JPH10228180A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a failure in peeling a recording sheet, without making a defect of an image worse and shortening the life of a device by making a nipping load heavy only when the top end part of the recording sheet passes through a secondary transferring region. SOLUTION: A bias roll 30 is arranged on a side facing a backup roll 29 across an intermediate transfer belt B, in the secondary transferring region Q4, around the intermediate transfer belt B. The backup roll 29 and the bias roll 30 are connected to a transfer power source circuit 32 and a bias is applied to the bias roll 30 by the transfer power source circuit 32, to transfer a toner image on the intermediate transfer belt B to the recording sheet S. The nipping load of a secondary transfer roll 31 on the intermediate transfer body B is changed according to a position where the top end of the recording sheet S passes through the secondary transferring region Q4 and the nipping load when the top end of the recording sheet S passes through the secondary transferring region Q4 is set to be heavier than that when the other part of the recording sheet S passes through the secondary transferring region Q4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, such as an electrophotographic copying machine or a laser printer, for transferring a toner image formed on the surface of an image carrier to a recording sheet surface via an intermediate transfer member. The present invention relates to an image forming apparatus using a transfer roll as a transfer device for transferring a toner image on an intermediate transfer member to a recording sheet surface.

[0002]

2. Description of the Related Art In a conventional image forming apparatus such as an electrophotographic copying machine provided with an intermediate transfer member, in order to record an image such as a character photograph written on an original on a recording sheet, first, different color components are used. Each of the separated light images is individually exposed on an image carrier to form an electrostatic latent image for each color component, and the electrostatic latent images for each color component are developed with a developer of a different color and individually. Image. The toner images of each color individually formed on the image carrier are successively superimposed on the intermediate transfer body and transferred to form a composite toner image. As a transfer means, a corotron using an electrostatic force or a transfer roller is used.

The composite toner image on the intermediate transfer member is transferred to the recording sheet by applying a transfer electric field for moving the toner to the recording sheet. After transfer, as a method of peeling a recording sheet from an intermediate transfer body, there is a method in which a separation corotron is conventionally used and an AC corona discharge is performed to remove electricity from the recording sheet and reduce the electrostatic attraction force to peel off the recording sheet.
Further, there is a printer in which a recording sheet is forcibly separated by sliding a peeling claw on an intermediate transfer member. Further, there is a type in which a separating corotron and a peeling nail are used in combination. After the recording sheet is peeled off using the above method, the composite image on the recording sheet is fused by a fixing device, thereby completing the copying.

[0004]

In the above-mentioned system, a device using a separated corotron requires an expensive AC power supply since a high AC voltage must be applied. Further, if the separation corotron is placed near the transfer area, an electrostatic force is applied to the transfer area in a direction opposite to that of the transfer, so that there is a problem that the toner returns to the intermediate transfer body. In the case of using a peeling claw, a scratch is generated on the surface of the intermediate transfer member by sliding the peeling claw. Further, when the electrostatic attraction force of the recording sheet is strong, there is a problem that a mark of the peeling claw remains on the leading end of the recording sheet, or the peeling nail contacts the toner image on the recording sheet to disturb the toner image. Was.

In order to solve these problems, the following techniques (J01) and (J02) are conventionally known. (J01) Technology described in Japanese Patent Publication No. H8-023719. In this publication, a conductive member is provided near the downstream side of the transfer unit, and when the recording sheet passes through the transfer area and approaches the conductive member, the recording sheet is transferred to the transfer unit. A method is described in which the recording sheet is peeled off by utilizing the electrostatic adsorption of the recording sheet to the conductive member because the charge of the opposite polarity to the electric charge given to the conductive member is induced in the conductive member. In this method, since the charge induced in the conductive member and the toner have the same polarity, if the recording sheet comes into direct contact with the conductive member, the toner image is disturbed due to the repulsion of the charge. An insulating guide member is provided on the side to be insulated. However, if the insulating guide member repeatedly contacts and separates from the recording sheet, charges of the opposite polarity to the recording sheet accumulate due to peeling discharge or the like, and the toner and the guide member repel each other, causing toner to scatter. Therefore, there is a problem that the toner image is disturbed as a result.

(J02) The technique described in Japanese Patent Application Laid-Open No. Hei 5-100576 discloses that an intermediate transfer belt is stretched to reduce a radius of a roll located at a peeling portion and increase a curvature to prevent peeling failure. Trying to prevent. However, there has been a problem that the belt is bent by reducing the diameter of the peeling roll on which the belt is stretched, and therefore a new bending prevention means must be provided.

The present invention has been made in view of the above-mentioned problems, and has the following (O)
The contents described in 01) shall be technical issues. (O01) Separation corotron for peeling, expensive AC power supply, peeling claw, conductive member for peeling, etc. are not required, and the chargeability of the recording sheet or the environment without damaging the intermediate transfer body, recording sheet, toner image, etc. To ensure that the recording sheet can be reliably peeled off irrespective of conditions.

[0008]

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, an image forming apparatus of the invention has the following requirements. (A01) A latent image is formed on a moving image carrier (16). A latent image forming device (ROS) for forming, (A02) a developing device (D) for developing the latent image into a toner image, and (A03) an intermediate transfer member for transferring the toner image formed on the surface of the image carrier (16); 1) arranged in the primary transfer area (Q3) for transfer to B)
A secondary transfer unit (21), (A04) a secondary transfer roll (31) disposed in a secondary transfer area (Q4) for transferring the toner image transferred to the intermediate transfer body (B) to a recording sheet (S) ,
(A05) Recording sheet (S) in the secondary transfer area (Q4)
(A06) The recording sheet (S) supplied to the secondary transfer area (Q4)
Secondary transfer power applying means (32) for applying transfer power for transferring a toner image to the secondary transfer roll (31);
(A07) The secondary transfer area (Q) at the leading end of the recording sheet (S)
4) The nip load of the secondary transfer roll (31) on the intermediate transfer body (B) is changed according to the passing position, and the nip when the leading end of the recording sheet (S) passes through the secondary transfer area (Q4). Secondary transfer load changing means (52 to 56) in which the load is set to be larger than when the other portion of the recording sheet (S) passes through the secondary transfer area (Q4), (A08) the secondary transfer area (Q4) A fixing device (41) for heating and fixing the toner image transferred to the recording sheet (S) in the above (1).

(Operation of the Present Invention) In the image forming apparatus of the present invention having the above-described features, the latent image forming apparatus (ROS) forms a latent image on the moving image carrier (16). The developing device (D) develops the latent image into a toner image. A primary transfer unit (21) arranged in the primary transfer area (Q3) transfers the toner image formed on the surface of the image carrier (16) to the intermediate transfer body (B). The sheet supply means (36 to 38)
The recording sheet (S) is supplied to the secondary transfer area (Q4). The secondary transfer power applying means (32) applies a transfer power for transferring the toner image to the recording sheet (S) supplied to the secondary transfer area (Q4) to the secondary transfer roll (31). A secondary transfer roll (31) arranged in the secondary transfer area (Q4) transfers the toner image transferred to the intermediate transfer body (B) to the recording sheet (S). Secondary transfer load changing means (52) for changing the nip load of the secondary transfer roll (31) on the intermediate transfer body (B) according to the position of the leading end of the recording sheet (S) passing through the secondary transfer area (Q4). ~ 56)
Is a secondary transfer area (Q4) at the leading end of the recording sheet (S).
The nip load at the time of passing is 2 in the other part of the recording sheet (S).
It is set to be larger than when passing through the next transfer area (Q4). Therefore, when the leading end of the recording sheet (S) passes through the secondary transfer area (Q4), the nip load is large, so that the leading end of the recording sheet (S) is easily separated from the intermediate transfer body (B). If the nip load is too large during the entire period in which the recording sheet (S) passes through the secondary transfer area (Q4), the life of the secondary transfer roll (31) due to image defects [missing of characters, etc.] and deformation of the diameter will occur. Causes a decline. However, in the present invention, the leading end of the recording sheet (S) is located in the secondary transfer area (Q).
Since the nip load is increased only when passing through 4), it is possible to prevent the recording sheet (S) from peeling failure. In addition, other than the leading end of the recording sheet (S), the secondary transfer area (Q
When passing through 4), the load on the nip is made smaller than when the leading end of the recording sheet (S) is passing, so that image defects are not deteriorated. Also, since a large load is not required for a long time, the life of the roll is not reduced. Fixing device (4
1) The toner image transferred onto the recording sheet (S) in the secondary transfer area (Q4) is heated and fixed.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) Embodiment 1 of the image forming apparatus of the present invention
Is characterized in that the image forming apparatus of the present invention has the following requirements. (A09) The nip load A when the leading end of the recording sheet (S) passes through the secondary transfer area (Q4),
The portion other than the leading end of the recording sheet (S) is the secondary transfer area (Q
4) The secondary transfer load set so that the nip load B when passing and the nip load C when the recording sheet (S) does not pass through the secondary transfer area (Q4) satisfy the following formula. Change means (52 to 56), A>B> C.

(Operation of the First Embodiment) In the first embodiment of the image forming apparatus of the present invention, the leading end of the recording sheet (S) is
Since the nip load A at the time of passing through the next transfer area (Q4) is large, the leading end of the recording sheet (S) is easily peeled from the intermediate transfer body (B) when passing through the secondary transfer area (Q4). The portion other than the leading end of the recording sheet (S) is the secondary transfer area (Q
4) Since the nip load B at the time of passing is set smaller than the nip load A, the image defect is not deteriorated, and a large load is not applied to the secondary transfer roll (31) for a long time. As a result, the life of the secondary transfer roll (31) is not reduced. Since the nip load C when the recording sheet (S) does not pass through the secondary transfer area (Q4) is still smaller than the nip load B, the intermediate transfer body (B) and the secondary transfer roll (31) Therefore, the deformation of the intermediate transfer body (B) and the secondary transfer roll (31) can be further reduced, and the life thereof can be prolonged.

[0013]

Next, examples (embodiments) 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 embodiments.

(Embodiment 1) Next, Embodiment 1 of the present invention will be described with reference to FIGS. FIG. 1 is an overall explanatory view of an embodiment of the image forming apparatus of the present invention. FIG. 2 is a schematic configuration diagram of a mechanism for pressing a transfer roll against an intermediate transfer belt in a secondary transfer area of the embodiment. FIG. 3 is a schematic view of a cam having three points of action for changing the pressing load of the secondary transfer roll and a disk for detecting the position of the cam in the embodiment.
FIG. 4 is an explanatory diagram of the state of the transfer roll being pressed against the intermediate transfer belt and the positional relationship of the cam in the secondary transfer area of the embodiment. FIG. 5 is a timing chart showing a secondary transfer process according to the embodiment. FIG. 6 is an explanatory diagram showing the relationship between the bleeding level of a character and the number of defective peels with respect to the nip load of the transfer roll on the intermediate transfer belt.

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 section, and the like on an upper part, and a transparent (not shown) on which a document (not shown) is placed. And a platen glass 2. 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 has 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 original image light reflected by the third mirror 8 is transmitted to an imaging lens 9.
Through the CCD (color image reading sensor)
The signals are read as G and B analog signals.

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 K, Y, M, C image data.

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 scans an electrostatic latent image writing position Q1 of the rotating image carrier 16 with a laser beam L modulated by the input laser drive signal. A charging roll 17 for uniformly charging the image carrier 16 is disposed along the rotating image carrier 16 and upstream of the latent image writing position Q1 in the moving direction of the image carrier 16. After the image carrier 16 is uniformly charged by the charging roll 17, an electrostatic latent image is written by the laser beam L at the latent image writing position Q1.

A rotary developing unit (developing unit) 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 unit D
Has developing units Dk, Dy, Dm, and Dc of four colors of Y, M, C, and K mounted around the rotating shaft 18.
8, the developing units Dk, Dy, Dm,
Dc is sequentially moved to the development area Q2. The developing devices Dk, Dy, Dm, and Dc are connected to the image carrier 16.
This device develops the above electrostatic latent image into toner images of each color of K (black), Y (yellow), M (magenta), and C (cyan). An intermediate transfer belt (intermediate transfer body) B and a primary transfer device (transfer roll) 21 are provided in a primary transfer area Q3 set on the downstream side of the developing area Q2 along the surface of the rotating image carrier 16. Is arranged. A static eliminator 22 and a cleaner unit 23 are arranged downstream of the primary transfer area Q3 along the rotating image carrier 16.

The intermediate transfer belt B includes a driving roll 2
6, an idler roll 27, a tension roll 28, and a backup roll 29, and are stretched by four rolls at a speed substantially equal to that of the image carrier 16 through the drive roll 26 by a drive unit (not shown). To rotate. In this embodiment, the intermediate transfer belt B includes
Resins such as polyimide, polycarbonate, polyester and polypropylene or various rubbers containing an appropriate amount of an antistatic agent such as carbon black are used. The intermediate transfer belt has a volume resistivity of 10 ⁶ to 10 ¹⁴ Ω · c.
m, and the thickness is, for example, 0.1 mm
Is set to

A bias roll 30 is arranged around the intermediate transfer belt B on the side opposite to the backup roll 29 with respect to the intermediate transfer belt B in the secondary transfer area Q4. From the backup roll 29 and the bias roll 30 to the secondary transfer roll 31 of the present invention
Is configured. The backup roll 29 and the bias roll 30 are connected to a transfer power supply circuit 32 as a secondary transfer power application unit. The bias is applied to the bias roll 30 by the transfer power supply circuit 32 and the toner on the intermediate transfer belt B is The image is transferred to the recording sheet S. The transfer power supply circuit 32 is controlled by the controller C.

Further, a belt cleaning device 34 for removing untransferred toner remaining on the surface of the intermediate transfer belt B is disposed downstream of the bias roll 30 in the transport direction of the intermediate transfer belt B. The bias roll 30 and the belt cleaning device 34
Are configured to be able to be pressed against and separated from the intermediate transfer belt B. A static eliminator 35 and a belt position sensor SN1 are arranged downstream of the belt cleaning device 34. The static eliminator 35 eliminates charges remaining on the surface of the intermediate transfer member after the secondary transfer. The belt position sensor SN1 controls the writing timing of the electrostatic latent image so that the unfixed toner images of yellow, magenta, cyan, and black are sequentially superimposed and transferred every one rotation of the intermediate transfer belt B. , A predetermined position of the intermediate transfer belt B (for example,
This is a sensor for detecting the next transferred yellow unfixed toner image (the leading end position).

The recording sheet S taken out of the paper feed tray 36 is temporarily stopped by the registration roll 37 and is conveyed to the secondary transfer area Q4 through the guide conveyance path 38 at a predetermined timing. The unfixed toner image on the intermediate transfer belt B is secondarily transferred to the recording sheet S when passing through the secondary transfer area Q4. In the transport direction of the recording sheet S, the recording sheet sensor SN2 disposed at the registration position (position of the registration roll 37) on the upstream side of the secondary transfer area.
Is detected by The position (contact position, separation position) of the bias roll 30 with respect to the backup roll 29 is adjusted by the sheet detection signal of the recording sheet sensor SN2. The secondary transfer of the unfixed toner image is performed immediately after the primary transfer to the intermediate transfer belt B in the case of a single-color image formation. However, in the case of a full-color image, the intermediate transfer belt B rotates four times and
After the toner images of each color (black), Y (yellow), M (magenta), and C (cyan) are primary-transferred on the intermediate transfer belt B, the secondary transfer is performed once in the secondary transfer area Q4. Is done. The bias roll 30 and the belt cleaning device 34 are disposed so as to be able to be separated from and contacted with the intermediate transfer belt B. When a color image is formed, the unfixed toner image of the final color is These members are separated from the intermediate transfer belt B until the next transfer is performed. 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 sheet feeding means (36 to 3) of the present invention is provided by the paper feed tray 36, the registration roll 37, and the guide conveyance path 38.
8) is configured.

Next, a bias roll position adjusting device for moving the bias roll 30 in the secondary transfer area Q4 forward and backward between a position separated from the backup roll 29 and a position in contact with the backup roll 29 will be described. 2 and 3, the bias roll 30 whose position is adjusted between the contact position and the separation position with respect to the backup roll 29 has a bias roll shaft 30a. The bias roll shaft 30a is rotatably supported by bearings 51,51. In order to move the bias roll 30 forward and backward with respect to the backup roll, both ends of the bias roll shaft 30a are guided by guide grooves (not shown) so as to be movable forward and backward with respect to the backup roll 29. A pair of eccentric cams 54, 54 are fixedly supported on a cam support shaft 53 driven to rotate by a cam rotation motor 52. The eccentric cams 54 are arranged so as to contact the lower surfaces at both ends of the bias roll shaft 30a. At one end of the cam support shaft 53, a disk 55 having notches 55a, 55b, and 55c formed on the outer periphery is fixed. A notch sensor 56 for detecting the rotational position of the notches 55a, 55b, 55c is disposed adjacent to the upper end of the outer periphery of the disk 55. The secondary transfer load change for changing the nip load of the secondary transfer roll 30 on the intermediate transfer body B according to the position of the leading end of the recording sheet passing through the secondary transfer area Q4 by the elements indicated by the reference numerals 52 to 56. Means (52 to 56) are configured.

As shown in FIG. 3, the eccentric cam 54 has an action point 54 corresponding to the notches 55a, 55b and 55c.
a, 54b, and 54c are determined. That is, for example,
When the notch 55a is rotationally moved to the upper end position, the action point 54a of the eccentric cam 54 is rotationally moved to the upper end position, the bearing 51 is raised, and the bias roll 30 is moved.
Is brought into contact with the backup roll 29 via the intermediate transfer belt B. When the cam rotation motor 52 rotates and the cam support shaft 53, the eccentric cam 54, and the disk 55 rotate, one of the notches 55a, 55b, and 55c of the disk 55 is detected by the detection sensor 56.
Is detected, the cam rotation motor 52 is stopped. The action point 5 of the eccentric cam 54 which is moving to the upper end position at that time
4a, 54b, and 54c determine the position of bearing 51 and 2
The bias roll 30 in the next transfer area Q4 moves up and down to obtain a predetermined nip load. That is, in FIG. 4, in the case of FIG. 4A in which the action point 54c is rotationally moved to the upper end,
The bias roll 30 in the secondary transfer area Q4 does not press against the intermediate transfer belt B. That is, the nip load of the bias roll 30 on the intermediate transfer belt B is a C load (C = 0). Next, in the case of the action point 54a shown in FIG. 4B, the bias roll 30 is pressed against the intermediate transfer belt B with the largest load (A load), and in the case of the action point 54b of FIG.
Bias roll 30 with load (B load) smaller than 4a
Presses against the intermediate transfer belt B.

(Operation of the Embodiment) Next, the operation of the embodiment of the image forming apparatus having the above configuration will be described. At the time of actual image creation, first, when the primary transfer is being performed, the eccentric cam 54 acts on the bearing 51 of the shaft of the bias roll 30 at the position of the application point 54c (see FIG. 4A).
The bias roll 30 is separated from the intermediate transfer belt B. In the timing chart shown in FIG. 5, when the recording sheet S is transported to the position of the registration roll 37, the recording sheet sensor SN2 detects the recording sheet S and outputs a sheet detection pulse signal. This recording sheet detection sensor S
At the fall of the sheet detection pulse of N2, the cam rotation motor 52 for rotating the cam support shaft 53 is turned on, and the eccentric cam 54 is slightly delayed from the ON time.
Rotates. When the eccentric cam 54 rotates, the bias roll 30 rises and comes into contact with the backup roll 29 via the intermediate transfer belt B. At this time, the nip load in the secondary transfer area increases from load C in FIG. 4A to load A in FIG. 4B. Thereafter, the notches 55a, 55b, 55
When the sensor 56 for detecting c detects the notch 55a of the disk 55 corresponding to the position of the action point 54a, the cam rotation motor 52 stops, and the bias roll 30 applies an A load ( The eccentric cam 54 acts so as to make pressure contact in FIG. 4B). As can be seen from FIGS. 5 and 4B, the action point at this time is 54a.

In FIG. 5, on the time axis where the time when the leading end of the recording sheet S is conveyed to the position of the registration roll 37 is 0, the leading end of the recording sheet S is moved to the secondary transfer area Q at time x.
It is transported to the center position of 4. Assuming that the operation speed (so-called process speed) of the image forming apparatus is 160 mm / s, for example, the leading end of the recording sheet S is moved to the secondary transfer area Q
After about 10 mm is discharged from the nip center between the bias roll 30 of No. 4 and the intermediate transfer belt B (in this case, about 62.5
After ms, that is, at time x + 62.5 ms), the cam rotation motor 52 operates and the eccentric cam 54 rotates.
Then, as in the case of the action point 54a, the notches 55a,
When the sensor 56 for detecting 55b, 55c detects the notch 55b of the disk 55 corresponding to the position of the action point 54b, the state shown in FIG. 4C is reached, and the cam rotation motor 52 stops,
The bias roll 30 moves the intermediate transfer belt B
The eccentric cam 54 acts so as to be pressed against by a load (see FIG. 4C).

Next, when the toner image is transferred onto the recording sheet S and the rear end of the recording sheet S has passed through the secondary transfer area Q4 (see time y on the time axis in FIG. 5), the cam rotation is resumed. The motor for operation 52 operates, and the eccentric cam 54 rotates. Thereafter, when the sensor 56 that detects the notches 55a, 55b, and 55c detects the notch 55c of the disk 55 corresponding to the position of the action point 54c, the cam rotation motor 52 stops, and the bias roll 30 is moved to the intermediate transfer belt B. The eccentric cam 54 acts so as to be pressed against, ie, separated by, a C load (see FIG. 4D). The bias roll 30 is separated from the intermediate transfer belt B to prepare for the secondary transfer process for the next recording sheet S.

FIG. 6 shows the relationship between the bleeding level of the character with respect to the nip load of the transfer roll on the intermediate transfer belt and the number of defective peels in the secondary transfer area Q4. FIG.
As shown in (1), when the nip load increases, the number of defective peels decreases, and the hollow level of characters deteriorates. Therefore, when the nip load is set to the A load when the recording sheet S passes through the secondary transfer area Q4, the releasability is improved. However, when the nip load is set to the A load in the entire area of the recording sheet S, the hollow level of the character approaches the lower limit of the allowable level, and other factors (for example, environment, , The resistance of the intermediate transfer belt, etc.) may fall below the permissible level of the hollow characters.

Further, if a large load is applied to the bias roll 30 for a long time, the shape of the roll may be changed to deteriorate the image quality or shorten the life of the roll. Accordingly, only the leading end of the recording sheet S is pressed against the load A and the peeling performance when the leading end passes through the secondary transfer area Q4 is improved. The releasability of the recording sheet can be greatly improved without deteriorating image defects.

(Modification) Although the embodiments of the present invention have been described in detail, the present invention is not limited to the above-described embodiments.
Various design changes can be made without departing from the invention as set forth in the claims. Modified embodiments of the present invention will be exemplified below. (H01) The primary transfer device 21 can employ a corotron (discharge device). (H02) When transferring the toner image onto the recording sheet supplied to the secondary transfer area Q4, the backup roll 29
Transfer power applying means 3 for applying transfer power to a secondary transfer roll 31 composed of
2 can apply a transfer power to the backup roll 29 instead of applying a transfer voltage to the bias roll 30.

[0031]

The above-described image forming apparatus of the present invention has the following effects. (E01) Separating corotron for peeling, expensive AC power supply, peeling claw, conductive member for peeling, etc. are not required, and the chargeability of the recording sheet or the environment without damaging the intermediate transfer member, the recording sheet, the toner image, etc. It is possible to provide an inexpensive recording sheet peeling apparatus capable of stably peeling a recording sheet regardless of conditions. (E02) Since the nip load is increased only when the leading end of the recording sheet passes through the secondary transfer area, the image defect is not deteriorated and the life of the device (part) is not reduced.
It is possible to prevent poor peeling of the recording sheet. Also,
Since only the nip load of the secondary transfer area is changed using the device configured in the conventional image forming apparatus, a new device for separation or an expensive and complicated device is not required. Therefore, the present invention can realize an inexpensive and simple recording sheet peeling apparatus.

[Brief description of the drawings]

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

FIG. 2 is a schematic configuration diagram of a mechanism for pressing a transfer roll against an intermediate transfer belt in a secondary transfer area according to the embodiment.

FIG. 3 is a schematic view of a cam having three points of action for changing the pressing load of a secondary transfer roll and a disk for detecting the position of the cam in the embodiment.

FIG. 4 is an explanatory diagram of a state in which a transfer roll is pressed against an intermediate transfer belt and a positional relationship of a cam in a secondary transfer area according to the embodiment.

FIG. 5 is a timing chart showing a secondary transfer process according to the embodiment.

FIG. 6 is an explanatory diagram showing a relationship between a hollow portion level of a character and the number of defective separations with respect to a nip load of a transfer roll on an intermediate transfer belt.

[Explanation of symbols]

B: intermediate transfer member (intermediate transfer belt), D: developing device, Q
3 ... primary transfer area, Q4 ... secondary transfer area, ROS ... latent image forming device, 16 ... image carrier, 21 ... primary transfer unit, 31 ... 2
Next transfer roll, 32 ... Secondary transfer power application means, 41 ... Fixing device (36-38) ... Sheet supply means, (52-56) ... 2
Next transfer load changing means.

Claims (2)

[Claims] 1. An image forming apparatus having the following requirements: (A01) a latent image forming apparatus for forming a latent image on a moving image carrier; and (A02) developing the latent image into a toner image. (A03) a primary transfer device disposed in a primary transfer area for transferring a toner image formed on the surface of the image carrier to an intermediate transfer member; and (A04) toner transferred to the intermediate transfer member. A secondary transfer roll disposed in a secondary transfer area for transferring an image to a recording sheet, (A05) sheet supply means for supplying a recording sheet to the secondary transfer area, and (A06) supplied to the secondary transfer area Secondary transfer power applying means for applying a transfer power for transferring a toner image to a recording sheet to the secondary transfer roll; (A07) an intermediate position between the secondary transfer roll according to a position of the leading end of the recording sheet passing through the secondary transfer area; Changing the nip load on the transfer body (A08) the secondary transfer load changing means, wherein a nip load of the leading end of the recording sheet when passing through the secondary transfer region is set to be larger than that when the other end of the recording sheet passes through the secondary transfer region. A fixing device that heats and fixes the toner image transferred onto the recording sheet. 2. The image forming apparatus according to claim 1, wherein the following conditions are satisfied: (A09) A nip load A when the leading end of the recording sheet passes through the secondary transfer area, and a part other than the leading end of the recording sheet. Is the nip load B when the portion passes through the secondary transfer area
And the nip load C when the recording sheet does not pass through the secondary transfer area is set to satisfy the following equation.
Next transfer load changing means, A>B> C.