JPH11161043A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control the triboelectrification of a toner after a toner electrifying means passes within an appropriate range under any environment. SOLUTION: This device is provided with an intermediate transfer drum 8 and an ICL roller 15 on the downstream side of a 2nd transfer area in the rotating direction of the drum 8. A bias voltage obtained by superposing an AC component on a DC component is impressed on the roller 15 from an electrification bias power source 14. Further, in the case of impressing the voltage, a bias value is changed in accordance with the environment where the device is used. Thus, the triboelectrification of a residual toner after passing the roller 15 is controlled within an appropriate range and an excellent image free from faulty cleaning and without generating a negative ghost is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus such as a printer or a copying machine.

[0002]

2. Description of the Related Art With the flow of computerization, needs for outputting documents and images in color have been widened, and various types of color printers are commercially available. As a color image forming method, a sublimation type, a thermal transfer type, an ink jet method and the like are used, and an electrophotographic method is said to be the most excellent for forming an image at high speed.

In recent years, among these electrophotographic systems, an intermediate transfer system, which can form an image without selecting a transfer material and is excellent in color registration, is becoming mainstream.

In an electrophotographic apparatus of an intermediate transfer system, a yellow image formed on a photosensitive drum 1, which is a first image carrier,
Each single-color image of magenta, cyan, and, in some cases, black is superimposed on the intermediate transfer member 8 which is a solid drum or belt-shaped second image carrier, and finally a full-color image is collectively transferred onto a transfer material. Perform

This method does not require the paper to be wound around the transfer drum, so it can be used for envelopes and thick paper, and has high versatility. Also, since the color registration does not change with the thickness of the paper, high image quality can be obtained. There is a merit that it can be obtained.

However, in the intermediate transfer method, an image is formed by directly transferring a toner image onto an intermediate transfer member. Therefore, it is necessary to clean residual toner that cannot be finally transferred to a transfer material in preparation for the next image formation. There is.

Generally, fur brush cleaning or blade cleaning is used as a method for cleaning the intermediate transfer member. However, in these methods, the surface of the intermediate transfer member is mechanically rubbed, so that the surface is deteriorated and the toner is fused. There was a problem that wearing was easy to occur. Further, a mechanism for collecting the cleaned toner and a container for storing the waste toner are required, and there is a problem that user maintenance is inferior.

Therefore, a method has been proposed in which the untransferred toner on the intermediate transfer body is recharged by a charging device and collected on a photosensitive drum.

According to this method, since the transfer residual toner can be collected by the cleaning device for the photosensitive drum, there is an advantage that an unnecessary waste toner container is not required and deterioration of the intermediate transfer member is small. Hereinafter, this cleaning method is referred to as an ICL method.

In the ICL system, it is possible to carry out transfer simultaneous cleaning in which toner is transferred from the photosensitive drum to the intermediate transfer member and at the same time, the transfer residual toner is collected. It is effective to superimpose the AC voltage on the bias applied to the charging roller for disturbance.

In general, a charging roller (hereinafter, referred to as an "ICL roller") is used as a toner charging means, and a positive voltage is applied to the ICL roller in an electrophotographic apparatus of an image exposure using a negative toner and a reversal developing system. The transfer residual toner is collected on the negatively charged photosensitive drum.

The toner is charged by discharging from the ICL roller. If the amount of charge on the toner is too small, the toner is not collected on the photosensitive drum and cleaning failure occurs.
Conversely, if the charge amount is too large, the positively charged toner collected during the simultaneous cleaning for transfer will return to the photosensitive drum with the negatively charged toner to be transferred, and a negative ghost will occur.

Therefore, an IC for charging the toner is provided.
There is an appropriate range for the bias applied to the L roller.

In general, if the toner tribo after charging by the ICL roller is about +20 to 50 μC / g, a good image can be obtained without occurrence of cleaning failure and negative ghost.

[0015]

However, it is difficult to control the toner tribo after passing through the ICL roller to about +20 to 50 .mu.C / g even under all conditions and environments. This is because toner is charged by discharging from the ICL roller.

The DC current (hereinafter, ICL current) flowing through the ICL roller by applying a bias is divided into a discharge current and an injection current flowing directly from the ICL roller into the intermediate transfer member.

In a normal environment, most of the ICL current becomes a discharge current (since the resistance of the ICL roller and the intermediate transfer member is high, so that the injection current flowing ohmic is limited).
By controlling the CL current at a constant current, the toner tribo can be set to a desired value.

However, in a high-temperature and high-humidity environment where the resistance values of the ICL roller and the intermediate transfer member decrease, the ratio of the injection current to the ICL current increases.

For this reason, if the control is performed at the same constant current value as in the normal environment, there is a problem that the discharge current is insufficient and the toner tribo after the ICL is charged is reduced, resulting in poor cleaning.

This phenomenon occurs because the injection current increases and the voltage applied to the ICL during the constant current control falls below a discharge threshold voltage at which a discharge contributing to toner charging is excited. Can be considered.

Conversely, if the same constant current control as in high temperature and high humidity is performed in a low temperature and low humidity environment where almost all of the ICL current is a discharge current, the toner is overcharged and a negative ghost is caused. there were.

Accordingly, an object of the present invention is to provide an image forming apparatus capable of controlling the toner tribo after passing through the toner charging means to an appropriate range in any environment.

[0023]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
A first image carrier, a second image carrier on which a toner image formed on the first image carrier is primarily transferred at a primary transfer portion between the first image carrier, A transfer unit for secondary-transferring a toner image from the second image carrier to a transfer material; and a toner charging unit for contact-charging a transfer residual toner remaining on the second image carrier. The secondary transfer residual toner charged by the means is transferred from the primary transfer portion to the first toner.
In the image forming apparatus, the toner charging unit includes a cleaning member, and a charging bias power supply for applying a voltage to the cleaning member, and the charging bias power supply is biased according to an environment in which the toner is used. An image forming apparatus characterized by changing a value.

It is preferable that the charging bias power supply applies a voltage in which an AC component is superimposed on a DC component to the cleaning member. According to another aspect, it is preferable that the charging bias power supply performs constant current control of a DC component, and further holds the voltage value when the DC voltage generated by the constant current control falls below a predetermined voltage. It is preferable that the charging bias power supply controls a DC component at a constant current and changes a constant current value according to an environment.

It is preferable that the charging bias power supply controls the DC component at a constant current, and increases the constant current value in an environment where the resistance value of the second image carrier decreases. The DC component of the charging bias power supply preferably has a configuration in which a constant voltage power supply and a constant current power supply are connected in series. Preferably, the second image carrier is an intermediate transfer drum.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

Example 1 In Example 1, an intermediate transfer drum is cleaned by an simultaneous transfer cleaning (ICL) method using an electrophotographic printer using an intermediate transfer drum.

A specific description will be given with reference to FIG. The printer of this embodiment has a diameter of 186 mm as the second image carrier.
Solid intermediate transfer drum 8 of the maximum paper passing size A3,
Process speed 100mm / sec, image exposure,
This is a full-color electrophotographic image forming apparatus of a reversal developing system.

In order to form a full-color image, yellow (Y), magenta (M), cyan (C), and black (Bk) images are formed on the photosensitive drum 1, and the respective toner images are transferred to the intermediate transfer drum 8. Lay on top. This step is called primary transfer, and one full-color image is formed by rotating the intermediate transfer drum 8 four times.

Next, the toner images on the intermediate transfer drum 8 are collectively transferred onto transfer paper. This step is called secondary transfer.

As a transfer means, two rollers 10 and 11 are used.
Using a transfer unit having a transfer belt 12 stretched over, the transfer roller 11 on the upstream side in the traveling direction of the transfer paper is brought into contact with the intermediate transfer drum 8 to transfer the toner, and at the same time, the transfer belt 12 and the transfer paper are attracted. To effect separation. The other roller is a driving roller 10 that drives the transfer unit so that the peripheral speed of the intermediate transfer drum 8 is equal to the peripheral speed of the transfer belt 12.

The toner image secondarily transferred onto the transfer paper is sent to a heat fixing roller unit (not shown), and after being fixed, is discharged out of the apparatus.

Next, each unit will be described.

The photosensitive drum 1 as the first image carrier is a negatively chargeable OPC drum having a diameter of 64 mm, rotates in the direction of arrow R1, and first uniformly charges its surface by the charging roller 2. The bias applied to the charging roller 2 is -600 V
Is a DC component of 2000 Vpp, 1000 Hz, and a sine wave AC component is superimposed. As a result, the photoconductor is charged to about -600 V in any environment.

Next, the charged surface of the photoreceptor is exposed by a laser exposure device. In this embodiment, image exposure is performed by using an exposure apparatus in which an infrared laser unit 4 having a wavelength of 60 nm and a reflection mirror 5 are combined.

Next, the electrostatic latent image formed by the laser exposure is developed with toner by a developing device. Although the full-color printer of this embodiment uses four color toners, specifically, a fixed black developing device 6 and a rotary color developing unit 7 are used.

The black developing device 6 uses a jumping developing method using a magnetic one-component toner. A conductive non-magnetic sleeve with a diameter of 20 mm containing a fixed magnet roll has a particle size of 6 mm.
μm toner is coated with an elastic blade, and the DC component applied to the sleeve is −350 V, the AC component is 1600 V
Reversal development is performed by jumping between the photoconductor and a rectangular wave having a pp frequency of 2000 Hz.

The color developing unit 7 has three developing units 7C and 7
Y and 7M are assembled in the rotary rotary 7a, and the rotary
C, 7Y, and 7M are brought into contact with the photosensitive drum 1 to perform development.

Each of the color developing units 7C, 7Y, and 7M performs development by a jumping development method using a non-magnetic one-component toner. The toner is a polymerized toner having a core / shell structure having a particle diameter of 6 μm and containing wax therein. The toner is coated on a developing sleeve by an application roller, the layer thickness is regulated by an elastic blade, and is sent to a developing section. Development is performed under the same bias conditions.

The primary transfer is performed by applying a voltage of +100 V from the bias power supply 16 to the intermediate transfer drum 8, and the primary transfer residual toner of the photosensitive drum 1 is scraped off by the cleaning unit 9 having the urethane cleaning blade 9a. .

The printer of this embodiment employs a process in which the secondary transfer residual toner on the intermediate transfer drum 8 is recharged by the charging roller 15 called an ICL roller and collected on the photosensitive drum 1. The secondary transfer residual toner collected on the drum 1 is also scraped off by the cleaning blade 9a.

Next, the intermediate transfer drum 8 will be described.
In the intermediate transfer drum 8, a conductive rubber layer 8b having a thickness of 5 mm is formed on an aluminum drum 8a, and a resistance layer 8c is further formed thereon.
Coat 0 μm. The conductive rubber layer 8b is formed by mixing epichlorohydrin rubber and NBR rubber to adjust the resistance value to a volume resistance value of 10 ⁶ Ωcm, and the resistance layer 8c is a urethane resin having a volume resistance value of 10 ¹² Ωcm. The resistance value of the entire intermediate transfer drum is 10 ⁶ Ω as a resistance value measured by applying a voltage of 1 kV with a metal electrode in contact with a longitudinal length of 310 mm and a nip width of 5 mm.

In the case of single-color printing, after the primary transfer is performed, the toner image is conveyed on the intermediate transfer drum 8 to the secondary transfer section as it is, and undergoes the secondary transfer.

In the case of full-color printing, the intermediate transfer drum makes four rotations and performs primary transfer by superposing the respective toners of YMCK. In the secondary transfer, a transfer material is supplied from a paper supply unit (not shown), and a transfer belt 12 that can be separated and brought into contact with the intermediate transfer drum 8. The secondary transfer bias is controlled at a constant current of +20 μA by the high-voltage power supply 13, and a charge is supplied to the transfer material from the transfer belt 12, so that the toner image moves to the transfer material.

The transfer unit includes a transfer roller 11, a drive roller 10, and a transfer belt 12. Both the transfer roller 11 and the drive roller 10 form a conductive rubber layer having a volume resistance of 10 ⁵ Ωcm on a core metal having a diameter of 14 mm. And diameter 2
The roller is 0 mm. The transfer roller 11 has a metal core connected to a high-voltage power supply via a power supply spring, and rotates following the transfer belt 12. The driving roller 10 has a gear attached to the end of the cored bar, and is driven by meshing with a gear train of the main body.

The transfer belt 12 is a seamless two-layer rubber belt. The base layer is made of urethane rubber having a thickness of 300 μm and having a volume resistivity of 10 ⁷ Ωcm by dispersing carbon.

Next, the ICL roller 15 will be described.
About 90% of the toner is transferred to the transfer material by the secondary transfer, but a part of the toner remains on the intermediate transfer drum 8 as transfer residual toner. This toner appears as a ghost in the next image formation and must be removed. Therefore, in the present embodiment, the transfer residual toner is charged by the charging roller 15 provided downstream of the secondary transfer portion in the rotation direction of the intermediate transfer drum 8, and the electric field formed between the intermediate transfer drum 8 and the photosensitive drum 1 To collect the toner on the photoreceptor.

The ICL roller 15 is, as shown in FIG.
A core bar 15a having a diameter of 8 mm and a sponge layer 1 having an outer diameter of 18 mm
This is a two-layer type in which 5b is coated as a surface layer 15c.

The sponge layer 15b is formed by dispersing carbon in urethane to adjust the volume resistance value to 10 ⁷ Ωcm and foaming in the mold. The surface layer 15c is formed by dispersing carbon in an acrylic resin to obtain a volume resistance value of 10 ¹³ Ωcm. The sponge layer 15b is coated on the sponge layer 15b with a dipping coat to a thickness of 200 μm.

The resistance of the roller as a whole was determined by contacting a metal roller having a diameter of 30 mm with a total load of 9.8 N while rotating the roller at +700 V
Converted from the current value measured by applying a DC voltage of 5 ×
10 ⁸ Ω.

A bias is applied to this roller to charge the toner.

The ICL roller 15 can be brought into contact with and separated from the intermediate transfer drum 8 by appropriate means. When cleaning is performed, the ICL roller 15 comes into contact with a cam (not shown) of the main body.
A bias is applied from the high voltage power supply 14.

The bias is obtained by superimposing an AC component on a DC component. This is because the transfer residual toner is reciprocated with the ICL roller by the AC electric field and is disturbed. When the transfer residual toner is small, it is possible to charge all of the transfer residual toner with only the DC component. However, in order to charge the multi-layer transfer residual toner from the upper layer to the lower layer, some disturbance means is required. In this embodiment, a rectangular wave of 2 kHz and 3 kVpp was used as the AC component.

Next, the DC component of the bias applied to the ICL roller will be described. DC to transfer residual toner is DC
Made by the ingredients. I contacting the intermediate transfer drum
When a voltage is applied to the CL roller, the intermediate transfer drum and IC
Discharge is excited in the minute air gap on both sides of the L roller nip. When the discharge starts, the voltage Vth is determined by Paschen's law, and Vth = 312 + 6.2z (z: gap interval). Since a discharge mainly occurs in a gap of several tens of μm, if the DC voltage is lower than about 1.0 kV, sufficient charging is not performed.

In this embodiment, an ICL having a high resistance of 500 MΩ is used.
Since a roller is used, the injection current from the ICL roller to the intermediate transfer member is sufficiently small in a normal environment or a low-temperature and low-humidity environment. Therefore, it is considered that most of the ICL current is a discharge current, and the toner tribo can be kept constant by performing DC constant current control.

FIG. 3 shows the relationship between the charging current under a normal environment and the toner tribo after passing through the ICL roller. By performing a constant current control of about 20 μA, a toner tribo free from image defects can be realized. Note that the DC voltage value for performing the constant current control of 20 μA was 1.5 kV.

On the other hand, in a high-temperature, high-humidity environment, the injection current becomes a value that cannot be ignored because the resistance values of the ICL roller and the intermediate transfer drum decrease. Specifically, 30 ° x 80% R
In the environment of H, the resistance value of the ICL roller is 500MΩ → 20
MΩ, the resistance value of the intermediate transfer drum is 10 ⁶ → 3 × 10 ⁵ Ω
Down to. In particular, the intermediate transfer drum is easily affected by temperature and humidity because the base rubber is ionic conductive epichlorohydrin rubber.

When the constant current control of 20 μA was performed under the same conditions as in the normal environment, the toner tribo after passing through the ICL roller was reduced to −8 μC / g, and cleaning failure occurred. At this time, the DC voltage applied to the ICL roller was +800 V. From this, it is considered that the injection current increased due to the decrease in the resistance of the member, the ratio of the discharge current to the constant current control value decreased, and the toner was not given a tribo.

From another viewpoint, it can be said that the DC voltage is reduced according to Ohm's law because the resistance value of the member is reduced, and is lower than the discharge threshold.

In order to prevent this, in this embodiment, the constant current value is changed by detecting the environment (temperature and humidity). Specifically, the ratio of the discharge current and the injection current occupying the ICL current is predicted for each environment, and the constant current value is controlled so that the discharge current becomes constant in each environment.

In each environment, the toner tribo after passing through the ICL roller was measured while changing the ICL current, and the result of finding the ICL current necessary for the value to become +30 μC / g is shown in Table 1 below.

[0062]

[Table 1]

It is considered that the discharge current from the ICL roller is the same under the condition that the toner tribo after passing through the ICL roller is constant.

According to this, assuming that the ratio of the discharge current to the ICL current in a low-temperature and low-humidity environment of 10 ° C. × 10% (hereinafter, L / L environment) is 100%, 30 ° C. × 80% RH
In the high temperature and high humidity environment (hereinafter, H / H environment), the discharge current is expected to be 45% of the ICL current and 90% in the normal environment of 24 ° C. × 50% RH.

Therefore, in this embodiment, according to Table 1, L /
In the L environment, the DC constant current value of the ICL bias is 18 μA, and in the normal environment, 20 μA, H
In a / H environment, it is 40 μA.

The environment is detected by A / D converting the signals of the temperature sensor and the humidity sensor provided in the main body and converting the signals into the main body CP.
U, and determine the environment, and ICL at the specified constant current value
The bias applied to the roller is changed.

When the environment sensor is not used, the voltage generated when a predetermined constant current control (or constant voltage control) is performed by bringing the ICL roller into contact with the intermediate transfer drum before forming an image. It is also possible to determine the constant current value by detecting (or flowing current) and detecting the environment in which the main body is placed from each relationship.

Specifically, a constant current control of +20 μA is performed at the time of the preceding multi-rotation, and a DC voltage required at that time is detected, and a table as shown in Table 2 can be created. The environment is predicted based on this table, and the constant current value actually used at the time of image formation is determined.

[0069]

[Table 2]

As described above, the configuration in which the environment where the main body is placed is detected in advance and the constant current value of the DC bias applied to the ICL roller is controlled based on the detected environment. As a result, the discharge current can be controlled to be constant in any environment, and the toner tribo after passing through the ICL roller can be stabilized to prevent an image defect such as a cleaning failure or a negative ghost.

Embodiment 2 Next, Embodiment 2 of the present invention will be described. In this embodiment, as in the first embodiment, an IC is used in accordance with the environment in which the main body is used.
Although the bias applied to the L roller is changed, the method is characterized in that constant current control is not performed in all environments, but the control method is changed according to the environment.

In the first embodiment, especially in an H / H environment, the ICL
The constant current value was set high in anticipation of a decrease in the ratio of the injection current occupying the current. However, when an ICL roller or an intermediate transfer drum having a low resistance value is used due to manufacturing variations, or when the environmental fluctuation of the resistance value of each member becomes larger than expected, the injection current further increases, and There was a possibility that the application of the tribo to the surface was insufficient and cleaning failure occurred.

In order to prevent such a situation, in the present embodiment, especially in the H / H environment, the ICL bias is changed to the constant voltage control from the viewpoint of guaranteeing a voltage necessary for exciting discharge. Features.

Since the discharge current becomes almost the same as the ICL current in the normal environment or the L / L environment, it is preferable to perform the constant current control to keep the toner tribo constant after passing the ICL roller. Similarly, constant current control is performed.

A specific example will be described below.

Table 3 shows the measurement results of the toner tribo after passing through the ICL roller when the temperature and humidity were changed and the ICL bias was controlled by +20 μA constant current control.

[0077]

[Table 3]

As a result, the toner tribo was +20 μC / g.
In an environment lower than, cleaning failure occurred.

Therefore, in this embodiment, the output signal values of the temperature and humidity sensors of the main body are used to switch from constant current control to constant voltage control in the underlined environment where the toner tribo is lower than +20 μC / g in Table 3. did. The constant voltage value is IC
The voltage was set at +1000 V, which is a voltage capable of exciting discharge between the L roller and the intermediate transfer drum and giving a tribo of at least +20 μC / g.

In this case, the constant current and the constant voltage control are switched by detecting the environment. However, while performing the constant current control, the voltage generated at the ICL roller at that time is detected.
Similar effects can be obtained by driving the high voltage circuit so that this voltage does not fall below +1000 V, or by increasing the constant current value so that this voltage does not fall below +1000 V.

Table 4 shows an example in which printing was performed in a configuration using constant voltage control in an H / H environment, and the toner tribo after passing through the ICL roller was measured.

[0082]

[Table 4]

As described above, the minimum toner tribo that enables cleaning in any environment is +20 μC
/ G can be maintained, and image defects can be prevented.

Third Embodiment Next, a third embodiment of the present embodiment will be described. In the present embodiment, as in the second embodiment, a high voltage power supply circuit capable of maintaining a voltage applied to the ICL roller to at least a minimum voltage for applying a toner tribo to enable cleaning is used.

In the second embodiment, the minimum voltage under the H / H environment is maintained by detecting the environment or the voltage at the time of the constant current control.
The same effect can be obtained by using a two-stage configuration in which a constant voltage power supply and a constant current power supply are connected in series as the high-voltage power supply for applying a bias to 5.

FIG. 4 is a schematic diagram of the circuit configuration in this embodiment.
Shown in

In this circuit configuration, the first-stage constant-voltage transformer 141 excites the discharge from the ICL roller under the H / H environment and generates a voltage that can provide the minimum toner tribo required for cleaning. In the present embodiment, the constant voltage value is set to +1000 V in accordance with the second embodiment.

The constant current transformer 142 of the second stage is an ICL
The DC current value flowing through the closed loop including the roller and the high voltage power supply is detected, and the bias is feedback-controlled so that this value is always +20 μA.

In a normal environment or an L / L environment, the voltage generated at the ICL roller 15 at the time of +20 μA constant current control is +1.5
Since the voltage is kV or more, the first-stage constant-voltage transformer 141 generates +1.0 kV, and the remaining 500 V is taken over by the second-stage constant current circuit 142.

On the other hand, in the H / H environment, the minimum voltage required for cleaning is guaranteed at +1.0 kV of the first-stage constant-voltage power supply 141. At this time, a current of +20 μA or more flows through the circuit. The constant current circuit 142 at the stage does not operate.

As described above, in the circuit of this embodiment, in the normal environment, and in the L / L environment, +20 μm
Since the A constant current control is performed, the toner is not excessively charged and a negative ghost can be prevented.
In the / H environment, the lowest tribo necessary for cleaning can be given by the first-stage constant voltage power supply 141, so that cleaning failure can be prevented, and a good image can be obtained in all environments. Became.

[0092]

As is apparent from the above description, according to the present invention, the toner charging means for contact-charging the transfer residual toner remaining on the second image bearing member includes the cleaning member and the cleaning member. A charging bias power supply for applying a voltage, and changing the bias value in accordance with the environment in which the charging bias power supply is used. It can be controlled to an appropriate range, so that the occurrence of poor cleaning and negative ghost can be prevented, and a good image can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an electrophotographic full-color printer used in Examples 1 to 3.

FIG. 2 is a schematic sectional view showing an ICL roller.

FIG. 3 is a graph showing a relationship between an ICL current in a normal environment and a toner tribo after passing through an ICL roller.

FIG. 4 is a conceptual diagram of an ICL high-voltage circuit according to a third embodiment.

[Explanation of symbols]

 Reference Signs List 1 photosensitive drum (first image carrier) 2 intermediate transfer drum (second image carrier) 12 transfer belt (transfer unit) 14 charging bias power supply 15 ICL roller (cleaning member)

Claims (7)

[Claims] A second transfer unit configured to transfer a toner image formed on the first image carrier at a primary transfer unit between the first image carrier and the first image carrier; An image carrier and the second
A transfer unit for secondary-transferring a toner image from the image carrier to the transfer material; and a toner charging unit for contact-charging the transfer residual toner remaining on the second image carrier. In the image forming apparatus which collects the remaining secondary transfer residual toner from the primary transfer unit to the first image carrier, the toner charging unit includes: a cleaning member; a charging bias power supply for applying a voltage to the cleaning member; An image forming apparatus comprising: a charging bias power supply that changes a bias value according to an environment in which the charging bias power supply is used. 2. The charging bias power supply includes an AC
2. The image forming apparatus according to claim 1, wherein a voltage in which components are superimposed is applied to the cleaning member. 3. The charging bias power supply according to claim 1, wherein the DC component is controlled by a constant current, and further, when the DC voltage generated by the constant current control falls below a predetermined voltage, the voltage value is maintained. 2 image forming apparatus. 4. The image forming apparatus according to claim 1, wherein the charging bias power supply controls a DC component at a constant current, and changes a constant current value according to an environment. 5. The image forming apparatus according to claim 4, wherein said charging bias power supply controls a DC component at a constant current, and increases the constant current value in an environment where the resistance value of the second image carrier decreases. . 6. The image forming apparatus according to claim 1, wherein the DC component of the charging bias power supply has a configuration in which a constant voltage power supply and a constant current power supply are connected in series. 7. The image forming apparatus according to claim 1, wherein said second image bearing member is an intermediate transfer drum.