JP2002099187A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device which forms an excellent image free of lengthwise density unevenness with inexpensive constitution even when an a-Si photoreceptor is used. SOLUTION: The lengthwise electrostatic charging potential of the a-Si photoreceptor drum 1 can be made uniform with the inexpensive constitution by providing a filter 21 with light transmission characteristics which adjusts the quantity of pre-exposure light irradiating the a-Si photoreceptor drum 1 from a pre-exposure lamp 7 according to lengthwise electrostatic charging characteristics and potential attenuation characteristics of the a-Si photoreceptor drum 1 between the pre-exposure lamp 7 and a-Si photoreceptor drum 1 and then the lengthwise density unevenness of the a-Si photoreceptor drum 1 is prevented, so that an excellent image can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, etc., which forms an image using an electrophotographic system or an electrostatic recording system.

[0002]

FIG. 13 is a schematic diagram showing an example of a conventional electrophotographic image forming apparatus (copier). In this figure, A is an apparatus main body, and B is an image reading unit (image scanner) mounted on the apparatus main body A.

In the image reading section B, reference numeral 10 denotes a fixed platen glass, which is placed on the upper surface of the platen glass 10 with the surface on which the document G is to be copied facing downward, and an unillustrated document is placed thereon. Set it over the board. An image reading unit 11 includes a document irradiation lamp 11a, a short focus lens array 11b, a CCD sensor 11c, and the like.

When the copy button (not shown) is pressed, the image reading unit 11 is moved from the home position on the left side of the original table glass 10 to the right side on the lower side of the original table glass 10 by pressing a copy button (not shown). Is driven forward, and when it reaches a predetermined reciprocating end point, it is driven backward to return to the initial home position.

In the forward drive process of the image reading unit 11, the downward image surface of the original G on the original platen glass 10 is sequentially illuminated and scanned from the left side to the right side by the original irradiating lamp 11a. The surface reflection light is transmitted to the CCD sensor 1 by the short focus lens array 11b.
1c.

The CCD sensor 11c includes a light receiving section, a transfer section, and an output section (not shown). The light signal is converted into a charge signal in the light receiving section, and the output section is sequentially synchronized with a clock pulse in the transfer section. The charge signal is converted to a voltage signal at the output unit, amplified, reduced in impedance, and output. The analog signal obtained in this manner is converted into a digital signal by well-known image processing and output to the exposure device 3 on the apparatus main body A side.

On the other hand, in the apparatus main assembly A, reference numeral 1 denotes a rotating drum type electrophotographic photosensitive member (hereinafter, referred to as a photosensitive drum) as an image carrier. The photosensitive drum 1 has a predetermined peripheral speed (process speed) around a center support shaft and an arrow a.
It is rotationally driven in the direction (clockwise), and is uniformly charged by the charger 2 during the rotation process.

[0008] Scanning exposure is performed on the uniformly charged surface of the photosensitive drum 1 by ON and OFF emission of laser light modulated in accordance with an image signal from the exposure device 3, so that an image reading unit is formed on the photosensitive drum 1. B forms an electrostatic latent image corresponding to the image information of the document G photoelectrically read.

The electrostatic latent image formed on the photosensitive drum 1 is
The developing device 4 develops the toner image. The developing method by the developing device 4 is, for example, a two-component contact developing method in which a mixture of toner particles and a magnetic carrier is used as a developer and conveyed by a magnetic force, and is developed in a state of contact with the photosensitive drum 1. It is preferably used.

A transfer material P such as paper stored in a paper cassette 12 is fed one by one by a paper feed roller 13, and is transferred between the photosensitive drum 1 and the transfer device 5 at a predetermined timing by a registration roller 14. The toner image on the photosensitive drum 1 is transferred to the transfer material P by the transfer blade 5d which is fed to the transfer nip N and to which the transfer bias of the transfer device 5 is applied.

The transfer material P on which the toner image has been transferred is conveyed between the pressure roller 8a and the fixing roller 8b of the fixing device 8 by the transfer belt 5a also serving as a conveyance belt. The transfer belt 5a is stretched between a driving roller 5b and a driven roller 5c, and the upper surface of the belt moves in the direction of the arrow by the rotation of the driving roller 5b. Pressure roller 8 of fixing device 8
The transfer material P conveyed between a and the fixing roller 8b is heated,
The toner image is thermally fixed on the surface by pressing, and is discharged onto the tray 16 through the paper discharge roller 15.

The photosensitive drum 1 after the transfer of the toner image is
Adhered contaminants such as untransferred toner adhering to the surface are removed by the cleaning blade 6 and further discharged by the pre-exposure lamp 7 to prepare for the next image forming operation.

As the photosensitive drum 1 used in the above-described image forming apparatus, an organic photosensitive drum, an amorphous silicon photosensitive drum (a-Si photosensitive drum) and the like are often used. Is used as an electrophotographic photoreceptor for high-speed copiers and laser beam printers (LBPs) because of its high surface hardness, high sensitivity to semiconductor lasers, etc., and little deterioration due to repeated use. .

[0014]

By the way, the above-mentioned a-
The method of manufacturing the Si-based photosensitive drum is as follows. Since the gas is solidified by turning the gas into a plasma with high frequency or microwave, and deposited on an aluminum cylinder to form a film, if the plasma is not uniform, film thickness unevenness in the circumferential direction or the longitudinal direction may occur. Composition unevenness is caused.

As a result, potential unevenness of about several tens of volts has occurred in the developing section of the a-Si photosensitive drum. This is due to the phenomenon that the difference in electrostatic capacity is caused by the unevenness of the film thickness and the difference in charging ability, and the pre-exposure of the pre-exposure lamp used to erase the optical memory on the surface of the a-Si photosensitive drum by the previous image formation. The potential decay (hereinafter referred to as dark decay) in the dark state between charging and development of the surface of the a-Si photosensitive drum due to the difference caused by the difference in film thickness and composition, thereby further increasing the potential unevenness in the developing section. Caused by

The above optical memory will be described.
When the photosensitive drum is charged and subjected to image exposure, photo carriers are generated and the potential is attenuated. However, at this time,
The a-Si photosensitive drum has a large number of tangling bonds (unbonded bonds), which become localized levels to capture a part of the optical carrier to lower its running property or to generate light. Decreases the probability of carrier recombination.

Therefore, in the image forming process, a part of the photocarriers generated by the exposure is released from the localized level at the same time when an electric field is applied to the a-Si photosensitive drum at the time of charging in the next step, and is released from the exposure level. There is a difference in the surface potential of the a-Si photosensitive drum between the non-exposed portion and the non-exposed portion, which finally becomes an optical memory.

The dark decay described above is very large in the dark state when an a-Si photosensitive drum is used as compared with an organic photosensitive drum, and the potential decay due to an optical memory for image exposure increases. For this reason, the dark decay between the charging and the development of the photosensitive drum surface becomes extremely large, and a potential decay of about 100 to 200 V occurs. At this time, potential unevenness of several tens of volts occurred due to the above-described unevenness in film thickness and composition.

When such potential non-uniformity occurs, the a-Si type photosensitive drum having a large capacitance is more affected since the contrast is smaller than that of the organic photosensitive drum.
Density unevenness also becomes noticeable.

In order to solve such a problem, for example, the amount of light of the pre-exposure lamp can be changed in the longitudinal direction and the circumferential direction so as to cope with potential unevenness due to the charging characteristics and potential attenuation characteristics of the individual photosensitive drums. A method of changing the light amount is also conceivable. However, in a configuration in which the amount of light of the pre-exposure lamp is variably driven in accordance with the characteristics of each photosensitive drum, there is a problem that the configuration is complicated and the cost is increased.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus capable of obtaining a good image free from density unevenness in the longitudinal direction with an inexpensive structure even when an a-Si photosensitive drum is used.

[0022]

In order to achieve the above object, the present invention provides a method for transferring a toner image formed on an image carrier having a photosensitive layer containing at least amorphous silicon on a conductive substrate onto a transfer material. And a pre-exposure unit for pre-exposing the image carrier to remove residual charges on the image carrier after transferring a toner image to a transfer material. And the image carrier is disposed along the longitudinal direction of the image carrier, and the pre-exposure means transfers the image carrier from the pre-exposure unit in accordance with the charging characteristics and potential attenuation characteristics in the longitudinal direction of the image carrier. Light attenuating means for adjusting the amount of pre-exposure for irradiation.

Further, the light attenuating means adjusts the amount of pre-exposure light applied to the image carrier from the pre-exposure means in accordance with a longitudinal charging characteristic and a potential attenuation characteristic of the image carrier. The filter is characterized by having excellent light transmission characteristics along the longitudinal direction of the image carrier.

Further, the light attenuating means adjusts the amount of pre-exposure light applied to the image carrier from the pre-exposure means in accordance with the longitudinal charging characteristics and potential attenuation characteristics of the image carrier. The slit width is a slit formed along the longitudinal direction of the image carrier.

[0025]

Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1 FIG. 1 is a schematic configuration diagram showing an image forming apparatus (copier in the figure) according to the present embodiment. The same members as those of the image forming apparatus of the conventional example shown in FIG. 13 are denoted by the same reference numerals, and redundant description will be omitted.

In FIG. 1, A is an apparatus main body of the image forming apparatus according to the present embodiment, and B is an image reading unit (image scanner) mounted on the apparatus main body A. The configuration of the image reading unit B is the same as that of the conventional example shown in FIG. 13, and a description thereof will be omitted in the present embodiment.

The apparatus body A is a positively chargeable a-Si photosensitive drum as an image carrier (hereinafter simply referred to as a photosensitive body).
1, a magnetic brush charging device 20, an exposure device 3, a developing device 4, a transfer device 5, a cleaning blade 6, a pre-exposure lamp 7, a fixing device 6, and the like.

In the photosensitive drum 1, as shown in FIG. 2, a charge injection blocking layer 1b and a photoconductive layer 1c constituting a photosensitive layer are sequentially deposited on the surface of a conductive support 1a made of aluminum.
Further, a surface layer 1d is formed thereon.

The charge injection blocking layer 1b comprises a conductive support 1a
For preventing the injection of electric charge from the substrate into the photoconductive layer 1c, and is provided as necessary. The photoconductive layer 1c is made of an amorphous material containing at least silicon atoms, and exhibits photoconductivity. The surface layer 1d contains silicon atoms and carbon atoms (and, if necessary, hydrogen atoms and / or halogen atoms) and has the ability to hold an electrostatic latent image. The surface resistance of the surface layer 1d is 10 ⁹ to 10 ¹⁴ Ω · cm.

As a charging member of the photosensitive drum 1, a device using corona charging has been practically used. However, the relative dielectric constant of an a-Si photosensitive drum is 11 to 12.
Therefore, the electrostatic capacity is increased, and accordingly, the charging ability is reduced, and the image flow due to the flow of the latent image due to the discharge easily occurs.

On the other hand, a contact charging member using a conductive roller, a fur brush roller, a magnet roller carrying magnetic particles, or the like is used as the charging member.
When charging the photosensitive drum 1 under conditions to maintain a sufficient contact state with the surface of the photosensitive drum 1 is 10 ⁹ ~10 ¹⁴ Ω · c
Since it has a resistance of m, it is possible to obtain on the surface of the photosensitive drum 1 a charging potential substantially equal to the DC component of the bias applied to the contact charging member.

Such a charging method is referred to as injection charging since charging is performed by directly injecting charges into the photosensitive drum 1 without using discharge. If this injection charging is used, the charging of the photosensitive drum 1 is not performed using a discharge phenomenon that is performed by using a corona charger, so that it is possible to perform complete ozoneless charging with low power. In addition, it is possible to prevent a reduction in charging ability and an image deletion, and it is easy to control the potential because the charging is performed in the vicinity of the applied voltage.

Therefore, in this embodiment, the magnetic brush charging device 20 is used as the contact charging means. As shown in FIG. 3, the magnetic brush charging device 20 is rotatably supported in a charging container 22 and has a charging sleeve 23 made of a non-magnetic material (for example, stainless steel) having a fixed magnet roller 24 inside. Conductive magnetic particles 25, which are carried on the outer peripheral surface of the sleeve 23 in a brush shape by the magnetic force of the magnet roller 24 and contact the surface of the photosensitive drum 1 to inject electric charge, and the magnetic particles 25 are uniformly distributed on the surface of the charging sleeve 23. A regulating blade 26 made of a non-magnetic material (for example, stainless steel) to be coated to a thickness is provided. The contact nip width of the magnetic particles 25 with the photosensitive drum 1 is 6 in this embodiment.
mm.

A charging bias power supply (not shown) is connected to the charging sleeve 23, and a predetermined charging bias (charging bias in which alternating current is superimposed on direct current) is applied. By applying a charging bias to the charging sleeve 23, a charge is given from the magnetic particles 25 onto the photosensitive drum 1, and charged to a value close to a potential corresponding to the charging voltage. The charging sleeve 23 rotates in the counter direction with respect to the photoconductor 1, and in the present embodiment, the charging sleeve 23 rotates at a peripheral speed of 250 mm / sec with respect to the photosensitive drum 1 having a peripheral speed of 200 mm / sec.

In the present embodiment, as the magnetic particles 25, the ferrite surface is oxidized and reduced to adjust the resistance. On the other hand, a carbon-based resin is dispersed in carbon black to adjust the resistance. One coated with 1.0% by weight was used. The core of the magnetic particles 25 has an average particle diameter of 10 to 100 μm and a saturation magnetization of 20 to 2 μm.
50 emu / cm ³ , resistance 1 × 10 ² to 10 ¹⁰ Ω · c
m. Further, considering that there is an insulation defect such as a pinhole in the photosensitive drum 1,
It is preferable to use one having a resistivity of 10 ⁶ Ω · cm or more.

In order to improve the charging performance, it is better to use one having as small a resistance as possible, and in order to perform uniform charging, it is preferable to use one having a resistance of 1 × 10 ⁹ Ω · cm or less. Therefore, in the present embodiment, the average particle size is 25 μm, the saturation magnetization is 200 emu / cm ³ , and the resistance is 5 μm.
× 10 ⁶ Ω · cm magnetic particles 25 were used.

As shown in FIG. 4, the developing device 4 is a two-component contact developing device (two-component magnetic brush developing device) in the present embodiment. In this figure, 27 is a developing container, 28
Is a rotatable developing sleeve as a developer carrier, 29
Is a magnet roller fixedly arranged in the developing sleeve 28, 30 and 31 are agitating screws, 32 is a toner hopper for replenishment, and 33 is a regulation arranged to form a thin layer of the developer T on the surface of the developing sleeve 28. It is a blade.

The developing sleeve 28 has a region closest to the photosensitive drum 1 at least at the time of development at about 500 μm.
Are set so that the developer T can be developed in a state of being in contact with the photosensitive drum 1. The toner t, which is the developer T used in the present embodiment,
A toner having an average particle size of 8 μm manufactured by a pulverization method was used, and magnetic particles having an average particle size of 45 μm were used as the carrier c. Further, the toner t and the carrier c are mixed at a weight ratio of 7:
A mixture of 93 (toner particles: magnetic particles) was used as the developer T.

Next, an electrostatic latent image formed on the surface of the photosensitive drum 1 by exposure of the exposure device 3 is
Step of Visualizing by Component Brush and Method of Developing Agent T
Will be described.

First, the developing sleeve 28 is
The developer T, which is rotated in the counter direction with respect to the rotation direction of the developer T, is conveyed, and the developer T pumped by the N2 pole is regulated by the regulating blade 33 arranged perpendicular to the developing sleeve 28 in the process of being conveyed. A thin layer is formed on the sleeve 28. Here, when the developer T formed in a thin layer is conveyed to the main development pole (S pole), a spike is formed by its magnetic force. The electrostatic latent image on the photosensitive drum 1 is developed with the developer T formed in the spike shape, and thereafter, the developing sleeve 28 is developed by the repulsive magnetic fields of two adjacent N poles.
The upper developer T is returned into the developing container 27.

A developing bias in which an AC voltage is superimposed on a DC voltage is applied to the developing sleeve 28 from a developing bias power supply (not shown).

The transfer device 5 is a belt transfer device in the present embodiment, and transfers the endless transfer belt 5a to the drive roller 5a.
b and the driven roller 5c, and is driven to rotate at a peripheral speed substantially equal to the peripheral speed of the photosensitive drum 1 in the direction of the arrow. The transfer belt 5a is brought into contact with the surface of the photosensitive drum 1 by a transfer blade 5d provided inside the transfer belt 5a. The transfer material P is conveyed to the transfer nip N on the upper surface of the ascending belt portion of the transfer belt 5a.

When the leading edge of the transfer material P enters the transfer nip N, a predetermined transfer bias is applied to the transfer blade 5d from a transfer bias power supply (not shown), so that the toner t And the toner image on the surface of the photosensitive drum 1 is transferred to the upper surface of the transfer material P.

Next, an image forming operation of the above-described image forming apparatus will be described.

At the time of image formation, the photosensitive drum 1 is driven to rotate in the direction of arrow a by driving means (not shown), and the surface is uniformly charged to a predetermined positive voltage by the above-described injection charging by the magnetic brush charging device 3. You. Then, image exposure is performed by the exposure device 3 on the charged photosensitive drum 1 to form an electrostatic latent image corresponding to image information input from the image reading unit 11 of the image reading unit B. The latent image is developed by the developing device 4 as a toner image as described above.

When the leading end of the toner image on the photosensitive drum 1 reaches the transfer nip portion N between the photosensitive drum 1 and the transfer belt 5a, the sheet feeding cassette 12 is synchronized with this timing.
The transfer material P, such as the paper inside, is fed by the feed roller 13 and conveyed to the transfer nip N by the registration roller 14, and the transfer blade 5 d to which the transfer bias is applied reverses the toner t on the back side of the transfer material P. A polarity charge is applied, and the toner image on the photosensitive drum 1 is transferred to the front surface side.
The transfer material P on which the toner image has been transferred is transferred to the transfer belt 5.
a, the toner image is thermally fixed on the surface of the transfer material P by heating and pressing by the heating roller 8a and the fixing roller 8b of the fixing device 8, and is discharged onto the tray 16 through the paper discharge roller 15. . Further, on the photosensitive drum 1 after the transfer of the toner image, the contaminants such as transfer residual toner adhering to the surface are removed by the cleaning blade 6 and collected.

The surface of the photosensitive drum 1 is uniformly exposed to light by the pre-exposure lamp 7, so that the number of photo carriers latent inside the photosensitive drum 1 becomes excessive and uniform over the entire surface. . At this time,
Increase the amount of pre-exposure emitted from the pre-exposure lamp 7,
The wavelength of the pre-exposure is set to the spectral sensitivity peak of the photosensitive drum 1 (about 68
(0 to 700 nm), it is possible to erase the optical memory (ghost) more effectively.

However, when the film thickness unevenness exists in the longitudinal direction of the photosensitive drum 1 as described above, the electric field applied between the photoconductive layers 1c is different. As a result, the potential decay is greater in a portion where the film thickness is smaller, and even if the charging portion is uniformly charged, the potential unevenness occurs in the developing portion. In addition, the chargeability is disadvantageous because the smaller the film thickness, the greater the capacitance, and the lower the chargeability, the more uneven the charging in the developing section becomes. This potential non-uniformity remains even when image exposure is performed, and appears as a remarkable density non-uniformity particularly in a low-density region that is easily recognized by the eyes during the development process.

The potential unevenness due to the film thickness unevenness or the composition unevenness which occurs in the longitudinal direction and the circumferential direction of the photosensitive drum 1 is not irregular unevenness but periodicity of circumferential potential unevenness. Is the same in the longitudinal direction, and the potential unevenness in the longitudinal direction has the same tendency in the circumferential direction.
For example, FIGS. 5A and 5B and FIGS. 6A and 6B show examples of the potential unevenness in the longitudinal direction and the circumferential direction of the photosensitive drum 1 used in the present embodiment.

Here, FIGS. 5A and 5B show the potential unevenness in the longitudinal direction at the developing position, and FIGS. 6A and 6B.
Indicates uneven potential in the circumferential direction at the developing position. The charging condition at this time is as follows.
A charging bias of V is applied, and a pre-exposure lamp 7 for erasing the optical memory is uniformly irradiated in the longitudinal direction of the photosensitive drum 1 before the charging step. By irradiating the pre-exposure lamp 7 in this manner, the dark decay described above increases during the period from the charging of the surface of the photosensitive drum 1 to the development area, causing a potential decay of about 150 V at the development position. If this potential decay is not constant in the longitudinal direction and the circumferential direction, potential unevenness will occur at the time of development even if the toner is uniformly charged.

The potential unevenness at each position will be described. For example, in the photosensitive drum 1 used in the present embodiment, as shown in FIGS. 5A and 5B, the potential unevenness in the longitudinal direction is shown in FIG. , (B) when the potential at the left end position a is low and the potential at the right end position a ″ is high, the potentials at the left end positions b, c and d are similarly low in the circumferential direction,
The potentials at the right end positions b ″, c ″, and d ″ become higher. That is, as shown in FIGS. 5A and 5B, the photoconductor 1 of the present embodiment is viewed from the left side in the longitudinal direction. It has potential unevenness whose potential gradually increases along the right side.

Further, as shown in FIGS. 6A and 6B, the potential unevenness in the circumferential direction of the photosensitive drum 1 is shown in FIGS. 6A and 6B.
In the case where the potential at the position a on the left end side is low and the potential at the position d is high, similarly in the longitudinal direction, the potentials at the positions a ′ and a ″ are high and the potentials at the positions d ′ and d ″ are low.

For this reason, in this embodiment, in order to prevent potential unevenness in the longitudinal direction of the photosensitive drum 1, as shown in FIGS.
Between them, a filter 21 as light attenuating means having different light transmittance in the longitudinal direction of the photosensitive drum 1 is disposed.

When the surface of the photosensitive drum 1 is uniformly pre-exposed by the pre-exposure lamp 7, the filter 21 has a position a, b, c on the left end side of the photosensitive drum 1 where the potential at the developing position in FIG. , D near the right end of the photosensitive drum 1 where the potential at the developing position becomes high, the amount of transmitted light increases so as to decrease the amount of transmitted light. It is set to be thin. That is, in the filter 21 shown in FIG. 7, the amount of transmitted light gradually increases from the left side to the right side in the longitudinal direction.

By using the filter 21 set such that the amount of transmitted light is different, the potential attenuation near the positions a, b, c and d on the left end side of the photosensitive drum 1 is reduced, and the photosensitive drum 1 Right end positions a ″, b ″, c ″,
Since the amount of potential attenuation near d ″ increases, as shown in FIG.
(B) and the charging characteristics and the potential decay characteristics shown in FIGS. 6A and 6B are canceled out to make the potential at the developing position uniform.

As described above, in the present embodiment, the filter 21 whose light transmittance is adjusted along the longitudinal direction of the photosensitive drum 1 so as to prevent potential unevenness in the longitudinal direction of the photosensitive drum 1.
Is arranged between the pre-exposure lamp 7 and the photosensitive drum 1, the potential at the developing position of the photosensitive drum 1 is made uniform with an inexpensive configuration, and the density unevenness in the longitudinal direction of the photosensitive drum 1 is prevented. Images can be obtained.

<Second Embodiment> In the first embodiment, FIG.
This is an example of preventing the potential unevenness in the longitudinal direction of the photosensitive drum 1 having the potential unevenness as shown in FIGS. 6A and 6B and FIGS. , FIG.
An example in which the potential unevenness in the longitudinal direction of the photosensitive drum 1 having the potential unevenness shown in FIGS. 9A and 9B and FIGS. 9A and 9B will be described. The image forming apparatus according to the present embodiment is the same as the image forming apparatus according to the first embodiment shown in FIG. 1 except for the configuration of the filter 21, and a description thereof will be omitted in the present embodiment.

The photosensitive drum 1 used in the present embodiment
In FIGS. 8A and 8B, positions a ', b', c ', and d' at the central portion are shown as potential unevenness in the longitudinal direction as shown in FIGS.
Is high, and positions a, b, c, d and a ″ on both ends are
This is the case where the potentials of b ″, c ″ and d ″ are low.
As shown in (a) and (b), as potential unevenness in the circumferential direction of the photosensitive drum 1, the potentials at the positions b, b ', and b "are high and the potentials at the positions d, d', and d" are low. It is. That is,
As shown in FIGS. 8A and 8B, the photosensitive drum 1 of the present embodiment has a high potential at the central portion, and has gradually lower potential unevenness along both sides thereof.

For this reason, in this embodiment, in order to prevent potential unevenness in the longitudinal direction of the photosensitive drum 1, FIG.
As shown in FIG. 0, a filter 21 a as light attenuating means having different light transmittance in the longitudinal direction of the photosensitive drum 1 was disposed between the pre-exposure lamp 7 and the photosensitive drum 1.

In this embodiment, when the surface of the photosensitive drum 1 is uniformly pre-exposed by the pre-exposure lamp 7, the filter 21 a reduces the potential at the developing position shown in FIGS. Positions a, b, c on the left and right ends of the drum 1
The vicinity of d and the vicinity of a ″, b ″, c ″, and d ″ are set to be high so that the amount of transmitted light is small, and the positions a ′, b ′, and c of the central portion of the photosensitive drum 1 where the potential at the development position becomes high. ', D'
The vicinity is set to be thin so that the amount of transmitted light increases. That is, in the filter 21a shown in FIG. 10, the amount of transmitted light is made to gradually decrease from the center to the both ends.

By using such a filter 21a having a different amount of transmitted light, the photosensitive drum 1
Near the positions a, b, c, d on the left and right sides of
Since the potential attenuation near b ″, c ″ and d ″ becomes smaller and the potential attenuation near the center a ′, b ′, c ′ and d ′ of the photosensitive drum 1 becomes larger, the potential attenuation shown in FIG. ), (B) and the charging characteristics and the potential decay characteristics as shown in FIGS. 9 (a) and 9 (b) cancel out the potential at the developing position.

As described above, also in this embodiment, the filter 21a whose light transmittance is adjusted along the longitudinal direction of the photosensitive drum 1 is used as a pre-exposure lamp so as to prevent potential unevenness in the longitudinal direction of the photosensitive drum 1. By disposing the photosensitive drum 1 between the photosensitive drum 1 and the photosensitive drum 1, the potential at the developing position of the photosensitive drum 1 is made uniform with an inexpensive configuration, thereby preventing the density unevenness in the longitudinal direction of the photosensitive drum 1 and obtaining a good image. it can.

<Embodiment 3> In Embodiments 1 and 2,
Filters 21 and 21a having different transmittances in the longitudinal direction of the photosensitive drum are arranged between the pre-exposure lamp 7 and the photosensitive drum 1 as light attenuating means corresponding to the charging characteristics and potential attenuation characteristics in the longitudinal direction of the photosensitive drum 1. However, in the present embodiment, as shown in FIG. 11, a slit 35 having a different slit width in the longitudinal direction of the photosensitive drum 1 is provided as a light attenuation unit. The image forming apparatus according to the present embodiment
Except for the slit 35, the image forming apparatus is the same as the image forming apparatus according to the first embodiment shown in FIG. 1, and a description thereof will be omitted in this embodiment.

The photosensitive drum 1 used in the present embodiment
Has potential unevenness in the longitudinal direction as shown in FIGS. 5 (a) and 5 (b). That is, the photosensitive drum 1 has potential unevenness whose potential gradually increases from the left side to the right side in the longitudinal direction.

For this reason, in the present embodiment, in order to prevent potential unevenness in the longitudinal direction of the photosensitive drum 1, FIG.
As shown in FIG. 1, between the pre-exposure lamp 7 and the photosensitive drum 1, a slit 35 as a light attenuating means having a different slit width in the longitudinal direction of the photosensitive drum 1 is arranged.

When the surface of the photosensitive drum 1 is uniformly pre-exposed by the pre-exposure lamp 7, the slits 35 are located at positions a, b, c on the left end side of the photosensitive drum 1 where the potential at the developing position in FIG. , D near the positions a ″, b ″, c ″, and d ″ on the right end side of the photosensitive drum 1 where the potential at the developing position is high, so that the amount of transmitted light is small. The slit width is set wide so as to increase. That is, in the slit 35 shown in FIG. 11, the amount of transmitted light gradually increases from the left side to the right side in the longitudinal direction.

By using the slits 35 set such that the amount of transmitted light is different, the potential attenuation near the positions a, b, c, and d on the left end side of the photosensitive drum 1 is reduced, and the photosensitive drum 1 Right end positions a ″, b ″, c ″,
Since the amount of potential attenuation near d ″ increases, as shown in FIG.
The charging characteristic and the potential decay characteristic as shown in FIG. 4B are offset, and the potential at the developing position can be made uniform.

As described above, in the present embodiment, the slit 3 whose slit width is adjusted along the longitudinal direction of the photosensitive drum 1 so as to prevent potential unevenness in the longitudinal direction of the photosensitive drum 1.
5 is arranged between the pre-exposure lamp 7 and the photosensitive drum 1, the potential at the developing position of the photosensitive drum 1 is made uniform with an inexpensive configuration, and the density unevenness in the longitudinal direction of the photosensitive drum 1 is prevented. Image can be obtained.

<Embodiment 4> In Embodiment 3, FIG.
8A and 8B show an example in which the potential unevenness in the longitudinal direction of the photosensitive drum 1 having the potential unevenness as shown in FIGS. 8A and 8B is prevented by the slit 35. In the present embodiment, FIGS.
An example in which the potential unevenness in the longitudinal direction of the photosensitive drum 1 having the potential unevenness as shown in FIG. It should be noted that the image forming apparatus of the present embodiment has the slit 3
Other than 5 is the same as the image forming apparatuses of the first and third embodiments shown in FIG. 1 and FIG. 11, and the description thereof is omitted in the present embodiment.

The photosensitive drum 1 used in the present embodiment
In FIG. 8, as shown in FIGS. 8 (a) and 8 (b), potential unevenness in the longitudinal direction is regarded as the potential at the central positions a ', b', c 'and d' in FIGS. 8 (a) and 8 (b). Is high, and the potentials at positions a, b, c, d and a ″, b ″, c ″, d ″ at both ends are low. That is, in the photosensitive drum 1 of the present embodiment, as shown in FIGS.
It has gradually lower potential unevenness along both sides.

For this reason, in this embodiment, in order to prevent potential unevenness in the longitudinal direction of the photosensitive drum 1, FIG.
As shown in FIG. 2, a slit 35a as a light attenuating means having a different gap in the longitudinal direction of the photosensitive drum 1 is arranged between the pre-exposure lamp 7 and the photosensitive drum 1.

In the present embodiment, when the surface of the photosensitive drum 1 is uniformly pre-exposed by the pre-exposure lamp 7, the slit 35 a is provided at the left end and the right end of the photosensitive drum 1 where the potential at the developing position in FIG. In the vicinity of positions a, b, c, and d, and in the vicinity of a ", b", c ", and d", the slit width is set to be narrow so that the amount of transmitted light is small, and the potential at the developing position is high. A ', b', c 'at the center of
In the vicinity of d ', the slit width is set wide so that the amount of transmitted light increases. That is, in the slit 35a shown in FIG. 12, the slit width is gradually narrowed from the center to the both ends.

By using the slit 35 set to such a slit width, the vicinity of the positions a, b, c, and d on the left end side and the right end side of the photosensitive drum 1 and a ″, b ″, c ″,
8 (a) and 8 (b), since the potential attenuation near d ″ becomes smaller and the potential attenuation near the positions a ′, b ′, c ′, and d ′ at the center of the photosensitive drum 1 becomes larger. The potential at the developing position can be made uniform by being offset by the charging characteristics and the potential decay characteristics as shown.

As described above, also in the present embodiment, the slit 35a whose slit width is adjusted along the longitudinal direction of the photosensitive drum 1 is connected to the pre-exposure lamp 7 so as to prevent potential unevenness in the longitudinal direction of the photosensitive drum 1. By disposing the photosensitive drum 1 between the photosensitive drum 1 and the photosensitive drum 1, the potential at the developing position of the photosensitive drum 1 is made uniform with an inexpensive configuration, thereby preventing density unevenness in the longitudinal direction of the photosensitive drum 1 and obtaining a good image. .

Further, in each of the above-described embodiments, the potential unevenness in the longitudinal direction of the photosensitive drum 1 has the characteristic as shown in FIG. 5 or FIG. 6. However, the present invention is not limited to this. The present invention can be applied to the photosensitive drum 1 having the characteristic of potential unevenness. Also in this case, the photosensitive drum 1
By using the filters 21 and 21a in which the amount of transmitted light is adjusted according to the characteristic of the potential unevenness in the longitudinal direction and the slits 35 and 35a in which the slit width is adjusted, the potential at the developing position of the photosensitive drum 1 is made uniform. Photosensitive drum 1
Is prevented, and a good image can be obtained.

In each of the above embodiments, a filter or a slit is used as the light attenuating means. However, other than this, for example, the transmittance of the imaging lens provided between the light emitting portion of the pre-exposure lamp and the photosensitive drum may be used. May be changed in the longitudinal direction. In other words, the present invention does not control the amount of light emitted from the pre-exposure means in the longitudinal direction, and provides light attenuation corresponding to the longitudinal charging characteristics and potential attenuation characteristics of the photosensitive drum between the light-emitting portion of the pre-exposure means and the photosensitive drum. The provision of the means cancels out potential unevenness in the longitudinal direction of the photosensitive drum, and includes all cases where the potential at the developing position can be made uniform.

In each of the above embodiments, the positively charged a-Si photosensitive drum is used.
The same effect can be obtained with a -Si photosensitive drum. In other words, regardless of the charging polarity and layer configuration of the photosensitive drum,
When potential unevenness in the longitudinal direction occurs in the a-Si photosensitive drum, by applying the present invention, unevenness in density in the longitudinal direction of the photosensitive drum can be prevented, and a good image can be obtained.

[0079]

As described above, according to the present invention, the image carrier is moved between the pre-exposure device and the image carrier in accordance with the charging characteristics and potential attenuation characteristics in the longitudinal direction of the image carrier. The provision of the light attenuating means for adjusting the amount of pre-exposure to irradiate the image carrier makes it possible to make the charging potential in the longitudinal direction of the image carrier uniform with an inexpensive structure, and to provide a longitudinal density of the image carrier. Unevenness can be prevented and a good image can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 illustrates an image forming apparatus according to Embodiment 1 of the present invention.
Sectional drawing which shows the layer structure of -Si photosensitive drum.

FIG. 3 is a schematic sectional view showing a magnetic brush charging device of the image forming apparatus according to the first embodiment of the present invention.

FIG. 4 is a schematic sectional view showing a developing device of the image forming apparatus according to the first embodiment of the present invention.

FIGS. 5A and 5B are views showing a state of potential unevenness in a longitudinal direction of the photosensitive drum according to the first embodiment of the present invention.

FIGS. 6A and 6B are diagrams showing a state of potential unevenness in a circumferential direction of the photosensitive drum according to the first embodiment of the present invention.

FIG. 7 is a perspective view showing a filter used in the first embodiment of the present invention.

FIGS. 8A and 8B are diagrams showing a state of potential unevenness in a longitudinal direction of a photosensitive drum according to a second embodiment of the present invention.

FIGS. 9A and 9B are diagrams showing a state of potential unevenness in the circumferential direction of the photosensitive drum according to the second embodiment of the present invention.

FIG. 10 is a perspective view showing a filter used in Embodiment 2 of the present invention.

FIG. 11 is a perspective view showing a slit used in Embodiment 3 of the present invention.

FIG. 12 is a perspective view showing a slit used in Embodiment 4 of the present invention.

FIG. 13 is a schematic configuration diagram showing an image forming apparatus in a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum (image carrier) 3 Exposure device 4 Developing device 5 Transfer device 5a Transfer blade 7 Pre-exposure lamp (pre-exposure means) 8 Fixing device 20 Magnetic brush charging device 21, 21a Filter (light attenuating device) 23 Charging sleeve 25 Magnetic particles 28 Developing sleeve 35, 35a Slit (light attenuating means)

Claims (3)

[Claims] 1. An image forming apparatus for forming an image by transferring a toner image formed on an image carrier having a photosensitive layer containing at least amorphous silicon on a conductive substrate onto a transfer material, wherein the toner image is transferred. A pre-exposure unit that pre-exposes the image carrier to remove residual charges on the image carrier after the image carrier has been transferred to a material, and a longitudinal length of the image carrier between the pre-exposure unit and the image carrier. Light attenuating means arranged along the direction, and adjusting the amount of pre-exposure to irradiate the image carrier from the pre-exposure means in accordance with the charging characteristics and potential attenuation characteristics in the longitudinal direction of the image carrier. An image forming apparatus comprising: 2. The method according to claim 1, wherein the light attenuating means adjusts the amount of pre-exposure irradiating the image carrier from the pre-exposure means in accordance with a longitudinal charging characteristic and a potential attenuation characteristic of the image carrier. 2. The image forming apparatus according to claim 1, wherein the filter has excellent light transmission characteristics along a longitudinal direction of the image carrier. 3. 3. The light attenuating means adjusts the amount of pre-exposure light applied to the image carrier from the pre-exposure means in accordance with a longitudinal charging characteristic and a potential attenuation characteristic of the image carrier. The image forming apparatus according to claim 1, wherein the slit width is a slit formed along a longitudinal direction of the image carrier.