JP2000147849A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a good image without deterioration in density by preventing a toner image on an intermediate transfer body from being transferred again to an image carrier. SOLUTION: In this image forming device, the potential by electrification of a photoreceptor 1 and/or the primary transfer potential of an intermediate transfer drum 6 are/is set by controlling a primary electrification power source 14 and/or a primary transfer bias power source 15 with a controller 17 so that the value of primary transfer current flowing between a photoreceptor 1 and the intermediate transfer drum 6 is not more then the specified value (1 μA). Thus, the good image without any deterioration in the density can be obtained by preventing toner on the intermediate transfer drum 6 from being transferred again to the photoreceptor 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile for forming an image.
Transfer the toner image to the intermediate transfer member on the image carrier, and then
The present invention relates to an image forming apparatus that transfers a toner image on an intermediate transfer member to a transfer material.

[0002]

2. Description of the Related Art Conventionally, a four-color full-color image forming apparatus using an intermediate transfer member has been known. The image forming process will be briefly described. First, a first color (yellow) toner image is formed on a photoconductor, and this toner image is primarily transferred onto an intermediate transfer body. Then, this primary transfer is transferred to another 3
Colors, that is, magenta, cyan, and black are sequentially performed, and four color toner images are superimposed on the intermediate transfer member. Thereafter, a full-color image can be obtained by collectively secondary-transferring the four color toner images onto a transfer material P such as paper by a secondary transfer member.

[0003]

In the image forming apparatus using the above-mentioned conventional intermediate transfer member, the primary transfer of the toner image formed on the photoreceptor to the intermediate transfer member is performed by yellow, magenta, cyan, and cyan. Black is performed four times,
At the time of the second magenta transfer, the yellow toner that has already been transferred onto the intermediate transfer body may be returned from the intermediate transfer body to the photoconductor side at the primary transfer portion. This is called retransfer. Similarly, during the third cyan transfer, the yellow toner and magenta toner already transferred on the intermediate transfer member are retransferred to the photoconductor, and the fourth black transfer is performed. At times, the yellow toner, magenta toner, and cyan toner that have already been transferred onto the intermediate transfer member are re-transferred to the photosensitive member.

As described above, the number of times of re-transfer, that is, the amount of re-transfer increases as the toner is primarily transferred earlier, which causes a problem that the density of an output image decreases. That is, the color unevenness of the output image occurs. This retransfer tends to occur particularly on a photoreceptor whose photosensitive layer has deteriorated due to abrasion or the like, and becomes remarkable under a high temperature and high humidity environment.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus capable of preventing the density of a toner image transferred from an image carrier to an intermediate transfer member from being reduced.

[0006] Other objects of the present invention will become apparent from a reading of the following detailed description.

[0007]

According to the present invention, the above object is achieved. The present invention provides an image carrier, a charging unit for charging the image carrier, an image forming unit for forming a toner image on the image carrier charged by the charging unit, an intermediate transfer member, and the image transfer device. Voltage applying means for applying a voltage to the intermediate transfer body to transfer the toner image on the image carrier formed by the forming means to the intermediate transfer body at a transfer position, and In an image forming apparatus for transferring a toner image transferred to the intermediate transfer body to a transfer material, a voltage applied to the intermediate transfer body by the voltage application unit is controlled at a constant voltage, and the voltage application unit controls the voltage applied to the intermediate transfer body. A voltage is applied to the detection means for detecting a current flowing from the voltage application means to the intermediate transfer member,
Control means for controlling at least one of a voltage applied to the image carrier by the charging means and a voltage applied to the intermediate transfer member by the voltage applying means based on a detection result by the detecting means. It is characterized by the following.

According to another embodiment of the present invention, a plurality of image carriers, a plurality of charging means for respectively charging the plurality of image carriers, and the plurality of images charged by the plurality of charging means are provided. A plurality of image forming means for respectively forming a plurality of color toner images on the carrier; an intermediate transfer member; and a plurality of color toner images on the plurality of image carriers formed by the plurality of image forming means. And a plurality of voltage applying means for applying a voltage to the intermediate transfer body to sequentially transfer the image onto the intermediate transfer body at the transfer position. In an image forming apparatus that transfers a toner image of a plurality of colors to a transfer material, a voltage applied to the intermediate transfer body by the plurality of voltage applying units is controlled by a constant voltage, charged by the charging unit, and By means A voltage is applied to the intermediate transfer member by the voltage application unit during a period in which the image carrier on which the toner image is not formed and the toner image transferred to the intermediate transfer member are at the transfer position; Detecting means for detecting a current flowing from the voltage applying means to the intermediate transfer member; a voltage applied to the image carrier by the charging means based on a detection result by the detecting means; An image forming apparatus, comprising: control means for controlling at least one of voltages applied to a body.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

<First Embodiment> FIG. 1 is a schematic configuration diagram showing an image forming apparatus (a four-color full-color laser beam printer in this embodiment) according to the present embodiment.

This image forming apparatus is a rotating drum type electrophotographic photosensitive member (hereinafter, referred to as a photosensitive drum) as an image carrier.
1 is provided. Around the photosensitive drum 1, a charging roller 2 as a charging unit and an exposure device (laser scanning unit)
3, a developing device 4, an intermediate transfer drum 6, which is an intermediate transfer body,
A cleaning device 7 is provided. Further, a secondary transfer belt 8 and a fixing device 9 are arranged in order from the upstream side in the transport direction of the transfer material P such as paper. Intermediate transfer drum 6
An intermediate transfer drum cleaning roller 10 is provided on the outer periphery of the printer 1, and a density detection sensor 11 for controlling density is provided so as to face the surface of the intermediate transfer drum 6.

As shown in FIG. 2, the photosensitive drum 1 has a cylindrical base 1b made of an aluminum cylinder having a thickness of 1 mm.
An organic photosensitive layer 1a using polycarbonate as a main binder is formed on the outer peripheral surface of the substrate, and has an outer diameter of 30 mm. In a normal image forming process, the photosensitive drum 1 has an arrow a at a peripheral speed of 100 mm / sec.
It is driven to rotate in the direction (counterclockwise).

The photosensitive layer has a charge transport layer (CT) as a surface layer.
Layer) and a charge generation layer inside the layer).
The layer preferably has a volume resistivity of 10 ¹² to 10 ¹⁵ Ω · cm.
Therefore, the volume resistivity of the entire photosensitive layer is 10 ¹² to 10 ¹⁵ Ω · c.
m is preferred.

A method for measuring the volume resistivity will be described with reference to FIG. As shown, conductive sheet with area S (aluminum, etc.)
Is applied to the surface of the photoreceptor, a predetermined voltage is applied between the conductive sheet and the substrate 1b, and a current value I flowing at that time is obtained by the following equation.

Here, the applied voltage V was 1000 V, and the measurement environment was 23 ° C. and 60% RH.

[0016]

[Outside 1] t: thickness of photosensitive layer

The charging roller 2 is disposed in contact with the surface of the photosensitive drum 1 and is driven to rotate. When a predetermined charging bias is applied to the charging roller 2 from a primary charging power source 14, the photosensitive drum 1 has a predetermined polarity and potential. (For example, -550 V). In this embodiment, a voltage obtained by superimposing an AC voltage and a DC voltage is applied.

The exposure device 3 forms an electrostatic latent image by performing exposure with laser light on the charged photosensitive drum 1 in accordance with input image information. In the present embodiment,
The unexposed portion (dark portion potential) on the surface of the photosensitive drum 1 after the exposure was set to about -550 V, and the exposed portion potential was set to about -180 V.

The developing device 4 includes a yellow (Y) developing device 4
a, cyan (C) developing device 4b, magenta (M) developing device 4
c and a black (Bk) developing device 4d. The yellow (Y) developing device 4a, the cyan (C) developing device 4b, and the magenta (M) developing device 4c are mounted on the rotating body 5, and the rotating driving device (not shown) moves the rotating body 5 in the direction of the arrow b (not shown). By the clockwise rotation, the yellow (Y) developing device 4a, the cyan (C) developing device 4b, and the magenta (M) developing device 4c are arranged at positions facing the photosensitive drum 1 in the developing process. The black (Bk) developing device 4d is fixedly arranged. The toner is adhered to the electrostatic latent image formed on the photosensitive drum 1 by the developing devices 4a, 4b, 4c, and 4d and developed as a toner image. In the present embodiment, a developing bias of about -350 V is applied to each of the developing units 4a, 4b, 4c, and 4d, and the exposed portion potential portion on the surface of the photosensitive drum 1 is developed with a negatively chargeable negative toner. Visualize the latent image.

The cleaning device 7 has a cleaning blade, and scrapes off the primary transfer residual toner remaining on the photosensitive drum 1 without being primarily transferred to the intermediate transfer drum 6 by the cleaning blade.

The intermediate transfer drum 6 includes a primary transfer nip N
, And further contacts the surface of the secondary transfer belt 8 at the secondary transfer nip M, and rotates in the direction of arrow c (clockwise). A primary transfer bias power supply 15 as a transfer unit is connected to the intermediate transfer drum 6, and a predetermined primary transfer bias (in this embodiment, a predetermined transfer bias) is applied from the primary transfer bias power supply 15 to a core metal (not shown) of the intermediate transfer drum 6. +200 V) is applied, and the toner image on the photosensitive drum 1 is thereby subjected to a potential difference (750 V) between the photosensitive drum 1 and the intermediate transfer drum 6 at the primary transfer nip N.
Is primarily transferred onto the intermediate transfer drum 6.

The intermediate transfer drum 2, as shown in FIG.
An elastic resistance layer 6a made of silicon rubber having a thickness of 5 mm is formed on the outer peripheral surface of a cylindrical base 6b formed of an aluminum cylinder having a thickness of 3 mm.
Has a resistance value adjusted to 10 ⁵ to 10 ¹² Ωcm by dispersing carbon of conductive particles in silicon rubber. The outer diameter of the intermediate transfer drum 6 is 100 mm, and the hardness of the elastic resistance layer 6a is 30 ° (JIS A). Further, the intermediate transfer drum 2 is provided with a pressing unit (not shown).
As a result, the photosensitive drum 1 is pressed against the photosensitive drum 1 at a total pressure of 500 gf, and is rotated at a peripheral speed substantially equal to the peripheral speed of the photosensitive drum 1.

The overall volume resistivity of the intermediate transfer member is 10 ⁵ to
It is preferably 10 ⁹ Ω · cm.

The measuring method is based on JIS K6911,
The measurement environment is 23 ° C. and 60% RH. Note that the applied voltage may be set as appropriate.

The secondary transfer belt 8 includes a secondary transfer roller 12
And the drive roller 13 is extended and suspended, and the upper surface of the belt is rotated in the direction of arrow d by the rotational drive of the drive roller 13. The secondary transfer belt 8 is provided so as to be able to contact and separate from the intermediate transfer drum 6. Further, a secondary transfer bias power supply (not shown) is connected to the secondary transfer roller 12, and applies a predetermined secondary transfer bias to the secondary transfer roller 12.

The fixing device 9 has a fixing roller 9a and a pressure roller 9b.
While the transfer material P having the unfixed toner image transferred to the fixing nip portion is sandwiched and conveyed, the transfer material P is heated and pressed to fix the toner image.

A bias power supply (not shown) is connected to the charging roller 10 for the intermediate transfer drum, and removes secondary transfer residual toner remaining on the surface of the intermediate transfer drum 6 without being transferred to the transfer material P. The intermediate transfer drum cleaning roller 10 charges the secondary transfer residual toner on the intermediate transfer drum 6 to the opposite polarity (plus) to the normal charge polarity of the toner. The untransferred toner is a toner image on the intermediate transfer drum 6 of the photosensitive drum 1.
Simultaneously with the primary transfer upward, the toner is transferred from the intermediate transfer drum 6 to the photosensitive drum 1 and removed by the cleaning device 7.

The density detecting sensor 11 has a light emitting unit and a light receiving unit (not shown), and detects a density detecting toner image (not shown) transferred from the photosensitive drum 1 onto the surface of the intermediate transfer drum 6. Light emitting unit (not shown) of the density detection sensor 11
Irradiates a spot light from the light source, receives the reflected light by a light receiving unit (not shown), and detects the density based on the received light amount. The density detection sensor 11 includes a control device (CP
U) 17 is connected.

As shown in FIG. 2, the intermediate transfer drum 6 detects a value of a current (primary transfer current) flowing when a primary transfer bias is applied to the intermediate transfer drum 6 from a primary transfer bias power supply 15. Device 16 is connected.

The control device 17 changes the image forming conditions such as the developing bias of the developing device 4 based on the received light amount information input from the density detecting sensor 11 and controls the image density to be appropriate.

In the present embodiment, the control device 17 controls the primary charging power supply 14 so that the value of the current (primary transfer current) flowing between the photosensitive drum 1 and the intermediate transfer drum 6 becomes equal to or less than a predetermined value. The control is performed such that the charging potential of the photosensitive drum 1 is set to a predetermined value (details will be described later).

Next, an image forming operation of the above-described image forming apparatus will be described.

At the time of image formation, the photosensitive drum 1 is driven to rotate at a predetermined peripheral speed (process speed) in the direction of the arrow.
It is charged to a predetermined polarity and potential by the charging roller 2 to which a predetermined charging bias has been applied from the primary charging power supply 14.

The charged photosensitive drum 1 is subjected to image exposure by a laser beam by the exposure device 3 to form an electrostatic image corresponding to a first color component image (for example, a yellow component image) of a target color image. A latent image is formed. Next, the electrostatic latent image is developed by a yellow (Y) developing unit 4a with a first color yellow toner.

The first first member formed and supported on the photosensitive drum 1
In the process of passing through the primary transfer nip N between the photosensitive drum 1 and the intermediate transfer drum 6, the yellow toner image of the color, the pressure at the primary transfer nip N and the primary transfer bias power supply 15 (constant voltage power supply) By an electric field formed by a primary transfer bias applied to the intermediate transfer drum 6 (the primary transfer bias is controlled at a constant voltage), primary transfer (intermediate transfer) is performed on the outer peripheral surface of the intermediate transfer drum 6.

The primary transfer residual toner remaining on the photosensitive drum 1 after the primary transfer of the yellow toner image is removed by the cleaning device 7 and used for forming a toner image of the next color.

Thereafter, similarly, the magenta (M) developing device 4
b, a second color magenta toner image, a third color cyan toner image, and a fourth color black formed and carried on the photosensitive drum 1 by a cyan (C) developing unit 4c and a black (Bk) developing unit 4d, respectively. The toner images are sequentially transferred to the intermediate transfer drum 6
A composite color toner image corresponding to the target color image is formed superimposed thereon.

At this time, the primary transfer bias applied from the primary transfer bias power supply 15 for sequentially superimposing transfer of the first to fourth color toner images from the photosensitive drum 1 to the intermediate transfer drum 6 has a polarity opposite to that of the toner. (Positive polarity). The secondary transfer belt 8 and the intermediate transfer drum cleaning roller 10 are separated from the intermediate transfer drum 6 in the process of sequentially superimposing and transferring the toner images of the first to fourth colors from the photosensitive drum 1 to the intermediate transfer drum 6. .

Then, a transfer material P such as paper is fed at a predetermined timing according to the leading end of the composite color toner image on the intermediate transfer drum 6.

Then, at the timing when the transfer material P passes through the paper feed path to the secondary transfer nip M, the secondary transfer belt 8 is moved from the separated position so as to contact the intermediate transfer drum 6, and the secondary transfer is performed. A predetermined secondary transfer bias is applied to the secondary transfer roller 12 by a bias power supply (not shown), and the composite color toner image is collectively and secondarily transferred onto the transfer material P.

The transfer material P on which the composite color toner image has been transferred is separated in curvature downstream of the secondary transfer belt 8 in the transport direction, and is fixed to the fixing roller 9 a and the pressure roller 9 of the fixing device 9.
b, and is heated and pressurized, and the composite color toner image is fixed on the surface and output.

The secondary transfer residual toner remaining on the intermediate transfer drum 6 without being subjected to the secondary transfer is converted to a positive polarity by the charging roller 10 for the intermediate transfer body to which the bias is applied, and the photosensitive drum 1 And the surface of the intermediate transfer drum 6 is cleaned. The secondary transfer residual toner transferred onto the photosensitive drum 1 is thereafter collected by the cleaning device 5.

Next, the control for preventing the occurrence of the retransfer will be described. In the present embodiment, the photosensitive drum 1
Was set to a predetermined value.

(1) In the control mode in which no image is formed (non-image formation), the secondary transfer belt 8 and the charging roller 1
0 is separated from the intermediate transfer drum 6, a first color yellow image (maximum density image) is formed on the photosensitive drum 1 over the entire thrust width, and is primarily transferred to the intermediate transfer drum 6.

(2) Assuming the primary transfer process of the magenta toner image of the second color, the surface of the photosensitive drum 1 is uniformly charged to the dark portion potential Vd [V] by the charging roller 2, and a primary transfer bias power supply is provided. A DC bias controlled to a predetermined voltage value Vt [V] by the constant voltage control 15 is applied to the intermediate transfer drum 6, and a primary transfer current (DC current) value I generated at this time is applied.
tm [μA] is detected by the current value detection device 16. When the primary transfer current value Itm is detected by the current value detection device 16, the intermediate transfer drum 6 is in contact with the photosensitive drum 1 via the yellow toner. At this time, a magenta image is not actually formed, but only a DC bias is applied.

(3) Third color cyan toner image and fourth color
Assuming the primary transfer process of the black toner image of the color similarly, the surface of the photosensitive drum 1 is uniformly charged to the dark portion potential Vd [V] by the charging roller 2, and a predetermined voltage value is set by the primary transfer bias power supply 15. A DC bias controlled at a constant voltage of Vt [V] is applied to the intermediate transfer drum 6, and the primary transfer current values Itc and Itk [μA] generated at this time are detected by the current value detection device 16. At this time, similarly, cyan and black images are not formed, and only a DC bias is applied.

The above (1) to (3) constitute one set of current measurement. In (1) to (3), Vd was set to, for example, -600 V, and Vt was set to, for example, 300 V.

(4) By changing the above Vd, the above (1) to
Repeat (3).

For example, Vd = −550 V, −500 V,
The DC current values Itm, Itc and Itk when changing to -450V, -400V and -350V are measured sequentially.

(5) Itm, Itc, It of each Vd
Of Vd in which k is equal to or less than Ith, Vd having the largest absolute value is set as the dark portion potential Vd of the photosensitive drum 1 during image formation.

For example, when Ith is 1 μA and the measurement result is Vd = −600 V, Itm = 20 μA, Itc = 21 μA, Itk = 22 μ
A Vd = −550 V, Itm = 12 μA, Itc = 13 μA, Itk = 14 μ
A When Vd = -500 V, Itm = 5 μA, Itc = 6 μA, Itk = 7 μA When Vd = −450 V, Itm = 1 μA, Itc = 1 μA, Itk = 2 μA When Vd = −400 V, Itm = 0 μA, Itc = 0 μA, Itk = 1 μA When Vd = −350 V, When Itm = 0 μA, Itc = 0 μA, Itk = 0 μA, all of Itm, Itc and Itk are Ith
Vd of = 1 μA or less is −400 V. At this time, the dark portion potential Vd of the photosensitive drum 1 during image formation is set to −400 V.

(6) Photosensitive drum 1 determined in (5) above
The density control is performed at the dark portion potential Vd.

In the density control, the density of a toner image (patch pattern) for density detection (not shown) formed on the intermediate transfer drum 6 is detected by the density detection sensor 11, and the density detection toner detected by the density detection sensor 11 is detected. Based on the density information of the image, a developing bias Vdc that provides an optimum density
Is determined by controlling the control device 17 to determine.

According to the study of the present inventor, as shown in FIG. 3, it is known that when the primary transfer current flowing from the primary transfer bias power supply 15 to the intermediate transfer drum 6 increases, the amount of toner for retransfer also increases. The amount of the toner for retransfer can be quantitatively measured by measuring the weight, or by peeling off the tape and attaching it to a transfer material and measuring the reflection density. In FIG. 3, “good” of retransfer on the vertical axis indicates that retransfer is small, and “bad” indicates that retransfer is large.

As described above, in the present embodiment, the charging bias by the primary charging power supply 14 is controlled to make the charging potential (dark portion potential) Vd of the photosensitive drum 1 about -400 V, so that the photosensitive drum 1 and the intermediate transfer drum By setting the primary transfer current value Ith flowing between them to 1 μA, the amount of retransfer can be reduced, and an output image without a decrease in density can be obtained.

In this embodiment, Ith = 1 μA
However, preferably, the primary transfer current value Ith = 0 μA further reduces retransfer.

The selection of the dark portion potential Vd of the photosensitive drum 1 whose absolute value is the largest when the primary transfer current Ith is equal to or less than a predetermined value is based on the contrast potential (developing biases _VDC and _VL).
And the fog potential (difference between V _D and developing bias V _DC ). As a result, the gradation of the output image can be ensured, and fogging can be suppressed.

<Embodiment 2> This embodiment will also be described using the image forming apparatus shown in FIG. In the present embodiment, since the image forming operation is the same as that in the first embodiment, only the control for preventing the occurrence of retransfer will be described. In the present embodiment, the primary transfer potential of the intermediate transfer drum 6 is set to a predetermined value.

(1) In the control mode in which no image is formed (non-image formation), the secondary transfer belt 8 and the charging roller 1
0 is separated from the intermediate transfer drum 6, a first color yellow image is formed on the photosensitive drum 1 over the entire width of the thrust, and primary-transferred to the intermediate transfer drum 6.

(2) Assuming the primary transfer process of the magenta toner image of the second color, the surface of the photosensitive drum 1 is uniformly charged to the dark portion potential Vd [V] by the charging roller 2, and the primary transfer bias power supply 15 is a predetermined voltage value (detection voltage)
A DC bias controlled at a constant voltage of Vt [V] is applied to the intermediate transfer drum 6, and the primary transfer current I
tm [μA] is detected by the current value detection device 16. When the primary transfer current value Itm is detected by the current value detection device 16, the intermediate transfer drum 6 is in contact with the photosensitive drum 1 via the yellow toner. At this time, a magenta image is not actually formed, but only a DC bias is applied.

(3) Third color cyan toner image and fourth color
Assuming the primary transfer process of the black toner image of the color similarly, the surface of the photosensitive drum 1 is uniformly charged to the dark portion potential Vd [V] by the charging roller 2, and a predetermined voltage value is set by the primary transfer bias power supply 15. A DC bias controlled at a constant voltage of Vt [V] is applied to the intermediate transfer drum 6, and the primary transfer current values Itc and Itk [μA] generated at this time are detected by the current value detection device 16. At this time, similarly, cyan and black images are not formed, and only a DC bias is applied.

The above (1) to (3) constitute one set of current measurement. In addition, in (1) to (3), Vd is, for example, −6.
00V and Vt were set to, for example, 300V.

(4) By changing Vt [V], the above (1)
Repeat (3).

For example, Vt = 250V, 200V, 15
DC current value It when changing to 0V, 100V, 50V
m, Itc and Itk are sequentially measured.

(5) Itm, Itc, It of each Vt
Of the Vd in which k is equal to or less than the Ith, Vt having the maximum absolute value is set as the primary transfer potential Vd at the time of image formation.

For example, when Ith is 1 μA and the measurement result is Vt = 300 V, Itm = 20 μA, Itc = 21 μA, Itk = 22 μ
When A Vt = 250 V, Itm = 12 μA, Itc = 13 μA, Itk = 14 μ
A When Vt = 200 V, Itm = 5 μA, Itc = 6 μA, Itk = 7 μA When Vt = 150 V, Itm = 1 μA, Itc = 1 μA, Itk = 2 μA When Vt = 100 V, Itm = 0 μA, Itc = 0 μA, Itk = 1 μA Vt = 50 V, Itm = 0 μA, Itc = 0 μA, Itk = 0 μA, Itm, Itc, Itk is all of Ith
Vt below = 1 μA is 100V. At this time, the primary transfer potential Vt at the time of image formation is set to 100V.

(6) Density control is performed with the primary transfer potential Vt determined in (5).

In the density control, the density of a density detection toner image (patch pattern) (not shown) formed on the intermediate transfer drum 6 is detected by the density detection sensor 11, and the density detection toner detected by the density detection sensor 11 is detected. Based on the density information of the image, a developing bias Vdc that provides an optimum density
Is determined by controlling the control device 17 to determine.

As described above, in this embodiment, by setting the primary transfer potential Vt of the intermediate transfer drum 6 to 100 V, the primary transfer current value Ith flowing between the photosensitive drum 1 and the intermediate transfer drum 6 is reduced to 1 μA. As a result, the amount of retransfer can be reduced, and an output image without a decrease in density can be obtained. In the present embodiment, Ith = 1 μA in the present embodiment, but preferably, Ith = 1 μA.
0 μA results in less retransfer.

In the present embodiment, the above-mentioned density control (6) need not always be performed.

The reason why It is equal to or smaller than a predetermined value and Vt having the maximum absolute value is selected is to maintain transferability. This is because when the transfer potential is lowered, the transfer efficiency is slightly lowered.

<Embodiment 3> This embodiment will also be described using the image forming apparatus shown in FIG. In the present embodiment, since the image forming operation is the same as that in the first embodiment, only the control for preventing the occurrence of retransfer will be described. In this embodiment, the charging bias (the charging potential of the photosensitive drum 1) by the primary charging power supply 14 and the primary transfer voltage of the intermediate transfer drum 6 are set to predetermined values.

The operations (1) to (3) of the first and second embodiments are performed in the same manner, and the charging bias (the charging potential of the photosensitive drum 1) by the primary charging power source 14 and the primary transfer of the intermediate transfer drum 6 are performed. The voltage was varied. That is, when Vd = -600V, Vt = 300V, 250V, 200V, 150V, 10
0 V, 50 V When Vd = −550 V, Vt = 300 V, 250 V, 200 V, 150 V, 10
0 V, 50 V When Vd = -500 V, Vt = 300 V, 250 V, 200 V, 150 V, 10
0 V, 50 V When Vd = −450 V, Vt = 300 V, 250 V, 200 V, 150 V, 10
0 V, 50 V When Vd = -400 V, Vt = 300 V, 250 V, 200 V, 150 V, 10
0 V, 50 V When Vd = -350 V, Vt = 300 V, 250 V, 200 V, 150 V, 10
The test was performed in 36 ways of 0V and 50V.

Among the above combinations, Embodiments 1 and 2
Similarly, all of Itm, Itc, and Itk have a predetermined value of It.
Select the Vd and Vt settings below h. Vd is selected so that the variable amounts of Vd and Vt do not change Vt as much as possible.
This is to maintain transferability.

As described above, in the present embodiment, Vd, Vt
Are both variable, the primary transfer current value Ith flowing between the photosensitive drum 1 and the intermediate transfer drum 6 is set to a predetermined value or less, whereby the retransfer amount can be more effectively reduced, and the density reduction No output images can be obtained.

In the first and second embodiments,
Itm, Itc, Itk by forming only yellow solid image
Is detected because the first color is yellow, and this is not the case when the color order is different. That is, an image of the first color is formed, and a current flowing at that time may be detected assuming a primary transfer process of the second to fourth colors.

After the transfer of the toner image, the toner image
As the number of times of passing through the next transfer portion N increases, the number of times of retransfer increases, and the toner amount of the first color toner image on the intermediate transfer drum 6 decreases. <Itk. For this reason, it is simpler to perform the above-described control by detecting only Itk, and in some cases, the effect on retransfer may be sufficiently obtained.

On the other hand, although complicated, a toner image of the second color may be formed to detect the current at the time of the primary transfer of the third color and the fourth color, or the toner image of the third color may be formed. An image may be formed to detect a current at the time of primary transfer of the fourth color. At this time,
A plurality of colors may be formed at different positions in the main scanning direction on the intermediate transfer drum 6 and currents of a plurality of colors may be detected at once by changing the timing in one image formation. Becomes shorter.

Further, the image formed during the control is a full-width thrust image, but if it is fixed for each control such as halftone, gradation patch, secondary color, and tertiary color,
Not limited to this.

When changing the values of Vd and Vt, 1
The current may be detected by setting a plurality of Vd and Vt at different timings in the image formation, and the tact time of this control can be shortened.

Further, the charged potential of the photosensitive drum 1 and the primary transfer potential of the intermediate transfer drum 6 can be monitored with an electrometer and fed back to control with higher precision.

In some cases, an upper limit is set for the absolute value of the difference between Vd and Vt, and the above-described control is performed within the upper limit.

The values of Vd, VL, and Vt are not limited to the present embodiment, and the same effects can be obtained by optimizing the respective systems.

<Embodiment 4> FIG. 4 is a schematic configuration diagram showing an image forming apparatus according to the present embodiment. FIG.
The same members as those of the image forming apparatus according to the first embodiment are denoted by the same reference numerals, and overlapping description will be omitted.

Since retransfer is likely to occur in a high-temperature, high-humidity environment, in this embodiment, a temperature / humidity detecting sensor 18 is provided in the image forming apparatus as shown in FIG. Is input to the control device 17. Control device 1
Reference numeral 7 denotes a case where the temperature and humidity are high and high based on the input temperature and humidity information (for example, a temperature of 30 ° C. and a humidity of 80%).
In addition, the charging bias (the charging potential of the photosensitive drum 1) and / or the primary transfer voltage by the primary charging power supply 14 are set to predetermined values, as in the control for preventing the occurrence of retransfer in the first, second and third embodiments. I did it.

As described above, also in this embodiment, the amount of retransfer can be reduced, and an output image without a decrease in density can be obtained.

<Embodiment 5> FIG. 5 is a schematic configuration diagram showing an image forming apparatus according to the present embodiment. FIG.
The same members as those of the image forming apparatus according to the first embodiment are denoted by the same reference numerals, and overlapping description will be omitted.

In the present embodiment, the retransfer is likely to occur as the photosensitive drum is durable and the film pressure of the photosensitive layer (that is, the CT layer) decreases, so in this embodiment, as shown in FIG. Life detection sensor 19 (membrane pressure detection sensor)
And inputs the detected photosensitive drum life information to the control device 17. The control device 17 turns on / off the control for preventing the occurrence of retransfer in the first, second, and third embodiments according to the progress of the life of the photosensitive drum 1 based on the inputted photosensitive drum life information.
By turning off, the primary transfer current value Ith flowing between the photosensitive drum 1 and the intermediate transfer drum 6 is set to a predetermined value or less.

As described above, also in the present embodiment, the amount of retransfer can be reduced, and an output image without a decrease in density can be obtained.

The temperature and the temperature in Embodiments 4 and 5
Humidity control and control based on the life of the photosensitive drum 1 are performed by reducing the electric resistance of the photosensitive drum 1 and the intermediate transfer drum 6 in a high-temperature and high-humidity environment, and by scraping the photosensitive layer of the photosensitive drum 1 due to durability of the photosensitive drum 1 This is because the current during the primary transfer increases due to a decrease in the electrical resistance and the like, and is not limited to the configuration of the image forming apparatus.

<Embodiment 6> FIG. 6 is a schematic configuration diagram showing an image forming apparatus according to the present embodiment. FIG.
The same members as those of the image forming apparatus according to the first embodiment are denoted by the same reference numerals, and overlapping description will be omitted.

In the present embodiment, as shown in FIG. 6, a toner image reflection density sensor 20 is provided opposite to the surface of the intermediate transfer drum 6 to control the detected reflection density information of the toner image before the secondary transfer. Enter 17. The controller 17 determines whether or not retransfer has occurred based on the input reflection density information of the toner image. If it is determined that retransfer has occurred, the controller 17 according to the first to fifth embodiments will be described. Is turned on / off so that the primary transfer current value Ith flowing between the photosensitive drum 1 and the intermediate transfer drum 6 is set to a predetermined value or less.

As described above, also in the present embodiment, the amount of retransfer can be reduced, and an output image without a decrease in density can be obtained.

In each of the above-described embodiments, the intermediate transfer drum has been described as an example of the intermediate transfer member. However, the present invention is not limited to a drum-shaped intermediate transfer member, but may be a belt-shaped intermediate transfer member. But the effect is the same.

<Seventh Embodiment> The present invention is also applicable to a tandem type image forming apparatus provided with a plurality of image forming units as shown in FIG. In FIG. 7, the same members as those in Examples 1 to 6 are denoted by the same reference numerals, and description thereof will be omitted.
The image forming apparatus will be briefly described. Toner images sequentially formed on the photosensitive drums 1a to 1d are sequentially superimposed on the intermediate transfer belt 35 by a power source (not shown) as a transfer unit and transfer blades (30a to 30d). Is transcribed. Thereafter, at the timing when the toner image is conveyed, the transfer material P is fed, and the toner image is electrostatically transferred from the intermediate transfer belt to the transfer material by the secondary transfer roller 33.

In the present embodiment, the volume resistivity of the intermediate transfer member and the photoreceptor is the same as in the first to sixth embodiments, and the volume resistivity of the transfer blade as the transfer means is smaller than 10 ⁵ Ω · cm. Is preferred. The measurement method is JIS K6911
The measurement environment was 23 ° C., 60 & RH. Note that the applied voltage may be set as appropriate.

That is, the same applies to the above-described first to sixth embodiments, but the present invention relates to the actual resistance value of the photosensitive member (the current flowing when a certain voltage (current) is applied (the generated voltage)).
Is determined in a system in which the resistance value of the intermediate transfer member (and the transfer blade) is 1/10 or less of the actual resistance value of the intermediate transfer member (and the transfer blade). Can be.

In such an image forming apparatus, the present invention is particularly effective, because the manufacturing error and the degree of deterioration (sharpness) of the photosensitive drum may be different.

That is, also in this image forming apparatus, similarly to Embodiments 1 to 6, the charging bias (the charging potential of the photosensitive drums 1a to 1d) and / or the transfer blades 30a to 30d by the primary charging power supplies 2a to 2d are changed. Via the intermediate transfer belt 3
5 is controlled by the control device.

Therefore, even in the present image forming apparatus, it is possible to obtain an output image without a decrease in density, that is, without color unevenness.

In the present embodiment, an intermediate transfer belt has been described as an example of the intermediate transfer member, but the present invention is not limited to this, and a drum-shaped intermediate transfer belt may be used.

In the above-described first to seventh embodiments, non-image formation refers to a period from the input of an image formation start signal to the start of image formation (exposure) on the photosensitive drum, that is, the so-called pre-rotation. This indicates the time or the time of post-rotation after image formation. However, in some cases, the effect can be further improved by performing more strict control at the time of so-called sheet interval during continuous image formation.

The first to seventh embodiments described above may be appropriately combined as long as the effects of the present invention can be obtained.

[0104]

As described above, according to the present invention,
It is possible to prevent the toner image transferred on the intermediate transfer member from returning to the image carrier, and it is possible to obtain a good image without a decrease in density. Further, it is possible to prevent the toner image transferred to the intermediate transfer member from returning to the image carrier, and it is possible to obtain a good image without color fluctuation and density reduction.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an image forming apparatus according to Embodiments 1, 2, and 3 of the present invention.

FIG. 2 is a diagram showing a photosensitive drum and an intermediate transfer drum.

FIG. 3 is a diagram showing the relationship between primary transfer current and retransfer.

FIG. 4 is a schematic configuration diagram showing an image forming apparatus according to Embodiment 4 of the present invention.

FIG. 5 is a schematic configuration diagram showing an image forming apparatus according to Embodiment 5 of the present invention.

FIG. 6 is a schematic configuration diagram showing an image forming apparatus according to Embodiment 6 of the present invention.

FIG. 7 is a schematic configuration diagram showing another image forming apparatus to which the present invention can be applied.

FIG. 8 is a schematic configuration diagram showing a measurement method.

Claims (31)

[Claims] An image carrier, a charging unit for charging the image carrier, an image forming unit for forming a toner image on the image carrier charged by the charging unit, an intermediate transfer body,
Voltage applying means for applying a voltage to the intermediate transfer body to transfer the toner image on the image carrier formed by the image forming means to the intermediate transfer body at a transfer position,
In an image forming apparatus for transferring a toner image transferred to the intermediate transfer body to a transfer material by the voltage application unit, a voltage applied to the intermediate transfer body by the voltage application unit is controlled by a constant voltage; A voltage is applied to the intermediate transfer member, and a detection unit detects a current flowing from the voltage application unit to the intermediate transfer unit. The charging unit applies a voltage to the image carrier based on a detection result by the detection unit. And a control unit for controlling at least one of the applied voltage and the voltage applied to the intermediate transfer body by the voltage application unit. 2. The image carrier, which is charged by the charging unit and on which a toner image is not formed by the image forming unit, and the toner image transferred to the intermediate transfer member exists at the transfer position. The image forming apparatus according to claim 1, wherein the detection unit performs a detection operation during a period. 3. The method according to claim 1, wherein the control unit controls at least one of a voltage applied to the image carrier by the charging unit and a voltage applied to the intermediate transfer member by the voltage applying unit. The image forming apparatus according to claim 2, wherein the image forming apparatus is provided once. 4. A voltage applied to the image carrier by the charging device and a voltage applied to the intermediate transfer member by the voltage application device based on a plurality of detection results by the detection device. 4. The image forming apparatus according to claim 3, wherein at least one of the image forming apparatus is controlled. 5. The image forming apparatus according to claim 1, wherein said voltage applying means includes a constant voltage power supply. 6. The voltage applying means includes an electrode which is in contact with a side of the intermediate transfer body opposite to a side where a toner image is transferred,
The image forming apparatus according to claim 5, wherein the constant voltage power supply supplies a voltage to the electrodes. 7. When the voltage application unit transfers the toner image on the image carrier to the intermediate transfer body, the control unit determines a predetermined absolute value of a current flowing from the voltage application unit to the intermediate transfer body. The image forming apparatus according to claim 1, wherein the control is performed so as to be equal to or less than a value. 8. The image forming apparatus according to claim 7, wherein the predetermined value is 1 μA. 9. The control unit sets a difference between a voltage applied to the image carrier by the charging unit and a voltage applied to the intermediate transfer member by the voltage applying unit within a predetermined range. 9. The image forming apparatus according to claim 1, wherein the image forming apparatus controls the image forming apparatus. 10. The image forming apparatus has a potential detecting means for detecting a charged potential of the image bearing member, and the control means controls the image bearing by the charging means based on a detection result by the potential detecting means. The image forming apparatus according to claim 1, wherein a voltage applied to a body is controlled. 11. The image bearing member is charged by the charging means using a voltage value set by the control means,
11. The image forming apparatus according to claim 1, wherein a toner image is formed on the image carrier by the image forming unit. 12. The image according to claim 11, wherein the toner image on the image carrier is transferred to the intermediate transfer member by the voltage applying unit using a voltage value set by the control unit. Forming equipment. 13. The image forming apparatus according to claim 1, further comprising: a density detecting unit configured to detect a density of the toner image transferred onto the intermediate transfer body, wherein the control unit performs the control based on a detection result by the density detecting unit. 13. The image forming apparatus according to claim 12, wherein the density of a toner image formed on the image carrier is controlled by an image forming unit. 14. The image forming apparatus has temperature and humidity detecting means for detecting temperature and humidity in the apparatus, and the control means determines whether or not to perform a control operation in accordance with a result of detection by the temperature and humidity detecting means. The image forming apparatus according to claim 1, wherein the determination is performed. 15. The image forming apparatus has a life detecting unit for detecting a life of the image carrier, and the control unit performs a control operation according to a detection result by the life detecting unit. The image forming apparatus according to claim 1, wherein it is determined whether or not the image forming apparatus is in the image forming apparatus. 16. The image forming apparatus according to claim 15, wherein said life detecting means detects a thickness of a photosensitive layer of said image bearing member. 17. A plurality of image carriers, a plurality of charging units for respectively charging the plurality of image carriers, and a plurality of color toner images on the plurality of image carriers charged by the plurality of charging units. A plurality of image forming means for respectively forming, an intermediate transfer body, and a plurality of color toner images on the plurality of image carriers formed by the plurality of image forming means are sequentially transferred to the intermediate transfer body at each transfer position. A plurality of voltage applying means for applying a voltage to the intermediate transfer body to transfer in an overlapping manner,
In an image forming apparatus for transferring a plurality of color toner images transferred to the intermediate transfer body by the plurality of voltage applying units onto a transfer material, a voltage applied to the intermediate transfer body by the plurality of voltage applying units is a constant voltage. In the period in which the image carrier, which is charged by the charging unit, and on which the toner image is not formed by the image forming unit, and the toner image transferred to the intermediate transfer member are present at the transfer position, A voltage is applied to the intermediate transfer body by the voltage application unit, a detection unit that detects a current flowing from the voltage application unit to the intermediate transfer body, and Control means for controlling at least one of a voltage applied to the image carrier and a voltage applied to the intermediate transfer member by the voltage applying means. An image forming apparatus comprising. 18. The time period is provided for each of the transfer positions. The detecting means applies a voltage to the intermediate transfer body by the plurality of voltage applying means, and outputs the voltage from the plurality of voltage applying means to the intermediate transfer body. 18. The image forming apparatus according to claim 17, wherein a current value flowing through the body is detected. 19. The control unit includes: a plurality of voltages applied to the plurality of image carriers by the plurality of charging units based on a plurality of detection results obtained by the plurality of detection units; 19. The image forming apparatus according to claim 18, wherein at least one of the voltages applied to the body is controlled. 20. An image forming apparatus according to claim 17, wherein said voltage applying means includes a constant voltage power supply. 21. An apparatus according to claim 21, wherein said voltage applying means includes an electrode in contact with a side of said intermediate transfer member opposite to a side on which the toner image is transferred, and said constant voltage power supply supplies a voltage to said electrode. Item 21. The image forming apparatus according to Item 20. 22. The control unit, when transferring the toner image on the image carrier to the intermediate transfer member by the voltage application unit, determines a predetermined absolute value of a current flowing from the voltage application unit to the intermediate transfer member. 22. The image forming apparatus according to claim 17, wherein the control is performed so as to be equal to or less than a value. 23. The image forming apparatus according to claim 22, wherein the predetermined value is 1 μA. 24. The control unit controls a difference between a voltage applied to the image carrier by the charging unit and a voltage applied to the intermediate transfer member by the voltage applying unit to be within a predetermined range. 18. A control method according to claim 17, wherein
24. An image forming apparatus according to any one of claims 23 to 23. 25. The image forming apparatus has a plurality of potential detecting means for detecting charged potentials of the plurality of image carriers, respectively, and the control means controls the charging based on a detection result by the potential detecting means. The means controls the voltage applied to the image carrier. 26. The image carrier is charged by the charging means using a voltage value set by the control means,
26. The image forming apparatus according to claim 17, wherein a toner image is formed on the image carrier by the image forming unit. 27. The image according to claim 26, wherein the toner image on the image carrier is transferred to the intermediate transfer member by the voltage applying unit using a voltage value set by the control unit. Forming equipment. 28. The image forming apparatus according to claim 28, further comprising: a density detecting unit configured to detect a density of the toner image transferred onto the intermediate transfer body, wherein the control unit performs the control based on a detection result by the density detecting unit. 28. The image forming apparatus according to claim 27, wherein the density of a toner image formed on the image carrier is controlled by an image forming unit. 29. The image forming apparatus has temperature and humidity detecting means for detecting temperature and humidity in the apparatus, and the control means determines whether or not to perform a control operation in accordance with a result of detection by the temperature and humidity detecting means. 18. The method of claim 17, wherein the determining is performed.
29. An image forming apparatus according to any one of claims 28 to 28. 30. The image forming apparatus has a life detecting means for detecting a life of the image carrier, and the control means performs a control operation according to a detection result by the life detecting means. The image forming apparatus according to any one of claims 17 to 29, wherein the image forming apparatus determines whether or not the image forming apparatus determines whether or not the image forming apparatus determines whether or not the image forming apparatus is operating. 31. An image forming apparatus according to claim 30, wherein said life detecting means detects a thickness of a photosensitive layer of said image bearing member.