JP2002132015A - Image forming device and process cartridge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of the problem of defective electrification, due to the decrease of the supply amount of electrification promoting particles Z from a developing means 3 to an electrifying nip part N, in accordance with the use endurance of a device in a transfer system, the image forming device of a toner recycling process (a cleaner-less system) and a process cartridge which is attachable/detachable to/from an image forming device body, in which a contact electrifying means 2 using the electrification acceleration particles Z, is adopted as the electrifying means of an image carrier 1. SOLUTION: This device possesses a means by which the nip width NP of the nip part N between a rotating/electrifying member (an electrifying roller) 21 and the image carrier 1 is increased according to the use endurance of the device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an electrophotographic photosensitive member.
The present invention relates to an image forming apparatus, such as a copying machine or a printer, for performing image formation by applying an image forming process including a step of uniformly charging an image carrier such as an electrostatic recording dielectric to a predetermined polarity and potential.

More specifically, an image forming apparatus of a transfer system, a toner recycling process (cleanerless system), and an image forming apparatus employing a contact charging device using charging promoting particles as a charging device of an image carrier. The present invention relates to a process cartridge that can be attached to and detached from an apparatus body.

[0003]

2. Description of the Related Art A contact charging means using charge accelerating particles is disclosed in Japanese Patent Application Laid-Open No. 10-307454 to 307459. This contact charging means is provided at a contact portion between at least both a member to be charged and a rotary charging member generally made of a conductive and elastic roller (charging roller) brought into contact with the member to be charged as a contact charging member. By interposing charge accelerating particles in a certain charging nip, the direct injection charging mechanism is more dominant than the discharge charging mechanism in the charging mechanism (charging mechanism, charging principle).

FIG. 7 is a schematic view of an example of this contact charging means, in which (a) is a front model diagram in which an intermediate portion is omitted, and (b).
Is an enlarged side view model diagram.

[0005] Reference numeral 1 denotes a member to be charged, and in this embodiment, a photosensitive drum as an image carrier in an electrophotographic apparatus. The photosensitive drum 1 is driven to rotate clockwise as indicated by an arrow a.

Reference numeral 21 denotes a charging roller as a rotating charging member, which is provided in contact with the photosensitive drum 1. The charging roller 21 includes a core 22, a conductive / elastic (flexible) layer 23 formed concentrically and integrally around the core, and a core at both ends of the conductive / elastic layer 23. Contact roller 24.2 provided by loose fitting on gold 22
Consists of four. Both ends of the cored bar 22 are bearing members 25 respectively.
The bearing 25 is freely rotatable on the bearing 25. Bearing member 25
Numeral 25 is free to slide in the radial direction of the photosensitive drum 1 along a guide member (not shown).
A spring 26 is contracted between the stationary member 25 and an immovable member 27 such as an apparatus frame or a process cartridge frame, so that the charging roller 21 is brought into contact with a contact roller (abutting roller) against the elasticity of the conductive and elastic layer 23. The contact rollers 24 are pressed against the surface of the photosensitive drum 1 until they are received.

The contact rollers 24 are circular members having a constant radius, the outer diameter of which is smaller than the outer diameter of the conductive / elastic layer 23 of the charging roller 21 when the conductive / elastic layer 23 is in a free state. When the charging roller 21 is pressed against the photosensitive drum 1, the charging roller 21 comes into contact with the surface of the photosensitive drum 1, and serves to regulate the axial distance CD between the charging roller 21 and the photosensitive drum 1 to a predetermined constant value.

As a result, the amount of penetration d of the conductive / elastic layer 23 of the charging roller 21 into the photosensitive drum 1 is regulated to a predetermined constant value, and the charging nip portion N serving as a contact portion between the charging roller 21 and the photosensitive drum 1 is defined. Of the nip is defined to be a predetermined constant.

For example, the conductive / elastic layer 2 of the charging roller 21 is so adjusted that the nip width NP of the charging nip N is 1 mm.
The outer diameter of the contact rollers 24 with respect to the outer diameter of No. 3 is set.

The outer peripheral surface of the charging roller 21 is coated in advance with rough electrifying particles Z, and the electrifying nip portion N has the electrifying particles Z interposed therebetween.

The charging roller 21 is driven to rotate at a predetermined peripheral speed in the clockwise direction of arrow b by a driving means (not shown).
Counter rotation while maintaining a predetermined relative speed difference, and rubs the surface of the photosensitive drum 1. A predetermined charging bias is applied to a core metal 22 of the charging roller 21 from a bias application power supply (not shown), and the peripheral surface of the rotating photosensitive drum 1 is directly charged to almost the same potential as the charging bias for the charging roller 21. Is charged.

The charge accelerating particles Z are conductive particles for the purpose of assisting charging. For example, the particle diameter is 0.1 to 5 μm, and the volume resistance is 1 × 10 ¹² Ω · cm or less, more preferably 1 × 10 ¹⁰ Ω · cm.
Various conductive particles, such as metal oxide fine particles such as conductive zinc oxide, Ω · cmm or less, other conductive inorganic fine particles, and a mixture with an organic substance can be used.

Due to the presence of the charge accelerating particles Z, the charging roller 21 can come into contact with the photosensitive drum 1 with a speed difference in the charging nip portion N, and at the same time, contact the photosensitive drum 1 densely via the charge accelerating particles Z. That is, the charge accelerating particles Z existing in the charging nip N rub the surface of the photosensitive drum 1 without gaps, thereby directly injecting charges into the photosensitive drum 1. That is, the charging of the photosensitive drum 1 by the charging roller 21 is dominated by the direct injection charging mechanism due to the presence of the charging promoting particles Z.

Accordingly, a high charging efficiency, which cannot be obtained by conventional roller charging or the like, can be obtained, and a potential substantially equal to the voltage applied to the charging roller 21 can be applied to the photosensitive drum 1. It is possible to realize direct injection charging with a simple configuration, and in an electrophotographic image forming apparatus or an electrostatic recording image forming apparatus, an image carrier such as an electrophotographic photosensitive member or an electrostatic recording dielectric has a predetermined polarity. This is effective as a charging means for uniformly direct charging at a potential.

In the direct injection charging using the above-mentioned charge accelerating particles, it is possible to uniformly charge the image carrier, which is a member to be charged, in an image forming apparatus of a cleanerless system. Specifically, the charge-promoting particles are mixed with the developer (toner) of the developing unit, and the charge-promoting particles are supplied together with the toner from the developing unit to the surface of the image carrier at the developing site. The image carrier is transferred to a recording medium (transfer material) and supplied to the charging nip, which is a contact portion between the rotating charging member and the image carrier, by the injection charging in the image forming apparatus of the cleanerless system. Can be uniformly charged.

Japanese Patent Application Laid-Open No. Hei 10-307455 discloses a configuration in which the charging promoting particles are supplied from the developing means to the charging nip portion, which is the contact portion between the rotary charging member and the image carrier.

Further, the transfer residual toner reaches the developing site via the charging nip portion with the subsequent rotation of the image carrier, and is cleaned (collected) at the same time as the development from the surface of the image carrier by the developing means (toner recycling process).

In the simultaneous cleaning with development, the toner remaining on the image carrier after transfer is developed in a subsequent image forming step, that is, the image carrier is subsequently charged and exposed to form a latent image, and the latent image is developed. In some cases, the fog is recovered by a fog removal bias for development, that is, a fog removal potential difference Vback which is a difference between a DC voltage applied to the developing means and a surface potential of the image carrier (Japanese Patent Laid-Open No. 10-30745).
No. 6).

[0019]

As described above, an image of a transfer system and a toner recycling process (cleanerless system) in which a contact charging unit using charge-promoting particles is employed as a charging unit of an image carrier. A charging device for supplying a charge-promoting particle to a charging nip portion, which is a contact portion between a rotating charging member and an image carrier, in which a charge-promoting particle is added and mixed in advance to a developer (toner) of a developing unit. In an image forming apparatus configured to be operated from the developing unit, the amount (weight ratio) of the charge-promoting particles added to the toner of the developing unit is such that the fog in the non-latent image area, which may be generated due to an excessive ratio, is reduced. It is set in advance to a value that does not cause various inconveniences such as poor charging that can occur due to too long.

However, as will be described later, the amount of the charge promoting particles added to the toner is relatively larger than the amount of the toner flying from the developing means to the image carrier.
As the use durability of the apparatus advances, the mixing ratio of the charge promoting particles to the toner in the developing means gradually decreases from the initially set mixing ratio.

By the time the toner in the developing means is exhausted, the supply amount of the charge-promoting particles from the developing means to the charging nip becomes insufficient, and the charge is directly injected from the rotary charging member to the image carrier. Poor charging may occur due to insufficient charging.

Accordingly, an object of the present invention is to secure charging performance in such an image forming apparatus irrespective of a decrease in the supply amount of the charge-promoting particles from the developing means to the charging nip portion due to the durability of the apparatus. I do.

[0023]

According to the present invention, there is provided an image forming apparatus and a process cartridge having the following constitution.

(1) An image carrier, charging means for charging the image carrier, image information writing means for forming an electrostatic latent image on a charged surface of the image carrier, and a toner image formed by toner And a transfer unit for transferring the toner image on the image carrier to a recording medium, wherein the charging unit is in contact with the image carrier and a voltage is applied to the flexible rotary charging unit. A charging member having conductivity at least in a nip portion between the rotating charging member and the image bearing member, and rotating the rotating charging member with a speed difference with respect to the surface of the image bearing member. Contact charging means for charging
The developing unit also serves as a cleaning unit that collects the toner remaining on the image carrier after transferring the toner image to the recording medium, and the developer of the developing unit includes toner and charge accelerating particles. The electrostatic latent image on the image carrier is developed, and the charge promoting particles adhered to the image carrier in the developing section and remaining on the transferred image carrier are carried to the nip between the rotating charging member and the image carrier. Image forming means for replenishing the nip portion with the charge accelerating particles, and having means for increasing the nip width of the nip portion between the rotating charging member and the image carrier with the endurance of use of the apparatus. apparatus.

(2) The means for increasing the nip width of the nip portion reduces the distance between the rotation center axis of the rotating charging member and the rotation center axis of the image bearing member against the elasticity of the rotating charging member. (1) The image forming apparatus according to (1), which is means for increasing the amount of penetration of the rotary charging member into the body.

(3) The image forming apparatus according to (1) or (2), wherein at least the image carrier and the rotary charging member are integrally formed as a process cartridge detachable from the image forming apparatus main body. Image forming apparatus.

(4) An image carrier, charging means for charging the image carrier, image information writing means for forming an electrostatic latent image on the charged surface of the image carrier, and a toner image formed by toner And a transfer unit for transferring the toner image on the image carrier to the recording medium, and recovering the toner remaining on the image carrier after the developing unit transfers the toner image to the recording medium. A process cartridge detachable from the apparatus main body of the image forming apparatus, which also serves as a cleaning unit, and includes at least an image carrier and a charging unit. It has a flexible rotary charging member to be applied, and at least nip portion between the rotary charging member and the image carrier has conductive charge-promoting particles interposed therebetween, and the rotary charging member is moved relative to the surface of the image carrier. Speed difference The charging means is a contact charging means for charging the image charging member by rotating the image charging member. The developer of the developing means includes toner and conductive charge-promoting particles, and the developer is used to develop the electrostatic latent image on the image carrier. In the developing unit, the charge-promoting particles remaining on the image carrier after the transfer and transferred to the image carrier are carried to the nip between the rotating charging member and the image carrier, so that the charge-promoting particles are supplied to the nip. A process cartridge having means for increasing a nip width of a nip portion between a rotating charging member and an image carrier as the device is used for a long time.

(5) The means for increasing the nip width of the nip portion reduces the distance between the rotation center axis of the rotating charging member and the rotation center axis of the image bearing member against the elasticity of the rotating charging member. (4) The process cartridge according to (4), which is a means for increasing an amount of the rotating charging member penetrating the body.

[Operation] In consideration of the fact that the supply amount of the charge-promoting particles from the developing means to the charging nip gradually decreases with the endurance of use of the apparatus, the image bearing member is used as the endurance of the apparatus is advanced. With a configuration in which the amount of the rotating charging member penetrating into the body, that is, the nip portion width is gradually increased, the deterioration of the charging performance due to the shortage of the charge accelerating particles is compensated by the increase of the nip width of the charging nip portion, and the charging failure is reduced. Problems can be prevented from occurring.

[0030]

FIG. 1 is a schematic structural diagram of an example of an image forming apparatus according to the present invention.

(1) General Description of Image Forming Apparatus This image forming apparatus uses a transfer type electrophotographic process, a contact charging system using charge accelerating particles, a reversal developing system, and a toner recycling process (cleanerless system). , A process cartridge detachable type laser beam printer.

Reference numeral 1 denotes an electrophotographic photosensitive drum as an image carrier, which is driven to rotate at a predetermined peripheral speed in a clockwise direction indicated by an arrow a.

The image carrier 1 is subjected to primary charging by a direct charging mechanism uniformly at a predetermined polarity and potential by a contact charging device 2 using the charge accelerating particles Z.

An image exposure L is performed on the charged surface by the exposure device 4 as image information writing means, and an electrostatic latent image of image information is formed.

The electrostatic latent image is reversely developed as a toner image by the developing device 3.

Next, the toner image is fed from a paper feed mechanism (not shown) to a transfer nip portion, which is a contact portion between the image carrier 1 and a transfer roller 5 as a transfer means, at a predetermined control timing. The images are sequentially transferred to a medium (transfer paper) P.

The recording medium P that has passed through the transfer nip is separated from the surface of the image carrier 1 and subjected to a fixing process of a toner image by a fixing device 6 to form an image formed product (copy, print).
Is discharged as

Further, there is no dedicated cleaning device for removing the transfer residual toner remaining on the surface of the image carrier after the recording medium is separated, and the transfer residual toner is developed via the charged portion by the subsequent rotation of the image carrier 1. The developer is carried to the site and cleaned (collected) simultaneously with development from the surface of the image carrier 1 by the developing device 3 (toner recycling process).

Further, the charge accelerating particles Z are added and mixed in advance to the developer (toner) T of the developing device 3 at a predetermined ratio. The toner is supplied to the surface of the carrier 1, and at the transfer portion, only the toner T is mainly transferred to the recording medium P, and the rotation of the image carrier 1 causes the charge promotion particles Z to be carried to the charging nip N, which is the charging portion. Supply.

Reference numeral 100 denotes a process cartridge. In this embodiment, the image carrier 1 and the rotary charging member 2 of the charging device 2 are used.
(1) A process cartridge which is assembled with three process devices of the developing device 3 in a predetermined mutual arrangement relationship and is collectively removable from the image forming apparatus main body. The process cartridge 100 is inserted and mounted in a predetermined manner by a mounting means (not shown) of the image forming apparatus main body, and can be removed from the image forming apparatus main body. The process cartridge 100 is mechanically and electrically connected to and integrated with the image forming apparatus main body by being mounted in the image forming apparatus main body in a predetermined manner.

(2) Image Carrier 1 It is desired that the image carrier 1 has a high charge injection efficiency and a high charge holding power. In this embodiment, a 3 μm-thick overcoat layer having low resistance and high hardness is further provided on the surface of the charge transfer layer which is a surface layer of a general organic photoreceptor. Thereby, higher charging performance than a general organic photoreceptor can be obtained.

(3) Charging Device 2 The charging device 2 includes a rotary charging member 21 as a contact charging member.
Is brought into contact with the image carrier 1, a charge nip portion N serving as the contact portion is interposed with electrically conductive charge-promoting particles Z, a voltage is applied, and the image carrier 1 rotates with a speed difference with respect to the surface of the image carrier 1. Then, the image charger 1 is charged by the direct injection charging mechanism.

In this embodiment, the rotating charging member 21 is a conductive roller (charging roller) composed of a core metal 22 and a conductive sponge layer 23 formed concentrically and integrally around the core metal in a roller shape. Hereinafter, it is referred to as a charging sponge roller. In the present embodiment, the hardness of the sponge layer 23 of the charging sponge roller 21 is 30 degrees, and the average foam diameter is 50 μm.

The outer peripheral surface of the charging sponge roller 21 is coated with the charging promoting particles Z in advance. Charge promotion particles Z
Has an average particle diameter of 3 μm including the secondary aggregate and a specific resistance of 10
Conductive zinc oxide particles of ⁶ Ω · cm are used. The charge polarity of the charge accelerating particles Z is determined by a developer (toner) described later.
The polarity of T is plus, which is the opposite polarity to the minus of the charge polarity. The charge accelerating particles Z mainly adhere to the air bubbles of the sponge, and cover the surface of the charge sponge roller 21.

The charging sponge roller 21 is arranged substantially parallel to the axis of the image carrier 1, and both ends of the core bar 22 are rotatably supported by bearing members shown in the drawing.
The pressing member (not shown) is arranged so as to be pressed against the image carrier 1 against the elasticity of the sponge layer 23.

N denotes the charging sponge roller 21 and the image carrier 1
(A charging nip). In this embodiment, the nip width NP of the nip portion N is 3 as an initial setting.
mm, and the nip width is gradually increased by the nip width gradually increasing means with the endurance of use of the apparatus. The means for gradually increasing the nip width will be described in detail in section (8).

Further, the charging sponge roller 21 is driven to rotate at a predetermined peripheral speed in the clockwise direction of the arrow b by a driving means (not shown), while maintaining a predetermined relative speed difference with respect to the image carrier 1 in the nip portion N. By rotating the counter, the surface of the image carrier 1 is rubbed. In this embodiment, the rotational surface speed of the charging sponge roller 21 is 0.6 times the speed of the image carrier 1 during image formation, that is, the relative speed with respect to the image carrier 1, It is moving at a speed of 60% of the surface speed.

Charging sponge roller 2 for image carrier 1
The relative speed difference of 1 can also be provided by rotating the charging sponge roller 21 at a different peripheral speed from the image carrier 1 in a direction opposite to the rotation of the image carrier 1 (forward direction of rotation of the image carrier 1). However, since the charging property of the direct injection charging depends on the ratio of the peripheral speed of the image carrier to the peripheral speed of the charging sponge roller 21, it is preferable that the charging sponge roller 21 be driven to rotate in the same direction as the image carrier 1. It is advantageous in this respect, and this configuration is preferable.

S1 is a charging bias application power source for the charging sponge roller 21. A predetermined charging bias is applied to the core metal 22 of the charging sponge roller 21 from the power source S1.

By the charging device 2, the peripheral surface of the rotating image carrier 1 is charged by the direct injection charging mechanism to almost the same potential as the charging bias for the charging sponge roller 21.

In this embodiment, a charging bias voltage of -610 V is applied to the charging sponge roller 21. For this reason, in a region where the image carrier 1 and the charging sponge roller 21 are in contact, that is, in the nip portion N, in the portion where the above-mentioned charge promoting particles Z, which are a low-resistance substance, are in direct contact with them, they tend to have the same potential. Then, an electric charge is induced on the surface of the image carrier 1 and tends to reach −610 V which is the same electric potential as the charging sponge roller 21 side. Thereafter, when the charging sponge roller 21 and the surface of the image carrier 1 are separated, again,
The movement of the charge also occurs, and the charge on the image carrier 1 tends to decrease, but the amount of the decrease depends on the resistance value of the charging sponge roller 21 and the charge accelerating particles Z, the resistance value of the image carrier 1,
This is determined by the layer configuration. In the present embodiment, a system that minimizes the amount of decrease is reduced by 10 V and a surface potential of -600 V is obtained.

(4) Exposure device 44 is an exposure device as image information writing means. In this embodiment, it is a laser beam scanner. The scanner 4 performs laser beam scanning exposure L corresponding to the image information on the uniformly charged surface of the image carrier 1, so that an electrostatic latent image of the image information is formed on the surface of the image carrier 1. It is formed.

That is, the exposed portion of the charged surface of the image carrier 1 has a lower potential as in a general electrophotographic process, and a potential difference is created between the exposed and unexposed portions.
A latent image is formed. In this embodiment, the so-called bright portion potential VL of the exposed portion is VL = -150 with respect to the so-called dark portion potential VD = -600 V of the unexposed portion.
V.

(5) Developing Device 3 In this embodiment, the developing device 3 using a so-called jumping developing method is used in which the electrostatic latent image formed on the image carrier 1 does not contact the image carrier 1. (Hereinafter referred to as toner) T.

The developing device 3 contains a rotatable developing sleeve 31 containing a fixed developing magnet 32, a developing blade 33 in contact with the developing sleeve 31, and a toner (one-component magnetic toner) T. Developing container 34
Formed by

The developing container 34 contains toner T
At the same time, the charge accelerating particles Z are mixed at a weight ratio of 2 parts, and when a strong electric force does not work, the toner T is moving in a state where most of the toner T adheres.

The surface of the developing sleeve 31 is roughened. The developing sleeve 31 holds the magnetic toner T on the surface thereof in accordance with the magnetic force of the developing magnet 32 contained therein and conveys it in the direction of arrow c. When the transported toner T passes through the contact surface with the developing blade 33, the height (layer thickness) on the developing sleeve 31 is regulated, and the toner T is charged by friction and receives charge. In this embodiment, most of the chargeability of the toner T at this time is negative due to the charge polarity of the material. At the same time, the charge promotion particles Z passing through this region are positively charged.

FIG. 2 shows how the charged toner T and the charge accelerating particles Z behave between the developing sleeve 31 and the image carrier 1.

When the negatively charged toner T reaches a region approaching the image carrier 1, the electrostatic latent image is formed by an electric field formed between the image carrier 1 and the developing sleeve 31. develop. In this embodiment, the developing sleeve 31 is supplied with -400 as a developing bias by the power source S2.
V DC voltage, frequency 1500Hz, 1600Vpp
A voltage obtained by superimposing a rectangular wave AC voltage is applied,
300 μm formed between the image carrier 1 and the developing sleeve 31
In the gap of m, the negatively charged toner T does not fly to the dark potential portion of VD = -600V, but does fly to the bright potential portion of VL = -150V.

(6) Supply of the charge-promoting particles Z from the developing device 3 to the charging nip portion N At this time, the positively charged charge-promoting particles Z are electrically opposite to the toner T. Although it is easy to fly to the dark potential portion, it often adheres to the toner T itself due to its size, and when the electrostatic force with the toner T is stronger, it does not show the opposite behavior to the toner T, The same manner of movement as the toner T is shown. Accordingly, the charge accelerating particles Z can fly to both the bright potential portion and the dark potential portion.

The toner T that has moved onto the image carrier 1 in the developing step is transferred to the recording medium P in the transferring step. A DC voltage of 2 KV is applied to the transfer roller 5 serving as a transfer device from the power supply S3 to the image carrier 1, and an electric field formed between the image carrier 1 and the transfer roller 5 is applied to the transfer roller 5. Most of the negatively charged toner T is transferred to the recording medium P because the toner T is attracted to the transfer roller 5 side.

On the other hand, the positively charged charge accelerating particles Z
In the light potential portion, most of the toner T adhered to the recording medium P is transferred to the recording medium P together with the toner T. However, electrically, the toner T is more stable when it is on the image carrier 1. In comparison, a larger amount remains on the image carrier 1. Most of the charge accelerating particles Z attached to the dark portion potential remain on the image carrier 1 as they are.

Therefore, on the image carrier 1 after the transfer step, the toner T slightly remaining in the transfer step at the bright potential portion is formed.
A relatively large amount of the charge accelerating particles Z are present on the entire surface of the image carrier 1.

With the subsequent rotation of the image carrier 1, the charge accelerating particles Z remaining on the entire surface of the image carrier 1 are carried to the charging nip N and supplied. That is,
The charge promotion particles Z are supplied from the developing device 3 to the charge nip N.

Since a voltage of −610 V is applied to the charging sponge roller 21, the positively charged charging promoting particles Z are transferred to the charging sponge roller 21 by the transfer process.
An attempt is made to move to the charging sponge roller 21 from the surface of the image carrier 1 that is more positively charged. And, by being held on the fine surface of the sponge, the sponge performs the function of the charging step as described above.

(7) Toner Recycling Process On the other hand, the toner T remaining on the image carrier 1 without being transferred
Is a so-called inversion component, which was originally positively charged and is difficult to be transferred, or because it has been subjected to a transfer voltage, most of it is positively charged. Accordingly, the toner T also adheres to the charging sponge roller 21, but while adhering, the image carrier 1 and the charging sponge roller 21 pass several times through the region where the charging process is performed, and the negative charge is applied. Since the grant is made,
Originally, the toner T, which tends to be negatively charged, becomes negatively charged in a relatively short time, returns to the image carrier 1 again, is carried to the developing site, and is in contact with the developing sleeve 31 where the developing process is performed. When passing through an adjacent area, the toner T is assimilated with the newly developed toner T, so that a toner recycling process is established.

(8) Means for gradually increasing the nip width of the charging nip N One of the important items in this system is the charging ability of the image carrier 1 by the charging sponge roller 21 and the charging promoting particles Z. In this embodiment, as described above, the relative speed between the image carrier 1 and the charging sponge roller 21 is controlled to obtain the required charging ability at all times.
Is set to 60% of the peripheral speed. The supply of the charge accelerating particles Z to the charge nip N is performed from the developing device 3. In consideration of the fact that the supply amount of the charge accelerating particles Z from the developing device 3 to the charging nip N gradually decreases with the endurance of use of the apparatus, the charging is performed as the endurance of use of the apparatus proceeds as described below. The configuration in which the nip width NP of the nip portion N is gradually increased compensates for the deterioration of the charging performance due to the shortage of the charge accelerating particles Z.

That is, as described above, the charge-promoting particles Z externally added at a weight ratio of 2 parts to the developer (toner) T contained in the developing container 34 of the developing device 3 in an actual use environment Actually, since it is difficult to always maintain the same mixing ratio in the developing container 34, the charging ability may be slightly reduced as the use durability of the apparatus advances. It is considered that the reason is as follows.

In the developing process of the jumping developing method of the present embodiment, not all the toner adhered to the developing sleeve 31 is consumed for the development, and a part of the toner which has flown to the dark potential portion of the image carrier 1 is re-used. The toner is returned to the developing container 34. Here, only the charge accelerating particles Z originally added to the returned toner fly to the dark portion potential portion of the image carrier 1,
Since almost all of the toner adheres to the image carrier 1, the returned toner becomes a toner having a relatively small amount of the charge accelerating particles Z.
The process returns to the developing container 34. Due to the circulation of the toner in the developing container 34, the toner whose charge accelerating particles Z have been reduced is mixed with the new toner, and when the developer T is completely consumed, the entire toner in the developing container 34 is The amount of the charge accelerating particles Z contained in T decreases. It is considered that the shortage of the charge accelerating particles Z makes it difficult to obtain stable charging performance.

In view of the fact that the amount of the charge accelerating particles Z in the toner T in the developing container 34 gradually decreases due to the image formation, the charging sponge roller 21 and the image bearing member are used by the nip width gradually increasing means with the endurance of use of the apparatus. 1 to gradually increase the nip width NP of the charging nip portion N, that is, increase the contact area to supplement the charging performance.

FIG. 3 is an explanatory view of the nip width gradually increasing means of this embodiment. The image carrier 1 is disposed in a housing of the process cartridge 100 so as to be rotatably held by a bearing. The charging sponge roller 21 is also used for the process cartridge 100.
In this case, both ends of the core bar 22 are rotatably held by bearings, and are always pressed against the image carrier 1 by an urging member (not shown).

In the image carrier 1, a rotational force is transmitted from a driving system (not shown) on the image forming apparatus main body side to a drum gear GD provided at one end thereof, and a predetermined force is applied in a clockwise direction indicated by an arrow a in FIG. It is driven to rotate at the peripheral speed.

The charging sponge roller 21 is rotated at a predetermined peripheral speed in a clockwise direction indicated by an arrow b in FIG. 1 by transmitting a rotational force from a driving system (not shown) on the image forming apparatus main body side to the cored bar 22. In the nip portion N, counter rotation is performed while maintaining a predetermined relative speed difference with respect to the image carrier 1 to rub the surface of the image carrier 1.

At both ends of the conductive / elastic layer 23 of the charging sponge roller 21, a core metal 22 is rotatably slidable with respect to the image carrier 1 independently of the charging sponge roller 21.
Contact cam roller (butting cam roller)
28 are provided.

The contact cam rollers 28 are different from the circular members having a uniform radius at each part like the contact rollers 24 of the prior art apparatus shown in FIG. Is a substantially circular (spiral) cam member having an outer peripheral surface that gradually decreases from the large diameter portion r1 to the small diameter portion r2. r0 is the radius of the charging sponge roller 21 in the free state, and is larger than the large diameter portion r1 of the contact cam roller 28 (r0> r
1> r2). The contact cam rollers 28 on both sides have the same shape, and gears G13 G9 are provided concentrically and integrally.

G1 is a flange gear provided at the end of the image carrier 1 opposite to the drum gear GD side.
And rotate together.

Numeral 7 denotes a speed reducing means, and the rotational force of the flange gear G1 which rotates integrally with the image carrier 1 is reduced.
Is transmitted to the concentric integral gear G9 of the one contact cam roller 28 via the reduction gear trains G2 to G7 and the relay gear G8, and the contact cam roller 28 is rotationally driven at a very low speed. FIG. 5A is a front view of the gear train on this side.

The contact cam roller 28 on the other side also rotates the relay gear G8 with the gear G10, the shaft 8, and the relay gear train G11.
The other contact cam roller 28 is transmitted to the other contact cam roller 28 via G12 to the concentric integral gear G13, and the corresponding contact cam roller 28 is driven to rotate at a low speed. FIG. 5B is a front view of the gear train on this side.

Each of the contact cam rollers 28 on both sides has a contact portion with the image carrier 1 from the large diameter portion r1 to the small diameter portion r.
2 so as to rotate and slide at a very low speed with respect to the image carrier 1 independently of the charging sponge roller 21 at the same speed and phase in the direction of shifting to the contact cam rollers 28. The speed reduction ratio of the speed reduction unit 7 is set so that the rotation of the developing device 3 provided in the process cartridge 100 is less than one rotation until the life of the developing device 3 (out of toner).

At the initial point of time when the use of the process cartridge 100 is started (early endurance), as shown in FIG. 6 (a), the contact cam rollers 28 have a large radius r.
1 is in contact with the image carrier 1. At this time, the axial distance CD1 between the charging sponge roller 21 and the image carrier 1 is a predetermined maximum, and the amount of penetration d1 of the charging sponge roller 21 into the image carrier 1 is maintained at a predetermined minimum.
The contact nip width NP1 is a predetermined initial setting width corresponding thereto. In this embodiment, the diameter of the large-diameter portion r1 of the contact cam rollers 28 is set so that the initial set width NP1 is 1 mm.

When the process cartridge 100 is used and the toner consumption in the developing device 3 is advanced, the contact cam rollers 28 become larger in contact with the image carrier 1 as the durability of the process cartridge 100 progresses. It is rotationally driven at a very low speed in the direction f from the part r1 to the small diameter part r2. Thereby, the contact nip width NP gradually increases.

Then, at the end of the endurance, as shown in FIG. 6B, the small radius r2 of the contact cam rollers 28, 28
The vicinity is in contact with the image carrier 1. At this time, the axial distance CD2 between the charging sponge roller 21 and the image carrier 1 is a predetermined minimum, and the penetration amount d2 of the charging sponge roller 21 into the image carrier 1 is maintained at a predetermined maximum. The contact nip width NP2 is a predetermined maximum width corresponding thereto. In the present embodiment, the diameter of the small diameter portion r2 of the contact cam rollers 28 is set so that the final maximum width NP2 is 4 mm.

As a result, as the endurance of the process cartridge 100 progresses, the contact cam rollers 28 and 28 rotate slightly less than one rotation before the life of the developing device 3, so that the axial distance between the charging roller 21 and the image carrier 1 is reduced. The CD gradually decreases (CD1 → CD2), and the nip width NP (penetration d) gradually increases (NP1 (d1) → NP2 (d2)).
That is, since the contact area between the charging sponge roller 21 and the image carrier 1 increases, it is possible to compensate for the above-mentioned problem of the deterioration of the charging performance due to the shortage of the charging promoting particles Z.

(9) Others Needless to say, the means for gradually increasing the nip width of the charging nip portion N is not limited to the configuration of the above-described embodiment. As another configuration example, for example, without the contact cam rollers 28, 28,
By gradually increasing the pressing force of the pressing member that presses the charging roller 21 against the image carrier 1 against its elasticity in accordance with the durability of the apparatus, the nip width of the charging nip portion N is gradually increased. Can also.

[0085] The process cartridge includes, for example, an electrophotographic photosensitive member and at least a charging unit. Therefore, as an aspect of the process cartridge, for example, an electrophotographic photosensitive member, a developing unit and a charging unit are integrally formed into a cartridge, and the cartridge is detachable from the apparatus main body. There are cartridges that can be attached to and detached from the apparatus main body. That is, the process cartridge is one in which the developing means, the charging means, and the electrophotographic photosensitive member are integrally formed into a cartridge, and this cartridge is detachably mountable to the main body of the image forming apparatus. In addition, the charging means and the electrophotographic photosensitive member are integrally formed into a cartridge so that the cartridge can be attached to and detached from the image forming apparatus main body.

Although the image forming apparatus of the embodiment with the process cartridge detachable system is for forming a single color image, a plurality of process cartridges are provided and a plurality of color images (for example, a two-color image, a three-color image or The present invention can be suitably applied to an image forming apparatus for forming a full-color image.

The present invention can be suitably applied to an image forming apparatus which is not of a process cartridge detachable type.

[0088] The electrophotographic photosensitive member as the image carrier is not limited to the photosensitive drum, and includes, for example, the following. First, a photoconductor is used as a photoconductor, and examples of the photoconductor include amorphous silicon, amorphous selenium, zinc oxide, titanium oxide, and an organic photoconductor (OPC). In general, a drum-shaped one is used, in which a photoconductor is deposited or coated on a cylinder of an aluminum alloy or the like.

[0089] An electrostatic recording dielectric may be used as the image carrier. The image information writing means in this case is not an exposure device but a selective charge removing device such as a charge removing needle array or an electron gun.

. In the embodiment, a laser beam printer is exemplified as an image forming apparatus. However, the present invention is not limited to this, and may be used in other image forming apparatuses such as an electrophotographic copying machine, a facsimile machine, or a word processor. Of course it is possible.

[0091] The rotary charging member, which is a contact charging member, is not limited to the roller type, but may be a rotary endless belt type. The conductive / elastic layer is not limited to sponge flesh, but may be solid flesh. Fur brushes, woven fabrics, non-woven fabrics, and the like can also be used.

[0092]

As described above in detail, according to the present invention, a transfer system, a toner recycling process (cleanerless system), which employs a contact charging device using charging promoting particles as a charging device for an image carrier. Regarding the image forming apparatus and the process cartridge detachably mountable to the main body of the image forming apparatus, regardless of the decrease in the supply amount of the charge promoting particles from the developing means to the charging nip portion due to the durability of the apparatus, A decrease in charging performance due to shortage is compensated for by an increase in the nip width of the charging nip portion, thereby making it possible to prevent the problem of poor charging.

[Brief description of the drawings]

FIG. 1 is a schematic configuration model diagram of an image forming apparatus according to an embodiment.

FIG. 2 is an explanatory diagram of the behavior of a toner and a charge accelerating particle at a development site.

FIG. 3 is an explanatory diagram of a configuration of a nip width gradually increasing unit.

FIG. 4 is an explanatory diagram of a configuration of a contact cam roller.

FIGS. 5 (a) and (b) are front views of a rotational force transmission gear train for one side and the other side of the contact cam rollers.

FIGS. 6 (a) and (b) are explanatory views of a nip width change at the beginning of the endurance and at the end of the endurance of the apparatus due to the operation of the nip width gradually increasing means, respectively.

FIG. 7 (a) is a front model diagram in which a middle part of a conventional example of a contact charging device using charge accelerating particles is omitted, and FIG. 7 (b) is an enlarged side model diagram.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Image carrier 2 ... Charging device 21 ... Charging roller 24 ... Contact roller 25 ... Bearing part 26 ... Spring 27 ... Device frame 28 ... Contact Cam roller 3 ・ ・ ・ Developing device 31 ・ ・ ・ Developing sleeve 32 ・ ・ ・ Developing magnet 33 ・ ・ ・ Developing blade 34 ・ ・ ・ Developing container 5 ・ ・ ・ Transfer device 6 ・ ・ ・ Fixing device 4 ・ ・ ・ Exposure device a , B, c, f ... rotation direction CD, CD1, CD2 ... center distance K ... drive transmission L ... exposure signal NP, NP1, NP2 ... nip width P ... transfer paper r0, r1, r2 ... radius S1, S2, S3 ... power supply

Claims (5)

[Claims] An image carrier; a charging unit configured to charge the image carrier; an image information writing unit configured to form an electrostatic latent image on a charged surface of the image carrier; A developing means for visualizing, and a transfer means for transferring the toner image on the image carrier to a recording medium, wherein the charging means is in contact with the image carrier and a flexible rotary charging member to which a voltage is applied Having at least a nip portion between the rotary charging member and the image carrier with conductive charge-promoting particles interposed therebetween, and rotating the rotary charging member with a speed difference with respect to the surface of the image carrier to form an image charger. The developing means is also a cleaning means for collecting the toner remaining on the image carrier after transferring the toner image to the recording medium, and the developer of the developing means is composed of the toner and the charge accelerating means. Containing particles,
With this developer, the electrostatic latent image on the image carrier is developed,
The charge-promoting particles that adhere to the image carrier in the developing unit and remain on the image carrier after transfer are carried to the nip portion between the rotating charging member and the image carrier, thereby replenishing the nip portion with the charge-promoting particles. An image forming apparatus, comprising: means for increasing a nip width of a nip portion between a rotating charging member and an image carrier in accordance with endurance of use of the apparatus. The means for increasing the nip width of the nip portion includes:
The distance between the rotation center axis of the rotating charging member and the rotation center axis of the image bearing member is reduced against the elasticity of the rotating charging member to increase the amount of penetration of the rotating charging member into the image bearing member. The image forming apparatus according to claim 1. 3. The image forming apparatus according to claim 1, wherein at least the image carrier and the rotary charging member are integrally formed as a process cartridge detachably mountable to the image forming apparatus main body. apparatus. 4. An image bearing member, charging means for charging the image bearing member, image information writing means for forming an electrostatic latent image on a charged surface of the image bearing member, and converting the electrostatic latent image into a toner image with toner Developing means for visualizing, and transfer means for transferring the toner image on the image carrier to a recording medium, and recovering the toner remaining on the image carrier after the developing means transfers the toner image to the recording medium. A process cartridge detachable from the apparatus main body of the image forming apparatus also serving as a cleaning unit, and includes at least an image carrier and a charging unit. The charging unit contacts the image carrier and applies a voltage. A charge-promoting particle having conductivity at least in a nip portion between the rotating charging member and the image carrier, and moving the rotating charging member relative to the surface of the image carrier. With a difference Is a contact charging means for charging the image charging member by rotating, the developer of the developing means includes toner and conductive charge-promoting particles, and the developer is used to develop an electrostatic latent image on the image carrier, The charge-promoting particles that adhere to the image carrier in the developing unit and remain on the image carrier after transfer are carried to the nip portion between the rotating charging member and the image carrier, thereby replenishing the nip portion with the charge-promoting particles. A process cartridge comprising means for increasing a nip width of a nip portion between a rotating charging member and an image carrier as the device is used for a long time. 5. The means for increasing the nip width of the nip portion includes:
The distance between the rotation center axis of the rotating charging member and the rotation center axis of the image bearing member is reduced against the elasticity of the rotating charging member to increase the amount of penetration of the rotating charging member into the image bearing member. The process cartridge according to claim 4, wherein