JPH10133497A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain a high image quality without exerting a load change to a belt driving system by preventing electric discharge derived from the gap between an image carrier in a belt shape and a recording medium. SOLUTION: In this image forming device, the position where the transferring roll is brought onto contact with the image carrier 2 at the first time are made to exist between a shifting locus of a transferring roll 10 shifting a transferring position and the non-transferring position, between the position where the back up roll is separated and the position where the rear side of the image carrier is held in contact with the back up roll 22, and a line that connects the center O2 of the transferring roll and the center O1 on the transferring position on which the transfer roll 10 is held in press contact with the back up roll 22 across the image carrier 2, and the surface of the image carrier 2 when the transferring roll 10 is retired on the non-transferring position is made below 90 degrees.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus, and more particularly, to a belt-shaped image carrier such as an endless belt-shaped intermediate transfer member or an endless belt-shaped photosensitive member in response to an image signal. The present invention relates to an image forming apparatus including a transfer device that transfers a formed toner image to a transfer material.

[0002]

2. Description of the Related Art An image forming apparatus such as an electrophotographic copying machine, a printer, or a facsimile machine transfers a toner image formed of a charged toner formed on an image carrier such as a photoreceptor to a recording medium such as transfer paper or a so-called OHP. And a transfer device for transferring the image to the printer. The transfer of the toner image to the recording medium is performed by applying an electric field having a polarity such that the toner constituting the toner image moves to the recording medium while simultaneously transporting the recording medium on the image carrier and electrostatically recording the toner image. The method of making it adsorb | suck to a medium is common.

As a means for applying the electric field, a roll-shaped member (transfer roll) is used so as to be opposed to and pressed against the image carrier such as the photoreceptor from the back surface of the recording medium, and to apply a voltage having a polarity opposite to the charging polarity of the toner. There is known a method of transferring a toner image to a recording medium by applying an electric field to a transfer roll and forming the electric field.
There is also a method in which heat is applied via a transfer roll in addition to the application of an electric field to move the toner to a recording medium.

When the above-described transfer roll is used for transfer, toner is not transferred to the transfer roll in order to avoid adhesion of toner to the transfer roll, deformation of the transfer roll due to pressing force at the time of transfer, or deterioration of the photoconductor due to heat. Normally, the transfer roll is separated from the image carrier at times other than the above. An image carrier such as a photoreceptor is generally in the form of an endless belt or a drum, but the endless belt has a greater degree of freedom in shape than the drum and has a larger surface curvature at the transfer position. Therefore, there is an advantage that after the toner image is moved to the recording medium, the recording medium can be easily peeled off from the image carrier such as the photoreceptor by utilizing the “waist” of the recording medium.

FIG. 8 is an explanatory view of a main part of an image forming apparatus using an intermediate transfer belt.
Is an intermediate transfer belt, 3 is a recording medium, 4 is a charging device, 5 is a black (Bk) developing device, 6 is a yellow (Y) developing device,
7 is a magenta (M) developing device, 8 is a Sian (C) developing device, 9 is a corona discharger as a primary transfer device, 10 is a secondary transfer roll, 11 is a feed roller, 12 is a recording medium tray, and 14 is a recording device. A medium transport belt, 15 a fixing device,
16 is an intermediate transfer belt cleaner, 17 is a belt position sensor, 18 is a photosensitive drum cleaner, 9 is a registration roll, 21 is a belt drive roll, 22 is a backup roll, 23 is a tension roll, 24 is a driven roll, 25
Is a secondary transfer roll cleaner.

In FIG. 1, a charger 4 uniformly charges the surface of the photosensitive drum 1 with a predetermined polarity around the photosensitive drum 1 rotating in the direction of arrow A. Image exposure means (not shown) for forming a latent image on the charged surface, developing devices 5 to 8 for a plurality of colors, and a photosensitive drum cleaner 18 are provided, and a toner image T is formed by an electrophotographic process.

The rotation of the photosensitive drum 1 causes the toner image T to reach a primary transfer position where the corona discharger 9 is disposed. On the other hand, the endless intermediate transfer belt 2 includes a driving roll 21, a driven roll 24, and a tension roll 2 having a tension control mechanism.
Backup Roll 22 Constituting 3 and Secondary Transfer Section
And rotates in the direction of arrow B in synchronism with the peripheral speed of the photosensitive drum 1.

At the primary transfer position, a corona discharger 9 is provided on the back surface of the intermediate transfer belt 2, and a toner image is intermediately transferred by applying a discharge electric field having a polarity opposite to the charging polarity of the toner T on the photosensitive drum 1. The primary transfer is performed on the belt 2. The intermediate transfer belt 2 on which the toner image has been primarily transferred rotates in the direction of arrow B to reach a secondary transfer position where the backup roll 22 and the transfer roll 10 are installed. After forming the next toner image, the photosensitive drum 1 is cleaned of residual toner by a photosensitive drum cleaner 18, and the remaining charge is removed by a static eliminator (not shown). Is made.

When a color image is formed, toner images corresponding to a plurality of image signals are sequentially formed on the photosensitive drum 1 and are transferred onto the intermediate transfer belt 2 in a superimposed manner. Also,
The intermediate transfer belt 2 returns to the primary transfer position again while carrying the toner image, and after the transfer of the final toner image, the secondary transfer roll is moved in a direction in contact with the intermediate transfer belt 2,
The recording medium is nipped to collectively transfer the toner images of the plurality of colors which are superimposed and transferred.

Until the final toner image is transferred to the intermediate transfer belt 2, the secondary transfer roll 10 is retracted to a position separated from the intermediate transfer belt 2. The recording medium 3 accommodated in the recording medium tray 12 includes a feed roller 1
1, the sheet is taken out one by one, and the sheet is fed between the intermediate transfer belt 2 and the secondary transfer roll 10 (nip) at a timing by the registration roll 19.

The recording medium 3 is nipped by the intermediate transfer belt 2 and the secondary transfer roll 10, and a transfer voltage having a polarity opposite to the charging polarity of the toner image is applied to the secondary transfer roll 10 and the backup roll 2.
2, the toner image carried on the intermediate transfer belt 2 is secondarily transferred to the recording medium 3. The recording medium 3 onto which the secondary transfer roll has been transferred is transferred to a recording medium transport belt 14.
Is sent to the fixing device 15 and is heated / pressurized to perform fixing.

Intermediate transfer belt 2 on which a toner image is secondarily transferred
The remaining toner and paper dust are removed by the intermediate transfer belt cleaner 16, and the toner adhered to the secondary transfer roll 10 by the cleaning blade 25 is removed.
FIG. 9 is an enlarged schematic view of the secondary transfer portion of the image forming apparatus shown in FIG. 8, where 10A is a position where the secondary transfer roll 10 is retracted from the intermediate transfer belt 2, and 10B is a secondary transfer at the time of the secondary transfer. The position 10C where the roll 10 first contacts the intermediate transfer belt 2 indicates the position where the secondary transfer roll 10 nips the intermediate transfer belt and the recording medium and presses against the backup roll 22.

The illustrated secondary transfer roll 10 is retracted to a position indicated by reference numeral 10A and separated from the intermediate transfer belt 2 except during the secondary transfer. And at the time of the secondary transfer, the position 10
A moves from A to the direction in contact with the intermediate transfer belt 2 and first contacts the surface of the intermediate transfer belt 2 at a position 10B as shown in FIG. 3A, and then moves to a position 10C shown in FIG. To contact the backup roll 22 via the intermediate transfer belt 2 and the recording medium 3. When the secondary transfer is completed, the secondary transfer roll 10 moves from the position 10C to the position 10A.
Evacuate to

As shown in the figure, the recording medium 3 is provided between the secondary transfer roll 10 and the intermediate transfer belt 2 as shown in FIG. Approach at an angle to. Even during the secondary transfer, there is a gap between the secondary transfer and the intermediate transfer belt as shown in FIG. Next, the configuration of an image forming apparatus employing a method in which an endless belt-shaped photosensitive member is used as an image carrier and a toner image is electrostatically adsorbed on a recording medium by applying an electric field by a transfer roll will be described.

FIG. 10 is a schematic view of an essential part of an image display device for transferring a toner image formed on a photoreceptor belt to a recording medium by a transfer roll.
7 is a developing device, 58 is a belt cleaner, 60 is a transfer roll, 61 is a roll cleaner, 62 is a photoreceptor belt, 7
1 is a driven roll, 72 is a backup roll, 74 is a drive roll, 81 is a transport mechanism, 82 is a fixing device, 83 is a registration roll, and 84 is a recording medium.

In this configuration, the photoreceptor belt 62 is wound around a driving roll 74, a driven roll 71 and a backup roll 72, and is rotated by the driving roll 62 in the direction of the arrow. The surface of the photoreceptor belt 62 is
2 uniformly charges at a predetermined polarity. A latent image is written on the charged surface with a laser beam 53 modulated with image information. The written latent image reaches the developing position where the developing device 57 is installed by rotation of the photoreceptor belt 62 in the direction of the arrow, and is developed with toner to be visualized as a toner image. The toner image reaches a transfer position where the transfer roll 60 and the backup roll 72 are installed.

On the other hand, the transfer medium 84 is taken out of the tray and fed by the registration roll 83 at a proper timing.
The fed recording medium is transferred to the photosensitive belt 62 and the transfer belt 6.
0 and the transfer roll and the backup roll 72
Is transferred from the photoreceptor belt 62 to a recording medium by a transfer electric field applied during the transfer. The transfer roll 60 is retracted from the photoreceptor belt 62 during non-transfer to prevent unnecessary toner from adhering.

The recording medium onto which the toner image has been transferred is transported by a transport mechanism 8.
1 and is conveyed to the fixing device 82, and is fixed by passing between the heating roll 82a and the pressure roll 82b. The photoreceptor belt 62 after the transfer is a belt cleaner 58.
Is performed to remove the remaining toner, to prepare for the next transfer cycle. Further, the toner adhered to the transfer roll 60 at the time of transfer is scraped off by the roll cleaner 61.

FIG. 11 is a schematic view of a main part of a color image display device in which toner images of a plurality of colors are superposedly formed on a photoreceptor belt and then transferred onto a recording medium by a transfer roll. Image writing laser light, 54 to 57 are yellow, magenta, sian, and black developing devices,
8 is a belt cleaner, 60 is a transfer roll, 61 is a cleaning blade, 62 is a photoreceptor belt, 71 and 73 are driven rolls, 72 is a backup roll, 74 is a drive roll, 81 is a recording medium transport belt, 82 is a fixing device, 8
3 is a registration roll, and 84 is a recording medium.

The color image forming apparatus of this type is basically the same as that shown in FIG.
Arrange the necessary number of developing devices in the image forming apparatus described in
After a required number of color toner images are formed on the photoreceptor belt 62 in a superimposed manner, the color toner images are collectively transferred onto a recording medium 84. Therefore, since a color image is obtained by rotating the photosensitive belt a plurality of times for charging the photosensitive belt and developing the toner, a small number of components, a small size, and a low price can be achieved.

In addition, since a plurality of color toner images are superimposed on a single photoreceptor, misregistration between the toner images is reduced, and as a result, a high quality color image with less color misregistration is obtained. be able to. FIG.
11 is an enlarged schematic diagram of a transfer unit or a secondary transfer unit in the image forming apparatus of the type described in FIG. 11, and is a schematic diagram similar to FIG. 9.

In FIG. 1, reference numeral 60A denotes a position at which a transfer roll or a secondary transfer roll (both are simply referred to as transfer rolls) is retracted from the photoreceptor belt, and 60B denotes a position at which the transfer roll is moved by the photoreceptor belt 62 during the secondary transfer. 10C indicates a position where the transfer roll nips the photosensitive belt 62 and the recording medium 3 and presses against the backup roll 72.

The transfer roll is retracted to the position indicated by 60 A and separated from the photosensitive belt 62 except during transfer. At the time of transfer, the photosensitive belt 62 is moved from the position 60A.
As shown in FIG. 6A, the roller first contacts the surface of the photoreceptor belt 62 at a position 60B, and then contacts the backup roll 72 at a position 60C shown in FIG. And presses against the photosensitive belt 62 via the recording medium 3. When the transfer is completed, the transfer roll or the secondary transfer roll retracts from the position 60C to the position 60A.

As shown in the drawing, the recording medium 3 is located between the transfer roll and the photosensitive belt 62 with respect to the toner carrying surface (the surface on the storage medium side) of the photosensitive belt 62 as shown in FIG. It enters at a certain angle and has a gap with the photosensitive belt 62 even during transfer, as shown in FIG. In the image forming apparatus described with reference to FIGS. 10 and 11, similarly to the image forming apparatus using the intermediate transfer belt, the occurrence of transfer failure due to many factors such as the storage state of the recording medium, waist, surface properties, and the like. Can be suppressed.

The transfer roll needs to faithfully transfer various toner images from the thin portion of the toner layer in the halftone portion to the thick portion of the thick toner layer in the solid portion on the photosensitive belt. A large transfer electric field is required to transfer a portion where the toner layer is thick. On the other hand, when a large transfer electric field acts on a portion of the halftone portion where the toner layer thickness is small, a transfer failure occurs because a portion of the toner becomes reverse polarity due to discharge in a gap between the photosensitive belt and the recording medium.
Particularly, when a high-resistance recording medium such as an OHP sheet is used, transfer failure is remarkable.

Japanese Patent Application Laid-Open Nos. 62-206567 and 6-317994 disclose the prior art of this type of image forming apparatus.

[0027]

In the above-mentioned conventional image forming apparatus, a recording medium is transferred to a secondary transfer roll or a transfer roll and a backup roll nip portion on an intermediate transfer belt or a photosensitive belt carrying a toner image at a transfer portion. At the time of carrying in, as shown in, for example, FIG. 9 or FIG. 12, since there is a gap between the intermediate transfer belt or the photoreceptor belt and the recording medium, transfer failure occurs due to discharge in this gap.

FIG. 13 is an enlarged view of the secondary transfer section shown in FIG. 8, in which the secondary transfer roll 10 is pressed against the backup roll 22 via the intermediate transfer belt 2 and the recording medium 3 and the transfer electric field 400 is applied. This shows a state where voltage is applied. As shown, the transfer electric field 400 is generated not only at the nip portion (the area where the toner image is actually transferred) formed between the secondary transfer roll 10 and the backup roll 22 but also between the recording medium 3 and the intermediate transfer belt. Is also formed in the gap. Improper transfer occurs due to the transfer electric field in the gap.

FIG. 14 is an explanatory diagram of the cause of the occurrence of transfer failure in the gap between the intermediate transfer belt and the recording medium formed immediately before the nip formed by the intermediate transfer belt and the backup roll shown in FIG. . When there is a gap between the intermediate transfer belt 2 and the recording medium 3 on the upstream side (immediately before) of the transfer nip, discharge occurs due to the transfer electric field 400 due to the transfer voltage applied to the secondary transfer roll. Of the charges generated by this discharge, a part 300 of the toner particles 200 carried on the intermediate transfer belt 2 has a reverse polarity, and a part of the toner particles that should be transferred to the recording medium 3 is transferred to the intermediate transfer belt 2. As a result, image defects such as so-called white spots occur in the toner image 210 on the recording medium 3.

In the transfer section described with reference to FIG. 12, the same phenomenon as described above occurs in the gap formed between the photosensitive belt and the recording medium, and the same image defect occurs. FIG. 15 is an explanatory diagram of the relationship between the gap between the intermediate transfer belt or the photoreceptor belt and the recording medium and the discharge electric field in the transfer unit according to the Passion rule.
E = 312 / d + 6.2, which indicates the pass law when the gap is d and the discharge electric field is E, and the upper right is the discharge region.

As shown in FIG. 3, when the gap d (μm) between the intermediate transfer belt or the photosensitive belt and the recording medium is increased, the discharge electric field E (V μm) is reduced, and the discharge is easily generated, and Image defects such as breakage occur. By the occurrence of this discharge, the positive ions and negative ions shown in FIG. 14 are generated, and these positive ions adhere to the negatively charged toner particles 200, and cause the negative toner to be neutral or low negative. In severe cases, the polarity is changed to a positively charged polarity, and a portion where toner particles cannot be transferred from the intermediate transfer belt 2 is formed. That is, a so-called white spot occurs, which deteriorates image quality.

In the configuration of the transfer unit in the conventional image forming apparatus, the load of the intermediate transfer belt or the photoreceptor belt fluctuates due to the position where the transfer roll is pressed against the backup roll and the direction thereof. Slip with the belt, especially in an image forming apparatus using an intermediate transfer belt, causes color shift and color unevenness in the primary transfer section,
In an image forming apparatus using an intermediate transfer belt or a photoreceptor belt, a shift in an image exposure position due to the load fluctuation at a transfer site or a secondary transfer roll transfer site, and uneven development at a development position occur.

This is because there is no backup roll at the position where the transfer roll first comes into contact with the intermediate transfer belt or the photoreceptor belt and starts to rotate. It is considered that the tension control mechanism cannot cope with the rapid increase in the tension. FIG. 16 is a schematic diagram for explaining the presence / absence of a load change on the belt driving roll due to the difference in the direction of the transfer roll contacting / separating from the intermediate transfer belt or the photosensitive belt.

FIG. 3A shows the backup roll 2 (7) on the back surface of the intermediate transfer belt 2 or the photosensitive belt 62 (hereinafter simply referred to as a belt) at which the transfer roll contacts first.
The case where 2) does not exist is shown. In this case, belt 2
A force F in the direction of the arrow is applied to (62) and the backup roll 22 (72). This force F causes a load in the opposite direction to the rotation of the backup roll 22 (72), causing uneven rotation of the belt, causing streaky color unevenness called banding in the transferred image, and in the case of color, The registration of each color is shifted.

An object of the present invention is to solve the above-mentioned problems of the prior art and to form a gap between an intermediate transfer belt or a photosensitive belt, which is an endless belt-shaped image carrier, and a recording medium in a transfer section. Provided is an image forming apparatus having a novel transfer mechanism that does not cause a load fluctuation on a drive system of the intermediate transfer belt or the photosensitive belt when the transfer roll is pressed against the intermediate transfer belt or the photosensitive belt. It is in.

[0036]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems in the prior art, and has an endless belt-shaped image carrier such as an intermediate transfer belt or a photosensitive belt stretched and supported inside. In the image forming apparatus including at least a backup roll and a secondary transfer roll or a transfer roll that forms a transfer position between the backup roll and a backup roll by pressing against the image carrier belt via a recording medium, the secondary transfer roll Or the secondary transfer roll when the transfer roll is at the transfer position or the line connecting the center of the transfer roll and the backup roll and the secondary transfer roll when the secondary transfer roll or the transfer roll is at the non-transfer position or If the angle formed by the line connecting the center of the transfer roll and the backup roll is smaller than 90 degrees is the transfer position, Next, between the trajectories where the secondary transfer roll or the transfer roll moves from the non-transfer position to the transfer position, the secondary transfer roll or the transfer roll first contacts the image carrier such as the intermediate transfer belt or the photosensitive belt. The contact position is within an area where the back surface of the image carrier such as the intermediate transfer belt or the photosensitive belt contacts the backup roll.

According to this configuration, the recording medium can be brought into close contact with the image carrier belt such as an intermediate transfer belt or a photoreceptor belt in the nip where the transfer electric field acts, and the image carrier belt and the recording medium are arranged upstream of the nip. The transfer failure caused by the discharge caused by the formation of the gap between the transfer roller and the secondary transfer roll or the transfer roll is determined by the position where the secondary transfer roll or the transfer roll first contacts the image carrier such as the intermediate transfer belt or the photoreceptor belt. Since the image carrier belt is supported by the backup roll, uneven rotation and slippage of the image carrier belt can be avoided, color shift and color unevenness can be prevented, and a high-quality image can be obtained.

Note that the configuration of the present invention can be configured without adding another device or the like, so that there is no increase in cost as compared with a conventional image forming apparatus. That is, a first aspect of the present invention is an endless belt-shaped image carrier, which is disposed inside a peripheral circuit of the endless belt-shaped image carrier and stretched from the back surface of the endless belt-shaped image carrier. An endless belt-shaped image carrier driving mechanism including a plurality of rolls such as a driving roll, a driven roll, a backup roll, and a tension roll to be supported; and the endless belt being in contact with the endless belt-shaped image carrier and the backup roll. In an image forming apparatus having at least a transfer position for sandwiching a belt-shaped image carrier and a transfer roll capable of moving a non-transfer position separated and retracted from the endless belt-shaped image carrier, the transfer position and the non-transfer position are The position where the transfer roll first comes into contact with the endless belt-shaped image carrier between the moving trajectories of the transfer roll moving is the back surface of the endless belt-shaped image carrier. The transfer roll is located between a position where the transfer roll is released from a position in contact with the backup roll and a transfer position of the transfer roll at a transfer position where the transfer roll presses against the backup roll via the endless belt-shaped image carrier. An angle between a line connecting the center and the center of the backup roll and the surface of the endless belt-shaped image carrier when the transfer roll is retracted to the non-transfer position is in an area smaller than 90 degrees. And

With this configuration, it is possible to prevent transfer failure due to discharge caused by the formation of a gap between the image carrier belt and the recording medium upstream of the nip between the image carrier and the transfer roll, and to prevent secondary transfer. Since the position where the roll or transfer roll first comes into contact with the image carrier such as the intermediate transfer belt or the photoreceptor belt is supported by the backup roll, uneven rotation and slip of the image carrier belt are avoided, and color misregistration and Color unevenness is prevented, and a high-quality image is obtained.

According to a second aspect of the present invention, in the first aspect, the endless belt-shaped image carrier carries a primary-transferred toner image, which is secondarily transferred onto a recording medium. Characterized in that the belt is an intermediate transfer belt. With this configuration, it is possible to prevent transfer failure due to discharge caused by a gap formed between the intermediate transfer belt and the recording medium upstream of the nip between the backup roll and the secondary transfer roll. Since the position where it first contacts the transfer belt is supported by the backup roll,
The occurrence of rotation unevenness and slippage of the intermediate transfer belt is avoided, and color shift and color unevenness are prevented, so that a high-quality image can be obtained.

Further, a third aspect of the present invention provides a third aspect of the present invention,
The endless belt-shaped image carrier according to the first invention is a photoreceptor belt that carries a toner image obtained by developing a latent image according to an image signal with toner. With this configuration, transfer failure due to discharge caused by formation of a gap between the photoreceptor belt and the recording medium upstream of the nip between the backup roll and the transfer roll is prevented, and
Since the position where the transfer roll first contacts the photoconductor belt is supported by the backup roll, uneven rotation and slippage of the photoconductor belt are avoided, and color shift and color unevenness are prevented, resulting in high-quality images. Can be

[0042]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a schematic diagram of a main part of a transfer unit and an operation explanatory view for explaining a first embodiment of an image forming apparatus according to the present invention, wherein 2 is an intermediate transfer belt, 2A is a secondary transfer roll 10 at a retracted position. 2C is the belt position when the secondary transfer roll 10 is at the transfer position, 3 is the recording medium, 10A, 10A
B and 10C are positions of the secondary transfer roll 10, 10A is a retreat position, 10B is a position where the secondary transfer roll first contacts the intermediate transfer belt,
10C indicates a transfer position. Reference numeral 22 denotes a backup roll.

In this embodiment, the intermediate transfer belt 2 moves in the direction of arrow B, the backup roll 22 rotates in the direction of arrow C, and the recording medium 3 is fed in the direction of arrow D. The secondary transfer roll 10 is located at the retracted position 10A, and moves from position 10A to position 10B to position 10C during transfer, and finally contacts the backup roll 22 via the intermediate transfer belt 2 and the recording medium 3 at the transfer position 10C. The transfer voltage is applied while rotating.

In the drawing, the center of the backup roll 22 is O ₁ , the center when the secondary transfer roll is at the retreat position 10A is O ₂ , and the center when the secondary transfer roll is in the position 10B where the secondary transfer roll first contacts the intermediate transfer belt 2 is O 1. _3. Assuming that the center at the transfer position 10C is O ₄ , the secondary transfer roll 10 moves from the retreat position 10A to 10B and comes into contact with the intermediate transfer belt 2 at the position 2C. The contact position between the secondary transfer roll 10 and the intermediate transfer belt 2, that is, the position X at which the secondary transfer roll 10 first contacts the intermediate transfer belt 2 is an intermediate position when the secondary transfer roll 10 is at the retreat position 10A. The back surface of the transfer belt 2 is in a region between A and B in contact with the backup roll 22. Actually, this position X is a position slightly shifted to the point A on the downstream side in the moving direction of the intermediate transfer belt 2.

At the position 10B, the secondary transfer roll 10 starts rotating following the movement of the intermediate transfer belt 2, and then moves to the position 10C to form a transfer nip with the backup roll 22. That is, the secondary transfer roll 1
The center of 0 moves along the locus of O ₂ → O ₃ → O ₄ . At this transfer position, an angle α formed between a straight line connecting the center O ₁ of the backup roll 22 and the center O ₄ of the secondary transfer roll 10 and the surface of the intermediate transfer belt 2 when the intermediate transfer belt 2 is at the original position 2A is formed. It is set to be smaller than 90 degrees.

As a result, the intermediate transfer belt 2 is moved to the position 2C, and the recording medium 3 is brought closer to the intermediate transfer belt 2 by the above-described moving operation of the secondary transfer roll 10, and is brought into close contact with the surface of the intermediate transfer belt 2. In this state, it is carried into the nip, that is, the transfer position. That is, the intermediate transfer belt 2
The recording medium 3 and the recording medium 3 are superimposed on each other immediately before the transfer position without a gap, and the discharge does not occur unlike the related art. Therefore, a high-quality transfer image can be obtained.

FIG. 2 is a diagram showing a main part of a transfer section and an operation explanatory view for explaining a second embodiment of the image forming apparatus according to the present invention, and the same reference numerals as those in FIG. 1 correspond to the same parts. In this embodiment, the secondary transfer roll 10 for the intermediate transfer belt 2 is used.
The trajectory of the push-contact and the retreat movement is different from that of the above embodiment. That is, the transfer in which the secondary transfer roll 10 presses the backup roll 22 and the intermediate transfer belt 2 through the recording medium 3 through the position 10B where the secondary transfer roll 10 retreats from the intermediate transfer belt 2 first passes through the position 10B where the secondary transfer roll 10 comes into contact with the intermediate transfer belt 2. The locus of the center of the secondary transfer roll 10 reaching the position 10C is on a straight line.

The secondary transfer roll 10 is at the retracted position 10A during non-transfer, moves from the position 10A to the position 10B to the position 10C at the time of transfer, and finally is transferred to the backup roll 22 at the transfer position 10C and the intermediate transfer belt 2 and the recording medium. The transfer voltage is applied while being pressed and rotated via 3. As in FIG. 1, the center of the backup roll 22 is O ₁ , the center when the secondary transfer roll is at the retreat position 10A is O ₂ , and the center when the secondary transfer roll is in the position 10B where the secondary transfer roll first contacts the intermediate transfer belt 2 is O 1. _3. The center at the transfer position 10C is O ₄
Then, the secondary transfer roll 10 is moved from the retracted position 10A by 1
The intermediate transfer belt 2 is moved to the position 0B and pushed up to the position 2C and pressed against the backup roll 22. This contact position between the secondary transfer roll 10 and the intermediate transfer belt 2, that is,
The position X where the secondary transfer roll 10 first comes into contact with the intermediate transfer belt 2 is such that when the secondary transfer roll 10 is at the retracted position 10A, the back surface of the intermediate transfer belt 2 is
2 is in the region between A and B that is in contact with 2. Actually, this position X is a position slightly shifted to the point A on the downstream side in the moving direction of the intermediate transfer belt 2.

At the position 10B, the secondary transfer roll 10 starts rotating following the movement of the intermediate transfer belt 2, and then moves to the position 10C to form a transfer nip with the backup roll 22. That is, the secondary transfer roll 1
The center of 0 moves along a linear locus of O ₂ → O ₃ → O ₄ . In the course from the position 10B to the position 10C, the secondary transfer roll 10 moves while crushing the surface thereof and pushing up the intermediate transfer belt 2 from the position 2A to the position 2C.

At this transfer position, the backup roll 2
The angle α between the straight line connecting the center O ₁ of the second transfer roller 2 and the center O ₄ of the secondary transfer roll 10 and the surface of the intermediate transfer belt 2 when the intermediate transfer belt 2 is at the original position 2A is smaller than 90 degrees. Set. As a result, the intermediate transfer belt 2
C, and the recording medium 3 is placed on the secondary transfer roll 1.
In the state of being moved toward the intermediate transfer belt 2 by the above-mentioned moving operation of No. 0, it is carried into the nip, that is, the transfer position in a state of being in close contact with the surface of the intermediate transfer belt 2.

That is, the intermediate transfer belt 2 and the recording medium 3
Are superimposed without a gap immediately before the transfer position, and there is no occurrence of discharge as in the prior art. Therefore, a high-quality transfer image can be obtained. FIG. 3 is a schematic diagram illustrating the configuration of the entire image forming unit of the color image forming apparatus to which the first embodiment and the second embodiment of the present invention are applied, and is the same as FIG. 8 illustrating the configuration of the related art. The symbols correspond to the same parts.

FIG. 5 shows a transfer state in which the secondary transfer roll 10 is pressed against and rotated by the backup roll 22 via the intermediate transfer belt 2 and the recording medium 3. Reference numeral 26 denotes a conductive roll for grounding the backup roll, which is not shown in FIG. Secondary transfer roll 1 at transfer site
0 is such that the position shown in FIG. 8 is pressed against the range of the area where the back surface of the intermediate transfer belt 2 is in contact with the backup roll 22 from the retracted position without changing the position of the intermediate transfer belt 2. On the other hand, in FIG. 3, the intermediate transfer belt 2 is pressed against the upstream in the manner shown in FIGS.

Further, since the position X where the secondary transfer roll 10 first comes into contact with the intermediate transfer belt 2 is located in a region where the back surface of the intermediate transfer belt 2 is in contact with the backup roll 22, the rotational unevenness of the image carrier belt is uneven. And the occurrence of slippage is avoided. Then, the recording medium 3 includes a recording medium tray 12
From the intermediate transfer belt 2 during batch transfer.
The sheet is fed to the transfer position in a state of being in close contact with the surface of the sheet.

As a result, a high-quality transfer image can be obtained as described above. FIG. 4 is a diagram showing a main part of a transfer section and an operation explanatory view for explaining a third embodiment of the image forming apparatus according to the present invention, wherein 60 is a transfer roll, 62 is a photoreceptor belt, 72 is a backup roll, and 84 is It is a recording medium. Incidentally, 60A indicates that the transfer roll 60 is
60B is a position where the transfer roll 60 first contacts the photoreceptor belt 62, and 60C is a position where the transfer roll 60 presses and rotates against the backup roll 72 via the photoreceptor belt 62 and the recording medium 84. Indicates the transfer position.

In this embodiment, the photosensitive belt 62 moves in the direction of arrow B, the backup roll 72 rotates in the direction of arrow C, and the recording medium 84 is fed in the direction of arrow D. The transfer roll 60 is located at the retreat position 60A,
0A → position 60B → position 60C, and finally the photoreceptor belt 6 is transferred to the backup roll 72 at the transfer position 60C.
The transfer voltage is applied while rotating while being pressed against the recording medium 2 via the recording medium 84.

In the figure, the center of the backup roll 72 is O ₁ , the center when the transfer roll is at the retracted position 60A is O ₂ , and the position 60 where the transfer roll _first contacts the photosensitive belt 62 is shown.
Assuming that the center at B is O ₃ and the center at transfer position 60C is O ₄ , the transfer roll 60 is moved to the retreat position 60.
It moves from A to 60B and contacts the photoreceptor belt 62 at the position of 6C. The contact position between the transfer roll 60 and the photoreceptor belt 62, that is, the position X where the transfer roll 60 first contacts the photoreceptor belt 62 is such that when the transfer roll 60 is at the retracted position 60A, the back surface of the photoreceptor belt 62 This is in the area between AB in contact with the backup roll 72. Actually, this position X is a position slightly shifted to the point A on the downstream side in the moving direction of the intermediate transfer belt 2.

At the position 60B, the transfer roll 60 starts to rotate following the movement of the photoreceptor belt 62.
The transfer nip is formed by moving to the position C and the backup roll 72. That is, the center of the transfer roll 60 moves along the locus of O ₂ → O ₃ → O ₄ . At this transfer position, the center O ₁ of the backup roll 72 and the transfer roll 1
The angle α between the straight line connecting the center O ₄ of 0 and the surface of the photosensitive belt 62 when the photosensitive belt 62 is at the original position 62A is set to be smaller than 90 degrees.

As a result, the photosensitive belt 62 is brought to the position of 62 C, and the recording medium 84 is moved toward the photosensitive belt 62 by the above-described movement of the transfer roll 60 and is brought into close contact with the surface of the photosensitive belt 62. At the transfer position. That is, the photoreceptor belt 62
The recording medium 84 and the recording medium 84 are overlapped with each other immediately before the transfer position without a gap, and the discharge does not occur unlike the related art. Therefore, a high-quality transfer image can be obtained.

FIG. 5 is a diagram showing a main part of a transfer section and an operation explanatory view for explaining a fourth embodiment of the image forming apparatus according to the present invention. The same reference numerals as those in FIG. 4 correspond to the same parts. This embodiment differs from the third embodiment in the trajectory of the pressing and retreating movement of the transfer roll 60 against the photoreceptor belt 62. That is, from the position 60A where the transfer roll 60 is retracted from the photoreceptor belt 62, a position 6 where the transfer roll 60 first contacts the photoreceptor belt 62
0B and the backup roll 72 and the photosensitive belt 6
The locus of the center of the transfer roll 60 reaching the transfer position 60C where the transfer roll 60 is pressed against the recording medium 84 via the recording medium 84 is on a straight line.

The transfer roll 60 is in the retracted position 6 during non-transfer.
0A, position 60A → position 60B → position 6 during transfer
The transfer voltage is then applied to the backup roll 72 at the transfer position 60C while pressing and rotating the backup roller 72 via the photosensitive belt 62 and the recording medium 84. 4, the center of the backup roll 72 is O ₁ , the center of the transfer roll at the retreat position 60A is O ₂ , the center of the backup roll 72 at the first contact position 60B with the photoreceptor belt 62 is O ₃ , Assuming that the center at the transfer position 60C is O ₄ , the transfer roll 60 moves from the retracted position 60A to 60B and presses against the backup roll 72 while lifting the photoreceptor imaging belt 62 to the position of 62C. Transfer roll 60
The position X at which the transfer roller 60 first contacts the photosensitive belt 62 is the photosensitive belt 62 when the transfer roll 60 is at the retracted position 60A.
Is in the area between A and B in contact with the backup roll 72. Actually, this position X is a position slightly shifted to the point A on the downstream side in the moving direction of the photosensitive belt 62.

At the position 60B, the transfer roll 60 starts to rotate following the movement of the photoreceptor belt 62.
The transfer nip is formed by moving to the position C and the backup roll 72. That is, the center of the transfer roll 60 moves along a linear locus of O ₂ → O ₃ → O ₄ . In the course of moving from the position 60B to the position 60C, the transfer roll 60 crushes the surface of the
Move while pushing up from the position to the position of 62C.

At this transfer position, the backup roll 7
The angle α between the straight line connecting the center O ₁ of the transfer roller 60 and the center O ₄ of the transfer roll 60 and the surface of the photoreceptor belt 62 at the original position 62A is set to be smaller than 90 degrees. . As a result, the photosensitive belt 62 is
C, and the recording medium 84 is transferred to the transfer roll 60.
Is moved toward the photoreceptor belt 62 by the above-described moving operation, and is carried into the nip, that is, the transfer position in a state of being in close contact with the surface of the photoreceptor belt 62.

That is, the photosensitive belt 62 and the recording medium 8
No. 4 is superimposed immediately before the transfer position without a gap, and the discharge does not occur unlike the above-mentioned prior art. Therefore, a high-quality transfer image can be obtained. FIG. 6 shows a third embodiment of the present invention.
FIG. 11 is a schematic diagram illustrating the configuration of the entire image forming unit of a single-color image forming apparatus to which the embodiment and the fourth embodiment are applied, and the same reference numerals as in FIG. .

FIG. 7 shows that the transfer roll 60 is
And a transfer state of pressing and rotating the backup roll 72 via the recording medium 3. Transfer roll 60 at transfer site
The position shown in FIG. 10 is such that the photosensitive belt 62 is pressed against the range of the area where the back surface of the photosensitive belt 62 is in contact with the backup roll 72 from the retracted position without changing the position of the photosensitive belt 62. On the other hand, in FIG. 6, the photosensitive belt 62 is pressed against the upstream side in a position shown in FIGS.

Further, the transfer roll 60 is
Is located in a region where the back surface of the photosensitive belt 62 is in contact with the backup roll 72,
The occurrence of uneven rotation and slippage of the photoreceptor belt as the image carrier is avoided. Then, the recording medium 84 is taken out one by one from the recording medium, and is fed to the transfer position in a state of being in close contact with the surface of the photoreceptor belt 62 at the time of transfer.

As a result, a high-quality transfer image can be obtained as described above. FIG. 7 is a schematic diagram illustrating the configuration of the entire image forming unit of a color image forming apparatus to which the third embodiment and the fourth embodiment of the present invention are applied, and is a colorized version of the image forming apparatus of FIG. The same reference numerals as those in FIG. 11 for explaining the configuration of the conventional technique correspond to the same parts.

FIG. 9 shows that the transfer roll 60 is
And a transfer state of pressing and rotating the backup roll 72 via the recording medium 3. Transfer roll 60 at transfer site
The position shown in FIG. 10 comes into contact with the range of the area where the back surface of the photosensitive belt 62 is in contact with the backup roll 72 from the retracted position without changing the position of the photosensitive belt 62. On the other hand, in FIG. 7, the photosensitive belt 62 is pressed against the upstream side in the manner shown in FIGS.

Further, the transfer roll 60 is
Is located in a region where the back surface of the photosensitive belt 62 is in contact with the backup roll 72,
The occurrence of uneven rotation and slippage of the photoreceptor belt as the image carrier is avoided. Then, the recording medium 84 is taken out one by one from the recording medium, and is fed to the transfer position in a state of being in close contact with the surface of the photoreceptor belt 62 at the time of transfer.

As described above, according to each of the above embodiments, it is possible to bring the recording medium into close contact with the image carrier belt such as the intermediate transfer belt or the photoreceptor belt in the nip where the transfer electric field acts, and the upstream of the nip This prevents transfer failures caused by electric discharge due to the formation of a gap between the image carrier belt and the recording medium, and also allows the secondary transfer roll or the transfer roll to carry an image on an intermediate transfer belt or a photoreceptor belt. Since the position where the belt first comes in contact with the body is supported by the backup roll, uneven rotation and slippage of the image carrier belt are avoided, and color shift and color unevenness are prevented, so that a high-quality image can be obtained.

[0070]

As described above, according to the present invention,
In the transfer section, no gap is formed between the intermediate transfer belt or the photosensitive belt, which is an endless belt-shaped image carrier, and the recording medium, and the secondary transfer roll is attached to the image carrier, such as the intermediate transfer belt or the photosensitive belt. Alternatively, a high-quality image without transfer unevenness is provided by providing a novel transfer mechanism that does not exert a load variation on the drive system of the image carrier such as the intermediate transfer belt or the photoreceptor belt when pressing the transfer roll. A forming device can be provided.

[Brief description of the drawings]

FIG. 1 is a main part configuration diagram and an operation explanatory diagram of a transfer unit for explaining a first embodiment of an image forming apparatus according to the present invention.

FIGS. 2A and 2B are a main part configuration diagram and an operation explanatory diagram of a transfer section for explaining a second embodiment of the image forming apparatus according to the present invention; FIGS.

FIG. 3 is a schematic diagram illustrating a configuration of an entire image forming unit of a color image forming apparatus to which the first embodiment and the second embodiment of the present invention are applied.

FIG. 4 is a main part configuration diagram and an operation explanatory diagram of a transfer unit for explaining a third embodiment of the image forming apparatus according to the present invention.

FIGS. 5A and 5B are a main part configuration diagram and an operation explanatory diagram of a transfer unit for explaining a fourth embodiment of the image forming apparatus according to the present invention; FIGS.

FIG. 6 is a schematic diagram illustrating a configuration of an entire image forming unit of a monochromatic image forming apparatus to which a third embodiment and a fourth embodiment of the present invention are applied.

FIG. 7 is a schematic diagram illustrating a configuration of an entire image forming unit of a color image forming apparatus to which a third embodiment and a fourth embodiment of the present invention are applied.

FIG. 8 is an explanatory diagram of a main configuration of an image forming apparatus using an intermediate transfer belt.

9 is an enlarged schematic diagram of a secondary transfer section of the image forming apparatus shown in FIG.

FIG. 10 is a schematic diagram of a main part of an image display device that transfers a toner image formed on a photosensitive belt to a recording medium by a transfer roll.

FIG. 11 is a schematic diagram of a main part of a color image display device in which toner images of a plurality of colors are superposedly formed on a photosensitive belt and then transferred to a recording medium by a transfer roll.

FIG. 12 is an enlarged schematic diagram of a transfer unit or a secondary transfer unit in the image forming apparatus of the type described in FIG. 10 or FIG.

FIG. 13 is an enlarged view of the secondary transfer section shown in FIG.

14 is an explanatory diagram of a cause of occurrence of transfer failure in a gap between an intermediate transfer belt formed immediately before a nip formed by the intermediate transfer belt and a backup roll illustrated in FIG. 13 and a recording medium.

FIG. 15 is an explanatory diagram of a relationship between a gap between an intermediate transfer belt or a photoreceptor belt and a recording medium and a discharge electric field in a transfer unit according to the Passion rule.

FIG. 16 is a schematic diagram illustrating the presence or absence of a load change on the belt driving roll due to a difference in the direction of contact of the transfer roll with the intermediate transfer belt or the photosensitive belt.

[Explanation of symbols]

1 ··· photoconductor drum, 2 ··· intermediate transfer belt,
3 ··· Recording medium, 4 ··· Charging device, 5 ···
Black (Bk) developing device, 6... Yellow (Y) developing device, 7... Magenta (M) developing device, 8... Sian (C) developing device, 9. Corona discharger as a vessel, 10... Secondary transfer roll, 11.
.Feed roller, 12... Recording medium tray, 14
····· Conveying belt of recording medium, 15 ··· Fixing device, 16 ··· Intermediate transfer belt cleaner, 17 ···
··· Belt position sensor, 18 ··· Photosensitive drum cleaner, 9 ··· Regi roll, 21 ··· Belt drive roll, 22 ··· Backup roll, 23
... Tension roll, 24 ... Driving roll, 2
5 Secondary transfer roll cleaner 52 Charger 53 Laser beam 54-57 Yellow, magenta, Sian, and black developing devices 5
8 ··· Belt cleaner, 60 ··· Transfer roll, 61 ··· Roll cleaner, 62 ··· Photoconductor belt, 71 ··· Followed roll, 72 ··· Backup roll, 74 .... Drive roll, 81 ...
A conveyance mechanism, 82, a fixing device, 83, a registration roll, 84, a recording medium, 54 to 57, a developing device for yellow, magenta, Sian, and black.

Claims (3)

[Claims] 1. An endless belt-shaped image carrier, and a driving roll, a driven roll, and a backup roll that are disposed inside a peripheral circuit of the endless belt-shaped image carrier and are supported by the back of the endless belt-shaped image carrier. An endless belt-shaped image carrier driving mechanism composed of a plurality of rolls such as a roll or a tension roll, and a transfer for holding the endless belt-shaped image carrier between the endless belt-shaped image carrier and the backup roll. An image forming apparatus including at least a transfer roll capable of moving a position and a non-transfer position retreating from the endless belt-shaped image carrier, wherein the transfer roll moves between the transfer position and the non-transfer position. The position where the transfer roll first comes into contact with the endless belt-shaped image carrier between the trajectories, and the back surface of the endless belt-shaped image carrier comes into contact with the backup roll. A line connecting the center of the transfer roll and the center of the backup roll at a transfer position where the transfer roll presses the backup roll via the endless belt-shaped image carrier, and the transfer roll An image forming apparatus, wherein an angle between the endless belt and the surface of the endless belt-shaped image carrier when retracted to a non-transfer position is smaller than 90 degrees. 2. The image according to claim 1, wherein the endless belt-shaped image carrier is an intermediate transfer belt that carries a primary-transferred toner image and secondary-transfers the toner image onto a recording medium. Forming equipment. 3. The image forming apparatus according to claim 1, wherein the endless belt-shaped image carrier is a photosensitive belt that carries a toner image obtained by developing a latent image corresponding to an image signal.