JPH0799440B2 - Color-Electrophotographic method - Google Patents

Description

The present invention relates to a color electrophotographic method applicable to a color copying machine or printer.

Conventional technology Conventionally, charging, exposure, and development are repeated multiple times to previously 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 plain paper. There have been proposed various color electrophotographic methods for obtaining a color image.

A conventional example of such a color electrophotographic method is shown in FIG. In the figure, 1 is a Se-Te photosensitive member that rotates in the direction of the arrow, 2 is a corona charger that uniformly positively charges the surface of the photosensitive member 1, 3 is a laser beam scanner, 4 to 7 are yellow (Y), respectively. Magenta (M), Cyan (C), Black (B
l) A developing device containing toner separately, 8 is plain paper,
9 is a discharge lamp for facilitating electrostatic transfer of the toner image onto the plain paper 8, 10 is a corona charger for electrostatically transferring the toner image onto the plain paper 8, 11 is a heat fixing device, and 12 is a toner image. Plain paper 8
A cleaning blade for removing the toner remaining on the photoconductor 1 after the electrostatic transfer to the photoconductor 1, and a charge eliminating lamp 13 for erasing the electrostatic latent image on the photoconductor 1 with light.

Next, FIG. 12 shows a concrete configuration example of the developing devices 4 to 7. In the figure, 14 is a two-component developer (hereinafter referred to as developer) composed of a mixture of positively charged toner and a magnetic carrier, 15 is a developing sleeve composed of a non-magnetic material such as aluminum, and 16 has a plurality of magnetic poles. Magn roll, 17 is a layer thickness regulating blade for regulating the layer thickness of the developer 14 on the developing sleeve 15, 18 is a scraping plate for scraping off the developer 14 on the developing sleeve 15 after development, and 19 is agitating the developer 14. Rotating blades,
Reference numeral 20 is a toner for replenishment, 21 is a toner replenishing roller, 1 is a photoconductor provided with a gap at a position not contacting the developer 14 on the developing sleeve 15, and 22 is toner from the developer 14 on the developing sleeve 15. It is a power supply for electrically flying toward the photoconductor 1.

When a voltage obtained by superimposing a high voltage AC voltage on a positive DC voltage generated from the power source 22 is applied to the developing sleeve 15 here, the toner flies toward the photoconductor.

Further, in order to put the developing device in a state where it is not used for development, the developing sleeve 15 is electrically floated, grounded, or a negative DC voltage is applied to the developing sleeve 15.

Next, a method for forming a color image using the above-mentioned color electrophotographic apparatus will be described. First, after the photoconductor 1 is positively charged by the corona charger 2, the yellow image signal is scanned and exposed by the laser beam scanner 3, and the negative electrostatic latent image (the image area is exposed and the surface potential of the photoconductor is attenuated). Form). Then, the electrostatic latent image is negatively and positively reversed-developed by the developing device 4 containing Y toner to form a yellow toner image on the photoconductor 1. At this time, only 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 toner does not fly. After developing with Y toner, remove the charge on the photoconductor 1
To irradiate the entire surface and photo-eliminate the electrostatic latent image of yellow.

Then, charging was performed by the same method as that for forming the yellow toner image. By repeating the steps of exposure, development and photo-erasing, toner images of Y, M, C and Bl are formed on the photoconductor 1. After all the toner development is completed, the electrostatic latent image is preliminarily photo-erased by the static elimination lamp 9, and the toner image is electrostatically transferred onto the plain paper 8 by the corona charger 10. The toner image transferred onto the plain paper 8 is heated and fixed by the heat fixing device 11. On the other hand, the toner remaining on the photoconductor 1 after electrostatic transfer is removed by the cleaning blade 12 and one cycle of color image formation is completed (for example, Japanese Patent Laid-Open No. 60-95456).

Problems to be Solved by the Invention When the conventional color electrophotographic apparatus described in FIG. 11 is continuously operated, there is a problem that the developing device is contaminated with different kinds of toner in proportion to the copy amount. When the cause of this problem was investigated, when the photoconductor bearing the toner image was recharged and image-exposed and then passed through a developing unit that should not contribute to development, part of the toner on the photoconductor was developed. It turned out to fly back to the sleeve. The toner reverse flight phenomenon will be described in more detail with reference to the drawings.

FIGS. 13 to 15 are schematic views showing the behavior of each toner on the photoconductor and the developing sleeve when the photoconductor having the toner image is recharged and image-exposed and then passes through the developing device which should not contribute to the development. FIG.

FIG. 13 shows a state in which the developing sleeve is grounded. A
The photoconductor 1 in the areas C and C is positively charged by recharging. Further, the toner 24 on the photoconductor 23 is more positively and strongly charged by the corona charger at the time of recharging. Therefore, the toner 24 in the area C is repulsed by the positive charge on the photoconductor 23, the photoconductor 23 and the developing sleeve 25.
Due to the action of the electric field generated between and, the particles flies backward toward the developing sleeve 25.

FIG. 14 shows a state in which a negative DC voltage is applied to the developing sleeve. In this case, the positively charged toner 25 on the developing sleeve 25 is electrically strongly attracted to the developing sleeve 25 to which a negative voltage is applied, so that the toner flying from the developing sleeve 25 to the photoconductor 23 is prevented. Is very effective to do. However, the electric field strength between the photoconductor 23 and the developing sleeve 25 in the C region is larger than that in the C region in FIG. Therefore, the amount of the toner 24 on the photoconductor 23 in the area C will fly more backward than in FIG.
Further, when the DC voltage applied to the developing sleeve 25 is increased, the toner 24 in the D area also starts to fly backward.

FIG. 15 shows a state in which the developing sleeve is electrically floated. The positive charge on the photoconductor 23 causes the developing sleeve 25 to undergo induction polarization as shown in the figure. Therefore, part of the toner 26 on the developing sleeve 25 in the area B flies toward the photoconductor 23. In addition, the toner on the photoconductor 23 in the area C
A part of 24 flies backward toward the developing sleeve 25.

As described above, the conventional method cannot prevent the contamination of the developing device due to the invasion of different kinds of toner, and there is a problem that a clear color copy cannot be stably obtained.

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 copy without the development fog caused by unnecessary toner. An object is to provide an electrophotographic apparatus.

Means for Solving the Problems In the present invention, a plurality of developing devices having means for flying toner on a toner carrier to develop an electrostatic latent image are provided with a constant gap between the photoconductor and the toner carrier. Placed, charging, exposure,
In a color electrophotographic method including a step of repeating development steps a plurality of times to superimpose toner images of a plurality of different colors on the same photoconductor, the photoconductor bearing the first toner image is charged and exposed to light. When the electrostatic latent image of No. 2 is formed and developed with the second toner, the toner on the toner carrier of another developing device, which should not contribute to the development, is removed, and the toner carrier of the other developing device is removed. By applying a DC voltage of approximately the same potential as the latent image potential of the non-image area to the toner, it is possible to prevent the toner from flying back from the photoconductor carrying the toner image and to make the development with unnecessary toner clear without blur. A stable color copy can be obtained.

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

FIG. 1 shows a state in which a photoreceptor having a toner image is recharged and image-exposed, and then passed through a developing device which is set to a state where it does not contribute to development. No toner is applied to the developing sleeve 25, and a positive DC voltage having substantially the same potential as the latent image potential of the non-image area of the photoconductor 23 is applied. Therefore, since there is almost no potential difference between the developing sleeve 25 and the photoconductor 23 in the region C, the toner 24 on the photoconductor 23 in this region does not fly. Further, in the area D, the direction of the electric field between the developing sleeve 25 and the photoconductor 23 is in the direction in which the flying of the toner 24 in this area is suppressed, so that the photoconductor 23 to the developing sleeve 25
The reverse flight of the toner to the toner does not occur.

Therefore, in the present invention, the reverse flight phenomenon of the toner from the photoreceptor having the toner image does not occur, and the contamination of the developing device with the different toner can be prevented.

Examples Examples of the present invention will be described below.

2 to 8 are schematic views showing the outline of the color electrophotographic method according to the present invention. First, the photoconductor 23 is positively charged by the corona charger 27 (FIG. 2). The photoconductor may be any ordinary electrophotographic photoconductor in which a photoconductive substance such as selenium tellurium, selenium arsenide, or amorphous silicon is deposited on a conductive substrate such as aluminum.

Next, the first light image is exposed to form a first negative electrostatic latent image on the photoconductor 23 (FIG. 3).

After the image exposure, the first toner carrier 28 carrying the positively charged first toner 24 is opposed to the photoconductor 23 so as not to come into contact with the toner 24. Then, a DC voltage having substantially the same potential as the latent image potential of the non-image area is applied to the toner carrier 28 to cause the toner 24 to fly toward the photoconductor 23, and the electrostatic latent image is negatively and positively reverse-developed. 1 toner image is formed (FIG. 4). Insulating toner is preferable, and its charge amount is 0.1 to 1
0 μc / g is preferable. Desirably, 1 to 6 μc / g is good. The gap between the toner carrier and the photoconductor is preferably 0.5 mm or less, and more preferably 0.3 mm or less.

Although the non-contact developing method utilizing the toner flying by the direct current electric field is used to obtain the first toner image here, other non-contact developing methods such as powder cloud developing method may be used and are not particularly limited. .

The photoconductor bearing the first toner image passes through a plurality of developing devices which should not be used for development. At this time, the toner carrier 25 of the developing device which should not be used for development is grounded (FIG. 5). Therefore, since there is no potential difference between the toner carrier 25 and the photoconductor 23, neither the toner 26 on the toner carrier 25 nor the toner 24 on the photoconductor 23 flies. At this time, the developing device that should not be used for development may be in the state described in FIG.

Next, the photoconductor 23 carrying the first toner is recharged again by the corona charger 27 (FIG. 6), and the second optical image is exposed to form the second negative electrostatic latent image. (Fig. 7).

The second negative latent image is developed by the same method as shown in FIG. 4 in which the toner carrier carries the second toner having a color different from that of the first toner.

Toner carrier of developing device that should not be used for other development
25 is a toner-free naked state and a photoconductor
A voltage of approximately the same potential as the non-image area of 23 is applied (8th
Figure). By doing so, the toner image on the photoconductor is held as it is on the photoconductor as described in detail in the operation of the present invention.

To form the third or fourth toner image on the photoconductor, the steps described with reference to FIGS. 2 to 8 are repeated to form a color image composed of a plurality of types of color toners on the same photoconductor. Is obtained.

The case of reversal development has been described above, but it goes without saying that the color electrophotographic method according to the present invention can be applied to regular development.

FIG. 9 is a schematic view of a color printer using the color electrophotographic method of the present invention.

29 is a photoconductor in which coelenterite is vapor-deposited on an aluminum drum, 30 is a corona charger for charging the photoconductor, 31 is a light emitting diode array with an emission wavelength of 670 mm, 32 is a converging rod array, and 33 to 35 are Y and M respectively. , A developing device containing C toner separately, 36 is a discharging lamp, 37 is a corona charger for transfer, 38 is an AC discharging device for peeling paper, 39 is plain paper, and 40 is a cleaning brush.

The construction of the developing units 33 to 35 is shown in FIG. 41 is a toner container, 42 is toner, 43 is a developing roller made of cylindrical aluminum, 44 is a fur brush in which rayon fibers containing carbon with a specific resistance of 10 ⁶ Ωcm are planted on an aluminum drum, and 45 is It is a rubber blade. The gap between the photoconductor 29 and the developing roller 43 was 0.15 mm. As the Y, M, and C toners, non-magnetic toner containing resin and pigment as main components was used.
The average particle size of each toner is 10 μm, the charge amount is 2-4 μc / g,
Non-resistance is 10 ¹⁴ or more Next, a method for forming a color image will be described.

While rotating the photoconductor 29 in the direction of the arrow, the corona charger 30
The photoconductor 29 was charged to +800 V with (corona voltage: 7 kV). Next, the yellow image signal was scanned and exposed by the light emitting diode array 31 to form an electrostatic latent image in which the non-image area was + 800V and the image area was + 80V. After exposure, the photoconductor 29 is transferred to three developing units 33.
.About.35 and the electrostatic latent image was reverse developed with Y toner.
The conditions of each developing device at this time are shown below.

+750 for the developing roller of the developing unit 33 containing Y toner
V, + 100V DC voltage was applied to the fur brush. Then, a thin layer of Y toner (about 40 μm) was formed on the developing roller, and the Y toner flew from the developing roller toward the photoconductor in the vicinity of the closest contact point with the photoconductor, and was developed with the Y toner.

On the other hand, developing units 34 and 35 containing M toner and C toner
When each of the developing rollers of No. 2 was grounded, there was no development fog on the photosensitive member due to the M toner and the C toner.

After the development, the photoconductor 29 carrying the Y toner image is removed from the discharge lamp 36.
After irradiating the entire surface with the light to remove static electricity from the electrostatic latent image, use the corona charger 30 (corona charging: +7 kV) to re-apply the photoconductor 2 from the top of the toner.
9 charged. The surface potential of the photoconductor 29 was +800 V regardless of the presence or absence of toner.

Next, the magenta image signal is subjected to scanning exposure with the light emitting diode array 31, and the surface potential of the non-image area is + 800V, the surface potential of the image area is + 80V in the portion without Y toner, and + 110V in the portion with Y toner. An electrostatic latent image was formed. After exposure, the developing device with the photoconductor 29 set under the following conditions
33 to 35, and the electrostatic latent image was reversely developed with M toner.

When a DC voltage of +750 V and a voltage of -200 V was applied to the developing rollers of the developing units 33 and 35 containing the Y toner and the C toner, respectively, the toner on the developing rollers was removed. A DC voltage of +750 V was applied to the developing roller of the developing device 34 containing M toner, and a DC voltage of +100 V was applied to the fur brush. On the photosensitive member 29, a toner image composed of Y toner and M toner was obtained. In addition, the reverse flight of Y toner to 33 and 35 developing devices was not recognized. Development device at this time
The state of development by 33 and 34 is shown in FIG.

The photoconductor 29 developed with M toner was discharged and recharged in the same manner as when the M toner image was formed, and the cyan image signal was scanned and exposed by the light emitting diode array 31. The surface potential of the non-image area is +80 regardless of the presence or absence of toner.
The surface voltage of the image area was + 110V in the area where only Y toner or M toner was present, and was + 120V in the area where Y toner and M toner were overlapped.

Next, the developing device 33 containing Y toner and M toner and
+ 750V to the developing roller of 34, -200V to the fur brush, and + 750V to the developing roller of the developing device 35 containing C toner.
A DC voltage of +100 V was applied to the fur brush, the photoconductor 29 was passed through each developing device, and reverse development was performed with C toner.

Next, after irradiating the entire surface of the photoconductor 29 with the discharge lamp 36, the photoconductor 2 is charged with the corona charger 37 (corona voltage: −5.5 kV) for transfer.
9 Transfer the toner image on 9 to paper 39, and use AC static eliminator 38 to
Was peeled off from the photoconductor 29. The toner image transferred onto the plain paper 39 was heated and fixed by a heat fixing device. After the transfer, the toner remaining on the photoconductor 29 was removed by the cleaning brush 40 and used for the next image formation.

After the above-described image forming process was repeated 1000 times, when the state of contamination of each developing device with the different toner was examined, the different toner could not be visually confirmed. Also, when the 1000th color copy was compared with the 1st color copy, it was clear that there was almost no difference in image quality.

EFFECTS OF THE INVENTION As described above, the present invention has an effect of preventing contamination of the developing device by different kinds of toner because the toner does not fly back from the photoconductor. Further, since the toner image previously developed does not fly backward, there is an effect that a clear color copy without a decrease in density can be stably obtained.

[Brief description of drawings]

FIG. 1 is a principle diagram of an apparatus for explaining a color electrophotographic method in one embodiment of the present invention, FIGS. 2 to 8 are principle diagrams for explaining the method, and FIG. 9 is a schematic view of the present invention. FIG. 10 is a principle diagram of a printer using the color electrophotographic method, FIG. 10 is a principle diagram of a developing device used in the printer of FIG. 9, FIG. 11 is a principle diagram of a conventional color electrophotographic apparatus, and FIG. FIG. 13 to FIG. 15 are principle diagrams of the developing device used in the apparatus shown in the figure, and are principle diagrams showing problems in the conventional color electrophotographic method. 29 …… photoreceptor, 43 …… developing roller, 44 …… fur brush.

Claims (3)

[Claims] 1. A plurality of developing devices having means for flying toner on a toner carrier to develop an electrostatic latent image are arranged with a constant gap between the photoconductor and the toner carrier, and charged and exposed. In a color electrophotographic method including a step of superposing toner images of different colors by repeating the developing process a plurality of times on the same photoconductor, charging and exposing the photoconductor carrying the first toner image When the second electrostatic latent image is formed and developed with the second toner, the toner on the toner carrier of another developing device, which should not contribute to the development, is removed, and the toner carrying of the other developing device is carried out. A color electrophotographic method comprising a step of applying a DC voltage having substantially the same potential as the latent image potential of a non-image area to the body. 2. When a first electrostatic latent image is developed with a first toner, a DC voltage having substantially the same potential as the latent image potential of the non-image area is applied to the toner carrier carrying the first toner. The color electrophotographic method according to claim 1, wherein the toner carrier of another developing device that does not contribute to development is grounded. 3. The color electrophotographic method according to claim 2, wherein the toner on the other toner carrier which does not contribute to the development is removed.