JP2010079004A - 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 a wet image forming method by which generation of rivulets is prevented for a long period of time and excellent image characteristics are stably obtained. <P>SOLUTION: The wet image forming apparatus includes a photoreceptor, a charging device for charging the photoreceptor to a predetermined potential, and a developing roller supplying a liquid developer prepared by dispersing a toner in an insulating liquid to the photoreceptor; the wet image forming method is carried out by using the apparatus. The Young's modulus on the developing roller is controlled to the range from 8 to 50 MPa. <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 occurrence of a riblet phenomenon (Rivulets).

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, since the entire surface of the photoconductor is partially covered with a water-insoluble solvent contained in the developer, when developing continuously, between the developing roller and the photoconductor, As shown in FIGS. 7 (a) to 7 (c), the occurrence of riblet phenomenon, which is a streaky non-uniform layer (unevenness) due to the liquid developer, becomes a serious problem. .
That is, there has been a problem that image characteristics are remarkably deteriorated and fog is easily generated due to the riblet phenomenon.

Here, in order to suppress the riblet phenomenon, in the liquid developing type developing roller, an electrode configuration constituted by a flexible sheet that is in contact with the toner layer on the developing roller before development and to which a bias voltage is applied. It is proposed to provide (for example, refer patent document 1).
More specifically, as shown in FIG. 8, according to the electrode configuration constituted by the flexible sheet 362, the toner layer is obtained by utilizing electrophoresis inside the toner layer by applying an electric field based on a bias voltage. Are substantially separated into a toner rich layer and a carrier rich layer.
Then, the surface of the developing roller 312 is attached to the surface of the developing roller 312 by utilizing the surface tension or wettability of the liquid developing solution between the flexible sheet 362 and the developing roller 312 as the developer carrying member. It has been proposed to contact by attracting.

In addition, in a developing roller used in a liquid developing electrophotographic apparatus, it has been proposed that a predetermined elastic body layer is provided on the outer periphery of a shaft body in order to suppress volume change due to a carrier (for example, see Patent Document 2). .
More specifically, for a liquid developing electrophotographic apparatus which is provided in a liquid developing electrophotographic apparatus using a liquid developer in which toner is dispersed in a carrier, and an elastic body layer is provided on the outer periphery of the shaft body. A liquid development characterized in that the elastic layer is a roller formed by reacting a bifunctional isocyanate and a polyester polyol having a sp value of 2 or more larger than the sp value of the carrier. It is a roller for an electrophotographic apparatus.
JP 2003-186308 A (Claims) JP 2008-8982 A (Claims)

However, the liquid developing type developing device described in Patent Document 1 must have a specific electrode configuration constituted by a flexible sheet to which a bias voltage is applied, and the configuration of the developing roller tends to be complicated. The problem was seen.
Further, even when a bias voltage is applied, there is a problem that separation between the toner-rich layer and the carrier-rich layer becomes insufficient, and suppression of the riblet phenomenon tends to be insufficient.
On the other hand, the development roller of the liquid development system described in Patent Document 2 does not consider any Young's modulus on the surface, so even if it can suppress the volume change due to the carrier, it does not prevent any suppression of the riblet phenomenon. The problem of not being able to be seen was seen.

As a result of intensive studies, the present inventors have found that the occurrence of the riblet phenomenon can be prevented over a long period of time by setting the Young's modulus at least on the surface of the developing roller to a value within a predetermined range.
That is, according to the present invention, the riblet phenomenon can be generated over a long period of time by generating a shearing force between the developing roller and the photoconductor so as to improve the liquid developer running out with a simple configuration. An object of the present invention is to provide a wet image forming apparatus and an image forming method capable of preventing occurrence and stably obtaining excellent image characteristics.

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,
The wet image forming apparatus is characterized in that the Young's modulus at least on the surface of the developing roller is set to a value in the range of 8 to 50 MPa.
That is, according to the present invention, the occurrence of the riblet phenomenon is prevented over a long period of time by generating a shearing force between the developing roller and the photoconductor so that the liquid developer is sufficiently drained. Excellent image characteristics can be obtained stably.

In constructing the present invention, the developing roller is configured to include a coating layer and a substrate, and the Young's modulus of the coating layer is preferably set to a value within the range of 8 to 50 MPa.
If comprised in this way, the Young's modulus in the surface of a developing roller can be finely adjusted with the combination of a structure of a coating layer and a base material.
In addition, although a coating layer may be called a surface layer, a conductive resin layer and a surface treatment layer may be further formed on it. Therefore, in such a case, the conductive resin layer or the surface treatment layer becomes the outermost surface layer, and the coating layer does not become the outermost surface layer.

Further, in constituting the present invention, it is preferable that the coating 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 Young's modulus in the surface of a developing roller can be finely adjusted with the combination of the coating layer of a developing roller, and the structural resin of a base material, and also predetermined durability can be obtained.

In constructing the present invention, the hardness of the coating layer of the developing roller (JIS-A hardness) is set to a value within the range of 50 to 100 °, and the hardness of the substrate (JIS-A hardness) is set to 30 to 100. A value within the range of ° is preferable.
If comprised in this way, the Young's modulus in the surface of a developing roller can be finely adjusted with the combination of the coating layer and base material which have predetermined | prescribed hardness, and also predetermined | prescribed riblet resistance and durability can be obtained. .
In addition, JIS-A hardness means the type A durometer hardness measured according to JIS K6253.

In configuring the present invention, the viscosity of the insulating liquid is preferably set to a value in the range of 15 to 300 mPa · sec (measurement temperature: 25 ° C.).
With this configuration, the liquid breakage is improved by the considerable shearing force generated between the developing roller and the photoconductor, and the riblet phenomenon is prevented from occurring for a long period of time. Can get to.

According to another aspect of the present invention, a photosensitive member, a charging device for charging the photosensitive member to a predetermined potential, and a liquid developer in which toner is dispersed in an insulating liquid are supplied to the photosensitive member. A wet image forming method using a developing roller,
A developing roller having at least a surface Young's modulus in the range of 8 to 50 MPa is used.
That is, according to the present invention, the occurrence of the riblet phenomenon is prevented over a long period of time by generating a shearing force between the developing roller and the photoconductor so that the liquid developer is sufficiently drained. Excellent image characteristics can be obtained stably.

Embodiments of the present invention, as illustrated in FIG.
A photoreceptor,
A charging device for charging the photoconductor to a predetermined potential;
A wet image forming apparatus comprising: a developing roller that supplies a liquid developer in which toner is dispersed in an insulating liquid to a photoreceptor;
The wet image forming apparatus is characterized in that the Young's modulus at least on the surface of the developing roller is set to a value in the range of 8 to 50 MPa.

That is, as shown in FIG. 2A, a shearing force generation model and the state of running out of liquid, the generated shearing force is small between the developing roller having a relatively large Young's modulus and the photosensitive member. The cutting characteristic is lowered and the spread width (l1) is reduced. Therefore, the riblet phenomenon is likely to occur, and the image characteristics are likely to be deteriorated.
On the other hand, as shown in FIG. 2 (b), a relatively large shearing force is generated between the developing roller having a relatively small Young's modulus and the photosensitive member, thereby improving the liquid breakage characteristics and the spreading width. (L2) becomes large. Thereby, the occurrence of the riblet phenomenon can be prevented over a long period of time, and excellent image characteristics can be stably obtained.
Hereinafter, as shown in FIG. 3, the wet image forming apparatus 10 illustrated in FIG. 1 will be described in detail by taking the case of 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. 3 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 photosensitive member will be described by taking the amorphous silicon photosensitive member 51 shown in FIG. 4 as an example.

(1) Conductive Substrate FIG. 4 shows a partial cross-sectional view of the amorphous silicon photoconductor 51. 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 Further, as shown in FIG. 4, 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. 4, as the photoconductive layer 51c made of an amorphous silicon-based 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) Covering Layer As shown in FIG. 4, the covering layer 51d is composed of amorphous silicon (Si) and / or carbon (C) atoms, and is formed of 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 coating 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.

(5) Diameter It is also preferable that the diameter (Dpc) of the photoreceptor is a value in the range of 30 to 300 mm.
The reason for this is that when the diameter (Dpc) of the photoreceptor is less than 30 mm, the shearing force generated between the developing roller and the developing roller becomes small, and it may be difficult to prevent the occurrence of the riblet phenomenon over a long period of time. Because.
On the other hand, when the diameter (Dpc) of the photosensitive member exceeds 300 mm, the wet image forming apparatus becomes large, or the shearing force generated between the photosensitive member and the photosensitive member becomes excessively large. This is because the image density may deteriorate and the image density may decrease.
Therefore, the diameter (Dpc) of the photoreceptor is more preferably set to a value within the range of 35 to 200 mm, and further preferably set to a value within the range of 40 to 100 mm.

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 near the contact portion between the anilox roller 13 and the drawing roller 14 and on the drawing 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.

The viscosity of the insulating liquid is preferably set to a value within the range of 15 to 300 mPa · sec (measurement temperature: 25 ° C.).
This is because by limiting the viscosity of the insulating liquid to such a range, the migration speed of the toner particles is increased, the leveling property is improved, and the riblet is eliminated.
That is, when the migration time is slow, the carrier liquid in which the toner particles remain moves to a shearing process (at the time of separation of the nip between the photosensitive member and the developing roller). Therefore, the liquid in which the toner particles remain has a high viscosity and tends to be a riblet.
The leveling property is expressed by the time that the undulated liquid surface becomes smooth. However, the good leveling property indicates that the time required for the undulating liquid surface to become smooth is short. . That is, riblets are eliminated in a short time.

(3) Developing roller As described above, the Young's modulus on the surface of the developing roller is set to a value in the range of 8 to 50 MPa.
The reason for this is that when the Young's modulus on the surface of the developing roller is less than 8 MPa, a predetermined shearing force is generated, but this time the mechanical strength and durability are lowered, and further, the developing roller is driven. This is because the development amount may not be constant in the initial state.
On the other hand, when the Young's modulus on the surface of the developing roller reaches a value exceeding 50 MPa, a predetermined shearing force is not generated between the developing roller and the photosensitive member, and the liquid developer is poorly drained. This is because the riblet phenomenon is likely to occur.
Accordingly, the Young's modulus on the surface of the developing roller is preferably set to a value within the range of 15 to 40 MPa, more preferably set to a value within the range of 15 to 35 MPa, and a value within the range of 15 to 30 MPa. Is more preferable.

Moreover, as shown to Fig.5 (a), the developing roller 12 is comprised including the coating layer 12a and the base material 12b, and the Young's modulus in the said coating layer 12a is in the range of 8-50 Mpa. It is preferable to use a value.
This is because, since the developing roller includes the coating layer and the base material, the Young's modulus on the surface of the developing roller can be finely adjusted only by selecting the coating layer.
In addition, the type of the constituent material of the base material is not particularly limited, and examples thereof include one or a combination of two or more of resin materials, rubber materials, metal materials, ceramic materials, glass materials, and the like. be able to.

Moreover, it is preferable that the coating 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.
This is because the Young's modulus on the surface of the developing roller can be finely adjusted by the combination of the coating layer of the developing roller and the constituent resin of the base material, and further, a predetermined durability can be obtained. It is because it can do.
That is, in the coating layer of the developing roller, a desired Young's modulus value can be easily obtained simply by changing the type and addition ratio of an alcohol compound (diol compound or the like) or an isocyanate compound (diisocyanate compound or the like) as a urethane resin raw material. This is because urethane resin can provide excellent durability as a developing roller.
Examples of the rubber material other than the urethane resin constituting the base material include natural rubber material, butyl rubber material, silicone rubber material, acrylic rubber material, chloroprene rubber material, fluororubber material, thermoplastic elastomer, etc. A combination of the above is preferable.

Further, the hardness (JIS-A hardness) of the coating layer of the developing roller is set to a value in the range of 50 to 100 °, and the hardness of the base material (JIS-A hardness) is set to a value in the range of 20 to 70 °. It is preferable to do.
This is because the Young's modulus on the surface of the developing roller can be finely adjusted by the combination of the coating layer of the developing roller and the hardness of the substrate, and further, a predetermined durability can be obtained. This is because it can.
That is, when the hardness of the coating layer of the developing roller becomes a value of less than 50 °, there is a case where the choice of the constituent material of the coating layer is excessively limited.
Further, when the hardness of the coating layer of the developing roller becomes a value exceeding 100 °, the shearing force becomes difficult to work at the nip, and riblets may be generated.
Moreover, it is because when the hardness of the base material of the developing roller is less than 20 °, the mechanical strength may be lowered and breakage may be easily caused.
In addition, when the hardness of the base material of the developing roller exceeds 70 °, it is difficult for the liquid to pass through, and the liquid can be accumulated, which may cause image defects.
Therefore, it is more preferable to set the hardness of the coating layer of the developing roller to a value within the range of 50 to 100 ° and the hardness of the substrate to a value within the range of 20 to 70 °. More preferably, the hardness is set to a value within the range of 60 to 100 °, and the hardness of the base material is set to a value within the range of 25 to 60 °.

Moreover, it is preferable to make the thickness of a coating layer into the value within the range of 0.01-50 mm.
This is because when the thickness of the coating layer is less than 0.01 mm, the spread width at the nip portion between the developing roller and the photosensitive member becomes small, and sufficient shearing force may not be obtained. is there.
On the other hand, when the thickness of the coating layer exceeds 50 mm, it may be difficult to form the coating layer uniformly.
Therefore, the thickness of the coating layer is preferably set to a value within the range of 1 to 20 mm, and more preferably set to a value within the range of 2 to 10 mm.

Further, as shown in FIG. 5B, a conductive resin layer 12c is preferably formed on the surface of the developing roller 12 ′. That is, in the case of the developing roller 12 ′ shown in FIG. 5B, the developing roller 12 ′ is configured to include the covering layer 12a and the base material 12b, and further, the conductive resin layer 12c is formed on the covering layer 12a. This is the configuration.
The reason for this is that, when configured in this way, the liquid developer between the developing roller and the photosensitive member is more electrically drained, and the occurrence of the riblet phenomenon is prevented over a long period of time. This is because image characteristics can be obtained stably.

Moreover, when providing a conductive resin layer, it is preferable to make the thickness into the value within the range of 5-50 micrometers.
This is because the mechanical strength may decrease when the thickness of the conductive resin layer is less than 5 μm.
On the other hand, when the thickness of the conductive resin layer exceeds 50 μm, the coat layer may become non-uniform.
Therefore, the thickness of the conductive resin layer provided on the coating layer of the developing roller is preferably set to a value in the range of 5 to 50 μm, and is preferably set to a value in the range of 10 to 30 μm.

Further, when the conductive resin layer is provided, it is preferable to mix a predetermined amount of conductive material with a resin such as fluororesin or urethane rubber as a constituent material.
This is because such a constituent material can control physical properties such as hardness, Young's modulus, rebound resilience, and wettability.

Further, the diameter (Ddr) of the developing roller constituting a part of the liquid developing device is not particularly limited, but it is usually preferable to set the value within a range of 10 to 280 mm.
This is because when the diameter (Ddr) of the developing roller is less than 10 mm, the shearing force generated between the developing roller and the photosensitive member increases, resulting in poor toner releasability and low image density. It is because there is a case to do.
On the other hand, if the diameter (Ddr) of the developing roller exceeds 280 mm, the shearing force generated between the developing roller is excessively small and it may be difficult to prevent the occurrence of the riblet phenomenon over a long period of time. Because.
Therefore, the diameter (Ddr) of the developing roller is more preferably set to a value within the range of 15 to 180 mm, and further preferably set to a value within the range of 20 to 50 mm.

(4) Relational Expression Further, it is preferable that the relational expression of (Dpc−Ddr)> 0 is satisfied when the diameter of the photoconductor is Dpc and the diameter of the developing roller is Ddr.
The reason for this is that by taking into consideration the diameter (Dpc) of the photoconductor and the diameter (Ddr) of the developing roller, shearing is performed so that the liquid developer runs out well between the developing roller and the photoconductor. This is to generate force.
That is, the high shearing force prevents the occurrence of the riblet phenomenon over a long period of time, and excellent image characteristics can be stably obtained.

However, in order to more effectively prevent the occurrence of the riblet phenomenon, it is more preferable that the relational expression (Dpc−Ddr)> 10 mm is satisfied, and it is more preferable that the relational expression (Dpc−Ddr)> 20 mm is satisfied.
On the other hand, considering that the size of the wet image forming apparatus does not become excessively large, it is preferable that the relational expression (Dpc−Ddr) <100 mm is satisfied, and it is more preferable that the relational expression (Dpc−Ddr) <80 mm is satisfied. It is preferable that the relational expression (Dpc−Ddr) <50 mm is satisfied.

[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, around a base material made of a urethane rubber material and having a base material hardness of 30 °, a Young's modulus is 25.6 MPa and a diameter is 20 mm from a diol compound and a diisocyanate compound. The developing roller in Example 1 was obtained by laminating a urethane resin coating layer having a thickness of 2 mm using a mold.
In order to finely adjust the Young's modulus of the coating layer, a predetermined amount of a fluorine compound (PFA) was added to the urethane resin, or a predetermined coating agent was applied to the surface of the urethane resin.

(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 A printing experiment (50% area ratio dot diagram, A4 paper, 300,000 continuous printing) was performed using the obtained wet image forming apparatus.
Next, as shown in the flow of the measurement method in FIG. 6, the difference between the density peak and the density average value in the obtained image was measured, and riblet evaluation was performed based on the obtained value. Three 10 mm square patch images with a 50% area ratio were formed on A4 size paper (transverse paper).
That is, each of the obtained patch images was photographed at a magnification of 100 times, and an arbitrary five points in the patch (one place is a range of 250 × 50 pixels) were averaged and peaked using image analysis software (Image J, free software). The value was determined, the peak value and the average value at five locations were determined for each patch image, and the average of the peak value and the average value at three locations in the patch image was determined to calculate the riblet value.
○: The density difference is less than 20.
Δ: Density difference is less than 20-25.
X: The density difference is 25 or more.

[Example 2]
In Example 2, a developing roller having a coating layer having a Young's modulus of 25.6 MPa made of urethane was used around a base material made of a urethane rubber material and having a base material hardness of 50 °. Otherwise, a wet image forming apparatus was prepared and evaluated in the same manner as in Example 1.

[Example 3]
In Example 3, a wet image forming apparatus was prepared and evaluated in the same manner as in Example 1 except that a developing roller having a Young's modulus of the coating layer of 31.9 MPa was used.

[Example 4]
In Example 4, a wet image forming apparatus was prepared and evaluated in the same manner as in Example 1 except that a developing roller having a Young's modulus of a coating layer of 19.6 MPa was used.

[Comparative Example 1]
In Comparative Example 1, a wet image forming apparatus was prepared and evaluated in the same manner as in Example 1 except that a developing roller having a Young's modulus of the coating layer of 56.1 MPa was used.

[Comparative Example 2]
In Comparative Example 2, a developing roller having a base material having a base material hardness of 25 ° and a coating layer having a Young's modulus of 300 MPa made of a fluororesin was used around the base material having a base material hardness of 25 °. Otherwise, a wet image forming apparatus was prepared and evaluated in the same manner as in Example 1.

[Comparative Example 3]
In Comparative Example 3, a developing roller provided with a coating layer having a Young's modulus of 300 MPa made of a fluororesin was used around a base material made of a silicone rubber material and having a base material hardness of 50 °. Otherwise, a wet image forming apparatus was prepared and evaluated in the same manner as in Example 1.

According to the wet image forming apparatus and the wet image forming method of the present invention, by limiting the Young's modulus on the surface of the developing roller to a predetermined range, the liquid developer runs out between the developing roller and the photoconductor. A predetermined shear force can be generated as much as possible.
Therefore, the occurrence of riblet phenomenon and fogging can be prevented over a long period of time, and excellent image characteristics can be stably obtained.
Therefore, the wet image forming apparatus of the present invention can be suitably applied as 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. (A)-(b) is a figure provided in order to demonstrate the mechanism and liquid cutting property which a shearing force generate | occur | produces between a photoconductor and a developing roller. 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. (A)-(b) is a figure provided in order to demonstrate the modification of a developing roller. (A)-(d) is a figure provided in order to demonstrate the evaluation procedure of a riblet phenomenon. (A)-(c) is a figure provided in order to demonstrate a riblet phenomenon. (A)-(b) 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)
12a: Covering layer (surface layer)
12b: substrate 12c: conductive resin layer 13: anilox roller 14: pumping roller 15: doctor blade 17: charging device 18: liquid developing device 18a: recovered 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: Photoconductor 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 the Young's modulus on the surface of the developing roller is set to a value in the range of 8 to 50 MPa.   2. The wet method according to claim 1, wherein the developing roller includes a coating layer and a base material, and the Young's modulus of the coating layer is set to a value in the range of 8 to 50 MPa. Image forming apparatus.   The coating 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 hardness (JIS-A hardness) of the coating layer of the developing roller is set to a value in the range of 50 to 100 °, and the hardness (JIS-A hardness) of the base material is set to a value in the range of 30 to 100 °. The wet image forming apparatus according to claim 2, wherein the wet image forming apparatus is an image forming apparatus.   The wet image forming apparatus according to claim 1, wherein the viscosity of the insulating liquid is set to a value within a range of 15 to 300 mPa · sec (measurement temperature: 25 ° C.). 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 Young's modulus of at least a surface within a range of 8 to 50 MPa.

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