JPH0428103B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a two-color electrophotographic method, specifically a two-color electrophotographic method.
A two-color image forming method in which latent images corresponding to each color of an original are formed with different polarities with respect to the background, and each latent image is developed with toner of a corresponding color of opposite polarity. In particular, it relates to transfer methods.

As a conventional method for obtaining two-color copies using a photoreceptor in which a photoconductive layer and an insulating layer are laminated on a conductive substrate, an example will be explained in which the two colors are red and black and the photoconductive layer is P-type. do.

First, as shown in FIG.
A negative charge is deposited on the surface, and an opposite positive charge is induced on the back surface. Next, as shown in FIG. 1b, primary image exposure is performed through a red complementary color filter (cyan filter) 6 while applying secondary charging with a positive polarity opposite to the primary charging. As a result, the photoconductive layer 3 becomes conductive in the region W corresponding to the white part of the original 5, and the positive charges on the back side of the insulating layer are discharged to the conductive substrate 2 side, so that the black part B and the red color are not exposed to light. Compared to portion R, positive charges flow into the surface of photoreceptor 1 more easily, and negative charges on insulating layer 4 are neutralized. On the other hand, in a black area that is not exposed to light or a red area that is exposed to a small amount of light, the induced positive charge on the back surface of the insulating layer is retained, so the amount of positive charge flowing into the photoreceptor 1 due to secondary charging is reduced, and the surface of the insulating layer is Although the negative charge in the area decreases, it is retained more than in the white area.

Next, as shown in FIG. 1c, when secondary image exposure is performed through the red filter 7, the photoconductive layer 3 becomes conductive in the white area W and the red area R, and some of the induced positive charges on the back surface of the insulating layer are Charges other than those corresponding to the negative charges on the surface of the insulating layer escape to the conductive substrate 2 side. Since the black part is not exposed to light, the previous state is maintained. As a result, the potentials of the black, color, and red areas are based on the white area (zero potential), and the black area: positive potential, the red area: negative potential, and the white area: zero potential. An electrostatic latent image is formed that corresponds to the color.

The thus obtained red and black latent images of different polarities are developed with toners of opposite polarity to the latent images to form a two-color image on the photoreceptor, and this two-color image is transferred. to obtain the final image (see Figure 1d).

In this case, in order to transfer the toner image to paper, the polarity of the black toner and red toner is usually aligned to one side by direct current corona discharge as a pretreatment, and then a direct current corona discharge of opposite polarity to the toner is applied from behind the transfer material. Transfer is performed by applying

However, according to this method, even the floating toner remaining in the white background area is transferred, resulting in fogging in the red and black areas, making it impossible to obtain good copies.

An object of the present invention is to solve the above-mentioned problems and provide a good transfer method without fogging.

An object of the present invention is to form electrostatic latent images on a photoreceptor, which correspond to the A color part and B color part of a document consisting of two colors A and B, and which have different polarities from each other with the white part as a reference. 2 electrostatic latent images with different polarities
Then, the photoreceptor carrying the toner image is subjected to direct current charging at the same time as the entire surface is exposed with an exposure amount that does not make the part developed with the toner conductive. This can be achieved by a two-color electrophotographic method characterized by applying alternating current corona discharge in which a polar direct current component is superimposed, and then transferring a toner image to a transfer member.

That is, in the present invention, a photoreceptor in which a photoconductive layer and an insulating layer are stacked on a conductive substrate is used to form a black part,
By changing the amount of charge remaining on the insulating layer in the red and white parts, and using the white part as a reference (zero potential), latent images with different polarities are formed in the black and red parts, and each latent image is After developing with a toner corresponding to the opposite polarity to the image, the potential of the red and black areas is changed by exposing the entire surface to light at a dose that does not make the area developed with the toner conductive and simultaneously applying DC charging. While changing the polarity to the same polarity, the absolute value of the potential is made larger than the absolute value of the potential of the white part, and then an AC corona discharge is performed by appropriately superimposing a DC voltage of the same polarity as the photoreceptor potential at this time. By doing this, the polarity of the black toner and red toner is made to be the opposite polarity to the photoreceptor potential after full-surface exposure and simultaneous DC charging, and the polarity of the toner attached to the background is set to the same polarity as the photoreceptor potential after full-surface exposure. By doing so, it is possible to prevent fogging in the background area during transfer by direct current corona discharge having the same polarity as the photoreceptor potential after the entire surface exposure after this treatment.

The process of the present invention will be described in detail below: (1) A photoreceptor made of a conductive substrate 2, a photoconductive layer 3, and an insulating layer 4 successively laminated is first charged as shown in FIG. 1a. In this case, if no charge is injected from the substrate, uniform exposure is performed at the same time or immediately after charging.

(2) Next, image exposure and simultaneous reverse polarity charging are performed through the red cut filter 6 (see FIG. 1b).
At this time, the amount of reverse polarity charge is approximately
Make it 0V.

(3) Imagewise exposure is then carried out through a red filter 7 (see FIG. 1c).

As a result, the potentials of the black, white, and red areas are based on the white area (zero potential), and the black area: positive potential, the red area: negative potential, and the white area: zero potential. An electrostatic latent image is formed that corresponds to the color.

(4) The thus obtained red and black latent image of opposite polarity is developed with toner of opposite polarity to the latent image as shown in Figure 1d (in the figure, the negatively charged black color is (represents positively charged red toner).

The process up to this point is the same as the conventional method, but in the present invention, next, (5) full-surface exposure and DC charging are performed simultaneously.
In this case, the exposure amount is such that in the background area (non-image area), the photosensitive layer becomes conductive due to light irradiation, and in the image area (black toner area and red toner area), the light does not reach the photosensitive layer because it is blocked or scattered by the toner. The amount should be such that it does not become conductive. This exposure amount varies depending on the photosensitive material used, the potential of the latent image, the toner on the photoreceptor, etc., and cannot be determined unambiguously, but it is used for image exposure during latent image formation to the extent that the image area does not become conductive. The entire surface is exposed at a value sufficiently lower than the exposure amount.

As a result, in the black and red image areas, light is blocked by the toner on them, and the photoreceptor is not exposed to light, but in the non-image areas, light is illuminated.
For this reason, a difference occurs in the capacitance of the photoreceptor between the image area and the non-image area, but by applying direct current charging at the same time in this state, the potentials of the red area and the black area become the same polarity, and the absolute value of the potential is The value is larger than the potential of the white area.

As a result, the surface potential of the photoreceptor changes from FIG. 2a to FIG. 2b. Although DC charging is used as charging in FIGS. 2a and 2b, the polarity may be either, and it is preferable to use a constant current power source. Furthermore, the polarity of the red toner and black toner is naturally the same as the polarity of the DC charging used at this time.

(6) Next, perform AC corona discharge by superimposing a DC voltage of the same polarity as the photoreceptor potential at this time. When an AC corona discharge with a superimposed DC voltage is applied, the polarity of the current flowing through the photoreceptor changes depending on the photoreceptor potential, for example.
In the case of DC superimposed AC corona discharge, the situation changes as shown in Figure 3.

Therefore, if the point at which the polarity of the photoreceptor changes (potential V ₀ ) is selected to be a voltage that is a little higher in absolute value than the background potential, the black and red areas will have the same voltage as shown in Figure 4. A current with the opposite polarity (+) to the potential of the black portion and the red portion flows, and a charge of the same polarity (−) as the potential of the black and red portions flows to the background portion. Therefore, a large amount of charge with the opposite polarity to the potential of the black and red parts is given to the black and red parts,
The polarity of the black toner and red toner is changed to make the black toner and red toner have the same polarity, and conversely, the background part is given a charge with the same polarity as the potential of the black and red parts.
The toner adhering to this area can be made to have the opposite polarity to the toner in the image area, so even when the black and red toner in the image area is transferred, the fog toner in the non-image area is not transferred, and there is no fog. Good two-color electrophotography can be obtained.

In addition, one method for obtaining a two-color copy from a two-color original, for example, black and red, is to use a photoreceptor in which two photosensitive layers with different spectral sensitivities are laminated. By changing the amount of charge remaining at the boundary between the two photosensitive layers, latent images with different polarities are formed in the black and red areas, using the white area as a reference (zero potential), and each latent image is converted into a latent image with a polarity opposite to that of the latent image. The method of the present invention can also be applied to a method of developing with a corresponding toner by exposing the entire surface after development to light to which the upper photosensitive layer has no sensitivity and the lower photosensitive layer has sensitivity.

Next, the present invention will be explained with reference to Examples.

As a photoconductor drum, a 110 μm thick selenium-tellurium photoconductor is placed in an aluminum cylinder with a diameter of approximately 120 mm.
vacuum evaporated to a certain extent, and then urethane on top of that.
A coating with a thickness of about 25 μm was used.

This photoreceptor was negatively charged by a first charger to uniformly charge its surface potential to about -2000 [V]. Next, while irradiating the photoreceptor with a light image through a cyan filter, it is charged with a second charger of positive polarity, and its surface potential is raised to +2000 [V].
It was charged to some degree.

The same light image was then illuminated through a red filter. This results in a black/white contrast of 900
[V], and a red/white contrast of 300 [V] was obtained.

Only the black area was developed by applying charged black toner to the load using the first developing device to which an appropriate bias voltage was applied to the surface of the photoreceptor. Subsequently, the second
By applying positively charged red toner to the developing device, only the red area was developed. Thereafter, the surface of the two-color developed photoreceptor was uniformly exposed to light over the entire surface and simultaneously charged with a direct current. The amount of light at this time was about 1 to 5 times the amount of light when image exposure was performed through the red filter 4. The distance between the DC charging corotron wire and the photoreceptor was approximately 10 mm, and a constant current power source was used as the power source. As a result, the polarity of the latent image in the black part was reversed and became the same as the polarity of the latent image in the red part. The potential of the photoreceptor at this time was about -200 [V] in the white part and about -400 [V] in the black and red parts.

Next, an AC discharge was applied to the entire surface of the photoreceptor with a DC bias appropriately superimposed. At this time, the DC bias and AC voltage are such that the surface potential of the photoreceptor immediately after the AC discharge is slightly smaller than the potential of the white part immediately before that (50
(about 100 [V]) was selected so that it was on the potential side of the black and red parts. As a result, the photoreceptor potential is approximately -250 ~
-300 [V].

Next, a two-color toner image was transferred onto a transfer paper using a negative transfer corotron, and this was fixed using a fixing device.

In this way, clear 2 images with no fog in the background can be obtained.
I was able to get a color copy.

[Brief explanation of drawings]

1A to 1D are process diagrams showing the process of latent image formation in a conventional two-color (black/red) electrophotographic method;
FIGS. 2a and 2b, 3 and 4 are explanatory diagrams of the process after latent image formation according to the method of the present invention. Codes in the figure: 1...photoreceptor; 2...conductive substrate;
3...Photoconductive layer; 4...Insulating layer; 5...Original; 6
...Red cut filter; 7...Red filter.

Claims (1)

[Claims] 1 Place A of the original consisting of two colors A and B on the photoreceptor.
Electrostatic latent images with mutually different polarities are formed with respect to the white portion corresponding to the color portion and the B color portion, and each electrostatic latent image is developed with two types of toner having mutually different polarities. After the image-bearing photoreceptor is fully exposed and simultaneously subjected to direct current charging with an exposure amount that does not make the portion developed with toner conductive, an AC corona discharge is generated in which a direct current component of the same polarity as the photoreceptor potential at this time is superimposed. A two-color electrophotographic method characterized in that the toner image is transferred to a transfer member.