JPS63172284A - Color electrophotographic device - Google Patents

Abstract

PURPOSE:To obtain a color image excellent in the color superposition of a thin line picture by setting up the light quantity of a light source for exposing a toner image from its surface to >=1.6 times the quantity of light required for dropping the initial surface potential of a naked photosensitive body by 500V. CONSTITUTION:In a color electrophotographing device forming plural toner images with different colors by repeating the cycle of charging, exposure and development plural times, the light quantity of the light source for exposing the photosensitive body is set up to >=1.6 times the quantity of light required for dropping the initial surface potential of the photosensitive body having no toner adhesion by 500V. When the light quantity of the light source is too much, a strong memory effect is generated in a photosensitive body and the memory of the preceding image is generated on the current image, so that the light quantity of the light source is suppressed to ten times or less. Even if much toner is tuck to the edge part of a line picture, sufficient light is radiated from the light source, the potential of the photosensitive body under the toner can be sufficiently dropped and another toner can be accurately superposed to the under toner and developed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a color electrophotographic device that can be used in a color hard copy device such as a color copying machine or a three-page color printer.

Conventional technology In recent years, charging, exposure, and development are repeated multiple times to form multiple toner images of different colors on an electrophotographic photoreceptor (hereinafter referred to as photoreceptor), and then the toner images are transferred all at once to paper to produce color images. Color electrophotographic methods for obtaining images are being actively studied. Unlike conventional color electrophotography, this method has the advantage that it does not require a transfer drum and the apparatus can be made smaller.

As this type of color electrophotographic device, for example,
There is a device proposed in the specification of No. 0-212927. This conventional device will be explained based on FIG. 2.

After charging the initial potential of the photoreceptor 2 to +800■ with the corona charger 1, the light emitting diode 3 is exposed to a yellow image signal, and a negative electrostatic latent image (the image area is exposed and the surface potential of the photoreceptor is forms an electrostatic latent image). And Y
A developing device 4 containing toner performs negative/positive reversal development of the electrostatic latent image to form a yellow toner image on the photoreceptor 1.

At this time, +700■ is added to the developing device 4 containing the Y toner.
A developing bias of 5 is applied, but other developing devices 5
and 6 are grounded and adjusted to prevent toner from flying away. After development with Y toner, the entire surface of the photoreceptor 2 is irradiated with a static eliminating lamp 7 to erase the yellow electrostatic latent image.

Next, the steps of charging, exposure, development, and optical static elimination are repeated using the same method and conditions as those used to form the yellow toner image (initial potential of the photoreceptor, development bias, etc.), and the number M , and C toner images are sequentially formed on top of the Y toner image. After the formation of all toner images is completed, the electrostatic latent image is erased using a static elimination lamp 8, and the toner image is electrostatically transferred onto a recording paper 10 using a corona charger 9.

Problems to be Solved by the Invention The method described in the previous section involves a new process not found in conventional electrophotographic methods, in which light is exposed through a single layer of toner formed on a photoconductor to form a new electrostatic image. Contains.

Because of this five-page exposure process through one layer of toner, many new problems arise that were completely unthinkable with conventional electrophotographic methods. This is caused by the fact that the thickness of a layer of toner adhering to the photoreceptor is not uniform, and that the shape of the toner is not constant but irregular. The newly encountered problems will be summarized and explained below.

In the following explanation, a photoreceptor having light attenuation characteristics as shown in FIG. 3 will be used. In this photoreceptor, the initial surface potential was 85 at an exposure dose of 0.8 μJ/cm2.
The surface potential decreases from 0V to 50V.

First, the first problem is that it becomes difficult to overlap colors in thin line areas and solid edge areas. In the method of overlapping colors on a photoreceptor, solid edges and thin lines, especially when the line width is 1
In line drawings with a diameter of 00 μm or less, it is difficult to overlay two colors, resulting in a problem that color unevenness tends to occur. In order to investigate the cause of this, we investigated the spectral transmittance (approximately 10 μm) of the toner used.
was measured (Figure 4). As shown in the figure, 85% or more of Page 6 is transmitted at the emission wavelength of the light emitting diode of 670 nm in both Yellow and Mazen 5≧. Therefore, the amount of light required to expose the yellow or magenta toner to lower the residual potential of the photoreceptor to the residual potential is calculated to be 1.0 μJ/em2, which is about 20% higher than that without toner. should be sufficient. However, when I actually print it,
Although I was able to overlap the colors on the solid areas, I was unable to overlap the colors on the thin lines and edges of the solid areas, resulting in unevenness. In order to find out the reason for this, we observed the state of adhesion of a layer of toner developed on the photoreceptor by this non-contact development method. The observation diagram is shown in Fig. 5. Therefore, due to the edge effect peculiar to the electrophotographic method, toner is 1.5 to 3 times as much toner in both thin line parts and the solid edge part (Fig. 5A) as in the solid part (Fig. 5A). It was found that the toner was particularly thick in that area. For this reason, the edge portions of the image have poor light transmission, and the photoreceptor beneath the image has an insufficient amount of light and the potential does not drop, making it difficult for toners with overlapping colors to be developed at the edge portions. This phenomenon in which the amount of toner adhesion increases at the edge of the image is characteristically emphasized in the developing method used in this conventional example on page 7 when a difference appears between the surface speed of the developing roller and the surface speed of the photoreceptor. appear after being treated. Even if the rotation speed of the developing device is initially adjusted so that edge enhancement of the image line does not occur as much as possible, as the amount of toner inside the developing device decreases, the toner will return to the rotating shaft. When the number of rotations of the developing roller changes due to a problem such as an increase in the rotational load caused by intrusion, an edge enhancement phenomenon immediately appears in the image. When this edge portion is emphasized in this way, as a side effect, it becomes difficult to overlap the colors, resulting in color unevenness. Another problem is that when the exposure amount is as small as about 1.2 times, close observation reveals that toner scatters around the image line, causing bleeding. When we investigated the cause of this, we found the following. Naturally, in a bare photoreceptor portion, the potential of the photoreceptor is sufficiently attenuated to approximately 50V with an amount of light 1.2 times the required amount of light. However, when a photoreceptor has a single layer of toner attached, the amount of light is attenuated by the single layer of toner, so
The photoreceptor potential decays only slightly. For example, in the case of the photoreceptor shown in FIG. 3, if the toner layer is thickly attached to the edge portion, the voltage is considered to be approximately 400V. In this state, as shown in Fig. 6, a potential difference of 350V is generated between the bare photoconductor (50V) and the photoconductor with a single layer of toner (400V) around the image line, and a new The toner scatters laterally on the photoreceptor along the generated lines of electric force (FIG. 7). Therefore, in addition to the above-mentioned problem of difficulty in overlapping colors, a new problem of blurring of toner images has arisen.

One possible solution to such a lack of light amount is to increase the amount of light from the light source, but it has been found that simply providing an excessive amount of light to the photoreceptor is not sufficient. For example, increasing the amount of light from a light source naturally shortens the life of the light source, impairing the reliability of the device. Furthermore, other problems regarding image quality also occur. This will be explained on page 9 using FIG.

For example, if the photoreceptor is irradiated with an exposure amount of 5 μJ/am2 (approximately 12 times the required exposure amount), the image will become thicker in the overlapping color areas where toner is thickly adhered to the photoreceptor, such as in thin line areas. did. For example, there are 2 red lines to be reproduced at 100 μm.
It had grown to nearly 0.00 micrometers, and the kanji written in Mincho font had been completely crushed. When we investigated the cause of this, we found the following. The first reason for this is that the toner used is amorphous. Because the toner has an amorphous shape and a variety of particle sizes, the incident light is scattered within a single layer of the toner, expanding the exposed area and thickening the electrostatic latent image.As a result, the toner stacked on top adheres to a wider area than the previous area. , the line drawing became thick.

It was also found that directly irradiating a bare photoreceptor with such an intense amount of light causes a memory effect on the photoreceptor, which interferes with the formation of the next electrostatic latent image.

In this way, there are 10 pages called exposure in the electrophotographic method of obtaining a color image by directly overlapping a layer of toner on the photoreceptor.

SUMMARY OF THE INVENTION An object of the present invention is to provide a color electrophotographic apparatus that produces color images with good color overlap in thin line areas.

Means for Solving the Problems The present invention provides a color electrophotographic apparatus that repeats charging, exposure, and development cycles multiple times to form a plurality of toner images of different colors on a photoreceptor. but,
This color electrophotographic apparatus is characterized in that the amount of light is 1.6 times or more the amount of light required to lower the initial surface potential of a bare photoreceptor by 500 μ.

According to the present invention, even if a large amount of toner adheres to the print edge area, the amount of light from the light source is irradiated with a margin, so the potential of the photoreceptor under the toner is sufficiently reduced, and furthermore, this It is possible to accurately overlay and develop toner of another color from above. Furthermore, problems such as blurring will not occur if the image line becomes thick due to excessive light intensity.

11<-- Example In the present invention, a developing method is used in which development is performed using a DC electric field without contacting the photoreceptor. The contrast potential between the image area and the non-image area must be approximately 500V or more. Therefore, it is essential that the potential of the photoreceptor is lowered by 500 μ from the initial surface potential. At this time, when the amount of toner deposited on the photoreceptor by this developing method was examined, it was found that the amount of toner deposited on the thin line side and the edge portion of the solid portion was 1.5 to 3 times the amount of deposited on the solid portion. When trying to attenuate the photoconductor by transmitting one layer of toner to obtain a contrast potential of 500V required for development, the amount of light from the light source that exposes the photoconductor will be lower than the initial surface potential of the photoconductor with no toner attached. The amount of light required is 1.6 times or more than the amount of light required to reduce the voltage by 500V. However, if the amount of light from this light source is too large, it will cause a strong memory effect on the photoreceptor, causing the image to have a memory of the previous image. Therefore, it is desirable to suppress the amount of light from the light source to 10 times or less. As mentioned above, the amount of toner adhering to solid areas is not so large, so the amount of light needs to be about 1.1 times that of bare areas, so basically areas where the amount of light needs to be 1.6 times or more are Only the boundary area between the drawing line and the non-printing part is sufficient. Further, in the present invention, the photoreceptor and the developing roller are not in contact with each other, and this is particularly effective in the case of a developing means that applies a DC voltage between the developing roller and the photoreceptor to evaporate toner. At this time, the developing conditions are particularly effective for images printed with the thickness of the toner on the developing roller being 100 μm or less and the gap between the developing roller and the surface of the photoreceptor being 300 μm or less. Furthermore, in this development method, the rotating direction of the developing roller is opposite to that of the photoconductor, that is, the surface of the photoconductor and the surface of the developing roller are in the same direction of movement, and the moving speed of the developing roller is 0% of the moving speed of the photoconductor. ．．
When the magnification is set within the range of 7x to 1.3x, no significant edge effect appears in the image, so a special sharp effect is exhibited. In the present invention, since the photoreceptor must be exposed from above the toner, a strong light source is desirable, and a light emitting diode (wavelength: 670 nm) or a semiconductor laser (wavelength: 800 nm) is preferable. At this time, toners that do not transmit the wavelengths of these light sources must be imaged at the end of the color stacking order. Therefore, the order of charging, exposing, and developing must be yellow, magenta, and cyan, or magenta, yellow, and cyan.

Of course, when using black toner, there is no need to overlap the colors, so it goes without saying that the black toner may be brought in any order.

Specific Example 1 Hereinafter, a specific example of the present invention will be described in detail using FIG. 1.

The developing devices 11, 12, 13 are non-contact type non-magnetic one-component developing devices that use a DC electric field to remove toner, and a blade 17 forms a thin layer of toner on aluminum developing rollers 14, 15, 16. It is configured to do this. Yellow (Y) in developer 11, magenta (M) in developer 12
, the developing device 13 contains cyan (C) insulating toner. Then, on page 14, the gap between the developing rollers 14, 15, 16 and the photoreceptor 18 (
The developing devices were placed facing each other around the photoreceptor 18 with a constant developing gap. Each developing device is attached with a separation mechanism that brings it close to the photoreceptor during development and separates it when not developing. The specifications and development conditions of the developer and the physical properties of the toner are shown below.

Developing unit specifications and developing conditions Developing roller diameter: 16 mm Developing roller circumferential speed: 130 mm/s Developing roller rotation direction: Opposite to photoreceptor Thickness of toner layer on developing roller:
30ttm developing roller rotation direction: Opposite direction from photoreceptor 18 Development gap: 150μm during development, 700μm when not developed Toner physical properties Toner charge amount: +3μC/g Average particle size: 10μm Long wavelength sensitized in the infrared region as a photoreceptor diameter 100mm
An amorphous 5e-Te photoreceptor drum 18 was used and rotated at a speed of 150 mm/s. This photoreceptor 18 was charged to a surface potential of 50V using a band 15-page electric device 19 (corona voltage: +7 kV). Next, output 5mW, wavelength 7
A semiconductor laser 20 of 80 nm was made to emit light. At this time,
The intensity of the laser beam on the photoreceptor surface was 2 mW. At this time, the surface potential of the bare photoconductor 18 is +50V from 1800cm.
0.8 mW on the photoreceptor surface was sufficient to lower the potential to . Therefore, the amount of laser light is 2.0% of the required amount of light.
I use it 5 times more.

Using this semiconductor laser 20, a negative yellow signal was exposed onto the photoreceptor 18 to form an electrostatic latent image. After the latent image is reversely developed in a yellow developing device 11 in a developing state in which +700 cm is applied to the developing roller 14, the photoreceptor 18 is passed through a magenta developing device 12 and a cyan developing device 13 in a non-developing state. A toner image was formed. At this time, the thickness of the yellow toner layer on the photoreceptor was one to two layers.

Next, the photoreceptor 18 is charged to +850V using the corona charger 19 again.
It was charged with electricity. Thereafter, the photoreceptor 18 was exposed to signal light corresponding to magenta by the semiconductor laser 20 to form a magenta electrostatic latent image. Next, the photoreceptor 18 is passed through a yellow developing device 11 in a non-developing state, a magenta developing device 12 in a developing state in which +800■ is applied to the developing roller 15, and a cyan developing device 13 in a non-developing state to form a magenta toner image. was formed. At this time, the thickness of the yellow and magenta toner layers that overlapped on the photoreceptor was 2 to 4 layers.

Next, the photoreceptor 18 is charged to +9 again by the corona charger 19.
It was charged to 50V. Thereafter, the semiconductor laser 20 was used to expose signal light corresponding to cyan to form a cyan electrostatic latent image. Here, the surface potential of the image area formed on the M toner image is +100V, and the surface potential of the image area formed on the image where Y toner and M toner are superimposed is +200V.
The contrast potential of the latent image was 750.

Next, the photoreceptor 18 is applied to the yellow developing device 11 and magenta developing device 12 in a non-developing state, and the developing roller 16 is applied with +900V.
A cyan toner image was formed by passing through a cyan developing device 13 in a developing state to which a cyan toner image was applied.

The color toner image thus obtained on the photoreceptor 18 was transferred onto paper 22 by a transfer charger 21, and 17 pages were thermally fixed. On the other hand, the surface of the photoreceptor 18 after the transfer was cleaned by pressing the fur brush 23 against the photoreceptor 18.

As a result, the color density of the composite color of the red, green, and blue solid areas is 1.
5 or more, and a clear color image with accurately overlapping line images was obtained.

Comparative Example 1 Using the apparatus described in FIG. 1, the output of the semiconductor laser 20 was reduced from 2 mW (on the surface of the photoreceptor) to 0.9 mW, which is 10% more than the required exposure amount of the photoreceptor 18. In edge portions and fine line drawings of 100 μm or less, it became difficult to overlap red, green, and blue-purple, and color unevenness occurred in the drawing lines.

Specific Example 2 Next, using the apparatus of Specific Example 1, a light emitting diode array (output 7 μW per dot) was used as a light source instead of the semiconductor laser 20, and a rod lens array (manufactured by Nippon Sheet Glass Co., Ltd., SELFOC lens) was used. An example will be described in which the present invention is used in combination with an array (5LA-20). The amount of exposure energy on the photoreceptor surface was 2.2 μJ/cm 2 for 18 pages. At this wavelength, the exposure energy required to reduce the potential of the photoreceptor to its residual potential is 0.4 μJ/cm 2 . Therefore, 5 times the exposure amount was given. When printed under these conditions, the color is red,
The color density of the composite color of green and blue solid areas is 1.5 or more, and Y
, M, and C color overlapping density was 1.7 or more, and a clear color image with overlapping line images was obtained.

Comparative Example 2 Using the apparatus of Example 2, a light emitting diode array (7 μW per dot) was used as the light source, and a rod lens array with higher resolution but darker (Selfoc manufactured by Nippon Sheet Glass Co., Ltd.) was used. Lens array, 5LA-
9) was used in combination. The amount of exposure energy on the photoreceptor surface was 0.4 μJ/cm 2 . This is the exposure amount at which the potential is completely reduced if the photoreceptor is bare. When printed under these conditions, the solid edges and 10
In fine line drawings of 0 μm or less, it became difficult to overlap red, green, and blue-purple colors, and color unevenness occurred in the drawing lines.

Page 19 Effects of the Invention According to the present invention, it is possible to obtain a color electrophotographic apparatus that allows colors to be superimposed not only on solid areas but also on the thin line side and that can stably obtain color images with high color density of composite colors.

[Brief explanation of the drawing]

FIG. 1 is a principle diagram of a color electrophotographic apparatus according to an embodiment of the present invention, FIG. 2 is a principle diagram of a conventional color electrophotographic apparatus, and FIG. 3 is a light attenuation characteristic of the photoreceptor used in the present invention. FIG. 4 is a characteristic diagram showing the measured spectral transmittance of the toner used in the present invention. FIG. 5 is a diagram schematically showing how the toner adheres to the solid area of the present invention. 7 and 7 are diagrams illustrating the blurring of the image line when a small exposure amount is used, and FIG. 8 is a diagram illustrating the thickening of the image line when an excessive exposure amount is used. 11.12.13...Developer, 14.15.16...
・Developing roller, 18... photoreceptor, 19... charger,
20... Name of Hikaru Gen's agent Patent attorney Toshio Nakachi (1 person) Figure 2 Figure 4 Figure 3 Figure 6 θ/ 17.2 1), 3 Q4 tl,
s 1.6 (1,71), 8 b, 9 /,
0 exposure amount (J-J/Rusty z7θ2 Yuji Figure 6 Figure 7 Figure 8

Claims (9)

[Claims] (1) In a color electrophotographic device that forms multiple toner images of different colors on a photoreceptor by repeating the cycle of charging, exposure, and development multiple times, the amount of light from a light source that exposes images from above the toner image is A color electrophotographic device characterized in that the amount of light is 1.6 times or more the amount of light required to lower the initial surface potential of a photoreceptor by 500V. (2) Claim 1 in which the required light amount is 10 times or less
The color electrophotographic device described in Section 1. (3) The development is a non-contact development method of the DC electric field type in which the toner is blown away by applying a DC voltage between the developing roller carrying a thin layer of toner and the photoreceptor. A color electrophotographic apparatus according to item 1 or 2. (4) The color electrophotographic apparatus according to claim 3, wherein the thickness of the toner on the developing roller is 100 μm or less, and the gap between the developing roller and the surface of the photoreceptor is 300 μm or less. (5) The rotating direction of the developing roller is opposite to that of the photoreceptor, and the moving speed of the developing roller is within a range of 0.7 to 1.3 times the moving speed of the photoreceptor. 3
The color electrophotographic device described in Section 1. (6) Claim 1 in which the light source is a semiconductor laser
3. The color electrophotographic apparatus according to item 1 or 2. (7) A color electrophotographic apparatus according to claim 1 or 2, wherein the light source is a light emitting diode. (8) A color electrophotographic apparatus according to claim 6 or 7, wherein the charging/exposure/developing cycle is in the order of yellow, magenta, and cyan. (9) A color electrophotographic apparatus according to claim 6 or 7, wherein the charging, exposing, and developing cycles are in the order of magenta, yellow, and cyan.