Abstract: An image forming apparatus having a tandem system configuration, includes: a multiple number of photoreceptors which each form an electrostatic latent image; and a multiple number of developing devices each holding a different color toner from the others for development of the corresponding static latent image, and is constructed so that the plural toners at least include a black toner, and the abrading force of the black toner or its carrier therein acting on the photoreceptor surface is adjusted so as to be smaller than that of the other developing toners or their carrier therein. Since, in a tandem type color image forming apparatus, the developing devices, photoreceptors and toners for all colors will reach the end of their life at the same time, the image forming apparatus can be operated at low cost.

Abstract: When an image signal is acquired, an encryption key is created, and the acquired image signal is encrypted with the created encryption key. An image based on the encrypted image signal is formed on a sheet having a memory, and the encryption key is written into the memory. The encrypted image formed on the sheet is read, and the encryption key is read from the memory. The image signal of the read encrypted image is decrypted with the read encryption key, and the original image based on the decrypted image signal is formed on a sheet.

Abstract: An image forming apparatus having a tandem system configuration, includes: a multiple number of photoreceptors which each form an electrostatic latent image; and a multiple number of developing devices each holding a different color toner from the others for development of the corresponding static latent image, and is constructed so that the plural toners at least include a black toner, and the abrading force of the black toner or its carrier therein acting on the photoreceptor surface is adjusted so as to be smaller than that of the other developing toners or their carrier therein. Since, in a tandem type color image forming apparatus, the developing devices, photoreceptors and toners for all colors will reach the end of their life at the same time, the image forming apparatus can be operated at low cost.

Abstract: An object of the invention is to improve the photosensitivity characteristics, characteristics on repeated use and stability of a photoreceptor. A photosensitive layer formed on a conductive support of a photoreceptor contains crystalline oxotitanylphthalocyanine having major peaks in an X-ray diffraction spectrum at Bragg angles (2&thgr;±0.2°) of 7.3°, 9.4°, 9.6°, 11.6°, 13.3°, 17,9°, 24.1° and 27.2°, wherein a peak bundle formed by overlapping the peaks at 9.4° and 9.6° is the largest peak, and the peak at 27.2° is the secondary largest peak as a charge generating substance. Furthermore, it contains a bisamine compound, an N,N′-bisenamine compound, a styryl compound, an amine-hydrazone compound, a benzofuran-bishydrazone compound, a bisenamine compound, a benzofuran-bishydrazone compound or a benzofuran-bis-cyclic hydrazone compound represented by the particular structural formulae as a charge transporting substance.

Abstract: An electrophotographic photoconductor comprises a charge generation layer containing a phthalocyanine compound as a charge generation material and a charge transfer layer containing a charge transfer material of a hole transfer type, the charge generation layer and the charge transfer layer are laminated on a conductive support, wherein the charge generation layer has an ionization potential of at least 5.6 eV.