JP2001092258A - Wet electrophotographic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilizes obtained image density by stably supplying liquid developer to a developing area. SOLUTION: By filling a space surrounded by a latent image-holding body 1, a developing roller 10 and a partition consisting of a developer supply part 11 with the liquid developer, not only the contact width between the liquid developer and the holding body can always be made constant, but also the obtained image density is made stable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art A wet type electrophotographic apparatus using a liquid developer has advantages which cannot be realized by a dry type electrophotographic apparatus, and its value is being reviewed in recent years. That is, in a wet electrophotographic apparatus, it is possible to use a very fine toner particle having a submicron size, so that high image quality can be realized. Further, since a sufficient image density can be obtained with a small amount of toner, printing is economical. The main advantages over the dry method are that printing can achieve the same level of texture and that toner can be fixed on paper at a relatively low temperature to save energy.

On the other hand, the conventional wet electrophotographic technique has some problems. One of the problems is that a high-resistance or insulating petroleum solvent for dispersing toner particles must be used as a carrier liquid as a developer for developing an electrostatic latent image. When a liquid developer using a carrier liquid is used, a mechanism for positively supplying the liquid developer to the photosensitive layer surface in the developing section is necessary in order to sufficiently adhere the liquid developer. At this time, if the supply speed of the liquid developer is too slow, the amount of toner carried to the image forming portion of the photosensitive layer is insufficient, so that color loss or insufficient contrast occurs. Further, if the supply speed is uneven, it causes unevenness in the density of the image, which causes a great inconsistency in the formation of a high quality image, which is the greatest advantage of the wet electrophotographic method.

FIG. 4 is an enlarged view of a developing section of a conventional wet electrophotographic apparatus.

A configuration is adopted in which the developing roller 30 is rotated to carry the liquid developer adhering to the surface to the developing section. The liquid developer is carried to a very small gap between the developing roller 30 and the photosensitive drum 31, and is supplied to the gap between the photosensitive drum 31 and the developing roller 30 to perform development. The lower portion of the developing roller 30 is immersed in the developer pool filled in the container, and the lower end thereof contacts a cleaning roller 32 for cleaning the toner attached to the developing roller during development. And serves to scrape off residues on the surface of the developing roller.

When the developing roller 30 rotates, the liquid developer adheres and is conveyed. The liquid developer transported to the very small gap between the photosensitive drum 31 and the developing roller 30 is transferred to both the photosensitive drum and the developing roller. A meniscus is formed in a minute area in contact, and the development phenomenon is performed in the meniscus. The larger the meniscus, the greater the amount of toner that can be involved in the development. Therefore, the density of the development can be easily obtained, and the gradation can be easily obtained. That is, development is performed favorably. The size of the meniscus is determined by the transport amount (thickness) of the developing solution carried to the surface of the developing roller 30 per unit time. Therefore, it is necessary to devise a method that does not change the transport speed of the developer. At the same time, it is important to maintain a large transport amount of the developer in order to increase the meniscus.

The transport amount of the developing solution is determined by the affinity of the surface of the developing roller 30 with the developing solution, the rotation speed of the developing roller 30, the contact width between the developing roller 30 and the liquid developer reservoir, that is, the level of the liquid developer with respect to the developing roller 30. It depends on the height of the building. Therefore, the developing roller 30 must rotate at a sufficient speed, and at the same time, the liquid level at which the developing roller 30 is immersed must be maintained at a predetermined position. On the other hand, the liquid developer is supplied to the pool by a circulating pump or the like. If the liquid surface is wavy, the contact width between the developing roller 30 and the developer changes, which affects the development density.

There is another problem in the method of dipping the developing roller 30 in such a liquid pool. For example, if an extremely small roller is used for the developing roller 30 in order to reduce the size of the apparatus, the effect of the error in the liquid level on the amount of adhesion to the surface of the developing roller 30 becomes extremely large, and the above-described control of the amount of adhesion becomes difficult. It is difficult to stabilize the liquid developer, and it is extremely difficult to stably supply the liquid developer. Another problem is that a relatively large amount of liquid developer must always be filled in the container.

[0009] There are other problems with the wet electrophotographic apparatus. The liquid developer is obtained by dispersing toner particles in a petroleum solvent as described above. This solvent evaporates relatively easily, and if it leaks out of the machine, odors and allergic effects on the human body pose problems. For this reason, in a wet developing mechanism, the exposure time of the developing solution to the air is minimized.
The liquid developer is supplied to the photosensitive drum only during development, and when not needed, the liquid developer is not supplied from the liquid developer pool, but is collected and stored in a tank to minimize the generation of solvent vapor. Is also necessary.

However, in the conventional wet electrophotographic apparatus, it is necessary to always stock a relatively large amount of liquid developer in the liquid developer pool in order to immediately carry out the development. The solvent evaporates relatively easily because it is exposed to water.
In particular, when trying to increase the diameter of the developing roller 30,
The opening area of the developer becomes extremely large, and the solvent is more likely to evaporate.

It is also conceivable to rotate the developing roller 30 at a very high speed to increase the filling amount of the developer. However, the fact that the developing roller 30 has a relatively high speed with respect to the photosensitive drum 31 does not necessarily have a good effect on the development result. For example, an image flows or blurs as the developing roller rotates.

In view of the above, there has been proposed another type of developing solution supply apparatus which is not of the type in which the roller is immersed in the developer pool.
For example, in US Pat. No. 5,585,900, there is one developing roller for four colors of liquid developer, and transfer is performed for each color. The supply of the liquid developer to the developing roller is performed directly on the roller surface by jetting from a plurality of nozzles arranged in the width direction of the developing roller. The ejected liquid developer adheres to the developing roller, is carried to the photosensitive drum, and is developed. This method makes it easy to control the amount of the developer carried in one development, and is less likely to cause uneven development density due to uneven amount of the developer. Further, since the required amount of the developing solution is jetted during the developing operation, there is an advantage that the amount of the solvent vapor generated from the liquid developer reservoir is reduced as compared with the above-described conventional example. However, this configuration requires a complicated liquid developer supply mechanism for uniformly ejecting the developing roller in the width direction, and the piping for that requires an extremely large volume. In particular, since the developing solution is supplied from the front side of the developing roller, the distance between the developing mechanisms must be increased in a structure in which a plurality of developing mechanisms are arranged in parallel. Attempting to reduce the size of the pipe itself results in a problem because the pipe diameter becomes small and the pipe is easily clogged. As a result, it is impossible to realize a small device such as a PPC with this mechanism.

[0013]

As described above, in a jet type wet electrophotographic apparatus having no liquid developer pool, there is a problem that the supply mechanism of the liquid developer becomes complicated, and the conventional liquid developer is disadvantageous. In the method using the pool, it is difficult to stabilize the shape of the meniscus obtained by supplying the liquid developer to the developing unit, so that the area where the development phenomenon occurs changes, and the resulting image density becomes stable. The problem of disappearing has arisen.

The present invention has been made in view of such a problem, and an object of the present invention is to provide a wet electrophotographic apparatus capable of obtaining a stable image density with a simple apparatus.

[0015]

SUMMARY OF THE INVENTION According to the present invention, there is provided a latent image holding member which forms an electrostatic latent image on a surface thereof, and moves the electrostatic latent image in a predetermined direction, and is arranged close to the latent image holding member. Developing means for holding a developing electrode on the surface of the roller,
A wet electrophotographic apparatus, comprising: a storage unit that is supplied to a gap between the latent image holding body and the developing unit and stores a liquid developer that develops the electrostatic latent image; wherein the storage unit includes at least the latent image holding unit; A liquid electrophotographic apparatus, wherein a liquid developer reservoir formed by a body and a part of the developing electrode is formed.

That is, in the conventional wet electrophotographic apparatus, since the liquid developer conveyed by the developing roller is conveyed to the gap between the latent image holding member and the developing electrode, the amount of the liquid developer conveyed Although the shape of the meniscus, that is, the width of the developing area was changed by the above, the reservoir according to the present invention is formed with a liquid developer reservoir in a state where the liquid developer is brought into contact with the latent image holding member in advance. Therefore, it is possible to reduce a change due to various conditions of the area of the development area.

Further, the storage section includes the latent image holding member,
It is preferable that the electrode is formed by the developing electrode and a partition wall provided in a region sandwiched between the latent image holding member and the developing electrode.

In order to prevent the liquid developer from volatilizing, when a system for collecting the liquid developer in the storage unit into a sub-tank or the like during non-development is employed, the storage unit must be newly filled with the liquid developer during development. With such a configuration, the volume of the storage unit can be reduced, so that the liquid developer can be quickly filled at the time of development.

That is, it is suitable for a wet electrophotographic apparatus for recovering the liquid developer in the storage section after the development step.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.

FIG. 1 is a schematic view of a wet electrophotographic apparatus according to the present invention.

The latent image holder 1 is a photosensitive drum having an organic or amorphous silicon photosensitive layer provided on a conductive substrate. This latent image carrier 1 is uniformly charged by a charger 2-1 such as a well-known corona charger or scorotron charger, and then is subjected to exposure 3-1 by an image-modulated laser beam to form an electrostatic latent on the surface. An image is formed.

Thereafter, a developing device 4- having a developing means comprising a storage section for storing the liquid developer and a developing roller.
The visualization of the electrostatic latent image is performed by 1.

The liquid developer has toner particles and a carrier liquid for dispersing the toner particles. As the carrier liquid, a non-polar solvent such as Isopar L (manufactured by DuPont) is used.

The developing roller may be constituted by a roller-shaped developing electrode disposed close to the latent image holding member, and a developing bias is applied to the developing roller. The liquid developer supplied to the gap between the electrostatic latent image and the developing roller electrically charges the toner particles according to the magnitude relationship between the developing bias and the surface potential of the electrostatic latent image formed on the surface of the latent image holding member. The electrostatic latent image is visualized by electrophoresis.

The developing means does not necessarily need to use roller-shaped electrodes. For example, a conductive belt serving as a developing electrode designated by a pair of roller bases may be used.

The visible image composed of the toner particles formed on the surface of the latent image holding member 1 may be directly transferred to a transfer step and transferred to a sheet by the transfer device 5. A second electrostatic latent image is formed by the second and second laser exposures 3-2, and a second developer of a different color from the liquid developer stored in the first developing device 4-1 is stored. Second developing device 4-
Develop this with 2. Therefore, after the second development, a visible image composed of toner particles of two colors is formed on the latent image holding member 1. Similarly, the third and fourth developments are performed, and a full-color visible image is formed on the latent image holding member 1.

The visible image is transferred to a sheet by a transfer device. In this case, the visible image may be transferred directly to the sheet.
As illustrated in FIG. 1, the image may be transferred to a recording medium such as a sheet 9 via the intermediate transfer medium 6. Transfer from the latent image carrier 1 to the intermediate transfer medium 6 and transfer from the intermediate transfer medium 6 to the paper 9
In the transfer to the substrate, either transfer by an electric field or transfer by pressure (pressure and heat as necessary) can be used. In general, many liquid developers can be fixed on paper at room temperature. However, fixing may be performed by heating the intermediate transfer medium 6 or a pressure roller 7 arranged by pressing the intermediate transfer roller 6. .

Further, the toner particles that have not been completely transferred by the transfer device 5 are removed by the cleaner 8, and the latent image holding member is subjected to the next image forming process.

The present invention is characterized in the developing device 4 in the wet electrophotographic apparatus shown in FIG. 1. FIG. 2 is an enlarged view of the developing device and will be described in more detail.

In FIG. 2, the developing device disposed around the latent image holding member 1 has a developing roller 10, a developer supply section 11, and a cleaning roller 12.

The developer supply section 11 also serves as a partition of the developer storage section, and the latent image holder 1 and the developing roller 1
0, the developer supply surface is brought close to the latent image holding member 1 and the developing roller, so that the developer supply portion 11
A region surrounded by the latent image holding member 1 and the developing roller 10 is a liquid developer storage portion, and the storage portion is filled with the liquid developer.

The latent image carrier 1 and the developing roller 10 are 50 μm
And 200 μm from each other, and move in the same direction at the facing portion.

The developing roller 10 is held rotatably in the direction of the arrow by a drive source (not shown), and the liquid developer filled in the storage portion is developed in a region in contact with the latent image holding member 1 and the developing roller 10. While being transported to the downstream side in the rotation direction by the rotation of the developing roller.

The amount of the liquid developer carried out of the storage unit by the rotation of the developing roller is supplied from a developer supply unit.
That is, the supply pipe 13 is connected to the developer supply unit 11, and the liquid developer adjusted to a predetermined concentration from the developer tank 15 is supplied to the storage unit through the supply pipe 13 through the developer supply unit 11. Is done.

The liquid developer is supplied from the developer tank 15 by a pump (not shown) or the like. The pump supplies the liquid developer to the developer supply unit 11 or the liquid remaining in the developer supply unit 11. It is also possible to collect the developer.

During standby after the development by the developing means, the liquid developer is collected from the storage section, and when the development is performed again, the storage section is filled with the liquid developer to prevent unnecessary evaporation of the liquid developer during standby. Can be prevented. According to the wet electrophotographic apparatus of the present invention, since the storage section can be a narrow space sandwiched between the latent image holding member 1 and the developing roller 10, the liquid developer is supplied to the storage section promptly. can do.

The liquid developer conveyed by the rotation of the developing roller 10 is scraped off from the surface of the developing roller 10 by the cleaning roller 12 and is collected in the developer container 14. A discharge hole for collecting excess liquid developer is provided in the lower part of the developing container 14, and the liquid developer is discharged to the developer tank through this discharge hole.

FIG. 3 is a view seen from the direction of arrow A in the drawing shown in FIG.

The developer supply section 11 has a plurality of supply pipes 13.
Is connected. Although the number of the pipes 13 may be increased, it has a drawback that the mechanism becomes complicated, and it is preferable to use as few pipes as possible. Developer supply unit 1
The width of the liquid developer supplied by 1 is wider than the development area, and stable and uniform development can be performed over the entire width of the development area. In this state, when the latent image holding member 1 and the developing roller 10 are rotated and the liquid developer is supplied from the developing solution supply section 11, the liquid developer becomes the latent image holding member 1, the developing roller 10,
It is filled in a pseudo triangular prism composed of three surfaces of the supply surface. When the supply is continued, a part of the liquid developer is
In the state of being attached to the surface of the developing roller 10, it is transported to the rear of the process through the small clearance between them, and a part of the material is dropped by the gravity from the clearance between the supply surface and the developing roller. Yes. However, if the amount of the liquid developer supplied per unit time is not too large, most of the liquid developer filled in the developing portion is carried to the rear of the process by the rotation of the developing roller 10 and the latent image holding member 1. . A developing operation is performed in the storage portion of the liquid developer, and a visible image is formed on the photosensitive drum.

The contact area of the storage section with the latent image holding member 1 is, for example, the area of the meniscus formed between the photosensitive drums by the liquid developer scraped up by the developing roller from the accumulation section shown in the conventional example. Much larger. Therefore, there is a sufficient number of toner particles to be used for development, and a sufficient development time can be obtained, which is extremely advantageous in obtaining image density and gradation.

A cleaning roller 1 is provided below the developing roller.
2 are in contact. The cleaning roller 12 has a surface layer formed of, for example, a soft rubber sponge.
It rotates at a relative speed to the developing roller 10 and scrapes off residual toner attached to the surface of the developing roller 10. After passing through the developing area, the liquid developer transported to and adhered to the roller also accumulates at the contact portion between the cleaning roller 12 and the developing roller 10. The scraped-off toner flows into this pool, passes along the surface of the cleaning roller 12, and is discharged from the lower portion of the developing container 14.

FIG. 4 shows a modification of the wet electrophotographic apparatus of the present invention.

In FIG. 4, a supply blade 16 for guiding a liquid developer to a developer supply section 11 is provided with a developing roller 10.
Is used so that the end is in contact with or close to the bus. With such a configuration, it is possible to reduce the gap between the partition and the developing roller and to prevent leakage of the liquid developer from the gap.

For example, the developing roller 10 of the supply blade 16
Is formed of an elastic body such as oil-resistant smooth urethane rubber or a thin PET (polyethylene terephthalate) plate, the supply blade 16 can be brought into contact with the developing roller 10 without damaging the surface. It is also expected that the supply blade 16 has a cleaning effect on the surface of the developing roller.

The developer supply section 11 and the supply blade 16
Is equivalent to at least the image forming portion on the developing roller 10,
Alternatively, it is arranged near the developing roller 10 with a width larger than that.

When the developing is performed by rotating the developing roller 10 in the direction shown in FIG. 2 in the same manner as in the wet electrophotographic apparatus shown in FIG. And a partition wall composed of a supply blade 16,
A space surrounded by the developing roller 10 and the latent image holding member 1 is filled.

In FIG. 4, the use of the supply blade 16 has an advantage that the contact area between the liquid developer and the latent image holding member 1 can be arbitrarily adjusted. For example, when a plurality of developing units have to be arranged on one circumference of one latent image holding member, the supply direction of the liquid developer has an inclination, but by providing such a guide, the leakage of the liquid in the direction of gravity can be achieved. Thus, the toner can be efficiently supplied to the developing unit.

As described above, according to the present invention, a necessary and sufficient amount of the liquid developer can be supplied to the developing portion of the wet electrophotographic apparatus in an easy and small configuration. Since the substantial amount of the liquid developer supplied to the developing unit becomes larger than before, the developed image quality is improved. In addition, the arrangement in the apparatus is easy, and there is no need to immerse the developing roller in the liquid developer. Therefore, a detection mechanism such as a detection of the liquid level of the liquid developer is not required. Unnecessary evaporation can be minimized.

[0050]

As described above, according to the present invention, it is possible to stabilize the density of an obtained image by keeping the contact area between the latent image holding member and the liquid developer constant.

Alternatively, since the volume of the storage section for storing the liquid developer can be reduced, a system for collecting the liquid developer from the storage section during non-development and supplying the liquid developer to the storage section during development can be provided. When employed, the reservoir can be quickly filled with the liquid developer.

[Brief description of the drawings]

FIG. 1 is a schematic view of a wet electrophotographic apparatus according to the present invention.

FIG. 2 is an enlarged view of a developing device used in the wet electrophotographic apparatus according to the present invention.

FIG. 3 is a plan view of the developing device shown in FIG. 2 as viewed from another direction.

FIG. 4 is a view showing a modification of the developing device used in the wet electrophotographic apparatus according to the present invention.

FIG. 5 is a schematic view of a developing device used in a conventional wet electrophotographic apparatus.

[Explanation of symbols]

 1, 31 ... Latent image holder 2 ... Charger 3 ... Exposure means 4 ... Developing device 5 ... Transfer device 6 ... Intermediate transfer medium 7 ... Pressurizing roller 8. ..Cleaner 9 ... Paper 10, 30 ... Developing roller 11 ... Developer supply unit 12,32 ... Cleaning roller 13 ... Supply pipe 14 ... Developer container 15 ... Developer tank 16 Supply blade

Claims (3)

[Claims] 1. A latent image holding member having an electrostatic latent image formed on a surface thereof, a developing device having a roller disposed close to the latent image holding member, and holding a developing electrode on the roller surface; A wet-type electrophotographic apparatus having a storage portion that is supplied to a gap between the latent image holding member and the developing unit and stores a liquid developer that develops the electrostatic latent image, wherein the storage portion includes at least the latent image holding member And a liquid developer reservoir formed by a part of the developing electrode. 2. The storage section is formed by the latent image holding member, the developing electrode, and a partition provided in a region sandwiched between the latent image holding member and the developing electrode. Item 6. A wet electrophotographic apparatus according to Item 1. 3. The wet electrophotographic apparatus according to claim 2, wherein the liquid developer in the storage section is recovered after the developing step.