JPH04149492A - Image formation device - Google Patents

Abstract

PURPOSE:To shorten the conveyance path for a recording material and obtain the image formation device which is small in size and low in cost by providing a rotary body for transfer which supports a conveying means at the most upstream position in the conveyance path where the recording material is conveyed by the conveying means and also at the position facing the image carrier on the most upstream side in the conveyance direction among image carriers. CONSTITUTION:The rotary body 12 for transfer which supports the conveying means 1 is provided on the most upstream position in the conveyance path where the recording material P is conveyed by the conveying means 1 and at the position facing the image carrier 4a on the most upstream side in the conveyance direction among the image carriers 4a-7a. The rotary body 12 can, therefore, serve as both a roller where the conveying means 1 is supported and wound and a transfer roller to decrease the number of rollers of a transfer device, shorten the peripheral length of a belt, and decrease the length of a transfer device unit. Consequently, the conveyance path for the recording material P can be shortened.

Description

Detailed Description of the Invention [Technical Field] The present invention includes a conveying means for carrying and conveying a recording material in order to sequentially transfer images formed on each of a plurality of image carriers onto a recording material. The present invention relates to an image forming apparatus, and particularly to an image forming apparatus suitable for forming color images.

[Background Art] Conventionally, as shown in FIG. 5, an image forming apparatus using a plurality of photosensitive drums 4a, 5a, 6a, 7a and a transfer belt 1 is known as a color electrophotographic printer. A toner image of each color is formed on each photosensitive drum by a respective toner image forming means. On the other hand, the transfer belt 1 is rotatable while being supported by a drive roller 3 and a driven roller 2, and paper as a recording material is attracted and held on this transfer belt 1 by an attraction corona charger IO.

When the transfer bell) 1 rotates to hold and convey the recording material, the timing is matched at the transfer position of each photosensitive drum,
The toner images on each photosensitive drum are sequentially superimposed and transferred onto the recording material by the respective transfer corona chargers 4e, 5e, 6e, and 7e. After the transfer, the toner image on the photosensitive drum is removed by a cleaner, making it possible to form the next image on the photosensitive drum.

[Problems to be Solved by the Invention] However, in the conventional example described above, as shown in FIG. 5, there are many corona chargers, and there is a problem that the amount of ozone generated and power consumption are large, resulting in high cost. Therefore, as shown in the image forming apparatus of FIG. 6 and FIG.
It is possible to use −. This makes it possible to reduce the power normally required by a corona charger by one or two orders of magnitude.

On the other hand, as shown in FIGS. 5 and 6, image forming apparatuses equipped with a plurality of photosensitive drums have a drawback in that the conveyance distance of the recording material cannot be shortened. In addition, in devices using transfer belts, it is especially effective to use seamless belts to achieve good image quality, but it is difficult to manufacture large diameter seamless belts as the diameter increases, resulting in high image quality. For high-precision products that can be obtained, there are further problems in terms of cost and productivity. Furthermore, even if a seamed belt is used, the longer the belt length, the higher the cost, and the longer the conveyance path of the recording material, the lower the speed of image formation on the recording material, and the more likely it is that the recording material will jam. This leads to a decrease in the production performance of the image-formed recording material as a device.

[Object of the Invention] The present invention has been made in view of the above-mentioned problems, and an object thereof is to provide an image forming apparatus in which a recording material conveyance path is shortened.

Another object of the present invention is to provide an image forming apparatus that efficiently forms an image on a recording material and improves the productivity of outputting the imaged recording material.

A further object of the present invention is to provide a compact and low cost image forming apparatus.

[Structure of the Invention] In order to achieve the above object, the present invention provides a conveying means for carrying and conveying a recording material in order to sequentially transfer images formed on each of a plurality of image carriers onto a recording material. In an image forming apparatus having the above, the recording material is located at the most upstream position in the conveyance path along which the recording material is conveyed by the conveyance means, and is opposed to the most upstream image carrier in the conveyance direction among the image carriers. The present invention is characterized in that it includes a transfer rotary body that is provided at a position and supports the conveyance means.

[Example] Embodiments of the present invention will be described below based on the drawings.

FIG. 1 shows a full-color electrophotographic printer showing an embodiment of the image forming apparatus of the present invention.

The photosensitive drums 4a, 5a, 6a, and 7a as image carriers are rotatable in the directions shown in the drawings, and each has a charger 4b.
, 5b, 6b, and 7b. Each of the charged photosensitive drums is exposed to a laser beam La by a laser scanner (not shown) in accordance with an image signal.

After the latent images are formed by irradiation with Lb, Lc, and Ld, a developing device 4d has toner of four different colors.

5d, 6d, and 7d, toner images of different colors are formed on each photosensitive drum.

On the other hand, the transfer belt 1 is an endless dielectric belt (seamless belt), and the recording material P such as paper that is fed toward the transfer belt 1 is transferred to the transfer belt 1, which is a recording material conveying means. Each photosensitive drum 4a, 5a is
, 6a, 7a, and transfer rollers 12, 5f, 6f, 7f, which are transfer rotating bodies facing each drum, toner images of different colors on each drum after passing through each transfer position. are sequentially superimposed and transferred at the same timing. As shown in the figure, this transfer belt (I) is wound around and stretched around a transfer roller 12 and a drive roller 3 that drives the belt. As the drive roller 3, a rubber roller with high surface friction resistance was used.

After the four color toners are transferred onto the recording material P carried and conveyed by the transfer belt 1, the recording material P passes through a belt drive roller 3, is separated from the belt 1, and then passes through a pair of heat rollers of a fixing device (not shown). The toner image on the recording material is thermally melted and mixed with color. Thereafter, the recording material on which the full color image has been formed is discharged from the apparatus.

The above transfer belt 11 transfer rollers 12, 5f, 6f, 7
The transfer device equipped with the f1 drive roller 3 will be further explained.

Each transfer roller is a conductive resin roller that applies a transfer voltage to the transfer roller, thereby sandwiching the transfer belt 1 and transferring the toner image formed on the photosensitive drum at the opposing portion of the photosensitive drum and the transfer roller onto the belt. so that it is transferred onto the upper recording material. Further, the transfer roller 12 that transfers the first color toner image onto the recording material is located at the most upstream position in the conveyance path along which the recording material is conveyed by the belt 1, and is located at the most upstream side in the conveyance direction. It is provided at a position facing the drum 4a. Therefore, the roller that supports and winds the belt 1 can serve both as a transfer roller, and the number of rollers in the transfer device, the circumferential length of the belt, and the length of the transfer device unit can be reduced.

Furthermore, if the recording material is fed toward the nip between the photosensitive drum 4a and the transfer roller 12 as shown in FIG. The recording material can be electrostatically attracted to the transfer belt l at the same time as the transfer by the transfer current at the time, and after the first color is transferred, the recording material or the recording material is conveyed while being electrostatically attracted to the transfer belt l. By employing the simultaneous transfer and attraction method as described above, a high-voltage attraction power supply for electrostatically attracting the recording material to the belt 1 is not required, so that it is possible to limit power consumption and reduce the cost of the power supply.

In addition, compared to a system in which the recording material is attracted to the transfer belt l in advance, the degree of freedom in the angle of entry of the recording material into the suction section is improved, making it possible to feed the recording material to the belt at the most suitable angle for each prefecture. can. For example, if the leading edge of a stiff recording material such as base paper is curled upward in Figure 1,
As shown in Figure 5, if the transfer belt extends to the upstream side of the recording material conveyance path from the transfer position, the leading edge of the curled recording material remains suspended from the belt and is conveyed to the transfer position. . Therefore, the leading edge of the stiff recording material hits the surface of the photosensitive drum, causing image disturbance and damage to the drum.

On the other hand, using the device shown in FIG.
The above phenomenon can be suppressed by feeding the recording material toward the curved portion.

Note that the transfer roller 12 of this embodiment is made of a soft material with a JISA hardness of about 20 to 30 degrees because if the pressure is increased to increase the adsorption force, the density in the central part of characters etc. will decrease and image deterioration will occur, such as white spots. It is preferable to use a different material and to increase the nip width.

On the other hand, in this embodiment, the material of the belt is made of polyurethane, which is easy to press and mold.
When changing the environment from a temperature and humidity of 60% °C to a temperature and humidity of 20 °C and 10%, there is an expansion and contraction of about 4 mm per 1 m. If the belt is shortened by 20 cm from 1 m in Fig. 5 using the configuration shown in Fig. 1, the expansion and contraction can be suppressed to 3.2 mm, which is approximately 1 m compared to the conventional belt in this embodiment.
This means that the expansion and contraction of mm can be reduced.

Next, another embodiment of the image forming apparatus of the present invention will be described with reference to FIG.

This embodiment is different from the embodiment shown in FIG. 1 in that a transfer roller 11 facing the photosensitive drum 7a is provided at the most downstream position in the conveyance path where the recording material is conveyed by the transfer belt 1. There is.

In FIG. 2, parts common to those in FIG. 1 are designated by the same numbers, and their explanations will be omitted.

The transfer roller/transfer belt drive roller 11 to which voltage is applied to transfer the toner image formed on the photosensitive drum 7a onto the recording material is made of a roller core material (5US303 in this case) and a conductive rubber and sponge coating. To maintain the insulation properties of the roller surface, the surface is coated with silicone rubber. The volumetric efficiency of the roller surface is 10I! -10"Ω'c
I made it m.

In this way, since the transfer roller 11 facing the photosensitive drum 7a located most downstream in the conveyance direction is provided at the most downstream position in the conveyance path where the recording material is conveyed by the transfer belt,
Compared to the apparatus shown in FIG. 1, the conveyance path of the recording material carried and conveyed by the belt can be further shortened, and the circumference of the belt can also be shortened.

Incidentally, as shown in FIG. 2, a suction roller 14 may be provided to charge the belt in advance before it reaches the transfer position of the photosensitive drum 4a.

FIG. 8 shows an example in which corona chargers 5f and 6f are used in place of the transfer rollers 5f and 6f for transferring the second and third colors onto the recording material in this embodiment, respectively.

In order to achieve effects such as reducing power consumption for transfer and reducing the amount of ozone generated, it is preferable to use rollers for transfer for all colors as shown in Figure 2, but rollers for transfer as shown in Figure 8 are preferred. Even if a corona charger is used in combination, the above-mentioned effect of shortening the length of the conveyance path and belt can be obtained.

In the embodiments described above, the belt tension is mainly controlled by the most upstream and most downstream rollers in the recording material conveyance direction in the recording material conveyance path by the belt. However, since the transfer belt generally has a large diameter, unless the circumference of the belt is finished with a high degree of accuracy, the tension will loosen and image quality deterioration such as speed unevenness will occur.

Therefore, in this embodiment, a case in which two tension rollers are provided will be described with reference to FIG. 3. In the figure, the tension roller 13 is an aluminum roller that applies tension by moving up and down its position, so that a certain degree of variation in the circumferential length of the transfer belt 1 can be adjusted by adjusting this position. The same thing can be said if there is only one tension roller instead of two. In addition, in the case where a tension roller is used, the tension roller 13
Even if the tension roller 13 is located on the right side in the figure from the roller 12 (which is the upper bottom (lower bottom when the belt shape shown is approximately trapezoidal)), the tension roller 13 is not in the recording material conveyance path by the transfer belt. Even in that case, roller I2 becomes the most upstream roller in the conveyance path.

FIG. 4 shows the case where there is one belt tension roller, that is, one roller 13, as described in the previous embodiment.

This is an example similar to when the belt shape in FIG. 3 explained in the previous embodiment is a trapezoid, and the upper and lower bases become upper and lower bases. In this case, since the recording paper is fed to the photosensitive drum 4a and the transfer roller 4f by the paper feed guide 9, the belt tension roller 13 is not in the recording conveyance path. Therefore, the roller 4f becomes the most upstream roller. The belt tension roller shown in FIG. 4 is a roller that adjusts the tension by moving up and down with respect to the drive roller. According to this embodiment, the recording material conveyance path on the transfer belt can be made shorter than in the conventional apparatus shown in FIG.
This leads to miniaturization of the apparatus, which tends to be long, especially in the recording material conveyance direction.

In the above embodiments, the case where toner images of four colors are superimposed and transferred to the recording material has been described, but it goes without saying that other cases, such as the case of three colors, etc., may also be used.

As in the embodiments described above, the most upstream position in the conveying path where the recording material is conveyed by the transfer belt, and the position facing the most upstream photosensitive drum in the conveying direction among the photosensitive drums. By providing a transfer roller in the transfer roller, the length of the recording material conveyance path and the transfer belt can be made shorter than in the past.

The configuration facilitates feeding of the recording material onto the transfer belt and facilitates simultaneous transfer and attraction, and there is no need to provide an attraction charger separate from the transfer means.

In addition, the circumferential length of the belt has been shortened, improving belt productivity with high precision and reducing costs. Furthermore, changes in the circumferential length of the belt due to environmental changes can be reduced by shortening the belt's overall circumferential length, making it possible to realize a device that is resistant to environmental changes.

Furthermore, since the recording material conveyance path can be shortened, the productivity of recording material output can also be improved.

[Effects of the Invention] As explained above, according to the image forming apparatus of the present invention,
The conveyance path for the recording material could be shortened.

Furthermore, it was possible to improve the productivity of outputting the recording material on which images were formed, and it was possible to realize miniaturization and cost reduction of the apparatus.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a sectional view showing one embodiment of the image forming apparatus of the present invention, and FIGS. 2 to 4, 7, and 8 are other embodiments of the present invention. 5 and 6 are cross-sectional views of a conventional image forming apparatus. 1 is a transfer (conveyance) belt, 3 is a drive roller, and 4a. 5a, 6a, 7a are photosensitive drums, 4f, 5f, 6f, 7
f, l 1, 12 are transfer rollers.

Claims (3)

[Claims] (1) In an image forming apparatus having a conveyance means for carrying and conveying the recording material, the recording material is conveyed by the conveyance means in order to sequentially transfer images formed on each of a plurality of image carriers onto the recording material. A transfer rotating body is provided at the most upstream position in the conveying path and at a position facing the most upstream image bearing member in the conveying direction among the image carriers, and supports the conveying means. An image forming apparatus comprising: (2) A voltage is applied to the transfer rotating body, and the recording material is electrostatically applied to the conveying means by passing between the transfer rotating body and the image bearing member on the most upstream side. The image forming apparatus according to claim 1, wherein the image forming apparatus is attracted to. (3) Claim (1) characterized in that images of different colors corresponding to the number of image carriers are superimposed and transferred onto the recording material.
) or the image forming apparatus according to (2).