JP2005148356A - Image forming apparatus and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain satisfactory image quality in an image forming apparatus that forms a color image through the superimposition of toner images of a plurality of colors on an intermediate transfer body, by restraining changes in conditions (primary transfer conditions) under which the toner images of the respective colors are transferred to the intermediate transfer body and also restraining changes in conditions (secondary transfer conditions) under which the color image is transferred from the intermediate transfer medium. <P>SOLUTION: A carrier quantity adjustment unit 80 includes squeeze rollers 81 to 83 and application rollers 881 and 882 and is disposed on and opposite an intermediate transfer belt 41 for each color. The squeeze rollers 81 to 83 scrape liquid carrier from liquid developer on the intermediate transfer belt 41, whereas the application rollers 881 and 882 apply liquid carrier onto the intermediate transfer belt 41. Thereby the quantity of liquid carrier in the liquid developer on the intermediate transfer belt 41 is adjusted. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electrophotographic image forming technique such as a printer, a copying machine, and a facsimile machine, and more particularly to an image forming technique that employs wet development as a developing method.

  Conventional electrophotographic image forming apparatuses include the following. A charged photosensitive member (latent image carrier) is exposed by an exposure unit to form an electrostatic latent image on the photosensitive member, and toner is attached to the photosensitive member by a developing unit to visualize the electrostatic latent image. Thus, a toner image is formed, and the toner image is primarily transferred onto an intermediate transfer medium such as an intermediate transfer belt or an intermediate transfer drum. The toner image on the intermediate transfer medium is conveyed to a secondary transfer position and secondarily transferred to a recording medium such as transfer paper. Here, as a developing method of the developing means, a wet developing method using a developer in which toner is dispersed in a liquid carrier is known. This wet development system has the advantages that the average particle diameter of the toner is as small as 0.1 to 2 μm, so that a high-resolution image can be obtained, and a uniform image can be obtained because of the high fluidity of the liquid. Therefore, various image forming apparatuses have been proposed (see, for example, Patent Document 1). This apparatus improves image quality by removing excess developer, particularly a liquid carrier, from the intermediate transfer medium before transferring the developed developed image (toner image) to a recording medium such as a transfer material. It is a thing.

JP 2002-296918 A (paragraph [0027], FIG. 1)

  By the way, for example, when images having a high image occupying ratio, which is the ratio of the image portion in the electrostatic latent image, are continuously formed, a large amount of toner adheres to the photoconductor, so that the liquid carrier that moves to the photoconductor is small. Conversely, when images with a low image occupation rate are continuously formed, only a small amount of toner adheres to the photoconductor, so that the number of liquid carriers that move to the photoconductor increases compared to when the image occupation rate is high. As described above, the amount of the liquid carrier contained in the developer that moves to the photoconductor greatly varies depending on the image occupancy rate. In particular, in a color image forming apparatus, the level of image occupancy varies for each color, so the amount of liquid carrier that moves to the photoreceptor varies for each color.

  However, the apparatus described in the above-mentioned conventional patent document 1 simply applies a liquid carrier according to the type of transfer material before secondary transfer of the visible image (toner image) transferred onto the intermediate transfer medium to the transfer material. However, the removal amount is not adjusted according to the amount of liquid carrier adhering to the toner image primarily transferred onto the intermediate transfer medium for each color. As a result, when the toner image of a predetermined color is primarily transferred onto the intermediate transfer medium and then the toner image of the next color is primarily transferred and superimposed, the amount of liquid carrier on the intermediate transfer medium varies. As a result, the primary transfer conditions may vary, making it difficult to perform suitable transfer. Further, it is conceivable that the secondary transfer conditions change due to the change in the amount of liquid carrier on the intermediate transfer medium, making it difficult to transfer the toner image onto the recording medium. Therefore, in order to obtain good image quality, it is an important issue to adjust the amount of liquid carrier attached to each color toner image for each color.

  The present invention has been made in view of the above problems, and in an image forming apparatus that forms a color image by superimposing a plurality of color toner images on an intermediate transfer medium, the transfer condition (1 And an image forming apparatus capable of obtaining good image quality by suppressing variations in color image transfer conditions (secondary transfer conditions) from an intermediate transfer medium while suppressing variations in secondary transfer conditions) The purpose is to do.

  In order to achieve the above object, according to a first aspect of the present invention, a developer in which toners of different N colors (where N ≧ 2 is a natural number) are dispersed in a liquid carrier for each color is used. A toner image is formed by developing the electrostatic latent images on N latent image carriers that are provided for each color corresponding to the toner and on which the electrostatic latent images can be carried, In the image forming apparatus for forming a color image by transferring the N color toner image onto the intermediate transfer medium in a predetermined order, the toner image on the latent image carrier is the intermediate image. An adjustment unit that adjusts the amount of liquid carrier contained in the uppermost attached developer that adheres to the intermediate transfer medium each time it is transferred to the transfer medium, and the toner on the intermediate transfer medium and the liquid carrier by the adjustment unit The ratio of It is characterized in that which enables us.

  In the invention (image forming apparatus) configured in this way, the intermediate transfer medium is already transferred before the toner image is primarily transferred for the M-th (2 ≦ M ≦ N) toner color among the N toner colors. The ratio of the toner in the developer of the (M-1) th toner color adhering to the liquid and the liquid carrier is adjusted. Then, the toner image of the Mth toner color is primarily transferred onto the intermediate transfer medium having such a ratio adjusted. Therefore, fluctuations in transfer conditions during primary transfer of the Mth toner image to the intermediate transfer medium are suppressed, and primary transfer processing can be performed satisfactorily and stably.

  Further, after primary transfer of each color, the ratio of the toner in the developer and the liquid carrier is adjusted for the toner color. That is, the above ratio is adjusted for all toner colors, and as a result, the ratio between the toner and the liquid carrier is adjusted even when viewed in the entire color image. Therefore, since the ratio of the color image is also adjusted in this way, fluctuations in the transfer conditions during the secondary transfer of the color image are reliably suppressed, and the secondary transfer process can be performed satisfactorily and stably.

  According to a second aspect of the present invention, each color corresponding to the N color toner is obtained by using a developer in which toners of different N colors (where N ≧ 2 is a natural number) are dispersed in a liquid carrier for each color. The electrostatic latent images on N latent image carriers that are provided on each surface and can carry electrostatic latent images are developed to form toner images, and the N color toner images In an image forming apparatus that forms a color image by superimposing images on the intermediate transfer medium by transferring them to the intermediate transfer medium in a predetermined order, the amount of liquid carrier contained in the attached developer adhering to the latent image carrier And adjusting the ratio of the toner and the liquid carrier on the latent image carrier by the adjusting means.

  Further, according to the third aspect of the present invention, an electrostatic latent image can be carried on the surface of a developer using N different color toners (however, a natural number of N ≧ 2) dispersed in a liquid carrier for each color. The electrostatic latent image on the latent image carrier is developed for each color to form a toner image, and the process of transferring the toner image onto the intermediate transfer medium at the transfer position is repeated for N colors. In an image forming apparatus that forms a color image by superimposing the N-color toner image on the intermediate transfer medium, an attached developer that adheres to the latent image carrier before transferring the toner image to the intermediate transfer medium Adjusting means for adjusting the amount of the liquid carrier contained in the toner, and the ratio of the toner and the liquid carrier on the latent image carrier can be controlled by the adjusting means.

  In the invention (image forming apparatus) configured as described above, for any toner color, a developer that forms a toner image formed on the latent image carrier before the primary transfer, that is, an attached developer. The ratio between the toner inside and the liquid carrier is adjusted. Then, the developer whose ratio has been adjusted moves to the intermediate transfer medium while the toner image in the developer is primarily transferred. Accordingly, the developer whose ratio is adjusted moves to the intermediate transfer medium and the toner image in the developer is primarily transferred, so that fluctuations in the primary transfer conditions are suppressed and primary transfer is suppressed. The treatment can be performed satisfactorily and stably.

  For each color, the ratio of the toner in the developer to the liquid carrier is adjusted on the latent image carrier before the primary transfer. Therefore, even when the entire color image formed by superimposing these toner images is viewed, the ratio between the toner and the liquid carrier is adjusted on the intermediate transfer medium. As a result, fluctuations in transfer conditions during secondary transfer of a color image are reliably suppressed, and secondary transfer processing can be performed satisfactorily and stably.

  In order to achieve the above object, the image forming method according to the present invention uses, for each color, a developer in which toners of different N colors (where N ≧ 2 is a natural number) are dispersed in a liquid carrier for each color. A developing process for forming an N-color toner image by developing an electrostatic latent image on the latent image carrier, and the intermediate transfer by transferring the N-color toner image onto an intermediate transfer medium in a predetermined order. A transfer step of superimposing N-color toner images on the medium; and an adjustment step of adjusting the amount of liquid carrier contained in the developer constituting the toner image for each color, and forming the toner image in the adjustment step It is characterized in that the ratio between the toner and the liquid carrier in the developer can be controlled.

  In the invention configured as described above (image forming method), the adjustment step is to adjust the ratio of the toner in the developer and the liquid carrier constituting each toner image. Either before primary transfer or after primary transfer to transfer the image to the intermediate transfer medium. Here, when the adjustment process is executed after the primary transfer, as in the above-described invention relating to the “first aspect”, when the M-th toner image is primarily transferred, it is already attached to the intermediate transfer medium. The ratio of the toner in the developer of the (M-1) th toner color and the liquid carrier is adjusted. Then, the toner image of the Mth toner color is primarily transferred onto the intermediate transfer medium having such a ratio adjusted. Therefore, fluctuations in transfer conditions during primary transfer of the Mth toner image to the intermediate transfer medium are suppressed, and primary transfer processing can be performed satisfactorily and stably. On the other hand, when the adjustment step is executed before the primary transfer, the ratio-adjusted development is performed for the intermediate transfer medium, as in the inventions according to the “second aspect” and the “third aspect”. As the liquid moves, the toner image in the developer is primarily transferred, and therefore, the primary transfer process can be performed satisfactorily and stably by suppressing fluctuations in the primary transfer conditions.

  Further, when viewed as a whole color image formed on the intermediate transfer medium as described above, the ratio of the toner and the liquid carrier is adjusted on the intermediate transfer medium. As a result, fluctuations in transfer conditions during secondary transfer of a color image are reliably suppressed, and secondary transfer processing can be performed satisfactorily and stably.

  One aspect of the adjusting means includes an applying member configured to be able to apply a liquid carrier to the attached developer, and the liquid contained in the attached developer by controlling the amount of liquid carrier applied by the applying member. The carrier amount is adjusted. According to this configuration, for example, when the toner concentration of the developer adhering to the intermediate transfer medium (or latent image carrier) increases with respect to a predetermined value, the liquid carrier is applied so that the toner concentration is predetermined. Decrease to become value. Thereby, the fluctuation | variation of transfer conditions is suppressed and favorable image quality can be obtained.

  Further, the applying member is disposed at a contact position in contact with the attached developer, thereby providing a liquid carrier to the attached developer, wherein the adjusting unit is configured to transport the attached developer. A plurality of application members arranged opposite to each other, and at least one of the application members is between the contact position and a separation position that is separated from the attached developer and does not apply a liquid carrier. The application amount may be controlled by controlling a combination of application members arranged at the contact position by position control of the application member configured to be movable. According to this configuration, at least one of the plurality of application members arranged for each color is configured to be movable between the contact position and the separation position, and by position control of the application member configured to be movable. Since the combination of the application members disposed at the contact position is controlled, the amount of liquid carrier applied for each color can be easily controlled by controlling the combination, for example, by increasing or decreasing the number of application members disposed at the contact position, and It can be done reliably.

  In addition, when the application amount is controlled by changing the relative speed of the contact surface of the application member with respect to the attached developer, the color is supplied from the application member for each color by changing the relative speed to a large value or a small value. The amount of liquid carrier to be controlled can be controlled, whereby the amount of liquid carrier applied for each color can be controlled easily and reliably.

  Another aspect of the adjusting means includes a stripping member configured to be disposed at a contact position in contact with the attached developer, and stripping off a liquid carrier on a surface layer of the developer by being disposed at the contact position. The amount of liquid carrier contained in the attached developer is adjusted by controlling the amount of liquid carrier removed by the stripping member. According to this configuration, the stripping member is arranged at the contact position for each color, and when contacting the attached developer constituting each color toner image, the liquid carrier on the surface layer of the developer adheres to the stripping member, and the liquid A part of the carrier is peeled off, but the amount of liquid carrier contained in the attached developer is adjusted by controlling the amount of peeling. For example, when the toner concentration of the developer adhering to the intermediate transfer medium (or latent image carrier) is reduced from a predetermined value, the liquid carrier is peeled off to increase the toner concentration to a predetermined value. To do. Thereby, the fluctuation | variation of transfer conditions is suppressed and favorable image quality can be obtained.

  Further, the adjusting means includes, as the peeling member, a plurality of peeling members that are arranged opposite to each other in the transport direction of the attached developer, and at least one of the plurality of peeling members is the A combination of a stripping member that is configured to be movable between a contact position and a separated position that is not in contact with the adhered developer, and is in contact with the adhered developer by controlling the position of the stripped member configured to be movable. The stripping amount may be controlled by controlling. According to this configuration, at least one of the plurality of stripping members arranged for each color is configured to be movable between the contact position and the separation position, and the position of the stripping member configured to be movable is configured. Since the combination of the stripping members that come into contact with the attached developer is controlled by the control, the amount of the liquid carrier stripped for each color can be controlled by controlling the combination, for example, by increasing or decreasing the number of stripping members arranged at the contact position. Control can be performed easily and reliably.

  Further, when the stripping amount is controlled by changing the relative speed of the contact surface of the stripping member with respect to the attached developer, the relative speed is stripped for each color by changing to a large value or a small value. The amount of liquid carrier adhering to the member can be controlled, whereby the amount of liquid carrier peel-off for each color can be controlled easily and reliably.

  Further, N containers for storing developers in which toners of different N colors (where N ≧ 2 is a natural number) are dispersed in a liquid carrier for each color and the liquid carrier removed by the stripping member are stripped off. A cleaning member that is removed from the member, and a recovery unit that recovers the liquid carrier removed by the cleaning member and returns it to the container that stores the developer of the same color as the attached developer may be further provided. . According to this configuration, the liquid carrier can be effectively used by removing the liquid carrier peeled off by the peeling member from the peeling member and returning it to the container.

  The recovery means is provided below the contact position of the cleaning member to the stripping member, and recovers the liquid carrier that is removed by the cleaning member and freely falls, and the recovery unit And a communication part that communicates with the container, and the liquid carrier recovered by the recovery part via the communication part may be returned to the container. According to this configuration, since the liquid carrier removed from the stripping member by the cleaning member is freely dropped and collected in the collection unit and returned to the container for storing each color developer, the liquid carrier is separately removed. Therefore, it is not necessary to provide a recovery device in the recovery unit, and the configuration of the device can be simplified.

  Further, the amount of liquid carrier contained in the attached developer may be adjusted so that the toner concentration of the attached developer remaining after the adjustment of the amount of liquid carrier by the adjusting means approaches a predetermined value. According to this configuration, for example, after the toner image of a predetermined color is primarily transferred onto the intermediate transfer medium, the amount of the liquid carrier contained in the developer that constitutes the toner image is adjusted. The toner density of the developer remaining on the intermediate transfer medium is always maintained at a value close to a predetermined value. Therefore, it is possible to suppress fluctuations in transfer conditions (primary transfer conditions) for primary transfer of the next color toner image. As a result, it is possible to prevent image disturbance during transfer. In addition, by adjusting the amount of liquid carrier contained in the developer constituting each color toner image, the toner concentration of the developer at the time of transfer to the recording medium is maintained at a predetermined value. Therefore, it is possible to suppress fluctuations in transfer conditions (secondary transfer conditions) from the intermediate transfer medium to the recording medium.

  The adjusting unit may adjust the amount of liquid carrier on the intermediate transfer medium in accordance with image information related to the toner image. As a result, the amount of liquid carrier is adjusted for each color in accordance with image information related to the toner image, so that fluctuations in transfer conditions can be suppressed and good image quality can be obtained. When the image information is obtained as an image occupancy ratio that is a ratio of the image portion in the electrostatic latent image and the liquid carrier amount contained in the attached developer is adjusted according to the image occupancy ratio, Since the occupation ratio is a value corresponding to the toner concentration in the developer on the latent image carrier, the liquid carrier amount can be easily adjusted according to the toner concentration without detecting the toner concentration. . As a result, fluctuations in the transfer conditions are reliably suppressed, and good image quality can be obtained.

<First Embodiment>
FIG. 1 is a diagram showing an internal configuration of a printer which is a first embodiment of an image forming apparatus according to the present invention, FIG. 2 is an enlarged view of a main part of FIG. 1, and FIG. 3 is a block diagram showing an electrical configuration of the printer. is there. This image forming apparatus is a so-called tandem type color printer, and the four-color photoconductors of yellow (Y), magenta (M), cyan (C), and black (K) are used as the “latent image carrier” of the present invention. 11Y, 11M, 11C, and 11K are arranged in the apparatus main body 2 side by side. This printer employs a wet development system to form a full-color image by superimposing the toner images on the photoconductors 11Y, 11M, 11C, and 11K, or a monochrome image using only a black (K) toner image. Is formed. In this printer, when a print command signal including an image signal is given to the main control unit 100 from an external device such as a host computer, the engine control unit 110 causes each part of the engine unit 1 to respond to the control signal from the main control unit 100. The image corresponding to the image signal is printed out on the recording medium 4 such as transfer paper, copy paper, and OHP paper conveyed from the paper feed cassette 3 disposed in the lower part of the apparatus main body 2.

  The engine unit 1 corresponds to each of the four photoconductors 11Y, 11M, 11C, and 11K arranged in parallel along the circumferential direction 47 of the intermediate transfer belt 41 corresponding to the “intermediate transfer medium” of the present invention. A charging unit 12, an exposure unit 20, a developing unit 30 (30Y, 30M, 30C, and 30K) and a cleaning unit 14 are provided. Each of the developing units 30Y, 30M, 30C, and 30K includes a tank 33 (33Y, 33M, 33C, and 33K) that stores a developer 32 in which each color toner is dispersed. Note that the configurations of the charging unit 12, the exposure unit 20, the developing unit 30, and the cleaning unit 14 are the same for all toner colors. Therefore, here, the configuration relating to yellow will be described, and the other toner colors will be denoted by the same or corresponding symbols, and description thereof will be omitted.

  As shown in FIG. 2, the photoconductor 11Y is provided so as to be rotatable in the direction of the arrow (clockwise in the figure). A charging unit 12, a developing roller 31, a charge eliminating unit (not shown) and a cleaning unit 14 are disposed around the photoconductor 11Y along the rotation direction. A surface area between the charging unit 12 and the developing position 16 (described later) is an irradiation area of the light beam 21 from the exposure unit 20. In this embodiment, the charging unit 12 includes a charging roller, and a charging bias is applied from the charging bias generation unit 111 to uniformly charge the outer peripheral surface of the photoreceptor 11Y to a predetermined surface potential Vd (for example, Vd = DC + 600V). It has a function as a charging means.

  A light beam 21 formed by a laser, for example, is irradiated from the exposure unit 20 toward the outer peripheral surface of the photoreceptor 11Y uniformly charged by the charging unit 12. The exposure unit 20 exposes the photoconductor 11Y by the light beam 21 in accordance with a control command given from the exposure control unit 112, and forms a yellow electrostatic latent image corresponding to the image signal on the photoconductor 11Y. Thus, it has a function as an exposure means. For example, when a print command signal including an image signal is given from an external device such as a host computer to the CPU 101 of the main control unit 100 via the interface 102, the CPU 113 controls the exposure control unit in response to a command from the CPU 101 of the main control unit 100. A control signal corresponding to the image signal is output to 112 at a predetermined timing. Then, in response to a control command from the exposure control unit 112, the light beam 21 is irradiated from the exposure unit 20 to the photoconductor 11Y, and an electrostatic latent image for yellow corresponding to the image signal is formed on the photoconductor 11Y. . When a patch image is formed as necessary, a control signal corresponding to a patch image signal of a predetermined pattern (for example, a solid image, a fine line image, a white line image, etc.) set in advance is controlled from the CPU 113. A yellow electrostatic latent image corresponding to the pattern is given to the portion 112 and formed on the photoconductor 11Y.

  The yellow electrostatic latent image formed in this way is visualized by yellow toner supplied from the developing roller 31 of the developing unit 30Y (developing step). In addition to the developing roller 31, the developing unit 30Y stores a tank 33Y that stores a developer 32 in which yellow toner is dispersed, and a coating roller 34 that pumps the developer 32 stored in the tank 33Y and applies it to the developing roller 31. And a regulating blade 35 that uniformly regulates the thickness of the developer layer on the application roller 34 and a cleaning blade 36 that removes the developer remaining on the developing roller 31 after supplying the toner to the photoreceptor 11Y. ing. The developing roller 31 rotates at a peripheral speed substantially equal to that of the photoconductor 11Y in the direction of following the photoconductor 11Y (counterclockwise in FIG. 2). On the other hand, the application roller 34 rotates in the same direction as the developing roller 31 (counterclockwise in the figure) at a peripheral speed of about twice.

  In the present embodiment, the developer 32 is a toner composed of a color pigment, an adhesive such as an epoxy resin that adheres the color pigment, a charge control agent that gives a predetermined charge to the toner, a dispersant that uniformly disperses the color pigment, and the like. Is dispersed in a liquid carrier. In this embodiment, for example, a silicone oil such as polydimethylsiloxane oil is used as the liquid carrier, and the toner concentration is 5 to 40% by weight. 2% by weight). The type of the liquid carrier is not limited to silicone oil, and the viscosity of the developer 32 is determined by the liquid carrier to be used, each material constituting the toner, the toner concentration, etc. In this embodiment, For example, the viscosity is 50 to 6000 mPa · s.

  In this embodiment, the distance between the photoconductor 11Y and the developing roller 31 (development gap = thickness of the developer layer) is set to, for example, 5 to 40 μm, and the development nip distance (the developer layer is the photoconductor 11Y and the developing roller 31). In this embodiment, the distance in the circumferential direction in contact with both is set to 5 mm, for example. In the case of the low-concentration developer described above, a development gap of 100 to 200 μm is required to increase the amount of toner, and in this embodiment using a high-concentration developer, the development gap can be shortened. Accordingly, the moving distance of the toner moving in the developer by electrophoresis is shortened, and a higher electric field is generated even when the same developing bias is applied, so that the developing efficiency can be improved and the developing can be performed at a high speed. It will be possible.

  In the developing unit 30Y having such a configuration, the developer 32 stored in the tank 33Y is pumped up by the application roller 34, and the thickness of the developer layer on the application roller 34 is uniformly regulated by the regulation blade 35. The developing solution 32 adheres to the surface of the developing roller 31 and is transported to the developing position 16 facing the photoconductor 11Y as the developing roller 31 rotates. For example, the toner in the developer is positively charged by the action of a charge control agent or the like.

  Then, the developing solution carried on the developing roller 31 at the developing position 16 is supplied from the developing roller 31 and adheres to the photoreceptor 11Y, and a developing bias Vb (for example, Vb) applied to the developing roller 31 from the developing bias generator 114. = DC + 400V), the yellow toner moves from the developing roller 31 to the photoreceptor 11Y, and the yellow electrostatic latent image is visualized. Further, the developer remaining on the developing roller 31 without adhering to the photoreceptor 11Y is scraped off by the cleaning blade 36 and returns to the tank 33Y by its own weight. Thus, in this embodiment, the tank 33 corresponds to the “container” of the present invention.

  The yellow toner image formed on the photoreceptor 11Y as described above is conveyed to the primary transfer position 42Y facing the primary transfer roller 53Y as the photoreceptor 11Y rotates. The primary transfer roller 53Y is disposed so as to sandwich the intermediate transfer belt 41 with the photoreceptor 11Y. The intermediate transfer belt 41 is stretched around a plurality of rollers 43 to 46, and is in contact with the photoconductor 11Y in a direction 47 (counterclockwise in FIG. 1) that is driven by the photoconductor 11Y by a drive motor (not shown). Drive around at the same peripheral speed. When a primary transfer bias (for example, DC-400 V) is applied from the transfer bias generator 115, the yellow toner image on the photoreceptor 11Y is primarily transferred to the intermediate transfer belt 41 at the primary transfer position 42Y ( Transfer process). The residual charge on the photoconductor 11Y after the primary transfer is removed by a charge removal unit such as an LED, and the residual developer is removed by a cleaning unit 14.

  The other toner colors are configured in the same manner as yellow (Y), and a toner image corresponding to the image signal is formed. The yellow (Y), magenta (M), cyan (C), and black (K) toner images formed on the photoconductors 11Y, 11M, 11C, and 11K are primary transfer rollers 53Y, 53M, and 53C. , 53K and primary transfer positions 42Y, 42M, 42C, and 42K, respectively, are superimposed on the surface of the intermediate transfer belt 41 to form a full-color toner image.

  Here, a part of the liquid carrier adhering to each of the toner images and the photoreceptors 11Y, 11M, 11C, and 11K on the intermediate transfer belt 41 is also moved to the intermediate transfer belt 41. It is conveyed with the rotation of the belt 41. In order to adjust the amount of liquid carrier on the intermediate transfer belt 41, a carrier amount adjustment unit 80, which will be described later, is disposed facing the intermediate transfer belt 41 for each color.

  The toner image formed on the intermediate transfer belt 41 is conveyed to a secondary transfer position 49 sandwiched between rollers 45 and 48 as the intermediate transfer belt 41 rotates. On the other hand, the recording medium 4 accommodated in the paper feed cassette 3 (FIG. 1) is conveyed to the secondary transfer position 49 by a conveyance unit 70 described later in synchronization with the conveyance of the primary transfer toner image. The roller 48 rotates in the direction of following the intermediate transfer belt 41 (clockwise in FIG. 1) at the same peripheral speed as the intermediate transfer belt 41, and a secondary transfer bias is applied from the transfer bias generator 115. Then, the toner image on the intermediate transfer belt 41 is secondarily transferred to the recording medium 4. In this embodiment, since roller transfer is adopted, the transfer condition can be set by constant voltage control, or the transfer condition can be set by constant current control. Further, instead of roller transfer, transfer may be performed by corona discharge. In this case, transfer conditions can be set by controlling the output of corona discharge. The residual developer on the intermediate transfer belt 41 after the secondary transfer is removed by the cleaning unit 51.

  The recording medium 4 onto which the toner image has been secondarily transferred as described above is conveyed along a predetermined conveying path 5 (the chain line in FIG. 1), and the toner image is fixed to the recording medium 4 by the fixing unit 60. Then, it is discharged to a discharge tray provided at the upper part of the apparatus main body 2. The fixing unit 60 includes a heating roller 61 incorporating a heater 61 h and a pressure roller 62 that contacts the heating roller 61. The heater controller 116 controls the operation of the heater 61h, so that the fixing temperature in the fixing unit 60 can be adjusted to an arbitrary temperature.

  In the image forming apparatus according to this embodiment, a transport unit 70 for transporting the recording medium 4 along a predetermined transport path 5 is provided. As shown in FIG. 1, the transport unit 70 is provided with a paper feed roller 71 corresponding to the paper feed cassette 3, and the recording medium 4 accommodated in the paper feed cassette 3 is received by the paper feed roller 71. Each sheet is taken out and conveyed to the feed roller 72. The feed roller 72 transports the recording medium 4 to the gate roller 73 and temporarily stands by at the gate roller position. Then, as described above, the gate roller 73 is driven at the timing corresponding to the secondary transfer operation, and the recording medium 4 is sent to the secondary transfer position 49. Further, on the discharge tray side, a pre-discharge roller 74, a discharge roller 75, and a reverse roller 76 are provided, and the secondary transferred recording medium 4 passes through the fixing unit 60, the pre-discharge roller 74, and the discharge roller 75. It is conveyed to the discharge tray side.

  Here, in order to perform double-sided printing, it is necessary to reverse the recording medium 4 and transport it to the gate roller 73 again, so that the discharge roller 75 can rotate forward and backward. That is, when the recording medium 4 is directly discharged to the discharge tray, the recording medium 4 continues to rotate forward and is completely conveyed to the discharge tray. On the other hand, when reversing and refeeding, when the rear end of the recording medium 4 reaches a predetermined position between the pre-discharge roller 74 and the discharge roller 75, the discharge roller 75 rotates reversely to reverse the recording medium 4. Feed into roller 76. As a result, the recording medium 4 is conveyed to the refeed intermediate roller 77 along the reverse path 5a. Then, the re-feed intermediate roller 77 and the pre-re-feed gate roller 78 transport the recording medium 4 to the gate roller 73 and temporarily stand by at the gate roller position. In this way, reverse refeeding of the recording medium 4 is performed.

  Next, the configuration of the carrier amount adjustment unit 80 will be described. A carrier amount adjustment unit 80 is disposed to face the intermediate transfer belt 41 for each color of yellow (Y), magenta (M), cyan (C), and black (K). That is, four carrier amount adjustment units 80 are provided, and these four units (80Y, 80M, 80C, 80K) are respectively disposed between the primary transfer position 42Y and the primary transfer position 42M on the intermediate transfer belt 41. Between the primary transfer position 42M and the primary transfer position 42C, between the primary transfer position 42C and the primary transfer position 42K, and between the primary transfer position 42K and the secondary transfer position 49. Yes. Note that the carrier amount adjustment unit 80 provided for each color has the same basic configuration except that the toner color is different. Therefore, here, the carrier amount adjustment unit 80Y for yellow (Y) will be described in detail, and the carrier amount adjustment unit 80 for the other colors will be given the same or corresponding reference numerals and description thereof will be omitted.

  FIG. 4 is a diagram illustrating the configuration of the carrier amount adjustment unit. The carrier amount adjustment unit 80Y removes the liquid carrier from the yellow developing solution 32 adhering to the intermediate transfer belt 41 or applies the liquid carrier to the intermediate transfer belt 41, thereby providing the liquid carrier amount on the intermediate transfer belt 41. Is to adjust. Thereby, the ratio of the toner and the liquid carrier in the developer on the intermediate transfer belt 41 can be controlled. In this carrier amount adjusting unit 80Y, the squeegee rollers 81, 82, 83 are provided as “peeling members” for removing the liquid carrier from the developer 32 adhering to the intermediate transfer belt 41, and the applying roller 881. , 882 are provided as “applying members” for applying a liquid carrier to the intermediate transfer belt 41. Thus, in this embodiment, the carrier amount adjustment unit 80 corresponds to the “adjustment means” of the present invention.

  The squeegee rollers 81 to 83 are arranged along the moving direction (developer transport direction) 47 of the intermediate transfer belt 41 and opposed to the intermediate transfer belt 41. The squeegee rollers 81 to 83 are supported so as to be movable in the contact / separation direction with respect to the intermediate transfer belt 41. That is, for example, when actuators 91, 92, and 93 (FIG. 3) made of solenoids or motors are driven by the contact / separation drive unit 118 (FIG. 3), the squeegee rollers 81 to 83 are in contact positions (in FIG. 4). , A solid line) and a reciprocating movement between a separated position (broken line in FIG. 4). The contact position is a position where the squeegee rollers 81 to 83 are in contact with the developer carried on the intermediate transfer belt 41, and the separation position is a position where the squeegee rollers 81 to 83 are not in contact with the developer.

  Further, the squeegee rollers 81 to 83 are driven in the direction of following the intermediate transfer belt 41 (in FIG. Around the intermediate transfer belt 41. Accordingly, the squeegee rollers 81 to 83 peel off the liquid carrier from the intermediate transfer belt 41 by contacting the liquid carrier on the surface layer of the developer 32 that is disposed at the contact position and is carried on the surface of the intermediate transfer belt 41. . The liquid carrier stripping operation by the squeegee rollers 81 to 83 will be described in detail later.

  The cleaning blade 84 is in contact with the squeegee rollers 81 to 83, and the liquid carriers peeled off from the intermediate transfer belt 41 by the squeegee rollers 81 to 83 are scraped off by the cleaning blade 84, respectively, from the squeegee rollers 81 to 83. Removed. Here, a receiving tray 85 for collecting the liquid carrier is installed below the position where each cleaning blade 84 contacts the squeegee rollers 81 to 83, and the liquid removed from the squeegee rollers 81 to 83 by the cleaning blade 84. The carrier is naturally dropped and collected in the tray 85. The recovered liquid carrier may be discarded, but it may be configured so as to be returned to the tank 33Y in order to effectively use the liquid carrier.

  In this case, the receiving liquid 85 and the tank 33Y are communicated with each other via the pipe 86, whereby the recovered liquid carrier flows down by its own weight via the pipe 86 and is returned to the tank 33Y. The return amount of the liquid carrier to be returned to the tank 33Y can be adjusted by opening and closing an on-off valve 87 provided in the pipe 86, and a part or all of the recovered liquid carrier is returned to the tank 33Y. Thus, in this embodiment, the tray 85 corresponds to the “recovery part” of the present invention, and the pipe 86 corresponds to the “communication part” of the present invention.

  Next, the configuration of the applying rollers 881 and 882 will be described. Like the squeegee rollers 81 to 83, the applying rollers 881 and 882 are supported so as to be movable toward and away from the intermediate transfer belt 41, respectively. That is, for example, when the actuators 95 and 96 (FIG. 3) composed of solenoids or motors are driven by the contact / separation driving unit 118 (FIG. 3), the applying rollers 881 and 882 are respectively in contact positions (solid lines in FIG. 4). ) And the separated position (broken line in FIG. 4). When the roller driving motor 94 (FIG. 3) is rotationally driven by the motor driving unit 119 (FIG. 3) at the contact position, the applying rollers 881 and 882 are in the same direction as the circumferential direction 47 of the intermediate transfer belt 41 (FIG. 4). Rotate at a predetermined peripheral speed (medium, counterclockwise). Accordingly, the application rollers 881 and 882 pump the liquid carrier 321 from the tanks 891 and 892 that store the liquid carrier 321 and supply the liquid carrier 321 to the intermediate transfer belt 41. Here, it is possible to control the application amount of the liquid carrier 321 by arranging both the application rollers 881 and 882 at the contact position or by arranging one of them at the contact position. On the other hand, when the liquid carrier 321 is not applied, the applying rollers 881 and 882 are retracted from the intermediate transfer belt 41 to the separated position.

  The liquid carrier applying means is not limited to this. For example, a supply nozzle or the like is disposed on the intermediate transfer belt 41 instead of the applying roller, and the liquid carrier 321 is discharged onto the intermediate transfer belt 41. May be. In this case, the application amount of the liquid carrier is adjusted by controlling the discharge amount.

  Further, the other toner colors are configured in the same manner as yellow (Y), and are respectively set by the carrier amount adjustment unit 80 provided for each color of magenta (M), cyan (C), and black (K). The amount of liquid carrier contained in each color developer 32 is adjusted. Thereby, the ratio of the toner and the liquid carrier in each color developer on the intermediate transfer belt 41 can be controlled.

  In the present embodiment, the liquid carrier 321 removed from the squeegee rollers 81 to 83 is configured to return to the tank 33Y by its own weight. However, the present invention is not limited to this, and a carrier feeding drive unit such as a pump is driven. Thus, it may be configured to forcibly return to the tank 33Y.

  In the present embodiment, the open / close valve 87 is configured to return a part or all of the liquid carrier 321 recovered by the tray 85 to the tank 33Y. However, the entire recovered liquid carrier 321 is returned to the tank 33Y. In this case, the liquid removed directly without providing the tray 85 and the pipe 86 by extending the opening of the tank 33Y to below the contact position of the cleaning blade 84 with the squeegee rollers 81-83. The carrier 321 may be configured to be naturally dropped and collected in the tank 33Y.

  Furthermore, in the present embodiment, the recovered liquid carrier 321 is returned to the tank 33Y. However, the recovered liquid carrier 321 is fed to the tanks 891 and 892, and the liquid carrier 321 is supplied to the applying rollers 881, It may be used as a source of 882. Thereby, the replenishment amount of the liquid carrier 321 to the tanks 891 and 892 can be minimized.

  In FIG. 3, the main control unit 100 includes an image memory 103 for storing an image signal given from an external device via an interface 102, and the CPU 101 receives a print command signal including the image signal from the external device. When it is received via the interface 102, it is converted into job data in a format suitable for the operation instruction of the engine unit 1 and sent to the engine control unit 110.

  The memory 117 of the engine control unit 110 includes a ROM that stores a control program of the CPU 113 including preset fixed data, a RAM that temporarily stores control data of the engine unit 1 and calculation results by the CPU 113, and the like. The CPU 113 stores data relating to the image signal sent from the external device via the CPU 101 in the memory 117.

  FIG. 5 is a view for explaining the operation of removing the liquid carrier from the intermediate transfer belt 41 by the squeegee roller 81. In the figure, in the area A, that is, upstream of the squeegee roller 81 in the circumferential direction 47 of the intermediate transfer belt 41, the developer 32 is supplied from the photosensitive member 11Y (FIG. 1) and adheres to the intermediate transfer belt 41. The toner image 322 (solid image in FIG. 5) moves in the liquid carrier 321 by the next transfer bias and is primarily transferred to the intermediate transfer belt 41. Note that the thickness of the toner image 322 is t1, and the thickness of the liquid carrier 321 is t2. That is, the thickness of the developer 32 on the intermediate transfer belt 41 is (t1 + t2).

  Then, the developer 32 on the intermediate transfer belt 41 is nipped between the squeegee roller 81 disposed at the contact position and the intermediate transfer belt 41, and the liquid carrier 321 on the surface layer of the developer 32 comes into contact with the squeegee roller 81. Adhere to. When the squeegee roller 81 and the intermediate transfer belt 41 are further rotated, the squeegee roller 81 and the intermediate transfer belt 41 are separated at substantially the center of the liquid carrier 321 layer. That is, the thickness of the liquid carrier 321 remaining on the intermediate transfer belt 41 and the thickness of the liquid carrier 321 moving to the squeegee roller 81 are both about t2 / 2.

  In this way, a part of the liquid carrier 321 is peeled off from the intermediate transfer belt 41 by the squeegee roller 81. In this embodiment, three squeegee rollers 81 to 83 are provided for each color, and the squeegee rollers 81 to 83 are controlled by the CPU 113 for each color. To be done. Then, by controlling the combination of the squeegee rollers arranged at the contact position among the squeegee rollers 81 to 83 for each color, the stripping amount of the liquid carrier 321 is controlled, thereby adjusting the liquid carrier amount on the intermediate transfer belt 41. Will be.

  6 to 9 are diagrams for explaining the relationship between the image occupancy rate and the amount of the liquid carrier peeled off. Since the liquid carrier stripping operation for each color is performed based on the same principle, here, the image occupancy ratio and the liquid carrier in the case where the yellow toner image 322 is transferred onto the intermediate transfer belt 41 are described. The relationship with the amount of stripping will be described in detail, and description of other toner colors will be omitted. (A) of each figure shows the yellow toner image on the intermediate transfer belt 41, and (B), (C), and (D) show the arrangement positions of the squeegee rollers 81 to 83 for yellow, respectively. 6 to 9, as in FIG. 4, the squeegee roller at the contact position is indicated by a solid line, and the squeegee roller at the separation position is indicated by a broken line.

  The image occupancy rate is the ratio of the image portion to the electrostatic latent image. The main control unit 100 (FIG. 3) includes, for example, a dot counter that counts the number of on dots to which toner adheres among the pixels constituting the electrostatic latent image, and the ratio of the number of on dots to the number of dots in the entire image Has the function to calculate as the image occupancy rate. For example, the image occupancy ratio of a solid image is 100%, and the image occupancy ratio of blank portions of the image is 0%. In place of the main control unit 100, the engine control unit 110 (FIG. 3) may include the dot counter.

  Here, in the present embodiment, as described above, the developer 32 in each color tank 33 uses a high concentration developer of 5 to 40% by weight, but the developer 32 is a value included in the range. For example, the toner density is set to 20 volume% (initial value of toner density). In FIG. 5, the thickness t1 of the toner image 322 transferred to the intermediate transfer belt 41 by the application of the primary transfer bias is set to 2 μm, and the thickness t2 of the liquid carrier 321 is set to 8 μm. That is, the thickness (t1 + t2) of the developer 32 on the intermediate transfer belt 41 = 10 μm.

  FIG. 6 shows a case where the image occupation rate is 100% (solid image) as shown in FIG. In this case, the toner concentration of the developing solution 32 on the intermediate transfer belt 41 is 20% by volume, which is equal to the initial value of the toner concentration in the tank 33Y. Therefore, as shown in FIGS. 5B to 5D, the liquid carrier 321 is not peeled off by disposing all the squeegee rollers 81 to 83 at the separated positions. That is, the stripping amount of the liquid carrier 321 is set to zero. As a result, all of the developer 32 on the intermediate transfer belt 41 is consumed. Since the toner concentration of the consumed developer is equal to the initial value of the toner concentration of the developer 32 in the tank 33Y, the tank 33Y. The toner density is maintained at 20% by volume of the initial value.

  FIG. 7 shows a case where the image occupation ratio is 50% as shown in FIG. In this case, the toner concentration of the developer 32 on the intermediate transfer belt 41 is 10% by volume, and t1 = 2 μm and t2 = 8 μm. However, on average, the thickness of the toner image 322 is 1 μm, and the liquid The thickness of the carrier 321 is 9 μm. Accordingly, more liquid carriers have moved to the intermediate transfer belt 41 than in the case of FIG.

  Therefore, as shown in FIG. 5B, when the squeegee roller 81 is disposed at the contact position, about half of the surface liquid carrier 321 is peeled off. As a result, the average thickness of the liquid carrier 321 remaining on the region B, that is, the intermediate transfer belt 41, is about 4.5 μm. Accordingly, the toner concentration of the developer 32 in the region B is about 18% by volume, which is substantially equal to the toner concentration in the tank 33Y.

  Then, as shown in FIGS. 4C and 4D, by arranging the squeegee rollers 82 and 83 in the separated positions, the toner concentration of the developer 32 remaining on the intermediate transfer belt 41 is about 18% by volume. Is maintained. Further, the toner concentration in the tank 33Y increased when many liquid carriers 321 moved to the intermediate transfer belt 41, but the liquid carrier 321 peeled off by the squeegee roller 81 is returned to the tank 33Y. It decreases and approaches the initial value of 20% by volume.

  FIG. 8 shows a case where the image occupation ratio is 20% as shown in FIG. In this case, the toner concentration of the developer 32 on the intermediate transfer belt 41 is 4% by volume, and t1 = 2 μm and t2 = 8 μm, but on average, the thickness of the toner image 322 is 0.4 μm. The thickness of the liquid carrier 321 is 9.6 μm. Accordingly, more liquid carriers have moved to the intermediate transfer belt 41 than in the case of FIG.

  Therefore, as shown in FIG. 5B, when the squeegee roller 81 is disposed at the contact position, about half of the surface liquid carrier 321 is peeled off. As a result, the average thickness of the liquid carrier 321 in the region B remaining on the intermediate transfer belt 41 is about 4.8 μm, and the toner concentration of the developer 32 in the region B is about 7.7% by volume. Further, as shown in FIG. 5C, when the squeegee roller 82 is disposed at the contact position, about half of the surface liquid carrier 321 is peeled off. As a result, the average thickness of the liquid carrier 321 in the region C remaining on the intermediate transfer belt 41 is about 2.4 μm. Accordingly, the toner concentration of the developing solution 32 in the region C is about 14% by volume, which approaches the toner concentration in the tank 33Y. As shown in FIG. 4D, the squeegee roller 83 is disposed at a separated position so as not to peel off the liquid carrier 321. This is because if the liquid carrier 321 is further peeled off, the toner image 322 on the intermediate transfer belt 41 may be adversely affected.

  As a result, the toner concentration of the developer 32 remaining on the intermediate transfer belt 41 is about 14% by volume. Further, the toner concentration in the tank 33Y increased when many liquid carriers 321 moved to the intermediate transfer belt 41. However, the liquid carrier 321 peeled off by the squeegee rollers 81 and 82 is returned to the tank 33Y. As a result, the value decreases and approaches the initial value of 20% by volume.

  FIG. 9 shows a case where the image occupation ratio is 0% as shown in FIG. In this case, the toner concentration of the developing solution 32 on the intermediate transfer belt 41 is 0% by volume, and only the liquid carrier 321 is consumed, and the toner concentration in the tank 33Y increases. Therefore, as shown in FIGS. 4B to 4D, the liquid carriers 321 are peeled off by disposing all the squeegee rollers 81 to 83 at the contact positions. As a result, the thickness in the region B after being peeled off by the squeegee roller 81 is about 5 μm, and the thickness in the region C after being peeled off by the squeegee roller 82 is about 2.5 μm. The thickness in the region D after being peeled off by the roller 83 is about 1.25 μm. Then, the liquid carrier 321 peeled off by the squeegee rollers 81 to 83 is returned to the tank 33Y, so that an increase in toner density in the tank 33Y is suppressed.

  As described above, by controlling the positions of the squeegee rollers 81 to 83, it is possible to control the amount of the liquid carrier 321 peeled off from the developer 32 adhering to the intermediate transfer belt 41. Therefore, by controlling the positions of the squeegee rollers 51 to 53, the ratio of the toner and the liquid carrier in the developer on the intermediate transfer belt 41 can be controlled. As a result, the toner density of the developer 32 on the intermediate transfer belt 41 can be adjusted to a value close to a predetermined value. As a result, the toner density of the developer 32 on the intermediate transfer belt 41 varies according to the image ratio of the yellow image. However, by controlling the positions of the squeegee rollers 51 to 53, a predetermined value (here, 20 It can be maintained at a value close to (volume%). As a result, it is possible to suppress fluctuations in transfer conditions (primary transfer conditions) during transfer of the toner image of the next color (in this embodiment, magenta). Further, by returning the peeled liquid carrier 321 to the tank 33Y, fluctuations in the toner concentration of the developer 32 in the tank 33Y can be suppressed and maintained at a value close to the initial value (20% by volume).

  Next, after the amount of liquid carrier attached to the yellow toner image 322 is adjusted, the toner image 322 of the next color (magenta) is primarily transferred onto the intermediate transfer belt 41 and superimposed on the yellow toner image 322. Here, since the toner concentration of the developing solution 32 on the intermediate transfer belt 41 is maintained at a value close to a predetermined value, it is possible to prevent the occurrence of image disturbance during the transfer of the magenta toner image 322.

  After the magenta toner image 322 is primarily transferred onto the intermediate transfer belt 41, the magenta (M) squeegee rollers 81 to 83 adhere to the intermediate transfer belt 41 in accordance with the image occupation ratio of the magenta image. The liquid carrier 321 in the outermost layer of the developer 32 is peeled off by being appropriately disposed at a contact position where it contacts the upper layer developer 32, that is, the magenta developer 32.

  Here, as in the case of yellow (Y), the amount of the liquid carrier 321 peeled off from the uppermost developer 32 adhering to the intermediate transfer belt 41 is controlled by controlling the positions of the squeegee rollers 81-83. Can be controlled. Therefore, by controlling the positions of the squeegee rollers 81 to 83, the ratio of the toner and the liquid carrier in the developer on the intermediate transfer belt 41 can be controlled. As a result, the toner density of the developer 32 on the intermediate transfer belt 41 can be adjusted to a value close to a predetermined value. As a result, the toner density of the developer 32 on the intermediate transfer belt 41 varies according to the image density of the magenta image. However, by controlling the positions of the squeegee rollers 51 to 53, a predetermined value (here, 20 It can be maintained at a value close to (volume%). As a result, it is possible to suppress fluctuations in the transfer conditions (primary transfer conditions) during the transfer of the toner image of the next color (cyan in this embodiment). Further, by returning the peeled liquid carrier 321 to the tank 33M, it is possible to suppress fluctuations in the toner concentration of the developing solution 32 in the tank 33M and maintain the value close to the initial value (20% by volume).

  Similarly, for cyan (C) and black (K), since the toner concentration of the developer 32 on the intermediate transfer belt 41 is maintained at a value close to a predetermined value before the primary transfer, cyan and black It is possible to prevent image disturbance during the primary transfer of the toner image 322. Further, by returning the liquid carrier 321 peeled off by the cyan (C) and black (K) squeegee rollers 81 to 83 into the tanks 33C and 33K, respectively, the toner concentration of the developing solution 32 in the tanks 33C and 33K is increased. Fluctuation can be suppressed.

  In this way, after the four color toner images are superimposed on the intermediate transfer belt 41, the full color toner image is transferred to the recording medium 4. The toner concentration of the developer 32 on the intermediate transfer belt 41 is a predetermined value. Since it is maintained at a value close to (20% by volume), fluctuations in the transfer conditions (secondary transfer conditions) from the intermediate transfer belt 41 to the recording medium 4 can also be suppressed.

  When the liquid carrier 321 peeled off from each color developer is returned to each color tank 33 as in this embodiment, it is necessary to use the same liquid carrier 321 for each color developer 32. This is because if the liquid carrier 321 is different for each color, it is difficult to maintain the identity of the components of the liquid carrier 321 included in the developer 32 stored in each color tank 33. Specifically, for the following reasons. Each color toner image 322 is superimposed on the intermediate transfer belt 41 and a liquid carrier 321 attached to each color toner image 322 is also mixed. For this reason, when the liquid carrier 321 is peeled off by the squeegee rollers 81 to 83, the liquid carrier 321 attached to the toner image 322 of other colors is also peeled off at the same time. This is because when the peeled liquid carrier 321 is returned to a predetermined tank, the components of the liquid carrier 321 that are different for each color are mixed.

  FIG. 10 is a flowchart showing an example of the stripping amount adjustment processing routine. Since the adjustment process of the stripping amount of the liquid carrier 321 for each color is the same, here, the stripping amount adjustment process of the liquid carrier 321 when the yellow toner image 322 is transferred onto the intermediate transfer belt 41 will be described. However, description of other toner colors is omitted. The memory 117 of the engine control unit 110 stores a stripping amount adjustment processing program for the liquid carrier 321 in advance. Then, the CPU 113 controls each part of the apparatus according to the program, whereby the following stripping amount adjustment processing is executed.

  First, the image occupancy rate P (%), which is the ratio of the image portion in the yellow electrostatic latent image, is obtained (# 10), and the obtained image occupancy rate level is determined. That is, it is determined whether or not 55 <P (# 12). If P ≦ 55 (NO in # 12), it is determined whether 30 <P ≦ 55 (# 14) and P ≦ 30. If (NO in # 14), it is determined whether or not 0 <P ≦ 30 (# 16). If NO in # 16, P = 0, so that all the squeegee rollers 81-83 are moved to the contact position as described in FIG. 9 (# 18).

  If 55 <P (YES in # 12), since the toner density on the intermediate transfer belt 41 is high, as described with reference to FIG. 6, the squeegee rollers 81 to 83 are all disposed at the separated positions. This routine ends. If 30 <P ≦ 55 (YES in # 14), the toner density on the intermediate transfer belt 41 is medium, so that the squeegee roller 81 is moved to the contact position, for example, as described with reference to FIG. (# 20). This movement may be one, and the squeegee roller 82 or 83 may be moved instead of the squeegee roller 81.

  If 0 <P ≦ 30 (YES in # 16), the toner density on the intermediate transfer belt 41 is low, and therefore, for example, the squeegee rollers 81 and 82 are moved to the contact position as described with reference to FIG. # 22). Two movements are sufficient, and the squeegee rollers 81 and 83 or the squeegee rollers 82 and 83 may be moved. Note that the threshold used to determine the level of image occupancy in steps # 12, # 14, and # 16 is an example, and other values may be used.

  Similarly, the stripping amount adjustment process described above is performed according to the image occupancy ratio for each color of magenta (M), cyan (C), and black (K). Specifically, the image occupancy rate is determined for each color, and the combination of the squeegee rollers 81 to 83 to be moved to the contact position for each color is determined.

  As described above, according to the operation of FIG. 10, the intermediate transfer is performed by controlling the combination of the squeegee rollers 81 to 83 that are moved to the contact position that contacts the developer 32 on the intermediate transfer belt 41 based on the image occupation ratio P. The amount of liquid carrier contained in the developer 32 on the belt 41 is adjusted. Thereby, even if the toner density of the developer 32 on the intermediate transfer belt 41 varies according to the variation of the image occupation ratio, the ratio of the toner in the developer on the intermediate transfer belt 41 to the liquid carrier Is controlled, the toner concentration of the developer 32 on the intermediate transfer belt 41 can be maintained at a value close to a predetermined value.

  As described above, according to this embodiment, the squeegee rollers 81 to 83 that are movable between the contact position that contacts the uppermost developer 32 adhering to the intermediate transfer belt 41 and the separation position that does not contact each color are provided. Since the combination of the squeegee rollers 81 to 83 arranged at the contact position is controlled for each color, the amount of the liquid carrier 321 peeled off from the uppermost developer 32 adhering to the intermediate transfer belt 41 is controlled. Can be controlled. In other words, the liquid carrier 321 can be controlled to decrease.

  Further, according to the present embodiment, since the applying rollers 881 and 882 are provided for each color, the applying rollers 881 and 882 that are moved to the contact positions for each color are controlled to be applied onto the intermediate transfer belt 41. The amount of liquid carrier 321 applied can be controlled. That is, it is possible to control the direction in which the liquid carrier 321 is increased. As described above, since the increase / decrease control of the liquid carrier 321 is possible, by controlling the amount of the liquid carrier on the intermediate transfer belt 41, the ratio of the toner in the developer on the intermediate transfer belt 41 to the liquid carrier can be adjusted. It becomes possible to adjust arbitrarily.

  Accordingly, even when the toner concentration of the developer 32 moving from each photoconductor to the intermediate transfer belt 41 is increased or decreased with respect to a predetermined value due to a difference in image occupancy ratio of each color image, each color toner The toner density of the developer 32 on the intermediate transfer belt 41 is close to a predetermined value by adjusting the ratio of the toner in the developer and the liquid carrier that adheres to the intermediate transfer belt 41 after the image 322 is primarily transferred. Value can be maintained. Specifically, among the four color toner images, the M-th (2 ≦ M ≦ N) color toner image 322 is already attached to the intermediate transfer belt 41 before the primary transfer (M−). 1) The toner density of the developer 32 on the intermediate transfer belt 41 can be maintained at a value close to a predetermined value by adjusting the ratio of the toner and the liquid carrier in the developer of the first color. Accordingly, fluctuations in transfer conditions (primary transfer conditions) when the M-th toner image 322 is primarily transferred to the intermediate transfer belt 41 are suppressed, and primary transfer processing can be performed satisfactorily and stably. .

  Further, by adjusting the amount of liquid carrier contained in the developer 32 constituting each color toner image 322, the toner and liquid in the developer on the intermediate transfer belt 41 after the respective color toner images 322 are overlaid. The ratio with the carrier has also been adjusted. Therefore, fluctuations in transfer conditions (secondary transfer conditions) from the intermediate transfer belt 41 to the recording medium 4 are suppressed, and the secondary transfer process can be performed satisfactorily and stably. Thereby, good image quality can be obtained.

  In addition, according to the present embodiment, the liquid carrier 321 scraped from the squeegee rollers 81 to 83 by the cleaning blade 84 is naturally dropped, collected in the tray 85, and returned to the color tank 33. It is possible to suppress a change in the toner concentration of the developing solution 32 and maintain the value close to the initial value. As a result, the peeled liquid carrier 321 can be used effectively, and the amount of liquid carrier, toner, etc. supplied from the outside can be minimized.

Second Embodiment
In the first embodiment, each color toner image on the photoconductors 11Y, 11M, 11C, and 11K is transferred (primary transfer) to the intermediate transfer belt 41, and then the developer 32 that adheres to the intermediate transfer belt 41 for each color. Although the liquid carrier amount included is adjusted, the liquid carrier amount included in the developer 32 attached to the photoconductors 11Y, 11M, 11C, and 11K may be adjusted.

  FIG. 11 is a diagram showing an internal configuration of a printer which is the second embodiment of the image forming apparatus according to the present invention. The second embodiment is different from the first embodiment in that the carrier amount adjusting unit 80 is disposed opposite to the intermediate transfer belt 41 and opposed to the photoreceptors 11Y, 11M, 11C, and 11K. The other configuration is basically the same as that of the first embodiment. Therefore, the same components are denoted by the same reference numerals and description thereof is omitted. In the following, the features of the present embodiment will be described focusing on the differences.

  In the second embodiment, a carrier amount adjustment unit 80 is disposed to face the photoreceptor 11 for each color of yellow (Y), magenta (M), cyan (C), and black (K). That is, four carrier amount adjustment units 80 are provided, and four units (80Y, 80M, 80C, 80K) are respectively provided between the development position 16 and the primary transfer position 42Y on the photoreceptor 11Y. Between the developing position 16 and the primary transfer position 42M above, between the developing position 16 and the primary transfer position 42C on the photoreceptor 11C, and between the developing position 16 and the primary transfer position 42K on the photoreceptor 11K. It is arranged to face each other. The basic configuration of each color is the same. Therefore, here, the configuration relating to yellow will be described, and the other toner colors will be denoted by the same or corresponding symbols, and description thereof will be omitted.

  The carrier amount adjustment unit 80Y for yellow (Y) can be disposed on the photoconductor 11Y so as to control the ratio of the toner of the developer 32 and the liquid carrier on the photoconductor 11Y. The configuration of the carrier amount adjustment unit 80 is basically the same as that of the first embodiment except that it is arranged on the photoconductor 11. That is, the yellow (Y) squeegee rollers 81 to 83 and the applying rollers 881 and 882 are arranged along the rotation direction (clockwise in the drawing) of the photoconductor 11Y and opposed to the photoconductor 11Y. ing. The squeegee rollers 81 to 83 are disposed at a contact position where the squeegee rollers 81 to 83 are in contact with the developing solution 32 on the photoconductor 11Y, thereby peeling the liquid carrier 321 from the photoconductor 11Y. At this time, the combination of the squeegee rollers 81 to 83 arranged at the contact position is controlled according to the image occupancy ratio of the yellow image, whereby the amount of the liquid carrier 321 removed is controlled. The operation of removing the liquid carrier 321 by the squeegee rollers 81 to 83 is the same as that shown in FIGS. On the other hand, the applying rollers 881 and 882 apply the liquid carrier 321 on the photoconductor 11Y by being disposed at a contact position that contacts the developing solution 32 on the photoconductor 11Y. At this time, the application amount of the liquid carrier 321 to be applied on the photoconductor 11Y is controlled by controlling the combination of the application rollers 881 and 882 arranged at the contact position on the photoconductor 11Y in contact with the developer 32. Thereby, even when the toner density of the developing solution 32 on the photoconductor 11Y varies depending on the image ratio of the yellow image, the liquid carrier amount of the developing solution 32 adhering to the photoconductor 11Y is adjusted. Thus, the toner concentration of the developer 32 on the photoconductor 11Y can be maintained at a value close to a predetermined value. Thereby, fluctuations in the transfer condition (primary transfer condition) of the yellow toner image 322 to the intermediate transfer belt 41 can be suppressed.

  Similarly, for other toner colors of magenta (M), cyan (C), and black (K), the amount of liquid carrier on each photoconductor is adjusted according to the image occupancy of each color image. Thus, the ratio of the toner and the liquid carrier in each color developer is controlled, and the toner concentration of the developer 32 on each photoconductor can be maintained at a value close to a predetermined value. The adjustment of the liquid carrier amount by each color carrier amount adjustment unit 80 is performed in the same manner as yellow (Y). That is, it is adjusted by controlling the combination of the squeegee rollers 81 to 83 arranged at the contact position in accordance with the image occupancy ratio of each color image, or by controlling the combination of the applying rollers 881 and 882 arranged at the contact position. The

  On the intermediate transfer belt 41, the toner images of the respective colors are sequentially transferred from the respective photoconductors to be superposed on each other, and the toner density of the developer 32 on the intermediate transfer belt 41 is a predetermined value. Therefore, fluctuations in the transfer conditions (primary transfer conditions) of the color toner images 322 to the intermediate transfer belt 41 can be suppressed. Therefore, it is possible to prevent the occurrence of image disturbance during the transfer (primary transfer) of each color toner image. Moreover, after the four color toner images are superimposed on the intermediate transfer belt 41, the full color toner image is transferred to the recording medium 4. The toner concentration of the developer 32 on the intermediate transfer belt 41 is a predetermined value. Therefore, fluctuations in the transfer conditions (secondary transfer conditions) from the intermediate transfer belt 41 to the recording medium 4 can be suppressed.

  As described above, according to the second embodiment, the carrier amount adjusting unit 80 is provided for each photoconductor (for each color), and the liquid carrier contained in the developer 32 on the photoconductor for each color. By adjusting the amount, the ratio of the toner and the liquid carrier in the developer on each photoconductor is adjusted. Thereby, the toner concentration of the developing solution 32 on each photoconductor is maintained at a value close to a predetermined value. Accordingly, the developer 32 whose ratio has been adjusted with respect to the intermediate transfer belt 41 is moved to the intermediate transfer belt 41 while the toner image in the developer is primarily transferred, so that the intermediate between the toner images 322 of the respective colors. Variations in the transfer conditions (primary transfer conditions) to the transfer belt 41 are suppressed, and the primary transfer process can be performed satisfactorily and stably.

  In each color toner image 322, the ratio between the toner in the developer and the liquid carrier is adjusted on each photoconductor side before the primary transfer. As a result, the ratio of the toner in the developer and the liquid carrier on the intermediate transfer belt 41 after the color toner images 322 are superimposed is also adjusted. Therefore, fluctuations in transfer conditions (secondary transfer conditions) from the intermediate transfer belt 41 to the recording medium 4 are suppressed, and the secondary transfer process can be performed satisfactorily and stably. Thereby, good image quality can be obtained.

  Also in the second embodiment, the liquid carrier 321 peeled off by the squeegee rollers 81 to 83 is returned to the respective color tanks 33, whereby the toner concentration of the developer 32 in each color tank 33 varies. Therefore, the replenishment of the toner or liquid carrier to each color tank 33 can be minimized.

<Third Embodiment>
FIG. 12 is a diagram showing an internal configuration of a printer which is the third embodiment of the image forming apparatus according to the present invention. This image forming apparatus is a so-called four-cycle color printer, and a photoreceptor 11 is provided to be rotatable in the direction of the arrow in FIG. A charging unit 12, a developing unit 30 (30C, 30M, 30Y, and 30K), a squeegee roller 81 to 83, a cleaning unit 14, and a charge eliminating unit (not shown) are provided around the photoconductor 11 along the rotation direction. Each is arranged.

  The surface area between the charging unit 12 and the developing unit 30 is an irradiation area of the light beam 21 from the exposure unit 20, and an electrostatic latent image corresponding to each color image signal is formed in the irradiation area. . The developing units 30C, 30M, 30Y, and 30K are stored in a tank 33 (33C, 33M, 33Y, and 33K) that stores a developing solution 32 in which each color toner is dispersed, and each color tank 33, in addition to the developing roller 31. The application roller 34 that draws up the developer 32 and applies it to the development roller 31, the regulation blade 35 that uniformly regulates the thickness of the developer layer on the application roller 34, and the development roller after the toner is supplied to the photoreceptor 11. And a cleaning blade 36 for removing the developer 32 remaining on the substrate 31.

  Each of the developing units 30C, 30M, 30Y, and 30K selectively selects the developing unit of the corresponding color only when the electrostatic latent image formed corresponding to each color image signal is developed with the toner of the corresponding color. And a predetermined developing position facing each other with a predetermined developing gap therebetween, and the toner carried by the developing unit is applied to the surface of the photoreceptor 11. As a result, the electrostatic latent image formed on the photoconductor 11 is visualized with the corresponding toner color. The developing portions of other colors not involved in the development are retracted to positions separated from the photoconductor 11.

  After the electrostatic latent image of a predetermined color is formed and developed in this manner, the developed toner image 322 is conveyed along with the rotation of the photoconductor 11 and transferred to the intermediate transfer belt 41 at the primary transfer position 42 (primary Transferred). In this embodiment, for example, a cyan (C) toner image 322 is first developed and then transferred to the intermediate transfer belt 41. Subsequently, for example, a magenta (M) toner image 322 is developed and then transferred to the intermediate transfer belt 41. Subsequently, for example, the yellow (Y) toner image 322 is developed and then transferred to the intermediate transfer belt 41. Finally, for example, the black (K) toner image 322 is developed and then transferred to the intermediate transfer belt 41. become. Thus, by rotating the photoconductor 11 four times, the respective color toner images 322 are sequentially superimposed on the intermediate transfer belt 41 to form a full-color toner image 322.

  The toner image 322 thus formed on the intermediate transfer belt 41 is conveyed to the secondary transfer position 49 sandwiched between the rollers 45 and 48 along with the rotation of the intermediate transfer belt 41 (clockwise direction in the figure), and the recording medium 4 Secondary transfer is performed. The recording medium 4 onto which the toner image 322 has been secondarily transferred is conveyed along a predetermined conveyance path 5 (indicated by a one-dot chain line in FIG. 12), and the toner image 322 is fixed to the recording medium 4 by a fixing unit (not shown). Discharged.

  Next, the configuration of the carrier amount adjustment unit 80 will be described. For each color of yellow (Y), magenta (M), cyan (C), and black (K), the carrier amount adjustment unit 80 is arranged along the rotation direction 15 of the photoconductor 11 and faces the photoconductor 11. Has been placed. That is, four carrier amount adjustment units 80 are provided, and these four units (80C, 80M, 80Y, 80K) are developed positions 16C, 16M, 16Y, which are opposed to the developing units 30C, 30M, 30Y, 30K, respectively. 16K and the primary transfer position 42 are arranged. Then, the carrier amount adjustment unit 80 corresponding to the developed color appropriately adjusts the amount of liquid carrier contained in the developer 32 on the photoconductor 11. The basic configuration of each color is the same. Therefore, here, the configuration relating to yellow will be described, and the other toner colors will be denoted by the same or corresponding symbols, and description thereof will be omitted.

  A yellow electrostatic latent image corresponding to the image signal is formed by the exposure unit 20 toward the outer peripheral surface of the photoconductor 11 charged by the charging unit 12. The electrostatic latent image for yellow is developed with yellow toner applied when the developing unit 30Y is disposed at the developing position 16Y, and a yellow toner image 322 is formed on the photoconductor 11. At this time, a part of the liquid carrier 321 adhering to the developing unit 30 </ b> Y together with the yellow toner has moved to the photosensitive member 11 and is conveyed along with the rotation of the photosensitive member 11. Note that the developing portions 30C, 30M, and 30K for the other colors not involved in the development are retracted to positions separated from the photoconductor 11.

  Then, the amount of liquid carrier adhering to the yellow toner image 322 is appropriately adjusted by the yellow (Y) carrier amount adjusting unit 80Y disposed to face the photoconductor 11, whereby the development on the photoconductor 11 is performed. The ratio of the liquid 32 toner to the liquid carrier is controlled. The configuration of the carrier amount adjustment unit 80 is basically the same as that of the first embodiment except that it is arranged on the photoconductor 11. That is, yellow (Y) squeegee rollers 81 to 83 and application rollers 881 and 882 are arranged along the rotation direction 15 of the photoconductor 11 and opposed to the photoconductor 11. The squeegee rollers 81 to 83 peel off the liquid carrier 321 from the photoconductor 11 by being disposed at a contact position on the photoconductor 11 that contacts the developer 32. At this time, the combination of the squeegee rollers 81 to 83 arranged at the contact position is controlled according to the image occupancy ratio of the yellow image, whereby the amount of the liquid carrier 321 removed is controlled. The operation of removing the liquid carrier 321 by the squeegee rollers 81 to 83 is the same as that shown in FIGS. On the other hand, the applying rollers 881 and 882 apply the liquid carrier 321 on the photoconductor 11Y by being disposed at a contact position that contacts the developing solution 32 on the photoconductor 11Y. At this time, the application amount of the liquid carrier 321 applied on the photoconductor 11 is controlled by controlling the combination of the application rollers 881 and 882 arranged at the contact position on the photoconductor 11Y in contact with the developer 32. Thereby, even when the toner concentration of the developer 32 on the photoconductor 11 varies depending on the image ratio of the yellow image, by adjusting the liquid carrier amount of the developer 32 attached on the photoconductor 11, The toner concentration of the developer 32 on the photoconductor 11 can be maintained at a value close to a predetermined value.

  Next, as the photoconductor 11 rotates, the yellow toner image 322 is conveyed to the primary transfer position 42 and transferred (primary transfer) to the intermediate transfer belt 41, but the toner concentration of the developer 32 on the photoconductor 11. Is maintained at a value close to a predetermined value, the fluctuation of the transfer condition (primary transfer condition) of the yellow toner image 322 to the intermediate transfer belt 41 can be suppressed. The residual charge on the photoconductor 11 after the primary transfer is removed by a charge removal unit (not shown) made of an LED or the like, and the residual developer is removed by the cleaning unit 14.

  Similarly, for other toner colors of magenta (M), cyan (C), and black (K), the amount of liquid carrier attached to each color toner image 322 formed on the photoconductor 11 as the photoconductor 11 rotates. Is adjusted by the carrier amount adjustment unit 80 corresponding to each color toner. Thereby, the ratio of the toner and the liquid carrier in each color developer is controlled, and the toner concentration of each color developer 32 can be maintained at a value close to a predetermined value. The adjustment of the liquid carrier amount by each color carrier amount adjustment unit 80 is performed in the same manner as yellow (Y). That is, it is adjusted by controlling the combination of the squeegee rollers 81 to 83 arranged at the contact position in accordance with the image occupancy ratio of each color image, or by controlling the combination of the applying rollers 881 and 882 arranged at the contact position. The

  As a result, each color toner image 322 formed on the photoconductor 11 is sequentially transferred onto the intermediate transfer belt 41 as the photoconductor 11 rotates, but the toner concentration of the developer 32 on the intermediate transfer belt 41 is transferred. Is always maintained at a value close to a predetermined value, so that fluctuations in the transfer conditions (primary transfer conditions) of the color toner images 322 to the intermediate transfer belt 41 can be suppressed. Therefore, it is possible to prevent the occurrence of image disturbance during the transfer (primary transfer) of each color toner image. In addition, after the four color toner images are superimposed on the intermediate transfer belt 41, the full color toner image is transferred to the recording medium 4. The toner concentration of the developer on the intermediate transfer belt 41 is close to a predetermined value. Since it is maintained, fluctuations in the transfer conditions (secondary transfer conditions) from the intermediate transfer belt 41 to the recording medium 4 can be suppressed.

  As described above, according to the third embodiment, each time the toner image 322 of each color is formed on the photoreceptor 11, the carrier amount adjusting unit 80 corresponding to each color is included in the liquid developer 32. By adjusting the amount, the ratio of the toner in the developer on the photoconductor 11 and the liquid carrier is adjusted. As a result, the toner concentration of the developer 32 on the photoreceptor 11 is maintained at a value close to a predetermined value. Accordingly, the developer 32 whose ratio has been adjusted with respect to the intermediate transfer belt 41 is moved to the intermediate transfer belt 41 while the toner image in the developer is primarily transferred, so that the intermediate between the toner images 322 of the respective colors. Variations in the transfer conditions (primary transfer conditions) to the transfer belt 41 are suppressed, and the primary transfer process can be performed satisfactorily and stably.

  In each color toner image 322, the ratio of the toner in the developer and the liquid carrier is adjusted on the photosensitive member 11 side before the primary transfer. As a result, the ratio of the toner in the developer and the liquid carrier on the intermediate transfer belt 41 after the color toner images 322 are superimposed is also adjusted. Therefore, fluctuations in transfer conditions (secondary transfer conditions) from the intermediate transfer belt 41 to the recording medium 4 are suppressed, and the secondary transfer process can be performed satisfactorily and stably. Thereby, good image quality can be obtained.

  Also in the third embodiment, the liquid carrier 321 peeled off by the squeegee rollers 81 to 83 is provided so as to return to the color tank 33 by providing “collecting means” such as a receiving tray 85 and a pipe 86. Also good. By configuring in this way, it is possible to suppress fluctuations in the toner concentration of the developer 32 in each color tank 33, and it is possible to minimize the replenishment of toner or liquid carrier to each color tank 33. .

  In the present embodiment, a carrier amount adjustment unit 80 is provided for each color, and the development on the photoreceptor 11 is performed by the carrier amount adjustment unit 80 of the corresponding color according to the color of the toner image formed on the photoreceptor 11. Although the liquid carrier amount contained in the liquid 32 is adjusted, the present invention is not limited to this. For example, when the liquid carrier 321 included in each color developer 32 is the same component and there is no possibility that other color toners adhere to the squeegee rollers 81 to 83 and the application rollers 881 and 882, Only one carrier amount adjusting unit 80 may be provided to adjust the amount of liquid carrier contained in each color developer 32.

  The present invention is not limited to the above embodiment, and various modifications can be made to the above without departing from the spirit thereof. For example, the following modifications (1) to ( 10) can be employed.

  (1) In the first embodiment, the three squeegee rollers 81 to 83 are provided for each color. However, the present invention is not limited to this, and two or four or more squeegee rollers may be provided. That is, if a plurality of squeegee rollers are provided, the amount of the liquid carrier 321 peeled off from the intermediate transfer belt 41 can be controlled by controlling the combination of squeegee rollers arranged at the contact position. Similarly, although two application rollers 881 and 882 are provided for each color, the present invention is not limited to this, and three or more application rollers may be provided. That is, if a plurality of application rollers are provided, the application amount of the liquid carrier 321 to the intermediate transfer belt 41 can be controlled by controlling the combination of the application rollers arranged at the contact position.

  (2) FIG. 13 is a diagram for explaining the stripping amount of the liquid carrier 321 at each contact position when three contact positions with different distances from the intermediate transfer belt 41 are provided as contact positions of the squeegee roller 81. is there. Although only the squeegee roller 81 is shown in FIG. 13, the same applies to the squeegee rollers 82 and 83.

  In this embodiment, the actuator 91 (FIG. 3) is configured by a motor, for example, and the contact positions of the squeegee rollers 81 to 83 are a plurality of contact positions having different distances from the surface of the developer 32 attached to the intermediate transfer belt 41. Further, the squeegee rollers 81 to 83 can be arranged. Here, it is assumed that a solid image is transferred to the intermediate transfer belt 41 as shown in FIG. Similarly to the above embodiment, the thickness of the toner image 322 is t1, and the thickness of the liquid carrier 321 is t2. The radius of the squeegee roller 81 is R.

  In FIG. 5B, the contact position is set to a position where the surface of the squeegee roller 81 barely contacts the developer 32 on the intermediate transfer belt 41. That is, the distance L1 between the center of the squeegee roller 81 and the surface of the developer 32 is set to L1≈R and L1 ≦ R. As a result, the thickness of the liquid carrier 321 remaining on the intermediate transfer belt 41 becomes t3, and a small amount of the liquid carrier 321 on the surface layer of the developer 32 on the intermediate transfer belt 41 is peeled off.

  In FIG. 8C, the contact position is set closer to the intermediate transfer belt 41 than in FIG. That is, the distance L2 between the center of the squeegee roller 81 and the surface of the developer 32 is set to L2 <L1. As a result, the thickness of the liquid carrier 321 remaining on the intermediate transfer belt 41 becomes t4 (<t3), and the surface of the liquid carrier 321 of the developer 32 on the intermediate transfer belt 41 is larger than in the case of FIG. Stripped off.

  In FIG. 4D, the contact position is set at a position closer to the intermediate transfer belt 41 than in FIG. That is, the distance L3 between the center of the squeegee roller 81 and the surface of the developer 32 is set to L3 <L2. As a result, the thickness of the liquid carrier 321 remaining on the intermediate transfer belt 41 becomes t5 (<t4), and the surface of the liquid carrier 321 of the developer 32 on the intermediate transfer belt 41 is further increased than in the case of FIG. Many are stripped off.

  As described above, according to the embodiment shown in FIG. 13, the squeegee rollers 81 to 83 can be arranged at a plurality of contact positions at different distances from the intermediate transfer belt 41 as the contact positions of the squeegee rollers 81 to 83. By changing the contact position of the squeegee rollers 81 to 83, the amount of the liquid carrier 321 peeled off from the intermediate transfer belt 41 can be controlled, whereby the same effect as in the above embodiment can be obtained. . In this embodiment, the number of squeegee rollers is not limited to a plurality, and only one squeegee roller may be provided. Even in this case, the stripping amount of the liquid carrier 321 can be controlled.

  (3) In the first embodiment, the rotational speed of the squeegee rollers 81 to 83 can be changed by the roller drive motor 94, and the contact surface of the squeegee rollers 81 to 83 is relative to the developer conveyed by the intermediate transfer belt 41. The speed may be changed. According to this embodiment, the amount of peeling of the liquid carrier 321 can be increased or decreased by increasing or decreasing the peripheral speed of the squeegee rollers 81 to 83 with respect to the peripheral speed of the intermediate transfer belt 41. The same effect as the form can be obtained. In this embodiment, the number of squeegee rollers is not limited to a plurality, and only one squeegee roller may be provided. Even in this case, the stripping amount of the liquid carrier 321 can be controlled. Similarly, the rotation speeds of the applying rollers 881 and 882 can be changed, and the relative speed of the contact surfaces of the applying rollers 881 and 882 with the developer conveyed by the intermediate transfer belt 41 may be changed. According to this embodiment, the application amount of the liquid carrier 321 can be increased or decreased by increasing or decreasing the peripheral speed of the applying rollers 881 and 882 with respect to the peripheral speed of the intermediate transfer belt 41. Also in this case, the application amount can be controlled by providing only one application roller.

  (4) Also in the second and third embodiments, the modifications shown in the above (1) to (3) can be adopted as in the first embodiment. That is, although three squeegee rollers 81 to 83 are provided for each color, two or four or more squeegee rollers may be provided. Further, the distance between the squeegee rollers 81 to 83 from the photosensitive member 11 may be varied, or the relative speed of the contact surface of the squeegee roller with respect to the developer conveyed by the photosensitive member 11 may be changed. In this case, the stripping amount can be controlled by providing only one squeegee roller for each color. Similarly, two application rollers 881 and 882 are provided for each color, but three or more application rollers may be provided. Further, the relative speed of the contact surface of the applying roller with respect to the developer conveyed by the photoconductor 11 may be changed. In this case, the application amount can be controlled by providing only one application roller for each color.

  (5) In the first embodiment, the color toner images 322 are superimposed on the intermediate transfer belt 41, and the liquid carrier 321 remaining without being peeled off by the squeegee rollers 81 to 83 is accumulated. Therefore, when the second to fourth color toner images 322 are transferred onto the intermediate transfer belt 41 and there is no possibility of adversely affecting the toner images 322, for example, in FIG. The liquid carrier 321 may be peeled off by arranging 83 at the contact position.

  (6) In the above embodiment, for example, as shown in FIG. 8A, the thickness t1 of the toner image 322 is set to 2 μm and the thickness t2 of the liquid carrier 321 is set to 8 μm. If the roller 83 is disposed at the contact position, the toner image 322 may be adversely affected. However, if there is no possibility of adversely affecting the toner image 322 even if the squeegee roller 83 is arranged at the contact position, for example, the thickness t1 of the toner image 322 is 1 μm, for example, the squeegee roller in FIG. You may make it arrange | position 83 in a contact position.

  (7) If there is no possibility of adversely affecting the toner image 322 even if the squeegee roller 83 is arranged at the contact position as in the cases (5) and (6) above, the image occupancy rate is not obtained in the operation of FIG. The maximum number of squeegee rollers that move to the contact position is 2 when the ratio is not 0%, whereas the comparison step is increased by one, and all three squeegee rollers 81 to 83 are arranged at the contact position. May be provided.

  For example, in the operation shown in FIG. That is, for example, if 0 ≦ P ≦ 20, the three squeegee rollers are moved to the contact position, and if 20 <P ≦ 35, the two squeegee rollers are moved to the contact position, and 35 <P ≦ 55. For example, one squeegee roller may be moved to the contact position.

  (8) In the above embodiment, a dot counter that counts the number of on-dots to which toner adheres among the pixels constituting the electrostatic latent image is provided, and the ratio of the number of on-dots to the number of dots in the entire image is used as the image occupation rate However, the method for obtaining the image occupancy rate is not limited to this. Since the image occupancy rate is a value corresponding to the amount of development, that is, the amount of toner movement from the developing roller 31 to the photoconductor 11, for example, the current flowing from the developing roller 31 to the photoconductor 11 is detected as the developing current. The amount of toner movement (development amount) may be obtained based on this and used as the image occupancy rate.

  (9) In the embodiment described above, the roller-shaped squeegee rollers 81 to 83 are used as the stripping member. However, the present invention is not limited to this, and for example, a belt-shaped member may be used. Similarly, the roller-shaped application rollers 881 and 882 are used as the application members, but the present invention is not limited thereto, and for example, a belt-shaped material may be used.

(10) In the above embodiment, the description has been given using a printer that prints an image provided from an external device such as a host computer on transfer paper. However, the present invention is not limited to this, and a copier, a facsimile machine, or the like is used. The present invention can be applied to a general electrophotographic image forming apparatus.
In short, a toner image developed using a developer in which toner is dispersed in a liquid carrier is temporarily carried on an intermediate transfer medium such as an intermediate transfer roller, an intermediate transfer belt, or an intermediate transfer drum, and then the toner image is recorded on the recording medium. The present invention can be applied to all image forming apparatuses that perform secondary transfer.

1 is a diagram illustrating an internal configuration of a printer that is a first embodiment of the present invention. FIG. The principal part enlarged view of FIG. 2 is a block diagram showing an electrical configuration of the printer. FIG. The figure which shows the structure of a carrier amount adjustment unit. Explanatory drawing of the peeling amount of the liquid carrier by a squeegee roller. The figure explaining the relationship between an image occupation rate and the amount of peeling of a liquid carrier. The figure explaining the relationship between an image occupation rate and the amount of peeling of a liquid carrier. The figure explaining the relationship between an image occupation rate and the amount of peeling of a liquid carrier. The figure explaining the relationship between an image occupation rate and the amount of peeling of a liquid carrier. The flowchart which shows an example of a peeling amount adjustment process routine. The figure which shows the internal structure of the printer which is 2nd Embodiment of this invention. The figure which shows the internal structure of the printer which is 3rd Embodiment of this invention. The figure explaining the peeling amount of the liquid carrier in a deformation | transformation form.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Photosensitive body (latent image carrier), 33Y, 33M, 33C, 33K ... Tank (container), 41 ... Intermediate transfer belt (intermediate transfer medium), 80Y, 80M, 80C, 80K ... Carrier amount adjustment unit (adjustment means) ), 81-83 ... squeegee roller (peeling member), 85 ... tray (collecting part), 86 ... piping (communication part), 881, 882 ... application roller (application member)

Claims (16)

A developer in which toners of different N colors (where N ≧ 2 is a natural number) are dispersed in a liquid carrier for each color is provided for each color corresponding to the N color toner, and an electrostatic latent image is formed on the surface thereof. The electrostatic latent images on the N latent image carriers that can carry the image are developed to form a toner image, and the N color toner images are transferred to the intermediate transfer medium in a predetermined order. In the image forming apparatus for forming a color image by superimposing on the intermediate transfer medium,
Adjusting means for adjusting the amount of liquid carrier contained in the uppermost attached developer that adheres to the intermediate transfer medium each time the toner image on the latent image carrier is transferred to the intermediate transfer medium;
An image forming apparatus characterized in that the ratio of the toner and the liquid carrier on the intermediate transfer medium can be controlled by the adjusting means. A developer in which toners of different N colors (where N ≧ 2 is a natural number) are dispersed in a liquid carrier for each color is provided for each color corresponding to the N color toner, and an electrostatic latent image is formed on the surface thereof. The electrostatic latent images on the N latent image carriers that can carry the image are developed to form a toner image, and the N color toner images are transferred to the intermediate transfer medium in a predetermined order. In the image forming apparatus for forming a color image by superimposing on the intermediate transfer medium,
Adjusting means for adjusting the amount of liquid carrier contained in the attached developer that adheres to the latent image carrier,
An image forming apparatus, wherein the ratio of the toner and the liquid carrier on the latent image carrier can be controlled by the adjusting means. Using a developer in which toners of different N colors (where N ≧ 2 is a natural number) are dispersed in a liquid carrier for each color, the electrostatic image is supported on the surface of the latent image carrier. The electrostatic latent image is developed for each color to form a toner image, and the process of transferring the toner image onto the intermediate transfer medium at the transfer position is repeated for N colors, thereby repeating the N color toner on the intermediate transfer medium. In an image forming apparatus that forms a color image by superimposing images,
Adjusting means for adjusting the amount of liquid carrier contained in the attached developer that adheres to the latent image carrier before the transfer of the toner image to the intermediate transfer medium;
An image forming apparatus, wherein the ratio of the toner and the liquid carrier on the latent image carrier can be controlled by the adjusting means. The adjusting means includes an applying member configured to be able to apply a liquid carrier to the attached developer.
The image forming apparatus according to claim 1, wherein the amount of liquid carrier contained in the attached developer is adjusted by controlling the amount of liquid carrier applied by the applying member. The applying member is provided at a contact position in contact with the attached developer, thereby giving a liquid carrier to the attached developer,
The adjusting means includes a plurality of application members arranged to face each other in the transport direction of the attached developer.
At least one of the plurality of applying members is configured to be movable between the contact position and a separated position that is separated from the attached developer and does not apply the liquid carrier,
The image forming apparatus according to claim 4, wherein the application amount is controlled by controlling a combination of application members arranged at the contact position by position control of the application member configured to be movable.   6. The image forming apparatus according to claim 4, wherein the application amount is controlled by changing a relative speed of a contact surface of the application member with respect to the attached developer. The adjusting means is configured to be disposed at a contact position in contact with the attached developer, and includes a stripping member that strips a liquid carrier on a surface layer of the developer by being disposed at the contact position.
The image forming apparatus according to claim 1, wherein the amount of liquid carrier contained in the attached developer is adjusted by controlling the amount of liquid carrier removed by the stripping member. The adjusting means includes, as the stripping member, a plurality of stripping members arranged opposite to each other in the transport direction of the attached developer,
At least one of the plurality of stripping members is configured to be movable between the contact position and a separated position that does not contact the attached developer.
8. The image forming apparatus according to claim 7, wherein the stripping amount is controlled by controlling a combination of the stripping members in contact with the attached developer by position control of the stripping member configured to be movable. The adjusting means includes, as the peeling member, a peeling member configured to be arranged at a plurality of contact positions that are in contact with the attached developer and that are different from each other in distance from the surface of the attached developer. ,
The image forming apparatus according to claim 7, wherein the stripping amount is controlled by changing a contact position of the stripping member.   The image forming apparatus according to claim 7, wherein the amount of peeling is controlled by changing a relative speed of a contact surface of the peeling member with respect to the attached developer. N containers for storing a developer in which toners of different N colors (where N ≧ 2 is a natural number) are dispersed in a liquid carrier for each color;
A cleaning member for removing the liquid carrier peeled off by the peeling member from the peeling member;
The image forming apparatus according to claim 7, further comprising a recovery unit that recovers the liquid carrier removed by the cleaning member and returns the liquid carrier to the container that stores the developer having the same color as the attached developer. .   The recovery means is provided below a contact position of the cleaning member to the stripping member, and recovers the liquid carrier that is removed by the cleaning member and freely falls, the recovery unit, and the recovery unit The image forming apparatus according to claim 11, further comprising: a communication unit that communicates with the container, wherein the liquid carrier recovered by the recovery unit is returned to the container via the communication unit.   The image according to claim 1, wherein the amount of liquid carrier contained in the attached developer is adjusted so that a toner concentration of the attached developer remaining after the adjustment of the amount of liquid carrier by the adjusting unit approaches a predetermined value. Forming equipment.   The image forming apparatus according to claim 1, wherein the adjustment unit adjusts an amount of liquid carrier contained in the attached developer according to image information related to the toner image.   The image formation according to claim 14, wherein the image information is obtained as an image occupancy ratio that is a ratio of an image portion occupied in the electrostatic latent image, and an amount of liquid carrier contained in the attached developer is adjusted according to the image occupancy ratio. apparatus. By developing an electrostatic latent image on a latent image carrier for each color by using a developer in which toners of different N colors (where N ≧ 2 is a natural number) are dispersed in a liquid carrier for each color, N color toner is developed. A development process for forming an image;
A transfer step of superimposing the N color toner image on the intermediate transfer medium by transferring the N color toner image onto the intermediate transfer medium in a predetermined order;
An adjustment step of adjusting the amount of liquid carrier contained in the developer constituting the toner image for each color,
An image forming method characterized in that the ratio of the toner and the liquid carrier in the developer constituting the toner image can be controlled in the adjustment step.

Images