JPS6354186B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrophotographic method, and particularly to an electrophotographic method suitable for two-color printing.

Currently, recording methods using electrophotography are being applied in many fields. Among these, laser beam printers are attracting attention as devices for printing information signals.

In such a printer, if the ruled lines of a slip, for example, and the calculated values or data values are printed in different colors, the printed matter becomes extremely clear and easy to understand. In addition, we often experience that it is easier to understand numerical values in calculations and the like if they are classified into two colors.

Therefore, a method as shown in FIG. 1 has been proposed as two-color printing using electrophotography. That is,
The photoconductive drum 1 is uniformly charged, for example, to a positive polarity by a charger 2. exposing the charged photoconductive drum 1 to a first light beam 3 carrying first information;
A first electrical latent image is formed, this electrical latent image is developed by the first developing device 4, and the first toner 5 is attached to the areas exposed to light, that is, the areas with low electric charge. 1 toner image is formed. Next, the second
to form a second electrical latent image;
The second toner 8 of a different color from the first toner 5 is adhered to areas with low electric charge, as described above, to form a second toner image. The two-color toner image thus formed is transferred onto recording paper 9 by a transfer device 10. The photoconductive drum 1 is cleaned with a cleaner 11 and used again.

However, in this method, when performing the second development, a second toner of a different color is deposited on the first toner image formed on the photoconductive drum by the first development, as shown in FIG. Since they overlap and adhere, and the second toner color is mixed with the first toner image, there is a drawback that clear two-color printing cannot be performed.

SUMMARY OF THE INVENTION An object of the present invention is to provide a two-color electrophotographic method that eliminates the drawbacks of the prior art described above and allows clear two-color printing.

The present invention has confirmed through experiments that the second toner adheres to the first toner image in an overlapping manner due to the potential difference between the surface potential of the photoconductive drum and the first toner image potential. As a means for solving this, a third exposing means and a charging means are provided after the first development, whereby the photoconductive drum is exposed once after the first toner image is formed, and the surface potential is reduced to approximately zero potential. By uniformly charging again,
The surface potential and the first toner image potential are made approximately equal.

Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 3 is a schematic configuration diagram of an example of a two-color electrophotographic method according to the present invention, and FIGS. 4 a to 4 d are process diagrams thereof, and the same parts as in FIG. 1 are designated by the same reference numerals. The photoconductive drum is positively charged, such as a Se photoreceptor,
An example with photosensitivity will be shown. An example in which the developer uses two components consisting of a carrier that is triboelectrically charged to a negative polarity and a toner that is electrically charged to a positive polarity will be shown. Fourth
The + sign in the figure indicates positive polarity potential, and indicates the first toner.
indicates a second toner having a different color from the first toner.

In FIG. 3, first, the photoconductive drum 1 is
The charger 2 uniformly charges the battery to a positive polarity. The surface potential _V1 of the drum 1 at this time is 700 to 800V. This charged drum 1 is exposed to a first light beam 3 carrying first information to be printed in a first color, and the charge at the exposed locations disappears as shown in FIG. 4a. The residual potential V _R of the exposed part is approximately 0 to 200V
It is.

Next, the first developing device 4 causes the first toner 5, which is positively charged, to adhere to the exposed area as shown in FIG. 4b. A first toner image is formed by so-called reversal development. This first toner image has a potential V _t (varies depending on the developer and development method) as shown in the figure due to the positive charge of the first toner 5.
have.

Subsequently, in a conventional manner, the photoconductive drum 1 is simply exposed to a second light beam 6 carrying second information in order to print in a second color, and the second exposed area is transferred to a second developing device 7. When reversal development is performed with a second toner 8 having a positive charge and a color different from that of the first toner 5, the first toner image previously deposited on the photoconductive drum 1 is removed as described above. The second toner 8 overlaps and adheres to the top, and the color of the first toner image becomes a mixture of the colors of the second toner 8, resulting in the inability to perform clear two-color printing. was.

The reason why the above phenomenon occurs is that, as shown in FIG. 4b, the potential V _t1 of the first toner image is lower than the surface potential V ₁ of the photoconductive drum 1, and the potential difference between the two enables reversal development. This is because the second toner further adheres to the first toner image during the second reversal development.

In order to solve the above-mentioned problems, the present invention provides an exposure means 1 after the first developing device 4, as shown in FIG.
First, the exposure means 12 exposes the photoconductive drum 1 on which the first toner image is formed, so that its surface potential V ₁ becomes approximately zero. Next, the photoconductive drum 1 is transferred to a second charger 1.
In Step 3, the battery is uniformly charged to positive polarity again. At this time, the voltage of the charger 13, that is, the surface potential V ₂ is as follows:
The toner 5 of the first toner image having the same polarity does not scatter and disturb the image, and the second light ray 6
The latent image potential required for reversal development can be formed at 500~
It is important to set the voltage to 600V.

Subsequently, the photoconductive drum 1 is exposed to a second light beam 6 carrying second information for printing in a second color. Then, as shown in FIG. 4c, the toner 5 forming the first toner image is also charged during the second charging, and the toner potential V _t becomes the surface potential.
V ₂ , and the charge at the second exposed location disappears (the residual potential V _R in this case is also 0 to 200 V as in the first exposure). Next, the developing brush is set to be close to or lightly touching the surface of the photoconductive drum 1, for example, with soft bristles, so as not to disturb the first toner image, or the second developing brush is set in a cascade manner so as not to disturb the first toner image. By the developing device 7 of
When reversal development is performed using a second toner 8 having a positive polarity different from that of the first toner 5, the second toner 8 becomes the first toner formed by the first toner 5, as shown in FIG.
The toner image does not adhere to the toner image, but adheres only to the areas exposed by the second light beam 6, forming a clear two-color toner image. If the toner image is transferred onto the recording paper 9 by the transfer device 10, there is an effect that clear two-color printing can be performed.

Note that the first surface potential V ₁ is the second surface potential V ₂
Although the case where the potential is higher has been described, the same effect can be obtained even when the potential V ₁ is lowered to be approximately equal to the potential V ₂ .

Although the case where the photoconductor is positively charged and has photosensitivity has been described, the same effect can be obtained when the photoconductor is negatively charged and has photosensitivity. In that case, of course, toner of negative polarity is used. Further, although the case where a two-component developer is used has been described, a single-component developer may also be used.

FIG. 5 is a block diagram showing another embodiment of the present invention. The same parts as in FIGS. 1 and 3 are indicated by the same symbols. In the figure, the first light beam 3 is a laser beam carrying the first information, and the exposure 14 carrying the second information is the ruled line of a slip or a predetermined pattern that is repeatedly printed on many pages, a so-called format. This is a case where overlay exposure consisting of a stored negative image overlay film 15, a light source 16, and an imaging lens 17 is used. In this case as well, exposure 12,
The effect of the charger 13 is exactly the same as described above.

Above, we have explained the case where both the first and second development are reversal development, but there is also a case where the second development is regular development, and the first development is regular development and the second development is reversal or regular development. The same effect can be obtained in the case of

As described above, according to the present invention, after the first development, the difference between the first toner image potential and the photoconductive drum surface potential is determined by applying the second toner image onto the first toner image during the second development. Since the second toner is made small enough to prevent it from adhering, it is possible to completely prevent the second toner from adhering to the first toner image, resulting in the effect of enabling clear two-color printing.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a two-color electrophotographic method according to the prior art, FIG. 2 is a schematic diagram of a two-color toner image according to FIG. 1, and FIG. 3 is a two-color electrophotographic method showing an embodiment of the present invention. FIG. 4 is a process diagram of the configuration shown in FIG. 3, and FIG. 5 is a configuration diagram of a two-color electrophotographic method showing another embodiment of the present invention. 1... Photoconductive drum, 5... First toner, 8
...Second toner, 12...Exposure means, 13...
Charger.

Claims (1)

[Scope of Claims] 1. A toner image of a first color is formed on a photoconductor whose surface has been uniformly charged by a first charging step by a first exposure step and a first reversal development step. and then erasing the charged potential of the photoconductor, lower than the charged potential of the first charging step,
and a second charging step of uniformly charging the toner forming the first color toner image and the surface potential of the photoconductor so that they are approximately equal to each other, and then a second exposure step. A two-color electrophotographic method, characterized in that a second color toner image different from the first color toner image is formed by a second reversal development step.