JPH08314228A - Try level developing method - Google Patents

Abstract

PURPOSE: To provide a try level developing method without the variation of an intermediate potential and the attraction of carriers at the time of developing of the second color. CONSTITUTION: A composite photoreceptor structured in such a manner that a second photoconductor layer 23 where an electrostatic latent image in the second color is formed, a polarizing plate 22 and a first photoconductor layer 21 where an electrostatic latent image in the first color is formed are laminated on a conductive substrate 24 in this order is used. After the composite photoreceptor is charged, the first photoconductor layer 21 is positively exposed with light in a polarization direction where the light to the second photoconductor layer 23 is intercepted by the polarizing plate 22 by using an exposure device capable of switching the polarization direction, to form the electrostatic latent image in the first color on the first photoconductor layer 21 when image information of the first color is inputted. When the image information of the second color is inputted, the second photoconductor layer 23 is negatively exposed with the light in the polarization direction where the light toward the second photoconductor layer 23 is transmitted, to form the electrostatic latent image in the second color on the second photoconductor layer 23 and a try level is formed. Moreover, after development for the first color is completed, the full surface of the photoreceptor is irradiated with the light in the polarization direction where the light toward the second photoconductor layer 23 is intercepted and then, the development for the second color is attained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic apparatus such as a copying machine, a printer and a facsimile, and more particularly to a tri-level developing method using a composite photoconductor.

[0002]

2. Description of the Related Art Several methods have been proposed and put to practical use for a color electrophotographic process. The mainstream of them is to form a single-color printing process such as charging, exposure and development by repeating the process a plurality of times. The single-color toner image is
On a photoreceptor as disclosed in JP-A-139598, on paper as described in JP-A-2-141778, or on an intermediate recording medium as described in JP-A-5-188789. This is a method of superimposing color images. However, in this method, a single-color printing process is performed a plurality of times for printing one color image, so that the printing speed becomes slow. In that respect, JP-A-48-57
The tri-level developing method described in Japanese Patent No. 637 or USP 4078929 is capable of printing two colors by one charging, exposing and developing, and is an effective developing method for speeding up. In this tri-level developing method, first, a photoconductor is charged to form a high potential level, and then one of the input image signals of the first color and the second color is weakly exposed to a positive light exposure by weakening the laser power to a white background. Is formed, and the other is subjected to negative strong exposure with an increased laser power to form a low potential level, and a ternary potential level as shown in FIG. 6 is formed. Next, the high potential level is subjected to normal development and the low potential level is subjected to reversal development to form two color toner images on the photoconductor, and the two color toners having different polarities are adjusted to one of the polarities by using a charger. In this method, a transfer device transfers the image onto a sheet, and a fixing device melts and fixes the sheet to obtain a two-color image.

As another method for forming a tri-level, there is a method using a composite photoconductor disclosed in Japanese Patent Laid-Open No. 2-113246. In this method, a composite photoconductor in which two types of photosensitivity layers having different spectral sensitivities are laminated is used, each photoconductor layer is charged with different polarities, and then two colors are exposed with light having different wavelengths to form a tri-level. To do.

[0004]

In the method of forming the tri-level by controlling the laser exposure amount, the intermediate potential level formed at the time of positive weak exposure becomes the background (white background) portion. However, in the relationship between the exposure intensity (laser power) and the photoconductor potential shown in FIG. 7, the potential of the photoconductor is saturated and stable at the residual potential of the photoconductor during strong exposure, whereas the potential of the photoconductor is stabilized during weak exposure. Uses an area that greatly depends on the exposure intensity,
The fluctuation of the exposure intensity makes the potential of the photoconductor unstable. As a result, problems such as partial fogging in the background portion tend to occur.

Further, in order to set a three-valued potential level as shown in FIG. 6 and to set a sufficient developing bias voltage for both normal development and reversal development, the potential of the initial charging is higher than that of the normal two-level system. Therefore, the potential difference ΔV ₁ between the normal development bias potential and the low potential level and the potential difference ΔV ₂ between the reverse development bias potential and the high potential level become large. Therefore, when a two-component developer is used, if these potentials are large, carrier pulling easily occurs. In particular, this phenomenon becomes noticeable when a low saturation magnetic carrier or the like having a small attraction force to the developing roller is used for the purpose of performing soft touch development for preventing scraping of the first color toner image in the second color development.

Further, in the system using the composite photoconductors having different wavelength sensitivities, the problem that the intermediate potential level becomes unstable can be solved, but a charger having a different charging polarity, an exposing device having a different wavelength, a different charging polarity and a wavelength sensitivity. Since a plurality of photoconductor layers having regions are required, the range of selection of the exposure device and the photoconductor material becomes very narrow, and the number of parts increases, which causes problems such as enlargement and complexity of the entire device.

The object of the present invention is to solve such a problem, and it is easy to eliminate the fluctuation of the intermediate potential and the carrier pulling during the development of the second color, which are problems in the conventional tri-level developing system. It is to provide a tri-level developing method that can be solved by the configuration.

[0008]

A second photoconductor layer for forming a second color electrostatic latent image, a polarizing plate, and a first photoconductor for forming a first color electrostatic latent image on a conductive substrate. Using a composite photoconductor having a structure in which layers are laminated in order, and using an exposure device capable of switching the polarization direction after charging the composite photoconductor,
When color image information is input, the second
By positively exposing light of a polarization direction in which light to the photoconductor layer is blocked, a first color electrostatic latent image is formed on the first photoconductor layer, and
When the image information of the color is input, the second photoconductor layer is negatively exposed to the light in the polarization direction that transmits the light to form a second color electrostatic latent image on the second photoconductor layer. Form a tri-level.

After the development of the first color is completed, the entire surface of the photoconductor is irradiated with light in the polarization direction in which the light to the second photoconductor layer is blocked by the polarizing plate, and then the second color is developed.

[0010]

By sandwiching a polarizing plate between the first photoconductor layer and the second photoconductor layer, when the light is irradiated from the first photoconductor layer, only the light in a certain polarization direction is provided in the second photoconductor. A composite photoreceptor can be constructed that is transparent to the layers. When this composite photoconductor is charged, the potential of the surface of the second photoconductor layer is determined according to the electrostatic capacities of the first photoconductor layer and the second photoconductor layer. Can be used as an intermediate potential level of During the positive exposure of the first color, if the second photoconductor layer is exposed to light having a sufficient intensity by the light of the polarization direction in which the light is blocked, the potential of the first photoconductor layer decreases to the residual potential. While being saturated, the potential on the surface of the second photoconductor layer is maintained without being affected by exposure,
The potential of the surface of the second photoconductor layer (more precisely, the potential of the potential of the surface of the second photoconductor layer plus the residual potential of the first photoconductor layer)
Can be used as a stable intermediate potential level that is not affected by variations in exposure dose.

After the completion of the development of the first color, the intermediate potential level is influenced by irradiating the photosensitive member with light in the polarization direction in which the light to the second photoconductor layer is blocked by the polarizing plate. However, only the high potential level corresponding to the image portion of the first color can be lowered, and the potential difference between the reversal development bias potential and the high potential level during the development of the second color can be reduced, so that carrier pulling can be prevented.

[0012]

【Example】

(Embodiment 1) FIG. 1 shows a two-color image forming apparatus used in this embodiment. A process of forming a two-color image by this two-color image forming apparatus will be described below by assuming that linearly polarized light in the main scanning direction is H polarized light and linearly polarized light in the sub scanning direction is V polarized light. First, Figure 2
As shown in FIG. 2, the second photoconductor layer 23, the H polarized light transmitting polarizing plate 22, the first photoconductor layer 2 are formed on the drum-shaped conductive substrate 24.
The composite photoconductor 1 in which 1 is laminated in order is charged to the negative electrode by the charger 2 installed around the photoconductor to form a high potential level as shown in FIG. Next, when the image signal of the first color is input as shown in FIG. 3B using the laser exposure device 3 capable of switching between V-polarized light and H-polarized light for exposure, positive-polarized light of V-polarized light is input. When exposure is performed to form an intermediate potential level and a second color image signal is input, negative exposure by H polarization is performed to form a low potential level and a three-value potential level is formed on the photoconductor. To do. Next, as shown in FIG. 3C, the high potential level is normally developed by the first developing device 4 using the positive toner, and the low potential level is reversely developed by the second developing device 5 using the negative toner. Then, two color toner images are formed on the photoconductor.
After that, two color toners having different polarities on the photoconductor are adjusted to a negative polarity by using the recharging device 6, transferred to the paper 7 by the transfer device 8, and the toner increase transferred to the paper 7 is performed by the fixing device 9. It is fused and fixed to obtain a two-color image. The toner remaining on the photoconductor without being transferred is removed by the cleaner 10.

Although the first-color V-polarized light exposure portion has a tri-level intermediate potential, the H-polarized light-transmitting polarizing plate 22 of the composite photoconductor 1 prevents the second photoconductor layer 23 from being exposed, so that the exposure intensity is increased. Regardless of this, the potential on the surface of the second photoconductor layer can be maintained. In addition, the potential of the first photoconductor layer 21, which is added to the potential of the surface of the second photoconductor layer, is saturated and stable at a slight residual potential if the intensity of the V-polarized light is sufficient. The fluctuation of the intermediate potential level due to the fluctuation of the exposure intensity, which is a problem, can be suppressed.

Next, details of the composite photoconductor 1 used in this embodiment will be described with reference to FIG. The photosensitive member includes a drum-shaped conductive substrate 24 made of aluminum, a negatively-charged OPC photosensitive layer to be the second photoconductive layer 23, a polarizing plate 22 transmitting H polarized light, and a second photoconductive layer. It has a structure in which the first photoconductor layer 21 made of the same material as 23 is sequentially laminated. When the composite photoconductor 1 is charged, the second potential becomes an intermediate potential level.
The surface potential of the photoconductor layer 23 is determined by the ratio of the capacitances of the first photoconductor layer 21 and the second photoconductor layer 23 when the capacitance of the polarizing plate 22 can be ignored. Therefore, the intermediate potential level can be optimized by a method such as adjusting the layer thickness of these capacitances. In this embodiment, both the first photoconductor layer 21 and the second photoconductor layer 23 are set to have a layer thickness of 20 μm.

The thickness of the polarizing plate 22 is 100 μm, and H
It is installed in the direction in which polarized light passes. As optical characteristics, it is desirable that the transmission loss of H-polarized light is as small as possible and the extinction ratio (ratio of transmitted light of H-polarized light and V-polarized light) is as large as possible. Further, when the electrostatic capacity of the polarizing plate 22 is small, the voltage applied to the polarizing plate 22 becomes large and the effective charging potential of the photoconductor decreases, so it is necessary to make the electrostatic capacity as large as possible.

Next, details of the laser exposure device 3 will be described with reference to FIG. The laser light oscillated by the semiconductor laser 31 based on the image signal information from the printer controller 37 is collimated by the collimator lens 32 into a parallel light flux, and then is polarized by the polarization switch 33 controlled by the printer controller 37. After being selected by any one of the above, the scanner motor 34 reflects the polygon mirror 35 rotating at high speed so as to scan the photoconductor, and after passing through the fθ lens 36, the photoconductor is irradiated with the electrostatic latent image. Form.

The light from the emission port of the semiconductor laser 31 is linearly polarized light, and reaches the photosensitive member as V polarized light when the polarization switch 33 using the Faraday effect is off.
In the ON state in which a magnetic field is applied to the polarization switch 33, the polarization direction is rotated by 90 ° and becomes H-polarized on the photoconductor. The polarization switch 33 is controlled by the printer controller 37 and is turned off to select the V polarization when the first color is reversely developed, and is turned on when the second color is normally developed to the H polarization. Select.

When a two-color image in which the first color is red and the second color is black is printed by using this two-color developing device, the intermediate potential level is stabilized, and printing by the conventional tri-level developing device is performed. The background fogging, which was partially seen at, was significantly reduced. The V-polarized light shown in the present embodiment,
It is clear that the same effect can be obtained even when the relationship of H-polarized light is exchanged.

In this embodiment, the drum-shaped photosensitive member has been used for explanation, but it is of course possible to obtain the same effect as a belt-shaped photosensitive member.

(Embodiment 2) In Embodiment 1, since the scraping phenomenon of the first color red toner image on the photoconductor by the second color black developing device was observed, the contact pressure of the magnetic brush to the photoconductor was lowered. For the purpose, we changed to a low saturation magnetic carrier. As a result, the mixture of toner due to scraping is reduced, but the low saturation magnetic carrier has a weak adsorption force to the developing roller, and the potential difference between the reversal developing bias potential and the high potential level is large as shown in FIG. 5A. , A carrier pulling phenomenon was observed in which the carrier adhered to the photoconductor due to electrostatic force. Therefore, for the purpose of lowering the high-potential level potential, the irradiation lamp 11 including an LED in which a V-polarized light transmitting polarizing plate is attached between the first developing device 4 and the second developing device 5 of the two-color image forming apparatus of the first embodiment.
Was installed, and the entire surface was irradiated with V-polarized light as shown in FIG. As a result, as shown in FIG. 5C, only the high potential level could be lowered without affecting the intermediate potential level, and the carrier pull could be prevented.

[0021]

The conventional tri-level development method has a problem by using a composite photoconductor having a structure in which a polarizing plate is sandwiched between photoconductor layers and an exposure device capable of switching the polarization direction. It has become possible to solve the fluctuation of the intermediate potential and the carrier pulling during the development of the second color.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a two-color image forming apparatus used in this embodiment.

FIG. 2 is a diagram showing a configuration of a composite photoconductor.

FIG. 3 is a diagram for explaining a tri-level formation process in a composite photoconductor.

FIG. 4 is a diagram showing a configuration of a laser exposure system.

FIG. 5 is a diagram for explaining the effect of V-polarized light irradiation before second color development.

FIG. 6 is a diagram showing a conventional tri-level forming method.

FIG. 7 is a diagram showing a relationship between laser power and a photoconductor potential.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Composite photoconductor, 2 ... Charger, 3 ... Laser exposure device, 4
... first developing device, 5 ... second developing device, 6 ... recharger, 7
... paper, 8 ... transfer device, 9 ... fixing device, 10 ... cleaner, 1
DESCRIPTION OF SYMBOLS 1 ... Irradiation lamp, 21 ... 1st photoconductor layer, 22 ... Polarizing plate, 23 ... 2nd photoconductor layer, 24 ... Conductive base | substrate, 31 ...
Semiconductor laser, 32 ... Collimator lens, 33 ... Polarization switch, 34 ... Scanner motor, 35 ... Polygon mirror, 36 ... f.theta. Lens, 37 ... Printer controller.

Claims (3)

[Claims] 1. A three-valued potential level is formed on a photoconductor by a charging and exposure process, two types of toner having different polarities are used to develop a high potential level by regular development, and a low potential level is inverted. In the tri-level development method of developing by development, in addition to using a composite photoconductor in which a plurality of photoconductor layers including a photoconductor layer that becomes a conductor only for light of a specific polarization direction are laminated, A tri-level developing method characterized in that the exposure is performed by an exposure means capable of switching the polarization direction according to the color to be printed. 2. The tri-level developing method according to claim 1, wherein the composite photoconductor has a structure in which a polarizing plate is sandwiched between laminated photoconductor layers. 3. The tri-level development method according to claim 1, wherein after the development of the first color is completed, the composite photoconductor is entirely irradiated with light of a specific polarization direction, and then the development of the second color is performed. A characteristic tri-level development method.