Kazutoshi Asano

Triboelectrification of plastic particles on a vibrating feeder laminated with a plastic film

Abstract The charging characteristics of polymer particles were investigated in order to develop an electrostatic separator for plastic-plastic mixtures which are to be recycled. The charging section of the proposed separator utilizes a vibrating feeder equipped with a charging plate. Plastic particles are charged by triboelectric charging while moving on the plastic plate. In order to increase the amount of a charge acquired by the plastic particles as well as to avoid an accumulation of a charge at the surface of the plastic plate, a plastic layer with a number of holes was formed by melting fine plastic powder over an aluminum plate. The charging characteristics of several kinds of plastic particles were investigated and the results show that the plastic-laminated vibrating plate is effective in charging plastic particles.

Electrification phenomena of pure water droplets dripping and sliding on a polymer surface

Abstract The streaming electrification of pure water is generally thought to be a less problem because of its high conductivity which is six orders of magnitude higher than that of a hydrocarbon liquid. However, due to the advancement of semiconductor industries, ultrapure water has been used for washing and rinsing processes and it turned out that high degree of electrification might be produced by using such ultrapure water. In order to clarify this phenomenon, the electrification of deionized water droplets dripping to and sliding on a polymer (PTFE) surface has been investigated. The surface potential distribution of the polymer plate after electrification is measured by moving a probe for two-dimensional scanning. The charge amount of the droplets after the sliding is measured by a Faraday cage. From these experiments, several interesting results were obtained. The potential distribution on the surface is not uniform, but varies along the streaming path. At the dripping point the surface potential of the polymer plate always becomes negative, then turns to positive downstream. However, the droplet, after sliding on the polymer surface, becomes electrified positively. This electrification phenomenon depends on the velocity and the conductivity of droplets. In order to explain this electrification process, a model based on the electric double layer is proposed.

Negative corona discharge at a tip of water cone deformed under dc field

Abstract The negative corona discharge phenomena occurring at a tip of water cone have been investigated focusing on the motion and the shape of the water surface using a high-speed video camera. The water cone is periodically formed from a water droplet located on a grounded electrode under dc field due to the electro-hydrodynamic instability. Negative corona discharge with trains of Trichel-like pulses occurred just after the formation of a cone jet. The magnitude and the pulse interval of the Trichel-like pulses gradually increase during the period that the conical surface returns to the initial ellipsoidal shape. The characteristics of the Trichel pulse occurring from the metal electrode simulating the shape of the water surface were also investigated. It is found that the increase in the magnitude and the interval of the trains of Trichel-like pulses with time at the tip of water drop are caused by the corona discharge from the tip of the water surface that deforms from a conical to an ellipsoidal shape.

Fundamental characteristics of electrostatic wafer chuck with insulating sealant

In the semiconductor industry, many manufacturing processes, such as CVD or dry etching, are performed in vacuum condition. The electrostatic wafer chuck is the most preferable handling method under such circumstances. It enables retention of a wafer flat and enhanced heat transfer through the whole surface area because the wafer can firmly contact with the chuck. We have investigated the fundamental study of an electrostatic chuck with comb type electrodes and a thin dielectric film. In order to remove the air gap between them, silicone oil is used as a filler to prevent breakdown. The experimental results proved the potential to use the electrostatic chuck for silicon wafer handling. There, however, is a problem which comes from using silicone oil as an insulating filler. The thin dielectric film is easily deformed by tension when the object starts moving. In this report experimental results of the electrostatic wafer chuck are shown when insulating sealant, instead of silicone oil, is used. The electrostatic force acting on the 4 inch silicon wafer is examined with several types of sealant and dielectric films. The electrostatic force increased with the square of the applied voltage for lower voltage and gradually saturated at higher voltage, and the maximum force obtained was approximately 30 N.

The behavior of charged conducting particles in electric fields

The presence of metal particles within gas insulated switchgear (GIS) might initiate a sparkover and lead to fatal failure of electric power transmission system. In order to investigate the behavior of a particle in GIS, model electrodes and a measuring system were constructed. The motion of a particle was investigated by using a CCD camera and a high-speed video camera. Different shapes of elongated particles were made from 0.1 mm and 0.25 mm diameter wires. The measured values of lift-off field strength of a particle lying on the electrode agreed quite well with the theoretical prediction. The initial raising up of particle usually started at the sharper edge as expected. There were two types of different mode of particle motions; one is bouncing motion between two electrodes or one electrode and the other the standing motion on the electrode. Interesting thing is that the standing motion on the upper electrode when a negative voltage is applied to the upper electrode. This phenomenon could be explained from the difference of positive and negative corona currents starting from both edges of a standing particle.<<ETX>>

Electrification of polymer surface caused by sliding ultrapure water

It has been thought that the conductivity of pure water is high enough to neglect the streaming electrification. However, with the advancement of semiconductor industries, even ultrapure water appeared to cause electrification problems at the washing and the rinsing processes of semiconductor wafers. The investigation on the electrification phenomenon of polymer (PTFE) surface with ultrapure water is described in this article. Water droplets are always charged positively after sliding on the PTFE surface, and the surface potential on PTFE is almost negative and varied along the path of droplets becoming positive downstream. As the conductivity of water becomes closer to that of ideal water, the amount of droplet charge increases drastically. This electrification phenomenon is also enhanced by decreasing the thickness of the PTFE plate. It suggests that the Coulomb force between the charge on the PTFE surface and the minor image charge is an important factor. The authors have proposed a model which is based on the electric double layer similar to conventional streaming electrification for insulating liquid, assuming that the charged droplet leaves the excess positive charge on the polymer surface.<<ETX>>

DC corona discharge of a metal filament particle within parallel-plate electrodes

When a metal particle accidentally exists within gas-insulated switchgear (GIS), it might lead to serious damage of a power transmission system. The authors have investigated and reported on the motion of a metal filament particle within parallel plate electrodes. When a metal particle on the electrode gained some charge by induction, it shows several different patterns of motion; such as simple standing, precession motion, jumping up-and-down, and so forth. Each case of such motion depended upon corona discharge from the particle itself. When the corona current from a fixed particle on the electrode was measured, either positive or negative corona takes place. The measured current showed different patterns of current depending on the polarity. The current characteristics also depends on the size of particle. Furthermore, when a particle is very short and the case of positive corona, strange characteristics of current were observed.

Observation of the electrorheological effect of silicone oil/polymer particles suspension

A liquid insulator that suspends small particles is one of the electrorheological fluids (ERF) whose apparent viscosity becomes larger under an electric field because of the formation of particle chains. Since many possible applications of ERF are expected, the development of a more practical ERF is required. We have investigated the ER effect of silicone oil in which small particles are suspended. Silica particles, silica particles coated by conductive polymer film, and polymer particles (microcrystalline cellulose), with a diameter between 5/spl sim/100 /spl mu/m, are investigated in order to clarify the difference between suspending materials. To measure the ER effect, a rotational viscometer was constructed. It became clear that the shear stress for cellulose particles is much stronger than that for other particles because of its peculiar particle chain formation due to the particle shape. >

Dynamic motion of a conductive particle in viscous fluid under DC electric field

When plastic waste is liquefied for recycling, the impurities present could influence the quality of the reprocessed products. In order to explore the possible method for removing solid impurities using electrostatic forces, the motion of spherical conductive particles under a uniform electric field has been carefully investigated. In this paper, a solid impurity and liquefied plastics are simulated by a conductive spherical particle and viscous insulating liquid, silicone oil, respectively. Experimental results indicate that the particle undergoes repeated motion between the parallel electrodes. The motion of the particle can be divided into four modes: settling on the lower electrode, moving upward, settling on the upper electrode, and moving downward. The higher the applied voltage, the faster the average particle velocity and the shorter the resting time of the particle. The particle accelerates after leaving the electrode and decelerates before reaching the other electrode. This deceleration could be explained by the viscous effect of the liquid layer between the particle and the electrode. The settling mode could be explained by the fact that there is a liquid flow induced by the particle motion and it pushes the particle against the electrode until the flow decreases. It is, therefore, suggested that the hydrodynamic effect is dominant in our case, as well as the electrostatic force.

Influence of the particle configuration on electrorheological effect

Abstract The electrical and rheological properties of model ER fluids consisting of small polymer particles (crystal cellulose) in silicone oil was investigated. The rheological properties were examined by using a cylindrical rotational viscometer under the applied electric field (0 – 3 kV / mm). We have investigated the ER effect of suspensions, focusing on the effect of different shapes of dispersed particle. The shear strain rate - shear stress characteristics with different shaped particles were compared: the sample in which elongated particles are dominant and the ones with rather round shaped particles, although their mean sizes are similar. The ER fluid with elongated particles shows much stronger shear stress than that with spherical particles. The effect of the shape of suspending particles is not simple. The observation of particle chain formation with a microscope suggests that elongated particles strengthen the particle chain formation. For spherical shaped particles, particle chain bundles are easily torn by shear strain, while they tend to stick to the electrode surface firmly. From these experimental results, it can be concluded that collaboration of elongated and spherical particles will produce stronger shear stress.