JP2002148893A - Color image forming device and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a color image forming device capable of easily forming a monochrome image concurrently with a color image excellent in gradation with thin and thick toner. SOLUTION: This image forming device is a tandem type color image forming device where the pairs of processing units 100Y to 100K for forming respective thin and thick toner images in yellow(Y), magenta(M), cyan(C) and black(K) are arranged in series on a transfer belt 14a. In the case of forming the color image, the respective thin and thick toner images formed by the respective processing units 100 are successively superposed on the belt 14a so as to form the color toner image, and in the case of forming the monochrome image, the carrying upstream side of the belt 14a is turned and retreated with a backup roller 30 as a fulcrum so as to form the image only by the processing unit 100K for black(K).

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,
In particular, the present invention relates to a color image forming apparatus and a color image forming method for forming an image by developing with two kinds of toners of the same color, a light color toner and a dark color toner.

[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. Particularly in a highlight portion (low-density portion), the attachment of a very small amount of toner per area is unstable due to the small size of the dot, so that image unevenness is likely to occur and it is difficult to obtain stable gradation. In the high-density portion, the toner is in an excessively toner-adhered state, and the image density is easily saturated.

The present invention is applied to a monochrome or color image forming apparatus, and includes two kinds of toners of the same color, a light color and a dark color (for example, cyan (C), magenta (M), yellow (Y), An image forming apparatus that performs development using any of black (K), and maintains the tone of color by arranging the image forming functions of a dark toner image and a light toner image of the same color adjacent to each other. A first object of the present invention is to provide a color image forming apparatus and a color image forming method capable of easily and efficiently forming a monochrome image at the same time as the formation of a sagging color is improved. A second object of the present invention is to provide a color image forming apparatus and a color image forming method which can form a color image by using either one of the dark and light toner images by being arranged adjacently.

[0006]

A first object of the present invention is to form a toner image by using different colored dark and light toners on a plurality of image forming members, and superimpose the toner images on an intermediate transfer member to form a color image. 2. A color image forming apparatus according to claim 1, wherein each of said toner images is formed by superimposing a dark toner image and a light toner image of the same color adjacent to each other. A color image forming apparatus that forms a color toner image by superimposing toner images of different colors of dark and light toners during one rotation of the image forming body and collectively transfers the color toner images; Is a color image forming apparatus (invention of claim 2) wherein a dark toner image and a light toner image of the same color are superimposed and formed adjacent to each other; Statue In a color image forming method for forming a color image by combining the color images, the respective toner images are formed by superimposing a dark toner image and a light toner image of the same color adjacent to each other. 3 invention).

A second object of the present invention is to form a color image by forming toner images of different colors of dark and light toners on a plurality of image forming members and superimposing the toner images on an intermediate transfer member to form a color toner image. In the image forming apparatus, each of the toner images is formed such that a dark toner image or a light toner image of a different color is superimposed on one another. In a color image forming apparatus that forms a color toner image by superimposing toner images of different colors of dark and light toners during one rotation, and collectively transfers the color toner images, each of the toner images is a different color dark toner image. Alternatively, a color image forming apparatus in which light toner images are formed adjacent to each other and overlapped with each other, and a toner image formed of dark and light toners of different colors on a transfer material. In a color image forming method for forming Align Te color images, each toner image color image forming method (claim 7, characterized in that the same color dark toner image or light toner image is formed by overlapping adjacent
Invention).

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention provides an image forming apparatus in which a reproducible area is widened by developing using light and dark toners, and excellent gradation is obtained and a good image is formed. A preferred embodiment of a color image forming apparatus according to each invention for forming a color image using light and dark toners will be described. (Embodiment 1) An embodiment of the invention according to claims 1 to 3 will be described with reference to FIGS.

The image forming apparatus shown in the cross-sectional view of FIG. 1 is a tandem type color image forming apparatus using an intermediate transfer member, and a yellow (Y), yellow (Y), Four process units 100 each including magenta (M), cyan (C), and black (K) are sequentially arranged in series from the upstream side in the belt conveyance direction.

Each of the above-mentioned process units 100 is a pair of photosensitive drums, each of which is a pair of image forming members, including a developing unit 13 (L) for storing light toner of each color and a developing unit 13 (H) for storing dark toner. 10, all of which have a common structure.

A photosensitive drum 10, which is an image forming body, has a light-transmitting conductive layer and an organic photosensitive layer formed on the outer periphery of a cylindrical base formed of a light-transmitting member such as glass or light-transmitting acrylic resin. (OPC) formed with a photoconductor layer.

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.

Numerals 11A and 11B denote scorotron chargers as charging means, which are mounted so as to be opposed to and close to the photosensitive drum 10 in a direction perpendicular to the moving direction of the photosensitive drum 10 and have the same polarity as the toner. A uniform potential is applied to the photosensitive drum 10 by the discharge.

The exposure optical systems 12 (L) and 12 (H)
Each is a linear exposure element (not shown) in which a plurality of LEDs (light emitting diodes) as light emitting elements for image exposure are arranged in an array in parallel with the axis of the photosensitive drum 10 and a selfoc as an equal-magnification imaging element. A lens (not shown) is configured as an exposure unit attached to a holder. Exposure optical systems 12 (L) and 12 (H) are attached to a cylindrical holding member and housed inside the base 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. Reference numeral 12 (L) denotes an image exposure unit that performs image exposure using image data for light toner, and 12 (H) denotes an image exposure unit that performs image exposure using image data for dark toner.

An exposure optical system 12 (L), which is an image exposure means for light toner, is provided with a scorotron charger 11A and a developing device 13 having light toner built therein.
Between (L) and the developing unit 13 (L), the photosensitive drum 10 is disposed inside the photosensitive drum 10 in a state provided on the upstream side in the rotation direction of the photosensitive drum 10. The exposure position of the exposure optical system 12 (H), which is an image exposure means for dark toner, on the photosensitive drum 10 is on the downstream side of the developing device 13 (H), and incorporates a scorotron charger 11 B and dark toner. Developing device 13
(H), the photosensitive drum 1 is provided on the upstream side in the rotation direction of the photosensitive drum 10 with respect to the developing device 13 (H).
0.

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

In forming an image, image data of each color of Y, M, C, and K is divided into image data for light toner and image data for dark toner, which will be described in detail later. Image exposure is performed by the optical system 12 (L), and the developing device 13 is placed on one of the photosensitive drums 10.
By (L), development with light toner is performed. The image data for the dark toner is subjected to image exposure by an exposure optical system 12 (H), and a developing device 13 is provided on the other light emitting drum 10.
By (H), the development with the dark toner is performed, and the toner image with the light toner and the toner image with the dark toner are individually formed on the respective photosensitive drums 10. This toner image is transferred onto a transfer belt 14a described later at a transfer position. Cleaning device 1 that electrostatically collects transfer residual toner remaining on the drum after transfer is completed.
9 performs cleaning.

Process unit 1 for four colors of Y, M, C and K
The transfer belt 14a in which 00 is opposed in parallel has a volume resistivity of 10 ¹⁰ to 10 ¹⁵ Ω · cm and a surface resistivity of 10 ¹⁰ to 10 ¹⁵ Ω.
Cm endless belt, for example, modified polyimide, thermosetting polyimide, ethylene tetrafluoroethylene copolymer, polyvinylidene fluoride, dispersed conductive material in engineering plastics such as nylon alloy, thickness 0.1 to 1.0 mm Outside the semiconductive film substrate of
Preferably, the toner filming preventing layer has a thickness of 5 to 5
This is a seamless belt having a two-layer structure and a fluorine coating of 0 μm. In addition, as the base of the transfer belt 14a, a semiconductive rubber belt having a thickness of 0.5 to 2.0 mm in which a conductive material is dispersed in silicon rubber or urethane rubber can be used. Transfer belt 14a
Are stretched in and out of contact with a driving roller 14d, a driven roller 14e, a tension roller 14k, and a backup roller 14j. During image formation, the driving roller 14d is rotated by a driving motor (not shown), and each color is rotated. At each transfer position, the photosensitive drum 1 is moved by the transfer roller 14c.
The transfer belt 14a is pressed to 0, and the transfer belt 14a is rotated in the direction indicated by the arrow in the figure.

A primary transfer device 14c, which is 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 having a polarity opposite to that of the toner (positive polarity in this embodiment) to c, and forming a transfer electric field in the transfer area, the toner image on the photosensitive drum 10 for each color is transferred onto the transfer belt 14a. Transfer to

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

When the image recording starts, the photosensitive drum driving motor (not shown) is started to rotate the photosensitive drum 10 of the yellow (Y) process unit 100 in the direction shown by the arrow in FIG. The application of a potential to the Y photoconductor drum 10 is started by the charging action.

After a potential is applied to the Y photosensitive drum 10, an electric signal corresponding to the first color signal, that is, image data for the Y light toner, is applied by an exposure optical system 12 (L) for the Y light toner. Is started, and an electrostatic latent image for light toner corresponding to the Y image of the original image is formed on the surface of the Y photosensitive drum 10.

The latent image for light toner is subjected to reversal development in a contact state by a developing device 13 (L) for light toner of Y, and the toner is formed by light toner of Y according to rotation of one photosensitive drum 10 of Y. An image is formed. Subsequently, charging by the scorotron charger 11B and the exposure optical system 1 for the Y dark toner
2 (H), an electrostatic latent image for dark toner corresponding to the image of Y is formed, and the developing device 13 (H) for dark toner forms a toner image with the dark toner of Y on the other photosensitive drum 10.
Formed on top.

The Y toner image formed of the light and dark toners formed on the pair of photosensitive drums 10 as the image forming bodies by the above-described image forming process is transferred to the K transfer area (no sign).
In step (1), the images are sequentially transferred onto the transfer belt 14a by the respective primary transfer units 14c as the first transfer unit.

Next, the transfer belt 14a is synchronized with the M toner image, and the magenta (M) process unit 1
In the M transfer area (no symbol), the respective primary transfer units 14c, which are the first transfer units, transfer the toner image composed of the M light and dark toners formed on the M photoconductor drum 10 by 00. A toner image composed of M light and dark toners is superimposed on the toner image composed of the Y light and dark toners.

In a similar process, the C and Y toner images are synchronized with the superposed toner images of Y and M, and are formed on the photosensitive drum 10 of C by the process unit 100 of cyan (C) by the third color signal. A toner image composed of light and dark toners of C corresponding to the image data of C is transferred by the respective primary transfer units 14c as the first transfer means in the transfer area of C (no symbol). A toner image composed of light and dark toners of C is superimposed on the toner image, and synchronized with the superimposed toner images of Y, M, and C, and the black (K) process unit 100 is used to form the black toner image. K based on the fourth color signal formed on the photosensitive drum 10
In the K transfer area (no sign), the respective primary transfer units 14c, which are the first transfer means, transfer the toner images composed of the K light and dark toners corresponding to the image data of Y, M, and A toner image composed of light and dark toners of K is superposed on the toner image of C to form a transfer belt 14.
A superimposed color toner image of Y, M, C and K is formed on a.

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.

In synchronization with the formation of the 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 transfer. The superimposed color toner image on the transfer belt 14a is recorded by the secondary transfer device 14g, which is conveyed to a transfer area (no symbol) of the secondary transfer device 14g, which is a unit, and to which a DC voltage having the opposite polarity to the toner is applied. It is transferred onto the paper P at once.

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 formed of a sawtooth electrode plate, conveyed to the fixing device 17, and heat and pressure are applied between the fixing roller 17a and the pressure roller 17b, so that the recording paper P After the toner image is fixed,
It is discharged to a tray outside the device.

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 across the transfer belt 14a. .

Further, a driven roller 30 is additionally provided on the inner peripheral surface of the transfer belt 14a between each of the process units 100 for cyan (C) and black (K), so that yellow (Y), magenta (M), and cyan ( C), the peripheral surface of the transfer belt 14a facing each process unit 100 is driven by a driven roller 14e.
The cleaning device 19a, the primary transfer devices 14c, and the static eliminator 14m have a structure that can be moved and retracted to a position indicated by a dashed line. The formation of a monochrome image by only the process unit 100) is efficiently performed.

In the present embodiment, Y, M,
Although the development using light and dark toners is performed for the four colors C, K, and C, the development is performed using only the dark toner for Y, M, and C, and the development using only the light and dark toners is performed only for K. Thus, the excellent effects of the present invention can be obtained. In this case, the developing device is an image forming apparatus provided with five sets.

Further, by omitting the image formed by the light toner of the specified color, for example, as shown in the sectional view of FIG.
Yellow (Y) and black (K) process units 100Y
And 100K may be process units for image formation using only dark toner. In this case, by appropriately setting the UCR in the image processing, a good image can be obtained for both a character image and a color image.

As shown in the sectional view of FIG. 2B, a developing unit 13 (T) for storing a transparent toner is provided on the upstream side of the process unit 100Y.
It is also free to provide the process units 100T and 100S each having the developing device 13 (S) for storing the white toner downstream of 0K. By providing a white toner layer between the recording paper and the toner image, the influence of the surface of the recording paper is removed, and by providing a transparent toner layer on the top surface of the toner image, a glossy high-quality image can be obtained. .

On the other hand, in the image forming apparatus shown in the sectional view of FIG. 3, the peripheral portion of the large-sized photosensitive drum 10 is provided with yellow (Y), magenta (M), cyan (C) and black (K).
Are sequentially arranged from the upstream side to the downstream side in the rotation direction of the drum to form a color toner image by superimposing the toner images of each color developed by each process unit 100 during one rotation of the drum. A color image forming apparatus of a type that transfers this onto a recording paper P via a transfer belt 14a, wherein each of the process units 100 includes a developing unit 13 (L) for storing light toner and a developing unit for storing dark toner. 13 (H).

Also in the case of this apparatus, as shown in FIG. 4A, the process units 10 for yellow (Y) and black (K) are used.
Each of 0Y and 100K can be a unit of an image forming unit using only dark toner, and FIG.
As shown in (1), process units 100T and 100S further provided with developing units 13 (T) and 13 (S) for accommodating transparent toner or white toner can be additionally provided. In this case, the image forming program is automatically changed together with the replacement of the process unit. (Embodiment 2) An embodiment of the invention according to claims 4 to 7 will be described with reference to FIGS.

The image forming apparatus shown in the sectional view of FIG. 5 is a tandem type color image forming apparatus using an intermediate transfer body similar to the above-described apparatus, and is a peripheral portion of a transfer belt 14a as an intermediate transfer body. Includes two process unit groups 100 each including yellow (Y), magenta (M), cyan (C), and black (K) process units 100.
(L) and 100 (H) are arranged in series before and after from the upstream side in the transport direction of the belt.

Each of the above process unit groups 100 (L)
And 100 (H) are developing units 13 (L) for storing light toners of respective colors or developing units 13 for storing dark toners.
(H) each comprising four sets of photoreceptor drums 10 serving as image forming members, all having a common structure, and all having the same structure and function as the process units of the apparatus shown above. It has been.

When the photosensitive drum drive motor (not shown) is started by the start of image recording, the transfer belt 14a moves in the direction of the arrow and the respective photosensitive drums 10 on the process unit group 100 (L) side move in the direction shown by the arrow in the figure. At the same time, application of a potential to the Y photoconductor drum 10 is started by the charging action of the Y scorotron charger 11A.

After a potential is applied to the Y photosensitive drum 10, an electric signal corresponding to the first color signal, that is, image data for the Y light toner, is applied by the Y light toner exposure optical system 12 (L). Is started, and an electrostatic latent image for light toner corresponding to the Y image of the original image is formed on the surface of the Y photosensitive drum 10.

The light toner latent image is subjected to reversal development in a contact state by the Y light toner developing unit 13 (L), and the Y toner is rotated by the Y photosensitive drum 10. A toner image is formed on the photosensitive drum 10. Subsequently, the electrostatic latent image for light toner corresponding to the image of M is formed by the exposure optical system 12 (L) for charging by the scorotron charger 11B and the light toner for M, and the developing device 13 (L) for light toner. ), A toner image of M light toner is formed on the photosensitive drum 10 located on the next downstream side.

The toner image composed of each light toner formed on each of the four photosensitive drums 10 of Y, M, C and K, which are image forming bodies, by the above-described image forming process is subjected to a first transfer in each transfer area. Primary transfer units 1 as means
By 4c, the toner image is sequentially superimposed and transferred onto the transfer belt 14a, and is formed as a color toner image including only a toner image using light toner.

Next, the transfer belt 14a is synchronized with the color toner image formed of the light toner image formed by the process unit group 100 (L), and Y, M, C by the process unit group 100 (H). A color toner image by each of the dark toners K and K is
The toner image is formed through the same process as in the case of the color toner image using the light toner of 0 (L), and is transferred while being superimposed on the color toner image of the light toner on the transfer belt 14a.

The transfer residual toner remaining on the peripheral surface of the photosensitive drum 10 of each process unit 100 after the transfer is cleaned by a cleaning device 19 which is a cleaning means of an image forming body for each color.

In synchronization with the formation of the color toner image on the transfer belt 14a, the recording paper P is transferred from the paper feed cassette 15 as a transfer material storage means to the second transfer means via a timing roller 16 as a transfer material transfer means. Is transferred to the transfer area (no symbol) of the secondary transfer device 14g, and a superimposed color toner image on the transfer belt 14a is recorded on the recording paper by the secondary transfer device 14g to which a DC voltage having a polarity opposite to that of the toner is applied. The image is transferred onto P at once.

The recording paper P on which the color toner image has been transferred is
An AC bias is applied by a neutralizing electrode 16b, which is a separating means composed of a saw-toothed electrode plate, to eliminate the charge, and the fixing device 17
After the toner image on the recording sheet P is fixed by applying heat and pressure between the fixing roller 17a and the pressure roller 17b, the sheet 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 cleaning means for the transfer belt 14a provided opposite to the driven roller 14e with the transfer belt 14a interposed therebetween. You.

Further, the transfer belt 14 between the process unit group 100 (H) and the process unit group 100 (L)
a driven roller 30 is additionally provided, and one peripheral surface of the transfer belt 14a facing the process unit group 100 (L) is driven by the driven roller 14e and the cleaning device 19a.
In addition, if each of the primary transfer devices 14c and the static eliminator 14m can be moved and retracted to a position indicated by a chain line,
The process unit group 100 (H) can form a color toner image of only the dark toner, and similarly, the transfer belt 14a facing the process unit group 100 (H).
Is configured to be able to move and retract together with the drive roller 14d, the tension roller 14k, and the respective primary transfer units 14c and the respective neutralizers 14m corresponding to the process unit group 100 (H).
It is also possible to form a color toner image of only light toner by 00 (L). A selection button for a gradation image, a dark color image, and a light color image is provided on the operation panel (not shown), and switching is performed by selection.

Further, the image formed by the light toner of the specified color is omitted and, for example, as shown in FIG.
The black and black (K) process units 100Y and 100K may be image forming units each using only dark toner, or as shown in FIG. 6B, a developing unit 13 (T) for further storing transparent toner or a white toner. Units 100T and 1 having a developing unit 13 (S) for storing
00S can be freely added.

On the other hand, the image forming apparatus shown in the sectional view of FIG. 7 uses yellow (Y), magenta (M), and cyan by the process units 100 arranged on the periphery of the large-sized photosensitive drum 10 during one rotation. (C) and black (K)
A color image forming apparatus of a type in which a color toner image is formed on a drum by superimposing respective toner images, wherein each of the process units 100 is a process unit group 100 (L) for forming a color toner image using light toner. And a process unit group 100 (H) for forming a color toner image using dark toner, and the process units 100 (L) and then the process units 100 (H) are arranged in this order from the upstream side in the rotation direction of the photosensitive drum 10. You.

Also in the case of this apparatus, as shown in FIG. 8A, the process unit group 100 (L) is constituted only by the process units 100M and 100C, and the toner image of the light toner is formed by magenta (M) and cyan ( It can also be formed only by C). In this case, by appropriately setting the UCR in the image processing, the same good gradation image as when all the dark and light toners are used can be obtained. Further, as shown in FIG. 8 (b), developing units 13 (T) and 13 which further contain transparent toner or white toner.
The process units 100T and 100S provided with (S) can be freely added.

The formation of the dark and light toner images in the embodiments described in the above embodiments is performed according to the block diagram of the image processing system shown in FIG.

An original image is read by image reading means using a solid-state image pickup device such as a CCD (F).
1). The output analog image signal from the CCD is 8
A / D conversion is performed to a digital signal of 10 to 10 bits, and shading correction and subsequent image processing (1) such as color space conversion, logarithmic conversion, black generation, and color correction are performed. 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 the 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. (F3).

The image data obtained in the image processing (1) is
The image data for light toner (F5A) and the image data for dark toner (F5B) are created based on the determination result of whether the image is a halftone image or a character image.
10A and 10B are explanatory diagrams showing a state in which image data is decomposed into light and dark toner image data. FIG. 10A is a halftone image, and FIG. 10B is a light and dark toner image for a character image. And shows a state in which the composition ratio of image data for light and dark toner is changed depending on whether the image data is a halftone image or a character image. That is, for halftone images, image data that uses more light toner is created, and for character images, image data that uses more dark toner is created.

The decomposed light and dark toner image data are subjected to γ correction for each toner (F6A, F6B),
MTF correction (F7A, F7B) and PWM modulation are performed (F
8A, F8B). In the PWM modulation, it is preferable to form large dots so as to improve dot reproduction in a highlight portion (low-density portion) and increase the recording unit. For example, the image data for light toner is subjected to two-pixel PWM in order to enhance the gradation, and the recording unit is increased. On the other hand, with respect to the image data for dark toner, since the emphasis is placed on the resolving power, this is performed with one pixel PWM.

The light toner image data after the PWM modulation is subjected to image exposure on the photosensitive drum 10 by the exposure optical system 12 (L) (F9A), and the dark toner image data after the PWM modulation is exposed to light. Image exposure on the photosensitive drum 10 is performed by the system 12 (H) (F9B).

It is preferable that these correction values are sequentially changed according to 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.

FIG. 11 is a graph showing the amount of toner adhered on the photosensitive drum 10 when the light toner and the dark toner of this embodiment are used. For the high-density portion, only the dark toner is used according to the image data for the dark toner, and the toner adhesion amount is reduced while the reproducibility is maintained. By increasing the size of the recording dots of the low-toner image data for low-density areas and using only light toner,
By maintaining a sufficient amount of toner adhesion, stable reproducibility is maintained. The light toner and the dark toner are used in combination with the image data for the low and dark toners in the middle between the high density portion and the low density portion, so that the gradation is maintained and the image unevenness is prevented.

FIG. 12 is an explanatory diagram showing the state of toner adhesion at the low to high density portions. According to the present invention, FIG.
As shown in (1), the difference in the amount of adhered toner between the high-density portion and the low-density portion is reduced, and transfer failure and fixing disturbance failure are eliminated.

The image forming apparatus using the light toner and the dark toner has been described above. In order to obtain a sufficient effect according to the present invention, for example, the image forming apparatus shown in FIG.
It is desirable that the relationship between the toner adhesion amount and the print image density shown in FIG. The density difference between the light and dark toners is caused by the difference in the amount of the 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, with respect to dark toner, the recording density becomes saturated when the amount of toner attached to white paper is about 1 mg / cm ² .
Saturated concentration value _Dmax (H) in a saturated state = 1.7 to 2.5
It is necessary to be. As shown in FIG. 13, 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, the recording density D of the light toner when the dark toner concentration is saturated.
It is necessary that (L) = between 0.2 and 0.8.
The recording density D _S (L) and the dark toner when the light toner is used when the toner adhesion amount to the white paper reaches the saturation density value, for example, when the toner adhesion amount is 0.5 mg / cm ² . Of the recording density D _S (H), that is, the inclination ratio D _S (L) / D of the recording density between the light toner and the dark toner.
_S (H) must be between 0.15 and 0.4.

The recording density needs to have the above relationship between the dark toner and the light toner, but the toner particle diameter and the charge amount may be the same for the light and dark toners. preferable. For toner particle size,
Because both light and dark 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 .mu.C / g for both the light and dark 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 light and dark toners, and the design can be made so that the sum of the adhesion amounts of the light toner and the dark toner in the middle to high density areas is almost the same and the change in the recording density is linear. It will be easier.

Note that the gradation characteristics shown in FIG. 13 also change depending on the toner particle size and the contained coloring material. In the case of a small particle size toner, the toner may be saturated even with a smaller amount of adhesion of 0.5 mg / cm ² , but the saturation density and the slope ratio are important in designing a light toner and a dark toner.

The light and dark toners have been described above. The image forming apparatus which uses a light and dark toner to extend the reproduction area, is small, and can easily perform color superposition has been described with reference to FIGS.

Next, a process of forming a T, S toner layer using a white (S) toner layer as a base of a color toner image and a transparent (T) toner formed thereon will be described.

In forming the T and S toner layers, T, S
An area where the S toner layer is formed is designated, and a white (S) toner layer is provided as a lower layer in the designated area, and a transparent (T) toner layer is provided as an upper layer.

Prior to image formation, by pressing a T, S toner layer area setting button on an operation panel (not shown),
The mode is the S toner area designation mode. To specify the area,
14 (a), the operator formulates the T and S toner layer formation ranges on the document D, and for example, formulates the ranges (X1Y1, X2Y2,
X3Y3, X4Y4) is designated by using the light pen LP, so that the designated T and S toner layer formation ranges indicated by oblique lines are temporarily stored in the RAM in the T and S image formation range setting circuit.

By pressing the copy button, the image formation is started in the manner already described, and called up from the RAM on each photosensitive drum 10 of the process units 100T and 100S (X1Y1, X2Y2, X3Y3, X4Y
Exposure is performed for the toner layer formation range of 4). The exposed latent image portion is subjected to reversal development by the developing device 13 (S) and the subsequent developing device 13 (T), transferred, and transferred onto the recording paper P (X1Y1, X2Y2, X3Y3, X4
A toner layer is formed in the range of Y4).

Here, T, S in the T, S toner layer forming range
The S toner layer is executed by a program provided in advance. That is, as shown in the enlarged cross-sectional view of FIG.
Exposure conditions set in advance in the exposure optical systems 12 (T) and (S) are such that the white toner layer and the transparent toner layer in the T and S toner layer formation ranges have the same thickness in the respective amounts. Image exposure of uniform intensity is performed. The latent image formed in this manner is applied to the developing device 1 under a predetermined developing condition.
The developing biases of 3 (S) and 13 (T) are set, and a white toner layer developed by the developing unit 13 (S) and a transparent toner layer developed by the developing unit 13 (T) are formed thereon. The thicknesses of the white toner layer and the transparent toner layer formed on the recording paper are preferably between 3 and 20 μm.

By providing a color toner layer on the T and S toner layers, light is reflected on a matt white toner surface,
The light transmitted through the color image thereon is observed in addition to the directly reflected light on the surface of the color image, and a high-quality image with a clear hue is obtained.

[0072] Here, preferred glossiness of the transparent toner and the white toner, the gloss G _T of the transparent toner is 25 ° to 60
, The gloss G _S of the white toner is 5 ° to 15 °, and the difference in gloss between the two is preferably 20 ° to 45 °.

By maintaining the above-described gloss relationship between the transparent toner and the white toner, a good image with a high gradation can be obtained in which the color becomes more transparent and a deep color image can be obtained. .

[0074]

The color image forming apparatus of the present invention has the effect of increasing the color reproduction area and improving the gradation of color images formed using light and dark toners. Accordingly, an image forming apparatus and an image forming method capable of forming a monochrome image in addition to a color image by using a light toner and a dark toner are realized. An image forming apparatus and an image forming method capable of forming a low-density or high-density color image with one of the toners have been realized.

[Brief description of the drawings]

FIG. 1 is a sectional configuration diagram of a tandem type color image forming apparatus.

FIG. 2 is a partial view showing an example of an arrangement of process units in a tandem format.

FIG. 3 is a cross-sectional configuration diagram of a drum-type color image forming apparatus.

FIG. 4 is a partial view showing an example of the arrangement of process units in a drum format.

FIG. 5 is a sectional configuration diagram of a tandem type color image forming apparatus.

FIG. 6 is a partial view showing an example of the arrangement of process units in a tandem format.

FIG. 7 is a cross-sectional configuration diagram of a drum-type color image forming apparatus.

FIG. 8 is a partial view showing an example of the arrangement of process units in a drum format.

FIG. 9 is a block diagram of an image processing system.

FIG. 10 is an explanatory diagram showing a state in which image data is decomposed.

FIG. 11 is a graph showing the amount of adhered toner.

FIG. 12 is an explanatory diagram showing the state of toner adhesion.

FIG. 13 is a graph showing a relationship between a toner adhesion amount and a print image density.

FIG. 14 is an explanatory diagram showing a unit for designating a formation area of each of transparent and white toners and a sectional layer of each formed toner.

DESCRIPTION OF SYMBOLS 10 Photoconductor drum 11 Scorotron charger 12 Exposure optical system 13 Developing device 14a Transfer belt 14c Primary transfer device (transfer roller) 14d Driving roller 14e Driven roller 14g Secondary transfer roller 14m Static eliminator 15 Paper cassette Reference Signs List 16 timing roller 17 fixing device 19, 19a cleaning device 30 driven roller 100 process unit 100 (L), 100 (H) process unit group

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04N 1/29 B41J 3/00 B (72) Inventor Yotaro Sato 2970 Ishikawacho, Hachioji-shi, Tokyo Konica Corporation F term (for reference) 2C262 AA04 AA24 AA26 BB03 BB16 DA07 GA40 GA42 2H027 DB01 DE07 EA18 EB01 EB02 EB04 EC00 EF09 FA28 FA35 FD01 FD08 ZA07 2H030 AA03 AB02 AD01 AD07 AD12 BB02 BB23 BB23 BB24 BB24 BB24 BB24 BB24 BB24 BB24 BB41 GA17 5C074 AA05 AA11 BB02 BB26 CC26 DD24 DD28 FF15 GG09 GG13

Claims (7)

[Claims] 1. A color image forming apparatus which forms toner images of different colors of dark and light toners on a plurality of image forming bodies and superimposes each of the toner images on an intermediate transfer body to form a color toner image. A color image forming apparatus wherein each toner image is formed by superimposing a dark toner image and a light toner image of the same color adjacent to each other. 2. A color image forming apparatus for forming a color toner image by superimposing toner images of different colors of dark and light toners during one rotation of an image forming body, and transferring the color toner images collectively. A color image forming apparatus wherein each toner image is formed by superimposing a dark toner image and a light toner image of the same color adjacent to each other. 3. A color image forming method for forming a color image by superimposing toner images of different colors of dark and light toners on a transfer material, wherein each of the toner images comprises a dark toner image and a light toner image of the same color adjacent to each other. A color image forming method, wherein the color image is formed by superimposing. 4. A color image forming apparatus which forms toner images of different colors of dark and light toners on a plurality of image forming bodies, and superimposes each of the toner images on an intermediate transfer body to form a color toner image. A color image forming apparatus, wherein each toner image is formed by superimposing a dark toner image or a light toner image of different colors adjacent to each other. 5. A color image forming apparatus for forming a color toner image by superimposing toner images of different colors of dark and light toners during one rotation of an image forming body, and transferring the color toner images collectively. A color image forming apparatus, wherein each toner image is formed by superimposing a dark toner image or a light toner image of different colors adjacent to each other. 6. The color image forming apparatus according to claim 4, wherein the different color dark toner image or light toner image is selectively formed. 7. A color image forming apparatus method for forming a color image by superposing toner images of different colors of dark and light toners on a transfer material, wherein each of the toner images is adjacent to a dark toner image or a light toner image of the same color. A color image forming method characterized by being formed by superimposing.