JP2002116594A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of reducing the number of developing means and image exposing means, preventing the occurrence of image roughness at a highlight part (low density part) and improving gradation reproduction at a dynamic range in a high density part. SOLUTION: In this image forming device, black toner consists only of thick toner, and the low density part of an achromatic color is formed at least by magenta and cyan thin toner, and the high density part of the achromatic color is formed by the black toner.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming an image using toner by electrophotography,
The present invention relates to an image forming apparatus that develops using two types of toner, a light color toner and a dark color toner, to form an image.

[0002]

2. Description of the Related Art In an image forming apparatus using an electrophotographic method, an image forming body is uniformly charged by a charging means and then exposed to an image to form a latent image. The latent image portion is developed by the subsequent developing means to form a toner image. In a digital image forming apparatus, image exposure is performed by, for example, dots that have been subjected to pulse width modulation, and reversal development in which toner adheres to the dot portions is performed. The amount of toner adhering to the dot portion is determined by the area and potential state of the dot portion on the image forming body, the developing bias for the dot portion, the state of the charge of the toner, and the like.

A high-density image portion recorded on an image forming body by an image exposure means has a large number of dots per area,
The size of the dots is also large. On the other hand, the low-density image portion has a small number of dots per area and a small size of one dot. Thus, after development, the amount of toner adhered to the high density image portion on the image forming body is large, and the amount of toner adhered to the low density image portion is small. The difference in the density of the recorded image is expressed by the amount of toner adhering to the area of the image formed on the image forming body by development.

[0004]

However, it is difficult to form an image with good gradation with one type of toner. Highlight part (low density part)
In this case, since the dots are small, the adhesion of a very small amount of toner per area is unstable, and image unevenness (image roughness) is likely to occur, and it is difficult to obtain stable gradation. Further, in the high-density portion, the toner is in an excessively adhered state, and the image density is likely to be saturated, and there is a problem that the gradation is not good in a wide area (dynamic range).

For this reason, an image forming apparatus which develops using two kinds of toners of yellow (Y), magenta (M), cyan (C), and black (K), respectively, is disclosed in Japanese Patent Application No. 2002-110,197. Although proposed in Japanese Patent Publication No. 2000-137089, there are problems that the number of developing means and image exposing means increases, and the size of the apparatus becomes large and the printing time becomes long.

The present invention solves the above problems, reduces the number of developing means and image exposing means, prevents the occurrence of image roughness in a highlight portion (low density portion), and reduces the number of developing portions and image exposure portions in a high density portion. It is an object of the present invention to provide an image forming apparatus which improves the reproduction of the gradation in the dynamic range.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus in which an image forming body is charged, image exposed, and developed with dark and light color toners, and sequentially transferred and superimposed. This is achieved by an image forming apparatus comprising only a dark toner, wherein an achromatic low-density portion is formed by at least magenta and cyan light toners, and an achromatic high-density portion is formed by the black toner. Is done.

[0008]

Embodiments of the present invention will be described below. Note that the description in this column does not limit the technical scope of the claims and the meaning of terms. Also, the following assertive description in the embodiment of the present invention indicates the best mode, and does not limit the meaning of the terms of the present invention or the technical scope.

An image forming process and each mechanism of an embodiment of the image forming apparatus according to the present invention will be described with reference to FIGS. FIG. 1 is a sectional view of a color image forming apparatus showing an embodiment of the image forming apparatus according to the present invention, FIG. 2 is a block diagram of an image processing system, and FIG. FIG. 4 is a graph showing a relationship with image density, FIG. 4 is a diagram showing redistributed achromatic image data, and FIG.
FIG. 6 is a diagram illustrating a CR process, FIG. 6 is a diagram illustrating image data for dark and light toners of each of the separated colors, and FIG. 7 is a diagram illustrating a state of toner adhesion to recording paper.

According to FIG. 1, the color image forming apparatus shown in FIG. 1 is a tandem type color image forming apparatus using an intermediate transfer member, and a transfer image is formed on a peripheral portion of a transfer belt 14a as an intermediate transfer member. From the upstream side in the rotation direction of the belt 14a,
Four sets of process units 100 including black (K), cyan (C), magenta (M), and yellow (Y) are provided. In the black (K) process unit 100, toner using only dark toner is used. An image is formed, and the other cyan (C), magenta (M), and yellow (Y) process units 100 use the dark and light toners C,
M and Y toner images are formed, the toner images are transferred in a superimposed manner on the transfer belt 14a, and the transferred color toner images are collectively transferred onto recording paper as a transfer material, fixed and discharged outside the apparatus. It is configured to be.

First, the three process units 100 of cyan (C), magenta (M) and yellow (Y) all have a common structure, and only one of them will be described. The photoreceptor drum 10 as an image forming body includes a light-transmitting conductive layer and an organic photosensitive layer (OPC) on the outer periphery of a cylindrical base formed of a light-transmitting member such as glass or light-transmitting acrylic resin. Is formed.

The photosensitive drum 10 is rotated in the counterclockwise direction indicated by an arrow with the light-transmitting conductive layer grounded by power from a driving source (not shown) or by the transfer belt 14a.

Scorotron charger 11 as charging means
The photoconductor drum 10 is attached to the photoconductor drum 10 in a direction orthogonal to the moving direction of the photoconductor drum 10 so as to be opposed to and close to the photoconductor drum 10.
To give a uniform potential.

An exposure optical system 12 (H) as an image exposure means for dark toner and an exposure optical system 12 (L) as an image exposure means for light toner each have an LED (light emission) as a light emitting element for image exposure. A linear exposure element (not shown) in which a plurality of diodes are arranged in an array in parallel with the axis of the photosensitive drum 10.
Selfoc lens (not shown)
Are configured as an exposure unit attached to the holder. An exposure optical system 12 (H) is provided on a cylindrical holding member,
12 (L) is attached and housed inside the base body of the photosensitive drum 10. In addition, as the exposure element, a linear element in which a plurality of light emitting elements such as FL (phosphor emission), EL (electroluminescence), and PL (plasma discharge) are arranged in an array is used. The exposure optical system 12 (H) is an image exposure unit that performs image exposure using image data for dark toner, and the exposure optical system 12 (L) is an image exposure unit that performs image exposure using image data for light toner.

The exposure optical system 12 (H) for the dark toner sets the exposure position on the photosensitive drum 10 to the scorotron charger 1.
Developing device 13 (H) for dark toner containing 1 and dark toner
Between the photosensitive drum 10 and the developing device 13 (H).
Is disposed inside the photoreceptor drum 10 in a state provided on the upstream side in the rotation direction. Exposure optical system 12 (L) for light toner
The exposure position on the photosensitive drum 10 is on the downstream side of the developing unit 13 (H) for the dark toner, and the developing unit 13 (H) and the developing unit 13 (L ), The developing unit 13 (L) is disposed inside the photosensitive drum 10 in a state provided on the upstream side in the rotation direction of the photosensitive drum 10 with respect to the developing unit 13 (L).

Developing device 13 as developing means for dark toner
(H) contains a one-component dark toner or a two-component developer of a dark toner and a magnetic carrier, and performs reversal development by contact or non-contact. The developing device 13 (L), which is a developing means for the light toner, incorporates a one-component light toner or a two-component developer of a light toner and a magnetic carrier that enables superposition development without destroying the toner image. Then, reversal development is performed by soft development or more preferably non-contact development.

In forming an image, the image data of each color of C, M and Y is divided into image data for dark toner and image data for light toner, respectively, as will be described in detail later. Is exposed by the exposure optical system 12 (H), and the developing roller 131 (H) of the developing unit 13 (H) performs development with the dark toner. Image exposure of image data for light toner is performed by the exposure optical system 12 (L), and development with the light toner is performed by the developing roller 131 (L) of the developing device 13 (L). A toner image of light toner is formed on the photosensitive drum 10 so as to be superposed thereon. The dark and light toner images are transferred at a transfer position onto a transfer belt 14a described later.

Since the blackest (K) process unit 100 located at the uppermost stream does not affect the color, the formation of the light toner image is omitted, and the scorotron charger 11 and the exposure optical system 12 (H) are omitted. Forming a toner image of only the dark toner using the developing device 13 (H)
The transfer is performed on the transfer belt 14a at the transfer position.

The untransferred toner remaining on each of the photosensitive drums 10 after the transfer is cleaned by a cleaning device 19 that electrostatically collects the remaining toner.

Process units for four colors of K, C, M and Y
The transfer belt 14a to which the rollers 100 face in parallel is a volume resistor.
Resistance rate is 10^Ten-10^FifteenΩ · cm, surface resistivity is 10^Ten~
10 ^FifteenΩ / □ endless belt, for example, modified polyimid
, Thermosetting polyimide, ethylene tetrafluoroethylene
Copolymer, polyvinylidene fluoride, nylon alloy, etc.
Disperse conductive materials in engineering plastics
Of a semiconductive film substrate having a thickness of 0.1 to 1.0 mm.
On the outside, preferably as a toner filming prevention layer
2 layer structure with fluorine coating of 5 to 50 μm
It is a seamless belt. Base of transfer belt 14a
Other than these, silicone rubber or urethane rubber
0.5-2.0mm thick semiconductive material with conductive material dispersed
An electrically conductive rubber belt can also be used. Transfer belt 1
4a is a driving roller 14d, a driven roller 14e,
External roller 14k and backup roller 14j
During image formation, a drive motor (not shown)
The drive roller 14d is rotated by the drive of
At the transfer position of the photosensitive drum 1 by the primary transfer device 14c.
0, the transfer belt 14a is pressed.
It is rotated in the direction indicated by the arrow in the figure.

A primary transfer device 14c composed of a transfer roller as a transfer means for each color is provided to face the photosensitive drum 10 for each color with the transfer belt 14a interposed therebetween, and the transfer belt 14a and the photosensitive member for each color are provided. A transfer area (no reference numeral) for each color is formed between the transfer area and the drum 10. Primary transfer unit 14 for each color
By applying a DC voltage of the opposite polarity (positive polarity in the present embodiment) to c, and forming a transfer electric field in the transfer area, the dark and light toner images on the photosensitive drum 10 for each color are transferred. The image is transferred onto the belt 14a.

The static eliminator 14m, which is a static eliminator for each color,
Preferably, the primary transfer unit 1 is constituted by a corona discharger.
The transfer belt 14a charged by 4c is neutralized.

The process unit 1 of black (K) is started by starting a photoconductor drive motor (not shown) by starting image recording.
The photoconductor drum 10 is rotated in the direction indicated by the arrow in the figure, and at the same time, the application of a potential to the K photoconductor drum 10 is started by the charging action of the K scorotron charger 11.

After the potential is applied to the K photosensitive drum 10, image writing by an electric signal corresponding to the image data for the K dark toner is started by the exposure optical system 12 (H) for the K dark toner. Then, an electrostatic latent image for dark toner corresponding to the K image of the document image is formed on the surface of the K photoconductor drum 10.

The latent image for dark toner is subjected to reversal development in a contact state by a developing device 13 (H) for dark toner of K, and a toner image of dark toner of K is formed in accordance with the rotation of the photosensitive drum 10 of K. It is formed.

The K toner image composed of the dark toner formed on the K photoreceptor drum 10 serving as an image forming member is used in a K transfer area (no reference numeral), and the first transfer means K 1
The image is transferred onto the transfer belt 14a by the next transfer device 14c.

Next, synchronization with the K toner image on the transfer belt 14a is established, and the cyan (C) process unit 1
00 is rotated in the direction indicated by the arrow in the figure, and at the same time, the application of a potential to the C photoconductor drum 10 is started by the charging action of the C scorotron charger 11.

After a potential is applied to the photosensitive drum 10 of C, an image is formed by an electric signal corresponding to image density data of image data of the dark toner of C by the exposure optical system 12 (H) for dark toner of C. Writing is started, and an electrostatic latent image for dark toner corresponding to the image C of the original image is formed on the surface of the photosensitive drum 10 of C.

The latent image for the dark toner is subjected to reversal development in a contact state by a developing device 13 (H) for the dark toner of C, and the toner image by the dark toner of C is formed according to the rotation of the photosensitive drum 10 of C. It is formed. Subsequently, a light-toner electrostatic latent image corresponding to the C image data is formed by the light-toner exposure optical system 12 (L), and the light-toner developing unit 13 is formed.
By (L), the toner image of the C light toner is formed so as to overlap the previously formed toner image of the C dark toner.

The C toner image formed of the dark and light toners formed on the C photoreceptor drum 10 as the image forming body by the above-described image forming process in the C transfer area (no sign). The C primary transfer unit 14c, which is a transfer unit, superimposes and transfers the toner image on the transfer belt 14a on the toner image composed of the K dark toner.

By the same process, the image is synchronized with the K and C superposed toner images, and corresponds to the M image data formed on the M photosensitive drum 10 by the magenta (M) process unit 100. A toner image composed of M dark and light toners is transferred from the top of the K and C toner images by the M primary transfer unit 14c, which is the first transfer means, in the M transfer area (no symbol). Are formed on top of each other, and are synchronized with the superposed toner images of K, C, and M, and the yellow (Y) process unit 100 forms a yellow toner image on the Y photosensitive drum 10. The formed toner image composed of the Y dark and light toners corresponding to the Y image data is transferred by the Y primary transfer unit 14c as the first transfer unit in the Y transfer area (no sign). K, , From the top Y dark toner image M, the light toner image formed of the toner is formed by overlapping, K, C, color toner image overlay M and Y are formed on the transfer belt 14a.

The transfer residual toner remaining on the peripheral surface of the photosensitive drum 10 for each color after the transfer is cleaned by a cleaning device 19 which is a cleaning means of the image forming body for each color.

On the other hand, in synchronism with the formation of the superimposed color toner image on the transfer belt 14a, the recording paper P is transferred from the paper supply cassette 15 as the transfer material storage means via the timing roller 16 as the transfer material supply means to the second. Is transferred to a transfer area (no symbol) of a secondary transfer unit 14g, which is a transfer unit, and a DC voltage having a polarity opposite to that of the toner is applied to the secondary transfer unit 14g.
Thereby, the superimposed color toner images on the transfer belt 14a are collectively transferred onto the recording paper P.

The recording paper P on which the color toner image has been transferred is
The charge is removed by a charge removing electrode 16b, which is a separating means composed of a saw-toothed electrode plate. After the toner image on the paper P is fixed, it is discharged to a tray outside the apparatus.

The transfer residual toner remaining on the peripheral surface of the transfer belt 14a after the transfer is cleaned by a cleaning device 19a which is a transfer belt cleaning means provided opposite to the driven roller 14e with the transfer belt 14a interposed therebetween. .

As described above, it is possible to provide a small-sized image forming apparatus in which color reproduction can be easily performed by widening the reproduction area by using dark and light toners.

In the above-described image forming process, development with light toner may be omitted for yellow (Y) having low visibility, and an image may be formed. Also,
Although a color image forming apparatus has been described as an example of the image forming apparatus, the present invention is not necessarily limited to this. The present invention is also applicable to a monochrome image forming apparatus using the same process as described with reference to FIG. Things.

According to FIG. 2, an original image is read by image reading means using a solid-state image pickup device such as a CCD (F1). The amplified analog image signal output from the CCD is converted to an 8- to 10-bit digital signal by A / D conversion.
After the conversion, image processing (1) such as shading correction and luminance conversion and subsequent color space conversion and density conversion are performed (F2). The image data may be read from the stored memory and subjected to the same processing.

The image data obtained in the image processing (1) is
By checking the density distribution of data and the density difference between adjacent dots, it is possible to determine whether the original image is a halftone image such as a photograph or a picture or a character image such as a character or a line drawing, and to determine color components. , The black component is determined (F31). Next, UCR processing level determination for determining the degree of UCR is performed from these (F32).

The image data obtained in the image processing (1) is
After image data of Y, M, C, and K is created (not shown) by image processing such as masking, a UCR processing level based on a determination result as to whether the image is a halftone image or a character image. UCR processing is performed based on the determination (F32) (F4). As the UCR processing (F4), the image data obtained in the image processing (1) (F2) is
It is output as% Y, M, C and K image data (F41). On the other hand, the difference of K and the redistribution to Y, M, and C are performed by the UCR process level determination (F32) (F42A). For example, in the case of UCR 100%, the image data of K UCR 100% is output as the difference of K.
Also, for example, the UC is determined by the UCR processing level determination (F32).
In the case of R40%, K image data of 40% UCR is output as a difference of K, and the remaining 60% of K is Y, M, C
For example, 100% UCR (F41) image data of Y and 60% of Y image data redistributed are added (F42B) and output (Similarly, for M and C, The 100% UCR (F41) M and C image data and the redistributed 60% image data are added and output). By the image data output by the addition processing (F42B) and the image determination (F31),
Image data decomposition of C, M and Y is performed (F51, F5
2, F53), and image data (F6) for dark toner, respectively.
1A, F62A, F63A) and image data (F61B, F62B, F63B) for light toner.

The K image data and the separated image data for dark and light toners of C, M and Y are subjected to γ correction, MTF correction and PWM modulation for each toner based on the image discrimination (F31). Is performed (F7), a printer output is performed (F8). In the PWM modulation, it is preferable to form large dots and increase the recording unit so as to improve dot reproduction in a highlight portion (low density portion). For example, with respect to the image data for dark toner, one pixel PWM is used because emphasis is placed on the resolution. On the other hand, for the light toner image data, two pixels PW
This is performed at M to increase the recording unit. Note that intensity modulation may be used instead of PWM modulation.

It is preferable that these correction values are sequentially changed according to the result of the image discrimination. That is, in the half tone, the form in which the γ correction is performed is used, the MTF correction is weakened, and the PWM recording unit is increased. On the other hand, for character images, it is preferable to make changes such as setting the γ correction higher, increasing the MTF correction, and reducing the PWM recording unit.

For an image forming apparatus using a dark toner and a light toner, in order to obtain a sufficient effect according to the present invention, the toner adhesion amount and the print image shown in FIG. It is desirable to have a relationship of concentration. The difference in density between the dark and light toners is caused by a difference in the amount of pigment contained in the toner particles. Further, the amount of toner adhered at the time of saturation depends on the toner particle size. For example, for dark toner, the amount of toner adhering to white paper is 1 mg /
The recording density becomes saturated at about cm ² . It is necessary that the saturated concentration value _Dmax (H) in the saturated state be 1.7 to 2.5. As shown in FIG. 3, the density value at the point of substantially saturation is defined as D _max (H). To be exact, the concentration gradually increases as shown by the broken line.

On the other hand, the density of the light toner does not reach a saturated state when the amount of toner attached to white paper is 1 mg / cm ² , for example. When the light toner has the same toner adhesion amount as the dark toner reaching the saturation density value, that is, when the density of the dark toner is saturated, the recording density D (L) of the light toner is D (L) = 0. It must be between 0.3 and 0.8. Before the toner adhesion amount to the white paper reaches the saturation density value, for example, the ratio to the recording density D _S (L) when using a light toner with the toner adhesion amount of 0.5 mg / cm ² , that is, the light toner DOO slope ratio of recording density of the dark toner _{D S (L) / D S} (H) = 0.2~0.
It must be between 5 and 5.

The recording density needs to have the above relationship between the dark toner and the light toner, but the toner particle size and the charge amount may be the same for the dark and light toners. preferable. For toner particle size,
Because both dark and light toners ensure image quality and developability,
It is preferable that the volume average particle size is between 3 and 10 μm, and even if there is a difference, it is ± 20% or less. The charge amount is between 5 and 30 μC / g for both the dark and light toners. In particular, when the toner particle size is small, a high charge amount is required. Preferably, there is. By satisfying these conditions,
A similar γ characteristic can be obtained between the dark and light toners, and the design can be made so that the sum of the adhesion amounts of the dark toner and the light toner in the middle to high density areas is substantially the same and the change in the recording density changes linearly. It will be easier.

Note that the gradation characteristics shown in FIG. 3 also change depending on the toner particle size and the contained coloring material. In the case of a toner having a small particle diameter, the toner may saturate even with a smaller amount of adhesion of 0.5 mg / cm ² , but is important in designing a toner having a high saturation density and a low slope ratio.

According to FIG. 4 or FIG. 5, FIG. 4 shows the relationship between the redistributed achromatic image data and the image data generated by 100% UCR. The achromatic image data redistributed by (F32 in FIG. 2) is composed of black (K) dark toner (UCR component) and black components to be redistributed to Y, M, and C, as shown in FIG. The low-concentration part is shown in FIG.
As shown in (A), halftone images such as photographs and prints are reproduced by superimposing a small amount of Y, M, and C components. At this time, for yellow (Y) having low visibility, development with light toner may be omitted, and image formation may be performed. The medium-density portion allows the creation conditions of Y, M, C, and K image data to be changed in accordance with the image density, and as shown in FIG.
Halftone images such as photographs and prints are reproduced by using the M and C toners and a small amount of K toner. The high-concentration part is shown in FIG.
As shown in (C), a character image such as a business document is reproduced by using 100% UCR and mainly using a large amount of K toner.

FIG. 6 shows the relationship between the image data for the separated dark and light toners of each color and the Y, M, and C image data after the redistribution of the high density portion, the middle density portion, and the low density portion. I have.

A high density portion using only K, Y, M and C dark toners is used for business documents. Since the light toner is not used, the reproducibility of low density is not good, but the reproducibility of non-glossy and high density portions such as characters is good. The amount of toner used is the smallest compared with the amount of toner used in the medium density part and the low density part.

By changing the image data for changing the usage ratio of the light and dark toners, the reproduction of the middle density portion is improved by using the light and dark toners of Y, M and C and the dark toner of K. I have. By increasing the amount of the light toner used, uniformity of the halftone image can be realized.

The low density portions using only the Y, M, and C light toners are used for OHP and photographic images. In this case, since the dark toner is not used, the saturation density value is not high. However, since the light toner has high translucency, a clear image can be obtained by using only the light toner as the OHP developer. Further, since the photographic image has a low image density and is faint, an image in which the gradation is emphasized can be obtained.

By the image forming process and the image processing, as shown in FIG. 7, a high-density portion corresponding to a character image of a business document or the like is formed as a toner image mainly on a recording paper P by a dark toner at the time of fixing. Maintain the gradation in the area (dynamic range). A medium density portion corresponding to a halftone image such as a photograph or a print is fixed on the recording paper P at the time of fixing.
A highly transparent light toner is formed on the toner image formed by the dark toner, and the transparency of the dark toner image is maintained. Also, low-density areas corresponding to halftone images such as photographs and prints
The toner image is formed on the recording paper P as a toner image composed of only a light toner having high transparency, and a stable gradation is maintained particularly in a highlight portion (low density portion).

As described above, the reproduction of gradation in a dynamic range in a high density portion corresponding to a character image of a business document or the like can be improved, and a highlight portion (low density portion) corresponding to a halftone image such as a photograph or print can be obtained. 2), it is possible to provide an image forming apparatus that prevents the occurrence of image roughness.

As the image forming apparatus, it is also possible to use a tandem structure in which a dark toner or a light toner is formed on each image forming body by charging, exposing, and developing one by one and superposed sequentially. At this time, the image exposure means can use external exposure, internal exposure using a transparent substrate as an image forming body, or the like. Further, an image forming process unit including a charging unit, an exposing unit and a developing unit
A method in which a plurality of toners are arranged around one image forming body, and a dark toner or a light toner is superposed on the image forming body by charging, exposing, and developing, and then transferred and fixed collectively on a transfer material. It is also possible to use the image forming apparatus described above.

[0055]

According to the present invention, the number of developing means and image exposing means is reduced to reduce the size of the apparatus and the printing time, and to improve the image quality in the highlight area (low density area). It is possible to provide an image forming apparatus capable of preventing the occurrence of roughness and improving the reproduction of gradation in a dynamic range in a high density portion.

[Brief description of the drawings]

FIG. 1 is a cross-sectional configuration diagram of a color image forming apparatus showing an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a block diagram of an image processing system.

FIG. 3 is a graph showing a relationship between a toner adhesion amount and a print image density.

FIG. 4 is a diagram showing redistributed achromatic image data.

FIG. 5 is a diagram showing UCR processing at each density in FIG. 4;

FIG. 6 is a diagram illustrating image data for dark and light toners of each color separated.

FIG. 7 is a diagram illustrating a state where toner adheres to recording paper.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 photoconductor drum 11 scorotron charger 12 (H), 12 (L) exposure optical system 13 (H), 13 (L) developing device 14 a transfer belt 14 c primary transfer device 14 g secondary transfer device 15 paper cassette 16 timing Roller 16b Static electricity removing electrode 17 Fixing device 100 Process unit

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Yotaro Sato 2970 Ishikawacho, Hachioji-shi, Tokyo Konica Corporation F-term (reference) 2H027 EA04 EA20 EB04 EC19 FD08 2H028 BD04 2H030 AA03 AB02 AD01 AD11 AD16 BB02 BB21 BB42

Claims (2)

[Claims] 1. An image forming apparatus in which an image forming body is charged, image-exposed, and developed with dark and light color toners, and sequentially transferred and superimposed. Wherein the low density portion is formed by at least a light toner of magenta and cyan, and the high density portion of achromatic color is formed by the black toner. 2. A method according to claim 1, wherein the image density is yellow, magenta,
2. The image forming apparatus according to claim 1, wherein conditions for creating cyan and black image data are changed.