JPH1020727A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize a photoreceptor charging voltage in an image forming device that uses a bipolar photoreceptor. SOLUTION: This reader-printer has a charger 32 whose discharge polarity can be switched between positive and negative, an exposure optical system 20 for projecting an optical image, a sub-eraser 35, a development counter 36 capable of reversal or normal development, a transfer charger 37, and a main eraser 39, all of which are disposed around a bipolar photoreceptor drum 31. The amount of light of the main eraser 39 is relatively large during the execution of the image forming mode, whereas during the execution of an operational mode in which charge and static elimination are repeated (e.g. the drum drying mode), either it is relatively small or short wavelength components are cut. Also, during the afterprocessing of an image forming process in the positive-charge reversal development mode, the main eraser 39 is turned off, and a charge of the opposite polarity is imparted from the transfer charger 37 or a special static eliminating charger to eliminate static electricity from the photoreceptor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus for forming an image on a sheet by an electrophotographic method using a bipolar photosensitive member.

[0002]

2. Description of the Related Art Electrophotography can be classified into a normal development mode in which a positive image is obtained from a positive document and a reversal development mode in which a positive image is obtained from a negative document, when classified according to the relationship between a document image and a reproduced image. In a reader printer that irradiates light on a microfilm and projects the light image on a screen or reproduces it on a sheet by electrophotography, the microfilm has a positive and a negative. It is required that the reversal development mode can be selectively executed.

[0003] Therefore, in the developing process, on the premise that one kind of toner charged to a specific polarity is used, a reader printer using an ambipolar photoreceptor capable of charging both positive and negative polarities is used. Is provided. For example,
When using an amphoteric photoreceptor containing a chilipyrylium dye, if the microfilm is positive, the amphoteric photoreceptor is charged to a negative polarity to form a positive electrostatic latent image, and the A positively charged toner is attached. On the other hand, in the case of a negative film, the bipolar photoreceptor is charged to a positive polarity to form a negative electrostatic latent image, and the toner (positively charged) is attached to a low potential image portion.

[0004]

By the way, the following problems have been encountered in the reader printer using the above-mentioned bipolar photosensitive member.

First, the photosensitive member charging voltage decreases during execution of the drum dry mode as an operation mode, and toner is consumed. In the drum dry mode, the photoconductor is rotated many times (about 500 times) for the purpose of rapidly supplying toner.
Rotation), and an operation mode in which charging and discharging are repeated for each rotation. In this case, the photoreceptor is charged to a positive polarity, passes through the developing unit with a predetermined developing bias applied, and is discharged by light irradiation. Next, when image formation is performed in the positive charge reversal development mode, the rise of the charging voltage of the photoconductor is poor and unstable, and black spots due to toner are generated on the image. When image formation is repeated, the charging voltage may decrease.

SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus which prevents a decrease in photosensitive member charging voltage when a function mode in which charging and discharging are repeated in a mode other than an image forming mode such as a drum dry mode is performed, and toner is not consumed. Is to provide. Further, another object of the present invention is to provide
An object of the present invention is to provide an image forming apparatus capable of improving the rise of the charging voltage of a photoconductor during image formation, preventing the charging voltage from lowering, and preventing black spots caused by toner.

[0007]

In order to achieve the above object, an image forming apparatus according to the present invention comprises a charging means provided around a photoreceptor having a bipolar chargeable photosensitive layer containing a thiapyrylium dye. An exposure unit, a developing unit, a transfer unit, and a light discharging unit are provided, and the light discharging conditions of the light discharging unit are switched between when the image forming mode is executed and when the other operation modes are executed.

The light neutralization condition is a neutralization light amount or a wavelength component, and can be switched to a relatively small neutralization light amount or a short wavelength component can be switched when an operation mode other than the image forming mode is executed. By reducing the light amount or cutting the short wavelength component, the occurrence of electron traps in the photosensitive layer is reduced, and the deterioration of the charge holding ability is prevented. Therefore, the charging voltage of the photoconductor is not reduced, and the consumption of toner is prevented. For example, it is extremely effective in a drum dry mode in which charging and discharging are repeated.

Furthermore, in the image forming apparatus according to the present invention,
A first light erasing unit that irradiates light to the photoreceptor to erase electric charges when the image forming mode is executed; and a shorter wavelength component distribution than light emitted from the first light erasing unit when an operation mode other than the image forming mode is executed. And a second photo-eliminator for erasing the charge by irradiating the photoreceptor with less light. In the same manner as described above, it is effective to prevent a decrease in the charging voltage when an operation mode in which charging and discharging are repeated in addition to the image forming mode is executed.

Further, the image forming apparatus according to the present invention has a control means for switching the light discharging means to a non-operating state when the photosensitive member is rotated and charged and discharged after the image forming process during the image forming mode. doing. Normally, the photosensitive member is rotated immediately after the image forming process to perform charging and discharging, and the charging characteristics of the photosensitive member are stabilized for the next image forming process. At this time, the charge is removed by another method instead of light removal, for example, by applying a charge of opposite polarity to the photosensitive member by a transfer unit or a dedicated charge removal unit to remove the charge, the photosensitive member charging voltage at the next image forming process Is stabilized, and the rising is improved. Moreover, since the charging voltage is prevented from lowering, the occurrence of black spots due to the toner can also be eliminated.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an image forming apparatus according to the present invention will be described below with reference to the accompanying drawings. In the embodiments described below, the present invention is applied to a microfilm reader printer.

(First Embodiment) In FIG. 1, a reader printer comprises a microfilm carrier 1, a light source unit 2, mirrors 11 and 12, a screen 15, a print exposure optical system 20, and a print unit 30. . The light source unit 2 includes a lamp, a condenser lens, and the like. The emitted light passes through the microfilm held by the carrier 1 and is reflected by the mirrors 11 and 12 through the imaging (magnifying) lens 5 and the prism 6 to be screened. 15 is projected onto the image.

On the other hand, during printing, the mirror 11 is set at the position shown by the dotted line, and the carrier 1 moves in the direction of the arrow a. The light transmitted through the microfilm is reflected by the mirror 11
Then, the light is reflected by the mirrors 21, 22, and 23 of the exposure optical system 20, and irradiates the photosensitive drum 31 rotating in the direction of the arrow b in a slit shape, thereby forming an electrostatic latent image of a film image on the surface.

The photosensitive drum 31 is formed by forming a laminated bipolar photosensitive member comprising a charge generation layer and a charge transport layer on the surface of a conductive support (drum). The conductive support is made of cylindrical aluminum having an outer diameter of 50 mm. The charge generation layer was prepared by adding 0.45 part of a trisazo pigment represented by the following chemical structural formula (A) as a charge generation material and 0.5 part of butyral resin together with 50 parts of cyclohexanone by a sand mill.
The dispersion was dispersed for 8 hours, and this dispersion was applied to the outer peripheral surface of the drum so as to have a dry film thickness of 0.5 g / m ² .

The charge transport layer comprises 50 parts of a diamino compound of the following chemical structural formula (B), 50 parts of a polycarbonate resin, 2.5 parts of a thiapyrylium salt (p type) of the following chemical structural formula (C), A solution prepared by dissolving 6 parts of hydroxytoluene in 400 parts of dichloromethane was vigorously stirred for 1 hour, and then applied on the charge generating layer so that the dry film thickness became 20 μm.

[0016]

Embedded image

The photoreceptor having the above structure can be charged to both positive and negative polarities. In this embodiment, when printing a negative film image, the negative electrostatic latent image is charged positively, and reversal development is performed on the negative electrostatic latent image with positive toner. When printing a positive film image, the image is charged to a negative polarity, and the positive electrostatic latent image is subjected to regular development with the positive toner.

Whether the film image is negative or positive is determined by scanning the carrier 1 (film) once once when the print key (not shown) is turned on, and optically reading the image. Then, the mode is automatically set to the normal development mode or the reverse development mode. Such a mode may be manually set by the operator, or a program may be set in advance including the frame number of the film to be printed and the number of prints.

The print unit 30 forms an image by a well-known electrophotography method. As shown in FIG. 2, the photosensitive drum 31 is arranged to be rotatable in the direction of arrow b. Around the charger, a charging charger 32, an exposure slit 33 and a shutter 34, a sub-eraser 35, a developing device 36, a transfer charger 37, a residual toner cleaner 3
8. A main eraser 39 is provided.

The charger 32 is of a scorotron type having a discharge wire, a mesh grid for adjusting a charged voltage, and a stabilizer, and charges the surface of the photoreceptor to a predetermined voltage by corona discharge from the wire. As shown in FIG. 3, the wires are connected to a power supply 40 via a high voltage relay 41. In the reversal development mode, a positive current of +300 μA is supplied to the wire, and the voltage applied to the wire at that time is about +7 kV. -300μ in regular development mode
A negative current of A is supplied to the wire, and the voltage applied to the wire at that time is about −6 kV. The supply current from the power supply 40 can be controlled to two or more values for both positive and negative polarities, and the output value is switched as needed.

The stabilizer is grounded via a resistor 42 and contributes to the improvement of the charging efficiency of the charger 32. Resistance 42
Is 5 MΩ, and the voltage applied to the stabilizer during discharge is 1
about kV. Further, the resistance value of the resistor 42 can be changed, and is switched as needed.

The grid is connected to a power supply 40, and in the reversal development mode, +740 V is applied, and the photosensitive member charging voltage at that time is +690 V. -62 in regular development mode
0V is applied, and the photosensitive member charging voltage at that time is -600.
V. The applied voltage from the power supply 40 is 2
Control is possible beyond the value, and the output value is switched as required.

The slit 33 guides the film light image from the exposure optical system 20 onto the photosensitive drum 31. Shutter 3
Numeral 4 can completely close the slit 33 by turning on a solenoid (not shown), and prevents unnecessary exposure of the photosensitive member to the area other than the image forming area during the reversal development mode, thereby preventing unnecessary toner consumption. On the other hand, shutter 3
Reference numeral 4 denotes an open state (solenoid off) during the printing operation in the normal development mode, and is closed when the printing operation is completed.

The sub-eraser 35 has a plurality of LEDs arranged in the axial direction of the photosensitive drum 31. In a normal developing mode, unnecessary toner consumption is achieved by irradiating light to an area other than the image area of the photosensitive body to erase electric charges. To prevent Further, since the sub-eraser 35 functions as masking or side erase, the sub-eraser 35 may be partially turned on with respect to the image forming area of the photoconductor.

The developing device 36 moves a two-component developer composed of a mixture of a carrier and a toner around the developing sleeve 36a, and performs development using a known magnetic brush method. The carrier and the toner are frictionally charged, so that the carrier is negatively charged and the toner is positively charged. This positive toner adheres to the negative image portion (low potential portion) on the positively charged photoconductor in the reversal development mode, and the positive image portion (high potential image) on the negatively charged photoconductor in the normal development mode. Part).

The developing sleeve 36a is connected to the power supply 40, and a developing bias voltage of + 540V is applied in the reverse developing mode and -150V in the normal developing mode. In the reversal development mode, the developing bias voltage is applied to the area immediately before and immediately after the charged area of the photoconductor in order to prevent carrier adhesion in the non-image forming area. In the normal development mode, the voltage is always applied during the printing operation to prevent the toner from adhering to the non-image forming area.

The transfer charger 37 applies a negative charge to the sheet by corona discharge in a corotron system, and transfers the positive toner to the sheet. The wire is connected to the power supply 40, and is -110 μm in the reversal development mode.
A current is supplied, and -190 μA in the normal development mode.
Is supplied. The reason why the supply current value to the transfer charger 37 is switched between the normal development and the reversal development is that the adhesion of the toner to the photoconductor varies depending on the development mode. In the reversal development, the supply current value is set low because the adhesion of the toner to the photoconductor is small and it is necessary to prevent the memory from being applied to the photoconductor due to the influence of the transfer electric field. The switching of the current value is performed by the power supply 40 or by changing the resistance value of the ground resistor 43 connected to the stabilizer. The current is supplied to the transfer charger 37 when the sheet passes between the photosensitive drum 31 and the transfer charger 37 so that the transfer charge does not directly act on the photosensitive member.

The cleaner 38 presses the blade 38a made of an elastic material against the photosensitive drum 31 in the forward direction to scrape off the residual toner after the transfer from the surface of the photosensitive member.

The main eraser 39 is a rod-shaped lamp, and is disposed in the axial direction of the photosensitive drum 31. The main eraser 39 irradiates the photosensitive body after transfer with light, thereby erasing the charge on the photosensitive body, and performing the next printing operation. Stabilizes charging at times. The light amount of the main eraser 39 is about 30 to 35 lx · s in both the normal development mode and the reversal development mode.

Further, the reader printer includes the print unit 30, the carrier 1, the light source unit 2, and the optical system 2.
It has a CPU 50 for controlling 0. The power supply 40, the relay 41, and the like are controlled by the CPU 50.

Incidentally, in the reader printer having the above configuration, the drum dry mode can be executed for the purpose of rapid toner replenishment and the like in addition to the image forming mode. In the drum dry mode, charging, development, and static elimination are usually set to the same conditions as in the reversal development mode, and the photosensitive drum 31
Rotate for a minute. With this, about 500 cycles of charging,
Static elimination is performed. Note that no exposure is performed, the transfer charger 37 is kept off, and no paper is passed.

According to the experiments by the present inventors, the intended purpose of the drum dry mode cannot be achieved if the amount of static elimination of the main eraser 39 is the same as that during image forming processing in the drum dry mode. A case has occurred.
Therefore, the light quantity of the main eraser 39 is set to 20 lx · s and 3
Switch to 5lx · s and execute drum dry mode,
The photoconductor charging voltage was measured. Table 1 shows the measured values and the presence or absence of toner consumption.

[0033]

[Table 1]

As is apparent from Table 1, when the drum dry mode is executed with the amount of static elimination set to a large value of 35 lx · s, the charging voltage of the photoconductor drops below the development threshold value.
Toner consumption occurred. In other words, if the amount of static elimination is large, the initial charging voltage may decrease, and the charging voltage of the photoreceptor decreases, causing a problem of toner consumption.

The amount of static elimination during image forming processing needs to be set to a large value (35 ls · x in the present embodiment) for reasons such as prevention of optical memory on the photosensitive member. However, in the drum dry mode, the charge voltage of the photoreceptor only needs to consider mainly the consumption of toner and the prevention of carrier adhesion, and the amount of charge removal can be greatly reduced. As shown in Table 1, when the static elimination light amount was set to 20 lx · s, the charging voltage at the end of the drum dry mode was 40 V higher than when 35 lx · s was set, and no wasteful toner consumption occurred. .

On the other hand, when the discharge light amount is 35 lx · s, when the normal reversal developing mode is executed after the drum dry mode, the charging voltage does not rise to a predetermined value for a while, and toner fogging occurs on the image background portion. . However, if the static elimination light amount is set to 20 lx · s in the drum dry mode,
No fogging of the toner occurred even when the reversal development mode was immediately executed. In addition, reducing the amount of static elimination in the drum dry mode is also effective for pre-processing in which charging and static elimination are performed to stabilize the characteristics of the photosensitive member prior to image forming processing. In the case of performing the processing, a decrease in the charging voltage can be suppressed.

Based on the above experimental results, in the present embodiment, a shutter 55 (see FIG. 4) for partially blocking the irradiation light from the main eraser 39 is installed as shown in FIGS. That is, the shutter 55 has a notch 55a having a length corresponding to the maximum sheet passing width, and is swingably mounted on the bracket 56 of the solenoid SL1 at the upper end of the support portion 55b with the pin 57 as a fulcrum. A torsion spring 58 is wound around the pin 57.
As a result, the shutter 55 is elastically urged clockwise. A long hole 55d formed in a protruding piece 55c protruding from the back surface of the support portion 55b is provided with a solenoid SL1.
Is loosely fitted to the pin 60 provided on the plunger 59 of the first embodiment.

When the solenoid SL1 is off,
As shown in FIG. 5, the plunger 59 is retracted, and the shutter 55 is retracted from the static elimination light radiated from the main eraser 39. This shutter-off state is maintained in the image forming process, and the light elimination light amount at that time is 35 lx · s. On the other hand, when the solenoid SL1 is turned on, as shown in FIG. 6, the plunger 59 moves forward, and the shutter 55 swings to a position where the discharging light is partially blocked. The drum dry mode is executed with the shutter on in this manner,
At this time, the amount of static elimination is about 20 lx · s, which is almost halved.
By setting the amount of static elimination light in the drum dry mode to be smaller than that in the image forming process, it is possible to prevent the above-described fogging of the toner and a decrease in the charging voltage in the preprocessing.

The amount of charge elimination during the drum dry mode can be set to various values based on the characteristics of the photosensitive member. However, if the static elimination light amount is too small, the charging voltage during execution of the drum dry mode tends to increase (although the increase stops when the voltage reaches a certain voltage).
It is preferable to secure s. Further, a mechanism for changing the area of the notch 55a of the shutter 55 may be provided, or a swing angle adjusting mechanism for the shutter 55 may be provided to enable correction of the amount of static elimination light.

(Second Embodiment) In the second embodiment, instead of the shutter 55 used in the first embodiment, a filter 61 (see FIG. 7) for blocking short-wavelength light of static elimination light from the main eraser 39 is used. ). The overall configuration as a reader printer and the configuration for moving the filter 61 forward and backward are the first.
This is the same as the embodiment. Table 2 below shows the results of experiments performed by the present inventors.

[0041]

[Table 2]

In Table 2, when there is no filter, the amount of static elimination is 35 lx · s. Under the condition of short-wavelength light cut, a filter having a transmittance of 40% at 680 nm (the characteristics are shown in FIG. 8A) was used. The amount of static elimination was reduced to 10 lx · s by actual measurement. Under conditions for cutting off long wavelength light, a bandpass filter having a peak at 550 nm was used. The characteristics of this bandpass filter are shown in FIG.
As shown in (B), the long wavelength region of 600 to 700 nm is substantially cut. The amount of static elimination is 10l
x · s.

The experimental results under the condition without a filter are the same as the results shown in Table 1 above. Under the condition of cutting off the short-wavelength light, the amount of decrease in the charging voltage was small and the most preferable result was obtained. No toner was consumed under the condition of cutting off the long wavelength light, but dissatisfaction remained because the amount of decrease in the charging voltage was slightly large.

Regarding the first and second embodiments, when the amount of charge removal is large or when light of a relatively short wavelength is irradiated, the light reaches deeper into the photosensitive layer as shown in FIG. Since the electrons generated in the reaching portion are easily trapped, the dark decay rate at the time of charging in the next step increases as a result. In other words, the charge holding ability is reduced. Therefore, it is considered that the charging voltage is likely to be reduced in the drum dry mode. FIG. 10 shows the state of occurrence of electron traps when the light elimination light amount is set small and when light of a relatively long wavelength is irradiated. Therefore, in the drum dry mode, it is desirable to perform charge elimination with a long wavelength light that does not reach the deep part of the photosensitive layer and with a small light amount.

(Third Embodiment) In the third embodiment, the same eraser printer as the first embodiment is used, and the main eraser 39 is turned off in the drum dry mode (the shutter 55 and the filter 61 are not used). 3
5 is turned on to perform light neutralization. Sub eraser 35 is red L
It is an ED, and has a shorter wavelength component distribution than the irradiation light of the main eraser 39 and a smaller light amount. In addition, at the time of the image forming process and at the time of a pre-process of performing charging and static elimination for stabilizing the characteristics of the photosensitive member prior to the image forming process, optical erasing is performed using the main eraser 39. Also in the third embodiment, the second
The same effect as the short-wavelength light cut shown in the table was obtained.

(Fourth Embodiment) In the fourth embodiment, the same reader printer as in the first embodiment is used (however, the shutter 55 and the filter 61 are not used), and the printing operation in the positive charge reversal development mode is performed. In the above, the light erasing area by the main eraser 39 is limited, and instead of this limitation, a charge of opposite polarity is applied to the photoreceptor by the transfer charger 37 to eliminate the charge.

The control sequence is as shown in FIG. When the printing operation is started, the photosensitive drum 3
Pre-processing is performed by rotating 1 once. In the preprocessing, the charging charger 32, the developing bias, and the main eraser 39 are turned on, and the exposure and transfer charger 37 is turned off. The conditions for charging and discharging are the same as in the image forming process in the reversal development mode. The development bias is applied to prevent the toner / carrier from adhering when the high potential portion of the photoconductor passes through the development unit, and is set to the same bias voltage as that at the time of reversal development. The developing sleeve 36a is driven to rotate.

Next, the photosensitive drum 31 is rotated twice to perform an image forming process. Here, one image is formed by two rotations of the photosensitive drum 31. Next, post-processing is performed by rotating the photoconductor drum 31 once to stabilize the characteristics of the photoconductor. In the post-processing, the charging charger 32 and the developing bias are turned on and the exposure is turned off in the same manner as in the pre-processing, except that the main eraser 39 is turned off and the transfer charger 37 is turned on. By turning on the transfer charger 37, a negative charge is directly applied to the photoconductor without passing through the sheet. The current supplied to the transfer charger 37 has the same value as in the image forming process. In this post-processing, the photosensitive member charging voltage charged to +690 V by the charging charger 32 was attenuated to +200 V by the reverse polarity discharge from the transfer charger 37. In the post-processing, it is desirable to attenuate the voltage to 0 to +300 V at which toner / carrier adhesion does not occur when the developing bias is at the ground potential. If the photosensitive member charging voltage is attenuated to 0 to +300 V, toner / carrier adhesion occurs in the developing section when image forming processing is performed next time, even immediately after the start of rotation of the photosensitive drum 31 and before the application of the developing bias. Nothing.

FIG. 12 shows a control sequence in the case where preprocessing is performed by rotating the photosensitive drum 31 twice in the fourth embodiment. In this preprocessing, the main eraser 39 is turned off at the first rotation, and the transfer charger 37 is turned on to apply a charge of the opposite polarity to the photoconductor, thereby performing charge elimination. In the second rotation of the preprocessing, the transfer charger 37 is turned off, and the main eraser 3 is turned off.
9 is turned on to remove electricity from the photoconductor.

In the fourth embodiment, the pre-processing and post-processing improve the short-term charging voltage stability including the rise of the photosensitive member charging voltage. further,
Compared with the case where the charge removal during post-processing is performed by light, it was confirmed that the occurrence of black spots due to the toner was reduced and the reduction in the charging voltage of the photoconductor during printing of a large number of sheets was suppressed.

The charge removal by the transfer charger 37 with the opposite polarity charge can be applied even in the drum dry mode. However, in the drum dry mode, continuous charging / discharging is repeated. To converge the charging voltage,
The transfer charger 37 is preferably a scorotron type provided with a grid electrode. This is because, when static elimination is performed with a corotron type charger, the voltage after static elimination tends to vary depending on the occasion, and it is difficult to predict the next charging voltage value.

On the other hand, in the fourth embodiment, FIG.
As shown in FIG. 5, a scorotron-type charge eliminator 65 for releasing negative charges is provided adjacent to the main eraser 39, and the charge eliminator 65 is operated in place of the transfer charger 37 to charge the photosensitive member. Good. Further, the static elimination charger 65 can also be used as a static elimination means in a drum dry mode.

(Fifth Embodiment) In the fifth embodiment, similarly to the above-described fourth embodiment, the charge is applied to the photosensitive member by the transfer charger 37 at the time of post-processing to remove electricity. However, pre-processing was omitted. The control sequence is as shown in FIG. 13, and the operation principle and the operation conditions of each element are the same as in the fourth embodiment.

In the fifth embodiment, the same applies to the fourth embodiment. However, since the light elimination is not performed in the post-processing, the rising charge voltage of the photosensitive member at the time of the next image formation is improved.
The occurrence of black spots due to the toner is prevented. This result is not lost even if the preprocessing is omitted.

If there is a problem with the rise of the charging voltage when switching from the negative charging normal development mode to the positive charging reversal development mode, the CPU 50 determines whether the charging polarity in the immediately preceding print mode was positive or negative. The pre-processing may be omitted only when the polarity is positive. Further, as shown in FIG.
, A static elimination charger 65 may be used.

By the way, if the print mode is terminated by light elimination, the generation of electron traps cannot be prevented, and the electrons are swept out by the charging electric field at the time of the next printing, so that the charging voltage decreases. That is, as shown in FIG. 9, when charging is performed in a state in which electrons are trapped, the voltage is controlled to a constant voltage by the grid electrode during charging. Electrons are swept out by the time they arrive, and the charging voltage drops. In addition, after the second rotation, the state becomes stable with respect to the sweeping out of electrons,
The charging voltage is higher than the first rotation and is stable. However, when the charging / discharging is repeatedly performed as in the drum dry mode, the number of trapped electrons increases, and it is considered that the charging voltage decreases as described above.

Further, when the light removal is performed excessively, electron traps are accumulated, the electric field is locally increased, and a local decrease in the charging voltage such as a decrease in the resistance value of the surface of the photoreceptor at high humidity is caused. This causes black spot noise in the reversal development mode.

As measures against the above two problems, in the fifth embodiment, the charge / discharge cycle is reduced during the formation of one print (the pre-processing is omitted), and the process is not terminated by the light discharge. . Omitting the preprocessing also leads to an improvement in the first print speed.

In the post-processing, the photosensitive drum 3
If 1 is rotated one or more times, the charge removal in the post-processing has substantially the same effect as the charge removal immediately before the image forming processing, but it is not necessary to perform the charge removal by light. At the end of the image forming process, the photoreceptor undergoes uniform light elimination from the main eraser 39 to form a uniform residual potential state, and is charged in post-processing. Because there is no. When the post-processing is not performed, it is necessary to end the print mode by performing the light elimination or to execute the pre-processing for performing the light elimination in order to eliminate the possibility of the optical memory.

(Sixth Embodiment) In the sixth embodiment, similarly to the fourth and fifth embodiments, the transfer charger 37 applies a charge of the opposite polarity to the photoreceptor at the time of post-processing, and the charge is removed.
In the continuous print mode, light elimination in the inter-image region is omitted.

The control sequence is as shown in FIG. FIG. 14 shows a sequence of the two-sheet continuous print mode. In this example, the pre-processing of the first sheet is performed in the same manner as in the fourth embodiment. Thereby, it is possible to cope with the rising failure of the charging voltage at the time of switching from the negative charging regular developing mode to the positive charging reversal developing mode. The image forming process is performed on the photosensitive drum 31
This is performed at a little over three rotations, and less than three rotations up to the image formation processing for the second sheet is an inter-image area. The less than two rotations in the first half of the inter-image area corresponds to post-processing after the first image forming process, and the main eraser 39 is turned off (light may be shielded by a shutter). One rotation in the latter half of the inter-image area corresponds to a pre-process of the second image forming process, and turns on the main eraser 39 (the shutter may be retracted). If possible, the transfer charger 37 may be turned off in a pre-process prior to the second image forming process.

As shown in FIG. 15, a charge removing charger 65 may be used in place of the transfer charger 37. Also, in the control sequence, the main eraser 39 may be turned off in all the inter-image regions of less than three rotations to omit the light neutralization.

The control sequence shown in FIG. 14 is a case where the diameter of the photosensitive drum 31 is 30 mm and two or more rotations are required for one image forming process due to the time required to return to the home position of the image exposure scan. It is. Traditionally,
Since the light neutralization was performed in the entire area between the images, the charging voltage was likely to decrease. However, the reduction of the charging voltage could be suppressed by at least partially omitting the light neutralization.

As in the sixth embodiment, in the continuous print mode, the light removal in the inter-image region is at least partially omitted, and the transfer charger 37 is kept on. This increases the process speed and increases the pressure in the inter-image region. This is effective when ON / OFF of the charging charger 32 and the transfer charger 37 cannot be precisely controlled due to restrictions on the rising and falling characteristics of the power supply unit.

(Other Embodiments) The image forming apparatus according to the present invention is not limited to the above embodiments, but can be variously modified within the scope of the invention. In particular, the relationship between the charging polarity of the bipolar photoconductor, the charging polarity of the toner, and the developing mode may be opposite to that of the above embodiments. Further, the present invention can be applied to a laser printer or the like that prints out image information transferred from a host computer, in addition to a reader printer using a microfilm as a document.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating a reader printer according to a first embodiment of the invention.

FIG. 2 is a sectional view showing a print unit mounted on the reader printer.

FIG. 3 is a block diagram showing a control circuit of the print unit.

FIG. 4 is a plan view showing a light-blocking shutter according to the first embodiment.

FIG. 5 is a side view showing an attached state of the shutter, showing a state where a shutter is off;

FIG. 6 is a side view showing a mounting state of the shutter, showing a state where a shutter is turned on.

FIG. 7 is a plan view showing a filter according to a second embodiment.

FIG. 8 is a graph showing characteristics of the filter.

FIG. 9 is a schematic diagram showing a state of an electron trap inside a photosensitive layer, and shows a case where a charge removal amount is large.

FIG. 10 is a schematic diagram showing a state of an electron trap inside a photosensitive layer, showing a case where a light elimination light amount is small.

FIG. 11 is a control sequence diagram in the fourth embodiment, showing a case of one rotation of preprocessing.

FIG. 12 is another control sequence diagram in the fourth embodiment, showing a case of two rotations of preprocessing.

FIG. 13 is a control sequence diagram according to the fifth embodiment.

FIG. 14 is a control sequence diagram in the sixth embodiment.

FIG. 15 is a sectional view showing a main part of a modification of the fourth, fifth, and sixth embodiments.

[Explanation of symbols]

 Reference Signs List 20 exposure optical system 30 print unit 31 photosensitive drum 32 charging charger 35 sub-eraser 36 developing device 37 transfer charger 39 main eraser 50 CPU 55 shutter 61 filter 65 charge removing charger

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Koji Niizawa 2-3-1-13 Azuchicho, Chuo-ku, Osaka-shi, Osaka Inside Osaka International Building Minolta Co., Ltd. (72) Akira Hirota Azuchi-cho, Chuo-ku, Osaka-shi, Osaka 2-3-13 Osaka International Building Minolta Co., Ltd.

Claims (8)

[Claims] 1. A photoreceptor having a photosensitive layer containing a thiapyrylium dye and capable of being charged to both polarities, a charging unit for uniformly charging the photoreceptor, and irradiating a light image onto the charged photoreceptor. Exposure means for forming an electrostatic latent image; developing means for developing the electrostatic latent image formed on the photoreceptor with toner; transfer means for transferring the developed toner image onto a sheet; Light erasing means for irradiating the body with light to erase electric charges, and control means for switching the light elimination conditions by the light erasing means between the execution of the image forming mode and the execution of other operation modes. An image forming apparatus comprising: 2. The image forming apparatus according to claim 1, wherein the control unit switches to a relatively small amount of static elimination light when an operation mode other than the image formation mode is executed. 3. The apparatus according to claim 1, wherein the control unit switches to a light neutralization condition in which short-wavelength light is blocked and a light amount is reduced when an operation mode other than the image formation mode is performed. Image forming device. 4. A photoreceptor having a photosensitive layer containing a thiapyrylium-based dye and chargeable to both polarities, a charging unit for uniformly charging the photoreceptor, and irradiating a light image onto the charged photoreceptor. Exposure means for forming an electrostatic latent image; developing means for developing the electrostatic latent image formed on the photoreceptor with toner; transfer means for transferring the developed toner image onto a sheet; execution of an image forming mode A first light erasing unit for irradiating the photosensitive member with light at a time to erase electric charges; and a light having a shorter wavelength component distribution than the irradiation light from the first light erasing unit when an operation mode other than the image forming mode is executed. And a second photo-eliminator for erasing the charge by irradiating the photoreceptor with a photoreceptor. 5. An operation mode other than the image forming mode includes:
3. A drum dry mode in which charging and discharging of a photoreceptor is repeated many times.
The image forming apparatus according to claim 3. 6. A photoreceptor having a photosensitive layer containing a thiapyrylium dye and capable of being charged to both polarities, a charging means for uniformly charging the photoreceptor, and irradiating a light image onto the charged photoreceptor. Exposure means for forming an electrostatic latent image; developing means for developing the electrostatic latent image formed on the photoreceptor with toner; transfer means for transferring the developed toner image onto a sheet; A light erasing unit that irradiates light on the body to erase the electric charge; and, when the photoreceptor is rotated to perform charging and static elimination after the image forming process during the image forming mode, switches the light erasing unit to a non-operation state. An image forming apparatus, comprising: a control unit. 7. The image forming apparatus according to claim 6, wherein the control unit switches the light discharging unit to a non-operation state and maintains the transfer unit in an operation state. 8. A static eliminator for applying charges of opposite polarity to erase charges on the photoreceptor, wherein the controller switches the light eliminator to a non-operating state and switches the static eliminator to an operating state. The image forming apparatus according to claim 6, wherein: