JP2004138853A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of uniformizing the electrification potential on a photoreceptor surface. <P>SOLUTION: The surface of the photoreceptor 21 is electrified by a scorotron electrifier 22 having a discharge electrode 22a, a back plate 22c and a grid 22b, and also, an air is made to flow along the back plate 22c so as to discharge the air. A ventilation opening 22c3 is formed in the side face 22c5 of the back plate 22c, and also, an insulating sheet 22k having nearly the same width (w) as that of the ventilation opening 22c3 is attached to the inner surface 22c6 of the side face 22c5 of the back plate 22c in the axial direction of the electrifier 22. Provided that the maximum image forming width of the photoreceptor 21 is expressed by (t), the length in the axial direction of the ventilation opening 22c3 is expressed by Th and the length in the axial direction of the insulating sheet 22k is expressed by Ts, t≤Th+Ts is established. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus such as a printer, a facsimile, and a copying machine that forms an image using an electrophotographic technique. In particular, the present invention relates to a technique for charging the photoreceptor with a corona discharger.
[0002]
[Prior art]
Generally, an image forming apparatus using an electrophotographic technique includes a photosensitive member having a photosensitive layer on an outer peripheral surface, a charging unit for uniformly charging the outer peripheral surface of the photosensitive member, and a uniform charging by the charging unit. Exposing means for selectively exposing the outer peripheral surface to form an electrostatic latent image, and applying a toner as a developer to the electrostatic latent image formed by the exposing means to form a visible image (toner image). And a transfer unit for transferring the toner image developed by the developing unit to a recording material such as paper as a transfer target.
As a charging unit for charging the outer peripheral surface of the photoreceptor, a charging unit using a corona discharger called a scorotron charger is known. The scorotron charger has a discharge electrode, a support member for supporting the discharge electrode, a back plate for performing stable discharge, and a grid for controlling a charging potential on the photoconductor. When charging, for example, a voltage of -4 KV to -6 KV is applied to the discharge electrode, -600 V (potential depending on the potential to be actually charged) is applied to the grid, and the back plate is the same as the ground or the grid. By setting the potential, a corona discharge is generated from the discharge electrode, and the photosensitive member can be charged to about -600V.
[0003]
Since the above-mentioned scorotron charger uses corona discharge, generation of ozone cannot be avoided. It is known that ozone degrades a photoreceptor and a charger and causes an image defect.
Therefore, conventionally, a ventilation opening is provided in the axial direction of the back surface of the charger, and a ventilation duct is provided on the back side of the charger, and air is blown from one end of the duct to exhaust ozone in the charger. Reference 1).
[0004]
[Patent Document 1]
Japanese Utility Model Publication No. 6-43815 (page 1, FIG. 1)
[0005]
[Problems to be solved by the invention]
In the conventional technology described above, in a low-temperature and low-humidity environment in which exhaustion of ozone is insufficient and corona discharge becomes unstable, partial deterioration of the discharge electrode is promoted, and the discharge becomes non-uniform. In some cases, image defects were caused.
The inventors of the present application have investigated the cause, and found that ozone partially stays in the charger (particularly on the downstream side of the airflow).
It has also been found that in order to solve this problem, it is only necessary to provide a ventilation opening on the side surface of the back plate (for example, the side surface on the downstream side of the airflow) to efficiently exhaust the ozone in the charger.
On the other hand, however, it has also been found that providing a ventilation opening on the side surface of the back plate lowers the absolute value of the charging potential of the photoconductor at the corresponding portion, and impairs the uniformity of the charging potential. For example, when an opening having a width of about 8 mm and a length of about 50 mm was provided on the side surface of the back plate, the absolute value of the charging potential was reduced by about 20 V at the corresponding portion. This is a difference that cannot be ignored in view of the recent demand for higher image quality in color image formation. Normally, in order to obtain a good color image in an image forming apparatus, it is desired that the in-plane variation of the charging potential (variation in the axial direction of the photoreceptor) be 20 V or less. It is difficult due to the tolerance of components constituting the container, and it is a serious problem that the potential difference in the axial direction of the photoconductor is about 20 V from the beginning in such a situation.
[0006]
SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus which can solve the above-described problems and can make the charged potential on the surface of a photoreceptor uniform.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, an image forming apparatus according to the present invention provides an image forming apparatus in which a photoreceptor surface is charged by a charger having a discharge electrode and a back plate, and exhaust is performed by flowing an air current along the back plate. A device,
A ventilation opening is provided on a side surface of the back plate, and an insulator sheet having substantially the same width as the width of the ventilation opening is attached to an inner surface of the side surface of the back plate in the axial direction of the charger. Features.
Further, when a maximum image forming width by the photoconductor is t, an axial length of the ventilation opening is Th, and an axial length of the insulator sheet is Ts,
t ≦ Th + Ts
It is desirable that
[0008]
[Effects]
The image forming apparatus according to the present invention is an image forming apparatus that discharges air by flowing an air current along the back plate while charging the surface of the photoconductor with a charger having a discharge electrode and a back plate,
A ventilation opening is provided on the side surface of the back plate, and an insulator sheet having substantially the same width as the width of the ventilation opening is attached to the inner surface of the side surface of the back plate in the axial direction of the charger. According to this image forming apparatus, the following operation and effect can be obtained.
That is, since the ventilation opening is provided on the side surface of the back plate, ozone in the charger is efficiently and sufficiently exhausted through the ventilation opening.
Therefore, even in a low-temperature and low-humidity environment where corona discharge becomes unstable, partial deterioration of the discharge electrode is prevented, and the discharge becomes uniform.
On the other hand, in the case where such an opening for ventilation is provided, if no measures are taken, as described above, the absolute value of the charging potential of the photoconductor at a portion corresponding to the opening may be different from that of another portion. Will be reduced as compared with.
On the other hand, according to the present invention, an insulator sheet having substantially the same width as the width of the ventilation opening is attached to the inner surface of the side surface of the back plate in the axial direction of the charger. Can be made uniform. In the portion provided with the ventilation opening, the amount of discharge by the charger decreases and the absolute value of the charging potential of the photoconductor at the portion corresponding to the portion decreases, but the side surface of the back plate in the axial direction of the charger. When an insulating sheet having a width substantially equal to the width of the ventilation opening is attached to the inner surface of the photosensitive member, the amount of discharge by the charger is reduced even at the attached portion, and the charging potential of the photoconductor surface at a portion corresponding to the portion is reduced. Is also reduced.
Therefore, according to the present invention, the charging potential on the surface of the photoconductor can be made uniform.
Therefore, when the maximum image forming width by the photoconductor is t, the axial length of the ventilation opening is Th, and the axial length of the insulator sheet is Ts,
t ≦ Th + Ts
By doing so, a uniform charging potential can be obtained over the entire maximum image forming width.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic front view showing an internal structure of an embodiment of an image forming apparatus according to the present invention.
This image forming apparatus is a color image forming apparatus capable of forming a full-color image on both sides of A3 size paper (recording material), and includes a case 10 and an image carrier unit 20 accommodated in the case 10. And an exposure unit 30 as an exposure unit, a developing unit (developing device) 40 as a developing unit, an intermediate transfer unit 50, and a fixing unit (fixing unit) 60 as a fixing unit.
The case 10 is provided with a frame (not shown) of the apparatus main body, and each unit is attached to this frame.
[0010]
The image carrier unit 20 includes a photoconductor (image carrier) 21 having a photosensitive layer on the outer peripheral surface, and a charging unit (scorotron charger) 22 for uniformly charging the outer peripheral surface of the photoconductor 21. The outer peripheral surface of the photoreceptor 21 uniformly charged by the charging unit 22 is selectively exposed to laser light L from the exposure unit 30 to form an electrostatic latent image. A toner as a developer is applied by a developing device 40 to form a visible image (toner image), and the toner image is primarily transferred to an intermediate transfer belt 51 of an intermediate transfer body unit 50 by a primary transfer portion T1. In the transfer section T2, secondary transfer is performed on the transfer target sheet.
The image carrier unit 20 includes a cleaning unit (cleaning blade) 23 for removing the toner remaining on the surface of the photoconductor 21 after the primary transfer, and a waste toner storage for storing the waste toner removed by the cleaning unit 23. A part 24 is provided.
[0011]
In the case 10, a transport path 16 for transporting the sheet on which an image is formed on one side by the secondary transfer unit T <b> 2 to a sheet discharge unit (discharge tray unit) 15 on the upper surface of the case 10, And a return path 17 for returning the sheet conveyed toward the sheet discharge section 15 to the secondary transfer section T2 in order to switch back the sheet and form an image on the other side.
A lower portion of the case 10 is provided with a sheet feed tray 18 for holding a plurality of sheets stacked and a sheet feed roller 19 for feeding the sheets one by one toward the secondary transfer portion T2.
[0012]
The developing device 40 is a rotary developing device, and a plurality of developing device cartridges each containing a toner are detachably mounted on the rotating body main body 41. In this embodiment, a yellow developing cartridge 42Y, a magenta developing cartridge 42M, a cyan developing cartridge 42C, and a black developing cartridge 42K are provided. Only the developing device cartridge 42Y is drawn directly), and the rotating body 41 is rotated at a 90-degree pitch in the direction of the arrow to selectively contact the developing roller 43 with the photosensitive member 21. The surface can be selectively developed.
[0013]
The exposure unit 30 irradiates the laser beam L toward the photoconductor 21 from an exposure window 31 made of a sheet glass or the like.
[0014]
The intermediate transfer body unit 50 includes a unit frame (not shown) and a driving roller 54, a driven roller 55, a primary transfer roller 56 rotatably supported by the frame, and a state for stabilizing the state of the belt 51 in the primary transfer unit T1. The intermediate transfer belt 51 includes a guide roller 57, a tension roller 58, and the intermediate transfer belt 51 stretched around the rollers, and the belt 51 is driven to circulate in a direction indicated by an arrow in FIG. The primary transfer portion T1 is formed between the photoreceptor 21 and the primary transfer roller 56, and the secondary transfer portion T2 is formed at a pressure contact portion between the drive roller 54 and the secondary transfer roller 10b provided on the main body side. It is formed.
The secondary transfer roller 10b is capable of coming into contact with and separating from the drive roller 54 (and thus to the intermediate transfer belt 51), and forms a secondary transfer portion T2 when it comes into contact therewith.
Therefore, when forming a color image, a plurality of color toner images are superimposed on the intermediate transfer belt 51 in a state where the secondary transfer roller 10b is separated from the intermediate transfer belt 51 to form a color image. The secondary transfer roller 10b contacts the intermediate transfer belt 51, and the sheet is supplied to the contact portion (secondary transfer portion T2), whereby a color image (toner image) is transferred onto the sheet. .
The sheet on which the toner image has been transferred passes through the pair of heating rollers 61 of the fixing unit 60 so that the toner image is fused and fixed, and is discharged toward the discharge tray unit 15.
The fixing device 60 is an oilless fixing device that does not apply oil to the heating roller 61.
[0015]
2A and 2B are diagrams showing a main part of this embodiment. FIG. 2A is a graph showing a change in the charging potential in the axial direction of the surface of the photoconductor 21 when no correction is made by attaching an insulator sheet, and FIG. FIG. 4C is a schematic left side view of the image carrier unit 20, FIG. 4C is a front view of the charger 22 when FIG. 4B is viewed from the front, and FIG. 4D is a front view of the insulator sheet 22k. 3 is a cross-sectional view (schematic diagram) taken along the line III-III in FIG. 2B, and FIG. 4 is a cross-sectional view (schematic diagram) taken along the line IV-IV in FIG.
As shown in FIG. 2B, the charger 22 of this embodiment controls a wire-like discharge electrode 22a, a back plate 22c for performing stable discharge, and a charging potential on the photoconductor 21. Charger having a grid 22b for charging.
A ventilation opening 22c3 is provided on one side surface 22c5 of the back plate 22c, and an inner surface 22c6 (see FIG. 4) of the one side surface 22c5 of the back plate 22c in the axial direction of the charger 22 (the left-right direction in FIG. 2). An insulating sheet 22k having a width w substantially equal to the width of the ventilation opening 22c3 is attached. The insulator sheet 22k is attached to the inner surface 22c6 (or an insulating paint is applied in the form of a sheet 22k) on the axial extension of the ventilation opening 22c3.
Further, when the maximum image forming width by the photoconductor is t, the axial length of the ventilation opening 22c3 is Th, and the axial length of the insulator sheet 22k is Ts,
t ≦ Th + Ts
Each length is configured so that
[0016]
In FIG. 2B, reference numeral 20a denotes a case of the image carrier unit 20, and the photosensitive member 21 is rotatably supported on the shaft 21c of the unit case 20a, and is driven to rotate by a driving mechanism (not shown). .
The charger 22 is attached to the unit case 20a. Reference numeral 22d denotes a pair of left and right support members that support the discharge electrode 22a and the grid 22b, and are attached to both ends of the back plate 22c.
[0017]
As shown in FIGS. 3 and 4, a duct 20 b is provided in the case 20 a of the image carrier unit 20. The duct 20b has a substantially U-shaped cross section so as to surround the lower part of the charger 22. An air inlet (blower) 20c (see FIG. 2B) is provided at one end of the duct 20b. An exhaust port 20d is provided at the end of the back plate 22c at a position facing the ventilation opening 22c3.
An opening 22c4 extending in the axial direction (a direction perpendicular to the plane of FIG. 3) is provided on the bottom surface 22c1 of the back plate 22c.
Accordingly, the airflow B enters the charger 22 from the inflow port 20c through the opening 22c4 at the bottom of the back plate 22c as shown by the arrow b in FIG. 2B, and the ventilation opening 22c3 on the side and the exhaust port of the duct. The sheet is discharged out of the image carrier unit 20 through 20d.
[0018]
In the image forming apparatus as described above, the surface of the photoconductor 21 is charged by the charger 22 having the discharge electrode 22a, the back plate 22c, and the grid 22b, and the air is discharged along the back plate 22c to exhaust the air. The image forming apparatus is provided with a ventilation opening 22c3 on a side surface 22c5 of a back plate 22c, and an inner surface 22c6 of the one side surface 22c5 of the back plate 22c in the axial direction of the charger 22. Since the insulator sheet 22k having substantially the same width w is attached, according to this image forming apparatus, the following operation and effect can be obtained.
That is, since the ventilation opening 22c3 is provided on the side surface 22c5 of the back plate 22c, the ozone inside the charger 22 is efficiently and sufficiently exhausted through the ventilation opening 22c3.
Therefore, even in a low-temperature and low-humidity environment where corona discharge becomes unstable, partial deterioration of the discharge electrode 22a is prevented, and the discharge becomes uniform.
On the other hand, in the case where such a ventilation opening 22c3 is provided, if no measures are taken, as described above, the absolute value of the charging potential of the photosensitive member 21 at the portion b1 corresponding to the opening 22c3, as described above. Is reduced as compared with the other part b2 (see FIG. 2A).
On the other hand, according to this image forming apparatus, the insulator sheet 22k having a width w substantially equal to the width of the ventilation opening 22c3 is provided on the inner surface 22c6 of the one side surface 22c5 of the back plate 22c in the axial direction of the charger 22. Since it is attached, the charging potential on the surface of the photoconductor 21 can be made uniform. At the portion where the ventilation opening 22c3 is provided, the amount of discharge by the charger 22 decreases, and the absolute value of the charging potential on the surface of the photoconductor 21 at the portion b1 corresponding to the portion decreases (see FIG. 2A). An insulator sheet 22k having a width w substantially equal to the width of the ventilation opening 22c3 is attached to the inner surface 22c6 of the side surface 22c5 of the back plate 22c in the axial direction of the charger 22 (or the insulating paint is applied in a sheet 22k shape). Then, the amount of discharge by the charger is reduced in the attached portion, and the absolute value of the charged potential on the surface of the photosensitive member at the portion b2 corresponding to the portion is similarly reduced.
Therefore, according to this image forming apparatus, the charging potential on the surface of the photoconductor can be made uniform.
When the maximum image forming width by the photoconductor 21 is t, the axial length of the ventilation opening 22c3 is Th, and the axial length of the insulator sheet 22k is Ts,
t ≦ Th + Ts
Therefore, a uniform charging potential can be obtained over the entire maximum image forming width t.
[0019]
Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and can be appropriately modified and implemented within the scope of the present invention.
[0020]
[Brief description of the drawings]
FIG. 1 is a schematic front view showing the internal structure of an embodiment according to the present invention.
FIGS. 2A and 2B are diagrams showing a main part, in which FIG. 2A is a graph showing a change in charging potential in the axial direction of the surface of a photoconductor 21 when no correction is made by attaching an insulator sheet, and FIG. 20 is a schematic left side view, (c) is a front view of the charger 22 when FIG. (B) is viewed from the front, and (d) is a front view of the insulator sheet 22k.
FIG. 3 is a sectional view (schematic view) taken along line III-III in FIG. 2 (b).
FIG. 4 is a sectional view (schematic view) taken along line IV-IV in FIG. 2 (b).
[Explanation of symbols]
21 photoconductor, 22 scorotron charger, 22a discharge electrode, 22b grid, 22c back plate, 22c3 ventilation opening, 22c4 bottom opening, 22c5 side surface, 22c6 inner surface, 22k insulator sheet.

Claims (2)

An image forming apparatus that discharges and charges a photoreceptor surface with a charger having a back plate, and exhausts air by flowing an air current along the back plate.
A ventilation opening is provided on a side surface of the back plate, and an insulator sheet having substantially the same width as the width of the ventilation opening is attached to an inner surface of the side surface of the back plate in the axial direction of the charger. Characteristic image forming apparatus. When the maximum image forming width by the photoconductor is t, the axial length of the ventilation opening is Th, and the axial length of the insulator sheet is Ts,
t ≦ Th + Ts
2. The image forming apparatus according to claim 1, wherein:

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