JPH06202430A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain an image of high image quality by forming conditions such as the shape of a transfer nip part and a pressing force, etc., suitable for all the stations. CONSTITUTION:In the image forming device provided with image forming stations which are constituted by arranging plural image carriers 1d, 1c,..., and for carrying a transfer material to each station by a carrying belt 61, the pressing force of transfer auxiliary members 80d, 80c,..., or of the transfer member against image carrier 1d and 1c,... at each transfer position is set different to every station. That means, as to a force necessary for forming a suitable transfer nip part, the pressing force of a backup member 80d as the transfer auxiliary member at a 4th station is larger than that of the backup member 80c at a 3rd station, then, this setting is applied. For example, flexible sheet material such as polyethylene terephthalate, etc., is generally used for the backup members 80d and 80c, and the stiffness is increased by increasing the thickness of the sheet material, and then the pressing force is adjusted. Thus, the occurrence of-transfer scattering, etc., is prevented and the image of high quality is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally forms a visible image (toner image) on an image carrier by an electrophotographic system or an electrostatic recording system and transfers the toner image onto a transfer material to obtain an image. The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that conveys a transfer material by a conveyor belt, and can be preferably embodied in a full-color electrophotographic copying machine, a laser beam printer, or the like.

[0002]

2. Description of the Related Art As one mode of a full-color image forming apparatus utilizing an electrophotographic process, a latent image is formed on an image carrier, which is a photoconductor, by utilizing light, magnetism, electric charge, etc., and the latent image is visualized. It has a plurality of image forming stations to obtain a visible image by image formation, and to transfer the images of each color on the photoconductor formed at each image forming station to the transfer material sequentially, to the transfer position of each image forming station. 2. Description of the Related Art There is widely known one that includes a transfer material conveying unit that conveys a transfer material and a fixing device that fixes an image that has been multi-transferred onto the transfer material onto the transfer material.

Further, the transfer material conveying means has a plurality of transfer positions, so that a belt-shaped conveying member,
That is, a transfer material transport belt is preferably used to transport the transfer material to the transfer position and further to the fixing device. Also, the transfer material is held on the transfer material transport belt by electrostatic attraction,
Be transported.

FIG. 10 is a sectional view of a main part of a transfer section in one image forming station. 1 is a photosensitive drum, 5
Numerals 1 and 52 are a shield plate and a transfer wire of the transfer charger. The backup member 80 urges the transfer material conveying belt 61 from below toward the photosensitive drum, which ensures contact between the photosensitive drum 1 and the transfer material 40. This contact area is called a transfer nip portion N.

[0005]

However, the conventional image forming apparatus has the following problems in the transfer process.

That is, in order to form an appropriate transfer nip in the transfer portion, the transfer material conveying belt is pushed up by using a backup member, but it is necessary to push up the transfer material conveying belt to form a predetermined transfer nip. The power is not always the same at each station. For example, as shown in FIG. 11, a driving roller (following roller) and a transfer section of the fourth station (transfer section of the first station).
If and are relatively close, the fourth station
The station (first station) requires a larger force to push up the transfer material transport belt. This is because the transfer material conveying belt is stretched by applying a predetermined tension to the rollers at both ends, and thus the relationship between the force and the displacement differs depending on the distance from the end portion, as in the case of the string.

Further, as shown in FIG. 12, when the driving roller 8 (following roller) and the transfer portion of the fourth station (transfer portion of the first station) are relatively distant from each other, l ₁ and l
_Since the ratio of ₂ becomes smaller, the difference between the stations in the force required for elastic deformation described above becomes smaller. In this case, the influence of the deflection of the transfer material transport belt due to its own weight increases,
The central station requires more force to push up the transfer material transport belt than the end stations.

Therefore, even if the force required to push up the transfer material conveying belt differs depending on the station, if the same backup member is provided in all stations, a suitable transfer nip portion cannot be formed depending on the position of the station. Things will occur. If the transfer nip portion is not properly formed, for example, pre-transfer occurs in the upstream portion of the transfer nip, which leads to deterioration of image quality such as the toner on the photosensitive drum being transferred to the transfer material in a scattered state. .

Therefore, an object of the present invention is to provide an image forming apparatus capable of obtaining a high quality image by suitably forming the conditions such as the shape of the transfer nip portion and the pressing force at all stations. It is in.

[0010]

In order to achieve the above object, the present invention provides an image forming station in which a plurality of image bearing members are arranged, and a transfer material for holding a toner image formed on each image bearing member. An image forming apparatus having a transfer material conveying belt that sequentially conveys the image to a transfer position of each image forming station, wherein a transfer assist member at each transfer position or a pressing force of the transfer member toward the image carrier is provided for each station. It is possible to set different pressing force.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

FIG. 3 shows an example of the present invention in which a plurality of photosensitive drums are used as an image carrier and a transfer material transport belt is used as a transfer material transport means. 1 illustrates an image format device, i.e., a color laser beam printer.

In this embodiment, the color laser beam printer has four image forming sections Pa, Pb, Pc and Pd arranged side by side in the main body 90 of the apparatus. The number of image forming units can be arbitrarily selected. Device body 9
On one side of 0, that is, on the right side of FIG. 1, the cassette 8 containing the transfer material 40 is arranged, and on the other side, that is, on the left side of FIG. 1, an external tray 19 for discharging the transfer material 40 is provided. . The fixing device 11 is arranged in the apparatus main body 90 adjacent to the external tray 19.

Further, these images are provided below the first, second, third and fourth image forming sections Pa, Pb, Pc and Pd from the cassette 8 in the apparatus main body 90 to the fixing device 11. An endless belt-shaped transfer material conveying unit, that is, a transfer material conveying belt 61, is provided which circulates to convey the transfer material through the forming portion. This transfer material transport belt 61
Is a driven roller 91 located near the cassette 8,
The drive roller 92 located close to the fixing device 11 is wound around the drive roller 92.

Here, the transfer material conveying belt is a film made of a dielectric resin such as a polycarbonate resin film sheet, a polyethylene terephthalate resin film sheet (PET sheet), a polyvinylidene fluoride film sheet or a polyurethane resin film sheet, and has a thickness. Is 1
The length is 25 μm and the circumference is 1650 mm.

The transfer material conveying belt 61 is a thin belt made of a dielectric material which is endlessly driven by a driving roller 92 in a direction shown by an arrow in FIG. 1. The transfer material conveying belt 61 is fed from the cassette 8 and is synchronized with a pair of registration rollers 12. The image forming portions Pa, Pb, and P that carry the transfer material 40 fed by
It is sequentially conveyed to c and Pd. The fixing device 11 receives the transfer material 40 fed from the drive roller 92 side, and collectively fixes the toner images of the respective colors transferred and superposed on the transfer material 40 at the image forming portions Pa, Pb, Pc, and Pd. , Form a permanent image.

The image forming sections Pa, Pb, Pc, and Pd have substantially the same structure and include photosensitive drums 1a, 1b, 1c, and 1d which are image carriers that are rotationally driven in the directions of the arrows in the drawing. Around the photosensitive drums, primary chargers 2a, 2b, 2c, 2d for uniformly charging the photosensitive drums, and developing devices 4a, 4b, 4 for developing electrostatic latent images formed on the photosensitive drums are provided.
c, 4d, transfer chargers 50a, 50b, 50c, 50d for transferring the developed color toner image to the transfer material 40, and cleaning devices 6a, 6b, 6c, 6d for removing the toner remaining on the photosensitive drums are drums. They are sequentially arranged in the rotating direction. In addition, each photosensitive drum 1a, 1b, 1c, 1d
An exposure lens system composed of an imaging lens and a laser beam scanner is provided above each of the above.

The developing device 4a contains yellow toner, the developing device 4b contains magenta toner, and the developing device 4c contains
Contains cyan toner, and the developing device 4d contains black toner.

In the color image forming apparatus having the above structure,
When the transfer material 40 is placed on the transfer material conveying belt 61, the image forming process for the corresponding photosensitive drums 1a, 1b, 1c, 1d is sequentially started as the transfer material conveying belt 61 moves in the arrow direction. To be done. That is, the yellow image (Y) is formed on the photosensitive drum 1a of the first image forming unit Pa, the magenta image (M) is formed on the photosensitive drum 1b of the second image forming unit Pb, and the third image forming unit Pc is formed. A cyan image (C) is formed on the photosensitive drum 1c, and a black image (BK) is formed on the photosensitive drum 1d of the fourth image forming unit Pd. By the movement of the transfer material transport belt 61, the transfer material 40 sequentially passes under the photosensitive drums 1a to 1d of the first to fourth image forming portions Pa to Pd and is transported toward the fixing device 11, and each image is transferred. Transferring chargers 50a, 5 in the forming section
The toner images of the respective colors formed by the respective image forming portions are sequentially transferred and superposed on the transfer material 40 by 0b, 50c, and 50d, and the color images are combined. The transfer material 40, after passing through the final fourth image forming portion Pd, is separated from the transfer material conveying belt 61 and is sent to the fixing device 11, and the color toner images superimposed and transferred in the fixing device 11 are melted. After being fixed, it is discharged to the external tray 19.

Next, the structure and operation of the image forming apparatus in this embodiment will be described with reference to FIGS. 1 and 2.

FIG. 1 is a partial detailed view of transfer portions of the third station and the fourth station of the image forming apparatus shown in FIG. In this example, the distance between the driving roller 92 having a diameter of 50 mm and the corona wire 51d at the transfer portion of the fourth station is relatively close to 80 mm, and the force required to form a suitable transfer nip portion is the backup member of the fourth station. 80d is needed more than 80c of the third station. Generally, PET is used as a backup material.
Although a sheet material having flexibility such as is used, in the example shown in FIG. 1, only the thickness is made 25 μm thicker than that of the third station without changing the size of the backup member of the fourth station. Thus, the bending stiffness of the sheet material is high, and the so-called strain is strengthened to increase the pressing force. In the above embodiment, the third and fourth
The difference in pressing force at the station was 100 gf.

In addition to the above-described method of changing the thickness of the sheet material, there are methods such as changing the free length l of the sheet material and the amount of penetration δ into the transfer material conveying belt (see FIG. 2: two points. The chain line shows the position of the transfer material transport belt when it is assumed that there is no backup member). To increase the pressing force, the free length 1 may be shortened or the penetration amount δ may be increased. Then, according to the method described above, the pressing of the backup member 80 may be set so as to form a suitable transfer nip portion at each station (the same applies to the first and second stations, and the second station side is the same). Weaken).

The above description corresponds to FIG. 11 in which the belt supporting roller to the image forming station of the conventional example is short, and next, an example corresponding to FIG. 12 in which the station of the conventional example is long. To do. In this case, as described above, the deflection of the transfer material transport belt itself due to its own weight is great, and the force required to push up the transfer material transport belt is greater at the central station than at the end stations. Therefore, it is necessary to set the pressing force of the backup members of the second and third stations to be stronger than that of the first and fourth stations. The setting of the pressing force is the same as the method described above.

Further, according to the above construction, the backup member 80 and the holder member 82 in which the backup member 80 is adhered and supported by the adhesive agent.
Only by replacing only the main body support frame 81 with the main body support frame 81, the pressing force at each station can be easily set. And
If the holder member 82 is attached to the frame 81 by using a locking member with a screw 83 or a sliding guide member as shown in the figure, the replacement work becomes easy.

[Other Embodiments] The corona transfer system has been described above. Next, an embodiment of the brush transfer system will be described.

FIG. 4 is a diagram showing a main part of the brush transfer system, which is used as a contact charging means. An electric charge is injected from the brush 91 to the transfer material conveying belt 61 to carry out the transfer process. The backup member 92, which is a flexible resin sheet, is for ensuring a sufficient transfer nip width as in the above-described example, and is also intended to prevent the brush 91 from being worn out (deformed) with time. It is a member.

FIG. 5 is an enlarged view of the brush 91 and the backup member 92. As in the above-mentioned example, the thickness t of the backup member, the free length l, or the penetration amount δ with respect to the transfer material conveying belt (shown by the chain double-dashed line) is changed. By doing so, the pressure is set for each station, and the transfer nip is appropriately formed in all the stations.

Next, examples of the blade transfer system will be described.

FIG. 6 is a diagram showing a main part of a transfer system using a blade electrode, in which electric charges are injected into the transfer material conveying belt 61 from a conductive blade 93 used as a contact charging means to perform a transfer step. Is.

FIG. 7 is an enlarged view of the blade 93 and the holder 94 to which the blade is adhered. As in the above-mentioned example, the blade thickness t, the free length l, or the amount of penetration δ into the transfer material conveying belt 61 (shown by the two-dot chain line). By changing
The pressure is set for each station, and the nip amount of the transfer portion is appropriately formed in all stations.

Next, an example of the roller transfer system will be described.

FIG. 8 is a diagram showing a main part of a transfer system using roller electrodes. A transfer process is carried out by injecting electric charges into the transfer material conveying belt from a roller 94 having a predetermined resistance as a contact charging means. It is a thing. The roller 94 is composed of a conductive cored bar 95 and a rubber layer 96. The roller 94 is biased toward the photosensitive drum by a spring or the like, so that the rubber layer 96
It deforms itself and secures the transfer nip width.

FIG. 9 is a view showing the structure of the shaft end portion of the roller 94. The roller 98 is urged toward the photosensitive drum by a spring 98 via a bearing 97. Since the biasing force of the elastic force of the spring is substantially proportional to the pressing force against the roller belt 61, a plurality of springs having different elastic forces are prepared and the biasing force of the spring is selected for each station by selecting these springs. Set,
A preferable transfer nip amount is appropriately formed in all stations. The above-mentioned method changes the elastic force for each spring, but it is also possible to change the rubber hardness of the roller 96 itself depending on the selection of the material, the amount of firing, and the like. Specifically, a roller having a higher hardness than that of the other stations may be arranged at the station where the pressing force needs to be increased.

[0034]

As described above, in the image forming apparatus according to the present invention, the pressing of the transfer auxiliary member or the transfer member toward the image carrier is set for each station.
The transfer nip portion is preferably formed in all stations, and a high-quality image can be obtained without causing problems such as transfer scattering due to precharging.

[Brief description of drawings]

FIG. 1 is a diagram showing a transfer section of a third and fourth station.

FIG. 2 is a detailed view of a backup member in corona transfer.

FIG. 3 is an overall view of the apparatus.

FIG. 4 is a cross-sectional view showing a main part of a brush transfer system.

FIG. 5 is a detailed view of a backup member in the brush transfer system.

FIG. 6 is a diagram showing a main part of a blade transfer system.

FIG. 7 is a detailed view of a blade.

FIG. 8 is a sectional view showing a main part of a roller transfer system.

FIG. 9 is a side view showing an end portion of a roller shaft.

FIG. 10 is a sectional view showing a main part of a corona transfer system.

FIG. 11 is an explanatory diagram for explaining a conventional problem.

FIG. 12 is an explanatory diagram for explaining a conventional problem.

[Explanation of symbols]

 1 Photosensitive Drum 40 Transfer Material 61 Transfer Material Conveying Belt 50 Transfer Charger 80 Backup Member

Claims (5)

[Claims] 1. An image forming station in which a plurality of image bearing members are arranged, and a transfer which holds a transfer material to transfer a toner image formed on each image bearing member and sequentially conveys it to a transfer position of each image forming station. An image forming apparatus having a material conveying belt, wherein the pressing force of the transfer assist member or the transfer member toward the image carrier at each transfer position is set to a different pressing force for each station. . 2. The means for setting the pressing force for each station prepares a plurality of transfer assisting members or transfer members having different pressing forces, and attaches the selected members to a predetermined portion of the main body apparatus. The image forming apparatus according to Item 1. 3. The transfer assisting member is a sheet-shaped backup member for corona transfer or brush transfer, and a predetermined pressing force is obtained by changing the thickness, the free length of the backup member, or the amount of intrusion into the transfer material conveying belt. The image forming apparatus according to claim 1, wherein the image forming apparatus is set to. 4. The transfer member is a blade member in blade transfer, and the blade member has a thickness, a free length,
Alternatively, the image forming apparatus according to claim 1, wherein the predetermined pressing force is set by changing the amount of penetration of the transfer material conveying belt. 5. The transfer member is a roller member in roller transfer, and is set to a predetermined pressure by changing the biasing force of the biasing member of the roller member or the hardness of the roller member. The image forming apparatus according to claim 1.