JP2018159764A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that suppresses a toner from passing through a worn part of a blade.SOLUTION: There is provided an image forming apparatus comprising: an image holding body; a charging device; a developing device; a cleaning device that includes a cleaning blade; a suction device that sucks all or part of a residual toner excluding an external additive isolated from the surface of toner particles on the upstream side in the direction of rotation of the image holding body with respect to the cleaning device; and a fixing device.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image forming apparatus.

  Methods for visualizing image information, such as electrophotography, are currently used in various fields. In electrophotography, an electrostatic charge image is formed as image information on the surface of an image carrier by, for example, charging and electrostatic charge image formation. Then, for example, a toner image is formed on the surface of the image holding member with a developer containing toner, the toner image is transferred to a recording medium, and then the toner image is fixed on the recording medium. Through these steps, the image information is visualized as an image. Then, for example, the image carrier is cleaned by a blade or the like before the toner image is formed again.

  For example, Patent Literature 1 discloses the following technique. Image formation is performed at the image forming portion of the photoreceptor facing the developing roll, and the toner remaining on the photoreceptor after the toner image is transferred to the transfer target is collected by the cleaning member, and the toner is replenished. Immediately before the process, the deteriorated toner in the non-image forming portion, which is the portion of the photoreceptor facing the conveyance roll, is removed by the cleaning member and collected. The collected residual toner is supplied as a collected toner together with unused toner to the developing device, and the charge amount distribution of the toner at the beginning of toner replenishment is set within an appropriate range. At this time, the control unit adjusts the supply amounts of the collected toner and the unused toner so that both are adjusted to the amount necessary for development.

  Patent Document 2 states that “a cleaning unit that removes and collects toner from the surface of the image carrier after the toner image is transferred to the transfer target by a transfer unit, and a developing unit that is unused. An image forming apparatus including a toner replenishing unit that replenishes toner and a recovered toner supply unit that supplies the toner collected by the cleaner to the developing unit and supplies more toner as the toner consumption in the developing unit increases is disclosed. ing.

  Further, Patent Document 3 states that “in the image forming method for cleaning the developer remaining on the image carrier, the image carrier contains a resin having a crosslinked structure on its surface, An image forming method is disclosed in which the developer contains a carrier, and the developer that has been collected after transfer is supplied to the developing means and reused.

JP 2010-224039 A JP 2010-170113 A JP 2004-109739 A

By the way, it contains toner particles having a volume average particle diameter of 3 μm or more and 5 μm or less and an external additive having a number average particle diameter of 70 nm or more and 200 nm or less, and a BET specific surface area A is 2.3 m ² / g or more and 4.0 m ² / g or less. A toner containing a toner containing a developer and a carrier containing a carrier having a volume average particle size of 20 μm or more and 35 μm or less; and an electrostatic latent image formed on the image carrier holding the developer on the surface thereof. In an image forming apparatus including a developing device having a developer holding body for developing as a low image density is repeatedly formed, toner consumption is reduced. Opportunities for repeated thermal loads are increased. Therefore, the toner of the developer stored in the storage unit of the developing device is likely to deteriorate.

  Accordingly, the problem of the present invention is that the BET specific surface area B of the developer toner accommodated in the developing device after outputting 1,000 images with an image density of 1% on A4 paper is less than 0.8 × BET specific surface area A. It is an object of the present invention to provide an image forming apparatus that suppresses “degradation of the toner of the developer contained in the developing device housing” that occurs when a low image density is repeatedly formed.

  The above problem is solved by the following means.

The invention according to claim 1
A developing device having an image carrier, a housing portion that contains a developer, and a developer carrier that holds the developer on the surface and develops an electrostatic latent image formed on the image carrier as a toner image. The developer includes toner particles having a volume average particle diameter of 3 μm or more and 5 μm or less and an external additive having a number average particle diameter of 70 nm or more and 200 nm or less, and a BET specific surface area A of 2.3 m ² / g or more. An image forming unit having a toner of 0 m ² / g or less and a developing device that is a developer containing a carrier having a volume average particle diameter of 20 μm or more and 35 μm or less;
A transfer device for transferring a toner image formed on an image carrier of the image forming unit to a recording medium;
With
The BET specific surface area B of the developer toner accommodated in the developing device after outputting 1,000 images with an image density of 1% on A4 paper as the recording medium is 0.8 × the BET specific surface area A or more. An image forming apparatus.

The invention according to claim 2
Replenishment including toner particles having a volume average particle size of 3 μm to 5 μm and external additives having a number average particle size of 70 nm to 200 nm and a BET specific surface area A of 2.3 m ² / g to 4.0 m ² / g A toner replenishing device having a housing portion that contains toner, and replenishing the replenishing toner to the housing portion of the developing device;
A recovery unit that is provided opposite to the developer holding body at a position downstream of the rotation direction of the developer holding body from a position facing the image holding body and that collects the toner of the developer held on the developer holding body. A toner recovery and supply device that has a member and supplies the toner recovered by the recovery member to a storage portion of the toner supply device;
A control device that controls the toner recovery and supply device when the toner image having a predetermined image density or less is formed on the image holding member, and recovers the toner of the developer held on the developer holding member;
The image forming apparatus according to claim 1, further comprising:

The invention according to claim 3
Replenishment including toner particles having a volume average particle size of 3 μm to 5 μm and external additives having a number average particle size of 70 nm to 200 nm and a BET specific surface area A of 2.3 m ² / g to 4.0 m ² / g A toner replenishing device having a housing portion that contains toner, and replenishing the replenishing toner to the housing portion of the developing device;
A cleaning device for cleaning residual toner on the surface of the image carrier;
A toner supply device that supplies residual toner cleaned by the cleaning device to a storage portion of the toner supply device;
A control device for controlling the image forming unit to form a toner image in a non-image forming area of the image carrier when forming a toner image having a predetermined image density or less on the image carrier;
The image forming apparatus according to claim 1, further comprising:

The invention according to claim 4
The image forming apparatus according to claim 2, wherein the toner image having a predetermined image density or less is a toner image having an image density of 5% or less.

The invention according to claim 5
The image forming apparatus according to claim 1, wherein a BET specific surface area B of the toner of the developer is 0.9 × the BET specific surface area A or more.

The invention according to claim 6
The image forming apparatus according to claim 1, wherein a volume average particle diameter of the carrier is 25 μm or more and 33 μm or less.

The invention according to claim 7 provides:
The image forming apparatus according to claim 1, wherein the number average particle diameter of the external additive is 80 nm or more and 180 nm or less.

According to the first aspect of the present invention, the BET specific surface area B of the developer contained in the developing device after outputting 1,000 images with an image density of 1% on A4 paper is 0.8 × BET specific surface area. An image forming apparatus is provided that suppresses “degradation of the toner of the developer stored in the storage unit of the developing device” that occurs when a low image density is repeatedly formed as compared with an image forming apparatus that is less than A.
According to the invention according to the second or fourth aspect, a belt-like toner image is formed other than during image formation, the belt-like toner image is collected by the cleaning device, and the collected toner is stored in the housing portion of the developing device. Image forming apparatus that suppresses “degradation of toner in developer contained in developing device housing”, which occurs when low image density is repeatedly formed, while suppressing toner consumption, as compared with an image forming apparatus of a direct supply type Is provided.
According to the third or fourth aspect of the present invention, a belt-like toner image is formed other than during image formation, and after the belt-like toner image is collected by the cleaning device, the collected toner is directly supplied to the housing portion of the developing device. An image forming apparatus is provided that suppresses “degradation of toner in a developer contained in a developing device housing portion” that occurs when a low image density is repeatedly formed, while suppressing toner consumption, as compared with a conventional image forming apparatus. The
According to the fifth aspect of the present invention, the BET specific surface area B of the developer contained in the developing device after outputting 1,000 images with an image density of 1% on A4 paper is 0.9 × BET specific surface area. An image forming apparatus is provided that suppresses “degradation of the toner of the developer stored in the storage unit of the developing device” that occurs when a low image density is repeatedly formed as compared with an image forming apparatus that is less than A.
According to the sixth aspect of the present invention, the BET specific surface area B of the developer contained in the developing device after outputting 1,000 images with an image density of 1% on A4 paper is 0.8 × BET specific surface area. Even when a carrier having a volume average particle diameter of 25 μm or more and 33 μm or less is applied as compared with an image forming apparatus of less than A, it occurs when a low image density is formed repeatedly. An image forming apparatus that suppresses “deterioration of toner” is provided.
According to the seventh aspect of the present invention, the BET specific surface area B of the developer contained in the developing device after outputting 1,000 images with an image density of 1% on A4 paper is 0.8 × BET specific surface area. Compared with an image forming apparatus of less than A, even when an external additive having a number average particle diameter of 80 nm or more and 180 nm or less is applied, the “development accommodated in the accommodating portion of the developing apparatus” occurs when a low image density is repeatedly formed. An image forming apparatus that suppresses deterioration of the toner of the agent is provided.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to an exemplary embodiment. 1 is a partially enlarged schematic configuration diagram illustrating an example of an image forming apparatus according to an exemplary embodiment. FIG. 3 is a block diagram illustrating an example of a control system in the image forming apparatus according to the present embodiment. 10 is a flowchart illustrating an example of a processing procedure of “toner recovery processing”. 10 is a flowchart illustrating another example of the processing procedure of “toner image forming processing on a non-image forming region of a photoreceptor”. It is a schematic diagram for demonstrating the non-image formation area of an image holding body. Image to be formed when measuring BET specific surface area B of developer toner

  Hereinafter, an embodiment which is an example of the present invention will be described in detail.

  An image forming apparatus according to the present embodiment includes an image forming unit having an image holding member and a developing device, and a transfer device that transfers a toner image formed on the image holding member of the image forming unit to a recording medium.

The developing device includes a storage unit that stores a developer, and a developer holding body that holds the developer on the surface and develops an electrostatic latent image formed on the image holding body as a toner image. The developer includes toner particles having a volume average particle size of 3 μm to 5 μm and an external additive having a number average particle size of 80 nm to 200 nm, and a BET specific surface area A of 2.3 m ² / g to 4.0 m ² /. g or less toner and a carrier having a volume average particle diameter of 20 μm or more and 35 μm or less.

In the image forming apparatus according to the present embodiment, the BET specific surface area B of the developer toner accommodated in the developing device after outputting 1,000 images with an image density of 1% on A4 paper as a recording medium is 0. 8 × BET specific surface area A or more. That is, the BET specific surface area B of the developer toner satisfies the formula: BET specific surface area B ≧ 0.8 × BET specific surface area A. Specifically, the BET specific surface area B of the developer toner is 0.8 × 2.3 m ² / g or more and 0.8 × 4.0 m ² / g or more.

  Here, in recent years, with respect to a developer used in an electrophotographic image forming apparatus, toner particles and carriers have been reduced in diameter in order to realize a high-definition image. On the other hand, the toner particles having a reduced diameter have a high adhesive force and tend to have low fluidity and transferability from an image carrier or the like. For this reason, external additives having a large diameter tend to be applied for the purpose of exerting a buffer function (spacer function) between toner particles or between toner particles and an image carrier.

From these points, toner particles having a volume average particle diameter of 3 μm or more and 5 μm or less and external additives having a number average particle diameter of 80 nm or more and 200 nm or less are included, and a BET specific surface area A is 2.3 m ² / g or more and 4.0 m. A developer containing ² / g or less of toner and a carrier having a volume average particle diameter of 20 μm or more and 35 μm or less is suitable for forming a high-definition image while ensuring transferability.

  However, when the diameter of the toner particles is reduced, the amount of toner consumption is reduced, and it is difficult for toner to be replaced in the housing portion of the developing device. Then, the time during which the same toner stays in the developing device becomes longer, and the tendency that the same toner continues to be mechanically and thermally loaded increases. In particular, when an image having a low image density (for example, an image having an image density of 5% or less) is repeatedly formed, the amount of toner consumption is further reduced, and the tendency for the same toner to continue to be subjected to mechanical and thermal loads increases. Therefore, the external additive is embedded in the toner particles due to mechanical and thermal loads, and the toner is likely to deteriorate.

  In addition, when the diameter of the toner particles is reduced, the amount of the external additive per unit area of the toner particles tends to increase. For this reason, the external load is embedded in the toner particles due to the mechanical load, and the tendency for the toner to deteriorate further increases.

  Specifically, in the developing device, the developer stored in the storage unit is held on the surface of the developer holding body from the storage unit while being stirred by the stirring and conveying member in the storage unit, and returns to the storage unit again. Circulate. At that time, the developer is given a regulating force by the layer regulating member that regulates the thickness of the developer layer held on the surface of the developer holding body, together with the stirring force by the stirring and conveying member. When the same developer stays in the developing device, a mechanical load due to the stirring force and the regulating force is repeatedly applied. As a result, toner deterioration tends to proceed.

Therefore, in the image forming apparatus according to the present embodiment, this image is formed with the BET specific surface area B of the developer toner contained in the developing device after outputting 1,000 images with an image density of 1% on A4 paper. The BET specific surface area is 80% or more of the BET specific surface area A of the developer toner accommodated in the previous developing device. That is, even after 1000 images with an image density of 1% are output on A4 paper, the external additive is difficult to be embedded in the toner particles, and fluctuations in the adhesion state of the external additive of the toner particles are reduced.
Therefore, in the image forming apparatus according to the present embodiment, “deterioration of the toner of the developer accommodated in the accommodating portion of the developing device” that occurs when the low image density is repeatedly formed is suppressed.

In the image forming apparatus according to the present exemplary embodiment, from the viewpoint of suppressing toner deterioration, the BET specific surface area B of the developer toner is preferably 0.9 × BET specific surface area A or more. That is, the BET specific surface area B of the toner of the developer preferably satisfies the formula: BET specific surface area B ≧ 0.9 × BET specific surface area A. Specifically, the BET specific surface area B of the developer toner is preferably 0.9 × 2.3 m ² / g or more and 0.9 × 4.0 m ² / g or more.

The BET specific surface areas A and B of the toner of the developer are the BET specific surface areas of the toner in the following state.
A developer containing new toner (unused toner) and a carrier is filled in a housing portion of the developing device of the image forming apparatus. A toner cartridge (an example of a storage unit of a toner replenishing device) containing the same new toner is loaded into the image forming apparatus. The BET specific surface area of this new toner is measured and set as the BET specific surface area A of the toner.
In this state, in a normal temperature and normal humidity environment (temperature of 25 ° C. and humidity of 55% RH), the amount of applied toner is 4 g / m ^{2 with} the pattern (one linear image pattern) shown in FIG. Output 1000 images of 1% density on A4 paper.
Here, when the image forming apparatus has a plurality of image forming units (for example, a tandem image forming apparatus), this image formation is targeted for image formation by one image forming unit. Further, when the image forming unit includes a plurality of developing devices (for example, in the case of an image forming unit including a rotary type developing device), image formation by one developing device is a target.
The image density is an area ratio of an image to be formed to the area of the surface (image forming surface) of a sheet (an example of a recording medium). Moreover, the arrow in FIG. 7 shows the paper feed direction of A4 paper.
Then, the BET specific surface area of the toner existing in the housing portion of the developing device after the image formation is measured and set as the BET specific surface area B of the toner.

  The BET specific surface area of the toner is determined by a nitrogen substitution method. Specifically, it is measured by a three-point method using an SA3100 specific surface area measuring device (manufactured by Beckman Coulter, Inc.).

In the image forming apparatus according to the present embodiment, examples of the aspect satisfying the relationship between the BET specific surface areas A and B of the toner of the developer include the following aspects.
Hereinafter, the toner to be supplied to the storage unit of the developing device is also referred to as “replenished toner”, and the toner recovered by the recovery member and the toner cleaned by the cleaning device are both referred to as “recovered toner”. As will be described later, the replenished toner may include a collected toner in a new toner (unused toner).

-Aspect (1)-
In the image forming apparatus according to the present embodiment,
Replenishment including toner particles having a volume average particle diameter of 3 μm to 5 μm and external additives having a number average particle diameter of 80 nm to 200 nm and a BET specific surface area A of 2.3 m ² / g to 4.0 m ² / g A toner replenishing device having a housing portion containing toner, and replenishing toner to the housing portion of the developing device;
A recovery member that is provided opposite to the developer holder on the downstream side in the rotation direction of the developer holder from a position facing the image holder and that collects the toner of the developer held on the developer holder; A toner recovery and supply device for supplying the toner recovered by the recovery member to the storage portion of the toner supply device;
A control device for controlling the toner collection and supply device when the toner image having a predetermined image density or less is formed on the image holding member, and collecting the toner of the developer held on the developer holding member;
The aspect which further comprises.

In the image forming apparatus according to the aspect (1), when a toner image having a predetermined image density or less is formed on the image holding member, the toner of the developer held on the developer holding member is collected, and the collected toner is supplied to the toner replenishing device. Supplied to the storage section. The collected toner is not directly returned to the housing portion of the developing device, but is once supplied to the housing portion of the toner replenishing device, so that it mixes with the replenishing toner in the housing portion of the toner replenishing device. In this state, the replenishment toner is replenished to the housing portion of the developing device. That is, the collected toner is supplied again to the housing portion of the developing device while being diluted with the supply toner.
These operations reduce the chance that the same toner is repeatedly subjected to mechanical and thermal loads in the developing device, and suppresses toner deterioration, compared to a method in which the collected toner is directly supplied to the housing of the developing device. The
In addition, the toner consumption is also reduced as compared with a method of forming a belt-like toner image other than during image formation.

-Aspect (2)-
In the image forming apparatus according to the present embodiment,
Replenishment including toner particles having a volume average particle diameter of 3 μm to 5 μm and external additives having a number average particle diameter of 80 nm to 200 nm and a BET specific surface area A of 2.3 m ² / g to 4.0 m ² / g A toner replenishing device having a housing portion containing toner, and replenishing toner to the housing portion of the developing device;
A cleaning device for cleaning residual toner on the surface of the image carrier;
A toner supply device that supplies residual toner cleaned by the cleaning device to a storage portion of the toner supply device;
A control device that controls the image forming unit to form a toner image in a non-image forming region of the image carrier when forming a toner image having a predetermined image density or less on the image carrier;
The aspect which further comprises.

Here, the “non-image forming area of the image carrier” refers to transferring the toner image formed on the image carrier among the image formable regions of the image carrier to a recording medium (hereinafter also referred to as “paper”). The area corresponding to the area through which the recording medium does not pass (non-passing area), depending on the size (size) of the recording medium and the paper feeding direction when the toner image is transferred to the recording medium, An area where a toner image is not formed is shown (see FIG. 6).
Specifically, for example, when outputting an image on A4 paper, the “non-image forming area of the image carrier” refers to an image on the entire surface of the A4 paper to be output from the image formable area of the image carrier. This is the area excluding the area that can be output.
Note that the “image formable area of the image carrier” may be the same area where an image can be formed on the entire surface of the largest sheet (for example, A3 sheet) on which an image is to be output in any paper feed direction. However, it may be a large area.

The code | symbol in FIG. 6 shows the following member or area | region.
PR: image carrier MIA: image formable area of the image carrier A4L1: 4A paper feed direction is “transverse feed direction (long side of paper intersects the paper transport direction (eg vertical) Area ”where the image can be formed on the entire surface of the 4A paper. A4L2: The paper feed direction of the 4A paper is the“ lateral feed direction (the direction in which the long side of the paper intersects the paper transport direction (eg, perpendicular) ”. ) ”, The area in which no image is formed on the 4A paper. The paper feed direction of the A4S1: 4A paper is“ vertical feed direction (a direction in which the short side of the paper intersects (for example, perpendicular) to the paper transport direction) ”. Area where an image can be formed on the entire surface of 4A paper. A4S2: When the paper feed direction of 4A paper is “vertical feed direction (a direction in which the short side of the paper intersects (for example, perpendicular) to the paper transport direction)” Area where no image is formed on 4A paper

In the image forming apparatus of aspect (2), when a toner image having a predetermined image density or less is formed on the image carrier, the toner image is formed in a non-image forming region of the image carrier. Thereafter, the toner image formed in the non-image forming region of the image carrier is cleaned by a cleaning device without being transferred from the image carrier. The cleaned collected toner is supplied to the storage unit of the toner replenishing device. The collected toner is not directly returned to the housing portion of the developing device, but is once supplied to the housing portion of the toner replenishing device, so that it mixes with the replenishing toner in the housing portion of the toner replenishing device. In this state, the replenishment toner is replenished to the housing portion of the developing device. That is, the collected toner is supplied again to the housing portion of the developing device while being diluted with the supply toner.
These operations reduce the chance that the same toner is repeatedly subjected to mechanical and thermal loads in the developing device, and suppresses toner deterioration, compared to a method in which the collected toner is directly supplied to the housing of the developing device. The
In addition, the toner consumption is also reduced as compared with a method of forming a belt-like toner image other than during image formation.

An image forming apparatus according to the present embodiment includes a tandem apparatus including a plurality of image forming units; an apparatus including a rotary image forming unit having a plurality of developing devices; and formed on the surface of an image carrier of the image forming unit. Direct transfer type device that directly transfers a toner image to a recording medium; the toner image formed on the surface of the image carrier of the image forming unit is primarily transferred to the surface of the intermediate transfer member and then transferred to the surface of the intermediate transfer member An intermediate transfer type apparatus that secondarily transfers a toner image onto the surface of a recording medium; a known apparatus such as an apparatus equipped with a charge removal device that discharges the surface of an image holding member with a discharge light before charging after the toner image is transferred. An image forming apparatus is applied.
In the case of an intermediate transfer type device, the transfer device includes, for example, an intermediate transfer body on which a toner image is transferred to the surface, and a primary transfer that primarily transfers the toner image formed on the surface of the image holding body to the surface of the intermediate transfer body. A configuration including an apparatus and a secondary transfer apparatus that secondary-transfers the toner image transferred onto the surface of the intermediate transfer member onto the surface of the recording medium is applied.
In the case of the intermediate transfer system including a plurality of image forming units, the transfer device includes a plurality of primary transfer devices that transfer the toner images formed on the image holding members of the plurality of image forming devices to the intermediate transfer member. Have.

  In the image forming apparatus according to the present embodiment, for example, the part including at least the image holding member may have a cartridge structure (process cartridge) that is detachable from the image forming apparatus.

  Hereinafter, an example of the image forming apparatus according to the present embodiment will be described, but the present invention is not limited thereto. In addition, the main part shown to a figure is demonstrated and the description is abbreviate | omitted about others.

<Overall configuration of image forming apparatus>
FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus according to the present embodiment.
An image forming apparatus 300 illustrated in FIG. 1 includes, for example, a rectangular parallelepiped housing 200. A paper tray 204 on which recording paper P is accumulated is loaded on the lower side of the housing 200, and a drawing roll 92 is provided on one end side of the rotating arm corresponding to the loading position of the paper tray 204. . On the other end side of the arm, a roll 94 disposed coaxially with the center of rotation of the arm and a roll 96 disposed corresponding to the roll 94 are provided.

  In forming an image, the drawing roll 92 is moved downward and rotated while the drawing roll 92 is in contact with the uppermost recording paper P, and the recording paper P is drawn out. The drawn recording paper P is guided to the rolls 94 and 96 and is conveyed while being sandwiched between the roll pair 82 arranged on the downstream side of the roll 96 in the paper conveyance direction. Further, on the downstream side of the roll pair 82 in the conveyance direction, a roll 84 and a roll 86 that are arranged to face each other, a roll 88 that changes the conveyance direction of the recording paper P by 90 °, and a roll pair 90 are sequentially arranged.

The image forming apparatus 300 includes the photoconductor 10 (an example of an image holding body) on the upper side in the housing 200.
The photosensitive member 10 (an example of an image holding member) has an image holding surface having a photoconductive layer (photosensitive layer) made of a photosensitive material on a peripheral surface, and rotates in a clockwise direction. A charging device 20 is provided above the photoconductor 10. The charging device 20 includes a charging roll 21 that is provided to face the photoconductor 10 and negatively charges the surface of the photoconductor 10. An exposure device 30 is provided adjacent to the charging device 20 to form an image-like electrostatic charge image to be formed with toner contained in the developer on the surface of the photoreceptor 10 charged by the charging device 20. ing. Further, adjacent to the exposure device 30, a developing device 40 is provided that forms a toner image on the surface of the photoreceptor 10 by attaching toner to the electrostatic image formed by the exposure device 30. A transfer device 50 is provided adjacent to the developing device 40. The transfer device 50 includes a transfer roll 52 that is provided to face the photoconductor 10 and transfers a toner image to the recording paper P. In addition, a neutralization device 60 is provided adjacent to the transfer device 50 for facilitating the removal of the toner remaining on the surface by neutralizing the surface of the photoconductor 10 after the toner image is transferred to the transfer roll 52 as necessary. It has been. Further, a cleaning device 70 is provided adjacent to the charge removal device 60 to clean the surface of the photoconductor 10 and remove residual toner.

  The image forming apparatus 300 is provided with a toner cartridge 46 for storing supply toner and a toner supply path 47. Then, toner is supplied from the toner cartridge 46 to the developing device 40 through the toner supply path 47.

Here, when the image forming apparatus 300 is viewed from the front, the charging device 20, the exposure device 30, the developing device 40, the transfer device 50, the charge removal device 60, and the cleaning device 70 are arranged on the photoconductor 10 in the clockwise direction. Are arranged sequentially.
A unit including the photoconductor 10, the charging device 20, the exposure device 30, the developing device 40, the charge eliminating device 60, and the cleaning device 70 corresponds to an example of an image forming unit.
A unit having a toner cartridge 46 (an example of a toner supply device) and a toner supply path 47 corresponds to an example of a toner supply device.

  In the image forming apparatus 300, the recording paper P conveyed to the transfer roll 52 provided facing the photoconductor 10 is pressed against the photoconductor 10 at the nip portion between the photoconductor 10 and the transfer roll 52, and the photoconductor. The toner image formed on the outer peripheral surface 10 is transferred.

  On the downstream side of the transfer roll 52 in the sheet conveyance direction, a fixing device 100 including a fixing roll 101 and a roll 102 arranged to face each other, and a cam 104 are sequentially arranged. The recording paper P onto which the toner image has been transferred is sandwiched between the fixing roll 101 and the roll 102 to fix the toner image, and reaches the portion where the cam 104 is disposed. The cam 104 is rotationally driven by a motor (not shown), and is fixed at a position indicated by a solid line or a position indicated by an imaginary line in FIG.

  When the recording paper P arrives from the fixing roll 101 side, the cam 104 is rotationally driven to the opposite side (position indicated by the solid line) of the fixing roll 101. As a result, the recording paper P coming from the fixing roll 101 side is guided to the roll pair 106 along the outer peripheral surface of the cam 104. At this time, roll pairs 106, 108, 112, and 114 are sequentially arranged on the downstream side of the guide direction of the recording paper P by the cam 104, and the paper receiver 202 is arranged on the downstream side of the roll pair 114 in the paper conveyance direction. Has been placed.

  Accordingly, the recording paper P coming from the fixing roll 101 side is sandwiched between the roll pairs 106 and 108, and the recording paper P is conveyed to the paper receiver 202 when the roll pairs 106 and 108 rotate continuously.

When the surface on which the image of the recording paper P once sandwiched between the roll pairs 106 and 108 is reversed to the reverse side of the surface on which the image is recorded, the cam 104 is positioned on the fixing roll 101 side (imaginary line). (Position indicated by). In this state, the rotation direction of the roll pairs 106 and 108 is reversed, so that the conveyance direction of the recording paper P is reversed in the reverse conveyance (hereinafter referred to as “switchback”) method, and the roll pairs 106 and 108 side. When the recording paper P is conveyed from the cam 104 toward the cam 104, the recording paper P is guided downward along the outer peripheral surface of the cam 104. At this time, the roll pair 120 is disposed on the downstream side in the conveyance direction of the recording paper P by the cam 104, and the recording paper P that has reached the portion where the roll pair 120 is disposed is given a conveyance force by the roll pair 120. Is further conveyed.
In FIG. 1, the conveyance path of the recording paper P is indicated by an imaginary line.

  Roll pairs 122, 124, 126, 128, 130, and 132 are sequentially arranged along the conveyance path of the recording paper P indicated by an imaginary line in FIG. These roll pairs constitute a recording paper reversing unit 220 together with the cam 104 and the roll pairs 106, 108 and 120 described above. The recording paper P switched back at the location where the roll pairs 106 and 108 are arranged is conveyed along the conveyance path indicated by an imaginary line in FIG. It is conveyed to the nip portion with the roll 52.

  At this time, the recording paper P is switched back by the recording paper reversing unit 220 as described above, so that the back surface of the surface on which the image has been recorded is reversed so that it faces the photoreceptor 10 side. When the toner image is transferred to the fixing roller 101 and fixed on the fixing roll 101, the image is recorded on both sides. The recording sheet P on which images are recorded on both sides is discharged to the sheet receiver 202 in a direction in which the side on which the images are recorded is turned to the back. In addition, when no image is recorded on the recording paper P in the subsequent image recording (image recording after the recording paper P is reversed by the recording paper reversing unit 220), the image is recorded on the recording paper P first. The sheet is discharged to the sheet receiver 202 with the front side facing up.

  Examples of the recording paper P onto which the toner image is transferred include plain paper used in electrophotographic copying machines, printers, and the like. In addition to plain paper, OHP sheets and the like are also included. As the recording paper P, for example, a coated paper in which the surface of plain paper is coated with a resin or the like, art paper for printing, and the like are preferably used.

<Developing device 40 and its peripheral devices>
Next, the developing device 40 and its peripheral devices will be described in detail with reference to FIG.
The developing device 40 is disposed to face the photoconductor 10 in the developing region, and has a developing container 41 (an example of a developing device housing portion) that houses a developer containing toner and a carrier.

The developing container 41 includes a developing container main body 41A and a developing container cover 41B that closes the upper end thereof.
The developing container main body 41A has a developing roll chamber 42A for accommodating the developing roll 42 inside thereof, adjacent to the developing roll chamber 42A, and adjacent to the first stirring chamber 43A and the first stirring chamber 43A. And a stirring chamber 44A. Further, a layer thickness regulating member 45 for regulating the layer thickness of the developer on the surface of the developing roll 42 when the developing container cover 41B is attached to the developing container main body 41A is provided in the developing roll chamber 42A. .

  The first stirring chamber 43A and the second stirring chamber 44A are partitioned by a partition wall 41C. Although not shown, the first stirring chamber 43A and the second stirring chamber 44A are arranged in the longitudinal direction of the partition wall 41C (the length of the developing device). Direction) Openings are provided at both ends, and the first stirring chamber 43A and the second stirring chamber 44A constitute a circulation stirring chamber (43A + 44A).

  In the developing roll chamber 42A, a developing roll 42 (an example of a developer holding body) is disposed so as to face the photoconductor 10. Although not shown, the developing roll 42 is provided with a sleeve outside a magnetic roll (fixed magnet) having magnetism. The developer in the first stirring chamber 43A is adsorbed on the surface of the developing roll 42 by the magnetic force of the magnetic roll and is transported to the developing area. Further, the developing roller 42 has a roll shaft supported rotatably on the developing container main body 41A. Here, the developing roll 42 and the photoconductor 10 rotate in the same direction, and the developer adsorbed on the surface of the developing roll 42 at the opposite portion is developed from the direction opposite to the traveling direction of the photoconductor 10. To be transported.

  A bias power source (not shown) is connected to the sleeve of the developing roll 42 so that a developing bias is applied (in this embodiment, a direct current component (AC) is applied so that an alternating electric field is applied to the developing region. A bias with an alternating current component (DC) superimposed thereon is applied).

In the first stirring chamber 43A and the second stirring chamber 44A, a first stirring member 43 (stirring / conveying member) and a second stirring member 44 (stirring / conveying member) that convey the developer while stirring are disposed. The first stirring member 43 includes a first rotating shaft that extends in the axial direction of the developing roll 42, and an agitating / conveying blade (protrusion) that is helically fixed to the outer periphery of the rotating shaft. Similarly, the second agitating member 44 includes a second rotating shaft and an agitating / conveying blade (protrusion). The stirring member is rotatably supported by the developing container main body 41A.
The first stirring member 43 and the second stirring member 44 are formed so as to be rotationally driven together with the developing roll 42 by a developing motor (not shown). The first stirring member 43 and the second stirring member 44 are arranged such that the developer in the first stirring chamber 43A and the second stirring chamber 44A is conveyed in opposite directions by rotation thereof.

  To the developing device 40, toner is supplied from the toner cartridge 46 through the toner supply path 47. Specifically, the toner replenishment path 47 is provided with a conveyance member (not shown) configured by conveyance blades (protrusions) that are spirally fixed to the outer periphery of the rotation shaft. In addition, a toner replenishing motor (not shown) that rotates the rotation shaft of the conveying member is provided. When the toner replenishing motor operates, the replenishing toner in the toner cartridge 46 is conveyed to the second stirring chamber 44A. That is, the replenishment toner is replenished from the toner cartridge 46 to the developing container 41 of the developing device 40.

On the other hand, a toner collection and supply device 55 is provided inside the developing device 40.
The toner collecting / supplying device 55 is opposed to the developing roller 42 on the downstream side in the rotation direction of the developing roller 42 with respect to the housing 58 and the position facing the photoconductor 10, and the collecting roller 56 (an example of a collecting member of the toner replenishing device). ) Is provided. The collection roll 56 collects the developer toner held on the development roll 42.
The collection roll 56 is composed of, for example, a metal roll, a metal roll having a resistance adjustment layer formed on the surface, and the like. For example, by applying a voltage opposite to the charging polarity of the toner from a power supply (not shown) to the collection roll 56, the developer toner held on the development roll 42 is electrostatically transferred to the surface of the collection roll 56. Let By this operation, the collection roll 56 collects the developer toner held on the development roll 42.

  A removal member 57 that removes the collected toner that has moved to the surface of the collecting roll 56 is provided on the downstream side in the rotational direction of the collecting roll 56 from a position facing the developing roll 42. The removal member 57 is configured by a blade, a brush, or the like.

  The collected toner removed by the removal member 57 is accommodated in the housing 58. One end of a toner supply path 59 for conveying the collected toner removed by the removing member 57 to the toner cartridge 46 is connected to the bottom of the housing 58. The other end of the toner supply path 59 is connected to the toner cartridge 46. The toner supply path 59 is shared on the cleaning blade 72 side with the toner supply path 74 for conveying the toner removed by the cleaning blade 72 to the developing device 40.

The collected toner removed by the removing member 57 and accommodated in the housing 58 is supplied to the toner cartridge 46 through the toner supply path 59.
Specifically, the toner supply path 59 is provided with a transport member (not shown) configured by transport blades (protrusions) that are spirally fixed to the outer periphery of the rotation shaft. Further, a toner supply motor (not shown) that rotates the rotation shaft of the conveying member is provided. When the toner supply motor operates, the collected toner accommodated in the housing 58 is conveyed to the toner cartridge 46. That is, the collected toner is supplied to the toner cartridge 46.
The collected toner supplied to the toner cartridge 46 is stirred together with the replenishment toner contained in the toner cartridge 46 and reused.

  Here, a unit having the collection roll 56, the removing member 57, the toner supply path 59, a conveying member (not shown), and a toner supply motor (not shown) corresponds to an example of the toner collection and supply device.

<Cleaning device 70 and its peripheral devices>
Next, the cleaning device 70 and its peripheral devices will be described in detail with reference to FIG.
The cleaning device 70 includes a housing 71 and a cleaning blade 72 provided so as to protrude from the housing 71. The cleaning blade 72 is a plate that extends to the rotation axis of the photoconductor 10, and is neutralized by the static eliminator 60 on the downstream side in the rotation direction (clockwise direction) from the transfer position of the photoconductor 10 by the transfer roll 52. A tip end portion (hereinafter referred to as an edge portion) is provided so as to be in pressure contact with the downstream side in the rotation direction.

  The cleaning blade 72 blocks the toner remaining on the surface of the photoconductor 10 without being transferred onto the recording paper P by the photoconductor 10 rotating in the clockwise direction, and removes the toner from the photoconductor 10.

  On the other hand, one end of a toner supply path 74 for conveying the collected toner removed by the cleaning blade 72 to the developing device 40 is connected to the bottom of the housing 71 of the cleaning device 70. The other end of the toner supply path 74 is connected to the toner cartridge 46.

The collected toner removed by the cleaning blade 72 and accommodated in the housing 71 is supplied to the toner cartridge 46 through the toner supply path 74.
Specifically, the toner supply path 74 is provided with a transport member (not shown) configured by transport blades (protrusions) that are spirally fixed to the outer periphery of the rotation shaft. Further, a toner supply motor (not shown) that rotates the rotation shaft of the conveying member is provided. When the toner supply motor operates, the collected toner accommodated in the casing 71 is conveyed to the toner cartridge 46. That is, the collected toner is supplied to the toner cartridge 46.
The collected toner supplied to the toner cartridge 46 is stirred together with the replenishment toner contained in the toner cartridge 46 and reused.

  Here, a unit having a toner supply path 74, a conveying member (not shown), and a toner supply motor (not shown) corresponds to an example of a toner supply device.

<Control system>
Next, an example of the configuration of the control system of the image forming apparatus 300 will be described with reference to FIG.
The image forming apparatus 300 includes a control device 400 that controls the operation of each device (each unit).
The control device 400 is configured as a computer that controls the entire device and performs various calculations. Specifically, as shown in FIG. 3, the control device 400 is a CPU (Central Processing Unit) 400A, a ROM (Read Only Memory) 400B that stores various programs, and is used as a work area when executing the programs. A random access memory (RAM) 400C, a nonvolatile memory 400D for storing various information, and an input / output interface (I / O) 400E. Each of CPU 400A, ROM 400B, RAM 400C, nonvolatile memory 400D, and I / O 400E is connected via a bus 400F.

  In addition to the control device 400, the image forming apparatus 300 includes an operation display unit 402, an image processing unit 404, an image memory 406, an image forming unit 408, a storage unit 410, and a communication unit 412. The operation display unit 402, the image processing unit 404, the image memory 406, the image forming unit 408, the storage unit 410, and the communication unit 412 are connected to the I / O 400E of the control device 400. The control device 400 exchanges information with each unit of the operation display unit 402, the image processing unit 404, the image memory 406, the image forming unit 408, the storage unit 410, and the communication unit 412, and controls each unit.

  The operation display unit 402 includes various buttons such as a start button and a numeric keypad, and a touch panel for displaying various screens such as a warning screen and a setting screen. With the above configuration, the operation display unit 402 receives operations from the user and displays various information to the user.

  The image processing unit 404 performs predetermined image processing on the image information acquired from the external device 414 via the communication unit 412, and generates image information to be output to the image forming unit 408. For example, PDL data described in a page description language is expanded and converted into raster data (RGB data) that has been expanded into RGB colors, and the RGB data is color-converted and reproduced by the image forming apparatus. Generates YMCK data expressed in color. Furthermore, screen processing, gamma correction processing, or the like may be performed.

  The image memory 406 stores various image information acquired by the image forming apparatus 300 such as image information acquired from the external device 414 and image information generated by the image processing unit 404. The image memory 406 stores, for example, at least image information after image processing by the image processing unit 404, that is, image information to be output to the image forming unit 408.

  The image forming unit 408 has been described as the main configuration of the image forming apparatus 300. The image forming unit 408 includes, for example, the photosensitive member 10 (its driving unit (not shown)), the charging device 20, the exposure device 30, the developing device 40, the transfer device 50, the charge eliminating device 60, the fixing device 100, and the toner collection and supply device ( And a toner supply motor (toner supply motor for the conveying member of the toner supply path 74), a toner supply device (toner supply motor for the conveying member of the toner supply path 74), and the like. Each of these units is connected to the control device 400. The control device 400 exchanges information with each of these units to control each unit and the like.

The storage unit 410 includes a storage device such as a hard disk. The storage unit 410 stores various data such as log data, various programs, and the like.
The communication unit 412 is an interface for communicating with the external device 414 via a wired or wireless communication line. For example, the communication unit 412 acquires image formation information from the external device 414 together with an image formation instruction or image information of an electronic document. The image formation information includes parameters representing attributes such as the type (size, etc.) of the recording paper P, the paper feed direction of the recording paper P, the number of copies, and the color mode.

  Various drives may be connected to the control device 400. Various drives are devices that read data from or write data to computer-readable portable recording media such as flexible disks, magneto-optical disks, CD-ROMs, DVD-ROMs, and USB memories. is there. When various types of drives are provided, a control program may be recorded on a portable recording medium, and this may be read and executed by a corresponding drive.

(Operation of image forming apparatus)
An example of the operation of the image forming apparatus 300 according to the present embodiment will be described. Various operations of the image forming apparatus 300 are performed by a control program executed in the control apparatus 400.

Here, in the image forming apparatus 300, for example, control programs for “image forming process”, “toner recovery process”, and “toner image forming process on the non-image forming area of the photoreceptor 10” are stored in the ROM 400 </ b> B in advance. Yes. The control program stored in advance is read out by the CPU 400A and executed using the RAM 400C as a work area. Further, in the image forming apparatus 300, for example, “non-volatile memory 400D stores“ image density range of the toner image that drives the toner collection and supply device 55 ”and“ image density range of the toner image that stops the toner collection and supply device 55 ”. "," Image density range of toner image for executing toner image formation on non-image forming area of photoconductor 10 "," Image density of toner image for stopping toner image formation on non-image forming area of photoconductor 10 " Various data such as “range” and “image forming conditions (various process control values)” are stored in advance.
These control programs and various data may be stored in the ROM 400B, the non-volatile memory 400D, or another storage device such as the storage unit 410, or may be acquired from the outside via the communication unit 412.

First, an image forming operation of the image forming apparatus 300 will be described. The image forming operation is performed by a control program of “image forming process” executed in the control device 400.
First, the surface of the photoreceptor 10 is charged by the charging device 20. The exposure device 30 exposes the surface of the charged photoreceptor 10 based on image information. As a result, an electrostatic charge image corresponding to the image information is formed on the photoreceptor 10. In the developing device 40, the electrostatic charge image formed on the surface of the photoreceptor 10 is developed by a developer including toner and a carrier. As a result, a toner image is formed on the surface of the photoreceptor 10. In the transfer device 50, the toner image formed on the surface of the photoreceptor 10 is transferred to the recording paper P. The toner image transferred to the recording paper P is fixed by the fixing device 100. On the other hand, the surface of the photoreceptor 10 after the transfer of the toner image is neutralized by the neutralization device 60 and cleaned (cleaned) by the cleaning device 70.

  On the other hand, in the image forming apparatus 300, when an image forming operation is being performed, the control apparatus 400 forms a toner image having a predetermined image density or less on the photoreceptor 10 (that is, the image density of the toner image is set in advance). When the value is equal to or less than a predetermined value), “collecting the toner of the developer held on the developing roll 42” by the toner collecting / supplying device 55 is started, and a toner image exceeding a predetermined image density is formed on the photoconductor 10. At that time (that is, when the image density of the toner image exceeds a predetermined value), a control for stopping the “collection of developer toner held on the developing roller 42” by the toner collection and supply device 55 is executed (see FIG. “Toner recovery operation by toner recovery and supply device 55”).

  A toner collecting operation by the toner collecting and supplying device 55 will be described. The toner collection operation by the toner collection and supply device 55 is performed by a control program for “toner collection processing” executed by the control device 400. The control program for “toner collection processing” is started when an image formation instruction or the like is received from the operation display unit 402 or the external device 414 via the communication unit 412, for example.

First, as shown in FIG. 4, in step S100, the image density of the toner image is acquired.
The method for obtaining the image density is not particularly limited. For example, a method for obtaining the image density obtained based on image data obtained by reading a toner image formed on the recording paper P with a reading device (not shown) is formed. There is a method of acquiring the image density obtained based on the image information of the image.

In step S102, it is determined whether the image density of the acquired toner image is equal to or less than a predetermined value.
Specifically, for example, the “image density range of the toner image for driving the toner collection and supply device 55” stored in advance in the nonvolatile memory 400D is acquired, and the acquired image density range and the acquired toner are stored. Compare the image density of the image.
The “image density range of the toner image that drives the toner collection and supply device 55” is, for example, a range of image density of 5% or less (preferably 2% or less). This image density range is a range in which the toner consumption of the developer contained in the developing device 40 decreases, the same toner stays in the developing device 40, and toner deterioration is likely to occur.

When the determination in step S102 is negative (when the image density of the acquired toner image exceeds a predetermined value, that is, the image density of the acquired toner image is an image of the toner image that drives the toner recovery and supply device 55) If it is determined that the density is out of the range), the process proceeds to step S112.
On the other hand, when the determination in step S102 is affirmative (when the image density of the acquired toner image is equal to or less than a predetermined value, that is, the image density of the acquired toner image is the toner that drives the toner collection and supply device 55) If it is determined that the image density is within the range of the image), the process proceeds to step S104.

Next, in step S104, the toner collecting / supplying device 55 (the driving unit and the power source (both not shown) of the collecting roll 56) is driven to remove all or part of the developer toner held on the developing roll 42. to recover.
Specifically, in a state where a voltage opposite to the toner charging polarity is applied to the collection roll 56 by a power supply (not shown), the collection roll 56 is rotated by a drive unit (not shown). As a result, the developer toner held on the developing roll 42 is electrostatically transferred to the surface of the collecting roll 56. Then, the collected toner transferred to the surface of the collecting roll 56 is removed by the removing member 57 along with the rotation of the collecting roll 56 and stored in the housing 58.

  Next, in step S106, the image density of the toner image is acquired.

Next, in step S108, it is determined whether or not the image density of the acquired toner image exceeds a predetermined value.
Specifically, for example, the “image density range of the toner image that stops the toner recovery and supply device 55” stored in advance in the nonvolatile memory 400D is acquired, and the acquired image density range and the acquired toner Compare the image density of the image.
The “image density range of the toner image for stopping the toner recovery and supply device 55” is, for example, a range where the image density exceeds 5% (preferably exceeds 2%). The range of the image density is a range in which the toner consumption of the developer accommodated in the developing device 40 is increased, and the same toner hardly stays in the developing device 40 and toner deterioration hardly occurs.

When the determination in step S108 is negative (when the image density of the acquired toner image is less than a predetermined value, that is, the image density of the toner image at which the acquired toner image stops the toner recovery and supply device 55) If it is determined that the density is out of the range), the process proceeds to step S114.
On the other hand, if the determination in step S108 is affirmative (when the image density of the acquired toner image exceeds a predetermined value, that is, the image density of the acquired toner image stops the toner collection and supply device 55) If it is determined that it is within the range of the image density, the process proceeds to step S110.

  Next, in step S110, the driving of the toner collection and supply device 55 (the drive unit of the collection roll 56 and the power source (both not shown)) is stopped. As a result, the collection of all or part of the developer toner held on the developing roll 42 is stopped.

  Here, in step S112, it is determined whether the image forming operation is finished. If it is determined in step S112 that the image forming operation has not ended, the process returns to step S100. On the other hand, if it is determined in step S112 that the image forming operation has been completed, the routine ends.

  On the other hand, also in step S114, it is determined whether or not the image forming operation is completed. If it is determined in step S114 that the image forming operation has not ended, the process returns to step S106. On the other hand, if it is determined in step S114 that the image forming operation has ended, the routine ends.

Here, the recovered toner accommodated in the housing 58 of the toner recovery and supply device 55 is supplied to the toner cartridge 46 through the toner supply path 59 by rotationally driving the conveying member by the toner supply motor.
The supply processing of the collected toner to the toner cartridge 46 is not particularly limited. For example, a detection device (sensor or the like) that detects the amount of collected toner accommodated in the housing 58 of the toner recovery supply device 55 is provided. When the amount of collected toner detected by the above reaches a predetermined amount, the process may be executed.
In addition, the recovered toner supply process is as follows: 1) In the toner recovery process, when the toner recovery supply device 55 (the drive unit and power source of the recovery roll 56) is driven; It may be executed for each output number (cumulative number) of the formed recording paper P, or 3) for each toner image formation time (accumulated time) equal to or lower than a predetermined image density.
The collected toner supply process may be executed during the image forming process or may be executed while the image forming process is not being performed.

In the “toner recovery process” described above, when a toner image having a predetermined image density or less is formed on the photoconductor 10, all or one of the developer toner held on the developing roll 42 by the toner recovery supply device 55 is used. Collect parts. By this operation, even when the toner consumption is reduced, the toner is collected from the developing device 40, and the mechanical and thermal load is repeatedly applied to the same toner. As a result, toner deterioration is suppressed. That is, the BET specific surface area B of the developer toner accommodated in the developing device 40 after outputting 1,000 images with an image density of 1% on A4 paper tends to be 0.8 × BET specific surface area A or more.
Then, the collected toner collected by the toner collecting and supplying device 55 is supplied to the toner cartridge 46 through the toner supply path 59 and mixed with the replenishing toner of the toner cartridge 46, and is supplied again to the developing device together with the replenishing toner. Used.

  Further, in the image forming apparatus 300, when an image forming operation is being executed, when the control apparatus 400 forms a toner image having a predetermined image density or less on the photoreceptor 10 (that is, the image density of the toner image is set in advance). When the developing device 40 starts “image formation on the non-image forming area” of the photoconductor 10 and forms a toner image exceeding a predetermined image density on the photoconductor 10 (that is, below the predetermined value) When the image density of the toner image exceeds a predetermined value), a control for stopping the “toner image formation on the non-image forming area of the photoconductor 10” by the developing device 40 may be executed (“developing device”). 40 ”is a toner image forming operation on the non-image forming area of the photoconductor 10).

  A toner image forming operation on the non-image forming area of the photoreceptor 10 by the developing device 40 will be described. The toner image forming operation on the non-image forming area of the photoconductor 10 by the developing device 40 is performed by a control program of “toner image forming process on the non-image forming area of the photoconductor 10” executed by the control device 400. The control program of “toner image forming process on the non-image forming area of the photoconductor 10” is started when an image forming instruction or the like is received from the operation display unit 402 or the external device 414 via the communication unit 412, for example.

First, as shown in FIG. 5, in step S200, the image density of the toner image, the size of the recording paper P, and the paper feeding direction of the recording paper P are acquired.
The method for obtaining the image density is not particularly limited. For example, a method for obtaining the image density obtained based on image data obtained by reading a toner image formed on the recording paper P with a reading device (not shown) is formed. There is a method of acquiring the image density obtained based on the image information of the image.
The method for acquiring the size of the recording paper P and the paper feeding direction is not particularly limited, and the recording medium information is extracted from the image forming information, and the “recording paper P to be formed” is formed based on the recording medium information. There is a method of acquiring “size and paper feed”.

Next, in step S202, it is determined whether the image density of the acquired toner image is equal to or less than a predetermined value.
Specifically, for example, the “image density range of the toner image for executing the toner image formation on the non-image forming area of the photoconductor 10” stored in advance in the nonvolatile memory 400D is acquired, and the image of the toner image is acquired. The density range is compared with the image density of the acquired toner image.
Note that “the range of the image density of the toner image for forming the toner image on the non-image forming area of the photoconductor 10” is, for example, a range of 5% or less (preferably 2% or less) of the image density. This image density range is a range in which the toner consumption of the developer contained in the developing device 40 decreases, the same toner stays in the developing device 40, and toner deterioration is likely to occur.

When the determination in step S202 is negative (when the image density of the acquired toner image exceeds a predetermined value, that is, the image density of the acquired toner image is a toner image on the non-image forming area of the photoreceptor 10). If it is determined that it is outside the range of the image density of the toner image to be formed), the process proceeds to step S212.
On the other hand, if the determination in step S202 is affirmative (if the image density of the acquired toner image is equal to or less than a predetermined value, that is, the image density of the acquired toner image is transferred to the non-image forming area of the photoconductor 10). If it is determined that the toner density is within the range of the image density of the toner image to be formed), the process proceeds to step S204.

Next, in step S <b> 204, toner image formation is performed on the non-image forming area of the photoreceptor 10.
Specifically, for example, non-image area information indicating which area on the surface of the photoreceptor 10 is a non-image area is associated with recording medium information including the size of the recording paper P and the paper feeding direction. Pre-stored in the nonvolatile memory 400D. Then, from the non-image area information, the non-image forming area of the photoreceptor 10 corresponding to the acquired size of the recording medium and the paper feeding direction is read and set. A belt-like toner image is formed in the set non-image forming area of the photoreceptor 10.
The belt-like toner image formed in the non-image forming area of the photoconductor 10 is not transferred by the transfer device 50, is cleaned by the cleaning device 70, and is accommodated in the casing 71 of the cleaning device 70.

  Next, in step S206, the image density of the toner image is acquired.

Next, in step S208, it is determined whether or not the image density of the acquired toner image exceeds a predetermined value.
Specifically, for example, the “image density range of the toner image for stopping the toner image formation on the non-image forming area of the photoconductor 10” stored in advance in the nonvolatile memory 400 </ b> D is acquired, and the image of the toner image is acquired. The density range is compared with the image density of the acquired toner image.
The “range of the image density of the toner image that stops forming the toner image in the non-image forming area of the photoconductor 10” is, for example, a range that exceeds 5% (preferably exceeds 2%) of the image density. The range of the image density is a range in which the toner consumption of the developer accommodated in the developing device 40 is increased, and the same toner hardly stays in the developing device 40 and toner deterioration hardly occurs.

When the determination in step S208 is negative (when the image density of the acquired toner image is less than a predetermined value, that is, the image density of the toner image at which the acquired toner image stops the toner recovery and supply device 55) If it is determined that the density is out of the range), the process proceeds to step S214.
On the other hand, if the determination in step S208 is affirmative (if the image density of the acquired toner image exceeds a predetermined value, that is, the image density of the acquired toner image is equal to the non-image forming area of the photoreceptor 10). If it is determined that it is within the range of the image density of the toner image for which the toner image formation is stopped), the process proceeds to step S210.

  Next, in step S210, toner image formation on the non-image forming area of the photoconductor 10 is stopped.

  Here, in step S212, it is determined whether or not the image forming operation is finished. If it is determined in step S212 that the image forming operation has not ended, the process returns to step S200. On the other hand, if it is determined in step S212 that the image forming operation has ended, the routine ends.

  On the other hand, in step S214, it is determined whether or not the image forming operation is finished. If it is determined in step S214 that the image forming operation has not ended, the process returns to step S206. On the other hand, if it is determined in step S214 that the image forming operation has ended, the routine ends.

Here, the collected toner accommodated in the casing 71 of the cleaning device 70 is supplied to the toner cartridge 46 through the toner supply path 74 by rotationally driving the conveying member by the toner supply motor.
The supply process of the collected toner to the toner cartridge 46 is not particularly limited. For example, a detection device (sensor or the like) that detects the amount of the collected toner accommodated in the casing 71 of the toner recovery supply device 55 is provided. When the amount of collected toner detected by the above reaches a predetermined amount, the process may be executed.
In addition, the recovered toner supply process is 1) when a toner image is formed on the non-image forming area of the photoconductor 10 in “a toner image forming process on the non-image forming area of the photoconductor 10”, and 2) predetermined. Executed for each output number (accumulated number) of recording paper P on which an image of a toner image having an image density or less is formed, or 3) for each formation time (accumulated time) of a toner image having a predetermined image density or less. May be.
The collected toner supply process may be executed during the image forming process or may be executed while the image forming process is not being performed.

In the “toner image forming process on the non-image forming area of the photoconductor 10” described above, when a toner image having a predetermined image density or less is formed on the photoconductor 10, the toner image is formed on the non-image forming of the photoconductor 10. Form. This operation prevents the toner consumption of the developer of the developing device 40 from increasing even when an image is formed in which the toner consumption is reduced, and the mechanical and thermal load is repeatedly applied to the same toner. Is done. As a result, toner deterioration is suppressed. That is, the BET specific surface area B of the developer toner accommodated in the developing device 40 after outputting 1,000 images with an image density of 1% on A4 paper tends to be 0.8 × BET specific surface area A or more.
The collected toner removed by the cleaning device 70 is supplied to the toner cartridge 46 through the toner supply path 74 and is mixed with the replenishment toner of the toner cartridge 46, and is supplied again to the developing device together with the replenishment toner and reused. The

In the “toner image forming process on the non-image forming area of the photoconductor 10”, the image can be formed on the entire surface of the largest sheet (for example, A3 sheet) on which an image is to be output in any sheet feeding direction. The case where the “image formable area of the photoconductor 10” is a large area has been described.
When the area where an image can be formed on the entire surface of the largest sheet (for example, A3 sheet) to which an image is output is the same in any paper feed direction and the “image formable area of the photoconductor 10”, In the “toner image forming process on the non-image forming region”, “toner image forming on the non-image forming region of the photoconductor 10” is not executed even if the image density of the acquired toner image is equal to or less than a predetermined value.

  In the image forming apparatus according to the present embodiment, either “toner recovery processing” or “toner image formation processing on the non-image forming area of the photoconductor 10” may be executed, or both may be executed. Good.

<Developer>
Next, the developer accommodated in the developing device 40 and the replenishment toner accommodated in the toner cartridge 46 will be described. Hereinafter, the developer toner accommodated in the developing device 40 and the replenishment toner accommodated in the toner cartridge 46 will be referred to as “toner”.

The developer contains toner and a carrier having a volume average particle diameter of 20 μm or more and 35 μm or less (preferably 25 μm or more and 33 μm or less).
The toner has a volume average particle diameter of 3 μm or more and 5 μm or less (preferably 3.5 μm or more and 4.5 μm or less), and a number average particle diameter of 70 nm or more and 200 nm or less (preferably 80 nm or more and 180 nm or less, more preferably Is 110 nm or more and 180 nm or less).
Here, the mixing ratio (mass ratio) of the toner and the carrier is preferably toner: carrier = 1: 100 to 30: 100, and more preferably 3: 100 to 20: 100.

The volume average particle size of the toner particles is measured using Coulter Multisizer II (manufactured by Beckman Coulter), and the electrolytic solution is ISOTON-II (manufactured by Beckman Coulter).
In the measurement, 0.5 mg to 50 mg of a measurement sample is added as a dispersant to 2 ml of a 5% aqueous solution of a surfactant (preferably sodium alkylbenzenesulfonate). This is added to 100 ml or more and 150 ml or less of the electrolytic solution.
The electrolyte in which the sample is suspended is dispersed for 1 minute with an ultrasonic disperser, and the particle size distribution of particles having a particle size in the range of 2 μm to 60 μm is measured using a 100 μm aperture with a Coulter Multisizer II. taking measurement. The number of particles to be sampled is 50,000.
A cumulative distribution is drawn from the small diameter side with respect to the particle size range (channel) divided based on the measured particle size distribution, and the particle size at which the product is 50% is defined as the volume average particle size D50v.

  On the other hand, the number average particle diameter of the external additive is measured by the following method. First, after adding an external additive to toner particles (toner), 100 primary particles of metal oxide particles are observed with a SEM (Scanning Electron Microscope) apparatus. Then, the longest diameter and the shortest diameter of each particle are measured by image analysis of primary particles, and the sphere equivalent diameter is measured from this intermediate value. The 50% diameter (D50p) in the cumulative frequency based on the number of sphere equivalent diameters obtained is taken as the number average particle diameter of the external additive.

The volume average particle diameter of the carrier is measured by the following method. First, the particle size distribution of the carrier is measured using a laser diffraction / scattering type particle size distribution analyzer (LS Particle Size Analyzer (manufactured by Beckman-Coulter)). As the electrolytic solution, ISOTON-II (manufactured by Beckman Coulter, Inc.) is used. The number of particles to be measured is 50,000.
Then, the measured particle size distribution of the carrier is drawn from the smaller diameter side with respect to the divided particle size range (channel), and the particle size that is 50% cumulative (expressed as “D50v”) is expressed as “volume”. It is defined as “average particle size”.

-Toner particles-
The toner particles include, for example, a binder resin. The toner particles may contain a colorant, a release agent, and other additives as necessary.

Examples of the binder resin include styrenes (eg, styrene, parachlorostyrene, α-methylstyrene, etc.), (meth) acrylic acid esters (eg, methyl acrylate, ethyl acrylate, n-propyl acrylate, acrylic acid). n-butyl, lauryl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, lauryl methacrylate, 2-ethylhexyl methacrylate, etc.), ethylenically unsaturated nitriles (for example, acrylonitrile, Methacrylonitrile, etc.), vinyl ethers (eg, vinyl methyl ether, vinyl isobutyl ether, etc.), vinyl ketones (vinyl methyl ketone, vinyl ethyl ketone, vinyl isopropenyl ketone, etc.), olefins (eg, ethylene, propylene, etc.) Emissions, a homopolymer of a monomer such as butadiene) and the like, or a vinyl-based resin composed of these monomers with two or more combinations copolymer.
As the binder resin, for example, epoxy resin, polyester resin, polyurethane resin, polyamide resin, cellulose resin, polyether resin, non-vinyl resin such as modified rosin, a mixture of these with the vinyl resin, or these Examples also include a graft polymer obtained by polymerizing a vinyl monomer in the coexistence.
These binder resins may be used alone or in combination of two or more.

  The content of the binder resin is, for example, preferably 40% by weight to 95% by weight, more preferably 50% by weight to 90% by weight, and more preferably 60% by weight to 85% by weight with respect to the entire toner particles. Further preferred.

Examples of the colorant include carbon black, chrome yellow, hansa yellow, benzidine yellow, sren yellow, quinoline yellow, pigment yellow, permanent orange GTR, pyrazolone orange, vulcan orange, watch young red, permanent red, brilliant carmine 3B, and brilliant. Carmine 6B, Dupont Oil Red, Pyrazolone Red, Resol Red, Rhodamine B Lake, Lake Red C, Pigment Red, Rose Bengal, Aniline Blue, Ultramarine Blue, Calco Oil Blue, Methylene Blue Chloride, Phthalocyanine Blue, Pigment Blue, Phthalocyanine Green, Various pigments such as malachite green oxalate, or acridine, xanthene, , Benzoquinone, azine, anthraquinone, thioindico, dioxazine, thiazine, azomethine, indico, phthalocyanine, aniline black, polymethine, triphenylmethane, diphenylmethane, thiazole, and other dyes Etc.
A colorant may be used individually by 1 type and may use 2 or more types together.

  As the colorant, a surface-treated colorant may be used as necessary, or it may be used in combination with a dispersant. A plurality of colorants may be used in combination.

  The content of the colorant is, for example, preferably 1% by mass or more and 30% by mass or less, and more preferably 3% by mass or more and 15% by mass or less with respect to the entire toner particles.

  Examples of release agents include hydrocarbon waxes; natural waxes such as carnauba wax, rice wax, and candelilla wax; synthetic or mineral / petroleum waxes such as montan wax; and ester waxes such as fatty acid esters and montanic acid esters. And so on. The release agent is not limited to this.

  The content of the release agent is, for example, preferably 1% by mass to 20% by mass and more preferably 5% by mass to 15% by mass with respect to the entire toner particles.

  Examples of other additives include known additives such as a magnetic material, a charge control agent, and inorganic powder. These additives are contained in the toner particles as internal additives.

The toner particles may be toner particles having a single layer structure, or toner particles having a so-called core / shell structure composed of a core (core particle) and a coating layer (shell layer) covering the core. May be.
Here, the core / shell structure toner particles include, for example, a core portion including a binder resin and, if necessary, other additives such as a colorant and a release agent, and a binder resin. It is good to be comprised with the comprised coating layer.

  The average circularity of the toner particles is preferably from 0.94 to 1.00, more preferably from 0.95 to 0.98.

The average circularity of the toner particles is obtained by (circle equivalent perimeter) / (perimeter) [(perimeter of a circle having the same projection area as the particle image) / (perimeter of the particle projected image)]. Specifically, it is a value measured by the following method.
First, the toner particles to be measured are collected by suction, a flat flow is formed, a flash image is instantaneously emitted, a particle image is captured as a still image, and the particle image is analyzed (Sysmex). FPIA-3000 manufactured by the company). The number of samplings for obtaining the average circularity is 3500.
When the toner has an external additive, the toner (developer) to be measured is dispersed in water containing a surfactant and then subjected to ultrasonic treatment to obtain toner particles from which the external additive has been removed. .

-External additive-
Examples of the external additive include inorganic particles. As the inorganic particles, SiO ₂ , TiO ₂ , Al ₂ O ₃ , CuO, ZnO, SnO ₂ , CeO ₂ , Fe ₂ O ₃ , MgO, BaO, CaO, K ₂ O, Na ₂ O, ZrO ₂ , CaO. _{SiO 2, K 2 O · (} TiO 2) n, Al 2 O 3 · 2SiO 2, CaCO 3, MgCO 3, BaSO 4, MgSO 4 , and the like.

The surface of the inorganic particles as an external additive is preferably subjected to a hydrophobic treatment. The hydrophobic treatment is performed, for example, by immersing inorganic particles in a hydrophobic treatment agent. The hydrophobizing agent is not particularly limited, and examples thereof include silane coupling agents, silicone oils, titanate coupling agents, aluminum coupling agents and the like. These may be used individually by 1 type and may use 2 or more types together.
The amount of the hydrophobizing agent is usually 1 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the inorganic particles, for example.

  Examples of external additives include resin particles (resin particles such as polystyrene, polymethyl methacrylate (PMMA), and melamine resin), cleaning activators (for example, metal salts of higher fatty acids typified by zinc stearate, fluorine-based high molecular weight substances). Particle) and the like.

  The external addition amount of the external additive is, for example, preferably 0.01% by mass or more and 5% by mass or less, and more preferably 0.01% by mass or more and 2.0% by mass or less based on the toner particles.

-Toner production method-
Next, a toner manufacturing method will be described.
The toner is obtained by externally adding an external additive to the toner particles after producing the toner particles.

The toner particles may be produced by any of a dry production method (for example, a kneading and pulverizing method) and a wet production method (for example, an aggregation coalescence method, a suspension polymerization method, a dissolution suspension method, etc.). The production method of the toner particles is not particularly limited, and a known production method is adopted. Among these, it is preferable to obtain toner particles by an aggregation and coalescence method.
The toner is produced, for example, by adding an external additive to the obtained dry toner particles and mixing them. Mixing may be performed by, for example, a V blender, a Henschel mixer, a Laedige mixer, or the like. Further, if necessary, coarse toner particles may be removed using a vibration sieving machine, a wind sieving machine, or the like.

(Career)
There is no restriction | limiting in particular as a carrier, A well-known carrier is mentioned. As a carrier, for example, a coated carrier in which the surface of a core made of magnetic powder is coated with a coating resin; a magnetic powder dispersion type carrier in which magnetic powder is dispersed and mixed in a matrix resin; a porous magnetic powder is impregnated with a resin Resin impregnated type carriers; and the like.
Note that the magnetic powder-dispersed carrier and the resin-impregnated carrier may be a carrier in which the constituent particles of the carrier are used as a core material and coated with a coating resin.

  Examples of the magnetic powder include magnetic metals such as iron, nickel, and cobalt, and magnetic oxides such as ferrite and magnetite.

Examples of the coating resin and matrix resin include polyethylene, polypropylene, polystyrene, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl ether, polyvinyl ketone, vinyl chloride-vinyl acetate copolymer, styrene-acrylic acid ester. Examples thereof include a straight silicone resin comprising a copolymer, an organosiloxane bond, or a modified product thereof, a fluororesin, a polyester, a polycarbonate, a phenol resin, and an epoxy resin.
The coating resin and matrix resin may contain other additives such as conductive particles.
Examples of the conductive particles include particles of metals such as gold, silver, and copper, carbon black, titanium oxide, zinc oxide, tin oxide, barium sulfate, aluminum borate, and potassium titanate.

Here, in order to coat the surface of the core material with the coating resin, a method of coating with a coating layer forming solution obtained by dissolving the coating resin and, if necessary, various additives in an appropriate solvent may be mentioned. The solvent is not particularly limited, and may be selected in consideration of the coating resin to be used, coating suitability, and the like.
Specific resin coating methods include a dipping method in which the core material is immersed in the coating layer forming solution, a spray method in which the coating layer forming solution is sprayed on the surface of the core material, and a state in which the core material is suspended by flowing air. Examples thereof include a fluidized bed method in which a coating layer forming solution is sprayed, a kneader coater method in which a carrier core material and a coating layer forming solution are mixed in a kneader coater, and the solvent is removed.

<Test example>
In the following, a test example is provided to support that “deterioration of toner is suppressed” by the image forming apparatus 300 according to the present embodiment.

(Preparation of developer)
For 100 parts by mass of polyester black toner particles having a volume average particle diameter D50v shown in Table 1, 1.5 parts by mass of an external additive (hydrophobic silica particles) having a number average particle diameter D50p shown in Table 1 was sampled. The mixture was mixed at 10,000 rpm for 30 seconds by a mill. Thereafter, each toner was prepared by sieving with a vibrating sieve having an opening of 45 μm.
Then, 4 parts of each toner and 96 parts of a carrier having a volume average particle diameter D50v shown in Table 1 changed in accordance with the following production method and stirred at 40 rpm for 20 minutes by a V-blender, The developers D1 to D9 were prepared by sieving with a sieve having an opening of 250 μm.

-Carrier manufacturing method-
Ferrite particles (average particle size: 30 μm): 100 parts Toluene: 14 parts Styrene-methyl methacrylate copolymer (component ratio: 90/10): 2 parts Carbon black (R330: manufactured by Cabot Corporation): 0. Part 2 First, the above components other than the ferrite particles are stirred with a stirrer for 10 minutes to prepare a dispersed coating solution. Next, the coating solution and ferrite particles are placed in a vacuum degassing kneader and stirred at 60 ° C. for 30 minutes. After that, the carrier 1 was produced by further depressurizing while heating and degassing and drying.

(Test example)
The DocuCentre-V C7775 manufactured by Fuji Xerox Co., Ltd. is modified by attaching a device corresponding to the toner collection and supply device 55 shown in FIGS. 1 and 2, and the toner of the developer held on the developing roll is collected, and the toner cartridge The collected toner can be supplied to the printer. In addition, a modification is made to attach a device corresponding to the toner supply device (toner supply path 74, conveying member, toner supply motor) shown in FIGS. 1 and 2, and the recovered toner cleaned by the cleaning device can be supplied to the toner cartridge. did.
Then, the developing device and toner cartridge of this apparatus were filled with developers D1 to D9, respectively, and the following test was performed.

In accordance with the presence / absence of “operation of toner collection and supply device” and “toner image formation operation on non-image forming area of photoconductor” shown in Table 1, the operation is performed when “present” and the operation is performed when “not present”. In a normal temperature and normal humidity environment (temperature 25 ° C. and humidity 55% RH), the amount of applied toner is 4 g / m ² in the pattern (one linear image pattern) shown in FIG. In addition, 1000 images with an image density of 1% were output on A4 paper.
Then, the BET specific surface area A of the toner accommodated in the developer before the image formation and the BET specific surface area B of the toner accommodated in the developer after the image formation were measured.

  The “operation of the toner collection and supply device” and “the toner image forming operation on the non-image forming area of the photoreceptor” are as follows.

-Operation of toner collection and supply device-
An operation of collecting the toner of the developer held on the developing roll by the toner collecting and supplying device 55 and supplying the collected toner to the toner cartridge.

-Toner image forming operation on non-image forming area of photoconductor-
An operation of forming a belt-like toner image with a toner applied amount of 4 g / m ² in a non-image forming area of the photosensitive member, cleaning it with a cleaning device, and supplying the recovered toner to the toner cartridge.

  These results are shown in Table 1.

From the above results, even when the low image density is repeatedly formed, when the toner collection and supply device is operated to collect the toner of the developer held on the developing roll and supply the collected toner to the toner cartridge, the BET ratio of the toner It can be seen that the fluctuation of the surface area is small and the toner deterioration is suppressed.
However, with the developers D7 to D9 in which the volume average particle diameter of the toner particles exceeds 5 μm, the image quality is lowered.
Even when low image density is repeatedly formed, if a belt-like toner image is formed in the non-image forming area of the photoreceptor, cleaned with a cleaning device, and the recovered toner is supplied to the toner cartridge, the BET specific surface area of the toner is increased. It can be seen that the fluctuation is small and toner deterioration is suppressed.

DESCRIPTION OF SYMBOLS 10 Photoconductor 20 Charging device 21 Charging roll 22 Cleaning device 30 Exposure device 40 Developing device 41 Developing container 42 Developing roll 46 Toner cartridge 47 Toner supply path 50 Transfer device 52 Transfer roll 55 Toner recovery supply device 56 Recovery roll 57 Removal member 58 Housing Body 59 Toner supply path 60 Neutralizing device 70 Cleaning device 72 Cleaning blade 74 Toner supply path 100 Fixing device 300 Image forming apparatus 400 Control device

Claims (7)

A developing device having an image carrier, a housing portion that contains a developer, and a developer carrier that holds the developer on the surface and develops an electrostatic latent image formed on the image carrier as a toner image. The developer includes toner particles having a volume average particle diameter of 3 μm or more and 5 μm or less and an external additive having a number average particle diameter of 70 nm or more and 200 nm or less, and a BET specific surface area A of 2.3 m ² / g or more. An image forming unit having a toner of 0 m ² / g or less and a developing device that is a developer containing a carrier having a volume average particle diameter of 20 μm or more and 35 μm or less;
A transfer device for transferring a toner image formed on an image carrier of the image forming unit to a recording medium;
With
The BET specific surface area B of the developer toner accommodated in the developing device after outputting 1,000 images with an image density of 1% on A4 paper as the recording medium is 0.8 × the BET specific surface area A or more. An image forming apparatus. Replenishment including toner particles having a volume average particle size of 3 μm to 5 μm and external additives having a number average particle size of 70 nm to 200 nm and a BET specific surface area A of 2.3 m ² / g to 4.0 m ² / g A toner replenishing device having a housing portion that contains toner, and replenishing the replenishing toner to the housing portion of the developing device;
A recovery unit that is provided opposite to the developer holding body at a position downstream of the rotation direction of the developer holding body from a position facing the image holding body and that collects the toner of the developer held on the developer holding body. A toner recovery and supply device that has a member and supplies the toner recovered by the recovery member to a storage portion of the toner supply device;
A control device that controls the toner recovery and supply device when the toner image having a predetermined image density or less is formed on the image holding member, and recovers the toner of the developer held on the developer holding member;
The image forming apparatus according to claim 1, further comprising: Replenishment including toner particles having a volume average particle size of 3 μm to 5 μm and external additives having a number average particle size of 70 nm to 200 nm and a BET specific surface area A of 2.3 m ² / g to 4.0 m ² / g A toner replenishing device having a housing portion that contains toner, and replenishing the replenishing toner to the housing portion of the developing device;
A cleaning device for cleaning residual toner on the surface of the image carrier;
A toner supply device that supplies residual toner cleaned by the cleaning device to a storage portion of the toner supply device;
A control device for controlling the image forming unit to form a toner image in a non-image forming area of the image carrier when forming a toner image having a predetermined image density or less on the image carrier;
The image forming apparatus according to claim 1, further comprising:   The image forming apparatus according to claim 2, wherein the toner image having a predetermined image density or less is a toner image having an image density of 5% or less.   The image forming apparatus according to claim 1, wherein a BET specific surface area B of the toner of the developer is 0.9 × the BET specific surface area A or more.   The image forming apparatus according to claim 1, wherein a volume average particle diameter of the carrier is 25 μm or more and 33 μm or less.   The image forming apparatus according to claim 1, wherein the number average particle diameter of the external additive is 80 nm or more and 180 nm or less.