JPH04238375A - Wet type developing device - Google Patents

Abstract

PURPOSE:To realize a wet type developing device which can carry out development with a small amount of developer while reducing the quantity of the developer required for the development, and which does not require an excess developer removing process after the development is completed. CONSTITUTION:The wet type developing device which develops an electrostatic latent image on an electrostatic latent image carrier with a wet type developer, has a developing roller 45 which carries the developer, elastically abuts on the electrostatic latent image carrier to supply the above-mentioned developer to the above-mentioned electrostatic latent image carrier, and is an electric conductor or has a thin exterminating layer on the most outside layer to obtain conductivity, and a developer coating part 40 which coats the developing roller 45 with the developer, as a characteristic.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] The present invention is used in recording devices such as electrophotographic copying machines and printers, and uses a wet type developer composed of charged particles dispersed in an insulating carrier liquid. The present invention relates to a wet developing device that visualizes an electrostatic latent image.

0002

[Prior Art] A conventional wet-type developing device is a system in which an electrostatic latent image carrier passes over a plate-shaped electrode containing developer to develop an image (Japanese Patent Publication No. 51466/1983, etc.) are known. In addition, a phenomenon roller made of a conductive material is placed close to the electrostatic latent image carrier through a small gap, and a developing roller is rotated at high speed to supply developer into the small gap to develop the image. There is a known method in which the

0003

[Problems to be Solved by the Invention] In the developing devices using these developing methods, the wet developer consists of a coloring agent (generally charged toner particles made of a pigment or resin), a carrier liquid, and other additives. A large amount of carrier liquid is required compared to the amount of colorant that will ultimately form the image. Therefore, in order to store a large amount of developer containing a large amount of carrier liquid, a large space is required, resulting in the problem that the entire image forming apparatus becomes large. In other words, the electrophoresis speed depends on the viscosity of the developer, so in order to obtain the required electrophoresis speed,
This is because it is necessary to keep the viscosity of the developer low, and for this purpose, it is necessary to disperse the charged toner particles in a large amount of carrier liquid to form a low-viscosity developer.

[0004] Further, at the end of development, excess developer adheres to the electrostatic latent image carrier, and in order to prevent background fog in non-image areas, a process for removing the excess developer is provided. There was a need.

The purpose of the present invention is to solve these problems, reduce the amount of developer required for development, and use a small amount of developer.
The object of the present invention is to realize a wet-type developing device capable of developing images.

[0006] Another object of the present invention is to realize a wet type developing apparatus that does not require a step of removing excess developer after the completion of development.

[0007]

[Means for Solving the Problems] The wet developing device of the present invention is a wet developing device for developing an electrostatic latent image on an electrostatic latent image carrier with a wet developer. A developing roller made of a conductive material or having a thin insulating layer provided as the outermost layer, which elastically contacts the image carrier and supplies the developer to the electrostatic latent image carrier; It is characterized by comprising a developer application section that applies developer to the development roller.

[0008]

[Example] An example of the present invention will be described.

FIG. 2 is a cross-sectional view of an electrophotographic printer equipped with the wet developing device of the present invention.

A charging device 2, an exposure device 3, a wet developing device 4, a transfer roller 5, a cleaning device 7, and a static eliminator 8 are arranged in this order around the photosensitive drum 1.

A photosensitive drum 1, which is an electrostatic latent image carrier, has an amorphous selenium photosensitive layer 101 deposited around an aluminum tube 100, as shown in FIG. This photosensitive drum 1 is configured to rotate in the direction of arrow A.

With the above configuration, image formation on recording paper is performed as follows. First, the pressure roller is placed in a pressure-released state at the position indicated by 9'. Next, an electrostatic latent image is formed on the photoreceptor drum 1 through a charging process by the charging device 2 and an exposure process by the exposure device 3. This electrostatic latent image is
The wet type developing device 4 uses a developer to develop the image as will be described later. That is, a toner image is formed. Thereafter, the toner image on the photosensitive drum 1 is electrostatically transferred to the transfer drum 5. Furthermore, it passes through a cleaning device 7 and a static eliminator 8, and then moves on to the charging process again.

On the other hand, the recording paper 21, which is carried out from the paper feeder 20 that stores the recording paper 21 as a recording medium, is conveyed to the transfer area in accordance with the formation of the toner image.

Next, the pressure roller is brought into the pressurized state shown at 9 and pressed, and the toner image is transferred from the transfer drum 5 to the recording paper 21.

After the recording paper 21 has undergone the transfer process, it is peeled off from the transfer drum 5 by the peeling claw 6, the carrier liquid on the recording paper 21 is evaporated in the heat fixing device 10, the toner image is fixed, and the recording paper 21 is discharged. The paper is stored in the paper tray 22.

The developer is a carrier liquid in which toner particles (colorant) consisting of a pigment and an acrylic resin are dispersed in a high-resistance petroleum solvent (for example, Isopar, manufactured by Esso) along with a charge control agent and a dispersion stabilizer. It is configured as follows. In this embodiment, a positively charged developer is used so that toner particles selectively adhere to the exposed portion of the positively charged photoreceptor drum 1. Here, the amount of carrier liquid in the developer is set to be as small as possible within a range that does not hinder the conveyance of the developer. That is, the amount of coloring agent (solid content concentration) in the developer is sufficiently increased.

FIG. 1 is a diagram showing the structure of a wet type developing device according to an embodiment of the present invention. A developer application head 40, which is a developer application section having a developer discharge slit 41, is provided with a slit opening 42 facing the developing roller 45. The developing roller 45 is constructed by disposing a conductive layer 47 made of conductive urethane rubber in which a conductive compound is dispersed as an elastic material having conductivity around a metal shaft 46, and having an elastic contact with the photoreceptor drum 1. The photosensitive drum 1 rotates in the direction of arrow B at the same speed as the photosensitive drum 1 while in contact with the photosensitive drum 1 .

Next, the developing operation will be explained. Photosensitive drum 1
The surface of the is uniformly charged with a positive charge through a charging process, and through an exposure process, the exposed area 105 is at approximately ground potential (for example, 40V), and the non-exposed area 104 is at a positive potential (for example, 500V).
) and enter the wet developing device 4. The developing roller 45 is
A power source 90 maintains the same positive potential as that of the non-exposed area (for example, 500 V).

Here, the developer 30 having a sufficiently high solid concentration is pumped up from the developer storage container 50 by the pump 51, passes through the developer discharge slit 41 of the developer application head 40, and is deposited on the developing roller 45. Applied evenly. The toner particles 31 in the developer 30 are positively charged and are ejected from the developer ejection slit 41 to form a layer on the development roller 45 in a minimally wet state that allows the toner to move along with the carrier liquid. It adheres to the developing roller 4.
It is conveyed along with the rotation of 5. The developing roller 45 elastically contacts the photoreceptor drum 1 in close contact with the photoreceptor drum 1 and rotates at the same speed as the circumferential speed of the photoreceptor drum 1 in the contact area 111 . In the vicinity of the contact area upstream 110, the gap between the developing roller 45 and the photosensitive drum 1 narrows as the rotation of both progresses. This also increases the strength of the developing electric field formed between the electrostatic latent image and the developing roller 45. Toner particles, which are charged particles in the developer introduced into the minute gap, are subjected to an electrostatic force depending on the strength and direction of the developing electric field. That is, the exposure section 1 of the photoreceptor drum 1
05, a large electrostatic force is applied toward the photoreceptor drum 1, and no electrostatic force is applied to the non-exposed area 104. As a result, on the photoreceptor drum 1, a large amount of toner particles 31 in the developer 30 are transferred only to the exposed area 105, and no toner particles 31 are transferred to the non-exposed area 104, leaving a toner image on the photoreceptor drum 1. is formed.

In experiments conducted by the present inventors, by using a developer with a solid content concentration (weight %) of 10 to 30%, which is 5 to 15 times higher than that of the conventional one, it was found that Visualization was achieved with sufficient image density without supplying a large amount of developer to the development area. Further, although the developing roller 45 and the photosensitive drum 1 rotate with each other, the contact area 11
In 1, they are in close contact. Therefore, the developer other than the toner particles 31 that has electrostatically adhered to the exposed portion 104 of the photoreceptor drum 1 cannot pass through the contact area 111 and is squeezed out. stay in. Therefore,
The toner image formed on the photoreceptor drum 1 after passing through the contact area 111 has the excess developer sufficiently removed, and is particularly free from the non-image area (in this case, the non-exposed area) on the photoreceptor drum 1. ) 104, so-called background fog does not occur even though a developer having a sufficiently high solid content concentration is used as described above. Therefore, in order to prevent background fog, there is no need to newly provide a process for removing excess developer after the development process is completed.

The amount of developer staying in the upstream part 110 of the contact region increases with time, and when it reaches a certain amount, it naturally flows down due to gravity, is guided to the lower part 49 of the wet type developing device, and is introduced to the developer storage container 50. It will be destroyed. In this embodiment, since a large amount of carrier solution is not used during development unlike in a conventional wet-type developing device, the developer storage container 50 is also miniaturized.

Further, the developing roller 45 has a
A thin insulating layer of about 30 μm may be provided. In this case, even if there is a pinhole on the photoreceptor drum 1,
No leak occurs between the developing roller 45 and the photosensitive drum 1, and it becomes possible to apply a bias potential to the developing roller 45.

Further, the potential applied to the developing roller 45 is
As mentioned above, it is desirable to make the surface potential equal to the surface potential of the non-exposed portion of the photoreceptor drum 1. However, in general,
In order to stably prevent background fog even when the photoreceptor drum deteriorates over time, changes in environmental conditions, etc., the potential applied to the developing roller 45 is set slightly higher than the surface potential of the non-exposed area (for example, between the exposed area and the non-exposed area). (approximately 10% of the potential difference) is set to a value shifted toward the surface potential of the exposed area. At this time, due to the potential difference between the developing roller 45 and the non-exposed portion of the photoreceptor drum 1, toner particles are transferred to the developing roller side, albeit slightly. Therefore, in order to stably prevent background fog, when setting the potential as described above, in order to remove toner particles transferred to the developing roller, the contact area 111 is
It is desirable to provide a developing roller cleaning member, such as a blade, downstream of the developer application head 40 and upstream of the area to be discharged by the developer application head 40.

[0024]

According to the present invention, an electrostatic latent image can be visualized without including a large amount of carrier liquid in the developer. Therefore, the volume capacity of the required developer can be reduced, and the space for storing the developer can be reduced.

Further, according to the present invention, excess developer is removed from the electrostatic latent image carrier at the time of completion of development;
There is no need to perform a new process for removing excess developer after development. Therefore, there is no need to provide a surplus developer removing device, and the electrostatic latent image carrier itself can also be miniaturized.

As described above, the final effect is that the size of the entire image forming apparatus can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the configuration of a wet developing device according to an embodiment of the present invention.

[Fig. 2] A cross-sectional view of an electrophotographic printer equipped with a wet developing device of the present invention.

[Explanation of symbols]

1 Photoreceptor drum 4 Wet developing device 30 Developer 31 Toner particles 40 Developer application head 45 Developing roller

Claims (2)

[Claims] 1. A wet type developing device that develops an electrostatic latent image on an electrostatic latent image carrier with a wet type developer (hereinafter referred to as developer) composed of charged particles dispersed in an insulating carrier liquid. , a conductive developing roller that carries a developer and comes into elastic contact with the electrostatic latent image carrier to supply the developer to the electrostatic latent image carrier; and a developer is applied to the developing roller. A wet-type developing device characterized by comprising a developer applying section. 2. The wet type developing device according to claim 1, wherein a thin insulating layer is provided on the outermost layer of the conductor constituting the developing roller.