JPH0447826B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a method for an electronic copying machine, and in particular, it forms positive and negative electrostatic latent images on a photoconductor and sequentially uses toners of two colors with different polarities. Develop 2
This invention relates to a developing method for a color electronic copying machine.

Prior Art In order to obtain a two-color copy from a two-color original image, electrostatic latent images with different polarities corresponding to each color are sequentially visualized using two-color toner charged with different polarities2. Color electronic copying machines are known.

One of these is that one color has a positive potential with respect to the white background.
For the other color, two developing machines are installed in the moving direction of the photosensitive drum on which a negative latent image potential has been formed, and the first developing machine develops the first color (for example, black), and the second developing machine develops the first color (for example, black). There is a method of developing a second color (for example, red) on the machine. In this method, the first and second developing devices contain a developer such that the toner is charged to a polarity opposite to that of the latent image. That is, the first toner and the second toner are each charged with opposite polarities.

However, a problem with this developing method is that the toner from one developing device gets mixed into the other developing device. For example, the electrostatic latent image of the first toner formed on the photosensitive drum by the first developing device is scraped off by the magnetic brush of the second developing device, and this is removed by the second developing device. The second toner is mixed with the second toner. If toner of a different color is mixed into the developing device, disadvantages such as deterioration of the quality of the developed underlying image and accelerated deterioration of the developer occur.

As a means to prevent color mixing of the developer due to mixed toner as described above, a metal roll to which a voltage is applied is provided in the developing device, and only different color toners are adhered to the roll, which is then removed by a blade.
A method of separation has been proposed.

However, although this method is effective in removing different color toner immediately after it enters the developing device, it has a drawback in that it is less effective in removing different color toner that has completely entered the developing device.

As a result of studying this phenomenon, the inventors found the following causes.

As shown in FIG. 2a, the first toner in a conventional two-color electronic copying machine is negatively charged with respect to the first carrier. On the other hand, the second toner is positively charged with respect to the second carrier, as shown in FIG. 2b.
After the positively charged first electrostatic latent image on the photoreceptor is developed with the first toner in the first developing device, the photoreceptor is guided to the second developing device. In the second developing device, the negatively charged second electrostatic latent image on the photoreceptor is visualized with the second toner. When this second electrostatic latent image is visualized, the first toner comes into contact with the magnetic brush formed between the photoconductor and the developing roll, and a part of the first toner is scraped off and the second toner is
It gets mixed into the developing device. In addition, the first toner that has entered the developing device and mixed with the second developer forms an electrical pair with the second carrier in the same way as the second toner, as shown in Figure 2c. This is because they float and accumulate in the water. The charging series of these developers was measured and was as shown in FIG. In other words, since charging conditions were applied to each of the first developer and the second developer individually without paying any attention to the correlated charging series, when the second carrier and the first toner are mixed, the first toner is positively charged. The reason was that I was exposed to it. Therefore, in such a state, even if an attempt is made to remove the mixed first toner by providing a bias roll to which a voltage of opposite polarity to that of the first toner is applied in the second developing device, the mixed first toner will be removed immediately after the mixed toner is charged. It has been found that, although the first toner that is retained can easily adhere, the first toner that has been mixed in the second developing device cannot be recovered by the bias roll.

Purpose of the Invention The present invention has been made in view of the above drawbacks, and
It is an object of the present invention to provide a developing method in which the first toner mixed in the second developer can be easily recovered by ordering the charging series of both the first developer and the second developer. .

Structure of the Invention The above object is a developing method for a two-color electronic copying machine that forms positive and negative electrostatic latent images on a photoreceptor and has different polarities, in which a first toner mixed in a second developing device is transferred to a second developing device. In the case where the toner and carrier are separated and removed using a means having a bias roll provided in the developing device, the charging series of toner and carrier is T ₁ <C < T ₂ (however, T ₁
This can be achieved by using a developer that satisfies the requirements (T is the first toner, T ₂ is the second toner, C is the first carrier, and C is the second carrier).

EXAMPLES The present invention will now be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic diagram of a two-color electronic copying machine according to the present invention. 1 around the photoreceptor drum 1.
Secondary charger 11, secondary charger 12, exposure section 13, first developing device 14, second developing device 15, pre-transfer charger 16, transfer charger 17, charge eliminating charger 18, cleaning device 19, and charge eliminating lamp 20 are arranged as shown.

Here, the first developing device 14, the second developing device 15
uses a magnetic brush developing device, and uses a two-component developer consisting of toner and carrier. For example, assume that the first developing device 14 uses black toner and the second developing device 15 uses red toner.

Here, in the case of the method of the present invention, the charging series of each developer is T ₁ <C < T ₂ (where T ₁ is the first toner, T ₂ is the first toner;
2nd toner, C; 1st carrier, 2nd carrier)
It is characterized by using a material that satisfies the following. Specifically, as shown in FIG. 5, the first toner has negative polarity with respect to the first carrier, the second toner has positive polarity with respect to the second carrier, and the first toner has negative polarity with respect to the second carrier. The charging series of the toner and carrier is selected so that the toner and carrier are charged in a specific manner. That is, if the combination of toner and carrier is expressed in terms of charging series, it is first toner, first carrier, second carrier, second toner, or first toner, second carrier, first carrier, second toner. be. However, the above-mentioned charging series includes a case where the first carrier and the second carrier are equal. The ordering of the charge series of toner and carrier is related to the carrier core material, coating material, toner binder, coloring agent, charge control agent, etc. used in them, and the present invention is directed to the materials used. It is not intended to limit this, so it will not be described in detail.

In the two-color electronic copying machine of the present invention in which the developer to be used is specified in this manner, the positively charged first electrostatic latent image on the photoreceptor is developed by the negatively charged first toner. and is guided to the second developing device.
In the second developing device, when the negatively charged second electrostatic latent image on the photoreceptor is visualized by the second toner, the photoreceptor and the developing roll of the second developing device When the first toner comes into contact with the magnetic brush formed between them, a portion of the first toner is scraped off and mixed into the second developing device, even if it is mixed with the second developer. Since the first toner is maintained in a negatively charged state by the charging series, it easily adheres to the bias roll, is peeled off by a blade, and can be collected by a spiral roll.
Generally, the bias roll has a direct current of 1kV or less with the opposite polarity to the first toner, an alternating current with an effective voltage of 1kV or less,
Alternatively, an AC voltage on which a DC voltage of opposite polarity to that of the first toner is superimposed is used. By doing so, even in the second developer, the second toner charged to the same polarity as the bias voltage does not adhere to the surface of the bias roll, and wasteful consumption is prevented.

In order to verify the method of the present invention as described above, the present inventors measured the removal rate of mixed toner using a conventional two-color electronic copying machine using the charging series developer shown in FIGS. 4 and 5. did. The toner used was a red developer (red toner _TR , carrier) as the second developer.
C _A ) are commonly used, including black toner A of the charging series shown in FIG. 4, and black toner B (B ₁ , B ₂ , B ₃ ) shown in FIG. 5 a, b, c. After mixing for 5 minutes so that the first toner and the second developer were sufficiently agitated, the removal rate of the mixed black toner by the bias roll was examined. The results are shown in FIG. As can be easily understood from FIG. 6, in the case of conventional charging series black toner A, a slight amount of mixed black toner is removed over time, but even after 5 minutes or more, the removal rate remains low. Almost no change was observed, about 10%. On the other hand, the mixed black toner according to the charging sequence according to the present invention is rapidly removed from the start of B (B ₁ , B ₂ , B ₃ ) operation, and the removal rate reaches about 90% after 5 minutes.

Furthermore, the present inventors measured the state of the amount of charge of the red and black toners during the above measurement. The results are shown in FIG. As can be easily understood from FIG. 7a, the developer using toner B is the first (black) toner while the second (red) toner is positively charged.
It can be seen that the toner is clearly negatively charged and easily adheres to the positively charged bias roll. On the other hand, as can be understood from FIG. 3b, in the mixed toner using toner A of the charging series shown in FIG. 4, both the first (black) and second (red) toners are charged to the same positive polarity. It was proven that bias rolls of the same polarity could hardly remove it.

Although the present invention has been described above, the present invention is not limited to the above-mentioned one, but can be applied to, for example, a developing device equipped with a roll coated with the same material as the overcoat material on the carrier surface in the second developing device. The same effect can be achieved even if

It goes without saying that a red toner can be used as the first toner and a black toner can be used as the second toner.

Effects of the Invention As described above, the developing method of the present invention significantly improves the performance of the conventional mixed toner separation/removal means having a bias roll without adding any special means. A copying machine with high image quality and high color saturation can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of a two-color electronic copying machine according to the present invention, FIG. 2 is a diagram showing the charging state of a conventional developer, and FIG. 3 is a diagram showing the charging state of a developer according to the present invention. FIG. 4 is a diagram showing a charging series of a conventional developer, FIGS. 5 a to c are diagrams showing a charging series of a developer according to the present invention, and FIG. 7 is a diagram showing the amount of charge of the mixed toner shown in FIG. 6. FIG. Symbols in the figure: 1...photosensitive drum, 11...primary charger, 12...secondary charger, 13...exposure section,
14...first developing device, 15...second developing device,
16...Pre-transfer charger, 17...Transfer charger, 1
8...Electrostatic charger, 19...Cleaning device,
20... Static elimination lamp.

Claims (1)

[Scope of Claims] 1. A developing method for a two-color electronic copying machine in which positive and negative electrostatic latent images are formed on a photoconductor and sequentially developed with two color toners having different polarities, the method comprising: When the mixed first toner is separated and removed using a means having a bias roll provided in the second developing device, the charge series of the toner and the carrier is as follows: T ₁ <C < T ₂ However, T A developing method for an electronic copying machine characterized by using a developer that satisfies the following conditions _{: 1} : first toner, T ₂ : toner C: first carrier, second carrier.