JP3233371B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming a toner image on a rotary member carrying a toner image and transferring the toner image to a recording medium via an intermediate transfer rotary member.

[0002]

2. Description of the Related Art A conventional image forming apparatus such as an analog copier, a digital copier, a laser printer, or a facsimile generally transfers a toner image formed on a rotary member carrying a toner image directly to a recording medium. It is configured as follows. On the other hand, the toner image on the toner image bearing rotating body is temporarily transferred onto the intermediate transfer rotating body once, and the intermediate image is transferred onto the recording medium pressed against the intermediate transfer rotating body by the pressing rotating body. 2. Description of the Related Art An image forming apparatus for secondary-transferring a toner image on a transfer rotary member has been proposed (for example, Japanese Patent Publication No.
41679 or JP-A-2-183288).

[0003]

In the image forming apparatus of this type, as a method of secondary-transferring the toner image on the intermediate transfer rotator to a recording medium, the toner on the intermediate transfer rotator is melted, and the intermediate transfer rotator is rotated. A fusing method in which the molten toner image is secondarily transferred to a recording medium by utilizing the releasability of the body surface, and an electric field is applied between a pressurizing rotator and an intermediate transfer rotator that presses the recording medium against the intermediate transfer rotator. And a method in which a toner image on the intermediate transfer rotating body is electrostatically secondarily transferred onto a recording medium, or a method in which a fusing method and an electrostatic method are used in combination.

[0004] Here, the above-mentioned electrostatic system alone or a system in which the electrostatic system is used in combination with the melting system is referred to as an electrostatic secondary transfer system. An electrode made of a conductive layer is provided around the entire circumference,
A voltage having the same polarity as the charge polarity of the toner on the intermediate transfer rotator is applied to this electrode, so that the toner image on the intermediate transfer rotator can be electrostatically transferred to the surface of the recording medium.

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.

[0006] In addition, when a voltage is applied to such an electrode, there is a possibility that other process operations will be adversely affected. For example, when the toner image on the toner image bearing rotating body is primarily transferred to the intermediate transfer rotating body, a voltage having a polarity opposite to that of the toner on the toner image bearing rotating body may be applied to the electrodes of the intermediate transferring rotating body. However, at this time, the polarity of the voltage applied to the electrode of the intermediate transfer rotating body for the purpose of the primary transfer,
As described above, the polarities of the voltages applied to the electrodes of the intermediate transfer rotator for the purpose of secondarily transferring the toner image on the intermediate transfer rotator to the recording medium are opposite to each other.

Therefore, when the toner image on the rotating rotary member is primarily transferred to the intermediate transfer rotating member while applying a voltage having a polarity opposite to that of the toner on the intermediate transferring rotating member to the electrode, Cannot be applied to the electrode of the intermediate transfer rotating body, and the secondary transfer must be performed after the primary transfer. For this reason, the disadvantage that the intermediate transfer rotating body becomes large and that the image forming operation requires a long time is required.

Therefore, the present inventor has used an intermediate transfer rotator having a plurality of electrodes divided and arranged in the circumferential direction,
When the toner image on the intermediate transfer rotator is secondarily transferred to the recording medium, a voltage having the same polarity as the charge polarity of the toner on the intermediate transfer rotator is applied to the electrode of the intermediate transfer rotator facing the pressure rotator. We proposed an image forming apparatus that applies a voltage. According to this configuration, the toner image on the intermediate transfer rotating body can be secondarily transferred to the recording medium by the electrostatic secondary transfer method without affecting other process operations, and the above-described disadvantage can be avoided. .

[0009]

[0010]

At this time, a plurality of toner images are successively formed successively on a toner image bearing rotating body, and these are primary-transferred one by one onto an intermediate transfer rotating body, and each of the toner images is transferred to the aforementioned electrostatic image bearing member. When a continuous image forming operation of sequentially performing secondary transfer on a recording medium by a secondary transfer method is performed, a toner image is not formed in a non-image area between image areas on an intermediate transfer rotator where each toner image is formed. Not formed.

However, since a small amount of unnecessary toner may adhere to the non-image area, when the non-image area is in contact with the pressing rotator or the recording medium, the non-image area is applied to the electrode of the intermediate transfer rotator. If a voltage having the same polarity as the charged polarity of the toner is kept applied, the unnecessary toner attached to the non-image area on the intermediate transfer rotating body is transferred to the surface of the pressure rotating body or to the recording medium. As a result, the pressing rotator is stained with the toner, or the background is stained on the recording medium, and the image quality of the final image is deteriorated.

SUMMARY OF THE INVENTION It is an object of the present invention to prevent a decrease in voltage application efficiency to an electrode of an intermediate transfer rotator, and to transfer a toner image on an intermediate transfer rotator to a recording medium without affecting other process operations. It is an object of the present invention to provide an image forming apparatus capable of performing a next transfer and suppressing a problem that unnecessary toner attached to a non-image area on an intermediate transfer rotator is transferred to a pressing rotator or a recording medium.

[0014]

[0015]

[0016]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a toner image bearing rotary member on which a toner image is formed, and an intermediate transfer on which the toner image on the toner image bearing rotary member is primarily transferred. A rotator, and a pressure rotator that presses against the intermediate transfer rotator when the toner image on the intermediate transfer rotator is secondarily transferred to a recording medium, in order to bring the recording medium into close contact with the intermediate transfer rotator. In the image forming apparatus, the intermediate transfer rotator has a plurality of electrodes divided and arranged in a circumferential direction thereof, and an intermediate transfer rotator is provided at a pressure contact portion between the intermediate transfer rotator and the pressure rotator. An image forming apparatus provided with voltage applying means for applying a voltage having the same polarity as the charging polarity of the toner on the intermediate transfer rotating body to the electrode facing the pressure rotating body only when the upper image area exists. Suggest.

At this time, it is advantageous to use a toner produced by a polymerization method.

It is advantageous that the intermediate transfer rotating body has elasticity.

[0019]

[0020]

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

The image forming apparatus shown in FIG. 1 has a drum-shaped photosensitive member 101 which is an example of a rotating member carrying a toner image, an intermediate transfer drum 102 which is an example of a structure of an intermediate transfer rotating member.
Similarly, the photosensitive drum 101 and the intermediate transfer drum 102 have a pressure roller 103 which is an example of a pressure rotating body, and are pressed against each other. The intermediate transfer drum 102 and the pressure roller 103 also come into pressure contact with each other, and these elements 101,
Each of 102 and 103 is driven to rotate 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 roller 103,
In order to maintain the respective press-contact forces in a predetermined state, a spring is provided, and, for example, the rotating shafts thereof are spring-connected. Further, the photosensitive member 101 and the intermediate transfer drum 102 or the intermediate transfer drum 102 and the pressure roller 103 can be pressed or separated according to a sequence.

It is also possible to form the toner image bearing rotating body, the intermediate transfer rotating body and the pressing rotating body from belt-shaped ones.

As will be described in detail later, the photosensitive member 101
A toner image is formed on the intermediate transfer drum 102 at the primary transfer position indicated by the symbol A in FIG.
The primary transfer is performed. Further, the toner image primarily transferred onto the intermediate transfer drum 102 is fed between the intermediate transfer drum 102 and the pressure roller 103 as described later, and the transfer paper 155 clamped by the pressure roller 103 by the clamper 150. The secondary transfer is performed at the secondary transfer position indicated by the symbol B above. Hereinafter, the configuration of the image forming apparatus shown in FIG. 1 will be clarified while an example of these series of operations is described in detail.

The photoreceptor 101 illustrated in FIG. 1 is an organic photoreceptor having relatively excellent pressure resistance and heat resistance. The photoreceptor 101 moves counterclockwise as described above with the start of the image forming operation. When the rotation starts, the photosensitive member 101 and the intermediate transfer drum 102 rotate at a constant linear speed without any difference 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 is set to about -800V.

Next, a laser beam 110 modulated based on an image signal by the laser optical system 106 exposes the surface of the uniformly charged photosensitive member 101 to an image, and a predetermined electrostatic latent image is formed on the photosensitive member 101. To form This latent image is a laser beam 1
The portion irradiated with No. 10 (surface potential is about -100 V) is used as the toner adhering portion, and the unexposed portion (surface potential is about -800 V).
V) is formed as a background portion.

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

The above-described electrostatic latent image 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, and the powdery developer in the developing device is transported by the rotation of the developing device. This developer is a two-component developer in which a high-resistance nonmagnetic toner and a magnetic carrier are mixed, and the toner and the carrier are frictionally charged to polarities opposite to each other. In this example, it is assumed that the toner is negatively charged.

The developer has a developing bias voltage of -60.
By the sleeve 104 rotating by applying 0 V, it is carried to a development area where the sleeve and the photoconductor 101 are opposed to each other, where reversal development is performed. That is, the negatively charged toner is electrostatically transferred to and adheres to the low potential portion of the electrostatic latent image formed on the photoconductor 101, and the high potential portion becomes a 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 to improve dot reproducibility.
It is desirable to use a toner having a particle size of not more than μm, and for this purpose, it is advantageous to use a toner having a narrow particle size distribution produced by, for example, a polymerization method.

As described above, a toner image composed of toner charged to a predetermined polarity is formed on the surface of the photosensitive member 101, and the photosensitive member portion on which the toner image is formed is subjected to primary transfer in pressure contact with the intermediate transfer drum 102. The position reaches the position A, where 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 method using the adhesive property on the intermediate transfer drum 102, an electrostatic method in which the toner on the photoreceptor 101 is electrostatically attracted to the intermediate transfer drum 102 and transferred. In this example, a combined use of an adhesive method and an electrostatic method is employed. Here, if the electrostatic method, or a method using the adhesive method together with the electrostatic method, is referred to as an electrostatic primary transfer method, in this example, the electrostatic primary transfer method using the adhesive method and the electrostatic method is used. It is.

In order to adopt this method, the intermediate transfer drum 102 is placed on a drum-shaped base 1 made of a rigid material such as aluminum as shown in FIG.
500-5000 μm thick and 30-80 rubber hardness
A sheet comprising an elastic layer 2, a conductive layer 3 having a thickness of 30 to 300 μm made of polyimide in which carbon black is dispersed, and an insulating layer 4 having a thickness of 10 to 300 μm.
The elastic layer 2 is adhered with the elastic layer 2 inside.

The above-mentioned conductive layer 3 is formed on the intermediate transfer drum 102
2 in the axial direction X of the intermediate transfer drum 102 as shown in FIG.
As shown in the figure, the plurality of electrodes 5 are divided in the circumferential direction Y and are insulated from each other. 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 a divided manner in the circumferential direction. The operation related to this will be described later.

When the insulating layer 4 constituting the surface of the intermediate transfer drum 102 is pressed against the photosensitive member 101,
It is desirable to use a material having appropriate elasticity so that a sufficient contact area and a uniform pressure can be obtained between them.
In addition, the surface of the insulating layer 4 exhibits tackiness with respect to the toner at room temperature, and exhibits releasability with respect to the toner which is in a molten state, more precisely, in a semi-molten state and is fluidized as described later. It is composed of materials. As a material satisfying such requirements, for example, silicone rubber can be cited.

Intermediate transfer drum 1 constructed as described above
02 and the photosensitive member 101, for example, 0.3 to 3.0 kg
A pressure of about / cm is applied, and the two pressure contact portions 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 intermediate transfer drum 102 in a manner to be described later. A contact portion of the drum 102,
That is, an electric field is formed at the primary transfer position A, and the toner on the photoconductor 101 moves from the photoconductor 101 to the intermediate transfer drum 102 by the action of the electric field.

At this time, since the surface of the intermediate transfer drum 102 has an adhesive property to the toner at room temperature as described above, the toner on the photosensitive member 101 also adheres to the intermediate transfer drum 102 by the adhesive force. Migrate effectively.

As described above, while the intermediate transfer drum 102 is in close contact with the photosensitive member 101, the toner image on the photosensitive member 101 is
The potential difference between the photoconductor 101 and the intermediate transfer drum 102 and the adhesive force of the surface of the intermediate transfer drum 102
The primary transfer is performed on the intermediate transfer drum 102. At this time,
In the contact portion between the photoconductor 101 and the intermediate transfer drum 102,
The toner hardly moves while being sandwiched between the two, and the toner is transferred to the intermediate transfer drum 10 by the electrostatic force due to the electric field formed therebetween and the adhesive force from the intermediate transfer drum 102.
2 and transfer to the intermediate transfer drum 102 almost without moving in the interface direction.

The photosensitive member 101 and the intermediate transfer drum 10
When the applied pressure between the two falls significantly below the above range,
The adhesion between the two is reduced, the transfer efficiency of the toner image to the intermediate transfer drum 102 is reduced, or transfer loss occurs. Conversely, if the pressure greatly exceeds the above range, the characteristics of the photoconductor 101 and the intermediate transfer drum 102 change, or an excessive load is applied to the driving source thereof, which is not desirable.

The toner remaining on the photosensitive member 101 after the primary transfer of the toner image onto the intermediate transfer drum 102 is removed by the cleaning device 112, and the surface of the photosensitive member 101 is cleaned. The photoconductor 101 is subjected to a charge removing operation by a charge remover (not shown).

On the other hand, the transfer paper 155, which is an example of a recording medium, 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 manner is transferred to the intermediate transfer drum 1 at a predetermined timing by the registration roller pair 126, that is, at a timing when the toner image on the intermediate transfer drum 102 matches the transfer paper 155.
02 and the pressure roller 103, and the leading end thereof is clamped by the pressure roller 103 by the clamper 150.
3 around.

Intermediate transfer drum 102 and pressure roller 103
Is 0.3 mm across the transfer paper 155 located between them.
At this time, the toner image on the intermediate transfer drum 102 is secondarily transferred onto the transfer paper 155. As described above, when the toner image on the intermediate transfer drum 102 is secondarily transferred onto the transfer paper 155, the pressure roller 103 makes contact with the intermediate transfer drum 102 so that the transfer paper 155 adheres to the intermediate transfer drum 102. And press-contact.

The secondary transfer is performed by utilizing the releasability of the surface of the intermediate transfer drum 102, or by electrostatically attracting the toner on the intermediate transfer drum 102 to the transfer paper 155, or by the action of both. However, in the present embodiment, the toner image on the intermediate transfer drum 102 is secondarily transferred to the transfer paper 155 by both the releasability of the surface of the intermediate transfer drum 102 and the electrostatic action. I have. The present invention can be applied to the case where the toner image on the intermediate transfer drum 102 is secondarily transferred to the transfer paper 155 only by the electrostatic action.

As described above, the surface of the intermediate transfer drum 102 is made of a material having a releasability from the melted and fluidized toner, for example, silicone rubber. Further, immediately before the toner image on the intermediate transfer drum 102 reaches the secondary transfer position B between the intermediate transfer drum 102 and the pressure roller 103 due to the rotation of the intermediate transfer drum 102, the toner image is opposed to the intermediate transfer drum 102. For example, the light from a heat source 132 such as an infrared lamp or a halogen lamp is irradiated to heat the toner on the intermediate transfer drum 102 and bring it into a semi-molten state. A heater (not shown) may be provided in the intermediate transfer drum 102 to heat the toner on the intermediate transfer drum 102. In any case, the toner constituting the toner image on the intermediate transfer drum 102 is heated. Because

On the other hand, the pressure roller 103 is formed of, for example, aluminum or the like, and is formed of a hollow rigid roller whose outer peripheral surface is covered with a compression-resistant resin. ) Are provided. For this reason, the transfer paper 155 clamped by the pressure roller 103 and passing through the secondary transfer position B between the intermediate transfer drum 102 and the pressure roller 103 pressed against each other,
Heated by a heat source inside the pressure roller 103. Further, heat may be applied to the transfer paper 155 being transported to the secondary transfer position B by a heat source (not shown) to heat the transfer paper 155. The pressure roller 103 is grounded in a normal operation state.

In this manner, heat is applied to the toner on the intermediate transfer drum 102 and the transfer paper 155 is also heated, so that the transfer paper 155 is transferred to the secondary transfer position B between the intermediate transfer drum 102 and the pressure roller 103. Paper 155 and intermediate transfer drum 102
When the upper toner image is reached, the toner is transferred to the transfer paper 155.
While being in contact with it. Since the surface of the intermediate transfer drum 102 exhibits releasability with respect to such a molten toner, the toner image on the intermediate transfer drum 102 is
55, and the toner permeates into the fibers of the transfer paper 155. As described above, while heating the toner on the intermediate transfer drum 102 and the transfer paper 155 or after heating them, the toner image on the intermediate transfer drum 102 is pressed while the pressing roller 103 and the intermediate transfer drum 102 are pressed against each other. Is secondarily transferred onto 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 in a manner described later, and the toner is applied to the surface of the transfer paper 155. Attracted electrostatically to the side. Due to this action and the above-described releasability of the surface of the intermediate transfer drum 102 from the molten toner, the toner image on the intermediate transfer drum 102 is efficiently secondary-transferred onto the transfer paper 155, and at the same time, on the transfer paper 155. Is established. Thus, the final image is formed on the transfer paper 155.

Intermediate transfer drum 102 and pressure roller 103
Transfer paper passing through the secondary transfer position B between
The clamp by 50 is released, separated from the pressure roller 103, and subsequently discharged to the paper discharge unit 131 by the paper discharge roller pair 128.

Since the toner on the intermediate transfer drum 102 is efficiently transferred to the transfer paper 155 during the secondary transfer,
The toner hardly remains on the intermediate transfer drum 102 after passing through the secondary transfer position B, and the toner transfer rate during the secondary transfer is usually 99% or more. However, a transfer rate of 100% is not guaranteed under any condition. Therefore, as shown in FIG. 5, the image forming apparatus shown in FIG. A cleaning device 113 for cleaning the intermediate transfer drum 102 is provided.
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 not sufficiently melted and soaks into the fibers of the transfer paper 155. That is, the melt transfer was not performed. Accordingly, the state of the toner remaining on the intermediate transfer drum 102 that has passed through the secondary transfer position B is a powder that has been slightly deformed by heat.

The cleaning device 113 illustrated in FIG.
Has a brush roller 114 that rotates while sliding on the surface of the intermediate transfer drum 102, and a casing 116 that stores the collected toner. Brush roller 114
Is constructed by implanting a brush 114b made of acrylic carbon or the like on the entire peripheral surface of a conductive core 114a, and the brush 114b is grounded through the core 114a. Such a brush 114b
Are in contact with the intermediate transfer drum 102 with a predetermined width.

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

At this time, in this embodiment, the intermediate transfer drum 102
A bias voltage having the same polarity as the charged polarity of the residual toner on the intermediate transfer drum 102 is applied to the conductive layer 3, and the residual toner on the intermediate transfer drum 102 is separated from the surface of the conductive layer 3 by the action of the electric field due to the bias voltage. Receiving the electrostatic force in the direction, the cleaning efficiency is improved. Thus, by applying an electric force to the powdery residual toner slightly deformed by heat at the time of cleaning,
The toner is easily peeled off toward the brush 114b against the adhesion of the residual toner to the intermediate transfer drum 102.

As described above, in the image forming apparatus shown in FIG. 1, the toner image on the photosensitive member 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 an electrostatic secondary transfer method.

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

As described above, the polarity of the voltage applied to the conductive layer 3 necessary for performing the electrostatic primary transfer, the conductive layer 3 necessary for performing the electrostatic secondary transfer and the cleaning of the intermediate transfer drum 102, and the like. The polarities of the voltages applied to are opposite to each other.
Therefore, if the above-described 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 ends. Thereafter, a voltage must be applied to the conductive layer 3 for electrostatic secondary transfer and cleaning. However, in this case, the diameter of the intermediate transfer drum must be increased, and each image forming operation requires a large amount of time, so that the image forming speed is inevitably reduced.

Therefore, in the image forming apparatus of this embodiment, as described above, the conductive layer 3 of the intermediate transfer drum 102
Are divided in the circumferential direction of the intermediate transfer drum 102, thereby forming a large number of electrodes 5 arranged along the entire circumference in the circumferential direction of the intermediate transfer drum 102.

As shown in FIG. 4, the electrodes 5 are electrically insulated from each other by the insulating elastic layer 2 located therebetween. At this time, if each electrode 5 is located at the interface between the elastic layer 2 and the insulating layer 4, there is a possibility that a current may easily flow through the interface. Therefore, each electrode 5 is arranged in a state embedded in the upper part of the elastic layer 2. Is preferred. Further, it is desirable that a sufficient interval be provided between the electrodes 5 so that the elastic substance between the electrodes 5 does not cause dielectric breakdown. The interval between the electrodes in the circumferential direction of the intermediate transfer drum 102 is, for example, 10 μm. About 500 μm, especially 20
Preferably, the thickness is about 0 μm. This interval depends on the electrode 5
In view of the relationship between the voltage applied to the substrate and the dielectric breakdown property of the insulator during that time, it is sufficient that the distance is sufficient to maintain the insulation. The width of each electrode 5 in the rotation direction of the intermediate transfer drum is set to, for example, about 1 mm. The width of each such electrode,
The number of electrodes 5 divided from each other is determined based on the distance between the electrodes, the outer diameter of the intermediate transfer drum 102, and the like.

FIG. 6 is a schematic view schematically showing a large number of electrodes 5 of the intermediate transfer drum 102. In this figure, among the above-mentioned many electrodes 5, the electrode 5 is located to face the photosensitive member 101. The electrode is denoted by reference numeral 5a, and the electrode facing the pressure roller 103 is denoted by reference numeral 5b. Similarly, the electrode 5c of the cleaning device 113 that faces the brush roller 114 is denoted by reference numeral 5c.
Since the intermediate transfer drum 102 is rotating, the photoconductor 10
1. The electrodes 5 facing the pressure roller 103 and the brush roller 114b change one after another.
Photoconductor 101, pressure roller 103, and brush roller 11
The electrodes facing 4 are 5a, 5b and 5c.

Here, at least when the above-described primary transfer is performed, a voltage for the primary transfer is applied only to the electrode 5a facing the photosensitive member 101. That is, the voltage applied to the electrode 5
A voltage having a polarity opposite to the charge polarity of the toner on the photosensitive member 101 is applied to a.

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

Similarly, at least the intermediate transfer drum 102
When the upper surface is cleaned as described above, the power supply 121
To the electrode 5c facing the brush roller 114 of the cleaning device 113 by the voltage applying means having the same polarity as the charge polarity of the residual toner on the intermediate transfer drum 102, for example, -0.3 KV to -0.7 KV. Are applied.

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, a voltage is not applied to the entire conductive layer 3 of the intermediate transfer drum 102 at once. , Separate them separately,
Photoconductor 101, pressure roller 103, and brush roller 11
The respective target voltages are applied only to the electrodes 5a, 5b, 5c facing each other. Electrodes other than these electrodes 5a, 5b, 5c are grounded.

In this way, when a voltage for secondary transfer of a toner image is applied to the electrode 5b facing the pressure roller 103, this applied voltage has no effect on other process operations. Never. That is, when this voltage is applied, voltages for primary transfer and cleaning can be applied to the electrodes 5a and 5c facing the photoconductor 101 and the brush roller 114, respectively, without any trouble. Therefore, the above-described respective voltage applications can be performed in parallel, so that the diameter of the intermediate transfer drum 102 is set small,
Further, the speed of the image forming operation can be increased. During one rotation of the intermediate transfer drum 102, primary transfer, secondary transfer, and intermediate transfer drum 102
Cleaning can be performed.

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

In the example shown in FIG. 6, each of the electrodes 5a, 5b, 5c to which a voltage is applied is composed of a plurality of electrodes separated from each other, but an intermediate electrode corresponding to each of the electrodes 5a, 5b, 5c. The electric field intensity on the surface portion of the transfer drum 102 is substantially uniform, so that the primary and secondary transfer and the cleaning operation of the intermediate transfer drum 102 can be reliably performed.

Next, the electrodes 5a,
A specific example of a device for applying a predetermined voltage to each of 5b and 5c will be described.

FIG. 2 shows the intermediate transfer drum 102 as described above.
FIG. 3 is a cross-sectional view of the intermediate transfer drum 102 cut along the axial direction. FIG. As shown in these drawings, at one end of the intermediate transfer drum 102, the conductive layer 3 and the insulating layer 4 are disposed outside the intermediate transfer drum 102 in the axial direction with respect to the drum-shaped base 1 and the elastic layer 2. The conductive layer 3 slightly protrudes, and a part of the inner surface of the conductive layer 3 is exposed to the outside. The conductive brushes 6a, 6b, and 6c for supplying a voltage contact the exposed portions of the electrodes 5a, 5b, and 5c formed by the conductive layer 3, respectively. Each power supply 115, 12
Voltages from 0 and 121 are applied to the electrodes 5a, 5b and 5c, respectively. That is, during the image forming operation, the intermediate transfer drum 102 rotates in the clockwise direction in FIG. 1 and the divided electrodes 5 also rotate with this, but each of the brushes 6a, 6b, 6
Since c is fixedly supported and fixed, these brushes sequentially come into sliding contact with the divided electrodes 5.

As described above, with the rotation of the intermediate transfer drum 102, different electrodes sequentially face the photosensitive member 101.
A predetermined voltage is applied to the opposed electrode 5a by the power supply 115 via the brush 6a. Pressure roller 103 and brush roller 11 of cleaning device 113
Similarly, a voltage of a predetermined polarity is applied to each of the electrodes 5b and 5c from the power sources 120 and 121 via the brushes 6b and 6c.

The width of the brushes 6a, 6b, 6c in the rotation direction of the intermediate transfer drum is set wider than the interval between the individual electrodes 5 so that a voltage can always be applied to the electrodes 5a, 5b, 5c.

In the embodiment shown in FIGS. 2 and 3, a voltage is applied from the inside of the conductive layer 3, and the exposed end of the conductive layer 3 is covered with the insulating layer 4 from the outside. . For this reason, external process equipment and structures are
, And the occurrence of voltage leakage and breakage can be prevented.

In order to apply a voltage to each of the electrodes 5a, 5b, 5c, elements other than the brushes 6a, 6b, 6c described above can be used. For example, as shown in FIG. 7 in which the intermediate transfer drum 102 is cut in the axial direction and FIG. 8 showing the appearance of the intermediate transfer drum 102, the insulating layer 4 at one end of the intermediate transfer drum 102 is provided over the entire circumference. Then, the conductive layer 3 is annularly exposed. Then, among the electrodes 5 constituted by the exposed conductive layer 3, the aforementioned electrodes 5a, 5b, 5
c, for example, conductive rubber rollers 7a, 7b, 7c are fixedly provided.
a, 7b, and 7c are driven to rotate with the rotation of the intermediate transfer drum 102, and the voltages from the power supplies 115, 120, and 121 are applied to the photosensitive members through the rollers 7a, 7b, and 7c as shown in FIG. The electrode 5a opposing the pressure roller 101, the electrode 5b opposing the pressure roller 103, and the brush roller 114
Is applied to the electrode 5c opposing the. Also in this case, the rubber rollers 7a, 7b, 7c and the conductive layer 3 are applied so that a voltage can be applied only to predetermined electrodes 5a, 5b, 5c.
Is set. By changing the contact width, the number of electrodes to which a voltage is applied can be selected.

In the embodiment shown in FIGS. 7 and 8, the conductive layer 3, that is, the divided electrode 5 is
It is desirable that the exposed portion of the electrode 5 be covered with a protective cover (not shown) since it is exposed to the outside at the end portion 2 to prevent other elements from coming into contact therewith.

The conductive brush 6 shown in FIGS. 2 and 3
a, 6b, and 6c, conductive rubber rollers 7a, 7b, and 7c shown in FIGS. 7 and 8 are disposed, and the conductive rubber rollers 7a, 7b, and 7c are disposed on the surface of the conductive layer 3 exposed toward the inside of the intermediate transfer drum 102. It is also possible to adopt a configuration in which a predetermined voltage is applied to each of the electrodes 5a, 5b, 5c by making the rolling contact between the electrodes 7a, 7b, 7c.

When a conductive roller such as conductive rubber rollers 7a, 7b, 7c is used to supply a voltage to the electrodes, a rubbing force between each roller and the electrode 5 becomes difficult to work. This has the advantage that premature abrasion can be prevented.

As shown in FIG. 2 and FIG. 4, instead of forming the insulating layer 4 and the insulating elastic layer 2 separately, as shown in FIG. The same intermediate transfer drum 102 as that shown in FIG. 4 can be formed by embedding a large number of conductive divided electrodes 5 in the homogeneous elastic insulating layer 4. Also in this case, some of the electrodes 5a, 5b, 5
A voltage is applied only to c (FIG. 6).

According to the configuration described above, problems such as a reduction in the efficiency of voltage application to the electrode 5 and an adverse effect on other process equipment and the toner image on the intermediate transfer drum 102 due to the voltage application to the electrode 5 are caused. No photoconductor 101
The toner image on the intermediate transfer drum 102 is primarily transferred onto the intermediate transfer drum 102 by an electrostatic primary transfer method.
Of the intermediate transfer drum 102 by applying a voltage to the electrodes, or the secondary transfer of the toner image on the intermediate transfer drum 102 to the transfer paper 155 by an electrostatic secondary transfer method.

Incidentally, in order to secondary-transfer the toner image on the intermediate transfer drum 102 onto the transfer paper 155 by using the electrostatic force as described above, one or more appropriate number of electrodes facing the pressure roller 103 are required. May be applied with a predetermined voltage. For example, even if a transfer voltage is applied to an electrode located in an outer region in the vicinity of a contact portion W (FIG. 6) between the intermediate transfer drum 102 and the transfer paper 155 on the pressure roller 103, the above-described operation is achieved. Obtainable.

However, as described above, when a voltage is applied to the electrodes existing in a range wider than the contact portion W, the gap S (see FIG. 7) on the upstream side of the contact portion W in the rotation direction of the intermediate transfer drum 102 is seen. Since the electric field is also formed in 6), the toner image on the intermediate transfer drum 102 immediately before the transfer is subjected to an electric force, the toner image is disturbed, and the image quality of the final image on the transfer paper 155 is deteriorated. There is a possibility that.

That is, since the intermediate transfer drum 102 has a releasability from the toner which has been in a semi-molten state by the irradiation energy from the heat source 132 (FIG. 1), the electric charge on the intermediate transfer drum 102 is The toner before secondary transfer is
Since the intermediate transfer drum 102 is in an unstable state, it can easily move on the surface of the intermediate transfer drum 102. Also, when the toner image on the intermediate transfer drum 102 before the secondary transfer is configured not to be melted, the intermediate transfer drum 1
02 is unstable and is in a state of being easily moved.

When the unstable toner image approaches the contact portion W, an electric force is applied to the toner on the intermediate transfer drum 102 by the electric field applied to the gap S, thereby causing It is inevitable that the toner image may be disturbed.

Therefore, as illustrated in FIGS. 10 and 11, when at least the secondary transfer is performed, the electrode 5b positioned corresponding to the area within the contact portion W between the intermediate transfer drum 102 and the transfer paper 155 is applied. On the other hand, a voltage having the same polarity as the charged polarity of the toner on the intermediate transfer drum 102 is applied. In this example, the power supply 120 and the brush 6b
(Or the conductive rubber roller 7b shown in FIGS. 7 and 8) constitutes a voltage applying means for applying such a voltage to the electrode 5b.

FIG. 10 and FIG. 11 are schematic views for explaining the above-mentioned structure. The ratio of the size of each component is different from the actual one, and the width and interval of each electrode 5 are shown larger than the actual one. is there.

In the example shown in FIG. 10, the conductive brush 6
A predetermined voltage is applied to the corresponding plurality of electrodes 5b by the power supply 120 via the terminal b so that an electric field is formed over substantially the entire contact portion W. On the other hand, FIG.
In the example shown in (1), a voltage is applied only to some of the electrodes 5b located inside the contact portion W so that an electric field is formed only in a portion inside the contact portion W. In any case, a voltage is applied to the electrode 5b located corresponding to the area inside the contact portion W, and the intermediate transfer drum 102 and the intermediate transfer drum 102 An electric field with the pressure roller 103, that is, a potential difference is generated. The range in which the electric field is formed is indicated by reference numeral a in FIGS.

The width of the contact portion W in the rotation direction of the intermediate transfer drum is determined by the elastic material of the intermediate transfer drum 102 or the pressure roller 103.
The thickness is usually about 7 mm, for example, though it varies depending on the hardness of the steel sheet.

According to the configuration described above, when the secondary transfer is performed, an electric field is formed only in the area of the contact portion W between the intermediate transfer drum 102 and the transfer paper 155 on the pressure roller 103, and the electric field is generated outside the area. No electric field is substantially formed in the region. Accordingly, when the toner image before the secondary transfer formed on the intermediate transfer drum 102 comes close to the contact portion W of the pressure roller 103 with the transfer paper 155 as the drum 102 rotates, this toner Until the image enters the inside of the contact portion W, the intermediate transfer drum 1 receives no force due to the electric field.
02 is not disturbed.

The toner on the intermediate transfer drum 102 enters the contact portion W, and only when the toner is sandwiched between the transfer paper 155 clamped by the pressing roller 103 and the intermediate transfer drum 102, the electric field is applied to the toner. Works. At this time, the melted toner does not move in the surface direction but is sucked into the fibers of the transfer paper 155, so that the toner image secondary-transferred onto the transfer paper 155 does not spread. In this way, it is possible to form a clear final image with no background stain on the transfer paper 155.

As described above, an electric field can be formed only at the contact portion W between the transfer paper 155 clamped by the pressure roller 103 and the intermediate transfer drum 102. At this time, as shown in FIG. When a voltage for secondary transfer is applied only to the electrode 5b located inside the contact portion W, the possibility that an electric field is formed in the region outside the contact portion W can be more reliably prevented than in the case of FIG. . In the example of FIG.
Voltage is applied only to the three electrodes 5b inside the contact portion W, and an electric field is generated only in the range indicated by a. As described above, when a voltage is applied only to the electrode 5b located in a region that is at least one electrode width (for example, several mm) inside the contact portion W from both ends of the contact portion W, the contact portion W It is possible to reliably prevent a problem that an electric field is formed in the outer region.

FIG. 12 shows that at least when the secondary transfer is performed, the intermediate transfer drum 102 and the transfer paper 155 clamped by the pressure roller 103 are positioned with respect to the electrode 5b located corresponding to the portion Z where they are separated from each other. A voltage having the same polarity as the charged polarity of the toner on the intermediate transfer drum 102 is applied by a voltage applying means including the power source 120 and the conductive brush 6b (or the conductive rubber roller 7b shown in FIGS. 7 and 8). An example is shown below.

In FIG. 12, three electrodes 5b facing the region including the portion Z, ie, the pressing roller 103
Paper 155 and intermediate transfer drum 102 clamped to
A voltage is applied to the electrode 5b located corresponding to a part of the contact portion W with the contact portion W and a region downstream of the contact portion W in the rotation direction of the intermediate transfer drum. An electric field is formed in a range indicated by reference numeral b in FIG. 12, that is, in a region on the exit side of the contact portion W. No voltage is applied to the electrode located on the upstream side in the rotation direction of the intermediate transfer drum from the contact portion W. Other configurations are the same as those shown in FIGS.

Even in the above configuration, no electric field is applied to the gap S on the upstream side of the contact portion W, so that the intermediate transfer drum 102 before the secondary transfer is completely similar to the embodiment shown in FIGS. The upper toner image is not disturbed.

Further, the transfer paper 155 and the intermediate transfer drum 1
Since the voltage is applied to the electrode 5b corresponding to the portion Z that is separated from the intermediate transfer drum 02, the electric field is concentrated on the moment the toner on the intermediate transfer drum 102 leaves the surface of the intermediate transfer drum 102 and transfers to the transfer paper 155. And the secondary transfer of the toner image on the intermediate transfer drum 102 to the transfer paper 155 can be performed effectively. The voltage can be applied efficiently. That is, in the portion Z where it is determined whether the toner existing between the intermediate transfer drum 102 and the transfer paper 155 adheres to either the intermediate transfer drum 102 or the transfer paper 155 based on the force relationship at the moment when the intermediate transfer drum 102 and the transfer paper 155 are separated. Since the potential difference is formed, the action of the electric field can be used efficiently, and a final image without any disturbance on the transfer paper 155 can be formed. At this time, the toner image is transferred in a short time when the intermediate transfer drum 102 and the transfer paper 155 are separated.
5, a stronger electric field needs to be generated at this portion.

FIGS. 10 to 12 show the conductive brush 6.
Although the example in which a voltage is applied to the electrode 5b through the electrode 5b is shown, when the conductive rubber roller 7b shown in FIGS. 7 and 8 is used, similarly to FIGS. What is necessary is just to set the contact width with 102.

Incidentally, in each of the examples shown in connection with FIGS. 1 to 12, a toner image is sequentially formed on the photoreceptor 101, and this is primary-transferred one by one onto the intermediate transfer drum 102. When a continuous image forming operation is performed in which images are sequentially and secondarily transferred onto the transfer paper 155, no toner image is formed in a non-image area between image areas on the intermediate transfer drum 102 where each toner image is formed. .

However, as described above, since a small amount of unnecessary toner may adhere to this non-image area, the non-image area is transferred to the transfer paper 155 or the transfer paper 155 clamped by the pressure roller 103. If a voltage of the same polarity as the toner charging polarity is applied to the electrode 5b facing the pressure roller 103 when the sheet is in contact with the peripheral surface of the pressure roller 103 where no paper is present, an intermediate Unnecessary toner attached to the non-image area on the transfer drum 102 is transferred onto the pressure roller 103 or the transfer paper 155 clamped by the pressure roller 103, and the image quality of the final image on the transfer paper deteriorates.

Therefore, only when the image area (the portion where the toner image is formed) on the intermediate transfer drum 102 is located between the pressure roller 103 and the intermediate transfer drum 102, When the non-image area on the intermediate transfer drum 102 comes between them, the pressure roller 103 and the intermediate transfer drum 102
May be separated from each other so that unnecessary toner adhering to the non-image area on the intermediate transfer drum 102 is not transferred onto the pressure roller 103 or the transfer paper 155 clamped thereto. When the pressure roller 103 and the intermediate transfer drum 102 are separated from each other every time a non-image area comes between the pressure roller 103 and the intermediate transfer drum 102, the structure of the apparatus becomes complicated, and the cost thereof increases significantly. .

Therefore, in this embodiment, in each of the above-described configurations, the pressure contact portion between the intermediate transfer drum 102 and the pressure roller 103 is opposed to the pressure roller 103 only when an image area on the intermediate transfer drum 102 exists. The power source 120 and the conductive brush 6b are applied so that a voltage having the same polarity as the charged polarity of the toner on the intermediate transfer drum 102 is applied to the electrode 5b.
(Or a conductive rubber roller 7b). That is, when the non-image area between the image areas on the intermediate transfer drum 102 where the toner image is formed is located at the pressure contact portion between the intermediate transfer drum 102 and the pressure roller 103, the pressure roller No voltage is applied to the electrode 5b opposite to the electrode 103. In this way, the unnecessary toner adhering to the non-image area on the intermediate transfer drum 102 can be removed without the pressure roller 103 and the intermediate transfer drum 102 being separated from each other. It can be prevented from being transferred onto the top, and a high quality final image can be obtained.

This configuration does not utilize the releasability of the surface of the intermediate transfer drum 102, but secondary-transfers the toner image on the intermediate transfer drum 102 to the transfer paper 155 clamped by the pressure roller 103 solely by electrostatic force. This is particularly effective when the configuration is made to perform the control. If the surface of the intermediate transfer drum 102 does not have releasability from the toner, the unnecessary toner on the non-image area of the intermediate transfer drum 102
03 or the transfer paper 155 can be more reliably prevented from being transferred.

The ON / OFF control of the voltage to the electrode 5b may be performed by, for example, providing a switching section for supplying voltage and selectively applying a voltage to the electrode 5b in a timely manner. Basically, whether or not an image area or a non-image area on the intermediate transfer drum 102 is located at a pressure contact portion between the intermediate transfer drum 102 and the pressure roller 103 is determined by other parts in the system. Judgment is made based on the created signal, and the electrode 5bb
Is controlled. FIG. 13 shows a specific example thereof.

The control section (not shown) determines whether or not the image on the photosensitive member 101 is an image area.
ON / OFF of voltage application to b is controlled. A signal P in FIG. 13 is an image area signal issued from the CPU, and the signal P controls writing of an image on the photoconductor 101. The signal P is a signal based on the time calculated from the size of the image to be formed, the distance between the images (distance between transfer papers), the linear velocity of the system, and the like, and the signal Q is the signal to the electrode 5b. 3 shows a voltage application signal.

At time t3 from the timing when the signal P enters the non-image area (H state), the leading end of the non-image area on the intermediate transfer drum 102 reaches the voltage application section in the contact portion W. Therefore, after the time t3, the voltage applied to the electrode 5b is turned off. Similarly, the voltage application to the electrode 5b is turned on at time t3 after the timing when the signal P enters the image area (L state). In the ON state, a voltage of, for example, -0.3 KV to -1.2 KV is applied to the electrode 5b, and in the OFF state, the electrode 5b is grounded.

The image area and the non-image area on the intermediate transfer drum 102 are determined by an image detection sensor (not shown) provided in the vicinity of the intermediate transfer drum 102, and the two are distinguished. It is also possible to perform on / off control of the voltage application.

In the image forming apparatus shown in FIG. 1, the transfer paper 155 on the pressure roller 103 and the intermediate transfer drum 10
Roller 103 and the transfer paper 1 before reaching the contact portion W with the transfer paper 1
Since the toner 55 is sufficiently heated, the toner is present in the non-image area on the intermediate transfer drum 102 and if the toner adheres to the pressure roller 103, the pressure roller 103 is not provided with a cleaning device. It is difficult to remove it.

Therefore, as described above, the voltage application to the electrode 5b is not merely turned on / off,
02 and the intermediate transfer drum 1
When a non-image area exists on the intermediate transfer drum 102, a voltage having a polarity opposite to that of the toner charged on the intermediate transfer drum 102 is applied to the electrode 5 b facing the pressure roller 103. The toner is applied to the pressure roller 103 or the transfer paper 1 clamped thereto.
It is also possible to configure so as to positively prevent adhesion to the surface 55.

Further, the releasability of the surface of the pressure roller 103 with respect to the toner in the semi-molten state is enhanced more than the releasability of the surface of the intermediate transfer drum 102, and the adhesion of the toner to the pressure roller 103 is more effectively performed. Prevention is also advantageous. The surface of the pressure roller 103 is made of a highly releasable substance such as silicone or Teflon.

As described above, the voltage application to the electrode 5b facing the pressure roller 103 is turned on / off, or a voltage having a polarity opposite to that of the toner is applied to this electrode 5b. Each of the above-described configurations, such as enhancing the moldability, is applicable not only to the image forming apparatus shown in FIGS. 12 and 13 but also to an image forming apparatus of a type in which a voltage is applied to the electrode 5b located in a wider area than the contact portion W. Is also applicable.

The transfer paper 155 is fed from the paper supply unit 124 to the pressure roller 103 via the pair of registration rollers 126, and is wound around the roller 103 to secondary transfer the toner image. For some reason,
The transfer paper 155 may not be fed to the secondary transfer unit B. When such a supply failure of the transfer paper 155 occurs, it is ignored and the electrode 5b of the intermediate transfer drum 102 is ignored.
When a voltage having the same polarity as the charging polarity of the toner is applied to the toner, the toner on the intermediate transfer drum 102 is transferred onto the pressure roller 102 where the transfer paper 155 does not exist, and the pressure roller 103 It gets dirty.

In the event that a transfer failure of the transfer paper 155 occurs, the pressing roller 103 and the intermediate transfer drum 10
2 may be separated so that the toner on the intermediate transfer drum 102 is not transferred to the surface of the pressure roller 103. However, immediately after the supply failure of the transfer paper 155 is detected, the intermediate transfer drum 102 and the pressure roller 10
It is structurally difficult to separate 3 from each other, and in such a configuration, the structure and control unit of the apparatus become complicated, and the cost increases.

Therefore, in this example, in each of the above-described configurations,
Only when the transfer paper 155 exists at the pressure contact portion between the intermediate transfer drum 102 and the pressure roller 103, the pressure roller 103
Is applied to the electrode 5b of the intermediate transfer drum 102, which is opposed to the toner, by a voltage applying means having a power source 120 and a conductive brush 6b (or a conductive rubber roller 7b). A voltage is applied, and the toner image on the intermediate transfer drum 102 is secondarily transferred onto the transfer paper 155 as described above.

More specifically, when a sensor not shown in FIG. 1 detects that the transfer sheet 155 is wound around the pressure roller 103 and is not clamped, a control unit (not shown) By the control, the voltage for the secondary transfer is not applied to the electrode 5b.
Thus, when transfer paper supply failure occurs, it is possible to prevent a problem that toner adheres to the pressure roller 103 without separating the pressure roller 103 and the intermediate transfer drum 102.

FIG. 14 shows an example of an image forming apparatus having a configuration slightly different from that of FIG. In this figure, the same or similar elements as those shown in FIG. 1 are denoted by the same reference numerals as those in FIG.

The operation relating to the formation of the toner image on the photosensitive member 101, the primary transfer of the toner image from the photosensitive member 101 to the intermediate transfer drum 102, and the configuration related thereto are substantially the same as those of the image forming apparatus shown in FIG. No change. The surface of the intermediate transfer drum 102 shows releasability from the toner in a semi-molten state, and the surface of the pressure roller 103 is also made of a material showing releasability.

Before writing (formation of an electrostatic latent image) by the laser beam 110 on the photoconductor 101 is started, the photoconductor 10
1 and the intermediate transfer drum 102 are brought into pressure contact with each other,
With the rotation of 01, the intermediate transfer drum 102 and the pressure roller 103 rotate. A power supply 132 such as a heating lamp disposed immediately before the secondary transfer position B from the intermediate transfer drum 102 to the transfer paper supplies a sufficient amount of heat to the toner on the intermediate transfer drum 102 to bring the toner on the intermediate transfer drum 102 into a semi-molten state. I do.

After a lapse of a predetermined time from the start of the formation of the electrostatic latent image on the photosensitive member 101, a paper feed motor (not shown) is turned on. Supplied in the direction, the registration roller pair 1
The liquid is temporarily stopped at 26 and then supplied to the pressure roller 103 at a predetermined timing.

It is preferable that the transfer paper is sufficiently heated on the pressure roller 103 before reaching the secondary transfer position B where the intermediate transfer drum 102 and the pressure roller 103 are opposed to each other. The transfer paper is supplied from the secondary transfer position B to the pressure roller 10 as much as possible.
It is desirable that it is located at a position distant to the upstream side in the rotation direction 3.

When the transfer paper needs to be supplied to the pressing roller 103 near the secondary transfer position B due to the layout of the components of the image forming apparatus, the pressing roller 1
It is desirable to heat the transfer paper before it is supplied to the transfer paper 03.
For example, when the transfer sheet is waiting at the registration roller pair 126, the transfer sheet is heated by a heating lamp or the like (not shown), or when the transfer sheet passes therethrough using a heating roller as the registration roller, The transfer paper is configured to be heated to some extent.

A registration sensor 151 is located immediately before the registration roller pair 126, and confirms the arrival of the transfer paper at the registration section. After a predetermined time from the start signal of the start of the formation of the electrostatic latent image on the photoconductor 101, a registration motor (not shown) starts, and the transfer paper starts to be fed.
The leading end of the transfer paper that has passed through the registration roller pair 126 is clamped by the pressure roller 103 by the clamper 150,
Heated by the heating lamp 153.

The transfer roller detecting sensor 1 is
When the transfer paper clamped by the pressure roller 103 is conveyed and reaches the sensor 152, the signal of the sensor 152 changes to confirm that the transfer paper has been successfully clamped.

At a predetermined time after the rise of this signal, the leading end of the transfer paper reaches the pressure contact portion (secondary transfer position B) between the intermediate transfer drum 102 and the pressure roller 103. A voltage is applied from a power supply to the electrode 5b (FIG. 6) in the intermediate transfer drum 102. This applied voltage is, for example, -0.3 KV to -1.0 KV.

If the signal of the sensor 152 does not change after a predetermined time, it is recognized that an abnormality has occurred. Even if an abnormal state occurs, the intermediate transfer drum 102 and the pressure roller 103
Since it is mechanically difficult to instantaneously separate the transfer paper, the toner remains on the intermediate transfer drum 102, and the rotation of the drum 102 causes the toner image on the intermediate transfer drum 102 to be pressed by the pressure roller 103 which does not clamp the transfer paper. Direct contact with the surface.

At this time, a bias voltage having a polarity opposite to that of the toner is applied to the electrode 5b (FIG. 6) in the intermediate transfer drum 102, and the toner is held on the intermediate transfer drum 102.
Moreover, since the surface of the pressure roller 103 has releasability from the toner in the semi-molten state, the toner on the intermediate transfer drum 102 does not transfer onto the pressure roller 103.
The intermediate transfer drum 102 and the pressure roller 103 rotate further, and before the toner image (image area) on the intermediate transfer drum 102 comes to the secondary transfer position B again, the intermediate transfer drum 102 and the pressure roller 103 Is released.

When an abnormal state is detected by the clamp detection, the detection signal is immediately sent to the CPU. When an abnormal state occurs, the heat source 132 for heating the toner on the intermediate transfer drum 102 is immediately stopped due to safety issues, and the heating of the pressure roller 103 and the transfer paper is also stopped.

By the above control, the intermediate transfer drum 102
Only when the transfer paper is present at the pressure contact portion (secondary transfer position B) of the pressure roller 103 and the pressure roller 103, a voltage having a polarity at which the toner image is secondarily transferred to the transfer paper is applied to the electrode 5b (FIG. 6). Unnecessary toner transfer to the pressure roller 103 can be prevented.

When a portion of the transfer sheet has passed the secondary transfer position B, the clamp on the transfer sheet is released, and the transfer sheet on which the toner image has been transferred and fixed is discharged out of the apparatus as indicated by an arrow D.

In each of the examples described above with reference to FIGS. 1 to 14, the transfer paper is clamped to the pressing roller 103 so that the toner image on the intermediate transfer drum 102 is secondarily transferred onto the transfer paper. Although the transfer paper fed from the paper feed unit is not clamped by the pressure roller 103, the transfer paper is simply passed between the pressure contact portions between the intermediate transfer drum 102 and the pressure roller 103. The toner image on 102 may be secondarily transferred to transfer paper.

In each of the above examples, the configuration of the image forming apparatus for forming a monochromatic image on transfer paper has been described. However, toner images of different colors are sequentially formed on the photoreceptor 101, and this is transferred to the intermediate transfer drum 102. Then, the multicolor toner image is secondarily transferred to the transfer paper 155 in a lump, or the toner images are primarily transferred one by one onto the intermediate transfer drum 102, and then transferred onto the transfer paper. The present invention is also applicable to an image forming apparatus that obtains a multicolor image by sequentially superimposing and secondary transferring.

[0126]

According to the present invention, unnecessary toner adhering to the non-image area on the intermediate transfer rotating body can be prevented from transferring to the pressure rotating body or the recording medium, and a high quality final image can be obtained. it can.

[0127]

[0128]

[0129]

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating 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 an axial direction thereof.

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

FIG. 4 is a sectional view showing the 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 an example in which a voltage is applied to an electrode via a conductive roller.

8 is an external perspective view of the intermediate transfer drum shown in FIG.

FIG. 9 is a sectional view similar to FIG. 4, showing another example of the intermediate transfer drum.

FIG. 10 is an explanatory diagram showing a relationship between a contact portion between a transfer sheet and an intermediate transfer drum on a pressure roller and an electrode of the intermediate transfer drum.

FIG. 11 is an explanatory diagram showing another example of a relationship between a contact portion between a transfer sheet and an intermediate transfer drum on a pressure roller and an electrode of the intermediate transfer drum.

FIG. 12 is an explanatory diagram showing still another example of a relationship between a contact portion between a transfer sheet and an intermediate transfer drum on a pressure roller and an electrode of the intermediate transfer drum.

FIG. 13 is a timing chart of an embodiment in which application of a voltage to an electrode is stopped when a non-image area of the intermediate transfer drum reaches between the intermediate transfer drum and a pressure roller.

FIG. 14 is a schematic configuration diagram illustrating another example of the image forming apparatus.

[Explanation of symbols]

 5 electrode 5b electrode

Claims (3)

(57) [Claims] 1. A toner image bearing rotary member on which a toner image is formed, an intermediate transfer rotary member on which a toner image on the toner image bearing rotary member is primarily transferred, and a toner image on the intermediate transfer rotary member are recorded. When performing secondary transfer to a medium, in order to bring the recording medium into close contact with the intermediate transfer rotator, in an image forming apparatus having a pressing rotator pressed against the intermediate transfer rotator, the intermediate transfer rotator is It has a plurality of electrodes divided and arranged in the circumferential direction, and only when there is an image area on the intermediate transfer rotator at a pressure contact portion between the intermediate transfer rotator and the pressure rotator, the pressure rotator An image forming apparatus comprising: a voltage application unit configured to apply a voltage having the same polarity as the charging polarity of the toner on the intermediate transfer rotator to the electrode facing the image forming apparatus. 2. The image forming apparatus according to claim 1, wherein a toner produced by a polymerization method is used. 3. The image forming apparatus according to claim 1, wherein the intermediate transfer rotator has elasticity.