JPH09304998A - Picture image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform cleaning of remaining toner in the secondary transfer which remains on an intermediate transfer body due to the secondary transfer of toner image having a plurality of colors from the intermediate transfer body to a transfer material and the primary transfer of toner image of each color from image hold body to the intermediate transfer body in the next picture image formation simultaneously to improve throughput when different manuscript is printed continuously. SOLUTION: Electrifying bias voltage is applied to a cleaning roller 8, an electric charge is given to toner which remains on an intermediate transfer body 5 in the secondary transfer, and toner which remains in the secondary transfer is returned on a photosensitive drum 1 in the electric field for cleaning. Charged bias to be applied on the cleaning roller 8 is bias in which an alternate current is superimposed on a direct current in order to perform the cleaning due to the return of toner which remains in the secondary transfer simultaneously with the primary transfer on the photosensitive drum 1 in the next picture image formation.

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 using an electrophotographic method, and in particular, an image of each color formed on a first image carrier is once transferred onto a second image carrier, Then, the present invention relates to an image forming apparatus for transferring images of respective colors to a transfer material in a lump and obtaining images of a plurality of colors on the transfer material.

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus is known in which an intermediate transfer member is used as a second image bearing member for a photosensitive drum which is an image bearing member. This image forming apparatus sequentially forms toner images of respective colors on the photosensitive drum of the first image carrier, and transfers the toner images of the respective colors on the intermediate transfer member one after another in order each time the toner images of the respective colors are obtained ( Primary transfer), and the toner images of the respective colors are collectively transferred onto a transfer material such as paper at one time (secondary transfer) to obtain an image of a plurality of colors on the transfer material.

According to such an image forming apparatus, it is possible to relatively easily obtain a color image without misregistration of image components of respective colors, that is, color misregistration, and an image reproduced by combining color image information is reproduced. A device that outputs a formed object,
It is useful as an image forming apparatus having a color image forming function.

However, when the toner image is secondarily transferred from the intermediate transfer body to the transfer material, the residual toner after transfer remains on the intermediate transfer body, and one of the good measures is to remove the residual toner after secondary transfer satisfactorily. It is a technical issue.

As a method for solving the above, (1) for example, JP-A-56-153357 and JP-A-5-303310.
Et al. Disclose that a cleaning blade, which can be freely contacted and detached from the intermediate transfer member, is brought into contact with the intermediate transfer member to scrape off the toner remaining after the secondary transfer on the intermediate transfer member.

(2) A fur brush is provided on the intermediate transfer member so as to be freely contacted and separated from the intermediate transfer member, and a bias having a polarity opposite to that of the secondary transfer residual toner on the intermediate transfer member is applied to the fur brush to collect the toner on the fur brush. There is also a cleaning method in which the collected toner is attached to a bias roller such as a metal roller and then scraped by a blade that is in contact with the bias roller.

(3) Further, in order to reduce the load on the cleaning blade, a corona charger or a bias roller is installed so that the toner remaining after the secondary transfer on the intermediate transfer member is charged to the opposite polarity to the potential of the photosensitive drum. However, a method of returning the residual toner after secondary transfer to the photosensitive drum by an electric field has been proposed, for example, in Japanese Patent Laid-Open Nos. 4-340564 and 5-29997739.

(4) Further, JP-A-1-105980
In order to avoid waste of providing similar cleaning means on both the intermediate transfer body and the photosensitive drum, and to simplify the cleaning means, a charger is provided and toner remaining after secondary transfer on the intermediate transfer body is provided. Discloses a cleaning technique in which the toner remaining after the secondary transfer on the intermediate transfer member is returned to the photosensitive drum only by charging the toner having a polarity opposite to the charging potential of the photosensitive drum.

In Japanese Patent Laid-Open No. 105980/1989, the steps of charging the residual toner such as the secondary transfer residual toner on the intermediate transfer member and returning it to the photosensitive drum are performed in one printing process.
Although it may be performed several times, it is stated that the intermediate transfer member can be made in a cleaner state by performing a plurality of times.

[0010]

However, the conventional cleaning method described above has the following problems.

In the method of (1) in which the blade is brought into contact with the intermediate transfer member to scrape off the toner remaining after the secondary transfer on the intermediate transfer member, the toner is deposited on the blade portion. In addition, there is a problem that toner remains on the intermediate transfer member and a blade mark is generated on an image in the next printing process. Further, due to long-term use, both the blade and the surface layer of the intermediate transfer member which is in contact with the blade are worn, and there are problems such as poor cleaning and deterioration of transfer efficiency due to deterioration of the surface layer of the intermediate transfer member.

In the method (2) of using a fur brush and applying a bias to the fur brush to collect the residual toner after the secondary transfer, the cleaning means becomes large and complicated, and therefore the overall size and cost of the image forming apparatus are increased. There was a drawback that led to an increase.

The method of providing a corona charger or a bias roller to assist the load of the cleaning blade of (3) is very effective, unlike the mechanical cleaning method of (1). In addition to the normal printing step, an intermediate transfer member cleaning step is required, which has a drawback that throughput (the number of prints per hour) is significantly reduced during continuous printing of different originals.

By providing the charging device of (4) to charge the toner remaining on the intermediate transfer member after the secondary transfer to the opposite polarity of the charging potential of the photosensitive drum, the transfer residue on the intermediate transfer member can be achieved only by the charging device. To return the toner of item 1 to the photosensitive drum (JP-A-1-
No. 105980) has a very simple cleaning means, and it seems promising.

However, this publication only mentions that one or a plurality of printing steps are performed once or a plurality of cleaning steps (sequential cleaning), and a sequence when continuous printing is performed on different originals. That is, it does not mention cleaning of the intermediate transfer member simultaneously with the primary transfer. In the method of the publication, the throughput is lowered similarly to the above by sequentially performing cleaning at the time of continuous printing of different originals.

An object of the present invention is to use the toner remaining after the secondary transfer remaining on the intermediate transfer member by the secondary transfer of the multi-color toner images from the intermediate transfer member onto the transfer material, and to form the image in the next image formation. 1 of each color toner image from the carrier to the intermediate transfer body
An object of the present invention is to provide an image forming apparatus in which the cleaning is simultaneously performed at the time of the next transfer and the throughput at the time of continuously printing different originals is improved.

[0017]

The above object is achieved by an image forming apparatus according to the present invention. In summary, according to the present invention, a plurality of color toner images are sequentially formed on the first image carrier from the first color, and the obtained toner images are sequentially formed from the first color to the second color.
Primary transfer onto the image carrier, and by applying a charging bias to the first charging means, charges are applied to the primary-transferred plural-color toner images, and the charged multi-color toner images are applied. Are collectively secondary-transferred onto the transfer material to obtain a color image on the transfer material, and by applying a charging bias to the second charging means, secondary transfer is performed onto the second image carrier. In an image forming apparatus in which an electric charge is applied to the remaining toner and is returned to the first image carrier by an electric field due to the applied electric charge of the remaining toner, the charging bias applied to the second charging unit is superposed on the direct current and the alternating current. By using the bias, the returning of the residual toner from the second image carrier to the first image carrier is performed by the second toner image from the first image carrier in the next image formation. Characterized by simultaneous primary transfer to the image carrier An image forming apparatus.

According to another aspect of the present invention, the charging bias applied to the first charging means is a bias in which an alternating current is superimposed on a direct current, so that the first residual toner from the second image carrier is removed. Is returned to the image carrier at the same time as the primary transfer of the toner image from the first image carrier to the second image carrier in the next image formation. According to still another aspect, the charging bias applied to the first charging unit and the charging bias applied to the second charging unit are biases in which alternating current is superimposed on direct current, whereby the second image carrier is The remaining toner is returned to the first image carrier at the same time as the primary transfer of the toner image from the first image carrier to the second image carrier in the next image formation.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

Embodiment 1 FIG. 1 is a schematic block diagram showing an embodiment of an image forming apparatus of the present invention, showing a color image forming apparatus such as a copying machine or a laser printer utilizing an electrophotographic process.

In addition to the photosensitive drum 1 which is an image carrier, this image forming apparatus is provided with an intermediate transfer member 5 which is an elastic roller having a low resistance as a second image carrier. Photosensitive drum 1
Is a drum type electrophotographic photosensitive member and is rotationally driven in the counterclockwise direction of the arrow at a predetermined peripheral speed (process speed), and the intermediate transfer member 5 is a primary transfer portion facing the photosensitive drum 1. It is rotationally driven at a predetermined peripheral speed in the clockwise direction of the arrow.

Around the photosensitive drum 1, a primary charging roller 2, an image exposing means (not shown), a rotary developing device 40, the above-mentioned intermediate transfer member 5 and a drum cleaner 13 are arranged. A pre-transfer charger 18, a transfer belt 6 and a cleaning roller 8 are arranged around the intermediate transfer body 5, a registration roller 11 and a guide 10 are provided in front of the transfer belt 6, and an extension of the transfer belt 6 is fixed. The vessels 15 are arranged respectively.

In order to perform color printing, the surface of the photosensitive drum 1 is uniformly charged by the charging roller 2 to a predetermined potential having a predetermined polarity in the course of rotation of the photosensitive drum 1, and then image exposure 3 is performed by the image exposure means. In response, the photosensitive drum 1
An electrostatic latent image corresponding to the image of the first color component of the target color image, for example, the image of the yellow component is formed on the surface of the.
The image exposure means includes a color separation / imaging exposure optical system for a color original image, a scanning exposure system using a laser scanner that outputs a laser beam modulated in accordance with a time series electric digital image signal of color image information, and the like. Is used.

Next, the first electrostatic latent image is the rotary developing device 4.
The developing device 41, which is a yellow developing device of 0, develops using the yellow toner charged to the opposite polarity to the electrostatic latent image. The rotary developing device 40 has developing devices 41, 42, 43, and 44 mounted at equal intervals in the circumferential direction. The developing devices 41, 42, 43, and 44 have yellow (Y) and magenta (, respectively). M), cyan (C), and black (BK) toners are stored. Developing devices 41 to 4
4 is rotated in the direction of the arrow in the drawing by a rotation driving device (not shown), and is sequentially moved to a developing position facing the photosensitive drum 1.

The first-color yellow toner image formed on the photosensitive drum 1 passes through the primary transfer nip portion between the photosensitive drum 1 and the intermediate transfer member 5, and rotates at the same peripheral speed as the intermediate transfer member. 5 is primarily transferred onto the surface of No. 5. The primary transfer of the toner image from the photosensitive drum 1 to the intermediate transfer body 5 is performed by the electric field formed by the primary transfer bias applied to the intermediate transfer body 5 by the transfer bias power supply 29, the photosensitive drum 1 and the intermediate transfer body 5.
And contact pressure with.

Thereafter, in the same manner, a magenta toner image of the second color, a cyan toner image of the third color, a black toner image of the fourth color are formed on the photosensitive drum 1, and these toner images are sequentially formed on the intermediate transfer member 5. Then, the images corresponding to the target color image are transferred by superimposing, and the four color toner images are superposed and combined.

The transfer belt 6 carries and conveys the transfer material P, and secondarily transfers the four color toner images superimposed on the intermediate transfer body 5 onto the transfer material P. It constitutes the next transfer means. The transfer belt 6 is formed as an endless belt having a width that is substantially the same as the axial length of the intermediate transfer body 5, and is supported by a tension roller 61 and a bias roller 62 that are parallel to the axial direction of the intermediate transfer body 5. ,
On the lower surface side of the intermediate transfer body 5 which is substantially opposite to the photosensitive drum 1, it is arranged so as to be inclined in a direction perpendicular to the axial direction of the intermediate transfer body 5. The upper surface of one end of the transfer belt 6 on the bias roller 62 side can be brought into and out of contact with the lower surface of the intermediate transfer body 5 by providing the bias roller 62 so as to be vertically movable. A transfer bias power supply 28 that applies a desired secondary transfer bias is connected to the bias roller 62.
The tension roller 61 is fixedly installed and grounded.

During the primary transfer process of the toner images of the first to fourth colors from the photosensitive drum 1 onto the intermediate transfer body 5, the transfer belt 6 is in contact with and separated from the intermediate transfer body 5. Similarly, the cleaning roller 8 of the intermediate transfer body 5 is also brought into contact with and separated from the intermediate transfer body 5 during the primary transfer process. The cleaning roller 8 will be described in detail later.

Prior to the secondary transfer of the four color toner images on the intermediate transfer body 5 to the transfer material P, a charging bias is applied from the bias power source 31 to the pre-secondary transfer charger 18 to expose the toner images. The toner is more strongly charged to the opposite polarity to the electrostatic latent image on the drum 1 so that the toner has a higher charge. Two
The pre-transfer pre-charger 18 includes a corotron, a scorotron, or the like.

In the secondary transfer, the transfer belt 6 is brought into contact with the intermediate transfer member 5, the transfer material P is fed from a paper feed cassette (not shown), passes through the resist roller 11 and the pre-transfer guide 10, Intermediate transfer member 5 and transfer belt 6
And are fed to the contact nip of the secondary transfer portion facing each other at a predetermined timing. At the same time, the bias power supply 28 to 2
The next transfer bias is applied to the bias roller 62. By applying the secondary transfer bias, a transfer electric field is formed between the intermediate transfer body 5 and the transfer belt 6, and the four color toners on the intermediate transfer body 5 are electrostatically transferred onto the transfer material P, The toner images of four colors are secondarily transferred onto the transfer material P collectively.

The transfer material P, which has undergone the secondary transfer of the four-color toner images, is introduced from the transfer belt 6 to the fixing device 15, where the four-color toners are heat-fixed to form a full-color print image and printed. Ends.

In the present invention, after the secondary transfer to the transfer material P is completed, the cleaning roller 8 is brought into contact with the intermediate transfer member 5,
The secondary transfer residual toner remaining on the surface of the intermediate transfer body 5 is charged, and then the intermediate transfer body 5 is returned to the photosensitive drum 1 at the primary transfer portion with the photosensitive drum 1, and the secondary transfer of the intermediate transfer body 5 is performed. The transfer residual toner is removed and cleaning is performed. According to the present invention, it is possible to simultaneously perform the cleaning of the residual toner after the secondary transfer and the primary transfer of the toner image from the photosensitive drum 1 to the intermediate transfer body 5 in the next image formation. What is done is a major feature.

The details will be described below. In the present embodiment, a toner having a negative chargeability is used, and therefore, the description will be given below by taking it as an example. However, in the case of a positive chargeable toner, the polarity is basically reversed and the same applies. is there.

When the four color toners are collectively secondarily transferred from the intermediate transfer member 5 to the transfer material (paper) P on the transfer belt 6,
Due to the secondary transfer bias that generates a transfer electric field in the direction in which the negative polarity toner having the regular charging polarity is ejected toward the transfer material P, the toner is strongly charged in the polarity opposite to the regular negative polarity and is inverted to the positive polarity. Therefore, the toner cannot be transferred to the transfer material P due to the transfer electric field and remains on the intermediate transfer member 5.
It is the toner remaining after the secondary transfer. However, not all of the toner remaining on the intermediate transfer member 5 is inverted to the positive polarity, and the toner that is partially neutralized and has no electric charge and the toner that maintains the negative polarity are also included. Intermediate transfer member 5
Exists on.

The fact that the polarity of the secondary transfer residual toner is reversed was confirmed by the following experiment. Using a laser printer having the configuration of the image forming apparatus shown in FIG. 1, one image of a single color text pattern and the other image of a solid white pattern were continuously printed one by one. When there is no cleaning means for the intermediate transfer body 5, the transfer residual toner of the text pattern of the previous print, that is, the first print appears in the second solid white pattern like a positive ghost. At this time, when the generation amount of positive ghosts was observed by changing the secondary transfer bias value, the generation amount of positive ghosts was different depending on the secondary transfer bias value and was higher than the transfer bias value showing the maximum transfer efficiency. It was recognized that the occurrence of positive ghosts was the smallest.

It is conventionally known that the transfer efficiency has a peak at a certain transfer bias value, and the transfer efficiency is lowered when an excessive bias is applied. That is, it is considered that the positive ghost increases at a transfer bias value higher than the transfer bias value showing the maximum transfer efficiency. This seems to be different from the positive ghost generation behavior described above.

Therefore, the toner on the intermediate transfer member 5 and the toner on the photosensitive drum 1 were observed after the secondary transfer. as a result,
When the secondary transfer was performed with an excessive transfer bias, a large amount of toner was present on the intermediate transfer body 5, but toner was also present on the photosensitive drum 1. From the state of those toner patterns, the secondary transfer residual toner generated on the intermediate transfer body 5 is obviously reversely transferred to the photosensitive drum 1, and the toner may return from the intermediate transfer body 5 to the photosensitive drum 1. confirmed.

However, among the toners remaining after the secondary transfer on the intermediate transfer member 5, there are neutralized toners and toners that maintain the negative polarity as described above. It does not return to the photosensitive drum 1 and appears as a positive ghost in the next print image during continuous printing. Also, using a transfer bias higher than the optimum transfer bias,
It is not practical to apply a strong secondary transfer bias because the transfer current becomes excessive and image deterioration becomes severe.

Therefore, as described above, the charging means after the secondary transfer, that is, the cleaning roller 8 is installed to charge the toner remaining after the secondary transfer on the intermediate transfer body 5 to remove the toner remaining after the secondary transfer. Even the toner which is neutralized and has no electric charge and the toner which maintains the negative polarity are also reversed to the polarity opposite to the normal polarity. as a result,
It has become possible to remove all the toner remaining after the secondary transfer from the intermediate transfer body 5 and return it to the photosensitive drum 1.

The reversely charged toner on the intermediate transfer member 5 and the normally charged toner primarily transferred on the photosensitive drum 1 do not cancel each other's charges in a short time contact. , 1 in which the photosensitive drum 1 and the intermediate transfer member 5 face each other
It was found that in the next transfer nip portion, the oppositely charged toner is transferred to the photosensitive drum 1 and the normally charged toner is transferred to the intermediate transfer member 5.

More specifically, by lowering the primary transfer bias, the electric field applied between the photosensitive drum 1 and the intermediate transfer member 5 at the primary transfer nip portion is weakened to discharge at the primary transfer nip portion. If the charging of the toner by the toner is suppressed, the toner on the photosensitive drum 1 and the toner on the intermediate transfer member 5 will not be canceled together with the fact that there is no cancellation of the charges when the passing time of the toner through the primary transfer nip portion is short. Each can behave independently.

Therefore, according to the present invention, the secondary transfer residual toner can be cleaned simultaneously with the primary transfer.

The charging means for the secondary transfer residual toner used in this embodiment, that is, the cleaning roller 8 will be described. The cleaning roller 8 is a contact-type charging unit including an elastic roller having a multi-layer structure. FIG. 2 shows a schematic cross section of the cleaning roller 8.

The cleaning roller 8 is provided with an elastic layer 82 made of at least rubber or resin on the surface of a conductive cylinder (core bar) 83, and 1
A coating layer 81 of more than one layer is provided.

The conductive cylinder 83 is used for the cleaning roller 8
Is a conductive material having rigidity such that the contact nip can be uniformly obtained without being bent in the longitudinal direction of the intermediate transfer body 5 when the intermediate transfer body 5 is brought into contact with the intermediate transfer body 5, aluminum,
A conductive metal or alloy such as iron, copper and stainless steel, or a resin in which carbon, metal particles or the like are dispersed to have conductivity can be used.

The elastic layer 82 has a hardness such that the cleaning roller 5 can be brought into contact with the intermediate transfer member 5 without a gap, and has a certain electrical withstand voltage against the applied bias. . The resistance value of the elastic layer 82 is preferably 10 ⁷ to 10 ¹¹ Ωcm (when 1 kV is applied) in terms of volume resistivity.

As the rubber used for the elastic layer 82, acrylonitrile-butadiene rubber (NBR), styrene-
Examples thereof include butadiene rubber, butadiene rubber, ethylene-propylene rubber, chloroprene rubber, chlorosulfonated polyethylene rubber, chlorinated polyethylene rubber, acrylic rubber, fluororubber, urethane rubber and the like.

The resin usable for the elastic layer 82 is polycarbonate (PC), nylon (PA), polyester (PET), polyethylene naphthalate (P).
EN), polysulfone (PSU), polyethersulfone (PES), polyetherimide (PEI), polyethernitrile (PEN), polyetheretherketone (PEEK), thermoplastic polyimide (TPI),
Thermosetting polyimide (PI), PES alloy, polyvinylidene fluoride (PVdF), ethylene tetrafluoroethylene copolymer (ETFE), etc. are available, and in the elastomer system, a polyolefin thermoplastic elastomer, a polyester thermoplastic elastomer, a polyurethane system. Thermoplastic Elastomer, Polyurethane Thermosetting Elastomer, Polystyrene Thermoplastic Elastomer, Polyamide Thermoplastic Elastomer, Fluorine Thermoplastic Elastomer, Polybutadiene Thermoplastic Elastomer, Polyethylene Thermoplastic Elastomer, Ethylene Vinyl Acetate Thermoplastic Elastomer, Poly Examples thereof include vinyl chloride thermoplastic elastomers.

A resistance adjusting agent such as carbon or metal oxide may be added to the elastic layer 82 in order to adjust the volume resistivity.

The material of the coating layer 81 is an important element for realizing the cleaning of the intermediate transfer member 5 by the cleaning roller 8. That is, the cleaning roller 8 is for charging the secondary transfer residual toner, and the cleaning roller 8 is required to have the same function as the charging roller 2 for charging the surface of the photosensitive drum 1.

If the resistance value of the charging roller 2 is very stable and there is no microscopic resistance unevenness on the surface, even if the charging roller 2 has a single-layer structure, the surface of the photosensitive drum 1 is uniformly charged. That function can be satisfied. This is because the charging of the photosensitive drum is caused by the discharge generated between the surface material of the photosensitive drum 1 and the material of the charging roller 2 by the application of voltage, and the electrostatic capacitance contributing to the discharge is the resistance of these materials. This is because it depends on the value.

Therefore, if the resistance value is not stable and the surface has microscopic resistance unevenness, the charging roller 2 having a single-layer structure does not satisfy the charging performance, and therefore the stable resistance value is obtained. It is preferable that the charging roller 2 has a two-layer structure so that the functions of the respective layers are separated in order to control the control and suppress the microscopic unevenness of resistance on the surface.

Similarly, if the cleaning roller 8 does not have a stable resistance value and has microscopic resistance unevenness on the surface, the cleaning performance is not satisfied with a single-layer structure, and therefore this stable cleaning roller 8 is stable. In order to control the resistance value and suppress microscopic resistance unevenness on the surface, the cleaning roller 8 is used.
It is preferable that each layer has a multi-layered structure to separate the functions of the layers. Specifically, as in this embodiment, the lower elastic layer 8
It is preferable that the coating layer 81 on the surface layer has a function of finely adjusting the resistance value, and the function of finely controlling the resistance value is assigned to the second step, and it is preferable from the viewpoint of manufacturing such as expansion of material choices and cost reduction.

As the material of the coating layer 81, it is preferable to use nylon resin, urethane resin, fluorine resin or the like in which a metal oxide such as titanium oxide or tin oxide is dispersed as a conductive agent to control resistance. The coating layer 81 may be formed by applying these resins on the elastic layer 82, or may be formed by winding a sheet or tube of these resins on the elastic layer 82. The coating layer 81 preferably has a thickness of 5 to 100 μm.

The coating layer 81 needs to have a surface resistance sufficient for contact with the intermediate transfer member 5 and discharging.
⁶ to 10 ¹⁵ Ω / cm ² (when 1 kV is applied) is effective.

The surface resistance of the coating layer 81 was measured by applying a coating layer to a conductive sheet having a length and width of 100 mm under the same conditions as the coating layer 81 to prepare a sample, and measuring the surface resistance of the coating layer. R8304 manufactured by Advantest
Using A and R12704, applied voltage 1 kV, non-application time (discharge) 5 seconds, application time (cha)
The measurement was carried out for 30 seconds for the RGE) and 30 seconds for the measurement time (measure).

Cleaning roller 8 used in this embodiment
Is a conductive cylinder 83 made of stainless steel having an outer diameter of 14 mm, on which an elastic layer 82 is formed by NBR to have a thickness of 3 mm and a volume resistivity of 10 ⁹ Ωcm (when 1 kV is applied), and a coating layer thereon. 81 was made by using titanium oxide dispersed in one kind of methoxymethylated polyamide of nylon resin and forming it to have a thickness of 30 μm and a surface resistance of 10 ⁸ Ω / cm ^2, and the outer diameter of the roller 8 is It is about 20 mm. If the outer diameter of the cleaning roller 8 is 12 to 30 mm, there is no problem in carrying out the method according to the present invention.

The actual use resistance of the cleaning roller 8 prepared above was measured by the method shown in FIG. Here, the actual use resistance is the resistance of the cleaning roller 8 as a whole including the elastic layer 82 and the coating layer 81.

In FIG. 3, the aluminum cylinder 71 is rotated by a rotation driving body (not shown), and the cleaning roller 8 contacted with the aluminum cylinder 71 is driven to rotate. The contact pressure is the same as in the actual state of use of the actual machine, and the total pressure is 1 kgf. The conductive cylinder 8 of the rotating cleaning roller 8
A DC voltage of 1 kV was applied to the No. 3 from the high voltage power source 73. As a result, the current i [A] flows through the elastic layer 82 and the coating layer 81 of the cleaning roller 8, flows into the aluminum cylinder 71, and flows to the ground through the standard resistor 72 (1 kΩ) connected to the cylinder 71. . The voltage Vr [V] generated across the standard resistor 72 is measured by the voltmeter 7.
Measure at 4.

The resistance of the cleaning roller 8 (actual use resistance) is Rc [Ω], and the resistance of the standard resistor 72 is Ro =
Assuming that [Ω] and the DC voltage of the power source 73 are E = 1 [kV], Rc · i + Ro · i = E is substituted for Ro · i = Vr → i = Vr / Ro to obtain Vr · Rc / Ro + Vr = E → Vr ・ Rc (1 / Ro +
1 / Rc) = E Rc = E / {Vr · (1 / Ro + 1 / Rc)} Since Rc is sufficiently large, 1 / Rc = 0 and Rc = E · Ro / Vr = (10 ³ ) [V] -(10 ³ ) [Ω] / Vr [V] ∴Rc [Ω] = 10 ⁶ / Vr [V]

As a result of the measurement by the above measuring method, the actual use resistance Rc of the cleaning roller 8 of this embodiment is 4 × 10.
It was ⁸ Ω. According to the study by the present inventors, the actual use resistance of the cleaning roller 8 is 5 × 10 ⁵ to 1 × 10 ⁹ Ω.
Is preferably within the range.

In the present embodiment, the intermediate transfer member 5 is also configured similarly to the cleaning roller 8. As shown in FIG. 4, the intermediate transfer member 5 is formed on the surface of a conductive cylinder (core bar) 53. An elastic layer 52 made of at least rubber, elastomer and resin is provided, and one or more coating layers 51 are provided on the surface of the elastic layer 52.

For the conductive cylinder 53, a conductive metal or alloy such as aluminum, iron, copper and stainless steel, or a resin in which carbon or metal particles are dispersed to have conductivity can be used. As the conductive cylinder 53,
In addition to a simple cylindrical body, one with a shaft passing through the center of the cylinder,
For example, the inside of the cylinder is reinforced with a supporting member.
In this embodiment, the conductive cylinder 53 is an aluminum cylinder having a thickness of 3 mm, which is reinforced.

The elastic layer 52 has a thickness in order to form a good transfer nip between the intermediate transfer member 5 and the photosensitive drum 1, prevent color misregistration of a transferred image due to rotation of the intermediate transfer member 5, and reduce material cost. The thickness is preferably 0.5 to 7 mm, and in this embodiment, the elastic layer 52 has a thickness of 5 mm.

From the viewpoint of placing importance on the resistance value, the elastic layer 52 is
Acrylonitrile-butadiene rubber (N
BR) was used, and Ketjen black was dispersed as a conductive agent therein to control the volume resistivity to a desired value.

Other rubber materials that can be used for the elastic layer 52 include the same rubber materials as those used for the elastic layer 82 of the cleaning roller 8.

As the conductive agent dispersed in the rubber material of the elastic layer 52, carbon black, aluminum powder, nickel powder or the like can be used. It is also conceivable to use a conductive resin which itself has conductivity, instead of dispersing a conductive agent in the resin. Examples of the conductive resin include quaternary ammonium salt-containing polymethylmethacrylate,
Examples thereof include polyvinylaniline, polyvinylpyrrole, polydiacetylene and polyethyleneimine.

The volume resistivity of the elastic layer 52 is measured by thinly cutting a 100 mm-long sheet from the elastic layer 52.
R8304A and R manufactured by Advantest mentioned above
12704, applied voltage 1 kV, non-application time (d
ischarge) 5 seconds, application time (charge) 3
The measurement was performed under the conditions of 0 seconds and a measurement time (measurement) of 30 seconds.

The material of the coating layer 51 is 2 on the intermediate transfer member 5.
This is important because it greatly affects the cleaning property of the toner remaining after transfer. In this example, a urethane resin was used as a binder, aluminum borate whiskers were used as the resistance controlling conductive agent, and PTFE powder was used as the mold release improving agent.

In order to convey the flexibility of the lower elastic layer 52 to the surface of the photosensitive drum 1 with which the coating layer 51 is in contact, the coating layer 5
The thickness of 1 is preferably thin, 50 to 200 μm
The degree is good. In this embodiment, the coating layer 51 has a thickness of about 50.
μm. The outer diameter of the intermediate transfer member 5 is 180 mm.

The surface resistance of the coating layer 51 in this example was measured by the same method as described above, and was 10 ¹⁰ Ω /
cm ² . According to a study made by the present inventors, the surface resistance of the coating layer 51 is 10 ⁸ to 10 ¹² Ω / cm ^2.
Within the range, it is possible to satisfactorily remove the secondary transfer residual toner remaining on the intermediate transfer member 5.

The actual use resistance of the intermediate transfer member 5 including the elastic layer 52 and the coating layer 51 was 10 ⁷ Ω (when 1 kV was applied). The actual resistance used was measured by the method shown in FIG. 3, as in the case of the cleaning roller 8.

The toner used in this embodiment will be described. In this embodiment, yellow toner, magenta toner,
The cyan toner is composed of a non-magnetic toner (a non-magnetic one-component developer), contains 5 to 30% by weight of a low softening point substance, has a shape factor SF1 of 116, SF2 of 109, and a particle size of 7 μm, and is substantially spherical. A non-magnetic toner (polymerized toner) manufactured by the suspension polymerization method was used.

The transfer efficiency increases as the shape of the toner approaches a sphere. This is because the more spherical the toner, the smaller the surface energy of the toner, the higher the fluidity of the toner, the weaker the attracting force (mirroring force) with respect to the photosensitive drum, etc., and the more likely it is to be transferred by the transfer electric field. it is conceivable that.

A schematic structure of the polymerized toner is shown in FIG. The polymerized toner 9 has a resin layer 92 laminated on a core 93 and a surface layer 91 laminated on the resin layer 92, and is spherical in terms of its manufacturing method. In this example, the core 93 was made to include an ester wax, styrene-butyl acrylate was used for the resin layer 92, and styrene-polyester was used for the surface layer 91. Its specific gravity is about 1.05.

The reason why the polymerized toner 9 has such a multi-layer structure is that the core 93 contains a wax to impart the effect of preventing offset in the fixing step, and the surface layer 9
This is because the charging efficiency was improved by forming 1 from resin. Yellow, magenta, and
The cyan toner was used by externally adding oil-treated silica in order to stabilize the triboelectric charge.

The black toner is a magnetic toner (magnetic one-component developer). This black toner uses a styrene-butyl acrylate-butyl maleate half ester copolymer as a binder, to which 100 parts of a magnetic substance such as magnetite is added, and kneaded and pulverized to obtain a coarse-grained toner. Spheroidizing treatment in dynamic impact force, hot air flow or high temperature liquid, shape factor SF1 is about 145, SF2
Was used, and a substantially spherical magnetic toner (sphericalized toner) having an average particle size of 7 μm was used. Similarly, in order to stabilize the triboelectric charge, black toner was used by externally adding oil-treated silica.

In the above, the shape factor SF1 is a numerical value indicating the roundness ratio of the shape of the spherical substance, as shown in FIG. 6, and is the maximum of the elliptical figure formed by projecting the spherical substance on the two-dimensional plane. It is defined as a value obtained by dividing the square of the long MXLNG by the graphic area AREA and multiplying by 100π / 4. In other words, the shape factor SF1 is: SF1 = {(MXLNG) ² / AREA} × (100π
/ 4).

As shown in FIG. 7, the shape factor SF2 is a numerical value showing the ratio of the unevenness of the shape of the substance, and is 2 for a spherical substance.
It is defined as a value obtained by dividing the square of the perimeter PERI of a figure formed on a dimensional plane by the figure area AREA and multiplying by 100π / 4. That is, the shape factor SF2 is: SF2 = {(PERI) ² / AREA} × (100π /
It becomes like 4).

In the present embodiment, the toner shape factor SF
1 and SF2 are electron microscopes FE-SEM manufactured by Hitachi Ltd.
By (S-800), the toner particle image is randomly changed to 10
Sampling was performed 0 times, and the image information was introduced into an image analysis device (LUSEX3) manufactured by Nikole Co. through an interface and analyzed, and calculated by the above formula.

The triboelectric charge amount of the black toner used in this embodiment is about −10 on the photosensitive drum 1 before the primary transfer.
μC / g.

The photosensitive drum 1 is an OPC having an outer diameter of 60 mm.
(Organic photoreceptor), the charge generation layer (CG layer: Carr)
The ier Generation Layer is formed of a phthalocyanine compound to have a thickness of 0.2 to 0.3 μm, and a charge transport layer (CT layer: Carrier Transfer) thereon.
er Layer) is used by dispersing a hydrazone compound in polycarbonate (PC) as a binder, and has a thickness of 1
The thickness was 5 to 25 μm.

As described above, the transfer belt 6 is used as the secondary transfer means, but the tension roller 61 and the bias roller 62 that support the transfer belt 6 may be made of the same material or different materials. The material of the rollers 61 and 62 has a volume resistivity of 1 × 10 ⁶ to 1 × 10 ¹⁰ Ωcm (1 k
It is only required that the voltage can be controlled when V is applied) and the voltage dependency of the resistance value is extremely large.

In this embodiment, the tension roller 61 and the bias roller 62 have a volume resistivity of 5 × 10 ⁷ Ωcm (1 k
NBR (when V was applied) was used. Its hardness is 30-35 degrees according to JIS-A. Both rollers 61, 62 have an outer diameter of 20 m
m, the central core metal is SUS stainless steel, and the outer diameter is 8 mm. Other materials for the rollers 61 and 62 include:
Other examples include those capable of dispersing a suitable conductive agent such as EPDM, urethane rubber, and CR.

The transfer belt 6 has a volume resistivity of 10 ¹¹ Ωc in which carbon is dispersed in silicone-modified polycarbonate.
m, a surface resistance of 10 ¹² to 10 ¹³ Ω / cm ² , a resin tube having a thickness of 100 μm, a width of 300 mm, and a peripheral length of 80.
mm. The volume resistivity of the transfer belt 6 is 10 ⁸ to 10
^It is preferably about ¹⁵ Ωcm (when 1 kV is applied).

Examples of materials that can be used as the transfer belt 6 include resin (polycarbonate (PC), nylon (PA), polyester (PET), polyethylene naphthalate (PEN), polysulfone (PS).
U), polyether sulfone (PES), polyetherimide (PEI), polyether nitrile (PE
N), polyetheretherketone (PEEK), thermoplastic polyimide (TPI), thermosetting polyimide (P
I), PES alloy, polyvinylidene fluoride (PVd
F), ethylene-tetrafluoroethylene copolymer (E
TFE) and the like; in the elastomer system, polyolefin-based thermoplastic elastomer, polyester-based thermoplastic elastomer, polyurethane-based thermoplastic elastomer, polyurethane-based thermosetting elastomer, polystyrene-based thermoplastic elastomer, polyamide-based thermoplastic elastomer, fluorine-based thermoplastic elastomer , A polybutadiene-based thermoplastic elastomer, a polyethylene-based thermoplastic elastomer, an ethylene-vinyl acetate-based thermoplastic elastomer, a polyvinyl chloride-based thermoplastic elastomer, and the like.

The other conditions of this embodiment are: contact pressure of the intermediate transfer member 5 with respect to the photosensitive drum 1: 2 kgf Contact pressure of the cleaning roller 8 with respect to the intermediate transfer member 5: 1 kgf With respect to the intermediate transfer member 5 of the transfer belt 6. Contact pressure: 5 kgf.

Dark potential on the photosensitive drum (primary charged non-image portion potential): V
d = -600V Bright potential on photosensitive drum (laser exposed image portion potential): V
I = -250V Development method: One-component jumping development Development bias: DC + AC. DC voltage Vdc = -40
0V AC voltage Vac = 1600Vpp, frequency = 1800H
z Sine wave Process speed: 120 mm / sec Primary transfer bias: +100 V Pre-secondary transfer charging bias (total current supplied from bias power supply 31): Idc = -200 μA Secondary transfer bias: +15 μA

Under the above conditions, the cleaning effect of the intermediate transfer member 5 was confirmed by using the laser beam having the apparatus configuration shown in FIG.

The timing of applying the charging bias to the pre-secondary transfer charger 18 was set just before the toner image on the intermediate transfer member 5 was subjected to the secondary transfer. That is, during printing of a continuous pattern of a single color, the pre-secondary transfer charging bias is applied simultaneously with the primary transfer, and during multi-transfer of four colors, the secondary pre-transfer charging bias is applied simultaneously with the primary transfer of the fourth color. I did it.

The cleaning roller 8 was brought into contact with the intermediate transfer member 5 at the same time as the primary transfer when printing a continuous pattern of a single color. This is to prevent the image from being disturbed due to the shock of contact. At the time of multi-transfer of four colors, the contact is made at the same time when the primary transfer of the fourth color is completed.

At this time, the toner amount of the toner image on the intermediate transfer member 5 before the secondary transfer is 0.8 mg / cm ² , and the toner triboelectric charge amount after the pre-second transfer charging is 30 μC /
g.

In order to clean the intermediate transfer body 5, it is preferable that the secondary transfer residual toner on the intermediate transfer body 5 is as small as possible. If the amount of residual toner remaining after secondary transfer is large, it is necessary to apply a strong charging bias to the cleaning roller 8 in order to charge the residual toner remaining after secondary transfer by the cleaning roller 8 and return it to the photosensitive drum 1. When cleaning the intermediate transfer member 5 with a strong bias,
Among the toners remaining after the secondary transfer, the toners already charged to the opposite polarity (positive polarity in this embodiment) due to the secondary transfer are further strongly charged, so that a toner having a very high positive charge amount is generated. To do.

FIG. 8 is a diagram schematically showing this situation. The black toner will be described as an example. The charge amount of the toner 94 on the photosensitive drum 1 before the primary transfer is about −10 μm.
C / g. Since the primary transfer bias has a low value of +100 V, the charge amount of the toner 94 hardly changes immediately after the primary transfer. The toner 95 transferred from the photosensitive drum 1 to the intermediate transfer member 5 by the primary transfer is further charged by the charge before the secondary transfer up to a charge amount of −30 μC / g, and then enters the secondary transfer step to form the transfer material P. Secondary transfer is performed.

The toner 96 left on the intermediate transfer member 5 by the secondary transfer is mainly the toner which is reversed to the positive polarity opposite to the normal due to the charging at the secondary transfer, and the toner 9
The charge amount of 6 was +10 to 20 μC / g. further,
When a bias is applied to the cleaning roller 8 to charge most of the toner 96 remaining after the secondary transfer to the positive polarity opposite to the normal polarity, the charge amount of the toner 97 after passing through the cleaning roller 8 is +30. Up to +40 μC / g.

As described above, since the toner 97 remaining after the secondary transfer on the intermediate transfer body 5 has a strong positive charge, the toner 97 is efficiently reverse-transferred between the intermediate transfer body 5 and the primary transfer portion of the photosensitive drum 1. , Can be returned to the photosensitive drum 1.

However, due to the charge imparted by the cleaning roller 5, the toner 9 remaining after the secondary transfer on the intermediate transfer member 5 is discharged.
Even if a portion of No. 7 has an excessively strongly positively charged toner, the toner 97 remaining after the secondary transfer has a larger amount of charge than the toner 94 primarily transferred. As shown in FIG.
4 and then again to the photosensitive drum 1. As a result, as an influence on the actual image, the traces of the residual toner at the time of the previous print appear like a negative ghost in the second and subsequent images of the continuous print. In the present invention, the negative ghost generated by the cleaning of the secondary transfer residual toner is called a cleaning ghost.

Therefore, in order to carry out cleaning of the intermediate transfer member 5, it is necessary to prevent both defective cleaning and cleaning ghost from occurring. As a bias applied to the cleaning roller 8, the present inventors
This has been achieved by using a bias that superimposes an AC voltage on a DC voltage.

Intermediate transfer member 5 by cleaning roller 8
Table 1 shows the difference in the cleaning characteristics of No. 1 depending on the presence or absence of AC superposition of the cleaning bias. Interchange is 10
μA (effective value rms; the same applies below), the toner used was a black toner, and the working environment was a high temperature and high humidity environment (H / H) of 30 ° C./80% R. The cleaning characteristics were examined for poor cleaning and cleaning ghost.

In Table 1, the meanings of the symbols are as follows.
○: Good with no occurrence. Δ: Occurrence occurs, but it reaches the end. X: Very bad and bad.

[0101]

[Table 1]

As shown in Table 1, in the H / H environment,
In the case of the cleaning bias of only DC, the cleaning failure disappears at 30 μA or more, but the cleaning ghost occurs, so that the primary transfer and the cleaning of the intermediate transfer member cannot be performed at the same time. On the other hand, in the case of a cleaning bias in which AC is superimposed on DC, DC is 40
Cleaning ghost occurs at μA or more, but H / H
Even in the environment, if the cleaning amount is 30 μA or more, the occurrence of cleaning failure can be prevented, and the primary transfer and the cleaning of the intermediate transfer member can be performed simultaneously.

The degree of occurrence of the cleaning ghost is different due to the superposition of the alternating current on the cleaning bias, that is, the charge amount of the secondary transfer residual toner 97 on the intermediate transfer member 5 after the charge is applied by the cleaning roller 8. It is thought that it is due to the difference of. FIG. 9 shows the difference in the charge amount distribution of the secondary transfer residual toner on the intermediate transfer member 5 after being charged by the cleaning roller 8 depending on the presence or absence of AC superposition of the cleaning bias. The conditions are black toner, H / H environment, DC = 30 μA, AC = 15
It is 00 μA. The distribution of the charge amount of the toner was measured with an E-Spurt analyzer manufactured by Hosokawa Micron.

As shown in FIG. 9, when the cleaning bias of only DC is applied to the cleaning roller 8, the distribution of the charge amount of the secondary transfer residual toner is broad and the charge amount is remarkably high. There is a large proportion of toner present. Since a cleaning ghost (negative ghost) is generated by the toner having the remarkably high amount of electric charge, by superimposing an alternating current on the cleaning bias so as not to generate such a toner,
The cleaning bias value that causes a cleaning ghost can be increased, and the margin with the cleaning bias value that causes defective cleaning can be expanded. That is, cleaning that is the same as the primary transfer is established.

As described above, according to this embodiment, since the alternating current is superimposed on the cleaning bias applied to the cleaning roller 8, the primary transfer to the intermediate transfer member 5 and the secondary transfer on the intermediate transfer member 5 are performed. It becomes possible to perform cleaning of the residual toner after the next transfer at the same time. Therefore, in the case of continuous printing with a color laser printer, a color copying machine, etc., the intermediate transfer member 5 is removed every time one image is output. There is no need to enter the cleaning step. Therefore,
When continuously printing different originals, it is possible to improve the throughput of print images.

Further, by applying the cleaning bias in which the alternating current is superimposed on the direct current, the secondary transfer residual toner can be cleaned simultaneously with the primary transfer even in the H / H environment. Further, compared to blade cleaning, fur brush cleaning, etc., since the parts used are not mechanically damaged, they can withstand long-term use and realize a stable cleaning means for the cleaning roller 8 etc. for the intermediate transfer member 5. be able to.

In the above, the cylindrical photosensitive drum 1 and the intermediate transfer member 5 are used, but it is needless to say that the same effect can be obtained even if a belt-shaped image carrier or intermediate transfer member is used. Nor. Although the belt transfer method using the transfer belt 6 is used as the secondary transfer means, the effect of the present invention is not changed even if the conventional corona transfer method or transfer roller method is used.

Example 2 In this example, a bias applied to the pre-secondary transfer charger 18 of the image forming apparatus of FIG.
The feature is that only direct current is used for the bias applied to the cleaning roller 8.

Bias power source 31 to pre-secondary transfer charger 1
The charging bias (total current from the bias power supply 31) supplied to 8 is: Idc = −50 μA, Iac = 60 μA Frequency = 1000 Hz, sine wave.

As in the case of Example 1, the toner remaining after the secondary transfer on the intermediate transfer body 5 is charged up to a charge amount of −30 μC / g by the charge before the secondary transfer. It should be noted that regardless of the presence or absence of AC superposition of the pre-secondary transfer charging bias, the toner on the intermediate transfer member is charged by the pre-secondary transfer charging up to a charge charge amount of −30 μC / g.
It has been confirmed that the amount of toner remaining on the intermediate transfer member after the next transfer is the same.

Intermediate transfer member 5 by cleaning roller 8
Table 2 shows the difference in the cleaning characteristics of the above-mentioned cleaning bias depending on the presence or absence of AC superposition of the pre-secondary transfer charging bias. Exchange is 6
0 μA. The conditions are black toner and H / H environment. The cleaning characteristics are poor cleaning and cleaning ghost. In Table 2, the meanings of the symbols are Table 1
It is the same as when.

[0112]

[Table 2]

As shown in Table 2, in the H / H environment,
30 μA when the pre-secondary transfer charging bias is DC only
Although the cleaning failure is eliminated by the above, a cleaning ghost is generated, so that the primary transfer and the intermediate transfer member cannot be cleaned at the same time. On the other hand, when the pre-secondary transfer charging bias is a superposition of direct current and alternating current, a cleaning ghost occurs when the direct current is 30 μA or more, but even in an H / H environment, it is possible to prevent the occurrence of cleaning failure at 20 μA or more. Next transfer and cleaning of the intermediate transfer member can be performed at the same time.

The degree of occurrence of cleaning failure differs due to the superposition of alternating current on the pre-secondary transfer charging bias.
It is considered that this is due to the difference in the charge amount of the secondary transfer residual toner 97 on the intermediate transfer member 5. Cleaning roller 8
FIG. 10 shows the difference in the charge charge amount distribution of the toner on the intermediate transfer member 5 after the application of the charge due to the presence or absence of AC superposition of the pre-secondary transfer charge bias. The conditions are black toner, H / H environment, DC = −200 μA when the pre-second transfer charging bias is DC, DC = −50 μA when AC is superimposed, AC = 60 μA, frequency 1000 H.
z, a sine wave.

As shown in FIG. 10, when the pre-secondary transfer charging bias is only direct current, the distribution of the charge amount of the secondary transfer residual toner after receiving the charge imparted by the cleaning roller 8 is broad. The average value of the amount of charge is also low. This toner with a low charge amount causes cleaning failure. Therefore, by superimposing direct current and alternating current on the pre-secondary transfer charging bias so as not to generate such toner, cleaning failure may occur even with a lower cleaning bias. It is possible to suppress, and it is possible to expand the margin with respect to the cleaning bias value that causes the cleaning ghost.

As described above, according to this embodiment, 2
By superimposing an alternating current on the direct current pre-transfer charging bias, the primary transfer to the intermediate transfer member 5 and the cleaning of the intermediate transfer member 5 can be performed at the same time. In a color laser printer, a color copying machine, etc. In the case of continuous printing, it is not necessary to enter the step of cleaning the intermediate transfer body 5 every time an image is output one by one, and the throughput in continuous printing can be improved.

Embodiment 3 In this embodiment, a bias applied to the pre-secondary transfer charger 18 of the image forming apparatus of FIG.
Further, it is characterized in that the bias applied to the cleaning roller 8 is also used by superimposing direct current on alternating current.

Bias power source 31 to pre-secondary transfer charger 1
The charging bias (total current from the bias power supply 31) supplied to 8 is: Idc = −50 μA, Iac = 60 μA Frequency = 1000 Hz, sine wave.

The alternating current of the charging bias (total current from the bias power source 30) supplied from the bias power source 30 to the cleaning roller 8 is Iac = 1500 μA, frequency = 1000 Hz, sine wave.

As in the case of Example 1, the toner on the intermediate transfer member 5 was rubbed with a charge amount of −30 due to pre-secondary transfer charging.
Receives electric charge up to μC / g. Regardless of whether or not the alternating current of the pre-secondary transfer charging bias is superposed, the toner on the intermediate transfer member is charged with an amount of −30 μC by the pre-secondary transfer charging.
It has been confirmed that the amount of toner left on the intermediate transfer body after the secondary transfer is the same as that of the charge applied up to / g.

Intermediate transfer member 5 by cleaning roller 8
Table 3 shows the difference in the cleaning characteristics between the case where both the pre-secondary transfer charging bias and the cleaning bias are DC only and the case where AC is superimposed on DC. The conditions are black toner and H / H environment. In Table 3, the meanings of the symbols are the same as in Table 1.

[0122]

[Table 3]

As shown in Table 3, in the H / H environment,
When both the pre-secondary transfer charging bias and the cleaning bias are DC only, the cleaning failure disappears at 30 μA or more, but a cleaning ghost occurs, so 1
Subsequent transfer and cleaning of the intermediate transfer member cannot be performed at the same time. On the other hand, when the pre-secondary transfer charging bias and the cleaning bias are both DC and AC superimposed,
A cleaning ghost occurs when the cleaning bias DC is 40 μA or more, but 20 μA even in the H / H environment.
By the above, the occurrence of cleaning failure can be prevented, and the primary transfer and the cleaning of the intermediate transfer member can be performed at the same time.

The degree of occurrence of cleaning failure and cleaning ghost differs due to the superposition of alternating current on the pre-secondary transfer charging bias and the cleaning bias. The reason why the intermediate transfer body 5 is after the charge is applied by the cleaning roller 8 is It is considered that the difference is due to the difference in the charge amount of the secondary transfer residual toner 97. FIG. 11 shows the difference in the charge amount distribution of the toner on the intermediate transfer member 5 after being charged by the cleaning roller 8 depending on the presence or absence of AC superposition of the pre-secondary transfer charging bias and the cleaning bias. The conditions are black toner, H / H environment, secondary pre-transfer charging bias is direct current (-200 μA) only, cleaning bias is direct current (+30 μA), and secondary pre-transfer charging bias is direct current (-50 μA). AC (60 μA, 100
0Hz, sine wave is superimposed, and cleaning bias is direct current (+ 30μA) and alternating current (1500μA, 1000H).
z, sine wave).

As shown in FIG. 11, when the pre-secondary transfer charging bias and the cleaning bias are DC only, the secondary transfer residual toner after the charge is applied by the cleaning roller 8 is charged. The quantity distribution is broad. By superimposing an alternating current on the secondary transfer charging bias and the cleaning bias, it is possible to sharpen the charge amount distribution of the secondary transfer residual toner, and it is possible to suppress the occurrence of cleaning failure even with a lower cleaning bias. Further, it is possible to suppress the occurrence of a cleaning ghost even with a higher cleaning bias, and thus it is possible to expand the margin of the cleaning bias value.

As described above, according to this embodiment, 2
By superimposing a direct current and an alternating current on the pre-secondary transfer charging bias and the cleaning bias, it is possible to simultaneously perform the primary transfer to the intermediate transfer body 5 and the cleaning of the secondary transfer residual toner on the intermediate transfer body 5. , Continuous printing with a color laser printer, color copier, etc.
It is not necessary to enter the step of cleaning the intermediate transfer body 5 every time an image is output one by one, and throughput improvement in continuous printing can be realized.

[0127]

As described above, according to the present invention,
Toner images of a plurality of colors are sequentially formed on the first image carrier from the first color, and the obtained toner images are primary-transferred on the second image carrier in order from the first color to perform the first charging. By applying a charging bias to the means, a plurality of color toner images that have been primary-transferred are charged, and the toner images of a plurality of colors that have been charged are collectively secondarily transferred onto a transfer material. In an image forming apparatus that obtains a color image on a material, by applying a charging bias to a second charging unit, a charge is applied to the toner remaining on the second image carrier by the secondary transfer, and the remaining toner Since the charging bias applied to the second and / or the first charging means is a bias in which an alternating current is superimposed on a direct current when the cleaning is performed by returning to the first image carrier by the electric field generated by the applied electric charge, Second image, even in a moist environment Primary transfer of the toner image from the first image carrier to the second image carrier in the subsequent image formation by returning and cleaning the remaining toner from the carrier to the first image carrier. It can be done at the same time.

Therefore, when different originals are continuously printed by a color laser printer, a color copying machine, etc.,
It is not necessary to enter the step of cleaning the second image carrier each time one sheet is printed out, and the throughput of printed images can be greatly improved. Further, as compared with blade cleaning, fur brush cleaning, etc., the parts used are not mechanically damaged, so that they can withstand long-term use and stabilize the second charging means etc. Can be realized as a cleaning means.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing one embodiment of an image forming apparatus of the present invention.

FIG. 2 is a schematic cross-sectional view showing a cleaning roller that cleans an intermediate transfer member installed in the image forming apparatus of FIG.

FIG. 3 is an explanatory diagram showing a method for measuring the actual use resistance of the cleaning roller performed in the present invention.

FIG. 4 is a schematic sectional view showing an intermediate transfer member.

FIG. 5 is a schematic sectional view showing a polymerized toner used in the present invention.

FIG. 6 is a diagram illustrating a shape factor SF1 of a spherical substance.

FIG. 7 is a diagram illustrating a shape factor SF2 of a spherical substance.

FIG. 8 is an explanatory diagram showing a mechanism of generation of a cleaning ghost.

FIG. 9 is a diagram showing the difference in the charge amount distribution of the toner on the intermediate transfer member after being charged by the cleaning roller, depending on whether or not AC of the cleaning bias is superposed.

FIG. 10 is a diagram showing the difference in the charge amount distribution of the toner on the intermediate transfer member after the charge is applied by the cleaning roller, depending on whether or not AC of the pre-secondary transfer charging bias is superposed.

FIG. 11 is a diagram showing the difference in the charge amount distribution of the toner on the intermediate transfer member after being charged by the cleaning roller, depending on the presence or absence of AC superposition of the pre-secondary transfer charging bias and the cleaning bias.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum 41-44 Developing device 5 Intermediate transfer body 6 Transfer belt 8 Cleaning roller 9 Toner 18 Pre-secondary transfer charger 30, 31 Bias power supply

Claims (3)

[Claims] 1. A toner image of a plurality of colors is sequentially formed on a first image carrier from the first color, and the obtained toner images are primarily transferred to the second image carrier in order from the first color. By applying a charging bias to the first charging means, charges are applied to the primary-transferred toner images of a plurality of colors, and the charged toner images of a plurality of colors are collectively secondary-transferred on the transfer material. By transferring, a color image is obtained on the transfer material, and by applying a charging bias to the second charging means, charges are applied to the toner remaining on the second image carrier by the secondary transfer, and the toner remains. In the image forming apparatus that restores the toner on the first image carrier by the electric field generated by the applied charge, the charging bias applied to the second charging unit is set to the bias in which the alternating current is superposed on the direct current to generate the second image. Return the remaining toner from the carrier to the first image carrier An image forming apparatus is characterized in that it is performed simultaneously with the primary transfer of the toner image from the first image carrier to the second image carrier in the next image formation. 2. A toner image of a plurality of colors is sequentially formed on the first image carrier from the first color, and the obtained toner images are primarily transferred to the second image carrier in order from the first color. By applying a charging bias to the first charging means, charges are applied to the primary-transferred toner images of a plurality of colors, and the charged toner images of a plurality of colors are collectively secondary-transferred on the transfer material. By transferring, a color image is obtained on the transfer material, and by applying a charging bias to the second charging means, charges are applied to the toner remaining on the second image carrier by the secondary transfer, and the toner remains. In the image forming apparatus for returning the toner onto the first image carrier by the electric field generated by the applied charge, the charging bias applied to the first charging unit is set to the bias in which the alternating current is superposed on the direct current, and thus the second image is formed. Return the remaining toner from the carrier to the first image carrier An image forming apparatus is characterized in that it is performed simultaneously with the primary transfer of the toner image from the first image carrier to the second image carrier in the next image formation. 3. A toner image of a plurality of colors is sequentially formed on the first image carrier from the first color, and the obtained toner images are primarily transferred to the second image carrier in order from the first color. By applying a charging bias to the first charging means, charges are applied to the primary-transferred toner images of a plurality of colors, and the charged toner images of a plurality of colors are collectively secondary-transferred on the transfer material. By transferring, a color image is obtained on the transfer material, and by applying a charging bias to the second charging means, an electric charge is applied to the toner remaining on the second image carrier by the secondary transfer and remains. In an image forming apparatus that returns onto a first image carrier by an electric field generated by an electric charge applied with toner, a charging bias applied to a first charging unit and a charging bias applied to a second charging unit are superimposed on a direct current and an alternating current. By setting the bias
The returning of the remaining toner from the second image carrier to the first image carrier is performed by returning the toner image from the first image carrier to the second image carrier in the next image formation. An image forming apparatus characterized by being performed simultaneously with the next transfer.