JPH01170956A - Color electrophotographic method - Google Patents

Abstract

PURPOSE:To prevent a waste cyan toner from attaching and to obtain red color of high purity by exposuring corona of polarity opposite to electrification polarity on a photosensitive body after the magenta developing process magenta and before the cyan electrifying process. CONSTITUTION:The corona of polarity opposite from the photosensitive body 40 is exposured on the photosensitive body 40 after the magenta developing process and before the cyan electrifying process. This corona exposure is effective when the photosensitive body 40 is an amorphous selenium based photosensitive body and an amorphous selenium arsenic based photosensitive body. In addition, when an organic photosensitive body such as azo based and phthalocyanine based bodies which are negatively electrified is used by reversal development, plus corona electrification is effective. Thus, the sticking of the waste cyan toner can be prevented and high pure red color can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a color electrophotographic method that can be used in hard copy devices such as color copiers or printers.

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. 62-4367. Hereinafter, an embodiment of the present invention will be described using FIG. 2.

Developing device L 2.3.4 is a non-contact type non-magnetic one-component developing device that uses a DC electric field to scatter toner, and rubs the toner with a conductive fur brush 5.6.7.8 that is in contact with the developing roller. charged, aluminum developing roller 9.10;
The blades 13, 14, 15, 16 are arranged to form a thin layer of toner on the 1L12. The developing device 1 contains yellow (Y) insulating toner, the developing device 2 contains magenta (M), the developing device 3 contains cyan (C), and the developing device 4 contains insulating toner of black (Bk). And developing roller 9.1O111
, 12 and the photoreceptor 17 (developing gap) is kept constant, and the developing units are disposed opposite to each other around the photoreceptor 17.

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.

Developer specifications and development conditions Developing roller diameter: 165w Peripheral speed of developing roller: 150++w/s.

Rotation direction of the developing roller: Opposite direction from the photoconductor Thickness of toner layer on the developing roller = 30 μm Development gap (gap between the surface of the developing roller and the surface of the photoconductor): 150 μm when developing, 700 μm when not developing Toner physical properties Toner charge Amount: +3μC/g Average particle size: 1011m Relative dielectric constant: Approximately 2 As a photoreceptor, an amorphous 5e-Te photoreceptor drum 17 with a diameter of 100cm (photosensitive layer thickness 60cm) is sensitized to long wavelengths in the infrared region.
μm, relative dielectric constant 6.3), and rotated at a circumferential speed of 150 m5/S. This photoreceptor 17 is connected to a charger 18 (Scorotron charger, corona voltage: +7 kV, grid voltage: 8
20V) to a surface potential of +700V. Next, the light emitting diode array 19 whose wavelength stops at 670 is caused to emit light and is exposed through a self-focusing rod lens array 20 (manufactured by Nippon Sheet Glass Co., Ltd., SELFOC Lens Array 5LA-20). At this time, the light intensity on the photoreceptor surface is 2.
It was 2 μJ/c-rl. Using this light emitting diode array 19, a negative yellow light signal was exposed onto the photoreceptor 17 to form an electrostatic latent image. The latent image is transferred to the developing roller 9
After reversal development is performed in a yellow developing device 1 in a developing state to which +600V is applied to the photoreceptor 17, the photoreceptor 17 is passed through a magenta developing device 2, a cyan developing device 3, and a black developing device 4 in a non-developing state.
Form a yellow toss image.

Next, the photoreceptor 17 is charged to +850V using the corona charger 18 again.
is charged with electricity. Thereafter, the photoreceptor 17 is exposed to signal light corresponding to magenta by the light emitting diode array 19 to form a magenta electrostatic latent image.

Next, the photoreceptor 17 is passed through a yellow developer l in a non-developing state, a magenta developer 2 in a developing state with +700V applied to the developing roller 10, and a cyan developer 3 and a black developer 4 in a non-developing state. Forms a magenta toner image.

Next, the photoreceptor 17 is charged by the corona charger 18 again to +8
Charge to 80v. After that, the light emitting diode array 19
A cyan electrostatic latent image is formed by exposing signal light corresponding to cyan. Next, the photoreceptor 17 is passed through a yellow developing device 1 and a magenta developing device 2 in a non-developing state, and a cyan developing device 3 in a developing state in which +800V is applied to the developing roller 11 to form a cyan toner image. Thereafter, the photoreceptor 17 is passed through the black developing device 4 in a non-developing state.

Next, the photoreceptor 17 is charged to +8 again by the corona charger 18.
Charge to 80v. After that, the light emitting diode array 19
A black electrostatic latent image is formed by exposing signal light corresponding to black. Next, the photoreceptor 17 is transferred to a yellow developing device l in a non-developing state.
, a magenta developing device 2, a cyan developing device 3, and a black developing device 4 in a developing state with +800V applied to the developing roller 12.
to form a black toner image.

The color toner image thus obtained on the photoreceptor 17 is transferred onto paper 22 by a transfer charger 21, and then thermally fixed by a fixing device 23. On the other hand, after the transfer, the surface of the photoreceptor 17 is
Pre-cleaning charger 24 (corona voltage +5.5kV)
After being positively charged, the conductive fur brush 25 to which a voltage of -150V has been applied is brought into pressure contact with the photoreceptor 17 for cleaning.

Problem to be Solved by the Invention In this method, when images are repeatedly and continuously formed on a photoreceptor,
It was found that the cyan toner developed and adhered to the red part to which the yellow and magenta toners had adhered even though it had not been exposed, and the color purity of the red gradually decreased.

When we investigated the cause of this decrease in color purity, we found the following facts. The cause of this problem will be explained using FIG. 3. FIG. 3 shows a portion of the photoreceptor 17 to which only magenta toner has adhered (M portion) and a red portion (R portion) to which yellow and magenta have overlapped, when corona charging is applied from above the toner layer. It shows the charged potential of the photoreceptor 26. As shown in this figure, even though the photoreceptor was corona charged under the same conditions, the bare photoreceptor was 800V and the M section was 850V.

It was found that the R part had a voltage of 500V, and had a different charging potential. If this photoreceptor is developed as it is with a cyan developer to which a developing via support of 800 V is applied, cyan toner will adhere to the R area where the charging potential has decreased even though it has not been exposed, and the color purity of red will decrease. That's what I found out.

A similar phenomenon also appeared when an azo-based or phthalocyanine-based organic photoreceptor was used as a photoreceptor.

In view of this, the present invention improves the charging ability of the surface of the photoconductor where yellow and magenta toner overlap when toner images are superimposed on the photoconductor to obtain a color image, thereby preventing unnecessary cyan toner from adhering to the photoconductor surface. It is an object of the present invention to provide a color electrophotographic method that prevents this from occurring and obtains red with high color purity.

Means for Solving the Problems The present invention consists of: - Repeating charging, exposing, and developing steps for each color image formation process of yellow, magenta, and cyan to form a color image on a photoreceptor, and then transferring it to paper. This color electrophotographic method includes a step of exposing a photoreceptor to corona having a polarity opposite to that of the photoreceptor after a magenta developing step and before a cyan charging step.

Effect: It has been found that the reason why the charging potential of the R portion of the photoreceptor to which the yellow and magenta toners overlap and adhere is lowered is due to the electrostatic history phenomenon of the photoreceptor. It is well known that if a photoreceptor is continuously irradiated with long wavelength light in the infrared region, such as the light emitting diode array or semiconductor laser used as a light source in this conventional example, electrostatic fatigue becomes significant. This is because when the charging/exposure cycle is repeated over a long period of time, a charge with a polarity opposite to that of the photoreceptor gradually accumulates in the photoreceptor, and this charge with the opposite polarity replaces the corona charge. It is thought that this cancels out the electrification potential of the photoreceptor and lowers the charged potential of the photoreceptor. However, this electrostatic fatigue phenomenon did not appear so conspicuously in images when used in a general black-and-white electrophotographic device. However, when a large amount of toner charged to the same polarity as that of the photoconductor adheres to the photoconductor as in this color electrophotographic method, a stronger electric field is applied to the photoconductor, resulting in damage to the photoconductor in the red area. It is thought that charges with a polarity opposite to that of the photoreceptor tend to accumulate. By exposing this electrostatically fatigued photoconductor to a corona with a polarity opposite to that of the charged polarity, the polarity of the toner attached to the photoconductor is made to be opposite to the polarity of the charged toner during development. It was found to be very effective in restoring charging capacity.

Example In the present invention, it is effective to expose the photoreceptor to corona at least after the magenta developing step and before the cyan charging step. A similar effect can be obtained even if the explosion continues during the period. This corona exposure effect was particularly effective when the photoreceptor was an amorphous selenium-based photoreceptor. It was also effective when the photoreceptor was an amorphous selenium arsenic photoreceptor. Further, when a negatively charged organic photoreceptor such as an azo or phthalocyanine type photoreceptor is used as a photoreceptor in a reversal development method, positive corona charging is effective.

Hereinafter, specific embodiments of the present invention will be described in more detail with reference to FIG.

The developing devices 26, 27, and 28 are non-contact type non-magnetic one-component developing devices that use a DC electric field to scatter the toner, and the toner is triboelectrically charged with a conductive fur brush 29, 30, 31 that is in contact with the developing roller. Aluminum developing roller 32.3
3.34, a thin layer of toner is formed by blades 35, 36, 37. The developer 26 is yellow (Y), the developer 27 is magenta (M), the developer 2 is
8 contains cyan (C) insulating toner. The developing device 38 is a contact type developing device containing a two-component developer consisting of an insulating toner and a magnetic carrier, which is widely used in electrophotographic devices. and developing roller 32, 33, 34.
The developing devices were disposed opposite to each other around the photoreceptor 40 with a constant gap (developing gap) between the photoreceptor 39 and the photoreceptor 4o. 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 black developer 38 and the physical properties of the toner are shown below.

・Developer specifications and developing conditions Diameter of developing roller 3″9: 22nnw developing roller 39
Peripheral speed: 3° 2oIII/s Developer layer thickness on the developing roller 39: 40011 m Rotation direction of the developing roller 39 2t% Opposite direction (same traveling direction) to the light body 4o Developing gap (between the developing roller surface and the photosensitive member 4o) Gap on body 4θ): 300 μm during development 2III+ C developer physical properties during non-development Type of developer: Two-component developer of toner and carrier Average particle size of carrier: Approximately 50 μm Type of carrier: Teflon coated ferrite toner Charge Amount: +10 μC/g Toner average particle size: 8 μI Toner dielectric constant: Approx. 2 The specifications and development conditions of yellow, magenta, and cyan developing devices and the physical properties of the toner are shown below.

・Developer specifications and development conditions Development roller diameter: 20cm Development roller circumferential speed: 160m/S Development roller rotation direction: Opposite direction (same traveling direction) as the photoreceptor 4o Toner layer thickness on the development roller: 30μm development gap (
Gap between image roller surface and photoconductor surface): 150 μm during development, 211III when not developed [Physical properties of toner] Toner charge amount: +3 μC/g Average particle size: 10 μm Relative dielectric constant: Approx. 2 Red as photoconductor Diameter 152a* with long wavelength sensitization in the outer region
Amorphous 5e-Te photoreceptor drum 4Q (photosensitive layer thickness 6
A functionally separated selenium photoreceptor with a dielectric constant of 0 μm and a relative dielectric constant of about 7, sensitized to long wavelengths in the infrared region was used and rotated at a circumferential speed of 160 μ/S. This photoreceptor 40 is charged to a charging potential of +900 V using a charger 41 (Scorotron charger, corona voltage: +7 kV, grid voltage: 1 kV).
The 0n- semiconductor laser 42 was emitted to perform exposure. At this time, the light intensity on the photoreceptor surface was 1.0 mW. Using this semiconductor laser 42, a negative black signal was exposed onto the photoreceptor 4θ to form an electrostatic latent image. The latent image was reversely developed by a black developing device 38 in a developing state in which +600V was applied to the developing roller 39 to form a black toner image, and then the photoreceptor 40 was neutralized by a neutralizing lamp 43 . At this time, the thickness of the black toner layer developed on the photoreceptor 4θ was 1 to 2 layers, and the thickness of the toner layer was 10 to 20 μm.

Next, the photoreceptor 40 was charged to +600V again using the corona charger 41 (Scorotron charger, corona voltage: +7kV, grid voltage: 6oov).

At this time, the charged potential of the photoreceptor 4o to which the black toner was attached reached 5oov, and then the photoreceptor 4o was exposed to signal light corresponding to yellow by the semiconductor laser 42 to form a yellow electrostatic latent image. . Here, the exposure amount of the semiconductor laser was set to 1.5 mW on the photoreceptor surface. Next, this photoreceptor is passed through a yellow developer 26 in a developing state where +600V is applied to the developing roller 32, a magenta developer 27 in a non-developing state, a cyan developer 2, and a black developer 38 to form a yellow toner. After forming the image, the photoreceptor 40 is then charged again with a corona charger 41 (scorotron charger, corona voltage: +7 kV, without photostatic charge removal).
Grid voltage: 8ooV) increases the photoreceptor 40 by +81
It was charged to 0V. At this time, the charged potential of the photoreceptor 4o to which the black and yellow toners were attached became 810V. Thereafter, a signal light corresponding to magenta was exposed to the semiconductor laser 4 (from the semiconductor laser 4) to form a magenta electrostatic latent image.
Magenta developer 2 in the developing state with +800■ applied to 3
7 to form a magenta toner image. At this time, the toner layer in the overlapping portion of yellow and magenta on the photoreceptor 40 has 2 to 4 layers, and its thickness is 20 to 40 mm.
It was μm. Thereafter, the photoreceptor 40 was passed through a cyan developer 28 and a black developer 38 in a non-developing state. Next, the photoreceptor 40 is connected to the corona charger 44 (applied voltage knee 5k).
After being exposed to V), the photoreceptor 40 was again charged to +800V by the corona charger 41. At this time, the charged potential of the photoreceptor 40 to which only black, yellow, and magentan toners were attached was 800V. In addition, the charged potential of the photoreceptor 40 in the area where the yellow and magenta toners overlap is 800.
V was closed.

Thereafter, the semiconductor laser 42 was used to expose signal light corresponding to cyan to form a cyan electrostatic latent image.

Next, the photoreceptor 40 is passed through a yellow developer 26 in a non-developing state, a magenta developer 27, and a cyan developer 28 in a developing state with +800V applied to the developing roller 34 to form a cyan toner image on the photoreceptor. Completed color image above.

The color toner image thus obtained on the photoreceptor 40 was transferred onto paper 46 by a transfer charger 45, and then thermally fixed by a fixing device 47. On the other hand, after the transfer, the surface of the photoreceptor 40 is
Charger 4 days before cleaning (corona voltage +5.5kV)
After being positively charged, a conductive fur brush 49 to which a voltage of -150 V was applied was brought into pressure contact with the photoreceptor 40 for cleaning.

As a result, the color density of the composite color of red, green, and blue is 1.
5 or higher, and a clear color image with high color purity was obtained without cyan toner being mixed into the red area. This image forming process was repeated for 100 sheets in succession, but no cyan fogging occurred in the red portion.

DETAILED DESCRIPTION OF THE INVENTION As described in detail, according to the present invention, when toner images are superimposed on a photoreceptor to obtain a color image, the charging ability of the surface of the photoreceptor in the area where yellow and magenta toners overlap is improved. It is possible to prevent unnecessary cyan toner from adhering, and to obtain a red color with high color purity, which has great practical effects.

[Brief explanation of the drawing]

The first part is a block diagram of an apparatus using a color electrophotographic method according to an embodiment of the present invention, FIG. 2 is a block diagram of an apparatus for performing a conventional color electrophotographic method, and FIG. FIG. 3 is an explanatory diagram showing the cause of toner development. 26.27.28...Developer, 38...Developer (black), 40...Photoreceptor, 41...Corona charger, 42
... Semiconductor laser, 44... Negative corona charger. Name of agent: Patent attorney Toshio Nakao (1 person) Figure 2

Claims (4)

[Claims] (1) A color electrophotographic method in which charging, exposure, and development steps are repeated for each color image formation process of yellow, magenta, and cyan to form a color image on a photoreceptor and then transferred to paper. 1. A color electrophotographic method comprising the step of exposing a photoreceptor to a corona having a polarity opposite to the charging polarity after the developing step and before the cyan charging step. (2) The color electrophotographic method according to claim 1, wherein the photoreceptor is an amorphous selenium-based photoreceptor. (3) The color electrophotographic method according to claim 1, wherein the photoreceptor is an amorphous selenium arsenic photoreceptor. (4) The color electrophotographic method according to claim 1, wherein the photoreceptor is an organic photoreceptor.