We have investigated the electrical conduction properties of transfer belts that are used for many color printers. The quantitative parameters based on the charge transport equation can be obtained from transient phenomenon.
At first, we demonstrated that the transfer belt had two regimes of electrical conduction properties by J-V characteristic. One is the ohmic conduction regime. The other is the space-charge limited current regime where a space-charge is formed in the bulk and the trap is filled up with carriers.
Next, we obtained the relaxation time and the carrier mobility by measuring charge decay characteristics. We found that the relaxation time and the carrier mobility depend mainly on the applied voltage. The voltage-dependence of carrier mobility lays dozens of volts higher than the voltage where the space-charge limited current occurs. This voltage-dependence of the carrier mobility can be approximated by the Pool-Frenkel type dependence.
A dielectric constant is obtained from a step response. This measuring circuit is a serial circuit with a resistance and the transfer belt. When an input voltage is applied to the resistance, the surface voltage of the transfer belt increases. After measuring these characteristics, we can calculate the dielectric constant.
These methods that we proposed are very effective to investigate electrical properties of transfer belts, and can be adapted to other materials.

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The transfer media used in electrophotographic printers are expressed by an electrical equivalent circuit in which a resistor and a capacitor are connected in parallel. Resistivity (or conductivity) and dielectric constant are measured with conventional measurements. However, an actual transfer process using a transfer roller is in their transient state. Thereby, a question arises as to whether the traditional parameters with conventional measurements are adequate for the actual transfer process.
We studied a new measuring method based on a charge transport equation, by which the parameters of transfer media were measured in their transient state. By our method, the transfer medium is charged and after that the voltage decay is measured as a function of time. Then, we can derive a relaxation time. The dielectric constant can be obtained by a step response, in which a step waveform is applied to a medium through a resistance. Conductivity is calculated with the relaxation time and the dielectric constant. New parameters were then compared to the values obtained by measuring with the conventional measurements.
As a result, we conclude that the dielectric constants don’ t depend on a voltage, but on values in a transient state, these values have been shown to be two or three times higher than those obtained from conventional measurements. Meanwhile, it remains true that conductivities, including those based on field dependence, agree with values with traditional measurements.

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An Intermediate transfer system features two transfer processes. In the first transfer process four different colors of toner that form the image are transferred onto the transfer belt in succession. In the second transfer process the four colors of toner are transferred to the paper in a single step. In this paper we focused the second transfer process and investigated the electrical properties of the transfer belt, the transfer medium and the transfer roller based on the charge transport equation.
We were able to demonstrate that the transfer belt has indeed an ohmic conduction regime and a space-charge limited current regime. The space-charge limited current regime itself characterizes a field independent carrier mobility regime and a field dependent carrier mobility regime. The conductivity of the transfer belt in the space-charge limited current regime can be defined as the relationship between a current density and a voltage. The field dependence of conductivity in the ohmic regime can also be found in the transfer roller and the transfer medium. These conductivities are expressed by approximated equations as a function of voltage.
The resulting parameters were applied to an electrical equivalent circuit model of the second transfer process in order to simulate the phenomenon. The volume charge density of toner layer was obtained experimentally.
Hence, we calculated the voltage evolutions of the transfer belt, the toner layer, the paper and the transfer roller. And the voltage distribution, the electric field distribution and the transfer efficiency were simulated. The calculated transfer efficiency proved to be in accordance with the experimental result.

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