JP2001125392A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively prevent white-dot-like image void caused by gap discharge. SOLUTION: This image forming device is equipped with plural image carriers 1 (for example, 1a to 1d) on which a toner image T in accordance with image information is formed and carried, a recording feeding body 2 whose part opposed to each image carrier 1 is circularly fed, and plural transfer devices 3 (for example, 3a to 3d) transferring the toner image T formed on the image carrier 1 to the feeding body 2 directly or through recording material K. In the device, the final transfer device 3d corresponding to the final image carrier 1d disposed on the most downstream side in the moving direction of the feeding body 2 is equipped with a discharge preventing means 4 preventing discharge between the image carrier 1d and the feeding body 2.

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 an electrophotographic copying machine, and more particularly, to an image formed by a plurality of image carriers on a recording carrier directly or sequentially via a recording material. The present invention relates to an improvement of a so-called tandem type image forming apparatus for transferring.

[0002]

2. Description of the Related Art Conventionally, as an image forming apparatus of this type, for example, a plurality of image forming units are arranged in parallel, and an intermediate transfer belt circulating and moving along the arrangement direction of each image forming unit is arranged. After each color component (for example, yellow, magenta, cyan, and black) image (toner image) formed by the forming unit is sequentially primary-transferred to the intermediate transfer belt, the color superimposed image on the intermediate transfer belt is secondarily transferred onto paper as a recording material. There is already known a device in which the next transfer (collective transfer) is performed, and then an unfixed image is fixed on a sheet by a fixing device (for example, see Japanese Patent Application Laid-Open No. 10-260593).

In order to obtain a full-color image, for example, with this image forming apparatus, it is necessary to superimpose toner images of a plurality of colors. (Toner pile height) becomes high, and white spot-shaped image omission (hereinafter, referred to as white spot omission) may occur around this image. This is due to a hollow character in which primary transfer cannot be physically performed due to a high toner pile height in an image portion, and a gap discharge in which primary transfer cannot be performed electrostatically. Here, for the former physical hollow character, as described in Japanese Patent Application Laid-Open No. H8-211755,
Techniques such as applying a lubricant to the surface of the intermediate transfer member have been proposed.

[0004]

However, studies on the latter countermeasures against gap discharge have been delayed, and no effective method has been established so far.

The present invention has been made to solve the above technical problem, and provides an image forming apparatus capable of effectively preventing white spot-like image omission due to gap discharge. is there.

[0006]

That is, as shown in FIG. 1, the present invention provides a plurality of image carriers 1 (for example, 1a to 1d) on each of which a toner image T corresponding to image information is formed and carried. A recording carrier 2 circulated and conveyed at a portion facing each image carrier 1 and a toner image T formed on each image carrier 1 transferred to the recording carrier 2 directly or via a recording material K; In an image forming apparatus provided with a plurality of transfer devices 3 (for example, 3a to 3d), a final transfer device 3d corresponding to a final image carrier 1d disposed on the most downstream side in the moving direction of the recording transport body 2 includes: A discharge preventing means 4 for preventing a discharge between the final image carrier 1d and the recording and conveying member 2.

In such technical means, the image forming apparatus to which the present invention is applied is of a so-called tandem type in which a plurality of image carriers 1 are arranged in parallel. As a method of forming the toner image T on the image carrier 1, an electrophotographic method, an electrostatic recording method, or the like is used, and the image transfer to the recording material 2 directly or to the recording material K on the recording material 2 is performed. As for the method, a method of transferring the toner image T formed on the image carrier 1 to the recording conveyance body 2 or the recording material K via the transfer device 3, such as an electrophotographic method or an electrostatic recording method, is used. In FIG. 1, the toner image transfer device 3 formed on the image carrier 1 sequentially transfers the toner image onto a recording carrier 2 (intermediate transfer member), and collectively transfers images superimposed on the recording carrier 2. An image forming apparatus in which transfer is collectively transferred to a recording material K via an apparatus 5 is illustrated. Then, the recording carrier 2
Is not limited to the embodiment as the intermediate transfer member shown in FIG. 1, but also includes a conveying member for carrying and conveying the recording material K. Here, regarding the specific mode of the recording conveyance body 2,
It does not matter whether it is a belt shape or a drum shape. For example, as shown in FIG. 1, in a so-called tandem type in which a plurality of image carriers 1 are arranged in parallel, from the viewpoint of the arrangement of the image carriers 1 and image alignment, A belt-shaped recording transport body 2 is often used.

Further, as the transfer device 3, for example, a contact transfer device such as a transfer roll or a non-contact transfer device such as a corotron may be appropriately selected.

In the case where the transfer device 3 is provided with a transfer roll that comes into contact with the recording and conveying member 2, the discharge prevention means 4 is connected to the final image carrier 1d and the final transfer device 3d. The transfer nip width formed between the transfer nip and the other transfer nip is set to be larger than the other transfer nip widths, so that the electric field per unit area of the transfer nip area between the final image carrier 1d and the final transfer device 3d is increased. Is reduced, and discharge is prevented accordingly.

As a specific embodiment, for example, the outer diameter of the transfer roll of the final transfer device 3d is made larger than that of the other transfer rolls, or the hardness of the transfer roll of the final transfer device 3d is made different from that of the other transfer rolls. Or smaller.

[0011] Further, by making the discharge preventing means 4 a bias applied to the final transfer device 3d smaller than that of the other transfer devices, the transfer between the final image carrier 1d and the final transfer device 3d can be performed. The electric field per unit area of the nip area is reduced, and accordingly, discharge is prevented.

[0012] From the viewpoint of preventing discharges caused by fluctuations in environmental conditions, the amount of bias applied to each of the transfer devices is reduced under conditions where the ambient temperature is low or the ambient humidity is low. It is preferable to provide a bias control unit.

Further, the transfer device 3 is used to
In the embodiment having a transfer roll that is disposed in contact with the transfer roll, from the viewpoint of preventing discharge generated due to the resistance change of the transfer roll, the resistance value of the transfer roll is a predetermined resistance value It is preferable to provide a bias control unit that reduces the amount of bias applied to each of the transfer rolls under a condition exceeding the condition.

The order in which the toner images are formed may be selected as appropriate, but from the viewpoint of obtaining a better image, the toner image T formed on the final image carrier 1d may be black toner. Preferably, it is an image.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the accompanying drawings. First Embodiment FIG. 2 shows a first embodiment of a color image forming apparatus to which the present invention is applied. In FIG. 1, a color image forming apparatus according to the present embodiment includes a plurality of image forming units 100 (specifically, 100Y, 100M, 100C, and 100K) on which respective color component toner images are formed by an electrophotographic method.
And an intermediate transfer belt 110 as a recording and transporting body for sequentially transferring (primary transfer) each color component toner image formed by each image forming unit 100, and an intermediate transfer belt 11
A batch transfer device 120 that batch-transfers (secondarily transfers) the superimposed image transferred onto the sheet P to a sheet P as a recording material, and a fixing device 150 that fixes the batch-transferred image onto the sheet P.
It is provided with.

In this embodiment, the image forming units 100 for the respective color components are arranged in the order from the upstream side in the conveying direction B of the intermediate transfer belt 110 to the yellow image forming unit 100Y, magenta image forming unit 100M, cyan image forming unit 100C, and black image forming unit. The forming units 100K are arranged in this order. Then, each image forming unit 10
0 denotes a uniform charging device 102 on which the photosensitive drum 101 is charged, and an electrostatic latent image is written on the photosensitive drum 101, around the photosensitive drum 101 as an image carrier rotating in the direction of arrow A. Laser exposure device 103 (indicated by an exposure beam Bm in the figure), and a developing device 10 in which toners of respective color components are stored and an electrostatic latent image on the photosensitive drum 101 is visualized.
4. For electrophotography, such as a primary transfer roll 105 as a transfer device for transferring each color component toner image on the photosensitive drum 101 to the intermediate transfer belt 110 and a drum cleaner 106 for removing residual toner on the photosensitive drum 101 Devices are sequentially arranged.

The primary transfer roll 105 of each image forming unit 100 (specifically, 105Y, 105M, 1M)
As shown in FIG. 3, transfer bias power supply 107 (specifically, 107C and 105K) to which a DC bias having a polarity opposite to the electrode resistance of the toner (positive in the present embodiment) is applied. , 107M, 107C, 107K). Each of these transfer bias power supplies 107
The voltage applied to each primary transfer roll 105 can be varied, and a constant current (30 μA in the present embodiment) is applied to each primary transfer roll 105.

Further, as shown in FIG. 2, the intermediate transfer belt 110 is stretched around a plurality of (five in this embodiment) support rolls 131 to 135. Here, the support roll 131 is a drive roll of the intermediate transfer belt 110, the support roll 132 is a driven roll, the support roll 133 is a tension roll for adjusting the tension of the intermediate transfer belt 110, and the support roll 134 is a collective transfer device 120 as described later. Backup roll.

The intermediate transfer belt 110 is made of a resin such as polyimide or polyamide containing an appropriate amount of an antistatic agent such as carbon black, and has a volume resistivity of 10 ¹⁰ to 10 ¹³ Ω · cm. The thickness is set to, for example, 0.1 mm.

Further, the collective transfer device 120 includes a secondary transfer roll 113 disposed in pressure contact with the toner carrying surface of the intermediate transfer belt 110 and a secondary transfer roll 113 disposed in contact with the back surface of the intermediate transfer belt 110. A backup roll 114 serving as an electrode (also used as a support roll 134) is provided. As shown in FIG. 3, the backup roll 114 stably receives a bias having the same polarity as the toner charging polarity from the bias power supply 112. A metal-made power supply roll 115 to be applied is disposed in contact with the metal.

In the present embodiment, the secondary transfer roll 1
13 is a tube of urethane rubber in which carbon is dispersed on the surface, the inside is made of urethane foam in which carbon is dispersed, and the surface of the roll is further coated with fluorine, the volume resistance is 10 ³ to 10 ¹⁰ Ω and the roll diameter is 28 mm. The hardness is set to, for example, 30 ° (Asuka C).

The backup roll 114 is made of a tube of EPDM and NBR blended rubber in which carbon is dispersed on the surface, and the interior is made of EPDM rubber. The surface resistivity is 10 ⁷ to 10 ¹⁰ Ω / □ and the roll diameter is 28 mm. The hardness is set to, for example, 70 ° (Asuka C).

The secondary transfer roll 113 is provided with a cleaning roll 161 made of, for example, urethane rubber, and removes stains attached to the secondary transfer roll 113 to prevent the back side of the paper P from being stained. Reference numeral 136 denotes a belt cleaner that cleans the surface of the intermediate transfer belt 110 after the secondary transfer, and 137 denotes an image density sensor that detects the image density of an image formed on the intermediate transfer belt 110.

Further, in the present embodiment, the paper transport system feeds out the paper P from the paper tray 116 at a predetermined timing by the pickup roll 117 and moves to the secondary transfer position via the transport roll 118 and the transport chute 119. The paper P after the secondary transfer is guided to a transport belt 140, and the transport belt 14
At 0, the sheet is conveyed to the fixing device 150.

Next, a method of arranging the primary transfer rolls 105 according to the present embodiment will be described in detail. The primary transfer roll 105 is made of urethane foam rubber in which carbon is dispersed, has a diameter of 28 mm, and has a volume resistance of 10 mm.
^It is formed so as to be ⁷ to 10 ⁹ Ω, and has a hardness of, for example, 30 °.
３５35 ° (Asuka C) is set. In the present embodiment, the photosensitive drums 101Y, 101M, 101C
Transfer rolls 105Y, 105M, 105 corresponding to
The mounting position of C is different from the mounting position of the primary transfer roll 105K corresponding to the photosensitive drum 101K.

The photosensitive drum 1 shown in FIG.
A description will be given by taking the example of 01C and the black photosensitive drum 101K. First, the mounting position of the cyan primary transfer roll 105C with respect to the cyan photosensitive drum 101C is a position 3 mm downstream of the moving direction of the intermediate transfer belt 110 with respect to a perpendicular line L0 indicating a direction directly below the cyan photosensitive drum 101C. In the present embodiment, the cyan primary transfer roll 105C is moved toward the rotation center 101Ca of the cyan photosensitive drum 101C, that is, the rotation center 10Ca.
1Ca and rotation center 10 of cyan primary transfer roll 105C
Pressing toward the center line L1 connecting 5Ca. The mounting position of the yellow primary transfer roll 105Y with respect to the yellow photosensitive drum 101Y and the mounting position of the magenta primary transfer roll 105M with respect to the magenta photosensitive drum 101M are the same as those of the cyan primary transfer roll 105C.

On the other hand, the mounting position of the black primary transfer roll 105K with respect to the black photosensitive drum 101K is perpendicular to the perpendicular line L0 'indicating the direction directly below the black photosensitive drum 101K.
(Parallel to the perpendicular L0) with respect to the intermediate transfer belt 110.
5 mm downstream of the moving direction. And
In the present embodiment, the black primary transfer roll 105
K is the rotation center 101K of the black photosensitive drum 101K.
The pressing force is directed toward a, that is, toward a center line L2 (not parallel to the rotation center line L1) connecting the rotation center 101Ka and the rotation center 105Ka of the black primary transfer roll 105K.

[0028] Thus, in this embodiment, the width of the black transfer nip region n _K formed between the black photosensitive drum 101K and the intermediate transfer belt 110, the cyan photosensitive drum 101C and the intermediate transfer belt 110 Are set wider than the cyan transfer nip area n _C (yellow transfer nip area and magenta transfer nip area) formed between the two.

Next, an image forming process of the color image forming apparatus according to the present embodiment will be described. Now, when a start switch (not shown) is turned on, a predetermined image forming process is executed. More specifically, for example, when the color image forming apparatus is configured as a digital color copying machine, a document set on a document table (not shown) is read by a color image reading device, and the read signal is read by an image signal processing unit. , And temporarily store the digital image signals in a memory. Based on the stored digital image signals of four colors (K, Y, M, and C), toner images of each color are formed. .

That is, the image forming unit 1 according to the digital image signal of each color inputted from the image signal processing means.
00 (specifically, 100Y, 100M, 100C, 10
0K). Then, each image forming unit 1
At 00, an electrostatic latent image corresponding to the digital signal is written on the photosensitive drum 101 uniformly charged by the uniform charger 102 by the laser exposure device 103, respectively. And
Each of these electrostatic latent images is developed by the developing device 104 containing the toner of each color to form a toner image of each color. When this color image forming apparatus is configured as a device such as a printer, it is only necessary to form toner images of each color based on an image signal input to the image signal processing means from the outside.

The toner image formed on each photosensitive drum 101 is transferred to a primary transfer roll 10 at a primary transfer position where each photosensitive drum 101 contacts the intermediate transfer belt 110.
5, from the photosensitive drum 101 to the intermediate transfer belt 11
0 is sequentially transferred to the surface. The toner remaining on the photosensitive drum 101 after the primary transfer is transferred to the drum cleaner 1.
It is cleaned at 06.

The toner image primarily transferred onto the intermediate transfer belt 110 in this manner is superimposed on the intermediate transfer belt 110, and is conveyed to the secondary transfer position as the intermediate transfer belt 110 rotates. On the other hand, the paper P is supplied to the secondary transfer position at a predetermined timing, and the secondary transfer roll 113 nips the paper P with respect to the backup roll 114.

Then, at the secondary transfer position, the transfer electric field formed between the secondary transfer roll 113 serving as the batch transfer device 120 and the backup roll 114 acts,
The toner image carried on the intermediate transfer belt 110 is
Is transferred in batch. Paper P on which this toner image has been transferred
Is transported by the transport belt 140 to the fixing device 150 to fix the toner image. Further, the toner remaining on the intermediate transfer belt 110 after the secondary transfer is cleaned by the belt cleaner 136.

In the present embodiment, as described above, each primary transfer roll 105 (specifically, 105Y, 105M,
105C, 105K), the constant current control is performed so that 30 μA always flows, but the width of the black transfer nip area n _K is set to be larger than the transfer nip area of another color (for example, the cyan transfer nip area n _C ). since the magnitude of the electric field per unit area in black transfer area n _K becomes possible induced to reduce than other colors. As a result, discharge when an image having a high toner pile height formed in multiple colors passes through the black photosensitive drum 101K at the most downstream is prevented, and while ensuring good transfer performance of the black toner image, It is possible to prevent white spots in an image around an image formed with multiple colors and having a high toner pile height.

Embodiment 2 This embodiment is almost the same as Embodiment 1, but as shown in FIG. 5, the outer diameter of the black primary transfer roll 105K is changed to the other primary transfer roll 105 (105Y). , 105
M, 105C, and in the figure, a cyan primary transfer roll 105C
Only shown).
Note that, of the components of the image forming apparatus according to the present embodiment, the same components as those of the image forming apparatus according to the first embodiment are denoted by the same reference numerals as those in the first embodiment, and detailed descriptions thereof will be given here. Description is omitted.

In the present embodiment, the primary transfer rolls 105 (specifically, 105Y, 105M, and 105C) except for the black primary transfer roll 105K have a diameter of 28 mm as in the first embodiment. As the black primary transfer roll 105K, a roll having a diameter larger than these, for example, 40 mm is used. The pressing direction of the cyan transfer roll 105C is set to L1, and the pressing direction of the black primary transfer roll 105K is set to L1 '(L1 and L1' are parallel).

[0037] In this embodiment, by increasing the diameter of the black primary transfer roll 105K, the width of the black transfer nip region n _K formed between the black photosensitive drum 101K and the intermediate transfer belt 110, the cyan This is set wider than the cyan transfer nip area n _C (yellow transfer nip area and magenta transfer nip area) formed between the photosensitive drum 101C and the intermediate transfer belt 110. Therefore, as in the first embodiment, the magnitude of the electric field per unit area in black transfer area n _K becomes possible induced to reduce than other colors. Therefore, also in the present embodiment, an image having a high toner pile height formed in multiple colors is transferred to the black photosensitive drum 101 at the most downstream side.
It is possible to prevent discharge when passing through K, and to prevent white spots in an image around an image having a high toner pile height formed of multiple colors while securing good transfer performance of a black toner image. Become.

Embodiment 3 The present embodiment is almost the same as Embodiment 1, but as shown in FIG. 6, the hardness of the black primary transfer roll 105K is changed to the other primary transfer rolls 105 (105Y, 105Y, 105
M, 105C, and in the figure, a cyan primary transfer roll 105C
Only shown).
Note that, of the components of the image forming apparatus according to the present embodiment, the same components as those of the image forming apparatus according to the first embodiment are denoted by the same reference numerals as those in the first embodiment, and detailed descriptions thereof will be given here. Description is omitted.

In the present embodiment, the primary transfer rolls 105 (specifically, 105Y, 105M, 105C) other than the black primary transfer roll 105K have a hardness of 35 ° (Asuka C) as in the first embodiment. The black primary transfer roll 105K has a smaller size, for example, 25 ° (Asuka C). The pressing direction of the cyan transfer roll 105C is L
1. The pressing direction of the black primary transfer roll 105K is L1 '.
(L1 and L1 'are set in parallel).

[0040] In this embodiment, by reducing the hardness of the black primary transfer roll 105K, the width of the black transfer nip region n _K formed between the black photosensitive drum 101K and the intermediate transfer belt 110, the cyan This is set wider than the cyan transfer nip area n _C (yellow transfer nip area and magenta transfer nip area) formed between the photosensitive drum 101C and the intermediate transfer belt 110. Therefore, as in the first embodiment, the magnitude of the electric field per unit area in black transfer area n _K becomes possible induced to reduce than other colors. Therefore, also in the present embodiment, an image having a high toner pile height formed in multiple colors is transferred to the black photosensitive drum 101 at the most downstream side.
It is possible to prevent discharge when passing through K, and to prevent white spots in an image around an image having a high toner pile height formed of multiple colors while securing good transfer performance of a black toner image. Become.

The black primary transfer roll 105K and the other primary transfer rolls 105 (105Y, 105M,
In case of setting the hardness of 5C in the same well, as shown in FIG. 6, the pressing force F _K for black primary transfer roll 105K, the other primary transfer roller 105 (105Y, 1
05M, 105C, and in the figure, a cyan primary transfer roll 10
If to be greater than only shown) pressing force F _C for 5C, the width of the black transfer nip region n _K formed between the black photosensitive drum 101K and the intermediate transfer belt 110, the cyan photoconductor This is set wider than the cyan transfer nip area n _C (yellow transfer nip area and magenta transfer nip area) formed between the drum 101C and the intermediate transfer belt 110. By doing so, it is also possible to prevent white spots in an image around an image formed with multiple colors and having a high toner pile height.

The present inventor has determined the width of the primary transfer nip area (hereinafter referred to as the primary transfer nip width) and the transferability when forming yellow (Y), magenta (M), cyan (C) and black (K) toner images. We investigated the relationship with FIG. 7 shows the results. As can be seen from the figure, when forming a color toner image (Y, M, C), the primary transfer nip width for obtaining good transferability is as narrow as 2 to 4 mm. Primary transfer nip width is 1
It is understood that it is as wide as 5 mm. Therefore, in Embodiments 1 to 3, a black toner image capable of obtaining good transferability even when the primary transfer width is widened is formed last.

Embodiment 4 This embodiment is almost the same as Embodiment 1, except that the primary transfer current applied to the black primary transfer roll 105K is changed to the other primary transfer rolls 105 (105Y, 105M,
105C).
Note that, of the components of the image forming apparatus according to the present embodiment, the same components as those of the image forming apparatus according to the first embodiment are denoted by the same reference numerals as those in the first embodiment, and detailed descriptions thereof will be given here. Description is omitted.

In this embodiment, the primary transfer roll 1
05 is made of foamed urethane rubber in which carbon is dispersed in the same manner as in the first embodiment, and has a diameter of 28 mm, a volume resistance of 10 ⁷ to 10 ⁹ Ω, and a hardness of, for example, 35 ° (Asuka C). ). Further, in the present embodiment, unlike the first embodiment, the photosensitive drum 101
Primary transfer roll 10 corresponding to Y, 101M, 101C
The mounting positions of the 5Y, 105M, and 105C and the mounting position of the primary transfer roll 105K corresponding to the photosensitive drum 101K are the same.

This is the same as the cyan photosensitive drum 1 shown in FIG.
A description will be given by taking the example of 01C and the black photosensitive drum 101K. First, the mounting position of the cyan primary transfer roll 105C with respect to the cyan photosensitive drum 101C is a position 3 mm downstream of the moving direction of the intermediate transfer belt 110 with respect to a perpendicular line L0 indicating a direction directly below the cyan photosensitive drum 101C. In the present embodiment, the cyan primary transfer roll 105C is moved toward the rotation center 101Ca of the cyan photosensitive drum 101C, that is, the rotation center 10Ca.
1Ca and rotation center 10 of cyan primary transfer roll 105C
Pressing toward the center line L1 connecting 5Ca.

On the other hand, the mounting position of the black primary transfer roll 105K with respect to the black photosensitive drum 101K is also perpendicular to the perpendicular line L0 'indicating the direction directly below the black photosensitive drum 101K.
(Parallel to the perpendicular L0) with respect to the intermediate transfer belt 110.
The position is 3 mm downstream of the moving direction. And
In the present embodiment, the black primary transfer roll 105
K is the rotation center 101K of the black photosensitive drum 101K.
A, that is, toward the center line L1 '(parallel to the rotation center line L1) connecting the rotation center 101Ka and the rotation center 105Ka of the black primary transfer roll 105K.

[0047] Thus, in this embodiment, the width of the black transfer nip region n _K formed between the black photosensitive drum 101K and the intermediate transfer belt 110, the cyan photosensitive drum 101C and the intermediate transfer belt 110 Are set to be the same as the cyan transfer nip area n _C (yellow transfer nip area and magenta transfer nip area) formed between the two.

Further, in the present embodiment, other primary transfer rolls 105 except for the black primary transfer roll 105K are used.
The transfer current applied to (specifically, 105Y, 105M, 105C) is 30 μA (constant current control) as in the first embodiment, but the transfer current applied to the black primary transfer roll 105K is 25 less than 30 μA
μA.

In this embodiment, as described above, the width of the black transfer nip area n _K is set to be the same as the transfer nip area of another color (for example, the cyan transfer nip area n _C ). since the transfer current flowing to the roll 105K is set lower than 25μA and other colors of transfer current (30 .mu.A), the magnitude of the electric field per unit area in black transfer area n _K, it induced to reduce than other colors Becomes As a result, discharge when an image having a high toner pile height formed in multiple colors passes through the black photosensitive drum 101K at the most downstream is prevented, and while ensuring good transfer performance of the black toner image, It is possible to prevent white spots in an image around an image formed with multiple colors and having a high toner pile height.

Fifth Embodiment This embodiment is almost the same as the first embodiment, except that the transfer current is controlled according to environmental conditions. Note that, of the components of the image forming apparatus according to the present embodiment, the same components as those of the image forming apparatus according to the first embodiment are denoted by the same reference numerals as those in the first embodiment, and detailed descriptions thereof will be given here. Description is omitted.

In this embodiment, the control device 200
As shown in FIG. 9, a temperature detection signal from a temperature sensor 171 and a humidity detection signal from a humidity sensor 172 are fetched into a CPU 202 via an input interface 201, and then, the CPU 202
After appropriately performing data processing with the black transfer bias power supply 1 via the output interface 205,
07K, yellow transfer bias power supply 107Y, magenta transfer bias power supply 107M, cyan transfer bias power supply 1
A bias control signal is transmitted to each of the 07Cs.

In the image forming apparatus according to this embodiment,
It is known that the relationship shown in FIG. 10 exists between the environment (temperature and humidity) and the primary transfer current. That is, if the transfer current is too small, insufficient transfer occurs due to insufficient transfer current,
On the other hand, if the transfer current is too large, discharge due to the excessive transfer current and white spots associated with the discharge occur. A region where such a defect does not occur (a region where no defect occurs) is slightly different between a low-temperature and low-humidity environment, a normal temperature and normal humidity environment, and a high-temperature and high humidity environment.

Therefore, in the present embodiment, the transfer current is made different depending on the temperature and the humidity. Specifically, the transfer current in a low-temperature and low-humidity environment is reduced as compared with a high-temperature and high-humidity environment. By doing this,
It is possible to prevent white spots in an image around an image having a high toner pile height in the lowermost black transfer area n _K , and also prevent discharge at the transfer area exit side of each color and associated white spots. .

The present embodiment can be applied not only to the image forming apparatus described in the first embodiment, but also to the image forming apparatuses described in the second to fourth embodiments.

Embodiment 6 This embodiment is almost the same as Embodiment 5, but instead of controlling the transfer current, each primary transfer roll 105 (specifically, 105Y, 105M, 105C, 105K) is used. The pressing force on the intermediate transfer belt 110 is made different so that the width of each primary transfer nip is made different.
Note that, of the components of the image forming apparatus according to the present embodiment, the same components as those of the image forming apparatus according to the fifth embodiment are denoted by the same reference numerals as those in the fifth embodiment, and detailed descriptions thereof will be given here. Description is omitted.

In this embodiment, the control device 200
As shown in FIG. 11, a CPU 202 receives a temperature detection signal from a temperature sensor 171 and a humidity detection signal from a humidity sensor 172 via an input interface 201, and then the CPU 202
After performing appropriate data processing with the M204, each primary transfer roll 105 is output via the output interface 205.
(Specifically, 105K, 105Y, 105M, 105
C) to each of the transfer roll drive cams 108 (specifically, the black transfer roll drive cam 108K, the yellow transfer roll drive cam 108Y, the magenta transfer roll drive cam 108M, and the cyan transfer roll drive cam 108C). It is designed to be sent.

In the image forming apparatus according to the present embodiment,
FIG. 12 shows the relationship between the environment (temperature and humidity) and the primary transfer nip width.
It is known that there is a relationship shown in FIG. That is, if the primary transfer nip width is too large, the intermediate transfer belt 110 and the photosensitive drum 101 are damaged and image quality defects occur.
If the primary transfer nip width is too small, the transfer current increases, and discharge due to excessive transfer current and white spots associated therewith occur. A region where such a defect does not occur (a region where no defect occurs) is slightly different between a low-temperature and low-humidity environment, a normal temperature and normal humidity environment, and a high-temperature and high humidity environment.

Therefore, in the present embodiment, the primary transfer nip width is made different depending on the temperature and humidity. Specifically, the pressing force in a low-temperature and low-humidity environment is made larger than that in a high-temperature and high-humidity environment to increase the primary transfer nip width. By doing so, it is possible to prevent white spots from being removed from the image around the image having a high toner pile height in the black transfer area n _K at the most downstream side, and also to cause discharge at the transfer area exit side of each color and associated white spots. Dropout can be prevented.

The present embodiment can be applied not only to the image forming apparatus described in the first embodiment but also to the image forming apparatuses described in the second to fourth embodiments.

Embodiment 7 This embodiment is almost the same as Embodiment 5, except that the resistance of the primary transfer roll 105 is measured at the start of image formation, and the transfer current is controlled based on the measured resistance value. It is like that. Note that, of the components of the image forming apparatus according to the present embodiment, the same components as those of the image forming apparatus according to the fifth embodiment are denoted by the same reference numerals as those in the fifth embodiment, and detailed descriptions thereof will be given here. Description is omitted.

In this embodiment, the control device 200
As shown in FIG. 13, a resistance detection signal from a resistance measuring device 173 that measures the resistance of the primary transfer roll 105 is taken into the CPU 202 via the input interface 201, and then the CPU 202 communicates with the ROM 203. After performing appropriate data processing, the output interface 20
5, a bias control signal is sent to each of a black transfer bias power supply 107K, a yellow transfer bias power supply 107Y, a magenta transfer bias power supply 107M, and a cyan transfer bias power supply 107C.

In this embodiment, at the start of image formation, a predetermined current (for example, 30 μA) is applied to each primary transfer roll 105 by each transfer bias power supply 107, and a voltage induced on the primary transfer roll 105 at this time. Is measured, and a resistance is calculated from the current and the voltage, and is input to the control device 200. In the present embodiment, the transfer current for each primary transfer roll 105 is made different based on the input resistance value.
Specifically, the transfer current at the time of high resistance is reduced as compared with the time of low resistance. By doing so, it is possible to prevent white spots from being removed from the image around the image having a high toner pile height in the black transfer area n _K at the most downstream side, and also to cause discharge at the transfer area exit side of each color and associated white spots. Dropout can be prevented.

The present embodiment can be applied not only to the image forming apparatus described in the first embodiment, but also to the image forming apparatuses described in the second to fourth embodiments.

[0064]

As described above, according to the present invention,
In a so-called tandem-type image forming apparatus, discharge between the final image carrier and the recording carrier is prevented by a final transfer device corresponding to the final image carrier disposed at the most downstream side in the moving direction of the recording carrier. Since the discharge prevention means is provided, white spot-like image omission due to gap discharge can be effectively prevented.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating an outline of an image forming apparatus according to the present invention.

FIG. 2 is a schematic configuration diagram of Embodiment 1 of the image forming apparatus to which the present invention has been applied.

FIG. 3 is an enlarged view of a primary transfer device of the image forming apparatus according to the first embodiment.

FIG. 4 is an explanatory diagram showing a method of arranging a black photosensitive drum and a black primary transfer roll and a cyan photosensitive drum and a cyan primary transfer roll in the first embodiment.

FIG. 5 is an explanatory diagram showing a method of arranging a black photosensitive drum and a black primary transfer roll, and a cyan photosensitive drum and a cyan primary transfer roll in the second embodiment.

FIG. 6 is an explanatory diagram showing a method of arranging a black photosensitive drum and a black primary transfer roll, and a cyan photosensitive drum and a cyan primary transfer roll in the third embodiment.

FIG. 7 is a graph showing a relationship between a primary transfer nip width and transferability.

FIG. 8 is an explanatory diagram showing a method of arranging a black photosensitive drum and a black primary transfer roll, and a cyan photosensitive drum and a cyan primary transfer roll in a fourth embodiment.

FIG. 9 is a block diagram of a control device of the image forming apparatus according to the fifth embodiment.

FIG. 10 is an explanatory diagram showing a relationship between an environment and a primary transfer current.

FIG. 11 is a block diagram of a control device of an image forming apparatus according to Embodiment 6.

FIG. 12 is an explanatory diagram illustrating a relationship between an environment and a primary transfer nip width.

FIG. 13 is a block diagram of a control device of the image forming apparatus according to the seventh embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Image carrier, 1d ... Final image carrier, 2 ... Recording conveyance body,
3 transfer device, 3d final transfer device, 4 discharge prevention means, 5 batch transfer device, K recording material, T toner image

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masaaki Takahashi 2274 Hongo, Ebina-shi, Kanagawa Fuji Xerox Co., Ltd. (72) Inventor Yukio Hayashi 2274 Hongo, Ebina-shi, Kanagawa Fuji Xerox Co., Ltd. (72) Inventor Yoko Miyamoto 2274 Hongo, Ebina-shi, Kanagawa Prefecture Inside Fuji Xerox Co., Ltd. (72) Inventor Makoto Katayama 2274 Hongo, Ebina-shi, Kanagawa Prefecture Fuji Xerox Co., Ltd. 2H030 AB02 AD16 BB02 BB23 BB42 BB54 2H032 AA05 AA15 BA01 BA05 BA09 BA23 CA02 CA14 DA23 DA28

Claims (8)

[Claims] A plurality of image carriers on which a toner image corresponding to image information is formed and carried; a recording carrier circulated and conveyed at a portion facing each of the image carriers; A plurality of transfer devices for transferring the toner images formed on the respective image carriers via a recording material, wherein a final image carrier disposed on the most downstream side in the moving direction of the recording carrier is provided. An image forming apparatus comprising: a final transfer device corresponding to a body; and a discharge prevention unit configured to prevent discharge between the final image carrier and the recording conveyance body. 2. The image forming apparatus according to claim 1, wherein
In a mode in which the transfer device is provided with a transfer roll that comes into contact with the recording conveyance body, the discharge prevention unit includes a transfer nip formed between the final image carrier and a transfer roll of the final transfer device. An image forming apparatus wherein the width is set to be larger than other transfer nip widths. 3. The image forming apparatus according to claim 2, wherein the discharge prevention unit is configured such that an outer diameter of a transfer roll of the final transfer device is larger than other transfer rolls. Forming equipment. 4. The image forming apparatus according to claim 2, wherein the discharge prevention unit has a hardness of a transfer roll of the final transfer device smaller than other transfer rolls. apparatus. 5. The image forming apparatus according to claim 1, wherein the discharge prevention unit reduces a bias applied to the final transfer device compared to other transfer devices. . 6. The image forming apparatus according to claim 1, further comprising: a bias control unit configured to reduce a bias application amount to each of the transfer devices under a condition in which the ambient temperature is low or the ambient humidity is low. Characteristic image forming apparatus. 7. The image forming apparatus according to claim 1, wherein
In the aspect in which the transfer device includes a transfer roll that is arranged in contact with the recording conveyance body, under the condition that the resistance value of the transfer roll exceeds a predetermined resistance value, the amount of bias applied to each of the transfer rolls is reduced. An image forming apparatus comprising: a bias control unit configured to reduce bias. 8. The image forming apparatus according to claim 1, wherein the toner image formed on the final image carrier is a black toner image.