JP2003207971A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device by which productivity is not reduced in image forming when the continuous images of originals where the full-color ones are mixed with the monochromatic ones are formed the excellent image is formed by preventing a hollow defect in the case of transferring and the life of an image carrier body, etc., is prolonged. <P>SOLUTION: A full-color image forming device is provided with a plurality of image carrier bodies 1a, 1b, 1c and 1d for forming developer images in different colors and a recording material carrier body 2 for abutting a recording material G onto the image carrier bodies 1a-1d and carrying it. Changeover is performed between a first image forming mode and a second image forming mode. In the first image forming mode, the developer images are formed in the whole image carrier bodies 1a-1d and a circumferential speed difference is made between the whole image carrier bodies 1a-1d and the recording material carrier body 2. In the second image forming mode, the absolute value of the circumferential speed difference between the image carrier bodies 1a-1c without forming the develop image and the recording material carrier body 2 is made to be smaller than the absolute value of the circumferential difference between the image carrier body 1d for forming the develop image among the image carrier bodies 1a-1d and the recording material carrier body 2. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copying machine, LBP,
The present invention relates to an image forming apparatus such as a facsimile, and particularly, an image forming mode in which a plurality of image carriers and a recording material carrier or an intermediate transfer member are provided, and image formation is simultaneously performed on all the plurality of image carriers, such as full-color image formation. And an image forming mode in which an image is formed only by a selected image carrier among a plurality of image carriers, such as black monochromatic image formation, and an image forming apparatus capable of forming two types of images. is there.

[0002]

2. Description of the Related Art Conventionally, for example, a drum-shaped electrophotographic photosensitive member, that is, a photosensitive drum has been used as an image bearing member. The surface of the photosensitive drum is uniformly charged, and the surface is exposed to light corresponding to an image signal to form an electrostatic latent image, and the electrostatic latent image is developed by a developing device using toner as a developer. To obtain a developer image (toner image) which is a visible image. Next, the toner image is transferred onto the recording material by using the transfer means, and then the unfixed toner image on the recording material is fixed by using the fixing device to form an image.

Here, for example, an image forming apparatus such as a copying machine printer is provided with a plurality of image forming units integrated with process means for forming an unfixed toner image on a recording material or an intermediate transfer member. In each image forming unit, toner images of different colors such as yellow, magenta, cyan, and black are formed on the respective photosensitive drums, and the respective toner images are carried and conveyed on the recording material carrier. Various image forming apparatuses have been proposed in which the color unfixed toner images superposed on the same recording material are sequentially superposed and transferred, and then the color unfixed toner images superposed on the recording material are collectively fixed to obtain a color image.

Such a plurality of image forming sections are provided, toner images of different colors are formed in the respective image forming sections, and the toner images are sequentially superimposed and transferred onto the same recording material to form a color image. An example of the image forming apparatus is shown in FIG.

The image forming sections Pa, Pb, Pc, and Pd form the toner images of the respective colors as one unit, and form the toner images of the respective colors, that is, the photosensitive drums 1a to 1a.
d and an image forming unit that acts on it.
Here, photosensitive drums 1a, 1b, 1c, and 1d that are rotatably supported and rotate in the directions of the arrows are provided, and primary chargers 12a to 12d and exposing means 16a to 1 are provided for the respective photosensitive drums.
6d, developing devices 13a to 13d, and transfer means 14a to
14d is integrated.

The photosensitive drums 1a, 1b, 1c, 1d are uniformly charged by the respective primary chargers 12a-12d,
Then, the light images that have been color-separated from the exposure units 16a to 16d are irradiated to form electrostatic latent images.

Next, the photosensitive drums 1a, 1b, 1c, 1d
The above electrostatic latent image is developed into a visible toner image by the developing devices 13a to 13d provided in each of the image forming units Pa to Pd.

On the other hand, in this image forming apparatus, the recording material G is accommodated in the cassette 4, and the recording material G fed into the image forming apparatus by the paper feed roller 10 is a belt-shaped recording material carrier. , From the first image forming unit Pa by the endless belt that cyclically moves, that is, the conveyor belt 2,
It is carried and conveyed to the fixing device 6 via the second and third image forming units Pb and Pc and the fourth image forming unit Pd.

The toner images formed on the photosensitive drums 1a, 1b, 1c, 1d of the image forming sections Pa to Pd are recorded on the recording material G carried on the conveyor belt 2 and the image forming sections Pa to Pd are formed. Transfer chargers 14a, 14b provided in the
The images are superimposed and transferred by 14c and 14d.

The transfer residual visible toner images which have not been completely transferred to the recording material G at the transfer portion to the recording material G of each image forming portion are collected by the respective developing portions and are used for the next image formation.

In an image forming apparatus using such a belt-shaped recording material carrier (hereinafter referred to as a "conveying belt"), a problem of a hollow defect which is a transfer process problem generally occurring in a conventional electrophotographic system. Was occurring.

The hollow image phenomenon is a phenomenon in which only the peripheral portion of a character or line image having a specific width is transferred to the recording material, and the toner in the central portion is not transferred and remains on the image carrier. is there. It is considered that this phenomenon occurs because an excessive pressure is applied to the transfer area, the toner in that portion is aggregated, and the releasability of the aggregated toner from the image carrier is deteriorated.

For such a hollowing-out phenomenon, Japanese Patent Laid-Open No.
As described in JP-A-7-78576 and JP-A-2-262175, this phenomenon can be prevented by providing a peripheral speed difference between the image carrier and the recording material. This prevention means is very effective in preventing the hollow defect in the image forming apparatus using the conveyor belt.

Incidentally, such a hollow phenomenon is not directly transferred to the recording material on the above-mentioned transport belt by using a belt-shaped intermediate transfer body (hereinafter referred to as "intermediate transfer belt"). The same occurs in the image forming apparatus in which the toner image is primarily transferred from the photosensitive drum to the intermediate transfer belt and then secondarily transferred to the recording material from the intermediate transfer belt. As a countermeasure, the method of providing the peripheral speed difference between the photosensitive drum and the intermediate transfer belt is effective in preventing the hollow defect.

In an image forming apparatus having an image forming unit for each of a plurality of photosensitive drums as shown in the above-mentioned conventional example, when using the single color mode instead of the full color mode,
In the image forming mode in which the toner image is formed only in the selected image forming section among the plurality of image forming sections, the conveyance belt or the intermediate transfer belt is separated from the photosensitive drum on which the image is not formed to form the image. An image forming apparatus has been proposed which prevents unnecessary wear of the photosensitive drum of the image forming unit that does not perform image formation by contacting only the photosensitive drum of the image forming unit that performs the image formation.

In this method, in order to prevent the hollow portion phenomenon in the transfer portion as described above, it is provided between the photosensitive drum and the conveying belt or the intermediate transfer belt (hereinafter collectively referred to as "transfer belt"). When the peripheral speed difference is provided, the photosensitive drum is heavily worn, which is particularly effective for such an image forming apparatus.

[0017]

However, in such a method in which one of the image carriers is separated from the transfer belt while the other image carrier is forming an image, a plurality of originals, for example, , When a black single color image and a full color image are mixed, when the copying operation is performed using an automatic document feeder called a feeder, the transfer belt contact / separation operation must be performed every time the black single color and the full color are switched. I won't. Therefore, there is a problem that an unnecessary time is increased in the image formation and the copying operation takes a very long time.

Therefore, in order to avoid such a problem, the transfer belt is subjected to image formation not only in the full color mode but also in the image forming mode in which only the selected image forming portion forms an image, such as the single color mode. The state of contacting not only the photosensitive drum on which the toner image is formed, but also the photosensitive drum on which the toner image is not formed, that is, not only the photosensitive drum on which the toner image is formed,
A method of forming an image without performing the separating operation of the transfer belt has also been proposed.

In this method, the image forming processes such as charging, exposure, development and transfer relating to the photosensitive drum are
Only the image forming unit that performs the selected image formation is performed.

Then, as a matter of course, if a peripheral speed difference is provided between the photosensitive drum and the transfer belt in order to prevent the hollow defect as shown in the above-mentioned conventional example, image formation by the photosensitive drum of the selected image forming portion is performed. At other times, the image carrier of the image forming unit that does not perform other image formation is worn or damaged even though it is not performing the image forming operation, resulting in a problem that the life is shortened. .

Therefore, an object of the present invention is to prevent a reduction in dropouts during transfer without reducing the productivity of image formation even in continuous image formation of full-color, single-color mixed originals, etc. An object of the present invention is to provide an image forming apparatus capable of performing formation, maintaining a long life of an image carrier and the like, and operating at low cost.

[0022]

The above object can be achieved by an image forming apparatus according to the present invention. In summary, the first aspect of the present invention is directed to a plurality of image carriers on the surface of which developer images of different colors are formed, and the plurality of image carriers sequentially from the upstream side to the downstream side along the moving direction. A recording material carrier that is arranged to convey the recording material in contact with the plurality of image carriers, and sequentially conveys the developer image onto the recording material carried by the recording material carrier. In an image forming apparatus that transfers and forms an image, in the first image forming mode, the developer images are formed on all of the image carriers, among the plurality of image carriers.
A peripheral speed difference is provided between all of the plurality of image carriers and the recording material carrier, and the developer image is formed in the plurality of image carriers in the second image forming mode. There is an image carrier and an image carrier on which the developer image is not formed, and the developer image is formed from the absolute value of the peripheral speed difference between the image carrier on which the developer image is formed and the recording material carrier. There is provided an image forming apparatus characterized by reducing the absolute value of the peripheral speed difference between the image carrier and the recording material carrier which is not operated.

According to a second aspect of the present invention, a plurality of image bearing members on the surface of which developer images of different colors are formed, and the plurality of image bearing members are sequentially arranged along the moving direction from the upstream side to the downstream side. An intermediate transfer member that is provided and moves itself, sequentially primary-transfers the developer image onto the intermediate transfer member, and collectively transfers the developer that is primarily transferred onto the intermediate transfer member to a recording material. Then, in the image forming apparatus that secondarily transfers and forms an image,
In the first image forming mode, the developer images are formed on all the image bearing members of the plurality of image bearing members, and there is a difference in peripheral speed between all of the plurality of image bearing members and the intermediate transfer member. In the second image forming mode, there are an image carrier on which the developer image is formed and an image carrier on which the developer image is not formed among the plurality of image carriers, and the developer image The absolute value of the difference in peripheral speed between the image carrier on which the developer image is not formed and the intermediate transfer member is made smaller than the absolute value of the difference in peripheral speed between the image carrier on which the image is formed and the intermediate transfer member. A characteristic image forming apparatus is provided.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION An image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Embodiment 1 FIG. 1 shows an embodiment of an image forming apparatus to which the present invention can be applied. In this embodiment, a color laser beam printer having a plurality of image forming units (hereinafter simply referred to as “printer”) is embodied, but the present invention is not limited to this.

Further, according to the present embodiment, the plurality of image forming units are the first, second, third and fourth image forming units Pa and P.
Although b, Pc, and Pd are arranged side by side, the present invention is not limited to this, and the number of image forming units can be arbitrarily selected from two or more.

As shown in FIG. 1, the printer of this embodiment has substantially the same image forming units Pa, Pb, and P.
Each of the image forming units c and Pd is an image forming unit that forms an image of yellow (Y), magenta (M), cyan (C), and black (Bk).

This printer has two image forming modes: (1) a full color image forming mode which is a first image forming mode, and (2) a black single color image forming mode which is a second image forming mode. However, these two modes can be switched by externally setting in advance, and the method of switching the image forming mode is selected according to the type and purpose of the image forming apparatus. In this embodiment, when a full-color, single-color mixed original or the like is continuously image-formed, the original fed by an original feeding device such as a feeder to the original reading unit is read by a so-called prescan, and the original is read. The control unit that controls the document reading unit determines whether the image is in full color or in black, and automatically switches the image forming mode.

In this embodiment, the image forming mode switching method for the printer equipped with the document reading section is described. However, in the case of a so-called simple printer having no document reading section, the host computer is changed to the printer. Even in such a printer, the image forming mode can be automatically switched by transferring the information of the full-color original or the black monochromatic original to the printer side separately from the image information in the image signal processing unit during the transfer of the image signal. Therefore, the present invention can be preferably applied.

(1) First Image Forming Mode: First, the image forming operation of the printer in the full color image forming mode for forming a full color image will be described.

A drum-shaped electrophotographic photosensitive member as an image bearing member, that is, photosensitive drums 1a, 1b, 1c, and 1d, which is rotationally driven in the direction of the arrow, is supported by each of the image forming portions Pa to Pd. Each photosensitive drum 1a to 1d has a peripheral speed of 100 m.
It is rotationally driven at m / sec.

The photosensitive drums 1a to 1d, primary chargers 12a, 12b, 12 arranged along the outer peripheral surfaces of the respective photosensitive drums 1a to 1d.
c and 12d are uniformly charged, and optical systems 16a and 16 including an imaging lens and a laser scanner are provided on the surfaces thereof, respectively.
b, 16c, 16d are scanned with spot laser light corresponding to the color-separated image signal, and the photosensitive drums 1a to 1d are scanned.
The surface is exposed, and an electrostatic latent image corresponding to each color of yellow (Y), magenta (M), cyan (C), and black (Bk) is formed on each surface.

The electrostatic latent images of the respective colors formed in this manner are developed as yellow (Y), magenta (M), cyan (C), as a developer as the photosensitive drums 1a to 1d rotate.
To a developing area facing the developing devices 13a, 13b, 13c, and 13d that store black (Bk) toners, respectively, and to be visualized by receiving electrostatic toner adsorption,
A developer image (toner image) of each color is formed on each of the photosensitive drums 1a to 1d.

On the other hand, in the printer of this embodiment, the recording material G is accommodated in the cassette 4, and the recording material G sent out into the image forming apparatus by the paper feed roller 10 serves as a recording material carrier and is the photosensitive drum. An endless belt that cyclically moves at a speed of 102 mm / sec, which is a moving speed that is 2% faster than the peripheral speed of 1a to 1d, that is, the conveyor belt 2 passes from the first image forming unit Pa to the fourth image forming unit Pd. Further, it is carried and conveyed up to the fixing device 6.

The conveyor belt 2 is a thin belt (dielectric sheet) of a dielectric material which is endlessly driven by the drive roller 7 in the direction of the arrow, and idler rollers 8a and 8b provided near the drive roller 7 and the cassette 4. , And the tension adjusting roller 9 are suspended.

When the image forming operation is started, the recording material G fed into the image forming apparatus is carried on the conveyor belt 2 in synchronization with the registration roller pair 11, and the conveyor belt carrying the recording material G is carried. With the movement of 2 in the direction of the arrow, the respective image forming portions Pa to Pd start forming the respective color toner images on the respective photosensitive drums 1a to 1d at desired timings.

That is, the recording material G is the photosensitive drums 1a to 1d.
And a blade-shaped transfer charging member as transfer means, that is, transfer charging blades 14a, 14b, 14c, 14d.
And sequentially pass through the transfer nip where they abut via the transport belt 2.

A transfer bias voltage is applied to the transfer charging blades 14a to 14d from a transfer bias high-voltage power source (not shown), and the toner images of the respective colors on the photosensitive drums 1a to 1d are sequentially printed on the same recording material G. After being transferred, a color unfixed toner image is synthesized on the recording material G.

The recording material G carrying an unfixed color image is
After passing through the final fourth image forming portion Pd, it is separated from the conveyor belt 2 and sent to the fixing device 6, and the unfixed color toner image is recorded on the recording material G by the fixing device 6 by heat and pressure.
It is fused and fixed on top to form a permanent image.

After that, the recording material G is discharged out of the image forming apparatus main body 3 and stored in the external tray 5. Further, the transfer residual toners on the photosensitive drums 1a to 1d, which have finished transferring the toner images of the respective colors, are developed by the developing devices 13a, 13b, 13 respectively.
The residual toner and the like are removed by c and 13d to prepare for the subsequent image forming operation.

(2) Second image forming mode: Next, the operation of the apparatus in the Bk single color image forming mode for forming the Bk single color image will be described.

The photosensitive drums 1a to 1c for forming images of yellow (Y), magenta (M), and cyan (C) are rotationally driven at a peripheral speed of 102 mm / sec which is the same as that of the conveyor belt 2 described later, and black ( The photosensitive drum 1d that forms the image Bk) is rotationally driven at a peripheral speed of 100 mm / sec.

The photosensitive drums 1a to 1d, the primary chargers 12a and 12b arranged along the outer peripheral surfaces of the photosensitive drums 1a to 1d,
Only the primary charger 12d corresponding to the photosensitive drum 1d for forming a black (Bk) image is operated to uniformly charge the photosensitive drum 1d, and 16d including an imaging lens and a laser scanner on its surface. Scans the spot laser light corresponding to the black monochromatic image signal to expose the surface of each photosensitive drum 1d to form an electrostatic latent image corresponding to the black monochromatic image.

The black monochromatic electrostatic latent image formed in this manner is developed by a developing device 13d that contains black (Bk) toner as a developer as the photosensitive drum 1d rotates.
Reaches a developing area opposite to and develops an image by receiving electrostatic attraction of toner, and a black toner image is formed on the photosensitive drum 1d.

On the other hand, the printer of this embodiment stores the recording material G in the cassette 4, and the recording material G fed into the image forming apparatus by the paper feed roller 10 is a photosensitive material for forming the black image. The conveyance belt 2 that circulates at a speed of 102 mm / sec, which is 2% faster than the peripheral speed of the drum 1d, passes from the first image forming unit Pa to the fourth image forming unit Pd, and then to the fixing device 6. It is carried and carried all the way.

At this time, even in the image forming portions Pa, Pb, and Pc where the image formation is not performed, the transfer belts 14a, 14b, and the transfer belts 2 are kept in contact with the photosensitive drums 1a, 1b, 1c at the respective transfer portions. 14c also keeps contact with the conveyor belt 2.

That is, even when a black monochromatic image is formed, the conveying belt is not separated from the photosensitive drum of the image forming section in which the image is not formed.

When the image forming operation is started, the recording material G fed into the image forming apparatus is carried on the conveyor belt 2 in synchronism with the registration roller pair 11, and the conveyor belt carrying the recording material G is carried. With the movement of 2 in the direction of the arrow, the image forming portion Pd starts forming the black toner image on the photosensitive drum 1d as described above at a desired timing.

That is, the recording material G is the photosensitive drums 1a to 1d.
And a blade-shaped transfer charging member as transfer means, that is, transfer charging blades 14a, 14b, 14c, 14d.
And sequentially pass through the transfer nip where they abut via the transport belt 2.

A transfer bias voltage is applied to the transfer charging blade 14d from a transfer bias high-voltage power source (not shown), and the black toner image on the photosensitive drum 1d is
It is transferred onto the recording material G, and a black unfixed toner image is synthesized on the recording material G.

Recording material G carrying an unfixed black image
Is separated from the conveyor belt 2 after passing through the final fourth image forming portion Pd and sent to the fixing device 6, and the black unfixed toner image is formed on the recording material G by the fixing device 6 by heat and pressure. It is fused and fixed to form a permanent image.

After that, the recording material G is discharged to the outside of the image forming apparatus main body 3 and stored in the external tray 5. The transfer residual toner on the photosensitive drum 1d, which has completed the transfer of the black toner image, is removed by the developing device 13d to prepare for the subsequent image forming operation.

Here, the dielectric sheet material for the conveyor belt 2 includes polyethylene terephthalate, polyacetal, polyamide, polyvinyl alcohol, polyether ketone, polystyrene, polybutylene terephthalate, polymethylpentene, polypropylene, polyethylene, polyphenylene sulfide, polyurethane. Thin films and belts of engineering plastics including silicone resin, polyamide imide, oricarbonate, polyphenylene oxide, polyether sulfone, polysulfone, aromatic polyester, polyetherimide, aromatic polyimide, etc. are generally used.

In this embodiment, the conveyor belt 2 includes
Aromatic polyimide was used from the viewpoint of mechanical properties, electrical properties, flame retardancy, etc., and a seamless type having a volume resistivity of 10 ¹⁷ Ω · m and a thickness of 75 μm was used.

In the image forming apparatus of this embodiment described in (1) and (2) above, the circumference of the transfer belt, which is the conveyor belt 2 in this case, is formed during image formation in the full color mode and the single color image forming mode. Speed and each photosensitive drum 1a
The peripheral speeds of 1d can be summarized as shown in Table 1.

[0056]

[Table 1]

In the present invention, as in the printer of this embodiment, in the black monochromatic image forming mode, image formation is carried out in a state where the conveyor belt is not separated from the photosensitive drum, and only the black image forming portion is charged and exposed. Image formation is performed by performing image forming processes such as development, transfer and the like.

As can be understood with reference to Table 1, in the printer of this embodiment, the image forming operation is performed in the full color image forming mode and in the single color image forming mode of the selected color, which is black here. A peripheral speed difference (102-100 = 2 mm / sec) is provided between the rotational speeds of the photosensitive drum and the transfer belt of the image forming unit.

In the single-color image forming mode, the peripheral speed difference of 2 mm / sec is provided between the photosensitive drum 1d and the conveyor belt 2 in the selected black image forming portion Pd, but at the same time, the yellow image is not formed. , Magenta and cyan image forming sections, the photosensitive drums 1a to 1
No peripheral speed difference is provided between c and the recording material conveying belt 2.

In other words, as a characteristic part of the present invention,
In the full-color image forming mode, all the photosensitive drums rotate at the same speed (100 mm / sec) and the peripheral speed difference with the transfer belt (102-100 = 2 mm / sec) is common. In the monochrome image forming mode, the absolute value of the difference in peripheral speed between the transfer belt and the photosensitive drum of the selected image forming unit (102-100 = 2 mm / sec) is larger than that of the transfer belt and other photosensitive drums. Absolute value of peripheral speed difference (102-1
02 = 0 mm / sec) is set small.

That is, in the present embodiment, in the selected black image forming portion Pd, the peripheral speed difference is provided between the image bearing member and the recording material to prevent the hollow defect which occurs at the time of transfer. At the same time, as a characteristic part of the present invention, in the image forming unit that does not form an image, the peripheral speed difference is not generated between the photosensitive drum and the conveyor belt, so that damage such as scratches and scrapes of the photosensitive member that is the image bearing member is prevented. To do.

As a result, when a Bk single-color image and a full-color image are mixed in a plurality of originals while enabling a low-cost operation, a copying operation is performed by using an automatic original feeding device called a feeder. Since it is no longer necessary to perform the contact / separation operation of the conveyor belt, high productivity can be ensured even when an image is formed on a full-color / black single-color mixed original.

In this embodiment, the black monochromatic mode has been described as an example of a system that does not use all the image forming portions, but the present invention is not limited to this, and monochromatic modes of other colors and two colors are used. It goes without saying that the same effect can be obtained in a system that does not use all image forming units such as modes.

Further, the peripheral speed difference between the image carrier and the conveyor belt for preventing the hollow defect is set to 2%, but the peripheral speed difference is not limited to this value and is a value having an equivalent effect. Can be appropriately adopted.

Further, in the image forming section where the image is not formed, the peripheral speed difference between the image carrier and the conveyor belt is set to 0%.
This value does not have to be exactly the same speed, and another value can be taken as long as the peripheral speed difference is at a level at which abrasion of the image carrier does not easily occur. Essentially, the effect of the present invention is made smaller by making the absolute value of the peripheral speed difference between the image carrier not forming an image and the conveyor belt smaller than the absolute value of the peripheral speed difference between the image carrier forming the image and the conveyor belt. Is obtained.

Embodiment 2 FIG. 2 shows another embodiment of the image forming apparatus to which the present invention can be applied.

The printer of this embodiment also has image forming portions Pa, Pb, Pc, and Pd of substantially the same structure as the printer shown in the first embodiment, and these image forming portions are respectively An image forming unit that forms images of yellow (Y), magenta (M), cyan (C), and black (Bk).

This printer has two image forming modes: (1) a full color image forming mode which is a first image forming mode, and (2) a black single color image forming mode which is a second image forming mode. These two modes can be switched by externally setting in advance, and the method of switching the image forming mode is selected according to the type and purpose of the image forming apparatus. When continuous images are formed on full-color, single-color mixed documents, etc., the image forming mode is automatically switched by the same method as the printer of the first embodiment.

(1) First Image Forming Mode: Also in this embodiment, the operation of the apparatus for forming a full-color image will be described first.

The image forming operation until the color toner images of yellow (Y), magenta (M), cyan (C) and black (Bk) are formed on the photosensitive drums 1a, 1b, 1c and 1d will be described. The description is omitted because it is the same as the full-color image forming mode in the printer of the first embodiment.

The image forming sections Pa, Pb, Pc, Pd
The photosensitive drums 1a to 1d are driven to rotate at a peripheral speed of 100 mm / sec.

In this embodiment, the intermediate transfer belt 3 is used as a transfer belt without using the conveyor belt 2 in the first embodiment, and the intermediate transfer belt 3 is an endless belt member as an intermediate transfer member. This intermediate transfer belt 3
Below the image forming units Pa, Pb, Pc, and Pd, the photosensitive drums 1a, 1b, 1c, 1 of the image forming units are provided.
It is stretched around three rollers of a drive roller 7, a secondary transfer counter roller 20, and a driven roller 9 so as to extend across the lower surface of d, and the photosensitive drums 1a, 1b, 1
It is rotationally driven at a peripheral speed of 102 mm / sec, which is a peripheral speed that is 2% faster than that of c and 1d.

Reference numerals 14a, 14b, 14c and 14d denote four primary transfer rollers, ie, first to fourth primary transfer rollers arranged inside the intermediate transfer belt 3. First primary transfer roller 14a
Forms a primary transfer portion 21a by abutting on the lower surface of the photosensitive drum 1a of the image forming portion Pa for yellow with the ascending side belt portion of the intermediate transfer belt 3 interposed therebetween. The second primary transfer roller 14b is in contact with the lower surface of the photosensitive drum 1b of the image forming portion Pb for magenta while sandwiching the ascending side belt portion of the intermediate transfer belt 3 to form a primary transfer portion 21b.

The third primary transfer roller 14c is in contact with the lower surface of the photosensitive drum 1c of the image forming portion Pc for cyan with the ascending side belt portion of the intermediate transfer belt 3 interposed therebetween to contact the primary transfer portion 2c.
1c is formed. The fourth primary transfer roller 14d is in contact with the lower surface of the photosensitive drum 1d of the black image forming portion Pd with the ascending side belt portion of the intermediate transfer belt 3 interposed therebetween to form a primary transfer portion 21d.

Each primary transfer roller 14a, 14b, 14
A transfer bias having a polarity opposite to that of the toner is applied to each of c and 14d from a transfer bias power source (not shown), whereby the toner images on the photosensitive drums 1a, 1b, 1c, and 1d side are transferred to the primary transfer portions 21a, 21b, and 21c. , 21d, the electrostatic latent image is transferred onto the ascending side belt surface of the intermediate transfer belt 3. In the case of the apparatus of this example, first, in the primary transfer portion 21a of the image forming portion Pa for yellow, the photosensitive drum 1a
Surface, the yellow image is transferred to the ascending side belt surface of the intermediate transfer belt 3.

Then, the magenta image, the cyan image and the black image are transferred in the same manner so as to be superposed on the ascending side belt surface of the intermediate transfer belt 3 to form a full color image in a composite manner.

The above-mentioned image forming portions Pa, Pb, Pc and Pd for yellow, magenta, cyan and black.
In the developing devices 13a, 13b, 13c,
Reference numeral 13d denotes the photosensitive drum 1 after the image is transferred from the photosensitive drums 1a, 1b, 1c, 1d surface to the intermediate transfer belt 3 surface.
The cleaning means (development simultaneous cleaning) for removing the transfer residual toner remaining on the surfaces a, 1b, 1c, and 1d is also used, and each of the image forming portions Pa, Pb, Pc, and Pd is exposed as a dedicated device. No drum cleaning device (cleanerless system).

Then, the surface of the intermediate transfer belt 3 on which the full-color image has been formed as described above is subjected to the secondary transfer formed by the secondary transfer counter roller 20 and the secondary transfer roller 17 by the subsequent rotation of the intermediate transfer belt 3. To section 18. The secondary transfer roller 17 is in contact with the secondary transfer counter roller 20 with the intermediate transfer belt 3 sandwiched therebetween to form a secondary transfer portion 18, and a transfer bias having a polarity opposite to that of the toner is applied from a transfer bias power source (not shown). Is applied.

Recording material G fed from paper feed cassette 4
Is fed from the paper feed roller 14 to the registration roller 11
Then, the sheet is fed to the secondary transfer portion 18 at a predetermined timing.

That is, when the leading end of the composite full-color image of each color formed on the surface of the intermediate transfer belt 3 by the rotation of the intermediate transfer belt 3 reaches the secondary transfer portion 18, the recording material G is fed and the secondary recording material G is fed. In the transfer section 18, the full-color image on the surface of the intermediate transfer belt 3 is transferred at once to the recording material G fed.

The recording material G exiting the secondary transfer portion 18 is separated from the surface of the intermediate transfer belt 3 and is subjected to heat fixing of the image introduced into the constant unit 6, and is discharged to the tray 5 outside the apparatus as an image formed product. To be paper.

The transfer residual toner left on the surface of the intermediate transfer belt 3 during the secondary transfer is removed from the surface of the intermediate transfer belt 3 by the intermediate transfer belt cleaner 19.

(2) Second image forming mode: Next, the operation of the apparatus in the Bk single color image forming mode for forming the Bk single color image will be described.

Photosensitive drums 1a, 1b, 1c for forming images of yellow (Y), magenta (M) and cyan (C).
Is rotationally driven at a peripheral speed of 102 mm / sec, which is the same peripheral velocity as that of an intermediate transfer belt 3 described later, and the photosensitive drum 1d for forming a black (Bk) image is rotationally driven at a peripheral velocity of 100 mm / sec.

Even here, the image forming operation is the same as that of the Bk single color image forming mode of the first embodiment until the black toner image is formed on the photosensitive drum 1d, and therefore the detailed description thereof will be omitted.

The intermediate transfer belt 3 includes the image forming portions Pa,
Below the Pb, Pc, and Pd, the three rollers of the drive roller 7, the secondary transfer counter roller 20, and the driven roller 9 are provided so as to extend between the lower surfaces of the photosensitive drums 1a, 1b, 1c, and 1d of the image forming units. The roller is suspended around the roller and is rotationally driven in a clockwise direction indicated by an arrow at a peripheral speed of 102 mm / sec, which is a peripheral speed 2% higher than that of the photosensitive drums 1a, 1b, 1c, and 1d.

At this time, even in the image forming portions Pa, Pb, and Pc where the image formation is not performed, the intermediate transfer belt 3 remains in contact with the photosensitive drums 1a, 1b, and 1c at the respective transfer portions, and the primary transfer rollers 14a and 14b. , 14c are also kept in contact with the intermediate transfer belt 3.

That is, the photosensitive drums 1a to 1c of the image forming portion, which does not form an image even when a black monochromatic image is formed.
The intermediate transfer belt 3 is not separated from.

A transfer bias having a polarity opposite to that of the toner is applied to the primary transfer rollers 14d from a transfer bias power source (not shown), so that the toner image on the surface of the photosensitive drum 1d is the ascending side belt of the intermediate transfer belt 3 at 21d. It is electrostatically transferred to the surface. In the case of the apparatus of this example, the black image is transferred from the surface of the photosensitive drum 1d to the ascending side belt surface of the intermediate transfer belt 3 at the primary transfer portion 21d of the image forming portion Pd for black.

Then, the surface of the intermediate transfer belt 3 on which the black image is formed as described above is formed by the secondary transfer counter roller 20 and the secondary transfer roller 17 by the subsequent rotation of the intermediate transfer belt 3. To section 18. The secondary transfer roller 17 is in contact with the secondary transfer counter roller 20 with the intermediate transfer belt 3 interposed therebetween to form a secondary transfer portion 18,
A transfer bias having a polarity opposite to that of the toner is applied from a transfer bias power source (not shown).

Recording material G fed from paper feed cassette 4
Is fed from the paper feed roller 14 to the registration roller 11
Then, the sheet is fed to the secondary transfer portion 18 at a predetermined timing.

That is, when the front end of the black image formed on the surface of the intermediate transfer belt 3 reaches the secondary transfer portion 18 by the rotation of the intermediate transfer belt 3, the recording material G is fed, and the secondary transfer portion 18 is fed. At 18, the black image on the surface of the intermediate transfer belt 3 is transferred to the fed recording material G at once.

The recording material G exiting the secondary transfer portion 18 is separated from the surface of the intermediate transfer belt 3 and undergoes thermal fixing of the image introduced into the fixing unit 6, and is discharged to the tray 5 outside the apparatus as an image formed product. To be paper.

The transfer residual toner left on the surface of the intermediate transfer belt 3 during the secondary transfer is removed from the surface of the intermediate transfer belt 3 by the intermediate transfer belt cleaner 19.

Here, as the material for the intermediate transfer belt 3, polyethylene terephthalate, polyacetal, polyamide, polyvinyl alcohol, polyether ketone,
Polystyrene, polybutylene terephthalate, polymethylpentene, polypropylene, polyethylene, polyphenylene sulfide, polyurethane, silicone resin, polyamide imide, oricarbonate, polyphenylene oxide, polyether sulfone, polysulfone, aromatic polyester, polyether imide, aromatic polyimide, etc. Engineering plastic thin films and belts containing are generally used.

In this embodiment, an aromatic polyimide is used for the intermediate transfer belt 3 from the viewpoint of mechanical properties, electrical properties, flame retardancy, etc., and the volume resistivity is 10 ¹⁴ Ω · m and the thickness is 75 μm. A seamless type was used.

The transfer belt, which is the intermediate transfer belt 3 in this case, is used for image formation in the full-color mode and the single-color image formation mode of the image forming apparatus of this embodiment described in (1) and (2) above. The peripheral speeds and the peripheral speeds of the photosensitive drums 1a to 1d can be summarized as shown in Table 1 as in the first embodiment.

In the present invention, as in the printer of this embodiment, in the black monochromatic image forming mode, image formation is carried out in a state where the intermediate transfer belt is not separated from the photosensitive drum, and only the black image forming portion is charged. exposure,
An image is formed by performing an image forming process such as development and transfer.

Also in this embodiment, as can be understood by referring to Table 1, even in the full-color image forming mode,
Here, even in the single-color image forming mode of the selected color, which is black, the peripheral speed difference (10) is generated between the rotational speeds of the photosensitive drum and the transfer belt of the image forming unit that performs the image forming operation.
2-100 = 2 mm / sec) is provided.

In the monochromatic image forming mode, the peripheral speed difference of 2 mm / sec is provided between the photosensitive drum 1d and the intermediate transfer belt 3 in the selected black image forming portion Pd, but at the same time, image formation is not performed. In the yellow, magenta, and cyan image forming portions Pa to Pc, the peripheral speed difference is not provided between the photosensitive drums 1a to 1c and the intermediate transfer belt 3.

Also in this embodiment, as a characteristic part of the present invention, in the full-color image forming mode, all the photosensitive drums rotate at the same speed (100 mm / sec), and the peripheral speed difference (102) with the intermediate transfer belt is increased. -100 = 2 mm / sec), the absolute value of the difference in peripheral speed between the intermediate transfer belt and the photosensitive drum of the selected image forming unit (102- 100 = 2mm / sec)
The absolute value (102-102 = 0 mm / sec) of the peripheral speed difference between the intermediate transfer belt and other photosensitive drums is set smaller than that.

That is, in the present embodiment, in the selected black image forming portion Pd, the peripheral speed difference is provided between the photosensitive drum and the intermediate transfer belt to prevent the hollow defect which occurs at the time of transfer. At the same time, as a characteristic part of the present invention, in the image forming unit that does not perform image formation, the peripheral speed difference is not generated between the photosensitive drum and the intermediate transfer belt, so that the photosensitive drum, which is an image bearing member, is not damaged or worn. To prevent.

As a result, when a Bk single-color image and a full-color image are mixed in a plurality of originals while enabling a low-cost operation, when a copying operation is performed using an automatic original feeding device called a feeder, Since it is not necessary to perform the contact and separation operation of the intermediate transfer belt, it is possible to ensure high productivity even when forming an image on a full-color / black single-color mixed original.

In the present embodiment, the black monochromatic mode has been described as an example of a system having an image forming portion that does not perform an image forming operation, but the present invention is not limited to this, and monochromatic modes of other colors are used. It is needless to say that the same effect can be obtained in a system having an image forming section that does not perform other image forming operations, such as a two-color mode.

Further, the peripheral speed difference between the photosensitive drum and the intermediate transfer belt is set to 2% in order to prevent the hollow defect, but the peripheral speed difference is not limited to this value and is a value having an equivalent effect. Can be appropriately adopted.

Further, in the image forming portion where the image is not formed, the peripheral speed difference between the photosensitive drum and the intermediate transfer belt is set to 0%, but this value does not have to be exactly the same speed, and the photosensitive drum is worn. Other values can be taken as long as it is a level difference that makes it difficult to do. Essentially, the effect of the present invention is obtained by making the absolute value of the peripheral speed difference between the photosensitive drum not forming an image and the intermediate transfer belt smaller than the absolute value of the peripheral speed difference between the photosensitive drum forming the image and the intermediate transfer belt. Is obtained.

Incidentally, as the recording material carrying member or the intermediate transfer member, the belt-shaped member was adopted in the first and second embodiments, but it is not limited to this.

[0108]

As described above, the image forming apparatus according to the present invention has a plurality of image bearing members on the surface of which developer images of different colors are formed and a plurality of image bearing members along the moving direction. A plurality of image carriers in the first image forming mode, the recording medium carriers being sequentially arranged from the upstream side to the downstream side, and transporting the recording material in contact with the plurality of image carriers. Among them, a developer image is formed on all of the image carriers, a peripheral speed difference is provided between all of the plurality of image carriers and the recording material carrier, and a plurality of image carriers are formed in the second image forming mode. Among them, there are an image bearing member on which a developer image is formed and an image bearing member on which a developer image is not formed, and the difference in peripheral speed between the image bearing member on which the developer image is formed and the recording material bearing member. Since the absolute value of the peripheral speed difference between the image bearing member on which the developer image is not formed and the recording material bearing member is made smaller than the absolute value, Even when forming continuous images of mixed-color, single-color mixed originals, etc., it is possible to prevent image dropouts during transfer without sacrificing image forming productivity, and to perform good image formation to reduce image dropouts during transfer. The effects of preventing the formation of a good image, maintaining the life of the image carrier and the like, and enabling low-cost operation are obtained.

Incidentally, in the first image forming mode, an image forming apparatus having an intermediate transfer member, which moves in place of the recording material carrying member and which primarily transfers the developed image on the image carrying member, is used in the first image forming mode. In the second image forming mode, a developer image is formed on all the image bearing members of the plurality of image bearing members, a peripheral speed difference is provided between all of the plurality of image bearing members and the intermediate transfer member, Among the plurality of image carriers, there are an image carrier on which a developer image is formed and an image carrier on which a developer image is not formed, and between the image carrier on which the developer image is formed and the intermediate transfer member. The same effect can be obtained by making the absolute value of the peripheral speed difference between the image carrier on which the developer image is not formed and the intermediate transfer member smaller than the absolute value of the peripheral speed difference.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an example of an image forming apparatus according to the present invention.

FIG. 2 is a schematic configuration diagram showing another example of the image forming apparatus according to the present invention.

[Explanation of symbols]

1a to 1d Photosensitive drum (image carrier) 2 Conveyor belt (recording material carrier) 3 Intermediate transfer belt (intermediate transfer member) Pa to Pd Process station (image forming unit) G Recording material

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03G 21/00 350 G03G 21/00 350 384 384 F term (reference) 2H027 ED02 ED24 EE03 FA28 FA35 2H030 AA01 AB02 AD07 AD17 BB02 BB23 BB42 BB44 2H035 CA07 CG01 2H071 CA02 CA05 DA09 DA15 DA31 EA18 2H200 FA04 FA09 GA12 GA23 GA34 GA44 GA47 GB25 GB37 HA02 HB12 HB14 JA02 JB07 JB45 JB46 JC04 JC12 JC15 JC16 MA04 MA20 MB

Claims (6)

[Claims] 1. A recording material comprising a plurality of image bearing members on the surface of which developer images of different colors are formed and a plurality of image bearing members sequentially arranged from the upstream side to the downstream side in the moving direction. And a recording material carrier for bringing the plurality of image carriers into contact with the plurality of image carriers, and transferring the developer images onto the recording material carried by the recording material carrier to form an image. In the image forming apparatus, the developer image is formed on all the image carriers of the plurality of image carriers in the first image forming mode, and all of the plurality of image carriers and the recording material carrier are formed. A peripheral speed difference is provided between the image carrier and the image carrier on which the developer image is formed and the image on which the developer image is not formed among the plurality of image carriers in the second image forming mode. There is an absolute difference in peripheral speed between the image carrier on which the developer image is formed and the recording material carrier. More, the image forming apparatus characterized by reducing the absolute value of the peripheral speed difference between the developer image with the image bearing member is not formed said recording material bearing member. 2. An image carrier on which the developer image is formed in the second image forming mode is an image carrier on which a black developer image is formed, and a black monochromatic image is formed on the recording material. The image forming apparatus according to claim 1, wherein the image forming apparatus forms an image. 3. The image forming apparatus according to claim 1, wherein the recording material carrier has a belt shape. 4. A plurality of image bearing members on the surface of which developer images of different colors are formed, and the plurality of image bearing members are sequentially arranged along the moving direction from the upstream side to the downstream side, and themselves. And an intermediate transfer member that moves, the primary transfer of the developer image onto the intermediate transfer member in sequence, and the secondary transfer of the developer primary transferred to the intermediate transfer member to a recording material all at once. In the first image forming mode, the developer image is formed on all the image carriers of the plurality of image carriers in the first image forming mode, and the image is formed on all of the plurality of image carriers. A peripheral speed difference is provided between the intermediate transfer body and the image carrier on which the developer image is formed and the developer image is formed in the plurality of image carriers in the second image forming mode. Between the image carrier on which the developer image is formed and the intermediate transfer member. Than the absolute value of the peripheral speed difference, the image forming apparatus characterized by reducing the absolute value of the peripheral speed difference between the intermediate transfer member and the image bearing member the developer image is not formed. 5. The image carrier on which the developer image is formed in the second image forming mode is an image carrier on which a black developer image is formed, and a black monochromatic image is formed on the recording material. The image forming apparatus according to claim 4, wherein the image forming apparatus is formed. 6. The image forming apparatus according to claim 4, wherein the intermediate transfer member has a belt shape.