JP2009145390A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus, where a recording material is easily separated on a downstream side of a transfer section and sticking again after separation is reduced, even in the case of a comparatively large curved surface with little burden to an intermediate transfer belt. <P>SOLUTION: A roller inside a secondary transfer roller 56 is provided with a plurality of conductive sections 561a which can independently apply voltages of different values. While the conductive section 561a which is positioned in a secondary transfer section T2 of the roller inside the secondary transfer roller 56 is connected to grounding potential, and a separating voltage which is the reverse polarity to charging polarity of a toner image is applied to a conductive section 561a positioned downstream of the secondary transfer section T2 by a power source D5. Since the curved surface of the intermediate transfer belt 51 on the downstream side of the secondary transfer section T2 is charged so as to have the reverse polarity to the charged polarity of the recording material, curvature separating effect in the curved surface is increased and the recording material P is drawn on the downstream side of the secondary transfer section T2 so as to allow the recording material P to be hardy stuck again to the intermediate transfer belt 51. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus in which a toner image transfer portion for a recording material is arranged on a curved surface obtained by curving an intermediate transfer belt in a rotational direction, and in particular, easily separates the curvature of a recording material on a curved surface downstream of the transfer portion. Concerning the structure to make.

  A toner image transfer portion for the recording material is disposed on a curved surface obtained by curving the intermediate transfer belt in the rotation direction, and the recording material on which the toner image is transferred is separated from the intermediate transfer belt by a curved surface downstream of the transfer portion. An image forming apparatus has been put into practical use.

  In an image forming device that separates the curvature from the intermediate transfer belt on the curved surface downstream of the transfer unit, if a thin and low-rigidity recording material or a recording material that is easily charged is used, the recording material sticks to the curved surface downstream of the transfer unit. The possibility of being carried away increases (see FIGS. 19 and 21).

  In view of this, a configuration for separating the curvature of the recording material from the intermediate transfer belt has been proposed (see FIGS. 22 and 23).

  In Patent Document 1, a plurality of color toner images formed on a common photosensitive drum using a rotary developing device are sequentially transferred and superimposed on an intermediate transfer belt, and then a plurality of color toners are transferred from the intermediate transfer belt to a recording material. An image forming apparatus that batch-transfers images is shown. Here, the diameter of the inner transfer roller is made smaller than that of the outer transfer roller to form a curved surface having a small radius of curvature.

  In Patent Document 2, toner images formed on a common photosensitive drum with different development colors are sequentially transferred and superimposed on an intermediate transfer belt, and then a plurality of color toner images are collectively transferred from the intermediate transfer belt to a recording material. An image forming apparatus to be transferred is shown. Here, a separating roller having a small radius of curvature is pressed against the inner surface of the intermediate transfer belt on the downstream side of the transfer portion (see FIG. 23B) to form a curved surface having a small radius of curvature.

  Patent Document 3 discloses an image forming apparatus in which a plurality of toner image forming units having different development colors are arranged on a linear portion of an intermediate transfer belt. Here, a transfer portion is formed by curving the intermediate transfer belt inward, and the recording material is guided to be wound around an outer transfer roller (see FIG. 23C), so that the transfer portion Curvature separation of the recording material from the intermediate transfer belt on the downstream side is facilitated.

JP 2003-122143 A JP-A-9-185268 JP 2003-91174 A

  In any of the methods disclosed in Patent Documents 1, 2, and 3, the intermediate transfer belt is greatly bent with a small radius of curvature, so that the burden on the intermediate transfer belt increases. The ribs adhered to the edge of the intermediate transfer belt may peel off, or the intermediate transfer belt may be bent due to a long-term stop under low temperature conditions.

  It is an object of the present invention to provide an image forming apparatus capable of easily separating a recording material on the downstream side of a transfer portion even with a relatively large curved surface with less burden on the intermediate transfer belt and reducing re-sticking after separation. It is aimed.

  An image forming apparatus according to the present invention includes an intermediate transfer belt that is formed endlessly and rotates, a toner image forming unit that forms a charged toner image to be carried on the intermediate transfer belt, and the intermediate transfer belt in a rotation direction. A transfer member that forms a toner image transfer portion between the curved transfer surface and the intermediate transfer belt, a feeding unit that feeds a recording material to the transfer portion, and a voltage applied to the transfer portion. And a transfer power source for transferring the toner image carried on the intermediate transfer belt to a recording material passing through the transfer portion. Then, the intermediate transfer belt is supported from the inside to form the curved surface on the downstream side of the transfer portion, and the intermediate transfer belt on the downstream side of the transfer portion has a polarity opposite to the charged polarity of the toner image. A separation voltage applying device for applying a voltage is provided.

  Since the image forming apparatus of the present invention applies a separation voltage having a polarity opposite to the charged polarity of the toner image to the curved surface downstream of the transfer unit, even a recording material that cannot be separated by only the curvature of the curved surface is forced to apply electrostatic force. Can be separated. In addition, since a separation voltage having a polarity opposite to the charging polarity of the toner image is applied to the curved surface downstream of the transfer portion, an electrostatic force is applied to the leading edge of the recording material separated by the curved surface in a direction to stick to the intermediate transfer belt. Does not work. For this reason, the recording material protruding from the secondary transfer portion is suppressed from being sucked and stuck to the intermediate transfer belt.

  Therefore, even with a relatively large curved surface with less burden on the intermediate transfer belt, the recording material can be easily separated on the downstream side of the transfer portion, and reattachment after separation can be reduced.

  Hereinafter, some embodiments of the present invention will be described in detail with reference to the drawings. As long as a voltage having a polarity opposite to the charging polarity of the toner image is applied to the curved surface spaced apart from the transfer unit to the downstream side, the present invention can partially or entirely replace the configuration of each embodiment. Another embodiment in which the configuration is replaced can also be implemented.

  Therefore, not only a tandem type image forming apparatus using a plurality of image carriers having different development colors but also a one-drum type image forming apparatus using a single image carrier.

  In the present embodiment, only main parts related to toner image formation / transfer will be described. However, the present invention includes a printer, various printing machines, a copier, a fax machine, a composite machine, in addition to necessary equipment, equipment, and a housing structure. It can be implemented in various applications such as a machine.

  In addition, about the general matter regarding the image forming apparatus shown by patent documents 1-3, illustration is abbreviate | omitted and the overlapping description is abbreviate | omitted. In the description, the reference symbols in parentheses attached to the component names used in the claims are examples for helping understanding of the invention, and are not intended to limit the configuration to the members of the embodiment. Absent.

<First Embodiment>
FIG. 1 is an explanatory diagram of the configuration of the image forming apparatus according to the first embodiment, and FIG. 2 is an explanatory diagram of the configuration of the image forming unit.

  As shown in FIG. 1, the image forming apparatus 100 according to the first embodiment has a tandem type in which image forming portions Pa, Pb, Pc, and Pd, which are examples of toner image forming means, are arranged in a straight section of an intermediate transfer belt 51. This is an intermediate transfer type full-color copier.

  In the image forming portion Pa, a yellow toner image is formed on the photosensitive drum 1 a and is primarily transferred to the intermediate transfer belt 51. In the image forming portion Pb, a magenta toner image is formed on the photosensitive drum 1 b and is primarily transferred to the yellow toner image on the intermediate transfer belt 1. In the image forming portions Pc and Pd, a cyan toner image and a black toner image are formed on the photosensitive drums 1c and 1d, respectively, and are sequentially transferred onto the intermediate transfer belt 51 in a primary manner.

  The four-color toner images primarily transferred to the intermediate transfer belt 51 are transported to the secondary transfer portion T2 which is an example of the transfer portion, and are collectively transferred to the recording material P fed to the secondary transfer portion T2. Is done. The recording material P on which the toner image has been secondarily transferred by the secondary transfer portion T2 is heated and pressurized by the fixing device 7 to fix the toner image on the surface, and then discharged to the outside of the image forming apparatus 100.

  The intermediate transfer belt 51 is supported by the tension roller 12, the driving roller 13, and the secondary transfer inner roller 56, and rotates in the direction of arrow R2 at a predetermined process speed. The intermediate transfer belt 51 is applied with a tension force of 30 N (3 kgf) by the tension roller 12 and is driven by transmitting a driving force from a driving motor (not shown) to the end of the driving roller 13.

  The separation device 22 separates the recording material P drawn from the paper feed cassette 20 by the pickup roller 21 one by one and sends it to the registration roller 23.

  The registration roller 23, which is an example of a feeding unit, accepts the recording material P in a stopped state and waits, and sends the recording material P to the secondary transfer portion T <b> 2 in time with the toner image on the intermediate transfer belt 51.

  The cleaning device 19 slides the cleaning blade against the intermediate transfer belt 51 to remove the transfer residual toner remaining on the intermediate transfer belt 51 after passing through the secondary transfer portion T2.

  The image forming portions Pa, Pb, Pc, and Pd are configured substantially the same except that the colors of toner used in the attached developing devices 4a, 4b, 4c, and 4d are different from yellow, magenta, cyan, and black. Hereinafter, the image forming unit Pa will be described, and the other image forming units Pb, Pc, and Pd will be described by replacing “a” at the end of the reference numerals with “b”, “c”, and “d”.

  As shown in FIG. 2, the image forming unit Pa includes a charging device 2a, an exposure device 3a, a developing device 4a, a primary transfer roller 5a, and a cleaning device 6a around the photosensitive drum 1a.

  The photosensitive drum 1a has a negatively charged photosensitive layer formed on the outer peripheral surface of an aluminum cylinder. The photosensitive drum 1a is rotatably supported at both ends, transmits a driving force from a driving motor (not shown) to one end, and rotates in the direction of the arrow R1 at a predetermined process speed.

  The charging device 2a presses the charging roller against the photosensitive drum 1a to be driven to rotate, and applies a voltage obtained by superimposing a DC voltage and an AC voltage to the charging roller from the power source D3, so that the surface of the photosensitive drum 1a has a uniform negative electrode. It is charged to a sex potential.

  The exposure device 3a scans the scanning line image data obtained by developing the yellow separated color image with a rotating mirror, and writes an electrostatic image of the image on the surface of the charged photosensitive drum 1a.

  The developing device 4a stirs and charges the two-component developer, and supports the photosensitive drum 1a around the fixed magnetic pole 4j in a stand-up state on the photosensitive drum 1a and the developing sleeve 4s that rotates in the counter direction. Let

  The power source D4 applies a developing voltage obtained by superimposing an AC voltage to a negative DC voltage to the developing sleeve 4s so that the electrostatic image on the photosensitive drum 1a having a relatively positive polarity relative to the developing sleeve 4s has a negative polarity. The electrostatic image is reversely developed by attaching a charged toner.

  Both ends of the primary transfer roller 5a are urged by spring members (not shown) to sandwich the intermediate transfer belt 51 between the photosensitive drum 1a, and the primary transfer portion T1 is interposed between the photosensitive drum 1a and the intermediate transfer belt 51. Form.

  The power source D1 applies a positive DC voltage to the roller shaft of the primary transfer roller 5a, and primary transfer the negative toner image carried on the photosensitive drum 1a to the intermediate transfer belt 51 passing through the primary transfer portion T1. To do.

  The cleaning device 6a slides the cleaning blade on the photosensitive drum 1a to remove the transfer residual toner that has passed through the primary transfer portion T1 and remained on the surface of the photosensitive drum 1a.

  The fixing device 7 includes a fixing roller 71 and a pressure roller 72, and a heater 73 is disposed inside the fixing roller 71. When the recording material P passes between the fixing roller 71 and the pressure roller 72, the recording material P is heated and pressurized by the heater 73, and the toner image is melted and fixed as a full-color image.

<Transfer section>
FIG. 3 is an explanatory diagram of the configuration of the secondary transfer unit in the first embodiment.

The intermediate transfer belt 51 as an example of the intermediate transfer belt is formed in an endless shape having a width of 370 mm and a peripheral length of 900 mm using a film material having a thickness of 50 to 150 μm in which carbon black is contained in a dielectric resin such as polyimide. ing. The intermediate transfer belt 51 has a volume resistivity adjusted to 1 × 10 ⁸ to 1 × 10 ¹² Ω · cm.

  The secondary transfer outer roller 57, which is an example of a transfer member, is in pressure contact with the secondary transfer inner roller 56, which is an example of a guide member, via the intermediate transfer belt 51, and the intermediate transfer belt 51, the secondary transfer outer roller 57, and the like. A secondary transfer portion T2 is formed between the two.

The secondary transfer outer roller 57 has an outer diameter of 24 mm by forming an elastic layer of 6 mm thick conductive rubber sponge on the outer periphery of a stainless steel roller shaft having a diameter of 12 mm. As the conductive rubber sponge, nitrile butadiene rubber, ethylene propylene diene rubber, urethane or the like mixed with an ionic conductive agent is used. The resistance value of the secondary transfer outer roller 57 is adjusted to 1 × 10 ⁷ to 1 × 10 ⁸ Ω. The resistance value is 10N (1 kgf) applied to the secondary transfer outer roller 57, pressed against the conductive cylinder, and 2kV is applied to the roller shaft while the secondary transfer outer roller 57 is driven to rotate by the rotation of the conductive cylinder. It was obtained from the current that flows. The surface hardness of the secondary transfer outer roller 57 is 35 degrees as an ASKER-C hardness value.

<Separation voltage application device>
In the secondary transfer inner roller 56, a cylindrical surface layer 561 is rotatably supported around a fixed columnar core roller 562, and the surface layer 561 rotates to form a curved surface on the intermediate transfer belt 51. Meanwhile, the intermediate transfer belt 51 is guided in the rotation direction.

  The fixed core roller 562 includes two semi-cylindrical conductive portions 562a and 562b. In the secondary transfer portion T2, the surface layer 561 is maintained at the ground potential through the conductive portion 562a connected to the ground potential. . On the other hand, in an area spaced downstream from the secondary transfer portion T2, the surface layer 561 has a separation potential having a polarity (positive polarity) opposite to the charging polarity of the toner image through the conductive portion 562b connected to the separation power source D5. It is kept.

  A power source D2 which is an example of a transfer power source outputs a positive constant voltage as a transfer voltage to the roller shaft of the secondary transfer outer roller 57, and the secondary transfer inner roller 56, the intermediate transfer belt 51, the recording material P, and the second transfer material. A transfer current is passed through a series circuit with the next transfer outer roller 57. As a result, the toner image is electrostatically moved from the intermediate transfer belt 51 to the recording material P in the process in which the recording material P passes through the secondary transfer portion T2 while being superimposed on the toner image of the intermediate transfer belt 51. The power source D <b> 2 applies a transfer voltage having a polarity opposite to the charging polarity of the toner image to the secondary transfer outer roller 57.

  A power supply D5, which is an example of a separation power supply, outputs a separation voltage having an absolute value smaller than the transfer voltage to the conductive portion 562b.

  Conductive portions 562a and 562b, which are examples of switching electrodes, connect the ground potential to the conductive portion 561a that has reached the secondary transfer portion T2 as the surface layer 561 rotates, and the conductive portion 561a that has reached the downstream region of the transfer portion T2. Is connected to the separation power source D5.

  In the process of passing through the secondary transfer portion T2, the recording material P is charged with an excessive charge through the secondary transfer outer roller 57 and charged to a potential (positive polarity) opposite in polarity to the toner image. When the recording material P which has been separated from the intermediate transfer belt 51 and protrudes from the secondary transfer portion T2 reaches a space slightly advanced downstream of the secondary transfer portion T2, the recording material P repels the separation voltage from the intermediate transfer belt 51. The course can be bent away.

  The control unit 15, which is an example of a first control unit, controls the power source D <b> 5 according to the image forming condition so that the separation voltage is set high when the transfer voltage is set high. When the absolute humidity decreases, the control unit 15 increases both the transfer voltage and the separation voltage.

  The control unit 15, which is an example of a second control unit, supplies a power source D <b> 5 according to the image forming condition so that the separation voltage is set higher as the image forming condition with a lower separation property of the recording material P downstream of the secondary transfer unit T <b> 2. To control. The controller 15 increases the separation voltage as the recording material P set through the operation panel 17 is thinner.

  The step motor M1, which is an example of a moving mechanism, rotates the core roller 562 at a rotation angle corresponding to the number of input pulses, and moves the position of the curved surface to which the separation voltage is applied in the rotation direction of the intermediate transfer belt 51.

  The control unit 15, which is an example of a third control unit, approaches the secondary transfer unit T <b> 2 to the position of the curved surface to which the separation voltage is applied in an image forming condition with poor recording material separation downstream of the secondary transfer unit T <b> 2. The step motor M1 is controlled according to the image forming conditions. The controller 15 brings the conductive portion 562b closer to the secondary transfer portion T2 as the recording material P set through the operation panel 17 is thinner.

  The controller 15 waits for the leading edge of the recording material P to pass through the secondary transfer portion T2 with the conductive portion 562b being close to the secondary transfer portion T2.

  Thereafter, the control unit 15 moves the conductive portion 562b to a position away from the secondary transfer portion T2 to the downstream side until the blank portion at the front end of the recording material P passes through the secondary transfer portion T2. After the marginal portion at the leading end of the recording material P charged to positive polarity cooperates with the curved surface and is reliably separated, the conductive portion 562b is retracted to a position where there is no fear of retransferring the toner image to the intermediate transfer belt 51. . The charged recording material P is pushed back at a position where there is no fear of retransferring the toner image to the intermediate transfer belt 51 to prevent the recording material P from reattaching to the intermediate transfer belt 51.

  As a result, the recording material P is not sucked and stuck to the intermediate transfer belt 51 after being once separated on the downstream side of the secondary transfer portion T2. Even the recording material P, which is thin and has low rigidity and cannot be separated only by the curved surface, can be forcibly separated by applying electrostatic force, so that the recording material P is rotated around the intermediate transfer belt 51 without being separated. There is nothing.

<Rotating electrode member>
4 is a side view of the secondary transfer inner roller, FIG. 5 is a sectional view of the secondary transfer inner roller in section A of FIG. 4, FIG. 6 is a sectional view of the secondary transfer inner roller in section B of FIG. FIG. 6 is a sectional view of the secondary transfer inner roller in section C in FIG. 5. FIG. 8 is a partially enlarged view of the cross section of the secondary transfer inner roller, FIG. 9 is an explanatory diagram of the electrostatic force relationship in the vicinity of the secondary transfer portion, and FIG. 10 is the static electricity in the vicinity of the secondary transfer portion of the comparative example. It is explanatory drawing of a typical force relationship.

  As shown in FIG. 4, when the secondary transfer inner roller 56 is viewed from a direction perpendicular to the axis, the secondary transfer inner roller 56 has a cylindrical shape with an outer diameter of φ16 to 20 mm. The cylindrical side surface of the secondary transfer inner roller 56 is formed to have the same width by crossing the cylindrical side surface in the axial direction and using a conductive material, and the plurality of conductive portions 561a (a plurality of electrode portions) are spaced in the circumferential direction. Is arranged. Insulating portions 561b that are formed to have the same width using an insulating material and are represented in white are arranged at intervals between the conductive portions 561a to insulate adjacent conductive portions 561a.

  The conductive portion 561a uses a metal such as aluminum or stainless steel or a conductive solid rubber such as conductive ethylene propylene diene rubber. The insulating part 561b uses a resin material such as polytetrafluoroethylene. The conductive portion 561 a and the insulating portion 561 b are arranged in parallel with the axis of the secondary transfer inner roller 56.

  As shown in FIG. 5, the conductive portion 561a on the cylindrical surface of the secondary transfer inner roller 56 is fitted in the recess of the insulating portion 561b whose surface is shaped like a gear. The width in the circumferential direction of the conductive portion 561a is 3 mm or more and 4 mm or less, and the width of the insulating portion 561b separating the two conductive portions 561a is 1.5 mm or less.

  A cylindrical core roller 562 is disposed in the cylindrical space inside the secondary transfer inner roller 56. The core roller 562 is provided with a pair of semi-cylindrical conductive portions 562a and 562b with an insulating layer 562c passing through the central axis of the secondary transfer inner roller 56 interposed therebetween. The insulating layer 562c and the conductive portions 562a and 562b are integrally fixed, and the insulating layer 562c divides the circular cross section of the core roller 562 into two.

  A resin such as polytetrafluoroethylene is used for the insulating layer 562c. A metal such as stainless steel is used for the conductive portions 562a and 562b.

  As shown in FIG. 6, a plurality of balls 563 a and 563 b surrounding the core roller 562 and rotating in contact with the outer periphery of the core roller 562 are arranged at both ends inside the secondary transfer inner roller 56.

  As shown in FIG. 7, at both ends inside the secondary transfer inner roller 56, a plurality of balls 563a (563b: 563b: 563b) are provided between the insulating portion 561 of the surface layer 561 and the insulating lid 564 fixed to the core roller 562. FIG. 6) is arranged.

  The plurality of spheres 563a and 563b are formed so as to be rotatable in respective positions on the outer periphery of the core roller 562, and rotate following the rotation of the surface layer 561. Accordingly, the cylindrical surface layer 561 is supported by a plurality of balls 563 a and 563 b that rotate around the core roller 562, and is rotatable around the core roller 562.

  The sphere 563a disposed on the surfaces of the conductive portions 562a and 562b is formed of a metal such as stainless steel and is conductive. The diameter of the sphere 563a is smaller than the width of the conductive portion 561a and larger than the width of the insulating portion 561b. In addition, twice the diameter of the sphere 563a is larger than the width of the conductive portion 561a. On the other hand, the sphere 563b disposed on the cylindrical side surface of the insulating layer 562c of the core roller 562 is formed of a resin material such as polytetrafluoroethylene and is insulative.

  As shown in FIG. 8, the insulating sphere 563b held in the depression of the insulating layer 562c rotates in a state where it is always in contact with the insulating layer 562c. Even if the surface layer 561 and the balls 563a and 563b rotate following the rotation of the intermediate transfer belt (51: FIG. 3), the core roller 562 does not rotate.

  As shown in FIG. 3, in the secondary transfer portion T2, the conductive portion 562a facing the upstream side of the secondary transfer portion among the conductive portions 562a and 562b of the core roller 562 of the secondary transfer inner roller 56 is grounded. Yes. On the other hand, a voltage having the same polarity as the voltage applied to the secondary transfer outer roller 57 is applied to the conductive portion 562b facing downstream of the secondary transfer portion.

  A transfer voltage of 2 to 7 kV is applied to the secondary transfer outer roller 57 so that 20 to 70 μA flows through the secondary transfer outer roller 57 when the recording material P passes through the secondary transfer portion T2.

  A separation voltage of 0.5 to 2 kV is applied to the conductive portion 562b of the secondary transfer inner roller according to the voltage applied to the secondary transfer outer roller 57.

  In the first embodiment, the secondary transfer inner roller 56, which is an example of a bending mechanism, rotates with the cylindrical surface in contact with the intermediate transfer belt 51. A surface layer 561, which is an example of a rotating electrode member, has a plurality of conductive portions 561 a and 561 b that are electrically conductive in the diameter direction of the cylindrical surface and can apply independent voltages to each other in the rotational direction of the secondary transfer inner roller 56. Arranged along.

  The core roller 562, which is an example of a separation voltage applying unit, includes conductive portions 562a, 562b, which are examples of a switching mechanism. The conductive portions 562a and 562b switch and apply a separation voltage to the conductive portion 561a that passes through the curved surface on the downstream side of the secondary transfer portion T2 as the surface layer 561 rotates.

  As shown in FIG. 9, an electric field of transfer voltage and an electric field of separation voltage are formed on the downstream side of the secondary transfer portion T2. In the figure, the white arrow represents the electric field, and the black arrow represents the electrostatic attraction force applied to the recording material P.

  As shown in FIG. 10, in the case of the comparative example in which the entire secondary transfer inner roller 56 having the same size is connected to the ground potential, as indicated by the black arrow on the downstream side of the secondary transfer portion T2. The recording material P is attracted to the intermediate transfer belt 51 by a strong electrostatic attraction force.

  As shown in FIG. 9, in the first embodiment, the electric field and pressure distribution of the transfer portion T2, the bending load on the intermediate transfer belt 51, and the transportability of the recording material P are the same as in the comparative example. However, since the electric field downstream of the secondary transfer portion T2 is suppressed, the electrostatic adsorption force acting on the positively charged recording material P is weakened, and the leading edge of the recording material P is stuck to the intermediate transfer belt 51. Can be prevented.

Second Embodiment
11 is an explanatory diagram of the configuration of the secondary transfer portion in the second embodiment, FIG. 12 is a cross-sectional view of the central portion in the axial direction of the secondary transfer inner roller, and FIG. 13 is along the axial direction of the secondary transfer inner roller. FIG. 14 is a cross-sectional view of the end portion in the axial direction of the secondary transfer inner roller.

  The image forming apparatus of the second embodiment is configured in the same manner as in the first embodiment except that the internal structure of the secondary transfer inner roller is different, and the electric field formed in the secondary transfer portion by the transfer voltage and the separation voltage is also the first. This is the same as the embodiment. Accordingly, here, only the difference in the configuration of the secondary transfer inner roller compared to the first embodiment will be described, and the description overlapping with the first embodiment will be omitted.

  As shown in FIG. 11, the secondary transfer outer roller 57 is pressed against the intermediate transfer belt 51 having a curved surface along the secondary transfer inner roller 56, and a toner image is transferred from the intermediate transfer belt 51 to the recording material P. A secondary transfer portion T2 for secondary transfer is formed. The secondary transfer outer roller 57 and the intermediate transfer belt 51 are the same as those in the first embodiment.

  Brush electrodes 562d and 562e for switching the potential of the conductive portion 561a are disposed at the end of the secondary transfer inner roller 56. Through the brush electrode 562d whose positional relationship is fixed with respect to the secondary transfer portion T2, the surface of the secondary transfer inner roller 56 positioned at the secondary transfer portion T2 is maintained at the ground potential. Through the brush electrode 562e whose positional relationship is fixed with respect to the secondary transfer portion T2, the surface of the secondary transfer inner roller 56 positioned downstream of the secondary transfer portion T2 is connected to the power source D5 and applied with a separation voltage. The

  As shown in FIG. 12, the outer diameter of the secondary transfer inner roller 56 is 16 to 20 mm, the conductive portion 561 a shown by hatching is conductive, and the white insulating portion 561 b is insulating. On the surface layer 561 of the secondary transfer inner roller 56, a plurality of conductive portions 561a are arranged in the circumferential direction, and insulating portions 561b are arranged at intervals between the conductive portions 561a.

  For the conductive portion 561a, a metal such as aluminum or stainless steel or a conductive solid rubber such as conductive ethylene propylene diene rubber is used. The insulating portion 561b uses a resin such as polytetrafluoroethylene.

  The conductive portion 561a is fitted into an insulating portion 561b whose cylindrical surface is molded into a gear shape, and is disposed in parallel with the axis of the secondary transfer inner roller 56. The core roller 562 is assembled integrally with the conductive portion 561a and rotates integrally. The width of the conductive portion 561a in the circumferential direction is 2 mm to 4 mm, and the width of the insulating portion 561b between the conductive portions 561a is 1.5 mm or less.

  As shown in FIG. 13, brush electrodes 562 d and 562 e for switching the potential of the conductive portion 561 a are disposed at one end of the secondary transfer inner roller 56. In FIG. 13, section A is FIG. 12, and section B is FIG.

  As shown in FIG. 14, the brush electrodes 562 d and 562 e are in contact with the conductive portion 561 a of the secondary transfer inner roller 56. The brush electrodes 562d and 562e have a circumferential width of 4 to 10 mm, and the circumferential interval between the brush electrodes 562d and 562e is larger than the circumferential width of the conductive portion 561a.

  For the brush electrodes 562d and 562e, a metal material that can withstand sliding such as aluminum, stainless steel, carbon, gold-plated phosphor bronze, conductive solid rubber such as conductive ethylene propylene diene rubber, a conductive brush, or the like is used. In FIG. 14, the cross section C is FIG.

  As shown in FIG. 11, when the intermediate transfer belt 51 rotates, the conductive portion 561a, the insulating portion 561b, and the core roller 562 rotate following the rotation of the intermediate transfer belt 51, but the brush electrodes 562d and 562e rotate. do not do.

  In the secondary transfer portion T2, the brush electrode 562d facing upstream of the secondary transfer portion is grounded, and the brush electrode 562e facing downstream of the secondary transfer portion is applied to the secondary transfer outer roller 57. A separation voltage having the same polarity as the transfer voltage is applied.

  A voltage of 2 to 7 kV is applied to the secondary transfer outer roller 57 so that 20 to 70 μA flows through the secondary transfer outer roller 57 when the recording material P passes through the secondary transfer portion T2.

  A separation voltage of 0.5 to 2 kV is applied to the conductive portion 562e of the secondary transfer inner roller in accordance with the transfer voltage applied to the secondary transfer outer roller 57.

  As a result, an electric field as shown in FIG. 9 is formed on the downstream side of the secondary transfer portion T2. Compared with the comparative example shown in FIG. 10, when the dimensions of the members constituting the secondary transfer portion T2 are the same, the pressure applied to the secondary transfer portion T2, the load on the intermediate transfer belt 51, the conveyance of the recording material P Sex is equivalent. However, as a result of suppressing the electric field downstream of the secondary transfer portion T2, the electrostatic attraction force acting on the charged recording material P is weakened, and the leading end of the recording material P can be prevented from sticking to the intermediate transfer belt 51.

<Third Embodiment>
15 is an explanatory diagram of the configuration of the secondary transfer unit in the third embodiment, FIG. 16 is a cross-sectional view along the axial direction of the secondary transfer inner roller, and FIG. 17 is a cross section perpendicular to the axial direction of the secondary transfer inner roller. FIG. 18 and FIG. 18 are explanatory views of the electrostatic force relationship in the vicinity of the secondary transfer portion.

  The image forming apparatus of the third embodiment is configured in the same manner as in the second embodiment except that the internal structure of the secondary transfer inner roller is different, and the electric field formed in the secondary transfer portion by the transfer voltage and the separation voltage is also the second. This is the same as the embodiment. Therefore, only the difference in the configuration of the secondary transfer inner roller compared to the second embodiment will be described here, and the description overlapping with the second embodiment will be omitted.

  As shown in FIG. 15, the secondary transfer outer roller 57 is pressed against the intermediate transfer belt 51 having a curved surface formed along the secondary transfer inner roller 56, and a toner image is transferred from the intermediate transfer belt 51 to the recording material P. A secondary transfer portion T2 for secondary transfer is formed. The secondary transfer outer roller 57 and the intermediate transfer belt 51 are the same as those in the second embodiment.

  As shown in FIG. 16, a surface layer support 562 h is fixed to the core roller 562 of the secondary transfer inner roller 56. The surface layer support portion 562h rotatably supports the cylindrical surface layer 561.

  The brush electrodes 562f and 562g are fixed to the surface layer support portion 562h and are disposed so as to slidably contact the inner side surface of the region continuous in the axial direction of the surface layer 561.

  As shown in FIG. 17, the outer diameter of the secondary transfer inner roller 56 is 16 to 20 mm, the hatched portion is conductive, and the white portion is insulating. In FIG. 17, the cross section C is FIG.

  The surface layer 561 indicated by a lattice does not have conductivity in the circumferential direction and the axial direction of the secondary transfer inner roller 56, but has conductivity in the thickness direction of the surface layer 561 (diameter direction of the secondary transfer inner roller 56). This is an anisotropic conductive member.

  For the brush electrodes 562f and 562g, a metal material that is resistant to sliding, such as aluminum, stainless steel, carbon, gold-plated phosphor bronze, conductive solid rubber such as conductive ethylene propylene diene rubber, a conductive brush, or the like is used.

  The brush electrodes 562f and 562g have a circumferential width of 4 to 10 mm and an axial length of 300 to 350 mm, and are insulated from each other in the circumferential direction by an insulating material constituting the surface layer support portion 562h.

  The surface layer support portion 562h is molded around the core roller 562 using an insulating resin material having a low friction coefficient such as polytetrafluoroethylene.

  In the surface layer 561, metal particles such as nickel particles are dispersed inside the rubber, and the metal particles are arranged so as to be in contact with each other in the thickness direction but not in the circumferential direction.

  As such an anisotropic conductive material, as disclosed in Japanese Patent Application Laid-Open No. 10-200242, a material in which metal particles are dispersed by molding and solidifying a resin material in which metal particles are dispersed in a magnetic field can be used. .

  As shown in FIG. 15, when the intermediate transfer belt 51 rotates, the surface layer 561 rotates following the rotation of the intermediate transfer belt 51, but the core roller 562 and the surface layer support portion 562h do not rotate. Of the surface layer 561 of the secondary transfer inner roller 56, the region in contact with the brush electrode 562f located upstream from the secondary transfer portion T2 is connected to the ground potential through the brush electrode 562f. On the other hand, the portion of the surface layer 561 located on the downstream side of the secondary transfer portion T2 is connected to the power source D5 through the brush electrode 562g and has the same polarity as the voltage applied to the secondary transfer outer roller 57. Is applied.

  A voltage of 2 to 7 kV is applied to the secondary transfer outer roller 57 so that 20 to 70 μA flows through the secondary transfer outer roller 57 when the recording material P passes through the secondary transfer portion T2.

  A voltage of 0.5 to 2 kV is applied to the brush electrode 562 g of the secondary transfer inner roller according to the transfer voltage applied to the secondary transfer outer roller 57.

  As shown in FIG. 18, at this time, an electric field due to the transfer voltage and the separation voltage is formed on the downstream side of the secondary transfer portion T2. Compared with the comparative example shown in FIG. 10, when the dimensions of the members constituting the secondary transfer portion T2 are the same, the pressure applied to the transfer portion T2, the load on the intermediate transfer belt 51, and the transportability of the recording material P are as follows. It is equivalent. However, it is possible to prevent the leading edge of the recording material P from sticking to the intermediate transfer belt 51 as a result of the electrostatic adsorption force acting on the charged recording material P being suppressed by suppressing the electric field downstream of the secondary transfer portion T2.

<Comparative Example 1>
19 is an explanatory diagram of the behavior of the recording material in the secondary transfer portion of Comparative Example 1, FIG. 20 is an explanatory diagram of the charging state of the recording material in the secondary transfer portion of Comparative Example 1, and FIG. 21 is another behavior of the recording material. It is explanatory drawing of.

  According to the observation of the present inventor, in the transfer portion in which the outer transfer roller is pressed against the curved surface of the intermediate transfer belt, the leading edge of the thin recording material is separated from the intermediate transfer belt and protrudes from the transfer portion. This is because as long as the protruding length is short, the bending resistance of the thin recording material is superior to the electrostatic force proportional to the protruding area.

  However, since the electrostatic force increases and the bending resistance of the thin recording material does not change as the protrusion length increases, the recording material is sucked by the intermediate transfer belt by the electrostatic force, and the intermediate transfer is performed again downstream of the transfer unit. Affixed to the belt.

  Therefore, if the protruding state can be maintained until the protruding length is sufficiently long and the weight of the recording material exceeds the electrostatic force, the recording material is attached to the intermediate transfer belt. It becomes difficult to turn.

  As shown in FIG. 19A, in Comparative Example 1, as in the conventional image forming apparatus, the secondary transfer inner roller 56 is formed of an aluminum cylinder and is connected to the ground potential as a whole. A transfer voltage is applied from the power source D2 to the secondary transfer outer roller 57 provided so as to contact the intermediate transfer belt 51 via the recording material P. Thus, the toner image carried on the intermediate transfer belt 51 is electrostatically moved to the recording material P by the electric field formed between the secondary transfer inner roller 56 and the secondary transfer outer roller 57.

  However, when the recording material P is thin or when the resistance of the recording material P is high as in the second side of double-sided printing, after the toner image on the intermediate transfer belt 51 is transferred to the recording material P, the recording material P is transferred to the intermediate transfer belt. In some cases, it may be pasted without being separated from 51.

  There are two types of behavior of the recording material P sticking to the intermediate transfer belt 51.

  One is that the leading edge of the recording material P is separated as shown in (a), but the recording material P is attracted to the intermediate transfer belt 51 downstream from the secondary transfer inner roller 56 as shown in (b). As shown in (c), it is a behavior that sticks at the end.

  Taking the case where the toner is negatively charged as an example, the state of the charge held by the recording material P and the intermediate transfer belt 51 at this time will be examined.

  As shown in FIG. 20 (a), in order to transfer the toner, a positive charge more than the charge necessary to hold the toner is applied from the secondary transfer outer roller 57. It is positively charged. On the other hand, the intermediate transfer belt 51 is negatively charged by the potential gradient at the secondary transfer portion T <b> 2 and is negatively charged downstream of the secondary transfer inner roller 56.

  Therefore, as shown in (b), the positive charge of the recording material P and the negative charge of the intermediate transfer belt 51 attract each other downstream of the secondary transfer inner roller 56, and sticking occurs as shown in (c). .

  The other is a behavior in which the recording material P does not separate from the intermediate transfer belt 51 downstream of the secondary transfer portion T2.

  As shown in FIG. 21A, the leading edge of the recording material P sticks to the intermediate transfer member immediately after passing through the secondary transfer portion T2, and is conveyed as it is as shown in FIG.

  As already described with reference to FIG. 10, the electrostatic attraction force received by the charged recording material P is near the outlet of the secondary transfer portion T <b> 2 where the secondary transfer outer roller 57 and the intermediate transfer belt 51 are in contact. Is the strongest. For this reason, the recording material P that is thin and has low rigidity and the recording material P that has high resistance and is easily charged are stuck without separation due to the electrostatic adsorption force at the secondary transfer portion T2. In FIG. 10, a white arrow indicates an electric field, and a black arrow indicates an electrostatic attraction force.

<Comparative example 2>
FIG. 22 is an explanatory diagram of the configuration of the secondary transfer unit in the image forming apparatus of Comparative Example 2.

  In Comparative Example 2, the recording material is separated from the intermediate transfer belt by reducing the electrostatic attraction between the intermediate transfer belt and the recording material while maintaining the curved state of the intermediate transfer belt in Comparative Example 1.

  As shown in FIG. 22A, a static eliminating member 58 for separation is disposed on the downstream side of the secondary transfer portion T2, and the static charge of the recording material P is eliminated by discharging excess charge on the recording material P. Decrease the adsorption power.

  As shown in FIG. 22B, the intermediate transfer belt 51 is neutralized by rubbing the electrode plate 59 connected to the ground potential on the inner peripheral surface of the intermediate transfer belt 51 on the downstream side of the secondary transfer inner roller 56. Or the potential rise is regulated.

  However, these methods are effective when the leading edge of the recording material P is once separated as shown in FIG. 19, but are effective when the recording material P is attached from the leading edge as shown in FIG. There was no.

<Comparative Example 3>
FIG. 23 is an explanatory diagram of a configuration of a secondary transfer unit in the image forming apparatus of Comparative Example 3.

  In Comparative Example 3, the recording material is separated from the intermediate transfer belt by increasing the curvature of the curved surface of the intermediate transfer belt in Comparative Example 1 and promoting the curvature separation of the recording material.

  As shown in FIG. 19A, the curvature of the intermediate transfer belt 51 is made smaller than that of the secondary transfer outer roller 57 by reducing the diameter of the secondary transfer inner roller 56 and the diameter of the secondary transfer outer roller 57. .

  However, in the method of reducing the diameter of the secondary transfer inner roller 56, the thinner the recording material P, the smaller the diameter, and the load on the intermediate transfer belt 51 increases, or the transfer area becomes narrow and the secondary transfer becomes narrower. May cause problems. The unevenness of the pressure applied to the secondary transfer portion T2 is likely to occur due to the deflection of the secondary transfer inner roller 56 and the misalignment.

  As shown in FIG. 23A, a separation static eliminating member 58 is disposed on the downstream side of the secondary transfer portion T2, and a ground potential is provided on the inner peripheral side of the intermediate transfer belt 51 on the downstream side of the secondary transfer portion T2. A separation roller 60 connected to is disposed. After the recording material P is adhered to the intermediate transfer belt 51 on the downstream side of the secondary transfer portion T2, the recording material P is neutralized by the separation neutralizing member 58 while the recording material P is intermediately bonded with a large curvature of the separation roller 60. The curvature is separated from the transfer belt 51.

  In this method, it is not necessary to prevent sticking of the leading end of the recording material P in the secondary transfer portion T2. However, the behavior of the recording material P from the secondary transfer portion T2 through the separation roller 60 impairs the image quality. When the recording material P is separated, the toner image easily returns to the intermediate transfer belt 51. Depending on the type and thickness of the recording material P, the traveling direction after separation of the recording material varies greatly. The addition of the separation roller 60 and the separation neutralizing member 58 complicates the periphery of the secondary transfer portion T2.

  As shown in (b) of FIG. 23, when the diameter of the separation roller 60 is reduced and brought close to the secondary transfer portion T2, curvature separation is further facilitated. The closer the secondary transfer portion T2 and the separation roller 60 are, the more the variation in behavior during separation due to the difference in the recording material P can be suppressed, and the recording material P can be easily separated in curvature by the reduction in diameter. However, if the intermediate transfer belt 51 is left as it is bent with a small radius of curvature, a bending wrinkle will occur and uneven density of the image will occur. Damage and fatigue of the intermediate transfer belt 51 accompanying the rotation also increase.

  As shown in FIG. 23C, when the intermediate transfer belt 51 is wound around the secondary transfer outer roller 57 to form the secondary transfer portion T2, the recording material P advances in a direction away from the intermediate transfer belt 51. Separation is facilitated. The intermediate transfer belt 51 is wound around the secondary transfer outer roller 57 by using the secondary transfer inner roller 56 and the separation roller 61, thereby stabilizing the variation in the separation angle due to the difference in the recording material P.

  However, in this case as well, the intermediate transfer belt 51 is curved, so that the load on the intermediate transfer belt 51 is increased. Since the recording material is curved, it is difficult to convey a thick recording material.

  In contrast, in the image forming apparatuses according to the first to third embodiments, the recording material conveyance stability and sufficient transfer can be achieved without increasing the load on the intermediate transfer belt 51 regardless of the type of the recording material. An area can be secured. Then, the leading edge of the recording material is guided downstream to the downstream side of the secondary transfer portion T2 without being attached to the intermediate transfer belt, and sent to the fixing device.

It is explanatory drawing of a structure of the image forming apparatus of 1st Embodiment. It is explanatory drawing of a structure of an image formation part. It is explanatory drawing of the structure of the secondary transfer part in 1st Embodiment. It is a side view of a secondary transfer inner roller. FIG. 5 is a cross-sectional view of the secondary transfer inner roller in cross section A of FIG. 4. FIG. 5 is a cross-sectional view of the secondary transfer inner roller in cross section B of FIG. 4. FIG. 6 is a cross-sectional view of the secondary transfer inner roller in cross section C of FIG. 5. It is a partial enlarged view of the cross section of the secondary transfer inner roller. It is explanatory drawing of the electrostatic force relationship in the vicinity of a secondary transfer part. It is explanatory drawing of the electrostatic force relationship in the vicinity of the secondary transfer part of a comparative example. It is explanatory drawing of the structure of the secondary transfer part in 2nd Embodiment. It is sectional drawing of the center part of the axial direction of a secondary transfer inner roller. It is sectional drawing along the axial direction of the secondary transfer inner roller. It is sectional drawing of the edge part of the axial direction of a secondary transfer inner roller. It is explanatory drawing of the structure of the secondary transfer part in 3rd Embodiment. It is sectional drawing along the axial direction of the secondary transfer inner roller. It is sectional drawing perpendicular | vertical to the axial direction of a secondary transfer inner roller. It is explanatory drawing of the electrostatic force relationship in the vicinity of a secondary transfer part. 6 is an explanatory diagram of the behavior of a recording material in a secondary transfer portion of Comparative Example 1. FIG. 6 is an explanatory diagram of a charging state of a recording material in a secondary transfer portion of Comparative Example 1. FIG. It is explanatory drawing of another behavior of a recording material. 6 is an explanatory diagram of a configuration of a secondary transfer unit in an image forming apparatus of Comparative Example 2. FIG. FIG. 10 is an explanatory diagram of a configuration of a secondary transfer unit in an image forming apparatus of Comparative Example 3.

Explanation of symbols

15 1st control means, 2nd control means, 3rd control means (control part)
23 Feeding means (registration roller)
51 Intermediate transfer belt 56 Bending mechanism (secondary transfer inner roller)
57 Transfer member (secondary transfer outer roller)
561 Separation voltage application device, rotating electrode member (surface layer)
561a Electrode part (conductive part)
562 Separation voltage application means (core roller)
562a, 562b Switching electrode (conductive part)
D2 Transfer power supply (power supply)
D5 Separate power supply (power supply)
M1 moving mechanism (step motor)
Pa, Pb, Pc, Pd Toner image forming means (image forming unit)
T2 transfer section (secondary transfer section)

Claims (6)

An intermediate transfer belt that is formed endlessly and rotates;
Toner image forming means for forming a charged toner image and carrying it on the intermediate transfer belt;
A transfer member that forms a toner image transfer portion between the intermediate transfer belt and the intermediate transfer belt by being pressed against a curved surface obtained by bending the intermediate transfer belt in a rotation direction;
A feeding means for feeding a recording material to the transfer section;
A transfer power source that applies a voltage to the transfer unit and transfers a toner image carried on the intermediate transfer belt to a recording material that passes through the transfer unit;
The intermediate transfer belt is supported from the inside to form the curved surface on the downstream side of the transfer portion, and a separation voltage having a polarity opposite to the charged polarity of the toner image is applied to the intermediate transfer belt on the downstream side of the transfer portion. An image forming apparatus comprising a separating voltage applying device for applying. The separation voltage application device includes:
A rotating electrode member that rotates by bringing a cylindrical surface on which a plurality of electrode portions capable of applying mutually independent voltages are arranged in contact with the intermediate transfer belt;
A separation power source for outputting the separation voltage;
The image forming apparatus according to claim 1, further comprising: a switching electrode that connects an output of the separation power source to the electrode unit that has reached the downstream side of the transfer unit as the rotating electrode member rotates. The transfer power supply applies a transfer voltage having a polarity opposite to the charging polarity of the toner image to the transfer member,
A ground potential is connected to the electrode portion that has reached the transfer portion as the rotating electrode member rotates,
The image forming apparatus according to claim 2, wherein the separation voltage has an absolute value smaller than the transfer voltage.   The image forming apparatus according to claim 3, further comprising a first control unit configured to control the separation power source in accordance with an image forming condition so as to set the separation voltage high when the transfer voltage is set high. apparatus.   And a second control unit that controls the separation power source according to the image forming condition so that the separation voltage is set higher in an image forming condition having a lower recording material separation property downstream of the transfer unit. The image forming apparatus according to claim 3 or 4. The separation voltage application device has a moving mechanism for moving a position where the separation voltage is applied to the curved surface in the rotation direction of the intermediate transfer belt,
Third control means for controlling the moving mechanism in accordance with the image forming condition so that the position where the separation voltage is applied is closer to the transfer part as the image forming condition is lower in the recording material downstream of the transfer part. The image forming apparatus according to claim 2, further comprising:

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