JPH1010846A - Electrifying device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow the uniform electrified body electrification processing being free from the electrification unevenness to maintain-execute over a long period under the various environment irrespective of soiling in accordance with the durability aging of a contact electrifying member, in an image forming device adopting the contact electrifying device of an AC bias impressing type, and to allow the output of excellent image being clear of the ground fogging to maintain over the long period under the various environment in the image forming device applying the contact electrification. SOLUTION: When this device executes the electrification of the electrified body 1 by holding the electrification member 2 applied a voltage while held in contact with the electrified body 1, the voltage for applying on the electrifying member 2 is provided with an AC bias component Vac and the DC bias component Vdc, and the AC bias component Vac is allowed so as to periodically repeat on/off. Moreover, the amplitude of the AC bias component Vac is made to become >=0.2kV<=6kV. Furthermore, the frequency fHz of the on/off period of the amplitude of the AC bias component Vac is allowed so as to become 2×V<=(f)<=200×V, corresponding to moving speed Vmm/sec of the electrified body 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device for charging (including charge elimination) an object to be charged, and more particularly, to a charging member (contact charging member) in which a voltage is applied to the object to be charged. The present invention relates to a contact-type charging device (contact charging device, direct charging device) for charging an object to be charged, and an image forming apparatus including the charging device.

[0002]

2. Description of the Related Art For convenience, an image forming apparatus will be described as an example.

Conventionally, in an image forming apparatus of an electrophotographic system or an electrostatic recording system, an image carrier such as an electrophotographic photosensitive member or an electrostatic recording dielectric is charged uniformly to a predetermined polarity and potential. In an image forming apparatus that performs image formation corresponding to target image information by a transfer method or a direct method by applying an image forming process including a processing step, as a device for charging an image carrier as a member to be charged, Conventionally, a corona charger has been generally used.

In this method, a corona charger is disposed opposite to an image carrier in a non-contact manner, and the surface of the image carrier is exposed to a corona shower generated from a corona charger to which a high voltage is applied. Is charged.

[0005] In recent years, it has advantages such as low ozone and low power over a corona charger. Therefore, as described above, a charging member is charged by contacting a contact charging member to which a voltage is applied. Contact type charging devices that perform the following have been put to practical use.

The contact charging member is a conductive member, and various types of members such as a roller (charging roller), a blade (charging blade), a magnetic brush, and a fur brush can be used. Magnetic brushes and fur brushes are preferably used in terms of charging and contact stability.

The magnetic brush has a magnetic brush portion of conductive magnetic particles that is magnetically constrained and supported by a supporting member also serving as a power supply electrode, and the magnetic brush portion is brought into contact with a member to be charged to supply power to the supporting member. Things. More specifically, the conductive magnetic particles are directly magnetically constrained as a magnetic brush on a magnet or a sleeve containing the magnet, and the magnetic brush portion is stopped or rotated to contact the member to be charged. Charging is started by applying a voltage.

The fur brush charger has a conductive fiber brush portion carried on a carrier member also serving as a power supply electrode, and the conductive fiber brush portion is brought into contact with a member to be charged to supply power to the carrier member. is there.

In contact charging, a system in which charging by a discharge phenomenon is dominant, and a system in which charging by direct injection (charging) of electric charge to a surface to be charged is dominant (charge injection charging system).
There is.

The charge injection charging method uses a charge injection chargeable material as an object to be charged.
In Japanese Patent No. 3921, an OPC photoreceptor as a member to be charged is coated with an acrylic resin as a charge injection layer in which SnO ₂ made conductive by antimony dope as a conductive filler (conductive particles) is applied (OCL photoreceptor). And a method of injecting a charge from a contact charging member, which is in contact with the surface of the photoreceptor and to which a voltage is applied, into conductive particles serving as a float electrode of a charge injection layer to perform charging. A photoreceptor having a surface layer of α-Si is also charge-injectable and chargeable. As the contact charging member in the case of the charge injection charging system, a magnetic brush or a fur brush is preferably used.

Such a charge injection charging method is substantially equivalent to a DC bias (DC voltage) applied regardless of the presence or absence of an AC bias (alternating voltage) superimposed on an applied voltage (charging bias) to a contact charging member. Surface potential of the member to be charged can be obtained. In addition, since a discharge phenomenon that is performed by using a corona charger to charge an object to be charged is not used, complete ozone-free and low-power-consumption charging is possible, and thus, attention has been paid.

[0012]

However, in the contact charging, the foreign matter is picked up from the surface of the member to be charged and becomes contaminated during repeated use of the contact charging member, so that the resistance of the contact charging member is locally or entirely increased. And the charging performance is degraded.

For example, in a transfer type image forming apparatus using a charge injection charging method, in a case where only a DC voltage is applied as a bias applied to a contact charging member of a magnetic brush or a fur brush (DC bias applying method), an image is formed. As the formation is repeated, a magnetic brush or fur brush, which is a contact charging member, removes foreign matters such as transfer residual toner and paper powder that have passed through a cleaner that cleans the image carrier as a member to be charged after transfer. When the particles are picked up and the foreign matter is mixed into the brush portion, the resistance of the contact charging member is increased, which may cause uneven charging. The uneven charging is mainly caused by unevenness of a brush of a magnetic brush or a fur brush which is a contact charging member.

Therefore, by superimposing an AC bias on the bias applied to the contact charging member (AC bias application method), the contact charging member is vibrated to increase the number of times of contact, thereby lowering the apparent resistance and charging. Techniques for preventing unevenness have been taken.

However, when an AC bias is superimposed on a bias applied to the contact charging member, when the resistance of the contact charging member is reduced in a high humidity environment or the like, a local potential level is generated on the surface of the member to be charged. In the image forming apparatus, a ground fog image is sometimes generated.

The present invention has been proposed in view of the above,
Regarding the contact charging device of the AC bias application type and the image forming apparatus using the charging device, uniform charging of the charged object is maintained for a long time in each environment regardless of the contamination due to the progress of the durability of the charging member. Accordingly, it is an object of the present invention to maintain a good image output without ground fog over a long period of time in each environment in an image forming apparatus using contact charging.

[0017]

SUMMARY OF THE INVENTION The present invention is a charging device and an image forming apparatus having the following constitutions.

(1) In a charging device for charging a member to be charged by contacting a charging member to which a voltage is applied with the member to be charged,
The voltage applied to the charging member has an AC bias component and a DC bias component, and the AC bias component is periodically turned on and off.
A charging device characterized by being repeatedly turned off.

(2) The charging device according to (1), wherein the voltage applied to the charging member is obtained by superimposing an AC bias and a DC bias.

(3) The charging device according to (1) or (2), wherein the AC bias component is a component that periodically turns on and off a square wave.

(4) The charging device according to (1) or (2), wherein the AC bias component is obtained by periodically turning on and off a sine wave.

(5) The charging device according to (1) or (2), wherein the AC bias component is a component that periodically turns on and off a triangular wave.

(6) The charging device according to (1) or (2), wherein the AC bias component is a component that periodically turns on and off a sawtooth wave.

(7) The amplitude of the AC bias component is 0.5.
It is 2 kV or more and 6 kV or less (1)
The charging device according to any one of (6) to (6).

(8) The frequency fHz of the ON / OFF cycle of the AC bias component is determined by the moving speed Vmm / s of the member to be charged.
The charging device according to any one of (1) to (7), wherein 2 × V ≦ f ≦ 200 × V with respect to ec.

(9) The charging member has a brush portion of conductive magnetic particles carried on a carrying member, and the brush portion is in contact with the member to be charged. 8) The charging device according to any one of 8).

(10) The charging member has a brush portion made of a conductive fiber carried on a carrying member, and the brush portion is in contact with the member to be charged (1) to (8). The charging device according to any one of (1) to (4).

(11) Any one of (1) to (10), wherein the member to be charged is charge-injection chargeable.
The charging device according to any one of the above.

(12) In an image forming apparatus for forming an image by applying an image forming process including a step of charging the surface of the member to be charged, the charging means for the member to be charged includes:
A charging device for charging an object to be charged by bringing a charging member applied with a voltage into contact with the object to be charged, wherein the voltage applied to the charging member has an AC bias component and a DC bias component.
An image forming apparatus wherein a C bias component is periodically turned on and off.

(13) A step of charging a member to be charged, a step of forming an electrostatic latent image corresponding to target image information on the charged surface, and a step of visualizing the electrostatic latent image as a toner image (12) The image forming apparatus according to (12), wherein the image forming is performed by an image forming process.

(14) A step of transferring the toner image formed on the member to be charged to a material to be transferred, wherein the member to be charged is repeatedly used for image formation, and the member to be charged after transfer of the toner image to the material to be transferred The image forming apparatus according to (13), wherein the image forming apparatus does not have a dedicated removing unit for removing residual toner.

(15) The image forming apparatus according to any one of (12) to (14), wherein the voltage applied to the charging member is obtained by superimposing an AC bias and a DC bias.

(16) The image forming apparatus according to any one of the above (12) to (15), wherein the AC bias component is obtained by periodically turning on and off a square wave.

(17) The image forming apparatus according to any one of (12) to (15), wherein the AC bias component is obtained by periodically turning on and off a sine wave.

(18) The image forming apparatus according to any one of (12) to (15), wherein the AC bias component is a component that periodically turns on and off a triangular wave.

(19) The image forming apparatus according to any one of (12) to (15), wherein the AC bias component is a component that periodically turns on and off a sawtooth wave.

(20) The image forming apparatus according to any one of (12) to (19), wherein the amplitude of the AC bias component is 0.2 kV or more and 6 kV or less.

(21) The frequency fHz of the ON / OFF cycle of the AC bias component is equal to the image forming speed Vmm / sec.
The image forming apparatus according to any one of (12) to (20), wherein 2 × V ≦ f ≦ 200 × V.

(22) The charging member has a brush portion of conductive magnetic particles carried on a carrying member, and the brush portion is in contact with the member to be charged. 21) The charging device according to any one of the above items 21).

(23) The charging member has a brush portion made of a conductive fiber carried on a carrying member, and the brush portion is in contact with the member to be charged. (12) to (21) The charging device according to any one of (1) to (4).

(24) The image forming apparatus according to any one of (12) to (23), wherein the member to be charged is charge-injectable.

(25) The object to be charged according to any one of (12) to (23), wherein the member to be charged has a photosensitive layer and a surface layer, and the surface layer has a resin and conductive fine particles. An image forming apparatus according to claim 1.

(26) The image forming apparatus according to (25), wherein the conductive fine particles are SnO ₂ .

(27) The image forming apparatus according to any one of (12) to (23), wherein the member to be charged has a surface layer made of amorphous silicon.

(28) The member to be charged has a surface resistance of 10 ⁹ or more.
It has a low resistance layer of 10 ¹⁴ Ω · cm.
The image forming apparatus according to any one of 2) to 23).

<Operation> That is, in the contact charging of the AC bias application method, the AC bias component is periodically turned on and off.
By repeating the OFF, that is, by applying the AC bias component in an intermittent form (blank pulse) instead of continuously applying it together with the DC bias component (hereinafter, AC bias component is applied).
As will be described in an embodiment to be described later, a contact charging device of an AC bias application type and an image forming apparatus using the charging device may be contaminated by the durability of the charging member. Regardless of the environment, it is possible to maintain and execute uniform charging of the charged object over a long period of time without unevenness in the charging environment, so that an image forming apparatus using contact charging can output a good image without fogging. Was maintained for a long time under each environment.

The reason is considered as follows.
That is,. Even though the AC bias component is applied intermittently to the contact charging member, the number of times of contact with the member to be charged increases due to the vibration of the charging member due to the AC bias component as in the AC bias application method, , The apparent resistance is reduced even if contamination occurs due to the endurance, and the treatment of the charged body without uneven charging is maintained. Even when the resistance of the charging member is reduced in a high-humidity environment, etc., the AC bias component is intermittently applied instead of being continuously applied, so that exchange of the AC current with the object to be charged per unit time is reduced, It is possible to reduce or substantially prevent the occurrence of a local potential variation following the peak of the AC bias on the surface potential of the member to be charged. It is possible to maintain and execute uniform charging of an object to be charged without charging unevenness over a long period of time, so that an image forming apparatus using contact charging of an AC application method can output a good image without ground fog. It can be maintained for a long time under each environment.

[0048]

BEST MODE FOR CARRYING OUT THE INVENTION

<Embodiment 1> (FIGS. 1 to 4) (1) Example of Image Forming Apparatus FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus. The image forming apparatus of this embodiment is a printer or a copying machine using a transfer type electrophotographic process.

Reference numeral 1 denotes an image carrier as a member to be charged. This example is a charge injection / negative / rotating drum type electrophotographic OPC photosensitive member having a diameter of 30 mm and a length of 300 mm, and has a process speed (peripheral speed) of 100 mm / sec in the clockwise direction of arrow a. It is driven to rotate. The layer configuration of the photoreceptor 1 will be described in detail in the section (2) below.

Reference numeral 2 denotes a magnetic brush roller as a contact charging member which is in contact with the photoconductor 1, and is provided with a magnetic brush portion in contact with the photoconductor 1, and is provided in a clockwise direction indicated by an arrow.
It is rotationally driven at a peripheral speed of mm / sec. The magnetic brush roller 2 will be described in detail in the section (3) below.

S 1 is a power supply for applying a charging bias to the magnetic brush roller 2. In the present embodiment, a predetermined charging bias is applied to the magnetic brush roller 2 from the power source S1 to apply a surface potential (primary charging potential) of −69 to the peripheral surface of the rotating photoconductor 1.
The charge injection and charging process is uniformly performed at 0V. The charging bias will be described in detail in (4) below.

Exposure of target image information (laser beam scanning exposure, slit exposure of a document image, etc.) L is performed on the charged surface of the rotary photoreceptor 1 by the exposure means 5, so that the surface of the rotary photoreceptor 1 is exposed. An electrostatic latent image corresponding to the exposure image information is formed.

Then, the developing device 6 applies toner to the electrostatic latent image, and the electrostatic latent image is sequentially visualized as a toner image.
The developing device 6 of this example is a device of a jumping developing type, in which a rotary developing sleeve 6a as a developer carrying member is disposed at a distance of 0.3 mm from the photoconductor 1, and a frequency of 1800 Hz is supplied to the developing sleeve 6a from a power source S2. An AC component of Vpp (amplitude, voltage between 13 peaks) of 1400 V, and -3
A developing bias on which a DC component of 00 V is superimposed is applied. In addition, a negative toner was used as the toner.

On the other hand, the transfer material P
Is transferred to a transfer portion t, which is a contact nip portion between the photoreceptor 1 and the transfer device 7, at an appropriate timing synchronized with the rotation of the photoreceptor 1, and the transfer portion t is nipped and conveyed. The transfer device 7 includes a rotatable transfer roller 7a.
A predetermined transfer bias having a polarity opposite to that of the toner is applied from the power source S3 to the transfer portion t while the transfer target material P is nipped and conveyed. As a result, the back side of the transfer material P is charged to the polarity opposite to that of the toner, and the toner images on the photoconductor 1 are sequentially electrostatically transferred to the front surface of the transfer material P. In this example, the transfer roller 7a
The transfer was performed by applying a DC voltage of +3500 V using a conductive rubber roller having a resistance of 5 × 10 ⁸ Ω and a diameter of 16 mm.

The transfer material P to which the toner image has been transferred at the transfer portion t is separated from the surface of the photoreceptor 1 and conveyed to a fixing device (not shown) where the toner image is fixed, and then discharged outside the apparatus main body. Alternatively, if an image is also formed on the back surface, the sheet is re-conveyed to the transfer unit t by a re-conveying unit (not shown).

Photoreceptor 1 after image transfer to transfer target material P
The residual toner (transfer residual toner) is removed by a cleaning blade 9a of a cleaning device (cleaner) 9, and the toner is repeatedly used for image formation.

(2) Photoconductor 1 The electrophotographic photoconductor 1 as a member to be charged in this example is a negative electrophotographic OPC photoconductor (OPC-OCL drum) having a surface layer having a charge injection / charging surface on its surface. It is. FIG. 2 is a schematic explanatory view of the layer structure of the photoreceptor 1. The outer peripheral surface of a conductive aluminum drum substrate (hereinafter referred to as an Al substrate) 1a has five functional layers 1b to 5th from a first layer to a fifth layer. 1f are sequentially laminated.

The first layer 1b is an undercoat layer, and
20 μm thickness provided to smooth out defects such as
Of the conductive layer.

The second layer 1c is a positive charge injection preventing layer.
play a role in positive charge injected from l substrate 1a is prevented from canceling the negative charge on the photoreceptor surface, 10 ⁶ Omega by Amilan resin and methoxy methylated nylon
A medium resistance layer having a thickness of 1 μm and a resistance adjusted to about cm.

The third layer 1d is a charge generating layer, and is a layer having a thickness of about 0.3 μm in which a disazo pigment is dispersed in a resin, and generates a positive and negative charge pair upon exposure.

The fourth layer 1e is a charge transport layer, in which hydrazone is dispersed in a polycarbonate resin, and is a P-type semiconductor. Therefore, the negative charges charged on the photoconductor surface cannot move through this layer, and only the positive charges generated in the charge generation layer 1d can be transferred to the photoconductor surface.

The fifth layer 1f is a charge injection layer (surface layer), and is a coating layer of a material in which ultrafine SnO ₂ particles are dispersed in a binder of an insulating resin. Specifically, SnO ₂ having a particle diameter of about 0.03 μm is obtained by doping an insulating resin with antimony, which is a light-transmitting conductive filler, to reduce the resistance (to make it conductive).
This is a coating layer of a material in which particles are dispersed in a resin by 70% by weight.

The coating solution thus prepared is applied to a thickness of about 3 μm by a suitable coating method such as dipping coating method, spray coating method, roll coating method, beam coating method, etc. And

In addition, in addition to the above, amorphous silicon (α-S
A photoreceptor (amorphous silicon) having a surface layer composed of i) can also be used as a photoreceptor having charge injection and charging properties.

(3) Charging member 2 Magnetic brush roller 2 as a contact charging member in this embodiment
Is a sleeve rotation type, and FIG. 3 is a model diagram of the configuration.

That is, reference numeral 2b denotes a conductive sleeve (referred to as an electrode sleeve, a conductive sleeve, a charging sleeve, or the like) of nonmagnetic SUS / aluminum having a diameter of 20 mm as a magnetic brush portion holding member.

Reference numeral 2a denotes a magnetic roller having a diameter of 16 mm and magnetized with S and N poles (each having a magnetic flux density of about 1000 gauss) serving as a magnetic field generating means inserted and disposed in the sleeve 2b. The magnet roller 2a is a non-rotating fixed member, and a sleeve 2b is rotatably driven concentrically in a clockwise direction indicated by an arrow at a predetermined peripheral speed by a drive mechanism (not shown) around the outer periphery of the magnet roller 2a.

Reference numeral 2c denotes a magnetic brush portion of conductive magnetic particles (magnetic carrier). The magnetic brush portion 2c is formed by attaching the conductive magnetic particles to the outer peripheral surface of the sleeve 2b by the magnetic force of the magnet roller 2a inside the sleeve. It is kept. The conductive magnetic particles form magnetic spikes on the outer surface of the sleeve 2b due to the magnetic restraining force of the magnet roller 2a, and these gather to form a brush. In this example, 40 g of conductive magnetic particles having a particle size of 25 μm and a resistance value of 2 × 10 ⁵ Ω (under an environment of 60% humidity) were attached to form the magnetic brush portion 2c.

As the conductive magnetic particles, magnetite is dispersed as a magnetic material in a resin, and a resin carrier formed by dispersing carbon black for conductivity and resistance adjustment, or a surface of magnetite alone such as ferrite is oxidized. A material which has been subjected to a reduction treatment to adjust the resistance or a material obtained by coating the surface of a single magnetite such as ferrite with a resin and adjusting the resistance can be used.

The magnetic brush roller 2 has a magnetic brush portion 2c formed in contact with a surface of the rotating photosensitive member 1 as a member to be charged by forming a contact nip portion (charging nip portion) n having a predetermined width.

The magnetic brush portion 2c is rotated and conveyed in the same direction with the rotation of the sleeve 2b, rubs the surface of the rotating photoreceptor 1 at the charging nip portion n, and moves from the power source S1 to the sleeve 2b.
In this case, the surface of the rotating photoconductor 1 is contact-charged by a charge injection charging method of an AC bias intermittent application method according to the present invention by a predetermined charging bias applied to the magnetic brush portion 2c via the magnetic brush section 2c. In the charging nip portion n, the sleeve 2
The rotation direction of b and the accompanying rotation and transport direction of the magnetic brush portion 2c are counter directions with respect to the rotation direction of the rotating photoreceptor 1 as a member to be charged. The sleeve 2b has a function of holding and transporting the magnetic brush portion 2c, and a function of a charging bias applying electrode.

(4) Charging bias. In the above-described image forming apparatus, when the image forming is performed by the DC bias applying method in which the applied bias (charging bias) to the magnetic brush roller 2 as the contact charging member is set to only DC-700V, 50,000 sheets of A4 paper are printed. Up to the level, the surface potential (primary charging potential) of the photoconductor 1 is −
690 V was obtained, and a good image was obtained without image defects due to charging unevenness such as sweeping unevenness.

However, a surface potential of -685 V could be obtained almost unchanged after passing over 60,000 sheets of image formation. However, when a halftone image such as halftone is formed, streaks are formed on the image. That is, image defects due to charging unevenness due to brush sweeping unevenness began to occur. When the number of sheets exceeded 70,000, an unacceptable image defect occurred.

This is because, with long-term image formation, residual toner and paper dust that have slipped through the cleaning device 9 adhere to or mix with the magnetic brush portion 2c of the magnetic brush roller 2 serving as a contact charging member. This is because the resistance locally increased.

[0075] Next, the charging bias for the magnetic brush roller 2 as the contact charging member is set to AC bias; frequency 1.5 kHz, Vpp = 1.0 kV.
(Square wave) DC bias; The same study was conducted using an AC bias application method with a superimposed voltage of -700 V. As a result, a good image could be obtained even after 80,000 sheets of image formation. .

This is because the AC bias is superimposed, and the contact charging member 2 vibrates and the number of times of contact increases, so that the apparent resistance of the magnetic brush roller 2 is reduced despite the contamination of the magnetic brush portion 2c by toner or the like. It is because it falls.

However, a similar study was conducted in a high humidity environment (80%
RH), a small amount of toner adheres to the non-image area from the early stage of image formation, that is, so-called background fog sometimes occurs.

In a high-humidity environment, the resistance of the photosensitive member 1 and the contact charging member 2 decreases and the charge injecting property increases, so that the surface potential of the photosensitive member 1 is charged to a potential following the peak of the AC bias. It is because.

[0079] Therefore, in this embodiment, the charging bias for the magnetic brush roller 2 which is a contact charging member is set to A according to the present invention.
The C bias intermittent application method, that is, the control in which the AC bias component is repeatedly turned on and off periodically.

Specifically, the charging bias applied to the magnetic brush roller 2 as a contact charging member is represented by an AC bias component Vac; Vpp as shown in FIG.
= 0.8 kV, blank pulse (square wave) with AC bias ON / OFF repetition cycle frequency f of 500 Hz and AC bias-ON frequency of 5 kHz DC bias component Vdc; did. Due to the applied charging bias, the surface potential (primary charging potential) of the photosensitive member 1 becomes -690V.

In this case, a good image free from image defects due to uneven charging such as sweeping unevenness could be obtained even after 80,000 sheets of image formation. In addition, even under a high humidity environment, a good image having no ground fog was obtained.

<Embodiment 2> (FIG. 5) In this embodiment, a rotating fur brush roller made of conductive fiber is used in place of the magnetic brush roller 2 as the contact charging member in the image forming apparatus of Embodiment 1. Other configurations of the image forming apparatus are the same as those of the image forming apparatus of the first embodiment.

The fur brush roller generally has a wire diameter of 1-1.
0 denier, resistance 10 ⁴ to 10 ⁷ Ωcm (10 ^{6 in} this example)
Ωcm) conductive fiber of 50000-500000 / inc
about h ² is a roll-shaped brush of approximately haired 2mm which is planted to a density of (50000 / inch ² in this example), is abutted by disposed rotating the photosensitive member 1 to the brush portion by a predetermined amount of intrusion Used.

[0084] Regarding the charging bias applied to the fur brush roller, (4)-of the first embodiment described above.
And (4)-, the same study was carried out. As a result, in the DC bias application method using only the DC bias, charging unevenness occurred, and D
In the AC bias application method in which the C bias and the AC bias are superimposed, the image may be fogged.

[0085] Therefore, as in (4)-of the first embodiment, the square pulse blank pulse shown in FIG. 4 is superimposed on the fur brush roller as the AC bias component Vac with the DC bias component Vdc (-700 V). A study was conducted by applying a charging bias (AC bias intermittent application method). As a result, a good image could be obtained even after the formation of 80,000 sheets of A4 paper. No ground fogging occurred in a high humidity environment.

However, in the middle tone such as halftone, two or three white spots were generated. This is because the fur brush is slightly inferior in contact with the photoreceptor as compared with the magnetic brush, so that an excessive discharge occurs in a portion where the contact is poor and the surface potential is partially increased.

[0087] Therefore, a similar study was conducted using the AC bias component Vac of the charging bias applied to the fur brush as a sine wave blank pulse as shown in FIG. 5, and there was no charging unevenness after long-term image formation and no spots in a high humidity environment. It did not occur.

This is because the peak time of the applied bias can be reduced by changing the AC bias component Vac from a square wave to a sine wave, thereby preventing excessive discharge.

In this example, the fur brush roller used had a fur length of 2 mm, a flocking density of 50,000 / inch ² , and a resistance of 10 ⁶ Ωcm.
By increasing the density to 00000 / inch ² , even if a square-wave blank pulse as in Embodiment 1 is used as the AC bias component Vac, a good image can be formed even after long-term image formation and under a high humidity environment. I got it.

<Third Embodiment> In the image forming apparatus of the first embodiment, an α-Si drum having a silicon amorphous layer as a surface layer is used as the photosensitive member 1, and the contact charging member 2 is used as the first embodiment. The case where the magnetic brush roller of Example 2 was used and the case where the fur brush roller of Embodiment 2 was used were examined.

As the charging bias applied to the contact charging member, an AC bias component Vac; Vpp = 0.6 kV, an ON / OFF repetition frequency of the AC bias of 1 kHz, and a frequency of 5 kHz when the AC bias is ON, is a square wave blank. Pulse When using an oscillating voltage with a DC bias component Vdc; +410 V superimposed thereon (AC bias intermittent application method), it is good for a long time in each environment both when using a magnetic brush roller and when using a fur brush roller. Images were obtained.

This is because α is smaller than that of the OPC-OCL drum.
This is because the -Si drum is more excellent in the charge injection property, so that the limitation on the applied bias is reduced. Α at this time
−Si drum surface potential (primary charging potential) is +4
00V.

Even when a sinusoidal blank pulse was used as the AC bias component Vac, a good image could be obtained over a long period of time under each environment.

Since the α-Si drum has a large dielectric constant, the charging current increases as compared with the OPC. Therefore, the charging current can be reduced by setting the blank pulse, which is the AC bias component Vac, to a triangular wave or a sawtooth wave, and a good image can be obtained over a long period in each environment. By reducing the charging current, the temperature rise due to the excess current can be reduced.

Fourth Embodiment (FIG. 6) FIG. 6 shows a so-called cleaner-less image forming apparatus in which the cleaning device 9 is removed from the image forming apparatuses of the first to third embodiments.

In the case of this cleanerless image forming apparatus, the transfer residual toner remaining on the surface of the photoconductor 1 after the transfer of the toner image from the rotary photoconductor 1 to the material P to be transferred reaches the developing device 6.
The toner is collected by the developing device 6 by a so-called simultaneous development cleaning action. The cleaner-less image forming apparatus can reduce the size and cost of the image forming apparatus by eliminating the provision of the dedicated cleaning device 9.

The same examination as in the first to third embodiments was conducted on such a cleaner-less image forming apparatus, and the same Vpp as that of the apparatus having the cleaning device 9 was obtained.
When the blank pulse is used as the AC bias component Vac of the charging bias applied to the contact charging member, charging unevenness and image unevenness sometimes occur due to poor charging at the time of 40,000 sheets of image formation.

This is because, in the case of a cleaner-less image forming apparatus, since the transfer residual toner on the photoreceptor 1 is directly mixed into the charging member 2, the contact charging member 2 is faster than the image forming apparatus having the cleaning device 9. Is increased and Vpp of the first to third embodiments causes insufficient vibration.

Therefore, in this embodiment, Vpp of the AC bias component Vac is set to 2 of Vpp in each of the first to third embodiments.
0% increase, that is, Vpp = 0.9 in the first and second embodiments.
By setting Vpp to 0.72 kV in Embodiment 3 and Vpp = 0.72 kV, it was possible to provide a good image even after long-term image formation under each environment even in a cleanerless image forming apparatus without the cleaning device 9. .

That is, by increasing the Vpp of the blank pulse as the AC bias component Vac and increasing the vibration force of the contact charging member 2, it was possible to prevent charging unevenness and ground fogging even in a cleanerless image forming apparatus. .

<Others> 1) The amplitude (peak-to-peak voltage) of the AC bias component Vac in the contact charging of the AC bias intermittent application method of the present invention.
Vpp and repetition frequency fHz (AC bias on / off)
OFF cycle frequency) depends on the type of contact charging member, resistance,
The optimum value differs in each case depending on the type, thickness, resistance, and the like of the photoreceptor as a member to be charged, and the presence or absence of a cleaning device.

In general, when the amplitude Vpp of the AC bias component Vac is smaller than 0.2 kV, the effect of the AC bias application, that is, the effect of preventing the charging unevenness becomes insufficient.
Above 6 kV, abnormal discharge starts to occur. Therefore, it is preferable to set the amplitude Vpp of the AC bias component to be 0.2 kV or more and 6 kV or less.

The repetition frequency fHz of the AC bias
Is generally the moving speed V (mm / sec) of the member to be charged, and the image forming speed (process speed) in an image forming apparatus.
If it is less than twice V (mm / sec), a streak of poor charging follows the frequency, and if it is more than 200 times, uneven charging occurs, so it is preferable to set 2 × V ≦ f ≦ 200 × V. .

When the frequency is 2 × V or less, the repetition frequency is slower than the image forming speed, so that there are portions where the AC effect appears and portions where the AC effect does not appear. As a result, uneven charging according to the frequency occurs. It becomes easier.

When the voltage exceeds 200 × V, the time constant of the charging member cannot keep up with the frequency. As a result, the vibration of the charging member is suppressed, and the charging unevenness is liable to occur as in the case where only the DC bias is applied. That's why.

In the embodiment, only one pulse is applied when the AC bias component Vac (blank pulse) is ON, but two pulses, three pulses... Are applied when the AC bias component Vac is ON. A similar effect was obtained.

The repetition frequency fHz of the AC bias can be fluctuated according to the situation.

2) In the present invention, the ratio between the ON time and the OFF time is 1 when the ON time is Tn and the OFF time is Tf.
It is desirable that / 100 ≦ Tn / (Tn + Tf) ≦ 4/5.

This is because the on-time Tn and the on-time Tn
When the ratio to the + off time Tf becomes 1/100 or less, AC
Is too short, and as in the case where only the DC bias is applied, the charging member is contaminated with the progress of durability.
Charging unevenness tends to occur. If the ratio is more than 4/5, the exchange of the AC current is too large.
This is because local ground fogging easily occurs as in the case of bias application.

3) In the above embodiment, the amplitude Vpp of the AC bias is set to zero at the time of off-state. However, the present invention is not limited to this. At that time, Vpp at the time of off is Vp at the time of on.
Desirably, it is 80% or less of p.

This is because Vpp at the time of off is 80% of that at the time of on.
Is exceeded, the exchange of AC current increases too much, and local ground fogging is likely to occur as in the case where a continuous AC bias is applied.

4) The contact charging device of the AC bias intermittent type according to the present invention is not limited to the charging process of the image carrier in the image forming apparatus of the embodiment, and is effective as a contact charging processing means for the charged object widely. Of course.

5) The magnetic brush serving as the contact charging member is not limited to the sleeve rotating type of the embodiment, but may be a type in which the magnet roller 2a rotates, or the surface of the magnet roller 2a may be used as a power supply electrode if necessary by a conductive treatment. Further, if necessary, a resistance layer is applied, and the conductive magnetic particles are directly magnetically restrained on the surface of the magnet roll 2a to form and hold the magnetic brush portion 2c, thereby rotating the magnet roller 2a. It can also be something. A fixed type magnetic brush that does not rotate can also be used.

The fur brush may be of a fixed type that does not rotate.

As the contact charging member, a rubber roller, a blade type, a wire type or the like other than the magnetic brush and the fur brush can be used.

6) It is preferable that the member to be charged has a low resistance layer having a surface resistance of 10 ⁹ to 10 ¹⁴ Ω · cm in the case of the injection charging method.

The charge by discharge may be dominant. A contact charging system based on discharge, and as a contact charging means of an AC bias application type, as disclosed in Japanese Patent Publication No. 3-52058, which was previously proposed by the present applicant, a predetermined DC voltage component is applied to the contact charging member. The method of applying an oscillating voltage having a predetermined alternating voltage component (alternating voltage having a peak-to-peak voltage that is at least twice the charging start voltage value of the member to be charged when a DC voltage is applied to the contact charging member) is applied to uniform charging. Excellent in nature.

As the alternating voltage component (AC bias component), those having an appropriate waveform such as a sine wave, a square wave (rectangular wave), a triangular wave, and a sawtooth wave can be used. It also includes a rectangular wave formed by periodically turning on and off a DC power supply.

In contact charging in which charging by discharge is dominant, the charging member does not necessarily need to be in contact with the member to be charged, and the charging member and the member to be charged can be discharged between the gap determined by the gap voltage and the corrected Paschen curve. Charging is performed (proximity charging) as long as they face each other in a non-contact manner with a small gap (gap) satisfying the conditions. In the present invention, such a proximity charging mode is also included in the category of contact charging.

7) Regarding the image forming apparatus, the image forming process is optional. The transfer system may be a direct system in which an image is formed directly on photosensitive paper (electrofax paper) or electrostatic recording paper without an image transfer process.

The image carrier may be an electrostatic recording dielectric or the like. In this case, after the dielectric surface is uniformly charged to a predetermined polarity and potential, the charge is selectively removed by a charge removing means such as a charge removing needle head or an electron gun to write and form a desired electrostatic latent image.

The method and means for developing an electrostatic latent image are arbitrary.
A reversal development system or a regular development system may be used.

The transfer method is not limited to the roller transfer shown in the embodiment, but may be a blade transfer or other contact transfer charging method. Needless to say, the present invention can be applied to an image forming apparatus that forms a multi-color or full-color image by multiple transfer or the like.

[0124] Arbitrary process equipment such as the image carrier 1, the charging member 2, the developing device 6 and the like can be configured so as to be detachable and replaceable with the image forming apparatus main body. .

An electrophotographic photosensitive member or an electrostatic recording dielectric as an image carrier is formed into a rotating belt type, and a toner image corresponding to required image information is formed on the rotating belt type by means of charging, latent image formation and development. There is also an image display device in which an image carrier is formed and the toner image forming unit is positioned in a reading display unit to display an image, and the image carrier is repeatedly used for forming a display image. The image forming apparatus of the present invention includes such an image display device.

[0126]

As described above, according to the present invention, AC
Regarding the contact charging device of the bias application type and the image forming apparatus using the charging device, the AC bias intermittent application method ensures uniform and uniform charging over a long period of time in each environment irrespective of contamination due to the durability progress of the contact charging member. It is possible to maintain and execute the charging process of the charged body, so that in an image forming apparatus using contact charging of an AC bias application method, a good image output without ground fog can be maintained for a long time in each environment. It is possible to achieve the intended purpose well.

[Brief description of the drawings]

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

FIG. 2 is a schematic diagram of a layer structure of a photoconductor as a member to be charged;

FIG. 3 is a schematic view of a configuration of a sleeve rotating type magnetic brush roller as a contact charging member.

FIG. 4 is a diagram showing a form of a blank pulse (square wave) as an AC bias component applied to a charging member.

FIG. 5 shows A applied to a charging member in a second embodiment.
Form of blank pulse (sine wave) as C bias component

FIG. 6 is a schematic diagram illustrating a configuration of a cleanerless image forming apparatus according to a fourth embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image carrier (charged body, photosensitive drum) 2 Contact charging member (magnetic brush) 5 Exposure means 6 Developing device 7 Transfer member (transfer roller) 9 Cleaning device P Transferred material

Claims (28)

[Claims] 1. A charging device for charging an object to be charged by bringing a charging member applied with a voltage into contact with the object to be charged, wherein the voltage applied to the charging member has an AC bias component and a DC bias component, The AC bias component is turned on periodically,
A charging device characterized by being repeatedly turned off. 2. The charging device according to claim 1, wherein the voltage applied to the charging member is obtained by superimposing an AC bias and a DC bias. 3. The charging device according to claim 1, wherein the AC bias component is obtained by periodically turning on and off a square wave. 4. The charging device according to claim 1, wherein the AC bias component is obtained by periodically turning on and off a sine wave. 5. The charging device according to claim 1, wherein the AC bias component is obtained by periodically turning on and off a triangular wave. 6. The AC bias component according to claim 1, wherein the sawtooth wave is periodically turned on and off.
Or the charging device according to 2. 7. An amplitude of the AC bias component is 0.2 k.
The charging device according to any one of claims 1 to 6, wherein the charging voltage is not less than V and not more than 6 kV. 8. The frequency fHz of the ON / OFF cycle of the AC bias component is equal to the moving speed Vmm / sec of the member to be charged.
The charging device according to claim 1, wherein 2 × V ≦ f ≦ 200 × V. 9. The method according to claim 1, wherein said charging member has a brush portion of conductive magnetic particles carried on a carrying member, and said brush portion is in contact with a member to be charged. The charging device according to any one of the above. 10. The charging device according to claim 1, wherein the charging member has a brush portion made of conductive fibers carried on a carrying member, and the brush portion is in contact with the member to be charged. A charging device according to any one of the preceding claims. 11. The charging device according to claim 1, wherein the member to be charged is charge-injectable. 12. An image forming apparatus for performing image formation by applying an image forming process including a step of charging a surface of a member to be charged, wherein a charging step of charging the member to be charged includes applying a voltage to the member to be charged. Is a charging device for charging a member to be charged by contacting a charging member to which the voltage is applied. The voltage applied to the charging member has an AC bias component and a DC bias component, and the AC bias component is periodically turned on and off.
An image forming apparatus characterized by repeating turning off. 13. A step of charging an object to be charged, a step of forming an electrostatic latent image corresponding to target image information on the charged surface, and a step of visualizing the electrostatic latent image as a toner image. 13. The image forming apparatus according to claim 12, wherein the image forming is performed by an image forming process. 14. A method for transferring a toner image formed on a member to be charged to a material to be transferred, wherein the member to be charged is repeatedly used for image formation, 14. The image forming apparatus according to claim 13, wherein there is no dedicated removing unit for removing the residual toner. 15. The image forming apparatus according to claim 12, wherein the voltage applied to the charging member is obtained by superimposing an AC bias and a DC bias. 16. The image forming apparatus according to claim 12, wherein the AC bias component is a signal that periodically turns on and off a square wave. 17. The image forming apparatus according to claim 12, wherein the AC bias component is obtained by periodically turning on and off a sine wave. 18. The image forming apparatus according to claim 12, wherein the AC bias component is obtained by periodically turning on and off a triangular wave. 19. The image forming apparatus according to claim 12, wherein the AC bias component is a component that periodically turns on and off a sawtooth wave. 20. The amplitude of the AC bias component is 0.2
2. A voltage of not less than kV and not more than 6 kV.
20. The image forming apparatus according to any one of 2 to 19. 21. The image forming apparatus according to claim 12, wherein the frequency fHz of the ON / OFF cycle of the AC bias component is 2 × V ≦ f ≦ 200 × V with respect to the image forming speed Vmm / sec. An image forming apparatus according to claim 1. 22. The charging device according to claim 12, wherein said charging member has a brush portion of conductive magnetic particles carried on a carrying member, and said brush portion is in contact with a member to be charged. The charging device according to any one of the above. 23. The device according to claim 12, wherein the charging member has a brush portion made of a conductive fiber carried on a carrying member, and the brush portion is in contact with the member to be charged.
The charging device according to any one of the above. 24. The image forming apparatus according to claim 12, wherein said member to be charged is charge-injectable. 25. The method according to claim 12, wherein the member to be charged has a photosensitive layer and a surface layer, and the surface layer has a resin and conductive fine particles. Image forming device. 26. The image forming apparatus according to claim 25, wherein the conductive fine particles are SnO ₂ . 27. An image forming apparatus according to claim 12, wherein said member to be charged has a surface layer made of amorphous silicon. 28. The object to be charged has a surface resistance of 10 ⁹ to 10.
13. A low-resistance layer having a resistance of ¹⁴ Ω · cm.
24. The image forming apparatus according to any one of claims 23 to 23.