JP5298107B2 - Density detector and image forming apparatus provided with the same - Google Patents

Description

  The present invention relates to a density detection apparatus that detects the density of a liquid developer and an image forming apparatus including the density detection apparatus.

  An image forming apparatus that forms an image on a sheet using a liquid developer collects the liquid developer that has not been used for image formation in an adjustment tank, and adjusts the collected liquid developer to an appropriate concentration in the adjustment tank. To do. As a result, the recovered liquid developer can be reused. The image forming apparatus includes a density detection device that detects the density of the liquid developer being adjusted (for example, Patent Document 1).

  The concentration detection device disclosed in Patent Document 1 is created by obtaining in advance a stirring member that rotates in a liquid developer, a torque meter that measures the rotational torque of the stirring member, and a relationship between the rotational torque and the concentration of the liquid developer. When detecting the concentration of the liquid developer, the concentration is detected by referring to the table data and converting the rotational torque into the concentration.

  In Patent Document 1, control is performed so that the conveyance of the liquid developer to the recovered developer storage tank is stopped while the concentration detection device detects the concentration of the liquid developer. This reduces the influence of flow unevenness caused by the operation of the pump that transports the liquid developer to the recovered developer storage tank. As a result, it is attempted to accurately detect the concentration of the liquid developer.

Japanese Patent Laid-Open No. 2007-21909

  However, the concentration detection device of Patent Document 1 uses a stirring member for concentration detection. Therefore, when the liquid developer has a high viscosity (that is, high concentration), the liquid developer may be entangled with the blade portion or the shaft portion of the stirring member. In that case, the rotational torque of the stirring member decreases regardless of the concentration of the liquid developer, and an accurate rotational torque cannot be obtained. As a result, the accuracy of detecting the concentration of the liquid developer is lowered.

  Accordingly, in view of the above circumstances, the present invention provides a density detection device that can maintain density detection accuracy even when the concentration of the liquid developer is high, and an image forming apparatus including the density detection device. Objective.

  In order to achieve the above object, a concentration detection apparatus according to the present invention detects a concentration of a liquid developer whose viscosity changes, and stores a storage container that stores the liquid developer at a predetermined liquid position. A rotating member rotatable in the liquid developer, a rotating shaft to which the rotating member is attached, a driving source for rotating the rotating shaft with a constant driving force, and a rotating speed for detecting the rotating speed of the rotating member A detecting means; a displacement member disposed at a predetermined position above the predetermined liquid position and in the vicinity of the rotation shaft; and a displacement member capable of being displaced from the predetermined position; and a displacement detection means for detecting that the displacement member is displaced. A heating means for warming the liquid developer; and a density detection unit that controls the heating means and detects the density of the liquid developer based on the rotation speed. Change of the displacement member There when detected, first, warmed the liquid developer by controlling the heating means, then, to detect the concentration of the liquid developer.

  The density detection apparatus according to the present invention uses the characteristics that the viscosity of the liquid developer changes according to the density and the characteristics that the rotation speed of the rotating member changes according to the viscosity of the liquid developer, and thereby adjusts the rotation speed. Based on this, the concentration is detected. When the displacement of the displacement member is detected, the concentration detection unit of the concentration detection device controls the heating means to warm the liquid developer. The displacement of the displacement member occurs when the liquid developer has a high viscosity (that is, concentration), the liquid developer is entangled with the rotation shaft beyond a predetermined liquid position, and the entangled liquid developer contacts the displacement member. . In the state where the liquid developer is entangled with the rotation shaft, the rotation speed cannot be accurately detected. However, in the present invention, the viscosity of the liquid developer is reduced by using the property that the viscosity changes according to the temperature and the liquid developer is warmed, and the entanglement of the liquid developer on the rotation axis is eliminated. . Thereby, the rotation speed is accurately detected. The density detection unit detects the density of the liquid developer based on the rotation speed after eliminating the entanglement of the liquid developer on the rotation axis. Thus, according to the concentration detection apparatus of the present invention, the displacement of the displacement member is detected as compared with the configuration in which the liquid developer is always warmed so that the liquid developer does not get entangled with the rotation shaft of the rotation member. Since the heating means is used only when the power consumption is low.

  In a preferred embodiment of the present invention, the density detection device further includes a first value created by previously obtaining a relationship between the rotation speed and the density of the liquid developer when the liquid developer is at a first temperature. A storage unit for storing a table and a second table created by previously obtaining a relationship between the rotation speed and the density when the liquid developer is at a second temperature higher than the first temperature; When the displacement of the displacement member is not detected, the concentration detection unit refers to the first table to convert the rotational speed into the concentration, and when the displacement of the displacement member is detected, The heating means is controlled to raise the temperature of the liquid developer to the second temperature, and then the rotation speed is converted into the density with reference to the second table.

  According to this configuration, the density detection unit obtains the relationship between the rotation speed and the density when the liquid developer is at the first temperature in advance, and the liquid developer is at the second temperature. In other words, the second table prepared by previously obtaining the relationship between the rotation speed and the density when the liquid developer is heated to such an extent that the liquid developer does not get entangled with the rotation axis is selectively referred to. Then, the rotation speed is converted into the concentration. As a result, the accuracy of density detection can be maintained even when the viscosity of the liquid developer is high.

  An image forming apparatus according to the present invention includes an image forming unit that forms an image on a sheet using a liquid developer, the density detecting device having the above-described configuration, and the concentration of the liquid developer based on detection by the density detecting device. And an adjusting unit for adjusting the.

  Since the image forming apparatus according to the present invention includes the concentration detection device having high detection accuracy even when the liquid developer has a high concentration (high viscosity), the concentration of the liquid developer is appropriately adjusted. . Thereby, a high quality image is obtained.

  In another preferred embodiment of the present invention, the liquid developer includes a carrier liquid, a pigment dispersed in the carrier liquid, and a dissolved resin dissolved in the carrier liquid. It is used to fix the pigment on the sheet, the concentration detection device detects the concentration of the dissolved resin, and the first table and the second table are respectively the rotation members. The relationship between the rotation speed and the concentration of the dissolved resin is created in advance, and the adjustment unit adjusts the concentration of the dissolved resin based on detection by the concentration detection device.

  According to this configuration, even when the concentration (viscosity) of the dissolved resin for fixing the pigment on the sheet is high, the concentration of the dissolved resin can be accurately detected by the concentration detection device. Therefore, the adjustment unit can appropriately adjust the concentration of the dissolved resin. As a result, a high-quality image with a good pigment fixing state can be obtained.

  The concentration detection apparatus according to the present invention detects the concentration of the liquid developer using the heating means only when the liquid developer is entangled with the rotating shaft, and thus consumes less power. Since the image forming apparatus according to the present invention includes the density detection device having high detection accuracy even when the liquid developer has a high density, the density of the liquid developer is appropriately adjusted. Thereby, a high quality image is obtained.

It is a figure which shows typically the structure of the density | concentration detection apparatus which concerns on embodiment of this invention. FIG. 6 is a schematic diagram illustrating a state where a liquid developer is entangled with a rotation shaft of a rotation mechanism of the density detection device. It is a flowchart which shows the operation | movement of the density | concentration detection of the melted resin by a density | concentration detection apparatus. 1 is an overall schematic cross-sectional view of a color printer according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of a color printer, excluding a portion of a liquid developer circulation device. 1 is a schematic cross-sectional view of a developing device used in a color printer and a peripheral portion thereof. It is a block diagram of a liquid developer circulation device.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram schematically illustrating a configuration of a concentration detection device 50 according to the present embodiment. The density detection device 50 is applied to a wet type image forming apparatus that forms an image on a sheet using a liquid developer, and is a device for detecting the density of the liquid developer. In particular, the liquid developer used in the present embodiment includes an electrically insulating carrier liquid, colored particles dispersed in the carrier liquid, and a resin dissolved in the carrier liquid (hereinafter referred to as a dissolved resin). The concentration detection device 50 is a device capable of detecting the concentration of the dissolved resin. The dissolved resin is an important element for fixing the colored particles on the sheet. The liquid developer will be described in detail later.

  Specifically, the density detecting device 50 is applied to a developer adjusting unit that adjusts the concentration of the liquid developer collected from the developing device 14 as described later. The concentration detection apparatus 50 includes a storage container 51, a rotation mechanism R, a rotation speed detection unit 57, a displacement detection unit D, a heater 61, a temperature detection sensor 62, a storage unit 63, and a concentration detection unit 66. Including.

  The storage container 51 stores the liquid developer LD at a predetermined liquid position LV. A liquid range LR in which the liquid developer LD is stored in the storage container 51 is defined by the predetermined liquid position LV. The liquid range LR is a range extending from the bottom of the storage container 51 to the liquid position LV.

  A supply pipe 52 and a discharge pipe 53 are connected to the storage container 51. A supply pump 54 is disposed in the supply pipe 52. When the supply pump 54 is driven, the liquid developer LD is supplied into the storage container 51 through the supply pipe 52. Although the supply pipe 52 is located above the liquid position LV in FIG. 1, the position is not particularly limited, and may be located below the liquid position LV.

  The discharge pipe 53 has a discharge port 53a at a position corresponding to the liquid position LV. The discharge port 53a is always open. Therefore, when the liquid developer LD is supplied to the storage container 51, the liquid developer LD is adjusted to a predetermined liquid position LV without requiring special control.

  The rotation mechanism R includes a rotation member 55, a rotation shaft 56 to which the rotation member 55 is fixed, and a drive source M. The rotating member 55 is disposed below the predetermined liquid position LV and within the liquid range LR. The rotating member 55 has a flat cylindrical shape in FIG. 1, but these shapes are not particularly limited, and may have a symmetric propeller shape around the rotating shaft 56 or a flat plate shape. You may have. A drive source M is connected to the rotating shaft 56. The drive source M is a motor, for example, and rotates the rotating shaft 56 with a constant driving force. Due to the rotation of the rotating shaft 56, the rotating member 55 rotates in the liquid developer LD in the liquid range LR.

  The rotating member 55 receives resistance from the liquid developer LD according to the viscosity of the liquid developer LD as it rotates. In particular, since the concentration of the dissolved resin greatly affects the viscosity of the liquid developer LD, when the concentration of the dissolved resin is high, the viscosity of the liquid developer LD increases, and the resistance that the rotating member 55 receives from the liquid developer LD is large. Become. As a result, the rotational speed of the rotating member 55 decreases. On the other hand, when the concentration of the dissolved resin is low, the viscosity of the liquid developer LD becomes low and the resistance becomes small. Thereby, the rotational speed of the rotating member 55 is increased. That is, as the resistance increases, the rotation speed of the rotation member 55 decreases, and as the resistance decreases, the rotation speed of the rotation member 55 increases.

  The rotational speed detector 57 (rotational speed detection means) detects the rotational speed of the rotating member 55. The rotational speed detection unit 57 includes, for example, a light emitting element, a light receiving element, and a light shielding plate attached to the rotating member 55 or the rotating shaft 56, and the number of times the light shielding plate shields light from the light emitting element in minutes. By measuring, the rotational speed of the rotating member 55 is obtained. The configuration of the rotation speed detection unit 57 is not particularly limited.

  The displacement detection means D includes a displacement member 58 and a displacement detection unit 60. The displacement member 58 is disposed to face the rotation shaft 56 at a home position that is a position above the predetermined liquid position LV of the liquid developer LD and in the vicinity of the rotation shaft 56. The displacement member 58 is supported by a wire 59 or the like, and can be displaced from the home position along the liquid surface of the liquid developer LD. Although the displacement member 58 has a flat columnar shape in FIG. 1, the shape is not particularly limited, and may be a flat plate shape or a rod shape. The displacement detector 60 is means for detecting whether or not the displacement member 58 is displaced from the home position. The displacement detection unit 60 is, for example, a reflection type optical sensor. The displacement detection unit 60 radiates light to a reflection surface provided on the surface of the displacement member 58, and detects the displacement of the displacement member 58 depending on whether the reflected light is received. To do. When the displacement member 58 is displaced from the home position, the reflective photosensor does not receive the reflected light. Thereby, the displacement of the displacement member 58 is detected. The configuration of the displacement detector 60 is not particularly limited.

  The heater 61 is disposed on the bottom side of the storage container 51 and warms the liquid developer LD in the storage container 51. The arrangement position of the heater 61 is not particularly limited, and may be within the liquid range LR of the storage container 51. The heater 61 is an example of the heating means of the present invention.

  The temperature detection sensor 62 is disposed within the liquid range LR of the storage container 51 and detects the temperature of the liquid developer LD.

  The storage unit 63 stores a first table 64 and a second table 65. The first table 64 is calibration curve data created by obtaining in advance the relationship between the rotation speed of the rotating member 55 and the concentration of the dissolved resin when the liquid developer LD is adjusted to the first temperature. The first temperature is a normal temperature of the liquid developer LD, and is about 25 ° C., for example.

  On the other hand, the second table 65 is created by previously obtaining a relationship between the rotation speed of the rotating member 55 and the concentration of the dissolved resin when the liquid developer LD is adjusted to a second temperature higher than the first temperature. Calibration curve data. Since the second temperature is higher than the first temperature, when the liquid developer LD is at the second temperature, the viscosity of the liquid developer LD decreases.

  When the concentration detector 50 is configured to detect the concentration of the liquid developer LD instead of the concentration of the dissolved resin, the first table 64 is rotated when the liquid developer LD is adjusted to the first temperature. This is calibration curve data created by obtaining in advance the relationship between the rotational speed of the member 55 and the concentration of the liquid developer LD, and the second table 65 is obtained when the liquid developer LD is adjusted to the second temperature. This is calibration curve data created by obtaining in advance the relationship between the rotation speed of the rotating member 55 and the concentration of the liquid developer LD.

  The density detector 66 has a characteristic that the viscosity of the liquid developer LD changes according to the density (particularly the concentration of the dissolved resin), and a characteristic that the rotation speed of the rotating member 55 changes according to the viscosity of the liquid developer LD. Utilizing this, the concentration of the dissolved resin is detected based on the rotational speed of the rotating member 55.

  Specifically, the concentration detection unit 66 controls the supply pump 54, the drive source M, and the heater 61, and controls the first table 64 and the second table 65 based on the displacement detection of the displacement member 58 by the displacement detection means D. With reference to it selectively, the rotational speed of the rotating member 55 is converted into the concentration of the dissolved resin.

  The displacement of the displacement member 58 occurs as follows. That is, when the viscosity of the liquid developer LD is high, the liquid developer LD is entangled with the rotation shaft 56 beyond the predetermined liquid position LV of the storage container 51 as shown in FIG. Easy to form a mass AD. Although not shown, the liquid developer LD is also entangled with the rotating member 55. At this time, the mass AD of the liquid developer LD contacts the displacement member 58 and moves the displacement member 58 from the home position H1 indicated by the two-dot difference line to the displacement position H2 indicated by the solid line. The displacement of the displacement member 58 that occurs in this way is detected by the displacement detection means D. In a state where the liquid developer LD is entangled with the rotation shaft 56, the rotation speed of the rotation member 55 is not accurately detected.

  Therefore, in the present embodiment, in order to cope with the entanglement of the liquid developer LD on the rotation shaft 56, the density detection unit 66 detects the displacement of the displacement member 58 (the liquid developer LD is applied to the rotation shaft 56). First, when the liquid developer LD is heated by controlling the heater 61 to raise the temperature of the liquid developer LD to the second temperature, then, referring to the second table 65, While the rotation speed of the rotating member 55 is converted into the concentration of the dissolved resin, when the displacement of the displacement member 58 is not detected (when the liquid developer LD is not entangled with the rotating shaft 56), referring to the first table 64, The rotation speed of the rotation member 55 is configured to be converted into the concentration of the dissolved resin.

  A specific detection operation by the concentration detection unit 66 will be described with reference to the flowchart of FIG. In detecting the concentration of the dissolved resin, the concentration detector 66 first controls the supply pump 54 to supply the liquid developer LD to the storage container 51 and adjust the liquid developer LD to a predetermined liquid position LV (step). S1). Next, the density detector 66 controls the driving source M to rotate the rotating member 55 with a constant driving force (step S2). The concentration detector 66 converts the rotational speed of the rotating member 55 into the concentration of the dissolved resin based on the detection by the displacement detector D.

  That is, when the displacement of the displacement member 58 is not detected (NO in step S3), the concentration detector 66 obtains the rotational speed of the rotary member 55 detected by the rotational speed detector 57 (step S4). Referring to the first table 64, the rotation speed of the rotating member 55 is converted into the concentration of the dissolved resin (step S5). Thereby, the density | concentration of melt | dissolution resin is obtained.

  On the other hand, when the displacement of the displacement member 58 is detected (YES in step S3), the concentration detecting unit controls the heater 61 (step S6) to raise the temperature of the liquid developer LD to the second temperature (step S7). ). The temperature of the liquid developer LD is increased based on the temperature detection of the liquid developer LD by the temperature detection sensor 62. When the liquid developer LD reaches the second temperature, the temperature rise by the heater 61 is stopped. The concentration detection unit 66 obtains the rotation speed of the rotation member 55 detected by the rotation speed detection unit 57 (step S8), and then refers to the second table 65 to determine the rotation speed of the rotation member 55 as a dissolved resin. (Step S9). Thereby, the density | concentration of melt | dissolution resin is obtained.

  According to the concentration detection apparatus 50 according to the present embodiment described above, when the displacement of the displacement member 58 is detected, the concentration detection unit 66 first controls the heater 61 to bring the liquid developer LD to the second temperature. Raise the temperature. Therefore, since the viscosity of the liquid developer LD decreases according to the characteristic that the viscosity changes according to the temperature, the lump AD (FIG. 2) of the liquid developer LD collapses, and the entanglement of the liquid developer LD on the rotating shaft 56 is eliminated. Is done. Thereby, the rotational speed of the rotating member 55 is accurately detected. In the present embodiment, the second temperature is a temperature at which the entanglement of the liquid developer LD with the rotation shaft 56 is eliminated, and is about 50 ° C., for example.

  Then, the concentration detector 66 eliminates the entanglement of the liquid developer LD on the rotating shaft 56, and then refers to the second table 65 to convert the rotational speed of the rotating member 55 into the concentration of the dissolved resin. Further, when the displacement of the displacement member 58 is not detected (that is, when the liquid developer LD is not entangled with the rotation shaft 56), the density detector 66 does not control the heater 61 and controls the first table. 64, the rotation speed of the rotating member 55 is converted into the concentration of the dissolved resin. As described above, according to the concentration detection apparatus 50 according to the present embodiment, the heater 61 is used only when the displacement of the displacement member 58 is detected, so that the liquid developer LD does not entangle with the rotation shaft 56 of the rotation member 55. Thus, the power consumption can be reduced as compared with the configuration in which the liquid developer LD is always warmed.

  Further, according to the concentration detection apparatus 50 according to the present embodiment, the concentration detection unit 66 preliminarily shows the relationship between the rotation speed of the rotating member 55 and the concentration of the dissolved resin when the liquid developer LD is at the first temperature. The first table 64 thus created and the rotation when the liquid developer LD is at the second temperature, that is, when the temperature of the liquid developer LD is raised to such an extent that the liquid developer LD does not entangle with the rotation shaft 56. The rotational speed is converted into a concentration by selectively referring to the second table 65 created by previously obtaining the relationship between the rotational speed of the member 55 and the dissolved resin concentration. Thereby, even when the viscosity of the liquid developer LD is high, the accuracy of the concentration detection of the dissolved resin can be maintained. As a result, the concentration detection device 50 can accurately detect the concentration of the dissolved resin in a wide viscosity range. In addition, since the developer adjustment unit of the image forming apparatus can adjust the concentration of the dissolved resin based on the accurate concentration of the dissolved resin detected by the concentration detection device 50, the colored particles are fixed in a good image quality. An image can be obtained.

  In the present embodiment, the configuration in which the second table 65 is added has been described in order to consider the amount of change in viscosity due to a temperature change when the liquid developer LD is heated to the second temperature. Instead of 65, the rotational speed of the rotating member 55 may be converted into the concentration of the dissolved resin by adding a correction coefficient corresponding to the amount of change in the viscosity to the calibration curve data as the first table 64.

(Wet image forming device)
FIG. 4 is a schematic configuration diagram of a color printer 1 (wet image forming apparatus) in which the above-described density detection device 50 is incorporated, and FIG. 5 is a schematic cross-sectional view of the color printer 1 excluding the liquid developer circulating device. FIG. 4 and 5 exemplify a color printer as the image forming apparatus.

  As shown in FIG. 4, the color printer 1 is arranged in an upper main body 1A in which various units and parts for image formation are stored, and a lower part of the upper main body 1A, and a liquid developer circulation for each color. It is comprised from the lower main-body part 1B in which apparatus LY, LM, LC, LB is accommodated.

  As shown in FIG. 5, the upper main body 1 </ b> A is formed by a tandem image forming unit 2 that forms an image based on image data, a sheet storage unit 3 that stores a sheet, and an image forming unit 2. A secondary transfer unit 4 that transfers an image onto a sheet, a discharge unit 6 that discharges a sheet on which an image is formed, and a sheet conveyance unit 7 that conveys a sheet from the sheet storage unit 3 to the discharge unit 6 are included. ing.

  The image forming unit 2 includes an intermediate transfer belt 21, a cleaning unit 22 for the intermediate transfer belt 21, and an image forming unit corresponding to each of yellow (Y), magenta (M), cyan (C), and black (Bk). FY, FM, FC, and FB.

  The intermediate transfer belt 21 is a wide endless belt member having conductivity, and is driven to circulate clockwise in FIG.

  The image forming units FY, FM, FC, and FB are arranged side by side along the lower running surface of the intermediate transfer belt 21.

  The image forming units FY, FM, FC, and FB include a photosensitive drum 10, a charging device 11, an LED exposure device 12, a liquid developing device 14, a primary transfer roller 20, a cleaning device 26, and a charge eliminating device 13. And a carrier liquid removing roller 30.

  The surface (circumferential surface) of the cylindrical photosensitive drum 10 can carry an image visualized with colored particles charged (charged to a positive polarity in this embodiment). The illustrated photosensitive drum 10 can rotate counterclockwise. The charging device 11 uniformly charges the surface of the photosensitive drum 10.

  The LED exposure device 12 has an LED as a light source, and irradiates light onto the uniformly charged surface of the photosensitive drum 10 based on image data input from an external device. As a result, an electrostatic latent image based on the image data is formed on the surface of the photosensitive drum 10.

  The liquid developing device 14 holds the liquid developer so as to face the electrostatic latent image formed on the surface of the photosensitive drum 10. As a result, the electrostatic latent image on the surface of the photosensitive drum 10 is visualized with the charged liquid developer and developed as an image.

  As shown in FIG. 6, the liquid developing device 14 includes a developing container 140, a developing roller 141, a supply roller 142, a support roller 143, a supply roller blade 144, a developing cleaning blade 145, a developer recovery device 146, and a developing roller charging device. 147.

  The developer container 140 is supplied with a liquid developer and stores the liquid developer. The liquid developer is supplied from the supply nozzle 278 to the inside of the developing container 140 after density adjustment is performed in advance. In that case, the liquid developer is supplied toward the nip portion between the supply roller 142 and the support roller 143, and the excess part falls below the support roller 143 and is stored in the bottom of the developing container 140. Excess liquid developer is recovered and reused.

  The support roller 143 is disposed substantially at the center of the developing container 140 and abuts against the supply roller 142 from below to form a nip portion. The supply roller 142 is not disposed directly above the support roller 143 but is shifted in a direction away from the supply nozzle 278. A groove for holding the liquid developer is provided on the peripheral surface of the supply roller 142. As indicated by dotted arrows in the figure, the support roller 143 rotates counterclockwise and the supply roller 142 rotates clockwise.

  The liquid developer supplied from the supply nozzle 278 is temporarily retained in the nip portion, and is conveyed upward while being held in the groove of the supply roller 142 as the rollers 142 and 143 rotate. The supply roller blade 144 is pressed against the peripheral surface of the supply roller 142 and regulates the amount of liquid developer held in the groove of the supply roller 142 to be a predetermined amount. Excess liquid developer scraped off by the supply roller blade 144 is stored at the bottom of the developing container 140.

  The developing roller 141 is disposed in the upper opening of the developing container 140 so as to be in contact with the supply roller 142. The developing roller 141 is rotated in the same direction as the supply roller 142. As a result, the surface of the developing roller 141 moves in the opposite direction to the surface of the supplying roller 142 at the nip portion where the developing roller 141 and the supplying roller 142 abut. As a result, the liquid developer held on the peripheral surface of the supply roller 142 is delivered to the peripheral surface of the developing roller 141. Since the amount of liquid developer held in the groove of the supply roller 142 (thickness of the thin layer of liquid developer) is regulated to a predetermined value, the amount of liquid developer carried on the surface of the developing roller 141 (liquid The thickness of the developer thin layer) is also kept at a predetermined value.

  The developing roller charging device 147 applies a bias potential having the same polarity as the charged polarity of the colored particles of the liquid developer (in this embodiment, a positive polarity bias potential) to the developing roller 141 from the outer surface side (developing corona charge). Then, the colored particles in the thin layer of the liquid developer carried on the surface of the developing roller 141 are moved to the surface side of the developing roller 141. As a result, the colored particles in the thin layer of the liquid developer are gathered and compressed on the developing roller 141 side by an electric field action (compaction treatment), and a layer of colored particles having a high concentration is formed on the developing roller 141 side. Thereafter, the thin layer of the liquid developer is supplied to the photosensitive drum 10 by the potential difference between the potential of the electrostatic latent image on the surface of the photosensitive drum 10 and the developing electric field applied to the developing roller 141, and The electrostatic latent image on the drum 10 is developed.

  The developing cleaning blade 145 is disposed so as to contact the downstream side in the rotational direction of the contact portion of the developing roller 141 with the photosensitive drum 10, and the liquid development on the surface of the developing roller 141 that has completed the developing operation on the photosensitive drum 10 Remove the agent.

  The developer recovery device 146 recovers the liquid developer removed by the development cleaning blade 145 and sends the liquid developer to the first pipe 771 of the liquid developer circulation device.

  The primary transfer roller 20 applies a voltage having a polarity opposite to that of the colored particles (minus in the present embodiment) to the intermediate transfer belt 21 at a position in contact with the intermediate transfer belt 21. Since the intermediate transfer belt 21 has conductivity, the applied voltage attracts colored particles to the surface side of the intermediate transfer belt 21 and its periphery. That is, the developed image on the surface of the photosensitive drum 10 is transferred to the intermediate transfer belt 21.

  The cleaning device 26 is a device for cleaning the liquid developer remaining without being transferred from the photosensitive drum 10 to the intermediate transfer belt 21. As shown in FIG. 6, the cleaning device 26 includes a residual developer conveying screw 261 and a cleaning blade 262. The residual developer transport screw 261 is scraped off by the cleaning blade 262 and transports the residual developer stored in the cleaning device 26 to the outside of the cleaning device 26.

  The static eliminator 13 has a light source for static elimination, and removes the liquid developer by the cleaning blade 262 and removes the surface of the photosensitive drum 10 with light from the light source in preparation for the next round of image formation.

  The substantially cylindrical carrier liquid removing roller 30 is disposed on the side where the secondary transfer unit 4 is disposed with respect to the position where the photosensitive drum 10 and the intermediate transfer belt 21 are in contact with each other. Remove the carrier liquid from

  The sheet storage unit 3 shown in FIG. 5 is disposed at the lower part of the upper main body 1A and includes a paper feed cassette (not shown) for storing sheets.

  The secondary transfer unit 4 secondarily transfers the image formed on the intermediate transfer belt 21 to a sheet. The secondary transfer unit 4 includes a support roller 41 that supports the intermediate transfer belt 21, and a secondary transfer roller 42 that is disposed to face the support roller 41.

  On the upper side of the secondary transfer unit 4, conveyance rollers 8 and 8 are provided. An image is transferred to a discharge unit 6 provided on the upper surface of the upper main body 1A, and a sheet on which image fixing has been completed is discharged. The sheet conveyance unit 7 includes a plurality of conveyance roller pairs, and conveys the sheet from the sheet storage unit 3 through the secondary transfer unit 4 to the discharge unit 6.

  In the upper main body 1A according to the present embodiment, by using the liquid developer described below, the sheet transferred to the sheet using heat or light energy is fixed without using a fixing process. The image transferred onto the sheet can be fixed on the sheet.

(Liquid developer)
The liquid developer according to this embodiment contains an electrically insulating carrier liquid, colored particles dispersed in the carrier liquid, and cellulose ether that is a dissolved resin dissolved in the carrier liquid.

In general, an electrically insulating carrier liquid serves as a liquid carrier, and is used for the purpose of enhancing the electrical insulating properties of the obtained liquid developer. As the electrically insulating carrier liquid, an organic solvent having an electrically insulating property and having a volume resistance at 25 ° C. of 10 ¹⁰ Ω · cm or more (in other words, conductivity of 100 pS / cm or less) is preferable. .

  As the carrier liquid that can be used in the present embodiment, in addition to the above physical properties, those capable of dissolving cellulose ether (those having relatively high solubility of cellulose ether) are preferable. Examples of such carrier liquids include oils such as vegetable oils, animal oils, and mineral oils. Among these, vegetable oils are preferable, and vegetable oils are more preferable. Among them, tall oil fatty acids (main components: oleic acid and linoleic acid) are preferable.

  In the present embodiment, the colored particles are not the toner in which the pigment is dispersed in the binder resin, but the pigment itself. As such a pigment, for example, a conventionally known organic pigment or inorganic pigment can be used without any particular limitation.

  In the present embodiment, the liquid developer contains cellulose ether that is a dissolved resin. Cellulose ether is a polymer in which a hydroxyl group in a cellulose molecule is substituted with an alkoxy group. The substitution rate is preferably 45 to 49.5%. Moreover, the alkyl part of the alkoxy group may be substituted with, for example, a hydroxyl group. A film formed of cellulose ether is excellent in toughness, thermal stability, and the like.

  In the liquid developer according to this embodiment, the cellulose ether exists in a state dissolved in the carrier liquid. As a result, the fixing mechanism of the image on the sheet is as follows. That is, the cellulose ether in the liquid developer stored in the developing container 140 of the liquid developing device 14 exists in a state dissolved in the carrier liquid. This state is the same on the developing roller 141, the photosensitive drum 10, and the intermediate transfer belt 21. However, the ratio of the carrier liquid in the liquid developer gradually decreases, but the cellulose ether in the liquid developer remains dissolved in the carrier liquid. When the image is transferred from the intermediate transfer belt 21 to the sheet by the secondary transfer unit 4, the cellulose ether and the colored particles (pigments) in the carrier liquid remain on the surface of the sheet, while the carrier liquid Absorbed inside. Along with this, the concentration of the cellulose ether in the carrier liquid increases on the surface of the sheet and exceeds the saturation dissolution amount. Cellulose ether exceeding the saturated dissolution amount stays on the surface of the sheet to form a film while coating the pigment remaining on the surface of the sheet. The pigment is fixed to the sheet by the cellulose ether film, and the image transferred to the pigment, that is, the sheet, can be fixed to the sheet without consuming heat energy or light energy. Energy saving is achieved. This is a very advantageous action in terms of environmental protection. Further, the wet image forming apparatus 1 according to the present embodiment does not require a fixing unit using heat or light energy that has been conventionally used, and simplification and cost reduction of the wet image forming apparatus 1 are achieved.

  The cellulose ether content in the liquid developer is preferably 1 to 6% by mass. More preferably, it is 2 mass% or more, More preferably, it is 3 mass% or more. Moreover, More preferably, it is 5 mass% or less, More preferably, it is 4 mass% or less. When the cellulose ether content is less than 1% by mass, the amount of the cellulose ether film remaining on the surface of the sheet becomes too small, and there is a possibility that the film-forming property and thus the fixing property is excessively insufficient. When the content of the cellulose ether exceeds 6% by mass, the amount of the cellulose ether film remaining on the surface of the sheet is excessively increased, the drying property of the film is excessively decreased, and the adhesiveness (tackiness) of the film is excessively increased. There is a possibility that the scratch resistance of the image is excessively lowered. In addition, developability may be insufficient, image density may be low, and fog may increase.

(Liquid developer circulation device)
Next, a liquid developer supply and recovery system will be described. FIG. 7 is a block diagram showing an outline of the entirety of one liquid developer circulating device LY. The other liquid developer circulating devices LM, LC, LB have the same configuration. The liquid developer circulating device LY is a device for supplying the liquid developer to the developing device 14 and circulating and recovering the liquid developer recovered without being used for development.

  The liquid developer circulation device LY includes a recovered developer tank 71, a developer adjusting unit 72, a pigment tank 73, a resin tank 74, a carrier tank 75, a developer reserve tank 76, and a plurality of pumps P1 to P8.

  The recovered developer tank 71 is a tank that is connected to the developing device 14 via the first pipe 771 and can store the liquid developer recovered from the developing device 14 side. The first pipe 771 is connected to the developer recovery device 146, and a first pump P1 is disposed in the middle of the first pipe 771, and is driven by the developer recovery device 146 through the first pipe 771 by driving the first pump P1. The recovered residual liquid developer is collected in the recovered developer tank 71. In addition, a pipe (not shown) extending from the developing container 140 is connected to the collected developer tank 71. With this pipe, the liquid developer remaining in the developing container 140 is collected in the collected developer tank 71.

  The developer adjustment unit 72 adjusts the concentration of the liquid developer LD based on the concentration detection of a concentration detection device 723 described later, while preparing the liquid developer LD with the concentration adjusted appropriately. A developer container 720 connected to the collected developer tank 71 is provided. The developer container 720 is a container for preparing the liquid developer LD whose concentration is adjusted to an appropriate range by adding the recovered residual liquid developer LD, the pigment, the resin solution, and the carrier liquid. . The developer container 720 is connected to the recovered developer tank 71 via a second pipe 772, and a second pump P 2 is attached to the second pipe 772. The liquid developer LD in the collected developer tank 71 is sent to the developer container 72 through the third pipe 83 by driving the second pump P2.

  In the developer container 72, a liquid level detection device including a rotary blade 721 and a drive shaft 722 for rotating the rotary blade 721 is disposed in order to detect the liquid developer amount LD. The rotary blade 721 is disposed so as to come into contact with the liquid developer LD when the liquid level of the liquid developer LD in the developer container 272 reaches a predetermined height position or more. The drive shaft 722 is rotationally driven by a motor (not shown), and the amount of liquid developer is detected based on the load change of the motor that accompanies the contact of the rotary blade 721 with the liquid surface of the liquid developer LD.

  The pigment tank 73 stores a dispersion of pigment that contributes to image formation of each color. In the binder resin tank 74, cellulose ether is stored in a state dissolved in an insulating organic solvent. A carrier liquid is stored in the carrier tank 75.

  The pigment tank 73 and the developer container 72 are connected by a third pipe 773, and the pigment dispersion is supplied to the developer container 72 by driving a third pump P3 provided in the middle of the third pipe 773. Is done. The binder resin tank 74 and the developer container 72 are connected by a fourth pipe 774, and the cellulose ether is transferred to the developer container 72 by driving a fourth pump P 4 provided in the middle of the fourth pipe 774. Supplied. The carrier tank 75 and the developer container 72 are connected by a fifth pipe 775, and the carrier liquid is supplied to the developer container 72 by driving a fifth pump P5 provided in the middle of the fifth pipe 775. The

  The developer reserve tank 76 is a tank that stores a liquid developer to be supplied to the developing device 14. The developer reserve tank 76 is connected to the developer container 720 by a sixth pipe 776, and the liquid developer is transferred from the developer container 720 by driving a sixth pump P 6 provided in the middle of the sixth pipe 776. Receive supply of LD. Further, the developer reserve tank 76 is connected to the above-described supply nozzle 278 for supplying the liquid developer into the developing device 14 by a seventh pipe 777, and the supply of the liquid developer is attached to the seventh pipe 777. It is executed by driving the seventh pump P7.

  The concentration of the liquid developer in the developer container 720 is adjusted based on the detection result of the concentration of the liquid developer LD by the concentration detection device 723, particularly the concentration of the dissolved resin. As the concentration detection device 723, the concentration detection device described with reference to FIGS. 1 to 3 is used. A circulation conduit 778 connected to the bottom of the developer container 720 is attached to the developer container 720. In the circulation line 778, a concentration detecting device 723 and an eighth pump P8 are disposed. By driving the eighth pump P8, the liquid developer LD is taken into the storage container 51 of the concentration detection device 723, and after measuring the concentration of the dissolved resin, the liquid developer LD is returned to the developer container 720. The control unit (not shown) prepares the liquid developer by appropriately driving the third to fifth pumps P3 to P5 based on the density measurement result of the density detector 723 to adjust the concentration of the liquid developer.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Image forming part 50 Density detection apparatus 51 Storage container 55 Rotating member 56 Rotating shaft 57 Rotational speed detection part 58 Displacement member 60 Displacement detection part 63 Memory | storage part 66 Density detection part AD Liquid developer lump LD Liquid developer LR predetermined liquid range LV predetermined liquid position M driving source R rotating mechanism

Claims (4)

A concentration detection device for detecting the concentration of a liquid developer whose viscosity changes,
A storage container for storing the liquid developer at a predetermined liquid position;
A rotating member rotatable in the liquid developer;
A rotating shaft to which the rotating member is attached;
A driving source for rotating the rotating shaft with a constant driving force;
A rotational speed detecting means for detecting the rotational speed of the rotating member;
A displacement member that is disposed at a predetermined position above the predetermined liquid position and in the vicinity of the rotation shaft, and is displaceable from the predetermined position;
Displacement detecting means for detecting that the displacement member is displaced;
Heating means for warming the liquid developer;
A concentration detector that controls the heating means and detects the concentration of the liquid developer based on the rotational speed;
With
When the displacement of the displacement member is detected, the density detector first controls the heating means to warm the liquid developer, and then detects the density of the liquid developer. . The concentration detection apparatus according to claim 1,
Further, a first table prepared by previously obtaining a relationship between the rotation speed and the concentration of the liquid developer when the liquid developer is at the first temperature, and the liquid developer from the first temperature. A storage unit for storing a second table created by previously obtaining a relationship between the rotation speed and the concentration in the case of a higher second temperature;
The concentration detector
When the displacement of the displacement member is not detected, the rotational speed is converted into the concentration with reference to the first table,
On the other hand, when the displacement of the displacement member is detected, first, the heating means is controlled to raise the temperature of the liquid developer to the second temperature, and then the rotation is made with reference to the second table. A concentration detector that converts the speed into the concentration. An image forming unit that forms an image on a sheet using a liquid developer;
The concentration detection apparatus according to claim 1 or 2,
An adjustment unit that adjusts the concentration of the liquid developer based on detection by the concentration detection device;
An image forming apparatus. The image forming apparatus according to claim 3.
The liquid developer includes a carrier liquid, a pigment dispersed in the carrier liquid, and a dissolved resin dissolved in the carrier liquid,
The dissolved resin is used to fix the pigment on the sheet;
The concentration detection device detects the concentration of the dissolved resin,
Each of the first table and the second table is created by obtaining in advance the relationship between the rotational speed of the rotating member and the concentration of the dissolved resin,
The image forming apparatus that adjusts the concentration of the dissolved resin based on detection by the concentration detection device.

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