JP2008116651A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To carry out stable circular conveyance of developer while maintaining image quality and performances such as durability and miniaturization, in a developing device equipped with three developer conveyance passages having separate developer supply, recovery and stirring functions and an image forming apparatus. <P>SOLUTION: The developing device is equipped with a supply conveyance passage 105 with a supply screw 104 which supplies developer to a developing roller under conveyance, a recovery conveyance passage 108 with a recovery screw 107 which recovers developer after development from the developing roller and conveys it in the same direction as the supply screw, and a stirring conveyance passage 109 with a stirring screw 108 which receives supply of surplus developer in the supply conveyance passage and recovered developer in the recovery conveyance passage and conveys these under stirring in the reverse direction to the supply screw, wherein the recovery conveyance passage is located above the stirring conveyance passage in the direction of gravitation force so that recovered developer is supplied to the stirring conveyance passage by free fall, wherein a recovered developer supply opening 114 in the recovery screw 107 becomes broader as proceeding to the downstream end of the recovery conveyance passage. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, a printer, and the like, and a developing device used therefor.

  Conventionally, as a developing device using a two-component developer, a supply conveyance path for supplying a developer to the developer carrier while conveying the developer in the axial direction of the developer carrier and a supply conveyance path for stirring the developer are opposite to each other. In some cases, a developer conveyance path that conveys the developer in the direction is provided, and the developer is circulated and conveyed between the supply conveyance path and the agitation conveyance path. In such a developing device, when the developer that has been supplied to the developer carrying member and has passed through the development region is collected in the supply conveyance path, the recovered developer in which toner is consumed in the development and the developer in the supply conveyance path are separated. It will be mixed in the supply conveyance path. At this time, since the amount of the collected developer that has passed through the development region and consumed the toner increases toward the downstream side of the supply conveyance path, the toner concentration of the developer supplied to the developer carrier decreases toward the downstream side. When the toner density of the developer supplied to the developer carrier decreases, the image density during development also decreases, and density unevenness differs in the image density on the upstream and downstream sides in the conveyance direction of the conveyance path supplied to the developer carrier. An abnormal image is generated.

  On the other hand, when the collected developer is collected in the stirring conveyance path, the developer collected on the downstream side in the conveyance direction of the stirring conveyance path becomes shorter in the stirring time. Since the developer that has reached the downstream end of the agitation transport path in the transport direction is delivered to the upstream end of the supply transport path in the transport direction, the developer collected immediately downstream in the transport direction of the agitation transport path is immediately It is supplied to the supply conveyance path. As a result, even if the toner is properly replenished according to the toner consumption amount, the developer is not sufficiently stirred, the toner density becomes uneven, and the toner charge amount becomes insufficient. Problems such as non-uniform density and low image density occur.

  As described above, the problems caused by collecting the collected developer in the supply conveyance path or the agitation conveyance path are the problems of the developing apparatuses described in Patent Document 1, Patent Document 2, Patent Document 3, Patent Document 4, and Patent Document 5. In this way, the problem can be solved by providing a collection conveyance path for collecting the collected developer separately from the supply conveyance path and the stirring conveyance path. These developing apparatuses include a supply conveyance path that supplies the developer to the developer carrier while conveying the developer, and a recovery conveyance path that conveys the recovered developer in the same direction as the supply conveyance path. Furthermore, an agitation conveyance path is provided for agitating the surplus developer that has reached the most downstream part in the conveyance direction of the supply conveyance path and the recovered developer that has reached the most downstream part in the conveyance direction of the recovery conveyance path. The supply conveyance path, the collection conveyance path, and the stirring conveyance path are each partitioned by a partition member. In addition, the partition member with the agitating and conveying path at the most downstream portion of the supply conveying path is a partitioning member with an excess opening for delivering excess developer to the agitating and conveying path and the agitating and conveying path at the downstream end of the collecting and conveying path. Is provided with a collection opening for delivering the collected developer to the stirring conveyance path. The partition member with the supply conveyance path at the most downstream portion of the agitation conveyance path is provided with an agitation opening for transferring the developer stirred in the agitation conveyance path to the supply conveyance path. The developer is transferred between the three developer conveying paths through the surplus opening, the collection opening, and the stirring opening, and the developer is circulated and conveyed. In this way, by separately performing the functions of supplying and collecting the developer to the developer carrying member, the toner concentration of the developer supplied to the developer carrying member becomes constant, and density unevenness is prevented. be able to. In addition, by separately performing the functions of stirring and collecting the developer, the developer can be sufficiently stirred and the image density can be stabilized.

  In this way, in the developing device that circulates and conveys the developer by providing the three developer conveyance paths of the supply conveyance path, the agitation conveyance path, and the recovery conveyance path, the retention of the developer in the developer conveyance path is suppressed, It is an important issue to stably circulate and convey the developer. This is because if the developer stays, excessive stress is applied to the developer, and the deterioration of the developer is accelerated, resulting in deterioration of fluidity. When the fluidity of the developer is deteriorated, the developer circulation property and the replenishment toner diffusibility are deteriorated. Especially in the staying part, the developer agitation becomes very poor, and the collected developer, surplus developer, and replenishment toner are not sufficiently agitated, and the developer has a non-uniform toner density or insufficient charge. There is a risk of being supplied to the developer carrying member. For this reason, the image density becomes unstable.

Here, it is considered that the three arrangements of the supply conveyance path, the agitation conveyance path, and the recovery conveyance path have a great influence on the circulation conveyance of the developer.
For example, in the developing devices disclosed in Patent Literature 1, Patent Literature 2, and Patent Literature 3, the recovery conveyance path and the agitation conveyance path are located in the lower part of the developing apparatus, and the supply conveyance path is located in the upper part of the developing apparatus. It is what is called a vertical arrangement type. In this vertical arrangement type developing device, the developer recovered from the developer carrying member in the recovery conveyance path and stirred in the stirring conveyance path is lifted and supplied to the supply conveyance path positioned above. For this reason, the developer is retained in the most downstream portion of the agitation conveyance path, and the developer overflows from the agitation opening to the supply conveyance path above the agitation conveyance path. In this way, in the vertical arrangement type developing device, the developer is retained in the most downstream portion of the agitation conveyance path, so that the developer and the replenishment toner are transferred to the supply conveyance path without being sufficiently agitated as described above. There is a risk that the developer carrying member may be supplied from the supply conveyance path.

  In the developing device proposed in Patent Document 4, the recovery conveyance path and the supply conveyance path, the supply conveyance path and the agitation conveyance path are adjacent to each other, and each conveyance path is arranged at substantially the same height. This is a so-called arrangement type developing device. In this lateral arrangement type developing device, the supply of the developer from the recovery conveyance path to the agitation conveyance path, the supply conveyance path to the agitation conveyance path, and the agitation conveyance path to the supply conveyance path is a substantially horizontal movement of the developer. As in the case of the above-described vertical arrangement type, it is not necessary to retain the developer in the vicinity of the stirring opening in order to lift the developer, and the above problems are reduced. However, since the collected developer must be transferred from the collection conveyance path to the stirring path across the supply conveyance path, the overall circulation stability is not good. In particular, at a position where the recovery conveyance path is passed over the supply conveyance path to the stirring conveyance path, the excess developer in the supply conveyance path may become a resistance and the collected developer may stay. For this reason, although not as much as the vertical arrangement type, there is a possibility that the developer and the replenishment toner may be supplied to the developer carrier without being sufficiently stirred as described above.

  On the other hand, in the developing device disclosed in Patent Document 5, the supply conveyance path and the agitation conveyance path are located in the lower part of the developing apparatus, and the collection conveyance path is located in the upper part of the developing apparatus. In this developing device, the recovered developer recovered from the developer carrying member in the recovery conveyance path is supplied to the agitation conveyance path by natural fall, and the substantially horizontal developer is transferred between the agitation conveyance path and the supply conveyance path. Do it. For this reason, it is possible to reduce the stay at the position where the developer is transferred, as compared with the above two types of developing devices.

Japanese Patent Laid-Open No. 11-167260 JP 2001-249545 A Japanese Patent No. 3127594 JP 2006-251440 A Japanese Patent Laid-Open No. 2002-72642

  As described above, in the developing device in which the supply conveyance path and the agitation conveyance path are located in the lower part of the developing device and the recovery conveyance path is located in the upper part of the developing device, there is a relative problem in terms of stabilizing the developer conveyance performance. Few. However, also in this developing device, when the amount of developer increases, stagnation tends to occur at a position where the developer is transferred between the conveyance paths, and it is desired to reduce this. As one of them, when the amount of the collected developer in the collection conveyance path increases, there is a problem that a large amount of the collected developer stays in the transfer section to the agitation conveyance path in the most downstream portion and the transfer is not smoothly performed. .

  As a method for solving this, it is conceivable to adjust the screw diameter of the developer collecting and conveying member and the screw of the developer agitating and conveying member, the number of rotations, etc. From the requirements of the image quality (development gap, agent density, etc.) In many cases, these adjustments alone cannot solve the retention.

  Therefore, it is considered effective to widen the size of the collection opening for delivery from the collection conveyance path to the agitation conveyance path so as to smoothly deliver and solve the retention. As a method of widening the collection opening, it is conceivable to widen the collection opening in the transport direction. Further, as a method of expanding in the conveyance direction, there are a method in which the image is expanded outside the image area along the conveyance direction, and the method is expanded toward the image area. Further, in the two-component developing device, in order to sufficiently supply the toner replenished by the development, the time required to stir the developer and the replenished toner in the developing device, This is performed at a position on the downstream side of the collection conveyance path. Here, if the collection opening is expanded outside the image area along the axial direction, the layout of the space extending in the axial direction and the toner replenishing portion becomes difficult, and as a result, the size of the developing device must be expanded in the axial direction. Therefore, the malfunction that a machine will enlarge will generate | occur | produce.

  On the other hand, if the recovery opening is expanded in the image area along the transport direction, the stirring time is shortened, and the supply transport path is maintained without sufficiently stirring the excess developer, the recovered developer, and the replenished toner. There is a possibility of being supplied to. For this reason, the toner density and the charge amount of the toner become non-uniform, causing problems such as non-uniform image density and low image density.

  Further, it is conceivable to widen the collection opening in the lateral direction perpendicular to the transport direction. However, if the collection opening is widened in the horizontal direction and a large amount of the collected developer is delivered all at once, stagnation occurs in the upstream portion of the stirring conveyance path.

  The present invention has been made in view of the above background, and an object of the present invention is to provide a developing device and an image forming apparatus provided with three developer conveying paths in which the functions of supplying, collecting and stirring the developer are divided. The present invention provides a developing device and an image forming apparatus that can stably convey and convey a developer and obtain a stable image density while maintaining performance such as image quality, durability, and downsizing.

In order to achieve the above object, the invention of claim 1 is characterized in that a developer composed of a carrier and a toner is carried on the surface and rotated, and the latent image carrier surface is latent in a region facing the latent image carrier. Supply carrier having a developer carrier for supplying toner to an image for development and a developer supply / conveying member for feeding the developer to the developer carrier while transporting the developer along the axial direction of the developer carrier A recovery transport path having a developer recovery transport member that recovers the developer after completion of development from the developer carrying member and transports the recovered developer in the same direction in parallel with the developer supply transport member And the surplus developer transported to the most downstream part in the transport direction of the supply transport path without being used for development, and recovered from the developer carrier and transported to the most downstream part in the transport direction of the recovery transport path The surplus developer and the recovered developer are supplied with the recovered developer. An agitating / conveying path having a developer agitating / conveying member that conveys in parallel and in the opposite direction to the developer supply / conveying member while agitating the toner, and a toner replenishing means for replenishing the recovered developer that has been consumed by development A partition member that divides each of the three developer transport paths of the recovery transport path, the supply transport path, and the stirring transport path, and the recovery transport path is located above the stirring transport path in the gravitational direction. The recovered developer in the recovery conveyance path is supplied to the agitation conveyance path by natural fall through a recovery developer supply opening provided in a partition member between the agitation conveyance path and the most downstream portion of the conveyance path, The surplus developer in the supply conveyance path is supplied to the agitation conveyance path through an excess developer supply opening provided in a partition member between the supply conveyance path and the stirring conveyance path, and the agitation A partition member between the supply conveyance path at the most downstream portion of the conveyance path In the developing device that circulates and conveys the developer by supplying the agitated developer after stirring the collected developer and the excess developer to the supply and conveying path through the agitated developer opening. The agent supply opening is configured to become wider as it goes downstream of the collection conveyance path.
According to a second aspect of the present invention, in the developing device of the first aspect, the recovered developer supply opening has a trapezoidal shape with a narrow upstream end and a wide downstream end.
According to a third aspect of the present invention, in the developing device according to the first aspect, the recovered developer supply opening includes a plurality of openings of a size that allows the developer to easily pass through. The number of openings is increased.
According to a fourth aspect of the present invention, in the developing device according to the first, second, or third aspect, the surplus developer supply opening is a partition member between the stirring conveyance path and the most downstream portion of the supply conveyance path. An opening is provided in the partition member, leaving at least a portion lower than the central axis of the developer stirring and conveying member below.
According to a fifth aspect of the present invention, in the developing device according to the first, second, third, or fourth aspect, an opening width of the excess developer opening is narrower than a screw pitch of the developer agitating / conveying member. It is what.
Further, the invention of claim 6 is the developing device of claim 1, 2, 3, 4 or 5, wherein the supply transport path is within half the height of the developer supply transport member relative to the stirring transport path. It is characterized by being provided at a high position.
The invention of claim 7 is the developing device of claim 1, 2, 3, 4, 5 or 6, wherein the developer is a two-component developer comprising a toner and a carrier, and the carrier has a volume average particle diameter. Is 20 to 60 [μm].
The invention of claim 8 is the developing device according to claim 1, 2, 3, 4, 5, 6 or 7, wherein the developer is a two-component developer comprising a toner and a carrier, and the toner has a volume average. The particle size is 3 to 8 [μm], and the ratio (D4 / D1) of the volume average particle size (D4) to the number average particle size (D1) is in the range of 1.00 to 1.40. To do.
According to a ninth aspect of the present invention, in the developing device according to the eighth aspect, the toner has a shape factor SF-1 in the range of 100 to 180 and a shape factor SF-2 in the range of 100 to 180. It is a feature.
The toner according to claim 10 is the developing device according to claim 8, wherein the toner is externally added with fine particles having an average primary particle size of 50 to 500 nm and a bulk density of 0.3 g / cm ³ or more on the surface of the toner base particles. The toner thus obtained is characterized by the following.
The invention according to claim 11 provides a latent image carrier that carries an electrostatic latent image, a latent image forming unit that forms an electrostatic latent image on the latent image carrier, and a static image on the latent image carrier. An image forming apparatus comprising: a developing unit that develops an electrostatic latent image into a toner image; and a transfer unit that transfers the toner image to a non-transfer body. , 6, 7, 8, 9 or 10 is used.
According to a twelfth aspect of the present invention, in the image forming apparatus of the eleventh aspect, a first image forming unit group having a plurality of image carriers and a developing device that forms toner images on the image carriers, A first image station having a first toner image carrying belt carrying a first superimposed toner image onto which toner images formed on a plurality of image carriers of the first image forming unit group are sequentially transferred; A second image forming unit group having an image carrier and a developing device for forming a toner image on the image carrier, and toner images formed on the plurality of image carriers in the second image forming unit group. A second image station having a second toner image carrying belt for carrying a second superimposed toner image transferred sequentially, and the first superimposed toner image formed by the first image station is a first image station. The second superimposed toner image formed by the second image station is transferred from the toner image carrying belt to the first surface of the recording medium simultaneously or sequentially from the second toner image carrying belt to the second surface of the recording medium. It is a double-sided transfer system for transferring.
According to a thirteenth aspect of the present invention, in the image forming apparatus according to the twelfth aspect of the present invention, the image forming apparatus further comprises a toner storage section that stores toner of each color to be supplied to the plurality of developing devices. The toner used in the image forming unit is supplied from the same color toner storage unit.

  In these inventions, by expanding the recovered developer supply opening as it goes downstream, the delivery amount is gradually increased as it goes downstream, enabling smooth delivery according to the recovered developer amount. . That is, even if the amount of the collected developer increases, the developer is prevented from staying in the downstream portion of the collection conveyance path by delivering a large amount in the wide portion of the downstream portion of the collected developer supply opening. it can. Further, in the collected developer supply opening having such a shape, the developer is not delivered all at once to the agitation transport path, so that the stay in the upstream part of the agitation transport path can be suppressed. Therefore, it is possible to stably convey and convey the developer. Further, even when it is necessary to widen the recovered developer supply opening along the transport direction depending on the amount of recovered developer, the size of the expanded developer can be reduced, so that problems such as an increase in size and insufficient stirring time can be suppressed.

  As described above, according to the present invention, in the developing device and the image forming apparatus provided with the three developer transport paths in which the functions of supplying, collecting, and stirring the developer are divided, the performance such as image quality, durability, and miniaturization is achieved. There is an excellent effect that the developer can be stably circulated and maintained, and a stable image density can be obtained.

Hereinafter, an embodiment in which the present invention is applied to a full-color image forming apparatus will be described.
First, a developing device employed in the image forming apparatus of the present embodiment will be described. FIG. 1 is a schematic configuration diagram of a developing device employed in the image forming apparatus of the present embodiment. The developing device 5 in FIG. 1 supplies toner to the latent image on the surface of the photoreceptor 1 while rotating, and develops the developing roller 103 as a developer carrying member to be developed and the developer supplied to the developing roller 103 for development. A developing doctor 112 is provided as a developer regulating member for regulating the thickness to an appropriate thickness. Further, a supply conveyance path 105 including a supply screw 104 as a developer supply conveyance member that conveys the developer in the depth direction of FIG. 1 while supplying the developer to the developing roller 103 upstream of the development unit, and a development unit A recovery conveyance path 107 provided with a recovery screw 106 as a developer recovery conveyance member that collects the developed developer from the developing roller 103 in the downstream portion of the developing roller 103 and conveys the recovered developer in the same direction as the supply screw 104; It has. Further, in parallel with the supply conveyance path 105, an agitation conveyance path 109 which is a developer agitation conveyance path is provided. These supply conveyance path 105, recovery conveyance path 107, and agitation conveyance path 109 are all disposed below the developing roller 103. The agitating and conveying path 109 includes an agitating screw 108 as a developer agitating and conveying member that conveys the developer to the front side in the figure, which is the opposite direction to the supply screw 104, while agitating the developer. The collection conveyance path 7 is arranged above the stirring conveyance path 109. The supply conveyance path 5 and the agitation conveyance path 109 are partitioned by a first partition wall 110 as a partition member. The portions of the first partition wall 110 that divide the supply conveyance path 105 and the agitation conveyance path 109 are openings 112 and 113 for transferring the developer at both ends of the front side and the back side in the figure. And the stirring and conveying path 109 communicate with each other. That is, the first partition wall 110 isolates portions other than the openings at both ends of the supply conveyance path 105 and the stirring conveyance path 109. Further, the supply conveyance path 105 and the collection conveyance path 107 are partitioned by a second partition wall 111 as a partition member. However, the supply conveyance path 105 and the collection conveyance path 107 of the second partition wall 111 are separated from each other. Does not have an opening. Further, the stirring and conveying path 109 and the recovery conveying path 107 located above are partitioned by the second second partition wall 111, but a place for partitioning the stirring and conveying path 104 and the recovery conveying path 107 of the second partition wall 111. An opening for delivering the developer is also provided below the back side in FIG.

  In the supply conveyance path 105, the developer supply amount to the developing roller 103 is set to an appropriate amount regardless of the position in the conveyance direction of the supply screw 104, and from above the developer conveyed in the supply conveyance path 105. In order to ensure that the supply to the developing roller 103 is performed, the shaft of the supply screw 104 is disposed within the range of the pumping magnetic force in the vicinity of the developing roller 103. In this way, the developer supplied from the supply conveyance path 105 onto the developing roller 103 is thinned by the developing doctor 102 and conveyed to a developing portion that is a portion facing the photoreceptor 1 for development. In the collection conveyance path 107, the developed developer is collected from the developing roller 103 by the collection screw 106 being rotated. At this time, it is preferable that the collection conveyance path 107 and the developing roller 103 are sufficiently close to each other, and the gap is preferably set to 1 mm or less so that the developer does not enter the supply conveyance path 105 from the collection conveyance path 107. By arranging in this way, the developed developer is separated from the developing roller 103 to the collection conveyance path 107 and does not enter the supply conveyance path 105 along with the development roller 103.

  The developer circulation in the three developer conveyance paths in the developing device 5 will be described. FIG. 2 is a perspective sectional view of the developing device for explaining the flow of the developer in the developer transport path. Each arrow in the figure indicates the moving direction of the developer.

  In the supply conveyance path 105, the developer is conveyed downstream in the conveyance direction of the supply screw 105 while supplying the developer to the developing roller 103. The surplus developer that is supplied to the developing roller 103 and is not used for development and is transported to the downstream end in the transport direction of the supply transport path 5 is stirred and transported from the surplus opening 112 that is the back opening of the first partition wall 110. 109 (arrow E in FIG. 4). In the collection conveyance path 107, the collected developer collected in the same direction as the supply screw 104 is conveyed downstream by the collection screw 106 while collecting the developed developer from the developing roller 103. The recovered developer recovered from the developing roller 105 and transported to the downstream end in the transport direction of the recovery transport path 107 by the recovery screw 106 is a recovery opening that is an opening provided on the lower surface of the second partition wall 111. From 114, it is supplied to the stirring and conveying path 104 arranged below by natural fall (arrow F in FIG. 4). The agitating and conveying path 109 agitates the supplied surplus developer and the recovered developer, conveys the agitating screw 108 to the downstream side in the conveying direction, and conveys it to the upstream side in the conveying direction of the supplying screw 105, and the first partition wall The ink is supplied to the supply conveyance path 105 from the supply opening 113 which is the front opening 110 (arrow D in FIG. 4).

  A toner concentration sensor 115 is provided in front of the collection opening 114 of the agitation transport path 107, and a toner replenishment control device (not shown) is operated by the sensor output. The toner is supplied to the toner supply position 116 indicated by. As shown in FIG. 2, by providing the toner concentration sensor 115 in the collection conveyance path 107 on the upstream side of the toner replenishment position 116, it is possible to accurately detect the toner concentration of the developer whose concentration has decreased after development. . As a result, an appropriate replenishment toner amount can be replenished according to the consumed toner amount, and toner density control is stabilized. Further, the toner replenishment position 115 is on the downstream side of the toner density sensor 115 in the collection conveyance path 107 and can be mixed more easily because the developer after development and the replenishment toner having a decreased toner density can be mixed. As a result, the time required for stirring with the developer increases and sufficient stirring is performed. The toner replenishing operation is performed as needed based on the detection result of the toner density sensor 115, so that a proper amount of toner can be quickly replenished quickly, so that on-demand toner replenishment is possible without a time lag. Further, as a toner replenishing means for replenishing toner, a system using a known MONO pump can be employed. The toner replenishing means using the Mono pump is advantageous for space distribution in the image forming apparatus because there are few restrictions on the installation location of the toner cartridge. Further, since the toner can be replenished in a timely manner, it is not necessary to provide a large toner storage space in the developing device, and the developing device can be downsized.

  As described above, the toner and the collected developer replenished from the toner replenishment position 116 on the downstream side of the collection conveyance path 107 spontaneously fall into the lower agitation conveyance path 109 through the collection opening 114. In the agitating and conveying path 109, the collected developer, surplus developer, and toner replenished as necessary are agitated and conveyed in the opposite direction to the developer in the collecting and conveying path 107 and the supply conveying path 105 by the agitating screw 108. Then, the sufficiently agitated developer is transferred to the upstream side in the conveyance direction of the supply conveyance path 109 communicating with the downstream side in the conveyance direction.

The supply screw 104, the recovery screw 106, and the stirring screw 108, which are developer conveying members, are the same as those in a general biaxial stirring method, and are made of resin or metal screws. These screws prevent the developer from being fed into the conveying screw part that stirs and conveys the developer in the developer conveying direction, the transfer paddle part that conveys the developer to the adjacent conveying path side, and the downstream bearing part. In addition, a reversing screw portion in the winding direction opposite to the conveying screw portion is provided. In this developing device, the following screws were used, but the values are not limited to these values.
Supply screw 104: outer diameter φ15, pitch 25 (1 item)
Recovery screw 106: outer diameter φ12, pitch 20 (2 items)
Stir screw 108: outer diameter φ15, pitch 25 (1 item)

  Since the developing device 5 includes a supply conveyance path 105 and a collection conveyance path 107 and supplies and collects the developer in different developer conveyance paths, the developed developer is mixed into the supply conveyance path 5. There is no. Therefore, it is possible to prevent the toner concentration of the developer supplied to the developing roller 3 from decreasing toward the downstream side of the supply conveyance path 5 in the conveyance direction. Further, since the recovery conveyance path 107 and the agitation conveyance path 109 are provided and the developer recovery and the agitation are performed in different developer conveyance paths, the developed developer does not fall during the agitation. Therefore, since the sufficiently agitated developer is supplied to the supply conveyance path 105, it is possible to prevent the developer supplied to the supply conveyance path 105 from being insufficiently agitated. As described above, the toner density of the developer in the supply conveyance path 105 can be prevented from decreasing, and the developer in the supply conveyance path 105 can be prevented from being insufficiently stirred. Can be constant.

  The developing device 5 is a developing device in which the supply conveyance path 105 and the agitation conveyance path 109 are located in the lower part of the development apparatus 5 and the recovery conveyance path 107 is located in the upper part of the development apparatus 5. For this reason, as indicated by an arrow in the figure, the developer does not move from the lower part to the upper part between the conveyance paths, and is only naturally dropped or moved substantially horizontally. Such movement of the developer can reduce stress applied to the developer. In addition, there are relatively few issues regarding stabilization of developer conveyance performance. However, even in the developing device 5, stagnation may occur at a position where the developer is transferred between the transport paths, and it is desired to reduce this. For example, when the amount of the collected developer in the collection conveyance path 107 increases, a large amount of the delivery section to the agitation conveyance path 109 in the most downstream portion stays, and the delivery by the collection opening 114 does not go smoothly. There are challenges.

  Therefore, in the present invention, the shape of the recovery opening 114 is as follows. For the delivery from the collection conveyance path 107 to the stirring conveyance path 109, it is considered effective to widen the size of the collection opening 114 and perform the delivery smoothly in order to solve the stay. Here, the collection opening 114 is shaped so as to become wider as it goes downstream of the collection conveyance path 107. As a result, the delivery amount is gradually increased as it goes downstream, and smooth delivery according to the collected developer amount is possible even if the amount of the collected developer increases. Further, in the opening of this shape, the collected developer is not delivered all at once to the stirring / conveying path 105, so that stagnation can be suppressed in the upstream portion of the stirring / conveying path 105. Furthermore, even when it is necessary to spread along the transport direction depending on the amount of the collected developer, the size of the spread can be reduced, so that problems such as an increase in size and insufficient stirring time can be suppressed. In this way, the developer is circulated stably, the developer is prevented from staying, the toner density is stabilized, and the developer is stably supplied to the developing roller.

  Note that the shape in which the collection opening 114 becomes wider as it goes downstream of the collection conveyance path 107 is a trapezoidal shape in which the upstream end of the collection opening 114 is narrow and the downstream end is wide, as shown in FIG. There is.

  Also, as shown in FIGS. 2 (b) and 2 (c), a plurality of square or circular openings having sides or diameters of about 1 mm to 10 mm of a size that allows easy passage of the developer are arranged. The number of openings is increased as it goes downstream. By adopting such a shape, it is possible to set the delivery amount according to the restrictions of the developing device such as the size of the developing device and the developer capacity.

  In the developing device 5, the surplus developer is transferred from the supply transport path 105 to the stirring transport path 109 via the surplus opening 112 in a substantially horizontal direction. Here, in the supply conveyance path 105, the developer that has not been supplied to the developing roller 103 is conveyed to the most downstream portion and is transferred to the agitation conveyance path 109 as an excess developer, so that the amount of excess developer is small. Further, in the upstream portion of the agitation transport path 109, as described above, a large amount of developer may be transferred from the collection transport path 107 or toner may be supplied, resulting in a large amount of developer. . For this reason, the developer may flow backward from the agitation transport path 109 to the supply transport path 105 through the excess opening 12. In order to prevent this, the surplus opening 112 is provided with an opening at the top of the first partition wall 110, leaving at least a portion below the center axis of the stirring screw 108 below the first partition wall 110. Shall. In this way, by leaving the first partition wall 110 below the surplus opening 112, the developer is prevented from flowing back from the agitation transport path 109 to the supply transport path 105 via the surplus opening 112. Thereby, the developer can be stably circulated and conveyed.

  Further, the opening width of the surplus opening 112 may be narrower than the screw pitch of the stirring screw 108. By setting such an opening width, the amount of developer sent to the excessive opening 112 side by the stirring screw 108 is reduced. This prevents the developer from flowing back to the supply conveyance path 105 from the agitation conveyance path 109 via the excess opening 112 on the downstream side of the supply conveyance path 105.

  Further, the height of the supply conveyance path 105 is set to be higher than that of the stirring conveyance path 109 within a range within half of the diameter of the stirring screw 108. With such an arrangement, the developer is prevented from flowing back from the agitation conveyance path 109 to the supply conveyance path 105 via the excessive opening 112. Thereby, the developer can be stably circulated and conveyed.

Next, characteristics of the two-component developer composed of the carrier and the toner used in the developing device of this embodiment will be described.
The carrier preferably has a volume average particle size of 20 to 60 [μm]. By using a carrier having a small particle diameter having a volume average particle diameter of 60 [μm] or less, the pumping amount can be reduced without lowering the developing ability. This is because the gap between the carriers is reduced, the magnetic brush in the development region becomes denser, and sufficient development can be performed with a small pumping amount. Further, the developer transportability in the collection transport path 7 is improved, which leads to an improvement in dispersibility of the replenished toner. On the other hand, if the average particle size of the carrier is larger than 60 [μm], the developer easily overflows in the collection conveyance path 7, and stable developer circulation cannot be performed, resulting in fluctuations in toner density. On the other hand, if it is smaller than 20 [μm], there arises a problem that the carrier adheres to the photosensitive member 1 or the carrier is easily scattered from the developing device. The average particle size of the carrier can be measured using a SRA type of a Microtrac particle size analyzer (Nikkiso Co., Ltd.) with a range setting of 0.7 [μm] or more and 125 [μm] or less.

  The toner preferably has a volume average particle diameter (D4) of 3 to 8 [μm]. By using a small particle diameter toner having an average particle diameter of 8 [μm] or less, the bulk density of the developer can be increased, and stable developer conveyance is possible. In addition, the diffusibility of the replenishment toner in the collection conveyance path is improved. In addition, since the particle size distribution is sharp, the developer fluidity is good, and the developer circulation can be performed stably over a long period of time, and the replenishment toner diffusibility is improved. On the other hand, since the gap between the toners is reduced and the toner is more satisfactorily contained in the image, it is possible to reduce the required toner adhesion amount and the height (pile height) of the toner image. Further, regarding the reproducibility of minute dots of 600 dpi or more, in this range, the toner particles having a sufficiently small particle diameter are obtained with respect to the minute latent image dots, so that the dot reproducibility is excellent. Therefore, the stability of the image is increased. On the other hand, when the volume average particle diameter (D4) 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 volume average particle diameter (D4) exceeds 8 [μm], the pile height of the image becomes large and it is difficult to suppress scattering of characters and lines.

  At the same time, the ratio (D4 / D1) of the weight average particle diameter (D4) to the number average particle diameter (D1) is preferably in the range of 1.00 to 1.30. The closer (D4 / D1) is to 1.00, the sharper the particle size distribution. With such a toner having a small particle size and a narrow particle size distribution, the toner charge amount distribution is uniform, a high-quality image with little background fogging can be obtained, and the electrostatic transfer method has a high transfer rate. can do.

Next, a method for measuring the particle size distribution of toner particles will be described.
Examples of the measuring device for the particle size distribution of toner particles by the Coulter counter method include Coulter Counter TA-II and Coulter Multisizer II (both manufactured by Coulter). The measurement method is described below.
First, 0.1 to 5 ml of a surfactant (preferably alkylbenzene sulfonate) is added as a dispersant to 100 to 150 ml of an aqueous electrolytic solution. Here, the electrolytic 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 for about 1 to 3 minutes with an ultrasonic disperser, and the volume and number of toner particles or toner are measured with the measurement device using a 100 [μm] aperture. Then, the volume distribution and the number distribution are calculated. From the obtained distribution, the weight average particle diameter (D4) and the number average particle diameter (D1) of the toner can be obtained. As a channel, it is less than 2.00-2.52 [micrometer]; 2.52-less than 3.17 [micrometer]; 3.17-less than 4.00 [micrometer]; 4.00-5.04 [micrometer] Less than 5.04 to 6.35 [μm]; 6.35 to less than 8.00 [μm]; 8.00 to less than 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]; 20.20 to less than 25.40 [μm]; 25.40 to less than 32.00 [μm]; Using 13 channels of 00 to less than 40.30 [μm], particles having a particle size of 2.00 [μm] or more to less than 40.30 [μm] are targeted.

The toner shape factor SF-1 is preferably in the range of 100 to 180, and the shape factor SF-2 is preferably in the range of 100 to 180. 3 and 4 are diagrams schematically showing the shape of the toner in order to explain the shape factor SF-1 and the shape factor SF-2. The shape factor SF-1 indicates the ratio of the roundness of the toner shape and is represented by the following formula (1). This is a value obtained by dividing the square of the maximum length MXLNG of the shape formed by projecting the toner on a two-dimensional plane by the figure area AREA and multiplying by 100π / 4.
SF-1 = {(MXLNG) 2 / AREA} × (100π / 4) Formula (1)
When the value of SF-1 is 100, the shape of the toner becomes a true sphere, and becomes larger as the value of SF-1 increases.

The shape factor SF-2 indicates the ratio of the unevenness of the toner shape, and is represented by the following formula (2). A value obtained by dividing the square of the perimeter PERI of the figure formed by projecting the toner onto the two-dimensional plane by the figure area AREA and multiplying by 100 / 4π.
SF-2 = {(PERI) 2 / AREA} × (100 / 4π) (2)
When the value of SF-2 is 100, there is no unevenness on the toner surface, and as the value of SF-2 increases, the unevenness of the toner surface becomes more prominent.
Specifically, the shape factor is measured by taking a photograph of the toner with a scanning electron microscope (S-800: manufactured by Hitachi, Ltd.), introducing it into an image analyzer (LUSEX 3: manufactured by Nireco) and analyzing it. Calculated. When the shape of the toner is close to a sphere, the contact state between the toners becomes a point contact, so that the attractive force between the toners is weakened and the fluidity is increased. Therefore, the circulation of the developer is improved and the diffusibility of the replenishment toner is improved. In addition, since the contact state between the toner and the photoconductor is a point contact, the attractive force between the toner and the photoconductor is weakened, and the transfer rate is increased, contributing to the improvement in image quality. On the other hand, if any of the shape factors SF-1 and SF-2 exceeds 180, the fluidity is deteriorated, and the agent circulation property and the replenishment toner diffusibility are poor. Further, the transfer rate is lowered, which is not preferable.

This toner is obtained by attaching fine particles (hereinafter simply referred to as fine particles) having an average primary particle size of 50 to 500 nm and a bulk density of 0.3 mg / cm 3 or more to the toner particle surface. In addition, although silica etc. are often used for a normal fluid improvement agent, for example, the average primary particle diameter of this silica is 10-30 nm normally, and a bulk density is 0.1-0.2 mg / cm < ³ >. As described above, the presence of fine particles having appropriate characteristics on the surface of the toner forms an appropriate gap between the toner particles and the object. In addition, fine particles have a very small contact area with toner particles, a photoconductor, a conveyance belt, etc., and are evenly contacted, so the effect of reducing adhesion is great, and toner of an unfixed image facing the conveyance belt adheres to the conveyance belt. There is little disturbance of the image because it is difficult. In addition, since the development / transfer efficiency is improved and the dot reproducibility is improved, the image is stabilized and a margin is increased against disturbance during conveyance. Furthermore, since it plays the role of a roller, it is difficult to be buried in toner particles even during cleaning under high stress (high load, high speed, etc.) between the cleaning blade and the photoconductor without wearing or damaging the photoconductor. Or, even if it is buried a little, it can be detached and returned, so that stable characteristics can be obtained over a long period of time. Further, the toner is moderately detached from the surface of the toner and accumulated at the tip of the cleaning blade, and the so-called dam effect has an effect of preventing a phenomenon that the toner passes from the blade. Since these characteristics have an effect of reducing the share received by the toner particles, the filming effect of the toner itself due to the low rheological component contained in the toner is exhibited for high-speed fixing (low energy fixing). In addition, when fine particles having an average primary particle size in the range of 50 to 500 [μm] are used, the excellent cleaning performance can be fully utilized and the particle size of the toner is extremely small. Does not reduce fluidity. Further, although the details are not clear, even if the surface-treated fine particles are externally added to the toner or the carrier is contaminated, the degree of developer deterioration is small. Therefore, since the change in the fluidity and charging property of the toner is small over time, the developer circulation and the replenishment toner diffusion can be stably performed over a long period of time. Also, the stability of image quality is increased.

  The average primary particle size (hereinafter referred to as the average particle size) of the fine particles is 50 to 500 nm, and particularly preferably 100 to 400 nm. If the thickness is less than 50 nm, the fine particles may be buried in the concave and convex portions on the toner surface to lower the role of the rollers. On the other hand, when the particle size is larger than 500 [μm], when the fine particles are positioned between the blade and the surface of the photoreceptor, the order of the contact area of the toner itself is on the same level, and the toner particles to be cleaned are allowed to pass through. It becomes easy to generate.

If the bulk density is less than 0.3 mg / cm ³ , it contributes to improvement of fluidity, but the scattering and adhesion of the toner and fine particles are increased, so that the toner and roller effect and the accumulation in the cleaning section are accumulated. As a result, the so-called dam effect that prevents toner cleaning failure is reduced.

As the fine particles, as the inorganic _{compound, SiO 2, TiO 2, Al} 2 O 3, MgO, CuO, ZnO, SnO 2, CeO 2, Fe 2 O 3, BaO, CaO, K 2 O, Na 2 O, ZrO ₂ , CaO.SiO ₂ , K ₂ O (TiO ₂ ) _n , Al ₂ O ₃ .2SiO ₂ , CaCO ₃ , MgCO ₃ , BaSO ₄ , MgSO ₄ , SrTiO _3, etc., preferably SiO ₂ , TiO ₂ , and Al ₂ O ₃ . In particular, these inorganic compounds may be hydrophobized with various coupling agents, hexamethyldisilazane, dimethyldichlorosilane, octyltrimethoxysilane, and the like.
The organic compound fine particles may be thermoplastic resins or thermosetting resins, such as vinyl resins, polyurethane resins, epoxy resins, polyester resins, polyamide resins, polyimide resins, silicon resins, phenol resins, melamine resins, Examples include urea resins, aniline resins, ionomer resins, and polycarbonate resins. As the resin fine particles, two or more of the above resins may be used in combination. Of these, vinyl resins, polyurethane resins, epoxy resins, polyester resins, and combinations thereof are preferred because an aqueous dispersion of fine spherical resin particles is easily obtained.
Specific examples of vinyl resins include polymers obtained by homopolymerization or copolymerization of vinyl monomers, such as styrene- (meth) acrylic acid ester copolymers, styrene-butadiene copolymers, (meth) acrylic acid. -Acrylic ester copolymer, styrene-acrylonitrile copolymer, styrene-maleic anhydride copolymer, styrene- (meth) acrylic acid copolymer, and the like.

The bulk density of the fine particles was measured by the following method. Using a 100 ml graduated cylinder, fine particles were gradually added to make 100 ml. At that time, no vibration was applied. The bulk density was measured by the difference in weight before and after placing the fine particles of the graduated cylinder.
Bulk density (g / cm ³ ) = fine particle amount (g / 100 ml) ÷ 100
The fine particles can be externally added and adhered to the toner surface by a method in which the toner base particles and the fine particles are mechanically mixed and adhered using various known mixing devices, or the toner base particles in the liquid phase. And a method in which the fine particles are uniformly dispersed with a surfactant or the like, and are dried after the adhesion treatment.

  Next, the entire image forming apparatus according to the present embodiment will be described. FIG. 5 is a schematic configuration diagram of an image forming apparatus in which the developing device is employed. This image forming apparatus is an image forming apparatus capable of forming a full-color image in one pass on both sides of a recording medium. In the image forming apparatus main body 100 shown in FIG. 5, the first image carrier unit 20 having the first image carrier belt 21 that moves endlessly in the direction of the arrow at the upper part with the recording material conveyance path 43A as a boundary, A second image carrier unit 30 having a second image carrier belt 31 that moves endlessly in the direction of the arrow is disposed at the bottom. Four first image forming units 80Y, 80C, 80M, and 80K are provided on the upper tension surface of the first image carrier belt 21, and four first image forming units 80Y, C, M, and K are provided on the inclined tension surface of the second image carrier belt 31. Two image forming units 81Y, 81C, 81M, and 81K are provided. Y, C, M, and K along the numbers of the first and second image forming units correspond to the colors of the toner to be handled. Y is yellow, C is cyan, M is magenta, and K is black. Means. Y, C, M, and K are also used in the same meaning with respect to the photoreceptor 1 provided in the first and second image forming units and rotating together with the first image carrying belt 21 and the second image carrying belt 31. . The photoreceptors 1Y, 1C, 1M, and 1K are arranged at the same interval, and at least at the time of image formation, are in contact with a part of the stretched portion with the image carrier belts 21 and 31, respectively. Here, the first and second image forming units are different only in the color of the accommodated toner, and other configurations and operations are the same. Therefore, the image forming unit will be described below with the suffix omitted.

  FIG. 6 is a schematic configuration diagram of the image forming unit. In FIG. 6, during operation of the image forming apparatus 100, charging means is provided around a cylindrical photosensitive member 1 rotatably supported so as to rotate in the direction of an arrow by a drive source (not shown) in accordance with an electrophotographic process. An image forming member such as a scorotron charger 3, an exposure device 4, a developing device 5, a cleaning device 2 and a photostatic device Q, a potential sensor S1, and an image sensor S2 are disposed. The photoreceptor 1 is obtained by forming an organic photosensitive layer (OPC), which is a photoconductive substance, on an aluminum cylinder surface having a diameter of about 30 to 120 mm. A photoconductor on which an amorphous silicon (a-Si) layer is formed can also be used. A belt-like photoreceptor can also be employed. The cleaning device 2 includes a cleaning brush 2a, a cleaning blade 2b, and a recovery member 2c, and removes and recovers foreign matters such as toner remaining on the surface of the photoreceptor. The exposure device 4 scans the light corresponding to the image data for each color on the surface of each photoreceptor 1 that has been uniformly charged by the charging means, and forms an electrostatic latent image. The exposure apparatus 4 in the illustrated example is an exposure apparatus that includes an LED (light emitting diode) array and an imaging element as light emitting elements, but uses a laser light source, a polygon mirror, etc., and beam light modulated according to image data to be formed. It is also possible to adopt a laser scanning type exposure apparatus. As the charging means, in addition to the charger 3, a type that contacts the surface of the photoreceptor 1, for example, a charging roller can also be used. The developing device 5 uses a two-component developer composed of toner and carrier. In this image forming apparatus 100, the electrostatic latent image for each color formed on the surface of each photoconductor 1 by a laser beam with respect to the negatively charged photoconductor 1 has the same polarity (minus polarity) as the charged polarity of the photoconductor. The toner is developed with a toner of a predetermined color and becomes a visible image, so-called reversal development is performed. The detailed description of the configuration of the developing device 5 is as described above.

  Also, a first image carrying belt 21 as an image carrier that is supported by a plurality of rollers 23, 24, 25, 26 (two), 27, 28, 29 and runs in the direction of the arrow is a first image forming unit. 80Y, C, M, K are provided below the photoreceptors 1Y, C, M, K. The first image carrying belt 21 is endless, and is stretched and arranged so that a part of each photoconductor after the developing process comes into contact. A primary transfer roller 22 is provided on the inner periphery of the first image carrying belt 21 so as to face the photoreceptors 1Y, 1C, 1M, and 1K. A cleaning device 20 </ b> A is provided on the outer periphery of the first image carrying belt 21 at a position facing the roller 23. The cleaning device 20 </ b> A wipes off unnecessary toner remaining on the surface of the first image carrying belt 21 and foreign matters such as paper dust. The members related to the first image carrier belt 21 are integrally configured as the first image carrier unit 20 and can be attached to and detached from the image forming apparatus 100.

  Further, a second image carrier belt 31 as an image carrier that is supported by a plurality of rollers 33, 34, 35, 36 (two), 37, 38 and runs in the direction of the arrow is provided in the second image forming unit 81Y, C, M, and K are provided in contact with the photoreceptors 1Y, C, M, and K. The second image bearing belt 31 is endless, and is stretched and arranged so that a part of each photoconductor after the developing process comes into contact. A primary transfer roller 32 is provided on the inner peripheral portion of the second image bearing belt 31 so as to face the photoreceptors 1Y, 1C, 1M, and 1K. A cleaning device 30 </ b> A is provided on the outer periphery of the second image carrying belt 31 at a position facing the roller 33. The cleaning device 30 </ b> A wipes off unnecessary toner remaining on the surface of the second image carrying belt 31 and foreign matters such as paper dust. The members related to the second image carrier belt 31 are integrally configured as the second image carrier unit 30 and can be attached to and detached from the image forming apparatus 100.

  Further, a secondary transfer roller 46 as a first secondary transfer unit is provided on the outer periphery of the first image carrying belt 21 and in the vicinity of the support roller 28. By applying a bias to the secondary transfer roller 46 while passing a recording medium (hereinafter referred to as paper P) between the first image carrier belt 21 and the secondary transfer roller 46, the toner is carried by the first image carrier belt 21. The image is transferred to the paper P.

  A secondary transfer charger 47 as a second secondary transfer unit is provided on the outer periphery of the second image carrying belt 31 and in the vicinity of the support roller 34. The secondary transfer charger 47 is a known type, and a thin wire of tungsten or gold is used as a discharge electrode, held by a casing, and a transfer current is applied to the discharge electrode from a power source (not shown). By applying a transfer current while passing the paper P between the second image carrier belt 31 and the secondary transfer charger 47, an image of toner carried by the second image carrier belt 31 is transferred to the paper P. The polarity of the transfer current applied to the secondary transfer roller 46 and the secondary transfer charger 47 is a positive polarity opposite to the polarity of the toner.

  On the right side of the image forming apparatus 100, a paper feeding device 40 that accommodates paper is provided, and only one sheet is reliably sent to the recording material conveyance paths 43B and 43A by a plurality of conveyance roller pairs 42B.

  A recording body for transporting the sheet that has passed through the second transfer station on the extension of the recording body transport path 43A to the fixing nip in the fixing device 60 provided downstream in the transport direction of the recording body while maintaining a flat state. The transfer means 50 is provided. The recording medium transporting unit 50 has rollers 52, 53, 54, 55, and 56 that support a conveyor belt 51 that moves endlessly in the direction of the arrow, and a cleaning device 50A that faces the roller 55 outside the conveyor belt 51. , An adsorption charger 57 for adsorbing the recording medium P facing the roller 56, and a charge eliminating / separating charger 58 facing the roller 57. The conveyance belt 51 that moves together with the recording medium P in contact with the unfixed toner image is negatively charged by the suction charger 57 with the same polarity as the polarity of the toner. As the conveyance belt 51, a metal belt, a polyimide belt, a polyamide belt, or the like can be employed. The surface is provided with releasability from the toner and has a chargeable resistance value. The traveling speed of the belt 51 is matched with the traveling speed of the recording medium in the fixing device.

  A fixing device 60 having a heating unit is provided on the downstream side of the recording material transport unit 50 in the paper transport direction. A type having a heater inside the roller, a belt fixing device that runs a heated belt, a fixing device that employs induction heating as a heating method, and the like can be employed. In order to make the color and glossiness of the images on both sides of the paper the same, the material, hardness, surface properties, etc. of the fixing roller and fixing belt are made equal. Further, the fixing conditions are controlled based on full-color and monochrome images, or single-sided or double-sided, or controlled by a control unit (not shown) so as to obtain an optimal fixing condition according to the type of paper. A cooling roller pair 70 having a cooling function is provided in the conveyance path after fixing in order to cool the sheet after fixing and stabilize the unstable toner state at an early stage. A heat pipe structure roller having a heat radiating portion can be employed. The cooled sheet is discharged and stacked by a discharge roller pair 71 on a discharge stack unit 75 provided on the left side of the image forming apparatus 100. The discharge stacking unit employs a mechanism in which a receiving member moves up and down according to a stack level by an elevator mechanism (not shown) so that a large amount of sheets can be stacked. It is also possible to pass the paper through the paper discharge stack unit 75 and transport the paper toward another post-processing apparatus. Another post-processing apparatus is an apparatus for bookbinding such as punching, cutting, folding, and binding.

  The toner cartridges 86Y, 86C, 86M, and 86K for each color in which unused toner is stored are detachably stored in the space 85. Toner is supplied to each developing device as necessary by toner conveying means such as a Mono pump or an air pump as described above. In the configuration of this embodiment, the toner cartridge is shared by the image forming units 80 and 81 arranged vertically. As a result, the replenishment toner having the same characteristics is transferred to the developing device corresponding to each surface and has the same diffusibility, so that it is possible to obtain a double-sided image with stable image quality. In addition, the toner cartridge 86K for black toner, which is highly consumed, can have a particularly large capacity. This storage space 85 is on the back side when viewed from the operation direction on the upper surface of the image forming apparatus, and a plane portion is secured on the front side of the upper surface of the image forming apparatus, so that it can be used as a work table.

  Next, the operation of the image forming apparatus 100 configured as described above will be described.

<Single-sided recording operation>
First, an operation during single-sided recording in which a full-color image is formed on one side of the paper P in the above configuration will be described. There are basically two types of single-sided recording methods that can be selected. One of the two types is a method in which an image carried on the first image carrying belt 21 is directly transferred to one side of the paper, and the other method is an image carried on the second image carrying belt 31 on the paper. This is a method of transferring directly to one side. In the present embodiment, due to the configuration of the image forming apparatus 100, when the image carried on the first image carrying belt 21 is directly transferred to one side of the paper, the image is placed on the upper surface of the paper and the second image carrying belt 31. When the carried image is directly transferred to one side of the paper, the image is formed on the lower surface of the paper. In the case where the data to be recorded is a plurality of pages, it is convenient to control the image forming order so that the pages are aligned on the paper discharge stack unit 75. An explanation will be given of a method in which an image is carried on the first image carrying belt 21 and then transferred onto a sheet so that the image order is recorded in order from the image data of the last page and the page order is aligned.

  When the image forming apparatus 100 is operated, the first image carrier belt 21 and the photoreceptors 1Y, 1C, 1M, and 1K in the first image forming units 80Y, 80C, 80M, 80K rotate. At the same time, the second image carrier belt 31 rotates. However, the photoreceptors 1Y, C, M, and K in the second image forming units 81Y, 81C, 81M, and 81K are separated from the second image carrier belt 31 and are not rotated. To be. First, image formation by the image forming unit 80Y is started. By the operation of the exposure device 4 composed of an LED (light emitting diode) array and an imaging element, light corresponding to image data for yellow emitted from the LED is irradiated onto the surface of the photoreceptor 1Y uniformly charged by the charging device 3. Thus, an electrostatic latent image is formed. The electrostatic latent image is developed with yellow toner by the developing roller 5a to become a visible image electrostatically on the first image carrying belt 21 that moves in synchronization with the photoreceptor 1Y by the transfer action of the primary transfer roller 22. Primary transfer is performed. Such latent image formation, development, and primary transfer operations are sequentially performed in the same manner on the photosensitive members 1C, 1M, and 1K. As a result, yellow, cyan, magenta, and black toner images are carried on the first image carrying belt 21 as sequentially overlapping full-color toner images, and are moved in the direction of the arrow together with the first image carrying belt 21. .

  At the same time, the paper P used for recording is fed out from the paper feed tray 40a or the paper feed cassettes 40b to 40d in the paper feed device 40 by one of the paper feed / separation means 41A to 41D for feeding the paper P. The pair 42B and 42C are conveyed to the recording material conveyance path 43C. Before the leading edge of the paper is picked up by the registration roller pair 45, the jogger 44 operates to push both sides of the paper from both lateral directions with respect to the paper conveyance direction, and the lateral alignment of the paper is not performed. I can be taken. The registration roller pair 45 is stationary, and the leading edge of the sheet is stationary while entering the nip of the registration roller pair 45, but the timing is set so that the position with the image on the first image carrier belt 21 is normal. Then, the registration roller pair 45 is rotated to convey the sheet to the transfer area.

  The full-color toner image on the first image carrying belt 21 is transferred to the upper surface of the paper P conveyed in synchronization with the first image carrying belt 21 by receiving a transfer action by the secondary transfer roller 46. The bias applied to the secondary transfer roller 46 has a positive polarity opposite to the charging polarity of the toner. Thereafter, the surface of the first image carrying belt 21 is cleaned by the belt cleaning device 20A. Further, foreign matters such as toner remaining on the surfaces of the photoreceptors 1Y, C, M, and K in the first image forming units 80Y, 80C, 80M, and 80K that have finished primary transfer are cleaned by the cleaning brush 2a and the cleaning blade 2b of the cleaning device 2. Is removed from the surface of each photoconductor. The surface of each photoconductor is neutralized by a residual potential by the static eliminator Q to prepare for the next image formation / transfer process. The removed foreign matter such as toner is sent to the collecting unit 87 by the collecting unit 2c. Sensors S1 and S2 detect whether the surface potential after exposure on the surface of the photoconductor and the concentration of toner attached to the surface of the photoconductor after the development process are appropriate, and appropriately set image forming conditions. Information is sent to a control means (not shown) for control.

  The paper P on which the toner image carried on the first image carrying belt 21 is transferred is transferred toward the fixing device 60 by the carrying belt 51 of the carrying device 50. The surface of the transfer belt 51 is charged in advance by a sheet suction charger 57 so that the sheet P can be reliably transferred together with the transport belt 51. The neutralization / separation charger 58 operates so that the paper P is separated from the transport belt 51 and is reliably sent to the fixing device 60. The toners of the respective colors superimposed on the paper P are subjected to the fixing action by the heat of the fixing device 60, and are melted and mixed to completely form a color image. Since toner is contained only on one side (upper surface) of the paper, less heat energy is required for fixing compared to double-sided recording having toner on both sides. A control means (not shown) optimally controls the power used by the fixing device according to the image. Until the fixed toner is completely fixed on the paper, it is rubbed by a guide member or the like on the conveyance path, and an image is lost or distorted. In order to prevent this problem, the cooling roller pair 70, which is a cooling means, operates to cool the toner and the paper. Thereafter, the paper is discharged by the paper discharge roller 71 onto the paper discharge stack 75 with the image surface facing upward. In the paper discharge stack section 75, the image forming order is programmed so that the recorded matter of the young pages is stacked so as to be sequentially stacked on top, so the page order is aligned. Since the paper discharge stack unit 75 is lowered as the number of discharged paper sheets increases, the paper sheets can be stacked in an orderly and reliable manner, and the page order is not disturbed. Instead of directly stacking the recorded paper on the paper discharge stack section 75, a punching process can be performed, or the paper can be conveyed to a post-processing device such as a sorter, a collator, a binding device, or a folding device.

  In another method for forming an image on one side of the paper P, image formation in the first image forming units 80Y, 80C, 80M, 80M, 80K is not performed, and image data of a young page is used for page alignment. Although the point of image formation is different in order, it is basically the same as the single-sided recording process described above, and therefore details are omitted.

<Operation during double-sided recording>
Next, the operation at the time of double-sided recording in which images are formed on both sides of the paper P will be described. When a start signal is input to the image forming apparatus, the images for the respective colors sequentially formed by the first image forming units 80Y, 80C, 80M, 80M, 80K described in the single-side recording operation are applied to the first image carrier belt 21. The image for each color sequentially formed by the second image forming units 81Y, 81C, 81M, and 81K is sequentially transferred to the second image carrier belt 31 in parallel with the step of carrying out the primary transfer sequentially and carrying it as the first image. Next, a process of transferring and carrying as a second image is performed. With the configuration shown in FIG. 5, in order for the first image and the second image to coincide with each other at the leading edge in the sheet conveyance direction, the second image is formed later than the start of the first image formation. Is started. Further, since the sheet is stopped and retransmitted by the registration roller pair 45, the sheet is fed in consideration of the time and is aligned by the jogger 44. The registration roller pair 45 transports the sheet to a first transfer station constituted by a transfer roller 46 as a first secondary transfer unit and the first image carrying belt 21 at a timing. A transfer current having a positive polarity is applied to the transfer roller 46, and the image is transferred from the first image carrying belt to one side (upper surface in the drawing) of the paper P. Thus, the sheet P having an image on one side is continuously sent to the second transfer station having the transfer charger 47 as the second secondary transfer means by the transfer action of the transfer roller 46. Then, by applying a positive transfer current to the charger, the full-color second image previously carried on the second image carrying belt 31 is transferred onto the lower surface of the paper P at a time.

  The paper P on which the full color toner images are transferred on both sides in this way is transported to the fixing device 60 by the transport belt 51. The surface of the transport belt 51 is charged with the same negative polarity as the polarity of the toner by the suction charger. The unfixed toner on the lower surface of the paper is prevented from transferring to the belt. An alternating current is applied to the charge removal / separation charger 58, and the sheet is separated from the belt 51 and transferred to the fixing device 60. The toner images on both sides of the sheet are melted and mixed in response to a fixing process by heat of the fixing device 60. The sheet subsequently passes through the cooling roller pair and is discharged onto the discharge stack unit 75 by the discharge roller 71. When double-sided recording is performed on a plurality of pages of paper, the image formation order is controlled so that the image of a young page becomes the bottom surface and is stacked on the paper discharge stack unit 75. The order of the pages is 1 page in order from the top, 2 pages on the back, 3 pages on the second sheet, and 4 pages on the back. Such control of image forming sequence and control such as increasing the power input to the fixing device compared to the one-side recording are executed by a control means (not shown). As for the single-sided recording and the double-sided recording operation, an example in which full-color recording is executed has been described, but monochrome recording using only black toner is also possible.

  By using the above-described image forming apparatus for such a one-pass double-sided transfer type image forming apparatus, productivity can be increased and a high-quality image with a stable density in the long term can be obtained. As a result, there is no difference in image quality between the front and back sides, and a stable double-sided image can always be obtained.

As described above, according to the image forming apparatus of the present embodiment, the recovery opening 114 is widened toward the downstream of the recovery conveyance path 107, and the transfer amount is gradually increased as it goes downstream. Enables smooth delivery according to the situation. That is, even if the amount of the collected developer increases, a large amount is delivered at a wide portion downstream of the collection opening 114, thereby enabling smooth delivery, and developer retention in the downstream portion of the collection conveyance path 107. Can be suppressed. Further, in the collection opening 114 having such a shape, the collected developer is not delivered all at once to the agitation transport path 109, so that the retention of the developer in the upstream portion of the agitation transport path 109 can be suppressed. it can. As a result, the developer can be stably circulated and conveyed. Further, depending on the amount of the collected developer, even when the collection opening 114 needs to be expanded along the transport direction, the size of the expansion can be reduced, so that problems such as an increase in size and insufficient stirring time can be suppressed.
Further, the recovery opening 114 has a trapezoidal shape with a narrow upstream end and a wide downstream end. Thereby, the collection opening 114 is formed into an integrated trapezoidal delivery opening that becomes wider as it goes downstream of the collection conveyance path 107, thereby simplifying the delivery of the developer from the collection conveyance path 107 to the stirring conveyance path 109. Can be carried out stably by a simple method.
Further, a plurality of square or circular openings having sides or diameters of about 1 mm to 10 mm, which are easy to pass the developer, are arranged, and the number of openings is increased toward the downstream. By adopting such a shape, it is possible to set the delivery amount according to the restrictions of the developing device such as the size of the developing device and the developer capacity.
Further, in the developing device 5, the surplus developer is transferred from the supply transport path 105 to the stirring transport path 109 through the surplus opening 112 in a substantially horizontal direction. Here, in the downstream portion of the supply conveyance path 105, the amount of excess developer that is conveyed to the downstream portion without being supplied to the developing roller 103 is small. On the other hand, in the upstream portion of the agitation conveyance path 109, a large amount of developer is delivered from the collection conveyance path 107 or toner is replenished, resulting in a large quantity of developer. For this reason, the developer may flow backward from the agitation transport path 109 to the supply transport path 105 through the excess opening 12. In order to prevent this, the surplus opening 112 is provided with an opening at the top of the first partition wall 110, leaving at least a portion below the center axis of the stirring screw 108 below the first partition wall 110. Shall. In this way, by leaving the first partition wall 110 below the surplus opening 112, the developer is prevented from flowing back from the agitation transport path 109 to the supply transport path 105 via the surplus opening 112. Thereby, the developer can be stably circulated and conveyed.
Further, the opening width of the surplus opening 112 may be narrower than the screw pitch of the stirring screw 108. By setting such an opening width, the amount of developer sent to the excessive opening 112 side by the stirring screw 108 is reduced. This prevents the developer from flowing back to the supply conveyance path 105 from the agitation conveyance path 109 via the excess opening 112 on the downstream side of the supply conveyance path 105.
Further, the height of the supply conveyance path 105 is set to be higher than the stirring conveyance path 109 within a range within half of the diameter of the stirring screw 108. With such an arrangement, the developer is prevented from flowing back from the agitation conveyance path 109 to the supply conveyance path 105 via the excessive opening 112. Thereby, the developer can be stably circulated and conveyed.
The volume average particle size of the carrier of the developer is 20 to 60 [μm]. By using a carrier having a small particle diameter, it is possible to reduce the amount of pumping to the developing roller 3 without reducing the developing ability. As a result, the developer amount in the downstream portion of the collection conveyance path 7 is excessive. Suppresses, makes it difficult to stay, and performs stable circulating conveyance. Therefore, the toner replenished in the collection conveyance path 7 is diffused efficiently, contributing to uniform toner density. If the average particle diameter of the carrier is larger than 60 [μm], overflow tends to occur in the collecting unit, and stable agent circulation cannot be performed, and the diffusibility of the replenishment toner deteriorates. On the other hand, if it is smaller than 20 [μm], there is a problem that the carrier easily adheres to the photosensitive member or the carrier is easily scattered from the developing device.
The volume average particle diameter of the toner is 3 to 8 [μm], and the ratio (D4 / D1) of the volume average particle diameter (D4) to the number average particle diameter (D1) is in the range of 1.00 to 1.40. Use what is in By using a small particle diameter toner having an average particle diameter of 8 [μm] or less, the bulk density of the developer can be increased, and the developer can be stably conveyed and developed at the downstream portion of the collection conveyance path 7. A problem that the agent overflows and enters the supply conveyance path 5 is also prevented. Therefore, the diffusibility of the replenishment toner in the recovery conveyance path is improved. In addition, since the particle size distribution is sharp, the developer fluidity is good, and the developer circulation can be performed stably over a long period of time, and the replenishment toner diffusibility is improved. On the other hand, since the gap between the toners is reduced and the toner is more satisfactorily contained in the image, it is possible to reduce the required toner adhesion amount and the height (pile height) of the toner image. Further, regarding the reproducibility of minute dots of 600 dpi or more, in this range, the toner particles having a sufficiently small particle diameter are obtained with respect to the minute latent image dots, so that the dot reproducibility is excellent. Therefore, the stability of the image is increased. On the other hand, when the volume average particle diameter (D4) 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 volume average particle diameter (D4) exceeds 8 [μm], the pile height of the image becomes large and it is difficult to suppress scattering of characters and lines. At the same time, the ratio (D4 / D1) of the weight average particle diameter (D4) to the number average particle diameter (D1) is preferably in the range of 1.00 to 1.30. The closer (D4 / D1) is to 1.00, the sharper the particle size distribution. With such a toner having a small particle size and a narrow particle size distribution, the toner charge amount distribution is uniform, a high-quality image with little background fogging can be obtained, and the electrostatic transfer method has a high transfer rate. can do.
Further, toner having a shape factor SF-1 in the range of 100 to 180 and a shape factor SF-2 in the range of 100 to 180 is used. By using a toner having a nearly spherical shape in this way, the flowability of the developer is improved, and the developer can be circulated and transported stably and the replenishment toner can be diffused stably over the long term.
The toner is obtained by externally adding fine particles having an average primary particle diameter of 50 to 500 nm and a bulk density of 0.3 g / cm ³ or more on the surface of the toner base particles. As a result, since the external additive is less buried and the change in the flowability of the developer is small over time, the developer can be circulated and transported stably and the replenishment toner can be diffused over a long period of time.
The first image carrier unit 20 having the first image carrier belt 21 that moves endlessly with the recording material conveyance path 43A as a boundary, and the second image carrier having a second image carrier belt 31 at the bottom. The unit 30 is disposed, and the four first image forming units 80Y, 80C, 80M, and 80K are opposed to the first image carrier belt 21 and four second image formations are opposed to the second image carrier belt 31. Units 8180Y, C, M, and K are arranged. Then, the first superimposed toner image formed on the first image carrying belt 21 by the first image forming unit is transferred from the first image carrying belt 21 to the surface of the recording medium, and the second image carrying belt by the second image forming unit. The developing device is employed in a one-pass double-side transfer type image forming apparatus that transfers the second superimposed toner image formed thereon onto the back surface of the recording body simultaneously or sequentially. Such a one-pass double-sided transfer system can increase productivity and obtain an image having excellent density stability in the long term. Accordingly, there is no difference in image quality between the front and back sides, and a stable double-sided image can always be obtained.
In addition, a toner storage unit that stores toner of each color to be supplied to a plurality of developing devices is provided, and the toner used in the first image forming unit and the toner used in the second image forming unit are stored in the same toner for each color. Supply from the department. Thereby, the toner of each color to be replenished to the developing device that forms an image on the front surface and the back surface is made the same, so that the diffusibility of the replenished toner becomes equal. Therefore, there is little difference in image quality on each side of the double-sided image, and a double-sided image with a stable image density can be obtained.

FIG. 3 is a cross-sectional view illustrating the flow of developer in the developing device employed in the image forming apparatus according to the present embodiment. FIG. 6 is a perspective view for explaining the flow of the developer in the developing device, wherein (a), (b), and (c) are diagrams showing examples of the shape of the collection opening. The figure which represented the shape of the toner typically in order to demonstrate shape factor SF-1. The figure which represented the shape of the toner typically in order to demonstrate shape factor SF-1. 1 is a schematic diagram of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram of an image forming unit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Cleaning apparatus 3 Charging apparatus 4 Exposure apparatus 5 Developing apparatus 20 1st image carrier unit 21 1st image carrier belt 30 2nd image carrier unit 31 2nd image carrier belt 43A, B Recording body conveyance path | route 46 Secondary transfer roller 47 Secondary transfer charger 80Y, C, M, K First image forming unit
81Y, C, M, K Second image forming unit 100 Image forming apparatus
DESCRIPTION OF SYMBOLS 102 Developing doctor 103 Developing roller 104 Supply screw 105 Supply conveyance path 106 Recovery screw 107 Collection conveyance path 108 Agitation screw 109 Agitation conveyance path 110 1st partition wall 111 2nd partition wall 112 Surplus opening part 113 Agitation opening part 114 Recovery opening part 115 Toner concentration sensor 116 Toner supply position

Claims (13)

A developer carrying member for carrying and developing a developer composed of a carrier and a toner on the surface, supplying the toner to the latent image on the surface of the latent image carrying member in a region facing the latent image carrying member, and developing; A supply conveyance path having a developer supply conveyance member that supplies the developer carrying member while conveying the developer along the axial direction of the developer carrying member, and a developer after completion of development from the developer carrying member A recovery transport path having a developer recovery transport member that transports the recovered developer in parallel and in the same direction as the developer supply transport member, and a transport direction of the supply transport path that is not used for development. The surplus developer transported to the most downstream portion and the recovered developer recovered from the developer carrier and transported to the most downstream portion in the transport direction of the recovery transport path are supplied, and the surplus developer and the In parallel with the developer supply and transport member while stirring the recovered developer An agitating / conveying path having a developer agitating / conveying member that conveys the toner in the opposite direction, toner replenishing means for replenishing the recovered developer that has been consumed by development, the collecting / conveying path, the supply / conveying path, and the stirring A partition member that partitions each of the three developer transport paths of the transport path, the recovery transport path is located above the stirring transport path in the gravitational direction, and is separated from the stirring transport path at the most downstream portion of the recovery transport path. The recovered developer in the recovery conveyance path is supplied to the agitation conveyance path by natural fall through a recovery developer supply opening provided in the partition member, and the agitation conveyance path is connected to the agitation conveyance path at the most downstream portion of the supply conveyance path. The excess developer in the supply conveyance path is supplied to the agitation conveyance path through an excess developer supply opening provided in the partition member between the two and the supply conveyance path at the most downstream portion of the agitation conveyance path. The recovered developer through a stirring developer opening provided in the partition member In the developing apparatus for circulating convey the developer stirring the developer after stirring the excess developer by supplying to the supply conveyance path,
A developing device characterized in that the recovered developer supply opening is configured to become wider toward the downstream of the recovery conveyance path.   2. The developing device according to claim 1, wherein the recovered developer supply opening has a trapezoidal shape with a narrow upstream end and a wide downstream end.   2. The developing device according to claim 1, wherein the recovered developer supply opening includes a plurality of openings each having a size that allows the developer to easily pass therethrough, and the number of the openings increases as it goes downstream. A developing device comprising:   4. The developing device according to claim 1, wherein the surplus developer supply opening is at least the developer agitating / conveying member below a partition member between the agitating and conveying path at a most downstream portion of the supply and conveying path. An image forming apparatus in which an opening is provided in the partition member, leaving a portion whose height is lower than the central axis of the partition member.   5. The developing device according to claim 1, wherein an opening width of the excess developer opening is narrower than a screw pitch of the developer stirring and conveying member.   6. The developing device according to claim 1, wherein the supply conveyance path is provided at a position higher than the agitation conveyance path in a range within half of the height of the developer supply conveyance member. Developing device.   7. The developing device according to claim 1, wherein the developer is a two-component developer composed of a toner and a carrier, and the carrier has a volume average particle diameter of 20 to 60 [μm]. A developing device.   8. The developing device according to claim 1, wherein the developer is a two-component developer composed of a toner and a carrier, and the toner has a volume average particle diameter of 3 to 8 [μm]. And a ratio of the volume average particle diameter (D4) to the number average particle diameter (D1) (D4 / D1) is in the range of 1.00 to 1.40.   9. The developing device according to claim 8, wherein the toner has a shape factor SF-1 in the range of 100 to 180 and a shape factor SF-2 in the range of 100 to 180. 9. The developing device according to claim 8, wherein the toner is a toner obtained by externally adding fine particles having an average primary particle diameter of 50 to 500 nm and a bulk density of 0.3 g / cm ³ or more to the surface of the toner base particles. A developing device. A latent image carrier that carries an electrostatic latent image, a latent image forming unit that forms an electrostatic latent image on the latent image carrier, and a development that converts the electrostatic latent image on the latent image carrier into a toner image An image forming apparatus comprising: a developing unit that transfers the toner image to a non-transfer body;
An image forming apparatus using the developing device according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 as the developing means.   12. The image forming apparatus according to claim 11, further comprising: a first image forming unit group having a plurality of image carriers and a developing device for forming a toner image on each of the image carriers, and a plurality of the first image forming unit groups. A first image station having a first toner image carrier belt carrying a first superimposed toner image onto which toner images formed on the image carrier are sequentially transferred; a plurality of image carriers; and the image carrier A second image forming unit group each having a developing device for forming a toner image, and a second superimposed toner onto which toner images formed on a plurality of image carriers of the second image forming unit group are sequentially transferred A second image station having a second toner image carrying belt for carrying an image, and recording the first superimposed toner image formed by the first image station from the first toner image carrying belt. A double-sided transfer system in which the second superimposed toner image formed by the second image station is simultaneously or sequentially transferred from the second toner image carrying belt to the second surface of the recording body on the first surface of the body. An image forming apparatus, comprising:   13. The image forming apparatus according to claim 12, further comprising a toner storage unit that stores toner of each color to be supplied to the plurality of developing devices, wherein the toner used in the first image forming unit and the toner used in the second image forming unit are The image forming apparatus is supplied from the same color toner storage unit.

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