JPH0255784B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preventing color mixing by removing toner from a first developing machine mixed into a second developing machine in a two-color electrophotographic system.

As a process for obtaining two-color copies using a photoreceptor with a three-layer structure in which a photoconductive layer and a transparent insulating layer are laminated on a conductive support, one conventionally known method is to use P-type light for convenience. A case will be described in which a two-color copy is obtained from a two-color original consisting of red and black using a conductive layer.

(1) First, a photoreceptor formed by sequentially laminating a conductive support 1, a photoconductive layer 2, and a transparent insulating layer 3 is negatively charged as shown in FIG.

(2) Next, image exposure is performed through a red cut filter (blue filter) 5, and at the same time, positive charging (secondary charging) is applied (see FIG. 2). The red color is cut out by a blue filter, so only the white color is exposed. That is, in the white portion, the photoconductive layer becomes conductive, and the positive charges of the photoconductive layer are discharged toward the conductive layer side. Therefore, this secondary charging is performed with the goal of eliminating the charge in the white portion. At this time, since the secondary charge in the red and black parts is positive, part of the negative charge on the transparent insulating layer is neutralized.
As a result, the apparent potential of the surface portion becomes positive due to the influence of the number of positive charges in the photoconductive layer.

(3) Next, as shown in FIG. 3, a second image exposure is performed through a red filter 6. As a result, light passes through the red part, the photoconductive layer becomes conductive, and supersaturated positive charges are discharged to the conductive layer side relative to the negative charges on the transparent insulating layer, so that the numbers of positive and negative charges match. Since the influence of negative charges near the surface increases, the apparent surface potential of the red portion becomes negative.

In the steps (1) to (3) above, when the potentials of the black and red parts are taken as a reference from the white part (zero potential), the black part has a positive potential and the red part has a negative potential, as shown in Figure 4. A sensimetry curve is obtained.

(4) Next, the latent image obtained in steps (1) to (3) above is developed.

A known method for this development is to perform development with a positively charged red toner, then uniformly expose the entire surface, invert the surface potential of the black area from positive to negative, and then develop with a positively charged black toner. There is. In this method, development is first performed with a positively charged red toner. As a result, the surface potential of the red portion is neutralized by the red toner, and the state changes from the solid line in FIG. 5 to the broken line.

Next, the entire surface is uniformly exposed. Due to this exposure, the surface potential of the black portion is reversed from positive to negative as shown in FIG. In this case, a process of applying an alternating current voltage superimposed on a direct current may be added prior to the uniform exposure of the entire surface. By applying this DC superimposed AC voltage, the surface potential can be controlled to an arbitrary value. This voltage is applied to balance the potential of the black area while replenishing the charge with alternating current, so that a high contrast can be obtained when it is later reversed.Also, due to the direct current component, the negative side generally tends to become dominant and charge The electric potential caused by a certain AC charging is corrected to the positive side so that the entire white part becomes close to zero.

Next, development is performed using a black toner having a positive charge. In this case, the cut-off potential of the developer is set at the level shown by the dashed line in FIG. Although this allows black development to be performed without disturbing the red development area, in reality, due to variations in the performance of the red developer, red toner gets mixed into the second developing machine. When developing with black toner of a different polarity without reversing the surface potential of the black part from positive to negative by uniform exposure over the entire surface, the mixed red toner is transferred to a bias roll with a polarity opposite to that of the red toner. It can be easily removed by applying a bias voltage, but this removal is difficult in the case of this method, which uses black toner with the same polarity as the red toner by inverting the surface potential of the black part by uniformly exposing the entire surface. be.

The present invention aims to remove mixed toner when the polarity of the red toner (first developer) mixed into the second developing device is the same as the polarity of the black toner (second developer).

The purpose of the present invention is to (a) uniformly charge (primary charge) a photoreceptor formed by laminating a photoconductive layer and a transparent insulating layer on a conductive support, and (b) charge a complementary color to a specific color to be reproduced. At the same time as image exposure (primary exposure) through a filter, charging (secondary charging) with the polarity of the primary charging is applied; (d) Develop only the specific color with a first developer (primary development), (e) perform AC corona discharge with a DC component superimposed (tertiary charging) if desired, and then (f) ) Uniform exposure (tertiary exposure) to the entire surface; In a two-color electrophotographic method for performing secondary development, a potential between the threshold potential of the second developer and the threshold potential of the first developer is applied to a bias roll provided in a developing device that performs secondary development. This can be achieved by a two-color electrophotographic color mixing prevention method characterized by removing the mixed first developer.

That is, the present invention uses two types of developers having different development threshold potentials, and removes mixed toner with a bias roll.

The present invention will be explained below based on the accompanying drawings. For convenience, it is assumed that a red developer is used as the first developer and a black developer is used as the second developer, and the polarities of the mixed red toner and black toner are both negative. However, in the method of the present invention, the polarity is not limited to this, and the polarity can be reversed depending on the image forming process.

FIG. 8 is a schematic diagram of the apparatus used in the method of the invention. A red developing machine (first developing machine) 7 and a black developing machine (second developing machine) 8 are provided facing the photoreceptor 10, and a bias roll 9 for removing mixed toner is provided in the second developing machine. It is. As shown in FIG. 9, the development threshold potential of the red toner after mixing is Va, the development threshold potential of the black toner is Vd,
Let Va<Vd. To change the development threshold potential so that Va<Vd, for example, a toner containing magnetite may be used as a black developer toner. In this case, since the iron powder of the commonly used carrier and the magnetite in the toner attract each other, the development threshold potential becomes higher than that of a toner made only of resin. For example, for a toner containing 35% by weight of magnetite, a simple test shows that the development threshold potential is
150V went high. If the voltage Vc applied to the bias roll is set between Va and Vb under the condition of Va<Vd, only the mixed red toner will be electrically developed on the bias roll, and the red toner mixed in the second developing machine will be developed. Can be removed. Note that when the developing bias voltage Vd is applied to the second developing device, mixed toner can be removed by making the value obtained by subtracting Vc from Vd fall between Va and Vb.

[Brief explanation of the drawing]

Figures 1 to 3 are explanatory diagrams when forming a red latent image in red/black two-color electrophotography, Figure 4 is a sensitometric curve of the red latent image, and Figure 5 is a sensitometric curve of the red latent image. The figure shows the red color before latent image development (solid line)
FIG. 6 is a graph showing potential curves after development (broken line), FIG. 6 is a potential curve before secondary development, and FIG. 7 is a graph showing the development start threshold of the developer when performing secondary development. FIG. 8 is a schematic diagram of an apparatus used in the method of the present invention, and FIG. 9 is an explanatory diagram of the method of the present invention. Codes in the figure: 1... Conductive support; 2... Photoconductive layer;
3... Transparent insulating layer; 4... Original; 5... Blue filter; 6... Red filter; 7... Red developing machine; 8...
Black developing machine; 9...bias roll; 10...photoreceptor.

Claims (1)

[Claims] 1. A photoreceptor formed by laminating a photoconductive layer and a transparent insulating layer on a conductive support, (a) uniformly charged (primary charging), and (b) a specific color to be reproduced. At the same time as image exposure (primary exposure) through a filter of a complementary color to the image, charging with the opposite polarity to the primary charging (secondary charging) is applied, and (c) image exposure through a filter that transmits only the specific color to be reproduced. (secondary exposure), (d) develop only the specific color with the first developer (primary development), (e) apply alternating current corona discharge (tertiary charging) with a direct current component superimposed as desired, Then (f) uniform exposure (tertiary exposure) to the entire surface, and (g) development with a second developer having a development threshold potential higher than the potential after the completion of primary development with the specific color toner (secondary development). In a two-color electrophotographic method, a potential between the threshold potential of the second developer and the threshold potential of the first developer is applied to a bias roll provided in a developing device that performs secondary development. 1. A method for preventing color mixing in two-color electrophotography, the method comprising removing the developer in step 1. 2. So that the value obtained by subtracting the developing bias potential of the device that performs secondary development from the potential applied to the bias roll is an intermediate value between the threshold potential of the second developer and the threshold potential of the first developer. 2. The method for preventing two-color electrophotographic color mixing according to claim 1, characterized in that a voltage of 100% is applied to the bias roll.