JP2001092275A - Image-forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image-forming device, capable of preventing image fogging caused by the positive electrification of a photoreceptor, the deterioration of electrostatic chargeability caused by the intrusion of a foreign matter into a charge injection electrifier, image deterioration caused by the re transfer of toner to the photoreceptor, and the color mixture of developer in a developing device, without spoiling the high speed output of a color image or the ease of use of the device. SOLUTION: An intermediate transfer belt 5 is installed as a 2nd image carrier, in addition to photoreceptor drums 1y, 1m, 1c and 1k. Four image forming units Uy, Um, Uc and Uk are arranged along the belt 5, and the drums 1y to 1k are provided with a charge injection layer on their surfaces, which are electrified by the charge injection electrifiers 2y to 2k and exposed by exposure devices 3y to 3k so as to form latent images. The latent images are developed and visualized as toner images by developing devices 4y to 4k, and the respective color toner images are superimposed and transferred to the belt 5 by transfer rollers 8y to 8k, then transferred to paper P by a secondary transfer roller 9 and fixed by a fixing device 11.

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 using an electrophotographic system, and more particularly, to a method for forming a color image by mounting a plurality of process units including a photosensitive drum, its charging means and developing means. The present invention relates to an image forming apparatus suitable for the present invention.

[0002]

2. Description of the Related Art In recent years, an image forming apparatus using an electrophotographic system has been reduced in size, enhanced in function, and colorized. Are increasing, and various image forming apparatuses have been proposed to satisfy those demands.

[0003] In particular, with respect to colorization, it is predicted that the frequency of use will increase in the future in the future due to the emergence of various color applications. In addition to the demand for networking, there is a demand for an apparatus capable of outputting a color image at a higher speed.

[0004] For this reason, as a method of increasing the speed of color image output, a plurality of image forming units or image forming cartridges (hereinafter, included in the image forming unit) including photoreceptors, charging means, developing means, and the like are loaded, A method in which a sheet for image formation called a transfer material is conveyed while electrostatically attracted by a belt-shaped conveying means, and toner images are sequentially superimposed and transferred from the units of each color on the sheet, that is, a four-drum method. (Tandem drum type) devices have been proposed.

According to the four-drum system, although the output speed of a color image is increased, a plurality of image forming units are stacked, and three or four developing units are arranged on one photosensitive member. This is disadvantageous in terms of size and cost reduction as compared with conventional color image forming apparatuses in which image formation is performed on a photoconductor one by one for a plurality of colors. In particular, it ’s very difficult to get a desktop printer size,
It is very disadvantageous in terms of paper handling (paper handling).

In order to reduce the size and simplification of the image forming unit for each color, Japanese Patent Application Laid-Open No.
As described in US Pat. No. 96997 or the like, it is effective to employ a charge injection method for charging the photosensitive member. This technology is characterized by the fact that charging does not involve a discharge phenomenon,
The voltage required for charging is also only the desired potential of the photoconductor surface, and no ozone is generated. Further, since no AC voltage is applied, no charging noise is generated, and the charging method is excellent in ozone-less and constant power as compared with the conventional roller charging method.

An additional effect is that the cleaning step of the photoconductor can be omitted. Since the cleaning means of the image forming unit for each color can be omitted, the image forming unit can be configured to be very compact, and the size of the image forming apparatus main body can be greatly reduced. Therefore, simplification of the apparatus and low cost can be achieved.

Further, in the charge injection charging system, since the transfer residual toner on the photoreceptor is collected by the developing device, the toner can be reused, and a product which is very environmentally friendly can be obtained.

FIG. 7 shows an example of such an image forming apparatus. Hereinafter, the operation will be described. Image forming units Uy, Um, Uc, Uk arranged along transfer belt 5
Have basically the same configuration.

In FIG. 7, image forming units Uy, U
m, Uc, and Uk, cylindrical photosensitive members as image carriers, that is, photosensitive drums 1y, 1m, 1c, and 1k are rotated in the direction of arrow a, and during the rotation process, charge injection chargers 2y and 2m. , 2c and 2k, the surface is uniformly charged, and then the images are exposed from the image exposure units 3y, 3m, 3c and 3k, and an electrostatic latent image is formed on the surface of the photosensitive drum 1 (1y to 1k). The electrostatic latent images formed on the respective photosensitive drums 1 are developed by the developing units 4y, 4m, 4c, and 4k, and are visualized as yellow, magenta, cyan, and black toner images, respectively.

The developing device 4 (4y to 4k) is a two-component non-contact developing device in this embodiment, and has a particle size of about 50, for example.
A two-component developer in which a magnetic carrier of μm and a non-magnetic toner of about 8 μm are mixed is accommodated. The developing sleeve 4
a from the developer carried on the developing sleeve 4a
The toner is caused to fly on the photosensitive drum 1 by applying a bias to the photosensitive drum 1 and is attached to the latent image and developed.

The paper P is supplied to the transfer belt 20 from a paper supply unit (not shown), and is electrostatically attracted to the rotating transfer belt 20 by a suction roller 19. The transfer belt 20
Driving roller 21 and a plurality of supporting rollers (driven rollers)
The sheet P is transported to the photosensitive drum 1y in synchronization with the rotation of the photosensitive drum 1y of the first unit Uy. The toner image on the photosensitive drum 1y is transferred to the conveyed sheet P by the action of the transfer bias applied to the transfer roller 23y.

After the transfer, the surface of the photosensitive drum 1y is uniformly discharged by a pre-exposure lamp (not shown) to initialize the surface of the photosensitive drum 1y, and then subjected to the next image formation. Also, the photosensitive drum 1
The transfer residual toner remaining on y is collected during the next developing operation by the developing device 4y and is used again for development.

The above operation is performed by the second to fourth units Um to U
For k, the toner images formed on the photosensitive drums 1m to 1k are sequentially transferred onto the paper P conveyed by the transfer belt 20 by the transfer rollers 23m, 23c, and 23k in a superimposed manner (multiple transfer). In the case of the full-color mode, the above-described four color toner images of yellow, magenta, cyan, and black are transferred in a multiplex manner,
In the case of the color mode, the required toner image is transferred onto the paper P singly or multiple transfer.

The paper P on which the toner image has been transferred is separated from the transfer belt 20, and then passed through a fixing device 11, where the toner image is fixed on the paper P by the action of heat and pressure. The surface of the transfer belt 20 from which the paper P has been separated is cleaned by a belt cleaner 32 and used for the next image formation.

[0016]

However, the above-described conventional image forming apparatus has the following three problems.

(1) First, in the step of transferring the toner image onto the paper P, a portion where the surface of the photosensitive drum 1 is positively charged occurs, and this portion is charged to a desired charging potential by the charge injection charger 2. Since it cannot be charged, fog occurs in the output image. Particularly, in a low humidity environment, if an image is formed by passing a sheet of a size smaller than A4 and then an image is formed by passing a sheet of A4 size or more, fogging is likely to occur on the image of the sheet of A4 size or more. . This is because the resistance value of the paper increases due to the decrease in the water content of the paper under a low humidity environment.

A specific situation will be described with reference to FIG. FIG.
FIG. 4 is a diagram illustrating potentials at various portions in a transfer section in an image forming apparatus using reversal development. In the figure, the potential (non-image portion potential) of the unexposed portion of the photosensitive drum is charged to -700V. The potential of the exposed portion (image portion potential) is about −50 V, but in actuality, −70 V to −70 V due to adhesion of the developing toner.
It is about 100V. A transfer material P and a transfer belt 20 supporting the transfer material P are sandwiched between the photosensitive drum 1 and the transfer roller 23. The transfer bias supplied from the transfer roller 23 is +300 V for the transfer roller 23y of the first unit.

Here, considering the case where small-size paper is passed, three current inflow paths from the transfer roller 23 to the photosensitive drum 1 are assumed to be an image portion, a non-image portion, and a non-sheet passing portion. . The currents IL and I flowing through these three paths
D and IP are different from each other because the potential difference and the resistance value between the surface of the photosensitive drum and the transfer roller are different. Transfer roller 23
Is the largest current flowing through the non-sheet passing portion, while the smallest current amount is the current IL flowing through the image portion.

Particularly, in a low humidity environment where the resistance value of the sheet P is high, the difference ΔI =
When ID-IL becomes very large and an attempt is made to transfer the toner in the image area with a bias that can transfer the toner satisfactorily, a very large current flows into the non-sheet passing area and the surface of the photosensitive drum is charged to a positive potential. Let me do it.

In full-color image formation, particularly when the transfer bias of each color is set to be gradually increased from the first color to the fourth color, the photosensitive drum is strongly charged to a positive polarity during the transfer of the third and fourth colors. At the time of outputting the next image, fogging of the image remarkably occurs.

(2) The second problem is that the image forming unit is made cleanerless. In the above four-drum color image forming apparatus, since the toner image is directly transferred from the photosensitive drum 1 of each of the image forming units Uy to Uk to the sheet P,
Paper dust or the like adheres to the photosensitive drum 1 from the paper. conventionally,
Although this was removed by a cleaner, it cannot be removed by a cleaner-less system. Therefore, when used for a long time, foreign matter such as paper dust enters the charge injection charger 2 and accumulates therein. Degrades the charging capability of the device.
When the charging ability is deteriorated, the surface of the photosensitive drum cannot be charged to a desired potential, and an image defect gradually occurs in the uncharged portion.

(3) Finally, there is a problem of retransfer. When a full-color image is output, 1
The color toner image is electrostatically attracted to the paper,
When the paper P passes through the gap between the second and subsequent photosensitive drums 1c to 1k and the transfer belt 20, a part of the first color toner is transferred to these photosensitive drums, that is, re-transferred.
In the image forming apparatus of this embodiment, since the simultaneous development cleaning method is employed, the re-transferred toner is developed by the developing device 4 at the time of development.
m to 4k, and color mixture occurs in the developer in the developing device. The color mixture of the developer becomes a fatal defect in color image formation. In addition, problems such as image unevenness, reduced density, and deviation of color balance (color) are caused.

In order to solve such a problem, Japanese Patent Laid-Open No. 2-2086 discloses a method of selectively controlling the urging and release of the transfer belt to the photosensitive drum for each image forming unit.
No. 69 and the like. In the single-color mode, for example, in the magenta single-color mode, control is performed so that only the photosensitive drum of the magenta unit and the transfer belt are in contact with each other. As a result, color mixing of the developer in the developing device due to retransfer and image rubbing do not occur.

However, a press release mechanism for the photosensitive drum is required for each image forming unit. There is also a drawback that various mechanical vibrations are generated during the operation of these release mechanisms and disturb the toner image.

An object of the present invention is to provide an image fogging due to the positive charging of the photoreceptor, a deterioration of the charging ability due to the inclusion of foreign matter into the charge injection charger, without impairing the high speed of the color image output and the simplicity of the apparatus. An object of the present invention is to provide an image forming apparatus capable of preventing image deterioration due to retransfer of toner to a photoreceptor and color mixing of a developer in a developing device.

[0027]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
An image carrier having a charge injection layer on its surface; a charging unit to which a charge bias is applied in contact with the surface of the image carrier and charged by a charge injection method; and an image on the surface of the charged image carrier. Developing means for developing the electrostatic latent image formed by the exposure using a developer and visualizing the electrostatic latent image as a toner image, forming a toner image on the image carrier, and forming the toner image on the image carrier. An image forming apparatus that transfers an image to a transfer material, and wherein the developing unit also serves as a cleaning unit that removes toner remaining on the surface of the image carrier after the transfer, an intermediate transfer that rotates along the image forming unit; Setting a toner image on the intermediate transfer member before transferring the toner image formed on the image bearing member to the transfer material, and then transferring the toner image from the intermediate transfer member to the transfer material. Image featuring It is formed apparatus.

According to the present invention, the intermediate transfer member is an endless belt, and the endless belt is a belt having a single-layer structure in which conductive particles are dispersed and resistance is adjusted, or an elastic layer and a resistance control layer thereon. And a belt having a multilayer structure having at least The intermediate transfer member may be a rotating drum. Further, the charging means includes a conductive rotating sleeve to which a charging voltage is applied, a magnet arranged in a non-rotating manner in the sleeve, and a magnetic brush held on the surface of the sleeve by the magnetic force of the magnet. And magnetic particles that are formed and contact the surface of the image carrier. The charging unit may be a conductive elastic roller to which a charging voltage is applied, which is in contact with the surface of the image carrier.
Preferably, the developer is a one-component developer that does not use a magnetic carrier in addition to the toner, and the toner is manufactured by a polymerization method. Further, the image forming apparatus can include a plurality of the image forming units.

[0029]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a first embodiment of the present invention.

Embodiment 1 FIG. 1 is a sectional view showing an embodiment of the image forming apparatus of the present invention. Hereinafter, the details will be sequentially described according to the image forming process.

The image forming apparatus includes an intermediate transfer belt 5 as a second image carrier in addition to a photosensitive drum as an image carrier, and four image forming units Uy, Um, Uc and Uk are arranged. These units Uy to Uk are basically configured the same.

Each image forming unit Uy, Um, Uc, U
The photosensitive drums (cylindrical photosensitive members) 1y, 1m, 1c, and 1k serving as the first image carriers of k are 100 m in the direction of arrow a.
The surface is uniformly charged by the charge injection chargers 2y, 2m, 2c and 2k during the rotation at a peripheral speed of m / sec. FIG. 2 shows details of the photosensitive drum 1 (1y to 1k) and the charge injection charger 2 (2y to 2k).

In this embodiment, the photosensitive drum 1 is
As shown in FIG. 1, a cylindrical drum base 1 made of aluminum is used.
A charge injection layer 1b, charge transport layer 1c, and charge injection layer 1d are formed on a. The charge injection layer 1d is formed of a material in which ultrafine particles of SnO ₂ are dispersed in a photocurable acrylic resin, and charges the photosensitive drum 1 by injecting charges into this layer 1d.

The charge injection charger 2 includes a rotatable non-magnetic conductive sleeve (electrode sleeve) 2a and a non-rotatable roller-like magnet 2b, and coats the peripheral surface of the sleeve 2a with magnetic particles 2c. It is doing. The coated magnetic particles 2c rise from the surface of the sleeve 2a by the magnetic force of the magnet 2b to form a magnetic brush, and the magnetic brush contacts the surface of the photosensitive drum 1 to form the magnetic brush.
A charge is applied to the charge injection layer 1d of the photosensitive drum 1 by the charging bias applied to a.

As the magnetic particles 2d, sintered magnetite, ferrite or the like is used. At the time of charging, the electrode sleeve 2a is rotated with respect to the photosensitive drum 1 in the counter direction indicated by the arrow b, and a DC voltage of -700 V is applied from the bias power supply 30 to the sleeve 2a as a charging bias. Thereby, the surface of the photosensitive drum 1 can be uniformly charged to a potential of -700 V without a discharge phenomenon.

As shown in FIG. 1, each photosensitive drum 1y, 1
Image exposure units 3y, 3m, 3 above m, 1c, 1k
c, 3k are arranged, and the exposure unit 3 (3y to 3k)
Forms an electrostatic latent image on the surface of the photosensitive drum 1 by exposing the charged photosensitive drum 1 according to image information. Exposure by the exposure device 3 is performed by a laser beam scanner, an LED, or the like. The electrostatic latent images formed on the respective photosensitive drums 1 are stored in respective developing units 4y, 4m, 4c,
In the present embodiment, the developing device 4 is a one-component non-magnetic contact developing device, and includes a developing roller 4a, a toner supply roller 4b, and a regulating blade. 4c, and contains a non-magnetic toner of a non-magnetic one-component developer. The developing device 4 includes a toner supply roller 4b.
Supplies the non-magnetic toner to the developing roller 4a, and the developing roller 4a carries the supplied toner.
And the regulating blade 4c regulates the amount of toner on the developing roller 4a during the conveyance.

The developing roller 4a is a photosensitive drum 1 at a developing section.
And the photosensitive drum 1 is rotated with a speed difference in the forward direction. The toner conveyed to the developing unit is applied to the latent image on the photosensitive drum 1 and developed by applying a DC voltage of -300 V from a developing power supply (not shown) to the developing roller 4a.

In the present embodiment, as described above, the developing device 4 is a one-component non-magnetic contact developing device, but may be a two-component contact developing device or a non-contact developing device.

The toner image formed on the photosensitive drum 1 of each of the image forming units Uy to Uk is transferred to a primary transfer section formed by the photosensitive drum 1 and the intermediate transfer belt 5.
Is transported according to the rotation of. The intermediate transfer belt 5 is
It is stretched around the driving roller 6 and supporting rollers (driven rollers) 7a and 7b, contacts the photosensitive drum 1, and is rotated in the direction of arrow c. The toner image that has reached the primary transfer portion is applied to primary transfer rollers 8 (8y, 8m, 8c, 8k) that are pressed against the respective photosensitive drums 1 via the intermediate transfer belt 5, and the toner image is reversed from a primary transfer power source (not shown). By applying a polarity voltage, the image is transferred onto the surface of the intermediate transfer belt 5 (primary transfer).

The primary transfer roller 8 is a conductive elastic roller using a conductive rubber having a resistance value of 10 ⁵ Ω or less. As the primary transfer unit, a conductive blade or a brush may be used in addition to the conductive roller. After the primary transfer, the transfer residual toner on the photosensitive drum 1 passes through the charger 2 and is collected by the developing device 4 to be used again for development.

The above operation is performed by the first to fourth units Uy to U
k, the toner images formed on the photosensitive drums 1y to 1k are transferred onto the intermediate transfer belt 5 by the primary transfer roller 8y.
Ｋ8k, superimposed and transferred sequentially (multiple transfer)
A color image is formed on the intermediate transfer belt 5 by superimposing toner images of four colors of yellow, magenta, cyan, and black.

The color image on the intermediate transfer belt 5 is conveyed to a secondary transfer section formed by the secondary transfer roller 9 and the intermediate transfer belt 5 according to the rotation of the intermediate transfer belt 5,
By applying a voltage having a polarity opposite to that of the toner to the secondary transfer roller 9 from a secondary transfer power supply (not shown), a four-color toner image is formed on the sheet P supplied from the paper supply unit 10 and conveyed to the secondary transfer unit. Are transferred together (secondary transfer). The secondary transfer roller 9 is made of an elastic rubber roller like the one transfer roller 8, but its resistance value is adjusted to about 10 ⁷ to 10 ¹³ Ω.

The paper P on which the full-color image has been sequentially transferred by passing through the secondary transfer section is continuously separated from the intermediate transfer belt 5 by the curvature of the support roller 7b at the moment of passing through the secondary transfer section. The toner image is conveyed to the fixing device 11 as it is, where the toner image is fixed on the sheet P by the action of heat or pressure, and then discharged outside the image forming apparatus. The transfer residual toner on the intermediate transfer belt 5 after the completion of the secondary transfer is
The intermediate transfer belt 5 is removed by a belt cleaner 12 provided on the downstream side of the secondary transfer portion.

As described above, in the present invention, the intermediate transfer member (intermediate transfer belt) is employed. By employing this, the fog due to the positive charging of the photosensitive drum and the charging due to the contamination of the charging device with the foreign matter are provided. The problems of reduced capacity and re-transfer of toner to the photosensitive drum are solved as follows.

(1) First, prevention of fogging caused by positive charging of the photosensitive drum 1 in the primary transfer section will be described. FIG. 3 shows the potential of each section in the primary transfer section of this embodiment.

Compared with the conventional transfer belt shown in FIG. 8, in the present embodiment, since the paper P does not exist between the photosensitive drum 1 and the intermediate transfer belt 5, the transfer bias and the photosensitive drum surface The region where the potential difference is generated is only the image portion and the non-image portion regardless of the size of the sheet. Therefore, the difference ΔI = ID−IL between the current amounts of the image portion and the non-image portion does not increase. Further, since there is no sheet whose resistance increases in a low humidity environment, the voltage applied to the transfer roller 8 can be reduced. By these two effects, the transfer roller 8
Current flowing from the photosensitive drum 1 to the photosensitive drum 1 can be kept low, and the photosensitive drum 1 does not become positively charged.
No fogging occurs in the next image when the image is output.

(2) Next, prevention of a decrease in charging ability due to entry of foreign matter such as paper dust into the charge injection charger will be described.

In the image forming apparatus of this embodiment, the photosensitive drum 1 and the paper P do not come into direct contact with each other, and the intermediate transfer belt 5 transfers an image to the paper P. The intermediate transfer belt 5 is cleaned by the belt cleaner 12 after completing the secondary transfer process to the paper P, so that the surface of the intermediate transfer belt is kept clean when the next image is formed. Has become. Therefore, foreign matter from the intermediate transfer belt 5 does not enter the charge injection charger 2 through the photosensitive drum 1, and even if the charger 2 is used for a long time.
Does not deteriorate. This makes it possible to output a good image over a long period of time.

(3) The last is the effect of preventing retransfer. In the present image forming apparatus, a transfer section (primary transfer section) for transferring a toner image from the photosensitive drum 1 includes a photosensitive drum 1 and an intermediate transfer belt 5.
And only the transfer roller 8 exists, and these have almost no change in resistance value with respect to environmental changes. In contrast, FIG.
In the conventional image forming apparatus shown in (1), since the sheet P whose resistance value greatly changes due to environmental fluctuations is present in the transfer portion of the toner image from the photosensitive drum 1, retransfer is suppressed low and transfer efficiency is increased. The setting of the transfer bias that can be performed changes each time.

In the present image forming apparatus, since the resistance values of the photosensitive drum 1, the intermediate transfer belt 5, and the transfer roller 8 are uniquely determined, the optimum transfer bias value is uniquely determined in relation to the transfer rate and the retransfer rate. The re-transfer can always be minimized. For this reason, the photosensitive drum 1 in each of the image forming units Uy to Uk is protected against various changes in the environment.
Thus, the color transfer of the toner in the developing unit 2 of each unit due to the retransfer can be suppressed.

In particular, in order to obtain the effect (3), the intermediate transfer belt 5 needs to have not only mechanical strength, flexibility and surface properties but also appropriate volume resistance and surface resistance. And an intermediate transfer belt as shown in FIG. 4 was used.

FIG. 4 shows a cross-sectional structure of the intermediate transfer belt 5 used in this embodiment. According to this embodiment, the intermediate transfer belt 5 is an endless belt having a single-layer structure. In order to control the resistance, a carbon or ammonium salt is applied to a base material 5a made of a resin or rubber such as polycarbonate, polyimide, or PTFE. In addition, conductive (including ion conductive) particles 5b such as metal salts and metal oxides are dispersed. The resistance value was 10 ⁷ to 10 ¹⁵ Ω, and the thickness was 0.1 to 1 mm. According to the transfer belt having this configuration, the effects (1) to (3) were successfully obtained.

In the present embodiment, the intermediate transfer belt is employed in the four-drum color image forming apparatus constructed as described above.
It is possible to solve three problems, that is, the lowering of the charging ability due to the intrusion of foreign matter into the charge injection charger and the retransfer of the toner to the photosensitive drum. Therefore, a good image can be output stably over a long period of time, and the speed of color can be increased and the size of the image forming unit can be reduced without impairing the ozoneless and cleanerless effects of the charge injection charger. .

Since the intermediate transfer belt does not need to adsorb a transfer material such as a transfer belt, flexibility with respect to the type of transfer material such as transfer paper can be increased. Further, since the toner images of each color are superimposed on the intermediate transfer belt, color shift caused by friction between the transfer material, the transfer belt, and the photosensitive drum, which occurs in the conventional image forming apparatus shown in FIG. There is no color shift due to the shock of the transfer material entering the transfer section, and the shift of the toner image of each color can be suppressed relatively easily.

Embodiment 2 This embodiment is characterized in that, in the image forming apparatus of Embodiment 1 shown in FIG. 1, an intermediate transfer belt 25 having a plurality of layers is used as shown in FIG.

In this embodiment, the intermediate transfer belt 25
Layer 25a and a resistance control layer 25b thereon
It is configured as an endless belt. The elastic layer 25a has a resistance value
10 ^Four-10¹¹Ω NBR, urethane, EPDM, etc.
Rubber material is used, and
In order to have elastic force, make it about 1-3mm thick
I have.

The resistance control layer 25 b is provided on the intermediate transfer belt 25.
This layer serves to control the overall resistance and to suppress the belt in the circumferential direction in order to prevent the occurrence of color misregistration during image formation due to the entire belt expanding and contracting in the circumferential direction. The resistance control layer 25b is formed by painting a resin such as polycarbonate, ETFE, polyimide, PTFE, or PFA, which has a relatively low elongation rate as compared with a rubber material, on the elastic layer 25a by spraying or dipping. The resistance value of the resistance control layer 25b is 10 ⁹ to 10 ¹⁴ Ω.
The thickness is adjusted to about 10 to 50 μm, which does not hinder the function of the elastic layer.

In order to suppress the circumferential elongation of the entire belt 25, a core material or the like may be inserted into the elastic layer 25a.

In this embodiment, the intermediate transfer belt 2
By making the surface roughness of R5 about 5 to 15 μm in Rz, the mechanical scraping property of the toner image from the surface of the photosensitive drum 1 is enhanced, and the transfer property is improved.

In the above, a conductive layer such as an aluminum material is provided as a base layer of the intermediate transfer belt 25, and the elastic layer 25a and the resistance adjusting layer 25b are provided thereon.
The intermediate transfer belt 25 can also be configured. However, in such a case, the current from the back surface of the intermediate transfer belt 25 may directly flow into the drive unit of the intermediate transfer belt 25 and the photosensitive drum 1 to affect the image at the time of transfer. It is necessary to pay attention to the specific configuration.

Also in this embodiment, by using the intermediate transfer belt, as in the first embodiment, the fog due to the positive charging of the photosensitive drum, the decrease in the charging ability due to the intrusion of foreign matter into the charge injection charger, and the decrease in the The three problems of toner retransfer can be solved, and the intermediate transfer belt has a multi-layer structure having at least an elastic layer and a resistance adjusting layer. It is possible to prevent the occurrence of voids in images such as images. Therefore, good image output over a long period can be performed more stably.

Example 3 This example is characterized in that, in Example 1, a polymerized toner produced by a polymerization method was used. The particle size of the polymerized toner was about 6 to 8 μm.

When the toner adheres to the photosensitive drum by development, the adhered toner exerts mainly a mirroring force and a Hunderwars force on the surface of the photosensitive drum.

The mirror power greatly depends on the charge amount of the toner and the distance from the photosensitive drum. As shown in FIG.
The pulverized toner R manufactured by the conventional pulverization method has an uneven surface shape, and the protrusions are intensively charged due to friction between the toners in the developing device (including friction with the developing sleeve). Is done. Since the shape of the crushed toner R is indefinite, the crushed toner R comes into contact with the photosensitive drum 1 at a plurality of points, and a large amount of electric charge exists in a region very close to the surface of the photosensitive drum. Power increases.

On the other hand, as shown in FIG. 6B, since the polymerized toner S has a spherical shape or a shape close to a spherical shape, the surface is uniformly charged by friction. Polymerized toner S
Has a spherical shape, it is almost in a point-contact state with the surface of the photosensitive drum 1, and the amount of charge in the proximity area is small.

The Van der Waals force is affected by the closest region and becomes very large in a state where the contact is made in a plane. In the pulverized toner R, among many toners, FIG.
As shown in (a), there are many toners that come into contact on a flat surface, and the van der Waals force becomes very large.
On the other hand, since the polymer toner S is almost in point contact, the van der Waals force is smaller than that of the pulverized toner R.

For the above reasons, the spherical toner S
The reflection force on the photosensitive drum and the van der Waals force, that is, the adhesion force are reduced, and the image can be easily transferred by the electric field generated by the primary transfer bias. For this reason, the transfer residual toner on the photosensitive drum can be reduced, and the primary transfer bias does not need to be increased and can be kept low.

Therefore, according to the present embodiment, the positive charging of the photosensitive drum in the non-image area can be more favorably suppressed, and a good image free from image disturbance, color mixing, etc. can be output more stably. can do.

Although the case where the polymerized toner is used in the image forming apparatus of the first embodiment has been described above, it can be used in the image forming apparatus of the second embodiment, and the same effect can be obtained.

[0070]

As described above, according to the present invention,
Before transferring a toner image on an image carrier to a transfer material in a miniaturized, cleaner-less image forming apparatus having a plurality of image forming units using a charge injection charger as a charging unit of the image carrier. The use of an intermediate transfer member that transfers images once causes image fogging due to positive charging of the photoreceptor, deterioration of charging performance due to foreign matter entering the charge injection charger, image deterioration due to re-transfer of toner to the photoreceptor, and development unit. The developer color mixture inside can be solved at the same time. Therefore, high-speed output of a color image and downsizing of an image forming unit can be achieved without deteriorating the ozone-less and cleaner-less effects of the charge injection charger, and a good image can be stably output over a long period of time. be able to. Further, when an intermediate transfer belt is used as the intermediate transfer member, there is no need to adsorb the transfer material as in an image forming apparatus having a conventional transfer belt, so that the flexibility with respect to the type of transfer material can be increased. In addition, since the toner images of each color are superimposed on the intermediate transfer belt, friction between the transfer material and the transfer belt and the image carrier, and transfer material, which occur in an image forming apparatus having a conventional transfer belt, are generated. Does not enter the transfer portion, and there is no color shift due to these.

[Brief description of the drawings]

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

FIG. 2 is a sectional view showing details of a photosensitive drum and a charge injection charger installed in the image forming apparatus of FIG. 1;

FIG. 3 is an explanatory diagram showing potentials of respective parts in a primary transfer unit of the image forming apparatus of FIG.

FIG. 4 is a sectional view showing an intermediate transfer belt in the image forming apparatus of FIG. 1;

FIG. 5 is a sectional view showing an intermediate transfer belt according to another embodiment of the present invention.

FIG. 6 is an explanatory diagram showing a charging state of a polymerized toner used in still another embodiment of the present invention in comparison with a charging state of a conventional pulverized toner.

FIG. 7 is a schematic diagram illustrating a conventional image forming apparatus.

FIG. 8 is an explanatory diagram showing potentials at various portions in a transfer section of the image forming apparatus of FIG. 7;

[Explanation of symbols]

 1y to 1k Photosensitive drum 2y to 2k Charge injection charger 4y to 4k Developing device 5 Intermediate transfer belt 8y to 8k Primary transfer roller 12 Intermediate transfer member cleaner 25 Intermediate transfer belt P Paper S Polymerized toner

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H003 BB11 CC04 EE11 EE18 2H030 AB02 AD01 AD02 AD03 AD05 AD17 AD19 BB02 BB23 BB26 BB34 BB42 BB44 BB46 BB54 BB71 2H032 AA05 AA15 BA01 BA02 BA05 BA08 BA11 BA30 AC16 AD06 AD24 AD35 EA11 GA13

Claims (9)

[Claims] An image carrier having a charge injection layer on a surface thereof;
A charging unit to which a charging bias is applied, which contacts the surface of the image carrier and is charged by a charge injection method; and a developer for applying an electrostatic latent image formed by image exposure on the charged surface of the image carrier to a developer An image forming unit having a developing unit for developing the toner image by using a developing unit, and forming a toner image on the image carrier, transferring the toner image to a transfer material, and the developing unit. However, in an image forming apparatus that also serves as a cleaning unit that removes toner remaining on the surface of the image carrier after transfer, an intermediate transfer body that rotates along the image forming unit is installed,
Before transferring the toner image formed on the image carrier to the transfer material, transferring the toner image onto the intermediate transfer member, and then transferring the toner image from the intermediate transfer member to a transfer material. Forming equipment. 2. The image forming apparatus according to claim 1, wherein said intermediate transfer member is an endless belt. 3. The image forming apparatus according to claim 2, wherein the endless belt is a belt having a single layer structure in which conductive particles are dispersed and resistance is adjusted. 4. The image forming apparatus according to claim 2, wherein the endless belt comprises a belt having a multilayer structure including at least an elastic layer and a resistance control layer thereon. 5. The image forming apparatus according to claim 1, wherein said intermediate transfer member is a rotary drum. 6. The charging means is held on a surface of the sleeve by a conductive rotating sleeve to which a charging voltage is applied, a magnet arranged non-rotatably in the sleeve, and a magnetic force of the magnet. The image forming apparatus according to claim 1, further comprising: magnetic particles formed on the magnetic brush and in contact with a surface of the image carrier. 7. The image forming apparatus according to claim 1, wherein said charging means comprises a conductive elastic roller to which a charging voltage is applied, which contacts a surface of said image carrier. 8. The image forming apparatus according to claim 1, wherein the developer is a one-component developer that does not use a magnetic carrier in addition to the toner, and the toner is manufactured by a polymerization method. . 9. The image forming apparatus according to claim 1, wherein a plurality of image forming units are provided.
Item 8. The image forming apparatus according to any one of Items 8.