JPH06301264A - Electrifying method - Google Patents

Abstract

PURPOSE:To provide an electrifying method using a magnetic brush capable of high speed, uniform electrification without causing fatigue and deterioration in image forming body due to corona ions, nor sticking of magnetic particles to the image forming body. CONSTITUTION:An electrifying sleeve 22 is disposed so that it can rotate around the periphery of a magnet body 23 with magnetic poles arranged and fixed in the periphery. The thickness of a layer of magnetic particles 21 sticking to the periphery of the electrifying sleeve 22 is restricted by a restricting plate 26. To the restricting plate 26 a DC voltage is applied by a DC power source 25. To the electrifying sleeve an AC bias voltage having an DC element between the photosensitive drum 10 and it is applied by a bias power source 24. A magnetic brush composed of the magnetic particles 21, whose resistance is made low by an alternating electric field 1 generated between the electrifying sleeve 22 and the restricting plate 26, is brought into contact with the photosensitive drum 10, and the photosensitive drum 10 is electrified by an alternating electric field 2 generated between the electrifying sleeve 22 and the photosensitive drum 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging method for charging an image forming body by a magnetic brush charging device incorporated in an image forming apparatus such as an electrophotographic copying machine or an electrostatic recording apparatus.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus, a corona charger has generally been used for charging an image forming body such as a photosensitive drum. This corona charger applies a high voltage to the discharge wire to generate a strong electric field around the discharge wire to perform gas discharge, and the charged ions generated at that time are adsorbed to the image forming body to charge. Done.

The corona charger used in such a conventional electrophotographic image forming apparatus can charge the image forming body without mechanically contacting the image forming body, so that the image forming body is damaged during charging. It has the advantage of never. However, since this corona charger uses a high voltage, there is a risk of electric shock or leakage, and ozone generated due to gas discharge is harmful to the human body,
It has the drawback of shortening the life of the image forming body. Further, the charging potential of the corona charger is unstable because it is strongly affected by temperature and humidity. Further, the corona charger has noise generation due to a high voltage, and it is necessary to obtain a stable charging potential after inputting a high voltage. It takes more than a second,
This is a major drawback when using an electrophotographic image forming apparatus as a communication terminal or an information processing apparatus.

Many drawbacks of such corona chargers are:
The cause is that the charging is mainly performed by gas discharge.

Therefore, as a charging device such as a corona charger, which is capable of charging an image forming body without performing high-voltage gas discharge and mechanically damaging the image forming body, for example, Japanese Patent Application Laid-Open No. In JP-A-59-133569, a magnetic brush is formed by adsorbing magnetic particles on a cylindrical carrier containing a magnetic body, and a DC brush voltage is applied to the carrier to apply an image forming body with the magnetic brush. A charging device has been disclosed in which charging is performed by rubbing the surface. Further, in Japanese Utility Model Application Laid-Open No. 59-192160, magnetic particles are adsorbed on a cylindrical carrier which is covered with a dielectric layer containing a magnet body to form a magnetic brush. Disclosed is a charging device configured to rotate a carrier at a constant speed while applying a DC bias voltage to a bristling regulating plate that regulates the bristling regulating plate, and to perform charging by rubbing the surface of an image forming body with a magnetic brush. There is.

Since the magnetic brush is a flexible brush made of magnetic particles, it can be charged without damaging the image forming body, such as a fur brush charging device or a charging device using a conductive elastic roll. Superior to other contact charging devices. However, even when the magnetic brush charging device is used, uniform charging is not always obtained.

Therefore, for example, Japanese Patent Laid-Open No. 4-21873 proposes a magnetic brush charging method for charging an image forming body by applying an AC bias voltage containing a DC component to the magnetic brush. In this publication, charging is performed by setting the AC bias voltage so that the peak-to-peak voltage V _PP exceeds twice the discharge limit value of the magnetic brush, and the charging is performed. The frequency of the AC bias voltage is preferably. It is set to 100 to 500 Hz. The magnetic particles used have a particle size of 20 to 200 μm and a resistivity of 10
It is described that iron, iron oxide, and ferrite particles having a size of ⁵ to 10 ⁹ Ω · cm are provided, whereby uniform charge can be imparted to the image forming body.

[0008]

However, the above publication does not recognize that the electric resistance of the magnetic brush changes depending on the strength of the electric field applied to the magnetic brush. Therefore, in the above-mentioned publication, the study of the strength of the electric field suitable for charging the magnetic brush, that is, the magnitude of the bias voltage, etc. is insufficient when paying attention to the point that the electric resistance of the magnetic brush changes depending on the strength of the electric field. No consideration has been given to high-speed charging for the high-speed copying that is being considered.

In consideration of these points, the present invention considers these points and charges by a magnetic brush capable of high-speed and uniform charging without causing fatigue deterioration of the image forming body due to corona ions and adhesion of magnetic particles to the image forming body. The purpose is to provide a method.

[0010]

The above-mentioned object is to form a magnetic brush made of magnetic particles on a carrier, and move the carrier to move the magnetic brush to a gap between the carrier and the spike-up regulating plate. In a charging method in which the image carrier is charged and rubbed after passing through it to charge the image carrier, an AC bias voltage having a DC component is applied to the carrier, and the spike control plate or the leveling plate is applied. It is achieved by a charging method characterized by applying a DC voltage to the plate.

As the magnetic brush, 1 × 10 ⁴ [V /
cm] or less, an alternating electric field in the gap between the carrier and the spike control plate or the leveling plate is used to generate a sudden change in electric resistance under the electric field. In a preferred embodiment, the charging method is characterized in that the bias voltage applied to the carrier and the gap between the carrier and the spike regulation plate or the leveling plate are set so as to be equal to or higher than the electric field that causes a change. is there.

[0012]

In the present invention, an AC bias voltage having a DC component is applied to the carrier of the magnetic brush, and a DC voltage is applied to the spike control plate or the leveling plate. An alternating electric field is formed between the carrier and the gap between the spike-up regulating plate or the leveling plate, and between the carrier and the image forming body. The magnetic brush has a low resistance state under an alternating electric field in a gap between the carrier and the spike-up regulating plate or the leveling plate, and then an image is formed between the carrier and the image forming body under an alternating electric field. Since the electric charges are injected into the formed body, uniform charging can be performed at high speed.

[0013]

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

FIG. 1 is a schematic sectional view of a copying machine which is an image forming apparatus equipped with a magnetic brush charging device to which the present invention is applied, and FIGS. 2 and 3 are enlarged sectional views showing examples of the magnetic brush charging device of FIG. FIG. 4 is a graph showing electric field dependence of electric resistance of a preferable magnetic brush used in the charging method of the present invention, and FIG.
3 is a graph showing a preferable range of an AC component of a bias voltage applied to the charging sleeve.

In FIG. 1, 10 is the peripheral speed in the direction of the arrow (clockwise).
An image forming body that rotates at 240 mm / sec.
The photosensitive drum is made of C, and a peripheral portion thereof is provided with a charging device 20 by a magnetic brush described later, an exposing portion on which image light L from the exposing device enters, a developing device 30, a transfer roller 13, a cleaning device 50, and the like. ing.

The basic operation of the copy process of this embodiment is as follows.
When a copy start command is sent from an operation unit (not shown) to a control unit (not shown), the control unit controls the photosensitive drum.
10 starts rotating in the direction of the arrow. As the photosensitive drum 10 rotates, its peripheral surface is uniformly charged by a magnetic brush charging device 20 described later and passes through. An image is written on the photoconductor drum 10 by image light L of a laser beam from an image writing device or the like, and an electrostatic latent image corresponding to the image is formed.

The developing device 30 is a two-component developing device in which a non-magnetic toner having an average particle diameter of 8.5 μm and iron spherical particles having a thin oxide film layer on the surface having a diameter of 45 μm are mixed at a weight ratio of 10: 1. After the agent is contained and agitated by the agitation screws 33A and 33B, it is outside the cylindrical magnet body 32 and is 360 mm / se.
A magnetic brush of developer is formed by adhering to the outer periphery of the developing sleeve 31 rotating at a peripheral speed of c, and a predetermined developing bias voltage is applied to the developing sleeve 31 in the developing area facing the photoconductor drum 10. Reverse development is performed.

From the paper feed cassette 40, the recording paper P which is a transfer material is fed one by one by the first paper feed roller 41. The fed recording paper P is sent onto the photosensitive drum 10 by the second paper feed roller 42 which operates in synchronization with the toner image on the photosensitive drum 10. And transfer roller
By the action of 13, the toner image on the photoconductor drum 10 is transferred onto the recording paper P and separated from the photoconductor drum 10. The recording paper P on which the toner image has been transferred is sent to a fixing device (not shown) via the conveying means 80, is sandwiched by a heat fixing roller and a pressure bonding roller, is fused and fixed, and is then discharged to the outside of the apparatus. The surface of the photosensitive drum 10 that has toner remaining without being transferred to the recording paper P and rotates, is scraped off and cleaned by a cleaning device 50 having a blade 51 and the like, and waits for the next copy.

FIG. 2 is a sectional view showing an example of a magnetic brush charging device 20 to which the present invention is applied. In the figure, 21 is a magnetic particle, 22 is a charging sleeve which is a carrier for carrying magnetic particles 21 made of non-magnetic and conductive metal such as aluminum, and the surface thereof is a surface for stable and uniform carrying of the magnetic particles 21. It is preferable that the average roughness of 2 to 15 μm. If it is smooth, it cannot be sufficiently conveyed, and if it is too rough, an overcurrent flows from the convex portions on the surface, and uneven charging tends to occur in either case. Sandblasting is preferably used to achieve the above surface roughness. The diameter of the charging sleeve 22 is 5 to
20 mm is preferable. With the above diameter, a contact area necessary for charging is secured. If the contact area is unnecessarily large, the charging current will be excessive, and if it is small, uneven charging is likely to occur.
Reference numeral 23 is a cylindrical magnet body fixedly arranged inside the charging sleeve 22, and this magnet body 23 has an S pole and an N pole so that the surface of the charging sleeve 22 has 900 Gauss on the periphery as shown in the figure. Are arranged and magnetized. The charging sleeve 22 is a magnet body 23.
It is rotatable relative to the photoconductor drum 10 and is held at a gap of 0.5 to 1.5 mm at a position facing the photoconductor drum 10 and rotates in the same direction as the photoconductor drum 10 moving direction at the same peripheral speed of 240 mm / sec. To be made.

Reference numeral 28 denotes a casing forming a storage portion for the magnetic particles 21, and the charging sleeve 22 is provided in the casing 28.
And a magnet body 23 are arranged, and 27 is a stirrer which is composed of a rotating body having a plate-like member around its axis to make the magnetic particles 21 uniform. Further, at the outlet of the casing 28, there is provided a regulating plate 26 which regulates the rising of the magnetic brush and which also serves as an electrode for applying a DC voltage, and is attached to the charging sleeve 22 and carried out. The thickness of the magnetic particle 21 layer is regulated, and the magnetic particles 21 are placed in the alternating electric field 1. A gap Dh between the tip of the regulation plate 26 and the charging sleeve 22 is a gap Dsd between the charging sleeve 22 and the photosensitive drum 10.
Is set to be almost equal to. As a result, the gap Dsd between the charging sleeve 22 and the photosensitive drum 10 is connected by the magnetic brush of the magnetic particles 21 whose thickness is regulated.

The photosensitive drum 10 comprises a conductive base material 10b and a photosensitive body layer 10a covering the surface thereof, and the conductive base material 10b is grounded.

Reference numeral 24 is composed of a DC power supply 24a and an AC power supply 24b, and a DC bias voltage V _DC equal to the charging voltage and an AC bias voltage V _DC are applied between the charging sleeve 22 and the conductive base material 10b.
Bias power source to be applied through the protective resistor R1 an AC bias voltage obtained by superposing an _AC, 25 is a DC power source for applying through a protective resistor R2 DC voltage V _h to the regulating plate 26. In addition,
The DC voltage V _h applied to the regulation plate 26 is the same as the charging sleeve 22.
It is preferably equal to the DC component V _DC of the AC bias voltage applied to. The bias power supply 24 and the DC power supply 25 perform constant voltage control for the DC component and constant current control for the AC component. Note that a DC voltage is applied V _h the regulating plate 26 may be used a DC power source 24a, preferably to simplify the configuration.

The magnetic brush charging device shown in FIG. 3 is another embodiment to which the present invention is applied, and is provided with a leveling plate 29 together with the regulating plate 26 of the magnetic brush charging device shown in FIG.

The leveling plate 29 regulates the gap between the charging sleeve 22 and the regulating plate 26 so as to be equal to the gap between the regulating plate 26 and the charging sleeve 22.
It is provided together with 26 and presses the layer of magnetic particles 21 toward the charging sleeve 22, and its tip is made not to contact the peripheral surface of the photosensitive drum 10, and is made of a conductive metal plate having a thickness of about 50 to 300 μm. An elastic material is used. By the leveling plate 29, the layer of the magnetic particles 21 is further leveled immediately before the charging region, and the unevenness of stripes which is likely to occur due to clogging of the spike control plate 26 is eliminated, and a uniform thin layer is conveyed to the charging region. The DC voltage V _h applied from the DC power supply 25 to the regulation plate 26 and / or the leveling plate 29 is applied to both the regulation plate 26 and the leveling plate 29 in this figure, but the DC voltage V _h is Regulation plate 26 or leveling plate 29
It may be applied to any one of the above. As in the embodiment of FIG. 2, the DC voltage V _h is preferably equal to the DC component V _DC of the AC bias voltage applied to the charging sleeve 22.

Next, the operation of the above-mentioned charging device 20 will be described.

When the charging sleeve 22 is rotated in the same direction as the arrow at the same speed as the peripheral speed of the photosensitive drum 10 while rotating the photosensitive drum 10 in the direction of the arrow, the magnetic particles adhered to and conveyed by the charging sleeve 22. The layer thickness of the layer 21 is regulated by the regulation plate 26, and at the same time, the regulation plate 26 or the leveling plate 29 and the charging sleeve 22.
Since an alternating electric field is formed between the magnetic particles 21
Is made to have a low resistivity, and is magnetically connected in a chain shape at a position facing the photosensitive drum 10 on the charging sleeve 22 by the magnetic lines of force of the magnet body 23 to form a kind of brush shape. Is formed. Then, this magnetic brush is conveyed in the rotation direction of the charging sleeve 22 and is transferred to the photosensitive layer of the photosensitive drum 10.
Contact 10a. Since another alternating electric field is formed between the charging sleeve 22 and the photoconductor drum 10, the charge is injected onto the photoconductor layer 10a through the magnetic brush having a low resistance, so that the charge is uniformly charged at high speed. Give.

Next, the magnetic brush preferably used in the charging method of the present invention will be described.

The magnetic brush which is preferably used in the charging method of the present invention is a magnetic brush which causes a rapid change in electric resistance under an electric field of 1 × 10 ⁴ V / cm or less. The electric resistance R under the low electric field of 1 × 10 ⁴ V / cm or less is 10 ⁵ to 10 ⁸ Ω, and the electric resistance R is 1 × 10 ⁴ V / c.
The electric resistance R under a high electric field exceeding m is 10 ³ Ω or less,
Further, for example, magnetic brushes B3 and B4 shown in FIG. 4 are used so as to rapidly change the electric resistance with an electric field of 1 × 10 ⁴ V / cm or less.

The horizontal axis of FIG. 4 represents the electric field E _D (V / cm), and the vertical axis represents the electric resistance R (Ω) of the magnetic brush.

Next, in the charging method of the present invention, in order to obtain a preferable electric field that gives a sudden change in resistance to the magnetic particles,
The alternating current (AC) bias voltage (1/2 of the peak-to-peak voltage V _PP of the alternating current component) V _AC (kV) applied to the charging sleeve and the gap D _h between the charging sleeve and the spike control plate or leveling plate.
(Cm) will be described.

The preferable range of the electric field in the charging method of the present invention is shown in FIG. 5, for example. In FIG. 5, the horizontal axis represents the AC bias voltage V _AC (kV), and V ₂ represents the preferable upper limit voltage. The vertical axis is the gap D
It represents the size (cm) of h, and D ₁ -D ₂ indicates its preferable range. E ₁ represents an electric field of 1 × 10 ⁴ V / cm, E ₂ represents a lower limit of a preferable electric field applied to the spike-height regulating plate portion, and a hatched area represents a range of the preferable electric field.

In the charging method of the present invention, the above (D ₁ -D
₂ ) is 0.01 to 1 cm, the upper limit of the AC bias voltage V _AC of the preferable electric field is ₂ kV, and the lower limit E _{2 of the} preferable electric field is 100 V / cm.

The magnetic brush preferably used in the present invention causes a rapid change in electric resistance under an electric field of 1 × 10 ⁴ V / cm or less, and the electric resistance of the magnetic brush is measured by a measuring method described later. Is measured under a DC electric field E _D based on a DC bias as shown by. The DC electric field E _D based on this DC bias is expressed by the following equation.

E _D = V _DC / Dh However, V _DC : DC bias voltage applied to the magnetic brush Dh: Gap between the charging sleeve and the spike-up regulating plate The graph of FIG. 4 shows changes in the DC electric field E _D. It shows a corresponding change in the electrical resistance R of the magnetic brush.

Next, let E _D * be the electric field that gives a sudden change in the magnetic brush electric resistance R when the DC electric field E _D in FIG. 4 is changed, and let this electric field E _D * and the alternating electric field E _r1 of the spike regulation part. The relationship will be described.

First, the alternating electric field E _r1 (this electric field is referred to as the alternating electric field 1) applied to the spike-height restricting portion during image formation is expressed by the following equation.

E _r1 = {(V _DC + V _AC ) −V _h } / _{D h} where V _{DC is} the DC bias voltage applied to the charging sleeve V _{AC is the AC} bias voltage applied to the charging sleeve by superimposing it on the DC bias voltage (V _PP / 2) V _h : DC voltage applied to the spike-rising restricting portion Dh: Gap between the charging sleeve and the spike-rising restricting plate By the way, in the present invention, preferably the DC bias voltage V _DC is applied to the spike-rising restricting portion. Since a voltage equal to is applied, V _h = V _DC , and the electric field of E _r1 = (V _DC + V _AC −V _DC ) / _{D h} = V _AC / _{D h} is applied to the magnetic brush.

Here, the AC bias voltages V _AC and Dh are set so that the alternating electric field E1 is equal to or higher than the electric field (E _D *) that causes a sudden change in the electric resistance R of the magnetic brush, and E _r1 ≈ ( the _{V AC / Dh) ≧ E D} *. As a result, before charging starts, A corresponding to Dh
By controlling the C bias V _AC , an electric field equal to or higher than the electric field E _D * that causes the electric resistance R of the magnetic brush to change rapidly is formed, and the electric resistance R of the magnetic brush is made low before the start of charging. The charging is performed later.

After that, the alternating electric field E _r2 (this electric field is referred to as the alternating electric field 2) applied to the charged area during image formation is expressed by the following equation.

E _r2 = {(V _DC + V _AC ) −V _S } / Dsd where V _DC : DC bias voltage applied to the charging sleeve V _AC : AC bias voltage (V applied to V _DC applied to the charging sleeve) _PP / 2) V _S: surface potential of the image forming body Dsd: the gap thereby the magnetic brush in the charging region of the charging sleeve and the image forming _{body, E r2 (t = 0)} = (V DC + V AC) / Dsd The electric field of is applied. However, as the charging time t elapses, the image forming body is charged and reaches the target potential V _s0 after an infinite time. However, at t ₁ (1 to
In 10 msec), the potential reaches a potential very close to the target potential V _s0 .

Since the charging of the image forming body is converged to the surface potential V _DC as the charging time elapses, the target surface potential V _SO = V _DC and E _r2 (t = t ₁ ) ≈ ( V
_AC / Dsd), and the electric field applied to the magnetic brush after the start of charging is regarded as an alternating electric field formed by almost only the AC bias voltage.

[0042] Thus, in the charging method of the present invention, the chain rising regulating portion, and a low resistance magnetic brush by an alternating electric field 1 be formed by controlling the AC bias voltage V _AC to be a V _AC / Dh ≧ E _D * After that, the charging is performed under the alternating electric field 2, whereby the image forming body is charged at high speed and uniformly.

The magnetic brush preferably used in the charging method of the present invention causes a rapid change in electric resistance under an electric field of 1 × 10 ⁴ V / cm or less. When it exceeds 1 × 10 ⁴ V / cm, it is necessary to increase the AC bias voltage for forming the electric field or to reduce the gap Dh between the carrier and the spike-height restricting portion.

In the charging method of the present invention, the upper limit of the AC bias voltage for forming a preferable electric field is 2 kV, because the ozone generation amount tends to increase when the AC bias voltage exceeds 2 kV. In addition, the gap Dh between the carrier and the spike-up regulating portion is preferably 0.01 to
At 1 cm, it is made equal to the gap Dsd between the image forming body and the carrier, but if it is less than 0.01 cm, the magnetic brush cannot be conveyed properly.
If it exceeds 1 cm, problems such as spikes of the magnetic brush may be found. Furthermore, the preferred lower limit of the electric field is
It is 100 V / cm, and if it is less than 100 V / cm, the alternating electric field 2 in the charging portion is also small, so that charging is insufficient and is likely to be non-uniform.

Next, general characteristics of the magnetic particles used in the present invention will be described.
As a property, the average particle size (weight average) of the magnetic particles is
30-100 μm, preferably 50-70 μm, saturation magnetization 20-100
emu / g, preferably 40-80 emu / g, apparent density 2-6 g /
cm³, Preferably 2.5-3g / cm ³And the ratio of the long axis to the short axis is 2
It is preferably double or less spherical particles.

The average particle size (weight average) of the magnetic particles is 30.
If it is less than μm, the particles tend to scatter or adhere to the surface of the image forming body. If it exceeds 100 μm, uneven charging tends to occur. If the saturation magnetization is less than 20 emu / g, the ears of the magnetic particles will be insufficient, and the particles will easily adhere to the image forming body.
If it exceeds 0 emu / g, the ears of the magnetic particles are hard and the image forming body is easily worn and damaged. Also, the apparent density of magnetic particles is 2
When it is less than g / cm ³ , the magnetic particles tend to adhere to the image forming body, and when it exceeds 6 g / cm ³ , the impact of the magnetic particles becomes strong and the image forming body is easily damaged. When the magnetic particles are spherical as described above, there are advantages that a uniform particle layer is formed on the charging sleeve of the carrier and the image forming body is not worn or damaged.

Such magnetic particles are the same as those used in the magnetic carrier particles of the conventional two-component developer as a magnetic material.
Ferromagnetism such as metals such as iron, chromium, nickel and cobalt, or their compounds and alloys such as ferric tetroxide, γ-ferric oxide, chromium dioxide, manganese oxide, ferrite and manganese-copper alloys. Body particles or the surface of these magnetic particles is coated with a resin such as styrene resin, vinyl resin, ethylene resin, rosin modified resin, acrylic resin, polyamide resin, epoxy resin, polyester resin, or It can be obtained by selecting the particle size of magnetic particles dispersed in a resin by a conventionally known average particle size selecting means.

Particularly preferred magnetic particles used in the present invention are, as described above, the magnetic brush made of the magnetic particles has an electric resistance of 10 ⁵ Ω or more under a low electric field and a high electric field. The electric resistance is 10 ⁴ Ω or less, and the abrupt change of the electric resistance is caused by an electric field of 1 × 10 ⁴ V / cm or less. For example, spherical particles made of the magnetic metal or alloys thereof have Those having a thin oxide film of 0.001 to 1 μm are used.

In order to measure the electric resistance of the magnetic brush, a copying machine, which is an image forming apparatus equipped with a magnetic brush charging device, is used. While the charging sleeve of the copying machine is rotated at a predetermined speed, the bristling regulating plate is used. The voltage V applied between the charging sleeve and the charging sleeve is changed, the current I flowing through the magnetic brush is measured, and the electric resistance of the magnetic brush is measured from the equation R = V / I. Further, the electric field dependency of the electric resistance is calculated from the voltage V at this time and the distance between the charging sleeve and the spike-rising regulating plate.

The carrier for carrying the magnetic brush in the charging method of the present invention comprises a magnet body having a plurality of magnetic poles and a charging sleeve rotatably provided on the outer periphery of the magnet body, and a particle layer is formed on the charging sleeve. While undulating in a wavy shape, new magnetic particles are supplied one after another,
Even if the particle layer on the surface of the charging sleeve has some unevenness in the layer thickness, the effect is sufficiently covered by the wavy undulation so as not to be a practical problem. It is preferable that the transport speed of the magnetic particles due to the rotation of the charging sleeve or the rotation of the magnet body is almost the same as or faster than the moving speed of the image forming body. Further, it is desirable that the conveying direction by the rotation of the charging sleeve is the same direction. The same-direction conveyance is superior to the opposite direction in charging uniformity. However, it is not limited thereto.

The carrier for carrying the magnetic particles is not limited to the one composed of a charging sleeve having a magnet body which is fixed or rotated inside, and is one in which the magnet body rotates without a charging sleeve, and N and S alternate. It may be composed only of the magnet body magnetized in the above.

As an image forming method using the charging method of the present invention, an inorganic photoreceptor such as ZnO, CdS, Se or the like, particularly an OPC photoreceptor of a function separation type having a charge generating layer and a charge transporting layer is used as an image forming body. Used as. The magnetic brush charging device according to the present invention is, for example, a magnet body to which a carrier carrying a magnetic brush is fixed and its outer periphery in the forward direction at a portion facing the image forming body, at 1.0 to 2.0 times the peripheral speed of the image forming body. It is composed of a charging sleeve that rotates at a peripheral speed, and the rotation of this sleeve rubs the above-mentioned specific magnetic brush on the image forming body to instantly give extremely uniform charging to the surface of the image forming body. Here, the peripheral speed V _S (mm / sec) of the image forming body during charging by this magnetic brush, the contact nip width L (mm) of the image forming body of the magnetic brush, and the frequency f of the AC bias applied to the magnetic brush. The relationship with (Hz) is preferably f ≧ (V _S / L) × 10, and the peripheral speed V _S of the image forming body is 50 to 500.
When the nip width L is 1 mm to 10 mm and the nip width L is 1 to 10 mm, the frequency f of the AC bias is 500 Hz to 4 kHz, and particularly preferably 1 to 2.5 kHz.

An electrostatic latent image is formed on the image-forming body which has been uniformly charged as described above by imagewise exposure, and the latent image is a one-component type developer composed of ordinary magnetic particles, preferably a one-component developer. A magnetic brush developing device containing a two-component developer composed of a magnetic carrier and a non-magnetic toner performs magnetic brush development to form a toner image. This toner image is transferred onto a transfer material by non-contact transfer using a corona discharger or contact transfer using a charging roller, and then fixed to form an image. The surface of the image forming body after the transfer is cleaned by a fur brush, a blade or the like, and is prepared for the next image formation.

(Example 1) Examples of the present invention will be specifically described below, but the embodiments of the present invention are not limited thereto.

First, as the magnetic particles 21 used in this embodiment, several kinds of magnetic particles were prepared by forming a thin oxide film of 0.001 to 3 μm on iron spherical particles having an average particle diameter of 45 μm. As shown in FIG. 6, three types of magnetic particles No. 1 to 3 in which the resistance of the selected magnetic particles made of a magnetic brush changed according to the electric field were obtained.

(Actual photo test 1) The above No. 1 was added to the copying machine.
The magnetic brush charging device 20 of FIG. 2 loaded with three kinds of magnetic particles of 3 to 3 is incorporated, and the gap Dh between the charging sleeve 22 and the regulating plate 26 and the gap Ds between the photosensitive drum 10 and the charging sleeve 22 are incorporated.
d, DC bias voltage V _h , DC bias voltage V _DC , AC
By changing the bias voltage V _AC (however, the frequency is constant at 2 kHz) and the like, the present invention tests No. 1 to 9 and the comparison test No. 1 to
Thirteen different imaging tests of 4 were performed. In this test, the image forming apparatus was left overnight in high humidity of 30 ° C. and RH 80%, and then a live-shooting test was performed in an atmosphere of 20 ° C. and RH 60%.
Image defects such as charging unevenness (image density unevenness) and magnetic particle adhesion (image defects due to magnetic particle adhesion) were measured.

For the measurement of the charging unevenness, the density of the high-density solid image portion was measured by using an image analyzer RT-2000 (manufactured by Yerman Co., Ltd.) at 100 points on a 100 μm × 100 μm square portion of the sample (data number 1
00), and the image defects due to the adhesion of the magnetic particles were measured by the optical densitometer for the occurrence of fog on the white background and evaluated according to the following evaluation criteria. The obtained results are shown in Table 2. .

Evaluation standard for uneven charging: “◎” ... The average density of 100 data is 1.3 or more,
And when the standard deviation of 100 data is 0.1 or less, "○" ... ・ The average density of 100 data is 1.3 or more,
And when the standard deviation of 100 data is more than 0.1 and 0.2 or less, “△” ・ ・ ・ ・ Average density of 100 data is 1.2 or more and 1.3
If the average concentration of 100 data is less than 1.2 or the standard deviation exceeds 0.2, the evaluation standard of magnetic particle adhesion is "○" ・ ・ ・ ・ When the white background fog is 0.01 or less "×" ・ ・ ・ ・ When the white background fog exceeds 0.01

[0059]

[Table 1]

From Table 1, in the test of the present invention, neither uneven charging nor adhesion of magnetic particles occurred, and an extremely high quality image was obtained, but in the comparative test with the regulation plate 26 in a floating state, any of the above image defects was found. Occur and are ineligible,
It turned out to have no practicality.

(Actual shooting test 2) Using a modified Konica 4045 copying machine in which the magnetic brush charging device shown in FIG. 3 was incorporated and the line speed was increased to 400 mm / sec, the conditions of No. 1 to 5 of the actual shooting test 1 were used. As a result of conducting a live-copy test 10,000 times each while sequentially charging the photoconductor with a magnetic brush, a clear image with high resolution and high density was obtained.

[0062]

According to the present invention, after the magnetic brush on the carrier is made to have a low resistance at the regulating plate portion, the electric charge is directly injected through the magnetic brush to give the image forming member with the electric charge. The voltage does not need to be higher than the charging voltage and can be lowered compared to the conventional method, and the generation of ozone and the fatigue of the image forming body due to corona ions are not accompanied by the uneven charging and the adhesion of magnetic particles to the image forming body. It is possible to provide a charging method using a magnetic brush capable of preventing deterioration and uniformly charging at high speed.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an image forming apparatus including a magnetic brush charging device to which the present invention is applied.

FIG. 2 is a sectional view showing an embodiment of a magnetic brush charging device to which the present invention is applied.

FIG. 3 is a sectional view showing another embodiment of the magnetic brush charging device to which the present invention is applied.

FIG. 4 is a diagram showing a relationship between an electric field and an electric resistance of a magnetic brush.

FIG. 5 is a diagram showing a relationship between a gap Dh, an AC bias voltage, and an electric field.

FIG. 6 is a diagram showing a relationship between an electric field and a resistance of a magnetic brush including each magnetic particle.

[Explanation of symbols]

 10 Photosensitive drum (image forming body) 20 Magnetic brush charging device 21 Magnetic particles 22 Charging sleeve (conveying carrier) 23 Magnet body 24 Bias power supply 24a, 25 DC power supply 24b AC power supply 26 Regulation plate (spike regulation plate) R1, R2 Protection resistance

 ─────────────────────────────────────────────────── ─── 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 magnetic brush made of magnetic particles is formed on a carrier, and the carrier is moved so that the magnetic brush passes through a gap between the carrier and the spike-up regulating plate, and then an image forming body is formed. In a charging method in which the image forming body is charged by contact and rubbing, an AC bias voltage having a DC component is applied to the carrier, and a DC voltage is applied to the spike control plate or the leveling plate. A charging method characterized by. 2. The magnetic brush as 1 × 10 ⁴ [V / cm]
Using a magnetic brush that causes an abrupt change in electrical resistance under the following electric field, an alternating electric field in the gap between the carrier and the spike control plate or leveling plate causes a sudden change in the electrical resistance of the magnetic brush. 2. The charging method according to claim 1, wherein the bias voltage applied to the carrier and the gap between the carrier and the bristling regulating plate or the leveling plate are set so as to be equal to or higher than the generated electric field.