JPH06102767A - Developing device - Google Patents

Abstract

PURPOSE:To obtain an image of high density and having no roughness without the occurrence of toner scattering by developing with two-component developer by use of a magnetic brush. CONSTITUTION:An electrode 20 is arranged on an upstream side position in the rotational direction of a developing sleeve 19 from a control blade 25 in a developing container 18 for containing the two-component developer T1, and by impressing a voltage on the electrode 20, toner among the developer T1 is biased on the side of the sleeve 19 when the developer T1 carried on the sleeve 19 passes by the electrode 20, thereafter, the toner is controlled by the control blade 25 so as to form a thin layer on the sleeve 19 with developer whose toner concentration is high. Even in the case of controlling the toner concentration in the developer T1 in the container 18 so that it may be suitable for electrostatic charging, the toner concentration in the developer carried to the developing part by the sleeve 19 is kept high, so that the image of high density and having no roughness is obtained by applying a magnetic brush developing method. Also, the occurrence of toner scattering is prevented by optimumly electrostatically charging the developer T1 in the container 18.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device for developing an electrostatic latent image formed by electrophotography or electrostatic recording.

[0002]

2. Description of the Related Art Conventionally, various devices have been proposed and put into practical use as a dry developing method for developing an electrostatic latent image formed by an electrophotographic method or an electrostatic recording method. It can be roughly divided into a one-component system and a two-component system. Most of the one-component methods are non-contact methods, but a typical method is a jumping developing method using magnetic toner. With this developing method, a high quality image can be obtained with a simple structure, but a color image cannot be obtained because the toner contains magnetic particles.

There is also a one-component developing method using a non-magnetic toner, whereby a color image can be obtained, but it is difficult to apply the toner onto the developing sleeve and it is applied by an elastic blade. At present, there are aspects that lack stability and durability.

On the other hand, in the two-component developing method, the toner is conveyed by a magnetic carrier, but since a non-magnetic toner can be used, a color image can be obtained and the image quality is high. A conventional two-component developing device is shown in FIG.

As shown in FIG. 9, the developing device is arranged so as to face the photosensitive drum 3 of the image forming apparatus. The developing device
A developing sleeve 19 opposed to the photosensitive drum 3 with a small gap is rotatably provided in an opening of a developing container 18 containing a two-component developer (not shown).
The magnet roller 22 in which the magnetic poles of S are alternately arranged is non-rotatably installed. Magnetic pole N of magnet roller 22
_The magnetic field generated by ₁ , N ₂ , N ₃ , S ₁ and S ₂ is formed as shown by the dotted curve Br in the figure. Development sleeve 19
Is rotated in the b direction by a driving device (not shown) with respect to the photosensitive drum 3 rotating in the a direction.

The inside of the developing container 18 is divided into a developing chamber 18a on the side of the developing sleeve 19 and a stirring chamber 18b on the opposite side by a partition wall 10 having an open upper end, and the developing chamber 18a and the stirring chamber 18b.
First screw 23 and second screw for stirring developer respectively
A screw 24 is installed. A regulating blade 25 that forms a thin layer of developer on the developing sleeve 19 is installed above the developing sleeve 19 in the developing container 18 with a small gap. In this example, the gap between the regulation blade 25 and the developing sleeve 19 is 800 μm, and the gap between the photosensitive drum 3 and the developing sleeve 19 is 500 μm.
It is set to μm.

The process of developing the electrostatic latent image on the photosensitive drum 3 by the two-component magnetic brush method using the above-described developing device and the circulation of the developer will be described. First, the developing sleeve is formed by the N ₂ pole of the magnet roller 22. The developer drawn up on and carried by S 19 is S _{2 as the} developing sleeve 19 rotates.
In the process of being conveyed from the pole to the N ₁ pole, a thin blade of developer is formed on the developing sleeve 19 by being regulated by the regulating blade 25 arranged perpendicularly to the developing sleeve 19. When the developer formed in a thin layer is conveyed to the S ₁ pole of the main developing pole (the peak of the magnetic field strength is 1000 gauss) located in the developing portion facing the photosensitive drum 3, the magnetic force of the developer causes The magnetic brush of the developer is formed by the spikes. The electrostatic latent image formed on the photosensitive drum 3 is developed by the developer formed on the magnetic brush coming into contact with the electrostatic latent image. The developed developer is returned into the developing container 18 as the developing sleeve 19 rotates, falls from the developing sleeve 19 by the repulsive magnetic field of the N ₃ pole and N ₂ pole of the magnet roller 22, and is collected in the container 18. To be done.

In this embodiment, the developer is a two-component developer in which a non-magnetic toner having an average particle diameter of 8 μm and a magnetic carrier having an average particle diameter of 50 μm are mixed, and the magnetic carrier has a magnetic field of the main developing electrode S ₁ . It has a magnetization strength of 200 emu per cubic centimeter when a strength of 1000 Gauss is applied. Toner concentration in developer is 6%
(% By weight; the same applies below).

[0009]

When the image is formed by developing under such conditions and copying is performed, the obtained image has a low density and becomes a dry image in the low density portion.

It has been found that when the toner density is increased to 10% to improve this, the image density is increased and a smooth low density portion is realized. This is because the developing efficiency of the developing device is increased, and the photosensitive drum 3 is used for developing the latent image.
It is considered that the developing efficiency is increased because the developing sleeve 19 carries an excessive amount of toner than the amount of toner to be supplied to the developing sleeve 19.

However, when the toner concentration of the developer is set to 10% and development is performed to form an image on several thousand sheets, the toner scatters the inside of the image forming apparatus, so-called toner scattering. Generally, toner scattering occurs when toner held on a magnetic carrier by electrostatic force is released from the carrier during transport of the developer.

The above-mentioned problems become more remarkable when a latent image is formed by a digital method. The digital latent image forms a dot-shaped latent image on the photosensitive drum using a laser beam or the like. This will be described below.

A photosensitive drum is scanned and exposed by a laser beam modulated in accordance with a recorded image signal to obtain a dot-distributed electrostatic latent image, that is, an electrostatic latent image in which dot-shaped latent images are distributed corresponding to the image. An image forming method for forming an image is known.
Among them, the so-called pulse modulation width (PWM) method, which modulates the width of the drive pulse current of the laser (that is, the duration time) according to the density of the image to be recorded, achieves high recording density (that is, high resolution). It is also possible to obtain high gradation.

However, when a dot distribution electrostatic latent image is formed on the photosensitive drum by using the PWM method, a magnetic brush of a two-component developer is brought into contact with the photosensitive drum, and the electrostatic latent image is reversely developed. In the image, the shading occurred in the halftone region where the reflection density was 0.3 or less. Roughness did not occur so much in text originals and the like, but occurred frequently in areas of low density such as photographic originals.

Then, when the cause of the rubbing was investigated, the following was found. Normally, when forming a low-density latent image by a dot distribution latent image, the latent image on the photosensitive drum is not a broad latent image like an analog latent image as shown in FIG. , A two-dimensional distribution of local dot-shaped latent images as shown on the left side. When attempting to reproduce a lower density, the dot-shaped latent image becomes blunt due to the influence of the photoconductor film thickness of the photosensitive drum. As shown in the right side of FIG. (Minimum potential difference in absolute value of the potential difference)
Gradually becomes smaller. For example, when an image having a reflection density of about 0.2 is to be reproduced, Vo of the dot-shaped latent image at that time becomes about 150 to 200V.

On the other hand, in the case of reversal development in which toner adheres to the light-exposed area of the photosensitive drum, the DC voltage component of the vibration development bias voltage is higher than the surface potential of the non-exposed area (non-image area) in order to prevent fogging. Is 100 to 200V lower in absolute value, the potential difference Vcont between the potential of the light exposure portion of the dot-shaped latent image and the DC voltage component of the developing bias when Vo is 150 to 200V is about 0 to 50V. turn into.

The Vcont value of 0 to 50 V is a very unstable contrast potential whether the toner reaches the photosensitive drum side or remains on the developing sleeve side. Therefore, when developing the above dot-shaped latent image with a two-component developer,
The contact state of the magnetic brush with the photosensitive drum has a great influence on the developing efficiency, and due to the lack of dots corresponding to the unevenness of the brush of the magnetic brush, density unevenness that is unevenly distributed is likely to occur. This is shown in FIG.

In FIG. 11, the symbol P indicates each pixel. A dot-shaped latent image L1 corresponding to a low-density image is formed on each pixel P by a laser beam modulated by the PWM method
To L5 are formed. D1 to D4 are dot-shaped latent images L
1 to L4 are areas of toner adhesion, that is, developed areas.

The dot-shaped latent image L2 is completely developed. However, the dot-shaped latent images L1, L3, and L4 are only partially developed. The dot-shaped latent image L5 is not developed at all.

Since the developed image having a defect in the development of the dot-shaped latent image is two-dimensionally distributed in this manner, the low-density area looks rough, and a color image is formed by superposing toner images of a plurality of colors. When formed, this graininess is very noticeable, resulting in deterioration of image quality.

An object of the present invention is to provide a developing device capable of obtaining an image with high density and without rubbing by developing a two-component developer with a magnetic brush without causing toner scattering. is there.

[0022]

The above object can be achieved by the developing device according to the present invention. In summary, the present invention supports a two-component developer housed in a developing container on a developer carrier having a built-in magnetic field generating means, and the carried developer is regulated by a regulating member to form a thin layer. While being formed, the developer carrying member conveys the developer to a developing unit facing the image carrying member, and in the developing unit, the magnetic brush of the developer is formed by the magnetic field generating means. In a developing device for developing an electrostatic latent image formed above, the toner of the developer carried on the developer carrying member is moved in the developing container in a moving direction of the developer carrying member rather than the regulating member. In the developing device, an electrode is provided at an upstream position so as to be unevenly distributed on the developer carrier side by an applied voltage.

In another aspect of the present invention, instead of the electrode, a developer different from the developer carrying body containing a magnetic field generating means for carrying a two-component developer housed in the developing container. A carrier and a toner applied from the developer carried on the other developer carrier by the voltage applied to the other developer carrier to carry the toner, and the carried toner is more than the regulating member. At a position on the downstream side in the moving direction of the developer carrying body, a toner carrying body which is transferred to the developer carried on the developer carrying body by the applied voltage was installed.

In still another aspect of the present invention, instead of providing the electrodes and the like, the regulating member is provided on the developer carrying member side by a voltage applied with toner of the developer carried on the developer carrying member. Built-in magnetic field generating means for uneven distribution and for separately carrying a part of the developer carried on the developer carrying member to form a thin layer of the developer on the developer carrying member. The developer carrier is different from the developer carrier.

The developing device of the present invention can be suitably used when the electrostatic latent image formed on the image carrier is a dot distribution electrostatic latent image.

[0026]

【Example】

Embodiment 1 FIG. 5 is an overall configuration diagram showing an example of an electrophotographic color printer to which the developing device of the present invention can be applied. This printer is provided with an electrophotographic photosensitive drum 3 which rotates in the direction of the arrow, and a primary charging device 4, a rotary developing device 1 having a plurality of developing devices around the photosensitive drum 3, a transfer charging device 10 and a cleaning means. 12 is provided, a laser scanner LS is provided above the photosensitive drum 3, and the image forming means is configured by these primary chargers 4 and the like.

The developing devices of the rotary developing device 1 are a magenta developing device 1M, a cyan developing device 1C, a yellow developing device 1Y and a black developing device 1K, which contain a two-component developer containing toner and carrier. Magenta toner, cyan toner, yellow toner, and black toner are used as toner.

The document to be copied is read by a document reading device (not shown). This reading device has a photoelectric conversion element such as a CCD that changes an original image into an electric signal, and outputs image signals corresponding to magenta image information, cyan image information, yellow image information, and monochrome image information of the original, respectively. To do. The semiconductor laser built in the scanner LS is controlled according to these image signals and emits the laser beam L. A laser beam can be emitted in response to an output signal from the computer.

The sequence of the entire color printer will be briefly described by taking the case of the full color mode as an example. First, the photosensitive drum 3 is uniformly charged by the primary charger 4. Next, scanning exposure is performed by the laser beam L modulated by the magenta image signal, and the photosensitive drum 3
A dot-distributed electrostatic latent image is formed on the latent image. The latent image is subjected to reversal development by the magenta developing unit 1M which is previously set at the developing position, and is visualized as a magenta toner image.

On the other hand, the recording material such as paper which is taken out from the cassette 2 and supplied through the paper feed guide 5a, the paper feed roller 6 and the paper feed guide 5b is gripped by the gripper 7 of the transfer drum 9 and abuts against it. It is electrostatically wound around and carried on the transfer drum 9 by the application roller 8 and its opposite pole. The transfer drum 9 is rotating in the direction of the arrow shown in the figure in synchronization with the photosensitive drum 3, and the recording material carried on the transfer drum 9 is conveyed to a transfer portion facing the photosensitive drum 3, where the photosensitive drum 3 is moved. The upper magenta toner image is transferred by the transfer charger 10. The transfer drum 9 continues to rotate as it is, and again conveys the recording material toward the transfer portion in preparation for transfer of the cyan toner image to be formed next.

After the transfer of the magenta toner image is completed, the photosensitive drum 3 is destaticized by the destaticizing charger 11, is cleaned by the cleaning means 12 to remove the untransferred toner, and is then charged by the primary charger 4 again. The dot distribution electrostatic latent image is formed on the photosensitive drum 3 by the exposure of the laser beam L modulated by the cyan image signal. During this time, the developing device 1 rotates by a quarter and the cyan developing device 1 rotates.
C is fixed in advance at the developing position, and the electrostatic latent image formed on the photosensitive drum 3 is reverse-developed by the cyan developing device 1C to be visualized as a cyan toner image. The obtained cyan toner image is transferred onto the recording material on the transfer drum 3 from the magenta toner image in an overlapping manner at the transfer portion.

The above-described steps are performed for yellow and black, and a dot distribution electrostatic latent image is formed on the photosensitive drum 3 by exposure of the laser beam L modulated by each image signal, and a yellow developing device. Magenta, cyan, yellow and black are formed on the recording material by forming a yellow toner image and a black toner image by development with 1Y and a black developing device 1K, and superposing and transferring the yellow toner image and the black toner image on the recording material. A color image is obtained by superimposing the four color toner images.

When the transfer of the four color toner images is completed, the recording material is discharged by the separation charge-eliminating chargers 13 and 14, the gripping by the gripper 7 is released, and then the recording material is separated from the transfer drum 9 by the separation claw 15 and then conveyed. Belt 16 to fixer 17
Sent to. The recording material sent to the fixing device 17 is heated and pressed there to fix the toner image, and the toner image is mixed and fixed to the recording material to form a full-color permanent image. Thus, a series of full-color mode sequences is completed, and the full-color print image obtained by fixing is discharged outside the printer.

FIG. 6 shows a laser beam scanner installed in the printer of FIG. This scanner includes a semiconductor laser element 102, and this element 102 is a generator (laser driver circuit) 5 of an emission signal which is a drive signal for generating a laser beam.
00, and blinks according to the light emission signal generated by the light emission signal generator 500. The laser beam L emitted from the laser element 102 by blinking is made into substantially parallel light by the collimator lens system 103 and is incident on a rotating polygon mirror, that is, a polygon mirror 105.

The polygon mirror 105 rotates in the direction of arrow B at a constant speed, so that the collimator lens system 103 is rotated.
The laser beam L of parallel light incident from is deflected and scanned in the direction of arrow C, which is the same 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 105 images the deflected laser beam L in a spot shape on the surface of the photosensitive drum 3, and the scanning speed thereof is constant on the surface of the photosensitive drum 3. And By scanning and exposing the photosensitive drum 3 with the laser beam L, a dot distribution electrostatic latent image is formed on the photosensitive drum 3.

Each of the developing devices 1M to 1K includes a primary charger 4
Since the reversal development is performed in which the toner charged to the same polarity as the charging polarity by the toner is attached to the bright portion potential portion of the latent image, the laser beam L exposes the area of the photosensitive drum 3 to which the toner should be attached.

In this embodiment, a dot distribution electrostatic latent image is formed by multi-valued recording in which the minimum recording unit is one pixel using the PWM (pulse width modulation) method. This will be described. 7 is a circuit block diagram showing an example of the pulse width modulation circuit, and FIG. 8 is a timing chart showing the operation of the pulse width modulation circuit.

In FIG. 7, reference numeral 401 is a TTL latch circuit for latching an 8-bit digital image signal, and 402.
Is a level converter for converting a TTL logic level into a high-speed ECL logic level, and 403 is an A / D converter for converting an ECL logic level into an analog signal. 404 is PWM
An ECL comparator for generating a signal, a level converter 405 for converting an ECL logic level into a TTL logic level,
406 is a clock oscillator that oscillates the clock signal 2f,
Reference numeral 407 is a triangular wave signal generator that generates a substantially ideal triangular wave signal in synchronization with the clock signal 2f, and 408 is a frequency divider that divides the clock signal 2f by ½ to generate an image clock signal f. As a result, the clock signal 2f has a cycle twice that of the image clock signal f. In order to operate the circuit at high speed, ECL logic circuits are arranged everywhere.

The circuit operation of such a configuration will be described with reference to the timing chart of FIG. Signal a is clock signal 2
The signal f and the signal b indicate the image clock signal f and are associated with the image signal e as shown in the figure. Also triangular wave generator 40
Even inside 7, the duty ratio of the triangular wave signal is set to 50
In order to keep the frequency at%, the clock signal 2f is once frequency-divided by 1/2 and then the triangular wave signal c is generated. Further, the triangular wave signal c is converted to the ECL level (0 to -1V) and becomes the triangular wave signal d.

On the other hand, the image signal is 00h (white) to FFh.
It changes up to (black), for example, in 256 gradation levels (the symbol "h" indicates hexadecimal display). The image signal e indicates an ECL voltage level obtained by D / A converting some image signal values. For example, the first pixel has the highest density pixel level of FFh, the second pixel has the halftone level of 80h, and the third pixel has the halftone level of 4h.
0h, the 4th pixel shows each voltage of 20h of the halftone level.

The comparator 404 compares the triangular wave signal d and the image signal e to generate a PWM signal such as a pulse width time table T, t ₂ , t ₃ , t ₄ according to the pixel density to be formed. This signal becomes narrower as the pulse width corresponding to the low-density pixel increases. This PWM signal is 0V or 5
The PWM signal f is converted into the V TTL level and is input to the laser driver circuit 500. By changing the exposure time per pixel in accordance with the PWM signal value obtained in this way, 256 gradations can be obtained for one pixel.

The beam effect h in FIG. 8 shows the laser beam exposure area shape of the photosensitive drum corresponding to each drive pulse width. The area shape of each dot latent image also substantially corresponds to this exposure area shape. In FIG. 8, for the signal waveforms a to g, the horizontal axis indicates time, and for h, the horizontal axis indicates the distance in the beam scanning direction.

FIG. 1 is a sectional view showing an embodiment of the developing device of the present invention. In the developing device according to the present embodiment, the electrode 20 is largely installed in the upper part of the developing container 18 containing the two-component developer T ₁ at a position upstream of the regulating blade 25 with respect to the rotation direction of the developing sleeve 19. It is a feature.

The two-component developer T ₁ contained in the developing container 18 is a toner having a volume average particle diameter of 8 μm made of a resin having a negative charging characteristic and a volume average particle diameter of 5
It is mixed with a magnetic carrier of 0 μm, and the toner concentration of the developer T ₁ is 6%. This toner concentration is detected by a toner concentration detection means such as light detection or magnetic detection (not shown), and based on this, an appropriate amount of toner is supplied from the toner hopper 31 in the upper part of the container 18, and the hopper 3
1 is supplied to the lower part of the container 18 by the rotation of the roller 30 at the lower end, and is made uniform with the developer by the developing chamber 18a and the first and second stirring rollers 23 and 24 in the stirring chamber 18b which are partitioned by the partition wall 10 thereof. After stirring and mixing, the toner concentration of the developer in the container 18 is constantly maintained at 6%.

Developing sleeve 1 for carrying and carrying the developer
9 includes a magnet roller 22 inside, and the magnet roller 22 is installed so as not to rotate with respect to the developing sleeve 19 which rotates in the direction of arrow b. By the N ₂ pole of the magnetic poles formed on the magnet roller 22, the container 1
The developer T ₁ in 8 is carried on the developing sleeve 19.
As the developing sleeve 19 rotates, the developer T ₁ carried on the developing sleeve 19 passes through the electrode 20 provided in the upper portion of the container 18.

The electrode 20 has a flat plate shape along the longitudinal direction of the developing sleeve 19 and is arranged with its width direction parallel to the tangential direction of the peripheral surface of the developing sleeve 19 and with a gap from the developing sleeve 19. It is kept at 1 mm. A DC bias of −650 V is applied to the electrode 20 by the power supply W.

As a developing bias, a voltage obtained by superimposing a DC bias of −450 V on an AC bias of Vpp = 2 kV and a frequency f = 2 kHz is applied to the developing sleeve 19, resulting in the electrode 20 and the developing sleeve 19. Between them, a potential difference of DC is 200 V and AC is 2 kV and 2 kHz. Therefore, in the developer T ₁ carried on the developing sleeve 19 and conveyed, the negatively charged toner in the developer T ₁ moves to the developing sleeve 19 side while passing through the portion of the electrode 20. Will be unevenly distributed.

A regulating blade 25 is provided at a position above the developing sleeve 19 in the upper part of the developing container 18, and in the present embodiment, the regulating blade 25 is also formed in a flat plate shape along the longitudinal direction of the developing sleeve 19. The width direction is arranged parallel to the tangential direction of the peripheral surface of the developing sleeve 29. The regulation blade 25 is spaced from the developing sleeve 19 by 8
The developer T ₁ on the developing sleeve 19 is maintained at 00 μm.
Is regulated to apply and form a thin layer. The developer T ₁ applied and formed in a thin layer by the regulation of the blade 25 is carried to the developing section facing the photosensitive drum 3 as the developing sleeve 19 rotates.

The regulating blade 25 may be perpendicular to the tangential direction of the peripheral surface of the developing sleeve 19, but the parallel to the tangential direction is the developing sleeve containing the developer containing the toner unevenly distributed due to the potential difference. 19 can be efficiently applied in a thin layer.

As mentioned above, the laser dot latent image is formed on the photosensitive drum 3, and the image portion is -150V.
The non-image area is charged to -650V, and the halftone area performs PWM area gradation according to the density between them. On the other hand, in the developing sleeve 19, as described above, Vpp = 2k
A developing bias in which a DC bias of −450 V is superimposed on an AC bias of V and a frequency f = 2 kHz is applied.

The toner contained in the developer T ₁ carried to the developing section reversely develops the electrostatic latent image on the photosensitive drum 3 by the developing bias. The developer, which has completed the development, passes through the developing section by the rotation of the developing sleeve 19 and passes through the developing container 18
Then, the magnet roller 22 in the developing sleeve 19 peels off the developing sleeve 19 by the action of the repulsive magnetic poles N ₃ and N ₂ and is collected in the container 18.

On the other hand, the developer which is not carried on the developing sleeve 19 side due to the regulation by the regulating blade 25 is carried to the upper portion of the regulating blade 25 and is conveyed in the longitudinal direction of the developing sleeve 19 by the conveying screw 21 installed thereon. It is carried and returned to the lower part inside the container 18.

In the present invention, as described above, the toner contained in the developer T ₁ carried on the developing sleeve 19 is changed to the electrode 20.
And the developing sleeve 19 due to the potential difference between the developing sleeve 19 and the developing sleeve 19.
The toner is unevenly distributed on the side and then applied in a thin layer on the developing sleeve 19 by the regulating blade 25. Therefore, the toner concentration of the applied developer of the thin layer is increased by the uneven distribution of the toner. Specifically, the toner concentration of the developer in the developing container 18 is 6
%, The toner concentration of the developer applied on the developing sleeve 19 was 10%.

In the present embodiment, when an image was formed by developing using such a developer, the conventional problems such as thinness of density and roughness were not generated, and a very smooth and high-quality high-quality image was obtained. An excellent image was obtained and toner scattering did not occur.

According to the present invention, since the developing portion facing the photosensitive drum 3 has a high toner density and a large amount of toner, an image having a high density can be obtained unlike the conventional case. Further, the reason why the high quality image is obtained without the toner scattering is that the toner in the developing section holds a necessary charge amount. That is, the toner concentration of the developer in the developing container 18 is 6%, and the carrier has an appropriate amount of toner for giving sufficient charging charge to the toner. However, if the toner concentration is simply increased, the toner charge amount per toner decreases, which causes toner scattering and image quality deterioration. However, in the present invention, it is necessary to impart a charged charge to the toner. Since the toner concentration of the developer in the developing container 18 to be performed is an appropriate concentration, the toner is sufficiently charged, and the toner is not scattered and the image quality is not deteriorated.

In the above, DC-45 is used as the developing bias.
Although AC of Vpp = 2 kV and f = 2 kHz was superposed on 0 V and applied, of course, so-called DC development with a developing bias of only a DC component having no AC component is also possible, and the same effect is obtained. However, application of an AC bias generally improves image quality, particularly development efficiency and highlight reproducibility. Therefore, it is preferable to apply a development bias superimposed with an AC bias. According to this, the electrode 2
Even if a DC bias is applied to 0, as a result, the electrode 20
Since the AC bias is also applied between the developing sleeve 19 and the developing sleeve 19, the toner in the developer carried on the developing sleeve 19 is efficiently moved to the developing sleeve 19 side.
It can be unevenly distributed, and the toner concentration in the developer applied by the regulation by the regulation blade 25 can be increased. For example, also in the DC development, the AC component can be superposed on the electrode 20.

As described above, in the present invention, the developing container 18
When the developer is properly charged while keeping the proper toner concentration in the developer, and the developer having the proper charge of the toner is carried on the developing sleeve 19 and regulated by the regulation blade 25, , The toner is unevenly distributed to the developing sleeve 19 side by the voltage applied to the electrode 20,
Since the toner concentration is increased and the developer is applied, it is possible to easily obtain a high-concentration image free of roughness by development without causing toner scattering.

Embodiment 2 FIG. 2 is a sectional view showing another embodiment of the developing device of the invention. In this embodiment, instead of providing the electrode 20 in the developing container 18, the developing sleeve 1 which is the first developer carrying member.
9, a second sleeve 41, which is a second developer carrying member, in which a magnet roller 42 is non-rotatably incorporated, and a third sleeve 43, which is a toner carrying member and does not have a magnet roller.
A major feature is the installation of.

According to this embodiment, the developing sleeve 19 described above is used.
The gap between the third sleeve 43 and the third sleeve 43 and the gap between the second sleeve 41 and the third sleeve 43 were both 500 μm.

The developing sleeve 19 has a DC bias-
A developing bias in which an AC bias of Vpp = 2 kV and f = 2 kHz is superposed on 450 V is applied to the second sleeve 41.
DC bias of -850V, Vpp = 2kV, f =
An AC bias of 2 kHz was superimposed and applied. A DC bias of −650V was applied to the third sleeve 43.

The second sleeve 41 is a magnet roller 42.
Thus, the two-component developer T ₁ in the developing container 18 is carried thereon, and the developer T ₁ is regulated by the regulation blade 40 provided below the sleeve 41, and the developer T ₁ is retained on the sleeve 41. Of the third sleeve 4 is formed by rotating the sleeve 41 in the c direction.
Transport in 3 directions. Then, due to the above bias applied to the second sleeve 41, the toner in the developer on the second sleeve 41 is transferred to the third sleeve 43, and a toner layer is formed on the third sleeve 43.

The third sleeve 43 rotates the toner layer formed on the third sleeve 43 in the direction d to convey the toner layer toward the developing sleeve 19, and the above-mentioned bias applied to the third sleeve 43 causes the toner to develop. Transfer to the developer above.

As in the conventional case, the developer T ₁ carried by the magnet roller 22 is regulated by the regulating blade 25 on the developing sleeve 19, and the developer T ₁ is applied and formed in a thin layer. Since the toner is transferred to the developer T ₁ from the third sleeve 43 as described above, the developing sleeve 1
The developer applied on the developer 9 has a toner concentration higher than that of the developer in the developer container 18.

The regulating blade 25 has a protruding portion bent in the direction of the developing sleeve 19 at the tip of a wide width direction portion parallel to the tangential direction of the peripheral surface of the developing sleeve 19, and the regulating blade 25 has a protruding portion. The developer is partitioned from the second sleeve 41 by the widthwise portion, and the developer on the developing sleeve 19 is regulated by the protruding portion.

Therefore, the same effect as in the above-described embodiment is obtained, and when the image is formed by developing with the above-mentioned developer, a high-quality image having high density and no roughness is obtained, and the toner is obtained. No scattering occurred.

Embodiment 3 FIG. 3 is a sectional view showing still another embodiment of the developing device of the present invention. The present embodiment is characterized in that a regulation roller 35, which is a developer carrying member that also serves as a regulation blade, is provided obliquely above the developing sleeve 19. The regulation roller 35 is
The magnet roller 36 is non-rotatably installed inside.

The developer carried on the developing sleeve 19 is conveyed to the portion facing the regulating roller 35 by the rotation of the developing sleeve 19. The regulation roller 35 is rotating in the direction of arrow e, and a part of the developer carried on the developing sleeve 19 is separated at the facing portion and carried by the magnet roller 36. As a result, the developer on the developing sleeve 19 is regulated, and a thin layer of the developer is applied and formed on the developing sleeve 19. The developer carried on the regulation roller 35 by the magnet roller 36 is stripped off by the stripping plate 45 provided obliquely below and returned to the lower part inside the developing container 18.

At this time, the developing sleeve 19 has Vpp =
DC bias to AC bias of 2 kV and f = 2 kHz-
A developing bias in which 450V is superimposed is applied, and a DC bias of -650V is applied to the regulation roller 35. Therefore, in the developer carried on the developing sleeve 19, the toner is unevenly distributed on the developing sleeve 19 side. Therefore, the developer applied in a thin layer on the developing sleeve 19 by the restriction of the restriction roller 35 has a toner concentration higher than that of the developer in the developing container 18.

Therefore, also in this embodiment, by developing with the above-mentioned developer, as in the previous embodiments,
It is possible to obtain a high-concentration, high-quality image with no roughness without causing toner scattering.

Embodiment 4 FIG. 4 is a sectional view showing still another embodiment of the developing device of the invention. In the present embodiment, unlike the first embodiment shown in FIG. 1, the regulation blade 25 is provided vertically to the developing sleeve 19, and the carrier return plate 37 is provided inside the regulation blade 25. ing. On the upstream side of the regulation blade 25 in the rotation direction of the developing sleeve 19,
As in the case of the first embodiment, the electrode 20 is provided in which the tangential direction and the width direction of the peripheral surface of the developing sleeve 19 are parallel to each other.

Since the developer carried on the developing sleeve 19 is biased to the electrode 20 as in the first embodiment, the toner is transferred to the developing sleeve 19 side while passing through the electrode 20. And unevenly distributed. The developer that has passed through the portion of the electrode 20 is separated by the return plate 37 at a portion far from the developing sleeve 19 and returns to the inside of the developing container 18 as indicated by an arrow f, and the residual developer remaining on the developing sleeve 19 is reached. The agent moves in the direction of arrow g and is applied in a thin layer on the developing sleeve 19 under the restriction of the restriction blade 25. Therefore, a thin layer of developer with increased toner concentration is obtained on the developing sleeve 19.

Therefore, also in this embodiment, as in the other embodiments, it is possible to obtain a high-density and high-quality image free of roughness, and toner scattering does not occur.

[0073]

As described above, according to the developing device of the present invention, by developing the two-component developer with the magnetic brush, it is possible to obtain an image having a high density and no greasiness without causing toner scattering. You can

[Brief description of drawings]

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

FIG. 2 is a sectional view showing another embodiment of the developing device of the invention.

FIG. 3 is a sectional view showing still another embodiment of the developing device of the present invention.

FIG. 4 is a sectional view showing still another embodiment of the developing device of the present invention.

FIG. 5 is an overall configuration diagram showing an example of an electrophotographic color printer to which the developing device of the present invention can be applied.

6 is an explanatory diagram showing a laser beam scanner installed in the printer of FIG.

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

8 is a timing chart showing the operation of the pulse width modulation circuit of FIG.

FIG. 9 is a cross-sectional view showing a conventional developing device.

FIG. 10 is an explanatory diagram showing the potential of a dot-shaped latent image formed on a photosensitive drum.

FIG. 11 is an explanatory diagram showing a developed image of a dot-shaped latent image.

[Explanation of symbols]

 3 Photosensitive Drum 18 Development Container 19 Development Sleeve 20 Electrode 22 Magnet Roller 25 Regulation Blade 35 Regulation Roller 37 Carrier Return Plate 42 Second Sleeve 43 Third Sleeve

Claims (4)

[Claims] 1. A two-component developer contained in a developing container is carried on a developer carrier having a built-in magnetic field generating means, and the carried developer is regulated by a regulating member to form a thin layer. Meanwhile, the developer carrying member conveys the developer to a developing unit facing the image carrying member, and in the developing unit, a magnetic brush of the developer is formed by the magnetic field generating means, and the magnetic brush is formed on the image carrying member. In the developing device for developing the formed electrostatic latent image, the toner of the developer carried on the developer carrying body is provided in the developing container at an upstream side of the regulating member in the moving direction of the developer carrying body. In the position, the developing device is characterized in that an electrode is installed which is unevenly distributed on the developer carrier side by the applied voltage. 2. A two-component developer contained in a developing container is carried on a developer carrier having a built-in magnetic field generating means, and the carried developer is regulated by a regulating member to form a thin layer. Meanwhile, the developer carrying member conveys the developer to a developing unit facing the image carrying member, and in the developing unit, a magnetic brush of the developer is formed by the magnetic field generating means, and the magnetic brush is formed on the image carrying member. In a developing device for developing the formed electrostatic latent image, a developer carrying member for carrying the contained two-component developer in the developing container, which is different from the developer carrying body containing the magnetic field generating means. Body and the toner applied from the developer carried on the another developer carrying body by the voltage applied to the other developer carrying body, and carrying the carried toner, and developing the carried toner with respect to the regulating member. Position on the downstream side in the moving direction of the agent carrier 2. A developing device, comprising: a toner carrier that transfers to the developer carried on the developer carrier by the applied voltage. 3. A two-component developer housed in a developing container is carried on a developer carrier having a built-in magnetic field generating means, and the carried developer is regulated by a regulating member to form a thin layer. Meanwhile, the developer carrying member conveys the developer to a developing unit facing the image carrying member, and in the developing unit, a magnetic brush of the developer is formed by the magnetic field generating means, and the magnetic brush is formed on the image carrying member. In the developing device for developing the formed electrostatic latent image, the regulating member causes the toner of the developer carried on the developer carrying body to be unevenly distributed to the developer carrying body side by the applied voltage, and A developer carrier having a built-in magnetic field generating means for forming a thin layer of the developer on the developer carrier by separating and supporting a part of the developer carried on the developer carrier; Is composed of another developer carrying member. Developing device. 4. The developing device according to claim 1, wherein the electrostatic latent image formed on the image carrier is a dot distribution electrostatic latent image.