JPS63279278A - Electrophotographic device - Google Patents

Abstract

PURPOSE:To faithfully reproduce an image having high resolution, high density and excellent color superposition by setting up specific relational inequalities among the diameter of spot light, recording density, thickness of a photosensitive body, and a distance between the photosensitive body and a developer carrier in DC field dispersing development. CONSTITUTION:In a device for developing an electrostatic latent image formed by exposing the photosensitive body with laser beams by dispersing toner by means of a DC field, the relation among the recording density X dot 1mm of spot light, the diameter Dmum of spot light, the thickness L1mum of the photosensitive body, and the distance L2mum between the developer carrier and the photosensitive body is set up as shown in the inequalities 1, 2. The inequality 1 shows a required range of the light diameter D inversely proportional to the thickness L1 and proportional to the distance L2 and the inequality 2 shows the range of the light diameter D at the time of setting up the dot X. Thereby, the picture line width of 1 dot or 1 line can be sufficiently reproduced, the image density can be improved, the superposing development of plural toner components on the photosensitive body can be accurately executed, and color reproducibility can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an electrophotographic device that can be used in a hard copy device such as a black-and-white copying machine, a color copying machine, or a 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. This method differs from conventional color electrophotography methods in that it does not require a transfer drum and has the advantage that the apparatus can be miniaturized.

An example of this type of color electrophotographic apparatus is an apparatus proposed by the inventors in Japanese Patent Application No. 80-212927.

This device uses a developing method in which toner is blown away using a direct current electric field. A conventional device will be explained based on FIG.

The initial potential of the selenium photoreceptor 2 is set to +5oo by the corona charger 1.
After being charged to v, a yellow image signal is exposed using a light emitting diode 3 (spot diameter 105 μm) with a dot density of 9.45 lines/mal, and a negative electrostatic latent image (the image area is exposed and the surface of the photoreceptor is form an electrostatic latent image whose potential is attenuated. Then, the electrostatic latent image is subjected to negative/positive reversal development using a developing device 4 containing Y toner using a DC electric field scattering development method to form a yellow toner image on the photoreceptor 2. At this time, a developing bias of +700 cm is applied to the developing device 4 containing the Y toner, while the other developing devices 5 and 6 are grounded and adjusted to prevent the 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, using the same method and conditions as those used to form the yellow toner image (initial potential of the photoconductor, development bias, etc.), the steps of charging, exposure, development, and optical static elimination are repeated to form M and M on the photoconductor 2. A C toner image is sequentially formed on a Y toner image. After the formation of all the toner images is completed, the electrostatic latent image is erased by the static elimination lamp 8, and the toner image is electrostatically transferred onto the recording paper 10 by the corona charger 9.

Problems to be Solved by the Invention When a light emitting diode array (spot diameter 65 μm) with a dot density of 16 dots/m was used as a light source and recording was performed using the apparatus described in Fig. 2, the reproducibility of the image was good. However, it was found that the image density became low. When an image is created with this device using an organic photoreceptor with a thickness of approximately 20 μm instead of a selenium photoreceptor, the image width of one dot or one line is significantly narrower than 65 μm despite the high density. The result was a poor image. Further, when overlapping development is performed, there is a problem in that the image line width of the overlying toner image is narrower than the image line width of the toner image below, and the toners do not overlap accurately, resulting in poor color reproducibility.

An object of the present invention is to provide a color electrophotographic apparatus that faithfully reproduces high-resolution dot and one-line images with high density and fidelity. Another object of the present invention is to provide a color electrophotographic apparatus that obtains high-resolution color images with good color overlapping.

Means for Solving the Problems The present invention uses a photoconductor provided with a photoconductor on a base, and an electrostatic latent image formed on the photoconductor, which is visualized by causing toner to fly away using a DC electric field. This is an electrophotographic apparatus having a DC electric field scattering developer and a light source for spot exposure, in which the recording density of the spot light is X dots/ffl, the spot light diameter is Dμm, and the thickness of the light body is L1μm. When the distance between the carrier and the photoconductor is #t-L2μm, the electrophotographic apparatus is such that 10<D-L1/L2<23[μml] and 1400<D-X<2000[μml].

The problems when using the organic photoreceptor described in the conventional example are: 1.
We presume that the cause is insufficient exposure for one dot or line, and instead of using a light emitting diode as a light source, we use a semiconductor laser light source that changes the light intensity for each dot (a spot with a light intensity of 1/e2 or more). The diameter was about 70 μm (where e is the base of the natural logarithm), and the light intensity for one dot or one line was increased to 1.5 times that for exposing a solid area. Shikaji, 1
The phenomenon of line thinning in dots and single-line images was not improved.

For comparison, when a spot exposed area of 70 μm was developed using this organic photoreceptor using a normal contact development type reversal development method, a high image density was obtained and there was no thinning of the image line. Therefore, it has been found that the phenomenon of decrease in image density and thinning of image lines is a phenomenon peculiar to the DC electric field scattering development method.

When we investigated the cause of this in more detail, we found the following facts. Figure 3 (A) and Figure 3 (B) show the potential distribution on the photoreceptor surface in the one-dot exposed area of the selenium photoreceptor and organic photoreceptor when using the DC electric field scattering development method.
), and the development electric field diagrams between the developer carrier and the photoreceptor are shown in FIGS. 4(A) and 4(B).

In the case of a selenium photoreceptor, even though the surface potential of the photoreceptor is completely attenuated to a residual level as shown in Figure 3 (A), the center position of the dot is affected by the charge existing around the dot. Because it is strongly affected, the potential rises to about 350V. Therefore, it was found that since the potential difference with the developing bias voltage (7!50V) is as small as 400V, the image density becomes low. On the other hand, for organic photoreceptors, Figure 3 (B
), it can be seen that the potential at the center of the spot drops to near the residual type level (150V), indicating that high density development is achieved.

However, in the developing electric field diagram in Figure 4, the selenium photoreceptor (
Comparing the organic photoreceptor (Fig. 4 (A)) and the organic photoreceptor (Fig. 4 (B)), it is found that in the organic photoreceptor, the lines of electric force wrap around the photoreceptor more in the lateral direction, and the developer carrier and the photoreceptor are It has been found that the width of the area where the electric lines of force connecting the lines reach the photoreceptor becomes narrower, that is, the width of the developed image becomes narrower.

To summarize the above, selenium photoreceptors have good image line width reproduction but result in low density, while organic photoreceptors have high density but result in thin image lines.

In order to solve this problem, we conducted various experiments and found that in order to obtain a good image width when using the DC electric field scattering development method, the spot diameter must be approximately inversely proportional to the thickness of the photoconductor. It has been found that it is best to establish a relationship that is approximately directly proportional to the distance between the developer carrier and the photoreceptor. In other words, as the thickness of the photoreceptor becomes thinner, and as the distance between the developer carrier and the photoreceptor increases, the spot diameter must increase. In an apparatus that develops an image by direct current electric field, the spot diameter of the exposing beam is inversely proportional to the film thickness of the photoreceptor, and the spot diameter is set larger when the photoreceptor is thinner. Further, when the distance between the developer carrier and the photoreceptor during development is large, the spot diameter is also increased. Therefore, 1
The image width of a dot or one line can be sufficiently reproduced, and the image density can be increased. At the same time, in a device that superimposes a plurality of toners on a photoreceptor, it is possible to achieve the effect of accurately superimposing toners and improve color reproducibility.

Embodiments In the present invention, the spot diameter of the light source is defined as a range of 1/e2 (e is the base of the natural logarithm) or more of the peak intensity of the light beam. The spot diameter of the laser beam is 90 μm.

In order to obtain a good line width, the recording density of the light source spot is X dots/@臘, and the spot diameter is Dμm1.
When the thickness of the photoconductor is L1 μm and the distance between the developer carrier and the photoconductor is 524 m, the spot diameter is approximately inversely proportional to the thickness of the photoconductor and relative to the distance between the developer carrier and the photoconductor. It is preferable to have a substantially directly proportional relationship; that is, as the thickness of the photoreceptor becomes thinner, and as the distance between the developer carrier and the photoreceptor increases, the spot diameter must increase; the range is 10. D−L1/L2×23 [μm] is desirable.

Usually, the relationship between spot diameter and resolution is 1000 D
-X [μm], but when DC electric field scattering development is performed under these conditions, 1IiI brocade becomes thinner. Therefore, in the present invention, the dot diameter is increased by approximately 40% in order to eliminate thinning of the image line. At this time, if the spot diameter is increased by more than twice, the exposed image will be crushed every other line. For example, if the thickness of the photoreceptor is 20 μm,
The distance between the developer carrier and the photoreceptor is 150 μm, and 11I
When exposing 16 dots per II11 (X=16)
, the spot diameter is 75<D<172.5 [
μm] and 87.5<D<125 [μm]. Therefore, the spot diameter is 87.5<D<125
[μm] range.

By controlling the size of the spot diameter in this way, the toner image formed on the reed can be When a toner of another color is newly superimposed on the top and developed, it has the effect of preventing thinning of the image line of the toner image that is superimposed on the top, and as a result, the color reproducibility is improved, which is particularly preferable.
When is about 6 to 10, the size of one dot is sufficiently large, so there is no need to particularly control the spot diameter. Furthermore, when X is 21 or more, it is no longer possible to reproduce one dot by controlling the spot diameter. Therefore, such spot diameter control is particularly effective when the number of exposures is 12 or more and 20 or less. The film thickness of the photoreceptor is preferably thin in order to increase image density, and thick in order to reproduce good image line width. Therefore, it is desirable that the film thickness be in the range of 10 μm or more and 35 μm or less. When this photoreceptor is developed using the DC electric field development method, the distance between the photoreceptor and the developer carrier is 100 μm.
It is necessary to set the thickness to not less than m and not more than 200 μm. In order to obtain a sufficiently high image density under these development conditions, the initial surface potential of the photoreceptor must be set high, but if it is too high, the surface charge of the photoreceptor tends to leak. Therefore, it is necessary to set the absolute value of the photoreceptor surface potential to a range of 700 V or more and 1100 V or less. At this time, in order to develop sufficiently densely, it is necessary to set the potential difference between the potential of the photoreceptor after exposure and the development bias to be in the range of 500 V or more and 1000 V or less. As a photoreceptor that can obtain a high surface potential even when the film thickness is reduced, there are organic photoreceptors that use azo pigments, phthalocyanine, or the like.

On the other hand, as the spot diameter increases, the patterns exposed every other line tend to become unclear.As a measure to prevent this, the light intensity distribution of the light source is made into a Gaussian distribution, which reduces the light intensity at the periphery of the spot. It has been found that because it gradually becomes weaker, even if the outer periphery of the spot overlaps to some extent, it is difficult for the lines to be blurred and the reproducibility of every other line is easily maintained.

As such a light source, for example, a He-He laser, a semiconductor laser, etc. can be used.

Hereinafter, embodiments of the present invention will be described in detail using FIG. 1.

The developing devices 11, 12, and 13 are non-contact type non-magnetic one-component developing devices that use a DC electric field to scatter toner, and form a thin layer of toner on aluminum developing rollers 14, 15, 16 using a blade 17. 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. The developing rollers 14, 15, 16 and the photoreceptor 18
The developing units were placed facing each other around the photoreceptor 18 while keeping the darkness W1 (developing gap) constant. 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 device specifications and developing conditions Diameter of developing roller: 16 mm Peripheral speed of developing roller: 150 mm/s Thickness of toner layer on developing roller = 30 μm Rotation direction of developing roller: Opposite direction from photoreceptor 18 Developing gap: 150 μm during development .

700 μm when not developed Toner physical properties Toner charge amount Nee 3 μC/g Average particle size: 10 μm As a photoreceptor, an azo pigment organic photoreceptor drum (dielectric constant: 2.7, thickness 225 μm) 18 with a diameter of 100 mm was used.
While rotating at a circumferential speed of 15 Qmm/s, the surface potential was set to -800V by the charger 19 (corona voltage: -7kV').
Using a semiconductor laser 20 with a photoreceptor surface light intensity of 3.5 mW and a wavelength of 790 nm, the spot diameter was set to 1.
00 μm and irradiated at a recording density of 16 lines per 1 m to expose a negative yellow signal onto the photoreceptor 18 to form an electrostatic latent image.

The contrast potential of the latent image was 750.

After the latent image is reversely developed in a yellow developing device 11 in a developing state in which -700V is applied to the developing roller 14, the photoreceptor 18 is passed through a magenta developing device 12 and a cyan developing device 18 in a non-developing state. A toner image was formed. The yellow drawing line was reproduced to approximately 70 μm.

Next, the corona charger 19 (corona voltage knee'l 3
The photoreceptor 22 was charged to -850 V with a voltage of 0.0 kV), and then the photoreceptor 18 was exposed to signal light corresponding to magenta by the semiconductor laser 20 to form a magenta electrostatic latent image. At this time, the spot diameter of the laser beam was set to be the same as when forming the yellow image. Here, the surface potential of the image area formed on the Y toner image was -100V, and the contrast potential of the latent image was 750V. 11. A magenta toner image was formed by passing through a magenta developing device 12 in a developing state with −800 V applied to the developing roller 15 and a cyan developing device 13 in a non-developing state. The magenta toner developed on top of the yellow toner overlapped accurately with no thinning of the image line.

Next, again the corona charger 19 (corona voltage knee 7.5k)
V), J: The photoreceptor 18t-950V was charged.

Next, the semiconductor laser 20 was used to expose signal light corresponding to cyan to form a cyan electrostatic latent image.

At this time, the spot diameter of the laser beam was set to be the same as when forming the yellow 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 -12V.
00■, the contrast potential of the latent image was 750V. Next, the photoreceptor 18 was transferred to the yellow developer 1 in an undeveloped state.
1 and magenta developer 12, developing roller 16 and 19
A cyan toner image was formed by passing through a cyan developing device 13 in a developing state to which 00■ was applied. When the cyan toner was developed on top of the yellow and magenta toners, the image lines did not become thin and overlapped accurately.

The color toner image thus obtained on the photoreceptor 18 was transferred onto paper 22 by a transfer charger 21 and then thermally fixed.

On the other hand, after the transfer, the fur brush 23 is pressed against the photoreceptor 18,
The photoreceptor whose surface had been cleaned was subjected to the next image forming step.

As a result, the size of the individual dots was approximately 40 microns in diameter, and the line width of one line was well reproduced as approximately 70 microns. In addition, the color density of the composite color of red, green, and blue is 1.5 or more,
In addition, the Y%M and C3 color overlapping densities were 1.7 or higher, and clear color prints with accurate color overlapping were obtained.

Effects of the Invention According to the present invention, it is possible to obtain an electrophotographic apparatus that can reproduce independent dots and fine line drawings well. Further, according to the present invention, it is possible to obtain an electrophotographic apparatus that produces color images with good color overlap.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an electrophotographic apparatus according to an embodiment of the present invention, FIG. 2 is a schematic diagram of a conventional electrophotographic apparatus, and FIG. 3 is a diagram showing potential distributions on the surfaces of a selenium photoreceptor and an organic photoreceptor. FIG. 4 is an analytical diagram of an electric field during development of a selenium photoreceptor and an organic photoreceptor, and FIG. 5 is an explanatory diagram of a light source having a substantially Gaussian distribution used in the present invention. 18... Photoreceptor, 19... Charger, 2o... Semiconductor laser, 11, 12, 13... Developer Name of agent Patent attorney Toshio Nakao 1 idiot Figure 1 Fur brush Figure 2 Figure 3 is a light pigeon Figure 4 U) Non-photobody (B)

Claims (10)

[Claims] (1) a photoconductor having a photoconductor provided on a base; a DC electric field splash developer that makes an electrostatic latent image formed on the photoconductor visible by scattering toner with a DC electric field; An electrophotographic apparatus having a light source for spot exposure, the recording density of the spot light is X dots/mm, and the spot light diameter is Dμm.
, when the thickness of the photoreceptor is L1μm and the distance between the developer carrier and the photoreceptor is L2μm, 10<D・L1/L2<23[μm] and 1400<D・X<2000[μm] ] An electrophotographic device. (2) A cycle of charging, exposure, and development is repeated multiple times to form a plurality of toner images of different colors on a photoreceptor, and then the toner images are transferred all at once to an image receptor. electrophotographic equipment. (3) Claim 1 in which X is 12 or more and 20 or less
The electrophotographic device described in Section 1. (4) The electrophotographic apparatus according to claim 1, wherein L1 is 10 μm or more and 35 μm or less. (5) The electrophotographic apparatus according to claim 1, wherein L2 is 100 μm or more and 200 μm or less. (6) The absolute value of the initial surface potential of the photoreceptor is 700 V or more1
The electrophotographic apparatus according to claim 4, which has a voltage of 100V or less. (7) The electrophotographic apparatus according to claim 6, wherein the potential difference between the surface potential of the photoreceptor after exposure and the developing bias is 500 V or more and 1000 V or less. (8) The electrophotographic apparatus according to claim 4, wherein the photoconductor of the photoreceptor is an organic photoconductor. (9) The electrophotographic apparatus according to claim 1, wherein the light intensity distribution of the light source is a substantially Gaussian distribution. (10) The electrophotographic apparatus according to claim 1, wherein the light source is a laser.