JPS6337378B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a latent image forming method in a multicolor electrophotographic method.

A two-color or multi-color electrophotographic method is known that uses a photoreceptor in which at least two photoconductive layers having different spectral sensitivities are laminated on a conductive substrate, and is capable of copying a color original of two or more colors. There is. Regarding the specific latent image forming method, many different types of methods have been proposed, and the method disclosed in Japanese Patent Application Laid-Open No. 54-3537 is known as a representative one. However, with this method, it is not possible to selectively reproduce color A or color B from a multicolor document having black on a white background, color A, and color B. In other words, the above method uses chromatic color A and color B (chromatic color or black) on a white background.
A method of forming a latent image in a color A part and a latent image in a color B part of a multicolor original with opposite polarities to make a two-color copy, in which black, color A, and color B are printed on the white background. When applied to multicolor originals, the polarity of the black latent image always matches only the polarity of the latent image of color B, so it is impossible to selectively reproduce color A or color B. be. Furthermore, the method described in Japanese Patent Application Laid-Open No. 146832/1983 has a problem in that image exposure must be performed twice.

An object of the present invention is to create a latent image in a multicolor original having black, color A, and color B on a white background by one image exposure, which corresponds only to a specific color with good contrast and opposite polarity to the background. An object of the present invention is to provide a latent image forming method that can selectively and easily form a latent image.

The present invention will be described below with reference to the attached drawings, but for the convenience of explanation, it is assumed that a multicolor original has black, red, and blue images on a white background, and the latent image to be selectively reproduced corresponds to red or blue. Make it a latent image.

FIG. 1 is a process diagram of an embodiment of the present invention, and FIG. 2 is a diagram showing changes in the surface potential of a photoreceptor in each step.

In FIG. 1, the photoreceptor P used includes a first photoconductive layer 2 having a panchromatic spectral sensitivity or a spectral sensitivity to blue light on a conductive substrate 1.
, a light-transmitting electrical insulating layer 3, and a second photoconductive layer 4 that has spectral sensitivity only to red light and does not transmit it. First, in step (1), the surface of the photoreceptor is uniformly and negatively charged by the corona charger 5 while the entire surface of the photoreceptor is exposed to white light. This charging polarity is determined by the physical properties of the photoconductive layer used. Due to this white light irradiation, the second photoconductive layer 4 becomes conductive, and the negative charge given by corona charging moves in the second photoconductive layer 4 to form an interface with the electrically insulating layer 3 below. At the same time, the first photoconductive layer 2 also becomes conductive, and positive charges equal to the negative charges injected from the conductive substrate 1 and given to the surface move through the first photoconductive layer 2. ,
It reaches the interface with the upper electrical insulating layer 3, forms an electrical double layer with the upper negative charges, and the electrical insulating layer 3 is negatively charged. This step (1) may be performed by irradiating light after primary charging, or may be performed by using chromatic light having spectral sensitivity to both the first and second photoconductive layers. Next, in step (2), the surface of the photoreceptor is irradiated with a light image of the multicolor original 6 while being positively charged by a corona discharger 7 to which a positive voltage of opposite polarity to the primary charging is applied. Secondary charging is performed uniformly on the As a result, the surface potential of the photoreceptor is reversed to positive, as shown in FIG. 2(2). The charging conditions in this case must satisfy the following conditions. That is, the capacitance of the first photoconductive layer 2 is
C ₁ is the capacitance of the electrical insulating layer 3, C ₂ is the capacitance of the second photoconductive layer ₄ , V ₁ is the absolute value of the surface potential of the photoreceptor after primary charging, and photosensitivity after secondary charging. When the absolute value of the body surface potential is V ₂ , C ₂ V ₁ > C ₁ V ₂ ………(1) and (C ₁ C ₂ + C ₁ C ₃ ) V ₂ > C ₂ C ₃ V ₁ … …(2) Must be. Equation (1) is the condition for reversing the latent image for the color to be reproduced to the same polarity as the primary charge, and equation (2) is the condition for reversing the latent image for the other colors as secondary charge. This is a condition for maintaining the same polarity. As a result of being charged based on these conditions and performing image exposure at the same time, the white background portion 6a, black image portion 6b, and red image portion 6 of the original 6 are
c. In the photoreceptor areas Pa, Pb, Pc, and Pd corresponding to the blue image area 6d, the surface potentials are the same, but the first photoconductive layer 2, the electrically insulating layer 3, and the second photoconductive layer The respective states of charge in layer 4 will be different. That is, in the white corresponding area Pa, only the electrical insulating layer 3 is charged, and in the black corresponding area Pb, the first photoconductive layer 2, the electrical insulating layer 3, and the second photoconductive layer 4 are each charged, and the red corresponding area Pb is charged. In area Pc,
the first photoconductive layer 2 and the electrically insulating layer 3 are charged;
In the blue corresponding region Pd, the electrical insulating layer 3 and the second photoconductive layer 4 are charged. In step (3), the entire surface of the photoreceptor is irradiated with blue light through the blue filter 8.
Since the second photoconductive layer 4 transmits sensitivity to blue light, the state of charge of the second photoconductive layer 4 does not change, and the electrically insulating layer 3 is not affected by light, so its state of charge does not change. Only the first photoconductive layer 2 is sensitive to blue light and the charges stored there are discharged through the conductive substrate 1. The charges accumulated in the first photoconductive layer 2 are the charges existing in the black corresponding area Pb and the red corresponding area Pc, and in the black corresponding area Pb, the amount of positive charge on the first photoconductive layer 2 is approximately Since it becomes zero, the positive surface potential in this region decreases significantly, but it does not become negative according to equation (2) above. In the red corresponding area Pc,
As the amount of positive charge on the first photoconductive layer 2 decreases to almost zero, its surface potential reverses to negative according to equation (1) above. White corresponding area Pa and blue corresponding area
In Pd, the respective surface potentials decrease due to dark decay of the photoreceptor or, if the second photoconductive layer 4 is slightly sensitive to blue light, due to its light decay; The percentage of black corresponding area is
less than that in Pb. Furthermore, since the electrical insulating layer 3 in the blue corresponding region Pd has a negative potential,
The rate of decrease in surface potential is the white corresponding area Pa
larger than that in . The color of the irradiation light in this step (3) is not limited to blue, and other chromatic colors other than red can be used, but among them, the chromatic light to which the first photoconductive layer 2 is most sensitive is particularly preferred. Further, it goes without saying that the light irradiation may be performed directly from a light source containing the color without using a filter.

FIG. 3 shows a process for forming a blue-only latent image using the same multicolor original 6. In FIG. Steps (1) and (2) are the same as shown in FIG. 1, but in step (3), the blue filter 8
A red filter 9 is used instead. Since the second photoconductive layer 4 is sensitive to red light and does not transmit it, only the charges accumulated in the second photoconductive layer 4 are discharged. As a result, as shown in FIG. 4, in the black corresponding region Pb, the positive surface potential decreases significantly but does not become negative, and in the blue corresponding region Pd, the positive surface potential becomes negative. Furthermore, the positive surface potentials in the white corresponding area Pa and the red corresponding area Pc also decrease slightly. In other words, the primary charging voltage and the secondary charging voltage are controlled so that each part has such a surface potential.

Of the positive and negative latent images obtained by these processes, only the negative latent image is developed with positively charged toner and, if necessary, transferred to transfer paper to obtain a copy image. The color of the toner may be the same as the color of the image to be selectively reproduced, or may be different.

The material of the photoreceptor used in carrying out this invention includes a conductive substrate 1 having a volume resistivity of 10 ¹⁰ Ωcm.
Those with the following conductive layers, such as Al, Cu,
Metal plates such as Pb, or SnO ₂ , In ₂ O ₃ , CuI,
A plate made of a metal compound such as CrO ₂ or a plastic film, paper, or cloth coated with the compound by vapor deposition or sputtering may be used. As the electrical insulating layer 3, polyethylene,
Polystyrene, polybutadiene, styrene-butadiene copolymer, acrylic ester or methacrylic ester polymer and copolymer, polyester, polyamide, polycarbonate, epoxy resin, urethane resin, silicone resin, alkyd resin, various polyvinyl resins, cellulose resin , polyimide resin, etc. can be used. The first photoconductive layer 2 and the second photoconductive layer 4 are selected from the following groups A and B in combination. Other than the light transmittance, the first and second
These may be used in any of the photoconductive layers.

Group A (photoconductive crystal powders such as zinc oxide and cadmium sulfide are used as photosensitive layers using resin as a binder, and chalcogenide substances such as Se, SeTe, and SeAs are formed by vacuum evaporation, or The above substance is used as a charge generation layer, and an electron donating substance such as polyvinylcarbazole, triphenylmethane, oxadiazole, etc. or an electron accepting substance such as trinitrofluorene is applied to the surface of this layer, and a resin is used as a binder to charge a charge. A transport layer is formed.) Group B (a photosensitive layer made of a pigment or dye such as β-copper phthalocyanine or methylene blue using a resin as a binder, or a eutectic formed from a resin such as polycarbonate and a thiapyrylium salt) (A photosensitive layer consisting of a complex and various electron-donating substances, or a charge-generating layer made of the above-mentioned substances, and a charge transport layer provided thereon.) According to this invention, only images of any color can be produced from a multicolor original. can be selectively extracted and reproduced.

[Brief explanation of the drawing]

FIG. 1 is a process diagram in one embodiment of the present invention, FIG. 2 is a diagram showing changes in the surface potential of the photoreceptor in each step, and FIG. 3 is a process diagram in another embodiment of the invention. FIG. 4 is a diagram showing changes in the surface potential of the photoreceptor in each step. P... Photosensitive paper, 1... Conductive substrate, 2... First
photoconductive layer, 3... translucent electrical insulating layer, 4... second
Photoconductive layer, 6...multicolor original, 8...blue filter, 9...red filter.

Claims (1)

[Claims] 1. On a conductive substrate, a first photoconductive layer sensitive to color A light but not sensitive to color B light, a translucent electrical insulating layer, and a first photoconductive layer sensitive to color B light; A second element that is sensitive to light of color A and is insensitive to light of color A.
A photoreceptor comprising photoconductive layers laminated in the above order is used, and the surface of the photoreceptor is uniformly charged with a primary charge, and at the same time or after that, a light beam is applied to make both of the two photoconductive layers conductive. a step of uniformly irradiating to form an electric double layer through the light-transmitting electric insulating layer; color A;
A step of performing secondary charging with a polarity opposite to the primary charging at the same time as image exposure with a multicolor original including two colors B, and reversing the polarity of the photoreceptor surface potential from the polarity after the primary charging; Alternatively, a latent image forming method including the step of selectively forming a latent image of color B or color A as a latent image of the same polarity as the primary charging by uniformly irradiating light of color B.