JP2003076164A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an image defect due to variation in the transfer material carrying power of a transfer member. SOLUTION: When a transfer roller 13 is cleaned by applying the transfer roller 13 with a cleaning bias having the opposite polarity from a transfer voltage when no image is formed, the transfer roller 13 is rotated and the cleaning is carried out longer than the time that the transfer roller 13 requires to make a 1.5 rotation and thus the transfer roller 13 is excellently cleaned to suppress the variation in the transfer material carrying power of the transfer roller 13, thereby preventing an abnormal image from being formed.

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, a printer or the like, which forms an image by an electrophotographic system or an electrostatic recording system.

[0002]

2. Description of the Related Art An image forming apparatus such as a copying machine, a facsimile, a printer, etc., which uses an electrophotographic system, has a process of transferring a toner image formed on a surface of a photosensitive drum as an image carrier to a transfer material such as paper. Although it is included, a method is known in which transfer is performed by using a transfer roller as a transfer member in this transfer step.

In such an image forming apparatus, the surface moving speed of the transfer roller at the transfer portion (transfer nip portion) formed by bringing the transfer roller into contact with the photosensitive drum is faster than the surface moving speed of the photosensitive drum. As described above, by providing a peripheral speed difference between the photosensitive drum and the transfer roller,
It has already been known that there is an improvement in voids (blank images) in the transfer.

In recent years, in order to reduce the size of the apparatus and shorten the time (first print time) when the first output image is obtained after the image formation start signal is input, the transfer from the paper feed unit to the paper discharge is performed. There is a demand for an apparatus in which a material (paper) transportation path is short.

[0005]

The transfer roller as the above-mentioned transfer member is usually composed of a metal shaft and an elastic body of a foam sponge made of conductive EPDM, NBR or the like around the shaft. There is. In general, in order to prevent transfer deviation and the like at the transfer portion, it is advantageous to increase the nip width between the transfer roller and the photosensitive drum.

However, if the contact pressure of the transfer roller with respect to the photosensitive drum is increased in order to increase the nip width, the photosensitive drum is rapidly worn and the life is shortened.

Therefore, a transfer roller having a hardness of a certain level or less is adopted, and a sponge-like elastic body is generally used. Further, since the outer diameter of the transfer roller affects the transfer performance, the tolerance of the outer diameter of the transfer roller is strictly controlled, and the transfer roller is generally mounted on the metal shaft when designed. It is manufactured by a method in which an elastic body having a diameter larger than the diameter is adhered and then the outer diameter is polished to a standard value with a grindstone.

However, even in the transfer roller manufactured by strictly controlling the outer shape tolerance in this way, the paper carrying ability of the transfer material such as a paper is greatly affected by the surface state of the transfer roller and changes.

That is, as shown in FIGS. 15 (a) and 15 (b), the surface of the transfer roller 101, which is in contact with the photosensitive drum 100 at the transfer portion (transfer nip portion) N, has an uneven polishing grain 101a.
Is in the direction opposite to the transport direction of the transfer material P transported in the direction of arrow a (FIG. 15A), and the direction of the uneven polishing eyes 101a on the surface of the transfer roller 101 is
It is known that the transfer force of the transfer material P is different from the state in which the transfer material P is transferred in the direction of the arrow a in the forward direction (FIG. 15B).

Further, especially as the number of images formed increases, the conveyance force of the transfer material changes due to wear and dirt on the surface of the transfer roller, which causes a magnification error (hereinafter referred to as image expansion) of the image transferred on the transfer material. An image defect may occur due to an increase in image size, or a change in the loop state during transfer material transfer.

The inventors of the present invention have studied the above problems, and have found the following.

As described above, by providing the peripheral speed difference between the photoconductor drum and the transfer roller, it is possible to prevent a hollow character (a hollow image) of characters at the time of transfer. When the peripheral speed difference between the drum and the transfer roller is large, the image transferred on the transfer material may be stretched, or the image may be defective due to changes in the loop condition during transfer material transfer. Occurs in.

Further, as shown in FIG. 16, the fixing roller 1
In the image forming apparatus having a short path in which the distance T between the transfer roller 101 and the fixing device 102 having the 02a and the pressure roller 102b is short, the fixing roller 10 of the fixing device 102 is used.
When the transfer material conveying speed by the transfer nip portion N between the transfer roller 102 and the photosensitive drum 100 is higher than the transfer material conveying speed by the fixing nip portion M between the 2a and the pressure roller 102b, the fixing is performed. When the leading end side of the transfer material P such as paper enters the nip portion M, a loop (slack) is formed in the transferred transfer material P.

Therefore, the pressure roller 10 of the fixing device 102
The transfer material P comes into contact with the surface of the conveyance guide 103 that guides the conveyance of the transfer material P provided between the transfer roller 101 and the transfer roller 101, and the transfer material P rubs against the conveyance guide 103 to cause an image defect.

It should be noted that the above-mentioned loop is generated when an A3 size or LDR size sheet is passed in an image forming apparatus having a large maximum sheet passing size, for example, an apparatus capable of passing A3 size or LDR size sheets, and the size is short. In the case of transfer material (paper), the transfer material is transferred to the transfer nip portion N before the loop grows.
There is almost no problem because it escapes.

Thus, the fixing roller 1 of the fixing device 102
If the distance N between the fixing nip portion M between 02a and the pressure roller 102b and the transfer nip portion N between the transfer roller 102 and the photoconductor drum 100 is large, there is no problem, but the fixing nip portion M and the transfer nip portion N. When the distance between them is set to 80 mm (1/4 or less of the maximum sheet-passing paper size), the loop (slack) of the transfer material P becomes considerably large as described above, and this loop protrudes 10 mm or more toward the conveyance guide 103 side. Therefore, the transfer material P comes into contact with the surface of the transport guide 103, and the transfer material P rubs against the transport guide 103, causing an image defect.

In the above situation, first, the change of the transfer material conveying speed in the transfer nip portion N will be described.

As the number of image forming sheets increases, for example, when foreign matter such as background dirt toner or paper dust on the surface of the photosensitive drum adheres to the transfer roller surface, or when a paper jam occurs, the amount of foreign matter such as toner increases. It will adhere to the surface of the transfer roller. When the transfer roller is a rubber roller, if toner, paper dust or the like adheres to the surface of the rubber, it is considered that the toner or paper dust has a smaller coefficient of friction than rubber, so that the friction force is reduced and the transfer material transport force is reduced. On the other hand, when the transfer roller is a sponge roller, the contact area is small because the holes occupy a considerable portion, and the friction force is smaller than that of rubber when the nip width is the same.

When the surface of the transfer roller composed of a sponge roller is contaminated with toner or paper powder, unlike solid rubber, the pores of the sponge rubber roller are filled with the toner or paper powder, and the contact area is reduced. It was found that the transfer material transporting power is increased by increasing the number.

Further, even when the transfer roller surface is not contaminated with toner or paper dust, when the transfer roller composed of a sponge roller is rotated in contact with the photosensitive drum, the minute convex portion of the sponge surface of the transfer roller is deformed to cause voids. The small convex portions are flattened and enter the concave portions because the fine convex portions enter the portions or are cut into pieces and enter the hole portions. It was also found that the surface roughness of the sponge of the transfer roller was reduced, the contact area was increased, and the transfer material conveying force was increased.

Further, it has been found that the increase of the transfer material conveying force is influenced by the cell diameter and the porosity of the transfer roller composed of a sponge roller. That is, when the porosity of the sponge is small and it is close to that of solid rubber, the contact area does not increase, so that the conveyance force of the transfer material is not increased so much. On the other hand, when the porosity of the sponge is extremely large, the outer diameter becomes smaller due to surface abrasion, and the pores cannot be filled sufficiently, so this also does not increase the transfer material conveyance force. I understood.

However, when a sponge roller is actually used as the transfer roller, basic rubber physical properties are appropriate, contamination by a plasticizer or the like does not occur, resistance value can be stably adjusted, and hardness is appropriate. Etc.
The range of cell diameter and porosity is limited.

For example, the cell diameter is usually about 50 μm to 200 μm, and the porosity is about 30 to 70%. In particular, when a roller having an average cell diameter of 120 μm or more and 170 μm or less and a porosity of 40% or more and 60% or less is used, the transfer material conveying force of the transfer roller increases as the number of image forming sheets increases, and Image elongation occurs in the transferred image, or an image defect occurs due to a change in the state of the loop when the transfer material is conveyed.

Therefore, according to the present invention, the transfer material conveying force of the transfer member changes, the image elongation of the image transferred on the transfer material becomes large, and an image defect occurs. An object of the present invention is to provide an image forming apparatus capable of preventing a change in image defect.

[0025]

To achieve the above object, the invention according to claim 1 is characterized in that a rotatable image carrier, charging means for charging the image carrier, and the charged image carrier. Exposing means for forming an electrostatic latent image according to image information, developing means for developing the electrostatic latent image to form a toner image, and a transfer nip portion abutting on the image carrier. A rotatable transfer member that is formed and contacts the back surface of the transfer material conveyed to the transfer nip portion, and transfers the toner image formed on the image carrier to the surface of the transfer material by applying a transfer voltage; A transfer material having the toner image transferred thereon is nipped and conveyed to a fixing nip portion formed between a pair of fixing rotating bodies having a heating means inside at least one of them to heat the toner image on the surface of the transfer material. Fixing means for fixing the transfer nip portion and the The distance between the wear nip, 1/4 of the maximum size of the transport transcriptional material to the transfer nip portion
The image carrier, the transfer member, and the fixing unit are arranged as follows, and the peripheral speed of the image carrier is 98.% of the writing speed of the image information to the image carrier by the exposing unit. It is less than 1%, and the peripheral speed of the outer periphery of the transfer member that contacts the transfer material is 103.6% of the writing speed.
The image forming apparatus of 104.3% or less has a cleaning unit for cleaning the transfer member, and rotates the transfer member when cleaning the transfer member by the cleaning unit during non-image formation, In addition, cleaning is performed for a time longer than the time when the transfer member rotates at least 1.5 times.

According to a third aspect of the present invention, a rotatable image carrier, charging means for charging the image carrier, and exposure of the charged image carrier are performed according to image information. An exposing unit that forms an electrostatic latent image, a developing unit that develops the electrostatic latent image to form a toner image, and a transfer nip portion that comes into contact with the image carrier and is conveyed to the transfer nip portion. And a rotatable transfer member for contacting the back surface of the transfer material and transferring the toner image formed on the image carrier to the surface of the transfer material by applying a transfer voltage, and a pair having a heating means in at least one of the inside. A fixing nip portion formed between the transfer material and the fixing rotating body, the transfer material having the toner image transferred thereon is nipped and conveyed, and the toner image is heat-fixed to the surface of the transfer material. The distance between the nip portion and the fixing nip portion is The image carrier, the transfer member, and the fixing unit are arranged so that the size of the transfer material that can be conveyed to the image nip portion is 1/4 or less, and the peripheral speed of the image carrier is the exposure. Is less than 98.1% of the writing speed of the image information to the image carrier by the means, and the peripheral speed of the outer periphery of the transfer member that contacts the transfer material is 103.6% or more and 104.3% or less of the writing speed. In the image forming apparatus, the peripheral speed of the surface of the fixing unit in contact with the transfer material of the pair of fixing rotary members is set to 10 times the writing speed.
It is characterized in that the speed is 0.02% or more and 100.5% or less.

According to the present invention, the rotatable image bearing member, the charging means for charging the image bearing member, the charged image bearing member are exposed, and the image bearing member is exposed according to the image information. An exposing unit that forms an electrostatic latent image, a developing unit that develops the electrostatic latent image to form a toner image, and a transfer nip portion that comes into contact with the image carrier and is conveyed to the transfer nip portion. And a rotatable transfer member for contacting the back surface of the transfer material and transferring the toner image formed on the image carrier to the surface of the transfer material by applying a transfer voltage, and a pair having a heating means in at least one of the inside. A fixing nip portion formed between the transfer material and the fixing rotating body, the transfer material having the toner image transferred thereon is nipped and conveyed, and the toner image is heat-fixed to the surface of the transfer material. The distance between the nip portion and the fixing nip portion is The image carrier, the transfer member, and the fixing unit are arranged so that the size of the transfer material that can be conveyed to the image nip portion is 1/4 or less, and the peripheral speed of the image carrier is the exposure. Is less than 98.1% of the writing speed of the image information to the image carrier by the means, and the peripheral speed of the outer periphery of the transfer member that contacts the transfer material is 103.6% or more and 104.3% or less of the writing speed. In the image forming apparatus, which is provided between the transfer nip portion and the fixing nip portion, the toner image of the transfer material, which has exited from the transfer nip portion, is provided so as to be in contact with the rear surface side,
A transfer guide that guides the transfer material discharged from the transfer nip portion to the fixing nip portion, and from the plane with respect to a direction orthogonal to a plane connecting the transfer nip portion and the fixing nip portion. The distance between the transfer nip and the surface of the conveyance guide, which is in contact with the back side of the transfer material on which the toner image is not transferred, is approximately 1 of the distance between the transfer nip and the fixing nip.
The feature is 6.25%.

The transfer member is a roller rotating body having a sponge-like elastic body on the surface, and the average cell diameter of the elastic body is 120 μm or more and 170 μm or less.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will now be described based on the illustrated embodiments.

<First Embodiment> FIG. 1 is a schematic configuration diagram showing an image forming apparatus according to a first embodiment of the present invention. The image forming apparatus according to the present embodiment is an electrophotographic copying machine,
It is a digital multi-function peripheral that has fax and printer functions.

This image forming apparatus is provided with a process cartridge 30 containing an image forming means for forming an image on a transfer paper as a transfer material by an electrophotographic method.
The process cartridge 30 includes an OPC photosensitive drum (hereinafter referred to as a photosensitive drum) 1 having a diameter of 30 mm as an image carrier, a charging roller 2 as a charging unit, a developing unit 3 as a developing unit, and a cleaning blade as a cleaning unit. 4 and the like are compactly integrated. The process cartridge 30 is detachably attached to the image forming apparatus main body 31.

A latent image writing unit (exposure device) 5 for writing an electrostatic latent image on the photosensitive drum 1 is provided above the process cartridge 30. The latent image writing unit 5 is, for example, an image reading device 6
A semiconductor laser (not shown) emits an optical signal (laser light) corresponding to the image information of the original document G read in, and the polygon mirror 5a which is rotationally driven scans the laser light, and a scanning optical path of the laser light. It is necessary to use one that writes an optical signal corresponding to image information on the photosensitive drum 1 through a lens 5b for converging and correcting a surface tilt of the polygon mirror 5a and a mirror 5c for deflecting a laser beam, which are provided inside. You can Document G read by the image reading device 6
Are transported from the document transport device 7.

Below the process cartridge 30, a paper feed cassette 8a or 8b in which a transfer paper P of a predetermined size is stored is installed. The transfer paper P stored in the paper feed cassette 8a or 8b is separated and fed one by one by the pickup roller 9, the retard roller 10, and the paper feed roller 11. The transfer sheet P fed by the sheet feeding roller 11 is fed upward by the vertical path roller pair 12 and is once on standby before the registration roller pair 14.

The registration roller pair 14 is the photosensitive drum 1
The leading edge of the image formed on the top and the leading edge of the transfer paper P are
The transfer paper P is synchronized with the rotation of the photosensitive drum 1 at the timings at which the transfer nip portion (transfer portion) between the photosensitive drum 1 and the transfer roller 13 rotating in pressure contact with the photosensitive drum 1 arrives at substantially the same time. To re-feed.

Further, above the transfer nip portion (transfer portion) between the photosensitive drum 1 and the transfer roller 13, a fixing roller 15a rotatably arranged so as to rotate in pressure contact with each other.
A fixing device 15 having a pressure roller 15b and a pressure roller 15b is provided. A heater (not shown) is built in the fixing roller 15a. The transfer paper P that has passed through the fixing nip portion between the fixing roller 15a and the pressure roller 15b is discharged to the stacker portion 16a or 16b as a discharge tray on the downstream side of the fixing device 15 in the transfer paper conveyance direction. A paper discharge roller pair 17a or 17b is provided for the purpose.

Further, between the transfer roller 13 and the fixing device 15, the transfer paper P discharged from the transfer nip portion between the photosensitive drum 1 and the transfer roller 13 is provided between the fixing roller 15a and the pressure roller 15b. A conveyance guide 25 for guiding the fixing nip portion is provided.

In the image forming apparatus having such a structure,
At the time of image formation, the photosensitive drum 1 is a driving device (not shown).
The charging roller 2 is rotated clockwise at a peripheral speed (process speed) of 94.25 mm / sec, and a charging bias is applied from a charging bias power source (not shown) during the rotation.
In the present embodiment, the negative charges are uniformly charged (-600 V) by the electric charges from the. Then, the latent image writing unit 5 is driven as described above on the basis of the image information of the document G conveyed from the document conveying device 7 read by the image reading device 6, whereby the charging area of the photosensitive drum 1 is charged. In the (image forming area), the image information is formed as an electrostatic latent image. At this time, the potential (bright potential) of the exposed portion of the surface of the photosensitive drum 1 is about -100V.

Then, the electrostatic latent image formed on the photoconductor drum 1 is statically imaged on the photoconductor drum 1 by the developing roller 3a to which a developing bias is applied from a developing bias power source (not shown) of the developing unit 3. Toner (negative toner) is attached to the electrostatic latent image and reversal development as a toner image (visualization)
To do. At this time, for example, -400V is applied to the developing roller 3a.
DC voltage of 16 to 2000Hz peak-to-peak voltage
A developing bias on which an AC voltage of 00V is superimposed is applied.

On the other hand, while the toner image is being formed on the photosensitive drum 1, the transfer sheet P is transferred from the sheet feeding cassette 8a or 8b by the rotation of the pickup roller 9, the retard roller 10 and the sheet feeding roller 11. Separately fed one by one,
The transfer paper P is conveyed upward by the vertical path roller pair 12.
The transfer paper P is once put on standby in a state where the leading end of the transfer paper P contacts the nip portion of the registration roller pair 14. The vertical path roller pair 12 is driven by a one-way clutch (not shown), and when the transfer sheet P is conveyed by the registration roller pair 14, the transfer sheet P is sandwiched and conveyed by the registration roller pair 14.

The registration roller pair 14 of the transfer sheet P starts to rotate in synchronization with the rotation of the photosensitive drum 1 at the timing when the front end of the transfer sheet P coincides with the front end of the toner image on the photosensitive drum 1. As a result, the toner is conveyed to the transfer nip portion (transfer portion) between the photosensitive drum 1 and the transfer roller 13, and the transfer bias power source 18 generates a transfer bias having a polarity (positive polarity) opposite to that of the negatively charged toner. The toner image on the photosensitive drum 1 is transferred onto the surface of the transfer paper P by the applied transfer roller 13.

The transfer roller 13 has a voltage of 500 to 6000V.
Transfer bias power source 18 for applying a transfer bias of a certain degree
A transfer roller cleaning bias power supply 19 for applying a transfer roller cleaning bias having a polarity (negative polarity) opposite to the transfer bias to the transfer roller 13 when the paper is not passed, and a transfer bias power supply 1 for bias applied to the transfer roller 13.
8 or a transfer roller cleaning bias power source 19 is connected to a changeover switch 20. The changeover switch 20 is controlled by a control unit (not shown), and the transfer bias power supply 18 is selected during transfer, and the transfer roller cleaning bias power supply 19 is selected during cleaning of the transfer roller 13.

Then, the transfer paper P on which the toner image is transferred
Is a fixing roller 15a and a pressure roller 15b of the fixing device 15.
In the process of being nipped and conveyed in the fixing nip portion between and, the transferred image is heated, pressurized and fixed, and is discharged onto the stacker unit 16a or 16b by the discharge roller pair 17a or 17b.

In the process of transferring the toner image onto the transfer paper P, the residual toner remaining on the photosensitive drum 1 without being transferred onto the transfer paper P is removed from the photosensitive drum 1 by the cleaning blade 4. Are collected and collected.

Further, an open / close cover 21 forming a side surface on the left side of the transfer path of the transfer paper P is attached to the image forming apparatus so as to be openable and closable. Inside the opening / closing cover 21, the transfer roller 13 and a static elimination brush 22 for eliminating static electricity from the transfer paper P on which the toner image has been transferred are provided. Further, a manual feeding unit 23 for manually feeding the transfer paper is attached to the lower part of the opening / closing cover 21 so as to be freely opened and closed.

The transfer sheet fed by using the manual feed unit 23 is conveyed to the registration roller pair 14 by the rotation of the manual feed roller 24 provided on the apparatus main body 31 side. Further, the manual feed unit 23 is configured to be stored in the outer portion of the opening / closing cover 21 when the manual feed unit 23 is not used.

Rollers (photosensitive drum 1, transfer roller 13, registration roller pair 14, fixing roller 15a) relating to transfer sheet transfer of the image forming apparatus in the above-described embodiment.
The rough peripheral speed ratio of is set as follows. Incidentally, here, the photosensitive drum 1 by the writing unit 5 is used.
The image writing speed to the image is 100% (the image writing speed here is the speed at which the original original image (original image) should be moved in the sub-scanning direction in order to reproduce it in the correct length. ).

The transfer paper is the transfer roller 13 and the photosensitive drum 1.
When the transport speed passing through the transfer nip portion between and corresponds to the image writing speed by the writing unit 5 described above, a 100% image without expansion and contraction is transferred onto the transfer paper. Therefore, in the present embodiment, in order to obtain the image of 100%, the photosensitive drum 1 is rotated at the peripheral speed of 97.5% of the image writing speed, and the transfer roller 13 is 103.9 of the image writing speed. % Peripheral speed (106.6% peripheral speed with respect to the peripheral speed of the photosensitive drum).

Whether or not the transfer paper conveyance speed at the transfer nip portion is 100% without loss depends on the frictional force between the photosensitive drum 1 and the transfer paper and the friction between the transfer roller 13 and the transfer paper. The peripheral speed of the photosensitive drum 1 (97.5% of the writing speed) and the peripheral speed of the transfer roller 13 (106.6% of the peripheral speed of the photosensitive drum) depend on the force. Can fluctuate between Further, in the present embodiment,
The peripheral speed of the fixing roller 15a is 99.
8%, and the peripheral speed of the pair of registration rollers 14 is 101.5% of the image writing speed.

FIG. 2 is a diagram showing a drive mechanism for driving the photosensitive drum 1 and the transfer roller 13 in the above-mentioned image forming apparatus.

As shown in this figure, flanges 1a and 1b are provided at both ends of the photosensitive drum 1 in the rotation axis direction. These flanges 1a and 1b are formed in a shape, for example, a gear shape, which allows transmission of driving force from other members or transmission of driving force of the photosensitive drum 1 to other members. In the image forming apparatus of the present embodiment,
Of the two flanges 1a and 1b, the left flange (hereinafter referred to as the left flange) 1a in FIG. 2 receives a driving force from a main motor (not shown) as a driving unit for the photosensitive drum 1, and as a result, The photosensitive drum 1 is rotationally driven.

The transfer roller 13 is rotationally driven by transmitting the driving force of the photosensitive drum 1 to the transfer roller drive transmission means. Specifically, the transfer roller drive transmission means includes a rotation of the right flange (hereinafter, referred to as a right flange) 1b in FIG. 2 of the two flanges 1a and 1b and a transfer roller 13 that meshes with the right flange 1b. Axis 13
and a drive gear 13b provided at the right end of a. Then, by transmitting the driving force from the right flange 1b to the drive gear 13b of the transfer roller 13, the transfer roller 13
Is driven to rotate.

In the present embodiment, the peripheral speed of the transfer roller 13 is set to be higher than the peripheral speed of the photosensitive drum 1 as described above.
And the transfer roller 13 rotate while slipping. The slip acts as a rotational force for rotating the photosensitive drum 1 from the transfer roller 13 due to friction, and at the same time, acts as a force against the rotational force on the right side flange 1b and the drive gear 13b.

Specifically, the right flange 1b receives a rotational force from the drive gear 13b in a direction opposing the rotational force. As a result, the right flange 1b and the drive gear 13b constantly apply a braking force to the photoconductor drum 1 due to the slip, and the front end side of the transfer paper in the transfer direction during transfer is, for example, the fixing roller 15a of the fixing roller 15. Even if an impact is generated by being sandwiched in the fixing nip portion between the pressure roller 15b and the pressure roller 15b, the impact transmits the driving force from the main motor (not shown) that drives the photosensitive drum 1 to the photosensitive drum 1. It will not be affected by backlash etc.

The transfer roller 13 used in this embodiment
In the above, the elastic layer is provided on the metal rotating shaft 13a, and the elastic layer is polished to have a predetermined diameter (16 mm in this embodiment). This transfer roller 13
The material of the elastic layer is 4 as an ionic conductive agent in order to impart conductivity to the base rubber such as EPDM or NBR.
A primary ammonium salt, an alkali metal peroxide, an alkaline earth metal peroxide salt, or an alkoxyethyl adipate can be contained and used.

In this way, the resistance value at room temperature and normal humidity was set to 0.
It is adjusted to 9 to 2.3 × 10 ⁸ Ω. Further, this elastic body has a hardness of about 20 to 35 °, preferably 26 ° (As
c-C: 4.9 N load), the cell diameter of the sponge at that time is about 120 μm to 170 μm, and the porosity is 40 to 60%. Preferably, the cell diameter is 150μ
m and porosity 50%.

The rotary shaft 13a of the transfer roller 13 is
The device body 31 is pressed against the photosensitive drum 1 by pressing springs 32a and 32b. In order to keep the width of the transfer nip portion between the transfer roller 13 and the photosensitive drum 1 constant while the transfer roller 13 is pressed against the photosensitive drum 1 by the pressing springs 31a and 31b, the transfer roller 13 has both ends. Gap rollers 33a and 33b are provided to manage the nip width. The diameter of the gap rollers 33a and 33b is set to 15.95 mm in the present embodiment. In the present embodiment, the pressing spring 32a uses the force of 7.8 N to transfer the roller 13
Is pressed against the photosensitive drum 1, and the pressing spring 32b on the drive gear 13b side presses the transfer roller 13 against the photosensitive drum 1 with a force of 11.8N.

Further, the transfer roller 13 of this embodiment is
Due to the polishing, since it has minute uneven polishing grains having a directivity in a predetermined direction inclined by a predetermined angle with respect to the direction perpendicular to the surface, and it is a sponge, holes are formed.
Further, since this polishing grain is a direction in which foreign matter does not easily enter, as shown in FIG. 15A, the direction of the polishing grain is opposite to the direction of the transfer paper P conveyed in the direction of arrow a, for example. It is in a state of becoming.

Further, in this embodiment, in order to reduce the size and shorten the first print time, FIG.
As shown in, the fixing roller 15 of the fixing device 15 is moved from the center of the transfer nip portion N between the transfer roller 13 and the photosensitive drum 1.
The distance T to the center of the fixing nip portion M between the a and the pressure roller 15b is 80 mm, which is 1/4 of the maximum sheet passing size.
Below is a short distance.

Therefore, as described in [Problems to be Solved by the Invention], an abnormal image is apt to occur due to a change in the transfer paper carrying force of the transfer roller 13. Further, since the vertical path roller pair 12, which is a paper feeding unit upstream of the registration roller pair 14, is driven by the one-way clutch, a reaction force is not generated much when the transfer paper P is pulled by the registration roller pair 14, so that an image Easily stretched.

Next, the bias application sequence including the transfer roller cleaning bias application to the transfer roller 13 will be described with reference to FIGS. 4 and 5. 4 and 5, the transfer roller cleaning bias application time to the transfer roller 13 at the time of post-rotation and the AC bias application time to the photosensitive drum 1 are substantially the same. Further, in the sequences of FIG. 4 and FIG. 5, the horizontal axis time represents the application timing of each bias of charging, development and transfer during continuous printing of two sheets.

In FIGS. 4 and 5, after the main motor (not shown) is turned on and the photosensitive drum 1 starts to rotate, a charging bias in which an AC bias and a DC bias are superimposed is applied to the charging roller 2 to The surface potential of 1 is -6
It becomes 00V. Then, the image is written on the photosensitive drum 1 by the exposure from the image writing unit 5.

At this time, as the developing bias, a DC bias with an AC voltage superimposed in the image area is applied, and the photosensitive drum 1
Develop the electrostatic latent image on top. Then, in a non-image portion such as a sheet interval, a DC bias is applied so that the toner does not fly onto the photosensitive drum 1.

Then, before applying a predetermined transfer bias, a predetermined voltage is first applied in order to detect the proper bias of transfer before the transfer paper is conveyed to the transfer nip portion, and then the transfer paper is transferred to the transfer roller. A predetermined transfer bias is applied as it is conveyed to the transfer nip portion between the photosensitive drum 1 and the photosensitive drum 1.

At the time of post-rotation after completion of the image forming operation,
In order to clean the toner attached to the transfer roller 13, a transfer roller cleaning bias having a polarity (negative polarity) opposite to that of the transfer bias is applied. This cleaning bias is the reverse of the transfer bias from the transfer bias power source 18 to the transfer roller 13 when, for example, a small amount of fog toner attached to the non-image forming area on the surface of the photosensitive drum 1 is transferred to the surface of the transfer roller 13. By applying a voltage having the same polarity as the charging polarity of the toner, the bias is such that the contaminated toner adhering to the transfer roller 13 is reversely transferred to the surface of the photosensitive drum 1 and the toner is removed from the transfer roller 13. Applies a voltage of about -1500V to -2300V.

In the case of FIG. 4, this transfer roller cleaning bias is applied for 0.78 seconds, and in the case of FIG. 5, this transfer roller cleaning bias is 3.
It was applied for only 1 second. At this time, the photosensitive drum 1 and the transfer roller 13 are rotating. Also, after post-rotation,
Before the photoconductor drum 1 is stopped, only the AC bias is applied to the charging roller 2 to eliminate the charge on the photoconductor drum 1.

Next, the initial rotation (power supply off / o
FIG. 6 shows a sequence of bias application including warm-up rotation at n hours, and application of a transfer roller cleaning bias to the transfer roller 13 at the time of rotation after opening and closing a door (not shown) of the apparatus main body 31 at the time of jam or the like. Will be described with reference to.

When the main motor (not shown) starts to rotate for preparation, the charging bias (AC + D) to the charging roller 2
C) is applied to charge the photosensitive drum 1 to -600V. Then, an AC bias of the developing bias is applied to the developing roller 3a of the developing unit 3, and a DC bias of the developing bias is also applied so that the toner does not fly to the photosensitive drum 1 at this time.

Then, a positive bias and a negative bias are alternately applied from the transfer bias power supply 18 and the transfer roller cleaning bias power supply 19 to the transfer roller 13 by switching the changeover switch 20, and both the normally charged toner and the reversed toner are applied. To clean. At this time, the negative transfer roller cleaning bias is applied for about 1.6 seconds.

The first positive bias applied to the transfer roller 13 at this time is applied to the photosensitive drum 1 at the portion where the voltage of -600 V is applied by the charging roller 2 to prevent the occurrence of memory or the like. Prevents defects. Also, 2
After the positive polarity bias is applied the next time, the AC charging bias is applied again to the place where the positive polarity bias is applied so that no charge remains on the photosensitive drum 1. In this way, the application of the transfer cleaning bias is
It is performed at the time of post-rotation and at the time of initial rotation.

Next, with respect to the cleaning time of the transfer roller 13 by the application of the above-mentioned transfer cleaning bias performed by the present inventors, the back side of the image on the back side of the transfer paper in contact with the transfer roller 13 is generated and the image is stretched. The experimental results for the generation of abnormal images are shown below.

(Study on Image Backside Staining) The time (length) of the cleaning process of the transfer roller 13 by applying the transfer cleaning bias during the subsequent rotation is 0.25 seconds (0.5 rotations of the transfer roller 13). 0.5 seconds (1 of transfer roller 13
2. Rotation), 0.78 seconds (1.5 rotations of the transfer roller 13), 1.54 seconds (3 rotations of the transfer roller 13), 3.
The backside of the image was checked for stains in 1 second (6 rotations of the transfer roller 13).

In the image backside stain checking method at this time, first, 99 sheets of A4R size paper were continuously printed with an image having a printing rate of 50%, and this was repeated 1000 sheets. After that, copying was performed at A3 size to check whether the back of the image was dirty. As a result, it was found that normal backside smearing does not cause a problem when the transfer cleaning bias application time is 0.78 seconds or more.

As described above, in terms of the backside of the image,
It was sufficient to apply the transfer cleaning bias for 0.78 seconds (1.5 rotations of the transfer roller 13) and perform the cleaning once. Next, when the time of the cleaning process of the transfer roller 13 by applying the transfer cleaning bias at the time of post-rotation is 0.78 seconds, 1.54 seconds, and 3.1 seconds, whether an abnormal image due to image stretching occurs is determined. Checked.

(Study of Abnormal Image) This study was carried out in a low humidity environment in which a large amount of toner is fogged and foreign matter such as toner is likely to adhere to the transfer roller 13.

The abnormal image checking method at this time is as follows. First, a predetermined image is continuously printed on 10 sheets of A4 size paper,
This was repeated. Then, the process was repeated until an abnormal image caused by image stretching occurred. The occurrence of abnormal images was examined by sampling a specific image (uniform halftone image) of A3 size after a certain number of sheets have passed. Also,
To determine the image stretch, print a line image at a predetermined interval,
It was examined how the line spacing changed.

The results are shown in FIG. As shown in FIG. 7, the time required for the cleaning process of the transfer roller 13 is 0.7.
The image stretches at 8 seconds (a in the figure) when the number of prints is 5
About 5,000 sheets exceeds about 100.8%, while the image elongation (b in the figure) when the cleaning time of the transfer roller 13 is 3.1 seconds is 15,000 sheets.
About 100.8% or less was maintained until about 0 sheets. Further, when the cleaning time of the transfer roller 13 is 1.54 seconds, the image extension (c in the figure) is 1200
About 100.8% or less was maintained until about 00 sheets.

As shown in FIGS. 8, 9 and 10,
The abnormal image in the halftone image occurs when the transfer cleaning bias application time is 0.78 seconds and the number of prints is about 60,000, and when the transfer cleaning bias application time is 1.54 seconds, the number of prints is small. 14
When the transfer cleaning bias application time is 3.1 seconds, the number of printed sheets is 16000.
It started to occur from 0 sheets. At this time, the image length was about 100.8% (100% is a state in which the original image length without image stretch is reproduced).

From the above results, by extending the application time of the transfer roller cleaning bias to the transfer roller 13, it is possible to suppress the expansion of the image and increase the number of prints until the abnormal image occurs. Do you get it. In particular, the application time of the transfer roller cleaning bias is 0.78 seconds (1.5 rotations of the transfer roller 13),
There is an effect on the dirt on the backside of the image on the transfer paper.
The cleaning bias application time of 0.78 seconds (1.5 rotations of the transfer roller 13) or less was sufficient, but an abnormal image occurs at 60,000 sheets, which is not practical as the life of the transfer roller. By making the cleaning bias application time longer than this, the practical life of 60,000 sheets or more is achieved.

As shown in FIG. 10, in order to satisfy the life of the transfer roller 13 having the number of prints of 150,000 or more, the cleaning bias application time is 3.1 seconds (equivalent to 6 rotations of the transfer roller 13). ) Cleaning was required. In addition, the abnormal image is A with a long image length.
Although it occurred in the 3 size, no abnormal image was observed in the B5 or A4 size transfer paper.

Next, the structure of the abnormal image was examined further.

(Relationship between the peripheral speed difference between the photosensitive drum 1 and the transfer roller 13) In the investigation of the relationship between the peripheral speed difference between the photosensitive drum 1 and the transfer roller 13, the photosensitive drum 1 is set to the latent image writing unit 5. It is rotated at a peripheral speed of 97.5% of the writing speed, and the transfer roller 13 is rotated at a peripheral speed of 103.9% (106% of the peripheral speed of the photosensitive drum 1) of the writing speed by the latent image writing unit 5. It was

From this state, the peripheral speed of the photosensitive drum 1 is 9 times the writing speed of the latent image writing unit 5.
9.1%, the peripheral speed of the transfer roller 13 is 101.8% of the writing speed by the latent image writing unit 5, and the peripheral speed of the photosensitive drum 1 is 98.1% of the writing speed by the latent image writing unit 5. The examination was conducted by changing the peripheral speed of the transfer roller 13 to 102.8% of the writing speed of the latent image writing unit 5.

As shown in FIG. 11, the peripheral speed of the photosensitive drum 1 is 9 times the writing speed of the latent image writing unit 5.
Those set to 7.5%, 98.1%, 99.1%
It was found that the image elongation can be reduced when the peripheral speed of the photosensitive drum 1 is set to 98.1% and 99.1%. Moreover, no abnormal image was generated due to an excessive loop of the transfer paper between the transfer nip portion and the fixing nip portion.

However, the peripheral speed of the photosensitive drum 1 is set to 98.1% of the writing speed by the latent image writing unit 5 to be 9%.
When the peripheral speed difference between the two is reduced by setting 9.1%,
It was found that a slight void in the transfer (intermediate void) occurred, and further, the toner was fused to the photosensitive drum 1 and cleaning could not be performed.

From the above results, the occurrence of an abnormal image caused by an excessive number of loops of the transfer paper between the transfer nip portion and the fixing nip portion due to the image expansion is caused by the peripheral speed of the photosensitive drum 1 being the latent image writing unit. Writing speed of 98.
It has been found that this is a phenomenon that occurs in the image forming apparatus set to less than 1%.

(Study of distance between transfer nip portion and fixing nip portion) Next, the relationship between the occurrence of an abnormal image due to image expansion and the distance between the transfer nip portion and the fixing nip portion was examined.

In the image forming apparatus shown in FIG. 1, a pedestal (not shown) is inserted so that the fixing device 15 having the fixing roller 15a and the pressure roller 15b can be moved upward, and the fixing device 15 is moved to the transfer roller. The presence / absence of an abnormal image was examined by setting the transfer nip portion between the photosensitive drum 1 and the photosensitive drum 1 at a predetermined distance.

The fixing roller 15a was rotated at a predetermined speed by using an independent motor for examination (not shown).
In this examination, the number of image formations (prints) is 160
The number of sheets was set to 000, and the presence or absence of an abnormal image due to image expansion was examined using the transfer roller 13 in which the above-described abnormal image occurred. The result is shown in FIG.

In this examination, as shown in FIG. 3, from the transfer nip portion N between the transfer roller 13 and the photosensitive drum 1 to the fixing nip between the fixing roller 15a and the pressure roller 15b of the fixing device 15. Distance to part M (distance between transfer and fixing) T
However, an abnormal image occurred in the configuration of 80 mm (1/4 or less of the maximum sheet passing size). On the other hand, when the transfer-fixing distance T was 120 mm and 180 mm, no abnormal image was generated. In this examination, as shown in FIG. 3, the distance L between the surface of the transport guide 25 provided between the transfer nip portion N and the fixing nip portion M and the surface connecting the transfer nip portion N and the fixing nip portion M is L. Is 9 mm, and this surface is parallel to the surface of the transport guide 25.

From the above results, an abnormal image is generated from the transfer nip portion N to the fixing nip portion M due to the excess of the loop of the transfer paper between the transfer nip portion N and the fixing nip portion M due to the image expansion. In the image forming apparatus having a short distance T of 1/4 or less of the maximum sheet passing size, the transfer nip portion N
It was found that this occurs when the trailing edge of the transfer paper separates.

(Study of Cell Diameter of Transfer Roller 13) Next,
An examination was conducted on the image elongation and the occurrence of abnormal images when the cell diameter and the porosity of the sponge forming the elastic layer of the transfer roller 13 were changed.

The sponge hardness was increased, but the cell diameter was reduced to reduce the porosity.
In this study, a transfer roller having a hardness of 26 ° (Asc-C: 4.9N load), a sponge cell diameter of 150 μm, and a porosity of 50%, a hardness of 35 degrees (Asc-C: 4.9N load), a sponge of Comparison was performed using a transfer roller having a cell diameter of 80 μm and a porosity of 30%.

As a result, with respect to the image elongation, the smaller the cell diameter is, the better. It is about 100.6% of the initial image length at the endurance of 150,000 sheets. However, when the hardness is high, the photosensitive drum is increased. 1 The surface was scraped, and voids in the transfer occurred during transfer.

As described above, in the present embodiment, from the results of the above studies, the distance from the transfer nip portion N to the fixing nip portion M is short for downsizing, which is 1 / maximum of the maximum sheet passing size.
It is set to a short distance of 4 or less, and the peripheral speed of the photosensitive drum 1 is less than 98.1% of the writing speed by the latent image writing unit 5, and the peripheral speed of the outer periphery of the transfer roller 13 that contacts the transfer paper. Is 103.6% or more and 104.3% or less of the writing speed of the latent image writing unit 5, a transfer roller cleaning bias is applied to the transfer roller 13 for at least 0.78 seconds,
That is, by applying the transfer roller cleaning bias for a time longer than at least 1.5 rotations of the transfer roller 13, it is possible to suppress the image expansion and prevent the occurrence of the abnormal image.

Particularly, the life of the transfer roller 13 is 15,000.
It is effective to apply a transfer roller cleaning bias of 3.1 seconds (six rotations of the transfer roller 13) or more in order to provide 0 or more durable paper passages.

In the above description, the transfer cleaning bias is applied after the image forming operation is completed, but the transfer cleaning bias is applied before the image forming operation is started or during the image forming operation. Alternatively, the process may be performed during the paper interval after the number of image formations reaches the predetermined number.

For example, except when the image forming operation is completed, the number of image forming sheets is increased by 3.1 seconds for every 20 sheets (transfer roller 1
A transfer roller cleaning bias of 6 rotations of 3) may be applied. As a result, it is possible to prevent problems such as image expansion from occurring even in the large-volume copy mode.

<Second Embodiment> In the first embodiment, the cleaning of the transfer roller is strengthened and the change of the transfer roller conveyance force is suppressed to suppress the image extension and prevent the occurrence of the abnormal image. In the present embodiment, in order to prevent the occurrence of this abnormal image, the peripheral speed of the fixing roller of the fixing device is adjusted to prevent the occurrence of this abnormal image.

The image forming apparatus of this embodiment also has the same structure as that of the image forming apparatus shown in FIGS. 1 to 3 except for the peripheral speed of the fixing roller of the fixing device.
From the fixing nip portion M to the fixing nip portion M is set to a short distance of 1/4 or less of the maximum sheet passing size, and the peripheral speed of the photosensitive drum 1 is 97.5 of the writing speed of the latent image writing unit 5. %, And the peripheral speed of the outer periphery of the transfer roller 13 in contact with the transfer paper is 103.6% or more and 104.3% or less of the writing speed by the latent image writing unit 5. In the present embodiment, the application time of the transfer roller cleaning bias when cleaning the transfer roller 13 is not specified.

In the present embodiment, the peripheral speed of the fixing roller 15a of the fixing device 15 is set to be higher than that at the normal time. In the first embodiment, the peripheral speed of the fixing roller 15a is set to 99.8% of the writing speed of the latent image writing unit 5, but in the present embodiment, the peripheral speed of the fixing roller 15a is set to the latent image writing. Writing speed by unit 5 is 100.02%, 100.2%, 100.5%, 10
It was changed to 1% respectively.

Then, in the above-described examination in the first embodiment, the transfer roller 13 in which an abnormal image is generated due to the endurance of 160000 sheets is used, and the outer shape of the fixing roller 15a is made slightly larger than that in the first embodiment. By changing the peripheral speed, the occurrence of abnormal images and their adverse effects (wrinkles on transfer paper, image stretch) were examined. The result is shown in FIG.

From this result, the peripheral speed of the fixing roller 15a is compared with the writing speed by the latent image writing unit 5.
By slightly increasing from 99.8% to 100.2%, the occurrence of abnormal images disappeared. This is the fixing roller 15
By increasing the peripheral speed of a, the transfer paper can be quickly pulled at the fixing nip portion between the fixing roller 15a and the pressure roller 15b, so that the transfer between the fixing nip portion and the transfer nip portion can be performed. This is because the paper loop becomes a little smaller.

On the other hand, if the transfer paper is conveyed faster in the fixing nip portion, the transfer paper is pulled faster in the fixing nip portion, so that the toner image transferred in the transfer nip portion is slightly expanded. In some cases, the image may be stretched by 1% or more on the trailing end side of the transfer paper in the transport direction.

Therefore, the peripheral speed of the fixing roller 15a is set to 10 with respect to the writing speed of the latent image writing unit 5.
When it is 0.5% or more, image elongation occurs, but 100.
In the cases of 02% and 100.2%, the occurrence of abnormal images did not occur, and the adverse effects (wrinkles on the transfer paper, image elongation) did not occur. Further, when the peripheral speed of the fixing roller 15a is set to 101.0% of the writing speed of the latent image writing unit 5, no abnormal image is generated, but
Occurrence of wrinkles and image stretch of the transfer paper was observed.

As described above, in the present embodiment, the distance from the transfer nip portion to the fixing nip portion is short for the purpose of downsizing, and is set to a short distance of 1/4 or less of the maximum sheet passing size. The peripheral speed of 1 is the latent image writing unit 5
Is less than 98.1% of the writing speed, and the peripheral speed of the outer periphery of the transfer roller 13 in contact with the transfer paper is 103.6% or more of the writing speed of the latent image writing unit 5.
In the image forming apparatus of 4.3% or less, by setting the peripheral speed of the fixing roller 15a to 1000.02% or more and 100.5% or less of the image writing speed of the latent image writing unit 5, the abnormal image It was possible to prevent the occurrence.

<Third Embodiment> In the first embodiment, as shown in FIG. 3, the surface of the conveyance guide 25 provided between the transfer nip portion N and the fixing nip portion M, the transfer nip portion N and the fixing are fixed. The distance L to the surface A connecting the nip portion M was set to 9 mm, and this surface was parallel to the surface of the transport guide 25. However, in the present embodiment, as shown in FIG. The concave portion 25 is formed on the surface on the side where the transfer paper is conveyed.
By forming a, the distance L between the transfer nip portion N and the surface A connecting the fixing nip portion M is adjusted to prevent the occurrence of an abnormal image.

The image forming apparatus of this embodiment also has the same structure as that of the image forming apparatus shown in FIGS. 1 to 3 except for the shape of the surface of the conveyance guide 25.
From the fixing nip portion M to the fixing nip portion M is set to a short distance of 1/4 or less of the maximum sheet passing size, and the peripheral speed of the photosensitive drum 1 is 97.5 of the writing speed of the latent image writing unit 5. %, And the peripheral speed of the outer periphery of the transfer roller 13 in contact with the transfer paper is 103.6% or more and 104.3% or less of the writing speed by the latent image writing unit 5. In the present embodiment, the application time of the transfer roller cleaning bias when cleaning the transfer roller 13 is not specified.

In this embodiment, as shown in FIG.
Fixing entrance guide 26 provided on the upstream side of the fixing nip portion M
In order to guide the leading edge of the transfer paper to the sheet, the curvature of the concave portion 25a formed on the surface of the transport guide 25 is small at a position close to the fixing entrance guide 26 and is large at a position near the transfer nip portion N side.

By changing the curvature of the concave portion 25a formed on the surface of the transport guide 25 in this way, the shock when the tip of the transfer paper coming out of the transfer nip portion N comes into contact with the surface of the transport guide 25 is reduced, and the transfer paper is transferred. It was possible to weaken the contact between the loop and the transport guide 25 that would occur when the second half of the transport guide was carried, and to suppress the occurrence of abnormal images.

As a result of examining the distance L between the position where the concave portion 25a of the surface of the transport guide 25 has the largest curvature and the surface A connecting the transfer nip portion N and the fixing nip portion M, this distance L is set to 1
By setting the thickness to 3 mm, the generation of abnormal images could be suppressed. In the present embodiment, the transfer nip portion N
The distance T from the fixing sheet to the fixing nip portion M is set to 80 mm (a short distance of ¼ or less of the maximum sheet passing size).

Therefore, the recess 25a on the surface of the transport guide 25 is formed.
The distance L between the position having the largest curvature and the surface A connecting the transfer nip portion N and the fixing nip portion M is 16.25% with respect to the distance T from the transfer nip portion N to the fixing nip portion M. Alternatively, by setting it to 16.25% or more, a loop formed when the latter half of the transfer sheet coming out of the transfer nip portion N is guided and the recess 25a on the surface of the transfer guide 25.
By weakening the contact with, it is possible to suppress the occurrence of abnormal images.

As described above, in the present embodiment, the distance from the transfer nip portion to the fixing nip portion is short and the distance T from the transfer nip portion N to the fixing nip portion M is 80 m for downsizing.
m (short distance of 1/4 or less of the maximum sheet passing size), the peripheral speed of the photosensitive drum 1 is less than 98.1% of the writing speed of the latent image writing unit 5, and the transfer roller 13 In the image forming apparatus in which the peripheral speed of the outer periphery contacting the transfer sheet is 103.6% or more and 104.3% or less of the writing speed by the latent image writing unit 5, the curvature of the concave portion 25a formed on the surface of the transport guide 25 is uniform. By setting the distance L between the largest position and the surface A connecting the transfer nip portion N and the fixing nip portion M to 16.25% with respect to the distance T from the transfer nip portion N to the fixing nip portion M, It was possible to prevent the occurrence of abnormal images.

[0113]

As described above, according to the first aspect of the invention, the distance between the transfer nip portion and the fixing nip portion is 1 which is the maximum size of the transfer material that can be conveyed to the transfer nip portion.
/ 4 or less, the image carrier, the transfer member, and the fixing unit are arranged, and the peripheral speed of the image carrier is less than 98.1% of the writing speed of the image information on the image carrier by the exposing unit. In the image forming apparatus in which the peripheral speed of the outer periphery of the transfer member that comes into contact with the transfer material is 103.6% or more and 104.3% or less of the writing speed, the image forming apparatus has a cleaning unit for cleaning the transfer member and does not perform image formation. In cleaning the transfer member by the cleaning means, the transfer member is rotated, and cleaning is performed for a time longer than at least 1.5 rotations of the transfer member, so that the transfer member is satisfactorily cleaned. By suppressing the change in the conveying force of the image, it is possible to suppress the image expansion and prevent the occurrence of the abnormal image.

According to the third aspect of the invention, the distance between the transfer nip portion and the fixing nip portion is set to 1/4 or less of the maximum size of the transfer material that can be conveyed to the transfer nip portion. An image carrier, a transfer member, and a fixing unit are arranged,
Further, the peripheral speed of the image carrier is less than 98.1% of the writing speed of the image information on the image carrier by the exposure means, and the peripheral speed of the outer periphery of the transfer member that contacts the transfer material is 10 the writing speed.
In the image forming apparatus of 3.6% or more and 104.3% or less, the peripheral speed of the surface of the fixing unit in contact with the transfer material of the pair of fixing rotators is 100.02% or more and 100.02% of the writing speed.
When the content is 5% or less, it is possible to suppress the image elongation and prevent the occurrence of an abnormal image.

According to the invention described in claim 4, the distance between the transfer nip portion and the fixing nip portion is set to 1/4 or less of the maximum size of the transfer material which can be conveyed to the transfer nip portion. An image carrier, a transfer member, and a fixing unit are arranged,
Further, the peripheral speed of the image carrier is less than 98.1% of the writing speed of the image information on the image carrier by the exposure means, and the peripheral speed of the outer periphery of the transfer member that contacts the transfer material is 10 the writing speed.
In the image forming apparatus in which the amount is 3.6% or more and 104.3% or less, the toner image of the transfer material, which has come out of the transfer nip portion, comes into contact with the back side not transferred between the transfer nip portion and the fixing nip portion. It has a transport guide that guides the transfer material from the transfer nip portion to the fixing nip portion. The distance to the surface of the transport guide where the back side where the toner image of the transfer material is not transferred contacts
By setting the distance between the transfer nip and the fixing nip to approximately 16.25%, it is possible to suppress the image expansion and prevent the occurrence of an abnormal image.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a photosensitive drum and a transfer roller of the image forming apparatus according to the first embodiment of the present invention.

FIG. 3 is a diagram for explaining a distance between a transfer nip portion and a fixing nip portion of the image forming apparatus according to the first embodiment of the present invention.

FIG. 4 is a diagram showing a sequence of bias application including application of a transfer roller cleaning bias to a transfer roller in the image forming apparatus according to the first embodiment of the present invention.

FIG. 5 is a diagram showing a sequence of bias application including application of a transfer roller cleaning bias to the transfer roller in the image forming apparatus according to the first embodiment of the present invention.

FIG. 6 is a diagram showing a bias application sequence including transfer roller cleaning bias application to the transfer roller during initial rotation in the image forming apparatus according to the first embodiment of the present invention.

FIG. 7 is a diagram showing a relationship between the number of prints and image stretch.

FIG. 8 is a diagram showing a result of examination of whether a transfer roller cleaning bias is applied and whether an abnormal image is generated with respect to the number of prints according to the first embodiment of the present invention.

FIG. 9 is a diagram showing a result of examination of whether a transfer roller cleaning bias is applied and whether or not an abnormal image is generated with respect to the number of prints according to the first embodiment of the present invention.

FIG. 10 is a diagram showing a result of examination of whether a transfer roller cleaning bias is applied and whether an abnormal image is generated with respect to the number of prints according to the first embodiment of the present invention.

FIG. 11 is a diagram showing a result of examination on the presence or absence of occurrence of image elongation, abnormal image, void in transfer, and toner fusion with respect to the peripheral speed of the photosensitive drum in the first embodiment of the present invention.

FIG. 12 is a diagram showing a result of examination on a distance between transfer and fixing and presence / absence of occurrence of an abnormal image in the first embodiment of the invention.

FIG. 13 is a diagram showing a result of examining whether or not an abnormal image, a paper wrinkle, and an image stretch occur with respect to the peripheral speed of the fixing roller according to the first embodiment of the present invention.

FIG. 14 is a diagram for explaining the shape of a conveyance guide of the image forming apparatus according to the third embodiment of the present invention.

15 (a) and 15 (b) are views for explaining the orientation of the polishing eyes on the surface of the transfer roller.

FIG. 16 is a diagram for explaining a loop of transfer paper formed between a fixing nip portion and a transfer nip portion.

[Explanation of symbols]

1 Photoreceptor Drum (Image Carrier) 2 Charging Roller (Charging Means) 3 Developing Unit (Developing Means) 4 Cleaning Blade 5 Writing Unit (Exposure Means) 6 Image Reading Device 13 Transfer Roller (Transfer Member) 14 Registration Roller Pair 15 Fixing Device (fixing means) 15a Fixing roller (fixing rotator) 15b Pressure roller (fixing rotator) 18 Transfer bias power supply 19 Transfer roller cleaning bias power supply (cleaning means) 25 Transport guide 25a Recess 26 Fixing entrance guide 30 Process cartridge 31 Device Body

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03G 21/00 350 G03G 21/00 350 F term (reference) 2H027 ED02 ED04 ED24 ED25 EE03 2H033 AA01 BB00 CA13 2H035 CA07 CB01 CG01 2H071 DA09 DA12 EA04 2H200 FA20 GA02 GA23 GA34 GA44 GB12 GB25 HA02 HA28 HB12 HB45 JA02 JA25 JA29 JB10 JB12 JB18 LA12 LB39 LB40 MA03 MA08 PA02 PB12

Claims (5)

[Claims] 1. A rotatable image carrier, charging means for charging the image carrier, and exposure means for exposing the charged image carrier to form an electrostatic latent image according to image information. And developing means for developing the electrostatic latent image to form a toner image,
The transfer nip portion is formed in contact with the image carrier, and the toner image formed on the image carrier by applying a transfer voltage to the back surface of the transfer material conveyed to the transfer nip portion is transferred to the transfer material. The transfer material on which the toner image has been transferred is nipped and conveyed in a fixing nip portion formed between a rotatable transfer member that transfers to the surface of a sheet and a pair of fixing rotating bodies that have heating means inside at least one of them. And a fixing unit that thermally fixes the toner image on the surface of the transfer material, and the distance between the transfer nip portion and the fixing nip portion is the maximum size of the transfer material that can be conveyed to the transfer nip portion. The image carrier, the transfer member, and the fixing unit are arranged so as to be ¼ or less, and the peripheral speed of the image carrier is the writing speed of image information to the image carrier by the exposing unit. Of 9
It is less than 8.1%, and the peripheral speed of the outer periphery of the transfer member in contact with the transfer material is 103.6% or more and 10% or more of the writing speed.
In the image forming apparatus of 4.3% or less, the image forming apparatus has a cleaning unit that cleans the transfer member, rotates the transfer member when cleaning the transfer member by the cleaning unit during non-image formation, and An image forming apparatus, wherein cleaning is performed for a time longer than at least 1.5 rotations of the transfer member. 2. The cleaning unit applies a transfer cleaning bias having a polarity opposite to that of the transfer voltage to the transfer member to electrostatically transfer the adhered toner adhering to the surface of the transfer member to the image carrier side. The image forming apparatus according to claim 1, wherein the transfer member is cleaned. 3. A rotatable image carrier, charging means for charging the image carrier, and exposure means for exposing the charged image carrier to form an electrostatic latent image according to image information. And developing means for developing the electrostatic latent image to form a toner image,
The transfer nip portion is formed in contact with the image carrier, and the toner image formed on the image carrier by applying a transfer voltage to the back surface of the transfer material conveyed to the transfer nip portion is transferred to the transfer material. The transfer material on which the toner image has been transferred is nipped and conveyed in a fixing nip portion formed between a rotatable transfer member that transfers to the surface of a sheet and a pair of fixing rotating bodies that have heating means inside at least one of them. And a fixing unit that thermally fixes the toner image on the surface of the transfer material, and the distance between the transfer nip portion and the fixing nip portion is the maximum size of the transfer material that can be conveyed to the transfer nip portion. The image carrier, the transfer member, and the fixing unit are arranged so as to be ¼ or less, and the peripheral speed of the image carrier is the writing speed of image information to the image carrier by the exposing unit. Of 9
It is less than 8.1%, and the peripheral speed of the outer periphery of the transfer member in contact with the transfer material is 103.6% or more and 10% or more of the writing speed.
In the image forming apparatus of 4.3% or less, the peripheral speed of the surface of the fixing unit in contact with the transfer material of the pair of fixing rotators is 100.02% or more of the writing speed.
An image forming apparatus characterized in that the content is 00.5% or less. 4. A rotatable image carrier, a charging unit for charging the image carrier, and an exposing unit for exposing the charged image carrier to form an electrostatic latent image according to image information. And developing means for developing the electrostatic latent image to form a toner image,
The transfer nip portion is formed in contact with the image carrier, and the toner image formed on the image carrier by applying a transfer voltage to the back surface of the transfer material conveyed to the transfer nip portion is transferred to the transfer material. The transfer material on which the toner image has been transferred is nipped and conveyed in a fixing nip portion formed between a rotatable transfer member that transfers to the surface of a sheet and a pair of fixing rotating bodies that have heating means inside at least one of them. And a fixing unit that thermally fixes the toner image on the surface of the transfer material, and the distance between the transfer nip portion and the fixing nip portion is the maximum size of the transfer material that can be conveyed to the transfer nip portion. The image carrier, the transfer member, and the fixing unit are arranged so as to be ¼ or less, and the peripheral speed of the image carrier is the writing speed of image information to the image carrier by the exposing unit. Of 9
It is less than 8.1%, and the peripheral speed of the outer periphery of the transfer member in contact with the transfer material is 103.6% or more of the writing speed 10
In the image forming apparatus of 4.3% or less, between the transfer nip portion and the fixing nip portion, the toner image of the transfer material, which has come out of the transfer nip portion, can be brought into contact with the back side not transferred. And a conveyance guide that guides the transfer material, which has come out of the transfer nip portion, to the fixing nip portion, and is perpendicular to a plane connecting the transfer nip portion and the fixing nip portion. The distance from the flat surface to the surface of the transport guide with which the back side of the transfer material on which the toner image is not transferred is in contact is about 16.25% of the distance between the transfer nip and the fixing nip. Image forming apparatus. 5. The transfer member is a roller rotating body having a sponge-like elastic body on the surface, and the average cell diameter of the elastic body is 120 μm or more and 170 μm or less. The image forming apparatus according to item 3 or 4.