JP2006099029A - Developing device, and process cartridge and image forming apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the occurrence of density unevenness attributed to the pitch of a developer stirring/transporting means as well as to maintain high image quality with high sharpness and high density without progressing carrier adhesion. <P>SOLUTION: A developing device is provided with: a developing roller 51 which scoops up, carries and transports a two-component developer comprising a toner and carrier in a developing case 55 stirred and transported by a first stirring/transporting screw 53; and a doctor blade 52 for regulating the amount of the two-component developer on the developing roller, wherein a maximum value of surface magnetic flux density in a normal line direction of a magnetic pole P5 which scoops up the two-component developer and transports it to a position opposite to the doctor blade in a magnetic field generating means of the developing roller is 75-95 mT, an average particle diameter of the carrier is 35-55 μm, and a carbon black is contained in a surface coating layer of the carrier. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a developing device used for a copying machine, a fax machine, a printer, and the like, and a process cartridge and an image forming apparatus using the developing device.

  2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine, a fax machine, or a printer, a two-component developer (hereinafter referred to as a developer) composed of a toner and a carrier as a developer for developing a latent image formed on an image carrier. Is used. An example of such a two-component developing device is disclosed in Patent Document 1. In the developing device disclosed as an example in Patent Document 1, a cross blade is provided as a developer agitating and conveying means in a developer container, and the developer is agitated by the developer agitating and conveying means, so that the developer is triboelectrically charged. In addition, the developer is transported to the vicinity of the developer carrying member. A developer carrying member comprising a non-magnetic developing sleeve having a magnet therein is pumped up by the magnetic force and carried on the surface of the developer, and is conveyed to a position facing the image carrying member by rotation of the non-magnetic sleeve. On the way, the amount of the developer on the developer carrying member is regulated by the developer regulating member. In the development area facing the image carrier, developer spikes are formed on the developer carrier by magnetic force, and toner is supplied from the developer spikes to the electrostatic latent image on the image carrier. develop.

  In such a two-component developing device, when solid images are continuously printed, image density unevenness due to pitch unevenness of the developer agitating / conveying means may occur. The cause is considered as follows. When continuously printing solid images that consume a lot of toner, the developer continuously replenished with a sufficient amount of toner is pumped up to the developer carrying member, sent to the portion facing the developer regulating member, and conveyed to the development area. There is a need. The low-concentration developer returned from the developer carrier to the developer container after contributing to the development is agitated with a new developer containing a lot of toner conveyed by the developer agitating and conveying means, and again. It is pumped up to the developer carrier. As the developer agitating and conveying means, a cross blade or a screw blade as disclosed in Patent Document 1 is used. However, in these developer stirring / conveying means, a difference in stirring / conveying ability due to the pitch of the developer stirring / conveying means is caused by the difference in the shape of the blade and the part without the blade or the blade. In the part where the stirring and conveying capability of the developer stirring and conveying means is low, stirring with a new developer becomes insufficient. Furthermore, the amount of developer transport to the vicinity of the developer carrying member is reduced. For this reason, there is a difference in the amount of developer supplied to the vicinity of the developer carrying member depending on the pitch of the developer stirring and conveying member. Here, a large amount of developer can be pumped up when the magnetic force of a magnet (hereinafter referred to as “pumping pole”) that pumps the developer onto the surface of the developer carrier is large. The difference in the developer supply amount due to the pitch of the agitating / conveying means does not have much influence. However, when the magnetic force of the pumping pole is weak, the difference in the developer supply amount due to the pitch of the developer agitating / conveying means greatly affects the amount of the developer carrying member. When the developer amount pumped up and carried by the developer carrier in this way has pitch unevenness and is sent to the portion facing the developer regulating member, the developer amount conveyed to the development area can also be uneven in pitch. This causes uneven image density. In the developing device disclosed in Patent Document 1, the maximum value of the surface magnetic flux density in the normal direction of the pumping pole is 650 gauss, and the magnetic force is relatively weak, so image density unevenness due to pitch unevenness is likely to appear. Further, in this developing apparatus, the developer agitating / conveying means has a cross-blade shape, so that there is no ability to agitate and convey the developer carrying member in the axial direction, which causes an increase in image density unevenness in the axial direction.

  The developing device disclosed as another embodiment of Patent Document 1 includes a toner feeding member, and the toner feeding member replenishes the toner by sprinkling the toner on the carrier on the developer carrying member. This is a configuration that does not have the developer conveying and stirring means, and does not cause unevenness due to the developer stirring and conveying means.

  Further, in order to suppress the occurrence of pitch unevenness in the developer agitating / conveying means, those which define the magnetic field strength of the magnetic field generating means of the developer carrier are proposed in Patent Document 2 and Patent Document 3. Yes.

Japanese Patent No. 2644489 JP 2001-194911 A JP 2002-148941 A

  In a two-component developing apparatus, there is a method using a small particle size carrier in order to obtain a sharp image quality. When a small particle size carrier is used, the action of rubbing the toner image with the developer spike immediately after development is reduced, and the overall image is less blurred. Therefore, there is no blurring feeling and the sharpness can be enhanced. However, as the particle size of the carrier is reduced, the margin for carrier adhesion decreases. When the carrier adheres, problems such as generation of a white-out image due to transfer loss and damage to the transfer device and the fixing device to shorten the entire life of the device occur. In particular, in a full-color image forming apparatus that superimposes four color toners, the possibility of occurrence of the above problems is four times as large as that in a single-color image forming apparatus. It has become.

  Further, in the two-component developing device, in order to suppress density unevenness due to the developer stirring and conveying means described above, when the magnetic force for conveying the developer to the developer amount regulating member is increased, the developer in the regulating unit The ironing becomes stronger and the frictional charging effect is increased. If the frictional charging effect becomes too large, carrier adhesion tends to deteriorate. Further, if the triboelectric charging effect is increased and the charge amount of the toner in the developer is excessively increased, the developing ability tends to be lowered, and the image density may be insufficient.

  As described above, in the two-component developing device, various demands are made to improve the image quality. However, the conventional developing devices such as the developing device described in the above-mentioned patent document cannot satisfy all of these requirements. There wasn't.

  The present invention has been made in view of such a background. The purpose is to use a developing device capable of maintaining high image quality with high sharpness and high density without deteriorating carrier adhesion, and suppressing density unevenness due to the pitch of the developer agitating and conveying means, and the use thereof. The present invention provides a process cartridge and an image forming apparatus.

In order to achieve the above object, a first aspect of the present invention is a developer containing portion that contains a two-component developer containing toner and a carrier, and a developer that stirs and conveys the two-component developer in the developer containing portion. A developer having a rotatable non-magnetic sleeve containing a stirring and conveying means and a magnetic field generating means having a magnet for forming a plurality of magnetic poles, and pumping and carrying the two-component developer in the developer accommodating portion In a developing device comprising a carrier and a developer regulating member that is disposed so as to face the surface of the developer carrier with a certain gap and regulates the amount of the two-component developer on the developer carrier. The maximum value of the surface magnetic flux density in the normal direction of the magnetic pole that pumps up the two-component developer of the magnetic field generating means of the developer carrying member and conveys it to the opposed portion to the developer amount regulating member is 75 to 95 mT. The average particle size of 35 to 35 A 5 [mu] m, and is characterized in that it contains carbon black in the surface coating layer of the carrier. Note that the surface magnetic flux density surface refers to the surface of the nonmagnetic sleeve.
According to a second aspect of the present invention, in the developing device of the first aspect, when the carrier has a volume resistance of R [Ω · cm] when a DC voltage of 1000 V is applied as a single carrier, the logR is 10 to 15th power. It is characterized by being.
According to a third aspect of the present invention, in the developing device according to the first or second aspect, the developer agitating / conveying means is disposed in parallel with the developer carrying member, and the two-component developer is arranged in the rotation axis direction of the developer carrying member. A developer transport and supply member capable of rotating the two-component developer in the vicinity of the developer carrier while transporting the developer, and a surface movement speed A of the developer carrier and a surface movement speed B of the developer transport member. The ratio B / A is 0.32 ≦ B / A ≦ 1.86.
According to a fourth aspect of the present invention, in the developing device of the first, second, or third aspect, the weight ratio of the carbon black to the resin of the surface coat layer of the carrier is 3% or less.
According to a fifth aspect of the present invention, in the developing device of the first, second, third, or fourth aspect, the toner has a weight average particle diameter of 3 to 10 μm.
A sixth aspect of the present invention is the developing apparatus according to the first, second, third, fourth or fifth aspect, wherein the toner has a spindle shape.
According to a seventh aspect of the present invention, in the developing device of the sixth aspect, the ratio (r2 / r1) of the major axis r1 to the minor axis r2 of the toner is 0.5 to 0.8, and the thickness r3 and the minor axis r2. (R3 / r2) is 0.7 to 1.0.
According to an eighth aspect of the present invention, there is provided a process cartridge which integrally supports an image carrier and at least one means selected from a charging means, a developing means, and a cleaning means, and is detachable from an image forming apparatus main body. As the developing means, a developer accommodating portion for accommodating a two-component developer containing toner and a carrier, a developer agitating / conveying means for agitating and conveying the two-component developer in the developer accommodating portion, and a plurality of magnetic poles A developer carrier having a rotatable non-magnetic sleeve containing a magnetic field generating means having a magnet for forming, pumping up and carrying the two-component developer in the developer container, and the developer carrier; A two-component developer that is disposed so as to face the surface with a certain gap and regulates the amount of the two-component developer on the developer-carrying member; Draw on The maximum value of the surface magnetic flux density in the normal direction of the magnetic pole conveyed to the portion facing the developer amount regulating member is 75 to 95 mT, the average particle size of the carrier is 35 to 55 μm, and the surface of the carrier The coating layer contains carbon black.
According to a ninth aspect of the present invention, in the process cartridge according to the eighth aspect, if the carrier has a volume resistance of R [Ω · cm] when a DC voltage of 1000 V is applied as a single carrier, the logR is 10 to the 15th power. It is characterized by being.
According to a tenth aspect of the present invention, in the process cartridge according to the eighth or ninth aspect, the developer agitating / conveying means is disposed in parallel with the developer carrying member, and the two-component developer is arranged in the rotation axis direction of the developer carrying member. A developer transport and supply member capable of rotating the two-component developer in the vicinity of the developer carrier while transporting the developer, and a surface movement speed A of the developer carrier and a surface movement speed B of the developer transport member. The ratio B / A is 0.32 ≦ B / A ≦ 1.86.
An eleventh aspect of the invention is the process cartridge according to the eighth, ninth or tenth aspect, wherein the weight ratio of the carbon black to the resin of the surface coat layer of the carrier is 3% or less.
According to a twelfth aspect of the present invention, in the process cartridge according to the eighth, ninth, tenth, or eleventh aspect, the toner has a weight average particle diameter of 3 to 10 μm.
According to a thirteenth aspect of the present invention, in the developing device according to the eighth, ninth, tenth, eleventh or twelfth aspect, the toner has a spindle shape.
According to a fourteenth aspect of the present invention, in the process cartridge of the thirteenth aspect, the ratio (r2 / r1) of the major axis r1 to the minor axis r2 of the toner is 0.5 to 0.8, and the thickness r3 and the minor axis r2. (R3 / r2) is 0.7 to 1.0.
An image forming apparatus comprising: an image carrier; a latent image forming unit that forms a latent image on the image carrier; and a developing unit that develops the latent image on the latent image carrier. The developing device includes the developing device according to claim 1, 2, 3, 4, 5, 6 or 7.

  According to the first to fifteenth aspects of the present invention, the maximum value of the surface magnetic flux density in the normal direction of the magnetic pole that pumps up the two-component developer of the magnetic field generating means of the developer carrying member and conveys it to the portion facing the developer amount regulating member. The average particle diameter of the carrier and the material of the carrier are defined. As a result, it is possible to satisfy a plurality of requirements of maintaining high sharpness and high density high image quality without deteriorating carrier adhesion and suppressing density unevenness due to the pitch of the developer stirring and conveying means. I found. Specifically, the following was found by experiments described later using Tables 1 to 8. First, when the magnetic force of the magnetic pole that draws up the two-component developer of the magnetic field generating means of the developer carrying member and conveys it to the opposed portion to the developer amount regulating member is small, the amount of developer carried by the developer carrying member is: It is easily affected by the difference in developer conveyance amount due to the pitch of the developer agitating and conveying means. If the maximum value of the surface magnetic flux density in the normal direction of the magnetic pole is 75 mT or more, the developer carrier can carry a large amount of developer, so the influence of the difference in the developer conveyance amount due to the pitch of the developer agitating and conveying means is affected. It becomes difficult to receive. Therefore, it has been found that the developer carrying member can convey the developer to the portion facing the developer regulating member with little unevenness, and image pitch unevenness due to the pitch of the developer agitating and conveying means does not occur. Further, it has been found that when the average particle size of the carrier is 55 μm or less, high image quality with high sharpness can be maintained. However, when the surface magnetic flux density in the normal direction is increased, the ironing of the developer at the restricting portion becomes stronger and the triboelectric charging effect of the developer increases, so that the degree of carrier adhesion deteriorates or the image density Or drop. Further, when the average particle diameter of the carrier is reduced, the carrier adhesion tends to be deteriorated. In the range where the average particle diameter of the carrier is 30 μm or less, no conditions satisfying the carrier adhesion could be found. Further, when the maximum value of the surface magnetic flux density in the normal direction of the magnetic pole is larger than 95 mT, the carrier adhesion margin is remarkably deteriorated. Furthermore, regarding the carrier material, the carrier adhesion margin is significantly improved in the carrier containing carbon black in the surface coat layer in Tables 4 to 8 as compared to the surface-coated carbonless carrier in Tables 1 to 3. To do. This is because the addition of a small amount of carbon to the carrier coat layer has the effect of extremely reducing the resistance of the carrier, and appropriate discharge is sequentially performed to improve the margin for carrier adhesion. Conceivable. In the case where a carrier in which carbon black is added to such a coat layer is used, the developer has a maximum surface magnetic flux density in the normal direction of 75 to 95 mT and an average particle diameter of the carrier of 35 to 55 μm. It was possible to obtain a high-definition and high-definition image with high sharpness in which unevenness in image density and carrier adhesion due to the pitch of the stirring and conveying means were substantially suppressed.

  According to the present invention, there is an excellent effect that high sharpness and high density high image quality can be maintained without deteriorating carrier adhesion, and density unevenness due to the pitch of the developer stirring and conveying means can be suppressed.

  Hereinafter, an embodiment when the present invention is applied to an image forming apparatus will be described. FIG. 1 is a configuration diagram showing a schematic configuration of the image forming apparatus. The central portion of the image forming apparatus includes image stations 15Y, 15C, 15M, and 15K for forming toner images of each color of yellow (Y), cyan (C), magenta (M), and black (K). ing. Hereinafter, the subscripts Y, C, M, and K of the respective symbols indicate members for yellow, cyan, magenta, and black, respectively. Each of the image stations 15Y, 15C, 15M, and 15K includes an optical unit 8 as an exposure unit that can irradiate the drum-shaped photoconductors 20Y, 20C, 20M, and 20K with laser light. Above the image station 15, an intermediate transfer unit 10 including an intermediate transfer belt 11 to which a toner image formed by each image station 15 is secondarily transferred is provided. Further, a fixing unit 6 for fixing the toner image transferred to the intermediate transfer belt 11 to the transfer paper 2 is provided. In addition, toner bottles 9Y, 9C, 9M, and 9K that store toner of each color of yellow (Y), cyan (C), magenta (M), and black (K) are loaded on the upper portion of the image forming apparatus.

  Since the image stations 15Y, 15C, 15M, and 15K have the same structure, only one image station 15 will be described. FIG. 2 is a block diagram showing the internal configuration of the image station. As shown in FIG. 2, the image station 15 includes a photosensitive member 20, a charging device 30 that charges the photosensitive member 20, a developing device 50 that develops a latent image formed on the photosensitive member 4, and residual toner on the photosensitive member 20. A cleaning device 40 for cleaning is provided. The charging device 30 is a charging roller, and includes a cleaning roller 31 that cleans the surface of the charging roller. The developing device 40 includes a developing roller 51 as a developer carrying member disposed in a developing case 55 as a developer containing portion having an opening so as to face and face the surface of the photoreceptor 20. The cleaning device 40 includes a cleaning case 43 having an opening, a cleaning blade 41 for cleaning the surface of the photoreceptor 20, a waste toner screw 42 for transporting the cleaned waste toner to a waste toner bottle (not shown), and the like. .

  Further, as shown in FIG. 1, the intermediate transfer unit 10 transfers toner images formed on the intermediate transfer belt 11 and the photoconductors 20Y, 20C, 20M, and 20K stretched by a plurality of rollers onto the intermediate transfer belt 11. Primary transfer rollers 12Y, 12C, 12M, and 12K for transferring are provided. These parts are integrally supported by the intermediate transfer belt case 14. The intermediate transfer unit 10 includes a secondary transfer roller 5 that transfers the toner image transferred onto the intermediate transfer belt 11 to the transfer paper 2, and a transfer residual toner on the intermediate transfer belt 11 that has not been transferred onto the transfer paper 2. A belt cleaning device 13 is provided.

  The transfer paper 2 in the paper feed cassette 1 is conveyed to a secondary transfer portion between the intermediate transfer belt 11 and the secondary transfer roller 5 by a paper feed roller 3 disposed in the vicinity of the paper feed cassette 2. . In the transfer paper conveyance path between the paper supply roller 3 and the secondary transfer roller 5, a pair of dies rollers 4 is arranged for timing the delivery of the supplied transfer paper 2 to the secondary transfer portion.

  The fixing unit 8 performs fixing by applying heat and pressure to the toner image transferred onto the transfer paper P. Then, the transfer sheet P that has been fixed is discharged out of the apparatus by the discharge roller pair 7.

  Next, a process of obtaining a color image in the image forming apparatus having the above configuration will be described. First, in the image stations 15Y, 15C, 15M, and 15K, the photoconductor 20 is uniformly charged by the charging device 30. Thereafter, the optical unit 8 scans and exposes the laser beam based on the image information to form a latent image on the surface of the photoconductor 20. The latent image on the photoconductor 20 is developed with each color toner carried on the developing roller 51 of the developing device 50 to be visualized as a toner image. The toner image on the photoconductor 20 is sequentially transferred onto the transfer belt 11 that is rotated counterclockwise by the action of each primary transfer bias roller 12. The image forming operation of each color at this time is shifted in timing from the upstream side toward the downstream side in the moving direction of the intermediate transfer belt 11 so that the toner image is transferred to the same position on the intermediate transfer belt 11. Executed. The surface of the photoreceptor 20 after the primary transfer is finished is cleaned by the cleaning device 40 and is prepared for the next image formation.

  On the other hand, the transfer paper 2 in the paper feed cassette 1 is transported by a paper feed roller 3 disposed in the vicinity of the paper feed cassette 1 and is transported to a secondary transfer section by a registration roller pair 4 at a predetermined timing. . In the secondary transfer portion, the toner image formed on the intermediate transfer belt 11 is transferred to the transfer paper 2. The transfer paper 2 onto which the toner image has been transferred passes through the fixing unit 6 to be fixed, and is discharged out of the apparatus by a discharge roller 7. Similar to the photoconductor 20, the untransferred toner remaining on the transfer belt 11 is cleaned by a belt cleaning device 13 that contacts the intermediate transfer belt 11. Further, a predetermined amount of toner filled in the toner bottle 9 is supplied to each developing device 50 through a conveyance path (not shown) according to necessity.

  Next, the developing device 50 will be described in detail. Since the developing devices 50Y, 50M, 50C, and 50K have the same configuration except that the toner colors are different, the configuration of one developing device 50 will be described. FIG. 3 is a configuration diagram showing an internal configuration of the developing device. As shown in FIG. 3, the developing device 50 includes a developing roller 51 disposed in the developing case 55 so as to face the photoconductor 20 through an opening of the developing case 55, and a developer on the developing roller 51. And a doctor blade 52 that regulates the amount carried. The developing roller 51 includes a magnet roller as a magnetic field generating means including a plurality of fixed magnets in a rotatable nonmagnetic aluminum developing sleeve. Further, in the developing case 55, a first agitating and conveying screw 53 and a second agitating and conveying screw 54 are provided as developer agitating and conveying means at a position facing the developing roller 51. As shown in FIG. 3, the pole disposed so as to face the center of the photosensitive drum 20 with the peak magnetic force is the main pole (P1 pole), and P2 in order of the rotation direction of the developing roller 51 from the P1 pole. The magnetic poles are arranged in the order of pole, P3 pole, P4 pole, and P5 pole. The P2 pole draws the developer used for development at the development position to the developing case 55 side by a synergistic action with the rotation of the developing roller 51, and draws the developer from the first agitating and conveying screw 53 to the developing roller 51. Is the P4 pole. It is constituted by the magnetic force of the same polarity as the P4 pole, and is located between the P2 pole and the P4 pole, and the developer attracted by the P2 pole by the repulsive magnetic field with the magnetic force of the P4 pole is separated from the developing roller 51. P3 pole. It is the P5 pole that draws and moves the developer restrained on the surface of the developing roller by the magnetic force of the P4 pole to the doctor blade 52 that regulates the thickness (amount) of the developer. The P5 pole also has a function of pumping up the developer conveyed by the first agitating and conveying screw 53 in the conveying process. Further, an angle obtained by shifting the center of the main pole from the straight line L connecting the center of the developing roller 51 and the point where the developing roller 51 is closest to the photoconductor 20 to the upstream side in the rotation direction of the developing roller 51 is referred to as a main pole angle. In this embodiment, since the photoconductor 20 is in a drum shape, the straight line L is a straight line connecting the center of the developing roller 51 and the center of the photoconductor 20, and an angle obtained by shifting the straight line from the center of the main pole is a main pole angle. Become.

A specific configuration and development conditions of the image forming apparatus according to the present exemplary embodiment will be described. The developing sleeve diameter is 18 mm, and the main pole angle is 7 °. The core material of the carrier is a ferrite core material, and a saturation magnetization of 72 Am ² / kg at an applied magnetic field of 5 KOe, and a silicone resin as a main component as a surface coat layer of the carrier. When the direct current resistance of the carrier is R [Ω · cm], the logR is set to the 13th power. The toner had an average particle size of 6.8 μm, and the toner concentration in the developer was 5 to 10% by weight. Here, the direct current resistance R [Ω · cm] means that a voltage of 1000 V was applied to the developing sleeve in an image forming apparatus that was actually used in a configuration using a grounded aluminum tube instead of the photoreceptor 20. It is the result of measuring the volume resistance at the time. The direct current resistance R [Ω · cm] can be adjusted by the prescription of the surface coat layer, but in the manufacturing process, about 2 to 3 is a value that tends to vary. Therefore, in terms of improving the yield and reducing the cost, it is important to obtain a stable high image quality even if this value fluctuates. The silicone resin here may be any conventionally known silicone resin, and includes straight silicone consisting only of an organosiloxane bond and silicone resin modified with alkyd, polyester, epoxy, urethane or the like. . The gap between the doctor blade 52 and the developing roller 51 is 0.45 mm, the gap (developing gap) between the surface of the developing roller 51 and the surface of the photoreceptor 20 is 0.30 mm, and the maximum value of the surface magnetic flux density in the normal direction of the P1 pole is 105 mT. The developing sleeve had a surface speed of 295 mm / s (rotation speed: 313 rpm) in the counterclockwise direction in FIG. The diameter of the photoconductor 20 was 30 mm, and the linear velocity was 155 mm / sec.

  FIG. 4 is a diagram showing a schematic configuration inside the developing case 55. As shown in FIG. 4, the first agitating and conveying screw 53 and the second agitating and conveying screw 54 extend in parallel with the developing roller 51 and are rotatably supported by a bearing member (not shown) provided in the developing case 55. . Of course, the developing roller 51 is also rotatably supported by the developing case 55 via a bearing member (not shown). The first agitating and conveying screw 53 and the second agitating and conveying screw 54 are partitioned by a partition wall 56. The first agitating and conveying screw 53 is disposed in the first space portion 57 located on the developer supply side to the developing roller 51 and rotates counterclockwise in FIG. 3 to remove the developer in the first space portion 57. In FIG. 4, it is conveyed in the longitudinal direction from the right to the left. The second agitating / conveying screw 54 is disposed on the second space 58 side that receives toner replenishment from a toner replenishing port (not shown), and rotates counterclockwise in FIG. 3 to show the developer in the second space 58. 4 Convey in the longitudinal direction from left to right in the middle. Between the one end of the partition wall 56 and the inner side surface of the developing case 55, a transfer portion 59a for sending the developer from the first space portion 57 to the second space portion 58 is formed. Between the other end of the partition wall 56 and the inner surface of the developing case 55, a transfer part 59b for sending the developer from the second space part 58 to the first space part 57 is formed. In addition, the diameter of the 1st stirring conveyance screw 53 and the 2nd stirring conveyance screw 54 which concern on this embodiment is formed in 15 mm. Moreover, the surface speed of the 1st stirring conveyance screw 53 was 333 mm / sec (rotation speed 424 rpm). Accordingly, (first conveying screw surface speed) / (developing sleeve surface speed) = 1.13.

  The movement of the developer in the developing device 50 having such a configuration will be described. The two-component developer in the developing case 55 is conveyed from the right to the left in FIG. 4 while being agitated by the first agitating and conveying screw 53, and the second agitating and conveying screw 54 is disposed from the transfer portion 59a of the partition wall 56. Is sent to the second space 58. The two-component developer sent to the second space 58 is agitated by the second agitating and conveying screw 54 and simultaneously conveyed from the left to the right in FIG. Sent to 57 side. The developer sent to the first space portion 57 is again stirred by the first stirring and conveying screw 53 and simultaneously conveyed to the left. By transporting the developer while stirring in this way, the toner and the carrier are frictionally charged by stirring while the developer circulates in the developing case 55.

  The first agitating / conveying screw 53 supplies a part of the developer in the first space portion 57 to the vicinity of the surface of the developing roller 51 near the P5 pole by its rotating action, and the developing roller 51 magnetically supplies the developer. Carry and carry. As shown in FIG. 3, the height (carrying amount) of the developer on the developing roller 51 is regulated by the doctor blade 52, and is conveyed to the developing area facing the photoconductor 20. As a result, the electrostatic latent image on the photoconductor 20 is developed at a portion facing the developing roller 51 to become a toner image. The developer on the developing roller 51 after contributing to the development is peeled off from the developing roller 51 by the repulsive force of the magnetic poles P2 and P3 in the developing roller 51 and returned to the first space portion 57 of the developing case 55. . The developer returned into the first space portion 57 is again transported by the first stirring and transporting screw 53, and the second space portion in which the second stirring and transporting screw 54 is disposed again via the transfer portion 59a of the partition wall 56. 58. When the toner concentration of the developer in the developing case 55 becomes a predetermined concentration or less, the toner is supplied from the toner supply port (not shown) to the second space 58 side. This toner is mixed with the developer by stirring by the second stirring and conveying screw 54. The developer adjusted to a predetermined concentration is carried on the developing roller 51, passes through the doctor blade 52, is thinned, and the above cycle is repeated.

  In such a developing device 50, the present inventors conducted the following experiment in order to obtain high-quality images with high sharpness by suppressing density unevenness and carrier adhesion due to the pitch of the first stirring and conveying screw 53. The conditions of the proper carrier material, particle size, and P5 pole magnetic flux density of the developing roller 51 were obtained.

First, in such a developing device 50, the maximum value of the surface magnetic flux density in the normal direction of the P5 pole was set to 55 mT, 65 mT, 75 mT, 85 mT, 95 mT, 105 mT, and 115 mT. The surface having the surface magnetic flux density refers to the surface of the nonmagnetic sleeve. The average particle size of the carrier was 30 μm, 35 μm, 40 μm, 50 μm, 55 μm, and 60 μm. Under these conditions, the screw pitch unevenness by the first stirring / conveying screw 53, carrier adhesion, feeling of blur, and image density were evaluated. The average particle diameter of the carrier can be measured by various methods. Here, 200 to 400 randomly extracted from an image obtained from a normal sieving method or an optical microscope is analyzed by an image processing analyzer. The method was used. In this confirmation experiment, the toner concentration was 5% by weight. This is because when the toner density is low, screw pitch unevenness, carrier adhesion, and insufficient image density are likely to occur, and good / bad judgment can be made with high sensitivity. As an evaluation method for screw pitch unevenness, 30 continuous A4 size solid images were continuously passed while maintaining a toner concentration of 5% by weight, and the degree of screw pitch unevenness was determined by observing the image at that time. . Rank 5 has no unevenness, and the lower the rank, the worse the degree of unevenness. Further, as a method for evaluating the carrier adhesion, a method of counting the number of carrier adhesions on the photoconductor 20 with an actual machine was used. After the background potential image (non-exposed white image) created by the photoreceptor background potential and the development potential is developed, the main power supply is turned off. Here, in the area after development and before transfer, the number of carriers attached on the photoconductor 20 is counted, and the number in the actual machine background potential control range is converted per 75 cm ² . This operation is carried out while shaking the ground potential. When the worst value of the number of carriers adhered on the photoreceptor (per 75 cm ² ) in the background potential control range is 30 or less, ○, and when 31 to 50, Δ, In the case of 51 or more, it determined with x. Regarding the decrease in image density, when the result of measuring the solid image density with X-Rite 938 when printing 100 sheets continuously at 10 ° C./15% environment is less than 1.2, NG It is indicated by a broken line area in the table. Note that the DC resistance R [Ω · cm] of the carrier is a value that is likely to vary in manufacturing, and in order to examine the margin, three types of logR, 12, 13, and 14th power, were examined.

この結果を表１〜表３にしめす。表１〜表３によると、平均キャリア粒径が６０μmより大きい場合は画像のボソツキが目立ち鮮鋭性に欠けるものとなった。一方、平均キャリア粒径が３０μmを下回った範囲ではキャリア付着余裕度を満足する範囲は見出せなかった。また、Ｐ５極が７５ｍＴを下回ると、Ｐ５極による現像剤の汲み上げが不十分になり、認識できるレベルのスクリュウピッチムラが発生した。一方、Ｐ５極を７５ｍＴ以上にすると、スクリュウピッチムラは解消する。ただし、Ｐ５極の上昇に伴って規制部での現像剤のしごきが強くなり、トナーの摩擦帯電効果が大きくなる。そのため、Ｐ５極の磁気力を大きくするほどキャリア付着の程度が悪化したり、画像濃度が低下したりする結果となった。

The results are shown in Tables 1 to 3. According to Tables 1 to 3, when the average carrier particle size is larger than 60 μm, the blur of the image is conspicuous and lacks sharpness. On the other hand, in the range where the average carrier particle size was less than 30 μm, a range satisfying the carrier adhesion margin could not be found. Further, when the P5 pole was less than 75 mT, the developer pumping by the P5 pole was insufficient, and a recognizable level of screw pitch unevenness occurred. On the other hand, when the P5 pole is 75 mT or more, screw pitch unevenness is eliminated. However, as the P5 pole increases, the ironing of the developer at the restricting portion becomes stronger, and the frictional charging effect of the toner increases. Therefore, as the magnetic force of the P5 pole is increased, the degree of carrier adhesion is deteriorated and the image density is decreased.

  In addition, the relationship between the direct current resistance of the carrier and the carrier adhesion is examined. It is considered that by increasing the resistance of the carrier, it is difficult to induce electrostatic induction, and the force that the carrier receives from the developing electric field in the developing region can be weakened, and the margin for carrier adhesion can be improved. However, if the direct current resistance of the carrier is too high, the effect of frictional charging of the toner is increased, and conversely, the carrier is likely to adhere. Further, if the toner triboelectric charging effect becomes too great, the developing ability is lowered, and the problem of insufficient image density occurs. In the experiments shown in Tables 1 to 3, when the carrier average particle size is 55 μm or less, which is considered to have good sharpness, in the range of 12, 13, and 14 with log R, the portion where the number of adhered carriers satisfies the circle is narrow. Further, in the vicinity of the carrier average particle diameter of 35 μm to 40 μm, which is considered to have the highest sharpness, there is no portion where the number of adhered carriers satisfies the circle. Thus, as shown in Tables 1 to 3, when a surface-coated carbonless carrier is used, the □ region in the figure satisfying all of the screw pitch unevenness, carrier adhesion, bumpiness, and ID is narrow. That is, the results are weak against variations such as the carrier DC resistance, the carrier particle size, and the surface magnetic flux density in the normal direction of the P5 pole.

  Therefore, the present inventor conducted the same experiment for the carrier in which carbon black was added to the surface coat layer, and evaluated the screw pitch unevenness, carrier adhesion, feeling of blur, and image density by the first stirring and conveying screw 53. The weight ratio of carbon black to resin of the surface coat layer of the carrier was 3%. Further, the direct current resistance R [Ω · cm] of the carrier was examined by changing the logR over a wide range of 9 to 16th power. By adding carbon black to the surface coat layer, the direct current resistance can be made relatively easy as compared with the case where no carbon black is added. For this reason, it was performed to confirm the margin for carriers having a wide range of DC resistance.

この結果を表４〜表８にしめす。表５〜表７によると、キャリアの表面コート層にカーボンブラックを添加した場合、スクリュウピッチムラ、キャリア付着、ボソツキ、ＩＤを全て満足する表５〜７中の領域は、表面コート層にカーボンブラックを添加しない場合と比較して広い。これは、キャリアの表面コート層にカーボンブラックを少量添加することで、キャリアの抵抗を極めて局所的に下げる効果が発生し、適度な放電が逐次行われて、キャリア付着に対する余裕度を向上させると考えられる。また、直流抵抗Ｒ[Ω・ｃｍ]に着目しても、logＲで１０〜１５乗の広い範囲でスクリュウピッチムラ、キャリア付着、ボソツキ、ＩＤを満足することができる。これは、キャリア製造上の抵抗バラツキに対する高画質という意味で余裕度が向上しているとも言える。ただし、表４に示すように、キャリアの直流抵抗Ｒ[Ω・ｃｍ]が、logＲで９乗まで低くなると、スクリュウピッチムラ、キャリア付着、ボソツキ、ＩＤを全て満足する領域は狭くなり、キャリア平均粒径のバラツキに対しては弱い結果となっている。また、キャリアの直流抵抗Ｒ[Ω・ｃｍ]が、LogＲで１６乗まで上昇してしまうとスクリュウピッチムラ、キャリア付着、ボソツキ、ＩＤを全て満足する領域は急激に狭くなり、Ｐ５磁気力のバラツキに対しては弱い結果となっている。以上のことから、ピッチムラがなく、ボソツキ感がなく鮮鋭感の高い、高濃度の高画質を高寿命で得つつ、キャリア付着に対して余裕度の高いシステムを得るためには、Ｐ５極の法線方向の表面磁束密度の最大値を７５ｍＴ以上、９５ｍＴ以下として、かつ平均粒径が３５〜５５μmの小粒径キャリアを用いて、かつ上記キャリアが少なくともシリコーン樹脂とカーボンブラックを主成分としたコート層から成るものを用いることが有効であることが判明した。さらに、キャリアの製造時の抵抗のばらつきを考慮すると、キャリアに１０００Ｖを印加したときの直流抵抗Ｒ[Ω・ｃｍ]を、logＲで１０〜１５乗の範囲に収めることが効果的であることが判明した。

The results are shown in Tables 4-8. According to Tables 5 to 7, when carbon black is added to the surface coat layer of the carrier, the regions in Tables 5 to 7 that satisfy all of the screw pitch unevenness, carrier adhesion, blur, and ID are carbon black in the surface coat layer. Compared to the case where no is added. This is because when a small amount of carbon black is added to the surface coat layer of the carrier, the effect of lowering the resistance of the carrier extremely locally occurs, and appropriate discharge is sequentially performed to improve the margin for carrier adhesion. Conceivable. Further, even if attention is paid to the direct current resistance R [Ω · cm], screw pitch unevenness, carrier adhesion, squeeze, and ID can be satisfied in a wide range of logR in the 10th to 15th power. This can be said that the margin is improved in the sense of high image quality against resistance variations in carrier manufacturing. However, as shown in Table 4, when the DC resistance R [Ω · cm] of the carrier decreases to the 9th power in logR, the region satisfying all screw pitch unevenness, carrier adhesion, bumpiness, and ID becomes narrower, and the carrier average This is a weak result against particle size variation. In addition, if the DC resistance R [Ω · cm] of the carrier rises to the 16th power of LogR, the region satisfying all of the screw pitch unevenness, carrier adhesion, bumpiness, and ID becomes abruptly narrow, and the P5 magnetic force varies. Is a weak result. From the above, in order to obtain a system with a high margin for carrier adhesion while obtaining a high density and high image quality with a long life without pitch unevenness, sharpness and sharpness, the P5 pole method is used. Coat in which the maximum value of the surface magnetic flux density in the linear direction is 75 mT or more and 95 mT or less, and a small particle carrier having an average particle diameter of 35 to 55 μm is used, and the carrier is composed mainly of at least silicone resin and carbon black. It has been found effective to use a layer. Furthermore, considering the variation in resistance during the manufacture of the carrier, it is effective to keep the DC resistance R [Ω · cm] when 1000 V is applied to the carrier in the range of 10 to 15 in terms of logR. found.

  Further, by mixing a small amount of carbon in the carrier coat layer, there is an effect that the resistance of the carrier can be easily adjusted. However, the amount of carbon black added is set to 3% or less by weight ratio of the surface coat layer of the carrier to the resin. If it is more than this, when printing with an image area ratio of 1% with a small toner balance is repeatedly performed, color mixing occurs due to the transfer of the carbon color of the carrier to the toner. That is, by keeping the amount of carbon added to 3% or less, the color transfer of the carbon black of the carrier coat layer to the color toner can be suppressed, so that it can be used in combination with a color toner other than black. These carbon blacks preferably have a particle size of about 0.01 to 10 μm, and are often added in an amount of 2 to 30 mm by weight, more preferably 5 to 20 mm by weight with respect to 100 parts by weight of the coating resin.

  Further, in order to examine the setting margin of the first stirring and conveying screw 53, the experiment was conducted by changing the surface speed of the first stirring and conveying screw 53 in the range of 94.2 to 549 mm / sec (120 to 700 rpm in rotation speed). went. As a result, it was confirmed that screw pitch unevenness and other image defects did not occur. When the speed was slower than this range, the replenished toner was not sufficiently stirred and mixed, resulting in a background image or density unevenness image. Further, when the speed was higher than this range, problems such as an increase in internal pressure due to screw rotation and toner scattering outside the developing machine occurred. It has also been confirmed that the carbon black coat of the carrier is damaged over time, leading to an increase in carrier adhesion due to carrier deterioration.

  Next, the toner suitably used for the developing device 50 according to the present embodiment will be described. First, the weight average particle diameter of the toner is preferably 3 to 10 μm. A toner having a toner weight average particle diameter in the above range has toner particles having a sufficiently small particle diameter with respect to a minute latent image dot, and thus has excellent dot reproducibility. When the weight average particle diameter is less than 3 μm, phenomena such as a decrease in transfer efficiency and a decrease in blade cleaning properties tend to occur. When the weight average particle size exceeds 10 μm, it is difficult to suppress scattering of characters and lines.

  Next, a method for measuring the particle size distribution of toner particles will be described. The particle size distribution of the toner particles can be measured by a measuring device using a Coulter counter method, for example, a Coulter counter TA-II or Coulter Multisizer II (both manufactured by Coulter). Specifically, first, 0.1 to 5 ml of a surfactant (preferably alkylbenzene sulfonate) is added as a dispersant to 100 to 150 ml of the electrolytic aqueous solution. The electrolytic aqueous solution is a solution prepared by preparing a 1% NaCl aqueous solution using primary sodium chloride. For example, ISOTON-II (manufactured by Coulter) can be used. Here, 2 to 20 mg of a measurement sample is further added. The electrolytic solution in which the sample is suspended is subjected to a dispersion treatment with an ultrasonic disperser for about 1 to 3 minutes, and the measurement device is used to measure the volume and number of toner particles or toner using a 100 μm aperture as the aperture. Volume distribution and number distribution are calculated. From the obtained distribution, the weight average particle diameter and the number average particle diameter of the toner can be obtained. Here, the following 13 channels are used for particles having a particle size of 2.00 μm or more and less than 40.30 μm. 2.00 to less than 2.52 μm; 2.52 to less than 3.17 μm; 3.17 to less than 4.00 μm; 4.00 to less than 5.04 μm; 5.04 to less than 6.35 μm; 6.35 to 8 Less than 0.000; less than 8.00 to 10.08 μm; 10.08 to less than 12.70 μm; 12.70 to less than 16.00 μm; 16.00 to less than 20.20 μm; less than 20.20 to 25.40 μm; .40 to less than 32.00 μm; 32.00 to less than 40.30 μm

  Furthermore, it is preferable that the toner used in this embodiment has a spindle shape. An irregular or flat toner having a non-uniform shape has the following problems due to poor powder flowability. Since frictional charging cannot be performed smoothly, problems such as background stains are likely to occur. When developing a minute latent image dot, the dot reproducibility is inferior because it is difficult to obtain a dense and uniform toner arrangement. In the electrostatic transfer method, the transfer efficiency is inferior due to being hardly affected by the lines of electric force. In addition, toner close to a true sphere has too good powder fluidity and excessively acts on external force, so that there is a problem that toner particles are likely to be scattered outside the dots during development and transfer. is there. Further, since the spherical toner easily rolls on the photoconductor, there is a problem that the toner often sinks between the photoconductor and the cleaning member, resulting in poor cleaning. On the other hand, the spindle-shaped toner has the powder flowability adjusted appropriately, so that the triboelectric charging is smoothly performed and the background stains are not generated. Further, the spindle-shaped toner is developed in an orderly manner with respect to a minute latent image dot, and then transferred efficiently, and the dot reproducibility is excellent. In this case, the powder flowability is moderately braked to prevent scattering. Further, the spindle-shaped toner has a limited rolling axis as compared with the spherical toner, and therefore, it is difficult to cause a cleaning failure such as to sink under the cleaning member.

  5A is a schematic diagram showing the toner shape on the coordinate axes x, y, and z, FIG. 5B is a schematic diagram showing the toner shape on the coordinate axes x, z, and FIG. 5C is a schematic diagram showing the toner shape on the coordinate axes y. , Z is a schematic diagram shown on z. As shown in FIGS. 7A, 7B, and 7C, the toner described above has a ratio (r2 / r1) of the major axis r1 to the minor axis r2 of 0.5 to 0.8 and a thickness r3. A spindle shape with a ratio (r3 / r2) to the minor axis r2 of 0.7 to 1.0 is preferable. By adopting a spindle-like shape close to this, it is a shape that is neither an irregular shape, a flat shape nor a true spherical shape, and it satisfies all of triboelectric chargeability, dot reproducibility, transfer efficiency, splash prevention, and cleaning properties. It becomes. When the ratio of the major axis r1 to the minor axis r2 (r2 / r1) is less than 0.5, the separation from the true spherical shape is high, but the cleaning property is high, but the dot reproducibility and the transfer efficiency are inferior, resulting in high quality image quality. It can no longer be obtained. When the ratio (r2 / r1) between the major axis r1 and the minor axis r2 exceeds 0.8, the shape approaches a spherical shape, so that cleaning failure may occur particularly in a low temperature and low humidity environment. Further, when the ratio of the thickness r3 to the minor axis r2 (r3 / r2) is less than 0.7, it is close to a flat shape and less scattered like an irregular toner, but a high transfer rate like a spherical toner is obtained. I can't. In particular, when the ratio (r3 / r2) between the thickness r3 and the minor axis r2 exceeds 1.0, a rotating body having the major axis as the rotation axis is formed, and cleaning failure is likely to occur. By making such a spindle shape, it is a shape that is neither an irregular shape, a flat shape nor a spherical shape, and both shapes have triboelectric chargeability, dot reproducibility, transfer efficiency, splash prevention, cleaning properties All can be satisfied.

  FIG. 6 is a configuration diagram showing the configuration of the process cartridge. As shown in FIG. 6, the image station 15 is configured as a process cartridge 60 that integrally supports the photosensitive member 20, the charging device 30, the developing device 50, and the cleaning device 40 and is detachable from the apparatus main body. FIG. 7 is a perspective view illustrating a state where the process cartridges 60Y, 60C, 60M, and 60K are removed from the apparatus main body 70. FIG. The user can easily remove the process cartridge 60 from the apparatus main body 70, and the user can replace the photosensitive member 20, the developing device 50, the charging device 30, or the cleaning device 40 in the form of a cartridge.

As described above, according to the image forming apparatus according to the present embodiment, the carrier in which the surface coat layer contains carbon black is used in the experiment described above, and the developer is pumped up and conveyed to the doctor blade 52 in the normal direction of the magnetic pole P5. The surface magnetic flux density and the average particle diameter of the carrier are defined as described above. As a result, it is possible to satisfy the requirement of maintaining high image quality with high carrier adhesion and high sharpness and suppressing density unevenness due to the pitch of the developer agitating and conveying means.
Further, a carrier having a logR in the 10th to 15th power is used, where R [Ω · cm] is a volume resistance when a DC voltage of 1000 V is applied as a single carrier. By using a carrier containing carbon black in the surface coat layer, carrier adhesion can be reliably suppressed even in the DC resistance range of such a carrier. Therefore, it is possible to improve the margin with respect to variation in resistance in manufacturing the carrier.
The developer agitating and conveying means is arranged in parallel with the developing roller 51 as a rotatable agent conveying and supplying member that supplies the two-component developer to the vicinity of the developing roller while conveying the developer in the rotation axis direction of the developing roller. The first stirring / conveying screw 53 is used. The ratio B / A between the surface movement speed A of the developing roller and the surface movement speed B of the first stirring and conveying screw is 0.32 ≦ B / A ≦ 1.86. According to the above-described experiment, when the ratio B / A is slower than the above range, the toner is not sufficiently stirred and mixed, and there is a possibility that a background image or a density unevenness image is generated. Further, when the ratio B / A is faster than the above range, there is a possibility that the internal pressure increases due to the screw rotation or the toner scatters outside the developing machine. It has also been confirmed that the carbon black coat of the carrier is damaged over time, leading to an increase in carrier adhesion due to carrier deterioration. In order to prevent such a side effect, the surface moving speed of the first stirring and conveying screw 53 is assumed to satisfy the above range at the ratio B / A.
Further, the weight ratio of carbon black to the resin of the surface coat layer of the carrier is 3% or less. If it is more than this, when printing with an image area ratio of 1% with a small toner balance is repeatedly performed, color mixing occurs due to the transfer of the carbon color of the carrier to the toner. That is, by keeping the amount of carbon added to 3% or less, the color transfer of the carbon black of the carrier coat layer to the color toner can be suppressed, so that it can be used in combination with a color toner other than black.
The weight average particle diameter of the toner is 3 to 10 μm. A toner having a toner weight average particle diameter in the above range has toner particles having a sufficiently small particle diameter with respect to a minute latent image dot, and thus has excellent dot reproducibility. When the weight average particle diameter is less than 3 μm, phenomena such as a decrease in transfer efficiency and a decrease in blade cleaning properties tend to occur. When the weight average particle size exceeds 10 μm, it is difficult to suppress scattering of characters and lines.
Further, the toner has a spindle shape. In the spindle-shaped toner, the powder fluidity is appropriately adjusted, so that the triboelectric charging is smoothly performed and the background stain is not generated. Further, the spindle-shaped toner is developed in an orderly manner with respect to a minute latent image dot, and then transferred efficiently, and the dot reproducibility is excellent. In this case, the powder flowability is moderately braked to prevent scattering. Further, the spindle-shaped toner has a limited rolling axis as compared with the spherical toner, and therefore, it is difficult to cause a cleaning failure such as to sink under the cleaning member.
Further, the ratio (r2 / r1) between the major axis r1 and the minor axis r2 of the spindle-shaped toner is 0.5 to 0.8, and the ratio (r3 / r2) between the thickness r3 and the minor axis r2 is 0. 7 to 1.0. By making such a spindle shape, it is a shape that is neither an irregular shape, a flat shape nor a spherical shape, and it satisfies all of triboelectric chargeability, dot reproducibility, transfer efficiency, splash prevention, and cleaning properties It becomes. When the ratio of the major axis r1 to the minor axis r2 (r2 / r1) is less than 0.5, the separation from the true spherical shape is high, but the cleaning property is high, but the dot reproducibility and the transfer efficiency are inferior, resulting in high quality image quality. It can no longer be obtained. When the ratio (r2 / r1) between the major axis r1 and the minor axis r2 exceeds 0.8, the shape approaches a spherical shape, so that cleaning failure may occur particularly in a low temperature and low humidity environment. Further, when the ratio of the thickness r3 to the minor axis r2 (r3 / r2) is less than 0.7, it is close to a flat shape and less scattered like an irregular toner, but a high transfer rate like a spherical toner is obtained. I can't. In particular, when the ratio (r3 / r2) between the thickness r3 and the minor axis r2 exceeds 1.0, a rotating body having the major axis as the rotation axis is formed, and cleaning failure is likely to occur. By making such a spindle shape, it is a shape that is neither an irregular shape, a flat shape nor a spherical shape, and both shapes have triboelectric chargeability, dot reproducibility, transfer efficiency, splash prevention, cleaning properties All can be satisfied.
Further, the process cartridge 60 according to the present embodiment is configured such that the photosensitive member 20, the charging device 30, the developing device 50, and the cleaning device 40 are integrated with each other so as to be detachable from the image forming apparatus main body. Yes. Therefore, maintainability and exchangeability can be improved even in long-term use.

1 is a configuration diagram showing a schematic configuration of an image forming apparatus according to an embodiment. 2 is a configuration diagram showing an internal configuration of an image station of the image forming apparatus. FIG. FIG. 2 is a configuration diagram illustrating a schematic configuration of a developing device of the image forming apparatus. FIG. 2 is a plan view showing an internal configuration of a developing device of the image forming apparatus. (A) Schematic diagram showing the shape of the toner on the coordinate axes x, y, z. (B) A schematic diagram showing the shape of the toner on the coordinate axes x and z. (C) A schematic diagram showing the shape of the toner on the coordinate axes y and z. FIG. 2 is a configuration diagram illustrating a schematic configuration of a process cartridge of the image forming apparatus. FIG. 3 is a perspective view showing a state where a process cartridge is mounted on the image forming apparatus main body.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Paper feed cassette 2 Transfer paper 3 Paper feed roller 4 Registration roller 5 Secondary transfer roller 8 Optical unit 8 Fixing unit 9 Toner bottle 10 Intermediate transfer unit 11 Intermediate transfer belt 12 Primary transfer roller 13 Belt cleaning device 15 Image station 20 Photoconductor DESCRIPTION OF SYMBOLS 30 Charging apparatus 40 Cleaning apparatus 50 Developing apparatus 51 Developing roller 52 Doctor blade 53 1st stirring conveyance screw 54 2nd stirring conveyance screw 55 Developing case 56 Partition wall 57 1st space part 58 2nd space part 59a, b Delivery part 60 Process Cartridge 70 Main unit

Claims (15)

A developer accommodating portion for accommodating a two-component developer containing toner and a carrier, developer agitating / conveying means for agitating and conveying the two-component developer in the developer accommodating portion, and a magnet for forming a plurality of magnetic poles A developer carrier having a rotatable non-magnetic sleeve containing the magnetic field generating means, pumping up and carrying the two-component developer in the developer container, and having a certain gap from the surface of the developer carrier; In a developing device provided with a developer regulating member that is disposed so as to oppose and regulates the amount of the two-component developer on the developer carrying member,
The maximum value of the surface magnetic flux density in the normal direction of the magnetic pole that draws up the two-component developer of the magnetic field generating means of the developer carrying member and conveys it to the opposed portion to the developer amount regulating member is 75 to 95 mT, A developing device characterized in that the carrier has an average particle size of 35 to 55 μm, and the surface coat layer of the carrier contains carbon black.   2. The developing device according to claim 1, wherein the carrier has a logR of 10 to 15th power, where R [Ω · cm] is a volume resistance when a DC voltage of 1000 V is applied to the carrier alone. apparatus.   3. The developing device according to claim 1, wherein the developer agitating and conveying means is arranged in parallel with the developer carrier, and the developer is conveyed while conveying the two-component developer in the rotation axis direction of the developer carrier. A rotatable agent conveyance supply member for supplying a two-component developer in the vicinity of the carrier is provided, and a ratio B / A between the surface movement speed A of the developer carrier and the surface movement speed B of the agent conveyance supply member is 0. ..32 ≦ B / A ≦ 1.86.   4. The developing device according to claim 1, wherein a weight ratio of carbon black to resin of the surface coat layer of the carrier is 3% or less.   5. The developing device according to claim 1, wherein the toner has a weight average particle diameter of 3 to 10 [mu] m.   6. The developing device according to claim 1, wherein the toner has a spindle shape.   7. The developing device according to claim 6, wherein a ratio (r2 / r1) between the major axis r1 and the minor axis r2 of the toner is 0.5 to 0.8, and a ratio (r3 / r2) between the thickness r3 and the minor axis r2. ) Is 0.7 to 1.0. In a process cartridge that integrally supports an image carrier and at least one means selected from a charging means, a developing means, and a cleaning means, and is detachable from an image forming apparatus main body,
As the developing means,
A developer containing portion for containing a two-component developer containing toner and a carrier;
Developer agitating and conveying means for agitating and conveying the two-component developer in the developer container;
A developer carrying member having a rotatable non-magnetic sleeve containing a magnetic field generating means having a magnet for forming a plurality of magnetic poles, pumping up and carrying the two-component developer in the developer containing portion; and A developer regulating member that is disposed so as to face the surface of the developer carrying body with a certain gap and regulates the amount of the two-component developer on the developer carrying body,
The maximum value of the surface magnetic flux density in the normal direction of the magnetic pole that draws up the two-component developer of the magnetic field generating means of the developer carrying member and conveys it to the opposed portion to the developer amount regulating member is 75 to 95 mT, A process cartridge, wherein the carrier has an average particle size of 35 to 55 μm, and the surface coat layer of the carrier contains carbon black.   9. The process cartridge according to claim 8, wherein the carrier has a logR of 10 to 15th power, where R [Ω · cm] is a volume resistance when a DC voltage of 1000 V is applied to the carrier alone. cartridge.   10. The process cartridge according to claim 8, wherein the developer agitating / conveying means is arranged in parallel with the developer carrying member and conveys the two-component developer in the direction of the rotation axis of the developer carrying member. A rotatable agent conveyance supply member for supplying a two-component developer in the vicinity of the carrier is provided, and a ratio B / A between the surface movement speed A of the developer carrier and the surface movement speed B of the agent conveyance supply member is 0. Process cartridge characterized in that 32 ≦ B / A ≦ 1.86.   11. The process cartridge according to claim 8, wherein the weight ratio of carbon black to resin of the surface coat layer of the carrier is 3% or less.   12. The process cartridge according to claim 8, wherein the toner has a weight average particle diameter of 3 to 10 [mu] m.   13. The process cartridge according to claim 8, wherein the toner has a spindle shape.   14. The process cartridge according to claim 13, wherein a ratio (r2 / r1) between the major axis r1 and the minor axis r2 of the toner is 0.5 to 0.8, and a ratio (r3 / r2) between the thickness r3 and the minor axis r2. ) Is 0.7 to 1.0. An image carrier;
Latent image forming means for forming a latent image on the image carrier;
In an image forming apparatus comprising: a developing unit that develops a latent image on the latent image carrier.
An image forming apparatus comprising the developing device according to claim 1 as the developing means.

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