JP2013190506A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device that prevents transferability from becoming unstable due to increase/decrease of effective transfer current at a secondary transfer nip.SOLUTION: An image forming device includes: effective transfer current detection means for detecting a value of an effective transfer current flowing in a secondary transfer nip from a transfer current application position where transfer current application means 50 applies the transfer current to an intermediate transfer belt 20 or a secondary transfer belt 93; and transfer current control means 51 for controlling the transfer current output from the transfer current application means so as to achieve a preset effective transfer current value, on the basis of a detection result of the effective transfer current detection means.

Description

  The present invention relates to an image forming apparatus such as a printer, a facsimile machine, and a copying machine.

  Conventionally, there is a so-called intermediate transfer type image forming apparatus that primarily transfers a toner image formed on a photosensitive member to an intermediate transfer belt and secondarily transfers the toner image transferred onto the intermediate transfer belt onto a transfer material. Are known.

  In the image forming apparatus described in Patent Document 1, the intermediate transfer belt is rotatably stretched by a plurality of stretching members. A toner image is primarily transferred from the photoreceptor to the intermediate transfer belt by forming a transfer electric field in the primary transfer nip formed by contact between the photoreceptor and the intermediate transfer belt by the primary transfer device. The transfer material onto which the toner image is secondarily transferred from the intermediate transfer belt is carried and conveyed by the secondary transfer belt that is rotatably stretched by a plurality of stretching members. By carrying the transfer material on the secondary transfer belt and transporting it, it is possible to make it difficult for wrinkles and deformations to occur on transfer materials with low rigidity such as thin paper, or to cause jamming. It is possible to pass through the secondary transfer nip stably. Then, in the secondary transfer nip formed by the contact between the intermediate transfer belt and the secondary transfer belt, a transfer electric field is formed by the secondary transfer device, so that the intermediate transfer belt is carried and conveyed to the secondary transfer nip by the secondary transfer belt. The toner image on the intermediate transfer belt is secondarily transferred onto the transfer material.

  The secondary transfer device is provided with a transfer power supply that applies a transfer current for secondary transfer to the intermediate transfer belt or the secondary transfer belt. The current that reaches the secondary transfer nip from the transfer current application position to the intermediate transfer belt or the secondary transfer belt by the transfer power source flows through the secondary transfer nip, and a potential difference is generated between the intermediate transfer belt and the secondary transfer belt. As a result, a transfer electric field is formed in the secondary transfer nip.

  In such an image forming apparatus, there is a problem that the transfer performance at the secondary transfer nip formed by the contact between the intermediate transfer belt and the secondary transfer belt becomes unstable. If the transfer performance at the secondary transfer nip becomes unstable, the transfer image transferred from the intermediate transfer belt to the transfer material may be uneven in density, or the density of the entire transfer image may become unstable. End up.

  Instability in transfer performance is largely related to the electrical resistance of a transfer belt such as an intermediate transfer belt or a secondary transfer belt. Specifically, the electrical resistance of the transfer belt varies in its initial value for each product, changes with time with deterioration, or changes with environmental fluctuations such as temperature and humidity. For this reason, the electric resistance of the transfer belt varies depending on the use state and use environment. When a transfer bias of a constant voltage is applied to such a transfer belt, the value of the electric current flowing through the transfer belt varies depending on the electric resistance value at the time of application, so the strength of the transfer electric field formed in the secondary transfer nip changes. Resulting in. This change makes the transfer performance unstable.

  As an image forming apparatus capable of suppressing such instability of transfer performance, there is an image forming apparatus that performs so-called constant current control that maintains a constant transfer current value applied to an intermediate transfer belt or a secondary transfer belt by a transfer power source. Are known. In this image forming apparatus, by applying a constant transfer current to the intermediate transfer belt or the secondary transfer belt regardless of the electric resistance value, a stable transfer electric field is formed in the secondary transfer nip. Instability of transfer performance can be reduced.

  However, even when such constant current control is carried out, the transfer performance may become unstable at the secondary transfer nip. Specifically, when the electrical resistance value on the back surface of the transfer belt is greatly reduced due to environmental changes, the transfer current is more likely to flow in the belt circumferential direction on the back surface than in the belt thickness direction. In this way, even if a constant transfer current is applied to the transfer belt, it is transferred to the belt circumferential direction on the back side of the transfer belt and flows into a roller or the like that stretches the transfer belt. The transfer current increases. Therefore, the effective transfer current flowing in the belt thickness direction, reaching the secondary transfer nip, and flowing through the secondary transfer nip is reduced. Then, the transfer performance at the secondary transfer nip deteriorates due to the decrease in the effective transfer current. On the other hand, when the electrical resistance on the back surface of the transfer belt rises to the original value due to environmental fluctuations, the amount of effective transfer current flowing through the secondary transfer nip increases and the transfer performance is restored to the original state.

  The transfer performance at the secondary transfer nip becomes unstable due to the increase or decrease in the effective transfer current flowing through the secondary transfer nip due to such environmental fluctuations. This phenomenon tends to cause instability of transfer performance particularly when a transfer current is applied to the transfer belt by an indirect application method. The indirect application method is a method in which a transfer current is applied to the back surface, which is the inner surface of the transfer belt loop, at a position different from the secondary transfer nip.

  Japanese Patent Application Laid-Open No. H10-260260 discloses that the destabilization of the transfer performance of the primary transfer nip caused by the increase or decrease of the effective transfer current flowing through the primary transfer nip formed by the contact between the photoconductor and the intermediate transfer belt is disclosed. Has been. However, Patent Document 1 does not disclose suppression of instability in transfer performance of the secondary transfer nip due to increase or decrease in effective transfer current in the secondary transfer nip.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus capable of suppressing instability of transfer performance due to increase / decrease in effective transfer current at the secondary transfer nip. is there.

  To achieve the above object, the invention of claim 1 is characterized in that the image carrier, a toner image forming means for forming a toner image on the image carrier, and a plurality of stretching members are rotatably stretched. An intermediate transfer belt to which a toner image on an image carrier is primarily transferred, and a toner image on the image carrier at a primary transfer nip formed by contact between the image carrier and the intermediate transfer belt. A primary transfer means for primary transfer, a secondary transfer belt that rotatably supports a transfer material on which a toner image on the intermediate transfer belt is secondarily transferred by a plurality of stretching members, and the intermediate transfer A secondary transfer unit that secondary-transfers the toner image on the intermediate transfer belt to the transfer material at a secondary transfer nip formed in contact with the belt and the secondary transfer belt, and the secondary transfer unit includes: The intermediate transfer belt or the two In the image forming apparatus having a transfer current applying unit that applies a transfer current for secondary transfer to the transfer belt, the transfer current is applied to the intermediate transfer belt or the secondary transfer belt from the transfer current applying position by the transfer current applying unit. An effective transfer current detection means for detecting an effective transfer current value that reaches the next transfer nip and flows through the secondary transfer nip, and an effective transfer current value is preset based on a detection result of the effective transfer current detection means. And a transfer current control means for controlling the transfer current output from the transfer current applying means so as to have a constant value.

  In the present invention, the transfer current output from the transfer current applying unit is set so that the value of the effective transfer current flowing through the secondary transfer nip becomes a predetermined constant value based on the detection result of the effective transfer current detecting unit. Is controlled by the transfer current control means. As a result, regardless of the electric resistance value of the intermediate transfer belt or the secondary transfer belt, the effective current that flows from the transfer current application position to the intermediate transfer belt or the secondary transfer belt to the secondary transfer nip and flows through the secondary transfer nip. The value of the transfer current can be kept constant. Therefore, it is possible to suppress the transfer performance from becoming unstable due to the increase or decrease of the effective transfer current in the secondary transfer nip.

  As described above, according to the present invention, there is an excellent effect that instability of transfer performance due to increase / decrease in effective transfer current at the secondary transfer nip can be suppressed.

The enlarged view of the secondary transfer part of a copying machine. 1 is a schematic configuration diagram of a copier according to an embodiment. The flowchart of the correction control of the transfer current value by temperature humidity environment. The enlarged view of a secondary transfer part at the time of positioning a secondary transfer roller in an indirect position. The figure which shows the case where an earth roller is earth | grounded via predetermined resistance. The figure which shows the case where an earth roller is earth | grounded directly. The figure explaining the influence of the pre-transfer in the case where the earth roller is grounded via a resistor and the case where it is grounded not via a resistor. The enlarged view of a secondary transfer part at the time of positioning a secondary transfer roller in an opposing position. The enlarged view of a secondary transfer part at the time of positioning a secondary transfer roller in an offset position. The figure which showed the case where the two secondary transfer members of a secondary transfer roller and a transfer brush were provided in contact with the back surface of a secondary transfer belt. The figure which showed the case where two secondary transfer members, a secondary transfer roller and a transfer brush roller, were provided in contact with the back surface of the secondary transfer belt. The figure which showed the case where the two secondary transfer members of a transfer brush roller and a transfer brush roller were made to contact on the back surface of a secondary transfer belt. FIG. 4 is an enlarged view of a secondary transfer portion when a ground roller is provided on the upstream side of the secondary transfer counter roller in the intermediate transfer belt rotation direction and a neutralizing roller is provided on the downstream side.

[Embodiment 1]
A first embodiment in which the present invention is applied to an image forming apparatus will be described below.
FIG. 2 is a schematic configuration diagram of the copying machine 1 which is the image forming apparatus according to the present embodiment. The copying machine 1 shown in FIG. 2 has a tandem configuration in which a plurality of photoreceptors as latent image carriers capable of forming a color image corresponding to color separation are juxtaposed, and a toner image formed on each photoreceptor. Is a full-color printer capable of forming a multicolor image by transferring the superimposed image onto the intermediate transfer belt 20 and transferring the superimposed image onto a transfer sheet as a transfer material.

  In the present invention, the image forming apparatus is not limited to a full-color printer, but of course includes a full-color copying machine, a facsimile machine, and a printing machine.

  In FIG. 2, in the copying machine 1, an image forming unit 100 is positioned at a central portion in the vertical direction, a document feeder 40 is provided below the image forming unit 100, and an original document table 31 is provided above the image forming unit 100. Each of the reading devices 30 is arranged.

  The image forming unit 100 is provided with a transfer unit composed of an intermediate transfer belt 20 having a horizontally extending surface. Above the intermediate transfer belt 20, an image of a color complementary to the color separation color is provided. The structure for forming is provided. In the present embodiment, photoreceptors 3B, 3Y, 3C, and 3M that can carry images of toners of complementary colors (black, yellow, cyan, and magenta) are juxtaposed along the extended surface of the intermediate transfer belt 20. Yes.

  In the following description, in the case of contents common to all the photoconductors, the photoconductor is denoted by reference numeral 3. Each of the photoconductors 3B, 3Y, 3C, and 3M is composed of a drum that can rotate in the same direction (counterclockwise in FIG. 2), and the periphery thereof is charged to perform image forming processing in the rotation process. A device 4, a writing device 5, a developing device 6, a primary transfer device 7, and a cleaning device 8 are arranged.

  The intermediate transfer belt 20 is applied to a primary transfer unit to which a visible image from an image forming unit including each photoreceptor 3 is sequentially transferred, a driven roller 21, a drive roller 22, a secondary transfer counter roller 23, and a tension roller 24. It has a configuration that is stretched in a rotatable manner and can move in the same direction at a position facing the photoconductors 3B, 3Y, 3C, and 3M. The driving roller 22 rotates in the clockwise direction in the figure by a driving force from a driving source (not shown), thereby driving the intermediate transfer belt 20 in the clockwise direction in the figure. The driven roller 21 is an intermediate transfer belt. Rotate with 20 rotations. The secondary transfer counter roller 23 faces the secondary transfer device 90 with the intermediate transfer belt 20 interposed therebetween. The tension roller 24 holds the intermediate transfer belt 20 so that a predetermined tension is applied to the intermediate transfer belt 20. It is energizing from the outside of the loop to the inside. Note that the secondary transfer counter roller 23 and the tension roller 24 also rotate as the intermediate transfer belt 20 rotates.

  Transfer residual toner remaining on the intermediate transfer belt 20 after the secondary transfer is removed by the intermediate transfer belt cleaning device 10. The intermediate transfer belt cleaning device 10 includes a cleaning blade and a rotatable roller-shaped application brush for applying a solid lubricant. The cleaning blade comes into contact with the intermediate transfer belt 20 and scrapes off transfer residual toner from the surface thereof. The application brush scrapes off and applies the solid lubricant pressed by the pressure spring to the intermediate transfer belt 20 while rotating. Thus, the intermediate transfer belt cleaning device 10 has a function as a cleaning device for cleaning the transfer residual toner on the intermediate transfer belt 20 and a function as a lubricant application device for applying the lubricant to the surface of the intermediate transfer belt 20. Have both.

  The intermediate transfer belt cleaning device 10 of the present embodiment is configured by a blade system, but may be an electrostatic cleaning system. In the case of the electrostatic cleaning method, a bias is applied to the cleaning roller or the cleaning brush, and the residual toner adhering to the intermediate transfer belt 20 is electrostatically adsorbed for cleaning.

  FIG. 1 is an enlarged view of a secondary transfer portion of the copying machine 1. The secondary transfer device 90 includes a secondary transfer belt 93 that is wound around the driving roller 91 and the driven roller 92 and can move in the same direction as the intermediate transfer belt 20 at the secondary transfer position where the secondary transfer device 90 is located. The secondary transfer belt 93 is driven by a drive roller 91. In the secondary transfer device 90, a multi-color image superimposed on the intermediate transfer belt 20 in the process of transporting the transfer paper by the secondary transfer belt 93 is transferred by batch transfer or a single color image carried on the transfer paper to the transfer paper. can do. Further, a secondary transfer belt cleaning device 60 for cleaning the front surface of the secondary transfer belt 93 by the cleaning blade 61 is provided, such as toner or paper dust adhered to the front surface of the secondary transfer belt 93. The deposits are removed.

  The driving roller 91 and the driven roller 92 are made of a conductive material so that a feedback current described later is returned to the transfer power supply 50.

  A secondary transfer roller 94 is in contact with the back surface of the secondary transfer belt near the secondary transfer nip N formed by bringing the intermediate transfer belt 20 and the secondary transfer belt 93 into contact with each other. The secondary transfer roller 94 is made of a conductive material, and is not shown connected to the transfer power supply 50 so as to give the secondary transfer belt 93 a charge having a polarity opposite to the charge polarity of the toner on the intermediate transfer belt 20. Connected to the switch. This switch is ON / OFF controlled by a control unit (not shown) and, when turned on, conducts a conduction path connecting the transfer power supply 50 and the secondary transfer roller 94. That is, in this printer, the secondary transfer roller 94, the transfer power supply 50, and the control unit constitute transfer current supply means.

  Further, the driving roller 91 and the driven roller 92 also have a function of detecting the current flowing on the secondary transfer belt 93 as a feedback current, and the current supplied from the secondary transfer roller 94 depends on the value of the feedback current. Be controlled. For this reason, the driving roller 91 and the driven roller 92 are control units that are transfer current control means in which a control circuit for setting a supply current to the secondary transfer roller 94 by the transfer power source 70 is set according to the feedback current value. A plate 51 is connected. A transfer power supply 50 is also connected to the control plate 51. The value of the effective transfer current flowing through the secondary transfer nip N obtained as a difference between the output current value of the transfer power supply 50 and the feedback current value detected by the drive roller 91 and the driven roller 92 is set to a predetermined constant value. The value of the output current value of the transfer power supply 50 is controlled so that the value becomes.

  As described above, by controlling the output current value of the transfer power supply 50 by the differential constant current method, it is possible to suppress instability of transfer performance due to increase or decrease of the effective transfer current in the secondary transfer nip N.

  Specifically, the differential constant current control is performed as follows. That is, a feedback current flowing on the back surface of the secondary transfer belt 93 is guided to the driving roller 91 and the driven roller 92, and this feedback current is supplied by the control plate 51 connected to the driving roller 91 and the driven roller 92. The value of is detected. The control plate 51 is configured to control the output current value of the transfer power supply 50 based on the detection result of the feedback current.

  Specifically, the value of the output current from the transfer power supply 50 is I1, and the values of the feedback currents flowing from the driving roller 91 and the driven roller 92 to the ground side via the secondary transfer belt 93 are I2 and I3. When the value of the effective transfer current flowing through the transfer sheet at the transfer nip N is indicated by IOUT, the output current value I1 is controlled so that the relationship expressed by the following equation 1 is obtained.

  When the resistance of the entire thickness of the secondary transfer belt 93 increases or decreases, the output current value I1 of Equation 1 increases or decreases accordingly. That is, the resistance value of the entire thickness of the secondary transfer belt 93 and the output current value I1 have a positive correlation. On the other hand, the effective transfer current value IOUT is constant regardless of the increase or decrease of the output current value I1.

  In such differential constant current control, the effective transfer current value IOUT is maintained constant regardless of environmental changes such as temperature and humidity, and resistance errors of each product of the secondary transfer belt 93, thereby stabilizing the transfer performance. Can be achieved.

  In the secondary transfer nip N, the toner on the intermediate transfer belt 20 is transferred to the transfer paper under the influence of the transfer current supplied from the secondary transfer roller 94 to the secondary transfer belt 93.

  When the toner image is transferred from the intermediate transfer belt 20 to the transfer paper, the transfer paper is charged. Accordingly, the transfer paper from the intermediate transfer belt 20 is electrostatically adsorbed on the secondary transfer belt 93 by the relationship between the true charge of the secondary transfer belt 93 and the polarization charge generated on the transfer paper side. Separation is made.

  Then, the separation from the intermediate transfer belt 20 is facilitated by the peeling operation from the intermediate transfer belt 20 by the strength of the transfer paper itself using the polarity separation of the intermediate transfer belt 20.

  However, when the environment is high temperature and high humidity (hereinafter referred to as H / H), the current easily flows through the transfer paper, so that the transfer paper cannot be separated from the intermediate transfer belt 20 successfully.

  Therefore, in this example, the secondary transfer roller 94 is positioned on the downstream side of the secondary transfer nip N, and the transfer of the true charge from the secondary transfer belt 93 to the transfer paper is delayed, so that the transfer to the intermediate transfer belt 20 is performed. The electrostatic adsorption of the transfer paper is suppressed.

  This “delaying the transfer of the true charge” means that the transfer sheet is not charged on the upstream side until the transfer sheet reaches the secondary transfer nip N. Thereby, winding of the transfer paper around the intermediate transfer belt 20 is suppressed.

  The secondary transfer belt 93 is formed of a material that exhibits a predetermined resistance characteristic so that a transfer bias is applied by the secondary transfer roller 94 that is in contact with the back surface thereof.

Specifically, each electrical resistance measured by JISK6911 is formed as follows when DC 100 [V] is applied. That is, the volume resistivity is set to 5 × 10 ⁸ [Ω · cm] to 5 × 10 ¹⁰ [Ω · cm]. Further, the volume resistivity may be set to be 1 × 10 ^7.5 [Ω · cm] to 1 × 10 ¹³ [Ω · cm] when DC 100 [V] is applied for 10 seconds.

The surface layer, which is a coating layer having a low friction coefficient, has a surface resistivity of DC 500 [V] set to 1 × 10 ⁸ [Ω / □] to 1 × 10 ¹² [Ω / □] when applied for 10 seconds. Has been. Furthermore, the surface resistivity of the inner layer is set to 1 × 10 ⁷ [Ω / □] to 1 × 10 ⁹ [Ω / □].

  The control plate 51 controls the output current value I1 from the transfer power supply 50 by the differential constant current method so as to have the relational expression shown in the following formula 2.

  As an example, when IOUT is set to 35 ± 5 [μA] under conditions of a conveyance speed of 330 [mm / sec] and an effective secondary transfer roller length of 310 [mm], an environment of normal temperature and normal humidity (M / M) is set. Below, good transfer results were obtained.

  Note that the effective transfer current value IOUT flowing to the intermediate transfer belt 20 side × correction coefficient value (hereinafter also referred to as a control target value of the control plate 51) is not unique and should be reduced when the conveyance speed is slow. Can do.

On the other hand, when the conveying speed is high, it is increased.
Further, the IOUT × correction coefficient may be varied so as to be optimal depending on the width and type of the transfer paper. Thereby, it is possible to prevent the transfer rate from changing due to the difference in width and type of transfer paper.

  In particular, when transferring a toner image onto small-size paper, a part of the current that should flow through the paper due to the application of a transfer bias flows to other than the paper due to the resistance of the paper itself. Defects will occur. In order to prevent this, the amount of current required to obtain the optimum transferability is set according to the paper width.

  On the other hand, even if the effective transfer current value IOUT is kept constant, various problems may occur depending on environmental fluctuations. For example, when the environment is relatively low temperature and low humidity (hereinafter referred to as L / L) in winter or the like, a phenomenon called pre-transfer may easily occur. This pre-transfer is a transfer before the electric charge of the secondary transfer belt portion before being sandwiched by the secondary transfer nip N attracts the toner on the intermediate transfer belt 20 electrostatically, and is sandwiched by the secondary transfer nip N. It is a phenomenon that the image is transferred to the paper portion, and it is known that the pre-transfer can be reduced by reducing the effective transfer current value IOUT.

  In addition, when the environment becomes relatively H / H in summer, for example, transfer paper separation from the intermediate transfer belt 20 may deteriorate. The cause of the deterioration of the transfer paper separation property in the H / H environment is considered as follows. That is, when the surface resistance of the secondary transfer belt decreases as the environment becomes H / H, current easily flows from the secondary transfer belt to the intermediate transfer belt 20 and the like, so that the charge holding amount of the secondary transfer belt is relatively low. Decrease. If the charge retention amount is reduced in this manner, the electrostatic force of the secondary transfer belt for attracting the transfer paper is weakened, so that it is considered that the transfer paper separability deteriorates. It is known that transfer paper separation can be improved by increasing the effective transfer current value IOUT.

  Further, for example, since the charge amount of the toner changes depending on the environment, the transfer rate also shifts, and problems such as insufficient transfer and overtransfer occur at the same current value. As described above, even if it depends on the environment (temperature, humidity), it is controlled to the optimum amount of current for obtaining the optimum transferability without various problems.

  In this embodiment, the temperature / humidity sensor is TDK / CHS-CSC-18, and the temperature can be detected from the thermistor output, and the humidity can be detected from the output of the temperature / humidity sensor. The temperature and humidity detection timing is sampled every 1 [min] after the power is turned on. Moreover, the timing which performs environmental correction is performed with the same period as a temperature / humidity detection timing.

  The location of the temperature / humidity sensor is not particularly limited, but is preferably located away from a heat source such as the fixing device 11. In this embodiment, the temperature / humidity sensor is provided below the paper feeding device 40.

  As a control example, a flowchart is shown in FIG. First, the thermistor output in the temperature / humidity sensor is detected, and the temperature is determined from the thermistor output-temperature conversion table based on the correlation between the thermistor output and the temperature (S1). Next, the humidity sensor output in the temperature / humidity sensor is detected, and the relative humidity is determined from the temperature obtained above and the humidity sensor output-relative humidity conversion table (S2). In this table, the relative humidity is obtained by setting the temperature to the horizontal and the humidity to the vertical. Next, the absolute humidity is calculated from the relative humidity obtained above and the relative humidity-absolute humidity conversion table (S3). In this table, relative humidity is set horizontally and temperature is set vertically, and absolute humidity is obtained. The absolute humidity can also be obtained from the temperature and relative humidity by a calculation formula. Next, the current environment is determined from the absolute humidity obtained above and the absolute humidity-current environment conversion table (S4).

  The current environment is, for example, L / L (19 [° C.] 30 [%]), M / L (23 [° C.] 30 [%]), M / M (23 [° C.] 50 [%]) , M / H (23 [° C.] 80 [%]), H / H (27 [° C.] 80 [%]), etc. However, the values and combinations of temperature and humidity are not limited to these. Absent.

  Finally, the transfer current value is corrected with the correction amount corresponding to the current environment obtained above (S5). The correction current value is determined from the relationship shown in Table 1, for example.

  In this embodiment, “α” in Table 1 is 5 [μA] and “β” is 10 [μA], but the relationship between the current environment and the correction current value is limited to this. is not.

  Since the detection by the temperature / humidity sensor does not require any machine operation, it can always be monitored and sequential control can be performed against environmental fluctuations. The transfer bias correction control based on the detection result of the temperature / humidity sensor and the voltage threshold correction control are performed by a control unit (not shown) in the apparatus main body.

  The transfer paper that has passed through the secondary transfer nip N is electrostatically attracted and conveyed in accordance with the movement of the secondary transfer belt 93, and the curvature separation is performed by the driven roller 92.

In this printer, fine 45K paper: and in view of (rigidity transverse ²¹ [cm 3/100]) experimental result that separation becomes possible to set the diameter of the driven roller 92 to 16 [mm] or less .

  The transfer paper that has passed through the secondary transfer nip N is separated from the secondary transfer belt 93 when it passes over the driven roller 92. Then, the driven roller 92 is guided by a guide plate toward a fixing device, which will be described later, disposed on the left side in the drawing.

  Transfer paper is fed from the paper feeding device 40 to the secondary transfer position. The paper feed device 40 includes a plurality of paper feed cassettes 41, a plurality of transport rollers 42 arranged in a transport path of transfer paper fed from the paper feed cassette 41, and a registration roller 44 positioned in front of the secondary transfer position. I have.

  In the present embodiment, in addition to the transfer path of transfer paper fed out from the paper feed cassette 41, the type of transfer paper that is not accommodated in the paper feed cassette 41 is fed to the paper feed device 40 toward the secondary transfer position. This configuration includes a manual feed tray 45 and a feeding roller 43 that are provided so that a part of the wall surface of the image forming unit 100 can be turned upside down.

  In the middle of the conveyance path of the transfer paper from the paper feed cassette 41 to the registration roller 44, the conveyance path of the transfer paper fed out from the manual feed tray 45 joins, and the transfer paper fed from any of the conveyance paths is registered roller. The registration timing is set by 44.

  In the writing device 5, writing light is controlled by image information obtained by scanning the document on the document placing table 31 included in the document reading device 30 or image information output from a computer (not shown), and the photosensitive members 3B, 3Y, An electrostatic latent image corresponding to image information is formed on 3C and 3M.

  The document reading device 30 is provided with a scanner 32 that exposes and scans the document on the document placement table 31, and an automatic document feeder 33 is disposed on the upper surface of the document placement table 31. The automatic document feeder 33 has a configuration capable of reversing the document fed on the document placement table 31, and can perform scanning on each surface of the document.

  The electrostatic latent image on the photoreceptor 3 formed by the writing device 5 is subjected to a visible image processing by the developing device 6 and is primarily transferred to the intermediate transfer belt 20. When the toner images for the respective colors are superimposed and transferred onto the intermediate transfer belt 20, the secondary transfer device 90 performs secondary transfer on the transfer paper at once.

  The untransferred image carried on the surface of the transfer paper that has been secondarily transferred is fixed by the fixing device 11. The fixing device 11 includes a belt fixing structure including a fixing belt heated by a heating roller and a pressure roller that contacts and contacts the fixing belt, and a contact area between the fixing belt and the pressure roller, that is, a nip area. By providing this, the heating area for the transfer paper can be expanded as compared with the roller type fixing structure.

  The transfer paper that has passed through the fixing device 11 is switched in its transport direction by a transport path switching claw 12 disposed at the rear of the fixing device 11. It is fed toward 44.

  In the copying machine 1 shown in FIG. 2, the primary transfer device 7 uses a roller for applying a transfer bias having a polarity opposite to that of the toner, and the intermediate transfer belt 20 is interposed by an elastic body such as a bearing and a compression spring (not shown). The photoconductor 3 is pressed against the photoconductor 3 with a predetermined pressure.

  Further, the primary transfer device 7B has an intermediate transfer belt at a position offset about 1 [mm] to 2 [mm] with respect to a position facing the center position of the photoreceptor 3 on the downstream side in the moving direction of the intermediate transfer belt 20. It is designed to rotate in conjunction with 20.

  This is to suppress pre-transfer that starts transfer by a transfer bias before the normal transfer position and generates an abnormal image such as an image flow.

Further, the primary transfer device 7 is configured in such a manner that a rubber material having a medium resistance electric characteristic is wound around a metal cored bar. In this embodiment, it is made of a foam rubber having a medium resistance, and its volume resistivity is 10 ⁶ [Ω · cm] to 10 ¹⁰ [Ω · cm], preferably 10 ⁷ [Ω · cm] to 10 ⁹ [ Ω · cm]. The material is not limited to foam rubber, and medium resistance solid rubber can be used as well.

Further, the secondary transfer counter roller 23 used in the present embodiment is configured in such a manner that a rubber material having an electric property of medium resistance is wound around a metal core. In this embodiment, it is made of medium resistance solid rubber, and its volume resistivity is 10 ⁶ [Ω · cm] to 10 ¹⁰ [Ω · cm], preferably 10 ⁷ [Ω · cm] to 10 ⁹ [Ω. · Cm] range. In the primary transfer step, the primary transfer bias is applied to the roller used as the primary transfer device 7 by using a constant current power source having a polarity of “+” and the current set value is in the range of approximately 20 [μA] to 40 [μA]. It is.

  Regarding the secondary transfer device 90, in this embodiment, the secondary transfer roller 94 is a metal roller made of a conductive material. However, the transfer brush is not limited to a rotary contact transfer system such as a transfer brush roller. The present invention can also be applied by using a contact transfer system such as a transfer blade or a transfer plate.

  Further, two or more secondary transfer members such as the secondary transfer roller 94 may be installed, and the installation location is not limited.

  In the present embodiment, as shown in FIG. 4, a secondary transfer roller 94 is provided at an indirect position downstream from the secondary transfer nip N. By positioning the secondary transfer roller 94 downstream of the opposed position, the secondary transfer nip N is formed before the normal transfer position, and the roller upstream of the secondary transfer nip N is grounded. Thus, pre-transfer can be prevented. The pre-transfer here refers to the charge before the paper transfer belt portion before being sandwiched by the secondary transfer nip N attracts the toner on the intermediate transfer belt 20 electrostatically and is sandwiched by the secondary transfer nip N. This is a phenomenon that the image is transferred to the transfer paper portion.

  In addition, when the environment is H / H, the current easily flows through the transfer paper, so that the transfer paper may not be separated from the intermediate transfer belt 20 in some cases. For this reason, the secondary transfer roller 94 is positioned downstream of the secondary transfer nip N, and the transfer of charge from the secondary transfer belt 93 to the transfer paper is delayed, whereby the transfer paper electrostatic to the intermediate transfer belt 20 is delayed. Is suppressed. Thereby, it is possible to suppress the winding of the transfer paper around the intermediate transfer belt 20.

  5 and 6, a transfer brush roller 96 is provided as a secondary transfer member at an indirect position downstream of the secondary transfer nip N, and further, an earth roller 52 upstream of the secondary transfer nip N is provided. Is located.

  The earth roller 52 may be grounded via a predetermined resistor 54 as shown in FIG. By grounding the earth roller 52 through a predetermined resistor 54, the potential gradient becomes gentler than when the earth roller 52 is directly grounded as shown in FIG. 6, and the pre-transfer OK range (secondary transfer nip N inlet side) If the resistance is selected such that the transfer margin is improved, the transfer margin is improved. That is, the potential in the area of the secondary transfer nip N can be increased as a whole, and the bias applied to the secondary transfer roller 94 can be suppressed, and the amount of charge required for transfer can be controlled. The range becomes wider and the control margin increases (see FIG. 7).

  In this embodiment, the secondary transfer roller 94 is installed at the indirect position. However, the secondary transfer roller 94 is opposed to the center position of the secondary transfer opposing roller 23 as shown in FIG. 8, or at the opposite position as shown in FIG. On the other hand, it may be a position offset by 1 [mm] to 2 [mm] upstream or downstream in the moving direction of the secondary transfer belt 93.

  FIG. 10 shows a case where two secondary transfer members of a secondary transfer roller 94 and a transfer brush 95 are provided in contact with the back surface of the secondary transfer belt 93. The output current from the transfer power supply 50 is diverted to the secondary transfer roller 94 and the transfer brush 95 at a predetermined ratio and supplied to the back surface of the secondary transfer belt 93.

  FIG. 11 shows a case where two secondary transfer members of a secondary transfer roller 94 and a transfer brush roller 96 are provided in contact with the back surface of the secondary transfer belt 93. The output current from the transfer power supply 50 is diverted to the secondary transfer roller 94 and the transfer brush roller 96 at a predetermined ratio and supplied to the back surface of the secondary transfer belt 93.

  FIG. 12 shows a case where two secondary transfer members of a transfer brush roller 96 and a transfer brush roller 97 are provided in contact with the back surface of the secondary transfer belt 93. The output current from the transfer power supply 50 is branched to the transfer brush roller 96 and the transfer brush roller 97 at a predetermined ratio and supplied to the back surface of the secondary transfer belt 93.

  As described above, the combination of the configuration, installation location, number, and the like of the secondary transfer member is not particularly limited, and any combination can be applied in the present invention.

The intermediate transfer belt 20 used in this embodiment includes PI (polyimide), PAI (polyamideimide), PC (polycarbonate), ETFE (ethylene-tetrafluoroethylene), polyvinylidene fluoride, PPS (polyphenylene sulfide), and the like. On the base layer 50 [μm] to 100 [μm] composed of carbon dispersion in the material or the resistance adjusted by blending the ionic conductive agent, carbon dispersion is similarly applied to rubber materials such as urethane, NBR, CR, Alternatively, an elastic layer made of a material whose resistance is adjusted by blending an ionic conductive agent is provided in a range of 100 [μm] to 500 [μm], and the surface layer has a thickness of about 1 [μm] to 10 [μm], or It consists of a three-layer belt with a coating of resin (or a hybrid material thereof). There. The volume resistivity is in the range of 10 ⁶ [Ω · cm] to 10 ¹⁰ [Ω · cm], preferably 10 ⁸ [Ω · cm] to 10 ¹⁰ [Ω · cm].

The surface resistivity is in the range of 10 ⁶ [Ω / □] to 10 ¹² [Ω / □], preferably 10 ⁸ [Ω / □] to 10 ¹² [Ω / □]. Further, the Young's modulus (longitudinal elastic modulus) of the base layer is desirably 3000 [MPa] or more, and sufficient mechanical strength is required to withstand elongation, bending, wrinkle, and waviness due to driving.

  By using the intermediate transfer belt 20 having such elasticity, a transfer paper such as a paper having a low density of paper fibers of the transfer paper or a so-called embossed paper having an unevenness of 20 [μm] to 30 [μm] on the surface. Is also known to have a solid filling improvement effect that toner transferability to the concave portion is improved because the elastic layer follows the concave portion.

  Examples of the other intermediate transfer belt 20 include PI (polyimide), PAI (polyamideimide), PC (polycarbonate), ETFE (ethylene-tetrafluoroethylene), polyvinylidene fluoride, PPS (polyphenylene) as a single layer belt. A medium resistance resin monolayer whose resistance is adjusted by carbon dispersion in a material such as sulfide) or an ionic conductive agent may be used.

  Also, carbon dispersion or ionic conductive agent blended in materials such as PI (polyimide), PAI (polyamideimide), PC (polycarbonate), ETFE (ethylene-tetrafluoroethylene), polyvinylidene fluoride, PPS (polyphenylene sulfide) Alternatively, a belt having a surface layer having a slightly higher resistance than the volume resistivity of the belt layer itself may be provided only on the surface side of the intermediate transfer belt 20 having a single-layer structure of medium resistance resin, the resistance of which is adjusted. The surface layer thickness is preferably about 1 [μm] to 10 [μm].

  This is a type of belt that controls resistance by dispersing carbon in the resin, especially in the secondary transfer process to paper that has passed through fixing once and the amount of moisture in the paper has decreased and resistance has increased. It is known that the phenomenon of “white spots” occurring is improved. The “white spot” is a phenomenon in which a transfer current concentrates due to variation in the carbon dispersion state, and the toner in that portion is repelled and whitened. By providing the high resistance layer on the surface, local concentration of the transfer current is alleviated, so that the abnormal image “white spot” is improved.

[Embodiment 2]
The second embodiment in which the present invention is applied to an image forming apparatus will be described below. The basic configuration of the image forming apparatus according to the present embodiment is substantially the same as that of the image forming apparatus according to the first embodiment, and elements common to the image forming apparatus according to the first embodiment are denoted by the same reference numerals. Since the same operation is performed, detailed description thereof is omitted.

  FIG. 13 is an enlarged view of a secondary transfer unit of the copying machine 1 that is the image forming apparatus according to the present embodiment. In the present embodiment, as shown in FIG. 13, a ground roller 52 is provided upstream of the secondary transfer nip N of the secondary transfer counter roller 23 in the intermediate transfer belt rotation direction, and downstream of the intermediate transfer belt rotation direction. A neutralizing roller 53 is provided.

  In the present embodiment, the secondary transfer counter roller 23, the earth roller 52, and the static elimination roller 53 are provided as three electrodes on the back surface that is the inner surface of the loop of the intermediate transfer belt 20, but the number of the electrodes is as follows. Two may be sufficient and three or more may be sufficient. Furthermore, it is good also as a float without earth | grounding.

  In addition, the earth roller 52 and the charge eliminating roller 53 may be anything as long as they can serve as electrodes without being a roller member. For example, a so-called neutralizing brush made of a bundle of conductive fibers of rayon or acrylic in which conductive particles of carbon or a metal complex are dispersed may be contacted with a width of several [mm] or more in the moving direction of the intermediate transfer belt 20. .

  In the present embodiment, the earth roller 52 and the static elimination roller 53 are made of a metal such as aluminum or stainless steel, and are two of a plurality of stretching rollers that rotatably stretch the intermediate transfer belt 20. Further, the earth roller 52 and the charge eliminating roller 53 may also have a function as a tension roller that applies tension to the intermediate transfer belt 20.

  The ground roller 52 and the charge removal roller 53 may be configured by laminating the same conductive rubber as the secondary transfer counter roller 23 as described in the first embodiment.

  In addition, if the tension roller that stretches the intermediate transfer belt 20 is made of metal, the back surface of the intermediate transfer belt 20 is scraped and the shavings accumulate, and there is a possibility that floating occurs between the tension roller and the intermediate transfer belt 20. is there. Therefore, in order to suppress the occurrence of such floating, a conductive resin or the like having a volume resistance or a thin layer thickness that is low enough not to cause a voltage drop may be laminated as a protective rod.

  The secondary transfer counter roller 23 is made of the conductive material of Embodiment 1 described above, and is supplied to the transfer power supply 50 so that a current (charge) having the same polarity as the charging polarity of the toner on the intermediate transfer belt 20 is applied. It is connected to a connected switch (not shown). This switch is ON / OFF controlled by a control unit (not shown), and when it is turned ON, a conduction path connecting the transfer power supply 50 and the secondary transfer counter roller 23 is conducted. That is, in this embodiment, the secondary transfer counter roller 23, the transfer power source 50, and the control unit constitute transfer current supply means.

  The earth roller 52 and the charge eliminating roller 53 also have a function of detecting a leakage current flowing on the intermediate transfer belt 20 without flowing into the secondary transfer nip N as a feedback current, and the transfer power supply 50 according to the value of the feedback current. Thus, the supply current supplied to the secondary transfer counter roller 23 is controlled.

  For this reason, the control plate 51 in which a control circuit for setting the supply current of the secondary transfer counter roller 23 is set according to the detected current is connected to the earth roller 52 and the charge removal roller 53. A transfer power supply 50 is also connected to the control plate 51. The effective transfer current is a value of an effective transfer current flowing through the secondary transfer nip N obtained as a difference between the output current value of the transfer power supply 50 and the feedback current values I2 and I3 detected by the earth roller 52 and the charge removing roller 53. The value of the output current value I1 of the transfer power supply 50 is controlled so that the current value IOUT becomes a predetermined constant value. In this way, by controlling the output current value I1 of the transfer power supply 50 by the differential constant current method, it is possible to suppress instability of transfer performance due to increase or decrease of the effective transfer current in the secondary transfer nip N. .

  In addition, if a transfer current is supplied to the intermediate transfer belt 20 to give a charge, and the resistance of the intermediate transfer belt 20 is selected so that the charge can move upstream in the intermediate transfer belt rotation direction, the charge is downstream in the intermediate transfer belt rotation direction. Also move on. For this reason, the charge moving to the downstream side in the intermediate transfer belt rotation direction is neutralized by the charge removal roller 53 so that the charge does not move downstream from the charge removal roller 53 in the intermediate transfer belt rotation direction. This avoids interference with the primary transfer that transfers the toner image on the photoreceptor 3 to the intermediate transfer belt 20.

  Note that the amount of current provided by the transfer power supply 50 may be varied so as to be optimal depending on the width and type of transfer paper, as in the previous embodiment. Similarly to the first embodiment, the combination of the configuration, installation location, number, and the like of the secondary transfer roller 94 is not particularly limited, and any combination can be applied in the present invention.

  In the first embodiment, the transfer bias is applied to the secondary transfer roller 94. However, in such a configuration, the transfer paper absorbs moisture and the resistance is reduced, or the resistance is low. When the transfer paper is used, a transfer current that should flow from the secondary transfer roller 94 to the secondary transfer counter roller 23 flows to the conveyance path through the transfer paper. For this reason, the transfer electric field may weaken and transfer defects may occur.

  On the other hand, in this embodiment, the secondary transfer is performed by applying a transfer bias to the secondary transfer counter roller 23 so that the toner image on the intermediate transfer belt 20 is transferred to the transfer paper by repulsion. Thereby, a stable image can be obtained even with respect to a decrease in transferability due to an environmental variation of the resistance value of the transfer paper. That is, it is possible to generate a sufficient transfer electric field on the toner carrying surface of the intermediate transfer belt 20 regardless of the resistance of the transfer paper, and it is possible to suppress the occurrence of transfer defects even when low resistance paper is used. It becomes possible.

What has been described above is merely an example, and the present invention has a specific effect for each of the following modes.
(Aspect A)
An image carrier such as the photoreceptor 3, a toner image forming unit that forms a toner image on the image carrier, and a plurality of tension members are rotatably stretched, and the toner image on the image carrier is primarily transferred. An intermediate transfer belt such as an intermediate transfer belt 20 and a primary transfer device 7 that primarily transfers a toner image on the image carrier onto the intermediate transfer belt at a primary transfer nip formed by contact between the image carrier and the intermediate transfer belt. Secondary transfer, such as a secondary transfer belt 93 that carries a transfer material such as a transfer sheet on which a toner image on an intermediate transfer belt is secondarily transferred by a primary transfer means and a plurality of stretching members. A secondary transfer means such as a secondary transfer device 90 for secondary transfer of a toner image on the intermediate transfer belt to a transfer material at a secondary transfer nip formed by contacting the belt with the intermediate transfer belt and the secondary transfer belt; Secondary transfer means In an image forming apparatus such as a copying machine 1 having a transfer current applying means such as a transfer power supply 50 for applying a transfer current for secondary transfer to the intermediate transfer belt or the secondary transfer belt, the intermediate transfer belt or the secondary transfer belt. Effective transfer current detecting means for detecting the value of the effective transfer current that reaches the secondary transfer nip such as the secondary transfer nip N from the transfer current applying position of the transfer current applying means, and flows through the secondary transfer nip, and effective transfer A transfer current control means such as a control plate 51 for controlling the transfer current output from the transfer current applying means so that the value of the effective transfer current becomes a predetermined constant value based on the detection result of the current detection means; Have According to this, as described in the above embodiment, it is possible to suppress instability of transfer performance due to increase or decrease in effective transfer current in the secondary transfer nip.
(Aspect B)
In (Aspect A), the effective transfer current detecting means includes a leakage current detecting means for detecting a value of a leakage current that flows outside the secondary transfer nip among the transfer current applied by the transfer current applying means, The effective transfer current value is detected from the difference between the transfer current value output from the transfer current applying means and the leakage current value detected by the leakage current detection means. According to this, as described in the above embodiment, it is possible to stabilize the transfer performance at the secondary transfer nip by controlling the output current value from the transfer power source by the differential constant current method.
(Aspect C)
In (Aspect A) or (Aspect B), the transfer current applying means applies a transfer current having a polarity opposite to the charging polarity of the toner to the secondary transfer belt. According to this, as described in the above embodiment, it is possible to obtain an image that is stable against variations in resistance value of the secondary transfer roller and environmental variations.
(Aspect D)
In (Aspect A) or (Aspect B), the transfer current applying means applies a transfer current having the same polarity as the toner to the intermediate transfer belt. According to this, as described in the above embodiment, it is possible to generate a sufficient transfer electric field on the toner carrying surface of the intermediate transfer belt regardless of the resistance of the transfer paper.
(Aspect E)
In (Aspect D), a plurality of electrodes are provided on the back surface, which is the surface opposite to the surface on which the toner image is carried, of the intermediate transfer belt, and a transfer current having the same polarity as the charge of the toner image is applied to the transfer current applying means. Is applied to the intermediate transfer belt through one of the plurality of electrodes, and the value of the current flowing out from the remaining electrodes is detected by the leakage current detection means as the value of the leakage current. According to this, as described in the above embodiment, interference with the primary transfer can be avoided.
(Aspect F)
In (Aspect A), (Aspect B), (Aspect C), (Aspect D) or (Aspect E), a predetermined constant value of the effective transfer current is varied depending on the width and type of the transfer material. According to this, as described in the above embodiment, stable transfer performance can be obtained for a wide variety of transfer materials.
(Aspect G)
In (Aspect A), (Aspect B), (Aspect C), (Aspect D), (Aspect E) or (Aspect F), a temperature / humidity detecting means for detecting temperature and humidity is provided, and temperature / humidity detection is performed. Based on the detection result of the means, a predetermined constant value of the effective transfer current is varied. According to this, as described in the above embodiment, it is possible to obtain a stable transfer performance against environmental fluctuations.
(Aspect H)
In (Aspect A), (Aspect B), (Aspect C), (Aspect D), (Aspect E) or (Aspect F), the intermediate transfer belt and the secondary transfer belt rotate more than the center position of the secondary transfer nip. A secondary transfer member such as a secondary transfer roller 94 is disposed on the downstream side in the direction, and an electrode member such as a ground roller 52 is disposed on the upstream side in the rotational direction from the center position of the secondary transfer nip, so that the electrode member is grounded. ing. According to this, as described in the above embodiment, it is possible to suppress pre-transfer or improve transfer paper separation.
(Aspect I)
In (Aspect H), the electrode member is grounded via a predetermined resistance such as the resistance 54. According to this, as described in the above embodiment, the margin of transfer performance can be increased.
(Aspect J)
In (Aspect A), (Aspect B), (Aspect C), (Aspect D), (Aspect E), (Aspect F), (Aspect G), (Aspect H) or (Aspect I), the intermediate transfer belt is used. Is an intermediate transfer belt having at least one elastic layer and a thin layer on the image forming surface. According to this, as described in the above embodiment, a high-quality transfer image can be provided for a wide variety of transfer sheets.

DESCRIPTION OF SYMBOLS 1 Copier 3 Photoconductor 4 Charging device 5 Writing device 6 Developing device 7 Primary transfer device 8 Cleaning device 10 Intermediate transfer belt cleaning device 11 Fixing device 12 Conveyance path switching claw 13 Paper discharge tray 20 Intermediate transfer belt 21 Drive roller 22 Drive roller 23 Secondary Transfer Counter Roller 24 Tension Roller 30 Document Reading Device 31 Document Placement Table 32 Scanner 33 Automatic Document Feeder 40 Paper Feed Device 41 Paper Feed Cassette 42 Transport Roller 43 Feed Roller 44 Registration Roller 45 Manual Tray 50 Transfer Power Supply 51 Control Plate 52 Ground roller 53 Static elimination roller 54 Resistance 60 Secondary transfer belt cleaning device 61 Cleaning blade 70 Transfer power source 90 Secondary transfer device 91 Driving roller 92 Driven roller 93 Secondary transfer belt 94 Secondary transfer roller La 95 transfer brush 96 transfer brush roller 97 transfer brush roller 100 image forming unit

JP 2001-305888 A

Claims (10)

An image carrier;
Toner image forming means for forming a toner image on the image carrier;
An intermediate transfer belt on which a toner image on the image carrier is primarily transferred by a plurality of stretching members and is rotatably rotated;
Primary transfer means for primarily transferring a toner image on the image carrier to the intermediate transfer belt at a primary transfer nip formed by contact between the image carrier and the intermediate transfer belt;
A secondary transfer belt that carries a transfer material on which a toner image on the intermediate transfer belt is secondarily transferred by a plurality of tension members,
A secondary transfer means for secondary transfer of the toner image on the intermediate transfer belt to the transfer material at a secondary transfer nip formed by contact between the intermediate transfer belt and the secondary transfer belt;
In the image forming apparatus, the secondary transfer unit includes a transfer current applying unit that applies a transfer current for secondary transfer to the intermediate transfer belt or the secondary transfer belt.
Effective transfer current for detecting the value of the effective transfer current that reaches the secondary transfer nip from the transfer current applying position by the transfer current applying means to the intermediate transfer belt or the secondary transfer belt and flows through the secondary transfer nip. Detection means;
Transfer current control means for controlling the transfer current output from the transfer current applying means so that the value of the effective transfer current becomes a predetermined constant value based on the detection result of the effective transfer current detection means; An image forming apparatus comprising: The image forming apparatus according to claim 1.
The effective transfer current detecting means has a leakage current detecting means for detecting a value of a leakage current flowing outside the secondary transfer nip out of the transfer current applied by the transfer current applying means. An image forming apparatus, wherein an effective transfer current value is detected from a difference between an output transfer current value and a leakage current value detected by a leakage current detection unit. The image forming apparatus according to claim 1 or 2,
The image forming apparatus, wherein the transfer current applying unit applies a transfer current having a polarity opposite to a charging polarity of the toner to the secondary transfer belt. The image forming apparatus according to claim 1 or 2,
The image forming apparatus, wherein the transfer current applying unit applies a transfer current having the same polarity as that of the toner to the intermediate transfer belt. The image forming apparatus according to claim 4.
A plurality of electrodes are provided on the back side of the intermediate transfer belt opposite to the surface on which the toner image is carried, and a transfer current having the same polarity as the charge of the toner image is applied by the transfer current applying means. Image formation characterized in that the leakage current detecting means detects the value of the current that is applied to the intermediate transfer belt through one of a plurality of electrodes and flows out from the remaining electrodes as the value of the leakage current. apparatus. The image forming apparatus according to claim 1, 2, 3, 4, or 5.
An image forming apparatus characterized in that a predetermined constant value of the effective transfer current is varied depending on the width and type of the transfer material. The image forming apparatus according to claim 1, 2, 3, 4, 5 or 6.
It has temperature and humidity detection means to detect temperature and humidity,
An image forming apparatus, wherein a predetermined constant value of the effective transfer current is varied based on a detection result of the temperature and humidity detection means. The image forming apparatus according to claim 1, 2, 3, 4, 5, 6 or 7.
A secondary transfer member is disposed downstream of the secondary transfer nip center position between the intermediate transfer belt and the secondary transfer belt in the rotational direction, and an electrode member is disposed upstream of the secondary transfer nip center position in the rotational direction. An image forming apparatus, wherein the electrode member is disposed and grounded. The image forming apparatus according to claim 8.
The image forming apparatus, wherein the electrode member is grounded through a predetermined resistance. The image forming apparatus according to claim 1, 2, 3, 4, 5, 6, 7, 8, or 9.
The intermediate transfer belt is an intermediate transfer belt having at least one elastic layer and a thin layer on an image forming surface.

Images