JPH08202109A - Electrophotographic recording device - Google Patents

Abstract

PURPOSE: To print a full color image with a stable density at a high speed by provided two light sources having a different wavelength and a light transmis sion system and driving the light sources based on image information in each printing color, at the time of forming a latent image. CONSTITUTION: The light sources 1a and 1b having the different wavelength are used and beams are obtained by collimating lenses 2a and 2b and then, synthesized by a PBS(polarizing beam splitter) 3. Then, the light beams are led to a rotary polygon mirror 6 by a lens 4 and a cylindrical lens 5. A photoreceptor 10 is irradiated with light 8 after passing through an f-θ lens 7 and an electrostatic latent image is formed on the surface of the photoreceptor. Printing data of magenta toner stuck to a part where a potential on the surface of the photoreceptor after being exposed is not drastically made lower than an initial potential by electrification is exposed with the light of the wavelength, emitted from the light source 1a and of cyan toner stuck to a part where the potential on the surface of the photoreceptor is drastically made lower than the initial potential by the electrification is exposed with the light of the wavelength, emitted from the light source 1b, based on the image information.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic recording apparatus such as a printer, a copying machine or a FAX which records an image by an electrophotographic method, and in particular, it exposes a photoconductor to form a three-level electrostatic latent image. And an exposure device for obtaining a color image.

[0002]

2. Description of the Related Art Electrophotographic recording devices such as copiers and printers that obtain color images by electrophotography are widely used. An image printing method using this recording device forms an electrostatic latent image by exposing a uniformly charged surface of a photoreceptor with one light source at an appropriate intensity, and the electrostatic latent image is formed. A method of developing an image with toner to obtain an image has been widely used. For the purpose of further increasing the printing speed and making the recording apparatus smaller than this method,
A method in which an electrostatic latent image composed of two printing potential levels and a non-printing potential level is formed by one exposure and development for two colors is performed (3
Level printing method) is shown in U.S. Pat. No. 4,078,929. FIG. 2 shows the state of the photoreceptor surface potential after exposure when printing is performed by this method. On the surface of the photoconductor after exposure, the portion where the initial charging potential V1 is maintained without being exposed by the exposure device is strongly exposed and the surface potential of the photoconductor is V3.
And a portion where the surface potential of the photosensitive member is V2 which is almost half the initial charging potential due to weak exposure.
After forming the electrostatic latent image on the surface of the photoconductor, two developing devices are used, one developing device stores positively charged toner, and the other developing device stores negatively charged toner. Various developing bias voltages Vb1 and Vb2 are applied to the developing roll to develop the electrostatic latent image to obtain a color image. The portion where the surface potential of the photosensitive member is approximately half the initial charging potential after weak exposure is a portion (background portion) where neither toner adheres. After the toner image is formed on the photoconductor, the charging polarity of the toner is adjusted by the charging device, and the toner image is transferred onto the recording paper by the transfer device. After that, the toner image is fused on the recording paper by heat and pressure by the fixing device. In this way, two-color printed images are obtained on the recording paper.

Further, in Japanese Patent Laid-Open No. 64-44462, a color image is produced by changing the exposure wavelength for each dot to distribute the surface potential and developing with toners of different charge polarities corresponding to the respective potentials. Is disclosed.

[0004]

The features of the above method are as follows:
Since latent images of two colors can be formed on the photoconductor by one exposure, two-color images can be printed at the same printing speed as the one-color machine without misalignment. Using this method, 2
By repeating the color printing twice, a full-color image can be obtained very quickly. Below, this method is 2 colors 3
Called the level printing method. In order to obtain an image by the two-color three-level printing method, the latent image potential of the first color after exposure is between V1 and Vb1 in FIG. 2, and the latent image potential of the second color is V3 and Vb2. Need to be formed between. A conventional color electrophotographic apparatus obtains a full-color image by repeating charging, exposure, and development four times. At the time of exposure by the conventional method, the electrostatic latent image potential after exposure is set to multiple levels, but since the printing data is for one color, the potential is
It was sufficient to form them in the range of V1 and Vb2 or V3 and Vb1 in the above. In the two-color three-level printing method, it is necessary to form the number of potential levels on the photoconductor after exposure in a number twice as compared with the conventional method and to form the potential level intervals finely. Since the photoreceptor surface potential after exposure depends on the exposure amount, it is necessary to control the exposure amount of the light source more precisely in order to accurately set the photoreceptor surface potential. FIG. 3 shows the relationship between the exposure amount and the photoconductor surface potential after exposure in the exposure apparatus used conventionally. The larger the exposure amount, the smaller the surface potential of the photoconductor after exposure and the smaller the change in the surface potential with respect to the change in the exposure amount. That is, the smaller the exposure amount is, the larger the fluctuation of the photosensitive member surface potential after the exposure is. When the fluctuation of the photoreceptor surface potential after exposure is large, the density fluctuation after printing is large. Therefore, when the two-color, three-level printing method is used to print by using the conventional exposure apparatus, there arises a problem that the density of the image of the first color in which the toner is attached to the portion where the exposure amount is small becomes unstable. Further, when a multicolor electrostatic latent image is formed at one time and developed with toners of different charging polarities as in JP-A-64-44462, it is difficult to control the charging of the toners and it is difficult to put them into practical use. Met.

SUMMARY OF THE INVENTION An object of the present invention is to provide an electrophotographic recording apparatus which solves the above problems that occur when a conventional exposure apparatus is used and is capable of printing a full-color image of stable density at high speed. .

[0006]

In order to achieve the above object, an electrophotographic recording apparatus according to the present invention, that is, by developing with a plurality of color toners having different charging polarities, a plurality of color toners are formed on the surface of a photoreceptor. In an electrophotographic recording device for forming a toner image, a light source driving device for driving two light sources having different wavelengths when forming a latent image and an optical transmission system and driving the light source based on image information for each color to be printed is provided. It is provided.

[0007]

Function The sensitivity of the photoconductor changes depending on the wavelength of the irradiation light. In order to form an electrostatic latent image of a color to be printed without lowering the potential more than the initial photoconductor charging potential, a light source that emits light of a wavelength with low sensitivity to the photoconductor is used. By irradiating with this light source, the change in the surface potential of the photoconductor after the exposure is reduced with respect to the change in the exposure amount, and the latent image potential is stabilized. A light source that forms an electrostatic latent image of a color to be printed by lowering the electric potential lower than the charging potential of the initial photoconductor is exposed using light having a wavelength that is sensitive to the photoconductor.

Further, the light source driving device appropriately selects the light source for emitting light based on the color information of the image to be printed when forming the electrostatic latent image, and sets the photosensitive member at an appropriate exposure amount. By controlling so as to expose, an electrostatic latent image having an appropriate potential can be formed on the surface of the photoconductor.

By exposing as described above, two colors of 3
At the time of printing by the level printing method, the surface potential of the photosensitive member after exposure is stable for both colors, so that the density of the printed image is stable.

[0010]

Embodiments of the present invention will be described below with reference to FIGS.

Embodiment 1 When printing a full-color image, color image information for each pixel is transmitted from the host computer to the electrophotographic recording apparatus. Printing pixels in the electrophotographic recording apparatus are printed in eight types of colors: white W, magenta M, red R, green G, cyan C, blue B, yellow Y, and black K. The intermediate color can be represented by setting an appropriate toner mixing ratio among magenta M, cyan C, and yellow Y by a known intermediate color creating method.

When a full-color image is obtained by using the two-color three-level printing method, two colors are combined from four toners of cyan, magenta, yellow, and black to form a two-color image by one exposure. This is repeated twice to obtain an image. FIG. 7 shows an example of the overall configuration of an electrophotographic recording apparatus that obtains a full-color image by this method.

Around the first photoconductor 10, along the rotation direction of the arrow, the first charging device 11, the first main exposure means 12, the first developing device 13, the second developing device 14, and the first toner adhesion amount. Sensor 15, auxiliary exposure means 16, first pre-transfer charging device 1
7, the first static eliminator 18, and the first cleaner 19 are arranged. Similarly, the second charging device 21, the second main exposure unit 22, the third developing device 23, the fourth developing device 24, and the second pre-transfer charging are arranged around the second photoconductor 20 along the rotation direction of the arrow. The device 27, the second static eliminator 28, and the second cleaner 29 are arranged. The intermediate transfer member 40 is provided at a position where it contacts the two photoconductors.
Is arranged, and the transfer roll 41 is arranged in contact with the intermediate transfer body 40. Further, between the intermediate transfer body 40 and the transfer roll 41, a recording paper conveying means 32 for conveying the recording paper 31 and a fixing device 37 for melting and fixing the toner on the recording paper 31 are arranged.

The printing process in the above electrophotographic apparatus will be described below. Here, the color of the toner of the developer contained in the first developing device 13 and the second developing device 14 is any two kinds of magenta, cyan, and yellow, and one of them is a toner that is positively charged. Yes, the other may be a negatively charged toner. In this embodiment, the first developing device 13 has a developer containing magenta toner which is positively charged, the second developing device 14 has a developer containing cyan toner which is negatively charged, and
The developing device 23 includes a developer containing black toner that is positively charged,
The fourth developing device 24 contains a developer containing yellow toner that is negatively charged. The developer may be a conventionally used one-component developer or two-component developer.

First, the surface of the first photoconductor 10 is uniformly charged by the first charging device 11, and the surface of the photoconductor is exposed by the first exposure means 12 according to the color information of magenta and cyan to form an electrostatic latent image. To form. Then, after developing by the first developing device 13 and the second developing device 14, the photosensitive member 1 is formed by the auxiliary exposure device 16.
0 By adjusting the potential of the surface, magenta and cyan toners are mixed as needed, the polarities of the toners are aligned by the first pre-transfer charging device 17, and then the magenta and cyan toners are formed on the intermediate transfer body 40. The transferred image is transferred. The surface of the first photoconductor 10 that has been transferred is destaticized by the first destaticizing device 18, and then cleaned by the first cleaner 19. At the same time, similar to the process around the first photoconductor 10, a black and yellow image is formed on the second photoconductor 20 and is superimposed on the image formed by the first photoconductor 10 on the intermediate transfer body 40. To match. The images superimposed on the intermediate transfer body 40 are transferred onto the recording paper 31 by the transfer roll 41. The recording paper 31 is conveyed to the fixing device 37 by the recording paper conveying means 32, and the toner is fused and fixed on the recording paper 31 by heat and pressure to complete a full-color image.

When an image is obtained by the above method, the first charging device 11 uniformly charges the first photoconductor 10 and the first exposure means 12 supplies information for two colors to the first photoconductor 10.
When recording on, the information of the magenta toner is formed so as not to lower the potential of the surface of the first photoconductor 10 after the exposure to a level lower than the initial charging potential, and the information of the cyan toner is the first information.
It is formed by greatly reducing the potential on the surface of the photoconductor 10. That is, in FIG. 3, the first color corresponds to magenta and the second color corresponds to cyan. In order to obtain a gradation color image, it is necessary to set the potential on the surface of the photoconductor after exposure to three levels as shown in FIG. The image density after printing is almost proportional to the difference between the latent image potential after exposure and the developing bias potential during development. Conventionally, the exposure device used in the electrophotographic recording device emits a light beam having a wavelength at which the photosensitivity of the photoconductor is large, and therefore the surface potential of the photoconductor after exposure is small even when a small amount of light is irradiated. Greatly reduced. The smaller the exposure amount, the greater the change in the potential of the surface of the photoconductor after the exposure with respect to the change in the exposure amount, and the greater the change in the density after printing. Since the amount of light emitted from the light source always fluctuates slightly, the surface potential of the photoconductor after exposure fluctuates and the image density changes in the area where the photoconductor is irradiated with a small amount of light to form an electrostatic latent image. The fluctuation of can be visually recognized. In the two-color multi-level printing method, it is necessary to set the surface potential after exposure in a narrower potential range than in the conventional method and to set twice as many potential levels. Therefore, it is difficult to obtain gradation with the magenta toner that is attached to the portion where the surface potential of the photoreceptor after exposure does not drop significantly below the initial charging potential. Therefore, in order to print an image with a desired density and gradation using magenta toner, it is necessary to devise a method of exposing the surface of the photoconductor.

FIG. 4 shows a photosensitive member (OP
The sensitivity of C) is shown. The unit of the vertical axis is the reciprocal of the half exposure amount of the photoconductor. It shows that the sensitivity is good in the wavelength range of 600 to 800 nm, and the sensitivity is lowered at the wavelengths on both sides of the range. Here, a method of exposing an image represented by each color of magenta toner and cyan toner with two light sources having different wavelengths to an exposure device for the purpose of expressing the image with desired density and good gradation Indicates.

FIG. 1 shows an example of an exposure apparatus used in the present invention. After using the light sources 1a and 1b having different wavelengths and shaping the beam by the collimating lenses 2a and 2b,
Combine the beams with PBS (Polarizing Beam Splitter) 3
The light beam is guided to the rotating polygon mirror 6 by the lens 4 and the cylindrical lens 5. The light 8 scanned by the rotary polygon mirror 6 passes through the f-θ lens 7 and is applied to the photoconductor 10,
An electrostatic latent image is formed on the surface of the photoconductor. Based on the image information, the printing data of the magenta toner, which is attached to a portion that does not significantly lower the surface potential of the photoreceptor after exposure from the initial charging potential, is exposed with the light of the wavelength emitted from the light source 1a to change the surface potential of the photoreceptor. By exposing the printing data of the cyan toner to be attached to the portion that is greatly reduced from the initial charging potential with the light of the wavelength emitted from the light source 1b, the density is stable for both colors and the gradation An image is obtained.

FIG. 5 shows the exposure amount and the surface potential of the photoreceptor after exposure when the photoreceptor is exposed using two light sources having different wavelengths. Here, the sensitivity of the photoconductor is better for the light of the wavelength of the light source 1b than for the light of the wavelength of the light source 1a. Light source 1a
Since the light having the wavelength of 1 has a low sensitivity to the photoconductor, the fluctuation of the surface potential of the photoconductor after the exposure with respect to the fluctuation of the exposure amount is small. The information on the magenta toner to be attached to the portion that does not significantly decrease the surface potential of the photosensitive body after exposure is provided as light source 1a
By exposing with the light of the wavelength emitted from, the fluctuation of the surface potential of the photosensitive member after the exposure with respect to the fluctuation of the output of the laser becomes small, so that an image with a stable density can be obtained.
Since the cyan toner is attached to a portion of the surface of the photoconductor that greatly reduces the potential after exposure, the printing information is exposed by a light source (light source 1b) having a wavelength conventionally used. Since it is small, the potential variation due to the light amount variation of the light source is small and the image density variation is small. Therefore, an image with stable density can be obtained for both magenta and cyan colors.

FIG. 6 shows the structure of a semiconductor laser used as a light source. The semiconductor laser has a structure in which semiconductors having an active layer of about 0.5 μm in the center are stacked in layers.
When a compound semiconductor made of Al, Ga, As is used as the laser material, the oscillation wavelength of the laser becomes 0.6 to 0.9 μm. By adjusting the mixing ratio of Al and Ga in the active layer, semiconductor lasers having different oscillation wavelengths can be manufactured. Light source 1a has a wavelength near 800 nm, and light source 1b has a wavelength of 870 n.
When a semiconductor laser near m is used, the difference in the transmittance and the refractive index of the lens due to the difference in wavelength is small, so even if two light beams are exposed with one optical axis, they can be exposed at a predetermined position, and a desired image can be obtained. Is obtained.

Embodiment 2 FIG. 9 shows an embodiment of an exposure system different from the embodiment 1.
When the wavelength difference of the light used for the light source 1a and the light source 1b is large, the reflection, refraction characteristics of the light beam at the PBS 3, the lens 4, and the cylindrical lens 5 used for the optical system are different, so the light from the two light sources is the same. Can not be transmitted on the optical axis. Therefore, it is necessary to provide one exposure system for one light source. This method is shown in FIG. As in FIG. 1, the light from the light source 1a is shaped by the collimator lens 2a and then guided to the rotary polygon mirror 6a by the lens 4a and the cylindrical lens 5a. The light 8a scanned by the rotating polygon mirror 6a passes through the f-θ lens 7a and enters the photoconductor 10. On the other hand, the light from the light source 1b is shaped by the collimator lens 2b, and then the lens 4
b, the rotary polygon mirror 6b by the cylindrical lens 5b
The light is guided to the f-θ lens 7b, the optical path is adjusted by the reflector 9, and the surface of the photoconductor is exposed.

By using an appropriate optical system for each of the light sources 1a and 1b, the object of the present invention can be achieved even when there is a large difference in the wavelengths of the light from the light sources.

Embodiment 3 FIG. 8 shows an embodiment of an electrophotographic apparatus different from the embodiment 1. The photoconductor is only the first photoconductor 10. The printing process of this embodiment will be described. After the surface of the first photoconductor 10 is uniformly charged by the first charging device 11, the electrostatic latent images of two colors are formed by the first main exposure unit 12. After developing by the first developing device 13 and the second developing device 14, the surface of the first photoconductor 10 is selectively exposed by the auxiliary exposure device 16. The pre-transfer charging device 17 aligns the charging polarities of the toners and transfers the toners onto the intermediate transfer body 40. At this point, the toner image on the intermediate transfer member 40 is not transferred to the recording paper 31, so the transfer roll 41 is retracted. After the toner image is transferred to the intermediate transfer body 40, the surface of the first photoconductor 10 is neutralized by the first static eliminator 18 and cleaned by the first cleaner 19. Next, after the surface of the first photoconductor 10 is uniformly charged by the first charging device 11, the electrostatic latent image printed by the remaining two colors is formed by the first main exposure unit 12. After developing by the third developing device 23 and the fourth developing device 24, the pre-transfer charging device 17 aligns the charging polarities of the toners, and transfers them so as to overlap the toner image on the intermediate transfer body 40 formed in the first process. To do. Then, the transfer roll 41 is brought into contact with the intermediate transfer body 40 and transferred onto the recording paper 31.

With the configuration of this embodiment, the first embodiment
Since the number of charging devices and main exposure devices can be reduced compared to the electrophotographic recording device shown in FIG. 1, the recording device can be downsized and the cost can be reduced. In this embodiment, the photosensitive member uses a drum, but it goes without saying that if the developing device is a belt and the developing device is arranged in the longitudinal direction of the belt, further downsizing can be achieved.

[0025]

EFFECTS OF THE INVENTION In a system in which electrostatic latent images for two colors are formed by one exposure and color images are obtained by using toners of plural colors having different charging polarities, light sources having different wavelengths are used for each color. By performing the exposure, the potential variation on the surface of the photoconductor after the exposure due to the variation in the light amount of the light source is reduced, and the variation in the image density after printing is reduced. Therefore, at the desired concentration,
Moreover, a color image having gradation can be obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram (1) of an exposure apparatus according to the present invention.

FIG. 2 is a photoconductor surface potential distribution after exposure by a three-level printing method.

FIG. 3 shows the relationship between the exposure amount and the surface potential distribution of the photoconductor after exposure.

FIG. 4 shows the relationship between the exposure light and the sensitivity of the photoconductor.

FIG. 5 shows the relationship between the exposure amount and the surface potential distribution of the photoconductor after exposure.
(2).

FIG. 6 is a sectional view of a semiconductor laser.

FIG. 7 is a configuration diagram (1) of the electrophotographic recording apparatus.

FIG. 8 is a configuration diagram (2) of the electrophotographic recording apparatus.

FIG. 9 is a configuration diagram (2) of the exposure apparatus according to the present invention.

[Explanation of symbols]

1 ... Light source, 2 ... Collimating lens, 3 ... PBS, 4 ... Lens, 5 ... Cylindrical lens, 6 ... Rotating polygon mirror, 7
... f-θ lens, 10 ... photoconductor.

Claims (5)

[Claims] 1. A light beam is irradiated onto a photosensitive member whose surface is uniformly charged by a charging device, so that at least 3 is obtained.
In an electrophotographic recording apparatus that forms a latent image potential level of a high level and records an image using a plurality of color toners having different charging polarities, two light sources having different wavelengths are provided to an exposure device that irradiates a photoreceptor with light. An electrophotographic recording apparatus comprising: a light source; and combining the light from the light source, and exposing the photoconductor with the combined light to form a latent image of at least three levels. 2. An optical system for exposing light beams on the photoconductor by transmitting the light beams from the two light sources according to claim 1 by using a beam splitter to align the optical axes and using a lens and a rotary polygon mirror. Characteristic electrophotographic recording device. 3. An electrophotographic recording method, wherein light beams from the two light sources according to claim 1 are transmitted using two optical systems consisting of a lens and a rotary polygonal mirror to expose on a photosensitive member. apparatus. 4. An electrophotographic recording apparatus, wherein the photoconductors have different sensitivities to the light beams from the two light sources according to claim 1. 5. An electrophotographic recording apparatus, wherein the image data exposed by the light beams from the two light sources according to claim 1 are image data of different colors.