JPH06171155A - Device for forming color image - Google Patents

Abstract

PURPOSE:To provide approximately constant transfer efficiency in any area by reducing differences in toner density and to from an improved gray level color image having less unevenness in transfer. CONSTITUTION:In a device for forming color image, wherein each color component electrostatic latent image formed on a photosensitive body 1 by the beam from a beam generating means 3 is developed by a multicolor development means 5 according to each color component toner so that each color component toner image is transferred once onto an intermediate transfer body 6 successively, following which the toner images are transferred at a time onto a recording medium 8, there are provided a beam intensity modulation means 9 for generating strong beam intensity modulation signals corresponding to gray levels of each color component image signal and a beam applying means 10 for applying a strong light beam corresponding to the beam intensity modulation signals.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital electrophotographic type color image forming apparatus, and more particularly, to charging, exposing and developing a photosensitive member a plurality of times, and successively transferring them onto an intermediate transfer member to form a multicolor toner. The present invention relates to an improvement in a color image forming apparatus of the type in which a color image is formed and then transferred onto a recording medium at once.

[0002]

2. Description of the Related Art As a color image forming apparatus adopting an electrophotographic system capable of providing high speed and high printing quality, a photosensitive member is charged, exposed and developed a plurality of times, and sequentially transferred to an intermediate transfer member to form a multicolor toner. After forming the color image by
It is known to collectively transfer color images onto a recording medium such as paper to form a color image (for example, JP-A-59-1257).
65, JP-A-62-206567).
According to this type, it is possible to suppress the occurrence of multiple transfer failure and color registration deviation due to many factors such as the holding state of a recording medium such as paper, the thickness and stiffness of the recording medium, and the surface property of the recording medium. In this respect, higher printing quality can be obtained as compared with the type that does not use the intermediate transfer member.

Further, in recent color printers and copying machines, binary information of ON / OFF is given to a predetermined location on a photosensitive member based on characters and image data, and when a halftone image is recorded, it is conventionally used. Area modulation methods such as a halftone dot structure and a line structure, which are often used in the field of printing, have been often 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.

[0004]

By the way, in a digital electrophotographic color image forming apparatus for obtaining a color image using an intermediate transfer member, transfer from the photosensitive member to the intermediate transfer member and further recording from the intermediate transfer member. One of the technical issues is how to form an image on a recording medium without sacrificing the transfer efficiency in order to obtain a good color image, because the transfer to the medium and the two transfer steps are required. Has become.
This is because, as described above, the area gradation method using the halftone dot structure or the line structure is used, and the difference between the high toner density and the low toner density on the photosensitive member affects the transfer efficiency. I know it's affected. In other words, as the toner density decreases, the transfer efficiency rapidly becomes unstable, and the difference from the high density area becomes noticeable, and the image quality on the recording medium (for example, graininess, color unevenness, etc.) is reduced. It was linked to dropping.

The present invention has been made in order to solve the above technical problems, and is based on the premise of a color image forming apparatus using an intermediate transfer member, which area is reduced by reducing the toner density difference. In the case of
Provided is a color image forming apparatus capable of obtaining a good density gradation color image with less transfer unevenness.

[0006]

That is, the present invention is
As shown in FIG. 1, a photoconductor 1 that is rotated by being charged by a charging unit 2 in each color component image forming cycle, a beam generating unit 3 that generates a light beam according to each color component image signal,
A scanning optical system 4 for forming an electrostatic latent image on the charged photosensitive body 1 by raster-scanning the light beam from the beam generating means 3 at a predetermined pixel pitch, and the scanning optical system 4 formed on the photosensitive body 1. A multicolor developing means 5 for sequentially developing the electrostatic latent image for each color component, an intermediate transfer body 6 for sequentially multiple-transferring each color component developed image sequentially developed by the multicolor developing means 5, and this intermediate transfer body. In the color image forming apparatus provided with the batch transfer means 7 for batch-transferring the color image formed on the recording medium 8 to the recording medium 8, the beam generating means 3 corresponds to the density gradation level for each color component image signal. A beam intensity modulation means 9 for generating a beam intensity modulation signal of intensity and a beam irradiation means 10 for irradiating a light beam of intensity according to the beam intensity modulation signal are provided.

In such technical means, the photoreceptor 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. It may be the one that has been adapted. In addition, as for the intermediate transfer member 6, if the toner images of the respective color components on the photosensitive member 1 can be temporarily transferred and held,
It does not matter whether it has a belt shape, a drum shape, or the like, and the transfer method can be appropriately selected such as pressure transfer and electrostatic transfer. Further, the batch transfer means 7 may be appropriately selected as long as it can transfer the color toner image on the intermediate transfer body 6 to the recording medium 8 side.

As the beam irradiating means 10 as the beam generating means 3, a semiconductor laser, a gas laser, a solid-state laser, or the like may be appropriately selected as long as it can irradiate a light beam. It may be irradiable, or may be composed of a light source with a constant light amount and a deflector that variably sets the transmission amount of the light amount.
The beam intensity modulating means 9 may be selected according to the beam irradiating means 10. For example, in the case where the beam irradiating means 10 is of a type in which the light amount level changes according to the drive current, it is driven according to the density gradation level. Any type of device that generates a beam intensity modulation signal that changes the current may be used, and the beam irradiation means 10 may be of a type that includes a constant light amount light source and a deflector that variably sets the light amount transmission amount. Is only required to generate a beam intensity modulation signal that changes the deflection degree of the deflector according to the density gradation level. Further, from the viewpoint of keeping the color image quality better, the beam intensity modulation means 9 corresponds to the transfer efficiency of the developed image of each color component onto the intermediate transfer body 6 and the recording medium 8 and outputs the beam intensity modulation signal. It is preferable to include the gradation correction unit 11 that variably corrects the intensity level. Further, the scanning optical system 4 may be appropriately selected as long as it can raster-scan the light beam from the beam generating means 3 along the main scanning direction on the surface of the photoconductor 1.

Further, as the multi-color developing means 5, any developing method may be adopted as long as toners of respective color components are used, and a parallel selecting method or a rotary selecting method or the like is also applied to the developing units for each color component. The design may be changed appropriately. In this case, in order to obtain a color image with good graininess, it is sufficient to develop with a toner having a particle diameter of 7 μm or less.

[0010]

According to the technical means as described above, the beam intensity modulating means 9 as the beam generating means 3 generates a beam intensity modulating signal having an intensity corresponding to the density gradation level for each color component image signal, The irradiation means 10 irradiates a light beam having an intensity corresponding to the beam intensity modulation signal. At this time,
When the light beam generated by the beam generating means 3 is guided onto the photoconductor 1 via the scanning optical system 4, the potential level of the electrostatic latent image according to the image signal of a predetermined density level is kept constant. Therefore, when the electrostatic latent image of this uniform density level is developed by the corresponding color component toner of the multicolor developing means 5, the toner of uniform layer thickness exists in the color component toner image. Therefore, the toner images of the respective color components on the photoconductor 1 are transferred to the side of the intermediate transfer body 6 with substantially uniform transfer efficiency, and the toner images of the respective color components transferred to the intermediate transfer body 6 are also substantially uniform. It is transferred to the recording medium 8 side with transfer efficiency.

[0011]

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 21 is a photosensitive drum that rotates in the direction of the arrow, 22 is a charging scorotron that charges the photosensitive drum 21 in each image forming cycle, and 23.
Is a laser ROS (Raster Output Scanner) for irradiating the photosensitive drum 21 with a light beam corresponding to an image signal, and 24 is a switching unit for each step rotation of the developing units 24a to 24d for cyan, magenta, yellow, and black toners. A rotary developing device 25, an intermediate transfer belt 25 for transferring and holding toner images of respective color components on the photosensitive drum 21, 26
Is a transfer corotron for transferring the toner image of each color component on the photosensitive drum 21 to the intermediate transfer belt 25 side, 27 is a drum cleaner for removing the residual toner on the photosensitive drum 21, 28
Is a discharge lamp for removing the residual charge on the photosensitive drum 21.

Reference numerals 30 to 32 are intermediate transfer belts 2.
5 is a drive roll and a driven roll that are rotationally driven, 33 is a belt cleaner that removes residual toner on the intermediate transfer belt 25, 34 is a driven roll 32 of one of the intermediate transfer belts 25 is a backup roll, and the intermediate transfer belt A bias applying transfer roll that transfers the toner images of the respective color components that have been multi-transferred onto 25 to the recording paper 35 side, 36 is a paper feed cassette that contains the recording paper 35, and 37 is a bias of the recording paper 35 from the paper feed cassette 36. A paper guide for guiding the application transfer roll 34 and 38 for the paper guide 3
7 is a sheet conveyance roll, 39 is a resist roll for adjusting the timing of entry of the recording sheet 35 into the bias application transfer roll 34, and 40 is an intermediate transfer belt 25.
The fixing device fixes the toner images of the respective color components transferred from the recording paper 35 to the recording paper 35.

Further, reference numeral 41 is a document 4 on the platen 42.
3 is a scanner for reading 3 and 44 is an image processing unit for converting the image information read by the scanner 41 into a digital image signal separated for each color component and sending it to the laser ROS 23. There is also a mode in which the image information from the computer is directly supplied to the image processing unit 43.

In this embodiment, the laser ROS2
3, numeral 3 designates a semiconductor laser 51 as a light source, a collimator lens 52 for collimating the light beam from the semiconductor laser 51, and an axial scanning of the photosensitive drum 21 with the light beam from the collimator lens 52. A polygon mirror 53 which raster-scans along a line, and a beam which is raster-scanned by the polygon mirror 53
And an fθ lens 54 for forming an image along the scanning line. Then, the semiconductor laser 51 irradiates the semiconductor laser 51 with a light amount according to the gradation signal (in this embodiment, a signal expressing the gradation density level in 256 gradations) from the image processing unit 43 by the light quantity control circuit 55. There is.

FIG. 4 shows a concrete example of the light quantity control circuit 55 used in this embodiment. In the figure, the light amount control circuit 5
Reference numeral 5 controls the laser drive current ILD so that the light quantity E proportional to the gradation signal is obtained based on the current characteristics of the semiconductor laser 51 as shown in FIG. 5, for example. The supply voltage V of the current control circuit 551 is changed to control the value of the laser drive current ILD passing through the resistor 552 portion serially connected to the semiconductor laser 51.

Next, the performance of the color image forming apparatus according to this embodiment will be evaluated. In the image forming process of this color image forming apparatus, the photosensitive drum 21 is charged by the charging scorotron 22 and the electrostatic latent image of the cyan component based on the original or the image information is generated on the photosensitive drum 21 by the laser ROS 23 as in the conventional case. After the image is formed, it is visualized by the cyan color developing unit 24a of the rotary developing device 24, and then transferred to the intermediate transfer belt 25. Then, after repeating the charging, exposing, developing, and transferring operations for each color of magenta, yellow, and black, the toner images of the respective color components on the intermediate transfer belt 25 are collectively transferred to the recording paper 35 and fixed. By fixing with the container 40, a color image is obtained on the recording paper 35.

FIG. 6A shows an exposure energy profile when uniform exposure is performed by variably setting the laser irradiation intensity in such an image forming process. On the other hand, as a comparative example, FIG. 6B shows an exposure energy profile when uniform exposure is performed by laser pulse width modulation based on the conventional area gradation method. In FIGS. 6A and 6B, the percentage display indicates the halftone image density level. At this time, the surface potential profile of the electrostatic latent image relating to the uniform exposure of the embodiment is maintained at a substantially constant level according to the exposure energy profile of FIG. 6A, as shown in FIG. 7A. It is understood that, as shown in FIG. 7B, the surface potential profile of the electrostatic latent image relating to the uniform exposure of the comparative example becomes uneven according to the exposure energy profile of FIG. 6B.

FIG. 8 shows the electrostatic latent image according to the embodiment for each color component toner TC (cyan), TM (magenta), TY (yellow), T.
After developing with K (black), the intermediate transfer belt 25
The toner image state when it is transferred to the recording sheet 35 and is collectively transferred to the recording paper 35 is divided into a high density area to an intermediate density area and an intermediate density area to a low density area. Incidentally, FIG. 9 shows a toner image state on the intermediate transfer belt 25 and the recording paper 35 according to the comparative example. According to the embodiment, as shown in FIG.
Since it becomes possible to make the toners of the respective color components uniformly exist on the intermediate transfer drum 1, there is no unevenness in the toner density, and the intermediate transfer drum 2
It is confirmed that the transfer of the toner image to No. 5 and the transfer of the toner image to the recording paper 35 are stable, and a good halftone image can be obtained. On the other hand, according to the comparative example, as shown in FIG. 9, since halftone is expressed by area gradation,
In the intermediate-density area to the low-density area, the transfer toner image on the recording paper 35 may be partially missing or missing, and the toner density on the intermediate transfer belt 25 may be high or low. It was confirmed that the uneven transfer after the transfer from the sheet to the recording paper 35 leads to the image disorder. this is,
In the intermediate density area to the low density area, since the amount of toner is smaller than that in the high density area, the adhesive force between the toners or between the toner and the intermediate transfer belt 25 becomes uneven, and as a result,
It is considered that random transfer will occur, and uneven transfer will lead to image distortion.

Further, when the transfer efficiency from the intermediate transfer belt 25 to the recording paper 35 of the embodiment and the comparative example with respect to the density gradation level of each input data was examined, the embodiment is sufficiently low density side as compared with the comparative example. It was confirmed that good transfer efficiency was obtained.

Next, how the particle size of each color component toner of the developing device 24 affects the granularity was examined. As an examination method, toner particles having respective particle diameters (12 μm, 10 μm, 7 μm, and 5 μm are selected in this example) are scattered on the intermediate transfer belt 25, and the granularity when transferred onto the recording paper 35 under the same conditions is visually observed. Evaluate. The results are shown in FIG. 11, and the quality of the graininess was evaluated by ◯. According to FIG. 11, it was confirmed that when the toner particle size was set to 7 μm or less, a good image quality was obtained in which human beings hardly perceive the granularity.

By the way, in the density gradation method according to the embodiment, the toner filled in the entire image area on the photosensitive drum 21 must be uniformly transferred onto the intermediate transfer belt 25 and onto the recording paper 35. Therefore, compared to the area gradation method according to the comparative example, it is more likely to be affected by the transfer condition and the state of the toner, which may affect the quality of the image. The influence of image quality can be avoided by reducing the toner particle size. That is, when the toner particle size is large, the surface and the inside of the toner image after transfer become rough, and even slight fluctuations at the time of transfer appear to be disturbed in the image due to the large particle size. However, when the toner particle size is 7 μm or less, the surface of the toner image after transfer becomes smooth and the inside becomes dense, and the effect of appearance becomes small, whereby uneven transfer and deterioration of graininess are suppressed. More specifically, as shown in FIG. 12B, the transfer unevenness of B when the toner T2 cannot be transferred when the toner particle size is large is visually observed in the image after transfer onto the recording paper 35 and fixing. However, as shown in FIG. 12A, the transfer unevenness of A when the toner T1 cannot be transferred when the toner particle size is small has almost no effect on appearance. In this way, by suppressing the physical properties of the toner on the photosensitive drum 21, a good image that is not affected by the transfer process can be obtained.

Example 2 FIG. 13 shows a light beam generator used in a color image forming apparatus according to Example 2. In the figure, the light quantity control circuit 55 of the light beam generation unit controls the laser drive current ILD passing through the resistor 552 connected in series to the semiconductor laser 51 by the current control circuit 551, as in the first embodiment. However, unlike the first embodiment, a gradation correction circuit 553 is added to the previous stage of the current control circuit 551. The gradation correction circuit 553 may be provided on either side of the image processing unit 43 or the laser ROS 23,
Intermediate transfer belt 25 for each color component toner image and recording paper 3
The gradation level of the gradation signal is corrected in advance in accordance with the transfer efficiency to No. 5, and in particular, the insufficient transfer of the color component toner image having poor transfer efficiency is compensated. Therefore, according to this embodiment, it is possible to further improve the image quality as compared with the first embodiment.

Example 3 FIG. 14 shows a light beam generator used in a color image forming apparatus according to Example 3. In the figure, the light beam generation unit differs from the first and second embodiments in that the semiconductor laser 61 to which a constant laser drive current is supplied by the constant current power supply 62 and the transmission amount of the light beam from the semiconductor laser 61 are transmitted. Based on the liquid crystal filter 63 to be changed and the voltage characteristic of the liquid crystal filter 63 (see, for example, FIG. 15), the liquid crystal filter 63 is controlled so that the transmittance of the liquid crystal filter 63 changes according to the density gradation level of the gradation signal. And a voltage control circuit 64 for controlling the applied voltage of. Therefore, also in this embodiment, similarly to the first embodiment, it is possible to irradiate the light beam having the intensity corresponding to the density gradation level of the gradation signal.
It should be noted that the gradation correction circuit 553 of the second embodiment is different from this embodiment.
Needless to say, may be added.

[0024]

As described above, according to the first aspect of the invention, in the color image forming apparatus using the intermediate transfer member, the difference in toner density between the toner images of the respective color components on the photosensitive member is reduced, Since a substantially constant transfer efficiency is obtained in any area, it is easy to obtain a density gradation color image with good image quality with little transfer unevenness even after two transfer steps of the intermediate transfer member and the recording medium. In addition, it is possible to eliminate the occurrence of image noise associated with the area gradation method (halftone dot structure, line structure).

According to the second aspect of the present invention, the transfer efficiency of the toner images of the respective color components is taken into consideration and the transfer shortage having poor transfer efficiency is compensated for in advance, so that an extremely good image with less transfer unevenness is obtained. It is possible to obtain a quality density gradation color image.

Further, according to the third aspect of the present invention, by devising the developing toner particle size of the multi-color developing means, the effect of transfer unevenness can be effectively suppressed, and the density gradation color having extremely good graininess. Images can be obtained.

[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 according to the first embodiment.

FIG. 4 is an explanatory diagram illustrating details of a light beam generation unit according to the first embodiment.

5 is an explanatory diagram showing an example of current characteristics of the semiconductor laser used in Example 1. FIG.

FIG. 6A is an explanatory diagram showing an exposure energy profile by a light beam according to Example 1, and FIG. 6B is an explanatory diagram showing an exposure energy profile by a light beam according to a comparative example.

7A shows a photosensitive drum surface potential profile according to an exposure energy profile by a light beam according to Example 1, and FIG. 7B shows a photosensitive drum surface according to an exposure energy profile by a light beam according to a comparative example. It is explanatory drawing which shows a potential profile.

FIG. 8 is an explanatory diagram illustrating a transfer state of toner images of respective colors according to the first exemplary embodiment onto an intermediate transfer belt and a recording sheet.

FIG. 9 is an explanatory diagram showing a transfer state of toner images of respective colors according to a comparative example onto an intermediate transfer belt and a recording sheet.

FIG. 10 is an explanatory diagram showing transfer efficiency from an intermediate transfer belt to a recording sheet for input data according to an example and a comparative example.

FIG. 11 is an explanatory diagram showing the relationship between toner particle size and graininess.

FIG. 12A is an explanatory diagram showing the influence on the transfer unevenness when the toner particle size is small, and FIG. 12B is an explanatory diagram showing the influence on the transfer unevenness when the toner particle size is large.

FIG. 13 is an explanatory diagram illustrating a light beam generation unit according to a second embodiment.

FIG. 14 is an explanatory diagram illustrating a light beam generation unit according to a third embodiment.

FIG. 15 is an explanatory diagram showing an example of voltage characteristics of the liquid crystal filter used in the third embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Photoconductor, 2 ... Charging means, 3 ... Beam generating means, 4 ...
Operation optical system, 5 ... Multicolor developing means, 6 ... Intermediate transfer body, 7 ...
Batch transfer means, 8 ... Recording medium, 9 ... Beam intensity modulation means, 10 ... Beam irradiation means, 11 ... Gradation correction means

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical indication location G03G 15/01 112 A (72) Inventor Yasuki Yamauchi 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd. (72) Inventor Yoshinori Machida 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd. (72) Inventor Kazuhiro Iwaoka 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd. (72) Inventor Yasuhiro Oda Kanagawa Prefecture 2274 Hongo, Ebina City, Fuji Xerox Co., Ltd. (72) Inventor, Kazuhiko Arai 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd. (72) Inventor, Kiyo Shigehiro 2274, Hongo, Ebina City, Kanagawa Prefecture Within

Claims (3)

[Claims] 1. A photoconductor (1) which is charged by a charging means (2) and rotates in each color component image forming cycle, and a beam generating means (3) which generates 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 generating means (3) at a predetermined pixel pitch, and the photoconductor. (1) Multicolor developing means (5) for sequentially developing the electrostatic latent image formed on each color component, and each color component developed image sequentially developed by this multicolor developing means (5) are sequentially multiplexed. In a color image forming apparatus comprising an intermediate transfer member (6) for transferring and a batch transfer means (7) for collectively transferring the color image formed on the intermediate transfer member (6) onto a recording medium (8), The beam generating means (3) is provided for density gradation for each color component image signal. Beam intensity modulation means (9) for generating a beam intensity modulation signal having an intensity corresponding to the level;
A color image forming apparatus comprising: a beam irradiating means (10) for irradiating a light beam having an intensity corresponding to the beam intensity modulation signal. 2. The beam intensity modulator according to claim 1, wherein the beam intensity modulator corresponds to the transfer efficiency of the developed image of each color component onto the intermediate transfer body (6) and the recording medium (8). A color image forming apparatus comprising: a gradation correcting unit (11) that variably corrects a signal intensity level. 3. The multicolor developing means (5) according to claim 1, wherein the electrostatic latent image on the photoconductor (1) has a particle size of 7 μm.
A color image forming apparatus, which develops with the following color component toners.