JPS59214070A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent the surface potential of a photosensitive body from going uneven after use by irradiating the photosensitive body with light from an image exposure part to overall image width for a specific time after image exposure on reversal development basis is completed. CONSTITUTION:The discharge of a transfer electrostatic charger and a predestaticizer 13 is stopped at the end point t1 of transfer to transfer paper, but the discharging of a primary electrostatic charger 2 and a secondary corona discharger 3 is carried on as it is. At this time, the light-part potential of an area (a) in a photosensitve body surface is almost 0V. A low-potential area (c) is charged electrostatically to a primary charging potential by the following rotation of the photosensitive body and held at the same potential with the area (a) through the discharging operation of the secondary corona discharger 3. Further, a high-potential area (d) is held at the same potential with the area (a) by passing by the position of the secondary corona discharger 3. An area (b), on the other hand, is held at the same potential with the area (a) through the discharging operation of the corona discharger 3 switched to weak discharge while passing by the position of the secondary corona discharger 3. Thus, the photosensitve body stops while the surface is almost at 0V, and the unevenness of surface potential is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses a photoreceptor having an electrically insulating layer on its surface as an image carrier, and applies an image forming process to this photoreceptor in which exposure is negative exposure and development is a reversal development method. This technology relates to image forming apparatuses (including recording devices and other applied devices) in which the formed image is transferred to a transfer material and the photoreceptor is used repeatedly. The purpose is to prevent the surface potential non-uniform state from having an adverse effect on the next image formation.

In this type of image forming apparatus, a plurality of corona dischargers/chargers are generally installed around a cylindrical or belt-shaped photoreceptor, and these devices can be placed in two states, either a charged state or a stopped state, in conjunction with the operation of the device. It is common practice to perform latent image formation, transfer, etc. by switching the state. In such devices, the surface potential of the photoreceptor is often uniform on each part immediately after the completion of one image formation, and if left in that state for a long time, the image may be defective during the next image formation. It is well known that this may cause adverse effects such as uniformity.

Therefore, in order to avoid such adverse effects, for example, as described in US Pat. No. 2,211,17892,
In the xerographic method, which uses a photoreceptor with a light-guiding insulating material provided on the surface of the conductor as an image carrier, when the photoreceptor is rotated after one image formation, the entire surface of the photoreceptor is irradiated with light to separate each part. Discharging residual charges.

However, Special Publication No. 42-23910, 43-247
In the electrophotographic method, which uses a photoreceptor having an insulating layer on its surface as an image carrier, as disclosed in Japanese Patent No. 48, the charge is retained in the insulating layer. Simply irradiating the body with light does not cause the charge to be lost.

The process disclosed in the above-mentioned publication includes a step of uniformly primary charging a three-layer photoreceptor whose basic structure is an electrically insulating layer, a photoconductive layer, and a conductive support, and irradiation of original image light. A latent image is formed by applying an alternating current corona discharge or a secondary corona discharge step of applying a corona discharge of opposite polarity to the primary charging, followed by a step of applying irradiation light almost uniformly to the surface of the photoreceptor. be.

In an image forming process using such a photoreceptor, in order not to leave any history on the photoreceptor while the photoreceptor is stopped, the surface potential of the photoreceptor surface is approximately Ov, and the voltage applied to the photoconductive layer of the photoreceptor is set to approximately Ov. It has been found that the best treatment method is to eliminate the electric field with light or the like so that no electric field is applied to either the photoconductive layer or the insulating layer.

As an example, a treatment method for the case where the development is normal development is proposed in Japanese Patent Laid-Open Nos. 57-83377 and 57-93378. This method will be explained using FIGS. 1 to 3.

In FIG. 1, reference numeral 1 designates a three-layer photosensitive drum having a photoconductive layer of a CdS binder on an aluminum substrate and a transparent insulating layer on top of the photoconductive layer, and rotates in the direction of arrow a around an axis 11. Driven. During the rotation process, the photoreceptor 1 is uniformly charged to about +1300V by the primary charger 2, and then subjected to static neutralization by the secondary corona discharger 3 to which a DC of about -7.BKV is applied. At the same time, it receives image exposure.

As a result, an electrostatic latent image is formed on the surface insulating layer of the photoconductor l due to the difference in surface charge density, and then the entire surface is uniformly exposed by the full-surface exposure lamp 4, so that the surface of the photoconductor is exposed according to the image exposure. A potential difference is generated, and the potential contrast of the electrostatic latent image formed above is greatly improved. At this time, the potential on the surface of the photoreceptor is +500 in the dark area and approximately Ov in the bright area. Then,
The high-contrast image a is visualized by positive development using negative toner by a developing device 5 to which a developing bias of approximately +100V is applied. The visible image is then corona-transferred onto the transfer paper P fed through the paper feed guide 20 by the corona discharger 6 to which a voltage of approximately +6.5V is applied. The transfer paper (±) on which the image has been transferred is separated from the photoconductor surface by a separating device 7, sent to a fixing device (not shown), and discharged outside the machine as an image-formed product.On the other hand, the photoconductor l after the transfer is Cleaner 8
The toner remaining on the photoreceptor 1 is removed by the photoreceptor 1, and then the charge on the photoreceptor is made uniform by exposure with the miniature light bulb 12 and corona action by the pre-discharge corona discharger 13.
Reused.

In the above-mentioned apparatus, the surface potential of the photoreceptor surface immediately after the series of operations is completed, that is, at the time when the rear end of the transfer material P passes through the transfer section 6, is extremely uneven in each part as shown in the graph of FIG. is in a state of In Figure 2, the surface potential of the photoreceptor surface area (A) is approximately -120V, which means that blank exposure (not shown) is performed at the same time as secondary corona discharge in this area (A), which is a non-image area. This is because a bright area potential is formed by applying this to prevent toner from adhering to non-image areas.

Now, in order to eliminate the non-uniform state of the photoreceptor surface potential as shown in Fig. 2 and to stop the photoreceptor after making it uniform,
JP-A-57-93378 discloses that it is sufficient to stop the machine at the timing shown in FIG. 3. That is, after the end of the predetermined copying process tl, at this point the discharge of the transfer charger 6 and the pre-static eliminator 13 is stopped, but the primary charger 2 and the secondary corona discharger 3 are allowed to continue their discharge state. Then, due to the continued rotation of the photoreceptor 1, 11
Discharging of the primary charger 2 is stopped at time t2 when the low potential area (c) on the photoreceptor surface in FIG. . Then, the surface potential of the region (c) becomes the primary charging potential as the primary charger 2 passes through the position in the discharged state. On the other hand, at time 11, the high potential area (d) on the photoreceptor surface in FIG.
As the area passes through the position, static electricity is removed and the surface potential becomes approximately the same as area (A).

The secondary corona discharger 3 continues the discharging state after time 12, and the area where the power is cut off to the primary charging potential (c)
At time t3 when the terminal end of the corona discharger 3 enters the action range of the secondary corona discharger 3, the discharge condition is switched to a weak discharge state to continue the discharge.

As the photoreceptor 1 continues to rotate, at time point 11, the terminal end of the photoreceptor surface potential area (b) in FIG. At a time point t4 within the range, the discharge of the secondary corona discharger 3 is completely stopped. Then, the photoreceptor surface area (c) charged to the above-mentioned primary charging potential is then subjected to the neutralizing action of the secondary corona discharger 3, and has approximately the same surface potential as the area (a). Furthermore, the middle surface potential region (b) that continues to enter and pass through the action range of the secondary corona discharger 3 is approximately the same as the region (a) due to the neutralization action of the secondary corona discharger 3 which has been switched to weak discharge. becomes the surface potential. t3 of secondary corona discharger 3
The strength of the weak discharge from t4 to t4 is such that the surface potential of region (b) is just lowered to the surface potential of region (a).

Incidentally, during the above-mentioned post-stroke, the entire surface exposure device 4 continues its operation for blank exposure.

By doing the above, in an apparatus that uses the normal development method for development,
It is possible to eliminate potential unevenness on the drum during post-rotation.

However, if this method is applied to a process in which an image area is exposed (negative exposure) and reversal development is performed, various problems arise. - As an example, the case of a laser beam printer (L/B/P) in which an image area is exposed to light by a laser and a visible image is obtained by a reversal development method will be explained.

The L-B-P is basically the same in configuration as an electrophotographic apparatus using the normal development method, so to explain only the differences using FIG. 1, first, the light source of the secondary corona discharge simultaneous image exposure section is The difference is that it is a laser, the polarity of the toner is positive because it develops the bright area exposed by the laser, the transfer blackout polarity is negative, and blank exposure is not used. The other details are as explained in the case of the normal development method described above.

Further, the bias applied to the developing device is approximately +400V.

Here, blank exposure is not used in the reversal development method because in the one-reversal development method, the background area is at the dark potential (on the other hand, in the normal development method, the background area is at the bright potential)
.

In such an apparatus, the surface potential of the photoreceptor surface immediately after a series of operations is completed, that is, when the trailing edge of the transfer material P passes the transfer section 6, is as shown in the graph of FIG. 4(a). Comparing the photoreceptor surface area (A) in this graph with the area (A) in Figure 2 for normal development, the area (A) for reversal development is about +500V, and in this state If the photoreceptor 1 is stopped and left as it is, the electric field remains applied to the insulating layer, causing stress.

On the other hand, in order to prevent toner from adhering to the photoreceptor surface,
It is necessary to keep the developing bias approximately 100 cm lower than the surface potential of the drum on the opposite surface of the developing device 5.

The present invention is to perform post-rotation in such an image forming apparatus including a reversal development process so as not to cause unevenness or stress on the photoreceptor. This will be explained in detail based on the device control timing chart shown in FIG.

First, after the writing of the trailing edge of the image by the laser is completed, the laser is turned on at the time point ○, after allowing a margin of about 30 to 100 mm on the circumference of the photoreceptor for switching the developing bias as described below. . Next, at stage 1o, when the exposure position of the laser 08 reaches a position facing the developing device 5 in FIG. 1 due to the continued rotation of the photoreceptor, the developing device
In order to eliminate fogging, the developing bias (51 is a bias application power source) for the image is changed to a different setting from that at the time of image production. For example, the difference between the value of the DC component of the developing bias and the potential of the surface of the photoreceptor is set to be approximately equal to the difference between the value of the DC component of the developing bias and the dark area potential of the photoreceptor during image formation (at the time of image formation). Change to

In the case of this embodiment, this value is approximately -100V. next,
At tl when the transfer to the rear end of the transfer paper P is completed, the discharge of the transfer charger 6 and the front static eliminator 13 is stopped, but the primary charger 2 and the secondary corona discharger 3 remain in the discharge state. Let it continue. At this time, the area (a) becomes Meito potential approximately OV. Then, due to the continued rotation of the photoreceptor 41, the low potential area (c) on the photoreceptor surface in FIG. The discharge of the primary charger 2 is stopped. Then, the surface potential of the region (c) becomes the primary charging potential as the primary charger 2 passes through the position in the discharged state. On the other hand, at time 11, the high potential area (d) on the photoreceptor surface in FIG. The surface potential is approximately the same as (a').

The secondary corona discharger 3 continues the discharging state even after time 12, and when the end of the area (/) charged to the above-mentioned primary charging potential enters the action range of the secondary corona discharger 3. At t3, the discharge condition is switched to a weak discharge state and the discharge is continued.

1 As the photoreceptor 1 continues to rotate, at time 11, the terminal end of the surface potential area (mouth') in the photoreceptor surface shown in FIG. 4 located between the transfer charger 6 and the pre-static eliminator 13 becomes a secondary corona discharger. At time t4 when the corona discharger 3 enters the action range of 3, the discharge of the secondary corona discharger 3 is completely stopped. Then, the photoreceptor surface area (c) charged to the primary power outage potential is then subjected to the static eliminating action of the secondary corona discharger 3, and becomes approximately the same surface potential as the area (a). The intermediate surface potential region (b) that enters and passes through the action range of No. 3 becomes approximately the same surface potential as the region (a) due to the neutralizing action of the secondary corona discharger 3 which has been switched to weak discharge. Corona discharger 3
The strength of the weak discharge from t3 to t4 is such that the surface potential of the region (mouth') is just lowered to the surface potential of the region (a5).

The laser continues to turn on while the drum l is rotating, and turns off when the rotation stops.

Incidentally, the relative operation timing control of each process execution device as shown in FIG. 5 is performed by a device control circuit programmed in advance, but this circuit is omitted from the diagram.

By doing the above, as shown in Figure 4(b), the entire area of the photoconductor stops at the bright area potential, which is approximately Ov, and since the developing bias is changed to remove fogging, the drum The above objectives are well achieved without causing any stains on the surface.

In addition, especially in laser beam printers that use a laser as a light source for image exposure, as in this embodiment, and other devices that use LEDs or liquid crystal shutters, it is possible to rotate the photoconductor rearward only by processing electrical signals. Although it is particularly preferable for carrying out the present invention because it can easily form a bright area potential, an analog device that performs reversal development using a negative original (for example, a microfilm hard copy device) is particularly preferable for carrying out the present invention. ), the present invention can be implemented by taking measures such as providing a light source in the secondary corona discharge section in order to form a bright area potential during post-rotation.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of the configuration of an example of an electronic copying machine, Fig. 2 is a surface potential graph of each part of the photoreceptor at the end of the copying process in the normal development method, Fig. 3 is a time chart of process equipment in the normal development method, and Fig. 4 Figure (a) is a graph of the surface potential of each part of the photoreceptor at the end of the copying process in the reversal development method, Figure 4 (b) is the same graph after the post-rotation of the photoreceptor according to the present invention, and Figure 5 is the graph according to the present invention. Time chart of process equipment for reversal development method. 1 is a photoreceptor, 2 is a primary charger, 3 is a secondary corona discharger,
4 is a full surface exposure device, 5 is a developing device, 6 is a transfer charger, 8 is a cleaner, and 13 is a pre-static eliminator. Figure 1 Figure 2 Figure 5 t. 577- Figure 4 (0) (b)

Claims (1)

[Claims] (1) A photoreceptor having an electrically insulating layer on the surface is used as an image carrier, and an image is formed on this photoreceptor by applying an image forming process in which image exposure is negative exposure and development is a reversal development method, In an image forming apparatus in which the formed image is transferred to a transfer material and the photoreceptor is used repeatedly, after the image exposure is completed, light is irradiated over the entire image width on the photoreceptor from the image exposure section for a certain period of time. An image forming apparatus characterized by: