JPH1165305A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of a streaky retransfer by providing a retransfer preventing member for applying a voltage having the same polarity as that of the charge of the toner of a toner image, so as to prevent a retransfer, that is, the retransfer to an image carrier, of the toner image after being once transferred to a transfer material. SOLUTION: In a wedge-shaped space formed between the transfer material B on the downstream side in the moving direction of the surface of the image carrier 16 adjacent to a transferring position Q3 and the image carrier 16, the retransfer preventing member Rt is arranged. An applied voltage means 32 applies the voltage having the same polarity as that of the charge of the toner of the toner image, to the retransfer preventing member Rt. This member Rt prevents the generation of the retransfer in the wedge-shaped space formed between the transfer material B on the downstream side of the transferring position Q3 and the image carrier 16. Thus, the retransfer does not occur so that a streaky void is not generated in the toner image after being transferred to the transfer material B.

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 using an electronic copying method, such as a copying machine or a printer, which electrostatically transfers a toner image formed on an image carrier to a transfer material. More particularly, the present invention relates to an image forming apparatus provided with a retransfer preventing member for preventing the occurrence of retransfer in which a part of the toner image on the transfer material returns to the image carrier again.

2. Description of the Related Art A full-color toner image formed on an image carrier such as a photosensitive drum is primarily transferred to an intermediate transfer member, and the toner image is secondarily transferred from the intermediate transfer member to a recording medium such as a recording sheet. An image forming apparatus is conventionally known (for example, see Japanese Patent Application Laid-Open No. 62-206567). FIG. 6 is a schematic explanatory view of a conventionally well-known technique using the intermediate transfer member.
6, developing devices Dk, Dy, Dm, and Dc corresponding to K (black), Y (yellow), M (magenta), and C (cyan) are arranged around the image carrier 01. While forming the toner image 02 of each color for each rotation of the image carrier,
The toner image 02 of each color is primarily transferred onto the intermediate transfer body 03 in a primary transfer area Q1 set on the movement path of the intermediate transfer body 03 that rotates synchronously with the image carrier 01,
Each color toner image is superimposed. The superimposed toner images are collectively and secondarily transferred onto the recording sheet S to form a desired image on the recording sheet S.

In the technique using the intermediate transfer member shown in FIG. 6, an intermediate transfer member 0 passing through the primary transfer area Q1 is used.
When the toner images of the respective colors are superimposed on the intermediate transfer member 3, the intermediate transfer member 03 is charged by the primary transfer electric field, and the force for attracting the toner onto the intermediate transfer member 03 increases. For this reason, at the time of the secondary transfer, a transfer failure occurs unless the secondary transfer charge is increased so that the toner on the intermediate transfer body 03 is transferred onto the recording sheet S. Further, if the intermediate transfer member 03 having a low volume resistivity is used so that the intermediate transfer member 03 is not charged, a transfer current leaks and a transfer failure occurs.

The following techniques (J01) and (J02) are conventionally known as techniques for preventing the transfer failure. (J01) (Technique described in JP-A-3-196172) According to the description of this publication, when the charge amount of the toner on the intermediate transfer member subjected to the primary transfer increases by a predetermined amount or more, a secondary transfer failure is likely to occur. Based on the experimental results, the cause of the increase in the amount of charge of the toner is due to the discharge generated between the surface of the image carrier and the surface of the intermediate transfer member when the surface is separated downstream of the primary transfer area. I am thinking. In order to prevent a discharge from occurring between the surface of the image carrier and the surface of the intermediate transfer member, a portion adjacent to the primary transfer region is located downstream of the primary transfer region where the image carrier and the intermediate transfer member are separated from each other. The static elimination corotron is placed at the location. Then, an attempt is made to perform a good secondary transfer without increasing the charge amount of the toner on the intermediate transfer body by a predetermined amount or more. (J02) (Technology described in JP-A-6-332321) In the technique described in this publication, a toner image on an image carrier is transferred onto an intermediate transfer member or a transfer material carrier at a transfer position. It is considered that the discharge generated when the transfer material separates from the surface of the image carrier is a cause of the transfer failure. Then, the transfer material on the intermediate transfer body or the transfer material carrier is discharged on the downstream side or the upstream side of the transfer position to prevent the occurrence of peeling discharge, thereby preventing transfer failure.

[0004]

However, the above-mentioned prior art is not so effective in generating streak-like image defects. The streak-like image defect is a streak-like transfer that occurs when the recording sheet on the intermediate transfer member or the transfer material carrier separates from the surface of the image carrier. (Transfer of the transferred toner onto the surface of the image carrier).
The retransfer is a phenomenon in which an unfixed toner image on the surface of an intermediate transfer member or a recording sheet or the like is blank (for monochrome) or missing (for color), and the retransfer occurs streaky. It is a streak transfer. The inventor studied, considered, and conducted experiments on the mechanism of the occurrence of streak-like retransfer and a method for preventing the occurrence.

Various inferences have been made regarding the above-mentioned examinations and considerations, and for example, the following has been estimated. (A) When a transfer electric field for primary transfer protrudes from the primary transfer region formed by pressing the surface of the intermediate transfer member against the surface of the image bearing member to the upstream side of the primary transfer region and discharge occurs,
Low-charged toner having a low charge amount is generated. At the time of primary transfer of the next color, the low-charged toner is supplied with electric charge in the primary transfer area to lower the charged potential or reverse polarity. Toner whose polarity has been reversed or whose charging potential has been lowered (for example, toner normally charged to-(minus) is replaced with + (plus) or +
Assuming that the toner charged to a potential close to that of the intermediate transfer member is streak-transferred from the intermediate transfer member to the image carrier, the toner having the opposite polarity or the charged potential lowered may be recharged. When the toner is recharged, for example, a corotron that generates negative ions is disposed downstream of the primary transfer area, or a discharge electrode to which a negative potential is applied is disposed, and the discharge electrodes and the intermediate transfer member or the image bearing member are disposed. A method of discharging between the body may be effective.

(B) After the primary transfer, residual toner remaining on the image carrier is removed by a cleaning blade or the like on the downstream side of the surface of the image carrier in the moving direction. However, some residual toner accumulates at the tip of the cleaning blade. The remaining toner includes a toner that is not sufficiently discharged and remains negatively charged, and a toner that is positively charged by the primary transfer and has a positive charge injected therein and has an opposite polarity. If the remaining charged toner is accumulated at the tip of the cleaning blade and left for a while, the portion of the image carrier surface where the toner is accumulated,
It is presumed that charging failure is caused and streaks occur when an image is formed. In this case, the streak defect of the image is not due to the retransfer, but in order to prevent the streak defect, it is necessary to solve the charging failure on the surface of the image carrier. In that case, a method of disposing a corotron that generates, for example,-ions or a discharge electrode to which a-potential is applied and causing a discharge between the discharge electrodes and the image carrier is disposed downstream of the primary transfer region. May be effective.

(C) It is assumed that a streak-like defective portion exists on the surface of the image carrier, and that the negatively charged toner transferred onto the intermediate transfer member is charged in a streaky manner on the surface of the image carrier. If it is to be re-transferred to the defective portion, in order to prevent the re-transfer, a corotron that generates, for example,-ions may be arranged downstream of the primary transfer area, or a discharge electrode to which a-potential is applied may be used. A method of arranging and discharging between the discharge electrode and the image carrier may be effective.

The present inventor has conducted various studies and considerations as exemplified in the above (a) to (c), but since the actual fact is unknown, various experiments were eventually conducted. As a result of the above experiment, a member or a corotron to which a voltage of the same polarity as the toner of the toner image was applied was placed in a space formed between the surface of the image carrier and the surface of the transfer material such as an intermediate transfer member downstream of the primary transfer area. Then, the result was obtained that the streak-like transfer was effective in preventing the occurrence.

[0009] In view of the above circumstances (and experimental results), the present invention is directed to the following content (O01). (O01) In an image forming apparatus for transferring a toner image on an image carrier onto a transfer material such as an intermediate transfer body or a recording sheet carried on a transfer material carrier, a part of the toner image is streaked. To prevent the occurrence of streak-like transfer returning to the carrier.

[0010]

Next, a description will be given of the present invention which has solved the above-mentioned problems. In the description of the present invention, reference numerals in parentheses added after constituent elements of the present invention denote constituent elements of the present invention. Reference numerals of corresponding components of the embodiment described later. The reason why the present invention is described in correspondence with the reference numerals of the components of the embodiments described later is to facilitate understanding of the present invention, and not to limit the scope of the present invention to the embodiments.

(Invention) In order to solve the above-mentioned problems, an image forming apparatus of the invention has the following requirements. (A01) The surface of an image carrier (16) which rotates and moves is provided. (A02) a latent image forming apparatus (ROS) for forming an electrostatic latent image on the surface of a uniformly charged image carrier (16), and (A03) a toner image (A04) a transfer device (21) disposed at a transfer position (Q3) for transferring a toner image formed on the surface of the image carrier (16) to a transfer material (B). (A05) A wedge-shaped space formed between the transfer material (B) and the image carrier (16) on the downstream side in the moving direction of the surface of the image carrier (16) adjacent to the transfer position (Q3). (We), and a voltage having the same polarity as the charge polarity of the toner of the toner image is applied to the transfer material (B). ), The toner image once transferred to the image carrier (16) is prevented from being retransferred.
t; Rt '; Rtk to Rtc), (A06) applying a voltage having the same polarity as the charging polarity of the toner to the retransfer preventing member (R
t; Rt '; applied voltage supply means (32) for supplying Rtk to Rtc). The transfer material means either an intermediate transfer member or a recording sheet.

(Operation of the Present Invention) In the image forming apparatus of the present invention having the above-described configuration, the surface of the image carrier (16) on which the charger (17) rotates is uniformly charged. A latent image forming apparatus (ROS) forms an electrostatic latent image on the surface of the uniformly charged image carrier (16). The developing device (D) develops the latent image into a toner image. The transfer device (21) arranged at the transfer position (Q3) transfers the toner image formed on the surface of the image carrier (16) to the transfer material (B). The transfer position (Q3)
A wedge-shaped space (We) formed between the transfer material (B) and the image carrier (16) on the downstream side in the moving direction of the surface of the image carrier (16) adjacent to the image carrier (16) has a retransfer prevention member. (Rt; Rt '; Rtk to Rtc). The applied voltage supply means (32) includes a retransfer prevention member (R
t; Rt '; Rtk to Rtc), a voltage having the same polarity as the charged polarity of the toner of the toner image is applied. The retransfer prevention member (Rt; Rt '; Rtk to Rtc) is a wedge-shaped space formed between the transfer material (B) and the image carrier (16) on the downstream side at the transfer position (Q3). (We) prevents occurrence of retransfer. Since the retransfer does not occur, no streak-like white spot occurs in the toner image transferred to the transfer material (B) and the toner image transferred on the transfer material (B) at the transfer position (Q3) The toner image has good image quality.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) The image forming apparatus according to Embodiment 1 of the present invention has the following requirements.
7) The transfer material (B), which is an intermediate transfer member (B).

(Operation of the First Embodiment) In the image forming apparatus of the first embodiment of the present invention having the above configuration, the toner transferred onto the intermediate transfer member (B) in the transfer position (Q3) region is Retransfer prevention member (Rt; R
t '; Rtk to Rtc) do not retransfer to the image carrier (16). Therefore, no streak-like transfer occurs, and a good image without streak-like image defects can be obtained.

(Embodiment 2) An image forming apparatus according to Embodiment 2 of the present invention is characterized by satisfying the following requirements in the present invention or Embodiment 1 (A08).
The retransfer prevention member (Rt; Rt '; Rtk to Rtc) disposed in the wedge-shaped space (We) and at a position close to the surface of the transfer material (B).

(Operation of the Second Embodiment) In the image forming apparatus of the second embodiment of the present invention, the retransfer prevention member (Rt; Rt '; Rtk to Rtc) is the wedge-shaped space (We) and the transfer material. (B) the retransfer prevention member (Rt; Rt '; Rtk to Rt) which is disposed at a position close to the surface;
Since c) is close to the transfer material (B), the streak-like transfer is more effectively prevented.

(Embodiment 3) An image forming apparatus according to Embodiment 3 of the present invention is characterized by satisfying the following requirements in the present invention or in Embodiment 1 or 2. A010) The applied voltage supply means (32) for supplying a DC voltage having the same polarity as the charged polarity of the toner of the toner image to the retransfer prevention member (Rt; Rt '; Rtk to Rtc).

(Operation of Third Embodiment) In the image forming apparatus of the third embodiment of the present invention, the applied voltage supply means (32) is provided with the retransfer prevention member (Rt; Rt '; Rtk to Rt).
In c), a DC voltage having the same polarity as the charged polarity of the toner of the toner image is supplied. This makes it possible to remove the toner remaining on the image carrier (16) due to the positive or negative charge, and to generate the streak-like transfer which is considered to be caused by the residual toner on the image carrier (16). Can be prevented.

(Embodiment 4) An image forming apparatus according to Embodiment 4 of the present invention is characterized by satisfying the following requirements in the present invention or any of Embodiments 1 to 3. A09) The anti-re-transfer member (Rt; Rt '; Rtk ~) composed of a sawtooth-shaped conductive member
Rtc).

(Operation of the Fourth Embodiment) In the image forming apparatus according to the fourth embodiment of the present invention, the anti-retransfer member (Rt; Rt '; Rtk to Rtc) is formed of a saw-tooth conductive member. Therefore, the electric field is concentrated on the sawtooth-shaped tip of the retransfer prevention member (Rt; Rt '; Rtk to Rtc), and a minute discharge is generated between the transfer material and the transfer material (B). At this time, since the toner is recharged, no toner charged to the opposite polarity is generated, and the force for holding the toner on the transfer material (B) is increased.
The streaky transfer of the toner to the image carrier is prevented.

(Embodiment 5) An image forming apparatus according to a fifth embodiment of the present invention is characterized in that the following requirements are satisfied in the present invention or any of the first to third embodiments. A011) The anti-retransfer member (Rt; Rt '; Rtk to Rt) constituted by a corotron
c), (A012) the applied voltage supply for supplying a voltage obtained by superimposing an AC voltage on a DC voltage having the same polarity as the charging polarity of the toner of the toner image to the retransfer prevention member (Rt; Rt '; Rtk to Rtc). Means (32).

(Operation of Embodiment 5) In the image forming apparatus of Embodiment 5 of the present invention, the applied voltage supply means (32) applies an AC voltage to a DC voltage having the same polarity as the charging polarity of the toner of the toner image. The superimposed voltage is supplied to the retransfer prevention member (Rt; Rt '; Rtk to Rtc). Thereby, the corotron (anti-transfer member, Rt; R)
t '; Rtk to Rtc) release-(minus) ions,
The poorly charged toner on the transfer material (B) has a correct charging potential, and can prevent the occurrence of streak-like transfer.

[0023]

Next, specific examples (embodiments) of the embodiment of the image forming apparatus of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments. (Embodiment 1) FIG. 1 is an overall explanatory view of an image forming apparatus according to Embodiment 1 of the present invention. In FIG. 1, an image forming apparatus F capable of performing color copying has a UI (user interface) having a copy start key, a numeric keypad, a display unit, and the like on an upper part thereof.
And a transparent platen glass 2 on which a document (not shown) is placed. A document illumination unit 3 that scans the document while illuminating the document is arranged below the platen glass 2. The document illumination unit 3 includes a document illumination light source 4.
And a first mirror 5. A mirror unit 6 that moves at half the speed of the original illumination unit 3 is disposed below the platen glass 2. The mirror unit 6 includes a second mirror 7 and a third mirror 8 which are emitted from the illumination light source 4 and reflected by the original, and reflect the original image light reflected by the first mirror 5. The document image light reflected by the third mirror 8 passes through the imaging lens 9 and is read as R, G, and B analog signals by a CCD (color image reading sensor).

The R (red), G (green), and B (blue) image signals read by the CCD are input to the IPS.
The operation of the IPS is controlled by the controller C.
Further, the IPS converts the analog electric signals of the R, G, B read images obtained by the CCD into digital signals and outputs the digital signals, and outputs the RGB image data to K (black), Y (Y). (Yellow), M (magenta), and C (cyan) image data that is converted into image data, subjected to data processing such as density correction and enlargement / reduction correction, and output as writing image data (laser drive data) Means 12 are provided. The image data output unit 1
2 has an image memory 13 for temporarily storing the image data of K, Y, M, C.

The IPS write image data output means 12
The image write data (laser drive data) of four colors of K, Y, M, and C output by the laser drive signal are input to the laser drive signal output device 14. The laser drive signal output device 14 outputs a laser drive signal of an image of each color component of K, Y, M, and C in accordance with the input image data at a predetermined timing to an ROS (optical scanning device, that is, a latent image forming device). ). The ROS is adjusted to 160 mm / mm by the laser beam L modulated by the input laser drive signal.
The electrostatic latent image writing position Q1 of the image carrier 16 rotating at the speed of sec is scanned. Along the rotating image carrier 16, the latent image writing position Q 1 is set in the moving direction of the image carrier 16.
A charging corotron (charging device) 17 for uniformly charging the image carrier 16 is arranged on the upstream side of. Although the charging device 17 is configured by a charging corotron in the first embodiment, it can be configured by a charging roll. After the image carrier 16 is uniformly charged by the charger 17, an electrostatic latent image is written by the laser beam L at the latent image writing position Q1.

A rotary developing device (developing device) for developing the electrostatic latent image into a toner image is provided in a developing area Q2 downstream of the latent image writing position Q1 along the moving direction of the image carrier 16. (Device) D is disposed. The developing device D includes developing devices D of four colors of K, Y, M, and C mounted around the rotation shaft 18.
k, Dy, Dm, and Dc, and the developing units Dk, Dy, Dm, and Dc of the four colors are sequentially moved to the developing area Q2 as the rotation shaft 18 rotates. I have. The developing devices Dk, Dy, Dm and Dc convert the electrostatic latent images on the image carrier 16 into K (black), Y (yellow), M (magenta),
This is a device for developing a toner image of each color of C (cyan).
The elements indicated by the reference numerals 14 to 17, ROS, D, etc., constitute a toner image forming apparatus (14 to 17 + ROS + D). A primary transfer position (transfer position) Q3 set on the downstream side of the developing area Q2 along the surface of the rotating image carrier 16 has an intermediate transfer member (intermediate transfer belt).
B and a primary transfer roll (transfer device) 21 are arranged.

A wedge-shaped space We (FIG. 2) formed along the rotating image carrier 16 and downstream of the primary transfer position Q3 and formed by the surface of the image carrier 16 and the surface of the intermediate transfer member B. ) Is provided with a retransfer prevention member Rt. The anti-retransfer member Rt of the first embodiment is constituted by a retransfer preventing electrode having a sawtooth-shaped tip. An image carrier cleaner 22 and a static elimination lamp 23 are arranged on the downstream side of the anti-retransfer electrode Rt having the serrated tip.
In addition, it is possible to use a static elimination roll instead of the static elimination lamp 23. The intermediate transfer member B includes a driving roll 2
5, an idler roll 26, a tension roll 27, a walk correction roll 28 (a roll for adjusting the position of the intermediate transfer body B in the width direction), and an inner transfer roll (backup roll) 29. The image carrier 16 is rotated in the direction indicated by an arrow A through the driving roller 25 at substantially the same speed as the image carrier 16 by a driving device (not shown).

The intermediate transfer member (intermediate transfer belt) B
A single-layer belt formed of a resin such as acrylic, polyester, polycarbonate, polyimide, urethane, nylon, vinyl chloride, or various rubber materials containing an appropriate amount of a conductive material such as carbon black, for example, having a thickness of 0.1 mm. .

At the periphery of the intermediate transfer member B, an outer transfer roll 30 grounded on the side opposite to the inner transfer roller 29 with respect to the intermediate transfer member B is disposed at a secondary transfer position Q4. Have been. A contact roll 31 (electrode roll) to which a bias having the same polarity as that of the toner is applied to the inner transfer roll 29 at a distance of 20 to 40 mm in the circumferential direction of the inner transfer roll 29 from the secondary transfer position Q4. ) Is in contact. The inner secondary transfer roll 29 is formed by covering an insulating roll with a semiconductive thin film. The semiconductive thin film is formed to have a thickness of 10 μm to 200 μm, and its surface resistivity is adjusted to 10 ⁷ to 10 ¹¹ Ω / □ (□: unit area). The outer secondary transfer roll 30 is a grounded conductive roll, and its volume resistivity is desirably as low as 10 ⁷ Ω · cm or less in order to keep its surface potential equal to the ground position. The elements indicated by the reference numerals 29 to 31 constitute the secondary transfer unit T of the first embodiment.

The outer transfer roll 30 is grounded, and the contact roll contacting the inner transfer roll 29 is connected to a transfer power supply circuit 32 (see FIG. 1) as a secondary transfer power applying means. The transfer power supply circuit 32 connects the inner transfer roll 29 via the contact roll 31.
To the intermediate transfer member B
The upper toner image is transferred to the recording sheet S. The transfer power supply circuit 32 is controlled by the controller C. A transfer roller cleaning blade 33 made of polyurethane rubber is always in contact with the surface of the outer transfer roll 30 to remove toner adhered to the surface of the outer transfer roll 30. Further, in the transport direction of the intermediate transfer body B,
On the downstream side of the secondary transfer position Q4, a separating claw H for separating the recording sheet S on which the toner image has been secondarily transferred from the intermediate transfer member B is disposed.
An intermediate transfer member cleaner 34 for removing untransferred toner remaining on the surface of the intermediate transfer member B is provided. The outer transfer roll 30 and the intermediate transfer body cleaner 34
Are configured so as to be able to press against and separate from the intermediate transfer member B.

The recording sheet S taken out of the paper feed tray 35 is conveyed by a feed roll 36, temporarily stopped by a registration roll 37, and then passes through a guide conveyance path 38 at a predetermined timing to the secondary transfer position Q4. Conveyed. The unfixed toner image on the intermediate transfer body B is secondarily transferred to the recording sheet S when passing through the secondary transfer position Q4. The recording sheet S to which the unfixed toner image has been transferred is
The sheet moves along the upper surface of the sheet guide member 39 and is further conveyed to the fixing position Q5 through the conveying belt 40. When the recording sheet S passes through the fixing position Q5, the unfixed toner image on the recording sheet S is fixed by the fixing device 41 and is discharged to the paper discharge tray 42. The elements indicated by the reference numerals 35 to 38 constitute the recording sheet conveying device (35 to 38) of the first embodiment.

Next, the retransfer prevention electrode (retransfer prevention member) Rt will be described. FIG. 2 shows a retransfer prevention electrode (retransfer prevention member) R
FIG. 2A is an enlarged explanatory view of a retransfer prevention electrode Rt disposed in a wedge-shaped space formed between the image carrier and the intermediate transfer body on the downstream side of the primary transfer position, and FIG. The distance from the point where the image carrier and the intermediate transfer member are separated to the sawtooth-shaped tip of the retransfer prevention electrode Rt, the applied voltage applied to the retransfer prevention electrode Rt, the destruction and streaking of the image carrier surface layer. 9 is a graph showing a relationship with occurrence of retransfer. In FIG. 2A, the sawtooth-shaped tip of the retransfer prevention electrode Rt arranged in a wedge-shaped space We formed by the image carrier 16 and the intermediate transfer member B downstream of the primary transfer position Q3 is It faces the primary transfer position Q3. In FIG. 2A, a curve P0 is a curve equidistant from the surface of the image carrier 16 and the surface of the intermediate transfer body B, an area P1 shows a space between the curve P0 and the surface of the intermediate transfer body B, and an area P2 shows the curve P0 and the image The space between the surfaces of the carrier 16 is shown. The sawtooth-shaped tip of the retransfer prevention electrode Rt is disposed on a line equidistant from the surface of the intermediate transfer member B and the curve P0 (on the center line of the region P1). Since the charge polarity of the toner is negative in the first embodiment, a negative DC voltage having the same polarity as the charge polarity of the toner is supplied from the transfer power supply 32 (applied voltage supply unit) to the retransfer prevention electrode Rt. Is done.

(Operation of Embodiment 1) In FIG. 1, the image carrier 16 rotates in the direction of the mark A, and the surface thereof is charged by the charger 17 in a uniform manner. ROS is applied to the charged image carrier 16
An electrostatic latent image of a first color (for example, K, that is, black) is formed by an image writing unit such as a (laser writing device). The electrostatic latent image is developed with toner by the developing device D to form a visualized toner image Im. The toner image Im is transferred to the primary transfer roll 21 by the rotation of the image carrier 16.
Is transported to the primary transfer position Q3 where is disposed. In the primary transfer area Q3, the image carrier 1
A voltage having a polarity opposite to that of the toner is applied to the primary transfer roll 21 pressed by 6. By applying an electric field having a polarity opposite to that of the toner image Im, the toner image Im is electrostatically attracted to the intermediate transfer body B and primary-transferred. Hereinafter, similarly, a toner image of a second color (for example, yellow Y), a toner image of a third color (for example, magenta M), and a toner image of a fourth color (for example, cyan C) are sequentially formed and superimposed on the intermediate transfer member B. As a result, a multiple toner image is formed.

The multi-toner image transferred to the intermediate transfer member B is conveyed to the secondary transfer area Q4 as the intermediate transfer member B rotates. The recording sheet S is conveyed to the secondary transfer area Q4 in time with the conveyance of the multiplex toner image to the secondary transfer area Q4. In the secondary transfer area Q4,
The multiple toner images on the intermediate transfer member B are formed by an outer secondary transfer roller 30 provided on the surface of the intermediate transfer member B on which the toner image is carried and an inner secondary transfer roller disposed on the back side of the intermediate transfer member B. Due to the secondary transfer voltage applied between the recording sheet S and the contact roll 31 contacting the recording sheet S,
Next is transferred. Recording sheet S on which multiple toner images have been transferred
Is peeled off from the intermediate transfer body B by operating the peeling claw H at the retracted position until the primary transfer of the final toner image is completed, is conveyed to the fixing device 41, and the toner image is fixed by the pressure / heat treatment. It is a permanent image. The intermediate transfer member B, on which the transfer of the multiple toner images to the recording sheet S has been completed, is subjected to removal of residual toner by an intermediate transfer member cleaner 34 provided downstream of the secondary transfer region Q4 to prepare for the next transfer. .

In the case of transferring a single-color image, the primary-transferred toner image Im is immediately secondarily transferred to the fixing device 41.
However, in the case of transferring a multi-color image by superimposing a plurality of colors, the rotation of the intermediate transfer body B and the rotation of the image carrier 16 are synchronized so that the toner images of each color exactly match at the primary transfer position Q3. Thus, the toner images of the respective colors do not shift. In the secondary transfer area Q4, a transfer voltage having the same polarity as the polarity of the toner image is applied to the contact roll 31 which comes into contact with the outer secondary transfer roll 30 and the inner secondary transfer roll 29 which is disposed to face the intermediate transfer body B via the intermediate transfer body B. Then, the toner image is transferred to the recording sheet S by electrostatic repulsion.

A part of the multi-color toner or the single-color toner transferred to the intermediate transfer member B is transferred from the intermediate transfer member B by the anti-retransfer electrode Rt to which a DC voltage having the same polarity as that of the multi-color or single-color toner is applied. There is no return to the carrier 16 again. In addition, when the retransfer prevention electrode Rt is used, in the step of charging the surface of the image carrier 16 after the primary transfer, uneven charging that occurs on the surface of the image carrier 16 is less likely to occur.

(Experimental Results) The inventor examined by experiment the DC voltage applied to the anti-retransfer electrode Rt and the arrangement position of the anti-retransfer electrode Rt suitable for preventing the occurrence of streak-like retransfer. In FIG. 2B, the vertical axis represents the DC voltage (-kV) applied to the retransfer prevention electrode Rt, and the horizontal axis represents the image carrier 16.
D1 (m
m). As described above, the sawtooth-shaped tip of the retransfer prevention electrode Rt is disposed on a line equidistant from the surface of the intermediate transfer member B and the curve P0 (on the center line of the region P1). As a result of the experiment, in the graph of FIG. 2B, the area above the straight line (solid line) L1 is an area where the surface layer of the image carrier 16 is broken, and the area below the straight line (dashed line) L2 is an area where streak-like transfer occurs. .

The straight line L2 indicating the boundary of the occurrence of the streak-like retransfer rises to the right, that is, the distance D1 (mm) from the separation position where the image carrier 16 and the intermediate transfer member B are separated from the retransfer prevention electrode Rt. Becomes larger, streak-like transfer easily occurs, and the lower limit of the applied voltage at which the streak-like transfer does not occur becomes larger. However, if the applied voltage becomes excessive, the image carrier 16
The surface layer is destroyed. Therefore, if the applied voltage is small, the cost of the power supply can be reduced, and the tip of the anti-retransfer electrode Rt should be arranged as close as possible to the separation position where the image carrier 16 and the intermediate transfer member B are separated. It turned out to be desirable. According to the experiment of the inventor, the distance D effective for preventing the streak-like retransfer is effective.
1 and the applied voltage are preferably 2 mm (applied voltage at this time: 0.5 kV to 4.5 kV) to 10 mm (applied voltage at this time: 6 kV to 6.5 kV).

FIG. 3 is an explanatory diagram of an experiment for examining the relationship between the arrangement position of the anti-transfer prevention electrode Rt and the applied voltage. FIG. 3A is an explanatory diagram of the arrangement position of the anti-retransfer electrode Rt, and FIG. The distance from the saw-toothed tip of the retransfer prevention electrode Rt to the point where the image carrier and the intermediate transfer member are separated when the retransfer prevention electrode Rt is arranged closer to the carrier or the intermediate transfer member, and the retransfer prevention electrode Rt 4 is a graph showing the relationship between the applied voltage applied to the substrate and the destruction of the image carrier surface layer and the occurrence of streak-like transfer. 3A, the saw-toothed tip of the anti-retransfer electrode Rt is arranged on a line equidistant from the surface of the intermediate transfer member B and the curve P0 (on the center line of the area P1) (that is, as shown in FIG. 2A). And the case where they are arranged on a line equidistant from the surface of the image carrier 16 and the curve P0 (on the center line of the area P2). The re-transfer prevention electrode Rt is disposed in each of the regions P1 and P2, and a distance D2 from the sawtooth-shaped tip of the re-transfer prevention electrode Rt to a point at which the image carrier 16 and the intermediate transfer member B are separated from each other.
The relationship between the applied voltage and the voltage applied to the retransfer prevention electrode Rt was examined.

In FIG. 3B, the upper part of the straight line (solid line) L1 is connected to the retransfer prevention electrode Rt in the region P1.
(The image carrier 1 when placed on the side closer to the intermediate transfer member B)
6 The area where the surface layer is broken, and the area below the straight line (broken line) L2 is the area where streaky retransfer occurs in the area P1, which is the same as FIG. 2B. Also, a straight line (solid line)
The area above L3 is the area where the surface layer of the image carrier 16 is broken when the anti-retransfer electrode Rt is arranged in the area P2 (the side closer to the image carrier 16), and the area below the straight line (dotted line) L4 is the area P2. This is a region where streak-like transfer occurs on the side (closer to the image carrier 16).

The straight line L2 which is the boundary of the streaky transfer in the area P1 (the side closer to the intermediate transfer member B)
The straight line L4, which is the boundary of the streaky transfer in the area P2 (the side closer to the image carrier 16), rises to the right. That is, as the distance D2 increases, streak-like transfer is more likely to occur, and the lower limit of the applied voltage at which the streak-like transfer does not occur increases. However, the straight line L2 is below the straight line L4. That is, when the distance D2 is the same, the lower limit of the applied voltage at which the line retransfer does not occur is lower in the straight line L2 than in the straight line L4. Therefore, it is more effective to arrange the anti-retransfer electrode Rt at a position close to the intermediate transfer member B (the area P2 in FIG. 3B) from the viewpoint of reducing the cost of the power supply and saving the power consumption. is there.

In the charging step of the surface of the image carrier 16 after the primary transfer, uneven charging may occur on the surface of the image carrier 16. However, another experiment examining the effect of the use of the retransfer prevention electrode Rt revealed that uneven charging on the surface of the image carrier 16 was less likely to occur. It is considered that this is because the residual charge on the surface of the image carrier 16, which is presumed to be the cause of the uneven charging on the surface of the image carrier 16, was removed by the retransfer prevention electrode Rt. The configuration in which a DC voltage having the same polarity as the toner is applied to the anti-retransfer electrode Rt has been described.
It has been found that applying a voltage obtained by superimposing an AC voltage on a C voltage is also effective in preventing streak-like transfer. In this case, the residual toner remaining on the image carrier 16 without being discharged after the primary transfer, which is presumed to be a cause of the occurrence of the streak-like transfer, becomes a DC having the same polarity as the toner.
It is considered that since the residual toner is removed by the retransfer prevention electrode Rt to which the voltage obtained by superimposing the AC voltage on the voltage is applied, the occurrence of the streak-like transfer is prevented.

(Embodiment 2) FIG. 4 is an explanatory view of a retransfer prevention corotron (retransfer prevention member) used in the image forming apparatus of Embodiment 2 of the present invention.
FIG. 4B is an enlarged explanatory view of a retransfer preventing member disposed in a wedge-shaped space formed between the image carrier and the intermediate transfer member on the downstream side of the next transfer position. FIG. 4B shows a point where the image carrier and the intermediate transfer member are separated from each other. 7 is a graph showing the relationship between the distance from a re-transfer prevention member to a discharge wire, the voltage applied to the re-transfer prevention member, and the destruction of the image carrier surface layer and the occurrence of streak-like retransfer. In the description of the second embodiment, components corresponding to the components of the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted. The image forming apparatus according to the second embodiment differs from the first embodiment in the following points, but has the same configuration as the first embodiment in other points.

In FIG. 4A, the anti-transfer member Rt 'used in the image forming apparatus of the second embodiment is formed of a corotron having a discharge wire (anti-transfer corotron). A voltage obtained by superimposing an AC voltage on a DC voltage having the same polarity as the toner is applied to the anti-retransfer corotron Rt '. The inventor of the present invention uses the same method as in the first embodiment to determine the distance D3 between the separation position where the image carrier 16 and the intermediate transfer member B are separated from the discharge wire of the retransfer preventing corotron Rt 'and the distance D3 between the retransfer preventing corotron Rt' Applied voltage and image carrier 1
6 The relationship between the surface layer destruction and the occurrence of streak-like retransfer was examined by experiments. The positions of the discharge wires are arranged on a line equidistant from the surface of the intermediate transfer member B and the curve P0 (on the center line of the region P1), similarly to FIG. In FIG. 4B, the area below the straight line (dotted line) L5 is an area where streak-like transfer has occurred. For comparison, a straight line L2 as an experimental result of Example 1 is also shown on the graph of FIG. 4B.

A straight line L5 indicating the boundary of the occurrence of the streaky retransfer rises to the right, that is, the distance from the separation position where the image carrier 16 and the intermediate transfer member B are separated from the discharge wire of the retransfer prevention corotron Rt '. D3 (m
As m) increases, streak-like transfer easily occurs, and the lower limit of the applied voltage at which the streak-like transfer does not occur also increases. Since the lower limit of the applied voltage at which the streak-like transfer does not occur in the second embodiment is lower than the lower limit of the applied voltage in the case of the first embodiment (L2 in FIG. 4B), the serrated shape of the first embodiment is used. The cost of the power supply can be reduced as compared with the case where the anti-retransfer electrode Rt made of a conductive member is used. According to the experiment of the inventor, the distance D effective for preventing the streak-like retransfer is effective.
3 and the applied voltage are 3 mm (at this time, the applied voltage is
5 kV to 4.7 kV) to 10 mm (at this time, the applied voltage is 4.5 kV to 6.5 kV).

(Embodiment 3) FIG. 5 is an explanatory view of an image forming apparatus according to Embodiment 3 of the present invention. In the description of the third embodiment, components corresponding to the components of the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.
The third embodiment differs from the first embodiment in the following points, but has the same configuration as the first embodiment in other points. The third embodiment is an example in which the anti-retransfer electrode Rt used in the first embodiment is applied to a tandem digital color copying machine F in which tandem is provided. In FIG. 5, in the third embodiment, the four image carriers 16k to 16c for forming the toner images of each color are arranged in tandem, so that K is set according to the image carriers 16k to 16c of each color.
An optical writing scanning device having a KY optical scanning device U1 for writing (black) and Y (yellow) images and an MC optical scanning device U2 for writing M (magenta) and C (cyan) images. U, image carriers 16k to 16c, chargers 17k to 17c, developing devices Dk to Dc, primary transfer rolls 21k to 21c, anti-retransfer electrodes Rtk to Rtc, and cleaner units 22k to 22c.

The primary transfer rolls 21k, 21y, 21
m, 21c, on the intermediate transfer member B,
(Black), Y (yellow), M (magenta), and C
The (cyan) toner image is transferred in an overlapping manner. In the secondary transfer area Q4, the multiplex toner on the intermediate transfer member B is secondarily transferred to the recording sheet S taken out of the paper feed tray 35, then fixed by the fixing device 41, and discharged to the discharge tray 42. In the third embodiment, the anti-retransfer electrodes Rtk to Rtc are also used in the first embodiment.
It has the same function as.

(Modifications) Although the embodiments of the present invention have been described in detail, the present invention is not limited to the above-described embodiments, but falls within the scope of the present invention described in the appended claims. Thus, various changes can be made. Modified embodiments of the present invention will be exemplified below. (H01) In the first embodiment, it is possible to apply a DC plus AC voltage to the retransfer prevention member. (H02) As the retransfer preventing member, various conductive members such as a conductive needle, a conductive film, and a conductive brush (used in a non-contact manner) other than the members exemplified in the embodiments can be used. (H03) The retransfer prevention member is also applicable to an image forming apparatus for directly transferring a toner image on an image carrier to a recording sheet. In this case, the present invention is also applicable to an image forming apparatus using a transfer material carrying drum that carries a transfer material on its surface and repeatedly passes through a transfer position. (H04) An intermediate transfer drum can be used in place of the intermediate transfer belt of the first or second embodiment.

[0049]

The above-described image forming apparatus of the present invention has the following effects. (E01) In an image forming apparatus for transferring a toner image on an image carrier onto a transfer material such as an intermediate transfer body, it is possible to prevent the occurrence of streak transfer in which a part of the toner image returns to the image carrier again. can do. (E02) The image forming apparatus of the present invention can prevent the occurrence of charging unevenness on the surface of the image carrier.

[Brief description of the drawings]

FIG. 1 is an overall explanatory diagram of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is an explanatory view of a retransfer prevention electrode (retransfer prevention member) Rt, and FIG. 2A is a wedge-shaped space formed between an image carrier and an intermediate transfer body downstream of a primary transfer position. FIG. 2B is an enlarged explanatory view of a retransfer prevention electrode Rt disposed at a distance from a point at which an image carrier and an intermediate transfer member are separated from each other to the sawtooth-shaped tip of the retransfer prevention electrode Rt and the retransfer prevention electrode Rt.
4 is a graph showing a relationship between an applied voltage applied to t and destruction of an image carrier surface layer and occurrence of streak-like transfer.

3 is an explanatory view of an experiment for examining a relationship between an arrangement position of a retransfer prevention electrode Rt and an applied voltage, FIG. 3A is an explanatory view of an arrangement position of the retransfer prevention electrode Rt, and FIG. The distance from the sawtooth-shaped tip of the retransfer prevention electrode Rt to the point where the image carrier and the intermediate transfer member are separated when the image transfer member or the intermediate transfer member is disposed closer to the image transfer member and the intermediate transfer member; 9 is a graph showing the relationship between the applied voltage to Rt and the destruction of the image carrier surface layer and the occurrence of streak-like transfer.

FIG. 4 is an explanatory diagram of a retransfer prevention corotron (retransfer prevention member) used in the image forming apparatus according to the second embodiment of the present invention. FIG. 4A is a view illustrating an image carrier and a downstream side of a primary transfer position. FIG. 4B is an enlarged explanatory view of a retransfer preventing member disposed in a wedge-shaped space formed between the intermediate transfer member and the intermediate transfer member. 5 is a graph showing a relationship between a distance and an applied voltage applied to the retransfer prevention member, and destruction of an image carrier surface layer and occurrence of streak-like retransfer.

FIG. 5 is an explanatory diagram of an image forming apparatus according to a third embodiment of the present invention.

FIG. 6 is a schematic explanatory view of a conventionally well-known technique using the intermediate transfer member.

[Explanation of symbols]

B: transfer material (intermediate transfer member), D: developing device, Q3: transfer position, ROS: latent image forming device, (Rt; Rt '; Rtk to Rt)
c) retransfer prevention member, We ... wedge-shaped space 16 ... image carrier, 17 ... charger, 21 ... transfer device, 32 ...
Applied voltage supply means

Continued on the front page (72) Inventor Keiji Yamamoto 2274 Hongo, Ebina-shi, Kanagawa Prefecture Fuji Xerox Co., Ltd. (72) Inventor Nobuyoshi Komatsu 2274 Hongo, Ebina-shi, Kanagawa Fuji Xerox Co., Ltd.

Claims (3)

[Claims] 1. An image forming apparatus having the following requirements: (A01) a charger for uniformly charging the surface of a rotating image carrier; and (A02) a uniformly charged image carrier. A latent image forming apparatus for forming an electrostatic latent image on the surface, (A03) a developing apparatus for developing the latent image into a toner image, and (A04) a transfer for transferring the toner image formed on the image carrier to a transfer material (A05) a transfer unit disposed in a wedge-shaped space formed between the transfer material and the image carrier on the downstream side in the moving direction of the surface of the image carrier adjacent to the transfer position; A retransfer prevention member for applying a voltage having the same polarity as the charged polarity of the toner of the toner image to prevent the toner image once transferred to the transfer material from being retransferred to the image carrier; A06) The same polarity as the charged polarity of the toner Applying voltage supply means for supplying a voltage to the retransfer preventing member; 2. The transfer material according to claim 1, wherein the transfer material is an intermediate transfer member of the image forming apparatus (A07). 3. The image forming apparatus (A08) according to claim 1 or 2, wherein the retransfer prevention is disposed in the wedge-shaped space and at a position close to the surface of the transfer material. Element.