JPH1165332A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device for forming a high quality image without a defect in an image such as a discharge mark by preventing an electric discharge caused by a transfer electric field on the upstream side of a transferring region, with a simple constitution. SOLUTION: In the image forming device, an image carrier 2 is held by two rotary bodies 22 and 10, so as to transfer a toner image to a recording medium 3 from the image carrier 2. One rotary body 22 is provided with a voltage applying means 30 for forming the transfer electric field, to rush the recording medium 3 into a holding part 230 from a guiding means 27. At this time, the image carrier 2 forms a first contact part 200, to obtain contact, on the side of the rotary body 10 which does not have the voltage applying means, prior to the side of the rotary body 22 for applying a voltage, on the upstream side of the holding part 230 and the recording medium 3 comes into contact with the image carrier 2 in the contact part 200 on the upstream side on which the transfer electric field is not exerted, to suppress a gap discharge.

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 and a facsimile, and more particularly to an apparatus having a transfer means provided with an image carrier such as an intermediate transfer member and a photosensitive member.

[0002]

2. Description of the Related Art A transfer device of an image forming apparatus using an intermediate transfer member having a pair of rollers for holding a recording medium and an intermediate transfer member immediately before a secondary transfer area on a conveyance path of a recording medium is disclosed in Japanese Patent Application Laid-Open No. 9-1990. No.-62116 (first document). Japanese Patent Application Laid-Open No. 4-188176 (second document) discloses a configuration in which the angle at which the intermediate transfer member enters the transfer device is set on the transfer roller side. Further, a configuration in which two transfer rollers are provided so as to increase the nip width in the transfer portion is disclosed in Japanese Patent Application Laid-Open No. 4-97186 (third document).
Is disclosed. An image forming apparatus using a belt-shaped photosensitive member has a similar configuration.

[0003]

In the apparatus disclosed in the above-mentioned first document, in order to maintain the close contact between the intermediate transfer member and the recording medium up to the transfer area, a pair of clamping rollers is arranged close to the transfer area. This necessitates the installation, which complicates the configuration and raises the cost. Further, in the gap region between the intermediate transfer member and the upstream side of the transfer device, there is an inconvenience that image quality defects occur due to discharge generated by the transfer electric field. Second
In the apparatus disclosed in the literature, since the recording medium protrudes between the roller for applying the electric field and the intermediate transfer member, the image quality is reduced by the transfer electric field in the cap region of the prenip portion (upstream of the holding portion) of the transfer portion. There was a problem that a defect (discharge mark) was generated. The above problem was remarkable especially in high-resistance paper under a low humidity environment. In the apparatus disclosed in the third document, it is difficult to separate the functions of the two transfer rollers.

Therefore, the present invention provides an image forming apparatus which has a simple structure, prevents discharge due to a transfer electric field on the upstream side of a transfer area, and forms an image of good image quality without image defects such as discharge marks.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an image forming apparatus includes an image carrier having two rotating members for transferring a toner image from an image carrier to a recording medium. Transfer means provided with a voltage applying means for generating a transfer electric field on one of the rotating bodies, and guide means for guiding the recording medium at the holding portion, and the image carrier has a voltage upstream of the holding portion. A configuration is provided in which the rotating body side on which the application means is not provided comes into contact with the rotating body side to which voltage is applied prior to the rotating body side.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. (Embodiment 1) This embodiment shows a color electrophotographic copying machine using a belt-shaped intermediate transfer member (see FIG. 4). An electrostatic latent image corresponding to image information is formed on the surface of the photosensitive drum (latent image carrier) 1 by a known electrophotographic process such as a charging device 4 as the photosensitive drum 1 rotates in the direction of arrow A. Black (Bk) around the photosensitive drum 1
Developing devices 5 to 8 corresponding to each color of yellow (Y), magenta (M), and cyan (C) are provided, and the electrostatic latent image formed on the photosensitive drum 1 is The toner image T is formed by development. Therefore, if the electrostatic latent image written on the photosensitive drum 1 corresponds to the yellow image information, this electrostatic latent image is developed by the developing device 6 containing yellow (Y) toner,
A yellow toner image is formed on the photosensitive drum 1.

A belt-like intermediate transfer member 2 is provided so as to be in contact with the surface of the photosensitive drum 1. The belt-shaped intermediate transfer member 2 includes a plurality of intermediate transfer member driving rollers 21, a secondary transfer opposing roller (backup roller) 22, a tension roller 23 for controlling the belt tension to be constant, and a driven roller 24. Stretched on the roller of
It is configured to rotate in the direction of arrow B. Then, the toner image T formed on the photosensitive drum 1 is
Is transferred from the photosensitive drum 1 to the surface of the intermediate transfer member 2 at a primary transfer position where the toner and the intermediate transfer member 2 are in contact with each other. At this primary transfer position, a transfer corona discharger 9 is disposed on the back side of the intermediate transfer body 2.
The toner image T on the photosensitive drum 1 is electrostatically transferred to the surface of the intermediate transfer member 2 by applying a voltage having a polarity opposite to the charge polarity of the toner.

In the case of forming a monochromatic image, the toner image T primarily transferred to the intermediate transfer body 2 is secondarily transferred to the recording medium 3 immediately. When a color image is formed by superimposing toner images of a plurality of colors, the steps of forming the toner image on the photosensitive drum 1 and the primary transfer of the toner image are repeated for the number of colors. For example, when a full-color image is formed by superimposing four color toner images, black BK, yellow Y, magenta M
And the toner images T of Sian C are supplied to the respective developing devices 5, 6, 7, 8
These toner images T are sequentially formed on the intermediate transfer member 2.
Is primary-transferred.

On the other hand, the intermediate transfer member 2 rotates at the same cycle as the photosensitive drum 1 while holding the first primary-transferred black toner image T on the surface. Are transferred toner images T of yellow, magenta and cyan. The toner image T primarily transferred onto the surface of the intermediate transfer body 2 in this manner is conveyed to a secondary transfer position facing the conveyance path of the recording medium 3 as the intermediate transfer body 2 rotates.

A semi-conductive transfer roller 1 is located at the secondary transfer position.
0 is disposed close to the intermediate transfer body 2 and comes into contact with the intermediate transfer body 2 at a predetermined timing. The recording medium 3 carried out of the tray 12 at a predetermined timing by the feed roller 11 is sandwiched between the transfer roller 10 and the intermediate transfer body 2 via the guide means 27. Further, on the back surface side of the intermediate transfer body 2 at the secondary transfer position, a backup roller 22 serving as a counter electrode of the transfer roller 10 is provided.
Are arranged. Then, when a transfer electric field having the same polarity as the charged polarity of the toner is generated in the backup roller 22,
The toner image T carried on the intermediate transfer body 2 is electrostatically transferred to the recording medium 3 at a secondary transfer position. Transfer roller 10
The cleaning blade 25 attached in contact with the roller removes dirt attached during the driven rotation of the transfer roller 10 over the entire circumference of the transfer roller 10 to prevent dirt on the back surface of the recording medium 3. In. And
The recording medium 3 onto which the toner image has been transferred is peeled off from the intermediate transfer body 2, sent to the fixing device 15 by the transport belt 14, and subjected to the toner image fixing process.

On the other hand, the residual toner is removed from the intermediate transfer body 2 on which the secondary transfer of the toner image has been completed by the belt cleaner 16, and the process proceeds to the next image forming step. Note that the transfer roller 10 and the belt cleaner 16 are disposed so as to be able to freely contact and separate from the intermediate transfer body 2, and when a color image is formed,
These members are separated from the intermediate transfer member 2 until the toner image before the final color passes through the transfer roller 10 and the belt cleaner 16.

The intermediate transfer member 2 is made of a resin such as polyimide, polycarbonate, polyester, polypropylene, polyethylene terephthalate or various rubbers containing an appropriate amount of carbon black or the like, and has a volume resistivity of 106 to 10%.
It is formed to have a thickness of 15 Ωcm, and its thickness is set to, for example, 0.1 mm. Backup roller 22
Is provided with a foamed elastic material layer 22b around the metal core material 22a and a conductive layer 2 outside the foamed elastic material layer 22b.
It has a two-layer structure covered with 2c. The outer conductive layer (surface layer) 22c is made of carbon black of 15 to 35.
It is made of semiconductive EPDM (ethylene propylene diene rubber) foam rubber dispersed in a wet%, and the thickness of the surface layer 22c is 0.5 to 1.5 mm. Further, the surface resistivity is controlled in a resistance region of 107 to 1010 Ω / □. Backup roller 2 configured as above
2, a metal roller 26 is brought into contact with the metal roller 26, and a predetermined voltage having the same polarity as that of the toner is applied to the metal roller 26 to generate a transfer electric field on the transfer roller 10 as a counter electrode.

The transfer roller 10 includes a metal core 10a and carbon black dispersed foam E fixed around the metal core 10a.
5 to 20 through a skin layer on a core layer made of a PDM material
It has a coating layer 10b coated with a carbon black-dispersed fluororesin-based material having a thickness of μm.
The volume resistivity of the core metal 10a and the coating layer 10b is 1
The roll hardness is 20 ° to 45 ° in terms of Aska C hardness. Transfer roller 10
The cleaning blade 25 attached to is made of urethane rubber.

In the secondary transfer section, the two rollers (rotating members) of the backup roller 22 and the transfer roller 10 constitute a transfer nip (nip) for holding the intermediate transfer member 2. Then, the recording medium 3 is configured to protrude into a winding portion between the intermediate transfer body 2 and the transfer roller 10 before reaching the transfer nip portion.

Here, the structure of the secondary transfer section will be described in detail with reference to FIG. The metal roller 26 in contact with the backup roller 22 is in communication with the voltage applying means 30. The transfer roller 10 is grounded. In this state, when a predetermined voltage having the same polarity as that of the toner is applied to the metal roller 26, the transfer roller 10 generates a transfer electric field as a counter electrode.
The intermediate transfer body 2 advances in the direction of the arrow x, and in a region where the transfer roller 10 and the backup roller 22 are in contact with each other,
It is pinched. At this time, first, the intermediate transfer body 2 is wound around the peripheral surface of the transfer roller 10 that is not provided with the voltage applying unit, and forms the first contact portion 200. The intermediate transfer body 2 advances along the peripheral surface of the transfer roller 10 and the transfer roller 10
Then, it moves to the downstream side after passing through the holding portion 230 between the roller and the backup roller 22.

The recording medium 3 is sent out of a guide plate 27 disposed on the upstream side of the secondary transfer portion and on the surface side of the intermediate transfer body 2. The sheet advances to the holding section 230 in contact with the intermediate transfer member 2.
At this time, the intermediate transfer body 2 is transferred to the recording medium 3 by the transfer roller 10.
The first contact portion 200 contacts the intermediate transfer member 2 and advances to the holding portion 230 between the transfer roller 10 and the backup roller 22 as the intermediate transfer member 2 advances. The toner image on the intermediate transfer body 2 is transferred to the recording transfer material 3 by the transfer electric field D at the holding portion 230.

The operation of the secondary transfer unit having this configuration will be described. The recording medium 3 is inserted from the roller 10 having no voltage application means, and the transfer roller 10 and the backup roller 22 are formed in contact with each other. At the upstream side of the next transfer area (holding portion 230), the sheet comes into contact with the intermediate transfer member 2 before receiving the action of the transfer electric field. And the recording medium 3
Is wound around the transfer roller 10 together with the intermediate transfer body 2 and advances to the secondary transfer area (see FIG. 2). In this configuration, in the secondary transfer area, the recording medium 3 is in a superposed state without any gap between the recording medium 3 and the intermediate transfer body 2, so that the discharge on the upstream side of the transfer area generated by the conventional apparatus does not occur. Does not occur. That is, as shown in FIG.
The discharge d generated in the gap G due to the transfer electric field D, which is generated when there is a gap G between the recording medium 3 and the recording medium 3, is prevented by eliminating the gap in the secondary transfer area.

Next, on the upstream side of the secondary transfer area, before the backup roller 22, the intermediate transfer body 2 is wound around a transfer roller having no application means. An example of the arrangement will be described. (1) A transfer roller is disposed upstream of the intermediate transfer body 2. ... See FIG. 5 The transfer roller 100 is moved to the upstream side of the intermediate transfer member 2 with respect to the backup roller 22 communicating with the voltage applying unit. The intermediate transfer body 2 that advances in the direction of the arrow winds around the peripheral surface of the transfer roller 100 disposed upstream of the backup roller 22 on the conveyance path reaching the secondary transfer portion (holding portion), and makes a first contact. The part 200A is formed. Next, on the downstream side of the first contact portion 200A, the transfer roller 100
And the backup roller 22 are held by the holding portion 230A where the contact is made. The recording medium 3 fed at the same timing comes into contact with the intermediate transfer member 2 at the first contact portion 200A on the upstream side of the secondary transfer region (holding portion) 230A. No gap with the recording medium 3 occurs.

(2) Soften the rubber hardness of the transfer roller. ... See FIG. 6. The transfer roller 100B is made of a foamed EPDM material in which the hardness of the core layer is softened. By softening the roll hardness, the holding portion 230 with the backup roller 22B is formed.
In B, the transfer roller 100B is recessed into the curvature shape of the backup roller 22B. Then, the intermediate transfer body 2 in the holding portion 230B first contacts the curved concave end face 110B of the transfer roller 100B to form a first contact portion, and advances along the recess of the transfer roller 100B. The recording medium 3 to be inserted into the holding portion according to timing is the intermediate transfer body 2
Collides with the first contact portion 110B that contacts the backup roller 100B, and proceeds to the holding portion 230B.
Further, in this case, the transfer roller 10 is made of a material which is easily deformed in the radial direction (normal direction) but not deformed in the axial direction (tangential direction) in response to an external force applied to the roller. .

Further, as shown in FIG. 7, the diameter γ2 of the transfer roller 100C is made larger than the diameter γ1 of the backup roller 22C. With this configuration, the first contact portion 110C of the intermediate transfer member 2 can be extended from the transfer area, and the recording medium 3 contacts the intermediate transfer member 2 before receiving the action of the transfer electric field, and the gap discharge occurs. Can be suppressed.

(Embodiment 2) In this embodiment, a voltage applying means is provided on the transfer roller (see FIG. 8). The transfer roller 120 in the secondary transfer unit is
, And the backup roller 220 is grounded. Toner image T carried on the surface of intermediate transfer body 2
Is transferred to the recording medium 3 sent to the holding portion at a proper timing by a voltage having a polarity opposite to that of the toner applied to the transfer roller 120 while passing through the holding portion 250 between the transfer roller 120 and the backup roller 220.

In this image forming apparatus, the intermediate transfer body 2 has a backup roller 220 having no application means.
To form a first contact portion 220 </ b> A and advance to the holding portion 250 while being wound around the backup roller 220. The recording medium 3 is conveyed onto the intermediate transfer member 2 from the guide means 27. The contact portion 270 with the intermediate transfer member 2 is located on the upstream side of the holding portion 250 and at the tangent line L of the contact portion 250. It is set on the side of the backup roller 220 which does not have a voltage applying means. In the secondary transfer unit configured as described above, the recording medium 3 abuts on the intermediate transfer member 2 at a position where the transfer electric field is weak on the side of the backup roller 220, which is not provided with the voltage applying means, and is overlapped with the intermediate transfer member 2 and clamped. Proceed to section 250. Also in this apparatus, no gap is formed between the intermediate transfer body 2 and the recording medium 3 in a region where the transfer voltage is applied, so that gap discharge is prevented.

(Embodiment 3) The color image forming apparatus shown in this embodiment forms toner images on a photoconductor in a required number of colors in a stacked state, and forms the toner images on the photoconductor. A color image forming method is adopted in which toner images of the number of colors are collectively transferred onto a recording medium. The configuration will be described with reference to FIG. A DC power supply is connected to the corona discharge wire of the charger 52 of the scorotron. A latent image corresponding to image information is formed on an image carrier belt 62 made of an organic photoreceptor by image exposure means 53 such as a semiconductor laser, and developing means 54, yellow, magenta, sian, and black toners are separately contained. Developed by 55, 56, 57.
The toner on the image carrier belt 62 is transferred to a recording medium by a transfer roller 60. The image carrier belt 62 is a belt having an insulating surface coat layer,
1. Transfer roller facing roller (backup roller) 7
2. The belt is stretched over a plurality of rollers such as a tension roller 73 and a driven roller 74 that control the tension of the belt to be constant, and rotates in the direction of arrow B.

The transfer roller 60 is formed by coating a core layer made of a carbon black dispersed and foamed EPDM material fixed around the core metal with a carbon black-dispersed fluororesin material having a thickness of 5 to 20 μm via a skin layer. And the volume resistivity between the core metal and the coating layer is 106Ωc.
m to 109 Ωcm, and the roll hardness is 20 ° to 45 ° in Asuka C hardness. The cleaning blade 61 attached to the transfer roller 60 is made of urethane rubber. The backup roller 72 is made of EPDM (ethylene propylene diene rubber) foam rubber.

First, as a first cycle, the image carrier belt 62 is uniformly charged by applying a DC bias to the grid of the charger 52. Thereafter, the first exposure is performed by the image exposure means 53 to form an image latent image. Then, a developing bias is applied to the yellow developing means 54 to cause the yellow developing means 54 to adhere on the image carrier belt 62. Subsequently, the second cycle is entered, and the charger 52 uniformly charges. Thereafter, a second image exposure is performed by the image exposure unit 53 to form an image latent image, and a developing bias is applied to the magenta developing unit 55 to cause the toner to adhere to the image carrier belt 62. The above steps are repeated to form Sian and Black images. Thereafter, the toner adhered to the image carrier belt 62 is collectively transferred to the recording medium by using the transfer roller 60 to which a voltage is applied. Until the toner image before the final color is formed on the image carrier belt 62 and passes through the transfer roller 60 and the cleaner position, the transfer roller 6
0, the cleaner 58 is separated from the image carrier belt 62, feeds a recording medium in accordance with the toner image forming position on the image carrier belt 62, makes the transfer roller 60 contact, and performs a transfer operation. The toner remaining on the body belt 62 is cleaned by the cleaner 58 which is brought into contact with the toner at the proper timing. A cleaning blade 61 is attached to the transfer roller 60.

In this image forming apparatus, the contact between the image carrier belt 62 and the backup roller 72 having no voltage applying means is backed up from the tangent line between the transfer roller 60 and the backup roller 72 on the upstream side of the transfer area. By setting the position on the roller 72 side, discharge occurring due to the gap between the image carrier belt 62 and the recording medium 3 on the upstream side of the transfer area can be prevented, and an image with good image quality can be formed.

Further, even when the voltage applying means is provided on the backup roller 72, the transfer roller 60 having no voltage applying means is arranged on the upstream side with respect to the backup roller 72. Alternatively, the transfer area may be formed by softening the hardness of the transfer roller 60 having no voltage applying means, or making the diameter of the transfer roller 60 larger than the diameter of the backup roller 72 having the voltage applying means. The discharge occurring due to the gap between the image carrier belt 62 and the recording medium 3 on the upstream side can be prevented, and an image can be formed with good image quality.

As described above, in the image forming apparatus shown in this embodiment, the recording medium comes into contact with the image carrier before receiving the action of the transfer electric field, and the transfer medium is generated by the transfer electric field on the upstream side of the transfer area. Discharge is prevented, and an image with good image quality without image defects such as discharge marks can be formed.

[0029]

As described above, in the image forming apparatus of the present invention, since the recording medium comes into contact with the image carrier on the upstream side of the area where the transfer electric field acts, image quality defects (discharge marks) are prevented. And high image quality can be achieved.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a transfer unit of an image forming apparatus according to the present invention.

FIG. 2 is a diagram illustrating the operation of a transfer unit of the image forming apparatus according to the present invention.

FIG. 3 is a diagram illustrating the operation of a conventional transfer unit.

FIG. 4 is a schematic configuration diagram of a color image forming apparatus to which the present invention is applied.

FIG. 5 is an explanatory view showing an embodiment of a transfer unit.

FIG. 6 is an explanatory view showing another embodiment of the transfer unit.

FIG. 7 is an explanatory view showing another embodiment of the transfer unit.

FIG. 8 is an explanatory view showing another embodiment of the transfer unit.

FIG. 9 is a schematic configuration diagram of a color image forming apparatus using a photosensitive belt to which the present invention is applied.

[Explanation of symbols]

1 photoreceptor, 2 intermediate transfer member, 3 recording medium,
4,52 charging device, 5,57 black developing device,
6,54 Yellow developing device, 7,55 Magenta developing device, 8,56 Sian developing device, 9 Transfer corona discharger, 10,60 Transfer roller, 11 feed roller, 12,84 tray, 14,81 conveyance Belt, 15,82 Fixing unit, 16,58 Belt cleaner, 17 Belt position sensor, 21,71
Drive roller, 22,72 backup roller, 2
3, 73 tension roller, 24, 74 driven roller, 25, 61 cleaning blade, 26 metal roller, 27 guide means, 62 photoreceptor belt.

Continued on the front page (72) Inventor Osamu Handa 2274 Hongo, Fuji Xerox Co., Ltd., Ebina City, Kanagawa Prefecture

Claims (8)

[Claims] 1. An image bearing member and a holding portion formed by holding the image bearing member by two rotating members in order to transfer a toner image from the image bearing member to a recording medium. On the other hand, in an image forming apparatus comprising a transfer means provided with a voltage applying means for generating a transfer electric field and a guide means for guiding a recording medium to the holding portion, the transfer means is provided at an upstream side of the holding portion. And an image forming apparatus configured to contact the image carrier with a rotating body not provided with the voltage applying unit prior to the rotating body provided with the voltage applying unit. 2. An image carrier and a holding portion formed by sandwiching the image carrier with two rotating members in order to transfer a toner image from the image bearing member to a recording medium. On the other hand, in an image forming apparatus comprising a transfer means provided with a voltage applying means for generating a transfer electric field and a guide means for guiding a recording medium to the holding portion, the transfer means is provided at an upstream side of the holding portion. The image carrier is brought into contact with a rotating body not provided with the voltage applying means prior to the rotating body provided with the voltage applying means, and the recording medium is placed on the upstream side of the holding portion, and the voltage applying means is provided. An image forming apparatus which is configured so that a tangential line of a holding portion is brought into contact with a rotator side provided with no voltage applying means prior to the provided rotator. 3. An image forming apparatus according to claim 2, wherein said transfer means comprises a rotator provided with a voltage applying means of a holding portion in contact with a toner image holding surface of the image carrier. 4. The image forming apparatus according to claim 1, wherein the rotator not provided with the voltage applying means is disposed upstream of the rotator provided with the voltage applying means. 5. The image forming apparatus according to claim 1, wherein the hardness of the rotating body provided with no voltage applying means is lower than the hardness of the rotating body provided with the voltage applying means. 6. The image forming apparatus according to claim 1, wherein the rotating body not provided with the voltage applying means is formed so that the diameter of the rotating body is larger than the diameter of the rotating body provided with the voltage applying means. 7. The material constituting the rotating body not provided with the voltage applying means has an anisotropy in a deformation amount with respect to an external stress in a normal direction and a tangential direction. 3. The image forming apparatus according to 2. 8. The image forming apparatus according to claim 1, wherein the rotating body not provided with the voltage applying unit has at least a surface layer and an elastic layer having a lower hardness than the surface layer.