JPH04345186A - Image forming device - Google Patents

Abstract

PURPOSE:To provide an image forming device which can obtain an excellent quality image without having linear irregularities in the density of an image, the missing of a discharging patter, linear color shade, color slurring, scattering, skipping in the transfer of an image leading edge, etc., by preventing the irregularities in the abutting of a transfer electric field forming means on a transfer material carrying member rear surface, a pretransfer, etc., does not have the occurrence of ozone at the time of transferring, as well, can reduce the capacity of the power source of the transfer electric field forming means and miniaturize it and a transfer device, as well. CONSTITUTION:The transfer electric field forming means 23 is composed of a conductive brush 20 being in contact with the rear surface of a dielectric sheet 93 at the time of transferring, and formed with fine fiber having elasticity and conductivity to which a transfer electric field forming voltage is applied a dielectric elastic sheet 21 supporting the brush 20 and pressing it to the rear surface of the sheet 93, and an electric field regulating member 22 interrupting a transfer electric field on the upstream side of the image transfer part provided on the side of the sheet 93 of the brush 20. Thus, the image forming device having the aimed performance can be obtained.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to an image forming apparatus, and particularly to an image forming apparatus for forming a toner image on an image carrier using an electrophotographic method or an electrostatic recording method.
The present invention relates to an image forming apparatus that obtains an image on a transfer material by applying a transfer electric field to the transfer material carried on a transfer material carrying member. Such image forming apparatuses include black-and-white, monochrome, or full-color electrophotographic copying machines, printers, and various other recording devices.

0002

2. Description of the Related Art Conventionally, various types of multicolor (full color) image forming apparatuses have been proposed. FIG. 5 shows a typical multicolor electrophotographic copying apparatus equipped with a developing device called a so-called rotary developing device.

As shown in FIG. 5, a multicolor electrophotographic copying apparatus has a photosensitive drum 3, which is an image bearing member that is rotatably supported and rotates in the direction of the arrow, approximately in the center, and an image forming apparatus is formed around the photosensitive drum 3. Means are placed. The image forming means may be any means, but in this example, it includes a primary charger 4 that uniformly charges the photosensitive drum 3, and a color-separated light image or a light image equivalent thereto that is irradiated onto the photosensitive drum 3. an exposure means 8 comprising, for example, a laser beam exposure device, for forming an electrostatic latent image on the
The photosensitive drum 3 includes a rotary developing device 1 that develops and visualizes an electrostatic latent image formed on a photosensitive drum 3.

The rotary developing device 1 includes a substantially cylindrical housing 1a that is rotatably supported, and a yellow developer, a magenta developer, a cyan developer, and a black developer held in the housing 1a. It consists of four developing units 1M, 1C, 1Y, and 1B each housing four different colors of developer. The rotary developing device 1 transports a desired developing device to a developing position facing the outer circumferential surface of the photosensitive drum 3 by rotating the housing 1a.
By sequentially developing the electrostatic latent image on the photosensitive drum 3 with developers of corresponding colors, full-color development of four colors is possible.

The image obtained by developing the latent image on the photosensitive drum 3, that is, the toner image, is carried by the transfer drum 9 of the transfer device 9A and conveyed to an image transfer section facing the photosensitive drum 3. It is designed to be transferred onto a transfer material P.

As shown in FIG. 6, the transfer drum 9 has a frame body in which cylinders 9a and 9b arranged at both ends are connected by a connecting member 9c, and a transfer material carrying sheet 93 is provided as a transfer material carrying member in an empty space on the outer peripheral surface of the frame body. It is stretched. As the transfer material carrying sheet 93, a dielectric sheet in the form of a film such as polyethylene terephthalate or polyvinylidene fluoride resin film is usually used. The connecting member 9c has a transfer material gripper 7 that grips the transfer material P fed from the paper feeding device.

Furthermore, on the inside and outside of the transfer drum 9, as shown in FIG.
is located.

A brief explanation of the process of forming a full-color image using the multicolor electrophotographic copying apparatus having the above configuration is as follows.

The primary charger 4 uniformly charges the photosensitive drum 3, and the exposure means 8 irradiates the photosensitive drum 3 with a light image E according to image information, thereby forming an electrostatic latent image on the photosensitive drum 3. be done. This electrostatic latent image is developed by a rotary developing device 1, and a toner image is obtained on the photosensitive drum 3 using resin-based toner having an average particle size of 12 μm, for example.

On the other hand, the transfer material P is conveyed to the transfer drum 9 by the registration roller 6 in synchronization with the image on the photosensitive drum 3, and its tip is gripped by a gripper 7 or the like, and the transfer material P is moved toward the transfer drum 9 in the direction of the arrow in the figure. The photosensitive drum 3 rotates with the rotation of the photosensitive drum 3 and is conveyed to an image transfer section facing the photosensitive drum 3 . There, the toner image on the photosensitive drum 3 is transferred onto the transfer material P by receiving a corona discharge of opposite polarity to the toner from the back side of the dielectric sheet 93 by the transfer charger 10.

As described above, the image transfer section transfers a first color, for example, a yellow toner image, a second color, a magenta toner image, a third color, a cyan toner image, and a fourth color, a black toner image. When all the transfer steps are completed, the transfer material P is separated from the transfer drum 9 by the action of the separation claw 15 while being neutralized by the chargers 11, 13, and 14, and is transported to the fixing device 17 by the transport belt 16. There, the four-color toner images on the transfer material P undergo heat fixation and color mixing to form a full-color permanent image, and then are discharged to the outside of the copying apparatus.

On the other hand, after the residual toner on the surface of the photosensitive drum 3 is cleaned by a cleaning device 12, the photosensitive drum 3 is subjected to the image forming process again. Further, the surface of the dielectric sheet 93 of the transfer drum 9 is similarly cleaned by the cleaning device 5 consisting of a fur brush or the like and the cleaning auxiliary means 5a, and then subjected to the image forming process again.

[0013]

By the way, in the above image forming apparatus, since the toner image on the photosensitive drum 3 is transferred onto the transfer material P by charging using the transfer charger 10, the following problem occurs. There was a drawback.

That is, in order to perform the transfer, it is necessary to apply a high voltage of usually 6 to 8 kV to the discharge wire of the transfer charger 10, and furthermore, only a part of the generated corona current flows toward the photosensitive drum 3. First, since the remainder of the corona current flows to the shield of the transfer charger 10 which is grounded, a corona current greater than the corona current that actually contributes to transfer is required.

Therefore, the transfer charger 10 requires a power source with a large voltage and current capacity, and the wiring also needs to have higher insulation voltage resistance, resulting in an increase in the size and cost of the transfer device 9A.

Furthermore, since the transfer charger 10 is used, ozone is generated as corona discharge occurs, which adversely affects not only the photosensitive drum 3 but also the human body.

Therefore, the present applicant has proposed a method for solving the above problem in Japanese Patent Application Nos. 2-29896 and 2-29898. In the above proposal, a contact conductive member consisting of a conductive metal sheet or blade provided at the tip of an elastic synthetic resin sheet or a conductive roller is brought into contact with the back surface of a dielectric sheet and a voltage is applied, thereby corona can be used as a means for forming a transfer electric field. It discloses generating a transfer electric field without using a charger. According to this, the contact injection current injected from the contact conductive member almost becomes a toner transfer current and a transfer material adsorption current during the transfer, and in order to efficiently contribute to the transfer, the corona charger transfers the toner. Unlike when using a charger, low voltage, low current, and high efficiency transfer is achieved without ozone generation.

However, since the contact conductive member used in the above proposal is in the shape of an elastic sheet, blade, or roller, the contact state with the dielectric sheet is a straight line contact or surface contact, and at first glance, the contact conductive member is in the form of an elastic sheet, blade, or roller. Although the contact of the member with the dielectric sheet is macroscopically uniform, microscopically the contact is quite uneven locally in the longitudinal direction of the photosensitive drum.

For this reason, if the voltage applied to the contact conductive member is low, the transfer injection current will be insufficient where the contact state is weak, resulting in a difference in transfer efficiency, and the toner image transferred onto the transfer material will not be affected by the movement of the transfer material. Line-like unevenness of light and shade with different toner densities occurs in parallel to the direction. In addition, when the applied voltage is high, especially in a low humidity environment, gap discharge may occur where the contact state is weak and there are microscopic gaps between the dielectric sheet and the contact conductive member, resulting in damage to the transfer material. Similarly, streak-like unevenness of light and shade occurs in the resulting toner image, and other problems such as discharge patterns and transfer omissions also occur. Therefore, the range of appropriate voltage to be applied to the contact conductive member is narrow.

[0020] Furthermore, even if the applied voltage is within the appropriate range, the above-mentioned difference in the contact state results in a difference in transfer efficiency, and in an image forming apparatus that obtains a monochrome image, it occurs as slight unevenness in density, which is not considered to be an acceptable level. However, in the case of an image forming device that obtains a multicolor image by overlapping toner images of multiple colors onto a transfer material, even slight density unevenness becomes noticeable as streak-like unevenness in color. It becomes a big problem because it appears in

[0021] In order to eliminate the above-mentioned difference in the contact state, the contact pressure of the contact conductive member to the dielectric sheet can be increased, but if the contact pressure is high, the kinetic frictional force with the dielectric sheet will increase. As the load on the dielectric sheet increases, the dielectric sheet becomes displaced or distorted, and the transfer material held thereon becomes displaced or distorted. Similarly to the above, this is not a big problem for image forming devices that produce monochrome images, but for image forming devices that produce multicolor images, color shifts and color unevenness may occur in the image. It becomes a problem. Furthermore, since the toner image is strongly pressed against the photosensitive drum during transfer, the transfer efficiency of the toner image onto the transfer material is reduced, and the life of both the dielectric sheet and the contact conductive member is shortened. It becomes necessary to frequently replace the image forming apparatus, which causes a problem that the cost of the transfer device and eventually the image forming apparatus increases.

Furthermore, members thicker than the dielectric sheet, such as the connecting member 9c that connects the cylinders 9a and 9b at both ends of the transfer drum 9 shown in FIG. When passing through the contact portion, if the contact pressure is high, the impact at the leading and trailing ends of the connecting member 9c, gripper 7, etc. will be large, causing the toner to scatter from the toner image on the transfer material, or toner image This also causes problems such as color misalignment. Since the contact conductive member is in the shape of an elastic sheet, blade, or roller, the responsiveness of the rear end portion of the connecting member 9c, gripper 7, etc. to the dielectric sheet immediately after passing is poor, especially Since it is difficult to make good contact with the boundary between the rear end of the connecting member 9c and the dielectric sheet, the transfer efficiency at the leading edge of the transfer material and therefore the leading edge of the image formed on the transfer material is reduced. There was also the problem that the condition deteriorated significantly and so-called image leading edge transfer failure occurred.

The purpose of the present invention is to eliminate unevenness in contact of the transfer electric field forming means with the back surface of the transfer material supporting member, unevenness in image density due to pre-transfer, etc., omission of discharge patterns, unevenness in color, and color shift. An image forming apparatus that can obtain images of good quality without image disturbances such as scattering, image leading edge transfer failure, etc., does not generate ozone during transfer, and can be made smaller and has a smaller capacity power source for applying transfer voltage. The goal is to provide the following.

[0024]

Means for Solving the Problems The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides an image transfer section that faces an image carrier of a transfer material carrying member, and transfers a toner image formed on the image carrier to a side of the transfer material carrying member opposite to the image carrier. An image forming apparatus that transfers an image onto a transfer material carried on the transfer material carrying member by applying a transfer electric field with a transfer electric field forming means disposed on the back side of the image forming apparatus. In this case, the transfer electric field forming means is disposed on the back side of the carrying member, contacts the back side of the carrying member at least when transferring the toner image onto the transfer material, and is applied with a transfer electric field forming voltage. a conductive brush made of fine fibers having elasticity and conductivity; an elastic sheet made of a dielectric material that supports the conductive brush and presses it against the back surface of the support member; and the support for the conductive brush. The image forming apparatus is characterized by comprising an electric field regulating member provided on a member side that blocks a transfer electric field generated from the conductive brush in an upstream region of the image transfer section. Typically, the carrier member is dielectric.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a sectional view of an image transfer section in an embodiment of an image forming apparatus of the present invention. This embodiment is applied to a multicolor electrophotographic copying apparatus having the rotary developing device 1 shown in FIG. 5, and the basic configuration of the image forming apparatus of this embodiment is the same as that of the image forming apparatus shown in FIG. It is. Therefore, explanations regarding the structure and operation of the image forming apparatus will be omitted except for those relating to the transfer electric field forming means. FIG. 1 is a drawing that best represents the features of the present invention, and specifically shows the transfer electric field forming means constructed according to the present invention in detail.

The image forming apparatus includes a transfer device 9A having the transfer drum 9 shown in FIG.
As explained earlier, the cylinders 9a arranged at both ends,
A dielectric sheet 93 is stretched as a transfer material carrying member in an open space on the outer peripheral surface of the frame body in which the frame members 9b are connected by a connecting member 9c. The dielectric sheet 93 can be a sheet using various dielectrics, or even a composite sheet, but in this embodiment, it has a volume resistivity of about 1015 Ωcm, a dielectric constant of about 8, and a thickness of about 150 μm. A sheet of polyvinylidene fluoride resin (PVdF) was used. The front and rear ends of the dielectric sheet 93 are fixed on the connecting member 9c. Connecting member 9
A gripper 7 is provided on c.

In this embodiment, the diameter of the transfer drum 9 is 16 mm.
0 mm, and the moving speed was set to 160 mm/sec. At the same time, the process speed, which is the moving speed of the photosensitive drum 3, etc., was also set to 160 mm/sec.

According to the present invention, as shown in FIG. 1, a conductive brush 20 and a dielectric elastic sheet 21 are provided inside the transfer drum 9 in the image transfer section where the transfer drum 9 and the photosensitive drum 3 face each other. A transfer electric field forming means 23 consisting of an electric field regulating means 22 is provided on a support member 19 made of a rigid body such as metal, and in this embodiment made of SUS.

The dielectric elastic sheet 21 is provided on the support member 19, the conductive brush 20 is provided on the elastic sheet 21 with the side opposite to the dielectric sheet 93 supported, and the electric field regulating means 22 is provided on the spacer 24. It is provided on the support member 19 via. The tip of the conductive brush 20 is inserted into the dielectric sheet 93 from between the elastic sheet 21 and the electric field regulating means 22.
It extends in the direction of. The transfer electric field forming means 23 is arranged to be inclined from the upstream side in the rotational direction of the transfer drum 9 toward the abutment area between the dielectric sheet 93 and the photosensitive drum 3, and rotates the support member 19 to generate a conductive brush. The tip end of the dielectric sheet 93 is configured to come into contact with the back surface of the dielectric sheet 93.

The conductive brush 20 is made of fine fibers having elasticity and conductivity, and comes into contact with the back surface of the dielectric sheet 93 at least during transfer, and generates a transfer electric field in the image transfer portion by an applied voltage from a power source (not shown). It is supposed to be done. The dielectric elastic sheet 21 is located upstream of the point where the conductive brush 20 comes into contact with the dielectric sheet 93, so as to block the transfer electric field generated from the conductive brush 20 in the upstream region of the image transfer section. It has become.

In this embodiment, the conductive brush 20 is made of conductive fibers obtained by dyeing acrylic fine fibers with copper sulfide to make them conductive. In addition, conductive fibers with a diameter of 8 to 15
μm stainless steel fiber or acrylic,
Fibers made of metal-plated resin fibers such as nylon, polyester, and rayon, fibers made by kneading conductive particles such as carbon and metal powder into resin, or composite fibers, and carbonized resin fibers. Carbon fiber or the like imparted with conductivity can be used. The volume resistivity of conductive fiber is 101
0Ωcm or less can be used, but preferably 1
08 Ωcm or less is preferable.

Further, polyethylene terephthalate (PET) sheets with thicknesses of 125 μm and 50 μm were used for the dielectric elastic sheet 21 and the electric field regulating means 22, respectively.
The material and thickness are not limited to these.

With the above configuration, the transfer electric field forming means 23 is such that the dielectric sheet 21 presses the conductive brush 20 in the direction of the dielectric sheet 93 during transfer, thereby causing the conductive brush 20, the dielectric sheet 93, and the dielectric sheet 93 and the transfer material P carried thereon and located in the transfer section, and the transfer material P and the photosensitive drum 3 are brought into close contact with each other so that no gap is created between them.

The electric field regulating member 22 blocks the transfer electric field generated by the conductive brush 20 in the upstream region of the transfer section by applying a voltage, and the area covered by the transfer electric field is shown in FIG. It is limited to the range of dE excluding the upstream region of the transcription area.

According to the conductive brush 20 used in the present invention, the state of contact with the dielectric sheet 93 is different from the linear contact made by the conventional contact conductive member in the shape of an elastic sheet, blade, or roller. Since each of the conductive fine fibers is in independent contact, the inclination of the contact pressure in the longitudinal direction of the contact area (direction perpendicular to the circumferential direction of the dielectric sheet 93) and the dielectric sheet 93 are It follows regardless of differences in surface roughness, differences in level of the connecting member 9c of the transfer drum 9, etc., and the state of contact of each fiber with the dielectric sheet 93 can be maintained uniformly and softly.

Furthermore, by adjusting the fiber diameter, fiber material, and fiber density, it is possible to easily achieve a more uniform and soft contact state without increasing the contact pressure.

The conductive brush 20 is arranged so that it extends from the introduction side of the dielectric sheet 93 toward the downstream side in the direction of movement thereof.
The dielectric sheet 93 corresponds to the position where the transfer material P supported on the dielectric sheet 93 has finished contacting the photosensitive drum 3, or the position where the contact has started, or a position as close as possible.
Place it so that it touches the position of. More precisely, the transfer electric field area is set within the so-called transfer nip area dN, which is the area where the transfer material P is in contact with the photosensitive drum 3. In particular, if the transfer electric field acts before the photosensitive drum 3 and the transfer material P come into contact, image disturbances such as toner scattering will occur due to so-called pre-transfer (pre-transfer), but with the transfer electric field forming means 23 of this configuration, Since the electric field regulating member 22 is provided to regulate the transfer electric field area and prevent the transfer electric field from acting before the photosensitive drum 3 and the transfer material P come into contact, it is possible to prevent image disturbance from occurring. .

Furthermore, as shown in FIG. 2, since the conductive brush 20 is in diagonal contact with the dielectric sheet 93,
There is no fear that the fine fibers of the brush 20 will fall, and the state of contact with the dielectric sheet 93 is good.

The present inventors incorporated the transfer device 9A having the above structure into the image forming apparatus shown in FIG. 5, and used it to transfer a toner image to form an image. A latent image was formed on a negatively charged photosensitive drum 3, and developed using a toner having an average particle size of 8 to 10 μm using a reversal development method in a rotary developing device 1 to obtain a toner image. Toner is composed of resin, coloring material, and small amounts of additives to improve charge control and lubricity, and is charged to a negative polarity by friction with carrier particles in a developing device. Ta.

The obtained toner image was then transferred onto the transfer material P by the above transfer device 9A. Next, in the case of a monochrome image, the transfer material P was separated from the dielectric sheet 93, and the toner image was fixed by the fixing device 17. In the case of a multicolor image, the same steps as above are repeated to transfer multiple color toner images in a superimposed manner onto the transfer material P,
The transfer material P was separated from the dielectric sheet 93, and the toner image was fixed.

As a result, in any case, the image obtained on the transfer material is free from uneven contact of the transfer electric field forming means with the back surface of the dielectric sheet 93 and pre-transfer, etc., as in the prior art. Images of good quality were obtained without any image disturbances such as streak-like unevenness in image shading, missing discharge patterns, streak-like unevenness in color, color shift, scattering, and missing transfer at the leading edge of the image.

Similar image forming experiments were conducted under a low humidity environment, which is a strict condition for preventing the discharge phenomenon, and similarly good images were obtained. The voltage applied to the conductive brush 20 (transfer bias voltage) is +0.7 to +3.0.
The kV and current value may be about several μ to 30 μA, and compared to transfer using a corona charger, no ozone is generated, leading to a significant reduction in power supply capacity and cost.

FIG. 3 is a schematic diagram showing another embodiment of the image forming apparatus of the present invention.

In this embodiment, the transfer material carrying member is an endless transfer belt 29, and the transfer belt 29 is wound around a plurality of rollers 25, 26, and 27 so as to run in synchronization with the photosensitive drum 3. It has become. The transfer belt 29 is in contact with or close to the photosensitive drum 3 to form an image transfer section therewith, and a transfer electric field forming means according to the present invention is provided inside (on the back side) of the transfer belt 29 of this image transfer section. 23 are provided. As in the previous embodiment, the transfer electric field forming means 23 includes a conductive brush 20, a dielectric elastic sheet 21 supporting the conductive brush 20, and a transfer belt 2 for the conductive brush 20.
The electric field regulating member 22 is provided on the supporting member 19.

The image forming operation of this image forming apparatus is basically the same except that the transfer belt 29 is used instead of the transfer drum 9 covered with a dielectric sheet 93, and the primary charger 4 charges the photosensitive drum. The surface of the photosensitive drum 3 is uniformly charged, and the exposure means irradiates the photosensitive drum 3 with a light image E according to the image information.
An electrostatic latent image is formed thereon, and the electrostatic latent image is developed by the developing device 1 to form a toner image on the photosensitive drum 3 . When the toner image reaches the image transfer portion between the transfer belt 29 and the photosensitive drum 3 as the photosensitive drum 3 rotates, a transfer electric field is applied to the image transfer portion by the transfer electric field forming means 23.
Transfer material P on which the upper toner image is carried on transfer belt 29
electrostatically transferred onto the surface.

After the toner image is transferred, the transfer material P leaves the image transfer section by being conveyed by the transfer belt 29 and reaches the rear end of the transfer belt 29 in the conveying direction, where it is separated from the transfer belt 29 and transferred to the fixing device 17. After the toner image is sent and fixed by the fixing device 17, it is discharged outside the image forming apparatus.

When the above-mentioned transfer material P is separated from the transfer belt 29, the toner may be scattered due to peeling discharge and polka dot-like scattering may be formed on the image, so in order to prevent this, transfer A static eliminator 14 is disposed near the transfer material separation portion of the belt 29 to separate the transfer material P and the transfer belt 2.
9 is discharged. The toner remaining after transfer on the photosensitive drum 3 is removed by the cleaner 12, and the photosensitive drum 3 enters the next image forming process.

In this embodiment, as in the previous embodiment, the transfer electric field forming means 23 is used to generate a conductive field that is pressed against the back surface of the dielectric sheet 93 in the image transfer section with the dielectric elastic sheet 21 during transfer. A voltage is applied from the power source to the transfer brush 20 to generate and apply a transfer electric field to the transfer section, and the toner image on the photosensitive drum 3 is blocked by the electric field regulation member 22 while blocking the transfer electric field in the upstream region of the transfer section. Since the image is transferred onto the transfer material P on the transfer belt 29, uneven contact with the back surface of the transfer belt 29 and streak-like unevenness in image density due to pre-transfer, missing discharge patterns, and color streaks are also avoided. Images of good quality are obtained without image disturbances such as unevenness, color shift, scattering, and transfer failure at the leading edge of the image, and no ozone is generated.

FIG. 4 is a block diagram showing the main parts of still another embodiment of the image forming apparatus of the present invention. This embodiment is applied to a multicolor image forming apparatus having four image forming units I, II, III, and IV.
It can also be used in such an image forming apparatus.

Image forming units I to IV each have photosensitive drums 3a to 3d, and around them are a primary charger, an exposing means, a developing device, and a transfer electric field forming means 23a to 23d.
, and a cleaner are arranged, and each image forming unit I
~IV photosensitive drums 3a to 3d in a manner penetrating
An endless transfer belt 29 which is a transfer material carrying member is placed below the
are arranged around rollers 25, 26, 27 and 28. Since the configuration of each image forming unit is the same as that of the image forming unit shown in FIG. 3, only the photosensitive drums 3a to 3d and the transfer electric field forming means 23a to 23d are shown in FIG. 4, and the primary charger and the like are omitted.

Similarly, the transfer electric field forming means 23a to 23d are provided on the conductive brushes 20a to 20d, the dielectric elastic sheets 21a to 21d supporting the conductive brushes, and the transfer belt 29 side of the conductive brushes 20a to 20d, respectively. The electric field regulating members 22a to 22d are provided on the supporting members 19a to 19d, respectively.

The transfer material P is fed by a paper feed roller, carried by the transfer belt 29, and passed through an image transfer section formed between the transfer belt 29 and the photosensitive drums 3a to 3d, where it is transferred. The toner images on the photosensitive drums 3a to 3d are sequentially transferred onto the transfer material P by applying a transfer electric field by the transfer electric field forming means 23a to 23d. Next, the transfer material P is separated from the transfer belt 29 at the end in the conveying direction, and transferred to the fixing device 17.
The toner image is fixed thereon and then discharged outside the image forming apparatus.

In this embodiment as well, the transfer electric field forming means 23a to
Since the transfer is performed using the transfer belt 29, uneven contact with the back surface of the transfer belt 29, streak-like unevenness in image density due to pre-transfer, missing discharge patterns, streak-like unevenness in color, color shift, scattering, image leading edge transfer. A good quality image without image disturbances such as omissions was obtained, and no ozone was generated.

[0054]

As explained above, in the image forming apparatus of the present invention, the transfer electric field forming means disposed on the back side of the transfer material carrying member opposite to the image carrier is placed on the back side of the carrying member. A conductive brush made of fine fibers having elasticity and conductivity, which is disposed in contact with the back surface of the supporting member during transfer and to which a voltage for forming a transfer electric field is applied, and a supporting member that supports the conductive brush. a dielectric elastic sheet pressed against the back surface of the
Since the structure includes an electric field regulating member that blocks the transfer electric field provided on the supporting member side of the conductive brush in the upstream region of the image transfer section, uneven contact of the transfer electric field forming means to the back surface of the supporting member and pre-transfer can be prevented. By eliminating this, a good quality image can be obtained without image disturbances such as streak-like unevenness in image shading, missing discharge patterns, streak-like unevenness in color, color shift, scattering, and missing transfer at the leading edge of the image. In addition, the transfer electric field forming means does not generate ozone unlike the case where a transfer charger consisting of a corona charger is used, and the voltage and current capacity of the power supply do not need to be increased, and the capacity and size of the power supply can be reduced. This is possible, and has the advantage of leading to downsizing of the transfer device.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an image transfer section in an embodiment of an image forming apparatus of the present invention.

FIG. 2 is an enlarged view of the image transfer section in FIG. 1;

FIG. 3 is a schematic configuration diagram showing another embodiment of the image forming apparatus of the present invention.

FIG. 4 is a configuration diagram showing main parts of still another embodiment of the image forming apparatus of the present invention.

FIG. 5 is a configuration diagram showing a conventional image forming apparatus.

6 is a perspective view showing a transfer drum of a transfer device provided in the image forming apparatus of FIG. 5. FIG.

[Explanation of symbols]

3 Photosensitive drum 9 Transfer drum 19 Support member 20 Conductive brush 21 Dielectric elastic sheet 22 Electric field regulating member 23 Transfer electric field forming means 29 Transfer belt 93 Dielectric sheet

Claims (2)

[Claims] 1. An image transfer section facing the image carrier of the transfer material carrying member transfers the toner image formed on the image carrier to the back surface of the transfer material carrying member opposite to the image carrier. An image forming apparatus that transfers an image onto a transfer material carried on the transfer material carrying member by applying a transfer electric field with a transfer electric field forming means disposed on the side, thereby obtaining an image on the transfer material, The transfer electric field forming means is disposed on the back side of the carrying member, contacts the back side of the carrying member at least when transferring the toner image onto the transfer material, and is applied with a voltage for forming a transfer electric field. a conductive brush made of fine fibers having elasticity and conductivity; an elastic sheet made of dielectric that supports the conductive brush and presses it against the back surface of the support member; and a side of the support member of the conductive brush. 1. An image forming apparatus comprising: an electric field regulating member disposed in an area for blocking a transfer electric field generated from the conductive brush in an upstream region of the image transfer section. 2. The image forming apparatus according to claim 1, wherein the supporting member is made of a dielectric material.