JPH10186878A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of minimizing the transfer dust at the time of transferring the toner image. SOLUTION: This device is at least, as toner image forming means, provided with electrifying means 2 uniformly electrifying a photoreceptor 1, exposing means (laser light (r)) forming a latent image on the photoreceptor 1 based on the image information, developing means 4 developing the latent image on the photoreceptor 1 by the toner charged in same polarity as the latent image, an endless belt shape transferring belt (intermediate transferring belt) 6 extended over plural rollers, a transferring nip part on which the transferring body 6 surface is held in contact with the photoreceptor 1 between two rollers 12 and 13, and the electric charge applying device (conductive brush 16 and power source 16A) applying the electric charge in polarity opposite to the toner on at least a part of the transferring body rear side of the transferring nip part. In this case, the device is provided with a conductive member 12 held in contact with the transferring body rear side and being electrically free from grounding on the upstream side of the transferring nip part, so that potential (Va) of the conductive member 12 becomes to zero or the potential in same polarity as the photoreceptor 1.

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 such as a copying machine, a printer, a facsimile or the like using an electrophotographic system, and more particularly, to a method for transferring a toner image formed on a photosensitive member onto a transfer member (or onto a transfer member). To transfer toner onto the transfer material).

[0002]

2. Description of the Related Art Conventionally, when a toner image formed on a photosensitive member is transferred onto a transfer member (or a transfer material on the transfer member), toner scatters due to pre-transfer (a transfer electric field is generated upstream of a transfer region. For example, in an image forming apparatus described in Japanese Patent Application Laid-Open No. 4-45470, an upstream side of a transfer area in a transfer / conveying belt system is known as a technique for preventing toner particles from being scattered due to discharge or electrostatic attraction. The pre-transfer is prevented by contacting the transfer material with the photoconductor. Further, in the image forming apparatus described in Japanese Patent Application Laid-Open No. 4-186387, in the transfer drum system, a means for blocking the transfer electric field is provided upstream of the transfer electric field forming means to prevent pre-transfer.

[0003]

Generally, in an image forming apparatus such as a copying machine or a printer using an electrophotographic system, a latent image is formed on a photoreceptor, and the latent image is developed with toner. Images are transferred and fixed on a transfer material such as recording paper to obtain an image. In recent years, a color image is obtained by superimposing and transferring a plurality of color toner images onto a transfer material such as recording paper. Image forming apparatuses such as color copiers have been developed. As one method of this color copier,
A color image is obtained by sequentially superimposing and transferring toner images formed for different color components on a photoreceptor onto an intermediate transfer body, and collectively transferring the superimposed and transferred toner images onto recording paper or the like. There is a method.

In this type of image forming apparatus, the transfer process of the toner image is performed twice or more, which is disadvantageous in that the final output image is blurred or blurred. The scattering of toner (hereinafter referred to as “transfer dust”) in the transfer process that causes image blur or the like changes depending on the transfer voltage value and the transfer current value.
Generally, initial settings of transfer conditions such as a transfer voltage value and a transfer current value are performed at the time of shipment from a factory so that transfer efficiency of toner is maximum and transfer dust is minimum. However, there are cases where the range of transfer conditions for completely satisfying both the transfer efficiency of the toner and the suppression of transfer dust is narrow, and it has been difficult to reduce the occurrence of transfer dust. Also, the optimum transfer conditions at that time will change due to changes in the environmental conditions in which the apparatus is used and changes in the characteristics of the photosensitive member and the intermediate transfer member over time. When environmental conditions such as temperature and humidity change, the charge amount of the toner and the resistance value of the intermediate transfer member change, and if the transfer conditions remain constant, transfer efficiency decreases or transfer dust occurs. In particular, when the resistance value of the intermediate transfer member decreases, the transfer voltage value becomes relatively larger than the optimum value, and transfer dust is deteriorated due to discharge at the transfer portion. Therefore, a temperature / humidity sensor is provided in the apparatus for environmental changes, and the transfer conditions are switched to experimentally determined transfer conditions in advance and corrected in accordance with the results. In addition, a medium-resistance material in which a conductive filler such as carbon black is dispersed in a resin has a tendency that the resistance value decreases with use time. It is possible to predict a rough deterioration tendency from empirical results and change the transfer conditions. However, with the correction based on the experimental and empirical results as described above, it is difficult to cope with a wide range of usage conditions of individual users, and the optimum correction is not always performed.

The present invention has been made in view of the above circumstances, and the objects of the invention described in each claim are as follows.
SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus with less transfer dust when transferring a toner image. Claims 4, 5, 7, 8, 14
SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus that always maintains a transfer condition with little transfer dust against a change in resistance of a transfer body due to a change over time. It is still another object of the present invention to provide an image forming apparatus for a color image, in which transfer dust during a toner transfer process from a photoreceptor onto an intermediate transfer belt is small. Furthermore, in the invention of claims 10, 17, and 18,
An object of the present invention is to provide an image forming apparatus in which transfer dust during transfer of toner onto a transfer material carried on a transfer conveyance belt is reduced.

[0006]

In order to achieve the above object, according to the first aspect of the present invention, as a toner image forming means,
At least a charging unit for uniformly charging the photoconductor, an exposure unit for forming a latent image on the photoconductor based on image information, and developing the latent image on the photoconductor with toner having the same polarity as the latent image. Developing means, an endless belt-shaped transfer member stretched over a plurality of rollers, a transfer nip portion where the transfer member surface and the photoconductor contact between the two rollers, and a transfer member of the transfer nip forming portion An image forming apparatus having at least a part of a back surface thereof and a charge supply device for supplying a charge having a polarity opposite to that of the toner, wherein a conductive member which is in contact with the back surface of the transfer member upstream of the transfer nip portion and is not electrically grounded And a potential (Va) of the conductive member at the time of transfer is zero or a potential having the same polarity as the charging polarity of the photoconductor.

According to a second aspect of the present invention, as a toner image forming means, at least a charging means for uniformly charging the photosensitive member, an exposing means for forming a latent image on the photosensitive member based on image information, Developing means for developing a latent image on the body with toner having the same polarity as the latent image; an endless belt-shaped transfer member stretched over a plurality of rollers; and a transfer member surface and a photoconductor between two rollers. And a charge supply device that supplies a charge of opposite polarity to the toner to at least a part of the back surface of the transfer body of the transfer nip forming portion, the transfer nip portion being upstream of the transfer nip portion. Providing a conductive member that is in contact with the rear surface of the transfer body and is electrically grounded,
And the current value (I) flowing from the conductive member to ground during transfer.
In the case of a), Ia ≦ 0 when the charging polarity of the photoconductor is negative, or Ia ≧ 0 when the charging polarity of the photoconductor is positive.

According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the image forming apparatus further includes a potential measuring means for measuring a potential (Va) of the conductive member.

According to a fourth aspect of the present invention, in the image forming apparatus of the first aspect, a potential measuring means for measuring a potential of the conductive member, and a potential of the conductive member during a transfer process using the potential measuring means. Operation control means for performing a measurement operation,
The operation control means controls the operation of the toner image forming means so that the potential of the conductive member becomes zero or a potential having the same polarity as the charging polarity of the photoconductor.

According to a fifth aspect of the present invention, in the image forming apparatus of the first or fourth aspect, the operation control means for controlling the operation of the toner image forming means is a power supply control means for controlling an output value of a transfer bias power supply. .

According to a sixth aspect of the present invention, in the image forming apparatus of the second aspect, a current measuring means for measuring a current value (Ia) flowing from the conductive member to the ground is provided.

According to a seventh aspect of the present invention, in the image forming apparatus of the second aspect, a current measuring means for measuring a current value (Ia) flowing from the conductive member to the ground, and transferring using the current measuring means. Operation control means for performing a current measurement operation during the process, wherein the operation control means is Ia ≦ 0 when the charging polarity of the photoconductor is negative, or when the charging polarity of the photoconductor is positive. The operation of the toner image forming means is controlled so that Ia ≧ 0.

According to an eighth aspect of the present invention, in the image forming apparatus of the second or seventh aspect, the operation control means for controlling the operation of the toner image forming means includes a power supply control means for controlling an output value of a transfer bias power supply. did.

According to a ninth aspect of the present invention, in the image forming apparatus according to any one of the first to eighth aspects, the transfer body is
An intermediate transfer belt for temporarily carrying the toner image and transferring the toner image from a transfer body onto a transfer material such as recording paper was used.

According to a tenth aspect of the present invention, in the image forming apparatus according to any one of the first to eighth aspects, the transfer member temporarily supports a transfer material such as a recording paper and transfers the transfer material on the transfer member. A transfer conveyance belt for transferring the toner image onto the material and conveying the transfer material in the next process was used.

In the eleventh aspect of the present invention, the first to tenth aspects are provided.
Wherein the transfer member has a volume resistivity of 10 ⁸ to 10 ¹² Ωcm.

According to a twelfth aspect of the present invention, in the image forming apparatus according to any one of the first to eighth aspects, the conductive member has a roller shape.

According to a thirteenth aspect of the present invention, in the image forming apparatus according to any one of the first to eighth aspects, an image is formed with a developer of two or more colors.

According to a fourteenth aspect of the present invention, in the image forming apparatus according to any one of the first to eighth aspects, an electric charge having a polarity opposite to that of the toner is supplied to at least a part of the back surface of the transfer member in the transfer nip forming portion. Conductive member constituting a charge supply device for the present invention is a brush-like member made of conductive fibers containing carbon fine particles in an acrylic resin.

According to a fifteenth aspect of the present invention, in the image forming apparatus of the ninth aspect, a non-exposed charging portion is formed on at least a part of the surface of the photoreceptor in the rotational direction, and after the charging portion has passed through a development process, the transfer is performed. When the sheet passes through the transfer nip without passing the paper, the potential of the conductive member that is placed upstream of the transfer nip and in contact with the rear surface of the transfer member and is not electrically grounded is set to Va. Was adopted.

According to a sixteenth aspect of the present invention, in the image forming apparatus according to the ninth aspect, at least a part of the surface of the photoreceptor in the rotational direction is formed with a non-exposed charging portion, and after the charging portion has passed through a developing process, a transfer is performed. When the sheet passes through the transfer nip without passing the paper, the current flowing through the electrically conductive member that is in contact with the back surface of the transfer member upstream of the transfer nip and is electrically grounded is defined as Ia. .

According to a seventeenth aspect of the present invention, in the image forming apparatus of the tenth aspect, at least a part of the surface of the photoreceptor in the rotation direction is formed with a non-exposed charging portion, and after the charging portion has passed through a development process, is transferred. When the sheet passes through the transfer nip portion in a state where the sheet is passed, the potential of the conductive member that is in contact with the back surface of the transfer body upstream of the transfer nip portion and is set so as not to be electrically grounded is changed. Va was adopted.

According to an eighteenth aspect of the present invention, in the image forming apparatus according to the tenth aspect, a non-exposed charging portion is formed on at least a part of the surface of the photoreceptor in the rotational direction, and after the charging portion has passed through a developing process, the transfer is performed. When passing through the transfer nip portion in a state where the material is passed, the current flowing through the electrically conductive member that is in contact with the back surface of the transfer body upstream of the transfer nip portion and is electrically grounded is defined as Ia. did.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail based on illustrated embodiments.

(Embodiment 1) FIG. 1 is a schematic diagram showing an example of an image forming apparatus according to the present invention. In the image forming apparatus having the configuration shown in FIG. 1, the color developing unit 4 faces four photosensitive drums 1 in the form of black (Bk), cyan (C), magenta (M), and yellow (Y). The color developing units are arranged side by side, and the toner images formed for the different color components on the photoconductor 1 are sequentially superimposed on the intermediate transfer belt 6 and transferred.
This is a one-drum intermediate transfer type color image forming apparatus that obtains a color image by collectively transferring the superposed and transferred toner images onto recording paper 14 or the like. The drum-shaped photoreceptor 1 has a function-separated type photosensitive layer formed on an aluminum tube by laminating an undercoat layer / a charge generation layer / a charge transport layer in this order. The thickness of this photosensitive layer is about 28 μm, and the capacitance is about 90 pF / cm ² .

When the image forming operation is started, the photosensitive member 1 is uniformly negatively charged by the scorotron charger 2 (about -650 V).
~ -700V), then a laser beam r corresponding to the image information
(Laser wavelength: 780 nm) is applied to the exposed portion 1A on the photoconductor 1 to form an electrostatic latent image of -100V to -500V.
At this time, the charging potential and the exposure portion potential of the photoreceptor 1 can be detected by the surface potential sensor 3 to control the charging condition and the exposure condition. In the color developing section 4, developing devices of four colors of Bk, C, M and Y are arranged side by side, and develop an electrostatic latent image for each color. Each developing unit uses a dry two-component developer composed of toner of each color and a magnetic carrier, and performs development by a reversal developing method in which a negatively charged toner is attached to a low potential portion on the photoconductor 1. The developing bias value is about -500V to -550.
V. An AC component may be superimposed on the developing bias. An image density sensor 5 is installed at the position after development,
The process conditions can be controlled by detecting the toner adhesion amount from the optical reflectance. The toner images formed for each color on the photoconductor 1 are sequentially superimposed and transferred onto the intermediate transfer belt 6.

The intermediate transfer belt 6 is stretched around a plurality of rollers (a driving roller and a plurality of driven rollers) and is rotated in a direction indicated by an arrow in FIG. In this embodiment, a belt portion stretched between two rollers of the entrance roller 12 and the exit roller 13 among the plurality of rollers is configured to be able to contact and separate from the photoconductor 1. The length of the belt portion stretched between the two rollers is 36 mm, and the width of the belt in the longitudinal direction is 350 mm.
And The distance from the entrance roller 12 to the contact start position was 8 mm, the transfer nip width L was 20 mm, and the distance from the separation start position to the exit roller 13 was 8 mm. Further, a conductive brush 16 was provided to be in contact with the back surface of the belt centered on a position 7 mm from the contact portion of the transfer nip portion. The width of the conductive brush 16 in the longitudinal direction is 340 mm, the width of the conductive brush 16 in the belt moving direction is about 4 mm, and the brush portion is made of 360 denier / 24 filament carbon-containing acrylic fiber, about 1 × 10 ⁷ Ωcm. With a resistance value of The conductive brush 16 and a transfer bias power supply 16A for applying a transfer voltage to the conductive brush 16 constitute a charge supply device for supplying charges of the opposite polarity to the toner on the back surface of the belt.

The intermediate transfer belt 6 is a single-layer medium resistor in which carbon black is dispersed in a fluorine-based resin.
The thickness is about 150 μm, and the new surface resistance is about 5 × 10 ⁹
Ω / cm ² and a volume resistivity of about 1 × 10 ¹¹ Ωcm were used. Other resins such as polycarbonate can be used as the belt material. Exit roller 13
Is not grounded, and a positive transfer voltage (Vt) is applied to the conductive brush 16 during transfer. The transfer voltage (Vt) is supplied by a transfer bias power supply 16A, and its output value is controlled by a control unit (not shown) of the image forming apparatus main body. Thereafter, from the photoconductor 1 to the intermediate transfer belt 6
The upward transfer is referred to as “belt transfer”. The residual toner on the photoreceptor 1 after the belt transfer is transferred to the charger 7 before cleaning.
The charging amount is controlled by the drum cleaning device 9.
Brush and blade. Further, the residual charge on the photoconductor 1 is removed by the charge removing lamp 10.

A toner image is formed on the photosensitive member 1 by an image forming operation of the first color, and the intermediate transfer belt 6 is transferred by belt transfer.
After the first color toner image is transferred thereon, the second color image forming operation is started, and the second color toner image is superimposedly transferred onto the intermediate transfer belt 6. At this time, the transfer voltage (Vt) may be increased for each transfer order. In the case of a full-color image, toner images of four colors of black (Bk), cyan (C), magenta (M), and yellow (Y) are sequentially superimposed on the intermediate transfer belt 6 and then belt-transferred, and then collectively recorded. The image is transferred onto paper 14. To transfer the toner image from the intermediate transfer belt 6 onto the recording paper 14, a positive voltage is applied from the back side of the recording paper 14 by the paper transfer roller 11. Hereinafter, the transfer from the intermediate transfer belt 6 onto the recording paper 14 is referred to as “paper transfer”. The toner remaining on the intermediate transfer belt 6 after the paper transfer is removed by a blade or the like of the belt cleaning device 8.

As the intermediate transfer member, a rigid intermediate transfer drum can be used instead of the intermediate transfer belt 6, but a color image forming apparatus of the intermediate transfer belt type has a free layout around the belt. There is an advantage that the degree is large and the device can be miniaturized.

In the present invention, the potential (Va) of the conductive member disposed upstream of the transfer nip portion and in contact with the back surface of the intermediate transfer belt 6 and not electrically grounded is zero or the photosensitive member 1 So that it has a potential of the same polarity as the charging polarity of
The charging conditions, the resistance value of the intermediate transfer belt 6, the output value of the transfer bias power supply 16A, and the like are set as the optimum transfer conditions.
The range in which the potential (Va) of the conductive member is zero or a potential having the same polarity as the charging polarity of the photoconductor 1 needs to be changed depending on mechanical conditions such as the transfer nip width L and the transfer characteristics of the toner itself. At this time, in order to prevent the transfer efficiency from decreasing, the charging conditions, the resistance value of the intermediate transfer belt 6, the output value of the transfer bias power supply 16A, and the like are set as the optimum transfer conditions. Hereinafter, a method for determining the optimum transfer condition will be described.

In the present embodiment, the entrance roller 12 is used as a conductive member which is arranged on the upstream side of the transfer nip portion, is in contact with the back surface of the intermediate transfer belt 6, and is not electrically grounded. The entrance roller 12 was provided with a potential sensor 15 for measuring the potential (Va) of the roller.

FIG. 2 shows a transfer voltage (Vt) applied to the conductive brush 16 for supplying electric charges to the belt back surface of the transfer nip portion.
5 shows the measurement results of the entrance roller potential (Va) with respect to FIG. As a measuring method, the potential of the entrance roller (Va) was measured by the potential sensor 15 when the charged portion of the photoreceptor 1 was passed through the transfer process without being exposed (similar to a blank image). In addition, due to the resistance unevenness of the intermediate transfer belt 6, the entrance roller potential (V
Since a) changed, the measurement was made for one round of the belt, and the average value was used as the measurement result. In the range of Vt ≦ 600V, the entrance roller potential (Va) is the same as the charging polarity of the photosensitive member 1 (Va).
≦ 0. According to the present invention, transfer conditions with less transfer dust can be obtained within this range.

FIG. 3 shows changes in the transfer dust level and transfer efficiency with respect to the entrance roller potential (Va). The transfer dust level is the toner image transferred on the intermediate transfer belt (about 0.3
(line image of mm width) was observed under magnification and ranked. The state with the least amount of transfer dust was evaluated as rank 5, and the poor state was evaluated as rank 1. The transfer efficiency was calculated by weighing the toner adhesion amount before and after the transfer of the solid toner image by a suction method. As shown in FIG. 3, the transfer dust rank tends to be rapidly deteriorated when the entrance roller potential (Va) is in the range of Va> 0, but becomes rank 4 or higher, which is practically no problem in the range of Va ≦ 0. Although the transfer efficiency decreases as the transfer voltage decreases, the transfer voltage of about 200 V or higher resulted in a transfer efficiency of 90% or higher, which is practically no problem.

In this embodiment, the photosensitive member for negative charging is used, but a photosensitive member for positive charging may be used. In the case of a photoconductor for positive charging, the charging polarity of the toner also becomes positive,
The transfer bias power supply has a negative polarity. Therefore, in this case, the transfer dust is reduced by setting the condition that the entrance roller potential (Va) satisfies Va ≧ 0. In this embodiment, the output value of the transfer bias power supply is controlled. However, the output value of the photosensitive member charging means and the resistance value of the intermediate transfer belt may be controlled to change the entrance roller potential (Va). .

(Embodiment 2) In the present embodiment, in the image forming apparatus having the structure shown in FIG. 1, the above-mentioned entrance roller (conductive material) is detected by the potential sensor 15 when the power of the machine is turned on or every time a fixed number of images are formed. The operation of measuring the potential (Va) of the member 12 was performed, and a control device (not shown) was installed as operation control means for controlling the toner image forming means based on the potential. As the control device, a power supply control device for controlling the output value of the transfer bias power supply 16A is used, and a control unit (a central processing unit (CPU), a memory such as a ROM or a RAM, a clock, a counter) of the image forming apparatus main body is used. , An input / output circuit (I / O), an interface circuit (I / F), and various control devices. Hereinafter, a case where a control device is added to the configuration of the first embodiment will be described.

In FIG. 1, after turning on the power of the image forming apparatus, the control device performs optimization setting such as charging conditions and developing conditions, and then performs a belt transfer voltage (transfer bias power supply 16).
(The output value of A). In this case, the photoreceptor 1 is charged to about -650 V and is passed through the development process without being exposed. However, in this embodiment, since the reversal development method is used,
Development (adhesion of toner) is not performed. The control device measures the potential (Va) of the entrance roller when the charged portion of the photoconductor 1 passes through the transfer process by the potential sensor 15. Then, in the transfer voltage setting operation, in order to eliminate the influence of the resistance unevenness of the intermediate transfer belt 6, a belt voltage value of 0V is applied as an initial value to one transfer voltage value, and the transfer voltage value is increased in 200V steps. However, the time of the setting operation may be shortened by setting the initial value to several hundred volts. The step-up interval is set to 5
Precise control becomes possible by narrowing the distance to about 0V. Finally, the maximum applied voltage value within the range of the condition that the entrance roller potential (Va) satisfies Va ≦ 0 is set as the optimum transfer voltage (Vt) at that time. For example, when the intermediate transfer belt 6 is new, the transfer voltage (Vt) is set to Vt = 600V.
(Va = 0 V, transfer chile rank = 4.5).

Then, a normal copy (or print)
After the operation was performed for 5,000 sheets, the transfer dust rank in the halftone portion deteriorated to 3.0. At this time, the surface resistance of the intermediate transfer belt 6 was reduced to about 5 × 10 ⁷ Ω / cm ² , and the volume resistance was reduced to about 5 × 10 ⁹ Ωcm. Further, when the entrance roller potential (Va) is measured by the potential sensor 15, Va =
+ 50V. When the setting operation of the optimum transfer voltage (Vt) was performed again by the control device, a characteristic like a white circle in FIG. 2 was obtained, and the optimum transfer voltage value (Vt) was Vt = 500.
V was detected and reset. Under these reset conditions, a uniform image with little transfer dust from the halftone portion to the solid portion could be obtained.

FIG. 4 shows the results obtained by rearranging the transfer dust ranks under various image forming conditions carried out as in the first embodiment and the above-described second embodiment with respect to the entrance roller potential. It is apparent from the results in FIG. 4 that if the entrance roller potential (Va) is controlled to zero or a potential having the same polarity as the charging polarity of the photoconductor by a power supply control device or the like, the occurrence of transfer dust is small. The volume resistance of the intermediate transfer belt 6 is about 1 × 10 ⁸ Ωc.
m or less, the current from the transfer bias flowing in the intermediate transfer belt 6 becomes large, and the entrance roller potential (Va) becomes Va.
The condition that ≦ 0 is lost. In this case, there was no range in which the transfer chile rank was 4 or more and the transfer efficiency was 90% or more.

(Embodiment 3) In this embodiment, as shown in FIG. 5, an ammeter 30 is connected between the inlet roller 12 and the ground instead of a potential sensor, and a DC power supply 31 is connected to the outlet roller 13. In this case, an equipotential voltage was applied to the outlet roller 13 and the conductive brush 16 which was in contact with the back surface of the belt at the transfer nip portion. (Vt) was set. That is, the current value (Ia) flowing from the entrance roller 12 to the ground when the transfer voltage value (Vt) is changed is measured by the ammeter 30, and the optimum transfer voltage value is determined and set from the current measurement result.

FIG. 6 shows the measurement results of the current value (Ia) flowing through the entrance roller 12 with respect to the transfer voltage (Vt) applied to the conductive brush 16 and the exit roller 13 that are in contact with the belt back surface of the transfer nip. FIG. 7 shows measurement results of the transfer efficiency and the transfer dust rank with respect to the entrance roller current. As a measuring method, the entrance roller 1 when the charged portion of the photoreceptor 1 is passed through the transfer process without being exposed (similar to a blank image)
The current value (Ia) flowing from No. 2 to the ground was measured by the ammeter 30. Further, since the current value changes due to the resistance unevenness of the intermediate transfer belt 6, the measurement was performed for one round of the belt, and the average value was used as the measurement result. Transfer voltage (Vt) is Vt ≦ 600
In the range of V, the current value (Ia) flowing through the ammeter 30 is Ia ≦
0 (current flows from the ground to the entrance roller, or electrons flow from the entrance roller to the ground). Within this range, transfer conditions with less transfer dust can be obtained. Therefore, by setting the transfer voltage value (Vt) under the condition that the current value (Ia) flowing from the inlet roller 12 to the ground is Ia ≦ 0, a transfer dust rank of 4.0 or more was obtained. Further, preferably, by setting the condition to be −3 μA ≦ Ia ≦ 0, the transfer dust rank is 4.0 or more and the transfer efficiency is sufficient.
0% or more was obtained.

In this embodiment, the photosensitive member for negative charging is used, but a photosensitive member for positive charging may be used. When a photoconductor for positive charging is used, the charging polarity of the toner also has a positive polarity, and the transfer bias power supply has a negative polarity. In this case, the current value (Ia) flowing from the entrance roller 12 to the ground is Ia ≧ 0. Set the condition to be

(Embodiment 4) In this embodiment, the optimum transfer voltage (Vt) was set under the same configuration and conditions as in Embodiment 3 except that the exit roller 13 was grounded as shown in FIG.
That is, the current value (Ia) flowing from the entrance roller 12 to the ground when the transfer voltage value (Vt) is changed is measured by the ammeter 30.
The optimum transfer voltage value is determined and set from the current measurement results. Also in this case, as shown in FIG.
By controlling the transfer voltage value (Vt) under the condition that the current value (Ia) flowing from No. 2 to the ground falls within the range of Ia ≦ 0, a good image with less transfer dust was obtained.

FIG. 10 shows the results obtained by rearranging the transfer dust ranks under various image forming conditions carried out as in the third embodiment and the fourth embodiment with respect to the entrance roller current. It is apparent from the results of FIG. 10 that the generation of transfer dust is small by controlling the entrance roller current to zero or to a current having the same polarity as the charging polarity of the photoconductor.

(Embodiment 5) In this embodiment, in the image forming apparatus having the configuration shown in FIG. 5 or FIG. A control device (not shown) was installed as an operation control unit for controlling the toner image forming unit based on the measurement of the current value (Ia) flowing from 12 to the ground. As the control device, a power supply control device for controlling the output value of the transfer bias power supply 16A or the like is used, and the control unit (central processing unit (C
PU), memories such as ROM and RAM, clocks, counters, input / output circuits (I / O), interface circuits (I
/ F) and various control devices). Hereinafter, a case where a control device is added to the configuration of the third embodiment in FIG. 5 will be described.

In this embodiment, the ammeter 30 is installed between the entrance roller 12 and the ground, and after the power supply of the image forming apparatus is turned on, the control device performs optimization settings such as charging conditions and developing conditions. Later, the current value (Ia) flowing from the entrance roller 12 to the ground when the transfer voltage value (Vt) is changed is measured by the ammeter 30 and the transfer voltage value is adjusted so that the entrance roller current (Ia) becomes optimal. (Vt) setting operation is performed. In this case, the photoconductor 1 is charged to about -650 V and is allowed to pass through the development process without being exposed. However, in this embodiment, development (adhesion of toner) is not performed because of the reversal development system. The control device measures the entrance roller current (Ia) when the charging section of the photoconductor 1 passes through the transfer process by the ammeter 30. The transfer voltage value (Vt) is set by measuring the current of one transfer voltage value for one rotation of the belt to eliminate the influence of the resistance unevenness of the intermediate transfer belt 6, and determining the average value for control. Is preferably adopted.

First, when the intermediate transfer belt 6 is new,
The transfer voltage (Vt) was adjusted, and the current value (Ia) flowing from the entrance roller 12 to the ground was set so that Ia = 0.
The transfer voltage (Vt) at this time was Vt = 600V. When an image was formed under these conditions, a clear image having a transfer dust rank of 4.0 was obtained.

Then, a normal copy (or print)
When 5000 operations were performed, the transfer dust rank in the halftone portion was deteriorated to 2.0. At this time, the surface resistance value of the intermediate transfer belt 6 was reduced to about 5 × 10 ⁷ Ω / cm ² and the volume resistance value was reduced to about 5 × 10 ⁹ Ωcm (the surface resistance value of a new article was about 5 × 10 ⁷ Ω / cm ^{2). 9} Ω / cm ² , volume resistance about 1 ×
10 ¹¹ Ωcm). At this point, the entrance roller 1
When the current value (Ia) of No. 2 was measured, Ia = + 2.0 μm
A. Therefore, the transfer voltage was adjusted by the control device so that Ia = -0.3 .mu.A and reset. The transfer voltage (Vt) at this time was Vt = 400V. When an image was created under these reset conditions, a clear image with less transfer dust from the halftone portion to the solid portion could be obtained.

Comparative Example 1 As a comparative example, a conductive brush 16 for contacting the back surface of the belt at the transfer nip and applying a transfer voltage was made of a SUS brush having a thickness of about 20 μm. The structure was the same as in Example 3. Although the operation of setting the transfer voltage in the initial stage was almost the same as that in Example 3, the back surface of the belt was damaged by using several hundred sheets. Then, the shavings of the flaws adhered to the roller surface and the like to form convex dirt, and transfer failure occurred in the belt transfer unit and the paper transfer unit. At this time, the current flowing from the entrance roller 12 to the ground was measured by the ammeter 30. As a result, the current value (Ia) varied greatly and it was difficult to set an appropriate transfer voltage value. From the above, the material of the conductive brush 16 is a conductive fiber (for example, 360 denier / 24 filament carbon-containing acrylic fiber or the like) containing carbon fine particles in an acrylic resin as described in the first embodiment. It is preferable that

The description of the first to fifth embodiments is directed to a technique for reducing transfer dust in an image forming apparatus using an intermediate transfer method. The present invention is applied to an image forming apparatus using an intermediate transfer method. The present invention is not limited to this. For example, the present invention can be similarly applied to an image forming apparatus using a transfer conveyance belt that carries and conveys a transfer material such as recording paper and transfers a toner image on a photoconductor to the transfer material. . Hereinafter, the embodiment will be described.

(Embodiment 6) FIG. 11 shows an example of an image forming apparatus using a transfer-conveying belt for carrying and conveying a transfer material such as recording paper. In FIG. 11, a drum-shaped photoreceptor 17 has a function-separated type photosensitive layer formed on an aluminum tube in the order of an undercoat layer / a charge generation layer / a charge transport layer.
The thickness of the photosensitive layer is about 28 μm, and the capacitance is about 90 pF / c.
m ² . When the image forming operation is started, the photosensitive member 17 is uniformly negatively charged by the scorotron charger 18 (about −65).
(0 V to -700 V), and then irradiates the exposed portion 17 </ b> A on the photoreceptor 17 with a laser beam r corresponding to the image information, and outputs -100 V
An electrostatic latent image of -500 V is formed. The developing unit 19 is of a reversal developing type in which a dry two-component developer including a toner and a magnetic carrier is used, and a negatively charged toner is attached to a low potential portion on the photoconductor 17. The developing bias value is -500V ~
-550V. Further, an AC component may be superimposed on the developing bias.

The transfer conveying belt 23 is stretched between the driving roller 21 and the driven roller 22. The recording paper 29 is fed from a paper feeding unit (not shown) in accordance with an image forming operation on the photoreceptor 17, is carried on a transfer conveyance belt 23 through a registration roller 20, and is conveyed to a transfer nip. A roller 24 is provided on the back side of the belt downstream of the transfer nip, and the photosensitive member 1 is brought into contact with the roller 24 and the belt portion stretched by the driven roller 22. Transfer nip width L is about 10
mm, the width of the transfer conveyance belt 23 in the longitudinal direction is 350 mm
And A conductive brush 25 was brought into contact with the belt back surface at the center of the transfer nip, and a transfer bias power supply 25A was connected to the conductive brush 25. In addition, the conductive brush 25
The brush portion was made of 360 denier / 24 filament carbon-containing acrylic fiber having a resistance value of about 1 × 10 ⁷ Ωcm. The conductive brush 25 and the transfer bias power supply 2
Reference numeral 5A designates a charge supply device for supplying charges of the opposite polarity to the toner to the belt back surface of the transfer nip portion during transfer, and a transfer voltage (Vt) is applied to the transfer conveyance belt 23 through the conductive brush 25.

The transfer / conveying belt 23 has a medium resistance rubber layer in which carbon black is dispersed in a blend rubber of chloroprene rubber and EPDM, and a fluorine-based coat layer is provided on the surface of the rubber layer. The thickness of the rubber layer is about 500 μm,
The volume resistance when new is about 1 × 10 ¹⁰ Ωcm, the thickness of the coating layer is about 10 μm, and the surface resistance when new is about 1 × 10
Those having a resistance of ¹¹ Ω / cm ² were used. The conductive roller 2 is provided on the back surface of the belt between the driven roller 22 and the conductive brush 25.
6 were brought into contact. The conductive roller 26 is grounded via an ammeter 30.

In the image forming apparatus of this embodiment, a positive transfer voltage (Vt) is applied to the conductive brush 25 during transfer. This transfer voltage (Vt) is applied to a transfer bias power supply 25.
The output value is supplied by a control unit (not shown) installed in the image forming apparatus main body in accordance with a current value (Ia) flowing from the conductive roller 26 to the ground measured by the ammeter 30 and the like. Processing unit (CPU), RO
M, a memory such as a RAM, a clock, a counter, an input / output circuit (I / O), an interface circuit (I / F), and various control devices. The conductive roller 26 is not electrically grounded, and a potential sensor is provided on the conductive roller. The potential sensor measures the potential of the conductive roller, and the control unit controls the transfer voltage according to the potential. It is also possible to adopt a configuration in which

When the recording paper 29 passes through the transfer process, the recording paper 29 is electrostatically attracted to the surface of the transfer / conveying belt 23, so that the recording paper 29 is easily separated from the photosensitive member 17. Therefore, the use of the transfer conveyance belt 23 has an advantage that troubles such as a paper jam are reduced. The residual toner on the photoconductor 17 after the transfer is removed by a brush and a blade of the drum cleaning device 27, and the residual charge on the photoconductor 17 is removed by a discharge lamp 28. Further, the recording paper 29 on which the toner image has been transferred is separated in curvature by the driving roller 21 and then conveyed to a fixing unit.
The heat is fixed by the fixing roller 32.

In the image forming apparatus having the above configuration, in this embodiment, the photosensitive member 17 is charged negatively (about -6).
50 V to -700 V), and when the recording paper 29 and the unexposed portion of the photosensitive member charging portion are passing through the transfer process (similar to a blank image), the current flowing from the conductive roller 26 to the ground is measured by the ammeter 30. The transfer voltage (Vt) was measured so that the current value (Ia) was Ia ≦ 0. Next, the control section controlled the transfer voltage (Vt) under these transfer conditions to form an image. As a result, a good image having a transfer dust rank of 4 to 5 was obtained. When the image was formed under the transfer condition where the current value (Ia) flowing from the conductive roller 26 to the ground was Ia = + 5 μA, the rank of the transfer dust was 2. From these results, the value of the current flowing from the conductive roller 26 to the ground (I
By controlling a) to zero or to a current having the same polarity as the charging polarity of the photoreceptor 17, it was clarified that the occurrence of transfer dust was small.

[0057]

As described above, in the image forming apparatus according to the first aspect, a conductive member that is in contact with the back surface of the transfer member and is not electrically grounded is provided upstream of the transfer nip portion. In some cases, a condition is set such that the potential (Va) of the conductive member is zero or a potential having the same polarity as the charging polarity of the photoconductor, so that discharge on the upstream side of the transfer nip portion is controlled, The movement of the toner in front of the transfer nip can be prevented, and the transfer dust can be reduced. Accordingly, it is possible to provide an image forming apparatus with less transfer dust during toner image transfer.

In the image forming apparatus according to the present invention, a conductive member which is in contact with the back surface of the transfer member and is electrically grounded is provided upstream of the transfer nip portion, and the conductive member is grounded during transfer. The current value (Ia) flowing to the photoconductor is controlled so that Ia ≦ 0 when the charging polarity of the photoconductor is negative, or Ia ≧ 0 when the charging polarity of the photoconductor is positive. The discharge on the upstream side of the transfer nip is controlled, and the movement of the toner in front of the transfer nip can be prevented.
Transfer dust is reduced. Accordingly, it is possible to provide an image forming apparatus with less transfer dust during toner image transfer.

According to the image forming apparatus of the third aspect, in addition to the configuration and effect of the first aspect, the potential (Va) of the conductive member
The transfer condition can be set at the time of machine shipment, trouble occurrence, machine maintenance, etc. by always installing the potential measurement means for measuring the potential (Va). A clear image with less transfer dust can be stably obtained.

According to a fourth aspect of the present invention, in addition to the structure and effect of the first aspect, a potential measuring means for measuring the potential (Va) of the conductive member, and a potential measuring means for measuring a potential (Va) of the conductive member during a transfer process are provided. Operation control means for performing a potential measurement operation of the conductive member, wherein the operation control means includes a toner image forming means such that the potential of the conductive member is zero or a potential having the same polarity as the charging polarity of the photosensitive member. Since the configuration of the operation is controlled, the potential (Va) of the conductive member is periodically measured,
The information can be fed back to reset the condition to reduce the transfer dust, so that even if the photoconductor potential and the electrical characteristics of the belt material deteriorate with time, an image with little transfer dust can always be obtained. it can.

According to a fifth aspect of the present invention, in addition to the configuration and effect of the first or fourth aspect, the operation control means for controlling the operation of the toner image forming means includes a power supply control for controlling an output value of a transfer bias power supply. As a result, the output of the transfer bias power supply can be controlled so as to reduce the transfer dust, and an image with little transfer dust can be always obtained even if the belt material deteriorates with time.

In the image forming apparatus according to the sixth aspect, in addition to the configuration and effect of the second aspect, a configuration is provided in which current measuring means for measuring a current value (Ia) flowing from the conductive member to the ground is provided. By always mounting the potential measuring means for measuring Ia), the transfer conditions can be set at the time of shipping the machine, at the time of occurrence of trouble, at the time of machine maintenance, etc., and a clear image with little transfer dust can be stably obtained.

According to a seventh aspect of the present invention, in addition to the configuration and effect of the second aspect, a current measuring means for measuring a current value (Ia) flowing from the conductive member to the ground, and using the current measuring means. Operation control means for performing a current measurement operation during the transfer process, wherein the operation control means is Ia ≦ 0 when the charging polarity of the photoconductor is negative, or when the charging polarity of the photoconductor is positive. Is configured to control the operation of the toner image forming means so that Ia ≧ 0. Therefore, the current (Ia) is measured periodically, and the information is fed back to return to a condition that reduces transfer dust. Since it can be set, a clear image with little transfer dust can always be stably obtained even if the potential of the photoconductor or the electrical characteristics of the belt material deteriorates with time.

According to an eighth aspect of the present invention, in addition to the configuration and effect of the second or seventh aspect, the operation control means for controlling the operation of the toner image forming means includes a power supply control for controlling an output value of the transfer bias power supply. As a result, the output of the transfer bias power supply can be controlled so as to reduce the transfer dust, and an image with little transfer dust can be always obtained even if the belt material deteriorates with time.

According to the image forming apparatus of the ninth aspect, in addition to the configuration and effect of any one of the first to eighth aspects, the transfer body is
An intermediate transfer belt that temporarily holds the toner image and transfers the toner image from a transfer body onto a transfer material such as recording paper, so a small image that can stably obtain a clear image with little transfer dust An image forming apparatus can be obtained.

In the image forming apparatus according to the tenth aspect, in addition to the configuration and effect according to any one of the first to eighth aspects, the transfer body temporarily supports a transfer material such as a recording paper and The transfer conveyance belt that transfers the toner image onto the transfer material and conveys the transfer material in the next process minimizes paper jams.
In addition, an image forming apparatus with less transfer dust can be obtained.

In the image forming apparatus according to the eleventh aspect, in addition to the configuration and effect of any one of the first to tenth aspects, the transfer body is a medium-resistance body having a volume resistance of 10 ⁸ to 10 ¹² Ωcm. The transfer condition can be controlled from the measurement result of the potential value on the back surface of the transfer body or the current value flowing on the back surface of the transfer body.

In the image forming apparatus according to the twelfth aspect, in addition to the configuration and effect of any one of the first to eighth aspects, since the conductive member is formed in a roller shape, damage due to scratches on the back surface of the belt is small, and the potential ( Since the measurement of Va) or the current (Ia) is stabilized, the reliability of setting the optimum transfer condition is increased,
It is possible to obtain an image having little transfer dust and no transfer abnormality over a long period of time.

In the image forming apparatus according to the thirteenth aspect, in addition to the configuration and effect of any one of the first to eighth aspects, an image is formed by using a developer of two or more colors. By applying the present invention to an image forming process having a transfer process, the effect of reducing transfer dust is further increased, and a clear color copy with less transfer dust can be obtained as compared with the related art.

In the image forming apparatus according to the present invention, in addition to the configuration and effect of any one of the first to eighth aspects, an electric charge having a polarity opposite to that of the toner is supplied to at least a part of the back surface of the transfer member in the transfer nip forming portion. Is a brush-like member made of conductive fibers containing carbon fine particles in an acrylic resin, so that damage due to scratches on the back surface of the belt is small, and the potential (V
Since the measurement of a) or the current (Ia) is stable, the reliability of the setting of the optimum transfer condition is improved, and an image free of transfer abnormalities with little transfer dust over a long period of time can be obtained.

In the image forming apparatus according to the fifteenth aspect, in addition to the structure and effect of the ninth aspect, a charging unit that is not exposed is formed on at least a part of the rotation direction of the surface of the photosensitive member, and the charging unit performs the development process. After passing through the transfer nip portion without passing the transfer material through the transfer nip portion, the conductive member is disposed upstream of the transfer nip portion so as to be in contact with the rear surface of the transfer body and not to be electrically grounded. Since the potential is set to Va, a simple and stable measurement of the potential (Va) is possible without using a special jig or the like, and a low-cost image forming apparatus can be provided.

In the image forming apparatus according to the present invention, in addition to the constitution and effect of the ninth aspect, at least a part of the surface of the photosensitive member which is not exposed is formed with a non-exposed charging portion, and the charging portion has passed through the developing process. Later, when the transfer material passes through the transfer nip without passing the paper, the current flowing through the electrically conductive member that is in contact with the back surface of the transfer body upstream of the transfer nip and is electrically grounded is defined as Ia. Therefore, a simple and stable measurement of the current (Ia) is possible without using a special jig or the like, and a low-cost image forming apparatus can be provided.

According to the seventeenth aspect of the present invention, in addition to the structure and effect of the tenth aspect, a non-exposed charging portion is formed on at least a part of the surface of the photosensitive member in the rotational direction, and the charging portion has passed through the developing process. After that, when the transfer material passes through the transfer nip portion in a state where the transfer material is passed, the conductive member is disposed upstream of the transfer nip portion so as to be in contact with the rear surface of the transfer body and not to be electrically grounded. Since the potential is set to Va, a simple and stable measurement of the potential (Va) is possible without using a special jig or the like, and a low-cost image forming apparatus can be provided.

In the image forming apparatus according to the eighteenth aspect, in addition to the structure and the effect of the tenth aspect, a charging portion which is not exposed is formed on at least a part of the rotation direction of the surface of the photoreceptor, and the charging portion has undergone a developing process. After that, when the transfer material passes through the transfer nip portion in a state where the transfer material is passed, the current flowing through the electrically conductive member that is in contact with the back surface of the transfer body upstream of the transfer nip portion and is electrically grounded is defined as Ia. With this configuration, a simple and stable measurement of the current (Ia) is possible without using a special jig or the like, and a low-cost image forming apparatus can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus showing one embodiment of the present invention.

FIG. 2 is a diagram illustrating a change in an entrance roller potential with respect to a transfer voltage applied to a conductive brush of the image forming apparatus illustrated in FIG. 1;

FIG. 3 is a diagram showing a change in a transfer chile rank and a transfer efficiency with respect to an entrance roller potential of the image forming apparatus shown in FIG. 1;

FIG. 4 is a diagram illustrating a change in transfer dust rank with respect to an entrance roller potential under various image forming conditions of the image forming apparatus illustrated in FIG. 1;

FIG. 5 is a schematic diagram illustrating a main part of an image forming apparatus according to another embodiment of the present invention.

FIG. 6 is a diagram illustrating a change in an entrance roller current with respect to a transfer voltage applied to a conductive brush of the image forming apparatus illustrated in FIG. 5;

FIG. 7 is a diagram showing a change in transfer chile rank and transfer efficiency with respect to an inlet roller current of the image forming apparatus shown in FIG. 5;

FIG. 8 is a schematic configuration diagram of a main part of an image forming apparatus according to still another embodiment of the present invention.

FIG. 9 is a diagram illustrating changes in transfer chile rank and transfer efficiency with respect to the entrance roller current of the image forming apparatus illustrated in FIG. 8;

FIG. 10 is a diagram showing the transfer dust rank with respect to the entrance roller current shown in FIGS. 7 and 9;

FIG. 11 is a schematic configuration diagram of an image forming apparatus showing still another embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 photoconductor 2 scorotron charger (charging means) 4 color developing section 6 intermediate transfer belt (transfer body) 8 belt cleaning device 9 drum cleaning device 10 static elimination lamp 11 paper transfer roller 12 entrance roller (conductive member) 13 exit roller 14 Recording paper (transfer material) 15 Potential sensor (potential measuring unit) 16 Conductive brush (charge supply unit) 16A Transfer bias power supply (charge supply unit) 17 Photoconductor 18 Scorotron charger (charging unit) 19 Developing unit 20 Registration roller 21 Driving roller 22 Driven roller 23 Transfer / transport belt (transfer) 24 Roller 25 Conductive brush (charge supply device) 25A Transfer bias power supply (charge supply device) 26 Conductive roller (conductive member) 27 Drum cleaning device 28 Static elimination lamp 29 Recording paper (transfer material) 30 Current (Current measuring means) 31 DC power supply 32 fixing roller r laser beam (exposure means)

Claims (18)

[Claims] At least as a toner image forming means,
Charging means for uniformly charging the photoreceptor, exposure means for forming a latent image on the photoreceptor based on image information, and development for developing the latent image on the photoreceptor with toner having the same polarity as the latent image Means, an endless belt-shaped transfer member stretched over a plurality of rollers, a transfer nip portion in which the surface of the transfer member and the photoconductor contact between the two rollers, and a transfer nip portion on the back surface of the transfer member of the transfer nip forming portion. An image forming apparatus having at least a charge supply device for supplying a charge having a polarity opposite to that of the toner, wherein the conductive member is in contact with the rear surface of the transfer member upstream of the transfer nip portion and is not electrically grounded. Wherein the potential (Va) of the conductive member during transfer is zero or a potential having the same polarity as the charging polarity of the photosensitive member. 2. A toner image forming means comprising:
Charging means for uniformly charging the photoreceptor, exposure means for forming a latent image on the photoreceptor based on image information, and development for developing the latent image on the photoreceptor with toner having the same polarity as the latent image Means, an endless belt-shaped transfer member stretched over a plurality of rollers, a transfer nip portion in which the surface of the transfer member and the photoconductor contact between the two rollers, and a transfer nip portion on the back surface of the transfer member of the transfer nip forming portion. An image forming apparatus having at least a charge supply device for supplying a charge having a polarity opposite to that of the toner, wherein the conductive member is in contact with the rear surface of the transfer member and electrically grounded upstream of the transfer nip portion And the current value (Ia) flowing from the conductive member to the ground during transfer is Ia ≦ 0 when the charging polarity of the photoconductor is negative, or Ia ≧ when the charging polarity of the photoconductor is positive. An image forming apparatus characterized by being 0. 3. The image forming apparatus according to claim 1, further comprising potential measuring means for measuring a potential (Va) of said conductive member. 4. An image forming apparatus according to claim 1, wherein a potential measuring means for measuring a potential of said conductive member, and an operation of measuring a potential of said conductive member during a transfer process using said potential measuring means. Control means for controlling the operation of the toner image forming means so that the potential of the conductive member becomes zero or a potential having the same polarity as the charging polarity of the photoconductor. Image forming device. 5. An image forming apparatus according to claim 1, wherein the operation control means for controlling the operation of the toner image forming means is a power supply control means for controlling an output value of a transfer bias power supply. Image forming device. 6. An image forming apparatus according to claim 2, further comprising current measuring means for measuring a current value (Ia) flowing from said conductive member to ground. 7. An image forming apparatus according to claim 2, wherein current measuring means for measuring a current value (Ia) flowing from said conductive member to ground, and a current measuring operation during a transfer process using said current measuring means. Operation control means for performing Ia ≦ when the charge polarity of the photoconductor is negative.
0, or Ia if the charging polarity of the photoreceptor is positive.
An image forming apparatus, wherein the operation of the toner image forming means is controlled so that ≧ 0. 8. An image forming apparatus according to claim 2, wherein the operation control means for controlling the operation of the toner image forming means is a power supply control means for controlling an output value of a transfer bias power supply. Image forming device. 9. An image forming apparatus according to claim 1, wherein said transfer member temporarily carries a toner image, and a toner image is transferred from said transfer member onto a transfer material such as recording paper. And an intermediate transfer belt for transferring the image. 10. The image forming apparatus according to claim 1, wherein the transfer member temporarily supports a transfer material such as a recording paper, and a toner is provided on the transfer material on the transfer member. An image forming apparatus, which is a transfer / conveying belt that transfers an image and conveys a transfer material in a next process. 11. An image forming apparatus according to claim 1, wherein said transfer member is 10 ⁸ Ω to 10 ¹² Ω.
An image forming apparatus having a volume resistance of 1 cm. 12. The image forming apparatus according to claim 1, wherein said conductive member has a roller shape. 13. An image forming apparatus according to claim 1, wherein an image is formed by using two or more colors of developer. 14. An image forming apparatus according to claim 1, wherein a charge having a polarity opposite to that of said toner is supplied to at least a part of a back surface of a transfer body of said transfer nip forming section. Wherein the conductive member is a brush-like member made of conductive fibers containing carbon fine particles in an acrylic resin. 15. The image forming apparatus according to claim 9, wherein
At least a part of the photosensitive member surface in the rotational direction is provided with a non-exposed charging portion, and after the charging portion has passed through the development process, passes through the transfer nip portion without allowing the transfer material to pass therethrough. An image forming apparatus, wherein the potential of a conductive member provided so as to be in contact with the rear surface of the transfer member further upstream and not electrically grounded is set to Va. 16. An image forming apparatus according to claim 9, wherein
At least a part of the photosensitive member surface in the rotational direction is provided with a non-exposed charging portion, and after the charging portion has passed through the development process, passes through the transfer nip portion without allowing the transfer material to pass therethrough. An image forming apparatus characterized in that a current flowing through a conductive member which is in contact with a rear surface of a transfer body further upstream and is electrically grounded is Ia. 17. An image forming apparatus according to claim 10, wherein at least a part of the surface of the photoreceptor in the rotation direction is provided with a non-exposed charging portion, and after the charging portion has passed through a developing process, a transfer material is passed. When passing through the transfer nip with
An image forming apparatus, wherein the potential of a conductive member provided in contact with the rear surface of the transfer member upstream of the transfer nip portion and not electrically grounded is set to Va. 18. An image forming apparatus according to claim 10, wherein at least a part of the surface of the photoreceptor in the rotation direction is provided with a non-exposed charging portion, and after the charging portion has passed through a development process, a transfer material is passed. When passing through the transfer nip with
An image forming apparatus characterized in that a current flowing through a conductive member that is in contact with the back surface of a transfer member upstream of the transfer nip portion and is electrically grounded is Ia.