JP3507246B2 - Magnetic brush charging device and image forming device - Google Patents

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 an object to be charged (including a charge removing process), and an image forming apparatus equipped with the charging device.

In particular, the present invention relates to a magnetic brush charging device using a magnetic brush charging member and an image forming apparatus equipped with the charging device.

[0003]

2. Description of the Related Art A means for charging a charged body is "non-contact type".
And "contact system".

A typical non-contact system is a corona charger.
This is because the corona charger is arranged so as to face the body to be charged in a non-contact manner, a high voltage is applied to generate corona discharge in the corona charger, and the surface of the body to be charged is charged by exposing the surface of the body to be charged to the corona discharge. It is what makes me.

Examples of the contact system include triboelectric charging and a contact charging device that charges a charged member by bringing a charging member such as a roller body or a brush member into contact with the charged member to apply a voltage.

Conventionally, for example, in an electrophotographic or electrostatic recording type image forming apparatus, a corona charging which is a non-contact system is used as a charging processing means for an image carrier such as an electrophotographic photosensitive member or an electrostatic recording dielectric. Although a container has been frequently used, a contact-type contact charging device has been put into practical use because of advantages such as low ozone and low electric power in recent years as ecological attention has been paid. There are various types of contact charging members such as a rubber roller type, a fixed brush type, and a roll-shaped fur brush type.

A) Roller charging system In particular, a roller charging system using a conductive roller as a contact charging member is preferably used in terms of charging stability.

In the roller charging type contact charging device, a conductive elastic roller (charging roller) as a charging member is brought into pressure contact with a member to be charged, and a voltage is applied to the member to charge the member to be charged. . Specifically, since the charging is performed by discharging from the charging member to the body to be charged, the charging is started by applying a voltage equal to or higher than a certain threshold voltage.

As an example, the member to be charged has a thickness of 25 μm.
When the charging roller is pressed against the OPC photosensitive member of m to perform the charging process, the surface potential of the photosensitive member starts to rise if a voltage of about 640 V or more is applied to the charging roller. After that, the surface potential of the photoconductor increases linearly with an inclination of 1 with respect to the applied voltage. This threshold voltage is defined as the charging start voltage Vth.

That is, in order to obtain the photoreceptor surface potential Vd required for electrophotography, Vd + Vth is applied to the charging roller.
More DC voltage is needed than is needed. A method of charging only by applying a DC voltage to the contact charging member in this way is called a "DC charging method".

However, in the DC charging method, the resistance value of the contact charging member fluctuates due to environmental fluctuations, etc. Further, the charging start voltage Vth fluctuates when the film thickness changes due to the abrasion of the photoconductor as the member to be charged. Therefore, it is difficult to set the potential of the photoconductor to a desired value.

Therefore, as disclosed in Japanese Patent Laid-Open No. 63-149669, a DC voltage corresponding to a desired Vd is provided with a peak-to-peak voltage of 2 × Vth or more in order to further uniformize the charging. An "AC charging method" is used in which a voltage on which a charged AC component is superposed is applied to a contact charging member to charge an object to be charged. This is for the purpose of leveling the potential by the AC, and the potential of the body to be charged converges on Vd which is the center of the peak of the AC voltage, and is not affected by disturbance such as the environment.

However, even in such contact charging, since the essential charging mechanism uses the discharging phenomenon from the charging member to the photosensitive member, as described above, the voltage required for charging is A value higher than the surface potential of the body to be charged is required, and a small amount of ozone is generated.

Further, when AC charging is performed to make the charging uniform, further generation of ozone amount and vibration noise of the charging member and the charged body due to the electric field of the AC voltage (AC charging sound).
And the deterioration of the surface of the member to be charged due to the discharge became remarkable, which was a new problem.

Here, in the characteristics required not only for the charging roller but also for the contact charging member, when a charging member having a low resistance value is used, there is a low withstand voltage defect portion such as a scratch or a pinhole on the member to be charged. Then, an excessive leak current flows from the charging member to the low withstand voltage defect portion, resulting in defective charging, enlargement of pinholes, and energization breakdown of the charging member in the portion to be charged around the low withstand voltage defect portion. In order to prevent this, the resistance value of the charging member needs to be about 1 × 10 ⁴ Ω or more. While 1
When the resistance is more than × 10 ⁷ Ω, the resistance value is too high, and the current required for charging cannot be passed. Therefore, the resistance value of the contact charging member must be in the range of 1 × 10 ⁴ Ω to 1 × 10 ⁷ Ω.

B) Injection charging method Further, a contact type charging method has been devised in which charging is performed by directly injecting an electric charge to an object to be charged (Japanese Patent Application Laid-Open No. 6-3921, Japanese Patent Application No. 5-1953). -66150).

In this injection charging method, only a DC voltage corresponding to a desired Vd is applied to a contact conductive member such as a roller type, a brush type, or a magnetic brush type, and charges are injected into a trap level on the surface of the charged body. Alternatively, a desired Vd is obtained by a method of charging the charged body having a protective film in which conductive particles are dispersed with electric charges.

Japanese Unexamined Patent Publication No. 6-3921 discloses a method of injecting electric charges into a float electrode of a charge injection layer of a member to be charged (photoreceptor) having a charge injection layer on the surface to perform contact charging. As a charge injection layer, S made conductive with antimony dope which is a conductive filler in acrylic resin on the surface of the photoreceptor
It is described that a dispersion of nO ₂ (tin oxide) particles can be applied and used.

In this injection charging method, since the discharge phenomenon is not used, the voltage required for charging is a DC voltage only for the desired surface potential of the member to be charged, and ozone is not generated.
Further, since the AC voltage is not applied, no charging noise is generated, and the charging method is superior in the low ozone property and the low voltage property as compared with the roller charging method.

In the contact charging method such as the CD charging method and the AC charging method described above, the charging mechanism is based on the discharge, so that the charging is performed even if some gap is generated between the charging member and the surface of the member to be charged. However, in the injection charging method, since the charging member and the member to be charged directly contact each other to transfer the electric charge,
It is necessary to adopt a configuration in which the two are in close contact with each other and are not microscopically charged and remain.

Further, it is preferable that the resistance of the charging member is lower so as not to hinder the transfer of charges, but as described above,
In the device using the contact charging member, when there is a low withstand voltage defect portion such as a scratch or a pinhole on the member to be charged, if the resistance of the charging member is low, leakage occurs, the power supply voltage drops, and charging failure occurs. Therefore, in practice, the charging member needs to have a certain level of resistance. When the resistance of the charging member is high as described above, the charge injecting property is deteriorated.Therefore, by increasing the contacting speed between the charging member and the member to be charged, a means such as rotating the charging member quickly is used. It is necessary to secure the charge injection capability.

As described above, the charging member used in the injection charging method can be in intimate contact with the member to be charged, and
From the viewpoint of a member capable of having a peripheral speed difference with respect to the body to be charged, a magnetically constrained charging member such as a magnetic brush or a magnetic fluid (magnetic brush charging member) is suitable.

C) Magnetic brush charging member The magnetic brush charging member is one in which magnetic particles are held by the magnetic particle supporting means by magnetic force so as to be attached and held as a magnetic brush. A voltage is applied to charge the body to be charged. More specifically, 1) The magnetic particle supporting means is a rotatable sleeve, and a fixed magnet roll (magnet) disposed in the sleeve.
The magnetic particles are bound to the outer surface of the sleeve by the magnetic force of and are attached and held as a magnetic brush (sleeve type), 2) the magnetic particle supporting means is a rotatable magnet roll (magnet), and For example, magnetic particles are directly bound to the outer surface by magnetic force and attached and held as a magnetic brush (magnetic roller type).

FIG. 9A is a schematic view of the sleeve type magnetic brush charging member 2 or the charging device of the above 1).

Reference numeral 21 denotes a non-magnetic conductive sleeve made of aluminum or the like (referred to as an electrode sleeve, a conductive sleeve, a charging sleeve, etc.) as a magnetic particle supporting means. Two
Reference numeral 2 denotes a magnet roll as a magnetic field generating means inserted and arranged in the sleeve 21. N and S are magnetized portions of the roll. The magnet roll 22 is a non-rotating fixed member, and the sleeve 21 is concentrically driven around the outer circumference of the magnet roll 22 in a clockwise direction b indicated by an arrow by a driving mechanism (not shown) at a predetermined peripheral speed. Reference numeral 23 is a conductive magnetic particle (hereinafter, referred to as a carrier), and the sleeve 2
The magnetic brush (conductive magnetic brush) 24 is constrained by the magnetic force of the magnet roll 22 inside the sleeve on the outer peripheral surface of the magnetic brush 24.
Is retained as attached. The carrier 23 forms a magnetic spike on the outer surface of the sleeve 21 due to the magnetic restraining force of the magnet roll 22, and these are gathered into a brush shape. E1 is a charging bias application power source for the sleeve 21.

Reference numeral 1 denotes a member to be charged, which is, for example, a drum type electrophotographic photosensitive member which is rotationally driven in the clockwise direction a indicated by an arrow at a predetermined process speed. The magnetic brush charging member 2 is arranged in a state where the magnetic brush 24 is brought into contact with the surface of the body 1 to be charged to form a contact nip portion (charging nip portion) D. The magnetic brush 24 is rotatably conveyed in the same direction as the sleeve 21 rotates, rubs the surface of the rotating photoconductor 1 at the contact nip portion D, and is charged by the power source E1 via the sleeve 21 to the magnetic brush 24. By the bias, the surface of the rotary photosensitive member 1 as the member to be charged is charged by the contact method.

In the contact nip portion D, the rotating direction of the sleeve 21 and the accompanying rotating and conveying direction of the magnetic brush 24 are counter to the rotating direction of the rotary photosensitive member 1 as the charged body.

The sleeve 21 has a carrying function for the magnetic brush 24, a carrying function, and a charging bias application electrode function.

FIG. 9B is a schematic view of the magnetic roller type magnetic brush charging member 2A or the charging device of the above 2).

The magnet roll 22 is rotationally driven at a predetermined peripheral speed by a drive mechanism (not shown) centering on a central core metal 25 that both drives and feeds power. The outer peripheral surface of the magnet roll 22 is covered with a conductive layer 22a as a charging bias applying electrode (power supply surface). The carrier 23 is restrained by the magnetic force of the magnet roll 22 and attached and held as a magnetic brush 24 on the outer peripheral surface of the conductive layer 22a. The magnetic brush 24 is rotatably conveyed in the same direction as the magnet roll 22 rotates, rubs the surface of the rotating photoconductor 1 at the contact nip portion D, and is applied to the central core metal 25 of the magnet roll 22 from the power source E1. By the charging bias, the surface of the rotary photosensitive member 1 as a member to be charged is charged by a contact method. The conductive layer 22a provided on the outer peripheral surface of the magnet roll 22 serves to stably and uniformly supply the charging bias to the magnetic brush 24.

[0031]

As described above, the charging device using the magnetic brush charging member and the image forming apparatus equipped with the charging device are capable of closely contacting the charging member and the member to be charged. Since it is possible to have a peripheral speed difference with respect to the body, the opportunity of contact between the charging member and the body to be charged can be increased, and the charge injection property is very advantageous.

In the magnetic roller type magnetic brush charging member 2A as shown in FIG. 9B, the spike shape of the magnetic brush 24 in the contact nip portion D changes as the magnet roll rotates. Compared to the sleeve type magnetic brush charging member 2 as shown in (a), the charging property is likely to be non-uniform, and charging failure may occur.

The sleeve-type magnetic brush charging member 2 is of a magnetic roller type because the magnetic brush 24 is basically unchanged in the shape of the spikes formed by the rotation of the sleeve 21 and the carrier 23 can be replaced. Charging uniformity is advantageous compared to magnetic brush charging members.

In any case, however, since the carrier 23 is restrained as the magnetic brush 24 by the magnetic force, if the magnetic restraining force acting on the carrier is insufficient, the following problems occur. . That is, (a) a problem caused by the detachment of the carrier 23 from the magnetic brush 24, and (b) a problem caused by the detached carrier 23 adhering to the surface of the body 1 to be charged.

The former problem (a) is that the carrier 23 constituting the magnetic brush 24 escapes from the magnetic restraining force and is detached to adhere to the surface of the body 1 to be charged and carried away, thereby contributing to the charging. The number of carriers 23 of 24 decreases with time, resulting in poor charging.

With regard to the latter problem (b), the harmful effect of the carrier 23 adhering to the surface of the member to be charged, for example, 1) in the image forming apparatus, is adhered to the photosensitive member as the member to be charged. Inhibition of image exposure by the carrier 2) Poor development at the carrier adhesion position on the photoconductor 3) Decrease in developability when the carrier is mixed in the developing device 4) When the carrier is transferred to the transfer material, after the transfer 5) Poor fixing because the carrier is not fixed in the fixing step of 5) There was a case where the carrier which was not transferred was caught between the cleaning blade and the photosensitive member at the cleaning position, resulting in damage to the photosensitive member.

In order to prevent the carrier from being detached from the magnetic brush and the carrier from being attached to the surface of the photosensitive member, the magnetic flux density on the sleeve and its distribution have been generally devised.
However, this does not always correspond to the removal of the carrier and the prevention of the carrier from adhering to the photoreceptor surface.

Therefore, according to the present invention, in the magnetic brush charging device and the image forming apparatus equipped with the charging device, the magnetic particles 23 are substantially detached from the magnetic brush 24 of the magnetic brush charging member 2 and adhered to the body 1 to be charged. The purpose of the present invention is to eliminate problems such as poor charging, harmful effects caused by adhesion of magnetic particles to a body to be charged, and occurrence of defective images in the image forming apparatus.

[0039]

The present invention provides a magnetic brush charging device and an image forming apparatus having the following features.

(1) A magnetic brush charging member in which magnetic particles are restrained by a magnetic force and attached and held as a magnetic brush on a rotatable conductive magnetic particle supporting means including a fixed magnet is provided. The magnetic brush of the brush charging member is brought into contact with the member to be charged and conveyed by the rotation of the magnetic particle supporting means,
In a magnetic brush charging device for applying a voltage to inject and charge an object to be charged through a magnetic brush, in a contact portion between the object to be charged and the magnetic brush, a moving direction of the magnetic particle carrying means and a moving direction of the object to be charged. Is the counter direction, and the position of the charging main pole of the magnetic pole of the magnet is provided on the downstream side with respect to the moving direction of the magnetic particle carrying means from the position closest to the charged body, and in the moving direction of the magnetic particle carrying means. , Charged body
The width of the contact portion between the magnetic brush and the magnetic brush is set to 4 mm or more, and the peak position of the magnetic force Fr in the normal direction on the magnetic particle supporting means is located downstream of the contact portion of the magnetic brush on the charged body in the rotation direction of the charged body. A magnetic brush charging device, characterized in that it is within ± 5 ° from the closest position on the magnetic particle carrying means with respect to the side end position.

[0041]

[0042]

(2) An image forming apparatus that forms an image by an image forming process including a step of charging the image carrier, wherein the charging means of the image carrier is the magnetic brush charging device described in (1). An image forming apparatus characterized by.

[0044] <work for> 1) That is, the peak position in the normal direction of the magnetic force Fr on the magnetic particle bearing section, come in contact of the magnetic brush on the member to be charged
Of the magnet with respect to the downstream end position of the charged body in the rotation direction.
By setting the position within ± 5 ° from the closest position on the conductive particle carrying means, the magnetic particles in the magnetic brush portion near the end position on the downstream side in the rotational direction of the charged body of the contact nip portion between the charged body and the magnetic brush are removed. Since the magnetic force attracted to the magnetic particle supporting means can be efficiently increased, the magnetic particles do not substantially adhere to the charged body, so that the magnetic particles are detached from the magnetic brush, and the magnetic force to the charged body is reduced. It is possible to solve the problem of adverse effects due to particle adhesion.

2) Further, in addition to the above configuration, the present invention
In the moving direction of the magnetic particle supporting means,
The width of the contact part between the electric body and the magnetic brush is especially large, 4 mm or more.
The contact machine between the magnetic brush and the charged object
Since there are many machines, the injection charging property is improved. Moreover also I'm a relative movement direction of the magnetic particle bearing section and the member to be charged to a counter direction, because it can be made large peripheral speed difference with respect to the member to be charged, the magnetic brush member to be charged the it is possible to increase the contact opportunity of contacting the charge injection property is improved, it is possible to improve the charging property, Note
It is advantageous for improving charging property.

[0046] 3) Further, in addition in addition to the above structure, the magnetic
Set the position of the charged main pole of the stone magnetic pole to the closest position to the charged body.
By providing the magnetic brush on the downstream side with respect to the moving direction of the magnetic particle carrying means, excessive retention of the magnetic brush at an upstream side portion of the contact nip between the charged body and the magnetic brush in the moving direction of the magnetic particle carrying means. Therefore, it is possible to prevent charging failure due to the retention of the magnetic brush.

4) Further, in the image forming apparatus using the magnetic brush charging device, detachment of the magnetic particles from the magnetic brush, adverse effects due to the adhesion of the magnetic particles to the member to be charged, and the resulting image defect are caused. The problem of can be solved.

[0048]

DETAILED DESCRIPTION OF THE INVENTION

<Embodiment 1> (FIGS. 1 to 7) (1) Example of image forming apparatus (FIG. 1) FIG. 1 is a diagram showing a transfer type electrophotographic process according to the present invention.
1 is a schematic configuration diagram of an example of a magnetic brush-contact charging type laser beam printer.

Reference numeral 1 denotes a rotary photosensitive drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum or drum) which is an image bearing member as a member to be charged. In this example, O with a diameter of 30 mm
100 mm in the clockwise direction as shown by the arrow a using a PC photoconductor
It is rotationally driven at a process speed (peripheral speed) of / sec. The layer structure of the photoconductor will be described in detail in item (2).

Reference numeral 2 denotes a sleeve-type magnetic brush charging member for uniformly charging the peripheral surface of the photosensitive drum 1 to a predetermined polarity and potential. The magnetic brush charging member 2 will be described in detail in section (3).

The sleeve 21 of the magnetic brush charging member 2
A −700V DC charging bias is applied to the charging bias applying power source E1 so that the outer peripheral surface of the rotary photosensitive drum 1 is uniformly charged to about −700V by charge injection charging.

A laser whose intensity is modulated corresponding to a time-series electric digital pixel signal of target image information output from a laser beam scanner 7 including a laser diode, a polygon mirror, etc. on the charged surface of the rotating photosensitive drum 1. Scanning exposure is performed by the beam 7a, and an electrostatic latent image corresponding to desired image information is formed on the peripheral surface of the rotary photosensitive drum 1.

The electrostatic latent image is developed as a toner image by the reversal developing device 3 using magnetic one-component insulating toner. Reference numeral 3a designates a non-magnetic developing sleeve having a diameter of 16 mm and containing a magnet 3b. The developing sleeve is coated with the above-mentioned negative toner so that the distance from the surface of the photosensitive drum is 300.
While being fixed to μm, the photosensitive drum 1 is rotated at a constant speed and a developing bias voltage is applied to the sleeve 3a from the developing bias applying power source E2. In this example, -500V DC
Voltage, frequency 1800Hz, peak-to-peak voltage 1600V
Using a rectangular AC voltage superimposed on the sleeve 3a
And jumping development is performed between the photosensitive drum 1 and the photosensitive drum 1.
That is, the negatively charged toner carried by the developing sleeve 3a is attached to the image portion of the latent image by an electric field to develop the latent image.

On the other hand, a transfer material 30, which is a recording material, is supplied from a paper feeding portion (not shown), and a medium resistance transfer is performed as a contact transfer means that is brought into contact with the photosensitive drum 1 with a predetermined pressing force. It is introduced into the pressure contact nip portion (transfer portion) T with the roller 4 at a predetermined timing.

A transfer bias application power source E is applied to the transfer roller 4.
A predetermined transfer bias voltage is applied from 3. In this example, a transfer roller 4 having a roller resistance value of 5 × 10 ⁸ Ω was used, and a DC voltage of +2000 V was applied to transfer.

The transfer material 30 introduced into the transfer portion T is nipped and conveyed by the transfer portion T, and the toner images formed and carried on the surface of the rotary photosensitive drum 1 are sequentially charged with electrostatic force and pressing force. Will be transcribed.

The transfer material 30 to which the toner image has been transferred is separated from the surface of the photosensitive drum 1 and is introduced into a fixing device 5 such as a heat fixing system to receive the toner image fixing, and an image formed product (print, copy). Is discharged outside the device.

The surface of the photosensitive drum 1 after the transfer of the toner image to the transfer material 30 is cleaned by the cleaning device 6 to remove adhered contaminants such as residual toner, and is repeatedly used for image formation.

The image forming apparatus of this embodiment includes a photosensitive drum 1, a magnetic brush charging member 2, a developing device 3, and a cleaning device 6.
The four process devices are collectively referred to as a process cartridge 10 which can be attached to and detached from the image forming apparatus main body. Reference numeral 9 is a cartridge housing in which the above-mentioned four process devices 1, 2, 3, and 6 are incorporated in a predetermined manner. Reference numeral 8 denotes a process cartridge insertion / removal guide / holding portion on the image forming apparatus main body side.

In a state where the process cartridge 10 is mounted in a predetermined manner on the image forming apparatus main body, the process cartridge 10 side and the image forming apparatus main body side are mechanically
The mutual coupling state is electrically established, and the lower surface of the photosensitive drum 1 on the side of the process cartridge 10 is brought into a predetermined contact with the transfer roller 4 on the side of the main body of the image forming apparatus, whereby the image forming can be executed.

The process cartridge 10 is one in which a charging unit, a developing unit or a cleaning unit, and an electrophotographic photosensitive member are integrated into a cartridge, and the cartridge can be attached to and detached from the main body of the image forming apparatus. . In addition, at least one electrophotographic photosensitive member including a charging unit, a developing unit, and a cleaning unit is integrally formed into a cartridge, which is attachable to and detachable from the main body of the image forming apparatus.
Further, it means that at least the developing means and the electrophotographic photosensitive member are integrally made into a cartridge so as to be attachable to and detachable from the main body of the image forming apparatus.

(2) Photoreceptor 1, Injection Charging a) Regarding Photoreceptor 1 (FIG. 2) FIG. 2 is a schematic diagram of the layer structure of the photoreceptor 1 as the member to be charged used in this example.

The photoreceptor 1 used in this example is a negatively charged OPC photoreceptor having a charge injection function on its surface. The following 1st to 5th are placed on a drum base 11 made of aluminum having a diameter of 30 mm.
5 functional layers 12 to 16 are sequentially provided from the bottom.

The first layer is the undercoat layer 12, which is provided for smoothing the defects on the outer peripheral surface of the aluminum drum substrate 11 and for preventing the generation of moire due to the reflection of laser exposure. Of the conductive layer.

The second layer is the positive charge injection preventing layer 13, which plays a role of preventing the positive charges injected from the aluminum base 11 from canceling out the negative charges charged on the surface of the photosensitive member, and the amylan resin and methoxymethyl. It is a medium resistance layer having a thickness of about 1 μm whose resistance is adjusted to about 10 ⁶ Ωcm by means of nylon.

The third layer is the charge generation layer 14, which is a layer having a thickness of about 0.3 μm in which a disazo pigment is dispersed in a resin, and positive and negative charge pairs are generated by laser exposure.

The fourth layer is the charge transport layer 15, which is a layer having a thickness of about 20 μm in which hydrazone is dispersed in polycarbonate resin, and is a P-type semiconductor. Therefore, the negative charges charged on the surface of the photoconductor cannot move in this layer, and only the positive charges generated in the charge generation layer can be transported to the surface of the photoconductor.

The fifth layer is the charge injection layer 16, which is made of a photocurable acrylic resin and ultrafine conductive particles (conductive filler).
16a is a coating layer of a material in which SnO ₂ is dispersed.
Specifically, antimony-doped SnO ₂ particles with a low resistance of about 0.03 μm are added to the resin in an amount of 70%.
It is a coating layer of a material in which weight percent is dispersed. The coating liquid thus prepared was applied by dipping to a thickness of about 3 μm to form a charge injection layer.

The volume resistance of the charge injection layer 16 which is the surface layer of the photoreceptor is 10 ⁹ to 10 ^{14 in} order to perform charge injection charging.
It is preferable to have a low resistance layer of Ω · cm, and in this example, the volume resistance of the charge injection layer 16 is 1 × 10 ¹³ Ω · cm.
And

The volume resistivity of the charge injection layer 16 is about 6 to 7 when the charge injection layer is formed on a conductive sheet (aluminum sheet).
It was applied at a voltage of 100 V by applying RESISTIVITY CELL 16008A to a high resistance meter 4329A manufactured by Yokogawa Hewlett-Packard Company.

The charge injection layer 16 intentionally creates injection sites for uniformly charging the surface by directly injecting charges from the magnetic brush charging device 2. However, the charges of the latent image flow on the surface. The surface resistance of the charge injection layer 16 needs to be 1 × 10 ⁸ Ω or more so as not to exist.

The surface resistance of the charge injection layer 16 is obtained by applying the charge injection layer on an insulating sheet and applying the charge injection layer to Yokogawa Hewlett
It is measured with a high resistance meter 4329A manufactured by Packard at an applied voltage of 100V.

B) Injection charging (FIG. 3) The principle of charging by using the above-mentioned photoreceptor 1 and the contact charging member will be described.

The charge injection charging in this example is a contact charging member having a medium resistance (magnetic brush charging member) for injecting charges on the surface of the photoconductor having a surface resistance of medium resistance. Instead of injecting charges into the trap potential, this is a method of charging the conductive particles 16a of the charge injection layer 16 with charges.

By applying a desired voltage to the magnetic brush charging member 2 at the time of charging, charges are injected into the charge injection layer 16 so that the surface of the photoconductor as the charged body is finally the magnetic brush 24.
Is charged (charged) to the same potential as.

Specifically, as shown in the model diagram and equivalent circuit diagram of FIGS. 3A and 3B, the photoconductor 1 is composed of the charge transport layer 1
5 can be regarded as a dielectric, and the aluminum drum substrate 11 and the conductive particles 16a (SnO ₂ ) in the charge injection layer 16 can be regarded as a parallel assembly of minute capacitors. It is based on the theory of charging a minute capacitor with a contact charging member.

At this time, the conductive particles 16a are electrically independent from each other and form a kind of minute float electrode. For this reason, the surface of the photoconductor looks macroscopically charged and charged to a uniform potential, but in reality, a large number of minute charged conductive particles 16a cover the photoconductor surface. Has become. Therefore, even if image exposure is performed with a laser, each conductive particle 16a is electrically independent, so that it is possible to hold an electrostatic latent image.

(3) Magnetic Brush Charging Device (FIG. 4) a) Magnetic Brush Charging Member 2 FIG. 4 (a) is a structural model diagram of the magnetic brush charging member 2 or the magnetic brush charging device of the present embodiment. It is of a sleeve type similar to that of 9 (a).

That is, 21 is a means for supporting magnetic particles,
It is a non-magnetic conductive sleeve (charging sleeve) made of aluminum or the like.

Reference numeral 22 is a magnet roll which is inserted and arranged in the sleeve 21 as a magnetic field generating means. N1
S1, N2 and S2 are magnetized portions of the roll. The magnet roll 22 is a non-rotating fixed member, and the outer circumference of the magnet roll 22 is concentrically driven by the sleeve 21 to rotate clockwise at a predetermined peripheral speed by a drive mechanism (not shown) in the clockwise direction shown by the arrow b. .

Reference numeral 23 is a conductive magnetic particle (carrier), which is bound to the outer peripheral surface of the sleeve 21 by the magnetic force of the magnet roll 22 inside the sleeve to be attached and held as a magnetic brush (conductive magnetic brush) 24. . Carrier 2
Reference numeral 3 forms a magnetic spike on the outer surface of the sleeve 21 due to the magnetic restraining force of the magnet roll 22, and these gather to form a brush shape.

A charging bias applying power source E1 is applied to the sleeve 21.
A charging bias is applied from (FIGS. 1 and 3). If the charging bias is too high, leakage occurs between the magnetic brush 24 and the photosensitive drum 1, and if it is too low, the charging potential becomes low and the developing contrast becomes small, so that the image becomes poor. Therefore, the charging voltage is preferably 100V to 1500V.

Reference numeral 26 is a magnetic brush layer thickness regulating blade (regulating blade) facing the sleeve 21 with a small gap,
The sleeve 21 regulates the thickness of the magnetic brush layer that is supported and conveyed to the charging area.

D is a contact nip portion (charging nip portion) formed by bringing the magnetic brush 24 into contact with the surface of the photosensitive drum 1.

The photosensitive drum 1 is rotationally driven in the clockwise direction indicated by the arrow a at a predetermined peripheral speed by a drive mechanism (not shown), and in the contact nip portion D, the rotational direction of the sleeve 21 and the magnetic brush 24 associated therewith. The rotational conveyance direction of is a counter direction with respect to the rotation direction of the photosensitive drum 1.

When the rotating and conveying direction of the magnetic brush 24 in the contact nip portion D is in the forward direction with respect to the rotating direction of the photosensitive drum 1, compared with the counter direction, the carrier 23 forming the magnetic brush 24 has the photosensitive drum. 1 tends to adhere. Further, in order to increase the relative speed between the sleeve 21 and the photosensitive drum 1, that is, the peripheral speed difference, the rotation speed of the sleeve 21 becomes high. Therefore, the carrier 23 is likely to be scattered and the rotation torque is increased,
The equipment cost is also high.

In the counter direction, the carrier adhesion to the photosensitive drum 1 can be suppressed, and the peripheral speed difference can be increased at a low speed. Therefore, the number of contact between the carrier and the photosensitive drum can be increased, so that the charging property becomes good.

The reason why the counter direction is better for attaching the carrier to the photosensitive drum has not been clarified yet, but the action of stripping the carrier on the photosensitive drum and pulling it back by the rubbing of the magnetic brush 24 works. I believe.

When the rotation of the sleeve 21 is stopped, the shape of the magnetic brush 24 remains uncharged and appears in the image.

For this reason, the rotating and conveying direction of the magnetic brush 24 is preferably the counter direction.

L is a virtual straight line connecting the center of rotation of the sleeve 21 and the center of rotation of the photosensitive drum 1, and indicates the facing center of the sleeve 21 and the photosensitive drum 1. At this portion, the sleeve 21 and the photosensitive drum 1 are It is the closest position.

H is the distance at the closest position between the sleeve 21 and the photosensitive drum 1. The minimum distance h between the sleeve 21 and the photosensitive drum 1 is preferably 0.15 to 2.0 mm,
3 to 1.0 mm is more preferable. If the interval h is too small, leakage easily occurs, it becomes difficult to uniformly regulate the thickness of the magnetic brush layer by the regulation blade 26, uneven charging is likely to occur, and a sufficient carrier amount is applied to the contact nip. It becomes impossible to supply it to the portion D, so that charging failure is likely to occur. On the other hand, if the interval h is too large, the thickness of the magnetic brush layer must be increased, and the magnetic binding force of the surface layer portion of the magnetic brush 24 becomes weak, so that the magnetic brush layer becomes rough and uneven charging occurs. Prone to occur,
In addition, the charge injection property is also lowered, and charging failure is likely to occur.

In the injection charging, the photosensitive member is charged by the charge injection caused by the contact between the carrier 23 forming the magnetic brush 24 and the photosensitive member, so that the carrier 23 is smoothly moved in the contact nip portion D. It is necessary to sufficiently contact the carrier and the photoconductor.

In order to improve the charge injection property, the volume ratio Mc of the carrier in the contact nip portion D, that is, the volume ratio of the carrier in the contact nip portion space is preferably 30 to 80%.

Here, the volume ratio Mc is based on the following equation.

Mc = (M / h) × (1 / ρ) × 100, where M is the carrier amount per unit area of the sleeve (in the non-brushing state) [g / cm ² ] and h is the charged area space. Is the true density [g / cm ³ ] of the carrier.

If the volume ratio Mc becomes too small,
The contact between the carrier and the photoconductor is likely to be insufficient, the contact nip portion D becomes non-uniform, and the chance of contact between the carrier and the photoconductor is reduced, so that the injection charging capability is lowered and the charging failure is likely to occur.

On the other hand, if the volume ratio Mc becomes too large, the carrier tends to stay in the contact nip portion D, which hinders the smooth movement of the carrier in the contact nip portion D, thus making the contact nip portion unsatisfactory. The chargeability becomes low due to the uniformity and the chance of contact between the carrier and the photoreceptor is reduced, and charging failure is likely to occur. Further, when the smooth movement of the carrier is obstructed and the movement of the carrier in contact with the surface of the photoconductor is impaired, the carrier itself is charged up, which hinders the injection of electric charges and easily causes charging failure. Here, the charge-up means a state in which the carrier in contact with the surface of the photoconductor charges the photoconductor to store a reverse charge and the actual applied voltage decreases.

The above-mentioned volume ratio Mc is the gap between the sleeve 21 and the regulating blade 26, the sleeve 21 and the photosensitive drum 1.
It can be set to a required value by correlatively setting the gap h, the true density of carriers, and the like.

Further, in order to improve the charge injection property, it is preferable that the width of the contact nip portion D is 2 mm or more, preferably 4 m.
More preferably, it is m or more. If the width of the contact nip portion D is too small, the chances of contact between the carrier and the photosensitive member are reduced, the charging becomes uneven, and the injection charging ability is deteriorated, so that charging failure is likely to occur.

In this example, the contact nip portion D is formed so that the charging is uniform, the injection charging ability is sufficient, and the charging property is improved.
The width of the contact nip is about 2 mm downstream from the closest position to the sleeve rotation direction, about 3 mm on the upstream side, and about 5 mm in total.
Set to.

B) Carrier 23 Carrier 2 which is magnetic particles constituting the magnetic brush 24
As for 3, a resin and a magnetic powder such as magnetite are kneaded and molded into particles, or a mixture of this with conductive carbon or the like for adjusting the resistance value, or sintered magnetite, ferrite, or these Those whose resistance value has been adjusted by reduction or oxidation, ・ Coating or N with the above-mentioned magnetic particles whose resistance has been adjusted (such as those in which carbon is dispersed in phenol resin)
It is considered that the resistance value is set to an appropriate value by plating with a metal such as i. In order to reduce damage to the photosensitive drum 1, it is desirable that the carrier 23 be spherically processed.

If the resistance value of these carriers 23 is too high, electric charges cannot be evenly injected into the photosensitive drum, resulting in a fog image due to minute charging failure. If it is too low, when there are pinholes on the surface of the photosensitive drum, current concentrates on the pinholes, the charging voltage drops, and the surface of the photosensitive drum cannot be charged, resulting in a charging nip-shaped charging failure.

Therefore, as the resistance value of the carrier 23,
It is preferably 1 × 10 ⁵ to 1 × 10 ⁸ Ω · cm. The resistance value of the carrier is the metal cell (bottom area 228
mm ² ), after putting 2 g of the carrier 23 into it, 6.6 kg / c
The measurement was performed by applying a weight of m ² and applying a voltage of 1 to 1000 V. For example, 100 V was applied, and it was defined by being normalized from the measured current flowing in this system.

It is also possible to improve the chargeability by mixing and using a plurality of types of carriers.

If the particle size of the carrier is too small, the magnetic binding force becomes small, and the carrier adheres to the surface of the photosensitive drum. On the other hand, if it is too large, the contact area with the photosensitive drum is reduced and charging failure increases. Therefore, the average particle size of the carrier is preferably about 5 to 50 μm from the viewpoint of chargeability and magnetic retention. The average particle size of the carrier was determined by randomly extracting 100 or more particles with an optical microscope or a scanning electron microscope, calculating the volume particle size distribution with the maximum chord length in the horizontal direction, and calculating the 50% average particle size.

Regarding the magnetic characteristics of the carrier 23, it is better to increase the magnetic force in order to prevent the carrier from adhering to the photosensitive drum, and the saturation magnetization is 30 (A · m ² / kg) or more,
More preferably, it is 50 (A · m ² / kg) or more.

In practice, the carrier 23 used in this example has an average particle size of 30 μm, a spherical shape, and a resistance value of 1 × 10 ^6.
Ω · cm, saturation magnetization was 64 (A · m ² / kg). The true density of the carrier 23 is about 5.8 g / cm ^3.
The magnetic permeability was about 5.0.

The saturation magnetization and the magnetic permeability were measured by using a vibrating sample magnetometer (trade name: VSM-P-1-type manufactured by Toei Industry Co., Ltd.) to magnetize magnetic particles placed in a magnetic field of maximum 10,000 oersteds. Was measured and determined based on the hysteresis curve drawn on the recording paper.

C) Magnet roll 22 (FIGS. 4 to 6) Regarding the magnet roll 22 used in this example, FIGS.
Will be described in detail. FIG. 4B is a diagram for explaining the positions of the contact nip portion D and the magnetic pole configuration.

L is an imaginary straight line connecting the center of rotation of the sleeve 21 and the center of rotation of the photosensitive drum 1, and indicates the opposing center of the sleeve 21 and the photosensitive drum 1. At this portion, the sleeve 21 and the photosensitive drum 1 are separated from each other. It is the closest position.

H is the distance at the closest position between the sleeve 21 and the photosensitive drum 1.

P is the closest position on the sleeve 21 to the photosensitive drum 1, and Q is the closest position on the photosensitive drum 1.

S is a sleeve 21 corresponding to the main charging pole S1.
In the upper position, θ is an angle formed by the virtual straight line L connecting the rotation center of the sleeve 21 and the charging main pole S1. That is, the main charging pole S1 is located downstream of the closest position P to the photosensitive drum 1 in the rotation direction of the sleeve 21.

A is the position of the contact nip portion D between the photosensitive drum 1 and the magnetic brush 24 on the photosensitive drum 1 on the downstream side in the photosensitive drum rotation direction.

L1 is an imaginary straight line connecting the downstream end position A of the nip portion on the photosensitive drum 1 and the rotation center of the sleeve 21.

B is the closest position on the sleeve 21 to the downstream end position A of the nip portion on the photosensitive drum 1, and is the position where the virtual straight line L1 and the surface of the sleeve 21 intersect.

When the position of the main charging pole S1 is located upstream of the closest position P to the photosensitive drum 1 with respect to the sleeve rotation direction, the magnetic brush stands on the upstream side of the nip portion and is conveyed by the rotation of the sleeve. The function of stopping the carried carrier from trying to pass through the closest nip part works,
The carrier easily stays in the nip portion. If the carrier stays in the nip portion, the contact nip portion D becomes non-uniform, or the chance of contact between the carrier and the photosensitive member is reduced, so that the injection charging ability is deteriorated and charging failure is likely to occur. In addition, the carrier itself is likely to be charged up, which hinders the injection of electric charges and easily causes a charging failure.

On the other hand, when the position of the main charging pole S1 is located downstream of the closest position P to the photosensitive drum 1 in the sleeve rotation direction, the distance between the sleeve 21 and the photosensitive drum 1 is the narrowest, and the carrier can be conveyed. Since the magnetic brush is not erected up to the most severe position P / Q, the carrier is conveyed smoothly, and the magnetic brush erears after the space passes through the position N / P closest to the nip portion to expand the space. The carrier of the magnetic brush is not hindered by the rising of the magnetic brush.

Therefore, the carrier does not stay,
The carrier in the nip portion D can move smoothly, the number of contact between the photoconductor and the carrier not charged up increases, and the charging failure does not occur.

The position of the main charging pole S1 is the photosensitive drum 1.
If the distance is too far from the closest position P to the carrier, the magnetic force for attracting the carrier in the nip portion toward the nip exit direction becomes weak, so that the carrier transportability may be slightly inferior.

The position of the main charging pole S1 is 0 ° downstream of the position P closest to the photosensitive drum 1 in the sleeve rotation direction.
-30 ° (θ) is preferable, and 0 ° -15 ° is more preferable.

FIG. 5 is a diagram for explaining the magnetic force Fr on the sleeve 21, where F is the magnetic force on the sleeve 21 and F
r represents a magnetic force in the normal direction of the sleeve surface on the sleeve 21, and Fθ represents a magnetic force in the tangential direction of the sleeve surface on the sleeve 21.

Here, the magnetic force Fr is the following proportional expression Fr∝ {B2 (r) -B2 (r + Δr)} / Δr, where B2 (r) = B2r (r) + B2θ (r) B2 (r + Δr) = B2r ( r + Δr) + B2θ (r +
Δr). Therefore, if {B2 (r) −B2 (r + Δr)} / Δr is obtained, the relative magnitude of the magnetic force Fr can be known, and the distribution form of the magnetic force Fr, the peak position of the magnetic force Fr, etc. can be known. be able to.

If Δr is fixed, Fr∝ {B2 (r) -B2 (r + Δr)} Next to {B2 (r) -B2 (r + Δr)} Will be required.

In practice, r is the radius of the magnetic particle carrying means (charging sleeve), Δr is 0.5 mm, and the magnetic flux densities Br (r), Br (r + Δr), Bθ (r), Bθ (r
+ Δr) was measured using a Gauss meter manufactured by Bell Co. as described later, and {B2 (r) −B2 (r + Δr)} was calculated and the relative value of the magnetic force Fr was calculated.

Here, Br (r) is the magnetic flux density [Gauss] in the vertical direction on the magnetic particle supporting means, Br (r + Δ).
r) is the magnetic flux density in the vertical direction [Gauss] at 0.5 mm on the magnetic particle supporting means, and Bθ (r) is the horizontal magnetic flux density [Gauss] on the magnetic particle supporting means, Bθ (r +
Δr) is the magnetic flux density [Gauss] in the horizontal direction at 0.5 mm on the magnetic particle supporting means.

Whether or not the carrier 23 separates from the magnetic brush 24 and adheres to the surface of the photosensitive drum 1, that is, whether or not carrier adhesion occurs, is not directly related to the magnetic flux density on the sleeve 21, but the carrier to the sleeve. It is related to the magnitude of the magnetic force that attracts it. This will be described with reference to FIGS.

The carrier 23 is detached from the magnetic brush 24 by a balance between the magnetic force for restraining the carrier to the sleeve and the Coulomb force, the mirroring force, the centrifugal force, etc. for peeling the carrier from the sleeve. By increasing the magnetic force that attracts the carrier to the sleeve at the contact nip portion D, it is possible to prevent the carrier from adhering to the drum.

Then, at what position in the contact nip portion D it is effective to increase the magnetic force, there is a balance with the Coulomb force, the mirror image force, the centrifugal force, etc. It is considered that the magnetic force in the area up to the contact position and the downstream end position in the drum rotation direction is related, and particularly the magnetic force in the downstream end position A in the drum rotation direction on the photosensitive drum is deeply related.

That is, the carrier at the downstream end position A may be attracted to the sleeve 21, and it is effective to increase the magnetic force Fr at the downstream end position A when viewed from the sleeve 21.

Further, the magnetic flux density decreases exponentially with distance from the sleeve, and the magnetic force further decreases with the magnitude of its square.

Therefore, when the photosensitive drum 1 and the sleeve 21 are close to each other, the carrier on the drum can be magnetically restrained to the sleeve relatively easily, but when the distance between the drum and the sleeve is large. It becomes difficult to magnetically restrain the carrier on the drum to the sleeve. In particular, the downstream end position A is the position farthest from the sleeve in the contact nip D, and in order to increase the magnetic force on the sleeve at position A, the magnetic pole configuration of the magnet roll 22 must be considered in advance. I have to.

That is, it can be achieved by setting the peak position of the magnetic force Fr in the normal direction on the sleeve 21 to be near the position B on the sleeve closest to the downstream end position A.

FIG. 6 is a diagram for explaining the distribution form of the magnetic flux density Br of the charging main pole S1 and the distribution form of the magnetic force Fr. In the horizontal direction, the position in the circumferential direction of the charging sleeve is shown as an angle, and in the vertical direction. direction indicates the magnitude of the magnetic force Fr on the strip conductive sleeve 21, or the magnitude of the magnetic flux density Br of the charging sleeve 21.

In this example, there are two peaks of the magnetic force Fr in the main charging pole S1, but the peak on the upstream side in the sleeve rotation direction is called F1 and the peak on the downstream side is called F2. α1 is the angle between the main charging pole S1 and the peak F1 of the magnetic force Fr.

For example, the outer diameter of the charging sleeve 21 is 16 m.
m, the outer diameter of the photosensitive drum 1 is 30 mm, the distance h between the photosensitive drum 1 and the sleeve 21 is 0.5 mm, and the width of the contact nip D is 2 mm on the upstream side of the photosensitive drum 1 and 3 mm on the downstream side. The angle between position Q and position A above is about 21.5
°, the angle between position P and position B on the sleeve is about 18.7 °
Becomes Then, the charging main pole S1 and the peak F of the magnetic force Fr
The angle α1 with respect to 1 is 25 °, and the position S of the charging main pole S1 is
Is located 6 ° downstream of the closest position P to the photosensitive drum 1 with respect to the sleeve rotation direction, the angle between the position P on the sleeve and the peak position F1 of the magnetic force Fr is “25-6 =
19 ° ”, which is almost the same position as the closest position B to the downstream end position A of the nip portion on the photosensitive drum 1.

The peak position F1 of the magnetic force Fr is preferably in the vicinity of the position B on the sleeve. Specifically ± 5 °
It is preferably within ± 3 °, more preferably within ± 3 °.

In particular, in order to reduce the size and cost of the magnetic brush charging device, the diameter of the charging sleeve 21 is reduced, and the contact nip portion D is enlarged to improve the charge injection property. When the width on the downstream side is increased, the position of the charging main pole S1 and the magnetic force F are used to prevent carrier adhesion.
Although intentionally increasing the peak position of r considerably has the great effect as described above, there has been a limit to downsizing and cost reduction of the magnetic brush charging device because such a device has not been conventionally devised. It was As will be described later, according to this example, it is possible to reduce the size and cost of the magnetic brush charging device while preventing carrier adhesion.

FIG. 7 is a diagram for explaining the method of measuring the magnetic flux density. This figure shows that the charging sleeve 21 or the sleeve 0.
This is for explaining the method of measuring the magnetic flux density Br in the normal direction and the magnetic flux density Bθ in the tangential direction at a position of 5 mm, and was measured using a Gauss meter model 9903 manufactured by Bell Co.

The sleeve 21 is fixed horizontally, and the magnet roll (magnet) 22 in the sleeve is rotatably attached.

42 is a two-axis probe (Bell YOA99-1
802) and is fixed so that the center of the sleeve 21 and the center of the probe 42 are substantially on the same horizontal plane with a slight distance from the sleeve 21, and is connected to the Gauss meter 41. The magnetic flux density in the normal direction at a position of 0.5 mm is measured.

The sleeve 21 and the magnet roll 22 are substantially concentric circles, and it can be considered that the distance between the sleeve 21 and the magnet roll 22 is equal everywhere.

Therefore, by rotating the magnet roll 22, the sleeve 21 or the sleeve 0.5 is rotated by 0.5.
The magnetic flux density Br at the position of mm in the normal direction can be measured in all circumferential directions.

Since the magnet roll 22 is rotated in the direction of the arrow, for example, the regulation pole N1 rather than the charging main pole S1 is used.
The angle of becomes a large value. That is, the measurement is performed in the direction in which the angle increases on the upstream side with respect to the moving direction b of the sleeve in FIGS. 1 and 4.

(4) Experimental Example In this example, the peripheral speed of the photosensitive drum 1 is 100 mm / sec, the outer diameter is 30 mm, and the peripheral speed of the charging sleeve 21 is 150 mm /.
sec, the outer diameter of the sleeve 21 was 16 mm. The rotating direction of the sleeve 21 was counter to the photosensitive drum 1. The distance h between the photosensitive drum 1 and the sleeve 21 was 0.5 mm. The position of the main charging pole S1 is the photosensitive drum 1.
And 6 ° (−6 °) downstream of the closest position P with respect to the sleeve rotation direction. At this time, on the sleeve surface of the charging main pole S1 which is a magnet fixed in the sleeve 21,
The peak value of the magnetic flux density in the direction normal to the sleeve surface was 950 × 10 ⁻⁴ T (Tesla). Magnetic brush 24
Carrier amount is about 15 g, the longitudinal width of the magnetic brush 24 is 210 mm, the thickness of the coat layer of the magnetic brush 24 on the charging sleeve 21 is about 1 mm, and the width of the contact nip D is about 2 mm on the upstream side. Width about 3mm on the downstream side, width about 5m overall
m. Table 1 shows the results obtained with respect to carrier adhesion and chargeability.

Further, as the magnet roll 22, the "roll A" in which the angle α1 between the main charging pole S1 and the peak F1 of the magnetic force Fr shown in FIG. 6 is 25 °, and the magnetic flux density of the main charging pole S1 is 940. × 10 ^-4 T (Tesla), charging main pole S1
Results obtained for carrier adhesion and chargeability when "Roll B" having an angle α1 of 5 ° with the peak F1 of the magnetic force Fr and various changes were made to the main charging pole position and the peak position of the magnetic force Fr. Table 1 shows (Experimental examples 1-1 to 1-6).
Shown in.

[0148]

[Table 1] In Table 1, the meanings of the symbols are as follows.

Regarding evaluation of "carrier adhesion": Very good prevention of "carrier adhesion" △: Good prevention of "carrier adhesion" X: Poor prevention of "carrier adhesion" ○: Evaluation of "transportability": Carrier No retention, very good transportability Δ: Carrier retention is practically no problem, good transportability x: Carrier retention, poor transportability As can be seen from Table 1, Experimental Example 1- 1, 1-2, 1
As shown in -6, if the peak position of the magnetic force Fr is near the closest position B to the downstream end position A of the nip portion on the photosensitive drum 1 (within ± 3 ° in this example), carrier adhesion Was hardly generated, and the results were good, but Experimental Examples 1-3 to 1-5
As shown in (3), when it was located at a position away from the closest position B, carrier adhesion occurred and it was defective.

If the position of the main charging pole S1 is upstream of the closest position P to the photosensitive drum 1 with respect to the sleeve rotation direction, retention of carriers occurs on the upstream side of the nip portion, resulting in poor charging. However, when it was on the downstream side, there was no retention of carriers, the transportability was very good, the chargeability was good, and the image was good.

At the closest position P, retention of the carrier was practically no problem, the transportability was good, the chargeability was relatively good, and the image was good.

By thus disposing the peak position of the magnetic force Fr in the vicinity of the closest position B to the downstream end position A of the nip portion on the photosensitive drum 1, it is possible to prevent the carrier from adhering to the drum. You can

Further, by utilizing the deviation between the position of the main charging pole S1 and the peak position of the magnetic force Fr as described above, the peak position of the magnetic force Fr can be adjusted to the downstream end position of the nip portion on the photosensitive drum 1. By disposing the carrier in the vicinity of the closest position B to A, the carrier is prevented from adhering to the drum, and the position of the charging main pole S1 is located downstream of the closest position P to the photosensitive drum 1 in the sleeve rotation direction. By arranging it on the side, it is possible to obtain a good image by improving carrier property without carrier retention and good chargeability, and satisfying both carrier adhesion prevention and charging failure prevention. Will be able to.

In particular, in order to reduce the size and cost of the magnetic brush charging device as in this example, the charging sleeve 21 is reduced in diameter and the contact nip portion D is enlarged in order to improve the charge injection property. When the width of the photosensitive drum 1 on the downstream side is increased, intentionally increasing the position of the charging main pole S1 and the peak position of the magnetic force Fr considerably large in order to prevent carrier adhesion, as described above. However, since such a device has not been conventionally made, there is a limit to downsizing and cost reduction of the magnetic brush charging device. According to this example, downsizing and cost reduction of the magnetic brush charging device can be achieved while preventing carrier adhesion.

<Embodiment 2> (FIG. 8) This embodiment is an application example of a so-called cleanerless system to an image forming apparatus. FIG. 8 is a schematic configuration diagram of an example of the image forming apparatus.

This image forming apparatus is different from the image forming apparatus shown in FIG. 1 in that the cleaning device 6 is omitted, the two-component magnetic brush developing device 3A is used as the developing device, and the magnetic brush charging device is set. The laser beam printer uses the transfer type electrophotographic process and has the same configuration as that of the image forming apparatus in FIG. 1 except that it is slightly different and not the process cartridge system, and thus the repetitive description will be omitted .

In the case of such an image forming apparatus of the cleanerless system, the transfer residual toner remaining on the surface of the photosensitive drum 1 after the toner image is transferred from the rotary photosensitive drum 1 to the transfer material 30 reaches the developing device 3A, which is so-called simultaneous development. By the cleaning action, the toner is collected in the developing device (developing device that also serves as cleaning). The image forming apparatus of the cleanerless system can be downsized and reduced in cost by omitting a dedicated cleaning device.

A) Developing Device 3A The developing device 3A in this image forming apparatus is a developing device using a two-component magnetic brush contact developing method which has been widely used conventionally. The developer used is a two-component developer consisting of a non-magnetic toner and a magnetic carrier, and the toner particles have a weight ratio of titanium oxide having an average particle size of 20 nm to negatively charged toner having an average particle size of 6 μm produced by a polymerization method. A magnetic carrier having a saturation magnetization of 66 (A · m ² / kg) and an average particle size of 35 μm was used as the carrier. A mixture of this toner and a carrier in a weight ratio of 6:94 was used as a developer.

Reference numeral 31 is a non-magnetic developing sleeve having a diameter of 16 mm, which encloses a magnet roll 32 fixedly arranged therein, and is driven in the forward direction at the same speed as the photosensitive drum 1 by a driving mechanism (not shown), that is, as shown by the arrow c. It is rotated counterclockwise as shown.

The developing sleeve 31 is coated with the above-mentioned developer so that the closest distance to the surface of the photosensitive drum 1 is 0.5 mm.
And is set so that development can be performed in a state where the developer is in contact with the photosensitive drum 1.

A developing bias applying power source E is applied to the sleeve 31.
A developing bias voltage is applied from 2. In this example, -50
A direct current voltage of 0 V and a rectangular alternating voltage having a frequency of 2000 Hz and a peak-to-peak voltage of 1500 V were superimposed and applied.

B) Magnetic Brush Charging Device 2 The magnetic brush charging device 2 used in this example is different from the one in the first embodiment only in the condition for applying the charging bias to the magnetic brush charging member, but is different in configuration. Is the same as that of the first embodiment, and thus the repetitive description will be omitted.

That is, in this example, a DC bias superimposed with an AC voltage was used as the charging bias for the magnetic brush charging member.

When only the DC voltage is used as the charging bias, a good charging property is initially obtained, but the image forming apparatus of the cleanerless system does not have a dedicated cleaning device like the image forming apparatus of this embodiment. In the case of, when the image formation is repeatedly performed (during durability), the transfer residual toner cannot be sufficiently collected in the magnetic brush charging member,
In some cases, charging failure may occur or image failure may occur.

However, when a DC voltage superimposed with an AC voltage is used as the charging bias, the transfer residual toner can be sufficiently collected by the magnetic brush charging member.
It is possible to improve the charging property and the image property.

The reason why the transfer residual toner can be sufficiently collected by the AC voltage is that positive and negative voltages are applied. Therefore, both the positively charged toner and the negatively charged toner are collected. It is considered possible. Further, when the AC voltage is superposed, the charging property can be improved even if the transfer residual toner is mixed in the magnetic brush charging member. The reason for this is considered to be that the carrier vibrates and actively moves due to the action of the AC voltage, so that the chances of contact with the photoconductor increase.

If the frequency of the AC voltage is too low,
Frequency unevenness appears and charging unevenness occurs. Too high,
The effect is diminished because it approaches the DC voltage. Therefore, the frequency is preferably 400 peak Hz to 4000 Hz. If the peak-to-peak voltage (Vpp, amplitude) of the AC voltage is too low, it approaches the DC voltage, and the effect is weakened. If it is too high, a leak may occur between the photosensitive drum and the carrier and the carrier may be attached. Therefore, the peak-to-peak voltage is 50-
5000V is preferable.

In this example, the charging sleeve 21 has -700V.
DC voltage, frequency 1000Hz, peak-to-peak voltage 80
A rectangular alternating voltage of 0 V was applied.

In this example, as the magnet roll 22, the "roll A" and "roll B" used in the first embodiment and the magnetic flux density of the charging main pole S1 are 950 × 10 ^-4 T.
In (Tesla), using the "roll C" in which the angle α1 between the charging main pole S1 and the peak F1 of the magnetic force Fr is 29 °, the charging main pole S1
The magnetic flux density of 1 is 940 × 10 ⁻⁴ T (Tesla), and the angle α1 between the main charging pole S1 and the peak F1 of the magnetic force Fr is 22 °.
Table 2 shows the results obtained with respect to carrier adhesion and chargeability when various positions of the charging main pole and the peak position of the magnetic force Fr were variously changed using "Roll D" of Example 2 (Experimental Example 2).
-1 to 2-19).

[0170]

[Table 2] In Table 2, the meanings of the symbols are as follows.

Regarding evaluation of "carrier adhesion": Very good prevention of "carrier adhesion" △: Good prevention of "carrier adhesion" X: Poor prevention of "carrier adhesion" ○: Evaluation of "transportability": Carrier No retention, very good transportability Δ: Carrier retention is practically no problem, good transportability ×: Carrier retention, poor transportability Regarding evaluation of "chargeability" ○: Very good chargeability Good: Fair: Chargeability is relatively good X: Poor chargeability Regarding evaluation of "ghost" O: No ghost, very good △: Some ghost, but practically no problem X: Ghost, bad Note) “Ghost” is a phenomenon that causes image unevenness in a pattern with a certain history.

As shown in Table 2, if the peak position F1 of the magnetic force Fr is within ± 5 ° in the vicinity of the closest position B to the end position A on the downstream side of the nip part on the photosensitive drum 1, carrier adhesion will not occur. Very good with almost no occurrence, especially ± 3 ° near position B
If it was within the range, it was very good, but when it was at a position (± 6 ° or more) away from the closest position B, carrier adhesion occurred and it was poor.

If the position of the main charging pole S1 is on the upstream side of the closest position P to the photosensitive drum 1 with respect to the sleeve rotation direction, carrier accumulation occurs on the upstream side of the nip portion, resulting in poor charging. Occurs, and a ghost image results in an image defect, but when it is on the downstream side, there is no carrier retention,
The transportability was very good, the chargeability was good, and the image was good. At the closest position P, retention of the carrier was not a practical problem, the transportability was good, the chargeability was relatively good, and the image was good.

As described above, by arranging the peak position of the magnetic force Fr in the vicinity of the closest position B to the downstream end position A of the nip portion on the photosensitive drum 1, the carrier is prevented from adhering to the drum. You can

Further, by utilizing the deviation between the position of the main charging pole S1 and the peak position of the magnetic force Fr as described above, the peak position of the magnetic force Fr is set to the downstream end position of the nip portion on the photosensitive drum 1. By disposing the carrier in the vicinity of the closest position B to A, the carrier is prevented from adhering to the drum, and the position of the charging main pole S1 is located downstream of the closest position P to the photosensitive drum 1 in the sleeve rotation direction. By arranging it on the side, it is possible to obtain a good image by improving carrier property without carrier retention and good chargeability, and satisfying both carrier adhesion prevention and charging failure prevention. Will be able to.

<Third Embodiment> In this embodiment, in the image forming apparatus of the cleanerless system of the second embodiment, the configuration of the magnetic brush charging device is slightly changed.

That is, the magnetic brush charging device of this example is different from the magnetic brush charging device of the second embodiment in that the carrier used is different, and the outer diameter of the charging sleeve 21 is 12 mm. Accompanying
The structure of the magnet roll 22 is slightly different. The configuration other than the magnetic brush charging device is the same as that of the image forming apparatus according to the second exemplary embodiment, and thus the repetitive description will be omitted.

In this example, the peripheral speed of the photosensitive drum 1 is 100 mm.
/ Sec, the outer diameter was 30 mm, the peripheral speed of the charging sleeve 21 was 150 mm / sec, and the outer diameter of the sleeve 21 was 12 mm. The rotating direction of the sleeve 21 was counter to the photosensitive drum 1. The distance h between the photosensitive drum 1 and the sleeve 21 is 0.5 mm, the width of the contact nip portion D is about 2 mm on the upstream side, about 3 mm on the downstream side, and the total width is about 5 m.
m. The bias voltage applied to the charging sleeve 21 is a DC voltage of −700 V superimposed on a rectangular AC voltage having a frequency of 1000 Hz and a peak-to-peak voltage of 800 V. The average particle size of the carrier 23 is 35 μm, the shape is spherical, the resistance value is 1 × 10 ⁶ Ω · cm, and the saturation magnetization is 66 (A
・ M ² / kg). The carrier 23 had a true density of about 5.8 g / cm ³ and a magnetic permeability of about 5.0.

In the magnet roll 22, the magnetic flux density of the charging main pole S1 is 750 × 10 ⁻⁴ T (Tesla), and the angle α1 between the charging main pole S1 and the peak F1 of the magnetic force Fr is 30 °.
Table 3 shows the results obtained with respect to carrier adhesion and chargeability when the charging main pole position and the peak position of the magnetic force Fr were variously changed using the roll E of No.

The closest position B on the charging sleeve 21 to the position A on the downstream side of the nip part on the photosensitive drum 1 in this example will be described. The outer diameter of the charging sleeve 21 is 1
6 mm, outer diameter of photosensitive drum 1 is 30 mm, photosensitive drum 1
Since the distance h between the sleeve 21 and the sleeve 21 is 0.5 mm, and the width of the contact nip portion D on the downstream side of the photosensitive drum 1 is 3 mm, the angle between the position Q and the position A on the photosensitive drum 1 is about 28.7 °. The angle between the position P and the position B on 21 is about 23.7 °. Then, the charging main pole S1 and the peak F1 of the magnetic force Fr.
Since the angle α1 with respect to is 30 °, if the position S of the charging main pole S1 is arranged 6 ° (-6 °) downstream of the closest position P to the photosensitive drum 1 in the sleeve rotation direction, the position on the sleeve The angle between P and the peak position F1 of the magnetic force Fr is “30
-6 = 24 ° ", which is almost the same position as the closest position B to the downstream end position A of the nip portion on the photosensitive drum 1.

[0181]

[Table 3] In Table 3, the meanings of the symbols are the same as those in Table 2 of the second embodiment.

As shown in Table 3, Experimental Example 3-1 in which the peak position F1 of the magnetic force Fr is within ± 3 ° in the vicinity of the closest position B to the downstream end position A of the nip part on the photosensitive drum 1 And 3-2 were very good with no carrier adhesion, but Experimental Examples 3-3 to 3-5 located at a position of ± 6 ° or more from the closest position B were defective due to carrier adhesion. It was

Further, in Experimental Example 3-5 in which the position of the main charging pole S1 is on the upstream side with respect to the closest position P to the photosensitive drum 1 in the sleeve rotation direction, the carrier is retained on the upstream side of the nip portion. Occurred, resulting in poor charging, resulting in a ghost image and poor image quality. 3-1 to 3-3 on the downstream side,
The carrier was not retained, the transportability was very good, the chargeability was good, and the image was good. 3 at the closest position P
In No. 4, carrier retention was practically no problem, the transportability was good, the chargeability was relatively good, and the image was good.

As described above, by arranging the peak position of the magnetic force Fr in the vicinity of the closest position B to the end position A on the downstream side of the nip portion on the photosensitive drum 1, it is possible to prevent the carrier from adhering to the drum. You can

Further, by utilizing the deviation between the position of the main charging pole S1 and the peak position of the magnetic force Fr as described above, the peak position of the magnetic force Fr is set to the downstream end position of the nip portion on the photosensitive drum 1. By disposing the carrier in the vicinity of the closest position B to A, the carrier is prevented from adhering to the drum, and the position of the charging main pole S1 is located downstream of the closest position P to the photosensitive drum 1 in the sleeve rotation direction. By arranging on the side, there is no retention of the carrier, the transportability is very good, the chargeability is good, and a good image can be obtained, and both carrier adhesion prevention and charge failure prevention are satisfied. Will be able to.

In particular, in order to reduce the size and cost of the magnetic brush charging device as in this example, the diameter of the charging sleeve is reduced, and in order to improve the charge injection property, the contact nip portion D is formed.
Is increased and the width is increased on the downstream side of the photosensitive drum 1, the positions of the main charging pole S1 and the peak position of the magnetic force Fr are intentionally made considerably large in order to prevent carrier adhesion, as described above. Although it has a great effect, there has been a limit to downsizing and cost reduction of the magnetic brush charging device because such a device has not been conventionally devised. According to this example,
It is possible to achieve downsizing and cost reduction of the magnetic brush charging device while preventing carrier adhesion.

<Others> 1) The magnetic brush charging device according to the present invention is not limited to the charging process of the image carrier in the image forming apparatus of the embodiment,
It is needless to say that it is widely effective as a contact charging treatment means for a body to be charged.

2) The charged body may be predominantly charged by discharge. A contact charging system by electric discharge,
As the contact charging means of the AC charging method, as disclosed in Japanese Patent Publication No. 2-52058 related to the applicant's previous proposal,
The contact charging member has a predetermined DC voltage component and a predetermined alternating voltage component (an 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). The method of applying the oscillating voltage is excellent in uniform charging property. As the alternating voltage component (AC bias component), a sine wave, a square wave (rectangular wave), a triangular wave, a sawtooth wave or the like having an appropriate waveform can be used. It also includes a rectangular wave formed by periodically turning on and off a DC power supply. The present invention can also be applied to such contact charging means.

3) The image forming process is optional for the image forming apparatus. The transfer method may be a direct method in which an image is directly formed on a photosensitive paper (electrofax paper) or an electrostatic recording paper without an image transfer step.

The image carrier may be an electrostatic recording dielectric or the like. In this case, after the primary surface of the dielectric surface is uniformly charged to a predetermined polarity and potential, the target electrostatic latent image is written and formed by selectively neutralizing with a neutralizing means such as a neutralizing needle head or an electron gun.

The developing method and means of the electrostatic latent image are arbitrary,
The reversal development method or the regular development method may be used.

As the transfer method, not only the roller transfer shown in the embodiment but also the blade transfer and other contact charging methods, and further the transfer drum, the transfer belt and the intermediate transfer member are used, and not only the single color image formation It goes without saying that it can be applied to an image forming apparatus that forms a multicolor or full-color image by multiple transfer or the like.

Further, an electrophotographic photosensitive member or an electrostatic recording dielectric as an image bearing member is made 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 forming / developing process means. There is also an image display device in which the toner image forming section is formed, the image is displayed by positioning the toner image forming section on the reading display section, and the image carrier is repeatedly used for forming the display image. The image forming apparatus of the present invention includes such an image display apparatus.

[0194]

As described above, according to the present invention,
The peak position in the normal direction of the magnetic force Fr on the magnetic particle bearing section, the magnetic particle bearing with respect to the rotational direction downstream side end position of the member to be charged against contact portion of the magnetic brush on the member to be charged
By setting the position within ± 5 ° from the closest position on the means, the magnetic particles of the magnetic brush portion near the end position on the downstream side in the rotation direction of the charged body of the contact nip portion of the charged body and the magnetic brush are carried by the magnetic particles. Since the magnetic force attracted to the means can be efficiently increased, the magnetic particles do not substantially adhere to the charged body, so that the magnetic particles are detached from the magnetic brush or adhered to the charged body. The problem of evil can be solved.

In addition to the above structure, the present invention
The charged body in the moving direction of the magnetic particle carrying means.
The width of the contact part between the and magnetic brush is large, especially 4 mm or more
By doing so, the contact machine between the magnetic brush and the charged body
Since the amount is large, the injection charging property is improved. Moreover also I'm a relative movement direction of the magnetic particle bearing section and the member to be charged to a counter direction, because it can be made large peripheral speed difference with respect to the member to be charged, the magnetic brush member to be charged It is possible to improve the charge injection property and the charge property by increasing the number of contacting points with the injection zone.
It is advantageous for improving electrical properties.

[0196] Moreover, further addition to the above structure, the magnetic poles
Set the position of the charging main pole from the position closest to the charged body to the magnetic particles.
The Rukoto provided on the downstream side with respect to the moving direction of the child carrying means, it is possible to prevent the excessive accumulation of the magnetic brush in the direction of movement upstream portion of the magnetic particle bearing section of the contact nip of the member to be charged and the magnetic brush Therefore, it is possible to prevent the charging failure due to the retention of the magnetic brush.

Further, in the image forming apparatus using the above magnetic brush charging device, there are problems such as separation of magnetic particles from the magnetic brush, adverse effects due to adhesion of magnetic particles to an object to be charged, and occurrence of image defects due to the problems. Can be eliminated.

[Brief description of drawings]

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

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

FIG. 3 is a diagram for explaining the principle of injection charging.

FIG. 4A is a structural model diagram of a magnetic brush charging device,
(B) is a figure for demonstrating the position of a contact nip part and a magnetic pole structure.

FIG. 5 is a diagram for explaining a magnetic force Fr on the charging sleeve 21.

FIG. 6 is a diagram for explaining a distribution form of a magnetic flux density Br and a distribution form of a magnetic force Fr of a main charging pole S1.

FIG. 7: Magnetic flux density Br in the normal direction on the charging sleeve 21
And a diagram for explaining a method of measuring the magnetic flux density Bθ in the tangential direction

FIG. 8 is a schematic configuration diagram of an image forming apparatus example of a cleanerless system according to the second embodiment.

9A is a schematic configuration model diagram of a sleeve type magnetic brush charging device, and FIG. 9B is a schematic configuration model diagram of a magnetic roller type magnetic brush charging device.

[Explanation of symbols]

1 Charged object (electrophotographic photoreceptor, photosensitive drum) 2 Magnetic brush charging member 21 Charging sleeve (magnetic particle carrier) 22 Magnet roll 23 Magnetic particles (carrier) 24 magnetic brush 25 regulation blade 3 developing device 4 Transfer roller 5 Fixing device 6 cleaning device 10 Process cartridge 30 Recording material (transfer material) E1 Power supply for charging bias

Front Page Continuation (72) Inventor Yasunori Kono 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) Reference JP-A-3-4262 (JP, A) JP-A-6-230647 (JP, A) JP 7-234567 (JP, A) JP 7-287432 (JP, A) JP 7-306568 (JP, A) JP 86401 (JP, A) (JP 58) Fields surveyed (Int.Cl. ⁷ , DB name) G03G 13/02 G03G 15/02

Claims (2)

(57) [Claims] 1. A magnetic brush charging member in which magnetic particles are restrained by a magnetic force and attached and held as a magnetic brush on a rotatable conductive magnetic particle supporting means containing a fixed magnet. In a magnetic brush charging device in which a magnetic brush of a charging member is brought into contact with an object to be charged and conveyed by rotation of a magnetic particle carrying means, a voltage is applied to inject and charge the object to be charged through the magnetic brush. In the contact portion with the magnetic brush, the moving direction of the magnetic particle carrying means and the moving direction of the charged body are counter directions, and the position of the charging main pole of the magnetic pole of the magnet is
It is provided on the downstream side with respect to the moving direction of the magnetic particle carrying means from the position closest to the charged body, and the magnetic body and the magnetic body are moved in the moving direction of the magnetic particle carrying means.
The width of the contact portion with the brush is set to 4 mm or more, and the peak position of the magnetic force Fr in the normal direction on the magnetic particle carrying means is defined as the downstream end of the contact portion of the magnetic brush on the charged body in the rotation direction of the charged body. A magnetic brush charging device, wherein the position is within ± 5 ° from the closest position on the magnetic particle carrying means with respect to the partial position. 2. An image forming apparatus for forming an image by an image forming process including a step of charging an image carrier, wherein the charging means of the image carrier is the magnetic brush charging device according to claim 1. A characteristic image forming apparatus.