JPS6013174B2 - Multiple copy method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for obtaining multiple copies from a single electrostatic latent image.

Erasing an electrostatic port image formed by a conventional method on an electrophotographic printing material such as an electrophotographic light-sensitive material having a photoconductive layer on a support, or an electrostatic recording material having a dielectric layer on a support. A method of obtaining multiple copies by repeating the development process and the transfer process of transferring the head image obtained by development onto a transfer sheet is disclosed in Hakama Kosho No. 44-30233 and Samurai Kosho No. 46-77.
No. 89, Japanese Patent Publication No. 49-17298, etc.

In these methods, multiple copies are obtained by repeating the steps of developing and transferring the electrostatic latent image formed on the photoconductive layer or dielectric layer. The electrostatic image attenuates over time due to attenuation and leakage of latent image charge due to development and transfer. As a result, the contrast of the electrostatic port image decreases, and the image quality of the resulting copy decreases.
In particular, there is a tendency for contrast to decrease. In order to prevent this decrease in contrast, a method has been proposed in which the voltage used for transfer is gradually increased to obtain an image with a constant contrast.
It has also been proposed to reduce the leakage of latent image charge during development by using a developer with high electrical resistance, thereby increasing the number of sheets that can be repeatedly copied.

However, if the transfer voltage is gradually increased during repeated copying, the latent image will eventually be destroyed by the transfer voltage, so there is a limit to the number of copies that can be repeated.

Furthermore, even if the leakage of latent image charges is reduced by selecting materials for development or transfer, it is impossible to avoid a decrease in the contrast of images upon repeated copying. Particularly when the number of repetitions is large, when the humidity is high, or when the material used for image formation becomes fatigued, the contrast decreases greatly. An object of the present invention is to provide a method for improving the deterioration in image quality caused by one repetition of development and transfer, and for obtaining a large number of copies.

The present invention has achieved this objective by detecting the state of the electrostatic latent image and changing the development and transfer states according to the state of the electrostatic latent image, thereby making it possible to obtain a constant image quality.

By detecting the attenuation of the latent latent image as the state of the electrostatic tank image and changing the efficiency of development and transfer according to the degree of attenuation, a large number of copies of a constant quality can be obtained from a single latent latent image. made it possible.

Experiments revealed that the potential attenuation of static fin latent images during repeated copying differs depending on the type of static fin latent image.

In other words, the potential attenuation of the latent image is large in post-latent areas where charges are distributed linearly, such as characters or lines, and in latent areas where charges are uniformly distributed over a relatively large area, such as in solid areas. The potential attenuation of the latent image is small in some areas. Furthermore, it has been found that the potential decay of a static latent image during repeated copying varies depending on the toner concentration of the developer. That is, when the toner density is high, the attenuation of the latent image is small, and when the toner density is low, the attenuation is large. This is thought to be due to the difference in electrical resistance between the carrier and the toner that constitute the developer. Further, the potential attenuation of the static latent image during repeated copying varies considerably depending on changes in temperature and humidity. Furthermore, if the photoconductive layer or dielectric layer holding the latent image becomes fatigued during use or its surface becomes dirty, the potential attenuation of the electrostatic latent image changes. As described above, the attenuation of the static latent image varies in various ways depending on the usage conditions and environment of the apparatus, and the degree of attenuation cannot be predicted in advance.

However, by detecting the level of the surface potential of a static latent image and performing development and transfer according to that level, it is possible to obtain many copies of a constant image quality from a single electrostatic tower image that is attenuated. I found out. Embodiments of the present invention will be described with reference to the drawings.

A drum 1 coated with amorphous selenium is charged and exposed to light using a known method to form a static latent image.

That is, it is uniformly charged by the corona chargers 2 and 3, and a light image of the original to be copied is irradiated at the exposure position 4 to form an electrostatic latent image corresponding to the light beam. Next, the surface potential of the static fin latent image is measured with an electrometer 5, and that value is used as a reference value. The potential may be detected by detecting a partial potential of the latent image or by detecting an average potential of the entire latent image. Thereafter, the image is developed in the developing section 6 by, for example, magnetic brush development. At this time, in the developing section, the magnetic brush is rotated at a preset speed, and the developing operation is performed under the set bias conditions. The developed image is transferred to paper in the transfer section 12, and the surface potential of the latent image after transfer is measured again by the electrometer 5.

When the measured value is attenuated with respect to the reference value, in order to improve the development efficiency of the development section, the rotation speed of the magnetic brush of the development section 6 is increased according to the degree of attenuation, and a means of lowering the bias voltage is also used. be done. As a result, an image of the same level as the first time can be formed on the drum surface 1 even after the potential decays, and copies of a constant quality can be produced from one static latent image whose potential gradually decays through repeated development and transfer. I was able to get it. In FIG. 2, the potential of the photosensitive drum 1 detected by the probe 15 of the electrometer 5 is amplified by an amplifier 17 and sent to a bias voltage 18, a motor drive power source 19, and a charger power source 211. When the potential attenuates, the bias voltage applied to the developing roll 16 from the bias power supply 18 is lowered, and the rotational speed of the developing roll 16 by the developing unit drive motor 201 is increased, and the transfer paper 23 is further pressed against the photoreceptor drum 1. The transfer voltage of the transfer roller 22 can be increased by the charger power source 21 for the corona charger 24.

Although development efficiency is limited and the number of copies to be made is limited, the copying ability can be increased by additionally increasing the transfer efficiency of the transfer section.

Methods for increasing the transfer efficiency include changing the contact pressure for transfer and increasing the transfer voltage. According to the present invention, a large number of copies of constant image quality can be obtained despite the potential attenuation of a static latent image, and can be obtained with simple operations.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the apparatus according to the present invention, and FIG. 2 is a diagram showing the speed and voltage of the developing roller and the voltage control system of the transfer roller. 1... Photosensitive drum, 5... Electrometer, 6.
...Development section, 12...Transfer section. Tsuyoshi I figure *2 figure

Claims (1)

[Claims] 1 In a method of obtaining a large number of copies by repeating development and transfer of a single electrostatic latent image, the potential of the electrostatic latent image is detected by an electrometer, and the development at the developing section is adjusted according to the degree of attenuation relative to a reference value. A multi-sheet copying method characterized by obtaining images of constant quality by varying the efficiency and/or transfer efficiency of a transfer section.