JP2003270972A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To always obtain an excellent image by reducing a current going along an intermediate transfer body and leaked away to a proximate member. <P>SOLUTION: An intermediate transfer belt 426 to which a toner image is primarily transferred from a photoreceptor drum 402 is laid between respective supporting members, that is, a primary transfer electrode roller 450 opposed to the drum 402, a driving roller 444, a secondary transfer counter roller 446 opposed to a secondary transfer roller 454, and a cleaning counter roller 448A opposed to a cleaning means 452 cleaning the surface of the belt 426. The roller 448A as the proximate member to the roller 446 has constitution that a high resistance layer 448A-2 is provided on the surface of a core bar 448A-1. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer and a facsimile, and more particularly to an image forming apparatus having a belt-shaped intermediate transfer member.

[0002]

2. Description of the Related Art In a color image forming apparatus, toner images formed on an image carrier are superposed (primary transfer) on an intermediate transfer belt for each color, and the superposed toner images are applied with a transfer voltage. Batch transfer (secondary transfer) is performed on a transfer material. For example, as shown in FIG. 5, the intermediate transfer belt 426 includes a primary transfer electrode roller 450 facing the photosensitive drum 402, a drive roller 444, a secondary transfer facing roller 446 facing the secondary transfer roller 454, and an intermediate transfer. Cleaning means 452 for cleaning the surface of the belt 426
Is supported and rotated by a cleaning facing roller 448 which faces the cleaning facing roller 448.

The toner image formed on the photosensitive drum 402 is transferred onto the intermediate transfer belt 426 by the primary transfer bias applied to the primary transfer electrode roller 450, transferred for each color, and superposed. The superimposed toner images are collectively transferred onto a sheet P as a transfer material by a secondary transfer bias having the same polarity as the toner applied to the secondary transfer counter roller 446 that contacts the inner surface (back surface) of the intermediate transfer belt 426. It When a secondary transfer electric field is formed by applying a constant-current-controlled voltage having a polarity opposite to that of the toner from the side of the intermediate transfer body to the transfer material, even when the resistance of the transfer material changes,
The secondary transfer electric field does not change significantly even when the resistance of the intermediate transfer body or the secondary transfer body (secondary transfer roller 454) changes, and therefore a stable image can be always formed on the transfer material. The cleaning facing roller 448 is generally formed of a conductive metal such as stainless steel, and is electrically connected to a housing as a main body of the apparatus.

[0004]

SUMMARY OF THE INVENTION Intermediate transfer belt 426.
If the resistance of the intermediate transfer belt 426 is sufficiently high, no problem occurs, but the resistance of the intermediate transfer belt 426, especially the secondary transfer counter roller 446 due to resistance shift or deterioration of energization due to changes in use environment.
When the surface resistivity of the back surface that comes into contact with the surface of the secondary transfer counter roller 446 falls below approximately 1010 Ω / □, the current applied to the secondary transfer counter roller 446 leaks to the cleaning counter roller 448 as a proximity member through the intermediate transfer belt 426, There was a problem that the secondary transfer electric field was weakened due to the shortage of the current to P, and a good image could not be obtained. Since the drive roller 444 is separated from the secondary transfer counter roller 446, the leakage current is small even in the above situation, and the influence on the secondary transfer electric field and the influence on the image can be ignored.

Therefore, an object of the present invention is to provide an image forming apparatus capable of always obtaining a good image by reducing a current leaking to a proximity member.

[0006]

In order to achieve the above object, in the invention described in claim 1, a toner image having a predetermined polarity is stretched between a plurality of supporting members and is rotatably driven. In an image forming apparatus for performing a primary transfer onto an intermediate transfer member having a sheet, and applying a transfer voltage from an electrode member located on the inner surface of the intermediate transfer member to secondarily transfer the toner image on the intermediate transfer member onto a transfer material. An electric resistance of an intermediate transfer member contact member that is in contact with the intermediate transfer member and is in a position close to the electrode member is increased,
Is adopted.

According to a second aspect of the invention, in the image forming apparatus according to the first aspect, the intermediate transfer member contact member has a high resistance layer on its surface.

According to a third aspect of the invention, in the image forming apparatus according to the first aspect, the intermediate transfer member contact member has an insulating layer on its surface.

According to a fourth aspect of the present invention, in the image forming apparatus according to the first aspect, a resistance element is provided between the intermediate transfer member contact member and the casing.

According to a fifth aspect of the invention, in the image forming apparatus according to the first aspect, a constant voltage element is provided between the intermediate transfer member contact member and the casing.

According to a sixth aspect of the present invention, the first to fifth aspects are provided.
In the image forming apparatus according to any one of items 1 to 5, a cleaning unit that cleans a surface of the intermediate transfer member is provided downstream of a secondary transfer portion, and the intermediate transfer member contact member sandwiches the intermediate transfer member. The configuration is such that it is provided so as to face the cleaning means.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION A first embodiment of the present invention will be described below with reference to FIGS. The same parts as those in the conventional technique are designated by the same reference numerals. First, an outline of the configuration of a color copying machine as an image forming apparatus in this embodiment will be described with reference to FIG. In a color copying machine, a writing optical unit 400 as an exposing unit converts color image data from the color scanner 200 into an optical signal and performs optical writing corresponding to a document image, and a photoconductor drum 402 which is an image carrier. An electrostatic latent image is formed on. The writing optical unit 400 includes a laser diode 404, a polygon mirror 406, a rotation motor 408 for the polygon mirror 406, an f / θ lens 410, a reflection mirror 412, and the like. The photoconductor drum 402 is rotated in the counterclockwise direction as shown by the arrow, and the photoconductor cleaning unit 414, the discharge lamp 416, and the potential sensor 42 are provided around the photoconductor drum 402.
0, the developing device selected from the rotary developing device 422 (developing device 438 in FIG. 2), and the developing density pattern detector 4
24, an intermediate transfer belt 426 as an intermediate transfer member, and the like are arranged.

The rotary developing device 422 includes a black developing device 428, a cyan developing device 430, and a magenta developing device 4.
32, a yellow developing device 434, and a rotation driving unit (not shown) for rotating each developing device. Each developing device has the same configuration as the developing device 4 shown in the above embodiment. The same applies to the conditions and specifications of the magnetic carrier. In the standby state, the rotary developing device 422 is set to the black developing position, and when the copy operation is started, the color scanner 200 starts reading the black image data at a predetermined timing. Based on the above, optical writing with a laser beam and formation of an electrostatic latent image (black latent image) are started.

In order to develop from the tip of the black latent image, the developing sleeve is started to rotate and the black latent image is developed with black toner before the tip of the latent image reaches the developing position of the black developing device 428. To do. Photoconductor drum 402
An image of negative polarity toner is formed on. After that, the developing operation of the black latent image area is continued, but when the trailing edge of the latent image passes the black developing position, the rotary developing is immediately performed from the developing position for black to the developing position of the next color. The device 422 rotates. The operation is completed at least before the leading edge of the latent image formed by the next image data arrives. When the image forming cycle is started, first, the photosensitive drum 402 is rotated counterclockwise as indicated by an arrow, and the intermediate transfer belt 426 is rotated clockwise by a drive motor (not shown). With the rotation of the intermediate transfer belt 426, black toner image formation, cyan toner image formation, magenta toner image formation, and yellow toner image formation are performed, and finally black (Bk), cyan (C), and magenta (M). , Yellow (Y) in this order, they are superposed on the intermediate transfer belt 426 (primary transfer), and a toner image is formed.

The intermediate transfer belt 426 is the photosensitive drum 4
Of the primary transfer electrode roller 450, the driving roller 444, the secondary transfer opposing roller 446 that faces the secondary transfer roller 454, and the cleaning opposing roller 448A that faces the cleaning unit 452 that cleans the surface of the intermediate transfer belt 426. It is stretched between the support members and is driven and controlled by a drive motor (not shown). The black, cyan, magenta, and yellow toner images sequentially formed on the photoconductor drum 402 are accurately aligned on the intermediate transfer belt 426, thereby forming a four-color belt transfer image. The belt transfer image is collectively transferred onto a sheet by the secondary transfer counter roller 446.

Each recording paper cassette 4 in the paper supply bank 456
58, 460 and 462 are cassettes 464 in the main body of the apparatus.
Various sizes of paper different from the size of the paper accommodated in the paper are stored in the paper storage roller 46.
The sheet 6 is fed and conveyed in the direction of the registration roller pair 470. In FIG. 2, reference numeral 468 indicates a manual paper feed tray for OHP paper, thick paper, and the like. At the time when image formation is started, the paper is fed from the paper feed port of any one of the above cassettes and stands by at the nip portion of the registration roller pair 470. When the front end of the toner image on the intermediate transfer belt 426 reaches the secondary transfer counter roller 446, the registration roller pair 470 is driven so that the front end of the paper coincides with the front end of the image, and the registration of the paper and the image is adjusted. Is done.

In this way, the paper is transferred to the intermediate transfer belt 4
26, and passes under the secondary transfer counter roller 446 to which a voltage having the same polarity as the toner is applied. At this time,
The toner image is transferred to the paper. Subsequently, the paper is destaticized, peeled off from the intermediate transfer belt 426, and separated from the paper conveyance belt 4
Move to 72. The sheet on which the four-color superposed toner images have been collectively transferred from the intermediate transfer belt 426 is conveyed to the fixing device 470 of the belt fixing system by the paper conveyance belt 472, and the fixing device 470 fixes the toner images by heat and pressure. The fixed paper is ejected to the outside of the apparatus by the ejection roller pair 480 and is stacked on a tray (not shown). This allows
A full color copy is obtained.

The intermediate transfer structure will be described in detail with reference to FIG. The intermediate transfer belt 426 used has a three-layer structure including a base layer, an intermediate layer, and a surface layer in order from the inside. The base layer has a thickness of 50
It was prepared by dispersing carbon in a polyimide-based resin that does not expand or contract an image of -100 μm. The intermediate layer has elasticity, and resistance was adjusted with carbon, titanium oxide, or the like to urethane-based or chloroprene-based rubber having a thickness of 100 to 300 μm. The surface layer was made of a fluorine-based or PVDF-based material having a releasability having a thickness of 1 to 20 μm. The resistance of the intermediate transfer belt 426 is such that the surface resistivity of the back surface is 1010Ω / □ to 1012Ω / □,
The volume resistivity measured is 1010 Ωcm to 1013 Ωcm, and the surface resistivity of the surface is 1010 Ω / □ to 1014 Ω / □.

The primary transfer electrode roller 450 facing the photosensitive drum 402 has a structure in which an elastic body 450b having a low resistance or a medium resistance is provided around a cored bar 450a.
A positive polarity voltage controlled to a predetermined current value is applied to 0a, and a negative polarity toner image is primarily transferred from the photosensitive drum 402 to the intermediate transfer belt 426. The secondary transfer roller 454 is provided with a core metal 454 from the inside.
a, an intermediate layer, and a surface layer. The intermediate layer has elasticity, and the resistance of the rubber was adjusted with chloroprene-based or NBR-based rubber material such as carbon or titanium oxide. The surface layer has a thickness of 1 to 20.
A material having a release property of μm of fluorine type or PVDF type was used. The core metal 454a of the secondary transfer roller 454 is connected to the housing, and no voltage is applied.

Contact with the inner surface of the intermediate transfer belt 426 2
The next transfer counter roller 446 is made of stainless steel having a surface roughness of 2 μm or less. When the sheet P is sandwiched between the intermediate transfer belt 426 and the secondary transfer roller 454 and a secondary transfer is performed, a voltage of a negative polarity whose constant current is controlled to a predetermined current value is applied to the secondary transfer counter roller 446,
The toner image having a negative polarity is transferred onto the paper P from the intermediate transfer belt 426. The cleaning unit 452 applies a lubricant such as zinc stearate to the surface of the intermediate transfer belt 426, or forms a cleaning electric field to transfer the toner on the intermediate transfer belt 426. It has a blade 452b for stripping the toner on 426 and a toner recovery screw 452c. Only one of the rotating brush 452a and the blade 452b may be provided.

The cleaning facing roller 448A has a core metal 448A-1 and a high resistance layer 448A-2 provided on the surface of the core metal 448A-1. High resistance layer 448
A-2 was finished to have a thickness of 0.5 to 5 mm and a surface roughness of 2 μm or less, was made of POM (polyacetal) resin in which barium titanate was dispersed as a conductive filler, and had a volume resistance value adjusted to 1011 Ωcm to 1014 Ωcm. Especially when the cleaning member is the blade 452b, the resin having no elasticity is used because the cleaning performance of the toner is deteriorated when the cleaning facing roller 448A escapes or deforms. The surface layer of the cleaning opposing roller 448 may be an insulating resin containing no conductive filler. Also, the cleaning facing roller 448
Is still metal conductive and is effective in preventing leakage current from the secondary transfer counter roller 446 even in a float state in which the housing is not grounded. However, when the electric charge is accumulated, a high electric field is easily formed, and an image unevenness of about 1 mm in diameter, which is considered to be discharged through the intermediate transfer belt 426 to the brush member of the cleaning unit 452, easily occurs. Noise is apt to cause malfunction of the image forming apparatus or failure to meet radio wave standards.

Next, a second embodiment will be described with reference to FIG. Note that the same parts as those in the above-described embodiment are denoted by the same reference numerals, and the description of the structural and functional features that have already been made will be omitted unless necessary, and only the essential parts will be described (the same applies to other embodiments below). The cleaning counter roller 448 in this embodiment is still a low resistance member such as a metal conductor as in the conventional case, but the resistance element 453 is provided between the cleaning counter roller 448 and the casing. The resistance value of the resistance element 453 is preferably 30 MΩ to 3 GΩ, and when the resistance value is low, the effect of preventing the leakage current from the secondary transfer counter roller 446 is weakened,
If it is high, the cleaning opposing roller 448 will have a high voltage,
The above-mentioned abnormal discharge is likely to occur. Further, if the resistance value is a proper value, the cleaning counter roller 448 has an absolute value of a voltage of about 1 to 4 kV, and this voltage is applied to both ends of the resistance element 453 as it is. Electricity is required. Also, this voltage is close to the voltage applied to the secondary transfer counter roller 446, and the potential difference between the secondary transfer counter roller 446 and the cleaning counter roller 448 is small, so it can be said that the leakage current is also small.

Next, a third embodiment will be described with reference to FIG. Cleaning counter roller 4 in this embodiment
48 is also a low resistance member such as a metal conductor as in the conventional case, but a constant voltage element 455 such as a Zener diode is provided between the cleaning facing roller 448 and the casing. The voltage of the constant voltage element 455 is the secondary transfer counter roller 44.
By setting the voltage close to the voltage applied to 6, the effect of reducing the leakage current can be obtained. In this case, a voltage of 1 to 4 kV in absolute value is preferable. Alternatively, if the voltage is higher than the voltage applied to the secondary transfer counter roller 446, the leakage current stops flowing. However, when the voltage is high, the above-mentioned abnormal discharge is likely to occur, and the absolute value is preferably about 4 kV, or at most about 7 kV or less.

In each of the above embodiments, one image carrier (photoconductor drum) is exemplified, but each photoconductor drum has a separate photoconductor drum, and each photoconductor drum has an intermediate transfer member.
The same function as described above can be obtained even in the configuration in which the color is superimposed on the intermediate transfer member by the subsequent transfer and the batch transfer is performed on the transfer material by the secondary transfer.

[0025]

According to the first aspect of the present invention, a toner image of a predetermined polarity is primarily transferred to a flexible intermediate transfer member which is stretched between a plurality of supporting members and driven to rotate. In an image forming apparatus for secondarily transferring a toner image on the intermediate transfer member to a transfer material by applying a transfer voltage from an electrode member located on the inner surface of the intermediate transfer member, the electrode member contacting the intermediate transfer member Since the electric resistance of the intermediate transfer member contact member located in the vicinity of the contact member is increased, the current leaking from the electrode member to the adjacent member is reduced, and the current flowing to the transfer material is not insufficient, so that a good image can be obtained. Can be stably obtained.

According to the second aspect of the invention, in the image forming apparatus according to the first aspect, the intermediate transfer member contact member has a high resistance layer on the surface thereof. The current that leaks to the transfer material is reduced, the current flowing to the transfer material is not insufficient, and a good image can be stably obtained.

According to the third aspect of the present invention, in the image forming apparatus according to the first aspect, the intermediate transfer member contact member has an insulating layer on the surface thereof. The leaking current is reduced, the current to the transfer material is not insufficient, and a good image can be stably obtained.

According to a fourth aspect of the invention, in the image forming apparatus according to the first aspect, the resistance element is provided between the intermediate transfer member contact member and the casing, so that the electrode member is close to the member. The current leaking to the member is reduced, the current to the transfer material is not insufficient, and a good image can be stably obtained.

According to the fifth aspect of the invention, in the image forming apparatus according to the first aspect, a constant voltage element is provided between the intermediate transfer member contact member and the casing. The current leaking to the proximity member is reduced, the current to the transfer material is not insufficient, and a good image can be stably obtained.

According to a sixth aspect of the invention, in the image forming apparatus according to any one of the first to fifth aspects, a cleaning means for cleaning the surface of the intermediate transfer member is provided downstream of the secondary transfer portion. Since the intermediary transfer member contact member is provided so as to face the cleaning means with the intermediary transfer member interposed therebetween, the electrode member travels through the intermediary transfer member and leaks to a roller facing the cleaning device. The leaving current is reduced, the current to the transfer material is not insufficient, and a good image can be stably obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram around an intermediate transfer member according to a first embodiment of the present invention.

FIG. 2 is a schematic front view of a color copying machine as an image forming apparatus.

FIG. 3 is a configuration diagram of a main part around an intermediate transfer member according to a second embodiment.

FIG. 4 is a configuration diagram of a main part around an intermediate transfer member according to a third embodiment.

FIG. 5 is a configuration diagram of a main part around a conventional intermediate transfer member.

[Explanation of symbols]

P Paper 426 as a transfer material Intermediate transfer belt 446 as an intermediate transfer member Secondary transfer counter roller 448, 448A as an electrode member Cleaning counter roller 448A-2 High resistance layer 453 Resistor element 455 as a constant contact member element

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hideki Ueyama             1-3-3 Nakamagome, Ota-ku, Tokyo, stock             Company Ricoh (72) Inventor Satoshi Uchida             1-3-3 Nakamagome, Ota-ku, Tokyo, stock             Company Ricoh (72) Inventor Yuji Sawai             1-3-3 Nakamagome, Ota-ku, Tokyo, stock             Company Ricoh F-term (reference) 2H200 FA18 GA23 GA34 GA45 GA47                       GA50 GB02 HA03 HB12 HB22                       JA02 JA21 JA25 JA28 JA29                       JC04 JC07 JC12 JC13 JC15                       JC16 JC17 JC18 LB02 LB12                       LB13 LB35 MA03 MA04 MA13                       MA14 MA20 MB04 MB05 MC06                       NA02 NA22 PA05 PA06 PA30                       PB02 PB39

Claims (6)

[Claims] 1. A toner image having a predetermined polarity is primarily transferred onto a flexible intermediate transfer member which is stretched between a plurality of supporting members and is rotationally driven, and the toner image is positioned on the inner surface of the intermediate transfer member. In an image forming apparatus for secondarily transferring a toner image on the intermediate transfer member to a transfer material by applying a transfer voltage from an electrode member, the intermediate transfer member is in contact with the intermediate transfer member and in a position close to the electrode member. An image forming apparatus having an increased electric resistance of a member. 2. The image forming apparatus according to claim 1, wherein the intermediate transfer member contact member has a high resistance layer on a surface thereof. 3. The image forming apparatus according to claim 1, wherein the intermediate transfer member contact member has an insulating layer on the surface thereof. 4. The image forming apparatus according to claim 1, wherein a resistance element is provided between the intermediate transfer member contact member and the casing. 5. The image forming apparatus according to claim 1, wherein a constant voltage element is provided between the intermediate transfer member contact member and the casing. 6. The image forming apparatus according to claim 1, further comprising a cleaning unit for cleaning a surface of the intermediate transfer member downstream of the secondary transfer portion, the cleaning unit contacting the intermediate transfer member. An image forming apparatus, wherein a member is provided so as to face the cleaning means with the intermediate transfer member interposed therebetween.