JP2000131966A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image forming device by which color mixing and a positive ghost do not occur inside a developing device in a cleanerless system color image forming device. SOLUTION: This image forming device has an image carrier PR whose rotating and moving surface is electrostatically charged, on the electrified surface of which an electrostatic latent image corresponding to toner images having different colors is sequentially formed, in which the electrostatic latent image corresponding to the toner image is sequentially developed to the toner image of a corresponding color by a non-contacting developing device D, in which the toner image is primarily transferred to an intermediate transfer body B, and on which a cleaner removing residual toner on the surface of the image carrier PR obtained after the primarily transferring along the rotating and moving surface is not provided; and also this image forming device has the body B on the surface of which the toner image on the carrier PR is primarily transferred, in which the toner image is secondarily transferred to a recording sheet, and removed by the intermediate transfer body cleaner, and whose circumferential length is the same as that of the surface of the carrier PR.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus in which toner images of different colors are formed on a rotatable image carrier by using developers of different colors, and the respective color toner images are sequentially transferred to a transfer medium. The present invention relates to a color image forming apparatus for forming an image.

[0002]

2. Description of the Related Art FIG. 12 is a view showing a schematic configuration of a general image forming apparatus provided with the above-mentioned intermediate transfer member. The surface of the image carrier (photosensitive drum) PR that rotates in the direction of the arrow Ya is uniformly charged by the charger CSC (charge scorotron) in the charging area Q0, and is charged by the laser beam L in the latent image writing position Q1. An electrostatic latent image is formed. For a full-color image, K (black), Y (yellow), M
Electrostatic latent images corresponding to the four color images (magenta) and C (cyan) are sequentially formed. In the case of a monochrome image, K (black) is used.
Only an electrostatic latent image corresponding to the image is formed. In the case of a full-color image, the electrostatic latent images of each color sequentially formed on the surface of the image carrier PR are K (black) and Y (black) of a rotary developing device D that rotates around a rotation axis Da in a developing region Q2. The developing devices DK, DY, DM, and DC of four colors of yellow), M (magenta), and C (cyan) are developed into toner images TNn of the respective colors.

A slide frame F1 (indicated by a two-dot chain line) is supported by a pair of right and left slide rails SR, SR disposed below the image carrier PR so as to be able to enter and exit the image forming apparatus main body. A belt module BM is supported on the frame F1 so as to be vertically rotatable. The belt module BM includes a plurality of belt supporting rolls (Rd, Rf, Rt,
Rw), the intermediate transfer belt B rotatably supported by
, A primary transfer roll T1, and the backup roll T2.
It has an electrode roll T2c abutting on a, and a belt frame F2 supporting them.

A transfer voltage having a polarity opposite to that of the toner is applied to the primary transfer roll T1 by a power supply circuit E controlled by a controller C, and the toner image TNn on the surface of the image carrier PR is transferred to the primary transfer area. In Q3, primary transfer is performed on the intermediate transfer belt B. In the case of a full-color image, the image carrier P
The toner images of the respective colors sequentially formed on the R surface are sequentially transferred onto the surface of the intermediate transfer belt B in the primary transfer area Q3. When a monochromatic monocolor image is formed, only one developing device is used, and the monochromatic toner image is primarily transferred onto the intermediate transfer belt B. After the primary transfer, transfer residual toner and retransfer toner on the surface of the image carrier PR (toner reversely transferred from the intermediate transfer belt B to the image carrier PR)
Is cleaned by the image carrier cleaner CL1. The charge is removed by the charge adjusting charger JSC.

[0005] Below the backup roll T2a,
A secondary transfer slide frame Fs slidable back and forth (in a direction perpendicular to the paper surface) by a pair of left and right slide rails SR, SR is detachably supported on the image forming apparatus main body. A secondary transfer lifting frame Ft of the secondary transfer unit Ut is supported on the secondary transfer slide frame Fs so as to be rotatable up and down around a hinge axis Fta. The secondary transfer unit Ut includes a secondary transfer roll T2b, a secondary transfer roll cleaner CL3, a roll support lever Lr,
A sheet guide SG2 after transfer, a sheet conveying belt BH,
And the secondary transfer lifting frame Ft for supporting them.

The roll support lever Lr is a lever that supports the secondary transfer roll T2b and the secondary transfer roll cleaner CL3. In a state where the secondary transfer unit Ut is moved to the use position, the roll support lever Lr is rotated around a hinge axis La by a motor (not shown), and the secondary transfer roll T2b is moved to the intermediate transfer belt B by the motor. It is moved between a contacting secondary transfer position and a standby position separated from the intermediate transfer belt B. The contact area between the secondary transfer roll T2b and the intermediate transfer belt B is
A secondary transfer area Q4 is formed, and the secondary transfer roll T2b,
The backup transfer roll T2a and the electrode roll T2c constitute a secondary transfer unit T2. The post-transfer sheet guide SG2 guides the recording sheet that has passed through the secondary transfer area Q4 to the downstream sheet transport belt BH.

The recording sheets stored in the paper feed tray are conveyed to the registration roll Rr at a predetermined timing. The recording sheet conveyed to the registration roll Rr is transferred to the pre-transfer sheet guide SG1 at the same time as the multiple toner image or the single color toner image primarily transferred to the intermediate transfer belt B moves to the secondary transfer area Q4. To secondary transfer area Q4
Transported to When the recording sheet passes through the secondary transfer area Q4, a secondary transfer voltage having the same polarity as the charged polarity of the toner is applied to the electrode roll T2c of the secondary transfer unit T2 from the power supply circuit E controlled by the controller C. You. The secondary transfer unit T2 secondary-transfers the monochrome or color toner image primarily transferred onto the intermediate transfer belt B onto a recording sheet.

After the secondary transfer, residual toner is removed from the intermediate transfer belt B by the belt cleaner CL2. The toner adhered to the surface of the secondary transfer roll T2b is collected by a secondary transfer roll cleaner CL3. The secondary transfer roller T2b and the belt cleaner CL2 are disposed so as to be able to be separated from and separated from the intermediate transfer belt B (to be separated and contacted), and when a color image is formed, the unfixed toner of the final color is formed. The image is separated from the intermediate transfer belt B until the image is primarily transferred to the intermediate transfer belt B. The secondary transfer roll cleaner CL3 moves away from and moves together with the secondary transfer roll T2b. The recording sheet on which the toner image has been secondarily transferred is heated and fixed by the fixing device F when passing through the fixing area Q5. The recording sheet on which the toner image has been fixed is
The recording sheet is discharged to a recording sheet discharge tray (not shown).

In recent years, in this type of image forming apparatus employing an electrophotographic process, the size of the apparatus has been reduced.
From the viewpoints of cost reduction, ecology, and the like, it has been demanded to further reduce the amount of discarded toner. In view of such a point, a device of a so-called cleaner-less system, which is provided between the transfer unit and the charging unit and removes and recovers the untransferred toner and omits a cleaning device such as a blade or a brush, has been proposed. Proposed. For example, Japanese Unexamined Patent Publication No. Hei 5-346751 discloses a system in which untransferred toner is collected by a developing device, thereby eliminating the need for a cleaning device and a container for storing the cleaned toner (waste toner). (Hereinafter, this course is called the developer collection system). According to this developing device collecting method, not only can the size of the apparatus be reduced, but also the untransferred toner after development can be collected by the developing device and reused. In particular, when the cleaning blade of the cleaning device is removed, there is no abrasion or scratching of the image carrier due to the sliding of the cleaning blade on the image carrier, so that the life of the image carrier can be extended. The effect is expected.

[0010]

When the above-mentioned cleaner-less system of the developing device collecting system is applied to a conventional color image forming apparatus, different colors of toner are used because different colors of developer are used. There is a problem that light enters and color is mixed. This problem will be described with reference to FIG. 12 in which there is no image carrier cleaning device. The first color toner image developed on the image carrier is transferred to the intermediate transfer body by a transfer unit, and the transfer residual toner image passes through the charging unit, and is then transferred to the second color developing unit. Collected. As a result, the toner of the first color is mixed with the developer of the second color. This color mixture progresses with each image formation, and it becomes difficult to accurately reproduce the color tone of the output image.

Another cause of color mixing is re-transfer (referred to as re-transfer) of a transfer image of an intermediate transfer member to an image carrier. This is a phenomenon in which, for example, when the first color toner image transferred onto the intermediate transfer member passes through the transfer portion again, a part of the transferred image is transferred to the image carrier. As a result of intensive studies by the present inventors, it has been found that retransfer occurs when a part of the transfer toner becomes a reverse polarity by the discharge of the transfer nip and is transferred to the image carrier by the action of the transfer electric field. In a normal transfer state, the transfer portion is in a discharge state due to a strong transfer electric field, so that it is difficult to avoid retransfer. Color mixing occurs when the retransfer toner is collected by the developing device of another color.

In order to solve such a problem, Japanese Patent Laid-Open No.
Japanese Unexamined Patent Publication No. 236962 proposes that four untransferred toners on an image carrier are electrostatically temporarily collected by four cleaning rollers, and then the collected toners of the respective colors are image-supported. This is a method of re-adhering to the body and recovering each with a four-color developing device. In the above configuration,
When the untransferred toner remaining on the image carrier has only one specific color in a certain area on the image carrier, that is, for example, when only a transfer residual image is generated, it is effective to prevent color mixing. However, there is a disadvantage that color mixing in the presence of retransfer cannot be prevented. That is, normally, the transfer residual toner and the retransferred toner are present in a mixed form on the image carrier, and in the above-described method, the toner collected by the cleaning roller cannot be separated and collected according to the toner color. Is not a fundamental solution.

In any of the above-mentioned systems, the recovery ability of the cleaning roller or the developing device is not perfect, so that there is a case where the recovery residual toner is generated, and the residual toner is transferred onto the intermediate transfer body at the transfer section. It is transferred again, and the image of the transfer residual toner appears thinly on the image of the recording medium at a position separated by the peripheral length of the image carrier in the rear end direction.
An image defect called a positive ghost occurs.

In view of the above circumstances, the present invention provides the following (O01)
Is the subject of the description. (O01) To provide an image forming apparatus which does not cause color mixture and positive ghost in a developing device even in a color image forming apparatus which is a cleanerless system.

[0015]

Next, the present invention devised to solve the above-mentioned problems will be described. Elements of the present invention are used to facilitate correspondence with elements of the embodiments described later. , The reference numerals of the elements of the embodiment are enclosed in parentheses. The reason why the present invention is described in correspondence with the reference numerals of the embodiments described below 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 problems, the image forming apparatus of the invention has the following requirements (A01) to (A05).
(A01) a charging area (Q0) in which a rotating surface is charged by a charger (CSC) that is not in contact with the surface, and the charged area is charged by a latent image forming device (ROS). A latent image writing position (Q1) where electrostatic latent images corresponding to toner images of different colors are sequentially formed on the surface, and a developing device (D) that is not in contact with the surface forms a static image corresponding to the toner images of different colors. A developing area (Q2) where the electro-latent image is sequentially developed into a toner image of a corresponding color; a primary transfer area where the toner image is primarily transferred to an intermediate transfer body (B) by a primary transfer unit (T1) ( Q3), wherein the image carrier (PR) sequentially passes through the rotating surface, wherein a cleaner for cleaning residual toner on the surface of the image carrier (PR) after the primary transfer is not provided. Image carrier (PR), (A
02) The developing device (D) having a plurality of non-contact type developing devices of different colors for developing the electrostatic latent image on the surface of the image carrier (PR) into a toner image in a non-contact manner, The surface of the transfer body (B) is a secondary transfer area (Q4) where the primary transfer toner image is secondarily transferred to the recording sheet (S) by the secondary transfer unit (T2). The intermediate transfer member (B), (A04) sequentially passing through the intermediate transfer member cleaning area cleaned by the intermediate transfer member cleaner (CL2), and the intermediate member having the same peripheral length as the peripheral length of the surface of the image carrier (PR). The transfer sheet (B), (A05) the recording sheet (S) stored in the paper feed tray (TR1) is transferred to the secondary transfer area (Q4), and the toner image secondary-transferred to the recording sheet (S) is The recording sheets are sequentially arranged in a fixing area (Q5) where the image is fixed by the fixing device (F). Recording sheet conveying apparatus for conveying a S) (SH).

(Operation of the present invention) In the image forming apparatus of the present invention having the above-described configuration, the rotating surface of the image carrier (PR) has a charging device (CSC) that is not in contact with the surface in the charging area (Q0). ). The charged surface is applied to the latent image forming device (RO) at the latent image writing position (Q1).
Due to S), electrostatic latent images corresponding to toner images of different colors are sequentially formed. The electrostatic latent images corresponding to the toner images of the different colors are sequentially developed into the corresponding color toner images by a non-contact type developing device that does not contact the surface in the developing area (Q2). When the toner images of each color sequentially formed on the surface of the image carrier (PR) pass through the primary transfer area (Q3), the primary transfer is sequentially performed on the intermediate transfer body (B) by the primary transfer unit (T1). Is done. The recording sheet transport device (SH) transfers the recording sheets (S) stored in the paper feed tray (TR1) to two
The sheet is sequentially conveyed to a next transfer area (Q4) and a fixing area (Q5). The toner images of each color primary-transferred onto the intermediate transfer body (B) by the primary transfer unit (T1) are transferred to a secondary transfer area (Q
4), the sheet is secondarily transferred collectively to the recording sheet (S) by a secondary transfer unit (T2). The toner image secondarily transferred to the recording sheet (S) is transferred to the fixing area (Q
When passing through 5), the toner is fixed by the fixing device (F).

In the present invention, no cleaner for cleaning residual toner on the surface of the image carrier (PR) after the primary transfer is provided. For this reason, residual toner remaining on the surface of the image carrier (PR) without being transferred from the image carrier (PR) to the intermediate transfer body (B) during the primary transfer, or the intermediate transfer during the primary transfer The reverse transfer toner on the surface of the image carrier (PR) reversely transferred from the body (B) next passes from the surface of the image carrier (PR) to the intermediate transfer body (B) when passing through the primary transfer area (Q3). ). At this time, since the circumference of the surface of the image carrier (PR) and the circumference of the intermediate transfer body (B) are set to be the same, the image is transferred from the surface of the image carrier (PR) to the intermediate transfer body (B). The remaining toner image (remaining toner or reverse transfer toner) is transferred to the original transfer position (position to be transferred at the time of first transfer) on the surface of the intermediate transfer member (B). For this reason, an excellent image free of positive ghost can be formed. Further, since a non-contact type developing device is used, color mixing in the developing device (D) can be prevented. The intermediate transfer member (B) having passed through the secondary transfer region (Q4) is cleaned by the intermediate transfer member cleaner (CL2) when passing through the intermediate transfer member cleaning region.

[0019]

(Embodiment 1) An embodiment 1 of an image forming apparatus of the present invention includes the following requirements (A) in the present invention.
(A06) After the last secondary transfer of the image forming operation, the intermediate transfer body cleaner (C) is rotated while rotating the image carrier (PR) and the intermediate transfer body (B).
A belt cleaning execution unit at the end of image formation for performing the cleaning of the surface of the intermediate transfer member (B) by L2) for a predetermined period.

(Operation of the First Embodiment) In the first embodiment of the image forming apparatus of the present invention having the above-described configuration, (A06) after the end of the last secondary transfer of the image forming operation, the image carrier (PR)
And a belt cleaning execution unit at the end of image formation in which the surface of the intermediate transfer member (B) is cleaned by the intermediate transfer member cleaner (CL2) for a predetermined period while rotating the intermediate transfer member (B).

(Embodiment 2) Embodiment 2 of the image forming apparatus of the present invention is characterized in that the following requirement (A07) is satisfied in the present invention or Embodiment 1 of the present invention. A07) The image carrier (P) is not transferred from the image carrier (PR) to the intermediate transfer body (B) during the primary transfer.
R) The charge of the remaining toner remaining on the surface or the charge of the reverse transfer toner reversely transferred from the intermediate transfer member (B) to the surface of the image carrier (PR) during the primary transfer is adjusted to a normal charge polarity. Charge control means.

(Operation of the Second Embodiment) In the second embodiment of the image forming apparatus of the present invention having the above-described configuration, the charge adjusting means performs the intermediate transfer from the image carrier (PR) during the primary transfer. Toner remaining on the surface of the image carrier (PR) without being transferred to the body (B), or reverse rotation reversely transferred from the intermediate transfer body (B) to the surface of the image carrier (PR) during the primary transfer The charge of the toner is adjusted to a normal charge polarity. The residual toner and the reverse transfer toner on the surface of the image carrier (PR) adjusted to the normal charge polarity next pass through the primary transfer area (Q3) to the intermediate transfer body (B).
It is easily transcribed. Then, the toner transferred to the intermediate transfer member (B) is secondarily transferred to the recording sheet (S). The toner remaining on the intermediate transfer member (B) without being secondarily transferred to the recording sheet (S) is cleaned by the intermediate transfer member cleaner (CL2).

(Embodiment 3) Embodiment 3 of the image forming apparatus of the present invention is the same as that of the present invention or Embodiment 1 of the present invention.
Or (2) wherein the following requirement (A08) is provided: (A08) The outer diameter shape factor KM which is the shape factor of the toner when the toner maximum diameter is ML and the toner projection area is A is When expressed by the equation (1), the outer diameter shape factor KM satisfies the following equation (2), and the toner circumferential length is PM,
When the circumferential shape factor KP, which is the shape factor of the toner when the projected area of the toner is A, is expressed by the following formula (3), the toner whose circumferential shape factor KP satisfies the following formula (4): KM = ( ML ² / A) (100π / 4) (1) 100 ≦ KM ≦ 140 ……………………………………………… ......... (2) KP = (PM 2 / A) (100 / 4π) ....................................... (3) 100 ≦ KP ≦ 120 .............................. ………………… (4).

(Operation of the Third Embodiment) In the third embodiment of the image forming apparatus according to the present invention having the above-described configuration, the toner has a maximum diameter of ML and a toner projection area of A. When a certain outer diameter shape factor KM is represented by the following equation (1), the outer diameter shape coefficient KM satisfies the following equation (2).
Further, when the circumferential shape factor KP, which is the shape factor of the toner when the toner circumferential length is PM and the toner projected area is A, is expressed by the following equation (3), the circumferential shape factor KP is expressed by the following equation (4). Meet). KM = (ML ² / A) (100π / 4) ………………………………… (1) 100 ≦ KM ≦ 140 ……………………………………… .................. (2) KP = (PM 2 / A) (100 / 4π) ....................................... (3) 100 ≦ KP ≦ 120 ..................... (4) Since the toner is nearly spherical, the amount of toner remaining after transfer is reduced, and a good image can be obtained. That is, since the toner is nearly spherical, the transfer efficiency is increased and the absolute amount of untransferred toner is reduced. Therefore, the amount of waste toner to be collected can be small. Also, since there is little untransferred toner,
It is possible to reduce the applied voltage at the charge control means (JSC). Furthermore, compared with the irregular toner, the formed image has excellent in-plane unevenness (mottle), and a good image can be obtained.

(Embodiment 4) An embodiment 4 of the image forming apparatus of the present invention is the same as that of the present invention or Embodiment 1 of the present invention.
(A09) wherein the primary transfer region (Q) has the following requirement (A09):
The charge control means having a charge control charger (JSC) disposed in the charge control area downstream of (3) and upstream of the charge area (Q0).

(Operation of the Fourth Embodiment) In the fourth embodiment of the image forming apparatus of the present invention having the above-described configuration, the downstream side of the primary transfer area (Q3) and the upstream side of the charging area (Q0). Charge adjustment charger (J
SC), the charge of the remaining toner and the reverse transfer toner is adjusted to the normal charge polarity.

(Embodiment 5) Embodiment 5 of the image forming apparatus of the present invention is the same as that of the present invention or Embodiment 1 of the present invention.
(A010) The charging area (Q0), which satisfies the following requirement (A010) in any one of (1) to (3).
The charger (CSC) configured by a scorotron disposed in the charger and a means for adjusting a grid potential of the charger (CSC).

(Effect of Fifth Embodiment) In the fifth embodiment of the image forming apparatus of the present invention having the above-described configuration, the charger (CSC) constituted by a scorotron arranged in the charging area (Q0). The charge of the remaining toner and the reverse transfer toner is adjusted to the normal charge polarity by the means for adjusting the grid potential.

(Examples) Next, specific examples (examples) of the embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following examples. (Embodiment 1) FIG. 1 is an overall explanatory view of Embodiment 1 of the image forming apparatus of the present invention. 1, the image forming apparatus U has a main body U1 and an automatic document feeder U2 placed on a platen glass PG on the upper surface of the main body U1. The automatic document feeder U2 has a document feed tray TG1 on which a plurality of documents G to be copied are stacked. The plurality of documents G placed on the document feed tray TG1 are sequentially passed through the copy position on the platen glass PG and discharged to the document discharge tray TG2.

The image forming apparatus main body U1 has a UI (user interface) through which a user inputs an operation command signal such as a copy start signal, and the UI has a display unit, a copy start key, and the like. . Copier body U
1 The IIT as a document reading device disposed below the transparent platen glass PG on the upper surface is located at the platen registration position (O
An exposure system registration sensor (platen registration sensor) Sp and an exposure optical system A are provided at the (PT position). Reflected light from a document conveyed to the platen glass PG by the automatic document feeder U2 or a document (not shown) manually placed on the platen glass PG passes through the exposure optical system A to a CCD (solid-state imaging device). R) (red), G (green),
It is converted into a B (blue) electric signal.

The IPS (image processing system) converts the RGB electrical signals input from the CCD into K (black), Y (yellow), M (magenta), and C (cyan) image data and temporarily stores the converted data. And outputs the image data to the laser drive circuit DL at a predetermined timing as image data for forming a latent image. Laser drive circuit DL
Changes the laser drive signal to R according to the input image data.
Output to OS (latent image forming apparatus).

Image carrier P composed of a photosensitive drum
R is rotated in the direction of the arrow Ya, and the surface thereof is adjusted by the charge adjusting charger JSC to adjust the charge (charge potential) of the toner adhered to the surface, and then in the charging area Q0 by the charger (charge scorotron) CSC. It is uniformly charged.
The charger CSC must be a charger that operates separately from the surface of the image carrier (photoreceptor drum) so that contamination by transfer residual toner does not occur. In this example, a scorotron charger is used. . -5.5 to corotron wire
By applying kV and -700V to the grit,
The surface of the image carrier was uniformly charged to -700V. If not in contact, another charger such as a pin scorotron charger may be used.

The surface of the image bearing member PR has a voltage of -700 V
After being uniformly charged, the wafer is exposed and scanned by the laser beam L of the ROS (latent image forming apparatus) at the latent image writing position Q1, and is -300V with respect to the -700V background potential.
Is formed. When forming a full-color image, K (black), Y (yellow), M (magenta), C
An electrostatic latent image corresponding to the image of four colors (cyan) is sequentially formed. In the case of a monochrome image, only an electrostatic latent image corresponding to a K (black) image is formed. The latent image is written on the image carrier PR by the laser beam L by using a reference mark Bm provided on a non-image portion of the intermediate transfer belt B with a belt position sensor SNb.
Is started after a lapse of a predetermined time from the detection of. In the case of a full-color image, the colors are superimposed, so that the time from when the belt position sensor SNb detects the reference mark Bm to when the laser beam L starts to write the latent image is the same for each color.

The surface of the image carrier PR on which the electrostatic latent image has been formed rotates and sequentially passes through the development area Q2 and the primary transfer area Q3. The rotary type developing device D rotates K in the developing area Q2 sequentially with the rotation of the rotation axis Da.
It has four color developing units DK, DY, DM and DC of (black), Y (yellow), M (magenta) and C (cyan).
The developing units DK, DY, DM, and DC of the respective colors are arranged in a developing area Q2.
The electrostatic latent image on the image carrier PR passing through the toner image TNn
Develop. The developing units DK, DY, DM, and DC will be described later in detail.

Below the image carrier PR, a slide frame F1 (2) is provided by a pair of left and right slide rails SR, SR.
(Indicated by a dashed line) is slidably supported back and forth (in a direction perpendicular to the paper surface). A belt frame F2 of the belt module BM is supported on the slide frame F1 so as to be rotatable around a hinge axis F2a. The belt module BM includes the intermediate transfer belt B, a plurality of belt support rolls (Rd, Rt, Rf, T2a) including a belt drive roll Rd, a tension roll Rt, an idler roll (free roll) Rf, and a backup roll T2a. , 1
It has a next transfer roll T1 and the belt frame F2 that supports them. The intermediate transfer belt B is rotatably supported by the belt support rolls (Rd, Rt, Rf, T2a).

The belt module BM is rotated around the hinge axis F2a, and the intermediate transfer belt B is moved to the image carrier PR.
1, and a maintenance position (a position where the intermediate transfer belt B is separated from the image carrier PR, and is moved into and out of the image forming apparatus main body U1). And the like, which can be moved up and down between maintenance work positions (not shown)).
When the belt module BM is rotated to the maintenance position, the slide frame F1 and the belt module F2 supported by the slide frame F1 are moved to the image carrier P.
It is configured such that it can be moved in and out of the image forming apparatus main body U1 without making frictional contact with R.
Such a configuration for moving the slide frame F1 back and forth and a configuration for moving the belt module F2 up and down are conventionally known (for example, see Japanese Patent Application Laid-Open No. 8-171248), and various conventionally known configurations may be adopted. Is possible.

When a full-color image is formed, a first-color electrostatic latent image is formed at the latent-image writing position Q1, and a first-color toner image TNn is formed at the developing region Q2.
This toner image TNn is electrostatically primarily transferred onto the intermediate transfer belt B by the primary transfer roll T1 when passing through the primary transfer area Q3. Thereafter, similarly, the second color, third color, and fourth color toner images TNn are sequentially superimposed on the intermediate transfer belt B carrying the first color toner image TNn, and primary-transferred. Is formed on the intermediate transfer belt B. When a monochromatic monocolor image is formed, only one developing unit is used, and the monochromatic toner image is primarily transferred onto the intermediate transfer belt B. A primary transfer voltage having a polarity opposite to the polarity of the toner charged in the developing device D is supplied to the primary transfer roll T1 (described in detail later) from a power supply circuit E. Controlled. After the primary transfer, the charge of the residual toner on the surface of the image carrier PR is adjusted by the charge adjusting charger JSC, and the original charge polarity of the used toner is adjusted.

Below the backup roll T2a,
A secondary transfer slide frame Fs slidable back and forth (in a direction perpendicular to the paper surface) by a pair of left and right slide rails SR, SR is detachably supported on the image forming apparatus main body U1. A secondary transfer lifting frame Ft of the secondary transfer unit Ut is supported on the secondary transfer slide frame Fs so as to be rotatable up and down around a hinge axis Fta. The secondary transfer unit Ut includes a secondary transfer roll T2b,
Next transfer roll cleaner CL3 and roll support lever Lr
, Sheet guide SG2 after transfer, and sheet transport belt BH
And the secondary transfer elevating frame Ft supporting them.
And

The roll support lever Lr is a rotatable lever that supports the secondary transfer roll T2b and the secondary transfer roll cleaner CL3. In a state where the secondary transfer unit Ut has been moved to the use position, the roll support lever Lr is rotated by a motor (not shown) to move the secondary transfer roll T2b to the intermediate transfer belt B.
Is moved between a secondary transfer position in contact with the intermediate transfer belt and a standby position separated from the intermediate transfer belt. The post-transfer sheet guide SG2 guides the recording sheet that has passed through the secondary transfer area Q4, which is the contact area between the secondary transfer roll T2b and the intermediate transfer belt B, to the downstream sheet transport belt BH.

An electrode roll T2c is in contact with the backup roll T2a.
The next transfer unit T2 is configured. A secondary transfer voltage having the same polarity as the charging polarity of the toner in the developing device D is supplied from the power supply circuit E to the contact roll T2, and the power supply circuit E is controlled by the controller C.

The recording sheets S stored in the paper feed tray TR1 are taken out by a pickup roll Rp at a predetermined timing, separated one by one by a separation roll Rs, and conveyed to a registration roll Rr. The recording sheet S conveyed to the registration roll Rr is transferred to the pre-transfer sheet guide SG in synchronization with the movement of the primary-transferred multi-toner image or single-color toner image to the secondary transfer area Q4.
It is transported from 1 to the secondary transfer area Q4. In the secondary transfer area Q4, the secondary transfer unit T2 electrostatically secondary-transfers the toner image on the intermediate transfer belt B onto the recording sheet S. 2
After the next transfer, the residual toner is removed from the intermediate transfer belt B by the belt cleaner CL2. The toner adhered to the surface of the secondary transfer roll T2b is collected by the secondary transfer roll cleaner CL3.

The secondary transfer roller T2b and the belt cleaner CL2 are disposed so as to be able to freely contact (separate and contact) with the intermediate transfer belt B, and when a color image is formed, the final color is not determined. It is separated from the intermediate transfer belt B until the applied toner image is primarily transferred to the intermediate transfer belt B. Note that the secondary transfer roll cleaner CL3 is
The separation / contact movement is performed together with the secondary transfer roll T2b. The recording sheet S on which the toner image has been secondarily transferred is fixed to a fixing area Q by a post-transfer sheet guide SG2 and a sheet conveying belt BH.
5 when passing through the fixing area Q5.
Heat fixing is performed by a fixing device F having a pair of fixing rolls constituted by h and a pressure roll Fp. The recording sheet S on which the toner image is fixed is a recording sheet discharge tray T
It is discharged to R2. The codes Rp, Rs, Rr, SG1, S
The recording sheet conveying device SH is constituted by the elements indicated by G2 and BH.
Is configured.

(Developing Apparatus D) FIG. 2 is an explanatory view of a developing apparatus according to Embodiment 1 of the image forming apparatus of the present invention. Each of the developing units DK to DC of the developing device D is a purge type developing unit, and performs development without contacting the image carrier PR. The developing unit DK,
DY, DM, and DC have a developer housing 1.
As shown in FIG. 2, a developer roll 2 as a donor member, a sleeve rotating type mag roll 3, and a trimmer 4 are sequentially arranged in the developer housing 1 from the image carrier PR side. The purge-type developing device of the first embodiment is conventionally known. Even when the developing device is stopped at a position facing the image carrier PR in the development area Q2, the toner is purged (retracted) from the surface of the developing roll 2 so that the image carrier is removed. It is possible to prevent the toner from moving on the PR. At the rear of the developer housing 1, toner is supplied from a toner supply unit, and the toner is mixed with a carrier by augers 6 and 7 to form a magnetic toner.
It circulates as a component developer. The surplus developer in the developer housing 1 is discharged through the inside of the rotation shaft Da. Part of the developer in the developer housing 1 is transported to the position of the mag roll 3, and adheres to the surface of the mag roll 3 by magnetic force and electrostatic force.

The mag roll 3 includes a rotatable sleeve 3a and a magnet 3b fixed inside the sleeve 3a. The magnet 3 b has at least a magnetic pole arranged at a position facing the trimmer 4 and a magnetic pole arranged at a position facing the developing roll 2. The mag roll 3 is biased to, for example, -400 V by a DC power supply E1, and at the same time, for example, to a frequency of 100 V by an AC power supply E2.
An alternating voltage of 0 Hz to 60000 Hz and 100 to 500 Vpp is superimposed. Then, after the amount of the developer attached to the mag roll 3 is controlled to an optimum amount by the trimmer 4, the mag roll 3 is conveyed in the arrow direction Yb as the sleeve 3a of the mag roll 3 rotates.

On the other hand, in the vicinity of the mag roll 3, the developing rolls 2 are arranged so as to face each other with an interval of, for example, 1.5 mm. The developing roll 2 has a lower voltage than the mag roll 3 by, for example, a DC power source E3.
It is biased to 200V to -400V, and at the same time, an AC voltage is superimposed by an AC power supply E4. The developer conveyed to the position facing the developing roll 2 with the rotation of the mag roll 3 becomes a magnetic brush by the magnetic pole 3b 'of the magnet 3b, and comes into contact with the surface of the developing roll 2. Moreover, the mag roll 3 and the developing roll 2
The electric field from the mag roll 3 toward the developing roll 2 is formed by the bias pressure applied to the developing roll 2, so that the toner in the developer attached to the mag roll 3 moves to the developing roll 2 side and Adhere to the surface,
A toner layer having a constant thickness is formed.

The toner adhering to the surface of the developing roll 2 is transported to a developing position facing the image carrier PR as the developing roll 2 rotates. In this developing position, the developing roll 2 is supplied with, for example, a frequency 1 by an AC power supply E4.
-200V to -400V from DC power supply E3 to AC components of 000Hz to 9000Hz, 500V to 2000Vpp
Is applied. The developing roll 2 and the image carrier PR are opposed to each other with a gap of 0.2 mm, and the toner adhered to the surface of the developing roll 2 is caused by an oscillating electric field formed between the developing roll 2 and the image carrier PR. The electrostatic latent image formed on the surface of the image carrier PR is developed by moving to the image carrier PR side. It should be noted that the developing device may be any device that operates without contact.
In addition to the non-contact type developing device D, a non-magnetic one-component type developing device or the like can be used.

(Backup Roll T2a) The backup roll T2a is formed by covering an insulating roll with a semiconductive thin film. This thin film is formed to a thickness of 10 μm to 200 μm, and its surface resistivity is adjusted to 10 ⁷ to 10 ¹¹ Ω. Further, the electrode roll T2c is in contact with the backup roll T2a at a distance of 20 to 40 mm in the circumferential direction from the contact position with the intermediate transfer body B.

[0048] (secondary transfer roll T2b) Meanwhile, the secondary transfer roll T2b is electrically conductive roll which is grounded, in order to keep always equipotential grounding position the surface potential, the resistance value of 10 ⁷ Omega · cm.
A cleaning blade (not shown) made of polyurethane rubber is always in contact with the peripheral surface of the secondary transfer roll T2b to remove the toner attached to the secondary transfer roll T2b.

(Intermediate Transfer Belt B) The intermediate transfer belt B contains an appropriate amount of an antistatic agent such as carbon black.
Polyimide 0.1mm thick, 263.9m circumference
m is an endless single-layer belt. As the intermediate transfer member belt, other than this embodiment, resins such as polycarbonate, polyester, urethane, nylon, acryl and vinyl chloride or various rubbers can be used. In the present invention, in order to set the image carrier PR and the intermediate transfer member B to the same peripheral length, the peripheral length of the intermediate transfer belt is set to 263.9 mm so as to correspond to the diameter φ of 84.0 mm of the image carrier PR. In order to accurately transfer the untransferred toner and the retransferred toner to the original toner image position on the intermediate transfer member B again, the circumferential length of the image carrier PR and the intermediate transfer belt must not be shifted. For this reason, among the intermediate transfer belt materials, polyimide having the lowest coefficient of thermal expansion is preferable.

(Toner) The toner of Example 1 is prepared by coagulating and coalescing fine particles of styrene acrylic resin and fine particles of yellow, magenta, cyan, and black pigments to an average particle size of about 6 μm. Agglomeration coalescence method (EA
Method). Particle size distribution index (GS
D) was 1.23. The average particle size is a value of a volume average particle size measured by a Coulter counter (manufactured by Coulter, Inc.). Then, the heating time and the heating temperature during the polymerization were adjusted to prepare four kinds of toners having substantially the same average particle size and particle size distribution but different shapes (Table 1).

[Table 1]

The outer diameter shape factor KM in Table 1 is a shape factor of the toner when the toner maximum diameter is ML and the toner projection area is A, and can be expressed by the following equation (1). KM = (ML ² / A) (100π / 4) (1) The circumferential shape factor K P in Table 1 above is based on the toner circumferential length PM,
This is the shape factor of the toner when the projected area of the toner is A, and can be expressed by the following equation (3). ^{KP = (PM 2 / A)} (100 / 4π) ....................................... (3) the KM, the value of KP is an optical microscope (micro Photo FX
A: A value calculated by performing the following image analysis on an enlarged photograph of the toner obtained by Nikon Corporation using an image analyzer Luzex3 (Nireco Corporation).

In the above equation (1), (ML ² / A) (π / 4)
Represents the ratio of the projected area (A) of the toner to the area (ML ² π / 4) of the circle circumscribing it, and PM ² / A in the above equation (3) is the projected area (A) of the toner. And the area (PM ² / 4π) of a circle having the same perimeter PM. In the case of a true sphere, the above equations (1) and (3) are both 1
00, which increases as the shape collapses. The shape coefficients KM and KP were calculated for a plurality of toner particles, and the average value was used as a representative value. The toner has an average particle diameter of 10
An appropriate amount of inorganic fine particles of silica and titania having an average particle size of 50 to 100 nm was added to a carrier composed of ferrite beads having an average particle diameter of 50 μm and used as a developer.

(Operation of Embodiment 1) FIG. 3 is a diagram showing a state before the second color toner image is primarily transferred. FIG. 4 is a diagram illustrating a state after the second color toner image is primarily transferred.
FIG. 5 shows that when the circumference of the intermediate transfer belt B and the image carrier PR are made equal, the transfer residual toner image remaining on the image carrier without being transferred to the intermediate transfer member B and the reverse transfer from the intermediate transfer member B are performed. The reverse-transferred toner image on the image carrier is then moved to the primary transfer area Q.
FIG. 4 is a view for explaining that an original toner image of the same image on an intermediate transfer member B is overlapped without being displaced when the toner image passes through No. 3; Next, an operation of transferring the untransferred toner and the retransferred toner on the image carrier PR onto the intermediate transfer member B again will be described in order with reference to FIGS. FIG. 3 shows a state before a second color toner image TN2a developed on the image carrier PR is transferred to, for example, a first color toner image TN1a transferred on the intermediate transfer belt B. I have. In FIG. 3, transfer residual toner TNRs1a of the first color toner image TN1a exists on the image carrier PR.

In FIG. 4, the operation proceeds from FIG. 3, and when the first color toner image TN1a passes again through the primary transfer area Q3, which is the contact area between the image carrier PR and the intermediate transfer belt B, the above-described transfer is performed. Due to the discharge phenomenon in the region Q3, a retransfer toner image TNRt1a of TN1a is generated on the image carrier PR. Further, when the second color toner image TN2a passes through the primary transfer position, TN2a is transferred from the image carrier PR onto the intermediate transfer belt B, and a transfer residual toner image TNRs2a is generated on the image carrier PR. FIG. 6 is a diagram showing a general relationship between a transfer current flowing in a transfer portion and a transfer efficiency of toner. FIG.
In (2), the transfer efficiency becomes the maximum transfer efficiency at the transfer current Ip (point P), and becomes a mountain-shaped curve having the peak there. P
In the area on the left side, the transfer electric field is insufficient, and the electrostatic force for transferring the toner from the image carrier PR to the intermediate transfer belt B is not sufficiently generated, so that the transfer efficiency is low. On the other hand, in the area on the right side of P, an electrostatic force sufficient to transfer the toner image is generated, but the electric field is large, so that the image carrier PR and the intermediate transfer belt B are moved before and after the primary transfer position. Discharge occurs in a minute gap formed between the toner particles, and the polarity of the charge of a part of the toner is inverted to the polarity originally possessed, and positively charged (reversely charged).

The oppositely charged toner generates an electrostatic force in the direction of moving from the intermediate transfer belt to the image carrier due to the transfer electric field, and remains on the image carrier as untransferred toner. The phenomenon that the toner image on the intermediate transfer belt B is re-transferred to the image carrier PR is also due to the above-described reason. Therefore, when the transfer current is set to a value close to or larger than Ip in FIG. 6, most of the re-transferred toner image TNRt1a of the first color and the untransferred toner image TNRs2 of the second color in FIG. (Positive charge). Even if the oppositely charged toner passes through the primary transfer area Q3 again with the same charge polarity, most of the toner is not transferred to the intermediate transfer belt B.
The oppositely charged toner images TNRt1a and TNRs2a can be returned to the normal polarity (negatively charged) by applying charges using the charge adjusting charger JSC.

In this embodiment, a scorotron type charger was used as the charge adjusting charger JSC for adjusting the polarity of the untransferred toner image or the retransferred toner image to the normal polarity (minus). As shown in FIG. 1, the charge adjusting charger JSC is 2 m away from the primary transfer position on the image carrier PR and upstream of the charger CSC with respect to the image carrier PR.
It is fixed at a position separated by m to 4 mm. As a result of examining the applied bias condition of the charger required to return the polarity of the transfer residual toner and the retransferred toner, the grid applied voltage of the toner used in this embodiment is optimally in the range of -500 V to -800 V. Was found. When the applied voltage is set in this range, the charge measurement value (peak value) by the toner charge spectrograph method is -3 to -6 m from +6 mm of the transfer residual toner and the retransfer toner.
m and could be inverted to normal polarity. Note that a current value of -400 μA was set for the wire.

The charge adjusting charger JSC is a charger CS.
As described above, in this embodiment, a scorotron charger is used as the charger CSC, and -700 V is applied to the wire to change the image carrier PR to -700 V.
Is charged. Therefore, when a grid voltage lower than -700 V is applied to the charge adjusting charger JSC (for example, -600 V), the charge adjusting charger JSC for the toner in the charger CSC can also be used. on the other hand,
When a grid voltage higher than -700 V must be applied to the charge adjusting charger JSC (for example, -800 V) because the electric resistance of the toner is not so high, for example,
Due to the charge adjusting charger JSC, the image carrier PR becomes higher than a desired surface potential. In this case, it is necessary to separately provide a static elimination lamp or the like between the charge adjusting charger JSC and the charger CSC.

In FIG. 4, the toner images TNRt1a and TNRs2a whose polarity has been adjusted by the charge adjusting charger JSC.
Is charged by the charger CSC, and the toner images TNRt1a and TNRt1a are charged by the laser beam L at the latent image writing position Q1.
An electrostatic latent image is formed from above NRs2a. Subsequently, the electrostatic latent image formed on the toner images TNRt1a and TNRs2a is transferred to the developing device DK by the developing device D in the developing area Q2.
To DC to develop a new toner image (third color toner image). (However, it is omitted in FIG. 4).

It has been found that, depending on the developing bias applied to the developing devices DK to DC in the developing area Q2, the untransferred toner image and the re-transferred toner image are collected by the developing device in spite of the non-contact developing method. . As a result of a detailed investigation by the present inventors, the occurrence / non-occurrence of collection is determined by the voltage (hereinafter referred to as a voltage) which is the difference between the background potential of the image carrier PR and the DC potential applied to the developing roll 2 of the developing units DK to DC. VCLN)
It has been found that it depends on the amount of untransferred toner. In the image forming apparatus of the first embodiment, as a result of an experiment,
By setting the CLN at 200 V or more, the collection did not occur.

The toner image TNRt1a that has passed through the development area Q2
Since the peripheral lengths of the image carrier PR and the intermediate transfer belt B are equal to each other, TNRs2a and TNRs2a are transferred onto the original toner images TN1a and TN2a of the same image without displacement in the primary transfer area Q3. (See FIG. 5). In this embodiment, since the circumferential lengths of the intermediate transfer belt B and the image carrier PR are made equal, the TNRt1a and TNRs2a are transferred without being displaced from the toner images TN1a and TN2a. No positive ghost-like image defect occurs even if the ghost image remains. Further, by re-passing the primary transfer position of TN1a and TN2a, a new image carrier P
A retransferred toner image is generated on R, but the amount of toner is
In the case of TN1a, the second retransfer toner image is almost equal to the amount of the first retransfer toner image TNRt1a, and the second retransfer image passes through the above-described process and is transferred to the intermediate transfer position at the next primary transfer position. Toner image TN1a or TN2a on belt B
, No positive ghost image defect occurs on the intermediate transfer belt B.

Next, after all the toners of each color necessary for the image to be formed are superimposed on the intermediate transfer belt B and primary-transferred, the primary-transfer toner image is collectively transferred to the recording sheet S in the secondary transfer area Q4. That is, the operation at this time is shown in FIG.
This will be described in order with reference to FIG. FIG. 7 shows the intermediate transfer belt B
Immediately after the full-color toner image transferred on the second transfer is secondary-transferred, the transfer residual toner at the time of the secondary transfer remains on the intermediate transfer belt B. In the primary transfer area Q3, the fourth color toner image TN4 Of the fourth transfer remaining toner image TNRs4a which is in the process of primary transfer and has already been primary transferred
FIG. 11 is a diagram illustrating a state in which (transfer residual toner at the beginning of the fourth color toner image) still remains on the toner image carrier. In FIG. 7, the secondary transfer roll T2b contacts the intermediate transfer belt B, a bias is applied, and the full-color toner image TNAa is secondary-transferred to the recording sheet S. The untransferred toner TNRsAa in the secondary transfer exists on the intermediate transfer belt B, and the fourth color toner image TN4b (the end portion of the fourth color toner image) in the primary transfer is formed on the image carrier PR. ) Still remains, and 4
The transfer remaining toner TNRs4a of the color toner image TN4a (the beginning of the fourth color toner image), the third color retransfer toner TN3a, and the like are present.

FIG. 8 is a view showing a state in which the secondary transfer of FIG. 7 is continuing and immediately after the primary transfer of the last portion TN4b of the fourth color toner image TN4 is completed. FIG. 9 shows a state in which the secondary transfer has been completed. In FIG. 8, until the secondary transfer ends, the secondary transfer roll T2b has been moved to the secondary transfer position pressed by the backup roll T2a via the intermediate transfer belt B. In addition, belt cleaner CL2
Means that the secondary transfer end portion of the intermediate transfer belt B has moved to a position separated from the intermediate transfer belt B until the secondary transfer end portion has moved to the belt cleaning region, but the secondary transfer end portion has moved to the belt cleaning region. When it reaches, the cleaning operation is started by contacting the intermediate transfer belt B.

In FIG. 9, when the secondary transfer is completed, the secondary transfer roll T 2 b is transferred to the toner image TN on the intermediate transfer belt B.
In order to prevent RsAa, TNRsAb, etc. from adhering, it moves to a standby position away from the intermediate transfer belt B. At this time, the belt cleaning operation of the belt cleaner CL2 is continued until immediately before the next primary transfer toner image on the intermediate transfer belt B reaches the belt cleaning area. After the final secondary transfer of the image forming operation is completed, cleaning of the intermediate transfer belt B by the belt cleaner CL2 is performed for a predetermined period while rotating the image carrier PR and the intermediate transfer belt B. The belt cleaning operation at the end of image formation is executed by a program of the control device of the image forming apparatus (a program having a function of executing the belt cleaning operation at the end of image formation). At this time, the untransferred toners TNRsAa and TNRsAb on the intermediate transfer belt B are removed by the belt cleaner CL2 in contact with the intermediate transfer belt B by the belt cleaning operation at the end of the image formation. Further, the primary transfer residual toner image TNRs4b or the retransferred toner image (not shown) of the fourth color on the image carrier PR is transferred to the intermediate transfer belt B after the completion of the entire transfer cycle as shown in FIG. And
It is removed and collected by the belt cleaner CL2.

When the obtained images were compared with the four types of toners shown in Table 1 (that is, the toners satisfying the above formulas (1) and (3)), a good image was obtained without any positive ghost. Obtained. On the other hand, when several hundred prints of each of the four types of toners in Table 1 were continuously printed, a change in color tone that was considered to be caused by color mixing in the developing device was observed as the shape factor was increased. Examination of the primary transfer efficiency of each toner revealed that the smaller the shape coefficient, the higher the primary transfer efficiency. As a result of the study of the present inventors, the adhesive force between the image carrier and the toner decreases as the toner becomes spherical,
This indicates that the spherical toner has a smaller contact area between the image carrier and the toner, facilitates the transfer of the toner from the image carrier, and improves transferability. From this result,
It is considered that the transfer efficiency deteriorated as the shape became more distant from the sphere and the amount of untransferred toner increased, so that the toner was collected by the developing device.

By increasing the VCLN (the difference between the potential of the background of the image carrier PR and the DC voltage applied to the developing roll 2 of the developing units DK to DC), transfer by the developing unit can be performed even for toner having a large shape coefficient. The collection of the remaining toner can be prevented. However, the toner C (KM: 13
2, KP: 111) and toner D (KM: 139, K
P: 112), VCLN at which developer collection does not occur
, The desired amount of toner development was not obtained as a side effect. The toner in which the recovery of the developing device hardly occurs was the toner in which the outer diameter shape coefficient KM and the circumference shape coefficient KP satisfy the following expressions (2) and (4). 100 ≦ KM ≦ 140 ……………………………… (2) 100 ≦ KP ≦ 120 …………………………………… ............ (4). However, in particular, in the case of the toner produced by the emulsion aggregation coalescence method used this time, it is desirable that the shape factor KM is 130 or less and KP is 110 or less from the viewpoint of preventing the recovery of the developing device and securing a predetermined or more development amount. It was correct.

By the way, the spherical toner has little friction and slips through the cleaning blade, so that cleaning is difficult. Therefore, when a spherical toner is used, it is essential to realize a cleanerless system. However, it has been difficult to realize an image forming apparatus with stable image quality due to problems such as color mixing of the developing device and positive ghost due to retransfer in the conventional cleaner-less system of the developing device collecting method. In the configuration of the present invention, a good image was obtained without generating a positive ghost in the image and without blurring of the image due to the transfer of the transfer residual toner image being slightly shifted. It was also confirmed that there was no change in color tone due to color mixing, and that there was excellent suitability for spherical toner. In addition, as a toner, a spherical toner formed by a suspension polymerization method, a dissolution suspension method, an emulsion polymerization method, or a kneading and pulverizing method may be used in addition to the emulsion aggregation method.

(Embodiment 2) FIG. 10 is an explanatory view of Embodiment 2 of the image forming apparatus of the present invention. 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 second embodiment differs from the first embodiment in the following points, but has the same configuration as the first embodiment in other points. In the second embodiment, the YC image carrier PR1 for forming Y (yellow) and C (cyan) toner images
(Magenta) and MK forming K (black) toner image
The image carrier PR2 is used. The YC image carrier PR1 and the MK image carrier PR2 have the same configuration as the image carrier PR of the first embodiment. The YC image carrier PR1 is connected to the YC image carrier PR1 by a retractable Y developing device DY and a C developing device DC that can be separated from and contacted with the YC image carrier PR1 (movable between a separated position or a contact position). The Y (yellow) and C (cyan) toner images are developed, and M (magenta) and K (black) are respectively applied to the MK image carrier PR2 by retractor-type M developing devices DM and DK. Is developed.

At the time of the first rotation of the intermediate transfer belt B,
On each of the image carriers PR1 and PR2, the first color Y toner image and the M toner image are developed by the developing devices DY and DM. At this time, the developing devices DC and DK are
It has moved to a position separated from R1 and PR2. During the second rotation of the intermediate transfer belt B, the second color C toner image and the K toner image are developed on the image carriers PR1 and PR2 by the developing units DC and DK. The developing units Dy and Dm for the first color have moved to positions separated from the image carriers PR1 and PR2. During the first rotation of the intermediate transfer belt B, each of the image carriers PR
The first color toner images (Y toner image and M toner image) formed on PR1 and PR2 respectively are primary transfer units T1, T1.
Is transferred to the intermediate transfer belt B by the first transfer, and during the second rotation, the toner images of the second color (C toner image and K toner image) are transferred by the primary transfer devices T1 and T1 to the first color of the intermediate transfer belt B. The primary transfer is performed on the toner image. That is, in the second embodiment, while the intermediate transfer belt B makes two rotations, the toner images of four colors of Y, M, C, and K are
Transcribed above.

The four-color toner images primary-transferred onto the intermediate transfer belt B are secondarily transferred collectively onto a recording sheet in a secondary transfer area Q4. In the course, YC
The image carrier PR1 and the image carrier PR2 for MK have an outer diameter equal to φ84.0 mm, and the peripheral length of the intermediate transfer belt B is set to 263.8 mm (=
π × 84.0 mm). The charge adjusting charger JSC provided in the first embodiment is omitted here due to the mounting space, and by setting the grid applied voltage of the charger (charge scorotron) CSC to -700 V, the polarity is reversed (positive). ) The charge of the toner was adjusted by using a charger. The development conditions and the transfer conditions were set to the same conditions as in Example 1.

The toner has an outer diameter shape factor KM (see the above equation (1)) of 119 and a circumferential shape factor KP of 107.
The spherical toner described in Example 1 was used. Also in the apparatus having the configuration of the second embodiment, an excellent image having no positive ghost due to the untransferred toner and the retransferred toner was obtained as in the first embodiment. Further, the developing device is not in contact with the image carrier, and by setting VCLN to the condition of the first embodiment, the transfer residual toner is not collected by the developing device, and therefore, the toner mixed color in the developing device also occurs. Did not.

(Comparative Example) FIG. 11 is an explanatory view of a comparative example of an image forming apparatus for comparison with the first embodiment. FIG.
, The peripheral length of the intermediate transfer belt B is 263.9 mm
1, but the diameter of the image carrier PR is 42.0 mm, which is half (132 mm) the outer diameter and outer circumference of the first embodiment of FIG. Other configurations of the comparative example of FIG. 11 are the same as those of the first embodiment of FIG. When an image was formed by the image forming apparatus of this comparative example, the obtained image was approximately 132 m on the opposite side to the paper traveling direction.
Positive ghost occurred at a distance of m.

(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 present invention, an intermediate transfer drum can be used instead of the intermediate transfer belt B shown in the first and second embodiments. (H01) In the present invention, a transfer corotron can be used instead of the transfer roll.

[0073]

The above-described image forming apparatus of the present invention has the following effects. (E01) An untransferred toner image remaining on the image carrier and a retransferred toner image from the intermediate transfer member can be transferred again onto the original toner image on the intermediate transfer member, and the cleaning device is provided. Even without this, it is possible to obtain a good image free from color mixing and positive ghost in the developing device. Therefore, since the image carrier cleaning means, the waste toner conveying device, and the toner storage container can be omitted, a small-sized and low-cost full-color image forming apparatus can be provided.

[Brief description of the drawings]

FIG. 1 is an overall explanatory diagram of Embodiment 1 of an image forming apparatus of the present invention.

FIG. 2 is an explanatory diagram of a developing device according to a first embodiment of the image forming apparatus of the present invention.

FIG. 3 is a diagram illustrating a state before a second color toner image is primarily transferred.

FIG. 4 is a diagram illustrating a state after a second color toner image is primarily transferred.

FIG. 5 is a diagram illustrating a case where the intermediate transfer belt B and the image carrier PR have the same circumferential length, the transfer residual toner image remaining on the image carrier without being transferred to the intermediate transfer member B and the intermediate transfer member B; A description will be given of the fact that the reverse-transferred toner image on the image carrier, which has been reverse-transferred, then overlaps with the original toner image of the same image on the intermediate transfer body B when it passes through the primary transfer area Q3 without displacement. FIG.

FIG. 6 is a diagram illustrating a general relationship between a transfer current flowing to a transfer unit and a transfer efficiency of toner.

FIG. 7 is a diagram showing a state in which the transfer residual toner at the time of the secondary transfer remains on the intermediate transfer belt B immediately after the secondary transfer of the full-color toner image superimposedly transferred on the intermediate transfer belt B; In the next transfer area Q3, the fourth color toner image T
N4 primary transfer in progress and already primary transferred 4
FIG. 10 is a diagram illustrating a state where a transfer residual toner image TNRs4a of a color remains on the toner image carrier.

FIG. 8 shows a state where the secondary transfer shown in FIG.
FIG. 11 is a diagram illustrating a state immediately after the primary transfer of the last portion of the color toner image TN4 is completed.

FIG. 9 shows a state where secondary transfer has been completed.

FIG. 10 is a second embodiment of the image forming apparatus of the present invention.
FIG.

FIG. 11 is an explanatory diagram of a comparative example of the image forming apparatus for comparison with the first embodiment.

FIG. 12 is a view showing a schematic configuration of a general image forming apparatus provided with the intermediate transfer member.

[Explanation of symbols]

B: intermediate transfer member (intermediate transfer belt), CL2: intermediate transfer member cleaner (belt cleaner), CSC: charger, D:
Developing device, F: Fixing device, JSC: Charger for charge adjustment,
PR: image carrier, Q0: charged area, Q1: latent image writing position,
Q2: development area, Q3: primary transfer area, Q4: secondary transfer area, Q5: fixing area, ROS: latent image forming apparatus, S: recording sheet, SH: recording sheet transporting apparatus, T1: primary transfer unit, T2: secondary transfer unit, TR1: paper feed tray.

 ──────────────────────────────────────────────────の Continuing from the front page (72) Inventor Kisho Kojima 2274 Hongo, Ebina-shi, Kanagawa Prefecture Inside Fuji Xerox Co., Ltd. (Reference) 2H030 AA04 AD01 AD03 AD04 AD05 BB02 BB24 BB42 BB44 BB46 BB54 2H032 AA05 AA15 BA02 BA05 BA09 BA18 BA21 BA23 BA26 BA30 CA13 DA19

Claims (4)

[Claims] 1. An image forming apparatus having the following requirements (A01) to (A05): (A01) a charging area in which a rotating surface is charged by a non-contact charger on the surface; A latent image writing position where an electrostatic latent image corresponding to a toner image of a different color is sequentially formed on the charged surface by the latent image forming device; A developing area in which the corresponding electrostatic latent image is sequentially developed into a toner image of a corresponding color; an image carrier that sequentially passes through a primary transfer area in which the toner image is primarily transferred to an intermediate transfer body by a primary transfer device Wherein the image carrier is not provided with a cleaner for cleaning residual toner on the surface of the image carrier after the primary transfer along the rotating surface; (A02) the electrostatic force on the surface of the image carrier; Color to develop latent image into toner image without contact A developing device having a plurality of different non-contact type developing devices; (A03) the surface of the rotating intermediate transfer member is secondarily transferred to the recording sheet by the primary transfer region and the secondary transfer device; Secondary transfer area,
An intermediate transfer member that sequentially passes through an intermediate transfer member cleaning area to be cleaned by the intermediate transfer member cleaner;
4) The intermediate transfer body having the same circumference as the circumference of the surface of the image carrier, (A05) The recording sheet stored in the paper feed tray is secondarily transferred to the secondary transfer area and the recording sheet. A recording sheet conveying device for sequentially conveying the recording sheet to a fixing area where the toner image is fixed by the fixing device. 2. The image forming apparatus according to claim 1, further comprising the following requirement (A06): (A06) the image bearing member and the intermediate transfer member after the completion of the last secondary transfer of the image forming operation. Means for performing belt cleaning at the end of image formation in which cleaning of the surface of the intermediate transfer member by the intermediate transfer member cleaner is performed for a predetermined period while rotating. 3. The image forming apparatus according to claim 1, wherein the image forming apparatus satisfies the following requirement (A07).
The toner remaining on the surface of the image carrier without being transferred from the image carrier to the intermediate transfer member at the time of the primary transfer, or reversely transferred from the intermediate transfer member to the surface of the image carrier at the time of the primary transfer Charge adjusting means for adjusting the charge of the reverse transfer toner to a normal charge polarity. 4. The image forming apparatus according to claim 1, wherein the following requirement (A08) is satisfied: (A08) The toner maximum diameter is ML, and the toner projection area is A. When the outer diameter shape factor KM, which is the shape factor of the toner at that time, is expressed by the following equation (1), the outer diameter shape coefficient KM satisfies the following equation (2), the toner circumferential length is PM, and the toner projection area is A When the circumferential shape factor KP, which is the shape factor of the toner, is expressed by the following formula (3), the toner whose circumferential shape factor KP satisfies the following formula (4): KM = (ML ² / A) (100π / 4) ……………………………………………… (1) 100 ≦ KM ≦ 140 ………………………… (2 ^{) KP = (PM 2 / A} ) (100 / 4π) ....................................... (3) 100 ≦ KP ≦ 120 .............................. ………………… (4).