JP3230171B2 - Developing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic copying machine or the like, in which magnetic carrier particles and toner particles are mixed.
The present invention relates to a developing device that develops an electrostatic latent image or a magnetic latent image using a component developer.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic copying machine or the like,
A magnetic brush developing type developing device using a two-component developer is used. This developing device has a cylindrical developing sleeve rotatably supported and provided with a magnet roll composed of a magnet body having a plurality of magnetic poles inside, and holds a magnetic carrier having toner particles adhered to the surface of the developing sleeve. The toner is transported to the development zone for development, and the frictional charge control of the toner particles is relatively easy, the aggregation of the toner particles is less likely to occur, and the magnetic brush has good ears, and the surface of the image carrier has excellent friction. In addition, it is widely used in spite of the necessity of controlling the amount of toner particles with respect to carrier particles, such that a sufficient cleaning effect is exhibited even when used also for cleaning. However, in the developing method in which the magnetic brush is rubbed against the surface of the image carrier to develop, conventionally, magnetic carrier particles having an average particle diameter of several tens μm to several hundred μm and non-magnetic toner particles having an average particle diameter of about 10 μm are generally used. Is used, and the toner particles and further the carrier particles are coarse, so that it is difficult to obtain a high-quality image that reproduces delicate lines, dots, differences in shading, and the like. Therefore, in order to obtain high image quality in this developing method, conventionally,
For example, many efforts have been made, such as resin coating of carrier particles and improvement of the magnet body in the developer carrier, but still it is still impossible to obtain a stable and satisfactory image. . Therefore, in order to obtain a high quality image, it is considered necessary to make the toner particles and the carrier particles finer. However, if the average particle diameter of the toner particles is 20 μm or less, particularly 10 μm or less, the influence of the van der Waals force relative to the Coulomb force during development appears, and the adhesion force between the image forming body and the toner And so-called fog in which toner particles adhere to the background portion of the image background occurs, and it becomes difficult to prevent fog even by applying a DC bias voltage to the developer carrier. It is difficult to control the triboelectric charging of the toner particles, and aggregation tends to occur. On the other hand, as the carrier particles become finer, the carrier particles also adhere to the electrostatic image portion of the image carrier. It is considered that this is because the magnetic bias force was reduced and the carrier particles adhered to the image carrier together with the toner particles. When the bias voltage increases, the carrier particles also adhere to the ground portion of the image background. Since the above-mentioned side effects are more conspicuous in micronization and clear images cannot be obtained, it is difficult to micronize toner particles and carrier particles. Was.

As a method for solving the above-mentioned problem, a developer is transported to a development area so as not to be in contact with an image forming body, and the toner in the developer is caused to fly by an oscillating electric field to develop a latent image. In the non-contact developing method, a horizontal magnetic field is formed in a developing area, and a leveling member is disposed between a central portion thereof and a regulating member that regulates the thickness of the developer layer. And applying a DC bias voltage having a polarity opposite to the charging polarity of the toner particles to the leveling member (Japanese Unexamined Patent Publication No.
No. 368).

Further, a toner cloud developing method using a plate-like electrode body (Japanese Patent Application Laid-Open Nos. Hei 3-31878 and Hei 3-131879) has been proposed.

[0005]

However, according to the above-mentioned solution, when the average particle diameter of the toner particles becomes 10 μm or less,
As described above, since the influence of the Van der Waals force becomes large, there arises a problem that the adhesive force between the carrier and the toner is increased and the developability is extremely reduced.

According to the above-mentioned solution, since the horizontal magnetic field causes the ears of the magnetic brush to fall and the developer layer to be dense, the toner is difficult to be pulled out by the leveling member, and in particular, the small particle diameter having an average particle diameter of 10 μm or less. When a toner is used, the developability is significantly reduced. Further, since a DC voltage having a polarity opposite to that of the toner is applied to the leveling member, there is a problem that the toner is deposited as the toner is used, and the image is stained.

In the method (1), since the electrode body is in the form of a wide plate, a toner cloud is generated even at a position upstream of the contact position or the closest position of the electrode body, and the developer conveyance amount is reduced. There is a problem that the development is not performed.

An object of the present invention is to solve the above-mentioned problems and to provide a developing apparatus which does not cause image contamination even when small-sized toner particles and carrier particles are used, and which can stably achieve high developability. With the goal.

[0009]

An object of the present invention is to transport a two-component developer to a developing area by a developing sleeve having a magnet body having a plurality of magnetic poles fixed therein, and to fly toner in an oscillating electric field. In a developing device for developing a latent image formed on an image forming body, a bias voltage obtained by superimposing an AC voltage on a DC voltage is applied to the developing sleeve, and a main magnetic pole of the magnet body is arranged in the developing area, An insulating plate-shaped member is disposed at a position on the upstream side in the rotation direction of the development sleeve with respect to the development area and in contact with or in proximity to the magnetic brush formed by the main magnetic pole, This is achieved by a developing device characterized in that a linear electrode to which a voltage can be applied is provided at the front end of the developing area, and a DC bias voltage is applied to the linear electrode.

The tip of the linear electrode is located upstream of the main pole in the direction of rotation of the developing sleeve, and when the maximum magnetic flux density of the main pole is Hr, the magnetic flux density is 0.2H.
The angle between the main magnetic pole and the closest position between the developing sleeve and the image forming body with respect to the rotation axis of the developing sleeve and the main magnetic pole around the rotation axis of the developing sleeve is θ1. And the angle between the tip of the linear electrode and θ
2, when the angle between the main magnetic pole and the upstream magnetic pole with respect to the rotation direction of the developing sleeve adjacent to the main magnetic pole is θ3, θ1 = −10 ° to 10 ° θ2 = (0.05 to 0.5) θ3 The developing device according to the preferred embodiment, characterized in that θ3 = 10 ° to 45 °.

[0011]

FIG. 2 is a sectional view showing an example of a color image forming apparatus provided with the developing device of the present invention as a suitable developing means.

In FIG. 2, reference numeral 1 denotes a photoreceptor belt which is a belt-shaped photoreceptor made of a flexible belt on which a photoconductor is coated or vapor-deposited. And is conveyed clockwise by the driving of the rotating roller 2.

Reference numeral 4 denotes a guide member fixed to the apparatus main body so as to be in contact with the photoreceptor belt 1. The photoreceptor belt 1 is tensioned by the action of a tension roller 5 so that the inner peripheral surface thereof becomes the guide member. 4 rub.

Reference numeral 6 denotes a scorotron charger as a charging means;
Is an optical writing device using a laser beam as an image exposure means,
Reference numerals 8A to 8D denote developing devices according to the present invention, each of which is a plurality of developing means accommodating a developer of a specific color. These image forming means are provided at a portion of the photosensitive belt 1 which is in contact with the guide member 4. You.

The developing devices 8A, 8B, 8C, and 8D, which will be described in detail later, contain, for example, yellow, magenta, cyan, and black developers, respectively, and maintain a predetermined gap with the photosensitive belt 1. Keep each developing sleeve
81, and has a function of visualizing a latent image on the photosensitive belt 1 by a non-contact reversal developing method. Unlike the contact development, the non-contact development has an advantage that the movement of the photosensitive belt 1 is not hindered.

Reference numeral 12 denotes a transfer unit, 13 denotes a cleaning device, and a blade 13a of the cleaning device 13 and a toner discharge roller.
13b is kept at a position separated from the surface of the photoreceptor belt 1 during image formation, and is brought into pressure contact with the surface of the photoreceptor belt 1 as shown in the drawing only during cleaning after image transfer.

The process of forming a color image by the color image forming apparatus is performed as follows.

First, the formation of a multicolor image according to the present embodiment is shown in FIG.
Performed in accordance with the imaging system. That is, an original image is obtained by a color image data input unit (a) scanned by an image sensor, and this data is obtained by an image data processing unit (b).
The image data is created by performing the arithmetic processing in and stored in the image memory (c) once. Next, the image data is taken out at the time of recording and is input to the recording unit (d), for example, the color image forming apparatus shown in FIG. That is, when image data, which is a color signal output from an image reading device separate from the color image forming device, is input to the optical writing device 7, the optical writing device 7 is a semiconductor which is a writing light source (not shown). A laser beam (writing light) generated by the laser passes through a collimator lens and a cylindrical lens (not shown), is rotationally scanned by a rotary polygon mirror 74 rotated by a drive motor 71, passes through an fθ lens 75 and a cylindrical lens 76, The optical path is bent by the mirrors 77 and 78 and projected onto the peripheral surface of the photoreceptor belt 1 to which a uniform charge is given in advance by the charger 6 of the scorotron as a charging means, and the main scanning is performed to form a bright line. I do.

On the other hand, when scanning is started, a laser beam is detected by an index sensor (not shown),
The laser beam modulated by the color signal scans the peripheral surface of the photosensitive belt 1. Therefore, a latent image corresponding to the first color is formed on the peripheral surface of the photosensitive belt 1 by the main scanning by the laser beam and the sub-scanning by the conveyance of the photosensitive belt 1. The latent image is developed by the developing device 8A loaded with yellow (Y) toner (visual medium) of the developing means, and a toner image is formed on the belt surface. The obtained toner image passes under the blade 13a of the cleaning device 13 and the toner discharge roller 13b, which is a cleaning means, which is separated from the peripheral surface of the photoreceptor belt 1 while being held on the belt surface. to go into.

That is, the photosensitive belt 1 is connected to the charger 6
Then, a second color signal is input to the optical writing device 7, and writing is performed on the belt surface in the same manner as in the case of the above-described first color signal to form a latent image. The latent image is developed by the developing device 8B loaded with magenta (M) toner as the second color.

The magenta (M) toner image is formed in the presence of the previously formed yellow (Y) toner image.

Reference numeral 8C denotes a developing device having cyan (C) toner, and forms a cyan (C) toner image on the belt surface similarly to the first and second colors.

Reference numeral 8D denotes a developing device having a black toner, which forms a black toner image on the belt surface by the same processing as the above-described color. A DC or further AC bias voltage is applied to each developing sleeve 81 of each of these developing devices 8A, 8B, 8C, and 8D, and non-contact development is performed by a two-component developer as a visualizing means.
The development is performed in a non-contact manner on the photosensitive belt 1 whose base is grounded.

The color toner image thus formed on the peripheral surface of the photoreceptor belt 1 is applied with a high voltage having a polarity opposite to that of the toner at the transfer portion, and is sent from the paper supply cassette 14 through the paper supply guide 15. Is transferred to the transfer material.

That is, one of the uppermost layers of the transfer material accommodated in the paper supply cassette 14 is carried out by the rotation of the paper supply roller 16, and the timing of image formation on the photosensitive belt 1 is adjusted via the timing roller 17. And is supplied to the transfer device 12.

The transfer material to which the toner image has been transferred is reliably separated from the photoreceptor belt 1 which suddenly changes its direction along the rotating roller 2 and goes upward, and the toner image is fused by the fixing roller 18. After being fixed, the sheet is discharged onto a tray 20 via a sheet discharge roller 19.

On the other hand, the photoreceptor belt 1 after the transfer to the transfer material is further conveyed to remove the residual toner in the cleaning device 13 in which the blade 13a and the toner discharge roller 13b are pressed against each other, and the process is completed. Then, the blade 13a is separated again, and a little later, the toner discharge roller 13b is separated to start a new image forming process.

As the color image forming apparatus using the developing device of the present invention, a belt-shaped image forming body has been described. However, an image forming apparatus having a drum-shaped image forming body can be similarly used. .

The developing devices 8A to 8D have the same structure, and are denoted by reference numeral 8 below. FIG. 1 is a schematic sectional view showing an embodiment of the developing device of the present invention. FIG.
(A) is sectional drawing of one Example of the apparatus of this invention, 81
Is a developing sleeve made of a non-magnetic material such as aluminum,
82 is fixed inside the developing sleeve 81 and has a plurality of N,
A magnetic body having an S magnetic pole in the circumferential direction. One of the magnetic poles is disposed in the vicinity of the closest position between the developing sleeve 81 and the photosensitive belt 1 and is referred to as a main magnetic pole 82a. The developing sleeve 81 and the magnet 82 constitute a developer carrying carrier. The developing sleeve 81 is rotatable with respect to the magnet 82, and the drawing shows that the developing sleeve 81 is rotated leftward as indicated by the arrow, and the magnet 82 is fixed. The main magnetic pole of the magnet body 82
82a and other N and S magnetic poles are usually magnetized to a magnetic flux density of 500 gauss to 1,500 gauss, and the magnetic force causes a layer of a developer D composed of toner particles and carrier particles on the surface of the developing sleeve 81, that is, a magnetic brush. To form This magnetic brush is rotated by the rotation of the developing sleeve 81 to form the developing sleeve.
It moves in the same direction as the rotation of 81 and is transported to the development area A. The gap between the developing sleeve 81 and the regulating blade 86 and the gap between the developing sleeve 81 and the photosensitive belt 1 are adjusted so that the magnetic brush formed on the developing sleeve 81 does not contact the surface of the photosensitive belt 1 and keeps a gap. Is done.

Reference numeral 83 denotes a plate-like member provided on the upstream side of the development zone A and also serves as a leveling member made of an electrical insulator such as polyester, polyimide, glass epoxy, polyethylene terephthalate, or polyamideimide, and 84 denotes a plate-like member. 85A, 85B linear electrodes made of a conductive material such as metal, which are linearly provided integrally with the plate member 83 on the front end of the plate member 83 to form an oscillating electric field at the front end of the member 83; Is a stirring screw that stirs the developer D to make the components uniform, 86 is a regulating blade that is a developer regulating means made of a non-magnetic material or a magnetic material provided for regulating the height and amount of the magnetic brush, 87 Is a cleaning blade that removes the magnetic brush that has passed the developing area A from above the developing sleeve 81, 88 is a reservoir for developer, and 89 is a casing.

As shown in FIG. 3, the linear electrode 84 is formed by bonding a conductive material such as a metal into a linear shape having a circular or quadrangular cross section to the tip of an insulating plate member 83. (A), (b), (g), (h) in FIG.
A notch 83a is provided at the tip of the plate-shaped member 83 and sandwiched between the cuts (FIGS. 3C and 3D).
In addition to the method of providing and embedding 83b (FIGS. 3 (e) and 3 (f)) and the like, as shown in FIG. A linear electrode 84 can be formed at the tip end of the plate-like member 83 by laminating a conductive member such as copper foil using polyimide, polyimide, paper phenol, or the like, and then performing etching. The linear electrode 84 may be covered with an insulating resin for preventing unnecessary discharge and for preventing rust.

At this time, in order to prevent generation of unnecessary clouds in the upstream portion of the transfer and obtain a stable transfer amount, the linear electrodes 84
Is formed only on the downstream side in the sleeve rotation direction from the closest contact point 81b between the plate member 83 and the developing sleeve 81 as shown in FIG. The circumferential length of the linear electrode 84 is
Depends on the diameter of 81 and the conveying speed, 0.05mm to 5mm, especially 0.1m
m to 1 mm is preferred. If it is less than 0.05 mm, a sufficient cloud cannot be generated, and if it is more than 5 mm, the toner is charged by vibration and becomes excessively charged, so that the developing property is deteriorated. The thickness of the linear electrode 84 is (2/3) g when the closest distance between the image forming body 1 in the development area and the development sleeve 81 is g.
To (1/10000) g, particularly (1/2) g to (1/1000) g. If it is larger than (2/3) g, the image forming body 1 and the linear electrode 8
Since the gap of 4 is narrowed, the linear electrode 84 easily comes into contact with the surface of the image forming body 1, and image disorder is easily generated.
On the other hand, if it is less than (1/10000) g, the current from the developing sleeve 81 tends to flow, causing a voltage drop and a decrease in developability. In the plate member 83, the upper end of the linear electrode 84 on the image forming body 1 side is (2/3) g or less, and the lower end of the linear electrode 84 on the developing sleeve side is (1/1).
A material capable of supporting the linear electrode 84 so as to have a weight of 0000) g or more is selected. From the viewpoints of strength, vibration prevention, and prevention of contact with the image forming body 1, (2/3) g to (1/100) g g are preferred. Assuming that the length of the linear electrode 84 is w3 and the width of the developer D layer on the developing sleeve 81 is w4, w3> w4 and
Terminal portion 81a for applying a DC voltage E ₃ to 4, provided than W ₄ of the linear electrodes 84 to the outer part, to prevent generation of unwanted cloud.

As shown in FIG. 1B, FIG. 3A and FIG. 5, the installation position of the linear electrode 84 is
83 between the contact point of the developing sleeve 81 and the closest contact point 81b, and the linear electrode 84 is connected to the main magnetic pole.
Assuming that the maximum magnetic flux density on the developing sleeve 81 by the main magnetic pole 82a is Hr, the magnetic flux density is in the range of 0.2Hr to 1Hr upstream of the rotation of the developing sleeve 81 from the rotation of the developing sleeve 81. This is because in a place where the magnetic flux density is 0.2 Hr or less, the magnetic binding force is insufficient and toner scattering and image fogging are likely to occur.

As a result of the experiment, assuming that a straight line connecting the closest position 81a of the developing sleeve 81 to the photoreceptor belt 1 and the rotation axis O of the developing sleeve 81 is the center line C, the distance between the center line C and the main magnetic pole 82a is The angle, that is, the angle between the closest position 81a and the main magnetic pole 82a around the rotation axis O of the developing sleeve 81 is θ1, and the angle between the main magnetic pole 82a and the tip of the linear electrode 84 is the same. θ2, when the angle between the main magnetic pole 82a and the upstream magnetic pole 82b adjacent to the main magnetic pole 82a is θ3 (the angle is + on the upstream side from the center line C and − on the downstream side), θ1 = − 10 ° to 10 ° θ3 = 10 ° to 45 ° θ2 = (0.05 to 0.5) × θ3 θ4 = 10 ° to 45 ° Was maintained at a high level to prevent toner scattering.

That is, when the angle θ1 from the center line C of the main magnetic pole 82a is ± 10 ° or more, the rising of the developer D in the development area A is deteriorated, and the distance between the tip of the linear electrode 84 and the main magnetic pole 82 is reduced. If the angle θ2 between them is 0.05 × θ3 or less, the ears of the developer D are hindered, and θ
When 2 is 0.5 × θ3 or more, the spikes of the developer D fall down and become dense, so that it is difficult to pull out the toner and the like, so that the developability is reduced. Note that a more preferable result was obtained when θ2 was in the range of (0.1 to 0.3) × θ3.

The magnetic pole 82b adjacent to the main magnetic pole 82a and
If the angles .theta.3 and .theta.4 with respect to 82c are out of the range of 10 DEG to 45 DEG, the developer D will not be uniform.

The developing sleeve 81 has a DC bias power source E1.
And a bias voltage in which an AC component is superimposed on a DC component is applied by a AC bias power source E2 via a protection resistor R1.
A bias voltage of only a DC component is applied to the linear electrode 84 from a DC bias power source E3 via a protection resistor R2. It is preferable to apply a DC voltage having the same polarity as the toner to the linear electrode 84 from the viewpoint of preventing toner adhesion.

When the DC voltage applied to the sleeve is equal to the DC voltage applied to the linear electrode 84, the DC bias power supply E1 can be shared as shown in FIG. Complications can be avoided.

In this embodiment, by applying the above-described bias voltage, the plate-like member 83 is formed together with the oscillating electric field formed between the photosensitive belt 1 and the developing sleeve 81 (this is referred to as a second oscillating electric field). A first oscillating electric field is generated between the linear electrode 84 and the developing sleeve 81 provided integrally with each other.

In the above-described color image forming apparatus, when the reversal development is performed using a negatively charged OPC photoreceptor as the photoreceptor of the photoreceptor belt 1, and the photoreceptor is charged to -800V, for example, the linear electrode A bias voltage of −500 V is applied to 84, and a bias voltage of −700 V + AC voltage component is applied to the developing sleeve 81. The AC component has a frequency of 100 Hz to 20 KHz, preferably 1 to 10 KHz, and a peak-to-peak voltage (V _PP ) of 200 V or more.
2,000V.

Since the linear electrodes 84 are provided closer to the developing sleeve 81 than the photoreceptor belt 1, the intensity of the first oscillating electric field is greater than the intensity of the second oscillating electric field.

Since the toner particles are vibrated by the first oscillating electric field in a direction perpendicular to the line of electric force, the toner particles are separated from the carrier and fly, so that a cloudy toner cloud can be sufficiently generated. This toner cloud is assisted by the second oscillating electric field to fly toward the latent image on the photoreceptor belt 1 and uniform development is performed.

At this time, since the AC bias is applied only to the developing sleeve 81, the first oscillating electric field and the second oscillating electric field have the same phase, and the toner particles are moved from the first oscillating electric field to the second oscillating electric field. Smooth transition to electric field.

A glass electrode having a thickness of 0.1 mm is used as the plate member 83. As shown in FIG. 8, a 0.3 mm linear electrode 84 is circumferentially provided at the tip of the image forming body side surface. Thickness 0.0
It was formed by a laminate etching method using a 2 mm copper foil. A DC voltage of -600 V was applied to the linear electrode 84.

The waveform of the AC component is not limited to a sine wave.
A rectangular wave or a triangular wave may be used. Also, although the frequency is related, the higher the voltage value, the more the magnetic brush of the developer D vibrates, so that the toner particles are easily separated from the carrier particles and fly, but on the other hand, such as fogging and lightning phenomena Dielectric breakdown easily occurs. The occurrence of fogging is prevented by a DC component, and the dielectric breakdown is caused by coating the surface of the sleeve 81 with an insulating or semi-insulating material such as a resin or an oxide film, or by applying an insulating property to the carrier particles of the developer D as described later. It can be prevented by using carrier particles.

As described above, the developing device of the present invention
The magnetic brush of the component developer is kept in non-contact with the photoreceptor belt 1 as an image forming body, and a toner cloud is generated by the first and second oscillating electric fields, thereby improving separation and flight to the photoreceptor belt 1. To improve the selective attraction to the electrostatic image to prevent carrier particles from adhering to the photoreceptor belt 1;
Therefore, it is possible to use fine particles for the toner particles and the carrier particles so that the development of a high-quality image is performed. It is preferable to use

In general, if the average particle size of the magnetic carrier particles is large, the state of the ears of the magnetic brush formed on the developing sleeve 81 becomes coarse. In addition, unevenness tends to appear in the toner image, and the toner density in the ears becomes low, so that high-density development is not performed. To solve this problem, it is sufficient to reduce the average particle size of the magnetic carrier particles. As a result of experiments, it has been found that the above problem does not occur when the weight average particle size is 50 μm or less. However, if the particle size of the magnetic carrier is too small, the magnetic carrier adheres to the surface of the photoreceptor belt 1 together with the toner particles, or easily scatters. These phenomena are related to the strength of the magnetic field acting on the carrier and the strength of the magnetization of the carrier.However, in general, when the weight average particle diameter of the magnetic carrier becomes 15 μm or less, the above tendency gradually appears. And remarkably appear below 5 μm. Therefore, in this developing device, a magnetic carrier of the developer D having a weight average particle diameter of preferably 50 μm or less, particularly preferably 30 μm or less and 5 μm or more is suitably used. When the magnetic carrier is spherical, the stirring property of the toner particles and the carrier particles and the transportability of the developer D are improved, and the charge controllability of the toner is further improved. This is preferable because the aggregation of particles hardly occurs.

Such a magnetic carrier is made of a metal such as iron, chromium, nickel, or cobalt, or a compound or alloy thereof, such as triiron tetroxide, γ-oxide, as in a conventional magnetic carrier. Ferromagnetic or paramagnetic spherical particles such as ferric oxide, chromium dioxide, manganese oxide, ferrite, and manganese-copper alloy, or the surfaces of these magnetic particles are made of styrene resin, vinyl resin, Resin such as ethyl resin, rosin modified resin, acrylic resin, polyamide resin, epoxy resin, polyester resin, silicone resin, etc., or spherically coated with these copolymer resins or fatty acid wax such as palmitic acid, stearic acid, or Particles obtained by forming spherical particles of resin or fatty acid wax containing magnetic fine particles dispersed in Obtained by a particle size selected in the average particle 径選 another means.

The use of the spherical carrier particles coated with a resin or the like as described above, in addition to the effects described above, makes the layer of the developer D formed on the developer carrier uniform, In addition, there is an effect that a high bias voltage can be applied to the developer carrier. That is, the fact that the carrier particles are spherical carrier particles coated with a resin or the like means that (1) the carrier particles are generally easily magnetized and adsorbed in the long axis direction, but the orientation is lost due to the spheroidization. Are formed uniformly to prevent locally low resistance and uneven thickness.
(2) With the increase in the resistance of the carrier particles, the edge portion seen in the conventional carrier particles disappears, and the electric field does not concentrate on the edge portion. As a result, a high bias voltage is applied to the developer carrier. Even if the photoreceptor belt 1
This has the effect that the surface is not discharged to disturb the electrostatic latent image and the bias voltage does not break down. The fact that the high bias voltage can be applied means that the above-described effects in the development under the oscillating electric field of the present invention can be sufficiently exerted. The above-described wax is also used for the spheroidization of the carrier particles having the above-described effects. However, from the viewpoint of the durability of the carrier and the like, it is preferable that the spherical magnetic particles are coated with a resin as described above. Further, it is preferable that the carrier particles are formed of magnetic particles having an insulating property with a resistivity of 10 ⁸ Ωcm or more, particularly 10 ¹³ Ωcm or more. The resistivity, the electric field of 1000V / cm between After tapping putting particles into a container having a cross section of 0.50 cm ^2, a load of 1Kg / cm ² on packed particles, the load and a bottom electrode Is a value obtained by reading the current value when a voltage is applied, and when the resistivity is low, when a bias voltage is applied to the developer carrier, charges are injected into the carrier particles and the photosensitive material is exposed to light. Carrier particles tend to adhere to the surface of the body belt 1 or breakdown of the bias voltage tends to occur.

In consideration of the above, the magnetic carrier particles are spherical so that the ratio of the major axis to the minor axis is at least three times or less. Is at least 10 ⁸ Ωcm, preferably at least 10 ¹³ Ωcm. Then, such magnetic carrier particles are used to increase the resistance of spherical magnetic particles by forming an oxide film or the like, and in the case of a magnetic fine particle dispersion system carrier, use magnetic fine particles as much as possible, and after forming the dispersed resin particles, It is produced by subjecting it to a spheroidizing treatment or obtaining dispersed resin particles by a spray drying method.

Next, the toner particles will be described. In general, as the average particle size of the toner particles decreases, the charge amount decreases qualitatively in proportion to the square of the particle size, and the adhesive force such as van der Waals force relatively increases, and the toner particles are easily scattered. While fogging is liable to occur, it is difficult to separate from the carrier particles of the magnetic brush. In the conventional magnetic brush developing method, when the average particle diameter is 10 μm or less, such a problem becomes conspicuous. In the developing device of the present invention, this problem is solved by performing the development with the magnetic brush under a double oscillating electric field. That is, the toner particles attached to the ears of the magnetic brush
Strongly vibrated in the first oscillating electric field and easily separated from the ear to form a toner cloud,
The toner particles are conveyed to the nearest developing area A by the inertia force due to the rotation of the sleeve, the centrifugal force due to the oscillating electric field, etc., and the toner particles are faithfully adsorbed to the electrostatic latent image under the second oscillating electric field. At this time, since the linear electrode 84 is provided only on the downstream side of the closest contact point 81b between the plate member 83 and the developing sleeve 81, no cloud is generated in an unnecessary portion other than the developing area. Further, the toner particles having a low charge amount hardly migrate to the image portion or the non-image portion, and the toner does not rub against the photoreceptor belt 1, so that the toner particles may adhere to the photoreceptor belt 1 by frictional charging. As a result, toner particles having a particle size of about 1 μm can be used. The oscillating electric field weakens the coupling between the toner particles and the carrier particles, so that the adhesion of the carrier particles to the photoreceptor belt 1 due to the toner particles is reduced, and the ears of the magnetic brush are kept out of contact with the surface of the photoreceptor belt 1. The selective transfer of the toner particles having a large charge amount to the carrier particles to the electrostatic latent image under the oscillating electric field as described above significantly reduces the adhesion of the carrier particles to the photoreceptor belt 1. Decrease.

When the average particle diameter of the toner becomes large, as already mentioned, the roughness of the image becomes conspicuous. Normally, a toner having an average particle diameter of about 20 μm is not a problem for development having a resolution of fine lines arranged at a pitch of about 10 lines / mm. However, when a toner having an average particle diameter of 10 μm or less is used, the resolution is reduced. Is significantly improved, and a sharp high-quality image with faithfully reproduced shade differences is provided. For the above reasons, the average particle diameter of the toner is 20 μm or less, preferably 10 μm or less, which is an appropriate condition. Since the toner particles follow the electric field, the charge amount of the toner particles is 1 μC /
g to more than 3 μC / g (preferably 3 μC / g to
100 μC / g) is desirable. In particular, when the particle size is small, a high charge amount is required.

Such a toner can be obtained by a method such as a pulverization-granulation method, a suspension polymerization method, or an emulsion polymerization method similar to the conventional toner. That is, a toner obtained by selecting spherical or irregular non-magnetic or magnetic toner particles in a conventional toner by an average particle size selecting means can be used. Further, the toner particles may be magnetic particles containing magnetic fine particles,
In this case, the amount of the magnetic fine particles is 60 wt% or less, particularly 30 wt%.
Is preferably not more than When the toner particles contain magnetic particles, the toner particles are affected by the magnetic force contained in the developer carrier, so that the uniformity of the magnetic brush is further improved, and the fogging is further improved. The generation is prevented, and the scattering of toner particles hardly occurs. However, if the amount of magnetic material contained is too large,
The magnetic force between the carrier particles becomes too large, so that a sufficient development density cannot be obtained.Moreover, the magnetic fine particles come to appear on the surface of the toner particles, and it becomes difficult to control the triboelectric charging. And the toner particles are easily damaged.

In summary, in the developing device of the present invention, preferred toner particles include the resin described above for the carrier particles and also fine particles of a magnetic material, and further include a coloring component such as carbon and a charged component if necessary. It is made of particles having an average particle size of 20 μm or less, particularly preferably 10 μm or less, which can be produced by a method similar to a conventionally known method for producing toner particles by adding a control agent and the like.

In the developing device of the present invention, a developer in which spherical carrier particles and toner particles as described above are mixed at the same ratio as in a conventional two-component developer is preferably used. If necessary, a fluidizing agent for improving the fluid sliding of the particles, a cleaning agent for cleaning the surface of the image carrier, and the like are mixed. As a fluidizing agent, colloidal silica, silicon varnish, metal soap, a nonionic surfactant, or the like can be used. As a cleaning agent, a surfactant such as a fatty acid metal salt, organic group-substituted silicon, or fluorine can be used. Can be.

(Example 1) A weight average particle diameter obtained by coating the surface of a spherical ferrite particle having a magnetization intensity of 50 emu / g with a methyl methacrylate / styrene copolymer resin in the developing apparatus as described above. Using a spherical magnetic carrier having a resistivity of 30 μm or more and a resistivity of 10 ¹⁴ Ωcm or more, 100 parts by weight of styrene / acrylic resin (Hymer up110 manufactured by Sanyo Chemical), 10 parts by weight of carbon black (MA-100 manufactured by Mitsubishi Kasei), and Nigrosine 5 Using a non-magnetic particle obtained by a pulverization granulation method having a weight average particle diameter of 8 μm
1 and 2, the toner particle ratio of each developer D in the developer pool 88 is 10% of the carrier particles.
The development was performed under the condition of wt%. The average charge amount of each toner was 18 μC / g.

In this case, the photosensitive belt 1 is an OPC photosensitive member, the peripheral speed of which is 180 mm / sec, the maximum potential of the electrostatic latent image formed on the photosensitive belt 1 is -800 V, and the outer diameter of the developing sleeve 2 is 3 mm.
0 mm, the number of revolutions is 150 rpm, the magnetic flux density of the main magnetic pole 82a facing the development area A of the magnet body 1,200 gauss, and the developer D
The thickness of the layer is 0.4 mm, the gap between the developing sleeve 81 and the photosensitive belt 1 is 0.7 mm, θ1 = 2 °, θ2 = 4 °, θ3 = θ4 = 30.
The bias voltage applied to the developing sleeve 81 was a DC component voltage of -700 V, an AC component frequency of 8 KHz, and a peak-peak voltage of 1,000 V. A DC component voltage of -700 V was applied to the linear electrode 84. In this embodiment, the developing sleeve 8
The developer D on 1 does not contact the surface of the photoreceptor belt 1.

By performing development under the above conditions, a superimposed color toner image is formed on a photoreceptor, which is transferred by corona discharge onto a transfer paper of plain paper, and a heat roller fixing device having a surface temperature of 140 ° C. As a result, the recorded image on the transfer paper obtained was extremely sharp with no edge effect or fog, and had a high density, and 50,000 sheets of recording were performed continuously, but it was stable from the beginning to the end. As a result, the same recorded image could be obtained.

FIG. 7 shows the result of changing the frequency and the effective value voltage of the AC component applied to the developing sleeve 81 in the above embodiment. In FIG. 7, a range shaded by a horizontal line is a range in which fogging is likely to occur, a range shaded by a vertical line is a breakdown in which dielectric breakdown easily occurs, and a range shaded by a diagonal line is a range in which image quality is likely to deteriorate. In this case, the range without shading is a preferable range in which a stable and clear image can be obtained. As is clear from the figure, the range in which fogging is likely to occur varies depending on the change in the AC component. The waveform of the AC component is
Not limited to a sine wave, a rectangular wave or a triangular wave may be used. Further, the low-frequency region shaded in the form of dots is a range in which development unevenness occurs due to the low frequency.

In the above embodiments, it is needless to say that a magnetic latent image can be visualized under the same developing conditions as long as the toner in the two-component developer has magnetism.

(Example 2) Development was carried out under the same conditions as in Example 1 except that θ1 was set to 0 °, and good results were obtained as in Example 1.

Example 3 Development was performed under the same conditions as in Example 1 except that θ was 0 ° and the DC voltage applied to the linear electrode 84 was −700 V. The result was obtained.

(Embodiment 4) θ1 = −2 °, θ2 = 6 °, θ
The development was performed under the same conditions as in Example 1 except that 3 = 30 ° and θ4 = 40 ° (the magnetic flux density at the position of the linear electrode 84 in this case was 800 gauss). The same good results as those described above were obtained.

[0064]

According to the construction described above, the developing device of the present invention is capable of: a) using a magnetic brush having good ears, a carrier having an average particle diameter of 30 μm or less, and a toner having an average particle diameter of 10 μm or less. It is possible to obtain stable and high developability by using an image forming apparatus that collectively transfers a multicolor image formed by superimposing a toner image on an image forming body onto a transfer material to obtain a color image. it can.

B) Since a plate-like member having a linear electrode is disposed upstream of the development area, a stable developer transport amount can be obtained without generating unnecessary cloud in the developer transport path.

C) Since a DC bias voltage having the same polarity as the toner charge can be applied to the linear electrodes, no toner accumulation occurs and no image contamination occurs.

D) A bias voltage in which an AC voltage is superimposed on a DC voltage is applied to the developing sleeve, and only a DC voltage is applied to the linear electrodes. Therefore, there is no phase disturbance of the AC bias voltage in the developing region, and smoothness is obtained. Development is performed. It is possible to provide an excellent developing device having the effects as described above.

[0068]

[Brief description of the drawings]

FIG. 1 is a sectional view showing one embodiment of a developing device of the present invention.

FIG. 2 is a cross-sectional view illustrating an example of a color image forming apparatus including the developing device of the present invention.

FIG. 3 is a sectional view showing another embodiment of the plate-like member and the linear electrode of FIG. 1;

FIG. 4 is a plan view showing still another embodiment of the linear electrode of FIG. 1;

FIG. 5 is a graph showing a preferred range of magnetic flux density at the tip of the linear electrode of FIG. 1;

FIG. 6 is a block diagram illustrating an image forming system.

FIG. 7 is a graph showing a preferable range of an AC component of a bias voltage.

FIG. 8 is a diagram showing a form of a plate-like member 83 and a linear electrode 84 of Examples 1 to 4.

[Explanation of symbols]

 Reference Signs List 1 photoconductor belt (image forming body) 4 guide member 6 charger 7 optical writing device 8, 8A, 8B, 8C, 8D developing device 81 developing sleeve 81b closest contact 82 magnet body 82a main magnetic pole 83 plate member 84 linear electrode 86 Regulator blade E1, E3 DC bias power supply E2 AC bias power supply R1, R2 Protection resistance A Development area D Developer N, S Magnetic pole

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G03G 15/09 G03G 15/08

Claims (3)

(57) [Claims] A latent image formed on an image forming member by conveying a two-component developer to a developing region by means of a developing sleeve in which a magnet body having a plurality of magnetic poles is fixed, and causing toner to fly in an oscillating electric field. In a developing device for developing an image, a bias in which an AC voltage is superimposed on a DC voltage is applied to the developing sleeve.
Applying a bias voltage, arranging the main magnetic pole of the magnet body in the developing area, and an upstream side in the rotation direction of the developing sleeve with respect to the developing area.
A is, disposed an insulating plate member in position abutting or adjacent to the magnetic brush more is formed on the main magnetic pole, the developing zone side leading end portion of the plate-like member, energizable line A linear electrode, and a DC bias voltage is applied to the linear electrode . 2. A front end of said linear electrode is located in front of said main magnetic pole.
When the maximum magnetic flux density of the main magnetic pole is Hr at an upstream portion with respect to the rotation direction of the developing sleeve and the magnetic flux density is 0.2Hr to 1H
2. The image forming apparatus according to claim 1 , wherein
The developing device as described in the above . 3. The image forming apparatus according to claim 2, wherein the rotation axis of the developing sleeve is centered.
The angle between the closest position of the developing sleeve and the image forming body and the main magnetic pole is θ1, the angle between the main magnetic pole and the tip of the linear electrode is θ2, and the main magnetic pole is the same. When the angle between the upstream magnetic pole and the upstream magnetic pole with respect to the rotation direction of the developing sleeve adjacent to the main magnetic pole is θ3, θ1 = −10 ° to 10 ° θ2 = (0.05 to 0.5) θ3 θ3 = 10 3. The developing device according to claim 1, wherein the angle is from 45 ° to 45 °.