JPH06202501A - Image forming device - Google Patents

Abstract

(57) [Abstract] [Purpose] In an image forming apparatus that electrostatically primary-transfers a toner image formed on a photoconductor to an intermediate transfer drum, and secondarily transfers the toner image on the intermediate transfer drum to a transfer paper. This prevents the electric field formed between the photoconductor and the intermediate transfer drum from adversely affecting other elements, and prevents uneven density in the transferred toner image. [Structure] A large number of electrodes 5 divided in the circumferential direction are provided on an intermediate transfer drum 102, and a voltage for primary transfer is applied to an electrode 5a of the electrodes 5 facing the photoconductor 101. Along with the electrode 5, the intermediate transfer drum 10
The two surfaces 102a are composed of two kinds of electrodes 5A and 5B having different depths.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention forms a toner image composed of toner charged to a predetermined polarity on the surface of a toner image bearing rotary member and transfers the toner image onto a recording medium via an intermediate transfer rotary member. And an image forming apparatus that operates.

[0002]

2. Description of the Related Art A conventional image forming apparatus such as an analog copying machine, a digital copying machine, a laser printer or a facsimile generally directly transfers a toner image formed on a toner image bearing rotary member onto a recording medium. Is configured. On the other hand, the toner image on the toner image bearing rotating body is temporarily transferred onto the intermediate transfer rotating body, and then on the recording medium pressed against the intermediate transfer rotating body by the pressing rotating body. An image forming apparatus for secondarily transferring a toner image on an intermediate transfer rotator has been proposed (for example, Japanese Patent Publication No. 46-41679 or Japanese Patent Laid-Open No. 2-1832).
88, etc.).

In this type of image forming apparatus, as a method of primary transfer of the toner image on the toner image bearing rotary member to the intermediate transfer rotary member, an adhesive system utilizing the adhesiveness of the surface of the intermediate transfer rotary member or a toner image is used. An electrostatic field that forms an electric field between the carrier rotating body and the intermediate transfer rotating body to electrostatically attract the toner on the toner image carrier rotating body to the surface of the intermediate transfer rotating body, or a combination of an adhesive system and an electrostatic system. The adopted method is adopted.

The above-mentioned electrostatic system alone or a system using the adhesive system together is collectively referred to as an electrostatic primary transfer system. When this system is adopted, an intermediate transfer rotary member is used. An electrode made of a conductive layer is provided all around the inside of the toner, and a voltage having a polarity opposite to the charging polarity of the toner on the toner image bearing rotary member is applied to the electrode to make the toner image bearing rotary member By utilizing the potential difference between the intermediate transfer rotator and the intermediate transfer rotator, the toner on the toner image bearing rotator can be electrostatically attracted to the surface of the intermediate transfer rotator.

However, when a voltage is applied to a large electrode provided over the entire circumference of the intermediate transfer rotator as described above, the voltage application efficiency decreases.

Not only the application of a voltage to such an electrode may adversely affect other process equipment arranged around the intermediate transfer rotator. For example, a cleaning device for cleaning the toner remaining on the surface of the intermediate transfer rotator after the secondary transfer may be provided around the intermediate transfer rotator. Since the toner is removed, if the voltage of the above-mentioned polarity is applied to the electrode of the intermediate transfer rotator during this cleaning operation, the cleaning efficiency of the cleaning device is significantly reduced. That is, the voltage applied to the electrode of the intermediate transfer rotator for the primary transfer of the toner image acts so as to attract the toner to the side of the intermediate transfer rotator. The toner is removed from the body, and the voltage applied to the electrode of the intermediate transfer rotator for the primary transfer of the toner image acts as a hindrance to the cleaning function of the cleaning device.

Under these circumstances, in order to remove the residual toner on the intermediate transfer rotator, the voltage applied to the electrode of the intermediate transfer rotator for the primary transfer of the toner image to the cleaning member of the cleaning device. It is necessary to apply a voltage having a large polarity opposite to that of the toner as described above, which increases the device cost and the maintenance cost.

Further, in order to facilitate removal of the residual toner on the intermediate transfer rotator by a cleaning device, a voltage having the same polarity as the residual toner on the intermediate transfer rotator is applied to the electrodes of the intermediate transfer rotator. It is also possible to adopt. At this time, the polarity of the voltage applied to the electrodes is opposite to the polarity of the voltage applied to the electrodes of the intermediate transfer rotator for the primary transfer of the toner image. Therefore, the voltage for cleaning cannot be applied to the electrodes during the primary transfer. After the primary transfer of the toner image is completed, a voltage for cleaning the surface of the intermediate transfer rotator must be applied to the electrodes of the intermediate transfer rotator. As described above, since the primary transfer of the toner image and the cleaning operation cannot be performed in parallel, the outer diameter of the intermediate transfer rotator is increased to increase the size thereof, or the time required for one image forming operation is lengthened. Must.

On the other hand, as a method for secondarily transferring the toner image on the intermediate transfer rotator to a recording medium, the toner on the intermediate transfer rotator is melted and the toner is melted by utilizing the releasability of the surface of the intermediate transfer rotator. A toner image is secondarily transferred onto a recording medium, or an electric field is formed between a pressure rotary member that pressurizes the recording medium onto the intermediate transfer rotary member and the intermediate transfer rotary member to remove the toner on the intermediate transfer rotary member. An electrostatic method in which secondary transfer is performed electrostatically on a recording medium, a method using both a melting method and an electrostatic method, or the like is adopted.

In this case as well, the electrostatic system alone or a system in which this system and the fusion system are used together is referred to as an electrostatic secondary transfer system. When this system is adopted, the entire intermediate transfer rotary member is covered. A voltage having the same polarity as that of the toner on the intermediate transfer rotator can be applied to the above-mentioned electrodes provided along the circumference. That is, the voltage of this polarity is applied to the electrodes to transfer the toner on the intermediate transfer rotator to the recording medium. The polarity of the applied voltage is such that the toner image on the toner image bearing rotator is rotated by intermediate transfer. The polarity is opposite to the polarity of the voltage applied to the electrodes of the intermediate transfer rotator for the primary transfer to the body.

Therefore, also in this case, when the toner image on the toner image bearing rotary member is primarily transferred to the intermediate transfer rotary member while applying a voltage having a polarity opposite to that of the toner on the intermediate transfer rotary member to the electrodes, The voltage for secondarily transferring the toner image on the transfer rotator to the recording medium cannot be applied to the electrode of the intermediate transfer rotator, and the secondary transfer must be performed after the completion of the primary transfer. For this reason, the intermediate transfer rotator becomes large,
In addition, it is inevitable that the image forming operation requires a long time.

Therefore, the inventor of the present invention uses an intermediate transfer rotator internally having a plurality of electrodes divided in the circumferential direction and has a polarity opposite to the charging polarity of the toner with respect to the electrode facing the toner image bearing rotator. A voltage is applied to primarily transfer the toner image on the toner image bearing rotating body to the intermediate transfer rotating body, and a voltage having the same polarity as the toner charging electrode is applied to the electrode facing the pressure rotating body to form an intermediate image. An image forming apparatus capable of secondarily transferring a toner image on a transfer rotating body onto a recording medium has been proposed. According to this configuration, the primary transfer operation or the secondary transfer operation can be executed without affecting other process operations, and the above-mentioned drawbacks can be avoided.

However, since the electrodes provided on the intermediate transfer rotator are arranged at a certain interval in the circumferential direction of the intermediate transfer rotator, they face the toner image bearing rotary member or the pressure rotary member. When voltage is applied to some electrodes,
The electric field strength on the surface of the intermediate transfer rotator becomes uneven, and the toner image is primarily transferred from the toner image bearing rotator onto the intermediate transfer rotator, or the toner image is secondarily transferred from the intermediate transfer rotator onto the recording medium. Uneven density may occur.

Specifically, for example, in the case of the primary transfer of the toner image from the toner image bearing rotary member to the intermediate transfer rotary member,
While the toner image bearing rotary member and the intermediate transfer rotary member rotate at the same peripheral velocity (surface linear velocity) and contact each other with a certain width in the circumferential direction, at this time, there are a plurality of electrodes within the width. , And when voltage is applied to the plurality of electrodes, the toner of the toner image portion corresponding to the electrodes is satisfactorily transferred onto the intermediate transfer rotator, whereas the toner image portion of the toner image portion corresponding to the electrodes is There is a possibility that the transfer rate of the toner is lowered and uneven density occurs in the toner image transferred onto the intermediate transfer rotator. A similar situation occurs at the time of secondary transfer.

If the voltage applied to the electrode is set to an appropriate value corresponding to the distance from the electrode to the surface of the intermediate transfer rotator, it is possible to prevent the above-mentioned problems from occurring. It is not easy to control the voltage application to the electrodes as described above, and when the value of the voltage applied to the electrodes at the time of primary or secondary transfer is changed according to the characteristics of the toner, etc. Controlling the voltage becomes extremely difficult.

[0016]

SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus which eliminates the above-mentioned drawbacks.

[0017]

In order to achieve the above object, the present invention provides a toner image bearing rotary member on the surface of which a toner image composed of toner charged to a predetermined polarity is formed, and a close contact with the rotary member. However, when the toner image on the rotator is primarily transferred and the toner image on the intermediate transfer rotator is secondarily transferred onto a recording medium, the recording medium is transferred onto the intermediate transfer rotator. In the image forming apparatus having a pressing rotary member that is pressed against the intermediate transfer rotary member, the intermediate transfer rotary member internally has a plurality of electrodes that are divided and arranged in the circumferential direction, and these electrodes are arranged in the intermediate transfer rotary member. At least two kinds of electrodes having different depths from the surface of the body are formed, and at least when the primary transfer is performed, the polarity of the toner charged on the toner image bearing rotating body with respect to the electrode facing the toner image bearing rotating body. And the reverse Voltage applying means for applying a positive voltage and at least the same polarity as the charging polarity of the toner on the intermediate transfer rotator with respect to the electrode facing the pressure rotator when the secondary transfer is performed. An image forming apparatus is proposed which is provided with at least one of the second voltage applying means for applying a voltage.

At this time, it is advantageous that the electrodes are arranged so that, as viewed from the surface side of the intermediate transfer rotator, there is no portion where the electrodes do not exist inside the intermediate transfer rotator.

Further, when the intermediate transfer rotator is brought into pressure contact with the toner image bearing rotary member or the pressure rotator, the electrodes are arranged so that the plurality of types of electrodes are at substantially the same distance from the surface of the intermediate transfer rotator. It is advantageous if it is arranged in the elastic layer of the intermediate transfer rotator.

Further, the first voltage applying means and the second voltage applying means apply a larger voltage to the electrode farther from the surface of the intermediate transfer rotor than to the electrode closer to the surface. Is advantageously configured.

Further, it is preferable that the plurality of electrodes are arranged in a zigzag pattern when viewed from the end face side of the intermediate transfer rotator.

Also, the first and second voltage applying means are
A voltage supply member for supplying a voltage to the electrodes is provided, and a part of each of the electrodes is exposed to the outside on the surface side of the intermediate transfer rotator, and the exposed electrode parts are contacted by the voltage supply member to generate a voltage. Is advantageously configured to supply

Further, the voltage supply member is composed of a conductive roller that rotates together with the rotation of the intermediate transfer rotator, and the contact width between the roller and the intermediate transfer rotator in the circumferential direction of the conductive roller. Is narrower than the contact width between the rotating body and the toner image carrying rotating body in the circumferential direction of the intermediate transferring rotating body, and the conductive roller and the intermediate transfer rotating body are connected to each other by the intermediate transfer rotating body and the toner image carrying rotating body. It is desirable to occupy a corresponding position within the range of the contact width.

Further, it is advantageous that the voltage supply member is composed of an elastic conductive roller, and the rubber hardness of the roller is set lower than the rubber hardness of the portion of the intermediate transfer rotator in contact with the roller. is there.

Further, each of the first and second voltage applying means has a plurality of voltage supply members respectively in contact with electrodes having different depths, and the plurality of voltage supply members of each voltage applying means are intermediate. It is advantageous that one end of the transfer rotary member in the axial direction is in contact with the electrode exposed to the outside.

Further, each of the first and second voltage applying means has a plurality of voltage supplying members respectively in contact with electrodes having different depths, and the plurality of voltage supplying members of each voltage applying means are intermediate. It is preferable that the one end and the other end of the transfer rotator in the axial direction are in contact with the electrodes exposed to the outside.

[0027]

Embodiments of the present invention will now be described in detail with reference to the drawings.

The image forming apparatus shown in FIG. 1 includes a drum-shaped photosensitive member 101 which is an example of a toner image bearing rotating member, an intermediate transfer drum 102 which is an example of a configuration of an intermediate transfer rotating member, and
Similarly, it has a pressure drum 103 which is an example of a pressure rotator, and the photoconductor 101 and the intermediate transfer drum 102 are in pressure contact with each other. The intermediate transfer drum 102 and the pressure drum 103 are also in pressure contact with each other, and these elements 101,
Each of 102 and 103 is rotationally driven in a direction indicated by an arrow in FIG.

Between the photosensitive member 101 and the intermediate transfer drum 102, and between the intermediate transfer drum 102 and the pressure drum 103,
In order to maintain the respective pressure contact forces in a predetermined state, a spring is provided, and for example, the rotating shafts are spring-coupled. Further, the photoconductor 101 and the intermediate transfer drum 102, or the intermediate transfer drum 102 and the pressure drum 103 may be configured to be pressed against each other or separated according to a sequence. Further, the toner image bearing rotary member, the intermediate transfer rotary member, and the pressure rotary member can be configured by belt-shaped members.

As will be described in detail later, the photoconductor 101
A toner image is formed on the intermediate transfer drum 102 at the primary transfer position indicated by reference character A in FIG.
Primary transcribed on. The toner image primarily transferred onto the intermediate transfer drum 102 is denoted by a symbol B on a transfer paper 155, which is an example of a recording medium fed between the intermediate transfer drum 102 and the pressure drum 103, as described later. Secondary transfer is performed at the secondary transfer position indicated by. Hereinafter, the configuration of the image forming apparatus shown in FIG. 1 will be clarified while describing an example of the series of operations in detail.

The photosensitive member 101 illustrated in FIG. 1 is an organic photosensitive member having relatively excellent pressure resistance and heat resistance, and the photosensitive member 101 rotates counterclockwise as described above with the start of the image forming operation. The rotation is started, and the photosensitive member 101 and the intermediate transfer drum 102 rotate at a constant linear velocity with no difference between them while being pressed against each other. At this time, the surface of the photoconductor 101 is uniformly charged by the charging charger (scorotron charger) 105, and the surface potential thereof is set to about −800V.

Next, the laser beam 110 modulated by the laser optical system 106 based on the image signal imagewise exposes the surface of the uniformly charged photoconductor 101, and a predetermined electrostatic latent image is formed on the photoconductor 101. To form. This latent image is laser light 1
The portion irradiated with 10 (surface potential is about −100 V) is the toner-adhered portion, and the unexposed portion (surface potential is about −800 V).
V) is used as the background portion.

The laser optical system 106 is composed of a semiconductor laser (not shown), a rotary polygon mirror 107, an fθ lens 108, a mirror 109, etc., and a laser modulation circuit controls the emission of the semiconductor laser according to an image signal.

The electrostatic latent image described above is visualized as a toner image by the developing device 111. The developing device 111 shown here is a non-magnetic sleeve 10 in which a magnet is provided.
4, the powdery developer in the developing device is conveyed by rotating this. This developer is a two-component developer in which a high resistance non-magnetic toner and a magnetic carrier are mixed, and the toner and the carrier are triboelectrically charged in opposite polarities. In this example, the toner is negatively charged.

Such a developer has a developing bias voltage of -60.
By the sleeve 104 which is rotated by applying 0V, the sleeve 104 is carried to the developing area where the sleeve and the photoconductor 101 face each other, and the reversal development is performed there. That is, the negatively charged toner electrostatically moves and adheres to the low potential portion of the electrostatic latent image formed on the photoconductor 101, and the high potential portion becomes the background portion. Of course, the toner adheres to the intermediate potential portion on the photoconductor 101 at a density corresponding to the intermediate potential portion. The toner used here is 5 in order to improve dot reproducibility.
It is desirable to use a toner having a particle diameter of not more than μm, and for this purpose, it is advantageous to use, for example, a toner produced by a polymerization method and having a narrow particle diameter distribution.

As described above, a toner image composed of toner charged to a predetermined polarity is formed on the surface of the photoconductor 101, and the photoconductor portion on which the toner image is formed is in primary contact with the intermediate transfer drum 102 in pressure contact. At the position A, the toner image on the photoconductor 101 is primarily transferred onto the surface of the intermediate transfer drum 102.

The primary transfer is performed by an adhesive system utilizing the adhesive property on the intermediate transfer drum 102, an electrostatic system in which the toner on the photoconductor 101 is electrostatically attracted to the intermediate transfer drum 102, or transferred. This can be carried out by a method using a combination of, but in this example, a combined method of an adhesive method and an electrostatic method is adopted.

In order to adopt this method, the intermediate transfer drum 102 has a thickness of 500 to 500 on a drum-shaped base 1 made of a rigid material such as aluminum, as shown in FIGS. 2 and 4. An insulating elastic layer 2 having a rubber hardness of 30 to 80 degrees and a thickness of 5000 μm, preferably about 2000 μm, and a thickness of 30 embedded in the elastic layer 2 and made of polyimide in which carbon black is dispersed.
To 300 .mu.m, preferably 50 .mu.m, and the insulating layer 4 having a thickness of 10 to 300 .mu.m, preferably 50 .mu.m, are bonded together with the elastic layer 2 inside.

The conductive layer 3 is the intermediate transfer drum 102.
2, which is continuous in the axial direction X of the intermediate transfer drum 102, as shown in FIG.
As shown in FIG. 4, the electrode is divided into a plurality of parts in the circumferential direction Y and is insulated from each other, and a plurality of electrodes 5 are constituted by these. These electrodes 5 are also insulated from the base 1. As described above, the intermediate transfer drum 102 has a plurality of electrodes 5 arranged in the circumferential direction in a divided manner, and these electrodes 5 are arranged on the surface 102 a of the intermediate transfer drum 102 to be mutually separated. At least two types of electrodes having different depths, in this example, reference numerals 5A and 5B
Although it is composed of two types of electrodes shown in, the operation related thereto will be described later.

The insulating layer 4 constituting the surface of the intermediate transfer drum 102, when pressed against the photoreceptor 101,
It is desirable to use a material having appropriate elasticity so that a sufficient contact area and uniform pressure can be obtained between them.
The surface of the insulating layer 4 is made of a material which exhibits adhesiveness to the toner at room temperature and exhibits releasability to the melted and fluidized toner as described later. As a material satisfying such requirements, for example, silicone rubber can be cited.

Intermediate transfer drum 1 constructed as described above
Between 02 and the photoconductor 101 is, for example, 0.3 to 3.0 kg.
A pressure of about / cm is applied, and the pressure contact parts of both are in close contact with each other. In this state, a voltage (transfer bias) having a polarity opposite to the charging polarity of the toner on the photoconductor 101 is applied to the conductive layer 3 of the intermediary transfer drum 102 in a manner described later, whereby the photoconductor 101 and the intermediate transfer are transferred. The close contact part of the drum 102,
That is, an electric field is formed at the primary transfer position A, and the photoconductor 10
The toner on No. 1 is transferred from the photoconductor 101 to the intermediate transfer drum 102 by the action of the electric field.

At this time, the surface of the intermediate transfer drum 102 exhibits adhesiveness to the toner at room temperature as described above, and thus the adhesive force also causes the toner on the photosensitive member 101 to adhere to the intermediate transfer drum 102. Migrate effectively.

In this way, the toner image on the photoconductor 101 is formed while the intermediate transfer drum 102 is in close contact with the photoconductor 101.
By the potential difference between the photoconductor 101 and the intermediate transfer drum 102 and the adhesive force on the surface of the intermediate transfer drum 102,
The image is primarily transferred onto the intermediate transfer drum 102. At this time, in the contact portion between the photoconductor 101 and the intermediate transfer drum 102, the toner is sandwiched between the two and hardly moves, and due to the electrostatic force due to the electric field formed between them and the adhesive force from the intermediate transfer drum 102. The toner has a large adhesive force with the intermediate transfer drum 102, and is transferred to the intermediate transfer drum 102 with almost no movement in the interface direction.

The photosensitive member 101 and the intermediate transfer drum 10
When the applied pressure between 2 and 1 is much lower than the above range,
When the adhesiveness between the two is reduced, the transfer efficiency of the toner image onto the intermediate transfer drum 102 is reduced, or the transfer omission occurs, and conversely, when the pressure greatly exceeds the above range, the photosensitive member 101 or the intermediate transfer drum 102 The polarity of 102 is changed and an excessive load is applied to its driving source, which is not desirable.

The toner remaining on the photoconductor 101 after the toner image is primarily transferred onto the intermediate transfer drum 102 is removed by the cleaning device 112, and the surface of the photoconductor 101 is cleaned. Further, the photoconductor 101 is subjected to static elimination action by a static eliminator (not shown).

On the other hand, the transfer paper 155 is fed in the direction of arrow C by the rotation of the paper feed roller 125 of the paper feed unit 124.
The transfer paper 155 sent out in this way is transferred by the registration roller pair 126 at a predetermined timing, that is, at a timing when the toner image on the intermediate transfer drum 102 is aligned with the transfer paper 155.
Delivered between and.

Intermediate transfer drum 102 and pressure drum 103
While being rotated at the same surface speed, they are pressed against each other with a pressure of 0.3 to 3.0 kg / cm sandwiching the transfer paper 155 fed between them, and at this time, the toner image on the intermediate transfer drum 102 is Secondary transfer is performed on the transfer paper 155. Pressure drum 103
Transfers the toner image on the intermediate transfer drum 102 to the transfer paper 155.
This is used to press the transfer paper 155 against the intermediate transfer drum 102 when the secondary transfer is performed. The transfer paper 155 may be wound around the peripheral surface of the pressure drum 103 and clamped to perform the secondary transfer of the toner image.

The above-mentioned secondary transfer is performed by the intermediate transfer drum 102.
The releasing property of the surface can be used, or the toner on the intermediate transfer drum 102 can be electrostatically attracted to the transfer paper 155, or both of them can be performed. In this example, the surface of the intermediate transfer drum 102 is used. The toner image on the intermediate transfer drum 102 is secondarily transferred to the transfer paper 155 by both of the releasing property and the electrostatic action.

As described above, the surface of the intermediate transfer drum 102 is made of a material having releasability for the melted and fluidized toner, for example, silicone rubber.
Further, for example, the toner image on the intermediate transfer drum 102 is placed opposite to the intermediate transfer drum 102 immediately before reaching the secondary transfer position B between the intermediate transfer drum 102 and the pressure drum 103 by the rotation of the intermediate transfer drum 102. The toner on the intermediate transfer drum 102 is heated by being irradiated with light from a heat source 132 composed of an infrared lamp or a halogen lamp, and the toner is brought into a semi-melted state. Intermediate transfer drum 1
No. 02 may include a heater (not shown) provided therein to heat the toner on the intermediate transfer drum 102. In any case, the toner forming the toner image on the intermediate transfer drum 102 is heated. .

On the other hand, the pressure drum 103 is a hollow rigid drum made of aluminum or the like, and the outer peripheral surface thereof is covered with a compression resistant resin. A heat source (not shown) such as a halogen lamp is also provided inside the pressure drum 103, and the transfer paper 155 passing through the secondary transfer position B between the intermediate transfer drum 102 and the pressure drum 103 which are in pressure contact with each other. Are heated by a heat source in the pressure drum 103. Further, the transfer sheet 155 conveyed to the secondary transfer position B may be heated by a heat source (not shown) to heat the transfer sheet 155.

In this way, heat is applied to the toner on the intermediate transfer drum 102 and the transfer paper 155 is also heated, so that the toner is transferred to the secondary transfer position B between the intermediate transfer drum 102 and the pressure drum 103. Paper 155 and intermediate transfer drum 102
When the upper toner image arrives, the toner is transferred to the transfer paper 155.
It will be in a molten state while coming into contact with. Since the surface of the intermediate transfer drum 102 exhibits releasability for such molten toner, the toner image on the intermediate transfer drum 102 is transferred onto the transfer paper 1.
55, and the toner penetrates into the fibers of the transfer paper 155. In this way, the toner image on the intermediate transfer drum 102 is formed while heating the toner on the intermediate transfer drum 102 and the transfer paper 155, or after heating the toner and the intermediate transfer drum 102 with pressure. The secondary transfer is performed on the transfer paper 155.

At this time, a bias voltage having the same polarity as the charging polarity of the toner on the intermediate transfer drum 102 is applied to the conductive layer 3 of the intermediate transfer drum 102, and the toner is electrostatically charged to the surface side of the transfer paper 155. Be attracted to. Due to this action and the releasability of the surface of the intermediate transfer drum 102 to the molten toner described above, the toner image on the intermediate transfer drum 102 is efficiently secondarily transferred onto the transfer paper 155, and at the same time, on the transfer paper 155. Is fixed in. In this way, the final image is formed on the transfer paper 155.

When the supply failure (jam) of the transfer paper 155 to the secondary transfer position B occurs, the toner on the intermediate transfer drum 102 is prevented from being directly transferred to the surface of the pressure drum 103. The pressure drum 103 may be separated from the intermediate transfer drum 102 when there is no transfer paper 155 in between.

Intermediate transfer drum 102 and pressure drum 103
The transfer sheet that has passed the secondary transfer position B between is discharged to the discharge unit 131 by the discharge roller pair 128.

Since the toner on the intermediate transfer drum 102 is efficiently transferred to the transfer paper 155 at the time of the secondary transfer,
Almost no toner remains on the intermediate transfer drum 102 after passing the secondary transfer position B. Normally, the toner transfer rate during the secondary transfer is 99% or more. However, since the transfer rate of 100% is not guaranteed under any condition, the image forming apparatus shown in FIG. 1 has the surface of the intermediate transfer drum 102 after the secondary transfer as shown in FIG. A cleaning device 113 that cleans the intermediate transfer drum 102 is provided to clean the toner remaining on the intermediate transfer drum 102.
When the cleaning device 113 is reached with the rotation of
The residual toner is removed from the surface of the intermediate transfer drum 102.

The reason why the toner remains on the intermediate transfer drum 102 after the secondary transfer is that a part of the toner on the intermediate transfer drum 102 is insufficiently melted and penetrates into the fibers of the transfer paper 155. The reason is that the melt transfer was not performed. Therefore, the state of the toner remaining on the intermediate transfer drum 102 that has passed the secondary transfer position B is a powdery state that is slightly deformed by heat.

The cleaning device 113 illustrated in FIG.
Has a brush roller 114 that rotates while slidingly contacting the surface of the intermediate transfer drum 102, and a casing 116 that stores the collected toner. Brush roller 114
Is composed of a conductive cored bar 114a having a brush 114b made of acrylic carbon or the like implanted therein. The brush 114b is grounded through the cored bar 114a. Such a brush 114b is in contact with the intermediate transfer drum 102 with a predetermined width W.
The brush roller 114 constitutes an example of a cleaning member that cleans the surface of the intermediate transfer drum 102.

The surface portion of the intermediate transfer drum 102 that has passed the secondary transfer position B is, for example, as shown in FIG. 5, the brush 114 of the brush roller 114 which is rotationally driven in the clockwise direction.
The toner remaining on the surface of the brush 11 is scraped off from the intermediate transfer drum 102 by being rubbed by b.
The toner adhering to 4b is removed by the scraping member 117.

At this time, in this example, the intermediate transfer drum 102
A bias voltage having the same polarity as the charge polarity of the residual toner on the intermediate transfer drum 102 is applied to the conductive layer 3 of No. 1, and the residual toner on the intermediate transfer drum 102 is separated from the surface thereof by the action of the electric field. The cleaning efficiency is improved by receiving the electrostatic force of the direction. In this way, by applying an electric force to the powdery residual toner slightly deformed by heat during cleaning,
This resists the adhesive force of the residual toner to the intermediate transfer drum 102, and facilitates the peeling of this toner toward the brush 114b.

As described above, in the image forming apparatus shown in FIG. 1, the toner image on the photoconductor 101 is primarily transferred onto the intermediate transfer drum 102 by the electrostatic primary transfer method, and the toner image on the intermediate transfer drum 102 is transferred. Is secondarily transferred onto the transfer paper 155 by the electrostatic secondary transfer method.

Here, in order to adopt the electrostatic primary transfer system, it is necessary to apply a voltage having a polarity opposite to the charging polarity of the toner to the conductive layer 3 of the intermediate transfer drum 102 as described above. On the other hand, to execute the electrostatic secondary transfer method,
It is necessary to apply a voltage having the same polarity as the charging polarity of the toner to the same conductive layer 3. Further, when cleaning the residual toner on the intermediate transfer drum 102, in order to improve the cleaning efficiency, a voltage having the same polarity as the charging polarity of the residual toner is applied to the conductive layer 3 of the intermediate transfer drum 102 during this cleaning operation. .

As described above, the polarity of the voltage applied to the conductive layer 3 required to execute the electrostatic primary transfer and the conductive layer 3 required to perform the electrostatic secondary transfer and the cleaning of the intermediate transfer drum 102. The polarities of the voltages applied to the electrodes are opposite to each other.
Therefore, if the above-mentioned respective voltages are applied to the entire conductive layer 3 of the intermediate transfer drum 102, the respective voltages cannot be applied simultaneously, and the electrostatic primary transfer operation is completed. After that, a voltage must be applied to the conductive layer 3 for electrostatic secondary transfer and cleaning. However, in such a case, the diameter of the intermediate transfer drum must be increased, and a large amount of time is required for each image forming operation, which inevitably results in a decrease in image forming speed.

Therefore, in the image forming apparatus of this embodiment, as described above, the conductive layer 3 of the intermediate transfer drum 102 is used.
However, a large number of electrodes 5 that are divided in the circumferential direction of the intermediate transfer drum 102 and are arranged over the entire circumference in the circumferential direction of the intermediate transfer drum 102 are configured.

As shown in FIG. 4, the electrodes 5 are electrically insulated from each other by the insulative elastic layer 2 located between them, and are also insulated from the base 1. The width of each electrode 5 in the rotation direction of the intermediate transfer drum 102 is, for example, about 1 to 2 mm.

FIG. 6 is a schematic diagram schematically showing a large number of electrodes 5 of the intermediate transfer drum 102. In this figure, among the aforementioned large number of electrodes 5, they are located facing the photoconductor 101. The electrodes are denoted by reference numeral 5a, and the electrodes facing the pressure drum 103 are denoted by reference numeral 5b. Similarly, reference numeral 5c is attached to the electrode located opposite to the brush roller 114 of the cleaning device 113. Since the intermediate transfer drum 102 is rotating, the photoconductor 101,
The electrodes 5 facing the pressure drum 103 and the brush roller 114 change one after another, but during such an operation, the electrodes facing the photoconductor 101, the pressure drum 103, and the brush roller 114 are changed to 5a, 5b, and 5c. To do.

The portion of the intermediate transfer drum 102 that is in pressure contact with the photoconductor 101 and the pressure drum 103 is elastically compressed and deformed, and is brought into pressure contact with the photoconductor 101 and the pressure drum 103 with a certain width in the circumferential direction of the drum 102. And a plurality of electrodes 5a
The plurality of electrodes 5b and the plurality of electrodes 5c face the photoconductor 101, the pressure drum 103, and the brush roller 114, respectively.

Here, at least when the above-mentioned primary transfer is performed, the voltage for this primary transfer is applied only to the electrode 5a facing the photoconductor 101. That is, the first voltage applying unit having the power supply 115 applies a voltage having a polarity opposite to the charge polarity of the toner on the photoconductor 101 to the electrode 5a.

Similarly, at least when the above-mentioned secondary transfer is performed, the charge polarity of the toner on the intermediate transfer drum 102 is applied to the electrode 5b facing the pressure drum 103 by the second voltage applying means having the power source 120. A voltage having the same polarity as is applied.

Similarly, in this example, at least when the surface of the intermediate transfer drum 102 is cleaned as described above,
A voltage having the same polarity as the charging polarity of the residual toner on the intermediate transfer drum 102 is applied to the electrode 5c facing the brush roller 114 of the cleaning device 113 by the third voltage applying unit having the power source 121.

As described above, for the purpose of the primary transfer, the purpose of the secondary transfer, and the purpose of cleaning the intermediate transfer drum 102, the voltage is not applied to the entire conductive layer 3 of the intermediate transfer drum 102 at once. , Separate these separately,
Photoconductor 101, pressure drum 103, and brush roller 11
The target voltage is applied only to the electrodes 5a, 5b and 5c facing the electrodes 4, respectively.

In this way, when the voltage for primary transfer is applied to the electrode 5a facing the photoconductor 101, it does not have any influence on other process equipment.
That is, even when voltages for secondary transfer and cleaning are applied to the electrodes 5b and 5c facing the pressure drum 103 and the brush roller 114, respectively, at the time of applying this voltage, the respective voltages are not applied. It does not interfere with the operation of. Therefore, it is possible to apply the above-mentioned respective voltages in parallel, so that the diameter of the intermediate transfer drum 102 can be set small and the speed of the image forming operation can be increased. While the intermediate transfer drum 102 is rotating once, the primary transfer, the secondary transfer, and the cleaning of the intermediate transfer drum 102 can be performed by using the electric field.

When a voltage is applied to the electrode 5c to clean the surface of the intermediate transfer drum 102, even if there is a toner image on the intermediate transfer drum 102 that has not been secondarily transferred to the transfer paper 155, The voltage application to the electrode 5c has no adverse effect on the toner image, and the disturbance of the toner image is prevented.

Further, since the voltage is not applied to the entire conductive layer 3 of the intermediate transfer drum 102 but to the local electrodes 5a, 5b, 5c of the electrodes 5, the voltage application efficiency is improved. be able to.

By the way, the above-described effects can be obtained by providing all the electrodes 105 at the same distance from the surface of the intermediate transfer drum 102 as shown in FIG. However, when the elastic material between the electrodes 105 causes a dielectric breakdown, for example, the voltage applied to the electrode facing the photoconductor affects the secondary transfer position and the position of the cleaning device, so that each electrode A sufficient space (for example, 10 to 500 μm, especially 200 μm) that does not cause dielectric breakdown must be provided between the electrodes. When a predetermined voltage is applied to each of the plurality of electrodes 105 facing each other, the potential of the surface of the intermediate transfer drum 102 corresponding to the electrodes 105 becomes non-uniform, which may cause unevenness of the electric field strength. As a result, density unevenness occurs in the toner image primarily transferred from the photoconductor onto the intermediate transfer drum or the toner image secondarily transferred from the intermediate transfer drum onto the transfer paper.

Therefore, in this example, as shown in FIG. 4 and briefly described above, the surface 10 of the intermediate transfer drum 102 is
The electrode 5 is composed of two types of electrodes 5A and 5B having different depths from 2a. In the example of FIG. 4, the electrode 5 as a whole is located inside the intermediate transfer drum 102 when viewed from the surface 102 a side of the intermediate transfer drum 102.
Are arranged so that there is no part that does not exist. That is, as shown in FIG. 4, the electrode 5A nearer to the surface 102a and the electrode 5B farther from the surface 102a are separated from each other as indicated by a symbol R when viewed from the side of the surface 102a. The electrodes 5 are arranged so as to overlap each other.

According to this structure, when the intermediate transfer drum 102 is viewed from the surface 102a, the electrodes 5 are present on the entire surface thereof. Therefore, when a predetermined voltage is applied to the electrodes 5a, 5b, 5c (FIG. 6), these Intermediate transfer drum 102 corresponding to
The electric potential of the surface portion of, that is, the electric field strength thereof can be made uniform. Therefore, it is possible to prevent a problem that density unevenness occurs in the toner image primarily transferred onto the intermediate transfer drum 102 and the toner image secondarily transferred onto the transfer paper 155, and it is possible to obtain a high quality image.

Moreover, it is possible to increase the distance between the individual electrodes, and it is possible to prevent the occurrence of dielectric breakdown between the electrodes to which a voltage is applied without any trouble. For example, the photoconductor 10
Even if a voltage of up to 3 KV is applied to the electrode 5a (FIG. 6) corresponding to the portion of the intermediate transfer drum 102 that is pressed against 1, it is possible to maintain the insulating state of each electrode 5, and thus
It is possible to apply the voltage for achieving the respective purpose to the predetermined electrodes 5a, 5b and 5c without affecting the other process operations at all.

Further, in this example, as shown in FIG. 4, the plurality of electrodes 5 are arranged in a zigzag pattern when viewed from the end face side in the axial direction of the intermediate transfer drum 102. According to this arrangement configuration, the intended purpose can be achieved and the cost of the intermediate transfer drum 102 can be reduced by simply arranging the electrodes 5 most simply.

Next, the electrodes 5a of the intermediate transfer drum 102,
A specific example of the first to third voltage applying means for applying a predetermined voltage to 5b and 5c will be described.

FIG. 3 shows the intermediate transfer drum 10 shown in FIG.
2 is an external perspective view of FIG. 2, but as shown in these drawings, a part of the electrode 5 is exposed to the outside on the surface side (transfer surface side) of the intermediate transfer drum 102.
Each electrode 5 is exposed to the outside at one end of the intermediate transfer drum 102 in the axial direction. The length of the intermediate transfer drum 102 in the axial direction is longer than the length of the photosensitive member 101 in the same direction as indicated by L in FIG. 2, and the electrode 5 is exposed to the outside at this L portion. . L
Is set to about 20 mm, for example.

On the other hand, each voltage applying means includes electrodes 5a, 5
b, having a voltage applying member for supplying a voltage to 5c,
In this example, each voltage applying member is connected to each power source 1 as shown in FIG.
It is composed of conductive rollers 6a, 6b, 6c electrically connected to 15, 120, 121, respectively. These conductive rollers 6a, 6b, 6c are connected to the electrode 5 described above.
The a, 5b, and 5c are fixedly supported so as to come into contact with the exposed portions thereof and rotate with the rotation of the intermediate transfer drum 102. Each conductive roller 6a, 6
b and 6c are in contact with the intermediate transfer drum 102 from the surface side thereof with a predetermined width (nip) in the circumferential direction. In this way, each power supply 115, 120, 121
Is applied to each of the electrodes 5a, 5b, 5c. As the intermediate transfer drum 102 rotates, the photoconductor 1
01, the pressure drum 103, and the cleaning brush 11
4, different electrodes face each other in sequence, but the conductive rollers 6a, 6 are connected to the facing electrodes 5a, 5b, 5c.
A predetermined voltage is applied from the power supplies 115, 120 and 121 via b and 6c.

In the embodiment shown in FIG. 7, the first voltage applying means is composed of two electrically independent conductive rollers 6 respectively.
a, 16a, and one of the conductive rollers 6a has the same voltage supply member as in the embodiment shown in FIG.
The electrode 5A of the exposed electrodes 5a is in contact, and the other conductive roller 16a is in contact with the electrode 5B of the exposed electrodes 5a, just as in FIG.

One conductive roller 6a is connected to the power supply 115, and the other conductive roller 16a is connected to the other power supply 1.
It is configured such that a larger voltage is applied to the electrode 5B that is connected to 15a and is closer to the surface 102a of the intermediate transfer drum 102 than to the electrode 5B that is farther from the surface 102a. For example, 500V is applied to the electrode 5A,
A voltage of 1.5 KV is applied to each of the electrodes 5B.

As described above, by applying voltages of different values independently to the electrodes 5A and 5B having different depths from the surface 102a of the intermediate transfer drum 102, the intermediate transfer drum at the primary transfer position A can be obtained. Surface 10 of 102
The potential of 2a can be made more uniform, and the intermediate transfer drum 10
The density unevenness of the toner image primarily transferred to No. 2 can be more reliably prevented.

As described above, the configuration in which different magnitude voltages are applied to the electrodes 5A and 5B can be applied to the second and third voltage applying means, and in particular, by adopting the second voltage applying means. The electric potential of the surface portion of the intermediate transfer drum 102 at the secondary transfer position B can be made highly uniform, density unevenness of the toner image transferred to the transfer paper 155 can be eliminated, and a high quality final image can be obtained. Of course, when this configuration is applied to the second voltage applying means, the polarity of the voltage applied to each electrode 5A, 5B is different from that of the first voltage applying means. This is the same when applied to the third voltage applying means.

A conductive brush or the like can be used as the voltage supply member of each voltage applying means instead of the conductive roller. However, when a conductive brush is used, these are applied to the intermediate transfer drum 102 including the electrode 5. Because of the rubbing, the rubbing portion of the intermediate transfer drum 102 may be worn relatively early, and the number of electrodes with which the conductive brush contacts may become unstable.

On the other hand, as shown in the above embodiment, when a conductive roller that rotates with the rotation of the intermediate transfer drum 102 is used as the voltage supply member, rubbing between these and the intermediate transfer drum 102 is avoided. Even when the intermediate transfer drum 102 is made of a soft material, its wear can be suppressed. Moreover, the number of electrodes in contact with each conductive roller can be kept constant at all times, and a voltage can be constantly applied to a predetermined range of the intermediate transfer drum 102. This allows
It is possible to always keep the quality of the final image constant.

As the conductive roller, a roller made of a rigid body or an elastic body, such as a rigid metal such as aluminum or a silicone rubber in which conductive particles such as metal or carbon are dispersed, can be appropriately used.

By the way, the electrodes 5a, 5b and 5c to which the voltage is applied as described above are, as shown in FIG. 6, the intermediate transfer drum 102, the photosensitive member 101 and the intermediate transfer drum 102.
And the pressure drum 103, and the electrodes located within the range of each contact portion W between the intermediate transfer drum 102 and the brush roller 114, or may be located across the contact portion W and the outer region in the vicinity thereof. It may be an electrode. In short, the photoconductor 101, the pressure drum 103, and the brush roller 114
It suffices to apply a voltage to the electrode facing the.

However, when a voltage is applied to the electrodes located in the region outside the contact portion W and outside the contact portion W, an electric field is also formed in the void S (FIG. 6) in the outside region, Photoconductor 101 or intermediate transfer drum 102
The upper toner may scatter due to the action of this electric field, which may disturb the toner image or cause cleaning failure.

Therefore, in this example, the conductive roller 6a or 6a and 16a of the first voltage applying means is the intermediate transfer drum 10
The state of contact with 2 is defined as follows.

That is, as schematically shown in FIG. 8, the conductive rollers 6a and 16a are arranged in the circumferential direction of the roller 6a.
a, 16a and the contact width a between the intermediate transfer drum 102 and the intermediate transfer drum 102 in the circumferential direction of the rotary member 102.
Is smaller than the contact width (contact width) W between the photosensitive member 101 and the photosensitive member 101, and the conductive roller 6a, 16a and the intermediate transfer drum 102 have a contact width W between the intermediate transfer drum 102 and the photosensitive member 101.
It occupies the corresponding position within the range. The same applies when one conductive roller 6a is used as in the embodiment shown in FIG.

According to the above structure, no electric field is formed in the space S outside the contact portion W between the photosensitive member 101 and the intermediate transfer drum 102, and the electric field is formed only inside the contact portion W. . Therefore, it is possible to prevent the problem that the toner on the photoconductor 101 scatters, prevent the occurrence of the discharge phenomenon in the space S, and prevent the disturbance of the toner image.

With the above-mentioned structure, the conductive rollers 6b and 6c on the secondary transfer position B and the cleaning device 113 are arranged.
Can also be applied to a contact portion with the intermediate transfer drum 102, which also effectively prevents toner scattering.

As in the embodiment shown in FIG. 7, the voltage applying means electrically connects the electrodes 5A and 5B having different depths electrically independently of each other. 16a, these conductive rollers are connected to the intermediate transfer drum 102 as shown in FIG.
The electrode 5 exposed to the outside at one end in the axial direction X of
By bringing them into contact with A and 5B, the conductive roller 6
Since a and 16a can be collectively arranged in a region on one side of the intermediate transfer drum 102 in the axial direction, the wiring can be easily performed and the structure of the apparatus can be simplified. Further, in particular, the conductive rollers 6a, 1 are provided at the rear end of the intermediate transfer drum 102.
By disposing 6a, the wiring that uses high voltage can be kept away from the operator, and the safety can be enhanced more reliably.

In the above structure, each of the second voltage applying means and the third voltage applying means electrically contacts the electrodes 5A and 5B having different depths electrically independently of each other. The present invention can also be applied to the case where the intermediate transfer drum 102 is provided with a conductive roller). In this case, all the conductive rollers of the first to third voltage applying means are connected to one end side of the intermediate transfer drum 102, particularly the back side. By arranging it at the end portion of, the above-mentioned advantages can be obtained more reliably.

As described above, when the conductive rollers are collectively arranged on one end side of the intermediate transfer drum 102, the structure of the apparatus can be simplified. On the other hand, the conductive roller is particularly preferable. When a plurality of conductive rollers are arranged at one end side of the intermediate transfer drum 102, the intermediate transfer drum 102 is largely compressed and deformed at this end side. , Photoconductor 101
In the area of the image portion of the intermediate transfer drum 102 to which the toner image is transferred from, a large distortion occurs on the surface thereof, which may disturb the toner image.

In such a case, as shown in FIG.
Electrodes 5A and 5B having different depths are exposed to the outside at one end and the other end of the intermediate transfer drum 102, and conductive rollers 6a and 16 are provided at the respective ends.
It is preferable that a is brought into contact with each other to apply a voltage to each of the electrodes 5A and 5B. By doing so, it is possible to prevent the one end side of the intermediate transfer drum 102 from being largely compressed and deformed, the distortion of the image portion surface of the intermediate transfer drum 102 is minimized, and the disturbance of the toner image is prevented. be able to.

In the above structure, a plurality of conductive rollers (voltage supply members) in which each of the second and third voltage application means electrically independently contacts the electrodes 5A and 5B having different depths from each other. The present invention can also be applied to the case where the above-mentioned condition is present, whereby the distortion of the surface of the image portion of the intermediate transfer drum 102 can be suppressed more reliably.

As shown in FIGS. 2 and 9, the length of the intermediate transfer drum 102 itself, or at least the electrode 5 inside the intermediate transfer drum 102 in the axial direction of the intermediate transfer drum, is the same as that of the photosensitive member 101. By making the length longer than the length, for example, a voltage supply member formed of a conductive roller can be brought into contact with the electrode 5 from the transfer surface side of the intermediate transfer drum 102, and the contact portion is in the axial direction of the intermediate transfer drum 102. Since it can be arranged in the region outside the image portion at the end portion, the structure of the intermediate transfer drum 102 can be simplified, and distortion on the image portion surface of the intermediate transfer drum 102 can be suppressed. If the conductive roller is configured to contact the electrode from the back surface side of the image portion of the intermediate transfer drum 102, the surface of the image portion is largely deformed, and the disorder of the toner image is inevitable.

In each of the above-mentioned configurations, in order to more surely prevent the distortion on the surface of the image portion of the intermediate transfer drum 102,
The voltage supply member is composed of an elastic conductive roller,
It is practical to set the rubber hardness of the roller to be lower than the rubber hardness of the portion of the intermediate transfer drum 102 that contacts the roller. The conductive rollers 6a, 6b, 6c; 16a are softer and more easily elastically deformed than the electrode 5 and the elastic layer 2 of the intermediate transfer drum 102, and the rubber hardness of these rollers is set to 2
It is set to about 0 to 80 °, especially about 50 °. By doing so, when the elastic roller and the intermediate transfer drum 102 come into contact with each other, the elastic roller is elastically deformed to a greater extent, so that the compressive deformation of the intermediate transfer drum 102 becomes extremely small, and the image portion surface thereof Can be effectively suppressed, and the disturbance of the toner image can be prevented more reliably.

The intermediate transfer drum 102 shown in FIG. 10 has a rigid drum-shaped base 1 made of aluminum or the like.
An insulating elastic layer 2 having a thickness of 150 μm to 5000 μm, preferably about 3000 μm is laminated, an insulating layer 4 made of, for example, a silicone rubber sheet is laminated on the surface thereof, and a large number of electrodes 5 are embedded in the elastic layer 2. The elastic layer 2 is
The elastic layer shown in FIG. 2 is made of a material that is more easily compressed and deformed, for example, a compressible polymer substance, especially a plastic sponge. The insulating layer 4 on the surface is 10 to 300 μm,
In particular, it has a thickness of about 50 μm, exhibits adhesiveness to toner at room temperature, and exhibits releasability to molten toner.

Also in this example, the electrode 5 is the intermediate transfer drum 102.
Is continuous in the axial direction, is divided into a large number in the rotational direction, and is composed of two types of electrodes 5A and 5B having different depths from the surface 102a. The thickness of each electrode 5 is 30 to 100
.mu.m, preferably 30 .mu.m, all of which are staggered. However, in this embodiment, when the electrodes 5 are viewed from the surface 102a side of the intermediate transfer drum 102, the electrodes 5 do not overlap with each other, and a minute gap R1 exists between the electrodes.

FIG. 10 shows a state in which the intermediate transfer drum 102 is in a non-compressed free state, and FIG. 11 shows the same intermediate transfer drum 102 as the photosensitive member 101 or the pressure drum as shown in FIG. It shows a state when it is pressed against 103 and elastically compressed and deformed.

When the electrode 5 is not compressed as shown in FIG.
A is 80 μm from the surface 102a, and electrode 5B is the surface 1
Since it is at a depth of from 02a to 120 μm, the electrodes 5 are positioned with a sufficiently large distance through the insulating elastic layer 2, and the insulation between the electrodes is secured.

When the intermediate transfer drum 102 is brought into pressure contact with the photosensitive member 101 or the pressure rotating member 103, and the elastic layer 2 is compressed and deformed in the thickness direction as shown in FIG.
Since the elastic layer 2 is larger than the elastic layer 2 and the amount of compressive deformation of the insulating layer 4 is extremely small, the electrode 5B that has been largely separated from the surface 102a up to then is relatively moved so as to float to the surface 102a side. Move to multiple types of electrodes 5A,
5B is almost the same distance from the surface 102a of the intermediate transfer drum 102. The thickness of the elastic layer 2 in the uncompressed state is about 3
If it is 000 μm, its thickness in a compressed state is, for example, about 2000 μm. Along with this, the distance between the upper electrode 5A and the lower electrode 5B in the thickness direction becomes, for example, 15 μm, all electrodes 5 are located at substantially the same distance from the surface 102a, and the intervals between the respective voltages are narrowed. As described above, the predetermined voltage is applied to the electrodes thus formed, and the primary or secondary transfer of the toner image is performed.

As described above, the intermediate transfer drum 102 is
The compressed state shown in FIG. 11 is applied only to the portion pressed against the photosensitive member 101 or the pressure drum 103, and voltage is applied to the compressed electrodes of the intermediate transfer drum 102. At this time, the respective electrodes come close to each other. Since they are located at the same position, the potential on the surface 102a of the intermediate transfer drum 102 corresponding to the electrode to which the voltage is applied becomes substantially constant, and the electric field intensity becomes uniform. Therefore, even if a voltage of the same strength is applied to the electrodes 5A and 5B, it is possible to prevent the problem that density unevenness occurs in the toner image that is primarily transferred to the intermediate transfer drum 102 or secondarily transferred to the transfer paper 155. It becomes possible.

The elastic layer 2 when compressed exhibits a particularly high insulating property and can prevent dielectric breakdown between the electrodes. Even if only a plurality of electrodes facing the photoconductor 101 or the pressure drum 103 are in the conductive state, the insulation between the electrodes of the uncompressed portion of the intermediate transfer drum 102 is ensured. Pressure drum 10
There is no possibility that the voltage applied to the electrode facing 3 will affect the operation of other processes.

Even if a rubber layer having a compressibility less than that of the elastic layer 2 is interposed between the elastic layer 2 and the base 1, the above-described effects can be obtained.

FIG. 12 shows an example in which the intermediate transfer rotator is constituted by an endless belt 102A wound around a plurality of rollers (not shown). This belt 102A comprises an insulating flexible base layer 1A and It is composed of an insulating layer 4A made of, for example, silicone rubber laminated on its surface and a large number of electrodes 5 embedded in the base layer 1A. The insulating layer 4A has a thickness of, for example, about 70 μm, and its rubber hardness is, for example, about 40 degrees. is there. Each electrode 5 is made of, for example, polyimide in which carbon is dispersed, and its thickness is, for example, about 50 μm.

Similar to the intermediate transfer drum 102 shown in FIG. 1, the belt 102A also comes into pressure contact with the photosensitive member 101 and the pressure drum 103 and rotates in the direction shown by the arrow P in FIG. In exactly the same manner as described above, the toner image is primarily transferred from the photoconductor 101, and the toner image on the belt 102A is secondarily transferred to the transfer sheet fed between the belt and the pressure drum.

As in the case of FIG. 4, each electrode 5 is divided into a large number in the circumferential direction (rotational direction P) of the belt 102A and is continuous in the width direction of the belt 102A.
It is composed of electrodes 5A and 5B having different depths from the surface of 02A. Further, as shown in FIG. 13, a part of the base layer 1A is
The conductive rollers 6a, 16a are rollingly contacted with the electrodes 5A, 5B, which are cut out along the entire circumference of the belt 102A, thereby supplying a voltage. In the areas of the primary transfer position B (FIG. 1) and the brush roller 114, the conductive roller is also in contact with the electrodes.

As described above, even when the intermediate transfer rotary member is composed of the belt 102A which does not have a rigid base as a base, as shown in FIG. For example, a voltage supply member composed of a conductive roller is brought into contact with the belt 102A and the photoconductor 10
By applying a voltage to the electrode in the area of the contact portion with No. 1, it is possible to prevent the image surface of the belt 102A from being distorted. Further, even if the voltage supply member is provided over the entire width of the image portion of the belt 102A, the distortion of the image portion can be suppressed.

In each of the embodiments described above, two types of electrodes 5 having different depths from the surface of the intermediate transfer rotator are used.
Although A and 5B are provided, three or more types may be provided. In the embodiment shown in FIG. 14, the intermediate transfer drum 102
Inside, the three types of electrodes 5A, 5B and 5C having different depths are provided from the surface 102a, and in this case as well, each configuration described above can be adopted respectively.

Further, a voltage supply member constituted by, for example, a conductive roller is supported so as to be movable between a position for supplying a voltage by contacting the electrode of the intermediate transfer rotator and a release position separated from the electrode. However, the voltage supply member may be configured to contact the electrode only when the voltage needs to be applied to the electrode.

The configuration relating to the voltage supply to the electrodes of the intermediate transfer rotator shown in each of the above embodiments is not limited to the case where the intermediate transfer rotator has a plurality of types of electrodes having different depths. As illustrated in FIG. 15, the present invention can also be applied to the case where a plurality of electrodes, which are divided in the circumferential direction and are located at the same depth position, are provided inside the intermediate transfer rotator.

The present invention relates to the above-mentioned first voltage applying means and second
If at least one of the voltage applying means is provided, the intended purpose can be achieved.

Further, toner images of different colors are sequentially formed on the toner image carrier, the toner images are superposed on the intermediate transfer rotator and primary-transferred, and then the multicolor toner images are collectively transferred to the transfer material to the secondary transfer. The present invention is also applicable to an image forming apparatus that obtains a multicolor image by transferring or primary transferring a toner image for each color onto an intermediate transfer rotator, and then sequentially superimposing the toner image on a transfer material and performing a secondary transfer. It is possible.

[0119]

According to the structure described in claim 1, the toner image on the toner image bearing rotary member is primary-transferred onto the intermediate transfer rotary member by the electrostatic primary transfer method without affecting other elements. Yes, or not only the toner image on the intermediate transfer rotator can be secondarily transferred to the recording medium by the electrostatic secondary transfer method, but the potential on the surface of the intermediate transfer rotator corresponding to the voltage-applied electrodes is not uniform. It is possible to form a high-quality toner image having no density unevenness by suppressing the problem that occurs.

According to the structure described in claim 2, the above effect can be obtained with a simple structure.

According to the third aspect of the invention, it is possible to easily achieve the potential uniformity on the surface of the intermediate transfer rotator corresponding to the electrode to which the voltage is applied.

According to the structure described in claim 4, the effect can be obtained more reliably by changing the magnitude of the voltage applied from the surface of the intermediate transfer rotator to the electrodes of different depths. it can.

According to the fifth aspect of the invention, the effect described above can be obtained by the simplest electrode arrangement, and the cost of the intermediate transfer rotary member can be reduced.

According to the structure of claim 6, a voltage can be applied to the electrodes simply and reliably.

According to the seventh aspect of the invention, it is possible to suppress the toner scattering on the toner image bearing rotary member or the intermediate transfer rotary member and form a high quality toner image.

According to the eighth aspect of the invention, since the conductive roller is made of an elastic material, it is possible to suppress the occurrence of distortion on the surface of the image portion of the intermediate transfer rotator and form a high quality toner image.

According to the ninth aspect, the voltage applying means can be compactly integrated.

According to the structure of the tenth aspect, it is possible to effectively suppress the distortion of the surface of the image portion of the intermediate transfer rotator and form a high quality toner image.

[Brief description of drawings]

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

FIG. 2 is a cross-sectional view showing the intermediate transfer drum cut in the axial direction thereof.

FIG. 3 is an external perspective view of an intermediate transfer drum.

FIG. 4 is a sectional view showing an intermediate transfer drum cut in a radial direction.

FIG. 5 is an explanatory diagram showing a relationship between a cleaning device for the intermediate transfer drum and electrodes in the intermediate transfer drum.

FIG. 6 is an explanatory diagram schematically showing electrodes of an intermediate transfer drum.

FIG. 7 is a sectional view similar to FIG. 2, showing another example in which a voltage is applied to an electrode via a conductive roller.

FIG. 8 is an explanatory diagram showing an example of a contact width between a conductive roller and an electrode and a contact width between a photoconductor and an intermediate transfer drum.

FIG. 9 is a cross-sectional view similar to FIG. 2, showing still another example in which a voltage is applied to electrodes via a conductive roller.

FIG. 10 is a sectional view showing another embodiment of the intermediate transfer drum.

11 is a cross-sectional view of a portion of the intermediate transfer drum shown in FIG. 10, which is in pressure contact with a photoconductor or a pressure drum.

FIG. 12 is a cross-sectional view showing an example in which the intermediate transfer rotary member is configured as an endless belt.

13 is a cross-sectional view of the endless belt shown in FIG. 12 cut in the width direction thereof.

FIG. 14 is a cross-sectional view showing an intermediate transfer drum having three types of electrodes having different depths.

FIG. 15 is a cross-sectional view showing an example of a conventionally proposed intermediate transfer drum.

[Explanation of symbols]

 2 elastic layer 5 electrode 5A electrode 5B electrode 5a electrode 5b electrode 6a conductive roller 6b conductive roller 16a conductive roller 102a surface a contact width W contact width X axial direction Y circumferential direction

Claims (10)

[Claims] 1. A toner image bearing rotating body having a toner image formed of toner charged to a predetermined polarity on its surface, and the toner image on the rotating body is primarily transferred while being in close contact with the rotating body. An image forming apparatus having an intermediate transfer rotator and a pressure rotator that presses the recording medium onto the intermediate transfer rotator when the toner image on the intermediate transfer rotator is secondarily transferred onto the recording medium. The intermediate transfer rotator has a plurality of electrodes inside which are divided and arranged in the circumferential direction, and these electrodes are formed from at least two kinds of electrodes having different depths from the surface of the intermediate transfer rotator. A first voltage applying unit that applies a voltage having a polarity opposite to the charging polarity of the toner on the toner image bearing rotary member to the electrode facing the toner image bearing rotary member when at least the primary transfer is performed, At least When the secondary transfer is performed, at least one of second voltage applying means for applying a voltage having the same polarity as the charging polarity of the toner on the intermediate transfer rotator to the electrode facing the pressure rotator. An image forming apparatus comprising a voltage applying unit. 2. The image forming according to claim 1, wherein the electrodes are arranged such that there is no portion where the electrodes do not exist inside the intermediate transfer rotator when viewed from the surface side of the intermediate transfer rotator. apparatus. 3. When the intermediate transfer rotary member is brought into pressure contact with the toner image bearing rotary member or the pressure rotary member, the plurality of types of electrodes are
So that the distance is almost the same from the surface of the intermediate transfer rotor.
The image forming apparatus according to claim 1, wherein the electrode is provided in an elastic layer of the intermediate transfer rotating body. 4. The first voltage applying means and the second voltage applying means apply a larger voltage to an electrode distant from the surface of the intermediate transfer rotor than to an electrode closer to the surface of the intermediate transfer rotator. The image forming apparatus according to claim 1, wherein the image forming apparatus is configured according to claim 1. 5. The plurality of electrodes are arranged in a zigzag pattern when viewed from the end face side of the intermediate transfer rotator.
The image forming apparatus according to any one of 1. 6. The first and second voltage applying means have voltage supply members for supplying a voltage to the electrodes, and a part of each electrode is exposed to the outside on the surface side of the intermediate transfer rotator. The image forming apparatus according to any one of claims 1 to 5, wherein the voltage supply member contacts the exposed electrode portion to supply a voltage. 7. The voltage supply member is composed of a conductive roller that rotates together with the rotation of the intermediate transfer rotary member, and the contact width between the roller and the intermediate transfer rotary member in the circumferential direction of the conductive roller. In the circumferential direction of the intermediate transfer rotator,
A position narrower than the contact width between the rotating body and the toner image carrying rotating body, and the conductive roller and the intermediate transfer rotating body correspond to the contact width range between the intermediate transfer rotating body and the toner image carrying rotating body. The image forming apparatus according to claim 6, wherein 8. The voltage supply member is formed of an elastic conductive roller, and the rubber hardness of the roller is set to be lower than the rubber hardness of a portion of the intermediate transfer rotator in contact with the roller. 7. The image forming apparatus according to item 7. 9. Each of the first and second voltage applying means has a plurality of voltage supply members that are in contact with respective electrodes having different depths, and the plurality of voltage supply members of each voltage applying means are intermediate. 9. The image forming apparatus according to claim 1, wherein one end of the transfer rotary member in the axial direction is in contact with an electrode exposed to the outside. 10. The first and second voltage applying means each have a plurality of voltage supply members that are in contact with respective electrodes having different depths, and the plurality of voltage supply members of each voltage applying means are intermediate. The image forming apparatus according to any one of claims 1 to 8, wherein the one and the other ends of the transfer rotator in the axial direction are in contact with the electrodes exposed to the outside.