JP4116530B2 - Image forming apparatus - Google Patents

Description

The present invention relates to an electrophotographic image forming apparatus, and in particular, includes a plurality of image forming units having an image carrier such as a photosensitive drum, and a toner image to be formed on these image forming units is conveyed by a belt or a belt. The present invention relates to an image forming apparatus that sequentially transfers images on a recording material.

An electrophotographic image forming apparatus, such as a laser printer, a laser fasque, or a digital copying machine, charges a photosensitive drum of an image forming unit substantially uniformly, exposes the photosensitive drum, and outputs an image signal on its surface. An electrostatic latent image is formed in accordance with the toner, and the toner charged by the developing device is supplied onto the photosensitive drum to be visualized, and the toner image is transferred to a recording material such as transfer paper and fixed by the fixing device. The image is formed. In particular, in a color image forming apparatus that forms a color image, for example, toner of four colors of yellow, magenta, cyan, and black is used, and a toner image of each color is converted into a plurality of image forming units based on the color-separated image signal. The toner image is formed on each photosensitive drum, and the toner images are sequentially transferred to a recording material, or transferred to an intermediate transfer member such as a belt and superimposed on the color, then transferred to the recording material, and then fixed. (For example, refer to Patent Document 1).
JP 2003-215941 A

Conventionally, in such an image forming apparatus, since a plurality of image forming units are arranged in series along the belt, the apparatus itself becomes large, handling is troublesome, and costs are high. .
Therefore, a so-called cleanerless system has been devised that removes the cleaning means for removing toner from the surface of the image carrier in the image forming unit.
However, the current cleaner-less system is established by a technique such as providing a toner collecting brush in each image forming unit or collecting toner at a developing position using a two-component developer. Yes, the cleaning means is not completely removed. Further, since the configuration as described above is added, there remains a problem that the control is complicated and expensive.

Here, the present inventors have attempted to completely remove the cleaning means from each image forming unit in the tandem image forming apparatus.
That is, as shown in FIG. 3, image forming units 2Y, 2M, 2C, and 2BK that form toner images of, for example, yellow, magenta, cyan, and black are arranged along the belt 1 transfer direction. An attempt was made to sequentially transfer the toner images formed by the image forming unit onto the recording paper conveyed by the belt 1 with the cleaning unit completely removed from the forming unit.
At this time, for example, an image formed on the first image forming unit 2Y (here, the numbers are defined as No. 1, No. 2 from the upstream side with reference to the belt transfer direction, respectively) and transferred onto the recording paper is A so-called retransfer in which part of an image is transferred to each of the image forming units 2M, 2C, and 2BK when sequentially passing through the second, third, and fourth image forming units 2M, 2C, and 2BK together with the recording paper. It was found that the phenomenon of (reverse transcription) occurs. (See FIG. 4).

  Specifically, for example, 10% of the image transferred by the first image forming unit 2Y is transferred to the image forming unit 2M when the recording paper passes through the second image forming unit 2M. 5% of the image is transferred to the image forming unit 2C when passing through the next third image forming unit 2C, and 2% of the image is transferred to the next fourth image forming unit 4BK. Was transferred to the image forming unit 2C.

This is because the image formed by the image forming units 2Y, 2M,... Is once transferred to the recording paper, but when the charged toner is transferred to the recording paper by a transfer roller or the like, a part of the toner is reversed by discharge or the like. This is considered to be caused by the reverse transfer of the toner having the opposite charge to the photosensitive drum of the image forming unit when passing the next image forming unit 2M,.
Further, the image formed by the second image forming unit 2M and transferred onto the recording paper causes retransfer when passing through the third and fourth image forming units 2C and 2BK, and the third image forming unit is formed. The image formed by the unit 2C and transferred onto the recording paper causes retransfer when passing through the fourth image forming unit 3BK. Therefore, retransfer does not occur only in the image formed by the final fourth image forming unit 2BK (see FIG. 4).

The downstream image forming units 2M, 2C, and 2BK that have undergone retransfer perform image formation with an excessive toner image attached thereto, so that the upstream toner image appears as it is or the photosensitive drum is exposed to light. A so-called ghost is generated in an image transferred by the photosensitive drum because the surface potential of the body drum is not uniform.
That is, when the cleaning unit is completely removed from each of the image forming units 2Y, 2M,..., It is possible to obtain an advantage that the size can be reduced and the cost can be reduced.

  The present invention has been made in view of the above circumstances, and provides an image forming apparatus capable of avoiding ghosts that tend to occur at the same time, in addition to obtaining advantages such as downsizing and low cost associated with removing the cleaning means. The purpose is to do.

In order to achieve the above object, according to the present invention, a circulating belt, a plurality of image forming units that are sequentially arranged in the transport direction along the belt, and each form a color component image, and each image forming unit A transfer unit that is arranged so as to contact the back surface of the belt facing the belt and electrostatically transfers a color component image formed on the corresponding image forming unit directly to the belt or to a recording material conveyed by the belt. And an image forming apparatus for forming a color image by sequentially transferring a color component image formed on each image forming unit onto the belt or a recording material conveyed by the belt by a transfer unit. . A black image is formed when the most upstream side of the plurality of image forming units arranged along the belt is numbered first and then numbered second, third,... The image forming unit is arranged on the most downstream side. The second image forming unit that forms a yellow image is provided with a cleaning unit that cleans the surface of the image carrier of the image forming unit, and at least the yellow image of the odd-numbered image forming units. The third image forming unit located on the downstream side of the second image forming unit to be formed is characterized in that no cleaning means is provided . Here, the image forming unit refers to a unit that includes a laser exposure device, an image carrier, a developing device, and a charging roller, and forms a monochromatic toner image on the image carrier.

In the present invention, since no cleaning means is provided in at least one image forming unit that is an odd number such as No. 1 or No. 3 counted from the upstream side, downsizing and cost reduction associated with a reduction in the number of parts can be achieved. Further, for example, in the case of an ghost image formed by the first image forming unit, the ghost generated due to the absence of the cleaning means has the greatest influence by the retransfer to the second image forming unit. And as it goes downstream, the effect of retransfer becomes smaller. Therefore, for example, when the cleaning unit is provided in the second image forming unit, retransfer to the second image forming unit can be avoided, so that the influence of the ghost can be reduced to some extent. That is, the ghost of the image formed by the first image forming unit can be avoided to some extent by providing the second image forming unit with the cleaning unit, and is not related to the provision of the cleaning unit in the first image forming unit. . In other words, the occurrence of ghosts is not affected even if the first image forming unit is not provided with cleaning means.
Considering the presence or absence of the cleaning means of the third image forming unit, when an image is formed by the second image forming unit, the influence of the retransfer is greatest on the next third image forming unit. However, when the image formed by the second image forming unit is yellow, since the yellow itself is an inconspicuous color, even if a ghost occurs, the ghost itself does not stand out. That is, when the third image forming unit is not provided with a cleaning unit, the influence of the ghost can be reduced by setting the image formed by the second image forming unit to yellow.
Further, in the image forming apparatus according to the present invention, it is preferable to form a black image by the most downstream image forming unit. In the present invention, the most conspicuous color black image is formed by the most downstream image forming unit, and the most downstream image forming unit has no image forming unit on the downstream side, so there is no need to consider retransfer. For this reason, the ghost accompanying black retransfer which is the most prominent color can be eliminated.

In the image forming apparatus according to the present invention, the most upstream side of the plurality of image forming units arranged along the belt is numbered first, and then sequentially numbered second, third,. When attached, it is preferable to provide a cleaning means for cleaning the surface of the image forming unit image carrier only in the second and fourth image forming units.
In the present invention, since the second and fourth image forming units are provided with cleaning means, it is possible to avoid the occurrence of image ghosting by the first and third image forming units. The ghost of the image by the second image forming unit can be made inconspicuous by making the color of the image drawn by the second image forming unit as inconspicuous as possible. Further, color image formation by an electrophotographic method usually forms an image using four colors of toner, and in this case, the fourth image forming unit is located on the most downstream side, and there is no need to consider retransfer. Ghost does not occur. That is, when the cleaning unit is provided only in the second and fourth image forming units, a ghost in which an image drawn by the second image forming unit is retransferred to the third image forming unit becomes a main problem. If the color of the image drawn by the second image forming unit is inconspicuous yellow, the problem of ghost can be cleared.

In the image forming apparatus according to the present invention, it is preferable that the second image forming unit forms a yellow image.
In the present invention, for example, when the cleaning unit is eliminated from the third image forming unit, the third image forming unit is most affected by the retransfer of the image formed by the second image forming unit. If the second image forming unit forms an inconspicuous yellow image, the ghost itself accompanying the retransfer of the image formed by the second image forming unit can be conspicuous.
Furthermore, the image forming apparatus according to the present invention may be formed to include four image forming units. Here, an image forming unit for forming a magenta or cyan image is arranged at the 1st or 3rd position. At this time, the cleaning means is not provided in the first and third image forming units. On the other hand, the image forming unit that forms the black image arranged at the position No. 4 which is the most downstream is provided with a cleaning unit. Thus, the ghost of the image formed by the first image forming unit is removed by the second cleaning unit, and the image formed by the second image forming unit is removed by the fourth cleaning unit. Further, by forming an inconspicuous yellow image by the second image forming unit, the ghost itself can be made inconspicuous without providing a cleaning means in the third image forming unit. Further, by disposing an image forming unit for forming a black image on the most downstream side, it is not necessary to consider the black retransfer which is the most prominent color.

Also, in the image forming apparatus according to the present invention, the cleaning unit is a blade-shaped, brush-shaped, rolled, it is preferable either pad-like or web-like, or a configuration that combines some of them. In the present invention, since the cleaning means such as blade shape, brush shape, roll shape, etc., which are generally well known, reliable, easy to obtain and inexpensive, are used, the reliability of cleaning can be improved and low cost. Can be achieved. In addition, the image forming apparatus according to the present invention preferably includes a control unit that applies a cleaning bias voltage and controls the cleaning bias voltage when the cleaning unit is used.
In the present invention, since cleaning can be performed while applying the cleaning bias voltage, the cleaning efficiency can be improved, and thus a clearer image can be obtained.
In the image forming apparatus according to the present invention, it is preferable that the developing unit for attaching the toner to the image carrier of the image forming unit is a one-component developing method.
In the present invention, since the one-component development method is adopted, it is simpler and the development cost can be reduced as compared with the two-component development method having a carrier other than the toner.
In the image forming apparatus according to the present invention, the developing means for attaching the toner to the image carrier of the image forming unit may be disposed in contact with the image carrier or through a certain gap. preferable.
In the image forming apparatus according to the present invention, it is preferable that the developing means for attaching the toner to the image carrier of the image forming unit uses toner formed by a pulverization method or a polymerization method as a developer.

  According to the present invention, in addition to obtaining advantages such as downsizing and low cost associated with removing the cleaning means, it is possible to avoid ghosts that tend to occur at this time.

Hereinafter, an embodiment of an image forming apparatus according to the present invention will be described with reference to the drawings.
FIG. 1 is a schematic diagram illustrating a schematic configuration of a main part of an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a schematic diagram for explaining the state of retransfer for explaining the operation of the image forming apparatus according to the present invention.
As shown in FIG. 1, the image forming apparatus 11 according to the present embodiment includes a transport unit 14, a plurality of image forming units 12M, 12Y, 12C, and 12BK disposed on the transport unit 14, a fixing device 26, and the like. Become.
Here, the plurality of image forming units 12M, 12Y, 12C, and 12BK are sequentially arranged in the transfer direction along the belt 19 described later, and the most upstream side is the first on the basis of the transfer direction. Then, the numbers 2, 3, and 4 are assigned to the downstream side. The first to fourth image forming units 12M, 12Y, 12C, and 12BK form magenta, yellow, cyan, and black toner images, respectively, and are photosensitive drums that are examples of image carriers. 15, a laser exposure device (not shown), a developing device 13, and a charging roller 24.
Hereinafter, the image forming units 12M, 12Y, 12C, and 12BK will be described by taking the image forming unit 12M as an example, but the other image forming units 12Y, 12C, and 12BK have substantially the same configuration.

  The laser exposure apparatus scans a laser beam 17 focused on a minute spot on a straight line parallel to the rotation axis of the photosensitive drum 15 in a fixed direction at an exposure position on the photosensitive drum 15.

A developing unit (developing unit) 13 triboelectrically charges a powder toner having a predetermined color to be negatively charged, and has a positive potential relative to a non-exposed portion by exposure. The toner is supplied to the exposed portion of the toner and the toner adheres to the surface of the photosensitive drum 15.
In the developing device 13, the toner, a stirrer 13 d that stirs and charges the toner, a supply roller 13 c that conveys the charged toner to the developing roller 13 a side, and the toner supplied by the supply roller 13 c are electrified and charged. A developing roller 13a that adheres to the surface by the Coulomb force generated by the toner and conveys it to the vicinity of the photosensitive drum 15 and a developing blade 13b for regulating the toner layer thickness on the developing roller 13a are provided.

Here, the developing method using the developing device 13 includes a one-component developing method using only toner and a two-component developing method using a carrier other than the toner. The one-component developing method is adopted because it is simple and low in cost. It is preferable to do this.
In the example shown in FIG. 1, the developing roller 13 a is in contact with the photosensitive drum 15. However, it is not always necessary to contact the developing roller 13 a, and when toner can be attached to the photosensitive drum 15,
The developing roller 13a may be arranged with a certain gap with respect to the photosensitive drum 15.
The toner used in the developing device 13 may be formed by either a pulverization method or a polymerization method.

The transport unit 14 includes an endless belt 19 that is circulated and moved in one direction by driven rollers 22 a, 22 b, 22 c and a tension roller 23 disposed on the inner peripheral portion, and an outer peripheral side of the belt 19. Via the driving roller 20 pressed to the driven roller 22a side, the transfer roller 18a held so that the belt 19 contacts the photosensitive drum 15 at the transfer position, and the belt 19 by contacting the belt 19 with a cleaning blade. A belt cleaning unit 21 having a space for scraping off the surface deposits and collecting the scraped deposits.
The driving roller 20 is pressed toward the driven roller 22a by an urging means such as a spring. When the driving roller 20 is rotationally driven by a driving means (not shown), the belt 19 sandwiched between the driving roller 20 and the driven roller 22a is circulated and moved in the direction of the arrow shown.

The belt 19 is made of, for example, a dielectric material that can attract the toner on the photosensitive drum 15 by a transfer voltage applied to the transfer roller 18a in contact with the back surface when facing the photosensitive drum 15 with a recording material interposed therebetween. A sheet is used.
The transfer roller 18a has, for example, a roller part formed of conductive or semiconductive synthetic rubber or the like on a metal rotation shaft, and a transfer high-voltage power supply (not shown) is connected to the rotation shaft. The surface potential of the part is controlled.
Here, the color component images formed by the image forming units 12M, 12Y, 12C, and 12BK are transferred onto the recording material conveyed by the belt by the transfer roller 18a and the control unit 18 that controls the surface potential of the roller unit. A transfer unit for electrostatic transfer is configured.

  The second and fourth image forming units of the image forming units 12M, 12Y, 12C, and 12BK are provided with a cleaning unit that cleans the surface of the photosensitive drum 15. The cleaning means is a photosensitive drum cleaning roller 16 that contacts the photosensitive drum 15 to remove toner on the surface of the photosensitive drum 15, and a box that is disposed near the cleaning roller 16 and collects toner removed by the cleaning roller. It consists of the body. Note that a required cleaning bias voltage may be applied to the photosensitive drum cleaning roller 16 by a control unit (not shown) as necessary.

The charging roller 24 is for setting the surface potential of the photosensitive drum 15 to a predetermined potential at the time of image formation. The roller portion is constituted by an elastic body having conductivity on the metal shaft, and the photosensitive drum cleaning roller 16 (photosensitive drum). When there is no body drum cleaning roller 16, it contacts the photosensitive drum 15 at a charging position downstream of the position where it is removed. The charging roller 24 is pressed against the photosensitive drum 15 with a predetermined pressure by pressing a bearing (not shown) by a biasing means such as a spring. As a result, the roller portion is deformed to form a nip portion that contacts the photosensitive drum 15 with a predetermined width in the circumferential direction. When a DC voltage is applied to the charging roller 24, the surface of the photosensitive drum 15 is set to a predetermined potential. Can be charged.
In addition, a charging roller cleaning roller 25 is in contact with the charging roller 24 so that dirt on the surface of the charging roller 24 is removed.

  The fixing device 26 includes a pair of rollers for thermally fixing the recording paper conveyed by the conveyance unit 14.

Next, the operation of the image forming apparatus 1 according to the present embodiment will be described.
Since the general operation of the image forming apparatus 10 is the same as that of a known printer or the like, the description thereof will be omitted as appropriate, and the operation of the image forming units 12M, 12C, 12Y, and 12BK will be mainly described.
First, in the first image forming unit 12M, when the photosensitive drum 15 is rotationally driven in a direction indicated by an arrow in FIG. 1 by a driving unit (not shown), the charging roller 24 that contacts the photosensitive drum 15 is It rotates following the direction opposite to that of the photosensitive drum 15. During this time, due to the discharge between the charging roller 24 and the photosensitive drum 15, the vicinity of the contact position on the surface of the photosensitive drum 15 is negatively charged almost uniformly.
When the photosensitive drum 15 is rotated from the contact position to the exposure position, the print image area is exposed by the laser beam 17, and the exposed portion loses its surface potential due to the discharge of electric charge. As a result, the surface potential difference between the exposed portion and the non-exposed portion is recorded on the surface of the photosensitive drum 15, and a so-called electrostatic latent image is formed.
When the photosensitive drum 15 rotates from the exposure position to the development position, toner selectively moves from the developing roller 13a to the photosensitive drum 15 based on the electrostatic latent image formed on the surface of the photosensitive drum 15, and the photosensitive body A visible image with magenta toner is formed on the surface of the drum 15.
Further, the photosensitive drum 15 rotates and moves to the transfer position, and at the same time, a recording material (not shown) is conveyed on the belt 9. At this time, the visible image formed by the magenta toner formed on the surface of the photosensitive drum 15 is transferred to the recording material, and then the transferred recording material is conveyed to the second image forming unit 12Y.
In the second image forming unit 12Y, the same operation as that of the first image forming unit 2M is repeated, and the visible image of yellow toner formed on the surface of the photosensitive drum 15 is transferred onto the recording material. Is done.

However, the second image forming unit 12C is provided with a cleaning means for cleaning the surface of the photosensitive drum 15, so that the photosensitive drum 15 here is made up of toner and recording material that is not transferred and remains on the drum surface. The toner retransferred to the drum surface is removed by the photosensitive drum cleaning roller 16 and then cleaned before being charged again by the charging roller 24.
Thereafter, the same operation is repeated in the image forming units 2C and 12BK, and finally, the visible image by the toner multiplex-transferred on the recording paper is melted and fixed on the recording paper by the fixing device 26, and a series of operations are performed. The printing operation ends.

In the image forming apparatus 10 according to the present embodiment, since the first and third image forming units 12M and 12C are not provided with a cleaning unit, the size and cost can be reduced by reducing the number of parts.
Further, the first and third image forming units 12M and 12C are not provided with a cleaning unit and may cause a ghost. However, since the first image forming unit 12M is located on the most upstream side, the retransfer is performed. Is not possible. Therefore, the problem is a ghost caused by retransfer of the third image forming unit 12C. As shown in FIG. 2, for example, 5% of the image transferred to the recording material by the first image forming unit 12M and the second image forming are transferred to the third image forming unit 12C. It is 10% of the image transferred to the recording material by the unit 12Y. 5% of the image transferred to the recording material by the first image forming unit 12M has a low reverse transfer ratio, and even if it appears in the form of a ghost, it does not matter much. On the other hand, 10% of the image transferred to the recording material by the second image forming unit 12Y has a high reverse transfer ratio, which is a problem. However, since the image formed by the second image forming unit 12Y is inconspicuous yellow, it does not stand out even if it appears as a ghost.
That is, the third image forming unit 12C is not provided with a cleaning unit and may cause ghosting. However, since the image formed by the second image forming unit 12Y is yellow, for example, ghosting occurs. However, the effect can be minimized.

As described above, the embodiments of the image forming apparatus according to the present invention have been described. However, the present invention is not limited to the above-described embodiments, and can be appropriately changed without departing from the scope of the present invention.
For example, in the above-described embodiment, the case where multiple transfer is performed on a recording sheet conveyed on the belt 19 has been described, but it is needless to say that the present invention can be applied to the case where intermediate transfer is sequentially performed on the belt 19.
In the above embodiment, four image forming units are provided. However, the present invention is not limited to this, and there may be three image forming units or five or more, for example, five.
In the above-described embodiment, the cleaning unit is excluded from both the first and third image forming units, but the cleaning unit is excluded from only one of them, and the cleaning unit is left in the other image forming units. May be.
In the above embodiment, a roller is used as a constituent member of the cleaning unit, but the present invention is not limited to this, and the cleaning unit constituent member is any one of a blade shape, a brush shape, a pad shape, and a web shape, Alternatively, some of them may be combined, or they may be combined with a roller.

1 is a schematic diagram illustrating a schematic configuration of a main part of an embodiment of an image forming apparatus according to the present invention. FIG. 4 is a schematic diagram illustrating a retransfer state of the image forming apparatus according to the present invention. FIG. 6 is a schematic diagram illustrating a transfer state of a general image forming apparatus. FIG. 3 is a schematic diagram illustrating a state of a reverse person in a general image forming apparatus.

Explanation of symbols

10 Image forming apparatus 12M, 12C, 12Y, 12BK Image forming unit 13 Developer (Developing means)
14 Transport unit 15 Photosensitive drum (image carrier)
16 Photosensitive drum cleaning roller (cleaning means)
17 Laser beam 18a Transfer roller (transfer unit)
18 Control means (transfer unit)
19 Belt 24 Charging roller 26 Fixing device

Claims (7)

A belt that circulates and is arranged in order in the transport direction along the belt, and is arranged so as to be in contact with a plurality of image forming units that respectively form color component images, and a back surface of the belt facing each image forming unit. And a transfer unit that electrostatically transfers the color component image formed on the corresponding image forming unit directly to the belt or on a recording material conveyed by the belt, and the color component formed on each image forming unit. In an image forming apparatus for forming a color image by sequentially transferring an image on the belt or a recording material conveyed by the belt by a transfer unit,
A black image is formed when the most upstream side of the plurality of image forming units arranged along the belt is numbered first, and then numbered second, third,. The image forming unit is arranged at the most downstream,
The second image forming unit for forming a yellow image is provided with a cleaning means for cleaning the surface of the image carrier of the image forming unit,
Of the odd-numbered image forming units, at least the third image forming unit positioned downstream of the second image forming unit that forms the yellow image is not provided with the cleaning unit. An image forming apparatus. The image forming apparatus includes four image forming units,
The image forming unit for forming a magenta or cyan image arranged at the 1st or 3rd position is not provided with the cleaning unit,
2. The image forming apparatus according to claim 1, wherein the cleaning unit is provided in the image forming unit that forms the black image arranged at the fourth position which is the most downstream side.   The image forming apparatus according to claim 1, wherein the cleaning unit has a blade shape, a brush shape, a roll shape, a pad shape, a web shape, or a combination of some of them. apparatus.   4. The image forming apparatus according to claim 3, further comprising a control unit that applies a cleaning bias voltage and controls the cleaning bias voltage when the cleaning unit is used.   The image forming apparatus according to claim 1, wherein the developing unit that attaches toner to the image carrier of the image forming unit employs a one-component developing method.   The developing means for attaching toner to the image carrier of the image forming unit is in contact with the image carrier or arranged through a certain gap. An image forming apparatus according to claim 1. The image forming unit according to claim 1, wherein the developing unit that attaches toner to the image carrier of the image forming unit uses toner formed by a pulverization method or a polymerization method as a developer. apparatus.

Images