JPS5897071A - Developing device - Google Patents

Abstract

PURPOSE:To reproduce a contact print and a line image adequately by forming a dielectric layer over the surface of a developing electrode, i.e. sleeve and providing an insulated electrode which is divided finely thereupon. CONSTITUTION:On the surface of a dielectric supporting body 12 made of stainless steel which houses a magnet 11 having numbers of, e.g. eight alternate poles N and S, an epoxy resin layer 13 with an about 300mum thickness is formed by powder coating as a dielectric layer. To the surface of the dielectric layer, spheroidized copper 14 is adhered with an epoxy adhesive. The spheroidized copper 14 forms a float electrode after the adherence of the spheroidized copper, the outer circumference surface of the dielectric layer 13 is polished to form the exposed surface of the spheroidized copper linearly in a plane shape. Respective electrodes of the spheroidized copper are insulated electrically from one another and a magnetic blade 18 for discharging is arranged in contact with the external circumferential surface of the dielectric layer 13.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a one-component developing device used in an electrophotographic copying machine or an electrostatic recording device.

Broadly speaking, two types of one-component developing methods have been proposed.

That is, using a toner with relatively low resistance as the toner,
There is a method called the dielectric development method, in which a latent image electric field induces charges of opposite polarity to the latent image to the toner on the latent image surface, and a method called the dielectric development method uses a relatively high-resistance toner as the toner. A method called a true charge developing method has been proposed in which a charge having a polarity opposite to that of the image is applied and development is performed by bringing this toner into contact with or close to the latent image surface.

The dielectric development method has advantages such as a simple device, but has the disadvantage that it is difficult to transfer onto plain paper because the toner has low resistance.

Although the true charge development method has the advantage of having the possibility of obtaining high image quality comparable to that of the two-component development method, it has not been widely commercialized due to the following problems. In other words, in order to pre-charge the toner with one polarity, it is difficult to charge the entire toner uniformly if the toner layer is thick, so it is necessary to make the toner layer thinner, and to obtain a true charge sufficient for development. It has been experimentally confirmed that it is desirable to form 4 to 5 layers of toner using normal toner particles of approximately 50μ or less in order to develop the toner in such a thin layer. When this is done, it is necessary to bring the sleeve very close to the latent image surface from the viewpoint of line image reproducibility.

9. A developing device in which a conductive brush is formed on the surface of a conductive sleeve and the flexibility of the brush bristles is used to keep the bristles always in contact with the surface of the photoreceptor has been known. In such a developing device, all the hairs on the plan are at the same potential, so the result is the same as if the developing electrode, such as the sleeve, were extremely close to the surface of the photoreceptor, and line images are well reproduced. Since the electric field due to a solid image increases rapidly compared to a line image, appropriate gradation cannot be obtained. When attempting to obtain the gradation of a solid image, the reproducibility of the line image is insufficient, making it difficult for conventional apparatuses to properly reproduce both images. To overcome this difficulty, it is conceivable to provide a dielectric layer on the sleeve surface to widen the substantial development gap between the sleeve and the photoreceptor surface, thereby reducing the electric field of the solid image. In this case, the electric field of the line image does not change much. However, if a thick dielectric layer is provided on the surface of the sleeve, it will cause wear and tear due to friction with the toner.
It is known that charges accumulate on the surface of the dielectric layer due to triboelectric charging and other causes, and this appears as uneven development.

Generally, when copying with an electrophotographic copying machine, it is desirable for solid images such as photographs to reproduce the background and gradation of the image as they are, and for line images such as characters and line drawings, for example, thin lines drawn with a pencil. However, it is desirable to be able to reproduce it clearly. Looking at the relationship between the density of the original (0, D) and the density of the copy (1, D), in a solid image, a certain value of ω is used to prevent staining of the background, as shown by the curve S in Figure 1. The image is reproduced from a certain point, and the image is advanced at an angle of 45 degrees until the saturation density is reached.In the case of a line image, as shown by the curved line in Fig. 1, the image is reproduced at 0. It is required that the curve 1 quickly rises from a small value of D to reach the saturation concentration. In the figure, the vertical axis is 1. D, horizontal axis is 0, D
'&-show.

Furthermore, in the exposure optical system of a copying machine, a transfer function (MrF
), the relationship shown by the curve in Figure 2 is obtained, and if the spatial frequency is 0 lines/1u1, that is, a solid image, M
When rF is 1, the original image is sent to the photoreceptor with the same contrast, but as the spatial frequency increases,
In other words, the thinner the line, the lower the MTF, and the dark image on the photoconductor tends to be a line with weak contrast, so even if the image has the same density on the original, the density of the latent image on the photoconductor changes.
The solid image has a higher potential than the line image, -1
Ru. For this reason, it is required to develop the latent image of the line image to be dense. The vertical axis of the figure shows MrF, and the horizontal axis shows spatial frequency /U.

As shown in FIG. 3, the developing electrode 1, for example, the developing sleeve, and the photoreceptor 2 are spaced apart from each other by a distance P. In the developing area opposed to each other, the potential of the developing electrode 1 is set to, for example, 200 V, and the dielectric constant ε of the photoreceptor 2 is set to
3.0, thickness d = 20μ, various charge patterns were created on the photoreceptor surface, and the magnitude of the electric field on the photoreceptor surface was determined by computer simulation, as shown in Figure 4. An example has been obtained. In the figure, the horizontal axis shows the distance P between the photoconductor writing development electrodes, and the vertical axis shows the developing electric field V/m', where the curve shown by the solid line is the curve for a black solid image, and the curve shown by the broken line is the curve HO,I)=0.2. Spatial frequency = 5 lines/Iu
represents a curve for a low contrast line image of . Charged potential of black solid image Va=800 Land surface potential Vs=2
It is 00V.

In a solid black image, charges are uniformly distributed over a wide area on the surface of the photoconductor, and an almost parallel electric field is formed between the photoconductor and the developing electrode, so when the distance PG becomes small, the developing electric field suddenly increases. However, in the case of a line image, there is a local charge on the surface of the photoreceptor, and the lines of electric force emitted from this component are directed toward the developing electrode; 1. The latent image adjacent to the charged portion of the photoreceptor The interval P is large because it has a considerable amount of components directed toward the skin area where no pores are formed. The potential hardly changes depending on the change in .

For example, a low contrast line image with O, D = 0.2 and a spatial frequency of 5/, is reduced to 1 of the saturation density of a black peta image.
In order to reproduce the value of approximately /2, the distance PG between the photoreceptor and the developing electrode must be selected to be approximately 2 Iu from FIG. However, when the toner layer is a thin layer of several tens of microns as described above, under these conditions, a large gap is created between the surface of the toner layer and the photoreceptor.

When the relationship between the distance from the photoreceptor/surface and the change in electric field magnitude was determined, the results shown in FIG. 5 were obtained. In the figure, the horizontal axis represents the spatial frequency V/, and the vertical axis represents the developing electric field V/
For m', a group of curves with distance μ from the photoreceptor surface as a parameter is shown. In the fifth case, an example is shown in which the distance PG between the photoreceptor surface and the developing electrode is 0.5. From the curve group, when the photoconductor is extremely close to < 5μ (for example, 5 μ), the line image (for example, 5 lines/U) is emphasized compared to the solid image (0 lines/U), but the photoconductor surface The electric field of the line image decreases rapidly as the distance from the line increases. Therefore, if development is performed with a larger gap between the toner surface and the photoreceptor, the reproducibility of line images will be extremely poor.

As a method to solve the above problem, as shown in FIG. 6, an alternating current magnetic field or an alternating electric field is applied to the toner.

A method has been considered in which a cloud is generated to bring the toner closer to the surface of the photoreceptor, but only a portion of the toner reaches the surface of the photoreceptor using this method. Therefore, the above problem could not be completely solved. In Fig. 6, l is a sleeve, 2 is a photoreceptor, 3 is a magnetic pole, 4 is an AC power supply,
5 indicates a doctor blade.

It has also been considered to provide a dielectric layer on the surface of the sleeve to bring the toner layer closer to the surface of the photoreceptor, which has largely solved the above problems, but the surface of this dielectric layer becomes statically charged due to friction with the toner, etc. Since this band 11 was used without being completely neutralized, uneven development occurred. It is quite difficult to completely eliminate static electricity from such a dielectric layer, which has the drawback of complicating the equipment.

SUMMARY OF THE INVENTION An object of the present invention is to provide a developing device capable of solving the above-mentioned drawbacks and properly reproducing solid images and line images with a thin layer of toner having a true charge.

This object has been achieved by the present invention by providing a dielectric layer on the surface of the developing electrode or sleeve, on which are provided finely divided electrodes which are insulated from each other.

According to the present invention, the sleeve electrode is completely floating during development, so it has little effect on the development electric field, and the charge accumulated on the sleeve can be easily removed.
The uneven development caused by incomplete charge removal when providing the dielectric layer described above is eliminated, and with this screen angle, even if the toner layer on the surface of the three 7 is brought quite close to the photoreceptor surface, the electric field of the solid image is not affected by the dielectric layer. The thickness of the layer makes it possible to obtain a suitable edge effect. The details of the present invention Mf3 will be explained in detail with reference to the embodiments shown in the drawings.

In Section 7 and FIG. 8, a dielectric support 12 made of stainless steel with a thickness of about 300 μm is coated on the surface of a dielectric support 12 made of stainless steel containing a multi-pole, for example, 8-pole S-stone 11 in which N and S poles are arranged alternately. An epoxy resin layer 13 is formed as a dielectric layer by powder coating. Spherical copper powder 14 with a diameter of approximately 100 mm is placed on the surface of the dielectric layer.
are bonded using epoxy adhesive. Spherical copper powder 14
forms a float electrode.

After adhering the spherical copper powder, the outer circumferential surface of the dielectric layer 13 is polished so that the surface exposed to the outer surface of the spherical copper powder is substantially flat. The electrodes made of each copper powder are electrically insulated from each other. A magnetic blade 18 that also serves as a charge remover is placed in contact with the outer peripheral surface of the dielectric layer 13.
(For example, SK material with a thickness of 0.11 IJ) is placed.

On the developing sleeve 16 shown in the seventh section, 15 layers of toner of about 1 mg/cj are formed using magnetic toner. The amount of toner charge at this time is approximately 7μ axis. The volume average particle diameter of the toner is approximately 7 μ, and the true specific gravity is 1.8.

For the developing sleeve 16, that is, the toner carrier formed as described above, the developing gap, which is the distance between the surface of the toner layer 150 and the surface of the photoreceptor, that is, the electrostatic latent image carrier, is 0.
．． The photoreceptor 17 is arranged so that the linear velocity ratio is 05+u, and the linear velocity ratio is 1.
When the image was developed at a ratio of 1:1, a good image with a suitable edge effect was obtained.

As a second example, when the development gap 1 between the photoreceptor and the surface of the toner layer 150 of the developing sleeve 16 was changed to 0.15+u, and the linear velocity ratio vt:a of the photoreceptor 17 and the developing sleeve 16 was used, almost the same result was obtained. An image with an even better signal-to-noise ratio was obtained due to the edge effect.

In the second embodiment, since the developing gap becomes narrower, the proportion of toner close to the surface of the photoreceptor decreases, but this is compensated for by increasing the linear velocity ratio of the developing sleeve. In other words, even more uneven toner on the sleeve surface appears in the image,
It is thought that the image quality improves by making the image smaller.

Similar effects can be obtained by increasing the thickness of the dielectric layer in the first embodiment to increase the relative linear velocity of the photoreceptor sleeve.

If the developing gap is made even smaller, an effect can be obtained in which the electrodes on the sleeve surface emphasize the electric field of the line image.

As shown in FIGS. 9 and 10, spherical iron having a diameter of approximately 100 μm is provided on the circumferential surface of the stainless steel non-fertile sleeve 12'.

It is also possible to use a developing sleeve 16' formed by applying a magnetic material 19 such as powder, uniformly dispersed and bonded with a boxy adhesive 20, and polishing the outer peripheral surface. 1i15' of a thin magnetic toner of about 1 mg/cA is applied to the surface of the developing sleeve 16'.
was formed and placed facing the photoconductor 17 with a development gap of 0.2U, and development was performed at a linear speed ratio of 1:2 between the photoconductor and the developing sleeve, and both the peta image and the line image were well reproduced. . The charge amount of the toner was approximately 10 μm in Example 1, the volume average particle size was approximately 7 μm, and the true specific gravity was 1.8. The effect of greatly improving the developing efficiency was obtained by dispersing magnetic material 19 on the surface as shown in FIG.
The lines of magnetic force are concentrated on this magnetic body and form a non-uniform magnetic field on the surface of the sleeve, so when the toner moves between the magnetic bodies due to the rotation of the magnet 11, the magnetic toner 15 is repelled from the sleeve. This is thought to be due to the fact that the amount of toner reaching the surface of the photoreceptor increases as the toner jumps under the force.

When compared with the case where a developing sleeve made of only a stainless steel sleeve was used under the same conditions as in the above example using the developing sleeve shown in FIG. 9, in this case, the solid image could be reproduced to a certain extent, but the line width was 0, A line image of about 1lIj was hardly reproduced, and it became clear that the developing sleeve shown in FIG. 9 exhibited an excellent effect.

By forming an a-type turn made of the magnetic material 19 and adhesive 20 shown in FIG. 10 on the dielectric layer 13 shown in FIG. The effect of electrodes can also be obtained.

According to the present invention, it has become possible to properly reproduce both solid images and line images.

[Brief explanation of drawings]

Figure 1 shows the image density characteristic curves of peta images and line images, Figure 2 shows the change in the transfer function of the exposure optical system of the copying machine with respect to the spatial frequency of the image, and Figure 3 shows the development area. An explanatory diagram indicated by twlI■, FIG. 4 is a diagram showing the relationship between the distance between the photoreceptor and the developing electric field and the magnitude of the developing electric field on the surface of the photoreceptor for black solid images and low contrast line images,
FIG. 5 is a diagram showing the relationship between the spatial frequency of an image and a developing electric field, FIG. 6 is a schematic illustration of an example of a conventional developing device, FIG. 7 is an explanatory diagram of a developing sleeve according to the present invention, and FIG. FIG. 7 is a partially enlarged view of FIG. 7, FIG. 9 is an explanatory view of another embodiment of the present invention, and FIG. 10 is a partially enlarged view of FIG. 11... Magnet 12... Conductive support 13
...Dielectric layer 14...Electrode 15...Toner 16.16'...Toner carrier 17...Electrostatic latent image carrier 1 Modification...S material 20...Adhesive, -to-ichiku〉\ε) / --N

Claims (3)

[Claims] (1) A toner carrier disposed adjacent to the electrostatic latent image carrier and containing a magnet having a large number of magnetic poles therein, and a charge of a predetermined polarity is applied to the toner on the toner carrier. In a developing device for developing an electrostatic latent image, a dielectric layer is formed on the surface of the toner carrier, and a large number of finely divided electrodes are provided on at least the surface of the dielectric layer in an insulating manner. A developing device characterized in that toner is attached as a thin layer to the outer surface of an electrode arrangement portion of a toner carrier. (2) The developing device according to claim 1, wherein a magnetic toner is used as the toner, and a magnet included in the toner carrier is rotated. (3) Claim 1 or 2, characterized in that the magnetic toner layer on the toner carrier is formed thinner than the distance between the toner carrier and the electrostatic latent image carrier. Developing device described in Section 1.