JP2002132017A - Electrifying device and image recorder using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a particle electrifying type contact electrifying device, by which the improvement of an electrifying performance and the elimination of the influence of particle fall-off are both coped with. SOLUTION: In an electrifying device 2, which is provided with electrifying particles (m) consisting mainly of conductive particles whose each grain size is 10 μm-10 nm and a surface having conductivity and elasticity and by which the surface of a body to be electrified 1 is electrified by bringing carried electrifying particles (m) into contact with the body to be electrified 1, by making an electrifying member 2A constituted of an electrifying particle carrier to carry the electrifying particles (m) abut on the body to be electrified 1, the resistance of the electrifying particles (m), carried on the electrifying particle carrier 2A, is 1012 to 10-1 Ω.cm, and the value obtained by dividing the carried amount of the electrifying particles (m) by the surface roughness Ra μm of the carrier of the electrifying particles is in the range of 0.005 to 1 mg/cm2/μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a charging device for charging an object to be charged. More specifically, the present invention relates to a contact-type charging device (contact charging device) for charging a surface of a member to be charged by bringing a charging member into contact with the member to be charged.

[0002] The present invention also relates to an image recording apparatus (image forming apparatus) such as a copying machine or a printer using the charging device as a charging means for charging an image carrier.

[0003]

2. Description of the Related Art Conventionally, a contact charging device includes a roller type (charging roller), a fur brush type,
A conductive charging member (contact charging member / contact charging device) such as a magnetic brush type or a blade type is brought into contact, and a predetermined charging bias is applied to the contact charging member to charge the surface to be charged to a predetermined polarity and potential. It is to let.

Although these charging devices are collectively expressed as a contact charging device, their charging mechanism (charging mechanism,
From the viewpoint of charging principle), individual devices are greatly different. The charging mechanism of contact charging includes. Discharge charging mechanism,
. There is a direct injection charging mechanism. The characteristics of the charging device depend on which charging mechanism is used. The principle and characteristics of each of the discharge charging mechanism and the direct injection charging mechanism will be described.

[0005] Discharge Charging Mechanism This is a mechanism in which the surface of a member to be charged is charged with a discharge product due to a discharge phenomenon generated in a gap between the contact charging member and the member to be charged.

Since the discharge charging system has a fixed discharge threshold value for the contact charging member and the member to be charged, as shown in FIG. It must be applied to the member. Although the amount of generation is significantly smaller than that of the corona charger, a discharge product is generated in principle.

A roller charging method (roller charging device) using a conductive roller (charging roller) as a contact charging member by discharge is preferable in terms of discharge stability and is widely used. The charging roller for discharging is formed into a roller shape using a conductive or medium-resistance rubber material or foam as a base layer, and the surface thereof is often formed of a high resistance layer. In this configuration, the discharge phenomenon occurs in a gap of several tens μm slightly away from the contact portion between the roller and the member to be charged. Therefore, in order to stabilize the discharge phenomenon, the surface of the roller is flat and has an average surface roughness R.
a is sub-μm or less, and the surface has a high roller hardness.

[0008] In addition, roller charging by discharge is high in applied voltage, and if there is a pinhole (exposed base due to damage to the film to be charged), the voltage drops to the periphery and poor charging occurs. Therefore, the voltage drop is prevented by setting the surface resistance of the surface layer to 10 ¹¹ Ω □ or more.

[0009] Direct Injection Charging Mechanism Direct injection charging is a charging mechanism that charges (charges) the surface of an object to be charged by directly transferring charges by contact between the contact charging member and the object to be charged at the molecular level. It is also called direct charging or injection charging.

In this charging mechanism, the potential difference between the contact charging member and the member to be charged is about several volts to several tens of volts. The charging characteristics are shown in FIG. 7B (magnetic brush charging device). The charging potential is equal to the applied voltage, and there is no voltage difference causing discharge. Also, the voltage required for charging can be kept low.

As described above, since the direct charging system does not involve generation of ions as a charging mechanism, no adverse effect is caused by the discharge products. That is, the charging method is excellent in terms of environmental safety, member deterioration, and low power.

Next, a charging device using a direct injection charging mechanism will be described.

In the direct charging mechanism, an important factor that determines the charging performance is the contact between the contact charging member and the member to be charged. The term "contactability" as used herein means the ability of the contact charging member to microscopically contact many surfaces while the charged object passes through the charging device. For this reason, the contact charging member is required to have a surface having both a dense surface structure and elasticity capable of making flexible contact.

As a form of the contact charging member used in the direct injection charging device, an attempt has been made with a discharge charging roller or the like, but direct injection charging was not possible with the discharge charging roller. The high hardness and smooth surface structure as described above appears to be in close contact with the charged object in appearance, but there is almost no contact in terms of the microscopic contact required at the molecular level for charge injection. is there.

At present, as a direct injection charging system proposed, there is a particle charging using a magnetic brush.

[0016] Particle charging Considering the improvement in contact density, a charging method using conductive particles (particle charging) is advantageous. The conductive particles used at this time are referred to as “charged particles”. Examples of the charged particles include conductive magnetic particles, and an example in which a magnetic brush charging member is formed by a magnet has been proposed.

FIG. 8 is a schematic structural diagram of an example of the magnetic brush charging device 100. Reference numeral 120 denotes a magnetic brush charging member, which is a fixedly supported magnet roll 122, a non-magnetic and conductive charging sleeve 121 concentrically and rotatably fitted around the outer circumference of the magnet roll 122, and a magnetic brush charging member 121. Magnetic brush layer (magnetic brush portion) 1 of conductive magnetic particles C formed on the outer peripheral surface by being attracted and held by the magnetic force of the magnet roll 122 inside the charging sleeve.
24. Reference numeral 123 denotes a casing, in which the above-described magnetic brush charging member 120 is assembled, and in which an appropriate amount of the conductive magnetic particles C is stored and stored. Reference numeral 125 denotes a magnetic brush layer thickness regulating blade provided on the casing 123.

Reference numeral 1 denotes an object to be charged, which in this embodiment is an electrophotographic photosensitive drum that is driven to rotate clockwise as indicated by an arrow. In the above-described magnetic brush charging device, the magnetic brush layer 124 of the magnetic brush charging member 120 is disposed in contact with the photosensitive drum 1 as a member to be charged with a predetermined width. n is a charging contact portion (charging nip portion) as the contact portion.

The charging sleeve 121 is, more specifically,
It is a non-magnetic conductive sleeve having an average surface roughness Ra of 1.2 μm, an outer diameter of 16 mm and a length of about 220 mm.

The magnet roll 122 has four magnetic poles N1, N2, S1, and S2 that generate a magnetic flux density peak of 800 G in the radial direction on the surface of the charging sleeve. One magnetic pole N1 is provided on the photosensitive drum 1 side. The magnet roll 122 was fixedly supported so as to face.

As the conductive magnetic particles C, which are charged particles constituting the magnetic brush layer 124, magnetic metal particles such as ferrite and magnetite, and particles obtained by binding these magnetic particles with a resin are used. Resistance value is 1 × 10 ⁶ -1
A thing of 0 ⁹ Ωcm is used. About 10 ~
50 μm is used.

The charging sleeve 121 is driven to rotate in the clockwise direction indicated by the same arrow as the photosensitive drum 1. Magnetic brush layer 124
Is conveyed in a clockwise direction together with the charging sleeve 121, is regulated to a predetermined layer thickness by the blade 125, and the magnetic brush layer 124 whose layer thickness is regulated contacts the photosensitive drum 1 and is exposed at the charging contact portion n. Rub the drum surface. The magnetic brush layer 124 that has passed through the charging contact portion n is returned and transported to the conductive magnetic particle reservoir in the casing 123 by the subsequent rotation of the charging sleeve 121, and is transported and used cyclically.

A predetermined charging bias is applied to the charging sleeve 121 from a charging bias applying power source S1, and the surface of the photosensitive drum 1 is rubbed by the magnetic brush layer 124 at the charging contact portion n, and is directly charged by the charging bias by the applied charging bias. It is uniformly charged to a predetermined polarity and potential.

In the above configuration, the magnetic brush layer 124
Consider the contact density of the conductive magnetic particles. When the outer diameter of the conductive magnetic particles is about 30 μm, the contact density is 10 ³
point / mm ² is obtained. Therefore, good charging characteristics shown in FIG. 7B are exhibited.

At this time, the amount of the conductive magnetic particles to be retained is required to be several hundred mg / cm ² , and the amount of the magnetic particles held by the magnetic force is 0.1 mg / cm ² .
A particle layer of 5 to 1 mm is formed. In the injection charging, the contact charging member is required to flexibly and densely contact the member to be charged. However, in the magnetic brush charging member 120, since the conductive magnetic particles need to be magnetically restrained, the charging sleeve as a particle carrier is required. 121 needs to use a rigid body. Accordingly, since the flexibility of the contact charging member needs to be provided in the magnetic brush layer of the conductive magnetic particles, the magnetic brush layer requires a certain thickness and the amount of the conductive magnetic particles carried.

Also, the particle charging is suitable for a toner recycling system. That is, in the toner recycling process, in a transfer type image recording apparatus, waste toner (transfer residual toner) is used again for image formation, so that toner is effectively used and a space for a cleaner container is eliminated, thereby realizing a compact apparatus. It is an excellent configuration.

The transfer residual toner is once taken into the contact charging member, brought into a reusable state (original charge amount of the toner), returned to the developing device via the image carrier, and used again for development, or collected if unnecessary. As a result, the toner can be recycled. In addition to charging the image carrier, the charging device used here needs to collect transfer residual toner and recharge the toner.

From the above viewpoint, the appropriateness of the toner recycle of the magnetic brush will be considered. The magnetic brush itself has the characteristics that it is composed of particles and can move with a degree of freedom and has a large specific surface area. Therefore, in the magnetic brush, for example, the transfer residual toner is collected from the image carrier, and the charge of the captured toner is adjusted appropriately.
Functions essential for toner recycling can be advantageously realized.

As described above, the magnetic brush charging device is an excellent charging device, but further improvement in toner recycling performance is required, and for that purpose, a reduction in the particle size of the charged particles is desired. Ideally, a denser and more flexible contact charging member is formed.

[0030]

However, in conventional particle charging using a magnetic brush, if the size of the conductive magnetic particles, which are charged particles, is simply reduced (10 μm or less), the magnetic coercive force of the magnetic particles is reduced. There is a problem that the magnetic particles fall off the surface. In the case of a magnetic brush charging member requiring a certain amount of particles to be supported, if the problem of falling off of magnetic particles, which are charged particles, occurs, the adverse effect is large. The magnetic particles that have fallen off the magnetic brush and adhere to the image carrier cause a leakage of a developing bias and poor development, and further transfer to paper to cause fogging, which causes various image defects. It is not a matter of simply supplying magnetic particles.

As described above, in the conventional magnetic brush charging, there is a limit in improving the contact density. For this issue,
The present inventors have departed from particle retention by magnetic force and reviewed particle charging from the viewpoint of positively utilizing the adhesive force between substances.

As a result, it is important to reduce the diameter of the particles and optimize the amount of the particles, and developed a charging device of a particle charging type capable of improving the charging performance and eliminating the adverse effects of falling off the particles. The present invention aims to provide this.

[0033]

According to the present invention, there is provided a charging device having the following constitution and an image recording apparatus using the charging device.

(1) Charged particles mainly composed of conductive particles having a particle size of 10 μm to 10 nm, and a charged particle carrier having a surface having conductivity and elasticity and carrying the charged particles. In a charging device in which a charged member is brought into contact with a member to be charged to bring charged particles in contact with the member to be charged to charge the surface of the member to be charged, the resistance of the charged particles carried on the charged particle carrier is 10%. ¹² to 10 ^-1 Ω · cm, and the loading amount of the particles is determined by the surface roughness Ra of the charged particle carrier.
A charging device characterized in that the value divided by μm is 0.005 to 1 mg / cm ² / μm.

That is, by reducing the particle size of the charged particles, the charged particles can be held at a high density on the charged particle carrier of the charging member, and the charging performance can be improved. Further, even when the charged particles fall off the charged object, the influence can be suppressed. In addition, by adjusting the carried amount of the charged particles to a certain range with respect to the surface roughness of the carrier,
It ensures both charging performance and reduction of falling off.

(2) When the ratio of the charged particles covering the charged particle carrier is defined as a coverage Rc, 1 ≧ Rc ≧
The charging device according to (1), wherein the value is 0.2.

That is, by adjusting the coverage of the charged particles to a certain range, a contact charging member that is stable against mixing other than the charged particles can be configured.

(3) The charged particle carrier has a surface resistance of 1
0 ⁴ from the charging device according to claim 1 or 2, characterized in that it is ¹⁰ 10 Ω □.

That is, by setting the surface resistance of the carrier to an appropriate range, a structure advantageous for the pressure resistance of the member to be charged against pinholes and the ability to retain particles is obtained.

(4) The charged particle carrier is an elastic body having a porous body surface (1) to (3).
The charging device according to any one of the above.

That is, it is advantageous that the charged particle carrier has a porous body surface, so that the charged particles can be reliably held in the cell.

(5) The charging member contacts the member to be charged with a speed difference, (1) to (4).
The charging device according to any one of the above.

That is, the contact property between the charging member and the member to be charged is improved, and the charging can be stably performed.

(6) The surface of the charged particle carrier has a resistance of 1
The charging device according to any one of (1) to (5), further including a charged particle supply unit configured to supply charged particles having a ^{value of} 0 ¹² to 10 ⁻¹ Ω · cm.

That is, it is possible to stably charge by applying a proper amount of the charged particles to the surface of the charged particle carrier.

(7) In an image recording apparatus for performing image formation by applying an image forming process including a step of charging the surface of the image carrier to the image carrier, a process means for charging the surface of the image carrier. Is the charging device according to any one of (1) to (6).

That is, an excellent image recording apparatus can be realized by the characteristics of the charging device described in any one of (1) to (6).

(8) An electrophotographic image comprising an image bearing member, a charging device, an image exposing device, a developing device, a transfer device, and a fixing device for fixing an image on a recording medium disposed around the image bearing member. A recording device, wherein a toner remaining on the surface of the image carrier after the transfer process is temporarily supported on at least a charging member of a charging device, transferred to the surface of the image carrier again, and collected again in the developing device. 5. The image recording apparatus according to claim 1, wherein the charging device is the charging device according to any one of claims 1 to 4, wherein a mixture of the charged particles and the developer is stored in the developing device. An image recording apparatus, wherein particles are transferred to an image carrier during development, carried to a charging device, and supplied to a charging member.

That is, even in a toner recycling configuration in which charged particles are mixed with a developer, it is possible to stably recover toner and normalize toner charge, thereby realizing an excellent image recording apparatus.

[0050]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is a schematic configuration diagram of an image recording apparatus using a charging device according to the present invention.
This image recording apparatus is a direct injection charging type laser printer utilizing a transfer type electrophotographic process.

(1) Overall Schematic Configuration of Image Recording Apparatus 1 is an image carrier, which in this example is a rotating drum type negative OPC photosensitive member of φ24 mm (negative photosensitive member, hereinafter referred to as photosensitive drum). is there. The photosensitive drum 1 has a peripheral speed of 47 mm / sec (= process speed PS,
(The printing speed).

The photosensitive drum 1 will be described in further detail in another section.

Reference numeral 2 denotes a charging device, which is a contact charging device of a particle charging type according to the present invention. The charging device 2 includes a charging roller 2A as a contact charging member, a charging bias application power source S1 for the charging roller, and a charged particle supply device 3 for the charging roller.

The charging roller 2A comprises a cored bar 2a and a rubber or foamed elastic / medium resistance layer 2 serving as a charged particle carrier formed concentrically and integrally with the outer periphery of the cored bar 2a.
b, and further comprises charged particles (conductive particles) m carried on the outer peripheral surface of the elastic / medium resistance layer 2b. The charging roller 2A is pressed against the photosensitive drum 1 with a predetermined intrusion amount to form a charging contact portion n having a predetermined width. The charged particles m carried on the charging roller 2A come into contact with the surface of the photosensitive drum 1 at the charging contact portion n.

The charging roller 2A is driven to rotate in the clockwise direction indicated by the same arrow as that of the photosensitive drum 1, and rotates in the opposite direction (counter) to the rotating direction of the photosensitive drum 1 at the charging contact portion n, so that the charging roller 2A passes through the charged particles m. It comes into contact with the surface of the photosensitive drum 1 with a speed difference.

The relative speed difference of the charging roller 2A with respect to the photosensitive drum 1 can also be provided by rotating the charging roller 2A at a different peripheral speed in a direction opposite to that of the charging roller 2A (forward rotation direction of the photosensitive drum 1). . However, since the charging property of the direct injection charging depends on the ratio of the peripheral speed of the photosensitive drum 1 to the peripheral speed of the charging roller 2A, it is better to rotate the charging roller 2A in the same direction as the photosensitive drum 1 in terms of the number of rotations. This configuration is advantageous and advantageous in terms of particle retention.

At the time of image recording by the image recording apparatus, a predetermined charging bias is applied from the charging bias applying power source S1 to the metal core 2a of the charging roller 2A.

Thus, the peripheral surface of the photosensitive drum 1 is uniformly charged to a predetermined polarity and potential by the direct injection charging method. In this example, a charging bias of -600 V was applied from the charging bias applying power supply S1 to the core metal 2a of the charging roller 2A, and a charging potential substantially equal to the applied charging bias was obtained on the surface of the photosensitive drum 1.

The charged particles m applied to the outer peripheral surface of the charging roller 2A adhere to the surface of the photosensitive drum 1 with the charging of the photosensitive drum 1 by the charging roller 2A and are carried away. Therefore, a charged particle supply device 3 for the charging roller 2A is required to compensate for this. When the charged particles m are applied to the charging roller 2A by the charged particle supplier 3, the charged particles m stored in the housing container 3a of the charged particle supplier 3 are agitated by the stirring blade 3b and supplied to the outer peripheral surface of the charging roller 2A. Done. Then, an excessive amount of the charged particles m in accordance with the target application amount is scraped off by the fur brush 3c to apply an appropriate amount of the charged particles. The control of the applied amount of the charged particles can be adjusted at any time by controlling the rotation speed of the fur brush 3c.

The charging device 2 and the direct injection charging will be described in detail in another section.

Reference numeral 4 denotes a laser beam scanner (exposure device) including a laser diode, a polygon mirror, and the like. The laser beam scanner 4 outputs a laser beam intensity-modulated in accordance with a time-series electric digital pixel signal of target image information, and scans and exposes the uniformly charged surface of the rotary photosensitive drum 1 with the laser beam. .

By the scanning exposure L, an electrostatic latent image corresponding to the target image information is formed on the surface of the rotating photosensitive drum 1.

Reference numeral 5 denotes a developing device (developing device). The developing device 5 of this embodiment holds a two-component developer T composed of a magnetic carrier Cd and a non-magnetic toner t, and coats a fixed amount on the developing sleeve 51. The toner t is the carrier Cd
, And a developing bias applied between the developing sleeve 51 and the photosensitive drum 1 by the developing bias applying power source S2 makes the electrostatic latent image on the photosensitive drum 1 visible in the developing area a. Image. The developing device 5 will be described in detail in another section.

Reference numeral 6 denotes a transfer roller of a medium resistance as a contact transfer hand throw, which is brought into pressure contact with the photosensitive drum 1 at a predetermined pressure to form a transfer nip portion b. A transfer material P as a recording medium is supplied to the transfer nip b from a paper supply unit (not shown) at a predetermined timing, and a predetermined transfer bias voltage is applied to the transfer roller 6 from a transfer bias application power source S3. As a result, the toner image on the photosensitive drum 1 side is sequentially transferred onto the surface of the transfer material P fed to the transfer nip portion b.

The transfer roller 6 used in this embodiment has a medium resistance foam layer 6b formed on a cored bar 6a, and has a roller resistance value of 5 × 10 ^8.
The transfer was performed by applying a voltage of +2.0 kV to the cored bar 6a. The transfer material P introduced into the transfer nip portion b is conveyed by nipping the transfer nip portion b, and the toner image formed and carried on the surface of the rotary photosensitive drum 1 on its surface side is sequentially reduced by electrostatic force and pressing force. Is transcribed.

Reference numeral 7 denotes a fixing device such as a heat fixing system. The transfer material P fed to the transfer nip portion b and receiving the transfer of the toner image on the photosensitive drum 1 side is separated from the surface of the rotary photosensitive drum 1 and is introduced into the fixing device 7, where the toner image is fixed. It is discharged out of the apparatus as an image formed product (print copy).

Reference numeral 8 denotes a photosensitive drum cleaning device.
The transfer residual toner remaining on the photosensitive drum 1 is scraped off by the cleaning blade 8a and collected in the waste toner container 8b.

Then, the photosensitive drum 1 is charged again by the charging device 2, and is repeatedly used for image formation.

(2) Photosensitive Drum 1 FIG. 2 is a schematic view of the layer structure of the photosensitive drum (electrophotographic photosensitive member) 1. (A) is a photosensitive drum 1a with a charge injection layer,
(B) is a schematic diagram of a layer configuration of the photosensitive drum 1b without a charge injection layer.

(B) Photosensitive drum 1b without charge injection layer
Is a general organic photoreceptor drum coated on an aluminum drum substrate (Al drum substrate) 11 in the order of an undercoat layer 12, a charge generation layer 14, and a charge transport layer 15.

(A) Photosensitive drum 1a with charge injection layer
Is an improvement in charging performance by further applying a charge injection layer 16 to the photoreceptor 1b.

The charge injection layer 16 is formed by adding a photo-curable acrylic resin as a binder to conductive particles (conductive filler).
SnO ₂ ultrafine particles 16a (having a diameter of about 0.03 μm)
m), a polymerization initiator and the like are mixed and dispersed, and after coating, a film is formed by a photocuring method.

In addition, by incorporating a lubricant such as tetrafluoroethylene resin, the surface energy of the surface of the photosensitive drum can be suppressed, and the adhesion of the charged particles m can be generally suppressed. The surface energy is preferably 85 degrees or more, more preferably 90 degrees or more, as represented by the contact angle of water.

The surface resistance of the surface is an important factor from the viewpoint of charging performance. In the direct injection charging method, it is considered that by reducing the resistance on the side of the charged body, the area of the surface of the charged body that can be charged per injection point (contact point) is increased. Therefore, even if the charging rollers are in the same contact state, when the resistance of the surface of the member to be charged is low, charges can be transferred efficiently. On the other hand, when the charge injection layer 16 is used as a photoreceptor, the electrostatic latent image must be held for a certain period of time.
A range of 10 ⁹ to 1 × 10 ¹⁴ (Ω · cm) is appropriate.
Further, even in the case of the photosensitive drum 1b in which the charge injection layer 16 is not used in (b), for example, when the charge transport layer 15 is within the above-described resistance range, the same effect can be obtained. Further, similar effects can be obtained by using an amorphous silicon photoreceptor having a surface layer having a volume resistance of about 10 ¹³ Ωcm.

The resistances of the surface layers of the photosensitive drum 1a and the photosensitive drum 1b used in this example are 10 ¹² Ω · cm and 10 ¹⁴ Ω, respectively.
-Cm or more.

(3) Charging Roller 2A The charging roller 2A as a contact charging member in this embodiment is
As described above, the core metal 2a and the elastic / medium resistance layer 2b of a rubber or foam as a charged particle carrier formed in a roller shape so as to be concentrically integrated with the outer periphery of the core metal 2a. The elastic / medium resistance layer 2 of the charging roller 2A
The charged particles (conductive particles) m are carried on the outer peripheral surface of b.

The elastic / medium resistance layer 2b is formulated with a resin (for example, urethane), conductive particles (for example, carbon black), a sulfide agent, a foaming agent, and the like, and is formed in a roller shape on the cored bar 2a. Thereafter, the surface was polished.

The charging roller 2A as the contact charging member in the present invention is different from the generally used charging roller for discharging in the following points.

1. 1. Surface structure and roughness characteristics for supporting high-density charged particles m on the surface layer Resistance characteristics (volume resistance, surface resistance) required for direct injection charging (3) -1 Surface structure and roughness characteristics Conventionally, the roller surface caused by discharge is flat and the average roughness R of the surface is
a is sub-μm or less, and the roller hardness is high. In charging using discharge, a discharge phenomenon occurs in a gap of several tens of μm slightly away from a contact portion between a roller and a member to be charged.
If the roller and the surface of the member to be charged have irregularities, the electric field intensity partially varies, so that the discharge phenomenon becomes unstable and uneven charging occurs. Therefore, the conventional charging roller requires a flat and hard surface.

Considering why injection charging cannot be performed with the discharging charging roller, it is apparent that the surface structure as described above appears to be in intimate contact with the drum, but the molecular structure required for charge injection is low. There is almost no contact in the sense of microscopic contact.

On the other hand, the charging roller 2A as the contact charging member in the present invention needs to have a certain degree of roughness in order to carry the charged particles m at a high density. With the average roughness Ra,
1 μm to 500 μm is preferred.

If it is smaller than 1 μm, the surface area for supporting the charged particles m is insufficient, and when an insulator (eg, toner) adheres to the surface of the roller, the periphery thereof cannot contact the drum, and the charging performance is reduced. .

In consideration of the ability to retain particles, it is preferable that the charged particles used have a roughness larger than the particle diameter.

On the other hand, if it is larger than 500 μm, the unevenness of the roller surface reduces the in-plane charging uniformity of the member to be charged. Ra in this example was 50 μm.

For the measurement of the average roughness Ra, the roller surface shape and Ra were measured in a non-contact manner using an objective lens of 250 to 1250 times using a surface profile measuring microscope VF-7500 and VF7510 manufactured by Keyence Corporation. .

(3) -2 Resistance Characteristics In a conventional charging roller using discharge, a low resistance base layer is formed on a metal core, and the surface is covered with a high resistance layer. Roller charging by discharge has a high applied voltage, and if there is a pinhole (exposed base due to damage to the film), a voltage drop will occur around the pinhole and poor charging will occur. Therefore, it is necessary to set it to 10 ¹¹ Ω □ or more.

On the other hand, in the direct injection charging system of the present invention, since the charging can be performed with a low voltage, the surface of the contact charging member does not need to have a high resistance, and the roller can be constituted by a single layer. Rather, in direct injection charging, the surface resistance of the charging roller 2A needs to be 10 ⁴ to 10 ¹⁰ Ω.

If the resistance is higher than 10 ¹⁰ Ω, a large potential difference is generated on the roller surface, so that a discharge bias acts on the charged particles, so that the charged particles are easily discharged. Further, the uniformity in the charged surface is reduced, and unevenness due to the rubbing of the roller appears in a halftone image as streaks, and the image quality is reduced.

On the other hand, when it is smaller than 10 ⁴ Ω, a peripheral voltage drop due to a drum pinhole occurs even in the case of injection charging.

Further, regarding the volume resistance, 10 ⁴ -1
It is preferably in the range of 0 ⁷ Ω. If it is smaller than 10 ⁴ Ω, a voltage drop of the power supply due to pinhole leakage is likely to occur. On the other hand, if it is larger than 10 ⁷ Ω, the current required for charging cannot be secured, and the charging voltage is reduced.

The surface resistance and volume resistance of the charging roller 2A used in this embodiment were 10 ⁷ Ω and 10 ⁶ Ω.

The resistance of the charging roller 2A was measured according to the following procedure. FIG. 3 shows a schematic diagram of the configuration at the time of measurement. The roller resistance is such that the total pressure of the core metal 2a of the charging roller 2A is 9.8N.
An electrode was applied to an insulator drum 93 having an outer diameter of 24 mm so that a load of (1 kgf) was applied, and measurement was performed. As for the electrodes, a guard electrode 91 was arranged around a main electrode 92, and the measurement was carried out with reference to the wiring diagrams shown in FIGS. The distance between the main electrode 92 and the guard electrode 91 was adjusted to approximately the thickness of the elastic / medium resistance layer 2b, and the main electrode 92 secured a sufficient width with respect to the guard electrode 91. The measurement is performed by applying +100 V from the power supply S4 to the main electrode 92.
Was applied and the current flowing through the ammeters Av and As was measured, and the volume resistance and the surface resistance were measured, respectively.

As described above, the charging roller as the contact charging member in the present invention is as follows. 1. Surface structure roughness characteristics to support high density charged particles on the surface layer The resistance characteristics (volume resistance, surface resistance) required for direct charging are required.

(3) -3 Other Roller Characteristics In the direct injection charging system, it is important that the contact charging member functions as a flexible electrode.

The magnetic brush is realized by the flexibility of the magnetic particle layer itself.

In the present charging device 2, the charging roller 2A
This is achieved by adjusting the elastic characteristics of the elastic / medium resistance layer 2b. A preferred range is 15 to 50 degrees in Asker C hardness. More preferably, 20 to 40 degrees is preferable.

If it is too high, the required penetration amount cannot be obtained, and the charging contact portion n cannot be secured with the member to be charged, so that the charging performance is reduced. In addition, since the contact property at the molecular level of the substance cannot be obtained, contact with the surroundings is hindered by the entry of foreign matter.

On the other hand, if the hardness is too low, the unevenness of the shape is not stable, so that the contact pressure with the member to be charged becomes uneven, causing uneven charging. Alternatively, charging failure occurs due to permanent deformation of the roller due to long-term storage.

In this example, the charging roller 2A having a Asker C hardness of 22 degrees was used. Further, the charging roller 2A is disposed with a penetration amount of 0.3 mm into the photosensitive drum 1, and in this example, a charging contact portion n of about 2 mm is formed.

(3) -4 Material, Structure and Dimension of Charging Roller The material of the elastic / medium resistance layer 2b of the charging roller 2A is as follows.
EPDM, urethane, NBR, silicone rubber, IR
For example, a rubber material in which a conductive substance such as carbon black or metal oxide for resistance adjustment is dispersed. It is also possible to adjust the resistance by using an ion conductive material without dispersing the conductive substance. Thereafter, if necessary, surface roughness is adjusted, and molding by polishing or the like is performed. Further, a configuration using a plurality of layers separated in function is also possible.

However, as the form of the elastic / medium resistance layer 2b of the charging roller 2A, a porous structure is more preferable. This is advantageous in terms of manufacturing in that the above-mentioned surface roughness can be obtained simultaneously with the molding of the roller. An appropriate cell diameter of the foam is 1 to 500 μm. After the foam molding, the surface is polished to expose the surface of the porous body, so that the surface structure having the above-described roughness can be formed.

Finally, a diameter of 6 mm and a longitudinal length of 240
A 3 mm thick elastic / medium resistance layer 2b having a porous body surface was formed on a 2 mm cored bar 2a to prepare a charging roller 2A having an outer diameter of 12 mm and a middle resistance layer longitudinal length of 220 mm.

The charging roller 2A is disposed with a penetration amount of 0.3 mm into the photosensitive drum 1 as a member to be charged. In this embodiment, a charging contact portion n having a contact width of about 2 mm is formed.

(4) Charged Particles m In this example, the charged particles m have a specific resistance of 10 ⁶ Ω · c.
m, conductive zinc oxide having an average particle diameter of 3 μm was used.

The charged particles m are stored in the housing container 3a of the charged particle supply device 3.

As a material of the charged particles m, a mixture with conductive inorganic particles such as other metal oxides or an organic substance, or
Various conductive particles such as those subjected to a surface treatment can be used. In addition, the charged particles m in the present invention do not need to be magnetically constrained, and thus need not have magnetism.

The particle resistance requires a specific resistance of 10 ¹² Ω · cm or less in order to transfer electric charges via the particles.
Preferably, it is 10 ¹⁰ Ω · cm or less.

The resistance was measured by the tablet method and normalized. That is, approximately 0.5 g of the charged particles m is placed in a cylinder having a bottom area of 2.26 cm ² and 147N (15
At the same time as the pressurization of kgf), the resistance was measured by applying a voltage of 100 V, and then normalized to calculate the specific resistance.

The particle diameter is desirably 10 μm or less in order to obtain high charging efficiency and charging uniformity exceeding magnetic brush charging devices. In the present invention, the particle size when the particles constitute an aggregate is defined as the average particle size as a pseudo-aggregate. The particle size was measured by observation using an electron microscope.
More than one sample was extracted, the volume particle size distribution was calculated with the maximum horizontal extension, and the 50% average particle size was determined.

There is no problem that the charged particles m exist not only in the state of primary particles but also in the state where secondary particles are quasi-collected. The form of the aggregated particles is not important as long as the function as the charged particles m can be realized as an aggregate.

It is desirable that the charged particles m be white or nearly transparent so as not to hinder the exposure of the latent image particularly when used for charging the photosensitive member. Further, considering that the charged particles m are partially transferred from the photoreceptor to the recording material, color recording is preferably colorless or white. Further, in order to prevent light scattering by particles during image exposure, the particle diameter is desirably equal to or smaller than the constituent pixel size, and further preferably equal to or smaller than the toner particle diameter. The lower limit of the particle size is considered to be 10 nm as a limit so that the particles can be obtained stably.

(5) Charged Particle Carrying Amount In the present invention, the charging performance is improved by reducing the particle size of the charged particles m in the particle charging. Become noticeable. Since the force capable of holding the charged particles m on the charging roller 2A is a weak adhesive force, it is difficult to restrain the particles even if a large number of particles are supplied. The effect of image defects on the development process and transfer paper is suppressed. Therefore, ideally, it is desirable to apply the coating uniformly on the surface of the charging roller. However, in practice, by adjusting the carrying amount, it is possible to secure the charging property and to reduce the amount of particles adhering to an harmless level. Becomes possible. It is necessary to appropriately maintain the amount of particles supported by the average roughness Ra of the roller surface. That is, it is desirable that the value obtained by dividing the supported amount by the average roughness Ra is 1 or less, more preferably 0.3 or less.

The carrying amount / Ra of the magnetic conductive particles used in the conventional magnetic brush charging device is approximately 167 mg / cm ² / μm.
(200 mg / cm ² , Ra = 1.2 μm), whereas the nonmagnetic charged particles of the present invention are 1 mg / c
m ² / μm (50 mg / cm ² , Ra = 50 μm) or less. More preferably, 0.3 mg / cm ² / μm (15
mg / cm ² , Ra = 50 μm) or less. On the other hand, the minimum loading amount is also 0.005 m in the value of the loading amount / Ra because it is necessary to secure the charging performance.
^{g / cm 2 /μm(0.25mg/cm 2, Ra} = 50μ
m). More preferably, 0.02 mg / cm ² /
μm (1 mg / cm ² , Ra = 50 μm). That is, it is desirable that the supported amount / Ra is 0.005 to 1, more preferably 0.02 to 0.3 mg / cm ² / μm. Details will be described later in Examples.

The adjustment of the carried amount was performed by adjusting the rotation speed of the fur brush 3c of the charged particle supply device 3.
The higher the brush speed, the lower the particle carrying amount can be set. In addition, adjustment was made according to the rotation speed of the stirring blade 3b, the density of the fur brush 3c, and the like as needed.

(6) Developing Device 5 The developing device 5 is a two-component developing device. The configuration will be described in detail. The developing device 5 is arranged to face the photosensitive drum 1, and the inside thereof is divided into a first chamber (developing chamber) 58 a and a second chamber (stirring chamber) 58 b by a partition wall 57 extending in the vertical direction. ing.

At the opening of the first chamber 58a, a non-magnetic developing sleeve 51 which rotates in the direction of the arrow is arranged so as to face the photosensitive drum 1. Inside the developing sleeve 51, a magnet 52 is provided.
Are fixedly arranged. The developing sleeve 51 is a blade 5
9 carries a layer of a two-component developer (including a magnetic carrier Cd and a non-magnetic toner t) T whose layer thickness is regulated, and supplies the developer to the photosensitive drum 1 in a development area a facing the photosensitive drum 1. To develop the electrostatic latent image as a toner image. To the developing sleeve 51, a developing bias voltage having a rectangular wave in which a DC voltage is superimposed on an AC voltage is applied from a power source S2.

The first chamber 58a and the second chamber 58b are provided with developer stirring screws 53a and 53b, respectively. The screw 53a stirs and transports the developer T in the first chamber 58a. The screw 53b is connected to the transfer screw 5 from a toner discharge port 55 of a toner supply tank (not shown).
By the rotation of 6, the toner t supplied to the second chamber 58b and the developer T already in the second chamber 58b are agitated and conveyed, and the toner concentration is made uniform. In the partition wall 57, a developer passage (not shown) for communicating the first chamber 58a and the second chamber 58b with each other is formed at the front and rear ends in FIG. 1, and the screws 53a and 53b are formed. The developer T in the first chamber 58a whose toner concentration has been reduced due to the toner t being consumed by the development due to the conveyance force of
The developer T, which moves into the chamber 58b and has the toner concentration recovered in the second chamber 58b, moves from the other passage into the first chamber 58a.

On the other hand, the developer concentration control device adjusts the ratio of the toner in the developer T in the developing device to be constant by monitoring the magnetic permeability of the developer using a magnetic force sensor. That is, the magnetic permeability differs depending on the mixing ratio of the toner t and the development carrier Cd due to the difference in magnetic permeability. Therefore,
The replenishment of the toner is controlled by comparing the output of the magnetic sensor measured in advance with the current output, and the ratio of the toner in the developer T in the developing device is kept constant.

The developer T is a two-component developer comprising a non-magnetic toner T which is negatively charged and magnetic carrier particles Cd which are positively charged. The toner mixture ratio of the developer T was such that the nonmagnetic toner was 5% by weight.

A) Toner t: The non-magnetic toner t is prepared by mixing a binder resin, a pigment, and a charge controlling agent, and performing kneading, pulverizing, and classifying processes, and further adding a fluidizing agent or the like as an external additive. It was created. Average particle size of toner (D
4) was 8 μm.

B) Carrier Cd: The magnetic carrier is composed of ferrite particles and has an average particle size of 50 μm and a resistance value of 10 ⁸ Ω · cm or more.

Embodiment 2 FIG. 4 is a schematic configuration diagram showing an image recording apparatus according to a second embodiment using the charging device of the present invention. The image recording apparatus of this embodiment is a laser printer using a transfer type electrophotographic process, a direct injection charging system, and a toner recycling process (cleanerless system). The same points as those of the image recording apparatus according to the first embodiment will not be described again, and only different points will be described.

The charging device 2 does not include a dedicated charged particle supplier 3 for the charging roller 2A. Instead, the charged particles m are added to the developer t of the developing device 60, adhere to the surface of the photosensitive drum 1 together with the toner when the electrostatic latent image is developed on the photosensitive drum 1, and are charged by the rotation of the photosensitive drum 1. By being carried to the section n, it is supplied to the charging roller 2A via the photosensitive drum 1.

The developing device 60 is a reversal developing device using a one-component magnetic toner (negative toner). The developing device contains a mixture t + m of the developer t and the charged particles m. The electrostatic latent image on the surface of the rotating photosensitive drum 1 is
By 0, the toner is developed as a toner image at the development site a.

That is, the image recording apparatus of this embodiment is a toner recycling process, and the transfer residual toner remaining on the surface of the photosensitive drum 1 after image transfer is not removed by a dedicated cleaner (cleaning device). Is carried to the charging contact portion n with the rotation of the photosensitive drum 1, and is temporarily collected by the charging roller 2A rotating counter to the rotation of the photosensitive drum 1 at the charging contact portion n. The toner charge thus generated is normalized, sequentially discharged to the photosensitive drum 1 and reaches the development site a, and is collected and reused in the developing device 60 by simultaneous cleaning with development.

(2) Charging device 2 Except that the charged particle supply device 3 is not provided, the configuration is the same as that of the first embodiment.

(3) The developing device 60 60a is a non-magnetic rotary developing sleeve as a developer carrying member carrying a magnet roll 60b.
The toner t in the pre-development mixture t + m provided in the developing container 60e is subjected to layer thickness regulation and charge application by the regulation blade 60c in the process of being transported on the rotary developing sleeve 60a. A stirring member 60d circulates the toner in the developing container 60e and sequentially transports the toner around the sleeve.

The toner t coated on the rotary developing sleeve 60a is rotated by the rotation of the sleeve 60a, so that a developing portion (developing area) which is an opposing portion between the photosensitive drum 1 and the sleeve 60a.
a. A developing bias voltage is applied to the sleeve 60a from a developing bias applying power source S5.

In this example, the developing bias voltage was a superposed voltage of the DC voltage and the AC voltage. Thus, the electrostatic latent image on the photosensitive drum 1 is reversely developed with the toner t.

A) Toner t: A one-component magnetic toner t, which is a developer, is prepared by mixing a binder resin, magnetic particles, and a charge controlling agent, and kneading, pulverizing and classifying the toner. And a fluidizer are added as an external additive. The average particle size (D4) of the toner was 7 μm.

B) Charged particles m: According to the first embodiment.

(4) Charged Particle Carrying Amount and Coverage In this embodiment, the toner is recycled, so that more toner contaminates the surface of the charging roller than in the first embodiment. The toner has a resistance of 10 ¹³ Ω · cm or more in order to maintain the charge due to frictional charging on the surface. Therefore, when the charging roller 2A is contaminated with the toner, the resistance of the particles carried on the charging roller 2A increases, and the charging performance decreases. For example, even if the resistance of the charged particles is low, the resistance of the powder carried increases due to the mixing of the toner, and the charging property is impaired. Therefore, even if the charged particle carrying amount is from 0.005 to 1, preferably from 0.02 to 0.3 mg / cm ² / μm in the carrying amount / Ra according to the first embodiment, a lot of toner is contained in the component. And the charging performance naturally declines. In this case, the resistance of the supported particles increases and the situation can be grasped. That is, in the actual use state, the resistance (including the contaminants such as toner and paper powder) of the particles carried on the charging roller 2A is measured by the above-described method, and the measured value is 10 ⁻¹ to 10 ¹² Ω · cm. It is. Preferably, it is required to be 10 ¹⁰ Ω · cm.

Further, it is more important to adjust the coverage of the charged particles m in order to grasp the effective amount of the charged particles m in charging. Since the charged particles m are white, they can be distinguished from black of the magnetic toner. The area presenting white in observation with a microscope is determined as the area ratio. When the coverage is 0.1 or less, the charging performance is insufficient even if the peripheral speed of the charging roller 2A is increased.
It is important to keep the coverage of the charged particles m in the range of 0.2 to 1.

The adjustment of the carried amount was basically performed by adjusting the amount of the charged particles m added to the developer t. Further, if necessary, the adjustment was performed by bringing an elastic blade into contact with a part of the outer periphery of the charging roller 2A. The contact of the members has the effect of normalizing the triboelectric charging polarity of the toner, and makes it possible to adjust the amount of particles carried on the charging roller 2A.

Embodiment 3 FIG. 5 is a schematic diagram showing an image recording apparatus according to a third embodiment using the charging device of the present invention. The present embodiment is an image forming apparatus in which a reversal developing device 60 using a one-component magnetic developer according to the second embodiment is combined instead of the two-component developing device 5 in the image forming apparatus according to the first embodiment. However, the developing device 60
No charged particles m are mixed in the developer t. The application of the charged particles m to the charging roller 2A is performed by the charged particle supply device 3
The coating is performed with. The details of the individual devices are in accordance with the first and second embodiments.

<< Examples and Comparative Examples >> (1) Example 1 The image forming apparatus according to the first embodiment uses the charged particles m of 10 ⁴ Ω as the charged particles m, and uses the charged particle supply device 3 to charge the charging roller 2A. Is applied. The resistance of the charged particles m carried on the charging roller 2A was also 10 ⁴ Ω.
The amount of the charged particles m carried was set to about 3 mg / cm ² .

(2) Comparative Example 1 An image forming apparatus according to a conventional example, in which a magnetic brush charging device is used as a charging device. FIG. 6 is a schematic view showing an image forming apparatus of Comparative Example 1, in which the charging device 2 in the image forming device of Embodiment 1 (FIG. 1) is changed to the magnetic brush charging device 100 of FIG. It is.

The conductive magnetic particles C constituting the magnetic brush layer 124 have an average particle diameter of 30 μm and a volume resistance of 10 ⁷ (Ω).
cm) of ferrite particles having a saturation magnetization of 60 (A ·
m ² / kg).

The average particle size of the conductive magnetic particles C is represented by the maximum chord length in the horizontal direction, and the measurement is performed by microscopically selecting 300 or more particles at random, measuring the diameter, and taking the arithmetic average. did.

Further, a particle layer 124 having a particle carrying amount of 200 mg / cm ² is formed on the charging sleeve 121.

(3) Comparative Example 2 This is an image forming apparatus according to a conventional example using the same magnetic brush charging device 100 as Comparative Example 1, but conductive magnetic particles having a particle diameter of 7 μm are used in order to improve charging performance. C is used. The loading amount was also 200 mg / cm ² .

(4) Comparative Example 3 The image forming apparatus according to the third embodiment is similar to the image forming apparatus of the third embodiment except that the charged particles m to be carried have a particle diameter of 0.05 μm and a resistance of 10 ¹³ (Ωcm).
Was used.

(5) Example 2 This is an image forming apparatus according to Embodiment 3, but uses alumina powder having a particle diameter of 0.2 μm and a resistance of 10 ¹² (Ωcm) for the charged particles m to be carried.

(6) Example 3 An image forming apparatus according to Embodiment 3, wherein tin oxide-doped titanium oxide having a particle diameter of 0.2 μm and a resistance of 10 ⁻¹ (Ωcm) for the charged particles m to be carried. Particles were used.

(7) Comparative Example 4 This is an image forming apparatus according to the third embodiment. Tin oxide doped with tin oxide has a particle diameter of 0.2 μm and a resistance of 10 ⁻² (Ωcm). Particles were used.

(8) Example 4, Example 5, Example 6, Example 7, Example 8, Comparative Example 5 In these examples, the image forming apparatus according to the third embodiment is used. Having a particle size of 0.01,
Zinc oxide particles having a resistance of 10 ⁴ (Ωcm) of 0.05, 0.1, 5, 10, and 30 μm were used.

(9) Comparative Example 6, Example 9, Example 10,
Example 11, Example 12, Example 13, Comparative Example 7 In these examples, the image forming apparatus according to the third embodiment is used.
⁴ (Ωcm) using zinc oxide particles, and the loading amount was 0.05, 0.25, 1, 5, 15, 50, and 100 mg, respectively.
/ Cm ² . (10) Comparative Example 8, Example 13, Example 14, Example 1
5, Example 16, Example 17, Comparative Example 9 In these examples, the image forming apparatus according to the third embodiment is used.
A roller having a particle diameter of 3 μm and a resistance of 10 ⁴ (Ωcm) was used as the charged particles m, and the amount of the particles carried was 0.01, 0.05, 0.2, 1, 3, 1, and 1.
It was set to 0.50 mg / cm ² . (11) Comparative Example 10 This is an example in which the image forming apparatus according to Embodiment 2 is configured without using the charged particles m at all. That is, there is no charged particle supplier 3 for the charging roller 2A, and no charged particles m are mixed in the developer t of the developing device 60.

(12) Example 18 In the image forming apparatus according to Embodiment 2, 0.5 parts by weight of charged particles m was added to developer t.

(13) Example 19 In the image forming apparatus according to Embodiment 2, 2 parts by weight of the charged particles m were added to the developer t. (13) Evaluation Method of Each Example and Comparative Example a) Measurement of Amount and Resistance of Carrying Particles For the measurement of the carrying amount, the particles carried on the charging roller were washed, and the weight and resistance of the particles were measured.

Ethanol and water (1: 1) were placed in the ultrasonic cleaner.
The cleaning liquid obtained in 2) was prepared, and a roller was immersed therein to perform cleaning. By repeating washing and repeating the washing while rubbing the roller surface with a blade or the like as necessary while checking the surface of the roller with an optical microscope or the like, it is possible to remove deposits on the roller.

The obtained washing solution is allowed to stand for 1 to 2 hours, and when the supernatant can be clearly separated from the supernatant, the supernatant is removed. afterwards,
After sufficiently drying at 105 ° C., the load on the roller was extracted.

The measurement of the particle resistance follows the above-mentioned tablet method.

The carried amount is determined as the carried amount per unit area from the total weight of the obtained particles and the surface area of the charging roller 2A (calculated from the longitudinal length and the outer diameter of the roller).

The amount of the magnetic brush carried is measured by directly collecting magnetic particles on the surface of the sleeve after coating and measuring the amount of coating.

B) Measurement of Coverage Regarding the measurement of the coverage, the area covered with the conductive particles was measured by microscopic observation under a condition close to the roller contact condition. Specifically, the rotation of the photosensitive drum 1 and the charging roller 2A is stopped without applying the charging bias, and the surfaces of the photosensitive drum 1 and the charging roller 2A are moved with a video microscope (O
Images were taken with a LYMPUS OVM1000N) and a digital still recorder (DELTS SR-3100).
With respect to the charging roller 2A, the charging roller 2A was brought into contact with the slide glass under the same conditions as the contact with the photosensitive drum 1, and the contact surface was photographed with a video microscope from the back of the slide glass with a 1000 × objective lens. Thereafter, the area covered with the particles having the color or luminance of the charged particles measured in advance was separated, and the area ratio was obtained as the coverage. When it is difficult to determine the color, the material on the outermost surface of the roller is measured using a fluorescent X-ray analyzer SYSTEM3080.
(Manufactured by Rigaku Denki Kogyo KK). First, the adhesive surface of the polyester tape (Nichiban No.550 (# 25)) is sandwiched between the charging roller and the drum covered with the charged particles in the initial state, and the drum and the roller are driven to rotate and the roller is brought into contact with the roller. Pass the drum nip once. At this time, particles on the outermost surface of the charging roller are further sampled on the tape surface. On the other hand, sampling is performed in the same manner for the roller that has completed the print test. The coverage can be determined by quantifying the content of the specific element contained in the conductive particles. That is,
Assuming that the tape sample of the roller carrying only the conductive particles is 1, the ratio of the sample after the print test is calculated, and the coverage can be obtained.

C) Evaluation of Charging Performance The charging performance was evaluated by ghost. Since the printer of each example performs image recording by a reversal developing system, the ghost means a portion (toner image portion) of the photosensitive drum 1 which has been exposed to the image in the first rotation and a second rotation of the photosensitive drum. , Which means that the previous image pattern on the photosensitive drum is more strongly developed and a ghost image is generated. Here, the image evaluation was performed based on the following criteria.

X: Ghost is observed in a white background after solid black. Δ: No ghost is observed in a white background after solid black, but a ghost pattern is slightly observed in a halftone portion. ○: White background after solid black. No ghost is observed in any of the halftone portions and the halftone portion. The evaluation was performed after 100 sheets and 4000 sheets including the following defective development and fogging.

A printing test was performed using a pattern having a printing ratio of 5% for the image pattern and no difference in the printing ratio in the longitudinal direction.

D) Poor Development (Evaluation of Image Defects) Image evaluation was performed by outputting a halftone image and evaluating the number of image defects. In each of the printers, image recording was performed using a 600 dpi laser scanner.

In this evaluation, the halftone image means a stripe pattern in which one line in the main scanning direction is recorded, and then two lines are not recorded, and expresses a halftone density as a whole.

Since the printer of each example performs image recording in the reversal development system, any of the cases where image exposure is hindered and a leak occurs during development appear as white points in the image. In particular, in the present invention, the number of these defect sites was evaluated based on the following criteria, and importance was placed on the uniformity of the halftone image, and defects of 0.3 mm or more were evaluated.

X: White spots with a diameter of 0.3 mm or more are present in the halftone image exceeding 50 Δ: 5 to 5 white spots with a diameter of 0.3 mm or more in the halftone image
0: Good: Less than 5 white spots with a diameter of 0.3 mm or more are present in the halftone image. E) Fog evaluation Fog is a phenomenon in which toner is slightly developed in a white portion (unexposed portion) where printing is not originally performed, and This is an image defect that appears as follows.

The fog amount is determined by measuring the optical reflectivity of a green filter using an optical reflectometer (TC-6DS manufactured by Tokyo Denshoku) and subtracting it from the reflectivity of only the recording paper to obtain the fog amount. Was evaluated. The fog amount was measured on 10 or more points on the recording paper, and the average value was obtained.

×: The fog amount exceeds 10% Δ: The fog amount is 2 to 10% ○: Both the fog amounts are less than 2% (14) Evaluation results Evaluation result table 1, evaluation result table 2, evaluation Results Table 3 summarizes the evaluation results of the examples and comparative examples.

[0165]

[Table 1]

[0166]

[Table 2]

[0167]

[Table 3]

[0168]

[Table 4]

Hereinafter, the evaluation results of the examples and comparative examples will be described, and the effectiveness of the present invention will be described.

Each of the examples and the comparative examples was evaluated in two configurations. In the evaluation result table, the upper part shows the case where the photosensitive drum 1a with the injection layer was used (FIG. 2A), and the lower part shows the case where the photosensitive drum 1b without the injection layer was used (FIG. 2B).

Since the photosensitive drum 1b without the injection layer has a high resistance on the surface of the photosensitive drum, a charging device having a higher density is required. In other words, the contactability of the charging member can be evaluated under more severe conditions.

Comparative Example 1 is an image forming apparatus equipped with a conventional charging device using a magnetic brush. However, the charging performance of the photosensitive drum 1b having no injection layer is particularly insufficient. Further, the amount of the charged magnetic particles C dropping off to the photosensitive drum 1 was large, causing a development leak or a problem in detecting the amount of toner in the developer.

Comparative Example 2 has a configuration in which the charged particle diameter is improved to 7 μm in order to compensate for the insufficient contact density of Comparative Example 1. Certainly, the charging performance was improved in the initial stage of charging, but at the time of printing 100 sheets, particles were already noticeable and the durability of the photosensitive drum with the injection layer was insufficient.

On the other hand, in Example 1, conductive zinc oxide particles having a particle diameter of 3 μm were used as the charged particles m, and the contact density was improved, and the amount of particles carried was 3 mg / cm ^2.
Thus, the amount of particles falling onto the photosensitive drum 1 could be reduced. The reduced amount of particles and the small particle size were able to improve poor development and fogging, which are adverse effects of the dropped particles.

Comparative Examples 3 and 4 and Examples 2 and 3 are examples showing appropriate resistance ranges of the charged particles. The resistance of the particles m carried on the charging roller 2A is preferably 10 ¹² to 10 ^-1 Ω. For Comparative Example 3 having a particle resistance of 10 ¹³ Ω,
In the first place, charge transfer cannot be performed, and charging performance is insufficient.
On the other hand, with respect to the charged particles of 10 ⁻² Ω, leakage of the developing bias occurred during the development, and image defects were remarkable.

In Comparative Example 5 and Examples 4 to 8, the charged particles m
Represents an appropriate particle size range. The preferable range of the particle size of the charged particles m is 0.01 μm to 10 μm. Further, considering the fog characteristics on paper, 0.1 to 5 μm is a particularly preferable range.

Example 4 is an example using tin oxide particles having the smallest particle size among general charged particles. Although it is slightly disadvantageous in terms of poor development and fogging, it shows a sufficient charging performance.

On the other hand, Comparative Example 5 using charged particles m of 30 μm is disadvantageous in terms of contact density and insufficient in charging performance because the particle diameter is large. Furthermore, since the particle diameter is large and the force of adhering to the charging roller 2A is weak, many particles fall off, resulting in poor development and fogging.

Comparative Examples 6, 7, 8, 9 and Examples 9 to 17 are examples showing an appropriate amount of charged particles m carried. As the amount of support, there is an appropriate amount of support according to the surface roughness Ra of the roller. Therefore, a good correlation with the image was obtained using the carried amount / Ra normalized by Ra as an index.

In Comparative Example 6, where 0.05 mg was carried, the charging performance was insufficient. On the other hand, Example 13
Has a roller surface roughness of 10 μm and a supported amount / Ra of 0.005 mg.
Which is more than 0.001 of Comparative Example 6. Therefore,
It can be understood that Example 13 was superior to Comparative Example 6 in terms of chargeability.

Comparative Example 7 is an example in which the carrying amount is 100 mg / cm ² . Although the charging performance is sufficient, the carrying amount is too large to sufficiently hold the charging roller 2A. Therefore, the toner is dropped on the photosensitive drum 1 and causes defective development and fogging. Therefore, as in Example 13, the loading amount was 50
By reducing the carrying amount / Ra to 1 as mg, the carrying amount becomes appropriate for the roller, and development defects and fog can be improved. On the other hand, even when the loading amount is 50 mg, the loading amount / Ra is 5 as in Comparative Example 9.
In the case of, the carried amount was too large with respect to the roller roughness, resulting in a remarkable development failure. In other words, the carrying amount has an appropriate range according to the roughness of the roller surface,
When these are arranged, the supported amount / Ra is 0.005 to 1
Preferably by adjusting from 0.02 to 0.3,
Excellent conditions can be set for both the charging property and the developing property.

Further, in the cleaner-less apparatus of Embodiment 2, Comparative Example 10 and Examples 18 and 19 show that there is an optimum configuration for the charged particle coverage when a plurality of particles are carried on the charging roller 2A. ing.

Comparative Example 10 is a case where charging was performed without using charged particles. 10mg / c as loading amount
m ² but all are toner and particle resistance is 10 ¹⁴ Ω
And high. Therefore, charging is insufficient.

On the other hand, in Examples 18 and 19, both the particle resistance and the carried amount were within the above-mentioned appropriate ranges, and although the coverage was slightly low, they exhibited sufficient chargeability, development and fog characteristics.

As described above, the coverage is preferably in the range of 0.2 to 1. << Other Embodiments >> 1) In the embodiments, a laser printer is exemplified as an image recording apparatus. However, the present invention is not limited to this, and other image recording apparatuses (image forming apparatuses) such as an electrophotographic copying machine, a facsimile apparatus, and a word processor may be used. Of course.

2) The image carrier as a member to be charged is an electrostatic recording dielectric in the case of an electrostatic recording device.

3) The image carrier is not limited to a drum type, but may be an endless type, an endless belt type, a sheet type, or the like.

4) The contact charging member is not limited to the roller type.
An endless or endless belt type may be used.

5) The charging device of the present invention is not limited to a charging device for an image bearing member (an electrophotographic photosensitive member, an electrostatic recording dielectric, etc.) of an image recording apparatus, but can be used for charging a wide range of charged objects to a charge processing means (for discharging electricity). Of course).

[0190]

As described above, in the present invention, for the purpose of enhancing the charging ability of the particle charging, the particle diameter, the resistance value, and the carrying amount of the charged particles for improving the contact density are configured. As a result, a high charge density is obtained, the amount of particles falling off is reduced, and even if the particles fall off, the problem is not caused.

[0191] Indeed, to be able to maintain a sufficient charging performance for the member to be charged with which was difficult 10 ¹⁴ [Omega] cm or more surface resistance in the conventional particle charging, the higher performance and stable charging device It was realized.

The surface resistance, structure, and resistance of the medium resistance roller as a particle carrier are also configured, and by maintaining a particle carrying amount suitable for the roller, a small particle diameter can be obtained without using a magnetic binding force. It is possible to hold charged particles. As a result, a dense and flexible ideal charging member was realized.

Further, the charging device of the present invention is also effective in an image recording device of a toner recycling system. By setting the coverage of the charged particles on the charging member in an appropriate range, high charging performance and toner recycling can be achieved. Excellent charging device was realized.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an image recording / recording apparatus according to a first embodiment.

FIG. 2 is a schematic diagram of a layer configuration of a photosensitive drum.

FIG. 3 is an explanatory diagram of a method for measuring a resistance value of a charging roller.

FIG. 4 is a schematic diagram of an image recording apparatus according to a second embodiment.

FIG. 5 is a schematic diagram of an image recording apparatus according to a third embodiment.

FIG. 6 is a schematic diagram of a conventional image recording apparatus.

FIG. 7 is a graph showing charging characteristics of a conventional roller charging device and a magnetic brush charging device.

FIG. 8 is a schematic diagram of an example of a magnetic brush charging device.

[Explanation of symbols]

1a. Photosensitive drum with injection layer, 1b. Photosensitive drum without injection layer, 2A. Charging roller, 2a. Cored bar, 2b. Conductive elastic roller; 2. charged conductive particles (charged particles); Charged particle feeder, 3b. Stirring blade, 3c. Fur brush, 4.
Laser exposure apparatus, 5.2-component developing apparatus, 51. Developing sleeve, 52. 5. Magnet roll, 60.1 component magnetic developing device, 6. transfer charger, Fixing device, 8. Drum cleaner

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Jun Hirabayashi 3-30-2 Shimomaruko, Ota-ku, Tokyo F-term in Canon Inc. (reference) 2H003 AA12 BB11 CC04 2H077 AA37 AC16 AD06 FA22 FA25 GA04

Claims (8)

[Claims] 1. A charged particle comprising a conductive particle having a particle diameter of 10 μm to 10 nm as a main component, and a charged particle carrier having a surface having conductivity and elasticity and carrying the charged particle. In a charging device for charging the surface of the charged object by bringing the charged particles into contact with the charged object by bringing the member into contact with the charged object, the resistance of the charged particles supported on the charged particle support is 10
¹² to 10 ^-1 Ω · cm, and the value obtained by dividing the supported amount of the particles by the surface roughness Ra μm of the charged particle carrier is from 0.005 to
A charging device having a concentration of 1 mg / cm ² / μm. 2. The charging device according to claim 1, wherein when the ratio of the charged particles covering the charged particle carrier is a coverage Rc, 1 ≧ Rc ≧ 0.2. . 3. The charged particle carrier has a surface resistance of 10 ⁴ to 10 ¹⁰ Ω □.
3. The charging device according to claim 1. 4. The charging device according to claim 1, wherein the charged particle carrier is an elastic body having a porous body surface. 5. The charging device according to claim 1, wherein the charging member contacts the member to be charged with a speed difference. 6. A charged particle supply means for supplying charged particles having a resistance of 10 ¹² to 10 ^-1 Ω · cm to the surface of the charged particle carrier. The charging device according to any one of the above. 7. An image recording apparatus which performs image formation by applying an image forming process including a step of charging the surface of the image carrier to the image carrier, wherein the step of charging the surface of the image carrier is performed by An image recording apparatus, comprising: the charging device according to claim 1. 8. An electrophotographic image recording system comprising an image carrier, and a charging device, an image exposure device, a developing device, a transfer device, and a fixing device for fixing an image on a recording medium, which are arranged around the image carrier. An apparatus having a toner recycling configuration in which the developer remaining on the surface of the image carrier after the transfer process is temporarily carried on at least the charging member of the charging device, transferred to the surface of the image carrier again, and collected again in the developing device. In the image recording apparatus, the charging device is the charging device according to any one of claims 1 to 5, wherein a mixture of the charged particles and a developer is stored in the developing device, and the charged particles are Is an image recording apparatus which transfers to an image carrier during development, is carried to a charging device, and is supplied to a charging member.