JPH0734130B2 - Color electrophotographic device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color electrophotographic apparatus that 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 of different colors are formed on an electrophotographic photosensitive member (hereinafter referred to as a photosensitive member) by repeating charging, exposure, and development a plurality of times, and then the toner images are collectively transferred to a paper to perform color printing. A color electrophotographic apparatus for obtaining an image has been actively studied. Unlike the conventional color electrophotographic method, this method has an advantage that the apparatus can be downsized without a transfer drum.

An example of this type of color electrophotographic apparatus is an apparatus proposed by the inventors in Japanese Patent Application No. 62-270664. An embodiment of the present invention will be described below with reference to FIG.

The developing devices 1, 2 and 3 are non-contact type non-magnetic one-component developing devices that fly the toner by a DC electric field, and the toner is triboelectrically charged by the conductive fur brushes 4, 5 and 6 in contact with the developing roller, A thin layer of toner is formed on the developing rollers 7, 8, 9 made of aluminum by the blades 10, 11, 12. The developing device 1 contains yellow (Y), the developing device 2 contains magenta (M), and the developing device 3 contains cyan (C) insulating toner. The developing device 13 is a contact type developing device containing a two-component developer. The developing units 7, 8 and 9, 14 and the photoconductor 15 are kept at a constant gap (development gap), and the respective developing devices are installed around the photoconductor 15 so as to face each other. Each developing device is provided with a separation / contact mechanism that is close to the photoconductor during development and is separated during non-development.

An amorphous Se-Te photosensitive drum 15 having a diameter of 152 mm, which is sensitized to a long wavelength in the infrared region, is used as a photosensitive member, and is rotated at a peripheral speed of 160 mm / s. The photoconductor 15 is charged to a charging potential + 900V by a charger 16 (scorotron charger, corona voltage: + 7kV, grid voltage: 1kV). Next, the semiconductor laser 17 having a wavelength of 790 nm is emitted and exposed. Using this semiconductor laser 17, a negative black signal is exposed on the photoconductor 15 to form an electrostatic latent image. The latent image is reversely developed by the black developing device 13 in the developing state in which + 600V is applied to the developing roller 14 to form a black toner image, and then the photoconductor 15 is neutralized by the static elimination lamp 18.

Next, the photoreceptor 15 is charged to + 600V again by the corona charger 16. After that, the semiconductor laser 17 exposes the signal light corresponding to the yellow to the photoconductor 15 to form a yellow electrostatic latent image. Next, this photoreceptor is passed through a yellow developing device 1 in a developing state in which + 600V is applied to a developing roller 7, a magenta developing device 2 in a non-developing state, a cyan developing device 3 and a black developing device 13 to form a yellow toner image. Form.

Next, the photoconductor 15 was again charged to + 810V by the corona charger 16 without discharging the photoconductor 15. Then, the semiconductor laser 17 exposes signal light corresponding to magenta to form a magenta electrostatic latent image. next,
The photoconductor 15 is a yellow developing device 1 and a developing roller 8 in a non-developing state.
Then, a magenta toner image is formed by passing it through the magenta developing device 2 in the developing state in which +800 V is applied to. Then the photoconductor
15 is passed through the cyan developing device 3 and the black developing device 14 in the non-developed state. Next, replace the photoconductor 15 with the AC corona charger
Corona exposure is performed at (applied voltage; 5 kVrms), and the photoconductor 15 is charged to +800 V by the corona charger 16 again. After that, the semiconductor laser 17 exposes signal light corresponding to cyan to form a cyan electrostatic latent image. Next, the photoconductor 15 is passed through the yellow developing device 1 in the non-developing state, the magenta developing device 2, and the developing cyan developing device 3 in which + 800V is applied to the developing roller 9 to form a cyan toner image to form the photoconductor. Complete the color image on top.

The color toner image thus obtained on the photoconductor 15 is transferred onto the paper 21 by the transfer charger 20, and then is thermally fixed by the fixing device 22. On the other hand, after the transfer, the surface of the photoconductor 15 is positively charged by the pre-cleaning charger 23 (corona voltage +5.5 kV), and then the conductive fur brush 24 to which a voltage of −150 V is applied is pressed against the photoconductor 15. To clean.

In this conventional example, when a color image formed on a photoconductor is transferred, the paper is brought into close contact with the dielectric belt, the surface of the paper is pressed against the photoconductor, and the toner image is transferred from the back surface of the dielectric belt by corona discharge. . It was found that when the paper on which the toner image was transferred in this manner was then fixed by a thermal fixing device, the toner was scattered at points A and B shown in FIG. 2 and the image was disturbed.

The toner scattering will be described below. On the corona-transferred paper, toners having two kinds of charged states are attached. That is, toner recharged on the photoreceptor by a corona charger 16 such as black, yellow, magenta,
Finally, there are two types of toner that are developed and not corona charged. Since the cyan toner is transferred to the paper as it is after development, it has a smaller charge amount than the first three types of toner.
When a sheet of toner having two kinds of charged states as described above is peeled off from the transfer belt at point A in FIG. 2, a peeling discharge occurs between the paper and the transfer belt, and as shown in FIG. A large amount of black. Yellow and magenta toner are scattered,
The image was distorted as shown in FIG.

To prevent this scattering, the AC corona charger is used to neutralize the electrostatic attraction between the paper and the transfer belt immediately before separation from the transfer belt. When the paper is decharged, such peeling discharge at point A disappears. It was

However, when the paper is rushed into the fixing device in the state where the charge is removed, the mechanical vibration causes the toner to be removed by the mechanical vibration immediately before the fixing device, that is, before reaching the point B in FIG. Moving up, the image was distorted.

In view of the above point, the present invention has an object to provide a color electrophotographic apparatus for producing a color image by synthesizing a toner image on a photoconductor, which is a clear image without toner scattering. .

Means for Solving the Problems The present invention uses a plurality of color toners to repeat a charging / exposure / reverse development process to form a color image on a photoconductor, and then the dielectric image is formed on a paper by a dielectric belt. A color electrophotographic apparatus for transfer using the color image, wherein the color image is transferred to the paper, the paper is charged by a charger a to which a direct current voltage is applied, and then separated from the dielectric belt, This is a color electrophotographic apparatus in which a sheet of paper is heat-fixed after passing through a pair of chargers having a charger b and a charger c at the bottom.

Effects According to the present invention, in a color electrophotographic apparatus for synthesizing a toner image on a photoconductor to obtain a color image, a color electrophotographic apparatus having a clear image without toner scattering can be obtained.

Example First, the electrostatic behavior of toner will be described. When the paper is separated from the dielectric belt after transferring the toner from the photoconductor to the paper, even if the paper is separated as it is or if the paper is positively charged, peeling discharge occurs violently and the toner image is disturbed. If the paper is discharged with an AC corona instead, the toner on the paper is also discharged, and the toner image is disturbed even by a slight mechanical vibration. At this time, it was found that the peeling discharge from the transfer belt can be completely prevented by using the minus corona charger when separating the paper from the transfer belt. In addition, the toner image on the paper is electrostatically fixed on the paper due to the negative charge, and the toner image is not disturbed by mechanical vibration before entering the fixing device. At this time, it is not clear whether the positive corona charge causes peeling discharge and the negative corona charge does not, but it is considered that the material or the structure of the dielectric belt used for the transfer is involved.

However, when the negatively charged corona was then irradiated and the negatively charged paper was rushed into the thermal fixing machine, the toner on the paper was scattered because the fixing machine was charged. To prevent this, it is sufficient to remove the charge from the charged fixing device, but it is difficult to completely remove the charge because the fixing device rotates at high speed while applying heat. In order to prevent the toner image on the paper from being disturbed by causing it to enter the fixing device in such a charged state, the electrostatic adhesive force between the paper and the toner may be increased. To this end, it has been found that toner scattering does not occur when corona charging is performed so that the paper is sandwiched from above and below and then the paper is rushed into the fixing device.

As the transfer belt used in this embodiment, a belt having a structure in which a high resistance material layer such as polytetrafluoroethylene or polyethylene terephthalate is applied to the surface of rubber made conductive by dispersing carbon black or the like is used. Since the conductive layer cannot be transferred when it is completely made into a conductive pair, its resistance value range is preferably in the range of 10 ⁴ to 10 ¹⁰ Ωcm. Further, the thickness of the transfer belt is preferably in the range of 200 μm to 2 mm. In order to separate the paper from the transfer belt having such a structure, it is desirable that the voltage applied to the separation charger be negative. After separating the paper, the voltage applied to the upper and lower chargers of the charger pair that charges the paper again may be any combination that electrostatically attracts the toner and the paper, that is, (1) Upper charger: Plus corona Lower charger: Minus corona (2) Upper charger: Minus corona Lower charger: Plus corona (3) Upper charger: Plus corona Lower charger: AC corona (4) Upper charger: Minus Corona lower charger: AC corona (5) Upper charger: AC corona Lower charger: Minus corona (6) Upper charger: AC corona Lower charger: Plus corona

An embodiment of the present invention will be described in more detail below with reference to FIG.

The developing devices 25, 26 and 27 are non-contact type non-magnetic one-component developing devices that fly the toner by a DC electric field. The conductive fur brushes 28, 29 and 30 in contact with the developing roller frictionally charge the toner, On the developing rollers 31, 32, 33 made of aluminum, blades 34, 35, 36 form a thin layer of toner. The developing device 25 contains yellow (Y), the developing device 26 contains magenta (M), and the developing device 27 contains cyan (C) insulating toner. The black developing device 37 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 electrophotographic apparatuses. The gap between the developing rollers 31, 32, 33, 38 and the photoconductor 39 (developing gap)
Was kept constant, and each developing device was installed opposite to the periphery of the photoconductor 39. Each developing device is provided with a separating / contacting mechanism that is close to the photoconductor 39 during development and separated when not developing.

The specifications and developing conditions of the black developing device 37 and the physical properties of the toner are shown below.

<Specifications and developing conditions of developing device> Diameter of developing roller 38: 22 mm Peripheral speed of developing roller 38: 320 mm / s Developer layer thickness on developing roller 38: 400 μm Rotating direction of developing roller 38: opposite to photoconductor 39 Direction (the same direction) Development gap (gap between the surface of the development roller and the surface of the photoconductor): 300 μm during development, 2 mm during non-development <Physical properties of developer> Type of developer: Two components, toner and carrier: Developer carrier Average particle size: Approx. 50 μm Carrier type: Teflon coated ferrite Toner charge amount: +15 μC / g Toner average particle size: 12 μm Toner dielectric constant: Approx. 2 Specifications of yellow, magenta and cyan developing devices and toner The physical properties are shown below.

<Developer specifications and development conditions> Development roller diameter: 20 mm Development roller peripheral speed: 160 mm / s Development roller rotation direction: Opposite photoconductor 39 (same direction) Toner layer thickness on development roller: 30 μm Development gap (gap between the surface of developing roller and the surface of photoconductor): 150 μm during development, 2 mm during non-development <Physical properties of toner> Toner charge amount: +3 μC / g Average particle size: 12 μm Dielectric constant: Approx. 152.8 mm diameter amorphous Se-Te photoconductor drum 39 (sensitized layer thickness 63 μm, relative dielectric constant of about 7, long-wavelength sensitized function-separated selenium photoconductor) , And a half-exposure amount of 0.6 μJ / cm ^{2 at} a wavelength of 790 nm was used, and rotation was performed at a peripheral speed of 160 mm / s. The photoreceptor 39 was charged to a charging potential of + 900V by a charger 40 (scorotron charger, corona voltage: + 7kV, grid voltage: 1kV). Next, the semiconductor laser 41 having a wavelength of 790 nm was emitted and exposed.
At this time, the light intensity on the photoconductor surface was set to 1.5 mW. Using this semiconductor laser 41, a negative black signal was exposed on the photoconductor 39 to form an electrostatic latent image. The latent image on the developing roller
After applying + 600V to 38, the black developing device 37 in the developing state reversely develops it to form a black toner image, and then the photoconductor 39 is once charged with the AC corona charger 42 (applied AC voltage; 5.0 kVrms, DC bias component; + 200V). ), And the photoconductor 39 was further discharged by the cyan light discharge lamp 43. The thickness of the black toner layer developed on the photoconductor 39 is 1 to 2 layers, and the thickness of the toner layer is 10 to
It was 20 μm.

Next, the photoconductor 39 was charged to + 600V again with the corona charger 40 (scorotron charger, corona voltage: +7 kV, grid voltage: +600 V). At this time, the charging potential of the photoconductor 39 to which the black toner adhered becomes + 600V. After that, photoconductor 39
Then, the semiconductor laser 41 was exposed to the signal light corresponding to yellow 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 photosensitive member is passed through a yellow developing device 25 in a developing state in which + 600V is applied to the developing roller 31, a magenta developing device 26 in a non-developing state, a cyan developing device 27, and a black developing device 37 to pass a yellow toner image. Was formed.

This photoconductor 39 is charged with an AC corona charger 42 (applied AC voltage; 5.0
Static electricity is removed with kVrms, DC bias component; + 200V, and then corona charger 40 (scorotron charger, corona voltage: + 7k)
V, grid voltage: + 940V) and photoconductor 39 + 810V
Charged. At this time, the charging potential of the photoconductor 39 to which the black and yellow toner adhered was + 840V. Then, the semiconductor laser 41 exposed a signal light corresponding to magenta to form an electrostatic latent image of magenta.

The photoconductor 39 is a non-developed yellow developing device 25 and a developing roller 32.
Then, a magenta toner image is formed by passing the toner through a magenta developing device 26 in the developing state in which +800 V is applied to the toner image. At this time the photoconductor
The toner layer where yellow and magenta overlap on 39 is
There were 2 to 4 layers, and the thickness was 20 to 40 μm.

After that, the photoconductor 39 was passed through the cyan developing device 27 and the black developing device 37 in the non-developed state. Next, the photoconductor 39 is charged with an AC corona charger 42 (applied AC voltage; 5.0 kVrms, DC bias component;
(+ 200V) to remove the charge, and then the corona charger 40 again
39 was charged to + 850V. At this time, the charging potential of the photoconductor 39 to which only black, yellow, and magenta toner adhere is +.
It became 870V. In addition, the charging potential of the photoconductor 39 in the portion where the yellow and magenta toners overlap each other becomes + 780V.

A signal light corresponding to cyan was exposed by the semiconductor laser 41 to form a cyan electrostatic latent image. Next, the photoconductor 39 is passed through the yellow developing device 25 in the non-developing state, the magenta developing device 26, and the cyan developing device 37 in the developing state in which + 830V is applied to the developing roller 33 to form a cyan toner image to form the photoconductor. Completed the color image on 39.

The transfer belt 44 has a structure in which the surface of a conductive rubber belt in which carbon black is dispersed is coated with Teflon, and its resistance value is 10 ⁸ Ωcm and its thickness is 1 mm. Paper 45,
The transfer belt 44 is previously passed between the paper adsorption charger 46 (applied voltage; −4 kV) and the grounded conductive brush 47 which is the opposite electrode.
Adsorbed on.

After transferring the color toner image obtained on the photoconductor 39 to the paper 45 by the transfer charger 48 (applied voltage; −6 kV),
After the paper is charged by the paper separation charger 49 (applied voltage; −6 kV), the paper is separated from the transfer belt 44, and the positive charger 50 (applied voltage; +4 kV) and the negative charger 51 (applied voltage; −5 kV).
(V) is passed between a pair of chargers and charged, and is further fixed by heat by a fixing device 52.

On the other hand, after transfer, the surface of the photosensitive pair 39 is
(Applied AC voltage: 5.0 kVrms, DC bias component: +800
V), the photosensitive drum was neutralized by the cyan light neutralizing lamp 43. Then, a conductive fur brush cleaner 53 (a fur with a specific resistance of 10 ⁵ Ωcm in which carbon black is dispersed in rayon fiber is wound around a stainless steel rod) to which a voltage of −350 V is applied is pressed against the photoconductor 39 for cleaning.

As a result, a clear image without toner scattering was obtained under both environments of 35 ° C relative humidity 85% and 10 ° C relative humidity 15%.

EFFECTS OF THE INVENTION According to the present invention, in a color electrophotographic apparatus for synthesizing a toner image on a photoconductor to obtain a color image, it is possible to obtain a color electrophotographic apparatus having a clear image without toner scattering.

[Brief description of drawings]

FIG. 1 is a side view of a color electrophotographic apparatus according to an embodiment of the present invention, FIG. 2 is a side view of a conventional apparatus, and FIG. 3 is a conceptual view showing a toner scattering state generated in the conventional apparatus. FIG. 4 and FIG. 5 are diagrams for explaining the toner scattering generated in the conventional apparatus. 25 …… yellow developing device, 26 …… magenta developing device, 27 …… cyan developing device, 37 …… black developing device, 39 …… photoconductor, 40 …… corona charger, 41 …… semiconductor laser, 44 …… Transfer belt,
49 ... Separation charger, 50 ... Charger, 51 ... Charger, 52 ...
… A heat fixing machine.

Front page continuation (72) Inventor Masahiko Nakamura 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP 55-38525 (JP, A) JP 62-186238 (JP, JP, 186238) A)

Claims (9)

[Claims] 1. A method for forming a color image on a photoconductor by repeating charging, exposure and reversal development steps using toners of a plurality of colors, and then transferring the color image onto paper by using a dielectric belt. Yes, after transferring the color image to the paper, the paper is charged by a charger a to which a direct current voltage is applied, then separated from the dielectric belt, a charger b is provided on the upper side, and a charger c is provided on the lower side. A color electrophotographic apparatus, characterized in that the paper is heat-fixed after passing through between the pair of chargers. 2. The color electrophotographic apparatus according to claim 1, wherein the dielectric belt is a belt having a structure in which a high resistance material layer is formed on the surface of conductive rubber. 3. The color electrophotographic apparatus according to claim 1, wherein the voltage applied to the charger a is negative. 4. The voltage applied to the charging device b is a DC voltage having the same polarity as the charging polarity of the toner, and the voltage applied to the charging device c is a DC voltage having the opposite polarity to the voltage applied to the charging device b. The color electrophotographic apparatus according to claim 3. 5. The voltage applied to the charging device b is a DC voltage having a polarity opposite to the charging polarity of the toner, and the voltage applied to the charging device c is a DC voltage having a polarity opposite to the voltage applied to the charging device b. The color electrophotographic apparatus according to claim 3. 6. The color electrophotographic apparatus according to claim 3, wherein the voltage applied to the charging device b is a DC voltage having the same polarity as the charging polarity of the toner, and the voltage applied to the charging device c is an AC voltage. 7. A color electrophotographic apparatus according to claim 3, wherein the voltage applied to the charging device b is a direct current voltage having a polarity opposite to the charging polarity of the toner, and the voltage applied to the charging device c is an alternating voltage. 8. A color electrophotographic apparatus according to claim 3, wherein the voltage applied to the charging device b is an alternating voltage, and the voltage applied to the charging device c is a direct current voltage having the same polarity as the charging polarity of the toner. 9. A color electrophotographic apparatus according to claim 3, wherein the voltage applied to the charging device b is an alternating voltage, and the voltage applied to the charging device c is a direct current voltage having a polarity opposite to the charging polarity of the toner.