JPH08146757A - Developing device - Google Patents

Abstract

PURPOSE: To obtain a high-quality image by developing a dot distributional latent image to a developed image whose roughness is restrained by the magnetic brush of two-component developer. CONSTITUTION: The magnetic carrier of the two-component developer has the magnetism of <=100emu/cm<3> in the magnetic field of 1000 gauss. A regulating blade is constituted of a non-magnetic plate and a magnetic plate provided on the upstream side of the non-magnetic plate in the rotating direction of a developing sleeve. The magnetic permeability μb (absolute number) of the magnetic plate and volume Vb(mm<3> ) per unit length (1mm) in a longitudinal direction are set to satisfy the relation of μb.Vb>=1050.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device used in an electrophotographic image forming apparatus, and more specifically, it uses a two-component developer having a non-magnetic toner and a magnetic carrier and a magnetic brush of the developer. The present invention relates to a developing device for performing development.

[0002]

2. Description of the Related Art A photosensitive drum, which is an electrophotographic photosensitive member, is scanned and exposed by a laser beam modulated corresponding to a recorded image signal to form a dot distribution electrostatic latent image, that is, a dot-shaped latent image as an image. There is known an image forming method for forming electrostatic latent images correspondingly distributed. Among them, the so-called pulse modulation width (PWM) method of modulating the width of the laser drive pulse current (that is, the duration time) in accordance with the density of the recorded image is
High recording density (that is, high resolution) can be obtained, and high gradation can be obtained.

However, 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. The image was shaky 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 rustle 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. When an even lower density is reproduced, the dot-shaped latent image becomes dull due to the influence of the photoconductor film thickness of the photosensitive drum, and as shown in FIG. 12, the maximum contrast Vo (the potential difference between the non-exposed portion potential and the potential difference in the dot-shaped latent image is reduced). The minimum potential difference of the absolute value) gradually becomes smaller. For example, when an image with a reflection density of about 0.2 is reproduced, Vo of the dot-shaped latent image at that time is 150
It becomes about 200V.

On the other hand, in the case of reversal development in which toner adheres to the light-exposed portion of the photosensitive drum, the DC voltage component of the vibration developing bias voltage is higher than the surface potential of the non-exposed portion (non-image portion) in order to prevent fogging. Also, since the absolute value is set to be 100 to 200 V lower, the maximum contrast Vo is 150 to
In the case of 200 V, 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 is 0 to 50.
It will be about V.

The Vcont of 0 to 50 V is a very unstable contrast potential as to whether the toner reaches the photosensitive drum side or remains on the developing sleeve side. For that 2
When developing the above dot-shaped latent image with a component developer,
The contact state of the magnetic brush with the photosensitive drum greatly affects the development efficiency, and it corresponds to the unevenness of the brush of the magnetic brush (where the magnetic brush is in contact with the photosensitive drum, it is not developed, and the area not in contact is developed. However, there is a tendency for the image to be loosened due to missing dots or the like. This is shown in FIG.

In FIG. 13, reference symbol P indicates one pixel.
The dot-shaped latent images L1 to L5 corresponding to the low-density image are formed on each pixel P by the laser beam modulated by the PWM method.
Are formed. D1 to D4 are dot-shaped latent images L1 to L
4 shows a toner adhesion area, that is, a developed area.

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 appears to be dull, and a color image is formed by superposing toner images of a plurality of colors. When forming the image, this roughness is very noticeable and the image quality is deteriorated.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to develop a dot distribution electrostatic latent image formed on an image bearing member with a magnetic brush of a two-component developer into a developed image in which roughness is suppressed, An object of the present invention is to provide a developing device capable of obtaining a high quality image.

[0011]

The above object can be achieved by the developing device according to the present invention. In summary, the present invention is directed to a developer carrier that carries a two-component developer having a toner and a magnetic carrier, rotates, and conveys the developer to a developing unit facing the image carrier, and a non-rotating developer carrier. A magnet arranged in
The developer carrying member is provided with a developer layer thickness regulating blade arranged with a tip and a small gap with respect to the developer carrying member, and in the developing unit,
In a developing device for forming a magnetic brush on a developer on a developer carrier to develop a dot distribution electrostatic latent image formed on the image carrier, the magnetic carrier is 100 emu / cm in a magnetic field of 1000 gauss. Has a magnetization of ³ or less,
The regulation blade is composed of a non-magnetic plate and a magnetic plate provided upstream of the non-magnetic plate in the rotation direction of the developer carrier, and has a magnetic permeability of μb (an innumerable number) and a longitudinal unit. When the volume per length (1 mm) is Vb (mm ³ ), the developing device satisfies the relationship of μb · Vb ≧ 1050.

According to the present invention, the magnetic pole arranged at the position of the regulating blade of the magnet has a peak value of the magnetic field strength of 500 to 2000 gauss on the surface of the developer carrying member. The regulation blade may be substantially perpendicular to the developer carrying body, or the rotational direction of the developer carrying body may be relative to the tangential direction on the circumferential direction of the facing portion of the developer carrying body. It is also possible to incline so as to form an angle of 0 to 30 ° in the opposite direction. When the regulation blade is inclined, a developer stirring member that rotates in the opposite direction to the developer carrying member can be provided above the regulation blade. The dot distribution electrostatic latent image on the image carrier is formed by modulating the light emission time of the light source per pixel in accordance with the image density value. At the time of developing the dot-distributed electrostatic latent image on the image carrier, a developing bias voltage in which a DC voltage is superimposed with an AC voltage is applied to the developer carrier.

[0013]

Embodiment 1 FIG. 8 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 around the photosensitive drum 3, a charging device 4, a rotary developing device 1 having a plurality of developing devices, a transfer charging device 10 and A cleaning unit 12 is provided, a laser scanner LS is provided above the photosensitive drum 3, and the charger 4 and the like constitute an image forming unit.

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 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, and this latent image is a magenta developing device 1M previously fixed at the developing position. The reversal development is carried out to visualize the image as a magenta toner image.

On the other hand, the recording material such as paper, which is taken out from the cassette C 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 is applied thereto. It is electrostatically wound around and carried on the transfer drum 9 by the contact 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 is moved. The magenta toner image on 3 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 charger 4 again. Exposure of the laser beam L modulated by the cyan image signal forms a dot-distribution electrostatic latent image on the photosensitive drum 3. During this period, the developing device 1 is rotated and the cyan developing device 1C is previously fixed and placed at the developing position, and the electrostatic latent image formed on the photosensitive drum 3 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 recording material on the transfer drum 3 from the magenta toner image in an overlapping manner at the transfer portion.

The steps described above are performed for yellow and black, and the dot distribution electrostatic latent image is formed on the photosensitive drum 3 by exposure of the laser beam L modulated by the respective image signals, and the 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.

After 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 gripper 7 releases the grip, and then the separation claw 15 separates the recording material from the transfer drum 9, and then the sheet is conveyed. It is sent to a fixing device (hot pressure roller fixing device) 17 by a belt 16. 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. 9 shows a laser beam scanner installed in the printer of FIG. This scanner is a semiconductor laser device 1
02, the element 102 is a generator (laser driver circuit) 50 of a light emission signal which is a drive signal for generating a laser beam.
It is connected to 0 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 the collimator lens system 1
At 03, the light is converted into substantially parallel light and is incident on the rotating polygon mirror, that is, the polygon mirror 105.

By rotating the polygon mirror 105 in the direction of arrow B at a constant speed, the collimator lens system 103
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 units 1M to 1K performs reversal development in which toner charged to the same polarity as the charging polarity of the charger 4 is attached to the bright portion potential portion of the latent image.
Exposes the area of the photosensitive drum 3 to which the toner is to be attached.

In the present 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. FIG. 10 is a circuit block diagram showing an example of the pulse width modulation circuit, and FIG. 11 is a timing chart showing the operation of the pulse width modulation circuit.

In FIG. 10, reference numeral 401 is a TTL latch circuit for latching an 8-bit digital image signal, and 40.
Reference numeral 2 is a level converter for converting a TTL logic level into a high-speed ECL logic level, and 403 is a D / A converter for converting an ECL logic level into an analog signal. 404 is PW
ECL comparator for generating M signal, 405 is ECL
A level converter that converts a logic level into a TTL logic level, 406 is a clock oscillator that oscillates a clock signal 2f, 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 clock signal. It is a frequency divider that divides 2f by 2 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 in the triangular wave signal generator 407, in order to keep the duty ratio of the triangular wave signal at 50%, the clock signal 2f is once 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 obtain a PW having a pulse width (time length) T, t ₂ , t ₃ , t _4, etc. according to the pixel density to be formed.
Generate the M signal. This signal becomes narrower as the pulse width corresponding to the low-density pixel increases. Then, this PWM signal is converted into a TTL level of 0V or 5V to become a PWM signal f, which 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. 11 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. 11, the horizontal axis of the signal waveforms a to g is time, and the horizontal axis of h is the distance in the beam scanning direction.

FIG. 1 is a block diagram showing an embodiment of the developing device of the present invention. Each developing device 1M to 1K of the printer of FIG.
Is configured like the developing device in FIG.

In this embodiment, the developing device is the partition wall 19
The developing chamber (first chamber) R1 and the stirring chamber (second chamber) R2
The toner container R3 is provided above the stirring chamber R2, and the toner container R3 is provided above the stirring chamber R2.
A reinforcing toner (non-magnetic toner) 20 is contained in the unit 3. A replenishment port 21 is provided below the toner storage chamber R3, and the reinforcing toner 20 drops and is replenished into the stirring chamber R2 through the replenishment port 21 in an amount commensurate with the toner consumed in the development. In the developing chamber R1 and the agitating chamber R2, a two-component developer 22 in which the above toner and magnetic carrier are mixed is stored.

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

Call counter TA-II as a measuring device
A model (manufactured by Coulter) was used, and an interface (manufactured by Nikkaki) that outputs a number distribution and a volume distribution and a CX-i personal computer (manufactured by Canon) were connected. First-grade sodium chloride was used as the electrolyte and 1% NaC
1 aqueous solution was prepared.

A surfactant, preferably 0.1 to 5 ml of alkylbenzene sulfonate is added as a dispersant to 100 to 150 ml of the above-mentioned electrolytic solution, and 0.5 to 50 mg of a toner measurement sample is further added and suspended. Then, the electrolytic solution in which the sample is suspended is dispersed by an ultrasonic disperser for about 1 to 3 minutes, and then 100 μm is obtained by the above-mentioned call counter.
The particle size distribution of particles having a size of 2 to 40 μm is measured using the aperture of, and the volume distribution of the toner is obtained therefrom. This volume distribution gives the volume average particle size of the sample.

On the other hand, as the magnetic carrier, those having an extremely thin resin coating on the surface of magnetic particles can be preferably used, and the average particle diameter is preferably 5 to 70 μm. The average particle size of this carrier is shown by the maximum chord length in the horizontal direction, and the measurement method was based on microscopy. The average particle size of the carrier can be obtained by randomly selecting 300 or more carriers, measuring the diameters and arithmetically averaging the diameters.

As the magnetic particles, for example, surface-oxidized or non-oxidized metals such as iron, nickel, cobalt, manganese, chromium, rare earths, alloys thereof or oxide ferrites, etc. are used. Is not particularly limited.

The resistance value of the magnetic particles is 10 ⁷ Ωcm or more, preferably 10 ⁸ Ωcm or more. To measure the resistance value of the magnetic particles, a sandwich type cell with an electrode area of 4 cm ² and an electrode gap of 0.4 cm was used. One electrode was applied with a pressure of 1 kg and an electric voltage E (V / cm) was applied between the electrodes. It is applied to obtain the resistance value of the magnetic particles from the current flowing in the circuit.

In the present developing device, a conveying screw 23 is installed in the developing chamber R1 of the developing container 18, and the rotation of the conveying screw 23 stirs the developer in the developing chamber R1 while the length of the developing sleeve 25 increases. It is conveyed in the direction. Conveyor screw 24 also in stirring chamber R2
Is installed, and the developer in the agitating chamber R2 and the toner supplied thereto are agitated by the rotational driving of the conveying screw 24, and are conveyed in the longitudinal direction of the developing sleeve 25. The conveying direction by the conveying screw 24 is opposite to that by the screw 23.

The partition 19 of the developing container 18 has openings on the front side and the back side, and the developer conveyed by the screw 23 is transferred to the screw 24 from one of the openings and conveyed by the screw 24. The developed developer is transferred to the screw 23 through the other one opening, and is conveyed while being stirred as described above. Due to the friction with the magnetic carrier due to this stirring, the toner is charged to the polarity for developing the latent image.

An opening is provided in a portion of the developing container 18 near the photosensitive drum 3, and the developing sleeve 25 is installed in the opening. The developing sleeve 25 is
It is made of a non-magnetic material such as aluminum or non-magnetic stainless steel.

Developer 22 contained in developer container 18
Is carried on the developing sleeve 25 by a magnet 29 installed in the developing sleeve 25, and the developing section 26 facing the photosensitive drum 3 by rotation of the developing sleeve 25 in the direction of arrow b.
Be transported to. Then, a magnetic brush is formed in the developing unit 26 and comes into contact with the photosensitive drum 3 rotating in the direction of arrow a,
The electrostatic latent image formed on the photosensitive drum 3 is developed.

At the time of development, a vibration bias voltage in which a DC voltage is superimposed on an AC voltage is applied to the developing sleeve 25 as a developing bias by the power source 27. The dark portion potential (non-exposed portion potential) and the bright 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 section 26. In this alternating electric field, the toner and the carrier of the developer violently vibrate, the toner shakes off the electrostatic restraint to the developing sleeve 25 and the carrier and flies to the photosensitive drum 3, and adheres to the photosensitive drum 3 corresponding to the latent image. To do.

The difference between the maximum and minimum values of the vibration bias voltage (peak-to-peak voltage) is preferably 1 to 5 kV, and the frequency is 1.
-10 kHz is preferable. The waveform of the vibration bias voltage is
Square wave, sine wave, triangle wave, etc. can be used. The DC voltage component of the vibration bias is a value between the dark part potential and the bright part potential as described above, but a value closer to the dark part potential than the minimum absolute bright part potential is closer to the dark part potential region. It is preferable for preventing the adhesion of the fog toner.

The minimum gap between the developing sleeve 25 and the photosensitive drum 3 (this minimum gap is in the developing section 26) is 0.2-.
It is preferably 1 mm.

A developer layer thickness regulating blade 28 is installed above the developing sleeve 25. This regulating blade 2
8 is a developer 22 which the developing sleeve 25 conveys to the developing section.
Layer thickness, that is, the amount of the developer 22 is regulated. The amount of developer regulated by the regulation blade 28 and conveyed to the developing section 26 is the height of the developer formed by the magnetic field in the developing section 26 by the developing magnetic pole S1 of the magnet 29 on the surface of the developing sleeve of the magnetic brush. However, the amount is preferably 1.2 to 3 times the minimum gap 0.2 to 1 mm with the photosensitive drum 3 removed.

According to the present invention, the regulation blade 28 includes a plate 28a of a non-magnetic material such as aluminum or SUS316,
And a magnetic plate 28b made of a ferromagnetic material such as iron, nickel, cobalt, or an alloy thereof.
Is attached to the developing sleeve 25 side of the non-magnetic material plate 28a and to the upstream side (inner side) in the rotational direction thereof. The magnetic plate 28b is narrower than the non-magnetic material plate 28a, and is located at the tip of the non-magnetic material plate 28, slightly retracted therefrom.

The magnet 29 in the developing sleeve 25 is formed in a roller shape, and is arranged concentrically and non-rotatably in the developing sleeve 25. The developing magnetic pole S1 of the magnet 29 is located in the developing section 26, and the developing magnetic field formed in the developing section 26 by the developing magnetic pole S1 forms a magnetic brush on the developer on the developing sleeve 25. The magnetic brush contacts the photosensitive drum 3, and the toner in the magnetic brush is transferred to the dot distribution electrostatic latent image formed on the photosensitive drum 3 to develop the latent image. Although the toner in the magnetic brush adheres to the brush (brush) of the magnetic carrier or adheres to the surface of the developing sleeve 25, any toner transfers to the exposed portion of the latent image and develops it.

The strength of the developing magnetic field by the developing magnetic pole S1 on the surface of the developing sleeve 25 (the magnetic flux density in the direction perpendicular to the developing sleeve surface) preferably has a peak value of 500 to 2000 gauss.

In this example, the magnet 29 has magnetic poles N1, N2, N3 and S2 in addition to the developing magnetic pole S1.

With this structure, as in the conventional case, the developing sleeve 25 is rotated, whereby the developer 22 in the developing container 18 is drawn up onto the developing sleeve 25 by the magnetic pole N3, and the drawn up developer is drawn from the magnetic pole S2. The toner is conveyed to N2 and regulated by the regulation blade 28 on the way to form a thin layer of the developer 22 on the developing sleeve 25. Then, as the developing sleeve 25 rotates, the developing sleeve 26 is conveyed to the developing unit 26, and as described above, a magnetic brush is formed by erected in the magnetic field of the developing magnetic pole S1, and the electrostatic latent image of the dot distribution on the photosensitive drum 3 is formed. Used for development.

After the development is completed, the developer is used as the developing sleeve 2.
When the magnetic poles N1 and N
The repulsive magnetic field between the developing sleeve 25 and the stirring chamber R
It falls within 1 and is collected. The collected developer is stirred by the stirring screws 23 and 24 as described above.
Be transported.

When the developing device as described above was used for the examination, the density of the magnetic brush of the developer in the developing portion (the magnetic brush per unit area of the surface of the developing sleeve 25) was reduced in order to eliminate the roughness of the image. It was found that it is necessary to increase the number. It is possible to increase the density of the magnetic brush by reducing the strength of magnetization of the magnetic carrier in the developing section.

The magnetic characteristics of the magnetic carrier are as follows: Riken Denshi KK BHH-50 DC magnetization BH characteristic automatic recording device
Can be measured using. At the time of this measurement, a cylindrical container (inner diameter 6.5 mm, height 10 mm) is filled with a carrier by applying a load of about 2 kg, and the strength of the magnetization is measured while the carrier does not move in the container. It is important to do so.

In this embodiment, the developing magnetic pole S of the magnet 9 is used.
Since the peak value of the magnetic flux density on the surface of the developing sleeve in the normal direction is 1000 gauss is used as 1, the developing magnetic field of 1000 gauss, that is, the carrier force when the magnetic force (magnetic flux density) is 1000 gauss is used. The value of magnetization,
The relationship with the density of the magnetic brush in the developing section was examined. The result is shown in FIG.

As shown in FIG. 2, carrier magnetization σ ₁₀₀₀ (e
mu / cm ³ ) and the density of magnetic brush ears α (books /
mm ² ) is in an inversely proportional relationship, and when the value on the curve of the inverse proportionality is read from FIG. 2 and expressed by an equation, α × σ ₁₀₀₀ = 600. As can be seen, carrier magnetization σ ₁₀₀₀
The smaller is the higher the magnetic brush ear density α.

Next, by changing the magnitude of the carrier magnetization σ ₁₀₀₀ to change the density α of the magnetic brush, the relationship between the density of the magnetic brush and the image quality of the output image (the highlight and halftone shading). Was examined and evaluated. The evaluation was performed on a developed image having a recording density of 200 dpi in the main scanning direction and 400 dpi in the sub scanning direction by a two-component developing method. Table 1 shows the results.

[0058]

[Table 1]

In Table 1, the meanings of the symbols are as follows.

Glossiness section: A: Very smooth image quality without "grassiness" B: Smoother image quality without "grassiness" C: Smoother image quality without "grassiness" D: "Grassiness" Conspicuous E: “Gasatsuki” is very conspicuous

As shown in Table 1, when the density of the ears of the magnetic brush is 6 lines / mm ² or more, a good image free from roughness can be obtained. In other words, referring to FIG. 2, if the magnitude of σ ₁₀₀₀ is 100 emu / cm ³ or less, a good image free from shakiness can be obtained. This is due to the visual limits of the human eye.

"Rattack" is noise when viewed by human eyes, and "visible" is that there is a large amount of noise in a period that is easily visible to human eyes. In the two-component contact development method, the toner is provided for development according to the pattern of the ears, but by making the magnetic brush dense, it is possible to make the toner pattern after development a cycle that is difficult for human eyes to see. Therefore, it is possible to reduce the roughness. In addition, since the magnetization of the magnetic carrier becomes small, the carrier is weakly restrained on the developing sleeve,
As a result, the fact that the magnetic brush rubs the photosensitive drum weakly in the developing section is also considered to be one of the factors for reducing the roughness.

However, the magnetization of the magnetic carrier is set to 10
When the magnetic field of 00 Gauss is used to reduce to 100 emu / cm ³ or less and the developer layer is regulated at the regulating blade position,
If the volume of the magnetic plate is set to 2.0 mm ³ per unit length (1 mm) in the longitudinal direction (thickness 0.5 mm × height 4 mm), the gap between the developing sleeve and the regulating blade (SB)
It becomes difficult to stably apply the toner onto the developing sleeve against the fluctuation of (gap).

This is because a magnetic carrier having a low magnetic permeability is inserted between the magnetic pole (corresponding to the magnetic pole S2 in FIG. 1) at the developer layer thickness regulating position of the magnet and the magnetic plate, so that the magnetic field near the magnetic plate is close to the magnetic plate. This is because the force with which the carrier is attracted to the magnetic plate weakens, and the effect on the application of the magnetic plate disappears.

The magnetization of the magnetic carrier was set to 205 emu / cm ³ with a magnetic field of 1000 gauss, and the magnetic plate 28b was formed.
Permeability is 300, and volume per unit length in the longitudinal direction is 2.
The toner coat amount (M / S) with respect to the SB gap in the case of using 0 mm ³ (0.5 mm ^t × 4 mm ^h ) (this condition is B) is as shown by the black circles in FIG. become. The desired amount of coat amount M / S is 40 to 50 mg / c.
If m ² is set, as shown in FIG.
/ S is in the range of 40 to 50 mg / cm ² over the variation of the S-B gap of 0.1 mm or more, and according to the condition B, with respect to the slight deviation of the S-B gap. A stable amount of developer layer can be formed.

Toner coat amount (M / M) for the SB gap in the same manner as above (this condition is A) except that the magnetization of the magnetic carrier was 100 emu / cm ³ or less in a magnetic field of 1000 Gauss. S) is as shown by white circles in FIG. In this case, when the developer conveyed by the developing sleeve passes through the developer layer thickness regulating position, a force (a force in a direction of separating from the developing sleeve) is exerted on the magnetic plate side. As shown, there is a large variation in the developer coating amount with respect to the slight deviation of the S-B gap (the S-B gap that gives an M / S in the range of 40 to 50 mg / cm ² is 0.1 mm. Variation is not allowed).

Then, the magnetization of the magnetic carrier was fixed to 100 emu / cm ³ or less in a magnetic field of 1000 gauss, and the magnetic plate was used with different magnetic permeability and volume. Permeability μb (unknown number),
Volume Vb (mm) per unit length (1 mm) in the longitudinal direction
^As shown in FIG. 4, when the relation ( ³ )) satisfies μb · Vb ≧ 1050, the developer coating amount M / S in the range of 40 to 50 mg / cm ² is 0. 1m
It was found that the coating amount was stably obtained over m or more, and the fluctuation of the coating amount of the developer due to the slight deviation of the SB gap could be reduced. In the range where the above relational expression holds, the peak value of the magnetic field strength on the surface of the developing sleeve of the magnetic pole S2 at the developer regulating position is 500 to 2000 gauss.

On the other hand, if the magnetization intensity of the carrier at the peak value of the developing magnetic field is less than ³⁰ emu / cm ³ , the developer transportability on the developing sleeve is poor and the quality of the developed image is deteriorated. The lower limit is preferably ³⁰ emu / cm ³ or more because the developer is easily scattered.

Above, the peak value d of the developing magnetic field is 1000.
With respect to the evaluation of carrier magnetization in the case of Gauss, the result was the same even when the peak value d was other than 1000 Gauss.

That is, the peak value d of the developing magnetic field is 500, 8
FIG. 5 shows the relationship between the magnetization intensity σ _d (emu / cm ³ ) and the magnetic brush density α (lines / mm ² ) in the case of 00, 1500, and 2000 gauss. In any case, it is understood that the relationship of σ _d × α = 600 is satisfied.

Therefore, the density of the ears of the magnetic brush and the preventiveness of the roughness of the image obtained by developing the dot distribution latent image do not depend on the peak intensity d of the developing magnetic field, but the magnetization of carriers in the magnetic field of d Gauss. It can be seen that it depends on the strength σ _d of.

As described above, in the present invention, the magnetic carrier having the magnetization of 100 emu / cm ³ or less in the magnetic field of 1000 gauss is used, and the non-magnetic plate 28a and the magnetic plate 28b are used.
Of the magnetic blade 28b provided on the upstream side in the rotation direction of the developing sleeve 25 of the regulating blade 28 including
(Unnamed number) and the volume Vb (mm ³ ) per unit length (1 mm) in the longitudinal direction were defined so as to satisfy the relationship of μb · Vb ≧ 1050.

In this embodiment, the developing device shown in FIG.
An image was formed on each of the developing devices 1Y to 1K of the image forming apparatus. Negatively charged toner is used as the toner of the two-component developer, the dark portion potential on the photosensitive drum 1 is -700 V, the light portion potential is -200 V, and the developing sleeve 3 is subjected to an alternating voltage (frequency 200 Hz, Vpp 2000 V alternating voltage). A direct current voltage of −550 V was applied) to perform reversal development.

The outer diameter of the photosensitive drum 1 is 80 mm, the outer diameter of the developing sleeve 3 is 32 mm, the distance between the developing sleeve 3 and the regulating blade 4 is 500 μm, the distance between the developing sleeve 3 and the photosensitive drum 1 is 500 μm, and the photosensitive drum is The peripheral speed of 1
The peripheral speed of the developing sleeve 3 was set to 60 mm / sec and 280 mm / sec.

As a result, a stable amount of the developer layer could be formed on the developing sleeve with respect to the variation of the SB gap, and the initial highlight of the image could be reproduced smoothly.

Embodiment 2 Another embodiment of the present invention will be described with reference to FIG. This embodiment differs from the first embodiment in that the regulating blade 28 is inclined with respect to the developing sleeve 28. The other structure of the present embodiment is basically the same as that of the first embodiment, and in FIG. 6, the same members as those of the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

That is, as in the first embodiment, the magnetic carrier has a magnetization intensity of 10 in a magnetic field of 1000 gauss.
Use a blade of 0 emu / cm ³ or less and control blade 2
Reference numeral 8 denotes a non-magnetic material plate 28a and a ferromagnetic material magnetic plate 28b.
The regulating blade 28 provided with was used. Similarly, in this magnetic plate 28b, the magnetic permeability μb (unnamed number) and the volume Vb (mm ³ ) per unit length (1 mm) in the longitudinal direction satisfy the relationship of μb · Vb ≧ 1050.

In this embodiment, the regulating blade 28 rotates about the tip thereof in the direction opposite to the rotating direction of the developing sleeve 25, and the circumferential tangent line of the portion of the developing sleeve 25 facing the regulating blade 28. 0 to the opposite direction
It is arranged so as to be inclined at an angle of 30 °. The distance between the tip of the regulating blade 28 and the developing sleeve 25 is 4
It was set to 00 μm.

According to this embodiment, since the regulating blade 28 is arranged so as to be inclined with respect to the developing sleeve 25 as described above,
With respect to the variation of the SB gap between the developing sleeve 25 and the regulation blade 28, not only can the developer be stably applied on the developing sleeve 25, but also unnecessary pressure is not applied to the developer, It is possible to prevent deterioration of the resin toner as a constituent component.

Image formation was carried out in the same manner as in Example 1. In this example as well, a stable amount of the developer layer could be formed with respect to the variation of the SB gap, and the image was high in the initial stage. The light could be reproduced smoothly, and an image with little deterioration could be obtained stably for a long period of time.

Embodiment 3 Yet another embodiment of the present invention is shown in FIG. In this embodiment,
The arrangement of the regulation blade 28 is the same as that of the second embodiment, and the developer stirring member 33 that rotates in the direction opposite to the developing sleeve 25 is arranged above the regulation blade 28. The tip of the regulation blade 28 has the developing sleeve 2
A gap of 5 and 800 μm was provided.

According to this embodiment, the stirring member 33 is made of a non-magnetic member such as SUS316. In this example, the stirring member 33 includes eight blades 33a made of a non-magnetic member.
Is attached to the rotating shaft 33b at a uniform interval. As for the position of the stirring member 33, the rotary shaft 33b is positioned at the regulating blade 2
The position of 8 is offset from the center of the developing sleeve 25 by 10 ° downstream of the developing sleeve 25 in the developing sleeve rotation direction. The rotating direction of the agitating member 33 is opposite to the rotating direction of the developing sleeve 25, as described above, in order to prevent the developer left over by the restriction of the restriction blade 28 from staying in the vicinity of the restriction blade 28.

The circulation of the developer in the developing device will be described. As in the first embodiment, the developer 22 drawn up onto the developing sleeve 25 by the magnetic force of the magnetic pole S2 of the magnet 29 in the developing sleeve 25 is The regulation blade 2 is conveyed by the rotation of the developing sleeve 25 and is positioned at the developer layer thickness regulating position.
8 and regulates the developer 22 on the developing sleeve 25.
A thin layer of is formed. After that, it is carried to the developing unit 26 and stands up in the magnetic field of the developing magnetic pole S1 to form a magnetic brush,
It is used for developing a dot distribution electrostatic latent image on the photosensitive drum 3.

The developer not applied on the developing sleeve 25 due to the regulation is returned to the inside of the developing container 18 by the rotation of the agitating member 33 at the location of the regulating blade 28, and the agitating screws 23 and 24 cause a uniform toner concentration. After being agitated, it is magnetically pumped again by the magnetic pole S2.

In the present embodiment, the regulating blade 28 is arranged so as to be inclined with respect to the developing sleeve, and the stirring member 33 which rotates in the opposite direction to the developing sleeve 25 is arranged above the regulating blade 28. Therefore, the developing sleeve 25 and the regulating blade 28 are arranged. Of S
With respect to the variation of the −B gap, not only can the developer be stably applied onto the developing sleeve 25, but it is possible to more effectively prevent unnecessary pressure from being applied to the developer, and the deterioration of the resin toner in the developer can be prevented. Prevention can be further improved.

Also in this embodiment, when an image is formed, it is possible to form a stable amount of the developer layer on the developing sleeve with respect to the variation of the SB gap, and the image has a smooth initial highlight. It was possible to obtain an image that was reproducible and that had little deterioration for a long period of time.

[0087]

As described above, in the present invention, the regulating blade comprises the non-magnetic plate and the magnetic plate provided on the upstream side in the rotation direction of the developer carrier, and the magnetic permeability of the magnetic plate. μb (unnamed number) and the volume Vb (mm ³ ) per unit length (1 mm) in the longitudinal direction are defined so as to satisfy the relationship of μb · Vb ≧ 1050, so that the strength of magnetization under a magnetic field of 1000 Gauss Even with a magnetic carrier of 100 emu / cm ³ or less, a stable amount of developer can be applied onto the developing sleeve against variations in the gap between the developing sleeve and the regulating blade. Therefore, the dot-distributed electrostatic latent image formed on the image carrier can be developed into a developed image in which blurring is suppressed, and a high quality image can be obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a developing device of the present invention.

FIG. 2 is a diagram showing the relationship between the carrier magnetization of the two-component developer used in the developing device of FIG. 1 and the density of the magnetic brush ears.

3 is a diagram showing a toner coating amount on a developing sleeve with respect to a gap between a developing sleeve and a regulating blade installed in the developing device of FIG.

FIG. 4 is a diagram showing the relationship between the magnetic permeability of the magnetic plate of the regulation blade and the volume of the magnetic plate per unit length in the longitudinal direction.

FIG. 5 is a diagram showing a relationship between carrier magnetization and peak magnetic field strength of a developing magnetic pole of a developing sleeve magnet.

FIG. 6 is a configuration diagram showing another embodiment of the developing device of the invention.

FIG. 7 is a configuration diagram showing still another embodiment of the developing device of the present invention.

FIG. 8 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.

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

FIG. 10 is an explanatory diagram of a PWM circuit.

FIG. 11 is an explanatory diagram of a signal waveform of the PWM method.

FIG. 12 is an explanatory diagram showing the potential of a dot-shaped latent image.

FIG. 13 is an explanatory diagram showing a developed image of a dot-shaped latent image.

[Explanation of symbols]

 3 photosensitive drum 18 developing container 22 two-component developer 25 developing sleeve 27 bias power supply 28 regulating blade 28a non-magnetic plate 28b magnetic plate 29 magnet S1 developing magnetic pole

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Claims (7)

[Claims] 1. A developer carrier for carrying a two-component developer having a toner and a magnetic carrier, rotating the carrier, and transporting the developer to a developing unit facing the image carrier, and a non-rotatably arranged developer carrier. A magnet provided, and a developer layer thickness regulating blade arranged with a small gap with respect to the developer carrying member,
In the developing device in which a magnetic brush is formed on the developer on the developer carrier in the developing unit to develop the dot-distributed electrostatic latent image formed on the image carrier, the magnetic carrier is 1000 gauss. 100 emu / cm in magnetic field
^The regulation blade has a magnetization of ³ or less, and is composed of a non-magnetic plate and a magnetic plate provided upstream of the non-magnetic plate in the rotational direction of the developer carrier, and has a magnetic permeability of μb.
A developing device characterized by satisfying the relationship of μb · Vb ≧ 1050 when (unnamed number) and the volume per unit length (1 mm) in the longitudinal direction is Vb (mm ³ ). 2. The magnetic pole arranged at the position of the magnet regulating blade is 500 to 2 on the surface of the developer carrying member.
A magnetic field strength peak value of 000 Gauss.
Developing device. 3. The developing device according to claim 1, wherein the regulating blade is substantially perpendicular to the developer carrying member. 4. The angle of the regulation blade is 0 to 30 ° in the direction opposite to the rotation direction of the developer carrier with respect to the circumferential tangential direction of the portion of the developer carrier facing the regulation blade. The developing device according to claim 1, wherein the developing device is inclined so as to form 5. A developer stirring member that rotates in a direction opposite to a direction of the developer carrying member is provided above the regulation blade.
Developing device. 6. The electrostatic latent image of dot distribution on the image carrier is formed by modulating a light emission time of a light source per pixel in accordance with an image density value. Or the developing device of 5. 7. A developing bias voltage in which a DC voltage is superposed with an AC voltage is applied to the developer carrying member during development of the dot-distributed electrostatic latent image on the image carrying member.
4, 5 or 6 developing devices.