Calculations of contact charging at metal/polymer interfaces were performed by a quantum chemical method (DV-Xα). In the calculations, model clusters with dangling bonds were used. The model clusters showed surface states in the density of states, and the electron transfer occurred at the contact interfaces between polymer and Al. Then, 0.3nm was a reasonable value as the contact distance in the present simulation.
Contact electrifications between PTFE and six metals such as Pt, Au, Cu, Al, Pb and Ca were simulated. The charge transferred from the metal to PTFE depended on the work function of the metals, and had a gap in the range of 4.25-4.28eV. According the gap the metals were classified into two groups. If Fermi level of a metal is lower than the LUMO level of PTFE, the electrons of metal transfer to the surface state (interface state). Electrons in a metal with a higher Fermi level transfer to the conduction band of PTFE.

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In dry powder processes, particles collide against each other and onto walls, and normally, electrostatic charge is generated. Such process is called triboelectrification or tribo-/contact-/impact- charging of particles. In this paper, the amount of maximum (or saturated, or equilibrium) charge on a particle in a powder flow of a pneumatic conveyer with a metal pipe was discussed. A theoretical discussion involving the space charge effect on the basis of ‘charge relaxation model, ’ in which the maximum charge is limited by the gas break down, is given. The result showed two regions, i. e., the region in which the space charge does not have any effect, and the other region where the space charge dominates the amount of the charge. The charge was proportional to the particle size to the power of 1.5 in the region of no space charge effect, and the power of 3 in the other region. An approximated analytical formula was empirically found, for the whole range, including these two regions. The maximum charge as a function of particle size pipe size and volume fraction of the powder, was given as: q/C=1.1×10^-4 (d_p/m)³/√[{Φ(D/m)}²+{17.1(d_p/m)^1.5}²], when the relative dielectric constant of the particle is 2. A comparison showed that the theory gives a certain overestimation to the data cited from literature. Additional detailed discussions are given in the paper.

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The control of electrostatic charge on particles in gas-solids flow has been studied both experimentally and theoretically. Micrometer-sized particles dispersed in air were charged with a charge control device, which consisted of an inverted truncated cone. Particles were introduced into the charger from the tangential direction on the top, flowing spirally downward and discharged from the bottom. The particles were electrostatically charged by contacting with the side wall because of the centrifugal force. The performance of particle charging was evaluated by analyzing the average specific charge of particles. It was found that the particle charging efficiency of a single device is about 90%, and 98-99% for a tandem system. The charge on particles was able to be controlled by contact with two different metal plates attached to the inner wall. Furthermore, to predict the charge on particles, an equation as the function of (i) the particle travel distance, (ii) the area fractions of the two metal plates, and (iii) the electrostatic properties was derived from the contact charging theory.

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When charged particles dispersed in air are introduced into a measurement cell, highly charged particles readily deposit on the surfaces, leading to a measurement error. To resolve this problem, a sampling device is designed and manufactured. The electrostatic force under AC field is used to control the motion of the particles close to the surfaces. The AC field is formed with many line electrodes arrayed on the surfaces by applying two AC voltages of a 180 degree phase difference. The effect of the operational conditions such as AC voltage and frequency on the particle deposition is studied and the performance of the sampling device is evaluated. Also, to verify the applicability of the device to actual measurement systems, an experiment is carried out by combining with a system to measure particle charge distribution.

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Many types of toner charge spectrometers have been designed because the measurement of toner charge distribution in an electrophotographic development system would be useful in evaluating and optimizing the system. However, some charge spectrometers cannot accurately measure the charge distribution; moreover, it is difficult to collect the toner particles classified by charge. We designed and manufactured a charge spectrometer using electrostatic field and gravity without air flow, which can classify the toner particles into different specific charge groups. The toner particles were analyzed by the particle analyzer measuring the composition and size of toner and additives. The analysis of a single-component toner showed that smaller sized toners with a large amount of additives resulted in a highly charged toner. The analysis method using the charge spectrometer and the particle analyzer together is very useful for studying the mechanism of toner charging and for producing a high-quality toner.

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The effect of surface composition of a development roll (mixture of the acrylic resin and the polyurethane) on the toner charge was investigated. The specific toner charge increased with the content of acrylic resin. The mass of toner layer coated on the development roll also increased with the content of acrylic resin because of the increased adhesion force between the toner and the development roll. The current was passed at the blade, the development roll and the supplying roll during the charging. The direction of current at the blade suggested that the blade worked for the charging to toner particles. On the other hand, the development roll worked for the discharging when the content of acrylic resin was less than 40%, while it worked for charging at the content higher than 40%. The charge distribution of toner particles was wider with increasing the acrylic resin because of the charging effect at the development roll.

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A novel flange-type electrostatic neutralizer has been developed, which can be used to effectively reduce the static charges on powder in pneumatic powder transport process. The flange-type electrostatic neutralizer, provided with eight nozzle neutralizers, blows ionized air (0.1MPa to 0.3MPa) toward the charged powder within the pipe as well as to protect the needle electrode from the deposition of powder. The current study aimed to improve the conventional version of flange type neutralizer for practical use by adding a function of explosion protection of pressurized type. The evaluation of the neutralizer was also conducted with a real industrial pneumatic powder transport process. As the results, it is shown that the improved version, the pressurized type of neutralizer is used for producing air ions to reduce the static charges on powder in an industrial situation with explosive atmosphere.

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Powder simulation which supports the design of electro photographic system is described. The simulation of the charging behavior of toner particles is performed by using the charge transfer equation obtained by impact experiments between plastic spheres and plastic or metal plate. This simulation method, which gives the relation between the charging properties and the chemical components of toner particles, can be applied to the design of toner particles with the optimum charging behavior.
The development and flow behavior of a two-component developer are simulated by large scale discrete element method taking into account the magnetic and electrostatic interactions between developing particles. The proposed simulation gives very useful information for the design of a two-component development system. New simulation methods of melting behavior of toner particles in fixing process and blade cleaning behavior are proposed.

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Factors affecting adhesion forces of charged particles are reviewed. First, fundamental forces, such as Coulombic force, gradient force, etc., working on charged particles are briefly described. Then recent studies on adhesion forces of charged particles with respect to particle size, particle charge, moisture content, etc. are introduced. Finally differences between calculated image forces and measured adhesion forces for charged particle are discussed in detail.

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