JPH0439071B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a float electrode type developing device in which a plurality of floating microelectrodes are arranged on the surface of a toner carrier, and in particular, the elasticity of the toner carrier is ensured, and the development characteristics can also be changed and set. This paper proposes a developing device that can

In an electrophotographic copying machine or an electrostatic recording machine, a developing device supplies toner to an electrostatic latent image formed on the surface of an image carrier to form a visible image. Therefore, the development characteristics required of the developing device are different depending on whether the document is a line image or a solid image. That is, as shown in Fig. 1, in the case of a solid image (indicated by solid line A in the figure), it is required to obtain a copy image density corresponding to the original image density, whereas in the case of a line image, it is required to obtain a copy image density corresponding to the original image density. (indicated by broken line B in the figure) requires high copy image density even when the original image density is low;
The rising slope of curve B is steep. In order to increase the density of the copied line image, a so-called edge effect has conventionally been used. That is, the intensity of the electric field in the image line portion of the electrostatic latent image is stronger than the intensity of the electric field in the central area of the image, resulting in a large amount of toner adhering to the edges of the image, resulting in an edge effect. In the case of a line image with a small image area, most of the latent image forming area is affected by the edge effect, resulting in a high image density after image processing.

However, this edge effect is sufficient when a two-component developer containing toner and carrier is used, but it is not effective when using a single-component toner that does not use a carrier. The problem is that a strong edge effect cannot be obtained.
For this reason, the applicant of the present application has already proposed a developing device using a float electrode type toner carrier 16, as shown in FIGS. 2 and 3. Toner carrier 16
In this example, a dielectric layer 18 is formed on a conductive medium 19, and a minute electrode 17 is arranged in a floating state on the surface of this dielectric layer 18, and a photosensitive layer 21 is formed on a conductive substrate 22. At a development position facing the photoreceptor 20, lines of electric force are formed by the positive charges of the electrostatic latent image formed on the surface of the photoreceptor layer 21, as indicated by arrows in the figure. Furthermore, Figure 2 is a line image.
In the case of L ₁ , Fig. 3 is the case of solid image L ₂ ,
In the figure, illustration of toner is omitted. Due to the presence of the electrode 17, the edge effect increases, the number of electric lines of force near the line image _L1 increases significantly, and toner adheres to the line image _L1 at a higher density than in the case of the solid image _L2 . do.

This edge effect (r-characteristic of a line image) remains approximately unchanged even if the thickness of the dielectric layer 18 is changed, but the r-characteristic of a solid image changes depending on the thickness of the dielectric layer 18. Therefore, in consideration of the balance between line images and solid images, the layer thickness of the dielectric layer 18 is preferably 400 to 1000 μm. However, with such a layer thickness, it is difficult to impart elasticity to the dielectric layer 18, and the surface of the toner carrier 16 is hard.

Therefore, when a hard image carrier such as a photosensitive drum is used, adhesion between the image carrier and the toner carrier cannot be obtained, and good development cannot be performed. Therefore, it is necessary to use an image carrier constructed on a belt, such as a photoreceptor belt, which limits its application to copying machines and the like.

The present invention has been made in view of the above points, and by sequentially laminating an elastic dielectric layer and a conductive layer on a base, the toner carrier itself has elasticity and is hard. It is an object of the present invention to provide a developing device that secures adhesion to an image carrier and improves adaptability to copying machines and the like. Furthermore, it is an object of the present invention to provide a developing device having a structure in which the r-characteristics of a capacitor composed of a float electrode, a dielectric layer, and a conductive layer can be arbitrarily changed, and the developing characteristics thereof can also be changed and set according to the type of document. purpose.

A developing device according to the present invention is a developing device that supplies toner to the surface of an image bearing member on which an electrostatic latent image is formed, and has a sleeve shape or an endless belt shape, and has a passage area in the vicinity of the image bearing member. The toner carrier has a toner carrier movably provided so as to be movable, and a toner replenishing means for replenishing the surface of the toner carrier with toner, and the toner carrier is made of an elastic insulating material and is disposed on a base. The toner carrier has a structure in which a first dielectric layer, a conductive layer made of a conductive material, and a second dielectric layer made of an insulating material whose surface is dotted with a plurality of microelectrodes are laminated in order, and A developing bias applying means for applying a bias power source to the conductive layer is provided.

Further, it is preferable that the base of the toner carrier is made of a conductive material, and that the developing bias applying means can selectively apply a bias voltage to the base of the toner carrier.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments in which a developing device according to the present invention is applied to an electrophotographic copying machine will be specifically described with reference to the accompanying drawings. FIG. 4 is a partially enlarged sectional view of the toner carrier 1 of the developing device according to the present invention, and FIG. 5 is a schematic diagram of the entire developing device. A photosensitive drum 11 serving as an image carrier is rotated at a constant speed in the direction of the arrow. The photosensitive drum 11 has a photosensitive layer made of a photoconductive substance formed on a conductive base on a sleeve, and while rotating at a constant speed, its surface is uniformly charged with, for example, a positive charge, and image exposure is performed. After the electrostatic latent image is formed, the developing device according to the present invention is located at a location.

The toner carrier 1 has a dielectric layer 3 made of an insulating material such as polyester resin or epoxy resin formed on the outer circumferential surface of a sleeve-shaped conductive base 2, and a dielectric layer 3 made of an insulating material such as polyester resin or epoxy resin is formed on the dielectric layer 3 to a predetermined thickness. conductive layer 4
A dielectric layer 5 made of an insulating material is formed on the conductive layer 4. That is, the toner carrier 1 includes a base 2 as a first conductive layer and a dielectric layer 3 as a first dielectric layer.
It has a four-layer structure including a conductive layer 4 as a second conductive layer and a dielectric layer 5 as a second dielectric layer. The dielectric layer 3 is preferably thick enough to have elasticity, and the insulating material forming the dielectric layer 5 is preferably highly flexible. On the circumferential surface of the toner carrier 1, that is, on the surface of the dielectric layer 5, a plurality of minute electrodes 6 are scattered over substantially the entire area of the toner carrier 1 in the width direction and circumferential direction. This electrode 6 is made of metal such as copper, and after embedding copper particles with a diameter of about 50 to 100 μm in the surface layer of the dielectric layer 5, the fourth
As shown in the figure, they are hemispherical minute metal grains, which are held in a floating state with appropriate distances from each other. The toner carrier 1 is installed so as to roll on the circumferential surface of the photosensitive drum 11 on the downstream side of an image exposure device (not shown) in the rotational direction of the photosensitive drum 11. body drum 1
It is designed to be rotationally driven in the direction of the arrow at the same peripheral speed as that of 1. A cylindrical magnet 7 is provided inside the toner carrier 1 coaxially with the toner carrier 1, and the magnet 7 is rotated together with the toner carrier 1 at a constant speed in the direction of the arrow.

A tank 8 storing toner 9 is disposed on the circumferential surface of the toner carrier 1 at a position opposite to the development position facing the photoreceptor 11 . Toner 9 is a so-called one-component toner (magnetic toner) in which magnetic powder is mixed in resin, and has an average particle size of about 9 μm, for example.
True specific gravity is adjusted to approximately 1.86. And tank 8
A layer thickness adjustment member 10 is disposed above.
The layer thickness adjusting member 10 is a metal plate made of SK material with a thickness of approximately 0.1 mm, and is provided so as to be in sliding contact with the circumferential surface of the toner carrier 1 over substantially the entire widthwise area of the toner carrier 1. After the toner supplied from the tank 8 to the peripheral surface of the toner carrier 1 passes through the layer thickness adjusting member 10, the layer thickness is regulated to approximately one layer. The layer thickness of the toner is regulated by the layer thickness adjusting member 10, and the toner is subjected to friction between the layer thickness adjusting member 10 and the circumferential surface of the toner carrier 1, so that the polarity determined by the triboelectrification series between these materials, e.g. It is charged with negative polarity.

Next, the operation of the apparatus of the present invention having such a configuration will be explained. While the toner carrier 1 rotates, the toner 9 is supplied from the tank 8 to the circumferential surface of the toner carrier 1, and the layer thickness adjusting member 10 regulates the toner layer thickness on the circumferential surface of the toner carrier 1 to a predetermined value. It is charged to a predetermined polarity by friction between the body 1 and the layer thickness adjusting member 10, and is attached to the peripheral surface of the toner carrier 1 by the magnetic force from the magnet 7. and,
As the toner carrier 1 rotates, this toner is transported to a development position where the toner carrier 1 rolls with the photoreceptor drum 11, and is supplied to the electrostatic latent image formed on the circumferential surface of the photoreceptor drum 11.

At this developing position, the peripheral surface of the toner carrier 1 is pressed by the photoreceptor drum 11 and is deformed by the elasticity of the dielectric layers 3 and 5 to follow the shape of the peripheral surface of the photoreceptor drum 11. Therefore, the adhesion between the toner carrier 1 and the photoreceptor drum 11 at the developing position is high, and even if the image carrier is a hard one, such as when the image carrier is a photoreceptor drum, the toner carrier 1
The image quality after development is extremely high. Furthermore, since the toner carrier 1 has minute electrodes 6 in a floating state disposed on its circumferential surface, when an electrostatic latent image corresponding to a line image is formed on the circumferential surface of the photosensitive drum 11. In this case, the electric lines of force coming out from the static latent image area not only go directly to the background area, but also go to the background area via the electrode 6 (see FIG. 2). That is, the presence of the electrode 6 increases the number of electric lines of force directed from the image area to the background area, resulting in a remarkable edge effect.
Therefore, the electric field near the latent image becomes significantly stronger, the amount of toner adhesion increases, and the density of the copied image becomes extremely high.

As the photoreceptor drum 11 rotates, the toner image formed on the circumferential surface of the photoreceptor drum 11 reaches a transfer device (not shown) disposed downstream of the developing device, and is transferred onto a transfer material by the transfer device. On the other hand, the toner that has not been consumed during development reaches the position of the tank 8 while remaining attached to the circumferential surface of the toner carrier 1 due to the magnetic force from the magnet 7, and new toner is deposited in the area where the toner was consumed. will be replenished. Note that the toner carrier 1
There is a risk that charge may accumulate on the electrode 6 due to the transfer of toner to and from the surface of the toner. , it is possible to avoid charge accumulation on the electrode 6.

Next, another embodiment of the developing device according to the present invention will be described based on FIG. Components that are the same as those in FIG. 5 are designated by the same reference numerals, and their description will be omitted.
In this embodiment, by controlling the application of bias voltage to the conductive layers 2 and 4, desired development characteristics are obtained depending on the type of document.
Although the illustrated example uses a belt-shaped photosensitive belt 12 as an image carrier, it goes without saying that a drum-shaped photosensitive drum shown in FIG. 5 may also be used. A photoreceptor 12 configured in the shape of an endless belt is stretched around a suitable roller 13 and is moved at a constant speed in the direction of the arrow by rotation thereof. The photoreceptor 12 has a photosensitive layer made of a photoconductive substance formed on a belt-shaped conductive substrate, and after an electrostatic latent image is formed on the surface of the photosensitive layer,
The location of the developing device according to the present invention is reached. The conductive layer 4 and the base 2 of the toner carrier 1 are connected to the switch 1
4, it is connected to a bias power supply 15 with a positive polarity that is opposite to the charged polarity of the toner, and when the switch 14 is switched to the terminal A side, a bias voltage is applied to the conductive layer 4, and the bias voltage is applied to the terminal B side. When switched, a bias voltage is applied to the base 2. Note that the conductive layer 4 or the base body 2 is maintained in an electrically insulated state when no bias voltage is applied.

FIG. 7a shows the r characteristics of line image B and solid image A when a voltage is applied to the conductive layer 4,
On the other hand, FIG. 7b shows similar r characteristics when a voltage is applied to the conductive substrate 2. As is clear from these figures, as the thickness of the dielectric layer increases, the r-characteristic of the line image B remains almost unchanged, but the r-characteristic of the solid image A changes greatly and its slope becomes gentler. This means that the dielectric layer should be
This is consistent with the finding that when the thickness is changed up to 1000 μm, the r-characteristic of a line image hardly changes, but the r-characteristic of a solid image becomes gentler as the layer thickness increases. Dielectric layer thickness is typically 600μm
However, even when the layer thickness is set to about 3000 μm or more as in this example, the r characteristic of the line image is almost unchanged, but the r characteristic of the solid image is It is conceivable that the r characteristic becomes very gentle, and development is not possible unless the original image density is quite high. In such a case, in this embodiment, even a solid image can be appropriately developed by applying a voltage to the conductive layer 4.

That is, when the switch 14 is switched to the terminal B side and a bias voltage is applied to the base 2, the conductive layer 4
Since is in a floating state, a capacitor is formed between the electrode 6 and the substrate 2 via the dielectric layers 3 and 5, and because the layer thickness of the dielectric layer (distance between the electrodes) is large, the r characteristic of the solid image is particularly weak. It becomes a kana curve. On the other hand, when the switch 14 is switched to the terminal A side and a bias voltage is applied to the conductive layer 4, the electrode 6 and the conductive layer 4
A capacitor is formed between the dielectric layer 5 and the r
The characteristic has a steep slope. As described above, since the present invention has two conductive layers, the first (substrate 2) and the second (conductive layer 4), the r characteristic can be selected depending on the type of document, etc. Because you can
Desired development characteristics can be easily obtained, and there is a large degree of freedom in the manner in which the development bias voltage is applied.

As explained in detail above, in the case of the present invention, since the toner carrier itself has elasticity, even if the image carrier is a hard one such as a photoreceptor drum, the adhesion between the two is extremely high. Since the image quality is high, the applicability of the device of the present invention to copying machines and the like is extremely high. Furthermore, since it is possible to appropriately select the layer thickness of the dielectric layer, it is possible to obtain desired development characteristics depending on the type of original image. It should be noted that the present invention should not be limited to the specific embodiments described above, and various modifications can be made within the technical scope of the present invention. As an example, the toner may be made of non-magnetic material.

[Brief explanation of drawings]

FIG. 1 is a graph showing the development characteristics, FIGS. 2 and 3 are schematic diagrams explaining the principle of development using the float electrode method, FIG. 4 is a partially enlarged sectional view of the toner carrier 1, and FIG. A schematic diagram showing an embodiment of the invention,
FIG. 6 is a schematic diagram showing another embodiment of the present invention, and FIG.
Figures a and 7b are graphs showing the r characteristics, respectively. Explanation of symbols, 1, 16... Toner carrier, 2,
19... Base, 3, 5... Dielectric layer, 4... Conductive layer, 6, 17... Electrode, 11... Photosensitive drum.

Claims (1)

[Scope of Claims] 1. A developing device that supplies toner to the surface of an image carrier on which an electrostatic latent image is formed, which is shaped like a sleeve or an endless belt and has a passage area near the image carrier. The toner carrier has a toner carrier disposed movably in the same manner as the toner carrier, and a toner replenishing means for replenishing the surface of the toner carrier with toner, and the toner carrier has a base made of an elastic insulating material. The toner carrier has a structure in which a first dielectric layer, a conductive layer made of a conductive material, and a second dielectric layer made of an insulating material whose surface is dotted with a plurality of microelectrodes are laminated in sequence, and the toner carrier 1. A developing device comprising: a developing bias applying means for applying a bias power source to the conductive layer. 2. Claim 1, wherein the base of the toner carrier is made of a conductive material, and the developing bias applying means is configured to selectively apply a bias voltage to the base of the toner carrier.
Developing device as described in section.