JP2010181736A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus equipped with a developing apparatus which achieves reduction in running cost by eliminating unnecessary carrier replacement and which provides image quality with stable density over a long period of time. <P>SOLUTION: A developer replenished from a replenishing apparatus has a higher ratio of the carriers to the developer at a later period of use than at an early period of use. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention replenishes a two-component developer containing a toner and a carrier, and applies a developing system developing device that performs development while recovering excess developer. The present invention relates to a forming apparatus.

  Conventionally, an image forming apparatus using an electrophotographic system, as shown in FIG. 11, has an electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) 1 generally in the form of a drum as an image carrier. I have. The surface of the photosensitive drum 1 is uniformly charged by a charger 2, the charged photosensitive drum 1 is exposed by an exposure device 3 according to image information, and an electrostatic latent image is formed on the photosensitive drum 1. Form. The electrostatic latent image formed on the photosensitive drum 1 is converted into a visible image (toner image) by using the developer toner using the developing device 4. The visualized image is transferred to the recording medium S by the transfer device 5. Thereafter, the toner image transferred onto the recording medium S is fused and fixed to the recording medium S by heat and pressure by the fixing device 6. Then, the toner remaining on the photosensitive drum 1 after the transfer process is removed by the cleaning device 7, and further, the charge remaining on the photosensitive drum 1 is removed by the charge eliminating device 8, so that the photosensitive drum 1 becomes the next time. Prepare for the image forming process.

  The developing device 4 uses a two-component developer containing non-magnetic toner particles (toner) and magnetic carrier particles (carrier) as a developer. In particular, in color image forming apparatuses, it is not necessary to include a magnetic substance in the toner, so that it is widely used for reasons such as good color.

  For example, the developing device 4 using a two-component developer is generally configured as shown in FIGS. The developing device 4 includes a developing container 41 that stores a developer. The developing container 41 is divided into a developing chamber (developer conveying path) 41a and an agitating chamber (developer conveying path) 41b by a partition wall 41c extending in the vertical direction. A first developer transport stirring member 42 and a second developer transport stirring member 43 are arranged in the developing chamber 41a and the stirring chamber 41b, respectively. In addition, delivery portions (developer transport paths) 41d and 41e that allow the developer to pass between the developing chamber 41a and the stirring chamber 41b are provided at the end in the longitudinal direction of the partition wall 41c. The first and second developer transport stirring members 42 and 43 transport the developer while stirring and circulate the developer container 41. A developing sleeve 44 as a developer carrying member is rotatably disposed at a position of the developing container 41 facing the photosensitive drum 1. The developing sleeve 44 incorporates a magnet 45 as a magnetic field generating means.

  The two-component developer conveyed while being agitated by the first and second developer conveying and agitating means 42 and 43 and having the toner adhered to the surface of the carrier due to frictional charging is developed by the magnetic field generated by the magnet 45. It is attracted and carried on the surface of the sleeve 44. Then, the developer passes through the developer layer thickness regulating means 46 by the rotation of the developing sleeve 44, is coated on the surface of the developing sleeve 44 as a thin layer, and is conveyed to a portion facing the photosensitive drum 1. At the facing portion, the developer forms a chain-like magnetic spike by the magnetic field generated by the magnet 45. The magnetic spikes are close to or in contact with the photosensitive drum 1, and only the toner is transferred to the electrostatic latent image formed on the surface of the photosensitive drum 1 by the developing bias applied to the developing sleeve 44, and the surface of the photosensitive drum 1. A toner image corresponding to the electrostatic latent image is formed.

  As described above, in the developing device 4 using the two-component developer used in the electrophotographic image forming apparatus, the toner and the carrier of the two-component developer contained in the developing container 41 are agitated and rubbed. Charge. Thereafter, the latent image on the image carrier is developed by supplying it to an image carrier such as a photosensitive drum by a developer carrier such as a developing sleeve. At this time, the toner is consumed and supplied, whereas the carrier is not consumed or supplied, and remains in the developing container. As the prints are used one by one, the durability deteriorates each time. Causes of deterioration include, for example, so-called “external additive adhesion” in which the external additive attached to the toner is released and adheres to the carrier, or so-called “toner spent” in which the toner itself adheres to the carrier. Both of them often cause deterioration of carrier charging ability. As a result, the charge amount of the toner decreases, and various problems such as white background toner fog and toner scattering outside the developing container occur.

  In order to avoid these problems, in the conventional developing device, before the above-described fogging or toner scattering occurs, for example, the number of printed sheets is 40k, and the two-component developer is replaced. However, it is of course not a desirable situation because it takes time and labor for replacement, and further downtime during replacement is inevitable.

  In view of this, a developing method in which not only toner but also a carrier is appropriately replenished into the developing container and the two-component developer that gradually becomes excessive due to the replenishment of the carrier is recovered, so-called “auto refresh” is disclosed in Patent Document 1. Has been proposed. With this developing method, it is possible to replenish the toner that decreases with consumption, and at the same time replace the deteriorated carrier in the developing container with a new carrier to be replenished.

  When this auto-refresh is used, supply and recovery of the two-component developer including the carrier is performed, so that the new (New) carrier and the durable carrier are gradually replaced together with the toner. For this reason, the deterioration of the carrier becomes saturated at a certain level.

  The deterioration level at the time of saturation can be arbitrarily changed by changing the mixing ratio of the toner and carrier of the replenishment developer. For example, when the carrier ratio of the developer for replenishment is increased, the frequency at which the New carrier is replaced with a deteriorated carrier in the developing container is increased, so that the carrier is saturated with little progress. By setting this mixing ratio to an appropriate value, the saturation level of carrier deterioration can be maintained at a level that does not cause problems such as fogging, so two-component developer replacement is not required or the life of the developer is extended. Will be possible.

  On the other hand, in the auto-refresh configuration, the carrier is replenished and discharged as a replenishment developer in addition to the toner, so there is also a demerit that leads to an increase in running cost. It is desirable to reduce the ratio.

  However, in the conventional auto-refresh configuration, the toner as a replenishment developer and the carrier mixing ratio are always replenished regardless of the degree of carrier deterioration. There is a case where it is exchanged wastefully, and there is room for improvement from the viewpoint of running cost.

  Furthermore, in the conventional auto-refresh configuration, the carrier deterioration is set to be suppressed by gradually repeating the supply / discharge of the carrier, but on the other hand, since the chargeability of the carrier gradually deteriorates, There is a problem that the charge amount becomes unstable.

  As a result, density fluctuations over a long period of time and control downtime for preventing density fluctuations occur, which is not desirable from that point of view.

  Further, in Patent Document 2, in addition to the case where the carrier is replenished corresponding to the toner replenishment amount replenished to correct the toner density, the carrier replenishment control is performed corresponding to the number of image formations or the development drive time. It has been proposed to do. As a result, a reduction in toner charging ability due to carrier deterioration is prevented in advance.

Japanese Patent Publication No. 2-21591 JP 2003-337469 A

  However, the carrier's ability to impart tribo usually varies with durability (use time). Therefore, in Patent Document 2, it is necessary to stabilize the image density by patch control or the like in order to stabilize the image density.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus provided with a developing device capable of reducing running costs by eliminating unnecessary carrier exchange and obtaining image quality with stable density over a long period of time. is there.

The above object is achieved by the image forming apparatus according to the present invention. In summary, according to a first aspect of the present invention, an image carrier and a developing device that develops a latent image formed on the image carrier into a toner image using a developer having toner and a carrier. An image forming apparatus provided in the developing device and having a discharge port for discharging the developer and a replenishing device for replenishing the developer to the developing device,
The developer replenished from the replenishing device is an image forming apparatus characterized in that the ratio of the carrier to the developer is higher in the late use than in the early use.

According to a second aspect of the present invention, an image carrier, a developing device that develops a latent image formed on the image carrier into a toner image using a developer having toner and a carrier, and the developing device An image forming apparatus having a discharge port for discharging the developer and a replenishing device for replenishing the developer to the developing device,
In the image forming apparatus, the developer replenished from the replenishing device is only toner at an early stage of use and a developer having toner and a carrier at a later stage of use.

  According to the present invention, in an auto-refresh configuration, running costs can be reduced by eliminating unnecessary carrier exchange, and stable image density reproduction can be achieved over a long period of time.

1 is a schematic configuration diagram of an embodiment of an image forming apparatus according to the present invention. 1 is a cross-sectional view illustrating a schematic configuration of a developing device according to an embodiment of an image forming apparatus according to the present invention. 1 is a schematic top view illustrating a schematic configuration of a developing device in an image forming apparatus according to the present invention. FIG. 6 is a diagram illustrating a carrier charge amount decrease amount (a decrease amount from an initial charge amount) and a carrier average print number with respect to the number of printed sheets in durability in Example 1. It is a figure explaining the problem of the conventional auto refresh type | system | group. FIG. 10 is a diagram illustrating a transition of the average number of printed sheets when the first supply developer and the second supply developer are switched in the first embodiment. FIG. 6 is a diagram illustrating a transition of the average number of printed carriers and a decrease in carrier charging ability when switching between a first supply developer and a second supply developer in Example 1. FIG. 10 is a diagram illustrating a transition of the average number of printed carriers in Example 2. It is sectional drawing which shows schematic structure of the image development apparatus of the other Example in the image forming apparatus which concerns on this invention. It is sectional drawing which shows schematic structure of the image development apparatus of the other Example in the image forming apparatus which concerns on this invention. It is a schematic block diagram of an example of the conventional image forming apparatus.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Example 1
[Overall Configuration and Operation of Image Forming Apparatus]
First, the overall configuration and operation of the image forming apparatus of this embodiment will be described. FIG. 1 shows a schematic cross-sectional configuration of the image forming apparatus of this embodiment.

  The image forming apparatus 100 according to the present embodiment is a full-color image according to image information from a document reading apparatus connected to the image forming apparatus main body (apparatus main body) 100A or a host device such as a personal computer connected to the apparatus main body so as to be communicable. Can be formed.

  That is, the image forming apparatus 100 according to the present exemplary embodiment is a quadruple tandem type image forming apparatus. In the present exemplary embodiment, a plurality of image forming apparatuses 100 include yellow (Y), magenta (M), cyan (C), and black (K). These four-color full-color images can be formed using an electrophotographic method.

  Accordingly, the image forming apparatus 100 includes, as a plurality of image forming units, first, second, third, and fourth image forming units (image forming stations) P (image forming stations) that form yellow, magenta, cyan, and black images, respectively. PY, PM, PC, PBk). Then, while the intermediate transfer member 51 included in the transfer device 5 moves in the direction of the arrow shown in the drawing and passes through each image forming unit, the images of the respective colors are superimposed on the intermediate transfer member 51 in each image forming unit. The multiple toner images superimposed on the intermediate transfer member 51 are transferred to a recording material (recording paper, plastic sheet, cloth, etc.) S to obtain a recorded image.

  In this embodiment, the configuration of each image forming station P is substantially the same except that the development colors are different. Accordingly, in the following, unless there is a particular need to distinguish, the subscripts Y, M, C, and Bk given to the reference numerals to indicate that they belong to any one of the image forming stations P are omitted, and a general description will be given. To do.

  The image forming station P includes a drum-shaped electrophotographic photosensitive member as an image carrier, that is, a photosensitive drum 1. On the outer periphery of the photosensitive drum 1, a charger 2 as a charging unit, an exposure device (a laser exposure optical system in this embodiment) 3 as an exposure unit, and a developing device 4 as a developing unit are arranged. Further, a transfer device 5 as a transfer means, a cleaning device 7 as a cleaning means, and a static elimination device 8 as a static elimination means are provided. The transfer device 5 has an intermediate transfer belt 51 as an intermediate transfer member. The intermediate belt 51 is wound around a plurality of rollers and rotates (circulates) in the direction of the arrow shown in the drawing. A primary transfer member 52 is disposed at a position facing each photosensitive drum 1 via the intermediate transfer belt 51. A secondary transfer member 53 is provided at a position facing one of the rollers around which the intermediate transfer belt 51 is wound.

  At the time of image formation, first, the surface of the rotating photosensitive drum 1 is uniformly charged by the charger 2. Next, an electrostatic image is formed on the photosensitive drum 1 by scanning and exposing the surface of the charged photosensitive drum 1 according to an image information signal by the exposure device 3. The electrostatic image formed on the photosensitive drum 1 is visualized as a visible image (toner image) with the developer toner using the developing device 4.

  The toner image formed on the photosensitive drum 1 has a primary transfer bias applied to the primary transfer member 52 at a primary transfer portion (primary transfer nip) N1 where the intermediate transfer belt 51 and the photosensitive drum 1 abut. Transfer (primary transfer) is performed on the intermediate transfer belt 51 by the action. For example, when a four-color full-color image is formed, a toner image is transferred from each photosensitive drum 1 onto the intermediate transfer belt 51 sequentially from the first image forming unit PY, and the four-color toner image is transferred onto the intermediate transfer belt 51. Is formed to form a multiple toner image.

  On the other hand, the recording material S is accommodated in a cassette 9 as a recording material accommodating portion. The recording material S is transferred to a secondary transfer portion (nip portion) N2 where the intermediate transfer belt 51 and the secondary transfer member 53 come into contact with each other by a recording material conveyance member such as a pickup roller, a conveyance roller, and a registration roller. The toner image is conveyed in synchronization with the upper toner image. The multiple toner images on the intermediate transfer belt 51 are transferred onto the recording material S by the action of the secondary transfer bias applied to the secondary transfer member 53 in the secondary transfer portion N2.

  Thereafter, the recording material S separated from the intermediate transfer belt 51 is conveyed to the fixing device 6. The toner image transferred onto the recording material S is melted and mixed by being heated and pressurized by the fixing device 6 and is fixed onto the recording material S. Thereafter, the recording material S is discharged out of the apparatus.

  Deposits such as toner remaining on the photosensitive drum 1 after the primary transfer step are collected by the cleaning device 7. The electrostatic image remaining on the photosensitive drum 1 is erased by the static eliminator 8. Thereby, the photosensitive drum 1 is prepared for the next image forming process. Further, deposits such as toner remaining on the intermediate transfer belt 51 after the secondary transfer step are removed by the intermediate transfer body cleaner 54.

  Note that the image forming apparatus 100 according to the present exemplary embodiment forms a single-color or multi-color image by using an image forming unit for a desired single color or some of four colors such as a black single-color image. Is also possible.

[Basic configuration of developing device]
Next, the developing device 4 will be further described.

  The developing device 4 has been described above in “Background Art” with reference to FIGS. 2 and 3, but will be described again as a developer containing portion that contains a two-component developer containing a non-magnetic toner and a magnetic carrier. Development container 41. A developing sleeve 44 as a developer carrying member is rotatably installed in the developing container 41, and a magnet roll (magnet) 45 as a magnetic field generating means is fixedly disposed in the developing sleeve 44. . Further, a regulating blade 46 as a developer amount regulating member for forming a thin layer of developer is disposed on or in contact with the surface of the developing sleeve 44, and the developer is stirred in the developing container 41. In addition, first and second developer conveying members 42 and 43 for conveying are arranged.

  The interior of the developing container 41 is divided into a developing chamber (developer transport path) 41a and an agitating chamber (developer transport path) 41b by a partition wall 41c extending in the vertical direction. The first developer conveying member 42 is disposed in the developing chamber 41a, and the second developer conveying member 43 is disposed in the stirring chamber 41b. At both ends in the longitudinal direction of the partition wall 41c (left side and right side in FIG. 3), communication portions (developer transport paths) 41d and 41e that allow the developer to pass between the developing chamber 41a and the stirring chamber 41b are provided. ing.

  In the present embodiment, the first and second developer conveying members 42 and 43 are both screw-like members (hereinafter referred to as “first screw” and “second screw”, respectively).

  In other words, in the present embodiment, the first and second screws 42 and 43 are provided with spiral blades 42b and 43b as conveying portions around the magnetic material shafts (rotating shafts) 42a and 43a, respectively. Is formed.

  In this embodiment, in addition to the blades 43b, the second screw 43 also has a stirring rib 43c that protrudes in the radial direction from the shaft 43a and has a predetermined width in the developer transport direction. . The rib 43c stirs the developer as the shaft 43a rotates. The first screw 42 agitates and conveys the developer in the developing chamber 41a. In addition, the second screw 43 is configured so that the toner supplied to the replenishing unit by the developer replenishing device 10 under the automatic toner replenishment control (ATR: Auto Toner Replenisher) and the developer already in the stirring chamber 41b. Is stirred and conveyed to make the toner concentration uniform.

  The first and second screws 42 and 43 are disposed substantially in parallel along the rotation axis direction (developing width direction) of the developing sleeve 44. The first screw 43 and the second screw 43 transport the developer in opposite directions along the rotation axis direction of the developing sleeve 44. Thus, the developer is circulated through the developing container 41 by the first and second screws 42 and 43 via the connecting portions 41d and 41e.

  That is, the developer in the developing chamber 41a in which the toner is consumed in the developing process due to the conveying force of the first and second screws 42 and 43 and the toner density is reduced is transferred to one connecting portion 41d (on the left side of FIG. 3). ) To move into the stirring chamber 41b. Further, the developer in the stirring chamber 41b which has been replenished with the toner is moved to the developing chamber 41a via the other connecting portion 41e (the right side of the paper surface in FIG. 3).

  The developing chamber 41a of the developing device 4 is opened at a position corresponding to the developing area facing the photosensitive drum 1, and the developing sleeve 44 can be rotated so as to be partially exposed to the opening of the developing container 41. Is arranged. In the present embodiment, the developing sleeve 44 is made of a nonmagnetic material and rotates in the direction of the arrow shown in the drawing operation. A magnet roll 45 having a plurality of magnetic poles is fixed inside the developing sleeve 44 along the circumferential direction as a magnetic field generating means.

  The developer in the developing chamber 41 a is supplied to the developing sleeve 44 by the first screw 42. A predetermined amount of developer supplied to the developing sleeve 44 is carried on the developing sleeve 44 by a magnetic field generated by the magnet roll 45 to form a developer pool. When the developing sleeve 44 rotates, the two-component developer on the developing sleeve 44 passes through the developer reservoir, the layer thickness thereof is regulated by the regulating blade 46, and the developing component facing the photosensitive drum 1. Be transported. In the developing area, the developer on the developing sleeve 44 spikes to form a magnetic spike. In this embodiment, the electrostatic brush is brought into contact with the photosensitive drum 1 and the toner of the developer is supplied to the photosensitive drum 1 so that the electrostatic image on the photosensitive drum 1 becomes a visible image (toner image). develop. In order to improve the developing efficiency, that is, the application rate of the toner to the latent image, the developing sleeve 44 usually receives a developing bias voltage obtained by superimposing a DC voltage and an AC voltage from a developing bias power source as a voltage applying unit. Applied.

  The developer on the developing sleeve 44 after supplying the toner to the photosensitive drum 1 returns to the developing chamber 41a when the developing sleeve 44 further rotates. The developing device 4 includes a developer discharging device 48 for discharging excess developer upstream of the stirring chamber 41b. The developer discharge device 48 includes a discharge port 48a, an excess developer conveying member 48b, and an excess developer storage portion (not shown). When the developer surface in the developing container reaches a predetermined height or more, excess developer is discharged over the discharge port 48a, and the discharged excess developer is conveyed by the excess developer conveying member 48b. And stored in the excess developer storage section.

  Further, the above-described developing device 4 has a developer replenishing device 10, and a developer container 41 connected to the replenishing developer container 20 has a predetermined ratio of toner and carrier as an initial developer, for example, 220 g of an initial developer in which the weight ratio is mixed with the toner 92 by the carrier 92 is filled. The replenishment developer container 20 may be a cartridge type that can be attached to and detached from the image forming apparatus main body, that is, a replenisher cartridge.

[Supply system]
Next, a replenishment mode that is a feature of the present embodiment will be described. First, the effect and reason of the conventional auto-refresh system will be described again in detail.

  In the auto-refresh system, as described above, unlike the conventional toner replenishment, by supplying and collecting a two-component developer containing a new (New) carrier, the carrier deterioration level is a constant level that can satisfy the development characteristics. Is saturated.

  When toner is consumed by the image forming operation, toner and carrier replenishment developer are supplied into the developing container by the amount of toner consumed by the developer replenishing device 10. However, since the developer in the developing container gradually increases by the amount of the carrier, the developer gradually becomes excessive. If the developer becomes excessive, the height of the developer surface increases, and therefore overflows and is discharged from the discharge port 48a. By repeating this, the New carrier replenished with the toner and the deteriorated carrier in the developing container discharged as the excess developer are exchanged, so that the average deterioration level of the carrier is saturated to a certain level.

  That is, in the auto-refresh system, instead of suppressing deterioration as a single carrier, by repeating supply / discharge of a New carrier and a deteriorated carrier with a certain probability, the average number of times of printing used for printing of all carriers (ie, By limiting the number of sheets (hereinafter referred to as “carrier average number of printed sheets”), carrier deterioration is suppressed.

  Note that the examination results described below support the fact that the average number of printed carriers and the degree of carrier deterioration are in a substantially proportional relationship.

  In this example, “carrier chargeability” is used as a physical property value indicating the degree of carrier deterioration, and the carrier chargeability is measured by the method described below.

  First, a two-component developer that has been subjected to a certain number of printed sheets is separated into a toner and a carrier. As a separation method, in this embodiment, a so-called electric field peeling method is used in which the toner is separated from the carrier by applying an electric field in the toner flying direction while the two-component developer is magnetically constrained by a magnet. . The separated carrier is again mixed with a New toner at a predetermined weight ratio, for example, a weight ratio of 8:92 and stirred for a predetermined time, and then the charge amount of the New toner is measured with E-SPART ANALYZER (manufactured by Hosokawa Micron). To do.

  Here, the measured toner charge amount indicates the charge ability of the carrier alone when a predetermined number of prints are made. Note that the toner charge amount when the durability is originally performed is determined by the durability deterioration of both the toner and the carrier. However, as described above, because the toner charge amount after the durable toner is separated from the two-component developer used for durability and replaced with New toner, the charging ability as a carrier alone during durability is exhibited.

  The reason why the charging ability is used as the degree of carrier deterioration is that “white background fogging” and “toner scattering” that occur remarkably during durability are phenomena that occur when the toner charge amount decreases.

  Using this carrier charge amount, FIG. 4 shows the carrier charge amount decrease amount (decrease amount from the initial charge amount) and the carrier average print number with respect to the number of prints during durability. As the durable print image, a commonly used A4 size 10% image ratio is used.

The 10% image ratio means that the amount of toner used when A4 is all solid is 100% image ratio. In this embodiment, the amount of toner used when A4 is all solid is about 0.4 g and about 10% when the ratio is 10%. .04g. As a developer for replenishment,
(1) a toner-only replenishment developer,
(2) A two-component developer for replenishment with a weight ratio carrier: toner = 20: 80 is used. Further, as described above, the developer filling amount in the developing container is 220 g.

  Next, a method for calculating the average number of printed carriers will be described.

  In auto refresh, the replenishment developer composed of toner and carrier enters the two-component developer in the developer container, so the toner is consumed, so there is no increase or decrease. Discharged as a quantity. That is, the carrier print number 0, that is, a new carrier dg is replenished, and excess dg is discharged from the two-component developer 220g having an average print number X. The average number of printed sheets of the two-component developer (220-d) g that has not been discharged is X + 1.

  By repeating these calculations, a curve of the average number of printed carriers can be obtained. In the case of a toner-only replenishment system, the number of prints and the average number of printed carriers are the same because there is no carrier replacement.

  As a result, it was found that both the above-mentioned replenishment developers (1) and (2) showed a tendency that the carrier average number of printed sheets and the carrier charging ability showed substantially the same tendency with respect to the print durability number. In other words, in the auto-refresh system, it was confirmed that the carrier chargeability is maintained by switching the number of carrier prints to a certain level or less by switching the New carrier / durable carrier.

  In the developing configuration used in this example, fog / toner scattering occurred when the average number of printed sheets of the carrier reached 40 k, that is, when the amount of decrease in the carrier charge amount reached 16 μC / g. (1) In the toner replenishment system, the developer needs to be replaced at this point.

  By the way, although the conventional auto-refresh system has the effects as described above, it cannot be said that the running cost for the exchange carrier, which is a potential problem of the auto-refresh system, is optimized. That is, in the conventional auto-refresh system, in order to maintain the development characteristics, there is a case where even a carrier that does not need to be replaced is replaced. The reason is that in the conventional auto-refresh system, the toner ratio of the developer for replenishment and the carrier ratio are made uniform regardless of the degree of carrier deterioration. Hereinafter, a description will be given with reference to FIG.

  In a conventional auto-refresh system, a replenisher with a constant carrier ratio is used in order to maintain the average number of printed carriers at a saturation level or less. Therefore, in the area (1) in FIG. 5, the carrier must be exchanged before the average number of printed sheets reaches the saturation level. In an extreme example, when the number of printed sheets is 0, the new carrier and the new carrier of the replenishment developer are completely replaced. That is, the carrier exchange in the broken line portion only extends the number of printed sheets until the carrier average printed number of sheets is saturated, and is meaningless from the viewpoint of maintaining the development characteristics.

  Further, in the area (1), the chargeability of the carrier is gradually deteriorating, and the toner charge amount gradually varies accordingly, so that the image density becomes unstable over a long period of time. Will be. This density fluctuation can be dealt with by, for example, known toner density control in which the toner charge amount is kept constant by changing the toner and carrier mixing ratio of the two-component developer. However, downtime occurs for control over a long period of time, which is not desirable from the viewpoint of usability.

  In consideration of the above problem, in this embodiment, two types of supply developers (first supply developer and second supply developer) are used. Then, by appropriately using these replenishment developers depending on the state of deterioration of the carrier in the developing container, it is possible to maintain development characteristics such as white background fog and toner scattering at a level that does not cause a problem in practical use, and is also useless. It becomes possible not to perform carrier exchange.

  The difference between the two types of replenishment developers is the mixing ratio of toner and carrier, and it is important that at least the first replenishment developer has a lower carrier ratio (including zero) than the second replenishment developer. It is. In this embodiment, as an example, the first replenishment developer is toner only, that is, the ratio of toner and carrier is 100: 0 by weight, and the second replenishment developer has a mixing ratio of toner and carrier. The weight ratio is 80:20.

  The toner used for the replenishment developer is the same as the toner of the initial developer, and is a toner that is negatively charged. The carrier used for the replenishment developer is the same as the carrier for the two-component developer previously stored in the developing device. The type of carrier is arbitrary. For example, in this embodiment, a magnetic material dispersion type having a core material in which magnetic fine particles are dispersed in a binder resin and the surface of the core material is coated with a resin. Uses a carrier.

  Next, a replenishment method and effect using the first replenishment developer and the second replenishment developer will be described with reference to FIG.

  In the present embodiment, the first replenishment developer is used and the number of prints reaches the saturation value of the average number of printed carriers until the “saturated value of average number of printed sheets” is reached as shown in the area (1) of FIG. Immediately before, the second supply developer is switched. That is, the developer to be replenished is switched so that the ratio of the carrier with respect to the developer is higher in the later stage of use than in the early stage of use.

  It should be noted that the saturation value of the average number of printed carriers can be estimated to be about 22,000 by the repeated calculation described above.

The two-component developer amount W (220 g in this embodiment) in the developing container, the carrier weight ratio T (20% in this embodiment) in the second replenishment developer, and the print per sheet. The expected average toner amount D to be used (in this embodiment, about 0.04 g). In this case, the saturation value is obtained by dividing the two-component developer Wg by the amount of carrier in the replenishment developer used in one replenishment (expected average toner amount Dg × carrier ratio T / toner ratio 100-T).
Average number of printed carriers = W / (D × (T / (100−T))
= 220 / (0.04 × (20/80)) = 22000
Is equivalent to

  When such replenishment is performed, the carrier average print number increases in proportion to the number of prints in the area (1) of FIG. 6 because there is no carrier replacement. When the carrier average print number reaches 22,000, and the toner is changed to the second replenishment developer with a toner / carrier ratio of 80:20, the carrier average print number is as shown in the area (2) of FIG. Saturates to a constant state.

  In other words, in this embodiment, the same carrier average print number, that is, the degree of carrier deterioration can be maintained as in the conventional auto-refresh system, without changing the carrier from the initial stage to the carrier average print number.

  In FIG. 7, the first replenishment developer and the second replenishment developer were switched according to the saturation value of the average number of printed carriers as described above, printing durability was performed, and the number of durable sheets and the change in carrier charging ability were evaluated. Results are shown. As comparative data, a change in durability-chargeability without changing the carrier ratio of the conventional developer for replenishment is also cited. As a result, as can be seen from FIG. 7, it can be seen that the charging ability changes with the same tendency as the average number of printed carriers, and the charging ability is maintained without causing fogging and toner scattering.

In addition, since the carrier charging performance is stabilized earlier than in the conventional auto-refresh control, good density stability can be realized. The charged developer amount of the first replenishment developer is set so that it is switched to the second replenishment developer just by the average number of printed carriers in order to eliminate useless carrier replacement. That is, in this embodiment, the carrier average print number described above is multiplied by the average toner usage amount D.
Average number of printed carriers x average amount of toner used = W / (D × (T / (100−T)) × D
= W / (T / (100-T))
= 220 / (20/80)
= 880 (g)
It is said.

  The first replenishment developer amount 880 g described here is a value set to eliminate any unnecessary carrier replacement. However, the first replenishment developer amount is 880 g or less. For example, as compared with the conventional auto-refresh system, there are certain advantages in terms of carrier running cost and density stability as described above. For example, when the first replenishment developer container cannot accommodate the above-described 880 g due to space requirements as in a small product, even if the replenishment developer capacity at that time is 500 g, at least Unnecessary carrier exchange can be avoided until 500 g of toner is consumed. For this reason, the advantages described above occur compared to the conventional auto-refresh system.

  Next, a method for switching between the first supply developer and the second supply developer will be described.

  For example, the first replenishment developer is accommodated in the replenisher cartridge included in the product, and is put into the replenishment developer container 20 when the operation of the apparatus is started. The second replenishment developer can be accommodated in the replacement replenisher cartridge after the toner is used up. Of course, when the replenishment developer container 20 itself is a replenisher cartridge, the replenisher cartridge containing the first replenishment developer is mounted on the apparatus main body as a replenishment developer container. Thereafter, after the first supply developer has been used up, a replacement supply cartridge containing the second supply developer is mounted on the apparatus main body.

  Further, as another method for switching between the first supply developer and the second supply developer, as shown in FIG. 9, the supply inside the supply developer container (supply cartridge) 20 as a storage portion is provided. The first replenishment developer is filled on the agent discharge port side, and the second replenishment developer is filled on the side opposite to the replenishment agent discharge port. Then, a configuration may be used in which the developer is switched to the second supply developer after that.

  As another method for switching between the first replenishment developer and the second replenishment developer, as shown in FIG. 10, the replenishment developer container 20 is filled with the second replenishment developer. In addition, the first replenishment developer may be filled in the hopper portion A that connects the replenishment developer container 20 and the developing device 4.

  As described above, according to this embodiment, two types of replenishment developers (first replenishment developer and second replenishment developer) are used, and the deterioration state of the carrier in the developing container That is, depending on the average number of printed sheets of the carrier, these replenishment developers are used properly. With this configuration, it is possible to maintain development characteristics such as white background fog and toner scattering at a level that does not cause a problem in practical use, and to avoid unnecessary carrier replacement. Furthermore, since the carrier charging ability is brought to a stable state faster than the conventional auto-refresh control, good density stability can be realized.

Example 2
Next, another embodiment of the image forming apparatus of the present invention will be described. Since the basic configuration of the image forming apparatus is the same as that of the image forming apparatus 100 of the first embodiment, elements having substantially the same or corresponding functions and configurations as those of the first embodiment are denoted by the same reference numerals. Detailed description will be omitted, and only the components specific to this embodiment will be described in detail.

  In Example 1, only the toner is used as the first replenishment developer. However, if the carrier ratio (that is, the carrier content) is lower than that of at least the second replenishment developer, the same effect as in Example 1 can be obtained. I can expect.

  For example, the first replenishment developer has a toner / carrier ratio of 95: 5, the second replenishment developer has a toner / carrier ratio of 80:20 as in Example 1, and the average number of printed sheets is 22,000. The first supply developer and the second supply developer may be switched.

  In this case, the carrier average print number shows a curve as shown in FIG. The area up to (1) in FIG. 8 increases toward the number of sheets that saturates when the first supply developer (T / C ratio = 95: 5) is continuously used. However, when the carrier average print number reaches 22,000, switching to the second replenishment developer causes the carrier average print number to saturate to a constant state as shown in area (2) of FIG. For this reason, problems such as fogging do not occur for the reason described in the first embodiment.

  In order to optimize the running cost, it is desirable to set the first replenishment developer having no wasteful carrier replacement at the end of durability to a toner ratio of 100%. However, if the carrier ratio in the replenishment developer is suddenly changed depending on the type of developer, the flowability of the replenishment developer may fluctuate and the replenishment performance may not be stable. In this case, it is preferable to prioritize stabilization of the replenishment performance even if the merit of running cost reduction is somewhat lost.

  For the above reason, in Example 2, the carrier ratio of the first supply developer is slightly close to the carrier ratio of the second supply developer.

  As described above, according to the second embodiment of the present invention, substantially the same effect as that of the first embodiment can be obtained, and stable even when the first supply developer is switched to the second supply developer. It becomes possible to realize the replenishment performance.

  In the above embodiment, the case where the present invention is applied to a tandem type intermediate transfer color image forming apparatus has been described. However, the present invention is not limited to this. The principle of the present invention can be applied to various image forming apparatuses known to those skilled in the art, and may be a monochrome image forming apparatus.

1 Image carrier (photosensitive drum)
2 Charging Device 3 Exposure Device 4 Developing Device 10 Developer Replenishing Device 20 Replenishing Developer Container 41 Developing Container 44 Developing Sleeve (Developer Carrier)
45 Magnet Roll 48 Developer Discharge Device 48a Discharge Port 48b Excess Developer Conveying Member 100 Image Forming Device 100A Image Forming Device Body

Claims (3)

An image carrier, a developing device that develops a latent image formed on the image carrier into a toner image using a developer having toner and a carrier, and a discharge port that is provided in the developing device and discharges the developer And an image forming apparatus having a replenishing device for replenishing developer to the developing device,
2. An image forming apparatus according to claim 1, wherein the developer replenished from the replenishing device has a higher carrier-to-developer ratio in the late use than in the early use. An image carrier, a developing device that develops a latent image formed on the image carrier into a toner image using a developer having toner and a carrier, and a discharge port that is provided in the developing device and discharges the developer And an image forming apparatus having a replenishing device for replenishing developer to the developing device,
2. An image forming apparatus according to claim 1, wherein the developer replenished from the replenishing device is toner only at an early stage of use, and a developer having toner and a carrier at a later stage of use.   The replenishing device has a housing portion that houses a developer that replenishes the developer to the developing device, and a replenisher discharge port for replenishing the developer from the housing portion, and the first replenishing developer is The second replenishment developer housed on the replenisher discharge port side and having a carrier content higher than that of the first replenishment developer is a replenisher discharge port inside the replenishment developer container. The image forming apparatus according to claim 1, wherein the image forming apparatus is accommodated on the opposite side.