JPH0447314B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a color electrophotographic method that can be used in color hard copy devices such as color copying machines and color printers.

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 paper. Various color electrophotographic methods for obtaining color images have been proposed.

A conventional example of an apparatus using such a color electrophotographic method is shown in FIG. In the figure, 1 is a Se-Te 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 and magenta, respectively. A developing device containing M, cyan C, and black B1 developers separately; 8 is plain paper; 9 is a static elimination lamp for facilitating electrostatic transfer of the toner image onto the plain paper 8; 10 is a toner image 11 is a heating fixing device; 12 is a cleaning blade for removing toner remaining on the photoconductor 1 after the toner image is electrostatically transferred to plain paper 8; 13 is a photoconductor; This is a static elimination lamp that returns the surface potential of the body to its initial state.

Next, a specific example of the structure of the developing devices 4 to 7 is shown in FIG. In FIG. 4, 14 is a two-component developer (hereinafter referred to as developer) made of a mixture of normally conductive toner and magnetic carrier, 15 is a developing sleeve made of a non-magnetic material such as aluminum, and 16 is a plurality of magnetic poles. The developing sleeve 15, the mag roll 16, and a rotating mechanism (not shown) constitute a toner carrier. 17
18 is a scraping plate that scrapes off the developer 14 on the developing sleeve 15 after development; 19 is a rotary blade that stirs the developer 14; ,
20 is a toner for replenishment, 21 is a toner replenishment roller, 1 is a photoreceptor installed with a gap at a position where it does not come into contact with the developer 14 on the developing sleeve 15, 22
is a power source for electrically causing toner to fly toward the photoreceptor 1 from the developer 14 on the developing sleeve 15 .

Here, in order to enable the developing device to develop, the power supply 22
Next, the developing sleeve 15 and the power source 22 are connected using a device that generates a voltage in which a high-voltage AC voltage is superimposed on a positive DC 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 the negative electrostatic latent image (the image area is exposed to light and the surface potential of the photoreceptor increases). (attenuated electrostatic latent image)
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, Y
Only the developing device 4 containing 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. 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, exposing, developing, and optically eliminating charges are repeated in the same manner as the method used to form the yellow toner image, to form Y, M, C, and B1 toner images on the photoreceptor 1. After the formation of all toner images is completed, the electrostatic latent images are optically neutralized in advance using a static eliminating lamp 9, and the toner images are electrostatically transferred onto plain paper 8 using a corona charger 10. The toner image transferred to the plain paper 8 is heated and fixed by a heating fixing device 11. On the other hand, after the electrostatic transfer, the toner remaining on the photoreceptor 1 is removed by the cleaning blade 12, completing one cycle of color image formation (for example, Japanese Patent Laid-Open No. 60-95456).

Problems to be Solved by the Invention When a conventional color electrophotographic apparatus is operated continuously, there is a problem in that the developing device is contaminated with different toners of different colors in proportion to the amount of copies to be made. After investigating the cause of this problem, we found that when the photoconductor carrying a toner image was recharged and imagewise exposed, and then passed through a developing device that was not used for development, part of the toner image on the photoconductor was transferred to the developing device. It turned out that it flew backwards into the sleeve. This reverse flight of toner will be explained in more detail based on the drawings.

Figures 5 to 7 show the behavior of each toner on the photoreceptor and the developing sleeve after the photoreceptor carrying the toner image has been recharged and imagewise exposed and has passed through a developing device that is not used for development. It is a diagram schematically shown.

FIG. 5 shows the situation when the developing sleeve 15 is grounded. The photoreceptor 1 in areas A and C is positively charged by recharging and image exposure. 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 charge 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, developing sleeve 1
The positively charged toner 20 on the photoreceptor 1 is strongly electrostatically attracted to the developing sleeve 15 to which a negative voltage is applied. effective. 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, more toner 20 on the photoreceptor 1 in area C flies back than in FIG. 5. Furthermore, as the DC voltage applied to the developing sleeve 15 is increased, the toner 20' on the photoreceptor 1 in the D area also flies backwards.

FIG. 7 shows the state when the developing sleeve is electrically floated. The developing sleeve 15 is polarized by the positive charge on the photoreceptor 1 as shown in the figure. Therefore, a portion of the toner 20 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 towards the developing sleeve 15.

As explained above, with the conventional method, it is not possible to prevent contamination of the developing device with foreign toner caused by toner flying back from the photoreceptor to the developing sleeve of the developing device, and it is not possible to stably obtain clear color copies. The problem was that I couldn't do it.

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

Means for Solving the Problems The present invention arranges a plurality of developing means around a photoreceptor, and repeats the steps of charging, exposure, and reversal development multiple times to form a plurality of toner images of different colors on the photoreceptor. A color electrophotographic method for forming a color electrophotographic image, which includes forming an image area exposed to an image signal in an exposure step and a developing area unrelated to the image signal outside the image area, and then developing the image area in a developing step. Stop the toner carrier of the developing means that does not contribute, and apply a voltage to the toner carrier that is approximately the same potential as the surface potential of the non-image area to cause the toner on the toner carrier to adhere to the developed area; This object is achieved by disabling the developing capability of the developing means for the image area.

Function Next, the function of the present invention will be explained using FIG. 1, which schematically shows the main parts of an apparatus using the color electrophotographic method of the present invention.

The first electrostatic latent image on the photoreceptor 1 has already been coated with toner 20.
a has been developed, and a second electrostatic latent image is formed after recharging. The first developer 23 is stationary and the second developer 23' is rotating. Photoreceptor 1
In order to prevent the upper toner a from flying back to the developing device 23, a voltage is also applied to the first developing device 23 by the bias power supply 22. At this time, the first developing device 23
When the developing device 23 rotates, toner is supplied and the electrostatic latent image is developed, so the developing device 23 is kept stationary. However, even if it is kept stationary in this way, the toner adhering to the surface of the developing device 23 facing the photoreceptor 1 will develop an electrostatic latent image and cause color turbidity in the image, so this toner must be removed in advance. It is necessary to keep it.
For this reason, a developed area 25, that is, an entire exposed area with a low potential in the case of reversal development, is formed in front of the area 24 where the electrostatic latent image is formed on the photoreceptor 1 in the advancing direction, and this The toner in the developing section on the surface of the first developing device 23 is removed in advance by the area 25, thereby eliminating the developing ability. In this way, the second electrostatic latent image is developed only by the second developing device 23', color turbidity does not occur due to the first developing device 23, and moreover, the second electrostatic latent image is already developed on the photoreceptor 1. A good image can be obtained without a decrease in density due to the toner 20a of the first developing device 23 flying backwards from the first developing device 23.

Furthermore, as in the present invention, if the area to be developed where the toner is removed in the area facing the photoconductor precedes the image area on the photoconductor, even if a problem such as a paper jam occurs, the next step can be carried out without any delay. It is possible to enter the print cycle, which is preferable.

Example Examples of the present invention will be described below.

Photoreceptors that can be used in the present invention include:
Amorphous selenium, arsenic selenide, CdS, ZnO, a-
Any ordinary electrophotographic photoreceptor in which a photosensitive layer such as Si or an organic photoconductor is provided on a conductive support can be used, but in particular, the capacitance of the photosensitive layer is 20 to 20.
Preferably it is within the range of 170 pF/cm ² .

Setting the capacitance of the photosensitive layer within the above range is possible by regulating the layer thickness of the photosensitive layer.
For example, the layer thickness may be 35 to 90 μm for a selenium photoreceptor, 60 to 90 μm for an arsenic selenide photoreceptor, and 15 to 50 μm for an organic photoreceptor.

Further, in the present invention, both a regular development method and a reversal development method can be used, but a reversal development method in which the polarity of the toner is not reversed during recharging is particularly preferred.

As a developing means, for the electrostatic latent image on the photoreceptor,
Any material can be used as long as it has a counter electrode effect and can develop the electrostatic latent image in a non-contact state between the developer layer and the electrostatic latent image. For example, a toner carrier carrying a thin layer of charged toner is placed opposite a photoconductor so that the several layers do not come into contact with each other, and a voltage is applied between the toner carrier and the photoconductor to remove the toner on the toner carrier. Electric field flying development is preferred. Particularly preferred is DC electric field flying development in which a DC voltage is applied between the toner carrier and the photoreceptor. In this DC electric field flying development, it is desirable that the contrast potential between the image area and the non-image area of the electrostatic latent image is 400V or more. Also,
The distance between the toner carrier and the surface of the photoreceptor is preferably 250 μm or less.

In addition, in order to prevent the potential of the toner layer from becoming high when the photoreceptor carrying a toner image is recharged, the thickness of the toner layer formed on the photoreceptor by one color development should be within the range of 5 to 30 μm. It is desirable to do so.

Furthermore, in order to prevent the toner layer on the photoreceptor from being overcharged, it is desirable to recharge the toner layer with a scorotron charger that allows easy control of the amount of charge.

Example 1 A specific example of the present invention will be described in detail with reference to FIG.

Photoreceptor 1 consisting of an amorphous Se-Te photoreceptor drum with a diameter of 100 mm (layer thickness of photosensitive layer 60 μm, electrostatic capacity 92 pF/cm ² ) is rotated at a peripheral speed of 75 mm/s, and a charger 2 (corona voltage: +7 KV) is rotated at a circumferential speed of 75 mm/s. , grid 26 voltage +850V)
was used to charge the surface potential to +800V. Then output
A light emitting diode 27 of 7 μW and a wavelength of 670 nm is emitted and exposed through a self-occurring lens 28 to form a solid area on the entire surface with a width of 10 mm in the direction of movement, which is used as an area to be developed. Thereafter, the light-emitting diode 27 was used to expose signal light corresponding to yellow to form an electrostatic latent image.

Next, in order to develop this electrostatic latent image, a toner carrier, that is, a developing roller 23a (diameter 16 mm, peripheral speed 75mm/s,
The direction of travel is the same as photoreceptor 1) and the developing gap
When a developing bias of +700V was applied from the DC power supply 22a, yellow toner was transferred from the developing roller 23a to the photoreceptor 1.
It flew towards the upper latent image area and attached to it. The thickness of the toner layer adhered to photoreceptor 1 was approximately 10 μm. After this,
Photoconductor 1, which has undergone yellow development, is charged with +850V while stationary.
The magenta developer 23 is applied with a bias voltage of
b and cyan developer 23c. At this time, since the magenta and cyan toner in the developing nip area has been removed in advance by the developed area in front of the image area on the photoreceptor 1, a bias (+850V) of approximately the same potential as the surface potential of the photoreceptor 1 is applied. Even if it is applied, the electrostatic latent image will not be developed. Thus 23b, 23
The toner image on the photoconductor 1 that has passed through the developing device c is not transferred to paper, but once the entire surface of the photoconductor 1 is neutralized by a static elimination lamp 13, and then charged again by a corona charger 2.
Due to the corona charging, the bare area on the photoreceptor 1 to which no yellow toner was attached was charged to +800V, and the area on the photoreceptor 1 to which the yellow toner was attached was also charged to +800V. Here, the area of the photoreceptor 1 to which the yellow toner is attached has a surface potential of +
The voltage was about 50V, and the photoreceptor 1 itself was charged with +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 approximately +30V.
In the area where the yellow toner was attached, the surface potential of the photoreceptor decreased to approximately +80V 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 a yellow developing device 23a. At this time, the yellow developing device 23a remains stationary with a bias of +850V applied, so the yellow toner on the portion of the yellow developing device 23a facing the photoreceptor 1 is previously absorbed by the solid area on the preceding photoreceptor. It has been removed. Therefore, the yellow toner on the photoreceptor 1 does not fly back to the yellow developing device 23a from the unexposed area and at the same time, the yellow toner on the photoreceptor 1
It also prevents the upper magenta electrostatic latent image from being developed with yellow toner. Next, the photoreceptor 1 passes through a magenta developer 23b (toner charge amount +3 μC/g, average particle size 10 μm, layer thickness 30 μm) to which a developing bias of +700 V is applied, and is developed with magenta toner. Finally, the photoreceptor 1 passes through the cyan developing device 23c.
At this time, like the yellow developer 23a, the cyan developer 23c is stationary with +850V bias applied, and the cyan toner in the area facing the photoreceptor 1 is preliminarily absorbed by the solid area on the photoreceptor 1. Since it has been removed, the magenta electrostatic latent image is not developed.

Next, the photoreceptor 1 was again charged to +800 V by the charger 2, and a solid latent image was again formed by the light emitting diode 27, and then a signal light corresponding to cyan was irradiated to form an electrostatic latent image. Next, the yellow and magenta developing units 23a and 23b are held stationary with a bias of +850 V applied to them so that the electrostatic latent image will not be developed and the toner will not fly back from the photoreceptor 1. cyan developer 23c (toner charge amount +3 μC/g, average particle size 10 μm, toner layer thickness) with +700 V developing bias applied.
30 μm).

The color toner image thus obtained on the photoreceptor 1 is discharged from the entire surface of the photoreceptor 1 by a pre-transfer static elimination lamp 9, transferred to paper 8 by a transfer charger 10, and then transferred to the photoreceptor by a peeling charger 29. Paper 8 was peeled off from 1 and then heat-fixed. After transferring the toner on the photoreceptor 1 to the paper 8, the surface of the photoreceptor 1 is removed using a static eliminator 30.
The charge was removed using a cleaning device 12, and the remaining toner was removed by a cleaning device 12, and the toner was reused. The color image obtained had a high maximum density of 1.7 and was of good quality with no color turbidity. Furthermore, even though this process was repeated 3,000 times, no different types of toner got mixed into the developing device.

Example 2 An arsenic selenide photoreceptor (photosensitive layer thickness: 90 μm, capacitance: 104 pF/cm ² ) was used instead of the Se-Te photoreceptor used in Example 1, and the other conditions were the same as in Example 1. and printed it. The color image obtained had a maximum density of 1.5 and was of good quality without color turbidity.

Example 3 An organic photoreceptor using an azo pigment (layer thickness of photosensitive layer 30 μm, capacitance 80 pF/cm ² ) was used as a photoreceptor.
Printing was carried out under the same conditions as in Example 1.
The color image obtained had a high maximum density of 1.7 and was of good quality with no color turbidity.

Effects of the Invention According to the present invention, there is an effect that contamination of a developing device with different toners can be prevented and clear color copies can be stably obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of the main parts of an apparatus shown for explaining the principle of the color electrophotographic method of the present invention;
Fig. 2 is a schematic sectional view of a color electrophotographic printer using the same method, Fig. 3, Fig. 4, Fig. 5, Fig. 6,
FIG. 7 is a diagram showing the behavior of an apparatus and toner for explaining a conventional color electrophotographic method. 1... Photoreceptor, 2... Charger, 20... Toner, 22... Bias power supply, 23... Developer, 2
5... Solid image area (area to be developed).

Claims (1)

[Scope of Claims] 1. A color electronic device in which a plurality of developing means are arranged around a photoconductor, and a plurality of toner images of different colors are formed on the photoconductor by repeating the steps of charging, exposure, and reversal development multiple times. In a photographic method, after forming an image area exposed to an image signal in an exposure step and a developing area unrelated to the image signal outside the image area, a developing means is provided that does not contribute to the development of the image area in a developing step. The toner carrying member is stopped, and a voltage of approximately the same potential as the surface potential of the non-image area is applied to the toner carrying member to cause the toner on the toner carrying member to adhere to the development area, and the developing to the image area is performed. A color electrophotographic method that disables the development capability of the means. 2. The color electrophotographic method according to claim 1, wherein the area to be developed precedes the image area. 3. The developing means places a toner carrier carrying a thin layer of toner facing the photoreceptor so that the toner does not come into contact with the photoreceptor, and applies a voltage between the toner carrier and the photoreceptor to remove the toner. 2. The color electrophotographic method according to claim 1, which is an electric field flying development method in which the colors are caused to fly by the action of an electric field. 4. The color electrophotographic method according to claim 3, wherein the voltage is a DC voltage, and the distance between the toner carrier and the photoreceptor is 250 μm or less.