JPH06175461A - Color image forming device - Google Patents

Abstract

PURPOSE:To provide a satisfactory color image having no image defect caused by inferior image-transfer. CONSTITUTION:A color image forming device comprises a latent image carrier 1 for carrying thereon a latent image, a multi-color image forming means 2 for forming latent images having different color components on the image carrier, a multi-color developing means 3 for toner-developing the latent images having different color components and formed on the latent image carrier 1, on either an image-transfer medium 5 or the latent image carrier 1, successively for different color components, a transfer means 4 for contacting and rolling the image-transfer medium 5 on the image carrier 1 so as to transfer the latent image having different color components or the developed images having different color components on the latent image carrier 1, onto the image-transfer medium 5, a fixing means 6 for successively fixing the developed images having different color components on the image-transfer medium 1, and an auxiliary developing means 7 for developing non-image areas in the images having different color components with the use of achromatic and transparent toner during developing for different color components by the multi-color developing means 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus such as a color copying machine or a color printer, and more particularly, to write an electrostatic latent image on a photoconductor and transfer the electrostatic latent image to another transfer medium. The present invention relates to an improvement in a color image forming apparatus that obtains a color image by transferring and developing it.

[0002]

2. Description of the Related Art The basic method of transferring an electrostatic latent image on a photosensitive member to another transfer medium (dielectric medium) was found by Walkup. After that, various methods were studied and R. M. It is described in Schaffert's Electrophotography. These methods are generally used for TESI (Tran
sfer of Electrostatic Image) method is called. This technology allows you to select an image-supporting recording medium with a high degree of whiteness compared to a method in which the electrostatic latent image on the photoconductor is directly developed with a developer and dried and fixed to obtain the final image. It has been conventionally known that there are advantages that the freedom of design of the photoconductor and the final image bearing recording medium is large, such as the selection options of (1) and the life of the photoconductor being extended. Further, it is already known to obtain a color image by repeating sequential transfer and development of an electrostatic latent image (JP-A-48-3546,
49-34838, 50-36128, 50-
62444, 52-35637 and 52-3603.
8, ibid. 52-35637, ibid. 53-67444). In these, the charge obtained by charging the photoconductor is exposed by a light source lamp to eliminate the charge, and an electrostatic latent image potential pattern that continuously changes depending on the light intensity is obtained.

On the other hand, digital electrophotographic printers and copying machines have already been used as recording systems capable of providing high speed and high print quality. In these printers and copiers, binary information of on / off is given as two-dimensional information of a predetermined location on the photoconductor based on characters and image data. Conventionally, when recording an image, an area modulation method using a halftone dot structure or a line screen structure has been widely used. Since this method has a relatively simple algorithm and is low in cost, it has been adopted in many digital electrophotographic printers and copying machines. It is possible to combine this with the TESI method to form binary information on a photosensitive member, transfer it to a transfer medium, and then develop and visualize it.
It is proposed in Japanese Patent No.

[0004]

However, the area modulation method has a basic structure in which the white portion of the paper as the transfer medium and the colored portion such as toner are repeated, and therefore, the repetition is detected by humans as image noise. Evaluation as good image quality cannot be obtained. In order to obtain good image quality, it is necessary to obtain a high-resolution image that cannot be detected by humans, and along with this, development of many technologies such as high response of development and narrowing of the light beam spot diameter. Is. When the area modulation method is used in the TESI method for obtaining a color image, the second, third, and fourth colors are respectively overlaid on the first-color, second-color, and third-color toner images developed on the transfer medium. When the electrostatic latent image is transferred, the basic structure is such that the white part of the transfer medium and the colored part of toner are repeated, so unevenness occurs on the surface of the transfer medium and the adhesion between the photoconductor and the transfer medium is improved. There is a concern that transfer defects of the electrostatic latent image may occur due to the unevenness, and there is a technical problem that image defects occur when the electrostatic latent image in the defective state is developed with each color developer. Was found.

The present invention has been made to solve the above technical problems, and provides a color image forming apparatus capable of obtaining a good color image free from image defects due to transfer defects.

[0006]

That is, the present invention is
As shown in FIG. 1, a latent image carrier 1 carrying an electrostatic latent image.
A multicolor latent image forming means 2 for forming an electrostatic latent image for each color component on the latent image carrier 1, and a transfer medium for transferring the electrostatic latent image for each color component formed on the latent image carrier 1. 5 or a multi-color developing means 3 for sequentially developing toner on the latent image carrier 1 for each color component, and a transfer medium 5 is brought into contact rolling with the latent image carrier 1.
A transfer unit 4 for transferring the electrostatic latent image of each color component or the developed image of each color component on the latent image carrier 1 to the transfer medium 5 side, and a fixing unit 6 for sequentially fixing the developed image of each color component on the transfer medium 5 are provided. In the color image forming apparatus, the auxiliary developing means 7 is provided for developing the non-image area of each color component image with colorless transparent toner when the multicolor developing means 3 develops each color component.

In such technical means, the latent image carrier 1 may be either a photoconductor or a dielectric as long as it can carry an electrostatic latent image. For example, a latent image carrier composed of a photoconductor. The specific form of the body 1 may be a drum or a belt having a photosensitive layer formed on the surface thereof, or a photosensitive sheet may be conveyed by a drum- or belt-like conveying means.

As the multicolor latent image forming means 2, if the electrostatic latent image of each color component can be formed, for example, the latent image carrier 1 is positively or negatively charged by the charging means, A latent image corresponding to an image signal may be written by the exposing means, or an electrostatic latent image may be appropriately written by an ion current writing head.

Further, as the multicolor developing means 3, a means for developing the electrostatic latent image on the transfer medium 5 (shown by the solid line in FIG. 1) and a means for developing the electrostatic latent image on the latent image carrier 1 are used. Liquid development using each color component toner (not necessarily limited to four colors).
Any of powder development may be used, and the development unit for each color component may be appropriately changed in design such as a parallel selection system or a rotary selection system. In this case, in order to obtain a color image with good graininess, liquid development or powder development may be performed with a toner having a particle diameter of 5 μm or less, preferably 3 μm or less.

Further, in the case where the transfer means 4 is a type in which the electrostatic latent image on the transfer medium 5 is developed by the multicolor developing means 3, the transfer medium 5 is held and the latent image is formed on the transfer medium 5. As long as the electrostatic latent image on the image carrier 1 is transferred, various methods such as an electrostatic latent image transfer method (TESI method) may be appropriately selected. On the other hand, for the type in which development is performed by the multicolor developing means 3, any type can be selected as long as it holds the transfer medium 5 and transfers the toner image developed on the latent image carrier 1 to the transfer medium 5. It doesn't matter. In this case, when the transfer means 4 is of the electrostatic latent image transfer method type, the transfer medium 5 usually used has a surface made of a dielectric material and has a desired whiteness or transparency. A transfer medium whose back surface is formed of an aluminum vapor-deposited layer or a transparent conductive layer of ITO (indium tin oxide), tin oxide, indium oxide, lead oxide, etc. It is also possible to use 5. Further, as a specific mode example of the transfer means 4 using the transfer medium 5 having the conductive layer formed on the back surface thereof, for example, the surface of the latent image carrier 1 and the surface of the transfer medium 5 are brought into contact with each other to make the latent image carrier 1 A voltage may be applied between the conductive layer and the conductive layer of the transfer medium 5, and the two surfaces may be separated as they are, or
There is one in which the latent image carrier 1 and the transfer medium 5 are brought into close contact with each other under pressure, the conductive layer of the latent image carrier 1 and the conductive layer of the transfer medium 5 are electrically connected, and then the two surfaces are separated. . still,
For the type that transfers the toner image to the transfer medium 5,
Plain paper can be used as the transfer medium 5.

Further, as the auxiliary developing means 7, as shown by a solid line or a dotted line in FIG. 1, after developing the electrostatic latent image on the transfer medium 5 or the latent image carrier 1 with each color component, each color component toner is added. The design may be changed as appropriate as long as the non-image area which is not developed by the development can be developed with the colorless transparent toner. In this case, as a simple and reliable embodying means, for example, when the multi-color developing means 3 reverses or normally develops each color component image portion with each color component toner, the auxiliary developing means 6 uses each color component toner image portion. It suffices to apply a bias potential slightly higher or lower than the potential to perform normal or reversal development on the non-image area of each color component image.

Further, the multi-color developing means 3 and the auxiliary developing means 7
After the development process by the
In general, it is necessary to fix the toner image of each color component and the transparent toner image on the transfer medium 5. Here, as the fixing unit 6, a unit having good fixing performance may be selected according to the developing system of the multicolor developing unit 3 and the auxiliary developing unit 7. In this case, the toner images may be permanently fixed after each of the developing steps of the multicolor developing means 3, or the toner image may be temporarily attached after each of the developing steps of the multicolor developing means 3, The main fixing may be performed after the toner images of the respective color components are all transferred to the transfer medium 5.

[0013]

In the above-mentioned technical means, the system shown by the solid line in FIG.
Sequentially forms an electrostatic latent image of each color component on the latent image carrier 1, and the transfer unit 4 transfers the electrostatic latent image of each color component on the latent image carrier 1 to the transfer medium 5 side. Then, the multicolor developing means 3 sequentially develops the electrostatic latent images of the respective color components on the transfer medium 5 with the corresponding color toners, and the auxiliary developing means 7 sequentially colorless and transparent the non-image area which is not developed with the respective color toners. After developing with toner, the fixing unit 6 fixes each color component developed image on the transfer medium 5. In such an image forming process, the corresponding color toner adheres to the image part of each color component and the colorless transparent toner adheres to the non-image part, so the toner image of each color component has a flat surface. Obtained as an image. Therefore, when the electrostatic latent image of the second color is transferred onto the toner image of the first color on the transfer medium 5, the toner image of the first color is flat. Adhesion with the latent image carrier 1 holding the electrostatic latent image is sufficiently high, and the electrostatic latent image is transferred without omission. Thereafter, the same applies to the third color and the fourth color, whereby a color image having a four-layer structure is formed.

The system shown by the dotted line in FIG. 1 (latent image carrier 1
In the system in which the multicolor developing means 3 and the auxiliary developing means 7 are provided on the side), the second color toner image is transferred onto the first color toner image on the transfer medium 5,
Since the first-color toner image is flat, the adhesion to the second-color toner image is sufficiently high, and the toner image is transferred without omission. Thereafter, the same applies to the third color and the fourth color, whereby a color image having a four-layer structure is formed.

[0015]

【Example】

Example 1 FIG. 2 shows a schematic configuration of Example 1 of a color image forming apparatus to which the present invention is applied. In the figure, reference numeral 11 is a photosensitive drum that rotates in the direction of the arrow, 12 is a charging scorotron that charges the photosensitive drum 11 for each image forming cycle, and 13
Is a laser ROS (Raster Output Scanner) for irradiating the photosensitive drum 11 with a light beam according to an image signal, 14 is a discharge lamp for removing residual charges on the photosensitive drum 11, and 15
Is a dielectric sheet on which the electrostatic latent image on the photosensitive drum 11 is transferred and a conductive layer is formed on the back surface, and 16 is a metal transfer drum on which the back conductive layer side of the dielectric sheet 15 is wound and held and grounded, Reference numerals 17 to 20 are fountain liquid developing devices for cyan, magenta, yellow and black for developing electrostatic latent images of respective color components on the dielectric sheet 15 by toner.
Reference numeral 21 denotes an auxiliary liquid developing device for developing the non-image portion of each color component electrostatic latent image on the dielectric sheet 15 with colorless transparent toner, 22
Is a drying and fixing device for drying and fixing each color component toner image on the dielectric sheet 15, and 23 is an AC or DC superposed AC corotron for removing residual charges on the dielectric sheet 15.

In this embodiment, the laser ROS 13
For example, as shown in FIG. 3, a semiconductor laser 31 as a light source, a collimator lens 32 for collimating the light beam from the semiconductor laser 31, and a light beam from the collimator lens 32 for scanning the photosensitive drum 11 in the axial direction. A polygon mirror 33 that raster-scans along the line, and an fθ lens 34 that forms an image of the beam raster-scanned by the polygon mirror 33 along the scanning line of the photosensitive drum 11. The semiconductor laser 31 is modulated by a light emission time control circuit 35 and turned on / off. The light emission time control circuit 35 uses, for example, a dither matrix method, and a cyan light from an image reading device or a computer. The photosensitive drum 11 is exposed by controlling the beam irradiation time of the semiconductor laser 31 according to the gradation signal based on the magenta, yellow, and black color component print signals.

Further, in this embodiment, the metal transfer drum 16 has a conductive layer on the surface thereof, and the back surface conductive layer of the dielectric sheet 15 is in contact with the photosensitive layer 11 so as to be dielectric with the conductive layer. The body sheet 15 is pressed and brought into close contact, the conductive layer of the photosensitive drum 11 and the conductive layer of the dielectric sheet 15 are electrically connected, and then the two surfaces are separated to transfer the electrostatic latent image. There is. In this embodiment, the dielectric sheet 15 is a polyester film containing a white pigment, and the back surface of the dielectric sheet 15 is a conductive layer 1 composed of an aluminum vapor deposition layer.
5a (see FIG. 5).

Further, in this embodiment, the fountain liquid developing devices 17 to 20 for the respective colors are movable in the horizontal direction, and are set to be moved to a predetermined developing position for each image forming cycle. . Then, as shown in FIG. 4, the fountain liquid developing devices 17 to 20 for the respective colors have the liquid toner T1 having a negative polarity and an average particle diameter of 0.5 μm.
At a predetermined developing bias VB1 (-250 in this embodiment).
V) is applied to reversely develop the electrostatic latent image portion. On the other hand, as shown in FIG. 4, the auxiliary liquid developing device 21 is a colorless transparent toner T2 having an average particle diameter of 0.5 μm and having a positive polarity in each image forming cycle, and is slightly larger in absolute value than the developing bias VB1. Predetermined developing bias V
The electrostatic latent image non-image area is normally developed while applying B2 (-260 V in this embodiment).

Next, the performance of the color image forming apparatus according to this embodiment will be evaluated. In the color image forming process by this color image forming apparatus, the photosensitive drum 11 is uniformly charged to about -900 V by the charging scorotron 12, and the electrostatic charge of the cyan color component based on the document or the image information by the laser ROS 13 on the photosensitive drum 11. After the latent image is formed, this electrostatic latent image is transferred to the dielectric sheet 15, and the image portion of the electrostatic latent image (in this embodiment, 100% exposure portion potential is obtained by the liquid developing device 17 for the corresponding cyan color component). VG = -70V), and at the same time, the non-image portion (non-exposed portion potential VH = -440V) of the electrostatic latent image is developed by the colorless transparent toner of the auxiliary liquid developing device 21, and the dry fixing device 22 is used. A cyan visible image is obtained by drying and fixing at, and thereafter, the electric charge on the dielectric sheet 15 is removed by the AC corotron 23. Furthermore, this charging, exposure,
After the operations of transfer, development, auxiliary development, and dry fixing are sequentially repeated for each color of magenta, yellow, and black, the dielectric sheet 15 is peeled from the metal transfer drum 16 and the color recorded on the dielectric sheet 15 is removed. Get the image.

In such an image forming process, each color component toner image T formed on the dielectric sheet 15 is formed.
As shown in FIG. 5, (C), T (M), T (Y), and T (K) are formed as a flat image together with the colorless transparent toner image T (A). Therefore, when the second color electrostatic latent image is transferred onto the first color toner image T (C) of the dielectric sheet 15, the first color toner image T (C) is flat, Adhesion with the photosensitive drum 11 holding the electrostatic latent image of the second color becomes sufficiently high, and the electrostatic latent image is transferred without omission. The same applies to the third and fourth colors thereafter. Then, when the electrostatic latent image transferred to the dielectric sheet 15 was developed by each developing device 17 and auxiliary developing device 21 and then dried and fixed, the image quality was examined, and there was no image defect and the graininess was good. In addition, it was confirmed that a color image with high saturation and high density was obtained because the toner image surface was flat.

Further, in this embodiment, each of the developing devices 17 to 2 is
No. 0 uses a liquid toner of 5 μm or less, and how the particle size of this liquid toner influences the graininess was examined. As a study method, as the particle size of the toner,
0.5 μm, 5 μm, 7 μm, and 20 μm were selected, calculations and experiments by theoretical formulas were carried out for these, and the calculation results and experimental results are shown in FIG. 6, and the range with good graininess was examined. In the figure, the theoretical formula is a formula for calculating the effect of the density gradation image on the graininess of the toner particle size (Roger P. Dool
“Noise Perception in Electroph” by y and Rodney Shaw
otography ”), the calculated values are shown by lines and the experimental values are shown by dots. It is confirmed that the experimental values are almost the same as the calculated values, and good image quality that humans hardly perceive graininess is obtained. It has been confirmed that the graininess for this purpose needs to be about 4 or less, and the toner particle size that satisfies this needs to be 5 μm or less.

Example 2 FIG. 7 shows a schematic configuration of Example 2 of a color image forming apparatus to which the present invention is applied. The same components as those in Example 1 are designated by the same reference numerals as those in Example 1. The detailed description thereof will be omitted here. Unlike the first embodiment, the color image forming apparatus shown in FIG. 9 uses powder toner as a developer, and as in the case of using the liquid toner of the first embodiment, on the dielectric sheet 15 as a transfer medium. After forming the toner image of the first color on the dielectric sheet 1
5. Toner is presumed to be attached to 5. After that, AC Corotron 23
The charges of the dielectric sheet 15 are removed by. Next, exposure for magenta, yellow, black, latent image transfer,
By repeating the steps of development using toner of each color and post-fixing, the images are overlapped to form a color image. Thereafter, the dielectric sheet 15 is peeled off from the metal transfer drum 16, and the heat fixing device 2
The toner image of each color component, which is supposedly attached on the dielectric sheet 15, is discharged through the heat fixing device 2.
Mainly fixed at 5. Also in this embodiment, the first embodiment
It was confirmed that the same action and effect as in (3) were obtained.

Example 3 FIG. 8 shows Example 3 of the color image forming apparatus to which the present invention is applied. The same components as those of the first embodiment are designated by the same reference numerals as those of the first embodiment, and the detailed description thereof is omitted here. The color image forming apparatus according to this embodiment is
Different from the first and second embodiments, liquid developing devices 17 to 20 for accommodating each color component toner are arranged around the photosensitive drum 11, and an auxiliary liquid developing device 21 for accommodating colorless and transparent toner is arranged at the subsequent stage. The image portion of each color component electrostatic latent image on the photosensitive drum 11 is developed with the corresponding color component toner of the liquid developing devices 17 to 20, and the non-image portion of each color component electrostatic latent image is supplemented with liquid development. The colorless and transparent toner in the container 21 is used for development. Further, in the figure, reference numeral 41 is plain paper as a transfer medium, 42 is a transport drum for holding and transporting the plain paper 41, 43 is incorporated in the transport drum 42,
A transfer corotron that transfers the toner image on the photosensitive drum 11 to the side of the plain paper 41, a pre-transfer corotron 44 that charges the toner image on the photosensitive drum 11 to one polarity, and 45 removes the residual toner on the photosensitive drum 11. It is a cleaner.

According to the color image forming apparatus of this embodiment, the photosensitive drum 1 is formed by the cyan toner of the liquid developing device 17.
The image portion of the electrostatic latent image of the first color on No. 1 is reversely developed, and then the non-image portion of the electrostatic latent image of the first color is normally developed by the colorless transparent toner of the auxiliary liquid developing device 21. As a result, an image having a flat surface in which the image portion is made of cyan toner and the non-image portion is made of colorless transparent toner is obtained. The polarity of the first toner image on the photosensitive drum 11 obtained as described above is adjusted by the pre-transfer corotron 44, and then the transfer corotron 4
3 is transferred onto the plain paper 41. The toner remaining on the photosensitive drum 11 without being transferred is removed by the cleaner 45. Subsequently, the steps of exposure for magenta, yellow, and black, development with each color toner, development with colorless transparent toner, pre-transfer charging, and transfer are repeated, and a four-layer structure in which toner images are superimposed on plain paper 41. A color image of is obtained. After that, the plain paper 41 is separated from the transport drum 42 and fixed by the heat fixing device 25. In the above case, since the toner image having a flat plane is obtained, the plain paper 41
When the toner image of the second color is transferred onto the toner image of the first color, the adhesion to the developed image of the second color is sufficiently high and the developed image is transferred without omission. The same applies to the third and fourth colors thereafter. As a result, a multi-layered color image having high image quality and high graininess and having a flat toner image surface and high saturation and high density can be obtained.

[0025]

As described above, according to the first aspect of the invention, when the electrostatic latent image or toner image of each color component on the latent image carrier is transferred to the transfer medium, the transfer is performed first. The electrostatic latent image or toner image is missing while ensuring the flatness of the toner image transferred to the medium side and maintaining close contact with the electrostatic latent image or toner image of each color component on the latent image carrier. Since the image is transferred to the transfer medium side without doing so, it is possible to surely obtain a color image with high saturation and high density without image defects due to defective transfer and because the toner image surface is flat.

According to the second aspect of the present invention, by a simple method of appropriately selecting the developing bias and the developing system, each color toner is applied to the image portion of the electrostatic latent image of each color component, and the non-image portion is colorless and transparent. The toner can be surely adhered, and the toner image surface of each color component can be easily flattened.

Further, according to the third aspect of the invention, by devising the developing toner particle size of the multicolor developing means, a color image having no image defect due to transfer failure and having extremely good graininess can be obtained. it can.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration of a color image forming apparatus according to the present invention.

FIG. 2 is an explanatory diagram illustrating an overall configuration of a color image forming apparatus according to a first embodiment.

FIG. 3 is an explanatory diagram showing details of a laser ROS of Example 1.

FIG. 4 is an explanatory diagram showing a developing process of each color component toner of Example 1 by a liquid developing device and an auxiliary liquid developing device.

FIG. 5 is an explanatory diagram showing a state of a color image formed on the dielectric sheet of Example 1.

FIG. 6 is a graph showing the relationship between toner particle size and graininess of the liquid developing device used in the examples.

FIG. 7 is an explanatory diagram illustrating an overall configuration of a color image forming apparatus according to a second embodiment.

FIG. 8 is an explanatory diagram showing an overall configuration of a color image forming apparatus according to a third embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Latent image carrier, 2 ... Multicolor latent image forming means, 3 ... Multicolor developing means, 4 ... Transfer means, 5 ... Transfer medium, 6 ... Fixing means, 7
... Auxiliary developing means

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuhiro Oda 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd. (72) Inventor Toru Teshigawara 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd. (72 ) Inventor Yasuki Yamauchi 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd. (72) Inventor Masahiko Kubo 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd. (72) Inventor Kazuhiro Iwaoka Hongo, Ebina City, Kanagawa Prefecture 2274 Fuji Xerox Co., Ltd. (72) Inventor Toshiaki Sagara 2274 Hongo, Ebina City, Kanagawa Fuji Xerox Co., Ltd.

Claims (3)

[Claims] 1. A latent image carrier (1) carrying an electrostatic latent image.
A multicolor latent image forming means (2) for forming an electrostatic latent image for each color component on the latent image carrier (1), and each color component static image formed on the latent image carrier (1). A multi-color developing means (3) for sequentially developing the latent image on the transfer medium (5) or the latent image carrier (1) for each color component, and a transfer medium (5) on the latent image carrier (1). On the transfer medium (5), and a transfer means (4) for contact-rolling the electrostatic latent image or the developed image of each color component on the latent image carrier (1) to the transfer medium (5) side. In a color image forming apparatus provided with a fixing unit (6) for sequentially fixing each color component developed image, a non-image area of each color component image is developed with a colorless transparent toner when each color component is developed by the multicolor developing unit (3). A color image forming apparatus, characterized in that the auxiliary developing means (7) is provided. 2. The apparatus according to claim 1, wherein when the multicolor developing means (3) reverses or normally develops each color component image portion with each color component toner, the auxiliary developing means (7) uses each color component toner image. A color image forming apparatus, characterized in that a non-image area of each color component image is subjected to normal or reversal development by applying a bias potential slightly higher or lower than the partial potential. 3. The multicolor developing means (3) according to claim 1, wherein the electrostatic latent image of each color component on the transfer medium (5) is liquid or powder developed with a toner having a particle diameter of 5 μm or less. And a color image forming apparatus.