JP2512393B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to improvement of a cleaning unit of an image forming apparatus.

(Prior Art) Conventionally, as an image carrier cleaning means of an image forming apparatus, an edge portion of an elastic body such as polyurethane is brought into contact with the image carrier to scrape off the toner remaining on the surface of the image carrier. While blade cleaning is performed, various means such as a Mylar blade, a urethane type, a chloroprene type, a silicone type foaming roll, and a magnetic brush roll are devised as means for collecting the scraped toner. FIG. 2 shows a side view of these collecting means. However, in all of these toner collecting means, the separated toner is pressed again on the surface of the image carrier to form a film of the toner, or toner leaks to cause deterioration and damage of the image carrier, and Was causing the breakdown of.

Therefore, the inventors have proposed an improvement in which a non-contact type bias roller system as shown in FIG. 1 is adopted, and a bias voltage having a polarity opposite to that of the toner is applied to the bias roller system (Japanese Patent Application No. Sho.
60-262183).

Such a non-contact bias roller toner collecting means to which a voltage having a polarity opposite to the electric charge of the toner is applied has an extremely high collecting efficiency, and an electric field is formed in the gap with the image carrier, so that toner spillage occurs. Was prevented, and a very good cleaning recovery performance was obtained.

(Problems to be Solved by the Invention) However, in this toner collecting means, when the transfer residual toner passes through the bias roller, it is charged with a reverse charge, so that the charge of the toner is destroyed and the original toner is lost. Toner that has a different charge from the charge is generated,
The charge disappears. Then, when the toner is reused, the toner having the opposite charge is generated and mixed one after another, which adversely affects a new development stage.

Further, when the electric charge of the toner disappears and becomes a non-charged state, neither the bias roller nor the image bearing member is attracted to it and it becomes a floating state, and the toner adhering to the image bearing member is also released from the image bearing member. As a result, the toner is scattered as a whole. It is self-evident that the above-mentioned adverse effects and toner scattering in the toner reuse stage will bring about a more remarkable result when an untransferred toner image passes due to a conveyance jam or the like. .

In view of the above-mentioned problems of the conventional technology, an object of the present invention is to eliminate the above-mentioned problems by setting the potential of the bias roller at a midpoint between the potential of the image portion and the potential of the non-image portion of the image carrier. An object is to provide an image forming apparatus including a cleaning unit.

(Means for Solving Problems) In order to achieve the above-mentioned object, the present invention has the following means configuration. That is, the image forming apparatus of the present invention transfers the charging means for charging the image carrier, the developing means for reversing and developing the electrostatic latent image on the image carrier, and the monochromatic toner image developed by the developing means. In order to clean the toner remaining on the surface of the image carrier after being transferred to the material, a cleaning unit that contacts the surface of the image carrier to clean it and collects the cleaned toner, and the image of the cleaning unit. An electric field forming unit that is rotatably provided on the upstream side in the moving direction of the carrier without contacting the image carrier, and that forms an electric field between the image carrier and the image carrier by applying a voltage; In an image forming apparatus having a toner conveying means for returning the toner collected by the cleaning means to the developing means, the charging polarity of the image carrier charged by the charging means and the charging polarity of the monochromatic toner are the same. And the electric field formation An image forming apparatus characterized by having a potential setting means for setting the potential of the stage to approximately intermediate potential between the potential of the potential and the non-image area of the image portion of said image bearing member.

(Operation) The cleaning action of the image forming apparatus of the present invention will be described below. The potential on the surface of the image carrier after the transfer in the reversal development is the same as the polarity of the primary charging in the non-image portion, and is a value slightly lower than the potential during the primary charging. The potential of the image area is still the same as the polarity of the primary charging, but the absolute value is low.

For example, if the primary charge is negative charge, the non-image part is -500 to -400V, the image part is -70 to -20V, and if the positive charge is positive, the non-image part is +500 to + 400V and the image part is -70V. ~ −2
It becomes 0V. Further, the residual adhered toner also has a charge of the same polarity as that of the primary charging.

An electric potential intermediate between these two electric potentials (for example, an electric potential of -250V for negative charging and + 250V for positive charging) is applied to the electric field forming unit by the electric potential setting unit.

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

There is a gap between the electric field forming means and the image carrier, and an electric field is formed in this gap. The direction of this electric field is as follows.

Now, the electric potential of the electric field forming means is −250V as described above, whereas the electric potential of the image portion on the image carrier on which the residual toner adheres is −50V, which is higher than that of the electric field forming means. The direction of the electric field is from the image carrier to the electric field forming means.

Therefore, the toner having a negative charge receives the force of being attracted toward the image carrier.

For this reason, the toner adhering to the image portion is less likely to be scattered from the image bearing member, but rather, the negatively charged toner floating in the gap and the negative charge that has fallen from the contact cleaning means in the upper portion are not scattered. The tinged toner comes to be attracted and attached to the image portion by the action of the electric field. On the other hand, the electric potential of the non-image portion is -500 to -400 V as described above and is lower than the electric potential of the electric field forming means, so that the direction of the electric field is from the electric field forming means to the non-image portion. Therefore, the negatively charged toner floating in the gap or the toner falling from the upper contact cleaning unit is attracted toward the electric field forming unit by the action of the electric field in the gap.

Since the electric field forming means is rotatable, the adhering toner is collected by another cleaning means (scraper) contacting the electric field forming means.

As described above, in the present invention, since the voltage applied to the electric field forming means is the same as the polarity of the electric charge of the toner used for the first development, the toner is charged with the opposite electric charge, or the electric charge is changed. It is not neutralized and disappears.

As a result, the transfer residual toner is cleaned and recovered in a stable state without adverse effects when cleaning and recovering the residual toner and reusing it.

(Examples) Examples of the present invention will be described below.

The structure is as shown in FIG. Reference numeral 1 is a bias roller as an electric field forming means, which is made of a conductor such as stainless steel. The image carrier 2 is an OPC (Organic Photo C
Onductor: photoconductor drum using organic photoconductor, 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 toner scraped by the scraper 4. And 6 is a screen for moving the toner accumulated in the toner reservoir to one side in the direction perpendicular to the paper surface.

After the transfer, the toner remaining on the image carrier 2 reaches the cleaning blade 3 by the rotation of the image carrier 2 and is scraped off by the edge of the cleaning blade 3 contacting the surface of the image carrier 2. In addition to the toner directly falling on the bias roller 1, the charged toner is charged either by the bias roller 1 or the image carrier 2 by the electric field formed in the gap between the bias roller 1 and the image carrier 2. Adsorbed to 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. . On the other hand, the toner held on the image carrier 2 side is scraped off at the cleaning blade 3 by the rotation of the image carrier 2, and the same process as described above is followed.

In this embodiment, the primary charging is performed in the negative polarity, and the reversal phenomenon is performed by the polyester resin toner having a diameter of 11 μm which is charged by the negative charge.

At this time, the potential of the non-image portion is −50 to −400 V and the potential of the image portion is −70 to −20 V when the image carrier 2 passes through the position facing the bias roller 1.
As a bias voltage of
Was applied by the potential setting means, and the gap between the bias roller 1 and the image carrier 2 was 0.2 mm. In addition, the image carrier 2
The linear velocity of the bias roller 1 was set to 58 mm / sec, and the toner adhesion amount for development was set to 1.0 mg / cm ² .

As a result, as compared with the conventional image forming apparatus in which the bias voltage having the polarity opposite to the polarity of the primary charging is applied to the bias roller, the toner scattering is extremely small, and the collected toner is reused for development. Most of the adverse effects have been eliminated.

(Effects of the Invention) As described above, in the image forming apparatus of the present invention, the bias voltage applied to the electric field forming means of the cleaning means is not applied when the image carrier passes a position facing the electric field forming means. Since the electric potential between the electric field forming unit and the non-image unit and the electric field between the electric field forming unit and the image unit are set so as to be substantially in the middle between the electric potential of the image unit and the electric potential of the image unit. However, the electric field strength is almost the same, and the charged toner is sufficiently attracted, while the toner is charged with an electric charge of the opposite polarity or neutralized to become an uncharged state. Never.

As a result, when the toner is reused, the adverse effect at the time of development due to the mixture of the oppositely charged toner is eliminated, and
Since there is no charge, there is an advantage that a floating state that is not attracted to either the electric field forming means or the image carrier, that is, toner scattering is reduced.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of a non-contact type bias roller type toner cleaning unit of an image forming apparatus of the present invention, and FIG. 2 is a block diagram of a toner collecting unit in a conventional image forming apparatus. 1 ... Bias roller, 2 ... Image carrier, 3 ... Cleaning blade, 4 ... Scraper, 5 ...
... Toner pool, 6 ... Screw, 7 ... Mylar blade, 8 ... Foaming roll, 9 ... Magnetic brush roll, 10 ... Potential setting means.

Claims (1)

(57) [Claims] 1. A charging means for charging an image carrier, a developing means for reversal developing an electrostatic latent image on the image carrier, and a monochromatic toner image developed by the developing means after being transferred to a transfer material. Cleaning means for contacting the surface of the image carrier and cleaning the collected toner to clean the toner remaining on the surface of the image carrier, and the moving direction of the image carrier of the cleaning means. And an electric field forming means for forming an electric field between the image carrier and the image carrier by being rotatably provided on the upstream side of the image carrier without contact with the image carrier, and recovered by the cleaning device. An image forming apparatus having a toner conveying unit for returning the toner to the developing unit, the charging polarity of the image carrier charged by the charging unit and the charging polarity of the monochromatic toner are the same, Before the potential of the forming means An image forming apparatus comprising: a potential setting means for setting a potential substantially intermediate between a potential of an image portion and a potential of a non-image portion of an image bearing member.