Triboelectrification in the two-components development system, and effects of the charge density on a toner surface and the toner size on electrophotographic image-quality factors have been investigated by varying (1) the toner median size d from 6.8 μm to 13.5 μm and the carrier median size D from 43 μm to 106 μm, and also varying (2) the carrier specific weight ρ_c by using different carrier core, (3) composition of methylmethacrylate/styrene copolymer resin (MMA/St) on the carrier surface, and (4) concentration of carbon black [C B] in the toner binder of polyester.
As regars triboelecrification of toners and a carrier in the two-components development system, it has been found that triboelectrification with n particles of toner on a carrier is more favorably describable by the charge density on a toner surface (q/s_t) as a function of surface-area ratio of n toners to a carrier (n_st/s_c), on bases of contact electrostatic field strength (E_k) and structural (or geometrical) factors of the toner and the carrier (f_t, f_c), rather than by the toner charge-to-mass ratio (q/m) as a function of mixing-weight ratio of toners to a carrier X (or toner concentration T_c) .
As regars the development efficiency of toners in solid area, it has been found that the development efficiency is determined by the charge density on a toner surface q/s_t, not by the toner charge-to-mass ratio q/m suggested by Schein and by others.
As regards the resolusion of line images reproduced by the two-components contact development in the rotating direction of the photoreceptor drum, the width of a line image Γ, of which the original line width Γ₀ is 100 μm, broadens by four particles of toner, ΔΓ= +4·d. The resultant resolution of line images R_e is determined by the reciprocal of the broadening width, ( R_e ∝ 1/4d). In the horizontal direction of the photoreceptor drum, the line-width Γ is reduced by the scavenging effect of ears of the developer. On the other hand, the broadening of a line image reproduced by the mono-component jumping development is certified to be isotropic in the rotating and horizontal directions of the photoreceptor drum, then, the reproduction of a dot image has been investigated by the mono-component jumping development. As regards the reproduction of dot images of 150 dots/inch; for a small original dot with dot-area percentage ≤ 5 %, the dot image disappeares; for an original dot with dot-area percentage of 12 %, the diameter of a dot D_d reduces isotropically by two particles of toner, (ΔD_d = -2·d); and for an original dot with dot-area percentage of 28-60 %, the diameter of a dot D_d broadens isotropically by six particles of toner, (ΔD_d = +6·d).
In conclusion, the correlation between the toner size4and the image-quality factors, i.e. resolusion of line images, reproduction of a dot image, and reproduction of gereration copies of a line image, has been quantitatively clarified, and utilization of toner particles of a smaller size have been persuaded in order to improve the electrophotographic image-quality factors furthermore.

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The phenomena of paper sheet adsorption to the photoreceptor are wellknown during the corona charge transfer process, in that corona charging is performed directly to the paper sheet. However, even in using the roller transfer and belt transfer methods in that the charging was made not directly to the sheet but to an insulator of the roller or belt, similar phenomena were often experienced due to the charge injection from the insulator to the paper sheet. For such a charge injection process from a charged insulator to a paper sheet, the process due to Paschen's discharge was considered and argued. As a result, theoretical consideration indicates that Paschen's discharge may occur through the air gap due to the proejction of the sheet edge, and actually we have succeeded in observing the Paschen's discharge in the air gap.

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