Having developed a prototype of a metallic-base thin-film thermal head, we compared its density irregularity characteristics in the main scanning direction, with those of the alumina-base thermal head, and found the metallic-base to be superior in terms of uniformity in transferred ink density.
By using thermal analysis of the finite element method, we found that the following factors are predominantly responsible:
(1) Distribution of the equivalent air gap determined by the contact between thermal head surface and ink sheet.
(2) Nonuniform distribution of the common resistance due to the fact that the heat elements closer to the middle have higher common electrode resistance.
The reasons the metallic-base type is superior are that, it ensuring a uniform distribution of the equivalent air gap layer, and also because the base itself can serve as a common electrode, resulting in uniform common resistance.

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Triboelectrification in two-component development systems employing toner and insulative carrier has been studied by varying toner surface-area median size (d₅₀), carrier surface-area median size (D₅₀), specific weight of carrier (ρc), composition of methyl-methacrylate (MMA) /styrene (St) copolymer resin on the carrier surface, and concentration of carbon black in the toner binder of polyester resin. It has been found that toner surface-charge density (q/s_t) generated by triboelectrification with n partices of toner on a carrier particle is describable as a function of surface-area ratio of n toners to a carrier (ns_t/s_c), on bases of contact electrostatic field (E_k) and geometrical or structural factors of toner and carrier (f_t, f_c).

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Aqueous coating method was applied for preparing layered photoreceptors. Electrophotographic measurements of a layered photoreceptor, consisting of a charge generation layer (CGL) of ε-type copper phthalocyanine (ε-CuPc) and a hole transport layer of hydrazone derivative, showed a fast dark decay rate, suggesting increased injection of holes from the aluminum substrate into the CGL. Measurements of work function(φ) of substrate aluminum revealed that deposition of CGL was accompanied by an increase in φ of the substrate during the processes and that the enhanced φ value was nearly equal to the ionization potential of ε-CuPc (5.16 eV). This resulted in the increase in dark decay rate.
An approach for retarding dark decay rate was made by forming carrier-injection barriers between the substrate and CGL. Use of some improved photoreceptors led to lowering of dark decay rate without decrease in photo-sensitivity. One of them was an electron-transport type receptor in which an sufficient injection barrier was developed between ε-CuPc and Al. Another was a hole-transport type receptor that employed a pelylene pigment that possesses a high ionization potential.

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