JPH02293881A - Image forming device - Google Patents

Abstract

PURPOSE:To attain uniform electrostatic charge on an image carrier by operating a destaticizing means every time a transfer material is made abut on the area, where an electrostatic latent image is not formed, of the image carrier and destaticizing the trailing edge of the transfer material. CONSTITUTION:An inside electrifier 5d and an outside electrifier 5e are operated at the pre-rotation time before the image forming processes of a image forming device are started, and a period from when a last coler separation image forming process is started until the last image formation process is completed, the transfer material P is sufficiently separated from a transfer drum 5, and the image forming processes are throughly completed. Moreover, when the trailing edge Pa is positioned at a transfer area where a transfer means is arranged, at the time of making the transfer material P abut on the area, where the electrostatic latent image is not formed, on the peripheral surface of the photosensitive drum 1, the inside electrifier 5d is operated and a voltage is impressed thereon, and the trailing edge Pa of the transfer material P holding a toner image is destaticized. Thus, peeling discharge due to the accumulation of charges on the trailing edge of the transfer material is prevented, and uniform electrostatic charge on the image carrier can be attained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention generally relates to image forming apparatuses, and more particularly to multicolor electrophotographic copying apparatuses equipped with a plurality of developing devices, and recording apparatuses constituting output units of facsimile machines, computers, etc. The present invention relates to an image forming apparatus that can be suitably implemented in color image forming apparatuses such as various color printers. In this specification, a multicolor electrophotographic copying apparatus will be described, but the image forming apparatus of the present invention is not limited to this as described above. A variety of multicolor electrophotographic copying devices have been proposed in the past. FIG. 5 shows a typical multicolor Iπ photocopying apparatus equipped with a developing device called a so-called rotary developing device. To briefly explain with reference to FIG. 5, a multicolor electrophotographic copying apparatus includes an image bearing member, that is, a photosensitive drum l, which is rotatably supported on a shaft and rotates in the direction of the arrow. is placed. The image forming means can be any means, but in the wooden example, it includes a primary charger 2 that uniformly charges the photosensitive drum 1, and a color-separated light image or an equivalent light image that is irradiated onto the photosensitive drum 1. The photosensitive drum 1k is provided with an exposure means 3 formed of, for example, a laser beam exposure device, for forming an electrostatic latent image on the photosensitive drum lk, and a rotary developing device 4 for converting the electrostatic latent image on the photosensitive drum lk into a visible image. The rotary developing device 4 includes four developing devices 4Y, 4M, and 4C each housing four color developers, namely, a yellow developer, a magenta developer, a cyan developer, and a black developer.
, 4BK, and these four developing devices 4Y, 4M, 4C. 4
It consists of a substantially cylindrical casing 4a that holds the BK and is rotatably supported. The rotary developing device 4 conveys a desired developing device to a position facing the outer peripheral surface of the photosensitive drum l by rotating the housing 4a, and develops the electrostatic latent image on the photosensitive drum. The structure is such that full-color development of so-called four colors is possible by one rotation of the housing. The visible image, that is, the toner image, on the photosensitive drum L-H is transferred onto a transfer material P carried by a transfer device @5 and conveyed. In the wooden example, the transfer device 5 is a rotatably supported transfer drum, and the transfer drum 5 includes cylinders 5a. A transfer charger 5b, a paper feeder (
It has a transfer material gripper 5C that grips the transfer material P fed from a source (not shown). Further, inside and outside of the transfer drum 5, an inner static elimination charger 5d and an outer static elimination charger 5e, which constitute a weight removing means, are arranged. A transfer material carrying sheet 50l is stretched over an opening area on the outer peripheral surface of the cylinder 5a,
The transfer material carrying sheet 501 is usually made of, for example, polyethylene terephthalate or polyvinylidene fluoride resin film. A brief explanation of the full-color image forming process using the multicolor electrophotographic copying apparatus configured as described above is as follows. First, the charger 2 and the image exposure stage 3 are operated to form a blue color-separated electrostatic latent image on the outer peripheral surface of the photosensitive drum 1, and the electrostatic latent image is stored in the developer 4Y. The image is developed using a yellow developer. On the other hand, the transfer material P fed to the transfer drum 5 is transferred to the gripper 5C.
As the transfer drum 5 rotates, it comes into contact with the toner image formed on the outer peripheral surface of the photosensitive drum 1. The toner image is transferred onto the transfer material P by the operation of the transfer charger 5b, and at the same time, the transfer material P is attracted to the transfer material carrying sheet 501. After the image formation and transfer operation described above are completed, the transfer material carrying sheet 50 is
As the transfer drum 5 rotates, the transfer material P attracted to the photosensitive drum 1 still comes into contact with the electrostatic latent image non-forming area on the outer peripheral surface of the photosensitive drum 1. The toner image already transferred onto the transfer material P by the above-described image formation and transfer operations is still held on the transfer material P by the operation of the transfer charger 5b. The above image formation and transfer operations are repeated for each color of magenta, cyan, and black. The operation of the charger 5b is also repeated. When the overlapping transfer of the visible images of four colors onto the transfer material P is completed, the transfer material P is transferred to the inner charger 5d.
The charge is removed by the outer charger 5e, and then the transfer drum 5
and is discharged outside the machine via the heat roller fixing device 6. On the other hand, residual toner on the photosensitive drum is removed by a cleaner 7, and the photosensitive drum is subjected to the next image forming process. Although the multicolor electrophotographic copying apparatus having the above-mentioned structure operates extremely well, research experiments conducted by the present inventors have shown that during the transfer process, the transfer material carrying sheet 5 of the transfer drum 5 is particularly affected.
It has been found that when a polyvinylidene fluoride resin film or the like is used as the transfer material P and transfer paper is used as the transfer material P, a problem occurs particularly when the humidity is high. This point will be explained next. As can be understood by referring to FIG. 7, the static eliminating means for neutralizing the transfer material P on which the toner image has been transferred is an inner static neutralizing corona charger 5d, which is usually an AC charger capable of applying a DC bias. , an outer charge eliminating corona charger 5e consisting of an AC charger, and the inner charger 5d and the outer charger 5e are configured as shown in FIG. During the pre-rotation before the image forming process starts (transfer drum rotation speed 2, 3),
and from the start of the image forming process for the last color separated image to the time when the image forming process is completed, the transfer material is separated from the transfer drum, and the entire image forming process is completed (transfer drum rotation a9, 10 ) is activated only in FIG. 7 is a partially enlarged detailed view showing the relationship between the transfer material P, the transfer means, and the static elimination means. Transfer drum 5L
A toner image of one color is transferred to the transfer material P,
The toner image is held on the transfer material P, and the transfer material P continues to be wound around the transfer drum 5 without being separated yet.
This shows the state of charge at the trailing end Pa of the transfer material P when it is being rotated together with the transfer drum 5 to transfer a toner image corresponding to the next color image. As described above in connection with FIG. 9, at the stage shown in FIG. 7 (for example, when the transfer drum rotation speed is 3), the operation of the inner charger 5d and the outer charger 5e is stopped, and the transfer means, that is, the transfer The charger 5b is still activated (photosensitive drum rotation speed is 5). The polarity of the transfer voltage supplied to the transfer charger 5b is determined, for example, when a latent image is formed with a negative charge and the toner of each developer is charged with a negative charge to reversely develop the latent image. is set to positive. According to research experiments conducted by the present inventors, when a polyvinylidene fluoride resin film is used as the transfer material carrying sheet 501 of the transfer drum 5 and a transfer paper is used as the transfer material P, the volume of the polyvinylidene fluoride resin film is resistance is 1
0Ω is also Cm, and the volume resistance of the transfer paper is 109 (at high humidity) to 10B (at low humidity) Ω・Cm, so the positive charge from the transfer charger 5b increases the transfer material carrying sheet}5
It has been found that the positive charges are injected into the transfer material P through 01 and accumulated on the surface bond of the terminal end Pa of the transfer material P. In addition, the inventors have discovered that the positive charge accumulated on the surface area of the transfer material trailing edge Pa generates a high electric field between the surface of the photosensitive drum l, and as shown in FIG. When the material end Pa separates from the photosensitive drum 1, a peeling discharge occurs, and the negative charges in the air are attracted by the positive charges on the transfer material P and move onto the transfer material P, but the positive charges in the air It was discovered that the photosensitive drum 1 moves onto the negatively charged photosensitive drum 1, causing damage to the photosensitive drum 1, that is, a memory effect. The memory effect causes the amount of primary charge on the photosensitive drum 1 by the primary charger 2 to decrease in a striped manner along the axial width direction of the photosensitive drum l, making uniform charging of the photosensitive drum l impossible. The present applicant has proposed a method of preventing such memory effects and achieving uniform charging (Japanese Patent Application No. 1983-1999).
No. 171654). According to the above proposal, the charge eliminating means is operated every time a toner image of each color is transferred onto the transfer material P, and the charge eliminating means is operated to eliminate charge from the end portion Pa of the transfer material to which the toner image has been transferred. The operation is started when the transfer charger 5b of the transfer means is located in the transfer region where the transfer charger 5b is disposed, or is located near the upstream side of the transfer region. According to this method, it is possible to eliminate the memory effect (positions of photosensitive drum rotation speed 7, 11, 15, l9 in FIG. 8) that occurs at the rear end Pa of the transfer material during toner image transfer. However, the memory effect (photosensitive drum rotation shown in FIG. number 9
, 13, l7. Although we are aware that there is a problem in that the next image formation process starts immediately after the position of
This problem could not be resolved using the method proposed above. In addition, in order to solve the above problem, the transfer material P is removed from the electrostatic latent image on the photosensitive drum 1 between the end of image formation and transfer operation of a certain color and the start of image formation of the next color. It has also been attempted not to operate the transfer charger 5b while the transfer material P is in contact with the forming area, but although this can reduce the memory effect, some of the toner images already held on the transfer material P There was a problem in that the image was transferred in the opposite direction to the photosensitive drum l, resulting in image defects such as image omission. Therefore, an object of the present invention is to prevent peel-off discharge caused by accumulation of charge at the end of a transfer material, to enable uniform charging on an image carrier, and to obtain a high-quality image without image omission. The objective is to provide an image forming device that can perform the following functions. Another object of the present invention is to provide a multicolor image forming apparatus that can obtain high quality multicolor images without color shift or image omission. ? The above objects are achieved by an image forming apparatus according to the present invention. To summarize, the present invention provides an image forming apparatus that forms an image by bringing a transfer material into contact with an image carrier carrying a toner image and transferring the toner image on the image carrier to the transfer material, wherein the transfer material is The toner image is carried by the transfer material carrying means and conveyed to the image carrier, and at a contact position where the image carrier and the transfer material abut, the toner image is transferred from the transfer material carrying means side. A transfer means for transferring the image onto a transfer material is disposed, and a static eliminator is disposed downstream of and adjacent to the transfer means, and the static eliminator is configured to prevent the transfer material from becoming static on the image carrier. This image forming apparatus is characterized in that it operates each time it comes into contact with a latent image non-forming area to remove static electricity from the terminal end of the transfer material. Support (1) Next, the image forming apparatus according to the present invention will be explained in more detail with reference to the drawings. The present invention can be preferably carried out in a multicolor electrophotographic copying machine having a rotary developing device as shown in FIG. Therefore, in this embodiment, the image forming apparatus is implemented as a multicolor electrophotographic copying apparatus as shown in FIG. The structure and operation are basically as described above, but the diameter of the photosensitive drum 1 is, for example, 80 mm, and the diameter of the transfer drum 5b is 160 mm (twice the diameter of the photosensitive drum). Further, the photosensitive drum 1 is rotated at 160 mm/sec in the direction of the arrow, and the surface of the photosensitive drum 1 is charged to -300 to -900V by the primary charger 2. Each developing device of the rotary developing device N4 has toner of each color having a negative charge, and visualizes the latent image formed on the photosensitive drum l by reversal development. As understood by referring to FIG. 1, the visible image, ie, the toner image, on the photosensitive drum L is transferred to the transfer material P carried by the transfer device 5 and conveyed. In this embodiment, the transfer device 5 has the same structure as the transfer device 5 shown in FIGS. 5 and 6 described above, and is a rotatably supported transfer drum. A cylinder 5a with a transfer material carrying sheet 50l stretched over the surface opening area.
, a transfer charger 5b constituting a transfer means disposed within the cylinder 5a, and a transfer material gripper 5c for gripping the transfer material P fed from a paper feeding device (not shown). Further, on the inside and outside of the transfer drum 5, an inner charger 5d and an outer charger 5e, which constitute charge eliminating means, are arranged. The transfer material carrying sheet 5ol has a thickness of, for example, 100 g.
A polyvinylidene fluoride resin film with a diameter of 175 gm and a volume resistivity of 10 Ω●am is used. As will be better understood with reference to FIG.
A voltage of kV is applied, and the transfer current is +100 μ8 to +5
It is considered to be 00 final A. As shown in FIG. 2 showing the operation sequence of the image forming apparatus, the transfer charger 5b performs the image forming and transfer operations of the image forming apparatus in the same way as in the conventional image forming apparatus, that is, the transfer material P is connected to the photosensitive drum. While the toner image formed on the outer peripheral surface of the transfer drum is in contact with the toner image formed on the outer peripheral surface of the transfer drum (transfer drum rotation speeds 2, 4, 6, and 8 positions), and after the above image formation and transfer operation are completed, the next color While the transfer material P is in contact with the electrostatic latent image non-forming area on the outer peripheral surface of the photosensitive drum L until image formation is started (transfer drum rotation speed 3
, 5, 7). Inner charger 5d
As shown in FIG. 2 showing the operation sequence of the image forming apparatus, the outer charger 5e is rotated during pre-rotation before the image forming process of the image forming apparatus is started, as in the conventional image forming apparatus. (transfer drum rotation speed 2, 3), and from the start of the image forming process operation of the last color separated image, the image forming process is completed, and the transfer material P is transferred to the transfer drum 5.
The transfer drum is separated from the transfer drum and operated until the entire image forming process is completed (transfer drum rotation speed 9, lO position). Further, according to the present invention, when the transfer material P comes into contact with the electrostatic latent image non-forming area on the outer peripheral surface of the photosensitive drum l, the terminal end Pa of the transfer material P is in the transfer area where the transfer means is arranged (
It! When the optical drum is located at a rotation speed of 9, 13, 17), the inner charger 5d of the static eliminating means is further activated;
In addition to this, the DC component (-4.OkV ~-5.OkV, -1
By applying a voltage of 03LA N-60gA), the terminal end Pa of the transfer material P on which the toner image is held is neutralized. In the image forming apparatus of this embodiment, which forms a multicolor image using a four-color image forming process, after the image formation of a yellow image, magenta image, and cyan image and the transfer to the transfer material P are completed, the next color image is formed. When the trailing edge Pa of the transfer material P comes into contact with the electrostatic latent image non-forming area of the photosensitive drum 1 (photosensitive Drum rotation speed 9.
13. Electricity is removed from the terminal end Pa of the transfer material P on which the toner image is held at position 17). According to the present invention, before the terminal end Pa of the transfer material P on which the toner image is held is separated from the photosensitive drum l, the terminal end P of the transfer material P
At the location a, a negative charge is placed on the transfer material carrying sheet 50l by the inner charger 5d. Also, at this time, some of the charge is injected into the transfer material P. The charge transferred from the transfer charger 5b to the transfer material carrying sheet 501 and the negative charge injected into the transfer material P through this charge absorb the positive charge accumulated in the surface area of the transfer material end Pa. suction,
The charges injected into the transfer material P combine with the above-mentioned positive charges, causing most of the positive charges to disappear. Therefore, according to the present invention, the positive charge that was conventionally accumulated in the surface area of the terminal end Pa of the transfer material P does not exist at the terminal end Pa.
As a result, the surface area of the end portion Pa of the transfer material and the photosensitive drum l
Therefore, as illustrated in FIG. This prevents positive charges from moving onto the negatively charged photosensitive drum l and causing damage to the photosensitive drum l, that is, a memory effect. FIG. 3 is a diagram showing another operation sequence of the transfer means and the static elimination means with respect to the rotational speed of the photosensitive drum and transfer drum in the present invention. This operation sequence differs from the operation sequence shown in FIG. 2 in that the inner static neutralization charger 5d is further activated at photosensitive drum rotational speeds of 7, 8 and 11.12, and at l5 and l6. The points are the same.
Inner static elimination charger 5d according to the sequence shown in Figure 3
This operation also prevents the presence of positive charges on the surface area of the trailing edge Pa of the transfer material P, thus causing a memory effect on the photosensitive drum 1 when the trailing edge Pa of the transfer material moves away from the photosensitive drum l. This can be prevented. In the above embodiment, static electricity at the end portion Pa of the transfer material was removed by applying only a DC component to the inner static electricity removal charger 5d, but the present invention is not limited to this. ) Only the AC component is applied to the inner static neutralization charger 5d. (2) Direct current and alternating current components are simultaneously applied to the inner charger 5d for neutralization. (3) The outer neutralization charger 5e is, for example, an AC charger capable of applying a DC bias, as shown in FIG. 4, and only a DC component of opposite polarity to that of the transfer charger 5b is applied. (4) Using the outer static elimination charger 5e having the configuration shown in FIG. 4, apply a DC component and an AC component of opposite polarity to the transfer charger 5b to the outside static elimination charger 5e. (5) Using the static eliminating means configured as shown in Figure 1 or Figure 4,
Both the inner static elimination charger 5d and the outer static elimination charger 5e are activated. The following methods can be adopted, and these methods can also suitably eliminate static electricity at the end portion Pa of the transfer material. As explained above, the image forming apparatus according to the present invention prevents peeling discharge caused by accumulation of charge at the end of the transfer material, and enables uniform charging on the image bearing member. , it is possible to obtain high-quality images without image omissions, and when the present invention is applied to a multicolor image forming apparatus, it is possible to obtain high-quality multicolor images without color deviations or image omissions. It has the following characteristics.

[Brief explanation of the drawing]

FIG. 1 is a partially enlarged detailed view showing the relationship between a transfer material, a transfer means, and a static elimination means in an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a diagram showing the operation sequence of the transfer means and the static elimination means with respect to the rotational speed of the photosensitive drum and transfer drum in the image forming apparatus of FIG. 1. FIG. 3 is a diagram showing another operation sequence of the transfer means and the static elimination means with respect to the rotational speed of the photosensitive drum and transfer drum in the image forming apparatus according to the present invention similar to FIG. 1. FIG. 4 is a partially enlarged detailed view showing the relationship between the transfer material, the transfer means, and the static eliminator when the static eliminator in the image forming apparatus according to the present invention is in another embodiment, similar to that shown in FIG. 1. FIG. 5 is a schematic diagram showing an example of a multicolor electrophotographic copying apparatus to which the present invention can be applied. FIG. 6 is a perspective view showing an example of a transfer device used in the image forming apparatus shown in FIG. 7 and 8 are partially enlarged detailed views showing the relationship between a transfer material, a transfer means, and a static elimination means in a conventional image forming apparatus. FIG. 9 is a diagram showing the operation sequence of the transfer means and the static elimination means with respect to the rotational speed of the photosensitive drum and the transfer drum in a conventional image forming apparatus. Figure 1: Image carrier: Transfer drum b: Transfer charger d, 5e: Charger for static elimination Ol: Transfer material carrier sheet Figure 4 Figure 5 bC Figure 6 Figure 7 Figure 8

Claims (1)

[Scope of Claims] 1) In an image forming apparatus that forms an image by bringing a transfer material into contact with an image carrier carrying a toner image and transferring the toner image on the image carrier to the transfer material, the transfer material is carried by a transfer material carrying means and conveyed to the image carrier, and at a contact position where the image carrier and the transfer material contact, a toner image is applied from the transfer material carrying means side. A transfer means for transferring the image onto the transfer material is disposed, and a charge eliminating means is disposed downstream of the transfer means and adjacent to the transfer means, and the charge eliminating means is arranged so that the transfer material is transferred to the image carrier. An image forming apparatus that operates to eliminate static electricity from a trailing end of the transfer material each time it comes into contact with an area where no electrostatic latent image is formed. 2) The image forming apparatus according to claim 1, wherein the charge eliminating means is disposed on the same side and/or on the opposite side of the transfer material carrying means as the transfer means. 3) The image forming apparatus according to claim 1, wherein the transfer means is a transfer corona charger, and the static elimination means is a static elimination corona charger.