JP2024070076A - Charge conditioning device and image forming apparatus - Google Patents

Abstract

[Problem] To provide a configuration capable of stably adjusting the charge of a sheet over a long period of time. [Solution] A charge adjustment device 9 adjusts the charge of a sheet on which a toner image has been 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, a lower power feed roller 911, a high voltage power feed 90, a high voltage power feed 91, and the like. The upper power feed roller 901 has a conductive core metal 902 and an elastic layer 903 containing an ion conductive material formed on the outer periphery of the core metal 902. The lower charge adjustment roller 910 is disposed so as to sandwich a sheet between the upper charge adjustment roller 900 and the lower charge adjustment roller 910. The amount of charge applied by the high voltage power feed 90 to the upper power feed roller 901 is set to a value close to the amount of charge applied by the high voltage power feed 91 to the lower power feed roller 911. [Selected Figure] Fig. 14

Description

The present invention relates to a charge adjustment device that adjusts the charge on a sheet and an image forming apparatus equipped with the same.

In an image forming device, a toner image formed in an image forming unit is transferred to a sheet in a transfer unit, and the toner image is fixed to the sheet in a fixing unit, after which the sheet is stacked on an output tray or the like. At this time, the sheets may stick together due to electrostatic forces between them. For this reason, a configuration has been proposed that includes a charge adjustment unit that applies a voltage to the sheet on which the toner image has been fixed by the fixing unit to adjust the charge of the sheet (Patent Document 1).

In Patent Document 1, the charge adjustment unit includes a pair of conductive rubber rollers arranged opposite each other and a power source that applies a voltage to the conductive rubber rollers, and is configured to apply a voltage to a sheet that passes through the nip between the pair of conductive rubber rollers.

JP 2016-122156 A

However, if a roller containing an ionically conductive material is used as the conductive rubber roller, the resistance of the roller increases when electricity is passed through it, and there is a risk that the charge adjustment of the sheet cannot be performed stably over a long period of time.

The present invention aims to provide a configuration that can stably adjust the charge of a sheet over a long period of time.

One aspect of the present invention is a charge adjustment device that adjusts the charge on a sheet on which a toner image is fixed, the charge adjustment device having a conductive shaft portion and an outer periphery including an ion-conductive material formed on the outer periphery of the shaft portion, a grounded first roller, a second roller arranged to sandwich a sheet between the first roller, a power supply rotor that is in contact with the first roller and capable of supplying a current to the first roller, a first power source that is capable of applying a voltage of one of positive and negative polarity to the power supply rotor, and a second power source that is capable of applying a voltage of one of positive and negative polarity to the second roller, wherein the amount of charge applied to the power supply rotor by the first power source during a period in which multiple sheets are continuously passed through a nip portion that sandwiches the sheet between the first roller and the second roller is 90% or more and 110% or less of the amount of charge applied to the second roller by the second power source.

According to the present invention, the charge of the sheet can be adjusted stably over a long period of time.

1 is a schematic cross-sectional view of an image forming apparatus according to a first embodiment. FIG. 2 is a cross-sectional view showing a schematic configuration of an image forming unit according to the first embodiment. 1 is a cross-sectional view showing a schematic configuration of a charge adjustment device according to a first embodiment; FIG. 13 is a cross-sectional view showing a schematic configuration of a charge adjustment device according to a comparative example. FIG. 2A is a schematic cross-sectional view showing the configuration of a charge adjustment device according to a first embodiment; FIG. 2B is a graph showing the measurement results of voltage fluctuations of the charge adjustment device according to the first embodiment; FIG. 4 is a cross-sectional view showing a schematic configuration of a charge adjustment device according to a first modified example of the first embodiment. FIG. 11 is a cross-sectional view showing a schematic configuration of a charge adjustment device according to a second modified example of the first embodiment. FIG. 11 is a cross-sectional view showing a schematic configuration of a charge adjustment device according to a second embodiment. 10A is a schematic cross-sectional view of a charge adjustment device according to a second embodiment; FIG. 10B is a graph showing the measurement results of voltage fluctuations in the charge adjustment device according to the second embodiment; FIG. 13 is a schematic cross-sectional view of a charge adjustment device according to a third modified example of the second embodiment. FIG. 13 is a schematic cross-sectional view of a charge adjustment device according to a fourth modified example of the second embodiment. FIG. 13 is a schematic cross-sectional view of a charge adjustment device according to a fifth modified example of the second embodiment. 13 is a graph showing the relationship between the static elimination current and the external power supply current in Example 3. 13A is a graph showing the amount of neutralized charge in Example 3, and FIG. 13B is a graph showing the amount of externally supplied charge in Example 3.

First Embodiment
A first embodiment will be described with reference to Figures 1 to 7. First, a schematic configuration of an image forming apparatus according to the present embodiment will be described with reference to Figures 1 and 2.

[Image forming apparatus]
1, an image forming apparatus 100 according to this embodiment is a laser beam printer that uses an electrophotographic method to form a full-color image on a sheet P (paper, an OHP sheet, cloth, etc.) as a recording material. The image forming apparatus 100 is an intermediate transfer tandem type in which image forming units Pa, Pb, Pc, and Pd, which are means for forming toner images of yellow, magenta, cyan, and black, are arranged along an intermediate transfer belt 51.

The image forming units Pa, Pb, Pc, and Pd each have an image carrier that carries an electrostatic latent image and photosensitive drums 1a, 1b, 1c, and 1d as photosensitive bodies. In the image forming unit Pa, a yellow toner image is formed on the photosensitive drum 1a and is primarily transferred to an intermediate transfer belt 51 as an intermediate transfer body. In the image forming unit Pb, a magenta toner image is formed on the photosensitive drum 1b and is primarily transferred and superimposed on the yellow toner image on the intermediate transfer belt 51. In the image forming units Pc and Pd, a cyan toner image and a black toner image are formed on the photosensitive drums 1c and 1d, respectively, and are similarly primarily transferred in sequence and superimposed on the toner image on the intermediate transfer belt 51. In this embodiment, the photosensitive drums and the intermediate transfer belt serve as image carriers that carry toner images.

The four-color toner image that has been primarily transferred onto the intermediate transfer belt 51 is then secondary-transferred all at once onto the sheet P that has been fed to the secondary transfer section N2 formed by the intermediate transfer belt 51 and the secondary transfer roller 56. The sheet P onto which the toner image has been secondary-transferred at the secondary transfer section N2 is heated and pressurized by the fixing device 7 as a fixing section, and the toner image is fixed onto the surface. The sheet P is then discharged to the outside and stacked on the discharge tray 86.

In the feeding device 8, the sheet P is pulled out of the cassette 81 by the pickup roller 82, separated one by one by the separation device 83, and sent to the registration rollers 84. The registration rollers 84 receive the sheet P in a stopped state and keep it waiting, and then send the sheet P to the secondary transfer section N2 in time with the toner image on the intermediate transfer belt 51.

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 wrapping it around a drive roller 52, support rollers 58 and 59, a tension roller 53, and an opposing roller 54. The opposing roller 54 is disposed in a position facing a secondary transfer roller 56 across the intermediate transfer belt 51. The outer peripheral surface of the intermediate transfer belt 51 wrapped around the opposing roller 54 and the secondary transfer roller 56 form a secondary transfer section N2 that nips a sheet.

A power source D2 is connected to the secondary transfer roller 56, and a secondary transfer bias is applied to it. When performing secondary transfer, a high-voltage positive (positive polarity) transfer voltage (secondary transfer bias) is applied to the secondary transfer roller 56, so that the negatively charged toner image is electrostatically attracted to the sheet. As a result, the toner image carried by the intermediate transfer belt 51 is secondarily transferred to the sheet P passing through the secondary transfer section N2.

The fixing device 7 presses a pressure roller 73 against a fixing roller 72, which is disposed around a lamp heater 71, to form a heating nip. Then, in the heating nip, 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 discharge rollers 85, which serve as a discharge section, and is stacked on a discharge tray 86.

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

The image forming units Pa, Pb, Pc, and Pd are configured almost identically, except that the colors of toner used in the developing devices 4a, 4b, 4c, and 4d attached to the photosensitive drums 1a, 1b, 1c, and 1d, respectively, are yellow, magenta, cyan, and black. In the following, the image forming unit Pa will be described with reference to FIG. 2, and the other image forming units Pb, Pc, and Pd will be described with the suffix a replaced with b, c, and d.

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

The charging roller 2a, which is a charging member, is formed by covering the surface of a metallic central shaft with a resistive elastic layer, and is pressed against the photosensitive drum 1a and rotates in response. The power source D3 applies a DC voltage superimposed on an AC voltage to the charging roller 2a, charging the surface of the photosensitive drum 1a to a uniform negative potential.

The exposure device 3a scans a laser beam that is ON-OFF modulated to represent scanning line image data that is a yellow separation color image, using a rotating mirror, to write an electrostatic image of the image onto the charged surface of the photosensitive drum 1a.

The developing device 4a stirs a two-component developer in which non-magnetic toner is mixed with a magnetic carrier, and charges 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 brush-like state on the developing sleeve 41a, which rotates around the fixed magnetic pole 42a in the counter direction to the photosensitive drum 1a, and rubs against the photosensitive drum 1a. The power source D4 applies a developing voltage, which is a negative DC voltage superimposed with an AC voltage, to the developing sleeve 41a, and moves the toner to the exposed portion of the photosensitive drum 1a, which is relatively more positive than the developing sleeve 41a, to reversely develop the electrostatic image.

The primary transfer roller 55a, which is the primary transfer member, is pressed against the photosensitive drum 1a side 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 source D1a is a transfer output section that applies a voltage to the primary transfer roller 55a, and applies a positive polarity DC voltage of +900V as a primary transfer bias to the primary transfer roller 55a. As a result, the negatively charged toner image carried by the photosensitive drum 1a is primarily transferred to the intermediate transfer belt 51 that passes through the primary transfer section N1a.

The primary transfer roller 55a used is semiconductive with a resistance value of ^1x102 to ¹⁰⁸ Ω when 2000 V is applied. Specifically, an ion-conductive sponge roller with an outer diameter of φ16 mm and a core metal diameter of φ8 mm, formed from a blend of nitrile rubber and ethylene-epichlorohydrin copolymer, is used. The resistance value of the primary transfer roller 55a is approximately ^1x106 to ¹⁰⁸ Ω when an applied voltage of 2 kV is applied in an environment of a temperature of 23°C and a humidity of 50% RH.

The cleaning device 6a rubs a cleaning blade against the photosensitive drum 1a to remove residual toner adhering to the surface of the photosensitive drum 1a that has passed through the primary transfer section N1a.

In recent years, the variety of sheets has increased, and the thickness and electrical resistivity of the sheets are also widely varied, so the intermediate transfer method is adopted. In addition, in order to prevent the amount of charge supplied to the toner image from changing due to differences in the image ratio in the main scanning direction, the width of the sheet, etc., constant voltage control is adopted in the transfer section (secondary transfer section in the above example) where the toner image is transferred to the sheet. Furthermore, the electrical resistance of the intermediate transfer belt and transfer roller, or the film thickness of the surface layer of the photosensitive drum, etc. change due to changes in the atmospheric environment such as temperature and humidity, or due to the accumulation of image formation. In response to these changes, ATVC control (Active Transfer Voltage Control) is executed to determine the control value of the constant voltage control prior to image formation in order to optimize the voltage applied to the transfer roller during image formation.

ATVC control is a control in which a number of different test voltages are applied to the secondary transfer roller 56 when there is no sheet at the secondary transfer section N, the current is detected by a current detection sensor at each transfer voltage to obtain the relationship between the transfer voltage and the current, and the transfer voltage (secondary transfer bias) to be applied to the secondary transfer section N is set based on this relationship. The entire image forming apparatus 100, including this ATVC control, is controlled by the control unit 110 (Figure 1).

The control unit 110 has a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory). The CPU controls each unit while reading out a program corresponding to a control procedure stored in the ROM. In addition, working data and input data are stored in the RAM, and the CPU performs control by referring to the data stored in the RAM based on the aforementioned programs, etc.

[Sheet charge adjustment]
In this embodiment, in order to prevent sheets stacked on the discharge tray from sticking together due to electrostatic force, a charge adjustment device 9 serving as a charge adjustment unit is disposed downstream of the fixing device 7 in the sheet conveying direction and upstream of the discharge roller 85 (FIG. 1) as shown in FIG. 3. The charge adjustment device 9 adjusts the charge of the sheet on which the toner image has been fixed by the fixing device 7.

[Comparative Example]
First, the configuration described in Patent Document 1 will be described as a comparative example. The charge adjustment device 60 of the comparative example has a first conductive rubber roller 61 and a second conductive rubber roller 62 arranged opposite to each other. The core metal 61a of the first conductive rubber roller 61 is connected to a power source 63, and the second conductive rubber roller 62 is grounded. The power source 63 applies a positive (positive polarity) 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, a negative charge of the same amount as the positive charge applied from the first conductive rubber roller 61 is induced in the second conductive rubber roller 62, and cancels out the positive (negative polarity) charge on the first surface (front surface) P1 of the sheet P. The power source 63 is constant current controlled, and applies a voltage controlled to a constant current at a predetermined current value to the sheet P. This adjusts the charge of the sheet P, and the sticking of the sheet during stacking can be suppressed.

However, when charge adjustment is performed by constant current control in the comparative example configuration shown in Figure 4, a constant charge adjustment current continues to flow when one type of sheet is continuously passed through in a constant temperature and humidity environment. Furthermore, if the conductive rubber roller (charge adjustment roller) being used is configured to contain at least an ionically conductive material and to increase in electrical resistance depending on the amount of current passing through it, measures such as increasing the applied voltage depending on the duration of use are required to impart the desired charge.

Generally, there is an upper limit to the high voltage capacity of a power supply, so if continued use is performed under the conditions of the comparative example, a constant charge adjustment current cannot be supplied, and the user must choose between lowering the charge adjustment current value or replacing the charge adjustment roller. If the charge adjustment current value is lowered, the amount of charge on the sheet will naturally change, resulting in unstable loading and other issues. If the charge adjustment roller is replaced, downtime and increased initial costs are unavoidable. Therefore, in this embodiment, the charge adjustment device is configured as follows:

[Charge Adjustment Device of the Present Embodiment]
FIG. 3 is an explanatory diagram of the charge adjustment device 9 of this embodiment. The broken line indicates the transport path of the sheet P, and the charge adjustment device 9 is disposed downstream of the fixing device 7. The charge adjustment device 9 has an upper charge adjustment roller 900 as a first roller and a lower charge adjustment roller 910 as a second roller. The charge adjustment device 9 further has an upper power supply roller 901 as a power supply rotor and a first power supply rotor, a lower power supply roller 911 as a second power supply rotor, a high voltage power supply 90 as a power supply and a first power supply, and a high voltage power supply 91 as a second power supply. The upper power supply roller 901, the upper charge adjustment roller 900, the lower charge adjustment roller 910, and the lower power supply roller 911 are disposed in this order from top to bottom. Adjacent rollers are biased by a spring member with a load of 1 kgf and are in contact with each other.

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

The upper charge adjustment roller 900 and the lower charge adjustment roller 910 are semiconductive rollers, and the elastic layers 903, 913 are made of an ionically conductive material formed by blending nitrile rubber and ethylene-epichlorohydrin copolymer. The upper charge adjustment roller 900 and the lower charge adjustment roller 910 are each electrically floating. In other words, the upper charge adjustment roller 900 and the lower charge adjustment roller 910 are not directly connected to a power source, and are not grounded.

The lower charge adjustment roller 910 is arranged to sandwich the sheet between it and 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 urged toward the other charge adjustment roller by a spring member. This causes the elastic layers 903 and 913 to come into pressure contact 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.

The upper power supply roller 901 is in contact with the upper charge adjustment roller 900 and can supply a 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 high voltage power supply 90 can apply a voltage of one of positive and negative polarity to the upper power supply roller 901. In this embodiment, the high voltage power supply 90 applies a positive (positive) voltage to the upper power supply roller 901. In this embodiment, the high voltage power supply 90 is a constant voltage power supply. However, the high voltage power supply 90 may also be a constant current power supply. In other words, one of the power supplies is a constant current power supply.

The lower power supply roller 911 is in contact with the lower charge adjustment roller 910 and can supply a 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 high voltage power supply 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 high voltage power supply 91 applies a negative (negative) voltage to the lower power supply roller 911. In this embodiment, the high voltage power supply 91 is a constant current power supply. However, the high voltage power supply 91 may also be a constant voltage power supply. In other words, one of the power supplies is a constant voltage power supply.

The high voltage power supply 90 and the high voltage power supply 91 are controlled by the control unit 110. The control unit 110 determines the amount of charge to be applied to the sheet depending on 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 to be formed on the sheet, and determines whether or not to apply a voltage to the sheet from the high voltage power supply 90 and the high voltage power supply 91, and if so, the current value to be supplied from the high voltage power supply 90 and the high voltage power supply 91. This makes it possible to adjust the charge appropriately depending on the coverage of the sheet.

In this embodiment, a current flows between the upper charge adjustment roller 900 and the lower charge adjustment roller 910 in the direction of the arrow by applying a voltage to the upper power supply roller 901 and the lower power supply roller 911 from the high voltage power supply 90 and the high voltage power supply 91, respectively. 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 as to be biased toward 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 at the nip portion with the second conductive rubber roller 62, and the electrical resistance of the conductive rubber roller is likely to increase.

Therefore, in this embodiment, in order to suppress the increase in electrical resistance caused by such polarization, a voltage is applied from the upper power supply roller 901 and the lower power supply roller 911 to the upper charge adjustment roller 900 and the lower charge adjustment roller 910, respectively. The polarization of ions generated at the nip portion between the upper charge adjustment roller 900 and the lower charge adjustment roller 910 in the elastic layers 903 and 913 is alleviated at the nip portion 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. The polarization of ions in the upper charge adjustment roller 900 and the lower charge adjustment roller 910 is suppressed, and the resistance of the upper charge adjustment roller 900 and the lower charge adjustment roller 910 due to use can be suppressed from increasing. As a result, the charge adjustment device 9 can stably adjust the charge of the sheet over a long period of time.

[Example 1]
Next, an experiment conducted to confirm the effect of the present embodiment will be described. In the experiment, the charge adjustment device 9A shown in FIG. 5A was used. The charge adjustment device 9A of Example 1 has a charge adjustment roller 900Aa as a first roller, a counter roller 910Aa as a second roller, a power supply roller 901Aa as a power supply rotor, and a high voltage power supply 90A as a power source. The charge adjustment roller 900Aa has a metal core (rotating shaft) 902Aa as a conductive shaft portion, and an elastic layer 903Aa as an outer periphery containing an ion conductive material formed on the outer periphery of the core 902Aa. The charge adjustment roller 900Aa is a semiconductive roller, and the elastic layer 903Aa is formed of an ion conductive material formed by blending nitrile rubber and ethylene-epichlorohydrin copolymer. The charge adjustment roller 900Aa is electrically floating.

The opposing roller 910Aa is arranged to sandwich the sheet between it 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 spring members, so that the elastic layer 903Aa is pressed against the opposing roller 910Aa to form a nip portion. The opposing roller 910Aa is grounded.

The power supply roller 901Aa is in contact with the charge adjustment roller 900Aa and can supply a current to the charge adjustment roller 900Aa. The high voltage power supply 90A can apply a voltage of one of positive and negative polarity to the power supply roller 901Aa. In the first embodiment, 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 may be a constant voltage power supply.

In the experiment, the voltage fluctuation was measured when a constant current was continuously applied from the high voltage supply 90A to the charge adjustment device 9A having such a configuration. The experimental conditions were as follows. The opposing roller 910Aa and the power supply roller 901Aa were metal rollers each having a diameter of 30 mm. The charge adjustment roller 900Aa was a semiconductive roller having a diameter of 20 mm. The high voltage supply 90A was a constant current source. Each roller rotated at 240 mm/sec in the direction of the arrow, and a current of 20 μA was continuously applied from the high voltage supply 90A.

Figure 5(b) shows the measurement results of Experimental Example 1. In Figure 5(b), the horizontal axis is time and the vertical axis is applied voltage. From this result, it can be seen that although short-term voltage fluctuations remain across days, long-term voltage fluctuations are hardly observed and 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 bottom to top in the figure, but it may be reversed.

[Modification 1]
FIG. 6 shows a modified example 1 of this embodiment. The charge adjustment device 9B of the modified example 1 has a charge adjustment roller 900A as a first roller, a counter roller 910A as a second roller, a power supply roller 901A as a power supply rotor, and a high voltage power supply 90A as a power source and a first power source, as in the case of the embodiment 1 shown in FIG. 5(a). 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 containing an ion conductive material formed on the outer periphery of the core 902A. The charge adjustment roller 900A is a semiconductive roller, and the elastic layer 903A is formed of an ion conductive material formed by blending nitrile rubber and ethylene-epichlorohydrin copolymer. In the case of the modified example 1, the charge adjustment roller 900A is also floating. However, in the modified example 1, unlike the embodiment 1, the counter roller 910A is not grounded but is connected to the high voltage power supply 91A as a second power source.

Furthermore, the opposing roller 910A and the power supply roller 901A are each a metal roller having an outer diameter of, for example, φ16 mm. The charge adjustment roller 900A is a semiconductive roller. The elastic layer 903A is made of an ionically conductive material formed by blending 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.

The high voltage power supply 90A connected to the power supply roller 901A can apply a voltage of one of positive and 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 counter roller 910A can apply a voltage of the other of positive and negative polarity to the counter 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.

In the case of this variant 1, by applying voltages from the high voltage power supplies 91A and 90A to the opposing roller 910A and the power supply roller 901A, respectively, a current flows in the direction of the arrow from the opposing roller 910A to the power supply roller 901A via the charge adjustment roller 900A. As a result, as in the case described in the first embodiment, the polarization of the ions in the charge adjustment roller 900A is suppressed, and the resistance of the charge adjustment roller 900A is prevented from increasing with use. As a result, the charge adjustment device 9B can stably adjust the charge of the sheet over a long period of time.

[Modification 2]
Fig. 7 shows a second modification of this embodiment. The charge adjustment device 9C of the second modification has an upper charge adjustment roller 900 as a first roller and a lower charge adjustment roller 910 as a second roller, similar to the first embodiment shown in Fig. 3. The charge adjustment device 9C also has an upper power supply roller 901 as a power supply rotator and a first power supply rotator, a lower power supply roller 911 as a second power supply rotator, a high voltage power supply 90 as a power supply and a first power supply, and a high voltage power supply 91 as a second power supply.

Here, the upper charge adjustment roller 900 is electrically floating, but the lower charge adjustment roller 910 is grounded. In this embodiment, the lower charge adjustment roller 910 is grounded, but 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. Current also flows 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 in the case 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 resistance of the upper charge adjustment roller 900 and the lower charge adjustment roller 910 can be suppressed from increasing due to use. As a result, the charge adjustment device 9B can stably adjust the charge of the sheet over a long period of time. 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 floating and the other may be grounded, or both may be grounded.

Second Embodiment
The second embodiment will be described with reference to Figures 8 to 12. In the first embodiment described above, the charge adjustment roller is floating, but in this embodiment, the charge adjustment roller is grounded. Since the other configurations and functions are the same as those of the first embodiment described above, the same reference numerals are used for the similar configurations, and the description will be omitted or simplified. The following description will focus on the points that are different from the first embodiment.

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

Furthermore, the opposing roller 910A and the power supply roller 901A are each a metal roller having an outer diameter of, for example, φ16 mm. The charge adjustment roller 900A is a semiconductive roller. The elastic layer 903A is made of an ionically conductive material formed by blending 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.

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

[Example 2]
Next, an experiment conducted to confirm the effect of the present embodiment will be described. In the experiment, a charge adjustment device 9E shown in FIG. 9A was used. The charge adjustment device 9E of Example 2 has a charge adjustment roller 900Aa as a first roller, an opposing roller 910Aa as a second roller, and a power supply roller 901Aa as a power supply rotating body, as in Example 1 shown in FIG. 5A. 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 a voltage to the power supply roller 901Aa is a constant current power supply, and the high voltage power supply 91B that applies a voltage to the opposing roller 910Aa is also a constant current power supply.

In the experiment, the voltage fluctuation was measured when a constant current was continuously applied from the high voltage power supplies 90B and 91A in the charge adjustment device 9E having such a configuration. The experimental conditions were as follows. The opposing roller 910Aa and the power supply roller 901Aa were each metal rollers with a diameter of 30 mm. The charge adjustment roller 900Aa was a semiconductive roller with a diameter of 20 mm. Each roller rotated at 240 mm/sec in the direction of the arrow, and a current of 20 μA was continuously applied from the high voltage power supplies 90B and 91A.

Figure 9(b) shows the measurement results of experimental example 2. In Figure 9(b), the horizontal axis is time and the vertical axis is applied voltage. Note that the solid line in Figure 9(b) shows the applied voltage of the high voltage feed 90B, and the dashed line shows the applied voltage of the high voltage feed 91A. From this result, it can be seen that although short-term voltage fluctuations remain across days, there is almost no long-term voltage fluctuation and the applied voltage is stable. Note that the charge adjustment device 9E shown in Figure 9(a) is an experimental configuration, so the current flows from bottom to top in the figure, but it may be reversed.

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

[Modification 4]
Fig. 11 shows a fourth modified example of this embodiment. The charge adjustment device 9G of the fourth modified example has a charge adjustment roller 900A as a first roller and an opposing roller 910A as a second roller, similar to the second embodiment shown in Fig. 8. Furthermore, the charge adjustment device 9G has a power supply roller 901A as a power supply rotor, a power supply 90B as a power source and a first power source, and a power supply 91A as a second power source. However, in the fourth modified example, the power supply 90B that applies a voltage to the power supply roller 901A is a constant voltage power source, and the power supply 91A that applies a voltage to the opposing roller 910A is also a constant voltage power source.

[Modification 5]
Fig. 12 shows a fifth modified example of this embodiment. The charge adjustment device 9H of the fifth modified example has a charge adjustment roller 900A as a first roller and an opposing roller 910A as a second roller, similar to the second embodiment shown in Fig. 8. Furthermore, the charge adjustment device 9H has a power supply roller 901A as a power supply rotor, a high voltage power supply 90A as a power source and a first power source, and a high voltage power supply 91B as a second power source. However, in the fifth modified example, the high voltage power supply 90A that applies a voltage to the power supply roller 901A is a constant current power source, and the high voltage power supply 91B that applies a voltage to the opposing roller 910A is also a constant current power source.

Third Embodiment
As a third embodiment, a preferable relationship between the external power supply current and the charge removal current in the configuration of each of the above-mentioned embodiments will be described. Here, the charge removal current is a current flowing into the sheet in the nip portion, and the external power supply current is a current flowing out of the sheet in the nip portion. Specifically, in Figs. 3 and 7, the power supply rotor to which a positive voltage is applied is the first rotor, and the power supply rotor to which a negative voltage is applied is the second rotor, among the first and second power supply rotors. In this case, the current flowing through the first rotor is the charge removal current, and the current flowing through the second rotor is the external power supply current. That is, in Figs. 3 and 7, the current flowing through the upper power supply roller 901 is the charge removal current, and the current flowing through the lower power supply roller 911 is the external power supply current. Also, in Fig. 5(a), the current flowing through the power supply roller 901Aa as the power supply rotor is the charge removal current, and the current flowing through the counter roller 910Aa as the second roller is the external power supply current.

Furthermore, in Figures 6, 8 to 12, of the power supply rotor and second roller, the power supply rotor or roller to which a positive voltage is applied is the first rotor, and the power supply rotor or roller to which a negative voltage is applied is the second rotor. In this case, the current flowing through the first rotor is the charge removal current, and the current flowing through the second rotor 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 charge removal 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 charge removal current, and the current flowing through the opposing roller 910Aa is the external power supply current.

[Example 3]
In the following, the charge adjustment device 9E of the second embodiment shown in FIG. 9A will be described as a representative example, but the same applies to other charge adjustment devices. FIG. 13 shows the relationship between the neutralization current and the external power supply current. When considering the sign of the current based on the sheet in the nip portion, the current flowing into the sheet (neutralization current) is generally positive, and the current flowing out of the sheet (external power supply current) is generally negative. However, in this example, in order to make it easier to compare the neutralization current and the external power supply current, the neutralization current and the external power supply current will be described in terms of absolute values. Also, in FIG. 13, the neutralization current is indicated by a thin line, and the external power supply current is indicated by a thick line.

The charge removal current and external power supply current are roughly classified into three processes over time: pre-rotation, charge adjustment, and post-rotation. Here, pre-rotation is the period during which the charge adjustment roller 900Aa, the opposing roller 910Aa, and the power supply roller 901Aa rotate before the leading edge of the first sheet enters the nip in an image forming job in which images are formed continuously on multiple sheets. Charge adjustment is the period during which multiple sheets pass through the nip, and includes not only the period during which the sheet actually passes through the nip, but also the period (between sheets) from when the trailing edge of the sheet passes through the nip until the leading edge of the succeeding sheet enters the nip, i.e., between sheets. Even during charge adjustment, the charge adjustment roller 900Aa, the opposing roller 910Aa, and the power supply roller 901Aa rotate. Post-rotation is the period during which the charge adjustment roller 900Aa, the opposing roller 910Aa, and the power supply roller 901Aa rotate after the trailing edge of the last sheet in an image forming job has passed through the nip portion.

Figure 14(a) is a graph showing the amount of charge removed, and Figure 14(b) is a graph showing the amount of charge supplied from an external source. Note that the amount of charge in this embodiment is the value obtained by integrating the current value over time, and is the area of the shaded portion in Figures 14(a) and 14(b). In this embodiment, the amount of charge supplied from an external source and the amount of charge removed from a static electricity source during charge adjustment are set to be close to each other. Specifically, the difference between the amount of charge supplied from an external source and the amount of charge removed from a static electricity source is set to be within a range of ±10%. In other words, the amount of charge removed from a static electricity source is set to be 90% or more and 110% or less of the amount of charge supplied from an external source. As for the range of integration, since there is a transient response, it is assumed that the rise occurs at 90% of the target value for the rise, and the same is true for the fall.

In this example, the value of the neutralization current during forward and backward rotation and the value of the external power supply current were set to the same value of 30 μA. During charge adjustment, the current value of the neutralization current while the sheet was passing through the nip portion was set to a constant value of 40 μA, and the current value of the neutralization current between the sheets was set to a constant value of 30 μA. The current value of the external power supply current during charge adjustment was set to 35 μA, which is between the current value of the neutralization current while passing, 40 μA, and the current value between the sheets, 30 μA.

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

Next, a durability test was conducted in which images were continuously formed using an image forming apparatus with a peripheral speed of 200 mm/sec in the same temperature and humidity environment. In the test, A4 size Canon Inc. paper GF-C081 (basis weight 81.4 g/m ² ) was used. In this test, a cumulative number of 600,000 sheets of this paper were passed through the nip portion of the charge adjustment device 9E, and 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 slightly higher than the initial resistance value and was 1.25 times higher. However, there was no increase in resistance to the extent that the resistance value changed by an order of magnitude as in the past, and sufficient effects were confirmed.

In this way, in each of the above-mentioned embodiments, the amount of charge present on the surface of the sheet is adjusted, which makes it possible to prevent sheets from sticking together due to electrostatic forces and to perform stable charge adjustment over a long period of time.

As described above, the absolute value of the externally supplied current during charge adjustment, which is a period that includes the passage and the paper gap, is set to a value between the absolute value of the neutralization current during passage and the absolute value of the neutralization current between the papers. This allows ions polarized due to the influence of the neutralization current to be suitably alleviated by the externally supplied current. Also, since the externally supplied charge amount and the neutralization charge amount during charge adjustment are close in value, ions polarized due to the influence of the neutralization current can be suitably alleviated by the externally supplied current.

Furthermore, as described above, the externally supplied current when the sheets are continuously passed through the nip of the charge adjustment device is set to a constant value between the current value during the passage of the neutralization current and the current value between the sheets. This makes it possible to obtain a high effect of alleviating the polarization of the conductive agent caused in the neutralization process with the externally supplied current, with simple control without complex control.

<Other embodiments>
The present invention is not limited to the above-described embodiments, but can be applied to other power supply members and other types of image forming apparatuses. Furthermore, the numerical values used in the description of the above-described embodiments are merely examples, and the present invention is not limited thereto.

The disclosure of this embodiment also includes the following configuration:

7 Fixing device (fixing section)
9, 9A, 9B, 9C, 9D, 9E, 9F, 9G, 9H Charge adjustment device 90, 90A, 90B High voltage power supply (power supply, first power supply)
91, 91A, 91B High voltage power supply (second power source)
100 Image forming apparatus 110 Control unit 900 Upper charge adjustment roller (first roller)
900Aa, 900A Charge conditioning roller (first roller)
901 Upper power supply roller (power supply rotor, first power supply rotor)
901Aa, 901A Power supply roller (power supply rotating body)
902, 902Aa Core metal (shaft portion, first shaft portion)
903, 903Aa Elastic layer (outer periphery, first outer periphery)
910 Lower charge conditioning roller (second roller)
910Aa, 910A opposing roller (second roller)
911 Lower power supply roller (second power supply rotor)
912 Core metal (second shaft part)
913 Elastic layer (second outer periphery)

Claims (4)

A charge adjustment device for adjusting the charge on a sheet on which a toner image is fixed,
a first roller having a conductive shaft portion and an outer circumferential portion including an ionically conductive material formed on the outer circumferential surface of the shaft portion, the first roller being grounded;
a second roller disposed to sandwich a sheet between the first roller and the second roller;
a current supplying rotor that is in contact with the first roller and is capable of supplying a current to the first roller;
A first power source capable of applying a voltage of one of a positive polarity and a negative polarity to the power supply rotor;
a second power source capable of applying a voltage of one of a positive polarity and a negative polarity to the second roller;
during a period in which a plurality of sheets are successively passed through a nip portion between the first roller and the second roller, an amount of charge applied to the power supply rotor by the first power source is 90% or more and 110% or less of an amount of charge applied to the second roller by the second power source;
16. A charge balancing device comprising: 2. The charge adjustment device of claim 1, wherein at least one of the first power supply and the second power supply is a constant voltage power supply. 2. The charge conditioning device of claim 1, wherein at least one of the first power supply and the second power supply is a constant current power supply. A charge adjustment device according to any one of claims 1 to 3;
A transfer unit that transfers a toner image onto a sheet;
a fixing unit that applies heat and pressure to the sheet onto which the toner image has been transferred by the transfer unit to fix the toner image onto the sheet, and conveys the sheet onto which the toner image has been fixed to the charge adjusting device.
1. An image forming apparatus comprising:

Images