1. Field of the Invention
The present invention relates to electrophotographic photoconductors, and more particularly to electrophotographic photoconductors comprising an electroconductive support and a photoconductive layer comprising at least one [2,2]para-cyclophane compounds, and [2,2]paracyclophane compounds which can be used as photoconductive materials in the photoconductor.
2. Discussion of Background
Conventionally, inorganic materials such as selenium, cadmium sulfide and zinc oxide are used as photoconductive materials of an electrophotographic photoconductor in the electrophotographic process. The above-mentioned electrophotographic process is one of the image forming processes, through which the surface of the photoconductor is charged uniformly in the dark to a predetermined polarity, for instance, by corona charge. The uniformly charged photoconductor is exposed to a light image to selectively dissipate the electrical charge of the exposed areas, so that a latent electrostatic image is formed on the photoconductor. The thus formed latent electrostatic image is developed by a developer comprising a coloring agent such as a dye and a pigment, and a binder agent such as a polymeric material, to a visible image.
Fundamental characteristics required for the photoconductor in such an electrophotographic process are: (11) chargeability to an appropriate potential in the dark, (2) minimum dissipation of electrical charge in the dark, and (3) rapid dissipation of electrical charge when exposed to the light.
However, while the above-mentioned inorganic materials have many advantages, they have several shortcomings form the viewpoint of practical use.
For instance, a selenium photoconductor, which is widely used at present, satisfies the above-mentioned requirements (1) to (3) completely, but it has the shortcomings that its manufacturing conditions are difficult, and accordingly its production cost is high. In addition, it is difficult to work it into the form of a belt due to its poor flexibility, and it is so vulnerable to heat and mechanical shocks that it must be handled with the utmost care.
A cadmium sulfide photoconductor and a zinc oxide photoconductor can be easily obtained by coating a dispersion of cadmium sulfide particles and zinc oxide particles in a binder resin on a support. However, they are poor in mechanical properties, such as surface smoothness, hardness, tensile strength and wear resistance. Therefore, they cannot be used in the repeated operation, as they are.
To solve the above-mentioned problems of the inorganic materials, various electrophotographic photoconductors employing organic materials are proposed recently and some are still put to practical use. For example, there are known a photoconductor comprising poly-N-vinylcarbazole and 2,4,7-trinitrofluorene-9-on, as disclosed in U.S. Pat. No. 3,484,237; a photoconductor prepared by sensitizing poly-N-vinylcarbazole with a pigment of pyrylium salt, as described in Japanese Patent Publication 48-25658; a photoconductor comprising as the main component an organic pigment, as described in Japanese Laid-Open Patent Application 47-37543; a photoconductor comprising as the main component an eutectic crystal complex of a dye and a resin, as described in Japanese Laid-Open Patent Application 47-10735; a photoconductor prepared by sensitizing a triphenylamine compound with a sensitizer pigment, as described in U.S. Pat. No. 3,180,730; and a photoconductor comprising poly-N-vinylcarbazole and an amine derivative as a charge transporting material, as described in Japanese Laid-Open Patent Application 58-1155.
These electrophotographic photoconductors have their own excellent characteristics and considered to be valuable for practical use. With various requirements of the electrophotographic photoconductor in electrophotography taken into consideration, however, the above-mentioned conventional electrophotographic photoconductors cannot meet all the requirements.
In U.S. Pat. No. 3,265,496, Japanese Patent Publication 39-11546 and Japanese Laid-Open Patent Application 53-27033, polyfunctional tertiary amine compounds, in particular benzidine compounds among them, are considered to be excellent as photoconductive materials for use in the electrophotographic photoconductor. However, these compounds have the shortcomings that the solubility in a binder resin is poor and they are easily crystallized in a photoconductive layer. To remove the above shortcomings, it is proposed in Japanese Laid-Open Patent Application 62-112164 that the above benzidine compound be used together with other low-molecular weight compounds in the photoconductive layer to minimize the crystallization of the benzidine compound.
Furthermore, 4-N,N-dimethylamino[2,2]paracyclophane is conventionally known as a [2,2]paracyclophane compound containing a tertiary amino group as reported in J. Am. Chem. Soc. , 80, p.3115(1958), but it does not sufficiently function as a photoconductive material.