JP2001194925A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a defective transfer at a 1st transfer part in an image forming device. SOLUTION: The image forming device is provided with an exposing means for irradiating a uniformly electrified photoreceptor drum 1a with laser light corresponding to image data and then forming an electrostatic latent image, a developing means for supplying toner to the electrostatic latent image and developing the electrostatic latent image, an endless belt type intermediate transfer belt 7 which is arranged so that it is stretched and supported by plural rollers so as to be rotated around the rollers and so as to be attached/detached to/from the photoreceptor drum 1a and a nip part is formed by alowing it to be in contact with the photoreceptor drum 1a, a 1st transfer roller 8a which is arranged on the downstream side of the nip part in the rotating direction so as to face the photoreceptor drum 1a across the intermediate transfer belt 7 and transfer the toner image to the intermediate transfer belt 7, and a conductive roller 16a which is arranged on the upstream side of the nip part in the rotating direction so as to face the photoreceptor drum 1a across the intermediate transfer belt 7 and on which a ground potential or a potential whose polarity is reverse to that of the 1st transfer roller 8a is applied.

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 electronic copying machine, a laser beam printer, and a facsimile.

[0002]

2. Description of the Related Art A conventional image forming apparatus will be described below.

FIG. 3 is an explanatory view showing a conventional image forming apparatus.
FIG. 4 is an explanatory diagram showing the photosensitive drum and its periphery in the image forming apparatus of FIG.

In the image forming apparatus, photosensitive drums 1a, 1
b, 1c, and 1d respectively, and four image forming stations S1, S2, S3, and S on which a black image, a cyan image, a magenta image, and a yellow image are respectively formed.
4 are arranged.

Around the photosensitive drums 1a, 1b, 1c, 1d, charging brushes 2a, 2b, 2c, 2d for uniformly charging the surfaces of the photosensitive drums 1a, 1b, 1c, 1d.
Exposure means 3 for forming an electrostatic latent image corresponding to a specific component among the color components on photosensitive drums 1a, 1b, 1c, 1d
a, 3b, 3c, 3d; developing rollers 4a, 4b, 4c, 4d for developing electrostatic latent images; 10a, 10b, 10c, 10
d are respectively arranged along the rotation direction.

[0006] Toner supply rollers 5a, 5b, 5c, and 5d for pressing the developing rollers 4a, 4b, 4c, and 4d to supply toner to the developing rollers 4a, 4b, 4c, and 4d, and the developing rollers 4a, 4b, and 4d. Doctor blades 6a, 6b, 6c for thinning the toner supplied to 4c, 4d;
6d are provided.

The image forming stations S1, S2, S3
Below S4, an endless intermediate transfer belt 7, which is supported by a plurality of rollers 17 and is rotated, is arranged so as to be able to contact and separate from the photosensitive drums 1a, 1b, 1c, 1d. . The intermediate transfer belt 7 is provided with an intermediate transfer belt cleaning device 9 for scraping residual toner on the surface of the intermediate transfer belt 7.

[0008] The photosensitive drum 1 via the intermediate transfer belt 7
a, 1b, 1c, 1d, the first transfer rollers 8a, 8 for transferring the toner image to the intermediate transfer belt 7
b, 8c and 8d are provided.

A second transfer roller 11 for transferring a composite image formed on the intermediate transfer belt 7 to a sheet is provided on a paper path on which an image is formed, and a fixing device 15 for fixing the transferred toner image to the sheet. Is arranged.

The second transfer roller 11 is brought into contact with
A cleaning roller 12 that removes toner attached to the transfer roller 11 is provided. Further, the fixing device 15
Is composed of a fixing roller 13 having a heater, and a pressure roller 14 which rotates while being pressed against the fixing roller 13. The composite image transferred by the nipping rotation of the fixing roller 13 and the pressure roller 14 is formed on a sheet. Fix it.

Next, the operation of the image forming apparatus configured as described above will be described.

First, a charging brush 2a connected to a high voltage power supply
To uniformly charge the surface of the photosensitive drum 1a to a predetermined potential.

Next, an electrostatic latent image corresponding to a predetermined color in the color components is formed on the surface of the charged photosensitive drum 1a by the exposure means 3a.

A predetermined bias is applied to the developing roller 4a on which the toner layer is formed, and toner is applied to the electrostatic latent image on the photosensitive drum 1a by an electric field acting on the surface of the developing roller 4a and the photosensitive drum 1a. Transfer and development is performed.

The toner image formed on the photosensitive drum 1a is transferred onto the intermediate transfer belt 7 by a predetermined bias applied to the first transfer roller 8a.

Such an image forming operation is sequentially performed for each color, and a composite image is formed by superimposing toner images of four colors of black, cyan, magenta, and yellow on the intermediate transfer belt 7.

Thereafter, while applying a high voltage having a polarity opposite to that of the toner to the second transfer roller 11, the second transfer roller 11
When the sheet is pressed against the intermediate transfer belt 7, the composite image formed on the intermediate transfer belt 7 is collectively transferred to the sheet.

The sheet on which the toner image has been transferred is fixed to a fixing device 15.
Where the heat and the fixing roller 13 and the pressure roller 14
The toner image is fixed by the pinching force, and a color image is formed.

[0019]

However, in such a conventional image forming apparatus, a photosensitive drum and an intermediate transfer belt are provided in a first transfer section where a toner image is transferred from a photosensitive drum to an intermediate transfer belt. An electric field acts in the direction of moving the toner image on the photoconductor drum to the intermediate transfer belt also on the upstream side in the rotation direction of the nip portion where the nip portion contacts.

For this reason, there is a problem in that the toner image on the photosensitive drum before the transfer is disturbed and the character dust is generated, and the transfer loss occurs due to the toner being exposed to the transfer electric field for a long time and the charge polarity of the toner being inverted. Have a point.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus capable of preventing occurrence of a transfer failure such as character dust or missing transfer in the first transfer portion.

[0022]

In order to solve this problem, an image forming apparatus according to the present invention comprises an electrostatic latent image carrier, and a charging unit for uniformly charging the surface of the electrostatic latent image carrier. An exposure unit that irradiates a laser beam corresponding to image data to the electrostatic latent image carrier charged by the charging unit to form an electrostatic latent image; and supplies toner to the electrostatic latent image to supply the electrostatic latent image to the electrostatic latent image carrier. Developing means for visualizing the image, a belt-like intermediate transfer member which is circumferentially rotatably adjusted by a plurality of rollers and is in contact with the electrostatic latent image carrier to form a nip portion, and rotation of the nip portion Is located at a position on the downstream side in the direction opposite to the electrostatic latent image carrier via the intermediate transfer member, and transfers a toner image to the intermediate transfer member.
A transfer unit disposed at a position upstream of the nip portion in the rotation direction and opposed to the electrostatic latent image carrier via the intermediate transfer member, and a ground potential or a potential having a polarity opposite to that of the first transfer unit applied to the transfer unit; And a member.

As a result, the generation of an electric field for moving the toner on the electrostatic latent image bearing member approaching the nip to the intermediate transfer member is prevented by the conductive member, so that the character dust in the first transfer portion can be reduced. It is possible to prevent transfer failure such as transfer omission.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the first aspect of the present invention, there is provided an electrostatic latent image carrier, a charging unit for uniformly charging the surface of the electrostatic latent image carrier, and a charging unit for charging the surface of the electrostatic latent image carrier. Exposure means for irradiating the electrostatic latent image carrier with laser light corresponding to the image data to form an electrostatic latent image, and supplying toner to the electrostatic latent image to visualize the electrostatic latent image A developing means, a belt-like intermediate transfer body which is circumferentially rotatably adjusted by a plurality of rollers, and which comes into contact with the electrostatic latent image carrier to form a nip portion; and an intermediate transfer member on the downstream side in the rotation direction of the nip portion. A first transfer unit that is disposed at a position facing the electrostatic latent image carrier via the body and transfers the toner image to the intermediate transfer body; and an electrostatic latent image via the intermediate transfer body upstream of the nip in the rotation direction. It is arranged at a position facing the image carrier, and has a ground potential or a voltage having a polarity opposite to that of the first transfer means. And a conductive member to which the toner is transferred from the electrostatic latent image carrier approaching the nip portion to the intermediate transfer member. Therefore, there is an effect that it is possible to prevent the occurrence of a transfer failure such as character dust or transfer omission in the first transfer portion.

According to a second aspect of the present invention, in the first aspect, the distance between the contact position between the first transfer means and the intermediate transfer member and the nip portion, the distance between the conductive member and the intermediate transfer member are reduced. In this image forming apparatus, the distance between the contact position and the nip portion is set to be equal to each other, and it is possible to prevent the occurrence of transfer defects such as character dust and missing transfer in the first transfer portion. Having.

Hereinafter, an embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. In these drawings, the same members are denoted by the same reference numerals, and duplicate description is omitted.

FIG. 1 is an explanatory view showing an image forming apparatus according to an embodiment of the present invention, and FIG. 2 is an explanatory view showing a photosensitive drum and its periphery in the image forming apparatus shown in FIG.

The image forming apparatus is provided with four image forming stations S1, S2, S3, and S4. Each of the image forming stations S1, S2, S3, and S4 has an organic photoconductor (OPC) mounted on a grounded metal drum. ) Are provided with photosensitive drums (photosensitive members) 1a, 1b, 1c, and 1d, respectively, which are electrostatic latent image carriers coated in a thin film form.

Around the photosensitive drums 1a, 1b, 1c, 1d rotatably provided in the direction of the arrow, the surfaces of the photosensitive drums 1a, 1b, 1c, 1d made of conductive fibers are uniformly charged. Charging brush (charging means) 2a, 2b, 2
c, 2d, which are controlled by signals from a host computer (not shown) to form electrostatic latent images corresponding to specific components among predetermined color components on the photosensitive drums 1a, 1b, 1c, 1
d, exposure means 3a, 3b, 3c, and 3d, and toner as a developer are stored therein.
developing rollers (developing means) 4a, 4b, 4c, 4d for developing the electrostatic latent image formed by the toners c, 3d with this toner;
Cleaning blades 10a, 10b, 10c, which are formed of urethane rubber or the like and scrape toner remaining on the photosensitive drums 1a, 1b, 1c, 1d after transfer of the toner image.
10d are respectively arranged along the rotation direction.

Each of the developing rollers 4a, 4b, 4c,
4d, the developing rollers 4a, 4b, 4c, 4d
Supply rollers 5a, 5b, 5 for supplying toner to the
c, 5d, and a doctor blade 6a for thinning the toner supplied to the developing rollers 4a, 4b, 4c, 4d.
6b, 6c and 6d are provided.

Here, the developing rollers 4a, 4b, 4c, 4
“d” is made of a metal such as stainless steel and a conductive elastic body such as urethane or silicon formed in a layer on the outer peripheral surface thereof.
It is installed in a state where it is in contact with 1c and 1d with a predetermined pressing force.

The toner supply rollers 5a, 5b, 5
Each of c and 5d is made of a metal such as stainless steel and a conductive layer made of an elastic body such as a foam such as urethane or silicon formed on the outer peripheral surface thereof in a layered form. 4a, 4b, 4c, and 4d are pressed against each other with a predetermined bite amount to stabilize the charge amount due to friction with the toner.

Then, the doctor blades 6a, 6b, 6
Reference numerals c and 6d denote a stainless steel leaf spring and a conductive member such as silicon or urethane molded simultaneously at the tip of the leaf spring.
The toner supplied by b, 5c, 5d is frictionally charged to form a thin toner layer on the outer peripheral surfaces of the developing rollers 4a, 4b, 4c, 4d.

Although a negatively charged toner is used here, a positively charged toner may be used.

Here, the image forming stations S1, S
At S2, S3, and S4, a black image, a cyan image, a magenta image, and a yellow image are formed, respectively. Is output.

Each image forming station S1, S2, S
An intermediate transfer belt (intermediate transfer member) 7 in the form of an endless belt, which is supported by a plurality of rollers 17 and is rotated around the belt, is provided below the photosensitive drums 1a, 1b, 1c, and 1d. They are arranged so that they can come and go.

The intermediate transfer belt 7 formed of a conductive resin or the like is provided with an intermediate transfer belt cleaning device 9 for scraping residual toner on the surface of the intermediate transfer belt 7. The intermediate transfer belt cleaning device 9 is separated from the intermediate transfer belt 7 while a synthetic image is formed on the intermediate transfer belt 7, and comes into contact with the intermediate transfer belt 7 only when performing cleaning.

The photosensitive drum 1 via the intermediate transfer belt 7
At positions opposite to the photosensitive drums 1a, 1b, 1c, 1d and the intermediate transfer belt 7, the nip portion is made of metal such as stainless steel at a position facing the photosensitive drums 1a, 1b, 1c, 1d. First transfer rollers (first transfer means) 8a, 8b, 8c, 8d for transferring a toner image to the intermediate transfer belt 7
And conductive rollers (conductive members) 16a, 16b, 16c, 16d made of metal such as stainless steel and abutting on the intermediate transfer belt 7 are arranged on the upstream side in the rotation direction. Then, the first transfer rollers 8a, 8b, 8
For example, a voltage of +500 V is applied to c and 8d, and the conductive rollers 16a, 16b, 16c and 16d are grounded.

The first transfer rollers 8a, 8b, 8c,
8d and conductive rollers 16a, 16b, 16c, 16
d rotates following the rotation of the intermediate transfer belt 7.

Here, the first transfer rollers 8a, 8b, 8
c, 8d, the distance between the contact position between the intermediate transfer belt 7 and the nip, and the conductive rollers 16a, 16b, 16c, 16d.
The distance between the nip portion and the contact position between the belt and the intermediate transfer belt 7 is, for example, 5 mm.

It is preferable that these distances are equal to each other as in this embodiment, but they need not be equal.

A second transfer roller 11 for transferring the composite image formed on the intermediate transfer belt 7 onto the paper is provided on a paper (recording medium) transport path on which an image is formed, and the transferred toner image is fixed on the paper. A fixing device 15 is provided.

Here, the second transfer roller 11 contacts and rotates with the intermediate transfer belt 7 only when the composite image is transferred to the sheet. In addition, a cleaning roller 12 that contacts the second transfer roller 11 and removes toner attached to the second transfer roller 11 is provided.

The fixing device 15 includes a fixing roller 13 having a heater such as a halogen lamp therein, and a pressure roller 14 which rotates while being pressed against the fixing roller 13. Then, the fixing roller 13 and the pressure roller 1
The composite image transferred by the pressure and heat generated by the pinching rotation with the fixing member 4 is fixed on a sheet to form a color image.

Next, the operation of the image forming apparatus configured as described above will be described.

First, the charging brush 2a connected to the high voltage power supply
Is applied to the surface of the photosensitive drum 1a at -600V.
To be charged.

Next, the photosensitive drum 1a is rotated in the direction of the arrow by a driving device (not shown), and the laser beam emitted from the exposure means 3a causes the charged surface of the photosensitive drum 1a to have a color component. An electrostatic latent image corresponding to a predetermined color, for example, a black image is formed. Here, the energy given by the laser beam per unit area of the surface of the photosensitive drum 1a is 1.0 μJ / cm ² , and the surface potential of the portion irradiated with the laser beam is reduced to −80V.

A bias of -250 V is applied to the developing roller 4a on which the toner layer of 0.5 mg / cm ² is formed, and the electric field acting on the surface of the developing roller 4a and the photosensitive drum 1a causes the photosensitive drum 1a to be charged. The toner is transferred only to the portion irradiated with the laser beam and development is performed.

The toner image formed on the photosensitive drum 1a is transferred to the + 500V applied to the first transfer roller 8a at the first transfer section where the toner image is transferred from the photosensitive drum 1a to the intermediate transfer belt 7. The image is transferred onto the intermediate transfer belt 7 by the bias.

In the case of a copier or printer using four colors, such an operation is sequentially performed for each color, and four color toner images of black, cyan, magenta, and yellow are superimposed on the intermediate transfer belt 7. Form a composite image.

When a sheet is pressed against the intermediate transfer belt 7 by the second transfer roller 11 while applying a high voltage of about +1 kV having a polarity opposite to that of the toner to the second transfer roller 11, a composite image formed on the intermediate transfer belt 7 is formed. Are collectively transferred to paper.

Thereafter, the sheet is sent to the fixing device 15, where the toner image is fixed by heat and the clamping force between the fixing roller 13 and the pressure roller 14, and a color image is formed.

Here, as described above, the conductive rollers 16a, 16 set to the ground potential are located upstream of the nip in the rotational direction.
6b, 16c and 16d are arranged in contact with the intermediate transfer belt 7, so that the electric field for moving the toner on the photosensitive drums 1a, 1b, 1c and 1d approaching the nip to the intermediate transfer belt 7 is Does not work. As a result, the toner images on the photosensitive drums 1a, 1b, 1c, and 1d before the transfer are not disturbed, and the toner is not exposed to the transfer electric field for a long time, so that the charge polarity of the toner is not inverted. In this case, it is possible to prevent the occurrence of transfer failure such as character dust and transfer omission.

In this embodiment, the first transfer rollers 8a, 8b, 8c, 8d and the conductive roller 16
Each of a, 16b, 16c, and 16d is made of metal, but may be made of a metal shaft whose outer peripheral surface is coated with a conductive elastic material such as conductive urethane rubber.

In this embodiment, the conductive rollers 16a, 16b, 16c and 16d are set to the ground potential, but the conductive rollers 16a, 16b, 16c and 16d
The photosensitive drums 1a and 1 approaching the nip portion.
It suffices that a voltage for preventing generation of an electric field for moving the toner on b, 1c and 1d to the intermediate transfer belt 7 be applied. That is, the conductive rollers 16a, 16b, 16c, 16d
A voltage having a polarity opposite to that of the first transfer rollers 8a, 8b, 8c and 8d, for example, a voltage of -100V is applied to the toner on the photosensitive drums 1a, 1b, 1c and 1d approaching the nip portion. A force may be generated in the direction from the intermediate transfer belt 7 to the photosensitive drum 1a. This makes it possible to obtain better transferability.

[0056]

As described above, according to the present invention, the generation of the electric field for moving the toner on the electrostatic latent image carrier approaching the nip to the intermediate transfer member is prevented by the conductive roller. Therefore, an effective effect that it is possible to prevent the occurrence of a transfer failure such as character dust or transfer omission in the first transfer portion is obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an image forming apparatus according to an embodiment of the present invention;

FIG. 2 is an explanatory diagram showing a photosensitive drum and its periphery in the image forming apparatus of FIG. 1;

FIG. 3 is an explanatory view showing a conventional image forming apparatus.

FIG. 4 is an explanatory diagram showing a photosensitive drum and its periphery in the image forming apparatus of FIG. 3;

[Explanation of symbols]

 1a to 1d Photoconductor drum (electrostatic latent image carrier) 2a to 2d Charging brush (charging means) 3a to 3d Exposure means 4a to 4d Developing roller (developing means) 7 Intermediate transfer belt (intermediate transfer body) 8a to 8d 1 transfer roller (first transfer unit) 16a to 16d conductive roller (conductive member)

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Minoru Yamaguchi 1006 Kadoma Kadoma, Kadoma City, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. 72) Inventor Shimazaki Daimitsu 1006 Kazuma Kadoma, Osaka Prefecture F-term in Matsushita Electric Industrial Co., Ltd.

Claims (2)

[Claims] An electrostatic latent image carrier, a charging unit for uniformly charging the surface of the electrostatic latent image carrier, and image data on the electrostatic latent image carrier charged by the charging unit. Exposure means for irradiating a corresponding laser beam to form an electrostatic latent image, developing means for supplying toner to the electrostatic latent image to visualize the electrostatic latent image, and rotating by a plurality of rollers A belt-shaped intermediate transfer member that is tunably supported and contacts the electrostatic latent image carrier to form a nip portion; and the electrostatic transfer device is provided via the intermediate transfer member on the downstream side in the rotation direction of the nip portion. A first transfer unit disposed at a position opposed to the latent image carrier and configured to transfer a toner image to the intermediate transfer body; and an electrostatic latent image carrier via the intermediate transfer body on a rotation direction upstream side of the nip portion. Placed at a position facing the body, the ground potential or the first transfer An image forming apparatus, comprising a conductive member potential of opposite polarity is applied and. 2. A distance between a contact position between the first transfer unit and the intermediate transfer member and the nip portion, and a distance between a contact position between the conductive member and the intermediate transfer member and the nip portion are different from each other. 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is set equal to: