JPH06166219A - Color image forming device - Google Patents

Abstract

PURPOSE:To form a stabilized density color image without image defects formed by defective transfer while the cost of the device is reduced. CONSTITUTION:Static latent images corresponding to respective color components are formed on a photoreceptor 1 by luster scanning light beam by means of beam emission means 3. In a color image forming device in which the static latent images of respective color components are transferred successively to a transfer medium 5 and then developed by respective color component toner of a multicolor developing means 8, a beam spot adjusting means 9 setting beam spot diameters in the main scanning direction on the photoreceptor 1 by 1.5 times more of the pixel pitches in the main scanning direction in the range of not damaging the static latent image pattern when the static latent images at least to respective color component images other than the final color component is provided. More preferably, the beam spot diameters in the scanning direction are set by 1.5 times or more of the pixel pitches in the scanning direction by the beam sport adjusting means 9.

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 writing an electrostatic latent image on a photosensitive member by a raster scanning light beam. The present invention relates to an improvement in a color image forming apparatus that obtains a color image by transferring a latent image onto another transfer medium 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. Further, as a method that does not use the area modulation method as described above, there is a method of modulating the intensity of the light beam (hereinafter referred to as an intensity modulation method). Specifically, it is a method of changing the drive current of a semiconductor laser as a light source or a method of using an ultrasonic light modulator. By using this intensity modulation method, a density modulation image can be obtained in a format in which the image noise generated when the area modulation method is selected is removed.

[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.

In the method of changing the current of the semiconductor laser by the intensity modulation method described above, the light output changes greatly even if the current is changed a little and the environment dependence is high.
There is a technical problem that it is difficult to make a stable system, and the method using the ultrasonic optical modulator is expensive and complicated due to the price of the ultrasonic optical modulator and the necessity of highly accurate mounting. There is a technical problem of becoming.

The present invention has been made in order to solve the above-mentioned technical problems, and realizes a stable density gradation color image free from image defects due to transfer defects while reducing the apparatus cost. Provided is a color image forming apparatus which can be obtained.

[0007]

That is, the present invention is
As shown in FIG. 1, a photoconductor 1 that is charged and rotated by a charging unit 2 in each color component image forming cycle, and a beam irradiating unit 3 that irradiates a light beam according to each color component image signal.
And the photoconductor 1 charged by raster scanning the light beam from the beam irradiation means 3 at a predetermined pixel pitch.
A scanning optical system 4 for forming an electrostatic latent image thereon, and the photoconductor 1
The transfer medium 6 is contact-rolled to the transfer medium 6 to transfer the electrostatic latent images of the respective color components formed on the photoconductor 1 to the transfer medium 6 in order, and the electrostatic latent image on the transfer medium 6. Multicolor developing means 7 for sequentially developing each color component, and this multicolor developing means 7
And a fixing unit 8 for sequentially fixing the developed images according to the above, and is premised on a color image forming apparatus that multiple-forms a developed image of each color component on the transfer medium 6, and at least an electrostatic latent image for a color component image other than the final color component. Beam spot adjusting means 9 for setting the beam spot diameter in the main scanning direction on the photoconductor 1 at least 1.5 times the pixel pitch in the main scanning direction within the range where the electrostatic latent image pattern is not damaged. Is provided.

In such technical means, the photosensitive member 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-like or belt-like conveying means. It may be the one that has been adapted. As the beam irradiating means 3, a semiconductor laser such as a semiconductor laser may be appropriately selected as long as it irradiates a light beam having a pattern corresponding to the gradation level of each color component image signal on and off. Further, the scanning optical system 4 may be appropriately selected as long as it can raster-scan the light beam from the beam irradiation means 3 along the main scanning direction on the surface of the photoconductor 1.

As the latent image transfer means 6, any electrostatic latent image transfer method (TESI method) can be used as long as it holds the transfer medium 5 and transfers the electrostatic latent image on the photoconductor 1 to the transfer medium 5. )
Various methods may be appropriately selected. In this case, the transfer medium 5 usually used has a surface made of a dielectric material and has a desired whiteness or transparency,
In addition, the back surface is an aluminum vapor deposition layer or ITO.
(Indium tin oxide), tin oxide, indium oxide, lead oxide, etc., which is a transparent conductive layer.
It is also possible to use the transfer medium 5 made of only a dielectric material by devising the above. In addition, as a specific mode example of the latent image transfer means 6 using the transfer medium 5 having the conductive layer formed on the back surface, for example, the surface of the photoconductor 1 and the surface of the transfer medium 5 are brought into contact with each other to form the conductive layer of the photoconductor 1. A voltage may be applied between the transfer medium and the conductive layer of the transfer medium to separate the two surfaces as it is, or alternatively, the photosensitive layer 1 and the transfer medium 5 may be brought into close contact with each other under pressure to form the conductive layer of the photosensitive layer 1. There is a method in which the two surfaces are separated after electrically connecting the conductive layer of the transfer medium.

Further, the multi-color developing means 7 may be either liquid development using each color component toner or powder development,
The design of the developing units for each color component may be changed appropriately such as the parallel selection method or the rotary selection method. 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, as the fixing means 8, one having good fixing performance may be selected according to the developing system of the multicolor developing means 7. In this case, the toner images may be permanently fixed after each developing process of the multicolor developing means 7,
Alternatively, the toner images may be temporarily put on after each development process of the multicolor developing means 7, and the main fixing may be performed after all the toner images of each color component are transferred to the transfer medium 5.

The beam spot adjusting means 9 may basically be one that adjusts the beam spot diameter in the main scanning direction, but from the viewpoint of obtaining an image without image defects, the electrostatic latent image is adjusted. The beam spot diameter in the sub-scanning direction is preferably set to 1.5 times or more the pixel pitch in the sub-scanning direction as long as the image pattern is not damaged. Then, as a specific mode example of the beam spot adjusting means 9, the beam emitting time of the beam irradiating means 3 may be adjusted, or the image forming position of the scanning optical system 4 may be finely adjusted, and the design may be appropriately changed. .

[0013]

According to the technical means described above, the beam spot diameter of the light beam emitted from the beam irradiating means 3 on the photosensitive member 1 is not damaged by the beam spot adjusting means 9. It is set to be at least 1.5 times the pixel pitch in the main scanning direction in the range. At this time, if the beam diameter is small with respect to the pixel pitch, the unevenness of the exposure energy profile of the exposed portion and the non-exposed portion on the photoconductor 1 increases, and the area modulation in which the exposed portion and the non-exposed portion repeat is obtained. As described above, when the beam diameter increases with respect to the pixel pitch, the unevenness of the exposure energy profile of the exposed portion and the non-exposed portion on the photosensitive member 1 decreases, and the electrostatic intensity due to intensity modulation causes pseudo exposure intensity change. A latent image is formed. When the beam spot diameter in the sub-scanning direction is adjusted, similar results can be obtained in the sub-scanning direction. Therefore, the electrostatic latent image obtained by the pseudo intensity modulation obtained when the beam diameter is 1.5 times the pixel pitch or more has a flat exposure profile as compared with the area modulation latent image, and after being transferred to the transfer medium 5. The developed image is also obtained as a flat image. Therefore, when the second-color electrostatic latent image is transferred onto the first-color toner image on the transfer medium 5, the second-color electrostatic latent image is formed because the first-color toner image is flat. Adhesion with the held photoconductor 1 is sufficiently high, and the electrostatic latent image is transferred to the transfer medium 5 without omission. After that, the electrostatic latent images of the third color and the fourth color are similarly transferred to the transfer medium 5 without omission.
In this way, the electrostatic latent image transferred onto the transfer medium 5 is successively developed by the multicolor developing means 7 with the toner of each color component, and the developed toner image is fixed onto the transfer medium 5 by the fixing means 8. It

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on the embodiments shown in the accompanying drawings. 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, Numerals 17 to 20 are fountain liquid developing devices for cyan, magenta, yellow and black for developing the electrostatic latent image on the dielectric sheet 15 by toner, and 21 is a drying method for drying and fixing each color component toner image on the dielectric sheet 15. The fixing device 22 is an AC or DC superposed AC corotron that removes 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 is supplied 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 in accordance with the gradation signals based on the cyan, magenta, yellow, and black color component print signals. In particular, in this embodiment, the light beam spot diameter on the photosensitive drum 11 is set to 1.5 times or more the pixel pitch in the main scanning direction and the sub scanning direction. More specifically, when the resolution in the main scanning direction is 400 spi and the resolution in the sub scanning direction is 400 spi, the light beam spot diameter is set to 96 μm or more in both the main scanning direction and the sub scanning direction.

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 has a conductive layer composed of an aluminum vapor deposition layer.

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. . The fountain liquid developing devices 17 to 20 for the respective colors have an average particle diameter of 0.5 μm.
The one provided with the liquid toner is used.

Next, the performance of the color image forming apparatus according to this embodiment will be evaluated. The color image forming process by this color image forming apparatus is similar to that of the conventional one.
1 is charged by the charging scorotron 12, and the photosensitive drum 11 is charged.
After forming an electrostatic latent image of a cyan color component based on an original or image information by the laser ROS 13, the electrostatic latent image is transferred to the dielectric sheet 15 and is transferred to the liquid developing device 17 of the corresponding cyan color component. To form a visible image, which is dried and fixed by the dry fixing device 21 to obtain a cyan visible image, and thereafter, the charge on the dielectric sheet 15 is removed by the AC corotron 22.
Then, the operations of charging, exposing, transferring, developing, and drying and fixing are sequentially repeated for each color of magenta, yellow, and black, and then the dielectric sheet 15 is peeled off from the metal transfer drum 16 and placed on the dielectric sheet 15. Obtain a recorded color image.

In such an image forming process, as shown in FIG. 4, the electrostatic latent image based on the document or the image information has a surface potential profile in accordance with the exposure energy profile of the exposed portion and the unexposed portion by the laser beam. Form. This figure shows an exposure energy profile on the photosensitive drum 11 when the main scanning pixel pitch is changed for a constant main scanning beam diameter. In the figure, d represents the ratio of the beam spot diameter / pixel pitch, and the% display in each figure represents the halftone image density level. As shown in FIGS. 9A and 9B, when the beam spot diameter is smaller than the pixel pitch, the unevenness of the exposure energy profile increases, and area modulation in which the exposed portion and the non-exposed portion are repeated is obtained. On the contrary, as shown in FIGS. 6C and 6D, when the beam spot diameter increases with respect to the pixel pitch, the unevenness of the exposure energy profile decreases and the exposure intensity changes to intensity modulation. Specifically, when the beam spot diameter becomes 1.5 times the pixel pitch or more, a pseudo electrostatic latent image is formed by intensity modulation. Similar results can be obtained in the sub-scanning direction.

Therefore, as shown in (c) and (d) of FIG.
The electrostatic latent image obtained by the pseudo intensity modulation obtained when the beam spot diameter is 1.5 times the pixel pitch or more is shown in FIG.
Since the exposure energy profile becomes flatter than that of the electrostatic latent image by area modulation shown in (b), the dielectric sheet 15
The toner image obtained when the electrostatic latent image transferred to is developed is also flat. Therefore, when the electrostatic latent image of the second color is transferred onto the toner image of the first color of the dielectric sheet 15, the toner image of the first color is flat, so that the electrostatic latent image of the second color is formed. Adhesion with the photosensitive drum 11 holding the toner is sufficiently high, and the electrostatic latent image is transferred without omission. After that, the third color,
The same applies to the fourth color. Then, the electrostatic latent image transferred to the dielectric sheet 15 is developed by each developing device 17 and then dried and fixed (corresponding to FIGS. 4C and 4D), and
When the image quality of the result obtained by applying the same image forming process to the comparative example corresponding to FIGS. 4A and 4B was examined, the results shown in Table 1 below were obtained.

[0022]

[Table 1]

In Table 1, image defects were found in the case where the beam spot diameter was 0.5 times and 1.0 times the pixel pitch, but the beam spot diameter was 1.5 times the pixel pitch.
No image defect was observed for the double and 2.0 times. Regarding the graininess, it was confirmed that the graininess deteriorates when the beam spot diameter is as small as 0.5 times the pixel pitch, but the beam spot diameter is 1.
When the beam spot diameter is 2.0 times and the pixel pitch is 2.0 times, the graininess is very good. A good image was obtained.

Further, in this embodiment, when the beam spot diameter is made extremely large with respect to the pixel pitch, a phenomenon may occur in which the original electrostatic latent image pattern is damaged, and this electrostatic latent image pattern is damaged. It is necessary to select the beam spot diameter within the range that does not exist.

Furthermore, in this embodiment, the beam spot diameter is set to 1.5 times or more the pixel pitch in the main scanning direction and the sub scanning direction, but the beam spot diameter is set to the image pitch in the main scanning direction. It was confirmed that a good color image having no image defects was obtained although the image quality was slightly deteriorated even if the value was set to 1.5 or more only for the above.

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 performed for these, and the calculation results and experimental results are shown in FIG. 5, and the range in which the graininess was favorable 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. 6 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 22
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 4. Also in this embodiment, the first embodiment
It was confirmed that the same action and effect as in (3) were obtained.

[0028]

As described above, according to the first aspect of the invention, the electrostatic latent image pattern is maintained at least when the electrostatic latent image of the color component other than the final color component is formed. In the range, the diameter of the light beam spot irradiated on the photoconductor is set to 1.5 times or more the pixel pitch in the main scanning direction, and the light beam is turned on and off to generate an electrostatic latent image similar to that when the pseudo intensity modulation method is used. An image is formed, and this electrostatic latent image is sequentially transferred to a transfer medium and developed by a multicolor developing means. Therefore, an electrostatic latent image of a color component other than the final color component is transferred to the transfer medium side. It becomes possible to maintain the toner image as a flat image during development by
It is possible to maintain good sequential multicolor transferability when sequentially transferring the electrostatic latent image of the next color component onto the toner image previously formed on the transfer medium. Therefore, in the color image forming apparatus using the latent image transfer method, a stable density gradation color image without an image defect due to transfer failure is used without using the intensity modulation method which is unstable in terms of cost and density gradation reproducibility. Can be obtained.

Further, according to the second aspect of the invention, the diameter of the light beam spot irradiated on the photosensitive member in the range where the electrostatic latent image pattern is maintained is 1.5 times the pixel pitch in the sub-scanning direction. Since the above settings are made, it is possible to completely eliminate image defects in the sub-scanning direction, and to that extent, it is possible to obtain a very good density gradation color image in which image defects due to defective transfer are completely eliminated.

Further, according to the third aspect of the present invention, by devising the developing toner particle size of the multicolor developing means, there is no image defect due to transfer failure and graininess in the latent image transfer type color image forming apparatus. It is possible to obtain a very good density gradation color image.

[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 an exposure energy profile with respect to a ratio between a beam spot diameter and a pixel pitch.

FIG. 5 is a graph showing the relationship between toner particle size and graininess of the developing device used in the examples.

FIG. 6 is an explanatory diagram showing an overall configuration of a color image forming apparatus according to a second embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Photoconductor, 2 ... Charging means, 3 ... Beam irradiation means, 4 ...
Scanning optical system, 5 ... Latent image transfer means, 6 ... Transfer medium, 7 ... Multicolor developing means, 8 ... Fixing means, 9 ... Beam spot adjusting means

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical display location G03G 15/01 112 A (72) Inventor Yasuhiro Oda 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd. (72) Inventor Toshi Teshigawara, 2274 Hongo, Ebina-shi, Kanagawa Fuji Xerox Co., Ltd. (72) Inventor, Yasuki Yamauchi 2274 Hongo, Ebina-shi, Kanagawa Fuji Xerox Co., Ltd. (72) Masahiko Kubo, Kanagawa Kanagawa Fujino Xerox Co., Ltd., 2274 Hongo, Ebina-shi, Japan (72) Inventor Kazuhiro Iwaoka 2274 Hongo, Ebina-shi, Kanagawa Fuji Xerox Co., Ltd. (72) Toshiaki Sagara 2274 Hongo, Ebina-shi, Kanagawa Fuji Xerox shares In the company

Claims (3)

[Claims] 1. A photoreceptor (1) which is charged and rotated by a charging means (2) in each color component image forming cycle, and a beam irradiation means (3) which irradiates a light beam according to each color component image signal. A scanning optical system (4) for forming an electrostatic latent image on the charged photoconductor (1) by raster-scanning the light beam from the beam irradiation means (3) at a predetermined pixel pitch; A latent image transfer means (5) for contact-rolling the transfer medium (6) to the body (1) to sequentially transfer the electrostatic latent images of the respective color components formed on the photoconductor (1) onto the transfer medium (6).
A multicolor developing means (7) for sequentially developing the electrostatic latent image on the transfer medium (6) for each color component, and a fixing means (8) for sequentially fixing the developed images by the multicolor developing means (7). ) And a color image forming apparatus that multiplex-forms each color component developed image on the transfer medium (6), at least when forming an electrostatic latent image for a color component image other than the final color component,
Photoconductor (1) within the range where the electrostatic latent image pattern is not damaged
A color image forming apparatus comprising a beam spot adjusting means (9) for setting a beam spot diameter in the main scanning direction above 1.5 times or more a pixel pitch in the main scanning direction. 2. The beam spot adjusting means (9) according to claim 1, wherein the beam spot diameter in the sub-scanning direction on the photoconductor (1) is sub-scanned within a range in which the electrostatic latent image pattern is not damaged. A color image forming apparatus, characterized in that the direction pixel pitch is set to 1.5 times or more. 3. The multicolor developing means (7) according to claim 1, wherein the electrostatic latent image of each color component on the transfer medium (6) is liquid or powder developed with toner having a particle diameter of 5 μm or less. And a color image forming apparatus.