JP2006084730A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily prevent transfer failures caused by the fluctuations in the resistance of a transfer roller, and to prevent increase in the output of a bias power supply. <P>SOLUTION: A toner image formed by an electrophotographic process is carried on a photoreceptor drum 11, a transfer roller 12 is brought into contact with the photoreceptor drum and a transfer nip part, and a transfer bias current is supplied to the transfer roller, to transfer the toner image onto a transfer material sent to the transfer nip part. The transfer roller comprises a conductive shaft core 12a and an ionic conductive material 12b, disposed on the outer peripheral face of the conductive shaft core, and a power feed roller 13 abuts against the surface of the transfer roller, and the power feed roller is connected to a transfer bias power supply 14. The transfer bias power supply is connected to the conductive shaft core through a resistor 15. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a composite machine using an electrophotographic process, and in particular, supplies a transfer bias current to a transfer roller to transfer a toner image on an image carrier. The present invention relates to a transfer device for transferring to a transfer material such as recording paper.

  In an image forming apparatus using an electrophotographic process, when a toner image formed on a photosensitive drum, which is an image carrier, is transferred to a transfer material such as recording paper, a voltage is applied to the corotron or scorotron charger for transfer. However, in recent years, transfer rollers have been used from the viewpoints of suppressing the amount of ozone generated, transport stability of a transfer material, lowering the output of a transfer bias transformer, and the like.

  Generally, an electroconductive transfer roller in which carbon having excellent environmental stability is dispersed in EPDM (ethylene propylene rubber) or the like is used as a transfer roller. If an amorphous silicon (a-Si) photosensitive drum is used, abnormal discharge due to charge concentration occurs due to uneven dispersion of carbon, and the Si-C layer that is a protective layer of the photosensitive member may be destroyed. In other words, so-called black spots are generated at the portion where the Si-C layer is destroyed.

  On the other hand, in the transfer roller (ion conductive type) using an ionic conductive material such as epichlorohydrin, the abnormal discharge as described above is difficult to occur. For this reason, although the generation of black spots is suppressed, There is a problem that the resistance value fluctuates greatly, and further, the ionic conductive material is biased with the energization time, which increases the resistance value and deteriorates the durability of the transfer roller.

  In order to prevent the above-mentioned problems, for example, a dielectric layer is disposed on the surface of the transfer roller so as to easily control the charge supply operation of the transfer roller, and charges are supplied to the surface of the dielectric layer. (See Patent Document 1).

  Furthermore, in order to obtain stable transferability regardless of changes in environmental conditions, a dielectric layer is formed on the elastic roller, and the back surface of the dielectric layer is electrically floated with respect to the surface of the elastic roller. There is one in which the back surface of the dielectric layer is grounded according to the fluctuation (see Patent Document 2).

  On the other hand, in order to prevent deterioration of the toner image due to electric discharge, the contact point with the transfer roller is located downstream of the extended line connecting the center point of the nip portion formed by the transfer roller and the image carrier and the center point of the transfer roller. The electrode member is arranged so that the transfer roller is biased, and a transfer bias is applied from the electrode member to the transfer roller to reduce the electric field change on the paper entrance side, and the total resistance value of the transfer roller as viewed from the power source side is reduced. Thus, the power source capacity is reduced (see Patent Document 3).

JP-A-6-138784 (pages 10 to 25, FIGS. 7 to 8) Japanese Patent Laid-Open No. 9-34278 (pages 7 to 9, FIGS. 2 to 4) JP 2003-5539 A (pages 4 to 6, FIGS. 2 to 3)

  As described above, the ionic conductive type transfer roller is unlikely to cause abnormal discharge due to charge concentration, but the resistance value of the ionic conductive material varies greatly due to environmental fluctuations. For example, the resistance value is 1.5 to 2 digits. It varies to some extent. Specifically, the resistance value increases in the order of low temperature and low humidity environment, normal temperature and normal humidity environment, and high temperature and high humidity environment. In the α-Si photosensitive drum, it is necessary to pass a larger transfer current than in the OPC photosensitive drum. For this reason, if the resistance value of the transfer roller greatly fluctuates due to environmental fluctuations, the transfer roller has a low temperature and low humidity environment. Since the resistance value increases, the output voltage of the transfer bias power supply must be increased in order to allow a specified current to flow through the transfer roller, and the upper limit value of the output voltage of the transfer bias power supply is set. May cause a transfer failure due to insufficient transfer current.

  On the other hand, in the image forming apparatuses described in Patent Documents 1 and 2, since the dielectric layer is formed on the surface of the image forming apparatus, unevenness in transfer charge accumulation of the dielectric layer is likely to occur. For this reason, it is necessary to perform a control operation for determining the voltage to be applied to the transfer roller and a control for detecting the resistance value of the transfer member during image formation, and there is a problem that the control at the time of transfer becomes complicated. .

  Furthermore, in the image forming apparatus described in Patent Document 2, it is necessary to perform control for grounding the back surface of the dielectric layer according to environmental conditions or the type of transfer material, and as a result, the control becomes more complicated. There is a problem of end.

  In the image forming apparatus described in Patent Document 3, the change in the electric field on the paper entry side is reduced to prevent the toner image from being deteriorated due to the discharge, but this is caused by the resistance value fluctuation of the transfer roller. Transfer defects cannot be prevented.

  In any case, in the conventional image forming apparatus, there is a problem that it is difficult to easily prevent a transfer failure due to a change in resistance value of the transfer roller.

  Therefore, an object of the present invention is to provide an image forming apparatus that can prevent transfer failure and increase in bias power output with a simple configuration.

  In order to solve the above-described problems, the present invention provides an image carrier that carries a toner image formed by an electrophotographic process, a transfer roller that is in contact with the transfer nip, and a transfer bias current applied to the transfer roller by constant current control. A transfer bias power supply for supplying the transfer roller, and transferring the toner image onto a transfer material sent to the transfer nip portion. An ionic conductive material disposed on an outer peripheral surface, and the transfer roller is connected to the transfer bias power source via a power supply member in contact with the surface of the transfer roller and a resistor connected to the conductive shaft core. It is characterized by being connected to.

  In the present invention, the power supply member is in contact with the transfer roller on the side opposite to the image carrier with the transfer roller interposed therebetween, and when the resistance value of the transfer roller varies due to temperature and humidity, the resistance The resistance value of the container is set to a value that is less than the upper limit and exceeds the lower limit of the fluctuation range of the resistance value of the transfer roller. The image carrier has, for example, an amorphous silicon photoconductor as a photoconductor.

  As described above, in the image forming apparatus of the present invention, the transfer roller has the conductive shaft core and the ion conductive material disposed on the outer peripheral surface of the conductive shaft core, and the transfer roller is further connected to the transfer roller. The transfer roller is connected to the transfer bias power source through a power supply member that abuts on the surface of the roller and a resistor connected to the conductive shaft, so that the resistance value of the transfer roller increases due to fluctuations in environmental conditions (temperature and humidity). When the resistance value of the resistor is exceeded, most of the transfer bias current is supplied to the conductive shaft core via the resistor, and the apparent resistance value of the transfer roller is reduced. As a result, the transfer roller In addition to preventing transfer failure due to the resistance value fluctuation, it is possible to prevent an increase in bias power supply output.

  In the present invention, since the resistance value of the resistor is set to a value that is less than the upper limit of the fluctuation range of the resistance value of the transfer roller and exceeds the lower limit, the fluctuation of the resistance value of the transfer roller is substantially suppressed and simplified. In addition, there is an effect that it is possible to prevent a transfer failure due to a change in resistance value of the transfer roller.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, but are merely illustrative examples. Not too much.

  Referring to FIG. 1, an illustrated transfer device 10 is used together with an image forming apparatus (not shown), and abuts an α-Si photosensitive drum 11 (hereinafter simply referred to as a photosensitive drum 11) as an image carrier. A transfer roller 12 is provided. A toner image is formed on the photosensitive drum 11 by an electrophotographic process, and the transfer roller 12 is in contact with the photosensitive drum 11 at the transfer nip portion. Then, a transfer bias current is supplied to the transfer roller, and the toner image is transferred to a transfer material sent to the transfer nip portion.

  For example, a power supply roller (power supply member) 13 using a conductive material such as SUS is in contact with the transfer roller 12. The power supply roller 13 is disposed on the side opposite to the photosensitive drum 11, and a transfer bias power supply 14 is provided. (The photosensitive drum 11 is grounded). The transfer roller 12 is made of an ion conductive material such as epichlorohydrin rubber, and the ion conductive material 12b is formed on the outer peripheral surface of the conductive shaft core 12a.

  For example, the ion conductive material 12b is wound around the conductive shaft core 12a as a single-layer solid or a foamed elastic body. As the ionic conductive material, in addition to the aforementioned epichlorohydrin rubber, a metal complex (for example, lithium perchlorate) or 1 ethyl-3methyl-imidazolium-bis (trifluoromethylsulfonyl) imide or the like added to NBR or the like Can be used.

  The ionic conductive material 12b is sandwiched between a plus electrode and a minus electrode (both not shown), and when a voltage is applied between the plus electrode and the minus electrode, the ion conductive material 12b is added by an electric field formed by the applied voltage. Ions and negative ions move in the transfer roller, and current flows. In the illustrated example, the conductive axis 12a is connected to a transfer bias power source 14 via a resistor 15, and this transfer bias power source 14 is grounded.

  Here, with reference to FIG. 2, first, a transfer operation when a transfer bias is directly applied to the transfer roller 12 will be described. When the transfer bias power source 14 is connected to the shaft core 12a of the transfer roller 12 and a transfer bias is applied, the transfer current is transferred from the shaft core 12a of the transfer roller 12 to the photosensitive drum 11 and the transfer roller as indicated by an arrow A. 12 flows in the direction of the transfer nip where the transfer material 16 is sandwiched. In this case, the ions in the ion conductive material 12b flow and polarize in the transfer nip portion toward the outer periphery of the transfer roller 12, and the resistance value increases with the passage of energization time. It should be noted that the influence of polarization becomes significant, and transfer defects appear after several tens of hours after use.

  On the other hand, when environmental conditions such as temperature and humidity vary, the resistance value of the transfer roller 12 varies greatly in the transfer apparatus shown in FIG. Referring to FIG. 3, if a transfer bias of 1 kV is applied to the shaft core 12a of the transfer roller 12, the roller resistance value is about 8 at log Ω at low temperature / low humidity (L / L). On the other hand, when it is normal temperature / normal humidity (N / N), logΩ = about 7, and when it is high temperature / high humidity (H / H), logΩ = about 6.5. Thus, when the ratio of ion mobility in the ion conductive material 12b changes due to the change in temperature and humidity, and the temperature and humidity change, the roller resistance value changes by about 1.5 to 2 digits. Will end up.

  4 and 5, when a transfer bias is applied to the transfer roller 12 via the power supply roller 13, the transfer current is transferred from the power supply roller 13 to the transfer roller 12 as indicated by an arrow B in FIG. Then, as shown by an arrow C, a transfer current flows from the shaft core 12 a to the transfer nip portion between the transfer roller 12 and the photosensitive drum 11 as indicated by an arrow C. At this time, since the transfer roller 12 is rotating, a portion of the transfer roller 12 that was initially in contact with the photosensitive drum 11 (hereinafter referred to as a specific portion) moves, and the transfer roller 12 is in an initial state. In this state, the specific portion is located on the power supply roller 13 side.

  That is, in the specific portion, when the transfer roller 12 rotates 180 degrees, the direction of the transfer current flowing from the shaft core 12a is reversed, and as a result, the electric field applied to the ion conductive material 12b is changed every half rotation of the transfer roller 2. In the opposite direction. For this reason, when viewed from the ions in the ionic conductive material 12b, the direction of the electric field is reversed every half circle. For example, as shown in FIG. When a negative voltage is applied, negative ions are collected at the specific portion from the shaft core 12a of the transfer roller 12 to the photosensitive drum 11 toward the photosensitive drum 11, and from the power supply roller 13 to the shaft core 12a toward the shaft core 12a. Thereafter, in a state where the transfer roller 12 makes a half turn, ions gathered on the photosensitive drum 11 side gather on the axial core 12a side, and ions gathered on the axial core 12a side gather on the photosensitive drum 11 side. Accordingly, the ions in the ion conductive material 12b are alternately moved to the outer peripheral portion and the axis 12a side every half circumference of the transfer roller 12, and polarization does not occur.

  In the transfer apparatus shown in FIG. 4, since polarization does not occur as described above, an increase in the roller resistance value due to energization can be suppressed even when a high voltage is applied to the transfer roller 12. When the environmental conditions such as are changed, as described with reference to FIG. 2, the ratio of the ion mobility in the ion conductive material 12b is changed, and the roller resistance value is changed by about 1.5 to 2 digits.

  Again referring to FIG. 1, as described above, in the illustrated example, the shaft core 12 a of the transfer roller 12 is connected to the transfer bias power source 14 via the resistor 15. Here, the resistance value of the resistor 15 is R2, and the resistance value of the transfer roller 12 is Rv (resistance value between the shaft core 12a and the transfer roller surface). As described above, the resistance value Rv changes according to changes in temperature and humidity, and the resistance value Rv decreases as the temperature and humidity become higher. The resistance value of the transfer roller 12 in N / N to H / H (N / N or more and H / H or less) is represented by Rvh, and the transfer roller 12 in L / L to N / N (L / L or more and less than N / N). Is represented by Rvl, and Rvh <R2 <Rvl is set.

  Therefore, in the N / N to H / H environment, the resistance value of the transfer roller 12 is lower than the resistance value of the resistor 15, so that most of the transfer current is supplied from the power supply roller 13 to the transfer roller 12. (See FIG. 6). On the other hand, under the L / L environment, the resistance value of the transfer roller 12 becomes large, and the resistance value of the transfer roller 12 becomes higher than the resistance value of the resistor 15, and as shown in FIG. Will flow directly to the shaft core 12a.

  As described above, the current flowing through the transfer roller 12 selectively flows through the resistor 15 according to the environmental conditions (temperature and humidity) in which the transfer device 10 is disposed. That is, as shown in FIG. 7, when the temperature and humidity are L / L, most of the transfer current is supplied to the shaft core 12a of the transfer roller 12 via the resistor 15, and the apparent transfer roller 12 The resistance value is Rvl + R2, and (Rvl + R2) <2Rvl.

  On the other hand, when the temperature / humidity is N / N to H / H, most of the transfer current is supplied to the transfer roller 12 via the power supply roller 13 as shown in FIG. Inversion does not occur and polarization does not occur (the ionic conductive material is not biased, and an increase in resistance value is suppressed).

  Here, using the transfer device shown in FIG. 1, the transfer device shown in FIG. 2, and the transfer device shown in FIG. 4, the variation of the transfer voltage when the environmental condition (temperature and humidity) changed was examined. The results are shown in FIGS. FIG. 8A shows the fluctuation of the transfer voltage in the transfer apparatus shown in FIG. 2, and FIG. 8B shows the fluctuation of the transfer voltage in the transfer apparatus shown in FIG. FIG. 8C shows the fluctuation of the transfer voltage in the transfer apparatus shown in FIG. Here, the resistance value of the resistor 15 is set to 10 MΩ.

  8A to 8C, when the temperature and humidity are L / L, N / N, and H / H, the transfer current (constant current control) is 50 μA, 80 μA, and 100 μA, respectively. 8A, when the transfer current is 50 μA, 80 μA, and 100 μA, the transfer roller resistance value is 8.1, 7.1, and 6.5 in logΩ (in FIG. 8A, the apparent value is shown). The resistance value is the same as the transfer roller resistance value). The transfer voltages were 6.3 kV, 1.0 kV, and 0.3 kV, respectively.

  Similarly, in FIG. 8B, when the transfer current is 50 μA, 80 μA, and 100 μA, the transfer roller resistance value is 7.8, 6.8, and 6.2 in logΩ (in FIG. 8B). Are apparent resistance values of 8.1, 7.1, and 6.5, respectively). The transfer voltages were 6.3 kV, 1.0 kV, and 0.3 kV, respectively.

  On the other hand, in FIG. 8C, when the transfer current is 50 μA, 80 μA, and 100 μA, the transfer roller resistance values are 7.8, 6.8, and 6.2 in logΩ (in FIG. 8C). The apparent resistance values were 7.9, 7.0, and 6.5, respectively). The transfer voltages were 3.6 kV, 0.8 kV, and 0.3 kV, respectively.

  In this way, the power supply roller 13 is brought into contact with the transfer roller 12 on the opposite side of the photosensitive drum 11 to perform power supply, and the shaft core 12a of the transfer roller 12 is connected to the transfer bias power supply 14 via the resistor 15 ( 1), even when the temperature and humidity are L / L, that is, when the resistance value of the transfer roller 12 fluctuates and becomes large (see FIG. 3), compared to the transfer device shown in FIGS. (See FIGS. 8 (a) and 8 (b)), an increase in transfer voltage can be suppressed (transfer voltage is reduced from 6.3 kV to 3.6 kV). As a result, by simply inserting the resistor 15 between the transfer bias power supply 14 and the shaft core 12a of the transfer roller 12, transfer defects caused by fluctuations in the resistance value of the transfer roller can be easily prevented, and transfer can be performed. An increase in the bias power supply output can be prevented. In a normal office environment, a low temperature and low humidity environment occurs only within a very limited time, such as immediately after the start of a cold district. Therefore, most of the transfer bias current is a resistor connected to the shaft core 12a of the transfer roller 12. 15, the ionic conductive material 12b constituting the transfer roller 12 is polarized and the influence thereof does not appear (as described above, the transfer is performed via the shaft core 12a of the transfer roller 12 for several tens of hours or more. If an electric current is continuously applied, an influence of polarization such as transfer failure occurs.

  That is, in the N / N environment to the H / H environment, the resistance value of the transfer roller is lower than the resistance value of the resistor, and the transfer bias current is applied to the transfer roller via the power supply roller, and the L / L environment. In this case, the resistance value of the transfer roller rises and becomes larger than the resistance value of the resistor, and the transfer bias current is supplied via the axis of the transfer roller (transfer bias via the power supply roller). When the current is supplied, the resistance layer is doubled as compared with the case where the transfer bias current is supplied via the shaft core, and the configuration of FIGS. Since it is assumed that the transfer bias power source 14 is used, the transfer current that can flow to the transfer roller in each environment is the same.In the case of the configurations of FIGS. Set it in half compared to the case Using ion conductive material). For this reason, the apparent transfer roller resistance value is low under the L / L environment.

  On the other hand, in the N / N environment to the H / H environment, the transfer bias current is supplied to the transfer roller via the power supply roller, and the electric field is reversed by one rotation of the transfer roller, so that the ion conductive material in the ion conductive material Bias, that is, polarization does not occur, and an increase in the resistance value of the transfer roller can be suppressed.

  Further, when the α-Si photosensitive drum is used as the photosensitive drum, it is necessary to increase the transfer bias current. However, as described above, it is possible to suppress fluctuations in the resistance value of the transfer roller with respect to temperature and humidity. In this case, an increase in transfer bias voltage (bias power supply output) can be suppressed.

  Since the transfer roller is connected to the transfer bias power source via a power supply roller that contacts the surface of the transfer roller and a resistor connected to the conductive shaft core, the resistance value of the transfer roller due to temperature and humidity fluctuations is reduced. When the resistance value exceeds the resistance value of the resistor, most of the transfer bias current is supplied to the conductive shaft core via the resistor to prevent transfer defects caused by fluctuations in the resistance value of the transfer roller. As a result, it is possible to prevent an increase in the bias power output, and as a result, it can be applied to an image forming apparatus such as a copying machine, a printer, or a facsimile machine using an electrophotographic process.

1 is a diagram schematically showing a transfer device used in an image forming apparatus according to Embodiment 1 of the present invention. It is a figure which shows roughly the transfer apparatus which applies a transfer bias directly to the axial center of a transfer roller. It is a figure which shows the change of the resistance value of a transfer roller by the fluctuation | variation of environmental conditions (temperature / humidity). It is a figure which shows schematically the transfer apparatus which applies a transfer bias to a transfer roller via a power feeding roller. FIG. 5 is a diagram for explaining a flow of a transfer current in the transfer device shown in FIG. 4. In the transfer apparatus shown in FIG. 1, it is a figure which shows the flow of the transfer electric current when temperature and humidity are high. In the transfer apparatus shown in FIG. 1, it is a figure which shows the flow of the transfer electric current when temperature and humidity are low. FIG. 5 is a diagram showing a change in transfer voltage due to a change in environmental conditions, (a) shows a change in transfer voltage when the transfer device shown in FIG. 2 is used, and (b) uses the transfer device shown in FIG. FIG. 6C is a diagram showing a change in transfer voltage when the transfer device shown in FIG. 1 is used.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Transfer apparatus 11 Photosensitive drum 12 Transfer roller 12a Conductive shaft core 12b Ion conductive material 13 Feed roller 14 Transfer bias power supply 15 Resistor 16 Transfer material

Claims (4)

An image carrier that carries a toner image formed by an electrophotographic process; a transfer roller that is in contact with a transfer nip; and a transfer bias power source that supplies a transfer bias current to the transfer roller by constant current control. In an image forming apparatus comprising a transfer device for transferring the toner image to a transfer material sent to a nip portion,
The transfer roller has a conductive axis and an ionic conductive material disposed on the outer peripheral surface of the conductive axis;
The image forming apparatus, wherein the transfer roller is connected to the transfer bias power source via a power supply member in contact with the surface of the transfer roller and a resistor connected to the conductive shaft core.   The image forming apparatus according to claim 1, wherein the power supply member is in contact with the transfer roller on a side opposite to the image carrier with the transfer roller interposed therebetween. The resistance value of the transfer roller fluctuates due to temperature and humidity,
The image forming apparatus according to claim 1, wherein the resistance value of the resistor is set to a value that is less than an upper limit and exceeds a lower limit of a fluctuation range of the resistance value of the transfer roller.   The image forming apparatus according to claim 1, wherein the image bearing member includes an amorphous silicon photosensitive member as a photosensitive member.

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