JP2010014918A - Developing device, process cartridge, and image forming apparatus - Google Patents

Abstract

It is possible to prevent the apparatus from being damaged and the occurrence of an image defect without causing the deflection of the magnetic field generating means. By recovering the carrier and returning it efficiently into the developing container, the image density can be lowered and the image defect can be prevented. Provided are a developing device, a process cartridge, and an image forming apparatus capable of preventing the occurrence.
In a developing device in which a plurality of magnetic particle carriers including a first developing magnetic field generating means are disposed, and the magnetic poles closest to each other of the adjacent magnetic particle supporting members are different in polarity, the second developing magnetic field generating means is provided. Including a magnetic particle collection body 115c adjacent to both the magnetic particle carrier 115b and the image carrier 108, and among the magnetic poles of the second magnetic field generating means, a magnetic pole closest to the magnetic particle carrier and A developing device, a process cartridge, and an image having a magnetic pole closest to the image carrier having the same polarity and adjacent to each other, and having a different polarity from the magnetic pole closest to the magnetic particle recovery body of the first magnetic field generating means A forming apparatus is provided.
[Selection] Figure 1

Description

  The present invention relates to a developing device, a process cartridge, and an image forming apparatus used for a copying machine, a facsimile, a printer, and the like. Specifically, the developer carried on the developer carrying member is conveyed to a developing area where the image carrying member and the developer carrying member face each other with a gap, and the electrostatic latent image on the image carrying member is developed to produce a toner image. The present invention relates to a developing device. The present invention also relates to a process cartridge and an image forming apparatus using such a developing device.

  An image forming apparatus such as a copying machine or a printer includes a charging unit that uniformly charges an image carrier, a latent image forming unit that forms a latent image on the image carrier, and a latent image on the image carrier. A developing means for developing with a developer comprising toner and carrier; and a transferring means for transferring a toner image formed by the developing means to a transfer material. As the developing means, a two-component developing device is attached to the image carrier. The developing device includes a fixed magnetic field generating means (hereinafter also referred to as “magnet roller”) and a rotating nonmagnetic hollow body (hereinafter also referred to as “sleeve”). In general, a magnetic particle carrier comprising means and a nonmagnetic hollow body is disposed opposite to the image carrier.

  With the recent increase in image forming speed, the surface moving speed of an image carrier such as a photoconductor tends to be further increased. In such a high-speed image forming apparatus, if the developing sleeve is not rotated at a relatively high speed, the toner supply amount per unit time to the developing area is insufficient, and the developing density is insufficient. However, if the developing sleeve is rotated at a relatively high speed, the wear of the image carrier and the developer due to the friction between the magnetic brush and the image carrier becomes significant, or the centrifugal force acting on the developer forming the magnetic brush. The increase in the developer increases the scattering of the developer, which may deteriorate the function of the apparatus, such as causing contamination inside the copying machine.

  Therefore, for example, a developing device that develops a latent image on a latent image carrier using a plurality of developing rollers has been proposed (see Patent Document 1). A developing device described in Patent Document 1 includes a developing chamber for developing a latent image, a first agent storage chamber for storing a developer, and a second agent storage chamber for storing the developer immediately below the developing chamber. Have. The developing chamber is disposed on the side of the first agent storage chamber and the second agent storage chamber, and has a first developing roller and a second developing roller disposed directly below the first developing chamber. is doing. The first developing sleeve, which is a developing sleeve of the first developing roller, carries a developer supplied from a first agent storage chamber disposed on the side of the developing sleeve, and displays a latent image on a photosensitive member as a latent image carrier. develop. The developer that has contributed to the development passes through the first development region where the first development sleeve and the photosensitive member face each other, and then the second development sleeve of the second development roller disposed below the first development sleeve. Is passed on. Then, along with the rotation of the second developing sleeve, the second developing sleeve and the photosensitive member are sent to the second developing region where they face each other, and here again contribute to the development. The developer that has completed the second developing process is collected from the second developing sleeve into the second agent containing chamber disposed on the side of the second developing sleeve, and after being replenished with toner, the developer is supplied into the first agent containing chamber. Returned. In such a configuration, by repeating the developing process twice with two developing sleeves, a sufficient developing density can be obtained without rotating the developing sleeve at a high speed.

  When a developing device using a plurality of developing rollers as described above is used, the developing device tends to increase in size, which counters the recent needs for downsizing of copying machines. Therefore, in order to achieve a reduction in the size of the developing device, there is an increasing need to reduce the diameter of the developing roller, and recently, a developing roller having a diameter of 14 mm or less has been used.

  However, by reducing the diameter of the developing roller, the magnet volume of the magnet roller is reduced, and there is a possibility that the magnetic force necessary for development cannot be obtained sufficiently. Further, if there is not enough magnetic force, the carrier adheres on the image carrier during development, which may cause uneven image density, white spots, and wear or breakage of the image carrier.

  Further, by reducing the diameter of the developing roller, there is a problem that the strength of the included magnet roller is reduced and the central portion of the magnet roller is easily bent. In particular, when the magnetic poles (N3 pole and S3 pole) adjacent to each other of the two developing rollers are different from each other, as shown in Patent Document 1, two magnets are used as shown in FIG. A magnetic attractive force acts between the rollers, and the problem that the central portion of the two magnet rollers bend with the fixed ends supporting the magnet rollers as fulcrums tends to occur. If these two poles are the same, the magnetic force acts so that the two poles repel each other, and there is a high possibility that the developer will not be smoothly transferred from the first developing roller to the second developing roller. In general, the electrodes are different from each other.

  When a deflection occurs in the magnet roller, a part of the magnet roller first comes into contact with the inner wall of the developing sleeve, and a frictional force is generated in that part, which requires a large force to drive the development. The magnet roller may be scraped off. Further, when the magnet roller is bent, the magnetic flux density distribution is not uniform in the axial direction of the developing roller, and the toner cannot be uniformly deposited on the image carrier, resulting in uneven image density. is there.

  Normally, a magnet roller is often made with a magnet around a shaft made of metal, so increasing the strength by increasing the diameter of the shaft core as one of the countermeasures against the deflection of the magnet roller. Can be considered. However, increasing the diameter of the shaft rod reduces the volume of the magnet portion, so it is likely that it will be difficult to obtain a magnetic force suitable for development. In particular, there is a problem that the carrier tends to adhere to the image carrier due to a decrease in magnetic force.

  Therefore, a rotating body is disposed so as to be close to the second developing sleeve, and the second mag roller is moved in the opposite direction of the first mag roller by the magnetic attraction between the third mag roller (magnet roller) and the second mag roller. A method for eliminating the deflection by pulling has been proposed (see Patent Document 2). In the case of the method described in Patent Document 2, the first mag roller is pulled toward the second mag roller, but the first mag roller is balanced with the magnetic attraction force of the magnetic plate disposed on the first developing roller. The mag roller of this does not bend.

JP 2004-163906 A JP 2004-151591 A

  According to the method of Patent Document 2, the carrier attached to the image carrier can be recovered by bringing the rotating body close to the image carrier, but the carrier recovered here is collected in a carrier recovery container. , It does not return into the developing container. For this reason, in the long term, the number of carriers in the developing container decreases, the amount of developer adhering to the first and second developing sleeves decreases, and there is a high possibility of causing a decrease in image density. Further, in order to peel the carrier from the third sleeve and collect it in the carrier recovery container, the developer scraping blade is brought into contact with the third sleeve and the developer is mechanically peeled off. There is a possibility that the blade is worn out and the carrier recovery efficiency is lowered.

  Therefore, in a developing device using a plurality of magnetic particle carriers, the magnetic field inside the magnetic particle carrier can be reduced even if the magnetic particle carrier has a small diameter and has a magnetic force that can be used to lubricate the developer. Without causing the deflection of the generating means, it is possible to prevent the occurrence of image defects due to the damage of the apparatus or the uneven adhesion of the toner to the image carrier, and further, the carrier adhered on the image carrier causes the apparatus to wear or break. There is a need for a developing device that can prevent the occurrence of a decrease in image density and the occurrence of image defects by efficiently collecting the collected carrier and returning the collected carrier into the developing container efficiently, but has not yet been provided.

  The present invention has been made in view of the above-described problems in the prior art, and even with a magnetic particle carrier having a reduced diameter, it does not cause deflection of the magnetic field generation means contained therein, and damage of the apparatus or image holding is performed. It is possible to prevent the occurrence of image defects due to uneven toner adhesion to the body, and to recover the carrier adhering to the image carrier without causing wear or damage to the apparatus, and to efficiently develop the recovered carrier It is an object of the present invention to provide a developing device, a process cartridge using the developing device, and an image forming apparatus capable of preventing a decrease in image density and occurrence of an image defect by returning them to the container.

The present invention provided to solve the above problems is as follows.
[1] A first developing magnetic field generating means in which a plurality of magnetic poles are fixedly arranged is contained in a rotatable nonmagnetic hollow body, and magnetic particles for developing an electrostatic latent image on the image carrier are carried on the surface. In a developing device in which a plurality of magnetic particle carriers are arranged along the image bearing surface of the image carrier, and the magnetic poles closest to each other between the adjacent magnetic particle carriers are different in polarity. A magnetic particle carrier A disposed in the most downstream portion in the rotation direction of the image carrier and the image carrier including the second developing magnetic field generating means having a magnetic pole fixedly arranged in a rotatable nonmagnetic hollow body A magnetic particle recovery body disposed in close proximity to both of the magnetic body and the magnetic field carrying body of the second magnetic field generating means. The contacting magnetic poles are adjacent and of the same polarity, and the magnetic particle bearing The developing device according to claim 1, wherein the first magnetic field generating means of the holder A has a polarity different from that of the magnetic pole closest to the magnetic particle recovery body.
[2] The magnetic flux density of the magnetic pole closest to the magnetic particle carrier A of the second magnetic field generator is such that the magnetic flux of the magnetic pole closest to the magnetic particle collector in the first magnetic field generator of the magnetic particle carrier A The developing device according to [1], wherein the developing device is smaller than the density.
[3] The magnetic pole closest to the image carrier of the second magnetic field generating means is located on a line segment connecting the rotation center of the magnetic particle recovery body and the rotation center of the image carrier. The developing device according to any one of [1] to [2], wherein the developing device is located upstream in the rotation direction.
[4] The nonmagnetic hollow body of the magnetic particle carrier disposed at the most downstream portion in the rotational direction of the image carrier is a linear velocity that is the rotational speed of the nonmagnetic hollow body of the magnetic particle recovery body. The developing device according to any one of [1] to [3], wherein the developing device is smaller than a linear speed that is a rotational speed of the above.
[5] A process cartridge comprising the developing device according to any one of [1] to [4].
[6] An image carrier that carries a latent image, a charging unit that charges the image carrier, a developing unit that develops the latent image on the image carrier, and an image formed by the developing unit is transferred to a transfer material An image forming apparatus comprising a transfer unit configured to include the developing device according to any one of [1] to [4] as the developing unit.

  According to the present invention, it is possible to prevent the occurrence of image defects due to damage to the apparatus or uneven adhesion of toner to the image carrier without causing the deflection of the magnetic field generating means contained in the magnetic particle carrier. In addition, the carrier adhering to the image carrier can be recovered without causing wear or damage to the apparatus, and the recovered carrier can be efficiently returned to the developing container to prevent image density deterioration and image defects. Development apparatus, a process cartridge using the development apparatus, and an image forming apparatus can be provided.

As an effect of the present invention, according to the first aspect of the present invention, the first developing magnetic field generating means in which a plurality of magnetic poles are fixedly arranged is enclosed in a rotatable nonmagnetic hollow body, and the electrostatic latent image on the image carrier is A plurality of magnetic particle carriers carrying magnetic particles for developing an image on the surface are arranged along the image bearing surface of the image carrier, and the magnetic poles closest to each other between the adjacent magnetic particle carriers are arranged. In the developing devices having different polarities, the second developing magnetic field generating means, in which a plurality of magnetic poles are fixedly arranged, is enclosed in a rotatable nonmagnetic hollow body and arranged at the most downstream portion in the rotation direction of the image carrier. A magnetic particle carrier disposed in the vicinity of both the magnetic particle carrier A and the image carrier, and the magnetic particle carrier among the plurality of magnetic poles of the second magnetic field generating means. The magnetic pole closest to A and the magnetic pole closest to the image carrier are: A plurality of magnetic particles arranged in contact with each other and having the same polarity and having a different polarity from the magnetic pole closest to the magnetic particle recovery body in the first magnetic field generating means of the magnetic particle carrier A The magnetic attractive force acting between the carrier and the magnetic attractive force acting between the magnetic particle collecting body and the magnetic particle carrier disposed at the most downstream portion in the rotation direction of the image carrier adjacent to the magnetic particle collecting body are balanced. Thus, the deflection of the first developing magnetic field generating means included in the magnetic particle carrier can be prevented, and the occurrence of image defects due to the damage of the apparatus due to the deflection or the uneven adhesion of the toner to the image carrier can be prevented. be able to.
In addition, since the magnetic particle collection body is close to the image carrier, the magnetic field of the magnetic pole closest to the image carrier among the plurality of magnetic poles of the second magnetic field generating means included in the magnetic particle collection body is included. Since the carrier adhering to the image carrier can be adsorbed onto the magnetic particle collection body by the attractive force, it is possible to prevent white spots in the image, density unevenness, wear and damage of the image carrier due to the carrier adhesion. .
Further, among the plurality of magnetic poles of the second magnetic field generating means included in the magnetic particle recovery body, the magnetic pole closest to the image carrier and the magnetic pole closest to the magnetic particle carrier are adjacent to each other, and Since they are of the same polarity, a repulsive magnetic field is formed between the magnetic poles, and when the magnetic particle collection body rotates in the direction opposite to the rotation direction of the image carrier, the magnetic particle collection body is attracted to the magnetic particle collection body. The carrier thus received is repelled between the magnetic poles and jumps to the magnetic particle carrier (magnetic particle carrier disposed at the most downstream portion in the rotation direction of the image carrier) close to the magnetic particle collector. The carrier is finally collected in the developing container. This eliminates the need to install a container for collecting the carrier, thereby reducing the size of the developing device. Further, since the number of carriers in the developing container can be kept constant, the image density can be maintained even when used for a long time. Decrease is less likely to occur.
Further, among the magnetic poles of the magnetic particle carrier disposed at the most downstream portion in the rotation direction of the image carrier, the magnetic pole closest to the magnetic particle recovery body has a different polarity from the repulsive magnetic field, so that the repulsive magnetic field It is necessary to worry about the influence of blade wear, because the carrier can be easily recovered without having to mechanically peel off the carrier with a blade that scrapes off the developer. The carrier can be recovered stably over a long period of time.

According to the second aspect of the present invention, in the developing device according to the first aspect, the magnetic flux density of the magnetic pole closest to the magnetic particle carrier A of the second magnetic field generating means is the first of the magnetic particle carrier A. Since the magnetic field density is smaller than the magnetic flux density of the magnetic pole closest to the magnetic particle recovery body in the single magnetic field generating means, the magnetic particle support body (the image carrier) close to the magnetic particle recovery body by the repulsive magnetic field formed. A developer container without adsorbing the magnetic particles (hereinafter also referred to as “carrier”) after jumping to the magnetic particle carrier disposed in the most downstream portion in the rotation direction of the body without adsorbing the magnetic particles again on the magnetic particle recovery body. Can be recovered. Therefore, it is possible to prevent image blanking, density unevenness, wear and damage of the image carrier due to carrier adhesion, and furthermore, the number of carriers in the developing container can be kept constant, so that it can be used for a long time. Also, it is possible to prevent a decrease in image density.
According to a third aspect of the present invention, in the developing device according to any one of the first to second aspects, the magnetic pole closest to the image carrier of the second magnetic field generating means contained in the magnetic particle recovery body is the magnetic field. Since the configuration is such that it is located upstream of the line segment connecting the rotation center of the particle recovery body and the rotation center of the image carrier, the image recovery body contains the magnetic particle recovery body. The repulsive magnetic field formed by reducing the distance between the magnetic pole closest to the magnetic particle carrier of the two magnetic field generator and the magnetic pole collector closest to the magnetic particle collector of the first magnetic field generator included in the magnetic particle carrier. Becomes stronger, so that the carrier is less likely to adhere to the image carrier. Accordingly, it is possible to prevent white spots in the image, density unevenness, and wear and damage of the image carrier due to adhesion of the carrier.
According to a fourth aspect of the present invention, in the developing device according to any one of the first to third aspects, a linear speed that is a rotational speed of the nonmagnetic hollow body of the magnetic particle collection body is a rotation speed of the image carrier. The carrier on the magnetic particle recovery body is blown away by a repulsive magnetic field because the magnetic particle carrier disposed at the most downstream portion in the direction is configured to be smaller than the linear speed that is the rotational speed of the nonmagnetic hollow body. , Can be smoothly transferred to the adjacent magnetic particle carrier (magnetic particle carrier disposed at the most downstream portion in the rotation direction of the image carrier), and white spots in the image due to carrier adhesion, density unevenness and It is possible to prevent the image carrier from being worn or damaged. In addition, since the carrier can be reliably collected in the developing container, the number of carriers in the developing container can be kept substantially constant, so that it is difficult for the density of the image to decrease even during long-term use.
According to the fifth aspect of the present invention, since the process cartridge having the developing device according to any one of the first to fourth aspects is provided, the magnetic field generating means included in the magnetic particle carrier is not deflected. In addition, it is possible to prevent the occurrence of image defects due to damage to the device or uneven toner adhesion to the image carrier, and to recover and collect the carrier adhering to the image carrier without causing wear or damage to the device. By efficiently returning the used carrier into the developing container, it is possible to prevent a decrease in image density and occurrence of image defects.
According to a sixth aspect of the present invention, the image carrier is formed by an image carrier that carries a latent image, a charging unit that charges the image carrier, a developing unit that develops the latent image on the image carrier, and the developing unit. 5. An image forming apparatus comprising a transfer means for transferring an image to a transfer material. The image forming apparatus having the developing device according to claim 1 as the developing means. It is possible to prevent the occurrence of image defects due to uneven toner adhesion to the toner, and to recover the carrier adhering to the image carrier without causing wear or damage of the apparatus, and to efficiently collect the recovered carrier. By returning to the inside, it is possible to prevent a decrease in image density and occurrence of image defects.

  A configuration of an embodiment of a copying apparatus of the present invention having means for executing an image processing method according to the present invention, an image processing method of the present invention, and a program for executing the processing method will be described below with reference to the drawings. explain. However, the present invention is not limited to the embodiments shown in the drawings, and other embodiments, additions, modifications, deletions, and the like can be modified within a range that can be conceived by those skilled in the art. The embodiment is also included in the scope of the present invention as long as the operations and effects of the present invention are exhibited.

  The developing device carries magnetic particles (for example, a developer) to a developing area facing the image carrier, and develops an electrostatic latent image formed on the image carrier to form a toner image. Has a body. The magnetic particle carrier includes, for example, a non-magnetic hollow body (for example, a developing sleeve) formed in a cylindrical shape, and a magnetic field generating means (for example, a magnetic field generating means for generating a spike of developer on the surface of the sleeve). , A magnet roller) inside the developing sleeve. When the developer is spiked, the carrier constituting the developer is spiked on the developing sleeve so as to follow the lines of magnetic force generated by the magnet roller, and charged toner is attached to the carrier. . In the magnet roller, a plurality of magnetic poles are fixedly arranged, but the magnets forming the respective magnetic poles are formed in a molded body such as a rod shape, and in particular, in the portion corresponding to the development region portion on the surface of the development sleeve, It has a developing main magnetic pole for making the developer spike. The developer that has risen can be moved in the circumferential direction by rotating at least one of the developing sleeve and the magnet roller. In general, in order to facilitate transport of the developer, the surface of the developing sleeve is subjected to roughing processing such as groove processing or sand blast processing. Such roughening processing such as grooving and sandblasting is performed in order to prevent the occurrence of a decrease in image density caused by the developer slipping and stagnation on the surface of the developing sleeve rotating at high speed.

Next, the configuration of the developing device 113 according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2.
As shown in FIGS. 1 and 2, the developing device 113 includes a magnetic particle (for example, developer) supply unit 114, a case 125, two developing rollers 115a and 115b as magnetic particle carriers, and a regulating member. The regulating blade 116 is provided at least.
As shown in FIG. 2, the developing roller 115 (115a and 115b) includes a cored bar 134, first magnetic field generating means (hereinafter also referred to as a magnet roller or a magnet body) 133a and 133b, and a nonmagnetic hollow body (hereinafter referred to as a development). 132a and 132b). The longitudinal direction of the cored bar 134 is arranged in parallel with the longitudinal direction of the image carrier (photosensitive drum) 108 and is fixed to the case 125 of the developing device 113 without rotating.

  As a material of the magnet roller 133, a plastic magnet or a rubber magnet is generally used. Ferrite as magnetic powder, Ne type (Ne-Fe-, etc.) or Sm type (Sm-Co, Sm-Fe-N, etc.), etc. for obtaining high magnetic properties, and 6PA or 12PA as polymer materials Heat of PA-based materials, ethylene-based compounds such as EEA (ethylene-ethyl copolymer) / EVA (ethylene-vinyl copolymer), chlorine-based materials such as CPE (chlorinated polyethylene), rubber materials such as NBR Examples of plastic resins and thermosetting resins include epoxy, silicone, and urethane, but when making a magnet roller with a small diameter as in the present invention, a ferrite magnet is mixed with a highly rigid PA resin. It is desirable to form a magnet roller using a material and to dispose a rare earth magnet block in a place where high magnetic force is required. As a kind of rare earth magnet, Nd—Fe—B or Sm—Fe—N is generally used as a magnetic powder. As a molding method, a method of injection molding by mixing with 6PA, or a method of compression molding by mixing with resin powder such as polyester can be employed. In this case, higher magnetic properties can be obtained by performing compression molding or injection molding in a magnetic field. Examples of the method for forming the magnet roller 133 include extrusion magnetic field molding, injection molding, and the like, but injection molding is desirable because a polymer material having high crystallinity and advantageous in rigidity can be used. In addition, when the cored bar 134 and the magnet roller 133 are integrally molded, since the diameters of the body part and the cored bar part are different, injection molding is desirable to realize this shape.

The magnet roller 133 is thus formed of a magnetic material, is formed in a cylindrical shape, and a plurality of fixed magnetic poles are attached thereto. The fixed magnetic pole is a long, rod-shaped magnet that extends along the longitudinal direction of the magnet roller 133, that is, the developing roller 115, and is provided over the entire length of the magnet roller 133. The magnet rollers 133a and 133b configured as described above are accommodated (enclosed) in the developing sleeves 132a and 132b, respectively.
The magnet roller 133a includes a plurality of fixed magnetic poles, for example, N2 (developer transport pole), N1 (developer pumping pole), S1 (developer pole), N3 (developer transport pole) and S2 (developer transport pole). Are provided. The fixed magnetic pole N1 is opposed to the stirring screw 118c accommodated in the third space 120c as a pumping magnetic pole for pumping up the developer, and the fixed magnetic pole S1 is opposed to the photosensitive drum 108 as the developing magnetic pole. . Since the developing sleeve 132a of the developing roller 115a rotates in the direction of arrow D, the developer moves on the surface of the developing sleeve 132a in the order of the fixed magnetic poles N1, S2, N3, S1, and N2. In this magnet roller 133a, since the fixed magnetic pole N2 (developer transport pole) and the fixed magnetic pole N1 (developer pumping pole) have the same polarity, a repulsive force is generated between the fixed magnetic pole N1 and the fixed magnetic pole N2. The developer 126 is easily separated from the developing roller 115a in the direction from the fixed magnetic pole N2 to the fixed magnetic pole S3 of the developing roller 115b.
Similarly, the magnet roller 133b is provided with a plurality of fixed magnetic poles, for example, N4 (developing pole), S4 (developer conveying pole), and S3 (developer pumping pole). The developing sleeve 132b of the developing roller 115b also rotates in the direction of arrow D, and the developer separated from the developing roller 115a is pumped onto the developing sleeve 132b by the magnetic force of the fixed magnetic pole S3 of the developing roller 115b, and shifts in the order of N4 and S4. . Since the fixed magnetic pole S3 and the fixed magnetic pole S4 have a wide gap and the same polarity, the developer is easily separated from the developing roller 115b and dropped into the second space 120b.

In the present invention, a magnetic particle recovery body (hereinafter referred to as “recovery roller”) is disposed so as to be close to the developing roller 115b, which is a magnetic particle support disposed in the most downstream portion in the rotation direction of the image support, and the photosensitive drum 108. 115c).
Of the magnetic poles of the second magnetic field generating means (second magnet roller) 133c included in the recovery roller 115c, the N5 pole is close to the S4 pole of the first magnetic field generating means (first magnet roller) 133b, and the N6 pole Is close to the photosensitive drum 108. The magnet roller 133b is deflected upward due to the magnetic attractive force of the S3 pole and the N2 pole, but the magnetic attractive force of the N5 pole and the S4 pole acts downward, so that each magnetic pole is canceled so as to cancel each magnetic attractive force. By adjusting the magnetic force (S3≈N2, N5≈S4), the deflection of the magnet roller 133b can be prevented.

Further, by preventing the magnetic force of the N5 pole from becoming larger than the magnetic force of the S4 pole, the developer 126 carried on the developing roller 115b between the S4 pole and the N5 pole is reliably accommodated without being attracted to the recovery roller. Can be transported to layer 117.
Further, since the N6 pole is close to the photosensitive drum 108, the carrier attached on the photosensitive drum 108 can be attracted to the outer surface of the recovery roller 115c by the magnetic attraction and recovered.
As shown in FIGS. 1 and 3, the adsorbed carrier is conveyed from the N6 pole to the N5 pole by the developing sleeve 132c rotating in the arrow E direction. Since the N6 pole and the N5 pole form a repulsive magnetic field, the carrier is blown off in the direction of arrow F while being conveyed from the N6 pole to the N5 pole, and is attracted to the S4 pole of the developing roller 115b. Furthermore, since the N5 pole faces and is close to the S4 pole, the repulsive magnetic field is strengthened by adding the magnetic force of the S4 pole to the magnetic force of the N5 pole, so that the carrier is more reliably developed from the collection roller 115c. It can be blown off to the roller 115b, and the carrier can be reliably recovered into the storage tank 117.

  Further, since a repulsive magnetic field is formed between the N6 pole and the N4 pole, the carrier adhering to the photosensitive drum 108 is blown off and the effect of being most adsorbed to the developing roller 115b can also be achieved. Carrier adhesion can be prevented.

  Further, as shown in FIG. 4, by disposing the magnetic pole N6 slightly above the line segment connecting the center of the photosensitive drum 108 and the center of the collecting roller 115c, the distance between the N6 pole and the N4 pole is shortened. Since the repulsive magnetic field between the N6 pole and the N4 pole is strengthened, the above effect can be further strengthened.

The developing sleeves 132a and 132b and the collecting sleeve 132c shown in FIG. 3 are formed in a cylindrical shape, and each of them includes (accommodates) a magnet roller 133, and is rotatably provided around the axis.
The developing sleeve and the collecting sleeve may be the same member.
The sleeve 132 is rotated so that the inner peripheral surface thereof is sequentially opposed to the fixed magnetic pole. The sleeve 132 is preferably made of a nonmagnetic material such as an aluminum alloy or stainless steel (SUS). As a base material for the developing sleeve 132, an aluminum alloy is excellent in terms of workability and lightness. When using an aluminum alloy, it is desirable to use A6063, A5056, and A3003. When using SUS, it is desirable to use SUS303, SUS304, and SUS316.
The outer diameter of the developing sleeve 132 is desirably about 9 mm to 18 mm, and the length of the developing sleeve 132 in the axis (axial center) direction is desirably about 240 mm to 350 mm.
The developing sleeve 132 is preferably subjected to a roughing process such as a groove process or a sandblast process.

  In addition, by setting the gap between the developing sleeve 132b and the collecting sleeve 132c to be slightly wide as 2 to 5 mm, it is possible to prevent the developer from being taken into the containing layer 117 and overflowing. Further, by protruding a part of the containing layer 117 so as to be connected to the second space 120b in the gap, the developer can be reliably conveyed from the developing roller 115b to the second space 120b.

  Further, it is preferable that the linear speed that is the rotational speed of the recovery sleeve of the recovery roller 115c is smaller than the linear speed that is the rotational speed of the development sleeve of the developing roller 115b.

  On the other hand, the magnet roller 133c, which is the second magnetic field generating means, bends due to the magnetic force from the first magnet roller 133b, but the recovery sleeve 132c of the magnet roller 133c is not coated with the developer and is not involved in the development, so it is somewhat distorted. But the image is not affected. Further, regarding the problem that the magnet roller 133c bends and comes into contact with the inner wall of the recovery sleeve 132c, the magnet roller 133c does not participate in image formation and therefore does not require a large magnetic force, so the outer diameter of the magnet roller 133c is reduced. Measures such as cutting the area of the magnet part to thicken the shaft core may be taken.

  The developer supply unit 114 includes a storage tank 117 and stirring screws 118a to 118c as stirring members. The storage tank 117 is formed in a box shape having a length substantially equal to that of the photosensitive drum 108. Further, a partition wall 119 extending along the longitudinal direction of the storage tank 117 is provided in the storage tank 117. The partition wall 119 partitions the storage tank 117 into a first space 120a, a second space 120b, and a third space 120c. Further, the first space 120a and the second space 120b communicate with each other on the front side, and both ends of the first space 120a and the third space 120c communicate with each other, and the second space 120b and the third space 120c. The front side is in communication.

  The storage tank 117 stores the developer 126 in the first space 120a, the second space 120b, and the third space 120c. The developer 126 contains toner and magnetic particles (also referred to as carrier or magnetic powder). The toner is appropriately supplied to the front side of the first space 120a. The toner is spherical fine particles produced by an emulsion polymerization method or a suspension polymerization method. The toner may be obtained by pulverizing a lump composed of a synthetic resin in which various dyes or pigments are mixed and dispersed. The average particle diameter of the toner is 3 μm or more and 7 μm or less. The toner may be formed by pulverization or the like.

  The stirring screw 118 is accommodated in each of the first space 120a, the second space 120b, and the third space 120c. The longitudinal direction of the stirring screw 118 is parallel to the longitudinal directions of the storage tank 117, the developing roller 115, and the photosensitive drum 108. The agitating screw 118 is provided so as to be rotatable around an axis, and rotates around the axis to agitate the toner and the magnetic carrier 135 and convey the developer 126 along the axis. Further, the stirring screw 118a in the first space 120a conveys the developer 126 from the near side to the far side. The stirring screw 118b in the second space 120b conveys the developer 126 from the back side toward the front side. The stirring screw 118c in the third space 120c conveys the developer 126 from the back side toward the front side.

  In the developer supply unit 114, the toner supplied to the front side of the first space 120a is conveyed to the back side while being stirred with the magnetic carrier 135, and is transferred from the back side to the back side of the third space 120c. . The developer supply unit 114 agitates the toner and the magnetic carrier 135 in the third space 120c and supplies the toner and the magnetic carrier 135 to the outer surface of the first developing roller 115a while being conveyed in the axial direction. The developer travels on the outer surface of the first developing roller 115a, travels to the outer surface of the second developing roller 115b, and finally is detached from the outer surface of the second developing roller 115b toward the second space 120b. The developer in the second space 120b is transported from the back side to the near side, and is transported to the near side of the first space 120a.

  The case 125 is formed in a box shape, is attached to the storage tank 117 of the developer supply unit 114 described above, and covers the two developing rollers 115a and 115b together with the storage tank 117. In addition, an opening 125 a is provided in a portion of the case 125 that faces the photosensitive drum 108.

  The two developing rollers 115a and 115b are formed in a cylindrical shape, and are provided between the second space 120b and the third space 120c and the photosensitive drum 108 and in the vicinity of the opening 125a described above. The developing rollers 115 a and 115 b are parallel to both the photosensitive drum 108 and the storage tank 117. The developing rollers 115a and 115b are spaced apart from the photosensitive drum 108. The space between the developing rollers 115a and 115b and the photosensitive drum 108 forms a developing area 131 in which the toner of the developer 126 is attracted to the photosensitive drum 108 to develop the electrostatic latent image to obtain a toner image. Yes. In the developing area 131, the developing roller 115 and the photosensitive drum 108 face each other.

  The regulating blade 116 is provided at the end of the developing device 113 near the photosensitive drum 108. The regulating blade 116 is attached to the case 125 described above with a space from the outer surface of the developing sleeve 132a. The regulating blade 116 scrapes the developer 126 on the outer surface of the developing sleeve 132a exceeding the desired thickness into the storage tank 117, and the developer 126 on the outer surface of the developing sleeve 132a conveyed to the developing region 131a. Adjust the amount. In addition, a magnetic plate is attached to the regulating blade 116, and the height of the rising of the developer is adjusted. Since a magnetic attractive force acts between the magnetic plate and the magnetic pole (S2 pole) of the developing roller 115a facing the magnetic plate, the magnet roller 133a as the first magnetic field generating means tries to bend upward, but the N2 pole and S3 Due to the magnetic attraction with the pole, a downward force also works. Therefore, the magnetic force of the magnetic plate, S2 pole, S3 pole and N2 pole is adjusted so that the magnetic roller 133a cancels the magnetic attractive force acting upward and downward (magnetic plate≈S2 pole, S3 pole≈N2 pole). Thus, the deflection of the magnet roller 133a can be prevented.

Next, an operation in which the developing device 113 conveys the developer 126 to the developing area 131 will be described.
In the developing device 113 configured as described above, the toner and the magnetic carrier 135 are sufficiently stirred by the developer supply unit 114, and the stirred developer 126 is fixed by a fixed magnetic pole included in the developing roller 115a through the third space 120c. Adsorb to the outer surface of the developing sleeve 132a. In the developing device 113, the developing sleeve 132a rotates in the direction of arrow D, and the developer 126 adsorbed by the plurality of fixed magnetic poles is conveyed toward the developing region 131a. The developing device 113 causes the photosensitive drum 108 to adsorb the developer 126 having a desired thickness by the regulating blade 116. The developer 126 is further conveyed and conveyed to the developing sleeve 132b by the magnetic force and gravity of the fixed magnetic pole included in the developing roller 115a and the magnetic force of the fixed magnetic pole included in the developing roller 115b. In the developing device 113, the developing sleeve 132b rotates, and the developer 126 adsorbed by the plurality of fixed magnetic poles is conveyed toward the developing region 131b. In the developing region 131b, the developer 126 is again adsorbed to the photosensitive drum 108. Thus, the developing device 113 carries the developer 126 on the developing rollers 115a and 115b, conveys the developer 126 to the developing regions 131a and 113b, develops the electrostatic latent image on the photosensitive drum 108, and forms a toner image. . Further, the developing device 113 separates the developed developer 126 toward the second space 120b. Further, the developed developer 126 stored in the storage tank 117 is sufficiently stirred again with the other developer 126 in the second space 120b and the first space 120a, and passes through the third space. It is used for developing the electrostatic latent image on the photosensitive drum 108.

  As described above, according to the present embodiment, the developing device 113 using a plurality of magnetic particle carriers has a magnetic force capable of lubricating the developer as a magnetic particle carrier corresponding to downsizing of the device. Even when using a developing sleeve having a small diameter, the deflection of the developing magnetic field generating means inside the magnetic particle carrier is prevented, preventing image defects due to damage to the apparatus and uneven adhesion of toner to the image carrier, The carrier attached on the image carrier is collected to prevent image defects such as wear and damage of the apparatus and white spots due to the carrier attachment, and the collected carrier is efficiently returned to the containing layer 117 for a long time. In addition, it is possible to prevent a decrease in image density.

Next, the configuration of a process cartridge according to an embodiment of the present invention will be described with reference to FIG.
The process cartridges 106Y, 106M, 106C, and 106K include a cartridge case 111, a charging roller 109 as a charging device, a photosensitive drum 108 as a photosensitive member (also referred to as an image carrier), and a cleaning blade 112 as a cleaning device. And a developing device 113.
The cartridge case 111 is detachably attached to the apparatus main body 102 and accommodates a charging roller 109, a photosensitive drum 108, a cleaning blade 112, and a developing device 113. The charging roller 109 uniformly charges the outer surface of the photosensitive drum 108. The photosensitive drum 108 is disposed with a gap from a later-described magnetic particle carrier (for example, a developing roller) 115 of the developing device 113. The photosensitive drum 108 is formed in a columnar shape or a cylindrical shape that is rotatable around an axis.

  The distance between the developing roller 115 (115a and 115b), that is, the developing sleeve 132 (132a and 132b), and the photosensitive drum 108 is preferably 0.1 mm or more and 0.4 mm or less. The toner can be reliably supplied to the photosensitive drum 108 from the developer 126 sprouting on the developing sleeve 132, and a high-quality image can be obtained. If the distance between the developing sleeve 132 and the photosensitive drum 108 is less than 0.1 mm, the electric field between the developing sleeve 132 and the photosensitive drum 108 becomes too strong, and the magnetic carrier 135 is formed on the photosensitive drum 108. It moves and is not desirable. If the distance between the developing sleeve 132 and the photosensitive drum 108 exceeds 0.4 mm, the electric field between the developing sleeve 132 and the photosensitive drum 108 becomes too weak, and the amount of toner that can be supplied to the photosensitive drum 108 is small. Development is not desirable because the development efficiency decreases and the edge effect of the electric field increases at the edge of the image and a uniform image cannot be obtained.

Next, the operation in which the process cartridges 106Y, 106M, 106C, and 106K transfer an image to the recording paper 107 will be described.
The photosensitive drum 108 in each process cartridge 106 forms an electrostatic latent image on its outer surface by the corresponding laser writing unit 122 shown in FIG. The photosensitive drum 108 is developed by adsorbing the toner supplied from the developing device 113 to the electrostatic latent image formed and carried on the outer surface, and the toner image thus obtained is conveyed between the photosensitive belt 108 and the conveyance belt 129. The image is transferred to the recording paper 107 positioned. The cleaning blade 112 removes the transfer residual toner remaining on the outer surface of the photosensitive drum 108 after the toner image is transferred to the recording paper 107.

  As described above, according to the present embodiment, since the process cartridge 106 has the developing device 113 described above, the apparatus is damaged due to the deflection of the developing magnetic field generating means inside the magnetic particle carrier, or the image carrier is used. Image defects due to uneven toner adhesion, etc., and further, the carrier adhering to the image carrier is collected, and image defects such as device wear, breakage, and white spots due to carrier adhesion are prevented and collected. By efficiently returning the carrier into the containing layer 117, it is possible to prevent the image density from decreasing for a long time.

Next, the configuration of the image forming apparatus 101 according to an embodiment of the present invention will be described with reference to FIG. The image forming apparatus of the present invention includes an image carrier that carries a latent image, a charging unit that charges the image carrier, a developing unit that develops the latent image on the image carrier, and an image formed by the developing unit. A transfer means for transferring the toner to a transfer material, and the developing device of the present invention as the developing means.
The image forming apparatus 101 forms an image of each color of yellow (Y), magenta (M), cyan (C), and black (K), that is, a color image, on a recording sheet 107 as a single transfer material. The units corresponding to the colors of yellow, magenta, cyan, and black are indicated by adding Y, M, C, and K at the end of the reference numerals.

  As shown in FIG. 5, the image forming apparatus 101 includes an apparatus main body 102. The main body is formed in a box shape, for example, and is installed on a floor or the like. The apparatus main body 102 accommodates a paper feed unit 103, a registration roller pair 110, a transfer unit 104, a fixing unit 105, a plurality of laser writing units 122, and a plurality of process cartridges 106Y, 106M, 106C, and 106K. Yes.

  The paper feed unit 103 is provided in the lower part of the apparatus main body 102. The paper feed unit 103 includes a paper feed cassette 123 that can accommodate the above-described recording paper 107 in a stacked manner and can be taken in and out of the apparatus main body 102, and a paper feed roller 124. The paper feed roller 124 is pressed against the uppermost recording paper 107 in the paper feed cassette 123. The paper feed roller 124 is used to transfer the above-described uppermost recording paper 107 between a transfer belt 129 (described later) of the transfer unit 104 and a photosensitive drum 108 of a developing device 113 (described later) of the process cartridges 106Y, 106M, 106C, and 106K. Send it in between.

  The registration roller pair 110 is provided in a conveyance path of the recording paper 107 conveyed from the paper supply unit 103 to the transfer unit 104, and includes a pair of rollers 110a and 110b. The registration roller pair 110 sandwiches the recording paper 107 between the pair of rollers 110a and 110b, and the transfer unit 104 and the process cartridges 106Y, 106M, 106C, and 106K at a timing at which the sandwiched recording paper 107 can be superimposed on the toner image. Send out in between.

The transfer unit 104 is provided above the paper feed unit 103. The transfer unit 104 includes a driving roller 128, a driven roller 12, a conveyance belt 129, and transfer rollers 130Y, 130M, 130C, and 130K. The drive roller 128 is disposed on the downstream side in the conveyance direction of the recording paper 107 and is rotationally driven by a motor or the like as a drive source. The driven roller 12 is rotatably supported by the apparatus main body 102 and is disposed on the upstream side in the conveyance direction of the recording paper 107. The conveyor belt 129 is formed in an endless annular shape and is stretched over both the driving roller 128 and the driven roller 12 described above. The transport belt 129 circulates (endless travel) counterclockwise around the drive roller 128 and the driven roller 12 described above as the drive roller 128 is rotationally driven.
The transfer rollers 130Y, 130M, 130C, and 130K sandwich the conveyance belt 129 and the recording paper 107 on the conveyance belt 129 between the photosensitive drums 108 of the process cartridges 106Y, 106M, 106C, and 106K, respectively. In the transfer unit 104, the transfer rollers 130Y, 130M, 130C, and 130K press the recording paper 107 fed from the paper supply unit 103 against the outer surface of the photosensitive drum 108 of each process cartridge 106Y, 106M, 106C, and 106K. The toner image on the photosensitive drum 108 is transferred to the recording paper 107. The transfer unit 104 sends the recording paper 107 onto which the toner image is transferred toward the fixing unit 105.

  The fixing unit 105 is provided downstream of the transfer unit 104 in the conveyance direction of the recording paper 107, and includes a pair of rollers 105a and 105b that sandwich the recording paper 107 therebetween. The fixing unit 105 presses and heats the recording paper 107 sent out from the transfer unit 104 between the pair of rollers 105a and 105b, thereby recording the toner image transferred from the photosensitive drum 108 onto the recording paper 107. Fix to paper 107.

  The laser writing unit 122 is attached to the apparatus main body 102. The laser writing unit 122 irradiates the outer surface of the photosensitive drum 108 uniformly charged by a later-described charging roller 109 of the process cartridges 106Y, 106M, 106C, and 106K with laser light to form an electrostatic latent image. .

  The process cartridges 106Y, 106M, 106C, and 106K are provided between the transfer unit 104 and the laser writing unit 122, respectively. The process cartridges 106Y, 106M, 106C, and 106K are detachable from the apparatus main body 102. The process cartridges 106Y, 106M, 106C, and 106K are arranged in parallel along the conveyance direction of the recording paper 107.

The conveyor belt cleaning device 15 collects residual toner on the conveyor belt 109 and stores it in a toner disposal container through a conveyor path (not shown).
The secondary transfer roller 16 is for transferring the toner image formed on the conveyance belt 109 to the recording paper 107, and a bias having a reverse sign to that of the toner is applied to attract the toner.
The paper discharge roller pair 24 is a roller for discharging the recording paper 107 on which the toner image is fixed.
The toner bottle 31 stores Y, M, C, and K replenishment toners, and from there through a conveyance path (not shown), the toner is supplied to the process cartridges 106Y, 106M, 106C, and 106K for each color by a predetermined replenishment amount. Replenish.

Next, an operation in which the image forming apparatus 101 forms an image on the recording paper 107 will be described.
First, the image forming apparatus 101 rotates the photosensitive drum 108 and uniformly charges the outer surface of the photosensitive drum 108 by the charging roller 109. Laser light is irradiated on the outer surface of the photosensitive drum 108 to form an electrostatic latent image on the outer surface of the photosensitive drum 108. When the electrostatic latent image is positioned in the developing area 131, the developer 126 adsorbed on the outer surface of the developing sleeve 132 of the developing device 113 is adsorbed on the outer surface of the photosensitive drum 108, and the electrostatic latent image is developed. Then, a toner image is formed on the outer surface of the photosensitive drum 108. In the image forming apparatus 101, the recording paper 107 conveyed by the paper supply roller 124 of the paper supply unit 103 is transferred to the photosensitive drum 108 of the process cartridges 106Y, 106M, 106C, and 106K and the conveyance belt 129 of the transfer unit 104. The toner image formed on the outer surface of the photosensitive drum 108 is transferred to the recording paper 107. The image forming apparatus 101 uses a fixing unit 105 to fix the toner image on the recording paper 107. Thus, the image forming apparatus 101 forms a color image on the recording paper 107.

  As described above, according to the present embodiment, since the image forming apparatus 101 includes the developing device 113 described above, the image carrier may be damaged or the image carrier may be damaged by the deflection of the developing magnetic field generating means inside the magnetic particle carrier. Prevents image defects due to uneven toner adhesion to the image carrier, and recovers the carrier adhering to the image carrier, preventing image defects such as wear and breakage of the device and white spots due to carrier adhesion. By efficiently returning the thus-prepared carrier into the containing layer 117, it is possible to prevent a decrease in image density over the long term.

Examples of the present invention will be described below.
For example, as shown in FIG. 1, in the developing device 113 in which the first developing roller 115a and the second developing roller 115b, which are magnetic particle carriers, and the collecting roller 115c, which is a magnetic particle collecting body, are arranged, the second developing roller The magnetic pole arrangement and magnetic force of the magnet rollers 115b and the collecting roller 115c (133b: first magnetic field generating means and 133c: second magnetic field generating means) are created and assembled under the following conditions, and the second developing sleeve 132b and the collecting sleeve are assembled. Evaluation of the deflection amount of the magnet roller (133a and 133b: first magnetic field generating means) of the developing roller, sensory evaluation of image density unevenness and white spot using a developing device in which the rotational speed of 132c is adjusted under the following conditions. Went.

Example 1
Of the magnetic poles of the magnet roller 133c of the collection roller 115c, the magnetic pole closest to the second developing roller 115b is an N pole (N5 pole), and is on a line segment connecting the center of the photosensitive drum 108 and the center of the magnet roller 113c. In addition, the magnetic pole closest to the photosensitive drum 108 is the N pole (N6 pole). The magnetic forces of the N5 pole and N6 pole were both 50 mT. The magnetic force of the magnetic pole (S4 pole) closest to the recovery roller 115c among the magnetic poles of the magnet roller 133b of the second developing roller was set to 50 mT. Further, the rotation speed of the second developing sleeve 132b was set to 800 rpm, and the rotation speed of the recovery sleeve 132c was set to 700 rpm. The developing device adjusted in this way was attached to the image forming apparatus 113.

As the image forming apparatus, a printer (trade name: IPSIO CX400 (manufactured by Ricoh Co., Ltd.)) attached with the developing device 113 was used.
The photosensitive drum 108 is charged to 550 V, a developing bias voltage of 385 V is applied, a cyan two-component developer (carrier average particle size 35 μm) is used as the developer 126, and the first developing sleeve of the first developing roller 115a. The amount of developer adhering to the outer surface of 132a was set to 40 mg / cm 2, the material of the developing sleeve and the recovery sleeve was A6063, the outer diameter was 10 mm, and the surface roughness Rz was 15 μm.
The three magnet rollers (133a, 133b, 133c) use TP-S68 manufactured by Toda Kogyo Co., Ltd., in which anisotropic nylon Sr ferrite powder as magnetic particles and 6 nylon as a binder are mixed. Injection molding was performed while applying a 7T magnetic field in one direction, and a groove having a diameter of 8.5 mm × 313 mm and a width of 3 mm × depth of 2.3 mm was prepared on the outer periphery. A groove having a width of 3 mm and a depth of 2.3 mm was realized by providing a convex shape on the core side nest. A separately manufactured rare earth magnet block was placed in the groove. The magnet roller was also integrally molded with the same material as the core.

  As for the rare earth magnet block, 950 g of Magfine MFP-13 (anisotropic Ne-Fe-B rare earth magnet) manufactured by Aichi Steel Co., Ltd. was weighed, and quaternary ammonium salt ( 1.5 parts by weight of charge control agent), 1.5 parts by weight of styrene acrylic resin (low softening point substance), 2.0 parts by weight of carbon black, and 1.5 parts by weight of silica (H2000) are externally added. 50 g of the thermoplastic resin was weighed and kneaded with a tumbler mixer under conditions of 22 rpm × 10 min. 12.0 g of the material is filled in a cavity (W2.2 mm × H10.0 mm × L313 mm) of a mold made of a magnetic material (SKS3), and 100 A as an orientation current flows in a direction perpendicular to the press direction. , 400 kN press pressure was applied for molding. Thereafter, the mold and the magnet block were demagnetized with a pulse voltage of 3500 V, the mold was opened, the magnet block was removed, and these magnet blocks were fired at 100 ° C. for 60 minutes. The completed magnet block was 2.8 mm wide x 2.2 mm high x 313 mm long.

  In addition, the S1 pole, S2 pole, N2 pole, S3 pole, and N4 pole were magnetized so that the magnetic forces were 100, 50, 50, 50, and 100 mT, respectively.

Using the image forming apparatus configured as described above, 250,000 solid images of 195 mm × 285 mm were output, and sensory evaluation and deflection amount evaluation were performed. The results are shown in Table 1.
(1) Sensory evaluation Sensory evaluation between the initial state and after outputting 250,000 sheets of images was performed for density unevenness and white spots in the image.
A: Image density is uniform and density unevenness and white spots are not visually recognized.
○: The image density is uniform, and density unevenness and white spots are hardly visually recognized.
Δ: Image density unevenness and white spots are slightly visible, but there is no problem in actual use.
X: Unevenness of image density and white spots are visually recognized and cannot be used practically.

(2) Deflection amount evaluation The deflection amount of the magnet rollers 133a and 133b after outputting 250,000 sheets of images was evaluated. The deflection amount is measured by assembling a bare magnetic roller without a developing sleeve into the developing device, measuring the gap at the center of the magnet rollers 133a and 133b with a thickness gauge, and bending from the gap that is not bent. The amount of deflection was calculated by dividing the difference in gap distance between the two states by two. The evaluation criteria for the amount of deflection were determined as follows.
○: Deflection amount is 0.0 mm or more and less than 0.2 mm.
Δ: Deflection amount is 0.2 mm or more and less than 0.5 mm.
X: Deflection amount is 0.5 mm or more.

(Example 2)
In Example 1, evaluation was performed in the same manner as in Example 1 using a developing device set in the same manner except that the magnetic force of the magnet roller N5 pole of the collecting roller was changed to 45 mT. The results are shown in Table 1.

(Example 3)
In Example 1, evaluation was performed in the same manner as in Example 1 except that the position of the N6 pole was shifted by 10 ° in the rotation direction of the recovery sleeve 132c and a developing device adjusted in the same manner as in Example 1 was used. The results are shown in Table 1.

Example 4
In Example 2, evaluation was performed in the same manner as in Example 1 except that the position of the N6 pole was shifted by 10 ° in the direction of rotation of the recovery sleeve 132c and a developing device adjusted in the same manner as in Example 2 was used. The results are shown in Table 1.

(Comparative Example 1)
In Example 1, among the magnetic poles of the magnet roller 133c of the collection roller, the magnetic pole closest to the second developing roller 115b was set as the S pole, and the magnetic force of the S pole was adjusted to 50 mT, and the same adjustment as in Example 1 was performed. Evaluation was performed in the same manner as in Example 1 using a developing device. The results are shown in Table 1.

(Comparative Example 2)
In the first embodiment, the magnetic pole closest to the second developing roller 115b among the magnetic poles of the magnet roller 133c of the collecting roller is the S pole, and is on the line segment connecting the center of the photosensitive drum 108 and the center of the third magnet roller. In the same manner as in Example 1, except that the magnetic pole closest to the photosensitive drum 108 is the S pole, and the magnetic force of both of these S poles is 50 mT. Evaluation was performed. The results are shown in Table 1.

(Comparative Example 3)
In Example 1, among the magnetic poles of the magnet roller 133c of the collection roller, the magnetic pole that is on the line connecting the center of the photosensitive drum 108 and the center of the magnetic roller 133c and is closest to the photosensitive drum 108 is the S pole, Evaluation was performed in the same manner as in Example 1 using a developing device adjusted in the same manner as in Example 1 except that the magnetic force of this S pole was set to 50 mT. The results are shown in Table 1.

(Comparative Example 4)
In Example 1, except that the magnetic force of the N5 pole was changed to 55 mT, evaluation was performed in the same manner as in Example 1 using a developing device adjusted in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 5)
In Example 1, except that the rotation speed of the second developing sleeve 132b was set to 800 rpm and the rotation speed of the recovery sleeve 132c was set to 900 rpm, evaluation was performed in the same manner as in Example 1 using a developing device adjusted in the same manner as in Example 1. went. The results are shown in Table 1.

  According to Table 1, in all of Examples 1 to 4, it was found that density unevenness and white spots in the image were not visually recognized, and the amount of deflection was small.

According to Table 1, in Comparative Example 1, since the magnetic pole closest to the second developing roller 115b is the S pole among the magnetic poles of the magnet roller 133c of the collecting roller, the S4 pole of the magnet roller 133b of the second developing roller As a result, the magnet roller 133b is scraped due to contact between the surface of the magnet roller 133b of the second developing roller and the inner wall of the developing sleeve 132b in the long term. Became.
Of the magnetic poles of the magnet roller 133c of the collecting roller, the magnetic pole closest to the second developing roller 115b is the S pole and is on a line segment connecting the center of the photosensitive drum 108 and the center of the magnet roller of the collecting roller. In addition, the magnetic pole closest to the photosensitive drum 108 is an N pole (N6 pole), that is, two adjacent magnetic poles have different polarities, so a repulsive magnetic field is not created between the two poles, and the photosensitive body Since the carrier adsorbed on the collection sleeve 132c from the drum 108 is not separated from the collection sleeve 132c, the carrier is not collected in the containing layer 117, and in the long term, density unevenness of the image or density reduction is caused. .

  According to Table 1, in Comparative Example 2, since the magnetic pole closest to the second developing roller 115b among the magnetic poles of the magnet roller 133c of the collecting roller is the S pole, the S4 pole of the magnet roller 133b of the second developing roller As a result, the magnet roller 133b is scraped due to contact between the surface of the magnet roller 133b of the second developing roller and the inner wall of the second developing sleeve 132b in the long term. became. Of the magnetic poles of the magnet roller 133c of the collecting roller, the magnetic pole closest to the second developing roller 115b is the S pole, and is on a line segment connecting the center of the photosensitive drum 108 and the center of the third magnet roller, The magnetic pole closest to the photosensitive drum 108 is also the S pole, that is, the two adjacent magnetic poles have the same polarity, so that a repulsive magnetic field is created between the two poles. Since a repulsive magnetic field is also formed between the magnetic roller S4 poles of the two developing rollers, the carrier adsorbed on the recovery sleeve 132c from the photosensitive drum 108 is not easily separated from the third sleeve 132c, and the carrier is accommodated. It was not collected in the layer 117, and in the long term, density unevenness and density reduction of the image were caused.

  According to Table 1, in Comparative Example 3, the deflection was good, but the magnetic pole closest to the second developing roller 115b among the magnetic poles of the magnet roller 133c of the recovery roller is the N pole (N5 pole). The magnetic pole that is on the line connecting the center of the photosensitive drum 108 and the center of the magnet roller of the recovery roller and that is closest to the photosensitive drum 108 is the S pole, that is, the two adjacent magnetic poles have different polarities. Therefore, a repulsive magnetic field is not created between the two poles, and the carrier adsorbed on the recovery sleeve 132c from the photosensitive drum 108 is not separated from the recovery sleeve 132c. Therefore, the carrier is not recovered in the accommodation layer 117. In the long term, it caused density unevenness and density reduction of images.

  According to Table 1, in Comparative Example 4, the relationship between the magnitudes of the magnetic forces of the N5 pole of the magnet roller of the collecting roller and the S4 pole of the magnet roller of the second developing roller is N5> S4. The developer carried by 115 is easily attracted to the collecting roller 115c between the N5 pole and the S4 pole, and in the long term, density unevenness and density reduction of the image are caused.

  According to Table 1, in Comparative Example 5, because the rotational speed of the recovery sleeve 132c is larger than that of the second developing sleeve 132b, that is, the linear speed of the recovery roller is larger than the linear speed of the second developing roller, the recovery roller 115c Carriers repelled by the repulsive magnetic field formed between the N5 pole and the N6 pole are not smoothly delivered to the second developing roller 115b, making it difficult for the carrier to be collected in the containing layer 117 for a long time. Caused density unevenness and density reduction of the image.

  In the image forming apparatus 101 described above, the process cartridges 106Y, 106M, 106C, and 106K include a cartridge case 111, a charging roller 109, a photosensitive drum 108, a cleaning blade 112, and a developing device 113. However, in the present invention, the process cartridges 106Y, 106M, 106C, and 106K need only include at least the developing device 113, and do not necessarily include the cartridge case 111, the charging roller 109, the photosensitive drum 108, and the cleaning blade 112. . In the above-described embodiment, the image forming apparatus 101 includes the process cartridges 106Y, 106M, 106C, and 106K that are detachable from the apparatus main body 102. However, in the present invention, the image forming apparatus 101 only needs to include the developing device 113 and does not necessarily include the process cartridges 106Y, 106M, 106C, and 106K.

  In addition, the above-mentioned embodiment only showed the typical form of this invention, and this invention is not limited to embodiment. That is, various modifications can be made without departing from the gist of the present invention. For example, the present invention can be applied not only to an image forming apparatus that forms a color image but also to a monochrome image forming apparatus.

1 is a cross-sectional view of a developing device and a process cartridge showing an embodiment of the present invention. 1 is a cross-sectional view of a developing device and a process cartridge showing an embodiment of the present invention. FIG. 2 is a cross-sectional view of a collecting roller of a developing device according to an embodiment of the present invention, a developing roller adjacent to the collecting roller, and an explanatory diagram showing a developer flow. It is explanatory drawing which shows arrangement | positioning of the magnetic pole (N6 pole) of the collection | recovery roller of the developing device in one Embodiment of this invention. 1 is a cross-sectional view of an image forming apparatus showing an embodiment of the present invention. It is a schematic diagram which shows the bending of a magnet roller.

Explanation of symbols

DESCRIPTION OF SYMBOLS 12 Drive roller 15 Conveyor belt cleaning apparatus 16 Secondary transfer roller 24 Paper discharge roller pair 31a, 31b, 31c, 31d Toner bottle 101 Image forming apparatus 102 Apparatus main body 103 Paper feed unit 104 Transfer unit 105 Fixing unit 105a, 105b Roller 106 ( 106Y, 106C, 106M, 106K) Process cartridge 107 Recording paper 108 Image carrier (photosensitive member, photosensitive drum)
109 Charging roller 110 Registration roller pair 111 Cartridge case 112 Cleaning blade 113 Developing device 114 Developer supply unit 115a, 115b Magnetic particle carrier (developing roller)
115c Magnetic particle collection body (collection roller)
116 Regulating blade 117 Storage tank 118 Stirring screw 119 Partition wall 120a First space 120b Second space 120c Third space 122 Laser writing unit 123 Paper feed cassette 124 Paper feed roller 125 Case 126 Magnetic particles (developer)
128 Driving roller 129 Conveying belt 130Y, 130C, 130M, 130K Transfer roller 132a, 132b Non-magnetic hollow body (developing sleeve)
132c Nonmagnetic hollow body (recovery sleeve)
133a, 133b First magnetic field generating means (magnet roller)
133c Second magnetic field generating means (magnet roller)
134 Core

Claims (6)

A magnetic particle having a first developing magnetic field generating means having a plurality of magnetic poles fixedly disposed in a rotatable nonmagnetic hollow body and carrying magnetic particles for developing an electrostatic latent image on the image carrier on the surface In a developing device in which a plurality of carriers are disposed along the image bearing surface of the image carrier, and the magnetic poles closest to each other between the adjacent magnetic particle carriers are different from each other,
A second developing magnetic field generating means having a plurality of magnetic poles fixedly disposed therein is enclosed in a rotatable nonmagnetic hollow body, and the magnetic particle carrier A disposed at the most downstream portion in the rotational direction of the image carrier and the above Having a magnetic particle recovery body disposed in close proximity to both the image carrier and
Of the plurality of magnetic poles of the second magnetic field generating means, the magnetic pole closest to the magnetic particle carrier A and the magnetic pole closest to the image carrier are adjacent and of the same polarity, and the magnetic particle carrier A A developing device having a polarity different from that of the magnetic pole closest to the magnetic particle recovery body in the first magnetic field generating means.   The magnetic flux density of the magnetic pole closest to the magnetic particle carrier A of the second magnetic field generator is greater than the magnetic flux density of the magnetic pole closest to the magnetic particle collector in the first magnetic field generator of the magnetic particle carrier A. The developing device according to claim 1, wherein the developing device is small.   The magnetic pole closest to the image carrier of the second magnetic field generating means is closer to the rotation direction of the image carrier than the line segment connecting the rotation center of the magnetic particle recovery body and the rotation center of the image carrier. The developing device according to claim 1, wherein the developing device is located upstream.   The linear velocity, which is the rotational speed of the nonmagnetic hollow body of the magnetic particle recovery body, is the rotational speed of the nonmagnetic hollow body of the magnetic particle carrier disposed at the most downstream portion in the rotational direction of the image carrier. The developing device according to claim 1, wherein the developing device is smaller than the linear velocity.   A process cartridge comprising the developing device according to claim 1.   An image carrier that carries a latent image, a charging unit that charges the image carrier, a developing unit that develops the latent image on the image carrier, and a transfer unit that transfers an image formed by the developing unit to a transfer material An image forming apparatus comprising: the developing device according to claim 1 as the developing unit.

Images