JP3084465B2 - 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 widely 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 particles are transported to the development area 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, the magnetic brushes have good standing, and the friction of the image carrier surface is excellent. It also has a feature that a sufficient cleaning effect is exhibited even when it is also used for cleaning, and is suitable for non-contact development in which development is performed without contact with the surface of the image carrier. It is widely used in spite of the need for management. 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 tens to hundreds of μm and non-magnetic toner particles having an average particle diameter of about 10 μm are generally used. Is used, and since the toner particles and further the carrier particles are coarse, there is a problem that it is difficult to obtain a high-quality image reproducing fine lines, dots, differences in shading, and the like. Therefore, in order to obtain high image quality in this developing method, conventionally, for example, resin coating of carrier particles, improvement of a magnet body in a developer carrier, and many efforts have been made, but still stable. At present, a satisfactory image cannot be obtained.
Therefore, in order to obtain a high quality image, it is considered necessary to make the toner particles and the carrier particles finer. However, the toner particles have an average particle size of 20 μm or less,
In particular, when the particle size is 10 μm or less, the influence of van der Waals force appears relative to the Coulomb force during development, so-called fogging occurs in which toner particles adhere to the background portion of the image background, and development occurs. It is also difficult to prevent fogging by applying a DC bias voltage to the agent 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 a clear image cannot be obtained, it is difficult to micronize toner particles and carrier particles. Was.

As a method for solving the above-mentioned problem, a control electrode for controlling the flight of toner particles is provided in a development area, which was filed by the present applicant, and developed under an oscillating electric field generated by applying a bias voltage having an AC voltage component. (Japanese Patent Laid-Open No. 59-2)
No. 23467), and disclosed in JP-A-1-94368.
A leveling member is provided between the central portion of the developing area and a regulating member that regulates the layer thickness of the developer layer, and a DC voltage having a polarity opposite to the charging polarity of the toner particles is applied to the leveling member. Has been proposed.

[0004]

However, in the former method, as the control electrode is used, dirt is generated and the control electrode vibrates during use. In addition, there is a problem that it is difficult to hold the control electrode in a straight line.

In the latter method, a bias voltage having a polarity opposite to the charging polarity of the toner particles is applied to the leveling member, so that the toner adheres to the leveling member, and the toner adheres to the photoreceptor. In addition, there is a problem that good development cannot be performed due to the change of the vibration condition of the developer.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and to provide a developing device which has a high developing efficiency and can perform development without unevenness.

Further, in a color image forming apparatus in which a multicolor image is formed by superimposing a toner image on an image carrier, and the multicolor image is collectively transferred onto a transfer material, color mixing between toner images is caused by an oscillating electric field. The purpose is to solve the problem of easy occurrence.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a developing apparatus which applies and transports a two-component developer onto a developing sleeve and flies toner in an oscillating electric field to perform reversal development on a latent image on a photoreceptor. in the plate-like member having electrodes on the developing area upstream portion (electrode plate) in contact with the developing sleeve, the electrode plate
Is a DC bias voltage, and the developing sleeve is a DC bias voltage.
Apply a bias voltage superimposed with AC and apply DC
The voltage component has the same polarity as the toner, and the electrode plate
DC voltage higher than the
A first oscillating electric field between the electrode plate and the developing sleeve, and a second oscillating electric field between the photoreceptor and the developing sleeve, wherein the first oscillating electric field is and sets stronger than the second oscillating electric field, click the between the photosensitive member and the electrode plate generated by the first oscillating electric field
This is achieved by a developing device that forms an electric field that moves the loud toner to the photoconductor.

In a preferred embodiment, the oscillating electric field is formed between the developing sleeve, the photoconductor and the electrode, and a unidirectional electric field is formed between the photoconductor and the electrode. It is an aspect.

[0010]

FIG. 4 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. 4, reference numeral 1 denotes a photoreceptor belt which is a belt-shaped photoreceptor made of a flexible belt on which a photoconductor is applied or vapor-deposited.
And 3 are 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 charging means, and 7
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.

Each of the developing devices 8A, 8B, 8C, and 8D, which will be described later in detail, contains, for example, yellow, magenta, cyan, and black developers, respectively, and has a predetermined gap with the photosensitive belt 1. Each developing sleeve 81 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 and a toner conveying roller 13b of the cleaning device 13
Is maintained at a position separated from the surface of the photoreceptor belt 1 during image formation, and is pressed against 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 this embodiment is shown in FIG.
Performed in accordance with the imaging system. That is, an original image is obtained at a color image data input unit (a) scanned by an image sensor, and the data is subjected to arithmetic processing at an image data processing unit (b) to create image data and temporarily stored in an image memory (c). Is done. Next, the image data is taken out at the time of recording and input to a recording unit (d), for example, a 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 apparatus, is input to the optical writing device 7, the optical writing device 7 is a semiconductor which is a writing light source (not shown). The laser beam (writing light) generated by the laser passes through a collimator lens and a cylindrical lens (not shown), is rotationally scanned by a rotating 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. This latent image is reversely developed by the developing device 8A in which yellow (Y) toner (visual medium) of the developing means is loaded, and a toner image is formed on the belt surface. The obtained toner image passes under the blade 13a of the cleaning device 13 which is a cleaning means and is separated from the peripheral surface of the photoreceptor belt 1 while being held on the belt surface, and enters the next image forming cycle.

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 reversely 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 a cyan (C) toner is formed on the belt surface similarly to the first and second colors.
Is formed.

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 AC bias is applied to each sleeve of each of these developing devices 8A, 8B, 8C, and 8D, non-contact reversal development is performed by a two-component developer as a visualizing means, and the base is grounded. The photoreceptor belt 1 is developed in a non-contact manner.

The color toner image thus formed on the peripheral surface of the photoreceptor belt 1 is fed from the paper feed cassette 14 via the paper feed guide 15 by applying a high voltage having a polarity opposite to that of the toner at the transfer section. 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 through the timing roller 17. And is supplied to the transfer device 12.

The transfer material to which the image has been transferred is surely separated from the photoreceptor belt 1 which suddenly changes its direction along the rotating roller 2 and heads upward. The paper is discharged onto the tray 20 via the paper discharge rollers 19.

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

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

The developing devices 8A to 8D have the same configuration and will be denoted by reference numeral 8 hereinafter. 1 to 3
1 is a schematic sectional view showing an embodiment of a developing device used in the present invention. FIG. 1A is a cross-sectional view of a first embodiment of the apparatus of the present invention, in which reference numeral 81 denotes a developing sleeve made of a nonmagnetic material such as aluminum, and 82 denotes a plurality of N, The developing sleeve 81 and the magnet 82 constitute a developer carrying carrier with a magnet having an S magnetic pole in the circumferential direction. The developing sleeve 81 is rotatable with respect to the magnet 82, and the drawing shows that the developing sleeve 81 rotates in the left direction indicated by the arrow. The N and S magnetic poles of the magnet body 82 in the developing section are usually magnetized to a magnetic flux density of 500 to 1,500 gauss, and the magnetic force causes the layer of the developer D composed of toner particles and carrier particles on the surface of the developing sleeve 81. That is, a magnetic brush is formed. The rotation of the developing sleeve 81 moves the magnetic brush in the same direction as the rotation of the developing sleeve 81, and is conveyed to the developing area A. The magnetic brush formed on the developing sleeve 81 is in a sleeping state by the N and S magnetic poles disposed near the developing machine, and is kept in contact with the surface of the photoreceptor belt 1 so as to maintain a gap without contacting the surface. The gap between the developing sleeve 81 and the photosensitive belt 1 is adjusted.

Here, θ ₁ and θ ₂ are angles between magnetic poles disposed close to the upstream and downstream in the moving direction of the developing sleeve from the position of the developing sleeve closest to the photosensitive. Θ ₃ is
This is the angle made with the tip of the electrode.

Here, it is desirable that each of θ ₁ and θ ₂ be 5 to 45 °. This makes it possible to form a magnetic brush that is uniformly raised.

[0031] Also, a plate-shaped member upstream of the poles, is set toward the downstream with respect to the preferred angle theta ₃ is theta ₂ 0.
From 2θ ₂ is a 0.9θ _2.

Reference numerals 83 and 84 denote stirring screws for circulating and stirring the developer D back and forth in the figure to make the components uniform, and 85 is provided upstream of the development area A to form an oscillating electric field. The electrode plate, which is a plate-like member, and the electrode plate 85, are insulating members made of an insulator such as rubber provided so as to contact the developing sleeve 81.
A plate-like electrode 85a made of a conductive material such as metal is integrally provided on 85b. Reference numeral 86 denotes a regulating blade which is a developer regulating means made of a non-magnetic material or a magnetic material provided to regulate the height and amount of the magnetic brush, and 87 removes the magnetic brush passing through the developing area A from the developing sleeve 81. Reference numeral 88 denotes a developer pool, and reference numeral 89 denotes a casing. A bias voltage obtained by superimposing an alternating current on a direct current is applied to the developing sleeve 81 via a protective resistor R1 by a direct current bias power source E1 and an alternating current bias power source E2. A bias voltage is applied to the electrode 85a of the electrode plate 85 from the DC bias power supply E3 via the protection resistor R2.

In the embodiment 1 shown in FIG. 1, the magnetic bodies 82 arranged close to the developing unit have substantially the same magnetic flux densities of the N and S magnetic poles and the magnet body 82 is fixed. The embodiment 2 of FIG. 2 differs from the apparatus of FIG. 1 in that the magnet body 82 rotates in the same direction or the opposite direction to the developing sleeve, and the embodiment 3 of FIG. Is different from the apparatus of FIG.

FIG. 2A is a sectional view of a second embodiment of the apparatus of the present invention, in which reference numeral 81 denotes a developing sleeve made of a nonmagnetic material such as aluminum, and reference numeral 82 denotes a rotatably provided inside the developing sleeve 81. A magnet body having a plurality of N and S magnetic poles on its surface at equal intervals in the circumferential direction. The developing sleeve 81 and the magnet body 82 constitute a developer carrying carrier. And the developing sleeve
Numeral 81 indicates that the developing sleeve 81 is rotatable in the left direction of the arrow, and the magnet body 82 is rotatable in the right direction. The N and S magnetic poles of the magnet body 82 of the developing section are usually magnetized to a magnetic flux density of 500 to 1,500 gauss, and the magnetic force causes the layer of the developer D composed of toner particles and carrier particles on the surface of the developing sleeve 81, that is, , Forming a magnetic brush. This magnetic brush is moved in the same direction as the rotation of the developing sleeve 81 by the rotation of the developing sleeve 81 and the magnet body 82,
It is transported to the developing 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 numerals 83 and 84 denote stirring screws for circulating and stirring the developer D in the drawing to make the components uniform, and reference numeral 85 is provided upstream of the development area A to form an oscillating electric field. The electrode plate, which is a plate-like member, and the electrode plate 85, are insulating members made of an insulator such as rubber provided so as to contact the developing sleeve 81.
A plate-like electrode 85a made of a conductive material such as metal is integrally provided on 85b. Reference numeral 86 denotes a regulating blade which is a developer regulating means made of a non-magnetic material or a magnetic material provided to regulate the height and amount of the magnetic brush, and 87 removes the magnetic brush passing through the developing area A from the developing sleeve 81. Reference numeral 88 denotes a developer pool, and reference numeral 89 denotes a casing. A bias voltage obtained by superimposing an alternating current on a direct current is applied to the developing sleeve 81 via a protective resistor R1 by a direct current bias power source E1 and an alternating current bias power source E2. A bias voltage is applied to the electrode 85a of the electrode plate 85 from the DC bias power supply E3 via the protection resistor R2.

The third embodiment shown in FIG.
Is rotatable with respect to the magnet body 82.
81 indicates that it rotates in the arrow left direction. The S and S magnetic poles of the magnet body 82 in the developing section are usually 500 to 1,
It is magnetized to substantially the same magnetic flux density of 500 gauss, and the magnetic force forms a layer of developer D composed of toner particles and carrier particles, that is, a magnetic brush, on the surface of developing sleeve 81. The rotation of the developing sleeve 81 moves the magnetic brush in the same direction as the rotation of the developing sleeve 81, and is conveyed to the developing area A. The magnetic brush formed on the developing sleeve 81 is brought into a cloud state by the repulsive magnetic field of the SS magnetic pole disposed near the developing machine, and moves in a cloud form without rubbing the surface of the photoreceptor belt 1. The gap between the regulating blade 86 and the gap between the developing sleeve 81 and the photosensitive belt 1 are adjusted.

Here, it is desirable that each of θ ₁ and θ ₂ be 5 to 45 °. This makes it possible to form a magnetic brush that is uniformly raised.

[0038] Also, a plate-shaped member upstream of the poles, is set toward the downstream with respect to the preferred angle theta ₃ is theta ₂ 0.
From 2θ ₂ is a 0.9θ _2.

Reference numerals 83 and 84 denote stirring screws for circulating and stirring the developer D back and forth in the drawing to make the components uniform, and 85 is provided upstream of the development area A for forming an oscillating electric field. The electrode plate, which is a plate-like member, and the electrode plate 85, are insulating members made of an insulator such as rubber provided so as to contact the developing sleeve 81.
A plate-like electrode 85a made of a conductive material such as metal is integrally provided on 85b. Reference numeral 86 denotes a regulating blade which is a developer regulating means made of a non-magnetic material or a magnetic material provided to regulate the height and amount of the magnetic brush, and 87 removes the magnetic brush passing through the developing area A from the developing sleeve 81. Reference numeral 88 denotes a developer pool, and reference numeral 89 denotes a casing. A bias voltage obtained by superimposing an alternating current on a direct current is applied to the developing sleeve 81 via a protective resistor R1 by a direct current bias power source E1 and an alternating current bias power source E2. A bias voltage is applied to the electrode 85a of the electrode plate 85 from the DC bias power supply E3 via the protection resistor R2.

In the present invention, a first oscillating electric field is generated between an electrode 85a integrally provided on an insulating member 85b abutting on the developing sleeve 81 and the developing sleeve 81, and the photosensitive member is formed by a conventional apparatus. The intensity of the first oscillating electric field is greater than the intensity of the second oscillating electric field as compared with the oscillating electric field formed between the belt 1 and the developing sleeve 81 (this is referred to as a second oscillating electric field). And the photoreceptor belt 1 and the electrodes
It is characterized in that an electric field for moving the toner to the photoreceptor is formed between it and 85a. Particularly preferably, the electrode plate 85a is set to 0.2d ₁ ～0.6D ₁ from the developing sleeve 81 side when the gap between the developing sleeve 81 and the photoreceptor belt 1 was d _1.

FIG. 1B is an enlarged sectional view showing the vicinity of the developing area A. As shown in FIG. 1 (a), a bias voltage in which alternating current is superimposed on direct current is applied to the developing sleeve 81.
A DC bias voltage is applied to 85. Electrode plate 85
Has a V-shaped notch at the end on the side of the developing sleeve,
A space for generating a toner cloud is provided between the developing sleeve 85 and the developing sleeve. The notch portion is provided than磁角theta ₂ of the upstream side to the downstream. The electrode plate 85 is also insulated on both sides and the tip. This configuration is also a preferable configuration in FIGS. In the above color image forming apparatus, reverse development is performed using a negatively charged OPC photoreceptor as a photoreceptor of the photoreceptor belt 1, and if the photoreceptor is charged to -800V, for example, the electrode plate 85 A bias voltage of a DC voltage component and an AC voltage component of −700 V is applied to the developing sleeve 81, which is − (800 to 1,500) V higher than the body potential.
The AC voltage component has a frequency of 100 Hz to 10 KHz, preferably 1
Peak to Peak of voltage is 200 to 4000 V at ５5 KHz.
Since a voltage higher than the potential of the photoconductor with the same polarity as the toner is applied to the electrode plate 85, no toner adheres to the electrodes, and in the superposition process, the toner image on the photoconductor adheres to the electrodes. Nor. Since the electrode plate 85 is provided closer to the developing sleeve 81 than the photoreceptor belt 1, the intensity of the first oscillating electric field is higher than the intensity of the second oscillating electric field. Closest gap d ₂ between the electrode plate and the developing sleeve with respect to the closest distance d ₁ between the developing sleeve and the photosensitive member, d ₂ =
(0.2~0.6) d ₁ is preferred. Incidentally, d ₁ is 0.2~1.0mm is preferred.

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.

Here, it is important that the first and second oscillating electric fields have the same phase. Since the phases are the same, the development is performed without causing undulation or the like due to the vibration of the toner. or,
There is no breakdown due to the strong electric field when the phase changes.

The waveform of the AC voltage component is not limited to a sine wave, but may be a rectangular wave or a triangular wave. Also, although the frequency is related, the higher the voltage value, the more the magnetic brush of the developer is vibrated, 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. Fogging is prevented by the DC voltage component, and dielectric breakdown is achieved by coating the surface of the developing sleeve 81 with an insulating or semi-insulating material such as a resin or an oxide film, or by insulating the carrier particles of the developer with an insulating material 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 out of contact with the photoreceptor belt 1 serving as an image carrier, 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 toner particles and carrier particles so that high-quality images can be developed. Preferably, it is used.

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 resulting strength of the magnetization of the carrier.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, the magnetic carrier of the developer D preferably has a weight average particle size of 50 μm or less,
Above, preferably those having a size of 15 μm or more are 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, cobalt or the like, or a compound or alloy thereof, such as triiron tetroxide, γ-oxide, as in a conventional magnetic carrier. Ferromagnetic spherical particles such as ferric iron, 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, etc., silicone resin, fluororesin, or spherical resin containing magnetic particles dispersed therein The particles obtained by producing or obtaining the particles are subjected to particle size selection by a conventionally known average particle size selection means.

Forming the carrier particles in a spherical shape with a resin or the like as described above, in addition to the above-described effects, makes the developer layer formed on the developer carrier uniform, This also has the effect that a high bias voltage can be applied to the carrier. That is, the fact that the carrier particles are spheroidized by resin or the like means that (1)
Generally, carrier particles are easily magnetized and adsorbed in the long axis direction,
Due to the spheroidization, the directionality is lost, so that the developer layer is formed uniformly, thereby preventing a locally low-resistance region 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 so, there is an effect that the electrostatic latent image is not disturbed by discharging to the electrode member or the surface of the photoreceptor belt 1 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, the use of the above-described resin is preferable. It is preferable to form insulating magnetic particles having 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. Body belt 1
Carrier particles are likely to adhere to the surface, or breakdown of the bias voltage is likely to occur.

In view of the above, the magnetic carrier particles are spherical so that the ratio of the major axis to the minor axis is at least 3 times or less, have no protrusions such as needle-like portions and edge portions, and have resistivity. Is at least 10 ⁸ Ω, preferably at least 10 ¹³ Ω. 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 adhering to the ears of the magnetic brush
Strongly vibrated in the oscillating electric field to easily separate from the ear to form a toner cloud, and is transported to the developing area A immediately adjacent to the cloud, where the toner particles are transferred to the electrostatic latent image under the second oscillating electric field. It will be adsorbed faithfully. 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. When the oscillating electric field weakens the coupling between the toner particles and the carrier particles, the adhesion of the carrier particles accompanying the toner particles to the photoreceptor belt 1 is reduced,
The ears of the magnetic brush are kept out of contact with the surface of the photoreceptor belt 1, and the toner particles having a large charge amount with respect to the carrier particles selectively shift to the electrostatic latent image under the oscillating electric field as described above. This greatly reduces the adhesion of carrier particles to the photoreceptor belt 1.

When the average particle diameter of the toner is increased, as already mentioned, the roughness of the image becomes conspicuous. Normally, for development having a resolving power of fine lines arranged at a pitch of about 10 lines / mm, a toner having an average particle diameter of about 20 μm is not a problem. However, when a fine particle toner having an average particle diameter of 1 to 5 μm is used, The resolving power is remarkably improved, and a clear high-quality image that faithfully reproduces the density difference is provided. For the above reasons, the appropriate condition is that the average particle diameter of the toner is 10 μm or less, preferably 1 to 5 μm. Further, since the toner particles follow the electric field, the charge amount of the toner particles is 1 to 3 μm.
It is desirable that it be larger than C / g (preferably 3 to 30 μC / g). In particular, when the particle size is small, a high charge amount is required.

Such a toner can be obtained in the same manner as a 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. Among them, it is preferable that the toner particles are magnetic particles containing magnetic fine particles, and it is particularly preferable that the amount of the magnetic fine particles is not more than 60 wt%, particularly not more than 30 wt%. 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 the magnetic material contained is too large, the magnetic force between the particles and the carrier particles becomes too large, so that a sufficient development density cannot be obtained. 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, preferable 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. A toner having a mean particle size of 20 μm or less, preferably 10 μm or less, particularly preferably 1 to 5 μm, which can be produced by a method similar to a conventionally known method for producing toner particles by adding a control agent or 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.

In the above-described developing device, a spherical ferrite treatment is performed by heat in which fine ferrite is dispersed at 50 wt% in a resin, the weight average particle diameter is 30 μm, the magnetization strength is 50 emu / g, and the resistivity is 10 ¹⁴ Ωcm or more. Styrene / acrylic resin (Hymer up110 manufactured by Sanyo Chemical Co., Ltd.) 100
Weight average particle diameter of 5 parts by weight and 10 parts by weight of color pigment
Using the non-magnetic particles obtained by the pulverization and granulation method of μm, each of the developer pools 88 was prepared by the apparatus shown in FIG.
The development was carried out under the condition that the toner particle ratio of each developer D in Example 1 was 10 wt% with respect to the carrier particles. The average charge amount of each toner was −15 μC / g.

In this case, the photosensitive belt 1 is an OPC photosensitive member, its peripheral speed 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 NS magnetic pole facing the development area A of the magnet body is 1,200 gauss, θ ₁ = 20 °, θ
₂ = 30 ° The thickness of the developer D layer is 0.4 mm, the gap between the developing sleeve 81 and the photoreceptor belt 1 is 0.7 mm, the bias voltage applied to the developing sleeve 81 is a DC voltage component of −700 V, an AC voltage component of 4 KHz, 1,000 V. Electrode member is 0.3mm from photoconductor
At the same polarity as the toner and higher than the charged potential of the photoreceptor.
A DC voltage component of 1000 V was applied. Note that θ ₃ = 20 °. In this embodiment, the developer D on the developing sleeve 81 does not contact the surface of the photosensitive belt 1.

By performing development under the above conditions, a superposed color toner image is formed on a photoreceptor, which is transferred by corona discharge onto a transfer paper of plain paper, and transferred to a heat roller fixing device having a surface temperature of 140 ° C. As a result, the recorded image on the transfer paper obtained was clear without edge effects or fog, and was very clear with high density. After recording 50,000 sheets continuously, it was stable from the beginning to the end. As a result, the same recorded image could be obtained.

In the second embodiment shown in FIG. 2, the photosensitive belt 1 is an OPC photosensitive member, its peripheral speed is 180 mm / sec, and the maximum potential of the electrostatic latent image formed on the photosensitive belt 1 is -800.
V, the outer diameter of the developing sleeve 2 is 30 mm, the number of revolutions is 150 rpm, and the magnet body 82 is an 8-pole magnet body, the number of revolutions is 1000 rpm, and the magnetic flux density is 1000
Gauss, the thickness of the developer D layer was 0.4 mm, the gap between the developing sleeve 81 and the photosensitive belt 1 was 0.7 mm, and the bias voltage applied to the developing sleeve 81 was a DC voltage component of -700 V, an AC voltage component of 4 KHz and 1,000 V. . Electrode member is 0.4mm from photoconductor
At the same polarity as the toner and higher than the charged potential of the photoreceptor.
A DC voltage component of 1000 V was applied. Note that θ ₃ = 20 °. In this embodiment, the developer D on the developing sleeve 81 does not contact the surface of the photosensitive belt 1.

By performing development under the above conditions, a superimposed color toner image is formed on the photoreceptor, which is transferred by corona discharge onto a plain paper transfer paper, and transferred to a heat roller fixing device having a surface temperature of 140 ° C. As a result, the recorded image on the transfer paper obtained was clear without edge effects or fog, and was very clear with high density. After recording 50,000 sheets continuously, it was stable from the beginning to the end. As a result, the same recorded image could be obtained. In the third embodiment shown in FIG. 3, the photoconductor belt 1 is an OPC photoconductor, and its peripheral speed is 180 mm.
/ Sec, the maximum potential of the electrostatic latent image formed on the photoreceptor belt 1 is -800 V, the outer diameter of the developing sleeve 2 is 30 mm, and the rotation speed is 150
rpm, the magnetic flux density of the SS magnetic pole facing the development area A of the magnet 82 is 1,200 gauss, θ ₁ = 25 °, θ ₂ = 25 °, the thickness of the developer D layer is 0.4 mm, the developing sleeve 81 and the photosensitive belt The bias voltage applied to the developing sleeve 81 is a DC voltage component of -700 V, an AC voltage component of 4 KHz, and 1,000 V.
And The electrode member was placed 0.3 mm from the photoreceptor, and applied a -1000 V DC voltage component having the same polarity as the toner and higher than the charging potential of the photoreceptor. Note that θ ₃ = 15 °. In this embodiment, the developer D on the developing sleeve 81 does not contact the surface of the photosensitive 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 plain paper transfer paper, and transferred to a heat roller fixing device having a surface temperature of 140 ° C. As a result, the recorded image on the transfer paper obtained was clear without edge effects or fog, and was very clear with high density. After recording 50,000 sheets continuously, it was stable from the beginning to the end. As a result, the same recorded image could be obtained.

In the above embodiment, while the specific developing device is being used, the rotation of the developing sleeve is stopped in the other unused developing devices, and the AC bias applied to the developing sleeve is stopped. That is, a bias having the same polarity or a different polarity as that of the toner in the floating state was applied. The electrode member maintained the same voltage as the toner during image formation. Thereby, the movement of the toner from the toner image on the photoconductor to the electrode member was prevented.

As an electrode member, between urethane rubbers
A structure with a 100 μm electrode plate interposed was used.

In the above embodiment, similar bias conditions were obtained. FIG. 6 shows the result of changing the frequency and voltage of the AC voltage component applied to the developing sleeve 81. FIG.
In the range, the range shaded by the horizontal line is the range where fogging is likely to occur, the range shaded by the vertical line is the range where insulation breakdown easily occurs, and the range shaded by the diagonal line is the range where the image quality is likely to deteriorate, The range without shading is a preferable range in which a clear image can be obtained stably. As is clear from the figure, the range in which fogging is likely to occur varies depending on the change in the AC voltage component. The waveform of the AC voltage component is not limited to a sine wave, but may be a rectangular wave or a triangular wave. 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 embodiment, 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.

A one-component magnetic developer can also be used in a similar configuration.

[0066]

As described above, the developing device of the present invention has a carrier having an average particle size of 30 μm or less and a carrier having an average particle size of 10 μm or less.
Even if the following toner is used, a developing device that can obtain high image quality using a small particle size toner having no carrier adhesion or the like can be provided.
Further, a weak oscillating electric field can be used during development even when used in an image forming apparatus in which a multicolor image formed by superimposing a toner image on an image carrier is collectively transferred onto a transfer material to obtain a color image. Therefore, it is possible to provide an excellent developing device which does not cause color mixing, has high developing efficiency, and can perform development without unevenness.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a developing device according to a first embodiment of the present invention.

FIG. 2 is a sectional view illustrating a developing device according to a second embodiment of the present invention.

FIG. 3 is a sectional view showing Embodiment 3 of the developing device of the present invention.

FIG. 4 is a cross-sectional view illustrating an example of a color image forming apparatus including the developing device of the present invention.

FIG. 5 is a block diagram illustrating an image forming system.

FIG. 6 is a graph showing a developing state when an AC component of a bias voltage is changed in the embodiment.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photoconductor belt (image carrier) 4 guide member 6 charger 7 optical writing device 8, 8A, 8B, 8C, 8D developing device 12 transfer device 13 cleaning device 81 developing sleeve 82 magnet body 83 stirring screw 84 fur brush 85 electrode Plate (plate-like member) 85a Electrode 85b Insulating member 86 Regulator blade (developer regulating member) E1, E3 DC bias power supply E2 AC bias power supply R1, R2 Protective resistor A Developing area D Developer N, S Magnetic pole

Claims (1)

(57) [Claims] 1. A two-component developer is attached on a developing sleeve.
It conveyed, latent on the photosensitive member by the toner to fly in the oscillating electric field
In the developing device for performing reversal development to the image, a plate-like member having electrodes on the developing area upstream portion (electrode plate) abuts on the developing sleeve, a DC bias voltage to the electrode plate, the developing sleeve
Apply a bias voltage in which DC and AC are superimposed on
The applied DC voltage component has the same polarity as the toner, and is applied to the electrode plate.
Applies a DC voltage higher than the photoconductor potential to the developing sleeve.
Applies a DC voltage lower than the photoconductor potential, and generates a first oscillating electric field between the electrode plate and the developing sleeve.
The second oscillating electric field formed between the developing sleeve and the photosensitive member, the first oscillating electric field is thereby set to be stronger than the second oscillating electric field, the in between the photosensitive member and the electrode plates the first
A developing device for forming an electric field for moving cloud-shaped toner generated by an oscillating electric field to a photoconductor.