JP2011197216A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus using wet developer in which toner is dispersed in carrier liquid, the apparatus being configured to stabilize an image for a long time by preventing charging capability degradation caused by carrier liquid with which a corona charger disposed opposite the developer holding member is soiled.SOLUTION: The image forming apparatus has a heater for heating the corona charger disposed opposite the developer holding member.

Description

  The present invention relates to an image forming apparatus that forms a toner image by developing a latent image using a wet developer in which toner is dispersed in a carrier liquid.

  2. Description of the Related Art An electrophotographic image forming apparatus that forms an electrostatic latent image on a photoconductor (image carrier), adheres toner to the image, and transfers and fixes the image on paper or the like is widely used. In particular, in an image forming apparatus that requires higher image quality and higher resolution, such as an office printer for large-scale printing and an on-demand printing apparatus, a wet process using a liquid developer that has a small toner particle diameter and is less likely to cause toner image disturbance. Development methods are being used.

  In recent years, an image using a high-viscosity, high-concentration liquid developer composed of high-concentration dispersion of a solid toner composed of a resin and a pigment in an insulating liquid “carrier liquid” such as silicone oil. Forming devices have been proposed.

  When developing using this liquid developer, a thin layer of developer is formed on a developer carrier such as a developing roller, and the thinned developer is brought into contact with the photoreceptor. It is common to develop.

  The latent image on the photoreceptor is developed by the developer thin layer, and after forming a toner image with a liquid developer, for example, the image is primarily transferred to an intermediate transfer member, and then secondarily transferred to a recording medium and fixed by a fixing device. Follow the process.

  In this process, the liquid developer remains on the developer holding member such as the developing roller, the photosensitive member, and the intermediate transfer member, which may adversely affect the next image formation or the like. Therefore, a cleaning device is disposed as appropriate.

  Further, in this process, one or more corona chargers are generally arranged at an appropriate location in order to form a latent image, to charge or remove the toner in the liquid developer.

  The corona charger is used as a photosensitive member charger, a pre-development charger, a development pre-cleaning charger, a pre-transfer charger, a pre-cleaning charger, and the like.

  The corona charger is composed of a mesh, a wire, a shield, and the like, and applies a high voltage to the wire to discharge and apply an electric charge to the opposing members.

  These corona chargers are easily soiled. In particular, if the photoreceptor charger, the pre-development charger, and the pre-development charger are contaminated, uneven charging occurs and image unevenness is likely to occur.

  Patent Document 1 discloses a technique in which air outside the apparatus is sent to a charging means (corona charger), and a blowing means is provided to exclude discharge products generated by discharge from the charging means.

Japanese Patent Laid-Open No. 2000-147962

  As described above, the image forming apparatus is provided with the corona charger for applying timely charges in the image process.

  In particular, a photoconductor charger for forming an electrostatic latent image, a pre-development charger that charges toner in a thin developer layer to be developed, and before developing cleaning that is charged to support the removal of residual developer from the developing roller When the charger becomes dirty, uneven charging occurs, and any of these tends to cause image unevenness.

  In particular, in a wet type image forming apparatus using a liquid developer, the carrier liquid of the liquid developer tends to adhere to the corona charger, and charging may become unstable.

  In Patent Document 1, air blowing means is provided, but this is for preventing the adhesion of discharge products in the air, and is hardly effective against contamination by the carrier liquid.

  The present invention has been made in view of the above technical problems.

  An object of the present invention is to prevent a decrease in charging ability due to carrier liquid contamination of a corona charger disposed opposite to a developer holding member in an image forming apparatus using a wet developer in which toner is dispersed in a carrier liquid. It is an object of the present invention to provide an image forming apparatus capable of stabilizing an image over a long period of time.

  In order to solve the above problems, the present invention has the following features.

1. In an image forming apparatus for developing a latent image using a wet developer in which toner is dispersed in a carrier liquid and forming a toner image,
A developer holding member carrying a thin layer of the wet developer;
A corona charger disposed opposite the developer holding member;
An image forming apparatus comprising: a heating unit that heats the corona charger.

2. A fixing device for fixing the developed toner image to the recording medium;
2. The image forming apparatus according to 1, wherein the heating unit heats the corona charger using heat of the fixing unit.

3. 3. The image forming apparatus according to 1 or 2, further comprising an exhaust port provided in the vicinity of the corona charger for collecting the carrier liquid volatilized by heating of the corona charger.

4). The image forming apparatus according to any one of claims 1 to 3, wherein the heating unit heats the corona charger in an end sequence or at predetermined intervals.

5. The image forming apparatus according to any one of 1 to 4, wherein the heating unit heats the corona charger by applying hot air.

6). The heating means has a heating member,
The image forming apparatus according to any one of 1 to 4, wherein the heating member is heated by contacting the corona charger.

7. The developer holding member is a photoreceptor for forming a latent image on the surface,
The image forming apparatus according to any one of 1 to 6, wherein the corona charger is a photoreceptor charger that charges a surface of the photoreceptor.

8). The developer holding member is a developing roller carrying a wet developer to be developed on the surface,
The image forming apparatus according to any one of 1 to 6, wherein the corona charger is a pre-development charger that charges toner before development on the surface of the developing roller.

9. The developer holding member is a developing roller carrying a wet developer to be developed on the surface,
The image according to any one of 1 to 6, wherein the corona charger is a pre-development charger that is charged to facilitate removal of toner remaining after development on the surface of the developing roller. Forming equipment.

  The image forming apparatus according to the present invention includes a heating unit that heats the corona charger disposed to face the developer holding member.

  As a result, in the image forming apparatus using the wet developer in which the toner is dispersed in the carrier liquid, the carrier liquid attached to the corona charger disposed opposite to the developer holding member is volatilized, and the charging ability due to the carrier liquid contamination is It is possible to prevent the deterioration and to stabilize the image over a long period of time.

1 is a configuration diagram illustrating a schematic configuration example of a wet image forming apparatus. 1 shows a schematic configuration of a wet type image forming apparatus used in first to fourth embodiments. FIG. 3 is a diagram illustrating a configuration of a heating unit of the image forming apparatus according to the first embodiment. It is a figure which shows the structure of the heating means of the image forming apparatus which concerns on 2nd Embodiment. It is a figure which shows the structure of the heating means of the image forming apparatus which concerns on 3rd Embodiment. It is a figure which shows the structure of the heating means of the image forming apparatus which concerns on 4th Embodiment. It is a graph which shows the change of the developing roller inflow electric current value about the charger before development. It is a graph which shows the change of the developing roller inflow electric current value about the charger before development cleaning. It is a graph which shows the change of the photoreceptor surface potential by a photoreceptor charger.

  Embodiments of an image forming apparatus according to the present invention will be described below with reference to the drawings.

(Configuration and operation of image forming apparatus)
FIG. 1 is a schematic configuration diagram illustrating a schematic configuration example of a wet image forming apparatus according to the present embodiment. First, the schematic configuration of the wet image forming apparatus according to the present embodiment and an example of the image forming operation will be described with reference to FIG.

  In FIG. 1, around a drum-shaped photoconductor (image carrier) 1, there are a photoconductor charger 2, an exposure device 3, a developing device 4, a pre-primary transfer charger 10, an intermediate transfer body 5, and a photoconductor cleaning device. (Including a pre-photoconductor cleaning charger 81) 8 is installed.

  Around the intermediate transfer member, a pre-secondary transfer charger 11, a transfer roller 6, and an intermediate transfer member cleaning device (including an intermediate transfer member pre-cleaning charger 91) 9 are provided.

  The developing device 4 is a liquid developing device, supplied with the liquid developer stored in the developer tank 42, and forms a thin developer layer on the developing roller 41. The developing roller 41 develops a latent image on the surface of the opposing photoreceptor 1.

  Further, a pre-development charger 43, a pre-development charger 44, and a development cleaning device 45 are arranged facing the developing roller 41.

  Each of the above chargers is generally disposed so that the corona charger faces a developer holding member (photosensitive member, intermediate transfer member, developing roller, etc.), and may be omitted as necessary. The role of each charger will be described later.

  Next, an example of the image forming operation will be described.

  The surface of the photoreceptor 1 is uniformly charged to a predetermined surface potential by the photoreceptor charger 2, and then image information is exposed by the exposure device 3 to form an electrostatic latent image on the surface of the photoreceptor 1. .

  Next, the electrostatic latent image on the photoreceptor 1 is developed with a liquid developer containing toner and carrier liquid by the developing roller 41 of the liquid developing device 4, and a toner image is formed on the surface of the photoreceptor 1. At this time, the liquid developer containing not only the toner but also the carrier liquid adheres to the surface of the photoreceptor 1.

  Next, the toner image on the photoreceptor 1 is primarily transferred to the intermediate transfer member 5 by applying a predetermined voltage to the intermediate transfer member 5. A voltage having a polarity opposite to that of the toner is applied to the intermediate transfer member 5, and the potential difference from the photosensitive member 1 is 300 V to 3 kV.

  After the primary transfer to the intermediate transfer member 5, the liquid developer remaining on the photosensitive member 1 is removed by the photosensitive member cleaning device 8, and the photosensitive member 1 is again subjected to the latent image formation.

  The liquid developer (toner image) transferred to the intermediate transfer member 5 is secondarily transferred to the recording medium 7 by the transfer roller 6. A voltage having a polarity opposite to that of the toner is applied to the transfer roller 6.

  The toner image on the recording medium 7 is fixed by the heat roller of the fixing device 12.

  The liquid developer remaining on the intermediate transfer member 5 after being transferred to the recording medium 7 is removed by the intermediate transfer member cleaning device 9.

(Developer composition)
A liquid developer used for development will be described. In a liquid developer, colored toner particles are dispersed at a high concentration in a carrier liquid that is a solvent. In addition, additives such as a dispersant and a charge control agent may be appropriately selected and added to the liquid developer.

  As the carrier liquid, an insulating solvent is used. The toner particles are mainly composed of a resin and a pigment or dye for coloring. The resin has a function of uniformly dispersing pigments and dyes in the resin and a function as a binder when being fixed to the recording material.

  The volume average particle diameter of the toner is suitably in the range of 0.1 μm or more and 5 μm or less. When the average particle diameter of the toner is less than 0.1 μm, the developability is greatly lowered. On the other hand, when the average particle diameter exceeds 5 μm, the quality of the image is deteriorated.

  The ratio of the toner particle mass to the liquid developer mass is suitably about 10 to 40%. If it is less than 10%, toner particles are liable to settle, and there is a problem with the stability over time during long-term storage. Further, in order to obtain a required image density, it is necessary to supply a large amount of developer, the carrier liquid adhering to the paper increases, and it must be dried at the time of fixing, and steam is generated, resulting in environmental problems. If it exceeds 40%, the viscosity of the liquid developer becomes too high, making it difficult to manufacture and handle.

(Configuration and operation of each charger)
As for the charger (corona charger), as shown in FIG. 1, the photoreceptor charger 2, the pre-development charger 43, the pre-development charger 44, the (primary and secondary) pre-transfer chargers 10, 11, (Photosensitive member, intermediate transfer member) Pre-cleaning chargers 81 and 91 are provided.

  The function of each charger and the degree of influence on dirt will be described. Although the present invention is effective in any place, particularly when the photosensitive member charger 2, the pre-development charger 43, and the pre-development charger 44 become dirty, image unevenness tends to occur.

<Photoconductor charger>
For charging the photoconductor for forming a latent image, when uneven charging occurs, the latent image becomes uneven and immediately causes image unevenness. The opposing developer holding member is the photoreceptor 1.

  The developer is charged before development, and basically there should be no developer thin layer at the opposite position.However, due to slight carrier liquid residue on the photoconductor after cleaning, volatilization from the developer, and splashing liquid, Contamination of carrier liquid occurs during use.

<Charger before development>
For toner charging of the developer used for development, when charging unevenness occurs, toner charging unevenness occurs and causes image unevenness. The opposing developer holding member is a developing roller 41.

  Since there is always a thin developing layer on the developing roller, it is easily soiled.

<Charger before development cleaning>
It is provided as necessary to assist with cleaning, and is used to remove toner before development cleaning. When the charging ability is lowered, cleaning becomes poor, and image unevenness (fogging) is caused. The opposing developer holding member is a developing roller 41.

  Since there is always a thin developing layer on the developing roller, it is easily soiled.

<Charger before transfer>
For toner charge adjustment at the time of toner image transfer, it is provided as needed to support primary transfer or secondary transfer. If the charging ability is reduced, transfer defects occur and image unevenness occurs. The opposing developer holding members are the photosensitive member 1 before the primary transfer and the intermediate transfer member 5 before the secondary transfer.

  Since the amount of liquid decreases toward the upstream side of the developing portion and the toner charge allowable width in transfer is wide to some extent, image unevenness does not easily occur, but gradually becomes dirty and becomes image unevenness after long-term use.

<Charger before cleaning>
It is provided for adjustment of toner neutralization at the time of cleaning, and is provided as needed to assist cleaning of the photosensitive member or intermediate transfer member. When the charging ability is lowered, cleaning becomes poor, and image unevenness (fogging) is caused. Opposing developer holding members are the photosensitive member 1 for the photosensitive member cleaning and the intermediate transfer member 5 for the intermediate transfer member cleaning.

  Since the amount of liquid decreases toward the upstream side of the developing unit, and the toner charge allowable width in cleaning is somewhat wide, image unevenness hardly occurs, but gradually becomes dirty and becomes image unevenness after long-term use.

(Prevents carrier liquid contamination of each charger)
As described above, in the image forming apparatus using the liquid developer in which the toner is dispersed in the carrier liquid, each of the corona chargers arranged facing the developer holding member is easily contaminated with the carrier liquid and has a charging ability. It was difficult to stabilize the image over a long period of time due to the reduction and unevenness.

  In this embodiment, each corona charger is provided with a heating unit as necessary, and the corona charger is heated to prevent the carrier liquid from adhering or to volatilize the adhering carrier liquid.

  As a result, it is possible to prevent a decrease in charging ability due to carrier liquid contamination of each corona charger disposed facing the developer holding member, and to stabilize an image for a long period of time.

<Heating means for charger>
Specific heating means will be described.

  The heating means includes contact heating by a heating member, hot air blowing, radiant heat and the like as a heating method, but heating member contact or hot air blowing is particularly preferable.

  The hot air type has advantages such as promoting the volatilization of the carrier liquid by the wind, and heating not only the shield but also the wire and mesh at the same time without contact.

  Further, it is preferable to provide an exhaust port for collecting the volatilized carrier liquid in the vicinity of the charger. Thereby, re-adhesion of the volatilized carrier liquid can be prevented.

  In the embodiment to be described later, air is blown from the lower position of the charger and the exhaust port is provided at the upper position. However, the present invention is not limited thereto, and for example, air may be blown from the front side of the figure and the exhaust port may be provided on the far side.

  The contact type is advantageous in that heat is not easily transmitted to the peripheral member and the peripheral developer, and the image is not adversely affected. Therefore, it is possible to heat during image formation.

  As for the heat, a heat source may be provided in the vicinity of the charger, but the heat of the fixing device 12 may be used. Since the periphery of the fixing unit is heated, it is necessary to release the heat, and using the heat is energy efficient.

  When using the heat of the fixing unit, there are various methods. For example, if it is a blowing type, air blowing, if it is a contact type, air circulation, oil circulation, connection with a material having good thermal conductivity, Etc.

  The heating timing of each charger is preferably performed in an end sequence of image formation or at predetermined time intervals.

  If heating is performed during image output, the peripheral members and the peripheral developer are warmed, and the image quality may fluctuate. Therefore, it is preferable to volatilize the accumulated carrier liquid periodically.

  The heating temperature is less effective if the temperature of the charger is too low, and if it is too high, heat is transmitted to the peripheral members and the peripheral developer, and it takes time until the image formation starts after releasing the heat.

  For safety reasons, when using the charger, it is better to set the temperature of the charger to be lower than the flash point of the carrier liquid.

  In addition, the effect depends on the volatility of the liquid, and the carrier liquid is a hydrocarbon solvent, for example, IP solvent 1620, IP solvent 2028, IP solvent 2835 (manufactured by Idemitsu Petroleum), Moresco White P-40, Moresco White P-70, Moresco White P-120 (manufactured by Matsumura Oil Co., Ltd.) and the like, and other silicone oils and animal and plant oils are available.

  In the IP solvent 2028 (flash point 86 ° C.) used in this embodiment, the heating temperature when the charger is stopped is preferably 60 ° C. to 150 ° C., and when the charger is used, it is preferably heated to about 60 ° C. to 80 ° C.

  The shield of the charger may be provided with a gap through which air flows in consideration of the flow of hot air blown or the vaporized carrier liquid exhaust air.

<First Embodiment>
FIG. 2 shows a schematic configuration of the wet image forming apparatus used in the first embodiment. In the first embodiment, the pre-development charger 43 and the pre-development charger 44 in FIG. 2 are each provided with hot air heating means.

  FIG. 3 is a diagram illustrating a configuration of a heating unit of the image forming apparatus according to the first embodiment. The heating means includes an air conveyance tube 47, a hot air blowing port 48, and an exhaust port 49.

  The heating method was a hot air blowing type, in which air in the vicinity of the heat source of the fixing device was sent by a fan through the air conveyance pipe 47 and hot air was applied from the hot air blowing ports 48 below the corona chargers 43 and 44.

  An exhaust port 49 was provided in the upper part of each corona charger, and the carrier liquid which volatilized through the air carrying tube 47 was collected.

  The image forming apparatus and the developer were continuously driven and heated for 3 minutes every hour. During the heating, the developing device driving and the corona charger output were stopped, and the developing device driving and the corona charger output were started 2 minutes after the completion of the heating. Moreover, after the continuous driving stop of the day, it heated for 5 minutes.

  The temperature of the shield at the end of heating was 80 ° C. to 120 ° C., and was 60 ° C. or less at the start of driving the developing device.

<Second Embodiment>
FIG. 2 shows a schematic configuration of the wet image forming apparatus used in the second embodiment. Also in the second embodiment, the pre-development charger 43 and the pre-development charger 44 in FIG. 2 are each provided with contact-type heating means.

  FIG. 4 is a diagram illustrating a configuration of a heating unit of the image forming apparatus according to the second embodiment. The heating means includes an air conveyance pipe 47, a heating member 46, and an exhaust port 49 as necessary.

  The heating method is a heating member contact type, and the heating member 46 is warmed by sending air in the vicinity of the fixing device with a fan through the air conveyance pipe 47 reciprocating from the vicinity of the fixing device heat source to the heating member 46. Was applied to each shield of the corona chargers 43 and 44.

  An exhaust port 49 was provided in the upper part of each corona charger, and the carrier liquid which volatilized through the air carrying tube 47 was collected.

  Heating was performed while continuously driving the image forming apparatus and the developing unit.

  The temperature was detected by a temperature sensor (not shown) attached to the shield, and the temperature of the shield was controlled by contact / separation of the heating member 46 so as to be 60 ° C. to 80 ° C.

<Third Embodiment>
FIG. 2 shows a schematic configuration of the wet image forming apparatus used in the third embodiment. In the third embodiment, the photoconductor charger 2 in FIG. 2 is provided with hot air type heating means.

  FIG. 5 is a diagram illustrating a configuration of a heating unit of the image forming apparatus according to the third embodiment. The heating means includes an air conveyance tube 47, a hot air blowing port 48, and an exhaust port 49.

  The heating method was a hot air blowing type, in which air in the vicinity of the heat source of the fixing device was sent by a fan through the air conveying tube 47 and hot air was applied from the hot air blowing port 48 on the lower side of the photosensitive member charger 2.

  An exhaust port 49 is provided in the upper part of the photosensitive member charger 2, and the carrier liquid that has volatilized through the air conveyance pipe 47 is collected.

  The image forming apparatus was driven continuously and heated for 3 minutes every hour. During the heating, the driving of the image forming apparatus and the photosensitive member charging output were stopped, and the driving of the image forming apparatus and the photosensitive member charging output were started 2 minutes after the completion of the heating. Moreover, after the continuous driving stop of the day, it heated for 5 minutes.

  The temperature of the shield at the end of heating was 80 ° C. to 120 ° C., and was 60 ° C. or less at the start of driving of the image forming apparatus.

<Fourth Embodiment>
FIG. 2 shows a schematic configuration of the wet image forming apparatus used in the fourth embodiment. Also in the fourth embodiment, a contact-type heating unit is provided in the photoreceptor charger 2 in FIG.

  FIG. 6 is a diagram illustrating a configuration of a heating unit of the image forming apparatus according to the fourth embodiment. The heating means includes an air conveyance pipe 47, a heating member 46, and an exhaust port 49 as necessary.

  The heating method is a heating member contact type, and the heating member 46 is warmed by sending air in the vicinity of the fixing device with a fan through the air conveyance pipe 47 reciprocating from the vicinity of the fixing device heat source to the heating member 46. Was applied to the shield of the photoreceptor charger 2.

  An exhaust port 49 is provided in the upper part of the photosensitive member charger 2, and the carrier liquid that has volatilized through the air conveyance pipe 47 is collected.

  Heating was performed while continuously driving the image forming apparatus.

  The temperature was detected by a temperature sensor (not shown) attached to the shield, and the temperature of the shield was controlled by contact / separation of the heating member 46 so as to be 60 ° C. to 80 ° C.

  For the first to fourth embodiments, the following charger stability evaluation was performed.

(Heating and charging stability of pre-development charger and pre-development charger)
Example 1 relates to the first embodiment (hot air type heating means) and Example 2 relates to the pre-development corona charger and the pre-development corona charger for the second embodiment (contact-type heating means), respectively. Stability evaluation was performed.

  As Comparative Example 1, the same stability evaluation was performed on a configuration similar to Example 1 or Example 2 and having no heating means.

<Evaluation method>
The image forming apparatus shown in FIG. 2 and the developing device shown in FIG. 3 (Example 1) or FIG. 4 (Example 2) are driven. The stability was evaluated by comparing the inflow current into the initial and post-endurance.

  However, when measuring the inflow current by the pre-development charger, the output of the pre-development charger is turned off, and when measuring the inflow current by the pre-development charger, the output of the pre-development charger is turned off. The inflow current value was measured.

  At the same time, the temperature of the shield was measured with a temperature sensor attached to the shield.

Setting conditions for each charger and the like are as follows.
Pre-development charger: a corotron (wire and shield) system configuration, with an applied voltage of 6 kv under constant voltage control.
Charger before development cleaning: a corotron (wire and shield) system configuration, and the applied voltage was set to 5 kv by constant voltage control.
Developing roller: φ4 cm elastic roller. Volume resistance 3E + 5Ω · cm.
Roller drive: 40 cm / s.
Developer: Toner particles (average particle size 2 μm) and a small amount of dispersant were added to a carrier liquid (IP solvent 2028). The solid content ratio Tc is 20%.

<Evaluation results>
The stability evaluation results for Example 1, Example 2, and Comparative Example 1 are shown in graphs in FIGS. The graph shows the initial ratio (vertical axis) indicating how much the developing roller inflow current value has decreased from the initial value 1 with the passage of the endurance time (horizontal axis).

  FIG. 7 shows the developing roller inflow current value for the pre-development charger. L1 is the stability evaluation result for Example 1, L2 is Example 2, and S1 is the stability evaluation result for Comparative Example 1.

  FIG. 8 shows the developing roller inflow current value for the pre-development charger. L1 is the stability evaluation result for Example 1, L2 is Example 2, and S1 is the stability evaluation result for Comparative Example 1.

  Both the inflow current to the developing roller by the pre-development charger and the inflow current to the development roller by the pre-development charger are compared with the first comparative example in the first and second embodiments (decrease). ) Is less.

  Even when a half image with a BW ratio of 50% was output after driving for 200 hours, density unevenness occurred in Comparative Example 1, but in Examples 1 and 2, good images without density unevenness were obtained.

(Photoconductor charger heating and charging stability)
Example 3 evaluated the stability of the photoreceptor charger in the third embodiment (hot air type heating means), and Example 4 evaluated the stability of the photoreceptor charger in the fourth embodiment (contact type heating means).

  As Comparative Example 2, the same stability evaluation was performed on a configuration similar to Example 3 or Example 4 and having no heating means.

<Evaluation method>
The image forming apparatus of FIG. 2 and FIG. 5 (Embodiment 3) or FIG. 6 (Embodiment 4) is driven, and the surface potential of the photoreceptor by the photoreceptor charger is compared with that after the endurance to ensure stability. Evaluated.

  At the same time, the temperature of the shield was measured with a temperature sensor attached to the shield.

Setting conditions for the charger and the like are as follows.
Photoconductor charger: a scorotron (wire, shield, and mesh) type configuration, and an applied voltage of 6.5 kv by constant voltage control.
Photoconductor: Amorphous silicon photoconductor.
System speed 40 cm / s.
Developer: Toner particles (average particle size 2 μm) and a small amount of dispersant were added to a carrier liquid (IP solvent 2028). The solid content ratio Tc is 20%.

<Evaluation results>
The stability evaluation results for Example 3, Example 4, and Comparative Example 2 are shown in a graph in FIG. The graph shows the initial ratio (vertical axis) indicating how much the photoreceptor surface potential has decreased from the initial value 1 with the passage of the endurance time (horizontal axis).

  FIG. 9 shows the stability evaluation results of Example 3 for L3, Example 4 for L4, and Comparative Example 2 for S2.

  As for the photoreceptor surface potential by the photoreceptor charger, it can be seen that the fluctuation (decrease) from the initial stage is less in Example 3 and Example 4 than in Comparative Example 2.

  Even when a half image with a BW ratio of 50% was output after driving for 200 hours, density unevenness occurred in Comparative Example 2, but in Examples 3 and 4, good images with no density unevenness were obtained.

  As described above, the image forming apparatus according to the present embodiment includes a heating unit that heats the corona charger disposed to face the developer holding member.

  As a result, in the image forming apparatus using the wet developer in which the toner is dispersed in the carrier liquid, the carrier liquid attached to the corona charger disposed opposite to the developer holding member is volatilized, and the charging ability due to the carrier liquid contamination is It is possible to prevent the deterioration and to stabilize the image over a long period of time.

  In addition, the above-mentioned embodiment is an illustration and restrictive at no points. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Photoconductor charger 3 Exposure apparatus 4 Developing apparatus 5 Intermediate transfer body 6 Transfer roller 7 Recording medium 8 Photoconductor cleaning apparatus 9 Intermediate transfer body cleaning apparatus 10 Primary transfer charger 11 Secondary pre-transfer charger 12 Fixing Development device 41 Development roller 42 Developer tank 43 Pre-development charger 44 Pre-development charging device 45 Development cleaning device 46 Heating member 47 Air transport tube 48 Hot air blowing port 49 Exhaust port 81 Pre-photoconductor cleaning charger 91 Before intermediate transfer member cleaning Charger

Claims (9)

In an image forming apparatus for developing a latent image using a wet developer in which toner is dispersed in a carrier liquid and forming a toner image,
A developer holding member carrying a thin layer of the wet developer;
A corona charger disposed opposite the developer holding member;
An image forming apparatus comprising: a heating unit that heats the corona charger. A fixing device for fixing the developed toner image to the recording medium;
The image forming apparatus according to claim 1, wherein the heating unit heats the corona charger using heat of the fixing unit. The image forming apparatus according to claim 1, further comprising an exhaust port provided in the vicinity of the corona charger in order to collect the carrier liquid volatilized by heating of the corona charger. The image forming apparatus according to any one of claims 1 to 3, wherein the heating unit heats the corona charger in an end sequence or at predetermined intervals. The image forming apparatus according to claim 1, wherein the heating unit heats the corona charger by applying hot air. The heating means has a heating member,
The image forming apparatus according to claim 1, wherein the heating member is heated by contacting the corona charger. The developer holding member is a photoreceptor for forming a latent image on the surface,
The image forming apparatus according to claim 1, wherein the corona charger is a photoreceptor charger that charges a surface of the photoreceptor. The developer holding member is a developing roller carrying a wet developer to be developed on the surface,
The image forming apparatus according to claim 1, wherein the corona charger is a pre-development charger that charges toner before development on the surface of the developing roller. The developer holding member is a developing roller carrying a wet developer to be developed on the surface,
7. The charger according to claim 1, wherein the corona charger is a pre-development charger that is charged in order to facilitate removal of toner remaining after development on the surface of the developing roller. Image forming apparatus.

Images