JPS6180177A - Formation of electrostatic latent image - Google Patents

Abstract

PURPOSE:To obtain a sharp image having medium contrast with good reproducibility by executing approximately simultaneously the irradiation of a light image and corona discharge on a photosensitive body, impressing a voltage to the shield electrode or grid electrode of a corona discharger or both thereof and making variable the voltage. CONSTITUTION:The photosensitive body 1 consisting of a conductive substrate 21 and a photoconductor layer 22 is subjected approximately simultaneously to the irradiation 3 of a light image and the corona discharge from the corona discharger 2. The voltage is impressed to the shield electrode 24 or grid electrode 71 of the discharger 2 or both thereof and is made variable. The irradiation of the light image and corona discharge are executed approximately simultaneously in the above-mentioned manner on condition that the electrostatic charge does not appear at the same point of the body 1 after the end of the irradiation of the light image. The medium contrast is reproduced by such electrostatic latent image forming stage and the contrast and density of the medium contrast image can be adjusted by making variable the quantity of the corona discharge. Since the quantity of such corona discharge is stable and is easily reproducible, the reproducibility of the image is improved and the deterioration of the image owing to the deviation of the light image and the deviation of the irradiating position of bias light, etc. are obviated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for forming an electrostatic latent image on an electrophotographic photoreceptor comprising a conductive substrate and a photoconductor layer.

[Technical background of the invention and its problems]

In an electrophotographic copying machine, the method of forming an electrostatic latent image corresponding to the density of the original on a normal electrophotographic photoreceptor consisting of a conductive substrate and a photoconductor layer is to first deposit the image on the photoreceptor in the dark. Generally, uniform charging is carried out by corona discharge, and then a light image is irradiated. FIG. 10 typically shows the relationship between the electrostatic latent image potential and the original density obtained by this method.

The electrostatic latent image thus formed on the photoconductor is developed using a well-known two-component magnetic developer, and the toner image is transferred and fixed onto plain paper, resulting in a copy image with a density of , the relationship is generally shown in FIG. 11 with respect to the density of the original, and extremely clear black and white copies can be obtained. Therefore, this method is suitable for office copying machines that mainly handle character images.

However, in recent years, the demands on copying machines have expanded, especially for copies that can faithfully reproduce halftones.

The demand for Reproduction of halftones is also important in realizing color copying that enables faithful color reproduction. Several methods have been proposed to enable reproduction of halftones. For example, 11oidF, Bean and I na
Chen reported that by devising the structure and materials of the photoreceptor, the relationship between the latent image potential and the exposure amount can be adjusted, making it possible to reproduce halftones (I E E E
I As 1977 Annual Meeting)
. Although this is an excellent method from a practical point of view, there are still points that need to be improved, such as improving the reliability of the photoreceptor. Another method is a halftone screening method.

This is a method of converting the density of the original into the size of halftone dots by, for example, placing a screen on the surface of the original, or placing the screen close to the surface of a photoreceptor where the light image is focused (R, N, Qoren” l-1ight-Qu
arity Pictorial Xerogra
phicReproduction by Half
tone 5cleanir+a” J.

AI) Dl, photogra, Eno,
L 233-238 [1982] et al.).

This method is the same as halftone images in printed matter, and is an excellent method for reproducing halftones, but if the original to be copied is formed with halftone images, there is a risk that so-called moire phenomenon may occur. However, it cannot be applied to all kinds of originals.2Also, another method is limited to the case of a photoreceptor with a three-layer structure consisting of a conductive substrate, a photoconductor layer, and a transparent insulator layer. For example, a method for forming an electrostatic latent image based on a series of steps of uniform primary charging, light image irradiation and simultaneous secondary charging (opposite polarity to the primary charging), and uniform light irradiation was disclosed in Japanese Patent Application Laid-open No. It is disclosed in Japanese Patent No. 59-30560. This method is considered to be one of the excellent methods for forming electrostatic latent images that can reproduce halftones, but the process is extremely complicated, and the equipment inevitably becomes larger and more expensive. There is a problem.

Furthermore, as an electrophotographic method that could express halftones,
As described in Japanese Patent No. 7-56070, an electrophotographic photoreceptor having a photoconductor layer is irradiated with a light image, corona charging, and bias light are irradiated simultaneously, and by adjusting the intensity of the bias light, intermediate A method of adjusting the contrast and density of a toned image has also been proposed. However, with this method, it is difficult to maintain a stable amount of bias light due to problems such as the stability of the light source, which causes poor reproducibility of image contrast and density. Moreover, in this method, it is important that the light image irradiation position and the bias light irradiation position on the photoreceptor are completely aligned in order to obtain a good image without contrast or even one-degree unevenness, and the position adjustment is necessary. The disadvantage is that it is difficult to

[Purpose of the invention]

The purpose of this invention is to be able to reproduce halftones through an extremely simple process, and to be able to adjust the density and contrast of an image with simple operations, and to maintain stability and reproducibility of the image density and contrast. An object of the present invention is to provide a method for forming a good electrostatic latent image.

[Summary of the invention]

According to the present invention, the above-mentioned object is to provide a method for forming an electrostatic latent image on an electrophotographic photoreceptor comprising a conductive substrate and a photoconductor layer, in which a photoreceptor is irradiated with a light image and a corona discharger is used. This is achieved by performing corona discharge from the corona discharger almost simultaneously, applying a voltage to the shield electrode and/or the grid electrode of the corona discharger, and making the voltage variable.

〔Effect of the invention〕

According to the present invention, halftones can be reproduced through a simple electrostatic latent image forming process in which irradiation of a light image onto an electrophotographic photoreceptor and corona discharge are performed almost simultaneously. Further, by varying the voltage applied to the shield electrode or grid electrode of the corona discharger, the amount of corona discharge can be changed, and as a result, the contrast and density of the halftone image can be adjusted. In this case, the amount of corona discharge, which depends on the voltage applied to these shield electrodes and grid electrodes, is very stable and has good reproducibility. There is no problem, and image contrast, density stability, and reproducibility can be significantly improved. In addition, the problem of conventional methods of deterioration of image quality due to the misalignment of the irradiation position of the optical image and the bias light is fundamentally solved.

[Embodiments of the Invention] FIG. 1 is a sectional view of a copying machine using the electrostatic latent image forming method according to the present invention, and FIG. 2 is a diagram for explaining the configuration of the main parts thereof. As shown in FIG. 2, the electrophotographic photoreceptor 1 includes a conductive substrate 21 and a photoconductor layer 22 formed thereon, and is configured as a rotatable drum. For example, the conductive substrate 21 includes a /l plate, and the photoconductor layer 2
For example, a 5e-Te alloy deposited to a thickness of about 70 μm is used for each of the layers 2 and 2.

First, a corona discharger 2 is installed around the photoreceptor 1. This corona discharger 2 has a structure that allows light to pass therethrough so that a light image 3 can be irradiated almost simultaneously with corona discharge onto the photoreceptor 1.

The optical image 3 is obtained by scanning an image on a document 5 illuminated by a light source 4 with an optical system 6.

The electrostatic latent image formed on the surface of the photoreceptor 1 by the irradiation from the light source 3 and the corona discharge from the corona discharger 2 is transferred to the developing device 7.
It becomes a toner image and is visualized.

The toner image formed on the photoreceptor 1 is transferred by a transfer charger 9 onto a transfer paper conveyed from a transfer paper storage cassette 8, and then passed through a fixing device 10 to become a copied image. The photoreceptor 1 is further sent to a cleaning device 11 to remove residual toner, and the memory is further removed by an erasing lamp 12, before entering the next image forming cycle.

As shown in detail in FIG. 2, the corona discharger 2 is composed of a corona discharge wire 23 and a shield electrode 24 placed between the wires, and the upper part of the shield electrode 24 in the figure is normally closed. However, in this invention, it is opened so that the optical image 3 can pass through. Corona discharge wire 2
3 is supplied with a DC high voltage from the high voltage power supply 25, for example +5.7.
KV is applied.

On the other hand, the shield electrode 24 is normally grounded, but in this embodiment, a suitable DC voltage having the same polarity as the high-voltage power supply 25 is applied from the power supply 26, for example, a voltage of about +200V. It is assumed that the voltage applied from this power source 26 to the shield power station 24 is variable.

The potential of the electrostatic latent image formed on the photoreceptor 1 by simultaneously performing light image irradiation and corona discharge via the corona discharger 2 as shown in FIG. It was experimentally confirmed that the relationship shown in the figure is established. In addition, the relationship between the electrostatic latent @potential and the density of the original when an electrostatic latent image is formed by irradiating a light image at 11 after performing corona discharge using the conventional general method is shown in Figure 10. As shown, this electrostatic latent image is developed, transferred, and fixed to form L5.
The relationship between the density of the copied image and the original density is as shown in FIG. On the other hand, when an electrostatic latent image having the document density-electrostatic latent image potential characteristics shown in FIG. 3 was developed using the same developing agent and developing method, the relationship shown in FIG. 4 was obtained by 1q. This result can be evaluated as an extremely good reproduction of halftones.

Further, according to this embodiment, the shield electrode 2 is connected to the power source 26.
By changing the voltage applied to 4, the slope of the original density-electrostatic latent image potential characteristic shown in FIG. 3 changes, and accordingly, the slope of the original density-copied image density characteristic shown in FIG. 4 changes. Since the slope of the image also changes, the image density and contrast can be adjusted. As mentioned above, this method is extremely advantageous in terms of image density, contrast stability, and reproducibility compared to the conventional method using bias light. Of course, there is no need to consider the problem of misalignment between the optical image and the irradiation position of the bias light, which is the case when bias light is used, and therefore better image quality can be obtained.

FIG. 5 shows another embodiment of the present invention, in which a corona discharger 2 having a grid electrode 51 on the front surface is used, and a suitable DC voltage is applied to the grid electrode 51 from a power source 52. This is what I did. The purpose of applying voltage to the grid electrode 51 is the same as applying voltage to the shield electrode 24 in the previous embodiment, and in fact, +7.6 kV is applied from the high voltage power supply 25 to the corona discharge wire 23 to The electrode 24 is grounded and the grid electrode 51
When +400V was applied from the power supply 52 to , almost the same characteristics as shown in FIGS. 3 and 4 were obtained. In this embodiment, an appropriate voltage may also be applied to the shield electrode 24.

In the process of irradiating the photoreceptor 1 with a light image and performing corona discharge almost simultaneously in the present invention, it is not advantageous in obtaining a good image if the corona discharge slightly precedes the start of the irradiation with the light image and the corona discharge. Yes, but it's especially strict!
There is no need to decide which one should take precedence; it is sufficient if they are done at the same time.

On the other hand, in order to obtain a clear image, it is preferable that the photoimage irradiation and the corona discharge end at the same time, or that the corona discharge end a little earlier. That is, it is desirable that the photoimage irradiation and the corona discharge occur almost simultaneously, provided that the corona discharge is not performed at the same location on the photoreceptor after the photoimage irradiation is completed.

FIG. 6 shows an embodiment made in consideration of this point, in which a transparent insulating film 61 is attached to the tip of the shield electrode 24.
is provided. If the traveling direction (rotation direction) of the photoreceptor 1 is the direction shown by arrow A, by providing this transparent insulating film 61 on the front side in the traveling direction as shown in the figure, the irradiation of the optical image 3 is prevented. Region B and corona discharge region C can be conveniently controlled to meet the above conditions.

Furthermore, in the embodiment shown in FIG. 7, a grid electrode 71 is provided at approximately the same position as the transparent insulating film 61 in FIG. It is something.

Furthermore, in the embodiment shown in FIG. 8, the corona discharge region C is controlled by applying voltages under different conditions to each of the grid electrodes 81881b from the power sources 82a and 82b. For example, when applying a positive high voltage to the corona wire 23 to generate corona ions, the grid electric eU8
When 1a is grounded or a negative voltage is applied, no corona ions are observed to pass through the grid electrode 81a.

By the way, in general, it is not always desired to reproduce halftones when copying. For example, there may be cases where it is desired to copy a relatively low-density document, such as a document created with a pencil, into a high-density copy. In such a case, it is almost impossible to perform copying without causing so-called fog using conventional methods that allow reproduction of halftones. However, in the method of this invention, by making the voltage applied to the shield Rh and the grid electrode variable,
It can be easily adjusted to the desired concentration.

FIG. 9 shows the original density-copied image density characteristic showing this situation. Characteristic 91 is the same as the characteristic shown in FIG.
This is the case when +200V is applied to each, but when the shield electrode 24 is grounded, characteristic 92 is obtained. This characteristic 92
When the electrostatic groove @ potential is as follows, a copy image with high density and high contrast can be obtained. Further, when -100V is applied to the shield electrode 24, the characteristic becomes 93, which makes it possible to prevent gabbiness in the case of a document that gabbles easily, and also makes it possible to reproduce halftones to a certain extent.

As described above based on the embodiments, the method of the present invention allows an electrostatic latent image that enables reproduction of halftones to be obtained through extremely simple steps, and the density and contrast of the image can also be adjusted. Also, image density.

It has the advantage of excellent contrast stability and reproducibility.

In addition, in the above embodiment, a case was explained in which a photoconductor having a 5e-Te alloy deposited thereon was used as a photoconductor layer.
The present invention can be applied to other materials as long as the photoconductor consists of a conductive substrate and a photoconductor layer. The voltage to be applied should also be determined based on various conditions, and the values given in the examples are just examples.In addition, the present invention can be modified in various ways without departing from the gist.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a copying machine to which an electrostatic latent image forming method according to an embodiment of the present invention is applied, FIG. 2 is a diagram showing the configuration of main parts in the same embodiment, and FIG. FIG. 4 is a diagram showing the relationship between the original density and the electrostatic latent image potential in the same embodiment, FIG. 4 is a diagram showing the relationship between the original density and the copied image density in the same embodiment, and FIGS. FIG. 9 shows the relationship between image density and electrostatic latent image density when voltage is applied to various electrodes of the corona discharger in this invention. Comparative diagram, No. 10
This figure shows the relationship between image density and electrostatic latent image potential in the conventional method, and FIG. 11 is a diagram showing the relationship between image@density and copied image density. 1... Photoreceptor for electrophotography, 2... Corona discharger, 3
... Light image, 4... Light source, 5... Original, 6... Optical system, 7... Developing device, 8... Transfer paper storage cassette, 9... Transfer charger, 10...・Fuser, 11・
...Cleaning device, 12...Erasing lamp, 21.
... Conductive substrate, 22... Photoconductor layer, 23... Corona discharge wire, 24... Shield electrode, 25...
High voltage power supply, 26... Power supply, 51... Grid electrode,
52... Power supply, 61... Transparent insulating film, 71
... Grid electrode, 72 ... Power supply, 81a, 81b
...grid 1ftffi, 82a, 82b...power supply. Applicant's agent Patent attorney Takehiko Suzue Figure 4 0. ') 10 1.5! , Calamity I
L Fig. 5 Fig. 6 Fig. 7 Fig. 9 Fig. 9 0.5 +, 5 1.5 & k

Claims (2)

[Claims] (1) In a method of forming an electrostatic latent image on an electrophotographic photoreceptor consisting of a conductive substrate and a photoconductor layer, the photoreceptor is almost irradiated with a light image and corona discharge from a corona discharger. At the same time, applying a voltage to the shield electrode or the grid electrode or both of the corona discharger,
A method for forming an electrostatic latent image, characterized in that the voltage is variable. (2) The irradiation of the photoreceptor onto the photoreceptor and the corona discharge from the corona charger are performed almost simultaneously on the condition that the same location on the photoreceptor is not charged after the irradiation of the photoreceptor is completed. A method for forming an electrostatic latent image according to claim 1.