JP2006091457A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress occurrence of image defects at a low cost while reusing recovered toner particles, with respect to an image forming apparatus in which an electrophotographic system is adopted to perform image formation. <P>SOLUTION: When a charge distribution of ≥5,000 toner particles is measured by a charge spectrograph method and the distance from the origin to a spot where the number of toner particles per mm<SP>2</SP>is 100-500 is defined as a maximum value, the following four expressions are satisfied at the same time; ¾8 mm¾<¾the above maximum value St in a charge distribution of toner particles in a toner image formed on an image bearing member 11¾≤¾15 mm¾; ¾5 mm¾<¾the above maximum value Dt in a charge distribution of toner particles immediately before fed to a stirring chamber 143 by fresh toner feeding means 141, 142, 1421¾; ¾5 mm¾<¾the above maximum value Dt' in a charge distribution of toner particles immediately before returned to the stirring chamber 143 by a toner recovery means 152¾; 0.9<¾St¾/¾the above maximum value Pt in a charge distribution of toner particles borne on a developer bearing member 145¾<1.1. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, or a facsimile, which forms an image by employing a so-called electrophotographic system.

  In the electrophotographic system, an electrostatic latent image is obtained by charging the surface of the image carrier and exposing the charged image carrier to exposure light, and developing the electrostatic latent image with toner particles. A toner image is formed on the image carrier by developing with toner particles in the developer using a developing device that holds the developer inside, and the toner image formed on the surface of the image carrier is transferred to a predetermined transfer surface ( An image composed of a fixed toner image is formed by an image forming process in which the image is transferred to the surface of a recording sheet or the surface of an intermediate transfer member and finally fixed on a recording medium.

  Here, since the untransferred toner particles remain on the surface of the image carrier that has been transferred onto the predetermined transfer surface, it is necessary to remove the residual toner particles prior to the next image forming process. . Various cleaning methods for removing residual toner particles are known, but the method of scraping the residual toner particles by rubbing the surface of the image carrier with an elastic plate-shaped cleaning blade is simple and inexpensive. More commonly used.

  In recent years, it has been important to reduce the amount of waste by effectively using resources in consideration of environmental problems. Therefore, the toner particles removed from the surface of the image carrier are collected from the cleaning device to the developing device and then statically again. It may be used for developing an electrostatic latent image (see, for example, Patent Document 1).

  By the way, in order to develop an electrostatic latent image using a so-called two-component developer including magnetic carrier particles and toner particles electrostatically attracted to the magnetic carrier particles, the two-component developer is held. A developing device is used. In the developing device that holds the two-component developer, a stirring chamber is provided in which the carrier particles and the toner particles are agitated to frictionally charge the toner particles and electrostatically adsorb the toner particles to the carrier particles. However, if the toner particles are insufficiently charged, “fogging” is likely to occur in the formed image. Also, if the toner particle charge distribution is too wide, the toner particles located at the end of the distribution are undercharged or overcharged, resulting in image quality defects such as 'fogging' and reduced image density. . For this reason, toner particles having externally added inorganic fine particles that increase the charge amount while suppressing the spread of the charge distribution of the toner particles are used (see, for example, Patent Document 2).

  When a toner image is formed on the surface of the image carrier with toner particles having such inorganic fine particles added externally to the surface, even the toner particles and the inorganic fine particles are externally added to the surface of the toner particles when the toner image is formed. In such a state, the image carrier moves to the surface of the image carrier.

Here, it is known that as the toner particles to which inorganic fine particles having a large particle size are externally used are used, the spread of the charge distribution of the toner particles is suppressed and the charge amount is also increased.
Japanese Patent No. 3435582 Japanese Patent Application Laid-Open No. 07-028276

  However, the inorganic fine particles that improve the charging characteristics of the toner particles have a large true specific gravity. Therefore, when inorganic fine particles having a particle size larger than a certain value with respect to the particle size of the toner particles are added to the developer, Separation from the toner particles is likely to occur. When this separation occurs due to the stirring action in the stirring chamber, not only the charge distribution of the toner particles is widened, but also the central value of the charge distribution becomes low, and image quality defects occur in the formed image. Even though the inorganic fine particles having a large particle size are much smaller than the toner particles, if such separation of the inorganic fine particles occurs on the image carrier, the inorganic fine particles are removed from the image carrier due to the small size of the inorganic fine particles. Is very difficult with an inexpensive cleaning means such as a cleaning blade. If image formation is performed with inorganic fine particles remaining on the surface of the image carrier, the image quality of the formed image is degraded. Therefore, if a complicated and expensive mechanism is provided as a cleaning means in order to remove any remaining inorganic fine particles, the cost of the image forming apparatus is increased.

  In addition, among the untransferred toner particles remaining on the surface of the image carrier collected up to the developing device, reversely charged toner particles having different charge polarities or weakly charged toners having a charge amount lower than the normal charge amount Contains a lot of particles. Further, if the toner particles removed from the surface of the image carrier stay in the cleaning device for a long time, the charge of the toner particles is lowered, and the charge may be further lowered in the process until it is conveyed to the developing device. . For this reason, the toner particles collected up to the developing device do not rise well when recharged in the stirring chamber and do not reach the desired charge amount. If development is performed using such collected toner particles, image quality defects such as fogging will occur. May occur. Further, even toner particles to which inorganic fine particles having a large particle diameter are externally added are often separated from the fine particles when collected up to the developing device, resulting in image quality defects in the formed image. .

  SUMMARY OF THE INVENTION An object of the present invention is to solve the above-described problems and to provide an image forming apparatus that can suppress the occurrence of image quality defects at low cost while reusing collected toner particles.

An image forming apparatus according to the present invention that solves the above-described object is to develop an electrostatic latent image formed on a predetermined image carrier including magnetic carrier particles and toner particles that are electrostatically attracted to the magnetic carrier particles. The toner is developed with toner particles in the developer using a developing device holding the developer inside to form a toner image on the image carrier, and the toner image is transferred to a predetermined transfer surface and finally recorded. In an image forming apparatus for forming an image composed of a fixed toner image on a recording medium by fixing on the medium,
A cleaning device for removing toner particles remaining on the surface of the image carrier after the toner image is transferred to the transfer surface;
The developing device is
Stirring the developer to frictionally charge the toner particles and electrostatically adsorb the toner particles to the magnetic carrier particles;
A developer carrying member that carries the developer stirred in the stirring chamber on the surface and conveys the developer to a development region facing the image carrier;
A fresh toner supply means for supplying new toner particles to the stirring chamber,
The cleaning device includes a toner recovery means for returning the toner particles removed from the surface of the image carrier to the stirring chamber;
This image forming apparatus further includes
When the charge distribution of 5000 or more toner particles is measured by the charge spectrograph method and the distance from the origin to the point where the number of toner particles per 1 mm ² is 100 or more and 500 or less is defined as the maximum value, the above image The maximum value of the charge distribution of the toner particles in the toner image formed on the carrier is St, and the maximum value of the charge distribution of the toner particles immediately before being supplied to the stirring chamber by the fresh toner supply means is Dt. The maximum value of the charge distribution of the toner particles immediately before being returned to the stirring chamber by the toner collecting means is Dt ′, and the maximum value of the charge distribution of the toner particles carried on the developer carrier is Pt. When
| 8 mm | <| St | ≦ | 15 mm |
| 5 mm | <| Dt |
| 5 mm | <| Dt ′ |
0.9 <| St | / | Pt | <1.1 Equation 4
The above-mentioned formula 1, formula 2, formula 3 and formula 4 are satisfied simultaneously.

  When a collection of a large number of toner particles is charged, a charge distribution is inevitably generated, and it is extremely difficult to accurately define the central value of the charge distribution. Even if it is defined, toner particles that cause image quality defects It is a toner particle located at the end and has little meaning. Therefore, in the image forming apparatus of the present invention, attention is paid to the fact that the charge distribution of the toner particles tends to become wider when the charge amount of the toner particles is increased by triboelectric charging, and the toner obtained using the charge spectrograph method is used. Specifies the maximum value of the particle charge distribution. Here, the charge distribution of new toner particles (hereinafter referred to as “fresh toner particles”) immediately before being supplied to the stirring chamber is defined by the above formula 2, and the value of | Dt | exceeds | 5 mm | In this case, the fresh toner particles are charged to some extent by the fresh toner supply means, and it is not necessary to increase the frictional charge in the stirring chamber even when inorganic fine particles having a large particle diameter are added. As a result, separation of the inorganic fine particles from the toner particles does not become a problem. If the | Dt ′ | value exceeds | 5 mm |, the toner particles immediately before being returned to the stirring chamber by the toner recovery means (hereinafter referred to as recovered toner particles) are also charged to some extent. Thus, the problems caused by the reversely charged toner particles having different charge polarities and the weakly charged toner particles having a charge amount lower than the regular charge amount, which are likely to be contained in the collected toner particles, are solved. Further, by limiting the range to the range defined by the above formula 1, the occurrence of image quality defects due to the charged state of the toner particles can be finally suppressed. That is, if the value of | St | exceeds 15 mm, there is a high possibility that toner particles that are insufficiently charged or toner particles that are overcharged will be present. Image quality defects are likely to occur. Further, white spots may occur during transfer, and image unevenness may occur due to deterioration in transfer efficiency. If the value of | ST | is 8 mm or less, the toner particles are likely to be insufficiently charged, and 'fogging' tends to occur in the formed image. Further, the above formula 4 defines the degree of transfer of the toner particles from the developer carrying body to the image carrying body. By suppressing the toner particles to the range defined by the above formula 4, stable developability can be obtained. Guaranteed. Thus, according to the present invention, by defining the conditions for suppressing the occurrence of image quality defects due to the charged state of the toner particles, the occurrence of image quality defects due to the recovered toner particles can be suppressed, and the large particle size Therefore, it is possible to provide a low-cost image forming apparatus that does not require an expensive cleaning device.

  Here, in the image forming apparatus of the present invention, a toner image composed of toner particles of each color is formed on the image carrier based on image signals corresponding to at least a plurality of colors of cyan, magenta, yellow and black. An image forming apparatus that forms an image on the recording medium by forming and finally transferring and fixing the toner images of the respective colors onto a predetermined recording medium, wherein the developing device is attached to the image carrier. The formed electrostatic latent image may be developed with at least one color toner particle of the plurality of color toner particles.

In the image forming apparatus of the present invention, the toner particles have a spherical coefficient of SF = (πL ² / 4A) × 100.
In the above formula, L is the maximum diameter (μm) of the toner particles, and A is the projected area (μm ² ) of the toner particles.
The SF value is preferably 135 or less.

  Of the toner particles held in the developing device, the shape close to a true sphere has a smaller contact area with the image carrier and good transferability, but the shape in which the true sphere is crushed or distorted The contact area with the image carrier is large and the transferability is poor. For this reason, in the image forming apparatus of the present invention, the shape of the toner particles is defined using a parameter called SF. When the SF value is larger than 135, the toner particles have a shape in which the true sphere is crushed or distorted, the transfer efficiency of the toner is lowered, and it is difficult to obtain a uniform image quality image.

  By the way, the developing device is provided with a transport amount regulating member facing the developer carrying member, and the developer carrying amount is controlled by adjusting the interval between the developer carrying member and the carrying amount regulating member. Things are known. The developer containing toner particles that are sufficiently spheroidized in this way has improved fluidity, and at the same time, solidified and increased in bulk density. As a result, there may be a phenomenon in which developer accumulation occurs at the conveyance amount regulating portion and the conveyance amount becomes unstable. For this phenomenon, it is conceivable to stabilize the transport amount by controlling the surface roughness of the developer carrier or by narrowing the distance between the transport amount regulating member and the developer carrier, The packing property due to the developer pool is further increased, and the stress applied to the toner particles is also increased. For this reason, when a fine structure change on the surface of the toner particles, especially when inorganic fine particles having a large particle diameter are added, the inorganic fine particles are easily detached from the toner particle surface. Sexuality will be impaired. However, according to the image forming apparatus of the present invention, it is not necessary to add inorganic fine particles having a large particle diameter, and thus toner particles that are sufficiently spherical can be used.

  Further, in the image forming apparatus of the present invention, the toner particles have an average particle size of 50% in a cumulative distribution from the smaller diameter side with respect to the particle size range divided based on the particle size distribution. When represented by the average particle diameter D, it is also preferable that the volume average particle diameter D falls within the range of 2 μm to 9 μm.

  Furthermore, in the image forming apparatus of the present invention, it is preferable that the toner particles are externally added with at least one inorganic fine particle having an average particle diameter of 10 nm to 100 nm on the surface.

  In the image forming apparatus of the present invention, it is not necessary to add inorganic fine particles having a large particle diameter exceeding 100 nm. However, by adding inorganic fine particles having an average particle diameter of 10 nm or more and 100 nm or less, the charging characteristics of the toner particles are improved. It will be better. If the average particle size of the inorganic fine particles to be added is less than 10 nm, improvement in charging characteristics of the toner particles cannot be expected. Conversely, if the average particle size exceeds 100 nm, the inorganic fine particles are likely to be detached from the toner particles.

In the image forming apparatus of the present invention, the surface of the image carrier is charged, and an electrostatic latent image is formed on the surface of the image carrier by irradiating the surface of the image carrier after charging with exposure light. Because
It may be provided with a charging roll for charging the surface of the image carrier by rotating in a state where a voltage is applied and in contact with the surface of the image carrier.

  According to the image forming apparatus of the present invention, since it is not necessary to add inorganic fine particles having a large particle diameter, the surface of the image carrier is not contaminated by the separation of the inorganic fine particles. The surface of the charging roll that comes into contact is not contaminated. Therefore, there is no inconvenience even if the charging roll is provided, and the image forming apparatus is preferably downsized.

Further, in the image forming apparatus according to the present invention, the carrier particle has a coating on the surface of the core portion which has excellent chargeability so that the toner particles are charged to a predetermined polarity by friction with the toner particles from the core portion. Coated with an agent,
The fresh toner supply means includes a coating member coated with the coating agent, and charges the new toner particles by relatively rubbing the new toner particles and the coating member.
The toner recovery means includes a coating member coated with the coating agent, and relatively rubs the toner particles removed from the surface of the image carrier and the coating member, thereby removing the toner from the surface of the image carrier. It is also preferable that the removed toner particles are charged.

  According to this aspect, new toner particles are charged to some extent before being supplied to the stirring chamber, the value of | Dt | is increased, and the toner particles removed from the surface of the image carrier are also stirred. It is charged to some extent before returning to the chamber, the value of | Dt ′ | is increased, and the toner particles are charged better.

Here, as an example of the toner collecting means in the above aspect,
The toner collecting means includes
The toner particles removed from the surface of the image carrier through the stirring chamber pass while contacting the inner peripheral surface, and the inner peripheral surface may have a conveyance path coated with the coating agent. And
The toner particles removed from the surface of the image carrier may be conveyed to the stirring chamber by rotating, and may have a screw-shaped conveying member whose surface is coated with the coating agent.
A blade in which toner particles removed from the surface of the image carrier are in contact with the surface, and the toner particles removed from the surface of the image carrier are rotated toward the agitating chamber while rotating in contact with the surface of the blade. It has a conveying member, and at least one of the surface of the blade and the portion of the rotating member that contacts the surface may be coated with the coating agent,
The surface of the image carrier is rotated by having a supply path leading to the stirring chamber and hair coated with the coating agent, with the tip of the hair in contact with the inner peripheral surface of the supply path. The toner particles removed from the hair may be provided with a brush that passes between the tip portion of the hair and the inner peripheral surface of the supply path and feeds the toner particles toward the stirring chamber, or
The mesh member having a surface provided with a mesh larger than the particle diameter of the toner particles removed from the surface of the image carrier and coated with the coating agent, the toner particles having the surface removed from the surface of the image carrier. The surface may be arranged so as to be able to vibrate freely in the direction in which the surface spreads toward the direction of sending.

  In any of these examples, relative rubbing with the toner particles removed from the surface of the image carrier occurs, and the toner particles removed from the surface of the image carrier are in a stage before being supplied to the stirring chamber. Charged to some extent.

  According to the present invention, it is possible to provide an image forming apparatus in which the occurrence of image quality defects is suppressed at a low cost while the collected toner particles are reused.

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

  FIG. 1 is a diagram schematically illustrating an image forming apparatus according to a first embodiment of the present invention.

  The image forming apparatus 1 of the present embodiment (first embodiment) is a small-sized image forming apparatus that employs a full-color tandem system, and includes four toners corresponding to yellow, magenta, cyan, and black toners, respectively. Using the toner image forming unit, each toner image forming unit forms a toner image of each color in synchronization with the feeding of the intermediate transfer belt, and superimposes the toner images on the intermediate transfer belt as an intermediate medium (1 (Next transfer), the toner image superimposed on the intermediate transfer belt is transferred (secondary transfer) to a sheet as a recording medium and fixed.

  An image forming apparatus 1 shown in FIG. 1 is a semiconductive intermediate transfer belt that is supported by four toner image forming units 10, four primary transfer rolls 20, and three support rolls 31 and circulates in a clockwise direction. 30, a batch transfer device 40 that performs secondary transfer, and a fixing device 50 that fixes an unfixed toner image on a sheet.

  The four toner image forming units 10 are arranged side by side in the circulation direction of the intermediate transfer belt 30, and each toner image forming unit 10 is provided with a multi-layered photosensitive drum 11 that rotates counterclockwise. Yes. The surface of each photosensitive drum 11 is in contact with the surface of the intermediate transfer belt 30. The primary transfer roll 20 is disposed at a position facing the photosensitive drum 11 with the intermediate transfer belt 30 interposed therebetween, and an area sandwiched between the photosensitive drum 11 and the primary transfer roll 20 becomes a primary transfer area. .

  Here, the toner image forming unit 10 will be described in detail with reference to FIG. 1 and FIG. 2.

  FIG. 2 is an enlarged view showing one toner image forming unit among the four toner image forming units provided in the image forming apparatus shown in FIG.

  FIG. 2 also shows a part of the intermediate transfer belt 30 and the primary transfer roll 20 in addition to the toner image forming unit 10. The toner image forming unit 10 shown in FIG. 2 includes a charging roll 12, a developing device 14, and a cleaning device 15 in addition to the photosensitive drum 11.

  The charging roll 12 has an outer diameter of 14 mm that rotates in contact with the photosensitive drum 11, which leads to downsizing of the image forming apparatus. The charging roll 12 has a semiconductive single-layer structure, and the photosensitive drum 11 is charged by generating a discharge in a minute gap near the contact portion with the photosensitive drum 11. Electric power having a voltage waveform in which an alternating voltage is superimposed on a DC voltage is supplied to the surface of the charging roll 12. Note that the image forming apparatus shown in FIG. 1 is not provided with a mechanism for cleaning the surface of the charging roll 12, thereby reducing the cost.

  The developing device 14 is disposed on the upstream side of the primary transfer region around the photosensitive drum 11. The charging roll 12 is disposed further upstream than the developing device 14. The charging roll 12 is disposed further upstream than the developing device 14. In addition, the cleaning device 15 is disposed around the photosensitive drum 11 and downstream of the primary transfer region. The developing device 14 shown in FIG. 2 includes a fresh toner supply tank 141, a fresh toner supply nozzle 142, a first stirring chamber 143, a second stirring chamber 144, and a developing roll 145. New toner particles are stored in the fresh toner supply tank 141. The fresh toner replenishing nozzle 142 has a pipe shape that connects the fresh toner replenishing tank 141 and the first agitation chamber 142, and has a conveying member 1421 disposed therein. The conveyance member 1421 shown in FIG. 2 is a rotating screw-like member. New toner particles stored in the fresh toner replenishing tank 141 are conveyed to the first stirring chamber 143 through the fresh toner replenishing nozzle 142 by the rotation of the conveying member 1421. Supply of new toner particles from the fresh toner supply tank 141 is appropriately performed. Each of the first stirring chamber 143 and the second stirring chamber 144 is a chamber that extends in parallel to the rotation shaft 11a of the photosensitive drum 11 (extends in a direction perpendicular to the paper surface of FIG. 2). The first stirring chamber 143 and the second stirring chamber 144 are partitioned by a partition wall 146 except for both ends in the extending direction, but both ends are connected. A developer is held in the stirring chambers 143 and 144. The developer includes magnetic carrier particles and toner particles that are electrostatically adsorbed to the magnetic carrier particles. The toner particles have a predetermined charging polarity, and the magnetic carrier particles are charged to the toner particles in which the surface of the core portion charges the toner particles to a predetermined polarity by friction with the toner particles from the core portion. It was coated with an excellent coating agent. A detailed description of the developer will be described later. In addition, in these stirring chambers 143 and 144, screw augers 147 extending in the extending direction of the stirring chambers are provided. The screw augers 147 arranged in any of the stirring chambers 143 and 144 are also rotatable, and the developer is stirred in each stirring chamber by rotating each screw auger 147. In the first stirring chamber 143, the toner particles are frictionally charged by the rotation of the screw auger 147 provided in the first stirring chamber 143 and electrostatically adhere to the magnetic carrier particles, and the magnetic carrier particles to which the toner particles are attached It is fed into the second stirring chamber 144. In other words, the toner particles supplied to the first stirring chamber 143 pass through the first stirring chamber 143 and are fed into the second stirring chamber 144 while being frictionally charged. In the second stirring chamber 144, the magnetic carrier particles to which the toner particles adhere are conveyed toward the developing roll 145 by the rotation of the screw auger 147 provided in the second stirring chamber 144. The developing roller 145 includes a developing sleeve 1451 that is provided to face the photosensitive drum 11 and rotates in the direction of the arrow. A region where the developing sleeve 1451 and the photosensitive drum 11 face each other is a developing region. Inside the developing sleeve 1451, a magnet roll (not shown) is provided. The magnet roll is arranged in a fixed state with respect to the rotating developing sleeve 1451, and a pickup magnetic pole for adsorbing the magnetic carrier particles (developer) to which the toner particles adhere to the developing sleeve 1451, or a developer is provided. It has a magnetic pole to be raised in the developing area, a pick-off magnetic pole for peeling off the developer after passing through the developing area from the developing sleeve 1451, and the like. Further, a voltage obtained by superimposing an AC voltage on a DC voltage is applied to the developing sleeve 1451 so as to form an electric field so that an electrostatic force acts on the toner particles on the developing sleeve 1451 toward the developing sleeve 1451 side. Has been. Such a developing roll 145 having a developing sleeve 1451 in which a magnet roll is disposed is configured to carry a developer on its surface and transport the developer to a development region. It corresponds to an example of a body. The developer that has not been adsorbed by the developing sleeve 1451 and the developer that has been peeled off from the developing sleeve 1451 after passing through the developing region are rotated by the rotation of the screw auger 147 provided in the second stirring chamber 144. Returned to

  Further, in the developing device 14 shown in FIG. 2, both the inner peripheral surface of the fresh toner supply tank 141 and the inner peripheral surface of the fresh toner supply nozzle 142 correspond to the toner particles coating the surface of the core portion of the magnetic carrier particles. It is coated with a coating agent having excellent chargeability. New toner particles stored in the fresh toner replenishment tank 141 are frictionally charged by moving and sliding with the inner peripheral surface of the fresh toner replenishment tank 141. In addition, new toner particles passing through the fresh toner supply nozzle 142 are further frictionally charged by rubbing against the inner peripheral surface of the fresh toner supply nozzle 142. As described above, in the developing device 14 shown in FIG. 2, new toner particles charged to some extent are replenished to the first stirring chamber 143. Note that the combination of the fresh toner supply tank 141, the fresh toner supply nozzle 142, and the conveying member 1421 corresponds to an example of the fresh toner supply means according to the present invention (hereinafter, these three members will be combined with the fresh toner supply means). Called). According to the present invention, both the inner peripheral surface of the fresh toner replenishing tank 141 and the inner peripheral surface of the fresh toner replenishing nozzle 142 need not be covered with the coating agent having excellent chargeability with respect to the toner particles. Only one inner peripheral surface may be covered.

  Further, the cleaning device 15 shown in FIG. 2 is an inexpensive device including the cleaning blade 151 and the toner collecting means 152. The cleaning blade 151 is a plate-shaped member made of urethane rubber or the like, and its tip is in contact with the surface of the photosensitive drum 11 and scrapes off toner particles remaining on the surface. The toner collecting unit 152 includes a screw auger 1521 and a conveyance path 1522. The screw auger 1521 is provided at the bottom of the cleaning device 15, and the toner particles scraped off from the surface of the photosensitive drum 11 are sent to the conveyance path 1522 by the screw auger 1521. The conveying path 1522 is a pipe-shaped member connecting the bottom of the cleaning device 15 and the first stirring chamber 143 of the developing device 14, and has a screw-shaped conveying member 1523 that rotates inside. The toner particles scraped off from the surface of the photosensitive drum 15 sent to the conveyance path 1522 by the screw auger 1521 are returned to the first stirring chamber 143 of the developing device 14 through the conveyance path 1522 when the conveyance member 1523 rotates. It is. The inner peripheral surface of the conveyance path 1522 of the toner collecting means 152 is the same as the inner peripheral surface of the fresh toner replenishing nozzle 142, and is a coating agent that is excellent in chargeability with respect to the toner particles coating the surface of the core portion of the magnetic carrier particles. It is covered by. Therefore, the toner particles scraped off from the surface of the photosensitive drum passing through the conveyance path 1522 are frictionally charged by sliding with the inner peripheral surface of the conveyance path 1522. As described above, the toner particles charged to some extent are returned to the first stirring chamber 143 after being scraped off from the surface of the photosensitive drum 11 by the toner recovery means 152 shown in FIG.

  Accordingly, the toner particles supplied from the toner replenishing tank 141 through the toner replenishing nozzle 142 and the toner collecting means 152 are returned to the first stirring chamber 143 of the developing device 14 shown in FIG. There are two types of toner particles, toner particles, and both toner particles are charged to some extent before reaching the first stirring chamber 143.

  Next, the configuration of the image forming apparatus 1 will be described in more detail while describing image formation in the image forming apparatus 1 shown in FIG.

  The surface of the photosensitive drum 11 is uniformly charged by the charging roll 12. The surface of the photosensitive drum 11 that is uniformly charged by the charging roll 12 is irradiated with laser light L, and an electrostatic latent image is formed on the surface of the photosensitive drum 11. The developing device 14 develops the electrostatic latent image on the photosensitive drum 11 with toner particles carried on the developing roll 145 in the developing region, and a toner image is formed on the photosensitive drum 11.

  A transfer bias having a polarity opposite to the charging polarity of the toner particles is applied to the primary transfer roll 20, and the toner image formed on the photosensitive drum 11 is intermediate from the surface of the photosensitive drum in the primary transfer region. Transition to the surface of the transfer belt 30. The toner images formed by the respective toner image forming units 10 become toner images that overlap one on the surface of the intermediate transfer belt 30.

  The batch transfer device 40 includes a secondary transfer roll 41 disposed in pressure contact with the surface (toner image carrying surface) side of the intermediate transfer belt 30 and a backup roll 42 disposed on the back surface side of the intermediate transfer belt 30. The intermediate transfer belt 30 is sandwiched between these two rolls 41 and 42. A region sandwiched between these two rolls 41 and 42 becomes a secondary transfer region.

  Further, the image forming apparatus 1 shown in FIG. 1 is provided with a paper tray 60, and the paper P accommodated in the paper tray 60 is sent out from the paper tray 60 by the feed roll 61, and is secondary at a predetermined timing. It is sent to the transfer area. In the secondary transfer region, the toner images overlapped on the intermediate transfer belt 30 are transferred onto the fed paper P. The fixing device 50 includes a fixing roll 51 having a heating mechanism 511 and a pressure roll 52 provided so as to face the fixing roll 51. Between the fixing roll 51 and the pressure roll 52 facing each other, the paper P that has passed through the secondary transfer region is conveyed. The toner constituting the toner image on the paper P is melted by the heating mechanism 511 of the fixing roll 51 and fixed on the paper P.

  A belt cleaner 70 for removing residual toner on the intermediate transfer belt 30 is provided on the downstream side of the batch transfer device 40. The belt cleaner 70 has a rubber blade 71. The tip of the blade 71 is pressed against the surface of the intermediate transfer belt 30, and when the intermediate transfer belt 30 circulates, the toner remaining on the surface is peeled off.

  Further, toner particles that are not transferred to the intermediate transfer belt 30 in the primary transfer region and remain on the photosensitive drum 11 are scraped off from the photosensitive drum 11 by the cleaning blade 151.

Here, when the charge distribution of 5000 or more toner particles is measured by a charge spectrograph method, and the distance from the origin to the point where 100 or more and 500 or less toner particles per 1 mm ² is defined as the maximum value. (Hereinafter the same), the maximum value of the charge distribution of toner particles in a toner image formed on the photosensitive drum 11 and having an image density of 1.2 or more in X-Rite 936 manufactured by X-Rite is St. The maximum value of the charge distribution of new toner particles immediately before being supplied from the fresh toner supply tank 141 to the first stirring chamber 143 through the fresh toner supply nozzle 142 is set to Dt, and passes through the conveyance path 1522 of the toner recovery unit 152. The maximum value of the charge distribution of the toner particles scraped off from the surface of the photosensitive drum immediately before being returned to the first stirring chamber 143 is D And ', when the maximum value of the charge distribution of the supported toner particles to the developing roller 145 was set to Pt,
| 8 mm | <| ST | ≦ | 15 mm |
| 5 mm | <| Dt |
| 5 mm | <| Dt ′ |
0.9 <| St | / | Pt | <1.1 Equation 4
In the image forming apparatus 1 in FIG. 1, the above Expression 1, Expression 2, Expression 3, and Expression 4 are satisfied simultaneously.

The number of toner particles per mm ² was measured using a laser microscope (manufactured by Keyence Corporation: VK8500).

Here, paying attention to the fact that the charge distribution of the toner particles tends to become wider as the charge amount of the toner particles increases due to frictional charging, and a new toner just before being supplied to the first stirring chamber 143 by the above equation 2 The charge distribution of the particles is defined, and the charge distribution of the toner particles scraped off from the surface of the photosensitive drum immediately before being returned to the first stirring chamber 143 is defined by the above equation 3. In the image forming apparatus 1 in FIG. 1, both the inner peripheral surface of the fresh toner supply tank 141 and the inner peripheral surface of the fresh toner supply nozzle 142 are covered with a coating agent that has excellent chargeability with respect to toner particles. The new toner particles immediately before being supplied to the first stirring chamber 143 are charged to the extent that | Dt | exceeds 5 mm due to the rubbing between the new toner particles to be replenished and the inner peripheral surfaces thereof. The Further, since the inner peripheral surface of the conveyance path 1522 of the toner collecting means 152 is also coated with a coating agent having excellent chargeability with respect to the toner particles, the toner particles passing through the conveyance path 1522 and their inner peripheral surfaces The toner particles scraped off from the surface of the photosensitive drum immediately before being supplied to the first stirring chamber 143 by the rubbing of the toner are also charged to the extent that | Dt ′ | exceeds 5 mm.

According to the image forming apparatus 1 in FIG. 1, if the maximum value of the charge distribution of new toner particles just added to the fresh toner supply tank 141 is Ft,
| Dt | = | Ft | × 1.65 Equation 5
The relationship of the above formula 5 is established. The coefficient of “1.65” in the above formula 5 is a coefficient representing how uniformly new toner particles can be charged by the fresh toner supply means.

Also, let Jt be the maximum value of the charge distribution of the toner particles scraped off from the surface of the photosensitive drum that has just been sent to the conveyance path 1522 of the toner collecting means 152.
| Dt ′ | = | Jt | × 1.65 Equation 6
The relationship of Equation 6 is also established. The coefficient of “1.65” in the above formula 6 is a coefficient representing how uniformly the toner particles scraped off from the surface of the photosensitive drum can be charged by the toner recovery unit 152.

  If the values of | Dt | and | Dt ′ | are less than | 5 mm |, the toner particles are likely to be insufficiently charged, and the toner particles fly to the non-image area on the photosensitive drum when the toner image is formed. Image defects such as non-image portions being cobbled easily occur. For this reason, in the new toner particles, it is necessary to add inorganic fine particles having a large particle size to increase the frictional charging in the first stirring chamber. However, if inorganic fine particles having a large particle size are added, the added inorganic particles The separation of the fine particles from the toner particles becomes a problem. However, if the value of | Dt | exceeds | 5 mm |, the toner particles are charged to some extent, and the triboelectric charge in the stirring chamber is increased even when inorganic fine particles having a large particle diameter are added. Is no longer necessary. As a result, separation of the inorganic fine particles from the toner particles does not become a problem. In addition, the toner particles scraped off from the surface of the photosensitive drum include a large number of reversely charged toner particles having different charge polarities and weakly charged toner particles having a charge amount lower than a normal charge amount. In addition, there is a known problem that when toner particles scraped off from the surface of the photosensitive drum stay for a long time in the bottom of the cleaning device 15 or in the conveyance path 1522 of the toner recovery unit 152, the charging of the toner particles is reduced. However, if the | Dt ′ | value exceeds | 5 mm |, these problems are solved by frictional charging in the conveyance path 1522.

  Further, by limiting the range to the range defined by the above formula 1, the occurrence of image quality defects due to the charged state of the toner particles can be finally suppressed. That is, if the value of | St | exceeds 15 mm, there is a high possibility that toner particles that are insufficiently charged or toner particles that are overcharged will be present. Image quality defects are likely to occur. Further, white spots may occur during transfer, and image unevenness may occur due to deterioration in transfer efficiency. On the other hand, if the value of | St | is 8 mm or less, the toner particles are likely to be insufficiently charged, and 'fogging' tends to occur in the formed image. Further, the above formula 3 defines the degree of transfer of the toner particles from the developing roll 145 to the photosensitive drum 11, and stable developability is assured by suppressing the toner particles to the range defined by the above formula 3. The

Further, when the maximum value of the charge distribution of the toner particles immediately before being stirred in the first stirring chamber 143 and sent into the second stirring chamber 144 is At,
| Dt | <| At | = | St |
In the image forming apparatus in FIG. 1, in addition to the above formulas 1 to 6, the above formula 7 is also satisfied. Here, the value of | St | is preferably in the range of 10 to 14 (mm), and more preferably in the range of 11 to 13 (mm).

  Next, the developer will be described in detail. As described above, this developer includes magnetic carrier particles whose core surface is coated with a coating agent having excellent chargeability to toner particles, and toner particles that are electrostatically adsorbed to the magnetic carrier particles. It is a waste.

  The toner particles are mainly composed of colored particles composed of a colorant and a binder resin and an external additive. As the binder resin, a known resin can be used. For example, styrenes such as styrene and chlorostyrene, monoolefins such as ethylene, propylene, butylene and isoprene, vinyl esters such as vinyl acetate, vinyl propionate, vinyl benzoate and vinyl butyrate, methyl acrylate, ethyl acrylate , Α-methylene aliphatic monocarboxylic esters such as butyl acrylate, decyl acrylate, octyl acrylate, phenyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, dodecyl methacrylate, vinyl methyl ether, vinyl Homopolymers and copolymers such as vinyl ethers such as ethyl ether and vinyl butyl ether, vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone and vinyl isopropenyl ketone can be used. Examples of the resin used include polystyrene, styrene-alkyl acrylate copolymer, styrene-alkyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, polyethylene, Examples include polypropylene. Furthermore, polyester, polyurethane, epoxy resin, silicone resin, polyamide, modified rosin, paraffin wax, and the like can be given.

  A known resin can be used as the colorant. For example, magnetic powders such as magnetite and ferrite, carbon black, aniline blue, calcoil blue, chrome yellow, ultramarine blue, dupont oil red, quinoline yellow, methylene blue chloride, phthalocyanine blue, malachite green oxalate, lamp black, rose bengal , C.I. I. Pigment red 48: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 57: 1, C.I. I. Pigment yellow 97, C.I. I. Pigment yellow 17, C.I. I. Pigment blue 15: 1, C.I. I. Pigment Blue 15: 3 can be exemplified as a representative one.

  Further, in the image forming apparatus 1 shown in FIG. 1, in order to make the offset resistance better, a color particle added with a release agent is used. A known resin can be used as the release agent. For example, hydrocarbon waxes such as low molecular weight polypropylene and low molecular weight polyethylene, microcrystalline wax, silicone resin, rosins, ester wax, rice wax, carnauba wax, Fischer-Tropsch wax, montan wax, candelilla wax, etc. Can be illustrated as representative. The addition amount of the release agent is preferably 1 to 15 parts by weight and more preferably 3 to 10 parts by weight with respect to 100 parts by weight of the binder resin. If the addition amount is less than 1 part by weight, the effect may not be exhibited. Conversely, if the addition amount is more than 15 parts by weight, the fluidity may be extremely deteriorated and the charge distribution may be very wide.

  Further, the image forming apparatus 1 shown in FIG. 1 uses colored particles to which a charge control agent is added. As the charge control agent, known ones can be used. For example, fluorinated surfactants, azo metal complex compounds, salicylic acid metal complex compounds, high molecular acids such as copolymers containing maleic acid as a monomer component, quaternary ammonium salts, azine dyes such as nigrosine, carbon Typical examples include black and resin-type charge control agents containing polar groups. In particular, when a toner is manufactured by a wet manufacturing method, it is preferable to use a material that is difficult to dissolve in water in terms of controlling ionic strength and reducing wastewater contamination.

  The colored particles may be magnetic particles containing a magnetic material or non-magnetic particles not containing a magnetic material. When the colored particles are magnetic particles, examples of the magnetic powder dispersed in the binder resin include known magnetic materials, for example, metals such as iron, cobalt, nickel, and alloys thereof, Fe3O4, γ-Fe2O3, cobalt Metal oxides such as added iron oxide, various ferrites such as Mn / Zn ferrite and Ni / Zn ferrite, magnetite, hematite, etc. can be used, and the surface treatment agents such as silane coupling agents and titanate coupling agents It is also possible to use a material treated with the above or a polymer-coated material.

  As the external additive of the colored particles, that is, the external additive constituting the toner particles, at least one kind of inorganic fine particles having a relatively small particle diameter of 10 nm or more and 100 nm or less can be used. It is preferably 80 nm or less, and more preferably 10 nm or more and 50 nm or less. In the image forming apparatus of the present invention, it is not necessary to add inorganic fine particles having a large particle diameter exceeding 100 nm, but toner particles are improved by adding inorganic fine particles having an average particle diameter of 10 nm to 100 nm. Charged. If the average particle size of the inorganic fine particles to be added is less than 10 nm, improvement in charging characteristics of the toner particles cannot be expected. Conversely, if the average particle size exceeds 100 nm, the inorganic fine particles are likely to be detached from the toner particles.

Known inorganic fine particles having a small particle diameter can be used, for example, silica, aluminum oxide, titanium oxide, TiO (OH) ₂ metatitanate, barium titanate, magnesium titanate, calcium titanate, titanate. Strontium, zinc oxide, silica sand, clay, mica, wollastonite, diatomaceous earth, cerium chloride, bengara, chromium oxide, cerium oxide, antimony trioxide, magnesium oxide, calcium phosphate, calcium carbonate, magnesium carbonate, zirconium oxide, silicon carbide And metal oxide particles such as silicon nitride, calcium carbonate, and barium sulfate, and ceramic particles such as alumina. In particular, when metatitanate TiO (OH) ₂ particles are externally added to the colored particles, the transparency is not affected and good chargeability, environmental stability, fluidity, caking resistance, stable negative chargeability, and stability Image quality maintainability can be obtained. In general, metatitanic acid can be produced by a sulfuric acid method (wet process) using the ilmenite ore shown below.
FeTiO ₂ + 2H ₂ SO ₄ → FeSO ₄ + TiOSO ₄ + 2H ₂ O
TiOSO ₄ + 2H ₂ O → TiO (OH) ₂ + H ₂ So ₄
Further, by adding a silane compound in a TiO (OH) ₂ state, preferably an aqueous dispersion of TiO (OH) ₂ , treating a part or all of the OH groups, filtering, washing, drying, and pulverizing Compared with conventional crystalline titanium oxide (calcined TiO (OH) ₂ obtained by the sulfuric acid method), a specific titanium oxide having a small true specific gravity can be obtained. That is, when the reaction is carried out in the solution as described above, TiO (OH) ₂ is treated with the silane compound during its hydrolysis. As a result, the specific titanium oxide generated from TiO (OH) ₂ is surface-treated with the silane compound in the state of primary particles. Thereby, it is possible to obtain a specific titanium oxide in a primary particle state without aggregation.

  In addition, the surface of these inorganic fine particles may be subjected to a known surface treatment according to the purpose. For example, a silane coupling agent, a titanate coupling agent, an aluminate coupling agent, a zirconium coupling agent, etc. Coupling agents, silicone oils and the like. Among these, a silane coupling agent and silicone oil can be preferably used. As the silane coupling agent, any type such as chlorosilane, alkoxysilane, silazane, and special silylating agent can be used. Specific examples thereof include methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, and phenyltrichlorosilane. , Diphenyldichlorosilane, tetramethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, phenyltrimethoxysilane, diphenyldimethoxysilane, tetraethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane , Ethyltriethoxysilane, propyltriethoxysilane, phenyltriethoxysilane, diphenyldiethoxysilane, butyltrimethoxysilane, Tiltriethoxysilane, isobutyltrimethoxysilane, hexyltrimethoxysilane, octyltrimethoxysilane, decyltrimethoxysilane, hexadecyltrimethoxysilane, trimethylmethoxysilane, hexamethyldisilazane, N, O- (bistrimethylsilyl) acetamide, N, N-bis (trimethylsilyl) urea, tert-butyldimethylchlorosilane, vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriacetoxysilane, γ-methacryloxypropyltrimethoxysilane, β- (3.4 Epoxycyclohexyl) ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropylme Rudiethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, etc., and trifluoropropyltrimethoxysilane, tridecafluorooctyltrimethoxysilane in which some hydrogen atoms are changed to fluorine atoms , Heptadecafluorodecyltrimethoxysilane, heptadecafluorodecylmethyldimethoxysilane, tridecafluoro-1,1,2,2-tetrahydrooctyltriethoxysilane, 3,3,3-trifluoropropyltrimethoxysilane, heptadeca Fluorine-based silane compounds such as fluoro-1,1,2,2-tetrahydrodecyltriethoxysilane, 3-heptafluoroisopropoxypropyltriethoxysilane, and amino-based silane compounds in which some hydrogen atoms are substituted with amino groups Etc., and the like. Silicone oils include dimethyl silicone oil, methyl hydrogen silicone oil, methylphenyl silicone oil, cyclic dimethyl silicone oil, epoxy-modified silicone oil, carboxyl-modified silicone oil, carbinol-modified silicone oil, methacryl-modified silicone oil, and mercapto-modified. Examples include silicone oil, polyether-modified silicone oil, methylstyryl-modified silicone oil, alkyl-modified silicone oil, amino-modified silicone oil, and fluorine-modified silicone oil. One of these hydrophobizing agents may be used alone, or two or more thereof may be used in combination.

  The adhesion state of the inorganic fine particles to the colored particle surface may be merely mechanical adhesion or may be loosely fixed to the surface. Further, the entire surface of the colored particles may be coated or a part thereof may be coated. The amount of the inorganic fine particles added is preferably 0.1 to 3.0 parts by weight, more preferably 0.2 to 2.0 parts by weight with respect to 100 parts by weight of the colored particles. When the addition amount is less than 0.1 parts by weight, there are cases where sufficient fluidity of the toner cannot be obtained, and blocking suppression due to thermal storage tends to be insufficient. On the other hand, when the addition amount is more than 3.0 parts by weight, an excessive coating state is caused, and the excessive inorganic fine particles may move to the contact member and cause a secondary failure. Moreover, you may pass a sieving process after external addition mixing.

  Next, a method for producing toner particles will be described. First, the colored particles constituting the toner particles are obtained by emulsion polymerization of a polymerizable monomer of a binder resin and mixing the formed dispersion with a dispersion of a colorant, a release agent, a charge control agent, and the like. It is produced by an emulsion polymerization aggregation method in which colored particles are obtained by aggregation, heat fusion. However, the production method of the colored particles is not limited to this emulsion polymerization aggregation method, and can be produced by any known method. For example, the particles obtained by kneading and pulverizing method, which knead, pulverize and classify binder resin, colorant, release agent, charge control agent, etc. Method of changing, suspension polymerization method in which a solution of a polymerizable monomer and a colorant, a release agent, a charge control agent, etc. for obtaining a binder resin is suspended in an aqueous solvent and polymerized, a binder resin, a coloring Examples thereof include a solution suspension method in which a solution of an agent, a release agent, a charge control agent and the like is suspended in an aqueous solvent and granulated. Moreover, you may perform the manufacturing method which makes the colored particle obtained by the said method a core, and also adheres agglomerated particle, heat-fuses, and has a core shell structure.

  Next, a method for forming toner particles by adding an external additive to the obtained colored particles will be described. As a production method for adding an external additive to the colored particles, it can be produced by any known method. For example, it can be obtained by mixing a colored particle with an external additive added, and can be mixed by a known mixer such as a V-type blender, Henschel mixer, or Redige mixer.

The toner particles thus produced become spherical toner particles. The “spherical shape” means both a perfect sphere and a shape close to a true sphere. The spherical toner particles can be obtained by an emulsion polymerization aggregation method, but the production method is not particularly limited as long as substantially spherical toner particles can be obtained. Such spherical toner particles are quantitatively expressed by the shape index (SF) represented by the following formula 8, and when this value is 100, it means a true sphere. It means close to a true sphere.
SF = (πL ² / 4A) × 100 Equation 8
In Equation 8, L is the maximum diameter (μm) of the toner particles, and A is the projected area (μm ² ) of the toner particles.
Here, the shape index (SF) is preferably 135 or less, and more preferably 125 or less. When the shape index (SF) exceeds 135, the adhesion force of the spherical toner particles to the surface of the photosensitive drum 11 increases, and the transfer efficiency may decrease. The value of the shape factor (SF) is determined for each of the obtained 100 toner particles using an image analyzer (manufactured by Nexus Corp .: NEXUS) and the maximum length of the projected image (the maximum diameter of the toner particles). ) L (μm) and the projected area A (μm ² ) of the toner particles are measured, and these values are substituted into Equation 6 to obtain an average value.

  Incidentally, although not shown in FIG. 2, the developing device 14 is provided with a conveyance amount regulating member facing the developing roll 145, and the interval between the conveyance amount regulating member and the developing roll 145 is adjusted. Thus, the transport amount of the developer is controlled. Developers containing sufficiently spheroidized toner particles have increased fluidity and at the same time solidified and increased bulk density. As a result, there may be a phenomenon in which developer accumulation occurs at the conveyance amount regulating portion and the conveyance amount becomes unstable. For this phenomenon, it is conceivable to stabilize the transport amount by controlling the surface roughness of the developing roll 145 or by narrowing the distance between the transport amount regulating member and the developing roll 145. Packing properties due to stagnation become stronger, and further, stress applied to the toner particles becomes stronger. For this reason, when a fine structure change on the surface of the toner particles, especially when inorganic fine particles having a large particle diameter are added, the inorganic fine particles are easily detached from the toner particle surface. It will damage the sex. However, according to the image forming apparatus 1 shown in FIG. 1, it is not necessary to add inorganic fine particles having a large particle diameter, and thus toner particles that are sufficiently spherical can be used.

  In addition, the toner particles used in the image forming apparatus 1 shown in FIG. 1 have an average particle size of 50% with a cumulative distribution drawn from the small diameter side with respect to the volume with respect to the particle size range divided based on the particle size distribution. When expressed by the volume average particle diameter D, the value of the volume average particle diameter D falls within the range of 2 μm to 9 μm, and preferably falls within the range of 5 μm to 8 μm. When the volume average particle diameter D is less than 2 μm, the desired charge distribution cannot be obtained, so that the toner particles are easily scattered from the developing device, causing contamination in the image forming apparatus, or the toner particles are magnetic carrier particles. In some cases, the toner chargeability may be reduced. On the other hand, even when the volume average particle diameter D exceeds 9 μm, a desired charged cloth cannot be obtained, and problems such as easy deterioration of image quality occur.

  In the present invention, toner particles to which no release agent or charge control agent is added may be used.

  As the core particles constituting the magnetic carrier particles, known particles such as metal powder exhibiting ferromagnetism such as ferrite, magnetite, iron, cobalt and nickel can be used. Among these, it is preferable to use a ferrite having a relatively low specific gravity in order to suppress carrier contamination and toner carrier peeling on the carrier surface due to stress received in the developing device.

As ferrite, a magnetic material formed by granulating and sintering an oxide of one or more elements selected from Li, Mg, Ca, Mn, Ni, Cu, and Zn and Fe ₂ O ₃ as main components. It is preferable in that the particles can easily obtain the desired magnetic susceptibility, and further, formed by granulating and sintering with an oxide of one or more elements selected from Li, Mg, and Mn and Fe ₂ O ₃ as main components. The obtained magnetic particles are more preferable because they can easily obtain both desired magnetic susceptibility and desired electric resistance.

  A well-known means can be used for the manufacturing method of a ferrite particle. For example, the pulverized ferrite composition is mixed with a binder, water, a dispersant, an organic solvent, etc., and particles are made using a spray drying method or fluidized granulation method, and then fired in a rotary kiln or batch incinerator. And a method of classifying by sieving to control the particle size distribution to obtain a carrier core material. In the firing stage, it is also possible to control the electrical resistance of the core material by controlling the oxygen partial pressure or by adding oxidation or reduction treatment on the particle surface after firing.

  The surface of the core particle is coated with a coating agent excellent in chargeability with respect to the toner particle that charges the toner particle to a predetermined polarity by friction with the toner particle than the core particle. Further, as described above, both the inner peripheral surface of the fresh toner supply tank 141 and the inner peripheral surface of the fresh toner supply nozzle 142 are covered with this coating agent. Coating agents include polyolefin resins such as polyethylene, polypropylene; polyvinyl and polyvinylidene resins such as polystyrene, acrylic resin, polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl carbazole, polyvinyl ether and polyvinyl. Ketone; Vinyl chloride-vinyl acetate copolymer; Styrene-acrylic acid copolymer; Straight silicone resin composed of organosiloxane bond or its modified product; Fluororesin such as polytetrafluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, poly Polyester; Polyurethane; Polycarbonate; Phenol resin; Amino resin such as urea-formaldehyde Fat, melamine resins, benzoguanamine resins, urea resins, polyamide resins, epoxy resins, and the like. In order to minimize the resistance change due to toner contamination on the carrier surface, it is preferable to use a resin having a critical surface tension (γc) of 30 dyn / cm or less for a part or the whole of the matrix resin. As resins having a critical surface tension of 30 dyn / cm or less, polyvinyl fluoride (γc = 28 dyn / cm), polyvinylidene fluoride (γc = 25 dyn / cm), polytrifluoroethylene (γc = 22 dyn / cm), polytetrafluoro There are ethylene (γc = 18 dyn / cm), polyhexafluoropropylene (γc = 16 dyn / cm), etc., and others are copolymers of vinylidene fluoride and acrylic monomers, vinylidene fluoride and vinyl fluoride And a resin having a critical surface tension of 35 dyn / cm or less, such as a terpolymer of tetrafluoroethylene, vinylidene fluoride and a non-fluorinated monomer. In particular, it is more preferable to contain a fluorine-containing resin, polymer, and / or silicone resin having a critical surface tension of 30 dyn / cm or less.

  Moreover, you may externally add electroconductive fine particles on a core particle with a coating agent. The conductive fine particles used here include metals such as gold, silver and copper; carbon black; and semiconductive oxides such as titanium oxide and zinc oxide; titanium oxide, zinc oxide, barium sulfate and aluminum borate. In addition, the surface of a potassium titanate powder or the like covered with tin oxide, carbon black, or metal can be used. In particular, carbon black is preferable from the viewpoints of production stability, cost, good conductivity, and the like. The type of carbon black is not particularly limited, and known ones can be used, and carbon black having a DBP (dibutyl phthalate) oil absorption in the range of 50 to 300 ml / g with good production stability is preferred. Furthermore, the average particle size of carbon black is preferably 0.1 μm or less, and the primary particle size is preferably 50 nm or less in order to obtain better dispersibility. Furthermore, for the purpose of charge control, coating strength control, etc., in addition to the coating agent and conductive fine particles, crosslinkable organic particles, magnetic fine particles and the like may be contained.

  As a method for forming a coating material such as a coating agent or conductive fine particles on the surface of the core particle, typically, a raw material solution for forming a coating layer (including a coating agent, resin fine particles, and conductive fine powder in a solvent) There are various coating methods using Specifically, for example, a dipping method in which the powder of the core particles is immersed in the raw material solution for forming the coating layer, a spray method in which the raw material solution for forming the coating layer is sprayed on the surface of the core particles, and the core particles are suspended by flowing air Examples thereof include a fluidized bed method in which the coating layer forming raw material solution is sprayed in a state, a kneader coater method in which the core particles and the coating layer forming raw material solution are mixed in a kneader coater, and the solvent is removed. The solvent used for the raw material solution for forming the coating layer is not particularly limited as long as it dissolves the coating agent. For example, aromatic hydrocarbons such as toluene and xylene, ketones such as acetone and methyl ethyl ketone, Ethers such as tetrahydrofuran and dioxane can be used.

  Further, a method for coating the inner peripheral surface of the fresh toner supply tank 141 and the inner peripheral surface of the fresh toner supply nozzle 142 with this coating agent is not particularly limited. For example, a known dip method or spray method is used. May be used.

  Next, the second to fifth embodiments of the image forming apparatus according to the present invention will be described. Any of the image forming apparatuses from the second embodiment to the fifth embodiment is an image forming apparatus adopting a full-color tandem system, and the rough configuration is the configuration of the image forming apparatus of the first embodiment shown in FIG. Is the same. The developing device provided in the toner image forming unit of any of the image forming apparatuses from the second embodiment to the fifth embodiment is provided with fresh toner supply means, and the cleaning apparatus is provided with toner recovery means. Has been. Each of the fresh toner supply means and the toner recovery means in these embodiments includes a coating member coated with a coating agent excellent in chargeability with respect to the toner particles coating the surface of the core portion of the magnetic carrier particles. The toner particles are charged by relatively rubbing the toner particles and the coating member, but the configuration is different. Hereinafter, the same constituent elements as those described in the first embodiment will be described with the same reference numerals as those used so far.

  First, an image forming apparatus according to a second embodiment will be described with reference to FIG. FIG. 2 is an enlarged view of the toner image forming unit provided in the image forming apparatus according to the first embodiment. However, the image forming apparatus according to the second embodiment also has a fresh toner supply tank 141 and a fresh toner supply nozzle 142. , And the configuration of the toner image forming unit provided in the image forming apparatus of the first embodiment, except for the configuration of the fresh toner supply unit having the three components of the conveyance member 1421 and the configuration of the toner recovery unit 152. A toner image forming unit is provided.

  In the fresh toner supply means in the second embodiment, the inner peripheral surface of the fresh toner replenishment tank 141 and the inner peripheral surface of the fresh toner replenishment nozzle 142 against the toner particles coating the surface of the core portion of the magnetic carrier particles. Instead of being coated with a coating agent having excellent chargeability, the surface of the conveying member 1421 is coated with the coating agent. New toner particles passing through the fresh toner replenishing nozzle 142 are frictionally charged by friction with the surface of the transport member 1421 while being transported to the first stirring chamber 143 by the transport member 1421 rotating.

  Further, in the toner collecting unit 152, instead of the inner peripheral surface of the conveyance path 1522 being covered with the coating agent, the surface of the conveying member 1523 is covered with the coating agent. The toner particles scraped off from the surface of the photosensitive drum passing through the conveyance path 1522 are frictionally charged by sliding against the surface of the conveyance member 1523 while being returned to the first stirring chamber 143 by the rotation of the conveyance member 1523. The

According to the image forming apparatus of the present embodiment, when the maximum value of the charge distribution of new toner particles just added to the fresh toner supply tank 141 is Ft,
| Dt | = | Ft | × 1.5 Equation 9
When the relationship of the above equation 9 is established and the maximum value of the charge distribution of the toner particles scraped off from the surface of the photosensitive drum just sent to the conveyance path 1522 of the toner collecting unit 152 is Jt,
| Dt | = | Jt | × 1.5 Equation 10
The relationship of Equation 10 is established, and in addition to the relationships of Equation 1 to Equation 4, the relationships of Equation 9 and Equation 10 are also established.

  Note that all three of the inner peripheral surface of the fresh toner supply tank 141, the inner peripheral surface of the fresh toner supply nozzle 142, and the surface of the conveying member 1421 may be covered with a coating agent. Both the peripheral surface and the surface of the conveying member 1523 may be covered with a coating agent.

  Next, an image forming apparatus according to a third embodiment will be described with reference to FIG.

  FIG. 3 is an enlarged view of the toner image forming unit provided in the image forming apparatus according to the third embodiment.

  In addition to the screw-like conveyance member 1421, the conveyance member constituting the fresh toner supply unit in the third embodiment also includes a roll member 1422 that rotates on the downstream side of the screw-like conveyance member 1421. Further, the fresh toner supply means in this embodiment also has a blade 1423. The blade 1423 is disposed inside the fresh toner replenishing nozzle 142, and new toner particles replenished from the fresh toner replenishing tank 141 disposed above the blade 1423 are disposed on the blade 1423. It falls on the surface 1423a. The roll member 1422 rotates while being in contact with the surface 1423 a of the blade 1423, and feeds the toner particles dropped onto the surface 1423 a of the blade 1423 toward the first stirring chamber 143.

  In addition to the screw-like conveyance member 1523, the conveyance member of the toner collecting unit 152 includes a roll member 1524 that rotates on the downstream side of the screw-like conveyance member 1523 in the same manner as the conveyance member constituting the fresh toner supply unit. I have. Further, the toner collecting unit 152 also has a blade 1525 disposed inside the conveyance path 1522. The toner particles removed from the surface of the photosensitive drum and conveyed by the screw-shaped conveying member 1523 fall on the surface 1525a of the blade 1525. The roll member 1524 rotates while being in contact with the surface 1525 a of the blade 1525, and returns the toner particles dropped on the surface 1525 a of the blade 1525 to the first stirring chamber 143.

  In the fresh toner supply means in the third embodiment, both the inner peripheral surface of the fresh toner supply nozzle 142 and the blade surface 1423a are charged to the toner particles coating the surface of the core portion of the magnetic carrier particles. Is coated with an excellent coating agent. New toner particles passing through the fresh toner replenishing nozzle 142 are frictionally charged by rubbing against the inner peripheral surface of the fresh toner replenishing nozzle 142 and at the same time, rubbing against the blade surface 1423 a by rotating the roll member 1422. Is also triboelectrically charged.

  In the toner collecting unit 152, both the inner peripheral surface of the conveyance path 1522 and the blade surface 1525a are covered with the coating agent. The toner particles scraped off from the surface of the photosensitive drum passing through the conveyance path 1522 are triboelectrically charged by rubbing against the inner peripheral surface of the conveyance path 1522, and the roll member 1524 rotates to rotate the blade surface 1525a. It is also triboelectrically charged by sliding.

According to the image forming apparatus of the present embodiment, when the maximum value of the charge distribution of fresh toner particles just added to the fresh toner supply tank 141 is Ft,
| Dt | = | Ft | × 1.1 Equation 11
When the relationship of the above equation 11 is established and the maximum value of the charge distribution of the toner particles scraped off from the surface of the photosensitive drum just sent to the conveyance path 1522 of the toner collecting unit 152 is Jt,
| Dt | = | Jt | × 1.1 Equation 12
The relationship of the above equation 12 is established, and in addition to the relationships of the above equations 1 to 4, the relationships of the equations 11 and 12 are also established.

  In both the fresh toner supply means and the toner recovery means, instead of the blade surfaces 1423a and 1525a being coated with the coating agent, the peripheral surfaces of the roll members 1422 and 1524, that is, the surfaces that contact the blade surfaces 1423a and 1525a. May be coated with a coating agent, or both the blade surfaces 1423a and 1525a and the peripheral surfaces of the roll members 1422 and 1524 may be coated with a coating agent.

  Next, an image forming apparatus according to a fourth embodiment will be described with reference to FIG.

  FIG. 4 is an enlarged view of the toner image forming unit provided in the image forming apparatus according to the fourth embodiment.

  The fresh toner supply means in the fourth embodiment has an acrylic carbon fiber roll brush 1424 in addition to the three components of the fresh toner supply tank 141, the fresh toner supply nozzle 142, and the screw-shaped conveying member 1421. The roll brush 1424 is disposed at the end (exit) of the fresh toner supply nozzle 142 on the first stirring chamber 143 side, and the tip portion of the acrylic carbon fiber is brought into contact with the inner peripheral surface of the fresh toner supply nozzle 142. It rotates in a state. New toner particles conveyed from above by the conveying member 1421 fall onto the roll brush 1424 and are carried on the front end portion of the acrylic carbon fiber, and the front end portion of the acrylic carbon fiber is rotated by the roll brush 1424 rotating. And the fresh toner replenishing nozzle 142 are supplied to the first stirring chamber 143.

  The toner recovery unit 152 also includes an acrylic carbon fiber roll brush 1526 disposed at the end (exit) of the conveyance path 1522 on the first stirring chamber 143 side. The roll brush 1526 rotates in a state where the tip end portion of the acrylic carbon fiber is in contact with the inner peripheral surface of the conveyance path 1522. The toner particles removed from the surface of the photosensitive drum conveyed by the conveying member 1523 fall on the roll brush 1526 and are carried on the tip portion of the acrylic carbon fiber. The carbon fiber passes between the front end portion of the carbon fiber and the inner peripheral surface of the conveyance path 1522 and is returned to the first stirring chamber 143.

  In the fourth embodiment, the surface of the acrylic carbon fiber of the roll brushes 1424 and 1526 is charged to the toner particles coating the surface of the core of the magnetic carrier particles in both the fresh toner supply means and the toner collection means. It is covered with a coating agent with excellent properties. The toner particles dropped on the rotating roll brush 1424 are carried on the tip portion of the acrylic carbon fiber and move to the inner peripheral surface of the fresh toner replenishing nozzle 142 or the inner peripheral surface of the conveying path 1522, and the inner peripheral surface thereof. And triboelectrically charged by rubbing when passing between the end portions of the acrylic carbon fibers.

According to the image forming apparatus of the present embodiment, when the maximum value of the charge distribution of new toner particles just added to the fresh toner supply tank 141 is Ft,
| Dt | = | Ft | × 1.25 Equation 13
When the relationship of the above equation 13 is established and the maximum value of the charge distribution of the toner particles scraped off from the surface of the photosensitive drum just sent to the conveyance path 1522 of the toner collecting unit 152 is Jt,
| Dt | = | Jt | × 1.25 Equation 14
The relationship of the above equation 14 is established, and in addition to the relationships from the above equations 1 to 4, the relationship of the equation 13 and the equation 14 is also established.

  In both the fresh toner supply means and the toner recovery means, the roll brushes 1424 and 1526 are not limited to acrylic carbon fibers but may be insulating or semiconductive fibers.

  Next, an image forming apparatus according to a fifth embodiment will be described with reference to FIG.

  FIG. 5 is an enlarged view of the toner image forming unit provided in the image forming apparatus according to the fifth embodiment.

  In the fifth embodiment, both the fresh toner supply means and the toner collection means 152 have mesh members 1425 and 1527, respectively, instead of the roll brush of the fourth embodiment. Similar to the roll brushes 1424 and 1526 shown in FIG. 4, the mesh members 1425 and 1527 are also arranged at the outlet of the fresh toner supply nozzle 142 or the outlet of the conveyance path 1522. The mesh members 1425 and 1527 are supplied with toner particles in which surfaces 1425a and 1527a having a mesh size of 500 μm larger than the particle diameter of the toner particles are removed from the upstream side in the supply direction of new toner particles or from the surface of the photosensitive drum. It vibrates in the direction in which its surfaces 1425a and 1527a spread (in the horizontal direction in FIG. 5) in a posture facing the coming direction. New toner particles conveyed from above by the conveying member 1421 fall on the vibrating surface 1425a of the mesh member 1425 and are supplied to the first stirring chamber 143 through the mesh. In addition, toner particles removed from the surface of the photosensitive drum, which have been transported from above by the transport member 1523, fall onto the vibrating surface 1527 a of the mesh member 1527, and are returned to the first stirring chamber 143 through the mesh. .

In the fifth embodiment, the surfaces 1425a and 1527a of the mesh members 1425 and 1527 are coated with a coating agent having excellent chargeability with respect to toner particles coating the surface of the core portion of the magnetic carrier particles. . The toner particles dropped on the vibrating surfaces 1425a and 1527a of the mesh members 1425 and 1527 are rubbed and frictionally charged with the surfaces 1425a and 1527a by the vibration. According to the image forming apparatus of the present embodiment, when the maximum value of the charge distribution of new toner particles just added to the fresh toner supply tank 141 is Ft,
| Dt | = | Ft | × 1.65 Equation 15
When the relationship of the above equation 15 is established and the maximum value of the charge distribution of the toner particles scraped off from the surface of the photosensitive drum just sent to the conveyance path 1522 of the toner collecting unit 152 is Jt,
| Dt | = | Jt | × 1.65 Equation 16
The relationship of the above equation 16 is established, and in addition to the relationships from the above equations 1 to 4, the relationships of the equations 15 and 16 are also established.

  In addition, each mesh member 1425,1527 should just be a thing of the mesh | network of 100 micrometers or more and 500 micrometers or less, it is preferable if it is a mesh of 200 micrometers or more and 500 micrometers or less, and it is more preferable if it is a thing of 400 micrometers or more and 500 micrometers or less. When the mesh is less than 100 μm, the mesh is clogged or the toner particles are blocked. On the other hand, when the mesh exceeds 500 μm, the frictional charging of the toner particles becomes insufficient, and a desired charge distribution cannot be obtained.

  The image forming apparatuses from the first embodiment to the fifth embodiment have been described above. However, all of these image forming apparatuses have toner fluidity, chargeability, developability, transferability, and fixability simultaneously and for a long time. In addition, it is possible to suppress the occurrence of image quality defects caused by the recovered toner particles, and in particular external fine particles having a certain large particle diameter that can improve toner fluidity, chargeability, developability, and transferability. Therefore, the image forming apparatus is small in size and low in cost, and can stably form clear images without fogging without providing a further cleaning mechanism on the charging roll or the like.

The image forming apparatuses from the first embodiment to the fifth embodiment are all image forming apparatuses adopting a full-color tandem method using four color toners. May be adopted. For example, the present invention can be applied to an image forming apparatus provided with a developing device having more than four colors. Further, the charging method of the photosensitive drum 11 is not limited to the contact charging method using the charging roll 12, and may be a non-contact charging method.
(Example)
Examples of the present invention will be described below, but the present invention is not limited to these examples.
Example 1
Using the image forming apparatus of the first embodiment described above, a running test of 60000 monochrome images was performed. That is, both the inner peripheral surface of the toner replenishing tank and the inner peripheral surface of the toner replenishing nozzle of the developing device, and the toner recovery means transport path are all against the toner particles coating the surface of the core portion of the magnetic carrier particles An image forming apparatus that is covered with a coating agent having excellent chargeability and does not have a mechanism for cleaning the surface of a charging roll having a single layer structure with an outer diameter of 14 mm was used. As the developer, a negatively chargeable two-component developer was used. As the K (black) toner particles contained in the developer, substantially spherical polymerization wet toner particles having a volume average particle diameter of 6.4 μm and a shape factor value (SF) of 132 were used. Further, two types of inorganic fine particles having an average particle diameter of 40 nm and one type of inorganic fine particles having a size of 50 nm were used as external additives for the toner particles.

The maximum charge distribution Dt of new toner particles immediately before being supplied from the fresh toner supply tank to the first stirring chamber through the fresh toner supply nozzle is returned to the first stirring chamber through the conveyance path of the toner collecting means. The maximum value Dt ′ of the charge distribution of the toner particles scraped off from the surface of the photosensitive drum immediately before, the maximum value St of the charge distribution of the toner particles in the toner image formed on the photosensitive drum, and carried on the developing roll. The maximum values Pt and St / Pt of the charge distribution of the toner particles are as shown in Table 1 below.
[Cover evaluation method]
The density of the background portion on the print and the density when the surface of the photosensitive drum was transferred to the OHP sheet with tape after the running test were visually evaluated. The evaluation criteria are as follows. The evaluation results are shown in Table 1 below.
○: No fogging was confirmed.
X: Background part fogging occurred.
[Halftone stripe evaluation method and charging roll contamination evaluation method]
After the running test, image quality defects such as streaks in the halftone on the print were visually evaluated. The contamination of the charging roll at this time was also evaluated visually. The evaluation criteria are as follows. The evaluation results are shown in Table 1 below.
○: Streaks or the like were not confirmed in the halftone on the print, and the charging roll was not contaminated.
X: Streaks or the like were confirmed in the halftone on the print, and the charging roll was contaminated.
[Solid density and unevenness evaluation method]
After the running test, the image quality defects such as the density and unevenness of the solid portion on the print were visually evaluated. The evaluation criteria are as follows. The evaluation results are shown in Table 1 below.
○: Concentration abnormality and unevenness were not confirmed in the solid part.
X: Abnormal density and unevenness were confirmed in the solid part.
(Example 2)
The charging roll provided in the toner image forming unit of the image forming apparatus in the first embodiment is replaced with a two-layer structure having an outer diameter of 10 mm, and K (black) toner particles having a volume average particle diameter of 6.8 μm. A running test of 60000 monochrome images was performed in the same manner as in Example 1 except that substantially spherical polymerization method wet toner particles having a shape factor value (SF) of 133 were used.

  The maximum value of each charge distribution and the value of St / Pt are as shown in Table 1 below.

Further, by the above-described methods, fogging evaluation, halftone streak evaluation, solid density and unevenness were evaluated. The results are shown in Table 1 below.
(Example 3)
As the K (black) color toner particles, substantially spherical polymerization method wet toner particles having a volume average particle diameter of 6.2 μm and a shape factor value (SF) of 130 are used. A running test of 60000 sheets of monochrome images was performed in the same manner as in Example 1 except that only two types of inorganic fine particles having an average particle size of 40 nm were used without using inorganic fine particles having a particle size of 50 nm.

  The maximum value of each charge distribution and the value of St / Pt are as shown in Table 1 below.

Moreover, various evaluation was performed by each method mentioned above. The results are shown in Table 1 below.
Example 4
Using the image forming apparatus of the second embodiment described above, a running test of 60000 monochrome images was performed. That is, both the surface of the conveying member provided in the fresh toner replenishing nozzle of the developing device and the surface of the conveying member of the toner collecting means are charged to the toner particles coating the surface of the core of the magnetic carrier particles. An image forming apparatus coated with an excellent coating agent was used. Except for this, a running test of 60000 monochrome images was performed in the same manner as in Example 1.

  The maximum value of each charge distribution and the value of St / Pt are as shown in Table 1 below.

Moreover, various evaluation was performed by each method mentioned above. The results are shown in Table 1 below.
(Example 5)
The charging roll provided in the toner image forming unit of the image forming apparatus in the second embodiment is changed from a single-layer structure having an outer diameter of 14 mm to a two-layer structure having an outer diameter of 10 mm, and K (black) toner A running test of 60000 monochrome images in the same manner as in Example 4 except that substantially spherical polymerization method wet toner particles having a volume average particle diameter of 6.8 μm and a shape factor value (SF) of 133 are used as particles. Went.

  The maximum value of each charge distribution and the value of St / Pt are as shown in Table 1 below.

Moreover, various evaluation was performed by each method mentioned above. The results are shown in Table 1 below.
(Example 6)
As the K (black) color toner particles, substantially spherical polymerization method wet toner particles having a volume average particle diameter of 6.2 μm and a shape factor value (SF) of 130 are used. A running test of 60000 sheets of monochrome images was performed in the same manner as in Example 4 except that only two types of inorganic fine particles having an average particle size of 40 nm were used without using inorganic fine particles having a particle size of 50 nm.

  The maximum value of each charge distribution and the value of St / Pt are as shown in Table 1 below.

Moreover, various evaluation was performed by each method mentioned above. The results are shown in Table 1 below.
(Example 7)
Using the image forming apparatus of the third embodiment described above, a running test of 60000 monochrome images was performed. That is, both the inner peripheral surface of the fresh toner replenishing nozzle and the surface of the blade disposed in the fresh toner replenishing nozzle of the developing device, the inner peripheral surface of the transport path of the toner recovery means, and the interior of the transport path An image forming apparatus in which both the surface of the deployed blade and the surface of the blade were covered with a coating agent was used. Except for this, a running test of 60000 monochrome images was performed in the same manner as in Example 1.

  The maximum value of each charge distribution and the value of St / Pt are as shown in Table 1 below.

Moreover, various evaluation was performed by each method mentioned above. The results are shown in Table 1 below.
(Example 8)
The charging roll provided in the toner image forming unit of the image forming apparatus in the third embodiment is changed from a single-layer structure having an outer diameter of 14 mm to a two-layer structure having an outer diameter of 10 mm, and K (black) toner A running test of 60000 monochrome images in the same manner as in Example 7 except that substantially spherical polymerization method wet toner particles having a volume average particle diameter of 6.8 μm and a shape factor value (SF) of 133 are used as particles. Went.

  The maximum value of each charge distribution and the value of St / Pt are as shown in Table 1 below.

Moreover, various evaluation was performed by each method mentioned above. The results are shown in Table 1 below.
Example 9
As the K (black) color toner particles, substantially spherical polymerization method wet toner particles having a volume average particle diameter of 6.2 μm and a shape factor value (SF) of 130 are used. A running test of 60000 monochrome images was performed in the same manner as in Example 7 except that inorganic fine particles having a particle diameter of 50 nm were not used and only two kinds of inorganic fine particles having an average particle diameter of 40 nm were used.

  The maximum value of each charge distribution and the value of St / Pt are as shown in Table 1 below.

Moreover, various evaluation was performed by each method mentioned above. The results are shown in Table 1 below.
(Example 10)
Using the image forming apparatus of the fourth embodiment described above, a running test of 60000 monochrome images was performed. That is, an image in which a roll brush coated with a coating agent is disposed at the outlet of the fresh toner replenishing nozzle of the developing device, and a roll brush coated with the coating agent is disposed at the outlet of the conveyance path of the toner recovery means. A forming device was used. Except for this, a running test of 60000 monochrome images was performed in the same manner as in Example 1.

  The maximum value of each charge distribution and the value of St / Pt are as shown in Table 1 below.

Moreover, various evaluation was performed by each method mentioned above. The results are shown in Table 1 below.
(Example 11)
The charging roll provided in the toner image forming unit of the image forming apparatus in the fourth embodiment is changed from a single-layer structure having an outer diameter of 14 mm to a two-layer structure having an outer diameter of 10 mm, and K (black) toner A running test of 60000 monochrome images in the same manner as in Example 10 except that substantially spherical polymerization method wet toner particles having a volume average particle diameter of 6.8 μm and a shape factor value (SF) of 133 are used as particles. Went.

  The maximum value of each charge distribution and the value of St / Pt are as shown in Table 1 below.

Moreover, various evaluation was performed by each method mentioned above. The results are shown in Table 1 below.
(Example 12)
As the K (black) color toner particles, substantially spherical polymerization method wet toner particles having a volume average particle diameter of 6.2 μm and a shape factor value (SF) of 130 are used. A running test of 60,000 monochrome images was performed in the same manner as in Example 10 except that only two types of inorganic fine particles having an average particle size of 40 nm were used without using inorganic fine particles having a particle size of 50 nm.

  The maximum value of each charge distribution and the value of St / Pt are as shown in Table 1 below.

Moreover, various evaluation was performed by each method mentioned above. The results are shown in Table 1 below.
(Example 13)
Using the image forming apparatus of the fifth embodiment described above, a running test of 60000 monochrome images was performed. That is, an image forming apparatus was used in which a mesh member having a 500 μm mesh surface coated with a coating agent was provided at each of the outlet of the fresh toner supply nozzle of the developing device and the outlet of the conveyance path of the toner collecting unit. Except for this, a running test of 60000 monochrome images was performed in the same manner as in Example 1.

  The maximum value of each charge distribution and the value of St / Pt are as shown in Table 1 below.

Moreover, various evaluation was performed by each method mentioned above. The results are shown in Table 1 below.
(Example 14)
The charging roll provided in the toner image forming unit of the image forming apparatus according to the fifth embodiment is changed from a single-layer structure having an outer diameter of 14 mm to a two-layer structure having an outer diameter of 10 mm. Further, as the K (black) color toner particles, substantially spherical polymerization method wet toner particles having a volume average particle diameter of 6.8 μm and a shape factor value (SF) of 133 were used. Except for these, a running test of 60000 monochrome images was performed in the same manner as in Example 13.

  The maximum value of each charge distribution and the value of St / Pt are as shown in Table 1 below.

Moreover, various evaluation was performed by each method mentioned above. The results are shown in Table 1 below.
(Example 15)
As the K (black) color toner particles, substantially spherical polymerization method wet toner particles having a volume average particle diameter of 6.2 μm and a shape factor value (SF) of 130 are used. Two types of inorganic fine particles with an average particle size of 40 nm were used without using inorganic fine particles with a particle size of 50 nm. Except for these changes, a running test of 60000 monochrome images was performed in the same manner as in Example 13.

  The maximum value of each charge distribution and the value of St / Pt are as shown in Table 1 below.

Moreover, various evaluation was performed by each method mentioned above. The results are shown in Table 1 below.
(Comparative Example 1)
The developing device provided in the toner image forming unit of the image forming apparatus according to the first embodiment covers both the fresh toner replenishing tank and the fresh toner replenishing nozzle and the transport path of the toner collecting means from those coated with a coating agent. I replaced it with something not done. Further, as the K (black) toner particles, substantially spherical polymerization method wet toner particles having a volume average particle diameter of 7.0 μm and a shape factor value (SF) of 130 are used. In addition to the use of one inorganic fine particle having an average particle diameter of 40 nm and one inorganic fine particle having a thickness of 50 nm, one kind of inorganic fine particle having an average particle diameter of 140 nm was used. Except for these changes, a running test of 60000 monochrome images was performed in the same manner as in Example 1.

  The maximum value of each charge distribution and the value of St / Pt are as shown in Table 1 below.

Further, by the above-described methods, fogging evaluation, halftone streak evaluation, solid density and unevenness were evaluated. The results are shown in Table 1 below.
(Comparative Example 2)
The charging roll provided in the toner image forming unit of the image forming apparatus used in Comparative Example 1 is changed from a single-layer structure having an outer diameter of 14 mm to a two-layer structure having an outer diameter of 10 mm. 60000 sheets of monochrome images were run in the same manner as Comparative Example 1 except that substantially spherical polymerization method wet toner particles having a volume average particle diameter of 7.4 μm and a shape factor value (SF) = 131 were used as toner particles. Tested.

  The maximum value of each charge distribution and the value of St / Pt are as shown in Table 1 below.

Further, by the above-described methods, fogging evaluation, halftone streak evaluation, solid density and unevenness were evaluated. The results are shown in Table 1 below.
(Comparative Example 3)
As the K (black) color toner particles, substantially spherical polymerization method wet toner particles having a volume average particle diameter of 6.4 μm and a shape factor value (SF) of 132 are used. 60,000 monochrome images in the same manner as in Comparative Example 1 except that one type of inorganic fine particle having an average particle size of 20 nm and one type of inorganic fine particle having a size of 40 nm were used without using inorganic fine particles having a large particle size of 140 nm. A running test was conducted.

  The maximum value of each charge distribution and the value of St / Pt are as shown in Table 1 below.

Moreover, various evaluation was performed by each method mentioned above. The results are shown in Table 1 below.
(Comparative Example 4)
In the developing device provided in the toner image forming unit of the image forming apparatus according to the second embodiment, both the conveying member provided in the fresh toner replenishing nozzle and the conveying member of the toner collecting unit are covered with a coating agent. The thing was replaced with the uncoated one. Further, as the K (black) toner particles, substantially spherical polymerization method wet toner particles having a volume average particle diameter of 7.0 μm and a shape factor value (SF) of 130 are used. In addition to the use of one inorganic fine particle having an average particle diameter of 40 nm and one inorganic fine particle having a thickness of 50 nm, one kind of inorganic fine particle having an average particle diameter of 140 nm was used. Except for these changes, a running test of 60000 monochrome images was performed in the same manner as in Example 4.

  The maximum value of each charge distribution and the value of St / Pt are as shown in Table 1 below.

Moreover, various evaluation was performed by each method mentioned above. The results are shown in Table 1 below.
(Comparative Example 5)
The charging roll provided in the toner image forming unit of the image forming apparatus used in Comparative Example 4 is changed from a single-layer structure having an outer diameter of 14 mm to a two-layer structure having an outer diameter of 10 mm. 60000 sheets of monochrome images were run in the same manner as Comparative Example 4 except that substantially spherical polymerization method wet toner particles having a volume average particle diameter of 7.4 μm and a shape factor value (SF) = 131 were used as toner particles. Tested.

  The maximum value of each charge distribution and the value of St / Pt are as shown in Table 1 below.

Moreover, various evaluation was performed by each method mentioned above. The results are shown in Table 1 below.
(Comparative Example 6)
As the K (black) color toner particles, substantially spherical polymerization method wet toner particles having a volume average particle diameter of 6.4 μm and a shape factor value (SF) of 132 are used. 60,000 monochrome images in the same manner as in Comparative Example 4 except that one inorganic particle having an average particle size of 20 nm and one inorganic particle having a particle size of 40 nm were used without using inorganic particles having a large particle diameter of 140 nm. A running test was conducted.

  The maximum value of each charge distribution and the value of St / Pt are as shown in Table 1 below.

Moreover, various evaluation was performed by each method mentioned above. The results are shown in Table 1 below.
(Comparative Example 7)
In the developing device provided in the toner image forming unit of the image forming apparatus according to the third embodiment, both the fresh toner replenishing nozzle and the blade disposed inside the fresh toner replenishing nozzle, and the conveying path of the toner collecting means, Both the blade disposed inside the conveyance path and the blade coated with the coating agent were replaced with those not coated. Further, as the K (black) toner particles, substantially spherical polymerization method wet toner particles having a volume average particle diameter of 7.0 μm and a shape factor value (SF) of 130 are used. In addition to the use of one inorganic fine particle having an average particle diameter of 40 nm and one inorganic fine particle having a thickness of 50 nm, one kind of inorganic fine particle having an average particle diameter of 140 nm was used. Except for these changes, a running test for 60000 monochrome images was performed in the same manner as in Example 7.

  The maximum value of each charge distribution and the value of St / Pt are as shown in Table 1 below.

Moreover, various evaluation was performed by each method mentioned above. The results are shown in Table 1 below.
(Comparative Example 8)
The charging roll provided in the toner image forming unit of the image forming apparatus used in Comparative Example 7 is changed from a single-layer structure having an outer diameter of 14 mm to a two-layer structure having an outer diameter of 10 mm. 60000 sheets of monochrome images were run in the same manner as in Comparative Example 7 except that substantially spherical polymerization method wet toner particles having a volume average particle diameter of 7.4 μm and a shape factor value (SF) = 131 were used as toner particles. Tested.

  The maximum value of each charge distribution and the value of St / Pt are as shown in Table 1 below.

Moreover, various evaluation was performed by each method mentioned above. The results are shown in Table 1 below.
(Comparative Example 9)
As the K (black) color toner particles, substantially spherical polymerization method wet toner particles having a volume average particle diameter of 6.4 μm and a shape factor value (SF) of 132 are used. 60,000 monochrome images in the same manner as in Comparative Example 7, except that one inorganic inorganic particle having an average particle diameter of 20 nm and one 40 nm inorganic particle were used without using a large inorganic particle having a particle diameter of 140 nm. A running test was conducted.

  The maximum value of each charge distribution and the value of St / Pt are as shown in Table 1 below.

Moreover, various evaluation was performed by each method mentioned above. The results are shown in Table 1 below.
(Comparative Example 10)
The roll brush covered with the coating agent is removed from the outlet of the fresh toner supply nozzle of the developing device provided in the toner image forming unit of the image forming apparatus in the fourth embodiment, and also from the outlet of the conveying path of the toner recovery unit. The image forming apparatus from which the roll brush coated with the coating agent was removed was used. Further, as the K (black) toner particles, substantially spherical polymerization method wet toner particles having a volume average particle diameter of 7.0 μm and a shape factor value (SF) of 130 are used. In addition to the use of one inorganic fine particle having an average particle diameter of 40 nm and one inorganic fine particle having a thickness of 50 nm, one kind of inorganic fine particle having an average particle diameter of 140 nm was used. Except for these changes, a running test of 60000 monochrome images was performed in the same manner as in Example 10.

  The maximum value of each charge distribution and the value of St / Pt are as shown in Table 1 below.

Moreover, various evaluation was performed by each method mentioned above. The results are shown in Table 1 below.
(Comparative Example 11)
The charging roll provided in the toner image forming unit of the image forming apparatus used in Comparative Example 10 is changed from a single-layer structure having an outer diameter of 14 mm to a two-layer structure having an outer diameter of 10 mm. 60000 sheets of monochrome images were run in the same manner as in Comparative Example 10 except that substantially spherical polymerization method wet toner particles having a volume average particle diameter of 7.4 μm and a shape factor value (SF) = 131 were used as toner particles. Tested.

  The maximum value of each charge distribution and the value of St / Pt are as shown in Table 1 below.

Moreover, various evaluation was performed by each method mentioned above. The results are shown in Table 1 below.
(Comparative Example 12)
As the K (black) color toner particles, substantially spherical polymerization method wet toner particles having a volume average particle diameter of 6.4 μm and a shape factor value (SF) of 132 are used. 60,000 monochrome images in the same manner as in Comparative Example 10 except that one inorganic particle having an average particle size of 20 nm and one inorganic particle having a particle size of 40 nm were used without using inorganic particles having a large particle diameter of 140 nm. A running test was conducted.

  The maximum value of each charge distribution and the value of St / Pt are as shown in Table 1 below.

Moreover, various evaluation was performed by each method mentioned above. The results are shown in Table 1 below.
(Comparative Example 13)
The mesh member covered with the coating agent is removed from the outlet of the fresh toner supply nozzle of the developing device provided in the toner image forming unit of the image forming apparatus in the fifth embodiment, and also from the outlet of the conveyance path of the toner recovery unit. An image forming apparatus from which the mesh member covered with the coating agent was removed was used. Further, as the K (black) toner particles, substantially spherical polymerization method wet toner particles having a volume average particle diameter of 7.0 μm and a shape factor value (SF) of 130 are used. In addition to the use of one inorganic fine particle having an average particle diameter of 40 nm and one inorganic fine particle having a thickness of 50 nm, one kind of inorganic fine particle having an average particle diameter of 140 nm was used. Except for these changes, a running test of 60000 monochrome images was performed in the same manner as in Example 13.

  The maximum value of each charge distribution and the value of St / Pt are as shown in Table 1 below.

Moreover, various evaluation was performed by each method mentioned above. The results are shown in Table 1 below.
(Comparative Example 14)
The charging roll provided in the toner image forming unit of the image forming apparatus used in Comparative Example 13 is changed from a single-layer structure having an outer diameter of 14 mm to a two-layer structure having an outer diameter of 10 mm. Similar to Comparative Example 13, 60000 sheets of monochrome images were run, except that substantially spherical polymerization method wet toner particles having a volume average particle diameter of 7.4 μm and a shape factor value (SF) = 131 were used as toner particles. Tested.

  The maximum value of each charge distribution and the value of St / Pt are as shown in Table 1 below.

Moreover, various evaluation was performed by each method mentioned above. The results are shown in Table 1 below.
(Comparative Example 15)
As the K (black) color toner particles, substantially spherical polymerization method wet toner particles having a volume average particle diameter of 6.4 μm and a shape factor value (SF) of 132 are used. 60,000 monochrome images in the same manner as in Comparative Example 13 except that one inorganic particle having an average particle size of 20 nm and one inorganic particle having a particle size of 40 nm were used instead of inorganic particles having a large particle diameter of 140 nm. A running test was conducted.

  The maximum value of each charge distribution and the value of St / Pt are as shown in Table 1 below.

  Further, by the above-described methods, fogging evaluation, halftone streak evaluation, solid density and unevenness were evaluated. The results are shown in Table 1 below.

  In Comparative Examples 3, 6, 9, 12, and 15 in which the maximum values Dt, Dt ′, St, and Pt of each charge distribution of the toner particles in the toner image are large, large particle diameters are used as external additives for the toner particles. Since no inorganic fine particles are added, the inorganic fine particles are not detached from the toner particles, and the charged roll is not contaminated by the separated fine inorganic particles, and the halftone streaks caused by this contamination are also recognized. I couldn't. However, since the charge distribution is wide, fog due to insufficient charging of the toner particles and abnormal density and unevenness of the solit portion due to overcharging of the toner particles were confirmed. Further, in other comparative examples except these comparative examples, since inorganic fine particles having a large particle diameter were added as external additives for toner particles, the inorganic fine particles were detached from the toner particles, and the separated inorganic particles were generated. Contamination of the charging roll with fine particles occurred. Furthermore, halftone streaks caused by this contamination were also confirmed. Further, the maximum value St is 8 (mm) or less, and an image quality defect occurs. The “fogging” means that the volume average particle diameter of the toner particles is large, and furthermore, the toner particles scraped off from the surface of the photosensitive drum include the reversely charged toner particles having different charge polarities and the charge lower than the normal charge amount. This is considered to be caused by insufficient charging of the toner particles distributed on the low charge amount side in the charge distribution due to the presence of a large amount of weakly charged toner particles having only a small amount. Further, it is considered that the abnormal density and unevenness of the solit portion are caused by contamination of the charging roll.

  On the other hand, in each Example, the said Formula 1 to Formula 4 is satisfied simultaneously. That is, the maximum value St in each example is in the range of more than 8 (mm) and not more than 15 (mm). Moreover, all the various evaluation results in each Example are favorable. As a result of the evaluation, the inorganic fine particles are not detached from the toner particles, and the collected toner particles are reused, but some of the charged toner particles existing with a certain charge distribution are insufficiently charged. It can be seen that neither toner particles nor overcharged toner particles were present. Further, when compared with the evaluation results of the respective comparative examples, in order to set the maximum value St to a value greater than 8 (mm) and not more than 15 (mm), supply fresh toner that rubs relatively with new toner particles. The member of the means is coated with a coating agent that is excellent in chargeability with respect to the toner particles coating the surface of the core portion of the magnetic carrier particles, and relative to the toner particles scraped off from the surface of the photosensitive drum. It can also be seen that the member of the toner collecting means that is rubbed can be covered with the coating agent.

1 is a diagram schematically illustrating an image forming apparatus according to a first embodiment of the present invention. FIG. 2 is an enlarged view showing one toner image forming unit of four toner image forming units provided in the image forming apparatus shown in FIG. 1. FIG. 10 is an enlarged view illustrating a toner image forming unit provided in an image forming apparatus according to a third embodiment. FIG. 10 is an enlarged view illustrating a toner image forming unit included in an image forming apparatus according to a fourth embodiment. FIG. 10 is an enlarged view of a toner image forming unit provided in an image forming apparatus according to a fifth embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 10 ... Toner image forming unit, 11 ... Photoconductor drum, 12 ... Charging roll, 14 ... Developing device, 141 ... Fresh toner supply tank, 142 ... Fresh toner supply nozzle, 1421 ... Conveying member, 1422 ... Roll member, 1423 ... blade, 1424 ... roll brush, 1425 ... mesh member, 143 ... first stirring chamber, 144 ... second stirring chamber, 145 ... developing roll, 1451 ... developing sleeve, 147 ... screw auger, 15 ... cleaning device 151 ... Cleaning blade, 152 ... Toner recovery means, 1521 ... Screw auger, 1522 ... Conveyance path, 1523 ... Conveyance member, 1524 ... Roll member, 1525 ... Blade, 1526 ... Roll brush, 1527 ... Mesh member, 20 ... Primary Transfer roll, 30 ... Intermediate transfer bell 40 ... collective transfer device, 50 ... fixing device, 60 ... Paper tray, 70 ... belt cleaner

Claims (8)

Development of an electrostatic latent image formed on a predetermined image carrier using a developing device in which a developer containing magnetic carrier particles and toner particles electrostatically attracted to the magnetic carrier particles is held. The image is developed with toner particles in the agent to form a toner image on the image carrier, the toner image is transferred to a predetermined transfer surface, and finally fixed on the recording medium, thereby fixing on the recording medium. In an image forming apparatus for forming an image composed of a toner image,
A cleaning device for removing toner particles remaining on the surface of the image carrier after the toner image is transferred to the transfer surface;
The developing device is
An agitating chamber for agitating the developer to frictionally charge the toner particles and electrostatically adsorbing the toner particles to the magnetic carrier particles;
A developer carrying member that carries the developer stirred in the stirring chamber on the surface and conveys the developer to a developing region facing the image carrier;
Fresh toner supply means for supplying new toner particles to the stirring chamber,
The cleaning device includes toner recovery means for returning the toner particles removed from the surface of the image carrier to the stirring chamber;
This image forming apparatus further includes
When the charge distribution of 5000 or more toner particles is measured by a charge spectrograph method and the distance from the origin to a point where 100 or more and 500 or less toner particles per 1 mm ² is defined as the maximum value, the image The maximum value of the charge distribution of the toner particles in the toner image formed on the carrier is St, and the maximum value of the charge distribution of the toner particles immediately before being supplied to the stirring chamber by the fresh toner supply means is Dt. The maximum value of the charge distribution of the toner particles immediately before being returned to the stirring chamber by the toner collecting means is Dt ′, and the maximum value of the charge distribution of the toner particles carried on the developer carrier is Pt. When
| 8 mm | <| St | ≦ | 15 mm |
| 5 mm | <| Dt |
| 5 mm | <| Dt ′ |
0.9 <| St | / | Pt | <1.1 Equation 4
An image forming apparatus characterized by satisfying the above expressions 1, 2, 3, and 4 simultaneously.   On the image carrier, based on image signals corresponding to at least a plurality of colors of cyan, magenta, yellow and black, a toner image composed of toner particles of these colors is formed, and the toner images of these colors are finally formed. An image forming apparatus for forming an image on a recording medium by transferring and fixing the image on a predetermined recording medium, wherein the developing device converts the electrostatic latent images formed on the image carrier into the plurality of electrostatic latent images. 2. The image forming apparatus according to claim 1, wherein development is performed with toner particles of at least one color among color toner particles. The carrier particles are coated on the surface of the core portion with a coating agent excellent in chargeability for charging the toner particles to a predetermined polarity by friction with the toner particles from the core portion,
The fresh toner supply means includes a coating member coated with the coating agent, and charges the new toner particles by relatively rubbing the new toner particles and the coating member.
The toner collecting means includes a coating member coated with the coating agent, and relatively rubs the toner particles removed from the surface of the image carrier and the coating member, thereby removing the toner from the surface of the image carrier. 2. The image forming apparatus according to claim 1, wherein the removed toner particles are charged.   The toner collecting means has a conveyance path that leads to the stirring chamber and passes through the toner particles removed from the surface of the image carrier while contacting the inner peripheral surface, the inner peripheral surface being coated with the coating agent. The image forming apparatus according to claim 3, wherein the image forming apparatus is an image forming apparatus.   The toner collecting means has a screw-like conveying member whose surface is coated with the coating agent, and which conveys toner particles removed from the surface of the image carrier to the stirring chamber by rotating. The image forming apparatus according to claim 3.   The toner collecting means rotates in a state where the toner particles removed from the surface of the image carrier are in contact with the surface and the surface of the blade, and removes the toner particles removed from the surface of the image carrier. A conveying member that feeds toward the stirring chamber, wherein at least one of the surface of the blade and the portion of the rotating member that contacts the surface is coated with the coating agent. The image forming apparatus according to claim 3.   The toner collecting means rotates with the supply path leading to the stirring chamber and the hair coated with the coating agent in contact with the inner peripheral surface of the supply path. A brush for feeding toner particles removed from the surface of the image carrier through the bristles and an inner peripheral surface of the supply path toward the agitating chamber; The image forming apparatus according to claim 3.   The toner collecting means includes a mesh member having a surface provided with a mesh larger than the particle diameter of the toner particles removed from the surface of the image carrier and coated with the coating agent, the surface from the surface of the image carrier. 4. The image forming apparatus according to claim 3, wherein the surface is arranged so as to vibrate in a direction in which the surface expands toward a direction in which the removed toner particles are sent.

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