JP2007241014A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus designed such that a defect such as nonuniform transfer resulting from bends in a plurality of bias rollers is prevented as well as an image defect caused by the bias rollers and longitudinal nonuniform pressure, particularly, image defects such as nonuniform transfer and worm hole image are effectively prevented, and therefore a high quality image can be formed. <P>SOLUTION: The image forming apparatus 1 includes: backup rollers 103 and 104 disposed in contact with the corresponding bias rollers 101 and 102 so as to be opposite to contact parts between the corresponding bias rollers and the image carrier. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a fax machine using electrophotographic technology. In particular, the present invention relates to an image forming apparatus that uses the technique of a bias applying device in primary transfer of a color electrophotographic apparatus using an intermediate transfer member. The present invention also relates to an image forming apparatus having a bias applying device in a secondary transfer unit or a neutralizing device such as an intermediate transfer belt.

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 the trade-off relationship. Since such adjustment is very fine, for example, it varies depending on slight fluctuations such as the transfer belt and the photoreceptor potential, which is a cause of variation in the transfer performance of the machine.
Incidentally, the cause of “reverse transfer” is a discharge in the vicinity of 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 as the toner polarity.
Here, as a technique related to the bias applying device, Patent Document 1 discloses an image forming apparatus that applies a (−) electric field downstream of the rear end of the nip. Further, 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 by applying a (−) bias to a mechanical nip entrance / exit roller. ing.

The current intermediate transfer belt is almost entirely kneaded with carbon or the like in a polymer body, and is electrically conductive. Since it is an electronic conductive resistor, the resistance has an electric field dependency. When such an intermediate transfer belt is used, the resistance is low in the primary transfer nip, but the resistance increases if the primary transfer nip is left. 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, reverse-polarity ions are generated and sucked into the image toner, causing the polarity to vary, and even after the transfer nip, the toner is irregularly shaken, resulting in worsening of dust. 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. For example, in Patent Document 1, an electrode is placed on the downstream side considerably away from the nip. However, this method has a problem in that electric charges often remain 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 a current that does not lower 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, but since the static elimination is performed at the outlet end of the mechanical nip, the static elimination time is insufficient.

In the primary transfer apparatus, a transfer system having a plurality of adjacent bias applying members has been proposed. 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 the biases having different polarities are applied to the adjacent bias members, the roller has a small-diameter configuration, and there has been a problem of preventing deflection.
Further, in Patent Document 2, there is no specific configuration for the method of pressing a plurality of bias rolls. If the pressure fluctuates, transfer defects and blurring occur in the low pressure region. In the high-pressure region, there is a concern that the problem of “worm biting” that the characters and lines fall out due to aggregation inside the toner layer.

JP 2003-057963 A Japanese Patent No. 3346063

  Therefore, the present invention has been made in view of the above-described problems, and its problem is to prevent the occurrence of transfer unevenness due to the deflection of the bias roller and to prevent the occurrence of abnormal images due to uneven pressing in the longitudinal direction. An image forming apparatus is provided. Another object of the present invention is to provide an image forming apparatus capable of effectively suppressing the occurrence of abnormal images such as uneven transfer and insect eaters and forming a high quality image.

The features of the present invention, which is a means for solving the above problems, are listed below.
According to the present invention, a toner image formed on an image carrier is primarily transferred to an intermediate transfer belt that is driven while being in contact with the image carrier, and the toner image on the intermediate transfer belt is secondarily transferred to a recording medium. An image forming apparatus for transferring and obtaining a recorded image, wherein the image carrier and the intermediate transfer belt are in contact with each other in a range between a most upstream side position and a most downstream side position in the intermediate transfer belt moving direction. As a primary transfer device that primarily transfers the toner image on the body to the intermediate transfer belt, a transfer voltage that is in contact with the back surface portion of the intermediate transfer belt within the contact range and has a polarity opposite to the normal charging polarity of the toner is applied. An intermediate transfer belt on the downstream side in the intermediate transfer belt movement direction from the position where the transfer roller contacts the intermediate transfer belt, and on the upstream side in the intermediate transfer belt movement direction from the most downstream position. In an image forming apparatus provided with a downstream bias roller that is in contact with the back surface portion and to which a voltage having the same polarity as the normal charging polarity of the toner is applied, the side opposite to the position in contact with the image carrier with respect to the bias roller The image forming apparatus is characterized in that a backup roller is provided in contact with the position.
The present invention is characterized in that the backup roller is provided in contact with a position opposite to a position in contact with the image carrier with respect to a plurality of bias rollers.
The present invention is characterized in that the plurality of bias rollers and the plurality of backup rollers apply contact pressures independently to the image carrier.
The present invention is characterized in that the deflection of the backup roller with respect to a predetermined load is smaller than the deflection of the bias roller.
The present invention is characterized in that the backup roller has an insulating layer on the surface.

  The present invention provides an image forming apparatus that prevents the occurrence of transfer unevenness due to the deflection of the bias roller and prevents the occurrence of abnormal images due to uneven pressing in the longitudinal direction. It became possible. In addition, it is possible to provide an image forming apparatus capable of effectively suppressing the occurrence of abnormal images such as uneven transfer and insect eaters and forming a high-quality image.

  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.

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 100 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 100 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 100. 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, developing device 8Y, primary transfer device 7Y, and 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 100 is configured so as to be able to move in the same direction at the facing position between the driving roller 2B and the driven roller 2A and the photosensitive members 3Y, 3M, 3C, and 3B. A cleaning device 10 that cleans the surface of the intermediate transfer belt 100 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 100 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 100 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 in order from the top. The conveyance roller pair 1B2 that conveys the fed paper P and the paper P are temporarily stopped and the oblique shift is corrected, and then the leading edge of the image on the intermediate transfer belt 100 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 100 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, and 3B onto the intermediate transfer belt 100 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 sheet P through the intermediate transfer belt 100 and the secondary transfer roller 9B by the action of an electric field. 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, based on FIG. 2 and FIG. 3, the detailed operation and operation of the primary transfer unit of the image forming apparatus in the present embodiment will be described.
Example 1
FIG. 2 shows an example in which two bias rollers and two backup rollers are provided. A winding roller 105 shown in FIG. 2 functions to expand a belt winding nip formed by the photosensitive member 3 and the intermediate transfer belt 100. The two bias rollers are provided in contact with the back side of the intermediate transfer belt 100 and opposed to the photosensitive member 3, and a (+) bias having a polarity opposite to that of the toner is applied to the entrance side when viewed from the moving direction of the intermediate transfer belt 100. A transfer bias roller 101 that performs the same operation as described above and an exit bias roller 102 that applies a (−) bias having the same polarity as that of the toner are provided in contact with the back side of the intermediate transfer belt 100. The electrical characteristics of the transfer bias roller 101 and the exit bias roller 102 are both in the middle resistance region (about 10 ⁸ to 10 ¹⁰ Ω / □), and in a specific embodiment, the core metal is made of a metal material of φ5. Further, a rubber layer or a resin layer having a thickness of 0.5 mm is formed on the surface layer.

In the primary transfer nip constituted by the photoreceptor 3 and the intermediate transfer belt 100 by the transfer bias roller 101 that applies the (+) polarity opposite to the (−) polarity toner, the (−) polarity toner is intermediate from the photoreceptor 3. Transferred to the transfer belt 100. Thereafter, the surface potential of the intermediate transfer belt 100 is lowered to around 0 V by the exit bias roller 102 that applies the (−) polarity of the same polarity as the (−) polarity toner to the back surface of the intermediate transfer belt 100, so A discharge phenomenon caused by a potential difference at the time when the transfer belt 100 peels is prevented.
In order to faithfully transfer the toner image on the photoreceptor 3 onto the intermediate transfer belt 100, the potential of the intermediate transfer belt 100 is changed at a position before the primary transfer nip formed by the photoreceptor 3 and the intermediate transfer belt 100. It is necessary to prevent “pre-transfer” in which the toner image is transferred due to the influence.

In the case where FIG. 2 is the first station of a multi-color station, it is necessary to prevent pre-transfer by dropping the surface potential of the intermediate transfer belt 100 to near 0V by a neutralizing device (not shown). When FIG. 2 shows the second and subsequent stations of the multi-color station, the exit bias roller 102 of the previous station functions as a static eliminating device for the intermediate transfer belt 100. If the residual potential still remains on the intermediate transfer belt 100, the surface potential of the intermediate transfer belt 100 drops to near 0 V by applying a reverse polarity (-) bias to the toner to the winding roller 105 of the previous station, and pre-transfer is performed. Is prevented.

The transfer bias roller 101 and the exit bias roller 102 have a small diameter because the primary transfer nip formed by the photosensitive member 3 and the intermediate transfer belt 100 is narrow and it is necessary to secure an insulating distance that does not leak because reverse polarity is applied to each other. A roller is used.
Therefore, by forming the transfer bias roller 101 for applying the transfer bias and the bias roller 102 for applying a bias having a polarity opposite to that of the transfer electrode by a small-diameter roller member, a stable electric field is formed in a narrow primary transfer region. It becomes possible.

Further, the transfer bias roller 101 and the exit bias roller 102 have an elastic layer of about 0.5 mm on the surface in order to secure a contact nip. On the other hand, the backup roller 103 and the backup roller 104 do not need to be particularly provided with an elastic layer, and have a thin insulating layer on the surface. In a specific embodiment of the backup roller 103 and the backup roller 104, the core metal is made of a metal material of φ10 to φ15, and further has an insulating layer on its surface layer.
Therefore, the deflection of the bias rollers 101 and 102 with respect to a predetermined load is larger than that of the backup rollers 103 and 104. Thus, by making the deflection of the backup rollers 103 and 104 under a predetermined load smaller than the deflection of the bias rollers 101 and 102, the deflection of the bias rollers 101 and 102 can be effectively reduced, and uneven transfer can be prevented. .

As a conventional method of applying pressure to the transfer roller, it is common to apply pressure to the journal portions at both ends of the roller. However, in the present invention, bending is likely to occur because of the small diameter roller. Therefore, when the backup roller 103 is pressed against the transfer bias roller 101, the transfer bias roller 101 is pressed against the photosensitive member 3 with a small amount of bending. Here, P in the figure indicates the direction of pressing, and P1 indicates pressing on the backup roller 103. Since the backup roller 103 can have a larger diameter than the transfer bias roller 101, the deflection can be reduced even when the journal portions at both ends are pressed. The backup roller 104 is pressed against the outlet bias roller 102 and performs the same function. P <b> 2 indicates the pressure on the backup roller 104.
The backup roller 103 is brought into contact with the transfer bias roller 101 and the backup roller 104 is pressed against the exit bias roller 102, so that the transfer bias roller 101 and between the exit bias roller 102 and the photosensitive member 3 are pressed. Uniform pressure distribution in the longitudinal direction can prevent uneven transfer due to poor contact. In addition, the transfer bias roller 101 and the exit bias roller 102 can independently set the pressing force, and thus can prevent insect biting caused by excessive pressure.

(Example 2)
FIG. 3 shows a primary transfer portion of the present invention, which is an example in which two bias rollers and one backup roller are provided.
The backup roller 103 is pressed between the transfer bias roller 101 and the exit bias roller 102. Since the surface of the backup roller 103 has an insulating layer, it is possible to prevent a leakage phenomenon due to current flowing between the transfer bias roller 101 and the exit bias roller 102. In the second embodiment, substantially the same operation as in the first embodiment can be obtained, and since there are fewer backup rollers compared to the first embodiment, there is an advantage that the cost can be reduced.

1 is a diagram showing an image forming apparatus (schematic diagram) of the present invention. It is a figure which shows the primary transfer part detail drawing (Embodiment 1) of this invention. FIG. 10 is a detailed view of a primary transfer portion of the present invention (second embodiment).

Explanation of symbols

1 Image forming device (color copier)
DESCRIPTION OF SYMBOLS 1A Image formation part 1B Paper feed part 1B1 Paper feed tray 1B2 Conveyance roller pair 1B3 Registration roller pair 1C Document conveyance part 1D Scanner part 2A Driven roller 2B Drive roller 3 Photoconductor 4 Charging device 5 Writing device 6 Cleaning device 7 Primary transfer device 8 Developing device 10 Cleaning device 11 Fixing device 12 Discharge roller 13 Discharge tray 100 Intermediate transfer belt 101 Transfer bias roller 102 Exit bias roller 103 Backup roller 104 Backup roller 105 Winding roller

Claims (5)

The toner image formed on the image carrier is primarily transferred to an intermediate transfer belt that is driven while being in contact with the image carrier, and the toner image on the intermediate transfer belt is secondarily transferred to a recording medium for recording. An image forming apparatus for obtaining an image,
When the image carrier and the intermediate transfer belt are in contact with each other in the range between the most upstream side position and the most downstream side position in the intermediate transfer belt moving direction, the toner image on the image carrier is primarily transferred to the intermediate transfer belt. As a primary transfer device, it has a transfer roller that is in contact with the back surface portion of the intermediate transfer belt within the contact range and to which a transfer voltage having a polarity opposite to the normal charging polarity of the toner is applied,
A downstream side of the intermediate transfer belt in the intermediate transfer belt movement direction downstream of the position where the transfer roller is in contact with the intermediate transfer belt, and a downstream side of the intermediate transfer belt in the intermediate transfer belt movement direction upstream of the downstream side position;
In addition, in the image forming apparatus provided with a downstream bias roller to which a voltage having the same polarity as the normal charging polarity of the toner is applied,
The image forming apparatus is provided with a backup roller in contact with a position opposite to a position in contact with the image carrier with respect to the bias roller. The image forming apparatus according to claim 1.
In the image forming apparatus, the backup roller is provided in contact with a position opposite to a position in contact with the image carrier with respect to a plurality of bias rollers. The image forming apparatus according to claim 1.
In the image forming apparatus, the plurality of bias rollers and the plurality of backup rollers respectively apply contact pressure to the image carrier independently. The image forming apparatus according to claim 2 or 3,
In the image forming apparatus, the deflection of the backup roller with respect to a predetermined load is smaller than the deflection of the bias roller. The image forming apparatus according to claim 1,
In the image forming apparatus, the backup roller has an insulating layer on a surface thereof.

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