JP3984739B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a transfer device for transferring a charged object from a reusable image carrier to a recording material by using electrostatic force, and in particular, a transfer device in an image forming apparatus such as an electrophotographic copying machine, a printer, and a fax machine. The present invention relates to an apparatus for electrostatically transferring a toner image onto a recording material using a charged toner by a suitable image forming process means such as electrophotography, electrostatic recording, and magnetic recording, directly or indirectly.
[0002]
[Prior art]
FIG. 5 shows a schematic configuration of a conventional image forming apparatus using an intermediate transfer belt as an intermediate transfer member. The image forming apparatus shown in the figure is an electrophotographic four-color full-color laser beam printer.
[0003]
The photosensitive drum 11 serving as an image carrier rotates in the direction of the arrow R11, is uniformly charged by the primary charger 12, and an electrostatic latent image is formed on the surface by the laser light from the scanner 13. The electrostatic latent image reaches the developing units 14a, 14b, 14c, and 14d by the rotation of the photosensitive drum 11, and the toner charged with the same polarity is attached and developed. A full-color image forming apparatus generally includes four-color developing devices 14a to 14d, and supplies yellow, magenta, cyan, and black toners, respectively. The full-color image forming apparatus described here synthesizes a toner image on a belt as an intermediate transfer member, and the electrostatic latent image on the photosensitive drum 11 is developed with a single color toner. First, the first color (yellow) toner is applied to the photosensitive drum 11 from the first developing device 14a according to the electrostatic latent image. At this time, the second to fourth developing units 14b to 14d are turned off, and the first color toner image is not affected by the second to fourth developing units 14b to 14d. And the primary transfer portion (primary transfer nip portion) T ₁ formed between the photosensitive drum 11 and the opposite polarity to the toner of the first color applied to the conductive primary transfer roller 1 c in contact with the back surface of the intermediate transfer belt 1. The primary transfer (intermediate transfer) is performed on the intermediate transfer belt 1 by the voltage of. The surface of the photosensitive drum 11 after the primary transfer of the first color toner image is cleaned by the cleaning device 16 and then enters the second color (magenta) image forming process.
[0004]
In the second color process, only the second developing device 14b is operated and the other developing devices 14a, 14c, and 14d are turned off, and the toner image of the second color is intermediately transferred by the procedure described above. Primary transfer is performed on the belt 1. Thereafter, the third color (cyan), the fourth color (black), and the primary transfer are sequentially performed on the intermediate transfer belt 1, and toner images of four colors are superimposed on the intermediate transfer belt 1. During this time, the intermediate transfer body cleaning device 18 of the intermediate transfer belt 1 is released so that the toner image on the intermediate transfer belt 1 is not disturbed.
[0005]
Then, the recording material P from the paper feed means (not shown) is the removed one, the secondary transfer portion (secondary transfer nip) is inserted into T _2. At this time, a voltage having a polarity opposite to that of the toner is applied to the conductive secondary transfer roller 3, and the first to fourth color toner images on the intermediate transfer belt 1 are secondarily transferred onto the recording material P all at once. Is done.
[0006]
The recording material P carrying the unfixed toner image that has passed through the secondary transfer portion T ₂ reaches the fixing device 17 and is heated and pressurized to obtain a permanent fixed image. The surface of the intermediate transfer belt 1 on which the first to fourth color toner images have been transferred to the recording material P is cleaned by the intermediate transfer body cleaning device 18 operating.
[0007]
In Japanese Patent Laid-Open No. 8-146706, a reverse bending roller that bends the intermediate transfer belt in the reverse direction downstream of the recording material separating roller of the secondary transfer portion is used as a winding method of the intermediate transfer belt that is the above-described intermediate transfer member. The structure to provide is disclosed. According to this, the degree of freedom of the layout of the intermediate transfer belt is increased, space can be saved, and the recording material can be easily separated.
[0008]
[Problems to be solved by the invention]
However, the above-described image forming apparatus has the following problems.
[0009]
In the configuration disclosed in Japanese Patent Application Laid-Open No. 8-146706, an intermediate transfer belt, which is an intermediate transfer member, is used in the process of synthesizing a full-color image in order to form an image using a single photosensitive member (image carrier). In this state, the above-described reverse bending roller passes a plurality of times while the toner image is carried, and at this time, the image is disturbed or the reverse bending roller becomes dirty.
[0010]
In addition, the load at the time of running of the intermediate transfer belt is increased due to the contact of the reverse bending roller, and particularly in an image forming apparatus that forms an image at a high speed, the intermediate transfer belt that is run by the driving roller has a separation roller portion (secondary roller). In some cases, uneven running occurred in the vicinity of the transfer portion, resulting in uneven image.
[0011]
The present invention has been made in view of the above circumstances, and is intended to achieve good separation of the recording material, prevention of toner image disturbance, and stabilization of the intermediate transfer belt when the intermediate transfer belt is used. An object of the present invention is to provide an image forming apparatus.
[0012]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, the invention of claim 1 includes a movable endless intermediate transfer belt, a plurality of rollers that support the intermediate transfer belt, a plurality of image carriers that carry a toner image, A toner image formed on the intermediate transfer belt by transferring a toner image onto the intermediate transfer belt at a plurality of primary transfer portions between the image carrier and the intermediate transfer belt. collectively onto the recording material by the secondary transfer in the next transfer section, one of said multiple rollers the intermediate transfer belt is passed over the said intermediate transfer recording medium after the secondary transfer of the toner image also it serves as a separation roller for separating from the belt surface, with respect to the common tangent of the outer connecting the last roller in the separating roller and the downstream side along the running direction of the intermediate transfer belt, than the common tangent Also the intermediate transfer belt In the image forming apparatus Ru comprising a pressing member for bending the side, the intermediate transfer belt on the downstream side of the primary transfer portion of the most downstream side of the upstream side and the plurality of primary transfer portion of the secondary transfer portion It has a driving roller for driving, and has a recording material conveying member that makes the conveying speed of the recording material in the secondary transfer portion larger than the traveling speed of the intermediate transfer belt .
[0014]
According to a second aspect of the invention, in the image forming apparatus according to claim 1, the two said recording material conveying member conveys the intermediate transfer belt及beauty Symbol recording material of the sandwich in record material between the separation roller order transferring a roller, and setting higher than the running speed of the intermediate transfer belt peripheral speed of the secondary transfer roller.
[0015]
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect , the recording material is caused to enter the secondary transfer portion while forming a loop in the recording material .
[0016]
A fourth aspect of the present invention, the cleaning in the image forming apparatus according to any one of claims 1 to 3, on the upstream side of the downstream side and the pressure member of the secondary transfer portion, the surface of the intermediate transfer belt characterized in that it has a cleaning member for.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0020]
<Embodiment 1>
FIG. 1 shows an example of an image forming apparatus according to the present invention. The image forming apparatus shown in FIG. 1 is an electrophotographic four-color full-color laser beam printer having four image forming units and an intermediate transfer belt (intermediate transfer member). FIG. FIG.
[0021]
Each image forming unit has photosensitive drums 11a, 11b, 11c, and 11d corresponding to toners of yellow, magenta, cyan, and black as image carriers. Transfer belt 1 as an intermediate transfer member forms a respective photosensitive respective primary transfer portion in contact with the drum 11 a to 11 d (primary transfer nip) T ₁ above.
[0022]
The intermediate transfer belt 1 preferably has a volume resistivity of 10 ⁶ to 10 ¹² Ω · cm, such as urethane resin, fluorine resin, nylon resin, polyimide resin, silicone rubber, hydrin rubber, or the like. An elastic material or a material in which resistance is adjusted by dispersing carbon or conductive powder in these materials can be used.
[0023]
As shown in FIG. 1, the intermediate transfer belt 1 is wound around three rollers including a driving roller 1a, a separation roller 1b, and a support roller 1c. A belt pressure roller (rotating body) 1d disposed outside the intermediate transfer belt 1 applies tension to the intermediate transfer belt 1 by applying pressure so as to curve the inner transfer belt 1 inward. Although the tension depends on the material of the intermediate transfer belt 1, it is desirable to set the elongation rate to be within 1% so that the intermediate transfer belt 1 is not broken or permanently deformed. In this embodiment, a polyimide resin-based intermediate transfer belt 1 is used and a load of 15 kgf is applied.
[0024]
In the primary transfer unit, a primary transfer roller 15a, 15b, 15c, 15d are photosensitive drums 11a, 11b, 11c, between the 11d, sandwiches the intermediate transfer belt 1, to form a primary transfer portion T ₁ . Each primary transfer roller is formed in a roller shape by coating the outer peripheral surface of a cored bar with an elastic material having a medium resistance (actual resistance in nip formation when applying 1 kV is 10 ⁶ to 10 ¹⁰ Ω).
[0025]
The secondary transfer roller 3 is obtained by coating the outer peripheral surface of a core metal with an EPDM foam layer having a resistance value of medium resistance, and is disposed at a position facing the separation roller 1b so as to be intermediate between the separation roller 1b. A secondary transfer portion (secondary transfer nip portion) T ₂ is formed between the transfer belt 1 and the intermediate transfer belt 1. The recording material P such as paper is nipped and conveyed by the secondary transfer unit.
[0026]
Hereinafter, the operation of the entire image forming apparatus will be described while appropriately adding a description of the configuration.
[0027]
The photosensitive drum 11a is rotationally driven counterclockwise in FIG. 1 by a driving means (not shown), is uniformly charged by a primary charger 12a, and is modulated by an image information signal sent from a host computer. An electrostatic latent image is formed on the surface by the laser beam from the laser beam. The intensity of the laser beam and the irradiation spot diameter at this time are appropriately set according to the resolution of the image forming apparatus and the desired image density, and the electrostatic latent image on the photosensitive drum 11a is the portion irradiated with the laser beam ( It is formed by maintaining the potential V _{L of the} bright portion) at about −100 V and the potential V _D of the non-irradiated portion (dark portion) at about −700 V charged by the primary charger 12a.
[0028]
The electrostatic latent image reaches a portion facing the developing device 14a by the rotation of the photosensitive drum 11a, and the toner charged with the same polarity (negative polarity in the present embodiment) is attached to the bright portion of the electrostatic latent image. Develop as a toner image. In four-color full-color image formation, toner images are similarly formed by the photosensitive drums 11a to 11d, the primary chargers 12a to 12d, the scanners 13a to 13d, and the developing devices 14a to 14d corresponding to the respective colors. Are primary-transferred sequentially on the intermediate transfer belt 1 at each primary transfer portion T ₁ and are combined so as to overlap on the intermediate transfer belt 1. In each primary transfer portion T ₁ , an electric field formed in the primary transfer portion T ₁ by a voltage (+100 to +1000 V) opposite in polarity to the toner applied to the conductive rollers 15 a to 15 d in contact with the back surface of the intermediate transfer belt 1. The toner image is primarily transferred. Four color toner images at the stage of the intermediate transfer belt 1 passes through the primary transfer portion T ₁ of the photosensitive drum 11d is supported on the intermediate transfer belt 1, the primary transfer process is completed. On the other hand, after the surfaces of the photosensitive drums 11a to 11d after the primary transfer of the toner images are cleaned by the cleaning devices 16a to 16d, they are prepared for the next image forming process.
[0029]
Then, the recording material P such as paper from the paper feed means (not shown) is taken out one sheet, it is inserted through the secondary transfer portion T _2. At this time, a voltage (+1 to +6 kV) having a polarity opposite to that of the toner is applied to the secondary transfer roller 3, so that four color toner images are collectively transferred from the intermediate transfer belt 1 onto the recording material P. Transcribed.
[0030]
The intermediate transfer belt 1 can increase the winding amount of the intermediate transfer belt 1 around the outer peripheral surface of the separation roller 1b in the separation portion A of the recording material P by the action of the belt pressure roller 1d. The curvature becomes almost the same as that of the separation roller 1b, and the recording material P can be separated well. As long as the diameter of the separation roller 1b is 30 mm or less, the thin recording material P can be handled. When the thickness is preferably 25 mm or less, good separation can be secured even with a paper having a basis weight of 60 g / m ² , and the reliability of the image forming apparatus can be improved.
[0031]
The recording material P carrying the unfixed toner image passing through the secondary transfer portion T ₂ reaches the fixing device 17 and is fixed as a permanent image by being heated and pressurized. On the other hand, the surface of the intermediate transfer belt 1 that has finished transferring the toner image to the recording material P is removed by the intermediate transfer body cleaning device 18. The intermediate transfer body cleaning device 18 causes a cleaning blade 18a formed of urethane rubber to come into contact with the surface of the intermediate transfer belt 1, and the secondary transfer residual toner adhering to the surface of the intermediate transfer belt 1 (recorded during secondary transfer). Toner remaining on the surface of the intermediate transfer belt 1 without being secondarily transferred onto the material P is scraped off and collected as waste toner in a waste toner box 18b.
[0032]
In the present invention, the toner image is carried by the intermediate transfer belt 1 on the downstream side of the primary transfer portion T ₁ (hereinafter, particularly referred to as “primary transfer portion Ta”) where the primary transfer roller 15a is located, and the secondary transfer portion T. ₂ , the intermediate transfer belt 1 does not carry a toner image on the downstream side of the secondary transfer portion T ₂ and the upstream side of the primary transfer portion Ta (however, the secondary transfer residual toner). May exist.) Accordingly, among the intermediate transfer belt 1, in the portion located between the secondary transfer portion T ₂ and the primary transfer portion Ta, no touching the toner image before secondary transfer, the belt pressing roller 1d There is no contamination with toner, and the toner image on the intermediate transfer belt 1 is not disturbed by the belt pressure roller 1.
[0033]
In this embodiment, a roller is used as a member that curves the intermediate transfer belt 1 inward, but as a further modification, an abutting roller that pressurizes both ends in the width direction of the intermediate transfer belt 1 instead of the roller, A slidable butting member that pressurizes the entire width in the width direction may be used. Even in this case, these members abut on a portion of the intermediate transfer belt 1 that does not carry the toner image. Therefore, the same effect as described above can be obtained.
[0034]
<Embodiment 2>
FIG. 2 shows a second embodiment. In addition, the same code | symbol shall be attached | subjected about the same member as Embodiment 1 shown in FIG. 1, and the description shall be abbreviate | omitted.
[0035]
In this embodiment, the collection roller 18c for collecting the secondary transfer residual toner also serves as a pressure member that curves the intermediate transfer belt 1 inward.
[0036]
The collection roller 18c is a hollow aluminum core (diameter 30 mm) coated with a PFA resin (thickness 20 to 30 μm) as an insulating layer. The collection roller 18c is pressurized so that the intermediate transfer belt 1 is curved inward, and the collection counter roller Positioned by 18d. In the figure, reference numerals 18e and 18f denote charge application rollers having an intermediate resistance elastic layer, and 18g denotes a charge application counter roller disposed at a position facing the charge application roller 18f with the intermediate transfer belt 1 interposed therebetween.
[0037]
The amount of winding of the intermediate transfer belt 1 around the separation roller 1c can be increased by the curvature of the intermediate transfer belt 1 by the collection roller 18c, and separation of the recording material P from the intermediate transfer belt 1 is facilitated. In addition, the recovery roller 18c has a relatively large diameter, thereby reducing the bending of the intermediate transfer belt 1 and preventing the durability of the intermediate transfer belt 1 from being deteriorated.
[0038]
In addition to the above-described operation, the collection roller 18c in the present embodiment also performs a collection operation of secondary transfer residual toner. The operation will be described below.
[0039]
The secondary transfer residual toner may be present on the intermediate transfer belt 1 after the secondary transfer depending on the type of the recording material P and the temperature and humidity of the atmosphere. If the secondary transfer residual toner is left as it is, problems such as a transfer failure in the next image formation (primary transfer process) or a ghost that disturbs the image occur.
[0040]
In the present exemplary embodiment, a voltage is supplied to the charge applying roller 18f to apply charge to the secondary transfer residual toner on the intermediate transfer belt 1, and the charge applying roller 18e that is in contact with the collection roller 18c is used as the above-described charge applying roller. A voltage having a reverse polarity to the voltage applied to 18f is applied to charge the collection roller 18c, and the secondary transfer residual toner is collected to the collection roller 18c by electrostatic force acting between them.
[0041]
The secondary transfer residual toner collected on the collection roller 18c becomes waste toner by the cleaning blade 18h positioned on the upstream side of the charge applying roller 18e along the rotation direction of the collection roller 18c (counterclockwise in the drawing). It is scraped off by the box 18b.
[0042]
In the present embodiment, there is no cleaning member that directly rubs against the intermediate transfer belt 1, and the intermediate transfer belt 1 can be used without being damaged for a long time. Further, the cleaning property of the intermediate transfer belt 1 can be efficiently cleaned because the mechanical distortion can be used by processing at the curved portion, and is high for fine toner, spherical toner, and the like. Cleanability can be ensured.
[0043]
<Embodiment 3>
FIG. 3 shows a third embodiment. In addition, the same code | symbol shall be attached | subjected about the same member as Embodiment 1 shown in FIG. 1, and the description shall be abbreviate | omitted.
[0044]
In the present embodiment, by applying a driving force to the secondary transfer roller 3 by the motor 3a, a secondary transfer roller 3 traveling speed of the peripheral speed V ₂ of the intermediate transfer belt 1 surface (rotational speed) 4% than V ₁ It is set so as to increase. In the present embodiment, the secondary transfer roller 3 is used as a recording material conveying member that applies a conveying force to the recording material P.
[0045]
In the secondary transfer portion T ₂ formed between the secondary transfer roller 3 and the intermediate transfer belt 1, the recording material P obtains a conveyance speed Vp larger than the traveling speed Vi of the intermediate transfer belt 1, and the intermediate transfer belt. An urging torque is applied to 1.
[0046]
In the present embodiment, a curved portion is given to the intermediate transfer belt 1 by the belt pressure roller 1d to ensure separation from the recording material P. The traveling load of the intermediate transfer belt 1 in this curved portion is described above. By offsetting with the urging torque, it is possible to stabilize the running of the intermediate transfer belt 1 from the primary transfer portion T ₁ to the secondary transfer portion T _2, thereby reducing problems such as color misregistration and pitch unevenness. be able to.
[0047]
The peripheral speed ratio (peripheral speed V ₂ of the secondary transfer roller 3 with respect to the travel speed Vi of the intermediate transfer belt 1) is effective if it is greater than 0.5%. In this embodiment, the intermediate transfer belt 1 travels. By rotating the peripheral speed V ₂ of the secondary transfer roller 3 4% faster than the speed Vi as described above, the conveyance speed Vp of the recording material P is 0.1 to 1.5% (from the intermediate transfer belt 1). The above-mentioned effect is obtained by giving a large item (which varies depending on the image and paper type).
[0048]
As a modification of the present embodiment, the same effect can be obtained by making the speed at which the recording material P is fed to the secondary transfer portion larger than the traveling speed of the intermediate transfer belt 1. Further, by forming a loop due to the waist of the recording material P upstream of the secondary transfer portion T ₂ , the above urging torque can be obtained even when the recording material P is fed at a constant speed, and the intermediate transfer belt. 1 traveling can be stabilized.
[0049]
<Embodiment 4>
FIG. 4 shows a fourth embodiment. In addition, the same code | symbol shall be attached | subjected about the same member as Embodiment 1 shown in FIG. 1, and the description shall be abbreviate | omitted.
[0050]
In this embodiment, the surface of the belt pressure roller 1d is blasted to give a grip force to the intermediate transfer belt 1, and an elastic layer is provided on the surface at a position facing the belt pressure roller 1d. A belt pressure opposing roller 1e is provided to sandwich the intermediate transfer belt 1, and the belt transfer roller 1d is driven to rotate by a motor (driving means) 1f to drive the intermediate transfer belt 1.
[0051]
This arrangement, to complete the toner image carrying on the intermediate transfer belt 1 between the present invention from the primary transfer portion Ta to the secondary transfer portion T _2, between the secondary transfer portion T ₂ and the primary transfer portion Ta The advantage is that a driving roller for pressing the intermediate transfer belt 1 from the outside can be provided.
[0052]
Therefore, in this embodiment, the surface speed can be ensured regardless of the thickness of the intermediate transfer belt 1, and the running performance can be improved. Further, the separation roller 1b and by placing the belt pressing roller 1d which also serves as a driving roller between the support rollers 1c, driving the intermediate transfer belt 1 two tension from the primary transfer portion T ₁ of the transfer portion T ₂ by Since it can be maintained in the pulling direction, there is an advantage that unevenness in traveling speed during this period can be reduced.
[0053]
【The invention's effect】
As described above, according to the present invention, yet as it can be improved separability of the recording material from the intermediate transfer belt after the secondary transfer, it is possible to stabilize the traveling of the intermediate transfer belt .
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view illustrating a schematic configuration of an image forming apparatus according to a first embodiment.
FIG. 2 is a longitudinal sectional view showing a schematic configuration of an image forming apparatus according to a second embodiment.
FIG. 3 is a longitudinal sectional view illustrating a schematic configuration of an image forming apparatus according to a third embodiment.
4 is a longitudinal sectional view showing a schematic configuration of an image forming apparatus according to Embodiment 4. FIG.
FIG. 5 is a longitudinal sectional view showing a schematic configuration of a conventional image forming apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Intermediate transfer belt 1a Drive roller 1b Separation roller 1c Support roller 1d Pressure member (rotating body, belt pressure roller)
1f Driving means (motor)
3 Recording material conveying member (secondary transfer roller)
11a, 11b, 11c, 11d
Image carrier (photosensitive drum)
18a Cleaning member (cleaning blade)
A Separation part P Recording material T ₁ Primary transfer part Ta Primary transfer part T ₂ Secondary transfer part

Claims (4)

A movable endless intermediate transfer belt; a plurality of rollers that support the intermediate transfer belt; and a plurality of image carriers that carry toner images; and the image carrier and the intermediate transfer belt. The toner image formed on the intermediate transfer belt is transferred onto the recording material at the secondary transfer portion by transferring the toner image onto the intermediate transfer belt at a plurality of primary transfer portions therebetween. and, wherein one of the multiple rollers the intermediate transfer belt is passed over is also serves as a separation roller for separating the recording material after the secondary transfer of the toner image from the intermediate transfer belt surface, the the separation roller along the conveying direction of the intermediate transfer belt and to the outside of the common tangent line connecting the last roller at the downstream side, with a pressing member for bending the intermediate transfer belt than the common tangent to the inside Image forming apparatus Oite,
A drive roller for driving the intermediate transfer belt on the upstream side of the secondary transfer unit and on the downstream side of the primary transfer unit on the most downstream side of the plurality of primary transfer units, and recording in the secondary transfer unit An image forming apparatus comprising: a recording material conveying member configured to make a material conveying speed larger than a traveling speed of the intermediate transfer belt . The recording material conveying member is a secondary transfer roller for transferring the intermediate transfer belt及beauty Symbol recording material of the sandwich in record material between said separation roller, said intermediate peripheral speed of the secondary transfer roller The image forming apparatus according to claim 1 , wherein the image forming apparatus is set to be larger than a traveling speed of the transfer belt. The image forming apparatus according to claim 1 , wherein the recording material is caused to enter the secondary transfer portion while forming a loop in the recording material . Wherein the upstream side of the downstream side a and the pressing member of the secondary transfer portion, a cleaning member for cleaning the surface of the intermediate transfer belt, claimed in any one of claims 1 to 3, characterized in Image forming apparatus.

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