JP2010085648A - Wet image forming apparatus and wet image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wet image forming apparatus and an image forming method which are less in occurrence of stripes even in an initial stage of operation after once stop that it stops for about several minutes or even in an initial stage of operation after long-term stop that it stops over a long term such that one day or more has passed. <P>SOLUTION: The wet image forming apparatus includes: a photoreceptor; an electrifying device for electrifying the photoreceptor to predetermined potential; and a developing roller for supplying liquid developer obtained by dispersing toner in insulating liquid to the photoreceptor. In the wet image forming apparatus and the image forming method, impact elastic modulus (measurement in conformity to JIS K 6255) on a surface of the developing roller is set to a value within 50 to 70%. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a wet image forming apparatus and a wet image forming method, and more particularly, to a wet image forming apparatus and a wet image forming method with less streaking in a formed image in an initial operation after stopping.

In the wet image forming apparatus, a liquid developing device is mounted as a developing device, and the electrostatic latent image formed on the photoconductor is developed with a liquid developer supplied from the liquid developing device.
At this time, it is presumed that the supply amount of the liquid developer obtained by dispersing the toner in the insulating liquid varies at the initial stage of the operation when the wet image forming apparatus is started. There was a problem that it was likely to occur.
That is, the liquid developing device employs a contact developing system, and forms a part of the liquid developing device, and the developing roller that supplies the liquid developer cooperates with a contact member such as a supply roller or a cleaning blade. Yes.
Since the developing roller is in contact with these contact members with a high load, the surface of the developing roller is distorted, which is considered to cause the supply amount of the liquid developer to vary. Has been.

In view of this, there has been proposed an electrostatic latent image liquid developing apparatus capable of supplying a liquid developer with a uniform thickness from the beginning to the surface of the developer support (see, for example, Patent Document 1). .
More specifically, as shown in FIG. 5, an electrostatic latent image liquid developing device for developing an electrostatic latent image formed on a photoreceptor with toner, and a developing belt 310 carrying a liquid developer. An application roller 322d for applying a liquid developer onto the developing belt 310, a conveying roller 322c for transferring the liquid developer to the application roller 322d, and the development belt 310 and the application roller 322d being separated from each other, and the application roller 322d and And a contact / separation means 353 for contacting / separating the transport roller 322c.
JP-A-8-137279 (Claims)

  However, in the liquid developing device described in Patent Document 1, it is necessary to provide a special separation mechanism, which not only makes the configuration of the liquid developing device complicated, but also the sealing performance becomes insufficient. There was a problem that liquid leakage was likely to occur.

Therefore, as a result of intensive studies, the present inventors have made the surface of the developing roller less likely to be distorted by setting the resilience elastic modulus on the surface of the developing roller to a value within a predetermined range. It was found that the generation of muscles can be reduced not only at times but also at the initial stage of movement.
That is, according to the present invention, it is an object to provide a wet image forming apparatus and an image forming method that prevent the occurrence of distortion on the surface of the developing roller with a simple configuration, and that cause little generation of streaks even in the initial operation. .

According to the present invention,
A wet image comprising a photoconductor, a charging device for charging the photoconductor to a predetermined potential, and a developing roller for supplying a liquid developer in which toner is dispersed in an insulating liquid to the photoconductor. A forming device,
There is provided a wet image forming apparatus characterized in that the rebound resilience (measured in accordance with JIS K 6255) on the surface of the developing roller is set to a value in the range of 50 to 70%, and the above-described problems can be solved. .
That is, according to the present invention, it is possible to provide a wet-type image forming apparatus that prevents the occurrence of distortion on the surface of the developing roller with a simple configuration, and that causes less streaking even in the initial operation.
The resilience modulus on the surface of the developing roller is measured according to JIS K 6255, using a prescribed test piece (a cylindrical shape with a thickness of 12.5 mm × diameter of 29 mm) at a temperature of 23 ° C.

Further, in configuring the present invention, the developing roller is configured to include a surface layer and a base material, and the rebound elastic modulus in the surface layer is set to a value within the range of 50 to 70%. preferable.
If comprised in this way, the resilience elastic modulus in the surface of a developing roller can be finely adjusted with the combination of a surface layer and the structure of a base material.
In addition, the surface layer in this invention shows the outermost surface layer in a developing roller.
For example, when an intermediate layer made of urethane resin or the like is interposed on the base material and a treatment layer is laminated thereon, the treatment layer becomes a surface layer.
The rebound resilience of the surface layer is measured in accordance with JIS K 6255 for a specified test piece made of the constituent material of the surface layer.

Further, in constituting the present invention, it is preferable that the surface layer of the developing roller contains a urethane resin as a main constituent material, and the base material contains a rubber material other than the urethane resin as a main constituent material. .
If comprised in this way, the resilience elastic modulus in the surface of a developing roller can be finely adjusted with the combination of the surface layer of a developing roller, and the constituent resin of a base material, and also predetermined durability can be obtained.

In constituting the present invention, the thickness of the surface layer of the developing roller is preferably set to a value in the range of 5 to 50 μm.
If comprised in this way, the resilience elastic modulus in the surface of a developing roller can be finely adjusted with the surface layer which has predetermined thickness, and also predetermined durability can be acquired.

Further, in constituting the present invention, it is preferable that the hardness (international rubber hardness) of the surface layer of the developing roller is set to a value within the range of 50 to 100 °.
If comprised in this way, the resilience elastic modulus in the surface of a developing roller can be finely adjusted with the surface layer which has predetermined hardness, and also predetermined durability can be obtained.
The international rubber hardness is measured in accordance with JIS K 6253, N or H method, using a prescribed test piece (8 mm thick, upper and lower surfaces are planar).

Another aspect of the present invention is as follows:
A photoreceptor,
A charging device for charging the photoconductor to a predetermined potential;
A developing roller for supplying a liquid developer in which toner is dispersed in an insulating liquid to the photoreceptor;
A wet image forming method using
A wet image forming method using a developing roller having a surface impact resilience value in a range of 50 to 70%.
That is, according to the present invention, it is possible to provide a wet image forming method with a simple configuration that prevents the occurrence of distortion on the surface of the developing roller and, in turn, produces less streaking even in the initial stage of operation.

Embodiments of the present invention, as illustrated in FIG.
A wet image comprising a photoconductor, a charging device for charging the photoconductor to a predetermined potential, and a developing roller for supplying a liquid developer in which toner is dispersed in an insulating liquid to the photoconductor. A forming device,
The wet image forming apparatus is characterized in that a rebound elastic modulus (measured in accordance with JIS K 6255) on the surface of the developing roller is set to a value in a range of 50 to 70%.

  Hereinafter, as shown in FIG. 2, the wet image forming apparatus 10 illustrated in FIG. 1 will be described in detail by taking a tandem type wet image forming apparatus (color printer) 150 for color image formation as an example.

1. Basic Configuration A color printer 150 shown in FIG. 2 is arranged in an upper main body 150A in which various units and parts for image formation are stored, and a lower part of the upper main body 150A, and a liquid developer circulating device for each color. LY, LM, LC, and LB (mixed liquid supply system) are comprised from the lower side main-body part 150B.

  In the upper main body 150A, a tandem-type image forming unit 2 that forms a toner image based on image data, a paper storage unit 3 that stores paper, and a toner image formed by the image forming unit 2 are printed on paper. From the secondary transfer unit 4 to be transferred upward, the fixing unit 5 for fixing the transferred toner image on the paper, the discharge unit 6 for discharging the fixed paper, and from the paper storage unit 3 to the discharge unit 6 And a paper transport unit 7 for transporting paper.

Here, the image forming unit 2 corresponds to the intermediate transfer belt 21, the cleaning unit 22 of the intermediate transfer belt 21, and each color of yellow (Y), magenta (M), cyan (C), and black (Bk). Image forming units FY, FM, FC, and FB.
Further, the intermediate transfer belt 21 is wider than the maximum length sheet in the direction perpendicular to the usable sheet transport direction and has an endless shape, that is, a loop-shaped member. It is circulated and driven.
Note that the surface facing outward in the circulation drive of the intermediate transfer belt 21 is hereinafter referred to as a front surface, and the other surface is referred to as a back surface.

Further, four image forming units FY, FM, FC, and FB are arranged in the vicinity of the intermediate transfer belt 21 and arranged between the cleaning unit 22 of the intermediate transfer belt 21 and the secondary transfer unit 4.
Note that the order of arrangement of the image forming units FY, FM, FC, and FB is not limited to this, but this arrangement is preferable in consideration of the influence of the color mixture on the completed image.

The image forming units FY, FM, FC, and FB include a photosensitive drum 51, a charging device 53, an LED exposure device 54, a developing device 18, a primary transfer roller 20, a cleaning device 58, and a static elimination device. 52.
Corresponding to the image forming units FY, FM, FC, and FB, liquid developer circulating devices LY, LM, LC, and LB are provided in the lower main body portion 150B to supply liquid developers of respective colors. In addition, collection is performed.

2. Photoreceptor As the photoreceptor to be mounted on the wet development image forming apparatus, there are a single layer type and a multilayer type, and any of them can be applied.
However, it can be used for both positive and negative chargeability, has a simple structure and is easy to manufacture, can suppress film defects when forming a photoreceptor layer, has few interface between layers, and can improve optical characteristics. For these reasons, it is more preferable to apply to a single layer type.

Moreover, it is preferable to use an amorphous silicon photoconductor because of its excellent durability.
Hereinafter, the details of the photoconductor will be described by taking the amorphous silicon photoconductor 51 shown in FIG. 3 as an example.

(1) Conductive Substrate As shown in the partial cross-sectional view of the amorphous silicon photoconductor 51 in FIG. 3, the amorphous silicon photoconductor 51 usually includes a conductive substrate 51a as a core, and a conductive member such as an aluminum alloy. The conductive film may be formed by vapor deposition or the like on the surface of resin or glass.

  Here, as a material constituting the conductive substrate, aluminum (Al), SUS (stainless steel), zinc (Zn), copper (Cu), iron (Fe), titanium (Ti), nickel (Ni), chromium Examples thereof include metal materials such as (Cr), tantalum (Ta), tin (Sn), gold (Au), and silver (Ag), and alloy materials thereof.

In addition, the surface of an insulating material such as resin, glass, or ceramic is subjected to conductive treatment with the above-described transparent conductive material such as metal, ITO, or SnO ₂ .
In particular, when an aluminum alloy material is used, it is possible to reduce the weight of the photosensitive member at low cost, and the adhesiveness to the a-Si photoconductive layer or the carrier injection blocking layer is high, thereby improving the reliability of the photosensitive member. This is preferable in terms of improvement.

(2) Carrier Injection Blocking Layer As shown in FIG. 3, the carrier injection blocking layer 51b uses an amorphous silicon-based material (a-Si-based material) as a base material, and hydrogen (H) or fluorine (F). In addition, it is preferable to further include at least one element selected from Group III, Group IV, and Group V of the periodic table.
It is also preferable to further contain elements such as C, N, and O as a constituent material of the carrier injection blocking layer.

(3) Photoconductive layer Further, as shown in FIG. 3, as the photoconductive layer 51c made of an amorphous silicon material, when the amorphous state is abbreviated as a-, for example, a-SiC, a-SiCN, It is preferably composed of a-SiNO, a-SiCO, a-SiN, a-Si, a-C, a-CN, a-SiO and the like.
It is also preferable to further contain an element such as hydrogen (H) or fluorine (F) as a part of the amorphous silicon material.

(4) Surface Layer As shown in FIG. 3, the surface layer 51d is composed of amorphous silicon (Si) and / or carbon (C) atoms, and oxygen (O) or nitrogen (N). Among these, it is preferable to contain at least one atom and at least one atom of hydrogen (H) or fluorine (F).
For example, when the ratio of Si atoms to C atoms is expressed as Si _1-x C _x , if x is in the range of 0.4 ≦ x ≦ 1.0, the Mohs hardness becomes 8-11. Has been confirmed.
In addition, it is preferable to make the film thickness of this surface layer into the value within the range of 0.1-10 micrometers, and it is further more preferable to set it as the value within the range of 0.3-5 micrometers.

4). Charging Device The charging device may be a known embodiment, but for example, a scorotron charging device is preferable.

5). Liquid Developing Device (1) Basic Configuration Further, as shown in FIG. 1, the liquid developing device 18 includes a liquid developer tank 45 for storing the liquid developer 11 containing the toner.
Further, inside the liquid developing device 18, a developing roller 12, an anilox roller 13, a pumping roller 14, a doctor blade 15, a cleaning blade 33, a charging device 17, a cleaning unit 32, and the like are provided. The developing roller 12, the anilox roller 13, and the scooping roller 14 are each driven to rotate by a driving means including a gear train or the like.
The liquid developer 11 having a predetermined toner concentration is supplied by the supply device 18c in the vicinity of the contact portion between the anilox roller 13 and the pumping roller 14 and on the pumping roller 14.

An anilox roller 13 is provided above the pumping roller 14. A developing roller 12 is further provided above the anilox roller 13.
The pumping roller 14 and the anilox roller 13, and the anilox roller 13 and the developing roller 12 are in contact with each other.

The doctor blade 15 is in contact with the upper part of the anilox roller 13 and on the upstream side in the rotational direction of the anilox roller 13 with respect to the developing roller 12 in the axial direction of the anilox roller 13. The liquid developer 11 supplied to the 13 roller surfaces is held in a groove (concave portion) carved on the surface to regulate the amount of the liquid developer 11.
The photosensitive drum 51 is outside the liquid developing device 18 and is in contact with the developing roller 12.

(2) Liquid Developer Further, a liquid developer storage tank (liquid developer tank) 45 provided outside the liquid developing device 18 stores a liquid developer 11 composed of toner particles and a carrier which is an insulating liquid. Has been.
The liquid developer 11 is adjusted so that toner particles are dispersed at a high concentration in a carrier liquid that is a nonpolar, ie, electrically neutral, solvent such as silicone oil.
The toner particles are composed of a resin (binder) such as epoxy, a charge control agent that gives a predetermined charge to the toner, a color pigment, and the like.
Then, the liquid developer 11 is supplied from a developing roller 12 as a developer carrying member to an electrostatic latent image of a portion irradiated with light by the LED exposure device 54 of the photosensitive drum 51, whereby a photosensitive member is obtained. A toner image can be developed on the drum 51.

(3) Developing roller In the present invention, the rebound resilience (measured in accordance with JIS K 6255) on the surface of the developing roller is set to a value in the range of 50 to 70%.
That is, with this configuration, distortion can be prevented from occurring on the surface of the developing roller even with a simple configuration. For example, even in the initial operation after a temporary stop of about several minutes, or for a long time after one day or more. This is because it is possible to provide a wet-type image forming apparatus with less streaking even in the initial operation after the stop.

More specifically, when the rebound resilience on the surface of the developing roller becomes a value of less than 50%, the contact member that is in contact with a high load causes distortion on the surface of the developing roller, which is the cause. This is because in the initial stage of operation, the amount of liquid developer supplied varies and streaks occur.
On the other hand, when the resilience modulus on the surface of the developing roller becomes a value exceeding 70%, the room for selection is excessively limited with respect to the configuration of the surface layer.
Therefore, the rebound resilience on the surface of the developing roller is more preferably set to a value within the range of 55 to 68%, and further preferably set to a value within the range of 60 to 65%.

As shown in FIG. 4, the developing roller 12 includes a surface layer 12a, a base material 12b, and an intermediate layer 12c. The rebound resilience of the surface layer 12a is 50 to 70%. It is preferable to set the value within the range.
The reason for this is that, if constituted in this way, the rebound resilience on the surface of the developing roller can be finely adjusted by the combination of the construction of the surface layer and the substrate.
That is, the rebound resilience on the surface of the developing roller can be finely adjusted within a predetermined range by a combination of the surface layer made of the predetermined material and the base material made of the predetermined material.

Moreover, it is preferable that the surface layer 12a of the developing roller 12 shown in FIG. 4 includes a urethane resin as a main constituent material, and the base material 12b includes a rubber material other than the urethane resin as a main constituent material. .
The reason for this is that the rebound elastic modulus on the surface of the developing roller can be finely adjusted by combining the surface layer of the developing roller and the constituent resin of the base material, and further, a predetermined durability can be obtained. Because it can.
That is, the rebound resilience on the surface of the developing roller can be finely adjusted within a predetermined range by the combination of the structure of the surface layer made of urethane resin and the base material made of aluminum or the like.

The urethane resin is a reaction product of an alcohol compound (such as a diol compound) and an isocyanate compound (such as a diisocyanate compound). The type of these alcohol compound (such as a diol compound) or isocyanate compound (such as a diisocyanate compound). In addition, it is easy to obtain a desired rebound resilience simply by changing the addition ratio. On the other hand, a urethane resin can provide excellent durability as a developing roller.
It has been found that the value of the resilience modulus of the developing roller can be adjusted to a desired range by forming at least a part of the outside of the developing roller from a urethane resin.

Moreover, it is preferable to make the thickness of the surface layer 12a of the developing roller 12 shown in FIG. 4 into the value within the range of 5-50 micrometers.
The reason for this is that, when configured in this way, the resilience modulus on the surface of the developing roller can be finely adjusted by the surface layer having a predetermined thickness, and further, a predetermined durability can be obtained. .
More specifically, when the thickness of the surface layer in the developing roller is less than 5 μm, the mechanical strength may decrease or it may be difficult to form a uniform thickness. .
On the other hand, when the thickness of the surface layer on the developing roller exceeds 50 μm, it may be difficult to form a uniform thickness, and the amount of liquid developer that passes therethrough may easily vary. Because there is.
Therefore, the thickness of the surface layer in the developing roller is more preferably set to a value within the range of 15 to 45 μm, and further preferably set to a value within the range of 20 to 40 μm.
In addition, an intermediate | middle layer can be comprised from a urethane resin etc., for example.

Moreover, it is preferable to set the hardness (international rubber hardness) of the surface layer 12a of the developing roller 12 shown in FIG. 4 to a value within the range of 50 to 100 °.
The reason for this is that, if configured in this way, the resilience modulus on the surface of the developing roller can be finely adjusted by a surface layer having a predetermined hardness, and further, a predetermined durability can be obtained.
More specifically, when the hardness of the surface layer in the developing roller is less than 50 °, the sealability of the liquid developer is reduced, and the choice of the constituent material of the surface layer is excessively limited. It is.
On the other hand, when the hardness of the surface layer in the developing roller reaches a value exceeding 100 °, when the liquid developer passes through the developing roller, the load and stress applied to the liquid developer increase, and the gap between the rollers This is because the liquid breakage at the nip is worsened and the so-called riblet phenomenon occurs.
Therefore, the hardness of the surface layer in the developing roller is more preferably set to a value within the range of 60 to 90 °, and further preferably set to a value within the range of 70 to 80 °.

[Example 1]
1. Preparation of wet image forming apparatus (1) Preparation of photoconductor An amorphous silicon photoconductor having a diameter of 40 mm was prepared.
The form of the amorphous silicon photoconductor conformed to the configuration shown in FIG.

(2) Preparation of developing roller Next, a urethane resin composed of a predetermined amount of a diol compound and a diisocyanate compound is laminated around a steel material using a mold, and then cut and polished, and a urethane resin layer having a thickness of 2 mm did.
Further, 100 parts by weight of an ether-based thermoplastic polyurethane solution is mixed with 4 parts by weight of a fluorine-based resin as a predetermined fluorine-based modifier and 40 parts by weight of Ketchin Black International Ketchin Black EC300J as a conductive agent (with a solid content of 10% by weight of tetrohydrofuran was added to the surface of the urethane resin and heat-treated at 130 ° C. for 2 hours to obtain a developing roller having a diameter of 20 mm having a surface layer with a thickness of about 30 μm.
The rebound resilience in the surface layer was measured to be 53%, and the hardness in the surface layer (international rubber hardness) was measured to be 88 °.
The rebound resilience in the surface layer is based on JIS K 6255, using a prescribed test piece (thickness 12.5 mm × column 29 mm in diameter) made of a constituent material of the surface layer at a temperature of 23 ° C. Measured.
In addition, the international rubber hardness was measured using a prescribed test piece (the upper and lower surfaces were 8 mm thick in a planar shape) in accordance with the N or H method of JIS K 6253.

(3) Preparation of Wet Image Forming Apparatus The prepared amorphous silicon photoconductor and developing roller were mounted on an experimental device of a wet image forming apparatus manufactured by Kyocera Mita, and the wet image forming apparatus of Example 1 was obtained.

2. Evaluation of wet image forming apparatus (1) Evaluation of streak generation at the initial stage of operation Using the obtained wet image forming apparatus, three printing experiments (predetermined pattern, A4 paper, 100 sheets of continuous printing three times, stop time 10 minutes) The predetermined image obtained at the initial stage of the operation was visually observed, and the generation of streaks was evaluated according to the following criteria.
○: No muscle development was observed at all.
Δ: Muscle development was observed once or twice.
X: Muscle development was observed in all three times.

[Example 2]
In Example 2, a wet image forming apparatus was prepared in the same manner as in Example 1 except that a developing roller having a rebound resilience of the surface layer of 59% and a hardness of the surface layer of 54 ° was used. And evaluated.
The rebound resilience and hardness of the surface layer in the developing roller were adjusted to predetermined values by changing the addition amount of the fluorine compound (PFA) and the processing amount of the coating agent.

[Example 3]
In Example 3, a wet image forming apparatus was prepared in the same manner as in Example 1 except that a developing roller having a surface layer rebound resilience of 55% and a surface layer hardness of 86 ° was used. And evaluated.
The rebound resilience and hardness of the surface layer in the developing roller were adjusted to predetermined values by changing the addition amount of the fluorine compound (PFA) and the processing amount of the coating agent.

[Example 4]
In Example 4, a wet image forming apparatus was prepared in the same manner as in Example 1 except that a developing roller having a surface layer rebound resilience of 66% and a surface layer hardness of 57 ° was used. And evaluated.
The rebound resilience and hardness of the surface layer in the developing roller were adjusted to predetermined values by changing the addition amount of the fluorine compound (PFA) and the processing amount of the coating agent.

[Comparative Example 1]
In Comparative Example 1, a wet image forming apparatus was prepared in the same manner as in Example 1 except that a developing roller having a rebound resilience of the surface layer of 47% and a hardness of the surface layer of 97 ° was used. And evaluated.
The rebound resilience and hardness of the surface layer in the developing roller were adjusted to predetermined values by changing the addition amount of the fluorine compound (PFA) and the processing amount of the coating agent.

[Comparative Example 2]
In Comparative Example 2, a wet image forming apparatus was prepared in the same manner as in Example 1 except that a developing roller having a surface layer rebound resilience of 73% and a surface layer hardness of 69 ° was used. And evaluated.
The rebound resilience and hardness of the surface layer in the developing roller were adjusted to predetermined values by changing the addition amount of the fluorine compound (PFA) and the processing amount of the coating agent.

According to the wet image forming apparatus and the wet image forming method of the present invention, by setting the rebound resilience on the surface of the developing roller to a value within a predetermined range, the surface of the developing roller is less likely to be distorted, and thus operates. It has become possible to provide a wet image forming apparatus and an image forming method with little streaking even in the initial stage.
In addition, since the rebound resilience on the surface of the developing roller is within a predetermined range, the torque when driving the developing roller can be reduced. As a result, the energy consumption of the wet image forming apparatus and the like is reduced, and the durability A wet image forming apparatus or the like rich in properties can be obtained.
Therefore, the wet image forming apparatus of the present invention can be suitably applied as a part of various printers, facsimiles, copiers, and the like.

It is a figure provided in order to demonstrate the wet image forming apparatus which concerns on this invention. FIG. 2 is a diagram for explaining a tandem wet color image forming apparatus equipped with a liquid developing device. It is a fragmentary sectional view provided in order to demonstrate an amorphous silicon photoconductor. It is a figure provided in order to demonstrate the aspect of a developing device. (A)-(c) is a figure provided in order to demonstrate the structure of the conventional liquid developing device.

Explanation of symbols

2: image forming unit 3: paper storage unit 4: secondary transfer unit 5: fixing unit 6: discharge unit 7: paper transport unit 10: wet image forming apparatus 11: liquid developer 12: developing roller (developer carrier)
13: Anilox roller 14: Pumping roller 15: Doctor blade 17: Charging device 18: Liquid developing device 18a: Collected liquid reservoir 18b: Waste liquid reservoir 18c: Supply device 20: Primary transfer roller 21: Intermediate transfer belt 22: Cleaning unit 32 : Cleaning roller 33: Cleaning blade 45: Liquid developer tank 51: Photosensitive drum 52: Static elimination device 53: Charging device 54: LED exposure device 57: Cleaning blade 58: Polishing device 150: Color printer (wet image forming device)

Claims (6)

A photoreceptor,
A charging device for charging the photoconductor to a predetermined potential;
A developing roller for supplying a liquid developer in which toner is dispersed in an insulating liquid to the photoreceptor;
A wet image forming apparatus comprising:
A wet image forming apparatus characterized in that a rebound resilience (measured in accordance with JIS K 6255) on the surface of the developing roller is set to a value within a range of 50 to 70%.   The said developing roller is comprised including the surface layer and the base material, and makes the rebound resilience rate in the said surface layer into the value within the range of 50 to 70%, It is characterized by the above-mentioned. Wet image forming apparatus.   The surface layer of the developing roller contains a urethane resin as a main constituent material, and the base material contains a rubber material other than the urethane resin as a main constituent material. Wet image forming apparatus.   The wet image forming apparatus according to claim 2 or 3, wherein the thickness of the surface layer of the developing roller is set to a value within a range of 5 to 50 µm.   The wet image forming apparatus according to any one of claims 2 to 4, wherein the hardness (international rubber hardness) of the surface layer of the developing roller is set to a value within a range of 50 to 100 °. A photoreceptor,
A charging device for charging the photoconductor to a predetermined potential;
A developing roller for supplying a liquid developer in which toner is dispersed in an insulating liquid to the photoreceptor;
A wet image forming method using
A wet image forming method using a developing roller having a surface rebound resilience (measured in accordance with JIS K 6255) having a value in the range of 50 to 70%.

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