JPH06161211A - Image forming device - Google Patents

Abstract

PURPOSE:To impart a uniform and sufficient quantity of charges to an image forming body without the generation of ozone and simultaneously to recover a magnetic grain without the damage of the image forming body by providing two magnetic brush electrifying members. CONSTITUTION:Electrifying members 23 and 24 are composed of fixed magnet bodies 27 and 28. rotary sleeves 25 and 26 and magnetic brushes 29 and 30, respectively. A DC voltage from a DC power source 63 and AC voltages from AC power sources 61 and 62 superimposed on the DC voltage are applied on the gaps of the sleeves 25 and 26 with respect to a photosensitive body 10, respectively. The AC voltage lower than that of a first electrifying member 23 is applied to a second electrifying member 24. On the other hand, magnetic force on the sleeve 26 is larger than that on the sleeve 25. The photosensitive drum 10 is electrified to correct electrification unevenness by the first electrifying member 23 by the second electrifying member 24. Moreover, the magnetic grain 22 stuck to the photosensitive drum 10 is stuck and recovered by the strong magnetic force of the second electrifying member 24.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as an electrophotographic copying machine, and more particularly to an image forming apparatus having a first charging magnetic brush and a second charging magnetic brush.

[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 is
A high voltage is applied to the discharge wire to generate a strong electric field around the discharge wire to perform gas discharge. Charging is performed by adsorbing the charge ions generated at that time to the image forming body.

Since the corona charger used in such a conventional image forming apparatus can be charged without mechanical contact with the image forming body, it is said that the image forming body is not damaged during charging. Have advantages. However, since this corona charger uses a high voltage, there is a risk of electric shock or leakage, and ozone generated by gas discharge is harmful to humans, which shortens the life of the image forming body. Had. In addition, the charging potential of the corona charger is unstable because it is strongly affected by temperature and humidity. Furthermore, it takes several seconds for the corona charger to obtain a stable charging potential after high voltage input. However, this is a major drawback when an electrophotographic image forming apparatus is used as a communication terminal or an information processing apparatus.

Many drawbacks of such corona chargers are:
The cause is that gas discharge is involved in charging.

Therefore, a cylinder containing a magnet body is used as a charging device capable of charging an image forming body without causing a gas discharge like a corona charger and without mechanically damaging the image forming body. A charging device that forms magnetic brushes by adsorbing magnetic particles on a sleeve and charges the surface by rubbing the surface of the image forming body with the magnetic brush is disclosed in, for example, JP-A-59-133569. And JP-A-63-18
It is described in each publication of No. 7267. In the inventions described in these publications, the surface of the image forming body is rubbed by a magnetic brush to charge the surface of the image forming body, and magnetic particles adsorbed on the image forming body from the magnetic brush are contacted with a blade on the surface of the image forming body. It is peeled off and collected on the magnetic brush side.

[0006]

However, in the charging device described in the above publication, charging is applied to the image forming body with one magnetic brush, so that it is difficult to set the charging condition, and uniform and sufficient charging can be obtained. There is a problem that you cannot do it. Furthermore, since the magnetic particles attached to the image forming body are collected by a blade or the like, there is a problem that the surface of the image forming body is damaged and a high quality image cannot be obtained.

As a result of earnest studies, the inventor of the present invention found a charging device capable of constantly providing stable charging to an image forming body and recovering magnetic particles without damaging the image forming body, thus completing the present invention. Of.

[0008]

(Object of the Invention) It is an object of the present invention to impart a uniform and sufficient amount of electric charge to an image forming body without generating harmful gas such as ozone. An object of the present invention is to provide an image forming apparatus having a magnetic brush charging device that can be used.

Still another object is that the magnetic particles adhering to the image forming body from the magnetic brush can be collected on the magnetic brush side without damaging the image forming body, and high image quality is stable in the process of repeated image formation. An object is to provide an image forming apparatus obtained by the above.

(Constitution of the Invention) The above-mentioned object is an image forming apparatus equipped with a charging means for applying a charge by bringing a magnetic brush made of magnetic particles into contact with an image forming body. An oscillating voltage having a direct current component and an alternating current component is applied to the first charging member, which has a first charging member arranged on the upstream side in the moving direction of the body and a second charging member arranged on the downstream side. At the same time, an oscillating voltage lower than the oscillating voltage applied to the first charging member is applied to the second charging member, and the image forming apparatus is composed of magnetic particles. In an image forming apparatus provided with a charging unit that applies a charge by bringing a magnetic brush into contact with the charging unit, the charging unit includes a first charging member arranged on the upstream side in the moving direction of the image forming body and a first charging member arranged on the downstream side. Two
And a DC voltage is applied to each of the first and second charging members and an AC voltage is applied to the first and second charging members to form an oscillating electric field with the image forming body. The oscillating electric field of the second charging member has the same phase as the oscillating electric field of the first charging member, and a magnetic brush made of magnetic particles is brought into contact with the image forming body to charge the image forming apparatus. In the image forming apparatus provided with a charging unit for applying, the charging unit has a first charging member arranged on the upstream side in the moving direction of the image forming body and a second charging member arranged on the downstream side. , A DC voltage is applied to each of the first and second charging members, and an AC voltage is applied to the first and second charging members to form an oscillating electric field between the first and second charging members and convey the second charging member. An image characterized in that the speed is smaller than the moving speed of the first charging member. It is accomplished by forming device.

In the image forming apparatus of the present invention, two magnetic brush charging members are integrally incorporated in the casing in order to uniformly and sufficiently charge the image forming body. Of the two charging members, a higher oscillating electric field is applied to the charging member on the upstream side in the rotation direction of the image forming body to apply sufficient charging to the image forming body. In this charging by the charging member on the upstream side, sufficient charging is imparted by the higher oscillating electric field, but on the other hand, the magnetic particles constituting the magnetic brush violently vibrate, so that uneven charging is likely to occur, and in the vicinity of the outlet of the charging member. Magnetic particles tend to adhere to the image forming body. Therefore, the charging member on the downstream side, to which a low oscillating electric field is applied, makes the charging uniform and collects the magnetic particles attached to the image forming body.
As a result, uniform and sufficient charging is imparted to the image forming body without the magnetic particles attached thereto.

If magnetic particles adhere to the image forming body,
In the next step, the toner image becomes uneven and the image quality becomes rough, and the image forming body is damaged.

The magnetic brush charging member according to the present invention comprises a magnetic particle carrier which comprises a magnet body and a sleeve which rotates relative to the outer periphery thereof, and a magnetic brush formed on the sleeve. The gap D between the sleeve of the magnetic brush charging member and the image forming member is in the range of 0.1 to 5 mm, and the charging member has a DC voltage of ± 500 to 1000 V and a frequency of 0.2 to 5 KHz, V _PP.
An alternating bias biasing an alternating voltage of 200 to 3500 V and 0.3 to 10 KHz is applied, and an oscillating electric field is formed between the AC bias and the image forming body.

Furthermore, since the magnetic particles forming the magnetic brush have a low resistance, it is desirable to apply an AC portion having the same phase in order to prevent an electric leak phenomenon between the first and second charging members. By doing so, the potential difference between the magnetic brushes can be reduced, and the voltage can be effectively applied.

Further, in order to prevent an electric leak phenomenon, it is preferable to provide an insulating shield member between the both charging members. The oscillating electric field is configured such that the first charging member on the upstream side in the rotational direction of the image forming body is large and the second charging member on the downstream side is small. The electric field strength is preferably 1.2 to 3 times.

As a control method of the oscillating electric field, (1)
A method of varying the alternating voltage to create an oscillating electric field,
(2) A method of changing the gap D between the sleeve and the image forming body without changing the AC bias is used. The above (1) and (2) are adjusted according to the ratio of the electric field.

That is, by setting the gap D ₂ between the sleeve of the second charging member and the image forming body to be larger than the gap D ₁ between the sleeve of the first charging member and the image forming body, The oscillating electric field is configured so that the oscillating electric field on the first charging member side is small.

Further, in a preferred embodiment of the present invention, the charging area of the second charging member is made wider than the charging area of the first charging member in order to enhance the recovery efficiency of the magnetic particles attached to the image forming body. . In addition, the second for the same purpose
It is preferable that the magnetic force of the charging member is larger than the magnetic force of the first charging member.

The magnetic particles forming the magnetic brush will be described below.

The magnetic particles have an average particle size (weight average) of 150 μm or less, preferably 100 μm or less, 30 μm or more.

Generally, when the average particle size (weight average) of the magnetic particles is large, (a) the state of the magnetic brush formed on the sleeve is rough, so that even if the magnetic particles are charged while vibrating, the magnetic The unevenness is likely to appear on the brush, and the problem of uneven charging occurs. To solve this problem, the average particle size of the carrier particles should be reduced.
It was found that the effect began to appear when the thickness was 0 μm or less, and particularly when the thickness became 100 μm or less, the problem (a) did not substantially occur. However, if the particles are too fine, they tend to adhere to the surface of the image forming body at the time of charging, or easily scatter. These phenomena are related to the strength of the magnetic field acting on the particles and the strength of the magnetization of the particles thereby, but generally, the average particle diameter of the particles becomes prominent at 30 μm or less. In addition,
A magnetized strength of 20 to 200 emu / g is preferably used.

From the above, the average particle size of the magnetic particles is
It is preferably 150 μm or less, particularly preferably 100 μm or less and 30 μm or more.

Such magnetic particles can be used as a magnetic substance, such as metals such as iron, chromium, nickel and cobalt as in the conventional magnetic carrier particles, or compounds or alloys thereof, such as iron tetroxide and γ-oxidized iron. The surface of ferromagnetic particles such as diiron, chromium dioxide, manganese oxide, ferrite, manganese-copper alloy, or the surface of these magnetic particles is styrene resin, vinyl resin, ethylene resin, rosin modified resin, acrylic The particles obtained by coating with a resin such as a system resin, a polyamide resin, an epoxy resin, a polyester resin, or by a resin containing magnetic particles dispersed therein are provided with a conventionally known average particle size selection means. It is obtained by selecting the particle size.

The formation of spherical magnetic particles is
The particle layer formed on the sleeve becomes uniform, and a high bias voltage can be uniformly applied to the sleeve. That is, the fact that the magnetic particles are spherical means that (1) generally, the magnetic particles are easily magnetized and adsorbed in the long axis direction, but due to the spherical shape, the directionality is lost, so that the layers are uniformly formed and local layers are formed. (2) Higher resistance of magnetic particles is eliminated, and the edge parts seen in conventional particles are eliminated, and the concentration of electric field on the edge parts does not occur. As a result, even if a high bias voltage is applied to the sleeve, there is an effect that the surface of the image forming body is uniformly discharged and charging unevenness does not occur. The resistivity of the carrier particles is 10 ³ Omega · cm or more spherical particles to achieve the above effects, 10 ¹²
It is preferable that the magnetic particles having electrostatic properties are formed so as to be Ω · cm or less. The resistivity after tapping putting particles in a container having a sectional area of 0.50 cm ^2, a load of 1 kg / cm ² on packed particles, between the load and a bottom electrode
This value is obtained by reading the current value when a voltage that generates an electric field of 1000 V / cm is applied. If this resistivity is low, electric charges are injected into the magnetic particles when a bias voltage is applied to the sleeve. The magnetic particles are likely to adhere to the surface of the image forming body, or the breakdown of the bias voltage is likely to occur. If the resistivity is high, charge injection is not performed and charging is not performed.

In summary, the magnetic particles are spherical so that at least the ratio of the major axis to the minor axis is 3 times or less, and there are no protrusions such as needles and edges, and the resistivity is high. 10 ³ Ω ・
cm to 10 ¹² Ω ・ cm, preferably 10 ⁴ Ω ・ cm to 10 ⁹ Ω ・ c
The proper condition is that it is m or less. Then, such spherical magnetic particles should be selected as spherical as possible for the magnetic particles, and in the particles of the magnetic material fine particle dispersion system, the fine particles of the magnetic material should be used as much as possible, and the spheroidizing treatment should be performed after the formation of the dispersed resin particles. It is manufactured by applying or by having dispersed resin particles by a spray drying method.

The conditions for magnetic particles have been described above. Next, a magnetic particle carrying carrier composed of a magnet body carrying a magnetic particle layer and carrying it and a sleeve will be explained. The magnet body has a plurality of N and S alternating magnetic poles, and the relative rotation between the magnet body and the sleeve causes the particle layer formed on the sleeve to undulate and move. The new magnetic particles are supplied one after another, and even if the particle layer on the surface of the sleeve has some non-uniformity of the layer thickness, its effect is sufficiently covered by the wavy undulation so that it is not a practical problem. The transport speed of the magnetic particles due to the rotation of the sleeve or the rotation of the magnet body may be slower than the moving speed of the image forming body, but is preferably almost the same or higher than that. Further, the transport direction by the rotation of the sleeve is preferably the same direction. Uniformity of charging is better in the same direction than in the opposite direction. However, it is not limited thereto. In particular, it is preferable to make the conveying speed of the second charging unit smaller than that of the first charging unit in terms of scattering of magnetic particles and adhesion to the image forming body. The conveying speed of the second charging unit may be slower than the moving speed of the image forming body.

Further, the thickness of the particle layer formed on the sleeve is preferably such that it is sufficiently scraped off by the regulating plate to form a uniform layer, and the gap between the sleeve and the image forming body is 100 to 5000 μm is preferable. If the surface gap between the sleeve and the image forming body becomes too narrower than 100 μm, it will be difficult to form the magnetic brush spikes that uniformly act on the surface, and sufficient magnetic particles must be supplied to the charging section. If it becomes impossible to perform stable charging, and if the gap exceeds 5000 μm, the particle layer will be rough and uneven charging will occur easily. You will not be able to get it.
As described above, when the gap between the sleeve and the image forming member becomes extreme, the thickness of the particle layer on the sleeve cannot be adjusted appropriately, but when the gap is in the range of 100 to 5000 μm, The particle layer can be formed to have an appropriate thickness. This is because it is possible to prevent the occurrence of sweeps due to the rubbing of the magnetic brush.

The magnetic force on the sleeves of the first and second charging members is 500 to 1500 Gauss, and the second charging member is preferably larger than the first charging member.

[0029]

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

FIG. 1 is a sectional view showing the outline of the construction of an electrophotographic image forming apparatus equipped with the charging device of the present invention.

In the figure, reference numeral 10 is an (-) charged OPC photosensitive drum which is an image forming body which rotates in the direction of the arrow (clockwise), and its peripheral portion has an image exposure from a charging device 20 and an exposing device which will be described later. L, a developing device 30, a transfer roller 13, a cleaning device 50 and the like are provided.

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, the peripheral surface of the photosensitive drum 10 is uniformly charged and passed by a charging device 20 described later. An image is written on the photosensitive drum 10 by, for example, a laser beam L from an image writing device or the like, and an electrostatic latent image corresponding to the image is formed.

There is a two-component developer in the developing device 30, which is agitated by the agitating screws 33A and 33B, and then adheres to the outer circumference of the developing sleeve 31 which is outside the magnet roll 32 and is a magnetic brush of the developer. Then, a predetermined bias voltage is applied to the developing sleeve 31, and reversal development is performed in the developing area facing the photoconductor drum 10.

The recording paper P is fed from the paper feed cassette 40 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. Then, by the action of the transfer roller 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. Recording paper P
The surface of the photosensitive drum 10 which has toner remaining without being transferred to and is rotated is scraped off and cleaned by a cleaning device 50 having a blade 51 and the like, and waits for the next copying.

FIG. 2 is a sectional view showing an embodiment of the charging device 20 of the present invention used in the image forming apparatus of FIG. In the figure, 22 is a magnetic particle, and spherical ferrite particles coated so as to have conductivity are used. In addition, conductive magnetic resin particles obtained by pulverizing the magnetic particles and a resin as main components after thermal smelting can also be used. The outer shape is a true sphere and the particle size is 50μ to ensure good charging.
It was adjusted to m and a specific resistance of 10 ⁸ Ω · cm, and the triboelectric charge amount with the toner was −5 μC / g under the condition that the toner concentration was 1%.

Reference numeral 21 denotes a casing of the charging device 20, in which a first charging member 23 and a second charging member 24 are incorporated.

The first charging member 23 has a fixed magnet body 27 having N and S alternating magnetic poles, and a sleeve forcibly rotating its outer periphery in the arrow direction (counterclockwise direction) at 1.5 times the peripheral speed of the photosensitive drum. 25 and a magnetic brush 29, and the magnetic force on the surface of the magnet 25 is 800 gauss. The gap between the sleeve 25 and the photosensitive drum 10 is D ₁ is a 500 [mu] m, 1 KHz from the AC power supply 61 to Ju疂DC voltage and to the -800V from the DC power supply 63 of the power supply 60 in the gap D _1, An AC voltage of V _PP voltage of 1500 V is applied, and the magnetic brush 29 regulated by the layer thickness regulating member 71 rubs the surface of the photoconductor drum 10 to inject charges into the photoconductor layer 10b of the photoconductor drum 10. A negative charge (-700V) is applied.

By the way, an oscillating electric field based on a high AC voltage injects charges into the charging member, so that uneven charging occurs or magnetic particles adhere to the photosensitive drum near the outlet of the magnetic brush. The uneven charging and the adhesion phenomenon of magnetic particles are eliminated by the second charging member 24.

As with the first charging member, the second charging member 24 has a circumferential velocity of 0.5 of the peripheral speed of the photosensitive drum in the arrow direction (counterclockwise direction) on the outer periphery of the fixed magnet body 28 in which N and S alternating magnetic poles are arranged.
The magnetic force of the magnet body 28 on the sleeve 26 is 1000 gauss, which is larger than that of the first charging portion. Also, the sleeve 26
The photosensitive member gap D ₂ between the drum 10 is a 500 [mu] m, an AC power source 6 from the DC power source 63 and the DC voltage of -800V power supply 60 to the gap D ₂ a wide charged region than the first charging section is provided
An AC voltage of 2 to 1 KHz and V _PP 800 V in the same phase as that of the first charging member is applied, and the magnetic brush 30 regulated by the layer thickness regulating member 72 slides on the photosensitive drum 10 to cause the first charging. The magnetic particles 22 attached to the photosensitive drum 10 are attached and collected by the strong magnetic force of the second charging member while being charged to correct the uneven charging of the member. Thus, the magnetic particles 22 do not adhere to the photoconductor drum 10 and extremely uniform charging is applied, and the image is sent to the next step of image exposure and development, and stable and high-quality image formation is always performed. Is obtained.

The stirring members 67, 68, 69 are rotating members provided around the plate-shaped member so that the magnetic particles are not biased. The insulative shield member 70 prevents current from flowing through the magnetic particles between the charging members.

AC power sources 61 and 62 in the power source 60
As for the voltage, the AC components of the same phase obtained by boosting the AC power supply 65 by the transformer 66 are applied.

[0042]

As is apparent from the above description, according to the image forming apparatus of the present invention, since the magnetic brush charging in which the electric charge is directly injected through the magnetic particles of the drum is employed, ozone is not generated and the characteristics are not generated. Since the charging is imparted by the first and second charging members having different values, extremely uniform and stable charging is possible, and there is no adhesion of magnetic particles to the surface of the image forming body. Played.

[Brief description of drawings]

FIG. 1 is a sectional view showing an outline of an image forming apparatus including a charging device according to the present invention.

FIG. 2 is a cross-sectional view showing an example of a charging device according to the present invention.

[Explanation of symbols]

 10 Photosensitive drum 20 Charging device 21 Casing 22 Magnetic particles 23 First charging member 24 Second charging member 60 Bias power supply 70 Insulating shield member

Claims (9)

[Claims] 1. An image forming apparatus comprising a charging means for applying a charge by bringing a magnetic brush made of magnetic particles into contact with the image forming body, wherein the charging means is provided on an upstream side in a moving direction of the image forming body. A first charging member arranged and a second charging member arranged on the downstream side, and a direct current voltage and an alternating current voltage are applied to each of the first and second charging members,
An image forming apparatus, wherein an oscillating electric field is formed between the image forming body and the oscillating electric field of the second charging member is smaller than that of the first charging member. 2. The charging area of the second charging member is the first area.
The image forming apparatus according to claim 1, wherein the charging area is wider than the charging area of the charging member. 3. The image forming apparatus according to claim 1, wherein the magnetic force of the second charging member is larger than the magnetic force of the first charging member. 4. An image forming apparatus comprising a charging means for applying a charge by bringing a magnetic brush made of magnetic particles into contact with the image forming body, wherein the charging means is provided on an upstream side in a moving direction of the image forming body. A first charging member arranged and a second charging member arranged on the downstream side, and a direct current voltage and an alternating current voltage are applied to each of the first and second charging members,
An image forming apparatus, wherein an oscillating electric field is formed between the image forming body and the oscillating electric field of the second charging member is in phase with the oscillating electric field of the first charging member. 5. The charging area of the second charging member is the first charging area.
The image forming apparatus according to claim 4, wherein the charging area is wider than the charging area of the charging member. 6. The image forming apparatus according to claim 4, wherein the magnetic force of the second charging member is larger than the magnetic force of the first charging member. 7. An image forming apparatus comprising a charging means for applying a charge by bringing a magnetic brush made of magnetic particles into contact with the image forming body, wherein the charging means is provided on an upstream side in a moving direction of the image forming body. A first charging member arranged and a second charging member arranged on the downstream side, and a direct current voltage and an alternating current voltage are applied to each of the first and second charging members,
An image forming apparatus, wherein an oscillating electric field is formed between the image forming body and a conveying speed of the second charging member is set to be lower than a moving speed of the first charging member. 8. The charging area of the second charging member is the first charging area.
The image forming apparatus according to claim 7, wherein the charging area is wider than the charging area of the charging member. 9. The image forming apparatus according to claim 7, wherein the magnetic force of the second charging member is larger than the magnetic force of the first charging member.