JP2000112190A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of forming a high quality image by reducing frictional force exerted on a sheet in the abutting part of an upper guide member against a sheet. SOLUTION: By using a sheet guide part 7 having a lower guide member 71 which guides the sheet S while abutting against the lower surface of the sheet S and the upper guide member 72, situated above the lower guide member 71, which curves the sheet S along an intermediate transfer body 5 while abutting against the sheet S, the sheet S is guided, along the intermediate transfer body 5, to the abutting part between the intermediate transfer body 5 to which a toner image formed on an image carrier is primarily transferred and a secondary transfer means 8b. Additionally, in the upper guide member 72 and lower guide member 71, the abutting part of at least the upper guide member 72 against the sheet S is coated with a resin, thereby reducing frictional force exerted on the sheet S in the abutting part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as an electrophotographic copying machine or a laser beam printer, and more particularly, to a method of first transferring a toner image formed on an image carrier to an intermediate transfer member. The present invention relates to an image forming apparatus that performs secondary transfer on a sheet.

[0002]

2. Description of the Related Art As an example of a conventional image forming apparatus, a plurality of toner images are formed on an intermediate transfer body by firstly transferring toner images sequentially formed on an image carrier onto an intermediate transfer body. 2. Description of the Related Art There is a color image forming apparatus configured so that secondary transfer is performed on a sheet by a secondary transfer unit that is in contact with an intermediate transfer member.

Next, an image forming operation of such a conventional color image forming apparatus will be described with reference to FIG.

At the time of image formation, first, a photosensitive drum 1 as an image carrier is driven in a direction indicated by an arrow by a driving means (not shown), and the surface of the photosensitive drum is uniformly charged by a primary charger 2. Next, the exposure device 3 applies a laser beam L, for example, first according to a yellow image pattern to the photosensitive drum 1.
To form a yellow electrostatic latent image on the photosensitive drum. Further, simultaneously with the formation of the electrostatic latent image, the developing devices 4a,
The developing device 4a containing the yellow toner is rotated by rotating the rotating support 4A supporting the photosensitive drums 4b, 4c, and 4d.
Then, the developing device 4a applies yellow toner to the electrostatic latent image for development.

Next, a primary transfer bias having a characteristic opposite to that of toner is applied to the primary transfer roller 8a to transfer the toner image formed and carried on the photosensitive drum to the driven roller 5a and the drive roller 5a.
b and the secondary transfer opposing roller 5c, and primary-transfers onto the outer peripheral surface of the intermediate transfer belt 5 which is an intermediate transfer member rotating in the direction of the arrow at substantially the same speed as the photosensitive drum 1. Further, thereafter, the above process is performed for magenta, cyan, and black, thereby forming toner images of a plurality of colors on the intermediate transfer belt in a superimposed manner.

Next, the transfer material S, which is a sheet stored in the transfer material cassette 12 at a predetermined timing, is fed by the pickup roller 13 and the transport roller pair 13a.
Thereafter, the transfer material S is moved along the intermediate transfer belt 5 through the pair of registration rollers 13b as shown in FIG.
Conveyed to the contact portion.

Here, the transfer material S is applied between the intermediate transfer belt 5 and the secondary transfer means between the contact portion N between the secondary transfer roller 8b and the intermediate transfer belt 5 and the registration roller pair 13b. A transfer lower guide 7b, which is a lower guide member that guides the transfer material S by contacting the lower surface of the transfer material S while guiding to the contact portion N, and is located above the transfer lower guide 7b and contacts the transfer material S. A sheet guide section 7 having an upper transfer guide 7a, which is an upper guide member that contacts and curves the transfer material S in a direction along the intermediate transfer belt 5, is provided.

The transfer material S is controlled by the upper transfer guide 7a and the lower transfer guide 7b, and the transfer material S is moved along the intermediate transfer belt 5 to a contact portion N between the secondary transfer roller 8b and the intermediate transfer belt 5. To be transported.

Next, when the transfer material S reaches the contact portion N, a secondary transfer bias is applied to the secondary transfer roller 8b, whereby the toner image is secondary-transferred from the intermediate transfer belt 6 to the transfer material S. Is done.

Next, the transfer material S is transported to the fixing device 6 by the transport belt 14 shown in FIG. 4, and the toner is melted and fixed in the fixing device 6 to fix the color image. Finally, the transfer material S on which the color image has been fixed is discharged onto a discharge tray 10 by a discharge roller 9.

The transfer residual toner on the intermediate transfer belt is charged by the intermediate transfer cleaning roller 15 and is reversely transferred onto the photosensitive drum at the next primary transfer.
On the other hand, the transfer residual toner on the photosensitive drum is cleaned by a known cleaning device.

[0012]

In such a conventional color image forming apparatus, the intermediate transfer belt 5
Is less likely to form a non-image portion potential than the photosensitive drum 1, and the formed potential also changes due to aging of the intermediate transfer belt 5 and environmental fluctuations. For this reason, when the intermediate transfer belt 5 is used, the transfer material S is made to follow the intermediate transfer belt 5 from an upstream of the photosensitive drum so that toner scattering does not occur.

Since the transfer material S moves along the intermediate transfer belt 5 as described above, the transport speed of the registration roller pair 13b among the intermediate transfer belt 5, the secondary transfer roller 8b, and the registration roller pair 13b is set to the highest. The transfer material S is curved upward as shown in FIG. 5 due to the difference in the transport speed.
Will move along.

However, the transfer material S is transferred to the intermediate transfer belt 5 using the upper and lower transfer guides 7a and 7b as in the conventional example.
If it is controlled so that the sheet is conveyed to the contact portion with the secondary transfer roller 8b along the path, there is a problem that banding (stripes) occurs in the transferred image.

The inventors of the present invention have investigated the cause of the banding in detail, and as shown in FIG.
Is curved upward, the pressure Fa applied to the transfer upper guide 7a
Becomes extremely large, and the frictional force of the upper transfer guide 7a acting on the transfer material S increases. As a result, the transport speed of the transfer material S changes, and the secondary transfer is disturbed and banding occurs. It has been found.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and has as its object to provide an image forming apparatus capable of forming a high-quality image without banding.

[0017]

According to the present invention, a toner image sequentially formed on an image carrier is sequentially transferred to an intermediate transfer member to form a plurality of toner images on the intermediate transfer member.
In an image forming apparatus which collectively and secondarily transfers the toner image to a sheet by a secondary transfer unit abutting on the intermediate transfer body, the intermediate transfer body and the secondary transfer unit are arranged while the sheet is along the intermediate transfer body. A lower guide member that guides the sheet by contacting the lower surface of the sheet while guiding the sheet to the abutting portion of the sheet. And a sheet guide portion having an upper guide member that bends in a direction along the body, and acts on the sheet at a contact portion of the upper guide member and the lower guide member at which the upper guide member contacts the sheet. The frictional force is reduced.

Further, in the present invention, at least a contact portion of the upper guide member and the lower guide member that contacts the sheet is coated with a resin so as to reduce a frictional force acting on the sheet. It is assumed that.

Further, the present invention is characterized in that the resin is a fluorine-based resin.

Further, according to the present invention, at least a portion of the upper guide member and the lower guide member, which is in contact with the sheet, is rotated in contact with the sheet so as to reduce a frictional force acting on the sheet. A rotating member is provided.

Also, as in the present invention, a lower guide member that contacts the lower surface of the sheet to guide the sheet, and is located above the lower guide member and contacts the sheet to bend the sheet along the intermediate transfer member. The sheet is guided along the intermediate transfer member by a sheet guide portion having an upper guide member to be brought into contact with an intermediate transfer member on which the toner image formed on the image carrier is primarily transferred and a secondary transfer means. While guiding. And, at least an upper guide member of the upper guide member and the lower guide member is coated with a resin at a contact portion with a sheet,
The frictional force acting on the sheet at the contact portion is reduced.

[0022]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a configuration of a color image forming apparatus as an example of the image forming apparatus according to the first embodiment of the present invention. 4, the same reference numerals as those in FIG. 4 denote the same or corresponding parts.

In FIG. 1, reference numeral 71 denotes a lower transfer guide, and the lower transfer guide 71 is a steel plate having a thickness of 1.0 mm.

Reference numeral 72 denotes an upper transfer guide having a 1.0 mm thick steel plate provided with a Teflon coat on the bottom surface which is in contact with the transfer material S. The friction coefficient on the bottom surface of the transfer upper guide can be reduced as compared with the case where the transfer upper guide is constituted only by the steel plate.

By reducing the coefficient of friction of the transfer upper guide surface, the transfer material S moves along the intermediate transfer belt 5 and the secondary transfer roller 8b as shown in FIG.
When the transfer material S is conveyed to the abutting portion N between the transfer guide S and the transfer material S, even if the pressure applied to the transfer upper guide 72 becomes extremely high due to the curvature of the transfer material S, the friction acting on the transfer material S of the transfer upper guide 72 The force is reduced, and the transfer speed of the transfer material S does not change.

As a result, the transfer material S is transferred to the upper transfer guide 72.
In addition, while being formed with a stable curve by the transfer lower guide 71, the sheet is conveyed to the contact portion N along the intermediate transfer belt 5 at a constant conveyance speed, so that occurrence of banding can be prevented.

In this embodiment, the intermediate transfer belt 5 is made of NBR (nitrile rubber) having a volume resistance of 10 ⁶ Ω · cm or less, a thickness of 1 mm, a width of 230 mm, and a circumference of 140π.
mm of volume resistivity of about 10 ¹⁴ Ω · cm on what was seamless molded into a cylindrical shape dielectric layer of high resistance was used as the 30μm coating.

When a strong transfer material S such as thick paper is used, when the transfer material S passes through the sheet guide portion 7, not only the transfer upper guide 72 but also the friction pressure Fb ( (See FIG. 5), and banding due to the lower transfer guide 71 may occur. Therefore, if the lower transfer guide 71 is coated with Teflon in the same manner as the upper transfer guide 72, banding caused by friction with the lower transfer guide 71 can be prevented, which is even better.

In this embodiment, the upper transfer guide 7 is used.
2 was coated with Teflon, but the same effect can be obtained by coating with another fluorine-based resin such as PFA or PTFE.

Instead of coating the transfer upper guide 72, the transfer upper guide 71 and the transfer upper guide 7 are not coated.
The same effect can be obtained by forming the second member 2 from a material having a small surface friction, such as a resin.

Next, a second embodiment of the present invention will be described.

FIG. 3 is an enlarged view of the secondary transfer section of the image forming apparatus according to the present embodiment. 2, the same reference numerals as those in FIG. 2 indicate the same or corresponding parts.

In the figure, reference numeral 73 denotes an upper transfer guide 72.
Is a rotating member provided at a contact portion with the sheet material S. By providing the roller 73 on the transfer upper guide 72 in this way, the frictional force acting on the sheet material S of the transfer upper guide 72 is reduced. Can be reduced.

As a result, the transfer material S is transferred to the upper transfer guide 72.
In addition, the belt is conveyed to the contact portion N at a constant conveyance speed along the intermediate transfer belt 5 while forming a stable curve by the transfer lower guide 71, so that banding can be prevented.

In this embodiment, a steel plate having a thickness of 1.0 mm is used as the transfer lower guide 71.
A 1.0 mm thick steel plate was used as the transfer upper guide 72, and a 2.0 mm diameter roller was used as the roller 73.

Also, as in the first embodiment described above,
If the lower transfer guide 71 is coated with Teflon or the like, banding caused by friction of the lower transfer guide 71 can be prevented, which is even better.

[0038]

As described above, according to the present invention, the sheet is intermediately transferred to the contact portion between the intermediate transfer member on which the toner image formed on the image carrier is primarily transferred and the secondary transfer means. High quality without banding by reducing the frictional force acting on the sheet at the abutting portion of the upper guide member of the sheet guide portion and the lower guide member that guides the body along the body, at least in the contact portion with the sheet. Image can be formed.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a schematic configuration of a color image forming apparatus as an example of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is an enlarged view of a secondary transfer unit of the color image forming apparatus.

FIG. 3 is an enlarged view of a secondary transfer unit of the image forming apparatus according to a second embodiment of the present invention.

FIG. 4 is a diagram showing a schematic configuration of a conventional color image forming apparatus.

FIG. 5 is an enlarged view of a secondary transfer portion of the conventional color image forming apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum 5 Intermediate transfer belt 7 Sheet guide part 7a, 72 Upper transfer guide 7b, 71 Lower transfer guide 8b Secondary transfer roller

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H030 AD05 BB42 BB44 BB46 BB53 2H032 AA05 BA09 BA19 2H072 CB07 3F101 FA02 FB04 FD01 FD02 LA02 LA07 LB03

Claims (4)

[Claims] 1. A method of forming a plurality of toner images on an intermediate transfer member by sequentially primary transferring toner images sequentially formed on an image carrier to an intermediate transfer member, and then transferring the toner images to the intermediate transfer member. In an image forming apparatus for performing secondary transfer to a sheet at a time by a contacting secondary transfer means, while guiding the sheet along the intermediate transfer body to a contact portion between the intermediate transfer body and the secondary transfer means, A lower guide member that contacts the lower surface of the sheet to guide the sheet, and an upper guide that is located above the lower guide member and contacts the sheet and curves the sheet in a direction along the intermediate transfer body. And a sheet guide portion having a member, wherein at least the upper guide member of the upper guide member and the lower guide member at the contact portion with the sheet reduces frictional force acting on the sheet. An image forming apparatus characterized in that: 2. At least a contact portion of the upper guide member and the lower guide member with respect to a sheet of the upper guide member,
2. The image forming apparatus according to claim 1, wherein a resin is coated so as to reduce a frictional force acting on the sheet. 3. The image forming apparatus according to claim 2, wherein said resin is a fluorine-based resin. 4. At least a portion of the upper guide member and the lower guide member that abuts on a sheet of the upper guide member,
3. The image forming apparatus according to claim 1, further comprising a rotating member that rotates in contact with the sheet so as to reduce a frictional force acting on the sheet.