JP3272208B2 - Developing method and 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 a developing method and a developing apparatus for developing an electrostatic latent image formed by electrophotography or electrostatic recording.

[0002]

2. Description of the Related Art Conventionally, various apparatuses have been proposed and put into practical use as developing apparatuses for electrophotographic apparatuses. Broadly speaking, it can be divided into a one-component development system and a two-component development system.

[0003] Most of the one-component developing devices are of the non-contact type, but a typical developing method is a one-component jumping developing method using magnetic toner. According to this developing method, a high-quality image can be obtained easily, but a color image cannot be obtained because the toner contains a magnetic substance.

In a one-component developing method using a non-magnetic toner,
Although color images can be obtained, and low cost and downsizing of the developing device are realized, it is difficult to apply the toner on the developing sleeve. , But lacks durability.

On the other hand, in the two-component developing method, a two-component developer in which a magnetic carrier and a toner are mixed is transported to a developing section facing a photosensitive drum in a state where toner is attached to the carrier, and a developing magnetic field of the developing section is applied. To form a magnetic brush of a developer, and contact the magnetic brush with the image carrier to develop an electrostatic latent image on the image carrier. In this development method, a non-magnetic toner can be used, so that a color image can be obtained and the image quality is high.

[0006]

Recently, it has been desired to reduce the space of a full-color copying machine, and the developing device of the two-component developing system has also been reduced in size. Accordingly, the diameter of the developing sleeve has been reduced.

However, as the diameter of the developing sleeve is reduced, a large amount of toner is developed at the rear end of a high-density solid image portion, that is, a so-called "sweep" occurs.

An object of the present invention is to develop a magnetic brush of a developer in a developing section and to develop a solid image of high density without sweeping, even if the developing sleeve is reduced in diameter. It is an object of the present invention to provide a developing method and a developing device capable of obtaining a stable image.

[0009]

The above object is achieved by a developing method and a developing apparatus according to the present invention. In summary,
According to the present invention, a developer including a toner and a magnetic carrier is carried and conveyed to a developing unit by a developer carrier, and a magnetic brush formed on the developer carrier is brought into contact with the image carrier in the developing unit by a developing magnetic field. And a developing method for developing the electrostatic latent image formed on the image carrier by an alternating electric field formed in the developing section, wherein the outer diameter of the developer carrier is 6 to 18 mm and the magnetic carrier is 1000 gauss. The intensity of magnetization in a magnetic field of 150 emu / cm ³ or less, and the directions of movement of the developer carrier and the image carrier in the developing section are opposite to each other. . According to another aspect of the present invention, there is provided a developer carrier that carries a developer including a toner and a magnetic carrier and transports the developer to a developing unit, and is formed on the developer carrier by a developing magnetic field. In a developing device in which a magnetic brush is brought into contact with an image carrier in the developing section and an electrostatic latent image formed on the image carrier is developed by an alternating electric field formed in the developing section, The outer diameter is 6 to 18 mm, and the intensity of magnetization of the magnetic carrier in a magnetic field of 1000 Gauss is 150 emu / cm ³ or less,
A developing device is provided, wherein the moving directions of the developer carrier and the image carrier in the developing section are opposite to each other.

In the present invention, the alternating electric field can be formed by applying a voltage obtained by superimposing a DC voltage and an AC voltage to the developer carrier.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The image forming method of the present invention will be described below in detail with reference to the drawings.

Embodiment 1 FIG. 3 is an overall configuration diagram showing an image forming apparatus to which the present invention can be applied. The image forming apparatus is an electrophotographic color printer. This printer includes an electrophotographic photosensitive drum 3 rotating in the direction of an arrow, and a rotary developing device 1 including a charger 4 and developing devices 1M, 1C, 1Y, and 1K around the photosensitive drum 3, a transfer charger 10 A cleaning unit 12 is provided, and a laser scanner LS is provided above the photosensitive drum 3. An image forming unit is configured by the charger 4 to the laser scanner LS and the like.

The developing devices of the rotary developing device 1, namely, a magenta developing device 1M, a cyan developing device 1C, and a yellow developing device 1Y
The black developing device 1K contains a two-component developer containing a toner and a carrier, and uses a magenta toner, a cyan toner, a yellow toner, and a black toner as the toner, respectively.

The semiconductor laser incorporated in the laser beam scanner LS is controlled in accordance with an input image signal and emits a laser beam L.

The sequence of the entire color printer will be briefly described by taking a full-color mode as an example. First, the photosensitive drum 3 is uniformly charged by the charger 4. Next, scanning exposure is performed by the laser beam L modulated by the magenta image signal, and a dot distribution electrostatic latent image is formed on the photosensitive drum 3. This latent image is reversely developed by a magenta developing device 1M fixed at a developing position in advance, and is visualized as a magenta toner image.

On the other hand, the transfer material such as paper taken out of the cassette C and supplied via the paper feed roller 6 is gripped by the gripper 7 of the transfer drum 9, and is statically moved by the contact roller 8 and its opposite pole. It is electrically wound around and supported on the transfer drum 9. The transfer drum 9 rotates in the direction of the arrow shown in FIG. 3 in synchronization with the photosensitive drum 3, and the transfer material carried on the transfer drum 9 is transported to a transfer unit facing the photosensitive drum 3, where the photosensitive drum 3 3 is transferred by the transfer charger 10. The transfer drum 9 continues to rotate as it is, and a toner image of the next color to be formed (FIG. 3)
In order to prepare for the transfer of the cyan toner image, the transfer material is again conveyed toward the transfer section.

After the transfer of the magenta toner image has been completed, the photosensitive drum 3 is cleaned by a cleaning unit 12 to remove the untransferred toner, and then charged again by the charger 4 to form a laser modulated by the next cyan image signal. The exposure of the beam L forms a dot distribution electrostatic latent image on the photosensitive drum 3. During this time, the developing device 1 is rotated, and the cyan developing device 1C is fixed at the developing position.
The upper latent image is reversely developed by the cyan developing device 1C and is visualized as a cyan toner image. The obtained cyan toner image is transferred onto the transfer material on the transfer drum 3 in the transfer section from above the magenta toner image.

The above-described steps are also performed for yellow and black to form an electrostatic latent image in a dot distribution by exposing the photosensitive drum 3 to a laser beam L modulated by respective image signals. 1Y, magenta, cyan, yellow, and black are formed on a transfer material by forming a yellow toner image and a black toner image by developing with a black developing device 1K and superimposing the transfer of the yellow toner image and the black toner image onto the transfer material. Are obtained by superimposing the four color toner images.

When the transfer of the four color toner images is completed, the transfer material is discharged by the separation charge removing devices 13 and 14, the gripping by the gripper 7 is released, and the transfer material is separated from the transfer drum 9. (Fixing device) 17. The transfer material sent to the fixing device 17 is heated and pressurized there to be fixed, whereby the toner images of each color are mixed and fixed to the transfer material to form a full-color print image. Thus, a series of the full-color mode sequence is completed, and the full-color print image obtained by fixing is discharged out of the printer.

FIG. 4 shows a laser beam scanner LS installed in the printer of FIG. The scanner includes a semiconductor laser element 102. This element 102 is connected to a light emission signal generator (laser driver circuit) 500 which is a drive signal for generating a laser beam. Flickers accordingly. The light beam of the laser beam L emitted from the laser element 102 by blinking is converted into substantially parallel light by a collimator lens system 103, and is turned into a rotating polygon mirror.
That is, the light enters the polygon mirror 104.

The polygon mirror 104 is rotated at a constant speed in the direction of arrow B, so that the collimator lens system 103 is rotated.
Deflects the parallel laser beam L incident thereon, and scans in the direction of the arrow C in the same direction as the axial direction of the photosensitive drum 3 which is the object to be scanned. The fθ lens group 100 provided in front of the polygon mirror 104 forms the deflected laser beam L into a spot image on the surface of the photosensitive drum 3 and sets the scanning speed at a constant speed on the surface of the photosensitive drum 3. And By scanning and exposing the photosensitive drum 3 with such a laser beam L, a dot distribution electrostatic latent image is formed on the photosensitive drum 3.

Each of the developing units 1M to 1K performs reversal development in which toner charged to the same polarity as the charging polarity of the charger 4 is adhered to the light portion potential portion of the latent image.
Exposes an area of the photosensitive drum 3 to which toner is to be attached.

In this embodiment, a dot distribution electrostatic latent image is formed by multi-value recording using a minimum recording unit of one pixel by using a PWM (pulse width modulation) method. This will be described. FIG. 5 is a circuit block diagram showing an example of the pulse width modulation circuit, and FIG. 6 is a timing chart showing the operation of the pulse width modulation circuit.

In FIG. 5, reference numeral 401 denotes a TTL latch circuit for latching an 8-bit digital image signal;
Is a level converter for converting a TTL logic level to a high-speed ECL logic level, and 403 is a D / A converter for converting an ECL logic level to an analog signal. 404 is PWM
An ECL comparator for generating a signal; a level converter for converting an ECL logic level to a TTL logic level;
406 is a clock oscillator for oscillating the clock signal 2f,
Reference numeral 407 denotes a triangular wave signal generator which generates a substantially ideal triangular wave signal in synchronization with the clock signal 2f, and 408 denotes a circuit which generates the image clock signal f by dividing the clock signal 2f by 1/2.
/ 2 frequency divider. Thus, the clock signal 2f has a cycle twice as long as the image clock signal f.
Note that ECL logic circuits are provided everywhere to operate the circuit at high speed.

The circuit operation of such a configuration will be described with reference to the timing chart of FIG. Signal a is clock signal 2
f and signal b indicate the image clock signal f, and are related to the image signal e as shown. Also, inside the triangular wave signal generator 407, the clock signal 2f is once reduced to １ ／ in order to maintain the duty ratio of the triangular wave signal at 50%.
After the frequency division, the triangular wave signal c is generated. further,
This triangular wave signal c is converted into an ECL level (0 to -1 V) to become a triangular wave signal d.

On the other hand, the image signal is from 00h (white) to FFh
(Black), for example, at 256 gradation levels (symbol "h" indicates hexadecimal notation). The image signal e indicates the ECL voltage level obtained by D / A converting some image signal values. For example, the first pixel is the highest density pixel level FFh,
The pixel has a halftone level of 80h, the third pixel has a halftone level of 40h, and the fourth pixel has a halftone level of 20h.

The comparator 404 compares the triangular wave signal d with the image signal e to obtain a pulse width (time length) T, t ₂ , t ₃ , t _4, etc. corresponding to the pixel density to be formed.
Generate an M signal. This PWM signal becomes narrower as the pulse width corresponds to the lower density pixel. And the PWM signal is 0V
Alternatively, the signal is converted into a TTL level of 5 V to be a PWM signal f, which is input to the laser driver circuit 500. By changing the exposure time per pixel according to the PWM signal value obtained in this way, it is possible to obtain 256 gradations with one pixel.

The beam effect h in FIG. 6 shows the laser beam exposure area shape of the photosensitive drum corresponding to each drive pulse width. The area shape of each dot distribution electrostatic latent image substantially corresponds to this exposure area shape. In FIG. 6, the horizontal axis represents time for the signal waveforms a to g, and the horizontal axis represents distance in the beam scanning direction for h.

Next, the developing units 1M to 1K of the rotary developing device 1 installed in the image forming apparatus of FIG. 3 have the same configuration, and have the developing unit configuration as shown in FIG. On the other hand, conventionally, the developing device has a configuration as shown in FIG. First, a conventional developing device will be described as a comparative example with reference to FIG.

The developing device 18 of the comparative example includes a developing container 30 in which a developing chamber R1 and a toner storage chamber R2 above the developing chamber R1 are formed. A replenishment toner (non-magnetic toner) 20 is stored in the toner storage chamber R2.
A replenishing roller 21 is provided at a lower replenishing port, and a replenishing toner 20 is dropped and replenished into the stirring chamber R1 in an amount corresponding to the toner consumed in the development.

A two-component developer 22 in which a toner and a magnetic carrier are mixed is accommodated in the developing chamber R1. The lower half of the developing chamber R1 is separated into two chamber areas by a partition wall 31, and stirring screws 23 and 24 are provided in each of the chamber areas along the longitudinal direction of the developing sleeve 25. By the rotation of the stirring screws 23 and 24, the developer 22 in the developing chamber 1 is transported while being stirred in the longitudinal direction of the developing sleeve 25.

A non-magnetic developing sleeve 25 made of aluminum, non-magnetic stainless steel, or the like is provided at an opening of the developing container 30 facing the photosensitive drum 3. The unit 26 is driven to rotate in the direction of arrow b so as to move in the same direction as the photosensitive drum 3 rotating in the direction of arrow a. A magnet 29 is fixedly arranged in the developing sleeve 25, and the magnet 29
The two-component developer 22 in the developing chamber R1 is carried on the developing sleeve 25 by the magnetic force of the magnetic pole N2 of
By the rotation of No. 5, it is conveyed toward the developing unit 26.

During the transfer, the toner on the developing sleeve 25 is regulated by the regulating blade 28 and the opposing magnetic pole S2 of the magnet roller 29 disposed close to and above the developing sleeve 25, and is coated on the toner layer having a predetermined thickness. . The toner conveyed to the developing unit 26 forms a magnetic brush in a developing magnetic field generated by the developing magnetic pole S1 of the magnet roller 29, and the magnetic brush contacts the photosensitive drum 3 to form an electrostatic latent image formed on the photosensitive drum 3. Develop the image.

Next, the developer is passed through the developing section 26 and returned into the developing container 28 by the rotation of the developing sleeve 25, and is peeled off from the developing sleeve 25 by the repulsive magnetic field of the magnetic poles N3 and N2 of the same polarity of the magnet 29. The developer is then dropped into the developing chamber R1 and collected. The collected developer is stirred and conveyed by stirring screws 23 and 24 in the developing chamber R1.

Referring to FIG. 1, the developing device of the present invention will be described.
A feature of the developing device 19 of the present invention is that the developing unit 26 is driven to rotate in the direction of arrow c so that the developing sleeve 25 moves in the opposite direction to the photosensitive drum 3 rotating in the direction of arrow a. . Accordingly, the regulating blade 28
Is disposed close to the position below the developing sleeve 25. The developer 22 carried on the developing sleeve 25 is regulated by the regulating blade 28 at the lower position, and is coated on the toner layer having a predetermined thickness.

The developer regulated by the regulating blade 28 is conveyed to the developing section 26 to be used for developing the latent image on the photosensitive drum 3, and then passes through the developing section 26 and returns into the developing container 28. Then, the magnets 29 are peeled off from the developing sleeve 25 by the repelling magnetic fields of the magnetic poles N2 and N3 having the same polarity, and fall into the container 28 to be collected. The collected developer is stirred and conveyed by stirring screws 23 and 24 in the developing chamber R1.

In the toner storage chamber R2 above the developing chamber R1 in the developing container 28, a replenishing toner 20 is stored, and an amount of the toner 20 corresponding to the toner consumed in the development is supplied via the replenishing roller 21 to the developing chamber R1. Will be replenished within.

First, when the developing device of the comparative example was subjected to development to form an image, the obtained image was swept. As described earlier, this sweeping is a phenomenon that occurs because toner adheres to the rear end of the high-density solid portion more than necessary, and an image in which toner sweeps to the rear end of a solid image. Presents abnormalities.

This phenomenon occurs when the diameter of the developing sleeve 25 is reduced. Table 1 shows how sweeping occurs when the diameter of the developing sleeve is reduced. In the study shown in Table 1, a magnetic carrier of a two-component developer having a magnetization intensity of 100 emu / cm ³ in a magnetic field of 1000 Gauss was used.

[0040]

[Table 1]

As shown in Table 1, in the comparative example, sweeping occurred when the diameter of the developing sleeve was reduced to 18 mm or less. This seems to be related to the fact that as the diameter of the developing sleeve is reduced, the nip formed between the photosensitive drum and the magnetic brush of the developer on the developing sleeve is reduced, but the detailed reason is unknown.

On the other hand, in the present invention, the developing system in which the developing sleeve is rotated on the photosensitive drum in the counter direction does not cause sweeping as shown in Table 1. It is also unknown why sweeping does not occur by using counter development, but counter development still contributes to development downstream of the development area where development ends in the direction of rotation of the development sleeve. It seems that there is no new developer coming.

Next, in both the comparative example and the present embodiment, the uniformity of the image and sweeping were examined by fixing the diameter of the developing sleeve to 14 mm and changing the intensity of magnetization of the magnetic carrier. Table 2 shows the uniformity of the image and the state of sweeping when the intensity of the magnetization of the magnetic carrier is changed.

[0044]

[Table 2]

One of the factors disturbing the uniformity of the image is unevenness of the ears of the magnetic brush on the developing sleeve. By reducing the magnetization strength of the magnetic carrier, the ears of the magnetic brush become denser, and the unevenness of the ears disappears. As shown in Table 2, in the comparative example, when the intensity of magnetization of the magnetic carrier of the magnetic carrier was reduced, the image uniformity was improved more than excellent, but sweeping occurred.

On the other hand, in the embodiment in which the counter development is performed, when the intensity of the magnetization of the carrier is as large as 200 or 170 emu / cm ³ , sweeping unevenness peculiar to the counter development is generated. Than in the case of rotating in the forward direction in which the photosensitive drum and the opposing part move in the same direction.
Poor image uniformity. However, when the magnetization of the carrier is weakened, the spikes of the magnetic brush become denser, the sweeping unevenness disappears, and the uniformity of the image is improved by improving the spikes of the magnetic brush. In the case of counter development, no sweeping occurs.

It can be said that reducing the diameter of the developing sleeve contributes to downsizing of the developing device from the diameter of 18 mm or less. However, considering the manufacturability and strength of the developing sleeve, 6 m
It is preferable that the diameter is not less than m diameter.

As described above, in the present invention, a developing sleeve having a small diameter of 6 to 18 mm is used, and accordingly, a magnetic carrier having a magnetization intensity of 150 emu / cm ³ or less in a 1,000 gauss magnetic field is used. Then, the developing sleeve is moved in the opposite direction at the portion facing the photosensitive drum to perform counter development. As a result, there is no sweeping of the image,
Further, it is possible to obtain a high-quality image having no spike unevenness and excellent image uniformity, and also to have a non-uniformity of sweeping characteristic characteristic of counter development, thereby realizing a small-sized developing device using a small-diameter developing sleeve.

In the developing device 19 of this embodiment shown in FIG. 1, at the time of development, an oscillating bias voltage superimposed on a DC voltage and an AC voltage is applied to the developing sleeve 25 by a power source 27 as a developing bias. The dark portion potential (non-exposed portion potential) and the light portion potential (exposed portion potential) of the latent image are located between the maximum value and the minimum value of the vibration bias voltage. As a result, an alternating electric field whose direction changes alternately is formed in the developing unit 26. In this alternating electric field, the toner and carrier of the developer vibrate violently, and the toner shakes off the electrostatic restraint on the developing sleeve 25 and the carrier, flies to the photosensitive drum 3, and adheres to the photosensitive drum 3 corresponding to the latent image. I do.

The difference (peak-to-peak voltage) between the maximum value and the minimum value of the oscillation bias voltage is preferably 1 to 5 kV, and the frequency is 1 kV.
-10 kHz is preferred. The waveform of the oscillation bias voltage is
A rectangular wave, a sine wave, a triangular wave, or the like can be used. The DC voltage component of the oscillating bias is a value between the dark portion potential and the bright portion potential as described above, but a value closer to the dark portion potential than the smallest bright portion potential in absolute value is transferred to the dark portion potential region. This is preferable from the viewpoint of preventing fog toner from adhering.

The minimum gap between the developing sleeve 25 and the photosensitive drum 3 (the minimum gap is in the developing section 26) is 0.2 to 0.2.
Preferably it is 1 mm.

The regulating blade 2 below the developing sleeve 25
Numeral 8 regulates the layer thickness of the developer 22 transported by the developing sleeve 25 to the developing section 26, that is, the amount of the developer 22. The amount of the developer conveyed to the developing unit 26 depends on the developing magnetic pole S1 of the magnet 29.
The height of the developer formed in the developing unit 26 from the surface of the developing sleeve of the magnetic brush is set to the minimum gap of 0.2 to 1 mm and 1.2 to 3 with the photosensitive drum 3 removed.
It is preferable that the amount is doubled.

The magnet 29 in the developing sleeve 25 is formed in a roller shape, and is disposed concentrically and non-rotatably in the developing sleeve 25. The developing magnetic pole S1 of the magnet 29 is
6, the developing magnetic pole S1 forms a magnetic brush on the developer on the developing sleeve 25 by the developing magnetic field formed in the developing section 26 as described above. The magnetic brush contacts the photosensitive drum 3, and the toner in the magnetic brush transfers to a dot distribution electrostatic latent image formed on the photosensitive drum 3 to develop the latent image. The toner in the magnetic brush adheres to the ears (brushes) of the magnetic carrier or adheres to the surface of the developing sleeve 25, and any toner can be transferred to the exposed portion of the latent image.

It is preferable that the peak value of the strength (magnetic flux density in the direction perpendicular to the surface of the developing sleeve) of the developing magnetic field by the developing magnetic pole S1 on the surface of the developing sleeve 25 is 500 to 2000 Gauss.

As the toner, known toners obtained by adding a colorant, a charge control agent, and the like to a binder resin can be used, and the volume average particle size is preferably in the range of 5 to 15 μm. The volume average particle size of the toner was measured by, for example, the following measurement method.

As a measuring device, a call counter TA-II is used.
Using a mold (manufactured by Coulter), an interface (manufactured by Nikkaki) for outputting the number distribution and volume distribution and a CX-i personal computer (manufactured by Canon) were connected. As the electrolytic solution, using reagent grade 1 sodium chloride, 1% Na
A Cl aqueous solution was prepared.

In 100 to 150 ml of the above electrolyte solution, 0.1 to 5 ml of a surfactant, preferably an alkylbenzenesulfonic acid salt, is added as a dispersant, and 0.5 to 50 mg of a toner measurement sample is further added and suspended. Then, the electrolytic solution in which the sample was suspended was subjected to dispersion treatment for about 1 to 3 minutes using an ultrasonic
Using an aperture of m, the particle size distribution of the particles of 2 to 40 μm is measured, and then the volume distribution of the toner is determined. This volume distribution gives the volume average particle size of the sample.

On the other hand, as the magnetic carrier, magnetic particles having a very thin resin coating on the surface thereof can be suitably used, and the average particle diameter is preferably 5 to 70 μm.
The average particle size of the carrier is indicated by the maximum chord length in the horizontal direction, and the measurement was performed by a microscope. An average particle size of the carrier can be obtained by randomly selecting 300 or more carriers, actually measuring the diameter, and arithmetically averaging the diameters.

The magnetic characteristics of the magnetic carrier were measured using a DC magnetization BH characteristic automatic recording apparatus BHH-5 manufactured by Riken Denshi Co., Ltd.
It can be measured using type 0. During this measurement,
A cylindrical container having an inner diameter of 6.5 mm and a height of 10 mm is filled with a carrier under a load of about 2 kgf, and the strength of the magnetization is measured while the carrier does not move in the container.

The magnetic carrier is made of ferrite, and IA, IIA, IIIA, IVA, V
A, IB, IIB, IVB, VIB, VIIB, VII
It contains at least one or more elements selected from Group I. For example, Ni-Zn-based, Li-based, Li-Zn
System, Mn-Cu ferrite can be used. The magnetization strength of the magnetic carrier in the magnetic field of the strength _d , that is, σ _d (emu / cm ³ ) can be appropriately adjusted by, for example, adjusting the composition. Of course, the material of the carrier is not limited to the above.

The present invention can be applied to an image expressing a gradation by the dither method.

Embodiment 2 Another embodiment of the present invention will be described. In this embodiment, the image forming apparatus shown in FIG. 7 was used. This image forming apparatus is a printer provided with four image forming stations on a transfer belt 40.

In each station, photosensitive drums 3M, 3C, 3Y, and 3K are installed, and primary chargers 4M, 4C, 4Y, and 4K and light emitting diodes (LEDs) 41M, 41C, 41Y, and 41K are provided around them. , Developing unit 1
M, 1C, 1Y, and 1K are arranged. The opposing portions of the photosensitive drums 3M, 3C, 3Y, and 3K and the transfer belt 40 are transfer portions, and the transfer belts 40 of these transfer portions are used as transfer portions.
Inside each of the transfer brushes 10M, 10C, 10C
Y, 10K are provided.

The transfer material, such as paper, taken out of the cassette C is fed onto a transfer belt 40 with registration by a registration roller 6, and is conveyed to the transfer section of the first station by the transfer belt 40. In the first station, after the photosensitive drum 3M is uniformly charged by the primary charger 4M, the LE blinks in response to the image signal.
By D41M, an electrostatic latent image is formed on the photosensitive drum 3M. This latent image is developed by a magenta developing device 1M to form a magenta toner image. The magenta toner image on the photosensitive drum 3M is transferred onto a transfer material conveyed to a transfer unit by applying a transfer voltage to the transfer brush 10M.

The transfer material onto which the magenta toner image has been transferred is
The transfer of the transfer belt 40 leads to the second station, where the transfer section transfers the cyan toner image formed on the photosensitive drum 3C. Similarly, in the third station, the yellow toner image on the photosensitive drum 3Y is transferred onto the transfer material, and in the fourth station, the black toner image on the photosensitive drum 3K is transferred. A color image obtained by superimposing images is obtained. The transfer material after the transfer is separated from the transfer belt 40 and sent to the fixing device 17.
Then, the toner image is fixed to form a full-color print image.

In this embodiment, no cleaner member is provided for each of the photosensitive drums 3M to 3K, and the transfer residual toner remaining on the photosensitive drums 3M to 3K is collected by the developing units 1M to 1K, that is, a so-called cleanerless process. Is adopted.

Also in this embodiment, each of the developing units 1M to 1K
The developing device having the configuration shown in FIG.
A magnetic carrier having a magnetization intensity of 70 emu / cm ³ in a magnetic field of 1000 Gauss was used as a magnetic carrier of a developer of M to 1K. The developing sleeve of each of the developing devices 1M to 1K is reduced in diameter and has an outer diameter of 16 mm or less. The developing sleeve was rotated in a direction opposite to the photosensitive drums 3M to 3K at a portion facing the photosensitive drums 3M to 3K to perform development. According to this embodiment, it is also possible to develop a high-density solid image and obtain a high-quality image without sweeping.

The toner used as the developer is a polymerized toner produced by suspension polymerization or the like. Since this polymerization toner is spherical, it has good releasability from the photosensitive drums 3M to 3K and high transfer efficiency. Accordingly, the above-described cleaner-less processing of the toner remaining on the photosensitive drum becomes possible.

[0069]

As described above, according to the present invention, a developer including a toner and a magnetic carrier is carried and transported to a developing section by a developer carrier, and a magnetic brush formed on the developer carrier by a developing magnetic field. Is brought into contact with the image carrier in the developing section, and in a developing method of developing an electrostatic latent image formed on the image carrier by an alternating electric field formed in the developing section, or a developer including a toner and a magnetic carrier. A developing device that carries a developer carrying member to be transported to the developing unit; and a magnetic brush formed on the developer carrying unit brought into contact with the image carrier in the developing unit by a developing magnetic field. In a developing device for developing an electrostatic latent image by an alternating electric field formed in a developing section, the outer diameter of the developer carrier is 6 to 1
Since the magnetization strength of the magnetic carrier in a magnetic field of 8 mm and 1000 gauss is 150 emu / cm ³ or less, the moving directions of the developer carrier and the image carrier in the developing section are opposite to each other. However, even if the development is performed by using a developer carrier having an outer diameter of 6 to 18 mm in order to reduce the size of the apparatus, and by making the magnetic brush contact the image carrier, a high density solid image can be obtained. A high-quality image with excellent image uniformity can be obtained by preventing a sweeping phenomenon in which a large amount of toner is developed at the rear end.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a developing device used in the present invention.

FIG. 2 is a cross-sectional view illustrating a conventional developing device used in a comparative example.

FIG. 3 is an overall configuration diagram illustrating an image forming apparatus to which the present invention can be applied.

FIG. 4 is an explanatory diagram illustrating a laser beam scanner of the image forming apparatus of FIG. 3;

FIG. 5 is a circuit block diagram illustrating an example of a pulse width modulation circuit used in the scanner of FIG.

6 is an explanatory diagram showing a signal waveform of the pulse width modulation circuit of FIG.

FIG. 7 is an overall configuration diagram illustrating another example of an image forming apparatus to which the present invention can be applied.

[Explanation of symbols]

 Reference Signs List 1 rotation developing device 1M to 1K developing device 3 photosensitive drum 19 developing device 25 developing sleeve 26 developing unit 28 regulating blade 29 magnet

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-7-175327 (JP, A) JP-A-62-43678 (JP, A) JP-A-7-175329 (JP, A) (58) Investigation Field (Int.Cl. ⁷ , DB name) G03G 15/08 G03G 15/09

Claims (4)

(57) [Claims] 1. A developer comprising a toner and a magnetic carrier is carried and transported to a developing unit by a developer carrier, and a magnetic brush formed on the developer carrier by a developing magnetic field is applied to the image carrier in the developing unit. In a developing method of contacting and developing an electrostatic latent image formed on the image carrier by an alternating electric field formed in the developing section, an outer diameter of the developer carrier is 6 to 18 mm and a magnetic carrier of 1000 is provided. The intensity of magnetization in a Gaussian magnetic field is 150 em
u / cm ³ or less, and the directions of movement of the developer carrier and the image carrier in the developing section are opposite to each other. 2. The developing method according to claim 1, wherein said alternating electric field is formed by applying a voltage obtained by superimposing a DC voltage and an AC voltage to said developer carrier. 3. A developer carrying member for carrying a developer including a toner and a magnetic carrier and transporting the developer to a developing portion, wherein a magnetic brush formed on the developer carrying member by a developing magnetic field is used in the developing portion. A developing device that is brought into contact with an image carrier and develops an electrostatic latent image formed on the image carrier by an alternating electric field formed in the developing unit; an outer diameter of the developer carrier is 6 to 18 mm; The magnetization intensity of the magnetic carrier in a magnetic field of 1000 Gauss is 150 em
u / cm ³ or less, and the directions of movement of the developer carrier and the image carrier in the developing section are opposite to each other. 4. The developing device according to claim 3, wherein the alternating electric field is formed by applying a voltage obtained by superimposing a DC voltage and an AC voltage to the developer carrier.