JPH10171253A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sufficiently remove toner remaining after a transfer and to form an image of high quality being highly accurate in the reproducibility of an image part by specifying the resistivity and magnetization of a magnetic carrier, so as to specify the relation among a developing sleeve, a photoreceptor drum and a magnetic brush. SOLUTION: The magnetic carrier has >=10<12> Ω resistivity at an electric field strength of 5×10<4> V/m and 30-200emu/cm<3> magnetization in a magnetic field of 1000G. Then, the developing sleeve 11, the photoreceptor drum 1 and the magnetic brush satisfy an equation of |VS1-Vdr|.Vdr.h.m.α>=7.0. In the equation, Vs1 denotes the circumferential speed (mm/second) of the developing sleeve, Vdr denotes the circumferential speed (mm/second) of the photoreceptor drum and (h) denotes the contact nip length (mm) of the magnetic brush with the photoreceptor drum. Further, (m) denotes the sectional area (mm<2> ) of the magnetic brush, αdenotes the density (number/mm<2> ) of the magnetic brush and |Vs1-Vdr| denotes the absolute value (mm/second) of the relative circumferential speed of the developing sleeve 11 with respect to the photoreceptor drum 1 in the part nearest to the drum 1, of the developing sleeve 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus which develops an electrostatic latent image formed on an image carrier with a magnetic brush of a two-component developer and visualizes it as a toner image, and more particularly, to the two-component development. The present invention relates to an image forming apparatus in which the means also serves as an image carrier cleaning means.

[0002]

2. Description of the Related Art Recently, digitalization of image forming apparatuses such as copying machines and printers has been progressing along with full-color images and systemization of the apparatuses.

For example, an image forming apparatus such as a laser beam printer for recording a desired image by scanning a photosensitive drum while turning on and off a laser beam to form a latent image, and developing and visualizing the latent image. However, it is becoming widely known. A typical application is binary recording of characters, figures, and the like. Since recording of characters, figures, and the like does not require a halftone, the printer structure can be simplified.

[0004] There is a printer that can form a halftone even with such a binary recording system. As such a printer, a printer employing a dither method, a density pattern method, or the like is well known. However, as is well known, high resolution cannot be obtained by the dither method, the density pattern method, or the like. Therefore, in recent years, a method of forming a halftone in each pixel without lowering the high recording density has been proposed. In this method, halftone is formed by modulating a laser beam with a pulse width (PWM) using an image signal. According to this method, a high-resolution and high-gradation image can be formed.

FIG. 4 shows an example of such a conventional image forming apparatus. In the present image forming apparatus, when a copy start signal is input, the photosensitive drum 1 is uniformly charged by the charger 3 so as to have a predetermined potential. On the other hand, with respect to the document G placed on the document table 10, a unit 9 in which a document illumination lamp, a short focus lens array, and a CCD sensor are integrated moves and scans while irradiating the document G with the illumination lamp. ,
The light reflected on the surface of the document G is imaged by the short focus lens array and is incident on the CCD sensor.

[0006] The CCD sensor comprises a light receiving section, a transfer section, and an output section. In the light receiving part of the CCD sensor,
The optical signal is converted into a charge signal, and is sequentially transferred to an output section in synchronization with a clock pulse in a transfer section. The output section converts the charge signal into a voltage signal, amplifies the voltage signal, lowers impedance, and outputs the signal. The analog signal obtained in this way is
After being converted into a digital signal by performing well-known image processing, it is sent to a printer unit.

[0007] In the printer section, as shown in FIG.
N, which is turned off, the light from the element 102 is scanned on the surface of the photosensitive drum 1 by the rotating polygon mirror 104 rotating at high speed, so that the electrostatic latent image corresponding to the image of the original G is formed on the surface 106 of the photosensitive drum 1. An image is formed.

FIG. 5 is a schematic configuration diagram of the laser scanning unit 100 of the image forming apparatus of FIG. When the laser scanning is performed by the laser scanning unit 100, first, the solid-state laser element 102 is caused to blink at a predetermined timing by the emission signal generator 101 based on the input image signal. The laser light emitted from the solid-state laser element 102 in this manner is converted into a substantially parallel light beam by the collimator lens system 103, and further the rotating polygon mirror 104 which rotates in the direction of arrow b
Scans in the direction of arrow c, and the fθ lens groups 105a, 105b, 105c form a spot-like image on the scanned surface 106 of the photosensitive drum 1. By such scanning of the laser beam, an exposure distribution for one scan of the image is formed on the scanned surface 106. Further, for each scan, the scanned surface 106 is scrolled by a predetermined amount in a direction perpendicular to the scanning direction. Then, an exposure distribution according to the image signal is obtained on the scanned surface 106. That is, an electrostatic latent image is formed.

When this electrostatic latent image is developed by the developing device 4, it is visualized as a toner image on the photosensitive drum 1.

Generally, there are roughly four types of developing methods.
One is a non-magnetic toner in which a non-magnetic toner of a one-component developer is coated on a developing sleeve with a blade or the like, and the non-magnetic toner is conveyed to the photosensitive drum by the developing sleeve and developed in a non-contact state with the photosensitive drum. The second is a one-component non-contact development method. The second one is a magnetic one-component contact development in which a magnetic toner of a one-component developer is coated on a developing sleeve by a magnetic force, and is similarly conveyed to a photosensitive drum and developed by contact. Is the law. The third and fourth uses a two-component developer in which a non-magnetic toner and a magnetic carrier are mixed, coats this on a developing sleeve by a magnetic force, and conveys it to a photosensitive drum by a developing sleeve. A two-component contact development method in which development is performed in a contact state, and a two-component non-contact development method in which development is performed in a non-contact state with respect to a photosensitive drum. From the aspects of high image quality and high stability, the two-component contact development method is often used.

FIG. 6 is a schematic structural view of the developing device 4. The developing device 4 is configured as a two-component magnetic brush developing device. The developing device 4 includes a developing container 16 containing a two-component developer 19, and a developing sleeve 11 is provided at an opening of the developing container 16 facing the photosensitive drum 1. The opposite portion rotates so as to move in the same direction, and transports the developer 19 to the developing portion facing the photosensitive drum 1. By setting the closest area between the developing sleeve 11 and the photosensitive drum 1 to a distance of about 500 μm, the developer 19 conveyed to the developing section is transferred to the photosensitive drum 1.
It is set so that development can be performed in a state of contact with. The peripheral speed ratio of the developing sleeve 11 to the photosensitive drum 1 is usually set to 1.5 to 2 times.

A magnet roller 1 for supporting a developer 19 on a developing sleeve 12 is provided in the developing sleeve 11.
2 are fixedly arranged. A magnetic blade 15 is provided above the developing sleeve 11.
Covers the developer 19 on the developing sleeve 11 by magnetically regulating the developer 19 carried on the developing sleeve 11. The lower half of the developing container 16 is provided with a partition wall 17.
The stirring chamber 13 is divided into a developing chamber R1 and a stirring chamber R2. Stirring screws 13 and 14 for stirring and transporting the developer 19 are installed in the developing chamber R1 and the stirring chamber R2.
Above the stirring chamber R2, a replenishing chamber R3 storing the replenishing toner 18 is provided.

As described above, the developing device 4 develops the electrostatic latent image on the photosensitive drum 1 to obtain a toner image.
The toner image on the photosensitive drum 1 is electrostatically transferred by a transfer charger 7 shown in FIG. Thereafter, the transfer material is electrostatically separated from the photosensitive drum 1 by the separation charger 8, and is conveyed to the fixing device 6, where the toner image is thermally fixed and output as a print image.

On the other hand, after transfer, the photosensitive drum 1 is cleaned with a cleaner 5 to remove residual contaminants such as transfer residual toner remaining on the surface thereof, is electrically initialized by a pre-exposure lamp 2, and then forms an image again. And the following process of charging by the charger 3 is performed.

The configuration of the above-described image forming apparatus is merely an example, and the charging unit 3 may be a charging roller other than a corona charging unit, or the transfer charging unit 7 may be a transfer roller. However, the image forming apparatus basically forms an image in the steps of charging, exposing, developing, transferring, fixing and cleaning, as described above.

In recent years, the size of image forming apparatuses has been reduced, but charging, exposure, development, transfer,
Just downsizing the equipment used in the fixing and cleaning processes has limited the downsizing of the apparatus.

Further, as described above, the transfer residual toner on the photosensitive drum 1 is removed by the cleaner 5 and collected as waste toner. However, such generation of waste toner is considered from the viewpoint of environmental protection. Preferably not. In view of this, a cleaner-less apparatus has been developed in which the cleaner 5 is eliminated and the developing device 4 performs cleaning simultaneously with the development of the photosensitive drum 1.

The cleaning at the same time as the development is to remove the transfer residual toner remaining on the photosensitive drum in the development area by applying a fogging bias Bback to the development sleeve at the time of developing the next image. It is a method of collecting in a container. According to this method, the transfer residual toner can be collected and used for development, so that waste toner is not generated, which is thicker in terms of environmental protection and saves space. It becomes possible.

[0019]

However, in the conventional image forming apparatus, when the cleaner 5 is removed and the image is formed while collecting the toner remaining after transfer by cleaning at the same time as the development, a portion of the transfer material having no image is removed. The positive ghost of the previous image occurred in the period of the photosensitive drum. This positive ghost occurs because the transfer residual toner of the previous image could not be removed and collected in the development area, and the transfer residual toner that could not be removed was transferred to the originally white background of the transfer material. It is a phenomenon that did.

Therefore, in an image forming apparatus employing cleaning at the same time as development, in order to prevent the occurrence of a positive ghost, the toner remaining after transfer during development is sufficiently removed and recovered by applying a fogging bias. Needed. Further, in the image portion, it was necessary to be able to perform high-definition development simultaneously with the recovery of the transfer residual toner. However, an image forming apparatus having such characteristics has not been proposed so far.

It is an object of the present invention to contact a magnetic brush of a two-component developer on a developer carrier of a developing means with an image carrier and to apply a developing bias including a fogging bias to the developer carrier. Thereby, at the same time as developing the electrostatic latent image on the image carrier, removing the transfer residual toner on the image carrier,
When collecting, it is possible to sufficiently remove the transfer residual toner, develop the latent image with high definition, and obtain a high-quality image with no positive ghost in the white background and high reproducibility of the image part. To provide an improved image forming apparatus.

[0022]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention applies a developing bias including a fogging bias to a developer carrier by bringing a two-component developer magnetic brush carried on a developer carrier of a developing unit into contact with an image carrier. Thereby, while developing the electrostatic latent image on the image carrier and visualizing it as a toner image, removing the transfer residual toner remaining on the image carrier, and recovering the image forming apparatus,
(I) the magnetic carrier has a specific resistance of at least 10 ¹² Ωcm at an electric field intensity of 5 × 10 ⁴ V / m, has a magnetization of ³⁰ to 200 emu / cm ³ in a magnetic field of 1000 gauss, and (ii)
The developing sleeve, the photosensitive drum, and the magnetic brush satisfy the following expression.

| Vs1−Vdr | · Vdr · h · m · α ≧ 7.0 where Vs1: peripheral speed of developing sleeve (mm / sec) Vdr: peripheral speed of photosensitive drum (mm / sec) h: magnetic brush and photosensitive Drum contact nip length (mm) m: magnetic brush cross-sectional area (mm ² ) α: magnetic brush density (pieces / mm ² ) | Vs1−Vdr |: development on the photosensitive drum at the closest point between the developing sleeve and the photosensitive drum Absolute value of sleeve relative peripheral speed (mm / sec)

According to the present invention, preferably, the developer carrying member of the developing means moves in a direction opposite to the image carrying member at a portion facing the image carrying member, and a peripheral speed ratio with the image carrying member is 1.5. More than double. Further, the developer carrier of the developing means can move in the same direction as the image carrier at a portion facing the image carrier, and the peripheral speed ratio with the image carrier is 3.5 times or more. The fogging bias is 150V. The developing bias is obtained by superimposing an AC voltage on a DC voltage. The non-magnetic toner is produced by a polymerization method.

[0025]

Embodiments of the present invention will be described below in detail with reference to the drawings.

Embodiment 1 FIG. 1 is a sectional view showing a schematic configuration of an embodiment of an image forming apparatus according to the present invention, and shows a color image forming apparatus. In the present invention, since the transfer residual toner is cleaned simultaneously with the development of the latent image on the photosensitive drum 1 by the two-component developing device 4, unlike the conventional image forming apparatus shown in FIG. Not. Other mechanical configurations of this image forming apparatus are basically the same as those of the image forming apparatus of FIG. 4, and the same reference numerals in FIG. 1 as those shown in FIG. 4 indicate the same members.

In this image forming apparatus, in order to form an image, first, an original G is set on an original platen 10 with the surface to be copied facing downward. Next, copying is started by pressing the copy button. The unit 9 in which the document illumination lamp, the short focus lens array, and the CCD sensor are integrated is moved with respect to the document G, scanned while illuminating the document G with the illumination lamp, and reflected on the surface of the document G. Light is imaged by the short focus lens array and is incident on the CCD sensor.

The CCD sensor comprises a light receiving section, a transfer section, and an output section. In the light receiving section, an optical signal is converted into a charge signal, and the transfer section sequentially transfers the charge signal to an output section in synchronization with a clock pulse. The output unit converts the charge signal into a voltage signal, and amplifies the signal to reduce the impedance, and outputs the signal. The analog signal thus obtained is subjected to well-known image processing, converted into a digital signal, and sent to a printer unit.

In the printer section, an electrostatic latent image is formed on the surface of the photosensitive drum 1 as follows. The photosensitive drum 1 is
It is rotated around the central axis at a predetermined peripheral speed, and is uniformly charged to a positive or negative polarity by the charger 3 during the rotation process. In response to the above image signal, the light emission of the solid-state laser element 102 is turned on and off as shown in FIG.
Rotating polygon mirror 1 that rotates light from the element 102 at high speed
By scanning the photosensitive drum 1 on the surface of the photosensitive drum 1 that has been uniformly charged, an electrostatic latent image corresponding to the image of the document G is formed on the surface of the photosensitive drum 1.

The electrostatic latent image formed on the photosensitive drum 1 is
Developed by the developing device 4 and visualized as a toner image,
The toner image is electrostatically transferred by a transfer charger 7 onto a transfer material (not shown). Thereafter, the transfer material is supplied to the separation charger 8
The toner image is sent to the fixing device 6 where the toner image is thermally fixed and output as a print image.

According to the present invention, the transfer residual toner remaining on the surface of the photosensitive drum 1 due to the transfer is removed and collected by the developing device 4 at the time of developing the next image.

The configuration of the above-described image forming apparatus is merely an example. The charging unit 3 may be a charging roller other than a corona charging unit, or the transfer charging unit 7 may be a transfer roller. However, the image forming apparatus basically forms an image in the steps of charging, exposing, developing, transferring, fixing and cleaning, as described above.

FIG. 2 is a configuration diagram showing the developing device 4 described above. The developing device 4 includes a developing container 16 containing a two-component developer 19 composed of a non-magnetic toner and a magnetic carrier.
At the opening of the developing container 16 facing the photosensitive drum 1,
A developing sleeve 11 made of a non-magnetic material is rotatably incorporated. The developing sleeve 11 carries the developer 19 and rotates in a direction (counter direction) in which a portion facing the photosensitive drum 1 moves in the opposite direction (counter direction), and conveys the developer 19 to a developing portion facing the photosensitive drum 1. The closest region between the developing sleeve 11 and the photosensitive drum 1 was a gap of about 500 μm.

Below the developing sleeve 11, a magnetic blade 15 is fixedly mounted on a developing container 16, and the distance between the magnetic blade 15 and the developing sleeve 11 is 500 μm.
And Magnetic blade 15 is aluminum, SUS31
6 and the like, and cooperates with the magnetic pole S3 of the magnet roller 12 to magnetically regulate the layer thickness of the developer 19 carried on the developing sleeve 11 so that a predetermined layer thickness is formed on the developing sleeve 11. Coat the developer layer.

In the developing sleeve 11, a magnet roller 12 as a magnetic field generating means is fixedly arranged. The magnet roller 12 has a developing magnetic pole N1, a magnetic pole S3 located downstream of the developing magnetic pole N1, and magnetic poles N2, S2, and S1 for carrying and transporting the developer 19. The developing magnetic pole N1 is
A magnetic field is formed in the vicinity of a developing section where the developing sleeve 11 and the photosensitive drum 1 are opposed to each other, and the magnetic brush is applied to the developer 19 carried to the developing section. Is formed.

The developer 19 formed on the magnetic brush contacts the photosensitive drum 1 to develop an electrostatic latent image on the photosensitive drum 1. At the time of development, an oscillating bias in which a DC voltage is superimposed on an AC voltage is applied between the developing sleeve 11 and the photosensitive drum 1 by the power supply 21. The dark portion potential (non-exposed portion potential) and bright portion potential (exposed portion potential) of the latent image formed on the photosensitive drum 1 are located between the maximum potential and the minimum potential of the vibration bias voltage. As a result, an alternating electric field whose direction alternates in the developing unit is formed, and the toner and the carrier of the developer 19 formed on the magnetic brush vibrate violently, and the toner shakes off the electrostatic restraining force of the developing sleeve 11 and the carrier. Then, the latent image adheres to the latent image on the photosensitive drum 1 in an amount corresponding to the latent image potential, and the latent image is developed.

The difference between the maximum value and the minimum value of the oscillation bias voltage,
That is, the peak-to-peak voltage (peak-to-peak voltage) is preferably 1 to 5 kV, and the frequency is preferably 1 to 15 kHz. As the waveform of the oscillation bias voltage, a rectangular wave, a sine wave, a triangular wave, or the like can be used. The DC voltage component of the oscillating bias voltage is between the dark portion potential and the bright portion potential of the latent image, and the absolute value of the dark portion potential is closer to the dark portion potential than to the minimum bright portion potential. This is preferable for preventing fog toner from adhering to the area.

The lower half of the developing container 16 is partitioned by a partition wall 17 into a developing chamber (first chamber) R1 and a stirring chamber (second chamber) R2. 19
Screws 13 and 14 for stirring and transporting are respectively provided. Above the stirring chamber R2, a replenishing chamber R3 storing the replenishing toner 18 is provided. Supply room R
3, an amount of toner 18 corresponding to the toner consumed in the development is supplied through the supply port 20 at the lower part of the supply chamber R3 to the stirring chamber R2.
Drops in and is replenished.

The stirring screw 13 installed in the developing chamber R1 is rotated in the direction of the arrow in the figure, and conveys in one direction along the longitudinal direction of the developing sleeve 11 while stirring the developer 19 in the developing chamber R1. I do. The stirring screw 14 installed in the stirring chamber R2 is rotated in a direction opposite to the direction of the stirring screw 13 while stirring the developer 19 in the stirring chamber R2.
It is transported in one direction opposite to the above. This stirring screw 1
The developer whose toner has been consumed by the development from the developing chamber R1 is transported to the stirring chamber R2 through the opening at the end of the partition wall 17, and the developer whose concentration has been recovered from the stirring chamber R2 is transferred from the developing chamber R1. Is transferred to the developing chamber R1 through the opening at the other end of the partition wall 17. The toner 18 supplied from the supply chamber R3 into the stirring chamber R2 is mixed with the developer by the stirring of the stirring screw 14, and the concentration of the developer is restored.

The magnetic carrier and the non-magnetic toner of the two-component developer 19 used in the present invention will be described.

The magnetic carrier used in the present invention is a small particle size carrier having a number average particle size of 100 μm or less. In general, the particle size of the magnetic carrier is required to be as small as possible from the demand of high image quality. In the present invention, from this viewpoint, the particle size of the magnetic carrier is 100 μm in number average particle size, preferably 10 to 60 μm. did.

In the above description, the number average particle diameter of the magnetic carrier is represented by the maximum chord length in the vertical direction of the magnetic carrier particles. In the present invention, the carrier powder is spread to disperse the particles.
Photographed with a microscope at a magnification of 500 to 1000 times,
At least 300 carrier particle images in the obtained micrograph are randomly selected, and the major axis of the particles (maximum chord length in the vertical direction) is selected.
Was measured and arithmetically averaged.

In the present invention, a magnetic material-dispersed resin carrier in which a magnetic powder is dispersed in a binder resin and coated with a high resin is used. As a magnetic material,
Examples thereof include ferromagnetic metals such as iron, cobalt, and nickel, and alloys and compounds such as ferrite, magnetite, and hematite that include ferromagnetic metals such as iron, cobalt, and nickel.

The magnetization of the magnetic carrier used in the present invention is not less than ³⁰ emu / cm ³ in a magnetic field of 1000 Gauss.
00 emu / cm ³ or less. The magnetic properties of the magnetic carrier
Oscillating magnetic field type magnetic characteristics automatic recording device B manufactured by RIKEN ELECTRONICS CO., LTD.
It measured using HV-30.

The specific resistance of the magnetic carrier is 5 × 10 ⁴ V /
It is necessary to be 10 ¹² Ωcm or more at an electric field strength of m. If the specific resistance is lower than this, the carrier adhesion and the image quality deteriorate, and the object of the present invention such as high image quality and high definition of the image cannot be achieved. In particular, when a carrier having a small magnetization is used and the carrier is magnetically weakly constrained on the developing sleeve as in the present invention, if the specific resistance of the carrier is low, the carrier is charged when the developing bias is applied. Is easily injected and carrier adhesion occurs.

The specific resistance of the magnetic carrier was measured by filling a cell with carrier powder, arranging two electrodes so as to be in contact with the upper and lower portions of the carrier-filled layer, and applying a load to the upper electrode. And a current was measured at that time. The measurement conditions were as follows: the contact area between the carrier and the electrode was about 2.3 cm ² , the thickness of the carrier-filled layer was about 2 mm, and the load applied to the upper electrode was 180
g, and the applied voltage was 1000 V. In this case, since the carrier is a powder, a difference occurs in the filling rate of the cell, and the measured value of the specific resistance may change with this.
Be careful.

As the non-magnetic toner, a known toner in which a colorant, a charge controlling agent and the like are added to a binder resin can be used, and its volume average particle diameter is preferably 5 to 15 μm. In the present invention, the photosensitive drum is cleaned at the same time as the development, and for this, it is preferable to use a toner having a high transfer efficiency such as a polymerization toner.

Since the polymerized toner produced by the polymerization method has a nearly spherical shape, an external additive can be uniformly coated on the toner surface. Therefore, the releasability of the toner from the photosensitive drum, Very good transferability to transfer material.
For example, when the toner on the photosensitive drum is transferred to paper, the ratio of the amount of toner per unit area on paper / the amount of toner per unit area on the photosensitive drum, that is, the transfer efficiency, is compared between the polymerized toner and the pulverized toner. In this case, the efficiency is as high as about 90% for the pulverized toner and 97% for the polymerized toner.

According to such a polymerized toner, since the transfer residual toner is extremely small and has a high mold release property, the transfer residual toner is easily removed by cleaning during development without using a cleaner. , Can be collected and the occurrence of positive ghosts can be eliminated.

In this embodiment, a non-magnetic toner obtained by externally adding 1% by weight of titanium oxide having an average particle diameter of 20 nm to a polymerized toner having an average particle diameter of 6 μm produced by a suspension polymerization method is used. . A magnetic carrier having a saturation magnetization of 205 emu / cm ³ and an average particle diameter of 50 μm was used. The mixing ratio of the toner and the carrier in the two-component developer was 7:93 by weight.

The volume average particle diameter of the toner can be measured, for example, by the following measuring method. A call counter TA-II type (manufactured by Coulter) was used as a measuring device, and an interface (manufactured by Nikkaki) for outputting a number average distribution and a volume average distribution and a CX-i personal computer (manufactured by Canon) were connected and used.

A 1% NaCh aqueous solution was prepared using primary grade sodium chloride as an electrolyte. 100 of this electrolyte
A surfactant (preferably an alkylbenzene sulfonate) was added in an amount of 0.1 to 5 mh as a dispersant in an amount of about 150 mh, and 0.5 to 50 mg of a toner as a measurement sample was further added.

The electrolytic solution in which the sample was suspended was subjected to dispersion treatment with an ultrasonic disperser for about 1 to 3 minutes.
Using a 100 μm aperture by type II, 2-40
The particle size distribution of the μm particles was measured, and the volume distribution of the toner was determined. This volume distribution gives the volume average particle size of the toner.

The triboelectric charge of the polymerized toner used here was
It was about 2.0 × 10 ^-2 C / kg. The measurement of the triboelectric charge amount of the toner was performed as follows.

FIG. 3 shows an apparatus for measuring the average charge amount of the toner. As shown in FIG. 3, the measuring device includes a metal measuring container 42 having a 500-mesh conductive screen 43 at the bottom. A two-component developer whose toner charge amount is to be measured is placed in a polyethylene bottle having a capacity of 50 to 100 mh, shaken by hand for about 10 to 40 seconds, and then about 0.5 to 1.5 g of the developer is added. Is placed in the measuring container 42 and a metal lid 44 is placed thereon. At this time, the entire measurement container 42 is weighed, and this is defined as W1 (kg).
Next, the measuring container 42 is set on the suction device 41 of the apparatus (at least the portion in contact with the measuring container 42 is an insulator), suction is performed through the suction port 47, and the air flow control valve 46 is adjusted to adjust the vacuum gauge 45. Is 250 mmAq. In this state, suction is sufficiently performed, preferably for 2 minutes, to remove toner (resin) by suction. At this time, the measuring container 4
Capacitor (capacitance C (μF)) 4 between 2 and ground
The potential of the electrometer 49 connected in parallel with 8 is read, and the reading is set to V (volt). In addition, the entire measurement container 42 after suction is weighed, and this is defined as W2 (kg). The average charge amount of the toner at this time is calculated as in the following equation.

Average charge amount of toner [C / kg] = C · V
× 10 ^-3 / (W1-W2)

In this embodiment, the image forming apparatus shown in FIG. 1 is used to develop the electrostatic latent image on the photosensitive drum 1 by the developing device 4 shown in FIG. While forming an image, the occurrence state of positive ghost and the image quality at that time were examined. The image quality was evaluated by highlight streaks.

The magnetic carrier of the two-component developer 19 of the developing device 4 has a magnetization of 300 emu /
cm ³ (σ1000 = 300 emu / cm ³ ) was used. The true density of the carrier of the developer 19 was 51 g / cm ³ , and the true density of the toner was 1.1 g / cm ³ . The triboelectric charge of the toner was 2.0 × 10 ⁻² C / kg. The developer 19 is applied on the developing sleeve 11 of the developing device 4 at a rate of 32 mg / unit area.
It was coated with cm ^2.

The diameter of the photosensitive drum 1 is 30 mm, the diameter of the developing sleeve 11 is 16 mm, and the closest distance (developing gap gap) between the photosensitive drum 1 and the developing sleeve 11 is 4 mm.
It was set to 00 mm. The rotation of the developing sleeve 11 was performed not only in the counter direction moving in the opposite direction at the opposing portion to the photosensitive drum 1 but also in the forward direction moving in the same direction at the opposing portion shown in the conventional example. Also, the peripheral speed (Vdr) of the photosensitive drum 1 and the peripheral speed (Vs1) of the developing sleeve 11 were variously changed.

The developing bias applied to the developing sleeve 11 has a frequency of 2 kHz and a peak-to-peak voltage of 2 kV.
And the fogging bias Vback is 15
It was fixed at 0V. If the value of Vback is too small, fog on a white background cannot be removed, and if it is too large, carrier adhesion occurs. Therefore, 150 V was selected as an appropriate value of Vback.

The peripheral speed (Vdr) of the photosensitive drum is 50 mm /
Second, 100 mm / sec, 200 mm / sec
The results are shown in Tables 1, 2, and 3, respectively. In Tables 1-3,
The symbol Y indicates a case where a positive ghost was visually observed, and the positive ghost which occurred extremely thinly was indicated by (Y). N is a case where a positive ghost could not be visually observed.

[0062]

[Table 1]

[0063]

[Table 2]

[0064]

[Table 3]

As shown in Tables 1 to 3, when the developing sleeve is of the developing type in which the developing sleeve is rotated in the forward direction (VS1 is indicated by +), the peripheral speed ratio Vs1 / Vdr (not shown) of the developing sleeve to the photosensitive drum is 3 At least 0.5 times, there was no occurrence of positive ghost and visual observation was not possible. On the other hand, in the case of the developing type in which the developing sleeve is rotated in the counter direction (VS1 is indicated by-), the peripheral speed ratio between the developing sleeve and the photosensitive drum is 1.5 times or more, and no positive ghost is generated, so that visual observation is not possible. .

As a result of several experiments, the removal and recovery of the transfer residual toner during the development were as follows: the surface properties of the photosensitive drum 1, the various physical properties of the toner (including the triboelectric charge), the fogging bias Vback, and the developing bias. It was found that, under certain conditions, the ratio was in proportion to the area of the magnetic brush contacting per unit area on the photosensitive drum per unit time.

The area of the magnetic brush contacting per unit area on the photosensitive drum per unit time will be described.

The peripheral speed of the developing sleeve is set to Vs1 (mm / sec)
(Accordingly, the peripheral speed of the magnetic brush on the developing sleeve is also Vs1
(Mm / sec)) and the peripheral speed of the photosensitive drum is Vdr (mm / sec).
Seconds). The absolute value of the relative peripheral speed of the developing sleeve with respect to the photosensitive drum at the closest portion between the developing sleeve and the photosensitive drum is | Vs1−Vdr |.

In the contact nip (NIP), which is the contact area between the magnetic brush and the photosensitive drum, the moving speed of the magnetic brush is always constant with respect to the contact plane of the photosensitive drum, and the magnetic brush contacts the photosensitive drum with the same thickness. Then it approximates.

The time t during which the transfer residual toner adhered per unit length in the longitudinal direction of the photosensitive drum passes through the contact nip.
(Seconds) is the contact nip length in the circumferential direction of the photosensitive drum h (m
m) is h / Vdr. The area of the magnetic brush contacting per unit area on the photosensitive drum per unit time is as follows: When the density of the magnetic brush on the developing sleeve is α (lines / mm ² ) and the cross-sectional area of the magnetic brush is m (mm ² / lines), m ・ α ・ ｜
Vs1−Vdr | (mm / sec). Therefore, the transfer residual toner adhered per unit length on the photosensitive drum is
The contact area S of the contacting magnetic brush is expressed as: S = (h / Vdr) · m · α · | Vs1−Vdr | (1)

The results in Tables 1 to 3 show that the contact nip length h is 7
mm, the magnetic brush cross-sectional area m is 0.125 mm ² , and the magnetic brush density α is 4 brushes / mm ² .

In this example, the contact nip length h was measured as follows. A double-sided tape was attached to the surface of the photosensitive drum, and a developing sleeve was opposed to the photosensitive drum with a gap from the double-sided tape being 400 μm, the same as the gap between the developing gaps. Then, while the photosensitive drum is stationary, only the developing sleeve is rotated in a state where no developing bias is applied, and the length of the developer attached to the double-sided tape on the surface of the photosensitive drum in the circumferential direction of the photosensitive drum is used to contact the photosensitive drum. The upper circumferential length was measured to obtain a contact nip length h.

The magnetic brush cross-sectional area and magnetic brush density were determined by compressing the magnetic brush raised on the developing sleeve at a gap of 400 μm between the developing sleeve and the photosensitive drum, and setting the 3 × 10 mm The area of No. ² was observed and measured with an optical microscope. The measurement was performed several times, and the average value was adopted. The method for measuring the contact nip length h, the cross-sectional area of the magnetic brush, and the density is not limited to the above.

From Tables 1 to 3, when the developing system is rotated in the forward direction of the developing sleeve, in order to collect 100% of the untransferred toner on the photosensitive drum by the developing unit, the rotation of the developing sleeve is performed by rotating the photosensitive drum about Although it is necessary to perform the rotation at 3.5 times the peripheral speed, there is a problem that the developer is easily deteriorated and the toner is scattered.

On the other hand, if the developing method is such that the developing sleeve is rotated in the counter direction, the peripheral speed difference between the magnetic brush and the photosensitive drum can be increased without rotating the developing sleeve at a high speed. A cleanerless / development simultaneous recovery system that simultaneously removes and recovers transfer residual toner is advantageous in terms of developer deterioration and toner scattering.

In the developing method of the counter rotation, depending on the image ratio of the image to be formed, the T / C ratio of the remaining development on the developing sleeve decreases when the transfer residual toner reaches the development area. Since the toner encounters the developer, there is an advantage that it is easy to remove and collect the transfer residual toner even in terms of charge.

As described above, according to the present invention, the positive ghost can be reduced to a level without any problem.
Regarding the image quality, if the relative speed between the photosensitive drum and the magnetic brush is too high, the toner image is scraped off by the magnetic brush, and the smoothness of the image is deteriorated, especially in a low density portion, thereby deteriorating the image quality, and the toner amount is reduced. In a highlight / halftone density region where the density is low, scratch-like stripes occur.

In Tables 1 to 3, the symbols in the image properties column are as follows: A: no streaks B: no streaks C: streaks are noticeable.

When the relative speed between the photosensitive drum and the magnetic brush is 30
When the speed is 0 mm / sec or more, uneven streaks are noticeable. As can be seen from Tables 1 to 3, this is disadvantageous in the cleanerless / development simultaneous recovery system of the present invention particularly when the peripheral speed of the photosensitive drum is increased.

As a result of the examination, the scraping of the toner image by the magnetic brush was carried out by the contact pressure that the magnetic brush formed by the developer on the developing sleeve in the magnetic field of the developing section presses the photosensitive drum,
It has been found that the magnetic brush greatly depends on the relative speed between the photosensitive drum and the developing sleeve, and particularly when the magnetic brush is located on the downstream side of the developing area. Therefore, in the development of the developing sleeve counter-rotation type in which the relative speed is large, scraping of the toner image is particularly likely to occur.

The contact pressure by the magnetic brush is determined when the packing density of the developer in the developing area is made the same (that is, the developer coated on the developing sleeve with the same volume in the same developing gap (SD gap)). ), The state of the bristles of the magnetic brush, that is, the magnetization intensity per volume of the magnetic carrier when the peak magnetic field intensity (d) of the developing magnetic pole is applied (d is the peak magnetic field) Suffix which indicates the strength of
It was found that the contact pressure decreased as d was reduced.

This is because when the carrier particles form ears in the developing magnetic field, each of the ears in the developing magnetic field behaves like a bar magnet, but when the magnetization intensity of the carrier decreases, It is considered that since the force acting between the carrier particles is reduced, the spikes are apt to collapse, and as a result, the brush pressure is reduced.

Therefore, in the present embodiment, in view of the necessity of increasing the area of the magnetic brush that contacts a unit area on the photosensitive drum with respect to the recoverability of the transfer residual toner,
The pressure for pressing the photosensitive drum was reduced by increasing the relative speed between the photosensitive drum and the magnetic brush and decreasing the intensity of magnetization of the magnetic carrier. Specifically, the intensity of the carrier magnetization is set to 30 emu /
cm ³ or more and 200 emu / cm ³ or less (σ1000 = ^{30 to} 200
emu / cm ³ ), so that 100
% Recovery and image quality were both compatible. When the magnetization intensity of the carrier is less than ³⁰ emu / cm ³ , the developer is poorly transported on the developing sleeve, and the image quality of the developed image is deteriorated or the developer is easily scattered.
Cannot be less than ³ . The results are shown in Tables 4 to 6.

[0084]

[Table 4]

[0085]

[Table 5]

[0086]

[Table 6]

In Tables 4 to 6, image formation was performed by changing the peripheral speeds of the developing sleeve and the photosensitive drum variously in the same manner as in Tables 1 to 3, using carriers having a magnetization of 150 emu / cm ³ in a magnetic field of 1000 Gauss. Then, the occurrence state of positive ghosts and the image quality (highlighted streaks) were examined. Here, since the magnetization of the carrier was made smaller than in Tables 1 to 3, the spike length of the magnetic brush became shorter, the cross-sectional area per magnetic brush became smaller, and the density of the magnetic brush became denser. The contact nip length is 7 mm, the magnetic brush cross-sectional area m is 0.05 mm ² , and the magnetic brush density α is 10
Book / mm ² .

In Tables 4 to 6, similarly to Tables 1 to 3, when the developing sleeve is of the forward rotation developing type, the peripheral speed ratio VS1 / Vdr (not shown) of the developing sleeve to the photosensitive drum is 3 At least 0.5 times, there was no occurrence of positive ghost and visual observation was not possible. In the case of the developing system in which the developing sleeve was rotated in the counter direction, the peripheral speed ratio between the developing sleeve and the photosensitive drum was 1.5 times or more, and there was no occurrence of positive ghost and visual observation was impossible.
Streaks did not occur even when the relative speed between the developing sleeve (magnetic brush) and the photosensitive drum was 800 mm / sec.

As described above, according to the present invention, the latent image formed on the photosensitive drum is developed by the magnetic brush of the two-component developer carried on the developing sleeve of the developing device,
An image is formed while removing and collecting the transfer residual toner on the photosensitive drum.

At this time, (i) the specific resistance is 10 ¹² Ω at an electric field intensity of 5 × 10 ⁴ V / m.
cm or more and 30 to 20 in a magnetic field of 1000 Gauss.
A magnetic carrier having a magnetization of 0 emu / cm ³ is used. (Ii) The peripheral speed of the developing sleeve and the photosensitive drum, the contact nip length of the magnetic brush, and the like satisfy the following expression (2).

| Vs1−Vdr | · Vdr · hm · α ≧ 7 (2) where Vs1: peripheral speed of developing sleeve (mm / sec) Vdr: peripheral speed of photosensitive drum (mm / sec) h: Contact nip length between magnetic brush and photosensitive drum (mm) m: Magnetic brush cross-sectional area (mm ² ) α: Magnetic brush density (pieces / mm ² ) | Vs1−Vdr |: Nearest point between developing sleeve and photosensitive drum Value of the relative peripheral speed of the developing sleeve to the photosensitive drum in the section (mm / sec)

In the present invention, by adopting the above-mentioned constitutions (i) and (ii), 100% of the transfer residual toner can be recovered, and a high-quality image without streaks can be obtained.

By setting the rotation direction of the developing sleeve to the counter direction in which the developing sleeve moves in the opposite direction at the portion facing the photosensitive drum, the above equation (2) can be obtained with a lower peripheral speed ratio to the photosensitive drum than in the forward direction. Can be satisfied. This leads to the provision of a highly stable developing device having a long life and a small amount of scattered developer.

Embodiment 2 In this embodiment, the developing sleeve 11 and the photosensitive drum 1
Is 300 μm, and the contact nip length h is 9.
This shows a case where the distance is 5 mm. Set the photosensitive drum speed to 100
mm / sec, and the conditions other than the contact nip length h were the same as those in Table 5 of Example 1.

Table 7 shows the evaluation results of the positive ghost in this example.

[0096]

[Table 7]

As can be seen from Table 7, in order to collect 100% of the transfer residual toner on the photosensitive drum 1 simultaneously with the development of the latent image, in the case of the forward rotation type development of the developing sleeve, the developing sleeve is At least about 3.0 times the speed of the photosensitive drum is required. On the other hand, in the case of development in the counter-rotation type of the developing sleeve, the speed may be about 1.0 times.

As compared with the first embodiment, by increasing the contact nip length, 100% of the transfer residual toner can be recovered at a lower peripheral speed ratio. Also in this case, no streaks were generated by using a magnetic carrier having a magnetization of 150 emu / cm ³ in a magnetic field of 100 Gauss.

That is, also in the present embodiment, the latent image on the photosensitive drum is developed by the magnetic brush of the two-component developer carried on the developing sleeve of the developing device, and at the same time, the toner remaining after transfer on the photosensitive drum is removed. When forming an image while collecting, (i) the magnetic carrier has a specific resistance of 10 ¹² Ωcm or more at an electric field strength of 5 × 10 ⁴ V / m and a magnetic carrier of 30 to 200 emu / Have a magnetization of cm ³ . (Ii) The peripheral speed of the developing sleeve and the photosensitive drum, the contact nip length of the magnetic brush, and the like are expressed by the following equation (2): | Vs1−Vdr | · Vdr · h · m · α ≧ 7.0 (2) where, Vs1: peripheral speed of developing sleeve (mm / sec) Vdr: peripheral speed of photosensitive drum (mm / sec) h: contact nip length between magnetic brush and photosensitive drum (mm) m: magnetic brush cross-sectional area (mm) ² ) α: Magnetic brush density (number / mm ² ) | Vs1−Vdr |: Satisfies the absolute value (mm / sec) of the relative peripheral speed of the developing sleeve with respect to the photosensitive drum at the closest point between the developing sleeve and the photosensitive drum. . By the above two methods, 100% of the transfer residual toner can be recovered, and a good image can be obtained.

Further, by setting the rotation direction of the developing sleeve to the counter direction in which the developing sleeve moves in the opposite direction at the portion facing the photosensitive drum, the above equation (2) can be obtained with a lower peripheral speed ratio to the photosensitive drum than in the forward direction. Therefore, it is possible to provide a highly stable developing device having a long life and a small amount of scattered developer.

[0101]

As described above, according to the present invention,
The magnetic brush of the two-component developer carried on the developer carrier of the developing means is brought into contact with the image carrier, and a developing bias including a fogging bias is applied to the developer carrier. When the electrostatic latent image is developed and visualized as a toner image, the specific resistance is 5 × 10 ⁴ V / when removing and collecting the transfer residual toner remaining on the image carrier.
Using a magnetic carrier having a magnetic field of 10 ¹² Ωcm or more at an electric field strength of m and a magnetization of ³⁰ to 200 emu / cm ³ in a magnetic field of 1000 gauss, the peripheral speed of the developing sleeve and the photosensitive drum, and the contact nip length of the magnetic brush | Vs1−Vdr | · Vdr · hm · α ≧ 7.0, where Vs1: peripheral speed of developing sleeve (mm / sec) Vdr: peripheral speed of photosensitive drum (mm / sec) h: magnetic brush and photosensitive drum Contact nip length (mm) m: magnetic brush cross-sectional area (mm ² ) α: magnetic brush density (pieces / mm ² ) | Vs1−Vdr |: developing sleeve for the photosensitive drum at the closest point between the developing sleeve and the photosensitive drum The absolute value (mm / sec) of the relative peripheral speed of the toner is satisfied, so that 100% of the untransferred toner can be recovered at the same time as the development, and high-definition development can be realized. What May reproducibility of an image portion also obtain a high-resolution high-quality image.

Further, by setting the rotation direction of the developing sleeve to the counter direction in which the developing sleeve moves in the opposite direction at the portion facing the photosensitive drum, the above expression can be satisfied at a lower peripheral speed ratio to the photosensitive drum than in the forward direction. Therefore, it is possible to provide a highly stable developing device having a long life and a small amount of scattered developer.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a schematic configuration of an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a cross-sectional view illustrating a schematic configuration of a developing device installed in the image forming apparatus of FIG.

FIG. 3 is a perspective view showing an apparatus used for measuring an average charge amount of a non-magnetic toner in a two-component developer in the present invention.

FIG. 4 is a cross-sectional view illustrating a schematic configuration of a conventional image forming apparatus.

5 is a schematic diagram illustrating a laser operation unit installed in the image forming apparatus of FIG.

6 is a cross-sectional view illustrating a schematic configuration of a developing device installed in the image forming apparatus of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum 3 Primary charger 4 Developing device 11 Developing sleeve 12 Magnet roller 19 Two-component developer

Claims (8)

[Claims] 1. A developing device comprising:
The electrostatic latent image on the image carrier is developed and visualized as a toner image by contacting the magnetic brush of the component developer with the image carrier and applying a developing bias including a fogging bias to the developer carrier. And (i) the magnetic carrier has a specific resistance of at least 10 ¹² Ωcm at an electric field intensity of 5 × 10 ⁴ V / m. And 1000
Having a magnetization of ³⁰ to 200 emu / cm ³ in a Gaussian magnetic field,
(Ii) The developing sleeve, the photosensitive drum and the magnetic brush satisfy the following expression. | Vs1−Vdr | · Vdr · hm · α ≧ 7.0 where Vs1: peripheral speed of developing sleeve (mm / sec) Vdr: peripheral speed of photosensitive drum (mm / sec) h: contact between magnetic brush and photosensitive drum Nip length (mm) m: Magnetic brush cross-sectional area (mm ² ) α: Magnetic brush density (pieces / mm ² ) | Vs1−Vdr | Absolute value of peripheral speed (mm / sec) 2. The image forming apparatus according to claim 1, wherein the developer carrier of the developing unit moves in a direction opposite to the image carrier at a portion facing the image carrier. 3. The image forming apparatus according to claim 2, wherein a peripheral speed ratio of the developer carrier to the image carrier is 1.5 times or more. 4. The image forming apparatus according to claim 1, wherein the developer carrying member of the developing unit moves in the same direction as the portion facing the image carrying member. 5. The image forming apparatus according to claim 4, wherein a peripheral speed ratio of said developer carrier to said image carrier is 3.5 times or more. 6. The image forming apparatus according to claim 1, wherein the fog removing bias is 150V. 7. The image forming apparatus according to claim 1, wherein the developing bias is obtained by superimposing an AC voltage on a DC voltage. 8. The image forming apparatus according to claim 1, wherein said non-magnetic toner is produced by a polymerization method.