JP3134904B2 - Image forming method in color image forming apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method in a color image forming apparatus of a copying machine having a plurality of image forming units.

[0002]

2. Description of the Related Art In a color image forming apparatus in a copying machine using an organic photoreceptor, discharge products such as ozone and nitride oxide generated by a minus discharge of a scorotron charger adhere to the surface of the photoreceptor. A catalyst is applied to the grid of the charger in order to cause an image defect due to an electrostatic leak. Some shields are coated with carbon fiber.

[0003]

Since these have maintainability, they have conventionally been required to increase the coating thickness of the catalyst,
Means such as area expansion can be considered, but there are drawbacks such as a problem of securing a space and an increase in cost. Also, Japanese Patent Application Laid-Open No. 1-9
As disclosed in Japanese Patent No. 6670, in a tandem color image forming apparatus which does not have a transfer auxiliary charging device and has a black developing device in a first image forming portion, a photosensitive member which does not form an image is Charging, developing bias,
While energizing the transfer, preventing fog on the photoconductor and preventing bead carrier over, it also works to eliminate the potential difference between the photoconductor and the toner image on the paper,
In the case of a color image forming apparatus having no transfer assisting charger, discharge cannot be stopped, and the maintainability of the ozone treatment means in the exhaust unit is shortened.

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and is directed to a color image forming apparatus capable of ensuring the maintainability of a means for treating a discharge product generated by the discharge of a negative charger and reducing the number of parts replacement steps. It is an object of the present invention to provide an image forming method.

[0005]

In order to achieve the above object, an image forming method in a color image forming apparatus according to the present invention comprises a charging device for uniformly charging a photosensitive member, and a developing device for developing a latent image on the photosensitive member. In a color image forming apparatus in which a plurality of image forming units having a developing device, a transfer assisting charger, a transfer charger, and a cleaning device are arranged in a traveling direction of a transfer material, each image is formed in a black and white copying mode. Forming unit
While the transfer auxiliary charger is operated , only the charger for uniform charging of the image forming unit for the monochrome copying mode is discharged, and the discharging of the charger for uniform charging of the other image forming units is stopped. I am trying to do it. Further, the developing bias applied to the developing device of the image forming unit that does not discharge by the charger for uniform charging is set to be lower than the photoconductor surface potential by 150 V or more.

[0006]

[Operation] Since the chargers for uniform charging of the image forming units other than the image forming unit for the selected copy mode do not discharge, the amount of discharge products generated in the entire image forming apparatus is small. In addition, the transfer assisting charger of the image forming unit in which the charger for uniform charging does not discharge operates in the same manner as in the full-color mode, and the surface of the photoconductor is negatively charged. Thus, the image formed on the sheet is not retransferred by an unselected image forming unit.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a color image forming apparatus of a color electronic copying apparatus to which the present invention is applied. In the color image forming apparatus, a plurality of, for example, black, yellow, Image forming units 2B, 2Y, 2M, and 2C for magenta and cyan are arranged. Each of the image forming units has the same configuration, and includes a drum-shaped photoconductor 3 and a scorotron charger 4, an exposure unit 5, a developing device 6,
A transfer auxiliary charger 7, a transfer charger 8, a neutralizer 9, a cleaning device 10, and a neutralization lamp 11 are arranged in this order.
The transfer charger 8 is located inside the transfer belt 1 and faces the photoconductor 3 via the transfer belt 1. As shown in FIG. 7, the scotron charger 4 includes a shield 12, a wire 13, and a grid 14, and the carbon fiber layer 1 is formed on the inner surface of the shield 12 for discharge product removing means.
5 is coated.

In this configuration, the paper 16 traveling along the transfer belt 1 in the color image forming apparatus, when in the full color mode, has the image units 2B, 2
Y, 2M, and 2C sequentially duplicate and color-copy. The timing chart of the color image forming apparatus at this time is as shown in FIG.

In this case, the photoconductor driving motors B, Y, M, and C of the respective image forming units are driven in the same manner during the entire copying process. Each scotron charger 4-B, Y, M, C is paper 1
6 are sequentially turned on in accordance with the movement timing of No. 6 and turned on. Similarly, each of the developing devices 6-B, Y, M, and C and each of the transfer auxiliary charging devices 7-B, Y, M, and C are sequentially shifted and turned on at respective timings.

In the black and white mode, that is, when copying is performed only by the black image forming unit on the most upstream side in the running direction, the copying operation is performed according to the timing charts shown in FIGS. In the case shown in FIG. 3, only the black scorotron charger 4-B among the scorotron chargers 4-B, Y, M and C for uniformly charging the photoconductor 3 in the full color mode shown in FIG. Is discharged, and the other scotron chargers 4-Y, M, and C do not discharge. Others are the same as in the full color mode. At this time, the bias voltages of the developing devices 6-Y, M, and C other than for black are set to be lower than those in the full-color mode. desirable. This prevents fogging due to the potential difference (cleaning field) between the photoconductor surface potential and the bias voltage of the developing device 6. This is because, as shown in FIG. 6, when the photoconductor surface potential is O (V), the cleaning field potential has a first-order correlation with the bias voltage. This is because the image is made more conspicuous by the photoconductor 3 to cause fogging, and the fog toner is preferably prevented from being transferred to the paper 16.

On the other hand, in the case shown in FIG. 4, a scorotron charger 4-B other than the black scorotron charger 4-B is used.
The discharge of Y, M, and C is stopped, and the application of the bias voltage to the developing devices 6-Y, M, and C other than the developing device 6-B for black is stopped. In any case in the black and white mode, the transfer assisting chargers 7-B and 7-B of each image forming unit are used.
Y, 7-M, and 7-C are output during operation of each image forming unit.
N, whereby the transferred image formed on the sheet by the black image forming unit 2B and the black developing device 6 is converted into the yellow, magenta, and cyan image forming units 2Y, 2M, and 2C. To each photoreceptor is prevented.

FIG. 5 shows the relationship between the surface potential of the photosensitive member 3 when the electrostatic latent image is formed on the photosensitive member 3 and the Bais voltage of the developing device 6. Further, the sustainability of the scorotron charger 4 against the discharge products is as follows. FIG. 8 shows the discharge product removal efficiency of the charger 4 with respect to the number of copies. As is clear from this figure, if the black-and-white and color copying are 4: 1, the maintainability of the scorotron charger 4 is quadrupled.

[0013]

According to the present invention, in the black and white mode, which is the most frequently used mode, only the black and white image forming unit 2B for selectively charging the photosensitive member 3 is selectively used. Discharge, the amount of discharge products generated by the discharge of the charger for uniform charging in the entire image forming apparatus is reduced, and the processing of the discharge products in the image forming apparatus is facilitated. Maintainability of the discharge product processing means provided in the scorotron chargers 4 of the image forming units 2Y, 2M, and 2C other than the image forming units 2Y, 2M, and 2C is secured, and the number of parts replacement in this part can be reduced. Also
According to the present invention, each image can be
The transfer assist charger of the image forming unit is operating
Transfer image on paper formed in black and white mode
Is transferred to each photoconductor of each image forming unit for other colors.
Suffering can be prevented.

By setting the developing bias voltage of the image forming unit in which the scorotron charger does not discharge to a value lower than a predetermined value, the transferred image formed on the sheet by the black image forming unit can be used to form an image other than black. Retransfer to the photoconductor of the unit is prevented.

[Brief description of the drawings]

FIG. 1 is a schematic structural explanatory view of an image forming apparatus to which the present invention is applied.

FIG. 2 is a timing chart of a full color mode.

FIG. 3 is a timing chart in the first embodiment in a monochrome mode.

FIG. 4 is a timing chart in a second embodiment in a monochrome mode.

FIG. 5 is a diagram illustrating a relationship between a photoconductor surface potential and a developing bias during image formation.

FIG. 6 is a diagram showing a relationship between a developing bias and a cleaning field potential.

FIG. 7 is a cross-sectional view showing a scorotron charger used in an image forming apparatus to which the present invention is applied.

FIG. 8 is a diagram showing discharge product removal efficiency with respect to the number of copies of the method of the present invention and the conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Transfer belt, 2B, 2Y, 2M, 2C ... Image forming unit, 3 ... Photoconductor, 4 ... Scorotron charger, 5 ... Exposure part, 6 ... Developing device, 7 ... Transfer auxiliary charger, 8 ... Transfer charger , 9 ... static eliminator, 10 ... cleaning device, 11 ... static elimination lamp, 12 ... shield, 13 ... wire, 14 ... grid, 15 ... carbon fiber layer, 16 ... paper.

Continuation of the front page (56) References JP-A-59-154465 (JP, A) JP-A-63-8665 (JP, A) JP-A-1-96670 (JP, A) JP-A-2-129665 (JP) , A) JP-A-63-8658 (JP, A) JP-A-62-299873 (JP, A) JP-A-60-188909 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB G03G 13/01 G03G 15/01-15/01 117

Claims (2)

(57) [Claims] 1. A plurality of image forming units having a charger for uniformly charging a photoconductor, a developing device for developing a latent image on the photoconductor, a transfer auxiliary charger, a transfer charger, and a cleaning device. In the color image forming apparatus arranged in the running direction of the material, each image forming
With the knit transfer assist charger in operation, only the charger for uniform charging of the image forming unit for the black and white copy mode is discharged, and the charger for uniform charging of the other image forming units is discharged. An image forming method in a color image forming apparatus, wherein the discharging of a charger is stopped. 2. The image forming apparatus according to claim 1, wherein the developing bias applied to the developing device of the image forming unit in which the charger for uniform charging does not discharge is lower than the surface potential of the photosensitive member by 150 V or more. Image forming method.