JP2004138849A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which can uniformize potential by electrification on the surface of a photoreceptor. <P>SOLUTION: The image forming apparatus is provided with a scorotron charger 22 which is disposed opposite to the photoreceptor 21 coating a photosensitive layer 21b by dipping, electrifies the surface of the photoreceptor 21 and has a discharge electrode 22a and a back plate 22c. Therein, the numerical aperture of the back plate 22c is made small on the dip upper side 21b side and is made large on the dip lower 21b2 side in the photoreceptor 21. Air discharging is performed while letting air to flow along the back plate. <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]
When the photoconductor is charged by the scorotron charger as described above, a parameter that strongly affects the charging potential of the photoconductor includes a distance between the discharge electrode or grid and the surface of the photoconductor.
Therefore, the conventional corona discharger has a mechanism for keeping the distance between the discharge electrode and the surface of the photoreceptor constant (for example, see Patent Documents 1 to 3).
There is also known a scorotron charger in which an opening pattern of a grid is formed by regular hexagonal fine holes so as to have an opening ratio in the isotropic direction with respect to the photoconductor moving direction (for example, see Patent Document 4).
[0004]
[Patent Document 1]
Japanese Patent Publication No. 2-10423 (page 1, left column, page 2, right column, FIGS. 2-5)
[Patent Document 2]
Japanese Utility Model Publication No. 2-3554 (left column of page 2, Figs. 2 and 3)
[Patent Document 3]
Japanese Utility Model Publication No. 5-14282 (left column of page 2, Fig. 5)
[Patent Document 4]
Japanese Utility Model Publication No. 4-53650 (page 1, left column, Fig. 3)
[0005]
[Problems to be solved by the invention]
The charging potential on the photoconductor surface is inversely proportional to the capacitance of the photosensitive layer. That is, the potential increases in proportion to the thickness of the photosensitive layer, and the thickness increases as the thickness increases.
On the other hand, the thickness of the photosensitive layer has a certain thickness deviation in manufacturing. For example, an organic photosensitive layer generally used as a photosensitive layer is usually applied by dipping (dip coating). The dip coating method has better film thickness stability than the ring coating method or the like, but it is not unusual to have a film thickness deviation of 1 to 2 μm between the upper part and the lower part of the dip. In particular, in the case of a large-sized printing photosensitive member having an A3 size or larger, the thickness deviation becomes remarkable.
When charging the photosensitive member, the distance between the discharge electrode and the surface of the photosensitive member is kept constant as in the above-described related art, or the opening pattern of the grid is isotropic with respect to the photosensitive member moving direction. Even if it is formed so as to have an appropriate aperture ratio, the charging potential on the photoconductor is not constant. For example, if there is a film thickness deviation of 1 to 2 μm between the upper part and the lower part of the dip of the photoconductor, the charging potential will have a difference of about 5 to 12 V in the axial direction of the photoconductor. 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 influence of the tolerance of the components constituting the container, and it is a serious problem that the potential difference in the axial direction of the photoreceptor is about 5 to 12 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 a first aspect of the present invention includes a photosensitive member coated with a photosensitive layer by dipping, and a discharge electrode and a back plate which are disposed to face the photosensitive member and charge the surface of the photosensitive member. An image forming apparatus comprising a charger having:
The aperture ratio of the back plate is smaller on the upper side of the dip of the photosensitive member and is larger on the lower side of the dip.
According to a second aspect of the present invention, there is provided a photoreceptor coated with a photosensitive layer by dipping, and a charger having a discharge electrode and a back plate, which is disposed to face the photoreceptor and charges the surface of the photoreceptor. An image forming apparatus that exhausts air by flowing an air current along a plate,
The photoreceptor is arranged so that the upper part of the dip is on the upstream side of the airflow and the lower part of the photoreceptor is on the downstream side of the airflow. Is smaller on the upper side of the dip and larger on the lower side of the dip of the photoreceptor.
[0008]
[Effects]
When the aperture ratio of the back plate is increased, the amount of discharge by the charger decreases. An image forming apparatus according to a first aspect of the present invention includes a photoconductor coated with a photosensitive layer by dipping, and a charger having a discharge electrode and a back plate, which is disposed to face the photoconductor and charges the photoconductor surface. Image forming apparatus,
Since the aperture ratio of the back plate is smaller on the upper side of the dip and larger on the lower side of the dip, the image forming apparatus can make the charged potential on the surface of the photoreceptor uniform.
An image forming apparatus according to a second aspect of the present invention includes a photoconductor coated with a photosensitive layer by dipping, and a charger having a discharge electrode and a back plate, which is disposed to face the photoconductor and charges the photoconductor surface. Since air is exhausted by flowing an air current along the back plate, ozone is discharged from the inside of the charger by this exhaust.
Therefore, the deterioration of the discharge electrode due to the stagnation of ozone is prevented, and a stable charging action can be obtained.
The photoreceptor is arranged so that the upper part of the dip is on the upstream side of the airflow, and the lower part of the dip is on the downstream side of the airflow, and the back plate is provided with an opening for ventilation, Since the aperture ratio of the back plate is small on the upper side of the dip and larger on the lower side of the dip, the charging potential on the surface of the photoconductor can be uniform.
In addition, since the ventilation opening is provided on the lower side of the dip in the photoconductor, that is, on the downstream side of the airflow, the flow of the airflow is smooth, and the ozone is more efficiently discharged from the inside of the charger. .
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
<First embodiment>
FIG. 1 is a schematic front view showing the internal structure of the first embodiment of the 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]
For example, in the above-described color image forming apparatus, the photosensitive layer of the photosensitive member 21 is formed by, for example, dipping (dip coating) as shown in FIG.
That is, as shown in FIG. 2, a photosensitive layer 21b is formed on the surface of the photosensitive member base 21a by gripping the photosensitive member base 21a with a jig J and immersing it in a coating solution A and pulling it up as indicated by an arrow. I do.
The photosensitive layer 21b thus formed has a film thickness deviation of 1-2 μm between the dip upper part 21b2 and the dip lower part 21b1. The film thickness of the upper dip 21b2 is smaller by 1 to 2 μm than the film thickness of the lower dip 21b1.
The charging potential on the photoconductor surface is inversely proportional to the capacitance of the photosensitive layer. That is, the potential increases in proportion to the thickness of the photosensitive layer, and the thickness increases as the thickness increases.
[0016]
FIG. 3 is a graph showing an example of the relationship between the photoconductor thickness and the charging potential.
This graph was created as follows.
(1) Three photosensitive drums were prepared in which a photosensitive layer was applied by changing the film thickness by about 5 μm.
(2) The film thicknesses of the three photosensitive drums were measured at the charging potential measurement position using an eddy current film thickness meter.
(3) The charge potential per 1 μm was calculated from each measured value, and a graph shown in FIG. 3 was created.
From the above results, it can be seen that there is a difference in the charging potential of about 5 to 6 V per 1 μm of the photoconductor thickness. For example, when the thickness of the photosensitive layer differs between the upper part and the lower part of the dip of the photosensitive drum by 2 μm, the charging potential has a difference of about 10 to 12 V.
Therefore, when charging such a photoconductor, the distance between the discharge electrode and the surface of the photoconductor is kept constant as in the above-described related art, or the opening pattern of the grid is set in the moving direction of the photoconductor. Even if it is formed so as to have a directional aperture ratio, the charged potential on the photoconductor is not constant.
Therefore, in this embodiment, the aperture ratio of the back plate is made smaller on the upper side of the dip and larger on the lower side of the dip.
[0017]
FIGS. 4A and 4B are diagrams showing a main part of this embodiment. FIG. 4A is a graph showing a change in the thickness of the photosensitive layer 21b in the axial direction of the photosensitive member 21, and FIG. 4B is a schematic diagram of the image carrier unit 20. (C) is a front view of the charger 22, (d) is a bottom view of the charger 22, and (e) is a plan view of the charger 22.
As shown in FIGS. 2B and 2C, the charger 22 of this embodiment includes a wire-like discharge electrode 22a, a back plate 22c for performing stable discharge, and a charging potential on the photoconductor 21. A scorotron charger having a grid 22b for control. As shown in FIG. 4D, the charger 22 has an elongated trapezoidal opening 22c2 in the bottom plate portion 22c1 of the back plate 22c, reduces the opening width t1 of the photoreceptor 21 facing the dip upper side 21b2, and reduces the dip lower portion. By increasing the opening width t2 facing the side 21b2, the aperture ratio of the back plate 22c is reduced on the dip upper side 21b2 side of the photoconductor 21, and is increased on the dip lower side 21b1.
When the aperture ratio of the back plate 22c is increased, the amount of discharge by the charger 22 decreases, and when the aperture ratio is reduced, the amount of discharge by the charger 22 increases.
Therefore, the charging ability (the ability to charge the photosensitive member 21) of the charger 22 is large on the dip upper part 21b2 side and small on the dip lower part 21b1 of the photosensitive member 21.
[0018]
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). . A1 is a photosensitive layer application area.
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.
[0019]
The image forming apparatus as described above includes a charger 21 having a photosensitive member 21 coated with a photosensitive layer 21b by dipping, and a discharge electrode 22a and a back plate 22c which are arranged to face the photosensitive member 21 and charge the surface of the photosensitive member. 22, the opening ratio of the back plate 22c is small on the upper side 21b2 of the photoreceptor 21 and is larger on the lower side 21b2 of the photoreceptor 21. According to this image forming apparatus, the charging potential on the photoreceptor surface is made uniform. Can be achieved.
That is, by adopting the above-described configuration, the distance between the discharge electrode and the surface of the photoreceptor is kept constant, as in the above-described conventional technique, or the opening pattern of the grid is made isotropic in the moving direction of the photoreceptor. The charging potential difference on the photoconductor, which would occur if the aperture ratio is formed, can be canceled, and the charging potential can be made uniform.
[0020]
<Second embodiment>
5A and 5B are diagrams showing a main part of an image forming apparatus according to a second embodiment of the present invention. FIG. 5A is a graph showing a change in the thickness of a photosensitive layer 21b in the axial direction of the photoconductor 21, and FIG. ) Is a schematic left side view of the image carrier unit 20, (c) is a front view of the charger 22 when FIG. (B) is viewed from the front, (d) is a bottom view of the same charger 22, and (e) is FIG. 3 is a plan view of the charger 22. FIG. 6 is a cross-sectional view (schematic diagram) taken along the line VI-VI in FIG. In these figures, the same or corresponding parts as those in the first embodiment are denoted by the same reference numerals.
The feature of this embodiment is that the airflow B is caused to flow along the back plate 22c to exhaust the inside of the charger 22, and the photoconductor 21 is moved so that its dip upper part 21b2 is upstream of the airflow B and the dip lower part 21b1 Is arranged on the downstream side of the airflow B, and an opening 22c3 for ventilation is provided in the back plate 22c, so that the aperture ratio of the back plate 22c is small on the side of the dip upper part 21b2 in the photoconductor 21 and is lower than the dip lower part. 21b1.
The ventilation opening 22c3 is provided in one side plate portion 22c5 of the back plate 22c at a portion facing the dip lower portion 21b1 of the photoconductor 21.
[0021]
As shown in FIG. 6, a duct 20b is provided in the case 20a of the image carrier unit 20. The duct 20b is provided with a substantially U-shaped cross section so as to surround the lower part of the charger 22. An air inlet 20c (see FIG. 5B) is provided at one end (on the upper side 21b2 of the photoreceptor 21). ) Is provided, and an exhaust port 20d is provided on the other end side (on the dip lower part 21b1 side of the photoconductor 21).
As shown in FIG. 5D, an opening 22c4 is also provided in the bottom plate portion 22c1 of the back plate 22c in the charger 22 of this embodiment, but the opening 224c is rectangular, and the first embodiment It is not an elongated trapezoid like the opening 22c2 in the embodiment. That is, the opening 22c4 is for introducing the airflow B into the charger 22. The airflow B enters the charger 22 from the opening 22c4 as shown by an arrow b in FIG. Through the opening 22c3 and the exhaust port 20d of the duct.
[0022]
According to this embodiment, since air is exhausted by flowing the airflow B along the back plate 22c, the exhaust discharges ozone from inside the charger 20.
Therefore, the deterioration of the discharge electrode 22a due to the stagnation of ozone is prevented, and a stable charging action can be obtained. In addition, deterioration of the photoconductor 21 due to stagnation of ozone is also prevented.
The photoreceptor 21 is arranged such that the dip upper part 21b2 is on the upstream side of the airflow B and the dip lower part 21b1 is on the downstream side of the airflow B, and the back plate 22c is provided with an opening 22c3 for ventilation. As a result, the aperture ratio of the back plate 22c is small on the upper side 21b2 of the dip of the photoconductor 21 and is larger on the side of the lower dip 21b1 of the photoconductor 21, so that the charging potential on the surface of the photoconductor 21 can be made uniform. it can.
Moreover, since the ventilation opening 22c3 is provided on the dip lower part 21b1 side of the photoreceptor 21, that is, on the downstream side of the airflow B, the flow of the airflow B is smooth, and the ozone from the inside of the charger 22 is further improved. Will be discharged.
[0023]
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.
[0024]
[Brief description of the drawings]
FIG. 1 is a schematic front view showing the internal structure of a first embodiment.
FIG. 2 is an explanatory diagram of dipping.
FIG. 3 is a graph showing an example of a relationship between a photoconductor thickness and a charging potential.
4A is a graph showing a change in the thickness of a photosensitive layer in the axial direction of the photosensitive member, FIG. 4B is a schematic diagram of an image carrier unit, FIG. 4C is a front view of a charger, and FIG. 3 is a bottom view of the charger, and FIG. 3E is a plan view of the charger.
5A and 5B are diagrams showing a main part of the second embodiment, in which FIG. 5A is a graph showing a change in the thickness of the photosensitive layer, FIG. 5B is a schematic left side view of the image carrier unit, and FIG. FIG. 2 is a front view of the charger when FIG. 2B is viewed from the front, FIG. 3D is a bottom view of the charger, and FIG. 3E is a plan view of the charger.
FIG. 6 is a sectional view (schematic diagram) taken along the line VI-VI in FIG. 5 (b).
[Explanation of symbols]
21 photosensitive member, 21b photosensitive layer, 21b1 dip lower part, 21b2 dip upper part, 22 charger, 22a discharge electrode, 22b grid, 22c back plate, 22c3 ventilation opening.

Claims (2)

A photosensitive member coated with a photosensitive layer by dipping, and an image forming apparatus including a charging device having a discharge electrode and a back plate, which is disposed to face the photosensitive member and charges the surface of the photosensitive member,
An image forming apparatus, wherein the aperture ratio of the back plate is smaller on the upper side of the dip and larger on the lower side of the dip. A photosensitive member coated with a photosensitive layer by dipping, and a charger having a discharge electrode and a back plate disposed opposite to the photosensitive member and charging the surface of the photosensitive member, and flowing an air current along the back plate. An image forming apparatus that exhausts air,
The photoreceptor is arranged so that the upper part of the dip is on the upstream side of the airflow and the lower part of the photoreceptor is on the downstream side of the airflow. Is smaller on the upper side of the dip and larger on the lower side of the dip of the photoreceptor.

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