JP2007241163A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus designed such that trouble arising from a leak caused by entry of foreign matter or powder resulting from wear is prevented even when the apparatus ages, insufficiency in belt discharge and an image defect are also prevented. <P>SOLUTION: The image forming apparatus comprises: a rotatable image carrier on the surface of which a toner image is formed; a belt-like primary transfer body rotated in contact with the image carrier in the same direction as the image carrier and used to transfer the toner image from the image carrier; and a transfer station disposed opposite the image carrier relative to the primary transfer body and including at least a bias application member of the same polarity as that of the toner and a bias application member of the reverse polarity to that of the toner. In the image forming apparatus, a cleaning member is disposed between the bias application members 71 and 72 of different polarities. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, and a fax machine using electrophotographic technology, and more particularly to an image forming apparatus having a bias applying device in primary transfer of a color electrophotographic apparatus using an intermediate transfer member. is there. Furthermore, the present invention relates to an image forming apparatus having a bias applying device for secondary transfer of a color electrophotographic apparatus and belt neutralization.

A conventional image forming apparatus, particularly a color image forming apparatus, has a configuration in which each color toner image sequentially formed on a photosensitive drum is superimposed and transferred to an intermediate transfer body system, and the color image is collectively transferred to a transfer material. Things have been used. In such an intermediate transfer body system, each color toner image is sequentially transferred onto the intermediate transfer body. In the process of transferring the second and subsequent colors to the intermediate transfer system, a “reverse transfer” phenomenon may occur in which the toner in the previous process returns from the intermediate transfer member to the photosensitive member. This is an electrophotographic industry term and is known as “reverse transfer” or “retransfer”.
This “reverse transfer” phenomenon is usually improved by lowering the transfer bias, but there is a problem that the toner transfer rate for the second and subsequent colors does not increase. Originally, “transfer residual” occurs when the transfer bias is not sufficiently increased. Therefore, “reverse transfer” and “remaining transfer” are a trade-off, and the person in charge adjusts the “remaining transfer” or “reverse transfer” reduction in consideration of this trade-off relationship. Since such adjustment is very fine, for example, it varies depending on slight fluctuations such as the transfer belt and the photosensitive member potential, which is a cause of variation in the transfer performance of the machine.
The cause of “reverse transfer” is discharge near the primary transfer nip. This discharge causes positive and negative ions to disperse, which directly causes the toner to accept and fluctuate the charge amount. When this discharge occurs, the image quality also deteriorates. From the above, it is important to perform transfer by applying a transfer electric field sufficiently to further reduce excessive discharge. In order to reduce both transfer residue and reverse transfer, it is important to provide a bias applying device at the entrance and exit of the transfer nip and to apply an electric field with the same polarity bias as the toner polarity.

  Therefore, in Patent Document 1, as a technique related to the bias applying device, a movable type that can move as a transfer unit facing each photoconductor drum with a transfer material and a transfer material conveying unit interposed therebetween. An image forming apparatus having a transfer unit different from a fixed transfer unit that is slidably disposed in contact with a transfer unit and a transfer material transport unit is disclosed. Patent Document 2 discloses an image forming apparatus in which a mechanical nip and an electrical nip have the same width so that a transfer electric field is not leaked outside by applying a (−) bias to an entrance / exit roller of the mechanical nip. ing. Further, Patent Document 3 discloses an image forming apparatus that applies a (−) electric field downstream of the rear end of the nip. Patent Document 4 discloses an image forming apparatus that applies a (−) bias having the same polarity as the toner to the transfer entrance away from the nip. Furthermore, Patent Document 5 discloses a transfer blade in which a blade member is provided along a longitudinal direction on one side of a plate-shaped holder, and both end portions are fixed to a portion closer to the inner side than the plate-shaped holder. There is disclosed a transfer blade in which an extended portion extending outward from the fixing portion is provided at both ends in the longitudinal direction on the end side, and a gap is provided between the extended portion and the plate-like holder.

However, almost all of the current intermediate transfer belts are made by kneading carbon or the like into a polymer body and conducting, and since they are electronic conductive resistors, the resistance has an electric field dependency. When such an intermediate transfer belt is used, the resistance is low in the primary transfer, but the resistance increases as it leaves the primary transfer nip. The transfer bias charge remaining in the belt moves when the resistance is low, but in this case, the charge remains because the resistance is increased, and an air discharge may be generated when the gap is widened when the intermediate transfer belt is peeled off. is there. Due to the occurrence of this discharge, ions of different polarity are generated and sucked into the image toner, and the polarity varies, and this irregularly fluctuates the toner even after the transfer nip. In addition, since the toner Q / M on the surface layer is fluctuated, there is a problem that the transfer rate is lowered.
Therefore, when using a belt having a high resistance when no electric field is applied, it is required to reduce the primary discharge outlet discharge.
Therefore, for example, in Patent Document 1, an electrode is placed on the downstream side considerably away from the nip. However, in this method, a charge is often left in a belt having a large capacity and high electric field dependency. There are two possible reasons for this.
First, as in Patent Document 2, even if a counter bias is applied to the exit peeling portion, an intermediate transfer belt having high voltage dependency of resistance loses electric field application and at the same time increases resistance. As a result, the current to the removed potential portion is reduced, and the current for lowering the belt potential cannot be supplied. In this case, it is considered that the charge removal is insufficient because the charge removal is performed at the outlet of the mechanical nip.
Second, the residual charge remaining in the medium resistance member tends to remain in the interior even after the neutralization to the surface is completed. In order to remove this, it is preferable to use AC charge discharge, but it is difficult to remove electricity by DC charge or the like. In such a case, the static elimination time is important. Here, since the static elimination is performed at the outlet end of the mechanical nip, the static elimination time is insufficient.

Therefore, a transfer system having a plurality of adjacent bias applying members has been proposed for the primary transfer apparatus. In this method, by arranging the plurality of bias applying members in the smallest possible area, the electric field in the process of transferring the toner image is restricted, and the discharge phenomenon at the time of peeling between the photosensitive member and the intermediate transfer belt can be suppressed. There are benefits.
However, since biases having different polarities are applied to adjacent bias members, it is essential to prevent leakage. The wear powder accumulated between the plurality of bias applying members over time is generated by wear of the intermediate transfer belt or the bias applying member, and has an intermediate resistance region (10 ⁸ to 10 ¹⁰ Ω) as electrical characteristics. / □ grade). Leakage does not occur when the amount of wear powder is small, but leakage may occur when a large amount of wear powder accumulates or when the resistance value between multiple bias application members decreases due to moisture absorption by the wear powder itself. There was a problem that the nature would be high. Also, if the adjacent electrodes are not reliably insulated, a large amount of leakage current flows, which is clearly a problem in terms of power supply specifications.

JP 2001-013759 A Japanese Patent No. 3346063 JP 2003-057963 A JP-A-8-202177 Japanese Patent Laid-Open No. 11-161058

  Therefore, the present invention has been made in view of the above problems, and the problem is that, even with the passage of time, the occurrence of problems due to leakage due to wear powder and foreign matter is prevented, and there is no shortage of belt neutralization. An object of the present invention is to provide an image forming apparatus that does not cause an image abnormality.

The features of the present invention, which is a means for solving the above problems, are listed below.
The present invention relates to an image carrier that rotates by forming a toner image on the surface, a belt-shaped primary transfer member that rotates in the same direction while contacting the image carrier and transfers the toner image from the image carrier. In the image forming apparatus having a transfer station having a bias applying member having at least the same polarity as the toner and a bias applying member having the reverse polarity of the toner, on the opposite side of the image bearing member with respect to the primary transfer body, An image forming apparatus, wherein a cleaning member is provided between a plurality of bias applying members.
The present invention is characterized in that the cleaning member is an insulating member provided between bias applying members having different polarities.
The present invention is characterized in that at least one of the plurality of bias applying members having different polarities performs a cleaning operation along with an operation of moving in a direction away from the primary transfer member.
The present invention is characterized in that the surface of the cleaning member and bias applying member is subjected to a surface treatment with a low friction coefficient.
The present invention is characterized in that an air generator for flowing air in the longitudinal direction of the bias applying member is provided.

  According to the present invention, there is provided an image forming apparatus that prevents the occurrence of problems due to leaks due to wear powder and foreign matter contamination over time, and does not cause belt abnormality, and does not cause image abnormalities. It became possible to provide.

  The best mode for carrying out the present invention will be described below with reference to the drawings. Note that it is easy for a person skilled in the art to make other embodiments by changing or correcting the present invention within the scope of the claims, and these changes and modifications are included in the scope of the claims. The following description is an example of the best mode of the present invention, and does not limit the scope of the claims.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
Based on FIG. 1, the configuration and operation outline of a tandem type color copier as an image forming apparatus in the present embodiment will be described. The color copying machine 1 includes an image forming unit 1A positioned at the center of the apparatus main body, a paper feeding unit 1B positioned below the image forming unit 1A, a document conveying unit 1C positioned above the image forming unit 1A, And a scanner unit.
An intermediate transfer belt 2 as an intermediate transfer body having a transfer surface extending in the horizontal direction is disposed in the image forming unit 1A. The upper surface of the intermediate transfer belt 2 has a color complementary to the color separation color. A configuration for forming an image is provided. That is, the photoreceptors 3Y, 3M, 3C, and 3B as image carriers capable of carrying an image of toners of complementary colors (yellow, magenta, cyan, and black) are juxtaposed along the transfer surface of the intermediate transfer belt 2. Has been.
Each of the photoconductors 3Y, 3M, 3C, and 3B is configured by a drum that can rotate in the same direction (counterclockwise direction), and around the charging device 4 that performs image forming processing in the rotation process, A writing device 5, a developing device 8, a primary transfer device 7, and a cleaning device 6 are arranged as optical writing means. The alphabet added to each symbol corresponds to the color of the toner as in the photosensitive member 3. In FIG. 1, symbols are added to the charging device 4Y, the developing device 8Y, the primary transfer device 7Y, and the cleaning device 6Y corresponding to yellow, but the same applies to other color devices. 5Y indicates the writing light of the yellow toner image.
Each developing device 8 contains respective color toners. The intermediate transfer belt 2 has a configuration that is wound around the driving roller 2B and the driven roller 2A and can move in the same direction at a position facing the photoconductors 3Y, 3M, 3C, and 3B. A cleaning device 10 for cleaning the surface of the intermediate transfer belt 2 is provided at a position facing the driven roller 2A.

The surface of the photoreceptor 3Y is uniformly charged by the charging device 4Y, and an electrostatic latent image is formed on the photoreceptor 3Y based on image information from the scanner unit. The electrostatic latent image is visualized as a toner image by a developing device 8Y containing yellow toner, and the toner image is primarily transferred onto the intermediate transfer belt 2 by a primary transfer device 7Y to which a predetermined bias is applied. The The other photoconductors 3M, 3C, and 3B also form similar images only with different toner colors, and the toner images of the respective colors are sequentially transferred onto the intermediate transfer belt 2 and superimposed. After the transfer, the toner remaining on the photosensitive member 3 is removed by the cleaning device 6Y, and after the transfer, the potential of the photosensitive member 3Y is initialized by a charge-removing lamp (not shown) to prepare for the next image forming process.
The paper feed unit 1B includes a paper feed tray 1B1 for stacking and storing paper P as a recording medium, and a paper feed roller for separating and feeding the paper P in the paper feed tray 1B1 one by one from the top. The conveyance roller pair 1B2 that conveys the fed paper P and the paper P are temporarily stopped and the oblique deviation is corrected, and then the leading edge of the image on the intermediate transfer belt 2 coincides with a predetermined position in the conveyance direction. It has a registration roller pair 1B3 that is sent out toward the nip at timing. In the vicinity of the registration roller pair 1B3, there is a sensor (not shown) for detecting the reflectance of the paper surface. When the value is different from the sensor output in the previous process, the intermediate transfer belt 2 or the transfer counter roller 2C is switched.
A toner image T (hereinafter, also simply referred to as “toner”) primarily transferred from the photoreceptors 3Y, 3M, 3C, 3B onto the intermediate transfer belt 2 is biased (AC, pulse, etc.) by a secondary transfer bias applying unit (not shown). Is applied to the transfer counter roller 2C, and is secondarily transferred onto the paper P by the action of an electric field with the secondary transfer roller 9B via the intermediate transfer belt 2. Thereafter, the sheet P on which the toner image T is secondarily transferred on the surface is firmly fixed on the surface by the action of heat and pressure in the fixing device 11 and is discharged from the discharge tray 13 through the discharge roller 12. .

Next, the detailed operation and operation of the primary transfer unit of the image forming apparatus according to this embodiment will be described with reference to FIGS.
FIG. 2 shows a primary transfer portion of the present invention, and an example in which two bias applying members are provided will be described. 2 is provided with a (−) bias roller 70 in contact with the back side of the intermediate transfer belt 2 in front of the entrance side of the transfer nip, and a (+) transfer bias inside the transfer nip. A blade 71 and a (−) bias blade 72 are provided in contact with the back side of the intermediate transfer belt 2.
A toner image (not shown) formed on the photoreceptor 3 is transferred onto the intermediate transfer belt 2. The toner image on the photoreceptor 3 is affected by the potential of the intermediate transfer belt 2 as it approaches the intermediate transfer belt 2. In order to faithfully transfer the toner image on the photoreceptor 3 onto the intermediate transfer belt 2, a position before the primary transfer nip formed by the photoreceptor 3 and the intermediate transfer belt 2 due to the influence of the potential of the intermediate transfer belt 2. Therefore, it is necessary to prevent “pre-transfer” in which the toner image is transferred.
Therefore, the toner image is moved before entering the primary transfer process by setting the surface potential of the intermediate transfer belt 2 to the same polarity (−) as that of the toner by the (−) bias roller 70 provided on the inner surface of the intermediate transfer belt 2. It prevents the image quality from deteriorating. In the primary transfer nip constituted by the photoreceptor 3 and the intermediate transfer belt 2 by the (+) transfer bias blade 71, (−) toner is transferred from the photoreceptor 3 to the intermediate transfer belt 2. Thereafter, the potential of the intermediate transfer belt 2 is dropped to about 0 V by the (−) bias blade 72 on the back surface of the intermediate transfer belt 2, thereby preventing a discharge phenomenon caused by a potential difference when the photoreceptor 3 and the intermediate transfer belt 2 are peeled off. is doing.
Since the (+) transfer bias blade 71 and the (−) bias blade 72 slide relative to the intermediate transfer belt 2, a small amount of wear powder 80 is generated with time, and the (+) transfer bias blade 71 (−) Since the bias blade 72 adheres to the upstream side of the moving direction of the intermediate transfer belt 2 and falls downward due to blade vibration during operation, the (−) wear powder 80 dropped from the tip of the bias blade 72 is It adheres to the space between the (+) transfer bias blade 71 and the (−) bias blade 72. Thereby, it is possible to effectively remove the wear powder accumulated between the plurality of bias applying members. However, although an insulating material of about 2 to 4 mm is provided between the (+) transfer bias blade 71 and the (−) bias blade 72, the intermediate transfer belt 2 is mainly formed by dispersing carbon in polyimide resin. Since it is a molded member having medium resistance electrical characteristics, the generated wear powder 80 accumulates with time, and a conduction path is formed between the (+) transfer bias blade 71 and the (−) bias blade 72. There is a risk of leakage.

Therefore, in the present invention, as shown in FIG. 3, the (+) transfer bias blade 71 and the (−) bias blade 72 can be independently released. Therefore, the wear powder adhering to the upstream side of the (−) bias blade 72 in accordance with the operation of releasing the (−) bias blade 72 is removed by the insulating member 72. However, the wear powder 80 remains attached to the upper part of the insulating member A73 only by being removed.
Therefore, as shown in FIG. 3, the insulating transfer member A73 and the insulating member B74 are the intermediate transfer belt in a state where the (+) transfer bias blade 71 and the (−) bias blade 72 are released by a blade switching mechanism (not shown). The top surface is inclined toward the traveling direction 2. Further, the top surfaces of the insulating member A73 and the insulating member B74 are subjected to a process for reducing the friction coefficient such as Teflon (registered trademark) coating, and the top surfaces of the insulating member A73 and the insulating member B74 are caused by the action of vibration caused by machine operation. The wear powder 80 that has fallen onto the surface moves out of the primary transfer region. A foreign material recovery member A76 is provided below the outermost insulating member A73, and is configured to store the worn powder 80 that has fallen. As a result, the wear powder adhering to the vicinity of the plurality of bias applying members falls along with the movement operation of the bias applying member, the insulation of the plurality of bias applying members can be maintained, and safety can be ensured. Further, by using the insulating member provided between the plurality of insulating members as the cleaning member, the configuration can be simplified, the number of parts can be reduced, and the cost can be reduced.
In addition, the timing of the bias blade contact / release switching operation is performed every predetermined number of prints, and the wear powder 80 does not accumulate even during long-time operation.
The Teflon (registered trademark) coating may be applied to the side surfaces of the (+) transfer bias blade 71 and the (−) bias blade 72, and the wear powder 80 that has dropped from the tip of the blade is less likely to adhere to the side surface of the blade. More advantageous against leaks.

As shown in FIG. 4, a nozzle 78 for supplying air to the gap between the two blades is provided at the front end portions of the (+) transfer bias blade 71 and the (−) bias blade 72. By supplying air by the air pump 79 at a predetermined timing, the wear powder 80 accumulated between the two blades is sent out toward the rear end portion on the opposite side to the nozzle 78. Since the upper surface of the insulating member A73 has been subjected to a process for reducing the friction coefficient such as Teflon (registered trademark) coating, the wear powder 80 moves out of the primary transfer region without staying. A foreign matter collecting member B77 is provided at the rear end, and is configured to store the worn powder 80 that has been sent out.
The timing of supplying air is performed every predetermined number of printed sheets, and the wear powder 80 does not accumulate even during long-time operation. As a result, the wear powder 80 that has dropped near the bias applying member moves to one end by the airflow, and therefore does not accumulate near the bias applying member.
Further, it has been found that the conditions under which the leak occurs depend on the humidity in the vicinity of the primary transfer portion, and the higher the humidity, the higher the possibility that the amount of moisture absorbed by the wear powder 80 increases and the leak occurs. In order to solve this problem, the side surfaces of the (+) transfer bias blade 71, the (−) bias blade 72, the insulating member A73, and the insulating member B74 are subjected to a treatment such as a water repellent coating so that dew condensation occurs. Since moisture hardly adheres to these side surfaces, it is more advantageous against leakage.

1 is a diagram illustrating a tandem type color copying machine as an image forming apparatus according to an exemplary embodiment. It is a figure which shows the primary transfer part which showed the form of the braid | blade contact of this invention. It is a figure which shows the primary transfer part which showed the form of the blade cancellation | release of this invention. It is a figure which shows the primary transfer part which showed the form of the abrasion powder removal by the air of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Color copier 1A Image formation part 1B Paper feed part 1B1 Paper feed tray 1B2 Conveyance roller pair 1B3 Registration roller pair 1C Document conveyance part 2 Intermediate transfer belt 2A Driven roller 2B Drive roller 2C Opposite roller 3 Photoconductor 4 Charging device 5 Writing device 6 Cleaning device 7 Primary transfer device 8 Developing device 9B Secondary transfer roller 10 Cleaning device 11 Fixing device 70 (-) Bias roller 71 (+) Transfer bias blade 72 (-) Bias blade 73 Insulating material A
74 Insulation B
75 Insulation C
76 Foreign matter recovery member A
77 Foreign matter recovery member B
78 Nozzle 79 Air pump 80 Abrasion powder

Claims (5)

An image carrier that rotates by forming a toner image on the surface, a belt-like primary transfer member that rotates in the same direction while contacting the image carrier and transfers the toner image from the image carrier, and the primary transfer In an image forming apparatus having a transfer station having a bias applying member having at least the same polarity as the toner and a bias applying member having the opposite polarity of the toner on the opposite side of the image carrier from the body,
In the image forming apparatus, a cleaning member is provided between a plurality of bias applying members having different polarities. The image forming apparatus according to claim 1.
In the image forming apparatus, the cleaning member is an insulating member provided between bias applying members having different polarities. The image forming apparatus according to claim 1.
In the image forming apparatus, at least one of the plurality of bias applying members having different polarities performs a cleaning operation along with an operation of moving in a direction away from the primary transfer body. The image forming apparatus according to claim 3.
In the image forming apparatus, the surface of the cleaning member and the bias applying member is subjected to a surface treatment with a reduced friction coefficient. The image forming apparatus according to claim 1,
The image forming apparatus is provided with an air generating device for flowing air in a longitudinal direction of a bias applying member.

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