JP2003307910A - Image recorder and process cartridge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve satisfactory image formation that is free of image failure until toner is used up, in an image recorder using particle electrification and a process cartridge. <P>SOLUTION: In order to maintain electrification performance at the completion of printing, the surface area of an electrifying member 2 and the volume of the first space 10 of a developing device 60 maintain a constant relationship. That is, the electrifying member 2 and the developing device 60 are provided around an image carrier 1 and its vicinity. The electrifying member 2 holds thereon conductive particles m, and is in contact with the image carrier 1. In a cross-section vertical to a longitudinal direction of the image carrier, a relationship satisfies the following expression: V<0.24×S<SP>2.3</SP>wherein S (cm<SP>2</SP>/cm) is a length along the surface of the electrifying member 2, that is, the member surface area per unit longitudinal length and V (cm<SP>3</SP>/cm) is an area occupied by the developer stored in the developing device 60, that is, the volume of the developer per unit longitudinal length. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image recording apparatus (image forming apparatus) and a process cartridge detachably mountable to the main body of the image recording apparatus.

More specifically, it has a charging device (charging device) for charging particles, and a replenishing system developing device for accumulating a developer in a second space of the developing device (developing device) and performing sequential development.
The present invention relates to an image recording device such as a copying machine and a printer, and a process cartridge.

[0003]

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

Although these charging devices are collectively referred to as a contact charging device, the charging mechanism (charging mechanism,
From the viewpoint of charging principle), each device is 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 are determined depending on which charging mechanism the charging device is. The principle and features of each of the discharge charging mechanism and the direct injection charging mechanism are described.

.. Discharge Charging Mechanism This mechanism charges the surface of the body to be charged with a discharge product generated by a discharge phenomenon that occurs in the gap between the contact charging member and the body to be charged.

Since the discharge charging system has a constant discharge threshold value between the contact charging member and the member to be charged, a voltage larger than the potential of the member to be charged is contact charged as shown in FIG. 14A (conventional roller charging device). It is necessary to apply it to the member. Further, compared with the corona charging device, the generated amount is remarkably small, but in principle, discharge products are generated.

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

Further, the roller charging due to the discharge has a high applied voltage, and if there is a pinhole (exposure of the substrate due to damage to the film to be charged), a voltage drop occurs around the pinhole and charging failure occurs. Therefore, the surface resistance of the surface layer is set to 10 ¹¹ Ω or more to prevent the voltage drop.

[0009]. Direct Injection Charging Mechanism The direct injection charging is a charging mechanism for directly charging and receiving (charging) the surface of the body to be charged by contact and transfer between the contact charging member and the body 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 body to be charged is about several volts to several tens of volts. The charging characteristics are shown in B (magnetic brush charging device) of FIG. The charging potential is equal to the applied voltage, and there is no voltage difference that causes discharge. In addition, the voltage required for charging can be kept low.

As described above, as a charging mechanism, this direct charging system does not generate ions, and therefore no harmful effects are caused by discharge products. That is, the charging method is excellent in environmental safety, member deterioration, and low power consumption.

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

In the direct charging mechanism, the contact between the contact charging member and the member to be charged is an important factor that determines the charging performance. The term "contact property" as used herein means the ability of the contact charging member to make microscopic contact with the surface of the body to be charged while passing through the charging device.

As a form of the contact charging member used in the direct injection charging device, attempts have been made to use a discharge charging roller or the like, but direct injection charging cannot be performed with the discharge charging roller. With the high hardness and smooth surface structure as described above, it looks like it is in close contact with the body to be charged, but in the sense of the microscopic contact property at the molecular level necessary for charge injection, there is almost no contact. is there.

At present, as a direct injection charging method which has been proposed, there is particle charging using a magnetic brush.

Particle charging: Considering improvement of contact density, a charging method using electrically conductive particles (particle charging) is advantageous. The conductive particles used at this time are called "charged particles". As an example of a charging type charging device using charged particles, A. A charging device using a magnetic brush charging member in which conductive magnetic particles as charged particles are magnetically restrained as a brush by a magnet; A charging device using a charging member in which a thin conductive particle layer is formed on an elastic roller has been proposed.

A. Magnetic Brush Charging Device FIG. 15 is a schematic configuration model diagram of an example of the magnetic brush charging device 100. Reference numeral 120 denotes a magnetic brush charging member, which includes a magnet roll 122 fixedly supported, a non-magnetic / conductive charging sleeve 121 concentrically and rotatably fitted around the outer circumference of the magnet roll 122, and a charging roller 121 of the charging sleeve 121. A magnetic brush layer (magnetic brush portion) 124 of conductive magnetic particles C is formed on the outer peripheral surface by attracting and holding by the magnetic force of the magnet roll 122 inside the charging sleeve. Reference numeral 123 denotes a casing, in which the above-mentioned magnetic brush charging member 120 is assembled, and an appropriate amount of conductive magnetic particles C is contained and stored. 125 is the casing 12
3 is a magnetic brush layer thickness regulating blade provided in FIG.

As the conductive magnetic particles C, which are the charged particles constituting the magnetic brush layer 124, magnetic metal particles such as ferrite and magnetite, and those obtained by binding these magnetic particles with a resin are used. Resistance value is 1 × 10 ⁶ -1
A material having a resistance of ⁰⁹ Ωcm is used. About particle size 10
50 μm is used.

The charging sleeve 121 is rotationally driven in the clockwise direction indicated by the same arrow as that of the photosensitive drum 1 as the member to be charged. The magnetic brush layer 124 is rotatably conveyed in a clockwise direction together with the charging sleeve 121, and is regulated to a predetermined layer thickness by the blade 125. The magnetic brush layer 124 whose layer thickness is regulated is brought into contact with the photosensitive drum 1 and a charging contact portion. The surface of the photosensitive drum is rubbed with n. Magnetic brush layer 1 passing through the charging contact portion n
24 is the rotation of the charging sleeve 121, and the casing 1 is rotated.
It is returned to the conductive magnetic particle reservoir in 23 and conveyed, and is conveyed in a circulating manner.

A predetermined charging bias is applied from the charging bias applying power source S1 to the charging sleeve 121, 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 injected by the applied charging bias. It is uniformly charged to a predetermined polarity and potential.

B. Charging Device Using Thin-Layer Conductive Particles FIG. 16 is a schematic configuration model diagram of an example of a charging device 20 using thin-layer conductive particles. The charging device 20 includes a charging roller 2 as a contact charging member, a charging bias application power source S1 for the charging roller, and a charged particle feeder 3 for the charging roller.

The charging roller 2 includes a core metal 2a and the core metal 2a.
The elastic / medium resistance layer 2b is made of rubber or foam as a charged particle carrier that is concentrically and integrally formed on the outer periphery of a, and the charged / conductive particles (conductive particles are formed on the outer peripheral surface of the elastic / medium resistance layer 202b). ) M is supported on a thin layer.

The charging roller 2 is pressed and brought into contact with the photosensitive drum 1 as the member to be charged with a predetermined amount of penetration to form a charging contact portion n having a predetermined width. The charged particles m carried on the charging roller 2 come into contact with the surface of the photosensitive drum 1 at the charging contact portion n.

The charging roller 2 is rotationally driven in the same clockwise direction as the arrow of the photosensitive drum 1 and rotates in the charging contact portion n in the opposite direction (counter) to the rotating direction of the photosensitive drum 1 to generate the charged particles m. The photosensitive drum 1 comes into contact with the surface with a speed difference.

The relative speed difference of the charging roller 2 with respect to the photosensitive drum 1 can also be provided by rotating the charging roller 2 in a direction opposite to the charging roller 2 (forward rotation direction of rotation of the photosensitive drum 1) with different peripheral speeds. . 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 2, rotating the charging roller 2 in the same direction as the photosensitive drum 1 results in a rotational speed. This configuration is preferable in terms of both the advantages and the retention of particles.

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

As a result, the peripheral surface of the photosensitive drum 1 is uniformly contact-charged to a predetermined polarity and potential by the direct injection charging method.

The charged particles m applied to the outer peripheral surface of the charging roller 2 adhere to the surface of the photosensitive drum 1 as the charging roller 2 charges the photosensitive drum 1 and are carried away. Therefore, the charged particle feeder 3 for the charging roller 2 is required to compensate for this. To apply the charged particles m to the charging roller 2 by the charged particle supplier 3, the charged particles m stored in the housing container 3a of the charged particle supplier 3 are stirred by the stirring blade 3b and supplied to the outer peripheral surface of the charging roller 2. Is done. Then, the fur brush 3c scrapes off excess charged particles m according to the target application amount, and an appropriate amount of charged particles m is applied. The control of the applied amount of charged particles can be adjusted at any time by controlling the rotation speed of the fur brush 3c.

C. Suitable for cleaner system of particle charging Particle charging is suitable for toner recycling system of image recording apparatus. In other words, the toner recycling process is that the waste toner (transfer residual toner) is used again for image formation in the transfer type image recording device, so that the toner is effectively used and the cleaner container space is eliminated to realize the downsizing of the device. It has an excellent configuration.

The transfer residual toner is once taken in the contact charging member and is returned to the developing device through the image carrier so that it can be reused (original toner charge amount), or used again for development, or collected if unnecessary. This allows toner recycling. The charging device used here needs to collect the transfer residual toner and recharge the toner in addition to charging the image carrier.

From the above viewpoints, let us consider the properness of toner recycling for particle charging. The magnetic brush itself is composed of particles and can move with freedom,
It is characterized by a large contact area. Therefore, in the magnetic brush, it is possible to advantageously realize the functions that are indispensable for toner recycling, such as collecting the residual toner after transfer from the image carrier and making the charge of the taken toner proper.

D. The performance of the developing device that visualizes the electrostatic latent image on the surface of the image carrier as a toner image is largely dependent on not only the sleeve as the developer carrier and the regulating blade but also the state of the toner supplied to the sleeve. to be influenced. Therefore, in a developing device having a particularly long life, a replenishing type developing device is often used to stabilize the characteristics of the developer.

In the replenishing system developing device, a first space is provided on the side closer to the image carrier, and a space in which the developing sleeve as the developer carrier is a part of the inner surface and a developer on the side far from the image carrier are provided. By configuring a second space for storing (toner) and supplying new toner from the second space as toner in the first space is consumed, the toner state in the first space is kept constant. It becomes possible to keep.

E. Maintaining Charged Particles Carried State In the above-described charging device using thin-layer conductive particles, there is a problem that the carried charged particles carried by the charging member fall off. Therefore, a means for supplying charged particles according to the life is required. Particularly in a cleanerless image recording apparatus, charged particles are mixed in the developer of the developing apparatus, and the charged particles are supplied to the image carrier as the toner is consumed, and the charged particles are supplied to the contact charging member of the charging apparatus through the transfer process. It is implemented from the viewpoint that the structure is simple and the amount that is suitable for consumption is supplied. That is, in the charging method using thin-layer conductive particles, stable supply of charged particles is very important for maintaining charging performance.

[0035]

However, there is a problem that the charging performance cannot be sufficiently maintained until the end of the life in the injection charging by the thin conductive particles as described above. In particular, the amount of toner in the developing device becomes small, and the charging performance is remarkably deteriorated immediately before the time when the image defect occurs due to the toner shortage (referred to as toner end).

Further, from the viewpoint of stabilizing the developing characteristics, it is very difficult to maintain the charging performance just before the toner end even if the replenishing type developing device is used.

As an actual image defect, a ghost image defect due to insufficient charging property, fog, and a problem in density uniformity in a halftone image appear.

It is an object of the present invention to perform good image formation in the image recording apparatus and the process cartridge using the particle charging without the above-mentioned image defect up to the toner end.

[0039]

SUMMARY OF THE INVENTION The present invention is an image recording apparatus and a process cartridge characterized by the following configurations.

(1) An image carrier and a charging member and a developing device arranged around the image carrier are provided. The charging member is a charging member carrying conductive particles and is perpendicular to the longitudinal direction of the image carrier. In a cross-sectional view, the length of tracing the surface of the charging member, that is, the surface area of the charging member per unit longitudinal length is S (cm ² / cm), and the area or unit occupied by the developer stored in the developing device is An image recording apparatus, wherein V <0.24 × S ^2.3, where V (cm ³ / cm) is the developer volume per longitudinal length.

With this configuration, it is possible to accurately guide the amount of toner corresponding to the decrease in charging performance due to the dropping of the charged particles, and it is possible to maintain good charging performance up to the toner end.

(2) In (1) above, V is V <0.24 × S ^2.3, where V is the area of the developing device in the sectional view, that is, the volume of the developing device per unit longitudinal length. An image recording device characterized by the above.

With this configuration, the toner amount can be set more accurately and the charge can be maintained.

(3) The image recording apparatus as described in (1) or (2) above, wherein V <0.16 × S ^2.3 .

With this configuration, the charging performance at the toner end can be realized at a higher level.

(4) The developing device accommodates a developer containing the conductive particles together with the toner, and the space for accommodating the developer is the first space near the image carrier and the image carrier. Is divided into a second space distant from the second space, and the developer is supplied by sequentially feeding from the second space to the first space, where V is the area of the first space in the sectional view, that is, per unit longitudinal length. From (1) to (3)
The image recording device according to any one of 1.

With this configuration, the life of the recording apparatus can be extended and the charging performance can be maintained up to the toner end.

(5) In any one of (1) to (4), the charging member has a roller shape, and the S is a circumference of the roller, that is, a surface area per unit longitudinal length. The image recording apparatus described.

With this structure, the charging performance can be maintained with a simple structure.

(6) At least the image carrier, the charging member, and the developing device are provided in a frame, and form a part of the image recording device described in any one of (1) to (5) to record an image. A process cartridge that is detachably attached to the main body of the apparatus.

With such a structure, it is possible to easily replace the replacement part having a relatively short life with the replenishment of the developer, and it is possible to set the charging member and the developing device structure for each cartridge.

[0052]

DESCRIPTION OF THE PREFERRED EMBODIMENTS << Embodiment 1 >> FIG. 1 is a schematic configuration diagram of an image recording apparatus according to the present invention. This image recording device uses transfer type electrophotographic process, direct injection charging system,
Toner recycling process (cleanerless system),
It is a laser printer with a detachable process cartridge.

(1) The overall schematic structure 1 of the image recording apparatus is an image carrier, and in this embodiment, it is a rotating drum type negative polarity OPC photosensitive member (negative photosensitive member, hereinafter referred to as photosensitive drum) of φ24 mm. is there. The photosensitive drum 1 has a peripheral speed of 47 mm / sec (= process speed PS,
It is rotated at a constant speed (printing speed). The photosensitive drum 1 will be described in detail in another section.

A charging device 20 uniformly charges the peripheral surface of the rotating photosensitive drum 1 to a predetermined polarity and potential.
This charging device is a particle charging type contact charging device similar to that shown in FIG. However, the charging device 20 of this example does not include the charged particle feeder 3 for the charging roller 2, but has the charging roller 2 as a contact charging member and the charging bias applying power source S1 for the charging roller. As will be described later, the charged particles m are supplied to the charging roller 2 by mixing the charged particles m with a developer (toner) t contained in the developing device 60 at a predetermined ratio, and then from the developing device 60 to the photosensitive drum. The charged particles m are attached to one surface and carried to the charging contact portion (charging nip portion) n so that the charging is performed.

The charging roller 2 includes a core metal 2a and the core metal 2a.
The elastic / medium resistance layer 2b is made of rubber or foam as a charged particle carrier, which is concentrically and integrally formed on the outer periphery of a, and the charged / conductive particles (conductive layer) are previously formed on the outer peripheral surface of the elastic / medium resistance layer 2b. (Particles) m are supported. The charging roller 2 is pressed and brought into contact with the photosensitive drum 1 with a predetermined amount of intrusion to form a charging contact portion n having a predetermined width.
The charged particles m carried on the charging roller 2 come into contact with the surface of the photosensitive drum 1 at the charging contact portion n.

The charging roller 2 is rotationally driven in the same clockwise direction as the photosensitive drum 1 in the arrow direction, and is rotated in the charging contact portion n in the direction (counter) opposite to the rotating direction of the photosensitive drum 1, so that the charged particles m are mediated. The photosensitive drum 1 comes into contact with the surface with a speed difference.

The relative speed difference of the charging roller 2 with respect to the photosensitive drum 1 can be provided by rotating the charging roller 2 in a direction opposite to that of the charging roller 2 (forward rotation direction of rotation of the photosensitive drum 1) with different peripheral speeds. . 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 2, rotating the charging roller 2 in the same direction as the photosensitive drum 1 results in a rotational speed. This configuration is preferable in terms of both the advantages and the retention of particles.

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 core metal 2a of the charging roller 2.

As a result, the peripheral surface of the photosensitive drum 1 is uniformly contact-charged to a predetermined polarity and potential by the direct injection charging method. In this example, a charging bias of −600 V was applied to the core metal 2a of the charging roller 2 from the charging bias applying power source Sl to obtain the same charging potential as the applied charging bias on the surface of the photosensitive drum 1.

The charged particles m applied to the outer peripheral surface of the charging roller 2 adhere to the surface of the photosensitive drum 1 as the charging roller 2 charges the photosensitive drum 1 and are carried away. Therefore, in this example, the charged particles m are mainly supplied from the developing device 60. The charged particles m are added to the developer t of the developing device 60, and 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 held at the charging contact portion n by the rotation of the photosensitive drum 1. By being carried, it is supplied to the charging roller 2 via the photosensitive drum 1.

The charging device 20 and the direct injection charging will be described in detail in another section.

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

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

The developing device 60 is a reversal developing device using a one-component magnetic toner (negative toner). A mixture t + m of the developer t and charged particles m is contained in the developing device. The electrostatic latent image on the surface of the rotating photosensitive drum 1 is transferred to the developing device 6
By 0, reversal development is performed as a toner image at the developing portion a.

The developing device 60 of this embodiment coats a fixed amount on the developing sleeve 60a. The toner t has a certain triboelectric charge due to the sliding friction with the developing sleeve 60a, and on the photosensitive drum 1 in the developing area a by the developing bias applied between the developing sleeve 60a and the photosensitive drum 1 by the developing bias applying power source S5. Visualize the electrostatic latent image. The developing device 60 will be described in detail in another section.

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

The transfer roller 6 used in this example has a roller resistance value of 5 × 10 ^{8 in} which a medium resistance foam layer 6b is formed on a core metal 6a.
The transfer was performed by applying a voltage of +2.0 kV to the core metal 6a. The transfer material P introduced into the transfer nip portion b is nipped and conveyed through the transfer nip portion b, and the toner image formed and carried on the surface of the rotary photosensitive drum 1 is sequentially transferred to the electrostatic force and the pressing force. Will be transcribed.

Reference numeral 7 is a fixing device such as a heat fixing system. The transfer material P that has been fed to the transfer nip portion b and transferred with the toner image on the photosensitive drum 1 side is separated from the surface of the rotating photosensitive drum 1 and is introduced into the fixing device 7, where it is fixed with the toner image. The image is discharged outside the apparatus as an image formed product (print copy).

Then, the photosensitive drum 1 is charged again by the charging device 20.
And is repeatedly used for image formation.

The image recording apparatus of this example is a toner recycling process, and the transfer residual toner remaining on the surface of the photosensitive drum 1 after image transfer is a dedicated cleaner (cleaning device).
Is carried to the charging contact portion n with the rotation of the photosensitive drum 1 without being removed by, and is temporarily collected by the charging roller 2 which counter-rotates with respect to the rotation of the photosensitive drum 1 at the charging contact portion n. As the toner goes around the outer circumference of the charging roller, the inverted toner charges are normalized, and are sequentially discharged to the photosensitive drum 1 to reach the developing portion a, and are collected and reused in the developing device 60 by the simultaneous cleaning of development.

Further, in the image forming apparatus of this embodiment, the three process equipments of the photosensitive drum 1, the charging roller 2 and the developing device 60 are framed independently from other parts (main body) constituting the image recording apparatus. The process cartridge 50 is formed by being integrated in the body 51, and is attachable to and detachable from the main body of the image recording apparatus collectively.

Here, the process cartridge is a cartridge in which the charging means, the developing means or the cleaning means and the image carrier are integrally formed, and the cartridge can be attached to and detached from the main body of the image recording apparatus. Further, at least one of the charging means, the developing means, and the cleaning means and the image carrier are integrally made into a cartridge so as to be attachable to and detachable from the main body of the image recording apparatus. Further, at least the developing means and the image carrier are integrally made into a cartridge so that it can be attached to and detached from the main body of the image recording apparatus.

(2) Photosensitive Drum 1 FIG. 2 is a schematic view of the layer structure of the photosensitive drum (electrophotographic photosensitive member) 1 used in this example. The photosensitive drum 1 includes an aluminum drum substrate (Al drum substrate) 11, an undercoat layer 12,
Positive charge injection prevention layer 13, charge generation layer 14, charge transport layer 1
The charge performance is improved by further applying the charge injection layer 16 to the general organic photoconductor drum that is coated in the order of 5.

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

By additionally including a lubricant such as tetrafluoroethylene resin, the surface energy of the surface of the photosensitive drum is suppressed and the adhesion of the charged particles m is generally suppressed. The surface energy is preferably 85 degrees or more, and more preferably 90 degrees or more when expressed by the contact angle of water.

From the viewpoint of charging performance, the resistance of the surface layer on the surface is an important factor. In the direct injection charging method, it is considered that by lowering the resistance on the side of the body to be charged, the area of the surface of the body to be charged that can be charged is widened per one injection point (contact point). Therefore, even if the charging rollers are in the same contact state, if the resistance of the surface of the member to be charged is low, it is possible to efficiently transfer charges. On the other hand, when it is used as a photoreceptor, it is necessary to hold the electrostatic latent image for a certain period of time, and therefore the volume resistance value of the charge injection layer 16 is 1 ×.
The range of 10 ⁹ to 1 × 10 ¹⁴ (Ω · cm) is suitable.

Even in the case of the photosensitive drum not using the charge injection layer 16, the same effect can be obtained when the charge transport layer 15 is in the above resistance range. Further, the same effect can be obtained by using an amorphous silicon photoconductor or the like having a surface layer having a volume resistance of about 10 ¹³ Ωcm.

The resistance of the surface layer of the photosensitive drum used in this example is 1
It was 0 ¹² Ω · cm.

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

The elastic / medium resistance layer 2b is formulated with a resin (for example, urethane), conductive particles (for example, carbon black), a sulfiding agent, a foaming agent, etc., and is formed in a roller shape on the core metal 2a. Then, the surface was polished.

The charging roller 2 as the contact charging member in the present invention is 1) different from the commonly used charging roller for discharging, and 1) the surface structure and roughness characteristics for carrying the high density charged particles m on the surface layer 2). The difference is in the resistance characteristics (volume resistance, surface resistance) required for direct injection charging.

1) Surface Structure and Roughness Characteristic Conventionally, the roller surface by discharge is flat and the average surface roughness R is
It is sub μm or less in a and the roller hardness is also high. In the charging using discharge, the discharge phenomenon occurs in a gap of several tens of μm, which is slightly apart from the contact portion between the roller and the body to be charged.
When the roller and the surface of the member to be charged have irregularities, the electric field strength is partially different and the discharge phenomenon becomes unstable, resulting in uneven charging. Therefore, the conventional charging roller requires a flat and hard surface.

The reason why injection charging cannot be performed by the discharge charging roller is as follows. It seems that the surface structure as described above is in close contact with the photosensitive drum as the member to be charged, but it is There is almost no contact in the sense of micro-contact at the required molecular level.

On the other hand, the charging roller 2 as the contact charging member in the present invention is required to have a certain degree of roughness because it needs to carry the charged particles m at a high density. 1 in terms of average roughness Ra
It is preferably from μm to 500 μm.

If it is smaller than 1 μm, the surface area for supporting the charged particles m becomes insufficient, and when an insulator (for example, toner) or the like adheres to the roller surface layer, its periphery cannot contact the photosensitive drum as the member to be charged. , The charging performance is reduced.

Further, in consideration of the particle holding ability, it is preferable that the charged particles have a roughness larger than the particle diameter of the charged particles.

On the other hand, when it is larger than 500 μm, the unevenness of the roller surface reduces the in-plane charging uniformity of the body to be charged. Ra in this example was 40 μm.

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

2) Resistance Characteristics In a conventional charging roller using electric discharge, a low resistance base layer is formed on a core metal, and then the surface is covered with a high resistance layer. The roller charging due to discharge has a high applied voltage, and if there is a pinhole (exposure of the substrate due to damage to the film), the voltage drops to the periphery thereof and charging failure occurs. Therefore, it is necessary to make it 10 ¹¹ Ω or more.

On the other hand, in the direct injection charging method, since charging at a low voltage is possible, it is not necessary to make the surface layer of the contact charging member have high resistance, and the roller can be composed of a single layer. Rather, it is necessary that the surface resistance of the charging roller 2 in direct injection charging is 10 ⁴ to 10 ¹⁰ Ω.

When it is larger than 10 ¹⁰ Ω, a large potential difference is generated on the roller surface, and a discharging bias acts on the charged particles, so that the charged particles are easily discharged. Further, the uniformity on the charging surface is reduced, unevenness due to the rubbing of the rollers appears as streaks in the halftone image, and the image quality is degraded.

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

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

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

The resistance of the charging roller 2 was measured by the following procedure. A schematic diagram of the structure at the time of measurement is shown in FIG. The roller resistance is such that the total pressure on the core metal 2a of the charging roller 2 is 9.8 N (1
Insulator drum 9 with an outer diameter of 24 mm so that
An electrode was applied to 3 and measured. As the electrode, a guard electrode 91 was arranged around the main electrode 92, and the measurement was performed with the wiring diagram shown in FIGS. 3 (a) and 3 (b). The distance between the main electrode 92 and the guard electrode 91 is adjusted to about the thickness of the elastic / medium resistance layer 2b,
The main electrode 92 has a sufficient width with respect to the guard electrode 91. In the measurement, +100 V was applied from the power source S4 to the main electrode 92, the currents flowing through the ammeters Av and As were measured, and the volume resistance and the surface resistance were measured, respectively.

As described above, regarding the charging roller as the contact charging member in the present invention, 1) surface structure roughness characteristics for carrying high density charged particles on the surface layer 2) resistance characteristics required for direct charging (Volume resistance, surface resistance) is required.

3) Other roller characteristics In the direct injection charging system, it is important that the contact charging member functions as a flexible electrode.

In the magnetic brush, this is realized by the flexibility of the magnetic particle layer itself.

In the charging device 20 of this example, the elastic characteristics of the elastic / medium resistance layer 2b of the charging roller 2 are adjusted and achieved. The Asker C hardness is preferably in the range of 15 to 50 degrees. More preferably, it is 20 to 40 degrees.

If it is too high, the required amount of penetration cannot be obtained, and the charging contact portion n cannot be secured between the member to be charged and the charging performance is deteriorated. Further, since the molecular level contact property of the substance cannot be obtained, the contact with the periphery thereof is hindered by the inclusion of foreign matter.

On the other hand, if the hardness is too low, the shape irregularity is not stable and the contact pressure with the body to be charged becomes uneven, resulting in uneven charging. Alternatively, a charging failure may occur due to permanent deformation strain of the roller due to long-term storage.

In this example, the charging roller 2 having an Asker C hardness of 20 degrees was used.

4) Material, Structure, and Size of Charging Roller The material of the elastic / medium resistance layer 2b of the charging roller 2 is E
Examples thereof include PDM, urethane, NBR, silicone rubber, and rubber materials in which a conductive material such as carbon black or metal oxide for resistance adjustment is dispersed in IR or the like. 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 is performed by polishing or the like. Further, a structure having a plurality of layers with separated functions is also possible.

However, the elastic / medium resistance layer 2 of the charging roller 2
The form of b is more preferably a porous structure. It is also advantageous in manufacturing in that the above-mentioned surface roughness can be obtained at the same time when the roller is molded. The cell diameter of the foam is 1 to 5
00 μm is suitable. After foam molding, the surface of the porous body is exposed by polishing the surface, so that the surface structure having the aforementioned roughness can be prepared.

Finally, a predetermined amount of an elastic / medium resistance layer 2b was formed on the surface of the porous body on a core metal 2a having a length of 240 mm to prepare a charging roller 2 having a length of the middle resistance layer of 220 mm.

(4) Charged particles m In this example, the charged particles m have a specific resistance of 10 ³ Ω · c.
Conductive zinc oxide having a particle size of m and an average particle size of 1.8 μm was used.

The charged particles m are applied to the outer peripheral surface of the charging roller 1 in advance and the developer t of the developing device 60 is used.
Has been added to.

The material of the charged particles m is a mixture with other conductive inorganic particles such as metal oxides or organic materials, or
Various conductive particles such as surface-treated particles can be used. Further, since the charged particles m in the present invention do not need to be magnetically restrained, they need not have magnetism.

The particle resistance needs to be 10 ¹² Ω · cm or less in order to transfer charges via particles.
It is preferably 10 ¹⁰ Ω · cm or less. On the other hand, if there is a pinhole on the drum,
It is desirable that it is 10 ⁻¹ Ω · cm or more, preferably 10 ² Ω · cm or more.

The resistance was measured by the tablet method and normalized. That is, approximately 0.5 g of charged particles m were put in a cylinder having a bottom area of 2.26 cm ² and 147 N (15
Simultaneously with the pressurization of kgf), a voltage of 100 V was applied to measure the resistance value, and then normalized to calculate the specific resistance.

The particle size of particles is measured by L
A liquid module is attached to the S-230 type laser diffraction type particle size distribution measuring apparatus, and a particle size of 0.04 to 2000 μm is set as a measurement range, and D50 is calculated from the obtained volume-based particle size distribution. The measurement was carried out by adding about 10 mg of particles to 10 ml of methanol and dispersing with an ultrasonic disperser for 2 minutes.
The measurement is performed under the condition that the measurement time is 90 seconds and the number of measurements is once.

The charged particles m may exist not only in the state of primary particles but also in the state of secondary particles in which primary particles are aggregated. However, the physical properties and functions of the charged particles m are realized as secondary particles. If possible, it can function as the charged particles. However, if it is composed of secondary particles,
While the charging performance may be improved, the fog and the deterioration in the uniformity of the halftone image may be remarkable. This is because secondary particles tend to aggregate further, which may cause image defects on the contrary, and it is necessary to adjust the degree of aggregation within an appropriate range. Details will be described in another section.

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

That is, the particle size is 0.01 to 10
μm can be used. Preferably 0.1 to 5.0μ
m is preferred. Small particle size causes manufacturing problems,
When attached to the toner, the toner is significantly deteriorated. If it is large, it becomes difficult to maintain the charging performance in consideration of environmental changes.

Further, in the present invention, from the viewpoint of the degree of aggregation, 0.5 to 3 μm is a preferable particle size range.

Further, the particles need to have an appropriate specific surface area. Specific surface area is 1 × 10 ^-5 to 100 × 10 ^-5 cm
² / cm ³ is required. More preferably, it is 1 × 10 ⁻⁵ to 100 × 10 ⁻⁵ cm ² / cm ³ .
If it is less than this range, the performance as charged particles will be deteriorated even if the charged particles have the same particle size. It is expected that this is because when the specific surface area is small, a relatively simple surface structure is formed, so that the number of contact points when contacting the charged body is reduced. On the other hand, if it is too large, the performance of the toner may deteriorate particularly in the second embodiment. Particles having a particularly large specific surface area tend to have a weak particle structure and cannot maintain a stable particle diameter.

Although the charging performance can be greatly improved by increasing the specific surface area, particles having a large specific surface area tend to increase aggregation of particles. As a result, image defects, which is the subject of the present invention, are likely to occur. Therefore, while increasing the specific surface area, pay attention to the degree of aggregation and select particles, or
By carrying out various surface treatments for weakening the cohesive force, higher-performance charged particles can be realized.

The specific surface area in the present invention was measured as follows.

First, according to the BET method, nitrogen gas was adsorbed on the sample surface using a specific surface area measuring device “Gemini 2375 Ver.5.0 (manufactured by Shimadzu Corporation), and the BET specific surface area (cm ² was measured using the BET multipoint method). / G) is calculated.

Next, a dry-type automatic densitometer "Accupyc1"
330 "(manufactured by Shimadzu Corporation) using true density (g / cm
³ ) Ask. At this time, a 10 cm ³ sample container was used, and a helium gas purge was performed at a maximum pressure of 19.5 as sample pretreatment.
Do 10 times in psig. After that, as a pressure equilibrium judgment value of whether or not the pressure in the container has reached equilibrium, the pressure fluctuation in the sample chamber is set to 0.0050 / min as a guide. Start and automatically measure true density. The measurement is performed 5 times, and the average value thereof is calculated to obtain the true density.

Here, the specific surface area of the powder is obtained as follows. Specific surface area (cm ² / cm ³ ) = BET specific surface area (cm
² / g) × true density (g / cm ³ ) (5) Charged particle carrying amount In particle charging, the charging performance is improved by reducing the particle size of the charged particles m.
Of the photosensitive drum 1 becomes noticeable. Since the force that can hold the charged particles m on the charging roller 2 is a weak adhesive force,
Even if a large number of particles are supplied, it is difficult to restrain the particles, and the particles fall onto the photosensitive drum 1 to suppress the influence of a defective image on the subsequent development process and transfer paper. Therefore, ideally, it is desirable to apply it more evenly on the surface layer of the charging roller, but in reality, it is possible to secure the charging property and reduce the adhered particles by adjusting the carrying amount.

The amount of particles carried is determined by the average roughness Ra of the roller surface.
Needs to be kept more appropriate. That is, the value obtained by dividing the carried amount by the average roughness Ra is preferably 1 or less, more preferably 0.3 or less.

In the present invention, the amount of non-magnetic charged particles carried per roughness is 1 mg / cm ² / μm (50 mg / cm ² ,
Ra = 50 μm) or less. More preferably 0.3 m
g / cm ² / μm (15 mg / cm ² , Ra = 50 μm)
The following results are good results.

On the other hand, the minimum carrying amount is 0.005 mg / cm in the same manner as the carrying amount / Ra value in order to ensure the charging performance.
² / μm (0.25 mg / cm ² , Ra = 50 μm). More preferably, 0.02 mg / cm ² / μm (1
mg / cm ² , Ra = 50 μm).

That is, the carried amount / Ra is 0.005 to 1, and more preferably 0.02 to 0.3 mg / cm ^2.
/ Μm is desirable.

In this example, 0.1 mg / cm ² / μm
The loading amount was adjusted to (4 mg / cm ² , Ra = 40 μm).

The carrying amount was adjusted in advance by the amount applied to the charging roller and the amount of charged particles mixed with the developer.

For the measurement of the carried amount, the particles carried on the charging roller were washed, and the weight and resistance of the particles were measured.

Ethanol and water (1:
The cleaning liquid consisting of 2) was prepared, and the roller was immersed therein for cleaning. It is possible to remove the deposits on the roller by repeating the cleaning and checking the surface of the roller with an optical microscope or the like, and repeating the cleaning while rubbing the surface of the roller with a blade or the like as necessary.

The obtained washing solution is allowed to stand for 1 to 2 hours, and when it can be clearly separated from the supernatant, the supernatant is removed. Then, the material carried on the roller was extracted by sufficiently drying at 105 degrees. The supported amount is calculated from the total weight of the obtained particles and the surface area of the charging roller 2 (calculated from the longitudinal length of the roller).
Calculated as the amount supported per unit area.

(6) The developing device 60 60a is a non-magnetic rotary developing sleeve as a developer carrying / conveying member which contains a magnet roll 60b therein.
The toner t in the pre-development agent provided in the developing container 60e is subjected to layer thickness regulation and electric charge imparted by the regulation blade 60c in the process of being conveyed on the rotary developing sleeve 60a. 60
Reference numeral d is a stirring member that circulates the toner in the developing container 60e and sequentially conveys the toner to the periphery of the sleeve.

The toner t coated on the rotary developing sleeve 60a is rotated by the rotation of the sleeve 60a, so that the developing portion (developing area portion) is a facing portion between the photosensitive drum 1 and the sleeve 60a.
It is transported to 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 superimposed voltage of DC voltage and AC voltage. As a result, the electrostatic latent image on the photosensitive drum 1 side is reversely developed by the toner t.

In the present embodiment, the developing device 60 is roughly classified into a replenishing type developing device and a non-replenishing type developing device.

1) Replenishing System Developing Device The developing device 60 of the image recording apparatus of FIG. 1 is a replenishing system developing device. In this configuration, the developing device 60 includes the developing container 60e.
The mixture t + m of the toner t and the charged particles m is stored in the container for development, and the space inside the container 60e is separated by the partition wall 60f.
It is divided into two spaces 10 and 11. The space closer to the image carrier 1 is called a first space 10, and the farther space is called a second space 11. Further, a partition wall 60f between the first space 10 and the second space 11 is provided with a communication opening portion (developer moving passage) 60g of both chambers 10 and 11, and a valve is provided in this communication opening portion 60g. The member 9 is arranged.

FIG. 4 is a perspective model view of the communication opening 60g and the valve member 9 portion. A partition wall 60f which forms a communication opening 60g through the upper part (long upper part) 9-1 of the valve member 9
It is attached to the upper frame of the and the lower part is free and the first space 1
It swings only to the 0 side. By doing so, the developer t + m can be moved from the second space 11 to the first space 10, but the opposite is not possible.

The valve member 9 used in this embodiment is a thin resin film made of PPS and having a thickness of 30 μm.

When there is a gap in the first space 10, the valve member 9 swings toward the first space 10 side as shown in FIG. To the first space 10 from the developer t + m.

On the other hand, when there is no gap in the first space 10, the valve member 9 does not swing as shown in (b), and therefore the developer does not move.

Furthermore, from the second space 11 to the first space 10
When the developer moves to, the density of the developer in the first space 10 is temporarily increased, and the rotation of the developing sleeve 60a causes the developer density in the first space 10 as shown by the arrow in (c). As the circulation occurs, a force that pushes the developer back into the second space 11 is generated. Then, as shown in (d), the valve member 9 swings in a direction that prevents the developer from moving from the first space 10 to the second space 11, and the first space 10 and the second space 11 communicate with each other. Since it will block the opening 60g,
It is possible to prevent the developer from moving from the first space 10 to the second space 11.

As described above, only the developer can be moved from the second space to the first space.

In Examples and Comparative Examples described later, the volume Vcm ³ / cm of the first space 10 is 1.8,
A printing test was conducted by changing the values in each example so that the values were 2.8, 4.5, 7.3, and 10.3. Further, at 4.5 or more, the circulation of the developer in the first space 10 was promoted by inserting and rotating the stirring member in the first space 10.

2) Non-Replenishment Type Developing Device FIG. 6 shows the image recording apparatus of FIG. 1 in which the developing device 60 is a non-replenishment type developing device. The configuration of the image recording apparatus other than this developing apparatus is the same as that of the image recording apparatus of FIG.

The non-replenishment type developing device 60 includes a developing container 60e.
Although the inside is divided into the first space 10 and the second space 11, the developer t + m moves back and forth between the first space 10 and the second space 11, and a large amount of development takes place in the developing container 60e as a whole. A developing device that circulates the agent. Therefore, the toner in the developing container 60e is in almost the same state in any place.

In Examples and Comparative Examples described later, the volume V of the developing device was adjusted to 2.8, 4.5, 7.3 and 10.3.

3) Prescribed toner t of developer t + m: A one-component magnetic toner t which is a developer is prepared by mixing a binder resin, magnetic particles and a charge control agent, and kneading, pulverizing and classifying the toner. Further, it is prepared by further adding charged particles m, a fluidizing agent and the like as external additives. The average particle diameter (D4) of the toner was 7 μm.

Charged particles m: Basically the same as the charged particles m previously applied to the charging roller 2, but the appropriate particle size range is slightly different. Further, the charged particles are mixed by adjusting the mixing state of each example including the case where the particles are desired to be mixed. Details are described in each example.

(7) Amount of Charged Particles and Coverage In the present embodiment, since the toner is recycled, many toners contaminate the surface of the charging roller. The toner has a resistance value of 10 ¹³ Ω · cm or more in order to maintain electric charges due to frictional charging on the surface. Therefore, when the charging roller 2 is contaminated with the toner, the resistance of the particles carried on the charging roller 2 increases and the charging performance deteriorates.
Even if the resistance of the charged particles is low, the resistance of the powder carried by the mixing of the toner rises and the charging property is impaired. Therefore, the amount of charged particles carried is 0.00 in terms of carried amount / Ra.
5 to 1, preferably 0.02 to 0.3 mg / cm ²
Even if it is / μm, a large amount of toner may be contained in the component, and naturally the charging performance is deteriorated. in this case,
The resistance of the supported particles rises and the situation can be grasped. That is, in actual use, the resistance of the particles (including the mixture of toner and paper powder) carried on the charging roller 2 is measured by the above-described method, and the value is 10 ^-1 to 10 ¹²
Ω · cm. It is necessary to preferably be 10 ¹⁰ Ω · cm.

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

The amount of the carried particles was basically adjusted by adjusting the amount of the charged particles m added to the developer t. Further, if necessary, an elastic blade was brought into contact with a part of the outer circumference of the charging roller 2 for adjustment. By abutting the members, there is an effect of normalizing the triboelectrification polarity of the toner, and the amount of particles carried on the charging roller 2 can be adjusted.

(8) Measurement of Coverage For the measurement of the coverage, the area covered with the conductive particles was measured by observing with a microscope under a condition close to the roller contact condition. Specifically, the rotation of the photosensitive drum 1 and the charging roller 2 is stopped without applying the charging bias, and the surfaces of the photosensitive drum 1 and the charging roller 2 are covered with a video microscope (OLY).
The images were taken with an MPM OVM1000N) and a digital still recorder (DELTS SR-3100).

The charging roller 2 is brought into contact with the slide glass under the same conditions as when the charging roller 2 is brought into contact with the photosensitive drum 1, and the contact surface is formed from the rear surface of the slide glass by a video microscope with an objective lens of 1000 times. I took a picture. Then, the area covered with the particles having the color or brightness of the charged particles measured in advance was separated, and the area ratio was calculated and used as the coverage.

If it is difficult to determine the color, the substance on the outermost surface of the roller is analyzed by the fluorescent X-ray analyzer SYSTEM308.
0 (manufactured by Rigaku Denki Kogyo Co., Ltd.).

First, between the charging roller covered with the charged particles and the drum in the initial state, the adhesive surface of the polyester tape (Nichiban No. 550 (# 25)) is sandwiched with the roller, and the drum and the roller are driven to rotate. The roller and 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, the roller for which the print test has been completed is similarly sampled. The coverage can be obtained by quantifying the content of a specific element contained in the conductive particles. In other words, it is possible to calculate the ratio of the sample after the printing test and obtain the coverage rate by setting the tape sample of the roller carrying only the conductive particles to 1.

<< Embodiment 2 >> This embodiment is schematically shown in FIG. In this embodiment, items other than the following are in accordance with the first embodiment.

1) Drum Cleaner 8 In this embodiment, the drum cleaner 8 for cleaning the surface of the photosensitive drum after the transfer process is provided. In this example, the transfer residual toner does not enter the charging roller 2 of the charging device 20.

2) Developing Device 60 In this embodiment, the developer contained in the developing device 60 contains only toner and does not contain charged particles. The charged particles m are only carried on the charging roller 2 in the initial stage.

<Examples and Comparative Examples> An object of the present invention is to maintain the performance of the charging device until the toner runs out (toner end). For that reason, the supply of the charged particles by the replenishing system developing device is indispensable. However,
The replenishing system developing device must be constructed so as to maintain a certain relationship with the charging device. It is the volume of the first space in the developing device and the surface area of the charging member. Next, the superiority of the present invention will be described through examples and comparative examples.

The structures of Examples and Comparative Examples are summarized in the evaluation result table. Next, each item in the table will be described first.

(1) Configuration a) Embodiment: Display which of the above-described Embodiments 1 and 2 is executed.

B) Presence or absence of addition of charged particles: The presence or absence of addition of charged particles to the developer stored in the developing device is displayed.

C) Developing device (developing device): It is indicated whether the constitution is a replenishing developing device which is separated into the first space and the second space.

D) Charging member surface area (outer diameter): For the charging member (charging roller) used in each example, the surface area of the charging member is the perimeter of the charging member surface in the cross section, that is, the surface area of the charging member per unit length. S was shown. The outer diameter of the roller at that time is also shown in parentheses.

E) Volume of first space: The volume of the first space of the developing device is expressed as the area in cross section.

F) Developer filling amount: The toner filling amount in each example is displayed.

(2) Evaluation Method of Examples and Comparative Examples Image evaluation was carried out by the following evaluation of halftone uniformity and chargeability at the end of toner.

A print test was conducted using a pattern having an image pattern print rate of 5% and no difference in print rate in the longitudinal direction.

A) Halftone Uniformity (Evaluation of Image Defects) For image evaluation, halftone images were output and evaluated from the number of image defects. Image recording was performed using a 600 dpi laser scanner in the printer of each example.

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

Since the printers of the respective examples carry out image recording by the reversal developing system, when the image exposure is obstructed or a leak occurs during development, they appear as white spots on the image. In the present embodiment, many charged particles are supplied to the photosensitive drum from the first space at the initial stage of printing, and the image exposure is blocked, so that an image defect of a white spot is likely to occur.

Particularly in the present invention, importance is attached to the uniformity of the halftone image, and the number of these defective portions is evaluated according to the following criteria. In the image defect evaluation, white dots were evaluated by counting points of 0.3 mm or more as defective parts.

◯: 10 to 50 image defects exist Δ: Image defects exceed 50 and less than 100 x: Image defects exceed 100 b) Charging property evaluation Due to insufficient charging as an index of charging performance The ghost image was evaluated. For evaluation, after writing an image pattern in which a black square of 5 mm to 25 mm square was arranged at the tip, the above-mentioned halftone image was arranged. When the charging performance is low, a square exposure pattern cannot be uniformly charged by the charger, so a light square pattern is confirmed in the halftone image area. The presence or absence of this pattern was used as an index of charging performance. Furthermore, in order to catch a slight change in charging performance, we paid attention to the uniformity of halftone images. When the charging performance is deteriorated, rubbing marks of the charging member appear as black short lines. In particular, the presence or absence of this streak in the halftone image was used as another index of charging performance.

Since the toner filling amount differs in each example, the life is not constant. In the present invention, since the problem of an image defect near the end of the toner is a particular problem, the evaluation was performed on the printed images at the toner end and 200 sheets before that.

◯: No ghost or streak is seen Δ: Minor ghost or streak is confirmed ×: Clear ghost and streak are confirmed Here, the toner end is the time when the image is removed for the first time after the start of printing. Refers to.

(3) Evaluation Results With respect to each of the examples and comparative examples, the evaluation results are summarized together with the constitution.

[0177]

[Table 1]

The evaluation results of the examples and comparative examples are described below, and the effectiveness of the present invention is described.

1) Comparative Example 1 is an example in which a conventional non-replenishment type developing device is used to construct an image recording device by particle charging (FIG. 6).
Is.

The non-replenishment type developing device is characterized in that the developer always circulates largely in the entire developing container to keep the state of the developer in the container constant. However, in the particle charging in which the charged particles are supplied from the developing device, there is a problem that the charged particles cannot be stably supplied through the durability.

FIG. 8A shows the total amount of toner in the developing device, and shows that toner is consumed to a certain extent according to the number of printed sheets. Further, (b) is a graph showing the total amount of charged particles in the developing device, and the consumption state of charged particles can be seen. (C) shows the amount of charged particles present on the charging member. It can be seen that while a certain amount of toner is developed and consumed according to the number of printed sheets, the amount of charged particles is drastically reduced in the initial stage. That is, it can be seen that a large amount of charged particles are transferred to the drum and supplied to the charging roller in the initial stage. However, the number of particles on the charging member has not increased. In other words, it can be seen that the supply is excessive. As a result, it can be seen from the results that in the initial stage, the charged particles cover the drum and block the image exposure, so that the uniformity of the image such as an intermediate image is significantly reduced.

Next, consider the reasons for these phenomena. Although the charged particles are contained in the developer in an amount of about 1%, the proportion of the charged particles in the developer transferred to the photoreceptor is considerably higher than 1%. That is, the charged particles have a characteristic that they are easily consumed in advance with respect to the toner. There is also a method of suppressing the advance consumption of the charged particles, but in order to efficiently supply the charged particles, it is necessary to have a property of the advance consumption to some extent. Therefore, it is a problem whether or not the charged particles that are consumed in advance are used stably, and stable supply can be realized by appropriately configuring a replenishing system developing device described later with respect to the charging member.

Further, in Comparative Example 1, since the non-replenishment type developing device is configured, the developer circulates largely in the container, the charged particles are supplied from all the developers in the container, and the concentration of the charged particles is entirely. Fall to. As a result, the charged particles are not supplied at all from the middle, and the amount of particles on the charging member decreases, so that the charging performance cannot be maintained. As a result of analyzing the remaining developer, it was found that the charged particles were reduced to a certain ratio, but almost no charged particles were transferred to the drum.
That is, the developing device is filled with the developer to which the charged particles cannot be supplied, so that the image cannot be further formed.

2) The first embodiment (FIG. 1) is configured as a replenishing system developing device in order to solve such a conventional problem.

In this example, the developing device performs image formation while moving the toner from the first space to the second space in one direction. FIG. 9 is a graph showing the state of this example, and it can be seen that the decrease of the charged particles is constant and the toner is stably transferred from the developing device to the drum throughout the durability. The decrease in the concentration of charged particles is limited to the first space, excess supply at the initial stage is eliminated, and a certain amount of charged particles can be supplied to the drum and the charging member as the toner is consumed.

Next, the state near the toner end, which is the most noticeable aspect of the present invention, will be examined. FIG. 9A shows the total toner amount, the toner amount in the first space, and the toner amount in the second space. It can be confirmed that when the number of printed sheets is A, the developer in the second space is exhausted, the supply of the charged particles is stopped, and the charged particles on the charging member are also decreased at this point. That is, it is expected that it is most difficult to maintain the charging performance in the situation where the toner remains only in the first space where the concentration of charged particles is low. In this example,
Even if the amount of charged particles carried was reduced, charging failure did not occur before the toner end. However, this is not achieved in any configuration.

For example, in Example 2 and Comparative Example 2, the same charging member was used as in Example 1, but the volume V of the first space of the developing device was 2.8 and 4.5 cm. ³ /
The configuration is changed to cm. In Comparative Example 2, a decrease in charging ability is confirmed in the result of evaluation of charging property at the end of toner. FIG. 10 is a graph showing changes in the amount of particles in Comparative Example 2. When viewed from the number of printed sheets A and thereafter, the amount of toner is larger than the charging life C of the charging member, and the charging performance cannot be maintained until the toner end B. Further, even in the initial stage, there is a tendency that the charged particles are excessively supplied in the initial stage due to the large amount of the developer in the first space. As a result, the initial halftone image uniformity is degraded.

In other words, in accordance with the life of the charging member, A-B
It is necessary to set the lifetime between the two, that is, to set the volume of the first space appropriately.

Here, the life of the charging member after the time point A greatly depends particularly on the surface area of the charging member. The charging member counter-rotates with respect to the photosensitive drum at a constant rotation speed. The charged particles also fall off at a constant rate, and the charged particles on the charging member decrease with charging. Therefore, in order to extend the life of the charging member, the surface area of the charging member should be large and many charged particles should be carried. It is desirable to do.

3) Next, an example in which the surface area of the charging member is changed will be described. Examples 3, 4, 5 and Comparative Example 3
The roller diameter of the charging member is increased to 16 mm to form a surface area S of 5.0 cm ² / cm charging member, and the volume V of the first space is 1.8 to 7.3 cm ³ / c as described above.
was subjected to the same printing test by changing to m, in Comparative Example 2, 4.5 cm ³ of decrease in charging property was observed
It was possible to maintain the charging performance even at / cm.

That is, by increasing the surface area S of the charging member from 3.8 to 5.0 cm ² / cm, the amount of charged particles carried on the charging member is increased, and the life of the charging member after the time point A can be extended. Became.

Therefore, even in the developing device having a larger first space, stable image recording can be performed up to the toner end. However, as seen in Comparative Example 3, at VV of 7.3 cm ³ / cm, the charging performance was deteriorated at the toner end. Furthermore, Example 5,
In Comparative Example 3, a decrease in uniformity in the halftone image was observed.

4) Examples 6, 7, 8, 9 and Comparative Example 4
Furthermore, the surface area S of the charging member is 6.3 cm.²/ Cm
This is an example of the case. By increasing the surface area of the charging member
It is possible to further extend the charging life, and Comparative Example 4
V is 10.3 cm ³Chargeability even at / cm
It has become possible to maintain Noh. However, early
The uniformity of the halftone image in the image was significantly deteriorated. Early on
Due to the excessive supply of charged particles,
Considering together with the results of 5 and Comparative Examples 2 and 3, V is large.
It tended to get worse.

5) From the above, it is desirable to maintain a constant relationship between the surface area S of the charging member and the volume V of the first space in order to maintain the charging performance especially up to the toner end. These results are shown in the graph of FIG. 11, and the relational expressions suitable for image evaluation are derived as follows from these relations. By setting V <0.16 × S ^2.3 , the toner end is charged. It is possible to maintain the performance.

Furthermore, it is preferable that V1 <0.10 × S ^2.3 is satisfied, so that the charging performance can be better maintained.

Further, in Example 1, white dot-like image defects were confirmed in the halftone image at the toner end time. This is presumably because paper dust adhered to the charging member to lower the charging uniformity and block the exposure. It is advantageous that the surface area of the charging roller is large in terms of capturing paper dust. Considering this.

By setting V <0.08 × S ^2.3 , a better charging device can be constructed.

From the above results, it is considered that the state between the number of printed sheets A and B is the same as the case where charged particles are not included in the developing device.

6) Next, the case where charged particles were not supplied from the developer was examined.

In comparison with the second and eighth embodiments, the tenth and eleventh embodiments have a non-replenishing type developing device and the developer filling amount is the same as the toner amount in the first space of the second and eighth embodiments. Was adjusted. Further, the developer is not mixed with charged particles. The charged particles are only carried on the charging member in the initial stage. As a result, in the evaluation of the charging property, Example 2,
The same result as 8 was shown.

FIG. 12 shows changes in the amount of particles. In other words, it is expected that the apparatus state after the number of printed sheets A in Examples 2 and 8 contains almost no charged particles in the first space, or hardly transfers to the drum even if they are included.

Comparative Examples 5 and 6 are examples in which V was further increased, and correspond to Comparative Examples 3 and 4 in the same manner.

7) In addition, Examples 12 and 13 correspond to Example 2,
5, the toner filling amount is increased from 130 g to 200 g. Although the total number of printable sheets is increased by increasing the toner filling amount, the charging performance at the initial stage of printing and at the end of printing shows the same results as in Examples 2 and 5 having the same S and V. It is expected that a slight difference in the filling amount will not have much relation to the performance at the toner end.

The characteristics at the end of printing do not depend much on the filling amount.

8) Further, in Example 14 and Comparative Example 8, V was made smaller to supply the charged particles more stably through durability, but when the volume of V was extremely small, the first space was formed. The toner circulation in the inside becomes very small,
The charging performance evaluation result was deteriorated due to deterioration of the developer and unevenness in the longitudinal direction of the developer. V must be at least 1.0 or more, and preferably 1.2 cm ³ / cm or more.

On the other hand, the structure in which the surface area of the charging member was increased to S7.5 (outer diameter 24 mm) was also evaluated, but no improvement in charging performance was observed as compared with Example 9. In this configuration, a photosensitive drum of φ24 mm is used, but the surface area increases as it approaches the outer diameter,
It is considered that it is not so effective in increasing the contact width to further expand the charging property. Further, considering the arrangement and the size of the cartridge, an outer diameter larger than that of the photoconductor is not preferable.

9) Next, the effects of the present invention will be described with respect to the configuration of the second embodiment. Examples 16 and 17 correspond to Comparative Examples 5 and 6 in S and V, but are different in having a drum cleaner. As a result of the evaluation, it was confirmed that the charging performance before completion of the toner was better than that of Comparative Example 5. In the image forming apparatus provided with the drum cleaner, it is possible to prevent the toner from mixing with the charging member, which is advantageous in terms of charging property. On the other hand, in Comparative Examples 9 and 10 in which V was further widened, a decrease in charging performance was observed.

From the above points, in the second embodiment, as shown in FIG. 13, when V <0.24 × S ^2.3 , the charging performance can be maintained up to the toner end.

Now, let's consider why V is proportional to S to the 2.3th power. Considering that a certain amount of charged particles carried on the charging member drops and is consumed as the drum rotates and the roller rotates, the charging life between A and B is expected to be proportional to the surface area of the roller. However, the result is 2.
3 showed a high dependency proportional to the above. Therefore, other effects are expected. In this example, since the surface area is improved by increasing the roller diameter, the roller outer diameter also affects the change in the state of the contact portion n. When the roller diameter increases,
The pressure distribution in the contact portion can be made uniform, and the area of the contact portion can be increased, so that the charging performance can be improved even with the same amount of charged particles. Also, at this time, the amount of the roller entering the drum can be set to be small. The roller will be less deformed upon contact. This has an advantageous effect on the dropout of particles from the charging member and has the effect of reducing the dropout amount. In other words, in addition to increasing the amount of supported particles, 1) increase the area of the contact area, and 2) have the secondary effect of suppressing particle detachment by charging with a low penetration amount. Expected to be proportional to the cube.

[0210] Now, let's consider another means for solving the problem of this case. For example, there is a method of increasing the peripheral speed of the charging roller. In injection charging, the charging property largely depends on the peripheral speed difference between the photoconductor and the charging member. However, if the peripheral speed of the charging member is increased, it becomes possible to charge with a small amount of charged particles carried, but the peripheral speed is increased. There is also a tendency for the number of particles to drop out to increase, and it cannot be improved simply by increasing the speed. Further, as a method of increasing the amount of charged particles as a whole, there is a method of increasing the amount of added particles. However, since excessive supply of charged particles in the initial stage increases, V of the present invention is also adjusted to be optimal. There is a need. It is difficult to improve the charging performance at the end of the toner by other means for improving the charging property.

(4) Others Regarding the definition of V in this example, in the present invention, it is assumed that the developer in the first space is circulated throughout the same space, and the circulating toner volume is almost the same as V. Although treated, the effect of the present invention is not limited to this. Originally, it should be defined as the actual circulating volume of toner. For example, when a dead space is formed especially in the space below, the developer may exist but the developer may hardly circulate. At this time, the effective toner volume as V is smaller than V. Therefore, at this time, it is desirable that the effective volume of toner circulation is V and that the above relationship with S is maintained. The state of circulation is
It can be predicted by measuring the content of charged particles in each part in the container. The charged particles are present in the non-circulating portion while maintaining the initial concentration. Further, more accurately, it is preferable to more accurately determine the density of each part after solidifying the toner at a high temperature.

Regarding the definition of the replenishing system developing device, it is preferable that the valve is arranged for reliable replenishment, but due to a device such as the arrangement of the openings connecting the spaces, the replenishment can be done without using the valve. It is also possible to achieve a system developing device. At this time, the developer may go backward from the first space to the second space. As a matter of course, when this amount is increased, the charged particle concentration is reduced to a constant amount in all the first and second spaces, as in the non-replenishment type developing device. In order to obtain the effects of the present invention, a certain degree of achievement as a replenishment type developing device is required. When the charged particle concentration of the developer in the second space was measured at the time when the first and second developer amounts became the same in the print test, at least 60% or more of the initial mixed amount, preferably It is necessary that 80% or more remains.

Regarding the surface area S of the charging member, the peripheral length of the roller is defined as the roller length when the charging member is the roller shape, and the belt length is defined when the charging member is the belt shape. It simply means the macroscopic surface area of the charging member.

<< Other Embodiments >> 1) In the embodiment, a laser printer is illustrated as an image recording apparatus, but the present invention is not limited to this, and other image recording apparatus (image forming apparatus) such as an electrophotographic copying machine, a facsimile machine, and a word processor. Of course, it may be an image display device (display device) such as an electronic blackboard.

2) The exposure means for forming an electrostatic latent image is not limited to the laser scanning exposure means 4 for forming a digital latent image as in the embodiment, but a usual analog type exposure means. Other light emitting elements such as image exposure and LEDs may be used, or a combination of a light emitting element such as a fluorescent lamp and a liquid crystal shutter may be used as long as it can form an electrostatic latent image corresponding to image information.

The image carrier as the member to be charged is an electrostatic recording dielectric in the case of an electrostatic recording device. In the case of an electrostatic recording dielectric, this is uniformly charged by a charging device to a predetermined polarity and potential, and the surface to be charged is selectively subjected to static elimination by static elimination means such as a static elimination needle array or electron gun, and then electrostatically charged. Write and form a latent image.

3) The image bearing member is not limited to the drum type, and may be an endless type, a belt type having an end, a sheet type or the like.

4) The contact charging member is not limited to the roller type,
An endless belt or an endless belt may be used. The belt expands the selection of charging nip and surface area. That is, even when the surface area is increased by using the same nip, the charging device can be configured with a margin because the amount of charged particles carried can be increased. Further, if the surface area is the same and the nip is improved, the charging performance can be further maintained.
However, the belt is disadvantageous in that it has a driving method and a problem of deviation, which makes the structure complicated.

5) The developing device in the embodiment is a reversal developing device using one-component magnetic toner, but the structure of the developing device is not particularly limited. It may be a regular developing device.

Generally, in the method of developing an electrostatic latent image, a non-magnetic toner is coated with a blade or the like on a developer carrying and conveying member such as a sleeve, and a magnetic toner is coated with the developer carrying and carrying member. A method of coating an electrostatic latent image on the image bearing member in a non-contact state by coating it with a magnetic force and developing it (one-component non-contact developing);
A method of developing an electrostatic latent image by applying the toner coated on the developer carrying member as described above to the image carrier (one-component contact development), and a carrier magnetic to the toner particles. And a method of developing an electrostatic latent image by applying a mixture of the above as a developer (two-component developer) by magnetic force and applying it in contact with an image carrier (two-component contact development); The two-component developer is applied to the image carrier in a non-contact state to develop an electrostatic latent image (two-component non-contact development).

6) The transfer means is not limited to roller transfer, but belt transfer, corona transfer, etc. may be used. An image forming apparatus that forms not only a single-color image but also a multi-color or full-color image by multiple transfer using an intermediate transfer member (intermediate transferred member) such as a transfer drum or a transfer belt may be used.

7) Direct injection charging uses a mechanism in which the charge is directly transferred from the contact charging member to the portion to be charged. Therefore, the contact charging member must sufficiently contact the surface of the member to be charged. It is desirable to rotate the contact charging member with a peripheral speed difference with respect to the charging body. Specifically, the speed difference between the contact charging member and the body to be charged is such that the surface of the contact charging member is driven to move to provide a speed difference between the body and the body to be charged.
It is preferable that the contact charging member is rotationally driven, and that the rotation direction thereof is opposite to the moving direction of the surface of the member to be charged. It is also possible to move the surface of the contact charging member in the same direction as the moving direction of the surface of the member to be charged to give a speed difference, but the charging property of direct injection charging is the peripheral speed of the member to be charged and the peripheral speed of the contact charging member. Since the rotation speed of the contact charging member in the forward direction is higher than that in the reverse direction in order to obtain the same peripheral speed ratio as in the reverse direction, it is better to move the contact charging member in the reverse direction. It is advantageous in terms of number. The peripheral speed ratio described here is the peripheral speed ratio (%) = (peripheral speed of contact charging member−peripheral speed of charged body) /
The peripheral speed of the charged body is 100 × (the peripheral speed of the contact charging member is a positive value when the surface of the contact charging member moves in the same direction as the surface of the charged body at the contact portion).

[0223]

As described above, according to the present invention, in order to maintain the charging performance at the end of printing, the surface area of the charging member and the volume of the first space of the developing device are kept constant. As a result, the charging performance was maintained at the end of the developer, the image uniformity performance was improved in the initial stage, and good image recording was realized over the entire life of the recording apparatus or the process cartridge.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an image recording device (developing device-replenishing system) according to a first embodiment.

FIG. 2 is a model diagram of the layer structure of a photosensitive drum.

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

FIG. 4 is a perspective model view of a communication opening and a valve member provided in a partition wall between the first and second spaces of the replenishing system developing device.

FIG. 5 is a view for explaining the operation of replenishing the developer from the first space to the second space of this developing device.

FIG. 6 is a schematic diagram of the image recording apparatus (developing apparatus-non-replenishing system) of the first embodiment.

FIG. 7 is a schematic diagram of an image recording apparatus according to a second embodiment.

FIG. 8 is a diagram (part 1) for explaining the evaluation of Examples and Comparative Examples.

FIG. 9 is a diagram (part 2) for explaining the evaluation of Examples and Comparative Examples.

FIG. 10 is a diagram (part 3) for explaining the evaluation of Examples and Comparative Examples.

FIG. 11 is a diagram (part 4) for explaining the evaluation of Examples and Comparative Examples.

FIG. 12 is a diagram (part 5) for explaining the evaluation of Examples and Comparative Examples.

FIG. 13 is a diagram for explaining evaluation of examples and comparative examples (No. 6).

FIG. 14 is a charging characteristic graph of a conventional roller charging device and a magnetic brush charging device.

FIG. 15 is a schematic view of an example of a magnetic brush charging device.

FIG. 16 is a schematic view of an example of a charging device using thin-layer conductive particles.

[Explanation of symbols]

1. Photosensitive drum with injection layer, 2. Charging roller, 2a. Core metal, 2b. Conductive elastic roller, m. 2. Conductive particles (charged particles) of the present invention, Charged particle feeder, 3b. Stirring blade, 3
c. Fur brush, 4. Laser exposure device, 60. One-component magnetic developing device, 6. Transfer charger, 7. Fixing device, 8.
Drum cleaner

Continued front page    F term (reference) 2H077 AA18 AA20 AA37 AB03 AB13                       AC16 AD06 AD13 AD31 AD35                       BA08 EA13 GA04                 2H171 FA02 FA11 FA13 GA01 JA23                       QB03 QB32 QB45 QB52                 2H200 FA02 FA14 FA19 GA16 GA18                       GA23 GA29 GA49 GB37 GB50                       HA03 HA21 HA28 HA29 HB12                       HB17 HB22 HB45 HB46 HB47                       LA38 LA40 MA03 MA04 MA12                       MA14 MB04 MC15 PA11

Claims (6)

[Claims] 1. An image carrier and a charging member and a developing device, which are arranged around the image carrier, the charging member carrying conductive particles and being in contact with the image carrier. In a sectional view perpendicular to the hand direction, the length of tracing the surface of the charging member, that is, the surface area of the charging member per unit longitudinal length is S (cm ² / cm), and the developer accumulated in the developing device is An image recording apparatus characterized in that V <0.24 × S ^2.3, where V (cm ³ / cm) is the area occupied, that is, the developer volume per unit length. 2. The V according to claim 1, wherein V <0.24 × S ^2.3, where V is a developing device area in a sectional view, that is, the developing device volume per unit longitudinal length. Characteristic image recording device. 3. The image recording apparatus according to claim 1, wherein V <0.16 × S ^2.3 . 4. The developing device accommodates a developer containing the conductive particles together with toner, and a space for accommodating the developer is defined by a first space near the image carrier and an image carrier. It is divided into a distant second space, and the developer is supplied by sequentially sending it from the second space to the first space, and the V is the area of the first space in the sectional view, that is, per unit longitudinal length. The image recording apparatus according to claim 1, wherein the image recording apparatus has a volume. 5. The image according to claim 1, wherein the charging member has a roller shape, and the S is a circumference of the roller, that is, a surface area per unit longitudinal length. Recording device. 6. An image recording apparatus main body comprising at least the image bearing member, the charging member, and the developing device, which constitutes a part of the image recording device according to claim 1. A process cartridge that is removable.