a material higher on the list. There are many different triboelectric series and they do not contain the same materials, so the order of following list of possible materials that can be used to create static electricity should not be read as a triboelectric series, but merely as a suggestion of materials that can be used: skin, asbestos, rabbit fur, acetate, plexiglass, bakelite, cellulose nitrate, glass, polyformaldehyde, polymethyl methacrylate, micra, hair, ethyl cellulose, polyamide, salt, melamine, quartz, silicone elastomer, nylon, wool, fur, lead, silk, aluminium, cellulose acetate, cotton, paper, steel, wood amber, resins (natural and manmade), metals in general, sealing wax, rubber (natural and manmade), MYLAR, nickel, copper, zinc, gold, silver, UV resist, brass, platinum, sulphur, acetate rayon, polyester, polyurethane elastomer, celluloid, dacron, orlon, polystyrene, styrene, acrylic, SARAN, polyethylene, polypropylene, PVC, KEL F, silicon, polytetrafloroethylene, teflon, polyvinyl chloride, silicone rubber, or other materials that can give or receive electrons when they come into contact with another material. The quantity of charge transfer is extremely complex and depends on many different things, among these: area of contact, the placement of the materials in the tribo series, the number of contacts and the surface contamination can be mentioned. The bigger the area of contact is, the bigger the gap between the two materials are in the tribo series and the higher the number of contacts are, the bigger a quantity of charge is transferred. If the surface of the materials are contaminated the degree of charging decreases. The charged object sets up an electric field. The strength of the electric field depends on the degree of charging of the object and how far away from the object the field is measured. The voltage of a charge object can be in the range of a few hundreds to several thousands volts.

Charging by induction is a process where a charged body can give another material a charge of opposite sign without loosing any of its own charge. If a grounded conductor is placed close to a charged object, the grounded conductor will either pull up or send electrons down into the ground depending on the polarity of the object. If the object is positively charged the conductor will pull up electrons from the ground and become negatively charged.

However, if the connection to the ground is broken while the conductor is still influenced by the electric field from the object, the excess charge will stay on the conductor. If the charged object is afterwards removed the conductor will stay negatively charged because it is insulated from the surroundings and can't get rid of the negative charge.

The present invention provides an improved electrostatic spray apparatus. The apparatus has a housing, wherein two members that are in contact with each other and a pipe for fluid conductions means are placed. At the end of the pipe droplets are created. A conducting element that connects the fluid with an electron reservoir and a source that drives the movement of the members can also be placed inside the housing. The members can be two insulating materials, one insulating and one conducting material or two pieces of the same insulating material. The materials are moved against each other and charge is transferred from one member to the other. The members are thereby charged, one negatively and one positively. The insulators will only be charged on the areas that have been in contact with the other member while conductors will conduct the excess charge to all parts of the member, and if the conductor is connected to other conducting elements the excess charge can be conducted further on. The movement of the members relatively to each other can be vertical, horizontal, rotating or any kind of movement that causes a transfer of electrons. The source that controls the movement can be a cylinder connected to a compressor, a spring driven by air one way, a motor placed inside or outside the housing, or any kind of motive force that can control the movement. The compressor can be placed on the back of a vehicle and it can get its power from the vehicle through the power plug. It is, therefore, an easy accessible power source. If a motor is used, the generator on the vehicle can be used as power source. The vehicle can for example be a tractor. The equipment is, therefore, easy to put on any kind of field sprayer.

One of the members is placed relatively to the fluid conduction means and it induces a charge in the fluid. The fluid is lead into the apparatus through a pipe. The pipe can be one of the members, it can be a pipe placed inside one of the members or the pipe can be placed near one of the members. When the fluid feels the electric field from one of the members it will either pulls up electrons or send electrons to an electron reservoir depending on the polarity of the member. The fluid gets thereby charged. The electron reservoir can be the ground or other parts on the sprayer that can be used as a reservoir. The fluid is connected to the electron reservoir through a conducting element. The conducting element can be placed inside or outside the housing; it just has to be in contact with the fluid. It can be placed in: the fluid conduction means, the tank, the bar or anywhere on the sprayer.

The compressor can also be used to produce an air stream that forces the droplets towards the target. Air from the compressor can be lead inside the housing at the rear end and out through the front end or the air-stream can be lead outside the housing. The big advantage of leading the air-stream in through the housing is that it keeps the two members dry. It's common knowledge that degree of charging by triboelectrification decreases with increasing humidity because the thickness moisture layer on the surfaces increases. The moisture layer contains electrolytic ions that provide neutralizing charges. Therefore, the relative air humidity has to be below 60 % inside the housing. The air- stream can leave the housing through small air holes or air slits which are positioned on two straight lines on both sides of the droplet-forming means e.g. a nozzle or in any pattern depending on the type of droplet forming means used. The air holes or slits create an air-stream that enforces the spray picture created by the droplet-forming means. The pattern of the air outlets can, therefore, vary depending on the droplet-forming means.

In an embodiment of the apparatus according to the present invention, pesticides are charged negatively by the use of induction. The pesticide is lead inside the housing through a pipe. The pipe is made of nylon. Inside the housing a copper ring slides up and down on all parts of the nylon pipe and electrons are transferred from the nylon pipe to the copper ring. The nylon pipe, thereby, sets up a strong positive electric field, which induces a charge in the fluid inside the pipe. The copper ring's negative electric field is much weaker than the positive electric field from the nylon because copper is an excellent conductor and the excess charge dissipates through the copper.

The nozzle is placed inside the nylon pipe and the copper ring goes 2 mm further down than the end of the nozzle. This is done to create an electric field in the droplet forming- zone as well. The pesticide is thereby influenced by the strong positive electric field from the nylon, from it enters in the rear section and until the droplets leave the apparatus. The positive electric field induces thereby a negative charge in the pesticide both before and in the droplet forming-zone. The pesticide is connected to the ground through a conducting wire and a harrow tooth. The harrow tooth digs into the ground in the spraying track. The pesticide pulls up electrons from the ground when it feels the positive field from the nylon pipe and the pesticide is thereby charged negatively. When the connection to the liquid is broken the droplets can't get rid of the excess charge and they, therefore, keep their charge. After they leave the nozzle they are assisted by air. A compressor can provide the air, which is lead through the housing. The air keeps the copper ring and the nylon pipe dry. The air is lead out at the front section through air holes or slits and the air stream forces the droplets downwards towards the crops or the soil. By using air drift is minimized. When the crops feel a stream of negatively charged droplets coming towards them, they send electrons away from the leaves and down in the roots. The crops are thereby positively charged and attract the negatively charged droplets. Then the droplets come down they start to neutralise the positively charged plant. When a droplet lands in an area on the plant, the plant's positive charge is neutralised by the negatively charged droplet. They other droplets, which at this point are only controlled by the electrostatic force, are not attracted to neutral areas and they, therefore, only move towards positively charged areas and the droplets will cover the plant. When the droplet lands on an area the droplet won't fall off because of the electric attraction force and because of the size of the droplet is small.

Brief description of the drawings

FIG 1: View of an apparatus from the side plus all its parts separate, i.e. exploded view, according to the present invention.

FIG 2: View of an apparatus from underneath according to the present invention.

FIG 3: View of an apparatus from the top according to the present invention. FIG 4: Shows a sprayer, the placement of the compressor and the ground connection according to the present invention.

Detailed description of the drawings.

FIG 1 shows the apparatus from the side and all its parts separate. In this type of apparatus a cylinder is used to make the copper ring slides up and down on the nylon pipe. Other kind of forces like a motor, a spring or other kind of motive forces can be used. The apparatus consists of a housing (1), a top piece that connects the apparatus with the sprayer, a nylon pipe (6), a copper ring (9), a cylinder (4), a conducting wire (10) that is connected to the ground, a nozzle (7), a nozzle hold (8), a fork that connects the copper ring and the cylinder (5), a pipe in the top lid where the air is added, a nylon top lid (2) and a nylon bottom lid (3) wherein there are air holes. A compressor is the energy source that drives the system. The compressor delivers the air that drives the cylinder (4) and the air, which is led into the housing through the pipe in the top lid. The air is first used the keep the nylon pipe and the copper ring dry. The air leaves through the air holes in the bottom lid (3) and is secondary used to force the droplets downwards. The cylinder (4) moves the copper ring (9) up and down on the nylon pipe by moving the fork (5) up and down. When the copper ring (9) and the nylon pipe (6) touch electrons are transferred from the nylon to the copper and thereby make the copper ring negatively charged and the nylon pipe positively charged. Since copper is an excellent conductor, the excess of electrons dissipating through the copper and the copper has a weak electric field. Nylon is an insulator and the charge can only be neutralised by charged air-molecules that plate out on the surface. Since this process is slower than the transfer of electrons between the copper and the nylon, the nylon will be positively charged. The pesticides run through the nylon pipe and are exposed to a strong electric field from the positively charged nylon pipe. The positive field attracts electrons and the pesticides pulls up electrons from the ground through the conducting wire (10). The conducting wire is connected to the ground through a harrow tooth (see FIG 4).

FIG 2 shows the apparatus from underneath. In the bottom nylon lid (3) there are air holes, which lie on both sides of the nozzle. The air holes lie parallel with the opening of the nozzle. The air holes can in other variants of the apparatus be placed different. The pattern of the air holes or slits depends on spray pattern of the nozzle. The pattern showed on figure 2 is, therefore, just one out of many variants that can be used. The lid around the nozzle is cut conic so that it doesn't interfere with the spread angle from the nozzle. The nozzle is placed inside the nylon pipe so that the copper ring goes 2 mm further down than the end of the nozzle. This is done to make sure that the area in which the droplets are made also has an electric field.

FIG 3 shows the apparatus from the top. In the top lid (2) there are made holes for the cylinder (4), the nylon pipe (6), the conducting wire and the air pipe. For practical conditions, the apparatus is too heavy to be carried only by the piece that connects the apparatus with the sprayer. Therefore, two grip arms are put on the lid and these grip arms are fastened on to the sprayer bar.

FIG 4 shows the sprayer (13) with the apparatuses, the placement of the compressor (14) and the ground connection (harrow tooth) (12). From each apparatus there is a conducting wire (10), which is connected from the apparatus through the bar (11) to the harrow tooth (12). The harrow tooth digs into the ground in the spraying track. The conducting wire can be disconnected from the apparatus via a plug. The conducting wire can thereby stay on the bar when the apparatus is removed from the sprayer. The compressor, which gets its power from the vehicle through a power plug, delivers all the air needed for all the apparatuses. The air that drives the cylinder (see FIG 1) and the air that is added to the inside of the housing, run in central pipes from the compressor through the bar and to the apparatuses where the pipes are split into smaller pipes at each apparatus. The pipes can be taken off the central pipes because they are fastened with a plug. The movement of the cylinders in the apparatuses can be switched on and off by a central switch. The pressure inside the apparatuses is also controlled central.

TEST RESULTS. Field tests on wheat. The tests were conducted with one apparatus. Area A and area B are split into 5 test areas: one area untreated, one area treated with a normal dose (100%), one area treated with 75% of normal dose, one area treated with 50% of normal dose and one area treated with 25% of normal dose. In area A the apparatus charged the pesticide and forced the droplets downwards towards the crops by the use of air. In area B the apparatus didn't charge the pesticides and didn't use air, so it was functioning like a normal nozzle. The Pesticides used: Boxer EC, Oxitril CM, Devrinol 45 FI. One month later the test areas were checked for weeds. The total number of weeds in a random chose rectangular (25.5*32.5 cm² split into 16 meshes of 6.5*4.5 cm²) was counted. Afterwards the weeds that were affected by the pesticide were counted (leaves losing colour). The success rate was found by taking the ratio between weeds affected/total number of weeds. The results are shown in table 1. As can be seen from the result there is a clear trend in the data, showing that more weed is affected when the apparatus charge the pesticide and the droplets are assisted by air. The result also indicates that the amount of pesticides used when using this new type of apparatus can be reduced to 50%-25% of normal dose.

Table 1. Although the present invention has been described in connection with the specified embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims. In the claims, the term comprising does not exclude the presence of other elements or steps. Additionally, although individual features may be included in different claims, these may possibly be advantageously combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. In addition, singular references do not exclude a plurality. Thus, references to "a", "an", "first", "second" etc. do not preclude a plurality. Furthermore, reference signs in the claims shall not be construed as limiting the scope.

List of references to Figure 1:

1. Housing

2. Top lid

3. Bottom lid

4. Cylinder 5. Fork that connects the cylinder and the copper ring

6. Nylon pipe

7. Nozzle

8. Nozzle hold

9. Copper ring 10. Conductive wire

List of references to Figure 4:

11. Bar 12. Harrow tooth

13. Sprayer

14. Compressor

Claims

1. An electrostatic spraying apparatus comprising:

- a housing having a front end and a rear section, the rear section having an inlet for a fluid, preferably a pressurised fluid,

- droplet forming means for providing a droplet stream from the fluid at an outlet at the front end of the housing,

- at least one air outlet, said at least one air outlet being positioned substantially circumferential or adjacent to the fluid outlet for assisting the displacement of the formed droplet steam in a preferred direction, and

- a first member and a second member capable of being relatively displaced during mutual physical contact so as to establish a charge transfer by triboelectricification from the first member to the second member,

wherein at least the first member or the second member is positioned relative to the fluid conduction means so as to electrostatically induce a charge in the fluid.

2. An electrostatic spraying apparatus according to claim 1, wherein at least the first member or the second member is positioned relative to the fluid conduction means so as to electrostatically induce a charge in the fluid before the fluid reach the outlet.

3. An electrostatic spraying apparatus according to claim 1, wherein at least the first member or the second member is positioned relative to the fluid conduction means so as to electrostatically induce a charge in the fluid when the fluid reach the outlet.

4. An electrostatic spraying apparatus according to claim 1, wherein the fluid conduction means and/or the droplet forming means comprises a conducting element, the conducting element providing an additional electrical contact from the fluid to an electron reservoir such as ground.

5. An electrostatic spraying apparatus according to claim 4, wherein the conducting element has a section positioned substantially within the fluid conduction means.

6. An electrostatic spraying apparatus according to claim 1, wherein a conducting element provides an additional electrical contact from the fluid to an electron reservoir, the conducting element being positioned outside of the housing, preferably the conducting element being in electrical contact to a liquid reservoir containing the fluid. 5

7. An electrostatic spraying apparatus according to claim 1, wherein the first member and the second member are capable of being reciprocating displaced by a motive force.

8. An electrostatic spraying apparatus according to claim 1, wherein the first member comprises a substantially tubular section.

10

9. An electrostatic spraying apparatus according to claim 1, wherein the first member and/or the second member comprises an electrically insulating materials such as PVC, , acetate rayon, polyester, polyurethane elastomer, celluloid, dacron, orlon, polystyrene, styrene, acrylic, SARAN, polyethylene, polypropylene, KELF, silicon, polytetrafloroethylene,

15 teflon, polyvinyl chloride, or silicone rubber.

10. An electrostatic spraying apparatus according to claim 1, wherein the second member comprises a substantially ring-shaped section.

20 11. An electrostatic spraying apparatus according to claim 1, wherein the first member and/or the second member comprises an electrically conducting materials such as Cu, Ag, Au, Ni, Zn, Al, Cr, Mn, Fe, Co or any alloys thereof.

12. An electrostatic spraying apparatus comprising: 25

- fluid conduction means for conducting the fluid from the inlet to or near the front end, 30

- droplet forming means for providing a droplet stream from the fluid at a fluid outlet at the front end of the housing, and

- a first member and a second member capable of being relatively displaced during mutual 35 physical contact so as to establish a charge transfer by triboelectricification from the first member to the second member,