JPH083671B2 - Color-Electrophotographic method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color electrophotographic method applicable to a color hard copy device such as a color copying machine or a color printer.

Conventional technology Conventionally, charging, exposure, and development are repeated multiple times to form a plurality of toner images of different colors on an electrophotographic photosensitive member (hereinafter referred to as a photosensitive member), and then the toner images are collectively transferred to paper. Various color electrophotographic methods for obtaining a color image have been proposed.

A conventional example of this type of color electrophotographic method is shown in FIG. In the figure, 1 is a Se-Te photoconductor that rotates in the direction of the arrow, 2 is a corona charger that uniformly charges the photoconductor 1, 3 is a laser beam scanner, 4-7 are yellow (Y), A developing device in which magenta (M), cyan (C), and black (B ₁ ) toners are separately contained, 8 is a recording paper, 9 is a discharge lamp for facilitating transfer of a toner image to the recording paper 8, 10 Is a corona charger for transferring a toner image onto a recording paper, 11 is a heat fixing device, and 12 is a photoreceptor 1 after toner transfer.
A cleaning blade for removing the toner remaining on the photosensitive drum 1, and a discharge lamp 13 for erasing the electrostatic latent image on the photosensitive member 1 with light.

FIG. 5 shows a specific structure of the developing devices 4 to 7 used in FIG. In the figure, 14 is a two-component developer (hereinafter referred to as a developer) made of a mixture of positively charged toner and a magnetic carrier, 15 is a developing sleeve made of a non-magnetic material such as aluminum, and 16 has a plurality of magnetic poles. A magnet roller, 17 is a layer thickness regulating blade for making the layer thickness of the developer 14 on the developing sleeve 15 uniform, and 18 is a developer 14 on the developing sleeve 15.
A scraping plate for scraping off the toner, 19 a rotary blade for stirring the developer 14, 20 a toner for replenishment, 21 a toner replenishing roller, 22
Is a power source for electrically flying only the toner from the developer 14 on the developing sleeve 15 toward the photoconductor 1.

To fly the toner from the developing sleeve, a voltage obtained by superimposing a positive DC voltage and an AC voltage is applied to the developing sleeve 15 using the power supply 22. Further, in order to stop the flying of the toner so as not to contribute to the development, the developing sleeve 15 is electrically floated, grounded, or a negative DC voltage is applied.

Next, a method of forming a color image using the above-described color electrophotographic apparatus will be described. First, after the photoconductor 1 is positively charged by the corona charger 2, the laser beam scanner 3
Then, the yellow image signal is subjected to scanning exposure to form a negative electrostatic latent image (an electrostatic latent image in which the image area is exposed and the surface potential of the photoconductor is attenuated). Then, the electrostatic latent image is subjected to negative / positive reversal development by the developing device 4 containing the Y toner to form a yellow toner image on the photoreceptor 1. At this time, the developing sleeve of the developing device 4 containing Y toner is connected to the power source 22, but the other developing devices 5 to 7 are adjusted so that the toner does not fly. This point will be discussed in detail later. After developing with Y toner, the surface of the photoconductor 1 is irradiated with the static elimination lamp 13 to erase the yellow electrostatic latent image.

Next, by the same method as the method for forming the yellow toner image, the steps of charging, exposure, development, and light removal are repeated,
Toner images of M, C, and B ₁ are sequentially formed on the photoreceptor 1 on the Y toner image. After formation of all toner images is completed, the electrostatic latent image is erased by the charge eliminating lamp 9, and the corona charger 10 is used.
Then, the toner image is electrostatically transferred onto the recording paper 8. The toner image transferred onto the recording paper 8 is fixed by the heat fixing device 11.

On the other hand, the toner remaining on the photoconductor 1 after the electrostatic transfer is removed by the cleaning blade 12, and the photoconductor 1 is used again for the next image formation (for example, Japanese Patent Laid-Open No. 60-95456).

Problems to be Solved by the Invention When color prints are continuously taken using the conventional color electrophotographic apparatus described in FIG. 4, the developing device is contaminated with different kinds of toner in proportion to the number of prints, and the color purity of the image gradually increases. There was a problem that the Upon investigating the cause of this, when the photoconductor carrying the toner image is recharged and imagewise exposed and passed through a developing device that should not contribute to development, the toner on the photoconductor flies back to the developing sleeve. It has been found. Why this toner reverse flight occurs
Next, description will be made with reference to the drawings.

FIGS. 6 to 8 show a developing device that does not contribute to the development after the photoconductor carrying the toner image is recharged and image-exposed (the development sleeve is grounded or a negative DC voltage is applied). FIG. 3 is a diagram schematically showing the behavior of toner on the photoconductor and the developing sleeve when the toner passes through the photosensitive drum and the developing sleeve.

FIG. 6 shows a state in which the developing sleeve is grounded.
The photoconductor 23 in the areas A and C has a positive charge. The toner 24 on the photoconductor 23 is positively and strongly charged by recharging the photoconductor. Therefore, toner in area C
The toner 24 is repelled by the positive charge of the photoconductor 23, and flies backward toward the developing sleeve 25 along the line of electric force from the photoconductor 23 to the developing sleeve 25. The reverse flight of this toner is
It increases as the potential difference between the photoconductor 23 and the developing sleeve 25 increases.

FIG. 7 shows a state in which a negative DC voltage is applied to the developing sleeve 25. In this case, the photoconductor 23 in the C area
The potential difference between the developing sleeve 25 and the developing sleeve 25 is larger than that in FIG. Therefore, the developing sleeve for toner 24 in this area
The reverse flight to 25 is more than in the case of FIG. 6, and the contamination of the developing device is more severe. Further, when the voltage applied to the developing sleeve 25 is increased, the toner in the D area also starts to fly backward.

FIG. 8 shows how the developing sleeve 25 is electrically floated. As shown in the figure, the developing sleeve 25 is opposed to the electrostatic latent image on the photoconductor 23 to induce a mirror image charge having a different polarity with respect to the latent image. Therefore, the toner 26 on the developing sleeve 25 in the region B flies toward the photoconductor 23, and the toner 24 on the photosensitive member 23 in the region C flies toward the developing sleeve 25 due to the repulsion of electric charges.

Therefore, an object of the present invention is to prevent the contamination of the developing device due to the backward flight of the toner from the photoreceptor, which is a conventional problem, and to stably obtain a clear color image without the development fog caused by unnecessary toner. To provide an electrophotographic method. Another object of the present invention is to provide a color electrophotographic method in which the developing device does not need to be mechanically separated from or contacted with the photoconductor when the photoconductor passes through the development device which should not be used for development. is there.

Means for Solving the Problems The present invention uses a device in which a charging unit for charging the photosensitive member, a single exposing unit, and a plurality of developing units are sequentially arranged around the photosensitive member, and the photosensitive member is moved in one direction. Move and charge / exposure /
After development to form a first toner image on the photoconductor, charging, exposure and development are performed by reversing the moving direction of the photoconductor to form a toner image on the photoconductor carrying the first toner image. By repeating the step of superimposing the second toner image to form toner images of a plurality of different colors on the photoconductor, the conventional problem is contamination of the developing device by the backward flight of toner from the photoconductor. And a stable color image without developing fogging due to unnecessary toner can be stabilized on the photoconductor.

Action The action of the present invention will be described with reference to the drawings.

FIG. 1 shows that after the photoconductor 25 is moved in the direction of the arrow and developed by the second developing device 26 to form the toner image 26 on the photoconductor 25,
The state of recharging and imagewise exposure and development by the third developing device 27 is shown. At this time, when the photosensitive member 25 is moved in the direction of the arrow, when passing through the first developing device 28 which should not be used for development, the developing roller 29 of the developing device 28 is moved as described in the section of conventional problems. Whether the toner of the toner image 26 flies backward to the developing roller 29 or the toner 30 on the developing sleeve 29 flies to the photoconductor 25 even if it is electrically floated, grounded, or a negative DC voltage is applied. Resulting in.

Therefore, the present invention solves the conventional problems by moving the photoconductor 25 in the direction opposite to the arrow and developing it first by the third developing device 27.

Examples Hereinafter, examples of the present invention will be described.

As the charge carrier that can be used in the present invention, any ordinary electrophotographic photoconductor such as selenium, phthalocyanine and amorphous silicon can be applied.

As a light source, ordinary lighting lamps, semiconductor lasers, H
A gas laser such as e-Ne, a combination of a liquid crystal switching element and an illumination lamp, or a light emitting diode may be used.

Further, as the toner, any toner used in ordinary electrophotography such as non-magnetic and magnetic one-component toner or two-component toner can be applied. In particular, for full-color use, the specific resistance that is transparent and has excellent color purity is 10
Non-magnetic insulating toner of ¹² Ωcm or more is good.

The developing method may be a generally well-known method and is not particularly limited, but among them, a method in which the toner photoconductor is caused to fly by the action of an electric field to perform development, and a propulsive force of an air flow generated by gas discharge is used. A non-contact developing method using a dry toner, such as a method of developing a toner in the vicinity of a photoreceptor or a toner cloud developing method is preferable. Further, a developing method is preferred in which the toner is ejected in one direction toward the photoconductor by the action of the DC electric field.

Embodiment 1 FIG. 2 is a schematic view of a color printer using the color electrophotographic method according to the present invention.

31 is a photoconductor having aluminum drum deposited with coelenteru, 32 and 33 are corona chargers for charging the photoconductor, 34 is a light emitting diode array with a main emission wavelength: 660 nm, pixel density: 16dot / mm, and a focusing rod. Light source for writing combined with array lens, 35 is a developing device containing yellow toner, 36 is a developing device containing magenta toner, 37
Is a developing device containing cyan toner, 38 and 39 are static eliminating lamps, 40 is a cleaning brush, 41 is a corona transfer device, 42 is a corona peeling device, and 43 is plain paper.

The developing devices 35, 36, and 37 have the same basic configuration and have developing rollers 44, 45, and 46, respectively. As a representative, FIG. 3 shows the structure of the developing device 35. 47 is a toner container, 48 is toner, 44 is a developing roller made of cylindrical aluminum, 49 is a conductive fur brush in which rayon fibers containing carbon with a specific resistance of about 10 ⁶ Ωcm are planted on an aluminum drum, and 50 is a rubber blade. Is. 20-80 μm on the developing roller 44 by adjusting the voltage (0 to +400 V) applied to the conductive fur brush 49.
Was adjusted so that the toner layer of Also, the photoconductor 31
The gap between the developing roller 44 and the developing roller 44 is set to 0.3 mm so that the toner on the developing roller does not directly contact the photoconductor.

As the toner, a non-magnetic toner containing a resin and a pigment as main components was used. The average particle size of each toner is 10 μm, and the charge amount is 2 to
The resistance is 5 μc / g and the specific resistance is about 10 ¹⁴ Ωcm.

Next, a method of forming a color image using this apparatus will be described.

The photoconductor 31 was rotated in the direction of arrow A starting from the point P, and charged to +800 V by the corona charger 32 (corona voltage: +7 kv). Then, the writing source 34 scan-exposed the magenta image signal to form a negative electrostatic latent image.
At this time, the surface potential of the non-exposed area (non-image area) was + 800V, and that of the exposed area (image area) was + 50V.

After exposure, the developing device 35 with the photoconductor 31 and the developing roller 44 grounded
Then, the developing roller 45 was passed through a developing device 36 to which a voltage of +750 V was applied. Next, after the static elimination lamp 39 is turned on to statically eliminate the electrostatic latent image of magenta by the light, the developing roller is
46 was passed through the developing device 37 which was grounded.

As a result, a magenta toner image developed by the developing device 36 was obtained on the photoconductor 31.

Next, the photoconductor 31 carrying the magenta toner image is set to P again.
Starting from the point, corona charger 32 (corona voltage: + 7kv)
After being exposed to scanning exposure of the yellow image signal with the light source 34, the developing roller 44 is applied with a voltage of + 750V.
Passed to 35. Subsequently, after the static elimination lamp 38 was turned on to statically eliminate the electrostatic latent image, each developing roller was passed through the developing device 36 and the developing device 37, which were grounded.
A toner image in which a yellow toner image is superposed on a magenta toner image is obtained.

Next, the photoconductor 31 is rotated in the direction of the arrow B starting from the point Q and charged by the corona charger 33 (corona voltage: +7 kv), and the cyan image signal is generated by the light source 34 with respect to the magenta and yellow image signals. Then, the writing order was reversed and scanning exposure was carried out, and then the developing roller 47 was passed through a developing device 37 to which a voltage of +750 V was applied. Then, after the charge eliminating lamp 39 is turned on to photo-electrify the electrostatic latent image, the developing device 36 and the developing device 35, in which the respective developing rollers are grounded, are passed through,
A color toner image in which magenta, yellow, and cyan toner images were sequentially superposed on the photoconductor 31 was obtained.

Next, after the color toner image on the photoconductor 31 was transferred to the plain paper 43 by the corona transfer device 41, the plain paper 43 was discharged by the corona peeling device 42 to be peeled from the photoconductor 31 and fixed by heating. On the other hand, after the toner remaining on the photoconductor 31 was removed by the cleaning brush 40, the photoconductor 31 was used again for the next image formation.

As a result, a clear color print having a resolution of 12 dots / mm and a background fog density of 0.01 and no color fog was obtained.

Further, when the above-mentioned image forming process was repeated 1000 times and the state of contamination of each developing device with the different toner was examined, the different toner could not be visually identified. Further, there was almost no difference in color purity between the first and 1000th prints.

Example 2 In Example 1, an AC corona charge eliminator was attached instead of the charge removal lamps 38 and 39, and the electrostatic latent image was removed by the AC corona charge eliminator (applied voltage: 5 to 7 kv). A clear color print similar to that obtained was obtained.

Example 3 In Example 1, images were formed by replacing the developing devices 35 and 36 with each other, and a clear color print similar to that in Example 1 was obtained.

Fourth Embodiment In the first embodiment, the developing devices 35 and 37 are replaced with each other, and the photosensitive member 31 is first rotated in the direction of arrow B starting from the point Q to form toner images of magenta and yellow. When the photoconductor 31 was rotated in the direction of arrow A starting from point P and developed with cyan toner, a clear color print similar to that in Example 1 was obtained.

Example 5 In the same manner as in Example 1, a semiconductor laser having an emission main wavelength of 780 nm was used as a light source in place of the light emitting diode, and a recording density in the main scanning direction was 16 dots / mm. When formed, resolution: 11dot
A clear color print without background fog of / mm was obtained.

Comparative Example In Example 1, the developing devices 35 and 37 were replaced with each other to form a magenta toner image first, then a cyan toner image was formed, and finally a yellow toner image was formed.
The color that should originally be reproduced in green was reproduced in blue-green, which is extremely strong in cyan.

This is because when the yellow signal light was imagewise exposed on the cyan toner, most of the light was absorbed by the cyan toner, and the surface potential of the photoconductor was hardly attenuated.

EFFECTS OF THE INVENTION As described above, according to the present invention, it is possible to prevent the developing device from being contaminated due to the backward flight of toner from the photoconductor and to stably obtain a clear color image without developing fogging due to unnecessary toner. There is an effect that can be.

Further, according to the present invention, when the photoconductor passes through the developing device that should not be used for development, it is not necessary to mechanically separate the developing device from the photoconductor, so that the mechanism of the developing device is simplified. This has the effect of improving the mechanical reliability of the container.

[Brief description of drawings]

FIG. 1 is a principle view of a color electrophotographic method according to the present invention,
FIG. 2 is a principle diagram of a color printer using the color electrophotographic method of the present invention, FIG. 3 is a principle diagram of a developing device used in the printer of FIG. 2, and FIG. 4 is a principle of a conventional color electrophotographic apparatus. 5 and 5 are principle diagrams of the developing device used in the apparatus of FIG. 4, and FIGS. 6 to 8 are principle diagrams showing the problems of the conventional color electrophotography. 25 …… photoreceptor, 26,27,28 …… developer, 29 …… developing roller, 31 …… photoreceptor, 32,33 …… corona charger, 34 …… writing light source, 35,36,37… … Developer, 38,39 …… Static discharge lamp, 44,45,46 …… Developing roller.

Claims (17)

[Claims] 1. A charging / exposure / charging / exposure unit is provided by moving a photosensitive member in one direction by using a device in which a charging unit for charging the photosensitive member, one exposing unit and a plurality of developing units are sequentially arranged around the photosensitive member.
After development to form a first toner image on the photoconductor, charging, exposure and development are performed by reversing the moving direction of the photoconductor to form a toner image on the photoconductor carrying the first toner image. A color electrophotographic method comprising repeating the step of superimposing a second toner image to form toner images of a plurality of different colors on a photoconductor. 2. A color electrophotographic method according to claim 1, further comprising a second charging means between the exposing means and the first developing means. 3. The color electrophotographic method according to claim 2, further comprising a surface potential control means for controlling the surface potential of the photoconductor between the developing means and the developing means. 4. The non-contact developing method according to claim 1, wherein the developing means has a toner carrier, and the toner on the carrier is a non-contact developing method in which the toner flies in the space toward the photoconductor by the action of an electric field. 4. A color electrophotographic method according to any one of item 3. 5. The electric field according to claim 4, which is a direct current electric field.
The color electrophotographic method described in the item. 6. The color electrophotographic method according to claim 1, wherein the toner is a non-magnetic one-component toner. 7. The color electrophotographic method according to claim 6, wherein the toner is light transmissive. 8. The color electrophotographic method according to any one of claims 2 to 7, wherein the surface potential control means is light irradiation. 9. The color electrophotographic method according to any one of claims 3 to 7, wherein the surface potential control means is AC corona discharge. 10. A first developing means, a first surface potential control means, a second developing means, a second surface potential control means, around the photosensitive member,
10. The method according to claim 3, further comprising the step of providing the third developing means in this order, and developing the first electrostatic latent image obtained by first charging and exposing the photoconductor with the toner of the second developing means. The method for color electrophotography according to any one of items. 11. The first electrostatic latent image is passed through a first or third developing means in which a voltage having substantially the same potential as the latent image potential of the image area is applied to the toner carrier, and then the toner carrier is carried to the toner carrier. After passing through the second developing means to which a voltage of substantially the same potential as the latent image potential of the non-image area is applied, the photosensitive member is made substantially the same as the latent image potential of the image area by the second or first surface potential control means. After the potential voltage is applied, a step of passing the toner through the third or first developing means in which a voltage of substantially the same potential as the latent image potential of the image area is applied to the toner carrying member and performing reversal development with the toner of the second developing means. Claims Including 10
The method for color electrophotography according to item. 12. A photosensitive member on which a second electrostatic latent image is formed by being charged and exposed again after being developed with the toner of the second developing means is substantially the same as the latent image potential of the non-image area on the toner carrier. The voltage of the potential is passed through the first or third developing means, and then the first
Alternatively, the second surface potential control means sets the photosensitive member to a voltage substantially equal to the latent image potential of the image area, and then applies a voltage substantially equal to the latent image potential of the image area to the toner carrier. The second step of passing through the developing means and the first or third developing means and performing reversal development with the toner of the first or third developing means, and then charging and exposing again to form a third electrostatic latent image. The photoconductor is made to pass through the third or first developing means in which a voltage of substantially the same potential as the latent image potential of the non-image area is applied to the toner carrier, and then the second or first surface potential control means is used to remove the photoconductor. Second developing means and third or first developing means in which a voltage of substantially the same potential as the latent image potential of the image area is applied and then a voltage of approximately the same potential as the latent image potential of the image area is applied to the toner carrier. Pass it to the third
12. The color electrophotographic method according to claim 11, further comprising a third step of performing reversal development with the toner of the first developing means. 13. The color electrophotographic method according to claim 11 or 12, wherein a voltage substantially equal to the latent image potential of the non-image area is ground potential. 14. Each of the toners contained in the first to third developing units is yellow, magenta, and cyan, and is obtained by superposing two kinds of toners selected from the three kinds of toners. The method according to any one of claims 10 to 13, wherein the exposure means having a dominant wavelength in the light transmission spectrum is used to develop with the selected two kinds of toners first, and then develop with the remaining toners. The color electrophotographic method described in Crab. 15. The dominant wavelength of the light source used for the exposure means is 640 nm.
15. The color electrophotographic method according to claim 14, which is the above and the toner to be developed first is yellow and magenta. 16. The color electrophotographic method according to claim 15, wherein the light source is a light emitting diode having a main wavelength of 650 to 680 nm. 17. The color electrophotographic method according to claim 15, wherein the light source is a semiconductor laser.