JP2008241862A - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of forming a high-quality image by destaticizing recording material that is low-stiffness thin paper to which an image has been transferred with simple constitution and preventing the recording material from being wound round a transfer body side. <P>SOLUTION: The image forming apparatus is equipped with: a transfer means which applies transfer bias between a transfer roller and a transfer body so as to transfer a toner image from the transfer body to the recording material; a destaticizing member which applies destaticizing bias having a reverse polarity to the transfer bias to the recording material to which the toner image has been transferred by the transfer means; and a destaticizing bias control means which controls output from the destaticizing member so that destaticizing bias higher than ordinary one may be applied only to the leading edge area of the recording material and ordinary destaticizing bias may be applied to areas other than the area when the recording material is the thin paper. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a printer, a facsimile machine, and a copying machine that forms an image on a recording material such as paper by using electrophotographic technology, and more particularly to transfer a toner image by applying a transfer bias from a transfer medium to the recording material. The present invention relates to an image forming apparatus and an image forming method including a transfer unit.

  The recording material onto which the unfixed toner image has been transferred in the transfer section is charged. If this charging is left undisturbed, problems such as hindering subsequent smooth conveyance of the recording material occur. There is a need. For this reason, a neutralizing member such as a neutralizing cloth, a neutralizing needle, and a corona discharger is provided close to the downstream side of the transfer roller, and a neutralizing bias having a polarity opposite to the transfer bias applied at the transfer portion is applied to the recording material. Has been implemented.

Japanese Patent Application Laid-Open No. 2006-235097 provides a static elimination unit for eliminating the charge of a recording material, and provides a static elimination bias having a predetermined first absolute value until the recording material reaches a passing position from a position reaching the static elimination unit. A neutralizing bias applying unit for applying the neutralizing bias, and the neutralizing bias applying unit applies a neutralizing bias having a second absolute value smaller than the first absolute value at least one of before and after the neutralization starts. An image forming apparatus is disclosed. Japanese Patent Application Laid-Open No. 2002-72715 provides a charge eliminating member that neutralizes a recording material in a transfer portion, and changes a control method of a transfer bias applied to the recording material when a charge eliminating bias is applied to the charge eliminating member. An image forming apparatus configured as described above is disclosed.
JP 2006-235097 A JP 2002-72715 A

  However, in the transfer means of the conventional image forming apparatus, consideration is insufficient when transferring thin paper (referring to a basis weight of 64 g / m2 or less). In general, when the shape of the transfer roller is a straight shape, the nip width at the end in the axial direction is larger than the nip width at the center due to the deflection of the transfer roller, and current easily flows at the end at the transfer portion. If the recording material at the end is charged and the charge removal member has a uniform charge removal capability in the axial direction of the transfer part, the charge at the end of the recording material is insufficient, and the recording material is wound around the transfer body by electrostatic force. Directional force is generated. In addition, since the end of the recording material passing through the transfer portion in the axial direction is a free end, the recording material is weak at the end, and the end of the recording material is easily wound around the transfer member. In particular, when the recording material is thin paper, the risk is great, and when the leading edge of the paper is wound, it sticks to the transfer body as it is and jam occurs. As in the prior art, if all the neutralization capability in the axial direction of the recording material after passing through the transfer portion is increased to prevent the recording material from being wound around the transfer body, the charging of the recording material becomes too small and the toner is attracted to the recording material. There arises a problem that power is weakened and an image is blurred, and that power consumption is increased.

  SUMMARY OF THE INVENTION The present invention provides an image forming apparatus that solves the above-described problems and eliminates the wrapping of a thin paper recording material after transfer with a simple structure, prevents the recording material from being wound around, and forms a high-quality image. For the purpose.

  In order to solve the above-described problems, the first invention provides a transfer unit that applies a transfer bias between a transfer roller and a transfer member to transfer a toner image from the transfer member to a recording material. A neutralizing member that applies a neutralizing bias having a polarity opposite to the transfer bias to the recording material onto which the image has been transferred, and when the recording material is thin paper, a higher neutralizing bias is applied only to the tip region of the recording material, In a region other than the above, a neutralization bias control means for controlling the output of the neutralization member so as to apply a normal neutralization bias is provided. By applying a higher neutralization bias than usual to only the leading edge of the recording material, it is possible to reduce jamming of thin paper while minimizing deterioration of the neutralization member (paper dust adhesion).

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect of the present invention, the charge removal capability at both ends in the transfer portion axial direction of the charge removal member is made larger than the charge removal capability at the central portion. Efficiently removes charge from non-uniform recording material in the axial direction due to deflection of the transfer roller and non-uniformity in the axial direction of the transfer roller in the axial direction. Winding can be prevented and jamming of thin paper can be reduced. Moreover, since the static elimination capability of only the part which is easy to wind is increased, the lifetime of the static elimination member can be improved.

  According to a third aspect of the present invention, in the image forming apparatus according to the second aspect of the invention, the distance between the charge eliminating member and the recording material is set such that the distance from both ends in the transfer portion axial direction is shorter than the distance from the central portion. It is characterized in that the charge eliminating ability at both ends of the is larger than the charge eliminating ability at the central part.

  According to a fourth aspect of the present invention, in the image forming apparatus according to the second aspect of the present invention, the magnitude of the resistance at both ends in the transfer portion axial direction of the charge eliminating member is made smaller than the magnitude of the resistance at the central portion, and both ends in the transfer portion axial direction. It is characterized in that the charge removal capability of the battery is larger than the charge removal capability at the center.

  According to a fifth aspect of the present invention, in the image forming apparatus according to the second aspect of the present invention, the neutralizing member is a neutralizing cloth, and the pasting area of the neutralizing cloth is the pasting area of both ends in the transfer portion axial direction. The neutralization capability at both ends in the transfer portion axial direction is made larger than the neutralization capability at the central portion.

  According to a sixth aspect of the present invention, in the image forming apparatus according to the second aspect of the invention, the static elimination bias control means divides the static elimination member into three in the transfer portion axial direction, and the static elimination bias higher than usual only in the static elimination members corresponding to both ends. It controls to apply.

  The seventh invention is characterized in that the neutralizing bias control means implements the control according to any one of the first to sixth inventions only on the second surface in the case of duplex printing.

  According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the first to seventh aspects of the present invention, the image forming apparatus includes a sensor for detecting temperature and humidity, and the neutralization bias control unit applies the neutralization member based on information from the sensor. The charge eliminating bias is controlled.

  According to a ninth aspect of the present invention, in the image forming apparatus according to any one of the first to eighth aspects of the present invention, the control of the static elimination bias at the time of thin paper is stored in a storage unit, and a thin paper mode is set in advance.

  According to a tenth aspect of the present invention, in the image forming method, a transfer bias is applied between the transfer roller and the transfer body, the toner image is transferred from the transfer body to the recording material, and the transfer bias is applied to the recording material on which the toner image is transferred. A neutralizing bias having a polarity opposite to that of the recording material is applied, and when the recording material is thin paper, a neutralizing bias higher than usual is applied only to the front end region of the recording material.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a view showing a transfer portion of the image forming apparatus of the present invention. For convenience of explanation, an example in which an intermediate transfer belt is used as a transfer member is shown, but the present invention is not limited to this.

  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 is transferred from the photosensitive member (primary transfer) at the nip portion with the photosensitive drum 5, and after the four color toner images are overlaid, at the nip portion with the secondary transfer roller 51. Batch transfer (secondary transfer) is performed on a recording material (not shown).

  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 later in detail, a bias voltage is applied from a power source (not shown) controlled at a constant current to perform transfer. 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 removal 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) obtained by processing innumerable conductive fibers 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 removal 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 the static elimination plate 55. In the embodiment shown in the figure, an example in which a neutralizing cloth is used as the neutralizing member 54 is shown. However, as the neutralizing member 54, a corona discharger such as a neutralizing needle or a scorotron may be used.

  In such a secondary transfer means, the attracting force by the charge eliminating plate 55 and the winding force due to the winding electric field generated between the intermediate transfer belt 21 and the recording material act on the recording material after the secondary transfer. . The winding electric field is affected by a change in resistance due to the environment of the transfer roller 51 by constant current control. If the recording material is not sufficiently neutralized by the neutralizing member 54, when the recording material is thin paper with low stiffness, the wrapping force with the intermediate transfer belt 21 becomes larger than the attractive force of the neutralizing plate 55, and the secondary transfer. A phenomenon in which the subsequent recording material is wound around the intermediate transfer belt 21 occurs. If the attracting force by the charge removal plate 55 is too strong, the recording material comes into contact with the guide and causes an image defect. Further, if the charge of the recording material is excessively removed, the force for attracting the toner to the recording material S becomes weak and the image is easily blurred. In order to prevent the recording material from being wound around the intermediate transfer belt 21 and to obtain a high-quality image, the attraction force by the neutralization plate 55 and the winding force from the winding electric field generated between the intermediate transfer belt 21 and the recording material. It is necessary to balance

  However, when the recording material is thin paper with a low stiffness, winding occurs even if a neutralizing bias is applied to a normal recording material. In particular, when the recording material is thin paper, the curl at the leading end of the recording material is the main cause of the winding.

  Further, the wrapping force of the recording material around the intermediate transfer belt 21 is different for each portion of the secondary transfer portion in the axial direction. Consider the occurrence of a difference in the partial winding force of the intermediate transfer belt 21 of the recording material. One reason is that the secondary transfer roller 51 is bent. When the secondary transfer roller 51 bends, the nip width at the end in the axial direction at the secondary transfer portion becomes larger than the central portion, and current easily flows at both ends in the axial direction of the secondary transfer portion. The neutralization due to is also insufficient at both ends of the recording material, and the recording material is easily wound around the intermediate transfer belt 21. This phenomenon is also remarkable when the recording material is thin paper.

  Further, since the secondary transfer roller 51 is pressed against the intermediate transfer belt 21 by urging means such as springs provided at both ends thereof, the axial pressing force at the secondary transfer portion is large at the end portion, and at the center portion. Get smaller. As a result, the nip width becomes large at the end of the secondary transfer roller 51 in the axial direction, current flows easily, and the nip shape becomes easy to wind around the intermediate transfer belt. Winding occurs. In general, since the end portion of the secondary transfer portion of the recording material in the axial direction is a free end, the end portion is weak and easily wound around the intermediate transfer belt. This phenomenon is also remarkable when the recording material is thin paper.

  FIG. 2 is a diagram showing a timing chart of the static elimination bias for solving the problem when the recording material is thin paper as described above. As shown in FIG. 2, when the recording material is thin paper, a high static elimination bias is applied only to the leading end, and a lower static elimination bias is applied in other areas. Since a high static elimination bias is applied only to the leading edge region of the thin paper, the curling does not occur at the leading end, does not wrap around the intermediate transfer belt 21, and the thin paper is conveyed to the fixing unit without curling. Winding is unlikely to occur in a region other than the tip without applying a high static elimination bias. A high static elimination bias may be applied until the thin paper as the recording material reaches the fixing means. This is because when the leading edge of the thin paper reaches the fixing unit, the thin paper is largely stiffened due to the difference in speed between the transfer process and the fixing process, and is difficult to wind.

  FIG. 3 shows an embodiment for dealing with the difference in the winding force of the recording material around the intermediate transfer belt 21 for each axial portion of the secondary transfer portion. In this embodiment, the height of both end portions in the axial direction of the static elimination member 54 attached to the static elimination plate 55 is made higher than the central portion, and the secondary transfer is performed between the secondary transfer roller 51 and the intermediate transfer belt 21. The distance between the recording material conveyed and the neutralization member 54 is set so that the distance from both axial ends is shorter than the distance from the central portion, and the neutralization capability at both axial ends is larger than the neutralization capability at the central portion. To do. The neutralization capability at both ends in the axial direction of a thin paper recording material having a large winding force on the intermediate transfer belt 21 side is increased to prevent winding. Also in this embodiment, as shown in FIG. 2, when the recording material is thin paper, a configuration in which a high static elimination bias is applied only to the leading end and a lower static elimination bias is applied in other areas is the same. It is.

  FIG. 4 shows another embodiment corresponding to the difference in the wrapping force of the recording material around the intermediate transfer belt 21 for each axial portion of the secondary transfer portion. In this embodiment, the thickness of the resistance layer 57 at both ends in the axial direction of the transfer portion of the static elimination member 54 is made smaller than the thickness of the resistance layer 56 at the center, and the resistance at both ends is made smaller than the resistance at the center. The neutralization capability at both ends in the transfer portion axial direction is made larger than the neutralization capability at the central portion. The neutralization capability at both ends in the axial direction of a thin recording material having a large winding force on the intermediate transfer belt 21 side is increased to prevent the occurrence of winding. Also in this embodiment, as shown in FIG. 2, when the recording material is thin paper, a configuration in which a high static elimination bias is applied only to the leading end and a lower static elimination bias is applied in other areas is the same. It is.

  FIG. 5 shows another embodiment corresponding to the difference in the wrapping force of the recording material around the intermediate transfer belt 21 for each portion in the axial direction of the secondary transfer portion. In this embodiment, the pasting area at both ends in the axial direction of the neutralizing member 54 to be pasted on the static eliminating plate 55 is made larger than the pasting area at the central portion, and the static eliminating capability at the axial end is set to the neutralizing capability at the central portion. Make it bigger. The neutralization capability at the axial end of the recording material having a large winding force on the intermediate transfer belt 21 side is increased to prevent the occurrence of winding. Also in this embodiment, as shown in FIG. 2, when the recording material is thin paper, a configuration in which a high static elimination bias is applied only to the leading end and a lower static elimination bias is applied in other areas is the same. It is.

  FIG. 6 shows still another embodiment corresponding to the difference in the winding force of the recording material around the intermediate transfer belt 21 for each axial portion of the secondary transfer portion. In this embodiment, the neutralization member 54 is divided into three in the transfer portion axial direction, and a higher neutralization bias is applied only to the neutralization members 54 corresponding to both ends, so that the neutralization capability at the axial end is central. Make it larger than the static elimination capacity of the part. The neutralization capability at the axial end of the recording material having a large winding force on the intermediate transfer belt 21 side is increased to prevent the occurrence of winding. Also in this embodiment, as shown in FIG. 2, when the recording material is thin paper, a configuration in which a high static elimination bias is applied only to the leading end and a lower static elimination bias is applied in other areas is the same. It is.

  In the case of double-sided printing, since the occurrence frequency of winding is higher on the second side, the neutralization bias control described in the above-described embodiment may be performed only on the second side during double-sided printing.

  Since the amount of charge after secondary transfer of the recording material varies greatly depending on environmental conditions such as temperature and humidity, a neutralization bias is applied to the recording material based on sensor measurement data by placing a sensor for temperature and humidity in the main body of the device. It is good to decide.

  If the control of the static elimination bias when the recording material is thin paper is stored in advance in the storage means of the apparatus main body and the thin paper mode is set in the apparatus main body, the operation becomes easy and a user-friendly apparatus can be provided.

  FIG. 7 is a diagram showing the main components of the image forming apparatus of the present invention.

  As shown in FIG. 7, the image forming apparatus 1 according to the present embodiment includes a charging unit 9, a rotary unit, and the like along the 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 a 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 the 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 this embodiment, the rotary developing unit 11 will be described as an example, but a tandem developing unit may be used.

  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.

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. 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 apparatus, 5: photosensitive drum, 9: charging unit, 11: rotary developing unit, 12K, 12M, 12C, 12Y: black, magenta, cyan, yellow developing apparatus, 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 support shaft, 54: Static elimination member, 55: Static elimination plate, 56: Thick resistance layer, 57: Thin resistance layer

Claims (10)

A transfer unit that applies a transfer bias between the transfer roller and the transfer member to transfer the toner image from the transfer member to the recording material, and a charge removal bias having a polarity opposite to the transfer bias is applied to the recording material on which the toner image is transferred. When the recording material to be applied is thin and the recording material is thin paper, an output of the neutralizing member is applied so that a higher neutralization bias is applied only to the tip region of the recording material and a normal neutralization bias is applied to the other regions. An image forming apparatus comprising a neutralizing bias control means for controlling. 2. The image forming apparatus according to claim 1, wherein the charge removal capability of both ends of the charge removal member in the axial direction of the transfer portion is greater than the charge removal capability of the central portion. The distance between the neutralization member and the recording material is set so that the distance from both ends in the transfer portion axial direction is shorter than the distance from the central portion, and the neutralization capability at both ends in the transfer portion axial direction is larger than the neutralization capability in the central portion. The image forming apparatus according to claim 2. The resistance of both ends in the transfer portion axial direction of the charge removal member is made smaller than the resistance in the central portion, and the charge removal capability at both ends in the transfer portion axial direction is made larger than the charge removal capability in the center portion. The image forming apparatus described in 1. The neutralizing member is a neutralizing cloth, the pasting area of the neutralizing cloth is set so that the pasting area at both ends in the axial direction of the transfer portion is larger than the pasting area at the central portion, The image forming apparatus according to claim 2, wherein the image forming apparatus is larger than a static elimination capability of the part. 3. The neutralization bias control means controls the neutralization member to be divided into three in the transfer portion axial direction so that a neutralization bias higher than usual is applied only to the neutralization members corresponding to both ends. The image forming apparatus described. The image forming apparatus according to any one of claims 1 to 6, wherein the neutralizing bias control unit performs the control according to any one of claims 1 to 6 only for the second side when duplex printing is performed. 8. The sensor according to claim 1, further comprising a sensor for detecting temperature and humidity, wherein the static elimination bias control unit controls a static elimination bias to be applied to the static elimination member based on information of the sensor. Image forming apparatus. The image forming apparatus according to any one of claims 1 to 8, wherein the thin paper mode is set in advance by storing in the storage means the control of the static elimination bias when the paper is thin. A transfer bias is applied between the transfer roller and the transfer body, a toner image is transferred from the transfer body to the recording material, a neutralizing bias having a polarity opposite to the transfer bias is applied to the recording material on which the toner image is transferred, An image forming method, wherein when the recording material is thin paper, a higher neutralization bias is applied only to a front end region of the recording material.

Images