JPH03249774A - Full color image forming method - Google Patents

Abstract

PURPOSE:To faithfully reproduce an original image by respectively separating and developing a full color image of the color area and a pure black tone image of a black-and-white area of the original image. CONSTITUTION:After electrostatically charging the respective layers U, M and L of a composite photosensitive body to be positive-negative-positive or negative-positive- negative, the color image information of cyanogen, magenta and yellow in the color area and the black-and-white image information in the black-and-white area are respectively put on respective wavelength light beams to simultaneously expose the composite photosensitive body, and an electrostatic latent image is formed so that the absolute value of the black image potential of the color area may be lower than that of the black-and-white image potential of the black-and-white area. Furthermore, by applying developing bias which is higher than the black image potential of the color area, the black-and-white area is developed with the black toner and then only the black-and- white area is uniformly exposed. After erasing the electrostatic latent image, the electrostatic latent images of the respective color of respective photoconductive layers are successively superposed and developed with the toner of the corresponding color. Thus, the black-and-white image part of the original image is faithfully reproduced in the pure black tone.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a full-color image forming method using a composite photoreceptor formed by laminating a plurality of photosensitive layers having photosensitivity to light of different wavelengths.

(Prior Art) Generally, in various full-color image forming apparatuses such as copying machines and printers that form full-color images, electrostatic latent images corresponding to each color image are formed on a photoreceptor, and
2 on the developing roller installed in the color developing device.
A component-based developer or a single-component developer is held, and color toner in this developer is supplied to the electrostatic latent images of each color in a development area that faces the photoreceptor to perform a development operation. ! ! The visible toner images of each color obtained by the images are superimposed on each other and transferred to the recording paper side, thereby obtaining a full-color image.

As a color image forming method in such a color image forming apparatus, (1) a method of forming a color image for each color on a plurality of installed photoreceptors (for example, a four-drum photoreceptor) (Japanese Patent Application Laid-Open No. 1983-1999-1);
38966).

(2) A method in which a recording sheet is conveyed and transferred multiple times in correspondence with each color image formed at different positions on one photoreceptor (Japanese Patent Application Laid-Open No. 78157/1983).

(1) A method in which a photoreceptor equipped with a mosaic filter is uniformly exposed to light, and the electrostatic latent images of each color are sequentially recalled and developed (Japanese Patent Application Laid-Open No. 58-82270, Japanese Patent Publication No. 59-1989)
-34:910 public relations etc.).

(2) A method in which a multi-layered photoconductor with different spectral sensitivities is charged and exposed once to form a multi-stage potential distribution, and developed with toner of a different color for each potential (Japanese Patent Laid-Open Publication No. 12451/1983).

A method of forming an electrostatic latent image corresponding to each color on each photoconductive layer of a composite photoreceptor formed by laminating 0.5 photoconductive layers (Japanese Patent Application Laid-Open No. 1983-59
-121356, JP-A-62-23417, etc.).

0. A method of performing charging, exposure, and development three times during one rotation of one photoreceptor (Japanese Unexamined Patent Application Publication No. 127755/1983), and a method of performing color images for each color by four rotations of one photoreceptor. After forming a
686 Public Relations).

Many methods have been proposed so far.

However, such conventional color image forming methods (
or equipment) has the following defects:

That is, the method (2) above results in a more complicated structure and higher cost, as well as slowing down the copying speed.

In method (2) above, image exposure is performed at different positions on one photoreceptor, so color shift occurs during image transfer, and a complete full-color image cannot be obtained.

In method (2) above, each color toner is developed in a mosaic pattern, so that the color density of one image becomes low.

Although it is possible to obtain a multicolor image using the method (2) above, it has not been possible to stably obtain a good full-color image.

With method (■) above, it is theoretically possible to form a full-color image with a simple structure and only one image-forming process, but in practice it is difficult to create a photoreceptor using this full-color image-forming method. This has become difficult, and many issues remain in terms of its practical application.

In method (2) above, positional deviations between colors are likely to occur during exposure, resulting in a decrease in the resolution of one image, resulting in discoloration due to color deviations and unnecessary patterns.

(Problem to be Solved by the Invention) By the way, in order to solve the above-mentioned problems of the conventional method, a composite layer in which three photoconductive layers having spectral sensitivities to light of different wavelengths are laminated is proposed. Electrostatic latent images of red, green, and blue, or black, red, and blue are formed on a photoreceptor, and the electrostatic latent images corresponding to these images are developed using toner of each color to create three-color images. A color image forming method was proposed to obtain an image (JP-A-61-15662 Publication, JP-A-63-5).
4185 Public Relations).

However, this conventional color image forming method is only capable of forming images in three colors of red, green, and blue, or black, red, and blue, and has not been able to obtain a complete full-color image.

Therefore, based on this most practical method, after uniformly charging a composite photoreceptor in which three photoconductive layers having spectral sensitivities to light of different wavelengths are laminated to a predetermined potential, Image information for each color of cyan, magenta, and yellow is exposed and written to form an electrostatic latent image corresponding to each color image, and the electrostatic latent image corresponding to each color image is developed with each color toner to create a full-color image. A full-power, color imaging method designed to obtain 200 nm was previously proposed.

However, in this full-color image forming method, a black image in the black and white area of the original image is reproduced by overlaying toner of each color cyan, magenta, and yellow on the same achromatic pixel. There was a problem in that the black image in the black area of this original image was not completely pure black and was developed into a colored image.

Such defects pose a major problem in obtaining high-quality images when reproducing original images in which the color area consisting of a full-color image and the black-and-white area consisting of an achromatic image are clearly separated. .

The present invention has been made in view of the above points, and its first object is to separately develop a full-color image in the color area and a pure black tone image in the black-and-white area of a document image. Therefore, it is an object of the present invention to provide a full-color image forming method that can faithfully reproduce a document image.

Incidentally, as described above, in a document image, a color area consisting of a full-color image and a black-and-white area consisting of an achromatic image are not necessarily clearly separated, and may be only a full-color image.

Color areas and black and white areas may be mixed.

For such original images, as described above.

It becomes difficult to develop the full-color image in the color area of the original image and the pure black tone image in the monochrome area separately, and the black image in the color area of the original image is not completely pure black but has only one color. There is a problem with the developed image.

The second object of the present invention was made in view of this point, and it is an object of the present invention to connect only pixels that require pure black tone reproduction to each of the three colors without separating the color area and black and white area. It is an object of the present invention to provide a full-color image forming method capable of faithfully reproducing an original image by adding black toner to toner and developing it.

(Means for solving problems) The present invention is intended to achieve the first object.

After uniformly charging a composite photoreceptor in which three photoconductive layers having spectral sensitivities to light of different wavelengths are laminated to a predetermined potential, image information for each color is written by exposure, and an image of each color is created. In a full-color image forming method in which a full-color image is obtained by forming electrostatic latent images corresponding to the respective color images and developing the electrostatic latent images corresponding to the respective color images with respective color toners, each layer of the composite photoreceptor is Positive/negative/positive or.

After being charged negatively, positively, and negatively, color image information consisting of each color of cyan, magenta, and yellow is placed in the color area, and black and white image information is placed in the black and white area on each of the wavelengths mentioned above, and the above composite photosensitive material is applied. The body is simultaneously exposed to light to form an electrostatic latent image such that the black image potential of the color area is smaller in terms of range value than the white image potential of the black and white area. Applying a developing bias higher than the black image potential, develop the above black and white area with black toner, then uniformly expose only the above black and white area to erase the electrostatic latent image in this black and white area, and then apply each of the above The method is characterized in that the electrostatic latent images of each color formed on the photoconductive layer are developed by sequentially overlapping them with toner of a color corresponding to the electrostatic latent image of each color.

Further, in order to achieve the second object, the present invention provides a composite photoreceptor in which three photoconductive layers having spectral sensitivities to light of different wavelengths are laminated, uniformly at a predetermined potential. After charging, image information for each color is exposed and written to form an electrostatic latent image corresponding to each color image, and these electrostatic latent images corresponding to each color image are developed with each color toner to form a full color image. In a method for forming a full color image.

After each layer of the composite photoreceptor is charged positive/negative/positive or negative/positive/negative, pixels that should be reproduced in pure black tone including black toner are not exposed, and are charged with cyan, magenta, and yellow. Only the other pixels that are reproduced in color with the three-color toner are exposed by adding image information of the three colors of cyan, magenta, and yellow and bias light for potential erasing of the pure black tone pixel valve to the light of each wavelength, Only the electrostatic latent image of the pixel to be reproduced in pure black tone is formed into an electrostatic latent image with a higher potential than other pixels, and first, the electrostatic latent image of the other pixels to be reproduced in color is Only the pure black tone pixels are selectively developed with black toner while applying a bias voltage that does not cause development, and then the electrostatic latent images of each color formed on each of the photoconductive layers are
It is characterized in that the electrostatic latent images of these colors are sequentially overlaid and developed using toners of colors corresponding to the electrostatic latent images.

(Function) According to the configuration described in claim 1 of the present invention, the electrostatic latent image in the black and white area and the electrostatic latent image consisting of each color of cyan, magenta, and yellow in the color area are formed by repeated image exposure. At the same time, among these four electrostatic latent images, an image in a color area and an image in a monochrome area are separated and sequentially developed separately with toner for each color.

Further, according to the configuration according to claim 2 of the present invention, the color area and the monochrome area are not separated.

Only pixels that require pure black tone reproduction are developed by adding black toner to each of the three toner colors.

(Example) EMBODIMENT OF THE INVENTION Below, one embodiment of the present invention will be described in detail based on the drawings.

However, the structure and structure within the range that can be clearly recalled from the following description.
The above-mentioned and other objectives and novel features of the present invention will be omitted from illustration and disclosure, omitted or simplified in order to avoid cluttering the description.

First, a full-color copying machine as an example of an apparatus for carrying out the present invention as set forth in claim 1 will be described with reference to FIG.

In FIG. 4, around the photoreceptor drum 1, along the rotation direction (clockwise direction in the figure), there is a charger 2 that performs initial charging of the photoreceptor drum 1, and a charger 2 that charges the photoreceptor drum 1 with electrostatic charge for each color. Digital exposure system (not shown) that forms a latent image
), a cyan developing device 4 for developing an electrostatic latent image corresponding to cyan, and a static elimination lamp 5 for removing an electrostatic latent image corresponding to cyan. Magenta developing device that develops an electrostatic latent image for magenta 6. The static elimination lamp 7 removes the electrostatic latent image corresponding to magenta, and the yellow developing device develops the electrostatic latent image corresponding to yellow! 8. A pre-transfer charger 9 that adjusts the charging state of each color toner attached to the photoreceptor drum 1 side by development, a transfer charger 11 that transfers a visible toner image onto recording paper, and a toner toner that remains on the photoreceptor drum 1 after transfer. a cleaning device 12 that removes the toner contained in the document; a black developer 13 that develops an electrostatic latent image corresponding to the achromatic image (image in the black and white area) of the document; and a black and white developer that removes the electrostatic latent image in the black and white area. Area erasing LEDs 14 and the like are arranged respectively.

As shown in FIGS. 1 and 2, the photoreceptor drum 1 includes:
Different wavelengths λ1. λ2. It has three photoconductive layers with sensitivity in each layer of λ, and the electrode la as a base body.
An L layer, a 1M layer, and a U layer are laminated on top in this order from the inside.

Here, the L layer is selenium (S) deposited on the electrode la.
e) layer, and has photosensitivity to blue light (wavelength λ).

Further, the M layer is made of microcrystal dispersed OPC overcoated on the five layers, and has photosensitivity to red light (wavelength λ).

Furthermore, the U layer is made of a functionally separated OPC formed by overcoating CTL and CGL on five layers by a spray method, and has photosensitivity to near-infrared light (wavelength λ2).

At this time, it is set in advance so that the light with the wavelength λ passes through the 1M layer and the U layer, and the light with the wavelength λ passes through the U layer.

The upper layer is set to be used with positive charge, the 1M layer is used with negative charge, and the U layer is set to be used with positive charge, and the capacitance of each layer is set to be equal to each other. ing.

The charger 2 shown in FIG. 4 includes a primary charger 2a equipped with a lamp that uniformly exposes light of wavelength λ3 and light of wavelength λ2, and a secondary charger 2a equipped with a lamp that uniformly exposes light of wavelength λ. Vessel 2
b, and a tertiary charger 2c which is not equipped with an exposure lamp.

On the other hand, the static elimination lamp 5 that removes the electrostatic latent image corresponding to cyan is constituted by a lamp that uniformly exposes light of wavelength λ.

In addition, a static elimination lamp 7 that removes the electrostatic latent image corresponding to magenta
is composed of a lamp that uniformly exposes light of wavelength λ2.

Further, the black and white area erasing LED 14 for removing the electrostatic latent image in the black and white area is configured by arranging a plurality of LEDs (light emitting elements) along the rotation axis direction of the photosensitive drum 1.

In addition, the exposure system (not shown) is λ1. λ2. λ, no 3
It is configured to simultaneously emit laser beams of different wavelengths, and by the exposure action thereof, three electrostatic latent images of cyan, magenta, and yellow are simultaneously written on the photoreceptor drum.

At this time, the light having a wavelength λ is set to 442 nm↓, and is configured to be emitted from a He-Cd laser.

In addition, the light with wavelength λ2 is set to 680 nm,
It is configured to emit light from a semiconductor laser.

Further, the light having a wavelength λ is set to 780 nm, and is configured to be emitted from a semiconductor laser.

Next, an image forming process in an embodiment of the present invention using the apparatus configured as described above will be described.

In the present invention, at the initial setting stage, it is determined whether the image forming process of the document is to be performed, color image processing or monochrome image processing.

In this initial setting stage, each pixel of the color document is first converted into an output signal of red (R), green (G), and blue (B) by a color scanner (not shown), and then these signals are By comparing the output signals with each other, it is determined whether each pixel of the color original is an achromatic color or a chromatic color.

Here, if the respective levels of the output signals are substantially the same, it is determined that the color is achromatic, and if the levels are different from each other, it is determined that the color is chromatic.

If most of the pixels (for example, about 90% or more of the pixels) in one unit of the black and white area (minimum unit of uniform exposure of LED 14 "1 x 1 m", or 2 x 2 x 2) are achromatic, black and white The settings are made to perform image processing, and vice versa, to perform color image processing.

At this time, the maximum tJ of uniform exposure (erase) of the LED 14
The percentage unit may be finer, but if the minimum erase unit is made finer, the configuration and control system will become complicated, leading to an increase in cost.

Also, in manuscripts for boat fishing, the black and white area consisting of a single character, etc., and the color area consisting of a design or photograph, etc. are often separated into two parts within the page, so it may be difficult to Between these two areas, there is usually a white background with a width of several millimeters.

Therefore, the minimum unit for erasing the LED 14 may be the above-mentioned erase unit without any inconvenience.

After the above-mentioned judgment is made, first, as shown in FIG. 1(a), the photoreceptor drum is exposed with a positive corona while being uniformly exposed to light of wavelength λ3 and light of wavelength λ2 by negative charger 2a. 1 primary charging is performed.

As a result, only the L layer of the photoreceptor drum 1 has a +1500
The surface potential of the photosensitive drum 1 becomes
It is charged to +1500V (see point a in Figure 3).

Next, as shown in FIG. 1(b), the photoreceptor drum 1 is secondary charged with a negative corona while being uniformly exposed to light of wavelength λ1 by the secondary charger 2b.

The charge density of the negative corona during this secondary charging is set higher than the charge density of the positive corona during the -order charging, and as a result, the M layer of the photoreceptor drum 1 is negatively charged, and the photoreceptor drum The surface potential of 1 is charged to -3500V (see the point in Figure 3).

Thereafter, tertiary charging is further performed in the dark using the positive corona of the tertiary charger 2C.

The charge density of the positive corona at this time is set higher than the charge density of the positive corona during negative charging, so that the U layer of the photoreceptor drum 1 is positively charged, and the surface potential of the photoreceptor drum 1 is increased. is charged to +1000V (third
(See point C in the figure).

As a result, the L layer of the photoreceptor drum 1 is charged to +500V, and the M layer is charged to +500V.
000V, and the U layer is charged (charged) to +1500V.

At this time, the surface potential of the photoreceptor drum 1 is charged to +500V.

Here, the +500V of the L layer is for forming a yellow electrostatic latent image, and the +500V of the 1,000V of the M layer is for forming a yellow electrostatic latent image.
is for magenta electrostatic latent image formation.

The remaining 500V is for forming a yellow electrostatic latent image.

This negative yellow electrostatic latent image of the M layer is different from the positive yellow electrostatic latent image of the L layer.
It is the same as that used for forming electrostatic latent images, and has the role of not allowing it to surface until the end of the process.

Similarly, +500V among the +1500V of the U layer is for forming a cyan electrostatic latent image, and the other +500V is for forming a positive magenta electrostatic latent image to neutralize the negative magenta electrostatic latent image of the M layer.

Furthermore, the remaining +500V of this U layer is for forming a black and white electrostatic latent image.

That is, in this embodiment, a black and white electrostatic latent image is newly formed using the extra +500V formed on this U layer.

When the photosensitive drum 1 is charged in this state, λ□
, λ2. Light images corresponding to three colors, cyan, magenta, and yellow, and light corresponding to a black and white area are simultaneously exposed by laser light having three wavelengths of λ.

At this time, in black and white areas, the black parts are not exposed.

The white part is exposed so that the L and M layers are exposed to oV and the U layer is exposed to +500V.

On the other hand, in the color area, the light with wavelength λ1 carries yellow image information, the light with wavelength λ2 carries yellow image information and magenta image information, and the light with wavelength λ carries yellow image information and magenta image information. Magenta image information and cyan image information are listed.

At this time, only the light with wavelength λ is transmitted by the extra +500
1/2 to erase the charge on V.

The output is added and exposed.

The light with wavelength λ2 is exposed at the output of I6, and the light with wavelength λ1 is exposed at 1/2 power. Exposure is performed with the output of
The layer is crab. Attenuates the light by 1000V and reduces the output to 1/2. Optical attenuation of 500V is performed at 500V.

The relationship between the reproduced color at this time and the way each laser is emitted is explained in the fifth section.
Shown in the table of figures.

As shown in Figure 3, the charge distribution after exposure is +100OV for black in the monochrome area, and +100OV for white in the black and white area.
The surface potential becomes 500V, and the color area becomes black (
Black) Cyan, Green
Pixels corresponding to each color of een) and Blue are +
As the surface potential becomes 5oov (point d in Figure 3), the color changes to magenta and yellow.
Pixels corresponding to each color, red and white, have a surface potential of OV (see point d' in Figure 3).
.

First, as shown in FIG. 2(a), +
A developing bias of 500 V is applied, and the black and white electrostatic latent image in the black and white area is developed with black toner.

Then, as shown in FIG. 2(b).

Only the LED 14 corresponding to the black and white area is turned on, and the black and white electrostatic latent image is selectively erased.

At this time, the electrostatic latent image in the area developed with black toner is generally difficult to erase with light.

This is fully possible by increasing the energy of the LED 14 to about 200 uw/a#.

Thereafter, as in the conventional method, first, as shown in FIG. 2(C), development is performed using negatively charged cyan toner, and black (B lac k),
Cyan toner is attached to pixels corresponding to each color of cyan, green, and blue as indicated by diagonal circles.

In addition, the pixels corresponding to white in FIG.

Since the charge is erased by lighting the LED 14, toner is not attached.

Next, after uniform exposure with light of wavelength λ (780 nm) is performed, development with magenta toner is performed.

At this time, since 90% or more of the light with wavelength λ3 passes through the cyan toner already attached, only the positively charged portion of the U layer is selectively attenuated, as shown in FIG. 2(d). This results in a charge distribution.

As a result, the positive magenta electrostatic latent image in the U layer disappears, and the negative magenta electrostatic latent image appears in the M layer. ), the surface potential of each color pixel becomes 1500V (see point e' in Figure 3), and the other colors cyan, green, yellow (
The pixels corresponding to each color (yellow) and white have a surface potential of ov (see point e in FIG. 3).

In this state, development is performed using positively charged magenta toner, resulting in black and magenta (Mag4!nta).

Magenta toner is applied to pixels corresponding to each color, red (Red) and blue (Blue), as indicated by black circles in FIG. 2(b).

Furthermore, as shown in FIG. 2(e), the wavelength λ3
After uniform exposure with light (680 nm), development with yellow toner is performed.

Here, this light with wavelength λ2 easily passes through the magenta toner that has already been attached, so that only the negatively charged portions of the M layer are selectively attenuated, resulting in the light as shown in FIG. 2(e). This results in a charge distribution.

That is, here, the positive yellow electrostatic latent image in the 1M layer disappears and the negative yellow electrostatic latent image appears in the L layer, thereby creating black, yellow (
Yellow), Red and Green (G
The pixels corresponding to each color (reen) are set to a surface potential of +5oov (see point f in FIG. 3), and the pixels corresponding to the other colors magenta and blue are set to a surface potential of +5oov (see point f in FIG. 3).

Iir* corresponding to each color, cyan (Cyan) and white (White), is set to the surface potential of ov (see point f in FIG. 3).

In this state, development is performed using negatively charged yellow toner, and as shown by the white circles in FIG.
), Red (Red) and Green
) yellow toner is attached to pixels corresponding to each color.

As a result, a black toner visible image and a full color toner visible image are formed on the photoreceptor drum 1.

Note that during such development, development with magenta toner and development with yellow toner are preferably performed by so-called non-contact development.

The full-color toner visible image formed on the photoreceptor drum 1 is transferred to the recording paper side by the transfer charger 11, but before that, the toner polarity adjustment is performed by the pre-transfer charger 9. It will be done.

That is, after development, the black toner, cyan toner, and yellow toner are negatively charged, and the mazeta toner is positively charged, so the pre-transfer charger 9 unifies the polarity of the toner to the negative side. It looks like this.

The transfer action by this transfer charger 11 is as follows.

This is the same as normal corona transfer, and the transferred image transferred by this transfer charger 11 is fixed onto the recording paper by heat fixing.

The full-color image obtained in this way is a high-density image with no misalignment at all. In particular, since the image in the black-and-white area is reproduced only with black toner, the image in the black-and-white area will not be colored. Furthermore, since there is no positional shift in the black image obtained by overlapping all of the cyan, magenta, and yellow toners in the color area, good reproducibility is possible.

Next, a second embodiment of the present invention as set forth in claim 2 will be described.

In this second embodiment, a full color copying machine as shown in FIG. 9 is used.

That is, in FIG. 9, around the photoreceptor drum 21, a charger 22. A digital exposure system (not shown) that forms an electrostatic latent image for each color on the photoreceptor drum 21 (the exposure optical path is indicated by 23), and a cyan developing device 24 that develops the electrostatic latent image corresponding to cyan.
, a static elimination lamp 25 for removing an electrostatic latent image corresponding to cyan, and a magenta developing device 26 for developing an electrostatic latent image corresponding to magenta. Static elimination lamp 2 that removes electrostatic latent images for magenta
7. A yellow developing device 28 that develops an electrostatic latent image corresponding to yellow, a pre-transfer charger 29 that adjusts the charging state of each color toner attached to the photosensitive drum 21 side by development. A transfer charger 31 that transfers the toner visible image onto the recording paper, and a cleaning device that removes the toner remaining on the photoreceptor drum 21 after the transfer! 32, and
A black developer 33, etc., which develops an electrostatic latent image corresponding to an achromatic image (image in a black and white area) of a document, etc. are arranged.

As shown in FIGS. 6 and 7, the photosensitive drum 21 has different wavelengths λ8. λ2. It has three photoconductive layers with sensitivity in each layer of λ.

An L layer and an M layer are formed from the inside on the electrode 1a as a base.

U layers are laminated in order.

Here, the L layer is selenium (Se) deposited on the electrode 1a.
) layer, and has photosensitivity to blue light (wavelength λ□).

The 1M layer is made of microcrystalline dispersed PC overcoated on the L layer, and has photosensitivity to red light (wavelength λ2).

Furthermore, the U layer is composed of a functionally separated type ○PC formed by overcoating CTL and CGL on the L layer using a single method, and has photosensitivity to near-infrared light (wavelength λ3). ing.

At this time, it is set in advance so that the light with the wavelength λ□ passes through the M layer and the U layer, and the light with the wavelength λ2 passes through the U layer.

The upper layer is set to be used with positive charge, the M layer is used with negative charge, and the U layer is used with positive charge, and the capacitance of each layer is set to be equal to each other. has been done.

The charger 22 shown in FIG. 9 includes a primary charger 22a equipped with a lamp that uniformly exposes light of wavelength λ3 and light of wavelength λ2, and a secondary charger 22a equipped with a lamp that uniformly exposes light of wavelength λ. 22b, and a tertiary charger 22c that does not include an exposure lamp.
It is made up of.

On the other hand, a static elimination lamp 25 that removes an electrostatic latent image corresponding to cyan
consists of a lamp that uniformly exposes light of wavelength λ.

In addition, a static elimination lamp 2 that removes electrostatic latent images for magenta
7 is composed of a lamp that uniformly exposes light of wavelength λ3.

Furthermore, the exposure system (not shown) is configured to simultaneously emit laser beams with three different wavelengths: λ□, λ2゜λ, and the exposure effect caused by this exposure causes three electrostatic charges of cyan, magenta, and yellow. The latent images are written on the photosensitive drum 21 at the same time.

At this time, the wavelength λ light is set to 442 nm, and is configured to be emitted from a He-Cd laser.

In addition, the light with wavelength λ2 is set to 680 nm,
It is configured to be emitted from a semiconductor laser.

Further, the light having a wavelength λ is set to 780 nm, and is configured to be emitted from a semiconductor laser.

Next, an image forming process in an embodiment of the present invention using the apparatus configured as described above will be described.

In this embodiment, at the initial setting stage, it is determined whether the image processing of the document should be performed using either color image processing or monochrome image processing.

In this initial setting stage, each pixel of the color document is first converted into an output signal of each color (red (R), green (G), blue CB) by a color scanner (not shown).
Next, by comparing these output signals with each other, it is determined whether each pixel of the color original is one of the five achromatic colors or the chromatic colors.

Here, if the respective levels of the output signals are substantially the same, it is determined that the color is achromatic, and if the levels are different from each other, it is determined that the color is chromatic.

In particular, here, if each level of each output signal matches the level of 1 reflected light amount zero, that pixel consists of black characters printed with black ink, and should be reproduced in pure black tone using black toner. It is determined that

Also, if there is a slight difference in the level of each output signal near zero amount of reflected light, that pixel is composed of a black part in a picture or photograph formed with cyan, magenta, and yellow ink, and .

It is determined that black with a subtle hue should be reproduced using toners of three colors, magenta and yellow.

After such a determination is made, first, as shown in FIG. 6(a), the photoreceptor drum is uniformly exposed to light of wavelength λ and light of wavelength λ2 by the -water charger 22a with a positive corona. 21 primary charging is performed.

As a result, only the L layer of the photoreceptor drum 21 is exposed.

The surface potential of the photosensitive drum 21 is charged to +1500V (see point a in FIG. 8).

Then, as shown in FIG. 6(b).

While being uniformly exposed to light of wavelength λ1 by the secondary charger 22b, the photoreceptor drum 21 is secondary charged with a negative corona.

The charge density of the negative corona during this secondary charging is set higher than the charge density of the positive corona during the negative charging, and as a result, the M layer of the photoreceptor drum 21 is negatively charged, and the photoreceptor drum The surface potential of 21 is charged to -3500V (see the point in Figure 8).

Thereafter, tertiary charging is further performed in the dark by the positive corona of the tertiary charger 22c.

The charge density of the positive corona at this time is set higher than the charge density of the positive corona at the time of negative charging, so that the U layer of the photoreceptor drum 21 is positively charged, and the surface of the photoreceptor drum 21 is The potential is charged to +1000V (
(See point C in Figure 8).

As a result, in the photosensitive drum 21, the L layer is charged (charged) to +500V, the M layer is charged (charged) to 11000V, and the U layer is charged (charged) to +1500V.

At this time, the surface potential of the photoreceptor drum 21 is +5oov
It is designed to be electrically charged.

Here, the +500V of the L layer is for forming a yellow electrostatic latent image, and the +500V of the M layer is for forming a yellow electrostatic latent image.
is for magenta electrostatic latent image formation.

The remaining 500V is for forming a yellow electrostatic latent image.

This negative yellow electrostatic latent image of the M layer is the same as that for forming the positive yellow electrostatic latent image of the L layer, and has the role of not allowing it to surface until the end of the process.

Similarly, +500V among the +1500V of the U layer is for forming a cyan electrostatic latent image, and the other +500V is for forming a positive magenta electrostatic latent image to neutralize the negative magenta electrostatic latent image of the M layer.

Furthermore, the remaining +500V of this U layer is for forming electrostatic latent images in pure black areas of monochrome images and black areas of color images.

That is, in this embodiment, a pure black electrostatic latent image is newly formed using the extra +500 cm formed on this U layer.

When the photosensitive drum 21 is charged to such a state, λ
8. λ2. Light images corresponding to three colors, cyan, magenta, and yellow, are simultaneously exposed by laser light having three different wavelengths of λ.

At this time, the pure black part of one image is not exposed, and the other parts are exposed so that the L layer and M layer are exposed to Ov and the U layer is exposed to 1500V.

Here, yellow image information is carried on the light of wavelength λ1, yellow image information and magenta image information are carried on the light of wavelength λ2, and furthermore, the light of wavelength λ,
The light carries magenta image information and cyan image information.

At this time, only the light with wavelength λ is transmitted by the extra +500
To erase the charge on V, +1/21. The output is added and exposed.

And light with wavelength λ2 is optical. Exposure is performed with an output of Exposure is performed with the output of
The U layer is crab. At the same time as performing optical attenuation of 1000V by

/2, optical attenuation of 500V is performed.

The relationship between the reproduced color and the output of each laser at this time is
It is shown in the table in Figure 0.

The charge distribution after exposure is as shown at point g in Figure 8, with pure black pixels at +1000V, and other pixels corresponding to black, cyan, green, and blue. The pixels corresponding to each color (Blue) have a surface potential of +500V (point d in Figure 8), and the pixels corresponding to each color of magenta (Magenta) and Izo -(Y
e l low) Red (Red) and White (
The pixels corresponding to each color (White) have a surface potential of Ov (
(See point d' in Figure 8).

First, as shown in FIG. 7(a), +
A development bias of 500V is applied to develop the pure black electrostatic latent image with black toner.

At this time, the potential of the pure black electrostatic latent image is slightly lowered as shown in FIG. 8g.

Here, if the potential difference between the pure black electrostatic latent image and the black electrostatic latent image is too large, the proportion of cyan toner adhering to the pure black electrostatic latent image will increase and the gray balance of the image will be disrupted. The smaller the potential difference, the better.

Hereinafter, similarly to the conventional method, first, as shown in FIG. 7(b), development is performed using negatively charged cyan toner, and black (B1. ), green, and blue, cyan toner is attached as indicated by diagonal circles.

Next, after uniform exposure with light of wavelength λ (780 nm) is performed, development with magenta toner is performed.

At this time, since the light having wavelength λ of 90% or more passes through the cyan toner already attached, only the positively charged portion of the U layer is selectively attenuated, as shown in FIG. 7(C). The charge distribution will be as follows.

As a result, the positive magenta electrostatic latent image in the U layer disappears, and the negative magenta electrostatic latent image appears in the M layer.
The pixels corresponding to each color (blue) have a surface potential of 1500V (see point e'' in Figure 8), and the other color cyan (
Cyan), Green, Yellow
The pixels corresponding to each color (low) and white have a surface potential of Ov (see point e in FIG. 8).

In this state, development is performed using positively charged magenta toner, and the pixels corresponding to each color of black, magenta, red, and blue are colored as shown in FIG. 7(c).
Magenta toner is attached as shown in the black circle inside.

Furthermore, as shown in FIG. 7(d), the wavelength λ2
After uniform exposure with light (680 nm), development with yellow toner is performed.

Here, since this light of wavelength λ2 easily passes through the already attached magenta toner, only the negatively charged portions of the M layer are selectively attenuated, resulting in the light as shown in FIG. 7(d). This results in a charge distribution.

That is, here, the positive yellow electrostatic latent image in the M layer disappears and the negative yellow electrostatic latent image appears in the L layer, thereby creating black, yellow (
Yellow), Red and Green (G
reen).

The pixels corresponding to each color are made to have a surface potential of +500V (see point f in Fig.
enta), Blue, Cyan
The corresponding pixels for each color are 0■
(See point f in Figure 8).

In this state, development is performed using negatively charged yellow toner, and as shown by the white circles in FIG. 7(d), black and yellow are produced.
ow), Red and Green
) yellow toner is attached to pixels corresponding to each color.

As a result, a black toner visible image and a full color toner visible image are formed on the photoreceptor drum 1.

Note that during such development, development with magenta toner and development with yellow toner are preferably performed by so-called non-contact development.

The full-color toner visible image formed on the photoreceptor drum 1 is transferred to the recording paper side by the transfer charger 11, but before that, the toner polarity adjustment is performed by the pre-transfer charger 9. It will be done.

That is, after development, the black toner, cyan toner, and yellow toner are negatively charged, and the mazeta toner is positively charged, so the pre-transfer charger 9 unifies the polarity of the toner to the negative side. It looks like this.

The transfer action by this transfer charger 11 is the same as normal corona transfer, and the transferred image transferred by this transfer charger 11 is fixed on the recording paper by thermal fixation.

The full-color image obtained in this way is a high-density image without any positional deviation, and in particular, the pure black electrostatic latent image is
The black electrostatic latent image is obtained by overlapping all of the black, cyan, magenta, and yellow toners, and the black electrostatic latent image is obtained by overlapping all of the cyan, magenta, and yellow toners, so it is possible to reproduce a good image without coloring. It becomes possible.

(Effects of the Invention) As described above, according to the invention described in claim 1, a full-color image in a color area of a document image and a pure black tone image in a black-and-white area can be developed separately. Therefore, the black and white image portion of the original image can be faithfully reproduced in pure black tone.

Further, according to the invention described in claim 2, the color area and the monochrome area are not separated.

Only the pixels that require reproduction of pure black tone can be developed by adding black toner to each of the three toner colors, so that the original image can be faithfully reproduced in pure black tone without color.

[Brief explanation of drawings]

FIGS. 1(a), (b), and (c) are schematic side views of a photoreceptor for explaining the charging process in the first embodiment of the present invention, and FIGS. 2(a), (b), and ( c). (d) and (e) are schematic side views of a photoconductor for explaining the developing process in the first embodiment of the present invention, and FIG. 3 is a surface potential variation of the photoconductor in the first embodiment of the present invention. 4 is a schematic side view of a full-color copying machine as a first embodiment of an image forming apparatus for carrying out the present invention,
Figure 5 is a table showing the relationship between reproduced colors and the output of each laser in the first embodiment of the present invention, and Figure 6 (,) (b
) and (c) are schematic side views of the photoreceptor for explaining the charging process in the second embodiment of the present invention, and FIGS. 7(a) and (b)
), (c), and (d) are schematic side views of a photoconductor for explaining the developing process in the second embodiment of the present invention, and FIG. 8 is a surface of the photoconductor in the second embodiment of the present invention. FIG. 9 is a schematic side view of a full-color copying machine as a second embodiment of an image forming apparatus for carrying out the present invention. FIG. 10 is a table showing the relationship between reproduced colors and outputs of each laser in the second embodiment of the present invention. 1.21... Photosensitive drum, 2, 22... Charger, 2
a, 22a...-Jiko Denki, 2b. 22b...Secondary charger, 2c, 22c...Tertiary charger, 4.24...Cyan developing device, 5°25.7,2
7... Static elimination lamp, 6.26... Macenter developing device, 8, 28... Ix o-Q image device, 9, 29...
・Pre-transfer charger, 11゜31...Transfer charger, 12.32...Cleaning device, 13.33
...Black developer, 14...LED for black and white area erasure. -2-4 Deputy Director Kabayama Torugokan (and 1 other person) Kozu (1) ()

Claims (1)

[Claims] 1. Having spectral sensitivity to light of different wavelengths 3.
After uniformly charging the composite photoconductor on which photoconductive layers are laminated to a predetermined potential, image information for each color is written by exposure to form an electrostatic latent image corresponding to each color image. In a full-color image forming method in which an electrostatic latent image corresponding to each color image is developed with each color toner to obtain a full-color image, each layer of the composite photoreceptor is , the composite photoreceptor is simultaneously exposed with color image information consisting of cyan, magenta, and yellow colors in the color area and black and white image information in the black and white area on each of the wavelength lights, and An electrostatic latent image is formed so that the black image potential of the color area is smaller in absolute value than the white image potential of the area, and a developing bias higher than the black image potential of the color area is first applied. Then, the electrostatic latent image in the black and white area is developed with black toner, and then only the black and white area is uniformly exposed to erase the electrostatic latent image in the black and white area. A full-color image forming method, which comprises sequentially overlapping and developing electrostatic latent images of each color with toners of colors corresponding to the electrostatic latent images of each color. 2. Has spectral sensitivity to light of different wavelengths 3.
After uniformly charging the composite photoconductor on which photoconductive layers are laminated to a predetermined potential, image information for each color is written by exposure to form an electrostatic latent image corresponding to each color image. In a full-color image forming method in which an electrostatic latent image corresponding to each color image is developed with each color toner to obtain a full-color image, each layer of the composite photoreceptor is After being charged to , the pixels that should be reproduced in pure black tone, including black toner, are not exposed, and only the other pixels that are to be reproduced in color with cyan, magenta, and yellow toners are exposed to the above cyan, magenta, and yellow. The three-color image information and potential erasing bias light for pure black tone pixels are added to each of the above wavelength lights for exposure, and only the electrostatic latent image of the pixel to be reproduced in pure black tone is set higher than that of other pixels. At the same time as forming an electrostatic latent image with a high potential, first, apply a bias voltage that does not develop the electrostatic latent image of the other pixels that will be reproduced in color, and apply black toner only to the pure black pixel. selectively developed, and then the electrostatic latent images of each color formed on each of the photoconductive layers are
A full-color image forming method characterized by sequentially overlapping development with toners of colors corresponding to these electrostatic latent images.