JP2002099148A - Image forming device and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize the amount of auxiliary particles in a developing means and to form an image of high picture quality for a long period as to a developing and cleaning system image forming device. SOLUTION: Toner T has toner particles and the auxiliary particles provided outside them. A developing and cleaning system collects residual toner by a developing roller 8 in development and at this time, more auxiliary particles than toner particles are collected to increase the amount of auxiliary particles in a developing container 4A, causing the density of a toner image to decrease. The auxiliary particles are discharged onto a photosensitive drum 1 by applying a discharging bias to the developing roller 8 by a developing bias power source 13 between sheets of paper and the auxiliary particles are temporarily stuck on a transfer roller 5 by applying a dislocation bias to the transfer roller 5 from a transfer bias power source 14. The auxiliary particles stuck on the transfer roller 5 are stuck on the reverse surface of a transfer material P in inext image formation and discharged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus and an image forming method such as an electrophotographic copying machine, a laser printer, and a facsimile.

[0002]

2. Description of the Related Art Conventionally, in a developing device for developing with a one-component developer, a developing roller for developing a toner image by attaching toner to an electrostatic latent image formed on a photosensitive drum (image carrier) is developed. Depending on whether the (developer bearing member) is in contact with or not in contact with the photosensitive drum, a distinction is made between a contact developing device and a non-contact developing device.

[0003] Among the contact developing devices, in recent years, a developing roller in which toner (developer) remaining on the photosensitive drum in the transfer process is arranged in contact with the photosensitive drum without providing a cleaning device in order to save energy and reduce running costs. A so-called development / cleaning system in which development is carried out while collecting at the same time has attracted attention.

FIG. 7 shows a schematic configuration of a conventional developing / cleaning type image forming apparatus in contact development using a non-magnetic one-component toner.

As shown in FIG. 1, a conventional image forming apparatus of this type includes a charging roller (charging device) 102 around a photosensitive drum (image carrier) 101 rotating in the direction of arrow X in FIG.
An exposing unit 103, a developing unit 104, and a transfer roller (transfer charger) 105 are provided. Further, a fixing device 107 is provided on the downstream side of the transfer roller 105 along the transfer direction of the transfer material P (the direction of the arrow Kp).

A developing device 104 is arranged in contact with the photosensitive drum 101 and performs development while rotating in the direction of arrow Y, and supplies non-magnetic toner T to the developing roller 108 by rotating in the direction of arrow Z. Roller (developer supply means) 109, toner T on developing roller 108
Regulating blade (developer regulating means) 110 for regulating the application amount and charge amount of the toner, a stirring member 11 for supplying the toner T to the supply roller 109 and stirring the non-magnetic one-component toner
1 and the like.

Next, the image forming operation of the above-described image forming apparatus will be described.

An external print signal (image forming signal)
As a result, the photosensitive drum 101 starts rotating in the arrow X direction.
First, the surface of the photosensitive drum 101 is uniformly charged by the charging roller 102. The charging roller 102 has a roller shape, and is rotated in a direction of an arrow W by a driving unit (not shown). Next, an electrostatic latent image is formed on the photosensitive drum 101 by the exposure L by the exposure device 103, and the electrostatic latent image reaches a contact portion with the developing device 104 by rotation of the photosensitive drum 101.

The developing device 104 performs the following operation in conjunction with the above operation.

The toner T stirred by the stirring member 111
Is supplied onto the developing roller 108 by sliding friction between the supply roller 109 rotating in the arrow Z direction and the developing roller 108 rotating in the arrow Y direction. The toner T on the developing roller 108 is provided with a desired amount of charge by the regulating blade 110 and the amount of toner (layer thickness) is regulated, and is carried on the developing roller 108. The toner in the developing device 104 is stirred by the stirring member 111, and
9 is conveyed.

When the toner carried on the developing roller 108 reaches a position where the toner contacts the photosensitive drum 101, a DC developing bias is applied to the developing roller 108 by a power source (not shown). Thus, the electrostatic latent image formed on the surface of the photosensitive drum 101 is developed (visualized) as a toner image by the toner T carried on the surface of the developing roller 108. At this time, the toner remaining on the surface of the developing roller 108 without contributing to the development is collected into the developing device 104 via the supply roller 109.

Usually, in this type of developing device 104,
The same developing bias potential as that during the image forming step is applied between one image forming step and the next image forming step during continuous printing.

In a contact developing device that uses a rigid photosensitive drum 101 and performs a developing and cleaning system by contacting a developing roller 102, the developing roller 102 is preferably a roller having an elastic body formed in a roller shape. As the elastic body, a solid rubber single layer or a solid rubber coated with a resin in consideration of the charging property to the toner is used.

In order to perform the contact development, in addition to the method in which the elastic developing roller 108 is brought into contact with the rigid photosensitive drum 101, a rigid developing roller is used for a belt-shaped photosensitive belt. There are ways.

The toner on the photosensitive drum 101 reaches the opposite portion of the transfer roller 105 by the rotation of the photosensitive drum 101, and is transferred onto the transfer material P by the transfer roller 105.
The transfer material P after the transfer of the toner image is conveyed to the fixing device 107, where the toner image on the surface is melted by heat and fixed, and then discharged out of the image forming apparatus main body.

On the other hand, the toner T (residual toner) remaining on the photosensitive drum 101 without being transferred onto the transfer material P during transfer.
Passes through the charging roller 102 and reaches a contact portion with the developing roller 108. At this time, the toner is collected by the developing roller 108 by the DC developing bias applied to the developing roller 108, and the collected toner is used for development at the next image formation.

By repeating the above operation, the image formation of the developing and cleaning system is repeated.

In the image forming apparatus of the developing / cleaning system described above, the residual toner remaining on the photosensitive drum 101 without being transferred to the transfer material P is collected by the developing device 104 and used again for development. . Therefore, for the purpose of reducing the stress applied to the toner particles, a toner in which auxiliary particles are externally added to the toner particles is preferably used.

The particle size of the auxiliary particles is set to be 0. 0 of the toner particles.
It is 0.5 to 0.5 times. The auxiliary particles adhere to the surfaces of the toner particles, function as spacers between the toner particles, and prevent friction between components such as the developing roller 108 and the toner and toner deterioration due to friction between the toner.

It is preferable that such auxiliary particles are particles having a negative imparting property to the toner (the auxiliary particles themselves are positively chargeable). This is because the toner has a stable tribo even under a high humidity environment.

[0021]

However, in the image forming apparatus of the developing and cleaning system using the toner to which auxiliary particles are externally added as shown in the above-mentioned conventional example, the following problems occur due to long-term use. .

Most of the toner externally added with auxiliary particles developed on the photosensitive drum 101 is transferred onto the transfer material P together with the auxiliary particles by the transfer bias applied to the transfer roller 105. However, some, especially the photosensitive drum 1
In the auxiliary particles that were in contact with 01, only the toner particles were separated from the auxiliary particles and transferred to the transfer material P side by the transfer electric field due to the adhesive force of the auxiliary particles themselves and the auxiliary particles being positively charged. The auxiliary particles are the photosensitive drum 1
01 may remain.

In the case of an image forming apparatus having a cleaning device, the auxiliary particles remaining on the photosensitive drum 101 are collected by the cleaning device and do not affect the developing device.

However, when the developing and cleaning system that reuses the toner is used, the remaining auxiliary particles pass through the charging roller 102 and are collected in the developing device 104. As a result, the ratio of the auxiliary particles to the toner amount in the developing device 104 increases. When the amount of the auxiliary particles is excessive with respect to the amount of the toner particles, the cohesiveness of the toner is increased, so that the density is reduced or the reproduction of minute dots becomes difficult. Or lower.

The present invention has been made in view of the above circumstances, and in an image forming apparatus of a developing / cleaning type having no cleaning device, the mixing ratio between toner and auxiliary particles in a developing device is stabilized. It is another object of the present invention to provide an image forming apparatus capable of stably outputting a high-quality image.

[0026]

According to a first aspect of the present invention, there is provided an electrophotographic photosensitive member, a charging unit for uniformly charging the electrophotographic photosensitive member, Exposure means for exposing the electrophotographic photoreceptor to form an electrostatic latent image; developing means for adhering toner to the electrostatic latent image with a developer carrier to develop the toner image; and transferring the toner image Transfer means having a transfer member for transferring to a material, the residual toner not transferred to the transfer material and remaining on the electrophotographic photoreceptor, after passing through the charging means, the developing bias during the developing step, In an image forming apparatus for collecting toner on a developer carrier, the toner includes toner particles that are frictionally charged to opposite polarities and auxiliary particles externally added to the toner particles. The second An ejection bias application unit that applies an ejection bias for ejecting the auxiliary particles in the developing unit from the developer carrier onto the electrophotographic photosensitive member during an image process, and corresponds to the first development process. First
Transfer bias applying means for applying a transfer bias for transferring auxiliary particles on the electrophotographic photoreceptor to the transfer member between the transfer step of (a) and the second transfer step corresponding to the second development step. , Is provided.

According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the discharge bias applying means applies a discharge bias of the same polarity as that of the auxiliary member to the developer carrier. It is characterized by.

According to a third aspect of the present invention, in the image forming apparatus of the first or second aspect, the transfer bias applying unit applies a transfer bias having a polarity opposite to that of the auxiliary member to the transfer member. It is characterized by the following.

The present invention according to claim 4 is based on claims 1, 2,
Or in the image forming apparatus of (3), a toner consumption detecting means for detecting the toner consumption, and an application time of the ejection bias applied by the ejection bias applying means based on a detection result of the toner consumption detecting means. And control means for controlling at least one of the applied voltage.

The present invention according to claim 5 is based on claims 1 and 2,
In the image forming apparatus of 3 or 4, the auxiliary particles have an average particle diameter of 0.01 to the average particle diameter of the toner particles.
0.5 times.

According to a sixth aspect of the present invention, there is provided a charging step for uniformly charging an electrophotographic photosensitive member, an exposing step for exposing the charged electrophotographic photosensitive member to form an electrostatic latent image, A developing step of attaching the toner to the electrostatic latent image by a developer carrying member to develop the toner image as a toner image; and a transfer step of transferring the toner image to a transfer material by a transfer member, and further, the image is not transferred to the transfer material. A cleaning step of passing the residual toner remaining on the electrophotographic photoreceptor through the charging unit, and then collecting the residual toner on the developer carrier by a developing bias during a developing step. Has toner particles frictionally charged to opposite polarities and auxiliary particles externally added to the toner particles, and is provided between the first developing step and the subsequent second developing step. A discharge step of discharging the auxiliary particles in the developing unit from the developer carrier onto the electrophotographic photosensitive member by applying a discharge bias by a discharge bias applying unit; and a first developing step. A corresponding first transfer step and a second transfer step corresponding to the second developing step.
A transfer step of transferring the auxiliary particles on the electrophotographic photosensitive member to the transfer member by applying a transfer bias by a transfer bias applying unit. .

According to a seventh aspect of the present invention, in the image forming method of the sixth aspect, the discharge bias applying means applies a discharge bias having the same polarity as that of the auxiliary member to the developer carrier. It is characterized by.

According to an eighth aspect of the present invention, in the image forming method of the sixth or seventh aspect, the transfer bias applying means applies a transfer bias having a polarity opposite to that of the auxiliary member to the transfer member. It is characterized by the following.

The present invention according to claim 9 is based on claims 6, 7,
Or the image forming method according to 8, wherein the toner consumption detecting means for detecting the toner consumption, and the application time of the ejection bias applied by the ejection bias applying means based on the detection result of the toner consumption detecting means. And control means for controlling at least one of the applied voltage.

According to a tenth aspect of the present invention,
In the image forming method according to 7, 8, or 9, the auxiliary particles have an average particle diameter of 0.01 to the average particle diameter of the toner particles.
０．５0.5 times.

[Operation] According to the above-described image forming apparatus, the auxiliary particles in the developing means are discharged from the developer carrying member onto the electrophotographic photosensitive member, and the discharged auxiliary particles are temporarily transferred to the transfer member. For example, it can be transferred to the back surface of the transfer material at the time of the next image formation. That is, it is possible to stably maintain the added amount of the auxiliary particles in the toner in the developing unit.

[0037]

Embodiments of the present invention will be described below with reference to the drawings.

<Embodiment 1> In this embodiment, the auxiliary particles externally added to the toner in the developing device are used to form the auxiliary particles between the time of forming one image and the next image forming (between sheets). Bias applied to the developing roller, and
In the transfer section, auxiliary particles are temporarily stored in a transfer roller, and the auxiliary particles are discharged to the back surface of the transfer material at the time of the next image formation, thereby stabilizing the ratio of the auxiliary particles in the developing device.

FIG. 1 shows an example of an image forming apparatus according to the present invention. The image forming apparatus shown in FIG. 1 is an image forming apparatus of a developing / cleaning type (for example, a copying machine or a laser beam printer), and FIG.

First, a schematic configuration and an overall operation of the entire image forming apparatus will be described.

The image forming apparatus shown in FIG. 1 includes a drum-type electrophotographic photosensitive member (hereinafter, referred to as "photosensitive drum") 1 as an image carrier. Around the photosensitive drum 1, a charging roller 2 (primary charger) 2 as a charging unit, an exposure unit 3 as an exposure unit, and a developing unit as a developing unit are arranged substantially in order along the rotation direction (the direction of the arrow X). (Developing device) 4,
A transfer roller (transfer member) 5 is provided as a transfer unit, and a fixing unit is provided on the downstream side of the transfer roller 5 along the transport direction (arrow Kp direction) of the transfer material P such as paper. Is provided.

As shown in FIG. 1, the charging roller 2 uniformly charges the photosensitive drum 1 rotating in the direction of the arrow X to a predetermined polarity and a predetermined potential while rotating in the direction of the arrow W. Then, laser or LE is applied to the surface of the charged photosensitive drum 1.
Exposure based on the information signal is performed by the exposure device 3 having the light emission blocking D to form an electrostatic latent image. This electrostatic latent image is
The toner is adhered by the developing device 4 and is developed (visualized) as a toner image. This toner image is transferred by the transfer roller 5 to the transfer material P conveyed by a feeding / conveying means (not shown). The transfer material P after the transfer of the toner image is
The toner is conveyed to the fixing device 7 where the toner is heated and pressed to fix the toner on the surface. On the other hand, on the photosensitive drum 1 after the transfer of the toner image, after the toner (residual toner) remaining on the surface without being transferred onto the transfer material P passes through the charging roller 2, the developing device 4
Is collected by the developing roller 8.

The description of the outline of the configuration and operation of the image forming apparatus has been completed. Then, each member etc. are explained in full detail.

The photosensitive drum 1 shown in FIG.
It rotates at the peripheral speed Vx. In the present embodiment, Vx
Was set to 48 mm / sec.

The charging roller 2 is a contact charging roller that contacts and charges the photosensitive drum 1 and is driven to rotate in the direction of arrow W at the same speed as the photosensitive drum 1. A charging bias power supply 12 is connected to the charging roller 2 so as to uniformly charge the surface of the photosensitive drum 1. The charging bias power supply 12
During the image forming operation, a voltage of about -1100 V is applied to the charging roller 2 to uniformly charge the surface of the photosensitive drum 1 to about -500 V.

Next, the light emitting element (laser or LE
D), the surface of the photosensitive drum 1 is exposed and scanned according to the information signal to form an electrostatic latent image. In the present embodiment, a so-called reversal developing system for forming a toner image by attaching negatively charged toner to an exposed portion on the photosensitive drum 1 will be described, but the present invention is not limited to this.

The developing device 4 includes a developing container 4A for storing a non-magnetic one-component toner T (hereinafter, simply referred to as “toner T”). The developing container 4 </ b> A has an opening at a portion facing the photosensitive drum 1.
A developing roller (developer carrier) 8 is provided. The developing roller 8 comes into contact with the photosensitive drum 1 and rotates at a peripheral speed Vy in the direction of arrow Y. The developing device 4 further includes a regulating blade 10 as a toner regulating member, a supply roller 9 rotating in the arrow Z direction, and a stirring member 11 for stirring the toner T. Here, the peripheral speed Vx of the photosensitive drum 1 and the developing roller 8
Is a relation of Vx <Vy. Where V
y is rotating at 81 mm / sec.

In order for the toner T accommodated in the developing device 4 to adhere to the developing roller 8, the toner T must be rubbed between the supply roller 9 and the developing roller 8 to apply a charge. The material of the supply roller 9 is urethane foam rubber,
A known material such as foamed EPDM rubber is used. In the present embodiment, the supply roller 9 made of urethane foam rubber is used.
Was rotated at a peripheral speed Vz in the counter direction (arrow Z direction) with respect to the rotation direction of the developing roller 8 (arrow Y direction).
As the rotation speed, Vz is 40 mm / sec. A supply bias power supply 15 is connected to the supply roller 9, and a DC voltage of about −460 V is applied to urge the negatively charged toner T from the supply roller 9 to the developing roller 8.

Next, the toner applied to the developing roller 8 by the supply roller 9 is regulated by the regulating blade 10 to regulate the toner amount and to perform tribo application by friction. The regulating blade 10 is a stainless steel thin plate (about 0.1 m thick).
The position about 2 mm from the tip of m) is bent in a direction opposite to the developing roller 8, and the bent portion is disposed so as to be in contact with the developing roller 8 with a slight bite.

The developing roller 8 has a developing bias power source 1.
3 is connected, while the photosensitive drum 1 is grounded. The developing bias power supply 13 is a negative DC power supply. In the present embodiment, a potential of −350 V is applied as a developing bias during image formation. The toner charged with the regulating blade 10 and carried on the developing roller 8 is charged with the developing bias (−350).
V), is supplied onto the photosensitive drum 1 and adheres to the electrostatic latent image, and the electrostatic latent image is developed as a toner image.

The toner image formed on the surface of the photosensitive drum 1 is transferred to the transfer material P. The transfer material P is supplied from a feeding / conveying device, for example, a sheet feeding cassette, a sheet feeding roller, a conveying roller,
The paper is supplied to a transfer section formed between the photosensitive drum 1 and the transfer roller 5 by a feeding / conveying device (neither is shown) constituted by a resist roller or the like. The transfer material P is supplied to the transfer unit in such a manner as to be synchronized with the toner image on the surface of the photosensitive drum 1, and the toner image on the photosensitive drum 1 is transferred by the transfer roller 5. The transfer roller 5 is a roller-type transfer charger in the present embodiment, and a transfer bias power supply 14 is connected to the transfer roller 5. A voltage of about 2 to 5 kV is applied to the transfer roller 5 by the transfer bias power supply 14 at the time of image transfer.

Further, the transfer bias power supply 14
In order to prevent the occurrence of an image defect called “paper mark” due to the leading end and the trailing end of the transfer material P to the transfer roller 5,
A transfer weak bias (approximately +500 V) for temporarily weakening the transfer bias is applied at the time of entry and discharge. In addition,
The “paper mark” is a kind of charge memory of the photosensitive drum 1 due to the transfer charge. As a result, the photosensitive drum 1 is abnormally positively charged due to the concentration of the electric field at the boundary of the transfer material P. Even if it receives a negative charge due to passing through the charging roller 2, a predetermined negative potential (charge potential: -50
0 V), when this portion is developed by the developing device 4, a black band-like horizontal stripe is generated on the transfer material P. For this reason, the black band-like horizontal stripes are present at a portion separated from the leading end on the transfer material P by the outer peripheral length of the photosensitive drum 1.

Similarly, when a weak transfer bias is not applied to the rear end of the transfer material P, the outer peripheral length of the photosensitive drum 1 from the rear end of the previous transfer material P on the transfer material P on which the next image is to be formed. Black streaks will be generated only at a distant portion.

The application timings of the above-described charging bias power supply 12, developing bias power supply 13, supply bias power supply 15, and transfer bias power supply 14 are controlled by a controller (control means) 16.

The transfer material P on which the toner image has been transferred is conveyed to the fixing device 7, where it is heated and pressed to thermally fuse (fix) the toner on the surface.

On the other hand, the residual toner remaining on the surface of the photosensitive drum 1 without being transferred onto the transfer material P reaches the charging roller 2. The residual toner that has reached the charging roller 2 is normally discharged by the transfer roller 5 and is therefore charged to a polarity opposite to the normal charging polarity. The residual toner charged to the opposite polarity has a regular charging polarity by rubbing with the charging roller 2 and the photosensitive drum 1 and discharging by the charging roller 2, and is discharged from the charging roller 2 onto the photosensitive drum 1.
Of the discharged toner, the toner present in the non-image portion at the contact portion between the photosensitive drum 1 and the developing roller 8 has a charging potential (= −500 V) and a developing bias (= −350 V) applied to the developing roller 8. Is collected by the developing roller 8 due to the potential difference.

Referring to FIG. 2, a method of developing and cleaning will be described.

In FIG. 2, “□” indicates residual toner existing on the photosensitive drum 1, and “「 ”indicates new toner that has passed through the regulating blade 10 and is carried on the developing roller 8. “−” In these “□” and “○” indicates the charging polarity of the toner.

The residual toner that has passed through the charging roller 2 or is discharged from the charging roller 2 is rubbed at the contact portion between the photosensitive drum 1 and the developing roller 8 to become negatively charged toner. Regarding the exposed portion (image portion) on the photosensitive drum 1, the potential on the photosensitive drum 1 is changed by receiving the exposure.
It becomes about -100V. At this time, the residual toner remains on the photosensitive drum 1 as it is, while the new toner on the developing roller 8 has a potential difference between the developing bias (= −350 V) and the potential of the exposed portion on the photosensitive drum 1 (= −100 V). Is developed on the photosensitive drum 1. At the same time, the negatively charged residual toner in the unexposed portion (non-image portion) is transferred onto the developing roller 8 by the potential difference between the charged potential (= -500 V) on the photosensitive drum 1 and the developing bias (= -350 V). At this time,
New toner on the developing roller 8 is used as it is.
Remain on top. Through the above steps, development and cleaning are achieved.

[Auxiliary Particle Discharge Sequence] The auxiliary particle discharge sequence, which is a feature of the present embodiment, will be described below. By using the discharge sequence of the auxiliary particles, the amount of the auxiliary particles with respect to the amount of the toner contained in the developing device 4 is stabilized, and the image quality is stably output.

FIG. 3 is a control sequence showing a charging potential (charging bias), a developing potential (developing bias), and a transfer potential (transfer bias) in the charging unit, the developing unit, and the transfer unit. Here, the vertical axis of each part indicates the polarity of the applied voltage, and has a negative polarity in the upward direction. The horizontal axis is the time axis. Hereinafter, the control sequence will be described with reference to FIGS.

First, when a print signal is input to the image forming apparatus and image data is processed for image formation by an image processing unit (not shown), the controller 16 controls the charging bias power supply 12 to charge the charging bias power supply 12 at time t _1. -1100V)
Is applied.

When the photosensitive drum 1 rotates in the direction of the arrow X and the portion of the photosensitive drum 1 charged by the above-described charging bias reaches the developing section, the developing bias power supply 13 applies a developing bias to the developing roller 8. -350V) is applied. At the same time, a transfer bias is applied to the transfer roller 5 by the transfer bias power supply 14. The transfer bias applied at this time is +500 lower than the transfer bias for transferring the toner image on the photosensitive drum 1 to the transfer material P.
A voltage of about V (hereinafter referred to as “transfer weak bias”) is applied.

Next, at time t ₃ (part A1), the transfer material P enters the transfer roller 5. Then, at time t _4, the transfer bias value is changed to the normal transfer bias from a transfer weak bias. Here, between the time t ₃ and time t ₄ corresponds to the leading end margin of the transfer material P (image top margin). Since the made when the leading edge margin time t ₄ has finished passing, the normal transfer bias (= + 2~4kV) is applied, the toner image is transferred onto the transfer material P. In the developing section,
Elapsed time t ₂ is a toner image is formed in accordance with an exposure unit from the portion that passed the end margin ( "image forming area" in FIG. 1).

At time t ₅ , the rear end margin of the transfer material P enters the transfer roller 5, so that the transfer bias is changed from the normal transfer bias to the weak transfer bias for the same reason as the prevention of the transfer memory of the front end margin. Then, the transfer material P completely comes out of the transfer roller 5 at time t ₆ (B1 portion).
That is, during the period from the time point (B1 parts) to the time t ₁₁ to the next transfer material P enters the transfer roller 5 (A2 parts) is sheet interval.

During the sheet interval, the developing bias and the transfer bias perform the following operations.

As shown in the developing bias of FIG. 3, the developing bias power supply 13 is switched at the time t ₇ between the sheets, and the developing bias is applied to the developing roller 8 from the developing bias (−350 V) during image formation. A bias having a large back contrast (hereinafter, referred to as “ejection bias”) is applied. The developing bias power supply 13 functions as an ejection bias applying unit by being switched as described above. That is, by increasing the absolute value of the back contrast (= charging bias−developing bias),
Auxiliary particles contained in the toner carried on the developing roller 8 are partially transferred to the photosensitive drum 1. here,
The reason is that some auxiliary particles adhere to the toner even when a bias is applied due to the adhesive force of the auxiliary particles themselves. As described above, by applying the ejection bias for increasing the back contrast as the developing bias, some auxiliary particles are transferred onto the photosensitive drum 1 and reach the transfer portion. Here, a broken line connecting the charging bias, the developing bias, and the transfer bias in FIG. 3 indicates that the photosensitive drum surface position of the bias applied in the development reaches the position of the transfer unit. At this time, there is no transfer material P in the transfer portion because of the paper interval, and the transfer roller 5 and the photosensitive drum 1 are in direct contact with each other.

When the auxiliary particles on the photosensitive drum 1 reach the transfer section, the transfer bias power supply 14 is switched,
A negative transfer reverse bias (transfer bias) is applied to the transfer roller 5 (time t ₉ ). Since the transfer reverse bias is more negative than the photosensitive drum 1, the photosensitive drum 1
The upper auxiliary particles are transferred onto the transfer roller 5. That is, the transfer bias power supply 14 functions as a transfer bias applying unit by being switched as described above.

The transfer of the auxiliary particles due to the transfer reverse bias is continued until the surface of the photosensitive drum 1 reaches the transfer unit while the developing bias is applied in the developing unit (from time t ₇ to time t ₈ ).

[0070] At time t _10, the transfer weak bias to the transfer roller 5 is applied in preparation for the transfer material tip rushes, rush leading edge of the transfer material P to the transfer roller 5 to the time t ₁₁ (A2 parts) I do. The normal transfer bias is applied at time t _12. At this time, the transfer roller 5
The auxiliary particles transferred to the transfer material P are transferred to the back surface of the transfer material P. The auxiliary particles attached to the back surface of the transfer material P
The transfer material P is directly adhered to the transfer material P and
Is discharged from the image forming apparatus main body.

As described above, the excessive amount of the auxiliary particles in the developing device 4 generated in the latter half of the long-term use is temporarily transferred to the transfer roller 5 using the paper interval, and adhered to the back surface of the next transfer material P. By discharging the toner, the amount of the auxiliary particles can be kept within a predetermined range even in an image forming apparatus using a developing and cleaning system.

In the above sequence, the period between time t ₂ and time t ₇ corresponds to the first developing step, and the period between time t ₈ and time t ₁₂ corresponds to the second developing step. Equivalent to. The first transfer step corresponding to the first development step corresponds to between the A1 part and the B1 part, and the second transfer step corresponding to the second development step includes the A2 part and the B2 part. And between

Hereinafter, the developing roller 8 and other members that come into contact with the developing roller 8, which are features of the present embodiment, will be described in detail.

[Configuration of Developing Roller] As shown in FIG. 1, the developing roller 8 is a so-called elastic developing roller having an elastic layer 8b on a cored bar 8a. In the present embodiment,
A solid silicone rubber layer of about 4 mm is formed as a low hardness elastic layer 8b on a stainless steel core 8a having a diameter of 8 mm. Further, a resin layer, for example, a polyamide resin of about 10 μm is provided thereon as the surface layer 8c, thereby constituting an elastic developing roller having a diameter of about 16 mm as a whole.

[Dynamic Coefficient of Developing Roller] Developing Roller 8
As the dynamic friction coefficient in the surface layer is 0.01 to
0.8 is suitably used. In order to apply a predetermined amount of electric charge to the toner T carried on the developing roller 8 by the supply roller 9, a kinetic friction coefficient of 0.01 or more is required. This is because the amount of toner passing through the blade 10 is increased, so that an appropriate charge is not applied to the toner, and transfer scattering occurs during the transfer process. More preferably, 0.
02 to 0.2.

The dynamic friction coefficient referred to here is a dynamic friction coefficient μ of the surface of the developing roller 8 with respect to a stainless steel plate, measured by the following method. The dynamic friction coefficient μ is shown in FIG.
Was determined as shown in FIG. A weight W1 is applied to one end, and a stainless steel thin plate 21 having a thickness of 0.03 mm connected to a digital force gauge 22 at the other end is set on the surface of the developing roller 8, and θ in FIG. Set. The digital force gauge 22 is adjusted to 0 when no load is applied to the weight W1 and the stainless steel plate.
After the value of the digital force gauge 22 is stabilized, the developing roller 8 is rotated in the direction of arrow R in FIG. 4, and the sliding force between the developing roller 8 and the stainless steel plate 21 at this time is measured by the digital force gauge 22. I do. The measured value is obtained by sampling a value output from the digital force gauge 22 in analog form at a frequency of 10 Hz by a recorder, calculating the sampled data by a computer 23 according to the following equation (1), and further calculating the data for one rotation of the developing roller 8. The calculated values were averaged.

Μ = (1 / θ) · ln (F / W) (1) where μ: dynamic friction coefficient, θ: contact between the surface of the developing roller and the stainless steel plate in the entire circumference of the developing roller Angle (90
Degree), W: total value of weight W1 (100 g) and weight of stainless steel thin plate 21 (5 g, including thin plate indicating member), F: measured value of digital force gauge.

The reason why the dynamic friction coefficient of the surface of the developing roller 8 was measured with respect to the stainless steel plate 21 as described above is that there is an example in which paper is used instead of the stainless steel plate 21. Coarse or smooth paper exists, and the coefficient of dynamic friction cannot be uniquely determined. Further, in the present embodiment, since the regulating blade 10 made of metal (in the present embodiment, a thin stainless steel plate) is brought into contact with the developing roller 8, the dynamic friction coefficient μ of the surface of the developing roller 8 is made of stainless steel. This is because the comparison using the thin plate 21 is close to the current situation and is more appropriate.

[Rubber Hardness of Developing Roller] The rubber hardness of the developing roller 8 was measured using an Asker C rubber hardness meter (manufactured by Kobunshi Keiki Co., Ltd.). The rubber hardness is 55 degrees (Aske
rC) The following are preferably used. 55 degrees (Ask
If erC) or more, the toner is melted due to the rubbing of the developing roller 8, and the fixing blade and the roller are fused, which is not preferable. More preferably, 35 to 45
When the hardness is low in this range, the stress applied to the toner is reduced, so that energy saving can be achieved by using a toner having a low melting point.

[Material of Elastic Layer of Developing Roller] As a material of the low hardness elastic layer 8b of the developing roller 8, silicone rubber is shown, but the material is not limited to this.
Commonly used rubbers such as BR rubber (nitrile rubber), butyl rubber, natural rubber, acrylic rubber, hydrin rubber, urethane rubber, or a mixture thereof can be used. Usually, the hardness is reduced by increasing the oil impregnation amount of the rubber material described above.

[Material of Surface Layer of Developing Roller] The resin used as the material of the surface layer 8c needs to consider the charge imparting property to the toner. Therefore, when a negatively chargeable toner is used, urethane resin, silicone resin, polyamide Resins, acrylic resins, and the like, and mixed resins thereof are suitably used.

[Resistance of Developing Roller] The resistance of the low-hardness elastic layer 8b and the resin layer 8c of the developing roller 8 is preferably conductive in order to prevent charge-up of toner due to frictional charging. However, for example, when a pinhole or the like is present on the surface of the photosensitive drum 1, an overcurrent may flow. Therefore, it is preferable that the elastic layer 8b and the resin layer 8c have some resistance. Resistance is 10 ^{2 in} volume resistance
The range is preferably about 10 to 10 ⁹ Ω · cm.

[Surface Roughness of Developing Roller] The surface roughness of the developing roller 8 depends on the particle size of the toner used.
The ten-point average roughness Rz is preferably 3 to 15 μm. If the particle diameter of the toner used is 6 μm in average volume particle diameter, 5 to 12 μm in ten-point average roughness Rz can be preferably used. When the toner particle size is smaller, it is preferable to make the ten-point average roughness Rz slightly smaller. If the ten-point average roughness Rz is 3 μm or less, sufficient toner conveying force cannot be obtained, resulting in insufficient density.
On the other hand, when the thickness is 15 μm or more, the toner is not sufficiently charged, and so-called “fogging” in which the toner adheres to the non-image portion.
Will occur. The ten-point average roughness Rz is JIS
Using the definition shown in B0601, a surface roughness tester “SE-30H” manufactured by Kosaka Laboratory was used for the measurement.

[Method of Manufacturing Developing Roller] An example of a method of manufacturing the developing roller 8 in the present embodiment will be described. Core 8
First, an adhesive for bonding rubber and ensuring conductivity is applied on a. Then, a low-hardness rubber is wound around the cored bar 8a and put into a mold. The mold is vulcanized by applying heat and pressure by a press machine, and the surface is polished after the vulcanization. The elastic layer 8b having a low hardness is formed by the above steps. Next, the developing roller 8 can be obtained by coating the polished semi-finished product of the developing roller 8 with the surface layer 8c by spray coating or the like.

[Regulatory Blade] The regulating blade 10 as a toner regulating member is a thin plate made of stainless steel (having a thickness of about 0.3 mm).
1 mm) is bent in a direction opposite to the developing roller 8 at a position of about 2 mm from the front end, and the bent portion comes into contact with the developing roller 8 slightly. The contact pressure at this time is preferably approximately 15 to 35 g / cm. 15g
/ Cm or less, the toner cannot be properly charged, resulting in fogging and deterioration of image quality. On the other hand, 35
When the g / cm is not less than g / cm, the external additive mixed with the toner is easily peeled off from the surface of the toner due to pressure or the like, so that the toner is deteriorated and the chargeability of the toner is reduced. Although the above-described regulating blade 10 is made of metal, the regulating blade 10 made of metal may be coated with a resin or the like in order to improve the chargeability of the toner. As the resin at this time, a polyamide resin, a urethane resin or the like is preferably used when the charge polarity of the toner is negative, and a fluororesin or the like is used when the charge polarity of the toner is positive.

The regulating blade 10 is not limited to the above-described shape. For example, an elastic member having rubber elasticity is attached to the tip of a thin metal plate, and this elastic member is brought into contact with the developing roller 8. It may be. The measuring method of the linear pressure is as follows:
× A stainless steel sheet with a width of 15 mm × a thickness of 30 μm and a stainless steel sheet with a length of 180 mm × a width of 30 mm × a thickness of 30 μm folded as half as a sandwich plate are prepared. The holding plate is inserted between the developing roller 8 and the regulating blade 10.
In this state, the drawing plate is pulled out at a constant speed with a spring scale or the like, and the value (unit: g) of the spring scale at that time is read.
The linear pressure when the unit is g / cm is obtained by dividing the value of the spring scale by 1.5.

[Contact Pressure between Developing Roller and Photosensitive Drum] The contact pressure of the developing roller 8 with respect to the photosensitive drum 1 is the same as the above-mentioned linear pressure measurement, and the linear pressure is 20 to 100 g.
/ Cm is preferred. When the linear pressure is 20 g / cm or less, the contact state becomes unstable, and when the linear pressure is 100 g / cm or more, the external additive mixed with the toner is easily embedded in the toner surface due to pressure or the like, and deteriorates the toner. This is because the chargeability of the toner by the blade 10 decreases.

[Toner] The toner used in the present embodiment is a non-magnetic one-component toner, and is a transmission electron microscope (TE).
In observation of the tomographic plane of the toner particles using M), it is preferable that the wax component is substantially spherical and / or spindle-shaped and dispersed in an island shape without being compatible with the binder resin. By dispersing the wax component as described above and encapsulating it in the toner, it is possible to prevent deterioration of the toner and contamination of the image forming apparatus, etc., so that good chargeability is maintained and excellent dot reproduction is achieved. It is possible to form a toner image for a long time. In addition, since the wax component acts efficiently during heating, low-temperature fixability and offset resistance are satisfied.

In this embodiment, as a specific method for observing the tomographic plane of the toner particles, a method in which the toner particles are sufficiently dispersed in a cold-setting epoxy resin, and then the temperature is reduced to 40 ° C.
After curing for 2 days in an atmosphere of ° C, the resulting effect is combined with ruthenium tetroxide and, if necessary, osmium tetroxide, dyed, and then flaked using a microtome with diamond teeth. Are cut out, and the tomographic morphology of the toner particles is observed with a transmission electron microscope. In the present embodiment, it is preferable to use a ruthenium tetroxide dyeing method in order to give a contrast between materials by utilizing a slight difference in crystallinity between the wax component used and the resin constituting the outer shell.

FIGS. 5A and 5B show typical examples. In the toner particles used in this embodiment, it was observed that the wax component Ta was encapsulated by the outer shell resin (binder resin) Tb. In the DSC curve measured by the differential scanning calorimeter, the wax component Ta
Those having the maximum endothermic peak in the range of 0 to 130 ° C are used. By having the maximum endothermic peak in the above-mentioned temperature range, it greatly contributes to low-temperature fixing, and also effectively develops releasability. When the maximum endothermic peak is less than 40 ° C., the self-cohesive force of the wax component becomes weak, and as a result, the hot offset resistance deteriorates and the gloss becomes too high. On the other hand, if the maximum endothermic peak exceeds 130 ° C., the fixing temperature becomes high, and it becomes difficult to appropriately smooth the surface of the fixed image. Absent.
Further, when the toner is directly obtained by a polymerization method by performing granulation and polymerization in an aqueous medium, a high maximum endothermic peak temperature is not preferable because a problem such as precipitation of a wax component mainly occurs during granulation. .

The measurement of the maximum endothermic peak temperature of the wax component Ta is performed in accordance with “ASTM D3418-8”. For the measurement, for example, DSC-
7 is used. The temperature correction of the device detection unit uses the melting points of indium and zinc, and the heat quantity correction uses the heat of fusion of indium. An aluminum pan was used as a measurement sample, an empty pan was set as a control, the temperature was raised and lowered once to obtain a pre-history, and then measurement was performed at a temperature raising rate of 10 ° C./min. Specific examples of the wax component include paraffin wax, polyolefin wax, Fischer-Tropsch wax, amide wax, higher fatty acid, ester wax, derivatives thereof, and graft / block compounds thereof.

The toner used in the present embodiment has a shape factor SF1 value of 100 to 160 measured by an image analyzer.
It is preferable that the value of the shape factor SF2 is 100 to 140, more preferably the value of the shape factor SF1 is 100 to 140, and the value of the shape factor SF2 is 100 to 120. Further, the above condition is satisfied and (SF
2) By setting the value of / (SF1) to 1.0 or less,
Not only the various characteristics of the toner, but also the matching with the image analyzer becomes very good.

The SF1 and SF2 indicating the above-mentioned shape factors are obtained by using FE-SEM (S-800) manufactured by Hitachi, Ltd.
100 toner images magnified by 500 times were randomly sampled, the image information was introduced into an image analyzer (Luzex3) manufactured by Nicole via an interface, analyzed, and calculated by the following equation. The values were defined as shape factors SF1 and SF2 in the present embodiment.

SF1 = ｛(MXLNG) ² / (ARE
A) {× (π / 4) × 100 SF2 = {(PERI) ² / (AREA)} × (1/4
π) × 100 where AREA: toner projection area, MXLNG: absolute maximum length, PERI: peripheral length.

The shape factor SF1 of the toner indicates the degree of roundness of the toner particles. 100 is a perfect spherical shape, and gradually changes from a spherical shape to an irregular shape as the numerical value increases. The shape factor SF2 indicates the degree of unevenness of the toner particles. 100 is the smoothest, and the unevenness of the toner surface becomes more remarkable as the numerical value increases.

When the shape factor SF1 exceeds 160, the shape of the toner becomes irregular, so that the charge amount distribution of the toner becomes broad and the toner surface is easily crushed in the developing device 4. This causes a reduction in image density and image fogging.

To increase the transfer efficiency of the toner image, the shape factor SF2 of the toner particles is 100 to 140,
The value of (SF2) / (SF1) is preferably 1.0 or less. The shape factor SF2 of the toner particles is larger than 140,
When the value of (SF2) / (SF1) exceeds 1.0, the surface of the toner particles is not smooth, and the toner particles have many irregularities, and the toner particles transfer from the photosensitive drum 1 to the transfer material P or the like. Transfer efficiency tends to decrease.

In order to faithfully develop minute latent image dots for higher image quality, the toner particles have a weight average particle size of 10 μm or less (preferably 4 to 8 μm), and the coefficient of variation A in the number distribution is It is preferably at most 35%. Toner particles having a weight average particle diameter of less than 4 μm tend to cause non-uniform unevenness of an image due to charge-up of the toner, which is not preferable as the toner used in the present embodiment. When the weight average particle diameter of the toner particles exceeds 10 μm, fusion to the surface of the photosensitive drum 1 is likely to occur, and the reproducibility of latent images of minute dots is inferior. When the coefficient of variation in the number distribution of toner particles exceeds 35%, the tendency is further enhanced. The particle size distribution of the toner particles can be measured by various methods. In the present embodiment, the measurement was performed using a Coulter counter.

For example, a Coulter Counter TA-II type (manufactured by Coulter) is used as a measuring device, and an interface (manufactured by Nikkaki) that outputs a number distribution and a volume distribution.
And a personal computer, and the electrolyte is 1
Adjust 1% NaCl aqueous solution using graded sodium chloride. For example, IS0T0NII (manufactured by Coulter Scientific Japan) can be used. As a measurement method, 0.1 to 5 ml of a surfactant (preferably an alkylbenzene sulfonate) is added as a dispersant to 100 to 150 ml of the above-described electrolytic aqueous solution, and the measurement sample is added to 2 to 50 ml.
Add 20 mg. The electrolyte in which the sample is suspended is subjected to a dispersion treatment for about 1 to 3 minutes by an ultrasonic disperser, and the above-mentioned Coulter counter TA-II type is used as an aperture, for example, 100%
Using a μm aperture, 2 to 40μ based on the number
The particle size distribution of m particles is measured, and then the value according to the present embodiment is determined.

Coefficient of variation A in number distribution of toner particles
Is calculated from the following equation.

A = (S / D ₁ ) × 100 In the formula, S represents a standard deviation value in the number distribution of toner particles, and D ₁ represents a number average particle diameter (μm) of the toner particles.

Further, as the toner particles used in the present embodiment, it is preferable to use a toner particle whose surface is coated with an external additive so that a desired charge amount is imparted to the toner. In that sense, the external additive coverage on the toner surface is preferably 5 to 99%, more preferably 10 to 99%.

The external additive coverage on the toner surface was determined by Hitachi, Ltd.
Using a FE-SEM (S-800) manufactured by
0 samples are randomly sampled, and the image information is
Image analysis device manufactured by Nicole (Luzex) through the face
Introduce in 3). The obtained image information is displayed on the surface of the toner particles.
Since the brightness of the part and the external additive part are different, it is binarized,
Area S of external additive_GAnd area of toner particles (external additive
(Including the area of the part) S _TDivided by the following formula.
calculate.

External additive coverage (%) = (S _G / S _T ) × 100 As the external additives used in the present embodiment, at least two types of external additives are used. As the first external additive, from the viewpoint of chargeability to toner particles when added to the toner,
Inorganic fine particles having an average primary particle size of 50 nm or less are preferred.
As the first external additive, for example, the following are used. Metal oxides (aluminum oxide, titanium oxide, strontium titanate, cerium oxide, magnesium oxide, chromium oxide, tin oxide, zinc oxide, etc.), nitrides (silicon nitride, etc.), metal salts (calcium sulfate, barium sulfate, calcium carbonate) Etc.) and silica.

These external additives are used in an amount of 0.01 to 10 parts by weight, preferably 0.05 to 5 parts by weight, based on 100 parts by weight of the toner particles. These external additives may be used alone or in combination. Those subjected to a hydrophobic treatment are more preferable.

If the amount of the external additive is less than 0.01 part by weight, the flowability of the one-component developer is deteriorated, and the chargeability of the toner is lowered, so that the efficiency of transfer and development is reduced. As a result, uneven density of the image occurs, or toner scatters around the image portion, that is, so-called scatter occurs.

On the other hand, when the amount of the external additive exceeds 10 parts by weight, an excessive amount of the external additive adheres to the photosensitive drum 1 or the developing roller 8 to deteriorate the chargeability of the toner or disturb the image. Or

Further, in the present embodiment, a second external additive as auxiliary particles is added to the toner particles in addition to the above-mentioned first external additive. The auxiliary particles are inorganic fine particles or polymer fine particles, such as spherical silica particles, spherical polymethylsilsesquioxane particles, and spherical resin particles. Auxiliary particles having an average particle size of 0.01 to 0.5 times the toner particle size can be used. The particle size of the polymer fine particles or the inorganic fine particles means an average particle size obtained by observing the surface of the toner particles with an electronic head microscope.

The auxiliary particles preferably have a charging polarity opposite to that of the toner particles. The auxiliary particles having the opposite polarity adhere better to the toner surface than the auxiliary particles having the same polarity, and uniform dispersion can be maintained for a long period of time. Furthermore, when the auxiliary particles are present in the form of agglomerates, if the auxiliary particles are of the same polarity as the toner particles, the chargeability of the toner particles may be inhibited depending on the size and amount of charge of the agglomerates, or one-component development In some cases, the stability of the toner coat on the developing roller may be impaired. From these reasons, it is desirable that the auxiliary particles have a polarity opposite to that of the toner particles.

In order to obtain polymer fine particles, a conventionally known method, that is, an emulsion polymerization method or a spray drying method can be used. Preferably, styrene, acrylic acid, methyl methacrylate, butyl acrylate, 2-
Fine resin particles having a glass transition point of 80 ° C. or higher obtained by homopolymerizing or copolymerizing monomer components such as ethylhexyl acrylate and melamine resin by an emulsion polymerization method exhibit a good effect. Further, it may be cross-linked with a cross-linking agent such as divinylbenzene, and for the purpose of adjusting the specific electric resistance and the amount of triboelectric charge, a metal, metal oxide, pigment, or the like whose resin particle surface does not damage the photosensitive drum surface. It may be treated with a surfactant or the like.

Examples of the inorganic fine particles include cerium oxide powder, strontium titanate, zinc oxide powder, tin oxide powder, boron nitride, hydrotalcite compounds,
Hydroxyapatite compounds can be used.

The functions and effects of the auxiliary particles are as follows: (1) The toner particles enter the toner particles as spacer particles to improve the developing characteristics in the developing section and the transfer efficiency in the transfer section.
(2) In the contact development, at the contact portion between the developing roller and the supply roller, the contact portion between the developing roller and the regulating blade, and the contact portion between the developing roller and the photosensitive drum, the toner stress due to rubbing is reduced. 3) Since the auxiliary particles have a weak positive property, when the residual toner in the transfer portion is rubbed with the toner in the rubbing portion between the charging roller and the photosensitive drum,
The friction between the toner and the auxiliary particles makes it easy for the toner to have a regular charge.

The external addition amount of the auxiliary particles may be set as follows.
0.02 to 1.0 part by weight is preferable with respect to 00 parts by weight. When the content is 0.02 or less, the above-mentioned effects cannot be obtained. On the other hand, when the content is 10 parts by weight or more, the amount of auxiliary particles becomes excessive and the density is reduced, or conversely, the reproducibility of one dot is reduced. .

The color of the auxiliary particles is preferably white or transparent and colorless. This is because if the image is colored, the color of the image changes.

As described above, the developing roller 8 is placed between the sheets.
Is applied to the transfer roller 5 to temporarily adhere the bias to the transfer roller 5, and the auxiliary particles are attached to the back surface of the transfer material P at the time of the next image formation, and the auxiliary particles are ejected to perform development and cleaning. Also in the image forming apparatus of the system, the amount of the auxiliary particles in the developing device 4 can be stabilized, and a high-quality image can be output for a long period of time.

<Embodiment 2> Next, referring to FIG.
Embodiment 2 of the present invention will be described. Members and devices having the same configuration and operation as those in the first embodiment are denoted by the same reference numerals, and redundant description thereof will be omitted.

In the first embodiment, the development reverse bias is applied for a predetermined time between sheets. In the present embodiment, the time for applying the development reverse bias is changed according to the number of pixels to be developed during image formation. as a result,
Even when the number of pixels for developing the toner is extremely large, that is, when the image is close to a solid image, the amount of the auxiliary particles can be stabilized.

FIG. 6 is a diagram showing a control sequence according to the present embodiment.

[Auxiliary Particle Discharge Sequence]
A discharge sequence of the auxiliary particles, which is a feature of the present embodiment, will be described.

FIG. 6 shows a control sequence showing a potential relationship in the charging section, the developing section, and the transfer section. Here, the vertical axis of each part indicates the polarity of the applied voltage, and has a negative polarity in the upward direction. The horizontal axis is the time axis.

First, a print signal is input to the image forming apparatus, and image data is processed by an image processing unit (not shown) for image formation. At this point, the number of pixels to be imaged is determined. That is, the image processing unit determines the toner consumption based on the number of pixels on which an image is formed for each transfer material P.
It functions as a toner consumption detecting means. FIG. 6 shows an example in which the printing rate of the first transfer material P is 80% and the printing rate of the second transfer material P is 5%, with reference to FIG. 1 as appropriate.

When the number of pixels has been calculated, the controller 16 (see FIG. 1) applies a charging bias (−1100 V) to the charging bias power supply 12 at time t ₂₁ .

[0123] the photosensitive drum 1 is rotated in the arrow X direction, the time t _22, the charged portion by the charging bias of the photosensitive drum 1 surface reaches the development portion, the developing bias (-350 V) is applied You. At the same time, a transfer bias is applied. The transfer bias applied at this time is
A voltage of about 500 V lower than a normal transfer bias for transferring the toner image on the photosensitive drum 1 to the transfer material P (hereinafter, referred to as “transfer weak bias”) is applied.

[0124] Then, the transfer material P at time t ₂₃ (C1 parts) enters the transfer roller 5. Then, at time t _24, the bias voltage is changed to the normal transfer bias from a transfer weak bias. Here, between the time t ₂₃ and time t ₂₄ corresponds to the end margin of the transfer material P (image top margin).
At time t ₂₄ the normal transfer bias (+ 2~4kV) is applied for the paper edge margins passes, the toner image is transferred onto the transfer material P. In the development unit, and the elapsed time t ₂₂ is, an image is formed from the portion that passed the end margin in accordance with an exposure unit (image forming area in FIG. 6).

[0125] At time t _25, since the trailing edge margin of the transfer material P (image trailing edge margin portion) enters the transfer roller 5, transfer weak from the normal transfer bias for the same reasons as the transfer memory prevention Edge Margin Changed to bias. The transfer material P is being withdrawn completely from the transfer roller 5 to the time t ₂₆ (D1 parts). In other words, until the time t ₃₁ to the next transfer material P from the point enters the transfer roller 5 (C2 parts) is sheet interval.

During the sheet interval, the developing bias and the transfer bias perform the following operations.

[0127] As shown in the developing bias of FIG. 6 (development potential), the developing bias between paper protruding bias having a developing bias (-350 V) is greater than back contrast in the image formation in t ₂₇ is applied. However, unlike the first embodiment described above in this embodiment, only the time corresponding to the printing rate protruding bias is applied (from time t ₂₇ to time t _28). The time applied to the projecting bias is set to be longer as the printing rate is higher. In other words, the higher the printing rate (the larger the toner consumption), the more auxiliary particles that are not transferred in the transfer unit, so that the amount of the auxiliary particles that are not transferred is discharged from the toner in the developing device 4 to the outside of the image forming apparatus. It is to be.

The auxiliary particles contained in the toner carried on the developing roller 8 are partially transferred to the photosensitive drum 1 and reach the transfer section.

When the auxiliary particles on the photosensitive drum 1 reach the transfer section, a negative transfer reverse bias is applied to the transfer roller 5 (time t ₂₉ ). Since the transfer reverse bias is more negative than the photosensitive drum 1, the auxiliary particles on the photosensitive drum 1 are transferred to the transfer roller 5.

[0130] At time t _30, the transfer material tip transcription weak bias is applied to the transfer roller 5 in order to prepare for rush is the leading edge of the transfer material P is transferred to the time t ₃₁ (C2 parts in FIG. 6) It enters the roller 5. Then at time t _32, the normal transfer bias is applied. At this time, the transfer roller 5
The auxiliary particles transferred to the transfer material P are transferred to the transfer material P side. Then, the auxiliary particles adhered to the back surface of the transfer material P adhere to the transfer material P as they are and are fixed to the transfer material P by the fixing device 7, so that they are discharged from the image forming apparatus main body.

Next, a description will be given of a case where a sheet interval (part D2 to part C3 in FIG. 6) between the second transfer material P and the third transfer material P similarly occurs.

[0132] While projecting bias between paper at time t ₃₃ is applied, the second sheet of printing rate for 5% and lower, it is not necessary to discharge the large amount of auxiliary particles. Therefore, (t ₃₄ from t ₃₃₎ the time for applying the protruding bias is shorter than the case of 80% printing rate described above. When the application time of the discharge bias is short, the amount of toner carried by the developing roller 8 and conveyed to the developing unit during that time is small, so that the amount of auxiliary particles discharged to the photosensitive drum 1 is naturally small.
In this way, it is possible to adjust the amount of auxiliary particles emitted from the developing device 4 according to the difference in printing rate, that is, the difference in toner consumption.

As described above, since the discharge amount of the auxiliary particles is determined according to the toner consumption amount, the amount of the auxiliary particles can be adjusted with extremely high accuracy. As a result, even when a large amount of an extremely high printing rate is formed, the amount of the auxiliary particles can be kept within a predetermined range, and a high-quality image can be stably formed.

Further, in the present embodiment, the application time of the projecting bias is determined in accordance with the number of pixels on which an image is formed. However, any means for controlling the toner consumption is limited to the number of pixels. It goes without saying that it is not.

Although the amount of auxiliary particles emitted from the developing unit 4 is determined by the application time of the projecting bias, the emission amount of auxiliary particles decreases when the back contrast is lowered, and the emission amount increases when the back contrast is increased. Is possible. That is,
It is also possible to adjust the emission amount of the auxiliary particles by adjusting the potential of the protruding bias while keeping the application time of the emission bias constant.

[0136]

As described above, according to the present invention, the discharge bias is applied to the developer carrier between the sheets to cause the auxiliary particles to be discharged onto the electrophotographic photosensitive member, and the discharged auxiliary particles to be discharged. A transfer bias is applied to the transfer member to temporarily attach the transfer member from the electrophotographic photosensitive member to the transfer member, and the auxiliary particles attached to the transfer member are attached to the back surface of the transfer material at the time of the next image formation, and are discharged by auxiliary discharge Also in an image forming apparatus of a developing and cleaning system, the amount of auxiliary particles in the developing means can be stabilized, and a high-quality image can be formed for a long period of time.

Further, the amount of the auxiliary particles can be adjusted with extremely high accuracy by determining the amount of the auxiliary particles to be discharged according to the toner consumption. As a result, for example, even when a large number of extremely high printing rates are formed, the amount of the auxiliary particles can be kept within a predetermined range, and a high-quality image can be stably formed.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view illustrating a schematic configuration of an image forming apparatus of a developing and cleaning system according to a first embodiment.

FIG. 2 is a schematic diagram illustrating the principle of a developing and cleaning system.

FIG. 3 is a diagram showing a control sequence of a charging potential, a developing potential, and a transfer potential in the first embodiment.

FIG. 4 is a diagram illustrating a method for measuring a dynamic friction coefficient.

FIG. 5 is a sectional view of a toner used in the image forming apparatus according to the first embodiment.

FIG. 6 is a diagram showing a control sequence of a charging potential, a developing potential, and a transfer potential in the second embodiment.

FIG. 7 is a longitudinal sectional view showing a schematic configuration of a conventional image forming apparatus of a developing and cleaning system.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 electrophotographic photosensitive member (photosensitive drum) 2 charging means (charging roller) 3 exposing means (exposing device) 4 developing means (developing device, developing device) 5 transfer means (transfer member, transfer roller) 8 developer carrier (developing) Roller) 10 regulating blade 13 developing bias power supply, discharge bias applying means 14 transfer bias power supply, transfer bias applying means 16 control means (control controller) P transfer material T toner 6

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03G 15/06 101 G03G 15/08 507B 2H077 15/16 9/08 344 21/10 21/00 312 (72 Inventor Manami Sekiguchi 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Makoto Nonomura 3-30-2 Shimomaruko 3-chome, Ota-ku, Tokyo F-term (reference) 2H005 AA08 DA02 DA03 DA07 EA05 2H027 DD02 EA09 EB01 EC12 EC14 ED09 ED15 ED24 ED27 EF12 2H032 AA05 BA03 BA05 BA23 BA30 CA13 CA15 2H034 AA06 CA00 2H073 AA07 BA02 BA09 BA13 BA22 BA43 BA45 CA03 AC15 DB03 AD03

Claims (10)

[Claims] An electrophotographic photosensitive member, charging means for uniformly charging the electrophotographic photosensitive member, exposure means for exposing the charged electrophotographic photosensitive member to form an electrostatic latent image, A developing unit for applying toner to the electrostatic latent image by a developer carrier to develop the toner image as a toner image; and a transfer unit having a transfer member for transferring the toner image to a transfer material. In an image forming apparatus, the residual toner remaining on the electrophotographic photoreceptor is passed through the charging unit, and then collected on the developer carrier by a developing bias during a developing process. A toner particle that is triboelectrically charged and auxiliary particles externally added to the toner particles, wherein the auxiliary particles in the developing unit are interposed between a first development step and a subsequent second development step. Developer Discharge bias applying means for applying a discharge bias for discharging from the carrier onto the electrophotographic photosensitive member; a first transfer step corresponding to the first development step; and a second transfer step corresponding to the second development step. And a transfer bias applying means for applying a transfer bias for transferring auxiliary particles on the electrophotographic photosensitive member onto the transfer member between the transfer step and the transfer step. 2. The image forming apparatus according to claim 1, wherein the discharge bias applying unit applies a discharge bias having the same polarity as the auxiliary member to the developer carrier. 3. The image forming apparatus according to claim 1, wherein the transfer bias applying unit applies a transfer bias having a polarity opposite to that of the auxiliary member to the transfer member. 4. A toner consumption detecting means for detecting the consumption of the toner, and an application time and an application voltage of an ejection bias applied by the ejection bias applying means based on a detection result of the toner consumption detection means. 4. The image forming apparatus according to claim 1, further comprising: a control unit configured to control at least one of the above. 5. The auxiliary particle according to claim 1, wherein the average particle diameter of the auxiliary particles is 0.01 to 0.5 times the average particle diameter of the toner particles. Image forming apparatus. 6. A charging step for uniformly charging the electrophotographic photosensitive member, an exposing step for exposing the charged electrophotographic photosensitive member to form an electrostatic latent image, and a developing agent for the electrostatic latent image. A developing step of applying toner by a carrier to develop the toner image as a toner image; and a transfer step of transferring the toner image to a transfer material by a transfer member. A cleaning step of, after passing the remaining toner through the charging unit, collecting the residual toner on the developer carrier by a developing bias during a developing step, wherein the toners have respective opposite polarities. And a toner particle that is frictionally charged and auxiliary particles externally added to the toner particle. Between a first development step and a subsequent second development step, A discharge step of discharging the auxiliary particles from the developer carrier onto the electrophotographic photosensitive member by applying a discharge bias by a discharge bias applying unit, and a first transfer step corresponding to the first developing step And transferring the auxiliary particles on the electrophotographic photosensitive member onto the transfer member by applying a transfer bias by means of a transfer bias applying unit between the second transfer step and the second transfer step corresponding to the second developing step. And a transfer step. 7. The image forming method according to claim 6, wherein the discharge bias applying unit applies a discharge bias having the same polarity as the auxiliary member to the developer carrier. 8. The image forming method according to claim 6, wherein the transfer bias applying unit applies a transfer bias having a polarity opposite to that of the auxiliary member to the transfer member. 9. A toner consumption detecting means for detecting the toner consumption, and an application time and an application voltage of an ejection bias applied by the ejection bias applying means based on a detection result of the toner consumption detecting means. 9. The image forming method according to claim 6, further comprising: control means for controlling at least one of the following. 10. The toner according to claim 6, wherein the auxiliary particles have an average particle diameter of 0.01 to 0.5 times the average particle diameter of the toner particles. Image forming method.