JPH0568703B2 - - Google Patents

Description

[Detailed description of the invention]

B. Purpose of the Invention [Field of Industrial Application] The present invention relates to electrophotography, and particularly to electrophotography using a photosensitive drum type transfer method. [Prior Art] An electrophotographic process is known in which a photosensitive drum is subjected to primary charging, image exposure, reversal development, transfer charging, cleaning, and pre-exposure in that order. [Problems to be Solved by the Invention] In the above conventional electrophotographic process, the transfer charge has a polarity opposite to the primary charge, that is, if the primary charge is negative, the transfer charge is positive. Therefore,
Unless you use a photoreceptor that is sensitive to both positive and negative charges,
During continuous copying, the surface potential of the drum becomes opposite in polarity to the primary charging due to the influence of transfer charging. Therefore, in order to erase the potential (hereinafter referred to as erasing), pre-exposure is performed before primary charging, but this has the disadvantage of increasing the memory rather than achieving the purpose. This invention aims to solve the above problems. B. Structure of the invention [Means for solving the problem] A photosensitive drum is charged to a constant potential with a primary charger (Fig. 2A showing potential fluctuations of the photosensitive layer), and an electrostatic latent image is formed by imagewise exposure. (FIG. 2B), and reverse development is performed in a developing device (FIG. 2C). A toner image is transferred onto plain paper using a transfer charger having a polarity opposite to the primary charging polarity, and a positive image is obtained from the negative image (FIG. 2D). After cleaning the residual toner, a potential of opposite polarity to the primary charging is applied using a pre-charging device having a grid (FIG. 2E), and when continuous copying is performed, the primary charging step is immediately started. When copying is finished, transfer charging and pre-charging are turned off.
Primary charging and pre-exposure are performed on at least one part of the photosensitive drum.
Let this happen during rotation. [Operation] Due to the transfer charging described above, the portion of the photosensitive drum that was at the bright area potential becomes the potential of the transfer charging polarity, and a charged portion with opposite polarity is generated on the drum surface (FIG. 2D). Conventionally, pre-exposure is applied to erase this potential, but since it does not become completely zero, the memory of the latent image from the previous process still remains, and erasing is not performed, degrading the image quality in the next cycle. Therefore, in this invention, pre-exposure is not performed during continuous copying. Instead, pre-charging with the opposite polarity to the primary charging (same polarity as the transfer charging) is performed to align the positive and negative charging potentials on the photosensitive drum surface to the pre-charging polarity and to make it uniform (Fig. 2 E). The memory is erased, that is, the potential is cleaned, and the primary charging in the next step is performed uniformly over the entire surface. At the end of the copying operation, only primary charging and pre-exposure are performed for at least one revolution of the photosensitive drum. Then, the surface of the photoreceptor, which has been potential-cleaned by pre-charging in the previous cycle, is primary charged at a constant potential and is pre-exposed, so that the surface potential becomes close to zero. [Example] Figure 1 shows a schematic diagram of an apparatus for carrying out the method of the present invention, in which 1 is a grounded conductive support 1a;
2 is a primary charger, 3 is an image exposure path for an original image or a light beam modulated by an image signal, and 4 is a toner drum in a bright potential area. (the toner is charged to the same polarity as the primary charger 2),
5 is a transfer charger with a polarity opposite to that of the primary charger, P is a transfer paper, 6 is a cleaner for removing residual toner, and 7 is a pre-charger with a polarity opposite to that of the primary charger 2, which converges the photoreceptor surface to a uniform potential. It has a grid 71 for
8 is a pre-exposure path. Note that the same effect can be obtained even if the pre-charger 7 described above is placed after the pre-exposure path 8. Since the apparatuses for each of the above processes are similar to those known in the art, explanations of their individual configurations will be omitted. As shown in the table below, for example, if primary charging is negative, transfer charging and pre-charging are positive, and pre-exposure 8 is turned off during continuous copying. When copying is completed, the transfer charger 5 is turned off by the end signal, and then the front charger 7 is also turned off, and only the charging by the primary charger 2 is continued for at least one revolution of the photosensitive drum 1. At that time, pre-exposure 8
administer. The above sequence control can be performed using a known method.

[Table] C. Effects of the Invention In the electrophotographic process using the drum type transfer method, as described in the section of the operation above, the potential on the photoreceptor is made uniform before primary charging, and potential unevenness on the photoreceptor due to primary charging is eliminated. This improves the image quality since most of the noise can be eliminated. Furthermore, since the entire surface of the photoreceptor is not pre-exposed during continuous copying, there is an effect of suppressing optical memory of the electrophotographic photoreceptor and sensitivity deterioration due to light to a lower level than usual.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an apparatus implementing the present invention, and FIG. 2 is a schematic diagram illustrating potential fluctuations in each process. 1 is a photosensitive drum, 2 is a primary charger, 3 is an image exposure optical path, 4 is a reversal developing device, 5 is a transfer charger, 6 is a cleaner, 7 is a pre-charger with a grid, and 8 is a pre-exposure optical path.

Claims (1)

[Claims] 1. Primary charging, image exposure, reversal development, and
In an electrophotographic process in which transfer charging, cleaning, and pre-exposure are performed in that order, a pre-charger with a polarity opposite to that of the primary charger is placed before or after the pre-exposed area, and during continuous copying, the pre-exposure is turned off and the copying process is performed. 1. An electrophotographic method characterized in that upon completion of the process, the transfer charging and pre-charging are turned off, and the primary charging and pre-exposure are performed for at least one rotation of the photosensitive drum.