JP2002258567A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that a cleaning blade is turned up because the photoreceptor of an image forming means not to be used is rotated in a state where toner is not supplied in the case of outputting an image only in black in a tandem color copying machine or printer. SOLUTION: The cleaning blade is prevented from being turned up by arranging a yellow image forming means on the most upstream side and a black image forming means on the most downstream side, developing and transferring yellow toner a little by the yellow image forming means and transferring the yellow toner to the photoreceptors of other color image forming means for cyan and magenta existing between the yellow image forming means and the black image forming means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of arranging a plurality of image forming means side by side, performing an image forming process on the image forming means to obtain a visual image of each color, and transferring the visual image to a transfer paper supplied from outside. The present invention relates to an image forming apparatus that obtains a color image by performing a cleaning blade in an image forming unit of another color when a black-only image is formed. is there.

[0002]

2. Description of the Related Art A document image is color-separated on a plurality of photoconductors,
2. Description of the Related Art A tandem-type image forming apparatus that forms an image by sequentially exposing and developing a visible image obtained by exposing and developing each recording information onto a transfer sheet conveyed by a transfer belt is known. Normally, in the case of full color, image forming means of four colors of cyan, magenta, yellow, and black are arranged, developed successively on a transfer belt, and transferred to a sheet. To form a color image. Until now, monochrome image forming devices such as copiers and printers have been the mainstream in offices, but by replacing color image forming devices, color image forming devices can copy black-only originals. There is a tendency to increase further. When a black image is copied by the color image forming apparatus, the unused cyan, magenta, and yellow image forming units use an image forming unit from the transfer belt so that the toner on the photoreceptor is not placed on the transfer paper. It has been considered that the evacuation mechanism can be evacuated, but the evacuation mechanism is costly and not a practical solution.

Recently, in such a case, generally, in order to prevent toner from being placed on the photoreceptor of the image forming means for cyan, magenta, and yellow other than black, for example, in the case of a positively charged photoreceptor, A method is adopted in which the toner is not placed on the photoconductor by means of rotating at a surface potential of 0 without charging and applying a negative bias potential to the positively charged toner for reversal development. However, if the photoconductor continues to rotate without toner, a large torque is applied between the photoconductor surface and the edge of the cleaning blade,
There was a problem that the blade finally rolled up.

[0004]

According to the present invention, in order to solve the above-mentioned problems, when a color image forming apparatus forms an image only with black, yellow is first developed, black is finally developed, and cyan, The magenta image forming means is arranged side by side in the middle, first developed slightly with yellow toner, and transferred to transfer paper.
By transferring the yellow toner onto the photoreceptor of the magenta image forming means, it is possible to prevent cleaning failure.

[0005]

According to the first aspect of the present invention, an electrostatic latent image is formed on a photosensitive drum and developed by a developing device. In an image forming apparatus having a plurality of image forming means for visualizing, a color developed by the image forming means on the upstream side and transferring the toner transferred to the transfer paper onto the photoreceptor of the image forming means on the downstream side An image forming apparatus, in which an image forming unit adjacent on the downstream side does not perform development because the original does not have a color and does not supply toner onto the photosensitive drum. This is to prevent it.

In the second aspect, the plurality of image forming units are arranged side by side so that the first is yellow development and the last is black development, and the image formation is performed only in black. The color image forming apparatus according to claim 1, wherein the yellow toner is slightly supplied to an image forming unit such as cyan or magenta positioned in the middle, but the image is formed even if mixed. , And cleaning failure can be prevented. In the third aspect of the invention, if the amount of development of the uppermost stream yellow toner is too small, the amount of toner to be supplied to the image forming means on the downstream side is insufficient, and the effect of winding up the cleaning blade is small. The feature is that the area ratio of the toner is less than 5% because many colors are mixed into the toner and the image is affected. 5. A transfer type color image forming apparatus according to claim 4, wherein said plurality of image forming means are arranged side by side in a tandem type, and said paper is placed on a transport belt and is sequentially transferred.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A tandem type color image forming apparatus employing the present invention will be described with reference to FIG. In FIG. 1, the tandem color image forming apparatus includes a sheet feeding unit 01,
Vertical transport path 2, registration roller pair 3, belt transport means 4, first image forming means 5, second image forming means 6, third image forming means 7, fourth image forming means 8, fixing means 9 , A discharge conveyance path 10, a discharge tray 11, and the like. The tandem-type color image forming apparatus sequentially superimposes the toners developed by the image forming means of each color.
There are two types: a type in which the image is transferred in degrees, and a type in which the image is transferred and superimposed for each color on a sheet placed on a transport belt. In the present invention, the latter type is used.

The paper feeding means 01 is composed of a paper feeding cassette 011, a paper stacking means 012, a paper feeding roller 013, etc., and the first of a plurality of papers stacked on the paper stacking means 012 in response to a paper feeding signal. Paper is fed one by one from the top. The registration roller pair 3 has a role of adjusting the leading edge of the conveyed sheet and a role of starting the sheet with respect to the transfer position in synchronization with the image timing. Belt conveying means 4
The belt charging means (not shown) comprises a driving roller 41, a tension roller 42, and a belt member 42 stretched over the two rollers. It is composed of The belt member 43 is stretched over the driving roller 41 and the tension roller 42, and rotates and moves at substantially the same speed as the paper transport speed while maintaining an appropriate tension. Since the material is close to the fixing means 9, in consideration of heat resistance, elasticity, strength, insulation property of the inner surface of the belt, releasability of toner on the outer surface of the belt, etc., the outer peripheral surface of the endless belt made of polyimide is coated with fluorine. Applied and suitable. Further, since the belt needs to also serve as the elastic layer, a material having a release layer of a fluorine-based resin such as PTFE on the surface of silicon rubber or EPDM may be used.

In this case, the first to fourth image forming means (5 to 8) are for yellow, cyan, magenta, and black from the right side in the figure, and are all units having almost the same configuration. Here, the image formation will be described with reference to FIG. 2 using the first image forming unit 5 as a representative. The first image forming means 5 includes a first photosensitive drum 51, a first main charging device 52, a first LPH (LED PRINT HEA).
D) 53, a first developing device 54, a first transfer unit 55,
The first cleaning device 56 and the first static elimination lamp 56 are combined into a resin housing to form a single unit, which is attached to the main body. The first photosensitive drum 51 uses an amorphous silicon drum, and is charged by the first main charging device 52 so that the dark potential at the developing position is approximately +450 V. The first main charging device 52 stretches a thin tungsten wire of 50 to 100 μm in the shield case opened toward the first photosensitive drum 51 in the longitudinal direction with respect to the drum.
The first photosensitive drum 32 is positively charged by applying a high voltage of about +5 KV thereto. The first LPH 53 irradiates the charged surface of the first photosensitive drum 51 with light according to image information, whereby an electrostatic latent image is formed on the surface of the first photosensitive drum 51. First LPH5
3 is used to reduce the size of the unit, but LSU
(Laser scanning unit) may be used.

The first developing device 54 uses a developer consisting of a positively charged toner and a carrier with stirring and mixing so as to have a predetermined concentration, and uses a developing roller having a magnet member therein to apply this developer to the first developing device. The toner image is formed on the photosensitive drum by applying to the electrostatic latent image of the portion of the photosensitive drum 51 irradiated with light. The dark potential of the first photosensitive drum 54 is +450 V, and the developing bias is +35.
0 V, and the potential after exposure is set to +20 V. That is, since the developing bias potential corresponds to the image white portion and the post-exposure potential corresponds to the image black portion, the so-called contrast potential is 330 V in this case. The toner image on which the electrostatic latent image formed as described above is developed is transferred to a sheet conveyed by the conveyance belt 4 to a nip with the first transfer unit 55. In the present embodiment, the first transfer unit 55 uses a transfer roller, and a voltage having a polarity opposite to the surface potential of the first photosensitive drum 51 is −1000 to −1.
The voltage is set in the range of 300 V and applied.

The untransferred toner on the first photosensitive drum 51 is removed by the first cleaning means 5 in the next process.
6 and scraped off by a rubber blade, and the charge is removed by a first charge removing lamp 57 in order to lower and make the residual potential on the surface uniform, and then prepare for the next series of processes. The optimal value for the potential setting for image formation in this manner changes depending on the characteristics of the photosensitive drum, the performance of the toner, and the environment. Since the dark potential, the developing bias potential, and the transfer potential are changed depending on whether or not each image forming unit forms an image, the first main charging device 52 receives a signal from the first main charging power source 521. First for turning on / off the output
The first developing device 54 is provided with a first developing bias switch SW541 for switching between an eleventh developing bias power source 541 and a twelfth developing bias power source 542, and the first developing device 54 is further provided with the first developing device 54. Transfer unit 55
Include the eleventh transfer power source 551 and the twelfth transfer power source 55
2 for the first transfer voltage switching SW553
Is provided. Here, each switch is provided to facilitate understanding of the invention. However, in practice, the developing bias voltage is controlled so that a plurality of voltages can be output in a stepwise manner, and the rising fog of the main charging is reduced. Prevent,
A transfer power supply that can variably control the voltage is used. The color image forming apparatus uses the same method as the above-described first image forming means, and performs cyan, magenta,
A full-color image is formed by developing an image corresponding to black on a photoreceptor and repeating the transfer on a sheet of paper sequentially without deviation.

The image formation after the return transfer in FIG. 1 will be described again. The fixing unit 9 includes a first fixing roller 91, a first fixing heater 911, a second fixing roller 92, and a second fixing heater 921. More specifically, the first fixing roller 91 may be formed by applying a fluorine coat to aluminum or the like having good thermal conductivity or by providing an elastic layer. By incorporating the first fixing heater 911, the temperature is controlled to a predetermined temperature required for fixing. The driving of the first fixing roller 91 may be driven by contact from the second fixing roller 92.
It is preferable to follow the fixing roller 92. The second fixing roller 92 faces and contacts the first fixing roller 91, and is driven by a driving unit (not shown). The fixing roller 92 has a base made of an aluminum roller having good thermal conductivity, and its periphery is covered with an elastic layer 922 in order to secure a fixing nip width.
The elastic layer 922 may be made of any heat-resistant rubber, but silicon rubber or the like is suitable. In this embodiment, in order to perform color fixing, a second fixing heater 921 is built in and is controlled to a predetermined temperature necessary for fixing. Although not shown, each roller is provided with a claw member for peeling off the sheet, and a roller or web for cleaning.

The case of forming an image only with black, which is a feature of the present invention, will be described with reference to FIGS. The present color image forming apparatus sequentially develops and transfers one color at a time, but also drives the photosensitive drum of the image forming means that is not performing image formation. The photosensitive drum is driven in the image forming means of the color of. In FIG. 3, a surface potential of +450 V is placed on the photosensitive drum 51 by applying a voltage of +5 KV to the main charging device 52 of the first image forming means 5, the potential after exposure is +20 V, and the area ratio of the print dots is 1 % To form an electrostatic latent image, and the developing unit 54 develops the yellow toner at a bias potential of +350 V. The developing area of the yellow toner is preferably A4 size or more, although it depends on the transfer efficiency, but also on the number of image outputs of black only. On the paper conveyed to the nip between the first image forming means 5 and the first transfer means 55, an image of yellow toner is transferred to the paper by the first transfer means 55 at a transfer voltage of -1000V, and subsequently In the nip between the second image forming means 6 and the second transfer means 65, the yellow toner on the paper is transferred to the photoconductor side. Further, in the nip between the third image forming means 7 and the third transfer means 75, the yellow toner on the sheet is transferred to the photoconductor similarly to the second image forming means. Finally, the black toner formed on the photosensitive drum 81 at the nip between the fourth image forming means 8 and the fourth transfer means 85 is transferred by the transfer means 85 to output an image of only black.
In this embodiment, a small amount of yellow toner is developed at the dot area ratio. However, it is also possible to reproduce halftone on the entire surface of the photoconductor by multi-value control and develop the yellow toner thinly over the entire surface.

Next, when outputting only the above-described black image, the first and second image forming units 6 and 7 which do not form an image are formed by the first image forming unit 5 and formed on paper. The transfer of the transferred yellow toner to the photosensitive drums 61 and 71 of the second and third image forming units 6 and 7 is described below.
A description will be given based on FIG. 4 using the second image forming unit 6. In the main charging device 62 of the second image forming means 6, since the second main charging SW 622 is OFF, no potential is applied to the surface of the second photosensitive drum 61, and thus the second photosensitive device 62 at the developing position The surface potential of the body drum 61 is 0V. Since the developing bias applied to the developing roller of the second developing device 64 is -150 V, the positively charged toner mixed with the developer is electrostatically pulled by the developing roller, and
Does not move to the surface of the photosensitive drum 61. The developing bias of -150 V is set to a value such that the positively charged toner is not developed and the carrier of the developer does not fly when the surface potential of the second photosensitive drum 61 is 0 V.

In the nip between the second photosensitive drum 61 and the second transfer means 65, the toner is not transferred to the sheet because no toner is loaded on the second photosensitive drum 61.
5 to 10% of the yellow toner already transferred to the paper by the first image forming means 5 on the upstream side is the second photosensitive drum 61
-1000V to the second transfer means 65 so that the
The above transfer voltage is applied. (Transfer is possible even when the applied voltage is 0 V or slightly positive.) In this way, the yellow toner in the first developing unit 54 is moved onto the second photosensitive drum 61 for cyan toner via the paper. And the second
To the image forming means 6. As the photosensitive drum 61 rotates, this yellow toner is supplied to the edge of the cleaning blade of the second cleaning unit 66,
The coefficient of friction between the photosensitive drum and the edge of the cleaning blade can be reduced to prevent the cleaning blade from rolling up. The yellow toner on the paper that has not been supplied to the second image forming means 6 is transferred to the third photosensitive member 7 of the third magenta image forming means 7 in the same manner.
After being supplied to 1, the cleaning blade reaches the cleaning blade edge of the third image forming unit 7, and similarly prevents the cleaning blade from being rolled up. In this series of processes, the yellow toner developed and transferred by the first image forming unit is evenly transferred onto the photoreceptors of the second and third image forming units, and the yellow toner of the third image forming unit is also transferred. After the image is transferred onto the photoreceptor, it is necessary to adjust the transfer voltage of the second and third image forming units so that the toner remains on the sheet as little as possible. However, when black is developed by the fourth image forming means, slight mixing of the yellow toner does not cause a problem on the image.

In this embodiment, a positively charged amorphous silicon photosensitive drum is used, but a positively charged OPC or a negatively charged photosensitive drum may be used. In the case of a negatively charged photosensitive drum, the polarity of the setting of the developing bias and the transfer voltage is naturally opposite to that of the present embodiment. Further, with respect to the curling up of the cleaning blade, it is more effective to add a lubricant such as zinc stearate to the toner side.

[0017]

According to the present invention, when a color image is formed, the blade roll-up that has occurred in the image forming means of a color that does not appear is mixed with other colors if the amount is small, such as yellow toner. By sending an image which has no effect on the image to the edge of the cleaning blade of the image forming means which does not develop color, it is possible to prevent the cleaning blade of the image forming means from rolling up.

[Brief description of the drawings]

FIG. 1 is a schematic view of a tandem color printer employing the present invention.

FIG. 2 is a diagram illustrating image formation in a first image forming unit of a tandem color printer employing the present invention.

FIG. 3 is a schematic diagram showing a case where a tandem color printer employing the present invention performs printing of only black.

FIG. 4 is a diagram illustrating a case where yellow toner is supplied to a cyan developing section on the downstream side when performing only black printing with a tandem color printer employing the present invention. 01; sheet feeding means CPU 2; vertical conveying path 3: registration roller pair 4: belt conveying means 5; first image forming means (yellow) 6; second image forming means (cyan) 7; third image forming Means (magenta) 8; fourth image forming means (black) 9; fixing means 10; discharge conveyance path 11; discharge tray

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03G 21/00376 G03G 21/00 384 384 318

Claims (4)

[Claims] An image forming apparatus having a plurality of image forming means for forming an electrostatic latent image on a photosensitive drum and developing and visualizing the latent image with a developing device, after developing in an upstream image forming section, A color image forming apparatus, wherein toner transferred to a sheet is transferred onto a photosensitive member of an image forming unit on a downstream side. 2. The image forming means according to claim 1, wherein said plurality of image forming means are arranged side by side so as to develop first with a yellow toner on a most upstream side and finally develop with a black toner on a most downstream side. 2. The color image forming apparatus according to claim 1, wherein the process is performed by: 3. The development of the yellow toner on the most upstream side is as follows:
3. The color image forming apparatus according to claim 2, wherein the area ratio is less than 5%. 4. The color image forming apparatus according to claim 2, wherein said plurality of image forming means are arranged in a tandem type, and said sheet is placed on a conveyor belt and transferred in order.