JP2002014591A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device which is constituted so that a contact electrifying means to use electrically conductive particles m is adopted as the electrifying means for uniformly electrifying image carrying bodies 1 to have the prescribed polarity and electrical potential and the particles m are supplied from a developing means 3 to a nip part (a) where the electrifying means 2 is brought into contact with the bodies 1 and in which stable electrification is realized during repetive passage of paper sheets by preventing the unbalance that the particles m are supplied to the electrifying member region part corresponding to the paper-impassable part region more excessively than to that corresponding to the paper-passable part region. SOLUTION: The unbalance that the particles m are supplied to the electrifying member zone part corresponding to the paper-impassable part region more excessively than to that corresponding to the paper-passable part region is prevented by setting the electrical potential of the image carrying body surface region corresponding to the paper-impassable part lower than the prescribed electrified potential of the image carrying body 1 by the means 2 to restrain the moving amount of the particles m from the means 3 to the image carrying body surface region corresponding to the paper-impassable part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an electrophotographic photosensitive member.
Conductive particles (charge accelerating particles) as charging means for uniformly charging an image carrier such as an electrostatic recording dielectric to a predetermined polarity and potential
The present invention relates to an image forming apparatus that employs a contact charging unit using a developing unit and supplies conductive particles to a contact nip between a charging member and an image carrier from a developing unit.

[0002]

2. Description of the Related Art FIG. 8 is a schematic structural diagram of an example of an image forming apparatus having the above-described structure disclosed in Japanese Patent Application Laid-Open No. Hei 10-307455. The image forming apparatus of this embodiment is a copying machine or printer using a transfer type electrophotographic process, a reversal developing method, and a cleaner-less type.

Reference numeral 1 denotes a drum-type electrophotographic photosensitive member (hereinafter, referred to as a photosensitive drum) as an image carrier, which is rotated at a predetermined peripheral speed (process speed) in a clockwise direction indicated by an arrow.

Reference numeral 2 denotes a charging roller (a conductive elasticity or sponge roller) as a charging member of the contact charging means, which is pressed against the photosensitive drum 1 with a predetermined pressing force. Reference symbol a denotes a charging nip portion (charging portion) that is a pressure contact portion between the charging roller 2 and the photosensitive drum 1.

[0005] Conductive particles m are applied to the outer peripheral surface of the charging roller 2 in advance, and the conductive particles m are applied to the charging nip portion a.
Intervenes. The charging roller 2 is driven to rotate in the clockwise direction indicated by an arrow, and moves in a direction opposite to the surface moving direction of the photosensitive drum 1 in the charging nip portion a. The surface of the charging roller 2 and the surface of the photosensitive drum 1 are electrically conductive particles m. And rubbing contact with speed difference. The charging roller 2 has a power supply S1.
, A predetermined DC charging bias is applied.

As a result, the outer peripheral surface of the rotating photosensitive drum 1 is directly subjected to direct injection charging at substantially the same potential as the charging bias applied to the charging roller 2.

Next, image exposure L is performed on the uniformly charged surface of the photosensitive drum 1 by image exposure means (not shown) in an exposure section b, and the potential of the exposed section on the uniformly charged surface of the photosensitive drum 1 is attenuated. (Light potential), and an electrostatic latent image corresponding to the image exposure pattern is formed on the surface of the photosensitive drum 1 by a potential contrast with the potential of the exposed dark portion (dark potential).

3 is a magnetic one-component insulating toner (negative toner)
Is a reversal developing device using as a developer T. The developer T contains a predetermined amount of conductive particles m by external addition and mixing. A thin layer of the developer T containing the conductive particles m is formed and carried on the rotary developing sleeve 3a, and is conveyed to the developing section c, which is a portion of the photosensitive drum 1 and the developing sleeve 3a which are in close proximity to each other. Further, a predetermined developing bias is applied to the developing sleeve 3a from the power source S2.

Thus, in the developing section c, the electrostatic latent image on the surface of the rotating photosensitive drum 1 is reversely developed with the negative toner (toner adheres to a light potential portion on the photosensitive drum surface). In addition, the conductive particles m contained in the developer are also attached and supplied to the surface of the photosensitive drum 1.

Reference numeral 4 denotes a transfer roller as transfer means. The photosensitive drum 1 is brought into contact with a predetermined pressing force, and rotates in the forward direction of the photosensitive drum at a peripheral speed substantially equal to the rotational peripheral speed of the photosensitive drum. d is a transfer nip portion which is a pressure contact portion between the transfer roller 4 and the photosensitive drum 1. A transfer material P as a recording medium is fed to the transfer nip d from a paper supply unit (not shown) at a predetermined control timing, and the transfer nip d is nipped and conveyed. A predetermined transfer bias is applied to the transfer roller 4 from a power source S3.

As a result, the toner image on the surface of the photosensitive drum 1 is sequentially electrostatically transferred to the surface of the transfer material P which is nipped and conveyed by the transfer nip d.

The transfer material P coming out of the transfer nip d is separated from the surface of the rotary photosensitive drum 1, introduced into a fixing device (not shown), and subjected to a fixing process of the transferred toner image to form an image formed material (print). , Copy).

The image forming apparatus of this embodiment is cleaner-less, and is a dedicated cleaner (cleaning device) for removing transfer residual toner slightly remaining on the surface of the photosensitive drum 1 after transfer.
Is not provided. The untransferred toner on the surface of the photosensitive drum 1 after the transfer is carried to the developing unit c via the charging nip part a with the subsequent rotation of the photosensitive drum 1, and the developing device 3
And cleaning (collection) at the same time as development.

Further, it is contained in the developer T of the developing device 3,
The conductive particles m attached and supplied to the surface of the photosensitive drum 1 during development
Is electrically conductive and its charge polarity is opposite to that of the developer (toner) T, so that it does not substantially transfer to the transfer material P in the transfer portion d, and most of the photosensitive drum By continuing rotation of the photosensitive drum 1 while being attached to one surface, the photosensitive drum 1 is carried to the charging nip portion a and is replenished and supplied to the charging nip portion a, so that a new injection site can always be obtained. For this reason, even if the toner is accumulated on the charging roller 2, it is possible to suppress the occurrence of charging failure by supplying the conductive particles m more than that.

A) Contact charging means using conductive particles m A contact charging means using conductive particles (charge accelerating particles) m is disclosed in JP-A-10-307454 and the like.
Japanese Patent Application Laid-Open No. 10-30 discloses a structure in which conductive particles are supplied to a contact nip portion between a charging member and an image carrier from a developing unit.
No. 7,455, and the like. In an electrophotographic image forming apparatus / electrostatic recording image forming apparatus, an electrophotographic photosensitive member
This is effective as a charging means for directly injecting and charging an image carrier (charged body) such as an electrostatic recording dielectric at a predetermined polarity and potential.

The conductive particles m are fine particles for the purpose of assisting charging, and are directly injected into the nip portion a of the photosensitive drum 1 as an image carrier and the charging roller 2 as a charging member by interposing the conductive particles m. It realizes electrification. That is, by interposing the conductive particles m in the nip portion a, the friction in the charging nip portion a between the charging roller 2 and the photosensitive drum 1 is reduced by the lubricating effect (friction reducing effect) by the particles m, and the rotation of the charging roller 2 The driving torque can be reduced, and the charging roller 2 can be brought into contact with the photosensitive drum 1 with a speed difference. m
Rubs the surface of the photosensitive drum 1 without gaps, so that even if a simple member such as a charging roller or a charging sponge roller is used as the charging member 2, the ozone-less direct injection charging at a low applied voltage becomes dominant. Can be. In addition, uniform charging without charge unevenness can be achieved even in a micro portion.

The direct injection charging is a charging system that charges the image carrier by directly injecting charge from the charging member into the image carrier, which is a member to be charged, without basically using a discharge phenomenon. Even when the voltage applied to the charging member is equal to or lower than the discharge threshold, the image carrier can be charged to a potential corresponding to the applied voltage. Since no generation of ions due to the discharge phenomenon is involved, there is no adverse effect due to the discharge products.

B) Cleanerless System (Toner Recycling System) In a transfer type image forming apparatus, the developer (toner) remaining on the image carrier after transfer is removed from the surface of the image carrier by a cleaner and discarded. Although it becomes toner, it is desirable that this waste toner does not come out from the viewpoint of environmental protection. Therefore, as in the image forming apparatus of the above-described example, the cleaner is eliminated, and the untransferred toner on the photosensitive drum 1 after the transfer is removed from the photosensitive drum 1 by “developing simultaneous cleaning” by the developing device 3 and collected and re-used by the developing device 3 An image forming apparatus of a cleanerless system having an apparatus configuration used has also appeared.

Simultaneous development cleaning means that the toner remaining on the image carrier after transfer is developed at the next and subsequent steps, that is, the image carrier is subsequently charged and exposed to form a latent image, and the latent image is developed. This is a method of recovering sometimes by a fog removal bias (fogging potential difference Vback which is a potential difference between a DC voltage applied to the developing device and a surface potential of the image carrier).
According to this method, the transfer residual toner is collected in the developing device and reused after the next process. Therefore, waste toner can be eliminated and troublesome maintenance can be reduced. In addition, the cleaner-less system has a great advantage in terms of space, and can greatly reduce the size of the image forming apparatus.

In the toner recycling system, the transfer residual toner is not removed from the surface of the image bearing member by a dedicated cleaner as described above, but is transferred to a developing device via a charging means and used again in the developing process. Therefore, when contact charging is used as the charging means of the image carrier, how is the state in which the insulative toner is interposed in the charging nip portion which is the contact portion between the image carrier and the contact charging member? An issue is whether to charge the image carrier. In the roller charging or the fur brush charging, the transfer residual toner on the image carrier is diffused to form a non-pattern, and a large amount of baisic is applied and the discharge charging is used in many cases. In magnetic brush charging, since conductive magnetic particles that are powder are used as a contact charging member, there is an advantage that the magnetic brush portion of the conductive magnetic particles can flexibly contact the image carrier and charge the image carrier. The equipment configuration is complicated,
The adverse effects caused by the drop of the conductive magnetic particles constituting the magnetic brush portion are great.

In the case of the contact charging means using the above-described conductive particles m, the presence of the conductive particles m in the charging nip portion a causes transfer residual toner to be mixed into the charging nip portion a, or a charging member to be charged. 2 is contaminated with toner,
And the contact resistance at the charging nip portion a with respect to the image carrier 1 can be maintained, and even if the toner is accumulated in the charging nip portion a or the charging member 2, the conductive particles m Is supplied, it is possible to suppress occurrence of charging failure.

In this type, after the transfer of the image on the image carrier 1, the transfer residual toner T passes between the conductive particles m of the charging nip a where the charging process is performed and the image carrier 1. Since the charge injection is performed in the same manner as in the image carrier 1 during the developing process, it is possible to have an appropriate charge, so that the developing device 3 does not pass through the developing section area where the developing process is performed without passing through. Will be collected. Therefore, an electrophotographic process without a cleaner can be realized. That is, it is effective for both environmental protection and miniaturization of the device.

C) Transfer of the conductive particles m from the developing device 3 to the photosensitive drum 1 The conductive particles m contained in the developer T of the developing device 3 are charged by the developing device 3 into an electrostatic latent image on the photosensitive drum 1 side. Shifts to the photosensitive drum 1 side during toner development.

FIG. 9 shows a DC voltage (-400 V) and an AC voltage (1.2 kV) as a developing bias applied to the developing sleeve 3a.
In the developing device to which the superimposed voltage of
4 schematically shows how the positive conductive particles m fly on the photosensitive drum 1.

Vmax · Vmin is the maximum potential and the minimum potential of the developing AC component, and in this embodiment, each is −1000 V
And + 200V. , Vd · VL are the dark potential (non-image portion) and the bright potential (image portion) of the electrostatic latent image, and are −600 V and −150 V, respectively, in this example. Vdc is development DC
Potential (−400 V). Since the conductive particles m tend to be weakly positive as an external additive, the use of the conductive particles m alone causes the developing sleeve 3a to act on the non-image portion (dark potential Vd portion) of the electrostatic latent image on the surface of the photosensitive drum 1. 800 V (| Vmin−Vd | = | 200 − (− 60)
0) Fly with the contrast of |).

Some of the conductive particles m adhere to the toner T, and the image portion (the bright potential VL portion) of the electrostatic latent image
850 V (| VL−Vmax | = | −150 − (− 10) from the developing sleeve 3a to the photosensitive drum 1
00) |).

That is, the conductive particles m contained in the developer T of the developing device 3 fly and move toward the photosensitive drum 1 when the developing device 3 develops the toner of the electrostatic latent image on the photosensitive drum 1 side.

The toner image on the photosensitive drum 1 is attracted to the transfer material P side by the influence of the transfer bias in the transfer nip d and is positively transferred.
Is positive and does not transfer to the transfer material P side by an electric force (Coulomb force), but some conductive particles are transferred by friction (contact, rubbing) with the transfer material. It is attached to and transferred to the material P and is taken away from the surface of the photosensitive drum 1. FIG. 10 is a schematic diagram showing this state. The amount of the conductive particles to be transferred significantly increases when a large amount of the transfer material P is continuously fed.

Since the image forming apparatus in the toner recycling process does not use a cleaner, the transfer residual toner and the conductive particles m remaining on the surface of the photosensitive drum 1 after the transfer are charged on the photosensitive drum 1 and the charging roller 2 as a contact charging member. The photosensitive drum 1 is carried to the nip portion a by the rotation of the photosensitive drum 1 as it is. The conductive particles m carried to the charging nip portion a are the photosensitive drum 1
Most of the conductive particles m are peeled off by the charging roller 2 rotating in the counter direction, so that the conductive particles m can be applied onto the charging roller 2. Thus, the conductive particles m applied to the charging roller 2 initially
Is reduced by increasing the number of sheets passed, the conductive particles m
From the developing device 3 via the photosensitive drum 1
, The direct injection charging is realized.

Due to the presence of the conductive particles m in the charging nip portion a, even when toner adheres to or mixes with the charging roller 2, it is possible to maintain the close contact property and contact resistance of the charging roller 2 with the photosensitive drum 1. The contact charging member is a simple member such as a charging roller.
Of the photosensitive drum 1 by direct injection. That is, the charging roller 2 comes into close contact with the photosensitive member via the conductive particles m, and the conductive particles m present in the nip portion between the charging roller 2 and the photosensitive drum 1 rub the surface of the photosensitive drum 1 without gaps. As a result, the charging of the photosensitive drum 1 by the charging roller 2 is controlled by stable and safe direct injection charging without using a discharge phenomenon due to the presence of the conductive particles m, and has a high charging efficiency that cannot be obtained by conventional roller charging or the like. Thus, a potential substantially equal to the voltage applied to the charging roller 2 can be applied to the photosensitive drum 1.

The transfer residual toner adhering to and mixed into the charging roller 2 is gradually discharged from the charging roller 2 onto the photosensitive drum 1 and moves to the developing unit c as the surface of the photosensitive drum 1 moves. (Collected) (toner recycling process). As described above, in the simultaneous cleaning with development, the toner remaining on the photosensitive drum 1 after the transfer is developed in the subsequent image forming process, that is, the photosensitive member is subsequently charged and exposed to form a latent image, and the latent image is developed. At this time, the toner is collected by a fogging bias of the developing device, that is, a fog removing potential difference Vback which is a potential difference between a DC voltage applied to the developing device and a surface potential of the photoconductor. In the case of the reversal development as in the printer in this embodiment, the simultaneous cleaning for development involves the electric field for collecting the toner from the dark potential portion of the photoconductor to the developing sleeve and the adhesion of the toner from the developing sleeve to the bright potential portion of the photoconductor. This is done by the action of the electric field.

Even if the conductive particles m fall off from the charging roller 2, the printer is operated and the developing device 3
The conductive particles m contained in the developer T are transferred to the surface of the photosensitive drum 1 in the developing section a and are carried to the charging nip section a via the transfer nip section d by the rotation of the photosensitive drum 1 so that the charging roller 2 To the conductive particles m
And good chargeability is stably maintained due to the presence of.

Thus, in the image forming apparatus of the contact charging system, the transfer system, and the toner recycling process, the charging roller is used as the contact charging member, and the charging roller 2 can be applied at a low applied voltage regardless of the contamination by the transfer residual toner. Ozone-less direct injection charging can be stably maintained over a long period of time, uniform chargeability can be provided, and there is no obstacle due to ozone products, failure due to charging failure, etc., simple configuration, low cost image formation A device can be obtained.

[0034]

As described above, a part of the conductive particles m transferred from the developing device 3 to the surface of the photosensitive drum 1 adhere to the transfer material P passed through the transfer portion d. The amount of the conductive particles which are transferred and carried away and relocated increases remarkably when a large amount of the transfer material P is continuously passed, so that the transfer material P to be passed is the width of the maximum paper passing area (paper passing). In the case where the transfer material is smaller in width than the direction perpendicular to the direction, the same applies hereinafter), the conductive particles m adhered to the photosensitive drum surface area corresponding to the paper passing area of the small size transfer material are part of the transfer material. Is attached to the transfer material and carried away,
A part of the conductive particles m attached to the photosensitive drum surface area corresponding to the non-sheet passing area does not adhere to the transfer material and is not carried away. More conductive particles m remain than the photosensitive drum surface area corresponding to the paper area and are carried to the charging nip part a.

As a result, the supply of the conductive particles m along the length of the charging nip portion a is not uniform, and the supply amount of the conductive particles to the charging nip portion corresponding to the non-sheet passing area is equal to the charging amount corresponding to the sheet passing area. The supply amount of the conductive particles is larger than the supply amount of the conductive particles to the nip portion, and the supply of the conductive particles to the charging nip portion corresponding to the non-sheet passing area becomes excessive.

FIG. 11 shows the photosensitive drum 1, the charging area Sc of the charging roller 2, the developing area Sd of the developing sleeve 3a, and the small-size paper passing area S when a small-sized transfer material is passed.
FIG. 7 is a diagram schematically illustrating a width relationship between p and a non-sheet passing portion region Sp ′. This figure is based on the central paper passing. Charging area S
c and the width of the development area Sd are the same.

From the above, the abundance of the conductive particles m along the roller length on the charging roller 2 depends on the area Sc1 corresponding to the small size paper passing area Sp and the non-paper passing area Sp ′.
The relationship Sc1 <Sc2 occurs with the region Sc2 corresponding to.

As described above, when the small-size transfer material is passed, the distribution of conductive particles along the length on the charging roller 2 is increased in the region Sc2 corresponding to the non-paper passing portion region Sp '. When the number of durable sheets increases, a part of the conductive particles that are excessively supplied to the non-sheet passing area Sc2 on the roller 2 and deposited are peeled off from the charging roller 2 to cause a problem that poor charging occurs.

Accordingly, the present invention provides an image carrier having a predetermined polarity.
An image forming apparatus that employs a contact charging unit using conductive particles as a charging unit for uniformly charging to a potential, and supplies the conductive particles to a contact nip portion between a charging member and an image carrier from a developing unit. In the above, to prevent imbalance in which conductive particles are excessively supplied to the charging member region portion corresponding to the non-sheet passing portion region compared to the charging member region portion corresponding to the paper passing portion region Another object of the present invention is to realize stable charging through paper passing durability.

[0040]

SUMMARY OF THE INVENTION The present invention is an image forming apparatus having the following configuration.

(1) An image carrier, and a charging member for forming a nip with the image carrier, and a charging member for charging the image carrier to a predetermined potential with conductive particles interposed at least in the nip portion. Means, image information writing means for forming an electrostatic latent image on the charged surface of the image carrier, developing means for visualizing the electrostatic latent image as a toner image with a developer containing toner and conductive particles, Transfer means for transferring a toner image to a member to be transferred, wherein the conductive particles contained in the developer adhere to the surface of the image carrier when the electrostatic latent image is developed by the developing means. In the image forming apparatus in which the conductive particles are supplied to the nip portion by being carried to the nip portion, the potential of the image carrier surface area corresponding to the non-sheet passing portion in the transfer portion of the transfer unit is charged. Image carrying by means An image forming apparatus characterized in that setting of lower than the predetermined charging potential.

(2) The image information writing means is an exposure means, and the exposure means is provided on a non-sheet passing portion of a transfer section of the transfer means of the image carrier charged to a predetermined potential by the charging means. The image according to (1), wherein the surface area of the image carrier is set lower than a predetermined charging potential of the image carrier by the charging unit by exposing a corresponding surface area in a shorter time than during image formation. Forming equipment.

(3) A surface area of the image carrier charged to a predetermined potential by the charging means is exposed to a surface area corresponding to a non-sheet passing portion in a transfer section of the transfer means to charge the image carrier surface area. (1) having a dedicated exposure means for setting the charging potential to be lower than a predetermined charging potential of the image carrier by the means.
An image forming apparatus according to claim 1.

(4) There is provided a detecting means for detecting the length of the member to be transferred passed through the transfer portion of the transfer means in the direction perpendicular to the sheet passing direction. (1) to (3) The image forming apparatus according to any one of the above.

(5) The voltage applied to the charging member is DC
The image forming apparatus according to any one of (1) to (4), wherein the image forming apparatus includes only a component.

(6) The conductive particles have a particle resistance of 10 ¹²
Ω · cm to 10 ⁻¹ Ω · cm and a particle size of 10 μm to
The image forming apparatus according to any one of (1) to (5), wherein the thickness is 10 nm.

(7) The image forming apparatus according to any one of (1) to (6), wherein the charging member rotates at a counter with respect to the image carrier.

(8) The charging member has a surface having conductivity and elasticity, and is constituted by a conductive particle carrier for supporting the conductive particles. (1) to (7)
The image forming apparatus according to any one of the above.

<Operation> The transfer amount of the conductive particles from the developing means to the image carrier is
The value increases or decreases in accordance with the level of the charged potential of the image carrier. The higher the charged potential of the image carrier, the larger the value.

The present invention focuses on this, and by setting the potential of the surface area corresponding to the non-sheet passing portion of the image carrier to a predetermined lower than the predetermined charging potential of the image carrier by the charging means. The transfer amount of the conductive particles from the developing means to the surface area corresponding to the non-sheet passing portion of the image carrier is determined by the transfer of the conductive particles from the developing means to the area corresponding to the paper passing portion of the image carrier. The supply amount of the conductive particles along the length of the nip portion between the image carrier and the charging member as a result of the region corresponding to the paper passing portion and the region corresponding to the non-paper passing portion. By making the two regions substantially uniform without any imbalance, the conductive particles are supplied in excess with respect to the charging member portion corresponding to the non-sheet passing portion compared to the charging member portion corresponding to the paper passing portion, and accumulated. To prevent poor charging due to peeling, and stable through paper passing durability It is obtained by realizing the electrostatic.

[0051] Means for lowering the potential of the surface area corresponding to the non-sheet passing portion of the image carrier below a predetermined charging potential of the image carrier by the charging means is used for forming image information for forming an electrostatic latent image on the charged surface of the image carrier. When the writing means is an exposure means, the exposure means can be used, and the exposure means forms an image on a surface area corresponding to the non-sheet passing portion of the image carrier charged to a predetermined potential by the charging means. Exposure in a shorter time than before can set the surface area of the image carrier corresponding to the non-sheet passing portion to be lower than a predetermined charging potential of the image carrier by the charging means, and it is necessary to provide new means and members. do not do.

Further, it is more desirable that the light emission time of the exposure means for exposing a surface area corresponding to the non-sheet passing portion of the image carrier is not more than 1/2 of that during image formation. Setting is possible.

[0053] The means for lowering the potential of the surface area corresponding to the non-sheet passing portion of the image carrier to a predetermined charging potential of the image carrier by the charging means may be a dedicated exposure means (second exposure means). By exposing the surface area corresponding to the non-sheet passing portion on the image carrier by the dedicated exposure means, it is possible to simultaneously and more stably set the potential for the non-sheet passing portion on the image carrier. Further, it is desirable that the spot diameter of the dedicated exposure means is about twice as large as the spot system of the exposure means for forming an image, so that the non-sheet passing portion of the image carrier can be exposed more uniformly. And unnecessary potential pitch unevenness on the surface of the image carrier is not caused.

[0054] By detecting the longitudinal length of the transfer-receiving member, the non-sheet passing area on the image carrier becomes clear, and exposure for lowering the potential of the non-sheet passing area to a predetermined value is performed more accurately.

[0055] By setting the voltage applied to the charging member to only the DC component, the electric circuit of the image forming apparatus main body can be simplified.

Further, a small amount of ozone products generated in the charging mechanism by the discharge of the AC voltage + DC voltage can be further reduced.

[0057] Particle resistance of conductive particles is 10 ¹² Ω · c
By setting the particle size to 10 μm to 10 nm with m to 10 ⁻¹ Ω · cm, uniform and stable charging in direct injection charging becomes possible.

[0058] The charging member is preferably rotated in the counter direction with respect to the image carrier. Since the charging property of direct injection charging depends on the ratio between the peripheral speed of the image carrier and the peripheral speed of the charging member, the same peripheral speed ratio as in the reverse direction is obtained when the rotation speed of the charging member is in the reverse direction in the forward direction. It will be larger than that.

Therefore, it is advantageous to rotate the charging member in the counter direction with respect to the image carrier in terms of the number of rotations.
The peripheral speed ratio described here is the peripheral speed ratio (%) = (charging member peripheral speed−image carrier peripheral speed) / image carrier peripheral speed × 100 (the charging member peripheral speed is the surface of the charging member in the nip portion. It is a positive value when moving in the same direction as the surface of the image carrier). This peripheral speed ratio is desirably 120% or more.

[0060] It is preferable that the charging member has a surface having conductivity and elasticity, and is formed of a conductive particle carrier that supports the conductive particles. The conductive particles can be reliably carried in the nip portion between the image carrier and the contact charging member, and good contact charging can be performed on the image carrier.

[0061]

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

<First Embodiment> (FIGS. 1 to 5) 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 The image forming apparatus of this embodiment employs a contact charging means using conductive particles as a charging means of a photosensitive drum as an image carrier, and a charging nip portion. This is a configuration in which conductive particles are supplied from a developing device, and is a laser beam printer using a transfer type electrophotographic process, a reversal developing type, a cleanerless type, and a process cartridge type.

The components, members, and portions common to the image forming apparatus shown in FIG. 8 are denoted by the same reference numerals, and redundant description will be omitted.

In the printer of this embodiment, the electrophotographic photosensitive drum 1 as an image carrier is driven by a driving means (not shown) in a clockwise direction indicated by an arrow to a predetermined peripheral speed (process speed).
Is driven to rotate.

[Charging] The charging roller 2 as a contact charging member is formed by forming a rubber or foam medium resistance layer 2b as a flexible member on a cored bar 2a. The medium resistance layer 2b was formulated with a resin (for example, urethane), conductive particles (for example, carbon black), a sulfide agent, a foaming agent, and the like, and was formed in a roller shape on the core metal 2a. Thereafter, the surface was polished as necessary to prepare a charging roller 2 as a conductive elastic roller.

Here, it is important that the charging roller 2, which is a conductive elastic roller, functions as an electrode. That is, it is necessary to obtain sufficient contact with the photosensitive drum 1 by providing elasticity, and at the same time, to have a resistance low enough to charge the moving photosensitive drum 1. On the other hand, when a defective portion such as a pinhole exists in the photosensitive drum 1, it is necessary to prevent a voltage leak. In order to obtain sufficient chargeability and leak resistance, the resistance of the charging roller 2 is desirably in the range of 10 ⁴ to 10 ⁷ Ω.

If the hardness of the charging roller 2 is too low, the shape is not stable and the contact with the photosensitive drum 1 is deteriorated. If the hardness is too high, the charging nip a between the charging roller 2 and the photosensitive drum 1 cannot be secured. However, since the microscopic contact with the surface of the photosensitive drum is deteriorated, the Asker C hardness is preferably in a range of 25 to 50 degrees.

The material of the charging roller 2 is not limited to an elastic foam.
Examples of the material include DM, urethane, NBR, silicone rubber, and a rubber material in which a conductive material such as carbon black or a metal oxide is dispersed in IR or the like for resistance adjustment, or a foamed material thereof. Further, it is also possible to adjust the resistance by using an ionic conductive material without dispersing the conductive substance.

The outer peripheral surface of the charging roller 2 is coated with conductive particles m in advance. The charging roller 2 is pressed against the photosensitive drum 1 with a predetermined pressing force against elasticity to form a charging nip portion a having a predetermined width. The charging roller 2 is driven to rotate so as to have a speed difference with respect to the surface of the photosensitive drum 1. In this embodiment, the rotating direction of the charging roller 2 is the charging nip a
Are rotated at a speed of 150% with a peripheral speed difference in the counter direction.

Further, a DC voltage of -600 V was applied as a charging bias from the charging bias applying power source S1 to the core 2a of the charging roller 2. In this example, as described above, the conductive particles m intervene in the charging nip portion a,
The surface of the photosensitive drum 1 is uniformly charged by a direct injection charging method at -600 V (dark potential Vd) substantially equal to the voltage applied to the charging roller 2.

[Exposure] 5 is a laser beam scanner (exposure device) including a laser diode and a polygon mirror as image exposure means. This laser beam scanner outputs a laser light intensity-modulated in accordance with a time-series electric digital pixel signal of the target image information, and scans the uniformly charged surface of the rotary photosensitive drum 1 with the laser light.
Do one. By this scanning exposure L1, an electrostatic latent image corresponding to the target image information is formed on the surface of the rotating photosensitive drum 1. The surface potential of the photosensitive drum 1 when the laser beam is uniformly irradiated on the photosensitive drum 1 is set to -150 V (bright potential VL).

[Current Image] The electrostatic latent image on the surface of the rotating photosensitive drum 1 is developed by the developing device 3 as a toner image. The developing device 3 of this embodiment is a reversal developing device using a magnetic one-component insulating toner (negative toner) as a developer T. The developer T contains a predetermined amount of conductive particles m by external addition and mixing.

The toner as the developer T is prepared by mixing a binder resin, magnetic particles, and a charge control agent, and performing the steps of kneading, pulverizing, and classifying. To this, the conductive particles m and a fluidizing agent are added as external additives.

In this embodiment, the toner base is composed of styrene resin.
Silica as an external additive to promote toner charging.
-2 parts with respect to the base, conductive particles m, particle resistance is
10 ⁶ Ω · cm, average particle size of 3 μm including secondary aggregates
Two parts of conductive zinc oxide particles are externally added. This conductive particle
The child m shows a weak positive tendency as an external additive.

Reference numeral 3a denotes a non-magnetic rotary developing sleeve as a developer carrying member carrying a magnet roll 3b. The developing sleeve 3a is formed by applying a coating agent on an aluminum tube and providing an appropriate roughness. As the coating agent, a binder (acrylic resin) in which a pigment and a roughening agent (PMMA particles) for providing an appropriate roughness on the surface are dispersed.

The developing sleeve 3a is arranged to face the photosensitive drum 1 with a gap of 100 to 300 μm, and is driven by a gear (not shown) of the photosensitive drum 1 to rotate in the rotation direction of the photosensitive drum 1. In the forward direction, the photosensitive drum rotates at a peripheral speed of 150% relative to the peripheral speed of the photosensitive drum. The developer T containing the conductive particles m is coated in a thin layer on the rotary developing sleeve 3a with a regulating blade 3c (plate-like urethane rubber or the like). The layer thickness of the developer T with respect to the rotary developing sleeve 3a is regulated by the regulating blade 3c, and an electric charge is applied.
The developer coated on the rotary developing sleeve 3a is rotated by the rotation of the developing sleeve 3a to cause the photosensitive drum 1 and the developing sleeve 3 to move.
It is conveyed to a developing section (developing area section) c which is an opposing section of a. The developing sleeve 3a has a developing bias applying power source S
2, a developing bias voltage is applied. The developing bias voltage is a superimposed voltage of an AC voltage of about 1.2 kV and a DC voltage of -400V. As a result, the electrostatic latent image on the photosensitive drum 1 is reversely developed with the toner.

Here, as the material of the conductive particles m, various conductive particles such as conductive inorganic particles such as other metal oxides and mixtures with organic substances can be used. In order to obtain uniform chargeability, the particle size of the conductive particles m is preferably 10 μm to 10 μm. It is considered that the lower limit of the particle size is 10 nm as a limit to obtain stable particles. Further, the particle resistance is 1 as a specific resistance because electric charges are transferred via particles.
0 ¹² Ω · cm or less is desirable, and more preferably 10 ¹⁰ Ω · cm
The following is desirable. There is no problem that the conductive particles m exist not only in the state of primary particles but also in the state of aggregation of secondary particles.

[Transfer] The transfer roller 4 is a medium-resistance roller, and a transfer material P as a member to be transferred (recording medium, recording material) is supplied to the transfer nip d from the paper supply unit 7 at a predetermined control timing. When a predetermined transfer bias voltage is applied to the transfer roller 4 from the transfer bias applying power source S3, the toner image on the photosensitive drum 1 is sequentially transferred onto the surface of the transfer material P fed to the transfer nip d. It is transcribed to.
That is, the transfer material P introduced into the transfer nip d is conveyed by nipping the transfer nip d, and the toner image formed and carried on the surface of the rotary photosensitive drum 1 is sequentially pressed against the transfer material P by the electrostatic force. It is transferred by pressure.

[Fixing] 6 is a fixing device such as a heat fixing method. The transfer material P fed to the transfer nip portion d and transferred with the toner image on the photosensitive drum 1 side is separated from the surface of the rotating photosensitive drum 1 and introduced into the fixing device 6, where the toner image is fixed. It is discharged out of the apparatus as an image formed product (print, copy).

The printer of this embodiment is cleaner-less, and the transfer residual toner remaining on the surface of the rotating photosensitive drum 1 after the transfer of the toner image onto the transfer material P is not removed by the cleaner, and is charged as the photosensitive drum 1 rotates. The developer reaches the developing section c via the nip section a, and is cleaned (collected) at the same time as the development in the developing device 3 (toner recycling process).

[Process Cartridge] In this embodiment,
The photosensitive drum 1, the charging roller 2, and the developing device 3 are
An integrated cartridge 10 is provided, in which each device is integrated by an exterior and can be replaced together with the printer body.
Reference numeral 11 denotes a process cartridge attaching / detaching guide / holding member on the printer main body side.

In the case of this integral type cartridge 10, when the toner T stored in the developing device 3 is used up, the other devices are designed to have almost the same life. Therefore, there is an advantage that the user can always obtain a stable image while the toner in the cartridge 10 is present, and since it is an integral type, the exchange can be easily performed.

Here, the process cartridge is a unit in which a charging unit, a developing unit or a cleaning unit and an electrophotographic photosensitive member are integrally formed into a cartridge, and this cartridge is detachable from the main body of the image forming apparatus.
In addition, at least one of the charging means, the developing means, and the cleaning means and the electrophotographic photosensitive member are integrally made into a cartridge, and this cartridge is made detachable from the image forming apparatus main body. Further, at least the developing means and the electrophotographic photosensitive member are integrally formed into a cartridge, and the cartridge is detachably mountable to the main body of the image forming apparatus.

(2) Lowering the electric potential of the non-sheet passing area of the photosensitive drum 1 FIG. 2 shows the conductive particles m contained in the developer T of the developing device 3.
Schematically shows a mechanism of shifting the electrostatic latent image on the photosensitive drum 1 side to the photosensitive drum 1 side by the developing device 3 when developing the toner, and the conduction of the electrostatic latent image to the image portion and the non-image portion is performed. The flight transfer of the conductive particles m is exactly the same as that described with reference to FIG. 9 for the above-described conventional device (FIG. 8).

When the small-size transfer material is passed, the distribution of the conductive particles along the length on the charging roller 2 is increased in the area corresponding to the non-paper passing area. As described above, the conductive particles that are excessively supplied to and deposited on the portion corresponding to the region are partially peeled off from the charging roller 2 as the number of durable sheets increases, resulting in poor charging.

In order to avoid this, in this embodiment, the size of the transfer material (paper size) passed through the transfer portion d is detected, and the photosensitive drum 1 is uniformly moved by the charging roller 2 according to the paper size information. The surface portion corresponding to the non-sheet passing portion area of the charging processing surface is subjected to scanning exposure processing (non-sheet passing portion exposure L2) using a laser beam having a short lighting time using the laser beam scanner 5 to correspond to the non-sheet passing portion region. The potential of the photosensitive drum surface portion is set to a predetermined lower potential than the potential of the photosensitive drum surface portion corresponding to the paper area (= the charging potential of the photosensitive drum 1 by the charging roller 2, that is, the photosensitive drum dark potential Vd).

FIG. 3 is a diagram schematically showing the laser exposure time of the laser beam scanner 5 as the exposure means and the state of the latent image formed on the photosensitive drum.

(A) shows one of the laser beams L1 during image formation.
The dot emission time t is shown. The one-dot emission time t is several tens of ns depending on the number of surfaces of the polygon mirror included in the laser beam scanner 5, the process speed, the resolution, and the like.

FIG. 9B is a conceptual diagram of a latent image formed by the one-dot emission time, and this latent image is visualized as a toner image by the developing device 3.

On the other hand, for the photosensitive drum surface portion corresponding to the non-sheet passing portion area, 1 dot as shown in FIG.
The scanning exposure (non-sheet passing portion exposure) of the laser beam L2 is performed at the light emission time t '.

The one-dot emission time t 'of the laser beam L2 is about one half of the one-dot emission time t of the laser beam L1 at the time of image formation, and a sufficient latent image cannot be formed. As a result, the potential of the photosensitive drum surface portion corresponding to the non-sheet passing portion region is such that a shallow latent image as shown in FIG. 4D overlaps, and the potential of the photosensitive drum surface portion corresponding to the sheet passing portion region (= dark). The potential becomes a predetermined lower than the potential Vd).

For the photosensitive drum surface portion corresponding to the non-sheet passing portion area, the positive conductive particles m in the developing portion c have a low contrast with the photosensitive drum dark potential Vd, and fly and adhere. It becomes difficult to do.

FIG. 2 shows the potential on the photosensitive drum 1 when the laser beam L2 having a short light emission time t 'is irradiated on the surface portion corresponding to the non-sheet passing area of the photosensitive drum 1 as described above. FIG. 4 is a diagram schematically illustrating how a toner T and conductive particles m fly in a developing unit c. As can be seen from the figure, the contrast of the conductive particles m with the photosensitive drum dark potential Vd in the non-sheet passing portion is small, and it is difficult for the conductive particles m to fly to the photosensitive drum surface portion.

Thus, by setting the potential of the surface area corresponding to the non-sheet passing portion of the photosensitive drum 1 to be lower than the photosensitive drum dark potential Vd by a predetermined amount, the surface area corresponding to the non-sheet passing portion of the photosensitive drum 1 is moved to The transfer amount of the conductive particles m from the developing device 3 is suppressed to a predetermined lower value than the transfer amount of the conductive particles m from the developing device 3 to a region corresponding to the paper passing portion of the photosensitive drum 1, and as a result, As a result, the supply amount of the conductive particles m along the length of the nip portion a between the photosensitive drum 1 and the charging roller 2 is substantially uncoupled between both the region corresponding to the paper passing portion and the region corresponding to the non-paper passing portion. By uniformizing without balance, the conductive particles m are supplied in excess to the charging roller portion corresponding to the non-paper passing portion compared to the charging roller portion corresponding to the paper passing portion, and accumulated and peeled off. Prevents charging failure, etc. It is obtained by realizing the charging.

The formation of the above-described latent image on the surface of the photosensitive drum 1 can be applied to a space between sheets when the sheet is continuously passed. FIG.
Shows a state in which the photosensitive surface on the photosensitive drum 1 is captured as a continuous surface, and small-size paper is continuously passed therethrough. Sg is a printing area, and Sp is a paper passing area. These S
The conductive particles m are excessively supplied to the transfer nip portion a, that is, the charging roller, without the area Sdr (the hatched portion in the drawing) other than g and Sp being in contact with the photosensitive material on the photosensitive drum 1 and the transfer material P. Area. That is, the non-sheet passing portion of the transfer material P and the sheet interval when the sheet is continuously passed. By performing exposure L2 corresponding to FIG. 2C on this region, the dark potential of this region can be reduced. That is, it is possible to suppress the positive conductive particles m from flying on the photosensitive drum surface portion in the developing section c, and to make the conductive particles m
Can be prevented from being excessively supplied to the charging roller 2.

Further, in the present embodiment, the non-sheet passing portion exposure L2 (including the inter-sheet area) as described above is performed according to the conditions of the detection means 100 (FIG. 1) for detecting the small size paper and the number of prints.
It is carried out. This will be described sequentially with reference to FIG.

Step 1: detecting the paper size step 2: not performing the non-paper passing portion exposure L2 when the paper size is not the small size step 3: reading the number of paper passing input by the user, and reading the non-paper passing portion if the number is less than the specified number. No exposure L2 is performed. Step 4: When the paper size is small and the specified number or more, the non-paper passing portion on the photosensitive drum is exposed L2. Thus, in this embodiment, the charging roller 2 of the conductive particles m is used.
Since the non-sheet passing portion exposure L2 is performed in consideration of the condition in which the supply to the sheet is likely to be excessive, that is, taking into account the sheet size and the number of sheets passed, an adverse effect such as an optical memory due to overexposing the photosensitive drum 1 is given. The conductive particles m can be prevented from being excessively supplied to the charging roller 2 without causing the problem.

<Second Embodiment> (FIG. 6) In this embodiment, a laser beam scanner 5 serving as an exposure means is used.
Is characterized by having a configuration having two light sources.

The latent image forming process according to the present embodiment is based on the image forming (printing area) Sg on the photosensitive drum 1 as shown in FIG. 4 used in the first embodiment. The photosensitive drum is exposed with a laser beam L1 for exposure (for image exposure) to obtain a photosensitive drum light potential (VL) (first), and is used for a non-sheet passing portion exposure in a non-sheet passing portion region and a space between sheets during continuous sheet passing. Laser beam L2 (for post-exposure on photoreceptor)
And the surface potential is set to Vd2. At this time, by setting the laser spot diameter of the laser light L2 for non-sheet passing portion exposure to be larger than the laser spot diameter of the laser light L1 for image formation exposure, unevenness due to background exposure is minimized.

In this embodiment, a semiconductor laser chip having two light-emitting points in one element is used as a light source for image formation exposure and non-sheet passing portion exposure, and two laser beams emitted from this chip are used. Through the same optics,
The two beams are imaged on the photoreceptor. The image may be formed at the same position on the photosensitive member, or the image may be formed at a position shifted intentionally. Further, it is possible to make the spot diameters of the two laser beams different from each other and to increase the spot diameter of the laser for non-sheet passing portion exposure as described above. When such a laser chip is used, the same optical system as that used in the conventional electrophotographic apparatus can be used for the optical system such as the collimator and the scanning optical system. Therefore, it is not necessary to consider the alignment and the like, so that a very inexpensive and stable two-beam optical system can be realized.

The optical system and the electrophotographic apparatus used in this embodiment will be described with reference to FIG. The optical system includes a laser chip 81 having two light emitting points 81a and 81b (a first laser light source and a second laser light source), and a collimator lens 8.
2, and a polygon scanner 83 and an imaging lens 84 constituting the first and second scanning optical systems. In the present embodiment, the first scanning optical system and the second scanning optical system are the same.

The laser chip 81 is a semiconductor laser. By forming two electrodes on the same substrate, there are two laser emission points in the active layer, and the laser beams L1 and L2 emitted from each are modulated. It can be done separately. These two emission points are the first laser light source 8
1a and the second laser light source 81b.

The spot diameter of the two laser beams L1 and L2 is determined by the characteristics of the laser chip 81 and the scanning optical system 83.8.
In this embodiment, since the two beams L1 and L2 pass through the same optical system, the ratio of the beam spot formed on the photoconductor is determined by the characteristics of the laser chip 81.

The beam spot of the image forming exposure laser beam L1 on the photosensitive member is determined by the resolution of the electrophotographic image to be formed. In this embodiment, since the image is formed at a resolution of 600 dpi, the beam spot on the photosensitive member is 50 × 40
The laser chip 81 for image formation exposure and the scanning optical systems 83 and 84 were designed to meet this requirement.

On the other hand, the purpose of the laser beam L2 for non-sheet passing portion exposure is to uniformly irradiate the potential of the non-sheet passing portion on the photosensitive member as Vd2 in order to avoid excessive supply of conductive particles. Therefore, any number of beam spots may be used as long as they are larger than the spot of the laser beam L1 for image formation exposure. Rather, if the laser beam L2 for exposing the non-paper passing portion is narrowed, the distribution of the laser beam L2 for exposing the non-paper passing portion becomes non-uniform due to the pitch unevenness of the scanner, causing a problem of causing potential non-uniformity. . In order to prevent such non-uniformity in non-sheet passing portion exposure, the laser beam L2 for non-sheet passing portion exposure is used.
It is desirable that the spot diameter is rather large. In this embodiment, the laser chip is designed such that the laser spot diameter for exposing the paper non-passing portion on the photoconductor is 150 × 120 μm.

By using the laser beam scanner 5 (exposure device) having the above-described configuration, the non-paper passing area and the continuous paper passing area on the photosensitive drum 1 shown in FIG. 4 used in the first embodiment are used. In the inter-sheet area at the time of paper, by exposing with the laser beam L2 for exposing the non-paper passing portion and setting the surface potential to Vd2, as described in the first embodiment, the conductive particles are moved outside the paper passing width in the photosensitive drum 1 as described in the first embodiment. The positive conductive particles m can be prevented from flying in the area of the sheet and the inter-sheet area during continuous paper feeding, and the conductive particles m can be prevented from being excessively supplied to the charging roller 2.

<Others> 1) It is desirable that the image carrier has a surface layer having a surface resistance of 10 ⁹ to 10 ¹⁴ Ω · cm in order to stably and uniformly perform direct injection charging.

FIG. 7 is a schematic diagram of a layer structure of a photoreceptor having a charge injection layer on the surface. That is, the photoreceptor 1 is a general one in which an undercoat layer 1b, a positive charge injection preventing layer 1c, a charge generation layer 1d, and a charge transport layer 1e are sequentially stacked and coated on an aluminum drum substrate (Al drum substrate) 1a. By applying the charge injection layer 1f to a suitable organic photoreceptor, the charging performance is improved.

The charge injection layer 1f is made of a photo-curable acrylic resin as a binder and conductive particles (conductive filler).
1g of SnO ₂ ultrafine particles (having a diameter of about 0.03 μm)
m) A film is formed by mixing and dispersing a lubricant such as tetrafluoroethylene resin (trade name: Teflon), a polymerization initiator, and the like, coating the mixture, and then performing photo-curing.

The important points for the charge injection layer 1f are the resistance and the surface energy of the surface layer. In the charging method by direct injection of electric charge, the electric charge can be transferred more efficiently by lowering the resistance on the photoconductor side. On the other hand, since it is necessary to hold the electrostatic latent image for a certain time, the charge injection layer 1f
Is 1 × 10 ⁹ to 1 × 10 ¹⁴ (Ω · c
The range of m) is appropriate.

Further, since the charge injection layer 1f contains a lubricant, the surface energy of the photoreceptor is reduced. Therefore, the toner easily moves to the transfer material, and the paper powder hardly adheres to the photoreceptor, so that the contact charging member is reduced in contamination of the toner, paper powder, and the like, and the charging ability of the charging roller is maintained for a long period of time. Further, since the frictional force between the conductive particles and the photoreceptor is reduced, shaving of the photoreceptor is greatly reduced.

Even when the charge injection layer 1f is not used,
For example, the same effect can be obtained when the charge transport layer 1e is in the above-described resistance range. Volume resistance of surface layer is about 10 ¹³ Ω · c
The same effect can be obtained with an amorphous silicon photosensitive member having m.

2) The flexible contact charging member 2 may be of a shape or material such as a fur brush, felt, cloth, etc. in addition to the charging roller. In addition, it is possible to obtain more appropriate elasticity, conductivity, surface properties and durability by combining various materials.

3) The charging bias applied to the charging member may include an alternating voltage component (AC component, a voltage whose voltage value changes periodically). As the waveform of the alternating voltage component, a sine wave, a rectangular wave, a triangular wave, or the like can be used as appropriate. It may be a rectangular wave formed by periodically turning on / off a DC power supply.

4) In the case of the image forming apparatus, the image exposure means as the information writing means on the charged surface of the photoreceptor as the image carrier is not limited to the laser scanning means of the embodiment, but may be a solid light emitting device such as an LED. Digital exposure means using an element array may be used. An analog image exposure unit using a halogen lamp, a fluorescent lamp, or the like as a document illumination light source may be used. In short, any device that can form an electrostatic latent image corresponding to image information may be used.

5) The image carrier may be an electrostatic recording dielectric or the like. In this case, after uniformly charging the dielectric surface,
The charged surface is selectively discharged by a discharging means such as a discharging needle head or an electron gun to write and form an electrostatic latent image corresponding to target image information. Further, a process for lowering the potential of the non-sheet passing portion area is performed.

6) In general, a method for developing an electrostatic latent image is to coat a non-magnetic toner on a developer carrying member such as a sleeve using a blade or the like, and to coat a magnetic toner on the developer carrying member. A method of developing an electrostatic latent image by applying it in a non-contact state to an image carrier by coating it on a conveying member by magnetic force and conveying the image (one-component non-contact development)
A method of applying the toner coated on the developer carrying member as described above to the image carrier in a contact state to develop an electrostatic latent image (one-component contact development); A method of developing an electrostatic latent image by using a mixture of the above carriers as a developer (two-component developer), conveying the mixture by magnetic force, applying the mixture to an image carrier in a contact state, and developing the electrostatic latent image (2)
Component development) and a method of applying the two-component developer to the image carrier in a non-contact state to develop an electrostatic latent image (two-component non-contact development). .

7) The image forming apparatus of this embodiment is a cleaner-less apparatus, but the image forming apparatus is provided with a dedicated cleaning device for collecting and removing transfer residual toner from the surface of the image carrier after transfer. It may be. Again,
Since the conductive particles supplied from the developing device to the image carrier are fine, the transfer residual toner is captured by the cleaning device, but the conductive particles relatively easily pass through the cleaning blade of the cleaning device and are held in the charging nip. It is carried and supplied to the charging member.

8) The transfer means is not limited to the roller transfer of the embodiment, but may be a blade transfer, a belt transfer, another contact transfer charging system, or a contact transfer charging system using a corona charger. .

9) The present invention can be applied not only to the formation of a single-color image but also to an image forming apparatus for forming a multi-color or full-color image by multiple transfer or the like using an intermediate transfer member such as a transfer drum or a transfer belt.

[0122]

As described above in detail, according to the present invention, a contact charging means using conductive particles is employed as a charging means for uniformly charging an image carrier to a predetermined polarity and potential. An image forming apparatus having a configuration in which the supply of conductive particles to a contact nip portion between an image carrier and an image carrier is performed from a developing unit.
The surface area corresponding to the non-sheet passing portion of the image carrier is set by setting the potential of the surface region corresponding to the non-sheet passing portion of the image carrier to a predetermined lower than the predetermined charging potential of the image carrier by the charging means. The transfer amount of the conductive particles from the developing means to the area corresponding to the paper passing portion of the image carrier is suppressed to a predetermined lower than the transfer amount of the conductive particles from the developing means to the area corresponding to the paper passing portion of the image carrier. The supply amount of the conductive particles along the length of the nip portion between the body and the charging member is made substantially uniform without any imbalance between the region corresponding to the paper passing portion and the region corresponding to the non-paper passing portion. hand,
Conductive particles are supplied in excess of the charging member portion corresponding to the paper passing portion for the charging member portion corresponding to the non-paper passing portion,
Poor charging and the like due to accumulation and peeling can be prevented, and stable charging can be realized through paper passing durability.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating the transfer of conductive particles from a developing device to a photosensitive drum.

FIG. 3 is an explanatory diagram of an image forming exposure and a latent image potential, and a non-sheet passing portion exposure and a post-exposure potential of a non-sheet passing portion.

FIG. 4 is an explanatory view of non-sheet passing portion exposure.

FIG. 5 is a flowchart of a control system.

FIG. 6 is a schematic diagram of a configuration of a two-beam scanning optical system (laser beam scanner).

FIG. 7 is a schematic diagram of a layer structure of a photoconductor provided with a charge injection layer.

FIG. 8 is a schematic configuration model diagram of a conventional image forming apparatus.

FIG. 9 is a view for explaining transfer of conductive particles from a developing device to a photosensitive drum.

FIG. 10 is an explanatory model diagram of transfer of conductive particles from a photosensitive drum to a transfer material.

FIG. 11 shows a charging area, a developing area, a small-size paper passing area,
Schematic diagram showing the relationship between the non-paper passing area

[Description of Signs] 1. Image carrier 2, Charge roller 3, Developing device 4, Transfer roller 5, Exposure device (laser beam scanner), 6 Fixing device, 7 Paper feed Part, 10 ...
Process cartridge, S1 to S3, high-voltage power supply, P
・ Transfer material, m ・ ・ Conductive particles (charge accelerating particles), T ・ ・
Developer (toner)

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) G03G 15/08 502 G03G 15/16 103 507 21/00 372 15/16 103 15/08 507B (72) Inventor Yasushi Shimizu 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Masahiro Yoshida 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Hiroyuki Oba, Inventor Ota-ku, Tokyo Shimomaruko 3-chome No. 30-2 Canon Canon Inc. F-term (reference) 2H003 BB11 CC05 DD03 DD16 EE12 2H027 DA45 DC10 EC10 EC12 ED02 ED03 ED07 ED16 ED24 EE02 EE03 EE04 EF09 EF12 FA32 FA33 FA35 ZA01 2H032 AB052 AB053 AB16 CA16 CA18 2H077 AA37 AC16 AD06 AD13 AD17 AD31 AD36 BA07 EA13 EA16 GA01 GA17

Claims (8)

[Claims] A charging member that forms a nip with the image carrier; and a charging unit that charges the image carrier to a predetermined potential with conductive particles interposed at least in the nip portion. Image information writing means for forming an electrostatic latent image on the charged surface of the image carrier, developing means for visualizing the electrostatic latent image as a toner image with a developer containing toner and conductive particles, the toner Transfer means for transferring an image to a member to be transferred, wherein the conductive particles contained in the developer adhere to the surface of the image carrier when the electrostatic latent image is developed by the developing means. In the image forming apparatus, the conductive particles are supplied to the nip portion by being carried to the nip portion. Image carrier An image forming apparatus characterized in that set lower than a predetermined charging potential. 2. The image information writing unit is an exposing unit, and the exposing unit corresponds to a non-sheet passing portion of a transfer unit of the transfer unit of the image carrier charged to a predetermined potential by the charging unit. 2. The image forming apparatus according to claim 1, wherein the image carrier surface area is set to be lower than a predetermined charging potential of the image carrier by the charging unit by exposing a surface area to be exposed in a shorter time than during image formation. apparatus. 3. The image bearing member charged to a predetermined potential by the charging means is exposed to a surface area corresponding to a non-sheet passing portion in a transfer portion of the transfer means, and the image carrier surface area is charged by the charging means. 2. The image forming apparatus according to claim 1, further comprising a dedicated exposure unit that sets the charging potential to be lower than a predetermined charging potential of the image carrier. 4. The apparatus according to claim 1, further comprising a detecting unit configured to detect a length of a member to be transferred passed through a transfer unit of the transfer unit in a direction perpendicular to a sheet passing direction. 1
An image forming apparatus according to any one of the preceding claims. 5. The image forming apparatus according to claim 1, wherein a voltage applied to the charging member is only a DC component. 6. The conductive particles have a particle resistance of 10 ¹² Ω ·
cm to 10 ⁻¹ Ω · cm, and the particle size is 10 μm to 10 μm.
The image forming apparatus according to any one of claims 1 to 5, wherein the value is nm. 7. The image forming apparatus according to claim 1, wherein the charging member rotates at a counter with respect to the image carrier. 8. The charging member according to claim 1, wherein the charging member has a surface having conductivity and elasticity, and is formed of a conductive particle carrier that carries the conductive particles. An image forming apparatus according to any one of the preceding claims.