JPH0636107B2 - Color image forming apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention is directed to forming a toner image on an image bearing member by repeating latent image formation on the image bearing member and development with color toner a plurality of times depending on the number of colors. The present invention relates to an improvement in cleaning means for residual toner after transfer on the surface of an image carrier of a color image forming apparatus, which forms a color toner image by forming a color toner image on a transfer material and fixing the color toner image on the transfer material.

(Prior Art) Conventionally, as an image carrier cleaning means of a color image forming apparatus, an edge portion of an elastic body such as polyurethane is brought into contact with the surface of the image carrier to cause residual adhesion on the surface of the image carrier after transfer. Blade cleaning is performed to scrape off the toner that is being used. At that time, as a means for collecting the separated toner, one using a Mylar blade 7 as shown in FIG. 2, urethane type, chloroprene type, Those using a foaming roller 8 such as a silicone type, or a magnetic brush roller 9
It has been considered to use a foam roller or a combination of a foam roller and a magnetic brush roller.

However, in all of these toner collecting means, the separated toner is pressed against the surface of the image carrier again to form a film of the toner, and in the case of using a Mylar blade or a foaming roller, the surface of the image carrier is cleaned. The rubbing causes problems such as deterioration and damage of the image carrier, and a device using a foaming roller or a magnetic brush roller has a complicated driving system and is expensive.

Therefore, the inventors have adopted a non-contact type bias roller system as shown in FIG. 1 and applied a bias voltage having a polarity opposite to the charging polarity (primary electrode property) of the latent image to the bias roller 1. (Japanese Patent Application No. 60-27031)
9).

The color image forming apparatus targeted by the present invention is the image carrier 2
A latent image is formed for each of a plurality of colors set in advance for each one rotation, and the process of being inverted by the color toner of the corresponding color is repeated for the set number of times. For example, when three colors are used, the first color toner image is formed at the first rotation, and the second color toner image is formed at the second rotation so as to overlap the first color toner image formed previously. At the third rotation, the third color toner image is formed on the superimposed image of the first color toner image and the second color toner image, and then transferred to the transfer material. Therefore, the blade is retracted backward so that the blade cleaning is not performed until the development of the three color toners and the transfer to the transfer material are completed, and after the transfer is completed, the edge of the blade contacts the surface of the image carrier. Contact them for cleaning.

On the other hand, the bias roller 1 is provided in a non-contact state with a predetermined gap from the surface of the image carrier 2, and the first color toner image is rotated by the first rotation and the first color toner image is rotated by the second rotation. The toner image in which the second color toner images are superposed on each other passes through the gap. Then, in the third rotation, the toner image of the third color is superposed and passed through the gap in a state after being transferred to the transfer material. At this time, the cleaning blade 3 comes into contact with the surface of the image carrier after the transfer so as to clean the surface.
Then, the toner remaining on the surface of the image carrier is separated by the cleaning blade 3 and drops onto the bias roller, or drops into the gap between the bias roller 1 and the image carrier 2.

Since a potential having a polarity opposite to the charge polarity of the latent image is applied to the bias roller 1, the direction of the electric field in the gap portion is the direction for attracting the charged toner toward the bias roller 1, and the bias roller 1 is separated from the toner. Adsorbs well.

As a result, toner spillage is prevented, the toner recovery efficiency is extremely high, and a very good cleaning recovery performance can be obtained.

(Problems to be Solved by the Invention) However, in the above technique, the bias roller 1 is applied with a voltage having a polarity opposite to the polarity of the latent image, that is, the polarity of the primary charging. As shown in FIG. 3, the first color toner image formed on the image carrier 2 and the first color toner image and the second color toner image are superposed on each other as shown in FIG. When the toner image faces the bias roller 1, the toner is charged with an opposite electric charge to obtain a degree of freedom, and the toner image is attracted and scattered toward the bias roller 1 side to which a reverse polarity bias voltage is applied. Since the image carrier collapses or the image carrier moves at a high speed, the toner that cannot move to the bias roller 1 and floats near the toner image of the first color latent images and image parts of the second and subsequent colors. So-called "fog" There is a problem that "or" stains are generated to prevent clear image reproduction.

An object of the present invention is to eliminate the above-mentioned problems, and in a color image forming apparatus in which recharging, uniform exposure, reversal development and image formation are repeated, a color toner image passes a position facing a cleaning unit. Provided is a color image forming apparatus provided with a cleaning device which does not have a bad influence such as toner scattering and image disturbance when being carried out, and is capable of obtaining a good quality toner image with good toner recovery over a long period of time. Especially.

(Means for Solving Problems) The present invention has the following means configuration in order to achieve the above object. That is, the color image forming apparatus of the present invention forms a color toner image on the image carrier by performing latent image formation and reversal development with color toner a plurality of times to form an image after transferring the color toner image to the transfer body. In order to clean the toner remaining on the surface of the image carrier, a means for contacting and cleaning the surface of the image carrier, and a means for cleaning the image carrier on the upstream side of the means in the moving direction of the image carrier. In a color image forming apparatus, which is rotatably provided in a contact state and has an electric field forming means for forming an electric field with an image carrier by applying a voltage, the electric potential of the electric field forming means is set to a color toner image. Is set to a level between the surface potential of the toner image formed in the first color on the surface of the image carrier and the potential of the non-image portion before the transfer, and the cleaning process is performed to clean the residual toner after the transfer. Is 1
The color image forming apparatus is characterized by having a potential setting unit that sets a potential having a polarity opposite to the polarity of the next charging.

(Operation) The cleaning action of the color image forming apparatus of the present invention will be described below.

The potential on the surface of the image carrier after transfer in the reversal development is the same as the polarity of the primary charging in the non-image area,
The potential is slightly lower than the potential of the secondary charge, and the potential of the image portion to which the toner of the first color is attached is also the same as the polarity of the primary charge, but the absolute value is low. .
For example, if the primary charging is negative charging,
560V, the image part on which the first color toner is attached-
At 100V, the toner is also charged with a negative electric charge. Conversely, if the toner is positively charged, the non-image portion is + 560V and the image portion is +.
At 100V, the toner is also positively charged.

The potential setting means sets the potential of the electric field forming means to a level between the surface potential of the toner image formed in the first color on the surface of the image carrier and the potential of the non-image portion before the transfer of the color toner image. In the cleaning stage of the residual toner after the transfer, the potential is set to the opposite polarity to the polarity of the primary charging.

Therefore, in the above-mentioned numerical example, the electric potential of the electric field forming means before transfer is, for example, −350 V if the primary charging is negative, and is +350 V if the primary charging is positive.
Will be set to the value. The potential of the electric field forming means at the stage of cleaning the residual toner after transfer is set to a value of, for example, + 500V if the primary charging is negative charging, and to a value of −500V if the primary charging is positive charging.

Hereinafter, for convenience of description, a case where the primary charging is the above-mentioned negative charging will be described.

Since the voltage applied to the electric field forming means has the same polarity as that at the time of the primary charging, the toner of the toner image on the image carrier is reversely charged or neutralized and the charges disappear. There is no freedom.

The electric field formed in the gap between the image carrier and the electric field forming means acts to stabilize the toner image on the image carrier.

Before the transfer, the electric potential of the electric field forming means is −350 V as described above, whereas the electric potential of the image portion where the first color toner adheres to the image carrier is −100 V.
Therefore, the toner having a negative charge is subjected to the force of being attracted toward the image carrier.

For this reason, the toner attached to the image portion is less likely to be scattered from the image carrier, and is stably held. On the other hand, the electric potential of the non-image portion is −560 V as described above, which is lower than the electric potential of the electric field forming unit, so that the negatively charged toner floating in the gap or the contact cleaning unit at the upper portion falls. The resulting toner is attracted toward the electric field forming means by the action of the electric field in the gap. Since the electric field forming means is rotatable, another cleaning means (scraper) that comes into contact therewith
The adhered toner is collected by.

In this way, before the transfer, that is, the first color toner image, the second color toner image,
When the toner image of the color passes through the position facing the electric field forming means, the toner scattering from the already formed toner image is suppressed and the toner image is stably maintained, while the toner adheres to the non-image area. Is suppressed.

Next, when the transfer of the toner image is completed and the residual toner on the surface of the image carrier is cleaned, the electric field forming means
Since the electric potential is set to the opposite polarity to the polarity of the primary charging, the toner remaining on the surface of the image carrier is absorbed toward the electric field forming means by the action of the electric field and is dropped by the blade cleaning. The incoming toner is also sucked toward the electric field forming means to prevent toner spilling, and a very good cleaning recovery performance can be obtained.

(Example) Hereinafter, the Example of this invention is described based on drawing. The structure is as shown in FIG.

A bias roller 1 as an electric field forming means is made of a conductor such as stainless steel. 2 is an image carrier, OP
A photosensitive drum using C (Organic Photo Conductor), 3 is a cleaning blade made of polyurethane or the like, 4 is a scraper for scraping off the toner adhering to the bias roller 1, and 5 is a scraper 4 A toner pool in which the taken toner is pooled, and 6 is a screen for moving the toner pooled in the toner pool in one of the directions perpendicular to the paper surface.

Before the transfer of the color toner image, the cleaning blade 3 is retracted, the bias roller 1 is applied with a voltage having the same polarity as the primary charging polarity, and the toner image is stabilized because the toner image is stabilized. There is no scattering and no cleaning operation is performed.

After the transfer, part of the toner remaining on the image carrier 2 is attracted to the bias roller when it reaches a position facing the bias roller 1, and the remaining toner is rotated by the cleaning blade 3 by the rotation of the image carrier. Of the bias roller 1 and the image carrier 2 are directly scraped off by the edge of the cleaning blade 3 that is in contact with the surface of the image carrier 2 and dropped downward to directly fall on the bias roller 1. Due to the electric field formed in the gap, the charged toner is again attracted to the bias roller 1. The toner that has landed on the bias roller 1 and the adsorbed toner are scraped off by the scraper 4 when the bias roller 1 rotates in the direction of the arrow and accumulated in the toner reservoir 5, and are moved to one side by the rotation of the scraper 6. .

In this embodiment, the primary charging is performed with negative polarity,
Reversal development is performed with a polyester resin toner having a diameter of 11 μm which is charged by negative charges. At this time, the potential of the non-image portion when the image carrier 2 passes the position facing the bias roller 1 is −560 V, and the potential of the image portion on which the first color toner is attached is −100 V, so that the transfer is performed. As the bias voltage of the front bias roller 1, -350V, which is approximately the middle of both potentials, is applied, and + 500V after transfer.
Was applied.

This switching of the bias voltage is performed by the cleaning blade 3
A signal for advancing and retreating is added to the potential setting means and is performed in conjunction with the advancing and retreating. That is, −350 V is applied when the image carrier 2 is moving backward and the image carrier 2 is moved forward.
+ 500V is applied when it is in contact with.

Besides, the gap between the bias roller 1 and the image carrier 2 is 0.2 m.
m, the linear velocity of the bias roller 1 and the image carrier 2 were both set to 58 mm / sec.

As a result, "roughness" due to toner scattering in the toner image was completely eliminated, a clear color image free from "fog" and "dirt" was obtained, and very good cleaning recovery performance was obtained.

(Effects of the Invention) As described above, in the color image forming apparatus of the present invention, the bias voltage applied to the electric field forming unit of the cleaning unit forms the first color on the surface of the image carrier before transfer. Since the toner image is set to a level between the surface potential of the toner image and the potential of the non-image portion, the toner is not reversely charged and the charge is not neutralized, and the toner is prevented from being scattered and scattered. The direction of the electric field in the gap between the image carrier and the image carrier is also the direction that presses the toner against the image carrier, so that both actions are combined and the toner image formed on the image carrier is kept stable. In the cleaning step, since the electric potential is set to the polarity opposite to that of the primary charging, the electric field forming means exerts the action of attracting the charged toner, and the toner remaining on the image carrier or Scratch by contact cleaning means Suck well the toner that has been removed and dropped.

As a result, it is possible to obtain a stable and clear high-quality color image free from so-called “fog” and “dirt”, while obtaining a color image forming apparatus having extremely high toner recovery efficiency and very good cleaning recovery performance. The advantage is that

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of a non-contact type bias roller type toner cleaning means of a color image forming apparatus of the present invention, FIG. 2 is a block diagram of a toner collecting means in a conventional color image forming apparatus, and FIG. The toner of the toner image on the image carrier is charged by the reverse polarity potential of the bias roller and is released,
FIG. 6 is a diagram showing a situation in which the toner is attracted to a bias roller or adheres to a latent image portion in the vicinity. 1 ... Bias roller, 2 ... Image carrier, 3 ... Cleaning blade, 4 ... Scraper, 5 ... Toner sump, 6 ... Screw, 7 ... Mylar blade, 8 ...
Foaming roller, 9 ... Magnetic brush roller, 10 ... Potential setting means.

Continuation of the front page (56) References Open 58-115763 (JP, U) Open 56-10655 (JP, U) Open 57-70259 (JP, U)

Claims (1)

[Claims] 1. A color toner image is formed on an image carrier by performing latent image formation and reversal development with color toner a plurality of times.
A means for contacting and cleaning the surface of the image carrier to clean the toner remaining on the surface of the image carrier after transferring the color toner image to the transfer body, and the means for moving the image carrier. Color image forming apparatus having an electric field forming unit that is rotatably provided in an upstream side in the direction without contacting the image carrier and that forms an electric field with the image carrier by applying a voltage. In, the electric potential of the electric field forming means,
Before the transfer of the color toner image, the level is set to a level between the surface potential of the toner image formed for the first color on the surface of the image carrier and the potential of the non-image portion, and the residual toner is cleaned after the transfer. A color image forming apparatus comprising a potential setting means for setting a potential having a polarity opposite to that of primary charging at a stage.