JP2008262145A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of securing developing capability without causing an abnormal image such as a brush mark or white halation at the rear end. <P>SOLUTION: In the image forming apparatus having a developing device 61 in which a prescribed DC voltage is applied between a photoreceptor 40 and a developing sleeve 65, a developer is brought into contact with the photoreceptor 40, the developer is conveyed with a speed difference in the same direction relative to the photoreceptor 40, and an electrostatic latent image on the photoreceptor 40 is developed, a ratio of an area where the magnetic carrier having toner carried on the surface is not brought into contact with the photoreceptor 40 to the surface area of the photoreceptor 40 is 40% or less in a region from a position where the developer starts to be brought into contact with the photoreceptor 40 to the position by 500 μm, and the relation of M/ρ<1.2×PG is satisfied, where PG [m] is a gap between the photoreceptor 40 and the developing sleeve 65, M [kg/m<SP>2</SP>] is an amount of carried developer per unit area on the developing sleeve 65 in a facing position to the image carrier, and ρ [kg/m<SP>3</SP>] is a bulk density of the developer. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus provided in an image forming apparatus such as a copying machine, a printer, or a facsimile.

  Currently, in image forming apparatuses such as copying machines, printers, facsimiles, etc., a toner image is formed by an image carrier (hereinafter referred to as “photosensitive member”) having a photoconductive layer on the surface and a developing device containing developer. Is done. In developing devices, a two-component developer (hereinafter simply referred to as “developer”) mainly composed of toner and a magnetic carrier is widely used because it can be easily colored. The developer is triboelectrically charged by stirring and mixing in the developing device, and the electrostatic charge causes the toner to electrostatically adhere to the surface of the magnetic carrier. The magnetic carrier to which the toner is attached is attracted to the surface of a developer carrying member (hereinafter referred to as “developing sleeve”) in which a magnet is disposed, and is conveyed on the rotating developing sleeve. The developing sleeve is disposed at a position facing the photosensitive member, and the developer conveyed is brought into contact with the photosensitive member, and the toner is applied to the photosensitive member by an electric field generated by a latent image on the photosensitive member and a voltage applied to the developing sleeve. To form an image.

  In such a developing device, the closer the distance between the photosensitive member and the developing sleeve (hereinafter referred to as “development gap”) is, the higher the development capability becomes and the higher the image density becomes. However, once the magnetic carrier has scraped off the toner adhering to the photoconductor, density unevenness (hereinafter referred to as “head trace”) and the trailing edge of a solid image or halftone image are whitened out (hereinafter referred to as “backward”). “Out-of-white”) An abnormal image is likely to occur. Even if the developer amount per unit area on the developing sleeve (hereinafter referred to as “agent transport amount”) is increased, the developing ability is increased, but an abnormal image is similarly generated. With respect to this problem, Patent Document 1 shows that by setting the half width of the main magnetic pole to be raised in the development region to 40 ° or more, the development region is widened and the development capability is increased. However, this method tends to cause rear end white spots. Further, according to Patent Document 2 and Patent Document 3, the decay rate of normal magnetic force in the development region, the angular interval between the main magnetic pole and the adjacent magnetic pole to be raised in the development region, the half-value central angle of the main magnetic pole, etc. It is shown that the trailing edge white spot is suppressed by prescribing to a predetermined value. However, this method has a problem that the developing ability is lowered.

JP 2001-34067 A Japanese Patent No. 3816267 JP 2000-305360 A

In recent years, the diameter of toner has been reduced for the purpose of improving image quality. However, as the diameter of the toner is reduced, the developing ability is reduced due to an increase in the adhesion between the magnetic carrier and the toner, and it becomes difficult to obtain a predetermined image density.
Therefore, increasing the developing ability without causing the above-mentioned problems is a big issue. In view of the above, the present invention has been made in view of these problems, and provides an image forming apparatus that ensures developing performance without causing abnormal images such as ear marks and trailing edge blanks. Is an issue.

As a result of studying the above problems, the inventors have found that the developing ability is increased by increasing the developer density in the vicinity of the position where the developer starts to contact the photoreceptor (hereinafter referred to as “development region entrance”). I understood.
This is thought to be due to the following mechanism.
FIG. 1 is a schematic diagram for explaining that the developing ability is increased by increasing the developer density in the vicinity of the position where the developer starts to contact the photoconductor. When the agent density at the developing area entrance is low, the toner adhesion amount transition from the developing area entrance to the exit has a gentle slope (FIG. 1 (1)). Further, since the photosensitive member and the developing sleeve rotate in the circumferential direction and the developing sleeve linear velocity is higher than the photosensitive member linear velocity, the developer moves so as to pass the photosensitive member. At this time, as shown in FIG. 1 (2), the electric field generated between the developer at the place (A) where the toner is not attached to the photosensitive member and the place (B) where the toner is attached to some extent is compared. As a result, the electric field (B) becomes weaker due to the electric field of the toner adhering thereto, and development becomes difficult. Therefore, by increasing the developer density at the entrance of the development region, the development is performed at a time with a strong electric field, so that the influence of the toner adhering to the photoreceptor is reduced and the development capability is increased (FIG. 1 (3)). )).
FIG. 2 is a schematic diagram for explaining the situation of the magnetic field and magnetic spike by the magnetic pole arrangement of the mag roll in the developing sleeve. The developer density at the entrance of the developing area can be increased by arranging the magnetic pole of the mag roll in the developing sleeve so that a magnetic field is not provided in the developing area and a tangential magnetic field is formed in the circumferential direction of the developing sleeve. all right. If a magnetic pole is provided in the development region, the developer density becomes sparse due to the magnetic spikes formed on the magnetic pole (FIG. 2 (1)). In order to increase the developer density forcibly, if the development gap is brought close or the amount of the agent transported is increased, an abnormal image such as an ear mark or a trailing white spot is generated. By adopting the above magnetic pole arrangement, the developer density can be increased without forcibly bringing the developing gap close or increasing the amount of the agent transported (FIG. 2 (2)). However, if the development gap is too close or the agent transport amount is increased too much, the abnormal image is generated.

From the above examination results, according to the present invention, the image carrier on which the electrostatic latent image is formed, and the development that carries and conveys the two-component developer composed of the toner and the magnetic carrier, disposed at a position facing the image carrier. A predetermined DC voltage is applied between the image carrier and the developer carrier, the developer contacts the image carrier, and the developer is the same as the image carrier. In a developing device that develops an electrostatic latent image on the image carrier that is transported with a speed difference in the direction, the developer is placed in a region of the image carrier from the position where the developer starts to contact the image carrier to 500 μm. On the other hand, the area ratio at which the magnetic carrier supporting the toner on the surface is not in contact with the image carrier is 40% or less, and the interval between the image carrier and the developer carrier is PG [m], the image The developer carrying amount per unit area on the developer carrying body at a position facing the carrying body is M [ g ^{/ m} 2], when the bulk density of the developer was ρ [kg / ^{m 3],} characterized by satisfying the relation M / ρ <1.2 × PG.
Furthermore, in the present invention, a magnetic pole is provided outside the region where the developer contacts the image carrier, and a tangential magnetic field with respect to the circumferential direction of the image carrier is formed in a region where the developer contacts the image carrier. It is characterized by that.
Furthermore, in the present invention, the magnetic carrier has a weight average particle diameter of 20 μm to 40 μm.
Furthermore, in the present invention, the volume resistivity of the magnetic carrier is 10 ¹⁰ to 10 ¹⁴ [Ω · cm].
Furthermore, the present invention is characterized in that the toner coverage of the developer on the magnetic carrier is 50 to 70 [%].
Further, the present invention is characterized in that Vr / Vp is 1.2 to 2.5 when the linear velocity of the image carrier is Vp and the linear velocity of the developer carrier is Vr.

  As described above, in the present invention, it is possible to obtain a predetermined image density without generating an abnormal image such as a head trace or a trailing edge blank. Further, a predetermined image density can be obtained without causing carrier adhesion. In addition, a predetermined image density can be obtained without causing toner scattering and background contamination. Further, a predetermined image density can be obtained without causing toner scattering and carrier scattering.

The best mode for carrying out the present invention will be described below with reference to the drawings. Note that it is easy for a person skilled in the art to make other embodiments by changing or correcting the present invention within the scope of the claims, and these changes and modifications are included in the scope of the claims. The following description is an example of the best mode of the present invention, and does not limit the scope of the claims.
Example 1
Hereinafter, as an image forming apparatus to which the present invention is applied, an embodiment of a tandem type color laser copying machine (hereinafter simply referred to as “copying machine”) in which a plurality of photoconductors are arranged in parallel will be described.
First, the basic configuration of the copying machine will be described.
[overall structure]
FIG. 3 is a schematic configuration diagram of the copying machine according to the present embodiment. The copier includes a printer unit 100, a paper feeding device 200 on which the printer unit 100 is placed, a scanner 300 fixed on the printer unit 100, and the like. An automatic document feeder (hereinafter referred to as ADF) 400 fixed on the scanner 300 is also provided.
The printer unit 100 forms an image including four sets of process cartridges 18Y, 18C, 18M, and 18K for forming an image of each color of yellow (Y), magenta (M), cyan (C), and black (K). A unit 20 is provided. Y, C, M, and K added after the numerals of the symbols indicate members for yellow, cyan, magenta, and black (the same applies hereinafter). In addition to the process cartridges 18Y, C, M, and K, there are an optical writing unit 21, an intermediate transfer unit 17, a secondary transfer device 22, a registration roller pair 49, a paper feed cassette 44, a belt fixing type fixing unit 25, and the like. It is arranged.

[Optical writing unit]
The optical writing unit 21 has a light source (not shown), a polygon mirror, an f-θ lens, a reflection mirror, and the like, and irradiates the surface of a photoreceptor to be described later with laser light based on image data.
[Process cartridge]
FIG. 4 is an enlarged view showing a schematic configuration of the process cartridge 18Y for yellow and the process cartridge 18C for cyan among the process cartridges 18Y, 18C, 18M, and 18K. The other process cartridges 18M and 18K have the same configuration except that the toner colors are different, and thus the description thereof is omitted. In the figure, a process cartridge 18Y, which is an image generating unit that generates a toner image, includes a drum-shaped photoreceptor 40, a charging device 60, a developing device 61, a drum cleaning device 63, a charge eliminating device 64, and the like.

The charging device 60 serving as a charging means opposes a photosensitive roller 40Y with a charging roller serving as a rotating charging member that is driven to rotate while a charging bias is being applied therebetween through a predetermined minute gap. Then, with this minute gap, a discharge is generated from the charging roller to the photoconductor 40Y, and the photoconductor 40Y is uniformly charged. The reason why the charging roller is rotated is that the roller surface immediately after the discharge is retracted from the minute gap and the roller surface that has not been discharged is caused to enter the minute gap, thereby generating a stable discharge. As the charging rotating member, a charging drum, a roller-shaped charging brush, or the like can be used in addition to the charging roller. In this copying machine, the surface of the photoreceptor 40Y is uniformly charged to about −600 [V] by the discharge from the charging roller.
The surface of the photoreceptor 40Y subjected to the charging process is irradiated with the laser light L modulated and deflected by the optical writing unit (21). Then, the potential of the irradiation part (exposure part) is attenuated to about −150 to −500 [V]. By this attenuation, an electrostatic latent image for Y is formed on the surface of the photoreceptor 40Y. The formed electrostatic latent image for Y is developed by a developing device 61 as developing means to become a Y toner image.
In the photoreceptor 40Y as a latent image carrier, for example, a base tube made of aluminum or the like is coated with a photosensitive layer made of an organic photosensitive material that exhibits photosensitivity, and a thickness of 3.5 to 5.0 [μm] is further formed thereon. ] Is a drum-like material coated with a filler-reinforced charge transport layer. Instead of the drum shape, a belt shape may be adopted.

The developing device 61 includes a developing unit 67 and a stirring unit 66 in the casing 70. The developing portion 67 is provided with a developing sleeve 65 that exposes a part of the peripheral surface from the opening of the casing 70, a doctor blade 73, and the like.
The cylindrical developing sleeve 65 as a developer carrying member is made of a non-magnetic material, and its surface is roughened to a 10-point average surface roughness Rz of about 10 to 12 [μm] by sandblasting or the like. is there. By this roughening, the developer conveying ability is enhanced. Instead of roughening, fine grooves may be provided on the surface. The developing sleeve 65 is rotated by driving means (not shown). Inside the developing sleeve 65 that is driven to rotate in this manner, the magnet roller 72 is fixed so as not to rotate around the sleeve. The magnet roller 72 has a plurality of magnetic poles divided in the circumferential direction. Due to the influence of these magnetic poles, a magnetic field is formed on the periphery of the developing sleeve 65.
The agitating unit 66 of the developing device 61 is provided with two conveying screws 68, a toner concentration sensor (hereinafter referred to as T sensor) 71, and the like, and includes a magnetic carrier and a Y toner (not shown) including negatively charged Y toner. Contains developer. The Y developer is agitated and conveyed in the depth direction in the figure by the two conveying screws 68 and is frictionally charged. During this agitation and conveyance, the surface of the developing sleeve 65 comes into contact with the axial direction thereof. Then, it is carried on the surface of the developing sleeve 65 due to the influence of the magnetic field extending from the sleeve surface toward the stirring portion 66, and is pumped up from the stirring portion 66 as the sleeve surface rotates. And it conveys to the position facing the doctor blade 73 with rotation of the sleeve surface. At this facing position, the Y developer is regulated in layer thickness when it passes through a doctor gap of about 500 [μm], which is the gap between the developing sleeve 65 and the doctor blade 73, and the frictional charging of the toner is promoted. .

The Y developer that has passed through the doctor gap reaches the developing region facing the photoreceptor 40Y as the sleeve surface rotates. In this development region, the photoconductor 40Y and the development sleeve 65 are opposed to each other with a development gap of about 350 [μm]. On the surface of the sleeve in the developing region, the magnetic carrier in the Y developer rises and forms a magnetic brush by the magnetic force from the developing magnetic pole (not shown) of the magnet roller 72. The formed magnetic brush moves while the tip of the magnetic brush is rubbed against the photoconductor 40Y to attach Y toner to the electrostatic latent image for Y on the photoconductor 40Y. By this adhesion, a Y toner image as a toner image is formed on the photoreceptor 40Y. The charge amount of Y toner in the Y developer conveyed to the development area is −10 to −40 [μC / g], preferably −15 to −35 [μC / g]. The magnetic force of the magnetic pole of the magnet roller 72, the stirring performance, the doctor gap, etc. are set so as to be in this range.
The developer that has consumed Y toner by development returns to the developing device 61 as the developing sleeve 72 rotates. Then, it is separated from the sleeve surface under the influence of a repulsive magnetic field and gravity formed in the apparatus, and returned to the stirring unit 66 disposed at a position lower than the developing unit 67.
In the stirring unit 66, a partition wall 69 is provided between the two conveying screws 68. By this partition wall 69, the inside of the stirring section 66 is partitioned into two. Of the two conveying screws 68, the one arranged on the right side in the figure is driven to rotate by a driving means (not shown), and the developer is supplied to the developing sleeve 72 while being conveyed from the near side to the far side in the figure. To do. The developer conveyed to the far end in the figure passes through an opening (not shown) provided in the partition wall 69 and is transferred to the conveyance screw 68 on the left side in the figure. Then, due to the rotational drive of the transport screw 68, the transport screw 68 is transported from the front side to the front side in the figure, and then passes through the other opening (not shown) provided in the partition wall 69 to the right side in the figure. Return to top. In this way, the developer is circulated and conveyed in the stirring unit 66.

  A T sensor 71 composed of a magnetic permeability sensor is provided below the right conveying screw 68 in the drawing, and outputs a voltage having a value corresponding to the magnetic permeability of the Y developer conveyed thereon. Since the magnetic permeability of the developer shows a certain degree of correlation with the toner concentration, the T sensor 71 outputs a voltage having a value corresponding to the Y toner concentration. This output voltage value is sent to a control unit (not shown). The control unit includes a RAM or the like, and stores therein a Y Vtref that is a target value of the output voltage from the T sensor 71. In addition, data of M Vtref, C Vtref, and K Vtref, which are target values of output voltage from a T sensor (not shown) mounted in another developing device 61, is also stored. The Y Vtref is used for driving control of a Y toner supply device (not shown). Specifically, the control unit drives and controls a Y toner supply device (not shown) in the stirring unit 66 of the developing device 61 so that the value of the output voltage from the Y T sensor 71 approaches the V Vref for Y. Y toner is replenished. By this replenishment, the Y toner concentration of the developer in the developing device 61 is maintained within a predetermined range. Similar toner replenishment control is performed for the developing devices of the other process cartridges.

[Drum cleaning device]
The Y toner image formed on the Y photoconductor 40Y is intermediately transferred to an intermediate transfer belt 10 described later. The surface of the photoreceptor 40Y after the intermediate transfer is cleaned of the transfer residual toner by the drum cleaning device 63. The drum cleaning device 63 includes a fur brush, a collection roller 77, a scraper blade 78, a collection screw 79, a cleaning blade 75, and the like.
The fur brush 76 is a roller-like brush in which an infinite number of brushes made of acrylic carbon are planted on a core material. Then, the tip of countless raised brushes (not shown) is driven to rotate counterclockwise in the figure, which is the surface movement in the counter direction, at the portion facing the photoconductor 40Y so as to be slid sequentially on the photoconductor 40Y. The collection roller 77 is applied with a positive cleaning bias from a power source (not shown) while being driven to rotate counterclockwise in the figure, which is the surface movement in the counter direction at the portion facing the brush so as to contact the fur brush 76. receive. The transfer residual toner on the photoreceptor 40Y is scraped off by the brushing of the fur brush 76 and captured in the fur brush 76, and then electrostatically adheres to the surface of the collecting roller 77 under the influence of the cleaning bias. Collected. The collected transfer residual toner is scraped off from the roller surface by a scraper blade 78 in contact with the collection roller 77 and falls onto the collection screw 79. The collection screw 79 that is rotationally driven by a driving means (not shown) receives the transfer residual toner falling in this way and sends it to the toner recycling device 89.
The transfer residual toner that has not been completely captured by the fur brush 76 is scraped off by the cleaning blade 75 disposed downstream of the brush in the drum rotation direction and is captured by the fur brush 76. The cleaning blade 75 is made of an elastic material such as polyurethane rubber.
In the Y process cartridge 18 </ b> Y, the photoreceptor 40 </ b> Y cleaned by the drum cleaning device 63 is discharged by the discharging device 64. Then, it is uniformly charged by the charging device 60 and returns to the initial state. The series of processes as described above is the same for the other process cartridges (18C, M, K).

[Intermediate transfer unit]
FIG. 5 is an enlarged configuration diagram showing the image forming unit 20, the intermediate transfer unit 17, the secondary transfer device 22, the registration roller pair 49, and the fixing unit 25. The intermediate transfer unit 17 includes the intermediate transfer belt 10 and a belt cleaning device 90. Further, the tension roller 14, the driving roller 15, the secondary transfer backup roller 16, the four intermediate transfer bias rollers 62 Y, C, M, and K, the three grounding rollers 74, and the like are also provided.
The intermediate transfer belt 10 has a base layer, an elastic layer, and a surface layer (not shown) from the inside of the belt loop. The base layer is a layer containing, for example, a fluorine-based resin having a small elongation or a rubber material having a large elongation and a material that is difficult to stretch, such as canvas, or laminated. The surface layer is a layer made of a material having a low surface energy and exhibiting good releasability from the toner, such as a fluorine resin. The elastic layer is a layer made of an elastic material such as fluorine-based rubber or acrylonitrile-butadiene copolymer rubber, and is provided in order to exert a certain degree of elasticity on the entire belt.

The intermediate transfer belt 10 is tensioned by ten rollers including a tension roller 14. Then, it is endlessly moved clockwise in the drawing by the rotation of the driving roller 15 driven by a belt driving motor (not shown). The four intermediate transfer bias rollers 62Y, C, M, and K are disposed so as to be in contact with the base layer side (inner peripheral surface side) of the intermediate transfer belt 10, respectively, and receive an intermediate transfer bias from a power source (not shown). . Further, the intermediate transfer belt 10 is pressed from the base layer side toward the photoconductors 40Y, 40C, 40M, and 40K to form intermediate transfer nips. At each intermediate transfer nip, an intermediate transfer electric field is formed between the photoreceptor and the intermediate transfer bias roller due to the influence of the intermediate transfer bias. The above-described Y toner image formed on the Y photoconductor 40Y is intermediately transferred onto the intermediate transfer belt 10 due to the influence of the intermediate transfer electric field and nip pressure. On the Y toner image, the C, M, and K toner images formed on the C, M, and K photoconductors 40C, M, and K are sequentially superimposed and transferred. By this intermediate transfer of superposition, a four-color superposed toner image (hereinafter referred to as a four-color toner image), which is a multiple toner image, is formed on the intermediate transfer belt 10.
In the intermediate transfer belt 10 as a belt member, a ground roller 74 is in contact with a portion located between the intermediate transfer nips from the base layer side. These grounding rollers 74 are made of a conductive material. Then, the current due to the intermediate transfer bias transmitted from the intermediate transfer bias rollers (62Y, C, M, K) to the belt at each intermediate transfer nip is prevented from leaking to other intermediate transfer nips and process cartridges.
The four-color toner image superimposed and transferred on the intermediate transfer belt 10 is secondarily transferred to a transfer sheet (not shown) at a secondary transfer nip described later. Transfer residual toner remaining on the surface of the intermediate transfer belt 10 after passing through the secondary transfer nip is cleaned by a belt cleaning device 90 that sandwiches the belt with the driving roller 15 on the left side in the drawing. In the figure, as the belt cleaning device 90, an example in which the fur brush method and the cleaning blade method are used together as in the drum cleaning device (63) described above is shown. However, either one of the methods may be used.

[Secondary transfer device]
Below the intermediate transfer unit 17 in the figure, a secondary transfer device 22 is provided in which a paper conveying belt 24 is stretched by two stretching rollers 23. The paper transport belt 24 is moved endlessly in the counterclockwise direction in the drawing in accordance with the rotational drive of at least one of the stretching rollers 23. Of the two stretching rollers 23, one roller arranged on the right side in the drawing has the intermediate transfer belt 10 and the paper transport belt 24 between the secondary transfer backup roller 16 of the intermediate transfer unit 17. It is sandwiched. By this sandwiching, a secondary transfer nip is formed in which the intermediate transfer belt 10 of the intermediate transfer unit 17 and the paper transport belt 24 of the secondary transfer device 22 are in contact with each other. Then, a secondary transfer bias having a polarity opposite to that of the toner is applied to the one stretching roller 23 by a power source (not shown). By applying the secondary transfer bias, the four-color toner image on the intermediate transfer belt 10 of the intermediate transfer unit 17 is electrostatically moved from the belt side toward the one stretching roller 23 side in the secondary transfer nip 2. A next transfer electric field is formed. The transfer paper fed into the secondary transfer nip so as to synchronize with the four-color toner image on the intermediate transfer belt 10 by a registration roller pair 49 described later has four colors affected by the secondary transfer electric field and nip pressure. The toner image is secondarily transferred. Instead of the secondary transfer method in which the secondary transfer bias is applied to one of the stretching rollers 23 as described above, a charger for charging the transfer paper in a non-contact manner may be provided.

[Registration roller pair]
A registration roller pair 49 is disposed upstream of the secondary transfer nip in the belt moving direction. A transfer sheet (not shown) fed into the printer unit 100 from a sheet feeding device 200 described later is sandwiched between rollers of the registration roller pair 49. On the other hand, in the intermediate transfer unit 17, the four-color toner image formed on the intermediate transfer belt 10 enters the secondary transfer nip as the belt moves endlessly. The registration roller pair 49 sends out the transfer paper sandwiched between the rollers at a timing at which the transfer paper can be brought into close contact with the four-color toner image at the secondary transfer nip. As a result, at the secondary transfer nip, the four-color toner image on the intermediate transfer belt 17 is in close contact with the transfer paper. Then, it is secondarily transferred onto the transfer paper and becomes a full color image on the white transfer paper. The transfer paper P on which the full-color image is formed in this way exits the secondary transfer nip as the paper transport belt 24 moves endlessly, and then is sent from the paper transport belt 22 to the fixing unit 25.

[Fixing unit]
The fixing unit 25 includes a belt unit that moves the fixing belt 26 endlessly while being stretched by two rollers, and a pressure roller 27 that is pressed toward one roller of the belt unit. The fixing belt 26 and the pressure roller 27 are in contact with each other to form a fixing nip, and the transfer paper received from the paper conveying belt 24 is sandwiched therebetween. Of the two rollers in the belt unit, the roller that is pressed from the pressure roller 27 has a heat source (not shown) inside, and pressurizes the fixing belt 26 by the generated heat. The pressed fixing belt 26 heats the transfer paper sandwiched in the fixing nip. The full color image is fixed on the transfer paper by the influence of the heating and the nip pressure.
In FIG. 2 described above, the transfer paper P that has passed through the fixing unit 25 is discharged to the outside of the apparatus through a pair of paper discharge rollers 56 and stacked on the stack unit 57 or below the fixing unit 25. It is sent to the arranged paper reversing unit. When sent to the paper reversing unit, it is turned upside down and then conveyed again to the secondary transfer nip, and the four-color toner image is secondarily transferred to the other surface. Then, after passing through the fixing unit 25, it is discharged outside the apparatus. Whether the transfer paper P is sent from the fixing unit 25 to the paper discharge roller pair 56 or the paper reversing unit is determined by switching the paper transport path by the switching claw 55.

[overall structure]
When a document (not shown) is copied, for example, a bundle of sheet documents is set on the document table 30 of the automatic document feeder 400. However, when the original is a single-sided original that is closed in a main form, it is set on the contact glass 32. Prior to this setting, the automatic document feeder 400 is opened with respect to the copying machine main body, and the contact glass 32 of the scanner 300 is exposed. Thereafter, the single-bound original is pressed by the closed automatic document feeder 400.
When a copy start switch (not shown) is pressed after the document is set in this way, the document reading operation by the scanner 300 starts. However, when a sheet document is set on the automatic document feeder 400, the automatic document feeder 400 automatically moves the sheet document to the contact glass 32 prior to the document reading operation. In the document reading operation, first, the first traveling body 33 and the second traveling body 34 start traveling together, and light is emitted from a light source provided in the first traveling body 33. Then, the reflected light from the document surface is reflected by a mirror provided in the second traveling body 34, passes through the imaging lens 35, and then enters the reading sensor 36. The reading sensor 36 constructs image information based on the incident light.

In parallel with the document reading operation, each device in each process cartridge (18Y, C, M, K), the intermediate transfer unit 17, the secondary transfer device 22, and the fixing device 25 start driving. Based on the image information constructed by the reading sensor 36, the optical writing unit 21 is driven and controlled, and Y, C, M, and K toner images are formed on the respective photosensitive members (40Y, C, M, and K). Is formed. These toner images become four-color toner images superimposed and transferred on the intermediate transfer belt 10.
Further, almost simultaneously with the start of the document reading operation, the paper feeding operation is started in the paper feeding device 200. In this paper feeding operation, one of the paper feeding rollers 42 is selectively rotated, and the transfer paper is sent out from one of the paper feeding cassettes 44 accommodated in the paper bank 43 in multiple stages. The fed transfer paper is separated one by one by the separation roller 45 and enters the paper feed path 46, and then fed to the paper feed path 48 in the printer unit 100 by the transport roller 47. In some cases, paper feeding from the manual feed tray 51 is performed instead of such paper feeding from the paper feeding cassette 44. In this case, after the paper feeding roller 50 is selectively rotated and the transfer paper on the manual feed tray 51 is sent out, the separation roller 52 separates the transfer paper one by one and feeds it to the manual paper feed path 53 of the printer unit 100. To do. The transfer paper fed to the paper feed path 48 or the manual paper feed path 53 in the printer unit 100 is secondarily transferred with a four-color toner image via the registration roller pair 49 and the secondary transfer nip. Then, after passing through the fixing unit 25, it is discharged outside the apparatus.

As the toner, it is desirable to use a toner obtained by further adding an additive or the like to base particles containing a binder resin and other materials such as a colorant, a charge control agent, and a release accelerator. About the said release accelerator, it is desirable to contain 1-15 weight part with respect to 100 weight part of binder resin, Preferably, 2-10 weight part of a release accelerator is contained. This is because if the content of the release accelerator is less than 1 part by weight, hot offset of the toner to the fixing belt 26 cannot be sufficiently suppressed. On the other hand, if the amount exceeds 15 parts by weight, the developing ability is reduced, the occurrence of abnormal images due to the agglomerated toner, the transferability is lowered, and the durability is lowered. When it is 2 to 10 parts by weight, a high-quality image with high image density in the solid part and good dot reproducibility can be obtained.
A conventionally well-known thing can be used as said mold release accelerator. For example, low molecular weight polyethylene wax, low molecular weight polyolefin wax such as low molecular weight polypropylene, synthetic hydrocarbon wax such as Fischer-Tropsch wax, natural wax such as beeswax, carnauba wax, candelilla wax, rice wax, montan wax, Petroleum waxes such as paraffin wax and microcrystalline wax, higher fatty acids such as stearic acid, palmitic acid and myristic acid, metal salts of higher fatty acids, higher fatty acid amides, synthetic ester waxes, and various modified waxes thereof. These mold release accelerators can be used alone or in combination of two or more. In particular, when carnauba wax or synthetic ester wax is used, good releasability of toner from the fixing belt 26 and the photoreceptor can be obtained.

  The amount of the additive added to the toner is preferably 0.6 to 4.0 parts by weight, more preferably 1.0 to 3.6 parts by weight, based on 100 parts by weight of the base particles. It is. When the amount of the additive is less than 0.6 parts by weight, the contact with the magnetic carrier as the magnetic particles is insufficient due to an increase in the degree of aggregation between the toner particles due to poor fluidity of the toner. In addition, sufficient chargeability of the toner cannot be obtained in the developing device 61. In addition, transferability and heat-resistant storage stability are insufficient, and it is easy to cause background contamination and toner scattering. On the other hand, when the amount is more than 4.0 parts by weight, the fluidity is improved, but the cleaning of the photosensitive member due to chattering or turning of the cleaning blade or the like, and filming on the photosensitive member due to the additive released from the toner are likely to occur. . As a result, the durability of the cleaning member such as a cleaning blade or the photosensitive member to be cleaned is lowered, and the fixing property is also deteriorated. In particular, when the content is 1.0 to 3.6 parts by weight, a high-quality image with high image density in the solid part and good dot reproducibility can be obtained. The background stain is a phenomenon in which toner adheres to the non-image portion of the photoreceptor.

Conventionally known additives can be used as additives to be added to the toner. For example, oxides such as Si, Ti, Al, Mg, Ca, Sr, Ba, In, Ga, Ni, Mn, W, Fe, Co, Zn, Cr, Mo, Cu, Ag, V, and Zr, and complex oxidation Thing etc. are mentioned. In particular, silica, titania and alumina which are oxides of Si, Ti and Al are preferably used. In addition, about an additive, it is desirable to surface-treat according to the objectives, such as hydrophobization, a fluid improvement, and charging control.
There are various methods for measuring the additive content, but it is generally determined by fluorescent X-ray analysis. In this method, a calibration curve is prepared by fluorescent X-ray analysis for a toner having a known additive content, and the additive content is determined using this calibration curve.
As the treatment agent used for the surface treatment of the toner, an organic silane compound or the like is preferable. Examples thereof include alkylchlorosilanes such as methyltrichlorosilane, octyltrichlorosilane, and dimethyldichlorosilane, alkylmethoxysilanes such as dimethyldimethoxysilane and octyltrimethoxysilane, hexamethyldisilazane, and silicone oil. As a method of surface treatment with a treating agent, there are a method of immersing an additive in a solution containing an organosilane compound and drying, a method of spraying and drying a solution containing an organosilane compound as an additive, and the like.

  The particle size of the additive added to the toner base particles is preferably 0.002 to 0.2 [μm] in terms of the average primary particle size from the viewpoint of imparting fluidity and the like, and particularly preferably, the particle size is 0.00. 005 to 0.05 [μm]. An additive having an average primary particle size smaller than 0.002 [μm] is likely to be aggregated because the additive is easily embedded in the surface of the base particle. Further, sufficient fluidity cannot be obtained, or filming on the photoreceptor or the like is likely to occur. These tendencies are particularly remarkable under high temperature and high humidity. In addition, if the average primary particle diameter is smaller than 0.002 [μm], the additives tend to agglomerate with each other, and this also makes it difficult to obtain sufficient fluidity. On the other hand, if the average primary particle size is larger than 0.2 [μm], sufficient chargeability cannot be obtained due to poor fluidity of the toner, which is likely to cause background contamination and toner scattering. On the other hand, if the average primary particle diameter is larger than 0.1 [μm], the surface of the photoreceptor is easily damaged, and filming and the like are likely to occur. The particle size of the additive can be determined by measuring with a transmission electron microscope.

  A conventionally well-known thing can be used as said binder resin. For example, polystyrene, styrene-butadiene copolymer, styrene-vinyl chloride copolymer, styrene-acrylic acid ester copolymer, styrene-methacrylic acid ester copolymer, acrylic resin, polyester resin, epoxy resin, polyol resin, Examples thereof include rosin-modified maleic resin, phenol resin, low molecular weight polyethylene, low molecular weight polypropylene, ionomer resin, polyurethane resin, ketone resin, ethylene-ethyl acrylate copolymer, polybutyral, and silicone resin. You may use these individually or in combination of 2 or more types. Particularly preferred are polyester resins and polyol resins. The method for producing the binder resin is not particularly limited, and any of bulk polymerization, solution polymerization, emulsion polymerization, suspension polymerization and the like can be used.

Various types of polyester resins can be used. In particular, it is preferable to use those obtained by mixing the following (a) to (c).
(A) at least one selected from any of divalent carboxylic acids, lower alkyl esters thereof, and acid anhydrides (b) a diol component represented by the following chemical formula 1

(C) At least one selected from any of trivalent or higher polyvalent carboxylic acids, lower alkyl esters thereof, acid anhydrides, and trivalent or higher polyhydric alcohols

  Examples of (a) include terephthalic acid, isophthalic acid, sebacic acid, isodecyl succinic acid, maleic acid, fumaric acid, monomethyl, monoethyl, dimethyl, diethyl ester, phthalic anhydride, maleic anhydride, etc. . In particular, terephthalic acid, isophthalic acid, and dimethyl esters thereof are preferable in terms of blocking resistance and cost. These divalent carboxylic acids, their lower alkyl esters, and acid anhydrides greatly affect the fixability and blocking resistance of the toner. Although depending on the degree of condensation, if a large amount of aromatic terephthalic acid, isophthalic acid or the like is used, the blocking resistance is improved, but the fixing property is lowered. Conversely, if a large amount of sebacic acid, isodecyl succinic acid, maleic acid, fumaric acid or the like is used, the fixing property is improved, but the blocking resistance is lowered. Therefore, it is desirable to select these divalent carboxylic acids as appropriate according to other monomer composition, ratio and degree of condensation, and use them alone or in combination.

  Examples of the above (b) include polyoxypropylene- (n) -polyoxyethylene- (n ′)-2,2-bis (4-hydroxyphenyl) propane, polyoxypropylene- (n) -2,2 -Bis (4-hydroxyphenyl) propane, polyoxyethylene- (n) -2,2-bis (4-hydroxyphenyl) propane and the like. In particular, polyoxypropylene- (n) -2,2-bis (4-hydroxyphenyl) propane satisfying 2.1 ≦ n ≦ 2.5, polyoxyethylene- (2.0 ≦ n ≦ 2.5) n) -2,2-bis (4-hydroxyphenyl) propane is preferred. Such a diol component has the advantage of improving the glass transition temperature and making it easier to control the reaction. In addition, it is also possible to use aliphatic diols such as ethylene glycol, diethylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, propylene glycol as the diol component. is there.

Examples of the trivalent or higher polyvalent carboxylic acid, its lower alkyl ester and acid anhydride in the above (c) include 1,2,4-benzenetricarboxylic acid (trimellitic acid), 1,3,5-benzenetricarboxylic acid. Acid, 1,2,4-cyclohexanetricarboxylic acid, 2,5,7-naphthylenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexa Tricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane, tetra (methylenecarboxy) methane, 1,2,7,8-octanetetracarboxylic acid, emporic trimer acid and their monomethyl, Examples include monoethyl, dimethyl, and diethyl ester.
Examples of the trihydric or higher polyhydric alcohol in the above (c) include sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, sucrose 1,2,4-butanetriol, 1,2,5-pentatriol, glycerol, diglycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane 1,3,5-trihydroxymethylbenzene and the like. The blending ratio of the trivalent or higher polyvalent monomer is suitably about 1 to 30 [mol%] of the whole monomer composition. This is because when it is less than 1 [mol%], the offset resistance of the toner is lowered and the durability is easily deteriorated. Further, if it exceeds 30 [mol%], the toner fixing property tends to deteriorate.
As for the above-described trivalent or higher polyvalent monomers, benzenetricarboxylic acids such as benzenetricarboxylic acid, anhydrides and esters of these acids are particularly preferable. When benzenetricarboxylic acids are used, both fixability and offset resistance can be achieved.

As the above-mentioned polyol resin, various types can be used, and it is particularly preferable to use those obtained by reacting the substances listed below.
(D) epoxy resin (e) alkylene oxide adduct of dihydric phenol or glycidyl ether thereof (f) compound having one active hydrogen in the molecule reacting with epoxy group (g) active hydrogen reacting with epoxy group in molecule Compound having two or more in the above (d) As the epoxy resin, those obtained by bonding bisphenol such as bisphenol A and bisphenol F and epichlorohydrin are preferable. In particular, in order to obtain stable fixing characteristics and gloss, the epoxy resin is at least two or more bisphenol A type epoxy resins having different number average molecular weights, the low molecular weight component has a number average molecular weight of 360 to 2000, and a high molecular weight component. The number average molecular weight is preferably 3000 to 10,000. Further, it is preferable that the low molecular weight component is 20 to 50% by weight and the high molecular weight component is 5 to 40% by weight. When there are too many low molecular weight components, or when the molecular weight is lower than 360, there is a possibility that the gloss will be too high or the storage stability may be deteriorated. Further, when the amount of the high molecular weight component is too large, or when the molecular weight is higher than 10,000, the gloss may be insufficient or the fixability may be deteriorated.

As the alkylene oxide adduct of dihydric phenol in (e) above, for example, the following can be used. That is, it is a reaction product of ethylene oxide, propylene oxide, butylene oxide, or a mixture thereof and a bisphenol such as bisphenol A or bisphenol F. The resulting adduct may be used after glycidylation with epichlorohydrin, β-methylepichlorohydrin, or the like. In particular, diglycidyl ether of an alkylene oxide adduct of bisphenol A represented by the following chemical formula is preferred.

About the alkylene oxide adduct of the dihydric phenol mentioned above or its glycidyl ether, it is preferable to make it contain in the range of 10-40 [weight%] with respect to polyol resin. This is because if the amount is less than this, problems such as an increase in curl occur. Further, if n + m is 7 or more or too much, there is a possibility of excessive glossiness and further deterioration in storage stability.

  As the compound (f), monohydric phenols, secondary amines, carboxylic acids and the like can be used. Among these, the following are mentioned as monohydric phenols. That is, phenol, cresol, isopropylphenol, aminophenol, nonylphenol, dodecylphenol, xylenol, p-cumylphenol and the like. Secondary amines include diethylamine, dipropylamine, dibutylamine, N-methyl (ethyl) piperazine, piperidine and the like. Examples of carboxylic acids include propionic acid and caproic acid.

Examples of the compound (g) include dihydric phenols, polyhydric phenols, and polycarboxylic acids. Among these, examples of the dihydric phenols include bisphenols such as bisphenol A and bisphenol F. Examples of the polyhydric phenols include orthocresol novolacs, phenol novolacs, tris (4-hydroxyphenyl) methane, and 1- [α-methyl-α- (4-hydroxyphenyl) ethyl] benzene. Examples of polyvalent carboxylic acids include malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, phthalic acid, terephthalic acid, trimellitic acid, and trimellitic anhydride.
About the polyester resin and polyol resin mentioned above, if a high crosslinking density is given, it will become difficult to obtain transparency and glossiness. For this reason, it is preferable to provide non-crosslinking or weak crosslinking (THF insoluble content is 5% or less).

  Conventionally known dyes and pigments can be used as the colorant to be contained in the toner. Examples of yellow colorants include naphthol yellow S, Hansa yellow (10G, 5G, G), cadmium yellow, yellow iron oxide, ocher, yellow lead, titanium yellow, polyazo yellow, oil yellow, Hansa yellow, (GR , A, RN, R), Pigment Yellow L, Benzidine Yellow (G, GR), Permanent Yellow (NCG), Vulcan Fast Yellow (5G, R), Tartrazine Lake, Quinoline Yellow Lake, Anthrazan Yellow BGL, Benzimidazo Long yellow, isoindolinone yellow, etc. are mentioned. Red colorants include Bengala, Pangdan, Lead Zhu, Cadmium Red, Cadmium Mercury Red, Antimony Zhu, Permanent Red 4R, Para Red, Fire Red, Parachloro Ortho Nitroaniline Red, and Resol Fast Scarlet. G, Brilliant Fast Scarlet, Brilliant Carmine BS, Permanent Red (F2R, F4R, FRL, FRLL, F4RH), Fast Scarlet VD, Belkan Fast Rubin B, Brilliant Scarlet G, Resol Rubin GX, Permanent Red (F5R, FBB), Brilliant Carmine 6B, Pigment Scarlet 3B, Bordeaux 5B, Toluidine Maroon, Permanent Bordeaux F2K, Helio Bordeaux BL, Bordeaux 10B, Bon Maroon Ito, Bon Maroon Medium, Eosin Lake, Rhodamine Lake B, Rhodamine Lake Y, Alizarin Lake, Thioindigo Red B, Thioindigo Maroon, Oil Red, Quinacridone Red, Pyrazolone Red, Polyazo Red, Chrome Vermilion, Benzidine Orange, Perinone Examples include orange and oil orange. Blue colorants include cobalt blue, cerulean blue, alkali blue rake, peacock blue rake, Victoria blue rake, metal-free phthalocyanine blue, phthalocyanine blue, fast sky blue, indanthrene blue (RS, BC), indigo , Ultramarine blue, bitumen, anthraquinone blue, fast violet B, methyl violet lake, cobalt purple, manganese purple, dioxane violet, anthraquinone violet, chrome green, zinc green, chromium oxide, pyridiane, emerald green, pigment green B, naphthol green B, Examples include green gold, acid green lake, malachite green lake, phthalocyanine green, and anthraquinone green. Examples of black colorants include azine dyes such as carbon black, oil furnace black, channel black, lamp black, acetylene black, and aniline black, metal salt azo dyes, metal oxides, and composite metal oxides. . Examples of other colorants include titania, zinc white, litbon, nigrosine dye, and iron black. Any colorant can be used alone or in combination of two or more. About the content rate, normally 1-30 weight part with respect to 100 weight part of binder resin, Preferably 3-20 weight part is good.

  If necessary, a charge control agent or the like may be added to the toner. As such a charge control agent, conventionally known charge control agents can be used. For example, nigrosine dye, chromium-containing complex, quaternary ammonium salt and the like. These are properly used according to the polarity of the toner particles. In particular, in the case of a color toner, a colorless or light-colored toner that does not affect the color tone of the toner is preferable. For example, a salicylic acid metal salt or a metal salt of a salicylic acid derivative (Bontron E84, manufactured by Orient) is preferable. The charge control agents exemplified so far can be used alone or in combination of two or more. About the content rate, 0.5-8 weight part with respect to 100 weight part of binder resin, Preferably 1-5 weight part is good.

As a toner production method, a pulverization method, a polymerization method, a capsule method, and the like are known. An example of the grinding method is as follows.
(1) A binder resin, a colorant, a charge control agent, a release accelerator, a magnetic material, and the like are sufficiently mixed by a mixer such as a Henschel mixer.
(2) The mixture is sufficiently kneaded by a batch type two roll, a Banbury mixer, a continuous twin screw extruder, a continuous single screw kneader or the like. As continuous twin screw extruders, KTK type twin screw extruder manufactured by Kobe Steel, TEM type twin screw extruder manufactured by Toshiba Machine Co., Ltd., KCK twin screw extruder, PCM type twin screw extruder manufactured by Ikegai Iron Works Co., Ltd. A KEX type twin screw extruder manufactured by Kurimoto Iron Works Co., Ltd. is known. Further, as a continuous type single-screw kneader, a bushing co-kneader or the like is known.
(3) The kneaded product is cooled, coarsely pulverized using a hammer mill or the like, and further pulverized by a fine pulverizer or a mechanical pulverizer using a jet stream. And it classifies to a predetermined particle size with a classifier using a swirling airflow or a classifier using the Coanda effect to obtain base particles.

An example of the polymerization method will be described as follows.
(1) A polymerizable monomer, a polymerization initiator (if necessary), a colorant and the like are granulated in an aqueous dispersion medium.
(2) The granulated monomer composition particles are classified to an appropriate particle size.
(3) The monomer composition particles having a prescribed inner particle diameter obtained by this classification are subjected to a polymerization reaction.
(4) After removing the dispersant by appropriate treatment, the polymerization product obtained by the polymerization reaction is filtered, washed with water and dried to obtain base particles.
An example of the capsule method is as follows.
(1) A resin, a colorant, and the like are kneaded with a kneader or the like to obtain a molten toner core material.
(2) The toner core material is placed in water and stirred vigorously to form a fine particle core material.
(3) The above core material fine particles are put in a shell material solution, and a poor solvent is dropped while stirring, and the surface of the core material is covered with the shell material and encapsulated.
(4) The capsules thus obtained are filtered and then dried to obtain base particles.

  Other additives different from the above-described additives may be added to the toner. Examples of such other additives include Teflon (registered trademark) that functions as a lubricant, zinc stearate, polyvinylidene fluoride, and the like. Further, cerium oxide, silicon carbide, strontium titanate and the like that function as an abrasive may be mentioned. In addition, zinc oxide, antimony oxide, tin oxide, and the like that function as a conductivity imparting material can be given.

Conventionally known magnetic carriers can be used as the magnetic carrier used in the developer. For example, magnetic powder such as iron powder, ferrite powder, nickel powder, glass beads, and the like. It is desirable to form a protective layer by covering these surfaces with a resin or the like.
Examples of the resin used for the protective layer include polyfluorocarbon, polyvinyl chloride, polyvinylidene chloride, phenol resin, polyvinyl acetal, acrylic resin, and silicone resin. Examples of the method for forming the protective layer include a method in which a resin is applied to the surface of the magnetic carrier by means such as spraying or dipping. About the usage-amount of resin, it is preferable to set it as 1-10 weight part with respect to 100 weight part of magnetic carriers. The thickness of the protective layer is preferably 0.02 to 2 [μm], particularly preferably 0.05 to 1 [μm], and more preferably 0.1 to 0.6 [μm]. . When the film thickness is thick, the fluidity of the carrier and the developer tends to decrease, and when the film thickness is thin, the film tends to be easily affected by film scraping over time.

It is desirable to use a magnetic carrier having a weight average particle diameter of 20 to 40 [μm].
Magnetic carriers include metals such as iron, nickel and cobalt, alloys of these and other metals, magnetite, γ-hematite, chromium dioxide, copper zinc ferrite, manganese zinc ferrite and other oxides, manganese-copper-aluminum, etc. Ferromagnetic particles such as Heusler alloys can be used. The ferromagnetic particles may be coated with a resin such as styrene-acrylic, silicone, or fluorine. The material of the ferromagnetic material is desirably selected as appropriate in consideration of the charging property with the toner containing the release accelerator. In addition, a charge control agent, a conductive substance, or the like may be added to the resin that coats the ferromagnetic particles. Moreover, what disperse | distributed these magnetic body particles in resin, such as a styrene-acrylic type and a polyester type, may be used. The strength of saturation magnetization of the ferromagnetic material is preferably 40 to 90 [emu / g]. This is because if it is less than 45 emu / g, the transportability deteriorates due to the weak saturation magnetization, and the carrier adheres to the photoreceptor more. On the other hand, if it exceeds 90 [emu / g], the magnetic brush and scavenging effect are strengthened due to the strength of saturation magnetization, and scavenging marks are generated in the halftone portion, thereby degrading the image quality.

An example of a method for manufacturing a magnetic carrier will be described as follows. That is, first, materials to be listed next are prepared.
-Core material: Cu-Zn ferrite particles (weight average diameter: 35 µm) 5000 parts by weight-Coating material: 450 parts by weight of toluene Silicone resin SR2400 (made by Toray Dow Corning Silicone, nonvolatile content 50%) 450 parts by weight Aminosilane SH6020 (Toray 10 parts by weight of carbon black (10 parts by weight) Dow Corning / Silicone 10 parts by weight Carbon black 10 parts by weight The above-mentioned mixture of toluene and the like is stirred with a stirrer for 10 minutes to obtain a coating material. This coating material is put into a coating apparatus that sprays while forming a swirling flow in a fluidized bed provided with a rotary bottom plate disk and stirring blades, and is applied to the core material. The obtained particles are baked in an electric furnace at 250 ° C. for 2 hours to obtain a magnetic carrier on which a coat film having a thickness of about 0.5 [μm] is formed.

Next, a characteristic configuration of the copying machine according to the present embodiment will be described.
FIG. 6 is an enlarged sectional view showing a photosensitive layer of the photoreceptor. Since the configuration of each device in each process cartridge is the same as described above, the following description will be made with the symbols Y, M, C, and K omitted. In the figure, the photoreceptor 40 has a photosensitive layer coated on a conductive support (not shown). This photosensitive layer is composed of a charge generation layer 40a, a charge transport layer 40b, and a filler-reinforced charge transport layer 40c coated thereon, from the conductive support side to the surface side.
As the conductive support, for example, a conductive material having a volume resistance of 10 ¹⁰ [Ω · cm] or less coated with film or cylindrical plastic or paper by vapor deposition or sputtering can be used. Examples of the conductive material to be coated include metals such as aluminum, nickel, chromium, nichrome, copper, gold, silver, and platinum, and metal oxides such as tin oxide and indium oxide. Also, instead of coating the conductive material, a metal plate made of aluminum, aluminum alloy, nickel, stainless steel, etc. is formed into a cylindrical shape by a method such as extrusion or drawing, and then a surface such as cutting, superfinishing, polishing, etc. You may use the pipe | tube which performed the process.

In this copying machine, a drum-shaped photosensitive member is used. However, when a belt-shaped photosensitive member is used, an endless nickel belt disclosed in Japanese Patent Laid-Open No. 52-36016 is used as a conductive support. An endless stainless steel belt can also be used. In addition to this, a conductive powder dispersed in a suitable binder resin on a support made of plastic or paper may be used. In this case, examples of the conductive powder include carbon black, acetylene black, metal powder such as aluminum, nickel, iron, nichrome, copper, zinc and silver, or metal oxide powder such as conductive tin oxide. It is done.
The binder resin used simultaneously is polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, polyester, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer. , Polyvinyl acetate, polyvinylidene chloride, polyarylate resin, phenoxy resin, polycarbonate, cellulose acetate resin, ethyl cellulose resin, polyvinyl butyral, polyvinyl formal, polyvinyl toluene, poly-N-vinyl carbazole, acrylic resin, silicone resin, epoxy resin, Thermoplastic, thermosetting resin or photo-curing resin such as melamine resin, urethane resin, phenol resin, alkyd resin and the like can be mentioned. The conductive layer formed on the support can be provided by dispersing and applying these conductive powder and binder resin in a suitable solvent such as tetrahydrofuran, dichloromethane, methyl ethyl ketone, toluene and the like. In addition, a conductive layer is provided on a suitable cylindrical substrate by a heat-shrinkable tube containing the conductive powder in a material such as polyvinyl chloride, polypropylene, polyester, polystyrene, polyvinylidene chloride, polyethylene, chlorinated rubber, and Teflon. Can also be used as a conductive support.

  The charge generation layer 40a of the photosensitive layer is mainly composed of a charge generation material, a solvent, and a binder resin. If necessary, a binder resin may be included. Further, any additive such as a sensitizer, a dispersant, a surfactant, and silicone oil may be contained. Either an inorganic material or an organic material can be used as the charge generation material. Among these, examples of inorganic materials include crystalline selenium, amorphous selenium, selenium-tellurium, selenium-tellurium-halogen, selenium-arsenic compounds, and amorphous silicon. As amorphous silicon, dangling bonds that are terminated with hydrogen atoms or halogen atoms, or those that are doped with boron atoms or phosphorous atoms are preferably used. On the other hand, organic materials include metal phthalocyanine, metal-free phthalocyanine and other phthalocyanine pigments, azulenium salt pigments, squaric acid methine pigments, azo pigments having a carbazole skeleton, azo pigments having a triphenylamine skeleton, and diphenylamine skeletons Azo pigments, azo pigments having a dibenzothiophene skeleton, azo pigments having a fluorenone skeleton, azo pigments having an oxadiazole skeleton, azo pigments having a bis-stilbene skeleton, azo pigments having a distyryl oxadiazole skeleton, distyrylcarbazole skeleton Azo pigments, perylene pigments, anthraquinone or polycyclic quinone pigments, quinoneimine pigments, diphenylmethane and triphenylmethane pigments, benzoquinone and naphthoquinone pigments, cyanine and Methine pigments, indigoid pigments, and bisbenzimidazole pigments. These charge generation materials can be used alone or as a mixture of two or more.

Examples of the binder resin that can be included in the charge generation layer 40a as needed include polyamide, polyurethane, epoxy resin, polyketone, polycarbonate, polyarylate, silicone resin, acrylic resin, polyvinyl butyral, polyvinyl formal, polyvinyl ketone, polystyrene, Poly-N-vinylcarbazole, polyacrylamide and the like can be mentioned. These binder resins can be used alone or as a mixture of two or more. A polymer charge transport material can also be used as the binder resin. Furthermore, you may add a low molecular charge transport material as needed. Such low molecular charge transport materials include electron transport materials and hole transport materials, and these include further low molecular charge transport materials and high molecular charge transport materials. Hereinafter, the polymer type charge transport material is referred to as a polymer charge transport material.
Examples of the electron transporting material include chloranil, bromoanil, tetracyanoethylene, tetracyanoquinodimethane, 2,4,7-trinitro-9-fluorenone, 2,4,5,7-tetranitro-9-fluorenone, 2,4 , 5,7-tetranitroxanthone, 2,4,8-trinitrothioxanthone, 2,6,8-trinitro-4H-indeno [1,2-b] thiophen-4-one, 1,3,7-tri Examples thereof include electron accepting substances such as nitrodibenzothiophene-5,5-dioxide. These electron transport materials can be used alone or as a mixture of two or more.
Examples of the hole transport material include oxazole derivatives, oxadiazole derivatives, imidazole derivatives, triphenylamine derivatives, 9- (p-diethylaminostyrylanthracene), 1,1-bis- (4-dibenzylaminophenyl) propane, Examples include styryl anthracene, styryl pyrazoline, phenylhydrazones, α-phenyl stilbene derivatives, thiazole derivatives, triazole derivatives, phenazine derivatives, acridine derivatives, benzofuran derivatives, benzimidazole derivatives, and thiophene derivatives. These hole transport materials can be used alone or as a mixture of two or more. In addition, the following polymer charge transport materials can be used. A polymer having a carbazole ring such as poly-N-vinylcarbazole, a polymer having a hydrazone structure exemplified in JP-A-57-78402, and a polysilylene heavy exemplified in JP-A-63-285552 A polymer having a triarylamine structure exemplified in JP-A-7-325409. These polymer charge transport materials can be used alone or as a mixture of two or more.

Known methods for forming the charge generation layer 40a include a vacuum thin film fabrication method and a casting method from a solution dispersion system. For the former method, vacuum deposition method, glow discharge decomposition method, ion plating method, sputtering method, reactive sputtering method, CVD method, etc. are used, and the above-mentioned inorganic materials and organic materials should be formed satisfactorily. Can do. Further, in order to provide the charge generation layer by the casting method, it can be formed as follows. That is, the inorganic or organic charge generating material described above is dispersed by a ball mill, attritor, sand mill or the like using a solvent such as tetrahydrofuran, cyclohexanone, dioxane, dichloroethane, or butanone together with a binder resin as necessary. Then, the dispersion is appropriately diluted and applied. For this application, a dip coating method, a spray coating method, a bead coating method, or the like may be used.
The thickness of the charge generation layer 40a provided as described above is suitably about 0.01 to 5 [μm], preferably 0.05 to 2 [μm].

The charge transport layer 40b can be formed by dissolving or dispersing a mixture or copolymer mainly composed of a charge transport component and a binder component in an appropriate solvent, and applying and drying the mixture. The film thickness is suitably about 5 to 50 [μm], and about 5 to 30 [μm] is appropriate when resolving power is required.
Examples of the binder component used for the charge transport layer 40b include the following polymer compounds. That is, polystyrene, styrene / acrylonitrile copolymer, styrene / butadiene copolymer, styrene / maleic anhydride copolymer, polyester, polyvinyl chloride, vinyl chloride / vinyl acetate copolymer, polyvinyl acetate, polyvinylidene chloride, Thermoplastic such as polyarylate resin, polycarbonate, cellulose acetate resin, ethyl cellulose resin, polyvinyl butyral, polyvinyl formal, polyvinyl toluene, acrylic resin, silicone resin, fluorine resin, epoxy resin, melamine resin, urethane resin, phenol resin, alkyd resin For example, a thermosetting resin. These polymer compounds can be used alone or as a mixture of two or more kinds, or can be used after being copolymerized with a charge transport material.
Examples of the material that can be used as the charge transport material include the above-described low molecular electron transport materials, hole transport materials, and polymer charge transport materials. Moreover, it is also possible to add an appropriate antioxidant, a plasticizer, a lubricant, a UV absorber, a low molecular compound such as a low molecular charge transport material, or a leveling agent as necessary. When a low molecular charge transport material is used, the amount used is 20 to 200 parts by weight, preferably about 50 to 100 parts by weight per 100 parts by weight of the polymer compound. When a polymer charge transport material is used, a material in which the resin component is copolymerized at a ratio of about 0 to 500 parts by weight with respect to 100 parts by weight of the charge transport component is preferably used.

Dispersing solvents that can be used in preparing the charge transport layer coating solution include ketones such as methyl ethyl ketone, acetone, methyl isobutyl ketone, and cyclohexanone, ethers such as dioxane, tetrahydrofuran, and ethyl cellosolve, and aromatics such as toluene and xylene. Group, halogens such as chlorobenzene and dichloromethane, and esters such as ethyl acetate and butyl acetate. These compounds can be used alone or as a mixture of two or more. The amount of the low molecular compound used is 0.1 to 200 parts by weight, preferably 0.1 to 30 parts by weight based on 100 parts by weight of the polymer compound, and the amount of the leveling agent used is 100 parts by weight of the polymer compound. On the other hand, about 0.001 to 5 parts by weight is appropriate.
The filler-reinforced charge transport layer 40c includes at least a charge transport component, a binder resin component, and a filler, and has both charge transport properties and mechanical resistance. It also functions as a surface layer in which the above charge transport layer is functionally separated into two or more layers.
Examples of the filler material used for the filler-reinforced charge transport layer 40c include inorganic materials, silica, titanium oxide, and alumina. Two or more of these may be mixed and used. In order to improve the dispersibility in the coating liquid and the coating film, the filler surface may be modified with a surface treatment agent. The filler material can be dispersed by a suitable disperser in a solvent mixed with a charge transport material or a binder resin. The average primary particle diameter of the filler material is preferably 0.01 to 0.8 [μm] from the viewpoint of the transmittance and wear resistance of the charge transport layer. As a coating method of the solution in which the filler material is dispersed, a dipping method, a spray coating method, a ring coating method, a roll coater method, a gravure coating method, a nozzle coating method, a screen printing method, or the like can be used. The film thickness of the filler-reinforced charge transport layer 40c is preferably 0.5 [μm] or more, more preferably 2 [μm] or more.

An undercoat layer may be provided between the conductive support and the photosensitive layer. This undercoat layer generally contains a resin as a main component. With regard to this resin, it is desirable to use a resin having high solvent resistance with respect to a general organic solvent, considering that the resin is applied to the charge transport layer 40b in a state of dispersion dispersed in a solvent. Examples of such resins include water-soluble resins such as polyvinyl alcohol, casein, and sodium polyacrylate, alcohol-soluble resins such as copolymer nylon and methoxymethylated nylon, polyurethane, melamine resin, phenol resin, alkyd-melamine resin, epoxy resin, and the like. And a curable resin that forms a three-dimensional network structure.
To the undercoat layer, a fine powder pigment of a metal oxide such as titanium oxide, silica, alumina, zirconium oxide, tin oxide, or indium oxide may be added in order to suppress moire and reduce the residual potential. Moreover, a silane coupling agent, a titanium coupling agent, a chromium coupling agent, etc. can also be used. In addition, those using Al2O3 by anodic oxidation, organic materials such as polyparaxylylene (parylene), or inorganic materials such as SiO2, SnO2, TiO2, ITO, CeO2 are also used. Is possible. The thickness of the undercoat layer is suitably from 0 to 20 [μm], preferably from 1 to 10 [μm].

Each layer described so far has an antioxidant, a plasticizer, a lubricant, an ultraviolet absorber, a low molecular charge transport material, in order to improve the environmental resistance, in order to prevent a decrease in sensitivity and an increase in residual potential, A leveling agent may be added.
The following can be illustrated as antioxidant which can be added to each layer.
(A) Phenolic compounds 2,6-di-t-butyl-p-cresol, butylated hydroxyanisole, 2,6-di-t-butyl-4-ethylphenol, n-octadecyl-3- (4'- Hydroxy-3 ', 5'-di-t-butylphenol), 2,2'-methylene-bis- (4-methyl-6-t-butylphenol), 2,2'-methylene-bis- (4-ethyl- 6-t-butylphenol), 4,4′-thiobis- (3-methyl-6-tert-butylphenol), 4,4′-butylidenebis- (3-methyl-6-tert-butylphenol), 1,1,3 -Tris- (2-methyl-4-hydroxy-5-t-butylphenyl) butane, 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxy Benzyl) benzene, tetrakis- [meth] -3- (3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) propionate] methane, bis [3,3′-bis (4′-hydroxy-3′-t-butylphenyl) buty Rick acid] glycol ester, tocopherols, etc.
(B) Paraphenylenediamines N-phenyl-N′-isopropyl-p-phenylenediamine, N, N′-di-sec-butyl-p-phenylenediamine, N-phenyl-N-sec-butyl-p-phenylene Diamine, N, N′-di-isopropyl-p-phenylenediamine, N, N′-dimethyl-N, N′-di-t-butyl-p-phenylenediamine and the like.
(C) Hydroquinones 2,5-di-t-octylhydroquinone, 2,6-didodecylhydroquinone, 2-dodecylhydroquinone, 2-dodecyl-5-chlorohydroquinone, 2-t-octyl-5-methylhydroquinone, 2 -(2-octadecenyl) -5-methylhydroquinone and the like.
(D) Organic sulfur compounds Dilauryl-3,3′-thiodipropionate, distearyl-3,3′-thiodipropionate, ditetradecyl-3,3′-thiodipropionate, and the like.
(E) Organic phosphorus compounds Triphenylphosphine, tri (nonylphenyl) phosphine, tri (dinonylphenyl) phosphine, tricresylphosphine, tri (2,4-dibutylphenoxy) phosphine and the like.

The following can be illustrated as a plasticizer which can be added to each layer.
(A) Phosphate ester plasticizer Triphenyl phosphate, tricresyl phosphate, trioctyl phosphate, octyl diphenyl phosphate, trichloroethyl phosphate, cresyl diphenyl phosphate, tributyl phosphate, tri-2-ethylhexyl phosphate, Triphenyl phosphate etc.
(B) Phthalate ester plasticizers Dimethyl phthalate, diethyl phthalate, diisobutyl phthalate, dibutyl phthalate, diheptyl phthalate, di-2-ethylhexyl phthalate, diisooctyl phthalate, di-n-octyl phthalate, phthalate Dinonyl acid, diisononyl phthalate, diisodecyl phthalate, diundecyl phthalate, ditridecyl phthalate, dicyclohexyl phthalate, butyl benzyl phthalate, butyl lauryl phthalate, methyl oleyl phthalate, octyl decyl phthalate, dibutyl fumarate, dioctyl fumarate Such.
(C) Aromatic carboxylic acid ester plasticizers Trioctyl trimellitic acid, tri-n-octyl trimellitic acid, octyl oxybenzoate, and the like.
(D) Aliphatic dibasic ester plasticizer dibutyl adipate, di-n-hexyl adipate, di-2-ethylhexyl adipate, di-n-octyl adipate, adipic acid n-octyl-n-decyl , Diisodecyl adipate, dicapryl adipate, di-2-ethylhexyl azelate, dimethyl sebacate, diethyl sebacate, dibutyl sebacate, di-n-octyl sebacate, di-2-ethylhexyl sebacate, di-2 sebacate -Ethoxyethyl, dioctyl succinate, diisodecyl succinate, dioctyl tetrahydrophthalate, di-n-octyl tetrahydrophthalate and the like.
(E) Fatty acid ester derivatives butyl oleate, glycerin monooleate, methyl acetylricinoleate, pentaerythritol ester, dipentaerythritol hexaester, triacetin, tributyrin and the like.
(F) Oxyacid ester plasticizers Methyl acetyl ricinoleate, butyl acetyl ricinoleate, butyl phthalyl butyl glycolate, tributyl acetyl citrate and the like.

(G) Epoxy plasticizer Epoxidized soybean oil, epoxidized linseed oil, butyl epoxy stearate, decyl epoxy stearate, octyl epoxy stearate, benzyl epoxy stearate, dioctyl epoxy hexahydrophthalate, didecyl epoxy hexahydrophthalate, etc. .
(H) Dihydric alcohol ester plasticizers such as diethylene glycol dibenzoate and triethylene glycol di-2-ethylbutyrate.
(I) Chlorinated plasticizer Chlorinated paraffin, chlorinated diphenyl, chlorinated fatty acid methyl, methoxychlorinated fatty acid methyl and the like.
(J) Polyester plasticizer Polypropylene adipate, polypropylene sebacate, polyester, acetylated polyester and the like.
(K) Sulfonic acid derivative
p-toluenesulfonamide, o-toluenesulfonamide, p-toluenesulfoneethylamide, o-toluenesulfoneethylamide, toluenesulfone-N-ethylamide, p-toluenesulfone-N-cyclohexylamide and the like.
(L) Citric acid derivatives Triethyl citrate, triethyl acetylcitrate, tributyl citrate, tributyl acetylcitrate, tri-2-ethylhexyl acetylcitrate, acetylcitrate-n-octyldecyl, and the like.
(M) Others Terphenyl, partially hydrogenated terphenyl, camphor, 2-nitrodiphenyl, dinonylnaphthalene, methyl abietate and the like.

The following can be illustrated as a lubricant which can be added to each layer.
(A) Hydrocarbon compounds Liquid paraffin, paraffin wax, microwax, low-polymerized polyethylene and the like.
(B) Fatty acid compounds Lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid and the like.
(C) Fatty acid amide compounds Stearylamide, palmitylamide, oleinamide, methylenebisstearamide, ethylenebisstearamide and the like.
(D) Ester compounds Lower alcohol esters of fatty acids, polyhydric alcohol esters of fatty acids, fatty acid polyglycol esters, and the like.
(E) Alcohol compounds Cetyl alcohol, stearyl alcohol, ethylene glycol, polyethylene glycol, polyglycerol and the like.
(F) Metal soap Lead stearate, cadmium stearate, barium stearate, calcium stearate, zinc stearate, magnesium stearate and the like.
(G) Natural wax Carnauba wax, candelilla wax, beeswax, whale wax, ivotaro, montan wax and the like.
(H) Others Silicone compounds, fluorine compounds, etc.

The following can be illustrated as a ultraviolet absorber which can be added to each layer.
(A) Benzophenone series 2-hydroxybenzophenone, 2,4-dihydroxybenzophenone, 2,2 ′, 4-trihydroxybenzophenone, 2,2 ′, 4,4′-tetrahydroxybenzophenone, 2,2′-dihydroxy-4- Such as methoxybenzophenone.
(B) Salsylates Phenyl salsylates, 2,4 di-t-butylphenyl 3,5-di-t-butyl 4-hydroxybenzoate, and the like.
(C) Benzotriazole series (2′-hydroxyphenyl) benzotriazole, (2′-hydroxy5′-methylphenyl) benzotriazole, (2′-hydroxy5′-methylphenyl) benzotriazole, (2′-hydroxy3) '-Tertiarybutyl 5'-methylphenyl) 5-chlorobenzotriazole (d) cyanoacrylate type ethyl-2-cyano-3,3-diphenyl acrylate, methyl 2-carbomethoxy 3 (paramethoxy) acrylate, and the like.
(E) Quencher (metal complex)
Nickel (2,2′thiobis (4-t-octyl) phenolate) normal butylamine, nickel dibutyldithiocarbamate, nickel dibutyldithiocarbamate, cobalt dicyclohexyldithiophosphate and the like.
(F) HALS (hindered amine)
Bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis (1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, 1- [2- [3- (3 5-di-t-butyl-4-hydroxyphenyl) propionyloxy] ethyl] -4- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyloxy] -2,2,6 6-tetramethylpyridine, 8-benzyl-7,7,9,9-tetramethyl-3-octyl-1,3,8-triazaspiro [4,5] undecane-2,4-dione, 4-benzoyloxy- 2,2,6,6-tetramethylpiperidine and the like.

In FIG. 4 described above, the copying machine according to the present embodiment includes a developing bias power source (not shown) that is a developing bias applying unit that applies a developing bias to the developing sleeve 65 of the developing device 61. In addition, a charging bias power source (not shown) serving as a charging bias applying unit that applies a charging bias to a charging roller as a rotating charging member of the charging device 60 is also provided. Among these power sources, the development bias power source is configured to supply the developing sleeve 65 with a DC developing bias consisting of only a DC component. On the other hand, the charging bias power source is configured to supply an AC charging bias including at least an AC component to the charging roller. This copier employs a combination of AC charging and DC developing. In such a configuration, as shown in FIG. 6, deterioration of the photoreceptor 40 due to film scraping of the filler-reinforced charge transport layer (40c) can be suppressed.
The present inventors performed an evaluation test of image density, ear mark, and trailing edge white spot using this printer tester. With respect to the image density, “◯” indicates that a predetermined image density is obtained, “Δ” indicates an acceptable range, and “x” indicates that the image density is not obtained. Subjective evaluation was performed on the head trace and the trailing edge white spot, and it was determined to be good (◯) and bad (×).

FIG. 7 shows the magnetic pole arrangement of the magnet roller 72 used in Example 1, Example 2, Comparative Example 1, and Comparative Example 2, and the perpendicular magnetic force distribution with respect to the sleeve circumferential direction formed by the magnetic poles around the developing sleeve 65. It is a figure which shows tangential magnetic force distribution. Two magnetic poles are arranged upstream and downstream of the development region, and the tangential magnetic force is dominant in the development region. Hereinafter, this magnetic pole arrangement is denoted as A. Next, FIG. 8 shows the magnetic pole arrangement of the magnet roller 72 used in Comparative Example 3 and Comparative Example 4, and the perpendicular magnetic force distribution and tangential magnetic force distribution formed around the developing sleeve 65 by the magnetic poles in the circumferential direction of the sleeve. FIG. There is a magnetic pole in the development area, and the normal magnetic force is dominant in the development area. Hereinafter, this magnetic pole arrangement is referred to as B.
In order to compare the developer density at the entrance of the development area, the magnetic carrier carrying the toner on the surface of the image carrier area from the position where the developer starts to contact the image carrier to 500 μm is imaged. The area ratio that was not in contact with the support was measured. The smaller the area ratio, the denser the developer.

The results of Example 1, Example 2, and Comparative Examples 1 to 4 are shown in Table 1. Moreover, the conditions which are not described in Table 1 are shown below. The developer bulk density was measured by a powder bulk density measuring method defined by JIS standards.
-Thickness of the filler-reinforced charge transport layer (40c) of the photoreceptor (40): 5.0 [μm]
-Linear speed of photoconductor (40): 245 [mm / s]
-Exposure portion potential (electrostatic latent image potential) of the photoreceptor (40): -150 to -500 [V]
The background potential of the photoreceptor (40): -600 [V]
・ Developing sleeve diameter: 25 [mm]
-Ten-point average roughness Rz of the developing sleeve surface: 10 [μm]
・ Linear speed of developing sleeve: 504.7 [mm / s]
-DC development bias: -500 [V]
-Developer capacity in the developing device (61): 500 [g]
・ Development gap: 350 [μm]
-Weight average particle diameter of magnetic carrier: 35 [μm]
-Volume resistivity of magnetic carrier: 10 ¹² [Ω · cm]
-Toner coverage on magnetic carrier: 60 [%]
-Volume average particle diameter of toner: 5.5 [μm]
Developer bulk density: 1.6 [g / cm ³ ]
Agent transport amount: 52 [mg / cm ² ]

A method for measuring the area ratio in the development region in the present embodiment will be described.
In order to obtain the area of the front end of the magnetic brush viewed from the photosensitive drum side, observation is performed using a magnetic brush visualization device in the development region. The visualization device includes a transparent glass drum having a diameter of 60 mm as a substitute for the photosensitive member, and a developing sleeve is disposed at a position separated by a predetermined developing gap. The glass drum is cut into ¼ so that the tip of the magnetic brush in the developing area can be observed from the cut portion. At this time, the glass drum can move at an actual machine linear speed. In addition, a transparent electrode was prepared on the surface of the glass drum so as to prevent the toner from adhering due to frictional charging, and was controlled by applying an external potential. Further, a surface layer of the photoconductor is coated on the outermost surface of the glass drum so that the friction coefficient and the like are the same as those of the actual photoconductor.
The tip of the magnetic brush observed with this visualization device was magnified with a stereo microscope (Olympus SZ60), and dynamic behavior was observed with a high-speed camera (Photolon ultima II). FIG. 9 is a photograph showing an example of the photographing result. The image for each frame of the observation video is binary-coded with an appropriate threshold that can distinguish between the area where the developer is in contact with the photoconductor and the area where the developer is not in contact with the image processing software (Image Hyper2). The magnetic brush is divided into a magnetic brush portion and a carrier-free portion. FIG. 9 shows a schematic diagram of the photosensitive member and a photograph showing the developer contact state seen through the photosensitive member under the photosensitive member. The developer starts to contact from the position of the left line of the two lines in the left direction. The position of 500 μm is indicated by the right line, and the behavior of the developer in this region becomes important. Therefore, since these parts change in the process of moving the magnetic brush, by processing the image within a certain period of time, each of the parts in this area that are not in contact with the parts that are in contact with the developer Statistical information such as area, average area, number, etc. was obtained to determine the area ratio.

(Example 2)
The evaluation was performed under the same conditions as in Example 1 except that the amount of the agent transported was changed to the following conditions.
Agent transport amount: 62 [mg / cm ² ]
(Comparative Example 1)
The evaluation was performed under the same conditions as in Example 1 except that the amount of the agent transported was changed to the following conditions.
Agent transport amount: 45 [mg / cm ² ]
(Comparative Example 2)
The evaluation was performed under the same conditions as in Example 1 except that the amount of the agent transported was changed to the following conditions.
Agent transport amount: 72 [mg / cm ² ]
(Comparative Example 3)
An evaluation test was performed under the same conditions as in Example 1 except that the magnetic pole arrangement was changed to B under the conditions shown below for the agent conveyance amount.
Agent transport amount: 45 [mg / cm ² ]
(Comparative Example 4)
An evaluation test was performed under the same conditions as in Example 1 except that the magnetic pole arrangement was changed to B under the conditions shown below for the agent conveyance amount.
Agent transport amount: 72 [mg / cm ² ]

Further, evaluation tests were conducted on the weight average particle diameter of the magnetic carrier, the volume resistivity of the magnetic carrier, the toner coverage with respect to the magnetic carrier, and the linear velocity ratio between the photoreceptor and the developing sleeve.
By setting the weight average particle diameter of the magnetic carrier to 20 μm to 40 μm, the area ratio was reduced, and an image density could be obtained without generating an abnormal image. When the thickness is 20 μm or less, the magnetic force of one magnetic carrier is reduced and carrier adhesion occurs. If it is 40 μm or more, it is difficult to reduce the area ratio.
Further, by setting the volume resistivity of the magnetic carrier to 10 ¹⁰ to 10 ¹⁴ Ω · cm, an image density could be obtained without generating an abnormal image. When it is 10 ¹⁰ or less, carrier adhesion occurs, and when it is 10 ¹⁴ or more, it is difficult to obtain image density.
Further, by setting the toner coverage with respect to the magnetic carrier to 50 to 70%, an image density could be obtained without generating an abnormal image. If it is 50% or less, the image density cannot be obtained, and if it is 70% or more, toner scattering and toner adhesion to non-image portions, so-called background smearing occurs.
By setting the linear velocity ratio between the photosensitive member and the developing sleeve to 1.2 to 2.5, it was possible to obtain an image density without generating an abnormal image. When the density is 1.2 or less, the image density cannot be obtained, and when the density is 2.5 or more, toner scattering and carrier scattering occur.

FIG. 6 is a schematic diagram for explaining that the developing ability is increased by increasing the developer density in the vicinity of a position where the developer starts to contact the photoreceptor. It is a schematic diagram explaining the situation of the magnetic field and magnetic spike by the magnetic pole arrangement of the mag roll in the developing sleeve. 1 is a schematic configuration diagram of a copier according to an embodiment. It is an enlarged view showing a schematic configuration of a yellow process cartridge and a cyan process cartridge among the process cartridges. FIG. 3 is an enlarged configuration diagram illustrating the image forming unit, the intermediate transfer unit, the secondary transfer device, a pair of registration rollers, and a fixing unit. It is an expanded sectional view which shows the photosensitive layer of a photoreceptor. The magnetic roller magnetic pole arrangement used in Example 1, Example 2, Comparative Example 1, and Comparative Example 2, and the perpendicular magnetic force distribution and tangential magnetic force distribution with respect to the sleeve circumferential direction formed by the magnetic poles on the periphery of the developing sleeve are shown. FIG. It is a figure which shows the magnetic pole arrangement | positioning of the magnetic roller used by the comparative example 3 and the comparative example 4, and the perpendicular magnetic force distribution and tangential magnetic force distribution which are formed on the circumference | surroundings of a developing sleeve by each magnetic pole with respect to the sleeve circumferential direction. It is a photograph which shows an example of the imaging | photography result observed with a visualization apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Intermediate transfer belt 17 Intermediate transfer unit 18 Process cartridge 20 Image forming unit 21 Optical writing unit 22 Secondary transfer device 25 Fixing unit 40 Photoconductor 60 Charging device 61 Developing device 100 Printer unit 200 Paper feeding device 300 Scanner 400 Automatic document conveyance apparatus

Claims (6)

An image carrier on which an electrostatic latent image is formed;
A developer carrying member disposed at a position facing the image carrying member and carrying and transporting a two-component developer comprising a toner and a magnetic carrier;
A predetermined DC voltage is applied between the image carrier and the developer carrier, the developer contacts the image carrier, and the developer has a speed difference in the same direction with respect to the image carrier. An image forming apparatus comprising: a developing device that is transported and develops an electrostatic latent image on the image carrier;
The area ratio in which the magnetic carrier carrying the toner on the surface is not in contact with the image carrier is 40% or less with respect to the area of the image carrier from the position where the developer starts to contact the image carrier to 500 μm. And
The interval between the image carrier and the developer carrier is PG [m], the developer carrying amount per unit area on the developer carrier at the position facing the image carrier is M [kg / m ² ], When the bulk density of the developer is ρ [kg / m ³ ], the following relationship is satisfied: M / ρ <1.2 × PG
An image forming apparatus. The developer carrier is
A magnetic pole is provided outside a region where the developer contacts the image carrier, and a tangential magnetic field with respect to the circumferential direction of the image carrier is formed in a region where the developer contacts the image carrier. The image forming apparatus according to claim 1. The image forming apparatus according to claim 1, wherein the magnetic carrier has a weight average particle diameter of 20 μm to 40 μm. The image forming apparatus according to claim 1, wherein the magnetic carrier has a volume resistivity of 10 ¹⁰ to 10 ¹⁴ [Ω · cm]. The image forming apparatus according to claim 1, wherein a toner coverage of the developer with respect to a magnetic carrier is 50 to 70 [%]. 6. The Vr / Vp is 1.2 to 2.5, where Vp is the linear velocity of the image carrier and Vr is the linear velocity of the developer carrier. 6. The image forming apparatus described in 1.