JPS6271970A - Color electrophotographic method - Google Patents

Abstract

PURPOSE:To prevent a developing unit from contamination due to a different kind of toner and to obtain stably a clear color copy by forming a solid image independent of an image signal in the axial direction of a photosensitive body in the front of an image area. CONSTITUTION:A solid part 25, i.e. a fully exposed part with low electric poten tial in case of inversional development, is formed in the front of an image area 24 on which an electrostatic latent image on the photosensitive body 1 is written in the advancing direction and toner in a developing part on the surface of the 1st developing unit 23 is previously removed by the solid part 25 to remove its developing capability. Consequently, the 2nd electrostatic latent image is developed only by the 2nd developing unit 23' and a fine image can be obtained without the generation of color turbidity due to the 1st developing device 23 and density reduction due to the reverse dispersion of toner 20a devel oped on the photosensitive body 1 to the 1st developing device 23.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a color electrophotographic apparatus that can be used in a color copying machine or printer.

Conventional technology Conventionally, charging, exposure, and development are repeated multiple times to form multiple toner images of different colors on an electrophotographic photoreceptor (hereinafter referred to as photoreceptor), and then the toner images are transferred all at once to plain paper. Various color electrophotographic apparatuses for obtaining color images have been proposed.

A conventional array of such color electrophotographic devices is shown in FIG. In the figure, 1 is an Sθ-To photoreceptor that rotates in the direction of the arrow, 2 is a corona charger that uniformly charges the surface of the photoreceptor 1, 3 is a laser beam scanner, and 4 to 7 are yellow (
Y), magenta (M).

Cyan (C) and black (Bl) toners are contained separately.
1o is a corona charger for electrostatically transferring the toner image onto plain paper 8; 11 is a heat fixing device; 12 is electrostatically transferring the toner image onto plain paper 8. A cleaning blade 13 is used to remove toner remaining on the photoreceptor 1, and a discharge lamp 13 is used to bring the surface potential of the photoreceptor to an initial state.

Next, a concrete arrangement of the developing units 4 to 7 is shown in FIG. In FIG. 4, 14 is a two-component developer (hereinafter referred to as developer) consisting of a mixture of positively charged toner and magnetic carrier.
, 16 is a developing sleeve made of a non-magnetic material such as aluminum, 16 is a mag roll having a plurality of magnetic poles, 17 is a layer thickness regulating grade for regulating the layer thickness of the developer 14 on the developing sleeve 15, and 18 is a developing sleeve after development. A scraping plate 19 scrapes off the developer 14 on the sleeve 15;
20 is a toner for replenishment, 21 is a toner replenishment roller, 1 is a developer 14 on the developing sleeve 15
A photoconductor installed with a gap at a position where it does not come into contact with the photoreceptor, 22
is a power source for electrically flying toner from the developer 14 on the developing sleeve 15 toward the photoreceptor 1.

To bring the developing device into a state capable of developing, the developing sleeve 15 and the power source 22 are connected using a power source that generates a voltage that is a combination of a positive DC voltage and a high-voltage AC voltage.

Further, in order to put the developing device into 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 of forming a color image using the color electrophotographic apparatus described above will be described. First, the photoreceptor 1 is positively charged with the corona charger 2, and then a yellow image signal is scanned and exposed using the laser beam scanner 3, and a negative electrostatic latent image (the image area is exposed and the surface potential of the photoreceptor is attenuated) form).

Then, the electrostatic latent image is reversely developed into a negative/positive state using a developing device 4 containing Y toner, thereby forming a yellow toner image on the photoreceptor 1. At this time, only the developing device 4 containing the Y toner is connected to the power supply 22, but the other developing devices 6 to 7 are connected to the power source 22.
is adjusted so that toner does not fly away. After development with the Y toner, the entire surface of the photoconductor 1 is irradiated with a discharge lamp 13 to optically eliminate the yellow electrostatic latent image.

Next, the steps of charging, exposure, development, and photostatic discharge are repeated in the same manner as the method used to form the yellow toner image, to form Y, M, C, and Bl toner images on the photoreceptor 1. .

After all toner development is completed, the electrostatic latent image is optically neutralized in advance using a static eliminating lamp 9, and the toner image is electrostatically transferred onto plain paper 8 using a corona charger 2. The toner image transferred to the plain paper 8 is heated and fixed by a heat fixing device 11. On the other hand, the toner remaining on the window light body 1 after electrostatic transfer is removed by a cleaning blade, completing one cycle of color image formation (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. 3 is operated continuously, there is a problem in that the developing device is contaminated with toner of different types in proportion to the amount of copies to be made. When we investigated the cause of this problem, we found that when the photoconductor containing toner (containing toner) passes through a developing device that is not used for development after being recharged and imagewise exposed,
It has been found that some of the toner in the toner image on the photoreceptor flies back to the developing sleeve. This reverse flight phenomenon of toner will be explained in more detail with reference to the drawings.

Figures 5 to 7 schematically show the behavior of each toner on the photoreceptor and the developing sleeve when the photoreceptor carrying a toner image is recharged and exposed to light and then passes through a developing device that is not used for development. FIG.

FIG. 5 shows the situation when the developing sleeve 16 is grounded. The photoreceptor 1 in the area C and area C is positively charged by recharging. Furthermore, the toner on the photoreceptor 1 is more positively charged by the corona charger during recharging. Therefore, the toner in area C flies back toward the developing sleeve due to the repulsive force of the positive charges on the photoreceptor and the electric field generated between the photoreceptor and the developing sleeve.

FIG. 6 shows the situation when a negative DC voltage is applied to the developing sleeve. In this case, the positively charged toner 2o on the developing sleeve 15 is strongly electrostatically attracted to the developing sleeve 15 to which a negative voltage is applied, so that the toner does not fly from the developing sleeve 16 to the photoreceptor 1. It is very effective in preventing.

However, the electric field strength between the photoreceptor and the developing sleeve in region C is greater than that in region C in FIG. Therefore, the toner 2o on the photoreceptor 1 in the C area is the fifth
Compared to the illustration, it will fly much more backwards. Further, as the DC voltage applied to the developing sleeve 15 is increased, the toner 20' on the photoreceptor 1 in the C region also flies backwards.

FIG. 7 shows the state when the developing sleeve is electrically floated. The developing sleeve 15 is caused by the positive charge on the photoreceptor 1.
is polarized as shown. Therefore, a portion of the toner 2° on the developing sleeve 15 in area B flies toward the photoreceptor 1. Further, a part of the toner 20' on the photoreceptor 1 in the C area flies back toward the developing sleeve 15.

As described above, the conventional apparatus has a problem in that it is not possible to prevent the developing device from being contaminated by different types of toner, and it is not possible to stably obtain clear color copies.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a color electrophotographic method that prevents contamination of a developing device with different types of toner and can stably produce clear color copies.

Means for Solving the Problems The present invention includes a plurality of developing devices arranged around the photoreceptor for developing a toner carrier carrying a powder toner layer in a non-contact manner while facing the photoreceptor. In electrophotography, which repeatedly forms toner images of multiple colors on a photoreceptor, a solid image unrelated to the image signal is formed in the axial direction of the photoreceptor prior to the image area, and This is a color electrophotographic method in which a developing bias voltage having approximately the same potential as the surface potential of a non-image area of a photoreceptor is applied to a toner carrier of a developing device that does not contribute to development, and the driving of the toner carrier that does not contribute to development is stopped. .

action The present invention will be explained in detail with reference to FIG.

The first electrostatic latent image on the photoreceptor 1 has already been developed with the toner 20a, and an electrostatic latent image on the cylinder 2 is formed after recharging. The first developer 23 is stationary and the second developer 23'
is rotating. Developing device 2 for toner 20a on photoreceptor 1
In order to prevent the reverse flight to 3, a bias 22 is also applied to the first developing device 23. At this time, when the first developing device 23 rotates, toner is supplied and the electrostatic latent image is developed, so this developing device 23 is kept stationary. However, even if it is kept stationary in this way, the surface of the developing device 23 facing the photoreceptor 1 is
It is necessary to remove this toner in advance because the toner that adheres to the image will develop the electrostatic latent image and cause the image to become cloudy. For this reason, a solid area 25, that is, an entire exposed area with a low potential in the case of reversal development, is formed on the front side of the image area 24 on which the electrostatic latent image is written on the photoreceptor 1, and this solid area 25, the toner in the developing section on the surface of the first developing device 23 is removed in advance to eliminate the developing ability. In this way, the second electrostatic latent image is developed only by the second developer 23';
A good image can be obtained without causing any color turbidity due to the toner 20a of the first developing device 23, which has already been developed on the photoconductor 1, and without any decrease in density due to the toner 20a of the first developing device 23 that has already been developed on the photoreceptor 1 flying back to the first developing device 23. It will be done.

EXAMPLE As the photoreceptor that can be used in the present invention, amorphous selenium, CdS, ZnO, a-8i, etc. can be used. As the developing device, any device can be used as long as it has a counter electrode effect with respect to the electrostatic layer (p) on the photoreceptor and can develop the electrostatic latent image without contacting the developer layer. For example, , a single-component developer in which a charged toner layer is supported on a developing roller, and a two-component developer in which a toner and a magnetic carrier are mixed.Also, in the embodiments of the present invention, the case of a reversal development method is explained. However, it can also be applied to regular development methods.

An embodiment of the present invention will be described in detail using FIG.

Amorphous 5e-To photosensitive drum 1 with a diameter of 100ffff
Rotate at a circumferential speed of 7 tsyttm/s, charger 2 (corona voltage +7 kV, glyph) '26 voltage element 850 V)
It was charged to a surface potential of 500 V using i. Next, the cuff μ
W, the light emitting diode 27 with a wavelength of 670 nH is emitted and exposed through the SELFOC lens 28, and the distance is 10 M in the traveling direction.
A solid surface of M was formed on the entire surface, and then the light emitting diode 2 was exposed to signal light corresponding to yellow to form an electrostatic latent image.

Next, this electrostatic latent image is transferred to a developing roller 23a (diameter 16 x 1 circumferential speed 75 MM/cm) carrying yellow toner (toner layer thickness 30 μm) with a charge amount of 3 μC/g and an average particle size of 10 μm on the surface.
S, the direction of travel is the same as the photoreceptor 1) and the developing gear,
When a developing bias of +700 V was applied from the DC power source 22&, the yellow toner flew from the developing roller 232L toward the latent image area on the photoreceptor 1 and adhered thereto. After this, the yellow-developed photoreceptor 1 stands still and +as
It passes through a magenta developer 23b and a cyan developer 23C'i to which a bias of ov is applied. At this time, since the toner in the developing nip of the magenta and cyan developing devices has been removed in advance by the solid area in front of the image area on the photoconductor 1, a bias (+5 sOV) of approximately the same potential as the surface potential of the photoconductor 1 is applied. Even if it is applied, the electrostatic latent image will not be developed. In this way, the toner image on the photoconductor 1 that has passed through the developing devices 23b and 23C is not transferred to paper, but is once applied to the photoconductor 1 by the static elimination lamp 13.
After completely eliminating static electricity, it is charged again by the corona charger 2. Due to corona charging, the bare photoconductor 1 with no yellow toner attached was charged to +5oOV, and the photoconductor 1 with yellow toner attached was also charged to -4-aooV. Among the surface potentials of the photoconductor 1, the potential of the toner was approximately SOV, and the photoconductor 1 itself was charged at 750V.

Next, a solid latent image was again formed on the photoreceptor 1 by the light emitting diode 27, and then a signal light corresponding to magenta was irradiated. The surface potential of the photoreceptor 1 to which yellow toner was not attached decreased to about 30V. In the area where the yellow toner was attached, the surface potential of the photoreceptor decreased to about soV due to exposure. This is because the wavelength of the light emitting diode 27 is 670 nm, so most of the yellow toner transmits light of this wavelength, and even if toner exists on the photoreceptor 1, it does not affect the optical attenuation of the surface potential of the photoreceptor 1. It's for a reason. Next, the photoreceptor 1, which has been developed with this yellow toner and has an electrostatic latent image corresponding to magenta, first passes through the yellow developer 2° 31L. At this time,
Since the yellow developing device 23'& remains stationary with a bias of +860V applied, the yellow toner on the portion of the yellow developing device 23a facing the photoreceptor 1 is removed in advance by the solid area on the preceding photoreceptor. has been done. Therefore, the yellow toner on the photoconductor 1 does not adhere and fly back to the yellow developing device 23a from the unexposed area, and at the same time, the magenta electrostatic latent image on the photoconductor 1 is developed with the yellow toner. It can also be prevented. Next, magenta development was performed by applying a developing bias of photoconductor 1 +7001 -23b (), toner charge amount 3 μC; /
g.

The average particle size is 10 μm and the thickness of each layer is 30 μm), and the magenta toner is developed. Finally, the photoreceptor 1 passes through a cyan developer 230. At this time, cyan current 1ψ device 230
Like the yellow developer 23 &, it stands still with a +85°V bias applied, and the cyan toner in the area facing the photoreceptor 1 has been removed by the solid area on the photoreceptor 1 in advance. , no magenta electrostatic latent image occurs. Next, put the photoconductor 1 back into the charger 2 for +5oov.
After the light emitting diode 27 was used to form a solid latent image, a signal light corresponding to cyan was irradiated to form an electrostatic latent image. This time, yellow and magenta developer 231L,
23b with a bias of +850V (7) applied to it so as not to develop the electrostatic latent image and to prevent the toner from flying backwards from the photoreceptor 1. Developing is carried out using a cyan developer 230 to which a developing bias of 7001 is applied.

The color toner image thus obtained on the photoreceptor 1 is discharged from the entire surface of the photoreceptor 1 by the pre-transfer static elimination lamp 9, transferred to the paper 8 by the transfer charger 1o, and then removed from the photoreceptor 1 by the peeling charger 29. Paper 8 was peeled off and then heat-fixed. After the toner on the photoreceptor 1 was transferred to the paper 8, the surface of the photoreceptor 1 was neutralized by the static eliminator 3o, and the remaining toner was removed by the cleaning device 12, and the photoreceptor 1 was reused. The color image obtained had a high maximum density of 1.7 and was of good quality with no color turbidity. Further, even though this process was repeated for 300Q sheets, no different types of toners were mixed into the developing device.

Effects of the Invention According to the present invention, in an electrophotographic process in which color prints are obtained by directly superimposing color toner images on a photoreceptor, contamination of a developing device by different types of toner can be prevented and clear color copies can be stably obtained. be able to.

[Brief explanation of drawings]

FIG. 1 is a sectional view of the main parts of an apparatus shown to explain the principle of the color electrophotographic method of the present invention, FIG. 2 is a sectional view of a color electrophotographic printer using the same method, and FIGS. 3 and 4. ,
FIG. 6, FIG. 6, and FIG. 7 are diagrams showing the behavior of an apparatus and toner for explaining a conventional color electrophotographic method. 1...Photoreceptor, 2...Charger, 2o...
... Toner, 22 ... Bias power supply, 23
...Developer, 25...Solid area, image area. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 12 Figure 3 Figure 4 Zθ Figure 5 Figure 7

Claims (1)

[Claims] A plurality of developing devices are arranged around the photoconductor to develop a toner carrier carrying a powder toner layer in a non-contact manner while facing the photoconductor, and charging, exposure, and development are repeated to form toner of multiple colors on the photoconductor. In the electrophotographic method of forming an image, a solid image unrelated to the image signal is formed in the axial direction of the photoreceptor in advance of the image area, and a solid image is formed on the toner carrier of the developing device that does not contribute to development. A color electrophotographic method in which a developing bias voltage having approximately the same potential as the surface potential of a non-image area of a photoreceptor is applied and driving of a toner carrier that does not contribute to development is stopped.