JPS6345596B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a transfer device, and more particularly, to a transfer device that circulates a transfer material and forms multiple transferred images on the transfer material from an image carrier. Conventionally, in image forming apparatuses such as transfer-type color electrophotographic apparatuses, which sequentially form different color images on an image bearing member such as a photoreceptor drum, and multiple-transfer each color image onto a transfer material, Various types of multiple transfer devices have been proposed. In particular, the corona discharge transfer method is effective because it does not impose any load on the image carrier. This method also includes a model that uses an insulating belt,
There is a type that uses a mesh-like perforated screen. In the former type, since transfer corona charges accumulate on the back surface of the insulating belt, there is a problem that the transfer efficiency decreases as the number of repeated transfers increases, and no satisfactory solution has yet been found. In addition, the same type had the problem that the accumulated charges tended to cause image disturbances when the transfer material was separated. On the other hand, in the latter type, the transfer corona passes through the mesh of the screen and acts directly on the transfer material, so the above-mentioned problem is solved. However, although the increase in the aperture ratio of the mesh of the screen improves the transfer and separation properties, the holding force of the transfer material weakens, and there are cases where the conveyance force is insufficient. If the conveyance force is insufficient, there is a risk that misalignment will occur between the multiple transferred color images, resulting in a decrease in image quality. For this reason, when the aperture ratio is lowered, the same problem as in the case of the insulating belt becomes noticeable. The present invention has been made in view of the above-mentioned points, and it is an object of the present invention to provide a transfer device that can maintain sufficient circulation conveyance force while maintaining good transfer efficiency. That is, the present invention relates to a transfer device that transfers a toner image formed on an image carrier onto a transfer material, and a transfer material conveyance device that supports and conveys the transfer material to a transfer position where the toner image on the image carrier is transferred. The transfer material conveying means is formed by calendering a mesh-like screen formed by knitting fibers to flatten the surface that contacts the transfer material, and the transfer material conveying means is disposed on the back side of the transfer material conveying means, It is characterized by having a transfer discharge means for applying discharge for transfer at the transfer position. Hereinafter, details of the present invention will be explained using specific examples with reference to the drawings. FIG. 1 shows an example of a specific transfer-type color electrophotographic apparatus to which the embodiment transfer apparatus of the present invention is applied. Reference numeral 1 denotes an electrophotographic photosensitive drum having an insulating layer on its surface, which is rotatably supported on a shaft 2. and starts rotating in the direction of arrow 3 in response to a copy command. When the drum 1 rotates to the normal position, the original 0 placed on the original platen glass 4 is illuminated by an illumination lamp 6 integrated with the first scanning mirror 5, and the reflected light is transmitted to the second scanning mirror 7. is scanned. The first scanning mirror 5 and the second scanning mirror 7 move at a speed ratio of 1:1/2, so that the original is scanned while the optical path length from the original 0 to the lens 8 is always kept constant. The reflected light image passes through a lens 8 and a third mirror 9, is color-separated by a color separation filter 10, and is further color-separated by a fourth mirror 1.
1. An image is formed on the drum 1 at the exposure section 13 through the dust-proof sealing glass 12. After the drum 1 is neutralized by the static eliminator 14 and then charged (for example, positive) by the primary charger 15,
In the exposure section 13, the image illuminated by the illumination lamp 6 is subjected to slit exposure. At the same time, AC or primary static electricity removal with a polarity opposite to that of the primary (for example, negative) is performed using a static eliminator 16, and then a high-contrast electrostatic latent image is formed on the drum 1 by full-surface exposure using a full-face exposure lamp 17. The electrostatic latent image on the photosensitive drum 1 is then developed into a toner image by a developing device 18. Developing device 18
is yellow 181, magenta 182, cyan 18
The developing device is composed of four developing devices, 3 and 184 black, and a developing device designated in accordance with the color separation filter used for exposure operates to obtain a toner image of the required color. The transfer paper 201 in the cassette 191 is fed into the machine by the paper feed roller 211, and the rough timing is taken by the first register roller 221, and then the precise timing is taken by the second register roller 23, so that its leading edge is It is gripped by the gripper 24 of the transfer drum 33. As the transfer drum 33 rotates, the transfer paper 201 is conveyed while being wrapped around a screen attached to the transfer drum, and while the transfer paper 201 passes between the transfer charger 5 and the photosensitive drum 1, a While the toner image is transferred, the transfer paper 201 is held on the Screeley surface by electrostatic attraction. In the first transfer, the transfer paper 201 is electrostatically attracted to the screen after the transfer charger 25, and the binding force until then is weak, so the transfer paper 201 is pulled against the photosensitive drum 1, causing color misalignment. Therefore, the presser roller 35 prevents this. The presser roller 35 and paper feed guide plate 34 move away from the transfer drum 33 after the first paper passes through them. The transfer drum 33 grips the leading edge of the transfer paper 201 with the gripper 24 and rotates the required number of times while electrostatically attracting the screen, thereby transferring an image of the required number of colors. The copying machine shown in the figure is equipped with two cassettes loaded with transfer papers of different sizes and types, and the papers are selectively combined. After the transfer is completed, the transfer paper is released from the gripper 24 and is moved to the separation claw 2 with the help of separation chargers 36 and 37.
6, and is guided to a conveyor belt 27, and further guided to a pair of fixing rollers 28 and 29, where it is pressurized and
The image is fixed by heating and then discharged onto the tray 30. After the transfer, the surface of the photosensitive drum 1 is cleaned by a cleaning device 31 composed of an elastic blade, and the process proceeds to the next cycle. On the other hand, the transfer drum 33 has cleaners 38 and 39.
Both sides of the screen are cleaned by the screen, and if necessary, the charge up on the screen is removed by the charge up prevention charger 40, and the process proceeds to the next cycle. Charge up is a state in which charges of opposite polarity are generated on the side opposite to the charged side of the screen, attracting each other and no longer exerting any force on the outside. As shown in FIG. 2, the transfer drum 33 has a cylinder 331 cut out in the center and a screen 332 attached to the cutout part. The screen 332 is a perforated insulator with at least one flat surface, and is stretched so that the flat surface is in contact with the transfer paper. As such a screen, for example, a screen made by knitting fibers of nylon, polyester, silk, polypropylene, etc. and whose surface is made flat by calendering can be used. Next, the difference between a screen made of fibers knitted by a conventional method and a perforated screen whose at least one side is flat will be explained. Screens made of ordinary fibers can be divided into plain weave, twill weave, satin weave, twill weave, and semi-twill weave depending on the weaving method, but plain weave is generally the most commonly used screen for printing. The explanation will be given in plain weave. The same applies to other knitting methods. When the plain weave screen is viewed from above, the warp yarns Sv and weft yarns Sh are woven alternately as shown in Figure 3a, and its cross section is as shown in Figure 3b. For this reason, the area in contact with the transfer paper is only a small portion of the actual fiber, as shown in Figure 3c.
Therefore, the electrostatic attraction between the paper and the screen is small.
In order to increase the electrostatic adsorption force, the screen aperture ratio must be reduced, and if this is done, as mentioned earlier, transfer and separation will not be successful. However, if a perforated screen with a flat surface in contact with paper is used as in the present invention, such a phenomenon does not occur. FIG. 4 shows, as an example of the screen of the present invention, one side of the same screen which has been calendered. Figure 4a is a view from above, and the overlapping parts of the screen are squashed and are slightly thicker. As a result, the aperture ratio becomes slightly smaller than before the treatment, but it does not change drastically, so there is no problem. This cross section is shown in FIG. The calendered surface is flat. As a result, the area in contact with the transfer paper becomes much larger than before processing as shown in FIG. 4c. Therefore, the electrostatic adsorption force between the paper and the screen becomes large. Moreover, the aperture ratio of the screen is reduced by at most 10% compared to before processing, so transfer and separation are not impaired. As can be seen from the above description, by using a perforated screen having at least one flat surface as in the present invention, it is possible to convey, transfer, and separate the transfer paper in a good manner. EXAMPLES Hereinafter, in order to further deepen the understanding of the present invention, examples will be described. Example 1 A 70-mesh screen was made by knitting polyester single fibers, and the surface was made flat by calendering. (The screen at this time was designated as Sample A) An experiment was conducted in which this screen was attached to the transfer drum of the primary device. At this time, the flat surface of the screen was set as the front side of the transfer drum. Commercially available 80 g/m ² high-quality paper was used as the transfer material. A voltage of +6.5KV is applied to the transfer charger 25,
The developed colors of yellow, magenta, and cyan were sequentially transferred. After completion of the transfer, the transfer material was separated from the transfer drum by a separation corona discharge in which an AC voltage of 5 KV was applied to each of the separation chargers 36 and 37, and by the cooperative action of the separation claw 26. First, the transportability of the transfer material during repeated multiple transfers was good in this example, and the transfer material was sufficiently electrostatically attracted to the screen. Further, the transferred image of this example was good with no color shift. In other words, yellow, magenta, and
The development of the three cyan colors coincides with each other, and there is no color shift that would cause a shift in the mutual color images. Further, in the transferred image of this example, there was no substantial difference in transfer efficiency between the first color yellow and the final cyan color, and an image with good color balance was obtained. That is, the image quality was good. Further, in the configuration of this embodiment, the transfer material was smoothly separated after the transfer was completed, and the transferred image was not disturbed. That is, the separability was good. Comparative Example 1 For comparison, a similar experiment was conducted using a polyester screen of the same mesh stretched over a transfer drum without calendering (that is, without flattening the surface). (Sample B of the screen at this time)
). At this time, the image quality of the transferred image (that is, the uniformity of the transfer efficiency between the first color and the third color) was approximately good, and the separability was as good as Example 1, with no color loss. However, the electrostatic adsorption force was insufficient when repeatedly guiding the transfer material to the transfer position, and the conveyance performance was somewhat inferior. Then, the respective color images of the transferred image did not match, and the color shift became noticeable. Table 1 below summarizes the results of each of the above Examples and Comparative Examples.

[Table] As is clear from Table 1 above, Sample A of Example 1, in which the screen surface was flat, obtained good results. As described above in detail in the specific examples, the apparatus of the present invention is excellent in that it enables good transfer, maintains sufficient transfer material conveying force, and obtains good transferred images without color misregistration.

[Brief explanation of the drawing]

FIG. 1 is a side view of a specific example color electrophotographic apparatus to which the present invention is applied. FIG. 2 is a perspective view of the transfer drum. 3A, 3B, and 3C are explanatory diagrams of a conventional transfer drum screen, in which a is a plan view, b is a side sectional view, and c is a portion in contact with a transfer material. FIGS. 4a, b, and c are explanatory diagrams of the screen for a transfer drum according to the present invention, in which a is a plan view, b is a side sectional view, and c is a partial view of a portion in contact with a transfer material. In the figure, 1...electrophotographic photosensitive drum (image carrier),
2...Shaft, 4...Original table glass, 33...Transfer drum (transfer material carrying means).

Claims (1)

[Scope of Claims] 1. In a transfer device that transfers a toner image formed on an image carrier onto a transfer material, a transfer device that supports and conveys the transfer material to a transfer position where the toner image on the image carrier is transferred. A transfer material conveying means, which is formed by calendering a mesh-like screen formed by knitting fibers to flatten the surface that contacts the transfer material; and a transfer material conveying means disposed on the back side of the transfer material conveying means. 1. A transfer device comprising: a transfer discharge means for applying discharge for transfer at a transfer position.