JP2012203254A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus configured to effectively restrict transfer failure in second transfer means.SOLUTION: The image forming apparatus comprises: an intermediate transfer belt 32 movable in circle; primary transfer means 102 for primarily transferring a toner image on an image holder 18 to the intermediate transfer belt; secondary transfer means 104 for supplying power for secondary transfer, thereby secondarily transferring the toner image, primarily transferred to the intermediate transfer belt 32, to a sheet member P in a secondary transfer nip part, the secondary transfer nip part N2 being formed by inserting the intermediate transfer belt and the sheet member P between a secondary transfer roll 42 provided downstream of the primary transfer means 102 in the moving direction of the intermediate transfer belt and a secondary transfer counter roll 40 provided opposite the secondary transfer roll; and a power supply part 110 provided downstream of the secondary transfer nip part in the moving direction of the intermediate transfer belt and configured to supply power to the secondary transfer nip part through the intermediate transfer belt.

Description

  The present invention relates to an image forming apparatus.

  As shown in FIG. 1, Patent Document 1 includes a transfer roll (5) that can freely contact and separate from the intermediate transfer belt (2), and an opposing roll (6) inside the intermediate transfer belt (2). When the transfer roll (5) hits the intermediate transfer belt (2), the angle α between the line connecting the center of the transfer roll (5) and the center of the opposing roll (6) and the intermediate transfer belt (2) is less than 90 degrees. An image forming apparatus is disclosed.

  In Patent Document 2, as shown in FIG. 1, a toner image forming apparatus that forms a toner image, an intermediate transfer member B that rotates, and a toner image is transferred to the intermediate transfer member B in a first transfer region Q3. The first transfer unit (21), the recording sheet conveying device (35 to 38) for conveying and passing the recording sheet S to the secondary transfer area Q4, and the intermediate transfer member B and the recording sheet S are sandwiched in the secondary transfer area Q4 Then, the inner transfer roll (29) constituted by the core material (29a) and the semiconductive layer (29b), which supports the back surface of the intermediate transfer body B and is electrically insulated, and the outer transfer which hits the back surface of the recording sheet S. Secondary transfer voltage application for applying a secondary transfer voltage for transferring the toner image on the intermediate transfer body B to the recording sheet S, a roll (30), an electrode member (31) in contact with the semiconductive layer (29b) An image forming apparatus comprising the means (32). It is.

  In Patent Document 3, as shown in FIG. 2, when the toner image (6) transferred to the intermediate transfer belt (21) is secondarily transferred to the transfer material (7), the secondary transfer belt (31) is attached. The intermediate transfer belt (21) is pressed between the two secondary transfer rollers (26, 27) of the primary transfer unit, and the secondary transfer belt (31) and the intermediate transfer belt (21) have a relatively large area. To reduce the pressure applied to the contact surface between the secondary transfer belt (31) and the intermediate transfer belt (21), and apply excessive pressure to the toner of the toner image formed on the intermediate transfer belt (21). An image forming apparatus is disclosed in which a good quality toner image free from defects is formed on a transfer material (7).

  In Patent Document 4, as shown in FIG. 1, a toner image is formed on an image carrier, and the toner image is transferred to a transfer material sandwiched and conveyed between the image carrier and the transfer material carrier. The image carrier and the transfer material holder are contact portions that are in contact with each other with the transfer material interposed therebetween. An electric field is formed between the surface of the upstream image carrier (11) and the surface of the transfer material (15) to move the toner image toward the image carrier (11). An image forming apparatus is disclosed that forms an electric field in a direction in which a toner image is moved to the transfer material (15) side between the surface of the holder and the transfer material surface.

JP-A-9-90780 Japanese Patent Laid-Open No. 10-228182 JP 2009-237430 A JP 2004-62050 A

  An object of the present invention is to provide an image forming apparatus that effectively suppresses transfer defects in a second transfer unit.

  An image forming apparatus according to a first aspect of the present invention includes an image holding member on which an electrostatic latent image is formed, a developing device that develops the electrostatic latent image formed on the image holding member, and a belt that can be moved around. A first transfer unit that includes a first transfer member and that transfers the toner image on the image carrier developed by the developing device to the belt; and a first transfer unit in the moving direction of the belt. A second transfer member provided on the downstream side and a counter member provided to face the second transfer member, and the belt and the recording medium are disposed between the second transfer member and the counter member. Electric power for secondary transfer is supplied to the transfer nip formed by the insertion, and the second transfer for secondary transfer of the toner image primarily transferred to the belt in the transfer nip to the recording medium Means and in the direction of movement of the belt. Wherein provided in contact with the belt on the downstream side of the transfer nip portion Te, and having a power feeding unit that supplies power to the transfer nip portion through the belt.

  The image forming apparatus according to a second aspect of the present invention is the image forming apparatus according to the first aspect, wherein the belt is suspended on a plurality of suspension rolls and can be moved around. In addition to serving as one of a plurality of suspension rolls, the suspension roll is made of an insulating material.

  According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the resistance of the second transfer member is arranged between the power feeding portion and the transfer nip portion. It is characterized by being set smaller than the resistance of the belt to be applied.

  The image forming apparatus according to a fourth aspect of the present invention is the image forming apparatus according to the third aspect, wherein the first transfer unit is disposed so as to sandwich the belt with the image holding member. One transfer member, and the total resistance of the resistance of the first transfer member and the resistance of the belt disposed between the first transfer member and the transfer nip portion is It is characterized in that it is set larger than the resistance of the belt arranged between the power feeding part and the transfer nip part.

  The image forming apparatus according to a fifth aspect of the present invention is the image forming apparatus according to the third aspect, wherein the first transfer unit is disposed so as to sandwich the belt between the image holding body and the first transfer unit. One transfer member, and the length of the belt disposed between the first transfer member and the transfer nip portion is disposed between the power feeding portion and the transfer nip portion. It is characterized by being set longer than the length of the belt.

  An image forming apparatus according to a sixth aspect of the present invention is the image forming apparatus according to any one of the first to fifth aspects, further comprising charge removing means for removing charges on the surface of the facing member.

  According to the image forming apparatus of the first aspect of the present invention, the power feeding unit that supplies electric power for performing the secondary transfer to the transfer nip portion is brought into contact with the belt on the downstream side of the transfer nip portion in the belt moving direction. Transfer failure in the second transfer means can be effectively suppressed as compared with the case where the power supply unit is not provided (when the power feeding portion is provided on the opposing member).

  According to the image forming apparatus of the second aspect of the present invention, it is possible to effectively suppress the transfer failure in the second transfer unit as compared with the case where the opposing member is not made of an insulating material.

  According to the image forming apparatus of the third aspect of the present invention, compared to the case where the resistance of the second transfer member is not set smaller than the resistance of the belt disposed between the power feeding unit and the transfer nip unit, Transfer defects in the second transfer unit can be effectively suppressed.

  According to the image forming apparatus of claim 4 of the present invention, the total resistance of the resistance of the first transfer member and the resistance of the belt disposed between the first transfer member and the transfer nip portion is: Compared with the case where the resistance is not set larger than the resistance of the belt arranged between the power feeding portion and the transfer nip portion, the current flowing from the second transfer means side to the first transfer means side can be suppressed. Transfer defects in the second transfer unit can be effectively suppressed.

  According to the image forming apparatus of the fifth aspect of the present invention, the length of the belt disposed between the first transfer member and the transfer nip portion is disposed between the power feeding portion and the transfer nip portion. The current flowing from the second transfer means side to the first transfer means side can be suppressed regardless of the material of the first transfer member, compared to the case where the length is not set longer than the length of the belt. Transfer defects in the transfer unit can be effectively suppressed.

  According to the image forming apparatus of the sixth aspect of the present invention, the transfer defect in the second transfer unit is effectively suppressed as compared with the case where the charge removing unit for removing the charge on the surface of the facing member is not provided. be able to.

1 is a configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention. 1 is a configuration diagram illustrating a transfer device of an image forming apparatus according to an embodiment of the present invention. FIG. 7 is an explanatory diagram illustrating a secondary transfer mode of the transfer device of the image forming apparatus according to the embodiment of the present invention. FIG. 5 is an explanatory diagram illustrating a secondary transfer mode of a transfer device as a comparative example with respect to the transfer device of the image forming apparatus according to the embodiment of the present invention. FIG. 6 is an explanatory diagram for explaining a secondary transfer mode of the transfer device of the image forming apparatus according to the embodiment of the present invention using an equivalent circuit.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, embodiments of an image forming apparatus according to the invention will be described with reference to the accompanying drawings.

(overall structure)
As illustrated in FIG. 1, an image processing unit 12 that performs image processing on input image data is provided inside the apparatus main body 10 </ b> A of the image forming apparatus 10.

  The image processing unit 12 processes the input image data into gradation data of four colors of yellow (Y), magenta (M), cyan (C), and black (K). An exposure device 14 that receives the gradation data and performs image exposure with the laser beam LB is provided in the center of the apparatus main body 10A.

  Above the exposure device 14, four image forming units 16Y, 16M, 16C, and 16K of yellow (Y), magenta (M), cyan (C), and black (K) are spaced substantially horizontally. Arranged. Hereinafter, when it is not necessary to distinguish between Y, M, C, and K, Y, M, C, and K are omitted.

  These four image forming units 16Y, 16M, 16C, and 16K are all configured in the same manner. A cylindrical image carrier 18 that is rotationally driven at a predetermined speed, and an outer periphery of the image carrier 18. The electrostatic latent image formed on the outer peripheral surface of the image holding member 18 by the image exposure of the exposure device 14 and the primary charging member 20 for charging the surface is developed with toner of a predetermined color. A developing device 22 that visualizes the toner image and a cleaning blade 24 that cleans the outer peripheral surface of the image carrier 18 are included. A cleaning member 64 that contacts the cylindrical charging member 20 and cleans the outer peripheral surface of the charging member 20 is provided below the charging member 20.

  In addition, the exposure apparatus 14 is provided with four semiconductor lasers (not shown) that are configured in common to the four image forming units 16Y, 16M, 16C, and 16K. From these semiconductor lasers, laser light LB-Y, LB-M, LB-C, and LB-K are emitted according to the gradation data.

  The laser beams LB-Y, LB-M, LB-C, and LB-K emitted from the semiconductor laser are irradiated to a polygon mirror 26, which is a rotating polygon mirror, through an f-θ lens (not shown). The mirror 26 is deflected and scanned. The laser beams LB-Y, LB-M, LB-C, and LB-K deflected and scanned by the polygon mirror 26 pass through the imaging lens (not shown) and a plurality of mirrors on the image carrier 18. The exposure point is scanned and exposed from obliquely below.

  Further, the exposure apparatus 14 is hermetically sealed by a rectangular parallelepiped frame 28. In the upper part of the frame 28, four laser beams LB-Y, LB-M, LB-C, and LB-K are directed onto the image carriers 18 of the image forming units 16Y, 16M, 16C, and 16K. And transparent glass windows 30Y, 30M, 30C, and 30K are provided.

  On the other hand, a transfer unit 21 is provided above the image forming units 16Y, 16M, 16C, and 16K. The transfer unit 21 includes an endless intermediate transfer belt 32, two suspension rolls 36 and 40 that suspend the intermediate transfer belt 32, a cleaning blade 38 that cleans the outer peripheral surface of the intermediate transfer belt 32, Primary transfer rolls 34Y, 34M, 34C, 34K disposed on the opposite side of the image carriers 18Y, 18M, 18C, 18K across the transfer belt 32. The suspension roll 36 is configured as a tension applying roll that applies tension to the intermediate transfer belt 32, and the suspension roll 40 is configured as a drive roll that rotates and rotates the intermediate transfer belt 32 in the arrow direction.

  Yellow (Y), magenta (M), and cyan (C) sequentially formed on the image carrier 18 of the image forming units 16Y, 16M, 16C, and 16K by the four primary transfer rolls 34Y, 34M, 34C, and 34K. , Black (K) toner images are transferred onto the intermediate transfer belt 32 in a multiple manner.

  A secondary transfer roll 42 is provided on the opposite side of the suspension roll 40 across the intermediate transfer belt 32. The yellow (Y), magenta (M), cyan (C), and black (K) toner images transferred onto the intermediate transfer belt 32 in a multiple manner are conveyed by the intermediate transfer belt 32 and are connected to the suspension roll 40. The sheet is sandwiched between the next transfer rolls 42 and is secondarily transferred to a sheet member P as an example of a recording medium conveyed along the conveyance path 56.

  Further, a fixing device 44 that fixes the toner image transferred to the sheet member P to the sheet member P by heat and pressure is provided on the downstream side in the transport direction of the sheet member P with respect to the secondary transfer roll 42.

  Further, on the downstream side of the fixing device 44, a discharge roll 46 for discharging the sheet member P on which the toner image is fixed to a discharge portion 48 provided on the upper portion of the apparatus main body 10A of the image forming apparatus 10 is provided.

  On the other hand, a sheet feeding member 50 on which the sheet members P are stacked is provided on the lower side in the apparatus main body 10A of the image forming apparatus 10. Further, a sheet feeding roll 52 for feeding the sheet members P stacked on the sheet feeding member 50 to the conveyance path 56 is provided, and the sheet members P are separated and conveyed one by one on the downstream side of the sheet feeding roll 52. A separation roll 54 is provided. Further, an alignment roll 58 for adjusting the conveyance timing is provided on the downstream side of the separation roll 54. Thus, the sheet member P supplied from the sheet feeding member 50 is moved to a position (secondary transfer position) where the intermediate transfer belt 32 and the secondary transfer roll 42 are in contact with each other by the alignment roll 58 that rotates at a predetermined timing. It is configured to be sent out.

  Further, next to the discharge roll 46, the sheet member P on which the image is fixed on one side by the fixing device 44 is not discharged onto the discharge unit 48 as it is by the discharge roll 46 but is conveyed to the double-side conveyance path 62. A roll 60 is provided. As a result, the sheet member P conveyed along the double-sided conveyance path 62 is conveyed again to the alignment roll 58 with the front and back sides reversed, and this time, the toner image is transferred to the back surface of the sheet member P. It is fixed and discharged onto the discharge unit 48.

  With this configuration, an image is formed on the sheet member P as follows.

  First, gradation data of each color is sequentially output from the image processing unit 12 to the exposure device 14, and the laser beams LB-Y, LB-M, LB-C, and LB emitted according to the gradation data from the exposure device 14 are output. -K is scanned and exposed on the outer peripheral surface of the image carrier 18 charged by the charging member 20, and an electrostatic latent image is formed on the outer peripheral surface of the image carrier 18. The electrostatic latent images formed on the image holding member 18 are yellow (Y), magenta (M), cyan (C), and black (K) toners by developing devices 22Y, 22M, 22C, and 22K, respectively. Visualized as an image.

  Further, yellow (Y), magenta (M), magenta (M), and magenta (M) formed on the image carrier 18 by the primary transfer roll 34 of the transfer unit 21 disposed above the image forming units 16Y, 16M, 16C, and 16K. Cyan (C) and black (K) toner images are transferred in multiple onto the rotating intermediate transfer belt 32.

  Further, the toner images of the respective colors transferred in a multiple manner on the rotating intermediate transfer belt 32 are transported by the secondary transfer roll 42 from the paper feed member 50 to the paper feed roll 52, the separation roll 54, and the alignment roll 58. Are secondarily transferred to the sheet member P conveyed at a predetermined timing.

  Further, the sheet member P to which the toner image has been transferred is conveyed to the fixing device 44. The toner image transferred to the sheet member P is fixed on the sheet member P by the fixing device 44 and fixed, and then discharged to the discharge portion 48 provided on the upper portion of the apparatus main body 10A of the image forming apparatus 10 by the discharge roll 46. Is done.

  Further, when images are formed on both sides of the sheet member P, the sheet member P, on which the image is fixed on one side by the fixing device 44, is not directly discharged onto the discharge unit 48 by the discharge roll 46, and the conveyance direction is switched. Then, the sheet is conveyed to the double-sided conveyance path 62 via the conveyance roll 60. Then, by conveying the sheet member P along the duplex conveyance path 62, the front and back of the sheet member P are reversed, and the sheet member P is conveyed again to the alignment roll 58. This time, the toner image is transferred / fixed on the back surface of the sheet member P, transferred and fixed, and then discharged onto the discharge portion 48 by the discharge roll 46.

(Main part configuration)
The transfer device 100 included in the image forming apparatus 10 will be described again. As shown in FIG. 2, the transfer device 100 is formed on an intermediate transfer belt 32 as an example of a movable belt and an image holding member 18. Primary transfer means (first transfer means) 102 for primary transfer of the toner image to the intermediate transfer belt 32, and secondary transfer means (secondary transfer means for secondary transfer of the toner image primarily transferred to the intermediate transfer belt 32 to the sheet member P). Second transfer means) 104.

The intermediate transfer belt 32 is made of a semiconductive material having a volume electrical resistivity of 1 × 10 ¹⁰ Ω · cm, for example.

  The primary transfer unit 102 includes a primary transfer roll 34 as an example of a first transfer member disposed opposite to the image carrier 18 so as to sandwich the intermediate transfer belt 32 with the image carrier 18, and a primary transfer roller 34. A primary transfer power supply unit 106 that supplies electric power for primary transfer at a primary transfer nip N1 formed by sandwiching the intermediate transfer belt 32 between the roll 34 and the image carrier 18. .

  2 shows the primary transfer unit 102 of black K that is arranged closest to the secondary transfer unit 104 among the colors, but the same applies to the primary transfer unit 102 of other colors. In the following, the primary transfer unit 102 having the primary transfer roll 34 and the primary transfer power supply unit 106 will be described with reference to black K as a representative.

  The primary transfer roll 34 is composed of a conductive mandrel 34a and a semiconductive foaming rubber material 34b provided therearound. The positive pole of the primary transfer power supply unit 106 is connected to the mandrel 34a of the primary transfer roll 34, whereby the intermediate transfer belt 32 in the vicinity of the primary transfer nip N1 of the foamed rubber material 34b is positively charged. In the primary transfer nip portion N <b> 1, negatively charged toner moves from the image carrier 18 to the intermediate transfer belt 32 by electrostatic action, so that the toner image is primarily transferred from the image carrier 18 to the intermediate transfer belt 32. The

  The primary transfer current I1 flows through the primary transfer power supply unit 106 → the mandrel 34a → the foam rubber material 34b → the intermediate transfer belt 32, charges the intermediate transfer belt 32 positively, transfers the toner, and is charged by the charging member 20. The surface charge of the image carrier 18 is canceled.

  The secondary transfer unit 104 is opposed to the secondary transfer roll 42 as an example of a second transfer member provided on the downstream side of the primary transfer unit 102 in the moving direction of the intermediate transfer belt 32, and the secondary transfer roll 42. A secondary transfer nip formed by inserting the intermediate transfer belt 32 and the sheet member P between the secondary transfer roll 42 and the suspension roll 40. It is configured that the toner image primarily transferred to the intermediate transfer belt 32 is secondarily transferred to the sheet member P by supplying power for performing the secondary transfer to the portion N2.

  The suspension roll 40 is one of the two suspension rolls 36 and 40 that suspend the intermediate transfer belt 32, but faces the secondary transfer roll 42 for forming the secondary transfer nip portion N2. Therefore, the suspension roll 40 is hereinafter referred to as “secondary transfer counter roll 40”.

The secondary transfer roll 42 includes a conductive mandrel 42a and a semiconductive foaming rubber material 42b provided around the secondary metal roll 42a. The foamed rubber material 42b has a volume electrical resistivity (for example, 1 × 10 ⁸ Ω · cm) that is smaller than the volume electrical resistivity (for example, 1 × 10 ¹⁰ Ω · cm) of the intermediate transfer belt 32.

The secondary transfer facing roll 40 is made of an insulating material. Here, the insulating material is a volume electrical resistivity (for example, 1 × 10 ^{12 to 13} Ω · cm) that is 100 to 1000 times larger than the volume electrical resistivity (for example, 1 × 10 ¹⁰ Ω · cm) of the intermediate transfer belt 32. A high resistance material having

  In the vicinity of the secondary transfer facing roll 40, a static eliminating cloth 108 as an example of a charge removing unit is provided. The neutralizing cloth 108 is provided so that one end thereof is in contact with the secondary transfer opposing roll 40 at a position upstream of the secondary transfer nip N2 in the rotation direction of the secondary transfer opposing roll 40, and the other end is provided. Connected to ground. The charge removal cloth 108 removes electric charges on the surface of the secondary transfer counter roll 40. A non-contact type may be used as the charge removing means.

  A power feeding unit 110 is provided on the downstream side of the secondary transfer nip N2 in the moving direction of the intermediate transfer belt 32. The power supply unit 110 includes a counter roll 112 provided in contact with the inner peripheral surface of the intermediate transfer belt 32 so as to face the cleaning blade 38, and a secondary transfer power supply unit 114 connected to the counter roll 112. Yes. The facing roll 112 is made of a conductive material such as a metal material. A negative pole of the secondary transfer power supply unit 114 is connected to the facing roll 112. The power feeding unit 110 supplies power for performing secondary transfer from the secondary transfer power supply unit 114 to the secondary transfer nip N2 through the opposing roll 112 and the intermediate transfer belt 32.

  As shown in FIG. 3, in the transfer device 100 of the present embodiment, a power feeding unit 110 is provided on the downstream side of the secondary transfer nip portion N <b> 2 and power is supplied to the secondary transfer nip portion N <b> 2 through the intermediate transfer belt 32. Therefore, the intermediate transfer belt 32 disposed between the power feeding unit 110 (specifically, the opposing roll 112) and the secondary transfer nip N2 is negatively charged. Along with this, the outer peripheral surface (the outer peripheral surface in the vicinity of the secondary transfer nip portion N2 and its upstream side) of the foamed rubber material 42b of the secondary transfer roll 42 facing through the secondary transfer nip portion N2 is positively charged. . As a result, in the secondary transfer nip N2, negatively charged toner moves from the intermediate transfer belt 32 to the sheet member P by electrostatic action, and the toner image is secondary transferred from the intermediate transfer belt 32 to the sheet member P. Is done.

  The core 42a of the secondary transfer roll 42 is grounded, and the secondary transfer current I2 is calculated from the core 42a → fired rubber material 42b → sheet member P → intermediate transfer belt 32 → opposed roll 112 → secondary transfer power supply unit. 114 flows through.

  FIG. 4 is an explanatory diagram illustrating a secondary transfer mode of the transfer apparatus 200 as a comparative example with respect to the transfer apparatus 100 according to the present embodiment.

  The secondary transfer facing roll 202 of the transfer device 200 is composed of a conductive mandrel 202a and a semiconductive foamed rubber material 202b provided around the cored bar 202a. The negative pole of the secondary transfer power supply unit 114 is connected to the core metal 202 a of the secondary transfer facing roll 202. Thereby, the outer peripheral surface of the foamed rubber material 202b is negatively charged. Along with this, the outer peripheral surface (the outer peripheral surface in the vicinity of the secondary transfer nip N2 and its upstream and downstream sides) of the foamed rubber material 42b of the secondary transfer roll 42 facing through the secondary transfer nip N2 is positively charged. The The secondary transfer current I2 flows through the core metal 42a → the foamed rubber material 42b → the sheet member P → the intermediate transfer belt 32 → the foamed rubber material 202b → the core metal 202a → the secondary transfer power supply unit 114.

  Here, in the transfer device 200, since the secondary transfer power supply unit 114 is provided on the secondary transfer counter roll 202 to charge the outer peripheral surface of the secondary transfer counter roll 202, the secondary transfer nip N2 Between the secondary transfer roll 42 and the secondary transfer counter roll 202 on the upstream side in the conveying direction of the sheet member P, an electric field E to the extent that discharge (Paschen discharge) 204 occurs due to the sheet member P interposed therebetween. Has occurred.

  When the discharge 204 occurs, the cations generated by the discharge 204 adhere to the toner particles and charge some toner particles to a positive polarity having a reverse polarity. As a result, toner particles that should be secondarily transferred to the sheet member P at the secondary transfer nip portion N2 remain attached to the intermediate transfer belt 32, and the sheet member P has an image defect (transfer defect) 206 called white spot. Arise.

  In particular, during double-sided printing, since the sheet member P passes through the fixing device 44 once and is dried to increase resistance, the power (secondary transfer voltage) supplied to the secondary transfer nip portion N2 is set high. In this case, a strong electric field E is generated between the secondary transfer roll 42 on the upstream side of the secondary transfer nip portion N2 and the secondary transfer counter roll 202. For this reason, the discharge 204 is likely to occur, and the image defect 206 is likely to occur.

  On the other hand, as shown in FIG. 3, in the transfer apparatus 100 according to the present embodiment, the power feeding unit 110 is provided on the downstream side of the secondary transfer nip portion N <b> 2 and power is supplied to the secondary transfer nip portion N <b> 2 through the intermediate transfer belt 32. Therefore, the amount of charge on the upstream side of the secondary transfer nip portion N2 is suppressed, and an electric field E is generated between the secondary transfer roll 42 and the secondary transfer counter roll 40. It is supposed to be suppressed. That is, it is possible to suppress the toner from being charged to a reverse polarity due to the electric field E generated on the upstream side of the secondary transfer nip portion N2.

  Further, since the secondary transfer counter roll 40 also functions as a suspension roll 40 for suspending the intermediate transfer belt 32, it is in contact with the intermediate transfer belt 32 over a half circumference. However, since the secondary transfer facing roll 40 is made of an insulating material, energization to the secondary transfer facing roll 40 is suppressed. Therefore, it is possible to prevent the outer peripheral surface of the secondary transfer counter roll 40 from being negatively charged, and as a result, between the secondary transfer roll 42 and the secondary transfer counter roll 40 on the upstream side of the secondary transfer nip portion N2. Generation of the electric field E is further suppressed. That is, the toner is further suppressed from being charged to a reverse polarity due to the electric field E generated on the upstream side of the secondary transfer nip N2.

  Further, since the secondary transfer counter roll 40 is provided with the charge removal cloth 108 on the upstream side of the secondary transfer nip portion N2 in the rotation direction, the outer peripheral surface of the secondary transfer counter roll 40 may be negatively charged. Even if it exists, the negative charge on the outer peripheral surface of the secondary transfer opposite roll 40 is removed by the static eliminating cloth 108. As a result, the generation of an electric field E between the secondary transfer roll 42 and the secondary transfer counter roll 40 on the upstream side of the secondary transfer nip portion N2 is further suppressed. That is, the toner is further suppressed from being charged to a reverse polarity due to the electric field E generated on the upstream side of the secondary transfer nip N2.

  FIG. 5 is an explanatory diagram for explaining the secondary transfer mode of the transfer apparatus 100 of the present embodiment using an equivalent circuit. Reference numeral 116 in the drawing indicates a contact position where the opposing roll 112 of the power supply unit 110 and the intermediate transfer belt 32 are in contact with each other. RbX indicates the resistance of the intermediate transfer belt 32 disposed between the contact position 116 and the secondary transfer nip portion N2. RbY indicates the resistance of the intermediate transfer belt 32 disposed between the primary transfer nip N1 (the primary transfer nip N1 of the black K primary transfer unit 102) and the secondary transfer nip N2. R1 indicates the resistance of the primary transfer roll 34 (mainly foamed rubber material 34b), and R2 indicates the resistance of the secondary transfer roll 42 (mainly foamed rubber material 42b) and the sheet member P.

  X schematically shows the length of the belt disposed between the contact position 116 and the secondary transfer nip portion N2 on the equivalent circuit. Y schematically shows the length of the belt disposed between the primary transfer nip portion N1 and the secondary transfer nip portion N2 on an equivalent circuit.

  In the transfer device 100 of the present embodiment, the resistance R2 is set smaller than the resistance RbX. That is, the voltage drop at the intermediate transfer belt 32 disposed between the contact position 116 and the secondary transfer nip portion N2 is set to be larger than the voltage drop at the secondary transfer roll 42, and the secondary transfer roll The potential induced on the outer peripheral surface 42 is reduced (the positive charge amount on the outer peripheral surface is reduced).

  For this reason, generation of an electric field E between the secondary transfer roll 42 and the secondary transfer counter roll 40 on the upstream side of the secondary transfer nip portion N2 is further suppressed. In addition, since the potential at the secondary transfer nip portion N2 is low, even if the intermediate transfer belt 32 is made of a semiconductive material, the flowing current from the primary transfer unit 102 side to the secondary transfer unit 104 side The generation of I12 is suppressed.

  Further, in the transfer apparatus 100 of the present embodiment, the total resistance of the resistor R1 and the resistor RbY is set larger than the resistor RbX. Therefore, the generation of the flowing current I21 from the secondary transfer unit 104 side to the primary transfer unit 102 side is suppressed.

  Further, in the transfer apparatus 100 of the present embodiment, the length Y of the belt disposed between the primary transfer nip portion N1 and the secondary transfer nip portion N2 is set between the contact position 116 and the secondary transfer nip portion N2. Is set to be longer than the length X of the belt disposed on the belt. Therefore, even if the primary transfer roll 34 is made of a low resistance material (for example, a metal material), the relationship of resistance RbY> resistance RbX is established, and the flowing current I21 from the secondary transfer means 104 side to the primary transfer means 102 side is The generation is suppressed.

  In the transfer device 100 of the present embodiment, the secondary transfer roll 42 is used as the secondary transfer member, but a belt-like member that can be conveyed while adsorbing the sheet member P may be used.

  Further, in the transfer apparatus 100 of the present embodiment, as shown in FIG. 1, the intermediate transfer belt 32 is suspended by two axes of a suspension roll 36 and a secondary transfer counter roll 40 in order to reduce the size of the entire apparatus. At the same time, the rolls are arranged so that the axes of the suspension roll 36, the secondary transfer opposite roll 40, and the secondary transfer roll 42 are aligned in a straight line, and in a direction substantially perpendicular to the plane including the axis of the rolls The conveyance path 56 is arranged so that the sheet member P is conveyed. In such an arrangement relationship, the discharge 204 is likely to occur because the sheet member P is interposed on the upstream side of the secondary transfer nip N2. Therefore, by configuring as in the present invention, it is possible to reduce the overall size of the apparatus and suppress the toner from being charged to the reverse polarity due to the electric field generated upstream of the transfer nip portion of the secondary transfer unit. It becomes possible.

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 14 Exposure apparatus 16 Image forming unit 18 Image holding body 20 Charging member 21 Transfer unit 22 Developing apparatus 32 Intermediate transfer belt (an example of belt)
34 Primary transfer roll (an example of a first transfer member)
34a Mandrel 34b Foamed rubber material 36 Suspension roll 38 Cleaning blade 40 Suspension roll, secondary transfer facing roll (an example of facing member)
42 Secondary transfer roll (example of second transfer member)
42a Mandrel 42b Foamed rubber material 44 Fixing device 56 Conveyance path 62 Conveyance path 100 for both sides Transfer device 102 Primary transfer means (first transfer means)
104 Secondary transfer means (second transfer means)
106 Primary transfer power supply unit 108 Neutralizing cloth (an example of charge removing means)
110 Power feeding unit 112 Opposite roll 114 Secondary transfer power source unit 116 Contact position 204 Discharge 206 Image defect E Electric field I1 Primary transfer current I2 Secondary transfer current I12 Inflow current I21 Inflow current N1 Primary transfer nip N2 Secondary transfer nip P Sheet Member (an example of a recording medium)
R1 resistor R2 resistor RbX resistor RbY resistor

Claims (6)

An image carrier on which an electrostatic latent image is formed;
A developing device for developing the electrostatic latent image formed on the image carrier;
A belt that can move around, and
A first transfer member comprising a first transfer member, and transferring a toner image on the image carrier developed by the developing device to the belt;
A second transfer member provided on the downstream side of the first transfer means in the moving direction of the belt, and an opposing member provided to face the second transfer member, the second transfer member and the Electric power for secondary transfer is supplied to the transfer nip formed by inserting the belt and the recording medium between the opposing members, and the toner image primarily transferred to the belt in the transfer nip. Second transfer means for secondary transfer to the recording medium;
A power feeding unit that is provided in contact with the belt on the downstream side of the transfer nip in the moving direction of the belt, and supplies power to the transfer nip through the belt;
An image forming apparatus. The belt is suspended around a plurality of suspension rolls and is movable around,
The image forming apparatus according to claim 1, wherein the facing member serves as one of the plurality of suspension rolls and is made of an insulating material.   The image forming apparatus according to claim 1, wherein a resistance of the second transfer member is set to be smaller than a resistance of a belt disposed between the power feeding unit and the transfer nip portion. The first transfer unit includes the first transfer member disposed so as to sandwich the belt with the image carrier.
A total resistance of the resistance of the first transfer member and the resistance of the belt disposed between the first transfer member and the transfer nip portion is disposed between the power feeding portion and the transfer nip portion. The image forming apparatus according to claim 3, wherein the image forming apparatus is set to be larger than a resistance of the belt to be applied. The first transfer unit includes the first transfer member disposed so as to sandwich the belt with the image carrier.
The length of the belt disposed between the first transfer member and the transfer nip portion is set longer than the length of the belt disposed between the power feeding portion and the transfer nip portion. Item 4. The image forming apparatus according to Item 3.   The image forming apparatus according to claim 1, further comprising a charge removing unit that removes charges on the surface of the facing member.

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