JP3478501B2 - Image forming device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a copying machine, a printer,
The present invention relates to an electrophotographic image forming apparatus such as a facsimile, and more particularly, to a transfer structure for secondary transfer of a toner image transferred from an image carrier to an intermediate transfer member by primary transfer onto a transfer paper or the like.

[0002]

2. Description of the Related Art In a color image forming apparatus which is one of image forming apparatuses, it is necessary to form toner images of three primary colors of subtractive color mixture on a recording paper in an overlapping manner.

Therefore, conventionally, a primary transfer is once performed from a photosensitive member carrying a toner image to an intermediate transfer member, and the primary transfer is performed on the intermediate transfer member in an overlapping manner, and then is collectively transferred to a transfer paper or the like by a secondary transfer. Various methods have been proposed.

As a constitution of the means for performing the above-mentioned secondary transfer, for example, as described in Japanese Patent Application Laid-Open No. 2-50170, 10 ⁷ to 10 ¹² intermediate transfer members are used.
There is a belt having a surface specific resistance of Ω / cm ² and a volume specific resistance of 10 ⁷ to 10 ¹² Ωcm.

The transfer roller is constituted as an electrode for generating a transfer electric field for secondary transfer from the intermediate transfer body, and is composed of a roller coated with a dielectric layer.

A back electrode located on the back surface of the intermediate transfer member,
There is a structure in which a conductive path is formed between the back electrode and the transfer roller facing the back electrode.

In this structure, part of the electric field for transfer to the intermediate transfer member is contributed by the current formation in the above-mentioned conductive path, and the transfer bias can be lowered.

Further, in the structure in which a member facing the intermediate transfer member is provided, a brush or a sponge is attached to the facing member in order to prevent the facing member from being gradually charged during repeated image formation. There has also been proposed a configuration in which a conductive member such as the above is brought into contact with the surface of the member to eliminate the charge so as to suppress a change in transferability over time (for example, Japanese Patent Application Laid-Open No. 1-288879).

[0009]

However, in the former structure, the resistance of the conductive path in the intermediate transfer member is determined by the positional relationship between the back electrode and the transfer roller. Therefore, in order to stabilize the current in this conductive path in order to suppress the transfer bias voltage for obtaining the electric field required for transfer, it is necessary to make the resistance between them extremely low. It is necessary to set the path length, that is, the distance between the back electrode and the transfer roller to an extremely short distance of several mm to 20 mm.

Therefore, there is a problem that such a positional relationship is a considerable constraint on the layout of the apparatus, and that the positioning accuracy that affects positional variations and the like must be made quite high.

Further, in the latter construction, although static elimination itself is possible in principle, the charging state of the facing member is non-uniform, and it is difficult to set and maintain the contact state uniformly. For this reason, it is undeniable that it is difficult to implement this configuration in reality.

It is also conceivable to use a charge eliminating charger, but it is expensive in cost because a high-voltage power supply for using the charger is required, and ozone and nitrogen generated when the charger is used are generated. There is a possibility that a new problem may occur that not only the opposing member but also the intermediate transfer member is deteriorated by the oxide.

Therefore, in view of the problem of the transfer structure in the conventional image forming apparatus, an object of the present invention is to ensure a stable transfer electric field without depending on the positional relationship of the back electrode with a simple structure, and to face the transfer surface. An object of the present invention is to provide an image forming apparatus having a structure capable of preventing a harmful effect due to electrification of a member and always obtaining stable transferability.

[0014]

The invention according to claim 1 is
After primarily transferred to an intermediate transfer member the toner image formed on an image bearing member, an image forming apparatus that secondarily transferred to the transfer paper or the like from the intermediate transfer member, row Nau the secondary transfer
Set the transfer area to the tension support of the intermediate transfer belt,
If there is no leak at the back of this transfer area during transfer,
From a roller that has a resistance value that prevents electrostatic charge over time
And the volume resistance of the electrode member is 10 ⁷ to
It is characterized in that it is set to 10 ¹² Ωcm .

According to a second aspect of the invention, in the image forming apparatus, after the toner image formed on the image carrier is primarily transferred to the intermediate transfer belt , the toner image is secondarily transferred from the intermediate transfer belt to the transfer paper . Above, connected to a bias power supply
A transfer roller which contacts the intermediate transfer belt, the transfer Low
It is installed at a position facing the
The attached electrode member to the tension support part of the intermediate transfer belt.
The above-mentioned electrode member does not leak during transfer,
And the volume resistance for preventing charging with time is 10 ⁷ to 10
^A resistance member consisting of rollers having a resistance value of ¹² Ωcm.
Characterized in that there.

[0016]

According to the present invention, the electrode member located on the back surface of the intermediate transfer member in the transfer area has a resistance value that prevents charging with time.
Roller Oh as they may be have a resistance in that, the current in the conductive path between the back electrode and the intermediate transfer member, regardless of the position of the back electrode, based on the resistance obtained by the presence of the electrode member Desired.

Therefore, even if there is a variation in the position of the back electrode, or even if the back electrode itself does not exist, the current in the conductive path is in a stable state and a stable transfer field can be obtained.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the embodiments of the present invention will be described below with reference to FIGS. FIG. 1 is a schematic configuration diagram of the entire copying machine when a belt (hereinafter referred to as an intermediate transfer belt) is used as an intermediate transfer member in a color copying machine which is one of image forming apparatuses, and FIG. FIG. 2 is an enlarged view around the photoconductor / intermediate transfer belt shown in FIG. 1. The configuration and operation of this device will be described below.

The color copying machine comprises a color image reading device 1 and a color printer 2 forming a printer section, which will be described later. Of these, the color image reading device (hereinafter referred to as a color scanner) 1 is a copy of a document 3. An image is formed on the color sensor 7 via the illumination lamp 4, the mirrors 5-1, 5-2, 5-3, and the lens 6, and the color image information of the document is, for example, blue (B
lue), green (Green), red (Red)
Each color separation light is read and converted into an electrical image signal. Note that these decomposed lights will be referred to as B, G, and R in the following description for convenience.

Then, on the basis of the B, G, and R color-separated image signal intensity levels obtained by the color scanner 1, color conversion processing is performed by an image processing unit (not shown), and black (hereinafter referred to as BK Note), cyan (same as C), magenta (same as M), and yellow (same as Y) color image data are obtained.

A color image recording device (hereinafter referred to as a color printer) 2 described below is used to
Visualization is performed using C, M, and Y toners, and these toner images are superimposed to form a four-color full-color image.

Next, the outline of the color printer 2 will be described. The writing optical unit is a unit that converts the color image data from the color scanner 1 into an optical signal and performs optical writing corresponding to the original image.
Scans through the polygon mirror 8-2 which is rotated with the laser beam by the drive motor 8-3 from over 1, f [theta] lens 8-1 4, guide the scanning light to the reflecting mirror 8 -5 depending on the photosensitive drum 9, It is designed to form an electrostatic latent image.

The photoconductor drum 9 rotates counterclockwise as indicated by the arrow, around which a photoconductor cleaning unit (including a pre-cleaning static eliminator) 10 and a static elimination lamp 1 are provided.
1, charger 12, potential sensor 13, BK developing device 14,
The C developing device 15, the M developing device 16, the Y developing device 17, the development density pattern detector 18, the intermediate transfer belt 19 and other devices for executing the electrophotographic copying process are arranged.

In FIG. 2, each developing device is rotated by a developing sleeve (14-1, 15-1, 16-1, 17) for rotating the developer so as to face the photoconductor 9 in order to develop the electrostatic latent image.
-1), a developing paddle (14-2, 15-2, 16-2, 17-2) that rotates to draw up and stir the developer, and a toner concentration detection sensor (14-3, 15-) of the developer. 3, 16-3, 17-3) and the like.

The case where the developing operation sequence (color image forming sequence) is BK, C, M, and Y will be described below. However, the image forming order is not limited to this.

When the copying operation is started, the color scanner 1 starts reading BK image data at a predetermined timing, and optical writing / latent image formation by laser light is started based on this image data (hereinafter, BK image data). The electrostatic latent image by BK is referred to as a BK latent image. The same applies to C, M, and Y).

In order to allow development from the tip of the BK latent image, the developing sleeve 14-1 is started to rotate before the tip of the latent image reaches the developing position of the BK developing device 14 to spout the agent. Then, the BK latent image is developed with BK toner. After that, the developing operation of the BK latent image area is continued, but when the rear end portion of the BK latent image passes the BK developing position, the BK developing sleeve 14-1 is cut to make the developing inoperative state. This is completed at least before the leading edge of the C latent image by the next C image data arrives.

Now, the BK toner image formed on the photoconductor 9 is transferred onto the surface of the intermediate transfer belt 19 which is driven at the same speed as the photoconductor (hereinafter, the toner image transfer from the photoconductor to the intermediate transfer belt will be described). Belt transfer).

The belt transfer is performed by applying a predetermined bias voltage to the transfer bias roller 20 while the photoconductor 9 and the intermediate transfer belt 19 are in contact with each other. In addition, on the intermediate transfer belt 19, BK sequentially formed on the photoconductor 9,
The C, M, and Y toner images are sequentially aligned on the same surface to form a 4-color overlapping belt transfer image, and then they are collectively transferred to a transfer paper. The structure and operation of this intermediate transfer belt unit will be described later.

By the way, on the side of the photosensitive member 9, the BK process is followed by the C process, but C image data reading by the color scanner 1 is started at a predetermined timing, and a C latent image is formed by laser light writing by the image data. To do.

The C developing device 15 is
After the trailing edge of the previous BK latent image has passed, and before the leading edge of the C latent image has arrived, the developing sleeve 15-1 is started to rotate so that the agent is spiked and the C latent image is converted to C toner. develop.

Thereafter, the development of the C latent image area is continued, but when the trailing edge of the latent image passes, the agent is cut off on the C developing sleeve 15-1 as in the case of the BK developing device. To do. This is also completed before the leading edge of the next M latent image arrives.

The steps of M and Y are the same as the steps of BK and C described above since the operations of reading image data, forming a latent image, and developing are the same as those of step BK and C, and the description thereof will be omitted.

Next, the intermediate transfer belt unit will be described. The intermediate transfer belt 19 is stretched around a drive roller 21, a belt transfer bias roller 20, and a group of driven rollers, and is drive-controlled by a drive motor (not shown) as described later.

The belt cleaning unit 22 is shown in FIG.
As shown in, the brush roller 22-1, the rubber blade 2
2-2, and a contact / separation mechanism 22-3 from the belt, and the like, while the second, third, and fourth colors are transferred to the belt after the BK image of the first color is transferred to the belt, It is designed to be separated from the belt surface by the mechanism 22-3.

The paper transfer unit 23 is composed of a paper transfer bias roller 23-1, a roller cleaning blade 23-2, and a belt contact / separation mechanism 23-3.

The bias roller 23-1 is normally separated from the surface of the belt 19, but the timing is set when collectively transferring the four-color superposed images formed on the surface of the intermediate transfer belt 19 to the transfer paper. The toner image is transferred to the paper while being pressed by the contact / separation mechanism 23-3 and applying a predetermined bias voltage by the roller 23-1.

The transfer paper 24 is, as shown in FIG.
The paper feed roller 25 and the registration roller 26 feed the four-color superimposed image on the surface of the intermediate transfer belt at the timing when the leading end of the four-color superimposed image reaches the paper transfer position.

The movement of the intermediate transfer belt 19 is 1
There are three possible operation methods after the belt transfer of the BK toner image of the color is completed up to the rear end, but one of them is effective, or it is efficient according to the copy size (in terms of copy speed, etc.). It operates by combining various methods.

(1) -Constant speed forward movement method This is a method in which the transfer belt continues to move at a constant speed even after the toner image of the first color is transferred. In the case of this method, The image processing is performed with the timing set so that the image front end of the toner image of the next color subjected to the visible image processing on the photoconductor 9 side and the image front end on the intermediate transfer belt 19 coincide with each other. And the process for that is as follows.

.. Even after the BK toner image is transferred on the belt, the forward movement is continued at a constant speed.

.. Then, when the front end position of the BK image on the surface of the belt 19 reaches the belt transfer position of the contact portion with the photosensitive member 9 again, the front end portion of the next C toner image on the photosensitive member 9 side is exactly at that position. In addition, the image is formed with a timing.

As a result, the C image is accurately aligned with the BK image and is transferred onto the intermediate transfer belt 19 in a superimposed manner.

.. After that, the same operation is performed to proceed to the M and Y image process, and a belt transfer image of four colors is obtained.

.. Following the fourth color Y toner image belt transfer process, the four-color superimposed toner image on the belt surface is collectively transferred onto the transfer paper 24 as described above while moving forward.

(2) Skip forward method This is more than the case where the transfer belt is separated from the photoconductor after the toner image of the first color is transferred and the toner image of the first color is transferred. This is a method in which the photosensitive member is moved at a high speed in the same direction as before, and when a predetermined amount is moved, the initial moving speed is changed and the photosensitive member is again brought into contact with the photosensitive member. This method is executed, for example, when the length of the image transferred is short with respect to the length of the transfer belt, and it is possible to prevent the cycle time for image formation on the photoconductor side from increasing. The process for this is as follows.

.. When the belt transfer of the BK toner image is completed, the belt 19 is separated from the surface of the photoconductor 9 and is skipped at a high speed in the forward direction as it is, and after moving a predetermined amount, the initial forward speed is restored. After that, the belt 1 is again attached to the photoreceptor 9 again.
9 is contacted.

.. When the leading edge position of the BK image on the surface of the belt 19 reaches the belt transfer position again, the image is formed on the photosensitive member 9 side with timing so that the leading edge portion of the next C toner image comes to that position. There is. As a result, C
The image is belt-transferred so as to be accurately aligned with the BK image and superimposed.

.. After that, the same operation is performed to proceed to the M and Y image process to obtain a belt transfer image of four-color overlapping.

.. Following the Y toner image belt transfer process for the fourth color, the four color superposed toner images on the surface of the belt 19 are collectively transferred onto the transfer paper 24 at the same forward speed.

(3) Reciprocating (quick return) system: This is to separate the transfer belt from the photoconductor after the toner image of the first color is transferred, and transfer belt in the reverse direction at a higher speed than before. Move to wait for the position of the previously transferred toner image to match the position of the toner image of the next color carried on the photoconductor, and then contact the transfer belt with the photoconductor again. In this method, the movement is started in the same direction as the photoconductor, and this operation is continued until the transfer of the toner image of the final color.

This system relates to control when the image position on the transfer belt is aligned with the image position on the photoconductor.
The control is easy if you consider that it is not necessary to secure the transfer belt so much because it does not move the transfer belt in the forward direction but reverses only the amount of movement that has progressed so far. Yes, the steps for this are as follows:

.. When the belt transfer of the BK toner image is completed, the belt 19 is separated from the surface of the photoconductor 9, and the forward movement is stopped, and at the same time, the belt 19 is returned at a high speed in the opposite direction. In the return, the front end position of the BK image on the surface of the belt 19 passes through the position corresponding to the belt transfer in the opposite direction, and after moving for a preset distance, it is stopped and put in the standby state.

.. Next, when the front end portion of the C toner image on the side of the photoconductor 9 reaches a predetermined position before the belt transfer position, the intermediate transfer belt 19 is restarted in the forward direction. Further, the belt 19 is brought into contact with the surface of the photoconductor 9 again. Also in this case, the belt C is transferred under the condition that the C image accurately overlaps the BK image on the surface of the belt 19.

.. After that, the same operation is performed to proceed to the M and Y image process to obtain a belt transfer image of four-color overlapping.

.. Subsequent to the belt transfer process for the Y toner image of the fourth color, the toner is moved forward at the same speed without returning, and the four-color superimposed toner image on the surface of the belt 19 is collectively transferred onto the transfer paper 24.

The transfer paper 24 to which the four-color superposed toner images have been collectively transferred from the surface of the intermediate transfer belt is conveyed to the fixing device 28 by the paper conveying unit 27 in FIG. 1, and the fixing roller 28 controlled to a predetermined temperature. -1 and the pressure roller 28-2 melt and fix the toner image and copy tray 29
Shipped to and get a full color copy.

The photosensitive member 9 after the belt transfer is processed by the photosensitive member cleaning unit 10 (pre-cleaning static eliminator 10).
-1, brush roller 10-2, rubber blade 10-3)
The surface is cleaned by, and the charge is removed uniformly by the discharge lamp 11.

Further, the intermediate transfer belt 19 after the toner image is transferred onto the transfer paper 24 is cleaned by the cleaning unit 22.
Is pressed again by the contacting / separating mechanism 22-3 to clean the surface.

During the repeat copy, the operation of the color scanner 1 and the image formation on the photoconductor 9 are performed at a predetermined timing after the first Y (fourth color) image process.
Proceed to the BK (first color) image process for the first sheet.

Further, in the intermediate transfer belt 19, following the step of collectively transferring the first four-color superimposed image onto the transfer paper,
The BK toner image of the second sheet is transferred to the area where the surface is cleaned by the cleaning unit 22. After that, the same operation as the first sheet is performed.

In FIG. 1, the transfer paper cassette 3
Transfer sheets of various sizes are stored in 0, 31, 32, and 33, and the sheets are fed toward the registration roller 26 at a timing from a storage cassette of the size sheet designated by the operation panel (not shown). Paper is transported. Reference numeral 34 indicates a manual feed tray for OHP paper, thick paper, or the like.

Up to this point, the copy mode for obtaining four full colors has been described, but in the case of the three-color copy mode and the two-color copy mode, the same operation as described above is performed for the designated color and the number of times. .

In the case of the single color copy mode, only the developing device of that color is set to the developing operation (agent standing) state until the predetermined number of sheets are finished, and the intermediate transfer belt 19 is used.
Is driven at a constant speed in the forward direction while being in contact with the surface of the photoconductor 9, and the copying operation is performed while the belt cleaner 22 is also in contact with the belt 19.

Next, the transfer structure in the paper transfer unit will be described in comparison with the conventional case. Figure 3
3A shows the conventional case, and FIG. 3B shows the case of this example.

In FIG. 3B, the paper transfer roller 23-
1 is a core metal 23-1 -1 connected to the bias power source 35.
Disperse the conductive agent in the EPDM rubber member to 10 ⁷ to 1
Elastic member 23-having a volume resistivity of 0 ¹⁰ Ωcm
It is covered with 1-2.

[0067] Other in thickness 5.7mm on cored epichlorohydrin rubber having a volume resistivity ¹⁰ 8 to 10 ⁹ [Omega] cm as a volume in a thickness of 50μm resistivity ¹⁰ 8 to 10 ⁹
A roller covered with a PFA tube of Ωcm may be used.

The intermediate transfer belt 19 has a thickness of 0.1 as in the paper transfer roller 23-1, in which a conductive material is dispersed in a resin such as polycarbonate, polyester, or fluorine.
The volume resistivity of 5 ± 0.015 mm is set to 10 ⁷ to 10 ¹² Ωcm.

On the other hand, a belt drive roller 21 is provided at a position facing the back surface of the paper transfer roller 23-1. This belt drive roller 21 has a resistance of 10 ⁷ to 10 ¹² Ωc.
It has a cored bar 21-1 made of metal or the like set to have a volume resistivity of m, and its peripheral surface has a polarity by itself, so-called,
It is a polar rubber and has a thickness of 0.
Coated with 3 mm epichlorohydrin rubber 21-2-2.

As is apparent from FIG. 3A, in the conventional example, the current flowing in the transfer belt 19 between the transfer portion of the transfer roller 23-1 and the installation roller 36 which is the back electrode is the same as the opposing roller dielectric. since it was covered with member 21 2 -1 rubber or the like, it flows into the ground roller 36, but are intended to be affected by the distance, in this embodiment, the belt is composed of a medium resistance driving It flows into the roller 21.

This will be described below with reference to the circuits of both examples shown in FIG. FIG. 4 is a schematic diagram of an electric circuit of the paper transfer portion, FIG. 4 (A) shows a conventional case, and FIG. 4 (B) shows a case of this embodiment.

The current on the intermediate transfer belt 19 that contributes to the formation of an electric field for transfer will be compared. The resistance (rPR) of the paper transfer roller 23-1 at the transfer portion, the resistance (rPA) of the transfer paper, the belt resistance (rB1) in the moving direction of the intermediate transfer belt 19 and the bias voltage (v1) depending on the distance to the ground roller. Then, the current (i1) in the circuit in the conventional case shown in FIG. 4A is obtained by the following equation.

I 1 = (rPR + rPA + rB1) / v1 (Equation 1) Therefore, the intermediate transfer belt 19 for contributing to electric field formation
It is clear that the current (i1) flowing through the belt depends on the belt resistance (rB1) determined by the distance between the paper transfer roller 23-1 and the ground roller 36 that is the back electrode.
In order to keep the bias voltage (v1) low, the belt resistance (rB1) should be small.

Since the belt resistance (rB1) is the belt resistance formed by the distance to the ground roller, it is necessary to bring the ground roller 36 closer to the vicinity of the transfer portion. However, this has the following drawbacks.

.. The belt resistance (rB1) affected by the position of the ground roller 36 is likely to vary depending on the positioning accuracy of the ground roller 36. For example, when the distance between the paper transfer roller 23-1 and the ground roller 36 is 5 mm,
If the distance changes by ± 1 mm, the resistance changes by ± 20%.

.. Since the belt resistance (rB1) is formed by the surface and volume specific resistance of the belt between the paper transfer roller 23-1 and the ground roller 36, their stability is also required. However, since the dispersion of the conductive material is not necessarily uniform in the entire belt and local unevenness is inevitable, even if the distance between the paper transfer roller 23-1 and the ground roller 36 is accurately determined, The resistance changes.

As a result, the ground roller 3 which is the back electrode
In the conventional example that depends on the position of 6, stable transfer cannot be performed.

On the other hand, in the case of this embodiment shown in FIG. 4B, instead of the belt resistance (rB1), the resistance of the belt driving roller 21 (rK) and the belt resistance in the transfer area in the volume direction (rBL ). ) Occurs. Therefore, the current to the bias voltage (v2) (i2) is, i2 = (rPR + rPA + rK + r BL) / v1 ···
It will be calculated by (Equation 2).

As a result, the present invention is superior to the conventional example in the following items. ． The resistance (rK) of the belt driving roller 21 is determined by the roller material 21-2-2 itself.

.. Since the belt resistance (rB L ) is determined only by the resistance in the transfer region in the volume direction as described above, it is stable because it is not affected by the surface resistance like the belt resistance (rB1) of the conventional example. Its value is obtained as resistance.

As described above, according to the present invention, the current value on the intermediate transfer belt 19 forming a part of the electric field can be stably obtained without depending on the distance to the ground roller 36 which is the back electrode. Moreover, since it is not necessary to set the position of the ground roller 36 near the transfer portion, the ground roller 3
An electric field for transfer can be formed without being affected by the positioning accuracy of 6, and stable transfer can be performed.

The inventor of the present invention conducted an experiment on the resistance of the belt driving roller 21 and its charging property, and obtained the results shown in the following table.

[0083] This result is obtained by measuring whether charged belt driving roller 2 1 with respect to the bias voltage occurs, the charging property in the table, a case that does not cause charge ○
The mark is shown, and the case where charging occurs is shown by Δ or X.

This depends on the resistance (rK) of the belt driving roller 21 shown in FIG.
The occurrence of charging means that not only a sufficient current does not flow into the roller, but also the transfer electric field is obstructed and the transferability is deteriorated.

[0085]

[Table 1]

From this table, it can be seen that the resistance not charged corresponds to the above-mentioned 10 ⁷ to 10 ¹² Ωcm. Furthermore, when the volume resistivity is less than 10 ⁷ Ωcm,
The current that contributes to the transfer becomes excessive, charge is injected into the toner on the intermediate transfer belt, the polarity of the toner is reversed, and transfer is not performed, so-called leak occurs. Further, in the belt driving roller 21, when the resistance forming means is based on dispersion of a conductive agent such as carbon (to be precise, only in a layer formed by dividing the conductive agent), the above resistance value is obtained macroscopically. Even if it is present, the conductive agent may be unevenly dispersed in a microscopic manner, and a portion having low resistance may be formed.

In this case, since discharge breakdown may occur at the coating portion, it is preferable that the resistance value does not include at least the layer in which the conductive agent is dispersed so as not to depend on the dispersion state. .

Although the configuration in which the paper transfer portion is constituted by the bias roller has been described above as an example, it is apparent that the contents of the present invention can be applied to the configuration in which the corona charger is constituted as shown in FIG. is there.

[0089]

As described above, according to the present invention, since the electrode member having the medium resistance is arranged in the secondary transfer area to the recording paper or the like so as to face the back surface of the intermediate transfer member, the transfer bias is used. When a back electrode is provided on the intermediate transfer member for the purpose of contributing to the formation of the electric field, stable electric field formation can be performed without depending on the position of the electrode, whereby stable transferability can be obtained. Moreover, by providing the electrode member with a resistance capable of preventing charging, it is possible to maintain the above-mentioned medium resistance state over time,
By stabilizing the current described above, stable transfer can always be performed.

[Brief description of drawings]

FIG. 1 is a layout diagram showing a schematic configuration of a color copying apparatus which is one of image forming apparatuses of the present invention.

FIG. 2 is a photoconductor in the color copying apparatus shown in FIG.
FIG. 6 is an enlarged view of an area around an intermediate transfer belt.

FIG. 3A is a schematic diagram for explaining the configuration of a conventional transfer portion in an image forming apparatus, and FIG. 3B is a schematic diagram for explaining the configuration of the transfer portion according to the present invention.

4A is a circuit diagram for explaining a configuration for forming an electric field in a conventional transfer portion, and FIG. 4B is a diagram for explaining a configuration for forming an electric field according to an embodiment of the present invention. It is a circuit diagram of.

FIG. 5 is a schematic diagram for explaining a configuration of a transfer unit according to the present invention.

[Explanation of symbols]

19 intermediate transfer belt 21 belt drive roller which is an electrode member located on the back surface of the intermediate transfer belt in the transfer area

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Toshiaki Motohashi               1-3-3 Nakamagome, Ota-ku, Tokyo               Inside the ceremony company Ricoh (72) Inventor Mitsuru Takahashi               1-3-3 Nakamagome, Ota-ku, Tokyo               Inside the ceremony company Ricoh (72) Inventor Hideki Ueyama               1-3-3 Nakamagome, Ota-ku, Tokyo               Inside the ceremony company Ricoh                (56) Reference JP-A-5-333723 (JP, A)

Claims (2)

(57) [Claims] 1. A secondary transfer is carried out in an image forming apparatus in which a toner image formed on an image carrier is first transferred to an intermediate transfer belt and then secondarily transferred from the intermediate transfer belt to a transfer paper. The transfer area of the intermediate transfer belt
Set it on the tension support part, and on the back of this transfer area,
Resistor that does not leak and prevents static charge over time
An electrode member including a roller having a value is provided, and the electrode member
The image forming apparatus is characterized in that its volume resistance is set to 10 ⁷ to 10 ¹² Ωcm . 2. A bias power source is connected to an image forming apparatus in which a toner image formed on an image carrier is primarily transferred to an intermediate transfer belt and then secondarily transferred from the intermediate transfer belt to a transfer paper . , Contact the above intermediate transfer belt
And a transfer roller that faces the transfer roller via the intermediate transfer belt.
The electrode member provided at the position of the intermediate transfer belt
In order to prepare for the tension support part, the above-mentioned electrode member does not cause a leak during transfer, and
Volume resistance to prevent temporal charging is 10 ⁷ to 10 ¹² Ωc
An image forming apparatus comprising: a resistance member including a roller having a resistance value of m .