JPH08146696A - Multicolor image forming device - Google Patents

Abstract

PURPOSE: To provide an image forming device capable of preventing the color mixture of toner in a developing unit caused by a deterioration in an image due to a retransfer and recovery simultaneous with development. CONSTITUTION: This multicolor image forming device is provided with plural image forming units for developing a latent image formed on an image carrier by a developing means, transferring a toner image visualized on the image carrier to an image receiving member and recovering residual transfer toner remaining on the image carrier after a transfer while using a developing device also as a cleaning member, and forms a multicolor image in such a manner that the toner images formed by plural image forming units are successively multiply transferred to the image receiving member. The toner used in each image forming unit is polymerized toner produced in a polymerizing method and the grain size of the polymerized toner in each image forming unit is equal to or smaller than that of the toner used in the image forming unit on the downstream side in the advancing direction of the image receiving member against each image forming unit and smaller than that of the toner used in the most downstream side image forming unit in the advancing direction of the image receiving member.

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 utilizing an image forming process such as an electrostatic recording system or an electrophotographic system, and more particularly, it multiplex-transfers visualized images on a plurality of image information carriers. Thus, the present invention relates to a multicolor image forming apparatus capable of obtaining a multicolor image, and can be embodied not only in an electrophotographic copying apparatus but also in various printers, facsimiles and the like.

[0002]

2. Description of the Related Art In recent years, image forming apparatuses such as electrophotographic apparatuses have been reduced in size, increased in function, and increased in color, but on the other hand, they have improved reliability, system development, maintenance-free, and are friendly to people and the environment. , Etc. are increasing,
Various image output devices have been proposed to meet those demands.

Among them, there has been proposed a device in which a plurality of photoconductors are stacked in order to speed up the color image output, and a transfer paper is conveyed by a belt-shaped conveying means, and the toner images are sequentially transferred in multiplex. Has been done. Further, in recent years, in particular, a cleanerless device that collects and reuses transfer residual toner and a printer that employs a simultaneous development cleaning method have been put into practical use in order to reduce the size of the toner and eliminate the waste toner and to provide ecology.

Therefore, here, the conventional model will be described with reference to FIG. 1 which shows an example of a color copying machine using the simultaneous transfer cleaning system. In this example, the image forming unit includes a plurality of image forming units, and a transfer belt, which is a transfer material conveying unit, is arranged vertically through the image forming units. The configuration and operation of the image forming apparatus using such a system will be described. The image forming units UM, UC, UY, and UBk are described below.
(Hereinafter, since all units for four colors are the same, they will be described by taking UC as a representative). In this case, a cylindrical photosensitive member 10C as an electrostatic latent image carrier is rotated and moved in the direction of arrow a. It 12C is a primary charger that uniformly charges the photoconductor 10C. An image exposure unit 14C exposes the photoconductor 10C to form an electrostatic latent image. 16C is a developing device, which contains a two-component developer composed of a mixture of magnetic carrier particles of about 50 μm and non-magnetic toner of about 8 μm,
The electrostatic latent image is developed to form a toner image on the photoconductor 10C. Reference numeral 18 is a copy sheet as a transfer material, and a paper feeding section 20.
Is supplied to the transfer belt 30. Transfer belt 30
Is transported by the drive roller 31 and the support roller 32 in synchronization with the rotation of the photoconductor 10C. A transfer blade 25 is applied to the transferred transfer paper 18.
The toner image is transferred by the action of the transfer electric field formed by C.

The above operation is performed in each image forming unit, and the toner images formed on the respective photoconductors are sequentially and multiple-transferred onto the transfer paper 18 held on the transfer belt 50. In the full color mode, M, C,
The toners are transferred in the order of Y and Bk, and also in the case of the single color mode or the two or three color mode, the necessary toners are multi-transferred onto the transfer paper 18 in the above order. The copy paper 18 on which the toner has been transferred is supplied to the fixing device 38 by the transfer belt 30 and is fixed on the copy paper 18 by the action of heat and pressure.

On the other hand, the photoreceptor 10C on which the toner is transferred
Is uniformly discharged by the pre-exposure lamp 13C,
The transfer residual toner remaining on the photoconductor 10C is simultaneously collected by the developing device 16C during the developing operation, and is used again for image formation. The surface of the transfer belt 30 that has finished supplying the copy paper 18 to the fixing device 38 is cleaned by the belt cleaner 51.

[0007]

In the four-drum full-color copying machine having the above-described structure, for example, in the two-color mode (magenta, cyan), the transfer material 18 supported on the transfer belt 30 is sequentially magenta. Unit UM,
The image forming section passes through the cyan unit UC, the yellow unit UY, and the black unit UBk, but the image forming section may be a desired unit, for example, only the magenta and cyan unit.

However, as described above, the transfer material is sequentially sent to the magenta, cyan, yellow, and black units and passes through the gap between the transfer belt and the photosensitive drum. When all operations of the image forming process of the unit are stopped, as described above, when the transfer material passes through the gap between the drum and the belt of each unit other than magenta and cyan, the magenta and cyan already formed on the transfer material. There is a problem that the image is rubbed by the yellow and black photosensitive drums, and the image is significantly damaged. In particular, when the spherical toner is used as in this example, the toner itself easily rolls, so that the damage caused by rubbing becomes large.

Furthermore, in such a case, when the transfer material passes through the gap between the drum and the belt, the transfer material is apt to jam (jam). Therefore, you can avoid these problems by activating undesired units, but by doing so, you can make unnecessary operations
The life of parts will be shortened, running costs will rise, and extra power will be wasted.

Further, at this time, the magenta and cyan toners transferred onto the transfer material are electrostatically attracted to the transfer material, but the transfer material passes through the gaps between the yellow and black photosensitive drums and the belt. At that time, a part of the magenta and cyan toner forming the magenta and cyan images may be retransferred to these photosensitive drums, in which case the image is significantly deteriorated, that is, image unevenness and density decrease. Then, there arises a problem of color balance deviation.

In order to solve such a problem, there is a system in which the biasing and releasing of the transfer belt to and from the photosensitive drum used for image formation are selectively controlled.
No. 669, etc. With such a configuration, in the monochromatic mode, for example, the magenta monochromatic mode, by controlling only the magenta drum and the transfer belt to contact each other, the toner image on the transfer material comes into contact with another drum. In addition, the problem of image rubbing and toner color mixture in the developing device due to retransfer described above does not occur.

However, in such a conventional example, a pressure contact releasing mechanism for the photosensitive drum of an undesired image unit is required for each unit. Further, there is a drawback that various mechanical vibrations are generated during the operation of these release mechanisms. Further, even when a full-color image is formed by using all the image forming units, the toner already transferred onto the transfer paper at the time of multiple transfer of the second and subsequent colors may be retransferred to the drum.

If the above-mentioned retransfer occurs, that is, if magenta and cyan toners are retransferred to the yellow and black photosensitive drums, they are collected at the same time of development because the drum cleaner is not used. There is a problem of toner color mixing in the developing device. The color mixture in the developing device becomes a fatal defect in multicolor image formation.

Therefore, in Japanese Patent Laid-Open No. 1-273076, the toner on the transfer paper is also charged to the transfer polarity by the transfer, and it is assumed that this is due to the repulsion of the same polarity as the charging of the belt. It has been proposed to transfer the toner by contacting it with a photoreceptor. However, in this method, it is necessary to constantly monitor the charging status of the belt and perform control so that proper charging is performed. It has a drawback that the device configuration becomes complicated and large and the cost increases.

Regarding the re-transfer phenomenon and its countermeasure, in US Pat. No. 4,093,547, it is assumed that the re-transfer phenomenon is caused by the attractive force of the electric field from the charged area of the photoconductor to the toner on the transfer paper, and the first color is sequentially applied. It teaches to set a continuous charge amount in which the charge amount of the toner becomes small over a wide range. However, in this case, since the charge amounts of the toners of the respective colors are greatly different, the design conditions of the image forming process are also greatly different, and there is a drawback that the design values and the components cannot be shared and the cost is increased. Was.

Therefore, an object of the present invention is to form an image which can prevent image deterioration due to retransfer and toner color mixture in the developing device due to simultaneous recovery of development without impairing the simplicity which is a feature of the present construction. To provide a device.

[0017]

In order to achieve the above object, the present invention forms a latent image on an image bearing member by an image forming unit and develops the latent image by a developing unit,
The developing device also serves as a cleaning unit that transfers the visualized toner image onto the image receiving member by the developing unit on the image carrier and collects the transfer residual toner remaining on the image carrier after the transfer. In a multicolor image forming apparatus that has a plurality of image forming units and sequentially multiplies toner images formed by the plurality of image forming units on an image receiving member to form a multicolor image, each image forming unit The toner used in is a polymerized toner produced by a polymerization method, and the particle size of the polymerized toner in each image forming unit is used in the image forming unit downstream in the image receiving member traveling direction with respect to each image forming unit. The same as or smaller than the particle size of the toner used, and smaller than the toner used in the most downstream image forming unit in the traveling direction of the image receiving member. And it is characterized in and.

That is, the present invention is configured as described above to prevent the re-transfer phenomenon of toner from the transfer material to the photoconductor at the time of multiple transfer at the time of forming a multicolor image.

[0019]

【Example】

(First Embodiment) A first embodiment of the present invention will be described below with reference to the drawings. In this example, a plurality of image forming units are provided, and a transfer belt, which is a transfer material conveying unit, is arranged vertically through each image forming unit, and a drum cleanerless using spherical toner formed by a polymerization method is used. An image forming process method is adopted in which development and collection are simultaneously performed.

Here, the reason why the toner recycling process by cleanerless cleaning and simultaneous cleaning can be achieved by the spherical toner produced by the polymerization method will be explained with reference to FIG. 3 from the aspect of the adhesive force between the toner and the photoconductor. To do. When the toner adheres to the photoconductor by the developing process (bias, latent image potential), the main forces acting on the toner contacting the surface of the photoconductor are the mirror image force and the Van der Waals force. The mirror image force largely depends on the amount of electric charge and its distance. The crushed toner produced by crushing, which is a conventional toner, has irregularities in the surface shape, and by triboelectrification,
The convex portions are concentratedly charged.

On the other hand, the spherical polymerized toner obtained by the polymerization method has a spherical surface or a shape close to a spherical surface, so that the surface is uniformly charged. For crushed toner,
The mirror image force increases due to the presence of many charges in the very close areas where the protrusions are in contact. On the other hand, when the toner has a spherical shape like the polymerized toner, the contact state becomes almost point-like, the amount of electric charge in the adjacent region is small, and the mirroring power is smaller than the above. The Van der Waals force is very large in the state where the contact is made in a plane due to the influence of the region closest to the van der Waals.

When the pulverized toner is used, many of the many toners come into contact with each other in the state shown in FIG. 3, and in this case, the van der Waals force is very high. growing. On the other hand, the polymerized toner has a spherical surface shape, and therefore contacts the toner at almost points. Therefore, the Van der Waals force is also smaller for the polymerized toner.

For the above reason, in the case of polymerized toner having a nearly spherical shape, the mirror image force, the Van der Waals force, and
That is, the adhesive force becomes small, the transfer residual toner in transfer is small, and the toner collecting effect at the time of simultaneous cleaning at the time of development becomes large, and cleanerless and simultaneous cleaning at the time of development become possible. Therefore, here, an example of the present invention will be described with reference to FIG. 1 which shows an example of a color copying machine using the simultaneous transfer cleaning method. Note that it is possible to use the image forming apparatus having the same configuration in the present embodiment and the conventional embodiment.

First, the structure of the image forming apparatus of the present invention will be described. Each image forming unit UM, UC, UY,
A cylindrical photosensitive member 10C as an electrostatic latent image carrier is rotatably moved in the direction of arrow a in UBk (hereinafter, units for four colors will be described by using UC as a representative). 12C is a primary charger, which is installed so as to come into contact with the photoconductor 10C. An image exposure unit 14C exposes the photoconductor 10C to the primary charger 12C on the downstream side in the rotation direction of the photoconductor 10C. Reference numeral 16C denotes a developing device, which is installed further downstream from the exposure position of the photoconductor 10C so as to be adjacent to the photoconductor 10C. Reference numeral 18 is a transfer paper as a transfer material. Reference numeral 20 denotes a paper feeding unit for feeding the transfer paper 18.

A transfer belt 30 is in contact with the photoconductor 10C and is driven in the direction a. The transfer belt 30 is
This is an endless belt in which conductive particles such as carbon are dispersed in a resin or rubber base material having mechanical strength and flexibility such as polycarbonate, and has a resistance value of 10 ⁹ to 10 10.
It is preferable to adjust the thickness to ¹³ Ω and the thickness to 0.1 to 1 mm. Three
Reference numeral 1 is a driving roller, and 32 is a supporting roller, which is a driving unit that stretches and drives the transfer belt 50. 25C is a transfer blade, which is installed so as to sandwich the transfer conveyance belt 30 at the transfer position and face the photoconductor 10C. The transfer blade 25C is formed of a semiconductor layer having a base material of 10 ⁹ to 10 ¹¹ Ωcm, and the surface layer on the side of the photoreceptor 10C is formed of a material having a small surface roughness and a small friction coefficient and excellent abrasion resistance, such as a fluorine resin.
Those made of nylon resin are suitable.

Reference numeral 38 denotes a fixing device, which is the transfer / conveyance belt 30.
Is disposed adjacent to the driving roller 31 of the. 13C is a pre-exposure lamp, which includes the transfer blade 25C and the primary charger 12
It is installed between C. The operation of the image forming unit of the electrophotographic apparatus configured as described above will be described using the unit UC. (The same applies to other units.) First, the photoconductor 10C has an optical semiconductor layer on the surface of a conductive substrate such as aluminum and rotates in the direction of arrow b. Then, the surface is uniformly negatively charged by the primary charger 12C, and then the image is exposed by the image exposure unit 14C to form an electrostatic latent image corresponding to the original.

The developing device 16C develops using a negatively charged polymerized toner produced by a polymerization method to form a toner image corresponding to the electrostatic latent image on the surface of the photoconductor 10C. The toner image formed on the surface of the photoconductor 10C is fed to the paper feeding unit 20.
Thus, in synchronization with the image formation at the rotation speed of the photoconductor 10C, the image is transferred onto the copy paper 18 supplied toward the transfer belt 30.

The above-described operation is performed in each image forming unit, and the toner images formed on the respective photoconductors are sequentially and multiple-transferred onto the transfer paper 18 held on the transfer belt 50. In the full color mode, M, C,
The toners are transferred in the order of Y and Bk, and also in the case of the single color mode or the two or three color mode, the necessary toners are multi-transferred onto the transfer paper 18 in the above order.

The copy paper 18 on which the toner has been transferred is supplied to the fixing device 38 by the transfer belt 30 and is fixed on the copy paper 18 by the action of heat and pressure. On the other hand, the photoconductor 10C to which the toner has been transferred is uniformly discharged by the pre-exposure lamp 13C, and the transfer residual toner remaining on the photoconductor 10C is simultaneously collected by the developing device 16C during the developing operation to form an image. Will be served again. The surface of the transfer belt 30 that has finished supplying the copy paper 18 to the fixing device 38 is cleaned by the belt cleaner 51.

With respect to the image forming operation of the electrophotographic apparatus configured as described above, the causes of multiple transfer and retransfer will be described in detail with reference to FIGS. The image formation before the transfer portion is the same as that described above, and is omitted here. The present inventor conducted various studies on the retransfer phenomenon, and as a result, as shown in FIG. 4, it was found that the peeling discharge between the photosensitive drum and the transfer paper (including the transfer belt) was the cause. As described above, the toner image Tm formed on the photosensitive drum 10M of the magenta unit UM by the well-known electrophotographic process.
Is carried on the transfer belt 30, and is brought into close contact with the transfer paper 18 supplied in synchronization with the rotation of the photosensitive drum 10M, and at the same time, the toner image Tm is transferred to the transfer belt 30 from its rear surface. A positive transfer charge Qb is supplied to the transfer belt 30 by the blade 25C. The transfer charge Qb exerts an electrostatic attraction on the toner image Tm having a negative charge, and the toner image Tm is attracted to the transfer paper 18.

On the other hand, a positive charge is induced on the photosensitive drum 10M by the positive transfer charge Qb, and an electrostatic attractive force acts on the transfer paper 18 carrying the transfer paper 18 and the photosensitive drum 10C by both of them, and the transfer paper is transferred. 18 and the photosensitive drum 10C come into close contact with each other. Then, at the next moment, due to the curvature of the photosensitive drum 10M, the toner image Tm is attracted to the transfer paper 18, the transfer paper 18 held on the transfer belt 30, and the transferred toner image on the transfer paper 18. Tm is peeled off from the photosensitive drum 10C. Due to this peeling, an air gap is formed between the photosensitive drum 10M and the toner image Tm, the electrostatic capacitance at that portion is rapidly reduced, and the potential difference is increased. Stripping discharge occurs.

Most of the positive and negative charges generated by this peeling discharge are generated in a slight air gap surrounded by the photosensitive drum 10M and the toner image Tm, but the positive charge Qb applied to the transfer belt 30. And, according to the electric field formed by the negative charge induced on the photosensitive drum 10M, the positive charge is applied to the photosensitive drum 10M.
To the toner Tm and the transfer paper 18
Jump into. However, a part of the positive charges also jumps into the toner Tm, the charging polarity is reversed by the positive charges, repels the positive charges Qb of the transfer belt 30, and transfers to the photosensitive drum 10M to cause retransfer. However, at this time, most of the remaining toner Tm whose charge polarity has not been reversed due to the positive charge is given a negative charge due to the peeling discharge, the charge amount increases, and the toner is transferred onto the transfer paper 18.

Actually, the change in the charge amount of the magenta toner transferred to the transfer paper 18 after the transfer and the change in the charge amount of the toner retransferred onto the photosensitive drum and remaining on the drum were measured by changing the transfer bias. This is shown in FIG. 5, and it can be seen from this graph that the charge amount of the transferred toner is larger than that before the transfer and the charge amount on the drum is reversed. Further, it is shown that as the transfer bias is increased, the degree thereof is increased and the peeling discharge is increased.

In this case, since it is the first color, some image deterioration due to retransfer is caused, but toner color mixture in the developing device due to simultaneous cleaning at the development does not occur. Further, since cyan, yellow, and black are additionally transferred in succession, the influence of image deterioration due to retransfer can be reduced. Then, next, a case where the cyan toner Tc is multi-transferred onto the transfer paper 18 to which the magenta toner Tm has been transferred will be considered with reference to FIG.

In this case as well, the operation is basically the same as when the magenta toner Tm of the first color is transferred, but the toner image Tm on the transfer paper 18 acts when it is transferred as described above. It should be noted that the charge amount is increased due to. When the cyan toner image Tc having a negative charge on the photoconductor 10 is transferred onto the transfer paper 18 to which the magenta toner image Tm has already been transferred, the transfer blade 25
A positive transfer charge Qb is supplied from C to the transfer belt 30, and the transfer charge Qb and the toner image Tc having a negative charge exert an electrostatic attractive force, and the toner image Tc is attracted to the transfer paper 18.

On the other hand, the positive transfer charge Qb induces a negative charge on the photosensitive drum 10C, and the electrostatic charge acts on the transfer paper 18 carrying the transfer paper 18 and the photosensitive drum 10C by both of them, and the transfer paper is transferred. 18 and the photosensitive drum 10C come into close contact with each other. Then, at the next moment, due to the curvature of the photosensitive drum 10C, the toner image Tc remains attracted to the transfer paper 18, the transfer paper 18 held on the transfer belt 30, and the transferred toner image Tc on the transfer paper 18. The photosensitive drum 10C is peeled off, but due to this peeling, an air gap is formed between the photosensitive drum 10C and the toner image Tc, the electrostatic capacitance at that portion is rapidly reduced, and the potential difference increases. Occurs, and a positive charge and a negative charge are generated.

Here, as the toner sandwiched between the photosensitive drum 10C and the transfer paper 18, the magenta toner Tm whose charge amount has been increased by the transfer action and the transfer paper 18 is transferred from the photosensitive drum 10C. There is cyan toner Tc which is about to be transferred and still maintains the charged amount as it is developed. And the normal charge amount T
c and Tm having a higher charge amount and the photosensitive drum 10C
However, at the moment of this peeling, they are exposed to the positive and negative charges generated by the peeling discharge.

Then, the positive charge is applied to the photosensitive drum 1.
The toner jumps to the magenta toner Tm having a larger charge amount of 0 C and inverts the charge amount of Tm, and Tm is selectively retransferred to the photosensitive drum 10C by the electric field between the discharge gaps, while the charge amount of Tm is small. Cyan toner Tc
Negative charge jumps into and increases the amount of charge.

At the time of multiple transfer, such an action works, and the magenta toner already on the transfer paper 18 becomes easy to be selectively retransferred. The same can be said for yellow and black multiple transfer. From the above, in order to mitigate and prevent the selective retransfer of the toner already on the transfer paper at the time of this multiple transfer, the toner already transferred on the transfer paper 18 and the toner to be transferred from now on are transferred. Make the tribo difference as small as possible,
This is achieved by causing positive charges of opposite polarity generated by the peeling discharge to jump into the photosensitive drum, thereby reducing the amount of toner whose polarity is reversed in the toner tribo even when the transfer action is performed.

Therefore, the present inventor has conducted various experiments so as to achieve the above-mentioned object, and found that the toner tribo change after being subjected to the transfer action becomes smaller by reducing the particle size of the toner. It was An example of this is shown in FIG.
It can be seen that the μ toner has less change in toner tribo before and after transfer.

From the above, in the multicolor image forming apparatus as shown in FIG. 1, since the magenta toner image, which is the most upstream of the multiple transfer, is transferred four times, the toner of other three colors is compared with the toner. It is effective to make the particle size the smallest and gradually increase the particle sizes of cyan, yellow, and black. Therefore, in the first embodiment of the present invention, as shown in FIG. 2, the average volume particle size of the magenta toner is 5 μm,
The cyan toner was 6 μm, the yellow toner was 7 μm, and the black toner was 8 μm.

Here, the method for measuring the particle size distribution in the present invention will be described. As a measuring device, Coulter Counter TA-2 type (manufactured by Coulter) is used, and an interface (manufactured by Nikkaki) that outputs a number average distribution and a volume average distribution and a CX-1 personal computer (manufactured by Canon) are connected to perform electrolysis. Use 1st class sodium chloride
% NaCl aqueous solution is prepared.

The measuring method is as follows:
Surfactant as a dispersant in 150 ml, preferably
0.1 to 5 ml of alkylbenzene sulfonate is added, and 0.5 to 50 mg of a measurement sample is further added. The electrolytic solution in which the sample is suspended is subjected to a dispersion treatment for about 1 to 3 minutes with an ultrasonic disperser, and is subjected to the Coulter Counter TA-2 type,
2 using the 100μ aperture as the aperture
The particle size distribution of 40 μm particles is measured to obtain the volume average distribution. The volume average particle size is obtained from the obtained volume average distribution.

As described above, when an image of a four-color full-color image is produced by using a toner having a smaller particle size as the toner on the upstream side of the multiple transfer, retransfer does not occur, image deterioration and density decrease. It was possible to obtain a good image in which the color balance was not shifted, and it was possible to prevent toner color mixture in the developing device due to simultaneous recovery during development. Further, since the polymerized toner produced by the polymerization method is used in this example, it is possible to finely control the particle size in the production method as compared with the conventional pulverization method.
It also has the feature that it can be simplified at low cost.

(Second Embodiment) A second embodiment of the present invention will be described with reference to FIG. Also in this embodiment, the first
In the same manner as in the above embodiment, an image forming unit including charging, exposure, development and pre-exposure centered on the photosensitive drum is provided with four units of UM, UC, UY and UBk for each toner color. ing. As the toner, a spherical toner formed by a polymerization method is used, and each image forming unit UM, UC, UY is made of a toner having a particle diameter of 6 μ, and UBk
For this, 8 μ toner is used. This is at a level at which retransfer is acceptable with 6 μ toner, and
This is because the final color does not need to consider retransfer.

Also in this embodiment, the image is formed by the process of collecting the toner on the drum by the developing device at the same time without developing the drum cleaning. However, the first difference from the embodiment is that, in terms of the structure of the apparatus, instead of carrying the transfer paper on the transfer belt and carrying out multiple transfer of the toner images of the respective colors onto the transfer paper, instead of using the transfer belt, The intermediate transfer member 50 is stretched by a driving roller 31, a support roller and a backup roller 27, the toner images of respective colors are transferred onto the intermediate transfer member in a multiple transfer manner, and the synthetic toner image is transferred by the paper feed roller 20 to the transfer paper 18. On the other hand, it is transferred by the backup roller 27 and the secondary transfer roller 26 and fixed by the fixing device 38.

As an intermediate transfer member, urethane rubber (10
PTFE as a dielectric layer on the surface of ³ to 10 ⁴ Ωcm)
It is composed of a flexible endless belt on which a (polytetrafluoroethylene) layer (10 ¹⁴ Ωcm or more) is formed. Since the other components are almost the same as those in the first embodiment, the description thereof is omitted here. The operation of image formation with the above configuration will be described below.

First, a magenta toner image having a particle size of 6 μ is formed on the photosensitive drum of the magenta unit UM by the same process as described above, and the toner image is transferred onto the intermediate transfer member 50 by the transfer electric field formed by the transfer blade. To be done. The cyan toner image of 6 .mu. Formed on the photoconductor by the cyan unit UC is transferred thereon. After that, 6μ yellow toner image is transferred in the same manner,
Finally, 8μ black toner is multi-transferred, but at this time, magenta, cyan, and yellow toners hardly cause re-transfer, so that finally, a multi-transfer image without re-transfer is formed on the transfer paper 18. An image is formed by being transferred by the secondary transfer roller 26 and being fixed by the fixing device 38.

By using the apparatus having such a structure as described above, an excellent image without image defects due to retransfer can be obtained, and color mixture of toner in the developing device due to simultaneous development recovery can be prevented. Further, since the particle diameters of the magenta, cyan, and yellow toners are made common, the above-mentioned object can be achieved more easily and at low cost in manufacturing the toner or making good use of it.

[0050]

As described above, according to the present invention,
By making the toner particle size of the image forming unit on the upstream side in the transfer material conveyance direction in multiple transfer smaller, it is possible to prevent the reversal of the charging polarity of the toner during multiple transfer and prevent the occurrence of retransfer. It is possible to obtain a good color image without deteriorating the density, the color balance, and the like, and it is possible to prevent the toner color mixture in the developing device due to the simultaneous recovery of the development.

Further, since the polymerized toner produced by the polymerization method is used, there is an effect that the particle size can be controlled easily and at low cost.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a color image forming apparatus to which a first embodiment of the present invention and a conventional example can be applied.

FIG. 2 is a schematic diagram showing a toner particle size distribution of each color in the first embodiment of the present invention.

FIG. 3 is an explanatory diagram of a relationship among a toner shape, a mirror image force, and a Van der Waals force.

FIG. 4 is a model diagram illustrating retransfer of the first color.

FIG. 5 is data obtained by measuring the transfer bias dependence of the charge amount of the transferred toner after transfer and the toner remaining on the drum due to retransfer.

FIG. 6 is a model diagram illustrating retransfer of the second color.

FIG. 7 is data obtained by measuring the particle size dependence of the charge amount of the transferred toner after transfer and the toner remaining on the drum due to retransfer.

FIG. 8 is a schematic sectional view of a color image forming apparatus to which a second embodiment of the invention is applied.

[Explanation of symbols]

 UM Magenta image forming unit UC Cyan image forming unit UY Yellow image forming unit UBk Black image forming unit 10 Photosensitive drum 12 Primary charger 13 Pre-exposure lamp 14 Image exposure unit 16 Developer 18 Transfer paper 20 Paper feed roller 25 Transfer blade 26 2 Next transfer roller 27 Backup roller 30 Transfer belt 31 Belt drive roller 38 Fixing device 50 Intermediate transfer body 51 Belt cleaner Tm Magenta toner image Tc Cyan toner image Qb Transfer charge

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Claims (3)

[Claims] 1. A latent image is formed on an image bearing member by an image forming unit, the latent image is developed by a developing unit, and a toner image visualized by the developing unit on the image bearing member is received on an image receiving member. The developing device also has a plurality of image forming units for performing the cleaning means for collecting the transfer residual toner remaining on the image carrier after the transfer, and the image forming units are formed on the image receiving member by the plurality of image forming units. In a multicolor image forming apparatus for forming a multicolor image by sequentially transferring the formed toner images, the toner used in each image forming unit is a polymerized toner generated by a polymerization method, and the toner is used in each image forming unit. The particle size of the polymerized toner is equal to or smaller than the particle size of the toner used in the image forming unit on the downstream side in the image receiving member traveling direction with respect to each image forming unit. And a toner that is smaller than the toner used in the most downstream image forming unit in the traveling direction of the image receiving member. 2. The multicolor image according to claim 1, wherein the image receiving member is a transfer material onto which the toner is transferred, and an endless belt-shaped transfer belt that carries and conveys the transfer material. Forming equipment. 3. The multicolor image forming apparatus according to claim 1, wherein the image receiving member is an intermediate transfer member to which the toner is transferred.