JPS5880675A - Developing device - Google Patents

Abstract

PURPOSE:To obtain satisfactory reproducibility and gradation to both flat part and line part, by providing a dielectric layer on a conductive supporting body of a sleeve, and also embedding a finely divided float electrode on its surface like an island o that its surface is exposed. CONSTITUTION:A developing sleeve 12 is provided in the vicinity of a photosensitive drum 11, and on the outside circumference of a conductive supporting body 13 of this developing sleeve 12, a dielectric layer 14 is laminated, and on this dielectric layer 14, a conductive brush 15 is provided on the whole circumferential surface. This conductive brush 15 consists of conductive fur bodies which are in an electrically insulating state to each other. In the developing sleeve 12, a magnet which rotates in the opposite direction is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention makes it possible to visualize an electrostatic latent image formed on the latent image carrier by toner conveyed by a toner conveying member disposed adjacent to the electrostatic latent image carrier. The present invention relates to a developing device for imaging.

As a developer for the above-mentioned curved type developing device used in an electrophotographic copying machine or an electrostatic recording device, a one-component developer consisting of toner is more expensive than a two-component developer containing toner and a carrier. Simplification of developing device.

It has attracted particular attention recently because it has advantages in terms of improved reliability and the like.

Conventionally proposed one-component developing methods can be broadly classified into the following two methods.

One of them is 1. This is a so-called induction development method, in which a toner having a relatively low resistance is used, and development is carried out by inducing charges of opposite polarity to the latent image to the toner on the latent image surface using a latent image electric field.

The other method is called a true charge development method, in which a relatively high-resistance toner is used, a charge of the opposite polarity to that of the latent image is given to the toner in advance, and this is applied to the surface of the latent image. Development is carried out by contacting or bringing them close together.

The former has advantages such as a simple device.

Since the toner has low resistance, it has the disadvantage that it is difficult to transfer to plain paper.

Although the latter has the possibility of obtaining high image quality comparable to that of the two-component development method, it has the following problems and has not been widely commercialized.

That is, in order to pre-charge the toner with one polarity, it is necessary to make the toner a thin layer, since it is difficult to uniformly charge the entire toner if the toner layer is thick. To provide sufficient true charge for development.

Up to 4 to 5 layers of toner (normal toner particle size is approximately 50μ)
It has been experimentally confirmed that it is desirable to use a sleeve (below), but when developing with such a thin layer of toner, it is necessary to use a sleeve from the viewpoint of reproducibility of one-line images, etc., as will be explained in detail later. This creates a need to bring the image very close to the latent image surface.

Therefore, a developing method is conventionally known in which a conductive brush is provided on the surface of a conductive sleeve, and the flexibility of the bristles of the brush is used to press the bristles so that they are always in contact with the surface of the photoreceptor. In the case of this device, - Since all the bristles of the brush have the same potential, the result is the same as if the developing electrode (sleeve) were very close to the photoreceptor surface, but the image is solid compared to a line image. Since the electric field due to the image increases rapidly, appropriate gradation cannot be obtained. When trying to obtain the gradation of a solid image, the reproducibility of a line image is insufficient, and it is difficult for conventional devices to properly reproduce both images.

To solve this problem, it may be possible to provide a dielectric layer on the sleeve surface to widen the substantial development gap and reduce 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 sleeve surface, charges may accumulate on the surface of the dielectric layer due to frictional charging with the toner or other factors, and this may be removed. or known.

The above-mentioned problem of reproducibility of solid images and line images will be explained in more detail below.

When copying with an electrophotographic copying machine, it is generally desirable for solid images such as photographs to have the background and gradation of the image reproduced as they are, and for line images, that is, information such as text and line drawings, to be reproduced with a pencil. A major desire of users is to clearly reproduce even the thin lines they draw. Therefore, as shown in Figure 1, the γ characteristic curve showing the relationship between the original density (0, D) and the copy image density (I, D) is As shown by the curve S shown in the figure, reproduction starts from a certain value of O and D in order to prevent dirt on the skin, and progresses at a slope of approximately 45°.
For line originals, the density is set to saturation, and for line originals, the curve is as shown by the broken line in the figure (0, 0).

It is required to quickly rise from a small value and reach the saturation concentration π.

Furthermore, there is a related problem in the exposure optical system of a copying machine. In other words, the transfer function (MTF) of the image gradation transmitted from the original to the photoreceptor according to the spatial frequency of the image.
changes as shown in FIG. The figure shows the spatial frequency on the horizontal axis and the MTF on the vertical axis.If the spatial frequency is 0 lines/IIJ, that is, if it is a solid image, the MTF is 1.

The original image is sent to the photoreceptor with the same contrast, but as the spatial frequency increases, that is, as the line becomes thinner, the MTF decreases, and the latent image on the photoreceptor becomes a line with weaker contrast. That is, even if the images have the same density on the original, the density of the latent image on the photoreceptor changes, and the potential of the solid image is higher than that of the line image. Therefore, it is required to develop the line latent image to be dense.

Now, as shown in Figure 3, the developing electrode (developing sleeve) 1
In a developing area where the and photoconductor 2 are placed opposite each other at a distance of KPo, the potential of the development electrode 1 is set to 200V, for example, and the photoconductor 2
Assuming that the dielectric constant 6 = 50 and the thickness d = 20p, the photoreceptor 2
FIG. 4 shows an example in which various charge patterns were created on the surface of the photoreceptor and the magnitude of the electric field on the surface of the photoreceptor was determined by computer simulation. In FIG. 4, the horizontal axis represents the distance P between the photoreceptor developing electrodes. The developing electric field is plotted on the vertical axis, and the solid line shows the curve for the black peta image, and the broken line shows the curve for the low contrast line image with O, D = 0.2 spatial frequency 5 lines/U (Charging potential Vs = 800V, skin potential Vs=200V)
. P for solid black images. As the developing electric field becomes smaller, the developing electric field increases rapidly, whereas in the case of a line image, there is almost no change. The reason for this is that in the case of a solid image, the charges are uniformly distributed over a wide area on the surface of the photoreceptor 20, as shown in FIG. , a parallel electric field is formed, whereas in the case of a line image, charges are localized on the surface of the photoreceptor 20, as shown in FIG. In addition to the components toward 1,
This is because the adjacent background portion (where no latent image is formed) of the photoreceptor 2 has a considerable amount of component opposite to it. This development is called the edge effect.

From FIG. 4, for example, O, D=0.2. 5 spatial frequencies/
If you try to reproduce a low-contrast line image of IIu+ to a solid black image with a strong saturation density.

Distance P between photoconductor developing electrodes. 0.2. It turns out that you need to choose accordingly. However, as described above, when the toner layer is a thin layer of several tens of micrometers, under this condition, a large gap is created between the surface of the toner layer and the photoreceptor.

Now, the change in the magnitude of the electric field depending on the distance from the photoreceptor surface will be explained. FIG. 6 is a group of curves showing the relationship between the spatial frequency and the developing electric field when the distance P between the developing electrodes on the surface of the photoreceptor is 0.51 wJ, using the distance from the surface of the photoreceptor as a parameter. As you can see, in the very vicinity of the photoconductor, the condition is that a line image (for example, 5 lines/, >) is emphasized compared to a solid image (0 lines/,), but the distance from the photoconductor surface is large. Therefore, if development is performed with a large gap between the toner surface and the photoreceptor, the reproducibility of the line image will be extremely poor.

In order to solve these problems, the present inventors first
As shown in FIGS. 7 and 8, a dielectric layer 5 is provided on the conductive support 4 of the sleeve 6, and finely divided float electrodes 6 are formed on the surface of the dielectric layer 5 so that the surface is exposed (in the form of islands). We proposed a buried developing device.The above-mentioned float electrodes are electrically insulated from each other, and are connected to the photoreceptor 9 through toner.
come into contact with Therefore, the float electrode is brought to a certain potential state by the electric field created between the electrostatic latent image on the photoreceptor and the conductive support 4 of the sleeve 3. By introducing the float electrode 6 as described above into the electric field for the line image previously explained with reference to FIG. 5(b), an effect of greatly reducing the dielectric thickness is produced. In the case of a parallel electric field due to the latent image of a solid image shown in FIG. 5(a), the float electrode 6 has the effect of slightly reducing the dielectric thickness. As a result, it has become possible to properly reproduce both line images and solid images.

As shown in FIG. 7, this developing device uses a belt-shaped photoreceptor 9 that is passed around a roller 7°8.
Since the float electrode 6 can be brought into close contact with the toner thin layer 10, a good image can be obtained, but it is difficult to obtain such conditions when a normal drum-type photoreceptor is used. In the case of a drum-type photoreceptor, there is also a method in which the dielectric layer is made of an elastic material to improve adhesion. Although it is not inconceivable, it has the disadvantage that the manufacturing method would be considerably difficult.

An object of the present invention is to provide a developing device that solves the above-mentioned problems when applying a true charge developing method using a high-resistance toner to a drum-shaped photoreceptor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to drawings showing embodiments thereof.

In the developing device according to the embodiment of the present invention shown in FIG. 9, a developing sleeve 12 is provided adjacent to the photosensitive drum 11. As shown in FIG. A dielectric layer 14 is laminated on the outer periphery of the conductive support 13 of the developing sleeve 12, and a conductive brush 15 is provided on the entire circumference of the dielectric layer 14. The conductive brush 15 is composed of conductive bristles that are insulated from each other in terms of gas. Inside the developing sleeve 12, a magnet 16 having a plurality of alternating north and south poles is provided, and is configured to rotate in a direction opposite to the direction in which the sleeve 120 rotates.

A toner supply section 17 is provided on the opposite side of the development sleeve 12 from the development position in contact with the photoreceptor drum 11, and an excess toner removal brush 18 is provided at a position where the peripheral surface of the development sleeve 7'12 comes out from the toner supply section 17. is provided.

Since this device is configured as described above, the photoreceptor 11
Even if the conductive brush 150 has a drum shape, its flexibility ensures that the bristles of the conductive brush 150 always come into contact with the surface of the photoreceptor drum 1-1 via the toner 10, and these bristles are not electrically connected to each other. Since it is in the V-insulated state and is also insulated from the conductive support 13 by the dielectric layer 14, it exhibits the effect of the float electrode described above, and produces low contrast line images,
Good reproducibility can be achieved across both solid images.

Further, since the electrode is brush-shaped, it has the effect of gently sweeping the surface of the photoreceptor, and this also has the effect of removing toner adhering to the background portion.

As a result of the above, it is possible to obtain copies with good reproducibility and without background stains. 1 Next, an example of the specific structure and manufacturing method of the conductive brush used in the present invention will be explained.

First, an epoxy resin layer (dielectric layer) 14 of about 500 μm is formed on the surface of a stainless steel sleeve (conductive support) 130 by known powder coating, and after baking, this is ground into a uniform layer of 300 μm. Next, epoxy adhesive is uniformly applied to the surface to a thickness of several tens of micrometers, and then a known conductive fiber (e.g.
Electrostatic flocking with Beltron (manufactured by Kanebo), etc. According to the results of experiments, the appropriate length of the conductive fibers (brush hairs) at this time was about 0.5 to 20 mm.

The developing sleeve made by the above method has a dielectric layer provided on the conductive sleeve, and a dielectric layer on the surface.

It has a configuration in which a conductive brush made of bristles that are substantially insulated from each other is provided on the surface. During electrostatic flocking, some of the bristles on the brush came into contact with each other and became conductive.
No particular problem was observed in the image when development was performed using the method described below.

An example of a developing method using a developing sleeve having a conductive brush made by the above method will now be described. This development method includes
A prototype toner with a magnetic content of 40% by weight, an average particle size of 68, and p was used.

Toner is supplied from the toner supply section 17 and adhered to the brushed sleeve 12. The excess toner is removed by the excess toner removal brush 18, and the toner is reduced to the extent that it adheres to the brush 15 in almost a single layer. As the excess toner removal brush mentioned above, a stainless steel brush provided on a non-magnetic stainless steel roller is used. This brush vibrates as the magnet 160 in the developing sleeve 12 rotates, and can effectively remove excess toner. Note that, as shown in FIG. 2, it is preferable to apply the same bias to this brush as to the stainless steel conductive support 13 of the developing sleeve 12.

The toner on the conductive brush 15 is negatively charged due to the relative movement between the toner and the brush due to the rotation of the magnet 160 and friction with the excess toner removal brush.

This charged toner is rubbed against the latent surface of the photoreceptor 11 by a brush 15 in the development area, thereby performing development. At this time, a bias voltage equal to g of the background potential of the latent image is applied to the developing sleeve.

The developed toner image is transferred by a transfer device (not shown) and then fixed by a fixing device.

Through the above process, a good image with excellent reproducibility of low-contrast line images and gradation was obtained on the transfer paper.

In addition to the materials shown in the above embodiments, various known materials can be used as the conductive fibers. It is also possible to use non-magnetic toner as the toner, and in that case, it goes without saying that the magnet inside the developing sleeve is not required (1°) Also, as a conductive brush for the developing sleeve, for example, stainless steel etc. By using a magnetic brush, the movement of the toner can be activated to improve development efficiency.

As described above, according to the present invention, it is possible to copy both solid portions and line portions with good reproducibility and gradation, and a remarkable effect is obtained in improving copy quality.

[Brief explanation of drawings]

Fig. 1 is a curve diagram showing desirable γ characteristic curves for solid images and line images, respectively. Fig. 2 is a curve diagram showing changes in transfer function with respect to spatial frequency of images of the exposure system of a copying machine. Fig. 3 4 is a cross-sectional view schematically showing the developing area, FIG. Figure 5 (, ) is a sectional view showing a developing sleeve having an electrode in the developing area of the solid image area, Figure 8 is an enlarged sectional view of two parts thereof, and Figure 9 is a sectional view showing an embodiment of the present invention. It is a diagram. 11... Electrostatic latent scratch carrier (photosensitive drum) 12...
Toner conveying member (developing sleeve) 13...Conductive support 14...Dielectric layer 15...Conductive brush 16...Rotating magnet JP-A-58-80-75(5) FIG. Figure 7 Figure 9 Procedural Amendments March 26, 1982 T,! Mr. Haruki Shimada, Director-General of the Japan Patent Office l Indication of the case 1982 Percentage [i No. 17896 2nd Name of the invention Developing device 3 Person making the amendment 1 (Relationship with the matter Patent Applicant 2) Name ( Name 1 (674) Ricoh Co., Ltd. 4 Agent address Kaji Kogyo Building, 2-32-4 Nishi-Shinbashi, Minato-ku, Tokyo Telephone (433) 4564 Postal code 105 Name Patent attorney (63] 3) Takeshi Ito 5 Attachment 11 of the supplementary market order (voluntary) 6. Column 7 of the detailed explanation of the invention in the specification subject to amendment, Contents of the amendment (1) ``The larger the size, the more In other words, the thinner the line, the lower the MTF.'' is corrected as follows: ``The thinner the line, the smaller the MTF value at that frequency. Therefore, for images with a wide spatial frequency distribution, such as point images and line images, , the high frequency components will no longer be reproduced."

Claims (2)

[Claims] (1) It has a toner transport member disposed adjacent to the electrostatic latent image carrier, and the electrostatic latent image formed on the electrostatic latent image carrier is transported by the toner transported by the toner transport member. In the developing device for visualizing images, the toner transport member includes a conductive support, a dielectric layer provided on the support, and a dielectric layer provided on the surface of the dielectric layer that are electrically insulated from each other. 1. A developing device comprising a conductive brush made of conductive bristles. (2) The toner conveying member includes a rotating magnet. The developing device according to claim 1, wherein the toner used is a magnetic toner.