JP2005227308A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus having a mode in which a speed in secondary transfer is lower than that in primary transfer, wherein electrical memory is restrained from being caused on a photoreceptor drum during the low-speed mode so as to prevent a drum ghost. <P>SOLUTION: A cleaning bias when the speed is low is made lower than a primary transfer bias when the speed is normal and, thereby, an amount of current per unit time is restrained for the photoreceptor drum. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a color image forming apparatus for forming an image on a recording medium.

  Conventionally, as a color image forming apparatus, various methods such as an electrophotographic method, a thermal transfer method, an ink jet method, and the like are known. Of these, an electrophotographic method is an image compared with other methods. It is excellent in terms of formation speed, image quality, and quietness.

  There are various types of image forming apparatuses that employ an electrophotographic system. For example, a multi-development method in which a color image (a plurality of color toner images) is superposed on the surface of a photoreceptor and then transferred to a transfer material at once to form an image, a multi-transfer method in which a development-transfer cycle is repeated, There is an intermediate transfer method in which toner images of respective colors are sequentially transferred onto an intermediate transfer member, and then transferred onto a transfer material at a time. Among these, the intermediate transfer type has an advantage that various transfer materials having different qualities and thicknesses can be used (see, for example, Patent Document 1).

  FIG. 8 shows an outline of a four-color full-color laser beam printer as an example of an intermediate transfer type image forming apparatus. As shown in FIG. 8, on the peripheral surface of the photosensitive drum 1 that is an image carrier, a charger 2 and an exposure device 3 that irradiates the photosensitive drum 1 with laser light in order along the rotation direction (arrow R1 direction). Developing devices 5, 6, 7, and 8, an intermediate transfer belt 9, and a photosensitive drum cleaner 16 are arranged.

  First, the surface of the photosensitive drum 1 is negatively charged by the charger 2. Next, an electrostatic latent image is formed on the surface of the charged photosensitive drum 1 by the exposure L of the exposure means 3 (the surface potential of the exposed portion is increased). The developing device 5 containing yellow toner of the first color mounted on the developing device support 4 attaches toner to the electrostatic latent image portion on the photosensitive drum to form a toner image.

  The intermediate transfer belt 9 is supported by two support shafts (secondary transfer counter roller 12 and tension roller 14), and is rotated in the direction of arrow R3 by the secondary transfer counter roller 12 rotating in the direction of arrow R4 in the figure. When a positive primary transfer bias is applied at a constant voltage from the primary transfer power source 17 to the primary transfer roller 10 that rotates following the intermediate transfer belt 9, the toner image on the photosensitive drum 1 is transferred to the primary transfer nip N1. The primary transfer is performed.

  The primary transfer residual toner on the surface of the photosensitive drum 1 after the primary transfer is removed by a photosensitive drum cleaner 16 having an elastic blade.

  The series of image forming processes of charging, exposure, development, primary transfer, cleaning, and charge removal are repeated for the second color magenta, third color cyan, and fourth color black toners stored in the developing devices 6, 7, and 8. Then, four color toner images are superimposed on the intermediate transfer belt 9. At the time of primary transfer in which four color toner images are superimposed on the intermediate transfer belt 9, the secondary transfer roller 11 is separated from the intermediate transfer belt 9, and a four color toner image is formed on the intermediate transfer belt 9. Then, the secondary transfer roller 11 abuts on the intermediate transfer belt 9 by the rotation of the secondary transfer roller abutment / separation cam 21 in the R5 direction 180 ° to form a secondary transfer nip portion N2.

  Next, when the transfer material P enters the secondary transfer nip portion N2, a positive secondary transfer bias is applied to the secondary transfer roller 11 from the secondary transfer power source 18, and the four color toner images are transferred to the transfer material P. Secondary transfer is performed collectively on the surface.

  The transfer material P carrying the four-color unfixed toner image on the surface is conveyed to a fixing device (not shown), and the toner image on the surface is fixed to complete the image formation.

  Here, the secondary transfer property and the fixability to the transfer material P vary depending on the thickness, material and surface property of the transfer material P. When the transfer material P is thick or when the resistance is higher than that of plain paper such as a film, the transferability is poor, and when the transfer material P has a rough surface or thick paper, the transferability is poor. In such a case, unit transfer is performed at a normal speed until the primary transfer in which the four color toner images are superimposed on the intermediate transfer belt 9, and the transfer speed of the transfer material P is reduced during the secondary transfer and the fixing. The charge amount and heat amount applied to the transfer material P per hit are maintained, and the secondary transfer property and the fixability are ensured. The deceleration of the transfer material P not only reduces the rotation speed of the secondary transfer roller 11 and the intermediate transfer belt 9 contributing to the conveyance of the transfer material P, but also the photosensitive drum 1 simultaneously reduces the rotation speed. The photosensitive drum 1 is prevented from being charged due to friction with the.

On the intermediate transfer belt 9, there is secondary transfer residual toner that remains without being transferred to the transfer material P after the secondary transfer. The secondary transfer residual toner is made positive by the secondary transfer residual toner charging roller 19 to which a positive DC voltage is applied from the secondary transfer residual toner charging roller power source 13 before reaching the primary transfer nip portion N1. Charged. The secondary transfer residual toner charged to the positive polarity is statically applied to the photosensitive drum 1 when a cleaning bias having the same polarity as the secondary transfer residual toner is applied from the primary transfer power source 17 at the primary transfer nip portion N1. The image is electrically transferred and removed from the intermediate transfer belt 9. The removal of the secondary transfer residual toner is hereinafter abbreviated as ICL (Intermediate Transfer Belt Cleaning Less) (see, for example, Patent Document 2). Unlike the cleaning method in which the residual toner on the intermediate transfer member is scraped off using a blade or the like, this ICL method has excellent advantages such as being hard to damage the intermediate transfer belt and eliminating the need for a separate waste toner container. ing.
Japanese Patent Laid-Open No. 2003-76099 (5th term Fig. 1) JP2003-241479 (10th term Fig. 1)

  However, in the above conventional example, if the transfer speed of the transfer material is reduced, a positive memory may be provided to the photosensitive drum during the ICL cleaning, and a defective image may be generated. This will be described in detail below.

  When the transfer speed of the transfer material is reduced, the surface movement speed of the intermediate transfer belt is reduced, so that the secondary transfer residual toner is also collected on the photosensitive drum by the ICL cleaning. For this reason, if the cleaning bias used at the normal speed is applied to the photosensitive drum whose surface moving speed is reduced, the amount of charge accumulated per unit area increases in the photosensitive drum, and the positive polarity memory is stored in the photosensitive drum. Will be given. A photosensitive drum that has received a positive-polarity memory cannot obtain a desired negative-polarity potential on the surface of the photosensitive drum when it is charged by a charger for the next primary transfer. (Hereinafter referred to as drum ghost). Particularly in a high-temperature and high-humidity environment, the resistance at the primary transfer nip portion decreases, so that a current easily flows through the photosensitive drum, and the above-mentioned image defect is remarkable.

  An object of the present invention is to provide an image forming apparatus that does not give memory to a photosensitive drum and does not have a drum ghost.

In order to solve the above object, the first invention provides:
An image carrier for carrying a toner image;
An intermediate transfer member to which a toner image on the image carrier is electrostatically transferred;
Transfer means for transferring a toner image on the image carrier to the intermediate transfer member;
Charging means for charging residual toner remaining on the intermediate transfer member to a predetermined polarity;
Transferring the residual toner on the intermediate transfer member charged to a predetermined polarity by the charging unit to the image carrier by applying a bias voltage having the same polarity as the residual toner by the transfer unit;
A first surface moving speed of the intermediate transfer member when transferring a toner image on the image carrier onto the intermediate transfer member and simultaneously transferring residual toner on the intermediate transfer member onto the image carrier; An image forming apparatus that only transfers the residual toner on the intermediate transfer member onto an image carrier and has a second surface moving speed of the intermediate transfer member that is lower than the first surface moving speed. In
The image forming apparatus according to claim 1, wherein the bias voltage of the transfer unit at the second surface moving speed is lower than the bias voltage of the transfer unit at the first surface moving speed.

  In a second aspect based on the first aspect, the bias voltage of the transfer means at the second surface movement speed is reduced by a predetermined voltage from the bias voltage of the transfer means at the first surface movement speed. An image forming apparatus.

  A third invention is the image forming apparatus according to the second invention, wherein the predetermined voltage to be reduced varies depending on the environment.

  According to a fourth invention, in the first invention, the transfer voltage at the first surface moving speed is controlled by controlling the bias voltage of the transfer means at the second surface moving speed to be a desired current amount. An image forming apparatus wherein the bias voltage of the means is reduced.

  As described above, according to the present invention, when the surface movement speed of the intermediate transfer belt is slower than that at the time of the primary transfer, the cleaning bias is reduced to suppress the generation of memory on the photosensitive drum and prevent image defects. We were able to.

(Example 1)
A first embodiment of the present invention will be described below. The configuration other than the transfer bias control is the same as that of the conventional example, and will be described with reference to the schematic diagram of FIG. 8, and description of the same members as those of the conventional example will be omitted.

  This embodiment is characterized in that the ICL cleaning bias is reduced by a predetermined voltage when the intermediate transfer belt surface moving speed is reduced. This will be described in detail below.

As in the conventional example, the toner image developed on the photosensitive drum 1 is primarily transferred to the intermediate transfer belt 9 via the primary transfer nip N1 formed by the primary transfer roller 10 facing the photosensitive drum 1. Here, the primary transfer bias used for the primary transfer is determined by the control immediately before the primary transfer. Before the primary transfer, a voltage is applied from the primary transfer power source 17 to the primary transfer roller 10 to detect a current flowing through the primary transfer nip portion N1. The output voltage from the primary transfer power supply 17 is changed so that the output current approaches the desired current value used for the primary transfer, and the voltage when the output current value reaches the desired value is used as the primary transfer bias, and is constant during the primary transfer. Applied as a voltage. The transfer bias control performed before the primary transfer is an existing control method described in Japanese Patent Laid-Open No. 05-006112 and is hereinafter abbreviated as “ATVC”. In this embodiment, the desired primary transfer current amount is 10 μA, and the output voltage is about 1 kV in a room temperature and normal humidity environment. At this time, the surface moving speed of the photosensitive drum 1 is 120 mm / second, and the surface moving speed of the intermediate transfer belt 9 is the same as the surface moving speed of the photosensitive drum 1 by the rotation of the secondary transfer counter roller 12 in the direction of arrow R4. (In the direction of arrow R3). The primary transfer roller 10 is an NBR ion conductive rubber having a diameter of 14.0 mm, adjusted to be an actual resistance of 1.0 × 10 ⁸ [Ω] using a conductive material or the like, and is driven by the intermediate transfer belt 9. Yes. As the intermediate transfer belt 9, a PVDF (polyvinylidene fluoride) resin belt having a thickness of 100 μm and a volume resistance of 1.0 × 10 ¹¹ [Ω · cm] was used. When the intermediate transfer belt 9 rotates four times and toner images of four colors yellow, magenta, cyan, and black are formed on the intermediate transfer belt 9, the secondary transfer roller 11 contacts the intermediate transfer belt 9 as in the conventional example. The secondary transfer nip N2 is formed. A schematic diagram in which the secondary transfer roller 11 is in contact with the intermediate transfer belt 9 is shown in FIG. As the secondary transfer roller, an NBR ion conductive rubber having a diameter of 18.0 mm and adjusted so as to have an actual resistance of 1.0 × 10 ⁷ [Ω] using a conductive material or the like was used.

  When the transfer material P enters the secondary transfer nip portion N2, a secondary transfer bias having a positive polarity is applied to the secondary transfer roller 11 from the secondary transfer power source 18, and a four-color toner image is formed on the surface of the transfer material P. Secondary transfer is performed at once. By the above-described ICL method, the residual toner that has not been secondarily transferred is charged to a positive polarity and collected on the photosensitive drum 1 at the primary transfer nip N1. Since the cleaning by the ICL method is usually performed simultaneously with the primary transfer of the next first color, the primary transfer bias used is the same, and the residual toner on the intermediate transfer belt 9 is transferred to the photosensitive drum 1 and the photosensitive drum 1. The toner image is transferred onto the intermediate transfer belt 9.

On the other hand, as described above, when the transfer material P is thick, when the resistance is high, or when the surface property is poor, the secondary transfer and fixing are performed at the same speed as the primary transfer. Next transferability and fixability are deteriorated. Therefore, when the transfer material P is thick, when the resistance is high, or when the surface property is poor, the speed at the time of secondary transfer and fixing is reduced, and the amount of charge applied to the transfer material P per unit time. In addition, the amount of heat and the amount of heat are maintained, and the secondary transfer property and the fixing property are secured. In this embodiment, when a thick paper having a transfer material P of 110 g / m ² or more is used, and when a high resistance paper such as a gloss film or OHT is used, the conveyance speed of the transfer material P at the time of secondary transfer and fixing. Is reduced to 60 mm / sec. The transfer speed of the transfer material P is reduced by reducing the surface speeds of the intermediate transfer belt 9 and the secondary transfer roller 11. Further, in order to prevent frictional charging of the photosensitive drum 1 due to the deceleration of the intermediate transfer belt 9, the photosensitive drum 1 is also decelerated simultaneously. In this case, since the timing of exposure L by the exposure means 3 is different from the normal speed and it is difficult to switch the latent image formation sequence, exposure L and development on the photosensitive drum 1 are not performed, and the intermediate transfer is performed at the primary transfer nip portion N1. Only the residual toner remaining on the belt is collected by the ICL method. At this time, if the primary transfer bias determined by ATVC is used as the recovery bias for recovering the residual toner, the surface movement speed of the photosensitive drum 1 is reduced by half, so that the photosensitive drum 1 has about twice the unit time. The charge will move. When a large amount of current flows through the photosensitive drum 1, a drum ghost may be caused as described above. In order to prevent this, in this embodiment, a bias lower by 500 V than the result of the primary transfer bias determined by ATVC is set as the ICL recovery bias.

  When the intermediate transfer belt 9 is decelerated to 60 mm / second, secondary transfer is performed, and the residual toner on the intermediate transfer belt 9 is collected on the photosensitive drum 1 by the collection bias, the intermediate transfer belt 9 is 120 mm / second. Returning to the normal speed of 1 second, ATVC is performed again to determine the primary transfer bias for the first color, and the primary transfer is started.

  A printing test was performed using the configuration of the present embodiment described above and the conventional configuration as a comparative example. The print test is performed in a low temperature and low humidity environment (temperature: 15 ° C./humidity: 10%), in a normal temperature and normal humidity environment (temperature: 23 ° C./humidity: 50%), and in a high temperature and high humidity environment where drum ghosts are likely to occur. The drum ghost level was checked in three environments (temperature: 30 ° C./humidity: 80%). FIG. 2 shows a comparison result between the configuration of this example and the configuration of the comparative example. ○ in the figure indicates that there is no drum ghost, △ in the figure indicates that drum ghost is slightly generated, and x in the figure indicates that drum ghost is remarkably generated. Is shown. In the configuration of the conventional example, the drum ghost is remarkably generated in a high-temperature and high-humidity environment, whereas in the configuration of the present embodiment, the generation of the drum ghost can be completely suppressed.

(Example 2)
A second embodiment of the present invention will be described below.

  According to the configuration of the first embodiment, when the intermediate transfer belt surface moving speed is decelerated, the drum ghost can be prevented from being generated in a high-temperature and high-humidity environment. Slightly occurred. This is because the resistance of the primary transfer roller 10 and the intermediate transfer belt 9 increases due to low temperature and low humidity. Therefore, just by reducing the ICL recovery bias by 500 V as in the configuration of the first embodiment. The amount of charge that moves to the photosensitive drum 1 could not be suppressed. Therefore, a slight amount of positive-polarity memory is left on the photosensitive drum 1, and the occurrence of drum ghost cannot be completely suppressed.

  The present embodiment is characterized in that the ICL cleaning bias to be reduced is changed according to the environment when the intermediate transfer belt surface moving speed is decelerated, and the occurrence of drum ghost is prevented even in a low temperature and low humidity environment. . This will be described in detail below.

  FIG. 3 is a schematic configuration diagram of the image forming apparatus according to the present embodiment. The same reference numerals are given to the same parts as those in the conventional example and the first embodiment, and the description thereof is omitted. The primary transfer roller 10 and the intermediate transfer belt 9 of this embodiment are the same as those of the first embodiment, and their resistance is low in a high temperature and high humidity environment and high in a low temperature and low humidity environment. Therefore, the current characteristic with respect to the primary transfer bias varies depending on each environment. FIG. 4 shows voltage-current characteristics of the primary transfer nip portion in each environment in this embodiment. In order to flow the primary transfer target current of 10 μA, the primary transfer bias is about 700 V in the high temperature and high humidity environment (temperature: 30 ° C./humidity: 80%), whereas the low temperature low humidity environment (temperature: 15 ° C./humidity). : 10%), it is understood that about 1500 V is necessary. Also, the points plotted with ● in the figure are points at which drum ghosts do not occur in each environment. As shown by the thick dotted lines in FIG. 4, there is a drum ghost generation threshold value in the vicinity of about 6 μA. Therefore, the amount of bias that must be reduced to prevent drum ghost differs depending on the environment. In the image forming apparatus of this embodiment, a temperature / humidity sensor 22 is mounted (FIG. 3). The result detected by the temperature / humidity sensor 22 is sent to the recovery bias control means 23 to control (reduce) the ICL recovery bias. The ICL recovery bias in each environment by the recovery bias control means 23 is shown in FIG. From the result of FIG. 4, in the environment of 30 ° C. and 80% humidity, the ICL recovery bias is reduced by 450V from the primary transfer bias of 700V to 250V, and in the environment of 15 ° C. and 10% humidity, 750V is reduced from the primary transfer bias of 1500V. did.

  With the above configuration, a printing test was conducted as in Example 1. The print test was performed in three environments: a low temperature and low humidity environment (temperature: 15 ° C./humidity: 10%), a normal temperature and normal humidity environment (temperature: 23 ° C./humidity: 50%), and a high temperature and high humidity environment. The level was confirmed. FIG. 6 shows a comparison result between the configuration of this example and the configuration of the comparative example. ○ in the figure indicates that there is no drum ghost, △ in the figure indicates that drum ghost is slightly generated, and x in the figure indicates that drum ghost is completely generated. Is shown. In this configuration, the occurrence of drum ghosts can be completely suppressed in all environments.

  In the above configuration, the temperature and humidity sensor is used to detect the environment, but the environment is detected from the ATVC result of the primary transfer using the resistance change due to the environment of the primary transfer member (primary transfer roller, intermediate transfer belt, etc.). However, the same effect can be obtained.

(Example 3)
A third embodiment of the present invention will be described below. The description of the same members as those in the conventional example and the first embodiment is omitted.

  According to the configuration of the second embodiment, it is possible to suppress the occurrence of drum ghost in each environment when the intermediate transfer belt is decelerated. However, due to variations in the resistance of the primary transfer member such as the primary transfer roller and the intermediate transfer belt, the drum Ghosts may occur. When the primary transfer roller and the intermediate transfer belt with high resistance are combined in the production variation, the primary transfer current is less than the primary transfer current for preventing the drum ghost just by reducing the constant bias as in the second embodiment. Lowering may not be possible. In addition, when the primary transfer roller and the intermediate transfer belt with low resistance are combined in the production variation, the current may decrease to the extent that residual toner cannot be collected by ICL if the constant bias is reduced. It was.

  This embodiment is characterized in that when the intermediate transfer belt surface moving speed is decelerated, control is performed so that a desired current flows when residual toner is collected by the ICL, and the resistance of the primary transfer member is increased or decreased due to production variations. Even so, it is characterized by preventing the occurrence of drum ghosts. This will be described in detail below.

  In this embodiment, the configuration other than the residual toner collecting bias when the intermediate transfer belt surface moving speed is reduced is the same as in the conventional example and the first embodiment, and the description thereof is omitted with reference to the schematic diagram of FIG. As in the conventional example, when the transfer material P is thick, when the resistance is high, or when the surface property is poor, the surface of the intermediate transfer belt 9 is brought into contact with the intermediate transfer belt 9 when the secondary transfer roller 11 contacts the intermediate transfer belt 9. The moving speed is reduced to 60 mm / sec. When the surface moving speed of the intermediate transfer belt 9 is reduced, the primary transfer portion performs ATVC to determine the residual toner collection bias at the ICL. From the results of FIG. 4 of Example 2, the target current value in this ATVC was set to 5 μA as a current that does not generate drum ghost in each environment. After the intermediate transfer belt 9 decelerates, the residual toner collection bias is separately determined by ATVC, so that a bias that does not generate drum ghost is selected even when the resistance of the primary transfer member varies or the environment changes. Be able to. Further, since this ATVC is performed every time printing is performed, it is possible to cope with the resistance fluctuation of the primary transfer member due to printing durability. When the collection bias of the residual toner is determined by ATVC, the transfer material P is conveyed to the secondary transfer nip portion N2, and the four color toner images on the intermediate transfer belt 9 are transferred onto the transfer material P at a conveyance speed of 60 mm / second. Secondary transferred. The residual toner remaining on the intermediate transfer belt 9 is positively charged by the secondary transfer residual toner charging roller 19 and is collected at the primary transfer nip portion N1 using the ATVC recovery bias performed before the secondary transfer. Collected on the photosensitive drum 1.

With the above configuration, a printing test was conducted as in Example 1. As the transfer member for the printing test, the upper limit resistance product and the lower limit resistance product within the production variation were used. The resistance upper limit product uses a primary transfer roller 10 having a resistance of 2.0 × 10 ⁸ [Ω] as an actual resistance and an intermediate transfer belt having a volume resistance of 2.0 × 10 ¹¹ [Ω · cm]. For the lower limit resistance, the primary transfer roller 10 has a resistance of 5.0 × 10 ⁷ [Ω] as the actual resistance, and the intermediate transfer belt has a resistance of 7.0 × 10 ¹⁰ [Ω · cm] as the volume resistance. It was. In addition, the print test was performed in three environments: a low temperature and low humidity environment (temperature: 15 ° C./humidity: 10%), a normal temperature and normal humidity environment (temperature: 23 ° C./humidity: 50%), and a high temperature and high humidity environment. The ghost level was confirmed. FIG. 7 shows a comparison result between the configuration of this example and the configuration of the comparative example. ○ in the figure indicates that there is no drum ghost, △ in the figure indicates that drum ghost is slightly generated, and x in the figure indicates that drum ghost is completely generated. Is shown. In this configuration, in all environments, even when a transfer member resistance upper and lower limit product is used, the occurrence of drum ghost can be completely suppressed.

  As described above, the structure in which the surface movement speed of the intermediate transfer belt is reduced from 120 mm / second to 60 mm / second has been described as a structure for suppressing the occurrence of drum ghost when the surface movement speed of the intermediate transfer belt is reduced. Even if the surface moving speed and its deceleration amount are different, the same effect can be obtained by adjusting and reducing the primary transfer bias reduction amount in accordance with the deceleration amount of the intermediate transfer belt.

FIG. 3 is a diagram illustrating a schematic configuration in which the secondary transfer roller of the first embodiment is in contact with an intermediate transfer belt. The figure which shows the result of the printing confirmation in a 1st Example. The figure which shows schematic structure of a 2nd Example. The figure which shows the voltage-current characteristic of the primary transfer nip part in each environment. The figure which shows the ICL collection | recovery bias reduced in each environment. The figure which shows the result of the printing confirmation in a 2nd Example. The figure which shows the result of the printing confirmation in a 3rd Example. The figure which shows schematic structure of a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging device 3 Exposure apparatus 4 Developing device support body 5, 6, 7, 8 Developing device 9 Intermediate transfer belt 10 Primary transfer roller 11 Secondary transfer roller 12 Secondary transfer counter roller 13 Secondary transfer residual toner charging roller Power supply 14 Tension roller 16 Photosensitive drum cleaner 17 Primary transfer power supply 18 Secondary transfer power supply 19 Secondary transfer residual toner charging roller 21 Contacting / separating cam 22 Temperature / humidity sensor 23 Recovery bias control means

Claims (4)

An image carrier for carrying a toner image;
An intermediate transfer member to which a toner image on the image carrier is electrostatically transferred;
Transfer means for transferring a toner image on the image carrier to the intermediate transfer member;
Charging means for charging residual toner remaining on the intermediate transfer member to a predetermined polarity;
Transferring the residual toner on the intermediate transfer member charged to a predetermined polarity by the charging unit to the image carrier by applying a bias voltage having the same polarity as the residual toner by the transfer unit;
A first surface moving speed of the intermediate transfer member when transferring a toner image on the image carrier onto the intermediate transfer member and simultaneously transferring residual toner on the intermediate transfer member onto the image carrier; An image forming apparatus that only transfers the residual toner on the intermediate transfer member onto an image carrier and has a second surface moving speed of the intermediate transfer member that is lower than the first surface moving speed. In
The image forming apparatus according to claim 1, wherein the bias voltage of the transfer unit at the second surface moving speed is lower than the bias voltage of the transfer unit at the first surface moving speed.   2. The image according to claim 1, wherein the bias voltage of the transfer unit at the second surface moving speed is reduced by a predetermined voltage from the bias voltage of the transfer unit at the first surface moving speed. Forming equipment.   3. The image forming apparatus according to claim 2, wherein the predetermined voltage to be reduced varies depending on an environment.   The bias voltage of the transfer unit at the second surface moving speed is controlled to be a desired amount of current, so that the bias voltage of the transfer unit at the first surface moving speed is higher than the bias voltage of the transfer unit at the first surface moving speed. An image forming apparatus characterized in that the image forming apparatus is reduced.

Images