JPH04104177A - Wet developing roller - Google Patents

Abstract

PURPOSE:To prevent a charge from running from a photosensitive body to the side of a roller on the contact surface of an insulating elastic member covering the surface of a roller with the photosensitive body by coating the surface of the roller main body at least whose outer circumferential part is formed of a conductive elastic member with the insulating elastic member. CONSTITUTION:As to a wet developing roller 10, the roller main body 2 made of the conductive elastic plastic foam is formed around a columnar metallic core 1, and the film 3 made of the insulating elastic plastic foam is uniformly formed on the surface of the roller main body 2, so that the charge of the photosensitive drum 13 does not run away through the roller on the contact part with the photosensitive drum 13. And also, the bias potential of the wet developing roller 10 is not influenced by the photosensitive body potential, so that the developing bias can be uniformly given to the whole image part. Thus, uniform developing can be performed, and the image excellent in the gradation can be outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a wet developing roller used in a wet developing type electrophotographic apparatus.

[Prior Art] In an electrophotographic apparatus, an electrostatic latent image formed on a photoreceptor based on image information using a photoconductive phenomenon is made visible and developed by applying toner. There are two types of development methods: a method called dry development in which powdered toner is used in a dry state, and a method called wet development in which toner is used in a state dispersed in an insulating liquid. Further, in the wet development method, methods for bringing the toner into contact with the photoreceptor include a dropping method, a jetting method, a contact method, and the like.

As an example of a contact type of wet development method, a wet development roller has a roller body made of a conductive elastic material such as conductive elastic plastic foam formed uniformly around a cylindrical metal core, and the developer is pumped up and developed. Some types perform development by bringing a liquid into pressure contact with a photoreceptor on which an electrostatic latent image has been recorded.

[Problems to be Solved by the Invention] However, in the wet type developing roller as described above, in order to provide the roller body with a sufficient developing electrode effect, the volume resistivity must be low, for example, 10<7 >Ω or less.

On the other hand, by lowering the resistance value of the roller body, the charge on the photoreceptor escapes through the roller at the contact portion between the photoreceptor and the wet type developing roller, making it impossible to perform sufficient development.

Furthermore, the bias potential of the wet developing roller at the contact portion between the photoreceptor and the wet developing roller is affected by the potential of the electrostatic latent image on the photosensitive belt, making it impossible to apply a negative developing bias to the entire image area. This makes it impossible to perform uniform development, which becomes a problem especially when gradation reproduction is required.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a wet type developing roller that can perform sufficient development and output images with excellent gradation.

[Means for Solving the Problems] In order to achieve this object, the wet developing roller of the present invention has the following features:
The surface of the roller main body, at least the outer peripheral portion of which was formed of a conductive elastic member, was coated with an insulating elastic member.

[Function] In the wet developing roller of the present invention having the above configuration,
The insulating elastic member on the surface prevents charges from escaping from the photoreceptor toward the roller at the contact surface with the photoreceptor.

[Example] Hereinafter, an example embodying the present invention will be described with reference to the drawings.

FIG. 2 is a schematic diagram of a wet development type electrophotographic apparatus to which the present invention is applied.

A rotating photoreceptor drum 13, a charger 14, an exposure device 15 for providing image information, and a developer 1 in the order of rotational direction of the photoreceptor drum as indicated by an arrow in the figure, facing the photoreceptor drum 13.
8, transfer roller 30, static eliminator 16 to which AC voltage is applied;
A cleaner 17 is arranged. On the other hand, recording paper 20 is supplied from a recording paper cassette 21 by a half-moon roller 22.

FIG. 1 shows an enlarged view of the vicinity of the developing device 18.

A wet developing roller 10 is provided to face the photosensitive drum 13, and the wet developing roller 10 has a roller body 2 made of conductive elastic plastic foam formed around a cylindrical metal core 1. A film 3 made of insulating elastic plastic foam is uniformly formed on the surface. Further, a voltage is applied between the core 1 and the photosensitive drum 13 by a power source 7.

The roller body 2 is preferably made of synthetic rubber such as polyurethane mixed with carbon black fibers or powder, and has a volume resistivity of 10'' to 10'' in order to have a sufficient developing electrode effect during development. The film 3 is suitably made of synthetic rubber such as polyurethane, and has a thickness of 0.5 to 2 mm since the photosensitive drum 13 and the roller body 2 are brought close to each other during development.
Good rank.

In addition, in order to squeeze the excess developer on the photoreceptor drum 13, the hardness of the roller body 2 and the film 3 is adjusted from 10 degrees to 2 degrees.
About 5 degrees is good.

The wet type developing roller 10 is immersed in a tank 5 containing a developer 4 with a portion slightly above the liquid level 1, and the developer 4 is sufficiently absorbed.

Next, the action will be explained.

The photosensitive drum 13 rotates in the direction of the arrow in FIG. 2, the photosensitive drum 13 is uniformly charged by the charger 14, and a latent image is formed by the exposure device 15.

During development, the tank 5 is raised by a tank elevator (not shown), and the photoreceptor drum 13 on which the electrostatic latent image has been recorded is lifted.
The wet developing roller 10 is brought into contact with a slight pressure and then rotated in conjunction with the wet developing roller 10 .

Due to this rotation, the developer 4 absorbed by the wet type developing roller 10 and the developer 4 in the liquid reservoir A drawn up by the wet type developing roller 10 come into contact with the photoreceptor drum 13, and development is performed. At this time, the photosensitive drum 13 and the roller body 2 are brought into close proximity to each other because the film 3 is compressed under pressure. Further, at this time, the photosensitive drum 13 and the roller body 2 are insulated by the insulating film 3. Therefore, a negative developing bias can be applied to the entire image area without being affected by the potential of the electrostatic latent image on the photoreceptor drum 13.

After the development is completed, the wet type developing roller 10 returns to its original state due to the restoring force of the elastic plastic foam and absorbs the excess developer attached to the photoreceptor drum 13, so that the wet type developing roller 10 and the photoreceptor drum 13 are separated. After this, the surface of the photoreceptor drum 13 is in such a dry state that a squeeze device is not necessary.

On the other hand, the recording paper 20 is transferred from the cartridge 21 to the half-moon roller 2.
2 to the transfer roller 30 along the guide plate 24, and the image on the photosensitive drum 13 is transferred onto the recording paper 20. On the other hand, the charge on the photosensitive drum 13 is removed by a static eliminator 16, and the residual toner is removed by a cleaner 17.

As is clear from the detailed description above, in the wet developing roller 10 of the electrophotographic apparatus of this embodiment, the roller body 2 made of conductive elastic plastic foam is formed around the cylindrical metal core 1. Since the film 3 made of insulating elastic plastic foam is uniformly formed on the surface of the roller body 2, the charge on the photoreceptor drum 13 does not escape through the roller at the contact portion with the photoreceptor drum 13.

Further, the bias potential of the wet developing roller 10 is not affected by the photosensitive belt potential, and a negative developing bias can be applied to the entire image area. Therefore, uniform development can be performed,
Images with excellent gradation can be output.

It should be noted that the present invention is not limited to the above embodiments, and modifications can be made without departing from the spirit thereof.

[Effects of the Invention] As is clear from the above detailed description, in the wet developing roller of the present invention, the surface of the roller main body, at least the outer peripheral portion of which is formed of a conductive elastic member, is coated with an insulating elastic member. Therefore, the charge on the photoreceptor does not escape through the roller at the contact portion with the photoreceptor. Furthermore, the bias potential of the wet developing roller is not affected by the photosensitive belt potential, and a negative developing bias can be applied to the entire image area. Therefore, uniform development can be performed and an image with excellent gradation can be output.

[Brief explanation of the drawing]

1 and 2 show an embodiment embodying the present invention. FIG. 1 is an enlarged front view showing the vicinity of the developing unit, and FIG.
The figure is a schematic configuration diagram of an electrophotographic apparatus to which the present invention is applied. In the figure, 1 is a core, 2 is a roller body, 3 is a film, 4 is a developer, 10 is a wet type developing roller, and 13 is a photosensitive drum.

Claims (1)

[Claims] 1. Provided opposite to the photoreceptor on which the electrostatic latent image is formed,
A wet developing roller that contacts the photoreceptor at least during development and develops the latent image by applying a developer to the photoreceptor, the roller body having at least an outer peripheral portion formed of a conductive elastic member. 1. A wet developing roller, the surface of which is coated with an insulating elastic member.