JP2002072709A - Image forming device - Google Patents

Abstract

(57) [Problem] To simplify a pre-transfer at a transfer material entrance portion of a transfer nip portion when a toner image is transferred to a transfer material entering a transfer nip portion. To provide an image forming apparatus provided with a transfer device having the above configuration. SOLUTION: A secondary transfer bias roller 605 in a secondary transfer section is arranged at a position upstream of a secondary transfer opposing roller 510 in a moving direction of an intermediate transfer belt 501.
As a result, the transfer material P conveyed toward the transfer nip portion of the secondary transfer portion is transferred to the intermediate transfer belt 50 in the pre-transfer area.
1 in advance. As a result, the occurrence of pre-transfer due to the gap G between the transfer material P and the intermediate transfer belt 501 in the pre-transfer area is prevented without complicating the apparatus.

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 a copying machine, a facsimile, and a printer.
A transfer nip portion is provided between the image carrier and the transfer member by a transfer member that contacts the surface of the image carrier formed in a belt shape and an opposing member that faces the transfer member with the image carrier interposed therebetween. The present invention relates to an image forming apparatus provided with transfer means for applying a transfer bias to a transfer material conveyed so as to enter the transfer nip portion, and transferring a toner image on the image carrier to the transfer material. Things.

[0002]

2. Description of the Related Art As this type of image forming apparatus, for example,
As shown in FIG. 7, the photosensitive drum 20 as a latent image carrier
The toner image charged to a predetermined polarity formed on 0 is
2. Description of the Related Art There is known an image forming apparatus that performs primary transfer using an electrostatic force on an intermediate transfer member (hereinafter, referred to as an “intermediate transfer belt 501”) including an endless belt as an image carrier. The toner image primarily transferred on the intermediate transfer belt 501 is secondarily transferred to a transfer material P such as a transfer paper or an OHP sheet fed by a registration roller 650 by using an electrostatic force.

An image forming apparatus having such an intermediate transfer belt 501 can form a toner image formed on the photosensitive drum 200 by superimposing the toner image on the intermediate transfer belt 501. It is widely used as a color image forming apparatus for forming a color image on P.

As shown in FIG. 8, a transfer means of the image forming apparatus includes a secondary transfer bias roller 605 as a transfer member which comes into contact with the surface of the intermediate transfer belt 501.
And a secondary transfer opposing roller 510 as an opposing member opposing the secondary transfer bias roller 605 with the intermediate transfer belt 501 interposed therebetween.
In this transfer device, the secondary transfer bias roller 6
A transfer nip portion N is formed between the intermediate transfer belt 501 and the secondary transfer bias roller 605 by the secondary transfer opposing roller 05 and the secondary transfer facing roller 510. Then, with respect to the transfer material P conveyed so as to enter the transfer nip portion N,
A transfer bias is applied by the secondary transfer bias roller 605. As a result, the toner image on the intermediate transfer belt 501 is transferred onto the transfer material P.

[0005]

However, in a conventional image forming apparatus provided with this type of transfer device, in FIG. 8, a transfer material P enters a transfer nip N and a toner image on an intermediate transfer belt 501 is formed. When the image is transferred onto the transfer material P, pre-transfer occurs in a region on the near side of the transfer material entrance portion of the transfer nip N, and an abnormality occurs in the image transferred on the transfer material P. Has been a major issue in the past.

That is, in the above-described conventional image forming apparatus, as shown in FIG. 8, the transfer of the transfer material P entering the transfer nip N and being conveyed to the intermediate transfer belt 501 at the transfer nip N A minute gap G is generated in a portion on the near side (upstream in the moving direction of the intermediate transfer belt 501) of the material entrance portion. When such a gap G occurs, discharge occurs between the transfer material P at the transfer material entrance portion of the transfer nip N and the intermediate transfer belt 501. Then, the discharge causes the toner image on the intermediate transfer belt 501 to fly on the transfer material P before reaching the transfer nip N, and the pre-transfer occurs. Hereinafter, a region on the near side of the transfer material entrance portion of the transfer nip where the pre-transfer occurs, is referred to as a “pre-transfer region”.

In particular, in a color image forming apparatus using the intermediate transfer belt 501, an overlapped image of a plurality of colors is collectively transferred from the intermediate transfer belt 501 to a transfer material P. The effect is so great that, for example, overlapping dust and dot dust of each color toner and excessive transfer of halftone occur.

As a method for preventing the occurrence of the pre-transfer as described above, it is effective to eliminate the gap G between the transfer material P and the intermediate transfer belt 501 in the pre-transfer area. Therefore, conventionally, for example, as shown in FIG. 8, the intermediate transfer belt 501 of the secondary transfer bias roller 605 is used.
A guide member 901 for guiding the transfer material P is disposed at a position on the upstream side in the moving direction of the transfer member P. The guide member 901 causes the transfer material P and the intermediate transfer belt 501 to come into close contact with each other in the pre-transfer area in advance. In this manner, a method for guiding the transfer material P is adopted. However, in such a conventional method, as shown in FIG.
01, the transfer material P is separated by its own weight.
In the pre-transfer area, the transfer material P and the intermediate transfer belt 501 do not adhere as expected.

On the other hand, there is a transfer device using a dielectric belt as a transfer material conveying means for conveying the transfer material P toward the transfer nip portion N. In this transfer device, the dielectric belt is disposed so as to contact the intermediate transfer belt 501 at the transfer nip portion N and at a portion of the transfer nip portion N near the entrance of the transfer material, and the transfer nip portion N The transfer material P is conveyed while being held between the intermediate transfer belt 501 and the dielectric belt. Although this transfer device is quite effective in eliminating the gap G as described above, since the nip between the dielectric belt and the intermediate transfer belt 501 becomes large, the transfer nip portion is caused by the speed unevenness of each belt. Causes a new problem that the image is easily disturbed. Further, this transfer device has a problem in that the configuration thereof is complicated, so that the transfer device is more expensive than the transfer device shown in FIG.

The above is an example of an image forming apparatus in which the image carrier is an intermediate transfer belt.
The image carrier may be a photoreceptor belt, and the same may occur in an image forming apparatus that directly transfers a toner image formed on the photoreceptor belt to a transfer material.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and has as its object to transfer a toner image to a transfer material that has entered a transfer nip portion. An object of the present invention is to provide an image forming apparatus provided with a transfer device having a simple configuration capable of preventing pre-transfer at an entrance portion.

[0012]

In order to achieve the above object, the present invention is directed to a belt-shaped image carrier which carries a toner image on a surface thereof, and comprises: A toner image forming means for forming a toner image on the image carrier; a transfer member in contact with the surface of the image carrier; and a facing member facing the transfer member with the image carrier interposed therebetween. A transfer nip portion between the transfer member and a transfer bias for applying a transfer bias to the transfer material conveyed so as to enter the transfer nip portion to transfer the toner image on the image carrier to the transfer material; Wherein the transfer member of the transfer means is arranged at a position upstream of the opposing member in the moving direction of the image carrier.

In this image forming apparatus, since the transfer member of the transfer means is arranged at a position upstream of the opposing member in the moving direction of the image carrier, the transfer member is conveyed toward the transfer nip portion. The transfer material is brought into close contact with the transfer member in the pre-transfer area in advance.

According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the opposed member has an opposed roller having a radius of Rt.
The image carrier includes an intermediate transfer belt having a thickness of Tb, and the transfer member includes a transfer roller having a radius of R2. When the distance between the center of the opposing roller and the center of the transfer roller is M, (Rt + Tb + R2) -M <0, and
The transfer roller is in contact with the surface of the intermediate transfer belt so as to bite into the opposing roller, and the center of the transfer roller when the surface of the intermediate transfer belt is tangent to the transfer roller; The distance between the roller and the center of the transfer roller in a state where the roller is in contact with the surface of the intermediate transfer belt so as to bite the opposite roller is 0.5 to 5 mm.
mm.

In this image forming apparatus, the transfer roller comes into contact with the surface of the intermediate transfer belt so as to bite into the opposing roller, and the surface of the intermediate transfer belt is wound around the peripheral surface of the transfer roller. To make contact. As a result, the contact width between the transfer roller and the intermediate transfer belt in the transfer material transport direction is increased, and the transfer material transported toward the transfer nip portion is applied to the intermediate transfer belt even in the pre-transfer area. It comes into close contact with it.
Here, when a transfer bias is applied from the transfer roller, a transfer current flows so as to concentrate on a portion biased toward the opposing roller side in a portion where the transfer roller and the intermediate transfer belt are in contact with each other. become. Therefore, no transfer electric field is generated in the pre-transfer region, and the occurrence of pre-transfer in the pre-transfer region is suppressed. If the separation distance is less than 0.5 mm, it may be difficult to secure a sufficient contact width (a contact width that can prevent pre-transfer) between the transfer roller and the intermediate transfer belt. On the other hand, if the distance exceeds 5 mm, the contact width between the transfer roller and the intermediate transfer belt becomes too large, and jitter is generated due to a difference in speed between the transfer rollers and the intermediate transfer belt.

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the transfer is performed at a position upstream of a contact portion between the image carrier and the transfer member in a moving direction of the image carrier. A transfer material guide member configured to allow the transfer material to enter the transfer nip after the material is brought into contact with the surface of the image carrier.

In this image forming apparatus, the transfer material guide member causes the transfer material to move toward the image carrier at a position upstream of the contact portion between the image carrier and the transfer member in the moving direction of the image carrier. The transfer material is brought into contact with the surface of the carrier, and then enters the transfer nip. Thereby, the contact width of the transfer material with respect to the transfer member in the transport direction is increased, and the transfer material transported toward the transfer nip portion is more securely adhered to the transfer member in the pre-transfer area. become.

According to a fourth aspect of the present invention, in the image forming apparatus of the third aspect, the transfer material guide member is located at a position 5 to 30 mm before the transfer material entrance of the transfer nip portion, and the transfer material is provided with the image. It is characterized in that it is configured to start contacting the surface of the carrier.

In this image forming apparatus, the transfer material guide member starts contact of the transfer material with the surface of the image carrier at a position 5 to 30 mm before the transfer material entrance of the transfer nip portion. Here, the minimum distance (5 mm) from the transfer material entrance of the transfer nip portion to the contact start position of the transfer material with the image carrier is determined by the thickness of the transfer material guide member and the image carrier (intermediate transfer belt). It is determined by the swing during movement. Further, when the maximum distance from the transfer material entrance of the transfer nip portion to the transfer material contact start position exceeds 30 mm, an image is easily blurred due to a difference between the transfer speed of the transfer material and the speed of the image carrier.

According to a fifth aspect of the present invention, in the image forming apparatus of the third or fourth aspect, the transfer material guide member is provided with respect to the image carrier when the transfer material starts to contact the surface of the image carrier. The transfer material is configured to have an angle of approach of 5 ° to 30 °.

In this image forming apparatus, the transfer material comes into contact with the surface of the image carrier at an angle of approach of 5 ° to 30 ° by the transfer material guide member. Here, when the approach angle is less than 5 °, the adhesion pressure utilizing the stiffness of the transfer material to the image carrier (intermediate transfer belt) in front of the transfer nip portion becomes weak. As a result, the flatness of the portion of the transfer material that is in contact with the image carrier (intermediate transfer belt) is reduced, and an abnormal image may occur at a portion of the transfer material that is not in contact with the image carrier (intermediate transfer belt). is there. Further, when the above-mentioned approach angle exceeds 30 °, the rear end of the transfer material
When the recording material comes out of the transfer material guide member, it jumps up and hits the image carrier (intermediate transfer belt). As a result, the toner image on the image carrier (intermediate transfer belt) may be disturbed, and the transferred image may become a horizontal band-shaped abnormal image.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to an electrophotographic color copying machine (hereinafter, referred to as a "color copying machine") as an image forming apparatus will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of a color copying machine according to this embodiment. This color copying machine includes a color image reading unit (hereinafter, referred to as "color scanner 1"), a paper feeding unit 3, and a control unit for controlling the driving of these units, in addition to an image forming unit 2 as a main unit as shown in FIG. It is constituted by.

The color scanner 1 reads color image information of a document for each color separation light of, for example, red, green, and blue (hereinafter, referred to as "R", "G", and "B", respectively). Convert to image signal. Then, based on the intensity levels of the R, G, and B color separation image signals obtained by this color scanner, a color conversion process is performed by an image processing unit (not shown), and black, cyan, magenta, and yellow (hereinafter, respectively) “Bk”, “C”, “M”, “Y”) are obtained.

The image forming section 2 includes a photosensitive drum 200 as a latent image carrier, a charging charger 201 as charging means, a photosensitive member cleaning device 210 including a cleaning blade and a fur brush, and a writing optical unit 220 as exposure means. , A revolver developing unit 400 as a developing unit, an intermediate transfer unit 500, a secondary transfer unit 600, and a fixing unit 700 using a fixing roller 701.

The photosensitive drum 200 rotates in a counterclockwise direction as indicated by an arrow in the drawing, and around the charging charger 201, the photosensitive member cleaning device 210, and the revolver developing unit 400 as shown in FIG. Each developing unit 40
A developing machine selected from among 1, 402, 403, and 404, an intermediate transfer belt 501 as an intermediate transfer body of the intermediate transfer unit 500, and the like are arranged.

The writing optical unit converts the color image data from the color scanner into an optical signal, and places a laser beam corresponding to the image of the original on the surface of the photosensitive drum 200 uniformly charged by the charger 201. Light L
To perform optical writing to form an electrostatic latent image on the surface of the photosensitive drum 200. The writing optical unit includes, for example, a semiconductor laser as a light source, a laser emission drive control unit, a polygon mirror and its rotation motor, f / θ
It can be constituted by a lens, a reflection mirror or the like.

The revolver developing unit 400
Are a Bk developing device 401 using Bk toner, a C developing device 402 using C toner, and an M developing device 40 using M toner.
3, a Y developing device 404 using Y toner, a developing revolver driving unit for rotating the whole unit counterclockwise, and the like. This revolver developing unit 40
0 each developing machine 401, 402, 403, 40
Reference numeral 4 denotes a developing sleeve as a developer carrier which rotates by bringing the ears of the developer into contact with the surface of the photosensitive drum 200 to develop the electrostatic latent image, and rotates to pump up and agitate the developer. It is composed of a developer paddle, a developing sleeve driving unit for rotating the developing sleeve clockwise as indicated by an arrow, and the like.

In this embodiment, each of the developing machines 401 and 40
The toner in 2,403,404 is negatively charged by agitation with the ferrite carrier, and each developing sleeve is turned into a negative DC voltage Vdc (DC component) by a developing bias power supply (not shown) as a developing bias applying unit. A developing bias voltage on which the AC voltage Vac (AC component) is superimposed is applied, and each developing sleeve is biased to a predetermined voltage with respect to the metal base layer of the photosensitive drum 200.

In the standby state of the main body of the color copying machine, the revolver developing unit 400 is stopped at the home position where the Bk developing machine 401 is located at the developing position. Then, when the copy start key is pressed, reading of the original image data is started, and light writing by the laser beam L, that is, formation of an electrostatic latent image is started based on the color image data (hereinafter, static image formation by Bk image data). The electrostatic latent image is referred to as “Bk electrostatic latent image. The same applies to C, M, and Y.)

In order to enable development from the front end of the Bk electrostatic latent image, before the front end of the electrostatic latent image reaches the Bk development position, the rotation of the Bk developing sleeve is started and the Bk electrostatic latent image is started. Is developed with Bk toner. After that, the developing operation of the Bk electrostatic latent image is continued. When the rear end of the Bk electrostatic latent image passes the Bk developing position, the revolver is immediately moved until the developing machine of the next color comes to the developing position. The developing unit 400 rotates. This is completed at least before the leading end of the electrostatic latent image based on the next image data reaches the developing position.

The intermediate transfer unit 500 includes an intermediate transfer belt 501, which is an intermediate transfer member stretched over a plurality of rollers described later. This intermediate transfer belt 50
1, a secondary transfer belt 601 as a transfer material carrier of the secondary transfer unit 600, a secondary transfer bias roller 605 as a secondary transfer charge applying unit, and a belt cleaning blade 504 as an intermediate transfer body cleaning unit. ,
A lubricant application brush 505 serving as a lubricant application means is disposed so as to face the lubricant application brush 505.

The intermediate transfer belt 501 includes a primary transfer bias applying roller 507, a belt driving roller 508, a belt tension roller 509, and a primary transfer charge applying means.
Secondary transfer opposed roller 510, cleaning opposed roller 5
11 and an earth roller 512. Each roller is formed of a conductive material, and each roller other than the primary transfer bias roller 507 is grounded.

The primary transfer bias roller 507 is supplied with a primary transfer power supply 801 controlled by a constant current or a constant voltage.
A transfer bias controlled at a predetermined current or voltage according to the number of superimposed toner images is applied. The intermediate transfer belt 501 is driven by a drive motor (not shown) in a direction indicated by an arrow.
8 is driven in the direction of the arrow. The intermediate transfer belt 501 is made of a semiconductor or an insulator and has a single-layer or multilayer structure.

A transfer section for transferring the toner image on the photosensitive drum 200 to the intermediate transfer belt 501 (hereinafter referred to as a “primary transfer section”)
In this case, the intermediate transfer belt 501 is stretched by the primary transfer bias roller 507 and the ground roller 512 so as to be pressed against the photosensitive drum 200 side, so that a predetermined distance is provided between the photosensitive drum 200 and the intermediate transfer belt 501. A nip portion having a width is formed.

The lubricant applying brush 505 grinds the zinc stearate 506 as a lubricant formed in a plate shape,
The polished fine particles are applied to the intermediate transfer belt 501. The lubricant application brush 505 is also configured to be adjacent to the intermediate transfer belt 501, and is controlled so as to contact the intermediate transfer belt 501 at a predetermined timing.

The secondary transfer unit 600 includes a secondary transfer belt 601 and the like stretched over three support rollers 602, 603, and 604, and a stretch between the support rollers 602 and 603 of the intermediate transfer belt 501 is formed. The secondary transfer opposing roller 510 can be pressed against the roller. One of the three support rollers 602, 603, and 604 is a driving roller that is rotationally driven by a driving unit (not shown), and the driving roller drives the secondary transfer belt 601 in a direction indicated by an arrow in the drawing.

The secondary transfer bias roller 605 is a secondary transfer means, and is disposed so as to sandwich the intermediate transfer belt 501 and the secondary transfer belt 601 between the secondary transfer opposing roller 510 and a constant current control. A transfer bias of a predetermined current is applied by a secondary transfer power supply 802 to be performed. Further, the supporting roller 602 and the secondary transfer bias roller 605 are arranged such that the secondary transfer belt 601 and the secondary transfer bias roller 605 can take a position where the secondary transfer belt 601 is pressed against the secondary transfer opposing roller 510 and a position where the secondary transfer bias roller 605 is separated therefrom. Is provided in the direction of the arrow. The secondary transfer belt 601 and the support roller 6 at the separated position
02 is indicated by a two-dot chain line in FIG.

The pair of registration rollers 650 includes an intermediate transfer belt 501 and a secondary transfer belt 60 sandwiched between a secondary transfer bias roller 605 and a secondary transfer opposing roller 510.
During the period 1, the transfer material P, which is a transfer material, is fed at a predetermined timing.

Fixing roller 701 of secondary transfer belt 601
A transfer sheet static elimination charger 606 as a transfer material static eliminator and a belt static eliminator 607 as a transfer material carrier static eliminator are opposed to a portion stretched around the supporting roller 603 on the side of the side. A cleaning blade 608, which is a transfer material carrier cleaning unit, is in contact with a portion of the secondary transfer belt 601 that is stretched around the lower support roller 604 in the drawing.

The transfer paper discharging charger 606 discharges the electric charges held in the transfer paper, so that the transfer paper can be satisfactorily separated from the secondary transfer belt 601 by the rigidity of the transfer paper itself. It is. The belt static elimination charger 607 eliminates electric charges remaining on the secondary transfer belt 601. Further, the cleaning blade 608 is for removing the adhered matter adhered to the surface of the secondary transfer belt 601 for cleaning.

In the color copier thus constructed, when the image forming cycle is started, the photosensitive drum 2
Reference numeral 00 denotes a counterclockwise rotation indicated by an arrow by a drive motor (not shown), and the intermediate transfer belt 501 is rotated clockwise by an arrow by a belt driving roller 508.

With the rotation of the intermediate transfer belt 501, Bk toner image formation, C toner image formation, M toner image formation,
The primary transfer is performed by the transfer bias by the voltage applied to the primary transfer bias roller 507 to form the Y toner image, and finally, the intermediate transfer belt 5 is moved in the order of Bk, C, M, and Y.
01 to form a toner image. For example, Bk toner image formation is performed as follows. Charger 201
The surface of the photosensitive drum 200 is uniformly charged to a predetermined potential with a negative charge by corona discharge.

Then, raster exposure with laser light is performed by a writing optical unit (not shown) based on the Bk color image signal. When this raster image is exposed, in the exposed portion of the surface of the photosensitive drum 200 that is initially uniformly charged, the charge proportional to the amount of exposure light disappears, and a bk electrostatic latent image is formed. The Bk developing device 4
01 contacts the negatively charged Bk toner on the Bk developing roller, the toner does not adhere to the portion of the photosensitive drum 200 where the charge remains, and the toner does not adhere to the portion having no charge, that is, the exposed portion. Is attracted to form a Bk toner image similar to the electrostatic latent image.

The B formed on the photosensitive drum 200
The k toner image is transferred onto the surface of the intermediate transfer belt 501 that is driven at a constant speed in contact with the photosensitive drum 200.
Hereinafter, the transfer of the toner image from the photosensitive drum 200 to the intermediate transfer belt 501 is referred to as “belt transfer”. A small amount of untransferred residual toner remaining on the surface of the photoconductor drum 200 after the belt transfer is cleaned by the photoconductor cleaning device 300 in preparation for reuse of the photoconductor drum 200.

On the photosensitive drum 200 side, the process proceeds to the C image forming process after the Bk image forming process, and reading of the C image data by the color scanner starts at a predetermined timing.
A C electrostatic latent image is formed on the surface of the photosensitive drum 200 by writing the laser light with the C image data. Then, after the rear end of the previous Bk electrostatic latent image has passed, and C
Before the leading end of the electrostatic latent image reaches, the rotation operation of the revolver developing unit 400 is performed, the C developing device 402 is set at the developing position, and the C electrostatic latent image is developed with the C toner.

Thereafter, development of the C electrostatic latent image area is continued.
When the rear end of the C electrostatic latent image has passed, the revolver developing unit is rotated in the same manner as in the case of the Bk developing device 401, and the next M developing device 403 is moved to the developing position.
This is also completed before the leading end of the next M electrostatic latent image reaches the developing position. Regarding the M and Y image forming processes, the operations of reading the color image data, forming the electrostatic latent image, and developing are the same as those of the above-described Bk and C processes, and thus the description is omitted.

On the intermediate transfer belt 501, Bk, C, M, and Y toner images sequentially formed on the photosensitive drum 200 are transferred while being sequentially aligned on the same surface. As a result, a toner image in which a maximum of four colors are superimposed on the intermediate transfer belt 501 is formed. At the time when the image forming operation is started, the transfer material P is fed from a paper feed unit such as a transfer paper cassette (not shown) or a manual feed tray, and stands by at the nip of the registration roller 650.

When the leading end of the toner image on the intermediate transfer belt 501 approaches the secondary transfer portion where the nip is formed by the secondary transfer facing roller 510 and the secondary transfer bias roller, the leading end of the transfer material P is just The registration roller pair 650 is driven so as to coincide with the leading edge of the image, and registration of the transfer material P with the toner image is performed.

Then, the transfer material P is transferred to the intermediate transfer belt 501.
The sheet passes through the secondary transfer portion while being superposed on the upper toner image. At this time, the four-color superimposed toner image on the intermediate transfer belt 501 is collectively transferred onto the transfer paper by the transfer bias by the voltage applied to the secondary transfer bias roller 605 by the secondary transfer power supply 802.

Then, when the transfer material P passes through a portion facing the transfer paper static elimination charger 606 disposed downstream of the secondary transfer portion in the moving direction of the secondary transfer belt 601, the transfer material P is neutralized and the secondary transfer belt 601 is moved. From the fixing roller pair 701. The toner image is fused and fixed at the nip portion of the pair of fixing rollers 701, sent out of the apparatus body by a pair of discharge rollers (not shown), and stacked face-up on a copy tray (not shown) to obtain a full-color copy.

On the other hand, the photosensitive drum 2 after the belt transfer
The surface of No. 00 is cleaned by the photoconductor cleaning device 300 and is uniformly discharged by a discharge lamp (not shown). Further, the toner remaining on the surface of the intermediate transfer belt 501 after the transfer of the toner image onto the transfer material P is cleaned by a belt cleaning blade 504 pressed against the intermediate transfer belt 501 by a separation / contact mechanism (not shown).

Here, at the time of the repeat copy, the operation of the color scanner and the image formation on the photosensitive drum 200 are performed as follows.
After the fourth color (Y) image forming process of the first sheet, the process proceeds to the second color (Bk) image forming process at a predetermined timing. Further, the intermediate transfer belt 501 transfers the second sheet of Bk toner to the area of the surface cleaned by the belt cleaning blade 504 following the batch transfer step of the first sheet of four-color superimposed toner image onto transfer paper. The image is transferred to the belt. Thereafter, the operation is the same as that of the first sheet.

The above is the copy mode for obtaining a four-color full-color copy. However, in the three-color copy mode and the two-color copy mode, the same operation as described above is performed for the designated color and the number of times. Become. In the case of the single-color copy mode, only the developing machine of the predetermined color of the revolver developing unit 400 is in the developing operation state until the predetermined number of sheets is completed, and the belt cleaning blade 504 is pressed against the intermediate transfer belt 501. The copy operation is performed with the position as it is.

Next, the structure of the secondary transfer section, which is a feature of the present invention, will be described. As shown in FIG. 3, the secondary transfer bias roller 605 in the secondary transfer unit of the present invention is disposed at a position upstream of the secondary transfer facing roller 510 in the moving direction of the intermediate transfer belt 501, as shown in FIG. I have. Therefore, the transfer material P conveyed toward the transfer nip portion of the secondary transfer portion is brought into close contact with the intermediate transfer belt 501 in the pre-transfer region described above. Thus, the occurrence of pre-transfer due to the gap G between the transfer material P and the intermediate transfer belt 501 in the pre-transfer area is prevented without complicating the apparatus.

The secondary transfer bias roller 605
4, is in contact with the surface of the intermediate transfer belt 501 so as to bite into the counter roller 510 side. Here, the center of the transfer roller 605 in a state where the surface of the intermediate transfer belt 501 is tangent to the transfer roller 605, and the transfer roller 605 is closer to the facing roller 510 than the surface of the intermediate transfer belt 501. The distance between the transfer roller 605 and the center of the transfer roller 605 in a state where the transfer roller 605 contacts the transfer roller 605 is set to 0.5 to 5 mm. As a result, the position of the surface of the intermediate transfer belt 501 that is in contact with the transfer roller 605 is higher than the position of the surface of the intermediate transfer belt 501 that is not in contact with the secondary transfer bias roller 605. The secondary transfer facing roller 5
The intermediate transfer belt 501 comes into contact with the intermediate transfer belt 501 so as to dig into the 10 side by 0.5 to 5 mm.

Accordingly, the transfer material P entering the secondary transfer nip N formed by the intermediate transfer belt 501 and the secondary transfer bias roller 605 is located on the front side of the secondary transfer nip N. Then, the intermediate transfer belt 501 and the
The sheet is sandwiched between the next transfer bias roller 605. Thus, as shown in FIG. 5, the transfer material P comes into close contact with the surface of the intermediate transfer belt 501 due to its stiffness.

Therefore, in the secondary transfer portion having such a configuration, a pre-transfer region (an interposing portion) where an electric field is not generated is sufficiently ensured, and before entering the transfer nip portion N, the intermediate transfer belt The transfer material P can be brought into close contact with 501.

Further, in the secondary transfer portion having this configuration,
The tangent of the transfer nip portion N on the nip entrance side is parallel to the surface of the intermediate transfer belt 501. Therefore, as in the configuration of the conventional secondary transfer portion shown in FIG.
Since the surface of the intermediate transfer belt 501 does not move upward from the tangential direction on the nip entrance side of the intermediate transfer belt 501, the intermediate transfer belt 501 and the transfer material P are more easily adhered to each other in the pre-transfer area. As a result, the effect of bringing the transfer material P in close contact with the surface of the intermediate transfer belt 501 before the transfer nip N can be sufficiently exhibited.

Here, when a transfer bias is applied from the transfer roller 605, no transfer electric field is generated in the pre-transfer area. That is, the transfer current does not flow unless the opposing roller 510 serving as a ground or the like is provided at the opposing portion of the transfer roller 605. Therefore, the actual transfer electric field is
As shown by the oblique lines in FIG. 4, the toner image is generated on the opposite roller 510 side, so that the occurrence of the pre-transfer in the pre-transfer area is suppressed.

As shown in FIG. 4, the transfer material P includes a pair of guide plates 910 as transfer material guide members.
920, the surface of the intermediate transfer belt 501 is contacted at a position upstream of the contact portion between the intermediate transfer belt 501 and the secondary transfer bias roller 605 in the moving direction of the intermediate transfer belt 501. The sheet enters the transfer nip N. Thereby, the intermediate transfer belt 501 is
The contact width of the transfer material P with respect to the transfer direction in the transport direction increases, and the transfer material P transported toward the transfer nip portion N comes into close contact with the intermediate transfer belt 501 in the pre-transfer area.

As shown in FIG. 6, the guide plates 910 and 920 move the transfer material P onto the surface of the intermediate transfer belt 501 at a position 5 to 30 mm before the transfer material entrance of the transfer nip N. It is arranged to start touching. Here, if the angle between the transfer material P passing through the registration roller 650 and heading toward the intermediate transfer belt 501 and the belt surface (surface) of the intermediate transfer belt 501 is small, the transfer nip N A portion where the close contact pressure in the front is weak and the transfer material P is not flat (the intermediate transfer belt 50).
An abnormal image is generated in a portion that rises from 1). Also, if the angle is large, the rear end of the transfer material P collides with the surface of the intermediate transfer belt 501 due to the jump of the rear end of the transfer material P when the transfer material P comes out of the guide plate 920. become. In this case, a lateral band-shaped abnormal image is generated in the transferred image. For this reason, the angle is preferably set in the range of 5 ° to 30 °.

[0062]

According to the present invention, the occurrence of pre-transfer due to the gap between the transfer material and the transfer member in the pre-transfer area can be prevented without complicating the apparatus. Has an effect.

In particular, according to the second and third aspects of the present invention, the contact width between the transfer roller and the intermediate transfer belt in the transfer material transport direction is increased, and the transfer material transported toward the transfer nip portion is removed. There is an excellent effect that the pre-transfer area can more reliably adhere to the intermediate transfer belt.

According to the fourth aspect of the present invention, the transfer material guide member allows the transfer material to enter the transfer nip at a distance of 5 to 30 m from the entrance of the transfer material.
Since the transfer material starts to come into contact with the surface of the image carrier at a position before m, there is an excellent effect that an image is not easily blurred due to a difference between the transfer speed of the transfer material and the speed of the image carrier. .

According to the fifth aspect of the present invention, an abnormal image due to a decrease in flatness of a portion of the transfer material that is in contact with the image carrier (intermediate transfer belt), or the rear end of the transfer material is connected to the transfer material guide member. There is an excellent effect that occurrence of an abnormal image due to hitting of the image carrier (intermediate transfer belt) by jumping up when the user comes out can be prevented.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a color copying machine showing an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is an enlarged view of an image forming unit of the color copying machine shown in FIG.

FIG. 3 is a schematic diagram for explaining a configuration of a secondary transfer unit which is a characteristic part of the image forming unit.

FIG. 4 is an enlarged view of a secondary transfer section shown in FIG.

FIG. 5 is a schematic diagram for explaining the behavior of a transfer material in the secondary transfer section.

FIG. 6 is a schematic diagram illustrating a configuration of a guide plate of the secondary transfer unit.

FIG. 7 is a schematic diagram illustrating a configuration of a secondary transfer unit of a conventional image forming unit.

FIG. 8 is an enlarged view of a conventional secondary transfer unit.

FIG. 9 is a schematic diagram for explaining the behavior of a transfer material in a conventional secondary transfer unit.

[Explanation of symbols]

 Reference Signs List 200 photoconductor drum 201 charging charger 210 photoconductor cleaning device 400 revolver developing unit 500 intermediate transfer unit 501 intermediate transfer belt 507 primary transfer bias roller 508 belt drive roller 600 secondary transfer unit 601 secondary transfer belt 605 secondary transfer bias roller 650 Registration roller 700 Fixing unit 801 Primary transfer power supply 802 Secondary transfer power supply 910,920 Guide plate G Gap between transfer material and intermediate transfer belt N Transfer nip P Transfer material

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Katsuya Kawagoe, Inventor 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (72) Inventor Hiroshi Ono 1-3-6, Nakamagome, Ota-ku, Tokyo Stock Inside Ricoh Company (72) Inventor Ryuta Takeichi 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Company Ricoh Company (72) Inventor Hiromi Ogiyama 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Company Ricoh Company ( 72) Inventor Toshiaki Motohashi 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (72) Inventor Shin Chihara 1-3-6 Nakamagome, Ota-ku, Tokyo F-term in Ricoh Co., Ltd. (Reference) 2H032 AA05 BA09 BA23 CA01

Claims (5)

[Claims] A belt-shaped image carrier that carries a toner image on the surface thereof; a toner image forming unit that forms a toner image on the image carrier; A transfer nip portion is formed between the image carrier and the transfer member by the transfer member that is in contact and the opposing member that faces the transfer member with the image carrier interposed therebetween so as to enter the transfer nip portion. A transfer means for applying a transfer bias to the transfer material conveyed to the transfer member to transfer the toner image on the image carrier to the transfer material. An image forming apparatus, wherein the image forming apparatus is arranged at a position upstream of a member in a moving direction of the image carrier. 2. An image forming apparatus according to claim 1, wherein said opposing member is an opposing roller having a radius of Rt, said image bearing member is an intermediate transfer belt having a thickness of Tb, and said transfer member is having a radius of Tb.
R2, and when the distance between the center of the opposing roller and the center of the transfer roller is M, (Rt +
Tb + R2) -M <0, and the transfer roller comes into contact with the surface of the intermediate transfer belt so as to cut into the opposite roller side, and the surface of the intermediate transfer belt is The separation distance between the center of the transfer roller in a state where the transfer roller makes a tangent to the center of the transfer roller in a state where the transfer roller is in contact with the surface of the intermediate transfer belt so as to bite into the opposite roller side. , 0.5 to 5 mm. 3. The image forming apparatus according to claim 1, wherein the transfer material is provided at a position upstream of a contact portion between the image carrier and the transfer member in a moving direction of the image carrier. An image forming apparatus comprising: a transfer material guide member configured to allow the transfer material to enter the transfer nip after being brought into contact with the surface of the body. 4. The image forming apparatus according to claim 3, wherein the transfer material guide member is provided at a position 5 to 30 mm before the transfer material entrance of the transfer nip, and the transfer material is disposed on the surface of the image carrier. An image forming apparatus configured to start contacting. 5. The image forming apparatus according to claim 3, wherein the transfer material guide member is configured to allow the transfer material to enter the image carrier when the transfer material starts to contact the surface of the image carrier. An image forming apparatus, wherein an angle is configured to be 5 ° to 30 °.