JP2005221780A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device which is capable of suppressing brush mark uneveness and attaining high speed while maintaining high picture quality as it is, and to provide an image forming apparatus provided with the developing device. <P>SOLUTION: The developing device 400 comprises a plurality of developer carriers where a developer containing magnetic carriers having the amount of magnetization of ≥3.0×10<SP>4</SP>A/m and ≤2.5×10<SP>5</SP>A/m in an external magnetic field of 100 mT is used. Therein, in a magnetic field generating means 12b incorporated in a downstream developer carrier 11b, at least one conveyance pole is arranged between a development pole and a repulsive magnetic pole on the upstream side and the down stream side in the developer carrier rotation direction of the development pole, the magnetic pole distance between the development pole and the downstream conveyance pole is set to be smaller than the magnetic pole distance between the development pole and the upstream conveyance pole and the development pole is arranged in the angle region within ±5° as an angle around the rotation center of the developer carrier 11b and with respect to the most proximity part 50 with the developer carrier 11b and the image carrier 1. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a developing device and an image forming apparatus for developing an electrostatic latent image formed on an image carrier with a two-component developer.

  Conventionally, in an image forming apparatus, an electrostatic latent image formed on a uniformly charged surface of an image carrier by a method such as an electrophotographic method or an electrostatic recording method is developed in one step of the image forming process. A developing device for developing with an agent is installed.

  As developing means for carrying out this developing operation, generally, three types of developing methods are generally known, one of which is a non-magnetic one-component developing method using a one-component developer, and a one-component developer. The non-magnetic toner contained in the toner is coated on the developing sleeve (developer carrier) with a blade or the like, and the non-magnetic toner is conveyed to the photosensitive drum whose image carrier is the developing sleeve and developed in a non-contact state with respect to the photosensitive drum. To do.

  The second is a magnetic one-component developing method using magnetic toner, in which magnetic toner contained in a one-component developer is coated on a developing sleeve by magnetic force, and similarly, conveyed to a photosensitive drum and developed by contact.

  Third, a two-component developer in which a magnetic carrier is mixed with non-magnetic toner is coated on the developing sleeve by magnetic force, conveyed to the photosensitive drum by the developing sleeve, and developed in contact with the photosensitive drum. This is a two-component contact development method, that is, a two-component magnetic brush development method.

  Of these three, the third two-component contact development method is a development method that enables high image quality with excellent density uniformity because the toner is reliably charged with a magnetic carrier. In addition, it is desirable that the distance (SD gap) between the surface of the developing sleeve and the surface of the photosensitive drum is always constant and constant at the facing portion between the developing sleeve serving as the developing unit and the photosensitive drum. Fluctuates easily due to rotational movement and durability. The two-component contact development method is capable of stable image formation without being relatively affected by such SD gap fluctuations.

  In this two-component contact development method, a development method for reducing the amount of magnetization of the carrier has been proposed as a development method for improving the micro image quality. According to this method, the rubbing force against the photosensitive drum is weakened, and the developer image (toner image) developed on the photosensitive drum is not disturbed, so that the roughness is reduced. As a result, a halftone image with less noise can be formed, and the output image can be improved in image quality.

  By the way, in recent years, with the progress of full color, systemization, and digitization, not only the high quality of output images but also the demand for high speed and high stability is increasing, and in the light printing market of copying machines and various printers Is also expected.

  In order to increase the speed, it is essential to increase the moving speed of the photosensitive drum, and at the same time, it is necessary to increase the moving speed of the developing sleeve.

  In general, developability (development performance) is the ratio of the developing sleeve moving speed (peripheral speed ratio) to the moving speed of the photosensitive drum in the developing section when the development hardware conditions including the characteristics of the developer and the photosensitive drum are common. For example, when the photosensitive drum moving speed is 100 mm / s and the developing sleeve moving speed is 250 mm / s, the peripheral speed ratio is 2.5. Further, when the moving speed of the photosensitive drum is 200 mm / s and the moving speed of the developing sleeve is 500 mm / s, the peripheral speed ratio is 2.5. Therefore, in these cases, when the hardware conditions are the same, there is an ability to produce almost the same concentration.

  However, when the speed is further increased, for example, when the photosensitive drum moving speed is 250 mm / s or more, the developing sleeve moving speed is set to 625 mm / s in order to increase the peripheral speed ratio by 2.5 times. Otherwise, a sufficient density cannot be ensured, and in this case, the moving speed of the developing sleeve becomes very high, which causes a new problem that the developer is deteriorated or the toner is scattered.

  Accordingly, various development methods have been proposed in which development opportunities are provided at least twice as a measure for realizing a high speed stably without increasing the rotation speed of the developing sleeve (see, for example, Patent Document 1).

  For example, a method in which two or more independent developing devices are provided around the photosensitive drum, or two or more developing sleeves are arranged in the developing device, and the developer in the developing device is sequentially placed on the developing sleeve. The method of coating.

  When this method is used, it is possible to make a configuration in which the moving speed of the developing sleeve is not greatly increased because there are two or more development opportunities for the electrostatic latent image. As a result, it is possible to realize a configuration that is strong against developer deterioration and toner scattering.

However, even if a magnetic carrier having a relatively low magnetization amount is used, there are two or more development opportunities, so that the toner image developed on the photosensitive drum is scraped off by the rubbing of the magnetic brush of the developing sleeve on the downstream side. In other words, the so-called kimchi-mura phenomenon tends to occur, and as a result, the image has a low granularity and a low quality.
JP 2003-295602 A

  The object of the present invention is to achieve high-speed response while suppressing high-quality image quality by suppressing the unevenness phenomenon that tends to occur by arranging two or more developing sleeves around the photosensitive drum for high-speed response. It is an object of the present invention to provide a developing device and an image forming apparatus having the same.

The above object is achieved by the developing device and the image forming apparatus according to the present invention. In summary, the first invention includes a non-magnetic toner and a magnetic carrier having a magnetization of 3.0 × 10 ⁴ A / m to 2.5 × 10 ⁵ A / m in an external magnetic field of 100 mT. The electrostatic latent image on the image carrier is formed by a developing means having a plurality of developer carriers having a built-in magnetic field generating means fixed to the rotation. In the developing device for developing,
The plurality of developer carriers are arranged side by side so as to face the moving surface of the image carrier, and the downstream developer carriers located on the downstream side of the image carrier surface movement direction among the plurality of developer carriers. The magnetic field generating means incorporated in the plurality has a plurality of magnetic poles along an outer periphery, and the plurality of magnetic poles includes a developing pole facing the image carrier and the developing pole in a rotation direction of the developer carrier. A repelling magnetic pole that forms a repelling magnetic field disposed on the downstream side of
The plurality of magnetic pole arrangements of the magnetic field generating means built in the downstream developer carrier are:
At least one transport pole is disposed between the repelling magnetic pole on each of the upstream side and the downstream side in the developer carrying member rotation direction of the developing pole,
Between the magnetic poles of the developing pole and the downstream transport pole, which is the transport pole adjacent to the downstream side in the rotation direction of the developer carrier, is the transport pole adjacent to the upstream side in the rotation direction of the developer carrier. It is set smaller than the magnetic pole between a certain upstream carrier pole and
The developing pole is disposed within an angle region within ± 5 ° with respect to the closest portion of the developer carrying body and the image carrying body at an angle centered on the rotation center of the developer carrying body. A developing device is provided.

  According to an embodiment of the present invention, in the plurality of developer carriers, the upstream developer carrier has a diameter that is the developer carrier that is located upstream in the rotation direction of the image carrier. It is shorter than the diameter of the carrier.

  According to a second aspect of the present invention, there is provided an image forming apparatus comprising: an image carrier on which an electrostatic latent image is formed on a surface; and the developing device according to the first aspect of the present invention that develops the electrostatic latent image. I will provide a.

The developing device and the image forming apparatus of the present invention contain a non-magnetic toner and a magnetic carrier having a magnetization amount of 3.0 × 10 ⁴ A / m or more and 2.5 × 10 ⁵ A / m or less in an external magnetic field of 100 mT. The electrostatic latent image on the image carrier is formed by a developing means having a plurality of developer carriers having a built-in magnetic field generating means fixed to the rotation. In the developing device for developing, the plurality of developer carriers are arranged side by side facing the moving surface of the image carrier, and the downstream developer located on the downstream side of the image carrier surface movement direction among the plurality of developer carriers The magnetic field generating means incorporated in the carrier has a plurality of magnetic poles along the outer periphery, and the plurality of magnetic poles are located on the downstream side of the development pole in the rotation direction of the developer carrier and the development pole facing the image carrier. Repelling magnetic poles forming a repelling magnetic field disposed in The plurality of magnetic pole arrangements of the magnetic field generating means incorporated in the downstream developer carrier further includes at least one between the repulsive magnetic pole on the upstream side and the downstream side in the developer carrier rotation direction of the developer pole. A transport pole is disposed, and the transport pole adjacent to the development pole and the upstream side in the rotation direction of the developer carrier is between the magnetic poles of the development pole and the downstream transport pole adjacent to the downstream side in the rotation direction of the developer carrier. The developing pole is set to be smaller than the distance between the upstream conveying pole and the upstream conveying pole, and the developing pole is at an angle around the rotation center of the developer carrying body with respect to the closest portion between the developer carrying body and the image carrying body. Since it is arranged within an angle region within 5 °, it is possible to cope with high speed while maintaining high image quality.

  Hereinafter, a developing device and an image forming apparatus including the developing device according to the present invention will be described in more detail with reference to the drawings.

Example 1
FIG. 3 is a schematic configuration diagram showing an example of an image forming apparatus using the developing device of the present invention.

  The image forming apparatus (copier) is an electrophotographic image forming apparatus, which reads image information from external information, for example, a document G, below a reader unit 100 having a document table 10 and an optical scanning unit 9, and a reader unit. Based on the image information transmitted from the printer 100, a printer unit 200 that performs image formation is installed. The printer unit 200 includes an image carrier (image carrier) that is an image forming unit in each image forming process. Photosensitive drum) 1, two developing devices (developing devices) 4 and 5, and a latent image forming unit, and in this embodiment, a laser scanning unit 100 a which is an exposure unit are provided. In this embodiment, an electrophotographic image forming apparatus is taken as an example, but the present invention can also be applied to an electrostatic recording type.

  When the reader unit 100 places the surface on which the document G is to be copied on the document table 10 and presses a copy button (not shown) from the outside, that is, when an image formation signal is transmitted, the document G is copied. That is, image formation is started.

  The optical scanning unit 9 is configured by integrating a document irradiation lamp 9a, a short focus lens array 9b, and a CCD sensor 9c, and when the copy button is pressed, the unit 9 is operated by the irradiation lamp 9a with the document G. The reflected light from the original surface is imaged by the short focus lens array and incident on the CCD sensor 9c.

  The CCD sensor 9c includes a light receiving unit, a transfer unit, and an output unit (not shown). The light receiving unit converts an incident light signal into a charge signal, and the transfer unit sequentially outputs the charge signal to the output unit in synchronization with a clock pulse. The charge signal is converted into a voltage signal at the output unit, amplified and reduced in impedance, and output.

  The image signal (analog signal) obtained in this way is converted into a digital signal by known image processing, and then sent to the printer unit 200.

  In the printer unit 200, an image forming process is performed. The photosensitive drum 1 is driven to rotate at a predetermined peripheral speed around the central support shaft, and in the rotation process, an image is formed on the surface by the peripheral surface passing through a portion facing each image forming unit.

  In the present invention, a commonly used organic photoreceptor is used as the photosensitive drum 1, but it is also possible to use an inorganic photoreceptor such as an amorphous silicon photoreceptor. If an amorphous silicon drum is used, the photosensitive drum will also have a long life.

  First, an electrostatic latent image is formed after the surface of the photosensitive drum 1 as an image carrier is uniformly charged. In the charging process, the charger 3 receives a uniform charging process so that the surface becomes, for example, −650V.

  In this embodiment, a corona charger is used as the charger 3. However, it is more preferable to use a contact charger, particularly a charge injection type magnetic brush charging type charger.

  Next, in the latent image forming step, the solid-state laser element 102 (FIG. 5) of the laser scanning unit 100a receives the image signal (digital signal) and generates a laser beam L by ON / OFF light emission, and the rotating polygon mirror is operated. Then, the surface of the photosensitive drum 1 is scanned by the laser beam L, and electrostatic latent images corresponding to the document image are sequentially formed on the surface of the photosensitive drum 1.

  FIG. 5 shows a schematic configuration of a laser scanning unit 100a including the solid-state laser element 102 described above. In the laser scanning unit 100a, first, the solid-state laser element 102 is blinked at a predetermined timing by the light emission signal generator 101 based on the input image signal. The laser light L0 emitted from the solid-state laser element 102 in this way is converted into a substantially parallel light beam L1 by the collimator lens system 103, and further scanned by the rotating polygon mirror 104 that rotates in the direction of the arrow b, and the fθ lens group Images are formed in spots on the scanned surface 106 of the photosensitive drum 1 by 105a, 105b, and 105c. By scanning with such laser light L, an exposure distribution for one image scan is formed on the scanned surface 106, and the scanned surface 106 is scrolled by a predetermined amount perpendicular to the scanning direction for each scan. As a result, an exposure distribution corresponding to the image signal is obtained on the surface 106 to be scanned. That is, an electrostatic latent image is formed.

  This electrostatic latent image is non-magnetic by a developing device adopting a two-component contact developing system installed around the photosensitive drum 1 in the developing process, in this embodiment, by two two-component developing devices 4 and 5. It is developed with a developer containing toner and a relatively low magnetization magnetic carrier, and visualized as a developer image (toner image). The developing units 4 and 5 will be described in detail later.

  The toner image formed on the photosensitive drum 1 is transferred onto the transfer material P conveyed from the paper feed cassette 80 in the transfer process.

  Here, on the lower side of the photosensitive drum 1, a transfer belt 71 that is wound around a driving roller 72 and a driven roller 73 and rotates in the direction of arrow D is installed as a transfer unit. The transfer material P is taken out from the paper feed cassette 80, and is fed onto the transfer belt 71 at an appropriate timing in synchronization with the rotation of the photosensitive drum 1. The photosensitive drum 1 and the transfer belt 71 come into contact with each other at a predetermined timing. Then, it is conveyed to the transfer section 70. A transfer charging blade 74 is installed inside the transfer portion 70 of the transfer belt 71. The transfer charging blade 74 presses the transfer belt 71 in the direction of the photosensitive drum 1, and the transfer charging blade 74 is supplied with a high voltage power supply (not shown). By supplying power, the transfer material P is charged from the back side with a polarity opposite to that of the toner, and the toner image formed on the photosensitive drum 1 is electrostatically transferred onto the transfer material P.

  In this embodiment, a polyimide resin sheet having a thickness of 75 μm was used as the transfer belt 71. Other examples of the transfer belt 71 include a polycarbonate resin, a polyethylene terephthalate resin, a polyvinylidene fluoride resin, a polyethylene naphthalate resin, a polyether ether ketone resin, a polyethersulfone resin, a polyurethane resin, or a fluorine-based or silicone resin. A rubber sheet of the type can be preferably used. The thickness of the transfer belt 71 is not limited to 75 μm, and a transfer belt having a thickness of about 25 to 2000 μm, preferably 50 to 150 μm can be suitably used.

A transfer charging blade 74 having a resistance of 10 ⁵ to 10 ⁷ Ω, a thickness of 2 mm, and a length of 306 mm was used. At the time of transfer, the current applied to the transfer charging blade 74 was +15 μA, and this was supplied with power controlled under constant current control.

  As described above, the transfer material P onto which the toner image has been transferred is separated from the transfer belt 71 and then conveyed to the fixing device 6 as fixing means. In the fixing step, the transfer material P is heated and pressed to form an image. Are fixed and output as a print image as an image formed product to the outside of the image forming apparatus.

  The photosensitive drum 1 after the transfer of the toner image is used for repeated image formation by removing contaminants such as residual toner remaining on the surface by the cleaner 9.

  Note that the configuration of the image forming apparatus is not limited to this, and the image forming apparatus can be applied to other configurations such as a plurality of image carriers and an intermediate transfer method.

In the image forming process performed by the image forming apparatus shown in FIG. 3 described above, in the present invention, as a developing means for performing the developing process, the developing apparatus includes two developing devices 4 and 5 as in the conventional case. Are provided with developing sleeves (developer carrying members) 11a and 11b each having a magnetic field generating means disposed therein, and a two-component developer containing toner and a magnetic carrier is carried on the surface thereof, and a photosensitive drum is provided. So-called two-component contact that develops the electrostatic latent image on the photosensitive drum 1 by transporting it to the developing unit opposite to the developing unit 1 and forming a developer magnetic brush on the developing unit by the developing pole of the magnetic field generating means Adopt development method. It should be noted that here, a relatively low magnetization magnetic carrier, that is, a magnetic carrier having a magnetization amount of 3.0 × 10 ⁴ A / m or more and 2.5 × 10 ⁵ A / m or less in an external magnetic field of 100 mT is included. A component developer is used to create a high-quality image without roughness.

  In order to cope with high speed, a plurality of developing sleeves 11a and 11b are arranged side by side along the surface of the photosensitive drum 1 in the moving direction. The developing sleeves 11a and 11b are composed of a rotatable conductive hollow cylinder, and are opposed to the photosensitive drum 1 by the magnetic force generated by the built-in magnetic field generating unit, here, the magnetic force of a cylindrical magnet roller and the rotation of the developing sleeves 11a and 11b. The developer is conveyed to the developing units 40 and 50 which are the units.

  Here, the developing device will be described in detail. Here, as the developing device, two developing devices 4 and 5 are provided, and the two developing means of the developing sleeves 11a and 11b provided in the developing devices 4 and 5 are configured so that there is two development opportunities in one image. .

  FIG. 2 is a schematic configuration diagram of an upstream developing device (hereinafter referred to as “upstream developing device”) 4 in the rotation direction of the photosensitive drum 1. The developing device 4 is configured as a two-component contact developing device. The developing device 4 includes a developing container 16 containing a toner and a two-component developer 19 containing the above-mentioned relatively low magnetization magnetic carrier, and the developer is provided in an opening facing the photosensitive drum 1 of the developing container 16. A developing sleeve 11a that carries 19 and conveys it to the developing unit facing the photosensitive drum 1 is installed, and the developing sleeve 11a is rotated in a direction in which the facing part to the photosensitive drum 1 moves in the same direction.

Here, the diameter of the developing sleeve 11a is 24.5 mm, the diameter of the photosensitive drum 1 is 80 mm, and the closest region, that is, the SD gap between the developing sleeve 11a and the photosensitive drum 1 is set to a distance of about 500 μm. It is set so that development can be performed in a state where the developer 19 conveyed to the unit 40 is in contact with the photosensitive drum 1. In this embodiment, the developer coating amount per unit area on the developing sleeve 11a is set to 30 mg / cm ² at this time. The developing sleeve 11a is made of a conductive material such as Al or SUS.

  In the developing sleeve 11a, a magnet roller 12a as a magnetic field generating means is fixedly arranged with respect to the rotation of the developing sleeve 11a, and the thickness of the developer layer carried on the developing sleeve 11a is substantially above the developing sleeve 11a. That is, in order to regulate the developer amount, a regulating blade 15 having a magnetic member is arranged. Normally, in this configuration, the gap between the regulating blade 15 and the developing sleeve 11a is set to 200 to 1000 μm, preferably 300 to 700 μm. In this embodiment, it is set to 600 μm.

  Further, developer agitating and conveying screws 13 and 14 are disposed in the developing container 16 constituting the developing device 4, and the developer composed of two components is agitated so as to be uniform.

  The electrostatic latent image formed on the photosensitive drum 1 is developed by the two-component contact developing method using the developing device 4 as follows. First, the developing sleeve 11a is rotated, and with the rotation, the developer 19 in the developing container 16 is pumped onto the developing sleeve 11a by the magnetic pole N3 of the magnet roller 12a, and the developer thus pumped is stored in the developing sleeve 11a. By rotation, it is conveyed from the magnetic pole S2 to N2. During this conveyance process, the developer is formed into a thin developer layer on the developing sleeve 11 a by magnetically regulating the thickness of the developer layer by the regulating blade 15. When the developer thin layer is conveyed to the developing pole S1 of the magnet roller 12a, the developer thin layer rises toward the photosensitive drum 1 by the magnetic force of the developing pole S1. The developer spike (magnetic brush) contacts the surface of the photosensitive drum 1 to develop the electrostatic latent image on the photosensitive drum 1, and the electrostatic latent image is visualized as a toner image.

  The developer that has passed through the developing unit 40 is transported to between the repulsive magnetic poles N1 and N3 that form a repelling magnetic field by the rotation of the developing sleeve 11a, and is separated from the developing sleeve 11a by the repelling magnetic field and returned into the developing container 16. .

  At the time of development, a developing bias in which a DC voltage and an AC voltage are superimposed is applied to the developing sleeve 11a from a bias power source (not shown) between the photosensitive drum 1 and the developing sleeve 11a. In this embodiment, a DC voltage of −500 V, an AC voltage having a peak-to-peak voltage Vpp of 2000 V, and a frequency f of 2000 Hz are used, but the DC voltage value and the AC voltage waveform are not limited thereto. In general, in the two-component contact development method, when a development bias including an AC voltage is applied, the development efficiency increases and the image becomes high-quality, but conversely, fogging easily occurs. For this reason, a fog is prevented by providing a potential difference between the DC voltage applied to the developing sleeve 11a and the charged potential of the photosensitive drum 1, that is, the white background potential.

  Next, a downstream developing device (hereinafter referred to as “downstream developing device”) 5 in the rotation direction of the photosensitive drum 1 will be described with reference to FIG. The configuration of the developing device 5 uses a magnet roller 12b whose magnetic pole pattern is changed from the magnet roller 12a as the magnet roller 12b built in the developing sleeve 11b with respect to the configuration of the upstream developing device 4.

  The developing device 5 is arranged on the downstream side of the developing device 4 in the surface moving direction, that is, the rotating direction of the photosensitive drum 1. Similarly to the upstream developing device 4, the developing device 5 also includes a developing container 16 containing a two-component developer 19 containing toner and a low-magnetization magnetic carrier, and an opening facing the photosensitive drum 1 of the developing container 16. A developing sleeve 11b having the same configuration as the developing sleeve 11a is installed in the unit, which carries the developer 19 and conveys it to the developing unit 50 facing the photosensitive drum 1. The developing sleeve 11b rotates so that the surface moving direction of the portion 50 facing the photosensitive drum 1 is the direction of moving in the forward direction, like the developing device 4.

Here, the diameter of the developing sleeve 11b is 24.5 mm, the closest area SD gap between the developing sleeve 11b and the photosensitive drum 1 is set to a distance of about 500 μm, and the same conditions as those of the developing device 4 are set. The developer coating amount per unit area is 30 mg / cm ² , and the developing sleeve 11b is formed of a conductive material such as Al or SUS.

  A magnet roller 12b is fixedly disposed in the developing sleeve 11b, and a conductive magnetic regulating blade 15 is disposed in the same manner as the developing device 4. The gap between the regulating blade 15 and the developing sleeve 11b is set to 200 to 1000 μm, preferably 300 to 700 μm. In this embodiment, it is set to 500 μm.

  Further, developer agitating and conveying screws 13 and 14 are disposed in the developing container 16. The electrostatic latent image formed on the photosensitive drum 1 is developed by the developing device 4 and further developed by a two-component magnetic brush developing method by the developing device 5.

  A developing bias in which a DC voltage and an AC voltage are superimposed from a bias power source (not shown) is applied between the developing sleeve 11 and the photosensitive drum 1, and this developing bias is also common to the developing device 4.

  That is, the configuration of the developing device 5 is essentially the same as that of the developing device 4 except for the magnetic pole arrangement of the magnet roller 12b, and the developing device 5 is caused by the difference in the position of the developing sleeve 11b with respect to the photosensitive drum 1. The positional relationship between the internal sleeve 11b and the screws 13, 14 is changed. The characteristic part in the present embodiment is the formation state of a magnetic pole pattern of a magnet roller 12b of the developing device 5 described later.

  The developer conveying method by the developing sleeve 11b is basically the same as that of the developing sleeve 11a which is an upstream developer carrying member. As the developing sleeve 11b rotates, the developer 19 in the developing container 16 is pumped onto the developing sleeve 11b by the magnetic pole S2 of the magnet roller 12b, and the developer thus pumped up is rotated by the rotation of the developing sleeve 11b. , Conveyed from magnetic pole S2 to N2. During this conveyance process, the developer is formed into a thin developer layer on the developing sleeve 11b by magnetically regulating the thickness of the developer layer by the regulating blade 15. When the developer thin layer is conveyed to the developing pole S1 of the magnet roller 12b, the developer thin layer rises toward the photosensitive drum 1 by the magnetic force of the developing pole S1. The developer spike (magnetic brush) contacts the surface of the photosensitive drum 1 to develop the electrostatic latent image on the photosensitive drum 1, and the electrostatic latent image is visualized as a toner image.

  The developer that has passed through the developing unit 50 is transported between the repulsive magnetic poles S2 and S3 that form a repelling magnetic field by the rotation of the developing sleeve 11b, and is separated from the developing sleeve 11a by the repelling magnetic field and returned into the developing container 16. .

  In the present specification, the developing sleeve 11a provided in the upstream developing device 4 provided on the upstream side with respect to the rotation direction of the photosensitive drum 1 is referred to as an “upstream developer carrier (upstream developing sleeve)”, and is downstream. The developing sleeve 11b provided in the downstream developing device 5 provided on the side is referred to as a “downstream developer carrier (downstream developing sleeve)”.

  In the developing regions 40 and 50, the outer circumferences of the developing sleeves 11a and 11b of the developing units 4 and 5 are both 1.3 mm on the photosensitive drum 1 with respect to 300 mm / s which is the moving speed of the outer circumference of the photosensitive drum 1. It is moving by double. In a normal configuration in which there is only one developing sleeve around the photosensitive drum 1, the moving speed ratio of the developing sleeve relative to the photosensitive drum 1 (hereinafter referred to as “peripheral speed ratio”) is set in the range of 1.5 to 3.0. However, in the configuration of the present invention, since there are two development opportunities, it can be set in the range of 1.0 to 2.0. Reducing the peripheral speed ratio is advantageous for problems such as toner scattering and agent deterioration. This makes it possible to increase the speed of the image forming apparatus. Such a configuration having a plurality of developing sleeves is considered particularly effective for a configuration in which the rotational speed of the photosensitive drum 1 is 250 mm / s or more.

  In the above configuration, the peripheral speed ratio of the developing units 4 and 5 to the photosensitive drum 1 may be different from each other. In this embodiment, the peripheral speed ratio of the sleeves 11a and 11b of the developing units 4 and 5 is set to 1.3.

By the plurality of developing units 4 and 5 having the developing unit configuration as described above, a magnetization amount of 3.0 × 10 ⁴ A / m or more and 2.5 × 10 ⁵ A / m or less in a 100 mT external magnetic field with a non-magnetic toner. When the development is carried out using a two-component developer containing a relatively low-magnetization magnetic carrier having a peripheral speed ratio of 1.3, the development is completely completed in the first development. It doesn't end in a state.

  The “development complete state” described here is defined as follows in this case. In other words, after the development is completed, the potential difference between the bright portion potential of the electrostatic latent image and the potential of the developing sleeve is filled by moving the toner, that is, zeroed. When the potential with the toner attached is measured later, the potential is converged to the DC potential (Vdc) applied to the developing sleeve 11.

  When the first development by the developing device 4 is completed, the amount of toner itself is small compared to the state in which the development is completely completed, so even though a carrier having a relatively low magnetization amount is used. A little bit of unevenness has occurred and is cramped. Of course, the roughness is slight compared with the case where a magnet with a large amount of magnetization is used.

  In the second development, the first development is insufficient, but the latent image potential is filled with the movement of the toner, that is, the potential of the outermost layer of the toner layer adhering to the bright latent image and the developing sleeve. In the state where the potential difference with respect to the potential is small, the second potential development is performed with the state as the initial potential state, so that even when the peripheral speed ratio is small, the development end stage can be easily reached.

  Here, conventionally, even when a magnetic carrier having a relatively low magnetization amount is used, there are two or more development opportunities, so that the toner image developed on the photosensitive drum 1 is a developing sleeve 11b which is a downstream developer carrier. However, there is a tendency that a so-called kimchi-mura phenomenon that is scraped off by the rubbing of the magnetic brush tends to occur.

  By the way, at the time of the second development, the toner adhering to the photosensitive drum 1 in the first development also flies following the AC electric field under the application of the development bias again, and the toner is rearranged on the latent image. In some cases, the correction is made so that the toner adheres faithfully to the latent image dots. Therefore, if the presence of the magnetic brush that hinders the re-adhesion of the toner in the vicinity of the photosensitive drum 1 in the downstream developing device 5 is reduced, it is considered that image quality degradation such as unevenness is less likely to occur.

  Therefore, the configuration of the present invention has a downstream developing sleeve as shown in FIG. 1 in order to reduce the presence of the magnetic brush on the most downstream side in the rotation direction of the photosensitive drum 1 in the developing region 50 during the second development. The developing pole S1 and the magnetic pole on the downstream side of the developing pole S1 in the rotating direction of the developing sleeve 11b (hereinafter referred to as “downstream conveying pole”) N1 with the angle reference centered on the developing sleeve 11b. Is made narrower than the pole angle α between the developing pole S1 and the magnetic pole N1 that is one upstream side of the developing pole S1 in the rotation direction of the developing sleeve 11b (hereinafter referred to as “upstream transport pole”). .

  Specifically, the magnetic pole arrangement of the magnet roller 12b arranged downstream of the development pole S1 in the rotation direction of the development sleeve 11b on the basis of the angle around the rotation center of the development sleeve 11b is the development pole S1 and the upstream transport pole N2. Is set so that the following conditions (1) and (2) are satisfied: α (°) and β (°) between the developing pole S1 and the downstream transport pole N1.

(1) Development pole S1 position: 5 ° upstream to 5 ° downstream in the direction of surface movement of the photosensitive drum 1
(2) α> β (however, 50 ° ≦ α ≦ 70 °, 20 ° ≦ β ≦ 60 °)

  That is, the magnetic pole arrangement of the downstream developing sleeve 11b is such that the developing pole S1 is arranged in the vicinity of the photosensitive drum 1 in order to maintain developability on the upstream side of the developing region 50 in the rotation direction of the developing sleeve 11b, and the value of α is increased. As a result, the magnetic brush is sufficiently brought into contact with the photosensitive drum 1.

  On the other hand, on the downstream side of the developing unit 50, in order to reduce unevenness due to the contact of the magnetic brush, the value of β is decreased while the position of the developing pole S1 is set to 5 ° downstream, and the magnetic brush is moved after development. It is set so as to be away from the photosensitive drum 1 immediately.

  In this embodiment, referring to FIG. 1, the position of the developing pole S1 is 5 ° upstream of the closest position between the developing sleeve 11b and the photosensitive drum 1 in the rotational direction of the photosensitive drum 1 (in FIG. 1). α = 5 °), an angle between the development pole S1 and the upstream transport pole N2, α is set to 60 °, an angle between the development pole S1 and the downstream transport pole N1, and β is set to 40 °.

  However, at this time, if the above-described configuration is formed between the developing pole S1 and the magnetic pole S3 that forms a repulsive magnetic field located on the downstream side of the developing pole S1, and the magnetic pole S3 on the upstream side of S2, The magnetic force proportional to the Gauss of the developing pole and the absolute value of the Gauss cannot be set to a desired value.

  That is, in order to ensure the developer stripping performance, if a Gaussian pattern such as a Gaussian repulsion field and a full width at half maximum is ensured, the Gauss of the development pole S1 corresponding to the adjacent pole cannot be set to a desired value, and the development performance. If the mag pattern of the developing pole S1 is ensured in order to secure the repulsive magnetic field, it becomes difficult to form a repulsive magnetic field.

  Therefore, in the present invention, at least one transport pole N1 is arranged in front of the magnetic pole forming the repulsive magnetic field on the downstream side of the developing pole S1 in the rotation direction of the developing sleeve 11b, and the downstream transport pole generates a repulsive magnetic field. I try not to form it. In FIG. 1, the N1 pole set between the development pole S1 pole and the S3 pole that is the upstream pole among the magnetic poles that form the repulsive magnetic field corresponds to this downstream transport pole.

  The polarities such as S and N are not limited to those described above, but are determined as appropriate.

  According to the study conducted by the present inventors, if the magnetic pole pattern of the magnet roller 12b in the downstream developer carrying member is set within the above range, the image density is sufficient even if the peripheral speed ratio is 1.3 times, and the roughness level is low. Also very good images were obtained. In addition, it is possible to continue outputting a stable image for a long time with less scattering.

As described above, the developing configuration uses a plurality of developing units, and has a relatively low magnetization amount of 3.0 × 10 ⁴ A / m or more and 2.5 × 10 ⁵ A / m or less in a magnetic field of 100 mT. In a developing device using a magnetic carrier, the angle between the developing pole of the developing sleeve located on the downstream side in the rotation direction of the photosensitive drum and the pole on the downstream side of the developing pole is set to the upstream side of the developing pole and the developing pole. Narrower than the angle between and the development main pole position within ± 5 ° from the photosensitive drum facing position, high speed image quality can be achieved while maintaining high quality image without unevenness. It was.

  Here, the developer used in the present invention will be described in detail.

In the present invention, the magnetic carrier in the two-component developer used in the developing process has a magnetization of 3.0 × 10 ⁴ A / m or more and 2.5 × 10 ⁵ A / m or less in a magnetic field of 100 mT. Is a major feature, and the physical property values of the magnetic carrier will be described below.

  In the present invention, as the magnetic carrier, for example, surface oxidation, unoxidized iron, nickel, cobalt, manganese, chromium, ferrite made of metal such as rare earth, or ferrite made of those oxides can be used, The manufacturing method is not asked. Of course, a resin carrier in which a magnetic material is dispersed may be used. This magnetic carrier can be resin-coated by a known method.

In this embodiment, the ferrite particles containing neodymium, samadium, barium and the like are coated with a resin, the weight average particle diameter is 20 to 100 μm, preferably 20 to 70 μm, and the volume resistance is 10 ⁶ to 10 ¹² Ω · cm. A magnetic carrier having a value was used.

  The average particle diameter of the magnetic carrier is shown by the maximum length in the vertical direction. In the present invention, the carrier is photographed with a microscope at a magnification of 50 to 1000 times, and 3000 or more of the carrier particles in the obtained photographic image are taken. The carrier particles were randomly selected, their long axes were measured, and the arithmetic average was taken.

With a carrier having a magnetic property greater than 2.5 × 10 ⁵ A / m, the magnetization amount of the carrier cannot achieve high image quality / high stability, which is the effect of the present invention. This is because, when a material having a large amount of magnetization is used, unevenness occurs particularly in the developing device on the downstream side in the moving direction of the photosensitive drum. Further, in the case of a carrier having characteristics of less than 3.0 × 10 ⁴ A / m, problems such as poor developer coating on the developing sleeve occur, and therefore, 3.0 × 10 ⁴ A / m or more is preferable. Therefore, the thing of the above-mentioned field was used.

The amount of magnetization is determined by determining the magnetization (Am ² / kg) of the carrier packed in an external magnetic field of 100 mT using the oscillating magnetic field type automatic magnetic recording device manufactured by Riken Denshi Co., Ltd. The amount of magnetization (A / m) was calculated by applying true specific gravity (kg / m ³ ).

  As the toner used in the developer together with the magnetic carrier, conventionally known toners such as pulverized toners can be used.

  The volume average particle size of the toner is preferably 4 to 15 μm. The volume average particle diameter of the toner can be measured by, for example, the following measurement method.

  A call counter TA-II type (manufactured by Coulter Inc.) is used as a measuring device, and an interface (manufactured by Nikka Ki) and CX-i personal computer (manufactured by Canon) for outputting the number average distribution and volume average distribution are connected thereto. As the electrolytic solution, 1% NaCl aqueous solution is prepared using sodium chloride (reagent grade 1).

  In 100 to 150 ml of the above electrolytic solution, 0.1 to 5 ml of a surfactant (preferably alkyl benzene sulfonate) is added as a dispersant, and 0.5 to 50 mg of a measurement sample toner is added and suspended. The electrolytic solution in which the sample is suspended is dispersed for about 1 to 3 minutes with an ultrasonic disperser, and then the particle size distribution of toner particles of 2 to 40 μm is obtained using the 100 μm aperture by the above-mentioned call counter TA-II type. Measure and determine the toner volume distribution. From the volume distribution of the toner thus obtained, the volume average particle diameter of the toner is obtained.

  Further, the external additive used in the present invention preferably has a particle size of 1/10 or less of the weight average particle size of the toner particles from the viewpoint of durability when added to the toner. The particle size of the external additive means the average particle size obtained by observing the surface of the toner particles with a microscope. The external additive is used in an amount of 0.01 to 15 parts by weight, preferably 0.05 to 12 parts by weight, based on 100 parts by weight of the toner.

  Examples of external additives include the following. Metal oxides such as aluminum oxide, titanium oxide, strontium titanate, cerium oxide, magnesium oxide, chromium oxide, tin oxide, and zinc oxide; nitrides such as silicon nitride; carbides such as silicon carbide; calcium sulfate, barium sulfate, carbonic acid Metal salts such as calcium; fatty acid metal salts such as zinc stearate and calcium stearate; carbon black; silica and the like. These external additives may be used alone or in combination. Those subjected to hydrophobic treatment are preferred.

The toner having the above components can be charged with either a negative polarity or a positive polarity, but in this embodiment, a toner having a negative charge polarity is used, and the average charge amount charged by friction with the carrier (per unit weight). the amount of the charge; hereinafter Q / M) was used as the ^{-1.0 × 10 -2 C / kg~-} 6.0 × 10 -2 C / kg.

As described above, in a developing device that uses a two-component developer including a non-magnetic toner and a magnetic carrier and has a plurality of developer carriers for speeding up, the magnetic carrier is used in an external magnetic field of 100 mT. A relatively low magnetization carrier having a magnetization amount of 0 × 10 ⁴ A / m or more and 2.5 × 10 ⁵ A / m or less, and a plurality of developing sleeves are arranged along the photosensitive drum surface in the moving direction and downstream. The development sleeve on the downstream side, the spacing between the development pole and the magnetic pole on the downstream side of the development pole is narrower than the gap between the development pole and the magnetic pole on the upstream side of the development pole, and the development pole Is kept within ± 5 ° with respect to the photosensitive drum, so that the magnetic brush softly rubs the photosensitive drum at the developing unit, so that the scavenging of the toner image developed on the photosensitive drum is performed. Grayed effect is reduced, can be prevented Hakimemura like by the magnetic brush, a high image quality, over a long period can be continuously output in a high speed state.

  The image formation is performed through the above steps. However, the present invention is not limited to the example in which image formation is performed by one developing unit and a photosensitive drum as described above. This is also applicable to the tandem system in which a photosensitive drum and four color (for example, yellow, magenta, cyan, Bk, etc.) developing devices are arranged around each other.

  In the present embodiment, the developing device constituted by two developing devices has been described. However, the number of developing devices is not limited to this, and three or more developing devices may be provided around the photosensitive drum, May comprise a developing sleeve. In this case, the downstream developing device is a developing device arranged on the most downstream side in the rotating direction of the photosensitive drum among the provided developing devices, and the magnetic pole arrangement is set as described above in the downstream developing sleeve. What is necessary is just to set suitably about the magnetic pole structure of another developing sleeve.

  The present invention can also be applied to an electrostatic recording type. It is effective to form the electrostatic latent image on the photosensitive drum by a digital method, but it may be formed by an analog method.

  The effective point that the electrostatic latent image is a digital latent image is particularly an effect on the feeling of roughness (graininess) in the low density portion, which is as follows.

  In order to form the same density between the analog latent image and the digital latent image, the latent image potential depth of the analog latent image is shallower. On the other hand, since the one-dot latent image is deeper in the digital latent image, the toner is surely adhered to the latent image, so that the level of unevenness by the magnetic brush is improved.

Example 2
In the developing device of the present embodiment, as shown in FIG. 4, in the first embodiment, two independent developing devices 4 and 5 are used as the developing device, but in one developing device 400. The developing means 11 includes two developing sleeves 11a and 11b, and one developer stirring member 14 is provided. Other configurations are the same as those in the first embodiment.

  Also in this embodiment, the magnetic pole pattern in the vicinity of the developing pole of the downstream developing sleeve 11b has the same conditions as in the first embodiment, that is, the angle between the developing pole and the downstream conveying pole on the downstream side of the developing pole is the same. The angle between the development pole and the upstream transport pole on the upstream side of the development pole is narrower than that, and the development pole is set within ± 5 ° with respect to the portion facing the photosensitive drum with respect to the development sleeve.

  If a developing device having a plurality of such developing sleeves is used, the object of the present invention can be achieved. As an example of such a developing device, the developing device used in this embodiment will be described with reference to FIG.

  The developing device 4a is configured as a two-component magnetic brush developing device, similar to the developing 4 and 5 of the first embodiment, and the two-component developer 19 containing the toner and the magnetic carrier described in the first embodiment is used. A developer container 16 is provided.

  As shown in FIG. 4, a developing sleeve 11 a that is a developer carrying member that carries a developer 19 in an opening facing the photosensitive drum 1 of the developing container 16 and conveys the developer 19 to the developing unit 40 facing the photosensitive drum 1. , 11b are provided adjacent to the photosensitive drum 1 adjacent to each other, and provided upstream and downstream along the moving direction. Here, both the developing sleeves 11a and 11b rotate in a direction in which a portion facing the photosensitive drum 1 moves in the same direction.

  As shown in FIG. 4, the developer layer thickness is regulated by the N1 pole of the mag roller 12a in the upstream developing sleeve 11a and the developer layer thickness regulating blade 15 located upstream of the developing portion in the rotation direction of the developing sleeve 11a. Similarly to the first embodiment, a developing bias is applied in common to both developing sleeves 11a and 11b from a power source (not shown). The same developing bias as that in Example 1 is applied.

  The configuration of each of the two developing sleeves 11a and 11b is the same as that of the developing sleeves 11a and 11b provided in the developing devices 4 and 5 of the first embodiment. Each of the developing sleeves 11a and 11b is a magnet roller 12a that is a magnetic field generating unit fixed inside. , 12b are arranged and rotatable nonmagnetic cylinders 11a and 11b.

  The two developing sleeves 11a and 11b are arranged close to each other, but may be arranged apart from each other.

  In this embodiment, the flow of the agent will be described when the two developing sleeves 11a and 11b are close to each other.

  In the process where the developer is pumped up to the upstream developing sleeve 11a at the position of the S1 pole in the magnet roller 12a incorporated therein, and is transported to the transport pole N1 pole S2 pole of the internal magnetic pole by the rotation of the developing sleeve 11a. The thickness of the developer layer is regulated by the blade 15 and conveyed to the first development pole N3 facing the photosensitive drum 1, and a magnetic brush is formed and used for development. The developer for which the first development has been completed is delivered to the developing sleeve 11b at the S3 pole disposed on the magnet roller 12a facing the downstream developing sleeve 11b. At this time, a repulsive magnetic field is formed with the S3 pole of the magnet roller 12a and the S1 pole that is a developer pumping magnetic pole disposed in the developing container 16 downstream in the rotation direction of the developing sleeve 11a. 11a and 11b are not slipped through, but are attracted to the N4 pole of the magnet roller 12b incorporated in the downstream developing sleeve 11b from the position of the S3 pole of the magnet roller 12a of the upstream developing sleeve 11a, and the downstream developing. It is carried on the sleeve 11b.

  The developer delivered to the downstream developing sleeve 11b becomes a magnetic brush at the S4 pole which is the second developing pole of the magnet roller 12b in the downstream developing sleeve 11b, and is used for the second development.

  As described above, in this embodiment, the developer is transferred between the developing sleeves 11a and 11b by receiving the S pole and the N pole provided in the mag rollers 12a and 12b in the developing sleeves 11a and 11b in an opposite manner. It is a configuration to pass.

  In this configuration, since the T / D ratio at the time of the second development is surely lowered, the developer after the first development is not reliably agitated, and the reverse induced by the carrier in the developer. If the charge (the reverse charge (+ side) induced on the carrier (ie, the counter charge) due to the toner being peeled off from the carrier) remains, peeling unevenness is likely to occur during the second development.

  However, according to the present configuration, the developed agent in which the counter charge has occurred moves on the upstream sleeve 11a and is further transferred to the downstream sleeve 11b until the second development is performed. Counter charge disappears due to the movement of toner and carrier. As a result, although the T / D ratio is decreased, no unevenness occurs.

  In the case of this system, two developing devices are not arranged around the photosensitive drum 1 and can be handled by one developing device, and the configuration can be simplified.

  In addition, in this embodiment, a configuration using a bucket roller 14 is adopted as an alternative to the stirring and conveying screw 13 in FIGS. 1 and 2. This configuration is not limited to this example, and a helical screw that performs stirring and conveyance in the longitudinal direction may be used as in the developing devices 4 and 5.

As described above, even in a developing configuration using a plurality of developing units, a magnetic carrier having a magnetization amount of 3.0 × 10 ⁴ A / m or more and 2.5 × 10 ⁵ A / m or less in a magnetic field of 100 mT is used. In addition, the angle between the developing pole of the downstream developing sleeve and the downstream conveying pole on the downstream side of the developing pole, which is arranged upstream of the upstream repelling magnetic pole among the magnetic poles forming the repelling magnetic field, is developed. Maintaining high image quality without unevenness by narrowing the angle between the pole and the upstream transport pole upstream of the development pole, and arranging the development pole position within ± 5 ° from the photosensitive drum facing position As a result, high-speed response was achieved. Moreover, a reduction in space / cost can be achieved at the same time.

  In this case, three or more developing sleeves may be provided. At that time, the developing sleeve arranged on the most downstream side in the rotating direction of the photosensitive drum becomes the downstream developing sleeve, and the magnetic pole arrangement in the downstream developing sleeve is as described above. What is necessary is just to set, About the magnetic pole structure of another developing sleeve, it sets suitably.

Example 3
In this embodiment, only the relationship between the diameters of the upstream developing sleeve 11a and the downstream developing sleeve 11b is different from that of the first embodiment, and all other configurations are the same as those of the first embodiment.

  Also in this embodiment, the magnetic pole pattern in the vicinity of the developing pole S1 of the downstream developing sleeve 11b is installed under the same conditions as in Embodiment 1 shown in FIG. 1, that is, the pole angle between the developing pole S1 and the downstream magnetic pole N1. β is made narrower than the angle α between the developing pole S1 and the upstream magnetic pole N2, and the developing pole S1 is set within ± 5 ° with respect to the portion facing the photosensitive drum 1 with respect to the developing sleeve.

  Further, in this embodiment, the diameter of the upstream developing sleeve 11a is 24.5 mm, the diameter of the downstream developing sleeve 11b is 20 mm, and the diameter of the downstream developing sleeve 11b is smaller than the diameter of the upstream developing sleeve 11a.

  By making the diameter of the downstream developing sleeve 11b smaller than the diameter of the upstream developing sleeve 11a as in the present embodiment, the effect of the configuration of the first embodiment can be further enhanced.

  When the number of developing sleeves is more than three, the developing sleeve arranged on the most downstream side in the rotation direction of the photosensitive drum is set as the downstream developing sleeve, and the diameter thereof is arranged to be the smallest among the provided developing sleeves. .

  That is, by reducing the diameter of the downstream developing sleeve 11b, it becomes easy to adopt a configuration in which the so-called magnetic brush lays down immediately after development, as described in the first embodiment. In order to maintain the developability, it is advantageous that the diameter of the upstream sleeve 11a is large. Therefore, in this embodiment, the relationship between the diameter of the upstream developing sleeve 11a and the diameter of the downstream developing sleeve 11b is as follows. It is set as described above.

  As a result of some studies, the effect was obtained by setting the diameter of the upstream developing sleeve to 16 mm or more and 50 mm or less, the diameter of the downstream developing sleeve to 10 mm or more and 40 mm or less, and setting the diameter relationship as described above.

  Here, if the diameter of the downstream developing sleeve is too small, the developer contact area (circumferential direction) is narrowed, so that developability is deteriorated and the peripheral speed ratio cannot be set low in a high-speed system. become. The upper limit is set to 50 mm from the upstream developing sleeve due to cost. However, since the developing configuration uses two developing sleeves, it is not necessary to use a developing sleeve having a diameter larger than 50 mm. The magnitude relationship between the sleeves may be set from this value.

As described above, even in a developing configuration using a plurality of developing units, a magnetic carrier having a magnetization amount of 3.0 × 10 ⁴ A / m or more and 2.5 × 10 ⁵ A / m or less in a magnetic field of 100 mT is used. And between the developing pole of the downstream developing sleeve and the downstream conveying pole on the downstream side of the developing pole, which is arranged upstream of the repelling pole upstream of the developing sleeve rotation direction among the magnetic poles forming the repelling magnetic field. By making the angle narrower than the angle between the development pole and the upstream transport pole on the upstream side of the development pole, and arranging the development pole position within ± 5 ° from the photosensitive drum facing position, high quality without unevenness High-speed response was achieved while maintaining high image quality.

  In the development process, the image quality (glossiness) is finally determined in the most downstream area of the development portion. Therefore, if the magnetic pole pattern of the downstream sleeve is set as described above, the spike on the downstream sleeve is determined. The standing magnetic brush can be laid down immediately after the development is completed, and further, unevenness is less likely to occur.

  By adopting this configuration, it is possible to continue outputting high-quality images without unevenness in a high-speed state over a long period of time.

FIG. 2 is a cross-sectional view illustrating an example of a downstream developing device that is a developing device according to the present invention. FIG. 2 is a cross-sectional view illustrating an example of an upstream developing device that is a developing device according to the present invention. 1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to the present invention. It is sectional drawing which shows the other example of the developing device which concerns on this invention. It is explanatory drawing which shows an example of a structure of a latent image formation means.

Explanation of symbols

1 Photosensitive drum (image carrier)
4 Upstream Development Unit 5 Downstream Development Unit 11a, 11b Development Sleeve (Developer Carrier)
12a, 12b Magnet roller (magnetic field generating means)
40, 50 Development section

Claims (12)

Rotating conductivity using non-magnetic toner and developer containing magnetic carrier having magnetization of 3.0 × 10 ⁴ A / m or more and 2.5 × 10 ⁵ A / m or less in an external magnetic field of 100 mT In a developing device that develops an electrostatic latent image on an image carrier by a developer having a plurality of developer carriers, each of which is composed of a cylinder and includes a magnetic field generator fixed with respect to the rotation.
The plurality of developer carriers are arranged side by side so as to face the moving surface of the image carrier, and the downstream developer carriers located on the downstream side of the image carrier surface movement direction among the plurality of developer carriers. The magnetic field generating means incorporated in the plurality has a plurality of magnetic poles along an outer periphery, and the plurality of magnetic poles includes a developing pole facing the image carrier and the developing pole in a rotation direction of the developer carrier. A repelling magnetic pole that forms a repelling magnetic field disposed on the downstream side of
The plurality of magnetic pole arrangements of the magnetic field generating means built in the downstream developer carrier are:
At least one transport pole is arranged between the repelling magnetic pole on each of the upstream side and the downstream side in the rotation direction of the downstream developer carrier of the developing pole,
The conveyance between the magnetic poles of the development pole and the downstream conveyance pole, which is the conveyance pole adjacent to the downstream side in the rotation direction of the downstream developer carrier, is adjacent to the development pole and the upstream side in the rotation direction of the downstream developer carrier. Is set smaller than the magnetic pole between the upstream conveying pole and the pole,
In addition, the developing pole is within an angle region within ± 5 ° with respect to the closest portion between the downstream developer carrier and the image carrier at an angle centered on the rotation center of the downstream developer carrier. A developing device arranged.   The angle between the rotation center of the developer carrier and the angle between the development pole and the upstream transport pole is 50 ° to 70 °, and the distance between the development pole and the downstream transport pole is 20 °. The developing device according to claim 1, wherein the developing device is at least 60 ° and at most 60 °.   In the plurality of developer carriers, the diameter of the downstream developer carrier is shorter than the diameter of the upstream developer carrier that is the developer carrier positioned upstream in the rotation direction of the image carrier. The developing device according to claim 1 or 2.   4. The developing device according to claim 3, wherein, in the plurality of developer carriers, the diameter of the upstream developer carrier is 16 mm or more and 50 mm or less, and the diameter of the downstream developer carrier is 10 mm or more and 40 mm or less. .   5. The development according to claim 1, wherein the developing unit is a unit that executes a contact development method in which a developing operation is performed in a state in which a developer is in contact with the image carrier. apparatus.   The developing device according to claim 1, wherein the plurality of developer carriers are divided into a plurality of developing devices.   The developing device according to claim 1, wherein all of the plurality of developer carriers are provided in one developing device.   The developing device according to claim 1, wherein the image carrier surface moving speed is 250 mm / s or more.   The moving speed ratio of the plurality of developer carrying member rotation speeds with respect to the image carrying member surface moving speed is 1.0 or more and 2.0 or less, according to any one of claims 1 to 8. The developing device described.   10. The development according to claim 1, wherein a developing bias including a DC voltage in which an AC voltage is superimposed is applied to a portion where the image bearing member and the developer bearing member are opposed to each other. apparatus.   The developing device according to claim 1, wherein the electrostatic latent image is a latent image formed by a digital method.   An image forming apparatus comprising: an image carrier on which an electrostatic latent image is formed; and the developing device according to claim 1 that develops the electrostatic latent image. .

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