JP4218330B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus having a contact charging device. More specifically, the present invention relates to an image forming apparatus having a contact charging device capable of removing foreign matter accumulated in the charging device.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, some electrophotographic image forming apparatuses include a contact charger (charging brush or the like) that charges the surface of an image carrier while being in contact with a rotating image carrier. The contact charging type charging brush has the advantage that the amount of ozone generated is small and can be operated with a low applied voltage, compared to a non-contact charging type corona discharger. The charging brush has a function of charging the photosensitive member and a function of disturbing residual toner on the photosensitive member.
[0003]
However, the charging brush tends to take in residual toner and paper dust into the gaps between the brush fibers. Then, as a result of taking in residual toner or the like, uneven charging performance may occur. Therefore, it is necessary to remove the captured residual toner as much as possible. For example, Patent Literature 1 discloses a charging device that cleans the surface of a charging brush by bringing a conductive sheet or a metal grid into contact with the charging brush. Is described. Further, for example, in Patent Document 2, an elastic material is provided inside a ring-shaped cleaning tool, and when the charging brush is not operating, the elastic material is moved in the axial direction of the charging brush while being in contact with the charging brush. A charger cleaner is described which cleans the surface of the battery.
[0004]
[Patent Document 1]
Japanese Patent No. 3325636 [Patent Document 2]
Japanese Patent Laid-Open No. 8-137207
[Problems to be solved by the invention]
However, the conventional charging device described above has the following problems. That is, in the charging device described in Patent Document 1, when a conductive sheet is used, the contact force to the charging brush is uneven and weak, and cleaning becomes insufficient. In addition, when a rigid body such as a metal grid is used, stress on the charging brush is large and there is a problem in durability. Further, the charger cleaner described in Patent Document 2 is troublesome because it is necessary to manually operate a ring-shaped cleaning tool. Further, when the dirt is detected and automatically cleaned, the apparatus itself becomes complicated. Furthermore, since the toner discharged in both Patent Documents 1 and 2 cannot be collected, the inside of the image forming apparatus may be soiled.
[0006]
The present invention has been made to solve at least one of the problems of the conventional charging device described above. That is, an object of the present invention is to provide an image forming apparatus having a contact charging device capable of performing stable charging over a long period of time by removing accumulated toner and collecting the removed toner. It is in.
[0007]
[Means for Solving the Problems]
An image forming apparatus for solving this problem is an image forming apparatus having an image carrier and a contact charging device that contacts the image carrier and charges the surface of the image carrier. Has a charging member for charging the surface of the object to be charged while rotating in proximity to or in contact with the object to be charged, and a foamed elastic body in contact with the charging member. Located on the upstream side in the moving direction of the carrier, contacts the image carrier, and the foamed elastic body has a surface on the opposite side of the surface in contact with the charging member at the center of the foamed elastic body in the axial direction. It is characterized by being provided with a convex portion that is located and projects from the surface of the opposite surface. In the contact charging device of the image forming apparatus of the present invention, the charging member and the foamed elastic body are brought into contact with each other. At the time of contact, the toner adhering to the charging member is scraped off by the foamed elastic body. That is, it is taken into the bubbles of the foamed elastic body. Thereby, the toner adhering to the charging member can be removed.
[0008]
In addition, the bubbles of the foamed elastic body of the contact charging device of the present invention are in the form of open cells, and the density of bubbles in the foamed elastic body is preferably in the range of 4 to 40 / cm. . Since the bubbles of the foamed elastic body are open-celled, the scraped toner or the like is taken into the foamed elastic body by vibration generated by the contact between the charging member and the foamed elastic body. Thereby, the removed toner and the like can be collected. Moreover, since the density of bubbles (cells) is in the range of 4 to 40 / cm, it is possible to efficiently remove toner and the like adhering to the charging member. If the number is less than 4, the cell itself becomes very large and the durability is impaired. In addition, the cell does not form a continuous bubble but becomes a single bubble. On the other hand, when there are more than 40 cells, the cell itself becomes very small. That is, since it becomes equivalent to simply pressing the charging member against the wall surface, the effect of scraping the entire foamed elastic body is weak. Also, the toner or the like is likely to be clogged in the cell. Therefore, the cell density is suitably in the range of 4 to 40 cells / cm.
[0009]
Further, the volume resistivity of the foamed elastic body of the contact charging device of the present invention is preferably in the range of 10 ³ to 10 ⁹ Ωcm. As a result, it is possible to appropriately charge the toner and the object to be charged that pass under the foamed elastic body. If the volume low efficiency of the foamed elastic body is smaller than 10 ³ Ωcm, the resistance value is too small, and an overcurrent flows to damage the object to be charged. On the other hand, if it is larger than 10 ⁹ Ωcm, the resistance value is too large to cause current to flow. Therefore, the volume low efficiency of the foamed elastic body is suitably in the range of 10 ³ to 10 ⁹ Ωcm.
[0010]
Further, the foamed elastic body of the contact charging device of the present invention includes a surface of the opposite surface, which is located at the center of the surface of the foamed elastic body on the opposite side of the surface in contact with the charging member. Convex shape part which makes the shape which protruded from is provided . This convex-shaped part is installed in a position where the amount of accumulated paper dust or the like is large. As a result, the paper dust or the like that accumulates at that position first accumulates under the convex portion . Therefore, a sufficient amount of contact between the foamed elastic body and the object to be charged is ensured. That is, the amount of toner passing between the foamed elastic body and the object to be charged has little variation in the axial position. Accordingly, the occurrence of uneven charging performance is suppressed.
[0011]
The image forming apparatus according to the present invention is an image forming apparatus having an image carrier and a contact charging device that comes into contact with the image carrier and charges the surface of the image carrier. A charging member that charges the surface of the object to be charged while rotating in proximity to or in contact with the charging member, and a foamed elastic body that contacts the charging member. Located on the upstream side of the foam elastic body , and in contact with the image carrier, the foamed elastic body is located on the opposite side of the surface in contact with the charging member at the center of the foamed elastic body in the axial direction. The convex part which makes the shape protruded from the surface of the side surface is provided . As a result, large-diameter foreign matter is blocked by the foamed elastic body, and can be prevented from being taken into the charging member. In addition, the toner and the object to be charged that pass under the foamed elastic body can be reliably charged.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will be described below in detail with reference to the accompanying drawings.
[0013]
As shown in FIG. 1, the image forming apparatus according to the present embodiment includes an image forming unit 10 that forms and transfers a toner image, a paper feed cassette 11 that holds a transfer material, and a transfer roller that transfers the toner image to the transfer material. 4 and a fixing device 12 for fixing the transferred toner image to the transfer material. Further, the image forming unit 10 has a photoreceptor 1 on which a toner image is formed as shown in FIG. The photoreceptor 1 can rotate in the direction of the arrow in FIG. Further, around the photosensitive member 1, a conductive sheet 6, a foreign matter removing member 5, and a charging brush 2 are sequentially arranged along the rotation direction. When the photoconductor 1 rotates, the charging brush 2 also rotates in the forward direction with the rotation direction of the photoconductor 1.
[0014]
The charging brush 2 charges the surface of the photoreceptor 1 uniformly. In addition, the charging brush 2 is obtained by implanting conductive fibers (for example, viscose rayon) on a conductive shaft at a density of about 9,300 fibers / square cm. The thickness of the fiber is in the range of 0.22 to 1.11 tex. The brush fibers of the charging brush 2 are in contact with the photoreceptor 1 while being curved. Further, the brush fibers of the charging brush 2 are in contact with the foreign matter removing member 5 while being curved. The conductive sheet 6 is a charged member having a volume resistivity of 10 ⁵ to 10 ⁷ Ωcm and a thickness of about 100 μm. A bias is applied to the conductive sheet 6 as necessary.
[0015]
The foreign matter removing member 5 is a foamed elastic body (for example, maltoplane (registered trademark)). The bubbles (cells) in the foreign matter removing member 5 form continuous bubbles and are in the range of 4 to 40 / cm. Here, “pieces / cm” represents the number of cells through which a 1 cm line segment drawn on an arbitrary cross section of the member passes. Further, the volume resistivity of the foreign material removing member 5 is in the range of 10 ³ to 10 ⁹ Ωcm. A bias is also applied to the foreign matter removing member 5 as necessary. A convex portion 51 is formed on the side surface of the foreign matter removing member 5 on the upstream side in the rotation direction of the photoconductor 1 (hereinafter, “upstream” means the upstream in the rotation direction of the photoconductor 1). The convex portion 51 is disposed at a position where a large amount of foreign matter such as paper dust is conveyed. For example, a place where the conveyance guide rib is installed corresponds to the place where the paper dust is likely to be generated. Further, the foreign matter removing member 5 is pressed against the photoreceptor 1. The foreign matter removing member 5 includes a holding plate 52 and is held by the holding plate 52. Further, the holding plate 52 can move in the axial direction of the photoreceptor 1. The foreign matter removing member 5 is pressed against the photosensitive member 1 but is not fixed. Therefore, the foreign matter removing member 5 can move in conjunction with the movement of the holding plate 52.
[0016]
Next, the operation of the image forming apparatus during the image forming process will be described. During the image forming process, a negative DC voltage is applied to the charging brush 2. As a result, the surface of the photoreceptor 1 is charged. Thereafter, exposure corresponding to the image data is performed by the exposure device, and an electrostatic latent image is formed on the photoreceptor 1. Next, development with negative polarity toner is performed by the developing device, and a toner image is formed on the photoreceptor 1. Thereafter, the toner image on the photosensitive member 1 is transferred to the transfer material at the position of the transfer roller 4. The transfer material onto which the toner has been transferred is discharged to the outside through the fixing device 12.
[0017]
The toner on the photoconductor 1 is transferred to the transfer material due to the positive polarity of the transfer roller 4, but a part of the toner remains on the photoconductor 1 without being transferred. The charging polarity of the residual toner is shifted to positive polarity. Further, the charging polarity of the paper dust adhering to the photoreceptor 1 after passing through the transfer roller 4 is also positive. Residual toner or the like moves to the position of the conductive sheet 6. At this time, a negative polarity bias is applied to the conductive sheet 6. Therefore, when passing through the conductive sheet 6, the charged polarity of the residual toner after transfer is shifted to negative polarity. Thereby, adhesion of residual toner or the like to the charging brush 2 is suppressed. Further, since the surface of the photosensitive member 1 is also charged to the negative polarity, the conductive sheet 6 also functions as a preliminary charging before the main charging by the charging brush 2.
[0018]
Thereafter, residual toner or the like reaches the position of the foreign matter removing member 5 as shown in FIG. And the large-diameter residue such as paper dust is blocked by the foreign matter removing member 5. Further, at a position where there are many large-diameter residues such as paper dust, the paper dust or the like is deposited while pushing up the foreign matter removing member 5. Further, the paper dust and the toner are deposited in an entangled state. Further, a part of the small diameter residue such as toner passes between the foreign matter removing member 5 and the photoreceptor 1. At this time, a negative polarity bias is also applied to the foreign matter removing member 5. Therefore, also when passing through the foreign matter removing member 5, the charged polarity of the residual toner after transfer is shifted to negative polarity. Thereby, adhesion of residual toner or the like to the charging brush 2 is further suppressed. Further, since the surface of the photosensitive member 1 is also charged to a negative polarity, the foreign matter removing member 5 also functions as preliminary charging. Note that the amount of the residue that reaches the foreign substance removing member 5 varies depending on the position of the photosensitive member 1 in the axial direction. That is, the amount of the residue deposited between the foreign matter removing member 5 and the photoreceptor 1 varies depending on the position.
[0019]
Here, FIGS. 4 and 5 show the accumulated state of the residue as viewed from the photosensitive member side. FIG. 4 shows, as a comparative example, a residue accumulation state when the foreign matter removing member 5 has a flat shape, that is, when the convex portion 51 is not formed. On the other hand, FIG. 5 shows the accumulation state of the residue in the case of the foreign matter removing member 5 of this embodiment, that is, when the convex portion 51 is formed. The shaded portion in the foreign matter removing member 5 in both figures indicates a portion where a large-diameter residue is accumulated and pushes up the foreign matter removing member 5 (hereinafter referred to as “foreign matter depositing portion 53”). Further, the other portions indicate the portions where the foreign matter removing member 5 and the photosensitive member 1 are in contact (hereinafter referred to as “nip portion 54”). When the foreign matter removing member 5 has a flat shape, the width in the rotational direction of the nip portion 54 varies greatly depending on the position in the axial direction as shown in FIG. In particular, in a place where there are many deposits, the width of the nip portion 54 in the rotation direction is narrow, and the minimum width L1 is very narrow. As a result, the amount of residual toner passing is uneven, resulting in uneven charging performance. However, in the case of this embodiment in which the convex portion 51 is provided in a portion where paper dust or the like is large, paper dust or the like is first deposited on the convex portion 51 as shown in FIG. Therefore, even if the total area of the foreign matter accumulation part 53 is equal to the total area of the foreign matter accumulation part 53 in FIG. The minimum width L2 is also wide. Therefore, the deviation of the passing amount of the residual toner is small, and the charging performance is not uneven.
[0020]
Thereafter, the toner or the like that has passed through the foreign matter removing member 5 is disturbed by the charging brush 2 and a part of the toner is scraped off by the charging brush 2. A part of the scraped toner is again discharged onto the photosensitive member 1 by a negative polarity bias applied to the charging brush 2. Further, the discharged toner and the toner that has passed without being scraped by the charging brush 2 are collected by the developing device.
[0021]
Further, the charging brush 2 contacts the foreign matter removing member 5 while rotating. At that time, the toner adhering to the brush fibers of the charging brush 2 is scraped off by the foreign matter removing member 5. The foreign matter removing member 5 is an open-cell foamed elastic body, so that the scraped toner can freely move between cells. Further, when the brush fiber of the charging brush 2 collides with the foreign matter removing member 5, the foreign matter removing member 5 vibrates. Furthermore, since the brush fibers collide one after another as the charging brush 2 rotates, the foreign matter removing member 5 continues to vibrate while the charging brush 2 is rotating. Thus, the scraped toner is taken into the foreign matter removing member 5 while moving between the cells. Note that the toner that has moved between the cells finally falls on the photoreceptor 1 and is collected by the developing device. In addition, aggregation of the toner scraped off by appropriate vibration is prevented. As a result, the aggregated toner is not collected by the charging brush 2, so that the deterioration of the charging brush 2 is suppressed.
[0022]
Further, the vibration due to the collision of the brush fibers is transmitted to the entire foreign matter removing member 5. That is, vibration is also transmitted to the upstream side of the foreign matter removing member 5. By this vibration, the residue accumulated in a state where the paper powder and the toner are entangled is separated into a large-diameter residue such as paper powder and a small-diameter residue such as toner. Only the small-diameter residue passes between the foreign matter removing member 5 and the photosensitive member 1 and is collected by the developing device. On the other hand, the large-diameter residue remains blocked by the foreign matter removing member 5. Thereby, the toner and the like can be selectively collected from the aggregated residue.
[0023]
Next, the operation at the time of non-image formation in the image formation process will be described. After the image forming process is completed, the holding plate 52 is moved in the axial direction of the photoreceptor 1. In conjunction with the movement of the holding plate 52, the foreign matter removing member 5 moves in the axial direction. Specifically, the foreign substance removing member 5 reciprocates together with the holding plate 52 and is returned to the original position during the image forming process. As a result, large-diameter residues (such as paper powder and agglomerated toner) accumulated on the convex portions 51 and the like are detached from the foreign matter removing member 5. The detached residue reaches the foreign matter removing member 5 again while being diffused. Thereby, concentration of the residue can be prevented.
[0024]
Next, the transition of the foreign matter accumulation amount of the charging brush 2 will be described based on the graph of FIG. The graph of FIG. 6 shows the transition of the amount of accumulated foreign matter in two patterns, when the foreign matter removing member 5 is in contact with the charging brush 2 and when it is not in contact. When the contact is not made, the amount of foreign matter accumulated on the charging brush 2 increases as the printing time (number of sheets) elapses, and exceeds the allowable line when 4 hours elapse. The chargeability of the charging brush 2 is extremely deteriorated when foreign substances of a certain value or more (over the allowable line in FIG. 6) accumulate. On the other hand, when the contact is made, the amount of accumulated foreign matter is remarkably smaller than when the contact is not made. From this result, it is recognized that when the foreign matter removing member 5 is brought into contact as in the present invention, a sufficient margin can be ensured up to a certain value, so that stable charging can be performed over a long period of time. .
[0025]
Next, the discharging performance of the charging brush 2 will be described based on the graph of FIG. The graph of FIG. 7 shows the discharge performance of two patterns, that is, the case where the foreign matter is electrically discharged and the case where the foreign matter is physically discharged by colliding the brush fiber with the foreign matter removing member 5. In the case of electrical discharge, the accumulated amount of foreign matter is about 50% of that at the start after 60 hours. On the other hand, in the case of physical discharge, the accumulated amount at the start is about 15% when 60 hours have passed. From this result, it is recognized that the foreign substance is efficiently discharged by the physical discharge as in the present invention.
[0026]
As described above in detail, the image forming apparatus according to the present embodiment includes the rotatable charging brush 2 and the foamed foreign material removing member 5 that contacts the charging brush. Then, when the charging brush 2 collides with the foreign matter removing member 5 while rotating, the toner or the like adhering to the brush fibers of the charging brush 2 is scraped off by the foreign matter removing member 5. Thereby, a contact charging device capable of removing toner and the like accumulated on the charging brush 2 and an image forming apparatus having the charging device are realized.
[0027]
In addition, the foreign matter removing member 6 is a continuous foamed elastic body. Therefore, the scraped toner is taken into the foreign matter removing member 5 by vibration or the like when the charging brush 2 collides with the foreign matter removing member 5. As a result, toner and the like can be reliably collected.
[0028]
Further, the foreign matter removing member 6 is disposed upstream of the charging brush 2 and is in pressure contact with the photosensitive member 1. Further, a convex portion 51 is formed on the upstream side surface. And the convex part 51 is supposed to be arranged at a position where a large-diameter residue such as paper dust is likely to accumulate. As a result, even if the residue accumulates while pushing up the foreign matter removing member 5, the nip portion 54 can have a sufficient width in the rotation direction of the photoreceptor 1. Therefore, the amount of toner passing between the foreign matter removing member 5 and the photosensitive member 1 has little variation in the position in the axial direction, and the occurrence of uneven charging performance can be suppressed.
[0029]
Note that this embodiment is merely an example, and does not limit the present invention. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof. That is, in the embodiment, a brush type device is used as the contact type charging device, but the invention is not limited to this. For example, a roller type charging device may be used.
[0030]
The image forming apparatus is applicable to any printer, copier, scanner, FAX, or the like that forms an image by electrophotography. Further, it may be one that forms a color image or one that is dedicated to a monochrome image. Further, a tandem method or a four-cycle method may be used.
[0031]
【The invention's effect】
As is apparent from the above description, according to the present invention, an image having a contact charging device capable of performing stable charging over a long period of time by removing accumulated toner and collecting the removed toner and the like. A forming apparatus is provided.
[Brief description of the drawings]
FIG. 1 is a configuration diagram illustrating an image forming apparatus according to an embodiment.
FIG. 2 is a configuration diagram illustrating an image forming unit according to the embodiment.
FIG. 3 is a cross-sectional view showing a state in which foreign matter is accumulated on a photoconductor.
FIG. 4 is a view showing a dirt state of a flat-shaped foreign matter removing member from the photosensitive member side.
FIG. 5 is a diagram showing a dirt state of a foreign matter removing member having a convex portion from the photosensitive member side.
FIG. 6 is a graph showing a foreign matter accumulation amount of a charging brush during durable printing.
FIG. 7 is a graph showing a transition of a foreign matter discharge amount of a charging brush.
[Explanation of symbols]
1 Photoconductor (image carrier)
2 Charging brush (charging member)
5 Foreign material removal member (foamed elastic body)
51 Convex (convex part)
52 Retaining plate

Claims (3)

In an image forming apparatus comprising: an image carrier; and a contact charging device that contacts the image carrier and charges the surface of the image carrier.
The charging device is
A charging member for charging the surface of the charged object while rotating in proximity to or in contact with the charged object;
A foamed elastic body in contact with the charging member;
The foamed elastic body is located upstream of the charging member in the moving direction of the image carrier and is in contact with the image carrier,
The foamed elastic body has a shape protruding from the surface of the opposite surface located on the center of the surface of the foamed elastic body opposite to the surface in contact with the charging member. An image forming apparatus having a convex portion. The image forming apparatus according to claim 1 ,
The foamed elastic bubbles are open-celled,
The density of bubbles in the foamed elastic body is in the range of 4 to 40 / cm. The image forming apparatus according to claim 1 or claim 2,
The volume resistivity of the foamed elastic body is in the range of 10 ³ to 10 ⁹ Ωcm.

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