WO2018124310A1

WO2018124310A1 - Image formation device

Info

Publication number: WO2018124310A1
Application number: PCT/JP2017/047419
Authority: WO
Inventors: 藤原　基裕
Original assignee: キヤノン株式会社
Priority date: 2016-12-26
Filing date: 2017-12-26
Publication date: 2018-07-05
Also published as: JP2018105985A

Abstract

A squeezing roller 52K compresses a toner layer in a liquid developer formed as a film on a developing roller 54K by a film-forming electrode 51K. A developing cleaning contrast is applied between a developing cleaning roller 58K and the developing roller 54K, whereby the developing cleaning roller 58K recovers a toner remaining on the developing roller 54K that has passed the development position. A recovery power supply 14K is capable of variably applying a recovery potential difference. A control unit is capable of controlling the recovery power supply 14K and changing the developing cleaning contrast according to information pertaining to the compression state of the toner layer on the developing roller 54K that has passed between the squeezing roller 52K and the developing roller 54K.

Description

Image forming apparatus

The present invention relates to an image forming apparatus that forms an image using a liquid developer containing toner and a carrier liquid.

As an image forming apparatus, a configuration is known in which image formation is performed using a liquid developer in which toner is dispersed in a carrier liquid. For example, a configuration is known in which a liquid developer stored in a developer storage tank is adsorbed on a developing roller by an electrode, and an electrostatic image formed on a photoconductor is developed with toner in the liquid developer adsorbed on the developing roller. (JP-A-10-28295).

A developing roller having a compression member disposed opposite to the developing roller, and applying an electric field between the compressing member and the developing roller to compress the toner in the liquid developer to the developing roller side by the electric field There is known a configuration of a cleaning roller that contacts a toner and cleans the developer on the developing roller by an electric field (Japanese Patent Laid-Open No. 2007-147976).

As described in Japanese Patent Application Laid-Open No. 2007-147976, in a configuration in which a constant voltage is applied to the cleaning roller and cleaning is performed, if the cleaning voltage is small and the state of the developer on the developing roller changes, it is necessary for cleaning. An electric field cannot be obtained.
Further, in order to eliminate such a concern, when a large voltage is applied in advance, the force that adheres to the developer on the cleaning roller increases, so that the developer may remain on the cleaning roller.

According to one aspect of the present invention, a developer carrying member that carries and rotates a liquid developer containing toner and a carrier liquid and develops an electrostatic latent image carried on the image carrying member, and the developer carrying member. A recovery roller that recovers the toner remaining on the developer carrier by forming a potential difference between the developer carrier and a potential difference between the developer carrier and the recovery roller. There is provided a developing device including a potential difference forming unit to be formed and a switching unit that switches a set value of a potential difference between the developer carrying member and the collecting roller during an image forming operation.
[The invention's effect]

According to the present invention, even if the state of the developer on the developing roller changes, it is possible to reduce the deterioration of the cleaning property by the cleaning roller.

FIG. 1 is a schematic sectional view of an image forming apparatus according to the first embodiment.

FIG. 2 is a schematic sectional view of the image forming unit.

FIG. 3 is a schematic sectional view of the developing device.

FIG. 4 is a conceptual diagram of film formation on the developing roller of the film formation electrode.

In FIG. 5, (a) shows the case where the compression state of the toner layer formed through the gap between the developing roller and the squeezing roller is appropriate, (b) shows the case where the compression is excessive, and (c) shows the case where the compression is the same. It is a schematic diagram which respectively shows the case of a shortage.

FIG. 6 is a diagram showing cleaning characteristics with respect to development cleaning contrast.

7A shows the behavior of the toner at the contact portion between the developing cleaning roller and the cleaning blade when the toner layer is compressed properly and FIG. 7B shows the case where the toner layer is excessively compressed. It is a schematic diagram.

FIG. 8 is a diagram showing the cleaning characteristics with respect to the development cleaning contrast when the compressed state of the toner layer is good and when the toner layer is excessively compressed.

FIG. 9 is a schematic diagram showing the electric field applied to the toner in the gap between the developing roller and the squeezing roller.

FIG. 10 is a graph showing the relationship between the conductivity of the liquid developer and the development cleaning contrast.

FIG. 11 is a control block diagram of the image forming apparatus according to the first embodiment.

FIG. 12 is a flowchart of control for determining a recovery voltage according to the first embodiment.

FIG. 13 is a control block diagram of the image forming apparatus according to the second embodiment.

FIG. 14 is a control block diagram of the image forming apparatus according to the third embodiment.

FIG. 15 is a control block diagram of the image forming apparatus according to the fourth embodiment.

<First Embodiment>
A first embodiment will be described with reference to FIGS. First, a schematic configuration of the image forming apparatus according to the present exemplary embodiment will be described with reference to FIGS. 1 and 2.

Image forming apparatus

As shown in FIG. 1, an image forming apparatus 100 includes four

image forming units

1Y, 1M, 1M, 4M provided corresponding to four colors of yellow (Y), magenta (M), cyan (C), and black (K). An electrophotographic full-color printer having 1C and 1K. In the present embodiment, the

image forming units

1Y, 1M, 1C, and 1Bk are tandem type arranged along the rotation direction of the intermediate transfer belt 70 described later. For example, the image forming apparatus 100 forms a toner image on the recording material P in accordance with an image signal from an external device that is communicably connected to the image forming apparatus main body. Examples of the recording material include sheet materials such as paper, plastic film, and cloth.

Each of the

image forming units

1Y, 1M, 1C, and 1K forms a toner image of each color on the

photoreceptors

20Y, 20M, 20C, and 20K as image carriers using a liquid developer containing toner and a carrier liquid. To do. A detailed configuration of the image forming unit will be described later.

The intermediate transfer belt 70 as an intermediate transfer member is an endless belt stretched around a driving roller 82, a driven roller 85, and a secondary transfer inner roller 86, and the

photoreceptors

20Y, 20M, 20C, and 20K, outside the secondary transfer. It is driven to rotate while contacting the roller 81.

Primary transfer rollers

61Y, 61M, 61C, and 61K are disposed at positions facing the

photoconductors

20Y, 20M, 20C, and 20K with the intermediate transfer belt 70 interposed therebetween, and primary transfer portions T1Y, T1M, T1C, and T1K are formed. is doing. Then, at each primary transfer portion T1Y, T1M, T1C, T1K, four color toner images are sequentially transferred onto the intermediate transfer belt 70 from the

respective photoreceptors

20Y, 20M, 20C, 20K, and transferred onto the intermediate transfer belt 70. A full-color toner image is formed. For example, only a single color toner image such as black can be formed on the intermediate transfer belt 70.

A secondary transfer outer roller 81 is disposed at a position facing the secondary transfer inner roller 86 across the intermediate transfer belt 70, and forms a secondary transfer portion T2. The single color toner image or full color toner image formed on the intermediate transfer belt 70 is transferred to the recording material at the secondary transfer portion T2. The liquid developer that has not been transferred to the recording material is cleaned by a cleaning device (not shown) that is in contact with the intermediate transfer belt 70. A blade 83 is in contact with the secondary transfer outer roller 81, and the liquid developer adhering to the secondary transfer outer roller 81 is scraped off by the blade 83 and collected by the collection unit 84. The toner image transferred onto the recording material is fixed on the recording material by a fixing device (not shown).

Image forming unit

The

image forming units

1Y, 1M, 1C, and 1K will be described with reference to FIGS. The

image forming units

1Y, 1M, 1C, and 1K have developing

devices

50Y, 50M, 50C, and 50K, respectively. The developing

devices

50Y, 50M, 50C, and 50K contain liquid developers containing toner particles that develop colors of yellow (Y), magenta (M), cyan (C), and black (K), respectively. The developing

devices

50Y, 50M, 50C, and 50K have a function of developing the electrostatic latent images formed on the

photoreceptors

20Y, 20M, 20C, and 20K with the liquid developers.

The four

image forming units

1Y, 1M, 1C, and 1K have substantially the same configuration except that the development colors are different. Therefore, hereinafter, the image forming unit 1K will be representatively described with reference to FIG. 2, and description of other image forming units will be omitted. In addition, about the code | symbol of each part of FIG. 1, the subscript (Y, M, C, K) corresponding to each color is attached | subjected and shown.

Around the photosensitive member 20K, along the rotation direction, a charging device 30K that charges the photosensitive member 20K, an exposure device 40K that forms an electrostatic latent image on the charged photosensitive member 20K, a developing device 50K, and a cleaning device 21K. Etc. are arranged.

The photoreceptor 20K is a photosensitive drum formed in a cylindrical shape, has a cylindrical base material and a photosensitive layer formed on the outer peripheral surface thereof, and is rotatable around a central axis. The photosensitive layer is composed of an organic photoreceptor or an amorphous silicon photoreceptor. The photoconductor 20K can carry an electrostatic latent image described below. In the present embodiment, the photoconductor 20K rotates counterclockwise as indicated by an arrow in FIG.

The charging device 30K is a device for charging the photoconductor 20K. In this embodiment, a corona charger is used. The exposure device 40K has a semiconductor laser, a polygon mirror, an F-θ lens, and the like, and irradiates the charged photoconductor 20K with a laser modulated in accordance with an image signal, thereby electrostatically forming the photoconductor 20K. A latent image is formed. That is, an electrostatic latent image is carried on the photoconductor 20K.

The developing device 50K is a device for developing the electrostatic latent image formed on the photoconductor 20K using black (K) toner. Details of the developing device 50K will be described later. The toner image formed on the photoreceptor 20K is primarily transferred to the intermediate transfer belt 70 by applying a transfer voltage between the primary transfer roller 61K and the photoreceptor 20K. The cleaning device 21K includes a cleaning blade 21Ka and a recovery unit 21Kb, and can recover the liquid developer on the photoreceptor 20K after the primary transfer.

Development device

Next, the configuration of the developing device 50K in the present embodiment will be described with reference to FIG. The developing device 50K includes a developing roller 54K as a developer carrying member that carries a liquid developer and conveys it to the photoreceptor 20K. Around the developing roller 54K, a developer tank 53K, a film forming electrode 51K, a compression roller and a squeezing roller 52K as a compression rotator, and a developing cleaning roller 58K as a recovery member and a recovery rotator are arranged.

The developing roller 54K rotates while carrying a liquid developer, and develops the electrostatic latent image carried on the photoconductor 20K with toner at a development position facing the photoconductor 20K. The developing roller 54K is a cylindrical member, and rotates clockwise around the central axis as indicated by an arrow in FIG. The developing roller 54K includes an elastic body such as conductive urethane rubber, a resin layer, and a rubber layer on the outer peripheral portion of a metal inner core such as stainless steel.

The developer tank 53K stores a liquid developer in which black toner particles are dispersed in a carrier liquid. The liquid developer used in the present embodiment is, for example, toner particles having an average particle diameter of 0.8 μm, in which a colorant such as a pigment is dispersed in a resin, in a carrier liquid such as an organic solvent, a dispersant, a toner charge control agent, It is added together with the charge directing agent. In this embodiment, the concentration of toner particles in the liquid developer is set to 7% by weight, for example. In this embodiment, the toner particle surface is charged with a certain amount of negative polarity.

The liquid developer stored in the developer tank 53K is supplied from the mixer 200K. In the mixer 200K, for example, the carrier liquid and the toner are appropriately replenished from the carrier tank in which the replenishment carrier liquid is stored and the toner tank in which the replenishment toner is stored. The mixer 200K contains stirring blades that are driven by a motor (not shown), mixes the supplied carrier liquid and toner by stirring, and disperses the toner in the carrier liquid.

In such a mixer 200K, a conductivity sensor 201K is accommodated as a conductivity detecting means capable of detecting the conductivity of the liquid developer. Based on the detection result of the conductivity sensor 201K, the carrier liquid and toner are replenished so that the conductivity of the liquid developer in the mixer 200K falls within a predetermined range. For example, the predetermined range of the conductivity of the liquid developer in the mixer 200K is 10 ⁻¹¹ [S / cm] or more and 10 ⁻⁹ [S / cm] or less. Since the liquid developer in the mixer 200K is supplied to the developer tank 53K, the conductivity of the liquid developer stored in the developer tank 53K is almost the same as the conductivity of the liquid developer in the mixer 200K. . Therefore, the conductivity of the liquid developer stored in the developer tank 53K can be detected by the conductivity sensor 201K. The conductivity sensor may be provided directly in the developer tank 53K.

The film forming electrode 51K is arranged with a predetermined gap from the developing roller 54K, and the liquid developer is developed so that a predetermined toner concentration is obtained by applying a predetermined film forming voltage from the film forming power source 12K. The film is formed on the developing roller 54K from the agent tank 53K.

The squeezing roller 52K is disposed downstream of the film forming electrode 51K and upstream of the developing position with respect to the rotation direction of the developing roller 54K, and the toner in the liquid developer formed on the developing roller 54K (on the developer carrier). Compress the layer. In other words, the squeezing roller 52K is applied with a predetermined squeezing voltage from the squeezing power supply 13K, thereby bringing toner particles contained in the liquid developer formed on the developing roller 54K toward the developing roller 54K, and at the same time extra Squeeze and collect the appropriate carrier liquid.

Such a squeeze roller 52K is a cylindrical member made of metal, and in this embodiment, a roller made of stainless steel is used. The squeezing roller 52K is in contact with the developing roller 54K and rotates counterclockwise around the central axis as shown by the arrow in FIG. A certain amount of the liquid developer pumped up in the developer tank 53K and passed through the film forming electrode 51K is carried on the developing roller 54K. Therefore, the liquid developer conveyed at a predetermined speed to the contact portion between the squeezing roller 52K and the developing roller 54K has a gap of approximately 6 μm and a rotational width of approximately 5 mm between the squeezing roller 52K and the developing roller 54K. A nip is stably formed.

The liquid developer is separated in the vicinity of the exit between the squeezing roller 52K and the developing roller 54K and is carried on each roller. At this time, as will be described in detail later, when the liquid developer passes between the squeeze roller 52K and the developing roller 54K, a predetermined potential difference is set so that the toner in the liquid developer approaches the developing roller 54K side. It is generated between both rollers. For this reason, the toner concentration in the liquid developer on the surface of the developing roller 54K after passing between the rollers greatly increases, for example, about 35% by weight. The liquid developer carried on the squeeze roller 52K is scraped off by the blade 56K.

The developing cleaning roller 58K is disposed downstream of the developing position in the rotation direction of the developing roller 54K, and is applied with a recovery voltage from a recovery power supply 14K as a potential difference applying unit. The remaining toner is collected. That is, the developing cleaning roller 58K collects the toner on the developing roller 54K by applying a recovery potential difference to the developing roller 54K. The developing cleaning roller 58K is in contact with the surface of the developing roller 54K and rotates counterclockwise as indicated by an arrow in FIG. 3, and is, for example, a stainless steel or aluminum roller.

The recovery power source 14K can variably apply a recovery voltage between the developing roller 54K and the developing cleaning roller 58K. In other words, the recovery power source 14K can variably apply the recovery potential difference between the development cleaning roller 58K and the development roller 54K. Thus, as will be described in detail later, a potential difference (that is, a recovery potential difference) is generated between the two rollers so that the toner on the developing roller 54K approaches the developing cleaning roller 58K. Then, the toner remaining on the surface of the developing roller 54K is removed by being collected by the developing cleaning roller 58K.

The toner collected by the developing cleaning roller 58K is removed by a cleaning blade 59K as a cleaning means. The cleaning blade 59K is disposed so as to contact the developing cleaning roller 58K downstream of the position facing the developing roller 54K with respect to the rotation direction of the developing cleaning roller 58K. The developing cleaning roller 58K from which the toner has been removed again removes the toner from the developing roller 54K. The cleaning blade 59K is made of aluminum having a thickness of 0.2 mm, and is in contact with the developing cleaning roller 58K in the counter direction.

Operation of developing device and image forming apparatus

Next, the operation of such a developing device and an image forming apparatus using the developing device will be described. Subsequently, the developing device will be described with reference to FIG. 3 taking the developing device 50K as an example. For example, a developing voltage of −400 V is applied to the developing roller 54K by the developing power supply 11K. Most of the liquid developer supplied from the mixer 200K to the developer tank 53K is supplied to the gap between the film forming electrode 51K and the developing roller 54K. Note that the conductivity of the liquid developer in the mixer 200K is detected by the conductivity sensor 201K as described above.

A liquid developer is carried on the surface of the developing roller 54K when passing through the film forming electrode 51K. A film-forming voltage of −600 V, for example, is applied to the film-forming electrode 51K by the film-forming power source 12K, and the negatively charged toner due to the potential difference between the film-forming electrode 51K and the developing roller 54K is the developing roller 54K. Compressed and supported on the side.

In the vicinity of the outlet of the film forming electrode 51K, the liquid developer is divided into one that moves along the surface of the developing roller 54K and one that flows down to the back surface of the film forming electrode 51K. The developing roller 54K carrying the liquid developer then comes into contact with the squeezing roller 52K, and the squeezing roller 52K rotates in the follower direction at a constant speed with respect to the surface of the developing roller 54K.

A diaphragm voltage that is 50 to 120 V higher in absolute value than the developing voltage applied to the developing roller 54K by the diaphragm power source 13K is applied to the diaphragm roller 52K. That is, if the developing voltage applied to the developing roller 54K is −400V, the diaphragm voltage applied to the diaphragm roller 52K is −450 to −520V. By the action of the squeezing roller 52K, a thin layer coat of liquid developer having a toner concentration of about 35% by weight is formed on the developing roller 54K. Thereafter, the thin coat is moved to the developing position with respect to the photoreceptor 20K by the rotation of the developing roller 54K.

Although illustration is omitted, the liquid developer flowing down to the back surface of the film forming electrode 51K falls on the developing trough, and then the toner concentration is adjusted by the mixer 200K or the like, and is supplied again to the developer tank 53K.

The developing roller 54K after passing through the developing position is next brought into contact with the developing cleaning roller 58K. For example, a recovery voltage of −250 V is applied to the developing cleaning roller 58K by the recovery power source 14K. Due to the potential difference between the developing cleaning roller 58K and the developing roller 54K, the toner that has not been developed at the developing position is electrophoresed on the developing cleaning roller 58K. Then, the toner is scraped off by the cleaning blade 59K. In the present embodiment, the recovery voltage applied by the recovery power supply 14K can be changed by the control described later.

Next, the operation of the entire image forming apparatus will be described with reference to FIGS. In the present embodiment, the photoconductor 20K uses amorphous silicon. The surface of the photoreceptor 20K is charged to about −800 V by applying about −4.5 kV to −5.5 kV to the wire of the charging device 30K that is a corona charger. After charging, an electrostatic latent image is formed by the exposure device 40K so that the potential of the image portion is approximately 50V.

Between the developing roller 54K and the photosensitive member 20K at the developing position, the developing voltage -400V applied to the developing roller 54K and the potential of the electrostatic latent image on the photosensitive member 20K (image portion -50V, non-image portion- An electric field is formed with a potential difference of 800V). Then, according to the formed electric field, the toner particles selectively move to the image portion on the photoconductor 20K. As a result, a toner image is formed on the photoreceptor 20K. Since the carrier liquid is not affected by the electric field, it is separated at the outlet between the developing roller 54K and the photosensitive member 20K at the developing position, and adheres to both the developing roller 54K and the photosensitive member 20K.

The photosensitive member 20K that has passed the development position reaches a primary transfer portion that is a nip portion with the intermediate transfer belt 70, and a toner image formed on the photosensitive member 20K is primarily transferred to the intermediate transfer belt 70. At this time, the primary transfer roller 61K is applied with a primary transfer voltage of about +200 V having a polarity opposite to the charging characteristics of the toner particles, and the toner particles on the photoconductor 20K are primarily transferred to the intermediate transfer belt 70 to be photosensitive. Only the carrier liquid remains on the body 20K. The carrier liquid remaining on the photoconductor 20K is scraped off by the cleaning blade 21Ka of the cleaning device 21K downstream of the primary transfer portion T1K and recovered by the recovery portion 21Kb.

The toner image primarily transferred onto the intermediate transfer belt 70 goes to the secondary transfer portion T2. In the secondary transfer portion T2, a secondary transfer voltage of +1000 V is applied to the secondary transfer outer roller 81, the secondary transfer inner roller 86 is maintained at 0 V, and the toner particles on the intermediate transfer belt 70 are Secondary transfer is performed on the surface of the recording material conveyed to the next transfer portion T2.

In such an image forming operation by the image forming apparatus, the toner transfer efficiency in each subsequent toner particle transfer process including the transfer from the developing roller 54K to the photosensitive member 20K is adjusted to be extremely high, approximately 95% or more. It is. Therefore, in each of the developing

devices

50Y, 50M, 50C, and 50K, the amount of toner contained in the liquid developer on the developing

rollers

54Y, 54M, 54C, and 54K before being developed on the

photoconductors

20Y, 20M, 20C, and 20K. Is desired to be stabilized with high accuracy. Thereby, the image quality of the image output on the recording material can be stabilized.

Film formation

Next, film formation of the liquid developer onto the developing roller 54K by the film forming electrode 51k will be described in detail with reference to FIGS. 4 and 5A to 5C. As described above, in each of the developing

devices

50Y, 50M, 50C, and 50K, the

film forming electrodes

51Y, 51M, 51C, and 51K are used to form the liquid developer on the developing

rollers

54Y, 54M, 54C, and 54K. A film forming voltage is applied to the substrate. The gaps between the

film forming electrodes

51Y, 51M, 51C, and 51K and the developing

rollers

54Y, 54M, 54C, and 54K are set to be 400 μm, respectively. Next, the developing device 50K will be described as an example.

First, the concept of film formation with the film forming electrode 51K will be described with reference to FIG. In FIG. 4, for the sake of explanation, the gap between the film forming electrode 51K and the developing roller 54K is shown large. At the entrance (in the drawing, the lower part) of the film forming area between the film forming electrode 51K and the developing roller 54K, the toner (indicated by black circles) is distributed substantially uniformly. As described above, the toner gradually moves to the developing roller 54K by applying the film forming voltage as it goes downstream (upper part in the drawing) of the film forming area. The reason why the liquid developer containing toner goes upward in the drawing is that it is lifted as the developing roller 54K rotates. In the film forming area, there are two directions of flow: a direction in which the toner moves along the rotation of the developing roller 54K, and a direction in which the toner moves to the developing roller 54K by an electric field.

As described above, in the film forming area, the toner approaches the developing roller 54K. Among the offset toners, the toner closer to the developing roller 54K than the gap between the developing roller 54K and the squeezing roller 52K is in contact with the squeezing roller 52K. After a short time, a thin film is formed. The aperture roller 52K is a regulating roller that presses the developing roller 54K and regulates the developer on the developing roller 54K. A schematic diagram of this thin film is shown in FIG. In FIG. 5, the toner is indicated by white circles. FIG. 5A shows a case where the film is appropriately formed on the developing roller 54K. FIG. 5B shows a state where the electric field at the squeeze roller 52K is too strong and the toner is compressed too much on the developing roller 54K, that is, when the film is formed due to excessive compression. FIG. 5C shows a case where the electric field on the squeezing roller 52K is too weak and toner is formed on the developing roller 54K due to insufficient compression.

As shown in FIG. 5C, when the compression is weak, the toner layer is not uniformly formed due to the influence of turbulence generated when the toner passes through the squeeze roller 52K, and a non-uniform image is formed. On the other hand, as shown in FIG. 5B, in the case of excessive compression, as can be seen from the drawing, there is no particular problem in film formation, and good uniform film formation is achieved. Here, as shown in FIG. 5A, it is difficult to always maintain a very good film formation. For this reason, in this embodiment, as shown in FIGS. 5A and 5B, an electric field is applied between the squeezing roller 52K and the developing roller 54K so that the compression is normal or excessively compressed. It is formed so as to obtain a good uniform film formation. However, in the case of excessive compression as shown in FIG. 5B, the following problem may occur in the toner recovery process (cleaning process) in the developing cleaning roller 58K. This point will be described.

Development CLN residual efficiency and development CLN blade residual efficiency

First, the thin toner layer formed on the developing roller 54K may or may not contribute to the development of the electrostatic latent image on the photoreceptor 20K according to the image signal. The toner that has not contributed to the development is removed from the developing roller 54K by the developing cleaning roller 58K. Here, a process in which toner that has not contributed to development is removed from the developing roller 54K by the developing cleaning roller 58K will be described.

In the undeveloped area of the photoreceptor 20K, an electric field in the direction toward the developing roller 54K is applied to the toner. As a result, the toner layer on the developing roller 54K is further compressed. Thereafter, electrophoresis is caused by a potential difference between the developing cleaning roller 58K and the developing roller 54K, and the toner moves to the developing cleaning roller 58K. Next, the toner on the developing cleaning roller 58K is scraped off by the cleaning blade 59K.

Here, the ratio (%) of the toner remaining on the developing roller 54K without moving to the developing cleaning roller 58K out of the toner on the developing roller 54K when passing through the developing cleaning roller 58K is the development CLN residual efficiency. I will call it. The development CLN residual efficiency is desirably 0%, and when it is 0%, all the toner on the development roller 54K has been removed by the development cleaning roller 58K.

Further, the ratio (%) of the toner remaining on the developing cleaning roller 58K without being scraped off by the cleaning blade 59K out of the toner on the developing cleaning roller 58K is referred to as developing CLN blade remaining efficiency.

FIG. 6 shows the relationship between the development CLN residual efficiency and the development CLN blade residual efficiency when the potential difference between the development cleaning roller 58K and the development roller 54K (recovery potential difference, hereinafter referred to as development cleaning contrast) is changed. The development CLN residual efficiency is indicated by a solid line on the Y1 axis, and the development CLN blade residual efficiency is indicated by a dotted line on the Y2 axis. As shown in the figure, when the development cleaning contrast is small, the development CLN residual efficiency is high, and a large amount of toner remains on the development roller 54K.

For this reason, it is desirable that the development CLN residual efficiency is increased as the development cleaning contrast is increased. However, if the development CLN residual efficiency is excessively increased, the development CLN blade residual efficiency is increased. In other words, if the development cleaning contrast is too high, the toner is brought closer to the development cleaning roller 58K, and the toner layer on the development cleaning roller 58K is excessively compressed. As a result, it becomes difficult for the developing cleaning roller 58K to scrape off the toner on the developing cleaning roller 58K, and a lot of toner tends to remain on the developing cleaning roller 58K. Therefore, in this embodiment, the development cleaning contrast is set within a range in which the two remaining efficiencies are substantially zero. This is shown as an appropriate range in the figure.

More detailed explanation. As described above, since the toner on the developing roller 54K is electrophoresed by the potential difference between the developing cleaning roller 58K and the developing roller 54K, a predetermined potential difference is required between them. When the development cleaning contrast is increased, the compression state of the toner layer on the development cleaning roller 58K changes in the same manner as in the cases shown in FIGS. When the development cleaning contrast is excessively increased, the toner layer is in a highly compressed state as in the case shown in FIG. As a result, the toner layer on the developing cleaning roller 58K slips through the cleaning blade 59K.

The schematic diagram is shown in FIGS. 7 (a) and 7 (b). FIG. 7A shows a case where the toner layer on the developing cleaning roller 58K is in an appropriate compression state, and FIG. 7B shows a case where the compression is excessive. In FIG. 7, the toner is indicated by white circles. As can be seen from the figure, when the compression is appropriate, the toner layer on the developing cleaning roller 58K is scraped off satisfactorily by the cleaning blade 59K. On the other hand, if the compression is excessive, the toner layer on the developing cleaning roller 58K pushes the cleaning blade 59K and the toner slips out.
[Relationship between compressed state of toner layer and development cleaning contrast]

On the other hand, the cleaning characteristics for the development cleaning contrast shown in FIG. 6 differ depending on the compression state of the toner layer formed on the developing roller 54K. For example, in order to cause the toner layer that is excessively compressed to be electrophoresed on the developing cleaning roller 58K, an electric field sufficient to overcome the compression is required. Here, FIG. 8 shows the cleaning characteristics with respect to the development cleaning contrast when compression is good and excessive as shown in FIGS. 5 (a) and 5 (b).

FIG. 8 shows the relationship between the development CLN residual efficiency and the development CLN blade residual efficiency when the development cleaning contrast is changed. The developed CLN remaining efficiency is indicated by a thick line on the Y1 axis, and the developed CLN blade remaining efficiency is indicated by a thin line on the Y2 axis. The solid line in the figure indicates the case where the toner layer on the developing roller 54K is well compressed, and the dotted line indicates the case where the toner layer on the developing roller 54K is excessively compressed. As can be seen from the figure, the appropriate range of the development cleaning contrast varies depending on the compression state of the toner on the development roller 54K.

In the present embodiment, by changing the development cleaning contrast according to the compression state of the toner layer on the development roller 54K, good cleaning from the development roller 54 and cleaning from the development cleaning roller 58K are performed. ing. In particular, the developer cleaning contrast is increased as the toner layer is excessively compressed.

Prediction of toner layer compression

In this embodiment, the development cleaning contrast is controlled according to the compressed state of the toner layer as described above, but it is difficult to directly detect the compressed state of the toner layer on the developing roller 54K. However, as described above, the compression of the toner layer is determined by the movement of the toner between the developing roller 54K and the squeezing roller 52K. Therefore, the toner compression state can be predicted by detecting or predicting the movement.

This point will be described with reference to FIG. The charge amount of the toner is Q, the force due to the electric field applied to the toner is F, the gap between the developing roller 54K and the squeezing roller 52K is d, the potential difference between the developing roller 54K and the squeezing roller 52K is ΔV, and the electric field is E. Then, Formula 1 is established.
F = Q × E = Q × ΔV / d (Formula 1)

When a large force is applied to the toner, the toner approaches the developing roller 54K, and the compressed state of the toner layer on the developing roller 54K becomes high. That is, the toner layer compression state is determined by the toner charge amount Q and the potential difference ΔV between the developing roller 54K and the squeezing roller 52K. In this embodiment, the toner compression state is predicted by detecting the charge amount Q of the toner.

The toner charge amount Q is detected by a conductivity sensor 201K in the mixer 200K. As described above, the mixer 200K stores the liquid developer and supplies the liquid developer to the film forming electrode 51K via the developer tank 53K. Since the charge amount of the toner affects the conductivity of the liquid developer, the conductivity of the liquid developer has a correlation with the charge amount of the toner. The toner concentration and the liquid developer amount of the liquid developer in the mixer 200K are controlled to be substantially constant. Therefore, the measurement result of the conductivity of the liquid developer in the mixer 200K has a correlation with the charge of the toner particles.

Here, if the toner concentration in the mixer 200K changes, the amount of toner in the liquid developer changes, so whether the change in conductivity in the mixer 200K is a difference in charge amount due to the difference in toner amount. The difference in the charge amount of the toner particles cannot be understood. However, since the toner concentration and the amount of liquid developer in the mixer 200K are substantially constant, the change in the conductivity in the mixer 200K can be regarded as a change in the charge amount of the toner. For this reason, in this embodiment, the compressed state of the toner layer on the developing roller 54K is predicted from the detection result of the conductivity sensor 201K. Therefore, the conductivity sensor 201K corresponds to an acquisition unit that can acquire information regarding the compression state of the toner layer on the developing roller 54K that has passed between the aperture roller 52K and the developing roller 54K.

Note that even if the toner concentration changes, it is possible to calculate the charge amount of the toner particles in view of the amount. Therefore, the toner charge amount is calculated from the detection result of the toner density sensor 202K (see FIG. 11 described later) for detecting the toner density in the mixer 200K and the detection result of the conductivity of the liquid developer, The compression state may be predicted.

Relationship between conductivity of liquid developer and development cleaning contrast

Next, the relationship between the conductivity of the liquid developer detected by the conductivity sensor 201K and the development cleaning contrast will be described with reference to FIG. FIG. 10 shows the relationship between the conductivity (S / cm) of the liquid developer and the development cleaning contrast, which is the measurement result of the conductivity sensor 201K. As the conductivity increases, the charge amount of the toner particles increases, and the toner is subjected to a force due to the electric field between the developing roller 54K and the squeezing roller 52K, so that the toner moves further toward the developing roller 54K and the toner layer is compressed. Becomes higher.

In this case, since the electrophoresis is performed from the compressed state as described above, the development CLN residual efficiency becomes high (development CLN residual efficiency NG) unless a higher development cleaning contrast is applied. That is, the range below the line α in FIG. 10 is the development CLN residual efficiency NG. On the other hand, when a high development cleaning contrast is applied, the toner layer on the development cleaning roller 58K is further compressed, so that cleaning with the cleaning blade 59K becomes difficult (development CLN blade residual efficiency NG). That is, the range above the line β in FIG. 10 is the development CLN blade remaining efficiency NG.

For this reason, the range between the line α and the line β shown in FIG. In the present embodiment, as described above, the conductivity of the liquid developer in the mixer 200K is adjusted to 10 ⁻¹¹ to 10 ⁻⁹ [S / cm] (1e-11 to 1e-9 [S / cm]). Has been. For this reason, the development cleaning contrast changes the recovery voltage applied to the development cleaning roller 58K within a range of 70 V or more and 280 V or less (within a predetermined range) according to the conductivity of the liquid developer. In this embodiment, since the developing voltage applied to the developing roller 54K is −400V, the recovery voltage applied to the developing cleaning roller 58K is in the range of −330V (−400 + 70) to −120V (−400 + 280). I am trying to change it within. In this embodiment, the polarity of the voltage applied to the developing cleaning roller 58K is the same as the normal charging polarity of the toner. Further, the absolute value of the recovery voltage is smaller than the absolute value of the development voltage.

Factors of change in conductivity of liquid developer

The conductivity of the liquid developer may change due to various factors. For example, when the environment such as the temperature and humidity where the image forming apparatus is placed changes, the temperature and humidity of the liquid developer change, the charge amount of the toner also changes, and the charge amount of the liquid developer also changes. . In addition, the toner charge imparting agent or toner added to the liquid developer is deteriorated by being compressed at the nip portion of each member when used at the time of image formation, and the charge amount of the toner is reduced. As a result, the charge amount of the liquid developer also changes. In the present embodiment, such a change in the conductivity of the liquid developer is detected, and the development cleaning contrast is controlled within the range shown in FIG. 10 according to the value.

Development cleaning contrast control

FIG. 11 and FIG. 12 are block diagrams and flowcharts for controlling the development cleaning contrast. As shown in FIG. 11, the control unit 110 as a control unit is provided with a CPU (Central Processing Unit) 111 that performs high-pressure control. Further, the memory 112 has a ROM (Read Only Memory) 112a. The ROM 112a stores a program corresponding to the control procedure. The CPU 111 controls each part while reading data and programs previously written in the ROM 112a. The memory 112 also includes a RAM (Randon Access Memory) 112b in which work data and input data read from each sensor and the like are stored. The CPU 111 performs control with reference to data stored in the RAM 112b based on the above-described program and the like.

The CPU 111 is also connected to a conductivity sensor 201K that detects the conductivity of the liquid developer in the mixer 200K that circulates the liquid developer to and from the developer tank 53K, and the results are sequentially controlled. It can be used. Further, the CPU 111 is also connected to a recovery power supply 14K as a control destination. Then, the CPU 111 changes the developing cleaning contrast as the recovery potential difference by controlling the recovery power supply 14K as the potential difference application unit according to the information (that is, the conductivity) acquired by the conductivity sensor 201K as the acquisition unit. Is possible. In FIG. 11, only the black image forming unit 1 </ b> K is shown, but the other image forming units are similarly connected to the CPU 111 with a conductivity sensor and a recovery power source and controlled in the same manner as described below. .

Next, a development cleaning contrast control flow will be described with reference to FIG. The development cleaning contrast can be controlled during image formation or at other timings. For example, it may be performed at any time after the image forming job is started, may be performed every predetermined number of times, or may be performed at a timing when an image is not formed on the recording material, such as pre-rotation at the start of the image forming job. Also good.

The image forming job is a period from the start of image formation to the completion of the image forming operation based on a print signal for forming an image on a recording material. Specifically, it refers to the period from the pre-rotation to the post-rotation after receiving the print signal (input of the image forming job), and includes the image forming period and the interval between sheets (during non-image forming). The pre-rotation is a period in which rotation of the photosensitive member and the intermediate transfer belt is started as a preparatory operation before image formation, and various voltages are sequentially raised and various voltages are adjusted. The post-rotation is a period in which various voltages are sequentially lowered while the rotation of the photosensitive member and the intermediate transfer belt is continued as an operation after image formation, and finally the rotation of the photosensitive member and the intermediate transfer belt is stopped. The interval between the sheets is a period corresponding to the interval between the recording material that continuously passes through the secondary transfer portion T2.

As shown in FIG. 12, when the control is started (S1), the CPU 111 detects the conductivity of the liquid developer in the mixer 200K by the conductivity sensor 201K (S2). Next, based on the detection result of the conductivity, the CPU 111 calculates an optimum development cleaning contrast using the table shown in FIG. 10 (S3). Next, a recovery voltage that achieves the calculated development cleaning contrast is determined and applied to the recovery power supply 14K (S4).

Specifically, when the conductivity detected by the conductivity sensor 201K is the first conductivity, the CPU 111 controls the recovery power supply 14K so that the development cleaning contrast becomes the first recovery potential difference. Further, when the conductivity detected by the conductivity sensor 201K is the second conductivity higher than the first conductivity, the CPU 111 causes the development cleaning contrast to be a high second recovery potential difference that is larger than the first recovery potential difference. The recovery power source 14K is controlled. In other words, the CPU 111 controls the recovery power supply 14K so that the higher the conductivity detected by the conductivity sensor 201K, the greater the development cleaning contrast. Thereafter, this control ends (S5). In this embodiment, this control is performed once for each recording material.

In addition, the control of the voltage for recovery may include limit control that applies a limit when the result of this control exceeds a desired value, control that suppresses the amount of change in voltage once, etc. .

In the case of the present embodiment, by performing the control as described above, the toner remains appropriately on the developing roller 54K regardless of the compression state of the toner layer on the developing roller 54K that has passed between the squeezing roller 52K and the developing roller 54K. Collected toner. That is, even when the charge amount of the toner particles changes due to various factors and the compression state of the toner layer on the developing roller 54K changes, the developing cleaning contrast is appropriately controlled. For this reason, it can suppress that the development CLN residual efficiency mentioned above becomes NG, and development CLN blade residual efficiency becomes NG.

Note that the development cleaning contrast may be controlled by changing the development voltage or by changing both the development voltage and the recovery voltage. However, when the development voltage is changed, other parts such as the aperture voltage are also affected. Therefore, it is preferable to control the development cleaning contrast by changing the recovery voltage as in this embodiment. However, the development voltage may be changed from the viewpoint of developability. In this case, the recovery voltage is changed so as to satisfy the development cleaning contrast table shown in FIG. 10 in accordance with the change in the development voltage.
<Second Embodiment>

A second embodiment will be described with reference to FIGS. 1 to 3 and FIG. In the first embodiment described above, the development cleaning contrast is controlled in accordance with the conductivity of the liquid developer detected by the conductivity sensor 201K. In contrast, in the present embodiment, the development cleaning contrast is controlled according to the potential difference (compression potential difference) ΔV between the developing roller 54K and the squeezing roller 52K. Since other configurations and operations are the same as those of the first embodiment described above, the following description will focus on portions that are different from the first embodiment. In this embodiment as well, as in the first embodiment, the black image forming unit 1K will be described as an example, but the same applies to other image forming units.

As shown in Equation 1 above, the force F due to the electric field applied to the toner in the gap between the developing roller 54K and the squeezing roller 52K also depends on the compression potential difference ΔV. The compression potential difference ΔV may be changed according to the environment such as temperature and humidity, or the detection result of the density of the formed toner image. For this reason, the force F due to the electric field applied to the toner also changes due to the change in the compression potential difference ΔV, which affects the compression state of the toner layer on the developing roller 54K that has passed between the squeezing roller 52K and the developing roller 54K. Therefore, in this embodiment, the development cleaning contrast is controlled according to the compression potential difference ΔV.

For this reason, the diaphragm power source 13K as the compression power source of the present embodiment can variably apply a compression potential difference between the developing roller 54K and the diaphragm roller 52K. That is, the diaphragm power supply 13K can variably apply the diaphragm voltage. Further, the image forming apparatus 100 includes an environment sensor 120 capable of detecting temperature and humidity in the apparatus main body. Further, the image forming apparatus 100 includes a density sensor 121 that can detect the density of the toner image formed on the intermediate transfer belt 70.

The density sensor 121 is disposed further downstream than the most downstream image forming unit 1K and upstream of the secondary transfer unit T2 with respect to the rotation direction of the intermediate transfer belt 70. The density sensor 121 has a light emitting portion and a light receiving portion, emits light from the light emitting portion toward the surface of the intermediate transfer belt 70, receives the reflected light by the light receiving portion, and detects the amount of reflected light. . Since the amount of reflected light changes according to the amount of toner applied to the toner image, the amount of toner applied, that is, the density of the toner image can be detected by detecting the amount of reflected light of the toner image by the density sensor 121.

The control for detecting the density of the toner image is performed, for example, between sheets in an image forming job. For example, a control toner image (patch) is formed on the intermediate transfer belt 70 for every predetermined number of sheets, and the density sensor 121 detects the density of the control toner image. Then, the CPU 111 controls the developing power supply 11K and the like so as to change the developing voltage, for example, according to the detection result. As a result, the compression potential difference also changes. Further, the CPU 111 may change the development voltage based on the detection result of the environment sensor 120.

As described above, when the compression potential difference is changed according to the detection result of the environmental sensor 120 or the detection result of the density sensor 121, the compression state of the toner layer is affected. Then, there is a possibility that the development CLN residual efficiency becomes NG or the development CLN blade residual efficiency becomes NG. Therefore, in the present embodiment, the control unit 110 that is also an acquisition unit can acquire the compressed potential difference. That is, the CPU 111 compares the compression potential difference, which is the potential difference between the diaphragm voltage and the development voltage, from the diaphragm voltage applied by the diaphragm power supply 13K and the development voltage applied by the development power supply 11K set based on the detection result of the environment sensor 120 or the like. To get. Then, the CPU 111 controls the development cleaning contrast according to the acquired compressed potential difference. Specifically, the recovery power source 14K is controlled so as to change the recovery voltage.

Specifically, when the acquired compression potential difference is the first compression potential difference, the CPU 111 controls the recovery power supply 14K so that the development cleaning contrast becomes the first recovery potential difference. Further, when the acquired compression potential difference is a second compression potential difference larger than the first compression potential difference, the CPU 111 controls the recovery power supply 14K so that the development cleaning contrast becomes a second recovery potential difference larger than the first recovery potential difference. To do. In other words, the CPU 111 controls the recovery power supply 14K so that the developing cleaning contrast increases as the compression potential difference increases.

Also in the present embodiment, by performing the control as described above, the developing roller 54K is appropriately set regardless of the compression state of the toner layer on the developing roller 54K that has passed between the squeezing roller 52K and the developing roller 54K. The remaining toner can be collected. That is, it is possible to prevent the development CLN remaining efficiency from becoming NG or the development CLN blade remaining efficiency from becoming NG. It should be noted that the development cleaning contrast may be determined from the above-described formula 1 in consideration of both the charge amount of the toner (that is, the conductivity detected by the conductivity sensor 201K) and the compression potential difference.
<Third Embodiment>

The third embodiment will be described with reference to FIGS. 1 to 3 and FIG. In the first embodiment described above, the development cleaning contrast is controlled in accordance with the conductivity of the liquid developer detected by the conductivity sensor 201K. In contrast, in the present embodiment, the development cleaning contrast is controlled according to the current flowing between the development roller 54K and the squeeze roller 52K. Since other configurations and operations are the same as those in the first embodiment or the second embodiment described above, the following description will focus on parts that are different from the first embodiment or the second embodiment. In this embodiment as well, as in the first embodiment, the black image forming unit 1K will be described as an example, but the same applies to other image forming units.

The main ions in the gap between the developing roller 54K and the squeezing roller 52K are toner, and the current that is the amount of movement of these ions per unit time is also a measure of toner movement. As the current is larger, the toner is closer to the developing roller 54K, which means that the compressed state of the toner layer on the developing roller 54K is higher.

For this reason, in the case of the present embodiment, an aperture current detector 130 is provided as a current detector capable of detecting the current flowing between the developing roller 54K and the aperture roller 52K. In the present embodiment, the aperture current detection unit 130 corresponds to an acquisition unit. The CPU 111 controls the development cleaning contrast in accordance with the current detected by the aperture current detection unit 130. Specifically, the recovery power source 14K is controlled so as to change the recovery voltage.

More specifically, when the current detected by the aperture current detector 130 is the first current, the CPU 111 controls the recovery power supply 14K so that the development cleaning contrast becomes the first recovery potential difference. In addition, the CPU 111 determines the power supply for recovery so that the development cleaning contrast becomes the second recovery potential difference larger than the first recovery potential difference when the current detected by the aperture current detection unit 130 is the second current larger than the first current. 14K is controlled. In other words, the CPU 111 controls the recovery power supply 14K so that the developing cleaning contrast increases as the current detected by the aperture current detection unit 130 increases.

Also in the present embodiment, by performing the control as described above, the developing roller 54K is appropriately set regardless of the compression state of the toner layer on the developing roller 54K that has passed between the squeezing roller 52K and the developing roller 54K. The remaining toner can be collected. That is, it is possible to prevent the development CLN remaining efficiency from becoming NG or the development CLN blade remaining efficiency from becoming NG.
<Fourth Embodiment>

The fourth embodiment will be described using FIG. 15 with reference to FIGS. 1 to 3. In the first embodiment described above, the development cleaning contrast is controlled in accordance with the conductivity of the liquid developer detected by the conductivity sensor 201K. On the other hand, in the present embodiment, the development cleaning contrast is controlled according to one or more currents flowing between the developing roller 54K and each part. Other configurations and operations are the same as those of any one of the first to third embodiments described above, and therefore the following description will focus on the differences from the first to third embodiments. To do. In this embodiment as well, as in the first embodiment, the black image forming unit 1K will be described as an example, but the same applies to other image forming units.

There are potential differences between the film forming electrode 51K and the developing roller 54K, between the developing roller 54K and the squeezing roller 52K, between the photosensitive member 20K and the developing roller 54K, and between the developing cleaning roller 58K and the developing roller 54K. is there. In addition, the toner moves between each of them by electrophoresis. The amount of toner movement between them has a high correlation with the current as described above, and also has a high correlation with the charge amount of the toner. That is, the current between each of them has a high correlation with the charge amount of the toner, and it can be known that the toner is compressed by the squeezing roller 52K toward the developing roller 54K.

Also in the case of the present embodiment, a film forming power source 12K, a diaphragm power source 13K, a developing power source 11K, and a recovery power source 14K are provided. The film-forming power source 12K as the first power source can apply a voltage between the developing roller 54K and the film-forming electrode 51K. The diaphragm power source 13K as the second power source can apply a voltage between the developing roller 54K and the diaphragm roller 52K. A developing power source 11K as a third power source can apply a voltage between the developing roller 54K and the photoconductor 20K.

Further, in the case of the present embodiment, a film forming current detection unit 131, an aperture current detection unit 130, and a cleaning current detection unit 132 are provided. The film forming current detector 131 detects a current flowing between the developing roller 54K and the film forming electrode 51K. The aperture current detector 130 detects the current flowing between the developing roller 54K and the aperture roller 52K. The cleaning current detector 132 detects a current flowing between the developing roller 54K and the developing cleaning roller 58K. It is difficult to directly detect the current flowing between the developing roller 54K and the photoconductor 20K. However, since the total current flowing through the developing roller 54K is 0, the current flowing between the developing roller 54K and the photoconductor 20K can be calculated by obtaining the sum of the currents flowing from other than the photoconductor 20K. .

The control unit 110 that is also an acquisition unit includes the current detected by the film forming current detection unit 131, the aperture current detection unit 130, and the cleaning current detection unit 132, and the calculated current between the developing roller 54K and the photoconductor 20K. One or more currents can be acquired. The CPU 111 controls the development cleaning contrast in accordance with one or more currents acquired in this way. Specifically, the recovery power source 14K is controlled so as to change the recovery voltage.

Here, since an electric field in the direction toward the developing roller 54K is applied between the developing roller 54K, the film forming electrode 51K, and the squeezing roller 52K, the toner layer on the developing roller 54K increases as the current increases. It becomes easy to be compressed. Further, as described above, an electric field in the direction toward the developing roller 54K is applied to the toner between the developing roller 54K and the photoconductor 20K in the area where the photoconductor 20K is not developed. Therefore, the larger the current during this period, the more the toner layer on the developing roller 54K is compressed.

Therefore, when one or more of these three currents are acquired to control the development cleaning contrast, the larger the detected or calculated current, the more the toner layer is compressed, so that the development cleaning contrast is increased. To do. Of these three currents, when controlling using a plurality of currents, the current values added together, or the current values added by weighting part of the currents, or An average value can be used.

On the other hand, an electric field is applied between the developing roller 54K and the developing cleaning roller 58K in the direction in which the toner moves toward the developing cleaning roller 58K. Therefore, when the current during this period is used for controlling the development cleaning contrast, the development cleaning contrast obtained by using one or more of the above three currents is corrected.

For example, when the development cleaning contrast obtained by using one or more of the three currents described above is applied, the cleaning current detection unit 132 detects the current flowing between the development roller 54K and the development cleaning roller 58K. In this case, for example, when more current flows than expected from the development cleaning contrast obtained using one or more of the three currents, control is performed to lower the obtained development cleaning contrast. On the other hand, when a current smaller than the current expected from the development cleaning contrast obtained using one or more of the three currents flows, control is performed to increase the obtained development cleaning contrast. That is, the development cleaning contrast is controlled so that the current detected by the cleaning current detection unit 132 has a preset current value.

Also in the present embodiment, by performing the control as described above, the developing roller 54K is appropriately set regardless of the compression state of the toner layer on the developing roller 54K that has passed between the squeezing roller 52K and the developing roller 54K. The remaining toner can be collected. That is, it is possible to prevent the development CLN remaining efficiency from becoming NG or the development CLN blade remaining efficiency from becoming NG.
<Other embodiments>

The embodiments described above can be implemented in combination as appropriate. For example, when the configuration of the first embodiment is combined with the configuration of any one of the second to third embodiments, the development cleaning contrast obtained with one of the configurations is corrected with the other configuration. .

In the above-described embodiments, the configuration using the squeezing roller as the compression member has been described. However, the compression member may be a non-rotating member such as a blade. However, considering the life of the developing roller, the compression member is preferably a rotating body that rotates at the same peripheral speed as the developing roller.

In each of the above-described embodiments, the configuration using the developing cleaning roller as the collecting member has been described. However, as long as the toner on the developing roller can be collected by a potential difference, other than the roller, for example, a blade that does not rotate may be used. However, in consideration of the life of the developing roller, the collecting member is preferably a rotating body that rotates at the same peripheral speed as the developing roller. In addition to the intermediate transfer belt, the intermediate transfer member may be, for example, an intermediate transfer drum.

According to the present invention, there is provided an image forming apparatus that forms an image using a liquid developer containing toner and a carrier liquid, and that can reduce a decrease in cleaning performance due to a cleaning roller.
[Explanation of symbols]
11K: Development power source (third power source) / 12K ... Film forming power source (first power source) / 13K ... Power source for diaphragm (second power source, compression power source) / 14K ... For recovery Power source (potential difference applying means) / 20Y, 20M, 20C, 20K... Photoconductor (image carrier) / 51Y, 51M, 51C, 51K .. Film forming electrode / 52Y, 52M, 52C, 52K. Roller (compression member, compression rotating body) / 53Y, 53M, 53C, 53K... Developer tank / 54Y, 54M, 54C, 54K... Development roller (developer carrier) / 58Y, 58M, 58C, 58K ... Developing cleaning roller (collecting member, collecting rotating body) / 59Y, 59M, 59C, 59K ... Cleaning blade (cleaning means) / 100 ... Image forming apparatus / 110 ... Control section (control means, Take Means) / 130 ... stop current detector (current detection means) / 201K ... conductivity sensor (acquisition means, the conductivity sensing means)

Claims

A developer carrying member that carries and rotates a liquid developer containing toner and a carrier liquid and develops an electrostatic latent image carried on the image carrier;
A collecting roller that contacts the developer carrying member and collects toner remaining on the developer carrying member by forming a potential difference with the developer carrying member;
A potential difference forming means for forming a potential difference between the developer carrying member and the collecting roller;
A developing device comprising switching means for switching a set value of a potential difference between the developer carrying member and the collecting roller during an image forming operation.
2. The image forming apparatus according to claim 1, wherein the potential difference forming unit has a power source for applying a voltage to the collecting roller, and the switching unit switches a voltage value to be applied to the collecting roller.
The image forming apparatus according to claim 1, further comprising a blade that removes toner collected by the collecting roller from the collecting roller.
A voltage having the same polarity as a normal belt electrode of toner is applied to the developer carrying member and the collecting roller, and an absolute value of a voltage value applied to the developer carrying member is applied to the collecting roller. The image forming apparatus according to claim 1, wherein the image forming apparatus is larger than an absolute value of the voltage value.
5. The image forming apparatus according to claim 1, wherein the developer carrying member has a conductive elastic layer.
6. The image forming apparatus according to claim 1, wherein the collection roller is a metal roller.
7. The apparatus according to claim 1, further comprising a regulating roller disposed downstream of the collection roller and upstream of the developing position in the rotation direction of the developer carrier and pressing the developer carrier. An image forming apparatus according to claim 1.
A voltage having the same polarity as a normal belt electrode of toner is applied to the regulating roller, and an absolute value of a voltage value applied to the developer carrying member is smaller than an absolute value of a voltage value applied to the regulating roller. Item 8. The image forming apparatus according to Item 7.
In the rotation direction of the developer carrier, an electrode portion is disposed downstream of the collecting roller and upstream of the regulating roller, and the electrode portion has a voltage having the same polarity as a normal band electrode. The image forming apparatus according to claim 1, wherein an absolute value of a voltage value applied to the developer carrying member is smaller than an absolute value of a voltage value applied to the electrode unit. .
A developer tank for storing a liquid developer to be supplied to the developer carrier;
Conductivity detecting means for detecting the conductivity of the developer stored in the developer tank,
The switching means is configured such that when the conductivity detected by the conductivity detection means is the first conductivity, the potential difference is the first potential difference, and the conductivity detected by the conductivity detection means is more than the first conductivity. 10. The developing device according to claim 1, wherein the potential difference is set so that the potential difference becomes a high second potential difference larger than the first potential difference when the second conductivity is high. 11.
Voltage application means for applying a voltage to the regulating roller;
When the potential difference between the regulating roller and the developer carrying member is a first regulating roller potential difference, the switching means sets the potential difference to the first potential difference, and the potential difference between the regulating roller and the developer carrying member is the first potential difference. The image forming apparatus according to claim 7, wherein the potential difference is set so that the potential difference becomes a second potential difference larger than the first potential difference in the case of a second regulation roller potential difference larger than the regulation roller potential difference.
A current detector configured to detect a current value between the recovery roller and the developer carrier, and the switching unit is configured to detect the developer carrier and the recovery during an image forming operation based on an output of the current detector. The developing device according to claim 1, wherein the potential difference between the rollers is switched.
13. The developing device according to claim 12, wherein a potential difference between the developer carrying member and the collecting roller during an image forming operation is set so that an output of the current detection unit becomes a preset value.