JP2825809B2 - Color electrophotographic method and apparatus - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color electrophotographic method and apparatus which can be used in a hard copy apparatus such as a color copying machine or a printer. 2. Description of the Related Art In recent years, a plurality of toner images having different colors are formed on an electrophotographic photosensitive member (hereinafter referred to as a photosensitive member) by repeating charging, exposing, and developing a plurality of times, and then the toner images are collectively transferred to paper to perform color printing. A color electrophotographic method for obtaining an image has been actively studied. This method has an advantage that, unlike the conventional color electrophotography, there is no transfer drum and the apparatus can be miniaturized. As this type of color electrophotographic apparatus, for example, there is an apparatus proposed by the inventors in Japanese Patent Application No. 62-4367. Hereinafter, an embodiment of the present invention will be described with reference to FIG. Developing units 1, 2, 3, 4 are non-contact, non-magnetic, one-component developing units for causing toner to fly by a DC electric field, and the toner is supplied by conductive fur brushes 5, 6, 7, 8 in contact with the developing roller. Triboelectrically charged, aluminum developing rollers 9, 10, 1
A thin layer of toner is formed on blades 1, 12 by blades 13, 14, 15, 16. Developing unit 1 contains yellow (Y), developing unit 2 contains magenta (M), developing unit 3 contains cyan (C), and developing unit 4 contains black (Bk) insulating toner. Then, the developing rollers 9, 10, 11, and 12 and the photoconductor 17
The developing units are opposed to each other around the photosensitive member 17 with a constant gap (developing gap). Each developing device is provided with a separation / contact mechanism that is close to the photoconductor during development and separated during non-development. The specifications of the developing device, the developing conditions, and the physical properties of the toner are shown below. Developing device specifications and developing conditions Developing roller diameter: 16 mm Developing roller peripheral speed: 150 mm / s Developing roller rotation direction: Opposite to photoconductor Thickness of toner layer on developing roller: 30 μm Developing gap (between developing roller surface and , Gap between photoreceptor surfaces): 150 μm during development, 700 μm during non-development Physical properties of toner Toner charge: +3 μC / g Average particle size: 10 μm Relative permittivity: about 2 Long wavelength sensitization in the infrared region as a photoreceptor The photosensitive drum 17 having a diameter of 100 mm (a photosensitive layer having a thickness of 60 μm and a relative dielectric constant of 6.3) is rotated at a peripheral speed of 150 mm / s. This photoreceptor 17 is charged with a charger (scorotron charger, corona voltage: +
(7 kV, grid voltage: 820 V) to charge to a surface potential of +700 V. Next, the light-emitting diode array 19 having a wavelength of 670 nm emits light and is exposed through a self-focusing rod range array 20 (Nippon Sheet Glass Co., Ltd., Selfoc lens array SLA-20). At this time, the light intensity on the photoconductor surface is 2.
It was ₂ μJ / cm ₂ . Using this light emitting diode array 19, a negative yellow signal was exposed on the photoreceptor 17 to form an electrostatic latent image. After developing the latent image in a developing state in which +600 V is applied to the developing roller 9 with the yellow developing device 1,
17 is passed through the magenta developing device 2, the cyan developing device 3, and the black developing device 4 in a non-developed state to form a yellow toner image. Next, the photoconductor 17 is charged again to +850 V by the corona charger 18. Thereafter, the photosensitive member 17 is exposed to signal light corresponding to magenta by the light emitting diode array 19 to form an electrostatic latent image of magenta. Next, the photoreceptor 17 is passed through the yellow developing device 1 in the non-developing state, the magenta developing device 2 in the developing state in which +700 V is applied to the developing roller 10, the cyan developing device 3 in the non-developing state, and the black developing device 4. A magenta toner image is formed. Next, the photosensitive member 17 is again charged to +880 V by the corona charger 18.
Charge. Thereafter, the signal light corresponding to cyan is exposed by the light emitting diode array 19 to form an electrostatic latent image of cyan. Next, the photoreceptor 17 is passed through the yellow developing device 1 in a non-developing state, the magenta developing device 2, and the cyan developing device 3 in a developing state in which +800 V is applied to the developing roller 11 to form a cyan toner image. Thereafter, the photoconductor 17 is passed through the black developing device 4 in a non-developed state. Next, the photosensitive member 17 is again charged to +880 V by the corona charger 18.
Charge. Thereafter, the signal light corresponding to black is exposed by the light emitting diode array 19 to form a black electrostatic latent image. Next, the photosensitive member 17 is applied to the yellow developing device 1, the magenta developing device 2, the cyan developing device 3, and the developing roller 12 in a non-developed state.
The toner is passed through a black developing device 4 in a developing state to which 800 V is applied to form a black toner image. The color toner image thus obtained on the photoreceptor 17 is transferred onto paper 22 by the transfer charger 21 and then thermally fixed by the fixing unit 23. On the other hand, after the transfer, the surface of the photoconductor 17 is positively charged by the pre-cleaning charger 24 (corona voltage +5.5 kV), and then the conductive fur brush 25 to which a voltage of 150 V is applied is pressed against the photoconductor 17 for cleaning. I do. Problems to be Explained by the Invention When the selenium-based photoreceptor is repeatedly and continuously imaged by this method, the red portion to which the yellow and magenta toners adhere is developed by the cyan toner even though it is not exposed. It was found that they adhered and the color purity of red gradually decreased. Examination of the cause of the decrease in color purity revealed the following facts. The cause of this problem will be described with reference to FIG. Third
The figure shows the photoreceptor when a portion (M portion) where only magenta toner adheres on the photoreceptor 17 and a red portion (R portion) where yellow and magenta overlap and adhere are charged with corona from above the toner layer. 26 shows a charging potential of 26. As shown in this figure, although the photoconductor was corona-charged under the same conditions, the naked photoconductor was 800 V, the M portion was 850 V, and the R portion was 500 V, indicating different charging potentials. When this photoreceptor is developed as it is in a cyan developing device to which a developing bias of 800 V is applied, cyan toner adheres to the R portion where the charging potential has decreased even though the R portion has not been exposed, and the red color purity decreases. I understood. In view of the above, the present invention improves the charging ability of the surface of the photoconductor where the yellow and magenta toners are overlapped when the toner image is superimposed on the photoconductor to obtain a color image, and unnecessary cyan toner adheres. It is an object of the present invention to provide a color electrophotograph and a device for obtaining red having high color purity by preventing the occurrence of color electrophotography. Means for solving the problem The characteristic color electrophotographic method repeats the image forming process consisting of DC corona charging, exposure and development steps in the order of yellow, magenta, cyan, and after forming a color image on the photoreceptor, The toner is transferred onto paper, and after at least the magenta image forming step, the photosensitive member and the insulating toner on the photosensitive member are neutralized by an AC corona by a corotron charger, and then a cyan charging step is performed. Next, the color electrophotographic apparatus includes a DC corona charger A for charging the photoreceptor, an exposure device for exposing the charged photosensitive material, a developer having yellow, magenta, and cyan developers, respectively, and the corona charger A. A charging machine, an exposing process by the exposing device, and a developing process by the color developing devices are repeated in the order of yellow, magenta, and cyan, and a transfer machine for transferring a color image formed on the photoreceptor to paper. hand,
At least after the magenta developing step and before the cyan charging step, a corotron charger B is provided which removes electricity from the photoconductor and the insulating toner on the photoconductor by an AC corona. Action It has been found that the reason why the charging potential of the photoconductor R portion to which the yellow and magenta toners overlap and adhere is lowered is the electrostatic hysteresis of the photoconductor. It is well known that if the selenium-based photosensitive member is continuously irradiated with long-wavelength infrared light such as a light emitting diode array or a semiconductor laser used as a light source in this conventional example, electrostatic fatigue becomes remarkable. This is because, when the charging / exposure cycle is repeated for a long time, negative charges are gradually accumulated in the selenium photoreceptor, and this negative charge cancels out the corona-charged positive charges, and the photoreceptor It is thought to lower the charging potential. However, this electrostatic fatigue phenomenon
When used in a general black-and-white electrophotographic apparatus, it did not appear so remarkably in the image. However, if a large amount of charged positive toner adheres to the photoconductor as in the color electrophotographic method, a strong electric field is applied to the photoconductor, and as a result, negative charges easily accumulate in the red photoconductor. Conceivable. In order to eliminate the negative space charge accumulated in the photoconductor, it has been found that removing the static electricity between the photoconductor and the toner on the photoconductor with an AC corona is very effective. In the present invention, at least after the magenta developing process and before the cyan charging process, it is effective to remove the charge on the photoreceptor and the toner on the photoreceptor with an AC corona. The same effect can be obtained even if the photosensitive member and the toner on the photosensitive member are neutralized by an AC corona during all the cyan image forming steps. This effect of removing static electricity between the photoreceptor and the toner on the photoreceptor using an AC corona was particularly effective when the photoreceptor was an amorphous selenium-based photoreceptor. It was also effective when the photosensitive member was an amorphous selenium arsenic-based photosensitive member. Hereinafter, a specific embodiment of the present invention will be described in more detail with reference to FIG. Developing units 26, 27, and 28 are non-contact non-magnetic one-component developing units that fly toner with a DC electric field, and triboelectrically charge toner with conductive fur brushes 29, 30, and 31 that are in contact with a developing roller. On the developing rollers 32, 32, 34 made of aluminum, a thin layer of toner is formed by blades 35, 36, 37. The developing unit 26 contains yellow (Y), the developing unit 27 contains magenta (M), and the developing unit 28 contains cyan (C) insulating toner. The developing device 38 is a contact-type developing device containing a two-component developer composed of an insulating toner and a magnetic carrier, which is widely used in an electrophotographic apparatus. Then, the gaps (developing gaps) between the developing rollers 32, 33, 34, 39 and the photoreceptor 40
, And each developing device was installed opposite to the periphery of the photoreceptor 40. Each developing device is provided with a separation / contact mechanism that is close to the photoconductor during development and separated during non-development. The specifications and development conditions of the black developing device 38 and the physical properties of the toner are shown below. ● Specifications of developing unit and developing conditions Diameter of developing roller 39: 22 mm Peripheral speed of developing roller 39: 320 mm / s Thickness of developer layer on developing roller 39: 400 μm Rotation direction of developing roller 39: opposite to photoconductor 40 (Same traveling direction) Developing gap (gap between developing roller surface and photoreceptor surface): 300 μm during development, 2 mm during non-development [Developer physical properties] Developer type: Two-component developer of toner and carrier Average of carrier Particle size: about 50 μm Carrier type: Teflon-coated ferrite Toner charge: +10 μC / g Average toner particle size: 8 μm Toner relative dielectric constant: about 2 The specifications, development conditions, and physical properties of the yellow, magenta, and cyan developing units It is shown below. ● Specifications of developing unit and developing conditions Diameter of developing roller: 20 mm Peripheral speed of developing roller: 160 mm / s Rotation direction of developing roller: opposite direction to photoconductor 40 (same traveling direction) Thickness of toner layer on developing roller: 30 μm Development gap (gap between development roller surface and photoreceptor surface): 150 μm during development, 2 mm during non-development [Physical properties of toner] Toner charge amount: +3 μC / g Average particle size: 10 μm Relative permittivity: about 2 Long-wave sensitized amorphous Se-Te photoconductor drum 40 with a long wavelength sensitized in the red street region (photosensitive layer thickness 60 μm, relative dielectric constant about 7, function-separated selenium photoconductor sensitized in the infrared region with a long wavelength) And rotated at a peripheral speed of 160 mm / s. This photoreceptor 40 is charged to a charger 41 (scorotron charger, corona voltage: +
(7 kV, grid voltage: 1 kV). Next, the semiconductor laser 42 having a wavelength of 790 nm was emitted and exposed. At this time, the light intensity on the photoconductor surface is 1.0 mW
Met. Using this semiconductor laser 42, a negative black signal was exposed on the photoreceptor 40 to form an electrostatic latent image. The latent image was reversal-developed by a black developing device 38 in a developed state in which +600 V was applied to the developing roller 39 to form a black toner image. At this time, the thickness of the black toner layer developed on the photoreceptor 40 was one to two, and the thickness of the toner layer was 10 to 20 μm. Next, the photosensitive member 40 is again charged with the corona charger 41 (scorotron charger, corona voltage: +7 kV, grid voltage: 600 V).
Charged to 600V. At this time, the photoconductor with the black toner attached
The charging potential of 40 became 600V. After that, the photosensitive member 40 was exposed to a signal light corresponding to yellow by the semiconductor laser 42 to form an electrostatic latent image of yellow. Here, the exposure amount of the semiconductor laser was set to 1.5 mW on the photoconductor surface. Next, the photoreceptor is passed through a yellow developing unit 26 in a developed state in which +600 V is applied to a developing roller 32 and a magenta developing unit 27, a cyan developing unit 28, and a black developing unit 38 in a non-developed state. Was formed. Next, the photosensitive member 40 was charged again to +810 V by the corona charger 41 (scorotron charger, corona voltage: +7 kV, grid voltage: 800 V) without discharging the photosensitive member 40. At this time, the charged area of the photoconductor 40 to which the black and yellow toners adhered was 810V.
Thereafter, signal light corresponding to magenta was exposed by the semiconductor laser 42 to form an electrostatic latent image of magenta. Next, the photosensitive member 40 is applied to the yellow developing device 26 and the developing roller 33 in the non-developed state by +
The toner was passed through a magenta developing device 27 in a developed state to which 800 V was applied to form a magenta toner image. At this time, the toner layer in the portion where yellow and magenta overlapped on the photoreceptor 40 was two to four layers, and the thickness was 20 to 40 μm. Thereafter, the photoconductor 40 was passed through the cyan developing device 28 and the black developing device 38 in a non-developed state. Next, the photoreceptor 40 and the toner on the photoreceptor are neutralized by an AC corona 44 (applied voltage: 5 kVrms).
The photoreceptor 40 was again charged to +800 V by the corona charger 41. At this time, the charging potential of the photoconductor 40 to which only the black, yellow, and magenta toners had adhered was 800 V. The charged potential of the photoconductor 40 at the portion where the yellow and magenta toners overlapped also became 800 V. Thereafter, signal light corresponding to cyan was exposed by the semiconductor laser 42 to form an electrostatic latent image of cyan. Next, the yellow developing device 26 with the photoconductor 40 in the non-developed state
Then, the toner was passed through a cyan developing unit 28 in a developing state in which +800 V was applied to the magenta developing unit 27 and the developing roller 34 to form a cyan toner image, thereby completing a color image on the photoreceptor. The color toner image thus obtained on the photoreceptor 40 was transferred to 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 photoconductor 40 is positively charged by a pre-cleaning charger 48 (corona voltage +5.5 kV), and then a conductive fur brush 49 to which a voltage of -150 V is applied.
Was pressed against the photoreceptor 40 for cleaning. As a result, the color density of the composite color of the solid parts of red, green and blue is 1.
A clear color image with a high color purity was obtained at a value of 5 or more and without mixing the cyan toner into the red portion. This image forming step was repeated continuously for 100 sheets, but no cyan fog occurred on the red portion. Effects of the Invention As described above, according to the present invention, when a color image is obtained by superposing a toner image on a photoconductor, the charging ability of the surface of the photoconductor at the portion where yellow and magenta toners overlap is improved. To prevent unnecessary cyan toner from adhering,
Red with high color purity can be obtained, and its practical effect is great.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of an apparatus using a color electrophotographic method according to an embodiment of the present invention, and FIG. 2 is for performing the color electrophotographic method described in the specification of the prior application. FIG. 3 is an explanatory view showing the cause of the cyan toner being developed in the red portion. 26, 27, 28: developing unit, 38: developing unit (black), 40: photoconductor, 41: corona charger, 42: semiconductor laser, 44: AC corona charger.

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Masahiko Nakamura               Matsushita, 1006 Kadoma, Kazuma, Osaka               Kiki Sangyo Co., Ltd.                (56) References JP-A-62-115172 (JP, A)                 JP-A-60-46575 (JP, A)                 JP-A-54-116929 (JP, A)                 JP-A-58-102250 (JP, A)                 JP-A-60-209755 (JP, A)

Claims (1)

(57) [Claims] A color electrophotographic method in which an image forming step including a DC corona charging, exposure, and developing steps is repeated in the order of yellow, magenta, and cyan, and a color image is formed on a photoreceptor and then transferred to paper. A color electrophotographic method, comprising: removing electricity from a photoreceptor and an insulative toner on the photoreceptor by an AC corona using a corotron charger after the image forming step; and then performing a cyan charging step. 2. A DC corona charger A for charging the photoreceptor, an exposure device for exposing the charged photoreceptor, a developer having yellow, magenta, and cyan developers, respectively; a charging step using the corona charger A; Exposure process by the device,
A color electrophotographic apparatus, comprising: a transfer device for transferring a color image formed on a photoreceptor to paper repeatedly in the order of yellow, magenta, and cyan in the order of the magenta development process. A color electrophotographic apparatus comprising: a corotron charger B for removing electricity from the photoreceptor and the insulating toner on the photoreceptor by an AC corona after the process and before the cyan charging process.