JPH08266949A - Ionizing system in electrostatic spray apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrostatically ionizing system capable of realizing very strong electrostatic field strength by a low impressed voltage. SOLUTION: The electrostatically ionizing system used in connection with a sprayer 10 for spraying an electrically conductive liquid is provided with an electrically conductive needle 20 disposed near the center of a spray pattern 24 of the sprayer 10. This needle 20 has not larger than about 0.025 cm (250 μm) diameter and the tip of the needle 20 is sharpened to have not larger than about 0.005 cm (50 μm) radius of curvature. A second grounding electrode is disposed at separated point from the needle 20 by about 10.16 cm (4 inches) and forms a part of the sprayer 10.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to electrostatic charging systems for atomizers and coating applicators, and more particularly to electrostatic paint applicators when the paint is electrically conductive. Ionization system. The electrostatic paint applicator is a hand-held spray gun or an automatic spray gun operated by remote control.

The present invention also relates to US patent application Ser. No. 08 / 380,970 filed January 31, 1995 in the United States of America by the same inventor. Whereas the previous patent application is directed to the inventive concept of spraying particles of a non-conductive liquid, the present invention is primarily directed to a spray device for spraying conductive liquid particles. .

[0003]

In electrostatic sprays, an electrostatic field is preferably created in the vicinity of the spray device and the target or object to be sprayed. The atomized particles pass through this electrostatic field, and each particle is charged as it passes through the field. Thus, the charged particles become attracted to the atomized object. The object to be sprayed is generally grounded to earth, ie, maintained at a zero volt potential, so that an attractive force is created between the grounded object and the charged particles.
By this process, it is possible to actually carry a very high proportion of atomized particles towards the object to be atomized, which results in a great improvement in the efficiency of atomization compared to conventional methods.

In a typical electrostatic spray system, the electrode for ionization is placed near the spray orifice of the spray gun, and the object to be coated is maintained at ground voltage to maintain the ionization electrode and the object. An electrostatic field is formed between them. The distance between the two electrodes is about 30.
It is 5 cm (1 foot). Therefore, an electrostatic field of sufficient strength is generated, causing a large number of ion / particle interactions,
The voltage applied to the spray gun electrodes must necessarily be very high in order to generate a sufficiently large attractive force between the paint particles and the target. Approximately 60,000-100,000v to the electrode of the spray device to achieve the appropriate efficiency in the spray operation
It is not uncommon to apply an electrostatic voltage of (60-100 kv). Typically, an ionizing current of about 0.00005 amperes (50 μa) will flow between a grounded object and the spray device electrode.

Electrostatic systems of the type described above are often referred to as corona charging systems. The reason is that at the electric field strength at this time, a corona current is generated from the electrodes. The electrodes ionize the air in their vicinity and the spray paint particles passing through the ionized area carry an ionized charge, making it easier for the grounded or neutral potential object to be coated. You will be attracted. The efficiency of this process depends on the number n of ions attached to a typical particle as it passes between the spray gun and the target,
It depends on the following relationships: n = k * E * t * I where n = number of ionic charges per particle k = constant E = electric field strength in charged region t = time particle stays in charged region I = ion concentration in charged region The strength of the electric field in the charged region must be large enough to ionize the air in the vicinity of the electrode (charged region) to generate the corona current described above.

The electrostatic voltage charging system can be applied to spray devices whether the main atomizing force is generated by compressed air, hydraulic pressure or centrifugal force. In any case, it is preferable that the ionization electrode is installed at or near the location where atomization is performed, and that as many atomized particles as possible pass through the ionization region. The electrostatic ionization system can be used with both conductive and non-conductive paints. However, in the case of conductive paint, it may be necessary to carefully place the electrostatic ionization system so that a conductive path is not formed in the column of liquid paint before the point where the paint is atomized.

Conventionally, the most commonly used electrostatic electrode structure for obtaining sufficient performance is a needle shape. With this structure, a very strong field can be formed at the tip of the needle. In this case, the needle is in the atomization area,
It will be installed near it. Traditionally, these needles are typically formed from hardened steel material (often stainless steel). The diameter of the needle is typically about 0.5 millimeters (mm) and projects forward a sufficient distance from the nozzle to avoid electrical contact with the conductive paint inside the spray device.
These needles are generally formed from wire rods cut to an appropriate length, but no attempt has been made to make the tips of the needles sharp. The end of the needle may be rounded. In this case, the voltage applied to such a needle is usually in the range of 40 to 100 kv, and this voltage forms a relatively strong electrostatic field in the vicinity of the needle. At this time, the lines of electric force of the electrostatic field are formed between the needle and the normally grounded object to be painted. The field gradient in Volts / centimeter (v / cm) is
It is determined by dividing the voltage applied to the needle by the distance (in centimeters) to the second electrode (typically the object) where the field is formed.

[0008]

In the field of electrostatic spraying, very strong electrostatic field strengths can be achieved with the electrodes installed such that they do not create a high voltage short circuit through the liquid column. It would be very advantageous if a structure could be provided. Factors that influence the design of a suitable electrostatic system include the distance between each electrode, the shape of the electrodes, the position of the electrodes with respect to the spray sprayed, and the type of material sprayed by the system.

[0009]

The present invention provides a sufficient electrostatic field for an electrostatic spray system by controlling the shape of the needle and by controlling the placement of the needle electrode relative to the second electrode. The structure provides strength E. The needle diameter is selected to be about 0.025 cm (250 μm) or less.
The tip of the needle is sharpened with a radius of curvature of about 0.005 cm (50 μm) or less. The needle is located relatively close to the spray area of the particular spray gun to which it is applied. In such an electrostatic system,
Depending on the applied voltage of 50-80 kv, 0.00002-
Ionizing currents in the range of 0.00008 amps (20-80 μa) can be generated.

[0010]

OBJECTS AND ADVANTAGES OF THE INVENTION The main objects and advantages of the present invention are:
An object is to provide an electrostatic system that directly charges the conductive coating material of a spray device without the use of any mechanical voltage isolator. Another object and advantage of the present invention is
It is to provide an electrostatic system in which a very strong electric field is formed from the sharp points of the electrodes, so that a large number of ions are generated in and around the spray area of the spray. Still another object and advantage of the present invention is about 0.025 cm (250
It is to provide a very strong electrostatic field in a controlled manner by means of a needle electrode with a diameter of less than μm) and a sharp tip. The above objects and advantages, as well as others, will be apparent from the following description, claims, and the accompanying drawings.

[0011]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a perspective view showing a typical electrostatic spray device related to the present invention. The electrostatic spray device 10 has a manually operated trigger 14 for spraying the liquid supplied via a feed tube 16 via a nozzle 12. The electrostatic high voltage is supplied internally from a high voltage power source provided in the spray device 10 or is supplied to the spray device 10 via a cable 15. Thus, finally the needle 2
A high voltage is applied on 0. Nozzle 12 for spray spray
Is sprayed from the orifice at the front of the to form spray pattern 24. The particles that form the spray pattern 24 are each ionized by the electrostatic field that they pass through as they exit the orifice in the nozzle 12.

The present invention is primarily directed to a spray device for spraying liquid particles when the liquid is electrically conductive. Therefore, the liquid column conducts electricity in exactly the same way as an electrical wire. When spraying such a liquid under the condition of an electrostatic field, if the liquid column flowing in the spray device is grounded,
Extreme care must be taken in the design of spray devices to avoid electrostatic high voltage shorts directly to the ground. Conventionally,
The spray device and its associated parts are all insulated from the ground, thus ensuring a voltage level equal to the electrostatic high voltage. In the case of the present invention, the spray device and its associated devices are maintained at ground potential, so that there must be continued insulation between the high voltage member and the spray device and its associated conductive liquid column. This is accomplished in the present invention by placing the needle 20 at the front tip of the insulating rod 25 and insulating the conductor passing through the insulating rod 25 to connect with the conductor in the cable 15. Needle 20 is approximately 10.16-1 from the front of nozzle 12.
2.70 cm (4-5 inches) apart, providing the requisite voltage isolation required for this application. With this technique, the electrostatic high voltage emitted at the tip of the needle 20 is always applied to the spray region. That is, it is not applied to the region where the liquid column exists, but to the region where the liquid particles pass.

An important result of the present invention is to find an improved ionization system which allows a very efficient coating process to be achieved without coating the electrodes with the spray material and fouling it. This results from a structure that causes the voltage electrode to have a very sharp ionization tip or edge outside the spray area, but from a structure that produces a sufficient number of ions in the spray area. This is derived from the fact that the required ionizing field strength is inversely proportional to the square root of the radius of curvature of the electrode from which the electric field is emitted. That is, when the same voltage is applied between the needle and ground, the pointed tip can locally create a much higher electric field strength around the tip than the more rounded ones. Higher electric field strength causes more electrons to be emitted from the tip, resulting in more ions being generated by the stronger corona current and passing through the ionization zone, even when the tip is outside the spray area. The charge on the paint particles is increased. By providing a gap between the voltage electrode and the ground electrode, a very strong ionization region is formed. If this ionization region is located in or near the atomization region, the number of highly charged particles will also increase. About 20 to the needle of this invention
The net result when a voltage of ~ 80 kv is applied results in a particle charge equivalent to conventional isolated electrostatic systems.

The corona current produced by this improved ionization system is between 0.00005 and 0.000.
It is in the range of 1 amp (50-100 μa) and may have a heating effect at the point of emission from the sharp tip or edge. Therefore, it is important to select a material with a relatively high melting point for the needle structure.

FIG. 2 is a partially enlarged partial view of a conventionally known general needle. Such needles are generally formed from hardened steel such as stainless steel. Its diameter D1 is usually about 0.5 mm.

FIG. 3 is a partially enlarged front view of the needle 20 according to the present invention. The needle 20 is preferably formed of an alloy having a high melting point of 2300 degrees Celsius (° C.) or higher. The preferred material for forming the needle 20 is tungsten, which is 3,410 tungsten.
It has a melting point of ° C. Needle 20 has a diameter D. This diameter D is about 0.025 cm (250 μm)
The following is preferred. Needle 20 has radius of curvature "
The tip is sharpened to R ". The radius" R "is 0.005
cm (50μm) or less, 0.0025cm (25μ
m) or less is preferable.

During operation, the high voltage supplied to the electrostatic needle 20 of the spray device 10 of this embodiment is about 40-80 kv.
Is. This voltage is at least 0.00002-0.
It produces a stable corona current in the range of 00008 amps (20-80 μa), all of which flow from the very sharp tip of the electrostatic needle 20. The relatively high corona current with the tip of the sharp needle 20
Heat is generated near the tip of the needle 20. Therefore, it is important that the needle 20 be made of a material with a high melting point in order to keep the tip of the needle 20 sharp when heated. Carbon, osmium and rhenium are also 30
Tungsten is preferred as the material used in connection with this application, although it has a melting point of 00 ° C or higher. Other materials having a high melting point and suitable for use in the present invention include boron, molybdenum, niobium, tantalum,
There is ruthenium. However, other factors such as cost limit the choice of materials. Needle 20 during operation
The strong electrostatic field emitted from the sharp tip of the spray device 10 reaches the grounded liquid column of the spray device 10 in such a manner that the electrostatic field is located relatively in the center of the flow of atomized particles emitted from the spray device 10. To be distributed. Therefore, most of the atomized particles are ionized and electrostatically attracted to the object to be painted, which itself is maintained at ground potential.

The magnitude of the high voltage that must be applied to the needle 20 of the present invention is determined by many factors, including the type of liquid material sprayed. For example, the distance between the needle 20 and the spray nozzle 12, the distance between the needle 20 and the article to be sprayed, the velocity of the sprayed particles passing through the spray region, and environmental factors such as humidity and temperature. It is desirable that the high voltage applied to the spray device 10 of the present invention be adjustable so that the user of the spray device 10 can, depending on the situation, select the electrostatic voltage that best suits the particular operating situation. An electrostatic ionization field occurs between the needle 20 and the grounded spray device 10 and between the needle 20 and a grounded object for coating.

The present invention can be implemented in other forms without departing from the spirit or essence of the invention.
Accordingly, the above-described embodiments are merely illustrative and not limiting of the invention. For the scope of the invention, reference should be made to the appended claims rather than to the embodiments described above. For example, the principles of the present invention can be achieved with electrodes of shapes other than needles that have a sharpened tip, provided that the ideas described herein are incorporated into the structure.

In this specification, the numerical values shown together with the numerical values in parentheses are the converted values of the numerical values in parentheses, and if there is a mismatch, the numerical values in parentheses should be regarded as correct.

[Brief description of drawings]

FIG. 1 is a perspective view of an electrostatic spray device according to an embodiment of the present invention.

FIG. 2 is a partial front view of an electrostatic needle according to the prior art.

FIG. 3 is a partial front view of the needle of the present invention. 10 Spray Device 12 Nozzle 14 Trigger 15 Cable 16 Feeding Tube 20 Needle 24 Spray Pattern 25 Insulating Rod

Claims (11)

[Claims] 1. A spray device having an ionization needle that cooperates with a second ground electrode, wherein an electrostatic field and a corona discharge are formed by a potential difference between the ionization needle and the second ground electrode. An ionization system in an electrostatic spray device adapted to electrify liquid particles from a conductive liquid that are emitted by a liquid and pass through an electric field, wherein: (a) the ionizing needle is emitted from the spray device. Positioned outside the pattern of particles to be sprayed but away from the spray device, the ionizing needle having a pointed tip with a radius of curvature of about 0.005 cm (50 μm) or less, (b) the second An electrostatic spray device ionization system, wherein electrodes form part of said spray device. 2. The ionizing needle is about 0.025.
The ionization system according to claim 1, having a diameter of cm (250 μm) or less. 3. The ionizing needle is about 2300 °.
A metal member having a melting point of C. 3.
The ionization system described. 4. The ionization system of claim 3, wherein the ionization needle is made of a tungsten material. 5. The ionization system of claim 1, wherein the potential difference is greater than about 40 kv. 6. An electrostatic ionization system attached to a spray device in the vicinity of an atomizing nozzle that emits a pattern of atomized particles of a conductive liquid, comprising: (a) a pointed electrode. The electrode is positioned such that its tip is outside the pattern of atomized particles and at a distance from the spray device, and the tip is 0.005
has a radius of curvature of cm (50 μm) or less, (b) the spray device has a second electrode, and (c) a potential difference between the pointed electrode and the second electrode. An electrostatic ionization system provided with means for providing. 7. The pointed electrode is at least 23.
The ionization system according to claim 6, which is formed of a material having a melting point of 00 ° C or higher. 8. The ionization system of claim 7, wherein the potential difference is greater than about 40 kv. 9. A spray device having an ionization electrode that operates in cooperation with a second electrode, wherein an electrostatic field and a corona discharge are formed by a potential difference between the ionization electrode and the second electrode. An ionization system in an electrostatic atomizer adapted to electrify a pattern of particles emitted by and passing through an electric field, wherein: (a) the ionizing electrode comprises: Located near the pattern but remote from the atomizer, and wherein the ionizing electrode has a pointed edge with a radius of curvature of about 0.005 cm (50 μm) or less; (b) the atomizer is A second electrode, wherein the needle is about 1 from the atomizer.
An ionization system located 0.16 cm (4 inches) apart. 10. The ionization electrode is about 2300 ° C.
The ionization system according to claim 9, comprising a metal member having the above melting point. 11. The ionization system of claim 10, wherein the ionization electrode is formed of a tungsten material.