JP4496831B2 - Image forming apparatus and static eliminating apparatus used therefor - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printer, and more particularly to an image forming apparatus that effectively eliminates charge from a belt member that carries and conveys a toner image and an improvement in the charge eliminating apparatus used in the image forming apparatus.

Conventionally, as an image forming apparatus of this type, for example, an intermediate transfer type image forming apparatus adopting an electrophotographic system is taken as an example, and each color component (for example, Y (yellow), M (magenta) is formed on an image carrier such as a photosensitive drum. ), C (cyan), K (black)) toner images are formed and temporarily transferred in multiple locations (primary transfer) at the same location on the intermediate transfer member. There are some which are designed to transfer (secondary transfer).
In an embodiment using this type of intermediate transfer member, the toner images of the respective colors sequentially formed on the intermediate transfer member are configured to be superimposed. Therefore, it is necessary to superimpose the color toner images on the intermediate transfer member with high accuracy.
Further, as this type of intermediate transfer member, a belt-like one is frequently used because of the high degree of freedom of layout in the apparatus and the small occupied area.

An intermediate transfer belt (hereinafter abbreviated as a belt) is stretched around a plurality of stretching rolls and circulates and conveys a multiple transfer toner image. It is necessary to hold the belt firmly on the belt until it is secondarily transferred to the recording material.
Therefore, generally, a toner holding force that uses a belt having a volume resistivity of about 10 ⁷ to 10 ¹² Ω · m and holds the toner on the belt by an electric charge having a polarity opposite to that of the toner generated in the belt at the time of primary transfer. (Coulomb power) is gained.
If the toner holding force is insufficient, the repulsive force between the toners overlaid with each other (mutual repulsive force due to the charge of the toner) cannot be suppressed, and the toner splatters (hereinafter referred to as blur). Occurs, resulting in image disturbance on the recording material. Therefore, the charged charge in the belt plays an important role in suppressing the occurrence of blur.

However, if the charged charge in the belt becomes extremely large and the toner holding force becomes too strong, it becomes a factor that hinders the toner from transferring (transferring) to the recording material during the secondary transfer. This phenomenon is noticeable when using a high-resistance belt that takes a long time to move charges, or at a high process speed that does not allow sufficient charge transfer time, and the secondary transfer rate deteriorates. The problem occurs.
In order to solve this problem, a method has been proposed in which the conductive member is brought into contact with the back surface of the belt before the secondary transfer, and the conductive member is grounded so as to reduce the charge in the belt (see, for example, Patent Document 1). . In addition, a method of reducing the charge in the belt by applying a bias having a polarity different from the charged charge of the belt to a roller in contact with the back surface of the belt has been proposed (see, for example, Patent Document 2).

Japanese Patent Laid-Open No. 4-115266 (Example, FIG. 1) JP 2003-280331 A (Embodiment of the Invention, FIG. 1)

However, in the inventions described in the above-mentioned Patent Documents 1 and 2, since the structure in which the charged charge in the belt is grounded or a member to which a bias of reverse polarity is applied is in contact with the belt back surface, only a part of the belt back surface is in contact. The electric charge can be absorbed and extinguished by the conductive member side, but the potential gradient cannot be sufficiently formed in the belt due to the configuration in which the single conductive member is in contact, and most of the electric charge remains in the belt. End up. Such a phenomenon is particularly noticeable when using a high resistance belt (a belt with a high volume resistivity) in which the occurrence of blur is suppressed or when transferring at a high process speed. A sufficient charge removal effect cannot be obtained, and a sufficient secondary transfer rate cannot be obtained.
The present invention is for solving the above-described technical problems, and is performed by effectively eliminating the charge of a belt member that is disposed before transfer to a recording material and carries and conveys a toner image. An image forming apparatus capable of ensuring a sufficient transfer efficiency at the time of transfer to a material is provided. Furthermore, it is an object of the present invention to provide a static eliminator that effectively removes static electricity from a belt member by providing an effective potential gradient between two conductive members.

That is, as shown in FIG. 1A, the image forming apparatus according to the present invention is an endless belt that is rotatably supported on a plurality of stretching members 5 and carries and conveys the formed toner image T. A member 1, a transfer unit 7 that transfers the toner image T on the belt member 1 onto a recording material 6, and a charge removal device 2 that removes the charged charges of the belt member 1 are provided. The transfer member 7 is provided between the stretching member 5 and the transfer unit 7 upstream of the transfer unit 7 with respect to the direction of travel of the belt member 1 and spaced apart from the direction of travel of the belt member 1 and in contact with the back surface of the belt member 1. two conductive members 3 (3a, 3b) and, the two conductive members 3 (3a, 3b) 1000V or more potential with different polarity of the potential to the other conductive member 3b on one of the conductive members 3a between that The neutralizing bias or one conductive member 3 ( It is characterized in further comprising a bias applying means 4 for applying an example, if 3a) to discharge bias to be 1000V or more potential gradient having a potential of 0V.

In such technical means, the image forming apparatus according to this aspect includes a multi-cycle method (4 cycles, etc.), a tandem method, and a double tandem method, and the belt member 1 used carries and conveys the toner image T. Any intermediate transfer member or dielectric may be used. Further, the transfer means 7 may be a roll member or the like arranged in contact with the belt member 1, or a corotron or the like arranged apart from the belt member 1.
Furthermore, the conductive member 3 only needs to have conductivity capable of applying a static elimination bias to the belt member 1, and may be, for example, a semiconductive member. Moreover, the aspect of the conductive member 3 may be a fixed aspect or a rotating aspect .
The neutralizing bias of the present invention provides a potential gradient between the two conductive members 3a and 3b from the viewpoint of neutralizing the charged charge of the belt member 1 . For this reason , as the charge removal bias applied to the two conductive members 3a and 3b to remove the charged charge of the belt member 1, a mode in which different polarities are applied is preferable. For example, even in a mode in which one side is grounded In terms of static elimination effect, there is no problem. In addition, as the static elimination bias, it is only necessary that a potential gradient is formed between the two conductive members 3a and 3b. For example, the static elimination bias is not limited to a direct current component to which only a direct current component or an alternating current component is applied. The direction of the potential gradient between the conductive members 3 is not particularly limited.

In the present embodiment, the bias applying means 4 is preferably provided with a neutralizing bias having a potential gradient of 500 V or more between the two conductive members 3a and 3b from the viewpoint of neutralizing the charged charge of the belt member 1, and more preferably 1000 V or higher. It is more preferable to provide a potential gradient. For this reason, the aspect which provides the electric potential gradient of 1000 V or more is employ | adopted in this invention.
The bias applying means 4 may apply a static elimination bias so that the polarity of the conductive member 3b disposed on the downstream side of the two conductive members 3a and 3b is in the same polarity direction as the charged charge of the toner. Even when the static eliminator 2 is provided in the vicinity of the transfer means 7, the influence of the transfer bias can be reduced. Here, “a polarity direction similar to the charged charge of the toner” means a bias in which the downstream side is in the negative direction when, for example, negatively charged toner is used. In particular, if the downstream side conductive member 3b is a tension member 5 that faces the transfer means 7 (opposing member of the transfer means 7), it is possible to prevent toner scattering in the transfer area. . In addition, the two conductive members 3a and 3b are preferably disposed so as to have a distance of 50 mm or less from the viewpoint of constructing an effective potential gradient for neutralizing the charged charge of the belt member 1, It is more preferable to arrange it to be 30 mm or less.
Furthermore, it is preferable that the two conductive members 3a and 3b have an insulating member interposed between the opposing portions so as to ensure a conduction path only on the belt member 1 side. In this case, the discharge start voltage is higher than that in the atmosphere. The discharge can be prevented when the two conductive members 3a and 3b are arranged close to each other, and the static eliminator 2 can be miniaturized. Further, by disposing the conductive members 3a and 3b close to each other, the static elimination bias can be reduced. The “insertion of an insulating member” may be an aspect in which the insulating member and the two conductive members 3a and 3b are arranged in contact with each other, or may be an aspect in which the insulating members and the two conductive members 3a and 3b are arranged apart from each other. For example, in the case of a combination of a roll shape and a plate shape, there may be a mode in which an insulating member is applied to a part of the plate shape.

Furthermore, examples of the image forming apparatus of the intermediate transfer type in the present invention include a multi-cycle method (4 cycles or the like) and a double tandem method. In this case, the following may be performed.
That is, as shown in FIG. 1B, the image carrier 8 on which toner images of a plurality of colors are formed, and a plurality of tension members 5 are rotatably supported and arranged opposite to the image carrier 8. Intermediate transfer belt 1a, primary transfer means 9 for multiple transfer of the toner image on the image carrier 8 onto the intermediate transfer belt 1a, and secondary transfer of the toner image T on the intermediate transfer belt 1a onto the recording material 6 collectively. The neutralization device 2 includes a transfer unit 7a and a neutralization device 2 that neutralizes the charge of the intermediate transfer belt 1a. The neutralization device 2 is a tension member 5 upstream of the secondary transfer unit 7a with respect to the traveling direction of the intermediate transfer belt 1a. When provided between the secondary transfer unit 7a, two conductive members 3a which is placed in contact with the spaced and intermediate transfer belt 1a backside to the traveling direction of the intermediate transfer belt 1a, a 3b, of the two conductive members 3a, one conductive member 3a between 3b Applying a charge eliminating bias to be 1000V or more potential gradient having a potential of 0V to the different polarities discharge bias or one conductive member 3 becomes more potential gradient 1000V having the potential of (e.g., 3a) and the other conductive member 3b What is necessary is just to provide the bias application means 4 and the switching means 2a which switches operation | movement and a stop of the static elimination apparatus 2.

In this case, the toner image T on the intermediate transfer belt 1a is preferably held on the intermediate transfer belt 1a until it is secondarily transferred to the recording material 6. For this reason, the neutralizing device 2 is placed upstream of the secondary transfer means 7a. More preferably, it is arranged near the side. In this embodiment, until the secondary transfer, there is a concern that blurring may occur if the neutralizing effect of the neutralizing device 2 is activated. Therefore, it is preferable that the static eliminating device 2 is not activated by the switching unit 2a.
Here, as the switching unit 2a, when neutralization of the intermediate transfer belt 1a is not required, for example, the neutralization device 2 may be retracted, or only the neutralization bias may be turned off.
In this embodiment, the image carrier 8 may be either a drum shape or a belt shape. The primary transfer unit 9 and the secondary transfer unit 7a may be in the form of a transfer roll that contacts the intermediate transfer belt 1a, or may be in the form of a corotron that is separated from the intermediate transfer belt 1a.

Furthermore, in the aspect of the static eliminator 2 used in the above-described image forming apparatus in the present invention, the static eliminator 2 that neutralizes the endless belt member 1 on which the toner image T is carried and conveyed, the belt member 1 two conductive members 3a, 3b and the other conductive member to one of the conductive member 3a is between the two conductive members 3a, 3b which are disposed spaced and the belt member 1 in contact with the back surface with respect to the traveling direction of the Bias applying means 4 for applying a neutralizing bias having a potential gradient of 1000 V or more having a potential different from that of 3b or a neutralizing bias having a potential gradient of 1000 V or more having a potential of 0 V to one conductive member 3 (for example, 3a). Can be provided.

According to the present invention, the belt member back side between the upstream side of the tension member from the transfer means for transferring the recording material and the transfer means, and two conductive members, one conductive Between the two conductive members Bias applying means for applying a neutralizing bias having a potential gradient of 1000 V or more having a potential of a polarity different from that of the other conductive member to the member or a neutralizing bias having a potential gradient of 1000 V or more having a potential of 0 V to one conductive member ; Therefore, the image forming apparatus can be realized which can efficiently remove the charged charges in the belt member and can achieve sufficient transfer efficiency without blurring until transfer.
In addition, an image forming apparatus having a multi-cycle intermediate transfer system configuration by disposing a charge eliminating device having a switching means for switching between operation and stop of the charge eliminating device before the secondary transfer means for transferring to a recording material, Blur can be prevented and sufficient secondary transfer efficiency can be obtained.
Furthermore, the two conductive members which are spaced apart with respect to the traveling direction of the contact and the belt member on the back side of the belt member, on one of the conductive member between the two conductive members and other conductive members A bias applying means for applying a neutralizing bias having a potential gradient of 1000 V or more having a potential of different polarity or a neutralizing bias having a potential gradient of 1000 V or more having a potential of 0 V to one of the conductive members. It is possible to realize a static eliminator that can effectively neutralize charged charges.

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
Embodiment 1
FIG. 2 shows Embodiment 1 of an image forming apparatus to which the present invention is applied.
In FIG. 1, the image forming apparatus includes a photosensitive drum 10 that carries a toner image, and an intermediate transfer belt 20 that is disposed to face the photosensitive drum 10 in order to transfer the toner image from the photosensitive drum 10. This is a so-called four-cycle type intermediate transfer type image forming apparatus that performs four times of multiple transfer on the intermediate transfer belt 20 in order to obtain four color images.
In the present embodiment, the photosensitive drum 10 includes a photosensitive layer whose resistance value is reduced by light irradiation. Around the photosensitive drum 10, a charging device 11 for charging the photosensitive drum 10 and An exposure device 12 for writing an electrostatic latent image of each color component (in this example, black (K), yellow (Y), magenta (M), cyan (C)) on the charged photosensitive drum 10, and a photosensitive member. A rotary type developing device 13 that visualizes each color component latent image formed on the drum 10 with each color component toner and a cleaning device 14 that cleans residual toner on the photosensitive drum 10 are provided. .

Here, as the charging device 11, for example, a charging roll is used, but a charging device such as a corotron may be used.
The exposure device 12 may be any device that can write an image on the photosensitive drum 10 with light. In this example, for example, a print head using LEDs is used, but the present invention is not limited to this. A scanner that scans with a polygon mirror may be selected as appropriate.
Further, the rotary type developing device 13 is rotatably mounted with developing units 13a to 13d containing respective color component toners. For example, the respective color component toners are attached to a portion of the photosensitive drum 10 where the potential is lowered by exposure. The toner to be used is not particularly limited in shape and particle size, and any toner may be used as long as it is accurately placed on the electrostatic latent image on the photosensitive drum 10. In this example, the rotary developing device 13 is used, but four developing devices may be used.
Furthermore, the cleaning device 14 may be appropriately selected as long as it cleans the residual toner on the photosensitive drum 10 and employs a blade cleaning method. However, there may be a mode in which the cleaning device 14 is not used when toner having a high transfer rate is used.

Further, the intermediate transfer belt 20 is stretched around six tension rolls 21 to 26, and circulates, for example, with the tension roll 21 as a drive roll. In the present embodiment, the intermediate transfer belt 20 moves 220 mm / sec. It is speed.
Here, as the intermediate transfer belt 20, a rigid belt using a resin material such as a polyimide resin or a polycarbonate resin or an elastic belt using a synthetic rubber material may be appropriately selected. From the viewpoint of stably holding the toner on the intermediate transfer belt 20, it is preferable to use a rigid belt shape capable of obtaining a high resistance.
Therefore, a polyimide rigid belt having a thickness of 90 μm and a volume resistivity of 10 ¹⁴ Ω · cm was used as the intermediate transfer belt 20 in the present embodiment.

Furthermore, in the present embodiment, a primary transfer roll 27 as a primary transfer unit is disposed from the back side of the intermediate transfer belt 20 at a portion facing the photosensitive drum 10 of the intermediate transfer belt 20, and a primary transfer (not shown) is performed. The toner image on the photosensitive drum 10 is transferred onto the intermediate transfer belt 20 by the bias.
Furthermore, a secondary transfer roll 28 as a secondary transfer means is disposed opposite to the tension roll 26 of the intermediate transfer belt 20 with the tension roll 26 as a backup roll, for example, secondary transfer. A predetermined secondary transfer bias is applied to the roll 28, and the stretching roll 26 that also serves as a backup roll is grounded.
A belt cleaner 29 is disposed between the tension roll 21 and the tension roll 26 so as to be able to come into contact with and separate from the intermediate transfer belt 20 so as to clean residual toner on the intermediate transfer belt 20 during cleaning. It has become.
Further, the sheet 30 such as a recording material is guided to a secondary transfer portion and then discharged to a discharge tray not shown through a fixing device not shown.

In particular, in the present embodiment, the neutralizing device 40 that is a feature of the present invention is disposed on the back surface side of the intermediate transfer belt 20 between the stretching roll 25 and the stretching roll (backup roll) 26. Has been.
The static eliminator 40 includes two plate-like conductive members 41 and 42 and bias power sources 44 and 45 connected to the plate-like conductive members 41 and 42, respectively. In this embodiment, an insulating member 43 having a thickness of 20 mm is sandwiched between the two conductive members 41 and 42, and the insulating member 43 and the two conductive members 41 and 42 are bonded. It is fixed. Of the two conductive members 41, 42, the bias power source 44 is connected to the upstream side conductive member 41, the bias power source 45 is connected to the downstream side conductive member 42, and the bias power source 44 is +500 V, the bias power source 45. Is applied with -500V, and the potential difference between them is 1000V. In the present embodiment, the static eliminator 40 is also configured to contact and separate from the back surface of the intermediate transfer belt 20 in accordance with the timing at which the secondary transfer roll 28 contacts and separates from the intermediate transfer belt 20.

Next, the operation of the image forming apparatus according to the present embodiment will be described.
In the present embodiment, the respective color component toner images are sequentially formed on the photosensitive drum 10, and are transferred onto the intermediate transfer belt 20 through the primary transfer by the primary transfer roll 27. Then, the multiple toner images are subjected to the secondary transfer. The images are collectively transferred onto the sheet 30 at the position.
In such an image formation / transfer process, the charge of the intermediate transfer belt 20 and the operation of the charge eliminating device 40 in the present embodiment will be described in detail with reference to FIGS.

In this embodiment, the toner to be used is a negatively charged toner, and a bias having a polarity opposite to that of the toner (a bias with the primary transfer roll 27 as a plus) is applied to the primary transfer roll 27, and the toner on the photosensitive drum 10. The image is transferred onto the intermediate transfer belt 20. At this time, the intermediate transfer belt 20 is charged with a polarity opposite to that of the toner (plus charge), and the toner image is stably held by the generated plus charge.
In the present embodiment, since the high-resistance intermediate transfer belt 20 is used, the charged charges (plus charges) generated in the intermediate transfer belt 20 are stretched rolls 21 while color superposition is performed. Even if it contacts -26, it hardly attenuate | damps and generation | occurrence | production of the blurring resulting from the repulsive force between the toner in the color-superposed toner image is prevented. When the fourth color is overlaid on the intermediate transfer belt 20 by the primary transfer roll 27, the static eliminator 40 moves so as to contact the back surface of the intermediate transfer belt 20 at a predetermined timing.

In the static eliminator 40, the back surface of the intermediate transfer belt 20 is energized by the static elimination bias applied to the two conductive members 41, 42, and the positive charges in the intermediate transfer belt 20 are effectively removed and static elimination is performed. At this time, in the present exemplary embodiment, since the resistance of the intermediate transfer belt 20 is high, the charge is not excessively removed, and the toner image T ′ is held sufficiently stably on the intermediate transfer belt 20 side.
Therefore, when secondary transfer is next performed on the sheet 30, the force (Coulomb force) that the toner images T ′ superimposed on the intermediate transfer belt 20 are attracted to the intermediate transfer belt 20 side is also small. A sufficient secondary transfer rate can be obtained.
In order to prevent the toner image T ′ from blurring and to obtain a sufficient secondary transfer rate, the neutralization device 40 is brought close to the secondary transfer portion so that the neutralization effect is activated immediately before the secondary transfer. Image stability is improved.
In the present embodiment, +500 V is applied to the conductive member 41 and −500 V is applied to the conductive member 42 as the neutralizing bias applied to the conductive members 41 and 42 of the static eliminator 40, but the applied bias is reversed. Even when −500 V is applied to the conductive member 41 and +500 V is applied to the conductive member 42, the same effect is obtained.

  Further, in the present embodiment, the static eliminator 40 is brought into contact with the intermediate transfer belt 20 in accordance with the timing of the secondary transfer. However, the present invention is not limited to this. By providing a change-over switch in the circuit between the two conductive members 41 and 42 and switching with an electric signal, it is possible to keep both the two conductive members 41 and 42 in a floating state before the timing of the secondary transfer. . In that case, the changeover switch may be switched when necessary so that a static elimination bias is applied between the two conductive members 41 and 42.

Embodiment 2
FIG. 4 shows a main part of the image forming apparatus according to the second embodiment to which the reference invention related to the present invention is applied.
The basic configuration of the image forming apparatus according to the present embodiment is the same as that of the first embodiment. However, the configuration of the static eliminator 40 is different from that of the first embodiment, and the downstream conductive member 42 is a tension roll (backup). Roll) 26 is also used. Components similar to those of the first embodiment are denoted by the same reference numerals as those of the first embodiment, and detailed description thereof is omitted here.

In the same figure, the static elimination apparatus 40 in this Embodiment is comprised by the plate-shaped electrically-conductive member 41, the stretching roll (backup roll) 26, and the bias power supplies 44 and 45 connected to each. An insulating member 43 is fixed to the surface of the conductive member 41 on the tension roll 26 side, so that a discharge start voltage between the conductive member 41 and the tension roll 26 is increased.
Further, in the present embodiment, the distance between the conductive member 41 and the stretching roll 26 is arranged so that the distance D in the drawing is 20 mm, the bias power supply 44 is +1000 V, and the bias power supply 45 is grounded. . Further, the conductive member 41 can be brought into and out of contact with the intermediate transfer belt 20 by means not shown.

Next, the operation in the present embodiment will be described based on FIG. 4 and FIG.
In the present embodiment, as in the first embodiment, the conductive member 41 is separated from the intermediate transfer belt 20 during the color superposition of the three color toners. When the four-color superimposed toner image T ′ approaches the secondary transfer portion, the conductive member 41 comes into contact with the intermediate transfer belt 20 and discharges the charged charge (plus charge) in the intermediate transfer belt 20.
At this time, a potential gradient is formed between the conductive member 41 and the tension roll 26 in a direction in which the tension roll 26 is negative, and current flows through the intermediate transfer belt 20. Therefore, immediately before the secondary transfer, the positive charge charged in the intermediate transfer belt 20 is effectively removed to the tension roll 26 side, and the neutral transfer belt 20 is neutralized.
In the present embodiment, since the stretching roll 26 is grounded during the secondary transfer, the secondary transfer is performed by applying a secondary transfer bias with a positive polarity on the secondary transfer roll 28 side. ing.
In addition, the force (Coulomb force) by which the four-color superimposed toner images T ′ on the intermediate transfer belt 20 are attracted to the intermediate transfer belt 20 side is reduced, and a sufficient secondary transfer rate can be obtained.

Embodiment 3
FIG. 6 shows Embodiment 3 of the image forming apparatus to which the present invention is applied.
The image forming apparatus in the present embodiment is a tandem type color image forming apparatus, and each color component toner of four colors (Y (yellow), M (magenta), C (cyan), K (black)) in the present embodiment). Four image forming units 50 (specifically 50a to 50d) for forming an image are arranged in parallel, and each color component toner image formed by the image forming unit 50 is sequentially transferred onto the intermediate transfer belt 60 as a primary transfer roll. Each color component toner image on the intermediate transfer belt 60 is transferred onto a sheet 30 as a recording material at a secondary transfer portion (specifically, a secondary transfer roll 65). The sheet 30 is secondarily transferred and the sheet 30 is guided to a fixing device (not shown).

Each image forming unit 50 includes a photosensitive drum 51 (specifically, 51a to 51d), and a charging roll (not shown) that charges the photosensitive drum 51 around the photosensitive drum 51. A laser exposure device (not shown) for writing an electrostatic latent image on the photosensitive drum 51, and a developing device (not shown) that stores each color component toner and visualizes the electrostatic latent image on the photosensitive drum 51. 1), a primary transfer device 52 for transferring each color component toner image on the photosensitive drum 51 onto the intermediate transfer belt 60, a cleaner (not shown) for removing residual toner and the like on the photosensitive drum 51, and the like. ing.
Further, the intermediate transfer belt 60 is stretched around a plurality of stretch rolls 61 to 64, and is circulated and conveyed, for example, using the stretch roll 61 as a drive roll.

In the present embodiment, a portion of the intermediate transfer belt 60 that faces the stretching roll 64 is set as a secondary transfer portion, and the secondary transfer roll is disposed on the surface of the secondary transfer portion of the intermediate transfer belt 60. 65 is arranged, and a secondary transfer bias is applied between the secondary transfer roll 65 and a tension roll 64 (functioning as a backup roll) facing the secondary transfer roll 65. A belt cleaner 66 for cleaning residual toner on the intermediate transfer belt 60 is disposed on the downstream side of the secondary transfer roll 65 so as to be able to contact and separate from the intermediate transfer belt 60.
Further, the static eliminator 40 in the present embodiment is disposed on the back side of the intermediate transfer belt 60 between the tension roll 63 and the tension roll (backup roll) 64.

  The static eliminator 40 in the present embodiment has the same configuration as that of the first embodiment, and the two conductive members 41 and 42 are disposed via the insulating member 43 having a thickness of 20 mm. A bias power supply 44 and a bias power supply 45 are connected to 42. At this time, the bias power source 44 is + 500V and the bias power source 45 is −500V. Further, unlike the first embodiment, the static eliminator 40 is always in contact with the intermediate transfer belt 60.

Next, the operation of the image forming apparatus according to the present embodiment will be described with a focus on the static eliminator 40 in particular.
The toner images sequentially transferred and overlaid on the intermediate transfer belt 60 by the image forming units 50 (specifically, 50a to 50d) pass through the most downstream image forming unit 50d, and then the tension roll 62 and the tension roller 62 are stretched. The static eliminator 40 is reached via the part of the gantry roll 63. At this time, the intermediate transfer belt 60 overlaid with primary transfer is positively charged, and the toner image on the intermediate transfer belt 60 is stably held on the intermediate transfer belt 60 side by this positive charging.
When reaching the static eliminator 40, a potential gradient of 1000 V is applied between the two conductive members 41 and 42, so the charged charge in the intermediate transfer belt 60 is removed and the toner image holding power is reduced. Then, the toner image with the reduced holding force is transferred onto a sheet 30 as a recording material conveyed from a sheet tray or the like (not shown) by the secondary transfer roll 65.
In this embodiment, since the toner image holding force on the intermediate transfer belt 60 before the secondary transfer can be reduced, a sufficient secondary transfer rate can be obtained.

Example 1
In this example, in the configuration of the first embodiment, the effect of the static eliminator of the present case is large in the secondary transfer rate in the relationship between the volume resistivity of the intermediate transfer belt and the process speed (equivalent to the speed of the intermediate transfer belt). It was evaluated and confirmed at the level of occurrence and blur.
The volume resistivity of the intermediate transfer belt in this embodiment was set to four levels of 10 ¹² , 10 ¹³ , 10 ¹⁴ , and 10 ¹⁵ Ω · m.
The process speed was set at two levels of 220 and 400 mm / sec.
The results of the obtained secondary transfer rate are shown in FIG. From this, the following points were confirmed.
(1) The secondary transfer rate is improved by performing static elimination (the static elimination apparatus of the present case is effective).
(2) When the process speed is increased, the secondary transfer rate decreases. By using the static eliminator of the present case, a secondary transfer rate of 80% or more was secured within the conditions used in this example.
(3) When the volume resistivity of the intermediate transfer belt increases, the secondary transfer rate decreases. However, if the static eliminator of this case is used, the allowable range of volume resistivity is expanded.

The result of the blur occurrence level is shown in FIG. From this, the following points were confirmed.
(1) A clear significant difference by performing static elimination cannot be confirmed.
(2) If the volume resistivity of the intermediate transfer belt is 10 ¹³ , 10 ¹⁴ , 10 ¹⁵ Ω · m, the occurrence of blur is not a problem.
(3) Process speed is not directly related to blurring.
As described above, in this example, the effectiveness when the volume resistivity of the intermediate transfer belt is 10 ¹² , 10 ¹³ , 10 ¹⁴ , 10 ¹⁵ Ω · m was confirmed. Furthermore, it was confirmed that a high-quality image forming apparatus can be constructed with no problems in both secondary transfer rate and blur even when the process speed is increased to 400 mm / sec, preferably 10 ¹³ , 10 ¹⁴ Ω · m. .

Example 2
In this example, the relationship between the potential difference of the bias applied between the two conductive members and the secondary transfer rate was evaluated and confirmed by changing the process speed in the configuration of the first embodiment.
The potential difference was set so that the upstream conductive member was the positive side and the downstream conductive member was the negative side, and the applied bias was set to have the same absolute value (for example, when the potential difference was 500 V, the two conductive members + 250V and -250V are applied).
The potential difference was set to four levels of 500, 1000, 1500, and 2000V.
The process speed was set at two levels of 220 and 400 mm / sec.
As a result, as shown in FIG. 9, at a potential difference of 500 V, a secondary transfer rate of 80% or more is obtained when the process speed is 220 mm / sec, and when the process speed is increased to 400 mm / sec, the secondary transfer rate is poor. became. However, if the potential difference is 1000 V or more, a sufficient secondary transfer rate can be obtained even if the process speed is changed.
From this, a sufficient secondary transfer rate can be obtained by applying a potential difference of 500 V or more between the two conductive members, and a secondary transfer rate of 90% or more can be obtained by setting the potential difference to 1000 V or more. It was confirmed that Therefore, the effectiveness of this case was confirmed.

Example 3
In this example, in the configuration of the first embodiment, the occurrence of blur when the distance between two conductive members was changed was evaluated and confirmed by changing the process speed.
In this example, the distance between the conductive members was set to four levels of 10, 30, 50, and 70 mm.
The process speed was set at two levels of 220 and 400 mm / sec.
As a result, as shown in FIG. 10, it was confirmed that the secondary transfer rate decreases when the distance between the conductive members is increased or the process speed is increased.
That is, the effect of eliminating the charge on the intermediate transfer belt between the two conductive members is reduced, resulting in insufficient charge removal. Therefore, the toner image holding force to the intermediate transfer belt is strong at the time of secondary transfer, and the secondary transfer rate is lowered.
In this embodiment, when the distance between the two conductive members is 50 mm or less, a sufficient secondary transfer rate can be obtained at a process speed of 220 mm / sec. It was confirmed that the next transfer rate was obtained. Therefore, the effect of the present invention was confirmed.

(A) is explanatory drawing which shows the outline | summary of the static elimination apparatus which concerns on this invention, (b) is explanatory drawing which shows the outline | summary of the image forming apparatus using the static elimination apparatus which concerns on this invention. 1 is an explanatory diagram showing Embodiment 1 of an image forming apparatus to which the present invention is applied. FIG. 3 is an explanatory diagram showing a charge eliminating action of the first embodiment. FIG. 3 is an enlarged view of a main part showing an image forming apparatus according to a second embodiment. FIG. 6 is an explanatory diagram showing a charge eliminating action of a second embodiment. 5 is an explanatory diagram illustrating an image forming apparatus according to Embodiment 3. FIG. 6 is an explanatory diagram showing a first result of Example 1. FIG. It is explanatory drawing which shows the 2nd result of Example 1. FIG. FIG. 6 is an explanatory diagram showing the results of Example 2. It is explanatory drawing which shows the result of Example 3. FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Belt member, 1a ... Intermediate transfer belt, 2 ... Static elimination apparatus, 2a ... Switching means, 3 (3a, 3b) ... Conductive member, 4 ... Bias application means, 5 ... Stretch member, 6 ... Recording material, 7 ... Transfer means, 7a ... secondary transfer means, 8 ... image carrier, 9 ... primary transfer means, T ... toner image

Claims (6)

An endless belt member that rotatably supports and conveys an imaged toner image that is rotatably supported by a plurality of stretching members, a transfer unit that transfers the toner image on the belt member onto a recording material, and a belt A neutralization device that neutralizes the charge of the member,
The static eliminator is provided between the transfer member and the tension member upstream of the transfer unit with respect to the moving direction of the belt member, and is separated from the moving direction of the belt member and contacts the back surface of the belt member. Two conductive members disposed; and
Between the two conductive members, one of the conductive members has a neutralization bias having a potential gradient of 1000 V or more having a potential of a polarity different from that of the other conductive member, or a potential gradient of 1000 V or more having a potential of 0 V on one conductive member. An image forming apparatus comprising: a bias applying unit that applies a neutralizing bias . The image forming apparatus according to claim 1 .
The image forming apparatus characterized in that the bias applying means applies a static elimination bias such that the polarity of the conductive member arranged on the downstream side of the two conductive members is in the same polarity direction as the charged charge of the toner. The image forming apparatus according to claim 1.
An image forming apparatus, wherein a distance between two conductive members is 50 mm or less. The image forming apparatus according to any one of claims 1 to 3 ,
2. The image forming apparatus according to claim 2, wherein the two conductive members are provided with an insulating member interposed between the two opposing members so as to ensure an energization path only on the belt member side. An image carrier on which toner images of a plurality of colors are formed and carried;
An intermediate transfer belt that is rotatably supported by a plurality of stretching members and is disposed opposite to the image carrier;
Primary transfer means for transferring multiple toner images on the image carrier onto the intermediate transfer belt;
Secondary transfer means for collectively transferring the toner image on the intermediate transfer belt to a recording material;
A neutralization device that neutralizes the charge on the intermediate transfer belt,
The static eliminator is provided between the secondary transfer unit and the tension member on the upstream side of the secondary transfer unit with respect to the traveling direction of the intermediate transfer belt, and is separated from the intermediate transfer belt in the traveling direction. Two conductive members arranged in contact with the back surface of the transfer belt;
Between the two conductive members, one of the conductive members has a neutralization bias having a potential gradient of 1000 V or more having a potential of a polarity different from that of the other conductive member, or a potential gradient of 1000 V or more having a potential of 0 V on one conductive member. A bias applying means for applying a static elimination bias to be
An image forming apparatus comprising: switching means for switching between operation and stop of the static eliminator. A static eliminator that neutralizes an endless belt member on which a toner image is carried and conveyed,
Two conductive members arranged apart from the traveling direction of the belt member and in contact with the back surface of the belt member;
Between the two conductive members, one of the conductive members has a neutralization bias having a potential gradient of 1000 V or more having a potential of a polarity different from that of the other conductive member, or a potential gradient of 1000 V or more having a potential of 0 V on one conductive member. And a bias applying unit that applies a neutralizing bias .

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