JPH04221982A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent the transfer positional deviation of a recording material in a transfer process on a multiple transfer system copying machine having plural image forming parts, a printer, etc. CONSTITUTION:Even if the recording material attracted/held on a transfer belt 6 passes the image forming part not participating in an image formation at the time of the execution of the transfer process of a visible image formed on the image forming part, a transfer/electrifying unit arranged opposite to a photosensitive drum is pressed to give an attracting charge enough to reach the next image forming part to the recording material. Thus, the range of the volume resistance of a raw material used as a recording material carrying means is expanded, and even if excessive attracting force is not given, the positional deviation of the recording material does not occur.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to image forming apparatuses such as copying machines and printers using electrophotography or electrostatic recording.
In particular, but not limited to, the present invention relates to a multiple transfer type image forming apparatus that includes a plurality of image forming sections and transfers visible images formed by each image forming section onto a recording material in an overlapping manner.

0002

[Prior Art] Conventionally, in a multi-transfer type image forming apparatus, in order to prevent transfer position shift, an adsorption force is applied before transfer so that the recording material is fixed to the recording material conveyance means from beginning to end. Or, the recording material was forcibly held down using a gripper or the like. Furthermore, as described in Japanese Patent Application Laid-Open No. 1-96669, there was also a method in which a transfer charge was applied to an image bearing member downstream of image formation, such as a photoreceptor.

0003

[Problems to be Solved by the Invention] However, in order to generate an electrostatic force that can generate an adsorption force that will not shift the position from beginning to end, as in the above-mentioned conventional example, it is necessary to
(1) Unnecessarily large power supply capacity is required; (2)
The charge caused by adsorption causes a negative effect on the charge for transfer (discharge leakage, etc.), and the transfer conditions become narrow especially at the end of multiple transfer. (3) Due to the excessive charge applied, the discharge during separation (4) The materials used for the recording material conveying means are considerably limited.

Further, even if charges are applied only downstream of the image bearing member involved in image formation, as in the invention described in Japanese Patent Application Laid-Open No. 1-96669, it is ineffective against positional deviation.

Therefore, an object of the present invention is to widen the selection range of materials that can be used as a recording material conveying means by energizing the charging means to apply adsorption force to the recording material even in a transfer process that does not involve image formation. To provide an image forming apparatus that enables the use of a relatively small capacity power source, reduces the cost of a recording material conveying means and power source, improves transfer efficiency, and prevents image distortion. It is to be.

[0006]

Means for Solving the Problems The above objects are achieved by an image forming apparatus according to the present invention. To summarize, the present invention provides the following advantages: when a recording material attracted and held on a recording material conveying means by electrostatic force passes between an image carrier and a charging means disposed opposite to the image carrier, a transfer step of energizing the charging means to transfer the visible image formed on the image carrier to the recording material; the transfer step can be performed a plurality of times; In an image forming apparatus provided with an image forming mode in which at least one of the transfer steps does not involve image formation, and at least one transfer step that does involve image formation is performed thereafter, the image forming mode is executed. The image forming apparatus is characterized in that the charging means is energized to apply adsorption force to the recording material even in a transfer process that does not involve the image formation.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic sectional view showing a first embodiment of an image forming apparatus according to the present invention, in which the present invention is applied to an electrophotographic color copying machine. This color copying machine has a configuration in which four image forming sections are linearly arranged, and each image forming section has photoreceptor drums 1 to 1 as image carriers.
Although not shown, an erase lamp, a primary charger, a developer, a cleaner, an image exposure section, etc. are arranged around the photoreceptor drums 1 to 4, respectively. In the color copying machine of this embodiment, for example, cyan, cyan, and
The second image forming section forms magenta, the third image forming section yellow, and the fourth image forming section forms black color-separated toner images on these photoreceptor drums, and these color-separated toner images are A full-color image is obtained by sequentially overlapping and transferring the images onto a recording material (not shown) and fixing them all at once using a fixing device 5.

The recording material is fed to the suction position along the paper feed guide 8, and is moved by the driving force of the drive roller 7, for example, 1
The recording material is electrostatically attracted by corona discharge by an attraction charger 9 onto a transfer belt 6, which is a recording material conveying means, and which is moving endlessly at a speed of 0.00 mm/sec. As described above, the toner images of cyan, magenta, yellow, and black formed on the photoreceptor drums 1 to 4 of the first to fourth image forming sections according to the image signal are moved by the movement of the recording material. Accordingly, multiple images are transferred onto the recording material by corona discharge from the transfer chargers 11 to 14 disposed at the respective transfer positions. Thereafter, the recording material is separated from the transfer belt 6 by a separation charger 10 and passes through a pair of fixing rollers 5 to output a recorded image. On the other hand, after the recording material is separated from the transfer belt 6, the charge is removed by a charge-eliminating charger 15 to prevent charge-up, and the transfer belt 6 returns to the potential state before transfer.

When multiple transfer is performed in the color image forming apparatus configured as shown in FIG.
The required material properties are that both toner transfer properties and recording material adsorption properties are good. However, in order to satisfy this condition, the materials used have been quite limited in the past. For example, in terms of adsorption, after the recording material is attracted to the recording material transport means by the adsorption charger 9, the recording material is firmly fixed on the transfer belt 6 until it passes the fourth color photosensitive drum 4. If this is not done, transfer positional deviation will occur between each color, leading to significant image quality deterioration, especially in color.

Adsorption force in the recording material conveyance direction when the recording material passes through the fourth photosensitive drum 4 when a recording paper of 80 g is used as the recording material and the volume resistance value of the transfer belt 6 is changed. Figure 2 shows the changes in . In Figure 2, curve A
is 200μA, curve B is 300μA, curve C is 500μA
This is a case where a current of A is applied to the adsorption charger 9. As can be easily understood from Figure 2, if the system requires an adsorption force of 600gf, if the material is 1014Ω・cm, then the
It is sufficient to apply a current of 00 μA to the adsorption charger 9, but 1
It can be seen that even if a current of 500 μA is applied to the material of 0.013 Ω·cm, the current is insufficient. However, even if the adsorption force is not maintained until after passing the photosensitive drum 4 of the fourth color, the recording material has an adsorption force when the toner image of each color is transferred, so in theory, the first color It should be sufficient to maintain an adsorption force that does not cause transfer deviation until the photoreceptor drum 1 passes through the photoreceptor drum 1. Here, the adsorption force required to prevent transfer misalignment depends on various factors such as the nip with the photoreceptor drum, friction between the photoreceptor drum and the transfer belt, the material of the recording material, etc., and each differs, for example. , 600g as an example
A case where an adsorption force of f is required will be explained.

FIG. 3 shows that when a belt material having a volume resistivity of about 1013 Ω·cm is used as the transfer belt 6, the fourth
The adsorption force of the 80 g transfer paper after passing between the photoreceptor drum 4 and the first photoreceptor drum 1 is shown. A curve X shown by a dotted line in FIG. 3 shows the adsorption force after passing through the first photoreceptor drum,
A curve Y shown by a solid line indicates the adsorption force after passing through the fourth photoreceptor drum. As described above with reference to FIG.
cm, in order to obtain an adsorption force of 600 gf, it was insufficient to apply a current of 500 μA to the adsorption charger 9 after passing the fourth photoreceptor drum 4; It can be seen that it is sufficient to flow a current of 250 μA until after the passage.

However, the problem here is how the color image forming apparatus is used. Color image forming apparatuses are not always used to form four-color toner images and transfer them multiple times to obtain a full-color image. In particular, when black monochrome is specified, no transfer current is applied to the transfer chargers 11 to 13 of the first to third image forming sections. Therefore, in the present invention, even when the recording material passes through the photoreceptor drum of an image forming section that is not involved in image formation, the recording material is firmly fixed to the transfer belt 6 until it reaches the photoreceptor drum of the next image forming section. to be able to pass through
The structure is such that, in the same way as the transfer current, a current is applied to the transfer charger of the image forming section that is not involved in image formation to provide the necessary attraction force.

With this configuration, even if a recording material conveying means having a volume resistivity of 1013 Ω·cm is used, it is sufficient to apply a current of 250 μA to the adsorption charger as described above, so that the recording material can be transported easily. The range of volume resistivity of materials that can be used as the conveying means is widened, and the material for the recording material conveying means can be selected from a fairly wide range. Furthermore, since it is not necessary to apply excessive suction force, transfer efficiency is improved and image disturbance does not occur. Further, there are advantages such as cost reduction of the power source, the material of the recording material conveyance means, etc.

In the above embodiment, an endlessly moving transfer belt was used as the recording material conveying means, but the recording material conveying means is not limited to an endlessly moving belt-like body. For example, as shown in FIG. The present invention can also be applied to a full-color copying machine using a drum. A second embodiment of the present invention shown in FIG. 4 will be described below.

This full-color copying machine adopts the electrophotographic method as in the first embodiment, and therefore has a photosensitive drum 17 as an image bearing member, and an image forming means is arranged on the outer periphery of the photosensitive drum 17. ing. This image forming means may be any means, but in this embodiment, a primary charger 24 that uniformly charges the photoreceptor drum 17, and a color-separated optical image or a light beam corresponding thereto are transferred to the photosensitive member at a predetermined timing. A laser beam exposure device including, for example, a polygon scanner 25 forms an image on the surface of the photoreceptor drum 17 and forms an electrostatic latent image on the photoreceptor drum 17, and converts the electrostatic latent image on the photoreceptor drum 17 into a visible image. and developing devices 16 are sequentially provided in the rotational direction of the photoreceptor drum 17.

In this embodiment, the developing device 16 is a rotary developing device that rotates and moves opposite to the outer peripheral surface of the photoreceptor drum 17. It is equipped with four developing devices each containing four color developers, including black color developer. The toner image formed on the photosensitive drum 17 is transferred onto a recording material (not shown) carried by a transfer drum 19 that is rotationally driven in the direction of the arrow in the drawing and is conveyed. This transfer drum 1
9 is located in the rotational direction of the photoreceptor drum 17 and faces the photoreceptor drum 17, either in contact with the surface of the photoreceptor drum 17 or in a slightly separated state.

The recording material is sent out from within the paper feed cassette 27 by the paper feed motor 26, and is fed to the transfer drum 19 through the registration roller pair 22 in a synchronous state. At the recording material adsorption position, an adsorption charger 9 is installed inside the transfer drum 19.
However, at the transfer position facing the photosensitive drum 17,
Similarly, transfer chargers 18 are provided inside the transfer drum 19, respectively. Furthermore, two static eliminators 20 are disposed opposite to each other adjacent to the downstream side of the transfer position, and downstream of the static eliminators 20 there is a separation charger 21 for separating the recording material held on the transfer drum 19. is arranged, and a separation blade is arranged near it. Further, a fixing device 28 is provided for fixing the toner image on the recording material that has been separated from the transfer drum 19 by a separation blade and conveyed by a conveyor. Note that a cleaner 23 for removing residual toner on the photoreceptor drum 17 is provided around the photoreceptor drum 17 .

Next, the operation of the full color copying machine of this embodiment having such a configuration will be explained.

When forming a multicolor (including full color) color image in the copying machine having the above configuration, the developing device 1
6 develops the electrostatic latent image of each color, the transfer drum 19 rotates for the number of times of development of each color. Therefore, in this embodiment, not only the attraction charger 9 applies an attraction charge to the recording material, but also the transfer charger 18 is applied to the transfer drum 1.
The transfer charger 18 is always energized every time the transfer charger 9 rotates, and a charge for attracting the recording material is applied from the transfer charger 18 even when a toner image is not being transferred.

In this embodiment, an adsorption charger 9 and a transfer charger 1 are used.
Since the transfer drums 8 and 8 are disposed at positions substantially diametrically opposed to each other, it is only necessary to apply suction force to the recording material to prevent transfer displacement while the transfer drum 19 rotates half a rotation. For example, even in the case of a two-color mode for the second and fourth colors, the transfer charger 1 also rotates when the transfer drums 19 for the first and third colors are rotated.
8, corona discharge is performed to provide charge for adsorption. The applied current value in this case does not necessarily have to be equal to the normal transfer current value, and in short, it is sufficient to flow only the current necessary for adsorption.

Generally, when the volume resistance of the recording material carrying sheet material of the recording material conveying means is low, the potential decays quickly, but by applying the present invention, transfer deviation on the recording material is prevented only during half a rotation of the transfer drum. All you have to do is give the adsorption force that does not occur.
Even materials with a lower resistance value than conventional materials can be used as the recording material carrying sheet material. The lower the volume resistance value, the less transfer current can be applied for transfer, so the use of a material with a low resistance value leads to a reduction in power supply capacity, which makes it possible to reduce the cost of the power supply and to Since the selection range of material-carrying sheet materials is widened, it is also possible to reduce the cost of the recording material conveying means. Of course, since it is not necessary to apply an excessive adsorption force, the transfer efficiency is improved and the image is not disturbed.

Although corotron type chargers are used as the adsorption and transfer chargers in the first and second embodiments, the present invention is not necessarily limited to corotron type chargers. For example, as shown in FIG. 5, the attraction charger 29 and the transfer charger 30 may each be roller-shaped contact charging type chargers. Since it is clear that the same effects as in the first and second embodiments can be obtained in this embodiment as well, the same reference numerals are given to the parts corresponding to those in FIG. 4, and the explanation thereof will be omitted.

Further, the present invention is not limited to a drum-shaped photoreceptor, but may be, for example, a belt-shaped photoreceptor that moves endlessly. Further, in each of the above embodiments, the present invention is applied to an electrophotographic color copying machine, but the present invention can be applied to various copying machines, printers, etc. using electrophotography, electrostatic recording, etc. other than the embodiments. It is equally applicable to the following image forming apparatuses. Further, as described above, it goes without saying that various modifications and changes can be made to the members, elements, etc. constituting the image forming apparatus as necessary.

[0025]

As explained above, in the image forming apparatus according to the present invention, the charging means disposed opposite to the image bearing member of the image forming section not involved in image formation is energized so that the recording material is carried on the recording material conveying means. By applying a charge for adsorption to the recording material, the range of volume resistivity of materials that can be used as a recording material conveying means is widened, and even materials with lower resistance values than before can be used as materials for recording material conveying means. Can be adopted. The lower the volume resistance value, the less transfer current can be applied for transfer, so the use of a material with a low resistance value leads to a reduction in power supply capacity, which makes it possible to reduce the cost of the power supply and to Since the selection range of materials for the material conveyance means is considerably widened, it is also possible to reduce the cost of the recording material conveyance means. Furthermore, since it is only necessary to provide enough adsorption force to firmly adsorb the recording material to the recording material conveying means until it passes the image carrier of the next image forming section, there is no need to apply excessive charge. Therefore, there are remarkable effects such as improved transfer efficiency and no image disturbance.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing a first embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a characteristic showing the change in adsorption force in the recording material conveyance direction when the recording material passes the fourth photosensitive drum when the volume resistivity of the transfer belt is changed in the image forming apparatus of FIG. 1; It is a diagram.

3] Recording when a belt material having a volume resistivity of about 1013 Ω·cm is used as the transfer belt in the image forming apparatus shown in FIG. 1, and when the belt material passes through the fourth photosensitive drum and the first photosensitive drum. It is a characteristic diagram showing the adsorption power of the material.

FIG. 4 is a schematic cross-sectional view showing a second embodiment of the image forming apparatus according to the present invention.

FIG. 5 is a schematic cross-sectional view showing a third embodiment of an image forming apparatus according to the present invention.

[Explanation of symbols]

1 to 4 Photosensitive drum 6 Transfer belt 9
Adsorption chargers 11 to 14 Transfer charger 16 Developing device 17 Photosensitive drum 18
Transfer charger 19 Transfer drum 29 Adsorption charger 30 Transfer charger

Claims (1)

[Claims] Claim 1: When the recording material attracted and held on the recording material conveying means by electrostatic force passes between an image carrier and a charging means disposed opposite to the image carrier, the charging means It has a transfer step of transferring the visible image formed on the image carrier to the recording material by energizing the image carrier, and the transfer step can be performed multiple times, and among these transfer steps, At least one transfer step does not involve image formation, and then at least one transfer step that does involve image formation
In an image forming apparatus provided with an image forming mode in which rotation is performed, when the image forming mode is executed, the charging means is energized to apply an adsorption force to the recording material even in a transfer process that does not involve the image formation. An image forming apparatus characterized in that: