JP2002278292A - Wet type electrophotographic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wet type electrophotographic device speedily forming meniscus of liquid developer at the start of driving of a developing roll. SOLUTION: In the device, a great quantity of liquid developer 43 is carried by rotating a developing roll 42 at a higher speed than in a normal image formation when the developing roll 42 is started and the meniscus of the liquid developer is speedily formed in between a latent image carrier 1 and a developing roll 42.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wet electrophotographic apparatus.

[0002]

2. Description of the Related Art A wet electrophotographic apparatus using a liquid developer can use extremely fine toner particles of a submicron size, so that high image quality comparable to offset printing can be realized, and a small amount of toner particles can provide a sufficient image. It has advantages that cannot be realized with a dry-type electrophotographic recording apparatus, such as the ability to reduce the copy cost because of obtaining the density, and the ability to fix the toner particles on the recording paper at a relatively low temperature to achieve energy saving. (For example, JP-A-11-249444).

FIG. 11 is a partial sectional view showing the vicinity of a developing roller of a wet electrophotographic apparatus using a liquid developer.

In a wet electrophotographic apparatus, a liquid developer 120 composed of a carrier liquid and toner particles dispersed in the carrier liquid is used. By rotating 110, the liquid developer is continuously supplied to the photosensitive drum 100.

In the vicinity of the developing roller 110 and the photosensitive drum (latent image holding member) 100, the meniscus 1 having a certain width A due to the surface tension of the two rollers.
Reference numeral 21 is formed uniformly in the axial direction of both rollers (the direction perpendicular to the plane of FIG. 11), and development of the electrostatic latent image is mainly performed in the range of the width A.

This meniscus is not formed in the initial state where the developing roller is stopped, and it takes a time from the start of rotation of the developing roller to the uniform formation in the axial direction of both rollers. During this time, it is necessary to rotate the latent image holding member at a predetermined potential, so that there is a problem that the time from the rotation of the latent image holding member to the start of image formation becomes long.

On the other hand, since the meniscus once formed exists relatively stably, the meniscus may continue to exist between the developing roller and the photosensitive drum even after the both are stopped. If this meniscus is left after the image forming process is completed and the photosensitive drum is stopped, the carrier liquid will eventually evaporate, and the toner particles will adhere to the place where the meniscus of the photosensitive drum was present, and in the subsequent image forming process, There is a problem that the obtained image quality is reduced.

[0008]

As described above, in the conventional wet-type electrophotographic apparatus, it takes a long time from the rotation of the latent image holding member to the start of image formation, or the developing roller and the photosensitive drum are not used. There has been a problem that the toner particles adhere to the latent image holding member due to the meniscus of the liquid developer existing between the two after the stop.

The present invention has been made in view of such a problem, and a wet electrophotography capable of shortening the time from the start of image formation after the rotation of the latent image holding member to the formation of a meniscus and, consequently, the wet electrophotography. An object of the present invention is to provide a wet electrophotographic apparatus in which contamination of the apparatus or the latent image holding member is reduced.

[0010]

According to the wet electrophotographic apparatus of the present invention, an electrostatic latent image is formed on a surface, and a latent image holder for moving the surface in a predetermined direction, and a liquid developer is rotated to rotate the developer. The developing roller that supplies the latent image holding member to the surface of the latent image holding member and develops the electrostatic latent image formed on the latent image holding member with the liquid developer, and the developing roller before the start of the development performs the development. A developing roller control unit that rotates at a higher speed than the developing roller at the time.

When the potential supplied to the developing roller is Vb and the charged potential of an image portion in the electrostatic latent image on the surface of the latent image holding member is V1, the latent image on which the electrostatic latent image is formed It is preferable to have a charge amount control unit that controls the charging potential V2 of the surface region of the latent image holding member upstream of the holding member surface region in the predetermined direction so as to satisfy Expression (1).

| Vb−V2 | − | Vb−V1 |> 0 (1) In the wet electrophotographic apparatus of the present invention, an electrostatic latent image is formed on the surface, and the latent image holder moves the surface in a predetermined direction. A latent image holder control unit that moves the surface of the latent image holder at a first speed and then moves at a second speed higher than the first moving speed; A charging device for charging the surface of the moving latent image carrier, an exposure device for selectively exposing the charged surface of the latent image carrier according to image information, and a liquid developer for the exposed latent image carrier Supply,
A developing roller for developing the electrostatic latent image with the liquid developer.

An electrostatic latent image is formed on the surface, and a latent image holding member for moving the surface in a predetermined direction, and a liquid developer is supplied to the surface of the latent image holding member by rotating the latent image holding member. A developing roller for developing the electrostatic latent image formed in the liquid developer, a transfer device for transferring an image obtained by developing the electrostatic latent image from the latent image holding member, and A latent image holding member control unit that stops the latent image holding member after the transfer, and the rotation of the developing roller for at least a certain period of time between the end of the development and the stop of the latent image holding member. And a developing roller control section for rotating in the reverse direction.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment A first embodiment of the present invention will be described below with reference to the drawings. Here, a case will be described in which a liquid developer containing positively charged toner particles is used and a reversal developing method is adopted.

FIG. 1 is a schematic sectional view showing an example of the wet electrophotographic apparatus of the present invention.

The latent image holding member 1 has a metal roller such as aluminum as a support, and a surface of the support roller
It is possible to use a photosensitive drum on which a photosensitive material made of amorphous silicon having a thickness of μm is formed.
A protective layer having a thickness of not more than m can be formed. It is also possible to use a photosensitive belt having a belt-shaped support, and the photosensitive material is not limited to an inorganic material such as amorphous silicon, but may be an organic photosensitive material having solvent resistance. It is. During the image forming process, the surface of the latent image holding member 1 is moved by rotating in the direction of the arrow at a constant speed.

A latent image holding unit control unit 11 is connected to the latent image holding unit 1, and a known rotation speed control means such as changing a drive voltage is used to hold the latent image at a predetermined timing using a computer or the like. The rotation speed of the body 1 can be controlled.

Around the latent image holding member 1, a charging device 2, an exposing device 3, a developing device 4, a squeezing device 5, a carrier liquid collecting device 6, and
A carrier liquid drying device 7, a transfer device 8, and a cleaning device 11 are provided, and latent image formation, development,
The steps of carrier liquid removal, transfer, and cleaning are sequentially performed to complete a series of image forming processes.

<Latent Image Formation> An electrostatic latent image composed of an unexposed portion (a region with a large amount of charge) and an exposed portion (a region with a small amount of charge) is formed on the surface of the charged latent image carrier. That is, the latent image holder 1 uniformly charged to the potential V1 by the charging device 2 is selectively exposed by the exposure device 3 in accordance with image information, and only the exposed portion has the potential V0 (0 ≦ V0 <V
Attenuate to 1).

The charging device 2 is connected to a charging controller 21 for controlling the amount of charge on the surface of the latent image holding member 1. The exposure device 3 can control the amount of light emitted from the exposure device. The exposure control unit 31 is connected as described above.

As the charging device 2, a known charger such as a scorotron charger, a corotron charger, and a corona charger can be used. For example, in the case of a scorotron charger, a voltage of about 6000 V is applied to the wire of the charger, and the surface potential V1 of the latent image holding member is set to 600 V to 800 V.
It should be about the degree.

The charging control section 21 changes the charging amount of the surface of the latent image holding member 1 by the charging device 2 at a predetermined timing. For example, a known charging method such as controlling a voltage value applied to a wire of a scorotron charger is used. The quantity control means may be started at a predetermined timing by a computer. The timing at which the amount of charge on the surface of the latent image holding member 1 is changed will be described in a second embodiment described later.

The exposure device 3 uses, for example, a laser optical device, and scans the surface of the latent image holding member 1 with laser light.
It is also possible to use a solid head that does not involve scanning of light, such as an LED head. For example, the light amount of the irradiation light from the exposure apparatus is a charging potential V of about 600 to 800V.
It is sufficient that the surface of the latent image holding member 1 having 1 can be attenuated to a potential V0 of about 50 to 550 V.

The exposure control section 31 changes the amount of light emitted from the exposure apparatus at a predetermined timing to attenuate the potential of the exposure section on the surface of the latent image holding member 1 to a potential lower than V0. And a known light amount control means,
It is started at a predetermined timing by a computer or the like to control the light amount. This timing control will be described in a third embodiment described later. This computer can be used in combination with the computer used for the above-mentioned charging control unit.

<Development> The electrostatic latent image formed on the surface of the latent image holding member 1 is developed by the developing device 4. The developing device 4 has a developing roller 42 to which a potential Vb (V0 <Vb <V1) is applied in a developing device 41, and rotates the developing roller 42 in the rotation direction opposite to the latent image holding member 1 (the surface at the opposing position). The liquid developer 4 in the developing device 41 is rotated in the same direction as the moving direction.
3 is conveyed and supplied to the surface of the latent image holding member 1.

In the gap between the developing roller 42 and the latent image holding member 1, a meniscus of the liquid developer 43 having a predetermined width is formed as shown in FIG. The image is developed (hereinafter, the area where the meniscus is formed during the development step is referred to as a development area).

That is, the liquid developer 43 contains an insulating and non-polar carrier liquid and toner particles (here, positively charged toner particles) dispersed in the carrier liquid. The toner particles are electrophoresed according to the electric field formed by the developing roller and the developing roller. Specifically, in the region of the surface potential V0 (0 ≦ V0 <Vb) of the latent image holding member 1, the positively charged toner particles move in a direction from the developing roller 42 toward the latent image holding member 1, and In the region where the surface potential is V1 (0 ≦ Vb <V1), the positively charged toner particles move in the direction from the latent image holding member 1 to the developing roller. As a result, the area of the surface potential V1 (unexposed portion in the reversal development) becomes a non-image portion where toner particles do not adhere, and the area of the surface potential V0 (the exposed portion in the reversal development) becomes an image portion where the toner particles adhere. An image corresponding to the latent image is developed.

As described above, an insulating and non-polar liquid is used as the carrier liquid, for example, a petroleum-based liquid such as Isopar L (manufactured by Exxon Chemical Company).

As the toner particles, a mixture of a colorant and a resin having good dispersibility in a carrier liquid is usually used.
Further, since the toner particles are held in the carrier liquid, the particle diameter can be reduced, and usually 0.1 μm to 2 μm.
By using a material having a size of about μm, it is possible to improve the quality of an obtained image and to eliminate the need for fixing to paper or the like. For example, a liquid developer as described in JP-B-5-87825 can be used.

The developing roller 42 is moved relative to the latent image
For example, they are closely arranged with a gap of about 20 to 300 μm. Further, the potential Vb is applied to the developing roller as described above.
(V0 <Vb <V1), for example, when V1 is 600
When V-800V and V0 are about 50V-550V, Vb may be set to about 400V-600V.

The surface speed of the developing roller 42 during development slightly varies depending on the viscosity of the liquid developer used.
Usually, it is rotated so as to be about 0.1 m / s to 0.35 m / s. The surface speed of the developing roller 42 is 0.35 m / s
If the speed is faster than that, the viscosity of the liquid developer increases and there is a risk of disturbing the image, or the supply amount of the liquid developer increases, so that toner particles adhere to non-image portions (unexposed portions in reverse development). There is fear. If the surface speed of the developing roller 42 is lower than 0.1 m / s, the width of the meniscus becomes small, so that the time during which the liquid developer is used for development is shortened, and a sufficient amount of toner particles adhere to the image area. It becomes difficult to make it.

The developing container 42 stores the liquid developer 43 so as to be in contact with the developing roller 42, functions as a supply source of the liquid developer to the latent image holding member 1, and furthermore, the liquid developer 43 used for development. It also functions as a collection container.

The developing roller 42 includes the developing roller 4
The developing roller controller 44 for controlling the rotation speed of the developing roller 2 is connected, and changes the rotation speed of the developing roller at a predetermined timing. For example, the rotation speed of the developing roller 42 may be controlled by using a rotation speed control unit that changes the driving voltage of the developing roller 42 and controlling the rotation speed of the developing roller 42 at a predetermined timing by, for example, a computer. The timing for changing the rotation speed of the developing roller 42 will be described later with reference to FIG.

<Removal of Carrier Liquid> A carrier liquid is present on the surface of the developed latent image holding member 1 together with toner particles forming a visible image. This carrier liquid is removed from the surface of the latent image holding member by a squeeze device 5, a carrier liquid recovery device 6, or a carrier liquid drying device 7 as necessary.

The squeezing device 5 is formed of a conductive roller disposed in the vicinity of the latent image holding member 1 and rotates in the same direction as the latent image holding member 1 (the surface moves in the opposite direction at the facing position). ). When the thickness of the carrier liquid is larger than the gap between the conductive roller and the latent image holding member 1, a part of the carrier liquid is scraped off the surface of the latent image holding member 1 by the squeezing device. By applying a potential Vs between the image portion potential and the non-image portion potential of the electrostatic latent image to the conductive roller, the toner liquid formed on the surface of the latent image holding member 1 can be disturbed without disturbing the carrier liquid. Can be removed.

The carrier liquid recovery device 6 is a cylinder made of an elastic porous material such as a sponge, and is arranged in contact with the latent image holding member. The carrier liquid on the surface of the latent image holding member 1 is absorbed by the absorptivity of the porous body, and the carrier liquid is recovered by depressurizing the inside of the cylinder. This method of collecting a carrier liquid is suitable for collecting a small amount of a carrier liquid. It is preferable that a potential higher than the ionization of at least the unexposed portion of the electrostatic latent image is supplied to the cylinder.

The carrier liquid drying device 7 is a device for drying the carrier liquid on the surface of the latent image holding member 1. For example, a blower for blowing air to the surface of the latent image holding member 1, a heater, or the like can be used. This method is suitable for removing a small amount of carrier liquid.

<Transfer> The toner image developed by the developing device 4 is transferred to a recording medium such as the paper 10 by the transfer device 8.

In FIG. 1, the intermediate transfer member 80 and the pressure member 90 are pressed by a transfer device including an intermediate transfer member 80 pressed against the latent image holding member 1 and a pressing member 90 pressed against the intermediate transfer member 80. Paper 10 supplied to a pressure contact portion with body 90
The secondary transfer is performed. The intermediate transfer member 80 has a heater 8 inside.
3 is provided with an elastic layer 82 of silicone rubber or the like on the surface of a metal roller 81 provided with the roller 3. The primary transfer from the latent image holding member 1 to the intermediate transfer member 80 is possible by utilizing the adhesive force of the toner image. I have to. Further, the pressure member 90 is also formed of a metal roller having a heater 92 inside, and similarly transfers a toner image to the sheet 10 supplied from the intermediate transfer member 80 using the adhesive force of the toner. Regarding the transfer method, a method of directly transferring from the surface of the latent image holding member to the paper without using the intermediate transfer member may be adopted, and other than the transfer method using the adhesive force of the toner image, An electric field transfer method using electrostatic force (including electrophoresis) of toner particles may be adopted.

When a color image is formed, a visible image of a plurality of colors may be stacked on the surface of the latent image holding member 1 and then collectively transferred to the intermediate transfer medium 80 or the paper 10.
The visible image formed on the surface of the latent image holding member 1 can be transferred to the intermediate transfer medium 80 or the paper 10 for each color.

<Cleaning> The toner image formed on the surface of the latent image holding member 1 is preferably transferred to a 100% recording medium, but some toner particles remain on the surface of the latent image holding member 1 without being transferred. May be. If the remaining toner particles are left as they are, they may be mixed into an image formed in the next image forming process or adhere to the surface of the latent image holding member 1 to adversely affect the subsequent image forming process. is there.

Therefore, after the transfer is completed and before the next image forming process is started, the cleaning device 12 removes toner particles (liquid developer in some cases) remaining on the surface of the latent image holding member 1. For example, a belt-shaped web wound on the roller surface may be continuously supplied to wipe off the toner particles.

Thus, a series of image forming steps is completed. Further, the latent image holding member 1 is supplied to the next image forming step. If necessary, a known static eliminator (not shown) such as a static elimination lamp is disposed between the cleaning device 12 and the charging device 2. Can also.

In the first embodiment of the present invention, as described above, the rotation speed of the developing roller 42 is changed at a predetermined timing by the developing roller control unit 44 that changes the rotation speed of the developing roller 42 at a predetermined timing. It is characterized by:

This timing control will be described with reference to FIG.

FIG. 2 is a diagram showing the drive timings of the charging device, the exposure device, and the developing roller at the start of development. The horizontal axis indicates the time axis, and the area charged by the charging device during the time T1 (hereinafter, referred to as the time period). , A spare area) is shown by a dotted line at the time of passing through the exposure position or the development area.

First, at the same time when the latent image holding member starts rotating and driving, the charging device is started (charging device ON), and the latent image holding member 1 starts to be charged uniformly. Charged latent image carrier 1
After T1 has passed through the exposure position by the exposure device, exposure by the exposure device is started (exposure device ON), and the formation of an electrostatic latent image is started.

The developing roller starts rotating within T1 from the time when the preliminary area reaches the developing area. At this time, the rotation speed of the developing roller is higher than the rotation speed during the image forming process, for example, 1.5 times the rotation speed during development.
Rotation is performed up to 3 times to form a meniscus uniformly in the direction of the rotation axis from the time when the electrostatic latent image reaches the development area to after T1. The rotation speed of the developing roller is changed to the rotation speed during the image forming process before the region where the electrostatic latent image is formed reaches the development region.

As described above, in the present invention, when the formation of the meniscus is completed while the preliminary area passes through the development area (during T1), the rotation speed of the development roller is higher than the rotation speed during development. By quickly forming the meniscus, the time T1 for forming the preliminary area can be reduced. As a result, the time from rotating the latent image holding member to performing the image forming process can be reduced.

Here, the reason why the meniscus formation speed is increased by increasing the rotation speed of the developing roller will be described.

This meniscus is not formed when the developing roller is stopped, but is formed by rotating the developing roller and transporting the liquid developer to the gap between the developing roller and the latent image holding member. This meniscus is not formed at the same time in the direction of the rotation axis of the developing roller, but is formed first in a part of the gap. By continuing the rotation of the developing roller, the meniscus spreads in the direction of the rotation axis, and finally has a uniform width. A meniscus is formed in the direction of the rotation axis. In the first embodiment, by increasing the rotation speed of the developing roller, the amount of the liquid developer supplied to the gap between the developing roller and the latent image holding member is increased.
The meniscus can be quickly spread in the rotation axis direction. For example, by increasing the rotation speed of the developing roller to about 2 to 3 times, the time for making the meniscus uniform can be reduced to 1/3.
It can be reduced to １ ／.

The supply of the potential Vb to the developing roller is as follows.
It is preferable to perform the process at the timing when the electrostatic latent image reaches the development area. If the potential Vb is supplied before that, the possibility that toner particles will adhere to the latent image holding member increases, which causes so-called ground fogging.

As in the first embodiment, when the rotation speed of the developing roller is increased, the amount of the liquid developer in the development region increases while the rotation speed is high. Is more likely to adhere.

The second embodiment of the present invention addresses such a problem. FIG. 3 shows the drive timings of the charging device, the exposure device, and the developing roller at the start of development in the second embodiment. The second embodiment will be described with reference to FIG.

As shown in FIG. 3, while the developing roller is rotating at a high speed, the surface of the latent image holding member (preliminary area) passing through the developing area is strongly charged by the charging device.
For example, the electrostatic latent image is charged to a potential V2 (0 <V0 <Vb <V1 <V2) which is 1.05 times or more the potential V1 of the non-image portion.

The electric field strength (||) formed between the developing roller and the latent image holding member in the strongly charged area as described above
V2−Vb | / d: where d is the distance between the developing roller and the latent image holding member) is stronger than the electric field (| V1−Vb | / d) between the developing roller and the non-image portion of the electrostatic latent image. Positively charged toner particles exert a stronger force to move to the developing roller side than when the latent image holding member surface potential is V1. As a result, it is possible to prevent toner particles from adhering to the latent image holding member 1.

On the other hand, for example, when toner particles are replaced with negatively chargeable toner particles and regular development is adopted, the latent image carrier 1 becomes higher as the latent image carrier surface potential becomes higher than the developing roller surface potential. The toner adheres to the surface.

The third embodiment of the present invention is intended to reduce the adhesion and contamination of toner particles to the latent image holding member by rotating the developing roller at a high speed when such regular development is employed. Things.

FIG. 4 shows the drive timing of the charging device, the exposure device, and the developing roller at the start of the development in the third embodiment, which will be described with reference to FIG.

As shown, the surface of the latent image carrier (the area charged during T1 in FIG. 4) passing through the developing area while the developing roller is rotating at a high speed is exposed by the exposure device. The amount of light irradiation is increased to further attenuate the amount of charge on the surface of the latent image holding member. That is, by setting the charge amount of the portion corresponding to the spare region in the first and second embodiments to be smaller than the exposed region of the electrostatic latent image (the region where the toner particles do not adhere), Adhesion of toner particles to corresponding portions can be reduced.

In order to achieve this, it is sufficient that the portion corresponding to the preliminary area is strongly exposed by an exposure device, and the timing of the electrostatic latent image is controlled by a computer using known exposure amount control means. Of the exposed portion (non-image portion), the charging potential V2 (0 <V2 <V1 <) of the portion corresponding to the spare area is compared with the charging potential V1 (0 <V1 <Vb <V0).
(Vb <V0) The charge amount is attenuated to a potential 0.95 times or less of the charge amount.

In the strongly exposed area, the electric field (| Vb−V2 | / d: d is the distance between the developing roller and the latent image holding member) formed between the developing roller and the latent image holding member Electric field (| Vb) formed between the non-image portion of the latent image carrier
−V1 | / d), and the force of moving the negatively charged toner particles toward the developing roller acts strongly, so that it is possible to prevent the toner particles from adhering to the latent image holding member 1.

That is, in the third and fourth embodiments, by setting | V2−Vb | − | V1−Vb |> 0, the spare area (the electrostatic latent image is formed The toner particles can be prevented from adhering to the region (the region on the upstream side in the rotation direction with respect to the rotated region).

Further, as shown in FIG. 4, during normal development, it is preferable to supply the developing roller with the developing potential Vb even while the developing roller is being rotated at a high speed. During the rotation of the developing roller at a high speed, a force to move the toner particles toward the developing roller acts, thereby making it possible to further reduce the contamination of the latent image holding member.

As a method of shortening the meniscus formation time of the liquid developer, in addition to increasing the rotation speed of the developing roller as described above, a method described in the following fourth embodiment can be adopted.

A fourth embodiment will be described.

FIG. 5 shows the drive timing of the charging device, the exposure device, the developing roller, and the latent image holding member at the start of development in the fourth embodiment.

The latent image holding member is rotated at a speed lower than the rotation speed at the start of the image forming process for a time T1 (latent image holding member ON). Increase to speed. This change in the rotation speed may be performed by, for example, the latent image holding unit control unit 11 shown in FIG.

At the same time as the latent image holder starts rotating, the charging device is started (charging device ON), and the latent image holder starts to be charged. The area charged during the time T1 is the first area.
Is a spare area in the embodiment.

After that, similarly to the first embodiment, after passing through the spare area, the exposure device is activated to form an electrostatic latent image, and after the spare area reaches the developing area, the rotation of the developing roller is started. . The developing roller may be rotated at a constant speed as shown in FIG. 5, or may be rotated at a high speed while the spare area passes through the developing area as in the first embodiment.

In the first embodiment, the rotational speed of the developing roller is increased to increase the amount of the liquid developer conveyed to the developing area, and the liquid developer is stored in the developing area in a short time to form a meniscus. Although the time was shortened, as in the fourth embodiment, by rotating the latent image holding member at a low speed, the amount of the liquid developer conveyed from the development area to the outside of the development area was reduced, thereby reducing the development area. The liquid developer can be stored in a short time in a short time, and the time for forming a meniscus can be shortened. Therefore, it is possible to shorten the time T1 for forming the spare area, and also to shorten the time from rotating the latent image holding member to completion of image formation.

It is preferable that the rotation speed of the latent image holding member that rotates at a low speed during T1 is set to about 0.7 to 0.3 times the rotation speed of the latent image holding member in the image forming process. If it is faster than 0.7 times, T1 cannot be sufficiently shortened, and if it is slower than 0.3 times, T1 can be further advanced. On the other hand, the rotation of the developing roller starts after the latent image holding member starts rotating. Therefore, the total time from rotation of the latent image holding member to completion of the image forming process cannot be reduced.

If the amount of charge by the charging device changes at two different speeds of the latent image holding member used here, the charging potential differs depending on the position on the latent image holding member when the above operation is applied. This is undesirable. In this case, the position on the latent image holding member at the time when the rotation speed of the latent image holding member is changed to the rotation speed during the image forming process may be set as the start point of image formation. Accordingly, the exposure start point may be changed from A to A 'as shown in FIG. 6, and the development start position also shifts from B to B'.

In the present embodiment, the speed of the latent image holding member is reduced from the start of rotation. The object of the invention can be achieved. Therefore,
As shown in FIG. 6, when the latent image holding member is rotated at a high speed until the leading end of the preliminary area reaches the developing position, and then rotated at a low speed only until a meniscus is formed in the developing area, the entire operation is completed. Time can be reduced.
In FIG. 6, the initial rotation speed of the latent image holding member is the same as the speed at the time of the image forming process. However, it is not always necessary, and the operation speed can be further increased to further shorten the operation time. When the speed is increased, the charge amount of the latent image holding member may decrease. In such a case, the charge amount may be adjusted by a charging device.

After the above-described image forming process is completed,
When the meniscus of the liquid developer formed between the latent image holding member and the developing roller remains, the concentration of the toner particle component in the meniscus increases due to volatilization of the carrier liquid component, and the surface of the latent image holding member There is a possibility that the toner particles adhere to a part of the toner and deteriorate the developing characteristics in the next and subsequent times.

The fifth embodiment is for solving such a problem, and the fifth embodiment will be described below with reference to FIG.

FIG. 7 is a diagram showing drive control of the developing roller and the electrostatic latent image holder after the development of the electrostatic latent image by the developing roller is completed.

In the latent image holding member on which the electrostatic latent image has been developed by the developing roller, at least the developed area reaches the transfer position (in FIG. 1, the opposing portion of the intermediate transfer medium and the latent image holding member). Meanwhile, as shown in FIG. 7, the rotation is continued at a constant speed and then stopped. On the other hand, the developing roller, which has been rotating at a constant speed, once reversely rotates and stops after the development of the electrostatic latent image is completed and before the latent image holding member is stopped.

After the development is completed, the liquid developer forming the meniscus is conveyed downstream from the developing area in the rotational direction by rotating the latent image holding member. On the other hand, during the developing process, as a result of the liquid developer being supplied by the developing roller, an excess liquid developer reservoir is formed on the upstream side of the meniscus in the developing roller rotation direction, and the amount of the liquid developer is reduced on the downstream side in the rotation direction. The amount is larger than the liquid developer amount. In the fifth embodiment, a large amount of liquid developer can be quickly removed from the development area regardless of the width between the development roller and the latent image holding member by rotating the development roller in the reverse direction after the development is completed. As a result, the meniscus can be more reliably eliminated.

The timing of stopping the latent image holding member is controlled, for example, by the latent image holding member control section 11 shown in FIG. Just do it.

When the developing roller is rotated in the reverse direction,
When the reverse rotation time is controlled so that the rotation angle from the start of the reverse rotation is 45 ° to 135 °, the rotation speed is −0.5 to −3 times the rotation speed of the developing roller during development. It is preferable that If the rotation speed is higher than -0.5 times (small as an absolute value), the removal speed of the liquid developer in the development area decreases. It is difficult to make the rotation speed smaller than -3 times (increase the absolute value) when performing reverse rotation in a short time. Rotation angle is 45
If it is smaller than °, the liquid developer cannot be sufficiently removed from the development area. If the angle is larger than 135 °, the transport amount of the liquid developer to the developing area due to the reverse rotation increases.
Therefore, when the rotation angle is set to be larger than 135 °, it is preferable that the rotation speed of the developing roller be set to be larger than -0.5 times.

FIG. 8 shows a modification of the developing device.
As shown in FIG. 8, the transport prevention member 63 is brought into contact with the developing roller 62 from a portion facing the latent image holding member 61 to a downstream side in a rotation direction (direction indicated by an arrow in the drawing) of the developing roller 62 during development. This arrangement can prevent the supply of the liquid developer 64 to the developing area A when the developing roller 62 is rotated in the reverse direction. Therefore, by setting the rotation angle of the developing roller to be larger than 135 ° and setting the rotation speed to be smaller than -0.5 times, the liquid developer 64 in the developing area A can be more reliably removed. .

As described above, after completion of the development, the latent image holding member continues to rotate until at least the developed area is transported to the transfer position, and the liquid developer transported from the development area is further cleaned by the cleaning device. It is desirable to stop the rotation after continuing the rotation until it is collected.
In this way, by waiting for the next image forming process in a state where the developer does not exist on the surface of the latent image holding member, it is possible to prevent toner particles from adhering to the latent image holding member during the waiting period.

Further, the wet electrophotographic apparatus of the present invention is not limited to the formation of a single color image, but can be applied to the case of forming a color image of a plurality of colors.

FIG. 9 is a diagram showing an example of a wet electrophotographic apparatus for forming a plurality of color images.

In this wet electrophotographic apparatus, the substrate 1
44, a plurality of developing devices 104a to 104d, an intermediate transfer medium 180, and a pressure roller 190.
Is a structure in which the intermediate transfer roller 181 and the latent image holding member 101 can be separated from each other, and the cleaner 112 is a movable structure. 1 is different from that shown in FIG.

Further, liquid developers of different colors are used for the respective developing devices 104a to 104d.
4a uses a yellow liquid developer, the developing device 104b uses a magenta liquid developer, the developing device 104c uses a cyan liquid developer, and the developing device 104d uses a black liquid developer.

First, the intermediate transfer medium 180 and the cleaning device 112 are separated from the latent image holding member 101.

In this state, a latent image forming process for a yellow image is performed on the latent image holding member 101 using the charging device 102 and the exposing device 103, and a developing process is performed using the developing device 104a. The carrier liquid is formed on the image holding member 101, and a carrier liquid removing step is performed using a squeezing device 105, a carrier liquid collecting device 106, and a carrier liquid drying device 107. Further, the developing devices 104a to 104a
In the configuration of 04d, similarly to the developing device shown in FIG. 1, a developing device 141 and a developing roller 142 each storing a liquid developer of a predetermined color are provided.

After the yellow developing step by the developing device 104b is completed, the gas 144 is moved in parallel to move the developing roller 104b to the position of the developing roller 104a shown in FIG. 9 to switch the developing device. In this state, the magenta image latent image forming, developing, and carrier liquid collecting steps are performed, and the magenta toner image is superimposed on the yellow toner image.

Similarly, after the magenta developing process is completed, the developing roller 1 is moved to the position of the developing device 104a shown in FIG.
04c is moved to form a cyan toner image, and after the magenta developing process is completed, the developing device 104a
Is moved to the position to form a black toner image, so that the four color toner images are superimposed on the latent image holding member, and the full color toner image is transferred to the latent image holding member 10.
Formed on one surface.

The latent image forming step, the developing step, and the carrier liquid removing step may be performed in the same manner as in the description of the wet electrophotographic apparatus shown in FIG. 1, and the description is omitted here.

The full-color toner image is transferred to the latent image carrier 10
After being formed on the intermediate transfer medium 1,
80 is pressed against the latent image holding member 101, and then the full-color toner image is transferred to the latent image holding member 1 as described with reference to FIG.
01 to the intermediate transfer medium 180, and further from the intermediate transfer medium 180 to the sheet 101.

Further, after the full-color toner image is formed, the cleaning device 112 is brought into contact with the latent image holding member 101 to remove the transfer residual toner after transferring the full-color toner image to the intermediate transfer medium.

When the wet electrophotographic apparatus of the present invention is used for a color image, a full-color toner image is formed on the surface of the latent image carrier 1 and the full-color toner image is collectively transferred from the latent image carrier to the transfer medium. In addition to the transfer method, it is also possible to transfer a single-color toner image formed on the surface of the latent image holding member 1 to a transfer medium (for example, an intermediate transfer medium), and to superimpose the toner images of each color on the transfer medium. .

In any case, in the process of forming such a color image, when the meniscus is not instantaneously eliminated when the developing device is switched, unnecessary toner remains on the latent image holding member. , May adversely affect image formation of the next color. In order to solve this, as shown in FIG. 10, the timing of the movement of the developing devices 104a to 104d and the timing of reversing the rotation direction of the developing roller is controlled. First, when the developing operation by the developing device 104a ends, the developing roller 1041 mounted on the developing device 104a
As in the fifth embodiment, a rotates reversely for a specific period, and instantaneously eliminates the meniscus. After the disappearance of the meniscus is completed, the developing station is moved to prepare for the next developing operation. Similarly, the operation timings of the developing roller and the developing station for three colors are adjusted as shown in FIG. By moving the developing station after the meniscus disappears, toner contamination of the latent image holding member can be prevented, and the image formation of the next color is not adversely affected.

[0097]

As described above, according to the present invention, it is possible to shorten the time from the start of rotation of the latent image holding member to the start of image formation. Alternatively, it is possible to reduce contamination of the latent image holding member caused by the meniscus.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of a wet electrophotographic apparatus according to the present invention.

FIG. 2 is a diagram illustrating driving timings of a charging device, an exposure device, and a developing roller at the start of development according to the first embodiment.

FIG. 3 is a diagram illustrating driving timings of a charging device, an exposure device, and a developing roller at the start of development according to a second embodiment.

FIG. 4 is a diagram illustrating drive timings of a charging device, an exposure device, and a developing roller at the start of development according to a third embodiment.

FIG. 5 is a diagram illustrating drive timings of a charging device, an exposure device, a developing roller, and a latent image holding member at the start of development according to a fourth embodiment.

FIG. 6 is a diagram illustrating a modification of the drive timing of the charging device, the exposure device, the developing roller, and the latent image holding member at the start of development according to the fourth embodiment.

FIG. 7 is a diagram illustrating drive timings of a latent image holding member and a developing roller at the end of development according to a fifth embodiment.

FIG. 8 is a diagram illustrating a modified example of the developing roller.

FIG. 9 is a view showing a modification of the wet electrophotographic apparatus of the present invention.

10 is a diagram showing rotation of a developing roller and movement timing of the developing device in the electrophotographic apparatus shown in FIG.

FIG. 11 is a partial cross-sectional view near a developing electrode of a wet electrophotographic apparatus using a liquid developer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 100 ... Latent image holder 11 ... Latent image holder controller 2 ... Charging device 21 ... Charging controller 3 ... Exposure device 31 ... Exposure controller 4 ... Developing device 41 ... Developing device 42, 110 ... Developing roller 43 Reference Signs List 120 liquid developer 44 developing roller controller 8 transfer device 10 paper 12 cleaning device 121 meniscus

 ──────────────────────────────────────────────────続 き Continuing on the front page F term (reference) 2H027 DA02 DA17 DA39 DE07 DE10 EA01 EC06 ED02 ED08 EE02 EE03 EE04 EE07 EF06 EF12 EF13 2H074 AA03 BB43 BB54 BB72 CC01 CC28 CC33 CC34 EE07 2H200 FA16 GA23 GA25 GB25 GA43 GB32 HA12 HA29 HA30 HB03 HB32 HB48 JA05 NA02 PA05 PA10 PB04

Claims (4)

[Claims] An electrostatic latent image is formed on a surface of the latent image holding member for moving the surface in a predetermined direction, and a liquid developer is supplied to the surface of the latent image holding member by rotating the latent image holding member. A developing roller that develops the electrostatic latent image formed on the holding member with the liquid developer; and a developing roller that rotates the developing roller before the start of the development at a higher speed than the developing roller when the development is performed. A wet electrophotographic apparatus, comprising: a control unit. 2. The method according to claim 1, wherein the potential supplied to the developing roller is Vb, and the charging potential of an image portion in the electrostatic latent image on the surface of the latent image holding member is V1. 3. A charge amount control unit for controlling a charge potential V2 of the surface region of the latent image carrier upstream of the surface direction of the latent image carrier with respect to the predetermined direction so as to satisfy Expression (1). 2. The wet electrophotographic apparatus according to 1. | Vb−V2 | − | Vb−V1 |> 0 (1) 3. An electrostatic latent image is formed on a surface of the latent image holding member for moving the surface in a predetermined direction, and the first latent image holding member is moved after moving the surface of the latent image holding member at a first speed. A latent image holder control unit that moves at a second speed higher than the moving speed, a charging device that charges the surface of the latent image holder that moves at the second speed, and a charged surface of the latent image holder An exposure device that selectively exposes the latent image holding member according to image information, and a developing roller that supplies a liquid developer to the exposed latent image holding member and develops the electrostatic latent image with the liquid developer. A wet electrophotographic apparatus characterized by the above-mentioned. 4. An electrostatic latent image is formed on a surface of the latent image holding member for moving the surface in a predetermined direction, and a liquid developer is supplied to the surface of the latent image holding member by rotating the latent image holding member. A developing roller for developing the electrostatic latent image formed on the holding member with the liquid developer; a transfer device for transferring an image obtained by developing the electrostatic latent image from the latent image holding member; A latent image holding unit control unit that stops the latent image holding unit after transferring an image, and that the developing roller rotates the developing roller for at least a certain period of time after the development is completed until the latent image holding unit stops. And a developing roller control unit for rotating the developing roller control unit in a direction opposite to the above.