JPS58217958A - Electrophotographing method - Google Patents

Abstract

PURPOSE:To perform dichroic printing efficiently by using a photoreceptor formed by stacking the 1st photoconductive layer (N type), the 2nd photoconductive layer (P type), and an insulating layer on a conductive base body, and carrying out electrostatic charge exposure, and development in specific methods. CONSTITUTION:The 1st photoconductive layer 11 made of an N type semiconductor, the 2nd photoconductive layer 12 made of a P type semiconductor, and the insulating layer 13 are laminated successively to form the photoreceptor 1. Then, while the surface of the photoreceptor 1 is charged electrostatically positively, a negative image of picture information in the 1st color is formed by the 1st optical image exposure L1 (i), and after the surface of the photoreceptor 1 is charged by an alternating current (or electrified negatively) (ii), a positive image of picture information in the 2nd color is formed by the 2nd optical image exposure L2 (iii) to form latent images with surface potentials corresponding to an unexposed part, the 2nd exposure part, and the 1st plus the 2nd exposure part. Then, the images are developed with the 1st and the 2nd toner materials charged to the opposite polarities at a specific bias voltage (iv) and transferred to obtain dichroic print.

Description

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

The two-color electrophotographic method is an electrophotographic method for outputting images in two colors on an image support, and is extremely convenient in terms of office processing, and various methods have been proposed in the past. For example, images from two separate originals are compositely copied on the same recording medium surface as images of different colors in the form of a side-by-side image, an inset image, a wheel image (for example, an overlapping image of a floor plan and a wiring diagram), etc. Image information output from computers, image photoelectric reading devices, etc.

This is an effective method in cases such as obtaining a copy in which a separately prepared format image to be combined is synthesized as an image of a different color, and there are two types of methods and configurations.

The purpose of the present invention is to provide a new practical two-color electrophotographic method having features and effects such as being able to obtain two-color prints in a single scratch forming process. shall be. That is, (1) a first photoconductive layer, a second photoconductive layer, and an insulating layer are laminated in this order on a conductive substrate, and the first photoconductive layer and the second photoconductive layer are N-type and P-type. It uses a photoreceptor made of different types of optical semiconductors.

C2) Primary charging is applied to the surface of the insulating layer with a polarity that allows charge injection into the first photoconductive layer, and at the same time, first exposure is applied (first step).

(3) Next, b, which is an alternating current, is a direct current with the opposite polarity to the primary charge.
Next, charging is performed (second step).

(4) Next, a second exposure is applied to form a latent image on the surface of the photoreceptor having surface potentials corresponding to the non-exposed area, the second exposed area, and the first and second exposed areas (third step).

(5) Visualize the above-mentioned potential (*) on the surface of the photoreceptor using two types of developers colored in different colors (fourth step).

The gist of this paper is a two-color electrophotographic method characterized by the following.

The gist of the present invention is a modified process in which the first step of charging and exposure of the above-mentioned process is performed to perform primary charging on a 1 g light body, followed by a 19th exposure.

The present invention will be described below with reference to nine drawings.

Figures 1 (T) to (1) schematically show the latent image forming process in the two-color electrophotographic method of the present invention, where 1 is 8.
□A first photoconductive layer 11. is formed on a conductive substrate 1o which is electrically grounded on a photoreceptor. Second photoconductive layer 12. Transparent insulation layer 1
It has a four-layer structure consisting of 6 stacked in this order.

However, the insulating layer 16 does not need to be highly transparent when photoimage exposure is performed using, for example, X-rays.

In this photoreceptor 1, when the first photoconductive layer 11 is an N-type semiconductor, the second photoconductive layer 12 is a P-type semiconductor, and conversely, when the first photoconductive layer 11 is a P-type semiconductor, the second photoconductive layer 12 is a P-type semiconductor. is configured to be an N-type semiconductor. Here, the first photoconductive layer is of N type, and the second photoconductive layer is of N type.
An example in which the photoconductive layer is of P type will be explained.

Accordingly, in the present invention, as a first step for the photoreceptor 1, as shown in FIG. give.

This first light image exposure L1 gave the first image information, one of the two image information to be combined and copied as a different color image, as a negative image. This process is referred to as primary charging simultaneous exposure, and the light image exposed area on the surface of the photoreceptor is referred to as first exposure area.

With this primary charging simultaneous exposure, the non-exposed area D1 (the first
In the background part of the image information), negative charges corresponding to the positive charges on the surface of the insulating layer 13 are injected from the conductive substrate 10 into the first photoconductive layer 11 of Nu, but the second photoconductive layer 12 is of P type. Since no negative charges are injected at this point, the injected negative charges from the substrate 10 are eventually uniformly distributed on the interface between the first photoconductive layer 11 and the second photoconductive layer 12. On the other hand, in the first exposed area L1 (image area #j of the first image information), both the first photoconductive layer 11 and the second photoconductive layer 12 have become conductive due to light irradiation, so the negative injected from the conductive substrate 10 The charges are uniformly distributed at the interface between the second photoconductive layer 12 and the insulating layer 13.

Next, as a second step, the photoreceptor 1 after the first step is subjected to alternating current charging using a charger B as shown in FIG. 1 (II). This process is called secondary charging. Through this step, the charges on the insulating layer 13 are transferred to the first photoconductive layer 11. Second photoconductive layer 12. The capacitance is divided according to the capacitance of each of the insulating layers 15, and the potential on the surface of the insulating layer 16 approaches the O potential in both the first exposed portion L1 and the non-exposed portion D1. However, the amount of charge remaining on the insulating layer 13 is larger in the first photosensitive area L1 than in the non-exposed area D1 due to the influence of negative trapped charges at the interface between the insulating layer 16 and the second photoconductive layer 12.

Next, as shown in FIG. 1 (
The second optical image exposure L2 is applied as in g).

This second light image exposure L2 gave the other of the two image information to be combined and copied as different color images as a positive image. In FIG. 1 [phase], L2 and D2 correspond to the ground portion and image portion of the second image information, respectively. This process is called the second exposure. This second exposure and the first M light are used so that the image part of the first image information and the image part of the second image information are synthesized into a composite image in a desired predetermined positional relationship on the final print surface. , it goes without saying that the exposure processing is carried out in a required positional relationship with respect to each other on the surface of the photoreceptor. That is, the image area on the photoreceptor 1 of the first image information is the exposure area L1 of the first exposure, and that of the second image information is the area of the second exposure area L1.
This is the light exposure dark area D2 area, and the exposure process is performed by adjusting the positional relationship between the L1 area and the D2 area.

This second exposure causes the 11th! ! Komei part L1
The areas receive an overlapping exposure L2. This area is 1st + 2nd
These are called exposure sections L1 and L2. The photoreceptor surface area other than the first exposed light area L1 area and excluding the exposed dark area D2 area of the second exposure is exposed to light L2 for the first time in this second exposure. This area is called a second exposure area L2. Further, the photoreceptor surface in the exposed dark area D2 in the second exposure is also the exposed dark area D1 in the first exposure. These areas are called non-exposed areas D1 and D2.

In the first and second exposure areas L1 and 2 and the second j1 light area L2, the first photoconductive layer 11 and the second photoconductive layer 12 are made conductive by the second exposure L2, so the first photoconductive layer 11 The charges held by the second photoconductive layer 12 are canceled except those corresponding to the charges held on the surface of the insulating layer 13, and the charges held by the second photoconductive layer 12 are canceled.
A surface potential develops according to the charge held by the filter. The surface potentials of the first and second exposed areas L1 and 2 and the second blind area -L2 are determined by the capacitance division of charges performed in the secondary charging step. Either method 1 or 2nd exposure
1' In the unexposed areas D1 and 2, which are exposed dark areas, the above 2
Since there is no change equivalent to that after the next charging, the surface potential is Ov.

Said first and second exposure sections L1 and 2. The capacitance division of the second exposure section L2 will be explained using a capacitor model as an equivalent circuit shown in FIG. Here, the capacitance of the first photoconductor 1-11 is C
Let the capacitance of the second photoconductive layer 12 be 02, and the capacitance of the insulating layer 13 be 03.

First, the first step is primary charging simultaneous exposure (= photoconductor 1
As shown in FIG. 2 (1), the non-exposed portion D1 is charged by applying a voltage V based on the discharge of the charger 2 to the series connection of the mini ○ and C. Since C is an N-type semiconductor, it has low resistance to negative charges and can be considered conductive.

On the other hand, the first exposed part L1 is electrically connected to the first and second photoconductive layers 11 and 12 by light irradiation, so as shown in FIG.
All of the voltage is applied to the insulating layer C3, and charging is performed.

Next, the second step, AC static elimination, brings the surface potential of the photoreceptor close to zero, so it can be considered isometrically that the surface of the insulating layer 13 is short-circuited to the ground.Therefore, in the first step, the first exposure In the non-exposed area D1 which has not been irradiated and is not irradiated, a part of the charges charged in C2 and 03 due to primary charging moves to 01 as shown in FIG. 2 (3). The potential difference vDI applied to the capacitor C3 corresponding to the insulating layer 13 is expressed by the following equation.

On the other hand, in the first exposure part L1, when a part of the charge charged in C3 due to primary charging moves to C1 and C2 as shown in FIG. 2 (4), the potential difference applied to C3 is given by the following equation. .

Next, the second exposure step, which is the sixth step, is the second exposure step in the equivalent circuit.
Exposure section L1 and 1st + 2nd j! CI and 02 of optical part L1/2
This means short-circuiting both terminals of each as shown in Fig. 2 (6) and (7'). As a result, the insulating layer 16 of the second exposed portion L2 and the first + second exposed portions L1 and 2
On the surface, there is a potential difference v1,2・vL□ held by C3,
2 and 2 appear as surface potentials, respectively. Regarding the non-exposed areas D1 and D2, there is no change at all after the Vi secondary charging, and the surface potential ゎゎゎ0.2 is 0 it.

Specifically, for example, C, :C2:C3=1 :2:1
If ゜V=900(V), then v = O(v) I
vL2 = D1·2 240 (V), V -540 (V).

Ll-2= Electrostatic latent image VDi@2 #■L formed in this way
Developing bias 1&: 2nd exposure area L for 21■L□, 2
A two-color visible image can be created by setting the surface potential near the surface potential VLZ of No. 2 and developing with toners T1 and T2 of different colors and charged with opposite polarities. That is, Figure 1 (5
), the negative toner T1 adheres to the first and second exposed areas L1 and 2VcF′i to develop and form a positive image of the first image information, and the positive toner T2 is deposited in the non-exposed areas D1 and 2. The second image information is also developed and formed as a positive image in a color different from that of the first image information.

Therefore, by transferring these visible images T1 and T2 to a recording sheet P using an appropriate transfer means and fixing them as shown in Fig. 1 (■), a two-color image can be obtained. A non-exposed area through the first step of primary charging and simultaneous exposure, the second step of secondary charging, and the third step of second exposure in the two-color electrophotographic method of the invention.

It is a graph of changes in the surface potential of the photoreceptor at the second exposure section and the first and second exposure sections. When secondary charging of the photoreceptor surface is performed by alternating current corona discharge, negative corona is more likely to be produced than positive corona.
The surface potential of the non-exposed areas D1 and D2 after the next charging is slightly biased toward the negative side as shown in the graph.

In this explanation, the first photoconductive layer 11 is an N-type semiconductor.

Although the second photoconductive layer 12 is made of a P-type semiconductor as an example, the first photoconductive layer is made of a P-type semiconductor, the second photoconductive layer is made of an N-type semiconductor, and the polarity of primary charging is negative. The principle of forming a latent image is exactly the same in the case of selecting .

That is, the 1st + 211th light section L1/20 surface position ■1□, 2
゜The surface potential vL2 of the second exposed part L2 is negative, and the surface potential V of the non-exposed part DI-2 is 0 or negative to '71
-2 Only a positive low value is obtained. ■ The absolute value of is Ll・
2 ■ thicker than that of (, if V is negative, then L2

The absolute value of D 1@2 is smaller than that of vL2. Positively charged toner is Ll・2 part, negatively charged toner is D1@
Develop the second part. In addition, when secondary charging in the second step is performed not with alternating current but with direct current of opposite polarity to the primary charging (it is preferable to use a charger equipped with a grid to stabilize the surface potential after secondary charging). is exactly the same.

In addition, instead of applying the first charge at the same time as the first exposure t-first charge, if the photoreceptor 1 is first charged first and then the first exposure is given, the surface potential of the exposed part of the chopstick 1 will be slightly different. However, the process is otherwise exactly the same. To explain this using the CO/DE/SAM moder shown in Fig. 2, each of the nine parts of the photoconductor base is charged by applying a voltage V to the series connection of C2 and C3 in the primary charging process (the first Figure (1)
v2 is omitted).

Next, when the first exposure is performed, the second photoconductive layer 12 of the photoreceptor portion that received the first exposure becomes conductive, and the charge held by C2 is discharged (Fig. 1 (2) t). The potential on the surface of part 03 is lowered by the potential difference held by C2.

Then, when capacitance division similar to the previous example is performed in the secondary charging process (Fig. 2 (3) and (4)), the potential difference VL□( (4) in FIG. 2 is given by the following equation.

Then, when the second exposure step, which is the sixth step, is performed, the first +
In the second exposed portions L1 and L2, ■1□ in FIG. 2 (4) appears as a surface potential. On the other hand, the photoreceptor surface area F'i other than this first + second g light section L1@2 is the first exposure square ξ/
It's not affected by Google at all.

Surface potential VD of non-exposed areas D1 and 2 and second exposed area L2
Yo, 2. ■ is expressed by the formula in the previous example.

2 For example, C1:C70:C3= 1:2:2,
If V = 1500, VDo, 2-0(v), v
L, = 250 (v).

VLl, 2=500M J7. Similar to mN, 31
By obtaining a 1N electrostatic latent image and developing it with positively charged toner and negatively charged toner with the developing bias set around vL2, 2.
Color presets can be obtained.

FIG. 4 is a graph of changes in the surface potential of the photoreceptor corresponding to the graph of FIG. 3 when the 11th I light is performed successively after the above-mentioned primary charging.

FIG. 5 shows an example of an apparatus for implementing the two-color electrophotographic method of the present invention, and 1 is constructed in a drum shape. The photoreceptor has a length of 4 m and is driven to rotate about axis 0 in the direction of the arrow. Hereinafter, this drum-type photoreceptor will be simply referred to as a drum.

Various necessary process execution devices are arranged around the drum 1 along the drum rotation direction Ki. i.e. 2-/H1
The first process equipment includes a primary charger (positive DC corona discharger if the first photoconductive layer is N type, negative DC corona discharger if the first photoconductive layer is P type) and a first exposure device. In this example, the first exposure device 4 is of a laser beam scanning type.

Laser beam B modulated on and off by time-series pixel signals
1 is scanned in the drum generatrix direction as main scanning, and 10 rotations of the drum are used as sub-scanning to expose a negative image of the first image information on the drum surface. The first exposure of the drum surface by scanning the beam B1 is performed simultaneously with the primary charging by passing through the primary charger 2. Since the laser beam scanning type exposure apparatus itself is already used in laser beam links and the like and is well known, a detailed explanation thereof will be omitted.

3 is a secondary charger (AC or DC corona discharger with opposite polarity to charger 2) as a second process equipment. Reference numeral 5 denotes a 21st optical device as a third process device, which, like the first exposure device 4, uses a laser beam scanning system. A positive image of the second image information is scanned and exposed on the drum surface by the oscillation laser beam B2 of the exposure device 4.

Reference numerals 7 and ρ denote first and second developing rollers, which respectively carry toner and rotate to supply the toner to the drum 1. Both developing rollers are made to carry toners of different polarities and colors. For example, ``Roller 7 carries black toner and roller 8 carries red toner. 14 is a charger for transferring the polarity of the toner charged to a uniform polarity by the charger 9 and reverse polarity; 15 is a drum surface cleaner; 16 is an eraser lamp; be.

During the rotation process of the drum IFi, the primary charger 2 applies corona discharge to the photoconductor, the first exposure device 4 performs first exposure, and the secondary charger B applies corona to the photoconductor. The second step of applying a discharge, the second exposure by the second image exposure device 5, and the sixth step of 2 are sequentially applied to the peripheral surface to form the first w! A composite latent image of the light image and the second exposure pattern is sequentially formed. Next, the first developing roller 7 and then the second developing roller 8tl are sequentially passed through.
The second exposed portions L1 and 2 are developed, for example, with the toner of the first developing roller 7, and the non-exposed portions D1 and 2 are developed with the toner of the second developing roller 8, and as a result, the drum 1 surface is developed with the toner of the first developing roller 7, as shown in FIG. )
A two-color toner image is formed as shown in FIG.

In this case, the developing roller 7 is supplied with a bias potential that is between V and vL and is close to vL2.
/ is preferably applied. Also, developing roller 8
FivD engineering 1. and vL, and is the potential between vL2F
Preferably, a developing bias "'" having a value close to c is applied by the power supply 8'.

Next, the two-color toner image on the drum surface is unified into positive or negative polarity as a whole in the process of passing through a charger 9 section. This is because when corona transfer is adopted as the transfer means in the next step, both of the two-color toner images (toners T1 and T2 in Fig. 1 (M)) can be transferred well to the transfer material surface. It is carried out.

Next, the two-color toner image on the surface of the drum 1 reaches the transfer charger 14, and between the charger 14 and the drum 1, the two-color toner image is sequentially transferred onto the surface of the recording sheet P, which is synchronously conveyed from a paper feed section not shown in the figure. transcribed. The sheet Pt to which the toner has been transferred is then sequentially separated from the first surface of the drum, passes through a fixing device (not shown), and is discharged outside the machine as a two-color print.

On the other hand, after the image has been transferred, the drum surface is cleaned by removing residual toner after transfer by a cleaner 15, and by an eraser lamp 16, the previous history (memory removal) is removed by the eraser lamp 16, and the drum surface is used repeatedly.

The first exposure device 4 has a primary charger 20 as shown by a two-dot chain line 4'.
As described above, the first exposure Li may be provided at a subsequent stage and perform the first exposure Li after the primary charging of the surface of the drum 1 by the charger 2.

Further, one or both of the first and second exposure devices 4 and 5 may be an exposure mechanism of a lens optical system that projects an original image by reflecting the drum surface pressure or forming a transmitted light image.

Example 1 An aluminum plate is used as a conductive substrate 10, and an amorphous silicon layer doped with 1500 PPM of boron is formed thereon to a thickness of 62 μm to form a first light guide T5 layer 11.
An amorphous silicon layer doped with boron i2QPPM was formed thereon to a thickness of 16 .mu.m to form a second photoconductive layer 12, and a polyethylene terephthalate film having a thickness of 8 .mu.m was adhered thereon to form an insulating layer 16. A photoreceptor 1 having a four-layer structure was made.

The photoreceptor 1 constructed in this way is charged at a discharge voltage of +6,5
Charger 2) is firstly charged by corona discharge of KV, and at the same time first exposure L1 (
Negative image exposure of the first image information) was performed. At this time, the surface potential of the non-exposed portion D1 of the photoreceptor surface was +940V.

Next, as the second step, discharge voltage ±7 KV, frequency 10
After applying secondary charging (charger 3) by alternating current corona discharge at 0 Hz, second exposure L2 (positive image exposure of second image information) was performed with a semiconductor laser beam B2 having a wavelength of 780 nm.

As a result, the non-exposed portions D1 and 2 on the photoreceptor surface have a voltage of 15V and a voltage of 5V.
fE2 exposure section L2 is +240V, 10th m2 exposure section L1
・A latent image with a surface potential of +540V was formed. Next, the surface of the photoreceptor was first developed using a first magnetic plan scratch roller 7 using a positively charged black toner. At this time, the first developing roller has a bias voltage of +220V' (i
= applied. Next, this photoreceptor was developed with a second magnetic brush developing roller 8 using negatively charged red toner. At this time, the bias voltage for the second current roller is +28.
0.

■ was applied. As a result, the first and second exposed portions L of the photoconductor
1 and 2 are developed with negative red toner (first image information positive compensation), and unexposed areas D1 and 2 are developed with positive black toner (second image information positive image) to form a two-color composite image. It was done.

Then, a corona discharge with a discharge voltage of +5.5 KV (discharger 9
) to correctly align the toner polarities of both the black and red toner images on the photoconductor surface, and then transfer the toner images on the photoconductor surface to plain paper using the positive transfer charger 14, and the result is clear and clear with no fogging. A two-color print was obtained.

Example 2 An aluminum plate is used as the conductive substrate 10, and a phosphor layer is placed on it.
An amorphous silicon layer doped with tr1200PPM is formed to a thickness of 16μ to form the first photoconductive layer 11, and an amorphous silicon layer doped with 1500PPM boron is formed to a thickness of 62μ to form the first photoconductive layer 11.
2, and a polyethylene terephthalate film with a thickness of 8 μm was further bonded thereon to form an insulating layer. A photoreceptor 1 having a four-layer structure was made.

The photoreceptor 1 configured as described above is used as the first step.
0 to 0 by corona discharge, and then the wavelength 780
nm semiconductor laser beam B1', the first n light l,1(
The first image information (negative image exposure) was given.

At this time, the surface potential of the photoreceptor 1 is 16
70V, non-n light part D1h-1300V.

Next, as a second step, a discharge voltage of +5.5KV is applied to the photoreceptor surface.
After applying a corona discharge of
isp1・2 is +28oV, 1st + 2nd exposure part L1・
A latent image with a surface potential of 2-250V was formed.

This photoreceptor was first developed using a first magnetic brush roller 7 using positively charged black toner. At this time, the first developing roller was grounded.

Next, development was performed using a second magnetic brush roller 8 using a negatively charged red toner. At this time, a bias voltage of ±40Ve was applied to the second developing roller. As a result, negative red toner adheres to the first and second M light areas L12 on the photoconductor surface, and a positive image of the first image information is developed and formed, and the non-exposed area D
Positive black toner was adhered to No. 1 and No. 2, and a positive image of the second image information was developed and formed.

Then, a corona discharge with a discharge voltage of +5.5 KV (discharger 9
) to make the toner polarities of both black and red toner images positive, and then transferred to plain paper using a negative transfer charger 14, resulting in a clear two-color print with no fogging.

In Example 1.2 above, development was carried out using developing devices dedicated to red toner and black toner, respectively. A method of performing two-color development in one development step may also be used.

Further, in Examples 1 and 2 of Jin, a two-component developer is used for both red and black, but it is also possible to use a one-component developer for either or both.

In some cases, as a direct method, the recording sheet P itself is constructed as a sheet having the above-mentioned four-layer structure.

The latent image forming process, development, and fixing described above may be directly performed thereon to obtain a two-color print.

As explained above, according to the present invention, a two-color composite print can be easily obtained in a single image forming process.

[Brief explanation of drawings]

Figures 1 (1) to (V) are schematic diagrams of the latent flaw formation process and the development/transfer process of the method of the present invention, and Figures 2 (1) to (7) are schematic diagrams of the latent image formation process. A capacitor model diagram as an equivalent circuit to explain the charge relationship of each part of the photoreceptor, Fig. 6 is a graph of surface potential changes of each part of the photoreceptor from the first step to the sixth step, and Fig. 84 is the same graph in the case of the deformation process. , FIG. 5 is a schematic configuration diagram of an example of device implementation. Lightning light or exposed areas t D 1 and DI・2 are non-exposed areas. Procedural amendment (method) January 27, 1980 Commissioner of the Japan Patent Office Kazuo Sugi 1, matter 11- Indication 1981 Tokuken Ku No. 101555 3, Supplement 1
1:Relationship with the person lr f'l who does the same thing as the applicant (, I income, (100) Canon Co., Ltd. 5; [2-2 Yoyogi, Shibuya-ku, Miyako)
Figure (υ (2)

Claims (1)

[Claims] (1) A first photoconductive layer, a second photoconductive layer, and an insulating layer are laminated in this order on a conductive substrate, and the first photoconductive layer and the second photoconductive layer are formed into N-type and P-type phase layers. It uses a photoreceptor made of different optical semiconductors. The surface of the insulating layer is 11th-order charged with a polarity that allows charge to be injected into the first photoconductive layer, and at the same time, first exposure is applied. Next, secondary charging is performed using alternating current or direct current having a polarity opposite to that of the 11th order charging. Next, by applying a second exposure, a latent image having surface potentials corresponding to the non-exposed area, the second exposed area, and the first and second exposed areas is formed on the surface of the photoreceptor. An electrophotographic method characterized in that the latent image is visualized using 2 fl of a developer colored in different colors. ■ A first photoconductive layer, a second photoconductive layer, and an insulating layer are laminated in this order on a conductive substrate, and the first photoconductive layer and the second photoconductive layer are laminated in this order.
A photoreceptor is used in which the photoconductive layer is composed of different N-type and P-type optical semiconductors. After the surface of the insulating layer is firstly charged with a polarity that allows charge to be injected into the first photoconductive layer, a first exposure is subsequently applied. Next, secondary charging is performed using alternating current or direct current having a polarity opposite to that of the primary charging. Next, by applying a second exposure, a latent image having surface potentials corresponding to the non-exposed area, the second exposed area, and the first and second exposed areas is formed on the surface of the photoreceptor. An electrophotographic method characterized in that the latent image is visualized using two types of developers colored in mutually different colors.