JP2006293259A - Developing apparatus, process cartridge and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing apparatus, a process cartridge and an image forming apparatus which can reuse toner, suppress increase in toner aggregation and decrease in the charging performance of the reused toner, and prevent deposition of a toner on an electrostatic conveying member. <P>SOLUTION: The developing apparatus 10 is equipped with a developing unit 20 to carry out development, a toner recovering unit 30 to recover residual toner, and a conveying unit 40 to send the residual toner recovered by the toner recovering unit to the developing unit so as to reuse the residual toner. Further, fluidity and charging property of a residual toner are recovered by adding rubbing force required for charging the toner or adding inorganic fine particles in the conveying unit 40. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a developing device, a process cartridge, and an image forming apparatus, and more particularly to a developing device, a process cartridge, and an image forming apparatus that collect residual toner after transfer and reuse it.

  In recent years, in electrostatic copying image forming apparatuses, attention has been paid to a technique for collecting and reusing residual toner remaining on a photoconductor after toner image formation in consideration of environmental considerations and running costs.

  However, since the toner easily deteriorates, when the collected residual toner is reused, there is a possibility that an adverse effect such as deterioration of a formed image may occur.

  By the way, in a developing device using an electrostatic conveyance member that moves toner particles by a phase-shift electric field, if the electrostatic conveyance member becomes dirty due to adhesion of toner particles, the toner particle conveyance efficiency is reduced and stable image formation is achieved. Will not be able to. Therefore, a mechanism for removing the toner particles adhering to the electrostatic transport member is necessary.

  Since the electrostatic transfer member itself does not rotate, it is difficult to peel off the adhered toner particles with a physical force / external device. Therefore, the toner particles adhering to the electrostatic conveyance member are removed using a phase-shift electric field formed by the electrostatic conveyance member.

  However, when the toner particles attached using a phase electric field are removed, it is difficult to remove the toner particles if the toner particles are weakly charged or uncharged. Further, even if the toner particles are sufficiently charged, it is difficult to transport and remove the toner particles by a phase-shifting electric field when the non-electrostatic adhesion force of the toner such as Van der Waals force is large or when the cohesion is high.

  In particular, those that recycle residual toner tend to lose their fluidity and chargeability, and such problems are likely to occur. Then, how to solve such a problem is considered.

  As a technology related to the developing device, a developing device technology that does not require a complicated toner density control device or the like and has less space and position restrictions formed by the unused developer accommodating portion, and a plurality of electrodes arranged at predetermined intervals Patent Documents 1 and 2 propose a developing device technology that conveys a developer by applying a multiphase voltage to form a traveling wave electric field.

  However, these techniques do not provide any solution to the above problems.

Further, as a method for solving the above-mentioned problems, there is a method of supplying toner / polluting substances using a magnetic brush developing method. In this method, an excessive force is applied to the toner by a magnetic force or a magnetic brush contact portion. As a result, the stability over time is impaired.
JP-A-8-185051 Japanese Patent No. 3530124

  The present invention has been made in view of the above-described problems. The toner can be reused, and an increase in toner cohesiveness and a decrease in charging performance of the reused toner are suppressed. An object of the present invention is to provide a developing device, a process cartridge, and an image forming apparatus that can prevent the toner from adhering.

  The invention according to claim 1 is a developing device that conveys toner to a photosensitive member using an electrostatic conveying member, and develops an electrostatic latent image on the photosensitive member with the toner to form a toner image. A residual toner remaining on the photoreceptor after transfer of the toner image, and mixing and stirring the recovered residual toner; and the recovered and mixed and stirred residual toner; And a conveying unit that conveys the toner from the toner collecting unit to the toner storage unit in the developing unit.

  According to a second aspect of the present invention, in the developing device according to the first aspect, the transport unit is a mono pump.

  According to a third aspect of the present invention, there is provided the developing apparatus according to the first or second aspect, further comprising an external additive adding portion for adding an inorganic fine particle external additive to the collected residual toner.

  According to a fourth aspect of the present invention, in the developing device according to the third aspect, the inorganic fine particle external additive contains at least silica.

  According to a fifth aspect of the present invention, in the developing device according to the fourth aspect, the silica is silica having a particle size of 10 to 30 nm.

  According to a sixth aspect of the present invention, in the developing device according to the fourth aspect, the inorganic fine particle external additive contains 0.1 to 1.0% by mass of silica having a particle size of 10 to 30 nm, and the particle size Is characterized by containing 0.5 to 2.0% by mass of silica of 50 to 200 nm.

  A seventh aspect of the present invention is the developing apparatus according to the fifth or sixth aspect, wherein the inorganic fine particle external additive contains 0.1 to 0.7 mass% of titanium oxide.

  According to an eighth aspect of the present invention, in the developing device according to any one of the third to seventh aspects, the external additive adding section is provided in the vicinity of a feeding port of the transport section. .

  According to a ninth aspect of the present invention, in the developing device according to any one of the third to seventh aspects, the external additive adding section is provided in a transport path inside the transport section. .

  According to a tenth aspect of the present invention, in the developing device according to any one of the third to seventh aspects, the external additive adding portion is provided in the vicinity of the portion where the mixing and stirring is performed in the toner recovery portion. It is characterized by being.

  According to an eleventh aspect of the present invention, in the developing device according to any one of the first to tenth aspects, the toner has an average circularity of particles of 0.98 to 1.00.

  According to a twelfth aspect of the present invention, at least one of a photosensitive member, a charging unit, and a transfer unit and the developing device according to any one of the first to eleventh aspects are integrated to form an image forming apparatus. It is a process cartridge that can be attached and detached.

  A thirteenth aspect of the present invention is an image forming apparatus comprising the developing device according to any one of the first to eleventh aspects.

  According to a fourteenth aspect of the present invention, there is provided an image forming apparatus having the process cartridge according to the twelfth aspect.

  According to the present invention, the developing device includes a developing unit that performs development, a toner collecting unit that collects residual toner, and a transport unit that sends the residual toner collected in the toner collecting unit to the developing unit. Can be reused. In addition, since the rubbing force necessary for charging the toner can be applied in the transport unit, it is possible to suppress the problem of toner deterioration during reuse.

  In addition, since the inorganic fine particles are added to the toner to be reused, the fluidity and chargeability of the reused toner can be recovered. Therefore, it is possible to suppress the occurrence of an abnormal image due to contamination of the electrostatic conveyance member due to charging failure, and it is possible to provide a long-life image forming apparatus that is highly stable in operation over time. Further, it is possible to efficiently supply toner, and it is possible to give the developing device high-speed response that can cope with a solid image or the like under high-speed driving.

<Developing device>
With reference to FIG. 1, the structure of the developing device of this embodiment will be described. The developing device 10 according to the present embodiment includes a developing unit 20, a toner recovery unit 30, and a transport unit 40.

  The developing unit 20 develops the electrostatic latent image on the photoconductor 11 with toner (developer) to form a toner image. The electrostatic latent image is formed by irradiating the photoconductor 11 charged by the charging device 12 with the writing light from the writing device 83. The toner collecting unit 30 collects the toner remaining on the photoconductor 11 after the toner image is transferred to the output paper. The conveying unit 40 conveys the residual toner collected by the toner collecting unit 30 to the developing unit 20 as a reuse toner.

<Developer>
In the developing device 10 of the present embodiment, a mixture of toner particles and a carrier is used as a developer. The toner particles are nonmagnetic particles having a volume average particle diameter of about 2 to 5 μm, and the carrier is magnetic particles.

<Toner particles>
The toner particles include those obtained by radical polymerization of a styrene or acrylic polymerizable monomer as a binder resin dispersed in water together with a polymerization initiator, or a polyester resin dispersed in water and subjected to a polyaddition reaction. Particles obtained by granulating by adding a colorant, a charge control agent, etc. to the molecularized material are used.

  There is a parameter called “average circularity” as a parameter indicating the characteristics of toner particles. The average circularity is the value obtained by dividing (division) the circumference of an equivalent circle (circumference length) with the same shape and projection area of the object by the circumference of the actual object. It is a real value that serves as a guideline for determining whether or not. “Average circularity = 1.00” indicates a perfect circle, and as it decreases from this value, it becomes different from the shape of a perfect circle.

  The toner particles used in the developing device 10 of this embodiment preferably have an average circularity of 0.98 to 1.00. That is, it is preferably a substantially spherical body. With such toner particles, the toner can be supplied efficiently.

  As a test result to support this, in the A3 version black solid image creation test with a modified “IMAGIO COLOR 5100 (our product)” in which the average circularity of the toner particles is within this range, the toner is free from abnormal images. It has been confirmed that replenishment was possible. When the average circularity is less than 0.98, satisfactory toner supply is not performed in the development process, and therefore, insufficient toner supply when creating a solid image (filled image) with a large amount of toner consumption. As a result, a spot-like abnormal image was generated due to a decrease in image density and a change in charge amount.

  Although the precise reasoning why the average circularity of the toner particles is within the above range increases the toner replenishment efficiency is still under investigation, spherical toner rolls more than irregular toner. This is presumably because, since the friction is low and the roller is easy to roll, it is possible to ensure the replenishment follow-up property for a large amount of toner consumption when a solid image is formed in the developing device using the electrostatic conveyance method.

  This average circularity can be measured, for example, by passing a suspension containing toner particles through an imaging unit detection zone on a flat plate, optically detecting a particle image with a CCD camera, and analyzing the particle image. . Further, it can be easily measured by a measuring apparatus such as a flow type particle image analyzer FPIA-2100 (manufactured by Sysmex Corporation).

<Career>
As the carrier, a resin magnetic carrier in which a magnetic material generated by a polymerization method including at least a binder resin and a magnetic metal oxide and a nonmagnetic metal oxide is dispersed is used. Specifically, magnetite (Fe ₃ O ₄ ) is used as a magnetic metal oxide, and a vinyl resin such as styrene or ethyl acrylate is polymerized as a binder resin for dispersing and binding the metal oxide. Resin is used.

  In addition, a carrier in which a magnetic material is dispersed in a binder resin can be used as it is. Also, a coated magnetic carrier in which a carrier in which a magnetic material is dispersed in a binder resin is used as a carrier core, and the surface of the carrier core is coated with an insulating resin can be used.

Note that if a magnetic carrier having a magnetization amount of less than ³⁰ emu / cm ³ in a 1 kilo-Oersted magnetic field is used, the developer transport performance is lowered. Therefore, the magnetization of the magnetic carrier, 30 emu / cm ³ or more and preferably is 80 emu / cm ³ or more.

In addition, if the magnetization amount is low magnetization of 200 emu / cm ³ or less, the magnetic interaction between adjacent magnetic brushes becomes small, so that the ears of the magnetic brush to be formed can be made dense and short, Uniform toner particles can be supplied to the electrostatic conveyance member 21. Therefore, the magnetization amount of the magnetic carrier is preferably 200 emu / cm ³ or less, more preferably 140 emu / cm ³ or less.

  The amount of magnetization of the magnetic carrier can be determined by placing the magnetic carrier packed in a cylindrical container in a 1 kilo-Oersted external magnetic field using an oscillating magnetic field type automatic magnetic recording device manufactured by Riken Denshi Co., Ltd. It can be calculated by multiplying the measured magnetization strength by the true specific gravity of the carrier.

<Carrier specific gravity / Toner specific gravity>
The carrier specific gravity / toner specific gravity is preferably 2 or more and 8 or less. This is because, when the carrier specific gravity / toner specific gravity is 2 or less, free toner is taken into the conveying unit 40, and toner scattering occurs, which adversely affects the resultant image. Further, when the carrier specific gravity / toner specific gravity is 8 or more, the stirring energy at the time of developing the developer becomes too large, and the fluidity due to the deformation of the toner, the burying of the external additive, etc. This is because a reduction in the conveyance efficiency of the toner to be conveyed occurs, resulting in a decrease in image density.

  Next, the configuration and operation control of each part of the developing device 10 will be specifically described.

<Development part>
First, the developing unit 20 will be described. The developing unit 20 includes an electrostatic conveyance member 21, a supply roller 22, a doctor blade 23, and a stirring screw 24.

  The agitating screw 24 agitates the developer (toner, carrier) in the developing unit 20 and pumps the developer to the supply roller 22. The supply roller 22 transports the developer pumped up by the stirring screw 24 to the electrostatic transport member 21. The doctor blade 23 regulates the amount of developer supplied to the electrostatic transport member 21 by the supply roller 22. The electrostatic conveyance member 21 conveys the developer conveyed from the supply roller 22 to the photoconductor 11.

  Hereinafter, the structure of each mechanism of the developing unit 20 will be described in detail.

<Electrostatic transfer member>
The electrostatic transport member 21 is opposed to the photosensitive member 11 in a non-contact manner with a gap of 50 to 1000 μm, more specifically 150 to 400 μm.

  With reference to FIG. 2, the structure of the electrostatic conveyance member 21 is demonstrated. FIG. 2 shows a cross section of the electrostatic transfer member 21. The electrostatic transport member 21 has a structure in which a plurality of electrodes 52 are arranged on a support substrate 51 at a predetermined interval along the toner moving direction, and a surface protective layer 53 is laminated thereon.

  The support substrate 51 is a substrate made of an insulating material such as a glass substrate, a resin substrate, or a ceramic substrate, or a substrate made of an electrically conductive material such as SUS, and a flexible film such as a polyimide film. It consists of a substrate made of a deformable material.

  The electrode 52 is formed of a conductive material such as Al or Ni—Cr on the support substrate 51 in a thickness of 0.1 to 10 μm, preferably 0.5 to 2.0 μm, and this is formed into a required electrode shape by photolithography technology or the like. It is formed by patterning. In this embodiment, the width of the electrode 52 with respect to the developer traveling direction is set to 1 to 20 times the average particle diameter of the developer, and the interval between the electrodes 52 in the developer traveling direction is also equal to the average particle diameter of the developer. 1 to 20 times.

The surface protective layer 53 is formed of, for example, SiO ₂ , TiO ₂ , TiO ₄ , SiON, BN, TiN, Ta ₂ O _5, etc. with a thickness of 0.5 to 10 μm, preferably 0.5 to 3 μm. Is formed.

  The circumferential surface of the electrostatic transport member 21 is divided into two regions, a “transport region” and a “development region”. In the transport region, toner particles are transported to the vicinity of the photoconductor 11 and toner particles that have not contributed to development after passing through the development region are collected. In the development area, toner particles are attached to the latent image on the photoconductor 11 to form a toner image. The development area indicates an area close to the photoreceptor 11, and the conveyance area indicates an area other than the development area on the circumference of the electrostatic conveyance member 21.

  The power supply unit 54 applies drive voltages having different n phases to the electrode 52. This n is an arbitrary natural number satisfying n> 2.

  The electrodes 52 are respectively connected to the contacts of the power supply unit 54, and drive waveforms V11, V12, and V13 are applied from the power supply unit 54 to the respective electrodes 52 in the transport region, and the drive waveforms V21 are applied to the respective electrodes 52 in the development region. , V22, V23 are applied. In the figure, among the overlapping portions of each line, the portion indicated by a black circle indicates a state where it is electrically connected, and the other portion indicates a state where it is not electrically connected.

<Principle of electrostatic conveyance>
Next, the principle of electrostatic conveyance of the toner of the electrostatic conveyance member 21 will be described with reference to FIGS. The electrostatic conveyance is to generate a phase-shift electric field (traveling wave electric field) and to convey the toner by using the repulsive force / attraction force of the charged toner against the electric field. Specifically, the toner is obtained by applying a voltage so that the upstream adjacent electrode is repelled and the downstream adjacent electrode is attracted to the target electrode and the upstream adjacent electrode and the downstream adjacent electrode in the traveling direction. Transport.

  The phase electric field is generated when an n-phase driving waveform is applied to the electrode 52 of the electrostatic transfer member 21. Specifically, as shown in FIG. 3, it is generated by applying a three-phase pulse drive waveform that changes between the ground G (0 V) and the positive voltage + to the electrode 52 at different timings. In FIG. 3, it can be seen that voltage application of “G”, “G”, and “+” is periodically performed.

  FIG. 4 shows a timing chart of electrostatic conveyance. When “G”, “G”, “+”, “G”, and “G” are respectively applied to the continuous electrodes 52 a to 52 e of the electrostatic conveyance member 21 (time 1), the negatively charged toner T is “+ ”On the electrode 52c. When “+”, “G”, “G”, “+”, and “G” are respectively applied to the electrodes 52 a to 52 e at the next timing (time 2), the negatively charged toner T is “G”. Since the repulsive force with the electrodes 52b and 52c and the attractive force with the electrode 52d which is “+” act, it moves to the electrode 52d. Furthermore, when “G”, “+”, “G”, “G”, and “+” are applied to the electrodes 52 a to 52 e at the next timing (time 3), “G” is applied to the negatively charged toner T. Since the repulsive force with the electrodes 52c and 52d and the attractive force with the electrode 52e that is “+” act, it moves to the electrode 52e.

  By applying a multi-phase driving waveform whose voltage changes to the electrode 52 in this way, a traveling wave electric field is generated in the electrostatic transport member 21, and the negatively charged toner moves in the traveling direction of the traveling wave electric field. In the case of positively charged toner, if the drive waveform change pattern is reversed, the toner moves in the same direction.

  In the developing device 10 of the present embodiment, in the “transport region” of the electrostatic transport member 21, the driving waveform shown in FIG. 5, that is, the application time ta of +100 V is approximately 33% which is 1/3 of the repetition period tf. Are applied as V11, V12, and V13. This waveform is called a “carrier voltage pattern”. It is known from the applicant's research that the transport voltage pattern is a waveform suitable for high-speed transport of toner particles in the transport region.

  In the “development area”, the driving waveform shown in FIG. 6, that is, a three-phase driving waveform in which the +100 V application time ta is set to about 67%, which is 2/3 of the repetition period tf, is applied as V21, V22, and V23. . This drive waveform is called a “development voltage pattern”. In the development area, it is necessary to positively launch toner particles toward the image carrier. However, it has been found from the applicant's research that this development voltage pattern is suitable for launching toner particles.

  Even when the development voltage pattern is applied, since the toner is also subjected to a lateral force other than the toner positioned at the center of the 0V electrode, not all the toners are launched at the same time, and the toner moving in the horizontal direction is also included. Exists. Even when the drive waveform of the carrier voltage pattern is applied, depending on the position of the toner, the toner may be launched obliquely at a large angle, and the rising distance may be larger than the horizontal movement. Therefore, the drive waveform pattern applied to each electrode 52 in the transport region is not limited to the transport voltage pattern shown in FIG. Further, the drive waveform pattern applied to each electrode 52 in the development region is not limited to the development voltage pattern shown in FIG.

  In the above description, the case of n = 3, that is, the case of three layers has been described, but this will be generalized to n phase.

  When an n-phase (n is an integer of 3 or more) pulsed voltage (driving waveform) is applied to each electrode 52 to generate a traveling wave electric field, the voltage application time per phase {repetition period time × ( n-1) / n} The voltage application duty is set to be less than n−1) / n}. Thereby, the efficiency of conveyance and development can be increased. For example, when a three-phase drive waveform is used, the voltage application time ta of each phase is set to less than about 67%, which is 2/3 of the repetitive cycle time tf, and when a four-phase drive waveform is used, The voltage application time for each phase is set to less than 75%, which is 3/4 of the repetition cycle time.

  The voltage application duty is set to {repetition cycle time / n} or more. For example, when a three-phase driving waveform is used, the voltage application time ta of each phase is set to about 33% or more which is 1/3 of the repetition cycle time tf. As described above, when the driving frequency is high and the voltage application duty is set within the range of {repeat cycle time / n} or more and less than {repeat cycle time × (n−1) / n}, the toner on the electrode of interest. It becomes easy to obtain the initial speed with respect to.

  The above description is based on one form of the electrostatic conveyance member 21, but is not limited to the above form as long as desired conveyance / development performance can be obtained. Therefore, even if the distance between the electrodes 52 is different between the development area and the transport area to adjust the direction of the electric field, the distance between the electrodes and the drive waveform may be the same in the development area and the transport area.

<Supply roller>
Next, the supply roller 22 will be described with reference to FIG. On the surface of the supply roller 22, a nonmagnetic sleeve 61 is formed in which a nonmagnetic material such as aluminum, brass, stainless steel, or conductive resin is formed in a cylindrical shape. The nonmagnetic sleeve 61 is configured to be rotatable and is driven to rotate clockwise.

  Inside the supply roller 22, a magnet roller body 62 that forms a magnetic field is provided in a fixed state so as to cause a rise of developer on the peripheral surface of the nonmagnetic sleeve 61.

  A magnetic field is generated along the normal line of magnetic force emitted from the magnet roller body 62, and the developer carrier rises in a chain shape on the nonmagnetic sleeve 61. A magnetic brush is formed by the charged toner adhering to the carrier having such chain-like spikes. The magnetic brush is formed in a portion where the supply roller 22 and the electrostatic conveyance member 21 face each other, and is conveyed in the same direction as the rotation direction as the supply roller 22 rotates.

  The magnet roller body 62 includes a plurality of magnets 63, and a magnetic field is generated by the magnets 63. However, the magnets 63 do not generate a uniform magnetic field, but generate different magnetic fields. This point will be specifically described with reference to FIG.

  FIG. 8 is a diagram for explaining a magnetic field generated by each magnet 63. A curve in the figure represents a magnetic field (normal magnetic force pattern) generated by the magnet 63. In addition, “S” and “N” in the drawing indicate that the polarities of the surface of the supply roller 22 of each magnetic field are the S pole and the N pole, respectively.

  The supply roller 22 of this embodiment has six magnets 63a to 63e, and each magnet generates a magnetic field of P1 to P6, respectively.

  The magnetic field indicated by P <b> 1 causes developer spikes on the surface of the nonmagnetic sleeve 61 of the supply roller 22. The magnetic fields represented by P4 and P5 pump the developer to the nonmagnetic sleeve 61. The magnetic field represented by P6 conveys the developer pumped up by the magnetic fields P4 and P5 to the magnetic field region P1. The magnetic field represented by P2 conveys the developer in the area after P1, and the magnetic pole of P3 separates the developer from the nonmagnetic sleeve 61.

  In the present embodiment, the magnet roller body 62 includes six magnets 63, but is not limited to such a configuration, and includes eight or twelve magnets 63. It may be.

<Doctor blade>
The doctor blade 23 will be described with reference to FIG. The doctor blade 23 is provided on the developer conveyance route of the supply roller 22, and regulates the height of chain-like spikes generated on the supply roller 22, that is, the amount of developer on the nonmagnetic sleeve 61. In the present embodiment, the doctor gap, which is the distance between the doctor blade 23 and the nonmagnetic sleeve 61, is set to 0.4 mm.

<Agitating screw>
The stirring screw 24 will be described with reference to FIG. The agitating screw 24 agitates the developing casing in which the developer is stored, and pumps up to the supply roller 22.

<Toner recovery unit>
Next, the toner recovery unit 30 will be described with reference to FIG. The toner collection unit 30 includes a cleaning blade 31, a waste toner storage unit 32, and a mixing and stirring screw 33.

  The cleaning blade 31 is in contact with the surface of the photoconductor 11 and collects toner particles (including carrier) remaining on the photoconductor 11 after the toner image is transferred. The waste toner storage unit 32 stores the toner particles collected by the cleaning blade 31. The mixing and stirring screw 33 is a screw provided in the waste toner storage unit 32, and performs mixing and stirring of toner particles and sending the toner particles to the conveying unit 40.

  In this embodiment, a blade cleaning system that collects toner particles using the cleaning blade 31 is employed. However, the present invention is not limited to the blade cleaning system, and the brush cleaning system, the belt cleaning system, and the bias application. The electrostatic cleaning method may be used. Further, a combination of a plurality of these cleaning methods may be used.

<Transport section>
Next, the transport unit 40 will be described with reference to FIG.

  The transport unit 40 spatially connects the waste toner storage unit 32 of the toner collection unit 30 and the developing unit 20, and sends the used developer in the waste toner storage unit 32 to the development unit 20.

  By configuring the developing device 10 in this way, the toner circulates semi-permanently in the developing device 10 until it is transferred onto the output paper, so that it is possible to reuse the toner and to efficiently use the toner. .

  In addition, it is preferable that the toner conveyed from the toner recovery unit 30 is sent to a developer storage unit provided with the stirring screw 24 of the development unit 20. With such a configuration, it is possible to increase the dispersion efficiency of the toner to be reused and to prevent the occurrence of image unevenness.

  As the transport unit 40, a member having a mechanism capable of delivering and circulating the developer can be used, and a “Mono pump” is particularly preferable. A Mono pump is a pump that pressurizes a fluid to deliver the fluid from the inlet to the outlet. When a Monopump is used as the conveyance unit 40, an appropriate rubbing force can be applied between the toner as the developer and the carrier, and the charge amount of the toner can be stabilized.

  In addition, when using a MONO pump as the conveyance part 40, it is preferable that the time required for MONO pump passage is 3 seconds or more and 10 seconds or less. If the required time is 3 seconds or less, it is difficult to sufficiently obtain the effect of imparting the rubbing force. If the required time is 10 seconds or more, stable toner charging can be obtained, but the inorganic fine particle external additive is buried. It is because it becomes easy to progress.

<External additive>
In addition, when the residual toner is circulated to the developing unit 20 via the conveying unit 40, inorganic fine particles may be added as an external additive. By mixing the inorganic fine particle external additive with the toner, the external additive recoats the surface of the toner particles that have been buried or peeled and deteriorated, so that the fluidity and charging performance of the toner particles can be recovered, It becomes possible to use the recycled toner while recycling the deteriorated toner.

  As the inorganic fine particle external additive, silica having a particle size of 10 to 30 nm (hereinafter referred to as “silica A”) is used. By using silica A having such a particle size range as an external additive, fluidity is improved and a stably charged toner can be obtained.

  When silica outside the above range is used, it is not preferable because the chargeability decreases with an increase in the degree of aggregation of the toner and the chargeability increases by 50 μC / g or more, and abnormal images are likely to occur.

  As the inorganic fine particle external additive, silica A and silica having a particle size of 50 to 200 nm (hereinafter referred to as “silica B”), silica A added in an amount of 0.1 to 1.0% by mass, silica B Can be used in a mixed amount of 0.5 to 2.0% by mass. Further, silica A or a mixture of silica A and silica B containing 0.1 to 0.7% by mass of titanium oxide can also be used. By using an external additive formulated in this range, the stability to the environment is improved, and the amount of charge is less likely to be unstable even when the temperature and humidity environment changes, so that the occurrence of abnormal images can be suppressed. It becomes possible.

  In the combination containing no silica A, the desired effect of recovering the deteriorated toner was not observed, and the fluidity and chargeability could not be improved.

  The addition mechanism for adding the external additive as described above can be provided in the vicinity of the inlet of the transport unit 40 or on the transport path in the transport unit 40. 9 shows the developing device 10 provided with an external additive addition unit 41 as an external additive addition mechanism in the vicinity of the inlet of the conveyance unit 40, and FIG. 10 shows the external additive addition unit 41 on the passage path in the conveyance unit 40. 1 shows a developing device 10 provided with.

  The external additive addition unit 41 can also be provided in the waste toner storage unit 32 of the toner recovery unit 30. FIG. 11 shows the developing device 10 in which the external additive addition unit 41 is provided in the waste toner storage unit 32. By comprising in this way, it becomes possible to disperse | distribute an inorganic fine particle external additive efficiently. At this time, if the external additive adding portion 41 is provided in the vicinity of the mixing and stirring screw 33, the external additive can be dispersed more efficiently.

<Process cartridge>
Next, a process cartridge using the developing device of this embodiment will be described with reference to FIG.

  In FIG. 11, the developing device 10, the photoconductor 11, and the charging device 12 are integrated to form a process cartridge 70. The process cartridge 70 is provided with a writing light path for guiding the writing light to the photoconductor 11.

  When writing light is irradiated from the writing device onto the photosensitive member 11 charged by the charging device 12, an electrostatic latent image is formed on the photosensitive drum 11. The electrostatic latent image is developed by the developing unit 20 of the developing device 10 to form a toner image, and the toner image is transferred onto the output paper. The toner recovery unit 30 cleans the photoreceptor 11 after transfer and reuses the toner.

  The process cartridge 70 is configured to be detachable from the image forming apparatus. Therefore, maintenance can be easily performed by removing the process cartridge 10 from the image forming apparatus and replacing it with a new process cartridge 70 during maintenance.

  In FIG. 12, the developing device 10, the photoconductor 11, and the charging device 12 are integrated to form the process cartridge 20, but the configuration of the process cartridge 20 is not limited to this configuration. Any configuration may be adopted as long as at least one of the photosensitive member, the charging device, and the transfer device is provided and integrated in the vicinity of the periphery of the developing device 10.

<Image forming apparatus>
Next, an image forming apparatus using the developing device 10 of the present embodiment will be described with reference to FIG.

  The image forming apparatus 80 includes a document table 81, a reading device 82, a writing device 83, a developing device 10 (C, M, Y, K), a photoconductor 11, a transfer device 84, a fixing device 85, A paper discharge roller 86, a paper discharge tray 87, a paper feed roller 88, and a paper feed tray 89 are configured. C, M, Y, and K are cyan, magenta, yellow, and black, respectively, and a color image is formed by arranging these toners in a superimposed manner.

  The reading device 82 reads the image data of the document placed on the document table 81 and transmits the read image data to the writing device 83 as an image signal. The writing device 83 irradiates a writing laser (writing light) based on the image signal to form an electrostatic latent image on the photoconductor 11. The developing device 10 develops the electrostatic latent image on the photoconductor 11 to form a toner image. The toner image is transferred by the transfer device 84 to the output paper conveyed from the paper feed tray 89 by the paper feed roller 88. The fixing device 85 thermally fixes the toner image transferred onto the sheet, and the output sheet on which the toner image is thermally fixed is discharged onto a discharge tray 87 via a discharge roller 86.

  Since the image forming apparatus 80 includes the above-described developing device 10 capable of reusing residual toner as the developing device 10, the toner can be recycled and a long-life image forming apparatus that is highly stable in operation over time is provided. be able to.

  In the image forming apparatus 80 described above, the developing device 10 may be configured as an integrated process cartridge provided with at least one of a photoreceptor, a charging device, and a transfer device. With this configuration, maintenance and replacement work can be easily performed.

<Additional notes>
The above-described embodiment is merely an example of a preferred embodiment of the present invention, and is not intended to limit the embodiment of the present invention. Therefore, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention.

  An embodiment of the developing device of the present invention will be described.

<Configuration>
In the developing device 10 of this embodiment, toner particles having an average circularity of 0.995 are used. The toner particles having an average circularity of 0.995 are the irregular toner used in “IMAGE COLOR 5100 (our product)” (toner base: polyol resin, weight average particle size [Dv] 6.9 μm, number average) Particle size [Dn] 5.8 μm, Dv / Dn = 1.19, average circularity 0.89, black) is passed through a thermal spheronizer that creates a hot air temperature atmosphere of 150 ° C., and this is pneumatically classified It is produced by repeating the process of classifying with a machine several times.

Further, a resin magnetic carrier is used as the carrier, specifically, magnetite (Fe ₃ O ₄ , volume average particle size 50 μm) is used as the magnetic metal oxide, and styrene or acrylic is used as the binder resin for dispersing and binding the metal oxide. A resin obtained by polymerizing a vinyl monomer such as ethyl acid is used, and a coated magnetic carrier in which an insulating resin is coated thereon is used as a carrier core. The amount of magnetization of this magnetic carrier is 120 emu / cm ³ .

  The electrostatic transport member 21 and the photoconductor 11 in the developing device 10 are installed so as to face each other in a non-contact manner with a gap of 350 μm.

The electrostatic transport member 21 has an electrode 52 made of ITO (Indium Tin Oxide / Indium Tin Oxide) disposed on a glass support substrate 51 at a predetermined interval along the moving direction of the toner, and has a surface protection thereon. The layer 53 is formed by laminating 0.5 μm of SiO ₂ .

  Further, in the “transport area” of the electrostatic transport member 21, the application time ta of +100 V for each phase is set to about 33%, which is 1/3 of the repetition period tf, as shown in FIG. Specifically, tf is set to 0.83 milliseconds and ta is set to 0.27 milliseconds.

<Comparison test>
In the image forming apparatus 70 using the developing device 10 of the present embodiment described above, the following test was performed in order to measure the developing characteristics. The following test was also performed on the image forming apparatus 70 using the developing device 10 ′ that differs from the above-described developing device 10 only in the value of the average circularity in the range of 0.89 to 0 · 98. Note that the base image forming apparatus 70 is “IMAGE COLOR 5100”.

  The first test is a black solid image output test that outputs a black solid image as a print image and measures the quality of the output black solid image. The quality of the output black solid image was quantitatively evaluated by an image densitometer “X-rite”. When the image density is 0.8 or more, the image is a good solid image (FIG. 14 / O), and when it is less than 0.2, the image is unusable (FIG. 14 / X). Further, when the image density is 0.2 to 0.8, the image can be used, but the image cannot be recommended in terms of image quality (FIG. 14 / Δ).

  The second test is a test in which the output operation is stopped in the process of outputting an image, the toner particles conveyed to the development area are sampled by the suction method, and the amount of the sampled toner particles is measured thereby. The amount of toner particles sampled here is hereinafter referred to as “toner scooping amount”.

FIG. 14 shows a graph representing the correlation between the average circularity and the toner pumping amount, which is obtained from the measurement results of the above two tests. From this graph, the density of the solid image depends on the toner pumping amount, a good image can be formed when the pumping amount is 0.8 mg / cm ² or more, and the toner pumping amount is correlated with the average circularity of the toner particles. It can be seen that high circularity toner may be used to maintain a high pumping amount.

  Further, the image forming apparatus 70 using the developing device 10 of this embodiment having an average circularity of 0.995 is more than the image forming apparatus using the developing device 10 ′ using toner particles having an average circularity smaller than this. It can be seen that a good solid image can be formed.

It is a figure which shows the structure of a developing device. It is a figure which shows the structure of an electrostatic conveyance member. It is a figure for demonstrating the principle of electrostatic conveyance. It is a figure which shows the timing chart of electrostatic conveyance. It is a figure which shows the waveform of an "electrostatic conveyance pattern." It is a figure which shows the waveform of a "developing voltage pattern." It is a figure which shows the structure of a supply roller. It is a figure for demonstrating the magnetic field of a supply roller. FIG. 6 is a diagram illustrating a developing device in which an external additive supply unit is provided in an introduction unit of a conveyance unit. FIG. 5 is a diagram illustrating a developing device provided with an external additive replenishment unit on a passage path in a conveyance unit. FIG. 4 is a diagram illustrating a developing device in which an external additive supply unit is provided in a waste toner storage unit. It is a figure which shows a process cartridge. 1 is a diagram illustrating an image forming apparatus. It is a graph showing the correlation between the average circularity and the toner pumping amount.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Developing apparatus 11 Photoconductor 20 Developing part 30 Toner collecting part 40 Conveying part 41 External additive replenishing part 70 Process cartridge 80 Image forming apparatus

Claims (14)

A developing device that transports toner to a photoreceptor using an electrostatic transport member,
Developing an electrostatic latent image on the photosensitive member with the toner, and forming a toner image;
A toner recovery unit that recovers residual toner remaining on the photoreceptor after the toner image transfer, and mixes and stirs the recovered residual toner;
And a transport unit that transports the collected and agitated residual toner from the toner recovery unit to the toner storage unit in the development unit.   The developing device according to claim 1, wherein the transport unit is a mono pump.   The developing device according to claim 1, further comprising an external additive addition unit that adds an inorganic fine particle external additive to the collected residual toner.   4. The developing device according to claim 3, wherein the inorganic fine particle external additive contains at least silica.   The developing device according to claim 4, wherein the silica is silica having a particle diameter of 10 to 30 nm.   The inorganic fine particle external additive contains 0.1 to 1.0% by mass of silica having a particle size of 10 to 30 nm, and 0.5 to 2.0% by mass of silica having a particle size of 50 to 200 nm. The developing device according to claim 4, wherein:   The developing device according to claim 5, wherein the inorganic fine particle external additive contains 0.1 to 0.7 mass% of titanium oxide.   8. The developing device according to claim 3, wherein the external additive adding section is provided in the vicinity of an inlet of the transport section. 9.   The developing device according to claim 3, wherein the external additive addition unit is provided in a conveyance path inside the conveyance unit.   8. The developing device according to claim 3, wherein the external additive addition unit is provided in the vicinity of the portion where the mixing and stirring is performed in the toner recovery unit. 9.   The developing device according to claim 1, wherein the toner has an average circularity of particles of 0.98 to 1.00. At least one of a photoconductor, a charging unit, and a transfer unit and the developing device according to any one of claims 1 to 11 are configured integrally.
A process cartridge that is detachable from the image forming apparatus.   An image forming apparatus comprising the developing device according to claim 1.   An image forming apparatus comprising the process cartridge according to claim 12.

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