JPH11125976A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device which ensures the satisfactory, steady transfer of toner image in an electrostatic primary-transfer part. SOLUTION: The image forming device develops an electrostatic latent image, formed on a photoreceptor 1 (electrostatic latent-image carrier), with liquid developer D, thereby forming a visible toner-image T1, primarily transfers the toner image T1 electrostatically onto an intermediate transfer drum 6 once, and then secondarily transfers the toner image T2 under heating to transfer paper S (transfer material) which is pressed to the intermediate transfer drum 6 by a pressing roller 9. The pressure roller 9 has a transfer-material pressing surface made of a conductive material, and is provided with a bias application device 15 for applying a bias voltage to the pressing roller 9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copier, a printer, and the like, in which an electrostatic latent image is developed using a developer, and the obtained visible toner image is once primarily transferred to an intermediate transfer member and then transferred to a transfer material. The present invention relates to an image forming apparatus that performs secondary transfer.

[0002]

2. Description of the Related Art In this type of image forming apparatus, generally,
A surface of an electrostatic latent image carrier such as a photoreceptor is charged, an electrostatic latent image is formed in the charged area by image exposure or the like based on image information, and the latent image is developed with a developer to form a visible toner image. The toner image is temporarily primary-transferred onto an intermediate transfer member such as an intermediate transfer drum, and secondary-transferred from the intermediate transfer member onto a transfer material such as paper and fixed.

In such an image forming apparatus, for example, a so-called electrostatic transfer system in which transfer is performed using electrostatic force in primary transfer, and a so-called thermal transfer system in which transfer is performed using heat in secondary transfer, are used. Things have been suggested. In such an image forming apparatus, when performing the primary transfer, an electric charge is applied to the intermediate transfer member, and the visible toner image on the electrostatic latent image carrier is attracted to the intermediate transfer member using the electrostatic force of the electric charge. Transcribe.
When performing the secondary transfer, the visible toner image on the intermediate transfer member is softened by using heat, and the softened toner image is transferred onto a transfer material pressed against the intermediate transfer member by a pressing roller (backup roller). Transcribe.

[0004]

However, such an image forming apparatus has the following problems. That is, when a charge is applied to the intermediate transfer body to attract the visible toner image on the electrostatic latent image carrier onto the intermediate transfer body in the primary transfer unit, the electrostatic latent image carrier and the intermediate transfer body During this period, a so-called inflow current (primary transfer current) flows. This primary transfer current is likely to affect the primary transfer. For example, when a roller made of a conductive material is used for the pressing roller in the secondary transfer section, the charge moves from the intermediate transfer body to the pressing roller, and the current is reduced. It is easy to flow, and the current flowing in the secondary transfer section is likely to be large, and it is difficult to stabilize.
The next transfer current is likely to fluctuate. Further, for example, when a roller made of a dielectric material is used as the pressing roller in the secondary transfer unit, the surface of the pressing roller is easily charged by the charge from the intermediate transfer body, and at this time, the space between the intermediate transfer body and the pressing roller That is, a so-called charging current easily flows. That is, when the capacitance of the dielectric of the pressing roller is equal to or smaller than the capacitance of the electrostatic latent image carrier, the charging current tends to be equal to or larger than the primary transfer current. For this reason, if the surface potential of the pressing roller fluctuates with the secondary transfer operation of the pressing roller, the charging current tends to fluctuate, and consequently the primary transfer current fluctuates.

As described above, the primary transfer current tends to fluctuate due to the flowing current or the charging current in the secondary transfer unit, so that the visible toner image on the electrostatic latent image carrier is electrostatically primary-transferred to the intermediate transfer body. When transfer is performed, transfer failure is likely to occur. Therefore,
According to the present invention, a visible toner image is formed by developing an electrostatic latent image formed on an electrostatic latent image carrier with a developer, and the visible toner image is temporarily primary-transferred to an intermediate transfer member, and then pressed. Provided is an image forming apparatus that thermally secondary-transfers to a transfer material pressed against the intermediate transfer body by a roller, wherein the toner image transfer in the electrostatic primary transfer unit is good and stable. The task is to

[0006]

An image forming apparatus according to the present invention for solving the above-mentioned problems develops an electrostatic latent image formed on an electrostatic latent image carrier with a developer to form a visible toner image. An image forming apparatus for temporarily transferring a visible toner image to an intermediate transfer member by electrostatic primary transfer, and then thermally secondary-transferring the transfer material pressed against the intermediate transfer member by a pressing roller, wherein the pressing roller is made of a conductive material. And a bias applying device for applying a bias voltage for stabilizing a transfer current in the electrostatic primary transfer to the pressing roller.

According to this image forming apparatus, a transfer voltage is applied in the primary transfer section, and the visible toner image on the electrostatic latent image carrier is electrostatically primarily transferred onto the intermediate transfer body. At this time, a primary transfer current flows between the electrostatic latent image carrier and the intermediate transfer body. In the secondary transfer section, a transfer material pressing surface made of a conductive material of the pressing roller is pressed against the intermediate transfer body via the transfer material, and the visible toner image on the intermediate transfer body is thermally secondarily transferred to the transfer material. . At the time of the primary transfer, the pressing roller and the intermediate transfer member are at least partially in contact with each other.
In this state, an unstable inflow current easily flows between the pressing roller and the intermediate transfer body in the secondary transfer portion, and the transfer current in the primary transfer portion tends to fluctuate accordingly. However, since the bias voltage can be applied to the pressing roller by the bias applying device, the current flowing into the secondary transfer portion can be suppressed by doing so. That is, by applying a bias voltage to the pressing roller in the secondary transfer section by the bias applying device, the potential difference between this bias voltage and the transfer voltage in the primary transfer section can be reduced, or this potential difference can be eliminated. .
As a result, the current flowing in the secondary transfer section can be suppressed, and the current flowing in the secondary transfer section can be reduced relative to the transfer current in the primary transfer section.

[0008] By reducing the inflow current in the secondary transfer section, the fluctuation of the transfer current in the primary transfer section can be suppressed correspondingly, the primary transfer current can be easily managed, and the primary transfer conditions can be adjusted. Can be kept constant. As a result, the toner image transfer at the electrostatic primary transfer portion is good and stable. As the bias voltage of the bias applying device, for example, a voltage having the same potential as the transfer voltage in the electrostatic primary transfer portion, a voltage having substantially the same potential as the transfer voltage in the electrostatic primary transfer portion, and the like can be given. The voltage having substantially the same potential is a voltage close to the transfer voltage in the primary transfer unit that enables good and stable transfer in the primary transfer unit. When the bias voltage of the bias applying device and the transfer voltage in the primary transfer unit are set to the same potential or substantially the same potential, the bias applying device and the device for applying the transfer voltage in the primary transfer unit are separately provided. The same or substantially the same voltage may be applied, and all or a part of the bias applying device may also serve as all or a part of a device for applying a transfer voltage in the primary transfer unit.

Further, the present invention has been made in order to solve the above-mentioned problems.
The following image forming apparatus is also provided. That is, the electrostatic latent image formed on the electrostatic latent image carrier is developed with a developer to form a visible toner image, and the visible toner image is once primarily transferred to an intermediate transfer body by electrostatic, and then pressed by a pressing roller. An image forming apparatus for thermally secondary transferring to a transfer material pressed against the intermediate transfer body,
The pressing roller has a transfer material pressing surface made of a dielectric material, and a charging device for charging the surface of the pressing roller so as to stabilize a transfer current in the electrostatic primary transfer is provided. The image forming apparatus is a feature.

According to this image forming apparatus, a transfer voltage is applied in the primary transfer section, and the visible toner image on the electrostatic latent image carrier is electrostatically primary-transferred onto the intermediate transfer body. At this time, a primary transfer current flows between the electrostatic latent image carrier and the intermediate transfer body. In the secondary transfer section, the transfer material pressing surface made of a dielectric material of the pressing roller is pressed against the intermediate transfer member via the transfer material, and the visible toner image on the intermediate transfer member is heated by the heat transfer member.
Next is transferred. At the time of the primary transfer, the pressing roller and the intermediate transfer member are at least partially in contact with each other, so that the surface of the pressing roller is charged by the charge from the intermediate transfer member. At this time, a charging current flows between the intermediate transfer member and the pressing roller. In this state, the surface potential of the charged pressure roller fluctuates due to the secondary transfer operation of the pressure roller, and an unstable charging current easily flows between the pressure roller and the intermediate transfer body in the secondary transfer portion. The transfer current in the primary transfer section is likely to fluctuate. However, the surface of the pressing roller can be charged by the charging device.
The charging current in the next transfer portion can be stabilized. That is, by charging the pressing roller by this charging device, the surface potential fluctuation of the pressing roller can be made constant,
As a result, the fluctuation of the charging current in the secondary transfer portion can be suppressed.

By stabilizing the charging current in the secondary transfer section in this manner, the fluctuation of the transfer current in the primary transfer section can be suppressed accordingly, and the primary transfer current can be easily managed, and the primary transfer current can be easily controlled. Conditions can be kept constant. Thereby, good and stable transfer at the electrostatic primary transfer portion can be achieved. Examples of the charging device include a device that charges the surface of the pressing roller with a corona discharge wire and a device that charges the surface of the pressing roller with a charging brush, but is not limited thereto.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of an electrophotographic image forming apparatus according to an embodiment of the present invention. FIG.
The image forming apparatus shown in FIG.
(An example of an electrostatic latent image carrier). Around the photoreceptor 1, a corona charging device 2, an exposure device 3, a liquid developing device 4, a squeeze roller 5, an intermediate transfer drum 6 (an example of an intermediate transfer member), a cleaning blade 7, and an eraser lamp 8 are arranged in this order. Have been.

The photosensitive member 1 is driven to rotate in a counterclockwise direction A in FIG. Here, the photoconductor 1 is a drum-shaped photoconductor drum, but may be a belt-shaped photoconductor belt or the like. The intermediate transfer drum 6 faces the photoreceptor 1, and an electrostatic primary transfer portion P1 in FIG.
Is formed. A pressure roller 9 and a cleaning blade 10 are arranged around the intermediate transfer drum 6.

The pressing roller 9 faces the intermediate transfer drum 6,
In the drawing, a thermal secondary transfer portion P2 is formed. Secondary transfer section P2
The guide plate 11 and the timing roller pair 1
2 is provided, and a paper supply unit (not shown) is provided. A guide plate 13 is provided on the left side, and a discharge roller pair and a discharge tray (not shown) are provided.

The charging device 2 can apply a high voltage from the power supply PW1 and thereby charge the photosensitive member 1.
The exposure device 3 can irradiate the photoconductor 1 with the laser beam L based on image information sent from an image reading device or the like (not shown), and thereby form an electrostatic latent image on the photoconductor 1.

The liquid developing device 4 includes a developing roller 41 and a developer tank 42, and stores the liquid developer D. The liquid developer D contains a carrier liquid and a toner. The developing roller 41 is driven to rotate clockwise B in the figure, and can apply a developing bias voltage from the power supply PW2. Thereby, the photosensitive member 1
The upper electrostatic latent image can be developed. The squeeze roller 5 is provided on the photoconductor 1 and is driven to rotate. As a result, excess carrier liquid adhering to the photoreceptor 1 can be removed. FIG.
While the squeeze roller 5 is provided separately from the liquid developing device 4, the squeeze roller 5 may be provided integrally at the same position as the liquid developing device 4.

The cleaning blade 7 is arranged in contact with the photosensitive member 1. As a result, the transfer residual toner remaining on the photoreceptor 1 without being primarily transferred to the intermediate transfer drum 6 can be removed.
The eraser lamp 8 can irradiate the photoreceptor 1 with light, so that the charges on the photoreceptor 1 can be removed by light. The intermediate transfer drum 6 has a surface layer 62 whose surface is made of a conductive material.
The intermediate transfer drum 6 includes a heater 61 and is driven to rotate in the direction B in the drawing. The heater 61 is built in the intermediate transfer drum 6 and can heat the surface of the intermediate transfer drum 6 to a predetermined temperature. Thereby, as described later, 1
The toner image T2 can be softened while evaporating the carrier liquid attached to the drum 6 together with the toner image T2 to be transferred next.

The pressing roller 9 has a transfer material pressing surface layer 91 made of a conductive material. The pressing roller 9 is pressed toward the intermediate transfer drum 6 by a pressing device (not shown), and is driven to rotate in the direction A in the drawing. As a result, a transfer sheet S (transfer material) to be described later is pressed against the intermediate transfer drum 6, and the toner image T2 on the intermediate transfer drum 6 can be thermally secondary-transferred and fixed to the transfer sheet S.

The image forming apparatus is provided with a bias applying device 15. The bias applying device 15 is connected to the intermediate transfer drum 6 and the photoconductor 1, and is connected to the primary transfer portion P
1 can be applied with a transfer voltage. As a result, the toner image T1 on the photosensitive member 1 can be primary-transferred electrostatically onto the intermediate transfer drum 6. The application device 15 is also connected to the pressing roller 9,
A bias voltage can be applied to the secondary transfer portion P2. That is, the same voltage is applied to the intermediate transfer drum 6 and the pressing roller 9, and the bias voltage to the pressing roller 9 is the same potential as the transfer voltage to the intermediate transfer drum 6. In addition, 1 here
The transfer voltage in the next transfer portion P1 and the bias voltage in the secondary transfer portion P2 are applied from one application device (bias application device 15), and the application devices are individually applied to the primary transfer portion P1 and the secondary transfer portion P2. The same voltage may be applied to each of them. The intermediate transfer drum 6 is a drum-shaped transfer drum, but may be a belt-shaped transfer belt.

The cleaning blade 10 is arranged in contact with the intermediate transfer drum 6. Thereby, the secondary transfer residual toner remaining on the intermediate transfer drum 6 without being secondary-transferred to the transfer sheet S can be removed. According to this image forming apparatus, the photoconductor 1 is driven to rotate, and is uniformly charged by the charging device 2.

The laser beam L emitted from the exposure device 3 exposes the charged area to form an electrostatic latent image. This electrostatic latent image is transferred to the liquid developing device 4 as the photosensitive member 1 rotates. In the liquid developing device 4, a part of the developing roller 41 is immersed in the liquid developer D, and the developer D is pumped up with the rotation of the developing roller 41, and is used as an electrostatic latent image on the photoreceptor 1. The image is developed under the application of a developing bias voltage to form a visible toner image.

The visible toner image moves to the squeeze roller 5 with the rotation of the photosensitive member 1, and the excess carrier liquid on the photosensitive member 1 is removed by the squeeze roller 5. Thereafter, the visible toner image T1 moves to the primary transfer portion P1. In the primary transfer section P1, a transfer voltage is applied, and the toner image T1 on the photosensitive member 1 is electrostatically primary-transferred onto the intermediate transfer drum 6. At this time, a primary transfer current flows between the photoconductor 1 and the intermediate transfer drum 6.

The electrostatically transferred toner image T2 is heated to a predetermined temperature on the intermediate transfer drum 6, and is conveyed to the secondary transfer section P2 while being softened while evaporating the carrier liquid.
The toner image T2 conveyed to the transfer portion P2 is secondarily transferred and fixed to the transfer sheet S. The transfer paper S is sent out from a paper feed tray (not shown) by a paper feed roller (not shown), and is sent to the timing roller pair 12. The timing roller pair 12 controls the toner image T on the intermediate transfer drum 6.
The transfer paper S is sent out in synchronization with the transfer paper S. The transfer paper S is
The sheet moves to the transfer portion P2 while being supported by the guide plate 11.

In the secondary transfer section P2, a surface layer 91 made of a conductive material of the pressing roller 9 is pressed against the intermediate transfer drum 6 to thermally secondary transfer the toner image T2 on the intermediate transfer drum 6 to the transfer paper S. . Since the pressing roller 6 and the intermediate transfer drum 6 are in contact with each other, the secondary transfer portion P2
, An unstable flowing current flows between the pressing roller 9 and the intermediate transfer drum 6, and accordingly, the primary transfer portion P1
The transfer current at the time fluctuates. However, since the same voltage as the transfer voltage in the primary transfer portion P1 can be applied to the pressing roller 9 by the bias applying device 15, the secondary transfer portion P2
Can be suppressed. That is, the secondary transfer portion P2 is
By applying a bias voltage to the pressing roller 9 at, the potential difference between this bias voltage and the transfer voltage at the primary transfer portion P1 can be eliminated. As a result, the inflow current in the transfer portion P2 can be suppressed, and the primary transfer portion P
The current flowing in the secondary transfer portion P2 can be reduced with respect to the transfer current in the first transfer portion.

As described above, since the inflow current in the secondary transfer portion P2 is reduced, the fluctuation of the transfer current in the primary transfer portion P1 can be suppressed accordingly, and the primary transfer current can be easily managed, and the primary transfer can be performed. Conditions can be kept constant. Thereby, good and stable transfer efficiency in the electrostatic primary transfer portion P1 can be obtained. After transfer toner S is transferred and fixed, transfer paper S is supported by guide plate 13 and is discharged to a discharge tray by a discharge roller pair (not shown).

The toner remaining on the intermediate transfer drum 6 without being transferred onto the transfer sheet S is held. The cleaning blade 10 removes the secondary transfer residual toner. Although the toner remaining on the photoconductor 1 without being transferred to the intermediate transfer drum 6 is held, the cleaning blade 7 removes the primary transfer residual toner. Thereafter, light is irradiated from the eraser lamp 8 to the photoconductor 1, and the electric charge on the photoconductor 1 is removed by light. Then, the photoconductor 1 is prepared for the next image formation.

An evaluation experiment was conducted on the transfer performance in the electrostatic primary transfer, which will be described below.
A comparative experiment was also conducted, and will be described together. The evaluation experiment was performed using an image forming apparatus of the type shown in FIG. Further, a comparative experiment was performed using an image forming apparatus of the type shown in FIG. The image forming apparatus shown in FIG. 4 is different from the image forming apparatus shown in FIG. 1 in that the pressing roller 9 is grounded instead of applying a bias voltage to the pressing roller 9 of the bias applying device 15. The other points are the same in configuration and operation as those of the image forming apparatus of the type shown in FIG. 1, and the same parts and the like are denoted by the same reference numerals.

The experimental conditions are as follows. Comment
Surface layer of the intermediate transfer drum 6
62 is made of conductive fluoro rubber, and its resistance is 0.5 ×
10 ⁶Ωcm, the layer thickness is 5 mm, and the intermediate transfer drum
The surface temperature of No. 6 was set to 100 ° C. The pressing roller 9
Of conductive fluorine rubber for the surface layer 91 of
10^FiveΩcm, the layer thickness is 2 mm,
The pressing force on the intermediate transfer drum 6 was set to 15 kgf. Ma
In addition, the liquid developer D stored in the liquid developing device 4 has a minus value.
A liquid developer containing a polar toner was used.

Further, the bias applying device 15 outputs the voltage +4
A bias voltage of 00 V to +680 V (varies depending on the development pattern) is controlled by a constant current of 30 μA,
In the evaluation experiment, the voltage was applied to the intermediate transfer drum 6 and the pressing roller 9, and in the comparative experiment, the voltage was applied only to the intermediate transfer drum 6. Under these conditions, the transfer speed at the electrostatic primary transfer portion P1 was examined by setting the process speed of the image forming apparatus to 20 cm / s at the peripheral speed of the photoconductor 1.

As a result, in the evaluation experiment, the primary transfer portion P1
The current flowing from the intermediate transfer drum 6 to the pressing roller 9 in the secondary transfer portion P2 sharply decreases with respect to the current flowing into the intermediate transfer drum 6 from the photoreceptor 1 (transfer current), and the transfer in the primary transfer portion P1 No failure occurred. On the other hand, in the comparative experiment, since the current flowing into the pressing roller 9 in the secondary transfer portion P2 was large and unstable, a transfer failure occurred in the primary transfer portion P1.

From the above, it can be understood that the image forming apparatus of the type shown in FIG. 1 can obtain good and stable transfer efficiency in the electrostatic primary transfer portion P1. FIG. 2 is a schematic configuration diagram of an electrophotographic image forming apparatus according to another embodiment of the present invention. FIG. 3 is a schematic configuration diagram of an image forming apparatus which is a modification of the image forming apparatus shown in FIG.

The image forming apparatus shown in FIG. 2 includes a power supply PW3 and a pressing roller 900 in place of the bias applying device 15 and the pressing roller 9 in the image forming apparatus shown in FIG.
Further, a charging device 16a is provided. The other parts are the same as those of the apparatus shown in FIG. 1, and the same parts are denoted by the same reference numerals. As shown in FIG. 2, the power supply device PW3 is connected to the intermediate transfer drum 6 and the photoconductor 1, and can apply a transfer voltage to the primary transfer portion P1. As a result, the toner image T1 on the photoconductor 1 can be primary-transferred electrostatically.

The pressing roller 900 has a transfer material pressing surface layer 910 made of a dielectric material. The capacitance of the dielectric layer 910 is smaller than the capacitance of the photoconductor 1. The pressing roller 900 is pressed toward the intermediate transfer drum 6 by a pressing device (not shown), and is driven to rotate in the direction A in the figure. As a result, the transfer paper S is pressed against the intermediate transfer drum 6, and the toner image T2 on the intermediate transfer drum 6 is thermally secondary-transferred to the transfer paper S,
Can be fixed.

The charging device 16a includes a corona discharge device 161a having a discharge wire and a power supply PW4. The discharge device 161a faces the pressing roller 900 and is connected to the power supply PW4. Power supply PW4 to discharge device 16
By applying a voltage to 1a, the dielectric layer 910 of the pressing roller 900 can be charged by corona discharge from the discharge device 161a.

The image forming apparatus shown in FIG. 3 is different from the image forming apparatus shown in FIG.
6b. The other parts are the same as those of the apparatus shown in FIG. 2, and the same parts are denoted by the same reference numerals.
As shown in FIG. 3, the charging device 16b includes a charging brush 16
1b and a power supply PW5. The brush 161b is arranged in contact with the pressing roller 900, and is connected to the power supply PW5. When a voltage is applied from the power source PW5 to the brush 161b, a charge is applied to the pressing roller 900 from the brush 161b, and the dielectric layer 910 of the pressing roller 900 can be charged.

The image forming apparatus shown in FIGS. 2 and 3 will be described below. Here, the configuration and operation different from those of the image forming apparatus shown in FIG. 1 will be mainly described. In the primary transfer section P1, a transfer voltage is applied, and the toner image T1 on the photosensitive member 1 is electrostatically primary-transferred onto the intermediate transfer drum 6. At this time, a primary transfer current flows between the photoconductor 1 and the intermediate transfer drum 6.

The electrostatically transferred toner image T2 is heated to a predetermined temperature on the intermediate transfer drum 6, and is conveyed to the secondary transfer section P2 while being softened while evaporating the carrier liquid.
The toner image T2 conveyed to the transfer portion P2 is secondarily transferred and fixed to the transfer sheet S. The transfer paper S is sent out from a paper feed tray (not shown) by a paper feed roller (not shown), and is sent to the timing roller pair 12. The timing roller pair 12 controls the toner image T on the intermediate transfer drum 6.
The transfer paper S is sent out in synchronization with the transfer paper S. The transfer paper S is
The sheet moves to the transfer portion P2 while being supported by the guide plate 11.

In the secondary transfer portion P2, the surface layer 910 made of a dielectric material of the pressing roller 900 is pressed against the intermediate transfer drum 6 to thermally secondary transfer the toner image T2 on the intermediate transfer drum 6 to the transfer paper S. Press roller 900 and intermediate transfer drum 6
And the surface of the pressing roller 900 is charged by the electric charge from the intermediate transfer drum 6. At this time, a charging current flows between the intermediate transfer drum 6 and the pressing roller 900. In this state, the charged pressing roller 9 is charged.
The surface potential of No. 00 fluctuates due to the secondary transfer operation of the pressing roller 900, and an unstable charging current flows between the pressing roller 900 and the intermediate transfer drum 6 in the secondary transfer portion P2. The transfer current at P1 fluctuates. However, since the surface of the pressing roller 900 can be charged by the charging devices 16a and 16b, the transfer portion P
2 can be stabilized. That is, the pressing roller 9 by the charging devices 16a and 16b
By the charging to 00, the surface potential of the pressing roller 900 can be made constant, and the fluctuation of the charging current in the transfer portion P2 can be suppressed.

By stabilizing the charging current in the secondary transfer section P2 in this manner, the fluctuation of the transfer current in the primary transfer section P1 can be suppressed accordingly, and the primary transfer current can be easily managed, and the primary transfer current can be easily controlled. Transfer conditions can be kept constant. Thereby, good and stable transfer at the electrostatic primary transfer portion P1 can be achieved. Note that the above-described image forming apparatuses shown in FIGS. 1 to 3 each employ a liquid developing system, but the present invention is also applicable to an image forming apparatus of a dry developing system.

[0040]

According to the present invention, an electrostatic latent image formed on an electrostatic latent image carrier is developed with a liquid developer containing toner to form a visible toner image, and the visible toner image is temporarily transferred to an intermediate transfer member. An image forming apparatus for performing a thermal secondary transfer to a transfer material pressed against the intermediate transfer body by a pressing roller after the electrostatic primary transfer to the toner, wherein the toner image transfer at the electrostatic primary transfer portion is good. An image forming apparatus that is stable can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a schematic configuration of an electrophotographic image forming apparatus according to an embodiment of the invention.

FIG. 2 is a diagram illustrating a schematic configuration of an electrophotographic image forming apparatus according to another embodiment of the present invention.

FIG. 3 is a diagram illustrating a schematic configuration of an image forming apparatus that is a modification of the image forming apparatus illustrated in FIG. 2;

FIG. 4 is a schematic configuration diagram of the image forming apparatus in which the pressing roller 9 is grounded to the ground level instead of applying a bias voltage to the pressing roller 9 of the bias applying device 15 in the image forming apparatus illustrated in FIG.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photoconductor (one example of electrostatic latent image carrier) 2 corona charging device 3 exposure device 4 liquid developing device 41 developing roller 42 developer tank D liquid developer 5 squeeze roller 6 intermediate transfer drum (one example of intermediate transfer member) 61) heater 62 surface layer 7 cleaning blade 8 eraser lamp 9 pressing roller 91 surface layer made of conductive material 900 pressing roller 910 surface layer made of dielectric material 10 cleaning blade 11 guide plate 12 timing roller pair 13 guide plate 15 bias applying device 16a, 16b Charging device 161a Corona discharge device 161b Brush P1 Electrostatic primary transfer unit P2 Thermal secondary transfer unit PW1, PW2, PW3, PW4, PW5 Power supply L Laser light T1, T2 Toner image S Transfer paper S (transfer material)

Claims (3)

[Claims] An electrostatic latent image formed on an electrostatic latent image carrier is developed with a developer to form a visible toner image, and after the visible toner image is temporarily primary-transferred to an intermediate transfer member, An image forming apparatus for thermally secondary-transferring a transfer material pressed against the intermediate transfer body by a pressing roller, wherein the pressing roller has a transfer material pressing surface made of a conductive material, An image forming apparatus, comprising: a bias applying device for applying a bias voltage for stabilizing a transfer current in an electro-primary transfer. 2. A bias voltage of the bias applying device,
The image forming apparatus according to claim 1, wherein the potential is equal to or substantially equal to a transfer voltage applied in the electrostatic primary transfer. 3. An electrostatic latent image formed on an electrostatic latent image carrier is developed with a developer to form a visible toner image. An image forming apparatus for thermally secondary transferring to a transfer material pressed against the intermediate transfer body by a pressing roller, wherein the pressing roller has a transfer material pressing surface made of a dielectric material, and the surface of the pressing roller is An image forming apparatus comprising: a charging device for charging so as to stabilize a transfer current in electrostatic primary transfer.