JPH0314185B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an electrophotographic method, more specifically,
This invention relates to an electrophotographic method that can perform stable charging. A photoreceptor in which a photosensitive layer and an insulating layer are successively laminated and integrated on a conductive substrate is considered to be very useful due to its effect of protecting the surface of the photosensitive layer, for example, and many proposals have been made in the past. When the photoreceptor is used repeatedly, the technique for handling the residual charge on the surface of the insulating layer is a key issue, and the process is significantly different from that in the case of using a photoreceptor without an insulating layer. A typical process is, for example, US Patent No.
This is typified by No. 3041167, and below:
The outline will be explained with reference to the drawings. FIG. 1 shows the structure of the photoreceptor. 11 represents a conductive substrate, 12 represents a photoconductive layer, and 13 represents a transparent insulating layer. FIGS. 2a to 2c show a method of forming a latent image using the photoreceptor described above. In FIG. 2a, the surface of the insulating layer of the photoreceptor is primarily charged using a corona charger. The photoreceptor is P like Se.
In the case of a type semiconductor, it is desirable that the primary charge be negative, and in this case the surface of the insulator layer will be negatively charged. When negative charges are placed on the insulator layer, positive charges are injected into the photosensitive layer from the substrate side and captured inside the photoconductive layer near the boundary between the photoconductive layer and the insulator layer, resulting in the state shown in Figure 2a. make. In this case, since there is no injection blocking layer between the conductive substrate and the photosensitive layer, or the injection blocking layer is small, charges are easily injected from the substrate side. On the other hand, if no charge is injected from the substrate side, the photoconductive layer can transport both positive and negative charges, and if light is absorbed by the entire photoconductive layer, the primary charging and the above-mentioned primary charging occur simultaneously. Alternatively, a state similar to the above state can be brought about by immediately uniformly exposing the photoreceptor to light. Next, in order to leave a charge only on the interface between the photoconductive layer and the insulator layer, as shown in Figure 2b, a charger is used in a dark place to charge the polarity opposite to the primary charge, that is, in this case, the positive polarity. At 2
Next, apply electrification. The charge on the surface of the insulator layer is removed by secondary charging, creating the state shown in FIG. 2b. After secondary charging, when image exposure is performed as shown in Figure 2c, the positive charges existing between the photoconductive layer and the insulating layer are discharged due to photoconductivity in the exposed areas, and the positive charges remain in the dark areas, causing latent charges. It becomes a statue. In this method, it is possible to make the charge on the insulator layer positive or negative by appropriately adjusting the strength of the primary and secondary charges, and the electrostatic contrast can be freely selected. . When the photoreceptor is repeatedly used in this method, it is necessary to erase both the charge remaining on the surface of the insulating layer and the charge remaining inside the photoreceptor layer before uniformly charging the photoreceptor. In this case, in the case of a conventional photoreceptor without an insulating layer, it was possible to discharge the photoreceptor only by light irradiation, but in order to eliminate the charge on the surface of the insulating layer, an additional static eliminator is required. It is preferable to eliminate static electricity inside the photoreceptor at the same time as eliminating static electricity from the insulating layer. Even if such static elimination is performed, if the latent image formation static elimination process is repeated for a long period of time, the internal charge of the photoconductor and the surface charge of the insulator layer cannot be sufficiently eliminated, and as a result, In particular, a phenomenon is observed in which the potential of non-image areas (bright areas = exposed areas) gradually increases. If the potential of the non-image area gradually increases, each time the phenomenon cycle is repeated, stains (fogging) will occur in the non-image area and the quality of the image will be significantly degraded. Therefore, in order to prevent the potential of the non-image area from increasing, the applicant has adjusted the strength balance of primary charging and secondary charging.
An application was previously filed for an invention in which correction is automatically made according to each other's intensities without using any detection means (Japanese Patent Application No. 5824/1983). This is done by electrically insulating the shield electrode and discharge electrode of each of the first corona charger and the second corona charger, and the power source that applies DC or AC voltage to these chargers from other devices, and An electrophotographic charging device in which a corona charger and a shield electrode of a second corona charger are electrically coupled, and one end of a power supply is electrically coupled to a discharge electrode and the other end is electrically coupled to a shield electrode. Since the first corona charging current value and the second corona charging current value can be made equal in absolute value with different numbers, a charging device in which the first corona charger and the second corona charger are provided independently. Compared to the above, it is possible to suppress the increase in the potential of the non-image area to a large extent, and stable charging can be performed. However, even if this charging device is used, as long as a method is adopted in which after toner development, the toner image is transferred to paper using an electric field, and then the photoreceptor is uniformly exposed and static electricity is removed at the same time. It is not possible to prevent the increase in the potential of the exposed area immediately before charging due to repeated processes, that is, the increase in the potential difference between the exposed area and the non-exposed area, and as a result, a pre-image effect appears, and this effect is noticeable during continuous copying. As a result, the stability of the copying cycle is impaired and fogging becomes noticeable. The inventors of the present invention have conducted further research and found that when using the above-mentioned charging device, after the development of the previous process is completed,
Applying a transfer electric field after uniformly exposing the unexposed area inside the photosensitive layer to the exposed area potential,
Next, by removing the surface charge of the insulating layer, the potential of the non-exposed area increases before entering the next process.
In other words, the present invention has been completed by discovering that it is possible to prevent the difference in potential between the exposed area and the non-exposed area from increasing. Therefore, an object of the present invention is to provide electrophotography that can prevent the residual potential in the non-image area (background area) of the photoreceptor from increasing with the copying cycle, and in which the residual charge on the photoreceptor does not vary locally. The purpose is to provide a method. An object of the present invention is to use a photoreceptor having an insulating layer on its surface to apply a DC or AC voltage to the shield electrode, discharge electrode, and these chargers of each of a first corona charger and a second corona charger. The power source is electrically insulated from other devices, the shield electrodes of the first corona charger and the second corona charger are electrically coupled, and one end of the power source is connected to a discharge electrode and the other end is connected to a shield electrode. In an electrophotographic method that sequentially repeats an electrostatic latent image forming step, a developing step, and a transfer step in which image exposure is performed after being charged by an electrically coupled charging device, the step of uniformly exposing the surface of a photoreceptor after development and prior to transfer. This can be achieved by an electrophotographic method characterized by comprising the following steps: and a step of removing the surface charge on the photoreceptor prior to recharging after transfer. In order to repeat copying continuously, after forming, developing and transferring an electrostatic latent image, the charge on the photoreceptor is discharged in preparation for the next copying cycle. A photoconductor having an insulating layer on its surface must eliminate not only the charge inside the photoconductor but also the charge on the insulating layer. For this reason, the conventional static elimination method is as shown in FIG.
4 was disposed between the transfer corotron 5 and a cleaning device 8 for removing residual toner from the surface of the photoreceptor. As the first charger 2 and the charger 3, shield electrodes 22 and 32 are electrically coupled together as shown in FIG.
A charging device is used in which the charging device is electrically coupled to the charging device and the entire charging device is electrically insulated. When this charging device recharges the photoreceptor 1 that has been neutralized by the above-described static eliminator, the recharging is locally unbalanced even though the charging value is the same on average. Therefore, in the present invention, instead of the conventional static eliminator, a static eliminator and a static eliminator are provided independently before and after the transfer process. FIG. 5 shows a schematic sectional view of the apparatus used in the method of the present invention. In other words, in this device, the static elimination lamp 1
5 is disposed between the developing device 9 and the transfer corotron 5, and a static eliminator 16 is disposed between the cleaning device 8 and the transfer corotron 5. In the method according to the present invention, after development by the developing device 9, charges in the photosensitive layer are removed prior to transfer by a transfer corotron, and charges on the insulating layer are removed by a static eliminator 16 prior to recharging after transfer. This is to eliminate static electricity from the photoreceptor. By performing recharging after static electricity removal in this manner, uniform charging without local variations can be obtained, and a copy without the foreground image effect can be obtained. Static eliminator 1 used in the conventional method shown in Fig. 3
In case 4, in the static elimination area, the charge inside the photoconductor disappears by uniform exposure, and then the charge on the insulator layer is gradually eliminated, but before it becomes completely uniform, the photoconductor Since it passes through this region, it becomes difficult to uniformly remove the charges on the surface of the insulating layer, and the uneven residual charges from the previous process remain on the surface of the insulating layer. In this state, even if the charging device shown in FIG. 4 performs recharging so that the absolute values of the inflow currents from the corotron wires 21 and 31 are equal, the residual potential from the previous process remains on the surface of the insulator layer. If it exists, the surface of the insulating layer will not be uniformly charged, which is considered to cause a pre-image effect or the like. In the method of the present invention, the charges in the photosensitive layer are removed before transfer, so it is thought that such an effect does not occur. The wavelength and light intensity of the charge eliminating lamp 15 used in the present invention for uniformly exposing the photoreceptor to light are determined so that the charges inside the photoreceptor can be removed. Further, as the static eliminator 16 for removing charges on the surface of the insulating layer, a static eliminating corotron or a static eliminating roller can be used. A preferred static eliminator is a static eliminator corotron to which an alternating current voltage is applied. The present invention will be explained below with reference to comparative examples and examples. Comparative Example As shown in FIG. 3, an Se-based photoreceptor 1 having an insulating layer 13 on its surface was used, and the photoreceptor was charged with negative corona as primary charging and positive corona as secondary charging. At this time, as the primary charger 2 and the tertiary charger 3, those with the wire connections shown in FIG. 4 were used. Next, image exposure was performed through the slit 4 to form an electrostatic latent image, which was developed using the magnetic brush developing device 9. After the toner image is transferred to the transfer paper by the transfer corotron 5, the charge on the photoreceptor is removed by a static eliminator 6 to which an alternating current is applied.
A static eliminator 14 consisting of a static eliminator (a static eliminator corotron) and a static eliminator lamp (tungsten lamp) 7 removed static electricity, and a cleaning device 8 removed toner remaining on the surface of the photoreceptor. The potential change and charge state of the photoreceptor at this time are shown in FIG. 6-A and FIG. 7-A, respectively. In the figure, a
is negative charging, b is positive charging, c is image exposure, d is transfer, and e is charge removal. In the figure, the solid line represents the potential of the non-exposed area M, and the broken line represents the potential of the exposed area L. Negative charging is performed at a, positive charging is performed at b,
After holding a positive charge in the photoconductive layer near the interface between the insulating layer 13 and the photoconductive layer 12, imagewise exposure is performed at c, the charge in the exposed area disappears, and the potential drops. The potential between the non-exposed parts becomes non-uniform (6,7-Ac). In this state, during subsequent transfer, more charge is supplied to the surface of the insulating layer to the exposed area than to the non-exposed area because the transfer corotron 5 discharges so that the potentials of the unexposed area and the exposed area are as equal as possible. It will be done. (Figure 7-A d).
As a result, the charge removal device 16 performs uniform exposure and simultaneous charge removal, but as shown in Fig. 7-A e,
The residual charges on the surface of the insulator layer in the exposed area and the unexposed area have opposite polarities, and the potential at this time is lower in the unexposed area. Also, when the latent image potential was measured, the initial charging potential after the secondary charging was +
900V, and the residual potential after static electricity removal is + at the exposed part.
50V, the unexposed area showed -70V, and there was a difference of 120V. When the copying material was further recharged and copied, a pre-image effect appeared in the obtained copy, and unevenness occurred in the image density and background density. Example 1 This example uses the conventional static eliminator 6 described in the comparative example.
As shown in FIG. 5, instead of the static eliminator 14 consisting of the static eliminator 7 and the static eliminator lamp 7, a static eliminator lamp (tungsten lamp) is installed between the developing device 9 and the transfer charger 5.
15, and a static eliminating corotron to which alternating current was applied was provided as a static eliminating device 26 between the transfer corotron 5 and the cleaning device 8, and the other devices were the same as in the comparative example. The steps up to development were carried out in the same manner as in the comparative example. After development, the surface of the photoreceptor is uniformly exposed to light by a static elimination lamp 15, the toner image is transferred to a transfer paper by a transfer corotron 5, and then the charge on the surface of the insulating layer of the photoreceptor is eliminated by a static eliminator 16, A cleaning device 8 removed residual toner. The potential change and charge state of the photoreceptor at this time are shown in FIG. 6-B and FIG. 7-B, respectively. a, b and c are the same as in the comparative example; f is uniform exposure after development and before transfer; d' is transfer; and e' is charge removal using a corotron for charge removal. As is clear from these figures, a to c are the same as the conventional method, but when exposed uniformly at f, both the non-exposed and exposed areas match the residual potential inside the photoconductor, which is almost close to OV. Become. Therefore, after the next toner image transfer, the same amount of charge is formed on the surface of the insulating layer in the exposed and non-exposed areas (7th-B).
Figure a′). Therefore, the next static elimination process is uniformly performed on the exposed and non-exposed areas, so that both areas are at approximately the same level after static elimination. That is, when the latent image potential was measured, the initial charging potential was +900V, and the residual potential was +20V in the exposed area and +10V in the non-exposed area, and the difference was
There was only 10V. Further, when the copying material was recharged and copied, no foreground effect was observed in the obtained copy, and both the image density and the background density were uniform. Example 2 In order to examine the effects of repeated copying, copies were made continuously for 10 minutes using the methods of Comparative Example and Example 1. The background potential at this time was as shown in the table below.

[Table] As is clear from this table, in the case of the present invention, the background potential increased by only 10 V after 10 minutes, and almost no change in the background density was observed. As described above, the method of the present invention has the advantage of good cycle stability of image potential and no fluctuation in image quality during continuous copying. Furthermore, as a side effect of the method of the present invention, the capacity of the static eliminator is reduced, and restrictions on the design of the copying machine are reduced. Furthermore, by performing uniform exposure before transfer, the transfer electric field can be reduced, and as a result, the transfer electric field is inevitably reduced due to water content in the transfer paper, resulting in transfer defects at high humidity. is eliminated, and high-quality images can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the basic structure of a part of a photoreceptor, FIG. 2 is an explanatory diagram of an image forming method using the photoreceptor shown in FIG. 1, and FIG. 3 is a schematic sectional view of a conventional electrophotographic apparatus. Figure 4 is a wiring diagram of the charger used in the method of the present invention, Figure 5 is a schematic cross-sectional view of the device used in the method of the present invention, and Figures 6-A and 6-B are photosensitizers according to the conventional method and the method of the present invention, respectively. Graphs 7-A and 7-B showing changes in the potential of the photoreceptor represent the state of charge at each step of the photoreceptor according to the conventional method and the method of the present invention, respectively. Symbols in the figure: 1...photoreceptor; 2...first charger;
3... Second charger; 4... Image exposure; 5... Transfer corotron; 6... Static eliminator; 7... Static elimination lamp;
8... Cleaning device; 9... Developing device; 11
... Conductive substrate; 12 ... Photoconductive layer; 13 ...
Transparent insulator layer; 14... Static eliminator; 15... Static eliminator; 16... Static eliminator; 21, 31... Discharge wire; 22, 32... Shield electrode; 23, 3
3... High voltage generator (power supply); M... Non-exposed part;
L...Exposed part.

Claims (1)

[Claims] 1 Using a photoreceptor having an insulating layer on the surface, the first
The shield electrode, the discharge electrode, and the power source for applying DC or AC voltage to each of the corona charger and the second corona charger are electrically insulated from other devices, and the first corona charger and the second corona charger are 2 Electrostatic latent image formation that performs image exposure after being charged by a charging device that is electrically connected to the shield electrode of the corona charger, and in which one end of the power source is electrically connected to the discharge electrode and the other end to the shield electrode. In an electrophotographic method that sequentially repeats a process, a development process, and a transfer process,
An electrophotographic method comprising the steps of uniformly exposing the surface of a photoreceptor after development and prior to transfer, and removing charges on the surface of the photoreceptor before recharging after transfer.