JP2010020006A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus less liable to cause irregularities of a carried toner image by making a change of an electrified state of a belt member when passing through a supporting rotating body connected to ground potential more similar to natural attenuation without adding an electrification power source. <P>SOLUTION: A primary transfer downstream roller 20 connected to the ground potential comes into contact with a surface opposite to a toner image carrying surface of the intermediate transfer belt 7 on a downstream side of a primary transfer part T1 for transferring a toner image to the intermediate transfer belt from a photoreceptor drum 1. A scattering phenomenon of the toner image carried on the intermediate transfer belt 7 is caused by rapidly discharging electrification charge of the intermediate transfer belt 7 through the primary transfer downstream roller 20 when passing through the primary transfer downstream roller 20. Then, spiral groove structure is formed on a cylindrical surface of the primary transfer downstream roller 20 to support the intermediate transfer belt 7 linearly by a ridge line of the groove structure. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to an image forming apparatus in which a toner image transferred from an image carrier is directly or indirectly carried on a belt member, and more specifically, the toner image carried on the belt member is less likely to be disturbed at a position passing through a support rotating body. The present invention relates to a structure of a support rotating body.

  The toner image formed on the image carrier is transferred to a belt member (intermediate transfer belt) that passes through the primary transfer portion, transported to the secondary transfer portion, and then collectively secondary to the recording material fed to the secondary transfer portion. An image forming apparatus for transferring is widely used. In addition, an image forming apparatus that transfers a toner image formed on an image carrier onto a recording material carried on a belt member (recording material conveyance belt) and indirectly carries it is widely used.

  These belt members are usually formed in an endless shape, and are supported in a tensioned state over one or more supporting rotating bodies (a driving roller, a tension roller, a steering roller, a stretching roller, etc.).

  In the transfer unit that transfers the toner image from the image carrier to the belt member side, the belt member is charged as the toner image is transferred. Therefore, the belt member carries and moves the toner image in a charged state. When the intermediate transfer belt carrying the toner image in the charged state passes through the support rotating body having the ground potential, the charged state of the intermediate transfer belt may change suddenly and the carried toner image may be disturbed.

  Patent Document 1 discloses a tandem type image forming apparatus in which a plurality of photosensitive drums are arranged along an intermediate transfer belt, and a one-drum type image forming apparatus in which a plurality of developing devices are provided on the photosensitive drum. Here, it is shown that the toner image carried on the intermediate transfer belt causes an image defect called “scattering” when passing through the support rotating body connected to the ground potential.

  In order to prevent “scattering”, it is effective to increase the distance between the primary transfer portion and the support rotator and naturally attenuate the charging state of the intermediate transfer belt before reaching the support rotator. Is shown. It is also effective to apply a voltage having the same polarity as that of the primary transfer portion to the support rotator and recharge the intermediate transfer belt when passing through the support rotator.

JP 2000-298408 A

  When the support rotator located downstream of the transfer unit is insulated from the ground potential or connected to the ground potential through a high resistance, the support rotator is charged up, and the charge state of the intermediate transfer belt can be controlled. Disappear. However, if charging is prevented by connecting the support rotator to the ground potential, as described above, the toner image carried on the intermediate transfer belt may be disturbed when passing through the support rotator.

  In recent years, with the downsizing of photosensitive drums, belt members, housings, and the like, it has become difficult to secure a sufficient distance between a support rotating body positioned downstream of the transfer unit and the transfer unit. In addition, if the process speed is increased to increase the productivity, the rotational speed of the belt member inevitably increases, and natural attenuation of the charged state of the belt member cannot be expected. For this reason, there is a possibility that the toner image carried directly on the belt member (or indirectly via the recording material) may be disturbed by the belt member entering the support rotating body having the ground potential in a charged state at a higher potential than before. Is high.

  However, as shown in Patent Document 1, when the charging power source is arranged on the support rotating body, even if the photosensitive drum and the belt member are downsized, the ground space of the charging power source prevents the image forming apparatus from being downsized. The power consumption of the charging power source increases the running cost, and the component cost of the charging power source increases the manufacturing cost.

  Further, in order to control the charged state of the belt member, it is necessary to control the voltage applied to the support rotating body according to the temperature and humidity, the process speed, the image ratio, and the like. This is because, if the voltage is not controlled, the natural decay of the charged state is prevented, so that the result is not much different from the case where the support rotating body is insulated from the ground potential and the support rotating body is allowed to be charged up. It is.

  The present invention provides an image forming apparatus in which a change in a charged state of a belt member when passing through a support rotating body connected to a ground potential is brought close to natural attenuation without adding a charging power source, and a carried toner image is hardly disturbed. The purpose is to provide.

  The image forming apparatus of the present invention includes an image carrier on which a toner image is formed, and a belt member that carries and moves the toner image transferred from the image carrier at a transfer portion. And a support rotator that supports the belt member such that a conductive cylindrical surface connected to a ground potential contacts an opposite surface carrying a toner image, and the support rotator is configured to support the belt member with respect to the belt member. It has a surface structure in which the continuous contact length in the axial direction of the cylindrical surface is divided.

  In the image forming apparatus of the present invention, since the surface structure divides the continuous contact length of the support rotator in the axial direction with respect to the belt member, the locally charged charge of the belt member is supported in the axial direction of the support rotator. Difficult to move through. For this reason, the toner image on the belt member is less disturbed as the charged charge moves in the axial direction of the support rotator.

  Further, the portion of the belt member that does not need to come into contact with the support rotator due to the surface structure is less likely to discharge charged charges to the support rotator connected to the ground potential.

  Therefore, without adding a charging power source, the change in the charged state of the belt member when passing through the support rotating body connected to the ground potential is brought close to natural attenuation, and the carried toner image is hardly disturbed.

  Hereinafter, some embodiments of the present invention will be described in detail with reference to the drawings. In the present invention, as long as the surface structure in which the charge is not easily diffused to the adjacent position on the belt member is formed on the support rotating body, a part or all of the configuration of the embodiment is replaced with the alternative configuration. This embodiment can also be implemented.

  Therefore, not only the intermediate transfer type in which the toner image is directly carried on the intermediate transfer belt, but also the direct transfer type in which the toner image is carried on the recording material on the recording material conveyance belt. The intermediate transfer type or the direct transfer type is not limited to the one-drum type in which one or more developing devices are attached to the photosensitive drum, but may be a tandem type in which a plurality of photosensitive drums are arranged along the belt member.

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

  In addition, about the general matter of the image forming apparatus shown by patent document 1, illustration is abbreviate | omitted and the overlapping description is abbreviate | omitted. In addition, the reference symbols in parentheses shown in the configuration names used in the claims are examples for assisting understanding of the invention, and are not intended to limit the configuration to the corresponding members in the embodiments. Absent.

<Image forming apparatus>
FIG. 1 is an explanatory diagram of a configuration of the image forming apparatus according to the first embodiment.

  As shown in FIG. 1, the image forming apparatus 100 is a monochrome image forming apparatus in which one photosensitive drum 1 is attached to the intermediate transfer belt 7. The toner image formed on the photosensitive drum 1 is primarily transferred to the intermediate transfer belt 7.

  A charging roller 2, an exposure device 3, a developing device 4, a primary transfer roller 5, and a cleaning device 6 are disposed around the photosensitive drum 1.

  The photosensitive drum 1 has a photosensitive layer of an organic photosensitive member (OPC) formed on the outer peripheral surface of an aluminum cylinder having an outer diameter of 84 mm, is rotatably supported, and rotates in the direction of arrow R1.

  The charging roller 2 is applied with an oscillating voltage obtained by superimposing an AC voltage on a negative DC voltage from the power source D3 to charge the surface of the photosensitive drum 1 to a uniform negative potential.

  The exposure device 3 scans a scanning beam image data obtained by developing the image data with a laser beam that is ON-OFF modulated by a rotating mirror (not shown), and writes an electrostatic image on the surface of the charged photosensitive drum 1.

  The developing device 4 charges a one-component developer containing magnetic toner to a negative polarity, and supports the photosensitive drum 1 on a developing sleeve 4S that rotates around the fixed magnetic pole 4M with a minute gap (300 μm). Supply to drum 1. The power source D4 applies an oscillating voltage obtained by superimposing an AC voltage to a negative DC voltage to the developing sleeve 4S, attaches toner to the exposed area of the photosensitive drum 1, and reversely develops the electrostatic image.

  The primary transfer roller 5 sandwiches the intermediate transfer belt 7 between the photosensitive drum 1 and forms a primary transfer portion (transfer portion) T 1 between the photosensitive drum 1 and the intermediate transfer belt 7. The power source D1 applies a positive direct current voltage (constant voltage) to the primary transfer roller 5 and primarily transfers the toner image of the image carried on the photosensitive drum 1 to the intermediate transfer belt 7 passing through the primary transfer portion T1. Let

  The cleaning device 6 rubs the cleaning blade 6B against the photosensitive drum 1 to remove transfer residual toner attached to the photosensitive drum 1 that has passed through the primary transfer portion T1.

  The intermediate transfer belt 7 carries the toner image N transferred from the photosensitive drum 1 at the primary transfer portion T1 and conveys it to the secondary transfer portion T2. The toner image N carried on the intermediate transfer belt 7 is secondarily transferred to the recording material P fed to the secondary transfer portion T2, and then heated and pressurized by the fixing device 8 to be applied to the surface of the recording material P. It is fixed.

  The secondary transfer roller 12 is in pressure contact with the intermediate transfer belt 7 supported from the inside by the opposing roller 10 to form a secondary transfer portion T <b> 2 between the intermediate transfer belt 7 and the secondary transfer roller 12. The secondary transfer roller 12 is a sponge roller in which an elastic layer based on foamed NBR (nitrile butadiene rubber) is provided on a steel cored bar having an outer diameter of 12 mm, and includes an outer layer including the elastic layer. The diameter was 24 mm. The resistance value of the secondary transfer roller 12 is 107.5Ω (when 2 kV is applied) in an environment of 23 ° C. and 50% Rh by dispersing an ion conductive resistance adjusting agent on the base material of the elastic layer. Adjusted.

  The power supply D2 applies a positive DC voltage (constant voltage) to the secondary transfer roller 12 to form a transfer electric field with the opposing roller 10 connected to the ground potential, and is carried on the intermediate transfer belt 7. The transferred toner image is secondarily transferred to the recording material P.

  The belt cleaning device 13 rubs the cleaning blade 13B against the intermediate transfer belt 7 to remove transfer residual toner attached to the intermediate transfer belt 7 that has passed through the secondary transfer portion T2.

  The potentials of the photosensitive drum 1, the developing sleeve 4S, and the primary transfer roller 5 in an environment of 23 ° C. and 50% Rh are set as follows.

  A DC voltage of −450 V and an AC voltage of 900 Vp-p are applied to the charging roller 2. As a result, the surface of the photosensitive drum 1 is charged with a dark portion potential VD of −450 V, and the portion subjected to laser exposure so as to form an electrostatic latent image with the maximum image density reaches a bright portion potential VL of −200 V. The potential drops.

  To the developing sleeve 4S, a DC voltage Vdc of −300 V, an AC waveform of 9 kHz, and an AC voltage of 1.2 kVp-p with a blank pulse waveform obtained by combining a 4.5 kHz blank are applied.

  When a constant voltage of +400 V is applied to the primary transfer roller 5, the potential difference (primary transfer contrast) between the primary transfer roller 5 and the light portion potential DL of the photosensitive drum 1 becomes 600V.

<Belt member>
The intermediate transfer belt 7 is supported across the drive roller 30, the opposing roller 10, the support roller 11, the primary transfer roller 5, and the primary transfer downstream roller 20, and is driven by the drive roller 30 to rotate in the direction of arrow R2. The intermediate transfer belt 7 is rotationally driven at the same time as the tension is applied by the driving roller 30. The tension of the intermediate transfer belt 7 is applied by a spring (not shown) that supports the drive roller 30. A silicon rubber having a thickness of 1 mm is wound around the surface of the driving roller 30, and slipping is avoided by increasing the frictional force with the intermediate transfer belt 7.

The intermediate transfer belt 7 has a polyimide resin film having a thickness of 85 μm as a base material, carbon black is dispersed in the base material, the surface resistivity is 1 × 10 ¹² Ω / □, and the volume resistivity is 1 × 10 ^9. It is adjusted to ⁵ Ω · cm. The peripheral length of the intermediate transfer belt 7 was 527.5 mm, and the rotation speed (process speed) was 130 mm / sec.

  The intermediate transfer belt 7 is applied with a tension by the driving roller 30, and the applied tension is 1.14 N / cm. The intermediate transfer belt 7 has a Young's modulus of 3.5 GPa.

<Support rotating body>
The support rotating body that first contacts the surface of the intermediate transfer belt 7 on which the toner image is transferred at the primary transfer portion T1 after passing the primary transfer portion T1 is the primary transfer downstream roller 20. . Then, the support rotating body that comes into contact with the opposite surface of the intermediate transfer belt 7 that carries the toner next to the primary transfer downstream roller 20 is a drive roller 30. The cylindrical surfaces of the primary transfer downstream roller 20 and the driving roller 30 are formed with a surface structure that divides the continuous contact length in the axial direction of the support rotating body with respect to the belt member (7).

  The primary transfer downstream roller 20 is a support rotator that is disposed immediately downstream of the primary transfer portion T1 among a plurality of support rotators that stretch and support the intermediate transfer belt. The primary transfer downstream roller 20 is opposed to the optical sensor 15 that detects a reference density toner image (color patch), a position information toner image (registration mark), and the like, and is indispensable to improve the reading accuracy of the toner image. It is a member.

  The primary transfer downstream roller 20 is formed of a stainless steel cylindrical tube having an outer diameter of 16 mm, which is a conductive material, and is connected to a ground potential. In the primary transfer portion T1, the primary transfer downstream roller 20 is charged up if it is not grounded because it contacts the opposite surface of the intermediate transfer belt 7 that is charged by the primary transfer roller 5 and carries the toner image. Sometimes. When the battery is charged up, it may leak to peripheral members and apply electrical stress to the electronic circuit of the image forming apparatus 100.

  At the moment when the opposite surface of the intermediate transfer belt 7 carrying the toner image comes into contact with the primary transfer downstream roller 20, the toner may be scattered from the toner image carried on the surface of the intermediate transfer belt 7 and the toner image may be disturbed. . This is due to the fact that the toner carrying charge supplied from the primary transfer roller 5 to the intermediate transfer belt 7 in the primary transfer portion T1 is rapidly discharged along the bus line of the primary transfer downstream roller 20 in contact therewith. . For this reason, a surface structure is formed on the cylindrical surface of the primary transfer downstream roller 20 to reduce the continuous contact length in the axial direction of the support rotating body with respect to the belt member (7), and before and after contacting the primary transfer downstream roller 20. The change in the charging state of the intermediate transfer belt 7 is reduced.

<Toner image scattering phenomenon>
FIG. 2 is an explanatory diagram of the charged state of the intermediate transfer belt that has passed through the primary transfer portion, and FIG. 3 is an explanatory diagram of the relationship between the primary transfer roller applied voltage and the primary transfer current. FIG. 4 is an explanatory diagram of natural decay of the toner carrying charge, FIG. 5 is an explanatory diagram of rapid discharge when passing through the primary transfer downstream roller, and FIG. 6 is an explanatory diagram of the charged state of the intermediate transfer belt in contact with the primary transfer downstream roller. is there. 4 and 5, (a) is a charge state inside the intermediate transfer belt, and (b) is an equivalent circuit diagram of charge attenuation in the intermediate transfer belt.

  As shown in FIG. 2, in the primary transfer portion T1, the toner carrying charge is injected from the primary transfer roller 5 to the intermediate transfer belt 7 and moves to the toner carrying surface, whereby the toner image N is transferred to the intermediate transfer belt 7. It is carried on the belt 7. Here, the + mark in FIG. 2 schematically represents the toner carrying charge, and the polarity of the toner carrying charge is a plus opposite to that of the negative toner charged to the minus polarity. Since the total amount of toner carrying charges is larger than the total charge amount of the toner image N, an excessive plus charge is present on the toner carrying surface of the intermediate transfer belt 7 immediately after the primary transfer. The amount of charge differs between where the toner is and where it is not.

  As shown in FIG. 3 with reference to FIG. 2, when primary transfer is performed, the value of current flowing from the primary transfer roller 5 is different between where the toner is present and where there is no toner. Where there is no toner, since the surface layer of the photosensitive drum 1 is an insulating layer, the charge moves only by discharge, and the primary transfer setting voltage at which discharge starts between the toner carrying surface of the intermediate transfer belt 7 and the photosensitive drum 1. Until this time, no current flows from the primary transfer roller 5 to the intermediate transfer belt 7.

  On the other hand, when an electric field is applied, the charged toner moves from the photosensitive drum 1 to the intermediate transfer belt 7 when an electric field is applied. Therefore, even when the primary transfer setting voltage at which discharge does not occur, current flows from the primary transfer roller 5 to the intermediate transfer belt 7. Flows in.

  For the above reasons, when the toner image N is primarily transferred to the intermediate transfer belt 7, a considerable amount of charge is injected into the intermediate transfer belt 7 where there is toner, but only a small amount of charge is injected where there is no toner. Not. Then, in the intermediate transfer belt 7 that has passed through the primary transfer portion T1, a large amount of charge is present at a location where toner is present, and a small amount of charge is present where no toner is present, resulting in a difference in the amount of charge.

  However, in actuality, in the toner, the charge amount equal to the total charge amount of the toner image N out of the toner carrying charge is offset with the charge of the toner image N, so that the macro has only an excess charge amount. Looks like it doesn't exist.

  That is, in the process of passing through the primary transfer portion T1, the intermediate transfer belt 7 is injected with charged charges where there is toner and where there is toner, and the amount of charge increases when there is toner. However, in some places where the toner is present, the charged charge equal to the total charge amount of the toner image N is offset macroscopically, so that only the surplus charge amount that exceeds the total charge amount of the toner image N appears in appearance. Not done. Therefore, the difference in effective charge amount between where the toner is present and where it is not is small, and a potential difference is generated inside the intermediate transfer belt 7 so that the charge moves from where the toner is present to where there is no toner. There are few things.

  As shown in FIG. 4, the toner carrying charge distributed inside the intermediate transfer belt 7 naturally attenuates gradually as the intermediate transfer belt 7 rotates. The intermediate transfer belt 7, which is a dielectric that retains electric charge, is equivalent to an open-ended RC parallel connection circuit.

  As shown in FIG. 4 (b), when a constant charge is held in the capacitor of the equivalent circuit, a potential difference occurs between both ends of the resistor, so that a current flows through the resistor and discharges the capacitor charge. The phenomenon of doing occurs. The spontaneous discharge phenomenon of the toner carrying charge is potential attenuation that occurs in a float state where the intermediate transfer belt 7 passes through the primary transfer portion T1 and does not contact the supporting rotating body connected to the ground potential. This potential decay is a phenomenon that depends on the conduction characteristics and dielectric characteristics of the dielectric itself, and is not affected by the presence of toner.

  In other words, when the intermediate transfer belt 7 passes through the primary transfer portion T1 and becomes in a floating state, the natural attenuation of the charge proceeds inside the intermediate transfer belt 7, but at this time, the potential drops depending on whether the toner is present or not. Have the same time constant. For this reason, in the primary transfer portion T1, the difference between the toner carrying charges generated between where the toner is present and where it is not is maintained, so that the toner is not scattered from where it is present.

  As shown in FIG. 5, the toner carrying charge distributed inside the intermediate transfer belt 7 rapidly escapes with the contact with the primary transfer downstream roller 20. The potential attenuation due to the toner carrying charge escaping from the intermediate transfer belt 7 to the support rotating body connected to the ground potential is greatly affected by the presence of toner.

  As shown in FIG. 5B, when the back surface of the intermediate transfer belt 7 contacts the primary transfer downstream roller 20 connected to the ground potential, one end of the RC parallel connection circuit equivalent to the intermediate transfer belt 7 is grounded. It is equivalent to being short-circuited to a potential.

  Since the toner carried on the intermediate transfer belt 7 is insulative, it can be regarded as a capacitor Ct holding a certain charge. One end of the capacitor Ct is connected in series with the RC parallel connection circuit of the intermediate transfer belt 7, and the other end is electrically floated. When electric charge flows out from such an RC parallel connection circuit to the ground potential, the attenuation of the electric potential is such that the more charge accumulated in the capacitor Ct connected in series with the RC parallel connection circuit, the longer the time constant of the attenuation. There is. That is, in the process of passing through the primary transfer downstream roller 20 connected to the ground potential, the potential attenuation caused by the electric charge escaping from the intermediate transfer belt 7 through the primary transfer downstream roller 20 is greater when the toner is present. It will be longer than where there is no.

  That is, when the intermediate transfer belt 7 rotates and comes into contact with the primary transfer downstream roller 20, potential attenuation caused by the toner carrying charge escaping to the ground potential through the primary transfer downstream roller 20 occurs. At this time, the charge is less likely to decay when the toner is present than when the toner is absent, and the potential decay time constant is longer.

  For this reason, as shown in FIG. 6, a large electric field is generated in the intermediate transfer belt 7 from the location where the toner is present to the location where the toner is not present. The part moves. The electric field from the presence of toner to the absence of toner is greatest when the intermediate transfer belt 7 is in contact with the primary transfer downstream roller 20.

  As a result, the toner scatters from where the toner is present on the toner image carrying surface to where there is no toner so as to follow the charge moving inside the intermediate transfer belt 7. Where there is toner in which the charge in the intermediate transfer belt 7 has been lost, the toner particles that repel each other cannot be retained by the toner image carrying surface. The rearrangement of the toner carrying charge occurs, and a part of the toner carrying charge existing where the toner is present moves to the place where there is no toner. As a result, the toner particles that can no longer be electrostatically held on the intermediate transfer belt 7 are repelled by the repulsion of the charge between the toners, and move according to the distribution of the rearranged toner carrying charges to scatter the toner. The phenomenon will occur.

  It has been proposed to connect the primary transfer downstream roller 20 to a ground potential via a resistor against the toner scattering phenomenon. When connected to the ground potential via a resistor, the time constant of potential attenuation when passing through the primary transfer downstream roller 20 is lengthened, the amount of attenuation of the toner carrying charge is reduced, and relocation is less likely to occur. (See (b) of FIG. 5). However, if the primary transfer downstream roller 20 is not directly grounded, the configuration may be complicated and the cost may be increased.

<Example 1>
7 is a perspective view of the primary transfer downstream roller in Embodiment 1, FIG. 8 is a partial sectional view in the longitudinal direction of the primary transfer downstream roller, and FIG. 9 is an explanatory view of a contact state between the primary transfer downstream roller and the intermediate transfer belt. is there. FIG. 10 is an explanatory diagram of the primary transfer downstream roller of Comparative Example 1, FIG. 11 is an explanatory diagram of the primary transfer downstream roller of Comparative Example 2, FIG. 12 is an explanatory diagram when the tension of the intermediate transfer belt is excessive, and FIG. It is a diagram of the amount of distortion of the intermediate transfer belt in the structure.

  As shown in FIG. 7, in Example 1, a spiral groove structure 21 was provided as the surface structure of the primary transfer downstream roller 20. The spiral groove structure 21 is substantially parallel to the circumferential direction, but has a slight inclination with respect to the tangential direction of the cylindrical surface of the primary transfer downstream roller 20, so that it rotates with respect to the intermediate transfer belt 7 as it rotates. The contact position moves.

  As shown in FIG. 8, the longitudinal cross section of the spiral groove structure 21 is composed of a large number of triangular grooves, and the groove structures 21 adjacent to each other in the axial direction of the cylindrical surface have respective in-groove slopes 21e. The ridgeline 22 is formed adjacently. The groove structure 21 is formed by cutting using a lathe, the groove depth D is 30 μm, and the groove pitch L is 200 μm.

  As shown in FIG. 9, in Example 1, the ridge line 22 of the spiral groove structure 21 is brought into linear contact with the inner side surface of the intermediate transfer belt 7, so that the toner image carried on the intermediate transfer belt 7. Can be effectively avoided.

  The valley portion of the groove structure 21 is not in contact with the intermediate transfer belt 7, and the portion where the intermediate transfer belt 7 and the primary transfer downstream roller 20 are in contact is limited only to the ridge line 22 of the groove structure 21. For this reason, the contact area between the intermediate transfer belt 7 and the primary transfer downstream roller 20 is greatly reduced as compared with the case where the primary transfer downstream roller 20 comes into surface contact with the intermediate transfer belt 7 with a flat cylindrical surface. .

  As a result, when the intermediate transfer belt 11 comes into contact with the primary transfer downstream roller 20, the position where the charge escapes to the ground potential through the primary transfer downstream roller 20 is divided, and the amount of charge that can escape before passing is very small. Therefore, although the primary transfer downstream roller 20 is connected to the ground potential and charge-up is prevented, the change in the charging state of the intermediate transfer belt 11 before and after contacting the primary transfer downstream roller 20 can be small. . Even after passing through the primary transfer downstream roller 20, the behavior of the charge inside the intermediate transfer belt 7 is close to that of the natural attenuation shown in FIG. 4, and the toner carrying charge is rearranged inside the intermediate transfer belt 7. Toner scattering is suppressed.

  In Example 1, in order to avoid scattering by reducing the contact area between the grooved support rotating body and the belt member, in the spiral groove structure, the in-groove slopes of adjacent groove structures are connected by ridge lines. It is desirable.

  As shown in FIG. 10, in the primary transfer downstream roller 20 </ b> H of Comparative Example 1, the in-groove inclined surface 21 e of the adjacent groove structure 21 is not connected. For this reason, the intermediate transfer belt 7 and the primary transfer downstream roller 20 are in contact with each other on the cylindrical surface between the groove structures 21, and the contact area is increased, so that the scattering cannot be effectively improved. Charge rearrangement occurs inside the intermediate transfer belt 7 in contact with the cylindrical surface between the groove structures 21, and scattering occurs.

  In Example 1, it is desirable that the tension applied to the intermediate transfer belt 7 is a linear pressure of 0.25 N / cm or more and 3.5 N / cm or less. When the linear pressure is less than 0.25 N / cm, there is a possibility that a sufficient frictional force cannot be ensured between the driving roller 30 and the intermediate transfer belt 7 when the rotational driving is performed, and slipping may occur.

  As shown in FIG. 11, when a tension higher than 3.5 N / cm is applied to the intermediate transfer belt 7, the intermediate transfer belt 7 greatly bites into the groove structure 21 of the primary transfer downstream roller 20.

  As shown in FIG. 12, when the intermediate transfer belt 7 to which excessive tension is applied is stretched around the primary transfer downstream roller 20, the belt surface undulates in the vicinity of the stretched portion, and due to an extremely large wave. Image defects may occur. The optical sensor 15 shown in FIG. 1 may cause a detection error of reflected light from the belt surface.

  If the amount of deflection is large enough to contact the in-groove inclined surface 21e of the groove structure 21, the contact area between the intermediate transfer belt 7 and the primary transfer downstream roller 20 increases, and the scattering of the toner image may deteriorate.

  In the first exemplary embodiment, when the tension is applied to the intermediate transfer belt 7, the amount of bending of the intermediate transfer belt 7 is estimated between the groove and the ridge line due to the presence of the groove structure 21 on the surface of the primary transfer downstream roller 20. Is possible.

  As shown in FIG. 8, in Example 1, the groove structure 21 provided in the primary transfer downstream roller 20 preferably has a groove pitch L of 25 μm to 400 μm and a groove depth D of 10 μm to 50 μm.

  When the groove pitch L is 25 μm or less, the contact area between the intermediate transfer belt 7 and the primary transfer downstream roller 20 cannot be sufficiently reduced, so that the scattering may not be improved sufficiently.

  As shown in FIG. 11, when the groove pitch L is 400 μm or more, the intermediate transfer belt 7 bent into the groove structure 21 enters extremely, so that the stretched portion by the primary transfer downstream roller 20H as shown in FIG. There is a possibility that a wave will occur.

Here, L is the groove pitch [mm], d is the thickness [mm] of the intermediate transfer belt 7, and b is the amount [mm] of the intermediate transfer belt 7 applied to the primary transfer downstream roller 20. Further, P is a tension [N] applied to the intermediate transfer belt, and E is a Young's modulus [N / mm ² ] of the intermediate transfer belt. At this time, the strain amount h [mm] is approximated by the following equation as the deflection amount of the both-end supported beam in which the rotation of both ends is restricted.
h = 1/4 × (L3 / (d3 × b)) × (P / E) × 10 ⁶ (1)

  FIG. 13 shows the amount of distortion of the intermediate transfer belt 7 calculated by the equation (1) when the amount b of the intermediate transfer belt 7 applied to the primary transfer downstream roller 20 is 25 mm and the groove pitch of the groove structure 21 is 400 μm. It is. According to FIG. 13, the tension of the intermediate transfer belt 7 is 1.14 N / cm, the Young's modulus is the maximum strain amount at 3.5 GPa, and the depth at which the intermediate transfer belt 7 bites into the groove is approximately 3.5 μm. The

  Actually, when the intermediate transfer belt 7 is driven to rotate, variations in Young's modulus within the belt surface and variations in tension in the longitudinal direction occur. For this reason, it is desirable that the groove depth D of the primary transfer downstream roller 20 has a margin with respect to 3.5 μm, preferably 10 μm or more.

  On the other hand, if the groove depth D is 50 μm or more, when the above-described tension is applied to the intermediate transfer belt 7, there is a possibility that the amount of deflection at the center of the primary transfer downstream roller 20 becomes excessive. This is because the circumferential groove processing is performed on the surface of the primary transfer downstream roller 20 which is a metal tube roller member, so that the bending rigidity in the longitudinal direction is lowered and the amount of bending is increased. For this reason, the groove depth is preferably 50 μm or less.

  The pitch of the adjacent ridge lines of the groove structure 21 is narrower than the limit width at which the belt member that contacts in the stopped state is not permanently deformed, and the depth of the groove structure 21 is the limit at which the belt member supported in the stopped state contacts the groove surface. Desirably deeper than depth.

  The intermediate transfer belt 7 uses a belt material having a Young's modulus of 3.5 GPa, and the Young's modulus of the belt material is desirably 0.5 GPa or more. When a soft belt material having a Young's modulus of 0.5 GPa or less is used, the intermediate transfer belt 7 can bite into the groove structure 21 of the primary transfer downstream roller 20 as shown in FIG. There is sex. There is a possibility that the contact area between the intermediate transfer belt 7 and the primary transfer downstream roller 20 is increased, and scattering is deteriorated.

  In Example 1, a polyimide resin was used as the base material of the belt material, but other resins such as polycarbonate, polyethylene terephthalate, nylon, and polyamide can also be suitably used.

<Example 2>
FIG. 14 is an explanatory diagram of the groove structure of the primary transfer downstream roller according to the second embodiment. The second embodiment differs from the first embodiment only in the groove structure on the cylindrical surface of the primary transfer downstream roller 20 of the image forming apparatus 100 shown in FIG.

  In the first embodiment, as shown in FIG. 8, the spiral groove structure 21 formed on the surface of the primary transfer downstream roller 20 has a triangular cross section. However, in the second embodiment, as shown in FIG. The cross section of the groove structure 21A is elliptical.

  Even if the spiral groove structure 21A formed on the surface of the primary transfer downstream roller 20 is an elliptical groove, the ridgeline 22A of the adjacent elliptical groove is brought into linear contact with the inner surface of the intermediate transfer belt 7, The scattering of the toner image can be effectively avoided.

<Example 3>
FIG. 15 is an explanatory diagram of the groove structure of the primary transfer downstream roller according to the third embodiment. The third embodiment is different from the first embodiment only in the groove structure of the cylindrical surface of the primary transfer downstream roller 20 of the image forming apparatus 100 shown in FIG.

  In Example 1, as shown in FIG. 8, the spiral groove structure 21 formed on the surface of the primary transfer downstream roller 20 has a triangular cross section, but as shown in FIG. The cross section of the groove structure 21B is an inverted trapezoid.

  Even if the spiral groove structure 21B formed on the surface of the primary transfer downstream roller 20 is an inverted trapezoidal groove, the ridgeline 22B of the adjacent inverted trapezoidal groove is brought into linear contact with the inner surface of the intermediate transfer belt 7. Thus, the scattering of the toner image can be effectively avoided.

  In Example 1, the triangular groove is provided when the spiral groove on the surface of the primary transfer downstream roller 20 is provided. However, an inverted trapezoidal groove as shown in FIG. 15 can be preferably used.

<Example 4>
As shown in FIG. 1, in Example 4, a groove structure was formed on the cylindrical surface of the drive roller 30 located downstream of the primary transfer downstream roller 20 of the image forming apparatus 100.

  The support rotating body that first contacts the intermediate transfer belt 7 to which the toner image has been transferred at the primary transfer portion T1 after passing through the primary transfer portion T1 is the primary transfer downstream roller 20. The support rotating body that contacts the intermediate transfer belt 7 next to the primary transfer downstream roller 20 is a drive roller 30. The cylindrical surfaces of the primary transfer downstream roller 20 and the driving roller 30 are formed with a surface structure in which the continuous contact length in the axial direction of the support rotating body with respect to the belt member (7) is reduced.

  A rubber elastic layer having a thickness of 1.5 mm is formed on the cylindrical surface of the drive roller 30, and the overall outer diameter is 38 mm. The rubber elastic layer is cut into a spiral shape as shown in FIGS. 7 and 8. The triangular groove is formed. The groove pitch L is 500 μm, and the groove depth D is 500 μm.

<Example 5>
FIG. 16 is an explanatory diagram of the groove structure of the primary transfer downstream roller according to the fifth embodiment. The fifth embodiment is different from the first embodiment in the axial arrangement of the groove structure of the cylindrical surface of the primary transfer downstream roller 20 of the image forming apparatus 100 shown in FIG.

  As shown in FIG. 16A, the spiral groove structure 21 is formed only in the region of the maximum image formation width of the intermediate transfer belt 7, and the outside of the maximum image formation width is a flat cylinder having no groove structure. It may be left on the surface. At both ends of the intermediate transfer belt 7, a detent guide portion 7g is attached to limit the movement in the axial direction.

  As shown in FIG. 16B, the groove structure 21 may be formed of a plurality of parallel grooves that are each independently closed. Further, two types of groove structures 21 having different inclinations with respect to the tangential direction of the primary transfer downstream roller 20 may be alternately arranged.

  As shown in FIG. 16C, the groove structure 21 may be formed by intersecting two types of groove structures having different inclinations with respect to the tangential direction of the primary transfer downstream roller 20. Such a groove structure may be formed by transfer processing (so-called knurling) without depending on cutting.

  As shown in FIG. 16 (d), the groove structure does not need to be continuous over one round of the cylindrical surface, and may be formed by a number of grooves intermittent in the circumferential direction.

  In any of the groove patterns (a) to (d), as in the first embodiment, in the axial section, the pitch of the adjacent ridge lines of the groove structure 21 is larger than the limit width at which the belt member in contact in the stopped state is not permanently deformed. Is too narrow. The depth of the groove structure 21 is deeper than the limit depth at which the belt member supported in the stopped state contacts the groove surface.

<Example 6>
FIG. 17 is an explanatory diagram of a configuration of the image forming apparatus according to the sixth embodiment. In the seventh embodiment, a groove structure is formed on the cylindrical surface of the stretching roller and the driving roller of the tandem type image forming apparatus in which a plurality of photosensitive drums are arranged on the intermediate transfer belt.

  As shown in FIG. 17A, the image forming apparatus 200 is an electrophotographic full color in which yellow, magenta, cyan, and black image forming portions Pa, Pb, Pc, and Pd are arranged along the intermediate transfer belt 7. It is a laser printer. The image forming portions Pa, Pb, Pc, and Pd are configured similarly except that the color of toner used in the developing devices 4a, 4b, 4c, and 4d is different from yellow, magenta, cyan, and black. For each configuration arranged in the image forming portions Pa, Pb, Pc, and Pd, reference numerals of the corresponding configurations shown in FIG. 1 indicate a, which indicates the distinction between the image forming portions Pa, Pb, Pc, and Pd. Reference numerals to which b, c, and d are added are attached.

  In the yellow image forming portion Pa, the photosensitive drum 1a is configured by applying an organic photoreceptor (OPC) to an aluminum cylinder having an outer diameter of 84 mm. After the surface of the photosensitive drum 1a is uniformly charged by the charging roller 2a, the photosensitive drum 1a is subjected to scanning exposure with a laser beam by the exposure device 3a, and an electrostatic image of a yellow image is formed.

  The developing device 4a stirs and charges the two-component developer, carries the developer on the developing sleeve, and supplies the yellow toner to the electrostatic image on the photosensitive drum 1a, thereby developing the yellow toner image. The yellow toner image formed on the photosensitive drum 1a is primarily transferred onto the intermediate transfer belt 7 by the primary transfer roller 5a. The surface of the photosensitive drum 1a having the yellow toner image transferred to the intermediate transfer belt 7 is cleaned by the cleaning device 6a and is used for the next and subsequent image forming operations.

  The magenta, cyan, and black color component toner images are formed by the same process as described above and are primarily transferred onto the intermediate transfer belt 7 in a superimposed manner. The four-color toner images formed on the intermediate transfer belt 7 are conveyed to the secondary transfer portion T2 including the opposing roller 10 and the secondary transfer roller 12, and onto the recording material P fed at a predetermined timing. Batch secondary transfer.

  The recording material P onto which the toner image has been secondarily transferred undergoes heat and pressure fixing by the fixing device 8 and becomes a permanent image. After the toner image is secondarily transferred to the recording material, the intermediate transfer belt 7 is cleaned by the belt cleaning device 13 and used for image formation from the next time.

  As shown in FIG. 17B, in the black monochrome mode in which a black and white image is formed using the black image forming portion Pd, the image forming apparatus 200 starts from the image forming portions Pa, Pb, and Pc from the intermediate transfer belt 7. Separate.

  The tension roller 11 and the primary transfer rollers 5a, 5b, and 5c that support the intermediate transfer belt 7 on the upstream side of the stretching roller 20 are moved downward to contact the photosensitive drums 1a, 1b, and 1c with the intermediate transfer belt 7. Is released.

  As shown in FIG. 17A, in the full color mode, the cylindrical surface of the stretching roller 20 connected to the ground potential is always in contact with the inner surface of the intermediate transfer belt 7. For this reason, when the intermediate transfer belt 7 on which the toner images are primarily transferred by the image forming portions Pa, Pb, and Pc passes the stretching roller 20, the toner images may be scattered.

  Therefore, in Example 6, a spiral triangular groove structure 21 as shown in FIGS. 7 and 8 was formed on the cylindrical surface of the tension roller 20. Similar to Example 4, a groove structure was also formed on the cylindrical surface of the drive roller 30 located downstream of the stretching roller 20.

  As described above, by providing a spiral groove structure on the surface layer of the tension member of the intermediate transfer belt, it is possible to suppress the toner-carrying charge from being attenuated from the intermediate transfer belt to the tension member, and to scatter the toner image. Can be effectively avoided.

  Therefore, it is possible to provide an image forming apparatus capable of maintaining high image quality without causing stable scattering.

It is explanatory drawing of a structure of the image forming apparatus of 1st Embodiment. FIG. 6 is an explanatory diagram of a charged state of an intermediate transfer belt that has passed through a primary transfer portion. It is explanatory drawing of the relationship between a primary transfer roller applied voltage and a primary transfer current. FIG. 6 is an explanatory diagram of natural decay of toner carrying charges. It is explanatory drawing of the rapid discharge at the time of a primary transfer downstream roller. FIG. 6 is an explanatory diagram of a charged state of an intermediate transfer belt that is in contact with a primary transfer downstream roller. 3 is a perspective view of a primary transfer downstream roller in Embodiment 1. FIG. FIG. 6 is a partial cross-sectional view in the longitudinal direction of a primary transfer downstream roller. FIG. 6 is an explanatory diagram of a contact state between a primary transfer downstream roller and an intermediate transfer belt. 6 is an explanatory diagram of a primary transfer downstream roller of Comparative Example 1. FIG. 10 is an explanatory diagram of a primary transfer downstream roller of Comparative Example 2. FIG. FIG. 10 is an explanatory diagram when the tension of the intermediate transfer belt is excessive. It is a diagram of the amount of distortion of the intermediate transfer belt in the groove structure. FIG. 6 is an explanatory diagram of a groove structure of a primary transfer downstream roller in Embodiment 2. FIG. 10 is an explanatory diagram of a groove structure of a primary transfer downstream roller in Embodiment 3. FIG. 10 is an explanatory diagram of a groove structure of a primary transfer downstream roller in Embodiment 5. FIG. 10 is an explanatory diagram of a configuration of an image forming apparatus according to a sixth embodiment.

Explanation of symbols

1 Image carrier (photosensitive drum)
2 Charging roller 3 Exposure device 4 Developing device 5 Primary transfer roller 6 Cleaning device 7 Belt member (intermediate transfer belt)
10 Counter roller 12 Secondary transfer roller 20 Rotating support (primary transfer downstream roller)
21 Groove structure 21e Slope 22 in groove 22 Ridge line 30 Drive roller

Claims (4)

An image carrier on which a toner image is formed;
A belt member that carries and moves the toner image transferred from the image carrier in the transfer unit, and an image forming apparatus comprising:
A support rotating body that supports the belt member so that a conductive cylindrical surface connected to a ground potential is in contact with an opposite surface carrying a toner image;
The image forming apparatus according to claim 1, wherein the support rotating body has a surface structure in which a continuous contact length in the axial direction of the cylindrical surface with respect to the belt member is divided.   2. The image forming apparatus according to claim 1, wherein the surface structure is a plurality of parallel groove structures inclined with respect to a tangential direction of the cylindrical surface.   3. The image forming apparatus according to claim 2, wherein the groove structures adjacent in the axial direction are adjacent to each other in a groove so that a ridge line comes into linear contact with the belt member. . The pitch of the adjacent ridgelines of the groove structure is narrower than the limit width at which the belt member in contact in the stopped state is not permanently deformed,
The image forming apparatus according to claim 3, wherein a depth of the groove structure is deeper than a limit depth at which the belt member supported in a stopped state contacts the groove surface.

Images