JP2007140121A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of preventing recording material from being wound round an intermediate transfer body side by destaticizing the recording material after secondary transfer with simple constitution. <P>SOLUTION: The image forming apparatus has: a secondary transfer means for secondarily transferring a toner image to the recording material from an intermediate transfer body by applying secondary transfer bias between a secondary transfer roller and the intermediate transfer body by a constant-current control means; a destaticizing member for eliminating the charge of the recording material to which the toner image has been transferred by the secondary transfer means; and a destaticizing voltage applying means for applying the destaticizing voltage to the destaticizing member. The destaticizing bias is controlled to be high only in a monochrome mode according as it is the monochrome mode or a color mode. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a printer, a facsimile, or a copying machine that forms an image on a recording material such as paper using electrophotographic technology, and in particular, applies a transfer bias from an intermediate transfer member to the recording material by constant current control. The present invention relates to an image forming apparatus including a secondary transfer unit that transfers a toner image.

  Japanese Patent Application Laid-Open No. 2004-241947 discloses an image forming apparatus that forms an image on a recording material such as paper using electrophotographic technology, and transfers a toner image on an intermediate transfer member such as an intermediate transfer belt or an intermediate transfer drum to paper or the like. In order to perform secondary transfer onto the recording material, secondary transfer means for applying a transfer bias to the secondary transfer roller by constant current control is disclosed. In this prior art, a secondary transfer roller that is separated from and brought into contact with the intermediate transfer belt by a separation and contact mechanism is provided at a position facing the driving roller (also serving as a secondary transfer backup roller) of the intermediate transfer belt. A transfer bias is applied to the secondary transfer roller from the constant current control means, and the four color toner images on the intermediate transfer belt are secondarily transferred to the recording material.

The recording material onto which the unfixed toner image has been transferred in the secondary transfer section is charged. If this charging is left undisturbed, problems such as hindering subsequent smooth conveyance of the recording material occur. It is necessary to remove static electricity. For this reason, there is provided a static elimination member made of a nonwoven fabric obtained by processing conductive fibers into a sheet in the vicinity of the downstream side of the secondary transfer roller. The neutralizing member is attached to a conductive plate that applies a neutralizing voltage to the neutralizing member, and neutralizes the recording material after the secondary transfer.
JP 2004-241947 A

  The recording material after the secondary transfer is subjected to an attracting force by the neutralizing plate and a winding force due to a winding electric field generated between the intermediate transfer member and the recording material. The winding electric field is affected by non-uniform charging of the recording material due to a change in resistance due to the environment of the secondary transfer roller by constant current control or a change in transfer bias due to the type of recording material. If the neutralization of the recording material by the neutralization member is insufficient, the wrapping force between the recording material and the intermediate transfer member becomes larger than the attraction force of the neutralization plate, and the recording material after the secondary transfer is wound around the intermediate transfer member. The sticking phenomenon occurs. On the other hand, if the attracting force by the charge eliminating plate is too strong, the recording material comes into contact with the guide and causes image defects. If the charge of the recording material is excessively removed, the force that attracts the toner to the recording material is weakened and the image is easily blurred. In order to prevent the recording material from being wrapped around the intermediate transfer member and to obtain a high-quality image, the attractive force by the neutralization plate and the winding force by the winding electric field generated between the intermediate transfer member and the recording material are It is necessary to balance.

  The cause of the winding of the recording material around the intermediate transfer member is frictional charging of the recording material and the guide member. In general, in an image forming apparatus, a recording material is conveyed while being in contact with various members such as a guide member. At this time, the recording material and the guide member rub against each other, whereby the guide member and the recording material are charged by frictional charging. I will take on it. Due to the frictional charging of the recording material and guide member, the recording material after secondary transfer by constant current control becomes overcharged, the charge removal by the charge removal member becomes insufficient, and the winding force due to the winding electric field becomes larger than the attracting force of the conductive plate. Then, the recording material is wound around the intermediate transfer member. It was found that the amount of triboelectric charge differs between when the output image is in color mode (4 cycles) and when it is in monochrome mode.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus that solves the above-described problems and eliminates non-uniform charging of a recording material after secondary transfer with a simple configuration, thereby preventing the recording material from being wound around an intermediate transfer member.

  In order to solve the above-described problems, the first aspect of the present invention applies a secondary transfer bias between the secondary transfer roller and the intermediate transfer member by the constant current control means in the image forming apparatus, and the recording material from the intermediate transfer member Secondary transfer means for secondary transfer of the toner image to the sheet, a charge removal member for removing the charge of the recording material onto which the toner image has been transferred by the secondary transfer means, and a charge removal voltage application means for applying a charge removal voltage to the charge removal member In the image forming apparatus having the above, the neutralization bias is controlled to be increased only during printing in the monochrome mode according to the monochrome mode or the color mode.

  The second aspect of the invention is characterized in that, in the image forming apparatus of the first aspect of the invention, the neutralization bias is controlled to increase when the number of printed sheets in the monochrome mode exceeds a predetermined number.

  According to a third aspect of the present invention, in the image forming apparatus according to the first aspect of the present invention, the neutralization bias is gradually increased in accordance with the number of printed sheets in the monochrome mode.

A secondary transfer unit that applies a secondary transfer bias between the secondary transfer roller and the intermediate transfer member by a constant current control unit to secondary-transfer the toner image from the intermediate transfer member to the recording material; and the secondary transfer unit. When printing in monochrome mode according to monochrome mode or color mode in an image forming apparatus having a charge removal member that removes the charge of the recording material onto which the toner image has been transferred and a discharge voltage application unit that applies a discharge voltage to the discharge member By controlling the discharge bias only to a high level, it is possible to prevent the recording material from winding around the intermediate transfer body due to the frictional charge of the recording material and guide member, etc. Since the bias is increased, power consumption can be reduced, and the life of the static elimination member can be improved.
By controlling the neutralization bias to be higher when the number of prints in the monochrome mode exceeds the specified number, the triboelectric charge increases when the specified number of continuous prints is exceeded. Only by increasing the charge removal bias, power consumption can be reduced and the life of the charge removal member can be improved.
With the configuration in which the neutralization bias is gradually increased in accordance with the number of prints in the monochrome mode, the frictional charge increases in proportion to the increase in the number of continuous prints, so the neutralization bias is increased accordingly. It is possible to efficiently prevent the recording material from being wound around the intermediate transfer member.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing main components constituting an image forming apparatus including a secondary transfer device according to the present invention.

  As shown in FIG. 1, the image forming apparatus 1 according to the present embodiment includes a charging unit 9 and a rotary unit along a rotation direction 7 of a photosensitive drum 5 as an example of an image carrier for carrying a latent image. The image forming apparatus includes a developing unit 11, an exposure unit 15, a primary transfer unit 19, and an intermediate transfer belt 21, and further includes a secondary transfer unit 23, a fixing unit 27, and a paper discharge tray unit 29.

  The photosensitive drum 5 has a cylindrical conductive substrate and a photosensitive layer formed on the outer peripheral surface thereof, and is rotatable around a central axis. In the present embodiment, the photosensitive drum 5 is indicated by an arrow in FIG. Rotate clockwise as shown.

  The charging unit 9 is a device for charging the photosensitive drum 5, and the exposure unit 15 is a device for forming a latent image on the charged photosensitive drum 5 by irradiating a laser. The exposure unit 15 includes a semiconductor laser, a polygon mirror, an F-θ lens, and the like, and charges the modulated laser based on an image signal input from a host computer (not shown) such as a personal computer or a word processor. Irradiation is performed on the photosensitive drum 5 thus formed.

  The rotary developing unit 11 converts a latent image formed on the photosensitive drum 5 into black (K) toner contained in the black developing device 12K, magenta (M) toner contained in the magenta developing device 12M, and cyan developing device. This is an apparatus for developing using cyan (C) toner contained in 12C and yellow (Y) toner contained in yellow developing device 12Y.

  In the present embodiment, the rotary developing unit 11 can move the positions of the four developing devices 12K, 12M, 12C, and 12Y by rotating. That is, the rotary developing unit 11 is rotatable with the four developing devices 12K, 12M, 12C, and 12Y about the rotation shaft 31 while maintaining their relative positions.

  Each time image formation for one page is completed, the photosensitive drum 5 is selectively opposed to the photosensitive drum 5, and the toner T accommodated in each of the developing devices 12K, 12M, 12C, and 12Y is placed on the photosensitive drum 5. The formed latent images are sequentially developed. Each of the four developing devices 12K, 12M, 12C, and 12Y described above can be attached to and detached from the holding portion of the rotary developing unit 11.

  The primary transfer unit 19 is a device for transferring a single color toner image formed on the photosensitive drum 5 to the intermediate transfer belt 21. When four color toners are sequentially transferred in a superimposed manner, the primary transfer unit 19 is full-colored onto the intermediate transfer belt 23. A toner image is formed. The intermediate transfer belt 21 is an endless belt and is driven to rotate at substantially the same peripheral speed as that of the photosensitive drum 5. In the present embodiment, the intermediate transfer belt 21 is used as the intermediate transfer member, but an intermediate transfer drum may be used. The secondary transfer unit 23 is a device for transferring a single color toner image or a full color toner image formed on the intermediate transfer belt 21 to a recording material such as paper, film, or cloth.

  The fixing unit 27 is a device for fusing a single color toner image or a full color toner image transferred onto a recording material onto a recording material such as paper to form a permanent image.

  FIG. 2 is an enlarged view of a main part of the secondary transfer unit 23. The intermediate transfer belt 21 is stretched by a driving roller 50 that also serves as a secondary transfer backup roller, a driven roller (not shown), a tension roller, and the like, and is conveyed by the driving roller 50 in a predetermined direction. The intermediate transfer belt 21 has a toner image transferred from the photosensitive member at the nip portion with the photosensitive member 5 (primary transfer), and after the four color toner images are overlaid, the intermediate transfer belt 21 is illustrated at the nip portion with the secondary transfer roller 51. Batch transfer (secondary transfer) to the recording material that is not. The secondary transfer roller 51 is brought into and out of contact with the intermediate transfer belt 21 by a separating and contacting means (not shown). When the secondary transfer roller 51 comes into contact with the intermediate transfer belt 21, the secondary transfer roller 51 is pressed against the intermediate transfer belt 21 by biasing means (not shown) such as springs provided at both ends of the secondary transfer roller 51. The recording material, which rotates following the intermediate transfer belt 21 around the shaft and is introduced at a predetermined angle through the transfer guide 52 at the time of contact, is sandwiched between the intermediate transfer belt 21 and the nip portion. At this time, as will be described in detail later, transfer is performed by applying a bias voltage from a power source (not shown) under constant current control. The recording material after the transfer is conveyed by a transfer guide 52 at a predetermined angle. The transfer guide 52 is configured to be rotatable about a guide support shaft 53.

  The transfer guide 52 is provided with a charge eliminating member 54 in the vicinity of the secondary transfer roller 51. The neutralizing member 54 is composed of a conductive non-woven fabric (static neutralizing cloth) in which countless conductive fibers are processed into a sheet shape, and the upper surface of the neutralizing member 54 composed of the neutralizing cloth passes through the secondary transfer portion. The recording material is discharged by discharging between the charge eliminating member 54 and the recording material. The neutralization member 54 is attached to the conductive neutralization plate 55. A static elimination voltage from a static elimination voltage application means (not shown) is applied to the static elimination member 54 via a static elimination plate 55.

  In such a secondary transfer means, as shown in FIG. 3, the recording material S after the secondary transfer includes an attractive force indicated by an arrow A by the neutralizing plate 55, the intermediate transfer belt 21, the recording material S, and the like. The winding force indicated by the arrow B due to the winding electric field generated during the period acts. The wound electric field is affected by a change in resistance due to the environmental change of the secondary transfer roller 51 by constant current control, the type of the recording material S, and the like. If the neutralization of the recording material S by the neutralizing member 54 is insufficient, the wrapping force between the recording material S and the intermediate transfer belt 21 becomes larger than the attracting force of the neutralizing plate 55, and the recording material S after the secondary transfer. Occurs around the intermediate transfer belt 21. If the attractive force by the charge removal plate 55 is too strong, the recording material S comes into contact with the guide and causes image defects. Further, if the charge of the recording material S is excessively neutralized, the force for attracting the toner to the recording material S becomes weak and the image is likely to be blurred. In order to prevent the recording material S from being wrapped around the intermediate transfer belt 21 and obtain a high-quality image, as shown in FIG. 4, the attracting force indicated by the arrow A by the neutralizing plate 55, the intermediate transfer belt 21, and the recording material. It is necessary to balance the winding force of the arrow B due to the winding electric field generated between the material S.

  It has been found that frictional charging during conveyance of the recording material has an influence as a cause of the winding of the recording material around the intermediate transfer belt 21. In general, in an image forming apparatus using electrophotographic technology, a recording material is conveyed while being in contact with various members such as a guide roller. By rubbing at this time, the member and the recording material are triboelectrically charged and charge is charged. Come on. At this time, if the output image is in the color mode (4 cycles), the recording material waits in front of the secondary transfer section every time one page is printed even if continuous printing is performed, so the frictional charge of the recording material and the guide member is increased. Hard to do. On the other hand, when the output image is in the monochrome mode, since the recording material does not stand by during continuous printing, the frictional charge amount of the recording material and the guide member increases.

  Further, it has been found that the charge amount of the recording material increases when the number of printed sheets exceeds a predetermined number when printing in the monochrome mode. FIG. 5 shows a flowchart of the control of the neutralization bias for preventing such a triboelectric charge amount of the recording material. First, in the first stage, it is determined whether or not the output image is in a color mode. If the determination at the first stage is YES, the static elimination bias Vj is controlled to Normal (−1000 V). If the determination at the first stage is NO, it is sent to the second stage. In the second stage, it is determined whether or not the number of continuous prints is X pages or more. In this embodiment, the X page is set to 10 pages. If the determination at the second stage is YES, the control is performed so that the charge elimination bias Vj = Vj (Normal) + [Vj (Normal) × {(Vj (Normal) × 0.01 × number of printed sheets)}]. However, the upper limit of Vj = Vj (Normal) × 2 ← the printing number of 200 sheets or more is controlled to a constant value. If the determination is NO in the second stage, the static elimination bias is controlled to Vj = Vj (Normal) × 1.1.

  As shown in the flowchart of the neutralization bias, it is determined whether the output image is in the color mode or the monochrome mode, and only in the monochrome mode, the neutralization bias is controlled to increase according to the number of continuous prints. When the number of printed sheets exceeds the predetermined number X, the triboelectric charge amount of the recording material increases in proportion, so that the neutralizing bias is controlled to increase in proportion to the number of printed sheets. By controlling the static elimination bias, it was possible to prevent the recording material from being wound around the intermediate transfer belt.

It is a figure which shows embodiment of this invention. It is a figure which shows embodiment of this invention. It is a figure which shows embodiment of this invention. It is a figure which shows embodiment of this invention. It is a figure which shows embodiment of this invention.

Explanation of symbols

1: image forming device, 5: photosensitive drum, 9: charging unit, 11: rotary developing device, 12K, 12M, 12C, 12Y: black, magenta, cyan, yellow developing device,
15: exposure unit, 19: primary transfer unit, 21: intermediate transfer belt, 23: secondary transfer unit, 27: fixing unit, 29: discharge tray section, 50: drive roller, 51: secondary transfer roller, 52: Transfer guide, 53: Guide spindle, 54: Static elimination member, 55: Static elimination plate

Claims (3)

A secondary transfer unit that applies a secondary transfer bias between the secondary transfer roller and the intermediate transfer member by a constant current control unit to secondary-transfer the toner image from the intermediate transfer member to the recording material; and the secondary transfer unit. When printing in monochrome mode according to monochrome mode or color mode in an image forming apparatus having a charge removal member that removes the charge of the recording material onto which the toner image has been transferred and a discharge voltage application unit that applies a discharge voltage to the discharge member An image forming apparatus, wherein only the static elimination bias is controlled to be high. 2. The image forming apparatus according to claim 1, wherein the neutralization bias is controlled to be increased when the number of printed sheets in the monochrome mode exceeds a predetermined number. 2. The image forming apparatus according to claim 1, wherein the neutralization bias is gradually increased in accordance with the number of prints in the monochrome mode.

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