JPS59178462A - Latent image forming drum - Google Patents

Abstract

PURPOSE:To obtain a secondary latent image having high image quality and high characteristic uniformly over the entire part of a drum-shaped image receiving body by forming the image in such a way that the difference in the distance between a screen photosensitive body and the image receiving body at the central art and both end parts of the drum is eliminated. CONSTITUTION:An image receiving drum E is so formed as to have the sectional shape in which both ends thereof are curved to the radius larger by 50-500mu than the radius in the central part. Then the drum can be made to conform to the shape of the displacement when the screen drum is impressed thereon with a bias and the specified space between the central parts and both ends of both drums is maintained. The bias voltage to be impressed on the screen drum is thus increased and the quality and characteristic of the transferred image are improved. Since the central parts and both end parts have the same space, the image which is uniform over the entire surface is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image forming drum used in screen electrophotography using a screen photoreceptor having a large number of fine apertures.

Using a screen photoreceptor, electrons modulate the corona ion flow based on the primary latent image, which is an electrostatic image, formed on the screen, and form a secondary latent image, which is also an electrostatic image, on the recording member. Various photographic methods are known. In such an electrophotographic method, secondary latent images can be formed many times from a single primary latent image formed on a screen photoreceptor, and therefore many copies can be obtained from one image exposure. It has the advantage of being However, the number of copies obtained from the primary latent image formed on the screen photoreceptor is controlled by the attenuation of the primary latent image and is a finite value if the screen photoreceptor has poor charge retention properties. It also has a large number of fine openings, as shown in JP-A-50-19455 and JP-A-51-341, and has a photoconductive layer and a surface insulating layer provided on a conductive base. When using a photosensitive screen with the basic cross-sectional shape, a primary latent image is formed on the insulating layer, so the attenuation of the formed latent image charge is extremely small, and the modulation corona source side Because of the presence of the conductive member, during modulation, excessive or unnecessary modulating corona will flow away from the conductive member and will rarely have an adverse effect on the primary latent image, but a small amount may circulate around the screen photoreceptor.
The primary latent image on the screen photoreceptor is gradually canceled out, which limits the number of copies that can be repeated.

Conventionally, in order to increase the number of copies, research has been conducted on methods to control the modulation corona ion flow in response to the attenuation of the primary latent image potential and the decrease in modulation ability due to the influence of the modulation corona. As the amount of secondary corona ion flow increases, the modulation ability due to the modulating corona shadow becomes more significant and eventually adjustment becomes impossible.

The above-mentioned screen electrophotography method will be explained in detail below with reference to the drawings.

FIG. 1 is a sectional view showing the structure of an example of a screen photoreceptor used in the above screen electrophotography method. A screen photoreceptor 1 shown in FIG. il1 has a photoconductive layer 3 provided on a conductive substrate 2 having a large number of openings, and an insulating layer 4 formed on the photoconductive layer. FIGS. 2 to 5 show an example of the process of forming primary and secondary latent images by screen electrophotography.

Figure 2 shows the primary voltage application process performed on the screen photoreceptor.
Figure 3 shows the image irradiation and secondary voltage processing process, and Figure 4 shows the entire surface irradiation process, and the secondary electrostatic process is performed by modulating the ion flow using the primary electrostatic latent image of the screen formed in each of the above steps. The electrolatent image forming process is shown in FIG.

FIG. 2 shows the primary voltage application process, in which the screen photoreceptor 1 is uniformly charged with positive (+) polarity by a corona discharger 5 as a voltage application means. Due to the above-mentioned charging, the surface of the insulating layer 4 is charged with positive polarity, and due to this charging,
In the vicinity of the insulating layer 4 of the photoconductive layer 3, a negative charge layer having a polarity opposite to that of the above charge is formed. Note that if the interface between the photoconductive layer 3 and the conductive substrate 2 and the photoconductive layer have a rectifying property such that majority carriers are injected but minority carriers are not injected, the injection causes the above-mentioned effect even in the dark area. It is possible to form a charge layer in the vicinity of the insulating layer 4 in the photoconducting layer 3, such as the one shown in FIG. Items that do not have the above rectifying properties or 1
In the case where a charge layer as described above is not formed by application of a voltage, charging is carried out as described in US Pat. No. 2,955,938, in which the insulating layer is charged in a bright area.

FIG. 3 shows the results of simultaneously performing image irradiation and a secondary voltage application process on the screen photoreceptor 1 that has undergone the above-mentioned primary voltage application process. Note that 6 in the figure is an original image, the D side shows a dark part, the L side shows a bright part, and an arrow 7 shows light from a light source (not shown). 8 is a corona discharger for applying a secondary voltage, and in the figure, corona discharge from a corona wire to which a DC voltage of negative (-) polarity is applied reverses the surface potential of the insulating layer 4 to negative polarity. It is polarly charged.

When the surface potential of the insulating layer 4 is made negative as described above, the substance of the photoconductive layer 3 becomes conductive on the bright side due to image irradiation, and as a result, the surface potential of the insulating layer 4 becomes negative. However, on the dark side, because of the negative charge layer existing on the insulating layer 4 side of the photoconductive layer 3, the charge on the surface of the insulating layer 4 remains positive.

Here, considering the polarity change rate of the potential on the insulating layer 4 of the screen 1 in the above process, the corona discharger 8 of the insulating layer
The portion facing the surface (front side) changes fastest, and the substantially side portions that sandwich this facing portion and constitute the opening change later. Therefore, in the image irradiation section, the conductive substrate 2
The potential on the exposed side surface is the potential of the conductive substrate 2,
The potential becomes gradually higher from the back side to the front side.

Figure 4 shows the results of uniform exposure as a whole-surface irradiation process on the entire surface of the screen 1 that has undergone the image irradiation and secondary voltage application processes, and arrow 9 in the figure shows the me light from the light source. . Due to this entire surface irradiation, the potential on the dark side of the screen photoreceptor changes to a potential proportional to the amount of charge on the surface of the insulating layer 4.

FIG. 5 shows a state in which the ion flow is modulated by the primary latent image to form a secondary latent image on the image receptor. In the figure 1
0 is the corona wire of the discharger, 11 is the counter electrode member, 12
is an image receptor such as a paper film which is a chargeable surface, and a secondary latent image is formed on this surface.

Reference numerals 13 and 14 denote a power supply unit that forms an electric field between the corona wire and the image receptor 12 in the direction in which corona ions flow. The image receptor 12 is placed close to the side of the screen photoreceptor facing the insulating layer 4, and an ion current is applied to the image receptor 12 from a corona wire 10 placed through the screen photoreceptor. At this time, an electric field due to the primary latent image of the screen photoreceptor acts, that is, an electric field that blocks the negative ion flow shown by the solid line α acts on the bright side of the image, and an electric field that accelerates the ion flow shown as the solid line β acts on the dark side. acts. As a result, a secondary latent image is formed on the image receptor 12 in the state of a positive image of the original image.

An example of an electrophotographic apparatus using such a screen electrophotography method is shown in FIG. In FIG. 6, numeral 1 indicates a screen photoreceptor as shown in FIG. 1, and in FIG. 6, this screen photoreceptor has a cylindrical shape. 5 is the second
8 is the corona discharger shown in FIG. 3, 10 is the corona discharger with the corona wire shown in FIG. 5, and 11 and 12 are the counter electrode member and image receiver shown in FIG. Show your body.

In the electrophotographic apparatus shown in FIG. 6, an image of a document 15 is formed on a screen photoreceptor 1 by an optical system 16,
A primary electrostatic latent image is formed on the screen photoreceptor 1 by the processes shown in FIGS. 2, 3, and 4. Image receptor 12
is supplied from a cassette 17, and a secondary latent image is formed on the image receptor 12 as shown in FIG. It is ejected outside the aircraft.

Separately from the above secondary image forming, a corona discharger 20 and a counter electrode member 21 are provided via the screen photoreceptor l, and the distance between the screen photoreceptor l and the counter electrode member 21 is set at 2 to 6 degrees. The electric field between the screen drum and the counter electrode member is set at 1.5 k'V/mm to 2.5 kV/l.
By adjusting the value within the range of an and passing a corona ion flow through the screen, the number of copies per copy can be dramatically increased.

Conventionally, when forming this secondary latent image, the smaller the distance between the screen photoreceptor and the image receptor, the better the reproduction of the original image, especially when the screen photoreceptor and image receptor are shaped like cylindrical drums. When the curvatures of the two are different, if the distance between the two is large, the length of the formed secondary latent image in the circumferential direction may not match the primary latent image, which is an undesirable phenomenon. Furthermore, when forming a secondary latent image, the screen photoreceptor is drawn toward the image receptor due to the electric field caused by the application of a noisy voltage between the screen photoreceptor and the image receptor, and the distance between the screen photoreceptor and the image receptor decreases. change.

This is called the amount of displacement, and this amount of displacement increases as the electric field becomes stronger. Furthermore, since the displacement due to the bias electric field differs depending on each part of the screen photoreceptor, the actual bias electric field increases by the amount due to this displacement, creating a difference between each part of the screen. This difference is large at the center of the screen photoreceptor and becomes smaller toward both ends. The difference between the former and the latter is 5()-300μ, and this difference affects the bias voltage.

In other words, the center part where the difference between the screen photoreceptor and the image receptor is reduced is less likely to be biased than both ends, and even if both ends can withstand the applied voltage, the center part will cause discharge. For this reason, only a low bias voltage can be applied, even though it is preferable for characteristics and image quality to use a bias voltage as high as possible.

As described above, when the screen photoreceptor and the image receptor are constructed of cylindrical drums, the present invention eliminates the difference in distance between the screen photoreceptor and the image receptor at the center and both ends of the drum, thereby increasing the bias voltage. An electric field can be applied to the entire drum-shaped image receptor, providing uniform high image quality.
The purpose is to obtain a secondary latent image with high characteristics.

For the above purpose, the present invention modulates a corona ion flow by a primary electrostatic latent image formed on a screen photoreceptor, and forms a secondary electrostatic latent image on a secondary latent image forming drum by the corona ion flow. To provide a latent image forming drum used in a screen electrophotographic system, characterized in that the drum has a curved cross-sectional shape in which the radius at both ends is larger than the radius at the center.

The present invention will be described below with reference to FIGS. 7 to 9.

FIGS. 7(a) and 7(o) are side and front views showing a conventional arrangement of a screen drum A that forms a primary electrostatic latent image and an image receptor drum B that forms a secondary electrostatic latent image. It is. The drum A is provided with a screen C, and a corona discharge device for latent image transfer is arranged inside the screen C. The drum B is made of a conductive member and an insulating member, and is formed, for example, by applying the insulating member onto an aluminum cylinder using a dipping method or a spray gun and curing it using heat or ultraviolet rays.

In the apparatus shown in FIG. 7, in the state before operation, a constant distance, for example, 2 m, is maintained between drum A and drum B, and at points indicated by F and G in the figure, a certain distance is maintained between drum A and drum B. The spacing is equal.

However, when a bias voltage is applied to the drum A for image formation, the screen IJ-C is pulled toward the drum B by the action of the electric field, and the distance between the screen C and the drum B changes. This state is shown in FIG. As shown in FIG. 8, the displacement due to the bias electric field is large at the center and becomes smaller toward both ends. In the illustrated example, before operation, the distance between the screen C of drum A and drum B is 2fKIn at both points F and G, but 3 kV is applied to drum A.
When applying a bias of
~1.95am. Therefore, when the bias voltage is further increased and 35 kV is applied to drum A, the distance from drum B further approaches 1.5 to 1.6 at point F, and screen C
A leak begins between drum B and drum B. In other words, the seventh
A bias of 3.5 kV cannot be applied to the drum configuration shown in the figure.

FIG. 9 shows one embodiment of a receiver drum according to the present invention. As shown in the drawing, the image receptor drum E according to the present invention has a curved cross-sectional shape in which the radius at both ends is 50 to 500 microns larger than the radius at the center. In the illustrated example, this difference is indicated by H, and the preferred range of this degree of curvature is H of 50 to 500μ.

Continuing with the example described with reference to FIGS. 7 and 8, using the drum configuration of FIG.
．． Even if a 5 kV bias is applied, the distance between screen C and drum E at point F remains almost 2 meters, and at point G it is still 2 meters, and there is no leakage. Therefore, images with high quality and high characteristics can be obtained.

If the distance between the screen drum A and the image receptor drum E is set to 1 mm in box 9 in the above embodiment, the bias voltage that can be applied to the screen drum without leaking will be approximately halved, but as the distance becomes shorter, the characteristics will also change. Image quality also improves.

In this case, the amount by which the screen is displaced by applying a bias to the screen drum can be measured using a micro-displacement meter using eddy current, so by making the central part of the image receptor drum concave in accordance with the amount of displacement, the bias can be applied. It is possible to maintain the same spacing between the center and both ends even if . It is also possible to further improve the accuracy and set the interval between the drums to 0.5w11.

As explained above, in the present invention, by making the central part of the image receptor drum concave by 50 to 500 μm, it is possible to match the displacement shape of the screen drum when bias is applied. It is possible to keep the spacing constant. This makes it possible to increase the bias voltage applied to the screen drum, which has the effect of improving the image quality and characteristics of the transferred image, and because the spacing is the same in the center and both ends, a uniform image can be obtained over the entire surface.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of a screen photoreceptor used in a screen electrophotographic method, and FIGS. 2 to 5 show sequential processes of the electrophotography method using the screen photoreceptor shown in FIG. 1. Figure 6 shows an example of an electrophotographic apparatus for performing electrophotography, and Figures 7 (a) and (b) show the relationship between the screen drum and image receptor drum in the screen electrophotography method described above. A side view and a front view, FIGS. 8(A) and 8(B) are diagrams showing a state in which a bias voltage is applied to the screen drum and image receptor drum shown in FIG. 7, and FIG. 9 is a diagram showing one embodiment of the present invention. FIG. 3 is a front view showing the relationship between the image receptor drum and the screen drum shown in FIG. DESCRIPTION OF SYMBOLS 1... Screen photoreceptor, 2... Conductive substrate, 3... Photoconductive layer, 4...
Insulating layer, 5...Corona discharger, 6...Original image, 8...Corona discharger, 10...Corona discharger, 11...Counter electrode, 12...Image receptor, 13. 14...power supply section, 15...manuscript,
16...Optical system, 17...Cassette,
18...Developer, 19...Fixer,
A... Screen drum, B... Image receptor drum,
C...Screen, D...Corona discharger, E
...Image receptor drum. r-“Agent Teru Taniyama J~ Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 1 □- Mourning Figure 6 J-2:

Claims (1)

[Claims] Used in screen electrophotography, in which the corona ion flow is modulated by the primary electrostatic latent image formed on the screen photoreceptor, and this corona ion flow forms a secondary electrostatic latent image on the secondary latent image forming drum. 1. A latent image forming drum characterized in that the latent image forming drum has a curved cross-sectional shape in which the radius at both ends is larger than the radius at the center.