Image forming apparatus and charge adjustment device

Abstract

To provide a configuration that can stably adjust electric charges on a sheet for a long period.SOLUTION: A charge adjustment device 9 adjusts electric charges on a sheet to which a toner image is fixed by a fixing device 7. The charge adjustment device 9 has an upper charge adjustment roller 900, a lower charge adjustment roller 910, an upper power feed roller 901, and a power feed high voltage 90. The upper power feed roller 901 has a core grid 902 that has conductivity, and an elastic layer 903 that is formed on an outer periphery of the core grid 902 and includes ion conductive material, and is electrically floated. The lower charge adjustment roller 910 is arranged to sandwich the sheet with the upper charge adjustment roller 900. The upper power feed roller 901 can be in contact with the upper charge adjustment roller 900 to supply current to the upper charge adjustment roller 900. The power feed high voltage 90 can apply, to the upper power feed roller 901, a voltage having one of a positive polarity and a negative polarity.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, and a multifunction machine having a plurality of these functions, and a charge adjusting device.

Background Art

[0002] In an image forming apparatus, a toner image formed in an image forming unit is transferred to a sheet in a transfer unit, and after the toner image is fixed to the sheet in a fixing unit, the sheet is stacked on a discharge tray or the like. At this time, the sheets may stick to each other due to the electrostatic force between the sheets. For this reason, a configuration including a charge adjusting unit that applies a voltage to a sheet on which a toner image has been fixed by a fixing unit to adjust the charge of the sheet has been proposed (Patent Document 1).

[0003] In Patent Document 1, the charge adjusting unit includes a pair of conductive rubber rollers arranged opposite to each other and a power source that applies a voltage to the conductive rubber rollers, and applies a voltage to a sheet passing through the nip portion of the pair of conductive rubber rollers.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, when a roller containing an ion conductive material is used as the conductive rubber roller, the resistance of the roller increases due to energization, so there is a risk that the charge adjustment of the sheet cannot be stably performed over a long period.

[0006] An object of the present invention is to provide a configuration capable of stably adjusting the charge of a sheet over a long period.

Means for Solving the Problems

[0007] The image forming apparatus of the present invention comprises a transfer unit for transferring a toner image onto a sheet, a fixing unit for heating and pressurizing the sheet onto which the toner image has been transferred in the transfer unit to fix the toner image to the sheet, and a charge adjustment unit for adjusting the charge on the sheet onto which the toner image has been fixed in the fixing unit, wherein the charge adjustment unit comprises a first roller having a conductive shaft portion and an outer peripheral portion including an ion-conductive material formed on the outer circumference of the shaft portion and being electrically floating, a second roller arranged to sandwich a sheet between itself and the first roller, a power supply rotating body that contacts the first roller and can supply current to the first roller, and a power supply capable of applying a voltage of one of positive or negative polarity to the power supply rotating body.

[0008] The image forming apparatus of the present invention comprises a transfer unit for transferring a toner image onto a sheet, a fixing unit for heating and pressurizing the sheet onto which the toner image has been transferred in the transfer unit to fix the toner image onto the sheet, and a charge adjustment unit for adjusting the charge on the sheet onto which the toner image has been fixed in the fixing unit, wherein the charge adjustment unit has a conductive shaft portion and an outer peripheral portion including an ion-conductive material formed on the outer circumference of the shaft portion, and is grounded to a first roller, a metal second roller arranged to sandwich a sheet between itself and the first roller, a power supply rotating body that contacts the first roller and can supply current to the first roller, a first power supply capable of applying a voltage of one of positive and negative polarity to the power supply rotating body, and a second power supply capable of applying a voltage of one of positive and negative polarity to the second roller.

[0009] The charge adjustment device of the present invention is a charge adjustment device for adjusting the charge on a sheet, and is characterized by comprising: a first roller having a conductive shaft portion and an outer peripheral portion including an ion-conductive material formed on the outer circumference of the shaft portion and being electrically floating; a second roller arranged to sandwich a sheet between itself and the first roller; a power supply rotating body that contacts the first roller and is capable of supplying current to the first roller; and a power supply capable of applying a voltage of one of positive or negative polarity to the power supply rotating body.

[0010] The charge adjustment device of the present invention is a charge adjustment device for adjusting the charge on a sheet, and is characterized by comprising: a grounded first roller having a conductive shaft portion and an outer peripheral portion including an ion-conductive material formed on the outer circumference of the shaft portion; a metal second roller arranged to sandwich the sheet between itself and the first roller; a power supply rotating body that contacts the first roller and is capable of supplying current to the first roller; a first power supply capable of applying a voltage of one of positive and negative polarity to the power supply rotating body; and a second power supply capable of applying a voltage of one of positive and negative polarity to the second roller. [Effects of the Invention]

[0011] According to the present invention, the charge of the sheet can be stably adjusted over a long period of time. [Brief explanation of the drawing]

[0012] [Figure 1] A schematic cross-sectional view of the image forming apparatus according to the first embodiment. [Figure 2] A schematic cross-sectional view of the image forming unit according to the first embodiment. [Figure 3] A schematic cross-sectional view of the charge adjustment device according to the first embodiment. [Figure 4] A schematic cross-sectional view of the charge adjustment device relating to a comparative example. [Figure 5] (a) A schematic cross-sectional view showing the charge adjustment device according to Example 1, and (b) a graph showing the measurement results of the voltage fluctuation of the charge adjustment device according to Example 1. [Figure 6] A schematic cross-sectional view of the charge adjustment device according to Modification 1 of the first embodiment. [Figure 7] A schematic cross-sectional view of the charge adjustment device according to a modified example 2 of the first embodiment. [Figure 8] A schematic cross-sectional view of the charge adjustment device according to the second embodiment. [Figure 9] (a) A schematic cross-sectional view of the charge adjustment device according to Example 2, and (b) a graph showing the measurement results of the voltage fluctuation of the charge adjustment device according to Example 2. [Figure 10] Schematic cross-sectional view of a charge adjustment device according to Modification 3 of the Second Embodiment. [Figure 11] Schematic cross-sectional view of a charge adjustment device according to Modification 4 of the Second Embodiment. [Figure 12] Schematic cross-sectional view of a charge adjustment device according to Modification 5 of the Second Embodiment. [Figure 13] Graph showing the relationship between the charge removal current and the external power supply current in Example 3.

Mode for Carrying Out the Invention

[0013] <First Embodiment> The first embodiment will be described with reference to FIGS. 1 to 7. First, the schematic configuration of the image forming apparatus of the present embodiment will be described with reference to FIGS. 1 and 2.

[0014] [Image Forming Apparatus] As shown in FIG. 1, the image forming apparatus 100 of the present embodiment is a laser beam printer that forms a full-color image on a sheet P (paper, OHP sheet, cloth, etc.) as a recording material using an electrophotographic method. The image forming apparatus 100 is an intermediate transfer type tandem type in which image forming units Pa, Pb, Pc, and Pd, which are yellow, magenta, cyan, and black toner image forming means, are arranged along an intermediate transfer belt 51.

[0015] The image forming units Pa, Pb, Pc, and Pd each comprise an image carrier that holds an electrostatic latent image and a photosensitive drum 1a, 1b, 1c, and 1d, respectively. In the image forming unit Pa, a yellow toner image is formed on the photosensitive drum 1a and primary transferred to an intermediate transfer belt 51, which acts as an intermediate transfer body. In the image forming unit Pb, a magenta toner image is formed on the photosensitive drum 1b and primary transferred over the yellow toner image on the intermediate transfer belt 51. In the image forming units Pc and Pd, cyan toner images and black toner images are formed on the photosensitive drums 1c and 1d, respectively, and are sequentially primary transferred over the toner images on the intermediate transfer belt 51. In this embodiment, the photosensitive drums and intermediate transfer belts serve as image carriers that hold toner images.

[0016] The four toner images, which have been primarily transferred to the intermediate transfer belt 51, are then collectively transferred to a sheet P fed into the secondary transfer section N2, which is formed by the intermediate transfer belt 51 and the secondary transfer roller 56. The sheet P, on which the toner images have been secondarily transferred in the secondary transfer section N2, is heated and pressurized in the fixing device 7, which acts as a fixing unit, to fix the toner images to its surface. After this, the sheet P is discharged to the outside and stacked on a discharge tray (not shown).

[0017] The feeding device 8 separates the sheets P, which have been pulled out from the cassette 81 by the pickup roller 82, one by one using the separation device 83, and sends them to the register roller 84. The register roller 84 receives the sheets P in a stationary state and waits, and then sends the sheets P to the secondary transfer section N2 in time with the toner image on the intermediate transfer belt 51.

[0018] The intermediate transfer unit 5 rotates an intermediate transfer belt 51, which is an example of an image carrier, in the direction of arrow R2 by stretching it over the drive roller 52, support rollers 58 and 59, tension roller 53, and opposing roller 54. The opposing roller 54 is positioned opposite the secondary transfer roller 56 via the intermediate transfer belt 51. The outer surface of the intermediate transfer belt 51 stretched over the opposing roller 54 and the secondary transfer roller 56 form a secondary transfer section N2 that nips the sheet.

[0019] Furthermore, the secondary transfer roller 56 is connected to the power supply D2, and a secondary transfer bias is applied. When performing secondary transfer, a high-voltage positive (positive polarity) transfer voltage (secondary transfer bias) is applied to the secondary transfer roller 56, thereby electrostatically attracting the negatively charged toner image to the sheet. As a result, the toner image supported on the intermediate transfer belt 51 is transferred to the sheet P as it passes through the secondary transfer section N2.

[0020] The fixing device 7 forms a heating nip section by pressing a pressure roller 73 against a fixing roller 72, which is positioned around a lamp heater 71. In the heating nip section, the sheet P, onto which the toner image has been transferred in the secondary transfer section N2, is heated and pressurized to fix the toner image to the sheet P. After the fixing process, the sheet P is discharged outside the machine by a discharge roller 85, which acts as a discharge section, and loaded onto a discharge tray or the like.

[0021] The belt cleaning device 57 rubs a cleaning blade against the intermediate transfer belt 51 to remove residual transfer toner, paper dust, etc. remaining on the surface of the intermediate transfer belt 51 from which the sheet P has been separated after passing through the secondary transfer section N2.

[0022] The image forming units Pa, Pb, Pc, and Pd are configured almost identically, except that the toner colors used by the developing units 4a, 4b, 4c, and 4d attached to the photosensitive drums 1a, 1b, 1c, and 1d, respectively, differ (yellow, magenta, cyan, and black). In the following description, the image forming unit Pa will be explained with reference to Figure 2, and the other image forming units Pb, Pc, and Pd will be described by replacing the 'a' at the end of the symbols with 'b', 'c', and 'd', respectively.

[0023] As shown in Figure 2, the image forming unit Pa has a charging roller 2a, exposure device 3a, developing device 4a, primary transfer roller 55a, and cleaning device 6a arranged around the photosensitive drum 1a. The photosensitive drum 1a has an organic photoconductor layer (OPC) with negative charge polarity formed on the outer surface of an aluminum cylinder and rotates in the direction of arrow R1 at a process speed of 240 mm / sec.

[0024] The charging roller 2a, which is a charging component, is formed by covering the surface of a metallic central shaft with a resistive elastic layer, and rotates in pressure against the photosensitive drum 1a. The power supply D3 applies a DC voltage superimposed on an AC voltage to the charging roller 2a, thereby charging the surface of the photosensitive drum 1a to a uniform negative potential.

[0025] The exposure apparatus 3a scans a laser beam, which is ON-OFF modulated with scan line image data obtained by unfolding a yellow separated color image, using a rotating mirror to write an electrostatic image of the image onto the surface of the charged photosensitive drum 1a.

[0026] The developing device 4a agitates a two-component developer, which is a mixture of non-magnetic toner and magnetic carrier, to charge the non-magnetic toner to a negative polarity and the magnetic carrier to a positive polarity. The charged two-component developer is supported in a pile-like manner on the developing sleeve 41a, which rotates in the counter direction around the fixed magnetic pole 42a and rubs against the photosensitive drum 1a. The power supply D4 applies a developing voltage to the developing sleeve 41a, which is a negative polarity DC voltage superimposed with an AC voltage, to move the toner to the exposure area of ​​the photosensitive drum 1a, which has become relatively more positive polarity than the developing sleeve 41a, and inverts the electrostatic image during development.

[0027] The primary transfer roller 55a, which is a primary transfer member, is pressed against the photosensitive drum 1a so as to sandwich the intermediate transfer belt 51, forming a primary transfer section N1a between the photosensitive drum 1a and the intermediate transfer belt 51. The power supply D1a is a transfer output unit that applies voltage to the primary transfer roller 55a, and applies a positive DC voltage of +900V as a primary transfer bias to the primary transfer roller 55a. As a result, the toner image, which is negatively charged and carried on the photosensitive drum 1a, is primary transferred to the intermediate transfer belt 51 passing through the primary transfer section N1a.

[0028] The primary transfer roller 55a has a resistance value of 1 × 10 when 2000V is applied. 2 ~10 8A semiconducting material with a resistance of Ω was used. Specifically, an ion-conductive sponge roller with an outer diameter of φ16 mm and a core diameter of φ8 mm, formed by a blend of nitrile rubber and ethylene-epichlorohydrin copolymer, was used. The resistance value of the primary transfer roller 55a was 1 × 10⁻¹⁰ when applied at a voltage of 2 kV in an environment of 23°C and 50% RH. 6 ~10 8 It's around Ω.

[0029] The cleaning device 6a rubs its cleaning blade against the photosensitive drum 1a to remove any remaining toner that has adhered to the surface of the photosensitive drum 1a after it has passed through the primary transfer section N1a.

[0030] In recent years, the variety of sheet types has increased, and the range of sheet thicknesses and electrical resistivity has also expanded, leading to the adoption of intermediate transfer methods. Furthermore, to avoid changes in the amount of charge supplied to the toner image due to differences in the image ratio in the main scanning direction and the width of the sheet, constant voltage control is employed in the transfer section (secondary transfer section in the above example) that transfers the toner image to the sheet. In addition, changes in ambient conditions such as temperature and humidity, or the accumulation of image formation, cause changes in the electrical resistance of the intermediate transfer belt and transfer rollers, as well as the film thickness of the surface layer of the photosensitive drum. In response to these changes, Active Transfer Voltage Control (ATVC) is performed to determine the control value of the constant voltage control prior to image formation in order to optimize the voltage applied to the transfer rollers during image formation.

[0031] ATVC control is a control method that applies multiple different test voltages to the secondary transfer roller 56 when there is no sheet in the secondary transfer section N, detects the current using a current sensing sensor at each transfer voltage to determine the relationship between the transfer voltage and the current, and sets the transfer voltage (secondary transfer bias) to be applied to the secondary transfer section N based on this. The control of the entire image forming apparatus 100, including this ATVC control, is performed by the control unit 110 (Figure 1).

[0032] The control unit 110 includes a CPU (Central Processing Unit), ROM (Read Only Memory), and RAM (Random Access Memory). The CPU controls each part while reading programs corresponding to control procedures stored in ROM. The RAM stores working data and input data, and the CPU performs control by referring to the data stored in RAM based on the aforementioned programs, etc.

[0033] [Adjusting the charge of the sheet] In this embodiment, in order to prevent the sheets loaded on the discharge tray from sticking together due to electrostatic force, a charge adjustment device 9 is positioned downstream of the fuser 7 in the sheet transport direction and upstream of the discharge roller 85 (Figure 1), as shown in Figure 3. The charge adjustment device 9 adjusts the charge on the sheets on which the toner image has been fixed by the fuser 7.

[0034] [Comparative Example] First, the configuration described in Patent Document 1 will be explained as a comparative example. The comparative example charge adjustment device 60 has a first conductive rubber roller 61 and a second conductive rubber roller 62 arranged opposite each other. The core metal 61a of the first conductive rubber roller 61 is connected to a power supply 63, and the second conductive rubber roller 62 is grounded. The power supply 63 applies a positive voltage to the first conductive rubber roller 61. When a positive voltage is applied to the first conductive rubber roller 61, a positive charge is applied to the second surface (back surface) P2 of the sheet P. In addition, an amount of negative charge equal to the positive charge applied from the first conductive rubber roller 61 is induced in the second conductive rubber roller 62, canceling out the positive charge on the first surface (front surface) P1 of the sheet P. The power supply 63 is constantly current controlled and applies a voltage controlled by a constant current at a predetermined current value to the sheet P. As a result, the charge on the sheet P is adjusted, and sticking of the sheet during loading can be suppressed.

[0035] However, if charge adjustment is performed by constant current control using the comparative example configuration shown in Figure 4, a constant charge adjustment current will continue to flow if one type of sheet is passed through continuously under a constant temperature and humidity environment. Furthermore, if the conductive rubber roller (charge adjustment roller) used contains at least an ionic conductive material and has a configuration in which electrical resistance increases with the amount of current flowing, measures such as increasing the applied voltage according to the usage time are required in order to impart the desired charge.

[0036] Generally, there is an upper limit to the high-voltage capacity of a power supply, so if the conditions of the comparative example are continued, a constant charge adjustment current cannot be supplied, and one must choose to either lower the charge adjustment current value or replace the charge adjustment roller. If the charge adjustment current value is lowered, the amount of charge on the sheet will naturally change, so the load capacity and other aspects will not be stable. If the charge adjustment roller is replaced, downtime and an increase in initial costs are unavoidable. Therefore, in this embodiment, the configuration of the charge adjustment device is as follows.

[0037] [Charge adjustment device of this embodiment] Figure 3 shows an explanatory diagram of the charge adjustment device 9 of this embodiment. The dashed line shows the transport path of the sheet P, and the charge adjustment device 9 is located downstream of the fixing device 7. The charge adjustment device 9 includes an upper charge adjustment roller 900 as a first roller, a lower charge adjustment roller 910 as a second roller, a power supply rotating body and an upper power supply roller 901 as a first power supply rotating body, a lower power supply roller 911 as a second power supply rotating body, a power supply and a high voltage power supply 90 as a first power supply, and a high voltage power supply 91 as a second power supply. The upper power supply roller 901, upper charge adjustment roller 900, lower charge adjustment roller 910, and lower power supply roller 911 are arranged in this order from top to bottom. Also, adjacent rollers are biased and in contact with each other by a spring member with a load of 1 kgf.

[0038] The upper charge adjustment roller 900 has a conductive shaft portion and a metal core (rotating shaft) 902 as a first shaft portion, and an outer peripheral portion formed on the outer circumference of the core 902 containing an ion-conductive material and an elastic layer 903 as a first outer peripheral portion. The lower charge adjustment roller 910 has a conductive second shaft portion, a metal core (rotating shaft) 912, and an elastic layer 913 formed on the outer circumference of the core 912 containing an ion-conductive material as a second outer peripheral portion.

[0039] These upper and lower charge adjustment rollers 900 and 910 are semiconducting rollers, and the elastic layers 903 and 913 are made of an ion-conductive material formed by a blend of nitrile rubber and ethylene-epichlorohydrin copolymer. Furthermore, the upper and lower charge adjustment rollers 900 and 910 are electrically floating. That is, the upper and lower charge adjustment rollers 900 and 910 are not directly connected to a power source and are not grounded.

[0040] Furthermore, the lower charge adjustment roller 910 is positioned to sandwich the sheet between the upper charge adjustment roller 900. Specifically, both ends of the core metal of either the upper charge adjustment roller 900's core metal 902 or the lower charge adjustment roller 910's core metal 912 are biased toward the other charge adjustment roller by a spring member, causing the elastic layers 903 and 913 to press against each other and form a nip portion. Therefore, the sheet that has passed through the fixing device 7 passes through the nip portion formed between the upper charge adjustment roller 900 and the lower charge adjustment roller 910.

[0041] The upper power supply roller 901 contacts the upper charge adjustment roller 900 and can supply current to the upper charge adjustment roller 900. The upper power supply roller 901 is biased toward the upper charge adjustment roller 900 by a spring member. The power supply high voltage 90 can apply a voltage of either positive or negative polarity to the upper power supply roller 901. In this embodiment, the power supply high voltage 90 applies a positive voltage to the upper power supply roller 901. In this embodiment, the power supply high voltage 90 is a constant voltage power supply. However, the power supply high voltage 90 may also be a constant current power supply.

[0042] The lower power supply roller 911 contacts the lower charge adjustment roller 910 and can supply current to the lower charge adjustment roller 910. The lower power supply roller 911 is biased toward the lower charge adjustment roller 910 by a spring member. The power supply high voltage 91 can apply a voltage of the other polarity of positive and negative polarity to the lower power supply roller 911. In this embodiment, the power supply high voltage 91 applies a negative voltage to the lower power supply roller 911. In this embodiment, the power supply high voltage 91 is a constant current power supply. However, the power supply high voltage 91 may also be a constant voltage power supply.

[0043] The power supply high voltage 90 and power supply high voltage 91 are controlled by the control unit 110. The control unit 110 determines the amount of charge to be applied to the sheet according to the coverage of both sides of the sheet (the ratio of the area of ​​the toner image to the area of ​​the sheet). For example, the control unit 110 calculates the coverage based on the image information formed on the sheet and determines whether or not to apply voltage to the sheet from the power supply high voltage 90 and power supply high voltage 91, and if so, the current value to be supplied from the power supply high voltage 90 and power supply high voltage 91. This makes it possible to adjust the charge appropriately according to the sheet coverage.

[0044] In this embodiment, by applying voltages from the high-voltage power supply 90 and the high-voltage power supply 91 to the upper power supply roller 901 and the lower power supply roller 911, respectively, a current flows between the upper charge adjustment roller 900 and the lower charge adjustment roller 910 in the direction of the arrow. At this time, the elastic layers 903 and 913 containing the ion-conductive material of the upper charge adjustment roller 900 and the lower charge adjustment roller 910 are polarized at the nip portion. That is, the ions in the ion-conductive material are polarized so that they are biased towards the roller surface side. Here, as in the comparative example, when a voltage is applied to the core metal 61a of the first conductive rubber roller 61, polarization occurs on the nip portion side with the second conductive rubber roller 62, and the electrical resistance of the conductive rubber roller tends to increase.

[0045] Therefore, in this embodiment, in order to suppress the increase in electrical resistance caused by such polarization, a voltage is applied to the upper charge adjustment roller 900 and the lower charge adjustment roller 910 from the upper power supply roller 901 and the lower power supply roller 911, which are in contact with the respective surfaces of the upper charge adjustment roller 900 and the lower charge adjustment roller 910. As a result, the polarization of ions generated on the nip side between the upper charge adjustment roller 900 and the lower charge adjustment roller 910 within the elastic layers 903 and 913 is mitigated on the nip side between the upper charge adjustment roller 900 and the lower charge adjustment roller 910 and the upper power supply roller 901 and the lower power supply roller 911. Thus, the polarization of ions in the upper charge adjustment roller 900 and the lower charge adjustment roller 910 is suppressed, and the increase in resistance of the upper charge adjustment roller 900 and the lower charge adjustment roller 910 due to use can be suppressed. As a result, the charge adjustment device 9 can stably adjust the charge of the sheet over a long period of time.

[0046] [Example 1] Next, we will describe an experiment conducted to confirm the effects of the embodiment described above. In the experiment, we used the charge adjustment device 9A shown in Figure 5(a). The charge adjustment device 9A of Example 1 has a charge adjustment roller 900Aa as the first roller, an opposing roller 910Aa as the second roller, a power supply roller 901Aa as the power supply rotating body, and a power supply high voltage 90A as the power supply. The charge adjustment roller 900Aa has a metal core (rotating shaft) 902Aa as a conductive shaft part, and an elastic layer 903Aa as the outer circumference part which includes an ion-conductive material formed on the outer circumference of the core 902Aa. The charge adjustment roller 900Aa is a semi-conductive roller, and the elastic layer 903Aa is formed of an ion-conductive material formed by a blend of nitrile rubber and ethylene-epichlorohydrin copolymer. Furthermore, the charge adjustment roller 900Aa is electrically floating.

[0047] The opposing roller 910Aa is positioned to sandwich the sheet between itself and the charge adjustment roller 900Aa. Specifically, both ends of the core metal 902A of the charge adjustment roller 900Aa are biased toward the opposing roller 910Aa by a spring member, causing the elastic layer 903Aa to press against the opposing roller 910Aa and form a nip portion. The opposing roller 910Aa is grounded.

[0048] The power supply roller 901Aa contacts the charge adjustment roller 900Aa and can supply current to the charge adjustment roller 900Aa. The high-voltage power supply 90A can apply a voltage of either positive or negative polarity to the power supply roller 901Aa. In Example 1, the high-voltage power supply 90A applies a positive voltage to the power supply roller 901Aa. The high-voltage power supply 90A is a constant current power supply, but it may also be a constant voltage power supply.

[0049] In the experiment, the voltage fluctuation was measured in a charge adjustment device 9A having the above configuration when a constant current was continuously supplied from the high-voltage power supply 90A. The experimental conditions were as follows: The opposing roller 910Aa and the power supply roller 901Aa are metal rollers with a diameter of 30 mm. The charge adjustment roller 900Aa is a semiconducting roller with a diameter of 20 mm. The high-voltage power supply 90A is a constant current source. Each roller rotates at 240 mm / sec in the direction of the arrow, and a current of 20 μA is continuously supplied from the high-voltage power supply 90A.

[0050] Figure 5(b) shows the measurement results for Experimental Example 1. In Figure 5(b), the horizontal axis represents time and the vertical axis represents applied voltage. From these results, it can be seen that although short-term voltage fluctuations remain when crossing days, long-term voltage fluctuations are hardly observed, indicating that the applied voltage is stable. Note that the charge adjustment device 9A shown in Figure 5(a) is configured for experimental purposes, so the current flows from the bottom to the top of the figure, but it can be reversed.

[0051] [Example 1] Figure 6 shows Modification 1 of this embodiment. The charge adjustment device 9B of Modification 1, like Embodiment 1 shown in Figure 5(a), has a charge adjustment roller 900A as a first roller, an opposing roller 910A as a second roller, a power supply roller 901A as a power supply rotating body, a power supply, and a high-voltage power supply 90A as a first power supply. The charge adjustment roller 900A has a metal core (rotating shaft) 902A as a conductive shaft portion, and an elastic layer 903A as an outer periphery portion including an ion-conductive material formed on the outer circumference of the core 902A. The charge adjustment roller 900A is a semi-conductive roller, and the elastic layer 903A is formed of an ion-conductive material formed by a blend of nitrile rubber and ethylene-epichlorohydrin copolymer. In Modification 1, as well, the charge adjustment roller 900A is floating. However, in Modification 1, unlike Embodiment 1, the opposing roller 910A is not grounded but connected to the high-voltage power supply 91A as a second power supply.

[0052] Furthermore, the opposing roller 910A and the power supply roller 901A are metal rollers, for example, with an outer diameter of φ16 mm. The charge adjustment roller 900A is a semiconducting roller. The elastic layer 903A is formed from an ion-conductive material formed by a blend of nitrile rubber and ethylene-epichlorohydrin copolymer, and has an outer diameter of, for example, φ20 mm. The outer diameter of the core metal 902A1 is, for example, φ16 mm.

[0053] The high-voltage power supply 90A connected to the power supply roller 901A can apply a voltage of either positive or negative polarity to the power supply roller 901A. In this embodiment, the high-voltage power supply 90A applies a negative voltage to the power supply roller 901A. On the other hand, the high-voltage power supply 91A connected to the opposing roller 910A can apply a voltage of the other polarity to the opposing roller 910A. In this embodiment, the high-voltage power supply 91A applies a positive voltage to the power supply roller 901A. In this embodiment, the high-voltage power supply 90A is a constant current power supply and the high-voltage power supply 91A is a constant voltage power supply, but the high-voltage power supply may be either a constant voltage power supply or a constant current power supply.

[0054] In this modified example 1, by applying voltage from the high-voltage power supply 91A and 90A to the opposing roller 910A and the power supply roller 901A, respectively, current flows from the opposing roller 910A to the power supply roller 901A via the charge adjustment roller 900A in the direction of the arrow. As a result, as described in the first embodiment, the polarization of ions in the charge adjustment roller 900A is suppressed, and the increase in resistance of the charge adjustment roller 900A due to use is suppressed. As a result, the charge adjustment device 9B can stably adjust the charge of the sheet over a long period of time.

[0055] [Differentiation 2] Figure 7 shows a modified example 2 of this embodiment. The charge adjustment device 9C of modified example 2 has, similar to the first embodiment shown in Figure 3, an upper charge adjustment roller 900 as a first roller, a lower charge adjustment roller 910 as a second roller, a power supply rotating body and an upper power supply roller 901 as a first power supply rotating body, a lower power supply roller 911 as a second power supply rotating body, a power supply and a high voltage power supply 90 as a first power supply, and a high voltage power supply 91 as a second power supply.

[0056] In this embodiment, the upper charge adjustment roller 900 is electrically floating, while the lower charge adjustment roller 910 is grounded. In this embodiment, although the lower charge adjustment roller 910 is grounded, current flows from the high voltage power supply 90 to the lower charge adjustment roller 910 via the upper power supply roller 901 and the upper charge adjustment roller 900, and also from the high voltage power supply 91 to the lower charge adjustment roller 910 via the lower power supply roller 911. Therefore, current flows from the upper power supply roller 901 to the lower power supply roller 911 in the direction of the arrow in the figure. As a result, as described in the first embodiment, the polarization of ions in the upper charge adjustment roller 900 and the lower charge adjustment roller 910 is suppressed, and the increase in resistance of the upper charge adjustment roller 900 and the lower charge adjustment roller 910 due to use is suppressed. As a result, the charge adjustment device 9B can stably adjust the charge of the sheet over a long period of time. Note that the upper charge adjustment roller 900 may also be grounded. That is, either the upper charge adjustment roller 900 or the lower charge adjustment roller 910 may be made floating and the other grounded, or both may be grounded.

[0057] <Second Embodiment> A second embodiment will be described with reference to Figures 8 to 12. In the first embodiment described above, a configuration in which the charge adjustment roller is floating was described, but in this embodiment, the charge adjustment roller is grounded. The other configurations and operations are the same as in the first embodiment described above, so the same reference numerals are used for similar components and their descriptions are omitted or simplified, and the following description will focus on the differences from the first embodiment.

[0058] First, a typical configuration of this embodiment will be described using Figure 8. The charge adjustment device 9D of this embodiment shown in Figure 8 has, similar to the modified example 1 shown in Figure 6, a charge adjustment roller 900A as the first roller, an opposing roller 910A as the second roller, a power supply roller 901A as the power supply rotating body, a power supply and a high-voltage power supply 90A as the first power supply, and a high-voltage power supply 91A as the second power supply. However, in this embodiment, unlike the modified example 1, the charge adjustment roller 900A is grounded. In this embodiment, the high-voltage power supply 90A that applies voltage to the power supply roller 901A is a constant current power supply, and the high-voltage power supply 91A that applies voltage to the opposing roller 910A is a constant voltage power supply. Note that the high-voltage power supply may be either a constant voltage power supply or a constant current power supply.

[0059] Furthermore, the opposing roller 910A and the power supply roller 901A are metal rollers, for example, with an outer diameter of φ16 mm. The charge adjustment roller 900A is a semiconducting roller. The elastic layer 903A is formed from an ion-conductive material formed by a blend of nitrile rubber and ethylene-epichlorohydrin copolymer, and has an outer diameter of, for example, φ20 mm. The outer diameter of the core metal 902A1 is, for example, φ16 mm.

[0060] In this embodiment, although the charge adjustment roller 900A is grounded, current flows from the high-voltage power supply 90A to the charge adjustment roller 900A via the power supply roller 901A, and also from the high-voltage power supply 91A to the charge adjustment roller 900A via the opposing roller 910A. Therefore, current flows from the power supply roller 901A to the opposing roller 910A in the direction of the arrow in the figure. As a result, as described in the first embodiment, the polarization of ions in the charge adjustment roller 900A is suppressed, and the increase in the resistance of the charge adjustment roller 900A due to use is suppressed. As a result, the charge adjustment device 9D can stably adjust the charge of the sheet over a long period of time.

[0061] [Example 2] Next, we will describe an experiment conducted to confirm the effects of the above-described embodiment. In the experiment, the charge adjustment device 9E shown in Figure 9(a) was used. The charge adjustment device 9E of Example 2 has a charge adjustment roller 900Aa as the first roller, an opposing roller 910Aa as the second roller, and a power supply roller 901Aa as the power supply rotating body, similar to Example 1 shown in Figure 5(a). However, in Example 2, the charge adjustment roller 900Aa is grounded. Also, a voltage is applied to the opposing roller 910A. In Example 2, the high-voltage power supply 90A that applies voltage to the power supply roller 901Aa is a constant current power supply, and the high-voltage power supply 91B that applies voltage to the opposing roller 910Aa is also a constant current power supply.

[0062] In the experiment, voltage fluctuations were measured in a charge adjustment device 9E having the above configuration when a constant current was continuously supplied from the power supply high voltages 90B and 91A. The experimental conditions were as follows: The opposing roller 910Aa and the power supply roller 901Aa are metal rollers with a diameter of 30 mm. The charge adjustment roller 900Aa is a semiconducting roller with a diameter of 20 mm. Each roller rotates at 240 mm / sec in the direction of the arrow, and a current of 20 μA is continuously supplied from the power supply high voltages 90B and 91A.

[0063] Figure 9(b) shows the measurement results for Experimental Example 2. In Figure 9(b), the horizontal axis represents time and the vertical axis represents applied voltage. The solid line in Figure 9(b) represents the application of high-voltage power supply 90B, and the dashed line represents the application of high-voltage power supply 91A, both in summer. From these results, it can be seen that although short-term voltage fluctuations remain when crossing days, long-term voltage fluctuations are hardly observed, indicating that the applied voltage is stable. Note that the charge adjustment device 9E shown in Figure 9(a) is configured for experimental purposes, so the current flows from the bottom to the top of the figure, but it can be reversed.

[0064] [Difference 3] Figure 10 shows Modification 3 of this embodiment. The charge adjustment device 9F of Modification 3 has, similar to the second embodiment shown in Figure 8, a charge adjustment roller 900A as the first roller, an opposing roller 910A as the second roller, a power supply roller 901A as the power supply rotating body, a power supply and a high-voltage power supply 90B as the first power supply, and a high-voltage power supply 91B as the second power supply. However, in Modification 3, the high-voltage power supply 90B that applies voltage to the power supply roller 901A is a constant voltage power supply, and the high-voltage power supply 91B that applies voltage to the opposing roller 910A is a constant current power supply.

[0065] [Differentiation Example 4] Figure 11 shows Modification 4 of this embodiment. The charge adjustment device 9G of Modification 4 has, similar to the second embodiment shown in Figure 8, a charge adjustment roller 900A as the first roller, an opposing roller 910A as the second roller, a power supply roller 901A as the power supply rotating body, a power supply and a high-voltage power supply 90B as the first power supply, and a high-voltage power supply 91A as the second power supply. However, in Modification 4, the high-voltage power supply 90B that applies voltage to the power supply roller 901A is a constant voltage power supply, and the high-voltage power supply 91A that applies voltage to the opposing roller 910A is also a constant voltage power supply.

[0066] [Difference 5] Figure 12 shows Modification 5 of this embodiment. The charge adjustment device 9H of Modification 5 has, similar to the second embodiment shown in Figure 8, a charge adjustment roller 900A as the first roller, an opposing roller 910A as the second roller, a power supply roller 901A as the power supply rotating body, a power supply and a high-voltage power supply 90A as the first power supply, and a high-voltage power supply 91B as the second power supply. However, in Modification 5, the high-voltage power supply 90A that applies voltage to the power supply roller 901A is a constant current power supply, and the high-voltage power supply 91B that applies voltage to the opposing roller 910A is also a constant current power supply.

[0067] [Third Embodiment] As a third embodiment, the preferred relationship between the external power supply current and the static elimination current in the configuration of each embodiment described above will be explained. Here, the static elimination current is the current that flows into the sheet in the nip section, and the external power supply current is the current that flows out from the sheet in the nip section. Specifically, in Figures 3 and 7, when the power supply rotating body to which a positive voltage is applied is the first rotating body and the power supply rotating body to which a negative voltage is applied is the second rotating body, the current flowing through the first rotating body is the static elimination current, and the current flowing through the second rotating body is the external power supply current. That is, in Figures 3 and 7, the current flowing through the upper power supply roller 901 is the static elimination current, and the current flowing through the lower power supply roller 911 is the external power supply current. Also, in Figure 5(a), the current flowing through the power supply roller 901Aa as a power supply rotating body is the static elimination current, and the current flowing through the opposing roller 910Aa as a second roller is the external power supply current.

[0068] Furthermore, in Figures 6, 8-12, if the power supply rotating body or roller to which a positive voltage is applied is designated as the first rotating body, and the power supply rotating body or roller to which a negative voltage is applied is designated as the second rotating body, then the current flowing through the first rotating body is the static elimination current, and the current flowing through the second rotating body is the external power supply current. That is, in Figures 6, 8, 10, 11, and 12, the current flowing through the opposing roller 910A is the static elimination current, and the current flowing through the power supply roller 901A is the external power supply current. Also, in Figure 9(a), the current flowing through the power supply roller 901Aa is the static elimination current, and the current flowing through the opposing roller 910Aa is the external power supply current.

[0069] [Example 3] In the following explanation, we will use the charge adjustment device 9E of Example 2 shown in Figure 9(a) as a representative example, but the same applies to other charge adjustment devices. Figure 13 shows the relationship between the static elimination current and the external power supply current. When considering the sign of the current with respect to the sheet in the nip section, it is common to consider the current flowing into the sheet (static elimination current) as positive and the current flowing out of the sheet (external power supply current) as negative. However, in this example, in order to facilitate comparison between the static elimination current and the external power supply current, the static elimination current and the external power supply current will be explained in terms of their absolute values. Also, in Figure 13, the static elimination current is shown by a thin line and the external power supply current by a thick line.

[0070] Regarding the static elimination current and external power supply current, the process can be broadly classified into three stages over time: pre-rotation, charge adjustment, and post-rotation. Here, pre-rotation refers to the period in an image forming job where images are formed on multiple sheets in succession, during which the charge adjustment roller 900Aa, opposing roller 910Aa, and power supply roller 901Aa are rotating before the leading edge of the first sheet enters the nip. Charge adjustment refers to the period during which multiple sheets pass through the nip, including not only the time while the sheets are actually passing through the nip, but also the period between sheets (between sheets) from when the trailing edge of a sheet passes through the nip until the leading edge of the subsequent sheet enters the nip. The charge adjustment roller 900Aa, opposing roller 910Aa, and power supply roller 901Aa are also rotating during charge adjustment. Post-rotation refers to the period in an image forming job when the charge adjustment roller 900Aa, the opposing roller 910Aa, and the power supply roller 901Aa are rotating after the trailing edge of the last sheet has passed the nip section.

[0071] In this example, the static elimination current and external power supply current values ​​during the preceding and succeeding rotations were set to the same value of 30 μA. During charge adjustment, the static elimination current value while the sheet was passing through the nip was set to a constant value of 40 μA, and the static elimination current value between the sheets was set to a constant value of 30 μA. Furthermore, the external power supply current value during charge adjustment was set to 35 μA, which is between the static elimination current value of 40 μA and the current value of 30 μA between the sheets.

[0072] With the current value set to the above conditions, and in a temperature and humidity environment of 23°C and 5%RH, the charge adjustment roller 900Aa was first left in this environment for one week. With no metal roller (i.e., the opposing roller 910Aa) in contact with the device shown in Figure 9(a) from above, the rotation speed was 15 rpm, and the applied voltage from the high-voltage power supply of 90A was 2kV, the initial resistance value was measured and was found to be 4.0E+7Ω.

[0073] Next, a durability test was conducted using an image forming apparatus with a peripheral speed of 200 mm / sec in the same temperature and humidity environment, performing continuous image formation. In the test, Canon Inc.'s A4 size paper GF-C081 (basis weight 81.4 g / m²) was used. 2 The following was used: In this test, 600,000 sheets of this paper were passed through the nip section of the charge adjustment device 9E, and then the resistance value of the charge adjustment roller 900Aa was measured under the same conditions as above. As a result, the resistance value was 5.0E + 7Ω, which was a slight increase from the initial resistance value to 1.25 times. However, the resistance increase was not so large as to change the order of magnitude of the resistance value as in the past, and a sufficient effect was confirmed.

[0074] Thus, in each of the embodiments described above, the amount of charge present on the surface of the sheets is adjusted, which suppresses the sheets from sticking together due to electrostatic force and makes it possible to perform stable charge adjustment over a long period of time.

[0075] Furthermore, as described above, by setting the absolute value of the external power supply current during charge adjustment, which includes the period during passage and between the sheets of paper, to a value between the absolute value of the static elimination current during passage and the absolute value of the static elimination current between the sheets of paper, ions polarized by the static elimination current can be suitably relaxed by the external power supply current.

[0076] Furthermore, as described above, the external power supply current when the sheet was continuously passed through the nip section of the charge adjustment device was set to a constant value between the current value during the passage of the static elimination current and the current value between the sheets. As a result, it was found that a high level of effectiveness could be obtained in mitigating the polarization of the conductive agent generated in the static elimination process with the external power supply current using simple control without requiring complex control.

[0077] [Other embodiments] The present invention is not limited to the embodiments described above, but can be applied to other power supply members and other types of image forming apparatus. Furthermore, the numerical values ​​and other information used in the descriptions of the embodiments described above are merely examples, and the present invention is not limited to them.

[0078] Furthermore, the disclosure of this embodiment includes the following configuration.

[0079] (Composition 1) A transfer unit that transfers the toner image onto the sheet, A fixing unit heats and pressurizes the sheet onto which the toner image has been transferred in the transfer unit to fix the toner image to the sheet, The system includes a charge adjustment unit that adjusts the charge on the sheet on which the toner image has been fixed in the fixing unit, The charge adjustment unit is A first roller having a conductive shaft portion and an outer peripheral portion including an ion-conductive material formed on the outer circumference of the shaft portion, and being electrically floating, A second roller is positioned to sandwich the sheet between the first roller and the second roller, A power supply rotating body that contacts the first roller and is capable of supplying current to the first roller, The power supply rotating body is provided with a power supply capable of applying a voltage of either positive or negative polarity. An image forming apparatus characterized by the following features. (Configuration 2) The aforementioned shaft portion is the first shaft portion, The aforementioned outer periphery is the first outer periphery, The second roller has a conductive second shaft portion and a second outer peripheral portion formed on the outer circumference of the second shaft portion, which includes an ion-conductive material. The power supply rotating body is the first power supply rotating body, The aforementioned power supply is the first power supply, The charge adjustment unit is A second power supply rotating body that contacts the second roller and is capable of supplying current to the second roller, The invention further comprises a second power supply capable of applying a voltage of the other polarity (positive or negative) to the second power supply rotating body. The image forming apparatus according to configuration 1, characterized in that it is a picture forming apparatus. (Composition 3) When multiple sheets are passed continuously through a nip portion that clamps a sheet between the first roller and the second roller, the period during which a sheet passes through the nip portion is defined as the time between sheets, from when the rear end of a sheet passes through the nip portion until the leading edge of a subsequent sheet continuous with the sheet enters the nip portion. Furthermore, when the first power supply rotating body to which a positive voltage is applied is defined as the first rotating body and the second power supply rotating body to which a negative voltage is applied is defined as the second rotating body, the absolute value of the current flowing through the second rotating body during the period including the passage and the time between sheets is defined as the value between the absolute value of the current flowing through the first rotating body during the passage and the absolute value of the current flowing through the first rotating body between sheets. The image forming apparatus according to configuration 2, characterized in that... (Composition 4) The second roller is electrically floating. The image forming apparatus according to configuration 2 or 3, characterized by the above. (Composition 5) The second roller is grounded An image forming apparatus according to any one of configurations 1 to 3, characterized by the above. (Composition 6) The power supply applies a positive voltage to the rotating power supply body. The second roller is grounded, When multiple sheets are passed continuously through a nip portion that clamps a sheet between the first roller and the second roller, if the period during which a sheet is passing through the nip portion is defined as the time between sheets from when the rear end of a sheet passes through the nip portion until the leading edge of a subsequent sheet continuous with the sheet enters the nip portion, then the absolute value of the current flowing through the second roller during the period including the passage and the time between sheets shall be the value between the absolute value of the current flowing through the power supply rotating body during the passage and the absolute value of the current flowing through the power supply rotating body between the sheets. The image forming apparatus according to configuration 1, characterized in that it is a picture forming apparatus. (Composition 7) The aforementioned power supply is the first power supply, The second roller is a metal roller, The charge adjustment unit further includes a second power supply capable of applying a voltage of the other polarity (positive or negative) to the second roller. The image forming apparatus according to configuration 1, characterized in that it is a picture forming apparatus. (Composition 8) When multiple sheets are passed continuously through a nip portion that clamps a sheet between the first roller and the second roller, the period during which a sheet passes through the nip portion is defined as the time between sheets, from when the rear end of a sheet passes through the nip portion until the leading edge of a subsequent sheet continuous with the sheet enters the nip portion. Furthermore, when the power supply rotating body and the second roller are defined as the first rotating body to which a positive voltage is applied and the second rotating body to which a negative voltage is applied, the absolute value of the current flowing through the second rotating body during the passage and the period including the time between sheets is defined as the value between the absolute value of the current flowing through the first rotating body during the passage and the absolute value of the current flowing through the first rotating body between sheets. The image forming apparatus according to configuration 7, characterized by the features described above. (Composition 9) The aforementioned power supply is a constant voltage power supply. An image forming apparatus according to any one of configurations 1 to 8, characterized by the above. (Composition 10) The aforementioned power supply is a constant current power supply. An image forming apparatus according to any one of configurations 1 to 8, characterized by the above. (Composition 11) A transfer unit that transfers the toner image onto the sheet, A fixing unit heats and pressurizes the sheet onto which the toner image has been transferred in the transfer unit to fix the toner image to the sheet, The system includes a charge adjustment unit that adjusts the charge on the sheet on which the toner image has been fixed in the fixing unit, The charge adjustment unit is A grounded first roller having a conductive shaft portion and an outer peripheral portion including an ion-conductive material formed on the outer circumference of the shaft portion, A second metal roller is positioned to sandwich the sheet between the first roller and the second roller, A power supply rotating body that contacts the first roller and is capable of supplying current to the first roller, A first power supply capable of applying a voltage of either positive or negative polarity to the power supply rotating body, The second roller is provided with a second power supply capable of applying a voltage of either positive or negative polarity. An image forming apparatus characterized by the following features. (Composition 12) When multiple sheets are passed continuously through a nip portion that clamps a sheet between the first roller and the second roller, the period during which a sheet passes through the nip portion is defined as the time between sheets, from when the rear end of a sheet passes through the nip portion until the leading edge of a subsequent sheet continuous with the sheet enters the nip portion. Furthermore, when the power supply rotating body and the second roller are defined as the first rotating body to which a positive voltage is applied and the second rotating body to which a negative voltage is applied, the absolute value of the current flowing through the second rotating body during the passage and the period including the time between sheets is defined as the value between the absolute value of the current flowing through the first rotating body during the passage and the absolute value of the current flowing through the first rotating body between sheets. The image forming apparatus according to configuration 11, characterized by the features described above. (Composition 13) At least one of the first power supply and the second power supply is a constant voltage power supply. The image forming apparatus according to configuration 11 or 12, characterized by the above. (Composition 14) At least one of the first power supply and the second power supply is a constant current power supply. The image forming apparatus according to configuration 11 or 12, characterized by the above. [Explanation of Symbols]

[0080] 7. Fixing device (fixing unit) 9, 9A, 9B, 9C, 9D, 9E, 9F, 9G, 9H... Charge adjustment device (charge adjustment section) 90, 90A, 90B... High voltage power supply (power supply, first power supply) 91, 91A, 91B... High-voltage power supply (second power supply) 100...Image forming apparatus 110... Control Unit 900... Upper charge adjustment roller (first roller) 900Aa, 900A... Charge adjustment roller (first roller) 901... Upper power supply roller (power supply rotating body, first power supply rotating body) 901Aa, 901A... Power supply roller (power supply rotating body) 902, 902Aa... Core metal (shaft section, first shaft section) 903, 903Aa... Elastic layer (outer periphery, first outer periphery) 910...Lower charge adjustment roller (second roller) 910Aa, 910A... Opposing roller (second roller) 911...Lower power supply roller (second power supply rotating body) 912... Core metal (second shaft part) 913...Elastic layer (second outer periphery) N2...Secondary transfer section (transfer section)

Claims

1. A transfer unit that transfers a toner image onto a sheet, A fixing unit that heats and presses the sheet onto which the toner image has been transferred by the transfer unit to fix the toner image onto the sheet, A charge adjustment unit that adjusts the charge of the sheet onto which the toner image has been fixed by the fixing unit, and The charge adjustment unit has a first roller having a shaft portion with conductivity and an outer peripheral portion containing an ion conductive material formed on the outer periphery of the shaft portion, a second roller arranged to sandwich the sheet whose charge is to be adjusted between the outer peripheral portion of the first roller, a power supply rotating body that abuts on the outer peripheral portion of the first roller and can supply an electric current to the first roller, and a power supply that can apply a voltage of one of a positive polarity and a negative polarity to the power supply rotating body. An image forming apparatus characterized by the above.

2. The shaft portion is a first shaft portion, The outer peripheral portion is a first outer peripheral portion, The second roller has a second shaft portion with conductivity and a second outer peripheral portion containing an ion conductive material formed on the outer periphery of the second shaft portion, The power supply rotating body is a first power supply rotating body, The power supply is a first power supply, The charge adjustment unit further has a second power supply rotating body that abuts on the second roller and can supply an electric current to the second roller, and a second power supply that can apply a voltage of the other of a positive polarity and a negative polarity to the second power supply rotating body. The image forming apparatus according to claim 1, characterized by the above.

3. When a plurality of sheets are continuously passed through a nip portion that sandwiches the sheet between the first roller and the second roller, during the period when the sheet is passing through the nip portion, the period from when the rear end of the sheet passes through the nip portion to when the front end of the subsequent sheet continuous with the sheet enters the nip portion is defined as the inter-sheet period. And, when the power supply rotating body to which a positive voltage is applied among the first power supply rotating body and the second power supply rotating body is defined as the first rotating body, and the power supply rotating body to which a negative voltage is applied is defined as the second rotating body, the absolute value of the current flowing through the second rotating body during the period including during the passing through and the inter-sheet period is set to be between the absolute value of the current flowing through the first rotating body during the passing through and the absolute value of the current flowing through the first rotating body during the inter-sheet period. The image forming apparatus according to claim 2, characterized by the above.

4. The second roller is electrically floating. The image forming apparatus according to claim 2 or 3, characterized by the above.

5. The second roller is grounded. The image forming apparatus according to any one of claims 1 to 3, characterized in that...

6. The power supply applies a positive voltage to the power supply rotating body, The second roller is grounded, When a plurality of sheets are continuously passed through a nip portion that sandwiches a sheet between the first roller and the second roller, during the period when the sheet is passing through the nip portion, from the time when the trailing end of the sheet passes through the nip portion until the leading end of the subsequent sheet continuous with the sheet enters the nip portion, when this period is defined as the inter-sheet period, the absolute value of the current flowing through the second roller during the period including during the passing and the inter-sheet period is set to be a value between the absolute value of the current flowing through the power supply rotating body during the passing and the absolute value of the current flowing through the power supply rotating body during the inter-sheet period. The image forming apparatus according to claim 1, characterized in that...

7. The power supply is a first power supply, The second roller is a metal roller, The charge adjusting unit further has a second power supply capable of applying a voltage of the other polarity out of positive and negative polarities to the second roller. The image forming apparatus according to claim 1, characterized in that...

8. When a plurality of sheets are continuously passed through a nip portion that sandwiches a sheet between the first roller and the second roller, during the period when the sheet is passing through the nip portion, from the time when the trailing end of the sheet passes through the nip portion until the leading end of the subsequent sheet continuous with the sheet enters the nip portion, this period is defined as the inter-sheet period, and when the power supply rotating body or roller to which a positive voltage is applied and the power supply rotating body or roller to which a negative voltage is applied among the power supply rotating body and the second roller are defined as a first rotating body and a second rotating body respectively, the absolute value of the current flowing through the second rotating body during the period including during the passing and the inter-sheet period is set to be a value between the absolute value of the current flowing through the first rotating body during the passing and the absolute value of the current flowing through the first rotating body during the inter-sheet period. The image forming apparatus according to claim 7, characterized in that...

9. The power supply is a constant voltage power supply. The image forming apparatus according to claim 1, characterized in that...

10. The power supply is a constant current power supply. The image forming apparatus according to claim 1, characterized in that...

11. The first roller is electrically floated. The image forming apparatus according to claim 1, characterized in that...

12. The first roller is grounded. The second roller is made of metal, The power source capable of applying a voltage of one of the positive and negative polarities to the power supply rotating body is the first power source, The apparatus further includes a second power source capable of applying a voltage of one of the positive and negative polarities to the second roller. The image forming apparatus according to claim 1, characterized in that.

13. When a plurality of sheets are continuously passed through a nip portion that sandwiches the sheet between the first roller and the second roller, during the period when the sheet is passing through the nip portion, from the time when the trailing end of the sheet passes through the nip portion until the leading end of the succeeding sheet continuous with the sheet enters the nip portion is defined as the inter-sheet period, and among the power supply rotating body and the second roller, when the power supply rotating body or the roller to which a positive voltage is applied is defined as the first rotating body and the power supply rotating body or the roller to which a negative voltage is applied is defined as the second rotating body, the absolute value of the current flowing through the second rotating body during the period including the passing period and the inter-sheet period is set to be between the absolute value of the current flowing through the first rotating body during the passing period and the absolute value of the current flowing through the first rotating body during the inter-sheet period. The image forming apparatus according to claim 12, characterized in that.

14. At least one of the first power source and the second power source is a constant voltage power source. The image forming apparatus according to claim 12 or 13, characterized in that.

15. At least one of the first power source and the second power source is a constant current power source. The image forming apparatus according to claim 12 or 13, characterized in that.

16. A charge adjustment device that adjusts the charge of a sheet fixed by heating and pressing the toner image transferred by a transfer unit by a fixing unit, A first roller having a shaft portion having conductivity and an outer peripheral portion containing an ion conductive material formed on the outer periphery of the shaft portion, A second roller arranged to sandwich the sheet whose charge is to be adjusted with the outer peripheral portion of the first roller, A power supply rotating body that abuts against the first roller and can supply current to the first roller, A power source capable of applying a voltage of one of the positive and negative polarities to the power supply rotating body. The charge adjustment device, characterized in that.

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