JPH1165300A - Liquid developing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form an image with good quality and also to effectively utilize liquid developer by adequately keeping the concentration of the liquid developer used in developing to fixed concentration. SOLUTION: The viscosity U of the liquid developer inside a developer storage tank 61 to which the liquid developer recovered from a developing belt 54 is added is detected; the liquid developer with high concentration and the liquid developer with low concentration are supplied when the viscosity U of the liquid developer exceeds an allowable viscosity range, so that the viscosity U of the liquid developer inside the tank 61 becomes initial viscosity Uo the electrostatic latent image formed on the photoreceptor 1 is visualized by the liquid developer always having the viscosity in the allowable viscosity range, and the image with the good quality can be stably formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid developing apparatus for visualizing an electrostatic latent image formed by an electrophotographic system or the like by using a liquid developer having a high viscosity and a high density, and more particularly to a development homogenizer. It is.

[0002]

2. Description of the Related Art An image forming apparatus for visualizing an electrostatic latent image using a high-viscosity, high-concentration liquid developer is disclosed in, for example, Japanese Patent Application Laid-Open No.
This is disclosed in, for example, JP-A-239614 and JP-A-8-123205. In this image forming apparatus, the surface of the photoreceptor is uniformly charged by a charging unit, and then the surface of the photoreceptor is releasable by a pre-wet liquid coating unit and has a chemically inert dielectric and light transmitting property. Apply the pre-wet liquid to a uniform thickness. Thereafter, the surface of the photoreceptor is exposed by the writing means in accordance with the image data to form an electrostatic latent image, which is visualized by the liquid developing device.

[0003] A liquid developing device is an electrostatic latent image formed by a high-viscosity liquid developer in which toner, which is visualized particles, is dispersed at a high concentration in a developer solvent made of an insulating liquid such as dimethylpolysiloxane oil. The liquid developer is applied to the developing belt or the developing roller with a uniform thickness by the developer applying means, and the thin layer of the liquid developer applied to the developing belt or the developing roller comes close to the photoconductor. When passing through the development area
The toner in the liquid developer thin layer transfers to the image area of the photoreceptor to form a toner image. The toner image formed on the photoreceptor is transferred to transfer paper by transfer means, and the toner image transferred to the transfer paper is fixed to form an image. After the transfer step, the toner and the pre-wet liquid remaining on the photoreceptor are removed by the cleaning unit, and the charge remaining on the photoreceptor is removed by the charge removing unit, thereby completing the image forming step. Further, the pre-wet liquid applied to the photoreceptor adheres to the developing belt and the developing roller passing through the developing area, and is mixed with the liquid developer which is not used for the development and remains. The liquid developer and the pre-wet liquid adhering to the developing belt and the developing roller passing through the developing area are collected and reused in the developer applying means, or collected in a waste liquid collecting tank and discarded or collected. The liquid developer and the pre-wet liquid are separated, and the separated liquid developer is reused.

If the liquid developer and the pre-wet liquid adhering to the developing belt and the developing roller passing through the developing area as described above are collected and discarded, the liquid developer is wasted and the operating cost increases. When the liquid developer and the pre-wet liquid are separated and reused, it may be practically difficult to provide a separation mechanism in the developing device, and in some cases, the liquid developer and the pre-wet liquid cannot be separated depending on the properties of the pre-wet liquid. is there. Therefore, the developer is usually collected and reused by a developer applying unit.

[0005]

When an electrostatic latent image is visualized using a liquid developer, the toner of the liquid developer is consumed in accordance with the presence or absence of an image or its ratio, but the amount of the solvent adhered is reduced. It does not depend much on the presence or absence of an image. Usually, a liquid developer in which a toner is dispersed in a solvent at a fixed ratio is used. For example, when an electrostatic latent image having a high image area ratio is repeatedly developed, the consumption of the toner is remarkably larger than the consumption of the solvent. The liquid developer having a larger ratio and a lower ratio of the toner to the solvent is collected by the developer application unit, and the concentration of the liquid developer in the developer application unit, which is the ratio between the solvent and the toner, decreases. When the density of the liquid developer decreases, the density of the formed image also decreases.

Conversely, when the development of an electrostatic latent image having a low image area ratio is repeated, a liquid developer having a high ratio of toner to solvent is collected by a developer application unit, and the liquid developer in the developer application unit is recovered. The concentration, which is the ratio between the solvent of the agent and the toner, increases. When the concentration of the liquid developer in the developer application unit increases, the viscosity of the liquid developer increases, and the amount of the liquid developer applied to the developing belt or the developing roller changes, so that the liquid developer having a uniform thickness is developed. In addition, it becomes difficult to form a thin agent layer, and unevenness or the like occurs in a developed image density, thereby deteriorating image quality.

SUMMARY OF THE INVENTION The present invention has been made to improve such disadvantages, and forms a high-quality image while maintaining the concentration of a liquid developer used for development at an appropriate constant concentration, and effectively utilizes the liquid developer. It is an object of the present invention to obtain a liquid developing device capable of performing the above-described operations.

[0008]

A liquid developing apparatus according to the present invention comprises a developing solution carrying a high-viscosity liquid developer in which visualized particles are dispersed at a high concentration in a developer solvent comprising an insulating liquid. This is a liquid developing device that applies a thin layer and visualizes the electrostatic latent image formed on the image carrier by visualized particles contained in a high-concentration liquid developer applied in a thin layer on the developer carrier. And a developer supply device for supplying a liquid developer having a viscosity adjusted to a predetermined range to a developer application unit for applying a liquid developer to a developer carrier to form a liquid developer thin layer. It is characterized by.

It is preferable to recover the liquid developer remaining on the developer carrier after passing through the developing area to the developer supply device.

Further, the viscosity of the liquid developer in the developer supply device is detected, and when the viscosity of the liquid developer falls below a predetermined lower limit, a liquid having a large ratio of visualized particles and a high viscosity is used. The developer is supplied to the developer supply device, and when the viscosity of the liquid developer becomes equal to or more than a predetermined upper limit, the liquid developer having a small ratio of the visualized particles and a low viscosity is supplied to the developer supply device. .

When the viscosity of the liquid developer in the developer supply device falls below a predetermined lower limit, the developing particles are supplied to the developer supply device, and the viscosity of the liquid developer is set to a predetermined upper limit. When the value becomes equal to or more than the value, a developer solvent made of an insulating liquid may be supplied to the developer supply device.

When the initial viscosity of the liquid developer in the developer supply device is Uo, and the viscosity of the developer solvent composed of an insulating liquid is Uc, the viscosity of the liquid developer in the developer supply device is expressed as Uo. To {Uo- (Uo-Uc) / 2} <U <{U
It is desirable to adjust so as to be in the range of o + (Uo−Uc) / 2 °.

Further, it is preferable that the liquid developer in the developer supply device is stirred to have a uniform viscosity.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A liquid developing device according to the present invention has a developing device main body and a developer supply unit. The developing device main body has a developing belt that moves at the same surface moving speed as the surface moving speed of the photoconductor, a developer applying unit, and a developer cleaning unit. The developer supply unit includes a developer storage tank, a developer recovery unit, a developer supply unit, a high-concentration developer supply unit, and a low-concentration developer supply unit. The developer storage tank has a viscometer and stirring means, and stores the liquid developer to be supplied to the developer applying means. The developer supply unit supplies the liquid developer stored in the developer storage tank to the developer application unit.
The high-concentration developer supply unit stores a high-concentration liquid developer having a high toner ratio and a high viscosity, and supplies the stored high-concentration liquid developer to a developer storage tank. The low-concentration developer supply unit stores a low-concentration liquid developer having a low toner ratio and a low viscosity, and supplies the stored low-concentration liquid developer to a developer storage tank.

When the electrostatic latent image formed on the photoreceptor is developed and visualized by the liquid developing apparatus, the liquid developer having a uniform thickness is applied to the rotating developing belt by a developer applying means. Form a thin layer of developer. The electrostatic latent image on the photoreceptor is visualized with the toner contained in the liquid developer thin layer having a uniform thickness formed on the developing belt. The liquid developer remaining on the developing belt after this developing step is removed by a developer cleaning unit, and the removed liquid developer is collected in a developer storage tank by a developer collection unit of a developer supply unit.

The developer solvent in the liquid developer collected in the developer storage tank is always consumed in a constant amount in the developing process, but varies depending on the area of the image developed by the toner. The ratio, that is, the concentration of the toner to the developer solvent of the liquid developer collected in the storage tank may be changed. Therefore, the viscosity of the liquid developer in the developer storage tank to which the liquid developer collected from the photoreceptor belt is added is detected by a viscometer in the developer storage tank, and the viscosity of the liquid developer in the developer storage tank is allowed. When the viscosity becomes lower than the lower limit of the viscosity range, the high-concentration developer supply section supplies a high-concentration liquid developer to the developer storage tank, and the liquid developer in the developer storage tank is stirred and supplied by the stirring means. The developer is mixed with a high-concentration liquid developer to obtain a uniform viscosity, and the viscosity of the liquid developer in the developer storage tank is adjusted to the initial viscosity. When the viscosity of the liquid developer in the developer storage tank becomes higher than the upper limit of the allowable viscosity range, the low-concentration liquid developer is supplied from the low-concentration developer supply unit to the developer storage tank, and the developer storage tank is supplied. The viscosity of the liquid developer inside is adjusted to the initial viscosity.

As described above, the viscosity U of the liquid developer in the developer storage tank to which the liquid developer collected from the developing belt is added is detected, and when the viscosity U of the liquid developer exceeds the allowable viscosity range, A liquid developer having a low concentration or a liquid developer having a low concentration is supplied, and the viscosity U of the liquid developer in the developer storage tank is increased.
Is set to the initial viscosity Uo, the electrostatic latent image formed on the photoreceptor can always be visualized with the liquid developer having a viscosity within the allowable viscosity range, and a high-quality image can be stably formed. .

Further, when the viscosity U of the liquid developer exceeds the allowable viscosity range, a high-concentration liquid developer or a low-concentration liquid developer is supplied, and the liquid in the developer storage tank is stirred by stirring means. Since the viscosity of the developer is made uniform,
It is possible to prevent density unevenness or the like from occurring in the formed image.

Further, the limit value ΔUo for defining the allowable viscosity range (Uo ± ΔUo) with respect to the initial viscosity Uo is as follows. Can be formed.

Further, a toner or a developing solution solvent may be supplied instead of the high-concentration liquid developer or the low-concentration liquid developer.

[0021]

FIG. 1 is a block diagram of a wet image forming apparatus using a liquid developing apparatus according to one embodiment of the present invention. As shown in the figure, the wet image forming apparatus includes a charging unit 2, a pre-wet liquid applying unit 3, a writing unit 4, a liquid developing unit 5, and a transferring unit 6, which are disposed along a photoreceptor 1 rotating clockwise. And a discharging unit 7 and a cleaning unit 8. After the surface of the photoreceptor 1 is uniformly charged by the charging means 2, the pre-wet liquid applying means 3 removes a pre-wet liquid having a releasing property and a chemically inert dielectric and light-transmitting properties to a uniform thickness. Is applied. The photoreceptor 1 having the surface uniformly charged and coated with the pre-wet liquid is exposed by the writing means 4 in accordance with image data to form an electrostatic latent image. The electrostatic latent image formed on the photoconductor 1 is visualized by the liquid developing device 5 to form a toner image, and the formed toner image is transferred to the transfer paper 9 by the transfer unit 6. The charge remaining on the photoreceptor 1 having transferred the toner image onto the transfer paper 9 is discharged by the charge removing means 7, and the remaining toner and pre-wet liquid are removed by the cleaning means 7 to start the next image forming step.

The liquid developing device 5 is a high-viscosity liquid developer in which toner, which is visualized particles, is dispersed at a high concentration in a developing solution solvent made of an insulating liquid such as dimethylpolysiloxane oil. It is for visualizing an image, and has a developing device main body 51 and a developer supply unit 52. The developing device main body 51 is wound around a plurality of rotating rollers 53a to 53e, and moves in a counterclockwise direction at the same surface moving speed as the surface moving speed of the photoreceptor 1; a developer applying means 55; Means 56. A potential between a minimum value and a maximum value of the latent image potential on the photoconductor 1 is applied to the developing belt 54 by a bias applying unit (not shown). The developer application means 55 has a developer storage section 58 in which a high-viscosity liquid developer 57 in which toner is dispersed in a developer solvent is stored, a supply roller 59, and an application roller 60. A thin liquid developer layer having a uniform thickness is formed on the surface. The developer cleaning unit 56 collects the liquid developer remaining on the developing belt 54 that has passed through the developing area.

As shown in FIG. 2, the developer supply unit 52 includes a developer storage tank 61, a developer recovery section 62, a developer supply section 63, a high-concentration developer supply section 64, and a low-concentration developer supply section 65. Having. The developer storage tank 61 has a viscometer 66 and a stirring means 67, and stores the liquid developer to be supplied to the developer application means 55. The developer recovery section 62 sends the liquid developer recovered by the developer cleaning means 56 to the developer storage tank 61. The developer supply unit 63 supplies the liquid developer stored in the developer storage tank 61 to the developer applying unit 55. The high-concentration developer supply unit 64 optimally adjusts the ratio of the toner to the developer solvent in order to form an image with an optimum image density, and the high-concentration liquid development having a higher toner ratio and a higher viscosity than the liquid developer having a viscosity of Uo. The developer 57a is stored, and the stored high-concentration liquid developer 57a is supplied to the developer storage tank 61. The low-concentration developer supply unit 65 stores the low-concentration liquid developer 57b having a lower toner ratio and a lower viscosity than the liquid developer having the viscosity Uo, and stores the stored low-concentration liquid developer 57b in the developer storage tank 61. To supply.

As shown in FIG. 3, the control section of the developer supply unit 52 includes a reference viscosity range setting section 68 and a comparison section 69.
And a drive control unit 70. Reference viscosity range setting section 6
Reference numeral 8 sets a reference viscosity range for controlling the liquid developer stored in the developer storage tank 61 to an appropriate viscosity, that is, an appropriate toner content. The comparison unit 69 compares the viscosity of the liquid developer stored in the developer storage tank 61 detected by the viscometer 66 with the reference viscosity range set by the reference viscosity range setting unit 68, and stores the comparison result in the developer storage tank 61. It is determined whether the viscosity of the stored liquid developer is within the reference viscosity range.
The drive control unit 70 drives one of the supply unit 641 of the high-density developer supply unit 64 and the supply unit 651 of the low-density developer supply unit 65 and the stirring unit 67 based on the determination result of the comparison unit 69.

In the liquid developing device 5 configured as described above, the developer storage tank 61 of the developer supply unit 52
Initially, a liquid developer having an initial viscosity Uo in which the ratio of the toner to the developing solution solvent is optimally adjusted in order to form an image having an optimum image density is stored. The developer is supplied to the developer storage unit 58. When the electrostatic latent image formed on the photoreceptor 1 is developed and visualized by the liquid developing device 5, the liquid developer 57 is applied to the developing belt 54 rotating counterclockwise by the developer applying means 55. A liquid developer thin layer having a uniform thickness is formed. The electrostatic latent image on the photoconductor 1 is visualized with the toner contained in the liquid developer thin layer having a uniform thickness formed on the developing belt 54.
When the electrostatic latent image on the photoconductor 1 is visualized, the toner adheres only to the image portion of the electrostatic latent image, and the developer solvent as a carrier adheres to the entire area of the photoconductor 1. The liquid developer remaining on the developing belt 54 after this developing step is removed by the developer cleaning means 56, and the removed liquid developer is collected in the developer storage tank 61 by the developer collecting section 62 of the developer supply unit 52. You.

The developer solvent in the liquid developer collected in the developer storage tank 61 is always consumed in a constant amount in the developing process, but varies depending on the area of the image to be developed by the toner. The ratio, that is, the concentration of the toner of the liquid developer collected in the developer storage tank 61 to the developer solvent, that is, the concentration may be changed, and the collected liquid developer is added to the liquid developer in the developer storage tank 61. Then, the concentration, that is, the viscosity of the liquid developer in the developer storage tank 61 changes from the initial viscosity Uo. The viscosity of the liquid developer, that is, the ratio of the toner to the developer solvent, is shown in FIG.
As shown in the characteristic diagram of the viscosity and the image density, the image density when the electrostatic latent image of the photoconductor 1 is visualized is directly affected, and the liquid developer in the developer storage tank 61, that is, the developer applying means 55 When the viscosity of the liquid developer supplied to the photosensitive member 1 decreases, the density of the image formed on the photoconductor 1 also decreases. When the viscosity of the liquid developer decreases to a certain limit, the quality of the image deteriorates. When the viscosity of the liquid developer in the developer storage tank 61 increases, the amount of the liquid developer applied to the developing belt 54 by the developer applying means 55 changes, and the liquid developer having a uniform thickness is formed. It becomes difficult to form a thin layer, and unevenness or the like occurs in image density.

Therefore, the viscometer 6 in the developer storage tank 61
In 6, the viscosity U of the liquid developer in the developer storage tank 61 to which the liquid developer collected from the developing belt 54 is added is detected constantly or at a certain time, and is sent to the comparison unit 69. The comparing unit 69 compares the viscosity U of the sent liquid developer with an allowable viscosity range (Uo ± ΔUo) for the initial viscosity Uo set in the reference viscosity range setting unit 68 in advance,
It is determined whether the viscosity U of the liquid developer in the developer storage tank 61 exceeds the allowable viscosity range (Uo ± ΔUo). As a result of this comparison, the comparison unit 69 determines that the viscosity U of the liquid developer in the developer storage tank 61 is within the allowable viscosity range (Uo ± Δ
If it exceeds (Uo), a signal indicating whether the viscosity U of the liquid developer is lower than the lower limit (Uo−ΔUo) of the allowable viscosity range or higher than the upper limit (Uo + ΔUo) is sent to the drive control unit 70. . Upon receiving a signal indicating that the viscosity U of the liquid developer is lower than the lower limit value (Uo-ΔUo) of the allowable viscosity range, the drive control unit 70 supplies the high concentration developer supply unit 64 with the supply unit 6.
The high-concentration liquid developer 57a is supplied to the developer storage tank 61 by driving the high-concentration liquid developer 57a. It is mixed with the liquid developer 57a to have a uniform viscosity. When the high-concentration liquid developer 57a is being supplied, the viscometer 66 detects and sends the viscosity U of the liquid developer in the developer storage tank 61 to the comparison unit 69. The comparison unit 69 sets the viscosity U of the liquid developer in the developer storage tank 61 to the initial viscosity U.
When it becomes o, a supply stop signal is sent to the drive control unit 70 to stop driving the supply means 641 of the high-density developer supply unit 64. When the drive control unit 70 receives a signal indicating that the viscosity U of the liquid developer is higher than the upper limit value (Uo + ΔUo) of the allowable viscosity range, the drive control unit 70 of the low-density developer supply unit 65
1 to supply the low-concentration liquid developer 57b to the developer storage tank 61, and drive the stirring means 67 to stir the liquid developer in the developer storage tank 61 to supply the low-concentration liquid. By mixing with the developer 57b to make the viscosity uniform, the viscosity U of the liquid developer in the developer storage tank 61 is changed to the initial viscosity Uo.
Adjust to

As described above, the viscosity U of the liquid developer in the developer storage tank 61 to which the liquid developer collected from the photoreceptor belt 54 is added is detected, and the viscosity U of the liquid developer is set in the allowable viscosity range (Uo ± When ΔUo) is exceeded, a high-concentration liquid developer 57a or a low-concentration liquid developer 57b is supplied to set the viscosity U of the liquid developer in the developer storage tank 61 to an allowable viscosity range (Uo ± ΔUo). Therefore, the electrostatic latent image formed on the photoconductor 1 can be visualized with the liquid developer having a viscosity within the allowable viscosity range (Uo ± ΔUo), and a high-quality image can be stably formed. . Further, when the viscosity U of the liquid developer exceeds the allowable viscosity range (Uo ± ΔUo), the high-concentration liquid developer 57a or the low-concentration liquid developer 57b is supplied, and the liquid developer 57 is stirred by the stirring means 67 to be uniform. Since the viscosity is set, it is possible to prevent density unevenness or the like from occurring in the formed image.

The limit value ΔUo for defining the allowable viscosity range (Uo ± ΔUo) with respect to the initial viscosity Uo set in the reference viscosity range setting section 68 is defined by the toner solid content ratio shown in FIG. As shown in the viscosity characteristic diagram, when ΔUo = (Uo−Uc) / 2 was set, a high-quality image could always be formed.

In the above embodiment, the developer storage tank 61 to which the liquid developer recovered from the photosensitive belt 54 is added.
Is within the allowable viscosity range (Uo ± ΔU).
o), the case where the high-concentration liquid developer 57a or the low-concentration liquid developer 57b is supplied has been described, but the viscosity U of the liquid developer is lower than the lower limit (Uo) of the allowable viscosity range.
−ΔUo), the toner is supplied to the liquid developer in the developer storage tank 61. When the viscosity U of the liquid developer is higher than the upper limit (Uo + ΔUo) of the allowable viscosity range, the toner in the developer storage tank 61 is supplied. A developer solvent having a viscosity Uc may be supplied to the liquid developer.

[0031]

As described above, according to the present invention, the viscosity of the liquid developer in the developer storage tank to which the liquid developer collected from the developing belt is added is detected, and the viscosity of the liquid developer falls within the allowable viscosity range. When it exceeds, the high-concentration liquid developer or the low-concentration liquid developer is supplied to set the viscosity of the liquid developer in the developer storage tank to the initial viscosity. The electrostatic latent image formed on the photoreceptor can be visualized with the agent, and a high-quality image can be stably formed.

When the viscosity of the liquid developer exceeds the permissible viscosity range, a high-concentration liquid developer or a low-concentration liquid developer is supplied, and the liquid developer in the developer storage tank is stirred by stirring means. Since the viscosity of the agent is made uniform, it is possible to prevent unevenness in the formed image from occurring.

Further, the limit value ΔUo for defining the allowable viscosity range (Uo ± ΔUo) with respect to the initial viscosity Uo is always good by setting ΔUo = (Uo−Uc) / 2 with the viscosity of the developer solvent as Uc. Image can be formed.

Further, by supplying a toner or a developing solution solvent in place of the high-concentration liquid developer or the low-concentration liquid developer, the viscosity of the liquid developer used for development can be easily adjusted.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a configuration diagram of a liquid developing device.

FIG. 3 is a block diagram illustrating a configuration of a control unit of the developer supply unit.

FIG. 4 is a characteristic diagram of viscosity and image density.

FIG. 5 is a characteristic diagram of toner solid content and viscosity.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photoreceptor 5 liquid developing device 51 developing device main body 52 developer supply unit 54 developing belt 55 developer applying unit 56 developer cleaning unit 61 developer storage tank 62 developer recovery unit 63 developer supply unit 64 high-concentration developer supply Section 65 Low-concentration developer supply section 66 Viscometer 67 Stirrer 68 Reference viscosity range setting section 69 Comparison section 70 Drive control section

Claims (6)

[Claims] 1. A high-viscosity liquid developer obtained by dispersing visualized particles at a high concentration in a developer solvent composed of an insulating liquid is coated on a developer carrier in a thin layer, and is formed on the image carrier. A liquid developing device for visualizing an electrostatic latent image with visualized particles contained in a high-concentration liquid developer coated in a thin layer on a developer carrier, wherein the liquid developer is applied to the developer carrier. A developer supply device for supplying a liquid developer having a viscosity adjusted to a predetermined range to a developer application unit for forming a liquid developer thin layer by applying the liquid developer. 2. The liquid developing device according to claim 1, wherein the liquid developer remaining on the developer carrier after passing through the developing region to the developer supply device is recovered. 3. A liquid having a large ratio of visualized particles and a high viscosity when a viscosity of the liquid developer in the developer supply device is detected and the viscosity of the liquid developer becomes a predetermined lower limit or less. The developer is supplied to the developer supply device, and when the viscosity of the liquid developer becomes equal to or more than a predetermined upper limit, the liquid developer having a small ratio of the visualized particles and a low viscosity is supplied to the developer supply device. The liquid developing device according to claim 1. 4. A method for detecting the viscosity of the liquid developer in the developer supply device, and supplying the visualized particles to the developer supply device when the viscosity of the liquid developer becomes equal to or less than a predetermined lower limit. 3. The liquid developing device according to claim 1, wherein a developer solvent comprising an insulating liquid is supplied to the developer supply device when the viscosity of the liquid developer becomes equal to or higher than a predetermined upper limit. 5. The viscosity of a liquid developer in a developer supply device when the initial viscosity of the liquid developer in the developer supply device is Uo and the viscosity of a developer solvent composed of an insulating liquid is Uc. U is expressed as {Uo- (Uo-Uc) / 2} <U <{Uo + (Uo-
The liquid developing device according to claim 3, wherein the adjustment is performed so that Uc) / 2ｃ. 6. The liquid developing device according to claim 5, wherein the liquid developer in the developer supply device is stirred to have a uniform viscosity.