JPH03264969A - Color image forming device - Google Patents

Abstract

PURPOSE:To obtain a picture without density unevenness by forming alternating charge density patterns on the entire surface of a transfer paper carrying means corresponding to transfer paper at the time of each color transfer stage. CONSTITUTION:A charge pattern forming electrode roller 22, whose opposite electrode is a roller 18, is made abut on a transfer belt 17 wound around the driving belt roller 18, and this electrode roller 22 is connected to an AC power source 23. On the other hand, a charge pattern forming electrode roller 22A, whose opposite electrode is a roller 19, is made abut on the transfer belt 17 wound around the follower belt roller 19, and this electrode roller 22A is connected to an AC power source 23A. Since the negative and positive charge density patterns are formed on the transfer belt 17 corresponding to the transfer paper at the time of the transfer stage, the comparative position of the transfer paper is not deviated from that of the transfer belt 17. Thus, transfer efficiency is made entirely uniform and a preferable picture without density unevenness can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an electrophotographic color image forming apparatus such as a copying machine, a printer, or a facsimile.

(Prior art) A transfer paper is held by a transfer paper conveying means that moves in the same direction as the moving direction of the image carrier on which the image is formed, and the transfer paper is brought into contact with the image carrier in the transfer section and moved forward. Color image forming apparatuses are already known in which images of each color are superimposed on a transfer paper by repeating the step of moving the transfer paper conveying means backwards as many times as the number of colors of the developer. For example, the device described in Japanese Patent Application Laid-open No. 118366/1983 is one such device. The apparatus described in this publication reciprocates a transfer paper held by a transfer paper conveyance means to sequentially transfer images in a transfer section of an image carrier. The leading edge of the transfer paper held by the transfer paper conveyance means separates from the conveyance means when it moves forward to transfer an image, and when it moves back and waits for the next image transfer, its leading edge separates from the conveyance means. The ends are separate from the conveying means.

(Problems to be Solved by the Invention) In the apparatus described in the above publication, a portion of the transfer paper is once separated from the transfer paper conveying means before and after the image transfer process. This is advantageous in making the transport means small and downsizing the image forming apparatus. However, when a plurality of images are superimposed and transferred, the conveying means and the transfer paper become misaligned, causing color shift in the transferred images and degrading the copy quality.

In order to prevent the transfer paper from shifting, it is possible to increase the holding power of the transfer paper by applying an electric charge to the part of the transfer belt that is separated from the transfer paper, but it is difficult to transfer the next image. When transferring, the potential of the belt surface in the previously separated area is different from the surface potential of other areas, resulting in a difference in transfer efficiency and uneven density in the final image. be.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a color image forming apparatus that can obtain images without uneven density.

(Means for Solving the Problems) A color image forming apparatus of the present invention holds a transfer paper in a transfer paper conveying means that moves in the same direction as the moving direction of an image carrier on which an image is formed, and the transfer paper is In a color image forming apparatus in which an image is transferred in a transfer section while moving forward in contact with the image carrier, and then an image of each color is superimposed on a transfer paper by repeating a step of moving a transfer paper conveying means backward.

It is characterized in that during the transfer process for each color, an alternating charge density pattern is formed on the entire surface of the transfer paper conveyance means corresponding to the transfer paper.

Furthermore, the color image forming apparatus of the present invention includes an alternating current voltage applying means for forming an alternating charge density pattern on the surface of a transfer paper conveying means that moves back after the transfer process for each color is completed, and an alternating current voltage applying means for forming an alternating charge density pattern on the surface of the transfer paper conveying means that moves back after the transfer process for each color is completed, It is characterized by comprising a DC voltage applying means for applying a DC voltage substantially equal to the surface potential of the subsequent transfer paper conveyance means.

(Function) When the transfer paper on which the image has been transferred is moved forward and backward, an alternating current voltage is applied to the entire surface of the transfer paper conveyance means that conveys it, forming a charge density pattern.

When the transfer paper on which the image has been transferred is moved back, an AC voltage with a DC voltage superimposed is applied to the transfer paper conveying means.
Forming a charge density pattern.

(Example) Hereinafter, the present invention will be described in detail based on the illustrated example.

First, the general configuration of a color image forming apparatus to which the present invention is applied will be explained with reference to FIG. Reference numeral 1 denotes an electrostatic latent image carrier which is wound around a drive belt roller 2 and a driven belt roller 3 which are rotationally driven by a photoreceptor drive motor (not shown), and which is rotated in the direction of the arrow at a speed P. The photoreceptor belt is shown. In the case of a negative-positive process, since the developer adheres to uncharged areas on the surface of the photoreceptor, the entire surface of the photoreceptor belt 1 is uniformly charged to a predetermined polarity by corona discharge from the charger 4. This discharge generates a small amount of ozone. Although this ozone decomposes in a short time when the discharge is stopped, it may have an adverse effect on the surface of the photoreceptor belt 1 and impair the sharpness of the image. Therefore, the influence of ozone is eliminated by blowing or suctioning air from behind the charger 4 using a fan (not shown) or the like.

A rotation detection sensor (not shown) is attached to the shaft of the drive belt roller 2, and outputs a detection pulse every time the belt roller 2 rotates once. This detection pulse drives and controls the semiconductor laser of the optical writing unit 5 to form an electrostatic latent image at the writing position E. The image data applied from the optical writing unit 5 is read by an image reading device (not shown) such as "r blue" and "r green".

We read each of the three color separated lights of "red" and perform image calculation processing based on the intensity level of each color light.
This is image data of each of the words "yellow", "magenta", "cyan", and "black" written in French. Instead of the unit 5 using a semiconductor laser, the image data may be image data output from another type of laser or an optical writing unit such as an LED array or an LCD array, and may be output from a color facsimile, a word processor, a personal computer, etc. It may also be image data output from. In the part where the photoreceptor belt 1 moves downward,
From top to bottom: a yellow developer 7 containing yellow developer and having a developing roller 6 facing the photoreceptor belt 1; Magenta developer 9 containing magenta developer and equipped with a developing roller 8
．． A cyan developer 11 containing a cyan developer and provided with a developing roller 10, and a black developing device 13 containing a black developer and provided with a developing roller 12 are provided. Each developing device is normally placed in a standby position with its developing roller separated from the photoreceptor belt 1, and the latent image surface of the corresponding color is
The left side in FIG. and is positioned at the developing position. The developing unit placed at the developing position rotates a developing roller and a roller that supplies developer thereto in order to perform a developing function. In FIG. 1, the yellow developing device 7 is placed at the developing position, and the other developing devices are placed at standby positions.

In the part where the photoreceptor belt 1 moves upward.

A cleaning group M29 for removing developer remaining on the surface of the photoreceptor belt 1 after image transfer, and a static eliminator 30 for removing static from the photoreceptor belt 1 are provided.

A transfer belt 17 serving as transfer paper conveyance means is disposed below the photoreceptor belt 1. The transfer belt 17 is wound around an LLE moving belt roller 18 and a moving belt roller 19, and is driven to move forward in the direction of the arrow at a speed VF and vice versa at a speed VR according to the copying process. controlled. A belt contact/separation roller 20 for bringing the belt into contact with the photoreceptor belt 1 of the transfer portion T and separating it from the photoreceptor belt 1 is disposed on the lower surface of the upper extending portion of the transfer belt 17.

The belt contact/separation roller 20 is driven and controlled by a drive means (not shown), and the transfer belt 17 that moves forward (VF) during image transfer is brought into contact with the photoreceptor belt 1, and after transfer, the transfer belt 17 moves backward (VR). The belt 17 is moved up and down so as to separate it from the photoreceptor belt 1. The drive belt roller 18 is driven to rotate in forward and reverse directions by a drive motor (not shown), and rotates the transfer paper after one image has been transferred forward to a position indicated by symbol PA, and then to a standby position indicated by symbol PB for image transfer of the next color. It can be rotated back and forth up to. Transfer section T
A transfer charger 21 is disposed below the transfer belt 17 with the transfer belt 17 in between.

Above the driven belt roller 19 is a paper feed tray 14 on which transfer papers P are stacked. A paper feeding device is provided, which includes a paper feeding roller 15 that takes out the transfer paper P from this tray one by one, and a registration roller 16 that sends out the taken out transfer paper P toward the transfer paper belt 17 according to the process.

A charge pattern forming electrode roller 22 with the roller 18 as a counter electrode is in contact with the transfer belt 17 which is wound around the drive belt roller 18 . This electrode roller 22 is connected to an AC power source 23, and the transfer belt 1
7 to form a charge pattern. The drive belt roller 18 as a counter electrode is grounded.

The electrode roller 22 and the AC power source 23 constitute a first charge applying means. On the other hand, the transfer belt 17 wound around the driven belt roller 19 is brought into contact with an electrode roller 22A for forming a charge pattern, with the roller 19 serving as a counter electrode. This electrode roller 22A is connected to an AC power source 23A and forms a charge pattern on the transfer belt 17. The electrode roller 22A and the AC power source 23A constitute a second charge applying means. A transfer belt cleaning device 25 is disposed at the lower extending portion of the transfer belt 17, and the belt is held between a counter electrode plate 24 and a cleaning roller 25a.

Further, the transfer belt 17 is passed between the counter electrode roller 44 for static elimination and the static elimination corona charger 45.

A transfer paper path switching member 26 is disposed to the left of the drive belt roller 18, and is placed at the position shown by the solid line until the transfer of all color images is completed, and the transfer of the image of the last color is completed. Then, the transfer paper is swung to the drainage position shown by the chain line 26A, and the transfer paper is guided toward the fixing device 31. On the left side of the switching member 26 is a guide plate 27 on which the leading end of the transfer paper PA is placed.
is installed.

A guide plate 28 is provided on the right side of the driven belt roller 19, on which the rear end of the transferred sheet PB is placed. The transfer paper PA having the length QP that has finished its forward movement is positioned with its leading end on the guide plate 27, its middle part on the switching member 26, and its rear end on the transfer belt 17. The backwardly moved transfer paper PB has its rear end positioned on the transfer belt 17 and its rear end positioned on the guide plate 28 .

Although the illustrated fixing device 31 is of a roller fixing type, other types of fixing devices may be used. The transfer paper that has been fixed is discharged to the paper discharge tray 32.

When a print switch (not shown) is turned on, the photoreceptor belt 1 rotates at a speed VP in the direction indicated by the arrow, and the transfer belt 1
7 starts forward rotation in the direction of the indicated arrow at a speed VF (=VP). An alternating charge density pattern is formed on the transfer belt 17 by an AC power source 23A via an electrode roller 22A. The photoreceptor belt 1 is irradiated with light or applied with a charge-eliminating corona to the surface of the belt from which developer has been removed in advance by the cleaning device 29 by the static eliminator 30 to bring the surface potential to approximately O volts. The entire surface is uniformly charged.

When the charged photoreceptor belt 1 moves to the optical writing position E, yellow image data is first written by the optical writing unit 5 to form an electrostatic latent image. Before the electrostatic latent image of the yellow image data moves to the developing section, the yellow developing device 7 is moved to the illustrated developing position, and the developing roller 6 is brought into contact with the surface of the photoreceptor belt 1. Therefore, the electrostatic latent image that has moved to the developing section is visualized. The photoreceptor belt 1 on which the yellow image is formed is
Since the transfer paper P is brought into contact with the transfer portion T, the paper feed roller 15 feeds the transfer paper P at an appropriate timing prior to this. The sent-out transfer paper is held by the registration rollers 16 and waits. At this time, the transfer belt 17 is brought into contact with the photoreceptor belt 1 by the raised belt contact/separation roller 20.

The transfer paper P held between the registration rollers 16 is moved to the transfer belt 17 when the leading edge of the yellow image on the photoreceptor belt 1 reaches the front position TS at a predetermined distance from the transfer section T.
It is sent out towards the transfer section T and advances to a position nearer IRT with a length Ql.

The distance between the transfer portion T and the front position TS on the photoreceptor belt is also the length ρ1. Then, when the leading edge of the yellow image and the leading edge of the transfer paper both move by a distance IQ1 and reach the transfer portion T, the yellow image is transferred to the transfer paper P by the corona charger of the transfer charger 21. As the yellow image transfer process progresses, the leading edge of the transfer paper P separates from the transfer belt 17, is guided by the switching member 26, and advances onto the guide plate 27. When the rear end of the transfer paper P has passed the transfer portion T by a distance Q2, the drive belt roller 18 is reversed, and the transfer belt 17 is moved back in the direction of the arrow at a speed VR (>VF). When the transfer belt 17 is made to return quickly, the belt contact/separation roller 20 descends and the transfer belt 1
7 is spaced apart from the photoreceptor belt 1.

When the forward movement of the transfer belt 17 is finished, the electrode roller 22A, which has been forming an alternating charge density pattern,
The power supply is cut off. When the transfer belt 17 starts to move backward, an alternating current voltage from the alternating current power supply 23 is supplied to the transfer belt 17 via the electrode roller 22 to form an alternating charge density pattern on the belt.

As a result, the portion of the transfer paper P that was away from the transfer belt 17 is held by the reciprocating transfer belt with a large adsorption force. Details regarding the timing of applying the AC voltage to the transfer belt 17 will be described later.

The transfer paper P conveyed by the backward motion of the transfer belt 17 is
It is placed at a standby position indicated by the symbol PB, and is kept on standby for the next magenta image transfer.

At this standby position, the leading edge of the transfer paper is at the transfer position T.
It is located at the front position RT at a distance Q1 from. At this time, the rear end of the transfer paper P is separated from the transfer belt 17 and positioned on the guide plate 28 .

When the return movement of the transfer belt 17 is completed, the supply of AC voltage by the AC power supply 23 is stopped. The cleaning device 29 removes untransferred developer from the surface of the photoreceptor belt 1 after the yellow image has been transferred, and then the static eliminator 30 removes residual charges.

On the other hand, on the photoreceptor belt 1, even during the transfer of the first color yellow image, the second color magenta image forming step has already been performed. When the development of the yellow image area is completed, the yellow developing device 7 retreats to the standby position, and before the leading edge of the magenta image area moves, the magenta developing device 9 brings its developing roller 8 into contact with the photoreceptor belt 1. is moved to the developed position.

When the leading edge of the developed magenta image area reaches the near position TS, the transfer belt 17 starts to move forward, and the transfer paper PB held thereon is conveyed toward the transfer position T. At the same time as and prior to the start of movement of the transfer belt, the belt contact/separation roller 2o is raised to bring the transfer belt into contact with the photoreceptor belt 1. The transfer belt 17, which is raised to the speed VF while holding the transfer paper and moving the distance Q1, transfers a magenta image in an overlapping manner to the transfer paper P on which the yellow image is formed. The reciprocating transfer belt 17 stops at a position where the rear end of the transfer paper to which the magenta image has been transferred has passed a distance Ω2 from the transfer position IT, and then its direction of movement is reversed and the transfer belt 17 is moved back at a speed VR.

Thereafter, the same steps as those described above are repeated. That is,
Cyan image data writing, cyan image development, cyan image transfer, transfer paper quick return.

Writing black image data, developing black image.

Execute the process of black image transfer. When the black image transfer process begins, the switching member 26 is switched to the ejection position 26A, and the transfer paper undergoing the transfer process is guided toward the fixing device 31. Distance Q from the transfer position T to the rear edge of the transfer paper
Even after moving forward two times, the transfer belt 17 is rotated in the forward direction to convey the transfer paper. The transfer paper on which the four-color images are superimposed and transferred is fixed by a fixing device 31 and then discharged onto a paper discharge tray 32 as a full-color copy. On the other hand, after the transfer of the black image, the photoreceptor belt 1 is cleaned of residual developer by a cleaning device 29, and its surface potential is reduced to approximately 0 volts by a static eliminator 30, thereby returning it to its initial state.

Further, the transfer belt 17 is also connected to the transfer belt cleaning device 2.
5, the static eliminating corona charger 4
5, the static electricity is removed and the state is returned to the initial state.

In the above explanation, the image formation order is "yellow".

"Magenta,""cyan," and "black" were used, and the order in which the developing units were arranged was also set in this manner; however, the developed color is also "blue".

It is also possible to use "green", "red" and other desired colors in combination as necessary.

Further, in the illustrated embodiment, image data subjected to digital image processing is transferred to the photoreceptor belt 1 by the optical writing unit 5.
However, a method of guiding an analog optical image to the optical writing position E and forming the image may be used. When obtaining a two-color or three-color copy instead of a full-color copy, image formation and transfer of the desired color may be performed two or three times in succession. If you want to obtain monopower,
A developing device of a desired color is placed in a developing position and activated;
The transfer belt 17 remains in contact with the photoreceptor belt 1,
The switching member is positioned in the ejection position indicated at 26A.

The timing of forming the charge density pattern on the transfer belt 17 will be explained in detail.

In FIG. 2, only the length QF of the transfer paper PA at the position where the first color (yellow image) has been transferred and the forward movement has been completed is on the transfer belt 17, and the transfer charger 2
It is adsorbed by the adsorption force caused by the transfer corona of No. 1. Therefore,
Transfer paper (7) rffR separated from transfer belt 17
J part and rffP-QF-uR' part have no adsorption force. Even when the transfer belt 17 starts to move back and the transfer paper that has been separated until now joins the transfer belt, the suction force of this part is weak, and at the standby position (PB) where the back movement has finished, , QF<ΩB, there is no adhesion force between the transfer paper PB and the transfer belt 17, so the transfer paper shifts with respect to the transfer belt, and accurate overlapping transfer cannot be expected.

Therefore, when the drive belt roller 18 is reversely rotated and the transfer belt 17 is made to move back at the speed VR, the AC voltage from the AC power source 23 is applied to the electrode roller with the drive belt roller 18 as a counter electrode. 22. As a result, a positive and negative charge density pattern is formed on the transfer belt 17 at a portion corresponding to the "flooding P-QF-QR" of the transfer paper PA, and an unequal electric field is generated.

This unequal electric field can attract the rI2P-QF-12RJ portion of the transfer paper that has moved away from the transfer belt and has lost its attraction force. Therefore, when the transfer belt 17 moves back at a rapid speed, it holds the transfer paper without shifting its holding position. If the AC voltage is not applied by the AC power supply 23A when the transfer belt 17 starts forward movement, the surface potential of the transfer belt 27 corresponding to the transfer paper will be:
As shown in Figure 3 (, ), if the next color transfer process is performed while the surface potential is still in this state, the ``ΩP-QF-QRJ area and other areas of the transfer paper will be Differences in transfer efficiency occur, resulting in uneven image density.Therefore, in order to eliminate this phenomenon, when the transfer belt 17 starts moving forward, an electrode is placed on the transfer belt wrapped around the driven roller. By applying an AC voltage from an AC power source 23A through the roller 22A, a positive and negative charge density pattern is formed in the QF+QRJ portion or a longer area, and the surface potential on the transfer belt corresponding to the entire surface of the transfer paper is changed. As shown in FIG. 3(b), the voltage distribution is made substantially uniform over the entire surface. By creating such a voltage distribution, the transfer efficiency of the second color (magenta) image becomes uniform.

In the re-adsorption described above, a charge pattern is formed using the drive belt roller 18 as a counter electrode, but unless the transfer belt 17 is moved while the transfer paper is in contact with the circumference of the drive belt roller, the attraction force due to the unequal electric field is not born. Therefore, in order to obtain suction power, as shown in Figure 1,
A portion of the switching member 26 placed in the guide position is kept in contact with the drive belt roller 18.

Next, when preparing to transfer a magenta image, that is, when the transfer belt 17 moves backward and the transfer paper is placed in the standby position indicated by the symbol PB, the transfer paper "ΩP-QF-flRJ
The portion is attracted and held by the belt by the attraction force of the unequal electric field, and the rear end portion is separated from the transfer belt 17 by a length uB. This separated part has weaker adsorption power.

When the transfer belt 17 starts moving forward to transfer the magenta image, the electrode roller 2
The AC voltage of the AC power supply 23A is applied to the transfer belt 1 through 2A.
7 to form a charge density pattern and generate an unequal electric field. The driven belt roller 19 acts as a counter electrode when voltage is applied.

The application of AC voltage via the electrode rollers 22, 22A and its stopping are repeated until the transfer process of each color is executed.
Each AC power source 23.
An AC voltage of 23 A may be continued to be applied.

Next, referring to FIG. 4, another embodiment will be described.

The feature of this example is that in addition to the AC voltage applying means consisting of the AC power supply 23 and the electrode roller 22, a DC voltage applying means 23V for applying a DC voltage is provided. Transfer belt 17
An electrode roller to which an AC voltage is applied is not provided below the driven belt roller 19 .

In FIG. 4, on the underside of the drive belt roller 18.

An electrode roller 22 in contact with the transfer belt 17 is provided, and a fifth
AC power supply 23 and DC power supply 23V at the timing shown in the figure.
As a result, a voltage obtained by superimposing a DC voltage on an AC voltage is applied to the electrode roller 22. The superimposed voltage is applied while the transfer belt 17 is making a backward movement (VR).

When no DC voltage is applied. As shown in FIG. 6(a), the surface potential of the transfer belt 17 when the first color image transfer is finished and the transfer paper PB is placed in the standby position is different from the average value of each part by VT volts. ing. Therefore, when an image is transferred while holding a transfer paper on the transfer belt 17 having such a surface potential, one image becomes uneven.

Therefore, when the first color (yellow) rotor is in use, the surface potential of the transfer belt 17 is changed by the transfer charger 21 as shown in FIG. 6(b).
As shown in FIG. 2, the transfer paper is charged to 1 volt, and at the timing when the drive belt roller 18 starts rotating in the VR force direction from the PA position, an AC voltage with a DC voltage v1 volt superimposed is applied to the electrode roller 22. As a result, the rQ of the transfer paper
A striped charge density pattern is formed on the transfer belt 17 corresponding to the P-ΩF-QRJ portion, and an unequal electric field is generated. This unequal electric field causes the rQP of the transfer paper to
The -QF-QRJ portion is attracted to the transfer belt 17 and is conveyed without slipping to the standby position (PB) at the end of the backward motion. Transfer belt 17 corresponding to the transfer paper at this time
Figure 6(b) shows the surface potential of the transfer belt 17 corresponding to the rQP-QF-QJ portion of the transfer paper. It is equal to the belt surface potential v1.

Therefore, during the image transfer process for the second color (magenta), the transfer efficiency of the rI2P-QF-QRJ portion and the rnF+QR'' portion of the transfer paper is the same, and a uniform image density can be obtained.

Next, in order to transfer the second color image, a current larger than the transfer charger current for the first color is required.

Therefore, the surface of the transfer belt after transferring the second color image is raised to -V volts. Therefore, the DC voltage v1 volts used in the first backward movement is changed to v2 volts and applied during the second backward movement. The surface potential of the transfer belt 17 when the second backward motion is completed is the average value of the surface potential of the transfer belt corresponding to the rQp-QF-QJ portion of the transfer paper, as shown in FIG. 6(c). is set to v2 volts, and even when transferring a third color image, an image with uniform density can be obtained over the entire surface.

Similarly, since the surface potential of the transfer belt becomes v3 volts due to image transfer of the third color (cyan), the DC voltage is changed to v3 volts and applied.

FIG. 6(d) shows the surface potential of the transfer belt 17 when the third backward motion is completed, and the average value is v.
3 volts, and the transferred image of the fourth color (black) also has uniform density over the entire surface, making it possible to obtain a full-color copy consisting of good overlapping images.

The processes such as image formation and image transfer in the example shown in FIG. 4 are the same as those described in FIG. 1, and therefore their description will be omitted to avoid duplication.

Further, the operation of the AC voltage applying means and the DC voltage applying means is controlled by respective control circuits (not shown).

(Effect of the invention) As described above, according to the first invention, during the transfer process,
Since a positive and negative charge pattern is formed on the transfer paper conveying means (transfer belt) corresponding to the transfer paper, the relative positions of the transfer paper and the transfer belt do not shift.

Therefore, the transfer efficiency is uniform over the entire surface, and a good image can be obtained. Further, since the surface potential of the transfer belt does not increase during each transfer process, the transfer current does not increase multiple times and there is no disturbance in one image.

Further, according to the second invention, since a charge density pattern is formed by applying an AC voltage with a DC voltage superimposed to the transfer belt that moves backward after each transfer process is completed, the relative position of the transfer paper and the transfer belt can be changed. It is possible to obtain an image with uniform density over the entire surface without any deviation.

By forming the charge density pattern that attracts the transfer paper to the transfer paper conveying means as described above, the effective length of the transfer belt can be shortened, and the image forming apparatus itself can be configured to be small.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a color image forming apparatus showing an embodiment of the present invention, FIG. 2 is a schematic configuration diagram showing only the main parts of the first invention, and FIG. 3 is a diagram showing the surface potential of the transfer belt. , FIG. 4 is a schematic configuration diagram showing only the main parts of the second invention, FIG. 5 is a timing chart showing the timing of voltage application, and FIG. 6 is a line showing changes in the surface potential of the transfer belt in the second invention. It is a diagram. DESCRIPTION OF SYMBOLS 1... Image carrier, 17... Transfer paper conveyance means, 7-
13...Developer, 22.22A...Electrode roller, 2
3, 23A...AC power supply, 23V...DC power supply, P
...Transfer paper, T...Transfer section. Form 40 (8) Ten Ikesa Cノ? '-1 and Ichinon f) e (EJ tp>

Claims (1)

[Claims] 1. A transfer paper is held by a transfer paper conveying means that moves in the same direction as the moving direction of the image carrier on which the image is formed, and the transfer paper is brought into contact with the image carrier in a transfer section. In a color image forming device that overlays images of each color on transfer paper by repeating the process of transferring the image while moving the transfer paper forward and then moving the transfer paper transport means backward, the transfer paper is transferred during the transfer process of each color. A color image forming apparatus characterized in that an alternating charge density pattern is formed on the entire surface of a transfer paper conveying means. 2. In claim 1, the first charge applying means forms an alternating charge density pattern on the surface of the conveyance means in an area where the transfer paper separates when the transfer paper conveyance means moves forward, and the transfer paper separates when the transfer paper conveyance means returns. a second charge applying means for forming an alternating charge density pattern on the surface of the conveying means in areas where the color image forming apparatus is provided. 3. A transfer paper is held by a transfer paper conveying means that moves in the same direction as the moving direction of the image carrier on which the image is formed, and the transfer paper is brought into contact with the image carrier in the transfer section and transferred while moving forward. In a color image forming apparatus that overlays an image of each color on a transfer paper by repeating the process of moving the transfer paper conveying means backward after transferring the image, the image is transferred to the surface of the transfer paper conveying means that moves backward after the transfer process for each color is completed. It is characterized by comprising an alternating current voltage applying means for forming an alternating charge density pattern, and a direct current voltage applying means for applying a direct current voltage which is superimposed on the alternating current voltage and is approximately equal to the surface potential of the transfer sheet conveying means after transfer. Color image forming apparatus.