JPH06258915A - Magnetic brush type electrostatic charger - Google Patents

Abstract

PURPOSE:To provide a magnetic brush type electrostatic charger which can stably and uniformly execute the sufficient electrostatic charge of an image forming body and prevent magnetic particles from being attached on the surface of the image forming body. CONSTITUTION:The magnetic brush type electrostatic charger is provided with a container 21 storing the magnetic particles 26, a magnetic brush cylinder 23 which is provided in the container 21 so that one part of the circumferential surface thereof is exposed from the aperture part of the container 21 and provided with a magnet body 22 obtained by disposing plural magnetic poles in the circumferential direction inside and which carries the magnetic particles by attaching them on the circumferential surface by relative rotation between the magnet body 22 and a bias power source 24 impressing a bias voltage having a DC component and an AC component on the cylinder 23. Then, the surface of a body to be electrostatically charged is electrostatically charged by bringing the magnetic particles carried by the cylinder 23 into contact with it. As the magnetic particles stored in the container 21, particles which are obtained by dispersing and including magnetic fine powder and electrical conductive carbon black whose particle diameter is within the range of 10-50mm, whose surface area by nitrogen attracting quantity is <=300m<2>/g and whose dibutyl phtalate oil absorption quantity is within the range of 100-200cc/100g in binder resin, whose saturation magnetization is within the range of 20-100emu/g, whose resistivity is within the range of 10<4>-10<10>OMEGAcm and whose average particle diameter is within the range of 10-50mum are used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic brush charging device used to uniformly charge an image forming body in an image forming apparatus such as an electrophotographic copying machine.

[0002]

2. Description of the Related Art A magnetic brush charging device is known from Japanese Patent Application Laid-Open No. 59-133569 as a charging device without a defect due to gas discharge like a corona charger, and magnetic particles are attached to the surface. A magnetic brush charging device that applies a bias voltage having a direct current component and an alternating current component to a magnetic brush cylinder that is conveyed in such a way that uniform charging is stably performed is disclosed in Japanese Patent Laid-Open No. 4-21873 and 4-116674. It is known from the publication.

[0003]

The conventional magnetic brush charging device as described above still has a problem that ring mark-shaped or sweep-shaped charging unevenness or magnetic particles are likely to adhere to the image forming body. .

The present invention has been made in order to solve the above-mentioned problems, and it is possible to uniformly apply a sufficient charge to an image forming body and prevent magnetic particles from adhering to the surface of the image forming body. A brush charging device is provided.

[0005]

The present inventors have found that the above-mentioned problems of the magnetic brush charging device are deeply related to the average particle size of magnetic particles and the magnitude of saturation magnetization. When the saturation magnetization increases, the magnetic brush ears become coarse and hard and ring-shaped or sweep-shaped charging unevenness is likely to occur on the image forming body. Conversely, when the average particle size of the magnetic particles and the saturation magnetization decrease, The ears of the magnetic brush are delicately flexible and eliminate the ring mark-shaped or sweep-shaped charging unevenness, but the magnetic particle binding force of the magnetic body of the magnetic brush cylinder is weakened, and the magnetic particles become image forming bodies. However, even if the magnetic particles have a small average particle diameter, they contain a specific conductive carbon black as described as a magnetic toner in JP-A-59-102250. Imager, if any It found that can give a uniformly homogeneous sufficient charge without adhering.

The present invention has been made on the basis of the above-mentioned findings, and is provided with a container for storing magnetic particles and a part of the peripheral surface exposed from the opening of the container in the container, A magnetic brush cylinder which has a magnet body having a plurality of magnetic poles arranged in the circumferential direction and carries magnetic particles by adhering to the magnet body on its peripheral surface, and a DC component and an alternating current component in the cylinder. A magnetic brush charging device for charging the surface of the body to be charged by contacting the magnetic particles carried by the cylinder with a bias power source for applying a bias voltage having a component. Magnetic fine powder inside, the particle size is in the range of 10 to 50 nm, the surface area due to the amount of nitrogen adsorption is 300 m ² / g or less, and the dibutyl phthalate (DBP) oil absorption is in the range of 100 to 200 cc / 100 g. With a certain conductive carbon black Containing dispersed, saturation magnetization 20
~ 200emu / g range, resistivity of 10 ⁴ ~ 10 ¹⁰ Ωcm, and an average particle size of 10 ~ 50μm in the magnetic brush charging device, characterized in that the above-mentioned object. To achieve.

Here, the particle diameter of the conductive carbon black is the maximum diameter measured by electron micrograph, the surface area is the value measured by the so-called BET method, and the DBP oil absorption is 10.
DB for making 0g of carbon black into paste
Minimum required amount of P, saturation magnetization of magnetic particles is 0.25
After tapping into a cm ² × 30 mm sample cell and filling it, attach the sample cell to the pickup coil and set it in the magnetizer, and use the DC magnetization characteristic automatic recording device “Type 3257” (Yokogawa Kitatsuden Electric Co., Ltd.) The value and resistivity obtained by drawing a hysteresis curve on the Y recorder
After tapping in a container having a sectional area of 0.50 cm ^2, a load of 1 kg / cm ² on packed particles, applying a voltage to the electric field of 1000V / cm is generated between the load and a bottom electrode The value obtained by reading the current value when
The average particle size is measured by the laser diffraction particle size distribution analyzer "HELOS" equipped with a wet dispersion machine (SYMPATE
The average particle size on a volume basis measured by C), and the number of magnetic particles before measurement with a wet disperser of HEROS
A pretreatment is carried out by dispersing 10 mg together with a surfactant in 50 ml of water, and then dispersing with an ultrasonic homogenizer (output 150 W) for 1 to 10 minutes while paying attention to reaggregation due to heat generation.

[0008]

In the magnetic brush charging device of the present invention, the average particle size of the magnetic particles forming the magnetic brush is as small as 10 to 50 μm, and the saturation magnetization is in the range of 20 to 200 emu / g. Does not cause ring mark-shaped or sweep-shaped charging unevenness, and the resistivity is in the range of 10 ⁴ to 10 ¹⁰ Ωcm, so that the image forming body is sufficiently charged from the magnetic brush cylinder through the magnetic brush. Since the specific conductive carbon black is dispersedly contained in the magnetic particles together with the magnetic fine powder so as to make the resistivity of the magnetic particles 10 ⁴ to 10 ¹⁰ Ωcm, the magnetic particles can be dispersed in the image forming body. The adhesion is prevented and the durability of the image forming body is improved.

Since the average particle size of the magnetic particles is 10 μm,
When the saturation magnetization is smaller than 20 emu / g, the magnetic particles may adhere to or scatter on the image forming body. Conversely, the average particle size is less than 50 nm and the saturation magnetization is 200 emu / g. When each is larger than g, ring mark-shaped or sweep-shaped charging unevenness appears on the image forming body.
If the resistivity of the magnetic particles is less than 10 ⁴ Ωcm, if there is a scratch on the photoconductor layer of the image forming body, a current leaks to the portion through the magnetic brush, so a magnetic brush called banding is formed on the image forming body. If the resistivity is higher than 10 ¹⁰ Ωcm, the charge injection from the magnetic brush cylinder to the image forming body via the magnetic brush will not be sufficiently performed and the bias will occur. The reversal development with voltage causes the magnetic particles to adhere to the image forming body. Further, even if the average particle size, the saturation magnetization, and the resistivity of the magnetic particles are in the above-mentioned ranges, when the specific conductive carbon black is not dispersedly contained in the magnetic particles, the magnetic particles adhere to the image forming body. Like

[0010]

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

FIG. 1 is a schematic sectional view of an image forming apparatus using a charging device of the present invention, FIG. 2 is a partially enlarged view of FIG. 1 showing a charging device portion of the present invention, and FIG. 3 is applied to a magnetic brush cylinder. It is a graph which shows the preferable range of the alternating current component of bias voltage.

In FIGS. 1 and 2, reference numeral 1 denotes an image forming body which rotates in the direction of the arrow (clockwise), around which an image exposure L from a charging device 2, a static eliminator 3 and an exposing device (not shown) which will be described later.
Is provided with a developing device 4, a transfer roller 5, a cleaning device 6, and the like.

The image forming process of this image forming apparatus is performed as follows. When a copy start command is input to the control unit (not shown) from the operation unit (not shown), the image forming body 1 rotates in the direction of the arrow under the control of the control unit, and the surface thereof is uniformly charged by the charging device 2. . The static eliminator 3 is, for example, LE
It consists of D array, driven by the control of the controller,
The charging of the frame portion outside the incident area of the image exposure L on the surface of the image forming body 1 is erased. In the static eliminator 3, the charging by the charging device 2 has the same polarity as the charging of the toner used in the developing device 4,
This is not necessary in the case of reversal development in which toner is attached to the portion of the surface of the image forming body 1 where the image exposure L is incident.

Image exposure L is made incident on the charged surface of the image forming body 1 by a slit exposing device or a laser beam scanner, and an electrostatic image is formed.
Regular development or reversal development is carried out with toner charged to the opposite polarity or the same polarity as the above-mentioned charge.

In the developing device 4 in the illustrated example, a magnetic brush composed of a two-component developer in which toner and a magnetic carrier are mixed is formed on the developing roller 41 and conveyed in the direction of the arrow, and the developing roller 41 is connected to the image forming body 1. This is a magnetic brush developing device that applies a bias voltage having a polarity opposite to that of charging to prevent fogging in the case of regular development and to promote adhesion of toner to an electrostatic image in the case of reversal development. Even when a developer is used, a developing agent layer which is not in contact with the image forming body 1 is formed on the developing roller 41 and conveyed, and an AC component is also added to the bias voltage applied to the developing roller 41 so that the developing roller 41 forms an image. It is also possible to perform non-contact development in which toner is ejected from the developer layer and adheres to the electrostatic image in the developing area close to the formed body 1.

The toner image formed on the image forming body 1 by development is sent from the paper feeding cassette 7 by the paper feeding roller 71, and is transferred by the registration roller 8 onto the recording paper P which is sent to the position opposite to the transfer roller 5. It is transcribed by the action of 5. Then, the recording paper P is separated from the image forming body 1 and sent to a fixing device (not shown) by the conveying means 9 to fix the toner image, and then discharged to the outside of the apparatus. The residual toner on the surface of the image forming body 1 after the transfer is removed by the cleaning device 6 and then used again in the next image forming process.

The charging device 2 shown in detail in FIG. 2 has a stationary magnet body 22 inside a container 21 made of a non-magnetic conductive material with a part of its peripheral surface seen through the opening of the container 21. A magnetic brush cylinder 23 is provided rotatably in the direction of the arrow, and the magnetic brush cylinder 23 is biased by a bias power source 24 through a protective resistor 25, which is composed of a DC component and an AC component having the same polarity as the charging of the image forming body 1. It is possible to apply a voltage, the magnetic particles 26 are stored in the container 21, and the magnetic brush cylinder 23 rotates in the direction of the arrow, so that the magnetic particles 26 are attracted to the surface and conveyed in the direction of the arrow, and the conveyance The magnetic particles 26 to be formed are regulated in quantity by a doctor blade 27 made of a non-magnetic or magnetic material to form a magnetic brush 26a.
26a rubs the surface of the image forming body 1 rotating in the direction of the arrow to charge the magnetic brush cylinder 23 to a voltage substantially equal to the DC component of the bias voltage applied from the bias power supply 24. 28
Is a stirring member provided in the container 21 and rotated, and prevents the magnetic particles 26 in the container 21 from being unevenly distributed.

Not limited to the example of FIG. 2, the magnet body 22 has N and S magnetic poles at equal positions in the circumferential direction and rotates in the direction opposite to the transport direction of the magnetic particles 26. It may be stationary or may rotate in the opposite direction to the magnet body 22. Further, the above-described rotation directions of the magnetic brush cylinder 23 and the magnet body 22 are
The transport direction of the magnetic brush at the position where the magnetic brush cylinder 23 faces the image forming body 1 may be opposite to the moving direction of the image forming body 1. However, the uniformity of charging of the image forming body 1 and the container 21 of the magnetic brush 26a that has passed the sliding position of the image forming body 1
In view of the reducibility to the inside and the durability of the image forming body 1 and the like, it is preferable that the conveying direction of the magnetic brush is the same as the moving direction of the image forming body 1 and the conveying speed is the image forming body. It is preferably 1.0 to 2.0 times the moving speed of 1.

The gap in which the magnetic brush cylinder 23 faces the image forming body 1 can be set in the range of 0.05 to 1 mm, and if it is narrower than this range, the durability of the image forming body 1 and the like deteriorates quickly. If it becomes so, it becomes difficult to form a magnetic brush for properly rubbing the image forming body 1, and conversely, if it becomes wider,
It becomes difficult to uniformly rub the image forming body 1 with the magnetic brush, and thus to uniformly charge the image forming body 1.
The bias voltage applied to the magnetic brush cylinder 23 is
The DC component is equal to the charging voltage of the image forming body −500 to −100
The range of 0 V is suitable, but it is preferable that the AC component is within the white range shown in FIG. 3 because stable charging is performed. In FIG. 3, the range shaded by the vertical lines is a range where dielectric breakdown is likely to occur, the range shaded by diagonal lines is a range where uneven charging is likely to occur, and the low frequency region shaded with dots is low in frequency. Therefore, it is the range where uneven charging occurs. The waveform of the AC component is not limited to a sine wave, and may be a rectangular wave, a triangular wave, or the like.

As the magnetic particles 26 stored in the container 21, fine magnetic powder in the binder resin, the particle size is in the range of 10 to 50 nm, the surface area by the nitrogen adsorption amount is 300 m ² / g or less, Conductive carbon black having a dibutyl phthalate oil absorption of 100 to 200 cc / 100 g was dispersed and contained.
Saturation magnetization in the range of 20 to 200 emu / g, resistivity of 10 ⁴ to 10 ¹⁰ Ωc
Particles having a size of m and an average particle size of 10 to 50 μm are used. Such magnetic particles 26 can be manufactured by the same method as the magnetic toner described in JP-A-59-102250. But,
Unlike toner, it is not necessary to use a colorant other than conductive carbon black or to consider transferability and fixability, and rather poor fixability in toner means better morphological stability as magnetic particles. As described above, the binder resin is preferably a resin having a high melting point or softening point.
There are some differences in the manufacturing method of 26.

That is, the magnetic particles 26 are styrene resin, vinyl resin, ethylene resin, rosin-modified resin,
100 parts by weight of a binder resin containing acrylic resin, polyamide resin, epoxy resin, polyester resin, etc., or a mixture of two or more kinds, a particle size in the range of 10 to 50 nm, a surface area by nitrogen adsorption amount of 300 m ² / g or less, DBP Oil absorption 100-200c
Conductive carbon black satisfying the range of c / 100 g, for example, 2 to 30 parts by weight of Conductex 900 beads manufactured by Columbia Carbon Co., and metals such as iron, chromium, nickel and cobalt, or compounds or alloys thereof, for example, 43 Iron oxide, γ-ferric oxide, chromium dioxide, manganese oxide,
30 to 130 parts by weight of fine particles having an average particle size of several μm or less of a ferromagnetic material such as ferrite and manganese-copper alloy are preferably heated in a heating roll, an overheating kneader or a heating cokneader, preferably a binder resin and a conductive carbon black. After kneading, kneading or directly kneading, then cooling, crushing,
It can be obtained by a method in which the saturation magnetization, the resistivity and the average particle diameter are measured and then selected after the classification, preferably by a method in which the spheroidizing treatment with hot air is performed simultaneously with the classification or after the classification.

The preferred magnetic particles 26 have an average particle size of 20-40.
μm range, saturation magnetization 20-100 emu / g range, resistivity
It is in the range of 10 ⁵ to 10 ⁷ Ωcm, and has a static bulk density of 0.6 mg / ml or more in a state of being gently stored in the container 21 and a solid bulk packed in a condition for measuring the resistivity. Density 0.8 mg / ml
The above particles make it possible to more stably and uniformly charge the image forming body 1, and there is no fear that the magnetic particles 26 adhere to the surface of the image forming body 1 or scatter.

[0023]

According to the magnetic brush charging device 2 as described above, the surface of the image forming body 1 can be uniformly charged to a uniform potential in the range of, for example, -500 to -1000 V, and the magnetic particles 26 are formed. It does not adhere to the surface of the image forming body 1 or scatter in the machine.

[Brief description of drawings]

FIG. 1 is a schematic configuration sectional view of an image forming apparatus using a charging device of the present invention.

FIG. 2 is a partially enlarged view of FIG. 1 showing a charging device portion of the present invention.

FIG. 3 is a graph showing a preferable range of an AC component of a bias voltage applied to a magnetic brush cylinder.

[Explanation of symbols]

 1 image forming body 2 charging device 21 container 22 magnet body 23 magnetic brush cylinder 24 bias power supply 25 protective resistance 26 magnetic particles 26a magnetic brush 27 doctor blade 28 stirring member

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Masakazu Fukuchi 2970 Ishikawa-cho, Hachioji, Tokyo Konica stock company (72) Inventor Shizuo Morita 2970 Ishikawa-cho, Hachioji, Tokyo Konica stock company (72) Invention Noriyuki Hiroshi Nomori 2970 Ishikawa-cho, Hachioji City, Tokyo Konica Stock Company

Claims (2)

[Claims] 1. A container for storing magnetic particles, and a container in which a part of a peripheral surface is exposed from an opening of the container in the container,
Having a magnet body with a plurality of magnetic poles arranged in the circumferential direction,
A magnetic brush cylinder for adhering and transporting magnetic particles on the peripheral surface by relative rotation with the magnet body, and a bias power supply for applying a bias voltage having a DC component and an AC component to the cylinder are provided. In a magnetic brush charging device that contacts the conveyed magnetic particles to charge the surface of the body to be charged, the magnetic particles stored in the container are a magnetic substance fine powder in the binder resin, and the particle diameter is in the range of 10 to 50 nm. , With a surface area of 300 m ² / g or less according to the amount of nitrogen adsorbed, and a conductive carbon black having a dibutyl phthalate oil absorption amount in the range of 100 to 200 cc / 100 g dispersedly contained, and a saturation magnetization of 20 to 200 emu.
/ g range, resistivity 10 ⁴ to 10 ¹⁰ Ωcm range, average particle size 1
A magnetic brush charging device characterized in that the particles are in the range of 0 to 50 μm. 2. The binder resin 100 in the magnetic particles
The content of conductive carbon black is 2 to parts by weight.
The magnetic brush charging device according to claim 1, which is 30 parts by weight.