JPH0962111A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten throughput time and to improve the cleaning performance by cleaning away residual toner by means of an intermediate transfer roller which is positioned at downstream side from a transfer nip part where toner image is transferred. SOLUTION: A transfer bias is applied to the intermediate transfer roller 6 provided with a cleaning roller 21 so as to be freely away from and nearer to the roller 6. In the transfer nip part, a toner image is transferred to transfer paper P from the intermediate roller 6 and, immediately after that, the removal of the residual toner sticking to the intermediate transfer roller 6 is started by the cleaning roller 21. Thus, the transfer and cleaning are carried out almost in parallel with each other. Also, by generating a potential difference between the intermediate transfer roller 6 and cleaning roller 21, the toner is removed from the transfer roller 6 to the cleaning roller 21 by the potential difference.

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 which, for example, temporarily transfers a toner image formed on an image bearing member to an intermediate transfer member and then finally transfers it to a recording material.

[0002]

2. Description of the Related Art Conventionally, as an image forming apparatus having an intermediate transfer member, for example, there is a color image forming apparatus as shown in FIG. This color image forming apparatus includes a photosensitive drum 1 as an image carrier, and the photosensitive drum 1 is indicated by an arrow R1 in the figure.
While being rotated in the same direction, it is uniformly charged by the charging roller 2, an electrostatic latent image is formed on the photosensitive drum 1 by the exposure device 3, and then a first color (magenta) is generated by the first developing device 5M of the developing device 5. Toner is attached to the electrostatic latent image.

In this case, the visible image of the first color (toner image)
Since the second developing device 5C, the third developing device 5Y, and the fourth developing device 5B are in the operation-off state, the intermediate transfer which is an intermediate transfer member is not affected by these and is accompanied by the rotation of the photosensitive drum 1. The transfer nip portion where the roller 6 and the photosensitive drum 1 contact each other is reached. Then, the toner image of the first color is formed in the transfer nip portion by the voltage applied to the cylindrical core metal 6a of the intermediate transfer roller 6 by the power source 7a, that is, the voltage 7a having the opposite polarity to the toner of the first color. By the electric field,
The image is transferred onto the intermediate transfer roller 6.

The intermediate transfer roller 6 is made of a solid or foamed elastic material made of silicon rubber, Teflon rubber, chloroprene rubber, urethane rubber, EPDM or the like on the core metal 6a, and this elastic material is made of carbon or metal. which was coated with a resistive elastic layer 6b in which regulate the resistivity powder and dispersed, the inside resistance elastic layer 6b is 10 ⁵ to 10
^It has a volume resistivity of ¹¹ Ω · cm.

When the transfer of the toner image of the first color is completed,
The residual toner on the surface of the photosensitive drum 1 is removed and cleaned by the cleaning device 9, and the image forming process of the second color (cyan) is started. In the second color process, only the second developing device 5C operates, and the other developing devices 5M, 5Y, 5B are in the operation-off state.
The color toner image is intermediately transferred onto the intermediate transfer roller 6. Thereafter, similarly, the toner images of the third color (yellow) and the fourth color (black) are sequentially intermediate-transferred onto the intermediate transfer roller 6, and the toner images of four colors are superimposed.

Next, the transfer paper P as a recording material is taken out from the cassette 10 one by one by the paper feed roller 11,
After being transferred through the transfer guide 12, it is carried into a transfer nip portion formed between the photosensitive drum 1 and the intermediate transfer roller 6. A voltage having the same polarity as the toner is supplied to the core metal 6a of the intermediate transfer roller 6 in synchronization with the transfer of the transfer paper P into the transfer nip portion.
The toner images of the first to fourth colors on the intermediate transfer roller 6 are collectively transferred onto the transfer paper P by the application. FIG. 7 shows a state in which the toner images intermediately transferred to the intermediate transfer roller 6 are collectively transferred to the transfer paper P.

Thereafter, the transfer paper P carrying the unfixed color image is carried out from the transfer nip portion, and is conveyed by the transfer guide 13.
The fixing device 15 is reached via. Then, the unfixed color image is heated and pressed by the fixing device 15 to become a fixed image.

On the other hand, after the transfer of the toner image onto the transfer sheet P, the cleaning bias voltage, which is a DC bias having the same polarity as the toner, is applied to the core metal 6a of the intermediate transfer roller 6 from the power source 7c, so that the intermediate transfer is performed. The untransferred (residual) toner on the roller 6 is returned to the photosensitive drum 1 and collected by the cleaning device 9.

As described above, according to the sequence shown in FIG. 8, the first developing device 5M, the second developing device 5C, the third developing device 5Y,
A bias is applied to each of the fourth developing device 5B and the intermediate transfer roller 6. The timing at which this bias is applied is such that the primary transfer bias is applied to the intermediate transfer roller 6 while the developing bias is sequentially applied to the four developing devices 5M, 5C, 5Y, and 5B. The toner image is transferred to the intermediate transfer roller 6. Then, after the final transfer from the intermediate transfer roller 6 to the transfer paper P, the intermediate transfer roller 6 is cleaned by the cleaning bias.

[0010]

However, in the above-mentioned conventional image forming apparatus, the toner remaining on the intermediate transfer roller 6 is cleaned after the secondary transfer from the intermediate transfer roller 6 to the transfer paper P. Even in the case of a single color, it takes time to clean the intermediate transfer roller 6, and there is a problem that the throughput time cannot be shortened.

When a large amount of toner remains on the intermediate transfer roller 6 as in a color image, or when the toner remaining on the intermediate transfer roller 6 contains a large amount of reversal toner, the intermediate transfer roller 6 may be used. There is a possibility that the cleaning cannot be sufficiently performed only by rotating 6 once.

Therefore, the present invention has been made in order to solve the above-mentioned problems, and while the toner image is finally transferred from the intermediate transfer member to the recording material, the intermediate transfer member downstream of the transfer nip portion is formed. It is an object of the present invention to provide an image forming apparatus in which the residual toner is cleaned to reduce the throughput time and improve the cleaning performance.

[0013]

In order to achieve the above object, an image forming apparatus according to the present invention transfers a toner image formed on an image bearing member to an intermediate transfer member and transfers the toner image at a transfer nip portion. A cleaning member configured to transfer from the intermediate transfer member to a recording material, which removes residual toner on the intermediate transfer member downstream of the transfer nip portion in the moving direction of the intermediate transfer member. Is provided.

Preferably, the cleaning member is an insulating roller member having a surface roughness Rz of Rz ≦ 5 μm.

Further preferably, the cleaning member is an elastic roller having a volume resistivity of 10 ⁵ to 10 ¹¹ Ω · cm.

Still more preferably, the cleaning member has a power source for applying a bias voltage, which is a DC voltage having a polarity opposite to that of the toner and an AC voltage superimposed thereon, in response to contact with the intermediate transfer member.

[Operation] Based on the above configuration, immediately after the transfer bias is applied to the intermediate transfer member provided with the cleaning member so as to be freely contactable and separable, and the toner image is transferred from the intermediate transfer member to the recording material at the transfer nip portion. Then, the toner remaining on the intermediate transfer member is removed by the cleaning member. This can reduce the throughput time.

Particularly, as the cleaning member, the surface roughness R
By using an insulating roller member having z of Rz ≦ 5 μm, the intermediate transfer member can be uniformly cleaned.

Further, an elastic roller having a volume resistivity of 10 ⁵ to 10 ¹¹ Ω · cm is used as the cleaning member, and a bias voltage in which an AC voltage is superimposed on a DC voltage having a polarity opposite to that of the toner is applied to the cleaning member. Therefore, the cleaning performance on the intermediate transfer member can be remarkably improved.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. <First Embodiment> FIG. 1 is a schematic vertical sectional view showing a first embodiment of an image forming apparatus according to the present invention, and FIG.
FIG. 3 is a sequence diagram illustrating the operation of FIG. 1.

In FIG. 1, the color image forming apparatus uniformly charges the photosensitive drum 1 around the photosensitive drum 1 as an image carrier rotating in the direction of arrow R1 in order along the rotation direction of the photosensitive drum 1. A charging roller 2 which is a charging member,
An exposure device 3 that irradiates a laser beam on the basis of an image signal corresponding to document information to form an electrostatic latent image on the photosensitive drum 1, and a developing device that attaches toner to the electrostatic latent image to form a toner image. The device 5, the intermediate transfer roller 6 which is an intermediate transfer member on which the toner image formed on the photosensitive drum 1 is primarily transferred, and the cleaning device 9 for removing the toner remaining on the surface of the photosensitive drum 1 after the transfer. Then, the cassette 10 for accommodating the transfer paper P, the paper feed roller 11 for taking out the transfer paper P one by one from the cassette 10, and the transfer paper P taken out and conveyed by the paper feed roller 11 from the photosensitive drum 1 A transfer guide 12 that carries in and guides the toner image to the intermediate nip portion in synchronization with the transfer of the toner image to the intermediate transfer roller 6.
And the rotation of the intermediate transfer roller 6 from the transfer nip portion in which the photosensitive drum 1 and the intermediate transfer roller 6 are in contact with each other, and the paper feed guide 13 that conveys the transfer paper P on which the toner image is transferred in the transfer nip portion to the fixing device 15. A cleaning device 20 disposed downstream of the intermediate transfer roller 6 in contact with the intermediate transfer roller 6
(See FIG. 3).

The photosensitive drum 1 is formed to have a diameter of φ = 30, and the intermediate transfer roller 6 has a urethane rubber elastic layer 6b on the surface of a solid rubber base layer of NBR on a core metal 6a of a drum base made of aluminum. Is formed by coating. In this case, the volume resistivity of the intermediate transfer roller 6 is 1.0.
× is 10 ⁶ Ω · cm, the toner to be used (using the same toner in the following embodiments) using the negatively charged toner single component non-magnetic. The intermediate transfer roller 6 has an outer circumference 35.
A 0 cm one was used.

The developing device 5 includes a first developing device 5M,
Second developing device 5C, third developing device 5Y and fourth developing device 5B
One of the developing devices 5M, 5C, 5Y and 5B is selectively operated by an image signal from the exposure device 3 to form a predetermined color image on the photosensitive drum 1.

The cleaning device 20 is provided with a cleaning roller (cleaning member) 21, which is provided so as to be capable of coming into contact with and separated from the intermediate transfer roller 6 by a driving means (not shown), a urethane blade 22 for scraping off the toner on the cleaning roller 21, and a cleaning. The cleaning roller 21 is provided with a destaticizing brush 23 for destaticizing the roller 21 and a housing 24 for accommodating toner. The cleaning roller 21 has a surface roughness Rz of Rz ≦ 5 μm by coating a polycarbonate resin layer 21b on an aluminum cored bar 21a. It is formed so that.

Then, the toner images of the respective colors image-formed on the photosensitive drum 1 are sequentially primary-transferred onto the intermediate transfer roller 6 by a transfer bias having a polarity opposite to that of the toner applied to the cored bar 6a. Thus, the intermediate transfer roller 6 repeats the transfer of the toner images four times by the photosensitive drum 1, so that the toner images of four colors are superimposed. Next, the transfer paper P fed from the cassette 10 is carried into the transfer nip portion between the intermediate transfer roller 6 and the photosensitive drum 1 at the image timing, and a bias having the same polarity as the toner is applied to the core metal 6a. Then, the toner images on the intermediate transfer roller 6 are collectively transferred (secondary transfer) onto the transfer paper P.

Almost at the same time as this batch transfer is performed,
The cleaning roller 21 arranged on the downstream side of the transfer nip portion comes into contact with the intermediate transfer roller 6 and is driven to rotate, and adsorbs the toner remaining on the intermediate transfer roller 6. That is, when the cleaning roller 21 applies a voltage for secondarily transferring a toner image from the intermediate transfer roller 6 to the transfer paper P,
The intermediate transfer roller 6 is contacted at almost the same time. As a result, the residual toner on the intermediate transfer roller 6 is removed by the cleaning roller 2
The electric field that is attracted to the 1st side is created, and the intermediate transfer roller 6
The toner is transferred to the cleaning roller 21 via the contact nip portion between the cleaning roller 21 and the cleaning roller 21. In this case, constant current control is performed so that the secondary transfer bias applied to the intermediate transfer roller 6 has the same current value as the current value in the primary transfer from the photosensitive drum 1 to the intermediate transfer roller 6. Specifically, the current value in the primary transfer is 5 μA for the first color, 10 μA for the second color, and 3
15μA for the 4th color and 2 for the 4th full color
A current of 0 μA is required. Since the secondary transfer voltage applied to the intermediate transfer roller 6 is changed according to the thickness of the toner layer transferred to the intermediate transfer roller 6 in this way, the voltage drop due to the thickness of the toner layer on the intermediate transfer roller 6 is reduced. Can be prevented.

Further, since the surface roughness Rz of the cleaning roller 21 is set so that Rz ≦ 5 μm, the intermediate transfer roller 6 can be uniformly cleaned.

After that, the residual toner adhering to the cleaning roller 21 is scraped off by the urethane blade 22 and collected in the housing 24. At this time, the aluminum cored bar 21a is electrically grounded, and the surface potential of the cleaning roller 21 is maintained at a constant potential (0 V) by the static elimination brush 23 that is in contact with the downstream side of the urethane blade 22. The cleaning performance is prevented from being deteriorated by the charging caused by the friction between the cleaning roller 21 and the cleaning roller 21.

Further, the cleaning roller 21 performs the intermediate transfer even after the transfer paper P has passed through the transfer nip portion until the trailing edge of the toner image formed on the intermediate transfer roller 6 passes through the contact nip portion. Since the secondary transfer bias is applied to the roller 6, the cleaning of the intermediate transfer roller 6 is continued.

As described above, according to the sequence shown in FIG. 2, the first developing device 5M, the second developing device 5C, the third developing device 5Y,
A bias is applied to each of the fourth developing device 5 and the intermediate transfer roller 6. According to this, since the cleaning roller 21 is configured to contact the intermediate transfer roller 6 in synchronization with the secondary transfer bias applied to the intermediate transfer roller 6, the throughput time can be shortened.

Further, in order to improve the cleaning performance, the contact pressure of the cleaning roller 21 to the intermediate transfer roller 6 is preferably set so that the contact nip width is 1 to 2 mm.

If the cleaning roller 21 is rotated faster than the intermediate transfer roller 6 by the driving means of the cleaning roller 21, the cleaning performance can be further improved.

The intermediate transfer roller 6 has a volume resistivity of 1.
Since the medium resistance of 0 × 10 ⁶ Ω · cm is used, it is possible to prevent the toner from charging up and improve the cleaning performance. In the above embodiment, the case where the constant current control is performed as the secondary transfer bias applied to the intermediate transfer roller 6 has been described, but the same effect can be obtained even when the constant voltage control is performed. In this case, there is an advantage that an appropriate secondary transfer bias can be selected even if the resistance value of the intermediate transfer roller 6 varies depending on the environment.

Further, in the above embodiment, an example in which an insulating roller is used as a cleaning member has been shown, but as the cleaning member, an elastic blade, an insulating belt,
Of course, the same effect can be obtained by using a fur brush. In particular, when the surface of the intermediate transfer roller 6 is smooth, it can be effectively cleaned by bringing an elastic blade or an insulating belt into contact with the intermediate transfer roller 6, and the intermediate transfer member has an uneven surface like a foamed elastic member. In this case, a fur brush can be used to clean even the toner clogged in the recess. <Second Embodiment> Next, a second embodiment will be described with reference to FIG.

In this embodiment, an elastic roller 25 having a medium resistance is used as the cleaning member, and a bias is applied to the core metal 25a to enhance the cleaning performance.

That is, the cleaning device 20 includes an elastic roller 25 having a medium resistance, a fur brush 26 for scraping the toner on the elastic roller 25, a housing 24 for collecting the toner, and a power source 2 for applying a bias to the elastic roller 25.
7a and 27b.

The elastic roller 25 of medium resistance is made of a cylindrical aluminum core metal 25a and an elastic layer 25b formed by foaming EPDM in which carbon is dispersed and the volume resistivity is adjusted to 1.0 × 10 ⁸ Ω · cm. Formed by and a core metal 25a
Is covered with an elastic layer 25b.

The secondary transfer bias (-
When 1 kV) is applied, the elastic roller 25 is moved in the direction of arrow B by a moving unit (not shown) to come into contact with the intermediate transfer roller 6 (dotted line in FIG. 3), and is driven by the intermediate transfer roller 6. Rotate. In addition, a bias (+) having a polarity opposite to that of the toner is applied to the aluminum core metal 25a by the power supply 27b.
(1.5 kV) is applied to electrostatically attract the toner remaining on the intermediate transfer roller 6. As a result, the intermediate transfer roller 6 and the elastic roller 25 are different from those of the first embodiment.
The potential difference between and can be increased. Further, the fur roller 26, which is constantly rotating, is in contact with the elastic roller 25, so that the residual toner adhering to the elastic roller 25 is scraped off into the housing 24 and the cleaning performance of the elastic roller 25 is maintained. . When the intermediate transfer roller 6 makes one rotation, the elastic roller 25 is separated from the intermediate transfer roller 6 in the direction of arrow A by a moving unit (not shown) (solid line in FIG. 3).

Next, when the intermediate transfer roller 6 is rotated in the direction of an arrow R6 in the figure by a driving means (not shown), at the same time, a bias (-1k) having the same polarity as the toner is supplied by the power source 27a.
V) is applied and the toner remaining on the elastic roller 25 can be completely collected in the housing 24.

Since the elastic roller 25 has an uneven surface formed by foaming, the cleaning performance can be remarkably improved as compared with the first embodiment.

In the above embodiment, the bias applied to the elastic roller 25 is a DC bias having a polarity opposite to that of the toner. However, a color image having a high printing ratio or toner remaining on the intermediate transfer roller 6 is a reverse toner. In the case of including many, the intermediate transfer roller 6 cannot be sufficiently cleaned even if cleaning is performed several times.

Therefore, the bias of the opposite polarity to the toner is applied to the elastic roller 25 in the first rotation of the intermediate transfer roller 6, and the bias of the same polarity as the toner is applied in the second rotation. As a result, the reverse toner on the intermediate transfer roller 6 can be satisfactorily removed.

Further, as shown in FIG. 4, the elastic roller 25
AC bias (Vpp = 500V, frequency f = 200Hz) to DC bias (+ 1kV) as a power source applied to
By using the power supply 28 capable of applying the superimposing bias in which the above is superposed, effective cleaning can be performed by one rotation of the intermediate transfer roller 6 without making the cleaning device 20 into a complicated configuration. <Third Embodiment> Next, a third embodiment will be described with reference to FIG.

In the first and second embodiments, the device for transferring the toner image onto the transfer paper P in the transfer nip portion between the photosensitive drum 1 and the intermediate transfer roller 6 is exemplified as the device for the secondary transfer. In this embodiment, as shown in FIG. 5, a secondary transfer device is separately provided. That is,
A case where a medium resistance transfer roller as shown in the figure is used as an image forming apparatus for performing secondary transfer will be described.

The process of forming a toner image on the intermediate transfer roller 6 is the same as in the first and second embodiments.

In the figure, the structure of the part for carrying out the secondary transfer of the toner image primarily transferred from the photosensitive drum 1 to the intermediate transfer roller 6 is different from that of the above-mentioned embodiment, and the transfer roller 30 for carrying out the secondary transfer is intermediate. It is brought into contact with the transfer roller 6. Since the cleaning device 20 such as the elastic roller 25 for cleaning the intermediate transfer roller 6 has the same configuration as that of the above-described embodiment, the duplicated description will be omitted.

The transfer roller 30 is made of an aluminum core metal 30.
a and carbon are dispersed to obtain a volume resistivity of 1.0 × 10
Elastic layer 30b made by foaming EPDM adjusted to ⁸ Ω · cm
And a cored bar 30a covered with an elastic layer 30b. The intermediate transfer roller 6 has an outer circumference of 350 cm as in the first embodiment.

Further, from the photosensitive drum 1 to the intermediate transfer roller 6
At the time of primary transfer to the intermediate transfer roller 6, the transfer roller 30 and the elastic roller 25 are not in contact with the intermediate transfer roller 6. When the primary transfer of the toner image to the intermediate transfer roller 6 is completed,
Transfer paper P of, for example, A4, is conveyed from the cassette 10 to the secondary transfer nip portion between the intermediate transfer roller 6 and the transfer roller 30 at the same timing, and at the same time, the transfer roller 30 and the elastic roller 25 are driven by a driving unit (not shown). Secondary transfer to the transfer paper P and cleaning of the intermediate transfer roller 6 are performed by the secondary transfer bias applied to the core metal 6a of the intermediate transfer roller 6 in contact with the intermediate transfer roller 6. In this case, since the outer circumference of the intermediate transfer roller 6 is made larger than the A4 size transfer paper P, the elastic roller 25 as a cleaning member does not disturb the toner image. Further, the secondary transfer onto the transfer paper P and the cleaning of the intermediate transfer roller 6 can be performed at the same time, and the time required for cleaning can be shortened.

Further, +1 kV is applied to the intermediate transfer roller 6,
When a bias of −2 kV is applied to the transfer roller 30 and a bias of −2.5 kV is applied to the elastic roller 25 as a cleaning member, when the toner images of a single color are continuously formed, the primary transfer from the photosensitive drum 1 is performed. After the transfer roller 30
Thus, the secondary transfer onto the transfer paper P is performed, and the cleaning of the intermediate transfer roller 6 is performed in parallel by the elastic roller 25, whereby the printing speed can be significantly increased.

As described above, the present embodiment is particularly effective when a single color image is continuously printed.

An insulating belt stretched by a transfer roller and a tension roller may be used as a device for the secondary transfer. In this case, there is an effect that the transfer material can be easily separated from the intermediate transfer body.

[0052]

As described above, according to the present invention, a transfer bias is applied to an intermediate transfer member provided with a cleaning member so that the cleaning member can be brought into contact with and separated from the intermediate transfer member at a transfer nip portion. Since the toner remaining on the intermediate transfer member is removed by the cleaning member on the downstream side of the transfer nip portion while transferring, the throughput time can be shortened.

Particularly, as the cleaning member, the surface roughness R
By using an insulating roller in which z is Rz ≦ 5 μm,
The intermediate transfer member can be uniformly cleaned.

Further, an elastic body having a volume resistivity of 10 ⁵ to 10 ¹¹ Ω · cm is used as the cleaning member, and a bias voltage in which an AC voltage is superimposed on a DC voltage having a polarity opposite to that of the toner is applied to the cleaning member. Therefore, the cleaning performance on the intermediate transfer member can be remarkably improved.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view showing an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a sequence diagram illustrating an operation of the first exemplary embodiment shown in FIG.

FIG. 3 is a vertical sectional view showing an image forming apparatus according to a second embodiment of the invention.

FIG. 4 is a schematic vertical cross-sectional view showing a main part of an image forming apparatus using a cleaning bias power source in which an alternating voltage is superimposed on a direct current voltage.

FIG. 5 is a vertical sectional view showing an image forming apparatus according to a third embodiment of the present invention.

FIG. 6 is a schematic vertical sectional view showing an example of a conventional image forming apparatus.

FIG. 7 is a cross-sectional view showing how toner on an intermediate transfer member is transferred to a transfer material.

8 is a sequence diagram showing an operation of the image forming apparatus shown in FIG.

[Explanation of symbols]

 1 image carrier (photosensitive drum) 6 intermediate transfer member (intermediate transfer roller) 7a power supply 7b power supply 21 cleaning member 25 cleaning member 50 transfer roller P recording material (transfer paper)

Claims (4)

[Claims] 1. An image forming apparatus in which a toner image formed on an image bearing member is transferred to an intermediate transfer member and transferred from the intermediate transfer member to a recording material at a transfer nip portion. An image forming apparatus, wherein a cleaning member for removing residual toner on the intermediate transfer member is provided so as to be freely contactable and separable on the downstream side of the transfer nip portion in the body moving direction. 2. The cleaning member has a surface roughness Rz.
The image forming apparatus according to claim 1, wherein Rz ≦ 5 μm is an insulating roller member. 3. The image forming apparatus according to claim 1, wherein the cleaning member is an elastic roller having a volume resistivity of 10 ⁵ to 10 ¹¹ Ω · cm. 4. The cleaning member has a power source that applies a bias voltage, which is a DC voltage having a polarity opposite to that of the toner, superimposed with an AC voltage, in response to contact with the intermediate transfer member. The image forming apparatus according to claim 1 or 2.