JPS61209466A - Electrophotographic device having plural developing devices - Google Patents

Abstract

PURPOSE:To suppress easily the mixture of different colors while the spatter of a developer is suppressed from a developer at the down stream side by disposing plural developing devices in the order of the developer controlled, so that the charge quantity of the developer can be larger, from the upstream side of the rotation of a picture carrier. CONSTITUTION:In order to suppress the spatter of the developer in the direction of a toner photosensitive body 1 on the sleeve 5a of the developing device 5 at the downstream, a higher current V than the surface current V0 of the photosensitive surface is always given to the developing device 5. In such a state, since an electric field E of (V-V0)/d arises between sleeve photosensitive surfaces, the toner image on the photosensitive surface generates a peeling off force F0 in the direction of the sleeve 5a of the developing unit 5 due to the electric field (d: interval between them). However, since the charge quantity of the toner image developed by the developing device 4 is larger than that of the developing device 5, the image force of an adhesive F is sufficiently large and the relationship F>F0 can be established. Namely the charge quantity of the toner of the developing device at the upstream side is set larger than that at the downstream side, whereby the spatter to the downstream developing device and color mixture can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrophotographic apparatus such as a color electrophotographic copying apparatus and a color recording apparatus of a computer output section, and particularly relates to an electrophotographic apparatus such as a color electrophotographic copying apparatus and a color recording apparatus of a computer output section, and more particularly to the above-mentioned electrophotographic apparatus in which a plurality of developing units are arranged on the circumferential surface of an image carrier. This invention relates to an electrophotographic apparatus such as the above. Although the following description will be made in connection with a copying apparatus, the present invention is not limited thereto.

Recently, the demand for color copying has increased rapidly not only in special fields but also in general office fields, and there is a desire to improve the quality of each image.

One of the important problems to be solved in order to meet such demands is how to configure the developing device that visualizes the electrostatic latent images of each color formed on the image carrier in full-color and multi-color copying machines. There's something to be said for it.

The most commonly used color electrophotographic copying apparatus at present employs a side-by-side multicolor developing device in which a plurality of developing devices each having a developer of each color are arranged along the surface of an image carrier.

However, when installing multiple developing devices as described above, the toner in one developing device may scatter or once adhere to the image carrier, i.e., the photoreceptor (developed toner). ) The problem is that the toner is attracted to another developing device by magnetic force or the like, causing color mixing.

Generally, toner is restrained on the sleeve of a developing device or on the surface of an image carrier by magnetic force and electrostatic force, so the weaker the restraining force, the more likely the colors will be mixed due to scattering, etc.0 For example, when a magnetic one-component developer is used Development method (Unexamined Japanese Patent Publication No. 54-4
No. 2141, etc.), the charge to the toner is generated by contact friction with the sleeve of the developing device, so the amount of charge is low (
4-8 p-c/g). When such toner is developed and the toner image on the image carrier is passed over another developing device, if the magnetic attraction of the magnet built in the developing sleeve of the other developing device is strong, the toner image will be Since the image has a low charge and therefore weak electrostatic adhesion to the image carrier,
A part of the toner image is peeled off from the image carrier by the magnetic attraction of the magnet of the other developing device and collected in another developing device. That is, a color mixture phenomenon occurs. This phenomenon will be easily understood if one considers that the other developing device employs the conventional two-component development method, that is, the magnetic brush development method.

Further, even if the conventional two-component development method is used in all developing devices, if the amount of charge of the toner is low, the binding force of the toner to the sleeve or image carrier will be weak.

Most of the scattered toner is collected by the downstream developing device due to gravity or the air flow over the image carrier as the image carrier moves, or it is so-called in-machine scattering that adheres everywhere inside the machine. This was causing problems such as.

In order to alleviate these problems, it may be possible to mechanically separate developing devices other than those in operation from the image carrier or other devices in operation, or to provide shutters on the sleeves of developing devices that are not in operation. However, all of these methods have the problem of making the device complicated, expensive, and large-sized.

11 Therefore, an object of the present invention is to be able to operate a plurality of developing units stably at all times without the need for any special equipment, and to avoid the above-mentioned toner scattering and resulting color mixing. An object of the present invention is to provide an electrophotographic apparatus that can prevent the above problems.

. The above purpose of the image carrier is to develop the electrostatic latent image formed on the image carrier using one of a plurality of developing devices arranged around the circumferential surface of the carrier, and then transfer it to a transfer material such as paper. In an electrophotographic apparatus having a system of This is achieved by an electrophotographic device characterized by the following.

Hereinafter, the electrophotographic apparatus according to the present invention will be described in detail with reference to the drawings.

As described above, the principle of the present invention can be applied to an electrophotographic apparatus for multicolor printing of two or more colors, and furthermore to an electrophotographic apparatus for gold color (full color). The embodiments will be described in connection with an electrophotographic copying apparatus having two developing devices for the sake of simplicity.

In FIG. 1, an electrophotographic reproduction apparatus is shown in a schematic cross-sectional view. A photoreceptor 1, which is one of the image carriers, is uniformly charged by a charger 2 and subjected to image exposure 3 to form an electrostatic latent image 1, which is then toned by toner from a developer 4 or 5. Visualized. This visualized toner image is transferred to a transfer material such as paper by a transfer charger 6, electrostatically peeled off from the photosensitive surface by a one-separation charger 7, and advances to a fixing device. The transferred residual toner image is removed by a cleaning hand yt8 such as a cleaning blade.

In an apparatus having a series of processes listed in L, a plurality of 1
In this embodiment, when two developing devices are used, multicolor printing or copying in a desired color (color selection) is possible by changing the coloring material of the toner used in each developing device.
For example, if the developing device 4 is black and the developing device 5 is red, by applying a developing bias to only one of the developing devices, it is possible to develop only black or red (color selection). If the same transfer material is provided after development, transfer, and fixing with black toner in the first process, and development is performed with red toner in the second process, multicolor printing becomes possible. Therefore, by arranging four developing units on three sides, it is possible to perform three-color, four-color printing, etc., without limiting to the above example.

In this embodiment, the developing unit 4 on the upstream side in the rotational direction of the image carrier l
A two-component development method using a mixture of carrier and toner is used for the development device 5, and a development method using magnetic l-component toner is used for the development device 5. However, in the upstream two-component development method, instead of developing by bringing a conventional magnetic (carrier) brush into contact with the photosensitive surface, the carrier is retained in front of the doctor blade, and only the toner passes between the carriers. A developing method in which a thin layer of toner is formed on the sleeve, and this is placed in a non-contact state with the photosensitive surface for jumping development (for details, see Japanese Patent Application No. 151028/1983);
Alternatively, a method is used in which the heights of carrier and toner brushes are regulated using a doctor blade so that they are in a non-contact state with the photosensitive surface, and development is performed by applying a bias. By these methods, when the developing device 4 is not in operation, unnecessary toner is prevented from adhering to the photosensitive surface by controlling the bias without separating the developing device or the sleeve from the photosensitive surface.

1. In the arrangement of the developing devices as described above, as mentioned above, both toner loads in the upstream and downstream developing devices are distributed.
r5. There is a significant difference between r. That is, in the one-component method, the toner is charged mainly by contact friction with the sleeve, so the average charge amount is small (4 to 7 JLc/g).
), On the other hand, in the two-component method, the toner is charged mainly by contact friction with the carrier, so the average amount of charge is larger (10
JLc/g or more).

Here, the adhesion force of charged particles to an adherend will be discussed with reference to FIG. 2. Generally, the adhesion force of charged particles to an adherend is caused by electrostatic attraction F1. It is expressed as the resultant force of the mirror image force F2 of the charged particle and the van der Waals force F3, and F=F, +Fl+F3, but the third term is smaller than the first and second terms and can be ignored. Further, the first term is proportional to the charge amount σ, and the second term is proportional to the square of the charge amount σ. In other words, the adhesive force increases as the amount of charge increases. On the other hand, while the upstream developer 4 is in operation, the downstream developer 5 is
In order to prevent the toner on the sleeve 5a from flying toward the photoreceptor 1, a potential V higher than the surface potential VO of the photosensitive surface is usually applied. In particular, since the amount of charge δ' of the toner possessed by the developing device 5 is small, the electrostatic attraction force in the first term must be increased in order to increase the adhesion force F' to the sleeve expressed by the above equation and prevent scattering. V is set as a much higher bias value than Vo. In such a state, there is a gap (V-Vo) between the photosensitive surfaces of the sleeve.
)/d is generated, so the toner image on the photosensitive surface is
The peeling force F in the direction of the sleeve 5a of the developing device 5 due to the electric field of
(here, d is the distance between the two).However, since the amount of charge of the toner image developed by the developing device 4 is larger than that of the developing device 5, the second term of the adhesion force F is The mirror image force expressed by becomes sufficiently large, F>F.

The relationship holds true. In other words, by making the amount of charge on the toner in the upstream developing device larger than that in the downstream side, even when a bias is applied to suppress toner scattering from the downstream developing device, the toner image produced by the upstream developing device is The adhesion force is greater than the peeling force associated with bias application to the downstream developing device, and therefore, scattering to the downstream developing device and color mixing can be prevented.

A copying experiment was conducted using an electrophotographic apparatus according to the above example. The surface potential of the photoreceptor is set to +400V at maximum, and the two-component method described above is applied to the developer 4, and the l-component method is applied to the developer 5.
In both cases, negative polarity toner was used. In this case, the amount of charge of the toner in the developing device 4 is -10 to -151Lc/g.
The amount of charge of the toner in the developing device 5 is -3 to -6 p-c.
/g, so d = 3001 on the sleeve of developing device 5.
A bias of +600V was applied as Lm. Under these conditions, even when 10,000 sheets of A4 paper are passed through, the color mixture in the developing device 5 is slight, and the characteristics of the developing device 5 are as follows.
It did not reduce the level of bass.

Next, another embodiment of the electrophotographic apparatus according to the present invention will be described. In this embodiment, as shown in FIG. , both use magnetic one-component toner, and the upstream developer is black and the downstream developer is sepia. As mentioned above, in the l-component method.

Since charge is applied to the toner mainly by contact friction with the sleeve, the larger the contact area, the larger the amount of charge. Therefore, in this embodiment, as shown in FIG. 3, the actual pressure fa of the toner material in contact with the sleeve is made larger in the upstream developing device 4 than in the downstream developing device 4. Specifically, with the sleeve diameter r being the same, the angle θ formed by the blade 10 and the stage lower surface 11 was approximately 1.5 times larger on the upstream side than on the downstream side. As a result, the amount of charge on the toner in the developing device 4 becomes sufficiently large compared to that in the developing device 5.
The same effects as in the previous example were obtained.

Conversely, in a system in which 0 was the same, the sleeve diameter r was increased on the upstream side, and the contact distance was increased, neither scattering nor color mixing occurred.

Furthermore, in this embodiment, which describes another embodiment of the electrophotographic apparatus according to the present invention, two developing units are used as in the previously described embodiments, and both use the previously described two-component method. 2
In the component method, the toner is generally charged by contact friction with the carrier. Therefore, in this example,
A different type of carrier agent is used in the reproducing device. Specifically, the specific surface area of the carrier in the upstream developer 4 is made larger than that of the downstream carrier. For example, a flat one (Japanese iron powder type EFV carrier) is used in the developer 4, and A spherical developing device (TSV carrier manufactured by Nippon Steel Powder) was used as the developing device 5. As a result, the uneven carrier takes in more toner than the spherical carrier, and the number of contacts and area becomes larger, and the amount of charge becomes correspondingly larger. In other words, the amount of charge on the toner on the upstream side is larger than that on the downstream side,
Effects similar to those of the previously described embodiments were obtained.

Alternatively, instead of making the shape of the carrier the same, the particle size of the carrier is made smaller on the upstream side. For example, the particle size of the carrier on the upstream side is 50 to 80 ILm, and that on the downstream side is 100 to 150 ILm.
m. The smaller the particle size of the carrier, the better it mixes with the toner, and the number of times the two come into contact increases.
The amount of triboelectric charge increases accordingly. Therefore, the amount of charge of the toner on the upstream side was larger than that on the downstream side, and it was possible to prevent scattering and color mixing as in the previously described embodiments.

In the present invention, when a plurality of developing devices are arranged on the circumferential surface of the image carrier, the image carrying device is sequentially arranged starting from the developing device in which the amount of charge of the developer is controlled to be large. By arranging the toner from the upstream side of the rotation of the image carrier, it is possible to prevent toner from scattering from the downstream developing device (even under such bias application) and prevent toner from scattering from the image carrier and the accompanying toner from the downstream developing device. The effect is that color mixing can be easily suppressed.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of an electrophotographic apparatus according to the present invention. FIG. 2 is a diagram illustrating the adhesion force of charged particles to an object to which they are attached. FIG. 3 is a diagram illustrating changes in contact between the sleeve and toner in the developing device. l: Image carrier? = Charger 4.5: Developer F-Fr + F2 10F3 F, Key-F
2°ri・no2 Figure 3

Claims (1)

[Claims] 1) An electrophotographic method in which an electrostatic latent image formed on an image carrier is developed by one of a plurality of developing devices arranged around the carrier, and then transferred to a transfer material such as paper. In the apparatus, the plurality of developing devices are arranged in order from the upstream side in the rotational direction of the image carrier to the downstream side in the rotational direction of the image carrier, starting with the developing device having a developer with a large amount of charge. Photographic equipment.