JPS62178275A - Two-color electrophotographic printing method - Google Patents

Abstract

PURPOSE:To obtain a clear two-color image even if a printer is used over a long period by using a carrier for a developer to use the 1st electrostatic latent image whose specific surface area is smaller than that of a carrier for a developer to develop the 2nd electrostatic latent image to attain developing processing. CONSTITUTION:A carrier having a small specific surface area is used as a carrier for a black developer to be the two-color developer for the 1st color. On the other hand, a carrier having a large specific surface area is used as a carrier for a red developer 8 to be a two-color developer for the 2nd color. The toner of the developer 5 adheres to the 1st electrostatic latent image formed by a light beam radiated from an exposure 3 with an electrostatic charging level higher than the 2nd developer and then the toner of the developer 8 adheres to the 2nd electrostatic latent image formed by a light beam radiated from an exposure 6. Even if the printer is used over a long period, always clear two-color images can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an improvement in a so-called two-color electrophotographic printing method in which two-color printing is performed continuously using an electrophotographic printing machine.

[Background of the invention]

Prior to explaining the present invention, the basic structure of a two-color electrophotographic printing machine will be explained based on FIG.

In FIG. 2, l is a photosensitive drum, 2 is a charger, 3 is a first exposure device, 4 is a first developing device, and 5 is a two-component developer for the first color consisting of toner and carrier (in this application, is a black developer for convenience), 6 is a second exposure device, and 7 is a black developer.
8 is a second developing device, 8 is a second color two-component developer (in this application, for convenience, it is referred to as a red developer), 9 is a transfer device, 10 is printing paper, and ■ is a cleaner. It shows.

In the above configuration, the surface of the rotating photosensitive drum 1 is
A first electrostatic latent image is formed by the charger 2, for example in a uniform manner, and by the light rays from the exposure device 3.

This first electrostatic M image is reversely developed by a two-component developer fl MIJ 5 of a developing device (hereinafter referred to as a black developing device) 4, and black toner is applied to the portion where ti has disappeared by the light beam from the exposing device 3. is attached. Subsequently, a second silent latent image is formed on the surface of the photosensitive drum l by the light beam from the exposure device 6, and this second electrostatic latent image is transferred to the developing device &, (hereinafter referred to as the red developing device). The toner is reversely developed by the two-component developer 8 (referred to as ) 7, and red toner adheres to the portion where the electric charge has been lost by the light beam from the exposure device 6.

After that, the two-color image is transferred to the transfer device 9,
The two-color toner image transferred to the printing paper p and remaining on the photosensitive drum 1 is cleaned by a cleaning unit,
Thereafter, repeat the above operations.

The operating system of a two-color electrophotographic printing machine is as described above.
In this type of printing press, when the red developing device 7t is used to develop the second dark NL latent image, the magnetic brush of the red developing device 7 comes close to the previously developed black image. (or the black image is rubbed), so conventionally there have been phenomena in which the above-mentioned black image is disturbed or the toner of the black image is scraped off.

However, when the above-mentioned phenomenon occurs, black toner may get mixed into the red image on the photosensitive drum 1, or black toner may fall into the red developing device 7. During use, the amount of black toner mixed into the red developing device 7 gradually increases, so that the red image developed on the photosensitive drum 1 and, by extension, the red image transferred to the printing paper p. It turns black.

[Purpose of the invention]

The present invention was made as a result of various studies in order to solve the above-mentioned problems of the prior art, and its purpose is to solve the problems of the prior art described above. An object of the present invention is to provide an improved two-color electrophotographic printing method that can always produce clear two-color images even when a printing press is used for a long period of time.

[Summary of the invention]

In order to achieve the first half of the objective, the present invention performs a first exposure on the surface of a uniformly charged photosensitive drum to form an electrostatic latent image, and converts this electrostatic latent image into an electrostatic latent image made of toner and carrier. The surface of the photosensitive drum is developed with a two-component developer of the first color, and then a second exposure is performed on the surface of the photosensitive drum to form an electrostatic latent image. Developed with a two-component developer for the second color, and then
In a two-color electrophotographic printing method in which the two-color image is transferred and fixed onto printing paper, a developer that develops the first electrostatic latent image is added to a developer that develops the second electrostatic latent image. The development process is carried out using a carrier having a smaller specific surface area than that of the carrier.

That is, the present invention focuses on the fact that the toner concentration of the two-component developer used in a two-color electrophotographic printing machine, and furthermore, the toner charge amount changes depending on the carrier specific surface area (particle size, shape, etc.), and the first By changing the carrier specific surface area of the developer that develops the electrostatic latent image and the second electrostatic latent image,
As will be described later, the present invention aims to provide an improved fC two-color electrophotographic developing method that can always produce clear two-color images.

[Embodiments of the invention]

Hereinafter, the present invention will be explained based on FIG. 1 and with reference to FIG. 2. FIG.
Relationship between toner concentration of component developer and carrier specific surface area,
Furthermore, K is a characteristic diagram showing the relationship between toner charge amount and carrier specific surface area. Among two-component developers consisting of toner and carrier, the specific surface area of the carrier changes depending on its particle size and shape. - As an example, considering the relationship between the specific surface area of a carrier and its particle size, the smaller the particle size of the carrier, the larger its specific surface area. On the other hand, as is clear from Fig. 1, the toner concentration tends to increase as the specific surface area of the carrier increases, but as for the amount of toner charge, as the toner concentration increases, the frictional effect with the carrier decreases. Therefore, it tends to be lower by that amount.

Here, the printing method of the present invention, which is carried out using a carrier indicated by the symbol A in FIG. 1 and a carrier indicated by the symbol B, that is, a carrier A having a small specific surface area and a carrier B having a large specific surface area, is illustrated in FIG. To explain based on this, carrier A having a small specific surface area is used as a carrier for black developer 5, which is a two-component developer of the first color. on the other hand,
Carrier B, which has a large specific surface area, is used as a carrier for red developer 8, which is a two-component developer of the second color. In that case, the toner concentration of the black developer 5 mixed with carrier A having a small specific surface area will be the value shown by O in FIG. 1, and the toner charge amount will be the value shown by Δ in FIG. value. On the other hand, the toner concentration of the red developer 8 mixed with the carrier B having a large specific surface area is higher than the toner concentration (○ mark) of the black developer 5, as shown in FIG. The toner charge amount is a value lower than the toner charge amount Δ of the black developer, as shown by the arrow mark in FIG.

In the above, the first electrostatic latent image formed by the light beam from the exposure device shown as 3 in FIG.
The toner of the red developer 8 then adheres to the second electrostatic latent image formed by the light beam from the exposure device 6. Therefore, using the red developing device 7, the second
When developing the electrostatic latent image, the magnetic brush of the red developing device 7 comes close to (or rubs against) the previously developed black image, as in the conventional case. In the present invention, the amount of toner band \i of the black developer 5 is set to a higher value than the toner charge amount of the red developer 8, as is clear from FIG. The adhesion of toner is strong. From the above, when developing the second electrostatic latent image using the red developing device 7, the phenomenon that the magnetic brush of the red developing device 7 disturbs the previously developed black image almost disappears. Also, KL in the red image! Even if - black toner is mixed in, this small amount of black toner can be considered to be almost equivalent to the density of red toner, and therefore, the amount of charge of the small amount of black toner mixed into a red image is:
It can be considered that the toner charge t of the red developer 8 mixed with carrier B has decreased to approximately the same value as the toner charge t (marked with a square mark) due to the decrease in the black toner's charge. As a result, the minute amount of black toner mixed into the red image is developed together with the red toner, which has a low charge amount and high developability, and furthermore, the amount of black toner mixed into the red image during the printing process is very small. Therefore, there is no problem in practice, but on the other hand, when the printing press is used for a long time, black toner gets mixed into the red developing device 7 and gradually increases. It is possible to effectively solve the problem that the red image developed on the printing paper 1 and, by extension, the red image transferred to the printing paper becomes black.

〔Effect of the invention〕

The present invention is as described above, and as is clear from the description of the above embodiments, according to the present invention, when printing is performed using a two-color electrophotographic printing machine, even if the printing machine is used for a long period of time, , can always obtain clear two-color images,
An improved two-color electrophotographic printing method can be obtained.

[Brief explanation of drawings]

FIG. 1 is a characteristic diagram showing the relationship between the toner concentration and the carrier specific surface area of the two-component developer used for carrying out the method of the present invention, and also the relationship between the toner charge amount and the carrier specific surface area;
Figure NX2 is an explanatory diagram of the basic structure of a two-color electrophotographic printing machine. 10. Photosensitive drum, 20. Charger, 39. first exposure device, 46. first developing device, 50. 1st color two-component developer, 6. , @2 exposure device, 7. . second developing device, 81. Second color two-component developer, 90
．． Transfer device, Koma6. Printing paper, no, cleaner.

Claims (1)

[Claims] 1. A first exposure is performed on the uniformly charged surface of the photosensitive drum to form an electrostatic latent image, and this electrostatic latent image is developed using a two-component developer of the first color consisting of toner and carrier. After development, a second exposure is performed on the surface of the photosensitive drum to form an electrostatic latent image, and this electrostatic latent image is
In a two-color electrophotographic printing method in which development is performed using a second color two-component developer consisting of toner and carrier, and then the two-color image is transferred and fixed onto printing paper, the first electrostatic latent 2, characterized in that the development process is carried out using a carrier that has a smaller specific surface area than the carrier of the developer that develops the second electrostatic latent image, as the developer that develops the image.
Color electrophotographic printing method.