JPS60209750A - Formation of electrostatic latent image - Google Patents

Abstract

PURPOSE:To reduce minute potential unevenness of an electrostatic latent image and to improve graininess and gradation of an obtained image by executing secondary electrostatic charging with a power supply of DC in the same polarity or DC-superposed AC, and uniformly exposing a photosensitive body with an illuminance not above that given to the body corresponding to the white background part of an original at the imagewise exposure. CONSTITUTION:The photosensitive drum 1 is provided with the surface of a photosensitive body composed of a conductive substrate 1a' and a photoconductive layer 1b' and rotates in the arrow direction. The drum 1 is uniformly positively charged on the photoconductive layer 1b' with a primary charging corotron 3. Then, it is subjected to secondary charging with a secondary charging corotron 4 positively same in polarity as the primary charging, while it is exposed 2 to an optical image, and further, it is uniformly exposed with an exposure lamp 11 with an illuminance not above that given through the white background part of the original at the time of exposure. The electrostatic latent image thus formed on the surface of a photosensitive body is processed with a developing step and a transfer step to give a toner image on a transfer paper, and it is fixed to obtain a desired copy.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an electrophotographic electrostatic latent image forming method, and more specifically to an electrophotographic electrostatic latent image forming method that produces copies with improved graininess and gradation. The present invention relates to a latent image forming method.

Conventional methods for making copies using electrophotographic technology include a charging process in which the surface of a photoconductive photoreceptor is uniformly charged, and an optical image of the original is exposed onto the photoreceptor to form an electrostatic latent image of the original. There is a so-called Carlson method, which consists of an exposure step, a developing step of developing an electrostatic latent image with toner, and a fixing step of transferring the obtained toner image onto a transfer paper and fixing the toner image transferred onto the transfer paper. However, the copies thus obtained from moths are not satisfactory in terms of graininess and gradation;
NP using a photoreceptor with a six-layer structure consisting of a conductive support (1a), a photoconductive layer (lb) and a transparent insulating layer (1c)
In the method (see Figures 1 and 2), a photosensitive drum (1) having this photoreceptor on its surface and rotating in the direction of the arrow is coated with a transparent insulating layer (1C) by a primary corotron (3).
For example, the upper surface is uniformly charged to ■ (Fig. 2 (I)) - Then, while irradiating a light image (2), a secondary charging corotron (4) is used to charge 2 to θ, which is the opposite polarity to the one. Figure 2 (1)
)), and then uniformly exposed to light using an exposure lamp (111) (Fig. 2 (1)) = The electrostatic latent material thus obtained on the surface of the photoreceptor is developed using a developer α value, and a corotron (111) is used before transfer. 5) and a transfer corotron (6) to transfer the developed image on the surface of the photoreceptor to the transfer paper sent onto the paper conveyance path <8), and fix it in the fixing device (9). The toner remaining on the surface is removed by a cleaner (7) and the photoreceptor enters the next imaging step. Koushi C
The obtained copies are improved in gradation, but are inferior in graininess1. A method has been developed in which after exposing the photoconductive layer to form an electrostatic latent image, the entire surface of the photoconductive layer is uniformly exposed to light of approximately 2 to 20 L x 8 ec, and this method eliminates the error-magnetic effect. A copy with improved gradation can be obtained, but the graininess deteriorates due to warping.Objective of the Invention The purpose of the present invention is to improve the problem of graininess and/or poor gradation in conventional electrophotographic methods. An object of the present invention is to provide a method for forming an electrostatic latent image.

Structure of the Invention The above-mentioned object of the present invention is to provide electrophotography in which a photoreceptor comprising a conductive substrate and a photoconductive layer is used, and the photoreceptor is subjected to primary charging, secondary charging at the same time as image exposure, uniform exposure, and development. In the method, secondary charging is performed using a DC or DC superimposed AC power source with the same polarity as the primary charging, and the amount of light for uniform exposure is equal to the illuminance of the white background of the document during image exposure. This is accomplished by forming an electrostatic latent image by lowering the image.

The method of the present invention will be explained with reference to FIGS. 1 and 6.
The photoconductive layer (I
b') Evenly press on the top (Fig. 6 (■)). .

Next, while irradiating the optical image (2), the secondary charged corotron (4)
) is secondarily charged to the ■ of the same polarity as the sea turtle and Figure 6 (
(2))), and then further uniformly exposed using an exposure lens Uυ at a light intensity that is less than the illuminance of the white background area of the document at the time of image exposure (Fig. 6 (I)).
)) If the illuminance is higher than that of the white background of the original, the Seidenko 1 image will disappear. The electrostatic latent image thus obtained on the surface of the photoreceptor undergoes development and transfer steps to form a toner image on transfer paper, which is then fixed to obtain a desired copy. In this way, by performing secondary charging using direct current or direct current superimposed alternating current of the same polarity as the primary charging according to the method of the present invention, minute potential unevenness of the electrostatic latent image on the surface of the photoreceptor is reduced and the graininess of the copy is improved. In addition, gradation can be improved by uniformly exposing the image with an amount of light that is less than the illuminance of the white background portion of the document during image exposure. The potential pattern and electric field pattern on the photoreceptor surface due to image exposure simultaneous secondary charging in the method of the present invention are schematically shown as the potential pattern and electric field ξ-turn on the photoreceptor surface according to the conventional Carlson method or NP method. As shown in Fig. 4, Fig. 4 (5) and (E are the potential pattern and electric field on the photoreceptor surface by Carlson method or NP method.
Figure 4 (Q and (Dl +'t) shows the state of each pattern due to the image exposure simultaneous secondary charging mechanism of the method of the present invention, and the dashed line in the tq diagram indicates the turn of the turn. It corresponds to the solid line pattern, and it can be seen from Figure 0 that the method of the present invention has improved the image gradation across the image and non-image areas. It can be seen that the electric field pattern obtained by the inventive method has a more uniform distribution of toner than the electric field pattern obtained by the conventional method, and it is possible to obtain copies with excellent graininess. Figure 6 shows the brightness attenuation curves of electrostatic images formed by the Carlson method and the NP method. Figure 6 shows the Carlson method, the Carlson method with a secondary charging process added on the same photoreceptor, and the present invention. From FIGS. 5 and 6, which show the bright decay curves of electrostatic latent images formed by each method, the method of the present invention shows that the linearity of the bright decay curve is higher than that of the conventional method. The present invention will now be explained in more detail by way of one or more examples in which it will be seen that the gradation of the resulting copies is improved.

Example 1 A first method using a photoreceptor consisting of a conductive support and a photoconductive layer
Using the equipment shown in the figure, charging, image exposure simultaneous secondary charging,
Copies of good image quality were obtained by uniform exposure, uniform development, transfer and fixing.

In addition, the secondary electrification is caused by the awakening pressure applied to the cocitron wire: 11.5
Kv (DC), 40 oHz:, 3. OKV (AC
(7) Using direct current superimposed alternating current, the distance between the corotron wire and the photoreceptor surface was set to 15 mm, and uniform exposure was performed such that the photoreceptor surface illuminance was 201 wx-sec.

Example 2 A copy with good image quality was obtained in the same manner as in Example 1 except that secondary charging was performed using a screen grid corotron under the following condition 1. Corotron wire applied voltage: +4
．． OKV (DC), screen green P applied voltage: +
40 (1 (DC)), distance between corotron wire and photoreceptor surface: 15 mm, distance between screen grit P and photoreceptor surface: 4 mm.

The results of the self-confidence evaluation of the copies obtained in Examples 1 and 2 are as follows.

granular? 5. 2 Gradation f　O, 61, 0 Yellow Carlson method (secondary charging, no uniform exposure).

++ The smaller the number, the better the image quality. Graininess was evaluated on a scale of 1 to 5.

Measurement of square gradation was performed using dynamic range.

Effects of the Invention According to the method of the present invention, in forming an electrostatic charge on a photoreceptor consisting of a conductive substrate and a photoconductive layer, after the second charge, a direct current of the same polarity as the next force is applied. ' or a secondary band ' due to direct current superimposition current is carried out at the same time as image exposure, and then by uniformly illuminating with a light intensity that is less than the illuminance of the sunny area of the document at the time of image exposure, minute potential unevenness in the electrostatic It image is eliminated. The effect is that the graininess of the resulting copy is significantly improved (secondary charging effect), and the potential in the shadow area is reduced, which greatly improves the gradation of the image area (uniform exposure effect). can get. .

[Brief explanation of drawings]

FIG. 1 is a diagram showing a schematic representation of the apparatus used in the method of the present invention, FIGS. Figures (I), (It), ([
) is a diagram for explaining the principle of electrostatic a-image formation according to the method of the present invention; FIG.
Figures (Q and (0) are diagrams showing the potential pattern and electric field pattern on the photoreceptor surface according to the method of the present invention, Figure 5 is a bright decay curve diagram of the photoreceptor surface potential according to the NP method and Carlson method, and Figure 6 is a diagram showing the bright decay curve of the photoreceptor surface potential according to the Carlson method. , a bright attenuation curve of the photoreceptor surface potential according to the Karun method twelfth band and the method of the present invention.Symbol in the figure = 1...photosensitive drum, 1a, 1a'... conductivity Substrate, 1b, 1b'...photoconductive layer, 1
C: Transparent insulating layer, 2: Emitted light, 3: -order charged corotron, 4: Secondary @ cage corotron, 5, ψ, pre-transfer corotron, 6: transfer corotron, 7... ... Cleaner, 8 ... Paper conveyance path, 9 ... Fixing device, 10
...Developer, 11...Ichimon Fukimitsu Unzo. Figure 1 Figure 2 Round 3 Figure 4 Figure 5 Figure 0.2 0.4 0.6 0.8 1.0 12 +,
4-thick stripe density 0.2 0.4 0.6 0.8 1.0 +, 2 1
．． 4R draft, M.

Claims (1)

[Claims] In the electrophotography method, which uses a photoreceptor that is powered by a conductive substrate and a photoconductive layer, the photoreceptor is subjected to primary i-electrification, secondary charging at the same time as image exposure, uniform exposure, and development. 1. A method for forming an image using a static image forming method, characterized in that the method is performed using a direct current or direct current superimposed alternating current power source having the same polarity as that of charging, and that the amount of light for uniform exposure is lower than the illuminance of a white background area of a document at the time of image exposure.