JP2001083818A - Image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To excellently clean a transfer roll by stipulating the relation of the dynamic sticking force of toner to the surface of the transfer roll and the dynamic sticking force of the toner to the surface of an image carrier with which the transfer roll is in press contact. SOLUTION: Both of the electrostatic sticking force and dynamic sticking force of a charged color material to a belt-like image carrier surface are set to be larger than the electrostatic sticking force and dynamic sticking force of the charged color material to the surface of the transfer roll at the time of cleaning the transfer roll. That is, in order to make the surface energy of an intermediate transfer belt 21 larger than the surface energy of a secondary transfer roll 27, the contact angle of the water of the surface of the secondary transfer roll 27 is set to be larger than the contact angle of the water of the surface of the intermediate transfer belt 21. By making the dynamic sticking force FFR of the toner to the secondary transfer roll 27 smaller than the dynamic sticking force FFB of the toner to the intermediate transfer belt 21 in such a manner, the toner is hardly moved from the intermediate transfer belt 21 to the secondary transfer roll 27.

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 to which a copying machine, a laser printer, and other electrophotographic systems are applied, and which transfers a toner image onto a recording medium from an intermediate transfer member onto which a toner image has been transferred. The present invention relates to an image forming apparatus for forming an image by performing a next transfer, and more particularly to a technique for cleaning a transfer unit in a secondary transfer unit.

[0002]

2. Description of the Related Art Conventionally, the above copying machines, laser printers,
Other image forming apparatuses applying an electrophotographic method include transferring toner images of yellow, magenta, cyan, black, and the like sequentially formed on a photosensitive drum in a state of being superimposed on an intermediate transfer belt, After the toner images of each color multiplexed on the intermediate transfer belt are collectively transferred onto the recording medium by the pressing force and the electrostatic attraction force between the backup roll and the secondary transfer roll, the unfixed toner of each color is transferred. 2. Description of the Related Art In some cases, a color image is formed by fixing an image on a recording medium by a fixing device.

In such an image forming apparatus, a secondary transfer roll is pressed against an intermediate transfer belt onto which a toner image of each color has been transferred, and the toner images transferred on the intermediate transfer belt in a multiplex manner are secondarily transferred onto a recording medium. Thus, a color image is formed. Therefore, in the image forming apparatus, when the toner image transferred onto the intermediate transfer belt comes into contact with the secondary transfer roll, the toner is transferred to the secondary transfer roll by a pressing force, and the toner attached to the secondary transfer roll Adheres to the back surface of the recording medium that is next conveyed to the secondary transfer position, causing stains on the back surface of the recording medium.

Therefore, in order to prevent the back surface of the recording medium from being stained due to the adhesion of the toner to the secondary transfer roll, an image forming apparatus using a transfer roll including the secondary transfer roll requires a secondary transfer roll or the like. Japanese Patent Application Laid-Open No. 8-272235 and Japanese Patent Application Laid-Open No. 8-32
Japanese Patent Application Publication No. 8401 and Japanese Patent Application Laid-Open No. 9-6146 have already been proposed.

The image forming apparatus according to the above-mentioned Japanese Patent Application Laid-Open No. 8-272235 discloses an image carrier that electrostatically carries a toner image, a transfer member that contacts a surface of the image carrier, and applies a transfer bias. Bias applying means for sequentially applying bias currents having different polarities to the transfer member when no transfer material is present at the transfer position, wherein the bias applying means is the same as the toner constituting the toner image. After applying a current of the same polarity, a reverse polarity current having a current value opposite to that of the toner and having an absolute value equal to or greater than the absolute value of the same polarity current is applied.

Further, the image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 8-328401 discloses an image carrier for electrostatically carrying a toner image, and a transfer member for applying a transfer bias by contacting the surface of the image carrier. And applying a transfer bias to the transfer member when the transfer material is passed between the image carrier and the transfer member to transfer the toner image formed on the surface of the image carrier to the transfer material and to transfer the toner image to the transfer material. A bias applying means for causing a current having the same polarity as the toner charging polarity to flow to the transfer member during cleaning when the transfer material does not exist, and then causing a current having the opposite polarity to flow to the transfer member. A structure in which a bias having the same polarity as the transfer bias is applied to the transfer member from the start of the first image formation immediately after the cleaning until the transfer bias is applied. A.

Further, the image forming apparatus according to Japanese Patent Application Laid-Open No. 9-6146 discloses a photoconductor on which a toner image corresponding to an image to be formed is formed, and a toner image on the photoconductor on an intermediate transfer member. A primary transfer member for transferring, a secondary transfer member provided so as to be able to be pressed against and separated from the intermediate transfer body and transferring a toner image on the intermediate transfer body onto recording paper, and rotationally driving the intermediate transfer body And an intermediate transfer member driving means, the cleaner blade being provided so as to be capable of being pressed against and separated from the intermediate transfer member and removing a toner image on the intermediate transfer member. A secondary transfer member holding means for selectively switching and holding the next transfer member to a pressure contact state or a separated state with respect to the intermediate transfer member; and Cleaner blade holding means for selectively switching and holding a contact state or a separated state, paper jam detection means for detecting a paper jam in a recording paper conveyance path, and paper jam release detection for detecting that the paper jam state has been released Means, a voltage applying means for applying a voltage to the secondary transfer member, and a detection signal from each of the detection means,
Control means for controlling the operation of the holding means, the driving means, and the voltage applying means, wherein the control means detects that the paper jam state has been released, and then controls the operation of the cleaner blade. Is held in a pressure-contact state with respect to the intermediate transfer member, and the secondary transfer member is held in a state of being separated from the intermediate transfer member.
The intermediate transfer member is cleaned by rotating the intermediate transfer member by at least one rotation, and after the intermediate transfer member is cleaned, the secondary transfer member is pressed and held against the intermediate transfer member while being held. By applying a voltage, the secondary transfer member is rotated by one or more turns to clean the secondary transfer member.

[0008]

However, the above-mentioned prior art has the following problems. That is, JP-A-8-272235 and JP-A-8-3
The technique disclosed in Japanese Patent No. 28401 applies a voltage having the same polarity as the charged polarity of the toner to the transfer unit during cleaning when a recording medium does not exist at the transfer position, and then applies a voltage having a polarity opposite to the charged polarity of the toner. By doing so, the toner adhering to the transfer means is completely reverse-transferred onto the image carrier, thereby preventing the back stain of the recording medium. Further, the technique disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 9-6146 discloses a technique in which the toner remaining on the intermediate transfer member and the secondary transfer member after the paper jam is cleared by controlling the contact and separation of the cleaner blade and the secondary transfer member. Cleaning can be performed efficiently, and in the image forming operation performed after the paper jam is cleared, a clean image can be formed without causing stains such as fog and stripes due to residual toner. The configuration is such that the image quality of the image is improved.

However, even if a constant cleaning voltage is applied to the transfer means, the dynamic adhesion of the toner to the surface of the secondary transfer roll or the like as the transfer means,
Unless the relationship with the mechanical adhesion of the toner to the surface of the image carrier against which the secondary transfer roll is pressed is considered, the toner attached to the surface of the secondary transfer roll or the like as a transfer unit is effectively removed. Therefore, there was a problem that the surface of the secondary transfer roll could not be cleaned well.

As a result, in an image forming apparatus such as a color copying machine, the cleaning means for applying the cleaning voltage to the secondary transfer roll is supplementary, and the blade for cleaning the surface of the secondary transfer roll is mainly used for cleaning. It is configured to be used as a means. For this reason, there has been a problem that the surface of the secondary transfer roll is worn by pressure contact of the blade, and the life is shortened. In particular, when a color image is formed, the amount of toner to be cleaned is about four times larger than that of a black and white image, and cleaning means for applying a cleaning voltage to the secondary transfer roll is insufficient. Heavy burden.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and it is an object of the present invention to provide a method for controlling the dynamic adhesion of toner to the surface of a transfer roll and the transfer roll. An object of the present invention is to provide an image forming apparatus capable of always cleaning the transfer roll satisfactorily by defining the relationship between the toner and the mechanical adhesion of the toner to the surface of the image carrier against which the toner is pressed.

[0012]

In order to solve the above-mentioned problems, a first aspect of the present invention is to provide a belt-shaped image carrier that carries a visible image of a charged color material and circulates, A transfer roll that is disposed so as to be pressed against the surface of the image carrier via a recording medium, and that collectively transfers a visible image on the image carrier to the recording medium; A backup roll that is disposed so as to be in pressure contact with the back side of the belt-shaped image carrier and forms a transfer nip area having a predetermined width with the transfer roll; and a transfer roll that is transferred to at least one of the backup roll and the transfer roll. An image forming apparatus provided with a transfer bias applying unit for applying a bias voltage, wherein when the transfer roll is cleaned, an electrostatic charge of the charged coloring material with respect to the surface of the belt-shaped image carrier is removed. Both adhesive strength and mechanical adhesive force,
An image forming apparatus characterized in that it is set to be larger than the electrostatic adhesion and the mechanical adhesion of the charged coloring material to the surface of the transfer roll.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the electrostatic adhesion of the charged coloring material to the surface of the belt-shaped image carrier is transferred to the image forming apparatus. Means for setting the charged color material to be larger than the electrostatic adhesion of the charged color material to the surface of the roll applies a cleaning bias voltage having a polarity opposite to a transfer bias voltage to at least one of the backup roll and the transfer roll. And an image forming apparatus.

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the dynamic adhesion of the charged coloring material to the surface of the belt-shaped image carrier is reduced. The means for setting to be larger than the mechanical adhesion of the charged coloring material to the surface of the transfer roll is a means for setting the surface energy of the belt-shaped image carrier to be larger than the surface energy of the transfer roll. An image forming apparatus characterized in that:

[0015] Still further, the invention described in claim 4 is:
4. The image forming apparatus according to claim 3, wherein a contact angle of water on the surface of the belt-shaped image carrier is set to 70 ° to 80 °, and a contact angle of water on the surface of the transfer roll is set to 85 ° to 100 °. An image forming apparatus characterized in that:

[0016]

According to the first aspect of the present invention, at the time of cleaning the transfer roll, both the electrostatic adhesion and the mechanical adhesion of the charged coloring material to the surface of the belt-shaped image carrier are reduced. Since it was set to be larger than the electrostatic adhesion and the mechanical adhesion of the charged coloring material to the surface of the transfer roll, the charged coloring material adhered to the surface of the transfer roll, the electrostatic adhesion and By both the mechanical adhesion and the transfer roll, the transfer from the surface of the transfer roll to the surface of the belt-shaped image carrier can be surely performed, and the transfer roll can always be cleaned well, and special cleaning means is used. Therefore, good cleaning properties of the transfer roll can be ensured.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the electrostatic adhesion of the charged coloring material to the surface of the belt-shaped image carrier is reduced. The means for setting the charged color material to be larger than the electrostatic adhesion of the charged color material to the surface of the transfer roll applies a cleaning bias voltage having a polarity opposite to a transfer bias voltage to at least one of the backup roll and the transfer roll. By setting a cleaning bias voltage to be applied to at least one of the backup roll and the transfer roll, the electrostatic adhesion of the charged coloring material to the surface of the belt-shaped image carrier is set. Larger and easier than the electrostatic adhesion of the charged coloring material to the surface of the transfer roll. It can be set.

Further, according to the invention described in claim 3, in the image forming apparatus according to claim 1 or 2,
Means for setting the mechanical adhesion of the charged coloring material to the surface of the belt-shaped image carrier so as to be greater than the mechanical adhesion of the charged coloring material to the surface of the transfer roll; The surface energy of the image carrier in the shape of a belt is configured to include a means for setting the surface energy of the transfer roll to be larger than the surface energy of the transfer roll. The dynamic adhesion of the charged coloring material to the surface of the belt-shaped image carrier can be easily and reliably set to be greater than the dynamic adhesion of the charged coloring material to the surface of the transfer roll.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1 FIG. 2 shows a color electrophotographic copying machine as an image forming apparatus according to Embodiment 1 of the present invention.

In FIG. 2, reference numeral 1 denotes a main body of a color electrophotographic copying machine, and an original 2 is automatically conveyed to the upper portion of the main body 1 of the color electrophotographic copying machine in a state where documents 2 are separated one by one. An automatic document feeder 3 and a document reading device 4 for reading an image of the document 2 conveyed by the automatic document feeder 3 are provided. This document reading device 4
The original 2 placed on the platen glass 5 is illuminated by the light source 6, and a reflected light image from the original 2 is transmitted through a reduction optical system including a full rate mirror 7, half rate mirrors 8 and 9, and an imaging lens 10. Scanning exposure is performed on an image reading element 11 composed of a CCD or the like, and the color reading light image of the original 2 is scanned by the image reading element 11 at a predetermined dot density (for example,
(16 dots / mm).

The color material reflected light image of the original 2 read by the original reading device 4 is, for example, original reflectance data of three colors of red (R), green (G), and blue (B) (8 bits each). Is sent to the image processing apparatus 12, and the image processing apparatus 12 performs shading correction, position shift correction, lightness / color space conversion, gamma correction, frame erasure, color / movement editing on the reflectance data of the document 2. And other predetermined image processing.

The image data subjected to the predetermined image processing by the image processing device 12 as described above includes yellow (Y), magenta (M), cyan (C), and black (B
K) ROS13 (Raster Output Scann) as four-color original color material gradation data (8 bits each)
er), and the ROS 13 performs image exposure using laser light according to the original color material gradation data.

An image forming means A capable of forming a plurality of toner images of different colors is provided inside the main body 1 of the color electrophotographic copying machine. The image forming means A mainly includes a photosensitive drum 17 as an image carrier on which an electrostatic latent image is formed, and a plurality of images having different colors by developing the electrostatic latent image formed on the photosensitive drum 17. And a rotary developing device 19 as developing means capable of forming a toner image.

As shown in FIG. 2, the ROS 13 modulates a semiconductor laser (not shown) according to the original reproduction color material gradation data, and emits a laser beam LB from the semiconductor laser according to the gradation data. The laser light LB emitted from the semiconductor laser is deflected and scanned by the rotary polygon mirror 14 and is scanned and exposed on the photosensitive drum 17 as an image carrier via the f · θ lens 15 and the reflection mirror 16.

The photosensitive drum 17 on which the laser beam LB is scanned and exposed by the ROS 13 is driven to rotate at a predetermined speed in a direction indicated by an arrow by a driving means (not shown). The surface of the photosensitive drum 17 is
After being charged to a predetermined polarity (for example, negative polarity) and potential by the primary charging scorotron 18 in advance, the electrostatic latent image is scanned and exposed to laser light LB in accordance with the original reproduction color material gradation data, thereby forming an electrostatic latent image. It is formed. The electrostatic latent images formed on the photosensitive drum 17 include yellow (Y), magenta (M), cyan (C), and black (B
K) Four-color developing units 19Y, 19M, 19C, 19BK
Is reversely developed by, for example, a toner (charged color material) charged to a negative polarity having the same polarity as the charged polarity of the photosensitive drum 17 to form a toner image of a predetermined color. The toner image formed on the photosensitive drum 17 is charged with a negative polarity by the pre-transfer charger 20 as necessary, and the charge amount is adjusted.

The toner images of the respective colors formed on the photosensitive drum 17 are transferred onto an intermediate transfer belt 21 as an intermediate transfer member disposed below the photosensitive drum 17 by a first transfer means, such as a first transfer means. Multiple transfer is performed by the next transfer roll 22. The intermediate transfer belt 21 is
3, driven roll 24a, tension roll 24b and 2
The photoconductor drum 17 is supported rotatably in the direction of the arrow at the same moving speed as the peripheral speed of the photosensitive drum 17 by a backup roll 25 as an opposing roll constituting a part of the next transfer unit.

On the intermediate transfer belt 21, yellow (Y), magenta (M), cyan (C), and black (BK) are formed on the photosensitive drum 17 according to the color of the image to be formed. All or some of the four color toner images are
The images are transferred by the primary transfer roll 22 in a state of being sequentially superposed. The toner image transferred onto the intermediate transfer belt 21 is provided on a recording paper 26 as a recording medium conveyed to a secondary transfer position at a predetermined timing, on a backup roll 25 supporting the intermediate transfer belt 21, and The transfer is performed by the pressing force and the electrostatic attraction force of the secondary transfer roll 27 that forms a part of the second transfer unit that presses against the backup roll 25. As shown in FIG. 2, the recording paper 26 includes a plurality of paper feed cassettes 28, 2 as a plurality of recording medium housing members disposed at a lower portion in the main body 1 of the color electrophotographic copying machine.
Sheets of a predetermined size from any one of 9, 30, and 31 are fed by feed rolls 28a, 29a, 30a, and 31a. The fed recording paper 26 is transported to the secondary transfer position of the intermediate transfer belt 21 at a predetermined timing by a plurality of transport rolls 32 and registration rolls 33. Then, as described above, the backup rolls 25 and 2 serving as secondary transfer units are provided on the recording paper 26.
By the next transfer roll 27, a toner image of a predetermined color is collectively transferred from the intermediate transfer belt 21.

The recording paper 26 on which the toner image of a predetermined color has been transferred from the intermediate transfer belt 21 is separated from the intermediate transfer belt 21 and then conveyed to a fixing device 35 by a conveyance belt 34. The toner image is fixed onto the recording paper 26 by heat and pressure by the fixing device 35, and in the case of one-sided copying, the toner image is discharged onto the paper discharge tray 36 as it is, and the copying process of the color image is completed.

On the other hand, in the case of double-sided copying, the recording paper 26 having the color image formed on the first surface (front surface) is not discharged onto the paper discharge tray 36 as it is, but is transported downward by a reversing gate (not shown). The direction is changed, and the three rolls are once conveyed to the reversing path 39 by the tri-roll 37 and the reversing roll 38 pressed against each other. Then, the recording paper 26 is conveyed to the two-sided passage 40 by the reversing roll 38 which is reversed this time, and once conveyed to the registration roll 33 by the conveying rolls 41 provided in the two-sided passage 40 and stopped. The recording paper 26 is conveyed again by the registration roll 33 in synchronization with the toner image on the intermediate transfer belt 21, and the toner image is transferred and fixed to the second surface (back surface) of the recording paper 26. After the operation is performed, the sheet is discharged onto the discharge tray 36.

In FIG. 2, reference numeral 42 denotes a cleaning device for removing residual toner, paper dust and the like from the surface of the photosensitive drum 17 after the completion of the transfer process, and reference numeral 43 denotes a device for cleaning the intermediate transfer belt 21. The intermediate transfer belt cleaner 44 indicates a manual feed tray.

FIG. 1 is a block diagram showing the image forming means A of the color electrophotographic copying machine.

In this color electrophotographic copying machine, as described above, after the surface of the photosensitive drum 17 is uniformly charged to a predetermined potential by the scorotron 18 for primary charging,
An image corresponding to a predetermined color is exposed on the surface of the photosensitive drum 17 by the ROS 13 to form an electrostatic latent image. The electrostatic latent images formed for the respective colors on the surface of the photosensitive drum 17 are developed by developing units 19Y and 19 of the corresponding colors.
M, 19C, and 19BK are developed, and a toner image T of a predetermined color is formed on the surface of the photosensitive drum 17.

For example, if the electrostatic latent image formed on the photosensitive drum 17 corresponds to yellow, the electrostatic latent image is developed by the yellow developing unit 19Y and On the surface 17, a yellow toner image T is formed. Further, for the other magenta, cyan, and black colors, toner images T of corresponding colors are sequentially formed on the photosensitive drum 17 by the same process.

The toner image T of each color sequentially formed on the photosensitive drum 17 is transferred from the photosensitive drum 17 to the intermediate transfer belt 21 at a primary transfer position where the photosensitive drum 17 and the intermediate transfer belt 21 are in contact with each other. Is transferred to the surface of
At this primary transfer position, a semi-conductive primary transfer bias roll 22 is provided on the back side of the intermediate transfer belt 21, and the intermediate transfer belt 21 is moved by the primary transfer bias roll 22. It comes into contact with the surface of the photosensitive drum 17. A voltage having a polarity opposite to the charge polarity of the toner is applied to the bias roller 22 for the primary transfer, and the toner image T formed on the photosensitive drum 17 is pressed onto the intermediate transfer belt 21 by a pressing force and electrostatic suction. Transcribed by force.

In the case of forming a monochromatic image, the toner image T of a predetermined color primary-transferred onto the intermediate transfer belt 21 is
Immediately after the secondary transfer onto the recording paper 26, when forming a color image in which a plurality of color toner images T are superimposed, the formation of the toner image T of a predetermined color on the photosensitive drum 17 and the toner The process of the primary transfer of the image T onto the intermediate transfer belt 21 is repeated for a predetermined number of colors.

For example, when a full-color image is formed by superimposing four color toner images T of yellow (Y), magenta (M), cyan (C), and black (BK), the photosensitive drum 17 , For each rotation, yellow (Y), magenta (M), cyan (C), black (B
K) The toner images T of each color are sequentially formed, and these four color toner images are sequentially primary-transferred onto the intermediate transfer belt 21 in a superimposed state.

At this time, the intermediate transfer belt 21 rotates at a cycle synchronized with the photosensitive drum 17 while holding the yellow-colored unfixed toner image T that has been primarily transferred first.
A position detection sensor 45 is provided on the intermediate transfer belt 21.
The magenta, cyan and black unfixed toner images T
Is transferred in a state of being sequentially superimposed on the unfixed yellow toner image T.

The unfixed toner image T primarily transferred to the intermediate transfer belt 21 in this manner is transported to a secondary transfer position facing the transport path of the recording paper 26 with the rotation of the intermediate transfer belt 21. Is done.

The recording paper 26 is fed from feed cassettes 28, 29, 30, and 31 by feed rolls 28a, 29a, 30a, and 31a as described above.
3 and the secondary transfer roll 27 and the intermediate transfer belt 21
Is fed between the nip portions.

On the back side of the intermediate transfer belt 21 at the secondary transfer position, a backup roll 25 serving as a counter electrode of the secondary transfer roll 27 is provided. At the secondary transfer position, the semi-conductive secondary transfer roll 27 is pressed against the intermediate transfer belt 21 at a predetermined timing, and a voltage having a polarity opposite to that of the toner is applied to the backup roll 25 to thereby perform the intermediate transfer. The unfixed toner image T transferred onto the belt 21 is secondarily electrostatically transferred onto the recording paper 26 at the secondary transfer position.

In this embodiment, as shown in FIG.
Instead of directly applying a voltage having the same polarity as the charging polarity of the toner to the secondary transfer roll 27, the transfer bias is applied by the bias roll 46 to the backup roll 25 which is pressed against the secondary transfer roll 27 via the intermediate transfer belt 21. From a transfer bias high voltage power supply 47 as a voltage applying means,
It is configured to apply a voltage having the same polarity as the charging polarity of the toner. However, a voltage having the same polarity as the charge polarity of the toner may be directly applied to the secondary transfer roll 27.

Then, the recording paper 26 onto which the unfixed toner image has been transferred is separated from the intermediate transfer belt 21 and is fixed by an electrode member 48, a guide plate 49 and a transport belt 34 disposed downstream of the secondary transfer portion. Sent to 35,
The fixing process of the unfixed toner image T is performed.

On the other hand, from the intermediate transfer belt 21 on which the secondary transfer of the unfixed toner image T has been completed, the residual toner is removed by the intermediate transfer belt cleaner 44.

The intermediate transfer belt 21 is made of a synthetic resin such as polyimide, polycarbonate, polyester, or polypropylene or various rubbers containing an appropriate amount of an antistatic agent such as carbon black. Is formed to be 10 ⁶ to 10 ¹⁴ Ω · cm. The thickness of the intermediate transfer belt 21 is set to, for example, 0.1 mm. The circumference of the intermediate transfer belt 21 is set to an integral multiple (for example, three times) of the circumference of the photosensitive drum 17.

The secondary transfer roll 27 and the intermediate transfer belt cleaner 44 are disposed so as to be able to contact and separate from the intermediate transfer belt 21. When a color image is formed, the unfixed final color is not fixed. The toner image T is transferred to the intermediate transfer belt 21
At least the intermediate transfer belt cleaner 44 is separated from the intermediate transfer belt 21 until the primary transfer is performed thereon.

Further, the secondary transfer roll 27 has a surface layer made of a urethane rubber tube in which carbon is dispersed, and an inner layer made of foamed urethane rubber in which carbon is dispersed. Is coated with fluorine. The secondary transfer roll 27 is formed such that its volume resistivity is set to 10 ³ to 10 ¹⁰ Ω · cm, and the roll diameter is 28 mm.
The hardness is set to, for example, 30 ° (Asuka C).

On the other hand, the backup roll 25 has a surface layer made of a blended rubber tube of EPDM and NBR in which carbon is dispersed, and an inner layer made of EPDM rubber, and has a surface resistivity of 10 ⁷ to 10 ⁷ . 10 ¹⁰ Ω
/ □, formed so that the roll diameter is φ28 mm,
The hardness is set to, for example, 70 ° (Asuka C).

The electrode member 48 disposed downstream of the nip portion of the secondary transfer position is preferably a sheet metal as a conductive plate-like member. In this embodiment, a 0.5 mm thick stainless steel plate is used. In this case, the recording paper 26 having a needle shape is used. Further, the electrode member 48-2
The leading end on the side of the next transfer area is disposed on the side of the secondary transfer roll 27 by 1 mm from a line formed by the nip portion of the backup roll 25 and the secondary transfer roll 27, and separated by 7 mm from the exit of the nip portion.

Further, in the color electrophotographic copying machine according to the first embodiment, the toner image transferred to the non-image area on the intermediate transfer member is located on the intermediate transfer member other than the area corresponding to the recording medium. In this case, the second transfer unit may include a transfer bias voltage application control unit that controls so as to apply a reverse transfer bias voltage (cleaning bias voltage) having a polarity opposite to that of the transfer bias voltage to at least an area other than the recording medium. Is configured.

That is, in the color electrophotographic copying machine according to the first embodiment, as shown in FIG. 3, the surface of the intermediate transfer belt 21 is divided into an image area 50 and a non-image area 51 in advance. The image area 50 is set corresponding to the maximum size (for example, A3 size) recording paper 26 that can be copied by the color electrophotographic copying machine. On the surface of the intermediate transfer belt 21, for example, two image areas 50 corresponding to the A3 size recording paper 26 are set, and a non-image area 51 is provided between these image areas 50. As shown in FIG. 1, the position of the image area 50 and the non-image area 51 of the intermediate transfer belt 21 are recognized by detecting the mark 52 provided at the reference position by the position detection sensor 45. , Image area 50
Is configured to transfer the toner image T corresponding to the original 2 to the original. When forming an image on the recording paper 26 of A4 size or less, which is half the A3 size, the color electrophotographic copying machine converts the image area 50 into two areas 50a and 50a.
0b (for example, an area corresponding to A4 size)
The toner image of the document 2 can be transferred to each of the areas 50a and 50b in the image area 50.

In the color electrophotographic copying machine, as the image quality increases, a patch for process control or a patch for registration control is required before the start of the image forming operation in order to guarantee the image quality of the color image. It is configured to transfer onto the intermediate transfer body at the timing between recording paper passes, detect these process control patches and registration control patches, and control the image forming operation based on the detection results. Have been.

That is, in the above color electrophotographic copying machine, when the power switch of the copying machine is turned on, when a predetermined number of copies are taken, or after the copy button for starting the copying operation is pressed. 4 during a setup operation before the actual copying operation starts.
As shown in FIG. 5, in the image area 50 of the intermediate transfer belt 21,
A plurality of process control patches 53Y, 53M, 53C, 53BK of each color of yellow (Y), magenta (M), cyan (C), and black (BK) are formed at different densities, and yellow (Y) , Magenta (M), cyan (C), and black (BK) color registration horizontal control V-shaped patches 54Y for registration control;
54M, 54C, and 54BK are formed at a predetermined pitch.

In the above color electrophotographic copying machine, as shown in FIG.
, Yellow (Y), magenta (M), cyan (C), black (B)
K) patch 55Y for process control of each color,
55M, 55C, and 55BK are formed at two types of concentrations, 60% and 20%, and are used for resist control of each color of yellow (Y), magenta (M), cyan (C), and black (BK). V-shaped patch 56
Y, 56M, 56C, and 56BK are formed at a predetermined pitch.

Process control patches 53Y, 53M, 53 formed on the intermediate transfer belt 21.
C, 53BK, 54Y, 54M, 54C, 54BK and patches 55Y, 55M, 55 for resist control
C, 55BK and 56Y, 56M, 56C, 56BK
Is detected by an optical sensor 57 disposed above the driven roll 24a, as shown in FIG.

Further, in the color electrophotographic copying machine, at least a part of the toner image transferred to the non-image area 51 and the image area 50 of the intermediate transfer belt 21
In the case of being located on the intermediate transfer belt 21 other than the area corresponding to the transfer bias voltage, the reverse transfer bias voltage (cleaning bias voltage) having the reverse polarity to the transfer bias voltage is applied to at least the area other than the recording paper 26 to the secondary transfer means. 60 as transfer bias voltage application control means for controlling
It is constituted so that it may be provided.

In the color electrophotographic copying machine, as shown in FIG. 1, a recording paper 2 is provided upstream of the secondary transfer position.
6, a paper detection sensor 58 for detecting
The sheet detection sensor 58 allows the intermediate transfer belt 2
The front end and the rear end of the recording paper 26 conveyed to the secondary transfer position in contact with the recording paper 1 are detected.

Further, in the above color electrophotographic copying machine,
A humidity sensor 59 and a temperature sensor 66 for detecting humidity are provided inside the intermediate transfer belt 21.

FIG. 6 is a block diagram showing a control circuit of the color electrophotographic copying machine.

In FIG. 6, reference numeral 60 denotes a CPU which controls the image forming operation of the color electrophotographic copying machine and also functions as transfer bias voltage application control means, and 61 denotes the number of copies, the copy magnification, the size of the recording paper 26 and the like. User interface to specify, 45 is intermediate transfer belt 2
A position detection sensor 57 for detecting the mark 52 provided on the first transfer belt 1 is provided with process control patches 53Y, 53M, 53C transferred onto the intermediate transfer belt 21.
53BK and 54Y, 54M, 54C, 54BK and patches 55Y, 55M, 55C for resist control,
An optical sensor for detecting 55BK and 56Y, 56M, 56C, 56BK, a paper detection sensor 58 disposed before the secondary transfer position, and a paper cassette 2
A cassette sensor for detecting the size of the recording paper 26 stored in the paper feed cassettes 28, 29, 30, 31 by a size detector provided in 8, 29, 30, 31. Reference numeral 1 denotes a humidity sensor for detecting humidity; 47, a high-voltage power supply for transfer bias voltage as transfer bias voltage applying means for applying a transfer bias voltage to a backup roll 27 as secondary transfer means; and 13, a photosensitive drum. 17, patches 53Y, 53M, 53C, 53BK, 54Y and 54Y for image exposure and process control corresponding to the image of the original 2
4M, 54C, 54BK and patches 55Y, 55M, 55C, 55BK and 56Y, 5Y for resist control.
ROS for performing image exposure for forming 6M, 56C, and 56BK, 63 is a belt drive motor for rotating and driving the intermediate transfer belt 21, and 64 is a CPU that controls the image forming operation of a color electrophotographic copying machine and the application of a transfer bias voltage. ROM storing a program for performing a control operation, 65
Denotes RAMs for storing data and the like for the CPU 60 to perform control operations.

In the color electrophotographic copying machine according to the first embodiment, at the time of cleaning the transfer roll, the electrostatic adhesion of the charged coloring material to the surface of the belt-shaped image carrier and the dynamic Both of the adhesive forces are set to be larger than the electrostatic and mechanical adhesive forces of the charged coloring material on the surface of the transfer roll.

In the first embodiment, the electrostatic adhesion of the charged coloring material to the surface of the belt-shaped image carrier is determined by the electrostatic adhesion of the charged coloring material to the surface of the transfer roll. The means for setting to be larger is configured to include means for applying a cleaning bias voltage having a polarity opposite to a transfer bias voltage to at least one of the backup roll and the transfer roll.

Further, in the first embodiment, the dynamic adhesion of the charged coloring material to the surface of the belt-shaped image carrier is determined by the dynamic adhesion of the charged coloring material to the surface of the transfer roll. The means for setting the surface energy of the transfer roller may be set to be larger than the surface energy of the transfer roller.

That is, in the color electrophotographic copying machine according to the first embodiment, since the surface energy of the intermediate transfer belt 21 is set to be larger than the surface energy of the secondary transfer roll 27, the water on the surface of the secondary transfer roll 27 is Is set to be larger than the contact angle of water on the surface of the intermediate transfer belt 21.

Specifically, the surface roughness Rz of the fluorine-coated secondary transfer roll 27 is set so that Rz <5 μm by polishing the surface or the like. At this time, the contact angle of water on the surface of the secondary transfer roll 27 is controlled to be in a range of 85 ° to 100 ° as shown in FIG. At this time, the contact angle of water on the surface of the intermediate transfer belt 21 is in the range of 70 ° to 80 °, and is configured to satisfy the above relationship. The surface of the secondary transfer roll 27 is formed in an arc shape, but since the water droplets attached to the surface of the secondary transfer roll 27 are small, the surface of the secondary transfer roll 27 can be approximated to a plane. Things.

By doing so, as shown in FIG.
Dynamic adhesion F of toner to secondary transfer roll 27
_FR is made smaller than the mechanical adhesive force _{FFB of} the toner to the intermediate transfer belt 21, so that the toner is less likely to transfer from the intermediate transfer belt 21 to the secondary transfer roll 27.

The CPU 60 is configured to apply a predetermined cleaning bias voltage to the backup roll 25 via the bias roll 46 by the transfer bias high voltage power supply 47.

The cleaning bias voltage applied to the backup roll 25 is such that when the secondary transfer roll 27 is cleaned, the toner electrostatic adhesion F _CB to the surface of the intermediate transfer belt 21 is applied to the surface of the secondary transfer roll 27. The toner is set to be larger than the electrostatic adhesion force F _{CR of the} toner.

In the above configuration, in the color electrophotographic copying machine according to the first embodiment, the dynamic adhesion of the toner to the surface of the transfer roll and the image bearing against which the transfer roll is pressed are as follows. By defining the relationship between the toner and the mechanical adhesion of the toner to the surface of the body, the transfer roll can always be cleaned satisfactorily.

That is, in the color electrophotographic copying machine according to the first embodiment, as shown in FIG. 2, the original 2 is set at a predetermined position, and the number of copies, the copy magnification, When a size or the like is specified and the copy button is pressed, the CPU 60
As a result, the photosensitive drum 17 is driven to rotate, and as shown in FIG. 9, the belt drive motor 63 for driving the intermediate transfer belt 21 is turned on, and the intermediate transfer belt 21 is driven to rotate. At the same time as the intermediate transfer belt 21 is rotated by the CPU 60 as the transfer bias voltage application control means, the backup roll 25 of the secondary transfer means is rotated in the reverse direction at +600 to 700 V via the transfer bias voltage high voltage power supply 47. A shooting bias voltage (cleaning bias voltage) is applied. In the first embodiment, the secondary transfer roll 27 is configured to be kept in pressure contact with the intermediate transfer belt 21 while the belt drive motor 63 is rotating.

Then, in the image area 50 of the intermediate transfer belt 21, after the copy button for starting the copying operation is pressed as shown in FIGS. 4 and 9, the copying operation actually starts. During the previous setup operation, patches 53Y, 53M, 53C for process control of each color of yellow (Y), magenta (M), cyan (C), and black (BK) formed on the photosensitive drum 17 are provided.
53BK is transcribed multiple times at different concentrations,
Horizontal V-shaped patches 54Y, 54M, 54C, 54BK for resist control of each color of yellow (Y), magenta (M), cyan (C), and black (BK)
Is transferred at a predetermined pitch. Intermediate transfer belt 2
Patches 53Y, 53M, 53C, 53BK for process control of each color transferred to one image area 50,
As shown in FIG. 1, the horizontal V-shaped patches 54Y, 54M, 54C, and 54BK for the resist control of each color are detected by the optical sensor 57, and the density of the process control patch and the resist control patch is determined. The position data is sent to the CPU 60 as shown in FIG. The CPU 60 determines whether or not the density and position data of the process control patch and the registration control patch are within a predetermined range, and the density and position data of the patch fall within the predetermined range. Thus, various parameters for image formation are controlled.

The process control patches 53Y, 53M, 53C and 53BK of each color transferred to the image area 50 of the intermediate transfer belt 21 and the patch control patches 54Y, 54M, 54C and 5
Even when the 4BK passes through the secondary transfer position, the CPU 60
As shown in FIG. 9, a state is maintained in which a reverse transfer bias voltage of, for example, +600 V is applied to the backup roll 25 via the transfer bias voltage high-voltage power supply 47. Therefore, the image area 50 of the intermediate transfer belt 21 is
5 for process control of each color transferred to
3Y, 53M, 53C, 53BK and patches 54Y, 54M, 54C, 54B for resist control of each color
K is transferred to the intermediate transfer belt 21 by the reverse transfer bias voltage applied to the backup roll 25 when passing through the secondary transfer position, and the secondary transfer K is pressed against the intermediate transfer belt 21. There is no transfer onto the roll 27. The process control patches 53Y, 53M, 53C, and 53BK of the respective colors transferred to the image area 50 of the intermediate transfer belt 21 and the registration control patches 54Y, 54M, and 54 of the respective colors.
Thereafter, C and 54BK are removed from the intermediate transfer belt 21 by the intermediate transfer belt cleaner 43.

Next, an image area 50 of the intermediate transfer belt 21 and an area corresponding to a space between the recording papers 26 are provided.
As shown in FIGS. 5 and 9, a toner image 70 corresponding to the image of the original 2 formed on the photosensitive drum 17 and yellow (Y), magenta (M), cyan (C), and black (BK) Patch 55 for process control of each color
Y, 55M, 55C, and 55BK are transferred at two different densities, and a horizontal V-shaped resist control for each color of yellow (Y), magenta (M), cyan (C), and black (BK) is performed. Patches 56Y, 56M, 5
6C and 56BK are transferred at a predetermined pitch.

At this time, when a full-color image is formed, yellow (Y), magenta (M), and cyan (C) are formed on the image area 50 of the intermediate transfer belt 21 every time the photosensitive drum 17 makes one rotation. ) And black (BK) toner images are transferred, and a photosensitive drum 17 is provided in an area corresponding to a space between recording papers 26 as shown in FIG.
Each rotation of yellow makes yellow (Y), magenta (M),
Patches 55Y, 55M, 55C, 55BK for process control of each color of cyan (C) and black (BK)
Are transferred at two different densities, and yellow (Y), magenta (M), cyan (C), black (B
The horizontal V-shaped patches 56Y, 56M, 56C, and 56BK for registration control of each color K) are transferred at a predetermined pitch.

When a final toner image 70, that is, a full-color image is formed in the image area 50 of the intermediate transfer belt 21, yellow (Y), magenta (M), cyan (C), and black ( A toner image 70 in which four toner images of BK) are transferred in a multiplex manner, or an image of one to three colors of yellow (Y), magenta (M), cyan (C), and black (BK) is formed. In this case, for example, ++ is applied to the backup roll 25 until these one to three color toner images 70 are transferred.
The reverse transfer bias voltage of 600 V remains applied.

By the way, when the final toner image 70 transferred to the image area 50 of the intermediate transfer belt 21 as described above passes through the secondary transfer position, as shown in FIG. For example, a transfer bias voltage of −2.2 KV is applied to the backup roll 25 via the high-voltage power supply 47. Therefore, the intermediate transfer belt 2
The final toner image 70 transferred to the first image area 50 is
When passing through the secondary transfer position, the image is transferred from the intermediate transfer belt 21 onto the recording paper 26 conveyed to the secondary transfer position in synchronization with the toner image by the transfer bias voltage applied to the backup roll 25. You.

At this time, the transfer bias voltage applied to the backup roll 25 of the secondary transfer means is -2.2.
The value is not limited to KV, and is set to an optimal value for transferring the final toner image 70 transferred on the intermediate transfer belt 21 onto the recording paper 26 when passing through the secondary transfer position. . Therefore, in the color electrophotographic copying machine according to this embodiment, as shown in FIG.
9 to detect the humidity inside the copier body 1
0 indicates that the transfer bias voltage applied to the backup roll 25 is -1.5 based on the detection result of the humidity sensor 59 so that the optimum transferability of the toner image 70 is obtained.
The control is performed in the range of KV to -3.0 KV.

On the other hand, as described above, the intermediate transfer belt 21
, The process control patches 55Y, 55M,
55C, 55BK and horizontal V-shaped patches 56Y, 56M, 56C, 56 for resist control of each color.
When the BK passes through the secondary transfer position, the CPU 60
As shown in the figure, the reverse transfer bias voltage of, for example, +600 V is applied to the backup roll 25 via the transfer bias voltage high-voltage power supply 47 over the entire non-image area 51 corresponding to the size of the selected recording paper 26. It is in the state of. Therefore, the intermediate transfer belt 2
A patch 55 for process control of each color transferred to the non-image area 51 corresponding to the interval between the passing of one recording sheet 26
Y, 55M, 55C, 55BK and patches 56Y, 56M, 56C, 56BK for resist control of each color
Is the backup roll 2 when passing through the secondary transfer position.
Due to the reverse transfer bias voltage applied to the transfer belt 5, the transfer is kept on the intermediate transfer belt 21, and the transfer is not performed on the secondary transfer roll 27 pressed against the intermediate transfer belt 21.

Thereafter, when the belt drive motor 63 for rotating the intermediate transfer belt 21 stops, the application of the bias voltage to the backup roll 25 is turned off.

In the first embodiment, as shown in FIG. 7, the contact angle of water on the surface of the secondary transfer roll 27 is
It is controlled to be in the range of 85 ° to 100 °.
At this time, the contact angle of water on the surface of the intermediate transfer belt 21 is in the range of 70 ° to 80 °, and is configured to satisfy the above relationship.

By doing so, as shown in FIG.
The mechanical adhesion of the toner to the secondary transfer roll 27 is made smaller than the mechanical adhesion of the toner to the intermediate transfer belt 21, making it difficult for the toner to transfer from the intermediate transfer belt 21 to the secondary transfer roll 27.

The cleaning bias voltage applied to the backup roll 25 is
At the time of cleaning, the toner electrostatic adhesion to the surface of the intermediate transfer belt 21 is set to be larger than the toner electrostatic adhesion to the surface of the secondary transfer roll 27.

As described above, at the time of cleaning the secondary transfer roll 27, both the electrostatic adhesion and the mechanical adhesion of the toner to the surface of the intermediate transfer belt 21 are reduced. Since it was set to be larger than the electrostatic adhesion and the mechanical adhesion,
While preventing the toner from transferring to the surface of the secondary transfer roll 27, the toner adhered to the surface of the secondary transfer roll 27 is subjected to the secondary transfer by both electrostatic adhesion and mechanical adhesion. From the surface of the roll 27 to the intermediate transfer belt 2
1 can be reliably transferred to the surface, and the secondary transfer roll 27 can always be favorably cleaned. Therefore, good cleaning performance of the transfer roll can be secured without using a special cleaning means such as a blade for cleaning the surface of the secondary transfer roll 27, and the surface of the secondary transfer roll 27 is Since it is not worn by the cleaning means, the reliability can be improved and the life of the secondary transfer roll 27 can be extended about twice. Further, since it is not necessary to use a special cleaning means such as a blade for cleaning the surface of the secondary transfer roll 27, a cleaning means for the secondary transfer roll 27 is not required, and the number of components can be reduced.

Second Embodiment FIG. 10 shows a second embodiment of the present invention. In the second embodiment, the structure of the image forming means is different from that of the first embodiment. A plurality of image forming units each including an image carrier on which an electrostatic latent image is formed, and developing means for developing the electrostatic latent image formed on the image carrier with toner of a predetermined color. Image forming units which sequentially form a plurality of toner images of different colors are used.

FIG. 10 shows a tandem type color electrophotographic copying machine as an image forming apparatus according to Embodiment 5 of the present invention.

In FIG. 10, reference numeral 101 denotes a main body of a tandem-type digital color copying machine, and a platen for pressing a document 102 onto a platen glass 105 is provided on an upper end of one end of the digital color copying machine main body 101. A cover 103 and a document reading device 104 that reads an image of the document 102 placed on the platen glass 105 are provided. The original reading device 104 illuminates an original 102 placed on a platen glass 105 with a light source 106, and reflects a reflected light image from the original 102 from a full-rate mirror 107, half-rate mirrors 108 and 109, and an imaging lens 110. Scanning exposure is performed on an image reading element 111 such as a CCD via a reduction optical system, and the image reading element 111 converts a color material reflected light image of the original 2 at a predetermined dot density (for example, 16 dots / mm). It is designed to read.

The color material reflected light image of the document 102 read by the document reading device 104 is, for example, red (R),
IPS 112 (Image Processes) is used as document reflectance data of three colors of green (G) and blue (B) (each 8 bits).
Sing System) and the IPS 112
Now, with respect to the reflectance data of the original 2, shading correction, positional deviation correction, lightness / color space conversion, gamma correction,
Predetermined image processing such as frame erasure and color / movement editing is performed.

The image data subjected to the predetermined image processing by the IPS 112 as described above includes yellow (Y), magenta (M), cyan (C), and black (K) (each 8 bits).
Are converted into original color material gradation data of four colors, and as described below, the image forming units 113Y of each color of yellow (Y), magenta (M), cyan (C), and black (K)
ROS 114Y of 113M, 113C, 113BK, 1
14M, 114C, 114BK (Raster Out
put Scanner) to send these ROS1
In 14Y, 114M, 114C, and 114BK, image exposure with laser light is performed in accordance with original color material gradation data of a predetermined color.

By the way, inside the tandem type digital color copying machine main body 101, four image forming units 113Y, 113M, 113C of yellow (Y), magenta (M), cyan (C), and black (K) are provided. , 113BK
Are arranged in parallel at a constant interval in the horizontal direction.

These four image forming units 113
Y, 113M, 113C, and 113BK have the same configuration, and are roughly divided into a photosensitive drum 115 that rotates at a predetermined rotation speed in the direction of an arrow, and a surface of the photosensitive drum 115 that is uniformly charged. And a ROS 1 for exposing an image corresponding to each color to the surface of the photosensitive drum 115 to form an electrostatic latent image.
14, a developing device 117 for developing the electrostatic latent image formed on the photosensitive drum 115, and a cleaning device 118.

As shown in FIG. 10, the ROS 114 modulates the semiconductor laser 119 according to the original color material gradation data, and emits a laser beam LB from the semiconductor laser 119 according to the gradation data. The laser beam LB emitted from the semiconductor laser 119 is deflected and scanned by the rotating polygon mirror 122 via the reflection mirrors 120 and 121, and is again image-bearing via the reflection mirrors 120 and 121 and the plurality of reflection mirrors 123 and 124. The photosensitive drum 115 as a body is scanned and exposed.

From the IPS 12, the yellow (Y),
Image forming units 113Y, 113M, 113C for each color of magenta (M), cyan (C), and black (BK)
113BK ROS 114Y, 114M, 114C, 1
Image data of each color is sequentially output to 14BK, and laser beams LB emitted from these ROSs 114Y, 114M, 114C and 114BK according to the image data are
Each photoconductor drum 115Y, 115M, 115
The surface of C, 115BK is scanned and exposed to form an electrostatic latent image. Each of the photosensitive drums 115Y, 115M, 11
The electrostatic latent images formed on 5C and 115BK are
According to 7Y, 117M, 117C and 117BK, yellow (Y), magenta (M), cyan (C),
It is developed as a toner image of each color of black (BK).

Each of the above image forming units 113Y, 113
M, 113C, 113K photoconductor drums 115Y, 11
The yellow (Y), magenta (M), cyan (C), and black (BK) toner images sequentially formed on 5M, 115C, and 115BK are image-forming units 11 respectively.
3Y, 113M, 113C, and 113BK, the primary transfer roll 126 is placed on the intermediate transfer belt 125.
Y, 126M, 126C, and 126BK are multiplexly transferred. The transfer belt 125 is a drive roll 1
27, the stripping roll 128, the steering roll 129, the idle roll 130, the backup roll 131, and the idle roll 132 are wound around with a constant tension, and are not shown. Is driven to rotate at a predetermined speed in a direction indicated by an arrow by a drive roll 127 which is rotationally driven by the drive motor of the above. As the transfer belt 125, for example, an endless belt is formed by forming a synthetic resin film such as PET having flexibility in a belt shape and connecting both ends of the synthetic resin film formed in a belt shape by means such as welding. What was formed in the shape is used.

The toner images of each color of yellow (Y), magenta (M), cyan (C), and black (BK) transferred on the transfer belt 125 in a multiplex manner are pressed against the backup roll 131 by a secondary transfer roll. 133, the toner image is secondarily transferred onto the recording paper 134 by the pressing force and the electrostatic force,
The recording paper 134 onto which the toner images of each color are transferred is 2
The sheet is conveyed to the fixing device 137 by a series of conveying belts 135 and 136. The recording paper 134 onto which the toner images of the respective colors have been transferred undergoes fixing processing by heat and pressure by a fixing device 137 and is discharged onto a discharge tray 138 provided outside the copying machine main body 101.

As shown in FIG. 10, the recording paper 134 has a predetermined size from one of a plurality of paper feed cassettes 139, 140, and 141.
And a registration roller 14 via a paper transport path 146 including a pair of paper transport rollers 143, 144, and 145.
7 once. The paper cassettes 139 and 14
Transfer paper 13 supplied from any one of 0 and 141
4 is fed onto the intermediate transfer belt 125 by a registration roll 147 that is driven to rotate at a predetermined timing.

Then, the four image forming units 113 of the yellow, magenta, cyan and black colors are used.
In the Y, 113M, 113C, and 113BK, as described above, yellow, magenta, cyan, and black toner images are sequentially formed at predetermined timings.

The photosensitive drums 115Y, 115
After the toner image transfer process is completed, the cleaning devices 118Y, 118M, and 11M
The residual toner and paper dust are removed by 8C and 118BK to prepare for the next image forming process. Further, residual toner is removed from the intermediate transfer belt 125 by the belt cleaner 148.

In the tandem-type color electrophotographic copying machine, as in the first embodiment, the electrostatic adhesion of toner to the surface of the intermediate transfer belt 125 is reduced when the secondary transfer roll 133 is cleaned. It is configured so that both the mechanical adhesion and the mechanical adhesion are larger than the electrostatic adhesion and the mechanical adhesion of the toner to the surface of the secondary transfer roll 133.

The other configuration and operation are the same as those of the first embodiment, and the description is omitted.

[0100]

As described above, according to the present invention,
The dynamic adhesion of the toner to the surface of the transfer roll,
By defining the relationship between the transfer roller and the mechanical adhesion of the toner to the surface of the image carrier against which the transfer roller is pressed, an image forming apparatus capable of always cleaning the transfer roller satisfactorily can be provided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an image forming unit of a color electrophotographic copying machine as an image forming apparatus according to Embodiment 1 of the present invention.

FIG. 2 is a configuration diagram showing a color electrophotographic copying machine as an image forming apparatus according to Embodiment 1 of the present invention.

FIG. 3 is an explanatory diagram illustrating an image area and a non-image area of the intermediate transfer belt.

FIG. 4 is an explanatory view showing a patch for process control and a patch for registration control transferred onto an intermediate transfer belt.

FIG. 5 is an explanatory diagram showing a patch for process control and a patch for resist control transferred onto the intermediate transfer belt.

FIG. 6 is a block diagram showing a control circuit of a color electrophotographic copying machine as an image forming apparatus according to Embodiment 1 of the present invention.

FIG. 7 is an explanatory diagram showing a contact angle of water on the surface of a secondary transfer roll.

FIG. 8 is an explanatory diagram showing a dynamic adhesive force of toner to an intermediate transfer belt and a secondary transfer roll.

FIG. 9 is a timing chart showing an image forming operation of the color electrophotographic copying machine as the image forming apparatus according to Embodiment 1 of the present invention.

FIG. 10 is a configuration diagram showing a tandem-type color electrophotographic copying machine as an image forming apparatus according to Embodiment 2 of the present invention.

[Description of sign]

17: photosensitive drum (image carrier), 21: intermediate transfer belt (intermediate transfer member), 22: primary transfer roll (primary transfer means), 25: backup roll (secondary transfer means),
26: recording paper (recording medium), 27: secondary transfer roll (secondary transfer means), 47: high voltage power supply for transfer bias (transfer bias voltage applying means).

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H030 AB02 AD05 AD17 BB02 BB23 BB34 BB42 BB46 BB54 BB56 2H032 AA05 AA14 AA15 BA02 BA05 BA09 BA30 CA02 CA12 CA13

Claims (4)

[Claims] 1. A belt-shaped image carrier that carries a visible image of a charged color material and circulates, and is arranged so as to be in pressure contact with the surface side of the image carrier via a recording medium, and that A transfer roll that collectively transfers the visible image on the carrier to the recording medium, and a transfer roll that is disposed so as to be in pressure contact with the back side of the belt-shaped image carrier in opposition to the transfer roll, and An image forming apparatus comprising: a backup roll that forms a transfer nip area having a predetermined width therebetween; and a transfer bias applying unit that applies a transfer bias voltage to at least one of the backup roll and the transfer roll. At the time of cleaning, both the electrostatic adhesion and the mechanical adhesion of the charged coloring material to the surface of the belt-shaped image carrier are charged to the surface of the transfer roll. An image forming apparatus characterized in that set to be larger than the electrostatic adhesion of wood and mechanical adhesion. 2. The image forming apparatus according to claim 1, wherein the electrostatic adhesion of the charged coloring material to the surface of the belt-shaped image carrier is changed by the static electricity of the charged coloring material to the surface of the transfer roll. Image forming means for applying a cleaning bias voltage having a polarity opposite to a transfer bias voltage to at least one of the backup roll and the transfer roll. apparatus. 3. The image forming apparatus according to claim 1, wherein a dynamic adhesion of the charged color material to the surface of the belt-shaped image carrier is adjusted by a charged color material to the surface of the transfer roll. An image forming apparatus configured to set the surface energy of the belt-shaped image carrier to be larger than the surface energy of the transfer roll. 4. The image forming apparatus according to claim 3, wherein the contact angle of water on the surface of the belt-shaped image carrier is 70 °.
~ 80 °, contact angle of water on the transfer roll surface is 85 ° ~
An image forming apparatus characterized in that the angle is set within a range of 100 °.