JPH05150608A - Full-color image forming method - Google Patents

Abstract

PURPOSE:To provide the full-color image forming method which obviates the generation of surface staining and degradation in color reproducibility even when the part of the surface of a composite photosensitive body where the texture part of the latent image for normal development is ought to be formed by irradiation with prescribed light is not irradiated with the light by a fluctuation in the moving speed of the photosensitive body, etc. CONSTITUTION:The U layer of the composite photosensitive body 30 is positively electrified and the L layer is negatively electrified to set the surface potential at about Ov (a, b). An N/P main latent image of cyan is formed on the U layer by 680nm light and the P/P latent image of magenta and the N/P covered latent image of cyan are formed on the L layer by 780nm light (c). The latent image is then subjected to normal development by a positively charged magenta toner (d). The part not irradiated with 780nm light by the speed fluctuation, etc., of the surface is electrified to about 0V at the time and, therefore, the magenta toner does not stick to the part. The magenta latent image, etc., of the L layer are then erased by uniform exposing with near IR light (e) and the cyan main latent image is subjected to reversal development by the positively charged cyan toner (f). Similarly, the visible images of yellow and black images are formed in the second rotation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a full-color image forming method used in an image forming apparatus such as a copying machine, a facsimile, a printer, etc., and an image forming apparatus suitable for carrying out the full-color image forming method. ..

[0002]

2. Description of the Related Art Conventionally, as a full-color image forming method of this kind, a first photoconductive layer is provided on a conductive substrate, and a second photoconductive layer is formed directly on the first photoconductive layer or through an intermediate layer. A conductive layer is provided, and the first photoconductor is adjusted such that one photoconductive layer is mainly irradiated with light of A color light, and the other photoconductive layer is mainly converted to light conductor with light of B color light. The second photoconductor is adjusted so that one of the photoconductive layers is mainly made into a conductor by the irradiation of C color light and the other of the photoconductive layers is mainly made into a conductor by the irradiation of D color light.
It is known to use one photoconductor (hereinafter referred to as a composite photoconductor) (for example, Japanese Patent Laid-Open No. 61-163349).

The present applicant previously used one composite photoconductor of this type and formed a toner image of two color toners out of four color toners at the first rotation, and formed this toner image. Patent application for a method for forming a full-color image by forming a toner image with the remaining two color toners after transferring onto a transfer material or while carrying the toner image with the two color toners on the composite photoconductor. I did. That is, the first photoconductive layer is provided on the conductive substrate, and the second photoconductive layer is provided on the first photoconductive layer directly or via the intermediate layer, and the light of A color light is emitted. One of the photoconductive layers is adjusted so that the photoconductive layer on the other side is mainly made into a conductor by the irradiation of the light of the B color, and the first and second photoconductive layers of the photoconductor are adjusted. By charging in opposite directions to set the surface potential of the photosensitive member to a predetermined potential, the three primary colors α, β,
When γ, the first image, which is one of the α-color image, β-color image, γ-image, and black image, is A-color light, and the α-color image, β-color image, γ-image, and black image The second image, which is one image other than the one image, is A-color light and B-color light, and either one of the first image and the second image is a latent image for regular development. Then, the other image is written as a latent image for reversal development, the one image is developed with toner of a predetermined color, uniform irradiation is performed with light of a predetermined color, and the latent image of both images written with A-color light is erased to B The latent image of the other image written with colored light is made to appear potential on the surface of the photoconductor, and the other image is developed with a predetermined color toner having the same polarity as the predetermined color toner, and then an α color image, β The first image that is one of the remaining two images of the color image, the γ image, and the black image. Image is the A color light and the other image is the fourth image is the A color light and the B color light, and one of the third image and the second image is the latent image for regular development and the other image Is written as a latent image for reversal development, one of the images is developed with toner of a predetermined color, uniform irradiation is performed with light of a predetermined color, and the latent image of both images written with A color light is erased and written with B color light. Patent application for full-color image forming method, characterized in that the latent image of the other image is visualized on the surface of the photoconductor in a potential manner, and the other image is developed with a predetermined color toner having the same polarity as the predetermined color toner. Was done. According to the full-color image forming method of the previous patent application, one composite photoconductor is rotated twice to form a full-color image, so that a full-color image can be formed with a relatively simple structure and at a relatively high speed.

However, in the above invention of the prior patent application, the first photoconductive layer is finally obtained in the step of charging the composite photoconductor, which is executed prior to writing the latent image on the composite photoconductor. And the second photoconductive layer are charged so that they have opposite potentials and different magnitudes of electric potential, whereby the surface potential of the composite photoconductor is set to a predetermined value depending on the polarity of the charged photoconductive layer. The potential is set to, for example, minus 500V. Then, when writing the latent image for regular development, predetermined light is applied to attenuate the minus 500V to 0V in order to form a portion to which toner is not attached. For this reason, when light is not irradiated to a portion to be irradiated with predetermined light in order to form a portion to which toner is not attached due to fluctuations in the moving speed of the surface of the composite photoconductor, the potential of that portion is minus 500 V. As a result, the problem remains that the toner may be adhered to this portion by the regular development with the positive polarity toner, resulting in background stain and deterioration in color reproducibility.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and its object is to:
By providing a full-color image forming method that does not cause background stains or deterioration in color reproducibility even when light is not irradiated to a site to be irradiated with predetermined light due to fluctuations in the moving speed of the composite photosensitive member. is there.

[0006]

In order to achieve the above-mentioned first object, the full-color image forming method of the present invention provides a first photoconductive layer on a conductive substrate, and the first photoconductive layer is provided. A second photoconductive layer is provided on the layer directly or via an intermediate layer, and one photoconductive layer is irradiated with light of A color light, and the other photoconductive layer is irradiated with light of B color light. Each of them is adjusted so as to be mainly a conductor, and the first and second photoconductive layers of the photoconductor are charged in opposite directions so as to have substantially the same potential so that the photoconductor surface potential becomes approximately 0V. ,
When the three primary colors are α, β, γ, α color image, β color image,
The first image, which is any one of the γ image and the black image, is A-color light, and is the one image other than the one image of the α-color image, the β-color image, the γ-image, and the black image. A certain second image is written with A-color light and B-color light, and the first image is written as a latent image for regular development and the second image is written as a latent image for reversal development. After developing, uniform irradiation with light of a predetermined color is performed to erase the latent images of both images written with the light of A color and the latent image of the second image written with the light of B color is exposed on the surface of the photoconductor in a potential manner. The second image is developed with a predetermined color toner having the same polarity as the predetermined color toner, and then with one of the remaining two images of the α color image, the β color image, the γ image and the black image. A third image is A-color light and the other image is a fourth image with A-color light and B-color light, and , The third image is written as a latent image for regular development, the fourth image is written as a latent image for reversal development, the third image is developed with toner of a predetermined color, and uniform irradiation is performed with light of a predetermined color. The latent images of the two images written by the above are erased, and the latent image of the fourth image written by the B color light is made to appear potential on the surface of the photoconductor, and the fourth image has the same polarity as the toner of the predetermined color. It is characterized by developing with color toner.

Here, after the first image and the second image are developed with toners of a predetermined color, respectively, these toner images are transferred to a transfer material such as an intermediate transfer body or a final transfer body, and then transferred. The charging process for writing latent images for the remaining third image and fourth image may be started, or this charging process may be started with these toner images carried on the composite photoconductor. good.

In writing the latent image, the potential of the surface of the photoconductor may be set to approximately 0 V without irradiating either the A-color light or the B-color light on the latent image portion to be reproduced in white.

Further, in writing the latent images of the first image and the second image, the latent image portion to be reproduced as a common background portion of the first image and the second image is also the above A.
The potential of the surface of the photoconductor is set to approximately 0 V without irradiating either the colored light or the B-colored light, and in writing the latent images of the third image and the fourth image, the third image and the fourth image are written. The latent image part that should be reproduced as the background part common to
The potential on the surface of the photoconductor may be set to approximately 0 V without irradiating either the colored light or the B-colored light.

[0010]

In the full-color image forming method of the present invention,
First, the first and second photoconductive layers of the photoconductor are charged in opposite directions so that they have approximately the same potential, and the surface potential of the photoconductor is approximately 0V.
To Next, when the three primary colors are α, β, and γ, the first image, which is any one of the α color image, the β color image, the γ image, and the black image, for example, the α image is A color light,
A second image that is one image other than the one of the α color image, the β color image, the γ image, and the black image, for example β
The image is A-color light and B-color light, and α is the first image.
The image is written as a latent image for regular development, and the β image which is the second image is written as a latent image for reversal development. As a result, a latent image of an α-color image and a coated latent image of a β-color image are formed on the first photoconductive layer, which is mainly made into a conductor by the light irradiation of the A-color light, and mainly by the light irradiation of the B-color light. The main latent image of the β-color image is formed on the second photoconductive layer which is the other photoconductive layer to be made into a conductor. For this β image, the main latent image and the coated latent image are written in the photoconductive layers of opposite polarities, so they do not cancel each other out and no potential appears on the surface of the photoconductor, and only the latent image of the α image appears. The surface appears in a potential on the surface of the photoconductor. Here, the main latent image is a latent image for development, and the coated latent image is a photoconductive layer on which the main latent image is formed until it is erased by uniform irradiation with light of a predetermined color later. A latent image formed on the photoconductive layer charged in the opposite direction so that the main latent image does not appear on the surface of the photoconductor in a potential manner.

Next, the α-color image appearing on the surface of the photosensitive member in terms of potential is developed with toner of a predetermined color.

Here, this .alpha. Image is a latent image for normal development in which the potential of the surface of the photoconductor at a portion to which toner is not attached is approximately 0 V, and is executed prior to writing of the latent image as described above. In the charging step, the first and second photoconductive layers are charged in opposite directions so as to have substantially the same potential, and the surface potential of the photoconductor is set to approximately 0V. Therefore, in the latent image writing process, when the surface potential of the photoconductor is set to approximately 0 V by irradiation of the color A light to form a portion where the toner is not attached,
Even if this A-colored light irradiation site is deviated due to speed fluctuations on the surface of the photoconductor, the photoconductor surface potential of the area where the A-colored light is not irradiated remains as approximately 0 V as a part to which toner is not attached. Therefore, the toner does not adhere to this portion.

Next, the latent image of the α-color image and the covered latent image of the β-color image, which are the two images written with the A-color light, are uniformly irradiated with the light of the predetermined color, and the β is written with the B-color light.
The main latent image of the image is visualized on the surface of the photoconductor in a potential manner, and the main latent image of the β image is developed with a predetermined color toner having the same polarity as the predetermined color toner.

Then, after the visible images of the α image and β image formed on the photoconductor are transferred onto the transfer medium, the surface of the photoconductor is initialized, or the toner images of the α image and β image are transferred to the photoconductor. While being carried on top, proceed to the next step.

Then, a third image which is one of the remaining two images of the α color image, the β color image, the γ image and the black image, for example, the γ image is converted into the fourth image by the A color light. The black image which is the A color light and the B color light, and the γ image which is the third image is written as a latent image for regular development, and the black image which is the fourth image is written as a latent image for reversal development. As a result, the first color is mainly converted into a conductor by the light irradiation of the A color light.
A latent image of a γ color image and a latent image of a black image are formed on the photoconductive layer, and a main latent image of a black image is formed on the second photoconductive layer which is mainly made conductive by light irradiation of B color light. It is formed.

Next, the γ image, which is one of the images appearing electrically on the surface of the photosensitive member, is developed with toner of a predetermined color.

Again, this γ image is a latent image for normal development in which the potential of the surface of the photoconductor at the portion where toner is not attached is approximately 0 V, and is executed prior to writing the latent image as described above. In the charging step, the first and second photoconductive layers are charged in opposite directions so as to have substantially the same potential, and the surface potential of the photoconductor is set to approximately 0V. Therefore, in the above-described latent image writing step, when a portion of the surface of the photoconductor that does not adhere to the toner is formed by irradiating the color A light with the color A light, a portion of the surface of the photoconductor where the color A light is irradiated due to fluctuations in speed of the photoconductor surface or the like. Even when the deviation occurs, the surface potential of the photoconductor at the portion where the color A light is not irradiated as the portion where the toner is not adhered remains approximately 0V. Therefore, the toner does not adhere to this portion.

Then, uniform irradiation is performed with light of a predetermined color to erase the latent image of the γ-color image written with the A-color light and the cover latent image of the black image, and the main latent image of the black image written with the B-color light is exposed. The black image is developed on the surface of the body with a potential, and the black image is developed with a predetermined color toner having the same polarity as the predetermined color toner.
As a result, a visible image of a γ image and a black image is formed on the surface of the photoconductor.

Then, when the visible images of the α image and β image formed on the photoconductor as described above are transferred onto the transfer medium, the γ image and the black image formed on the photoconductor are transferred. Image is transferred to the transfer medium by aligning it with the α image and β image on the transfer medium, and the visible α image and β image formed on the photoconductor as described above. When the γ image and the black image are formed while carrying the image, these four-color visible images are collectively transferred onto the transfer medium to form a full-color image on the transfer medium. (Hereafter, margin)

[0020]

EXAMPLE First, a first photoconductive layer and a second photoconductive layer were formed on a conductive substrate.
A specific example of the photoconductor in which the photoconductive layer is laminated will be described. As such a photoreceptor, the above-mentioned JP-A-61 is used.
No. 163349, etc., and Japanese Patent Application No. 2
Those described in No. -100976 can be used. The one described in Japanese Patent Application No. 2-100976 is shown in FIG.
As shown in FIG. 3, a charge transport layer (CTL) and a charge generation layer (CGL) are formed on an aluminum drum, which is a conductive substrate (not shown).
The first photoconductive layer consisting of the L layer, the two-layer structure (lower layer M
I, upper layer MII) intermediate layer M layer, second photoconductive layer U
The layers are constructed by laminating in this order.

The CTL consists of 18 g of an alpha-phenyl stilbene compound having the following structural formula (1) and 20 g of a polycarbonate resin having the structural formula (2) below, and dichloromethane (methylene chloride) having the structural formula (3) below. ) Dispersed to 185.5 g, applied to an aluminum drum by a spray method and then dried to a thickness of 15 ± 1 μm.

CGL is prepared by coating a solution prepared by dispersing 1 gram of trisazo pigment having the following structural formula (4) in 99 grams of methylhexanone on the CTL so that the light transmittance at 720 nm is 10 ± 2%. It was formed by. Lower layer MI constituting an intermediate layer provided on the CGL layer
Is a thermosetting phenolic resin having the following structural formula (5) 0.8 g, butanol 50 g and methanol 30 g
A solution dispersed in gram of a mixed solvent was applied on CGL to form a thickness of 0.39 ± 0.03μ. The upper layer MII which constitutes the intermediate layer is composed of 0.8 g of quinacridone having the structural formula (6) below and 0.8 g of thermosetting phenolic resin having the structural formula (5) below, represented by the structural formula (7) below. It is formed by applying a solution dispersed in 80 g of tetrahydrofuran having the above to the lower layer MI so that the transmittance of light of 565 nm is 80 ± 4%.

The U layer is a thiapyrylium salt (4- (p-dimethylaminophenyl) -2) having the following structural formula (8).
-6-diphenylthiabylium perchlorate) 0.
127 grams and 7.51 grams of the polycarbonate resin having the structural formula (2) above and 5.07 grams of the alpha-phenyl stilbene compound having the structural formula above (1) were added to dichloromethane (chlorination) having the structural formula above (3). Methylene) 67.0 g and 1, having the following structural formula (9)
A solution prepared by dispersing 47.5 g of 1,2 trichloroethane in a mixed solvent was applied onto the intermediate layer so that the thickness was 30 ± 3 μm.

In this composite photoreceptor, the U layer and the upper layer MI
The I and the lower layer MI each have a transmittance of 94%, 96%, and 100% with respect to the light of 780 nm, and the L layer is sensitive to this light.
When irradiated with 80 nm light, this light reaches the CGL and makes it conductive. U layer alone is 680 nm
Has a transmittance of 0.3 to 0.4%, and
Since it has sensitivity to this light, when the light of 680 nm is irradiated on the composite photoconductor, this light makes the U layer conductive and is substantially absorbed by this. Therefore, in the laminated state, the L layer becomes a photoconductive layer having sensitivity to 780 nm light and not to 680 nm light, and the U layer has 680 nm.
Is a photoconductive layer having a sensitivity to the light of 780 nm and not to the light of 780 nm. The U layer and the L layer each have sensitivity to the red light of the red LED which is the back lamp of the primary chargers 11 and 12 described later, but this light is absorbed by the U layer, It does not reach the L layer. The intermediate layer (M layer) can be omitted, and U
An overcoat layer may be provided on the surface of the layer.

Examples using the composite photoconductor will be described below. The apparatus shown in FIG. 2 can be used as the embodiment apparatus. In FIG. 2, the photosensitive drum 30
Is a composite photoconductor provided with a U layer and an L layer as in the above-mentioned respective examples. Around the photosensitive drum 30, a primary charger 11, a secondary charger 12, a cyan developing device 17, a yellow developing device 15, a near-infrared light uniform exposure device 16a, and a magenta developing device equipped with a back lamp. 27, black developing device 25, AC
Simultaneous charging white uniform exposure device 19 and cleaning device 1
0 are sequentially arranged along the movement path on the surface of the photosensitive drum 30. And 780nm laser light source (LD)
13 and a 680 nm laser light source (LD) 14 and a two-wavelength simultaneous writing optical system including a polygon mirror 1 and the like, and the writing position on the photoconductor drum by this is the secondary charging device 12 and the cyan developing device 17. It is set in between. Further, an intermediate transfer belt 18 is provided so as to come into contact with the surface of the photosensitive drum 30 between the black developing device 25 and the AC charging simultaneous white uniform exposing device 19, and the intermediate transfer belt 18 is intermediately transferred at the bottom of the intermediate transfer belt 18. The backup roller 18b faces the belt 18 and forms a transfer portion onto the transfer paper 2. A cleaner 18a is provided so as to face the surface of the intermediate transfer belt 18.
Further, a conveyor belt device 3 for conveying the transfer paper 2 that has passed through the transfer section is also provided.

In the above construction, the magenta developing device 27 and the cyan developing device 17 in which the near-infrared light uniform exposure device 16a is sandwiched are used on the photosensitive drum 30 at the first rotation of the photosensitive drum 30. 2 of yellow image and magenta image
A color toner image is formed. The toner images of the two colors are collectively transferred to the intermediate transfer belt 18. After the transfer, the surface of the photosensitive drum 30 is discharged by the AC uniform simultaneous white uniform exposure device 19 and then the residual toner is removed by the cleaning device 10. Then, at the second rotation of the photoconductor drum 30, a yellow image and a black image are formed on the photoconductor drum 30 by using the yellow developing device 15 and the black developing device 25, which are also arranged with the near-infrared light uniform exposure device 16a interposed therebetween. To form two color toner images.
The two color toner images are aligned with the magenta and cyan images that have already been transferred, and the intermediate transfer belt 18
Is transferred onto the intermediate transfer belt 18, and
With the color toner images superposed, the four color toner images are transferred onto the transfer paper 2 to form a full-color image.

The process of forming a full-color image will be specifically described below with reference to FIGS. 3 and 4. FIG. 3 is a process drawing of the first rotation of the photosensitive drum 30, and FIG. 4 is a process drawing of the second rotation of the photosensitive drum 30.

First, the charging process using the primary charger 11 and the secondary charger 12 of the photosensitive drum will be described. While rotating the photosensitive drum 30A in a direction of an arrow (counterclockwise) at a predetermined linear velocity, negative corona discharge by the primary charging charger 11 is performed under uniform exposure of the red LED which is the back lamp. At this time, as shown in FIG. 3A, the negative charge that has reached the surface of the photosensitive drum 30A by corona discharge is a positive charge (hole) in the photocarrier generated in the U layer that is sensitive to red light. The negative charges (electrons), which are the other photocarriers, move in the U layer and are uniformly accumulated on the M layer, which is the insulating layer, while the L layer, which the red light does not reach, is electrically insulating. Without loss, positive charges are induced and uniformly distributed on the boundary surface between the L layer and the aluminum drum. As a result, the L layer is charged to −2000 V (strictly speaking, the combined voltage of the L layer and the M layer is 2000 V, but it is ignored because the M layer is sufficiently thin. The negative charge accumulated on the L layer is referred to as the negative charge accumulated on the L layer.). From the primary charging charger 11 to the rotation direction of the photoconductor drum 30 at a predetermined distance along the peripheral surface thereof,
In the dark, positive corona discharge by the secondary charger 12 is performed. At this time, as shown in FIG. 3B, the U layer does not lose its electrical insulating property, so that positive charges are accumulated on the surface of the U layer and are charged to plus 1000V. At this time, a part of the lines of electric force (determined by the ratio of the electrostatic capacities of the U layer and the L layer) that were all directed toward the aluminum drum from the negative charges accumulated at the boundary between the U layer and the L layer, Since the surface of the photoconductor drum 30 is turned to the positive charge side, the L layer becomes −1000V. As a result, the potential on the surface of the photoconductor drum 30 is approximately 0 V, which is the sum of plus 1000 V of the charge accumulated in the U layer and minus 1000 V of the charge accumulated in the L layer.

Writing by the dual wavelength simultaneous writing optical system will be described below. As is well known, the masking equation is used to convert the R, G, B reflection densities of the original into C, M,
The toner concentration of Y is obtained, the photoconductor surface potential for obtaining the toner concentration is obtained in consideration of the relationship between the toner concentration and the toner adhesion amount per unit area, the photoconductor characteristics, and the photoconductor surface potential. In order to simplify the explanation, here, as shown in Table 1 as the development amount, C, M and Y are set in order to simplify the explanation.
Each original color is reproduced when the adhered amount of each toner is 100% or 0%. For example, as shown in Table 1, the cyan color of the original document is reproduced only by attaching 100% of the cyan toner, and the blue-violet color of the original document is reproduced by attaching 100% of the cyan toner and the magenta toner.
The areas to which the C, M, and Y toners are attached are the cyan image that is the image component obtained by color-separating the document with the red filter, and the image component obtained by color-separating the document with the green filter. It is determined using image data of each of the magenta image and the yellow image, which is an image component obtained by color-separating the original with a blue filter. Even with such division, almost faithful color reproduction is possible except for blue-violet. Table 1 shows the latent image potential and the image exposure amount (exposure amount) for each original color when a latent image for regular development is formed. %, A development amount of 5% can be obtained, and the surface potential of the photoconductor is set to 5 at an exposure amount of 0.5 (unit is arbitrary).
It is supposed to be attenuated by 00V.

[Table 1]

Under the above assumptions, this embodiment is based on the above assumption that a latent image of a cyan image (hereinafter, referred to as a cyan latent image) on the positively charged U layer is used for reversal development on the first rotation of the photosensitive drum 30. As an image (hereinafter referred to as N / P latent image), a latent image of a magenta image (hereinafter referred to as magenta latent image) on a negatively charged L layer is used as a latent image for normal development (hereinafter referred to as P / P latent image). At the second rotation of the photosensitive drum 30, a latent image of a yellow image (hereinafter referred to as a yellow latent image) is written as a P / P latent image on the negative L layer. Table 2 shows the latent image potential and the exposure amount of the photoconductive layer forming a latent image for each original color in this case.

[Table 2]

Here, in this embodiment, the black portion of the original is registered with the black portion (hereinafter, the original color in this black portion is one black color) in the gradation image having a relatively large registration tolerance. Black areas of characters and diagrams with relatively small tolerances (hereinafter, the original color in this black area is black 2
It is reproduced by distinguishing it from (color). That is, black 1
The colors are reproduced with four colors of yellow toner (Y), magenta toner (M), cyan toner (C), and black toner, and the two black colors are reproduced with only black toner. To distinguish between the black 1 color and the black 2 colors, a known process such as pictogram separation process can be used. Then, at least black 1 to which black toner is attached
The image areas of two colors and black are treated as black images, and the image area of one black is treated as a part of each of the yellow image, the magenta image, and the cyan image. Then, at the second rotation of the photosensitive drum 30, the latent image of the black image (hereinafter, referred to as a black latent image) is N / N on the positively charged U layer.
Write as a P latent image.

Further, in this embodiment, as described later, first, the negative P / P latent image of the L layer is normally developed with the positive toner, so at this time, the positive N / P latent image of the U layer is formed. In order to prevent the positive polarity toner from adhering to the image, the positive polarity N / N of the U layer is
A negative polarity N / P latent image having the same shape as the P latent image and having the opposite polarity to that of the P latent image is formed as a coated latent image. This coating latent image may be formed on a photoconductive layer different from the U layer and the L layer and formed on the photoconductive layer. However, in this embodiment, in order to simplify the structure of the photoconductor. Then, the coated latent image is formed together with the negative P / P latent image on the L layer having a polarity opposite to that of the N / P latent image (corresponding to the main latent image) of the U layer.

Specifically, for the first rotation of the photosensitive drum 30, the N / P main latent image of the cyan image is formed on the U layer, and the P / P latent image of the magenta image and the cyan image are formed on the L layer. Form an N / P coating latent image of the image. For this purpose, a 680 nm laser beam sensitive to the U layer is used for N / C of the cyan image.
Image data for forming a P / P latent image of a magenta image and image data for forming an N / P latent image of a cyan image, which is modulated with image data for forming a P latent image and has a sensitivity of 780 nm for the L layer. Modulate with. On the other hand, 2 of the photosensitive drum 30
For the rotation eye, the N / P main latent image of the black image is formed on the U layer, and the P / P latent image of the yellow image and the N / P covered latent image of the black image are formed on the L layer. For this purpose, a laser beam of 680 nm having sensitivity to the U layer is modulated with image data for forming an N / P latent image of a black image, and 780 having sensitivity to the L layer.
A laser beam of nm is modulated with image data for forming a P / P latent image of a yellow image and image data for forming an N / P latent image of a black image.

Table 3 is for explaining the potential of each layer of the photoconductor 30 by the above latent image formation and the exposure amount at the time of latent image formation for each document color. Column (a) shows a cyan image (C
Image), magenta image (M image), black image, and yellow image (Y image), the toner adhesion area of each original color is shown. The main latent image (C (N / P)) of the cyan image for reverse development to be formed, the covered latent image (C (N / P)) of the cyan image for reverse development to be formed on the L layer, and magenta for normal development. It shows the potential of each original color portion of the latent image (M (P / P)) of the image and the exposure amount for obtaining the potential,
In column (c), the potential of each original color portion on the surface of the photoreceptor after writing a latent image (after image exposure) and the near-infrared uniform exposure device 1 described later.
6 shows the potential of each original color portion on the surface of the photoconductor after the uniform light irradiation by No. 6 in FIG. In column (d), the main latent image (black (N / P)) of the black image for reversal development formed on the U layer and the black image for reversal development formed on the L layer at the second rotation of the photosensitive drum. Showing the potential of each original color portion of the coated latent image (black (N / P)) and the latent image (Y (P / P)) of the yellow image for normal development and the exposure amount for obtaining the potential. And
In column (e), the potential of each original color portion on the surface of the photoconductor after writing a latent image (after image exposure) and the near-infrared uniform exposure device 1 described later.
6 shows the potential of each original color portion on the surface of the photoconductor after the uniform light irradiation by No. 6 in FIG. (Hereafter, margin)

[Table 3]

As is clear from Table 3, for example, for the first rotation of the photosensitive drum 30, a concrete example used for modulation of a 680 nm laser beam for writing the main latent image of the cyan image for reversal development on the U layer. As the image data, image data that is driven so as to irradiate a laser with an exposure amount of 1.0 for a toner-attached pixel and with an exposure amount of 0.5 for a non-toner-attached pixel is generated from cyan image data and used. be able to. Further, as concrete image data used for modulation of a 780 nm laser beam for writing a covered latent image of a cyan image for reversal development and a latent image of magenta for regular development on the L layer, for example, a toner-attached pixel of a cyan image is used. For the cyan image data, and for the cyan toner image non-toner-attached pixels, the image data for driving the laser to be irradiated with the laser light at the exposure amount 0 (no laser irradiation) is generated from the cyan image data. Data is generated from the magenta image data to drive so that the toner-attached pixels of the image are irradiated with laser light at an exposure amount of 0 (no laser irradiation) and the toner-non-adhered pixels of the magenta image are exposed at laser light amount of 0.5. Then
An image signal obtained by adding both of these image data can be used.

At the writing position on the photosensitive drum 30, a mixed beam of a 780 nm laser beam and a 680 nm laser beam, which is modulated according to the image data as described above, is a one-dimensional light beam in the axial direction of the photosensitive drum 30. The latent image of the magenta image and the cyan image is scanned for the first rotation of the photosensitive drum 30, and the latent image of the yellow image and the black image is scanned for the second rotation of the photosensitive drum 30, respectively. Image exposure is performed simultaneously at the same position. 780
As described above, the laser beam of nm has a U layer and an upper layer MI.
I, through the lower layer MI, reaches the CGL, is absorbed, generates photocarriers, and discharges −1000 V accumulated on the L layer. The 680 nm laser beam is absorbed in the U layer and generates photocarriers in it,
The electric charge of plus 1000 V accumulated here is discharged.

Here, in the first rotation of the photosensitive drum 30, the magenta latent image which is an N / P latent image is a 0V of the main latent image of the U layer and a covered latent image of the L layer at a portion to which toner is attached. Minus 0 V, and for the part where toner is not adhered, plus 500 V of the main latent image of the U layer and minus 500 V of the covered latent image of the L layer cancel each other out, so that any part of the surface potential of the photoconductor is reduced. The contribution is 0 V, and no potential appears on the surface of the photoconductor. As a result, in the first rotation of the photosensitive drum 30, the P / P of the magenta image is formed on the surface thereof.
Only the latent image, the part to which the toner adheres is minus 500
V, a portion to which toner is not attached appears as a P / P latent image of 0 V on the surface of the photoconductor in a potential manner.

Next, as the development of the first color, a magenta developing device 27 using positively charged magenta toner applies a developing bias of 0 V to normally develop the P / P latent image of the magenta image, and then, as shown in FIG. As shown in d), magenta toner is attached to the surface of the photoconductor corresponding to the areas of one color of black, magenta, red, bluish purple, etc. of the original forming the magenta image.

Next, as shown in FIG. 3 (e), the near-infrared light uniform exposure device 16a performs uniform exposure with near-infrared light, which is light having sensitivity to the L layer, and charges accumulated in the L layer. To discharge almost uniformly. As a result, the magenta latent image formed on the L layer and the covering latent image of the cyan image are erased, and the main latent image of the cyan image formed on the U layer is made to appear on the photoconductor in a potential manner.

Next, as the second color development, a plus 500 is applied by the cyan developing device 17 using positively charged cyan toner.
A developing bias of V is applied to reverse develop the N / P main latent image of the cyan image. As a result, as shown in FIG. 3F, the cyan toner is attached to the surface of the photoconductor corresponding to the areas of one color of black, cyan, green, blue-violet, etc. of the original forming the cyan image.

The toner images of the magenta image and the cyan image are carried on the photosensitive drum 30, and the intermediate transfer belt 1
3 (g), the surface of the photoconductor drum 30 after the transfer is removed by the exposure device 19 so that the residual charge is removed. The residual toner is removed while passing through the portion facing the cleaning device 10. During this first rotation, the yellow developing device 15 and the black developing device 25 which are not used are retracted from the photosensitive drum 30.

Next, in the second rotation, as shown in FIG.
As shown in (b), the photosensitive drum 30 is charged in the same manner as in the first rotation, and the potential on the surface of the photosensitive drum 30 is increased by plus 500 V of the charge accumulated in the U layer and the charge accumulated in the L layer. Approximately 0V is added to the minus 500V.

Next, as shown in FIG. 4C, the cyan latent image and the black latent image are written by the dual wavelength simultaneous writing optical system. Form N / P main latent image of black image on U layer
A yellow image P / P latent image and a black image N / P covered latent image are formed on the layer. For this reason, the sensitivity of the U layer is 68
A 0 nm laser beam is modulated with image data for forming an N / P latent image of a black image, and a 780 nm laser beam having sensitivity in the L layer is used for image data for forming a P / P latent image of a yellow image and a black image. Modulate with image data for N / P latent image formation.

As a result, the potential of each layer of the photoconductor drum 30 is lowered according to the exposure amount as shown in column (e) of Table 3 above, and as shown in column (f) of Table 3 above. On the surface of the photosensitive drum 30, the main latent image of the black image formed on the U layer does not appear to be covered with the covered latent image of the black image formed on the L layer, and only the P / P latent image of the yellow image appears. So that the potential appears.

Next, as the development of the third color, a yellow developing device 15 using positively charged yellow toner applies a developing bias of 0 V to normally develop the N / P latent image of the yellow image, and then, as shown in FIG. ), The yellow toner is attached to the surface of the photoconductor corresponding to the areas of one black color, the yellow color, the red color, the green color, and the like of the original forming the yellow image.

Next, as shown in FIG. 4 (e), the near-infrared light uniform exposure device 16a performs uniform exposure by the near-infrared light, which is light having sensitivity to the L layer, and is formed on the L layer. By erasing the yellow latent image and the covered latent image of the black image, the main latent image of the black image formed in the U layer as shown in column (f) of Table 3 above is electrically potential on the photoconductor. The state that appears in.

Next, as the development of the fourth color, a developing bias of plus 500 V is applied by the black developing device 25 using positively charged black toner to reverse develop the N / P main latent image of the black image, As shown in FIG. 4 (d), black toner is attached to the surface of the photoconductor corresponding to the black 1 color and black 2 color regions of the original forming the black image.

As described above, when the two color toner images of the yellow image and the black image formed on the photoconductor drum 30 pass through the portion facing the intermediate transfer belt 18, the magenta image and the cyan image already transferred. The toner image of the image is aligned and transferred onto the intermediate transfer belt 18, and the surface of the photoconductor drum 30 after the transfer is discharged by the exposure device 19 to remove residual charges, and passes through a portion facing the cleaning device 10. Sometimes residual toner is removed. On the other hand, the four-color toner images on the intermediate transfer belt 18 are collectively transferred to the transfer paper 2, thereby forming a full-color image on the transfer paper 2. The magenta developing device 27 and the cyan developing device 17 which are not used during the second rotation are retracted from the photosensitive drum 30.

Then, the transfer paper 2 to which the toner image is transferred is discharged to the outside of the machine after the toner image is fixed by a fixing device (not shown). On the other hand, the surface of the photosensitive drum 30 is charged by the simultaneous white uniform exposure device 19 for charging and then cleaned by the cleaning device 10 to prepare for the next image formation.

In the above embodiment, for example, when a full-color image is formed in synchronization with the image reading by the image input device (scanner), the development reading is performed at the first rotation and the second rotation of the photosensitive drum 30, respectively. By
Image memory requirements can be reduced while using a single photoreceptor drum.

In the above embodiment, the toner image formed on the photosensitive drum 30 was transferred onto the transfer paper 2 via the intermediate transfer belt 18. However, instead of such an intermediate transfer belt 18, a transfer paper is used. A transfer drum for holding or a transfer belt device capable of switchback transfer may be used to directly transfer the image from the photosensitive drum 30 onto the transfer sheet.

It is also possible to form the toner images of four colors on the photosensitive drum and then collectively transfer the toner images onto a transfer paper or the like. In this case, 2 formed in the first rotation
The intermediate transfer belt 18 is retracted so that the intermediate transfer belt 18 does not come into contact with the surface of the photoconductor drum 30 while the color toner image passes through a portion facing the intermediate transfer belt 18, and
White uniform exposure device 1 for simultaneous charging of the surface of the photoconductor drum 30
The remaining two color toner images are formed in the second rotation as they are without performing the charging and cleaning by the charging device 9 and the cleaning device 10, and then the four colors are collectively transferred onto the transfer paper via the intermediate transfer belt 18. To do it. Also in this case, instead of using the intermediate transfer belt 18, a transfer drum holding the transfer paper or a transfer belt device capable of switchback transfer is used to transfer directly from the photosensitive drum 30 to the transfer paper. It may be configured.

When the two-color toner images are superposed on the intermediate transfer belt 18 or the transfer paper on the transfer drum to form four-color toner images, the peripheral lengths of the intermediate transfer belt 18 and the transfer drum are set. , Maximum copy length, eg, A-3 size 4
Set longer than 20mm.

In the above embodiment, in the white part of the original at the first rotation, the surface potential of the photosensitive member is 0 in the latent image of the magenta image for normal development which is first developed.
Since it is V, the surface potential of this photoconductor is 0 V after the charging step.
It can be realized as it is. The latent image of the cyan image for reversal development, which is developed after uniform light irradiation, has a photoreceptor surface potential of plus 500V, which is sufficiently higher than 0V, which is the photoreceptor surface potential of the toner adhering pixel. If the potential has a large absolute value), U layer plus 100 after the charging process
Plus 1000 which is obtained by neutralizing the L layer minus 1000V by uniform light irradiation from 0V and L layer minus 1000V
Toner does not adhere even if it is V. This also applies to the white part of the document in the second rotation. Therefore, it is possible to form a full-color image on the white portion of the document by image exposure such that neither the 680 nm laser beam nor the 780 nm laser beam is irradiated. And, according to this, there is also an advantage that the cumulative amount of the laser beam irradiation to the photoconductor can be reduced correspondingly, and thereby the deterioration of the photoconductor can be reduced.

Table 4 is for explaining the potential of each layer of the photoconductor 30 and the exposure amount at the time of forming a latent image for each original color in such image exposure, and corresponds to Table 3 in the above embodiment. To do.

[Table 4]

In order to perform such image exposure, for example, by using cyan image data or the like, a white part in which the data value of the pixel in the white part of the original is 0 and the data value of other pixels is 1 Generate image data. For this purpose, for example, the background level determination value that is predetermined for each image such as a cyan image is compared with the data of each image such as a cyan image, and the pixels that are determined to be the background for all images are white areas. It is determined that the pixel is a medium pixel, and the white area image data value is determined as described above. Then, for example, regarding the first rotation of the photosensitive drum 30, as concrete image data used for modulation of the 680 nm laser beam for writing the main latent image of the cyan image for reversal development on the U layer, the above-mentioned cyan image data is used. The image data generated from the image data and the white area image data value are integrated. Further, specific image data used for modulation of a 780 nm laser beam for writing a covered latent image of a cyan image for reversal development and a magenta latent image for regular development on the L layer is generated from the above cyan image data. Image data obtained by adding the image data obtained by adding the image data and the image data generated from the magenta image data ({C (N / P) + M
(P / P)} × (white image data)) is used.

Further, not only in the white portion of the original, but also in the latent image portion where the toner does not adhere at all during the first and second rotations of the photosensitive drum 30, as in the white portion of the original, A full color image can also be formed by image exposure in which neither the 680 nm laser beam nor the 780 nm laser beam is irradiated.

Table 5 is for explaining the potential of each layer of the photoconductor 30 and the exposure amount at the time of forming a latent image for each original color in such image exposure, and corresponds to Table 3 in the above embodiment. To do. (Hereafter, margin)

[Table 5]

To perform such image exposure, for example, the following image data is generated in place of the white area image data generated using the cyan image data or the like. That is,
For the first rotation of the photoconductor drum 30, the data value for the pixel in the common background portion corresponding to the background portion is 0 and the data value for the other pixels is 1 in both the magenta image and the cyan image. Common background image data of a magenta image and a cyan image is generated. For this,
The image data of each of the magenta image and the cyan image is compared with the background level determination value to determine the background portion of each image, and the common portion is determined by an appropriate calculation. Similarly, common background image data of the yellow image and the black image is generated for the second rotation of the photosensitive drum 30. Then, for example, for the first rotation of the photosensitive drum 30,
Writing the main latent image of the cyan image for reversal development on the U layer 68
As specific image data used for modulation of the 0 nm laser beam, image data obtained by integrating the image data generated from the cyan image data and the common background image data of the magenta image and the cyan image are used. Also,
The specific image data used to modulate the 780 nm laser beam for writing the cyan latent image for reversal development and the magenta latent image for regular development on the L layer are the image data generated from the above cyan image data. The image data obtained by adding the image data generated from the magenta image data and the common background image data of the yellow image and the black image are used.

In each of the above embodiments and the like, the photosensitive member is formed on the surface of the drum-shaped substrate, but instead of this, it may be formed on the surface of the belt-shaped substrate.

[0061]

According to the present invention, for example, the α image which is the first image is a latent image for normal development in which the potential of the surface of the photoconductor at a portion where toner is not attached is approximately 0V. In the charging step performed prior to the writing of the first and second photoconductive layers, the first and second photoconductive layers are charged in opposite directions so as to have substantially the same potential, and the surface potential of the photosensitive member becomes approximately 0 V.
In the latent image writing process, when a portion of the surface of the photoconductor that does not adhere to the toner is formed by irradiating the light of A color with the light of A color, a region where the light of A color is irradiated is displaced due to speed variation of the surface of the photoconductor. Also, the surface potential of the photoconductor is about 0 V in the area where the A color light is not irradiated as the area where the toner is not attached.
Since it can be left as it is, toner does not adhere to this portion. Therefore, even if the light irradiation position in writing the latent image for regular development shifts due to speed fluctuations on the surface of the photoconductor or the like, it is possible to prevent the occurrence of background stains and deterioration in color reproducibility due to toner adhesion.

Further, according to the invention of claim 2 or 3, since the light irradiation amount for forming a latent image on the photoconductor is reduced, deterioration of the photoconductor can be reduced.

[Brief description of drawings]

FIG. 1 is a sectional view of a photosensitive member according to an example.

FIG. 2 is a schematic configuration diagram of an image forming apparatus according to an embodiment.

FIG. 3 is a process diagram of image formation for a first rotation of a photosensitive drum in the image forming apparatus.

FIG. 4 is a process diagram of image formation for a second rotation of the photosensitive drum in the image forming apparatus.

[Explanation of symbols]

2 Transfer paper, 3 Conveyor belt device 10 Cleaning device, 11 Primary charger 12 Secondary charger, 13 Laser light source (780 nm) 14 Laser light source (680 nm), 15 Yellow developing device 16 Uniform exposure device, 17 Cyan developing device 18 Intermediate Transfer belt, 19 Laser light source (780 nm) 25 Black developing device, 26 Yellow developing device 27 Magenta developing device

Claims (3)

[Claims] 1. A first photoconductive layer is provided on a conductive substrate, and a second photoconductive layer is formed on the first photoconductive layer directly or through an intermediate layer.
And the photoconductive layer is adjusted so that one of the photoconductive layers is irradiated with light of A color and the other of the photoconductive layers is irradiated with light of B color. The first and second photoconductive layers of the photoconductor are charged in opposite directions so that they have approximately the same potential, and the surface potential of the photoconductor is approximately 0V.
And the three primary colors are α, β, γ, α color image, β color image,
The first image, which is any one of the γ image and the black image, is A-color light, and is the one image other than the one image of the α-color image, the β-color image, the γ-image, and the black image. A certain second image is written with A-color light and B-color light, and the first image is written as a latent image for regular development and the second image is written as a latent image for reversal development. After developing, uniform irradiation with light of a predetermined color is performed to erase the latent images of both images written with the light of A color and the latent image of the second image written with the light of B color is exposed on the surface of the photoconductor in a potential manner. The second image is developed with a predetermined color toner having the same polarity as the predetermined color toner, and then one of the remaining two images of the α color image, the β color image, the γ image and the black image is used. A third image is A-color light and the other image is a fourth image with A-color light and B-color light, and , The third image is written as a latent image for regular development, the fourth image is written as a latent image for reversal development, the third image is developed with toner of a predetermined color, and uniform irradiation is performed with light of a predetermined color. The latent images of the two images written by the above are erased, and the latent image of the fourth image written by the B color light is made to appear potential on the surface of the photoconductor, and the fourth image has the same polarity as the toner of the predetermined color. A full-color image forming method comprising developing with color toner. 2. When writing the latent image, the potential of the surface of the photoconductor is set to approximately 0 V without irradiating either the A-color light or the B-color light on the latent image portion to be reproduced in white. The full-color image forming method according to claim 1. 3. When writing the latent images of the first image and the second image, the latent image portion to be reproduced as a common background portion of the first image and the second image is also the A color light. And the B-color light are not irradiated, the potential on the surface of the photoconductor is set to about 0.
V and when writing the latent images of the third image and the fourth image, the latent image portion to be reproduced as a common background portion of the third image and the fourth image is also the A color light. The potential of the surface of the photoconductor is set to approximately 0 without irradiating with the B color light.
3. The full-color image forming method according to claim 2, wherein V is set.