1. Field of the Invention
The present invention relates to an apparatus for atomizing and ionizing a conductive liquid, which enables direct application of a high voltage to a liquid system. The present invention is applicable to all industries subject to disasters and troubles caused by static electricity, and coating industries which desire to improve the environment by using a water coating.
2. Description of the Related Art
Measures for static electricity control in industrial fields are known. However, at present, risks of disasters and troubles remain due to changes in materials and production and processing steps and uses of plastics. The primary measures for such static electricity control include a lowering of electric resistance of materials for products, the use of antistatic agents, an increase of environmental humidity, a suppression of production speed, use of a discharge and self-discharging type discharger, and grounding.
Among these, a discharge type discharger for ionizing air to irradiate and neutralize a charged object is relatively easily installed in various production processes. This discharger is widely used for the reasons that an object to be irradiated is not damaged, and the charger is simple in maintenance and is relatively inexpensive.
The discharge type discharger may be a DC high voltage type. The DC system has a large irradiation distance but has a drawback in that, since either a positive or a negative ion is produced, the object to be discharged may be charged in reverse polarity depending on the irradiation time. It is also difficult to set up a suitable irradiation time in the DC system.
For these reasons, an AC system which has no limitation as to the irradiation time is the leading discharging system. However, the AC system also has disadvantages. There is a limitation as to the range for ion generation. An effective amount of ions can be delivered over only a short distance, say 3 cm. Discharge of a charged object spaced 3 cm or more is reduced to half, and when spaced 10 cm or more, almost no discharge is effected. Further, it is difficult to discharge a charged object which moves at a speed of 30 cm/sec or more even when it is within 3 cm of the irradiation source.
In the coating industry, use of electrostatic coating systems has been steadily increasing. Electrostatic coating systems include air atomizing systems, airless atomizing systems, and electrostatic atomizing systems, various ones of which are used depending on the required characteristics. Liquid coatings may generally be divided into a solvent type and a water type.
The water type is now widely used in consideration of environmental pollution. Since the electric resistance of the water coating is roughly of from 10.sup.4 to 10.sup.5 .OMEGA..multidot.m, when coating is carried out by an electrostatic coating system which uses a solvent type coating, grounding is made via a coating route from a high voltage generator, whereby the voltage drops to the extent that electrostatic coating is not adequately performed. For this reason, in the case of electrostatic coating, components such as a coating tank and a coating pump are electrically insulated, posing a problem of electric insulation.
When a conductive coating is applied by cup-type or disk-type electrostatic coating machines which are of the electrostatic atomizing type, the electrostatic atomization becomes disabled since the high voltage power supply is grounded. An air atomizing type electrostatic coating machine is a system in which a coating is jetted and atomized from a nozzle using a compressed air flow, and a high voltage is applied to a needle electrode provided at the tip of a nozzle to generate a corona, thereby ionizing coating particles. In this system, a water coating which is relatively high in electric resistance can be used. However, if resistance is low, a coating tank system needs to be electrically insulated.
It is known that ionized air generated by a discharge in air is brought into contact with vapor-like fine droplets jetted out of a nozzle to obtain a charged vapor, and the vapor is brought into a clean room to enable discharging (Japanese Patent Laid Open No. 47488/1993). This method uses a high frequency (1 KHz) AC power supply and charges vapor indirectly, so that power consumption becomes high. Furthermore, the discharge electrode tends to be contaminated, requiring troublesome maintenance.
On the other hand, in the production process, movement is speeded up with the enhancement of production efficiency. In particular, discharge of a charged substance which moves at a high speed has been desired.