JPWO2012102244A1 - Liquid toner concentration sensor device, electrophotographic printing apparatus, and liquid toner concentration measurement method - Google Patents

Abstract

The liquid toner concentration sensor device 30 includes a dispersion tank 31, a stirring tank 32, a concentration sensor 33, a control device 34, and a charge adjustment unit 35. The agitation tank 32 is a container that stores the liquid toner T conveyed from the dispersion tank 31, the high-concentration liquid toner T1 conveyed by the concent pump 25a, and the carrier conveyed from the carrier pump 25b. The density sensor 33 measures the density of the liquid toner T conveyed from the stirring tank 32 to the supply pan. The control device 34 controls the concentrate pump 25a and the carrier pump 25b based on the measurement result of the concentration sensor 33. The charge adjusting unit 35 can remove the charge of the charged liquid toner.

Description

  The present invention relates to a liquid toner concentration sensor device, an electrophotographic printing apparatus, and a liquid toner concentration measurement method for measuring a liquid toner concentration.

  Conventionally, a liquid toner concentration sensor can measure the liquid toner concentration by passing the liquid toner between an electric conduction plate and an opposing plate.

  In Patent Document 1, liquid toner guided to a developing unit is collected in a stirring tank, and the liquid toner concentration is measured using a capacitance type density sensor. Based on the measurement result of the liquid toner concentration, control is performed so as to keep the liquid toner concentration constant.

International Publication No. 2009/036504

  The liquid toner concentration sensor described in Patent Document 1 measures the charge of the liquid toner, thereby calculating the value of the liquid toner concentration from the relationship between the charge of the liquid toner and the liquid toner concentration. However, the liquid toner is charged by passing through the conveyance path and the collection path or being stirred by the impeller of the stirring tank. The charged liquid toner passes through the dispersion tank and is stirred in the stirring tank together with new liquid toner. When the density of the charged liquid toner is measured by a capacitance type liquid toner concentration sensor device, the liquid toner concentration may not be accurately measured due to the charge charged in the liquid toner.

  The present invention has been made in view of the above, and an object thereof is to suppress a decrease in measurement accuracy of liquid toner concentration.

  In order to solve the above-described problems and achieve the object, the liquid toner concentration sensor device according to the present invention is a stirrer capable of agitating both the liquid toner collected from the developing unit and the new liquid toner. A tank, a concentration sensor that measures the concentration of the liquid toner stirred in the stirring tank, and a charge adjustment unit that maintains the charge amount of the stirred liquid toner at a predetermined size before the measurement of the concentration sensor; It is characterized by including.

  With the above configuration, the liquid toner concentration sensor device according to the present invention can keep the charge amount of the liquid toner at a predetermined level. Thereby, when the density | concentration of the circulating liquid toner is measured, the fall of the measurement precision of a liquid toner density | concentration can be suppressed.

  In order to solve the above-described problems and achieve the object, a liquid toner concentration sensor device according to the present invention includes a dispersion tank to which liquid toner recovered from a developing unit is guided, and the liquid toner in the dispersion tank and a new one. An agitating tank capable of agitating the liquid toner, a concentration sensor for measuring the concentration of the liquid toner agitated in the agitating tank, and the agitated liquid toner before the concentration sensor is measured And a charge adjusting unit that keeps the amount of charge at a predetermined level.

  With the above configuration, the liquid toner concentration sensor device according to the present invention can keep the charge amount of the liquid toner at a predetermined level. Thereby, when the density | concentration of the circulating liquid toner is measured, the fall of the measurement precision of a liquid toner density | concentration can be suppressed.

  As a preferred aspect of the present invention, it is desirable that the charge adjusting unit includes a conductor that contacts the liquid toner.

  With the above configuration, the liquid toner concentration sensor device according to the present invention can accurately reduce the charge of the charged liquid toner. Thereby, when the density | concentration of the circulating liquid toner is measured, the fall of the measurement precision of a liquid toner density | concentration can be suppressed.

  As a preferred aspect of the present invention, it is preferable that the charge adjusting unit includes a conductive wire for grounding the conductor.

  With the above configuration, the liquid toner concentration sensor device according to the present invention can accurately reduce the charge of the charged liquid toner. Thereby, when the density | concentration of the circulating liquid toner is measured, the fall of the measurement precision of a liquid toner density | concentration can be suppressed.

  As a preferred aspect of the present invention, it is desirable that the charge adjusting unit is provided with the conductor in a path of the liquid toner between the stirring tank and the concentration sensor.

  With the above configuration, the liquid toner concentration sensor device according to the present invention can accurately reduce the charge of the charged liquid toner. Thereby, when the density | concentration of the circulating liquid toner is measured, the fall of the measurement precision of a liquid toner density | concentration can be suppressed.

  As a preferred aspect of the present invention, it is desirable that the charge adjusting unit is provided with the conductor in the stirring tank.

  With the above configuration, the liquid toner concentration sensor device according to the present invention can accurately reduce the charge of the charged liquid toner. Thereby, when the density | concentration of the circulating liquid toner is measured, the fall of the measurement precision of a liquid toner density | concentration can be suppressed.

  As a preferred aspect of the present invention, it is desirable that the charge adjusting unit is provided with the conductor at a suction port of a transport pump that transports the liquid toner from the stirring tank.

With the above configuration, the liquid toner concentration sensor device according to the present invention can accurately reduce the charge of the charged liquid toner. In addition, the charge of the liquid toner that is reliably charged can be collected. Thereby, when the density | concentration of the circulating liquid toner is measured, the fall of the measurement precision of a liquid toner density | concentration can be suppressed.

  As a preferred aspect of the present invention, it is desirable that the charge adjusting unit is provided with the conductor so as to cover the concentration sensor provided in the stirring tank.

  With the above configuration, the liquid toner concentration sensor device according to the present invention can accurately reduce the charge of the charged liquid toner. In addition, the charge of the liquid toner that is reliably charged can be collected. Thereby, when the density | concentration of the circulating liquid toner is measured, the fall of the measurement precision of a liquid toner density | concentration can be suppressed.

  As a preferred aspect of the present invention, it is desirable that the charge adjusting section has a conductive wire for grounding a conductive portion of the circulation path of the liquid toner.

  With the above configuration, the liquid toner concentration sensor device according to the present invention can remove the charge of the charged liquid toner even in the circulation path of the liquid toner. Thereby, when the density | concentration of the circulating liquid toner is measured, the fall of the measurement precision of a liquid toner density | concentration can be suppressed.

  In order to solve the above-described problems and achieve the object, an electrophotographic printing apparatus according to the present invention includes a developing unit that transfers a liquid toner onto a photoreceptor on which an electrostatic latent image is formed, and performs development. An intermediate transfer member that transfers the liquid toner developed by the developing unit; a pressure member that forms a nip by contacting the intermediate transfer member and applies a voltage for transferring the liquid toner; and the liquid toner And a density sensor device.

  With the above configuration, the electrophotographic printing apparatus according to the present invention can maintain the charge amount of the liquid toner at a predetermined level. Thereby, when the density | concentration of the circulating liquid toner is measured, the fall of the measurement precision of a liquid toner density | concentration can be suppressed.

  As a preferred aspect of the present invention, a procedure for introducing the liquid toner collected from the developing unit, a procedure for stirring the liquid toner and the new liquid toner, and a charge amount of the stirred liquid toner are set to a predetermined magnitude. And a procedure for measuring the concentration of the liquid toner in which the charge amount is maintained at a predetermined level.

  With the above configuration, the liquid toner measuring method according to the present invention can keep the charge amount of the liquid toner at a predetermined level. Thereby, when the density | concentration of the circulating liquid toner is measured, the fall of the measurement precision of a liquid toner density | concentration can be suppressed.

  The present invention has an effect of suppressing a decrease in measurement accuracy of the liquid toner concentration.

FIG. 1 is an explanatory diagram schematically illustrating the electrophotographic printing apparatus according to the first embodiment. FIG. 2 is an explanatory diagram schematically illustrating the liquid toner concentration sensor device according to the first embodiment. FIG. 3A is a diagram illustrating an output voltage of the density sensor when the liquid toner is circulated. FIG. 3B is a diagram illustrating a state in which charged liquid toner adheres in the circulation path. FIG. 4 is a diagram illustrating an output voltage of the density sensor when the liquid toner is circulated when the charge adjusting unit is provided. FIG. 5 is an explanatory diagram schematically illustrating the charge adjustment unit according to the first embodiment. FIG. 6 is an explanatory diagram schematically showing a charge adjustment unit provided in the circulation path of the first embodiment. FIG. 7 is an explanatory diagram schematically illustrating a liquid toner concentration sensor device according to the second embodiment. FIG. 8 is an explanatory diagram schematically illustrating a liquid toner concentration sensor device according to the third embodiment. FIG. 9 is an explanatory diagram schematically illustrating a modification of the liquid toner concentration sensor device according to the third embodiment.

  Hereinafter, the present invention will be described in detail with reference to the drawings. The present invention is not limited to the following description. In addition, constituent elements in the following description include those that can be easily assumed by those skilled in the art, those that are substantially the same, and those in a so-called equivalent range. Furthermore, the constituent elements described below can be appropriately combined.

(Embodiment 1)
FIG. 1 is an explanatory diagram schematically illustrating the electrophotographic printing apparatus according to the first embodiment. Hereinafter, the electrophotographic printing apparatus 10 of Embodiment 1 will be described. The electrophotographic printing apparatus 10 is a liquid development electrophotographic printing apparatus. The electrophotographic printing apparatus 10 includes a paper feed unit, a printing unit 11, and a paper discharge unit. For example, the paper supply unit can supply print sheets, which are sheets of paper, one by one from the paper supply tray to the printing unit. The printing unit 11 can perform printing on one side or both sides of the supplied printing sheet. The discharge unit can discharge the print sheet printed on one or both sides by the printing unit to a discharge tray.

  The electrophotographic printing apparatus 10 includes a printing unit 11, an intermediate transfer member 12, a backup roller 13, developing units 14a, 14b, 14c, and 14d, a liquid toner supply device 20, a cleaning device 40, and a liquid toner recovery device. 50 and a solid content separation device 60. Each developing unit 14a, 14b, 14c, 14d corresponds to each ink color C (blue), M (red), Y (yellow), K (black).

  The printing unit 11 performs printing using liquid toner. The liquid toner T contains a carrier liquid, toner particles, and a small amount of a charge accelerator. The toner particles are particles containing a thermoplastic material and a pigment (pigment or dye). The carrier liquid is a petroleum-based melt. In the liquid toner, a particulate toner having an average particle diameter of about 1 μm to 2 μm is contained in the carrier at a concentration of about 10% to 40% by weight. The viscosity (toner viscosity) of the liquid toner T is 10 cp (centipoise) to 120 cp, and particularly preferably 80 cp or less.

  The intermediate transfer body 12 has a bias voltage difference with respect to the photosensitive drum 15 and contacts the backup roller 13 at the nip portion N1. A blanket 12 a is wound around the outer peripheral surface of the intermediate transfer body 12. In the first embodiment, the blanket 12a is urethane conductive rubber.

  The backup roller 13 is configured to apply a predetermined pressure to the intermediate transfer body 12. The print sheet S is conveyed between the backup roller 13 and the intermediate transfer body 12, so that a predetermined nip pressure is applied. Since a bias voltage is applied to the backup roller 13, a force that attracts the intermediate transfer member 12 to the backup roller 13 side is applied to the liquid toner T due to a voltage difference between the intermediate transfer member 12 and the backup roller 13. In this way, the liquid toner T is transferred from the intermediate transfer body 12 to the print sheet S.

  Each developing unit 14a, 14b, 14c, 14d is disposed along the intermediate transfer body 12. Here, the developing unit 14a will be described in detail.

  The developing unit 14a includes a photosensitive drum 15, a supply pan 16a, and a liquid toner conveying roller 16b. The photosensitive drum 15 has a photosensitive layer on the outer peripheral surface, and forms a nip portion N <b> 2 with the intermediate transfer body 12. The supply pan 16 a is a container that stores the liquid toner T. The liquid toner transport roller 16 b transports the liquid toner T from the supply pan 16 a to the photosensitive drum 15.

  The liquid toner supply device 20 includes a concentrated tank 21, a concentrated pump 25a, a carrier tank 22, a carrier pump 25b, a liquid toner concentration sensor device 30, a recovery blade 26, a liquid toner pump 25c, and a recovery pump 25d. And a recovery pump 25e.

  The conc tank 21 is a container for storing a liquid toner T1 having a higher concentration than the normal liquid toner T. When the high-concentration liquid toner T1 is insufficient, the concentrate tank 21 is replenished with the high-concentration liquid toner T1 from the bottle toner 21a. The carrier tank 22 is a container for storing carriers. The carrier tank 22 is replenished with carriers from the carrier can 22a when the carrier capacity is insufficient.

  The liquid toner concentration sensor device 30 includes a dispersion tank 31, a stirring tank 32, and a concentration sensor 33. The dispersion tank 31 is a container for storing the liquid toner T collected from the liquid toner conveying roller 16b. Since the collected liquid toner T is an excess liquid toner T that is not transferred from the photosensitive drum 15 to the intermediate transfer body 12, the carrier ratio is lower than before the collection. Also, the liquid toner concentration is 130% to 140% higher than that before collection.

  The dispersion tank 31 can disperse the collected liquid toner T by the impeller 31 a in the dispersion tank 31. The liquid toner T in the dispersion tank 31 is conveyed to the agitation tank 32 by overflowing from the dispersion tank 31, for example.

  The agitation tank 32 is a high-concentration liquid toner T1 supplied from the concentrated tank 21, a carrier supplied from the carrier tank 22, a liquid toner T supplied from the dispersion tank 31, and a liquid toner collected from the supply pan 16a. A container for storing T. Further, the liquid toner T collected from the liquid toner conveying roller 16 b may be stored in the stirring tank 32 directly without passing through the dispersion tank 31.

  The concentric pump 25 a is a pump for conveying the high-concentration liquid toner T <b> 1 from the concent tank 21 to the stirring tank 32. The carrier pump 25 b is a pump that conveys the carrier from the carrier tank 22 to the stirring tank 32. The recovery pump 25d is a pump that conveys excess liquid toner T from the supply pan 16a to the stirring tank 32. The liquid toner pump 25c is a pump that conveys the liquid toner T stirred from the stirring tank 32 to the supply pan 16a.

  The collection blade 26 collects excess liquid toner T on the outer peripheral portion of the liquid toner transport roller 16b. Excess liquid toner T is one that has not been transferred onto the outer peripheral portion of the photosensitive drum 15. The recovery pump 25 e is a pump that conveys the liquid toner T recovered from the recovery blade 26 to the stirring tank 32.

  The concentration sensor 33 is provided, for example, in the conveyance path between the agitation tank 32 and the supply pan 16a. The density sensor 33 measures the density of the liquid toner T conveyed from the stirring tank 32 to the supply pan 16a. The control device 34 controls the concentrate tank 21 and the carrier tank 22 so that the concentration of the liquid toner T becomes a predetermined target concentration based on the measurement result of the concentration sensor 33.

  Each developing unit 14a, 14b, 14c, 14d includes a conc tank 21, a conc pump 25a, a dispersion tank 31, a stirring tank 32, a liquid toner pump 25c, a recovery pump 25d, and a recovery pump 25e. In the first embodiment, the developing units 14a, 14b, 14c, and 14d share the carrier tank 22 and the carrier pump 25b. A carrier tank 22 and a carrier pump 25b may be provided for each developing unit.

  The cleaning device 40 includes a carrier nozzle 41, a carrier pump 42, a collection blade 43a, a first cleaning roller 44b, a collection blade 43b, a second cleaning roller 44c, and a collection blade 43c. The carrier nozzle 41 is disposed between the backup roller 13 and the photosensitive drum 15. The carrier nozzle 41 discharges the carrier conveyed from the carrier tank 22 to the intermediate transfer body 12. The carrier pump 42 is a pump that conveys the carrier from the carrier tank 22 to the carrier nozzle 41.

  The first cleaning roller 44b and the collection blade 43b are disposed between the photosensitive drum 15 of the developing unit 14b and the photosensitive drum 15 of the developing unit 14c. The first cleaning roller 44 b is disposed so as to contact the intermediate transfer body 12 and collects the liquid toner T on the outer peripheral surface of the intermediate transfer body 12. The collection blade 43b collects the liquid toner T on the outer peripheral surface of the first cleaning roller 44b.

  The second cleaning roller 44c and the collection blade 43c are disposed between the backup roller 13 and the photosensitive drum 15 of the developing unit 14d. The second cleaning roller 44 c is disposed so as to contact the intermediate transfer body 12 and collects the liquid toner T on the outer peripheral surface of the intermediate transfer body 12. The collection blade 43c collects the liquid toner T on the outer peripheral surface of the second cleaning roller 44c.

  The collection blade 43 a is disposed so as to contact the intermediate transfer body 12. The collection blade 43 a collects the liquid toner T on the outer peripheral surface of the intermediate transfer body 12. The liquid toner T here is diluted by the carrier discharged from the carrier nozzle 41 to the intermediate transfer body 12.

  The liquid toner recovery device 50 includes a liquid toner recovery pump 51a, a liquid toner recovery pump 51b, and a liquid toner recovery pump 51c. The liquid toner recovery pump 51a is disposed between the recovery blade 43a and the solid content separation device 60. The liquid toner recovery pump 51b is disposed between the recovery blade 43b and the solid content separation device 60. The liquid toner recovery pump 51c is disposed between the recovery blade 43c and the solid content separation device 60.

  The liquid toner recovery pump 51 a conveys the liquid toner T recovered from the carrier nozzle 41 to the solid content separation device 60. The solid content separation device 60 is a device that mainly collects excess liquid toner T and recovers the carrier. The solid content separation device 60 promotes the separation of the toner as the solid content contained in the conveyed liquid toner T and the carrier as the liquid. The liquid toner recovery pump 51b conveys the liquid toner T recovered from the first cleaning roller 44b by the recovery blade 43b to the solid content separation device 60.

  The electrophotographic printing apparatus 10 shown in FIG. 1 reuses the carrier separated from the solid content separation device 60. In the first embodiment, the recycled carrier supply pump 17 is disposed between the solid content separation device 60 and the carrier tank 22. The recycle carrier supply pump 17 conveys the carrier separated by the solid content separation device 60 to the carrier tank 22. Next, the liquid toner concentration sensor device 30 will be described in more detail.

  FIG. 2 is an explanatory diagram schematically illustrating the liquid toner concentration sensor device according to the first embodiment. The liquid toner concentration sensor device 30 includes a dispersion tank 31, a stirring tank 32, a concentration sensor 33, a control device 34, and a charge adjustment unit 35. The charge adjusting unit 35 is for keeping the charge amount of the liquid toner T at a predetermined level.

  As described above, the agitation tank 32 is a container that stores the liquid toner T conveyed from the dispersion tank 31, the high-concentration liquid toner T1 conveyed by the concentric pump 25a, and the carrier conveyed from the carrier pump 25b. . The stirring plate 38 is disposed in the stirring tank 32 in order to stir the liquid accumulated in the stirring tank 32.

  The liquid toner pump 25c conveys the liquid toner T stirred in the stirring tank 32 to the supply pan 16a. The density sensor 33 is disposed, for example, between the liquid toner pump 25c and the supply pan 16a, and measures the density of the conveyed liquid toner T. The concentration sensor 33 may be disposed between the liquid toner pump 25 c and the stirring tank 32. In the first embodiment, the density sensor 33 employs a capacitance method.

  Capacitance method means that the insulated plates are fixed so that they face each other at regular intervals, and the liquid toner to be measured is passed between the plates so that the capacitance between the plates can be reduced. It is to be measured. For example, the liquid toner concentration can be obtained from the measurement result of the electrostatic capacity using a calibration curve.

  The control device 34 controls the concentrate pump 25a and the carrier pump 25b based on the measurement result of the concentration sensor 33. The concent pump 25a conveys the high-concentration liquid toner T1 from the conch tank 21 to the stirring tank 32 by the control device 34. The carrier pump 25b also conveys the carrier from the carrier tank 22 to the stirring tank 32.

  The liquid toner T is charged due to friction or the like when passing through the circulation path of the liquid toner T. Further, even when the liquid toner T is stirred by the stirring plate 38 disposed in the stirring tank 32, the liquid toner T is charged due to friction with the stirring plate 38.

  FIG. 3A is a diagram illustrating an output voltage of the density sensor when the liquid toner T is circulated. The output result indicated by the concentration sensor 33 is that the liquid toner T is circulated through a circulation path composed of the stirring tank 32, the concentration sensor 33, the liquid toner pump 25c, the concentric pump 25a, and the carrier pump 25b. Is. The density sensor 33 converts the measured electrostatic capacitance of the liquid toner T into a voltage V and outputs it. Since the circulating liquid toner T is negatively charged with time due to friction in the circulation path, the output voltage V of the concentration sensor 33 decreases with time.

  Here, the voltage V output from the density sensor 33 increases as the electrostatic capacity of the liquid toner T increases. Further, when the liquid toner concentration of the liquid toner T increases, the electrostatic capacity of the liquid toner T increases. Therefore, when the liquid toner concentration of the liquid toner T increases, the voltage V output from the concentration sensor 33 increases, and when the liquid toner concentration of the liquid toner T decreases, the voltage V output from the concentration sensor 33 decreases. When the liquid toner T is charged (negative charge in this example), the capacitance type density sensor 33 detects the capacitance of the liquid toner T lower. As a result, even when the liquid toner T has the same liquid toner concentration, when the liquid toner T is charged, the concentration sensor 33 sets the liquid toner concentration more than when the liquid toner T is not charged. It will be measured low.

  The liquid toner concentration of the liquid toner T does not normally change only by circulating in the circulation path. However, when the liquid toner T is charged by circulating through the circulation path, the density sensor 33 measures the liquid toner density of the liquid toner T lower than the actual value. For this reason, the control device 34 that has acquired the liquid toner concentration of the liquid toner T measured by the concentration sensor 33 controls to increase the liquid toner concentration of the circulating liquid toner T.

  The voltage V output from the concentration sensor 33 starts to approach a certain value after decreasing with time. Since the liquid toner T has an upper limit on the amount of charge that can be charged to the liquid toner itself, the charge amount of the liquid toner T becomes saturated as time passes.

  FIG. 3B is a diagram illustrating a state in which the charged liquid toner adheres to the circulation path. The charged liquid toner T adheres to the circulation path due to electrostatic force. In particular, as shown in FIG. 3B, the liquid toner T adheres in the circulation path at the inner peripheral surface of the stirring tank 32 and the liquid toner transport tube 36 that transports the liquid toner T from the stirring tank 32 to the concentration sensor 33. The suction port. Since the solid content Ta of the charged liquid toner T adheres in the transport path, the solid content contained in the liquid toner T decreases.

  FIG. 4 is a diagram illustrating an output voltage of the density sensor when the liquid toner T is circulated when the charge adjusting unit is provided. The output result indicated by the density sensor 33 indicates that the liquid toner T is circulated by the stirring tank 32, the density sensor 33, the liquid toner pump 25c, the concentric pump 25a, the carrier pump 25b, and the charge adjusting unit 35. The route is circulated. The charge adjusting unit 35 of the first embodiment removes the charge (negative charge in the present embodiment) of the charged liquid toner T.

  In this example, the negative charge of the charged liquid toner T is removed by the charge adjusting unit 35. For this reason, the output voltage V of the density sensor 33 is substantially constant regardless of the passage of time. By providing the charge adjustment unit 35 in the area before the density sensor 33 measures, the density sensor 33 can measure the capacitance of the liquid toner T without being affected by the electric charge. It is possible to avoid measuring the concentration below the actual level. As a result, the density sensor 33 can suppress a decrease in the measurement accuracy of the liquid toner density due to the influence of the electric charge charged on the liquid toner T. In this embodiment, the control device 34 that has acquired the liquid toner concentration of the liquid toner T measured by the concentration sensor 33 can be prevented from being controlled to increase the liquid toner concentration excessively.

  FIG. 5 is an explanatory diagram schematically illustrating the charge adjustment unit according to the first embodiment. The charge adjusting unit 35 includes a conductor 35a that contacts the charged liquid toner T, and a conductive wire 35b for grounding the conductor 35a. In the first embodiment, the meaning of grounding the conductor 35a means that the conductor 35a is connected to a reference potential point in the electrophotographic printing apparatus 10 (for example, a metal housing or frame of the electrophotographic printing apparatus 10). This includes both the case of being electrically connected at 35b and the case of being electrically connected to the ground by the conductive wire 35b. The conductor 35a that comes into contact with the charged liquid toner T is, for example, metal or conductive plastic.

  For example, the conductor 35a can be wound around the concentration sensor 33 from the stirring tank 32 so as to cover the suction port of the liquid toner pump 25c that transports the liquid toner T. When the conductor 35a is a metal mesh, if the metal mesh is wound so as to cover the suction port of the liquid toner transport tube 36, the area for collecting the charge of the charged liquid toner T is increased. The charge can be removed well. By connecting the conductive wire 35b to the conductor 35a and grounding it, the charge charged in the liquid toner T can be removed. For example, when the conductive wire 35b is connected to the ground, the charge charged to the liquid toner T can be removed from the liquid toner T by letting it escape to the ground. The charge adjusting unit 35 is not limited to the above-described embodiment as long as the conductor 35a is provided in the path of the liquid toner T between the stirring tank 32 and the concentration sensor 33.

  FIG. 6 is an explanatory diagram schematically showing a charge adjustment unit provided in the circulation path of the first embodiment. The charging adjustment unit 35A includes a conductive wire 35b for grounding a portion having conductivity in a circulation path through which the liquid toner T circulates. The conductive wire 35b constituting the charge adjusting unit 35A may be provided at any location having conductivity in the circulation path. For example, in the example shown in FIG. 6, the conductive wire 35 b is connected to the dispersion tank 31 having conductivity, the impeller 31 a of the dispersion tank 31, the stirring tank 32, the liquid toner transport tube 36, and the stirring plate 38. To ground. By connecting the conductive portion in the circulation path and the ground or the reference potential point of the electrophotographic printing apparatus 10 with the conductive wire 35b, the charge charged in the liquid toner T can be removed from the liquid toner T. Further, by connecting a plurality of conductive locations in the circulation path and the ground or the reference potential point of the electrophotographic printing apparatus 10 with the conductive wire 35b, the charge charged to the liquid toner T from the plurality of locations to the ground or the like. I can escape. As a result, the liquid toner T can be in an uncharged state throughout the circulation path. Alternatively, the conductor 35a may be grounded by wrapping the conductor 35a so as to cover the suction port of the liquid toner conveying tube 36 and electrically connecting the conductive portion in the circulation path.

  The liquid toner concentration measurement method according to the present embodiment is executed in the following procedure. First, the stirring plate 38 executes a procedure of stirring the liquid toner T transported from the dispersion tank 31 and the high-concentration liquid toner T1 transported by the concentric pump 25a in the stirring tank 32. Next, the charge adjusting unit 35 in the circulation path executes a procedure for keeping the charge amount of the stirred liquid toner T at a predetermined level. Then, the density sensor 33 executes a procedure for measuring the density of the liquid toner T kept at a predetermined size. The controller 34 controls the density of the circulating liquid toner T based on the density of the liquid toner T measured by the density sensor 33.

  As described above, in the present embodiment, the charge amount of the stirred liquid toner is maintained at a predetermined size (0 in the present embodiment) before the measurement by the density sensor 33. By doing so, the charge of the liquid toner circulating in the circulation path becomes zero. Therefore, even when a capacitance type density sensor is used, the measurement of the liquid toner concentration due to the influence of the charge charged on the liquid toner is performed. A decrease in accuracy can be suppressed. The configuration according to the first embodiment can also be applied as appropriate in the following.

(Embodiment 2)
FIG. 7 is an explanatory diagram schematically illustrating a liquid toner concentration sensor device according to the second embodiment. The liquid toner concentration sensor device 30 includes a dispersion tank 31, a stirring tank 32, a concentration sensor 33, a control device 34, and a charge adjustment unit 35B. The agitation tank 32 may store the liquid toner T collected directly from the liquid toner conveying roller 16b without passing through the dispersion tank 31. In addition, the charge adjusting unit 35B gives an electric charge so that the charged amount of the charged liquid toner T becomes equal. The charge adjustment unit 35B uses, for example, a constant voltage power supply device 37. The constant voltage power supply device 37 applies a charge to the liquid toner T, and keeps the charge amount of the liquid toner T at a predetermined level.

  The constant voltage power supply device 37 includes a power supply 37a for applying a voltage and an electrode 37b electrically connected to the power supply 37a. The constant voltage power supply device 37 is a device that generates a constant DC voltage. The charge adjustment unit 35B arranges, for example, electrodes 37b and 37b connected to the positive electrode and the negative electrode of the power source 37a in the stirring tank 32, respectively. Then, the electrodes 37b and 37b are brought into contact with the charged liquid toner T in the stirring tank 32, and a DC voltage is applied to the liquid toner T existing between the electrodes 37b and 37b. In this way, electric charge is given to the liquid toner T in the stirring tank 32.

  Since the constant voltage power supply device 37 of the charge adjustment unit 35B generates a constant DC voltage, if the electrodes 37b and 37b are brought into contact with the liquid toner T in the stirring tank 32, the liquid existing between the electrodes 37b and 37b. The toner T can be charged with the same amount of charge. Then, the liquid toner T in the agitation tank 32 is agitated and charged by the power supply 37a of the charge adjustment unit 35B, whereby the amount of charge charged in the liquid toner T in the agitation tank 32, that is, the charge amount, is expressed as time. It can be kept at a predetermined size regardless of the passage of time.

  In the second embodiment, the density sensor 33 measures the density of the charged liquid toner T. For this reason, the relationship between the charge amount (for example, saturation charge amount) charged to the liquid toner T and the liquid toner concentration is obtained, and the liquid toner concentration measured by the concentration sensor 33 is corrected based on this relationship. It is preferable to determine the toner concentration. In the present embodiment, by applying a charge to the liquid toner T from the power source 37a of the charge adjustment unit 35B, the density sensor 33 allows the liquid toner T to remain in a constant state regardless of the passage of time. Capacitance of T can be measured. By doing in this way, the density sensor 33 can avoid measuring the liquid toner concentration of the liquid toner T lower than actual. As a result, in the present embodiment, it is possible to avoid the control device 34 that has acquired the liquid toner concentration of the liquid toner T measured by the concentration sensor 33 from controlling the liquid toner concentration to be excessively high.

  As described above, in the present embodiment, the charged amount of the stirred liquid toner is kept at a predetermined magnitude (a value other than 0 in the present embodiment) before the measurement by the density sensor. In this way, the liquid toner circulating in the circulation path can have a constant charge amount regardless of the passage of time. Therefore, even when a capacitance type density sensor is used, the liquid toner The influence of the charged electric charge can be made constant regardless of changes in time. As a result, this embodiment can suppress a decrease in measurement accuracy of the liquid toner concentration. The configuration according to the second embodiment can also be applied as appropriate in the following.

(Embodiment 3)
FIG. 8 is an explanatory diagram schematically illustrating a liquid toner concentration sensor device according to the third embodiment. The liquid toner concentration sensor device 30 includes a dispersion tank 31, a stirring tank 32, a concentration sensor 33, a control device 34, and charge adjustment units 35 and 35B. The agitation tank 32 may store the liquid toner T collected directly from the liquid toner conveying roller 16b without passing through the dispersion tank 31. The concentration sensor 33 is provided in the stirring tank 32. For example, the concentration sensor 33 is provided between the stirring plate 38 and the central axis on which the stirring plate 38 rotates when the stirring plate 38 stirs the inside of the stirring tank 32. The liquid toner T in the agitation tank 32 is transported to the liquid toner transport tube 36 through the density sensor 33.

  FIG. 9 is an explanatory diagram schematically illustrating a modification of the liquid toner concentration sensor device according to the third embodiment. The configuration of the liquid toner concentration sensor device 30 is the same as that shown in FIG. The concentration sensor 33 is provided in the stirring tank 32 but is not provided in the circulation path of the liquid toner T. The liquid toner T in the agitation tank 32 is conveyed from the agitation tank 32 through the liquid toner conveyance tube 36 to the liquid toner pump 25C. For example, the concentration sensor 33 is provided between the stirring plate 38 and the central axis on which the stirring plate 38 rotates when the stirring plate 38 stirs the inside of the stirring tank 32. The density sensor 33 measures the density of the liquid toner T by using the flow of the liquid toner T generated along the central axis of the stirring tank 32.

  As in the first embodiment, the charge adjusting unit 35 includes a conductor 35a that contacts the charged liquid toner T and a conductive wire 35b for grounding the conductor 35a. In this modification, the conductor 35 a is provided in the stirring tank 32. More specifically, the conductor 35a can be wound so as to cover the concentration sensor 33 provided in the stirring tank 32, for example. That is, the conductor 35 a surrounds the concentration sensor 33 provided in the stirring tank 32. When the density sensor 33 is not provided in the circulation path of the liquid toner T, for example, the liquid toner T is transferred from the stirring tank 32 to the density sensor 33 together with the density sensor 33 provided in the stirring tank 32. It may be wound (enclosed) so as to cover the suction port of the liquid toner pump 25c to be conveyed. When the conductor 35a is a metal mesh, the area for collecting the charge of the charged liquid toner T is increased, so that the charge can be efficiently removed from the liquid toner T. By connecting the conductive wire 35b to the conductor 35a and grounding it, the charge charged in the liquid toner T can be removed. For example, when the conductive wire 35b is connected to the ground, the charge charged to the liquid toner T can be removed from the liquid toner T by letting it escape to the ground.

  Similarly to the second embodiment, the charge adjusting unit 35B applies charges so that the charged amount of the charged liquid toner T becomes equal. The charge adjustment unit 35B uses, for example, a constant voltage power supply device 37. The constant voltage power supply device 37 applies a charge to the liquid toner T, and keeps the charge amount of the liquid toner T at a predetermined level. The constant voltage power supply device 37 includes a power supply 37a for applying a voltage and an electrode 37b electrically connected to the power supply 37a.

  The electrode 37 b is provided in the stirring tank 32. For example, similarly to the concentration sensor 33, the stirring plate 38 is provided between the central axis of the stirring plate 38 and the stirring plate 38 when the stirring plate 38 stirs the inside of the stirring tank 32. The electrode 37 b may be provided at a position opposite to the concentration sensor 33 with respect to the central axis around which the stirring plate 38 rotates, or may be provided at the same position as the concentration sensor 33.

  In the third embodiment, even when the concentration sensor 33 is provided in the agitation tank 32, the charge amount of the agitated liquid toner T is set to a predetermined magnitude (this embodiment) before the liquid toner concentration of the charged toner T is measured. In the form, it can be kept at a value other than 0). Either one of the charge adjustment units 35 and 35B may be provided, and a charge adjustment unit 35A may be newly provided in the circulation path.

DESCRIPTION OF SYMBOLS 10 Electrophotographic printing apparatus 11 Printing part 12 Intermediate transfer body 12a Blanket 13 Backup roller 14a, 14b, 14c, 14d Development unit 15 Photosensitive drum 16a Supply pan 16b Liquid toner conveyance roller 17 Recycle carrier supply pump 20 Liquid toner supply apparatus 21 21a Bottle toner 22 Carrier tank 22a Carrier can 25a Concent pump 25b Carrier pump 25c Liquid toner pump 25d Recovery pump 25e Recovery pump 26 Recovery blade 30 Liquid toner concentration sensor device 31 Dispersion tank 31a Impeller 32 Stirring tank 33 Concentration sensor 34 Control device 35 Charge adjusting unit 35a Conductor 35b Conductive wire 36 Liquid toner transfer tube 37 Constant voltage power supply device 37a Power source 37b Electrode 38 Stirring plate 41 Carrier nozzle 42 Carrier pump 43a, 43b, 43c Recovery blade 44b First cleaning roller 44c Second cleaning roller 50 Liquid toner recovery device 51a, 51b, 51c Liquid toner recovery pump 60 Solid content separation device

Claims (11)

An agitation tank capable of agitating the liquid toner collected from the developing unit and the new liquid toner,
A concentration sensor for measuring the concentration of the liquid toner stirred in the stirring tank;
A charge adjusting unit that maintains a predetermined charge amount of the stirred liquid toner before the measurement of the density sensor;
A liquid toner concentration sensor device comprising: A dispersion tank to which liquid toner recovered from the developing unit is guided;
An agitation tank in which the liquid toner and the new liquid toner in the dispersion tank are guided and capable of agitating both;
A concentration sensor for measuring the concentration of the liquid toner stirred in the stirring tank;
A charge adjusting unit that maintains a predetermined charge amount of the stirred liquid toner before the measurement of the density sensor;
A liquid toner concentration sensor device comprising:   The liquid toner concentration sensor device according to claim 1, wherein the charge adjustment unit includes a conductor that contacts the liquid toner.   The liquid toner concentration sensor device according to claim 3, wherein the charge adjusting unit includes a conductive wire for grounding the conductor.   5. The liquid toner concentration sensor device according to claim 3, wherein the charge adjusting unit is provided with the conductor in a path of the liquid toner between the stirring tank and the concentration sensor. 6. .   The liquid toner concentration sensor device according to claim 5, wherein the charge adjusting unit is provided with the conductor in the stirring tank.   6. The liquid toner concentration sensor device according to claim 5, wherein the charge adjusting unit is provided with the conductor at a suction port of a transport pump that transports the liquid toner from the stirring tank.   The liquid toner concentration sensor device according to claim 5, wherein the charge adjusting unit is provided with the conductor so as to cover the concentration sensor provided in the stirring tank.   3. The liquid toner concentration sensor device according to claim 1, wherein the charge adjusting unit is provided with the conductive wire for grounding a conductive portion of the circulation path of the liquid toner. 4. A developing unit that performs development by transferring liquid toner onto a photoreceptor on which an electrostatic latent image is formed; and
An intermediate transfer member for transferring the liquid toner developed by the developing unit;
A pressurizing member that forms a nip portion by contacting the intermediate transfer member and applies a voltage for transferring the liquid toner;
A liquid toner concentration sensor device according to any one of claims 1 to 9,
An electrophotographic printing apparatus comprising: A procedure for stirring the liquid toner collected from the developing unit and new liquid toner;
A procedure for maintaining the charge amount of the agitated liquid toner at a predetermined level;
A procedure for measuring the concentration of the liquid toner in which the charge amount is maintained at a predetermined magnitude;
A liquid toner concentration measuring method comprising:

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