JP2537983B2 - Color electrophotographic device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color electrophotographic apparatus which can be used in a hard copy apparatus such as a color copying machine or a color printer.

2. Description of the Related Art Conventionally, charging, exposure, and development are repeated several 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 (Japanese Patent Application No. 60-
95456) is shown in FIG. In FIG. 2, 21 is a Se-Te photoconductor that rotates in the direction of the arrow, 22 is a corona charger that uniformly positively charges the photoconductor 21, 23 is a laser beam scanner, and 24-27 are yellow, respectively. A developing device in which developer of magenta (hereinafter referred to as M), cyan (hereinafter referred to as C), and black (hereinafter referred to as B) are separately contained, 28 is a recording paper, and 29 is toner. A discharge lamp for facilitating the transfer of the image to the recording paper 28, 30 a corona charger for transferring the toner image onto the recording paper, 31 a heat fixing device, 32 for the toner remaining on the photoreceptor 21 after the toner transfer. A cleaning blade for removing 33 is a charge eliminating lamp for erasing the electrostatic latent image on the photoconductor 21 with light.

Next, FIG. 3 shows a concrete configuration diagram of the developing devices 24-27.
In FIG. 3, 34 is a two-component developer (hereinafter referred to as developer) made of a mixture of positively chargeable toner and magnetic carrier, 35 is a developing sleeve made of non-magnetic material such as aluminum, and 36 is a plurality of magnetic poles. The mag roll has 37, a layer thickness regulating blade that regulates the layer thickness of the developer 34 on the developing sleeve, 38 a scraping plate that scrapes off the developer 34 on the developing sleeve 35 after development, and 39 stirs the developer 34. Rotating blades,
Reference numeral 40 is toner to be replenished, 41 is a toner replenishing roller, 21 is a photoconductor placed at a position not contacting the developer 34 on the developing sleeve 35, and 42 is toner from the developer 34 on the developing sleeve 35. A power supply for electrically flying toward the photoconductor 21.

In order to make the developing device ready for development, the developing sleeve 35 and the power source 42 are connected by using a power source 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 in a state where it is not used for development, the developing sleeve 35 is electrically floated, grounded, or a negative DC voltage is applied to the developing sleeve.

Next, a method of forming a color image using the above-described color electrophotographic apparatus will be described. First of all, corona charger
After positively charging the photoconductor 21 with 22, laser beam scanner
The image signal of Y is exposed at 23, and a negative electrostatic latent image (an electrostatic latent image in which the image portion is exposed and the surface potential of the photoconductor is attenuated)
To form. Then, the electrostatic latent image is subjected to negative / positive reversal development by the developing device 24 containing Y toner to form a Y toner image on the photoconductor 21. At this time, the developing device containing Y toner
Only 24 is connected to the power supply 42, but the other developers 25
To 27 is adjusted so that the toner does not fly. After developing with Y toner, the photoconductor 21 is entirely illuminated by the static elimination lamp 33 to erase the yellow electrostatic latent image.

Next, by the same method as the method for forming the Y toner image, the steps of charging, exposing, developing, and removing light are repeated, and the M, C, and B toner images are formed on the photoconductor 21 on the Y toner image. Are sequentially formed. After the formation of all the toner images is completed, the static latent image is erased by the static elimination lamp 29, and the toner images are collectively electrostatically transferred onto the recording paper 28 by the corona charger 30. On the other hand, after the electrostatic transfer, the toner remaining on the photoconductor 21 is removed by the cleaning blade 32, and one cycle of color image formation is completed.

Problems to be Solved by the Invention When the conventional color electrophotographic apparatus described with reference to FIG. 2 is used, toner may be mixed in a developing device having a different color (hereinafter referred to as color mixing). For example, the toner developed on the photoconductor flies backward from the photoconductor to a developing device of a different color. In addition, development occurs in which toner spills from a developing device and mixes with another developing device. At this time, the toner mixed in is mixed with the regular toner, so that the original characteristics of the toner are lost,
In some cases, the mixed color toner has a charging polarity opposite to that of the regular toner due to frictional charging. Therefore, when copying an original, the mixed color toner adheres to the non-image portion, resulting in an image with a lot of background fog.

Means for Solving the Problems In order to solve the above problems, in a color electrophotographic apparatus of the present invention, toner mixed in the course of initialization of a copying machine is developed and adhered to a photoconductor, and the toner adhered to the photoconductor. Are removed from the photoreceptor during the cleaning process. That is, yellow (hereinafter referred to as Y), magenta (hereinafter referred to as M), cyan (hereinafter referred to as C), and black (hereinafter referred to as B) developing devices are brought close to the photoconductor, and Y, M, C, and B
In the process of initializing the copying machine in which the developing device is in operation, the surface potential of the photoconductor is Vo, and the developing bias at the time of Y, M, C, and B development is V1, V2, V3, and V4, respectively. A means for setting the relationship between the surface potential of the photoconductor and the developing bias of each color developing device is set as follows.

100V <| Vo | − | V1 | <500V 100V <| Vo | − | V2 | <500V 100V <| Vo | − | V3 | <500V 100V <| Vo | − | V4 | <500V Action The present invention has been described above. Since the toner that has mixed colors can be removed during the initialization process of the copying machine due to the configuration, the amount of the mixed toner that adheres to the non-image area can be significantly reduced in the actual copying process, and the background fog due to the mixed toner can be controlled. It becomes possible to do.

Embodiment A color electrophotographic apparatus according to an embodiment of the present invention will be described below with reference to the drawings.

Embodiment 1 FIG. 1 shows a color electrophotographic apparatus of the present invention. Developer
A non-contact type non-magnetic one-component developing device for flying toner by 1,2,3 DC electric field and a two-component magnetic brush developing device 4 composed of a contact type toner and carrier. A thin layer of toner is formed on the developing rollers 101, 201, 301 made of aluminum by the blades 102, 202, 302. Further, the non-magnetic blade 402 regulates the spikes of the developer layer conveyed onto the developing roller 401.

Further, the developing units 1, 2, 3 are provided with fur brushes 103, 104, 105 to enhance the effect of toner triboelectric charging.

The developing device 1 contains Y, the developing device 2 contains M, the developing device 3 contains C, and the developing device 4 contains B insulating toner. Developing roller 101,
The developing devices are arranged around the photoconductor 5 so as to face each other, with a constant gap (development gap) between the photoconductors 201, 301, and 401. Each developing device is provided with a separation / contact mechanism that is close to the photoconductor during development and is separated during non-development.

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

Specifications of developing units 1, 2, and 3 and developing conditions Diameter of developing roller: 16mm Peripheral speed of developing roller; 160mm / sec Toner layer thickness on developing roller; 30μm Rotating direction of developing roller; Opposite direction to photoconductor 1 Development gap During development; 150 μm Non-development; 700 μm Physical properties of toner; Electric charge of toner; +3 μc / g Average particle size of toner; 10 μm Specifications and development conditions of developing device 4 Development roller diameter; 24.56 mm Development roller peripheral speed; 320 mm / sec Development roller rotation direction: Opposite to photoconductor 1 Development gap Development: 500 μm Non-development: 3 mm Blade-developing roller distance: 350 μm Toner physical properties Toner charge amount: +15 μc / g Average toner particle size: 8 μm The image forming process in the full color mode will be described.
An amorphous Se-Te photosensitive drum with a diameter of 152 mm is used as a photosensitive member, and the surface potential +850 V is charged by a charger 6 (corona voltage; 7 kV, grid voltage 900 V) while rotating at a peripheral speed of 160 mm / sec.
Charged to.

Next, a semiconductor laser 7 having an output of 1.5 mW and a wavelength of 780 nm was caused to emit light, and a negative B signal was exposed on the photoconductor 5 to form a B electrostatic latent image. The photoconductor 5 is passed through the Y developing device 1, the M developing device 2, and the C developing device 3 in the non-developing state, and the electrostatic latent image is developed on the developing roller 4.
After carrying out reversal development by the B developing device 4 in the developing state in which + 500V was applied to 01, a B toner image was formed. After development static elimination lamp 8
Then, the entire surface was irradiated with, and an AC voltage was applied to the AC corona charger 9 to erase the electrostatic latent image.

Next, the photoconductor 5 was charged again by the corona charger 6, and the photoconductor 5 was exposed to the signal light corresponding to Y by the semiconductor laser 7 to form an electrostatic latent image of Y. The electrostatic latent image is subjected to reversal development by a Y developing device in a developing state in which +800 V is applied to the developing roller 101, and then passed to a non-developing M developing device 2, a non-developing C developing device 3 and a B developing device 4. And a Y toner image was formed. Similarly, M and C toner images are formed, and the full-color toner image obtained on the photoconductor is transferred onto the paper by the transfer charger 11.
After transferring to 12, the image was thermally fixed by the fixing device 13. Transfer voltage is −
5kV was applied.

In this embodiment, a non-contact type non-magnetic one-component developing device was used for Y, M and C, and a contact type magnetic brush two-component developing device was used for B. However, in some cases, Y, M, C and B are also used. A non-contact type non-magnetic one-component developing device may be used. The above is the color image forming process.

Due to the arrangement of the developing units, toner may overflow from the developing units located above and mix with the developing units located below.

For example, when a copied image was obtained with a B developing device mixed with M toner, M toner adhered to the non-image portion. It can be seen that as the difference between the surface potential of the photoconductor and the developing bias of B increases, the amount of adhesion increases, and the M toner is charged in the opposite polarity to the B toner.

Next, an image was formed in the full-color mode, and it was examined how much color toner dropped to the B developing device.
It was about 0.5 g per 1000 sheets.

Therefore, 0.5 g of M toner was mixed in the B developing device, and it was examined how much it was removed in the initialization operation state. That is, B
A developing bias is applied to the developing device in the developing state, the developing device is close to the photosensitive drum, and the developing roller is rotating. The photoconductor drum is charged and rotating. No laser exposure was performed.

In Table 1, the discharge state of the color toner was examined by using the surface potential (Vo (V)) of the photoconductor and the developing bias (V4 (V)) of B development as parameters. C indicates carrier adhesion, K indicates B
This shows that a large amount of toner adhered. The numerical value indicates how many rotations of the photosensitive drum the color toner is discharged. Almost no M toner adhesion to the drum is observed above the stated rotation.

As described above, when the surface potential of the photosensitive member and the developing bias are in the range of 100V <| Vo |-| V4 | <500V, the adhering color toner can be eliminated without carrier adhesion and B toner fogging.

This result showed almost the same result when the Y and C toners were mixed in the B developing device. The same applies to other color developing devices, with respect to the photoconductor surface potential (Vo) and the developing bias (Y; V1, M; V2, C; V3) of each color, 100V <| Vo | − | V1 | <500V 100V The mixed color toner can be eliminated by performing in the range of <| Vo | − | V2 | <500V 100V <| Vo | − | V3 | <500V.

As a means for setting the photoreceptor surface potential, there are a method of controlling the voltage applied to the grid electrode of the scorotron charger, and a method of controlling the voltage applied to the corona charging line. The method of controlling the voltage applied to the grid electrode was used.

According to the present invention, when the different color toner is mixed by the above configuration, the mixed different color toner can be discharged in the initialization operation state of the copying machine, and the non-image portion can be obtained when a copy image is obtained. It is possible to control the adhesion of the different color toner to the toner and obtain a clear color print.

[Brief description of drawings]

FIG. 1 is a schematic view of a color electrophotographic apparatus according to the first embodiment of the present invention, and FIGS. 2 and 3 are schematic views of a conventional color electrophotographic apparatus. 1,2,3,4 …… Y, M, C, B developer, 101,201,301,40
1 ... Developing roller, 102,202,302,402 ... Blade for regulating the toner layer on the developing roller, 5 ... Photosensitive drum, 6 ... Corona charger, 7 ... Semiconductor laser, 8 ...
Static eliminator, 9 ... AC corona charger, 10 ... Cleaning fur brush, 11 ... Transfer charger, 13 ... Fixer.

Claims (3)

(57) [Claims] 1. A reversal development for developing an electrostatic latent image in which the surface potential of a photoconductor and the charging polarity of a toner are the same, and an image area is exposed and the surface potential of the photoconductor is attenuated. A color electrophotographic apparatus that repeats charging, exposing, and developing on a photoconductor to superimpose toners of at least one color of yellow, magenta, cyan, and black.
The magenta, cyan, and black developing units are brought close to the photoconductor, and the photoconductor and the yellow, magenta, cyan, and
During the process of initializing the copying machine in which the black developing device is operating, the surface potential of the photoconductor is Vo, and the developing biases at the time of yellow, magenta, cyan, and black development are V1, V2, V3, and V4, respectively. Then, the color electrophotographic apparatus is characterized in that the following conditions are set. 100V <| Vo | − | V1 | <500V 100V <| Vo | − | V2 | <500V 100V <| Vo | − | V3 | <500V 100V <| Vo | − | V4 | <500V 2. A color electrophotographic apparatus according to claim 1, wherein the means for setting the surface potential of the photosensitive member is a power source for controlling the voltage applied to the grid electrode of the scorotron charger. 3. A color electrophotographic apparatus according to claim 1, wherein the means for setting the surface potential of the photosensitive member is a power source for controlling the voltage applied to the corona charging line.