JP6187068B2 - Wet development apparatus and wet image forming apparatus - Google Patents

Description

  The present invention relates to a printer, a copier, a facsimile machine, and other electrophotographic image forming apparatuses, and more particularly to a wet developing apparatus and a wet image forming apparatus that employ wet development as a developing system.

  In a wet electrophotographic system in which development is performed by externally charging toner particles dispersed in an insulating carrier liquid, the toner particles are charged on a supply member and electrostatically transferred to the surface of the developer carrier. A wet developing apparatus and a wet image forming apparatus are disclosed in, for example, Japanese Patent Laid-Open No. 2008-299065 (Patent Document 1).

  According to the wet developing apparatus and the wet image forming apparatus, the toner particles are charged on the supply member, and the toner particles are transferred to the developer carrier using the potential difference under the rotation of the width (rotation in the same direction). The conveyance amount is controlled by changing the rotation speed ratio between the supply member and the developer carrier.

JP 2008-299065 A

  In recent years, further improvement in image quality has been demanded in wet developing apparatuses and wet image forming apparatuses.

  The present invention has been made in view of the above problems, and an object thereof is to provide a wet developing apparatus and a wet image forming apparatus that can further improve image quality.

  The wet developing apparatus of the present invention is a wet developing apparatus that uses a wet developer in which toner particles are dispersed in a carrier liquid, and includes a developer carrier that develops an electrostatic latent image and the developer carrier. A supply member that rotates in the same direction at the contact portion and supplies the wet developer to the surface of the developer carrying member; a charge imparting device that charges the toner particles in the wet developer on the supply member; and Power supply means for providing a potential difference between the developer carrier and the supply member;

The resistivity per surface area [Ω · cm ² ] of the supply member is lower than the resistivity [Ω · cm ² ] per surface area of the developer carrier, and the surface roughness [Rz] of the supply member is the developer. It is larger than the surface roughness [Rz] of the support.

In another embodiment, the resistivity [Ω · cm ² ] per surface area of the supply member is less than 1 × 10 ⁶ , and the resistivity [Ω · cm ² ] per surface area of the developer carrier is 1 × 10 ^6. it is 1 × 10 ⁸ hereinafter more.

  In another embodiment, the surface roughness [Rz] of the supply member is greater than twice the average particle diameter [D50] of the toner particles and 20 μm or less, and the surface roughness [Rz] of the developer carrier is Or less than twice the average particle size [D50] of the toner particles.

In another embodiment, the developer carrier includes a conductive elastic layer and a coat layer provided on the surface of the conductive elastic layer, and has a resistivity [Ω · cm ² ] per surface area of the coat layer. The resistivity per surface area of the conductive elastic layer is higher than [Ω · cm ² ].

In another embodiment, the resistivity [Ω · cm ² ] per surface area of the coat layer is higher than the resistivity [Ω · cm ² ] per surface area of the supply member.

In another form, the supply member has an elastic layer on the surface.
In another embodiment, a thin layer forming member for forming a predetermined amount of developer thin layer on the supply member is further provided.

  The wet image forming apparatus of the present invention includes an image carrier, an image forming mechanism for forming an electrostatic latent image on the image carrier, and the electrostatic latent image formed on the image carrier by the image forming mechanism. A wet developing apparatus according to any one of the above, which develops an image.

  According to the present invention, it is possible to provide a wet developing apparatus and a wet image forming apparatus that can further improve image quality.

1 is a diagram illustrating an overall configuration of a wet image forming apparatus according to Embodiment 1. FIG. FIG. 10 is a diagram showing another form of the wet developing apparatus in the first embodiment. It is a figure which shows the form of the wet developing apparatus used when measuring the surface potential of a toner particle layer. FIG. 3 is a first diagram showing a relationship between time from charging and a toner layer surface potential (V). FIG. 3 is a second diagram showing the relationship between the time from charging and the toner layer surface potential (V). FIG. 10 is a transverse cross-sectional view illustrating configurations of a supply member and a developer carrier in Embodiment 2. FIG. 6 is a diagram schematically showing the position of an electric charge immediately after reaching a nip between a supply member and a developer carrier, and FIG. 5A shows a case where the conductive elastic layer of the developer carrier is only one layer; ) Has two conductive elastic layers (a first conductive elastic layer and a second conductive elastic layer (coat layer)), and the second conductive elastic layer on the surface layer side is the first on the base material side. The case where the resistivity [Ω · cm ² ] per surface area is higher than that of the conductive elastic layer is shown. (C) shows the resistivity of the conductive elastic layer of the supply member as compared with the second conductive elastic layer of the developer carrier. It is a figure which shows the case where it lowered | hung. It is a figure which shows the magnitude | size of the resistivity of (A), (B), (C) in FIG. 7 by a ratio. It is a figure which shows the image pattern containing two types of charts in an Example. It is a figure which shows the evaluation result of Comparative Example 1-9 and Example 1-7.

  Various wet image forming apparatuses using a wet electrophotographic system that performs high-quality printing on demand have been proposed. As one of them, there has been proposed a wet image forming apparatus configured to charge toner particles in a carrier liquid using an external charging device such as a corona charger.

  As another method, the material of the wet developer is selected so that the toner particles in the wet developer are always charged in charge transfer between the carrier liquid and no particular charge is applied during the process. Non-external charging type toner particle charging method may be mentioned. In a dry type image forming apparatus, a charging method of an electrophotographic developer that charges toner particles by frictional charging with carrier particles and members is also known.

  Advantages of a wet image forming device that charges toner particles using an external charging device include changes in the external environment, changes in durability, and paper type compared to other methods in which the basic charge amount is determined at the time of material selection. It is possible to easily change the charge of the toner particles to an optimum state according to the above.

  As means for forming a developer thin layer containing externally charged toner particles on the developer carrier, the following two methods are mainly used. As a first method, there is a method in which toner particles are charged on the developer carrier after non-electrostatic transfer of the wet developer from the supply member to the developer carrier.

  When the wet developer is transferred non-electrostatically, if the supply member and the developer carrying member are rotated in the same direction at the opposing portion, the liquid (at the nip outlet) when the wet developer passes through the opposing nip. In some cases, a uniform thin layer may not be formed on the developer carrying member due to the influence of disturbance of the wet developer.

  On the other hand, when the opposite portion is rotated in the opposite direction, the wet developer does not pass between the nips and the liquid is not disturbed, so that a uniform thin layer can be formed on the developer carrier. Therefore, in the first method, it is indispensable to rotate the supply member and the developer carrying member in opposite directions at the opposing portions.

  However, since the rotation is performed in the opposite direction at the facing portion, in the first method, the friction generated between the supply member and the developer carrying member becomes large, and there is a problem of an increase in torque and a reduction in member life.

  Next, as a second method, a method of electrostatically transferring the wet developer by providing a potential difference between the supply member and the developer carrier after charging the toner particles on the supply member will be described. When the wet developer is electrostatically transferred, the toner particles are not affected by the disturbance of the liquid at the nip outlet, even if the supply member and the developer carrying member are rotated in the same direction at the opposed portions. Electrotransfer. As a result, a uniform thin layer can be formed on the developer carrier. Further, the friction between the members can be suppressed by rotating in the same direction at the facing portion.

  In consideration of these, when the wet developer is transferred electrostatically, it is desirable to rotate the supply member and the developer carrying member in the same direction at the facing portion.

  Here, two requirements necessary for obtaining a uniform image in the method of forming a wet developer thin layer containing externally charged toner particles on the developer carrier will be described below.

  First, since the toner particles are forcibly charged from the outside, the charge amount of the toner particles attenuates with time. If the charge amount of the toner particles is excessively attenuated on the developer carrying member, the moving speed due to the electric field is lowered during development on the image carrying member. Disturbances are particularly noticeable in images with a weak electric field such as small-diameter dots. Therefore, in order to prevent excessive attenuation of the charge amount of the toner particles, the developer carrier needs to have a certain resistance value or more.

  When the wet developer is delivered from the supply member to the developer carrying member, if the surface roughness of the supply member is small, the surface area of the supply member is reduced, so that the amount of wet developer that can be held on the surface is reduced. Therefore, the thin layer unevenness of the wet developer tends to occur.

  Furthermore, it becomes difficult for the developer to be drawn into the facing portion between the supply member and the developing portion carrier, and the amount of the developer thin layer transferred onto the developer carrier is likely to decrease. Therefore, the supply member needs to have a surface roughness of a certain level or more according to the wet developer type.

  From such a background, in particular, in the method of electrostatically transferring the wet developer by providing a potential difference between the supply member and the developer carrying member after charging the toner particles on the supply member, Provided are a wet developing apparatus and a wet image forming apparatus for obtaining a uniform image at a desired image density by a measure unique to a system for transferring a developer. The outline will be described below.

  As described above, the supply member needs to have a certain surface roughness. On the other hand, since the toner particles are charged on the supply member, the remaining toner particles on the supply member that have passed through the portion facing the developer carrying member are charged. The charged residual toner particles are electrostatically attached to the surface of the supply member having a certain surface roughness. For this reason, the toner particles are likely to stay on the supply member without being replaced with new toner particles in the wet developer thin layer newly formed on the supply member.

  When the charged residual toner particles stay on the supply member, the amount of the wet developer thin layer on the supply member becomes non-uniform toner particles, and the uniformity of the developer thin layer transferred to the developer carrier is impaired. Therefore, it is necessary to achieve both the securing of the wet developer transfer amount to the developer carrier and the suppression of the accumulation of residual toner particles.

For this reason, the residual toner particles are replaced with new toner particles by lowering the resistance of the supply member having a surface roughness of a certain level or more to quickly attenuate the charge of the residual toner particles and weaken the electrostatic adhesion amount. Need to be promoted. As described above, as a result of considering the charge attenuation of the toner particles, the resistivity per surface area of the supply member [Ω · cm ² ] needs to be smaller than the resistivity per surface area of the developer carrier.

  Since the toner particles are electrostatically transferred from the supply member to the developer carrier, if the electric field between the supply member and the developer carrier is nonuniform, the wet developer thin layer on the developer carrier is not uniform. Become. Since the surface roughness of the supply member needs to be a certain level or more, if the resistance of the supply member is high, the electric field becomes non-uniform due to the surface roughness between the developer carrying member and the supply member.

  Even when the surface of the developer carrying member having high resistance is large, the electric field becomes non-uniform for the same reason. Further, in the case of the developer carrying member, if the surface roughness is large, the electric field is non-uniform even at the portion facing the image carrying member, and the dot image is disturbed. In addition, the thickness of the toner particle layer on the developer carrying member becomes non-uniform due to only the surface roughness regardless of the resistance of the developer carrying member, and the image uniformity decreases.

Therefore, in order to ensure the electric field uniformity of the supply unit and the development unit and the wet developer thin layer uniformity on the developer carrier, the resistance of the supply member having a surface roughness of a certain level or more is low, On the contrary, a developer carrier having high resistance needs to have a small surface roughness. In other words, as described above, the resistivity per surface area of the developer carrying member needs to be larger than the resistivity per surface area [Ω · cm ² ] of the supplying member, and the developer carrying is higher than the surface roughness [Rz] of the supplying member. It is necessary to reduce the surface roughness [Rz] of the body.

  Further, the supply member has an elastic layer as compared with the case where the surface is a rigid body, so that the supply efficiency can be increased because the nip width of the supply portion facing the developer carrier can be increased. Further, since the pressure contact force for securing the necessary nip width is also reduced, damage to the developer carrying member can be reduced.

Based on these requirements, in the present embodiment, the supply member and the developer carrier are rotated in the same direction at the opposing portion, and after charging the toner particles on the supply member, the supply member and the developer carrier are In the method of electrostatically transferring the developer by providing a potential difference therebetween, the supply member has an elastic layer on the surface, and the resistivity per surface area of the supply member [Ω · cm ² ] is the surface area of the developer carrier. By making the surface roughness [Rz] of the supply member smaller than the per-resistivity and larger than the surface roughness [Rz] of the developer carrier, it is possible to obtain a uniform image with a desired image density.

  In addition to the above-mentioned requirements, by increasing the electric field strength at the supply unit to reduce the amount of residual toner particles, the residual toner particles on the supply member can be further suppressed and the image density can be controlled more easily. A more uniform image can be obtained.

  In order to increase the electric field strength at the supply unit, the developer carrying member has a multi-layer structure, and the surface is provided with a coat layer having a higher resistivity per surface area than the base material, so that the charge injected from the voltage application unit can be quickly absorbed. It can be moved to near the surface of the developer carrying member. As a result, the electric field strength of the supply unit can be increased to increase the supply efficiency, and the residual toner particles can be reduced, thereby making it easier to ensure the image density and further improving the image uniformity.

  In addition, by making the resistivity per surface area of the coat layer of the developer carrier higher than the resistivity per surface area of the supply member, the electric field strength of the supply part can be increased, so the above effect can be obtained more easily. To do.

Accordingly, the supply member and the developer carrying member are rotated in the same direction at the opposing portion, and after charging the toner particles on the supply member having the elastic layer on the surface, a potential difference is provided between the supply member and the developer carrying member to static In the method of electrically transferring the developer, by defining the relationship between the resistivity [Ω · cm ² ] and the surface roughness [Rz] per surface area of the supply member and developer carrier, it is uniform at a desired image density It is important to obtain a clear image.

  Hereinafter, a wet developing apparatus according to an embodiment and a wet image forming apparatus including the wet developing apparatus will be described with reference to the drawings. In each embodiment described below, when referring to the number, amount, and the like, the scope of the present invention is not necessarily limited to the number, amount, and the like unless otherwise specified. The same parts and corresponding parts are denoted by the same reference numerals, and redundant description may not be repeated.

(Embodiment 1: Example of overall configuration and operation of wet image forming apparatus 100)
A configuration example of a wet image forming apparatus 100 according to the present embodiment is shown in FIG. FIG. 1 is a diagram illustrating an overall configuration of a wet image forming apparatus according to an embodiment.

  The wet image forming apparatus 100 has an image carrier 1. The image carrier 1 rotates in the direction of arrow a in the figure. The image carrier 1 is charged to a uniform potential by the charging device 2. Thereafter, exposure is performed by the exposure device 3, the potential of the image portion is attenuated, and an electrostatic latent image is formed.

  The image carrier 1 on which the electrostatic latent image is formed is conveyed to a developing unit n1 that is a portion facing the developer carrier 4. In the developing unit n1, the wet developer 41 on the developer carrier 4 contacts the image carrier 1. The wet developer 41 includes toner particles having a colorant and a resin, and a dispersion medium (carrier liquid) for dispersing the toner particles. The toner particles on the developer carrier 4 are charged, and the toner particles move to the image carrier 1 side in the printing portion on the image carrier 1, and move to the developer carrier 4 side in the background portion.

  The toner particles developed on the image carrier 1 are conveyed to a transfer portion which is a portion facing the transfer roller 11 (rotated in the direction of arrow d in the figure). In the transfer portion, the transfer target (paper) 15 is conveyed in the direction of arrow e in the figure, and the toner particles on the image carrier 1 are transferred to the transfer target 15 by the voltage having the opposite polarity to the toner particles applied to the transfer roller 11. Is done. The transferred object 15 to which the toner particles are transferred is conveyed to a fixing unit (not shown), and the toner particle image is fixed.

  On the other hand, a cleaning unit 12 is provided on the image carrier 1 after passing through the transfer unit, and collects transfer residual toner particles and carrier liquid remaining after transfer. The image carrier 1 from which the toner particles and the carrier liquid have been collected is exposed by the eraser lamp 13 and the latent image potential is cancelled.

  Toner particles and carrier liquid that remain without being developed are also present on the developer carrier 4 after passing through the developing section. In order to remove them, a cleaning blade 16 may be provided.

  By repeating the above steps, images are sequentially printed on the transfer target 15. FIG. 1 shows a monochromatic wet image forming apparatus 100 having only one set of the image carrier 1 and the wet developing device 110. Four sets of these are prepared, and cyan (light blue), magenta (red purple), It is also possible to use a color image forming apparatus in which yellow (yellow) and black (black) images are formed and superimposed on the intermediate transfer member. In addition, the conventional electrophotographic process technologies can be combined with any configuration according to the purpose of the image forming apparatus.

(Developer composition)
The wet developer 41 used for development will be described. The wet developer 41 disperses colored toner particles at a high concentration in a carrier liquid as a solvent. Further, additives such as a dispersant and a charge control agent may be appropriately selected and added to the wet developer 41.

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

  Any toner particles that are generally used in the wet developer 41 can be used without particular limitation. As the binder resin for toner particles, for example, thermoplastic resins such as polystyrene resin, styrene acrylic resin, acrylic resin, polyester resin, epoxy resin, polyamide resin, polyimide resin, and polyurethane resin can be used. It is also possible to use a mixture of a plurality of these resins.

  Commercially available pigments and dyes used for coloring the toner particles can also be used. The volume average particle diameter of the toner particles is suitably in the range of 0.1 μm or more and 5 μm or less. When the average particle diameter of the toner particles 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 wet developer 41 can be prepared based on a commonly used technique. For example, the binder resin and the pigment are melt-kneaded using a pressure kneader, a roller mill or the like at a predetermined blending ratio and uniformly dispersed, and the obtained dispersion is finely pulverized by, for example, a jet mill. By classifying the obtained fine powder with, for example, an air classifier, colored toner particles having a desired particle diameter can be obtained. Thereafter, the obtained toner particles are mixed with an insulating liquid as a carrier liquid at a predetermined blending ratio. This mixture can be uniformly dispersed by a dispersing means such as a ball mill to obtain the wet developer 41.

  The ratio of the toner particles to the wet developer 41 is appropriately about 10% by mass to 50% by mass. When the amount is less than 10% by mass, the toner particles are liable to settle, and there is a problem in stability over time during long-term storage. Furthermore, 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, generating steam and causing environmental problems. When it exceeds 50% by mass, the viscosity of the wet developer 41 becomes too high, making it difficult to manufacture and handle.

  In this embodiment, 100 parts of a polyester resin and 15 parts of copper phthalocyanine are sufficiently mixed with a Henschel mixer (registered trademark), and then melt kneaded using a co-rotating twin-screw extruder having a heating temperature in a roll of 100 ° C. The obtained mixture was cooled and coarsely pulverized to obtain coarsely pulverized toner particles. 75 parts of IPS2028 (manufactured by Idemitsu Kosan Co., Ltd.), 25 parts of coarsely pulverized toner particles, 0.8 part of V216 (manufactured by IPS) as a dispersant were mixed, and wet pulverized with a sand mill for 4 days to obtain a wet developer 41. . The particle size at that time was 2.0 μm. The particle size was measured with a laser diffraction particle size distribution analyzer (SALD-2200 (manufactured by Shimadzu Corporation)).

(Details of development process)
The operation of the development process will be described in detail. The wet developing device 110 includes a supply member 5 and a developer carrier 4. As the supply member 5 and the developer carrier 4, an elastic conductive roller is used in which an elastic layer is provided on a base material such as metal to give a certain conductivity.

  The wet developer 41 is stored in the developer tank 8. Part of the supply member 5 is immersed in the wet developer 41 and rotates in the direction of arrow C in the figure. The rotation causes the wet developer 41 to be pumped up and regulated to a constant film thickness by the thin layer forming member 7 provided in contact with the supply member 5. After the film thickness is regulated to a certain value, the toner particles in the wet developer 41 are charged by the charge applying device 6 such as a corotron charger and a charging roller.

  The wet developer 41 charged by the charge applying device 6 moves to a portion facing the developer carrier 4. The developer carrier 4 is in contact with the supply member 5 at the nip portion, and the surface of the developer carrier 4 rotates in the same direction as the surface of the supply member 5 (direction b in the drawing) at the same speed.

  An electric field is formed between the developer carrier 4 and the supply member 5 by the power source means 9 so that the toner particles are transferred to the developer carrier 4 side. The toner particles that have entered the nip portion move from the surface of the supply member 5 to the surface side of the developer carrier 4. The toner particle thin layer formed on the developer carrier 4 by the electric field is brought into contact with the image carrier 1 by the rotation of the developer carrier 4 to develop the electrostatic latent image on the image carrier 1.

  The wet developer 41 that is not used for development and remains on the developer carrier 4 is collected by the cleaning member 10. Since the wet developer collected by the cleaning member 10 has a toner particle concentration different from that of the original wet developer 41, the wet developer is collected in a tank (not shown) separate from the developer tank 8, and after adjusting the toner particle concentration, It is returned to the developer tank 8 again.

  FIG. 2 is a view showing another type of wet developing apparatus 110A. As shown in FIG. 2, instead of the thin layer forming member 7 that forms a predetermined amount of developer thin layer on the supply member 5, a roller-shaped application member 21 may be used as the thin layer forming member. Part of the coating member 21 is immersed in the wet developer 41 in the developer tank 8. The application member 21 is in contact with the supply member 5 with a constant force, and rotates in the direction of arrow d in the figure at the same linear velocity as the supply member 5.

  The wet developer pumped up by the rotation of the coating member 21 is regulated to a certain film thickness by the regulation blade 22 that is in contact with the coating member 21. Thereafter, the coating member 21 moves to a nip that faces the supply member 5, and transfers the wet developer 41 to the supply member 5. When an anilox roller having a minute concave portion on the surface is used as the application member 21, a wet developer amount corresponding to the volume of the concave portion can be applied by the regulating blade 22, so that a more accurate thin layer of wet developer can be formed on the supply member 5 Can be formed.

(Regarding the relationship between the resistance of each member and the charge decay of the toner particles on each member)
The relationship between the charge amount of the toner particles in the wet developer 41 charged by the charge applying device 6 and the image will be described. The charge amount of the toner particles charged by the charge applying device 6 decreases with time. The state of this phenomenon can be indirectly grasped by the surface potential of the toner particles measured with the supply member 5 or the metal substrate of the developer carrier 4 as a reference by grounding.

  FIG. 3 shows the configuration of the wet developing device 110B used when measuring the surface potential of the toner particle layer, and FIG. 4 shows the relationship between the time from charging and the toner layer surface potential (V). 3 shows how the surface potential of the toner particle layer changes with time by stopping the rotation of the supply member 5 or the developer carrier 4 after passing through the charge applying device 6 in the wet developing device 110A shown in FIG. Measure with an electrometer 19. As a result, as shown in FIG. 4, the process in which the toner particles charged by the charge applying device 6 lose their potential with time is observed as the attenuation of the surface potential.

  The degree of decrease in the charge amount of the toner particles charged by the charge applying device 6 depends on the characteristics of the toner particles to be used, but also changes depending on the resistance of the supply member 5 or the developer carrier 4. .

FIG. 5 shows the relationship between the time from charging and the toner layer surface potential (V). FIG. 5 shows the attenuation characteristics of the toner particle layer surface potential when the developer carrier 4 having different resistance is used. The resistance of the developer carrier 4 was 2.6 × 10 ⁶ Ω · cm ² , 3.2 × 10 ⁷ Ω · cm ² , and 3.1 × 10 ⁸ Ω · cm ² . For convenience, each developer carrier 4 is referred to as a resistance 6th power roller, a resistance 7th power roller, or a resistance 8th power roller. The resistance of each developer carrier 4 was measured by the method described later.

  As shown in FIG. 5, when the roller resistance changes, the charge decay characteristics of the toner particles change. If the resistance of the developer carrying member 4 is too low, the charge of the toner particles is excessively attenuated at the developing portion facing the image carrying member, and electrostatic transfer cannot be performed faithfully to the developing electric field. As a result, image disturbance occurs particularly in a latent image portion having a low electric field strength such as a dot portion.

  On the other hand, if the resistance of the developer carrier 4 is too high, sufficient charge is not injected into the surface of the developer carrier at the nip portion with the supply member 5 or the nip portion with the image carrier, and toner particle movement in the nip portion As the electric field is weakened, the supply efficiency or the development efficiency is lowered and the image quality is lowered.

In order to solve these problems, although the optimum range varies depending on the charge decay characteristics of the toner particles, the size of the wet developing device used, and the system speed, the resistivity per surface area of the developer carrier 4 is particularly 1 × 10. It is desirable to adjust so that it may be in the range of ⁶ to 1 × 10 ⁸ [Ω · cm ² ].

  On the other hand, if the resistance of the supply member is too high, the residual toner particles that have passed through the portion facing the developer carrying member are electrostatically attached to the surface of the supply member while maintaining a charge on the supply member. As will be described later, since the surface of the supply member 5 needs to have a predetermined ten-point average roughness [Rz], the residual toner particles are unevenly distributed corresponding to the roughness.

  However, if electrostatic adhesion does not work, when a new developer thin layer is formed by the thin layer forming member, the remaining toner particles are replaced with new toner particles, and the amount of transferred toner particles and the amount of residual toner particles And a constant amount of a uniform developer thin layer is formed on the developer carrier 4.

  However, if the residual toner particles retain electric charge and electrostatic adhesion acts, the replacement with new toner particles is inhibited, and the residual toner particles stay and accumulate in a state where the residual toner particles are unevenly distributed on the surface of the supply member 5. Will continue. As a result, the amount of the developer thin layer that is electrostatically transferred onto the developer carrying member 4 becomes non-uniform, and image unevenness particularly occurs in a solid (single-sided printing) image.

In order to solve this problem, although the optimum range varies depending on the charge decay characteristics of the toner particles, the size of the wet developing apparatus to be used, and the system speed, the resistivity per surface area of the supply member 5 is particularly less than 1 × 10 ^6. It is desirable to adjust so that.

(About the surface roughness of the supply member 5)
Next, the relationship between the surface roughness of the supply member 5 and the image will be described. Referring again to FIG. 1, in the case of the configuration of the wet developing device 110 shown in FIG. 1, a part of the supply member 5 is immersed in the wet developer 41 and rotates in the direction of the arrow C in the drawing to rotate the wet developer 41. Pump up.

  The amount of wet developer pumped up depends on the surface area of the supply member 5. When the supply member 5 having a smooth surface is used, the amount of pumping is reduced, the developer amount on the supply member 5 is insufficient, and a uniform thin layer cannot be formed, and / or wet development for obtaining a required image density. There is a case where the amount of the agent cannot be secured.

  In the nip portion facing the developer carrier 4, the amount of wet developer that can enter the nip as the supply member 5 rotates depends on the surface area of the supply member 5. The amount of wet developer that can enter the ink is reduced. As a result, the amount of wet developer transferred to the developer carrier 4 is reduced, and the necessary image density cannot be obtained.

  As in the case of the wet developing apparatus 110A configured as shown in FIG. 2, even when the application member 21 is separately provided, even if the amount of wet developer can be secured on the supply member 5, it is within the nip with the developer carrier 4. A sufficient amount of wet developer cannot penetrate and the same problem occurs. The penetration amount of the wet developer into the nip also depends on the peripheral speed of the supply member 5, and the penetration amount of the wet developer decreases as the speed decreases.

  In order to form a uniform developer thin layer on the supply member 5 regardless of the system speed and to obtain a necessary image density, the surface roughness [Rz] of the supply member 5 is determined by the average particle diameter [D50 of toner particles]. ] Is preferably larger than 2 times.

(Relationship between resistance and surface roughness of developer carrier 4 and supply member 5)
Since the toner particles are electrostatically transferred from the supply member 5 to the developer carrier 4, if the electric field between the supply member 5 and the developer carrier 4 is not uniform, the developer thin layer on the developer carrier 4 Becomes non-uniform. The surface roughness of the supply member 5 needs to be a certain level or more. However, if the surface roughness is too large, depending on the resistance of the supply member 5 and the developer carrier 4 opposed thereto, When the electric field is weakened due to the surface roughness and / or a portion where the toner particle moving distance is long occurs at the nip portion between them.

  In this case, particularly when the system speed is high or the nip width between the supply member 5 and the developer carrier 4 is small, sufficient nip passage time cannot be ensured. The developer cannot be transferred to the carrier 4, and the developer thin layer on the developer carrier 4 becomes non-uniform. From this viewpoint, the surface roughness [Rz] of the supply member 5 is desirably smaller than 20 μm. Even when the surface roughness of the developer carrier 4 having high resistance is large, the developer thin layer on the developer carrier 4 becomes non-uniform for the same reason.

  Further, in the case of the developer carrier 4, if the surface roughness is large, the electric field is nonuniform in the nip portion facing the image carrier 1. In particular, a dot image or the like is formed on the image carrier 1 in a planar direction. Since latent images having different electric field strengths are formed, the latent image is not faithfully developed even by slight electric field unevenness in the nip portion, and dot reproducibility is lowered. Since the thickness of the toner particle layer on the developer carrier 4 becomes non-uniform due to only the surface roughness regardless of the resistance of the developer carrier 4, the image uniformity is also lowered.

  As described above, the surface roughness of the developer carrying member 4 acts on the developing unit more directly than the supply member 5. Therefore, in order to ensure the electric field uniformity of the developing portion and the thin layer uniformity on the developer carrier 4, the surface roughness of the developer carrier 4 needs to be smaller than that of the supply member.

    In particular, if a sufficient nip passage time cannot be ensured because the system speed is high or the nip width between the developer carrier 4 and the image carrier 1 is small, the toner particles are not sufficiently developed in time, Dot reproducibility and image uniformity are reduced. From this viewpoint, it is desirable that the surface roughness [Rz] of the developer carrier 4 is not more than twice the average particle size [D50] of the toner particles.

(Configuration of supply member 5 and developer carrier 4 of the present embodiment)
From the above, in the present embodiment, in order to uniformly form a desired amount of developer thin layer on the developer carrier 4 and to make the electric field in the nip uniform in the developing portion, The developer carrier 4 is configured as follows.

That is, the resistivity [Ω · cm ² ] per surface area of the supply member 5 is made smaller than that of the developer carrier, and the 10-point average roughness [Rz] of the surface of the supply member is made larger than that of the surface of the developer carrier 4. With this configuration, it is possible to ensure the reproducibility of the required image density and dots and the uniformity of the image.

(Embodiment 2)
FIG. 6 shows specific configurations of the supply member 5 and the developer carrier 4. FIG. 6 is a cross-sectional view showing the configuration of the supply member 5 and the developer carrier 4. In the first embodiment, the supply member 5 and the developer carrier 4 are made of an elastic conductive roller provided with an elastic layer on a base material such as metal to give a certain conductivity. In this embodiment, in addition to the requirements of the first embodiment, the conductive elastic layer of the developer carrier 4 has a multilayer structure.

With reference to FIG. 6, the supply member 5 is provided with a conductive elastic layer 5b on the surface layer of a base material 5a such as metal. The developer carrying member 4 is provided with a conductive elastic layer having a multi-layer structure including a first conductive elastic layer 4b and a second conductive elastic layer (coat layer) 4c on a surface layer of a substrate 4a such as metal. Yes. Comparing the resistivity per surface area between the first conductive elastic layer 4b closer to the substrate 4a and the second conductive elastic layer (coat layer) 4c on the surface layer side, the surface area of the second conductive elastic layer 4c is larger. Per unit resistivity [Ω · cm ² ] is high.

  By setting it as said structure, the electric field strength of the nip part where the supply member 5 and the developer carrier 4 oppose can be enlarged in a short time. As a result, the supply efficiency from the supply member 5 to the developer carrier 4 is increased, and the residual toner particles are reduced, so that it is easier to ensure the image density and the image uniformity is further improved.

  The relationship between the electric field strength at the nip portion and the layer structure of the developer carrier 4 will be described. The electric field strength E at the nip portion where the supply member 5 and the developer carrier 4 face each other is determined by the position of the electric charges in the conductive elastic layer of the supply member 5 and the developer carrier 4.

  FIG. 7 schematically shows the position of the electric charge immediately after reaching the nip between the supply member 5 and the developer carrier 4. A charge amount corresponding to the potential difference is injected into the conductive elastic layer 5b and the first conductive elastic layer 4b from the supply member 5 and the base material 5a of the developer carrier 4 and the base material 4a. The position of each charge is determined by the resistances of the conductive elastic layer 5b and the first conductive elastic layer 4b, and the lower the resistance, the faster the surface moves.

FIG. 7A shows a case where the developer carrier 4 has only one conductive elastic layer, and FIG. 7B shows two conductive elastic layers (the first conductive elastic layer 4b and the second conductive layer). In this case, the resistivity [Ω · cm ² ] per surface area of the second conductive elastic layer 4c on the surface layer side is higher than that of the first conductive elastic layer 4b on the base material side. .

7A and 7B, when the resistivity [Ω · cm ² ] per surface area of the entire developer carrier 4 is equal, the resistivity of the conductive elastic layer 4b in FIG. Since the resistivity of the first conductive elastic layer 4b in FIG. 7B can be made smaller, the charge can move faster to the surface side in the case of FIG. As a result, the electric field strength at the nip portion is stronger in FIG. 7B than in FIG. 7A.

In addition to this configuration, when the resistivity [Ω · cm ² ] per surface area of the second conductive elastic layer 4 c on the surface layer side of the developer carrier 4 is higher than that of the conductive elastic layer 5 b of the supply member 5, it is further described above. The effect of increases. As an example, the case where the relationship of the resistivity per surface area of each conductive elastic layer corresponding to FIG. 7 is as shown in FIG. 8 will be described.

  FIG. 8 shows the ratio of the resistivity per surface area of each of the conductive elastic layers of the supply member 5 and the developer carrier 4 when the resistivity per surface area of the entire developer carrier 4 is 10. Is. As can be seen from FIG. 8, in FIG. 7B, although the resistivity per surface area of the entire developer carrier 4 is higher than that of the conductive elastic layer 5b of the supply member 5, the second conductivity of the developer carrier 4 close to the surface layer. The elastic elastic layer 4 c is lower than the conductive elastic layer 5 b of the supply member 5.

  Therefore, by lowering the resistivity of the conductive elastic layer 5b of the supply member 5 from that of the second conductive elastic layer 4c of the developer carrier 4 (the layer thickness is reduced in FIG. 7C), FIG. ), The position of the charge in the second conductive elastic layer 5b of the developer carrier 4 reaches the surface side of the supply member 5 earlier. For this reason, the relative positions of the electric charges in the conductive elastic layer of the supply member 5 and the developer carrier 4 are closer than in the case of FIG. 7C, and as a result, the electric field strength in the nip is increased more quickly. Can do.

  Examples of materials for forming the supply member 5 and the developer carrier 4 include the following. As a material of the base materials 4a and 5a, for example, a metal material such as aluminum, stainless steel, or iron, or an alloy thereof can be used.

  As the material of the conductive elastic layer 5b and the first conductive elastic layer 4b, rubber materials such as silicone rubber, urethane rubber, nitrile rubber, natural rubber and isoprene rubber, foaming of thermosetting resin such as polyurethane, epoxy resin, acrylic resin, etc. Examples thereof include foam materials such as rubber foams of thermoplastic resins such as polyethylene and polystyrene.

  The material of the second conductive elastic layer 4c includes polyester resin, polycarbonate resin, acrylic resin, polyethylene resin, polypropylene resin, urethane resin, polyamide resin, polyimide resin, porsulfone resin, polyether ketone resin, vinyl chloride resin, vinyl acetate. Resin materials such as resin, silicone resin, and fluororesin can also be used.

  As the filler used for imparting conductivity to each layer, carbon black such as kettin black, acetylene black and furnace black, metal powder, fine particles of metal oxide, etc., or a mixture thereof can be used.

  In this embodiment, the outer diameter (diameter) of the supply member 5 in the case shown in FIG. 7A is about 100 mm, and the thickness of the conductive elastic layer 5b is about 3 mm. The developer carrier 4 has an outer diameter (diameter) of about 100 mm, and the conductive elastic layer 4b has a thickness of about 3 mm.

  The outer diameter (diameter) of the developer carrier 4 in the case shown in FIG. 7B is about 100 mm, the thickness of the first conductive elastic layer 4b is about 3 mm, and the layer of the second conductive elastic layer 4c. The thickness is about 30 μm.

(Measurement method of resistivity per surface area)
The resistivity [Ω · cm ² ] per surface area of the supply member 5 and the developer carrier 4 was measured by the following method. The supply member 5 or developer carrier 4 was brought into contact with a flat metal plate with a weak force of about 0.4 N / cm ² to form a nip with the metal plate.

In this state, a voltage of V = 100 V was applied between the roller base (core metal) and the metal plate, and current I [A] was measured. Separately, the nip area S [cm ² ] between the metal plate was measured, and based on the following formula, a resistance value R of the following formula (1) was derived from the substrate per unit area of the roller surface.

Resistance value per unit area: R = [V / I] × S (Formula 1)
From this equation (1), the resistance value through the thickness direction per unit area, which is not influenced by the nip area and the thickness of the resistance layer of the roller, is derived. The calculated value of R was used as the resistivity [Ω · cm ² ] per surface area.

(Example)
In order to confirm the effect of the above embodiment, an experiment was performed under the following conditions. As the wet developer 41, the cyan developer having the average particle diameter of 2.0 μm described in the first embodiment was used. The peripheral speed of the supply member 5 and the developer carrier 4 was set to be constant.

  Each condition of member resistance (resistance value per unit area), member surface roughness, and peripheral speed of each example and each comparative example was set as shown in FIG. The surface roughness of the supply member 5 and the developer carrier 4 was a value obtained by measuring 10-point average roughness Rz (JIS B 0633: 2001) using a surface roughness meter manufactured by Mitutoyo Corporation.

  As an experimental procedure, the wet image forming apparatus 100 shown in FIG. 1 is used, and an image pattern including two types of charts shown in FIG. 9, 10% area ratio dot printing (P11) and solid (entire) printing (P12). P1 was output, and dot reproducibility and solid uniformity were visually confirmed, and pass / fail was determined according to the following criteria. For image density, solid printing ID measurement was performed using a spectral densitometer manufactured by X-rite, and pass / fail was determined based on the following criteria for target ID 1.5.

  The dot shape was evaluated as “A: shade in the dot is uniform”, “B: shade in the rotation direction (the tip is thin and the back end is dark)”, and “C: shape in the rotation direction is severely broken”.

  The solid uniformity was evaluated as “A: the whole is uniform”, “B: a portion is shaded”, and “C: the whole is shaded”.

  Regarding the deviation from the solid ID target value (target 1.5 3-point measurement), “AA: 1.48-1.52”, “A: 1.45-1.55”, “B: 1 point only 1” .45-1.55 out of range "and" C: all 3 points out of 1.45 to 1.55 range ".

The outer diameters of the supply member 5 and the developer carrier 4 are φ100. A corotron charger was used as the charge imparting device 6. Regarding the charge amount of the toner particles, the charge imparting device 6 has a charge amount according to the peripheral speed of the developer carrier 4 so that the surface potential of the toner particle layer at the position where the supply member 5 faces the developer carrier 4 is about 50V. The current was adjusted. The toner particle concentration of the wet developer 41 in the developer tank 8 was adjusted to 25%, and the transport amount of the wet developer 41 on the developer carrier 4 was adjusted to 6 g / m ² .

  The bias applied to the developer carrier 4 was 400 V, the non-image part potential of the image carrier (photoreceptor) 1 was 600 V, and the image part potential was 20 V. The bias applied to the supply member 5 was adjusted to be in the range of 500V to 800V so that the toner particle transfer amount to the developer carrier 4 was saturated.

(result)
The results of Comparative Examples 1-9 and Examples 1-7 are shown in FIG. Comparative Examples 1 to 3, 6, and 7 and Examples 1 to 3 in which the combination of the surface roughness of the supply member 5 and the developer carrier 4 are the same will be described. “SR” in FIG. 10 means the supply member 5, and “DR” means the developer carrier 4.

In Comparative Example 1, the resistivity per surface area of the supply member 5 and the developer carrier 4 is 1 × 10 ⁵ [Ω · cm ² ] (indicated as “5th power” in FIG. 10; the same applies hereinafter). Due to the resistance, the wet developer is transferred onto the developer carrier 4 with high efficiency at the supply nip portion, and the ID is easily adjusted. However, since the charge amount of the toner particles on the developer carrier 4 is excessively attenuated, the dot shape was evaluated as “C”.

In Comparative Example 2, the resistivity per surface area of the supply member 5 and the developer carrier 4 is 1 × 10 ⁶ [Ω · cm ² ], and the toner particles on the developer carrier 4 at a peripheral speed of 400 mm / s. The charge amount was attenuated and the dot shape was disturbed, and the evaluation was “C”.

  On the other hand, at a peripheral speed of 1000 mm / s, the charge of the residual toner particles was held on the supply member 5 and the solid uniformity due to the residual toner particle accumulation was lowered, and the evaluation was “C”. Thus, when the supply member 5 and the developer carrier 4 have the same resistance, it becomes difficult to satisfy both quality requirements required for an image.

In Comparative Example 3, the resistivity per surface area of the supply member 5 and the developer carrier 4 is relatively high at 1 × 10 ⁸ [Ω · cm ² ], and the supply member 5 even at a peripheral speed of 400 mm / s. The charge of the residual toner particles was maintained above, and the solid uniformity due to the residual toner particle accumulation was lowered, and the evaluation was “C”.

In Comparative Example 6, since the resistivity per surface area of the supply member 5 and the developer carrier 4 is relatively low resistance of 1 × 10 ⁵ [Ω · cm ² ] or less, the wet developer is highly efficient at the supply nip portion. It transfers on the developer carrier 4 and the solid part ID is easy to adjust. However, since the charge amount of the toner particles on the developer carrier 4 is excessively attenuated, the dot shape was evaluated as “C”.

In Comparative Example 7, since the resistivity per surface area of the supply member 5 and the developer carrier 4 is as high as 1 × 10 ⁵ [Ω · cm ² ] or more, the formation of an electric field is delayed in the supply nip portion, and the transition rate is reduced. As a result, the amount of the wet developer on the developer carrier 4 is reduced, and the solid part ID may be out of the target (evaluation is “C”). Since the charge amount of toner particles on the developer carrier 4 is excessively attenuated, the dot shape is evaluated as “C”. Further, since the resistance of the supply member 5 is high, the charge of the residual toner particles is held on the supply member 5 and the uniformity of the solid portion due to the accumulation of the residual toner particles is lowered, and the evaluation is “C”.

In Example 1, although the resistivity per surface area of the developer carrier 4 is 1 × 10 ⁶ [Ω · cm ² ], the resistivity per surface area of the supply member 5 is 1 × 10 ⁵ [Ω · cm ² ]. Therefore, the electric field strength is strong at the supply nip portion, and the wet developer 41 is transferred onto the developer carrier 4 with high efficiency to form a more uniform developer thin layer. As a result, the developing electric field becomes more uniform at the nip portion between the developer carrier 4 and the image carrier 1, and the toner particles are charge-damped on the developer carrier 4 when the peripheral speed is 400 mm / s. However, the influence on the dot shape was smaller than in Comparative Example 2.

  In Example 2, both the supply member 5 and the developer carrier 4 have the resistivities within the optimum range, and can achieve each quality requirement required for the image regardless of the peripheral speed.

In Example 3, the resistivity per surface area of the developer carrier 4 is 1 × 10 ⁹ [Ω · cm ² ], and the electric field formation is delayed at the nip portion with the supply member 5 when the peripheral speed is 1000 mm / s. In some cases, the transfer rate was decreased, the amount of the wet developer 41 on the developer carrier 5 was decreased, and the solid part ID was not within the target (evaluation “B”).

  Next, Comparative Examples 4 to 5 and Examples 4 to 6 in which the combinations of resistivity per surface area of the supply member 5 and the developer carrier 4 are the same will be described.

  In Comparative Example 4, since the developer carrier 4 has a large surface roughness, the electric field is non-uniform at both the nip portion with the supply member 5 and the nip portion with the image carrier 1, and the dot shape does not depend on the peripheral speed. Disturbance (evaluation "C") and solid uniformity degradation (evaluation "C") occurred.

  In Comparative Example 5, since the surface roughness of the supply member 5 is as small as that of the developer carrier 4, the amount of the wet developer 41 drawn up is insufficient, and the developer thin layer is not uniform on the supply member 5. A reduction in solid uniformity (evaluation “C”) and insufficient ID (evaluation “C”) occurred regardless of the peripheral speed.

  In Comparative Example 8, since the developer carrier 4 has a large surface roughness, the electric field is non-uniform in both the nip portion with the supply member 5 and the nip portion with the image carrier 1, and the dot shape does not depend on the peripheral speed. Disturbance and a decrease in the uniformity of the solid portion occurred, and the evaluation was “C”.

  In Comparative Example 9, since the surface roughness of the supply member 5 is small, the amount of the wet developer pumped up is insufficient, and the developer thin layer is not uniform on the supply member 5, and the solid portion is uniform regardless of the peripheral speed. Decreased (evaluation “C”) and insufficient ID (evaluation “C”). Because the surface roughness of the developer carrier 4 is large, the electric field is non-uniform in both the nip portion with the supply member 5 and the nip portion with the image carrier 1, and the dot shape is disturbed regardless of the peripheral speed. (Evaluation “C”).

  In Example 4, since the surface roughness of the developer carrier 4 is larger than twice the average particle size of the toner particles, electric field formation is delayed at the nip portion with the image carrier 1 when the peripheral speed is 1000 mm / s. The electric field became non-uniform, and the dot shape was affected (evaluation “B”).

  In Example 5, when the surface roughness of the supply member 5 is 20 μm, when the peripheral speed is 1000 mm / s, the electric field formation is delayed at the nip portion with the developer carrier 4 and the electric field becomes non-uniform. As a result, the developer thin layer on No. 4 was shaded and affected the uniformity of the solid portion (evaluation “B”).

  In Example 6, since the surface roughness of the supply member 5 is smaller than twice the average particle diameter of the toner particles, the amount of developer conveyed into the nip with the developer carrier at a peripheral speed of 400 mm / s is It decreased and the influence (evaluation "B") appeared on solid part ID.

  Example 7 has the same structure as in Example 2 described above, except that the conductive elastic layer of the developer carrier 4 has a two-layer structure. By adopting this configuration, the electric field formation is accelerated at the nip portion between the supply member 5 and the developer carrier 4, and the wet developer is transferred onto the developer carrier 4 with high efficiency. Can be adjusted to the target value more easily.

As described above, according to the wet developing apparatus and the wet image forming apparatus in the present embodiment, the resistivity per surface area of the supply member 5 [Ω · cm ² ] in consideration of the charge decay of the toner particles that are forcibly charged from the outside. Is less than the resistivity per surface area of the developer carrying member, thereby preventing residual toner particles from staying on the supply member and at the same time preventing excessive charge decay of the pre-development toner particles on the developer carrying member, A uniform image can be obtained.

Considering that the surface roughness of the supply member 5 needs to be a certain level or larger in order to hold the wet developer on the surface, the developer is supported by the resistivity per surface area of the supply member 5 [Ω · cm ² ]. Considering that the resistivity [Ω · cm ² ] per surface area of the body is large, the surface roughness [Rz] of the developer carrying member 4 is made smaller than the surface roughness [Rz] of the supply member 5 to supply Therefore, it is possible to ensure the uniformity of the electric field in the area and the development area and the uniformity of the thin layer on the developer carrier 4, so that a uniform image can be obtained with a desired image density.

  The developer carrier 4 has a multi-layer structure, and a coating layer having a higher resistivity per surface area than the base material and the supply member 5 is provided on the surface, so that the charge injected from the voltage application unit can be quickly transferred to the developer carrier 4. Since it is moved to the vicinity of the surface, the electric field strength of the supply unit can be increased and the supply efficiency can be increased. As a result, the supply residual toner particles are reduced, whereby the image density can be further easily adjusted, and the image uniformity is further improved.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. 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 Image carrier, 2 Charging device, 3 Exposure apparatus, 4 Developer carrier, 4a, 5a Base material, 4b 1st electroconductive elastic layer, 4c 2nd electroconductive elastic layer, 5 Supply member, 6 Charge provision apparatus, 7 Thin layer forming member, 8 Developer tank, 9 Power supply means, 10 Cleaning member, 11 Transfer roller, 12 Cleaning means, 13 Eraser lamp, 15 Transfer object, 16 Cleaning blade, 19 Surface potential meter, 21 Coating member, 22 Regulation blade, 41 Wet developer, 100 Wet image forming apparatus, 110, 110A, 110B Wet developing apparatus.

Claims (8)

A wet developing apparatus using a wet developer in which toner particles are dispersed in a carrier liquid,
A developer carrier for developing the electrostatic latent image;
A supply member that rotates in the same direction at a contact portion with the developer carrier and supplies the wet developer to the surface of the developer carrier;
A charge imparting device that charges the toner particles in the wet developer on the supply member;
Power supply means for providing a potential difference between the developer carrier and the supply member,
The resistivity [Ω · cm ² ] per surface area of the supply member is lower than the resistivity [Ω · cm ² ] per surface area of the developer carrier,
The wet developing apparatus, wherein the surface roughness [Rz] of the supply member is larger than the surface roughness [Rz] of the developer carrier. The resistivity per surface area of the supply member [Ω · cm ² ] is less than 1 × 10 ⁶ ,
The surface area per resistivity of the developer carrying member [Ω · cm ^2] is 1 × 10 ⁸ hereinafter 1 × 10 ⁶ or more, a wet developing device according to claim 1. The surface roughness [Rz] of the supply member is greater than twice the average particle diameter [D50] of the toner particles and 20 μm or less.
3. The wet developing apparatus according to claim 1, wherein a surface roughness [Rz] of the developer carrying member is not more than twice an average particle diameter [D50] of the toner particles. The developer carrier includes a conductive elastic layer and a coat layer provided on the surface of the conductive elastic layer,
The surface area per resistivity of the coat layer [Ω · cm ^2], the conductive elastic layer surface area per resistivity [Ω · cm ^2] is higher than, wet development according to any one of claims 1 3 apparatus. The surface area per resistivity of the coat layer [Ω · cm ^2] is higher than the surface area per resistivity of the supply member [Ω · cm ^2], a wet developing device according to claim 4.   The wet developing apparatus according to claim 1, wherein the supply member has an elastic layer on a surface thereof.   The wet developing apparatus according to any one of claims 1 to 6, further comprising a thin layer forming member that forms a predetermined amount of a developer thin layer on the supply member. An image carrier;
An image forming mechanism for forming an electrostatic latent image on the image carrier;
The wet developing apparatus according to any one of claims 1 to 7, wherein the electrostatic latent image formed on the image carrier by the image forming mechanism is developed.
A wet image forming apparatus.

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