JP2014059436A - Transfer device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the occurrence of abnormal images by maintaining constant transfer pressure to a transfer body such as an intermediate transfer belt, even when a linear velocity of the transfer body is changed.SOLUTION: A transfer device includes primary transfer bias rollers 11a to 11d for transferring toner images to an intermediate transfer belt 10 from respective photoreceptors 1a to 1d for respective colors of Y, M, C, and K. During monochrome image formation, only the primary transfer bias roller 11d is pressed to the photoreceptor 1d with the intermediate transfer belt 10 therebetween. The primary transfer bias roller 11d is held by a primary transfer bias roller holder 15 that is rotatable around a support shaft; and the support shaft is provided on the downstream side of the primary transfer bias roller 11d in a direction of movement of the intermediate transfer belt 10. The primary transfer bias roller holder 15 suppresses a reduction in transfer pressure of the intermediate transfer belt 10 to the photoreceptor 1d, even when the belt linear velocity of the intermediate transfer belt 10 is changed.

Description

  The present invention relates to a transfer device that transfers a toner image from a plurality of image carriers that carry toner images to a transfer member, and an image forming apparatus that includes the transfer device.

There are image forming apparatuses such as a copying machine, a printer, a facsimile machine, or a multifunction machine having at least two of these functions.
Such an electrophotographic image forming apparatus employs a toner image (also referred to as a “toner image”) from a plurality of image bearing members such as a photosensitive member, and the toner image is transferred by an intermediate transfer belt or a transfer material such as paper. A transfer device for transferring to a certain transfer body is provided.

For example, in an intermediate transfer type color image forming apparatus including an intermediate transfer belt, an electrostatic latent image corresponding to image data of each color is formed on each photoconductor for each color provided in an image forming unit. The electrostatic latent image on each photoconductor is developed by a developing device for each color to form a toner image of each color. Each color is generally four colors, yellow, magenta, cyan, and black.
The toner image of each color is primary-transferred by superimposing the respective toner images on the intermediate transfer belt sequentially from each photosensitive member at the primary transfer portion where each photoconductor and the primary transfer unit are opposed to each other with the intermediate transfer belt interposed therebetween. Form.
Further, the full-color toner image carried on the intermediate transfer belt is secondarily transferred to a recording medium such as a sheet as a transfer body at a secondary transfer nip formed by the intermediate transfer belt and the secondary transfer roller. . The recording medium is passed through a fixing device, and pressure and heat are applied to fix the toner to form an image.

However, in the transfer method as described above, as the thickness of the recording medium conveyed to the secondary transfer nip portion increases, the stiffness of the recording medium increases, or the curling of the recording medium increases, The impact generated at the time of collision or contact when entering the next transfer nip is increased.
The impact due to the impact is such that when the toner image carried on the photoconductor as the image carrier is primarily transferred onto the intermediate transfer belt, the recording medium is moved in the sub-scanning direction (moving direction of the intermediate transfer belt). This may disturb the steady transfer linear velocity.

Further, the primary transfer pressure is disturbed due to the disturbance of the transfer linear velocity, and as a result, the so-called shock jitter is a factor that causes image misalignment, color misregistration, density unevenness and the like.
Furthermore, the resistance generated when the recording medium is sandwiched in the secondary transfer nip portion may reduce the linear speed of the intermediate transfer belt, which is the transfer linear speed, and this also causes an image called a shock jitter. Misalignment, color misregistration, density unevenness, and the like.

  When a problem such as shock jitter occurs due to such a change in the transfer linear velocity, when the recording medium enters the secondary transfer nip portion when forming a plurality of images, the impact is transferred to the intermediate transfer belt. Propagate to. At that time, during the primary transfer, there is a problem that the toner image (intermediate image) to be primarily transferred to the intermediate transfer belt is disturbed in the sub-scanning direction.

  Therefore, for example, Patent Document 1 (Japanese Patent Application Laid-Open No. 2010-113280) describes that an impact on an endless belt (corresponding to an intermediate transfer belt) when a recording medium enters the secondary transfer nip is buffered. ing. Furthermore, by reducing the linear velocity fluctuation of the endless belt as much as possible, a configuration for secondary transfer of a stable image to various recording media such as thick paper, a recording medium having high rigidity, or a recording medium with strong curl, etc. It is disclosed.

However, as described above, in the image forming apparatus in which the impact when the recording medium enters the secondary transfer nip portion is buffered to reduce image disturbance, the configuration for buffering the impact is complicated. As a result, there has been a problem that the cost of manufacturing the apparatus becomes high.
Further, even if the change in the belt linear velocity of the intermediate transfer belt is reduced, the change in the belt linear velocity cannot be completely eliminated, so that the problem that the primary transfer pressure is disturbed cannot be solved. Such a problem also occurs in a direct transfer type image forming apparatus that directly transfers a toner image on a photoconductor as an image carrier to a recording medium as a transfer body conveyed by a transfer conveyance belt.

  The present invention has been made to solve the above-described problems. Even when the linear velocity of the transfer body changes when the toner image is transferred from the image carrier to the transfer body, the transfer can be performed with a simple and low-cost configuration. An object of the present invention is to keep the transfer pressure to the body constant and suppress the occurrence of abnormal images.

In order to achieve the above object, the transfer device of the present invention comprises a plurality of transfer means for transferring each toner image to a transfer body from a plurality of image carriers each carrying a toner image, and the plurality of transfer means A state in which only a part of the transfer means on the downstream side in the moving direction of the transfer body is pressed against the corresponding image carrier through the transfer body, and the plurality of transfer means are all connected to the transfer body. And a state in which the image carrier is pressed against the corresponding image carrier.
The part of the transfer means is held by a transfer means holding means that can rotate around a support shaft, and the support shaft is disposed downstream of the transfer means in the moving direction of the transfer body. On the other hand, all other transfer means except the above-mentioned part of transfer means are movably held in a direction orthogonal to the moving direction of the transfer body by a fixed transfer means holding means.

  When transferring a toner image from an image carrier to a transfer body, the transfer device according to the present invention keeps the transfer pressure to the transfer body constant even if the linear speed of the transfer body changes, and suppresses the occurrence of abnormal images. can do. Moreover, since it has a simple configuration, it can be implemented at low cost.

1 is a side view showing a mechanism part of an embodiment of an image forming apparatus according to the present invention. FIG. 2 is an enlarged side view showing the configuration of a primary transfer bias roller 11d and a primary transfer bias roller holder 15 shown in FIG. FIG. 2 is an enlarged side view showing a configuration of a primary transfer bias roller 11a and a primary transfer bias roller holder 16a shown in FIG. FIG. 2 is a side view showing an arrangement of primary transfer bias rollers during monochrome printing of the transfer device in the image forming apparatus shown in FIG. 1. It is a side view which shows arrangement | positioning of the primary transfer bias roller at the time of monochrome printing of other embodiment of the transfer apparatus by this invention. It is a side view which shows the mechanism part of other embodiment of the image forming apparatus by this invention. FIG. 6 is a diagram schematically illustrating a toner shape for explaining a toner shape factor SF1. FIG. 6 is a diagram schematically illustrating a toner shape for explaining a toner shape factor SF2.

Hereinafter, embodiments for carrying out the present invention will be specifically described with reference to the drawings.
First, an embodiment of an image forming apparatus according to the present invention will be described. FIG. 1 is a side view showing a mechanism portion of the image forming apparatus.
This image forming apparatus is an intermediate transfer type color image forming apparatus using an intermediate transfer belt as an intermediate transfer member.

In the image forming apparatus 30, drum-shaped photoconductors 1 a to 1 d for yellow (Y), magenta (M), cyan (C), and black (K) images are provided as image carriers. Yes.
Around each of the photoreceptors 1a to 1d, the photoreceptor cleaning units 2a to 2d, the chargers 4a to 4d, the intermediate transfer belt 10, and the like are arranged, respectively.
The blades 3a to 3d in the photosensitive member cleaning units 2a to 2d are members for removing the transfer residual toner from the corresponding photosensitive members 1a to 1d.

Above these, an exposure unit (not shown) is disposed, and the laser light source in the exposure unit is modulated and driven based on the image information to emit laser light from the laser light source.
While the laser beam is scanned in the main scanning direction by the polygon mirror, the respective photoconductors 1a to 1d charged with the respective exposure laser beams 5a to 5d through the plurality of optical lenses and mirrors by the respective chargers 4a to 4d. Each surface is irradiated and exposed.

By the exposure, electrostatic latent images of yellow, magenta, cyan, and black images are formed on the surfaces of the photoreceptors 1a to 1d, respectively.
The image forming apparatus 30 uses a yellow developing unit 6, a magenta developing unit 7, a cyan developing unit 8, and a black developing unit 9 to convert the electrostatic latent images formed on the surfaces of the photoreceptors 1a to 1d into full-color images. To develop toner images of respective colors.

The toner images of the respective colors are sequentially superimposed and transferred onto the intermediate transfer belt 10 to form a full-color toner image on the intermediate transfer belt 10. That is, each of the photoconductors 1a to 1d corresponds to a plurality of image carriers that respectively carry toner images.
The intermediate transfer belt 10 is stretched between a secondary transfer counter roller 12 that also serves as a driving roller and a tension roller 13 in a tensioned state, and is provided below the respective photoreceptors 1a to 1d.

Then, the secondary transfer counter roller 12 also serving as a drive roller is driven to rotate by a drive motor (not shown), so that the intermediate transfer belt 10 rotates in the direction indicated by the arrow A (hereinafter referred to as “rotation”). . The process speed (linear speed) is adjusted to 150 mm / sec, for example.
Primary transfer bias rollers 11a to 11d are disposed at positions facing the respective photoreceptors 1a to 1d with the intermediate transfer belt 10 interposed therebetween.

A predetermined transfer bias, for example, +1800 V is applied to each of the primary transfer bias rollers 11a to 11d from the primary transfer bias power supply unit 22 during the primary transfer operation.
With the transfer bias from the primary transfer bias power supply unit 22, the primary transfer bias rollers 11a to 11d sequentially transfer the toner images formed on the photoreceptors 1a to 1d onto the intermediate transfer belt 10.

That is, the primary transfer bias rollers 11a to 11d function as a plurality of transfer units that transfer the toner images to the intermediate transfer belt 10 as a transfer body.
In full color printing, as shown in the figure, all the primary transfer bias rollers 11a to 11d are brought into contact with the intermediate transfer belt 10 and are pressed against the photoreceptors 1a to 1d with the intermediate transfer belt 10 interposed therebetween. To do.

On the other hand, during monochrome printing, the primary transfer bias rollers 11 a to 11 c for transferring toner images of yellow, magenta, and cyan are lowered by a mechanism (not shown) to a position away from the intermediate transfer belt 10. As a result, only the primary transfer bias roller 11d for transferring the black toner image, which is located on the most downstream side in the moving direction of the intermediate transfer belt 10, is pressed against the photoreceptor 1d via the intermediate transfer belt 10. .
In this way, during monochrome printing, the primary transfer bias rollers 11a to 11c are not pressed against the unused photoreceptors 1a to 1c, thereby extending the life of the photoreceptors 1a to 1c.

The primary transfer bias rollers 11a to 11d, the secondary transfer counter roller 12, and the tension roller 13 are arranged on both sides of the intermediate transfer belt 10 (front side and back side in FIG. 1) by an intermediate transfer belt unit side plate (not shown). ) Is supported.
The intermediate transfer belt 10 is composed of single layer or multiple layers of PVDF (vinylidene fluoride), ETFE (ethylene-tetrafluoroethylene copolymer), PI (polyimide), PC (polycarbonate), and the like.

The conductive material containing carbon black is dispersed, and the volume resistivity is adjusted to be 10 ⁸ to 10 ¹² Ωcm and the surface resistivity is adjusted to be in the range of 10 ⁹ to 10 ¹³ Ωcm. Note that a release layer may be coated on the surface of the intermediate transfer belt 10 as necessary.

As a material used for the coating, a fluororesin can be used, but is not limited thereto.
The fluororesin includes ETFE (ethylene-tetrafluoroethylene copolymer), PTFE (polytetrafluoroethylene), and PVDF (vinylidene fluoride).
Further, PEA (perfluoroalkoxy fluororesin), FEP (tetrafluoroethylene-hexafluoropropylene copolymer), and PVF (vinyl fluoride) are also included.

There are various methods for producing the intermediate transfer belt 10 including, for example, a casting method and a centrifugal molding method, and the surface thereof may be polished as necessary.
If the volume resistivity of the intermediate transfer belt 10 exceeds the upper limit of 10 ⁸ to 10 ¹² Ωcm within the above-described range, the bias necessary for transfer increases, which is not preferable because the power supply cost increases.
Further, since the charging potential of the intermediate transfer belt 10 becomes high and the self-discharge becomes difficult in the transfer process, the transfer paper peeling process, etc., it becomes unnecessary to newly provide a static elimination means, which causes an increase in the cost of manufacturing the apparatus. .

Furthermore, if the volume resistivity and surface resistivity are below the lower limits of the above ranges, the charge potential decays faster, which is advantageous for static elimination by self-discharge, but the toner flows because the current during transfer flows in the surface direction. Spattering will occur.
Therefore, it is preferable that the volume resistivity and the surface resistivity of the intermediate transfer belt 10 be within the above ranges.

  In measuring the volume resistivity and surface resistivity, an HRS probe (inner electrode diameter 5.9 mm, ring electrode inner diameter 11 mm) was connected to a high resistivity meter (manufactured by Mitsubishi Chemical Corporation: Hiresta IP, registered trademark) A voltage of 100 V (500 V when measuring the surface resistivity) was applied to the front and back of the intermediate transfer belt 10. And the measured value measured 10 seconds later is shown.

The belt cleaning unit 19 is a unit that cleans the surface of the intermediate transfer belt 10, and a cleaning blade 20 made of urethane rubber is disposed.
The cleaning blade 20 is pressed against the intermediate transfer belt 10 to block the residual toner on the intermediate transfer belt 10 and clean it.

A lubricant 29 is applied to the belt cleaning unit 19 by the lubricant application member 18 in order to facilitate cleaning of residual toner on the intermediate transfer belt 10.
As the lubricant 29, for example, a fatty acid metal salt having a linear hydrocarbon structure is used. The lubricant 29 is supplied in minute amounts in the form of powder.
As a specific supply method, there is a method in which the lubricant 29 is solid-molded into a block shape, the lubricant application member 18 is made into a brush shape, and the solid lubricant 29 is scraped off and applied.

A secondary transfer roller 21 is provided at a position facing the secondary transfer counter roller 12 across the intermediate transfer belt 10. The secondary transfer roller 21 is formed by coating an elastic body such as urethane adjusted to a resistance value of 10 ⁶ to 10 ¹⁰ Ω with a conductive material on a metal core such as stainless steel (SUS). Has been.

If the resistance value of the secondary transfer roller 21 exceeds the upper limit of the above range, it becomes difficult for the current to flow. Therefore, a higher voltage must be applied in order to obtain the required transfer property, which increases the power supply cost. Invite. In addition, since a high voltage is applied, a discharge occurs in the gap before and after the nip portion of the transfer portion, so that white spots are lost on the halftone image due to the discharge.
On the other hand, if the resistance value of the secondary transfer roller 21 is below the lower limit of the above range, transferability between a multicolor image portion (for example, a three-color superimposed image) and a single color image portion existing on the same image cannot be achieved. .
This is because the resistance value of the secondary transfer roller 21 is low, and a sufficient current flows to transfer the monochrome image portion at a relatively low voltage.

However, since a voltage value higher than the optimum voltage for the single color image portion is required to transfer the multiple color image portion, if the voltage is set so that the multiple color image portion can be transferred, the transfer current will be excessive for the single color image, and transfer efficiency will be increased. This leads to a reduction.
The resistance value of the secondary transfer roller 21 is set, for example, by placing the secondary transfer roller 21 on a conductive metal plate and applying a load of 4.9 N on one side (total of 9.8 N on both sides) to both ends of the core metal. In this state, it is calculated from the value of the current that flows when a voltage of 1000 V is applied between the core metal and the metal plate.

The secondary transfer roller 21 is given a driving force by a known driving gear (not shown), and its peripheral speed is adjusted to be substantially the same as the peripheral speed of the intermediate transfer belt 10. The secondary transfer by the secondary transfer roller 21 is controlled by a constant current, and in this embodiment, the set value is set to, for example, -30 μA.
Further, the secondary transfer roller 21 is grounded, and the secondary transfer counter roller 12 has a second bias voltage for transferring the toner image formed on the intermediate transfer belt 10 onto a transfer sheet 25 such as a sheet or a recording sheet. It is applied from the next transfer bias power supply unit 23.

In addition, the transfer paper 25 is fed by the paper feed roller 26, the transfer paper transport roller 27, and the positioning roller 28 at the timing when the leading end of the four-color superimposed image on the surface of the intermediate transfer belt 10 reaches the secondary transfer position. Make paper.
The transfer paper 25 is fed from a paper feed cassette 31 by a feed roller 26 as transfer paper feeding means, separated one by one by a separating means (not shown), and passed through a transfer paper transport roller 27. Be fed.

  Thereafter, the front end of the transfer paper is temporarily stopped by the nip portion of the positioning roller 28 to correct the oblique displacement, and the front end of the four-color superimposed toner image on the intermediate transfer belt 10 reaches the secondary transfer position. It is conveyed by the positioning roller 28 in accordance with the timing.

The four-color superimposed toner image on the intermediate transfer belt 10 is transferred to the transfer nip formed by the secondary transfer counter roller 12 and the secondary transfer roller 21 to which a predetermined voltage is applied via the secondary transfer bias power supply unit 23. The images are transferred to the transfer paper 25 at once.
The four-color superimposed toner image transferred to the transfer paper 25 is discharged by a discharging means (not shown) and then conveyed along the fixing inlet guide to the fixing unit 32 where the toner is fixed by heating and pressing. Thereafter, the paper is discharged onto a paper discharge tray (not shown) by a paper discharge roller 33.

Next, the transfer device in the image forming apparatus will be described in detail.
FIG. 2 is an enlarged side view showing the configuration of the primary transfer bias roller 11d and the primary transfer bias roller holder 15 shown in FIG.
FIG. 3 is an enlarged side view showing the configuration of the primary transfer bias roller 11a and the primary transfer bias roller holder 16a shown in FIG.
4 is a side view showing the arrangement of primary transfer bias rollers during monochrome printing of the transfer device in the image forming apparatus shown in FIG.

First, the primary transfer bias rollers 11a to 11d and the primary transfer bias roller holders 15 and 16a to 16c constituting the transfer device will be described with reference to FIGS.
As shown in FIG. 2, the primary transfer bias roller 11d for transferring the black toner image is applied with a pressing force from below in the drawing of the intermediate transfer belt 10 by a spring 14d, and is applied to the photoreceptor 1d with the intermediate transfer belt 10 interposed therebetween. It is pressed.

The primary transfer bias roller 11d is installed in a state of being offset by about 0.5 to 3 mm on the downstream side in the moving direction of the intermediate transfer belt 10 with respect to the photoreceptor 1d.
The primary transfer bias roller 11d for transferring the black toner image is held by a movable primary transfer bias roller holder 15 which is transfer means holding means that can rotate around a support shaft 15a.

Holder arms 15b are respectively provided at both ends (front side and back side in the figure) of the support shaft 15a, and a primary transfer bias roller 11d is rotatably attached to the tip of the holder arm 15b.
The movable primary transfer bias roller holder 15 has a support shaft 15a disposed downstream of the primary transfer bias roller 11d in the moving direction of the intermediate transfer belt 10 (in the direction of arrow B).

On the other hand, the primary transfer bias rollers 11a to 11c for transferring the yellow, magenta, and cyan toner images are held as representative of the primary transfer bias roller 11a for transferring the yellow toner image in FIG.
That is, the primary transfer bias roller 11a is moved in a direction orthogonal to the moving direction of the intermediate transfer belt 10 by a fixed primary transfer bias roller holder 16a which is a channel-shaped transfer means holding means fixed to a lifting member (not shown). It is held movably in the vertical direction in the figure.

The primary transfer bias roller 11a is pushed upward by the spring 14a built in the fixed primary transfer bias roller holder 16a so as to be pressed against the photoreceptor 1a via the intermediate transfer belt 10.
This is a transfer means holding means of a conventional general primary transfer bias roller.

The primary transfer bias roller 11a receives force due to speed fluctuation and tension fluctuation via the intermediate transfer belt 10 when there is speed fluctuation and tension fluctuation in the intermediate transfer belt 10 during full color printing.
Since the primary transfer bias roller 11a is directly pressurized by the spring 14a, the force in the arrow E direction due to the speed variation and the force in the arrow F direction due to the tension variation are superimposed to reduce the primary transfer pressure. Work in the direction to let you.

The transfer means holding means of the primary transfer bias rollers 11b and 11c for transferring magenta and cyan toner images are the same. Therefore, when the intermediate transfer belt 10 has a speed fluctuation and a tension fluctuation, it similarly works to reduce the pressurization of the primary transfer pressure.
However, during full-color printing, the primary transfer bias rollers 11 a to 11 d are all pressed against the corresponding photoreceptors 1 a to 1 d via the intermediate transfer belt 10.
Therefore, the speed fluctuation of the intermediate transfer belt 10 hardly occurs due to the adsorption force between the intermediate transfer belt 10 and the photoreceptors 1a to 1d.

At the time of monochrome printing, as shown in FIG. 4, the primary transfer bias rollers 11a to 11c for transferring the toner images of yellow, magenta, and cyan are not brought into contact with the intermediate transfer belt 10 by a lifting member (not shown). Lower.
Therefore, only the primary transfer bias roller 11d, which is a part of transfer means, arranged on the most downstream side in the moving direction of the intermediate transfer belt 10 is pressed against the photoreceptor 1d via the intermediate transfer belt 10. Become.

As described above, during monochrome printing, the number of primary transfer bias rollers pressed against the photosensitive member via the intermediate transfer belt 10 is reduced. It becomes easy to receive.
However, in the transfer device of this image forming apparatus, as shown in FIG. 2, the primary transfer bias roller 11d that can rotate the primary transfer bias roller 11d for transferring the black toner image about the support shaft 15a is movable. Is held by. The support shaft 15a is disposed downstream of the primary transfer bias roller 11d in the moving direction of the intermediate transfer belt 10.

With this configuration, the force in the direction indicated by the arrow C due to the speed fluctuation of the intermediate transfer belt 10 and the force in the direction indicated by the arrow D due to the fluctuation in tension are opposite to the primary transfer bias roller 11d. Both work and balance.
Accordingly, the pressing force of the primary transfer bias roller 11d against the photoreceptor 1d via the intermediate transfer belt 10, that is, the transfer pressure is hardly reduced.
For this reason, when the intermediate transfer belt 10 has speed fluctuations and tension fluctuations, it is possible to make it difficult for belt movement disturbance of the intermediate transfer belt 10 to occur, and shocks such as black toner image misalignment during monochrome printing. Image degradation due to jitter can be reduced.

  That is, according to this image forming apparatus, even if the speed fluctuation of the intermediate transfer belt 10 occurs when the transfer paper enters the secondary transfer nip portion, the temporary transfer pressure fluctuation due to the primary transfer bias roller with respect to the photosensitive member is suppressed. Therefore, the occurrence of abnormal images on the intermediate transfer belt 10 can be reduced.

In this case, the installation space of the primary transfer bias roller holder 15 that holds the primary transfer bias roller 11d for transferring the black toner image needs to be slightly increased. However, since no new space is required for the other primary transfer bias roller holders 16a to 16c, miniaturization of the transfer device is not hindered.
Therefore, it is possible to simultaneously suppress the influence of shock jitter during monochrome printing and to reduce the size of the transfer device.

  Furthermore, since only the holder of the primary transfer bias roller for transferring the black toner image is changed in order to reduce the change in the belt linear velocity of the intermediate transfer belt, the number of newly added components can be minimized. Therefore, the configuration of the transfer device is not complicated, and the cost for manufacturing the device is not increased.

Next, another embodiment of the transfer device of the image forming apparatus according to the present invention will be described.
FIG. 5 is a side view showing the arrangement of the primary transfer bias roller during monochrome printing of the transfer device.
The transfer apparatus shown in FIG. 5 is also mounted on an image forming apparatus having the same configuration as that of the image forming apparatus shown in FIG. 1, but a photoreceptor 1 e and a primary transfer capable of transferring a transparent toner image in monochrome and full color printing, respectively. A bias roller 11e is provided.
That is, as shown in FIG. 5, a transparent image photosensitive member 1e and a transparent toner image transfer primary transfer bias roller 11e are disposed downstream of the black image photosensitive member 1d in the moving direction of the intermediate transfer belt 10. However, they are arranged so as to face each other with the intermediate transfer belt 10 interposed therebetween.

The primary transfer bias roller 11e is also set so that a predetermined transfer bias is applied from the primary transfer bias power supply unit 22 shown in FIG.
The primary transfer bias roller 11e is also held rotatably around a support shaft 17a by a primary transfer bias roller holder 17 having the same configuration as the primary transfer bias roller holder 15 shown in FIG. The support shaft 17a is also installed downstream of the primary transfer bias roller 11e in the moving direction of the intermediate transfer belt 10.

In monochrome printing, as shown in FIG. 5, only the primary transfer bias rollers 11 d and 11 e installed on the downstream side in the moving direction of the intermediate transfer belt 10 are respectively connected to the corresponding photoreceptors 1 d and 11 via the intermediate transfer belt 10. 1e is pressed.
At this time, even if the intermediate transfer belt 10 has speed fluctuations and tension fluctuations, belt running disturbance of the intermediate transfer belt 10 hardly occurs for the same reason as in the above-described embodiment.
Therefore, it is possible to reduce image deterioration due to shock jitter such as a position shift of a black toner image during monochrome printing.

Next, another embodiment of the image forming apparatus according to the present invention will be described with reference to FIG. 6. The image forming apparatus 40 shown in FIG. 6 uses a toner image on a photoconductor as an image carrier as a transfer material such as paper. This is a direct transfer type color image forming apparatus for direct transfer. However, there are many parts in common with the intermediate transfer type color image forming apparatus shown in FIG. Therefore, in FIG. 6, the same reference numerals are given to portions corresponding to FIG. 1, and description thereof is omitted.

  In the image forming apparatus 40 shown in FIG. 6, the transfer paper 25 as a transfer member is attracted to the belt surface by the transfer conveyance belt 42 and conveyed to the toner image transfer position from the photoconductors 1 a to 1 d. The yellow, magenta, cyan, and black toner images are directly transferred to the superimposed state to form a full-color image.

The transfer / conveying belt 42 is stretched by the tension roller 13, the driving roller 45, and the driven rollers 43 and 44, and is disposed below the photoconductors 1 a to 1 d.
The drive roller 45 disposed at the inlet portion on the upstream side in the transfer paper moving direction is arranged on the outer peripheral surface side of the transfer conveyance belt 42 so that the electrostatic adsorption roller 46 to which a predetermined voltage is applied from a power supply (not shown) is opposed. Has been placed.

The transfer paper 25 fed between the drive roller 45 and the electrostatic adsorption roller 46 is electrostatically adsorbed on the surface of the transfer conveyance belt 42 charged by a charging means (not shown), and the left side (transfer body in the drawing) In the moving direction).
Transfer bias rollers 51a to 51d to which a transfer bias from a transfer bias power supply unit 47 is applied are provided at respective transfer positions corresponding to the respective photoreceptors 1a to 1d so as to be pressed via a transfer conveyance belt 42. .

  The transfer bias rollers 51a to 51c are respectively held by fixed transfer bias roller holders 16a to 16c similar to those shown in FIG. 3, and the transfer bias roller 51d is similar to that shown in FIG. It is held by a movable transfer bias roller holder 15. Since each of these transfer bias roller holders 16a to 16c and 15 has the same configuration as each of the primary transfer bias roller holders 16a to 16c and 15 in the above-described embodiment, the same reference numerals are given for convenience.

Therefore, similarly to the primary transfer bias roller holder 15 shown in FIG. 2, the transfer bias roller holder 15 is also a transfer means holding means that can rotate around the support shaft 15a. The support shaft 15a is a transfer bias roller. It is installed on the downstream side in the moving direction of the transfer sheet 25 as a transfer body from 51d.
At the time of full color printing, as shown in FIG. 6, the transfer bias rollers 11 a to 11 d are all pressed against the corresponding photoreceptors 1 a to 1 d via the transfer conveyance belt 42. Transfer pressure fluctuations caused by speed fluctuations of the transfer / conveying belt 42 can be suppressed by the adsorption force with the bodies 1a to 1d.

On the other hand, as in the above-described embodiment, only the transfer bias roller 51d for transferring the black toner image is pressed against the photoconductor 1d.
Therefore, at the time of monochrome printing, the number of transfer bias rollers pressed against the photosensitive member is small, and therefore, when the transfer conveyance belt 42 is fluctuated in speed, it is easily affected.

  However, since the transfer bias roller 51d is held by the movable transfer bias roller holder 15, the same effect as the case of the primary transfer bias roller holder 15 described with reference to FIG. 2 can be obtained. That is, the pressing force (transfer pressure) of the transfer bias roller 51d against the photoreceptor 1d via the transfer conveyance belt 42 is hardly reduced.

In this way, even in the image forming apparatus provided with the transfer device that directly transfers the toner image on the photosensitive member while the transfer paper 25 is conveyed by the transfer conveyance belt 42, the image forming apparatus of the intermediate transfer method described above is also used. The same effect can be obtained.
That is, even when there is a speed fluctuation in the transfer / conveying belt 42 during monochrome printing, it is possible to suppress a change in the transfer pressure caused by the speed fluctuation, and image deterioration due to shock jitter such as a positional deviation of the black toner image. Can be reduced.
The same applies to other effects.
Also in this image forming apparatus, the intermediate transfer belt 10 of the transfer apparatus shown in FIG. 5 can be mounted in place of the transfer conveyance belt 42. Thereby, the transparent toner can be transferred.

Here, the toner used in the image forming apparatus of each embodiment described above will be described.
The toner used in the image forming apparatus of each embodiment is a polymerized toner generated by a polymerization method.
The toner preferably has a shape factor SF1 in the range of 100 to 180 and a shape factor SF2 in the range of 100 to 180.

FIG. 7 is a diagram schematically showing the shape of the toner for explaining the shape factor SF1, and FIG. 8 is a diagram for explaining the shape factor SF2.
The shape factor SF1 indicates the ratio of the roundness of the toner shape and is represented by the following formula (1).
SF1 = {(MXLNG) ² / AREA} × (100π / 4) (1)

As shown in FIG. 7, this is a value obtained by dividing the square of the maximum length MXLNG of the shape formed by projecting the toner on a two-dimensional plane by the figure area AREA and multiplying by 100π / 4.
When the value of the shape factor SF1 is 100, the shape of the toner becomes a true sphere, and the toner shape becomes indefinite as the value of SF1 increases.
The shape factor SF2 indicates the ratio of the unevenness of the toner shape and is represented by the following formula (2).

SF2 = {(PERI) ² / AREA} × (100π / 4) Expression (2)
This is a value obtained by dividing the square of the perimeter PERI of the figure formed by projecting the toner on the two-dimensional plane by the figure area AREA and multiplying by 100π / 4, as shown in FIG.
When the value of SF2 is 100, there is no unevenness on the toner surface, and as the value of SF2 increases, the unevenness of the toner surface becomes more prominent.

Specifically, the shape factor is measured by taking a photograph of the toner with a scanning electron microscope (S-800: manufactured by Hitachi, Ltd.), introducing it into an image analyzer (LUSEX 3: manufactured by Nireco), and analyzing it. Calculated.
When the shape of the toner is close to a sphere, the contact state between the toner and the toner or the toner and the photoconductor becomes a point contact, so that the adsorption force between the toners becomes weak.

Therefore, the fluidity of the toner is increased, and the adsorption force between the toner and the photoreceptor is also weakened, so that the transfer rate is increased.
If either of the shape factors SF1 and SF2 exceeds 180, the transfer rate is lowered and the cleaning property when attached to the transfer means is also lowered, which is not preferable.
The toner particle size is preferably in the range of 4 to 10 μm in terms of volume average particle size.

In the case of a smaller particle diameter than this, it becomes a cause of background stain at the time of development, fluidity is deteriorated, and further, it tends to agglomerate, so that voids are likely to occur.
On the other hand, when the particle diameter is larger than this, it becomes impossible to obtain a high-definition image due to toner scattering and resolution deterioration.
In this embodiment, a toner having a volume average particle diameter of 6.5 μm was used.

Although the description of the embodiment has been completed above, in the present invention, the specific configuration of each unit, the content of processing, the data format, and the like are not limited to those described in the embodiment.
Further, it goes without saying that the configurations of the embodiments described above can be implemented in any combination as long as they do not contradict each other.

1a to 1d: photoconductors 2a to 2d: photoconductor cleaning units 3a to 3d: blades 4a to 4d: chargers 5a to 5d: laser light for exposure 6: yellow developer 7: magenta developer 8: cyan developer 9: Black developing device 10: Intermediate transfer belts 11a to 11d: Primary transfer bias roller 12: Secondary transfer counter roller 13: Tension rollers 13a, 14a to 14d, 54a to 54d: Spring 15, 17: Movable (primary transfer) bias roller Holders 15a and 17a: Support shaft 15b: Holder arms 16a to 16c: Fixed (primary transfer) bias roller holder 18: Lubricant application member 19: Belt cleaning unit

20: Cleaning blade 21: Secondary transfer roller 22: Primary transfer bias power supply unit 23: Secondary transfer bias power supply unit 25: Transfer paper 26: Paper feed roller 27: Transfer paper transport roller 28: Positioning roller 29: Lubricant
30, 40: Image forming apparatus 31: Paper feed cassette 32: Fixing unit
33: paper discharge roller 42: transfer conveyance belt 43, 44: driven roller
45: Driving roller 46: Electrostatic attracting roller 47: Transfer bias power supply unit
51a to 51d: transfer bias roller

JP 2010-113280 A

Claims (6)

A plurality of transfer means for transferring each toner image to a transfer body from a plurality of image carriers each carrying a toner image;
Either of the plurality of transfer means is a state in which only a part of the transfer means on the downstream side in the moving direction of the transfer body is pressed against the corresponding image carrier through the transfer body; In a transfer device that can take a state of pressing the corresponding image carrier through the transfer body,
The part of the transfer means is held by a transfer means holding means that is rotatable about a support shaft, and the support shaft is installed downstream of the transfer means in the moving direction of the transfer body,
The transfer apparatus, wherein all other transfer means except the transfer means are movably held in a direction orthogonal to the moving direction of the transfer body by a fixed transfer means holding means. A plurality of transfer means for transferring each color toner image to a transfer body from a plurality of image carriers each carrying a toner image of each color for creating a full color image;
A state in which only the transfer means used for forming a monochrome image downstream of the transfer body in the moving direction of the plurality of transfer means is pressed against the corresponding image carrier through the transfer body; In the transfer apparatus capable of taking a state in which any of the transfer means is pressed against the corresponding image carrier through the transfer body,
The transfer means used for forming the monochrome image is held by a transfer means holding means that can rotate around a support shaft, and the support shaft is installed downstream of the transfer means in the moving direction of the transfer body. ,
The transfer means other than the transfer means used for forming the monochrome image are all held movably in a direction perpendicular to the moving direction of the transfer body by a fixed transfer means holding means. Transfer device.   3. The transfer means used for forming the monochrome image is a transfer means for transferring a black toner image to the transfer body and a transfer means for transferring a transparent toner image to the transfer body. The transfer apparatus described.   The transfer device according to claim 1, wherein the transfer body is an intermediate transfer belt.   The transfer apparatus according to claim 1, wherein the transfer body is a recording medium, and a transfer conveyance belt for conveying the recording medium is provided.   An image forming apparatus comprising the transfer device according to claim 4.

Images