JPS58102251A - Prevention for mixing of colors in two color electrophotography - Google Patents

Abstract

PURPOSE:To obtain sharp two color copies by applying the potential at the intermediate of the threshold potential of the 2nd developer and the threshold potential of the 1st developer upon a biasing roll provided in a developing device which performs secondary development thereby removing the 1st developer mixed therewith. CONSTITUTION:The 1st developing machine 7 (for example, a red color) and the 2nd developing machine 8 (for example, a black color) are provided so as to face a photoreceptor 10. A biasing roll 9 for removing the mixed toners is provided in the machine 8, and if the developing threshold potential of the red toner after the mixing is defined as Va as shown in the graph and the developing threshold potential of the black toner as Vb, and if these potentials are assumed to be Va<Vb, the voltage Vc at the intermediate of Va and Vb is applied upon the roll 9 by which only the mixed red toner is developed electrically on the roll 9, so that the red toner mixed in the machine 8 is removed.

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 a Pfi photoconductive method 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 layers.

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

) Next, red cut filter (blue filter) 5
Positive charging (secondary charging) is applied at the same time as image exposure is carried out through (see FIG. 2). The red color is cut off by the 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 to the conductive layer 11. Therefore, this secondary charging is performed with the aim of dissipating the charge in the white portion.

At this time, for the red and black areas, since the secondary charge is positive, part of the negative charge on the transparent insulating layer is neutralized, and as a result, the apparent potential of the surface area becomes positive in the photoconductive layer. It becomes positive due to the influence of the number of charges.

(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 0) 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. A metric curve is obtained.

(4) Next, the # obtained in steps (1) to (3) above
Develop the image.

This developing method uses a positively charged red toner.
A known method is to uniformly expose the entire surface after Agll, invert the surface potential of the black portion from positive to negative, and develop with a black toner having a positive charge. In this method, iAgll is first performed with a positively charged red toner. The surface potential of the bright red part of the ridge K is neutralized by the red toner, and changes from the state shown by the solid line to the state shown by the broken line in FIG.

Next, the entire surface is uniformly exposed. As a result of this exposure, the surface area of the black portion at about ms 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 the DC superimposed AC voltage, #I! Surface potential can be controlled to any value. This voltage is applied so that the electric potential of the black part is balanced while replenishing the charge with alternating current, so that a high conotrast can be obtained when it is later reversed, and the negative voltage is generally dominant due to the direct current component. The electric potential due to alternating current charging, which tends to be charged, is corrected to the positive side so that the entire white part becomes close to OK.

Next, development is performed using a black toner having a positive charge. In this case, the force/off potential of the developer is set to the level shown by the dashed line in FIG.

As a result, it is possible to perform spot color development without messing up the red developer area, but due to variations in the performance of the red developer during printing, the second development fII! Red toner gets mixed into the seashore. When developing with black toner of different polarity without reversing the surface potential of the black area from positive to negative by uniform exposure over the entire surface, the mixed red toner is removed by bias roll K.
.

Red toner can be easily removed by applying a bias voltage of opposite polarity, but this method 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. In some cases, this removal is difficult.

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

The object of the present invention is to (a) uniformly charge (-order charge) a photoreceptor formed by laminating a photoconductive layer and a transparent insulating layer on a conductive support, and to charge a photoreceptor with a complementary color to a specific color to be reproduced. Simultaneously with the image exposure (-missing exposure) through the filter of -
Perform secondary charging and polar local charging (secondary charging), perform image exposure (secondary exposure) through a filter that transmits only the specific color to be reproduced (-9), and (2) apply only the specific color mentioned above. Developed with the first developer (-second development), (e) AC corona discharge with a DC component superimposed as desired (
(tertiary charging), then (f) uniform exposure (tertiary exposure) to the entire surface, and (g) potential (absolute value) after completion of primary development with the specific color toner.
In a two-color electrophotographic method in which development is performed using a second developer having a higher development threshold potential (secondary development), a second bias roll is placed on a bias roll Kjl in the developing device that performs the second development.
removing the mixed first developer by applying a potential between the threshold i potential of the developer and the threshold potential of the first developer;
This can be achieved by a two-color electrophotographic color mixing prevention method using I mold.

That is, in the present invention, mixed toner is removed by a bias roll using 2 m of developers having different developing potentials.

The present invention will be explained below based on the accompanying drawings.

For convenience, it is assumed that the first developing machine uses a red developer and the second developing machine uses a black developer, and that 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,
Depending on the image formation process, the polarity can be opposite.

FIG. 2 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) S are provided facing the photoreceptor N, and a bias roll t for removing mixed toner is provided in the second developing machine. It is provided.

As shown in the figure, the iAg#I threshold potential of the red toner after mixing is Va, the current threshold potential of the black toner is vb, and Vm(Wb).
To change the image threshold potential, for example, a toner containing magnetalite may be used as a black developer toner.

In this case, the overused iron powder of the carrier and the magnetite in the toner attract each other, so that the development threshold potential becomes higher than that of a toner made only of resin. For example, in a toner containing 35% of magnetite by weight, a simple test showed that the potential at the end of development was 150 V high (Va<vb).
and vb, only the mixed red toner is electrically developed on the bias roll, and the red toner mixed into the second developing machine is removed. Incidentally, when the developing/cleaning pressure Vd is applied to the second developing device, the mixed toner can be removed if the value obtained by subtracting Vc from Vd falls between Va and vb.

[Brief explanation of drawings]

Figures 1 to 3 are explanatory diagrams for forming a latent image corresponding to red in red/black two-color electrophotography, and Figure 4 is the sensitometric (IJ-) curve of the latent image corresponding to red; Figure 5 is a graph showing the potential white line during development (solid line) and after development (broken line) of a red corresponding latent image, Figure 6 is the potential curve before secondary development g11, and Figure 7 is This 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. Symbols in the figure: l... 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; lO...photoreceptor.

Claims (2)

[Claims] (1) A photoreceptor consisting of a photoconductive layer and a transparent insulating layer laminated on a conductive support is subjected to 0) uniform charging (-order charging), and (b) a complementary color filter for the specific color to be reproduced. Simultaneously with the imagewise exposure (-missing exposure) through the imagewise exposure (-missing exposure), the above-mentioned -order charging and freezing polarity charging (secondary charging) are applied, and the imagewise exposure (secondary charge) is performed through a filter that transmits only a specific color of f→ reproduction plate fIi. (next exposure), (2) develop the aforementioned specific color with a first developer (-next development), (2) apply alternating current corona discharge (tertiary charging) with a direct current component superimposed as desired, and then ( ()) Perform full uniform exposure (tertiary exposure), ()) I
Secondary development is performed in a two-color electrophotographic method in which the material is developed at a higher %A than the potential after primary development with fixed color toner (HT) and developed (secondary development) with a second fAgII agent having a potential. The 21st bias roll in the developing device
A method for preventing color mixing in two-color electrophotography, characterized in that the mixed 1011L developer is removed by applying a potential between the threshold potential of the first developer and the threshold potential of the first developer. (2) 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 the second
The two-color electrophotographic color mixture according to claim 1, characterized in that a voltage is applied to the bias roll so as to have an intermediate value between the threshold potential of the developer and the threshold potential of the 11th HI agent. How to prevent it.