JP2003043769A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photoreceptor which has excellent wear resistance when images of only the black are formed with a color image forming device and more preferably a tandem type image forming device which does not require a mechanism of attaching and detaching a transfer belt to and from the photoreceptor by using amorphous silicon and pressing the transfer belt with a suitable pressure. SOLUTION: A photoreceptor selected from amorphous silicon, selenium arsenide and an organic photoreceptor of Vickers hardness >=45 is used as the photoreceptor and the suitable pressing pressure is set between the photoreceptor and the transfer belt, by which the use of the transfer belt without spacing the belt from the photoreceptor is made possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus such as a tandem copying machine and a printer, and more specifically, a plurality of image forming units including a photoconductor drum and a developing device are arranged along a sheet conveying path. In an image forming apparatus arranged in a single row, when forming an image only in black, the photoconductors of the image forming units of other colors rotate in an appropriate pressing state without being separated from the transfer belt. .

[0002]

2. Description of the Related Art An original image is color-separated on photoconductors of a plurality of image forming units, exposed for each record information, and developed by a toner of each color to obtain a visible image on a transfer paper conveyed by a transfer belt. There is known a tandem type color image forming apparatus that forms an image by sequentially transferring the images. Normal,
The tandem-type full-color image forming apparatus has four color image forming units of cyan, magenta, yellow, and black arranged side by side, and is sequentially superposed on a transfer belt for development, and is transferred to a sheet in a batch and the sheet is placed on a conveyor belt. There is a method in which a color image is formed by transferring each color and transferring each color. Until now, even in offices, image forming apparatuses such as copiers and printers were mainly of the monochrome type, and there were only a few color machines, but due to an increase in the number of color originals, they are being replaced by color image forming apparatuses. There is a tendency for color image forming apparatuses to output black only originals. In this way, when outputting only black originals with a color image forming apparatus, even if the photoreceptors of unused cyan, magenta, and yellow image forming units continue to rotate while being pressed by the transfer belt, There is a problem that the body surface is worn and the life is shortened. In order to solve such a problem, JP-A-3-288173, JP-A-6-258194, and JP-A-6-258194
As proposed in -102776, Japanese Patent Laid-Open No. 10-181927, etc., a method is adopted in which the driving of the photoconductor of an image forming unit other than black is stopped and the photoconductor is separated from the transfer belt. However, the above method requires not only a mechanism for separating and contacting the transfer belt from the photosensitive member, but also in the case where monochrome and color originals are mixed,
The image forming process needs to be temporarily interrupted when the transfer belt is separated and the pressure contact is switched, which results in poor productivity.

[0003]

In order to solve the above problems, the present invention uses a photoreceptor having excellent abrasion resistance, particularly amorphous silicon, when a black image is formed by a color image forming apparatus. An object of the present invention is to provide a tandem type image forming apparatus that does not require a mechanism for separating and contacting the transfer belt with respect to the photoconductor by pressing the transfer belt with an appropriate pressure.

[0004]

According to a first aspect of the present invention, a plurality of image forming units including a photosensitive drum and a developing device are arranged in a line along a paper transport path, and the plurality of image forming units are arranged. A tandem-type color image forming apparatus that forms a color image by sequentially transferring a toner image developed on a photoconductor drum onto a transfer paper conveyed by a transfer belt so as to form a black image only. In the case of performing, after the image forming unit corresponding to black forms a toner image on the photoconductor, the toner image is transferred onto a transfer paper conveyed by a transfer belt, and in the image forming units other than black, The photoreceptor is characterized in that it rotates in a pressed state with the transfer belt and conveys a sheet. According to the invention of claim 1, the transfer belt can be used in a pressure contact state without requiring a mechanism for separating and contacting the transfer belt from the photoreceptor. The invention according to Claim 2 is Claim 1
Is characterized by being selected from amorphous silicon, selenium arsenide, and an organic photoreceptor having a Vickers hardness of 45 or more. According to the second aspect of the present invention, by using the photoconductor selected from amorphous silicon, selenium arsenide, and Vickers hardness of 45 or more, since the abrasion is extremely small, the life can be extended more effectively and the photosensitivity can be improved. The body and the transfer belt can be used while being in pressure contact with each other. Further claim 3
The invention according to claim 1 is characterized in that the pressing force of the transfer belt to the photoconductor of claim 1 is 2 to 10 N (Newton). According to the third aspect of the invention, if the pressing force of the transfer belt on the photoconductor is set in this range, the transfer can be efficiently performed and the photoconductor can be used without being worn.

[0005]

DETAILED DESCRIPTION OF THE INVENTION A tandem type color image forming apparatus adopting the present invention will be described with reference to FIG. In the figure, this tandem color image forming apparatus is provided with a sheet feeding means 0.
1, vertical conveyance path 2, registration roller pair 3, belt conveyance means 4, first image forming unit 5, second image forming unit 6, third image forming unit 7, fourth image forming unit 8, fixing Means 9, discharge conveyance path 10, discharge tray 1
1 and the like. In the tandem type color image forming apparatus of the present invention, an amorphous silicon drum is used as the photoconductor of each of the first to fourth image forming units 5 to 8 of the embodiment. To form a color image, the toners developed by the image forming units 5 to 8 of the respective colors are sequentially overlapped, but a method of transferring and superimposing each color on a sheet placed on a conveyor belt is used. ing.

The paper feeding means 1 is composed of a paper feeding cassette 011, a paper stacking means 012, a paper feeding roller 013, etc.
The plurality of sheets stacked on the sheet stacking unit 012 are fed one by one from the top of the sheets in accordance with a sheet feeding signal. The belt conveying means 4 includes a driving roller 41 and a tension roller 4.
2 and a transfer belt 43 stretched over these two rollers, and is composed of a belt charging unit (not shown) for adsorbing a sheet on the surface of the transfer belt 43. The transfer belt 43 is stretched over the drive roller 41 and the tension roller 42, and rotates and moves at a speed substantially the same as the sheet conveyance speed while maintaining an appropriate tension. In this case, all of the first to fourth image forming units 5 to 8 have substantially the same configuration, and therefore the first image forming unit 5 will be used as a representative for the image formation in FIG. I do.

The image forming unit 5 includes a photoconductor 51, a main charging device 52, and an LPH (LED PRINT HEAD).
53, a developing device 54, a transfer device 55, a cleaning device 56, and a charge eliminating lamp 56, and when assembled in a housing made of resin, it becomes one unit and is attached to the main body. The main charging device 52 extends a thin tungsten wire of 50 to 100 μm in the longitudinal direction with respect to the drum in a shield case that opens toward the photoconductor 51, and applies a high voltage to the wire to positively charge the photoconductor 51. Let By irradiating the surface of the charged photoconductor 51 with light according to image information from the LPH 53,
An electrostatic latent image is formed on the surface of the. The developing device 54 uses a developer composed of positively charged toner and carrier,
The toner image is formed on the photoconductor 51 by applying it to the electrostatic latent image of the portion of the photoconductor 51 irradiated with light. The toner image on which the electrostatic latent image formed on the photoconductor 51 is developed as described above is transferred to the sheet conveyed by the conveyor belt 4 at the nip position with the transfer unit 55. In this embodiment, the transfer means 55 uses a transfer roller, and a voltage having a polarity opposite to the surface potential of the photoconductor 51 is set in the range of −1000 to −2500V and applied. The toner that has not been transferred on the photoconductor 51 is scraped off by the rubber blade of the cleaning means 56 in the next process, discharged by the discharge lamp 57 to reduce the residual potential on the surface and make it uniform, and then the next series of steps. Prepare for the process. The color image forming apparatus develops images corresponding to cyan, magenta, and black on the photoconductor by the second to fourth image forming units 6 to 8 in the same manner as the first image forming unit 5 described above. A full-color image is formed by sequentially repeating and transferring on a sheet of paper that has been sent. The image formation after the return transfer of FIG. 1 will be described again. The fixing unit 9 includes a first fixing roller 91,
The first fixing heater 911, the second fixing roller 92, the second
It is composed of a fixing heater 921. First fixing heater 91
By incorporating No. 1 therein, the temperature is controlled to a predetermined temperature required for fixing. In this embodiment, since the color is fixed,
A second fixing heater 921 is built in and controlled to a predetermined temperature necessary for fixing.

Next, the case of forming an image only in black, which is a feature of the present invention, will be described with reference to FIG. In the color image forming apparatus of this embodiment, the yellow, cyan, and magenta image forming units 5, 6, and 7 are arranged in this order from the upstream side of sheet conveyance.
And the black image forming unit 8 on the most downstream side
Are located on the photoconductors 511, 512, 51.
Amorphous silicon is used for 3, 514, and positive charging is performed. These image forming units 5, 6,
The order of 7 and 8 is not particularly limited to this. When outputting only a black image, the upstream yellow, cyan, and magenta image forming units 5 and 6, which do not form an image,
The developing sleeves of the developing units 541, 542, and 543 of No. 7 are stopped, and a negative developing bias opposite to the developing at the time of normal image formation is applied so that the toner does not adhere to the photoconductor side. On the other hand, the photoconductors 511, 512, and 513 of the image forming units 5, 6, and 7 are rotated while being pressed by the transfer belt 43 with an appropriate force, and convey the paper. Further, in this embodiment, the transfer rollers 551, 552, 5 are used in the transfer area.
Although a bias is not applied to 53, a bias having a reverse polarity to that in normal image formation may be applied so that the toner is not transferred to the paper. The sheet that has passed through the upstream image forming units 5, 6, and 7 that does not form an image is charged with a positive polarity in the black image forming unit 8 that forms an image, and after the image exposure, the developing device 544. Reversal development is performed with the positive polarity toner, and the toner is transferred to the sheet with the negative polarity by the transfer roller 554 to obtain a black image.

In the case of forming an image only in black according to the present invention,
The mechanism of the photosensitive member of the image forming unit that does not form an image other than black and the pressing portion of the transfer belt are shown in FIG.
Shown in. Bearings 62, into which the rotary shaft 61 of the transfer roller 55 is fitted, are rotatably attached to both ends of the transfer roller 55 on a side plate of a transfer belt unit (not shown) about a fulcrum 63, and are attached to the bearings 62. The pressure contact force of the pressure contact spring 64 presses the photoconductor 51 via the transfer belt 43. With respect to the pressing force, the point A of the bearing 62 is pressed by the push-pull gauge, and the transfer roller 55 causes the photosensitive member 5 to move.
It was measured by reading the value at the position in contact with 1.
Regarding the setting of the pressing force, if the pressing force at the transfer position in the most upstream image forming unit is set to be higher than the other pressing forces on the downstream side, the sheet will be conveyed more reliably,
In the first image forming unit 5, the pressing force was set to 9 N, and in the second to fourth image forming units 6 to 8, the pressing force was set to 4 N, and 10000 sheets of black images were continuously printed. There was no problem on the image, and the abrasion of the photosensitive layer was not measured. Next, when the pressing force was changed and the same experiment was conducted, when the pressing force was less than 2N, the transfer tended to be insufficient, and conversely, when the pressing force was more than 10N, there was a tendency that the image dropped out. Because it was recognized,
By setting the pressing force in the range of 10 N, good image formation became possible.

Experiments were carried out using the same mechanical structure as described above, using only the photoconductors and single-layer photoconductors having different Vickers hardnesses of 15 to 60. As a result, when a single layer photoreceptor having a general hardness of Vickers hardness of 25 is used, a black image is 1000.
When 0 sheets were continuously printed, there was a film scraping of 8 μm.
Since it was 4.5 μm when printing 0 sheets, it was estimated that there was 3.5 μm scraping due to the rubbing between the photoconductor and the transfer belt. This result indicates that scraping is a problem level. It was On the other hand, when an experiment similar to the above is carried out using a photoreceptor having a Vickers hardness of 45, the abrasion caused by rubbing is 0.3 μm.
There was no problem with m. In the case of an organic photoconductor, the Vickers hardness is 30 or less when a thermoplastic polycarbonate such as Z type is used as the binder resin.
The Vickers hardness can be adjusted by using a thermosetting resin or providing an overcoat layer. Further, an arsenic selenium photoreceptor having a Vickers hardness of usually 45 or more can also be used.

[0011]

According to the present invention, in a tandem type color image forming apparatus, when a black only image is formed, the transfer belt is separated so that the photoconductors of the image forming units of other colors do not wear. Because it was necessary
When not only the separation and contact mechanism is required, but also when full-color and black image formation are mixed, productivity was poor by performing pressure contact and separation, but amorphous silicon, arsenic selenium, Vickers hardness 45 or more. In addition to using a photoconductor selected from the above-mentioned organic photoconductors, the photoconductor and the transfer belt are brought into contact with each other with an appropriate pressing force of 2 to 10 N, so that it is possible to perform constant pressure contact.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a tandem color printer that employs the present invention.

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

FIG. 3 is a schematic diagram for explaining image formation of only black color in a tandem color printer adopting the present invention.

FIG. 4 is a sectional view showing a pressing mechanism for a photoconductor and a transfer belt of a tandem color printer adopting the present invention.

[Explanation of symbols]

5: First image forming unit (yellow) 6; Second image forming unit (cyan) 7: Third image forming unit (magenta) 8: Fourth image forming unit (black) 43; Transfer belt 51; photoconductor 55; Transfer roller 61; Transfer roller rotating shaft 62: Transfer roller rotary shaft bearing 63: Rotation fulcrum of transfer roller rotary shaft bearing 64; Pressure contact spring

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H030 AA05 AB02 AD05 AD07 AD08                       AD16 BB22 BB43 BB53 BB56                       BB71                 2H068 AA08 AA28                 2H200 GA12 GA18 GA23 GA44 GA47                       HA02 HB12 JA01 JA08 JA29                       JB06 JB22 JB32 JB49 LA18                       PA14 PA26

Claims (3)

[Claims] 1. A plurality of image forming units including a photoconductor drum and a developing device are arranged in a line along a paper transport path, and a toner image developed on the photoconductor drums of the plurality of image forming units is A tandem-type color image forming apparatus that forms a color image by sequentially superposing and transferring the image on a transfer paper conveyed by a transfer belt, and in the case of forming an image only in black, the image forming corresponding to black is performed. After the unit forms a toner image on the photoconductor, the toner image is transferred onto the transfer paper conveyed by the transfer belt, and in the image forming unit other than black, the photoconductor rotates in a pressed state with the transfer belt. A tandem-type color image forming apparatus characterized in that it also conveys paper. 2. The tandem type color image forming apparatus according to claim 1, wherein the photosensitive member is selected from amorphous silicon, selenium arsenide, and an organic photosensitive member having a Vickers hardness of 45 or more. 3. The pressing force of the transfer belt against the photoconductor is 2 to 10.
The tandem color image forming apparatus according to claim 1, wherein the tandem color image forming apparatus is N (Newton).