JP2019053243A - Developing device and image forming apparatus - Google Patents

Abstract

To increase a control width in which the amount of toner transferred to a developing body can be controlled.SOLUTION: A developing device comprises: a holding body that is supplied with liquid developer and holds the liquid developer; a developing body that supplies the liquid developer transferred from the holding body to a latent image to develop the latent image; an application unit that applies, to a toner in the liquid developer held on the holding body, an electric charge having a polarity opposite to that of the electric charge of the toner; and a transfer unit that generates a potential difference between the holding body and the developing body to transfer the toner applied with the electric charge having the opposite polarity by the application unit from the holding body to the developing body.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a developing device and an image forming apparatus.

  Patent Document 1 discloses a configuration in which a liquid developer is transferred from a supply roll to a development roll by generating a potential difference between the supply roll and the development roll. In this configuration, the charging member disposed on the supply roll controls the inflow current flowing into the toner of the liquid developer held on the supply roll, thereby controlling the amount of toner on the development roll.

JP 2014-219539 A

  Here, in the configuration in which a potential difference is generated between the holding body and the developing body to transfer the liquid developer toner from the holding body to the developing body, the applying unit has the liquid developer toner held on the holding body. In addition, when a charge having the same polarity as that of the toner is applied, the control range in which the amount of toner transferred to the developing body can be controlled may be narrow.

  The present invention provides a control that can control the amount of toner transferred to the developer compared to a configuration in which the applying unit applies a charge having the same polarity as the charge of the toner to the liquid developer toner held on the holding member. The purpose is to widen the width.

  The invention according to claim 1 is a developer that is supplied with a liquid developer and holds the liquid developer, and a developer that develops the latent image by supplying the liquid developer transferred from the holder to the latent image. A potential difference between the holder and the developer, and an applying portion that applies a charge having a polarity opposite to the charge of the toner held by the holder to the liquid developer toner. And a transfer section that transfers the toner, to which the charge having the reverse polarity is applied by the applying section, from the holding body to the developing body.

  According to a second aspect of the present invention, there is provided a detection unit that detects the polarity of the charge of the toner before the charge having a reverse polarity is applied by the application unit, and the application unit is held by the holding body. A charge having a polarity opposite to the polarity detected by the detection unit is applied to the toner of the liquid developer.

  According to a third aspect of the present invention, the detection unit includes a measurement unit that measures a characteristic amount based on the amount of toner held on the developing member, and the measurement unit is configured to stop the application operation of the application unit. A measured value of the characteristic amount based on the amount of toner transferred from the holding body to the developing body due to a potential difference generated between the holding body and the developing body, and the applying unit Measured value obtained by the measuring means in a state in which the application operation of is stopped, and transferred from the holding body to the developing body in a state where the direction of the electric field between the holding body and the developing body is reversed. The polarity is detected from the difference between the measured value of the characteristic amount based on the amount of toner.

  According to a fourth aspect of the present invention, the detection unit includes a measurement unit that measures an optical density of the liquid developer held on the developer, and the measurement unit causes the measurement unit to stop the application operation of the application unit. The acquired measured value, the measured value of the optical density of the liquid developer containing the toner transferred from the holding body to the developing body due to the potential difference generated between the holding body and the developing body, and the application Measured value obtained by the measuring means in a state where the application operation of the part is stopped, and transferred from the holding body to the developing body in a state where the direction of the electric field between the holding body and the developing body is reversed. The polarity is detected from the difference between the measured value of the optical density of the liquid developer containing the toner.

  The invention of claim 5 includes a first application unit as the application unit, and a second application unit that applies electric charge to the toner of the liquid developer held on the developer, and the detection unit includes: Measuring means for measuring the surface potential of the liquid developer held on the developer, and the measuring means is arranged downstream of the second application unit in the rotation direction of the developer and stops the application operation of the application unit. And the measured value obtained by the measuring means in a state in which the second application unit is operated, and is transferred from the holding body to the developing body due to a potential difference generated between the holding body and the developing body. A measured value of the surface potential of the liquid developer containing the toner, and a measured value acquired by the measuring means in a state where the applying operation of the applying unit is stopped and the second applying unit is operated, and the holding Between the body and the developer. Detecting a measurement value of the orientation from the retaining member in an inverted state of the surface potential of the liquid developer containing toner transferred to the developing member, the polarity of the difference in the.

  According to a sixth aspect of the present invention, the detection unit is configured to provide a supply path for recovering the liquid developer from the developer after supplying the liquid developer to the latent image and supplying the liquid developer to the holder. Has been placed.

  According to a seventh aspect of the present invention, when the charge of the liquid developer toner held on the holding body has a first polarity, the applying portion has a polarity opposite to the first polarity. When the charge of the liquid developer toner held on the holding body is the second polarity when the first state is to apply the second polarity charge, the first polarity charge is given to the toner. Switch to the second state.

  The invention according to claim 8 includes a supply path for recovering the liquid developer from the developer after supplying the liquid developer to the latent image and supplying the liquid developer to the holding member, Is in the first state, the liquid developer is supplied to the holding body through the supply path, so that the charge of the liquid developer toner held on the holding body becomes the first charge. When the polarity is changed to the second polarity, the applying unit switches from the first state to the second state.

  The invention of claim 9 adjusts the amount of charge applied to the toner of the liquid developer held on the holding body based on the acquired information. And an image forming body on which a latent image is developed by the developing device to form a toner image, and a transfer section that transfers the toner image formed on the image forming body to a recording medium.

  According to the configuration of claim 1 of the present invention, the applying portion is transferred to the developer compared to the configuration in which the toner of the liquid developer held on the holding body is given a charge having the same polarity as the charge of the toner. The control range in which the amount of toner to be controlled can be controlled can be widened.

  According to the configuration of the second aspect of the present invention, the applying unit has a reverse polarity charge compared to the configuration in which the applying unit applies a charge having a reverse polarity to the known polarity regardless of the polarity detected by the detecting unit. Even when the polarity of the charge of the toner is changed before the toner is applied, it is possible to suppress the toner having the same polarity as the charge of the toner from the liquid developer held on the holding body.

  According to the configuration of the third aspect of the present invention, the polarity of the toner charge can be detected by using the measuring unit that measures the characteristic amount based on the amount of toner held on the developing member.

  According to the configuration of the fourth aspect of the present invention, the polarity of the toner charge can be detected by using the measuring means for measuring the optical density of the liquid developer held on the developer.

  According to the configuration of the fifth aspect of the present invention, the polarity of the toner charge can be detected by using the measuring means for measuring the surface potential of the liquid developer held on the developer.

  According to the configuration of the sixth aspect of the present invention, it is not necessary for the applying unit to stop the applying operation when the detecting unit detects the polarity of the toner charge.

  According to the configuration of the seventh aspect of the present invention, the charge of the toner of the liquid developer held on the holding body is changed from the first polarity to the second polarity as compared with the case where the applying portion is only in the first state. Even in this case, it is possible to suppress the liquid developer toner held on the holding body from being charged with the same polarity as the charge of the toner.

  According to the configuration of the eighth aspect of the present invention, the liquid developer is supplied to the holding body via the supply path when the applying portion is in the first state as compared with the case where the applying portion is only in the first state. Thus, even when the charge of the liquid developer toner held on the holding body changes from the first polarity to the second polarity, the toner of the liquid developer held on the holding body is added to the toner of the liquid developer. Giving a charge having the same polarity as the charge can be suppressed.

  According to the ninth aspect of the present invention, the toner amount of the toner image transferred to the recording medium can be controlled based on the acquired information.

1 is a schematic diagram illustrating a configuration of an image forming apparatus according to an exemplary embodiment. FIG. 2 is a schematic diagram illustrating a configuration of an image forming unit of a toner image forming unit according to the exemplary embodiment. FIG. 10 is a schematic diagram illustrating a configuration of an image forming unit of a toner image forming unit according to a modified example.

  Below, an example of an embodiment concerning the present invention is described based on a drawing.

(Image forming apparatus 10)
First, the configuration of the image forming apparatus 10 according to the present embodiment will be described. FIG. 1 is a schematic diagram illustrating a configuration of an image forming apparatus 10 according to the present embodiment.

  As shown in FIG. 1, the image forming apparatus 10 includes an image forming unit 14 that forms a toner image on a continuous paper P (an example of a recording medium) conveyed in the direction of arrow A, and fixes the toner image to the continuous paper P. And a controller 19 that controls each part of the image forming apparatus 10. The recording medium is not limited to paper such as continuous paper P, and may be, for example, a film.

(Fixing device 16)
As shown in FIG. 1, the fixing device 16 includes a heating roll 16 </ b> A that heats the continuous paper P and a pressure roll 16 </ b> B that pressurizes the continuous paper P. In the fixing device 16, the continuous paper P is sandwiched between the heating roll 16 </ b> A and the pressure roll 16 </ b> B, and the continuous paper P is pressurized while being heated, so that the toner image on the continuous paper P is fixed to the continuous paper P.

(Image forming unit 14)
As shown in FIG. 1, the image forming unit 14 forms toner images of yellow (Y), magenta (M), cyan (C), and black (K) toner images forming units 14Y, 14M, and 14C. , 14K (hereinafter referred to as 14Y to 14K). The toner image forming units 14Y, 14M, 14C, and 14K are arranged in this order from the upstream side in the transport direction of the continuous paper P.

  Each of the toner image forming units 14Y to 14K includes an image forming unit 18 and a transfer unit 20 (an example of a transfer unit). Since the toner image forming units 14Y to 14K are configured similarly except for the toner to be used, the reference numerals of the toner image forming units 14M, 14C, and 14K are omitted in FIG.

  Each of the toner image forming units 14Y to 14K includes a supply mechanism 110 and a recovery mechanism 70, as shown in FIG. Since the toner image forming units 14Y to 14K are basically configured in the same manner except for the toner to be used, in FIG. 2, the toner image forming units 14Y to 14K are collectively referred to as one toner image forming unit. It is shown.

  Hereinafter, a specific configuration of each of the toner image forming units 14Y to 14K (the image forming unit 18, the transfer unit 20, the supply mechanism 110, and the recovery mechanism 70) will be described.

(Image forming unit 18)
The image forming units 18 of the toner image forming units 14Y to 14K are units that form toner images using the liquid developer G. Specifically, as shown in FIG. 2, the image forming unit 18 rotates in one direction (for example, the clockwise direction in FIG. 2) and also holds an image holding member 22 (image) such as a photosensitive member that holds a toner image. An example of a formed body), a charging device 24 that charges the image holding body 22, an exposure device 26 that exposes the image holding body 22 to form an electrostatic latent image (an example of a latent image), and the image holding body 22 A developing device 40 that develops the electrostatic latent image and forms a toner image. The image carrier 22 is an example of an image forming body on which an electrostatic latent image is developed by the developing device 40 to form an image.

(Developing device 40)
As shown in FIG. 2, the developing device 40 includes a chamber 46 serving as a storage unit, a supply roll 44 (an example of a holding body), a developing roll 42 (an example of a developing body), and a charging device 45 (an application unit). An example, an example of a first application unit), a charging device 48 (an example of a second application unit), a power source 17 (an example of a transfer unit), a power source 15, and a detection unit 60 are included.

(Chamber 46)
The chamber 46 contains the liquid developer G therein. The liquid developer G used in the present embodiment is a liquid type liquid developer in which toner (particles) is dispersed in a volatile carrier liquid. As the carrier liquid, for example, an insulating liquid such as vegetable oil, liquid paraffin oil, or silicone oil is used. Further, as an example, the liquid developer G in the chamber 46 has toner (particles) dispersed in a carrier liquid at a concentration of 20% by mass. In addition, an additive may be added to the liquid developer G.

(Supply roll 44)
The supply roll 44 is an example of a holding body that is supplied with the liquid developer and holds the liquid developer. Specifically, the supply roll 44 is a roll that is supplied with the liquid developer G from the chamber 46 and holds the liquid developer G. More specifically, the supply roll 44 is a roll that supplies the held liquid developer G to the development roll 42.

  A part of the outer peripheral surface of the supply roll 44 is in contact with the liquid developer G in the chamber 46, and the other part of the outer peripheral surface is in contact with the outer peripheral surface of the developing roll 42. The contact position with the developing roll 42 is a supply position where the liquid developer G is supplied from the supply roll 44 to the developing roll 42. For example, the supply roll 44 rotates in one direction (for example, the clockwise direction in FIG. 2) following the development roll 42.

  As the supply roll 44, for example, an anilox roll having a plurality of recesses (cells) arranged on the outer peripheral surface and recessed radially inward is used. In the anilox roll, the liquid developer G is held in the recess (cell).

(Developing roll 42)
The developing roll 42 is an example of a developing body that supplies the liquid developer transferred from the holding body to the latent image and develops the latent image. Specifically, the developing roll 42 is a roll that supplies the liquid developer G supplied from the supply roll 44 to the electrostatic latent image formed on the image holding member 22 and develops the electrostatic latent image. .

  A part of the outer peripheral surface of the developing roll 42 is in contact with the outer peripheral surface of the supply roll 44, and the other part of the outer peripheral surface is in contact with the outer peripheral surface of the image carrier 22. The contact position with the image carrier 22 is a development position where development by the development roll 42 is performed. In other words, this is a supply position where the liquid developer G is supplied from the developing roll 42 to the image holding member 22. For example, the developing roll 42 rotates in one direction (for example, counterclockwise in FIG. 2) following the image carrier 22.

(Charging device 45)
The charging device 45 is an example of an applying unit (first applying unit) that applies to the toner of the liquid developer held on the holding body a charge having a polarity opposite to that of the toner. Specifically, the charging device 45 is a device that applies a charge having a polarity opposite to the charge of the toner to the toner of the liquid developer G held on the supply roll 44. More specifically, the charging device 45 is a device that charges the toner of the liquid developer G held on the supply roll 44 to a reverse polarity. The charging device 45 charges the toner with a reverse polarity to give the toner a charge with a polarity opposite to that of the toner. As the charging device 45, for example, a device that charges the toner of the liquid developer G by non-contact discharge is used. Specifically, as the charging device 45, for example, a corotron for charging the toner of the liquid developer G by corona discharge is used.

  Note that “the polarity opposite to the charge of the toner” means “a polarity opposite to the polarity of the toner having a large amount of charge”. Therefore, for example, when the amount of charge on the positive electrode in the toner is larger than the amount of charge on the negative electrode, the charging device 45 imparts the charge on the negative electrode to the toner. Specifically, the polarity of the charge of the toner is detected by, for example, a detection unit 60 described later.

  The charging device 45 is disposed to face the outer peripheral surface of the supply roll 44. Specifically, the charging device 45 is disposed downstream of the chamber 46 in the rotation direction of the supply roll 44 and upstream of the supply position for supplying the liquid developer G to the developing roll 42.

(Power supply 17)
The power source 17 is an example of a transfer section that generates a potential difference between the holding body and the developing body, and transfers the toner to which the charge having the reverse polarity is transferred from the holding body to the developing body. Specifically, the power source 17 generates a potential difference between the supply roll 44 and the developing roll 42, and transfers the toner, which has been charged with the reverse polarity by the charging device 45, from the supply roll 44 to the developing roll 42. Device. More specifically, the power source 17 applies a voltage between the supply roll 44 and the developing roll 42 to generate a potential difference between the supply roll 44 and the developing roll 42. As a result, the toner provided with the reverse polarity charge by the charging device 45 is transferred from the supply roll 44 to the developing roll 42 by electrostatic force.

  It should be noted that components other than the toner of the liquid developer G (such as carrier liquid) are also transferred from the supply roll 44 to the development roll 42 due to adhesion force due to contact with the development roll 42.

(Charging device 48)
The charging device 48 is an example of a second application unit that applies a charge to the toner of the liquid developer held on the developer. Specifically, the charging device 48 is a device that applies a charge to the toner of the liquid developer G held on the developing roll 42. More specifically, the charging device 48 is a device that charges the toner of the liquid developer G held on the developing roll 42. As described above, the charging device 48 charges the toner, so that the toner is charged.

  The charging device 48 is disposed to face the outer peripheral surface of the developing roll 42. Specifically, the charging device 48 is disposed downstream of the supply position where the liquid developer G is supplied from the supply roll 44 and upstream of the development position in the rotation direction of the development roll 42. As the charging device 48, for example, a device for charging the toner of the liquid developer G by discharge without contact is used. Specifically, as the charging device 48, for example, a corotron for charging the toner of the liquid developer G by corona discharge is used.

(Power supply 15)
The power supply 15 is a device that causes a potential difference between the developing roll 42 and the image holding body 22 to transfer the toner to which the charge is applied by the charging device 48 from the developing roll 42 to the image holding body 22. Specifically, the power supply 15 generates a potential difference between the developing roll 42 and the image holding body 22 by applying a voltage between the developing roll 42 and the image holding body 22. As a result, the toner charged by the charging device 48 is transferred from the developing roll 42 to the image holding member 22 by electrostatic force. The toner is transferred from the developing roll 42 to the image holding member 22, whereby the electrostatic latent image on the image holding member 22 is developed and a toner image is formed.

  It should be noted that components other than the toner (such as carrier liquid) of the liquid developer G are also transferred from the developing roll 42 to the image holding member 22 due to adhesion force due to contact with the image holding member 22. Further, the power source 15 may be a common power source with the power source 17.

(Detector 60)
The detection unit 60 is an example of a detection unit that detects the polarity of the charge of the liquid developer before the charge having the opposite polarity is applied by the application unit. Specifically, the detection unit 60 is a detection unit that detects the polarity of the charge of the liquid developer G before the charge of the reverse polarity is applied by the charging device 45.

  The detection unit 60 includes a detection sensor 62 (an example of a measurement unit) and an acquisition unit 64. The detection sensor 62 is an example of a measurement unit that measures a feature amount based on the amount of toner held on the developing member. Furthermore, the detection sensor 62 is also an example of a measuring unit that measures the optical density of the liquid developer held on the developer. Specifically, the detection sensor 62 is a sensor that measures the optical density of the liquid developer G held on the developing roll 42 as a feature amount based on the amount of toner held on the developing roll 42.

  The optical density of the liquid developer G represents how much light is not transmitted or reflected with respect to the liquid developer G. As the amount of toner held on the developing roll 42 increases, light does not transmit or reflect on the liquid developer G held on the developing roll 42. Accordingly, the higher the value of the optical density of the liquid developer G, the more toner is held on the developing roll 42.

  Specifically, for example, a sensor that irradiates the liquid developer G on the developing roll 42 with light and receives reflected light of the irradiated light is used as the detection sensor 62.

  The detection sensor 62 is disposed to face the outer peripheral surface of the developing roll 42. Specifically, the detection sensor 62 is disposed on the downstream side of the supply position where the liquid developer G is supplied from the supply roll 44 in the rotation direction of the development roll 42 and on the upstream side of the charging device 48. .

  The acquisition unit 64 acquires a measured value of the optical density measured by the detection sensor 62. The acquisition unit 64 detects the polarity of the charge of the toner before the charge having the opposite polarity is applied by the charging device 45 based on the acquired measurement value. Specifically, detection is performed as follows. Note that the detection operation related to the detection is executed in advance before executing the image forming operation for forming an image on the continuous paper P, for example.

  In the detection operation, first, in a state in which the application operation of the charging device 45 is stopped, a potential difference is generated between the supply roll 44 and the development roll 42 by applying a voltage of the power supply 17, and the supply roll 44 to the development roll 42 The toner is transferred (this operation is hereinafter referred to as a first transfer operation). In other words, toner in a state where no charge is applied from the charging device 45 is transferred from the supply roll 44 to the developing roll 42. In other words, the toner before the reverse polarity charge is applied by the charging device 45 is transferred from the supply roll 44 to the developing roll 42.

  It should be noted that components other than the toner of the liquid developer G (such as carrier liquid) are also transferred from the supply roll 44 to the development roll 42 due to adhesion force due to contact with the development roll 42.

  Next, the detection sensor 62 measures the optical density of the liquid developer G containing the toner transferred to the developing roll 42. The measurement unit (hereinafter referred to as the first measurement value) acquires the measurement value. The liquid developer G transferred to the developing roll 42 is removed by a scraping blade 72 described later.

  Next, in a state where the application operation of the charging device 45 is stopped, the toner is transferred from the supply roll 44 to the development roll 42 in a state where the direction of the electric field between the supply roll 44 and the development roll 42 is reversed from the first transfer operation. (This operation is hereinafter referred to as a second transfer operation).

  That is, in a state where the application operation of the charging device 45 is stopped, the power source 17 reverses the direction of the electric field between the supply roll 44 and the development roll 42, and applies a voltage between the supply roll 44 and the development roll 42. Apply. As a result, a potential difference is generated between the supply roll 44 and the developing roll 42, and the toner is transferred from the supply roll 44 to the developing roll 42.

  It should be noted that components other than the toner of the liquid developer G (such as carrier liquid) are also transferred from the supply roll 44 to the development roll 42 due to adhesion force due to contact with the development roll 42.

  In the second transfer operation, the direction of the electric field is reversed from the direction of the electric field in the first transfer operation described above. Therefore, in the first transfer operation, toner having a polarity opposite to the polarity of the toner transferred to the developing roll 42 is obtained. Transfer to the developing roll 42. In other words, in the first transfer operation, the toner of the first polarity (one of the positive electrode and the negative electrode) is transferred from the supply roll 44 to the developing roll 42, and in the second transfer operation, the polarity is opposite to the first polarity. The toner of the second polarity (the other of the positive electrode and the negative electrode) is transferred from the supply roll 44 to the developing roll 42.

  Next, the detection sensor 62 measures the optical density of the liquid developer G containing the toner transferred to the developing roll 42. The acquisition unit 64 acquires this measurement value (hereinafter referred to as a second measurement value).

  Then, from the difference between the first measured value and the second measured value, the charge polarity of the toner before the charge having the opposite polarity is applied by the charging device 45 is detected. Specifically, if the first measurement value is larger than the second measurement value, the charge polarity of the toner before the charge having the opposite polarity is applied by the charging device 45 is detected as the first polarity. On the other hand, if the second measured value is larger than the first measured value, the charge polarity of the toner before the charge having the opposite polarity is applied by the charging device 45 is detected as the second polarity.

(Applying operation of charging device 45)
The charging device 45 imparts to the toner of the liquid developer G held on the supply roll 44 a charge having a polarity opposite to the polarity detected by the detection unit 60. Specifically, the charging device 45 imparts a charge having a polarity opposite to the charge of the toner to the toner of the liquid developer G held on the supply roll 44 based on the detection result of the detection unit 60.

  Here, the charge polarity of the toner of the liquid developer G held on the supply roll 44 may change after a specific period. Specifically, in the present embodiment, as described later, the liquid developer G is collected from the developing roll 42 and then supplied to the chamber 46. For this reason, the charge of the reverse polarity is given by the charging device 45 and the charge is accumulated in the toner, so that the polarity of the charge of the toner may be reversed.

  Therefore, the charging device 45 is configured to be able to switch the polarity of the charge applied to the toner. That is, when the charge of the toner of the liquid developer G held on the supply roll 44 is the first polarity, the charging device 45 charges the toner with the second polarity charge that is opposite to the first polarity. When the charge of the toner of the liquid developer G held on the supply roll 44 is the second polarity, the first state is switched to the second state where the charge of the first polarity is applied to the toner. It is configured.

  In the present embodiment, specifically, when the charging device 45 is in the first state, the liquid development is performed via a supply path (a container 74, a recovery path 76, a storage section 112, a supply path 114, and a chamber 46) described later. When the charge of the toner of the liquid developer G held on the supply roll 44 is changed from the first polarity to the second polarity by supplying the agent G to the supply roll 44, the charging device 45 Switch from one state to the second state. In the present embodiment, whether or not the first polarity is changed to the second polarity is detected by the detection unit 60.

  Then, the control unit 19 controls the driving of the charging device 45 based on the acquired information, thereby adjusting the amount of charge applied by the charging device 45 to the toner of the liquid developer G held on the supply roll 44. . The acquired information includes image information to be formed and the type of recording medium on which the image is formed. The image information includes information such as the image density of the image to be formed.

(Transfer unit 20)
The transfer unit 20 is an example of a transfer unit that transfers the toner image formed on the image carrier 22 of the image forming unit 18 to the continuous paper P. Specifically, the transfer unit 20 has a transfer roll 50 as a transfer body and a backup roll 52.

  The transfer roll 50 is placed in contact with the image carrier 22 and rotates, and a voltage is applied to the image carrier 22 to transfer the toner image on the image carrier 22 with an electrostatic force. The backup roll 52 is disposed on the opposite side of the transfer roll 50 across the continuous paper P. Further, the transfer roll 50 transfers a toner image on the transfer roll 50 to the continuous paper P with an electrostatic force when a voltage is applied between the transfer roll 50 and the backup roll 52.

(Supply mechanism 110)
The supply mechanism 110 is a mechanism that supplies the liquid developer G to the chamber 46. Specifically, the supply mechanism 110 includes a storage unit 112 that stores the liquid developer G, and a supply path 114 that supplies the liquid developer G from the storage unit 112 to the chamber 46. The liquid developer G stored in the storage unit 112 is supplied to the chamber 46 through the supply path 114 by a pump (not shown) provided in the supply path 114.

(Recovery mechanism 70)
The recovery mechanism 70 is a mechanism for recovering the liquid developer G from the developing roll 42 after the liquid developer G is supplied to the electrostatic latent image on the image carrier 22. Specifically, the recovery mechanism 70 includes a scraping blade 72, a container 74, and a recovery path 76.

  The scraping blade 72 is a member that scrapes off the liquid developer G remaining on the developing roll 42. The scraping blade 72 is configured by, for example, a plate-like rubber blade having a length along the axial direction (the depth direction of the paper surface) of the developing roll 42. The tip portion of the scraping blade 72 is in contact with the developing roll 42 on the downstream side with respect to the developing position in the rotation direction of the developing roll 42 and on the upstream side with respect to the contact position with the supply roll 44.

  The container 74 receives the liquid developer G scraped by the scraping blade 72 and functions as a storage unit that temporarily stores the liquid developer G. The container 74 is configured by a container having an upper opening, and the liquid developer G scraped by the scraping blade 72 flows from the upper opening.

  The recovery path 76 has one end connected to the container 74 and the other end connected to the storage part 112. The liquid developer G flowing into the container 74 is sent to the storage unit 112 through the recovery path 76 by a pump (not shown) provided in the recovery path 76. In the process of sending the collection path 76 to the storage unit 112, the aggregated toner may be redispersed in the carrier liquid by passing through a dispersion device (not shown).

  As described above, in this embodiment, the electrostatic latent image of the image carrier 22 is constituted by the container 74 and the collection path 76 of the collection mechanism 70, the storage unit 112 and the supply path 114 of the supply mechanism 110, and the chamber 46. A supply path for collecting the liquid developer G from the developing roll 42 after supplying the liquid developer G to the supply roll 44 and supplying the liquid developer G to the supply roll 44 is configured.

(Operation of this embodiment)
In the image forming apparatus 10, after the detection operation by the detection unit 60 is executed, the image formation operation is executed. Hereinafter, the detection operation and the image forming operation will be described.

(Detection operation)
First, in a state where the application operation of the charging device 45 is stopped, a potential difference is generated between the supply roll 44 and the developing roll 42 by applying a voltage of the power supply 17, and the toner is transferred from the supply roll 44 to the developing roll 42. It should be noted that components other than the toner of the liquid developer G (such as carrier liquid) are also transferred from the supply roll 44 to the development roll 42 due to adhesion force due to contact with the development roll 42.

  Next, the detection sensor 62 measures the optical density of the liquid developer G containing the toner transferred to the developing roll 42. The measurement unit (hereinafter referred to as the first measurement value) acquires the measurement value.

  Next, in a state where the application operation of the charging device 45 is stopped, the toner is transferred from the supply roll 44 to the development roll 42 in a state where the direction of the electric field between the supply roll 44 and the development roll 42 is reversed. It should be noted that components other than the toner of the liquid developer G (such as carrier liquid) are also transferred from the supply roll 44 to the development roll 42 due to adhesion force due to contact with the development roll 42.

  Next, the detection sensor 62 measures the optical density of the liquid developer G containing the toner transferred to the developing roll 42. The acquisition unit 64 acquires this measurement value (hereinafter referred to as a second measurement value).

  Then, from the difference between the first measured value and the second measured value, the charge polarity of the toner before the charge having the opposite polarity is applied by the charging device 45 is detected.

(Image forming operation)
In the image forming operation, in the developing device 40, the liquid developer G in the chamber 46 is supplied to the supply roll 44 and is held by the supply roll 44. The liquid developer G held on the supply roll 44 is charged by the charging device 45 with a charge having a polarity opposite to that of the toner of the liquid developer G. Specifically, the charging device 45 applies a charge having a polarity opposite to the polarity detected by the detection unit 60 to the toner of the liquid developer G held on the supply roll 44.

  The toner to which the charge of reverse polarity is applied is transferred from the supply roll 44 to the development roll 42 due to a potential difference between the supply roll 44 and the development roll 42. It should be noted that components other than the toner of the liquid developer G (such as carrier liquid) are also transferred from the supply roll 44 to the development roll 42 due to adhesion force due to contact with the development roll 42.

  The liquid developer G transferred to the developing roll 42 is charged by the charging device 48 to the toner of the liquid developer G. The charged toner is transferred from the developing roll 42 to the image holding body 22 due to a potential difference between the developing roll 42 and the image holding body 22. It should be noted that components other than the toner (such as carrier liquid) of the liquid developer G are also transferred from the developing roll 42 to the image holding member 22 due to adhesion force due to contact with the image holding member 22 or the like.

  The electrostatic latent image on the image carrier 22 is developed by the liquid developer G transferred to the image carrier 22 to form a toner image.

  In the present embodiment, as described above, the charging device 45 imparts a charge having a polarity opposite to the charge of the toner to the toner of the liquid developer G held on the supply roll 44.

  As a result, the charging state of the toner is higher than that in the configuration in which the charging device 45 imparts the charge of the same polarity as the charge of the toner to the toner of the liquid developer G held on the supply roll 44 (first comparative example). Can be adjusted over a wide range. That is, in this embodiment, by applying a reverse polarity charge and reversing the polarity of the toner, the absolute value of the charge amount (charge amount) of the toner is close to O (zero) as compared with the first comparative example. Since the value can be taken, the charged state of the toner can be adjusted in a wide range.

  For this reason, in the configuration of the present embodiment, the control range in which the amount of toner transferred to the developing roll 42 can be controlled is wider than in the first comparative example.

Further, in the present embodiment, as described above, the detection unit 60 detects the polarity of the charge of the toner before the charge having the reverse polarity is applied by the charging device 45, and the charging device 45 is held by the supply roll 44. A charge having a polarity opposite to the polarity detected by the detection unit 60 is applied to the toner of the liquid developer G that has been detected.
As a result, in this embodiment, when the charge of the toner of the liquid developer G held on the supply roll 44 is the first polarity, the charging device 45 has a polarity opposite to the first polarity. When the charge of the toner of the liquid developer G held in the supply roll 44 is the second polarity when the charge is charged with the second polarity, the charge of the first polarity is applied to the toner. Switch to the second state to be granted.

  In the present embodiment, specifically, when the charging device 45 is in the first state, the liquid developer G passes through the supply path (the container 74, the recovery path 76, the storage unit 112, the supply path 114, and the chamber 46). Is supplied to the supply roll 44, so that the charge of the toner of the liquid developer G held on the supply roll 44 changes from the first polarity to the second polarity. To the second state. Whether the first polarity has changed to the second polarity is detected by the detection unit 60.

  For this reason, compared with the case where the charging device 45 is only in the first state, the liquid developer G is supplied to the supply roll 44 through the supply path when the charging device 45 is in the first state. Thus, even when the charge of the toner of the liquid developer G held on the supply roll 44 is changed from the first polarity to the second polarity, the toner of the liquid developer held on the supply roll 44 is changed. It is possible to suppress the charge having the same polarity as that of the toner.

(First Modification of Detection Unit 60)
In the present embodiment, the detection unit 60 is configured to measure the optical density of the liquid developer G held on the developing roll 42, but is not limited thereto. As an example of the detection unit, as shown in FIG. 3, for example, a detection unit 160 that measures the surface potential of the liquid developer G held on the developing roll 42 may be used.

  The detection unit 160 includes a detection sensor 162 (an example of a measurement unit) and an acquisition unit 164. The detection sensor 162 is an example of a measurement unit that measures a feature amount based on the amount of toner held on the developing member. Further, the detection sensor 162 is an example of a measuring unit that measures the surface potential of the liquid developer held on the developing member. Specifically, the detection sensor 162 is a sensor that measures the surface potential of the liquid developer G held on the developing roll 42 as a feature amount based on the amount of toner held on the developing roll 42.

  The detection sensor 162 is disposed to face the outer peripheral surface of the developing roll 42. Specifically, the detection sensor 162 is disposed downstream of the charging device 48 and upstream of the developing position in the rotation direction of the developing roll 42.

  The acquisition unit 164 acquires a measured value of the surface potential measured by the detection sensor 162. The acquisition unit 164 detects the polarity of the charge of the toner before the charge having the opposite polarity is applied by the charging device 45 based on the acquired measurement value. Specifically, detection is performed as follows. Note that the detection operation related to the detection is executed in advance before executing the image forming operation for forming an image on the continuous paper P, for example.

  In the detection operation, first, the application operation of the charging device 45 is stopped, and in the state where the charging device 48 is operated, a potential difference is generated between the supply roll 44 and the developing roll 42 by the voltage application of the power supply 17. The toner is transferred from the supply roll 44 to the developing roll 42 (this operation is hereinafter referred to as a third transfer operation). In other words, toner in a state where no charge is applied from the charging device 45 is transferred from the supply roll 44 to the developing roll 42. In other words, the toner before the reverse polarity charge is applied by the charging device 45 is transferred from the supply roll 44 to the developing roll 42.

  It should be noted that components other than the toner of the liquid developer G (such as carrier liquid) are also transferred from the supply roll 44 to the development roll 42 due to adhesion force due to contact with the development roll 42.

  In the third transfer operation, since the charging device 48 is operated, charge is applied to the toner transferred to the developing roll 42.

  Next, the detection sensor 162 measures the surface potential of the liquid developer G containing the toner transferred to the developing roll 42. The measurement unit (hereinafter referred to as the third measurement value) acquires the measurement value. The liquid developer G transferred to the developing roll 42 is removed by the scraping blade 72 or the like.

  Next, in a state where the application operation of the charging device 45 is stopped and the charging device 48 is operated, the direction of the electric field between the supply roll 44 and the development roll 42 is reversed, and the supply roll 44 to the development roll 42. Toner is transferred (this operation is hereinafter referred to as a fourth transfer operation).

  That is, in a state where the application operation of the charging device 45 is stopped, the power supply 17 reverses the direction of the electric field between the supply roll 44 and the development roll 42 with respect to the third transfer operation, and the supply roll 44 and the development roll 42. A voltage is applied between As a result, a potential difference is generated between the supply roll 44 and the developing roll 42, and the toner is transferred from the supply roll 44 to the developing roll 42.

  It should be noted that components other than the toner of the liquid developer G (such as carrier liquid) are also transferred from the supply roll 44 to the development roll 42 due to adhesion force due to contact with the development roll 42.

  In the fourth transfer operation, since the charging device 48 is operated, the toner transferred to the developing roll 42 is charged.

  In the fourth transition operation, since the direction of the electric field is reversed from the direction of the electric field in the third transition operation described above, in the third transition operation, toner having a polarity opposite to the polarity of the toner transferred to the developing roll 42 is obtained. Transfer to the developing roll 42. In other words, in the third transfer operation, the toner having the first polarity (one of the positive electrode and the negative electrode) is transferred from the supply roll 44 to the developing roll 42, and in the fourth transfer operation, the polarity is opposite to the first polarity. The toner of the second polarity (the other of the positive electrode and the negative electrode) is transferred from the supply roll 44 to the developing roll 42.

  Next, the detection sensor 162 measures the surface potential of the liquid developer G containing the toner transferred to the developing roll 42. The acquisition unit 164 acquires this measurement value (hereinafter referred to as a fourth measurement value).

  Then, based on the difference between the above-described third measurement value and the above-described fourth measurement value, the polarity of the toner charge before the charge having the opposite polarity is applied by the charging device 45 is detected. Specifically, if the third measurement value is larger than the fourth measurement value, the charge polarity of the toner before the charge having the opposite polarity is applied by the charging device 45 is detected as the first polarity. On the other hand, if the fourth measured value is larger than the third measured value, the charge polarity of the toner before the charge having the opposite polarity is applied by the charging device 45 is detected as the second polarity.

(Second Modification of Detection Unit 60)
The detection unit 60 is disposed on the developing roll 42, but is not limited thereto. For example, the liquid developer G is collected from the developing roll 42 after the liquid developer G is supplied to the electrostatic latent image on the image holding member 22, and the liquid developer G is disposed in a supply path for supplying the liquid developer G to the supply roll 44. A detection unit may be used.

  The detection unit is disposed, for example, in any of the container 74, the collection path 76, the storage unit 112, the supply path 114, and the chamber 46 that constitute the supply path.

  As the detection unit, for example, the liquid developer G is passed between opposing transparent electrodes to which an electric field is applied, and the reflectance of the transparent electrode is measured, so that the toner of the liquid developer G moves to either the positive electrode or the negative electrode The polarity of the toner is detected depending on whether the toner is used.

(Other variations)
In the present embodiment, the detection unit 60 detects the polarity of the toner charge before the charge having the opposite polarity is applied by the charging device 45, and the charging device 45 is held in the supply roll 44 by the liquid developer G. Although the toner having the opposite polarity to the polarity detected by the detection unit 60 is applied to the toner, the present invention is not limited to this. For example, in a configuration in which the polarity of the toner of the liquid developer G held on the supply roll 44 is constant (does not change), the charging device 45 is connected to the supply roll 44 regardless of the polarity detected by the detection unit 60. A configuration may be employed in which a charge is imparted to the toner of the liquid developer G that is held. In this configuration, for example, the detection unit 60 is not included. In this configuration, the charging device 45 may be configured such that the polarity of the charge applied to the toner is not switchable.

  In the present embodiment, the detection sensor 62 measures the optical density of the liquid developer G held on the developing roll 42 as a feature amount based on the amount of toner held on the developing roll 42. Further, the detection sensor 162 measures the surface potential of the liquid developer G held on the developing roll 42 as a feature amount based on the amount of toner held on the developing roll 42. The feature amount is not limited to these, and may be a physical property value that changes with a change in the amount of toner, for example.

  In the present embodiment, the charging device 45 is configured as a single device, and applies a charge of a second polarity that is opposite to the first polarity to the toner of the liquid developer G held on the supply roll 44. Although the configuration is switched to the first state and the second state in which the first polarity charge is applied to the toner, the present invention is not limited to this. For example, the charging device 45 includes a first applying unit (first device) that applies a second polarity charge opposite to the first polarity to the toner of the liquid developer G held on the supply roll 44. A second application unit (second device) that applies a first polarity charge to the toner, and the application unit to be operated is switched between the first application unit and the second application unit. Good.

  The present invention is not limited to the above-described embodiment, and various modifications, changes, and improvements can be made without departing from the spirit of the present invention. For example, the modification examples described above may be appropriately combined.

<Example>
EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.

Example 1
[Liquid developer G]
As the liquid developer G, a polyester colored resin having a volume average particle diameter of 1.7 μm dispersed in Isopar L manufactured by ExxonMobil Corporation was used, and the solid content concentration was adjusted to 20% by mass.

[Charging devices 45 and 48]
As the charging device 45 and the charging device 48, a corotron for charging the toner of the liquid developer G by corona discharge was used.

[Determination of toner charging polarity]
Two ITO vapor-deposited glasses (10 mm × 50 mm × 0.8 mm) connected to the power supply device were immersed in the liquid developer G with a 50 μm gap so that the ITO surfaces face each other, and a potential difference of 50 V was applied. After 30 seconds, the ITO vapor-deposited glass was taken out from the liquid developer G with a potential difference applied, and was gently submerged in Isopar L. Thereafter, the power was turned off, the ITO-deposited glass was taken out from the liquid developer G, and the adhered liquid was dried. The ratio of the optical density of the negative electrode to the positive electrode of the ITO-deposited glass colored by toner adhesion (the optical density of the negative electrode / (the sum of the optical densities of both electrodes)) is 0.5, and the toner of the liquid developer G is electrically neutral. It was confirmed that.

[Initial evaluation of toner amount control range]
A potential difference is applied so that the potential of the supply roll 44 is 600 V higher than that of the developing roll 42, and the output of the charging device 45 is changed in a range where the inflow current to the supply roll 44 is 10 μA to 100 μA. When the toner amount above was measured, the toner amount could be controlled in the range of 0.6 g / m ² to 1.45 g / m ² .

[Continuous printing test]
Next, while supplying the liquid developer G to the chamber 46 at a flow rate of 0.3 kg / min, a test pattern having a dot area ratio of 20% was continuously printed at a printing speed of 40 m / min for 1 hour. At this time, a potential difference is applied so that the potential of the supply roll 44 is 600 V higher than that of the developing roll 42, the output of the charging device 45 is 30 μA as an inflow current to the supply roll 44, and the output of the charging device 48 is the developing roll. The inflow current to 42 was set to 400 μA.

[Determination of toner charging polarity]
When the polarity of the toner was evaluated in the same manner as the previous method, the ratio of the optical density of the negative electrode to the positive electrode (the optical density of the negative electrode / (the sum of the optical densities of both electrodes)) was 0.9, and the toner of the liquid developer G Was positively charged.

[Toner amount control width after printing history]
After adjusting the solid content concentration of the used liquid developer G to 20% by mass, the toner amount control width was re-evaluated.

At this time, a potential difference is applied so that the potential of the supply roll 44 is 600 V lower than that of the developing roll 42, and the output of the charging device 45 is changed in a range where the inflow current to the supply roll 44 is −20 μA to −240 μA. When the toner amount on the developing roll 42 was measured, the toner amount could be controlled in the range of 0.5 g / m ² to 1.45 g / m ² , and a control range equivalent to that before the print test was obtained.

(Comparative example)
[Toner amount control width after printing history]
A potential difference is applied so that the potential of the supply roll 44 is 600 V higher than that of the developing roll 42, and the output of the charging device 45 is changed in a range where the inflow current to the supply roll 44 is 10 μA to 100 μA. When the toner amount was measured, the control range of the toner amount with respect to the output of the charging device 45 was 1.15 g / m ² to 1.45 g / m ² , which was narrower than before the printing test.

(Example 2)
[Determination of Toner Charging Polarity by Optical Density Sensor on Developing Roll 42]
An optical density sensor was installed facing the developing roll 42 of the image forming apparatus used in Example 1. The installation position was set downstream of the contact position with the image carrier 22 and upstream of the contact position with the scraping blade 72 in the rotation direction of the developing roll 42. The supply roll 44 and the developing roll 42 are brought into contact with each other, the developing roll 42 and the image carrier 22 are separated from each other, the charging device 45 is not used, and the potential of the supply roll 44 is increased by 400 V with respect to the developing roll 42; The developing roll 42 is rotated under the lowered condition, and the optical density of the liquid developer G transferred onto the developing roll 42 is measured. When the optical density is high under the condition where the potential of the supply roll 44 is high, it is determined that the toner polarity is positive, and in the opposite case, it is negatively charged. This toner charge polarity detection can be performed even during a printing operation. For example, based on input image information, when a blank state without image output continues, the charging device 48 on the supply roll 44 is stopped and the applied potential of the supply roll 44 is reversed.

[Print test]
While supplying the liquid developer G to the chamber 46 at a flow rate of 0.3 kg / min, a test pattern having a dot area ratio of 20% was continuously printed at a printing speed of 40 m / min for 1 hour. A potential difference is applied so that the potential of the supply roll 44 is 600 V higher than that of the developing roll 42. The output of the charging device 45 is 30 μA in terms of the current flowing into the supply roll 44, and the output of the charging device 48 is output to the developing roll 42. The inflow current was 400 μA. At this time, the toner polarity detection was performed by providing a non-printing area of 300 mm every 10 minutes. After 30 minutes, the toner charging polarity was determined to be positive, and the power supply caused the potential of the supply roll 44 to be 600 V lower than that of the developing roll 42, and the output of the charging device 45 was changed to −50 μA by the inflow current to the supply roll 44. . Throughout the printing test for one hour, the image density was a stable value.

10 Image forming apparatus 17 Power supply (an example of a transfer section)
20 Transfer unit (an example of transfer unit)
22 Image carrier (an example of an image forming body)
40 Developing Device 42 Developing Roll (Example of Developer)
44 Supply roll (an example of a holding body)
45 Charging device (an example of an application unit, an example of a first application unit)
48 Charging device (an example of a second application unit)
60 detector 62 detection sensor (an example of measuring means)
160 detector 162 detection sensor (an example of measuring means)
G Liquid developer

Claims (9)

A holder to which the liquid developer is supplied and holds the liquid developer;
A developer for supplying the liquid developer transferred from the holder to the latent image and developing the latent image;
An imparting unit that imparts, to the toner of the liquid developer held by the holder, a charge having a polarity opposite to the charge of the toner;
A transfer section that generates a potential difference between the holding body and the developing body, and transfers the toner to which the charge of the opposite polarity is applied by the applying section from the holding body to the developing body;
A developing device comprising: A detection unit that detects the polarity of the charge of the toner before the charge of reverse polarity is applied by the application unit;
The developing device according to claim 1, wherein the applying unit applies an electric charge having a polarity opposite to the polarity detected by the detecting unit to the toner of the liquid developer held on the holding body. The detector is
Measuring means for measuring a feature amount based on the amount of toner held on the developer,
Toner transferred from the holder to the developer due to a potential difference generated between the holder and the developer, which is a measurement value acquired by the measuring unit in a state where the application operation of the applying unit is stopped Measured values of features based on the amount of
The measured value obtained by the measuring means in a state where the applying operation of the applying unit is stopped, and the developer from the holder in the state where the direction of the electric field between the holder and the developer is reversed. Measured value of the feature amount based on the amount of toner transferred to
The developing device according to claim 2, wherein the polarity is detected from a difference between the two. The detector is
Measuring means for measuring the optical density of the liquid developer held on the developer,
Toner transferred from the holder to the developer due to a potential difference generated between the holder and the developer, which is a measurement value acquired by the measuring unit in a state where the application operation of the applying unit is stopped A measured value of the optical density of the liquid developer containing
The measured value obtained by the measuring means in a state where the applying operation of the applying unit is stopped, and the developer from the holder in the state where the direction of the electric field between the holder and the developer is reversed. Measured value of optical density of liquid developer containing toner transferred to
The developing device according to claim 2, wherein the polarity is detected from a difference between the two. A first grant unit as the grant unit;
A second application unit for applying an electric charge to the toner of the liquid developer held on the developer;
With
The detector is
Measuring means for measuring the surface potential of the liquid developer held on the developer,
The measuring unit is arranged downstream of the second applying unit in the rotation direction of the developer,
The measurement value obtained by the measurement means in a state where the application operation of the application unit is stopped and the second application unit is operated, and the potential difference generated between the holding body and the developing body A measured value of the surface potential of the liquid developer containing toner transferred from the holder to the developer;
The measurement value obtained by the measurement means in a state where the application operation of the application unit is stopped and the second application unit is operated, and the direction of the electric field between the holding body and the developing body is reversed. The measured value of the surface potential of the liquid developer containing the toner transferred from the holding body to the developing body in the
The developing device according to claim 2, wherein the polarity is detected from a difference between the two. The detector is
The developing device according to claim 2, wherein the developing device is disposed in a supply path for recovering the liquid developer from the developer after supplying the liquid developer to the latent image and supplying the liquid developer to the holding member. . The grant unit is
A first state in which when the charge of the liquid developer toner held on the holding body has a first polarity, the toner is given a charge of a second polarity that is opposite to the first polarity; ,
A second state in which when the charge of the liquid developer toner held on the holding body is the second polarity, the toner is given the first polarity charge;
The developing device according to any one of claims 1 to 6. A supply path for recovering the liquid developer from the developer after supplying the liquid developer to the latent image and supplying the liquid developer to the holder;
When the application unit is in the first state, the liquid developer is supplied to the holding body through the supply path, whereby the charge of the liquid developer toner held on the holding body is increased. When changing from the first polarity to the second polarity,
The developing device according to claim 7, wherein the applying unit switches from the first state to the second state. The developing device according to any one of claims 1 to 8, which adjusts an amount of charge applied to the toner of the liquid developer held on the holding body based on the acquired information.
An image forming body in which a latent image is developed by the developing device to form a toner image;
A transfer unit that transfers the toner image formed on the image forming body to a recording medium;
An image forming apparatus comprising: