The intermediate transfer belt plays very important roles in the electrophotographic color printer. But, the characteristics of the transfer belt have not been investigated sufficiently. Generally speaking, the transfer belt is treated as the resistance and the capacitance, assuming ohmic conduction model. In this study, we examine the characteristics of the transfer belt, and the independent roles played by additional transport parameters, including a dielectric constant, carrier density, field dependent mobility, are elucidated. The dielectric constant is obtained by frequency characteristics in high electric field. The electric circuit that we measured is that a series resistance is connected to the transfer belt. The frequency characteristics of the dielectric constant is decreasing slightly together with the frequency, but is independent on the applied voltages. Carrier mobility is calculated by the dielectric constant and J-V characteristics, and we have clarified that three carrier transport states exist in the transfer belt. The first state is the ohmic conduction state, the second state is a space charge limited current state where carrier mobility is independent on the field, and the third state is a space charge limited current state where carrier mobility is dependent on the field.
In the print system that water-based ink is transported from the free surface of the ink layer to the paper with electrostatic forces, conditions that independently control ink transportation of adjacent pixels have been approved through 3-D numerical analysis. The following conclusions have been obtained from this study. (1) Individual control of ink transportation of each pixel requires at least 254μm distance (correspond to 100dpi) between centers of any adjacent electrodes. (2) When a distance between centers of adjacent electrodes is 254μm, the bias voltage of adjacent electrodes which do not process ink transportation must be 0V in order to avoid Cross-Talk when the switching voltage is added. (3) When a distance between centers of adjacent electrodes is 254μm, a volume of ink transportations may vary over 7 times depending on influences from adjacent electrodes. It is necessary to reduce the influences of adjacent electrodes in order to make this print system practicable.
Biased roller transfer is attracting attention because it does not generate ozone and because it has a greater operating range than corona transfer. Conventional roller transfer with constant voltage biasing has a drawback in that paper thickness affects the transfer ratio. We previously proposed constant current biasing as an alternative. In this work, we examined the basic and useful characteristics of conductive roller transfer using constant current biasing, both theoretically and experimentally. Our investigation produced the following results. First, similar to the main transfer factor in constant voltage biasing, the transfer charge on paper determines the transfer characteristics, where the charge corresponds to the electric field between the paper and a layer of toner on the photoconductor. Paper thickness does not affect the transfer ratio if biasing is done with a constant current corresponding to an optimum transfer charge of 500μC/m2. Second, the effect of paper width can almost be eliminated by using a transfer roller with a resistivity of over 109Ωcm. Third, the optimum transfer pressure is in a range of 25 to 50gf/cm. Finally, ensuring that the speed difference between the transfer roller and photoconductor is no more than a few percent prevents the omission of characters during printing.
A set of wax-based pigmented solid inks (Y, M, C, and K) was developed as a potential alternative to the standard water-based inks currently used in colored inkjet printing with plain paper. First, the stability of pigment dispersion was analyzed with respect to particle size, functional groups, and melt viscosity. Long-chained alcohol-based waxes were particularly suitable for uniform and stable (no sedimentation) dispersion in the molten stage. Next, the color gamut, optical density, and show-through were evaluated and were found to be superior to these associated with water-based inks. In addition, light fastness was evaluated by the color change (Δab*) associated with Xe lamp exposure. The color print of this ink set was stable even after 700h, which corresponded to over a year under direct sunlight (Arizona sun) and was far better than Δab* of conventional prints.
We have developed a multi-channel print head for electrostatic inkjet printers using a microfabrication process. Its performance was assessed in gray-scale printing tests. The print head recorded 10-60μm dots on print media as the width of the pulse signal varied from 50 to 400μs. The optical density varied from approximately 0.3 to 1.2 on the gray scale print samples, indicating that our print head can achieve tone control by dot size. The variance of the dot size recorded by each electrode (channel) was found to be±9.9μm (±16.5%) at the maximum dot size (60μm). Finally, the print head was used to print a full color image using yellow, magenta and cyan ink. It successfully produced a full color sample with a resolution of 600 dpi.