JP2006091629A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device which can obtain a high-quality image suitable for a high-speed print processing, is free from toner leakage and uses a two-component developer. <P>SOLUTION: A first electrode member 43, a first developer carrier 41, a second developer carrier 42, and a second electrode member 44 are disposed in order from an upstream side in proximity to a rotating photoreceptor 1, and the first developer carrier 41 is rotated in a forward direction, and the second developer carrier 42 is rotated in the opposite direction, and a developing bias where a DC voltage and an AC voltage are superposed is applied to the developer carriers 41 and 42, and a control voltage is applied to electrode members 43 and 44. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a developing device that develops an electrostatic latent image using a two-component developer, and an image forming apparatus such as a printer, a copying machine, and a facsimile machine using the developing device.

  2. Description of the Related Art Conventionally, in an image forming apparatus that forms an image by an electrophotographic method, a magnetic brush developing type developing device using a two-component developer is used. This developing apparatus includes a magnet roll including a magnet body having a plurality of magnetic poles therein, a developer carrying body having a cylindrical developing sleeve that is rotatably supported, and causes toner to adhere to the surface of the developing sleeve. The magnetic carrier is held and transported to a developing area close to the image carrier, where the toner is separated from the magnetic carrier to develop the electrostatic latent image on the image carrier.

  A developing device using such a two-component developer can control the triboelectric charge of the toner relatively easily, hardly causes aggregation of the toner particles, has a good brushing of the magnetic brush, and is rubbed by the magnetic brush on the surface of the image carrier. It is excellent in that a good toner image can be obtained by development.

  In recent years, there has been a demand for image forming apparatuses that perform high-speed print processing with high image quality similar to offset printing. In order to perform high-speed printing processing, it is necessary to perform good development with a charged toner on an electrostatic latent image on an image carrier that rotates at a high speed and passes through the development area. .

  In Patent Document 1, as a method for good development, an electrode member is provided on the upstream side of the development region in addition to the magnetic brush formed by the magnetic pole of the developer carrier in the development region, and an electrode bias is applied to the electrode member. It is described that high-concentration toner regions are formed by applying the toner to perform efficient development in the development region.

Patent Document 2 describes a developing device suitable for high-speed processing by providing two developer carriers opposite to an image carrier and providing a double development area.
JP-A-8-30090 JP-A-10-26879

  A problem imposed on the developing device in high-speed processing is a problem of high-speed development processing and toner scattering.

  The toner is developed away from the magnetic carrier in the development area, and the toner adheres to the electrostatic latent image portion on the image carrier, but at the same time, a cloud-like toner is generated and floats, and a part is developed. Although it contributes, it also flows out of the developing device. The toner that has flowed out in a floating state adheres to the charger and the image carrier and the like, and lowers the image quality of the formed image.

  Patent Documents 1 and 2 are both developing devices suitable for high-speed processing, but do not describe means for preventing toner scattering.

  An object of the present invention is to provide a developing device that has high-speed processing and development performance suitable for high image quality and that can suppress toner scattering, and an image forming apparatus including such a developing device.

The developing device having the above object is achieved by the inventions according to claims 1 to 3.
(Claim 1)
An image carrier;
A first developer carrier that is upstream in the rotational direction of the image carrier and rotates in the forward direction;
A second developer carrier that is downstream in the rotational direction of the image carrier and rotates in the opposite direction;
A plate-like first electrode member disposed upstream of the first developer carrier and disposed in proximity to the image carrier and the first developer carrier;
A plate-like second electrode member disposed on the downstream side of the second developer carrier and in proximity to the image carrier and the second developer carrier;
A developing device comprising:
(Claim 2)
A developing bias in which a DC voltage and an AC voltage are superimposed is applied to the first developer carrier and the second developer carrier, so that the latent image formed on the image carrier is developed. The developing device according to claim 1, wherein:
(Claim 3)
The first electrode member is applied with a control voltage having the same polarity as the direct current voltage applied to the first developer carrier and having an absolute value equivalent to or close to the absolute value.
3. The development according to claim 2, wherein a control voltage having the same polarity as the DC voltage applied to the second developer carrying member and having a larger absolute value is applied to the second electrode member. apparatus.
(Claim 4)
In an image forming apparatus having an image carrier and a developing device that visualizes the electrostatic latent image formed on the image carrier using a two-component developer,
In the developing device, a first electrode member, a first developer carrier, a second developer carrier, and a second electrode member are disposed from the upstream side in the vicinity of the image carrier.
The first developer carrier rotates in the forward direction, the second developer carrier rotates in the opposite direction, and a development bias in which a DC voltage and an AC voltage are superimposed on each is applied.
The first electrode member is a plate-like member that is also close to the first developer carrier, and has the same polarity as the DC voltage applied to the first developer carrier, and an absolute value equal to or close to the control voltage. The second electrode member is a plate-like member close to the second developer carrier, and has the same polarity as the DC voltage applied to the second developer carrier and a larger absolute value. An image forming apparatus to which a control voltage is applied.

The developing device according to the first to third aspects of the present invention has the following function and effect, is suitable for high-quality development with high-speed processing, and has the effect of preventing contamination with toner.
-Two developer carriers opposite to the image carrier are overlaid in the first and second development areas at two locations, resulting in insufficient development for the image carrier that moves at high speed. Development without any effect.
-Since the two developer carriers are both rotated toward the inside of the two developer carriers, they are generated by rubbing with the photoconductor in the first and second development areas. The floating toner is between the two developer carriers and contributes to high-fidelity development with high fidelity without flowing out.
The first developer carrier rotates in the same direction as the image carrier, so that the required amount of toner adheres to the latent image portion and good development is performed, and the second developer carrier is the image carrier. By rotating in the opposite direction to the body, the surface of the image bearing member is rubbed by a magnetic brush, and development is performed. Toner that is excessively attached to the image portion and toner attached to the non-image portion is removed and cleaned. A toner image is formed.
The first electrode member is disposed with a slight gap from the image carrier, and a control voltage is applied, so that the toner does not flow out to the upstream side of the rotating image carrier. Further, at a position of the first electrode member close to the first developer carrier, the toner is removed from the magnetic carrier attached to the first developer carrier by the AC bias applied to the first developer carrier. The released toner moves to the first development area as the first developer carrying member rotates without adhering to the first electrode member, and good development is achieved by the toner having a high density. Is helping to be done.
The second electrode member is disposed with a slight gap from the image carrier, and a control voltage is applied, so that the toner does not flow through the gap portion downstream of the rotating image carrier. Further, when the second electrode member is close to the second developer carrier, the floating toner is electrostatically pressed and collected to the second developer carrier to prevent toner contamination. is doing.

  In the image forming apparatus according to the fourth aspect of the present invention, the toner is not scattered and contaminated, and the high-speed printing machine does not cause development failure, and a good high-quality image free from contamination can be obtained.

  The image forming apparatus of the present invention will be described with reference to the drawings.

  (1) The image forming apparatus shown in the cross-sectional configuration diagram of FIG. 1 illustrates an image forming unit of a copying machine using an electrophotographic process for forming a monochrome image using the developing device of the present invention. However, the present invention is not limited to the configuration shown in FIG. 1, and a color image forming apparatus using a plurality of multicolor developing devices is also applicable.

  Reference numeral 1 denotes a drum-shaped photoconductor of an image carrier, which is a negatively charged organic semiconductor layer in which a phthalocyanine pigment dispersed in polycarbonate is coated on a grounded metal cylindrical substrate, and is used for charge transport. The photosensitive layer including the layer has a film thickness of 30 μm, and is driven to rotate at a peripheral speed (Vp) of 500 mm / s in the direction of the arrow with a drum diameter of φ100 mm.

  Reference numeral 2 denotes a scorotron charging means for uniformly charging the periphery of the rotating photosensitive member 1 to a predetermined polarity and potential. The distance between the wire and the grid is 7.5 mm, the distance between the grid and the photosensitive member is 1 mm, and the distance between the wire and the back plate. It has a 12 mm band electrode configuration, the applied voltage of the grid is -780V, a bias voltage is applied with a constant charging current value, and the charging potential of the photosensitive member 1 is -800V.

  Reference numeral 3 denotes an image exposure means using a laser scanning system, which uses a semiconductor laser (LD) having a laser wavelength of 780 nm, and its output power is 500 μW. The image exposure means 3 emits a laser beam and scans and exposes the uniformly charged surface of the photoreceptor 1 to form an electrostatic latent image.

  As will be described in detail later, the developing device 4 develops the electrostatic latent image on the photoconductor 1 as a toner image by two developer carriers 41 and 42 that rotate to face the photoconductor 1. Development by contact or non-contact is performed using a two-component developer in combination with image exposure and reversal development.

  As a toner of a two-component developer containing a nonmagnetic toner and a magnetic carrier, a polymerized toner having a volume average particle diameter of 3 to 9 μm, and in this embodiment, 6 μm is used. By using the polymerized toner, an image forming apparatus having a high resolving power and a stable density and a very small occurrence of fog can be realized.

  The polymerized toner is manufactured by the following manufacturing method.

  The formation of the binder resin for toner and the toner shape are obtained by polymerization of the raw material monomer or prepolymer of the binder resin and subsequent chemical treatment. More specifically, it is obtained through a polymerization reaction such as suspension polymerization or emulsion polymerization and a subsequent fusing step between particles. In the polymerization toner, the raw material monomer or prepolymer is uniformly dispersed in an aqueous system and then polymerized. Thus, a toner having a uniform particle size distribution and shape can be obtained.

  If the toner has a volume average particle size of less than 3 μm, fogging and toner scattering are likely to occur. The upper limit of 9 μm is the upper limit of the particle size that enables the high image quality targeted by the present embodiment to be formed.

  As the carrier, a ferrite core carrier made of magnetic particles having a volume average particle size of 30 to 65 μm and a magnetization of 20 to 70 emu / g is preferable. Carrier adhesion tends to occur with a carrier having a particle size smaller than 30 μm. In addition, a carrier having a particle diameter larger than 65 μm may not form a uniform density image.

  Reference numeral 5 denotes a pre-transfer exposure light source which is irradiated to improve the transferability of the toner image. The light source is an LED having a light wavelength of 700 nm and is irradiated with a light output of 10 lux.

  Reference numeral 6 denotes a corotron transfer pole having a wire-to-photosensitive member distance of 8 mm and a wire-to-back plate distance of 12 mm. The toner image on the photosensitive member 1 is transferred onto the transfer paper by constant current control of a transfer current of 200 μA. Transcription.

  Reference numeral 7 denotes a corotron separation pole, which has a configuration in which the distance between the wire and the photoreceptor 1 is 8 mm and the distance between the wire and the back plate is 12 mm. The separation current of the AC component is 100 μA and the DC component is −200 μA. Encourage separation.

  The transfer paper P fed from the paper feed unit is fed in synchronism with the toner image formed on the photosensitive member 1 by the registration roller 21, and the toner image is transferred by the transfer pole 6 at the transfer nip portion. . The transfer paper P that has passed through the transfer nip is separated from the surface of the photosensitive member 1 by the separation pole 7 and is transported to the fixing device 23 by the transport belt 22.

  The fixing device 23 includes a heating roller 23a and a pressure roller 23b in which a heater is disposed. The transfer paper P holding a toner image is heated and pressed between the heating roller 23a and the pressure roller 23b. The transfer paper P, to which the toner image has been fixed, is discharged onto a discharge tray outside the apparatus by a discharge roller 24.

  On the other hand, the toner remaining on the surface of the photoreceptor 1 after the transfer of the toner image onto the transfer paper P is cleaned by the cleaning device 8. In this embodiment, a blade made of urethane rubber is used as the cleaning means, and the cleaning blade is a counter type for cleaning by sliding on the circumferential surface of the photosensitive member 1. The peripheral surface of the photosensitive member 1 whose surface has been cleaned by passing through the cleaning device 8 is irradiated by a pre-charge exposure (PCL) means 9 using a light wavelength of 700 nm and a light output of 10 lux light source to reduce the residual potential and then Shift to the image forming cycle.

  (2) Next, the developing device 4 of the present invention which performs development by being arranged in the image forming apparatus described with reference to FIG. 1 will be described.

  FIG. 2 shows a cross-sectional view of the developing device 4 of this embodiment. A first developer carrier 41 and a second developer carrier 42 are provided from the upstream side facing the photosensitive member 1, and are located close to the upstream side of the first developer carrier 41. On the downstream side of the plate-like first electrode member 43 and the second developer carrier 42, there is a plate-like second electrode member 44 located close to the plate-like first electrode member 43.

  Behind the first and second developer carriers 41 and 42, stirring members 45A, 45B, and 45C having water wheel-like stirring blades that stir the developer without having an axial conveying force. Is provided.

  The first developer carrying member 41 includes a developing roller 41A having a magnet roll 41B having a plurality of N and S magnetic poles in the circumferential direction, and having a stainless sprayed surface processed around the developing roller 41B. 41A faces the photosensitive member 1 with a gap (development gap) of 0.25 to 1.0 mm, and forms a first developing region 41G in which the developer on the developing sleeve 41A is in contact with the photosensitive member 1. . The developing sleeve 41A has an outer diameter of 15 to 40 mm, and in this embodiment has an outer diameter of 20 mm. The developing sleeve 41A rotates in the forward direction with respect to the photosensitive member 1, and the linear speed ratio with respect to the photosensitive member 1 is 1.0 to 2.5. In the embodiment, the motor rotates in the forward direction at a linear speed ratio of 1.5.

  A plurality of N and S magnetic poles of the magnet roll 41B are magnetized to a magnetic flux density of 0.05 to 0.15 T on the sleeve surface, and one of the magnetic poles is developed with the rotating shaft of the photosensitive member 1 in the first developing region 41G and the developing. A main magnetic pole is formed between 10 ° and −10 ° with respect to a line connecting the rotation axis of the sleeve 41A.

  The developing sleeve 41A is connected to a first developing bias power supply E1 that superimposes a DC voltage and an AC voltage and applies a bias voltage via a protective resistor. In this embodiment, a developing bias having a DC voltage of −500 V, an AC voltage of an effective value of 0.5 to 0.9 kV, and a vibration frequency of 1 to 5 kHz is applied. For example, it adheres to -50V) and is developed.

  The plate-like first electrode member 43 covers a nonmagnetic metal plate with an insulating film such as polyethylene to prevent discharge, and one end surface of the first electrode member 43 is a circumferential surface of the photoreceptor 1. And with a gap of 0.1 to 0.2 mm to prevent the toner from flowing through the gap to the upstream side of the developing device 4. Further, a part of the side surface of the first electrode member 43 is disposed with a gap 43G of 0.25 to 1.0 mm from the first developer carrier 41.

  The first electrode member 43 is controlled to a direct current voltage having the same polarity as the direct current voltage applied to the developing sleeve 41A and having an absolute value equal to or close to this (for example, ± 100V). A control voltage of −500 V is applied by the electrode power supply E3. By applying such a control voltage, an oscillating electric field is formed in the gap 43G, and the negatively charged toner electrostatically attached to the magnetic carrier on the developing sleeve 41A is released into a cloud shape, and the first electrode member 43 does not stick to the first developing area 41G, and part of the toner flies to the electrostatic latent image portion, and the toner density is increased to assist development.

  The second developer carrying member 42 has the same dimensions as the first developer carrying member 41, and the developing sleeve 42A rotating around the magnet roll 42B is the same as the photosensitive member 1 and 0.25 to 1.. A second developing region 42G is formed to face each other with a gap (development gap) of 0 mm, and the developing sleeve 42A rotates in the opposite direction to the photosensitive member 1, and the linear speed ratio is 1.0 to 2.5. It is rotating in the opposite direction at a linear speed ratio of 1.5.

  One of the plurality of N and S magnetic poles of the magnet roll 42B is between 10 ° and −10 ° with respect to a line connecting the rotation axis of the photosensitive member 1 and the rotation axis of the developing sleeve 42A in the second development region 42G. It has a main pole.

  The developing sleeve 42A is connected to a second developing bias power source E2 that superimposes a DC voltage and an AC voltage and applies a bias voltage via a protective resistor. In this embodiment, the second developing bias power supply E2 is shared with the first developing bias power supply E1, and the developing bias applied to the developing sleeve 42A is the same DC voltage −500 V and AC voltage as the developing bias applied to the developing sleeve 41A. Is applied with a developing bias having an effective value of 0.5 to 0.9 kV and a frequency of 1 to 5 kHz, and the toner negatively charged by frictional charging adheres to the image exposure portion and is developed and rotated in the opposite direction. Scraping with a magnetic brush is performed.

  Similarly to the first electrode member 43, the second electrode member 44 is a member obtained by coating a nonmagnetic metal plate with an insulating film such as polyethylene, and one end surface of the second electrode member 44 is a circumferential surface of the photoreceptor 1. With a gap of 0.1 to 0.2 mm to prevent the toner from flowing through the gap to the downstream side of the developing device 4. Further, a part of the side surface of the plate-like second electrode member 44 is installed with a gap 44G of 0.25 to 1.0 mm from the second developer carrier 42.

  The second electrode member 44 is controlled with a DC voltage having the same polarity as the DC voltage applied to the developing sleeve 42A and a larger absolute value. In this embodiment, the second electrode power supply E4 controls -1200V. A voltage is applied. By applying such a control voltage to the second electrode member 44, an electric field is formed in the gap 44G so as to press the toner in the free state toward the developing sleeve 42A, and the downstream direction of the rotating photoreceptor 1 is formed. The floating toner that is about to flow out of the toner is collected.

  FIG. 3 is an explanatory diagram showing the positional relationship among the first developer carrier 41, the second developer carrier 42, the first electrode member 43, and the second electrode member 44 that have already been described.

  As shown in the figure, the first developer carrier 41 and the second developer carrier 42, the first electrode member 43 and the second electrode member 44 are substantially symmetrically arranged. The two electrode members 43 and 44 are respectively attached to the upstream and downstream wall surfaces of the opening of the casing 49 that forms the outer shell of the developing device 4. When the angle formed by the flat first and second electrode members 43 and 44 and the line connecting the first and second developer carriers 41 and 42 is θ, θ is between 30 ° and 70 °. The position where the gaps 43G and 44G are formed is preferably near the development areas 41G and 42G.

  However, the first and second electrode members 43 and 44 do not necessarily have a flat plate shape. If the first electrode member 43 is illustrated, the cross-sectional shape as shown in FIG. Good. In this case, it is possible to prevent the toner from flowing out in a more complete form by widening the range of the gap portion for preventing the toner leakage facing the photoreceptor 1. In addition, since the gap 43G between the developing sleeve 41A and the first developing area 41G can be selected and set, a cloud is generated prior to development in the developing area 41G, and the toner density is increased. Development is performed more favorably.

  The first developer carrier 41 and the second developer carrier 42 that rotate in the forward direction and inward from each other are disposed with an interval of H, and the interval H is between 2 and 4 mm. This is desirable because it prevents floating toner from moving freely. In the developing areas 41G and 42G, the toner scatters in the rotation direction of the developing sleeves 41A and 42A. Therefore, in the developing range 4D indicated by the diagonal lines, there is a dense floating toner, and the electrostatic force of the photosensitive member 1 rotating at a high speed therebetween. The toner adheres to the latent image (for example, a potential portion of −50 V), and development is performed.

  Reference numerals 461 and 462 denote layer thickness regulating members. The developer agitated by the agitating members 45A, 45B, and 45C in the developer reservoir 49D, and the toner that has been agitated and frictionally charged adheres to the magnetic carrier is attracted to the developing sleeves 41A and 42A by a magnetic force, Although the layers are formed, the layer thickness regulating members 461 and 462 regulate the thickness of the developer layer adhering to the outer periphery of the developing sleeves 41A and 42A to a thickness suitable for developing in the developing regions 41G and 42G.

  (3) In the developing device 4 of the present invention, even when developing using a developer containing a polymerized toner having a volume average particle size of 3 to 9 μm, the development is performed in cooperation with the developing regions 41G and 42G. In addition, since cloud-like toner is generated on the upstream side of the development area 41G to assist development, high resolution can be achieved even when used as a developing device of an image forming apparatus that performs high-speed print processing with high image quality. Thus, it is possible to provide a clean image forming apparatus in which a necessary image density is obtained and a good image free from image smearing is formed and the toner is not discharged from the developing device 4 and contaminates the inside of the apparatus.

1 is a cross-sectional configuration diagram of an image forming apparatus. Sectional drawing of a developing device. FIG. 3 is an explanatory diagram showing the arrangement relationship of members in the developing device. Sectional drawing which shows one Example of an electrode member.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor 4 Developing apparatus 41 1st developer carrier 41A Developing sleeve 41B Magnet roll 42 2nd developer carrier 42A Developing sleeve 42B Magnet roll 43 1st electrode member 44 2nd electrode member 45A, 45B, 45C Stirring member 49 Housing 461, 462 Layer thickness regulating member

Claims (4)

An image carrier;
A first developer carrier which is upstream of the image carrier and rotates in the forward direction;
A second developer carrier that is downstream in the rotational direction of the image carrier and rotates in the opposite direction;
A plate-like first electrode member disposed upstream of the first developer carrier and disposed in proximity to the image carrier and the first developer carrier;
A plate-like second electrode member disposed on the downstream side of the second developer carrier and in proximity to the image carrier and the second developer carrier;
A developing device comprising: A developing bias in which a DC voltage and an AC voltage are superimposed is applied to the first developer carrier and the second developer carrier, so that the latent image formed on the image carrier is developed. The developing device according to claim 1, wherein: The first electrode member is applied with a control voltage having the same polarity as the direct current voltage applied to the first developer carrier and having an absolute value equivalent to or close to the absolute value.
3. The development according to claim 2, wherein a control voltage having the same polarity as the DC voltage applied to the second developer carrying member and having a larger absolute value is applied to the second electrode member. apparatus. In an image forming apparatus having an image carrier and a developing device that visualizes the electrostatic latent image formed on the image carrier using a two-component developer,
In the developing device, a first electrode member, a first developer carrier, a second developer carrier, and a second electrode member are disposed from the upstream side in the vicinity of the image carrier.
The first developer carrier rotates in the forward direction, the second developer carrier rotates in the opposite direction, and a development bias in which a DC voltage and an AC voltage are superimposed on each is applied.
The first electrode member is a plate-like member that is also close to the first developer carrier, and has the same polarity as the DC voltage applied to the first developer carrier, and an absolute value equal to or close to the control voltage. The second electrode member is a plate-like member close to the second developer carrier, and has the same polarity as the DC voltage applied to the second developer carrier and has a larger absolute value. An image forming apparatus to which a control voltage is applied.

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