JP3346063B2 - Image transfer device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image transfer apparatus in an image forming apparatus using an electrophotographic system, and more particularly, to a method of transferring a toner image to a belt-shaped secondary transfer member once.
The present invention relates to an image transfer device configured to transfer a toner image from a secondary transfer member to a sheet.

[0002]

2. Description of the Related Art An image forming apparatus using an electrophotographic method, such as a copying machine, a facsimile, and a printer, is disclosed in, for example, Japanese Patent Application Laid-Open No. 62-20667.
A toner image is formed on the surface of a photoreceptor drum serving as an image carrier, and the toner image is once electrostatically transferred to an endless belt-shaped secondary transfer member, and is to be transferred from the secondary transfer member. There is a configuration in which electrostatic transfer is performed on a sheet. The method using such a secondary transfer member is mainly used for forming a color image.

[0003] This device is, for example, yellow, magenta,
A multicolor developing device such as cyan and black is provided, and a single color toner image is formed on the photosensitive drum for each developing device during one rotation, and the toner image is secondary Primary transfer to transfer body. Such a process is performed for each color, the toner images of each color are superimposed on the secondary transfer body, and the combined color image is secondarily transferred collectively to a sheet. In order to transfer the color image of the electrostatically synthesized toner to the sheet by contacting the sheet with the secondary transfer body only once finally,
There is an advantage that troubles such as jamming and displacement during sheet conveyance can be reduced.

FIG. 4 shows an image forming apparatus using a conventional secondary transfer member. In FIG. 4, reference numeral 1 denotes a photosensitive drum as an image carrier. Although not shown, a charger, an exposure unit, and a developing unit are arranged around the photosensitive drum 1. Then, as the photosensitive drum 1 rotates as shown by the arrow, the surface of the photosensitive drum 1 is uniformly charged by the charger, and a latent image is formed on the surface by exposure means, and the latent image is formed by the developing device. An image is formed by attaching toner T to the image.

An endless belt-shaped secondary transfer member 2 is brought into contact with the photosensitive drum 1. This secondary transfer body 2 is
It is wound around pulleys 12, 13, 14, and 15 and is rotated around pulleys 12 to 15 as shown by arrows in synchronization with the rotation of the photosensitive drum 1. A corona discharger (electrostatic transfer means) 11 is disposed inside the secondary transfer member 2, that is, on the side opposite to the photosensitive drum 1 of the secondary transfer member. The corona discharger 11 discharges by applying a voltage having a polarity opposite to the charging polarity of the toner T on the photosensitive drum 1, whereby the toner T is attracted and adheres to the secondary transfer member 2. Then, by repeating the formation of the image of the toner T and the transfer to the secondary transfer member 2 for each rotation of the photosensitive drum 1, images of a plurality of colors are superimposed on the surface of the secondary transfer member 2. , A color image is obtained.

On the other hand, the sheet 5 to be transferred is stored in a paper feed tray 4, taken out of the sheet by a feed roll 3, passed through a transport path 16, and
It is transported between the secondary transfer member 2 and the bias roll 8. A voltage having a polarity opposite to the charging polarity of the toner T is applied to the bias roll 8. By the discharge of the bias roll 8, the combined color image is attracted and adheres to the sheet 5.

[0007] The sheet 5 on which the toner T has been transferred and passed between the secondary transfer body 2 and the bias roll 8 in this manner is placed on the transport belt 7 and transported toward the fixing device 20. You. Then, in the fixing device 20, the toner T
Is fixed on the sheet 5. Reference numeral 6 denotes a peeling nail. The tip of the peeling claw 6 can be moved toward and away from the secondary transfer member 2.
Is separated from the secondary transfer member 2.

[0008]

FIG. 5 is an enlarged view showing the vicinity of a transfer area from the photosensitive drum 1 to the secondary transfer body 2. FIG. Here, the toner T is attracted to the secondary transfer body 2 by the discharge from the corona discharger 11, but the electric field from the corona discharger 11 always has a certain extent.
Therefore, before the photosensitive drum 1 completely contacts the secondary transfer member 2, the toner T is charged in the region (gap region) G where there is a gap between the photosensitive drum 1 and the secondary transfer member 2. Transfer to the transfer body 2 starts.

Here, there is a positional deviation between the peripheral surfaces of the photosensitive drum 1 and the secondary transfer member 2. Also, not all the toners T start to be transferred at once, but the transfer start timing of the toner T also differs due to the difference in the charge amount. Therefore, the transferred image of the toner T is disturbed, or the transfer efficiency is reduced in the contact area between the photosensitive drum 1 and the secondary transfer body 2 where transfer is desired. As a result, image quality has been degraded.

In order to solve this problem, Japanese Patent Laid-Open No. 4-208 is disclosed.
According to the invention described in Japanese Patent Application Publication No. 970, a bias member is provided in a gap region G between the photosensitive drum and the secondary transfer member, and a voltage having the same polarity as that of the toner is applied to the bias member. An attempt is made to prevent the upper toner from scattering toward the secondary transfer member. However, in this case, once the toner has passed through the bias member, there is a problem that the toner starts to be transferred to the secondary transfer member before the photosensitive drum completely contacts the secondary transfer member. .

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has as its object to provide an image transfer apparatus for preventing image disturbance at the start of transfer of a toner image to a secondary transfer member. I do.

[0012]

In order to solve the above problems, according to the present invention, there is provided an image carrier having a toner image formed on a surface thereof, and an image carrier arranged so as to be in contact with the image carrier. A belt-like secondary transfer member that carries a sheet from which a toner image is to be transferred from the support member, and a transfer electric field that is disposed on a side of the secondary transfer member opposite to the image carrier. An electrostatic transfer unit for transferring the image of the toner from the image carrier to the secondary transfer body; and a side opposite to the image carrier of the secondary transfer body, and a traveling direction of the secondary transfer body. And an early transfer prevention unit disposed upstream of the electrostatic transfer unit, pressing the secondary transfer member against the image carrier, and applying a bias voltage having the same polarity as the toner. The image carrier of the secondary transfer member
On the opposite side and in the direction of travel of the secondary transfer body,
Disposed downstream of the electrotransfer unit, and
While pressing against the image carrier, the toner having the same polarity as the toner
A residual toner transfer preventing means to which an ass voltage is applied .

[0013]

In the present invention, a bias voltage having the same polarity as that of the toner is applied to the early transfer preventing means. The early transfer prevention means is disposed on the side opposite to the image carrier of the secondary transfer body and on the upstream side of the electrostatic transfer means in the traveling direction of the secondary transfer body. It is possible to cancel the transfer electric field of the electrostatic transfer means upstream of the middle of the means. Therefore, it is possible to prevent the transfer from starting early. In addition, the present invention
In other words, the toner of the same polarity as the toner
An ass voltage is applied. The residual toner transfer means is
The opposite side of the image carrier from the image carrier, and the traveling direction of the secondary transfer body
Because it is located downstream of the electrostatic transfer means in
Downstream from the middle between the electrostatic transfer unit and the residual toner transfer unit
Then, the transfer electric field of the electrostatic transfer means is canceled. But
Therefore, the image is not attracted to the transfer electric field of the electrostatic transfer means.
Toner remaining on the carrier adheres to the secondary transfer body
Can be prevented.

Further, when the early transfer preventing means presses the secondary transfer member against the image carrier, the image carrier and the secondary transfer member are brought into contact without any gap downstream of the early transfer preventing means. Therefore, when the transfer electric field thus transfer the electrostatic transfer means is started, there is no deviation between the image carrier and the secondary transfer member. Therefore, it is possible to prevent the disturbance of the transferred toner image. In addition,
In the invention of the third aspect, the residual toner transfer preventing means is used for secondary transfer.
Means for preventing early transfer by pressing the body against the image carrier
Secondary transfer body, from to the residual toner transfer prevention means
It can be brought into contact with the image carrier without any gap. Therefore, stable
The transfer can be performed in a state where the transfer is performed.

[0015]

【Example】

(1) First Embodiment A. Configuration examples below, with reference to the drawings will be described embodiments of the present invention. First, FIG. 1 is a schematic diagram of an image forming apparatus provided with an image transfer device according to a first embodiment of the present invention. In the drawings, parts corresponding to the respective parts in FIGS. 4 and 5 are denoted by the same reference numerals, and description thereof will be omitted. In this embodiment, the outer side of the secondary transfer member 2, that is, the side opposite to the photosensitive drum (image carrier) 1, and the upstream of the corona discharger 11 (electrostatic transfer means) in the traveling direction of the secondary transfer member 2. On the side, a bias roll (early transfer prevention means) 22 is disposed.

The bias roll 22 is formed in a cylindrical shape from a conductive material or a semiconductive material, and a bias voltage having the same polarity as that of the toner T on the photosensitive drum 1 is applied. In this embodiment, the toner T is negatively charged, and a negative bias voltage is applied to the bias roll 22 from the power supply 24 so that the toner T is not sucked. Corona discharger 11
, A positive voltage is applied from the power supply 26 and the toner T
Is sucked toward the secondary transfer member 2.

The bias roll 22 is urged by a spring (not shown) to press the secondary transfer member 2 against the photosensitive drum 1. As is clear from FIG. 1, the secondary transfer body 2 is pushed rightward by the bias roll 22 and the pulley 12, so that the secondary transfer body 2 is moved from the bias roll 22 to a position where the secondary transfer body 2 has passed the corona discharger 11. It is in contact with the photosensitive drum 1 without any gap.

In this embodiment, the diameter of the photosensitive drum 1 is 200 mm, and the diameter of the bias roll 22 is 20 mm. Then, the secondary transfer member 2 stretched between the pulleys 12 and 13 and forming the tangent plane of the photosensitive drum 1 is slightly pushed rightward by the bias roll 22 so that the secondary transfer member 2 and the photosensitive member The length of the area in contact with the drum 1 was about 25 mm. The width of the corona discharger 11 is 25 mm, and the distance from the corona discharger 11 to the bias roll 22 is 5 mm.
mm.

The voltage applied to the corona discharger 11 was 5 to 8 KV. The reason why the distance from the corona discharger 11 to the bias roll 22 was set to 5 mm was that the current when the corona discharger 11 was discharged was
To prevent the voltage value of the bias roll 22 from fluctuating. The voltage value applied to the bias roll 22 will be described later.

B. In this embodiment, as the photosensitive drum 1 rotates as indicated by the arrow, the surface of the photosensitive drum 1 is uniformly charged by the charger, and the latent image is charged on the surface by the exposure means. Is formed, and a toner T is adhered to the latent image by a developing device to form a visible image.

The toner T passes through the bias roll 22 with the rotation of the photosensitive drum 1, and the corona discharger 11
And is attracted and adhered to the secondary transfer body 2 by the transfer electric field of the corona discharger 11. Here, since a bias voltage having the same polarity as the toner T is applied to the bias roll 22, the corona discharger 11 and the bias roll 22
The electric field for transfer of the corona discharger 11 is canceled on the upstream side of the middle of the above. Thus, it is possible to prevent the transfer of the toner from being started early.

The bias roll 22 is used for the secondary transfer member 2.
Is pressed against the photoconductor drum 1 so that the secondary transfer body 2 contacts the photoconductor drum 1 without gaps from the bias roll 22 to a position where the photoconductor drum 1 has passed. Therefore, when the transfer is started by the transfer electric field of the bias roll 22, there is no displacement between the photosensitive drum 1 and the secondary transfer body 2. Therefore, as shown in FIG. 2, the transfer is not started in a state where there is a gap between the photosensitive drum 1 and the secondary transfer body 2, and the transferred toner T image is disturbed. Can be prevented.

The toner image thus transferred to the secondary transfer member 2 passes through the photosensitive drum 1 and then reaches the bias roll 8 by rotation of the secondary transfer member 2. A voltage having a polarity opposite to the charging polarity of the toner T is applied to the bias roll 8, and the image of the toner T is attracted by the discharge of the bias roll 8 and adheres to the sheet 5.
Thus, the secondary transfer of the toner T is performed. In this embodiment, every time an image of one color toner T is formed on the secondary transfer member 2, this image can be secondarily transferred from the secondary transfer member 2 to the sheet 5, or the secondary transfer member can be used. After a color image is obtained by superimposing a plurality of color toner images on the sheet 2, the color image can be secondarily transferred to the sheet 5 from the secondary transfer body.

The sheet 5 to which the toner T has been transferred is peeled off by the peeling claw 6, is placed on the transport belt 7, and is transported toward the fixing device 20. Then, the fixing device 20
, The toner T is fixed on the sheet 5.

FIG. 2 shows the secondary transfer member 2 in this embodiment.
The experimental results of changing the bias voltage applied to the secondary transfer member 2 and examining the amount of toner T scattered on the secondary transfer member 2 are shown. The applied voltage was a DC voltage. In this experiment, a plurality of determination samples having different amounts of scattered toner were prepared, and the sheet on which the image was formed and these samples were visually compared to determine the amount of scattered toner on the sheet on which the image was formed. Was evaluated as appropriate or unsuitable for use.
Here, only a DC voltage was applied so as not to cause a voltage change. The toner used was a positively charged toner having a standard particle size of 7 μm. As shown in FIG. 2, when the bias voltage applied to the secondary transfer body 2 is 250 V or less,
The amount of toner scattered was small, and it was found to be suitable for use.

[0026] (2) Second Embodiment C. Diagram 3 embodiment illustrates a second embodiment. In this embodiment, a bias roll 32 is provided in addition to the first embodiment. The bias roll 32 is located outside the secondary transfer member 2, that is, on the side opposite to the photosensitive drum (image carrier) 1, and on the downstream side of the corona discharger 11 (electrostatic transfer unit) in the traveling direction of the secondary transfer member 2. Are located in The bias roll 32 is formed in a cylindrical shape from a conductive material or a semiconductive material, similarly to the bias roll 22, and a bias voltage having the same polarity as that of the toner T on the photosensitive drum 1 is applied. .
That is, the same negative bias voltage as that of the bias roll 22 is applied to the bias roll 32 from the power supply 34.

The bias roll 32 is urged by a spring (not shown) to press the secondary transfer member 2 against the photosensitive drum 1. As is clear from FIG. 3, the secondary transfer body 2 is pushed to the right side by the bias rolls 22 and 32, so that the secondary transfer body 2 is wider than in the first embodiment.
From the bias roll 22 to the bias roll 32, the secondary transfer body 2 is in contact with the photosensitive drum 1 without any gap.

In this embodiment, the diameter of the bias roll 32 is set to 20 mm. By slightly pushing the secondary transfer body 2 rightward with the bias rolls 22 and 32, the length of the area where the secondary transfer body 2 and the photosensitive drum 1 are in contact was set to about 35 mm. The distance from the corona discharger 11 to the bias roll 32 was 5 mm. The distance from the corona discharger 11 to the bias roll 32 is 5 m
The reason for setting m is to prevent the current when the corona discharger 11 discharges from flowing into the bias roll 32 and to prevent the voltage value of the bias roll 32 from fluctuating. The dimensions of the other members are the same as in the first embodiment.

D. Operation of Embodiment In this embodiment, a large area where the photosensitive drum 1 and the secondary transfer member 2 come into contact with no gap can be ensured by the bias roll 32. Therefore, it is possible to perform the transfer in a more stable state than in the first embodiment.

Further , the same as the toner T is applied to the bias roll 32.
Since the bias voltage having the polarity is applied, the electric field for transfer of the corona discharger 11 is canceled on the downstream side of the middle between the corona discharger 11 and the bias roll 32. When the bias roll 32 is not provided, depending on the charged state of the toner T, the toner T remains on the photosensitive drum 1 without being attracted to the transfer electric field of the corona discharger 11 when approaching the corona discharger 11 most. And the residual toner T
May be attracted and adhere to the secondary transfer member 2 to induce image disturbance.

[0031] However, according to the second embodiment, since the bias roll 32 bias voltage of the toner T and the same polarity is applied, and this <br/> residual toner T adheres to the secondary transfer member 2 There is no. Therefore, it is possible to further prevent the disturbance of the transferred toner T image. That is, the bias roll 32 serves as a transfer prevention unit for the residual toner.

(3) Modification In the above-described embodiment, the corona discharger 11 is used as an electrostatic transfer unit for transferring the toner T on the photosensitive drum 1 to the secondary transfer body 2. The present invention is not limited to this, and may be a bias roll to which a bias voltage having a polarity opposite to the charging polarity of the toner T on the photosensitive drum 1 is applied.

[0033]

As described above, according to the image transfer apparatus of the present invention, the early transfer preventing means is provided on the side opposite to the image carrier of the secondary transfer body and in the traveling direction of the secondary transfer body. Since it is arranged on the upstream side of the electrostatic transfer unit, it is possible to cancel the transfer electric field of the electrostatic transfer unit upstream of the middle between the electrostatic transfer unit and the early transfer prevention unit.
Therefore, it is possible to prevent the transfer from starting early. In addition, the residual toner transfer preventing means is
The opposite side of the image carrier from the image carrier, and the traveling direction of the secondary transfer body
Because it is located downstream of the electrostatic transfer means in
Lower than the middle between the electrostatic transfer means and the residual toner transfer prevention means
On the downstream side, the transfer electric field of the electrostatic transfer means can be canceled
Noh. Therefore, residual toner adheres to the secondary transfer body
Can be prevented. Further, when the early transfer preventing means presses the secondary transfer body against the image carrier, the image carrier and the secondary transfer body are contacted with no gap downstream of the early transfer preventing means. Therefore, when the transfer electric field thus transfer the electrostatic transfer means is started, there is no deviation between the image carrier and the secondary transfer member. Therefore, it is possible to prevent the disturbance of the transferred toner image. As described above, the transfer start time and the transfer end time of the toner image on the secondary transfer body can be optimized, the transfer state can be stabilized, and the image can be prevented from being disturbed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating an image forming apparatus including an image transfer device according to a first embodiment of the present invention.

FIG. 2 is a graph showing a relationship between a voltage applied to an early transfer prevention unit (bias roll) and a degree of toner scattering in the first embodiment.

FIG. 3 is a schematic diagram illustrating an image forming apparatus provided with an image transfer device according to a second embodiment of the present invention.

FIG. 4 is a schematic view of an image forming apparatus provided with a conventional image transfer device.

FIG. 5 is an enlarged view showing the vicinity of a transfer area from a photosensitive drum to a secondary transfer body for explaining a problem at the time of transfer of a conventional image transfer apparatus.

[Explanation of symbols]

T toner, 1 photoconductor drum (image carrier), 2nd transfer body, 5 sheets, 11 corona discharger (electrostatic transfer means), 22 bias roll (early transfer prevention means), 3
2 bias roll

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Taku Fukuhara 2274 Hongo, Ebina-shi, Kanagawa Fuji Xerox Co., Ltd. (56) References JP-A-2-179670 (JP, A) JP-A-5-273872 ( JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G03G 15/16

Claims (1)

(57) [Claims] An image bearing member having a surface on which a toner image is formed; and a belt-shaped member arranged to be in contact with the image bearing member and carrying a sheet from which the toner image is to be transferred from the image bearing member. A secondary transfer member, disposed on the side opposite to the image carrier of the secondary transfer member,
An electrostatic transfer unit that transfers the toner image from the image carrier to the secondary transfer body by generating a transfer electric field; and an opposite side of the secondary transfer body to the image carrier, and A bias voltage having the same polarity as that of the toner is applied while the secondary transfer body is disposed on the upstream side of the electrostatic transfer unit in the traveling direction of the secondary transfer body and presses the secondary transfer body against the image carrier.
Was the early transfer prevention means, the side opposite to the image bearing member of the secondary transfer member, and the two
The downstream side of the electrostatic transfer unit in the traveling direction of the next transfer body
And presses the secondary transfer member against the image carrier.
At the same time, a bias voltage having the same polarity as the toner is applied.
An image transfer device comprising: a residual toner transfer preventing means .