JPS6248227B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a developing device for a two-color copying system.

The electrostatic latent image portions corresponding to each color image of a two-color document with two-color images written in two colors A and B on a white background are placed on a latent image carrier with a positive surface potential distribution and a negative surface potential distribution. Due to the distribution, two types of toners are formed coexisting, and are colored with different colors and charged with opposite polarities.
A two-color copying method for sequential visualization has been proposed.

The formation of an electrostatic latent image is achieved by a special combination of charging and exposure when the latent image carrier is a photoconductive photoreceptor, or by a special combination of charging and exposure when the latent image carrier is dielectric. In some cases, this is accomplished by selective charging, such as with a multi-stylus.

The process shown in FIG. 1 is a typical example of a two-color copying process using a photoconductive photoreceptor.

In principle, the combination of colors A and B in a two-color image to be copied is arbitrary, but for the sake of concreteness, below, the combination of two colors A and B will be explained as two colors, black and red. . Although either A or B may be black, let us assume that A is black for the time being. Also, the color α, β of the toner used for development
does not have to be the same as the colors A and B of the two-color image, but assuming a common sense case,
Let us assume that colors A and α are the same color, and colors B and β are also the same color. Then, the color α is black and the color β is red.

Now, in line with this situation, let us briefly explain the process shown in Figure 1.

The photoreceptor 1 has a photoconductive layer 1 on a conductive substrate 10.
It has a three-layer structure in which layers 1 and 12 are laminated.
For forming the photoconductive layer 11, a photoconductive material that is not sensitive to red light due to its spectral sensitivity characteristics is used, and for forming the photoconductive layer 12, a material that is sensitive to red light is used.

This photoreceptor 1 is irradiated with red light to form a photoconductive layer 1.
With only 2 made into a conductor, the charger 2 sets the polarity to a predetermined polarity, for example, 1 to positive polarity as shown in the figure.
Next, it will be charged. As a result, positive charges are uniformly distributed on the interface between the photoconductive layers 11 and 12.

Next, using the charger 3, secondary charging with a polarity opposite to that of the primary charging is performed in the dark, thereby uniformly distributing negative charges on the surface of the photoreceptor 1. The amount of negative charge given by secondary charging is small compared to the positive charge given by primary charging, and
After the next charging, the polarity of the photoreceptor surface potential is reversed from the initial positive polarity to negative polarity.

In this state, the photoreceptor 11 is exposed to the light image of the two-color original.
When exposure is performed, the photoreceptor parts corresponding to the white background part of the document and the red image are irradiated with white light and red light, respectively, and the parts corresponding to the black image remain unexposed. Therefore, in the area corresponding to the white background area, both the photoconductive layers 11 and 12 become conductive and the retained charge disappears, so the surface potential becomes approximately O.
In the area corresponding to the red image, only the photoconductive layer 12 is made conductive. Therefore, in the area corresponding to the red image, the negative charge on the surface of the photoreceptor is transferred to the photoconductive layers 11 and 12.
The surface potential of the photoreceptor at this location becomes positive polarity by canceling out a part of the positive charge between them. On the other hand, in the area corresponding to the black image, the photoreceptor surface potential maintains the negative polarity state after secondary charging.

In this way, electrostatic latent image portions corresponding to a red image and a black image are formed on the photoreceptor 1 due to the positive polarity photoreceptor surface potential distribution and the negative polarity photoreceptor surface potential distribution, respectively. FIG. 2 shows a model of the changes in the photoreceptor surface potential up to this stage.

In this way, among the electrostatic latent image parts corresponding to the respective color images formed coexisting on the photoconductor 1, the part corresponding to the black image is visualized by the black positively charged toner TBr, and the part corresponding to the red image is visualized. If this is visualized using red negatively charged toner T _R , a two-color visible image corresponding to the two-color image is obtained on the photoreceptor 1 . All that is left is to transfer this two-color visible image to photoreceptor 1.
(if the photoreceptor 1 is in the form of a sheet), or may be transferred and fixed onto a suitable recording sheet and used for copying.

FIG. 3 schematically shows only the main parts of an example of an apparatus for realizing such a two-color copying process. In order to avoid complication, the same reference numerals as in FIG. 1 are used for items that are unlikely to be confused.

The photoreceptor 1 is formed into a drum shape, rotates in the direction of the arrow, and is primarily charged by a charger 2 . At this time, the red light lamp 21 emits light, and 1
Next, the portion of the photoreceptor to be charged is irradiated with red light. Next, secondary charging by the charger 3 and exposure by the exposure optical system 4 are performed in succession, and an electrostatic latent image in which electrostatic latent image portions corresponding to the red and black images coexist is formed. Of this electrostatic latent image, the electrostatic latent image portion corresponding to the black image is visualized by the developing device 5 with a developer D _Br containing black toner T _Br , and then the electrostatic latent image portion corresponding to the red image is visualized by the developing device 5. The image part is
The toner is developed by the developing device 6 using developer D _R containing red toner T _R . In this way, the photoreceptor 1
A two-color visible image is obtained on the circumferential surface of the , but since one of these visible images is charged with positive polarity and the other with negative polarity, the charger 7 changes the charged polarity to positive polarity, for example. After being aligned, the images are electrostatically transferred onto the recording sheet S by the transfer charger 8.
Thereafter, the transferred two-color visible image is transferred to the recording sheet S.
The image is fixed upward by a fixing device (not shown).
After the visible image has been transferred, the photoreceptor 1 is transferred to a static elimination charger 9.
After that, the cleaning device 13 cleans the peripheral surface to complete the copying process.

By the way, in such a two-color copying method, or in general, in a two-color copying method in which electrostatic latent image portions of opposite polarity are coexisted, there are the following problems with regard to development.

Since this problem occurs with respect to the developing device 6, that is, the second developing device, the developing mechanism of the developing device 6 will be briefly explained before explaining this problem. In the example of the apparatus shown in FIG. 3, the developing mechanism itself is exactly the same in the developing device 5.

A developer tank 61 of the developing device 6 stores a developer D _R that is a mixture of red toner T _R and magnetic carrier powder.
The carrier and the toner T _R rub against each other as they are stirred by the toner, and the carrier and the toner T R are frictionally charged to opposite polarities. This frictional charging causes the toner T _R
However, the carrier and toner materials are selected so that they are negatively charged. Now, the agitated developer D _R
is held on the circumferential surface of the magnetic brush roll 63 by magnetic force and conveyed in the direction of the arrow, and in the developing section, a so-called magnetic brush is formed, and the tip of this magnetic brush sweeps the circumferential surface of the photoreceptor 1. Development is performed in this manner. In this way, the developer D _R that has contributed to the development is separated from the magnetic brush roll 63 by the separation plate 64 and recovered into the developer tank 61 again.

Well, the problem is this. As mentioned above, development by the developing device 6 is carried out by sweeping the circumferential surface of the photoreceptor 1 with the tip of the magnetic brush. A black visible image is formed, and inevitably this black visible image and the developing device 6
The magnetic brushes rub against each other, and at this time, a portion of the black toner _TBr , which is the toner constituting the black image, is inevitably peeled off from the circumferential surface of the photoreceptor 1. Peeled off black toner T _Br
Since the toner T Br is carried by the flow of the developer D _R and collected in the developer tank 61, as copying is repeated, the black toner T _Br gradually gets mixed in and accumulates in the developer Dr in the developing device 6. will be done. When the accumulated amount of the mixed black toner increases to a certain extent, it affects the charging characteristics of the red toner T _R , impairs the original developing function of the developing device 6, and reduces the image quality of the red visible image. Problems such as color mixing and color mixing may occur.

SUMMARY OF THE INVENTION An object of the present invention is to improve a developing device for a two-color copying system in order to solve such problems.

The present invention will be described below with reference to illustrated embodiments.

The developing device according to the present invention has a first developing device and a second developing device.
The first developing device may be any type as long as it is of a dry type developing system. Suppose that the second developing device performs development using red negatively charged toner T _R . FIG. 4 schematically shows the second developing device in the developing device according to the invention. In the figure, code 1 is
As before, the photoreceptor is shown.

The developer D _r stored in the developer tank 61A of the developing device 6A is magnetically held on the circumferential surface of the magnetic brush roll 63A and conveyed in the direction of the arrow.
After contributing to development, it is separated from the magnetic brush roll 63A by a separating plate 64A. Various types of magnetic brush rolls are known, and any of them may be used. In addition, the code|symbol 62A has shown the stirring tool in the figure.

Now, the developer separated from the magnetic brush roll 63A by the separating plate 64A is separated from the magnetic brush roll 63A by the separating plate 64A.
The developing device 6A flows from the upper end of the developing device 6A.
The developer flows down to the bottom of the developer tank 61A. That is, after the developer Dr is separated from the magnetic brush roll, it flows through a recovery channel and is recovered, but this developer contains black toner used in the first developing device (not shown). Contains T _Br .

Now, the feature of the present invention is that a sorting device is provided in the recovery flow path for the developer separated from the magnetic brush roll, more precisely, in the portion of the recovery flow path after the end of the separation plate. The point is that

In the embodiment shown in FIG. 4, the main parts of this sorting device are composed of two pulleys P, a belt 30 that is passed around the pulleys P, a blade 31, and the like. One of the pulleys P is driven by a drive mechanism (not shown), which constitutes one end of the configuration of the sorting device, and rotates the belt 30 in the direction of the arrow. The belt 30 forms a part of the developer recovery channel by placing a portion thereof in the developer recovery channel. The belt 30 is made of conductive rubber, and is supplied with a potential opposite to the charging polarity of the black toner _TBr , that is, a negative polarity in this example, from a power source that is part of the sorting device, although this is also not shown. A potential is applied. The value of this applied potential is 50 to 1000V in absolute value, preferably 200 to 1000V.
Approximately 800V is appropriate. The conductive rubber that makes up the belt has a volume resistivity of 10 ³ to 10 ⁶ Ω.
It is preferable to use a material on the order of cm, with a thickness of 0.5 to 2 mm.

In this way, the belt 30 selectively attaches and captures the positively charged black toner T _Br mixed in the developer while coming into contact with the developer to be collected. That is, the belt 30 is a capture member for the toner T _Br . In addition, due to charging abnormality,
It also captures red toner that has been positively charged and is no longer able to contribute to development.

The captured toner is conveyed by the rotation of the belt 30, is scraped off from the belt 30 by a blade 31 whose edge is in contact with the belt, and is formed into a part of the developing device. It falls into a groove 32 that is part of the sorting device, is conveyed perpendicular to the drawing by the rotation of a spiral conveying member 33 that is also a part of the sorting device, and is collected in a collecting section (not shown). In this way, mixed black toner can be sorted out and removed in the middle of the recovery channel.
In the developer collected in the developer tank 61A,
Black toner does not exist at all, or even if it exists, it can be kept in a very small amount, and the accumulation of black toner in the developer Dr, which has been a problem in the past, can be effectively prevented or reduced. .

As a capture member, instead of the above belt, a fifth
As shown in the figure, a roller 30A may be used. Of course, the roller 30A is conductive, and a potential of opposite polarity to that of the black toner _TBr to be sorted is applied thereto. In the figure, the reference numeral 31A indicates a blade, and the reference numeral 34 indicates a recovery member. These constitute a black toner removal and collection means. roller 3
0A may be constructed using metal or the above-mentioned conductive rubber, and the applied potential may be approximately the same as in the case of the belt. Alternatively, the peripheral surface of a metal roller may be coated with conductive rubber to form the roller 30A, and a potential of about 100 to 700 V may be applied to the metal roller.

The gap between the separation plate 64A and the roller 30A is set to be equal to or less than the particle size of the carrier in the developer Dr, thereby preventing the carrier from being mixed into the collection member 34. Of course, the roller 30A is rotated in the direction of the arrow by a drive mechanism (not shown).

In the embodiment shown in FIG. 6, the main parts of the sorting device are comprised of a mesh roller 40 and a rotating electrode 41.

The mesh roller 40 is a hollow roller whose peripheral surface is made of a mesh member, and is rotated in the direction of the arrow by a drive mechanism (not shown). The material of the mesh roller 40 is metal,
Although plastics or the like may be used as appropriate, the roughness of the mesh should be smaller than the particle size of the carrier in the developer Dr. Then, only the toner in the developer Dr flowing down toward the mesh roller 40 flows into the mesh roller 40.

The rotating electrode 41 is a capturing member, and is provided inside the mesh roller with its rotating axis parallel to the roller, and is applied with an electric potential having a polarity opposite to that of the black toner _TBr to be selected and captured. The absolute value of the potential may be the same as in the case of the belt, roller, etc. described above. In this embodiment, as shown in FIG. 7, the spiral shape is kept stationary while the toner is being sorted, and is rotated from time to time. The accumulated black toner is transported and collected in a direction perpendicular to the drawing.

8 and 9 show the mesh roller 40
An example is shown in which a roller 42 is used as a rotating electrode as a capturing member provided therein. In the figure, code 44
indicates a blade, numeral 45 indicates a wire blade, and numeral 43 indicates a collection member. Since the collecting member 43 is disposed directly below the roller 42, only the toner captured by the roller 42 is collected by the collecting member 43. In addition, the 8th
As shown in the figure, a guide 46 for the developer Dr.
A cleaning blade 47 for the mesh roller 40 may be provided. Of course, a potential with a polarity opposite to that of the black toner is applied to the roller 42, and the roller 42 always rotates in the direction of the arrow.

[Brief explanation of the drawing]

1 and 2 are diagrams for explaining an example of a conventionally proposed two-color copying method, and FIG. 3 is an example of an apparatus for realizing the two-color copying method shown in FIG. 1. FIG. 4 is a partially sectional front view showing only the essential parts of one embodiment of the present invention, and FIG. 5 is a partially sectional front view schematically showing only the essential parts of another embodiment of the present invention. , FIG. 6 is an explanatory front view showing still another embodiment of the present invention, FIG. 7 is a perspective view showing the shape of the rotating electrode indicated by reference numeral 41 in FIG. 6, and FIG. FIG. 9 is an explanatory front view schematically showing only the essential parts of yet another embodiment of the invention. FIG. 9 is an explanatory front view schematically showing only the essential parts of still another embodiment of the invention. 1... Photoreceptor (an example of a latent image carrier), 64A...
...Separation plate, 30...Belt, 30A...Roller, 40...Mesh roller, 41...Rotating electrode, Dr...Developer.

Claims (1)

[Scope of Claims] 1. Electrostatic latent image portions corresponding to each color image of a two-color document in which two-color images are written in colors A and B on a white background are placed on a latent image carrier with a positive polarity surface. A two-color copying method in which potential distributions and negative surface potential distributions coexist and are visualized sequentially using two types of toners colored in different colors and charged with opposite polarities. , a device for developing an electrostatic latent image, comprising: a first developing device that dry-develops an electrostatic latent image portion corresponding to an A-color image with an α-color toner; and a second developing device that magnetically develops the electrostatic latent image portion corresponding to the B color image with β color toner after development, and after contributing to the development in the second developing device, A sorting device for α-color toner is provided in the recovery flow path for the developer separated from the magnetic brush roll by the separation plate, and a potential of opposite polarity to the α-color toner is applied to the capture member in this sorting device, so that the above-mentioned A developing device that selectively captures α-color toner mixed in a developer. 2. In claim 1, the sorting device comprises a plurality of pulleys, a conductive rubber belt that is stretched around the pulleys and serves as a capture member, and a mechanism that rotates the belt in a predetermined direction. A developing device comprising: a means for applying a potential having a polarity opposite to the charge polarity of the α-color toner to the belt; and a means for removing and collecting the adhered α-color toner from the belt. 3. In claim 1, the sorting device includes a conductive roller serving as a capturing member, a mechanism for rotating this roller in a predetermined direction, and a charging polarity opposite to the charged polarity of the α-color toner to the roller. A developing device comprising means for applying an electric potential and means for removing and recovering adhering α-color toner from the roller. 4. In claim 1, the sorting device comprises a mesh roller, a rotating electrode member serving as a capture member, which is provided inside the mesh roller with its rotating shaft parallel to the mesh roller, and A developing device comprising means for applying a potential of opposite polarity to the α-color toner to an electrode member, and a mechanism for rotating the mesh roller and the rotating electrode member.